JP4797516B2 - Power steering device - Google Patents

Description

  The present invention relates to a power steering apparatus that performs steering assist by driving a hydraulic pump with an electric motor.

As a power steering device, for example, a device disclosed in Patent Document 1 is known. This device is a device that generates an assist steering force by guiding discharge pressure of a hydraulic pump driven by an electric motor to two power cylinder chambers separated by pistons of a power cylinder, and each power cylinder chamber A pair of bypass oil passages that communicate with each other and a fail-safe valve that can switch these bypass oil passages to a communication / non-communication state are provided. When any abnormality occurs, the fail-safe valve is gradually opened to maintain a certain level. Fully open after time.
JP 2004-276664 A

By the way, in the case of failure of the failsafe valve or failure of the circuit that drives the failsafe valve, the failsafe valve becomes uncontrollable, so a so-called normally open type failsafe valve that is opened at the time of failure is adopted. There are many cases. However, in a power steering device equipped with a normally open type fail-safe valve, when a failure occurs, the high pressure side hydraulic pressure flows into the low pressure side power cylinder chamber of the two power cylinder chambers of the power cylinder. An assist steering force in a direction opposite to the operation direction is generated, and the steering force of the steering wheel may fluctuate, which may cause the driver to feel uncomfortable.
The present invention has been made to solve such inconveniences, and when the fail-safe valve is opened at the time of a failure, the power steering that suppresses the fluctuation of the steering force of the steering wheel and does not give the driver a sense of incongruity. An object is to provide an apparatus.

In order to solve the above problems, a power steering device according to the present invention is divided into two chambers by a piston and connected to a steering wheel, and a hydraulic pump that gives a hydraulic pressure difference between the two chambers of the power cylinder, In a power steering apparatus comprising: an assist steering control means for driving the hydraulic pump so as to apply an assist steering force in accordance with an operation of a steering wheel; a bypass path communicating between the two chambers of the power cylinder; And a fail-safe valve for opening and closing the bypass path, and an abnormality detecting means for detecting an abnormality of the power steering apparatus, wherein the assist steering control means is configured to detect the abnormality of the power steering apparatus but the hydraulic pump Is detected by the abnormality detecting means to be drivable The addition to the fail-safe valve to the open state, to operate the hydraulic pump such that the liquid in the chamber of the high pressure side of the two chambers of the power cylinder is discharged, the high-pressure side of the two chambers of the power cylinder A hydraulic pressure calculating means for calculating the hydraulic pressure of the chamber, wherein the assist steering control means is configured to apply a hydraulic pressure to the higher pressure side chamber as the hydraulic pressure increases based on the hydraulic pressure calculated by the hydraulic pressure calculating means. Control is provided to increase the discharge amount, and hydraulic pressure difference calculating means for calculating the hydraulic pressure difference between the two chambers of the power cylinder is provided. The assist steering control means is configured such that the hydraulic pump after detected by the abnormality detecting means that can be driven, when the pressure difference was calculated by the fluid pressure differences calculating means is equal to or less than a predetermined threshold value, a device for stopping the operation of the hydraulic pump A.

  According to the power steering device of the present invention, since the hydraulic pump is operated so that the hydraulic pressure is supplied to the chamber on the high pressure side of the power cylinder when the fail safe valve is opened at the time of failure, the steering wheel is steered. Does not cause power fluctuations and does not give the driver a sense of incongruity.

Hereinafter, an embodiment of an electric power steering apparatus of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus according to the present invention, in which a steering wheel 4 is connected to an upper end portion of a steering shaft 2 extending in a slanting vertical direction, and a pinion shaft is connected to a lower end portion of the steering shaft 2. 6 are connected. A rack 8 disposed in the vehicle width direction meshes with the pinion provided at the lower end of the pinion shaft 6, and the rotational motion of the steering wheel 4 steered by the driver is a linear motion (translation) of the rack 8 as a steering force. Motion). A power cylinder 12 of the power steering mechanism 10 is connected to an inner end of the rack 8 in the vehicle width direction.

  The power cylinder 12 of the power steering mechanism 10 includes a piston 22 that divides the inside of the cylinder tube 16 into a first cylinder chamber 18 and a second cylinder chamber 20, and a piston rod 24 that is integrated with the piston 22 and moves within the cylinder tube 16. The rack 8 and the piston rod 24 are connected coaxially. The steering wheel WLR is connected to the outer side in the vehicle width direction of the rack 8 via a tie rod 14 and a knuckle, and the steering wheel is connected to the outer end in the vehicle width direction of the piston rod 24 of the power cylinder 12 via the tie rod 14 and the knuckle. WLL is connected.

