JP5824376B2 - Electric power steering apparatus and program - Google Patents

Description

  The present invention relates to an electric power steering apparatus and a program.

In recent years, there has been proposed an electric power steering device that includes an electric motor in a steering system of a vehicle and assists a driver's steering force with the power of the electric motor.
This electric power steering device is controlled by a control device. For example, the control device (microcomputer) described in Patent Document 1 includes an open control unit that executes open control (open loop control) in addition to each F / B control unit that executes current feedback control, and feedback by each of these control units. The switching determination part which performs switching determination between control and open control is provided.

JP 2008-259265 A

In the electric motor, since the resistance of the winding changes according to the temperature, the difference between the actual current that actually flows and the target current may increase depending on the temperature. When performing feedback control, even if the difference between the actual current and the target current is large, the difference is reduced so that the actual current approaches the target current. The difference between the actual current and the target current remains large. Therefore, depending on the temperature of the electric motor, the actual current supplied to the electric motor may greatly differ before and after switching between the feedforward control and the feedback control. If the actual current is different before and after the switching, the output torque of the electric motor is also different, which makes the steering feeling uncomfortable.
An object of the present invention is to provide an apparatus that makes it difficult to cause a difference in current supplied to an electric motor before and after switching between feedforward control and feedback control regardless of the temperature of the electric motor.

For this purpose, the present invention sets an electric motor for applying a steering assist force to a rack shaft connected to rolling wheels and a target current to the electric motor based on a steering torque applied to the steering wheel. Based on the target current setting means, the current detection means for detecting the actual current actually supplied to the electric motor, the target current set by the target current setting means, and the actual current detected by the current detection means Feedback control means for determining a control command value for the electric motor; feedforward control means for determining a control command value for the electric motor based on a target current set by the target current setting means; and the target current setting means. Based on the set target current, the final control command value of the electric motor is changed to the control command value determined by the feedforward control means. Switching means for switching between the control command value determined by the feedback control means and the feedforward control means even if the target current set by the target current setting means is the same. The control command value of the electric motor is changed according to the temperature of the electric motor, and the switching unit is configured to change the final control command value of the electric motor in a region where the target current set by the target current setting unit is small. the control command value feedforward control means decides, when the target current is increased, an electric power steering apparatus according to claim switch Rukoto the control command value, wherein the feedback control means is determined.

Here, it is preferable that the feedforward control means determines the control command value such that a current supplied to the electric motor decreases as the temperature of the electric motor decreases.
The feedforward control means includes a base current determination unit that determines a base current to be supplied to the electric motor according to a target current set by the target current setting unit, and a base current determined by the base current determination unit. A correction unit that corrects the base current by multiplying the correction coefficient and determines a value corresponding to the corrected value as the control command value, and the correction coefficient reduces the temperature of the electric motor. It is preferable to become smaller according to

From another point of view, the present invention relates to an electric motor for applying a steering assist force to a rack shaft connected to a rolling wheel based on a steering torque applied to a steering wheel to a computer that controls an electric power steering device. Feedback control for determining a control command value for the electric motor based on a function for setting the target current, a target current set by the function for setting the target current, and an actual current actually supplied to the electric motor A function for performing feedforward control for determining a control command value for the electric motor based on a target current set by a function for setting the target current, and a target current set by the function for setting the target current Control command value determined by the function for performing the feedforward control based on the control command value of the electric motor based on Or a function for switching between the control command value determined by the function for performing the feedback control, and the function for performing the feedforward control sets the target current. Even if the target current set by the function is the same, the control command value of the electric motor is changed according to the temperature of the electric motor , and the switching function is used to change the final control command value of the electric motor to the target current. In a region where the target current set by the function for setting is small, the control command value determined by the function for performing the feedforward control is set, and when the target current increases, the control command for the function for performing the feedback control is determined. is a program characterized switched Rukoto the value.

  According to the present invention, a difference in current supplied to the electric motor before and after switching between feedforward control and feedback control can be made difficult regardless of the temperature of the electric motor.

