JP2001171540A - Motor-driven power steering device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep favorable steering feeling for a driver when current limitation is released, in a motor-driven power steering device. SOLUTION: A command current calculating part 50 calculates a command current value I* in response to a steering condition of a steering wheel. An electric motor for assisting a turn operation of the steering wheel is drive- controlled in response to the current value I*. A command current limiting value calculating part 60 calculates a current limiting value IL* in response to a change of an ambient temperature, a power source voltage for the motor or the like to limit the command current value I* in response to the limiting value IL*. Increase of the value IL* is allowed only when steering torque is a prescribed value or more, in the calculation of the value IL*. An increasing speed of the value IL* is slowed down with increase of a vehicle speed V to evade thereby an abrupt change of assisting force before noticed by the driver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for a vehicle which assists a steering operation of a steering wheel by rotating an electric motor.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Utility Model Registration Publication No. 2
As shown in Japanese Patent No. 58620, an electric power having a magnitude corresponding to the steering state of a steering wheel is supplied to an electric motor to obtain an assist force for the turning operation of the steering wheel by rotation of the electric motor. 2. Description of the Related Art In a steering apparatus, it is known that the magnitude of a current flowing through an electric motor is limited in accordance with a driving current amount of the electric motor in order to protect the electric motor from overheating. And in this case,
The amount of heat generated by the electric motor is calculated by squaring the drive current of the electric motor, and the value determined by the first-order lag of the amount of heat is set as the upper limit of the magnitude of the current flowing through the electric motor.

[0003]

However, in the above conventional apparatus, the limit value changes only depending on the drive current of the electric motor. For example, the limit of the drive current of the electric motor is released. As described above, the way of changing the limit value when the limit value greatly changes is not considered. Therefore, before the driver notices, if the limit value is largely changed, that is, if the drive current of the electric motor is released and the drive current of the motor is changed from a small state to a large state, the previous time, There is a problem that the steering wheel, which is somewhat heavy, suddenly becomes lighter, and the driver feels uncomfortable with the steering wheel operation.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to address the above problems, and has as its object to reduce the driver's feeling of discomfort as to the operation of the steering wheel even if the limit value of the drive current for the electric motor changes. An object of the present invention is to provide an electric power steering device that does not make a user feel.

[0005] In order to achieve the above object, the structural features of the present invention include an electric motor for applying an assist force to the turning operation of the steering wheel, and an electric current having a magnitude corresponding to the steering state of the steering wheel. Power steering apparatus for a vehicle, comprising: motor control means for controlling the rotation of the electric motor by causing the electric motor to flow to the electric motor; and current limiting means for restricting a current value to be supplied to the electric motor to a limit value according to a predetermined condition. , A steering torque detecting means for detecting a steering torque, and a limit value control means for allowing an increase in a limit value limited by the current limiting means when the detected steering torque is equal to or more than a predetermined value. .

[0006] According to the structural feature, the limit value control means allows the limit value limited by the current limit means to increase when the steering torque detected by the steering torque detection means is equal to or more than a predetermined value. Therefore, even when the limit value changes greatly, such as when the limit on the drive current of the electric motor is released, the limit value increases while the driver turns the steering wheel, and during this steering, It is difficult for the driver to feel the change in the steering operation, so the driver does not feel great discomfort with the steering operation,
The driver's steering feeling is improved.

Another feature of the present invention is that the limit value control means is configured to gradually increase the limit value over time when the limit value is allowed to increase. It is in. According to this, the driver does not feel any more uncomfortable with the steering operation, and the steering feeling of the driver is further improved.

Another feature of the present invention is that the limit value control means is configured to make the increasing speed of the limit value dependent on the vehicle speed. According to this, for example, the increasing speed can be reduced as the vehicle speed increases, or the increasing speed can be increased when the vehicle stops, and the increasing speed can be decreased during traveling. As a result, a change in the steering operation at a high vehicle speed is suppressed as much as possible, so that the steering feeling of the driver is improved and the running stability of the vehicle is secured.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows an electric power steering apparatus for a vehicle according to the embodiment.

In this electric power steering apparatus, the turning operation of the steering handle 11 is performed by the rack and pinion mechanism 1.
Steering shaft 1 transmitting to left and right front wheels FW1 and FW2 via
3 is provided with the electric motor 14 assembled. The electric motor 14 is constituted by a DC motor, and provides an assisting force to the turning operation of the steering handle 11 in accordance with its rotation. The rotation is transmitted to the steering shaft 13 via the speed reduction mechanism 15. It has become so.

An electric control device 20 is electrically connected to the electric motor 14. The electric control device 20 controls the rotation of the electric motor 14 in accordance with detection outputs of a steering torque sensor 21, a vehicle speed sensor 22 and a temperature sensor 23. Control. The steering torque sensor 21 is mounted on the steering shaft 13 and operates the steering wheel 11 and the steering shaft 1 when steering the steering wheel 11.
3 is detected as a steering torque (steering reaction force) TM.
The steering torque TM represents the torque generated on the steering wheel 11 and the steering shaft 13 when the steering wheel 11 is turned to the right, and the steering wheel 11 is turned to the left. In this case, the torque generated in the steering wheel 11 and the steering shaft 13 is represented by a negative value. The vehicle speed sensor 22 detects a vehicle speed V. Temperature sensor 23
Detects the temperature Tp of the board on which the electric circuit components constituting the electric control device 20 are assembled.