  The power steering mechanism 10 drives a reversible rotation type oil pump 28 disposed in the middle of a hydraulic pipe 26 communicating with the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12, and the oil pump 28. An electric motor 30, a bypass pipe 32 connected to the hydraulic pipe 26 so as to communicate with the first cylinder chamber 18 and the second cylinder chamber 20 without passing through the oil pump 28, and a fail-safe valve disposed in the middle of the bypass pipe 32 34.

  When the driver operates the steering wheel 4, the rotation direction of the electric motor 30 is switched according to the operation direction, and a differential pressure is generated between the first cylinder chamber 18 and the second cylinder chamber 20, thereby causing the piston. 22, and the piston rod 24 moves in the vehicle width direction together with the piston 22, thereby assisting the rack 8 to move in the vehicle width direction.

  A fail-safe valve 34 arranged in the middle of the bypass pipe 32 is in a closed state when a voltage is supplied in response to a command signal from the controller 36, and is a normally open solenoid valve that is open in a state where no voltage is supplied. Is used. Thereby, when some abnormality occurs and the supply of power is stopped, the first cylinder chamber 18 and the second cylinder chamber 20 can be brought into a communication state, and normal steering without assistance is ensured. I try to do it.

A connecting portion between the steering shaft 2 and the pinion shaft 6 is provided with a torque sensor 38 that detects the steering torque of the driver, and the steering torque Tq detected by the torque sensor 38 is input to the controller 36.
In addition, the vehicle speed V from the vehicle speed sensor 40 mounted on the vehicle and the motor position θf from the electric motor 30 are input to the controller 36, and the electric motor 30, based on the input steering torque Tq, vehicle speed V, and motor position θf. A command signal is output to the bypass valve 34.

2 and 3 are diagrams more specifically showing the power steering mechanism 10 of the present embodiment.
Reference numerals 26 a to 26 d are hydraulic pipes connecting the first and second cylinder chambers 18, 20 and the oil pump 28. Reference numerals 32a, 32a ′, 32b, and 32b ′ are bypass pipes that connect the hydraulic pipes 26b and 26c. Reference numerals 60a, 60b, and 60c denote reservoir tanks that supply oil to the oil pump 28 and store drained oil. Reference numerals 62a and 62b are check valves that are closed when hydraulic pressure is generated by the oil pump 28 and opened when negative pressure is generated.

Reference numeral 64 is a return check valve, reference numeral 66 is a check valve for supplying oil drained from the return check valve 64 to the reservoir tank 60c, and reference numeral 68 is connected via the check valve 66 to the return check valve 64, the reservoir tank 60c. It is a drain oil passage.
As shown in FIG. 3A, the return check valve 64 includes a first return check valve 64a, a second return check valve 64a, a spool valve 70, and return springs 72a and 72b that urge the spool valve 70 to the center. It is composed of

  The first return check valve 64a is provided with a first hydraulic chamber 74a having a connection port with the hydraulic pipes 26a and 26b, and a first piston chamber 208a having a connection port with the drain oil passage 68 and the bypass oil passage 32a ′. ing. Similarly, the second return check valve 64b includes a second hydraulic chamber 74b having a connection port for the hydraulic pipes 26c and 26d, and a second piston chamber having a connection port for the drain oil passage 68 and the bypass oil passage 32b ′. 76b is provided.

  The spool valve 70 is acted on by the urging force on the right side in the figure by the urging force of the return spring 72a, the oil pressure of the first hydraulic chamber 74a, and the oil pressure of the first piston chamber 76a. On the other hand, as the biasing force on the opposite side (left side in the figure), the biasing force by the return spring 72b, the hydraulic pressure in the second hydraulic chamber 74b, and the hydraulic pressure in the second piston chamber 76b act. Thereby, the position of the spool valve 70 is determined.

