JP7567201B2 - Steering device - Google Patents

Description

The present invention relates to a steering device that steers the steered wheels of a vehicle.

Steering devices of the so-called steer-by-wire type, which mechanically separates the power transmission between the steering wheel and the steered wheels, are known. For example, in the steering device of Patent Document 1, two motors are provided coaxially with respect to a steering shaft that steers the steered wheels. A ball nut is integrally provided on each rotor of the two motors, and the ball nuts are screwed via a number of balls into a ball screw portion provided on the steering shaft. The rotational motion of the two motors is converted into linear motion of the steering shaft via a ball screw mechanism including the ball nuts.

JP 2006-347209 A

In the steering device of Patent Document 1, one steered shaft is operated using two motors. For this reason, the two motors need to be controlled in a coordinated manner. Depending on the product specifications, it may be necessary to control the power supply to the two motors using separate control devices. In this case, however, there is a concern that the controls by the two control devices may interfere with each other. Depending on the degree of this control interference, it may become difficult to properly steer the steered wheels.

The object of the present invention is to provide a steering device that can steer the steered wheels more appropriately.

A steering device that can achieve the above object includes two motors that generate driving forces for steering the steered wheels of a vehicle, and two control devices that individually control the two motors. One of the two control devices calculates a command value according to the total torque to be generated by the two motors so as to eliminate the difference between the target position and the actual position of the steered wheels. The command value is distributed at a changeable ratio that is set for each of the motors. Each of the two control devices supplies a current to the motor that is the object of its control according to the individual command value distributed to the motor.

According to this configuration, when two motors operate in coordination, the current supplied to these motors is determined by one of the control devices. The other control device simply operates to supply a current corresponding to an individual command value unilaterally determined by one of the control devices to the motor that is the object of its control. In other words, the two control devices are in a relationship of master and slave. For this reason, unlike a case in which, for example, two control devices each individually calculate a command value for the motor that is the object of its control, and control the power supply to the motor that is the object of its control based on these individually calculated command values, interference between the controls of the two control devices is suppressed. This allows the steered wheels to be steered more appropriately.

In the above steering device, a distribution ratio of the command values to the two motors may be set by one of the control devices.
The above-mentioned steering device may include a steering shaft for steering the steered wheels, and two transmission mechanisms for transmitting the driving forces of the two motors individually to the steering shaft, and when a predetermined execution condition for an abnormality detection process is satisfied, one of the control devices may set the distribution ratio of the command values for the two motors to an unequal distribution ratio and switch the set distribution ratio between the two motors, and detect an abnormal increase in friction of the transmission mechanism by comparing the total values of the currents detected as being supplied to the two motors before and after the switch of the distribution ratio.

There is a risk of an abnormal increase in friction in the transmission mechanism due to wear of the components of the transmission mechanism. In this case, the smooth operation of the transmission mechanism is hindered, and the force required to operate the transmission mechanism increases accordingly. As a result, the load torque of the motor increases according to the degree of increase in friction in the transmission mechanism. The current flowing through the motor increases in proportion to the magnitude of the load torque. Therefore, it is possible to detect an abnormal increase in friction in the transmission mechanism based on the motor current.

For example, in the case where the distribution ratio of command values for two motors is set to an unequal distribution ratio and the set distribution ratio is instantly switched between the two motors as in the above-mentioned steering device, if the total value of the currents of the two motors changes before and after the switching of the distribution ratio, it can be said that the friction of one of the two transmission mechanisms has abnormally increased.

The reason why the distribution ratio of the command value is set to an unequal distribution ratio is that the effect of increased friction in the transmission mechanism is more easily reflected in the motor current value when the distribution ratio of the command value is larger. For example, when switching between large and small distribution ratios for two motors, the change in the motor current value due to increased friction is larger when the distribution ratio is set to a larger value than when the distribution ratio is set to a smaller value. This larger change in the motor current value appears as a change in the total value of the current values of the two motors before and after the distribution ratio is switched. Therefore, when detecting an abnormal increase in friction in the transmission mechanism, it is preferable to set the distribution ratio of the command value to an unequal distribution ratio.

Incidentally, when the conditions for executing the abnormality detection process are met, if the distribution ratio of the command values for the two motors is set to an equal distribution ratio, the value of the distribution ratio for the two motors does not change before and after the swap of the distribution ratios, so there is a risk that the total value of the currents of the two motors will not change significantly before and after the swap of the distribution ratios. For this reason, when detecting an abnormal increase in friction in the transmission mechanism, it is preferable to set the distribution ratio of the command values to an unequal distribution ratio.

In the above steering device, the one control device may determine that the friction of one of the two transmission mechanisms has abnormally increased when the absolute value of the difference between a first sum of the currents of the two motors before the switching of the distribution ratio and a second sum of the currents of the two motors after the switching of the distribution ratio is outside a threshold range set to detect an abnormal increase in friction of the transmission mechanism.

If the friction of one of the two transmission mechanisms has increased abnormally, the total value of the currents of the two motors before and after the switching of the distribution ratio changes according to the degree of increase in friction of the transmission mechanisms. Therefore, as with the above-mentioned steering device, it is possible to easily detect that the friction of one of the two transmission mechanisms has increased abnormally based on whether the absolute value of the difference between the first total value and the second total value of the currents of the two motors is outside the threshold range.

In the above steering device, when the execution condition is satisfied, the one control device can determine that friction in the transmission mechanism corresponding to the second motor has abnormally increased if, after swapping the allocation ratios, the first allocation ratio for the first motor corresponding to the one control device is set to a value smaller than the second allocation ratio for the second motor, the absolute value of the difference is outside the threshold range, and the second total value is greater than the first total value.

In the above steering device, when the execution condition is satisfied, the one control device sets the first allocation ratio for the first motor corresponding to itself to a value smaller than the second allocation ratio for the second motor after the allocation ratio swap, and when the absolute value of the difference is outside the threshold range and the second total value is smaller than the first total value, the one control device can determine that friction in the transmission mechanism corresponding to the first motor has abnormally increased.

In the above steering device, when an abnormality is detected in one of the two transmission mechanisms, the one control device may stop driving the motor corresponding to the transmission mechanism in which the abnormality is detected, or may reduce the current supplied to the motor corresponding to the transmission mechanism in which the abnormality is detected compared to the current supplied to the motor corresponding to the normal transmission mechanism.

According to this configuration, it is possible to protect the ball screw in which friction has abnormally increased, and also to extend the life of the ball screw in which friction has abnormally increased.
In the above steering device, a first transmission mechanism of the two transmission mechanisms may have a first ball nut screwed into a first ball screw portion provided on the steering shaft, and a second transmission mechanism of the two transmission mechanisms may have a second ball nut screwed into a second ball screw portion provided on the steering shaft.

As with this configuration, the ball screw section and the ball nut, which are components of the transmission mechanism, may experience an abnormal increase in friction when the ball nut rotates relative to the ball screw section due to wear and tear caused by long-term use. In this case, the smooth rotation of the ball nut relative to the ball screw section is hindered, and the force required to rotate the ball nut relative to the ball screw section increases accordingly. As a result, the load torque of the motor increases according to the degree of increase in friction between the ball screw section and the ball nut. The current flowing through the motor increases in proportion to the magnitude of the load torque. Therefore, as with the above-mentioned steering device, an abnormality in the transmission mechanism corresponding to the first motor or the transmission mechanism corresponding to the second motor can be determined by comparing the total current value of the two motors before and after switching the distribution ratio of the command values for the two motors.

In the above steering device, the first ball screw portion and the second ball screw portion may have a mutually reverse thread relationship.
According to this configuration, when the turning shaft is to be moved in a specific direction, the two ball nuts rotate in opposite directions. Therefore, the torque acting on the turning shaft due to the rotation of the first ball nut and the torque acting on the turning shaft due to the rotation of the second ball nut, which are torques in opposite directions, are offset. Therefore, it is possible to suppress the torque about the axis from acting on the turning shaft.

In the above steering device, the distribution ratio of the command values to the two motors may be set by another control device provided outside the two control devices.
The above-mentioned steering device may include a steering shaft for steering the steered wheels, and two transmission mechanisms for transmitting the driving forces of the two motors individually to the steering shaft, and another control device provided outside the two control devices may, when a predetermined execution condition for an abnormality detection process is satisfied, set the distribution ratio of the command values for the two motors to an unequal distribution ratio and switch the set distribution ratio between the two motors, and detect an abnormal increase in friction of the transmission mechanism by comparing the total values of the currents of the two motors before and after the switch of the distribution ratio.

According to this configuration, it is possible to detect an abnormal increase in friction in the power transmission mechanism based on the motor current as described above.
In the above steering device, the command value may be a torque command value indicating a total torque to be generated by the two motors.

In the above steering device, the command value may be a current command value corresponding to a total torque to be generated by the two motors.
In the above steering device, the command value may be a voltage command value corresponding to a total torque to be generated by the two motors.

The steering device of the present invention allows the steered wheels to be steered more appropriately.

FIG. 1 is a configuration diagram of a first embodiment of a steering device. FIG. 2 is a block diagram of a control device according to the first embodiment. FIG. 11 is a block diagram of a control device according to a second embodiment. 13 is a flowchart showing the procedure of an abnormality detection process according to the second embodiment. FIG. 13 is a block diagram of a control device according to a fourth embodiment. FIG. 13 is a block diagram of a control device according to a fifth embodiment. FIG. 13 is a block diagram of a control device according to a sixth embodiment. FIG. 13 is a block diagram of a current control circuit according to a sixth embodiment. FIG. 13 is a block diagram of a control device according to another embodiment.