It is a figure showing the schematic structure of the electric power steering device concerning an embodiment. It is a schematic block diagram of the control apparatus of an electric power steering apparatus. It is a schematic block diagram of a target current calculation part. It is a schematic block diagram of a control part. It is a block diagram of a feedback control part and a feedforward control part. It is a figure which shows the correlation of a target electric current and a base duty ratio. It is a figure which shows the correlation of a duty ratio and the actual electric current which actually flows into an electric motor according to temperature. It is a figure which shows the target electric current of an electric motor when an electric motor is low temperature, and the actual electric current of an electric motor when the drive of an electric motor is controlled by the motor drive control part which concerns on a comparative example. It is a figure which shows the correlation with a correction coefficient and the temperature of an electric motor.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an electric power steering apparatus 100 according to an embodiment.
An electric power steering device 100 (hereinafter, also simply referred to as “steering device 100”) is a steering device for arbitrarily changing the traveling direction of a vehicle. In the present embodiment, the configuration applied to an automobile is used. Illustrated.

  The steering device 100 includes a wheel-like steering wheel (handle) 101 operated by a driver, and a steering shaft 102 provided integrally with the steering wheel 101. The steering device 100 includes an upper connecting shaft 103 connected to the steering shaft 102 via a universal joint 103a, and a lower connecting shaft 108 connected to the upper connecting shaft 103 via a universal joint 103b. . The lower connecting shaft 108 rotates in conjunction with the rotation of the steering wheel 101.

  Steering device 100 includes tie rods 104 connected to left and right front wheels 150 as rolling wheels, and rack shaft 105 connected to tie rods 104. Further, the steering device 100 includes a pinion 106 a that constitutes a rack and pinion mechanism together with rack teeth 105 a formed on the rack shaft 105. The pinion 106 a is formed at the lower end portion of the pinion shaft 106.

  The steering device 100 also has a steering gear box 107 that houses the pinion shaft 106. The pinion shaft 106 is connected to the lower connection shaft 108 via a torsion bar (not shown) in the steering gear box 107. A torque sensor 109 that detects the steering torque of the steering wheel 101 based on the relative angle between the lower connecting shaft 108 and the pinion shaft 106 is provided inside the steering gear box 107.

The steering device 100 includes an electric motor 110 supported by the steering gear box 107, and a speed reducing mechanism 111 that decelerates the driving force of the electric motor 110 and transmits it to the pinion shaft 106. The electric motor 110 is a motor with a brush. The speed reduction mechanism 111 includes, for example, a worm wheel (not shown) fixed to the pinion shaft 106, a worm gear (not shown) fixed to the output shaft of the electric motor 110, and the like.
In addition, the steering device 100 includes a motor current detection unit 33 (see FIG. 4) as an example of a current detection unit that detects the magnitude and direction of the actual current that actually flows through the electric motor 110, and the voltage between the terminals of the electric motor 110. Has a motor voltage detection unit 160 for detecting.

  The steering device 100 includes a control device 10 that controls the operation of the electric motor 110. The output value of the torque sensor 109, the output value of the motor voltage detector 160, and the output value of the vehicle speed sensor 170 that detects the vehicle speed of the automobile are input to the control device 10.

  The electric power steering apparatus 100 configured as described above detects the steering torque applied to the steering wheel 101 by the torque sensor 109, drives the electric motor 110 to correspond to the detected torque, and the electric motor 110. Is generated and transmitted to the pinion shaft 106. Thereby, the torque generated by the electric motor 110 assists the driver's steering force applied to the steering wheel 101.

Next, the control device 10 will be described.
The control device 10 is an arithmetic and logic circuit composed of a CPU, ROM, RAM, backup RAM, and the like.
FIG. 2 is a schematic configuration diagram of the control device 10 of the electric power steering device 100.
The control device 10 includes a torque signal Td in which the steering torque detected by the torque sensor 109 described above is converted into an output signal, and a vehicle speed signal v in which the vehicle speed detected by the vehicle speed sensor 170 is converted into an output signal. Is entered.
Since the detection signal from the torque sensor 109 or the like is input as an analog signal, the control device 10 converts the analog signal into a digital signal by an A / D conversion unit (not shown) and takes it into the CPU.