  In the electric power steering apparatus having the above-described configuration, when the steering wheel 4 starts to be steered, when the hydraulic pressure in the first cylinder chamber 18 of the power cylinder 12 and the hydraulic pressure in the second cylinder chamber 20 are in a balanced state, the rack 8 in FIG. Is assisted to the right in the vehicle width direction, the oil pump 28 is driven to supply hydraulic pressure to the second cylinder chamber 20. Then, the hydraulic pipe 26c and the hydraulic pipe 26d become high hydraulic pressure. This high oil pressure is also supplied to the bypass oil passages 32b and 32b ', and the second piston chamber 76b becomes a high oil pressure. At this time, since the fail safe valve 34 is closed, as shown in FIG. 3 (b), the first piston chamber 76a and the second piston chamber 76b, and the first hydraulic chamber 74a and the second hydraulic chamber 74b are different. Pressure is generated, and the spool valve 70 moves to the left in the figure. As a result, the bypass oil passage 32a 'and the drain oil passage 68 are communicated with each other, and the first cylinder chamber 18 has a low hydraulic pressure released to the atmosphere. Using this differential pressure, an assist force is generated in the power cylinder 12 so that the rack 8 moves to the left in the vehicle width direction. Although not shown, when assisting the rack 8 to the left in the vehicle width direction, the oil pump 28 is driven in the reverse direction to supply hydraulic pressure to the first cylinder chamber 18.

Next, FIG. 4 is a control block diagram showing the controller 36 according to the first embodiment of the present invention. The basic assist command value calculation unit 42, the switchback detection unit 44, the turning speed calculation unit 46, and the failure detection unit 48 are illustrated. , A changeover switch 50, a motor control unit 52, a power cylinder pressure estimation unit 54, a failure motor command value calculation unit 56, and a fail-safe valve control unit 58.
The basic assist command value calculation unit 42 calculates an assist pump command value Ta at normal time based on the vehicle speed V obtained from the vehicle speed sensor 40 and the steering torque Tq obtained from the torque sensor 38.

Based on the steering torque Tq obtained from the torque sensor 38 and the motor position θf obtained from the electric motor 30, the switch detection unit 44 determines whether or not the steering wheel 4 is turned back. Specifically, when the turning operation of the steering wheel 4 is performed, the turning flag Rf = 1 is output to the motor command value calculation unit 56 at the time of failure, and when the turning operation of the steering wheel 4 is not performed, The switching flag Rf = 0 is output to the motor command value calculation unit 56 at the time of failure.
The steered speed computing unit 46 computes the steered wheel WLR and the steered speed ω of the steered wheel WLL based on the change amount of the motor position θf obtained from the electric motor 30 and outputs it to the failure detecting unit 46.

  The failure detection unit 48 monitors the failure of the device (electric power steering device) based on the information on the vehicle speed V, the steering torque Tq, and the steering speed ω, and determines whether the electric motor 30 is in a drivable state. Then, the determination result is output to the changeover switch 50, the motor command value calculation unit 56 at the time of failure, and the fail safe valve control unit 58. That is, when the apparatus is normal, the failure flag Fc = 0 is output. In addition, when it is determined that the electric motor 30 can be driven based on the change in the steering speed ω, although the device has failed, a failure flag Fc = 1 is output. Further, when it is determined that the apparatus is out of order and the electric motor 30 cannot be driven, a failure flag Fc = 2 is output.

  Based on the normal assist pump command value Ta calculated by the basic assist command value calculation unit 42, the power cylinder pressure estimation unit 54 has a higher pressure side of the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12. While calculating the pressure Pmax of the cylinder chamber, the differential pressure Psub of the first cylinder chamber 18 and the second cylinder chamber 20 is calculated, and the pressure P and differential pressure Psub of the cylinder chamber on the high pressure side are calculated as a motor command value calculation unit at the time of failure. To 56.

  The motor command value calculation unit 56 at the time of failure calculates a gain from the differential pressure Psub between the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12 by referring to the map M1. This gain becomes 0 (zero) when the differential pressure Psub is equal to or less than a predetermined threshold value Pα. The predetermined threshold value Pα is set to such a value that the steering force fluctuation caused by the assist in the reverse direction that occurs when the failsafe valve 34 is opened does not cause the driver to feel uncomfortable. Further, by referring to the map M2, a motor command value corresponding to the pressure Pmax in the cylinder chamber on the high pressure side is calculated, and an assist pump command value Ta ′ at the time of failure is calculated by multiplying the motor command value by a gain. . Here, the above-described map M2 is set to calculate a larger motor command value as the pressure Pmax in the high-pressure side cylinder chamber is higher.