First Embodiment
A first embodiment of a vehicle steering device will now be described.
As shown in Fig. 1, the steering device 10 has a housing 11 fixed to a vehicle body (not shown). A steering shaft 12 extending in the left-right direction of the vehicle body (left-right direction in Fig. 1) is accommodated inside the housing 11. Steered wheels 14, 14 are connected to both ends of the steering shaft 12 via tie rods 13, 13, respectively. The steering angles θw, θw of the steered wheels 14, 14 are changed by moving the steering shaft 12 along its axial direction.

The steered shaft 12 is provided with a first ball screw portion 12a and a second ball screw portion 12b. The first ball screw portion 12a is a portion in which a right-handed screw is provided over a predetermined range near the first end (left end in FIG. 1) of the steered shaft 12. The second ball screw portion 12b is a portion in which a left-handed screw is provided over a predetermined range near the second end (right end in FIG. 1) of the steered shaft 12.

The steering device 10 has a first ball nut 15 and a second ball nut 16. The first ball nut 15 is screwed to the first ball screw portion 12a of the steering shaft 12 via a plurality of balls (not shown). The second ball nut 16 is screwed to the second ball screw portion 12b of the steering shaft 12 via a plurality of balls (not shown). The first ball screw portion 12a of the steering shaft 12, the balls (not shown), and the first ball nut 15 constitute a first ball screw _BS1 . The second ball screw portion 12b of the steering shaft 12, the balls (not shown), and the second ball nut 16 constitute a second ball screw _BS2 .

The steering device 10 has a first motor 17 and a second motor 18. The first motor 17 and the second motor 18 are sources of steering force, which is the power for steering the steered wheels 14, 14, and may be, for example, a three-phase brushless motor. The first motor 17 and the second motor 18 are each fixed to an outer portion of the housing 11. The output shaft 17a of the first motor 17 and the output shaft 18a of the second motor 18 each extend parallel to the steering shaft 12.

The steering device 10 has a first belt transmission mechanism 21 and a second belt transmission mechanism 22 .
The first belt transmission mechanism 21 has a driving pulley 23, a driven pulley 24, and an endless belt 25. The driving pulley 23 is a toothed pulley having teeth 23a on its outer circumferential surface, and is fixed to the output shaft 17a of the first motor 17. The driven pulley 24 is a toothed pulley having teeth 24a on its outer circumferential surface, and is fixed in a state of being fitted on the outer circumferential surface of the first ball nut 15. The belt 25 is a toothed belt having teeth 25a on its inner circumferential surface, and is stretched between the driving pulley 23 and the driven pulley 24. Therefore, the rotation of the first motor 17 is transmitted to the first ball nut 15 via the driving pulley 23, the belt 25, and the driven pulley 24.

The second belt transmission mechanism 22, like the first belt transmission mechanism 21, has a drive pulley 26, a driven pulley 27, and an endless belt 28. The drive pulley 26 is a toothed pulley with teeth 26a on its outer circumferential surface, and is fixed to the output shaft 18a of the second motor 18. The driven pulley 27 is a toothed pulley with teeth 27a on its outer circumferential surface, and is fixed in a state of being fitted onto the outer circumferential surface of the second ball nut 16. The belt 28 is a toothed belt with teeth 28a on its inner circumferential surface, and is stretched between the drive pulley 26 and the driven pulley 27. Therefore, the rotation of the second motor 18 is transmitted to the second ball nut 16 via the drive pulley 26, the belt 28, and the driven pulley 27.

The first belt transmission mechanism 21 and the first ball screw _BS1 constitute a first transmission mechanism that transmits the driving force of the first motor 17 to the steered shaft 12. The second belt transmission mechanism 22 and the second ball screw _BS2 constitute a second transmission mechanism that transmits the driving force of the second motor 18 to the steered shaft 12. Incidentally, the reduction ratio between the first motor 17 and the steered shaft 12 (reduction ratio of the first transmission mechanism) and the reduction ratio between the second motor 18 and the steered shaft 12 (reduction ratio of the second transmission mechanism) are the same value. In addition, the lead of the first ball screw portion 12a and the lead of the second ball screw portion 12b in the steered shaft 12 are the same value. Therefore, the movement amount of the steered shaft 12 when the first motor 17 rotates once and the movement amount of the steered shaft 12 when the second motor 18 rotates once are the same value.

The steering device 10 has a first rotation angle sensor 31 and a second rotation angle sensor 32. For example, resolvers are used as the first rotation angle sensor 31 and the second rotation angle sensor 32. The detection range of the first rotation angle sensor 31 and the second rotation angle sensor 32 is 360°, which corresponds to one period of the electrical angle of the first motor 17 and the second motor 18.

The first rotation angle sensor 31 is provided on the first motor 17. The first rotation angle sensor 31 detects the rotation angle (electrical angle) α of the first motor 17. The first rotation angle sensor 31 generates a first sine signal (sine signal) that changes in a sine wave shape as an electrical signal corresponding to the rotation of the first motor 17, and a first cosine signal (cosine signal) that changes in a cosine wave shape according to the rotation of the first motor 17. The first rotation angle sensor 31 calculates the arctangent based on the first sine signal and the first cosine signal as the rotation angle α of the first motor 17. This rotation angle α changes in a sawtooth wave shape with a period corresponding to the shaft multiplication angle of the first rotation angle sensor 31. In other words, the rotation angle α changes in a manner that repeatedly rises and steeply falls according to the rotation of the first motor 17.

The second rotation angle sensor 32 is provided on the second motor 18. The second rotation angle sensor 32 detects the rotation angle β (electrical angle) of the second motor 18. The second rotation angle sensor 32 generates a second sine signal that changes in a sine wave shape as an electrical signal corresponding to the rotation of the second motor 18, and a second cosine signal that changes in a cosine wave shape according to the rotation of the second motor 18. The second rotation angle sensor 32 calculates the arctangent based on the second sine signal and the second cosine signal as the rotation angle β of the second motor 18. This rotation angle β changes in a sawtooth wave shape with a period corresponding to the shaft multiplication angle of the second rotation angle sensor 32.

The first rotation angle sensor 31 and the second rotation angle sensor 32 have different shaft multiplier angles. The shaft multiplier angle refers to the ratio of the electrical angle of the electrical signal to the rotation angle (mechanical angle) of the first motor 17 and the second motor 18. For example, if the first rotation angle sensor 31 generates one cycle of the electrical signal while the first motor 17 rotates once, the shaft multiplier angle of the first rotation angle sensor 31 is one cycle (1X). Also, if the first rotation angle sensor 31 generates four cycles of the electrical signal while the first motor 17 rotates once, the shaft multiplier angle of the first rotation angle sensor 31 is four cycles (4X).

Since the first rotation angle sensor 31 and the second rotation angle sensor 32 have different shaft angle multiplication factors, the number of periods of the rotation angle α per rotation of the first motor 17 and the rotation angle β per rotation of the second motor 18 are different from each other. In other words, the values of the rotation angles (mechanical angles) of the first motor 17 and the second motor 18 per period of the electrical signals generated by the first rotation angle sensor 31 and the second rotation angle sensor 32 are different from each other.

The first motor 17 is connected to the steered shaft 12 and thus to the steered wheels 14, 14 via a first belt transmission mechanism 21. The second motor 18 is connected to the steered shaft 12 and thus to the steered wheels 14, 14 via a second belt transmission mechanism 22. Therefore, the rotation angle α of the first motor 17 and the rotation angle β of the second motor 18 are values that respectively reflect the absolute axial position of the steered shaft 12 and thus the steering angle of the steered wheels 14, 14.

The steering device 10 has a first control device 41 and a second control device 42. The first control device 41 can be configured by a processing circuit including (1) one or more processors that operate according to a computer program (software), (2) one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC) that executes at least some of the various processes, or (3) a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute the processes. The memory, i.e., a non-transitory computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. The configurations of the second control device 42 and the higher-level control device 43 described later are also similar to those of the first control device 41.

The first control device 41 controls the first motor 17. The first control device 41 receives a target steering angle θ ^* calculated by, for example, an on-board higher-level control device 43 in response to the steering state or running state of the vehicle. The first control device 41 also receives a rotation angle α of the first motor 17 detected via the first rotation angle sensor 31 and a rotation angle β of the second motor 18 detected via the second rotation angle sensor 32.

The first control device 41 executes steering control for steering the steered wheels 14, 14 according to the steering state through drive control of the first motor 17. The first control device 41 calculates an actual absolute position of the steered shaft 12 using the rotation angle α of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle β of the second motor 18 detected through the second rotation angle sensor 32. The first control device 41 also calculates a target absolute position of the steered shaft 12 based on the target steering angle θ ^* . The first control device 41 obtains a difference between the target absolute position and the actual absolute position of the steered shaft 12, and executes position feedback control for controlling power supply to the first motor 17 so as to eliminate this difference. The first control device 41 calculates current command values for the first motor 17 and the second motor 18 according to the difference between the target absolute position and the actual absolute position of the steered shaft 12, and supplies a current according to the calculated current command value to the first motor 17.

