JP2013006595A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device that can perform alternative steering assistance by active control of a differential gear when the abnormality occurs in the electric power steering device and the steering assistance is stopped without giving sense of incompatibility to the steering feeling of a driver.SOLUTION: There are provided an abnormality detection part that detects the abnormality of the electric power steering and a differential gear to adjust difference of rotation speeds of right and left wheels. When the abnormality detection part detects the abnormality of the electric power steering device, the differential gear performs the alternative steer assistance based on the vehicle condition.

Description

  The present invention relates to an electric power steering apparatus configured to control a motor that applies a steering assist force to a steering system, and in particular, when an abnormality (including a failure) is detected in the electric power steering apparatus, a differential gear is used. The present invention relates to an electric power steering apparatus in which alternative steering assistance is performed by adjusting a rotational speed difference between a left wheel and a right wheel.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor energizes an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate steering assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  The general configuration of the electric power steering apparatus will be described with reference to FIG. 106. The column shaft 102 is provided with a torque sensor 110 that detects the steering torque of the handle 101, and a motor 120 that assists the steering force of the handle 101 is connected to the column shaft 102 via the reduction gear 103. Electric power is supplied from the battery 113 to the control unit 130 that controls the electric power steering device, and an ignition key signal is input via the ignition key 111. The control unit 130 calculates the steering assist command value I of the steering assist (steering assist) command based on the steering torque T detected by the torque sensor 110 and the vehicle speed V detected by the vehicle speed sensor 112. Based on the steering assist command value I, the current supplied to the motor 120 is controlled.

  The control unit 130 is mainly composed of a CPU (or MPU or MCU). FIG. 6 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 130 will be described with reference to FIG. 6. The steering torque T detected by the torque sensor 110 is phase-compensated and phase-compensated by the phase compensator 131 in order to improve the stability of the steering system. The steering torque TA is input to the steering assist command value calculation unit 132. Further, the vehicle speed V detected by the vehicle speed sensor 112 is also input to the steering assist command value calculation unit 132. The steering assist command value calculation unit 132 refers to the steering assist map (lookup table) 133 based on the input steering torque TA and the vehicle speed V, and a steering assist command that is a control target value of the current supplied to the motor 120. The value Iref is determined.

  The steering assist command value Iref is input to the subtraction unit 130A and is also input to the feedforward differential compensation unit 134 for increasing the response speed, and the deviation (Iref-i) obtained by the subtraction unit 130A is the proportional calculation unit 135. And is input to an integral calculation unit 136 for improving the characteristics of the feedback system. The output of the proportional calculation unit 135 and the output of the integration calculation unit 136 are respectively input to the addition unit 130B, the output of the differential compensation unit 134 is also added to the addition unit 130B, and the current command value E that is the addition result in the addition unit 130B is obtained. The motor drive signal 137 is input as a motor drive signal. The motor current value of the motor 120 is detected by the motor current detection circuit 138, and the detected motor current detection value i is input to the subtraction unit 130A and fed back. Electric power is supplied from the battery 113 to the motor drive circuit 137, and the motor drive circuit 137 is configured by an H bridge circuit (in the case of a two-phase motor) or a three-phase bridge circuit (in the case of a three-phase motor) composed of drive elements such as FETs. The

  Japanese Patent No. 3564696 discloses a steering control device for preventing a driver from feeling uncomfortable when an abnormality occurs in such an electric power steering device and steering assistance by the electric power steering device is stopped. No. 1 (Patent Document 1). In the device described in Patent Document 1, an abnormal state of the steering reaction force applying unit is detected by the abnormal state detecting unit, and when the abnormal state is detected, the braking device for the left and right wheels is detected by the steering torque detecting unit. By applying a braking force difference based on the steering torque thus applied, a force for assisting steering of the steering wheel in the steering intention direction is applied.