  When the apparatus is normal (when the failure flag Fc = 0), the changeover switch 50 outputs the assist pump command value Ta at the normal time to the motor control unit 52. In addition, when the apparatus has failed but the electric motor 30 is in a driveable state (when the failure flag Fc = 1), the assist pump command value Ta ′ at the time of failure is sent to the motor control unit 52. Output. Furthermore, when the apparatus is out of order and the electric motor 30 cannot be driven (when the failure flag Fc = 2), the assist pump command value is not output to the motor control unit 52.

The motor control unit 52 calculates the motor control command value Tr corresponding to the assist pump command value Ta at the normal time or the assist pump command value Ta ′ at the time of failure, and outputs it to the electric motor 30.
The fail safe valve control unit 54 stops the output of the drive signal Vr to the fail safe valve 34 and opens the fail safe valve 34 when the apparatus is out of order but the electric motor 30 can be driven. State. Further, when the apparatus is malfunctioning and the electric motor 30 cannot be driven, the drive signal Vr is output to the fail safe valve 34 and the fail safe valve 34 is closed.

  The oil pump 28 of the present embodiment corresponds to the hydraulic pump of the present invention, and the motor control unit 52, the motor command value calculation unit 56 at the time of failure, and the fail safe valve control unit 58 correspond to the assist steering control unit of the present invention. The failure detection unit 48 corresponds to the abnormality detection unit of the present invention, the power cylinder pressure estimation unit 54 corresponds to the hydraulic pressure difference calculation unit of the present invention, and the switchback detection unit 44 corresponds to the steering wheel steering detection unit of the present invention. is doing.

  Next, the fail safe control process performed by the controller 36 of the present embodiment will be described with reference to the flowchart of FIG. Note that the flowchart processing shown in FIG. 5 is executed by timer interruption every predetermined sampling time ΔT set to, for example, about 10 msec. In this flowchart, no particular communication step is provided, but the results obtained by the arithmetic processing are updated and stored in the storage device as needed, and necessary information and programs are read from the storage device as needed.

  In the processing flow of FIG. 5, first, in step S2, it is determined whether or not the failure flag Fc is “0” (Fc = 0). If the failure flag Fc is “0” (Fc = 0), it is determined that the device (electric power steering device) is normal and has failed, and the process proceeds to step S18, and the failure flag Fc is not “0”. In that case, it is determined that the device has failed, and the process proceeds to step S4.

  In step S4, it is determined whether or not the failure flag Fc is “1” (Fc = 1). If the failure flag Fc is “1” (Fc = 1), it is determined that the apparatus has failed but the electric motor 30 can be driven, and the process proceeds to step S6, where the failure flag Fc is “1”. If not, it is determined that the apparatus is out of order and the electric motor 30 cannot be driven, and the process proceeds to step S22.

In step S6, the fail safe valve 34 is opened by outputting the drive signal Vr to the fail safe valve 34.
Next, the process proceeds to step S8, where the differential pressure Psub between the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12 calculated by the power cylinder pressure estimation unit 54 is compared with the threshold value Pα. When the relationship between the differential pressure Psub and the threshold value Pα is Psub> Pα, the process proceeds to step S10, and when Psub ≦ Pα, the process proceeds to step S24 described later.

In step S10, it is determined whether the return flag Rf is “1” (Rf = 1). When the return flag Rf indicating the state where the steering wheel 4 is turned back is “1” (Rf = 1), the process proceeds to step S24, and the return flag Rf where the steering wheel 4 is not turned back is “ If “0” (Rf = 0), the process proceeds to step S12.
In step S12, a motor command value corresponding to the pressure Pmax in the cylinder chamber on the high pressure side is calculated, and an assist pump command value Ta ′ at the time of failure is output by multiplying this motor command value by a gain.

  Next, the process proceeds to step S14 to determine whether or not the maximum timer counter CNTmax exceeds the timer counter CNT. If the maximum timer counter CNTmax exceeds the timer counter CNT, the process proceeds to step S16 and the maximum timer counter CNTmax exceeds the timer counter CNT. When the counter CNTmax does not exceed the timer counter CNT, the process proceeds to step S15. The timer counter CNT accumulates the actual elapsed time in units of 10 msec, for example.