As shown in FIG. 2, the electric control device 20
It comprises a drive circuit 30 for driving the electric motor 14 and a control circuit unit 40 for controlling the drive circuit 30. The driving circuit 30 includes switching elements 31 to 34 such as FETs.
Is connected to a positive voltage terminal (+) of a battery 37 via a shunt resistor 35 and a relay switch 36 at one of a pair of diagonal positions facing each other. The relay switch 36 is normally turned on, is controlled by a fail detector (not shown) for detecting a failure of the electric power steering device, and is turned off when a failure is detected. The negative voltage terminal (-) of the battery 37 is grounded. The other of the pair of diagonal positions is grounded via a shunt resistor 38. In the other diagonal position of the bridge circuit,
Both terminals of the electric motor 14 are connected to each other.

The control circuit unit 40 is constituted by a microcomputer and its peripheral circuits. The control circuit unit 40 is operated by a voltage from a positive voltage terminal (+) of a battery 37 through an ignition switch IG and a diode 41, and is connected to a relay switch 36. It operates also by the voltage supplied from the connection point with the shunt resistor 35 via the diode 42. The control circuit unit 40 actually realizes various functions by program processing, but FIG. 2 shows various functions by the program processing in a functional block diagram.

The control circuit unit 40 includes a voltage detector 4
3, a current detector 44, a steering speed calculator 45, a command current value generator 46, and a drive controller 47.

The voltage detecting unit 43 receives the voltage of both terminals of the electric motor 14, and detects and outputs the voltage Vm between the terminals of the motor 14 based on the difference between the two terminal voltages.
The current detection unit 44 inputs the both terminal voltages of the shunt resistor 38, and based on the both terminal voltages, the drive current Im
Is calculated. The steering speed calculation unit 45 calculates the rotational angular speed ω of the electric motor 14 by executing the calculation of the following equation 1 using the terminal voltage Vm and the drive current Im of the electric motor 14.

[0016]

Ω = (Vm−Rm · Im) / K

The above equation (1) is an approximate expression for calculating the rotational angular velocity of a DC motor that does not consider the inductance (the inductance is small and can usually be ignored), and K and Rm are constants determined by the motor. Since the electric motor 14 and the steering wheel 11 rotate integrally, the rotational angular speed ω is equal to the steering speed of the steering wheel 11, and the same rotational angular speed ω is hereinafter used as the steering speed.

As will be described in detail later, the command current value generator 46 includes a steering torque TM from the steering torque sensor 21, a vehicle speed V from the vehicle speed sensor 22, a temperature Tp from the temperature sensor 23, and a command from the steering speed calculator 45. , And calculates an output command current value Io * that defines the amount of current flowing to the electric motor 14 based on the steering torque TM, the vehicle speed V, the temperature Tp, and the steering speed ω. 4
7 is output. The command current value generator 46 is also supplied with an ignition off signal IGOF indicating that the ignition switch IG is turned off and a fail signal FAIL indicating a failure of the electric power steering device.
Both of these signals IGOF and FAIL are supplied from a detection unit (not shown).

The drive control unit 47 inputs the drive current Im of the motor 14 detected by the current detection unit 44 for feedback control and outputs a difference Io * from an output command current value Io *.
−Im and the calculated difference Io * −Im
A control signal is formed by PID control using Also,
The drive control unit 47 also has a pulse width modulation (PWM) function, supplies a pulse train signal pulse-width modulated according to the control signal to the switching elements 31 to 34, and turns the elements 31 to 34 on and off. Control. As a result, a drive current Im equal to the output command current value Io * flows through the electric motor 14. The switching elements 31, 34
Is turned on and off, the electric motor 14 rotates forward to assist the rightward turning of the steering wheel 11. If the switching elements 32 and 33 are controlled to be turned on and off, the electric motor 14 rotates in the reverse direction to assist the left-handed steering of the steering wheel 11.

The command current value generator 46 includes a command current value calculator 50, a command current limit value calculator 60, and a current limit storage 70, as shown in detail in FIG.

The command current value calculation unit 50 includes a steering wheel 1
In order to cause the electric motor 14 to generate an assist force corresponding to the steering state of the electric motor 1, the electric motor 1 corresponding to the assist force
The controller calculates a command current value I * with respect to No. 4 and includes a basic assist controller 51, a differentiator 52, an inertia compensation controller 53, a steering wheel return controller 54, a damping controller 55, and an adder 56.

The basic assist control unit 51 includes a conversion table for converting the steering torque TM into a basic command current value Ia for each of a plurality of vehicle speed ranges.
Torque TM from vehicle and vehicle speed V from vehicle speed sensor 22
And outputs a basic command current value Ia corresponding to the steering torque TM and the vehicle speed V. The basic command current value Ia increases as the steering torque TM increases and decreases as the vehicle speed V increases, as shown in FIG.

The differentiating section 52 differentiates the steering torque TM from the steering torque sensor 21 to obtain the same differential value TM ′ (= dTM
/ Dt) is output. The inertia compensation control unit 53 performs a turning operation of the steering handle 11 (in particular, the steering handle 1 at the start of turning).
(1 rotation operation) to calculate an inertia compensation current value Ib for compensating an inertial force of the electric motor 14;
The differential value TM ′ of the steering torque TM from the differentiator 52 and the vehicle speed V from the vehicle speed sensor 22 are input, and the differential value TM ′ is input.
The inertia compensation current value Ib increases as the vehicle speed V increases and decreases as the vehicle speed V increases.