  Then, the control device 10 calculates a target auxiliary torque based on the torque signal Td, a target current calculation unit 20 that calculates a target current necessary for the electric motor 110 to supply the target auxiliary torque, and a target current And a control unit 30 that performs feedback control and the like based on the target current calculated by the calculation unit 20.

Next, the target current calculation unit 20 will be described in detail. FIG. 3 is a schematic configuration diagram of the target current calculation unit 20.
The target current calculation unit 20 converts the motor current signal Im obtained by converting the actual current detected by the motor current detection unit 33 into an output signal and the voltage detected by the motor voltage detection unit 160 into an output signal. The motor terminal voltage signal Vm is input.

  The target current calculation unit 20 includes a base current calculation unit 21 that calculates a base current that serves as a reference for setting the target current, an inertia compensation current calculation unit 22 that calculates a current for canceling the inertia moment of the electric motor 110, and It has. The target current calculation unit 20 calculates the rotation speed of the electric motor 110 based on the damper compensation current calculation unit 23 that calculates a current that limits the rotation of the motor, the motor current signal Im, and the voltage signal Vm between the motor terminals. And a motor rotation speed calculation unit 24. Further, the target current calculation unit 20 includes a final target current determination unit 25 that determines a final target current based on outputs from the base current calculation unit 21, the inertia compensation current calculation unit 22, the damper compensation current calculation unit 23, and the like. I have.

  The base current calculation unit 21 calculates a base current based on the torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26 and the vehicle speed signal v from the vehicle speed sensor 170, and information on the base current is obtained. The base current signal Ims including it is output. Note that the base current calculation unit 21, for example, displays a map indicating the correspondence between the torque signal Ts and the vehicle speed signal v and the base current, which is created in advance based on empirical rules and stored in the ROM, and the torque signal Ts and the vehicle speed. The base current is calculated by substituting the signal v.

  The inertia compensation current calculation unit 22 calculates an inertia compensation current for canceling out the moment of inertia of the electric motor 110 and the system based on the torque signal Td and the vehicle speed signal v, and generates an inertia compensation current signal Is including information on this current. Output. For example, the inertia compensation current calculation unit 22 generates a torque signal Td on a map indicating the correspondence between the torque signal Td, the vehicle speed signal v, and the inertia compensation current, which is previously created based on an empirical rule and stored in the ROM. And the inertia compensation current is calculated by substituting the vehicle speed signal v.

  The damper compensation current calculation unit 23 calculates a damper compensation current for limiting the rotation of the electric motor 110 based on the torque signal Td, the vehicle speed signal v, and the rotation speed signal Nm of the electric motor 110, and information on this current A damper compensation current signal Id including is output. The damper compensation current calculation unit 23 indicates the correspondence between the torque compensation signal Td, the vehicle speed signal v, the rotation speed signal Nm, and the damper compensation current, which are previously created based on empirical rules and stored in the ROM, for example. The damper compensation current is calculated by substituting the torque signal Td, the vehicle speed signal v, and the rotational speed signal Nm into the map.

The final target current determination unit 25 includes the base current signal Ims output from the base current calculation unit 21, the inertia compensation current signal Is output from the inertia compensation current calculation unit 22, and the damper compensation output from the damper compensation current calculation unit 23. A final target current is determined based on the current signal Id, and a target current signal IT including information on this current is output. For example, the final target current determination unit 25 previously created a compensation current obtained by adding the inertia compensation current to the base current and subtracting the damper compensation current based on an empirical rule, and stored it in the ROM. The final target current is calculated by substituting it into a map indicating the correspondence between the compensation current and the final target current.
As described above, the target current calculation unit 20 functions as an example of a target current setting unit that sets a target current to be supplied to the electric motor 110 based on the steering torque detected by the torque sensor 109.

Next, the control unit 30 will be described in detail. FIG. 4 is a schematic configuration diagram of the control unit 30.
The control unit 30 includes a motor drive control unit 31 that controls the operation of the electric motor 110, a motor drive unit 32 that drives the electric motor 110, and a motor current detection unit 33 that detects the actual current that actually flows through the electric motor 110. And a motor temperature detection unit 34 for detecting the temperature of the electric motor 110.