In step S16, the timer counter CNT is incremented and the process proceeds to step S8. In step S15, the output of the assist pump command value Ta ′ at the time of failure is stopped, and then the fail safe control process is terminated.
On the other hand, in step S18 that is shifted to when the failure flag Fc is “0” in step S2 (Fc = 0), the output of the drive signal Vr to the fail safe valve 34 is stopped to close the fail safe valve 34. State. And it transfers to step S19, the assist pump command value Ta at the time of normal is output, and then it transfers to step S20, and after clearing the timer counter CNT to zero, a fail safe control process is complete | finished.

  In step S22, which is a transition to the case where the failure flag Fc is not “1” in step S4, the output of the drive signal Vr to the fail safe valve 34 is stopped, so that the fail safe valve 34 is closed. Next, the process proceeds to step S24, where the timer counter CNT is cleared to zero and the fail safe control process is terminated.

Next, a specific operation of the fail-safe control process shown in FIG. 5 when a failure occurs during execution of assist steering will be described with reference to FIGS.
First, when the driver steers the steering wheel 4 at a certain rudder angle and the second cylinder chamber 20 of the power cylinder 12 is at a high hydraulic pressure relative to the first cylinder chamber 18, the electric power steering device is A time chart when a failure occurs is shown in FIG.

  As shown in FIG. 6, when it is determined that the apparatus is abnormal and it is determined that the electric motor 30 can be driven (steps S2 and S4), the fail valve 34 is opened (step S6). Drive control of the electric motor 30 is performed. The drive control of the electric motor 30 is performed by calculating a motor command value corresponding to the pressure Pmax of the high-pressure side cylinder chamber, and multiplying the motor command value by a gain to control the assist pump command value Ta ′ at the time of failure. It outputs to the part 52 (step S8, step S12). Then, when the predetermined time CNTmax has elapsed, the driving of the electric motor 30 is stopped (step S14, step S16, step S15).

Next, FIG. 7 shows the oil flow of the power steering mechanism 10 at the time chart of FIG.
When high hydraulic pressure is generated in the second cylinder chamber 20 of the power cylinder 12, the high hydraulic pressure is supplied to the hydraulic pipes 26c and 26d and the bypass pipes 32b and 32b ′. At this time, the return check valve 64 has a relationship of (hydraulic pressure of the first hydraulic chamber 74a <hydraulic pressure of the second hydraulic chamber 74b). Therefore, the spool valve 60 of the return check valve 64 has moved to the left side, and the bypass oil passage 32a ′ and the drain oil passage 68 are in communication with each other, so the first piston chamber 76a is open to the atmosphere.
In this state, when a certain fail is detected in the power steering device and the fail safe control is started, when the fail safe valve 34 is opened, the oil pump 28 is operated by the drive of the electric motor 30, and the high hydraulic pressure of the bypass pipe 32b is reached. Is supplied to the bypass pipe 32a through the fail-safe valve 34.

  Thereby, the bypass pipes 32b and 32b are connected to the hydraulic pipe 26d connected to the second cylinder chamber 20 of the power cylinder 12 and the hydraulic pipe 26a connected to the first cylinder chamber 18 via the return check valve 64. The hydraulic pressure supplied from ', 32a, 32a' flows and is supplied to the first cylinder chamber 18 and the second cylinder chamber 20. As a result, the power cylinder 12 balances the assist force that faces the left side in the vehicle width direction and the assist force that faces the right side in the vehicle width direction. Thereby, when the fail safe valve 34 is opened, the hydraulic pressure of one of the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12 does not rapidly increase.

  In the prior art, when the fail-safe valve 34 is opened, the driving of the electric motor 30 is stopped at the same time (refer to the time chart of the electric motor indicated by the broken line in FIG. 6), so that the oil pump 28 does not operate. In addition, the internal pressures of the first cylinder 18 and the second cylinder chamber 20 of the power cylinder 12 are also reduced (refer to the time chart of the high-pressure side cylinder pressure and the low-pressure side cylinder pressure indicated by broken lines in FIG. 6). As a result, an assist force is generated when a failure occurs, causing a fluctuation in the steering force on the steering wheel 4 and giving the driver a sense of incongruity (see the steering wheel steering angle time chart shown by the broken line in FIG. 6). .

  In contrast, in the present embodiment, the fail-safe valve 34 is opened, and at the same time, the electric motor 30 is driven and controlled so that the hydraulic pressure is supplied to the high-pressure side cylinder (the second cylinder 20 in the present embodiment). Since the pump 28 is operated, the power cylinder 12 is generated such that the assist force facing the left side in the vehicle width direction and the assist force facing the right side in the vehicle width direction are balanced, and the steering wheel 4 causes fluctuations in the steering force. And does not give the driver a sense of incongruity.