The second control device 42 controls the second motor 18. The second control device 42 executes steering control to steer the steered wheels 14, 14 according to the steering state through drive control of the second motor 18. The second control device 42 takes in a current command value calculated by the first control device 41, and controls the power supply to the second motor 18 based on this taken-in current command value.

The second control device 42 also receives the target turning angle θ ^* calculated by the above-mentioned higher-level control device 43, as well as the rotation angle α of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle β of the second motor 18 detected through the second rotation angle sensor 32. The second control device 42 has a first function of calculating an actual absolute position of the turning shaft 12 using the rotation angle α of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle β of the second motor 18 detected through the second rotation angle sensor 32. The second control device 42 also has a second function of calculating a target absolute position of the turning shaft 12 based on the target turning angle θ ^* . The second control device 42 also has a third function of executing position feedback control that determines a difference between the target absolute position of the turning shaft 12 and the actual absolute position, and controls the power supply to the second motor 18 so as to eliminate this difference. However, when the first control device 41 is operating normally, the second control device 42 maintains these first to third functions in a stopped state. At this time, the target steering angle θ ^* , the rotation angle α of the first motor 17, and the rotation angle β of the second motor 18 are not used.

Incidentally, as the first ball nut 15 and the second ball nut 16 rotate relative to the steered shaft 12, a torque around the axis acts on the steered shaft 12. When the steered shaft 12 is to be moved in a specific direction, the first ball nut 15 and the second ball nut 16 rotate in opposite directions, and the operation of the first motor 17 and the second motor 18 is controlled so that the torque acting on the steered shaft 12 as the ball nuts rotate is the same value. Therefore, the torque acting on the steered shaft 12 as the first ball nut 15 rotates and the torque acting on the steered shaft 12 as the second ball nut 16 rotates, which are torques in opposite directions, are offset. Therefore, no torque around the axis acts on the steered shaft 12.

<Control device>
Next, the first control device 41 and the second control device 42 will be described in detail.
As shown in FIG. 2, the first control device 41 has a position detection circuit 51, a position control circuit 52, a distribution calculation circuit 53, a multiplier 54, a current control circuit 55, and a subtractor 56.

The position detection circuit 51 takes in the rotation angle α of the first motor 17 detected through the first rotation angle sensor 31 and the rotation angle β of the second motor 18 detected through the second rotation angle sensor 32, and calculates the absolute position P1 of the turning shaft 12 based on these taken-in rotation angles α and β. The shaft multiplier angle of the first rotation angle sensor 31 and the shaft multiplier angle of the second rotation angle sensor 32 are set so that the rotation angle α detected by the first rotation angle sensor 31 and the rotation angle β detected by the second rotation angle sensor 32 do not match within the maximum movement range of the turning shaft 12. Therefore, the combination of the value of the rotation angle α and the value of the rotation angle β corresponds one-to-one to the absolute position P1 of the turning shaft 12. Therefore, it is possible to instantly detect the absolute position P1 of the turning shaft 12 based on the combination of the two rotation angles α and β. The midpoint of the calculation range of the absolute position P1 calculated by the position detection circuit 51 is set as the origin, that is, the neutral steering position (steering angle θw = 0°), which is the position of the steering shaft 12 when the vehicle is traveling straight ahead.

The position control circuit 52 calculates a target absolute position of the turning shaft 12 based on the target turning angle θ ^* calculated by the above-mentioned higher-level control device 43. Since the turning shaft 12 and the turning wheels 14, 14 are linked to each other, there is a correlation between the turning shaft 12 and the turning angle θw of the turning wheels 14, 14. Using this correlation, the target absolute position of the turning shaft 12 can be obtained from the target turning angle θ ^* . The position control circuit 52 obtains a difference between the target absolute position of the turning shaft 12 and the actual absolute position P1 of the turning shaft 12 calculated by the position detection circuit 51, and calculates a current command value I ^* for the first motor 17 and the second motor 18 so as to eliminate this difference. This current command value I ^* is a command value corresponding to the total torque to be generated by the first motor 17 and the second motor 18.

The allocation calculation circuit 53 calculates a first allocation ratio _DR1 of the current command value I ^* calculated by the position control circuit 52 to the first motor 17. The first allocation ratio _DR1 is set to a value within a range of "0" to "1". In this embodiment, the value of the first allocation ratio DR1 is set to "0.5" from the viewpoint of canceling out the torque acting on the steered shaft 12 with the rotation of the first ball nut 15 and the torque acting on the steered shaft ₁₂ with the rotation of the second ball nut 16, which are torques in opposite directions. This value corresponds to 50% when the current command value I ^* calculated by the position control circuit 52 is set to 100%.

The multiplier 54 multiplies the current command value I ^* calculated by the position control circuit 52 by the first distribution ratio DR ₁ calculated by the distribution calculation circuit 53 to calculate a first current command value I ₁ ^* for the first motor 17 .

The current control circuit 55 supplies power according to the first current command value _I1 ^* calculated by the multiplier 54 to the first motor 17. This causes the first motor 17 to generate torque according to the first current command value _I1 ^* .

The subtractor 56 calculates a second allocation ratio DR2 of the current command value I* to the second motor 18 by subtracting the first allocation ratio _DR1 calculated by the allocation calculation circuit 53 from "1", which is a fixed value stored in the storage device of the first control device ^41. In this embodiment, since the first allocation ratio DR1 is set to "0.5", the value of the second allocation ratio _DR2 is "0.5 _" .

In this manner, the first control device 41 includes the allocation calculation circuit 53 that calculates the first allocation ratio _DR1 and the subtractor 56 that calculates the second allocation ratio _DR2 . That is, in this embodiment, the first allocation ratio _DR1 and the second allocation ratio _DR2 that allocate the current command value I ^* , which is a command value, are set by the first control device 41.

As shown in FIG. 2, the second control device 42 has a position detection circuit 61 , a position control circuit 62 , a multiplier 63 and a current control circuit 64 .
The position detection circuit 61 receives the rotation angle α of the first motor 17 detected via the first rotation angle sensor 31 and the rotation angle β of the second motor 18 detected via the second rotation angle sensor 32, and calculates the absolute position P2 of the steered shaft 12 based on these received rotation angles α, β. However, the position detection circuit 61 is a backup for the first control device 41, and is kept in a stopped state in the normal state where the first control device 41 is operating normally.

The position control circuit 62 calculates a target absolute position of the steered shaft 12 based on the target steering angle θ ^* calculated by the above-mentioned higher-level control device 43. The position control circuit 62 determines the difference between the target absolute position of the steered shaft 12 and the actual absolute position P2 of the steered shaft 12 calculated by the position detection circuit 61, and calculates a current command value I ^* according to the total torque to be generated by the first motor 17 and the second motor 18 so as to eliminate this difference. However, the position control circuit 62 is used as a backup for the first control device 41, and is kept in a stopped state in the normal state in which the first control device 41 is operating normally.

The multiplier 63 calculates a second current command value I2* for the second motor 18 by multiplying the second ^distribution ratio _DR2 calculated by the subtractor 56 of the first control device 41 by the current command value _I ^* calculated by the position control circuit 52 of the first control device 41.

The current control circuit 64 supplies power according to the second current command value _I2 ^* calculated by the multiplier 63 to the second motor 18. This causes the second motor 18 to generate torque according to the second current command value _I2 ^* .

<Functions and Effects of the First Embodiment>
Therefore, according to the first embodiment, the following actions and effects can be obtained.
(1) A current command value I ^* is calculated as a total for the first motor 17 and the second motor 18 through feedback control of the absolute position P1 of the steered shaft 12 by the position control circuit 52 of the first control device 41. The calculated current command value I _* is allocated as a first current command value _I1 ^* for the first motor 17 based on a first allocation ratio _DR1 calculated by an allocation calculation circuit 53, and is also allocated as a second current command value _I2 ^* for the second motor 18 based on a second allocation ratio _DR2 calculated by a subtractor 56. Then, a current corresponding to the allocated first current command value _I1 ^* is supplied to the first motor 17, and a current corresponding to the second current command value _I2 ^* is supplied to the second motor 18.

In this way, when the first motor 17 and the second motor 18 operate in cooperation with each other, the currents supplied to the first motor 17 and the second motor 18 are determined by the first control device 41. The second control device 42 only operates to supply a current corresponding to an individual current command value ( _I2 ^* ) based on the second distribution ratio _DR2 unilaterally determined by the first control device 41 to the second motor 18, which is the object of control of the first control device 41. That is, the first control device 41 and the second control device 42 are in a relationship of a master and a slave. For this reason, unlike a case in which the first control device 41 and the second control device 42 each perform position control to individually calculate a current command value for the motor, which is the object of control of the first control device 41, and control the power supply to the motor, which is the object of control of the second control device 42, based on the individually calculated current command values, the control of the first control device 41 and the control of the second control device 42 are prevented from interfering with each other.

As a specific example, due to lead errors of the first ball screw portion 12a and the second ball screw portion 12b of the steered shaft 12, the position feedback control of the steered shaft 12 by the first control device 41 and the position feedback control of the steered shaft 12 by the second control device 42 do not interfere with each other. Therefore, the first motor 17 and the second motor 18 operate appropriately in coordination with each other, so that the steered wheels 14, 14 can be steered more appropriately.