The steering wheel return control unit 54 calculates a steering wheel return current value Ic for compensating that the steering wheel 11 returns to the neutral position quickly when the steering wheel 11 is turned back. And the vehicle speed V from the vehicle speed sensor 22, and outputs a steering wheel return current value Ic that increases as the steering speed ω increases and decreases as the vehicle speed V increases.

The damping control unit 55 includes a steering wheel 1
This is for calculating a damping current value Id for compensating that a resistance is given to one rotation operation, and inputs the steering speed ω from the steering speed calculation unit 45 and the vehicle speed V from the vehicle speed sensor 22. The damping current value Id acts in the direction opposite to the steering speed ω, the absolute value increases as the absolute value | ω | of the steering speed ω increases, and the absolute value increases as the vehicle speed V increases. Is output.

The adder 56 adds the basic command current value Ia, the inertia compensation current value Ib, the steering wheel return current value Ic, and the damping current value Id to obtain the basic command current value Ia.
A command current value I * obtained by correcting a with the inertia compensation current value Ib, the steering wheel return current value Ic, and the damping current value Id is output.

The command current limit value calculating section 60 operates the electric power steering system including the electric motor 14, the electric control device 20, the drive circuit 30, and the like (ambient temperature,
The determined command current value I * is limited depending on the supply voltage, etc.), the operation state (immediately after the start of operation, occurrence of an abnormality, etc.). , An ignition-off limit value calculator 63, a fail limit value calculator 64, a minimum value calculator 65,
It comprises a current limit return section 66 and a command current value limit section 67.

The temperature limit value calculating section 61 includes the electric motor 1
4. In order to prevent overheating of the drive circuit 30 and the control circuit unit 40 due to a rise in temperature, the upper limit value of the current Im flowing through the electric motor 14 is set.
Is provided with a conversion table for converting the current Im into a temperature limit value ILt that defines an upper limit value of the current Im based on the temperature Tp detected by the above. As shown in FIG. 5, the conversion table stores a temperature limit value ILt that decreases as the temperature Tp increases.

When the voltage of the battery 37 drops, the motor power supply voltage limit value calculation unit 62 reduces the influence of the voltage drop on other systems, or allows the electric motor 14 to supply an appropriate current as long as it is allowed. Therefore, the upper limit value of the current Im flowing through the electric motor 14 is set.
The power supply voltage limit value ILe that defines the upper limit value of the current Im flowing through the electric motor 14 is calculated by repeatedly executing the motor power supply voltage restriction program of FIG. The power supply voltage Em may be any voltage that represents the voltage of the battery 37, such as the voltage on the cathode side of the diodes 41 and 42, the voltage on the positive voltage terminal of the battery 37, and the voltage on the anode side of one of the diodes 41 and 42. Voltage and others can be used. The motor power supply voltage limit value calculation unit 62
Has a conversion table for converting the power supply voltage Em into the power supply voltage limit value ILe with characteristics as shown in FIG. 7, and the conversion table is used when the program is executed.

The ignition-off limit value calculating section 63
To ensure the application of assist force to the driver's steering operation immediately after the ignition switch IG is turned off, and to set an upper limit value of the current Im flowing to the electric motor 14 in order to cut off the power supply to the electric motor 14 thereafter. Then, based on the ignition-off signal IG, an ignition-off limit value ILi that defines the upper limit of the current Im flowing to the electric motor 14 after the ignition switch IG is turned off is calculated. In this case, the ignition switch-off signal IG is given from a detection unit (not shown) that detects the turning-off of the ignition switch IG, and the ignition-off limit value ILi is gradually increased with time from the turning-off of the ignition switch IG, as shown in FIG. To "0". When the ignition switch IG is turned on, the ignition-off limit value ILi is set to the maximum allowable current value Imax.

A fail limit value calculating section 64 ensures the application of assist force to the driver's steering operation after the occurrence (failure) of the electric power steering apparatus, and interrupts the power supply to the electric motor 14 thereafter. For this purpose, an upper limit value of the current Im flowing to the electric motor 14 is set. Based on the fail signal FAIL, a fail limit value ILf for defining the upper limit value of the current Im flowing to the electric motor 14 at the time of a failure is calculated. in this case,
The fail signal FAIL is given from a detection unit (not shown) that detects the occurrence of an abnormality (fail) in the electric power steering device, and the fail limit value ILf is immediately set to “0” when the failure is detected, as shown in FIG. (See the solid line in FIG. 9), is set to a small predetermined value after the failure is detected (see the broken line in FIG. 9), and gradually decreases to “0” over time (see the dashed line in FIG. 9). The reason why the fail limit value ILf is variously limited depends on the type of the fail. Also in this case, before a failure occurs, the fail limit value ILf is set to the allowable maximum current value Imax.

The minimum value calculating section 65 includes a temperature limit value calculating section 6
1. Limit values ILt, ILe, ILi, ILf supplied from the motor power supply voltage limit value calculation unit 62, the ignition off limit value calculation unit 63, and the fail limit value calculation unit 64
Is determined as the minimum limit value ILmin.