Next, FIG. 8 shows a time chart when a failure occurs in the electric power steering apparatus and the driver turns the steering wheel 4 back.
As shown in FIG. 8, when it is determined that the apparatus is abnormal and it is determined that the electric motor 30 can be driven (step S2 and step S4), the fail valve 34 is opened (step S6). The drive control of the electric motor 30 is performed (step S8, step S12, step S14, step S16). Here, when the steering wheel 4 is turned back, the driving of the electric motor 30 is stopped (step S10, step S24, step S15).

Next, the flow of oil in the power steering mechanism 10 at the time of the time chart of FIG. 8 is shown in FIG.
When the driving of the electric motor 30 is stopped when the steering wheel 4 is turned back, the high hydraulic pressure of the bypass pipe 32b is supplied to the bypass pipe 32a via the failsafe valve 34, and the hydraulic pressure supplied from the bypass pipes 32a and 32a ′ is returned. It is supplied to the first cylinder chamber 18 of the power cylinder 12 through the check valve 64 and the hydraulic pipe 26a. On the other hand, the hydraulic pressure in the second cylinder chamber 20 of the power cylinder 12 is returned to the bypass pipes 32b and 32b ′ via the hydraulic pipe 26d and the return check valve 64.

As a result, when the steering wheel 4 is turned back, the hydraulic pressure in the first cylinder chamber 18 of the power cylinder 12 rises to generate assist force in the turning direction, and the hydraulic pressure in the second cylinder chamber 20 decreases. The steering force at the time of turning the wheel 4 is reduced, and a smooth steering operation can be performed.
Next, FIG. 10 shows a time chart when a certain failure occurs in the electric power steering device and the differential pressure Psub between the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12 becomes small.

  As shown in FIG. 10, when it is determined that the apparatus is abnormal and it is determined that the electric motor 30 can be driven (steps S2 and S4), the fail valve 34 is opened (step S6). The drive control of the electric motor 30 is performed (step S8, step S12, step S14, step S16). Thereafter, when the differential pressure Psub becomes equal to or less than the threshold value Pα (Psub ≦ Pα), the driving of the electric motor 30 is stopped (step S8, step S24, step S15).

Next, the flow of oil in the power steering mechanism 10 at the time chart of FIG. 10 is shown in FIG.
When the differential pressure Psub is equal to or less than the threshold value Pα (Psub ≦ Pα), the fail valve 34 is opened, and the steering force of the steering wheel 4 is reduced without operating the oil pump 38 by driving the electric motor 30. The assist force that faces the left in the vehicle width direction and the assist force that faces the right in the vehicle width direction that cause fluctuations are not generated in the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12. Further, when the electric motor 30 is continuously driven, there is a possibility that a problem may occur in terms of heating.

Therefore, when the differential pressure Psub between the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12 becomes equal to or less than the threshold value Pα (Psub ≦ Pα), the driving of the electric motor 30 is stopped to Heating of the motor 30 can be prevented.
As described above, the electric power steering apparatus according to the present embodiment opens the fail-safe valve 34 and simultaneously controls the electric motor 30 to operate the oil pump 28 so that the hydraulic pressure is supplied to the high-pressure side cylinder. Therefore, the steering wheel 4 does not cause a change in the steering force, and the driver does not feel uncomfortable.

Further, when the steering wheel 4 is turned back, the hydraulic pressure in the cylinder on the high pressure side of the power cylinder 12 is reduced, so that the steering force when the steering wheel 4 is turned back can be reduced, and a smooth steering operation can be performed.
Further, when the differential pressure Psub between the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12 becomes equal to or less than the threshold value Pα (Psub ≦ Pα), the electric motor 30 is stopped to drive The durability of the motor 30 can be improved by preventing the motor 30 from being heated.

  Further, the failure motor command value calculation unit 56 constituting the controller 36 refers to a map M2 that calculates a larger motor command value as the pressure Pmax of the cylinder chamber on the high pressure side is higher. Since the assist pump command value Ta ′ at the time of failure is calculated based on the obtained motor command value, the steering force of the steering wheel 4 can be obtained even when the pressure Pmax in the cylinder chamber on the high pressure side is extremely high. Can be reliably prevented.