  The motor drive control unit 31 performs feedback control based on the deviation between the target current calculated by the target current calculation unit 20 and the actual current supplied to the electric motor 110 detected by the motor current detection unit 33. A feedback (F / B) control unit 40 as an example of feedback control means is provided. Further, the motor drive control unit 31 includes a feed forward (F / F) control unit 50 as an example of a feed forward control unit that performs feed forward control based on the target current calculated by the target current calculation unit 20. ing. In addition, the motor drive control unit 31 uses the duty ratio determined by the feedback (F / B) control unit 40 as the duty ratio for the current electric motor 110 control, or the feed forward (F / F) control unit 50 A switching unit 45 for switching whether to use the determined duty ratio is provided. The feedback control unit 40, the feedforward control unit 50, and the switching unit 45 will be described in detail later.

  Further, the motor drive control unit 31 includes a PWM signal generation unit 60 that generates a PWM (pulse width modulation) signal for PWM driving the electric motor 110. The PWM signal generation unit 60 generates a PWM signal 60 a based on the output values from the feedforward control unit 50 and the feedback control unit 40, and outputs the generated PWM signal 60 a to the motor drive unit 32.

  The motor drive unit 32 drives a motor drive circuit 70 in which four power field effect transistors are connected in an H-type bridge circuit configuration, and drives the gates of two field effect transistors selected from the four. And a gate drive circuit unit 80 for switching the field effect transistor. The gate drive circuit unit 80 selects two field effect transistors according to the steering direction of the steering wheel 101 based on the drive control signal (PWM signal) 60a output from the PWM signal generation unit 60, and selects the selected 2 The field effect transistors are switched.

The motor current detection unit 33 detects the value of the motor current (armature current) flowing through the electric motor 110 from the voltage generated at both ends of the shunt resistor 71 connected in series with the motor drive circuit 70, and outputs the motor current signal Im. To do.
The motor temperature detection unit 34 can exemplify detecting the temperature of the electric motor 110 based on an output value from a thermistor attached inside the electric motor 110. Alternatively, the motor temperature detection unit 34 may detect the temperature of the electric motor 110 based on the atmospheric temperature of the electric motor 110 and the amount of heat generated by the electric motor 110.

Next, the feedback control unit 40 and the feedforward control unit 50 will be described.
FIG. 5 is a block diagram of the feedback control unit 40 and the feedforward control unit 50.
The feedback control unit 40 includes an F / B base duty ratio determination unit 41 that determines a base duty ratio that is a base of a duty ratio that is finally determined from the target current calculated by the target current calculation unit 20, and a target current calculation. A deviation calculating unit 42 for obtaining a deviation between the target current calculated by the unit 20 and the actual current detected by the motor current detecting unit 33; and determining a final duty ratio so that the deviation becomes zero. / B final duty ratio determining unit 43.

FIG. 6 is a diagram showing a correlation between the target current and the base duty ratio. In the following description, it is assumed that the current that assists the rotation of the steering wheel 101 in the right direction is positive and the current that assists in the left direction is negative.
The F / B base duty ratio determination unit 41 substitutes the target current determined by the target current calculation unit 20 into a function that calculates the base duty ratio from the target current, which shows a correlation as shown in FIG. Thus, it is determined by calculating the base duty ratio. Alternatively, the F / B base duty ratio determination unit 41, for example, a map indicating the correspondence between the target current and the base duty ratio, which is created in advance based on empirical rules and stored in the ROM, and the target current calculation unit 20 The base duty ratio may be determined based on the target current calculated in (1).

The deviation calculation unit 42 outputs a deviation value between the output value IT from the target current calculation unit 20 and the output value Im from the motor current detection unit 33 as a deviation signal 42a.
The F / B final duty ratio determining unit 43 determines the final duty ratio so that the target current and the actual current match. For example, the input deviation signal 42a is proportionally processed with a proportional element, integrated with an integral element, and these values are added to the base duty ratio determined by the F / B base duty ratio determining unit 41. A feedback processing signal 43a corresponding to the obtained value is generated and output.

