JP6744572B2 - Steering control device - Google Patents

Description

The present invention relates to a steering control device.

BACKGROUND ART Conventionally, there is an EPS (electric power steering device) that applies a motor torque as an assist force to a vehicle steering mechanism. For example, an EPS control device described in Patent Document 1 calculates an assist control amount based on a plurality of state quantities indicating steering states such as steering torque and steering angle, and controls power supply to a motor based on the assist control amount. To do. The control device individually sets a limit value (upper limit value and lower limit value) for limiting the change range of the assist control amount according to each state amount, for each state amount. The control device sets a value obtained by summing these individually set limit values as the final limit value for the assist control amount. In this way, when the EPS control device is provided with the limiting function for the abnormal assist control amount, when the assist control amount indicating the abnormal value is calculated, the value of the abnormal assist control amount is the final limit value. Is limited to an appropriate value according to each state quantity.

In the EPS of Patent Document 1, a rack and pinion mechanism is adopted as a steering mechanism. The mechanism changes the direction of the steered wheels by converting the rotation of the pinion accompanying the operation of the steering wheel into the linear movement of the rack shaft meshing with the pinion. The rack shaft is slidably accommodated in the housing. Normally, when the rack shaft reaches the limit of its movable range, so-called "end contact" occurs in which the end (rack end) of the rack shaft hits the housing, and the movement range of the rack shaft is physically restricted. As a result, the operating range of the steering wheel is also restricted.

When the end is applied, the torsion bar is twisted by the inertia of the steering wheel, so that a larger steering torque is instantaneously detected. The assist control amount calculated based on the steering torque also has a larger value. Further, the rotation speed of the motor, and consequently the counter electromotive force (induced voltage), sharply decreases due to the occurrence of the end contact. For this reason, the electric current flowing through the motor becomes excessively large, and an unnecessarily large assist force may be applied to the steering mechanism. Therefore, the impact at the end contact may be greater.

Therefore, in order to mitigate the impact at the time of end contact, for example, the control device of the EPS described in Patent Document 2 determines the surplus assist current value from the current assist current value when it is determined that the end contact has occurred. The motor is controlled based on the current command value obtained by the subtraction. A current according to the current command value is supplied to the motor. The current assist current value here is the assist current value for the motor immediately before the end contact occurs. Further, the surplus assist current value is stored in the control device as a correction waveform obtained by measuring a change in the counter electromotive force of the motor from the occurrence of the end contact to the elapse of a predetermined time. According to this configuration, the excess assist current value is subtracted from the current assist current value, so that the current command value for the motor is prevented from becoming excessively large. Further, the current command value for the motor is corrected to an appropriate value for maintaining the maximum steering angle of the steering wheel. Therefore, the impact at the time of hitting the end is reduced.

JP, 2005-163498, A JP, 2009-143312, A

When the EPS control device is provided with both the protective function for limiting the abnormal assist control amount of the cited document 1 and the buffer function for alleviating the impact at the end hit of the cited document 2 as the protection function, the following is performed. Is concerned. That is, since the electric current supplied to the motor is suppressed while the EPS control device is executing the buffer function for the end contact, the steering torque is likely to be larger. Therefore, when the limit function for the assist control amount is executed, for example, an individual limit value according to the steering torque that is one of the state quantities indicating the steering state, and finally a final limit value that reflects the individual limit value. The value may spread excessively with respect to the assist control amount reduced through the execution of the buffer function. Under this circumstance, if an excessive assist control amount indicating an abnormal value is calculated, it is feared that the abnormal assist control amount cannot be properly limited. At this time, a larger change in the motor torque or self-steering may occur.

An object of the present invention is to provide a steering control that can more appropriately limit an excessive assist control amount that indicates an abnormal value, even if it has a protection control function that reduces the assist control amount for controlling power supply to a motor. To provide a device.

A steering control device that can achieve the above object includes an assist control unit, a protection control unit, and a restriction processing unit. The assist control unit calculates an assist control amount for controlling power supply to a motor that is a generation source of the assist force applied to the steering mechanism of the vehicle, based on a plurality of state quantities including the steering torque. The protection control unit executes protection control to decrease the value of the assist control amount when a specific condition is satisfied. The limit processing unit individually sets a limit value for limiting the change range of the assist control amount according to the plurality of state quantities for each of the state quantities, and the assist obtained by adding these limit values together. The change range of the assist control amount is limited based on the final limit value for the control amount. Further, when the specific condition is satisfied, the limit processing unit limits the change range of the assist control amount by using the final limit value immediately before the protection control is executed.

According to this configuration, the limit value of the assist control amount is set individually for each state amount used for the calculation of the assist control amount, and the value obtained by adding these limit values is the final value for the assist control amount. It is set as a limit value. Therefore, even when an excessive assist control amount indicating an abnormal value is calculated for some reason, the abnormal assist control amount is limited to an appropriate value according to each state amount by the final limit value. By controlling the power supply to the motor, which is the source of the assist force, based on the assist control amount limited to an appropriate value, it is possible to prevent the unintended assist force from being applied to the steering mechanism.

Here, while the protection control is being executed, the original assist control amount calculated according to the steering state at that time is forcibly reduced, so that the value of the steering torque tends to become larger. Therefore, the individual limit value according to the steering torque, and eventually the limit width of the final limit value that reflects the individual limit value, may be excessively widened relative to the reduced actual assist control amount. ..

In this respect, according to the above configuration, when the specific condition is satisfied, the final limit value immediately before the protection control is executed is used to limit the change range of the reduced assist control amount. The final limit value immediately before the protection control is executed is calculated based on the steering state immediately before the assist control amount is decreased through the execution of the protection control, that is, immediately before the steering torque is increased as the assist control amount is decreased. It is a thing. Therefore, the limit width of the final limit value immediately before the protection control is executed is narrower than the limit width of the final limit value calculated after the protection control is executed. Therefore, by using the final limit value immediately before the protection control is executed as the final limit value for the reduced assist control amount, the limit width for the reduced assist control amount may be unnecessarily widened. Suppressed. It is possible to more appropriately limit the excessive assist control amount indicating the abnormal value.