  In the first embodiment, the power cylinder pressure estimating unit 54 is provided, and the assist pump command value Ta ′ at the time of failure is output according to the cylinder pressure Pmax on the high pressure side, and the differential pressure Psub is equal to or less than the predetermined threshold value Pα. However, the power cylinder pressure estimation unit 54 is not provided, and the assist pump command value Ta ′ at the time of failure and the duration CNT of the assist pump command at the time of failure are determined and output from the steering position of the steering wheel. May be.

Next, FIGS. 12 to 14 are control block diagrams showing the controller 36 of the second embodiment according to the present invention. The same components in the controller 36 of the present embodiment and the controller 36 shown in FIG.
The controller 36 of the present embodiment includes a vehicle acceleration calculation unit 80 in addition to the configuration shown in FIG.

The vehicle acceleration calculation unit 80 calculates the vehicle acceleration G based on the vehicle speed V obtained from the vehicle speed sensor 40 and outputs the vehicle acceleration G to the failure motor command value calculation unit 56.
Based on the normal assist pump command value Ta calculated by the basic assist command value calculation unit 42, the power cylinder pressure estimation unit 54 has a higher pressure side of the first cylinder chamber 18 and the second cylinder chamber 20 of the power cylinder 12. The cylinder chamber pressure Pmax is calculated and output to the motor command value calculation unit 56 at the time of failure.

  The motor command value calculation unit 56 at the time of failure refers to the map M3, and when a negative acceleration (deceleration: G <0) is input from the vehicle acceleration calculation unit 80, the gain is determined according to the deceleration G. Calculate. At positive acceleration (acceleration: G ≧ 0), the gain is set to 1, and the assist pump command value Ta ′ at the time of failure similar to the first embodiment is output. Similarly to the first embodiment, by referring to the map M2, a motor command value corresponding to the pressure Pmax in the cylinder chamber on the high pressure side is calculated, and this motor command value is multiplied by the gain to obtain a failure time. The assist pump command value Ta ′ is calculated.

The power cylinder pressure estimation unit 54 of the present embodiment corresponds to the hydraulic pressure calculation unit of the present invention, and the motor command value calculation unit 56 at the time of failure corresponds to the acceleration calculation unit.
Next, the fail safe control process performed by the controller 36 of the present embodiment will be described with reference to the flowchart of FIG.
In the flowchart of this embodiment, step S26 is inserted between step S10 and step S12 as compared to the flowchart of the first embodiment shown in FIG.
In step S26, the acceleration G calculated by the vehicle acceleration calculation unit 80 is read, and the process proceeds to step S12.

Next, the fail-safe control process of this embodiment when a failure occurs when assist steering is executed will be described.
FIG. 14 shows that when the second cylinder chamber 20 of the power cylinder 12 is at a high hydraulic pressure with respect to the first cylinder chamber 18 and the vehicle is traveling while decelerating, there is some failure in the electric power steering device. It is a time chart when it occurs.

  When it is determined that the apparatus is abnormal and it is determined that the electric motor 30 can be driven (step S2 and step S4 in FIG. 13), the fail valve 34 is opened (step S6), and the electric motor 30 Drive control is performed. The drive control of the electric motor 30 calculates the pressure Pmax of the cylinder chamber on the high pressure side and the acceleration G of the vehicle. Here, when the acceleration G of the vehicle is a positive value, the gain is 1. When the acceleration G of the vehicle is a negative value (deceleration), the gain is calculated according to the deceleration G, and the high-pressure side The motor command value corresponding to the cylinder chamber pressure Pmax is calculated. Then, by multiplying the motor command value and the gain, the assist pump command value Ta ′ at the time of failure is calculated and output (step S22 and step S12).

When the vehicle is traveling at a reduced speed, the steering force for steering the steered wheels WLR and WLL is larger than when traveling at a constant speed, and the variation in the assist steering force when a failure occurs is greater. Therefore, in this embodiment, when the vehicle decelerates, the fail safe valve 34 is opened, and at the same time, a motor command value corresponding to the pressure Pmax in the high-pressure side cylinder chamber is calculated, and the change in the deceleration G to this motor command value is calculated. When a failure occurs during deceleration of the vehicle, the assist pump command value Ta ′ at the time of failure is increased from that at the time of constant speed and output to the motor control unit 52 by multiplying the gain according to However, fluctuations in the assist steering force can be prevented more reliably.
Therefore, according to the present embodiment, even if a failure occurs when the vehicle decelerates, the assist steering force can be gradually generated to alleviate the shock, as indicated by the area within the circle indicated by C in FIG. it can.