The current limit restoring unit 66 repeatedly executes the current limit restoring program of FIG. 10 using the steering torque TM detected by the steering torque sensor 21 and the vehicle speed V detected by the vehicle speed sensor 22 every predetermined short time. Thus, the change state of the minimum limit value ILmin calculated by the minimum value calculation section 65 is changed and controlled to change the current limit value Imin.
Output as L *. Further, the current limit return unit 66
Is provided with a table that stores a count-up value CNTup that defines the rate of change of the current limit value IL * in relation to the vehicle speed V. The count-up value CNTup is shown in FIG.
As shown in FIG. 1, the vehicle speed V increases accordingly.

The command current value limiting section 67 repeatedly executes the command current value limiting program of FIG. 12 every predetermined short time, thereby limiting the command current value I * with the current limit value IL *. The output command current value I * is output as the output command current value Io *.

The storage unit 70 repeatedly executes the current limit storage program of FIG. 13 every predetermined short time to store the history of the command current I * in the command current value limit unit 67 when the limit is large. I do.

Next, the operation of the embodiment configured as described above will be described. When the driver turns on the ignition IG, the various sensors 21 to 23 and the control circuit unit 40
At the beginning, the microcomputer constituting the control circuit unit 40 performs an initial check operation of each part, and controls the rotation of the electric motor 14 in parallel with the initial check to rotate the steering wheel 11. The operation of applying the assist force to the moving operation is started. The relay switch 36 is on unless a failure occurs, and is turned off only after a predetermined time has elapsed from the occurrence of the failure.

In the assisting force applying operation, the command current value calculation unit 50 calculates a command current value I * according to the turning operation of the steering wheel 11, and the calculated command current value I * is used as the command current value. It is output to the drive control unit 47 as an output command current value Io * via the current value limiting unit 67. The drive control unit 47 cooperates with the current detection unit 44 to
And a drive current Im equal to the output command current value Io * is supplied to the electric motor 14. The electric motor 14 starts rotating in response to this, and the output command current value Io *
The drive torque corresponding to (drive current Im) is reduced by the reduction mechanism 15.
Through the steering shaft 13.

In this case, the basic assist control unit 51 receives the steering torque TM and the vehicle speed V from the steering torque sensor 21 and the vehicle speed sensor 22, respectively, and increases as the steering torque TM increases. The basic command current value Ia that decreases is calculated and output. The differentiating unit 52 and the inertia compensation control unit 53 receive the steering torque TM and the vehicle speed V from the steering torque sensor 21 and the vehicle speed sensor 22, respectively, and calculate an inertia compensation current value Ib for compensating the inertial force of the electric motor 14. Output.
The steering wheel return control unit 54 receives the steering torque TM and the vehicle speed V from the steering speed calculation unit 45 and the vehicle speed sensor 22, respectively, and calculates a steering wheel return current value Ic for compensating that the steering wheel 11 is returned to the neutral position. Output. The damping control unit 55 receives the steering torque TM and the vehicle speed V from the steering speed calculation unit 45 and the vehicle speed sensor 22, respectively, and compensates for giving resistance to the turning operation of the steering wheel 11. Calculate and output Id.

The adder 56 calculates these current values I
Since a, Ib, Ic, and Id are added and output as the command current value I *, in the steering operation by the driver, an appropriate assist force is applied to the steering operation. In this case, in the basic command current value Ia, the vehicle speed V is considered in addition to the steering torque TM, the inertia force of the electric motor 14, the return of the steering handle 11 to the neutral position, and the resistance to the turning operation of the steering handle 11 are performed. Therefore, a good steering feeling is obtained for the driver.

The command current value I * output from the adder 56 is limited by the command current limit value calculator 60. In this case, the temperature limit value calculation unit 61, the motor power supply voltage limit value calculation unit 62, the ignition off limit value calculation unit 63, and the fail limit value calculation unit 64 include the limit value ILt,
Ile, ILi, and ILf are calculated respectively, and the minimum value calculator 65 calculates these limit values ILt, ILe, ILi, and IL
calculating the minimum value of f as the minimum limit value ILmin;
The current limit return section 66 changes and controls the change state of the minimum limit value ILmin and outputs the current limit value IL *, and the command current value limit section 67 converts the command current value I * into the current limit value IL *.
Limited by *.

The temperature limit value calculating section 61 is provided with the temperature sensor 23
Is input, and a temperature limit value ILt that decreases as the temperature Tp increases is calculated and output. Therefore, the drive circuit 30 and the control circuit unit 4
When the temperature such as 0 rises, the current Im flowing to the electric motor 14 is limited to suppress the temperature rise, so that the electric motor 14, the drive circuit 30, the control circuit unit 40, and the like are protected from overheating. become.

The motor power supply voltage limit value calculation unit 62
Execute the motor power supply voltage restriction program of
The power supply voltage limit value ILe corresponding to m is calculated and output.
Execution of this program is started in step 100,
In step 102, the power supply voltage Em is input, and in step 1
At 04, low-pass filter processing (smoothing processing) is performed to remove noise, and it is determined whether the processed power supply voltage Em is equal to or lower than a predetermined voltage value Em1. The predetermined voltage value Em1 is set slightly higher than the voltage at which the operation of the microcomputer constituting the control circuit unit 40 becomes unstable, and is set to, for example, 7.0 V.