  The feedforward control unit 50 includes an F / F base duty ratio determination unit 51 that determines a base duty ratio that is a base of a duty ratio that is finally determined from the target current calculated by the target current calculation unit 20; It has the correction | amendment part 52 which correct | amends the base duty ratio which F base duty ratio determination part 51 determined using the correction coefficient (alpha), and the correction coefficient setting part 53 which sets the correction coefficient (alpha).

  The F / F base duty ratio determination unit 51 assigns the target current determined by the target current calculation unit 20 to a function that calculates the base duty ratio from the target current, which shows the correlation as shown in FIG. Thus, it is determined by calculating the base duty ratio. Alternatively, the F / F base duty ratio determination unit 51, for example, a map indicating the correspondence between the target current and the base duty ratio, which is previously created based on empirical rules and stored in the ROM, and the target current calculation unit 20 The base duty ratio may be determined based on the target current calculated in (1).

The correction unit 52 generates and outputs a feedforward processing signal 52a corresponding to a value obtained by multiplying the base duty ratio determined by the F / F base duty ratio determination unit 51 by the correction coefficient α.
The correction coefficient setting unit 53 will be described later.

Next, the switching unit 45 will be described in detail.
When the absolute value of the final duty ratio determined by the feedback control unit 40 and the feedforward control unit 50 is equal to or less than a threshold value that is a predetermined duty ratio, the switching unit 45 causes the PWM signal generation unit 60 to The duty ratio determined by the feedforward control unit 50 is output as the output duty ratio. On the other hand, when larger than the threshold value, the duty ratio determined by the feedback control unit 40 is output as the duty ratio output to the PWM signal generation unit 60. This is due to the following reason.

  The feedback control unit 40 performs feedback control based on the deviation between the target current determined by the target current calculation unit 20 and the actual current of the electric motor 110 detected by the motor current detection unit 33. However, since the electric motor 110 according to the present embodiment is a brushed motor, the detection accuracy of the motor current detection unit 33 is poor in a region where the current supplied to the electric motor 110 is small (low) (low current region). . Therefore, when feedback control is performed in the low current region (when the duty ratio determined by the feedback control unit 40 is output to the PWM signal generation unit 60), the current supplied to the electric motor 110 may greatly deviate from the target current. There is. Therefore, in the present embodiment, the duty ratio determined by the feedforward control unit 50 is used as the duty ratio to be output to the PWM signal generation unit 60 in the low current region, where the absolute value of the duty ratio is small. In other areas, the duty ratio determined by the feedback control unit 40 is used as the duty ratio output to the PWM signal generation unit 60.

Next, the correction unit 52 and the correction coefficient setting unit 53 will be described in detail.
FIG. 7 is a diagram showing the correlation between the duty ratio and the actual current actually flowing through the electric motor 110 for each temperature. The relationship when the temperature is 20 degrees is indicated by a thin solid line, the relationship when the temperature is −30 degrees is indicated by a thick broken line, and the relationship when the temperature is 90 degrees is indicated by a thick two-dot chain line. In FIG. 7, only the portion where the current and the duty ratio are positive is shown, but the portion where the current and the duty ratio are negative is symmetrical with respect to the zero point.

As a characteristic of the electric motor 110, when the temperature of the electric motor 110 increases, the resistance of the winding increases, so that it becomes difficult for the current to flow. When the temperature decreases, the resistance value decreases, so that the current flows easily.
Therefore, as shown in FIG. 7, even when the duty ratio output to the PWM signal generation unit 60 is the same, the current value when the temperature of the electric motor 110 is 90 degrees is high, the temperature is 20 degrees. The current value is smaller than the current value at a certain time, and the current value when the temperature of the electric motor 110 is −30 degrees is larger than the current value when the temperature is 20 degrees.