  In addition to the electric power steering device, recent vehicles have a differential gear (differential gear, differential device) and LSD (Limited Slip Differential) to improve the vehicle's stable turning characteristics and driving performance. There is something provided. These function to prevent the left and right driving wheels from being always driven at the same rotational speed by the engine output by rotating the driving wheels on the turning inner wheel side without slipping when the vehicle turns.

  Japanese Laid-Open Patent Publication No. 8-99652 (Patent Document 2) discloses a steering assist device for a vehicle having an LSD. In this steering assist device, when the LSD is activated, the steering assist force is appropriately controlled in order to eliminate a sense of incongruity such as a heavy steering operation by the driver when the LSD is activated.

Japanese Patent No. 3564696 Japanese Patent Laid-Open No. 8-99652

  When an abnormality occurs in the electric power steering apparatus and the abnormality is detected, it is necessary to stop the steering assist by the electric power steering apparatus depending on the situation in order to prevent an unexpected abnormality of the steering operation. However, when the steering assist is stopped, it is felt that the steering loses control because it is necessary to hold the steering to return to the straight traveling state by the driver alone. For this reason, the driver may feel a sense of incongruity and may feel dangerous to the driver.

  In order to prevent this, in the electric power steering device described in Patent Document 1, when an abnormality is detected in the electric power steering device, a braking force difference is applied to the left and right wheels by the braking device. However, there is a problem in that the turning characteristics and the running performance are poor because the mechanism for performing alternative steering assistance when an abnormality is detected in the electric power steering apparatus does not use a differential gear.

  Further, Patent Document 2 discloses an electric power steering apparatus provided with an LSD, but this LSD is used for applying an alternative steering assist force when an abnormality is detected in the electric power steering apparatus. It is not a thing. Therefore, it is not possible to perform steering assistance that exhibits the characteristics of LSD.

  The present invention has been made under the circumstances as described above, and an object of the present invention is based on the vehicle state when the steering assist is stopped due to an abnormality (including a failure) in the electric power steering apparatus. Provided an electric power steering device that performs alternative steering assistance by active control of the differential gear and can continue the steering assistance without causing a sense of incongruity to the driver even when an abnormality occurs in the electric power steering device There is to do.

  The present invention includes a control unit that calculates a steering assist command value based on the steering torque and the vehicle speed, and controls a motor that applies a steering assist force to the steering mechanism based on the steering assist command value. Regarding the electric power steering apparatus, the object of the present invention includes a differential gear for adjusting a difference in rotational speed between left and right wheels, and a differential gear control unit for controlling the differential gear, the control unit comprising: An abnormality detection unit that detects an abnormality of the electric power steering device, and a first determination as to whether or not steering assistance by the electric power steering device can be continued when an abnormality is detected by the abnormality detection unit A steering assist switching determination unit that performs If the continuation of the steering assist is determined to be impossible, the differential gear is achieved by performing an alternate steering assist based on the vehicle state.

  Further, the above-described object of the present invention is that the differential gear control unit includes a differential gear normal determination unit that determines whether or not the differential gear is normal, and the differential gear is determined by the differential gear normal determination unit. If it is determined that the differential gear is normal, or if the differential gear normal determination unit determines that the differential gear is not normal, the alternative steering assist is not performed. The steering assist switching determining unit determines whether the electric power steering apparatus has returned to normal after a predetermined time after the alternative steering assist is performed, by stopping the steering assist, and Electric power steering according to the judgment When it is determined that the vehicle has returned to normal, the steering assist is restored, or the control unit includes a vehicle safety ensuring condition determination unit, and the determination performed by the steering assist switching determination unit When it is determined that the electric power steering device has not returned to normal, the vehicle safety ensuring condition determining unit determines the conditions for ensuring the safety of the vehicle. If the vehicle condition is not confirmed, the alternative steering assistance is continued, or the vehicle state is the vehicle speed, the steering torque, and the steering angle signal. .