When the power supply voltage Em is normal and the predetermined voltage value E
If it is larger than m1, "NO" is determined in the step 106, and it is determined whether or not the flag F is "1" in a step 108. The flag F sets the power supply voltage limit value ILe to "0" by "1" and sets the limit value ILe to any other value by "0", and is initially set to "0". ing. Therefore, initially, "NO" is determined in step 108, and step 120
It is determined again whether or not the flag F is "0". In this case, since the flag F is set to "0" as described above, "YES" is determined in the step 120, and the program proceeds to the step 122 and thereafter.

In step 122, the power supply voltage Em subjected to the low-pass filter processing in the step 104 is subjected to a low-pass filter processing whose cutoff frequency is much lower than that in the low-pass filter processing in the step 104. Therefore, at the beginning of this low-pass filter processing, if the initial value is set low,
In order to prevent a low value from being output despite the power supply voltage Em being somewhat high, the previous value is used as the initial value. At the time of the first calculation, a method of using the voltage obtained this time as the previous value is used. The lower the cutoff frequency of the low-pass filter processing, the lower the power supply voltage limit value IL
e (and thus the minimum limit value ILmin) changes slowly,
Suppressing of the hunting phenomenon of the power supply voltage Em and the power supply voltage limit value ILe caused by the sudden decrease of the power supply voltage Em due to the large current consumption near the steering end when the steering wheel 11 is stationary, and vice versa. That is, the steering vibration of the steering handle 11 can be suppressed.

After the processing in step 122, step 1
At 24, the power supply voltage limit value ILe is derived with reference to the conversion table (Em-ILe table). As shown in FIG. 7, this conversion table indicates that the power supply voltage Em has a predetermined voltage value E
When the power supply voltage Em is equal to or lower than m2 (for example, 10.0 V), it is maintained at "0". When the power supply voltage Em is higher than the predetermined voltage value Em2 and equal to or lower than the predetermined voltage value Em3, it is set to "0" as the power supply voltage Em3 increases. The power supply voltage limit value ILe that gradually rises from the maximum current value Imax to the allowable maximum current value Imax and becomes the maximum current value Imax when the power supply voltage Em is higher than the predetermined voltage value Em3 is stored. The above-mentioned predetermined voltage value Em1 is a value smaller than the predetermined voltage value Em2. In this conversion table, the smaller the slope of the power supply voltage limit value ILe between the predetermined voltage values Em2 to Em3 of the power supply voltage Em, the smaller the
Suppressing of the hunting phenomenon of the power supply voltage Em and the power supply voltage limit value ILe caused by the sudden decrease of the power supply voltage Em due to the large current consumption near the steering end when the steering wheel 11 is stationary, and vice versa. That is, the steering vibration of the steering handle 11 can be suppressed.

As a result, the power supply voltage Em becomes the predetermined voltage value E
When it is larger than m1, the power supply voltage limit value ILe is basically set to a value according to the above-described characteristic according to the power supply voltage Em. As a result, when the power supply voltage Em decreases due to the rotation of the electric motor 14, the drive current Im for the motor 14 is limited in accordance with the power supply voltage Em. As a result, the influence of the rotation of the motor 14 on other systems can be reduced.

When the power supply voltage Em becomes equal to or lower than the predetermined voltage value Em1, "YES" is determined in step 106, and the state continues in step 116 for a predetermined time T1 (for example, 20 milliseconds) or more. Is determined. If the state does not continue for a predetermined time T1 or more,
At step 116, “NO” is determined, and the processing of step 120 and thereafter is executed.

On the other hand, if the state has continued for the predetermined time T1 or more, "YES" is determined in step 116, and
At step 118, the flag F is set to "1". When the flag F is set to "1" in this manner, "NO" is determined in step 120, and the power supply voltage limit value ILe is set to "0" in step 126. Then, if the state where the power supply voltage Em is equal to or lower than the predetermined voltage value Em1 continues, it is determined to be “YES” in steps 106 and 116, and
The power supply voltage limit value ILe is kept set to “0”.

Further, even if the power supply voltage Em becomes higher than the predetermined voltage value Em1 from the above-mentioned state, steps 108 to 11 are executed.
By the process of 2, the power supply voltage limit value ILe does not immediately return. That is, when the power supply voltage Em has the predetermined voltage value E
If it is larger than m1, it is determined "NO" in step 106, but "YES" in step 108, that is, it is determined that the flag F is "1", and in step 110, the power supply voltage Em is It is determined whether or not the voltage value is equal to or higher than Em2. If the power supply voltage Em is less than the predetermined voltage value Em2,
At step 110, “NO” is determined, and the program proceeds to step 120 and thereafter. Therefore, in this case, the flag F is maintained at "1" and the power supply voltage limit value ILe is also maintained at "0".

When the power supply voltage Em becomes equal to or higher than the predetermined voltage value Em2, "YES" is determined in step 110, and the state in which the power supply voltage Em is equal to or higher than the predetermined voltage value Em2 is determined in step 112 for a predetermined time T2 (for example, , 20 milliseconds) or more. Predetermined time T2
If not, "NO" in step 112.
In this case, the flag F is maintained at "1" and the power supply voltage limit value ILe is also maintained at "0".