  When the feedback control unit 40 performs feedback control based on the deviation between the target current and the actual current of the electric motor 110 detected by the motor current detection unit 33, even if the temperature of the electric motor 110 is high or low, Even if the actual current deviates from the target current, it is corrected. On the other hand, for example, when the feedforward control is performed by the feedforward control unit 50 that does not correct the base duty ratio determined by the F / F base duty ratio determination unit 51 by the correction unit 52, the actual current Regardless, for example, the duty ratio is determined based on the correlation between the duty ratio and the target current when the temperature is 20 degrees. Therefore, in the low current region described above, the actual current of the electric motor 110 may greatly deviate from the target current due to the temperature of the electric motor 110.

FIG. 8 shows the target current of the electric motor 110 when the electric motor 110 is at a low temperature, and the actual current of the electric motor 110 when the drive of the electric motor 110 is controlled by the motor drive control unit 31 according to the comparative example. FIG. (A) shows the target current, (b) shows the actual current, and (c) is an enlarged view of the VIIIC section in (b).
The motor drive control unit 31 according to the comparative example is different in the configuration of the feedforward control unit 50 from the motor drive control unit 31 according to the present embodiment. Unlike the feedforward control unit 50 according to this embodiment, the feedforward control unit 50 according to the comparative example does not correct the base duty ratio determined by the F / F base duty ratio determination unit 51 by the correction unit 52. That is, the feedforward control unit 50 according to the comparative example outputs the base duty ratio determined by the F / F base duty ratio determination unit 51 to the switching unit 45 as the final duty ratio.

  The feedforward control unit 50 according to this comparative example determines the duty ratio based on the correlation between the duty ratio and the target current when the temperature is 20 degrees, for example, regardless of the actual current. In the current region, the actual current of the electric motor 110 may deviate greatly from the target current due to the temperature of the electric motor 110. On the other hand, in the region where the output from the feedback control unit 40 is output to the PWM signal generation unit 60 and the duty ratio is larger than the threshold value, the actual electric motor 110 detected by the target current and motor current detection unit 33 is detected. Since feedback control is performed based on the deviation from the current, the actual current of the electric motor 110 tends to be the target current.

  As a result, the switching unit 45 uses the duty ratio determined by the feedback control unit 40 from the state where the duty ratio determined by the feedforward control unit 50 according to the comparative example is used as the duty ratio for controlling the electric motor 110. In the region where the duty ratio determined by the feedforward control unit 50 according to the comparative example is used from the state where the duty ratio determined by the feedback control unit 40 is used and the duty ratio determined by the feedforward control unit 50 according to the comparative example is used, End up.

  For example, when the electric motor 110 is at a low temperature, the switching unit 45 uses the duty ratio determined by the feedforward control unit 50 according to the comparative example as the duty ratio for controlling the electric motor 110 from the feedback control unit. When switching to use the duty ratio determined by 40, the state is shifted from the state where the actual current is shifted upward from the target current to the state where it becomes the same as the target current by feedback control. As a result, a step as shown in FIG. 8C is generated in the actual current of the electric motor 110, and a step is also generated in the assist torque of the electric motor 110, so that the steering feeling is uncomfortable.

  On the other hand, when the electric motor 110 is at a low temperature, the switching unit 45 uses the duty ratio determined by the feedback control unit 40 as the duty ratio for controlling the electric motor 110, so that the feedforward control unit according to the comparative example is used. When switching to use the duty ratio determined by 50, the state shifts from the state where the actual current is the same as the target current to the state shifted upward from the target current by feedforward control. That is, a step is generated in the actual current of the electric motor 110 before and after the switching point by the switching unit 45, and a step is also generated in the assist torque of the electric motor 110, so that the steering feeling is uncomfortable.

  Further, when the electric motor 110 is at a high temperature, the feedback control unit 45 switches from the state in which the switching unit 45 uses the duty ratio determined by the feedforward control unit 50 according to the comparative example as the duty ratio for controlling the electric motor 110. When switching to use the duty ratio determined by 40, the state is shifted from the state where the actual current is shifted downward from the target current to the state where it becomes the same as the target current by feedback control. That is, a step is generated in the actual current of the electric motor 110 before and after the switching point by the switching unit 45, and a step is also generated in the assist torque of the electric motor 110, so that the steering feeling is uncomfortable.