  In the electric power steering apparatus of the present invention, the steering wheel to the steered wheel are mechanically disconnected, the control unit controls the steered actuator according to the steering angle of the handle, and the steered wheel is steered by the driving force. The above object is achieved by the steer-by-wire type electric power steering apparatus.

  According to the electric power steering apparatus according to the present invention, when an abnormality occurs and the steering assist is stopped, the alternative steering assist is performed by actively controlling the differential gear based on the vehicle state. Even when an abnormality occurs, steering assistance can be continued without causing the driver to feel uncomfortable. In particular, in large vehicles, when steering assistance is stopped, there is a risk of sudden deterioration in steering feeling, but this can be prevented by performing alternative steering assistance using a differential gear.

  The present invention can achieve the same effect in a steer-by-wire type electric power steering apparatus.

It is a figure showing an example of composition of an electric power steering device concerning the present invention. It is a block diagram which shows the structural example of the electric power steering apparatus control unit which concerns on this invention. It is a block diagram which shows the structural example of the differential gear control unit which concerns on this invention. It is a flowchart which shows the operation example of this invention. It is a figure showing an example of composition of a general electric power steering device. It is a block diagram which shows the structural example of the control unit of an electric power steering apparatus.

10 Electric power steering device control unit 11, 31 CPU
DESCRIPTION OF SYMBOLS 12 Motor drive circuit 13 Motor phase current detection circuit 14 Motor total current detection circuit 16 Abnormality detection part 17 Steering assistance switching determination part 18 Steering assistance condition setting part 19 Vehicle safety ensuring condition determination part 30 Differential gear control unit 32 Rotational speed difference calculation part 33 Drive circuit 34 Differential gear normality determination unit 40 Differential gears 41R, 41L Transmission capacity variable clutches 42R, 42L Hydraulic pressure generator 52 Left wheel speed sensor 53 Right wheel speed sensor 54 Engine speed sensor 55 CAN bus 55A, 55B CAN processing Circuit 110 Torque sensor 112 Vehicle speed sensor 120 Motor 311 Differential limiting torque calculation unit 312 Alternative steering assist necessary amount calculation unit 314 Control amount setting unit 315 Left / right distribution setting unit

  Electric power steering device when an abnormality occurs in a current detection circuit such as a motor phase current detection circuit or a motor total current detection circuit, when an abnormality occurs in a CPU in a control unit, when an abnormality occurs in a torque sensor, etc. When an abnormality occurs, the steering assist by the electric power steering device is usually stopped in order to avoid danger. On the other hand, in the electric power steering device according to the present invention, even when the steering assist is stopped when such an abnormality occurs, the vehicle state (steering torque, left and right wheel rotational speed, engine rotational speed, vehicle speed, steering angle) is maintained. Based on the differential gear, the alternative steering assist is performed by adjusting the rotational speed difference between the left wheel and the right wheel. For this reason, even when an abnormality occurs in the electric power steering apparatus, the steering assist can be continued without causing the driver to feel uncomfortable.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration example of an electric power steering apparatus according to the present invention corresponding to FIG. 5, and the same members are denoted by the same reference numerals and description thereof is omitted. The vehicle has a structure viewed from the front, and the front wheels 50R and 50L and the rear wheels 51R and 51L of the driving wheels are displayed in a state of overlapping in view.

The electric power steering device control unit 10 calculates the steering assist command value I based on the steering torque T and the vehicle speed V, and controls the current supplied to the motor 120 based on the calculated steering assist command value I. , CAN (Controller
(Area Network) bus 55 is connected to differential gear control unit 30.