If the state in which the power supply voltage Em is equal to or higher than the predetermined voltage value Em2 continues for the predetermined time T2 or longer, "YES" is determined in the step 112, and the flag F is determined in the step 114.
Is set to “0” and the program proceeds to step 120. In step 120, “YES” is determined based on the flag F set to “0”, and the processing of steps 122 and 124 described above is executed.
The power supply voltage limit value ILe is set to a value according to the characteristic of FIG. 7 according to the power supply voltage Em. By the processing of steps 106 to 126, the power supply voltage E
While a large decrease and return of m are reliably detected,
Even if there is a large drop in the power supply voltage Em, the power supply voltage limit value ILe is set to a value other than "0" for a predetermined time, so that the effect of this voltage drop on other systems is reduced and the electric motor 14 As long as driving is allowed.

In this embodiment, the flag F
Is changed from “0” to “1”, step 1
26, the power supply voltage limit value ILe is suddenly changed to “0”.
e may be gradually changed to “0”. In this case, in step 126, the power supply voltage limit value ILe may be gradually changed to “0” as time passes. As a result, the change of the minimum limit value ILmin becomes slower, and the power supply voltage Em is sharply reduced due to a large current consumption near the steering end when the steering wheel 11 is stationary, and vice versa. Further, it is possible to suppress the occurrence of the hunting phenomenon of the power supply voltage limit value ILe, that is, to suppress the vibration of the steering of the steering wheel 11.

In this embodiment, the power supply voltage limit value ILe is determined by using the conversion table (Em-ILe table) in the process of step 124. The power supply voltage limit value ILe may be set to the maximum current value Imax without using it. In this case, the flag F is set to "
When the power supply voltage limit value ILe is changed from "0" to "1", it is necessary to gradually change the power supply voltage limit value ILe to "0" as time elapses in step 126 as described above.
Thus, also in this case, the change of the minimum limit value ILmin becomes slow, and the steering vibration of the steering wheel 11 can be suppressed. Further, in order to improve the steering feeling, the power supply voltage limit value ILe is set to the maximum current value Ima in step 124.
Also in the process of setting x, the flag F is changed from “1” to “1”.
Immediately after the power supply voltage limit value ILe is changed to "0", the power supply voltage limit value ILe may be gradually changed to "0" as time passes.

The ignition-off limit value calculating section 63
In response to the arrival of an ignition off signal IGOF indicating that the ignition switch IG has been turned off from a detection unit (not shown), as shown in FIG.
The ignition-off limit value ILi, which gradually decreases from time x as time passes, is calculated and output. As a result, the application of the assist force to the driver's steering operation immediately after the ignition switch IG is turned off is ensured, and the power supply to the electric motor 14 thereafter is cut off.

The fail limit value calculating section 64 calculates and outputs a fail limit value ILf having various characteristics as shown in FIG. 9 in response to a fail signal FAIL from a detection section (not shown). As a result, the application of assist force to the driver's steering operation after the occurrence of an abnormality (fail) in the electric power steering device is ensured, and the power supply to the electric motor 14 thereafter is cut off. If a plurality of types of abnormalities occur and are detected simultaneously, the smallest limit value is output as the fail limit value.

By executing the current limit return program of FIG. 10, the current limit return unit 66 allows the change of the minimum limit value ILmin and outputs the current limit value IL * in a manner corresponding to the steering torque TM and the vehicle speed V. I do. The current limit recovery program is started in step 200, and in step 202, it is determined whether or not the microcomputer constituting the control circuit unit 40 is performing an initial check. If the initial check is being performed, step 202
Is determined to be “NO” at step 226, and the current limit value IL * is set to the minimum limit value I supplied from the minimum value calculation unit 65 at step 226.
Set to Lmin. On the other hand, if the microcomputer finishes the initial check operation, step 202
Is determined to be "YES" in step 204 and the program is executed.
Proceed to the following.

In step 204, it is determined whether or not the current minimum limit value ILmin supplied from the minimum value calculation section 65 is larger than the previous current limit value IL *. If the current minimum limit value ILmin is equal to or smaller than the previous current limit value IL *, it is determined "NO" in step 204, and in step 226, the current limit value IL * is calculated in the same manner as described above. It is set to the minimum limit value ILmin supplied from 65. When the current limit value IL * should be reduced in this way, by immediately responding to this, the electric power steering device can be protected and the influence on other systems can be minimized. .

On the other hand, if the current minimum limit value ILmin is larger than the previous current limit value IL *, that is, if the current limit value IL * should be increased, "YES" is determined in step 204, and The program proceeds to step 206 and subsequent steps. In step 206, the steering torque TM from the steering torque sensor 21 and the vehicle speed V from the vehicle speed sensor 22 are input. Then, in step 208, it is determined whether or not the absolute value | TM | of the steering torque TM is equal to or greater than a predetermined value TMo. Absolute value of steering torque TM | TM |
Is less than the predetermined value TMo, at step 208
In step 228, the execution of the current limit return program is terminated without changing the current limit value IL *, that is, while keeping the current limit value IL * at the previous value.

If the absolute value | TM | of the steering torque TM is equal to or greater than the predetermined value TMo, "YES" is determined in step 208, and in step 210, the V-CNTup conversion table is referred to and Count up value CNTup
To determine. The count-up value CNTup is a time value for determining the increase rate of the current limit value IL * (decreasing the increase rate of the current limit value IL * as it increases), and as shown in FIG. Increases with increase. That is, the count-up value CNTup is a time value for slowly returning the current limit value IL * as the vehicle speed V increases. After the processing in step 210, a predetermined small value ΔCNT is added to the count value CNT in step 212, and the count value CNT is increased by the determination processing in step 214 to the count-up value CNTup.
Until the above, the program proceeds to step 220 and subsequent steps. The count value CNT is initially set to “0”.