In the above steering control device, it is preferable that the restriction processing unit includes a holding unit and a switching unit. The holding unit holds the used final limit value each time the final limit value is used. The switching unit determines the final limit value to be used according to the success or failure of the specific condition as the final limit value calculated this time and the last limit value calculated last time held in the holding unit. Switch between and.

According to this configuration, when the specific condition is satisfied, the final limit value to be used is changed from the final limit value calculated this time to the final limit value (previously calculated) held in the holding unit ( It is switched to the final limit value immediately before the protection control is executed). Further, when the specific condition is not satisfied, the final limit value to be used is switched from the last limit value calculated previously held in the holding unit to the last limit value calculated this time. In this way, the final limit value used in the limit processing unit can be appropriately switched according to the success or failure of the specific condition.

In the above steering control device, it is preferable that the protection control unit sets a value of a flag according to a determination result of success or failure of the specific condition. Further, at this time, it is preferable that the restriction processing unit recognizes whether or not the specific condition is satisfied based on the value of the flag.

With this configuration, the restriction processing unit can easily recognize the success or failure of the specific condition based on the value of the flag set in the protection control unit.
In the above steering control device, the specific condition may be a determination that the steering mechanism has reached its physical steering limit.

When it is determined that the steering mechanism has reached its physical steering limit, the assist force is weakened by the amount by which the assist control amount is forcibly reduced. Therefore, the impact when the steering mechanism reaches its physical steering limit is mitigated.

In the above steering control device, the specific condition may be a determination that the motor is in an overheated state.
When it is determined that the motor is overheated, the current supplied to the motor is reduced by the amount by which the assist control amount is forcibly reduced. Therefore, overheating of the motor is suppressed.

According to the steering control device of the present invention, it is possible to more appropriately limit an excessive assist control amount indicating an abnormal value even when the steering control device has a protection control function for reducing the assist control amount for controlling power supply to a motor. You can

The block diagram which shows an example of the electric power steering apparatus which has an electronic controller. The control block diagram which shows an example of an electronic control unit. The control block diagram which shows an example of an assist control part. The control block diagram which shows an example of the upper and lower limit calculation part. The map which shows an example of the relationship between steering torque and a limit value. The map which shows an example of the relationship between the derivative of steering torque, and a limit value. The map which shows an example of the relationship between a steering angle and a limit value. The map which shows an example of the relationship between steering speed and a limit value. The map which shows an example of the relationship between steering angular acceleration and a limit value. The graph which shows an example of change of assist control amount (current command value).

An embodiment in which the steering control device is embodied in an ECU (electronic control device) of an electric power steering device will be described below.
<Outline of EPS>
As shown in FIG. 1, an electric power steering apparatus 10 includes a steering mechanism 20 that steers steered wheels based on a steering operation of a driver, a steering assist mechanism 30 that assists the steering operation of a driver, and a steering assist mechanism 30. The ECU 40 is provided for controlling the operation of the.

The steering mechanism 20 includes a steering wheel 21 operated by a driver and a steering shaft 22 that rotates integrally with the steering wheel 21. The steering shaft 22 includes a column shaft 22a connected to the center of the steering wheel 21, an intermediate shaft 22b connected to the lower end of the column shaft 22a, and a pinion shaft 22c connected to the lower end of the intermediate shaft 22b. .. The lower end of the pinion shaft 22c is meshed with a rack shaft 23 (to be precise, a portion 23a having rack teeth) extending in a direction intersecting with the pinion shaft 22c. Therefore, the rotational movement of the steering shaft 22 is converted into a reciprocating linear movement of the rack shaft 23 by the rack and pinion mechanism 24 including the pinion shaft 22c and the rack shaft 23. The reciprocating linear motion is transmitted to the left and right steered wheels 26, 26 via the tie rods 25 respectively connected to both ends of the rack shaft 23, so that the steered angles θta of the steered wheels 26, 26 are changed. R.

As shown by the chain double-dashed line in FIG. 1, the lower ends of the rack shaft 23 and the pinion shaft 22c are housed in the housing 27. When the rack shaft 23 reaches the limit of its movable range through the operation of the steering wheel 21, a so-called "end contact" occurs in which the end (rack end) of the rack shaft 23 hits the housing 27, so that the rack shaft 23 The movement range of is physically restricted. As a result, the operation range of the steering wheel 21 is also restricted.

As shown in FIG. 1, the steering assist mechanism 30 includes a motor 31 that is a source of a steering assist force. As the motor 31, for example, a three-phase brushless motor is adopted. The motor 31 is connected to the column shaft 22a via a reduction mechanism 32. The deceleration mechanism 32 decelerates the rotation of the motor 31 and transmits the decelerated rotational force to the column shaft 22a. That is, the torque of the motor is applied to the steering shaft 22 as a steering assist force (assist force) to assist the driver's steering operation.

The ECU 40 acquires the detection results of various sensors provided in the vehicle as information indicating the driver's request or the traveling state, and controls the motor 31 according to the various information acquired.

The various sensors include, for example, a vehicle speed sensor 51, a steering sensor 52, a torque sensor 53, and a rotation angle sensor 54. The vehicle speed sensor 51 detects a vehicle speed (vehicle traveling speed) V. The steering sensor 52 is provided on the column shaft 22a and detects the steering angle θs. The torque sensor 53 is provided on the column shaft 22a and detects the steering torque τ. The rotation angle sensor 54 is provided in the motor 31 and detects the rotation angle θm of the motor 31.

The ECU 40 calculates a target assist force based on the vehicle speed V, the steering angle θs, the steering torque τ, and the rotation angle θm, and supplies the motor 31 with drive power for causing the steering assist mechanism 30 to generate the target assist force.

<ECU configuration>
Next, the hardware configuration of the ECU will be described.
As shown in FIG. 2, the ECU 40 includes a drive circuit (inverter circuit) 41 and a microcomputer 42.

The drive circuit 41 converts DC power supplied from a DC power supply such as a battery into three-phase AC power based on a motor control signal Sc (PWM drive signal) generated by the microcomputer 42. The converted three-phase AC power is supplied to the motor 31 via the power supply path 43 for each phase. A current sensor 44 is provided in the power supply path 43 for each phase. These current sensors 44 detect the actual current value Im generated in the power supply path 43 of each phase. Note that in FIG. 2, the power supply path 43 of each phase and the current sensor 44 of each phase are collectively shown as one for convenience of description.