  The vehicle according to the present invention includes a differential gear 40 between the left and right wheels 51 </ b> R and 51 </ b> L of the drive wheel, and includes a differential gear control unit 30 for controlling the differential gear 40. The drive wheel is either a front wheel or a rear wheel, and in the case of a four-wheel drive vehicle, it is both a front wheel and a rear wheel. In this example, description will be made assuming that the rear wheels 51R and 51L are driving wheels. An engine speed sensor 54 for detecting the engine speed Rs is provided which includes a left wheel speed sensor 52 for detecting the left wheel speed Lr and a right wheel speed sensor 53 for detecting the right wheel speed Rr. It has. The left wheel rotation speed Lr, the right wheel rotation speed Rr, the engine rotation speed Rs, and the vehicle speed V are input to the differential gear control unit 30, and the differential gear control unit 30 can communicate with the electric power steering device control unit 10 via the CAN bus 55. It is connected. The vehicle speed V may be given from CAN.

  The differential gear control unit 30 is based on the steering torque T, the left wheel rotation speed Lr, the right wheel rotation speed Rr, the engine rotation speed Rs, the vehicle speed V, and the steering angle signal Ss from the steering angle sensor (not shown). Then, a gear control voltage Vd for controlling the differential gear 40 is calculated, and the obtained gear control voltage Vd is input to the differential gear 40. The differential gear 40 adjusts the rotational speed difference between the left wheel 51L and the right wheel 51R based on the input gear control voltage Vd.

  The differential gear 40 adjusts the difference between the rotational speeds of the left and right wheels 51L and 51R in order to rotate the driving wheel on the turning inner wheel side without slipping when the vehicle is turning, and the electric power steering device has an abnormality. When the steering assist cannot be continued and the steering assist cannot be continued, the rotational speed difference between the left and right wheels 51L and 51R is adjusted in order to perform the alternative steering assist. The differential gear control unit 30 controls the differential gear 40 when performing slip prevention and alternative steering assistance during vehicle turning.

  The electric power steering device control unit 10 and the differential gear control unit 30 are connected by a CAN bus 55. For example, when an abnormality occurs in the electric power steering device and steering assistance by the electric power steering device cannot be continued, A switching signal or the like for switching to alternative steering assistance by the differential gear 40 is transmitted via the CAN bus 55.

  Next, a configuration example of the electric power steering apparatus control unit 10 will be described with reference to FIG.

  The electric power steering device control unit 10 calculates a steering assist command value I based on the vehicle speed V and the steering torque T, inputs the compensated current command value E to the motor drive circuit 12, and performs overall control. A CPU 11 to be executed, a motor phase current detection circuit 13 for detecting each phase current ip flowing in the motor 120, and a motor total current detection circuit 14 for detecting the sum total of each phase current are provided. Electric power is supplied to the motor drive circuit 12 from the battery 113 via the power supply relay 111, and the power supply relay 111 is turned on / off by a switching signal SW <b> 1 from the CPU 11. Motor current is supplied from the motor drive circuit 12 to the motor 120 via the motor relays 15A and 15B, and the motor relays 15A and 15B are turned on / off by a switching signal SW2 from the CPU 11. Furthermore, when abnormality is detected by the abnormality detection unit 16 for detecting abnormality of the CPU 11, the motor phase current detection circuit 13, the motor total current detection circuit 14, and the torque sensor 110, the abnormality detection unit 16 An abnormality detection signal AD indicating the abnormal part and the degree of abnormality is output from the steering assist switching determination unit 17 for determining whether or not the steering assist by the electric power steering device can be continued based on the abnormality detection signal AD; Is provided. The abnormality detected by the abnormality detection unit 16 is to detect an abnormality in the vehicle speed sensor 112, the CAN signal, the voltage of the battery 113, the motor drive circuit 12, the temperature sensor, the overheat protection means, etc. in addition to the above. May be.

  When the steering assist switching determination unit 17 determines that the steering assist by the electric power steering device is impossible, the switching signal SW3 for switching to the alternative steering assist is sent to the CPU 11 so as to perform the alternative steering assist by the differential gear 40. While being input, it is transmitted to the differential gear control unit 30 via the CAN processing circuit 55A and the CAN bus 55.