(2) Furthermore, the steering device 10 has the first ball screw _BS1 and the second ball screw _BS2 as elastic elements, and while the first control device 41 executes position feedback control of the steering shaft 12, the second control device 42 does not execute position feedback control of the steering shaft 12. Therefore, unlike a case in which position feedback control of the steering shaft 12 is executed in both the first control device 41 and the second control device 42, resonance is unlikely to occur in the steering device 10. Therefore, it is possible to suppress the generation of vibrations or abnormal noises accompanying the steering operation of the steering device 10.

Second Embodiment
Next, a second embodiment of the steering device will be described. This embodiment has a configuration basically similar to that of the first embodiment shown in Fig. 1, and the same components are denoted by the same reference numerals as in the first embodiment, and the description thereof will be omitted.

In the steering device 10, the first ball screw portion 12a and the first ball nut 15 of the steering shaft 12, and the second ball screw portion 12b and the second ball nut 16 of the steering shaft 12 may wear or rust due to long-term use. There is a concern that wear or rust of the first ball screw _BS1 and the second ball screw _BS2 may cause an abnormal increase in friction when the first ball nut 15 and the second ball nut 16 attempt to rotate relative to the steering shaft 12. In other words, wear or rust of the first ball screw _BS1 and the second ball screw _BS2 reduces the motion transmission characteristics of the steering device 10, and therefore has a significant effect on the positioning accuracy of the steering shaft 12, and therefore on the motion accuracy of the steering device 10, or on the accuracy of the steering operation of the steered wheels 14, 14.

Therefore, in this embodiment, in order to detect an abnormal increase in friction in the first ball screw _BS1 or the second ball screw _BS2 , the following configurations are adopted for the first control device 41 and the second control device 42.

As shown in Fig. 3, the first control device 41 has a first current sensor 57. The first current sensor 57 is provided in a power supply path 58 between the current control circuit 55 and the first motor 17. The first current sensor 57 detects a current value _I1 which is a value of a current supplied from the current control circuit 55 to the first motor 17. The second control device 42 has a second current sensor 65. The second current sensor 65 is provided in a power supply path 66 between the current control circuit 64 and the second motor 18. The second current sensor 65 detects a current value _I2 which is a value of a current supplied from the current control circuit 64 to the second motor 18.

The allocation calculation circuit 53 of the first control device 41 has an abnormality detection function that detects an abnormal increase in friction in the first ball screw BS ₁ or the second ball screw BS _2. The allocation calculation circuit 53 starts executing the abnormality detection process when a predetermined execution condition is satisfied. The execution condition may be, for example, the following condition (A).

(A) The vehicle is being steered while the vehicle is stationary. Stationary steering refers to operating the steering wheel while the vehicle is stationary, and thus steering the steered wheels 14, 14. When stationary steering is being performed, the load axial force of the steered shaft 12 becomes greater, and therefore an increase in friction of the first ball screw _BS1 or the second ball screw _BS2 is more likely to be reflected by the current values of the first motor 17 and the second motor 18.

The distribution calculation circuit 53 receives the vehicle speed V detected by a vehicle speed sensor (not shown) provided on the vehicle and the absolute position P1 of the steering shaft 12 calculated by the position detection circuit 51 to determine whether the conditions for executing the abnormality detection process are met. The distribution calculation circuit 53 calculates the movement speed of the steering shaft 12 by differentiating the absolute position P1 of the steering shaft 12 obtained through the position detection circuit 51. The distribution calculation circuit 53 determines that stationary steering is being performed, for example, when the vehicle speed is "0" and the movement speed of the steering shaft 12 is not "0".

Furthermore, in order to detect an abnormal increase in friction in the first ball screw _BS1 and the second ball screw _BS2 , the distribution calculation circuit 53 takes in the current value _I1 of the first motor 17 detected via the first current sensor 57 and the current value _I2 of the second motor 18 detected via the second current sensor 65. The distribution calculation circuit 53 detects an abnormal increase in friction in the first ball screw _BS1 and the second ball screw _BS2 based on these taken-in current values _I1 , _I2 .

When the friction of the first ball screw _BS1 or the second ball screw _BS2 increases abnormally, the smooth operation of the first ball screw _BS1 or the second ball screw _BS2 is hindered, and the force required to operate the first ball screw _BS1 or the second ball screw _BS2 increases accordingly. Therefore, the load torque of the first motor 17 and the second motor 18 increases according to the degree of increase in friction of the first ball screw _BS1 and the second ball screw _BS2 . The load torque refers to a force that tries to stop the rotation of the output shaft 17a of the first motor 17 and the output shaft 18a of the second motor 18. Here, the current flowing through the first motor 17 and the second motor 18 becomes large in proportion to the magnitude of the load torque (T-I characteristic). Therefore, it is possible to detect an abnormal increase in friction of the first ball screw _BS1 and the second ball screw _BS2 based on the current flowing through the first motor 17 and the second motor 18. In detail, the q-axis current value flowing through the first motor 17 and the second motor 18 is calculated, and this calculated q-axis current value is used to detect abnormalities in the first ball screw BS ₁ and the second ball screw BS _2. The abnormality detection process executed by the distribution calculation circuit 53 will be described in detail later.

When an abnormal increase in friction in the first ball screw _BS1 or the second ball screw _BS2 is detected, the allocation calculation circuit 53 generates an alarm command signal Sw for an alarm device 70 provided in the vehicle cabin, for example. The alarm command signal Sw is a command for causing the alarm device 70 to perform a predetermined alarm operation. The alarm device 70 performs the alarm operation based on the alarm command signal Sw. Examples of the alarm operation include emitting an alarm sound and displaying a warning on a display provided in the vehicle cabin.

<Procedure for abnormality detection process>
Next, the procedure of the abnormality detection process executed by the distribution calculation circuit 53 will be described with reference to the flowchart of Fig. 4. The process of this flowchart is executed when a predetermined execution condition such as the above-mentioned condition (A) is satisfied. During normal vehicle running when the abnormality detection process is not executed, the first distribution ratio _DR1 and the second distribution ratio _DR2 are each set to "0.5". This is based on the viewpoint of canceling out the torque acting on the steered shaft 12 with the rotation of the first ball nut 15 and the torque acting on the steered shaft 12 with the rotation of the second ball nut 16, which are torques in opposite directions.

As shown in the flowchart of FIG. 4, the distribution calculation circuit 53 changes the first distribution ratio DR ₁ of the current command value I ^* for the first motor 17 and the second distribution ratio DR ₂ of the current command value I ^* for the second motor 18 from equal distribution ratios to unequal distribution ratios (step S101).

The allocation calculation circuit 53 sets either one of the first allocation ratio _DR1 for the first motor 17 and the second allocation ratio _DR2 for the second motor 18 to a value exceeding "0.5", and sets the other allocation ratio to a value less than the remaining "0.5". However, the sum of the first allocation ratio _DR1 and the second allocation ratio _DR2 is "1". Here, the allocation calculation circuit 53 changes, for example, the first allocation ratio _DR1 from "0.5" to "0.7", and changes the second allocation ratio _DR2 from "0.5" to "0.3".

Next, the allocation calculation circuit 53 receives the current value _I1 of the first motor 17 detected by the first current sensor 57 and the current value _I2 of the second motor 18 detected by the second current sensor 65 (step S102), and calculates a first sum _IΣ1 of the received current values _I1 and _I2 (step S103). The allocation calculation circuit 53 temporarily stores the first sum _IΣ1 calculated in step S103 in a storage device (not shown).

Next, the allocation calculation circuit 53 replaces the value of the first allocation ratio _DR1 of the current command value I ^* for the first motor 17 set in the previous step S101 with the value of the second allocation ratio _DR2 of the current command value I ^* for the second motor 18 (step S104). Here, the allocation calculation circuit 53 changes the first allocation ratio _DR1 for the first motor 17 from "0.7" to "0.3", and changes the second allocation ratio _DR2 for the second motor 18 from "0.3" to "0.7".

Next, the allocation calculation circuit 53 takes in the current value _I1 of the first motor 17 detected by the first current sensor 57 and the current value _I2 of the second motor 18 detected by the second current sensor 65 (step S105), and calculates a second sum _IΣ2 of these taken current values _I1 and _I2 (step S106).

However, the processes from step S101, in which the distribution ratio of the current command value I ^* to the first motor 17 and the second motor 18 is changed to an unequal distribution ratio, to step S106, in which the second total value _IΣ2 is calculated, are performed within a time or movement distance in which the load axial force of the steered shaft 12 accompanying the movement of the steered shaft 12 can be regarded as constant. Incidentally, in order to eliminate bias due to the detection order, the processes of steps S101 to S106 may be repeated multiple times. In this case, the order in which the two distribution ratios (DR ₁ , DR ₂ ) are set to values exceeding "0.5" or less than "0.5" may be alternated.

Next, the allocation calculation circuit 53 calculates the difference ΔI _Σ between the first total value I _Σ1 calculated in the previous step S103 and the second total value I _Σ2 calculated in the previous step S106 (step S107), and determines whether the absolute value of the calculated difference ΔI _Σ is within a defined threshold range ΔI _th (S108).

The threshold range _ΔIth is set according to the detection accuracy of an increase in friction of the first ball screw _BS1 and the second ball screw BS2 required for the steering device _10. The threshold range _ΔIth is defined by an upper limit value and a lower limit value that are set based on the absolute value of the difference _ΔIΣ between the first total value _IΣ1 and the second total value _IΣ2 in an ideal state in which no wear or the like is occurring in the first ball _{screw BS1} and the second ball screw BS2.