The microcomputer 42 takes in the detection results of the vehicle speed sensor 51, the steering sensor 52, the torque sensor 53, the rotation angle sensor 54, and the current sensor 44 at predetermined sampling periods. The microcomputer 42 generates a motor control signal Sc on the basis of the detection results thus taken in, that is, the vehicle speed V, the steering angle θs, the steering torque τ, the rotation angle θm, and the actual current value Im.

<Microcomputer>
Next, the functional configuration of the microcomputer will be described.
The microcomputer 42 has various arithmetic processing units realized by executing a control program stored in a storage device (not shown).

As shown in FIG. 2, the microcomputer 42 includes a current command value calculation unit 61 and a motor control signal generation unit 62 as these calculation processing units. The current command value calculation unit 61 calculates the current command value I ^* based on the steering torque τ, the vehicle speed V and the steering angle θs. The current command value I ^* is a command value indicating the current to be supplied to the motor 31. To be precise, the current command value I ^* includes the q-axis current command value and the d-axis current command value in the d/q coordinate system. In this embodiment, the d-axis current command value is set to zero. The d/q coordinate system is rotation coordinates according to the rotation angle θm of the motor 31. The motor control signal generation unit 62 uses the rotation angle θm to convert the three-phase current value Im of the motor 31 into a two-phase vector component, that is, a d-axis current value and a q-axis current value in the d/q coordinate system. .. Then, the motor control signal generation unit 62 obtains the deviation between the d-axis current value and the d-axis current command value and the deviation between the q-axis current value and the q-axis current command value, respectively, and the motor is controlled to eliminate these deviations. The control signal Sc is generated.

<Current command value calculator>
Next, the current command value calculator will be described.
As shown in FIG. 2, the current command value calculation unit 61 includes an assist control unit 71, an upper/lower limit limit calculation unit 72, and an upper/lower limit guard processing unit 73. Further, the current command value calculation unit 61 has three differentiators 74, 75, 76. The differentiator 74 calculates the steering speed ωs by differentiating the steering angle θs. The differentiator 75 calculates the steering angular acceleration αs by further differentiating the steering speed ωs calculated by the differentiator 74 at the preceding stage. The differentiator 76 calculates the steering torque differential value dτ by differentiating the steering torque τ with time.

The assist control unit 71 calculates the assist control amount I _as ^* based on the steering torque τ, the vehicle speed V, the steering angle θs, the steering speed ωs, the steering angular acceleration αs, and the steering torque differential value dτ. The assist control amount I _as ^* is calculated to control the power supply to the motor 31. The assist control amount I _as ^* is a value (current value) of the amount of current that should be supplied to the motor 31 in order to generate a target assist force having an appropriate magnitude according to various state amounts.

The upper and lower limit calculation unit 72 is based on various signals used in the assist control unit 71, here, steering torque τ, steering angle θs, steering torque differential value dτ, steering speed ωs, and steering angular acceleration αs. _An upper limit value I _UL ^* and a lower limit value I _LL ^* are calculated as limit values for _as ^* . The upper limit value I _UL ^* and the lower limit value I _LL ^* are final limit values for the assist control amount I _as ^* .

The upper/lower limit guard processing unit 73 executes the limiting process of the assist control amount I _as ^* based on the upper limit value I _UL ^* and the lower limit value I _LL ^* calculated by the upper and lower limit calculation unit 72. That is, the upper/lower limit guard processing unit 73 compares the value of the assist control amount I _as ^{* with} the upper limit value I _UL ^* and the lower limit value I _LL ^* . Upper and lower limit guard processing unit 73, when the when the assist control amount _{I the as} ^* exceeds the upper limit _{I UL} ^* limits the assist control amount _{I the as} ^* to the upper limit value _{I UL} ^*, the lower limit _{I LL} ^* Limits the assist control amount I _as ^* to the lower limit value I _LL ^* . The assist control amount I _as ^* subjected to the limiting process becomes the final current command value I ^* . When the assist control amount I _as ^* is within the range between the upper limit value I _UL ^* and the lower limit value I _LL ^* , the assist control amount I _as ^* calculated by the assist control unit 71 remains the final current command value. It becomes I ^* .

<Assist control unit>
Next, the assist control unit 71 will be described in detail.
As shown in FIG. 3, the assist control unit 71 includes a basic assist control unit 81, a compensation control unit 82, an adder 83, and an end contact control unit 87.

The basic assist control unit 81 calculates the basic assist control amount I ₁ ^* based on the steering torque τ and the vehicle speed V. The basic assist control amount I ₁ ^* is a basic component (current value) for generating a target assist force having an appropriate magnitude according to the steering torque τ and the vehicle speed V. The basic assist control unit 81 calculates the basic assist control amount I ₁ ^* using an assist characteristic map stored in a storage device (not shown) of the microcomputer 42, for example. The assist characteristic map is a vehicle speed sensitive three-dimensional map for calculating the basic assist control amount I ₁ ^* based on the steering torque τ and the vehicle speed V. The larger the steering torque τ (absolute value), the more the vehicle speed V becomes. The smaller the value, the larger the absolute value of the basic assist control amount I ₁ ^* is set to be calculated.

The compensation control unit 82 executes various compensation controls for the basic assist control amount I ₁ ^* in order to realize a better steering feeling. The compensation control unit 82 includes an inertia compensation control unit 84, a steering wheel return control unit 85, and a torque differential control unit 86.

The inertia compensation control unit 84 calculates a compensation amount I ₂ ^* (current value) for compensating the inertia of the motor 31 based on the steering angular acceleration αs and the vehicle speed V. By correcting the basic assist control amount I ₁ ^* using the compensation amount I ₂ ^* , the feeling of catching (following delay) at the start of turning the steering wheel 21 and the feeling of flow at the end of turning (overshoot) are reduced. It

The steering wheel return control unit 85 calculates a compensation amount I ₃ ^* (current value) for compensating the return characteristic of the steering wheel 21 based on the steering torque τ, the vehicle speed V, the steering angle θs, and the steering speed ωs. By correcting the basic assist control amount I ₁ ^* using the compensation amount I ₃ ^* , the excess or deficiency of the self-aligning torque due to the road surface reaction force is compensated. This is because the assisting force is generated in the direction of returning the steering wheel 21 to the neutral position according to the compensation amount I ₃ ^* .