  The determination state of the steering assist switching determination unit 17 is input as the switching signal SW3 to the steering assist condition setting unit 18 and the vehicle safety ensuring condition determination unit 19, and the steering assist switching determination unit 17 performs steering assist by the electric power steering apparatus. Is not impossible, that is, when it is determined that the steering assist is continued, the steering assist condition setting unit 18 sets a certain condition according to the abnormality detected by the abnormality detecting unit 16, and inputs this certain condition to the CPU 11. Continue steering assistance.

  The certain condition is a condition imposed when steering assistance is performed as follows according to the abnormality detected by the abnormality detection unit 16. When the abnormality detected by the abnormality detection unit 16 is a minor failure such as an abnormality in the vehicle speed sensor 112 or an abnormality in the CAN signal, the restriction on the steering assist is loosened. For example, it takes a long time from the detection of abnormality to the limitation of steering assist, or the upper limit of the steering assist amount when limiting the steering assist amount is increased. When the abnormality detected by the abnormality detection unit 16 is an intermediate abnormality such as an abnormality of the torque sensor 110 or an abnormality of the voltage of the battery 113, the limitation of steering assist is set to an intermediate level. For example, the time from when an abnormality is detected until the steering assist is limited is set to a medium level, or the upper limit value of the steering assist amount when the steering assist amount is limited is set to a medium level. When the abnormality detected by the abnormality detection unit 16 is a high-level abnormality such as an abnormality in the motor drive circuit 12 or an abnormality in the CPU 11, the restriction on steering assistance is tightened. For example, the time from when an abnormality is detected until the steering assist is limited is shortened, or the upper limit value of the steering assist amount when the steering assist amount is limited is reduced.

  Further, after the abnormality is detected by the abnormality detection unit 16, when the alternative steering assistance is performed or when the steering assistance is performed under a certain condition, the abnormality detection unit 16 detects the abnormality after a predetermined time. The steering assist switching determination unit 17 determines whether or not the electric power steering apparatus has returned to normal depending on whether or not it is. When it is determined that the electric power steering device has returned to normal, normal control by the electric power steering device returns. On the other hand, when it is determined that the electric power steering device has not returned to normal, the vehicle safety ensuring condition determining unit 19 determines conditions for ensuring vehicle safety. Conditions for ensuring the safety of the vehicle include, for example, a numerical value that is equal to or less than a predetermined value at which the vehicle speed V can be determined to be sufficiently low, or the steering torque T is neutral, or the battery voltage detection signal of the battery 113 Is recognized as being within a predetermined normal range, or the engine signal received by the CAN signal is stopped. When it is confirmed, the steering assistance and the alternative steering assistance are stopped via the CPU 11.

  In the embodiment shown in FIG. 2, the steering assist condition setting unit 18 and the vehicle safety condition determination unit 19 are provided outside the CPU 11, but may be configured to be provided in the CPU 11.

  Next, a configuration example of the differential gear control unit 30 will be described with reference to FIG. 3, but the vehicle of this example has a planar structure as viewed from above, and an electric power steering is provided between the left and right wheels 50R, 50L of the front wheels. The apparatus is loaded, and the differential gear 40 is loaded between the left and right wheels 51R and 51L of the rear wheels that are drive wheels.

  The differential gear control unit 30 includes a CPU 31 for performing alternative steering assistance. The CPU 31 has at least functions of a differential limit torque calculation unit 311, an alternative steering assist necessary amount calculation unit 312, an addition unit 313, a limit amount setting unit 314, and a left / right distribution setting unit 315. Further, the rotational speed difference calculation unit 32 in the differential gear control unit 30 includes a left wheel rotational speed Lr detected by the left wheel rotational speed sensor 52 and a right wheel rotational speed Rr detected by the right wheel rotational speed sensor 53. And the rotational speed difference Rd is calculated. The CPU 31 detects the rotational speed difference Rd, the vehicle speed V, the engine rotational speed Rs detected by the engine rotational speed sensor 54, the steering torque T transmitted via the CAN bus 55 and the CAN processing circuit 55A, and the steering angle sensor. The steering angle signal Ss is input.