When the distribution calculation circuit 53 determines that the absolute value of the difference ΔI _Σ is within the threshold range ΔI _th (YES in step S108), that is, when the absolute value of the difference ΔI _Σ is greater than or equal to the lower limit value and less than or equal to the upper limit value of the threshold range ΔI _th , it determines that no abnormality has occurred in the first ball screw _BS1 and the second ball screw _BS2 (step S109), and terminates the processing.

On the other hand, when it is determined that the absolute value of the difference _ΔIΣ is not within the threshold range _ΔIth (NO in step S108), that is, when the absolute value of the difference _ΔIΣ exceeds the upper limit value or falls below the lower limit value, the distribution calculation circuit 53 determines that an abnormality has occurred in the first ball screw _BS1 and the second ball screw _BS2 (step S110). Specifically, the distribution calculation circuit 53 determines that the abnormality in the first ball screw _BS1 and the second ball screw _BS2 is that the friction of either the first ball screw _BS1 or the second ball screw _BS2 has abnormally increased.

Then, the allocation calculation circuit 53 generates a notification command signal Sw for the notification device 70 (step S111) and ends the process. The notification device 70 performs a predetermined notification operation in response to receiving the notification command signal Sw. The driver of the vehicle can become aware of the abnormality in the ball screw through the notification operation of the notification device 70.

<Technical significance of unequal distribution processing>
Next, the technical significance of the process executed in step S101 above to change the first allocation ratio _DR1 and the second allocation ratio _DR2 from equal allocation ratios to unequal allocation ratios will be described.

That is, the larger the value of the first distribution ratio _DR1 , the more likely the influence of the increase in friction of the first ball screw _BS1 is reflected in the current value _I1 of the first motor 17. Also, the larger the value of the second distribution ratio _DR2 , the more likely the influence of the increase in friction of the second ball screw _BS2 is reflected in the current value _I2 of the second motor 18. For example, assuming that the friction of the second ball screw _BS2 is increasing, the total value of the current value _I1 of the first motor 17 and the current value _I2 of the second motor 18 is larger when the value of the second distribution ratio _DR2 is set to the previous "0.7" than when it is set to the previous "0.3". The increase in the total value of the current value _I1 of the first motor 17 and the current value _I2 of the second motor 18 appears as the difference _ΔIΣ between the first total value _IΣ1 before the distribution ratio exchange and the second total value _IΣ2 after the distribution ratio exchange. Therefore, when detecting an abnormal increase in friction in the first ball screw _BS1 and the second ball screw _BS2 , it is preferable to change the first distribution ratio _DR1 and the second distribution ratio _DR2 from an equal distribution ratio to an unequal distribution ratio.

In addition, if the process of the previous step S101 is not executed and the first distribution ratio _DR1 and the second distribution ratio _DR2 remain set to "0.5", which is the standard operating condition of the steering device 10, it may be difficult to detect the increase in friction of the first ball screw _BS1 and the second ball screw BS2. This is because the values of the first distribution ratio _DR1 and the second distribution ratio _DR2 do not change before and after the switching of the distribution _ratios , so there is a risk that the total value of the current of the first motor 17 and the second motor 18 does not change significantly before and after the switching of the distribution ratios. In other words, the increase in friction of the first ball screw _BS1 and the second ball screw _BS2 is not easily reflected as the value of the difference _ΔIΣ between the first total value _IΣ1 before the switching of the distribution ratios and the second total value _IΣ2 after the switching of the distribution ratios. For this reason, when detecting an abnormal increase in friction in the first ball screw _BS1 and the second ball screw _BS2 , it is preferable to change the first distribution ratio _DR1 and the second distribution ratio _DR2 from an equal distribution ratio to an unequal distribution ratio.

<Advantages of the Second Embodiment>
Therefore, according to the second embodiment, in addition to the effects (1) and (2) of the first embodiment, the following effect can be obtained.

(3) Based on the current value _I1 of the first motor 17 and the current value _I2 of the second motor 18, an abnormal increase in friction caused by wear of the first ball screw _BS1 and the second ball screw _BS2 , etc., can be detected.

(4) When an abnormal increase in friction in the first ball screw _BS1 and the second ball screw _BS2 is detected, the fact is notified via the notification device 70. As a result, for example, the driver can be prompted to take some kind of measure, such as inspecting or repairing the steering device 10.

Third Embodiment
Next, a third embodiment of the steering device will be described. This embodiment basically has the same configuration as the second embodiment shown in Figures 1 and 3, and the same components are denoted by the same reference numerals as in the second embodiment, and the description thereof will be omitted.

In the judgment process of step S108 in the flowchart of Fig. 4, it is possible to judge that the friction of either the first ball screw _BS1 or the second ball screw _BS2 has increased abnormally, but it is difficult to identify the ball screw with the increased friction. Therefore, in this embodiment, the ball screw with the abnormally increased friction is identified as follows.

For the sake of simplicity, assume that, for example, as represented by the following formula (B1), in the previous step S101, the first allocation ratio _DR1 is changed from "0.5" to "1" and the second allocation ratio _DR2 is changed from "0.5" to "0". In this case, as represented by the following formula (B2), the value of the first allocation ratio _DR1 and the value of the second allocation ratio _DR2 are swapped in the previous step S104, so that the first allocation ratio _DR1 is changed from "1" to "0" and the second allocation ratio _DR2 is changed from "0" to "1".

DR ₁ :DR ₂ =1:0...(B1)
DR ₁ :DR ₂ =0:1...(B2)
In step S108, when the following two conditions (C1) and (C2) are both satisfied, the distribution calculation circuit 53 determines that the friction of the second ball screw _BS2 corresponding to the second motor 18 is abnormal. It is determined that the number of cases has increased.

(C1) The absolute value of the difference ΔI _Σ between the first total value I _Σ1 before the allocation ratio is swapped and the second total value I _Σ2 after the allocation ratio is swapped is a value outside the threshold range ΔI _th .
(C2) The second total value _IΣ2 after the allocation ratio is switched is greater than the first total value _IΣ1 before the allocation ratio is switched.

When both conditions (C1) and (C2) are satisfied, the following situation is assumed. That is, the load torque of the second motor 18 increases abnormally due to an abnormal increase in friction of the second ball screw _BS2 , and the current value _I2 of the second motor 18 becomes abnormally large accordingly. As a result, it is assumed that the second total value _IΣ2 after the allocation ratio is switched becomes larger than the first total value _IΣ1 before the allocation ratio is switched. When the friction of both the first ball screw _BS1 and the second ball screw _BS2 is normal, the first total value _IΣ1 before the allocation ratio is switched and the second total value _IΣ2 after the allocation ratio is switched are considered to be ideally the same value.

In addition, in the previous step S108, when both of the following two conditions (D1) and (D2) are satisfied, the distribution calculation circuit 53 determines that the friction of the first ball screw _BS1 corresponding to the first motor 17 has abnormally increased.

(D1) The absolute value of the difference ΔI _Σ between the first total value I _Σ1 before the allocation ratio is swapped and the second total value I _Σ2 after the allocation ratio is swapped is a value outside the threshold range ΔI _th .
(D2) The second total value _IΣ2 after the allocation ratio is switched is smaller than the first total value _IΣ1 before the allocation ratio is switched.

When both conditions (D1) and (D2) are satisfied, the following situation is assumed: An abnormal increase in friction of the first ball screw _BS1 causes an abnormal increase in the load torque of the first motor 17, and the current value _I1 of the first motor 17 becomes abnormally large accordingly. As a result, it is assumed that the second total value _IΣ2 after the allocation ratio exchange becomes smaller than the first total value _IΣ1 before the allocation ratio exchange.

<Advantages of the Third Embodiment>
Therefore, according to the third embodiment, in addition to the effects (1) and (2) of the first embodiment and the effects (3) and (4) of the second embodiment, the following effects can be obtained.

(5) Based on the current value _I1 of the first motor 17 and the current value _I2 of the second motor 18, it is possible to identify which of the first ball screw _BS1 and the second ball screw _BS2 has an abnormal increase in friction.

<Fourth embodiment>
Next, a fourth embodiment of the steering device will be described. This embodiment basically has the same configuration as the first embodiment shown in Fig. 1, and the same components are denoted by the same reference numerals as in the first embodiment, and the description thereof will be omitted.

As shown in Fig. 5, the first control device 41 does not have the distribution calculation circuit 53 and the subtractor 56. The higher-level control device 43 provided outside the first control device 41 and the second control device 42 has a distribution calculation circuit 72 and a subtractor 73 in addition to a target turning angle calculation circuit 71 that calculates the target turning angle θ ^* . The target turning angle calculation circuit 71 calculates the target turning angle θ ^* based on signals input from various sensors mounted on the vehicle.

The allocation calculation circuit 72 calculates a first allocation ratio DR ₁ of the current command value I ^* to the first motor 17 , similarly to the allocation calculation circuit 53 of the first embodiment.
The subtractor 73 calculates a second allocation ratio DR2 of the current command value I* for the second motor ₁₈ by subtracting the first allocation ratio _DR1 calculated by the allocation calculation circuit 72 from “1”, which is a fixed value stored in the memory device of the higher-level control device ⁴³ .

The multiplier 54 of the first control device 41 calculates a first current command value I1* for the first motor 17 by multiplying the first distribution ratio _DR1 calculated by the distribution calculation circuit 72 by the current command value _I ^* calculated by the position control circuit 52. Then, the current control circuit 55 supplies power according to the first current command value _I1 ^* calculated ^by the multiplier 54 to the first motor 17, similar to the first embodiment.