The torque differentiation control unit 86 detects a reverse input vibration component as a steering torque differential value dτ, and based on the detected steering torque differential value dτ, a compensation amount I ₄ ^* (current) for compensating for disturbance such as reverse input vibration. Value) is calculated. By correcting the basic assist control amount I ₁ ^* using the compensation amount I ₄ ^*, disturbance such as brake vibration generated due to the braking operation is suppressed. This is because an assisting force in the direction of canceling the reverse input vibration is generated according to the compensation amount I ₄ ^* .

The adder 83 compensation amount _I ^{2 *} as a correction processing for the basic assist control amount _I ^{1 *,} generates the assist control amount _{I the as} ^* by adding a compensation amount _I ^{3 *} and the compensation amount _I ^{4 *.}
The end contact control unit 87 determines whether or not the end contact of the rack shaft 23 has occurred, based on the steering torque τ detected by the torque sensor 53 and the vehicle speed V detected by the vehicle speed sensor 51. The end contact control unit 87 determines that the end contact has occurred, for example, when the following determination conditions (a) to (d) are satisfied.

(A) The vehicle speed V is less than the threshold value. Generally, as the vehicle speed V increases, it becomes more difficult to steer the steering wheel 21 to the steering limit.
(B) The absolute value of the steering torque τ is greater than or equal to the threshold value. When the end contact occurs, the steering torque τ generally increases.

(C) The absolute value of the changing speed of the steering torque τ is equal to or more than the threshold value. The change speed of the steering torque τ greatly changes due to the steering being attempted even though the steering wheel 21 reaches the steering limit.

(D) The steering torque τ and the changing speed of the steering torque τ have the same sign. When the steering torque τ and the changing speed of the steering torque τ have different signs, the steering wheel 21 is being operated in the direction in which the end contact is avoided.

The end contact control unit 87 executes so-called end contact control when it is determined that the end contact has occurred. The end contact control is a normal assist in which the torque (assist force) generated in the motor 31 is adjusted according to the steering torque τ in order to reduce the impact when the end contact is generated on the rack shaft 23 through the operation of the steering wheel 21. Control that weakens rather than force. When it is determined that the end contact has occurred, the end contact control unit 87 decreases the original assist control amount I _as ^* calculated by the adder 83, for example, by the set amount. The set amount is set through an experiment or the like based on, for example, how much the current supplied to the motor 31 should be reduced in order to reduce the impact at the time of hitting the end. Since the current supplied to the motor 31 is reduced by the amount by which the assist control amount I _as ^* is reduced according to the set amount, the assist force generated by the motor 31 is the original amount required for the steering torque τ. It becomes weaker than the assist power. As the assist power is weakened, the impact when hitting the end is alleviated.

Further, the end contact control unit 87 sets the end contact determination flag F to “1” when it is determined that the end contact has occurred. When it is determined that the end contact has not occurred, the end contact control unit 87 sets the end contact determination flag F to “0”.

<Upper and lower limit calculation section>
Next, the upper and lower limit calculation unit 72 will be described in detail.
As shown in FIG. 4, the upper and lower limit calculation unit 72 includes an upper limit value calculation unit 90 and a lower limit value calculation unit 100.

<Upper limit calculator>
The upper limit value calculation unit 90 includes a steering torque sensitive limiter 91, a steering torque differential value sensitive limiter 92, a steering angle sensitive limiter 93, a steering speed sensitive limiter 94, a steering angular acceleration sensitive limiter 95, and an adder 96. Further, the upper limit value calculation unit 90 has an upper limit value holding unit 97 and an upper limit value switching unit 98.

The steering torque sensitive limiter 91 calculates an upper limit value I _UL1 ^* for the assist control amount I _as ^* according to the steering torque τ. The steering torque differential value sensitive limiter 92 calculates an upper limit value I _UL2 ^* for the assist control amount I _as ^* according to the steering torque differential value dτ. The steering angle sensitive limiter 93 calculates an upper limit value I _UL3 ^* for the assist control amount I _as ^* according to the steering angle θs. The steering speed sensitive limiter 94 calculates an upper limit value I _UL4 ^* for the assist control amount I _as ^* according to the steering speed ωs. The steering angular acceleration sensitive limiter 95 calculates an upper limit value I _UL5 ^* for the assist control amount I _as ^* according to the steering angular acceleration αs.

The adder 96 generates the upper limit value I _UL ^* for the assist control amount I _as ^* by adding the five upper limit values I _UL1 ^{* to} I _UL5 ^* . The upper limit value I _UL ^* is supplied to the upper and lower limit guard processing unit 73 via the upper limit value switching unit 98.

The upper limit value holding unit 97 takes in the upper limit value I _UL ^* supplied from the upper limit value switching unit 98 to the upper and lower limit guard processing unit 73, and holds the taken upper limit value I _UL ^* . The upper limit value I _UL ^* held in the upper limit value holding unit 97 is updated every time the upper limit value I _UL ^* is supplied to the upper and lower limit guard processing unit 73. That is, the upper limit value I _UL ^* held in the upper limit value holding unit 97 is the previous value (the upper limit value I one cycle before the upper limit value I _UL ^* as the current value supplied to the upper and lower limit guard processing unit 73. _UL ^* ).

The upper limit value switching section 98, as a data input, captures the upper limit I _UL ^* held in the upper limit I _UL ^* and the upper limit value storing unit 97 is calculated by an adder 96. Further, the upper limit value switching unit 98 takes in the value of the end hit determination flag F set by the end hit control unit 87 as a control input. The upper limit value switching unit 98 sets the upper limit value I _UL ^* supplied to the upper and lower limit guard processing unit 73 to the upper limit value I _UL ^* (current value) calculated by the adder 96 based on the value of the end hit determination flag F. , And the upper limit value I _UL ^* (previous value) held in the upper limit value holding unit 97. When the value of the end hit determination flag F is “0”, the upper limit value switching unit 98 supplies the upper limit value I _UL ^* calculated by the adder 96 to the upper and lower limit guard processing unit 73. The upper limit value switching unit 98 holds in the upper limit value holding unit 97 when the value of the end hitting determination flag F is “1” (more accurately, when the value of the end hitting determination flag F is not “0”). The upper limit value I _UL ^* is supplied to the upper/lower limit guard processing unit 73.