  The differential limiting torque calculator 311 in the CPU 31 calculates the differential limiting torque Tdl based on the steering torque T and the rotational speed difference Rd. The differential limiting torque Tdl is a torque necessary for adjusting the rotational speed difference between the left and right wheels 51L and 51R in order to rotate the driving wheel on the turning inner wheel side without slipping when the vehicle is turning. The alternative steering assistance necessary amount calculation unit 312 calculates an alternative steering assistance torque St necessary for performing the alternative steering assistance based on the vehicle speed V, the steering torque T, and the steering angle signal Ss. The differential limiting torque Tdl and the alternative steering assist torque St are added by the adding unit 313 and input to the control amount setting unit 314. The control amount setting unit 314 calculates a necessary control torque Ct based on the input addition value, and the left / right distribution setting unit 315 applies the left / right transmission capacity variable clutches (actuators) 41L and 41R based on the control torque Ct. The gear control voltages VdL and VdR are calculated, and the drive signal Ds is input to the drive circuit 33.

  The drive circuit 33 applies gear control voltages VdL and VdR to the left and right transmission capacity variable clutches 41L and 41R based on the drive signal Ds. Usually, the drive circuit 33 includes a logic circuit because the drive signal Ds transmitted from the CPU 31 is weak. The transmission capacity variable clutches 41L and 41R are always applied with a constant pressure by the hydraulic pressure generators 42L and 42R, and distribute their outputs CoR and CoL to the differential gear 40.

  Note that the differential gear normality determination unit 34 provided in the differential gear control unit 30 determines whether or not the differential gear 40 is normal before performing the alternative steering assist by the differential gear 40. When it is determined that the differential gear 40 is normal, the alternative steering assist is performed by the differential gear 40, and when it is determined that the differential gear is not normal, the alternative steering assist is not performed, and electric power is supplied via the CAN bus 55. A steering assistance stop signal is transmitted to the power steering device control unit 10 to stop steering assistance by the electric power steering device.

  In the electric power steering apparatus having such a configuration, an example of an action to be taken when an abnormality occurs will be described with reference to a flowchart shown in FIG.

  In the electric power steering device, whether or not an abnormality has occurred is constantly monitored by the abnormality detection unit 16 (step S1). If no abnormality is detected in the electric power steering device by the abnormality detection unit 16, the electric power Normal control by the steering device is continued (step S2).

  On the other hand, when an abnormality of the electric power steering device is detected by the abnormality detection unit 16 in step S1, the steering assist switching determination unit 17 determines whether or not the steering assist by the electric power steering device can be continued (step S1). S3) When the steering assistance by the electric power steering device can be continued, the steering assistance condition setting unit 18 sets a certain condition according to the abnormality detected by the abnormality detection unit 16, and the electric power is set under this certain condition. Steering assistance by the steering device is continued (step S4). Then, depending on whether or not an abnormality is detected in the abnormality detection unit 16 after a predetermined time, the steering assist switching determination unit 17 determines whether or not the electric power steering device has returned to normal (step S5).

  When it is determined in step S5 that the electric power steering device has returned to normal, the process proceeds to step S2 and normal control by the electric power steering device is returned. On the other hand, if it is determined in step S5 that the electric power steering device has not returned to normal, the vehicle safety ensuring condition determining unit 19 sets conditions for ensuring vehicle safety, and the vehicle safety ensuring conditions are determined. It is determined whether or not it has been completed (step S6). If it is determined that the vehicle safety ensuring condition has been determined, the steering assist by the electric power steering device is stopped (step S7). If it is determined that the vehicle safety ensuring condition has not been determined, the above step is performed. Returning to S4, the steering assist by the electric power steering device under a certain condition is continued.