The multiplier 63 of the second control device 42 calculates a second current command value I2 ^{* for the second motor 18 by multiplying the current command value I*} by the second distribution ratio _DR2 calculated by the subtractor 73 of the higher-level control device 43. Then, the current control circuit 64 supplies power according to the second current command value _I2 ^* calculated ^by the multiplier ₆₃ to the second motor 18, similar to the first embodiment.

Similar to the third embodiment, the distribution calculation circuit 72 detects an abnormal increase in friction caused by wear of the first ball screw _BS1 and the second ball screw _BS2 , based on the current value _I1 of the first motor 17 and the current value I2 of the second motor 18. The distribution calculation circuit 72 receives the current value _I1 of the first motor 17 and the current value _I2 of the second motor 18 from the first control device ₄₁ and the second control device 42 using a communication path not shown. The distribution calculation circuit 72 starts executing the abnormality detection process when, for example, the above condition (A) is satisfied.

According to the fourth embodiment, it is possible to obtain the same actions and effects as those of (1) and (2) in the first embodiment, (3) and (4) in the second embodiment, and (5) in the second embodiment.

Fifth embodiment
Next, a fifth embodiment of the steering device will be described. This embodiment basically has the same configuration as the first embodiment shown in Fig. 1, and the same components are denoted by the same reference numerals as in the first embodiment, and the description thereof will be omitted.

As shown in FIG. 6, the first control device 41 has a position detection circuit 51, a position control circuit 52, an allocation calculation circuit 53, a multiplier 54, a current control circuit 55, and a subtractor 56, as well as a current command value calculation circuit 81.

As in the first embodiment, the position control circuit 52 determines the difference between the target absolute position of the steered shaft 12 and the actual absolute position P1 of the steered shaft 12 calculated by the position detection circuit 51. The position control circuit 52 then calculates a torque command value T ^* for the first motor 17 and the second motor 18 so as to eliminate this difference. This torque command value T ^* is a command value that indicates the total torque to be generated by the first motor 17 and the second motor 18.

The multiplier 54 multiplies the torque command value T ^* calculated by the position control circuit 52 by the first allocation ratio _DR1 calculated by the allocation calculation circuit 53 to calculate a first torque command value _T1 ^* which is an individual command value for the first motor 17.

The current command value calculation circuit 81 calculates the first current command value I _{1 * by dividing the first torque command value T 1 *} ^calculated by the multiplier 54 by a coefficient (torque constant) according to the motor constant of the first motor ¹⁷ .

The current control circuit 55 supplies the first motor 17 with electric power according to the first current command value I ₁ ^* calculated by the current command value calculation circuit 81 , in the same manner as in the first embodiment.
The second control device 42 has a position detection circuit 61 , a position control circuit 62 , a multiplier 63 , and a current control circuit 64 , as well as a current command value calculation circuit 82 .

The position control circuit 62 calculates the torque command value T ^* in the same manner as the position control circuit 52 of the first control device 41. However, the position control circuit 62 is a backup for the first control device 41, and is kept in a stopped state in the normal state in which the first control device 41 is operating normally.

The multiplier 63 calculates a second torque command value T2*, which is an individual command value for the second motor 18, by multiplying the torque command value _T ^* calculated by the position control circuit 52 of the first control device 41 by the second distribution ratio _DR2 calculated by the subtractor ⁵⁶ of the first control device 41.

The current command value calculation circuit 82 calculates the second current command value I _{2 * by dividing the second torque command value T 2 *} ^calculated by the multiplier 63 by a coefficient (torque constant) according to the motor constant of the second motor ¹⁸ .

The current control circuit 64 supplies, to the second motor 18, electric power according to the second current command value I ₂ ^* calculated by the current command value calculation circuit 82, in the same manner as in the first embodiment.
According to the fifth embodiment, it is possible to obtain the same functions and effects as those (1) and (2) of the first embodiment.

Sixth embodiment
Next, a sixth embodiment of the steering device will be described. This embodiment basically has the same configuration as the first embodiment shown in Fig. 1, and the same components are denoted by the same reference numerals as in the first embodiment, and the description thereof will be omitted.

As shown in FIG. 7, the first control device 41 has a position detection circuit 51, a position control circuit 52, an allocation calculation circuit 53, a current control circuit 55, and a subtractor 56, as well as a first current sensor 91. The first control device 41 of this embodiment does not have a multiplier 54.

The position control circuit 52 calculates a d-axis current command value I _d ^* and a q-axis current command value I _q ^* in the dq coordinate system. The q-axis current command value I _q ^* is a command value corresponding to the total torque to be generated by the first motor 17 and the second motor 18. The d-axis current command value I _d ^* is basically set to zero.

The first current sensor 91 is provided in a power supply path 92 between the current control circuit 55 and the first motor 17. The first current sensor 91 detects current values _Iu1 , _Iv1 , _Iw1 of each phase supplied from the current control circuit 55 to the first motor 17. For ease of explanation, the power supply path 92 of each phase and the first current sensor 91 of each phase are illustrated as being one each in FIG.

The current control circuit 55 takes in the d-axis current command value _Id ^* and the q-axis current command value _Iq ^* calculated by the position control circuit 52, the allocation ratio _DR1 calculated by the allocation calculation circuit 53, and a second d-axis current value _Id2 and a second q-axis current value _Iq2 calculated by a current control circuit 64 of the second control device 42 as described below. The current control circuit 55 also takes in the rotation angle α of the first motor 17 detected by the first rotation angle sensor 31, and the current values _Iu1 , _Iv1 , and _Iw1 detected by the first current sensor 91. The current control circuit 55 supplies current to the first motor 17 based on the execution of current feedback control (hereinafter also referred to as "current F/B control") in the dq coordinate system.

The second control device 42 has a second current sensor 93 in addition to the position detection circuit 61, the position control circuit 62, and the current control circuit 64. The second control device 42 of this embodiment does not have a multiplier 63.

The position control circuit 62 calculates the d-axis current command value I _d ^* and the q-axis current command value I _q ^* , similar to the position control circuit 52 of the first control device 41. However, the position control circuit 62 is a backup for the first control device 41, and is kept in a stopped state in the normal state in which the first control device 41 is operating normally.

The second current sensor 93 is provided in a power supply path 94 between the current control circuit 64 and the second motor 18. The second current sensor 93 detects current values _Iu2 , _Iv2 , _Iw2 of each phase supplied from the current control circuit 64 to the second motor 18. For ease of explanation, the power supply paths 94 of each phase and the second current sensors 93 of each phase are illustrated as being one each in FIG.

The current control circuit 64 takes in the d-axis current command value _Id ^* and the q-axis current command value _Iq ^* calculated by the position control circuit 52, the distribution ratio _DR2 calculated by the subtractor 56, and the first d-axis current value _Id1 and the first q-axis current value _Iq1 calculated by the current control circuit 55 of the first control device 41 as described below. The current control circuit 64 also takes in the d-axis current command value _Id ^* and the q-axis current command value _Iq ^* calculated by the position control circuit 62, the rotation angle β of the second motor 18 detected by the second rotation angle sensor 32, and the current values _Iu2 , _Iv2 , _Iw2 detected by the second current sensor 93. The current control circuit 64 then supplies a current to the second motor 18 based on the execution of current F/B control in the dq coordinate system.

Next, we will explain the current feedback control by the current control circuits 55 and 64. The current control circuits 55 and 64 supply current to the first motor 17 and the second motor 18, respectively, by executing the calculation processes shown in the following control blocks at each predetermined calculation cycle.

8, the current control circuit 55 of the first control device 41 includes a first three-phase to two-phase conversion unit 101, a first current F/B control unit 102, first multipliers 103 and 104, a first two-phase to three-phase conversion unit 105, a first PWM conversion unit 106, a first control signal generation unit 107, and a first inverter unit 108. The current control circuit 64 of the second control device 42 includes a second three-phase to two-phase conversion unit 111, a second current F/B control unit 112, second multipliers 113 and 114, a second two-phase to three-phase conversion unit 115, a second PWM conversion unit 116, a second control signal generation unit 117, and a second inverter unit 118. The first inverter unit 108 and the second inverter unit 118 each use a well-known PWM inverter having multiple switching elements such as FETs.

The first three-phase to two-phase conversion unit 101 receives the current values _Iu1 , _Iv1 , _Iw1 of each phase and the rotation angle α. The first three-phase to two-phase conversion unit 101 maps the current values _Iu1 , _Iv1 , _Iw1 of each phase onto the dq coordinate system based on the rotation angle α to calculate a first d-axis current value _Id1 and a first q-axis current value _Iq1 .

The second three-phase to two-phase conversion unit 111 receives the current values _Iu2 , _Iv2 , and _Iw2 of each phase and the rotation angle β. The second three-phase to two-phase conversion unit 111 calculates a second d-axis current value _Id2 and a second q-axis current value _Iq2 by mapping the current values _Iu2 , _Iv2 , and _Iw2 of each phase onto the dq coordinate system based on the rotation angle β.