By repeatedly executing the current limit return program, the count value CNT becomes the count-up value CNT.
If it is not less than “up”, the current limit value IL * is determined in step 216 based on the determination of “YES” in step 214.
To the provisional current limit value IL * '
, The count value CNT is cleared to “0” in step 218, and the program proceeds to step 220 and subsequent steps.

In step 220, the provisional current limit value IL * 'is compared with the minimum limit value ILmin supplied from the minimum value calculation section 65. If the provisional current limit value IL * 'is less than the minimum limit value ILmin, it is determined "NO" in step 220, and the current limit value I is determined in step 224.
L * is set to the provisional current limit value IL * '. This allows
The current limit value IL * is gradually increased with time. As the current limit value IL * increases, the provisional current limit value IL * 'calculated in step 216 also increases. When the current limit value IL *' exceeds the minimum limit value ILmin, the current limit value IL * 'is increased.
* Is set to the minimum limit value ILmin. Thus, the current limit value IL * does not increase beyond the minimum limit value ILmin. During the process of returning the current limit value IL * to the minimum limit value ILmin in the steps 208 to 224, the vehicle speed V suddenly changes and the count-up value CNTup
Is changed, there is a possibility that a sense of incongruity may occur in the return. Therefore, when the return process is started, the count-up value CNTup may be held.

In the current limiting / recovery section 66 operating as described above, the steering torque T
As long as the absolute value | TM | of M does not exceed the predetermined value TMo, the current limit value IL * is not increased. This means that the absolute value | TM |
As long as it does not exceed o, it means that the output command current value Io * is not increased, that is, the assist force by the electric motor 14 is not increased.
(Temperature limit value ILt, motor power supply voltage limit value ILe, ignition off limit value ILi, and fail limit value ILf)
If the driver greatly increases the steering wheel 11
During the turning operation, the current limit value IL * increases, and during this steering, the driver hardly feels a change in the steering operation, so that the driver does not feel great discomfort with the steering operation. Thus, the driver's steering feeling is improved.

Even when the increase of the current limit value IL * is detected, the current limit value IL * is gradually increased with the passage of time by the processing of steps 212 to 224. Therefore, the driver does not feel any more uncomfortable with the steering operation, and the steering feeling of the driver is further improved.

Further, in the control for increasing the current limit value IL *, the speed of increase of the current limit value IL * is made to depend on the vehicle speed V, and is made slower as the vehicle speed V increases, by the processing of step 210. Therefore, a change in the steering operation at a high vehicle speed is suppressed as much as possible, and the driving stability of the vehicle is secured while improving the steering feeling of the driver.

In the current limit return program, the increasing speed of the current limiting value IL * (output command current value Io *) is made to change continuously as the vehicle speed V increases. Alternatively, the speed at which the current limit value IL * is increased may be switched between two stages, that is, when the vehicle speed V is equal to or lower than the reference vehicle speed Vo with the predetermined reference vehicle speed Vo interposed therebetween and when the vehicle speed V is higher than the reference vehicle speed Vo. As the reference vehicle speed Vo,
If “0” or a predetermined minute value is set, the increasing speed of the current limit value IL * is fast only when the vehicle is stopped or running at extremely low speed, and the increasing speed of the current limit value IL * is slow during normal running of the vehicle. Become. Further, the reference vehicle speed Vo is set to 20 km / km so that the increasing speed of the current limit value IL * is increased at a low vehicle speed.
h, 30 km / h. In this case, instead of the processing of step 210, the vehicle speed V is compared with the reference vehicle speed Vo, and if the vehicle speed V is equal to or less than the reference vehicle speed Vo, the count-up value CNTup is set to a small value, and the vehicle speed V
Is greater than the reference vehicle speed Vo, the count-up value CN
What is necessary is just to employ | adopt the process which sets Tup to a large value.

In the current limit return program, the count-up value CNTup is increased at step 210 to reduce the increasing speed of the current limit value IL * (output command current value Io *) as the vehicle speed V increases. It was changed according to V. However, the predetermined value ΔCNT to which the count value CNT is added in step 212 may be changed according to the vehicle speed V, or the time interval at which the current limit recovery program is executed may be changed according to the vehicle speed V. . In this case, if the predetermined value ΔCNT is made smaller as the vehicle speed V increases, or if the time interval is made larger as the vehicle speed increases, the current limit is increased as the vehicle speed V increases. The increasing speed of the value IL * (output command current value Io *) decreases.

The command current value limiting section 67 limits the absolute value | I * | of the command current value I * to be equal to or less than the current limit value IL * by executing the command current value limiting program shown in FIG. The final output command current value Io * is output.
The command current value limiting program is started in step 300, and in step 302, it is determined whether or not the command current value I * is equal to or less than the negative current limit value -IL *. It is determined whether or not I * is equal to or greater than the positive current limit value IL *.

If the command current value I * is equal to or less than the negative current limit value -IL *, "YES" is determined in step 302.
In step 306, the output command current value Io * is set to a negative current limit value -IL *. If the command current value I * is equal to or greater than the positive current limit value IL *, it is determined to be "YES" in step 304, and the output command current value Io * is set to the positive current limit value IL * in step 308. If the command current value I * is a value between the two current limit values -IL *, IL *, both are determined to be "NO" in steps 302 and 304, and in step 310, the output command current value Io * is set to the command current. Set to the value I *. As a result, the absolute value | Io * | of the output command current value Io * supplied to the drive control unit 47 is limited within the current limit value IL *, and the electric motor 14 is controlled by the limited output command current value Io *. It will be driven.