  When it is determined in step S3 that it is impossible to continue steering assistance by the electric power steering device, first, the differential gear normal determination unit 34 determines whether or not the differential gear 40 is normal (step S8). When it is determined that the differential gear 40 is normal, alternative steering assist is performed by the differential gear 40 (step S9), and the steering assist switching is performed depending on whether or not an abnormality is detected in the abnormality detection unit 16 after a predetermined time. The determination unit 17 determines whether or not the electric power steering apparatus has returned to normal (step S10). If it is determined that the electric power steering apparatus has returned to normal, the process proceeds to step S2, and the electric power steering apparatus Normal control returns.

  On the other hand, if it is determined in step S10 that the electric power steering device has not returned to normal, the vehicle safety ensuring condition determining unit 19 determines whether or not the conditions for ensuring vehicle safety have been determined ( Step S11) If it is determined that the vehicle safety ensuring condition has been determined, the alternative steering assist is stopped (step S12). If it is determined that the vehicle safety ensuring condition has not been determined, the process returns to step S9. Then, the alternative steering assist by the differential gear 40 is continued.

  When the differential gear normality determination unit 34 determines in step S8 that the differential gear 40 is not normal, steering assist by the electric power steering device is stopped (step S13).

  In the above-described embodiment, when an abnormality occurs in the electric power steering device, the alternative gear assist is performed by the differential gear. However, when the abnormality occurs in the steer-by-wire type electric power steering device, the alternative steering assist by the differential gear is performed. You may make it carry out. The steer-by-wire type electric power steering device does not mechanically connect the steering wheel to the steered wheel, but electrically detects the steering angle of the steering wheel. Based on this detection signal, the control unit detects the steered angle of the steered wheel. The steering wheel is driven and controlled by driving an actuator that is mechanically independent from the steering wheel.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to this, In the range which does not deviate from the meaning, it can change suitably.

Claims (7)

An electric power steering apparatus including a control unit that calculates a steering assist command value based on the steering torque and the vehicle speed, and controls a motor that applies a steering assist force to the steering mechanism based on the steering assist command value. In
A differential gear for adjusting the difference in rotational speed between the left and right wheels, and a differential gear control unit for controlling the differential gear,
The control unit is
An abnormality detection unit for detecting an abnormality of the electric power steering device;
A steering assist switching determination unit that performs a first determination as to whether or not the steering assist by the electric power steering device can be continued when an abnormality is detected by the abnormality detection unit;
The electric power steering apparatus according to claim 1, wherein when the first determination determines that the steering assist cannot be continued, the differential gear performs an alternative steering assist based on a vehicle state. The differential gear control unit includes a differential gear normal determination unit that determines whether or not the differential gear is normal,
The electric power steering apparatus according to claim 1, wherein the alternative steering assist is performed when the differential gear normality determining unit determines that the differential gear is normal.   The electric power steering apparatus according to claim 2, wherein when the differential gear normality determination unit determines that the differential gear is not normal, the steering assist is stopped without performing the alternative steering assist.   The steering assist switching determination unit determines whether or not the electric power steering apparatus has returned to normal after a predetermined time after the alternative steering assist is performed, and the electric power steering apparatus is normally returned by the determination. The electric power steering apparatus according to claim 2, wherein when it is determined that the vehicle has returned, the steering assist is returned. The control unit includes a vehicle safety ensuring condition determining unit,
If it is determined by the determination performed by the steering assist switching determination unit that the electric power steering device has not returned to normal, the vehicle safety ensuring condition determining unit determines the condition for ensuring vehicle safety. 5. The electric power steering apparatus according to claim 4, wherein the alternative steering assist is stopped when the determination is confirmed and the alternative steering assist is continued when the determination is not possible.   The electric power steering apparatus according to any one of claims 1 to 5, wherein the vehicle state is the vehicle speed, the steering torque, and a steering angle signal.   The electric power steering apparatus mechanically disconnects from the steering wheel to the steered wheel, the control unit controls the steering actuator according to the steering angle of the steering wheel, and steers the steered wheel by the driving force. 7. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is a by-wire type electric power steering apparatus.

Images