<Lower limit value calculation part>
The lower limit value calculation unit 100 includes a steering torque sensitive limiter 101, a steering torque differential value sensitive limiter 102, a steering angle sensitive limiter 103, a steering speed sensitive limiter 104, a steering angular acceleration sensitive limiter 105, and an adder 106. Further, the lower limit value calculation unit 100 has a lower limit value holding unit 107 and a lower limit value switching unit 108.

The steering torque sensitive limiter 101 calculates a lower limit value I _LL1 ^* for the assist control amount I _as ^* according to the steering torque τ. The steering torque differential value sensitive limiter 102 calculates a lower limit value I _LL2 ^* for the assist control amount I _as ^* according to the steering torque differential value dτ. The steering angle sensitive limiter 103 calculates a lower limit value I _LL3 ^* for the assist control amount I _as ^* according to the steering angle θs. The steering speed sensitive limiter 104 calculates a lower limit value I _LL4 ^* for the assist control amount I _as ^* according to the steering speed ωs. The steering angular acceleration sensitive limiter 105 calculates a lower limit value I _LL5 ^* for the assist control amount I _as ^* according to the steering angular acceleration αs.

The adder 106 generates a lower limit value I _LL ^* for the assist control amount I _as ^* by adding five lower limit values I _LL1 ^{* to} I _LL5 ^* . The lower limit value I _LL ^* is supplied to the upper/lower limit guard processing unit 73 via the lower limit value switching unit 108.

The lower limit value holding unit 107 takes in the lower limit value I _LL ^* supplied from the lower limit value switching unit 108 to the upper and lower limit guard processing unit 73, and holds the taken lower limit value I _LL ^* . The lower limit value I _LL ^* held in the lower limit value holding unit 107 is updated every time the lower limit value I _LL ^* is supplied to the upper/lower limit guard processing unit 73. That is, the lower limit value I _LL ^* held in the lower limit value holding unit 107 is the previous value (the lower limit value I one calculation cycle before ^{) with} respect to the lower limit value I _LL ^* as the current value supplied to the upper and lower limit guard processing unit 73. _LL ^* ).

Lower limit switch 108, as a data input, captures the lower limit _{I LL} held in the lower limit _{I LL} ^* and the lower limit value storage unit 107 is computed by an adder 106 ^*. Further, the lower limit value switching unit 108 takes in the value of the end hit determination flag F set by the end hit control unit 87 as a control input. The lower limit value switching unit 108 sets the lower limit value I _LL ^* supplied to the upper and lower limit guard processing unit 73 to the lower limit value I _LL ^* (current value) calculated by the adder 106 based on the value of the end hit determination flag F. , And the lower limit value I _LL ^* (previous value) held in the lower limit value holding unit 107. When the value of the end hit determination flag F is “0”, the lower limit value switching unit 108 supplies the lower limit value I _LL ^* calculated by the adder 106 to the upper and lower limit guard processing unit 73. The lower limit value switching unit 108 holds the lower limit value holding unit 107 when the value of the end hitting determination flag F is “1” (more accurately, when the value of the end hitting determination flag F is not “0”). The lower limit value I _LL ^* is supplied to the upper/lower limit guard processing unit 73.

<Upper and lower limit map>
The upper limit value calculation unit 90 and the lower limit value calculation unit 100 respectively use the first to fifth limit maps M1 to M5 to set the respective upper limit values I _UL1 ^{* to} I _UL5 ^* and the respective lower limit values I _LL1 ^{* to} I _LL5 ^*. Is calculated. The first to fifth limit maps M1 to M5 are stored in a storage device (not shown) of the microcomputer 42. The first to fifth limit maps M1 to M5 each allow the assist control amount I _as ^* calculated according to the steering operation of the driver, and the abnormal assist control amount I _as ^* due to any other cause is It is set based on the point of not allowing.

As shown in FIG. 5, the first limit map M1 is a map in which the horizontal axis represents the steering torque τ and the vertical axis represents the assist control amount I _as ^*, and the upper limit for the steering torque τ and the assist control amount I _as ^* . The relationship between the value I _UL1 ^* and the relationship between the steering torque τ and the lower limit value I _LL1 ^* for the assist control amount I _as ^* are defined. The steering torque sensitive limiters 91 and 101 respectively use the first limit map M1 to calculate the upper limit value I _UL1 ^* and the lower limit value I _LL1 ^* according to the steering torque τ.

Setting the first limit map M1 is assist control amount I _{the as} in the same direction as the steering torque tau (positive or negative sign) ^* is allowed, the steering torque tau a different direction of the assist control amount I _{the as} ^* based on the viewpoint that does not permit By doing so, it has the following characteristics. That is, when the steering torque τ has a positive value, the upper limit value I _UL1 ^* of the assist control amount I _as ^* increases in the positive direction as the steering torque τ increases, and becomes a positive constant value with a predetermined value as a boundary. Maintained. Further, when the steering torque τ is a positive value, the lower limit value I _LL1 ^* of the assist control amount I _as ^* is maintained at “0”. On the other hand, when the steering torque τ has a negative value, the upper limit value I _UL1 ^* of the assist control amount I _as ^* is maintained at “0”. When the steering torque τ has a negative value, the lower limit value I _LL1 ^* of the assist control amount I _as ^* increases in the negative direction as the absolute value of the steering torque τ increases, and becomes negative with a predetermined value as a boundary. It is maintained at a constant value.

As shown in FIG. 6, the second limit map M2 is a map in which the horizontal axis represents the steering torque differential value dτ and the vertical axis represents the assist control amount I _as ^*, and the steering torque differential value dτ and the assist control amount I The relationship between the upper limit value I _UL2 ^* with respect to _as ^* and the relationship between the steering torque differential value dτ and the lower limit value I _LL2 ^* with respect to the assist control amount I _as ^* are defined. The steering torque differential value sensitive limiters 92 and ₁₀₂ calculate the upper limit value I _UL2 ^* and the lower limit value I _LL2 ^* according to the steering torque differential value dτ using the second limit map M2.