It is a figure showing the outline of the electric power steering device concerning the present invention. It is the figure which showed the structure of the power steering mechanism which comprises an electric power steering apparatus. It is a figure which shows the return check valve which comprises a power steering mechanism. It is a control block diagram which shows the controller which comprises an electric power steering apparatus. It is a flowchart which shows the fail safe control process of 1st Embodiment which concerns on this invention. It is a time chart of each apparatus when a failure generate | occur | produces when steering a steering wheel with a fixed rudder angle. It is a figure which shows the flow of the hydraulic pressure of a power steering mechanism when a failure generate | occur | produces when steering a steering wheel with a fixed steering angle. It is a time chart of each device when a failure occurs when the steering wheel is turned back. It is a figure which shows the flow of the hydraulic pressure of a power steering mechanism when a failure generate | occur | produces at the time of steering wheel turning-back. 6 is a time chart when a certain failure occurs in the electric power steering apparatus and the differential pressure between the first cylinder chamber and the second cylinder chamber of the power cylinder becomes small. It is a figure which shows the flow of the hydraulic pressure of a power steering mechanism when a certain failure generate | occur | produces in an electric power steering apparatus and the differential pressure | voltage of the 1st cylinder chamber of a power cylinder and a 2nd cylinder chamber becomes small. It is a control block diagram which shows the controller of the other structure which comprises an electric power steering apparatus. It is a flowchart which shows the fail safe control process which the controller of another structure performs. It is a time chart of each apparatus at the time of the controller of another structure performing fail safe control processing.

Explanation of symbols

4 Steering wheel 10 Power steering device 12 Power cylinder 14 Tie rod 16 Cylinder tube 18 First cylinder chamber (one chamber of the power cylinder)
20 Second cylinder chamber (the other chamber of the power cylinder)
22 Piston 24 Piston rod 26 Hydraulic pipe 28 Oil pump (hydraulic pump)
30 Electric motor 32 Bypass pipe (bypass path)
34 Fail-safe valve 36 Controller 38 Torque sensor 40 Vehicle speed sensor

Claims (3)

A power cylinder that is divided into two chambers by a piston and connected to a steering wheel, a hydraulic pump that provides a hydraulic pressure difference between the two chambers of the power cylinder, and an assist steering force that is applied according to the operation of the steering wheel, An assist steering control means for driving the hydraulic pump;
A bypass path communicating between the two chambers of the power cylinder and a fail safe valve for opening and closing the bypass path, and an abnormality detection means for detecting an abnormality of the power steering device,
The assist steering control means opens the fail-safe valve when the abnormality detecting means detects that the power steering device is abnormal but the hydraulic pump can be driven, and The hydraulic pump is operated so that the liquid is discharged into the high pressure chamber of the two chambers of the cylinder,
Fluid pressure calculating means for calculating the hydraulic pressure of the high pressure side chamber of the two chambers of the power cylinder is provided, and the assist steering control means is configured to control the hydraulic pressure based on the hydraulic pressure calculated by the hydraulic pressure calculating means. Control to increase the hydraulic pressure discharge amount to the high-pressure side chamber as it increases,
A hydraulic pressure difference calculating means for calculating a hydraulic pressure difference between the two chambers of the power cylinder is provided, and the assist steering control means detects the abnormality detecting means that the hydraulic pump can be driven although the power steering device is abnormal. The power steering device is characterized in that the hydraulic pump is stopped when the pressure difference calculated by the hydraulic pressure difference calculating means is equal to or smaller than a predetermined threshold value after being detected by the above . An acceleration calculating means for calculating the acceleration of the vehicle, wherein the assist steering control means is configured such that when the calculation result of the acceleration calculating means is a negative acceleration, the liquid to the high pressure side chamber increases as the negative acceleration increases. The power steering device according to claim 1, wherein the pressure discharge amount is controlled to be increased. A steering wheel steering detection unit configured to detect a steering direction of the steering wheel, wherein the assist steering control unit detects that the power steering device is abnormal but the hydraulic pump can be driven by the abnormality detection unit; The operation of the hydraulic pump is stopped when the steering wheel steering detection unit detects that the steering wheel is turned back from one steering direction to the other steering direction. The power steering apparatus described.

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