The first current F/B control unit 102 receives the d-axis current command value _Id ^* and the q-axis current command value _Iq ^* calculated by the position control circuit 52, the first d-axis current value _Id1 and the first q-axis current value _Iq1 calculated by the first three-phase to two-phase conversion unit 101, and the second d-axis current value _Id2 and the second q-axis current value _Iq2 calculated by the second three-phase to two-phase conversion unit 111. The first current F/B control unit 102 calculates the d-axis current value _Id by adding the first d-axis current value _Id1 and the second d-axis current value _Id2 , and calculates the q-axis current value _Iq by adding the first q-axis current value _Iq1 and the second q-axis current value _Iq2 . The first current F/B control unit 102 executes a current F/B control calculation to make the d-axis current value _Id follow the d-axis current command value _Id ^* and the q-axis current value _Iq follow the q-axis current command value _Iq ^* , thereby calculating a d-axis voltage command value _Vd ^* and a q-axis voltage command value _Vq ^* , which are command values. The first current F/B control unit 102 executes a PID control calculation as an example of a current F/B control calculation.

The first multiplier 103 multiplies the d-axis voltage command value V _{d * by the first allocation ratio DR 1 calculated by the allocation calculation circuit 53 to calculate a first d-axis voltage command value V d1 * which is an individual command value for the first motor 17. The first multiplier 104 multiplies the q-axis voltage command value V q} ^* _{by the} ^first _allocation ^ratio DR ₁ to calculate a first q-axis voltage command value V _q1 ^* which is an individual command value for the first motor 17.

The first two-phase to three-phase conversion unit 105 takes in the first d-axis voltage command value V _d1 ^* and the first q-axis voltage command value V _q1 ^* as well as the rotation angle α. The first two-phase to three-phase conversion unit 105 calculates three-phase first voltage command values V _u1 *, V _v1 ^* , V _w1 ^* by mapping the first d-axis voltage command value V _d1 ^{* and} the first q-axis voltage command value V _q1 ^* onto a three-phase AC coordinate based on the rotation angle α.

The first PWM conversion unit 106 calculates first duty command values D _u1 ^* , D _v1 ^* , D _w1 ^* based on the first voltage command values V _u1 ^* , V _v1 ^* , V _w1 ^* . The first duty command values D _u1 ^* , D _v1 ^* , D _w1 ^* specify the duty ratio of each switching element constituting the first inverter unit 108. The duty ratio refers to the proportion of the on-time of a switching element in a pulse period.

The first control signal generating unit 107 generates a control signal having a duty ratio indicated by the first duty command values D _u1 ^* , D _v1 ^* , D _w1 ^* through ^comparison with a PWM _carrier which is a carrier wave such as a _triangular wave or a sawtooth wave. The control signal calculated in this manner is output to the first _inverter unit 108, ^which supplies power to the first motor ¹⁷ according to the control signal.

The second current F/B control unit 112 takes in the d-axis current command value I _d ^* and the q-axis current command value I _q ^* calculated by the position control circuit 62, the first d-axis current value I _d1 and the first q-axis current value I _q1 calculated by the first three-phase to two-phase conversion unit 101, and the second d-axis current value I _d2 and the second q-axis current value I _q2 calculated by the second three-phase to two-phase conversion unit 111. The second current F/B control unit 112, like the first current F/B control unit 102, calculates a d-axis voltage command value V _d ^* and a q-axis voltage command value V _q ^* , which are command values.

The second multiplier 113 multiplies the d-axis voltage command value V _d ^* by the second allocation ratio DR ₂ calculated by the subtractor 56 of the first control device 41 to calculate a second d-axis voltage command value V _d2 ^* which is an individual command value for the second motor 18. The second multiplier 114 multiplies the q-axis voltage command value V _q ^* by the second allocation ratio DR ₂ to calculate a second q-axis voltage command value V _q2 ^* which is an individual command value for the second motor 18.

The second two-phase to three-phase conversion unit 115 takes in the second d-axis voltage command value _Vd2 ^* and the second q-axis voltage command value _Vq2 ^* as well as the rotation angle β. The second two-phase to three-phase conversion unit 115 calculates three-phase second voltage command values _Vu2 *, _Vv2 ^* , _Vw2 ^* by mapping the second d-axis voltage command value Vd2 ^* and the second q-axis voltage command value _Vq2 ^* onto the three-phase AC coordinate _system based on the rotation angle ^β .

The second PWM conversion unit 116 calculates second duty command values D _u2 ^* , D _v2 ^* , D _w2 * based on the second voltage command values V _u2 ^* , V _v2 ^* , V _w2 ^* . The second duty command values D _u2 ^* , D _v2 ^* , D _w2 ^* specify the duty ^ratios of the switching elements constituting the second inverter unit 118.

The second control signal generating unit 117 generates control signals having duty ratios indicated by the second duty command values D _u2 ^* , D _v2 ^* , and D _w2 ^* , similarly to the first control signal generating unit 107. The control signals calculated in this manner are output to the second inverter unit 118, whereby power corresponding to the control signals is supplied to the second motor 18.

According to the sixth embodiment, it is possible to obtain the same functions and effects as those (1) and (2) of the first embodiment.
<Other embodiments>
The first to sixth embodiments may be modified as follows.

- In the sixth embodiment, the voltage command value is allocated to individual command values corresponding to the first motor 17 and the second motor 18, but this is not limited thereto. For example, the duty command value may be allocated to individual command values corresponding to the first motor 17 and the second motor 18.

In the first to fifth embodiments, current may be supplied to the first motor 17 and the second motor 18 based on the execution of current feedback control in the dq coordinate system.
In the fourth embodiment, similarly to the second embodiment, the distribution calculation circuit 72 may detect only that the friction of either the first ball screw _BS1 or the second ball screw _BS2 is abnormally increased, and may not need to identify the ball screw with the increased friction. Also, the distribution calculation circuit 72 may not need to detect the abnormal increase in friction of the first ball screw _BS1 or the second ball screw _BS2 .

In the fifth or sixth embodiment, the allocation calculation circuit 53 may detect an abnormal increase in friction caused by wear of the first ball screw _BS1 and the second ball screw _BS2 , or the like, based on the current value _I1 of the first motor 17 and the current value _I2 of the second motor 18, as in the second or third embodiment.

In the third embodiment, when an abnormal increase in friction of the first ball screw _BS1 and the second ball screw _BS2 is detected, the drive of the motor corresponding to the ball screw in which the abnormality is detected may be stopped. Also, when an abnormal increase in friction of the first ball screw _BS1 and the second ball screw _BS2 is detected, the current supplied to the motor may be made less than the current that should be supplied. That is, the current supplied to the motor corresponding to the ball screw in which the abnormality is detected is made less than the current supplied to the motor corresponding to the normal ball screw. The distribution calculation circuit 53 transmits a command to the current control circuit 55, 64 of the control device corresponding to the ball screw in which the abnormality is detected to stop or limit the power supply to the motor. In this way, the ball screw in which the friction is abnormally increased can be protected. Also, the life of the ball screw in which the friction is abnormally increased can be extended.

In the second and third embodiments, the distribution calculation circuit 53 of the first control device 41 has an abnormality detection function for detecting an abnormal increase in friction in the first ball screw _BS1 and the second ball screw _BS2 , but a dedicated abnormality detection circuit having this abnormality detection function may be provided separately from the distribution calculation circuit 53. When this configuration is adopted, the abnormality detection circuit supplies a command to change the distribution ratio to the distribution calculation circuit 53 when the execution condition for the abnormality determination process is established. Then, the abnormality detection circuit detects an abnormal increase in friction in the first ball screw _BS1 and the second ball screw BS2 based on the current value _I1 of the first motor 17 and the current value _I2 of the second motor ₁₈ according to the flowchart of FIG. 4. When an abnormality in the first ball screw _BS1 and the second ball screw _BS2 is detected, the abnormality detection circuit generates a notification command signal Sw for the notification device 70.

In the second and third embodiments, the condition for determining an abnormality is that the absolute value of the difference ΔI _Σ between the first total value I Σ1 before the allocation ratio is replaced and the second total value I _Σ2 after the allocation ratio is replaced is outside the threshold range ΔI _th. However, the abnormality of _{the first ball screw BS 1 and} the second ball screw BS ₂ may be determined as follows. That is, the allocation calculation circuit 53 of the first control device 41 calculates the first total value I _Σ1 before the allocation ratio is replaced and the second total value I Σ2 after the allocation ratio is replaced through the execution of the processes of steps S101 to _S106 in the flowchart of FIG. 4. Then, when the first total value I _Σ1 and the second total value I _Σ2 are different values, the allocation calculation circuit 53 determines that the friction of either the first ball screw BS ₁ or the second ball screw BS ₂ has abnormally increased.

- In the first to sixth embodiments, the first ball screw portion 12a may be a left-handed thread, and the second ball screw portion 12b may be a right-handed thread. That is, the first ball screw portion 12a and the second ball screw portion 12b may have a reverse-thread relationship. In addition, both the first ball screw portion 12a and the second ball screw portion 12b may be right-handed or left-handed. However, if this configuration is adopted, the steering shaft 12 is provided with a rotation restriction portion for restricting the relative rotation of the steering shaft 12 with respect to the housing 11.

In the first to sixth embodiments, when the steered shaft 12 is provided with a rotation restricting unit, the first control device 41 may set the first allocation ratio _DR1 and the second allocation ratio _DR2 to unequal allocation ratios even during normal vehicle driving, regardless of whether the execution condition for the abnormality detection process is satisfied. This allows the manner of control of the first motor 17 and the second motor 18 to be flexibly adapted to the product specifications or the vehicle driving state. Furthermore, when this configuration is adopted, the determination of whether the execution condition (A) for the abnormality detection process described above is satisfied can be omitted, and the process of the flowchart in FIG. 4 can be executed.