The second limit map M2 allows the assist control amount I _as ^{* in the} same direction (positive or negative sign) _as the steering torque differential value dτ and does not allow the assist control amount I _as ^{* in the} direction different from the steering torque differential value dτ. By being set based on the viewpoint, it has the following characteristics. That is, when the steering torque differential value dτ is a positive value, the upper limit value I _UL2 ^* of the assist control amount I _as ^* increases in the positive direction as the steering torque differential value dτ increases, and becomes positive at a predetermined value. Is maintained at a constant value. When the steering torque differential value dτ is a positive value, the lower limit value I _LL2 ^* of the assist control amount I _as ^* is maintained at “0”. On the other hand, when the steering torque differential value dτ is a negative value, the upper limit value I _UL2 ^* of the assist control amount I _as ^* is maintained at “0”. When the steering torque differential value dτ is a negative value, the lower limit value I _LL2 ^* of the assist control amount I _as ^* increases in the negative direction as the absolute value of the steering torque differential value dτ increases, and a predetermined value is set. The boundary is maintained at a constant negative value.

As shown in FIG. 7, the third limit map M3 is a map in which the horizontal axis is the steering angle θs and the vertical axis is the assist control amount I _as ^*, and the upper limit for the steering angle θs and the assist control amount I _as ^* . The relationship between the value I _UL3 ^* and the relationship between the steering angle θs and the lower limit value I _LL3 ^* for the assist control amount I _as ^* are defined. The steering angle sensitive limiters ₉₃ and ₁₀₃ respectively use the third limit map M3 to calculate the upper limit value I _UL3 ^* and the lower limit value I _LL3 ^* according to the steering angle θs.

Setting a third limit map M3 is assist control amount I _{the as} the steering angle θs opposite direction (positive or negative sign) ^* is allowed, the steering angle θs assist control amount in the same direction as I _{the as} ^* based on the viewpoint that does not permit By doing so, it has the following characteristics. That is, when the steering angle θs has a positive value, the upper limit value I _UL3 ^* of the assist control amount I _as ^* is maintained at “0”. When the steering angle θs has a positive value, the lower limit value I _LL3 ^* of the assist control amount I _as ^* increases in the negative direction as the steering angle θs increases. On the other hand, when the steering angle θs has a negative value, the upper limit value I _UL3 ^* of the assist control amount I _as ^* increases in the positive direction as the absolute value of the steering angle θs increases. Further, when the steering angle θs is a negative value, the lower limit value I _LL3 ^* of the assist control amount I _as ^* is maintained at “0”.

As shown in FIG. 8, the fourth limit map M4 is a map in which the horizontal axis represents the steering speed ωs and the vertical axis represents the assist control amount I _as ^*, and the upper limit for the steering speed ω s and the assist control amount I _as ^* . The relationship with the value I _UL4 ^* and the relationship between the steering speed ωs and the lower limit value I _LL4 ^* with respect to the assist control amount I _as ^* are respectively defined. The steering speed sensitive limiters 94 and 104 respectively use the fourth limit map M4 to calculate the upper limit value I _UL4 ^* and the lower limit value I _LL4 ^* according to the steering speed ωs.

Setting fourth limit map M4 is assist control amount I _{the as} the steering speed ωs opposite direction (positive or negative sign) ^* is allowed, the steering speed ωs assist control amount in the same direction as I _{the as} ^* based on the viewpoint that does not permit By doing so, it has the following characteristics. That is, when the steering speed ωs has a positive value, the upper limit value I _UL4 ^* of the assist control amount I _as ^* is maintained at “0”. When the steering speed ωs has a positive value, the lower limit value I _LL4 ^* of the assist control amount I _as ^* increases in the negative direction as the steering speed ωs increases, and becomes a negative constant value with a predetermined value as a boundary. Maintained. On the other hand, when the steering speed ωs has a negative value, the upper limit value I _UL4 ^* of the assist control amount I _as ^* increases in the positive direction as the absolute value of the steering speed ωs increases, and becomes positive with a predetermined value as a boundary. It is maintained at a constant value. Further, when the steering speed ωs is a negative value, the lower limit value I _LL4 ^* of the assist control amount I _as ^* is maintained at “0”.

As shown in FIG. 9, the fifth limit map M5 is a map in which the horizontal axis represents the steering angular acceleration αs and the vertical axis represents the assist control amount I _as ^*, and the steering angular acceleration αs and the assist control amount I _as ^*. To the upper limit value I _UL5 ^*, and the relationship between the steering angular acceleration αs and the lower limit value I _LL5 ^* to the assist control amount I _as ^* . Steering angular acceleration-sensitive limiter 95, 105 calculates the upper limit value _{I UL5} ^* and the lower limit _{I LL5} ^* corresponding to the steering angular acceleration αs using fifth limit map M5, respectively.

In the fifth limit map M5, the assist control amount I _as ^{* in the} direction opposite to the steering angular acceleration αs (positive and negative signs) is allowed, and the assist control amount I _as ^{* in the} same direction as the steering angular acceleration αs is not allowed. By being set based on the above, it has the following characteristics. That is, when the steering angular acceleration αs has a positive value, the upper limit value I _UL5 ^* of the assist control amount I _as ^* is maintained at “0”. In addition, when the steering angular acceleration αs has a positive value, the lower limit value I _LL5 ^* of the assist control amount I _as ^* increases in the negative direction as the steering angular acceleration αs increases, and _remains constant at a predetermined value. Maintained at the value. On the other hand, when the steering angular acceleration αs has a negative value, the upper limit value I _UL5 ^* of the assist control amount I _as ^* increases in the positive direction as the absolute value of the steering angular acceleration αs increases, and the predetermined value is taken as a boundary. It is maintained at a positive constant value. Further, when the steering angular acceleration αs has a negative value, the lower limit value I _LL5 ^* of the assist control amount I _as ^* is maintained at “0”.

<Operation and effect of ECU>
Next, the basic operation and effect of the ECU 40 will be described. When the end contact has not occurred, the current upper limit value I _UL ^* calculated by the adder 96 and the current lower limit value I _LL ^* calculated by the adder 106 are used as final limit values. When the end contact occurs, the previous upper limit value I _UL ^* held in the upper limit value holding unit 97 and the previous lower limit value I _LL ^* held in the lower limit value holding unit 107 are the final limit values. Used as.