  On the other hand, when the electric motor 110 is at a high temperature, the switching unit 45 uses the duty ratio determined by the feedback control unit 40 as the duty ratio for controlling the electric motor 110, so that the feedforward control unit according to the comparative example is used. When switching to use the duty ratio determined by 50, the state shifts from the state where the actual current is the same as the target current to a state where it shifts downward from the target current by feedforward control. That is, a step is generated in the actual current of the electric motor 110 before and after the switching point by the switching unit 45, and a step is also generated in the assist torque of the electric motor 110, so that the steering feeling is uncomfortable.

  Therefore, in the feedforward control unit 50 according to the present embodiment, a feedforward processing signal corresponding to a value obtained by multiplying the base duty ratio determined by the F / F base duty ratio determination unit 51 by the correction coefficient α. The correction part 52 which produces | generates / outputs 52a and the correction coefficient setting part 53 which sets the correction coefficient (alpha) are provided. And the correction coefficient setting part 53 sets the correction coefficient (alpha) so that it may become a value according to the temperature of the electric motor 110. FIG.

FIG. 9 is a diagram showing a correlation between the correction coefficient α and the temperature of the electric motor 110.
As shown in FIG. 9, the correction coefficient setting unit 53 sets the correction coefficient α when the temperature of the electric motor 110 is a reference temperature (for example, 20 degrees) to 1, and the correction coefficient α as the temperature becomes lower than the reference temperature. Is set to be smaller than 1 and the correction coefficient α is set to be larger than 1 as the temperature becomes higher than the reference temperature. Further, the correction coefficient setting unit 53 uses the temperature detected and output by the motor temperature detection unit 34 as the temperature of the electric motor 110.

  For example, the correction coefficient setting unit 53 substitutes the temperature input from the motor temperature detection unit 34 for a function that calculates the correction coefficient α from the temperature of the electric motor 110 that shows the correlation as shown in FIG. This is determined by calculating the correction coefficient α. Alternatively, the correction coefficient setting unit 53 includes, for example, a map that indicates the correspondence between the temperature of the electric motor 110 and the correction coefficient α that is created in advance based on empirical rules and stored in the ROM, and the motor temperature detection unit 34. The correction coefficient α may be determined based on the input temperature.

  In the feedforward control section 50 configured as described above, the correction coefficient α is set to a value smaller than 1 by the correction coefficient setting section 53 when the temperature of the electric motor 110 is lower than the reference temperature. Then, the correction unit 52 corrects the base duty ratio determined by the F / F base duty ratio determination unit 51 using the correction coefficient α having a value smaller than 1. Thus, when the temperature of the electric motor 110 is lower than the reference temperature, the final duty ratio output from the feedforward control unit 50 is smaller than the base duty ratio, so that the actual current of the electric motor 110 is the target current. Get closer to.

  On the other hand, when the temperature of the electric motor 110 is higher than the reference temperature, the correction coefficient setting unit 53 sets the correction coefficient α to a value larger than 1. Then, the correction unit 52 corrects the base duty ratio determined by the F / F base duty ratio determination unit 51 using the correction coefficient α having a value larger than 1. Thereby, when the temperature of the electric motor 110 is higher than the reference temperature, the final duty ratio output from the feedforward control unit 50 is larger than the base duty ratio, so that the actual current of the electric motor 110 becomes the target current. Get closer to.

  And in steering apparatus 100 provided with feedforward control part 50 concerning this embodiment, since change according to temperature of electric motor 110 is performed in the low current field where feedforward control is performed, switching part Before and after the switching point by 45, a step is hardly generated in the actual current of the electric motor 110. As a result, the assist torque of the electric motor 110 is less likely to be stepped, so that it is possible to suppress a feeling of strangeness in the steering feeling.