In the first to sixth embodiments, the on-board host control device 43 may calculate a target absolute position of the steered shaft 12 according to the steering state of the vehicle or the running state of the vehicle, instead of the target steering angle θ ^* . In this case, the first control device 41 and the second control device 42 receive the target absolute position of the steered shaft 12 calculated by the host control device 43, and use this received target absolute position to control the power supply to the first motor 17 and the second motor 18.

- In the first to sixth embodiments, a configuration may be adopted in which the first belt transmission mechanism 21 is omitted as the first transmission mechanism that transmits the driving force of the first motor 17 to the steering shaft 12, and a configuration may be adopted in which the second belt transmission mechanism 22 is omitted as the second transmission mechanism that transmits the driving force of the second motor 18 to the steering shaft 12. In this case, for example, the first motor 17 and the second motor 18 are provided coaxially with the steering shaft 12. The output shaft 17a of the first motor 17 is connected to the first ball nut 15 so as to be rotatable together with the first ball nut 15, and the output shaft 18a of the second motor 18 is connected to the second ball nut 16 so as to be rotatable together with the second ball nut 16. Even when this configuration is adopted, the same effects as those of the first to sixth embodiments can be obtained.

As shown in FIG. 9, in the first to third, fifth and sixth embodiments, the allocation calculation circuit 67 and the subtractor 68 may be provided not only in the first control device 41 but also in the second control device 42. In this way, the second control device 42 can be configured in the same manner as the first control device 41 and can be used as a backup device for the first control device 41. Incidentally, the allocation calculation circuit 67 calculates the second allocation ratio DR ₂ of the current command value I ^* calculated by the position control circuit 62 to the second motor 18. The subtractor 68 calculates the first allocation ratio DR 1 of the current command value I ^* to the first motor 17 by subtracting the second allocation ratio DR ₂ calculated by the allocation calculation circuit ₆₇ from "1", which is a fixed value stored in the storage device of the second control device 42. However, the allocation calculation circuit 67 and the subtractor 68 are for backup of the first control device 41, and are maintained in a stopped state when the first control device 41 is operating normally.

- In the first to sixth embodiments, the second control device 42 may be configured without the position detection circuit 61 and the position control circuit 62. In this way, the configuration of the second control device 42 can be simplified.

The steering device 10 in the first to sixth embodiments may be applied to a by-wire type steering device in which power transmission between the steering wheel and the steered wheels is separated. A by-wire type steering device has a reaction motor which is a generating source of a steering reaction force applied to a steering shaft, and a reaction force control device which controls the drive of the reaction force motor, and some reaction force control devices calculate a target steering angle of the steering wheel based on the steering state of the vehicle or the running state of the vehicle. In this case, the first control device 41 and the second control device 42 take in the target steering angle calculated by the reaction force control device which is a higher-level control device as the target turning angle θ ^* .

<Other technical ideas>
Next, the technical ideas that can be understood from each embodiment will be additionally described below.
(A) A control system for a vehicle, comprising: a first motor (17) that generates a first driving force for steering the steered wheels of the vehicle; a second motor (18) that generates a second driving force for steering the steered wheels of the vehicle; a first control device (41) that controls the first motor; and a second control device (42) that controls the second motor, wherein the first control device includes a first circuit (52) that calculates a command value according to a total torque to be generated in the first motor and the second motor; a second circuit (53) that calculates a first distribution ratio of the command value to the first motor; and a second circuit (54) that calculates a second distribution ratio of the command value to the second motor according to the first distribution ratio calculated by the second circuit. a third circuit (56) that calculates a second allocation ratio of the command value to be supplied to the first motor, a fourth circuit (54) that calculates a first command value for the first motor by multiplying the command value by the first allocation ratio, and a fifth circuit (55) that supplies a current corresponding to the first command value calculated by the fourth circuit to the first motor, while the second control device has a sixth circuit (63) that calculates a second command value for the second motor by multiplying the command value by the second allocation ratio, and a seventh circuit (64) that supplies a current corresponding to the second command value calculated by the sixth circuit to the second motor.

10... steering device, 12... steering shaft, 12a... first ball screw section, 12b... second ball screw section, 14... steering wheel, 15... first ball nut, 16... second ball nut, 17... first motor, 18... second motor, 21... first belt transmission mechanism constituting first transmission mechanism, 22... second belt transmission mechanism constituting second transmission mechanism, 41... first control device, 42... second control device, 43... higher control device, BS ₁ ... first ball screw constituting first transmission mechanism, BS ₂ ... second ball screw constituting second transmission mechanism, DR ₁ ... first distribution ratio, DR ₂ ... second distribution ratio, I ^* ... current command value, I ₁ ^* ... first current command value, I ₂ ^* ... second current command value, _IΣ1 ... first total value, _IΣ2 ... second total value, ΔI _th ...threshold range.

Claims (13)

Two motors that generate driving forces for steering the steered wheels of a vehicle;
Two control devices each individually controlling the two motors,
One of the two control devices calculates a command value according to a total torque to be generated by the two motors so as to eliminate a difference between a target position and an actual position of the steered wheels ;
The command values are distributed at a changeable ratio set for each of the motors,
The two control devices are steering devices that supply currents to the motors that are their own control targets according to individual command values that are allocated to the motors that are their own control targets,
The steering device includes a steering shaft that steers the steered wheels, and two transmission mechanisms that transmit driving forces of the two motors individually to the steering shaft,
When a predetermined execution condition for an abnormality detection process is satisfied, the one of the control devices sets the distribution ratio of the command values for the two motors to an unequal distribution ratio and swaps the set distribution ratio between the two motors, and detects an abnormal increase in friction in the transmission mechanism by comparing the total values of the currents detected as being supplied to the two motors before and after the swapping of the distribution ratio. The steering device according to claim 1, wherein the distribution ratio of the command values to the two motors is set by one of the control devices. The steering device according to claim 1 or 2, wherein the one control device determines that the friction of one of the two transmission mechanisms has abnormally increased when the absolute value of the difference between a first sum of the currents of the two motors before the switching of the distribution ratio and a second sum of the currents of the two motors after the switching of the distribution ratio is outside a threshold range set to detect an abnormal increase in friction of the transmission mechanism. When the execution condition is satisfied, the one control device sets a first allocation ratio for a first motor corresponding to the one control device to a value smaller than a second allocation ratio for a second motor corresponding to the one control device after the swapping of the allocation ratios,
4. The steering device according to claim 3, wherein when the absolute value of the difference is outside the threshold range and when the second sum is greater than the first sum, it is determined that friction in a transmission mechanism corresponding to the second motor is abnormally increased. When the execution condition is satisfied, the one control device sets a first allocation ratio for a first motor corresponding to the one control device to a value smaller than a second allocation ratio for a second motor corresponding to the one control device after the switching of the allocation ratios,
5. A steering device as described in claim 3 or claim 4, wherein when the absolute value of the difference is outside the threshold range and when the second sum is smaller than the first sum, it is determined that friction of a transmission mechanism corresponding to the first motor is abnormally increased. The steering device according to claim 4 or 5, wherein when an abnormality is detected in one of the two transmission mechanisms, the one control device stops driving the motor corresponding to the transmission mechanism in which the abnormality is detected, or reduces the current supplied to the motor corresponding to the transmission mechanism in which the abnormality is detected to less than the current supplied to the motor corresponding to the normal transmission mechanism. a first transmission mechanism of the two transmission mechanisms has a first ball nut that is screwed into a first ball screw portion provided on the steering shaft,
A steering device as described in any one of claims 1 to 6, wherein a second transmission mechanism of the two transmission mechanisms has a second ball nut that screws into a second ball screw portion provided on the steering shaft. The steering device according to claim 7, wherein the first ball screw portion and the second ball screw portion have a reverse thread relationship with each other. Two motors that generate driving forces for steering the steered wheels of a vehicle;
Two control devices each individually controlling the two motors,
One of the two control devices calculates a command value according to a total torque to be generated by the two motors so as to eliminate a difference between a target position and an actual position of the steered wheels ;
The command values are distributed at a changeable ratio set for each of the motors,
The two control devices are steering devices that supply currents to the motors that are their own control targets according to individual command values that are allocated to the motors that are their own control targets,
The steering device includes a steering shaft that steers the steered wheels, and two transmission mechanisms that transmit driving forces of the two motors individually to the steering shaft,
Another control device, which is provided outside the two control devices, sets the distribution ratio of the command values for the two motors to an unequal distribution ratio when a specified execution condition for an abnormality detection process is satisfied, and swaps the set distribution ratio between the two motors, and detects an abnormal increase in friction in the transmission mechanism by comparing the total values of the currents detected as being supplied to the two motors before and after the swapping of the distribution ratio. The steering device according to claim 9, wherein the distribution ratio of the command values to the two motors is set by another control device provided outside the two control devices. The steering device according to any one of claims 1 to 10, wherein the command value is a torque command value indicating the total torque to be generated by the two motors. The steering device according to any one of claims 1 to 10, wherein the command value is a current command value corresponding to the total torque to be generated by the two motors. The steering device according to any one of claims 1 to 10, wherein the command value is a voltage command value corresponding to the total torque to be generated by the two motors.