Each signal limit value for the assist control amount I _{the as} ^* (upper limit and lower limit) is used when calculating the assist control amount I _{the as} ^*, the steering torque τ here a state quantity indicating a steering state, the steering torque differential The value dτ, the steering angle θs, the steering speed ωs, and the steering angular acceleration αs are individually set. The microcomputer 42, when calculating a final current command value I ^* based on the assist control amount I _{the as} ^*, a limit value for limiting the assist control amount I _{the as} ^* in the variation range in accordance with the value of each signal Set for each signal. Microcomputer 42, limit value ^{_{(I UL1 * ~I UL5 *,}} I LL1 * ~I LL5 *) final limit value summed values for the assist control amount _{I the as} ^* a set for each of these signals (I _UL ^* , _ILL ^* ).

Incidentally, the limit value for each signal, and thus the final limit value, allows the normal assist control amount I _as ^* calculated according to the steering operation by the driver, and allows an abnormal assist control amount I _as due to some cause. ^* Is set based on the viewpoint of restriction. The microcomputer 42 allows a compensation amount by various compensation controls such as a torque differential control and a steering return control with respect to the steering input of the driver, but limits an abnormal output or an erroneous output exceeding the value of each compensation amount.

When the assist control amount I _as ^* exceeds the limit range defined by the final upper limit value I _UL ^* and the lower limit value I _LL ^* , the microcomputer 42 determines the assist control amount I _as ^* or the lower limit exceeding the upper limit value I _UL ^*. The assist control amount I _as ^* below the value I _LL ^* is restricted so as not to be supplied to the motor control signal generation unit 62 as the final current command value I ^* . Individual limit values (upper limit value and lower limit value) set for each signal are reflected in the final upper limit value I _UL ^* and lower limit value I _LL ^* . That is, even when the assist control amount I _as ^* indicating an abnormal value is calculated, the value of the abnormal assist control amount I _as ^* is limited to an appropriate value according to each signal value by the final limit value. To be done. Then, the appropriate assist control amount I _as ^* is supplied to the motor control signal generation unit 62 as the final current command value I ^* , so that an appropriate assist force is applied to the steering mechanism 20. Even if the excessive assist control amount I _as ^* indicating an abnormal value is calculated for some reason, the motor control signal generator 62 receives the final current command value I ^* based on the abnormal assist control amount I _as ^*. Supply is suppressed. Therefore, application of unintended assisting force to the steering mechanism 20 is suppressed. For example, the occurrence of so-called self-steering is suppressed.

Here, although it is possible to continuously limit the assist control amount I _as ^* _as long _as the abnormality of the assist control amount I _as ^* continues, the following may be performed from the viewpoint of further improving safety.

As shown in the graph of FIG. 10, when the value of the assist control amount I _as ^* falls below the lower limit value I _LL ^* (time T _L0 ), the value of the assist control amount I _as ^* is limited by the lower limit value I _LL ^*. It The microcomputer 42 gradually decreases the lower limit value I _LL ^* toward “0” when the restricted state continues for a certain period ΔT (time T _L1 ) (hereinafter, referred to as “gradual decrease process”). The value of the assist control amount I _as ^* becomes “0” at the timing (time T _L2 ) when the lower limit value I _LL ^* reaches “0”. As a result, the application of the assist force to the steering mechanism 20 is stopped. The gradual reduction process is performed based on the viewpoint that it is preferable to stop the application of the assist force when the abnormal state continues for a certain period ΔT. Since the value of the assist control amount I _as ^* gradually decreases, the assist force also gradually decreases accordingly. Therefore, when the application of the assisting force to the steering mechanism 20 is stopped, a sudden change in the steering feeling does not occur. Safety is also improved.

The same applies when the value of the assist control amount I _as ^* exceeds the upper limit value I _UL ^* . That is, the microcomputer 42 gradually decreases the upper limit value I _UL ^* toward “0” when the limited state of the assist control amount I _as ^* continues for a certain period ΔT.

The gradual reduction process is forcibly performed regardless of the calculation process of the upper limit value I _UL ^* and the lower limit value I _LL ^* . The microcomputer 42 performs the gradual reduction process when the value of the assist control amount I _as ^* returns to a value within the normal range between the upper limit value I _UL ^* and the lower limit value I _LL ^* during the execution of the gradual reduction process. The execution may be stopped. As a result, the upper limit value I _UL ^* or the lower limit value I _LL ^{*, which} is forcibly reduced toward “0”, returns to the original value.

<Significance of switching the limit value between the current value and the previous value>
Next, the technical significance of switching the final limit values (I _UL ^* , I _LL ^* ) between the current value and the previous value according to the value of the end hit determination flag F will be described.

First, when the end hit has not occurred, the value of the end hit determination flag F is set to "0". At this time, the current limit values (I _UL ^* , I _LL ^* ) calculated by the adders 96 and 106 are used to limit the assist control amount I _as ^* . The assist control amount I _as ^{* at} this time is not forcibly reduced, and has a value according to the steering state at that time. Further, the current limit value (I _UL ^* , I _LL ^* ) is also calculated according to the steering state at that time. Therefore, the limit width of the current limit value (I _UL ^* , I _LL ^* ) with respect to the assist control amount I _as ^* is not unnecessarily expanded.

Next, when the end contact occurs, the microcomputer 42 executes the end contact control as protection control. While the end contact control is being executed, the original assist control amount I _as ^* calculated by the adder 83 is reduced by the set amount, so that the value of the steering torque τ detected by the torque sensor 53 is further increased. Easy to grow. Therefore, the individual limit values (I _UL1 ^* , I _LL1 ^* ) corresponding to the steering torque τ, and eventually the final limit values (I _UL ^* , I _LL ^* ) that reflect the individual limit values are the end values. There is a risk that the actual assist control amount I _as ^* that has been reduced through the execution of the hit control may be excessively expanded.