  In the above-described embodiment, the switching unit 45 switches the duty ratio output to the PWM signal generation unit 60 based on the final duty ratio determined by the feedback control unit 40 and the feedforward control unit 50. It is not limited to such an embodiment. For example, the switching unit 45 generates a PWM signal based on the duty ratio determined by the F / B base duty ratio determination unit 41 of the feedback control unit 40 and / or the F / F base duty ratio determination unit 51 of the feedforward control unit 50. The duty ratio output to the unit 60 may be switched. That is, when the duty ratio determined by the F / B base duty ratio determination unit 41 and / or the F / F base duty ratio determination unit 51 is equal to or less than the threshold value, the duty ratio finally determined by the feedforward control unit 50 May be output to the PWM signal generation unit 60, and the duty ratio finally determined by the feedback control unit 40 may be output to the PWM signal generation unit 60 when it is larger than the threshold value.

  Further, the duty ratio determined by the feedforward control unit 50 is equal to or smaller than the threshold value, and the duty ratio becomes larger than the threshold value from the state where the electric motor 110 is controlled using the duty ratio determined by the feedforward control unit 50. In such a case, the duty ratio determined by the feedback control unit 40 from the next time when it exceeds may be used, and the duty ratio used immediately before exceeding may be used immediately after exceeding.

DESCRIPTION OF SYMBOLS 10 ... Control apparatus, 20 ... Target electric current calculation part, 30 ... Control part, 33 ... Motor current detection part, 34 ... Motor temperature detection part, 40 ... Feedback control part, 45 ... Switching part, 50 ... Feed forward control part, 51 DESCRIPTION OF SYMBOLS F / F base duty ratio determination part 52 ... Correction part 53 ... Correction coefficient setting part 60 ... PWM signal generation part 100 ... Electric power steering apparatus 101 ... Steering wheel 102 ... Steering shaft 109 ... Torque sensor 110: Electric motor

Claims (4)

An electric motor for applying a steering assist force to the rack shaft connected to the rolling wheels ;
Target current setting means for setting a target current to the electric motor based on a steering torque applied to the steering wheel;
Current detection means for detecting an actual current actually supplied to the electric motor;
Feedback control means for determining a control command value for the electric motor based on the target current set by the target current setting means and the actual current detected by the current detection means;
Feedforward control means for determining a control command value of the electric motor based on the target current set by the target current setting means;
Based on the target current set by the target current setting means, the final control command value of the electric motor is set to the control command value determined by the feedforward control means, or the control command determined by the feedback control means Switching means for switching between values or
With
The feedforward control means changes the control command value of the electric motor according to the temperature of the electric motor even if the target current set by the target current setting means is the same .
The switching means sets the final control command value of the electric motor to a control command value determined by the feedforward control means in a region where the target current set by the target current setting means is small, and the target current is increased. if it becomes, the electric power steering apparatus according to claim switch Rukoto the control command value in which the feedback control means is determined.   2. The electric power steering apparatus according to claim 1, wherein the feedforward control unit determines the control command value so that a current supplied to the electric motor decreases as a temperature of the electric motor decreases. .   The feedforward control means determines a base current to be supplied to the electric motor according to the target current set by the target current setting means, and multiplies the base current determined by the base current part by a correction coefficient. A correction unit that corrects the base current and determines a value corresponding to the corrected value as the control command value, and the correction coefficient decreases as the temperature of the electric motor decreases. The electric power steering apparatus according to claim 1 or 2, wherein In the computer that controls the electric power steering device ,
A function of setting a target current of an electric motor for applying a steering assist force to a rack shaft coupled to a rolling wheel based on a steering torque applied to the steering wheel ;
A function of performing feedback control for determining a control command value of the electric motor based on a target current set by the function of setting the target current and an actual current actually supplied to the electric motor;
A function of performing feedforward control for determining a control command value of the electric motor based on a target current set by the function of setting the target current;
Based on the target current set by the function for setting the target current, the final control command value for the electric motor is set to the control command value determined by the function for performing the feedforward control, or the feedback control is performed. A function to switch between the control command value determined by the function and
Is a program for realizing
The function of performing the feedforward control is to change the control command value of the electric motor according to the temperature of the electric motor, even if the target current set by the function of setting the target current is the same .
The function of switching the final control command value of the electric motor to a control command value determined by the function of performing the feedforward control in a region where the target current set by the function of setting the target current is small, when the target current is increased, the program characterized by switching Rukoto the control command value function for the feedback control is determined.

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