When the command current I * is greatly limited by the execution of the current limit storage program of FIG. 13, the current limit storage unit 70 stores the history of the limitation. The current limit storage program is started in step 400, and in step 402, the absolute value | I * of the command current value I *
By subtracting the absolute value | Io * | of the output command current value Io * from |, it is determined whether or not a value | I * | − || Io * | is equal to or greater than a predetermined value Iref, thereby increasing the command current I *. Detect restricted conditions. That is, if the command current I * is greatly limited and the value | I * | − | Io * |
In step 404, the current limit information is stored in the nonvolatile memory. As this current limit information,
The subtracted value | I * |-| Io * |, the limited date and time by a program processing (not shown), the time from when the ignition switch IG is turned on, and the like are increased. In this case, if the cause of the current limitation, that is, the current limitation is caused by any of the temperature limitation value ILt, the motor power supply voltage limitation value ILe, the ignition off limitation value ILi, and the fail limitation value ILf, is further stored. Good.

When the absolute value | I * | of the command current value I * is subtracted from the absolute value | Io * | of the output command current value Io *, the value | I * | − || Io * | If there is, the determination in step 402 is “NO”, and the execution of the current limiting program is terminated in step 406.

By storing the history in which the output command current value Io * is greatly limited, the presence or absence of a failure of the electric power steering device and the analysis of the occurrence are appropriately performed even at a later date. be able to.

In the above embodiment, the ignition-off limit value ILf calculated by the ignition-off limit value calculation unit 63 is output to the minimum value calculation unit 65. However, instead of this, the ignition-off limit value ILf is output to the command current value limiting section 67, and the limiting section 67 converts the command current value IL * from the adding section 56 into its absolute value | IL * | May be limited to a smaller value of the ignition-off limit value ILf and the current limit value IL * from the current limit return unit 66, whichever is smaller.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a block diagram of the electric control device of FIG.

FIG. 3 is a detailed block diagram of a command current value generator of FIG. 2;

FIG. 4 is a graph showing a relationship between a steering torque and a basic command current value.

FIG. 5 is a graph showing a relationship between a temperature and a temperature limit value.

FIG. 6 is a flowchart of a motor power supply voltage restriction program executed by a motor power supply voltage restriction value calculation unit of FIG. 3;

FIG. 7 is a graph showing a relationship between a motor power supply voltage and a motor power supply voltage limit value.

FIG. 8 is a graph showing a change over time of an ignition-off limit value.

FIG. 9 is a graph showing a change of a fail limit value over time.

FIG. 10 is a flowchart of a current limit restoring program executed by the current limit restoring unit of FIG. 3;

FIG. 11 is a graph showing a relationship between a vehicle speed and a count-up value.

FIG. 12 is a flowchart of a command current value limiting program executed by a command current value limiting unit in FIG. 3;

FIG. 13 is a flowchart of a current limit storage program executed by the current limit storage unit of FIG. 3;

[Explanation of symbols]

FW1, FW2: left and right front wheels, IG: ignition switch, 11: steering wheel, 13: steering shaft, 14: electric motor, 20: electric control device, 21: steering torque sensor, 22: vehicle speed sensor, 23: temperature sensor, 30 ... Drive circuit, 37 ... Battery, 40 ... Control circuit unit, 43
... voltage detector, 44 ... current detector, 45 ... steering speed calculator, 46 ... command current value generator, 50 ... command current value calculator, 51 ... basic assist controller, 52 ... differentiator, 53 ...
Inertia compensation control unit, 54: handle return control unit, 55: damping control unit, 56: addition unit, 60: command current limit value calculation unit, 61: temperature limit value calculation unit, 62: motor power supply voltage limit value calculation unit, 63: ignition-off limit value calculator, 64: fail limit value calculator, 65: minimum value calculator, 66: current limit return unit, 67: command current value limit unit,
70: Current limit storage unit.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Eiji Kasai 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3D032 CC08 DA09 DA15 DA23 DA64 DA65 DA73 DD17 EA01 EB12 EC23 EC29 3D033 CA03 CA13 CA16 CA19 CA21 CA28

Claims (3)

[Claims] An electric motor for applying an assist force to a turning operation of a steering wheel, and a current having a magnitude corresponding to a steering state of the steering wheel is supplied to the electric motor to control the rotation of the electric motor. A motor control unit; and an electric power steering apparatus for a vehicle, comprising: a current limiting unit configured to limit a current value flowing to the electric motor to a limit value according to a predetermined condition; a steering torque detecting unit configured to detect a steering torque; An electric power steering apparatus for a vehicle, further comprising: a limit value control unit that allows an increase in a limit value limited by the current limiting unit when the detected steering torque is equal to or more than a predetermined value. 2. An electric power steering apparatus for a vehicle according to claim 1, wherein said limit value control means gradually increases said limit value over time when increase of said limit value is permitted. An electric power steering device for a vehicle. 3. An electric power steering apparatus for a vehicle according to claim 2, wherein said limit value control means makes an increasing speed of said limit value dependent on a vehicle speed. .