In this regard, in this example, when the end hit occurs, that is, when the value of the end hit determination flag F is “1”, the current limit values (I _UL ^* , I _LL ^*) calculated by the adders 96 and 106 ^. ), the previous upper limit value I _UL ^* held in the upper limit value holding unit 97 and the previous lower limit value I _LL ^* held in the lower limit value holding unit 107 are used as final limit values. The previous upper limit value I _UL ^* and the previous lower limit value I _LL ^* are the upper limit value I _UL ^* calculated by the adders 96 and 106 immediately before the end hit occurs (for example, one calculation cycle before this time) ^. And the lower limit value I _LL ^* .

The final limit value (I _UL ^* , I _LL ^* ) immediately before the end contact is steered before the assist control amount I _as ^* is increased by the end contact control unit 87, and eventually the steering force is increased due to the decrease in the assist force. The individual limit values (I _UL1 ^* , I _LL1 ^* ) according to the torque τ are reflected. Therefore, previous final limit ^{_{(I UL *, I LL *}} ) limit width due to the time of the final limit ^{_{(I UL *, I LL *}} ) is narrower than the limit width due. That is, with respect to the assist control amount I _as ^* reduced through the end contact control unit 87, it is possible to prevent the limit width due to the final limit values (I _UL ^* , I _LL ^* ) from being excessively widened.

Therefore, even when the ECU 40 is provided with the end contact control function as a protection function, the restriction function for the assist control amount I _as ^* indicating an abnormal value can be more appropriately exerted. When the excessive assist control amount I _as ^* indicating an abnormal value is calculated when the end abutting control is executed, the abnormal assist control amount I _as ^* is more appropriately limited, so that the motor torque of the motor torque is reduced. It is possible to suppress a larger change or the occurrence of self-steering. The safety is also improved.

When the value of the end hit determination flag F is switched from "1" to "0", the final limit values (I _UL ^* , I _LL ^* ) used are the upper limit value holding unit 97 and the lower limit value holding. The previous final limit value held in the unit 107 is switched to the current final limit value calculated by the adders 96 and 106.

<Other Embodiments>
The present embodiment may be modified as follows.
In the present example, the end contact control section 87 is provided as a component of the assist control section 71, but it may be provided in the calculation path between the assist control section 71 and the upper/lower limit guard processing section 73, for example.

In the present example, when the end contact occurs, the assist control amount I _as ^* calculated by the adder 83 is reduced _as the end contact control. However, for example, each compensation amount I ₂ ^* , I ₃ ^* , At least one of I ₄ ^* may be decreased. In this case, the end contact control section 87 is provided on the calculation path between at least one of the inertia compensation control section 84, the steering wheel return control section 85 and the torque differentiation control section 86 and the adder 83. Further, as the end contact control, instead of decreasing the assist control amount I _as ^* calculated by the adder 83, the total value of the compensation amounts I ₂ ^* , I ₃ ^* , I ₄ ^* is decreased. May be. In this case, for example, an adder for adding the respective compensation amounts I ₂ ^* , I ₃ ^* , I ₄ ^* is additionally provided. Then, the end hit control unit 87 is provided on the calculation path between the added adder and the adder 83. Even in this case, the assist control amount I _as ^* can be reduced when the end contact occurs.

The ECU 40 of the EPS 10 may have a function of protecting the motor 31 from overheating. The ECU 40 determines the overheated state of the motor 31 based on, for example, the current value Im supplied to the motor 31 detected by the current sensor 44 or the temperature of the motor 31 detected by a temperature sensor (not shown). The determination of the overheated state is performed, for example, by comparing the detected current value Im with the current determination threshold value or by comparing the detected temperature of the motor 31 with the temperature determination threshold value. When it is determined that the motor 31 is in the overheated state, the ECU 40 reduces and corrects the value of the assist control amount I _as ^* . Even in this case, the limit width of the final limit values (I _UL ^* , I _LL ^* ) with respect to the assist control amount I _as ^* may be excessively widened _{as in the} case where the end contact control function is executed. For this reason, when the overheat protection function is being executed, it is effective to reduce the value of the assist control amount I _as ^* , like the present example. By the way, it is effective not only for the end contact control function and the overheat protection function but also for various protection control functions for reducing and correcting the value of the assist control amount I _as ^* when a specific condition is satisfied. The ECU 40 may have a single type of protection control function or a plurality of types of protection control functions as the protection control functions including the end contact control function and the overheat protection function.

In this example, the ECU 40 is applied to the electric power steering device of the type that applies the assist force to the steering shaft 22, but the ECU 40 is applied to the electric power steering device of the type that applies the assist force to the rack shaft 23, for example. You may apply.

20... Steering mechanism, 31... Motor, 40... ECU (steering control device), 71... Assist control unit, 72... Upper/lower limit limit calculation unit that constitutes a limitation processing unit, 73... Upper and lower limit guard processing that constitutes a limitation processing unit , 87... end contact control section (protection control section), 97... upper limit value holding section, 98... upper limit value switching section, 107... lower limit value holding section, 108... lower limit value switching section.

Claims (5)

An assist control unit that calculates an assist control amount for controlling power supply to a motor that is a generation source of an assist force applied to the steering mechanism of the vehicle, based on a plurality of state quantities including the steering torque,
When a specific condition is satisfied, a protection control unit that executes protection control to reduce the value of the assist control amount,
A limit value for limiting the change range of the assist control amount is individually set for each state amount according to the plurality of state amounts, and a final value for the assist control amount obtained by adding these limit values is finally set. A limit processing unit that limits the change range of the assist control amount based on a limit value
The steering control device, wherein when the specific condition is satisfied, the limit processing unit limits a change range of the assist control amount by using a final limit value immediately before the protection control is executed. The steering control device according to claim 1,
The limit processing unit, a holding unit that holds the used final limit value each time the final limit value is used,
Depending on the success or failure of the specific condition, the final limit value to be used is set between the final limit value calculated this time and the last limit value calculated last time held in the holding unit. A steering control device having a switching unit for switching. The steering control device according to claim 1 or 2,
The steering control device, wherein the protection control unit sets a value of a flag according to a determination result of success or failure of the specific condition, and the restriction processing unit recognizes success or failure of the specific condition based on the value of the flag. The steering control device according to any one of claims 1 to 3,
The steering control device, wherein the specific condition is that it is determined that the steering mechanism has reached its physical steering limit. The steering control device according to any one of claims 1 to 4,
The steering control device, wherein the specific condition is that it is determined that the motor is overheated.

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