JP2007050828A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently reduce an impact caused when each steering angle of steered wheels is limited at the maximum in high-speed steering. <P>SOLUTION: When an absolute value of each steering angle of the steered wheels 101L and 101R exceeds a predetermined angle in the vicinity of the maximum steering angle, a bypass valve 3b is opened, and an oil pump 3a is driven so as to send liquid to a power cylinder chamber on a low pressure side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power steering apparatus that performs steering assist.

Conventionally, as this type of technology, for example, a piston connected to a steering rack and movable in the left-right direction is provided, and liquid is supplied to one of the left and right chambers of the power cylinder partitioned by the piston. Thus, in a power steering device that generates a hydraulic pressure difference and performs steering assist, when a handle is turned back, there is a device that opens a bypass valve of a bypass passage that communicates the two left and right chambers for a predetermined time (for example, Patent Documents). 1). According to the technique described in Patent Document 1, the differential pressure between the left and right chambers can be sufficiently reduced when the steering wheel is turned back, and the steering feeling can be improved.
JP 2004-306721 A

However, in the above prior art, if the turning speed is high, the steered wheel reaches the maximum steered angle before the differential pressure in the two chambers is not sufficiently reduced, and the steered wheel is turned. When the rudder angle is limited by the maximum steered angle, there is a risk of causing an impact.
The present invention aims to solve the above-mentioned unsolved problems of the prior art, and when the turning speed is high, the turning angle of the steered wheels is limited to the maximum turning angle. It is an object of the present invention to provide a power steering device that can sufficiently reduce an impact caused by steering assist when the operation is performed.

  In order to solve the above-described problems, a power steering device according to the present invention includes a power cylinder that is connected to a steering rack and that is movable in the left-right direction and is divided into two left and right chambers, and a liquid is fed to one of the two left and right chambers. A pump that controls the driving of the pump based on a steering operation state of the driver, an assist steering control unit that performs steering assist of the driver, a bypass path that communicates between the left and right two chambers, A bypass valve capable of opening and closing the bypass path, and the assist steering control means opens the bypass valve when the steered wheel is near the maximum turning angle, and opens the bypass valve in the power cylinder chamber on the low pressure side. The maximum turning time control for driving the pump so as to feed the liquid is executed.

  According to such a configuration, when the steering angle of the steered wheels is near the maximum steering angle, the hydraulic pressure in the power cylinder chamber on the low pressure side is increased, and the force pushing the piston on the power cylinder chamber side on the low pressure side is increased. Can be bigger. Therefore, by actively pushing out (pulling out) the fluid in the high-pressure side power cylinder chamber, the differential pressure between the cylinder chambers, that is, the steering assist force can be sufficiently reduced in a short time. As a result, the steering assist force can be made sufficiently small until the steered wheel reaches the maximum turning angle, and the steered wheel has the maximum turning angle even if the turning speed is high. The impact that occurs when limited by the turning angle can be made sufficiently small.

Hereinafter, an embodiment in which a power steering device of the present invention is mounted on a vehicle will be described with reference to the drawings.
<First Embodiment>
That is, this vehicle is equipped with the power steering device of the present embodiment, so that, normally, based on the steering torque applied to the steering wheel, the left and right two chambers of the power cylinder are separated by the pistons connected to the steering rack. Among them, the driver assists the steering by supplying the liquid to the power cylinder chamber on the opposite side to the direction of assisting the steering.

<Configuration of power steering device>
FIG. 1 is a configuration diagram showing an embodiment of a power steering apparatus of the present invention. As shown in FIG. 1, the power steering apparatus 1 includes a power steering mechanism 2, a pump unit 3, a torque sensor 4, a vehicle speed sensor 5, and an EPS controller 6.
The power steering mechanism 2 includes a piston 2a and a power cylinder 2b. The piston 2 a is connected to the steering rack 100 and is configured to be movable in the left-right direction in the power cylinder 2 b integrally with the steering rack 100. When the steering rack 100 moves leftward, the steered wheels 101L and 101R are steered to the right turning side. When the steering rack 100 moves rightward, the steered wheels 101L and 101R are steered to the left turning side.

The power cylinder 2b has a piston 2a disposed therein, and a left power cylinder chamber 2L and a right power cylinder chamber 2R defined by the piston 2a are formed.
When a differential pressure is generated between the power cylinder chambers 2L and 2R, the power steering mechanism 2 generates a force to push the piston 2a from the high pressure power cylinder chamber side to the low pressure power cylinder chamber side, thereby reducing the steering rack 100 to a low pressure. Push forward toward the power cylinder chamber.

The pump unit 3 includes an oil pump 3a and a bypass valve 3b. The oil pump 3a is disposed at the other end of the left hydraulic pipe 3L and the right hydraulic pipe 3R, one end of which is connected to the left power cylinder chamber 2L and the right power cylinder chamber 2R, and is driven by the electric motor 3c to be driven to the left hydraulic pipe 3L. And right hydraulic pipe 3R.
The electric motor 3c drives the oil pump 3a based on a motor control signal Tr (described later) output from the EPS controller 6. Further, the electric motor 3 c outputs a motor angle signal θf indicating the rotation angle of the electric motor 3 c to the EPS controller 6.

  The bypass valve 3b is provided at the center of a bypass passage 3d that connects the left hydraulic pipe 3L and the right hydraulic pipe 3R without passing through the oil pump 3a, and is based on a valve control signal Vr (described later) output from the EPS controller 6. Open and close the bypass 3d. As the bypass valve 3b, a normally open valve that is closed when a voltage is supplied by a control signal from the EPS controller 6 and is open when no voltage is supplied is used.

Then, as shown in FIG. 2, when the pump unit 3 acquires the motor control signal Tr with the bypass valve 3b closed, the pump unit 3 drives the oil pump 3a to either the left hydraulic pipe 3L or the right hydraulic pipe 3R. And a differential pressure is generated between the power cylinder chambers 2L and 2R.
Further, when the pump unit 3 obtains the valve control signal Vr from the EPS controller 6, the pump unit 3 opens the bypass valve 3b and allows oil to flow from the high pressure power cylinder chamber to the low pressure power cylinder chamber. The differential pressure between the chambers 2L and 2R is reduced.

The torque sensor 4 is disposed on the steering shaft 102 and detects a driver's steering torque applied to the steering wheel 103. Then, the torque sensor 4 outputs a steering torque signal Tq indicating the detection result (steering torque) to the EPS controller 6.
The vehicle speed sensor 5 detects the vehicle speed of the host vehicle. The vehicle speed sensor 5 outputs a vehicle speed signal V indicating the detection result (vehicle speed) to the EPS controller 6.

  The EPS controller 6 is a motor for assisting steering based on the motor angle signal θf output from the electric motor 3c, the steering torque signal Tq output from the torque sensor 4, and the vehicle speed signal V output from the vehicle speed sensor 5. The control signal Tr and the valve control signal Vr are calculated. Then, the EPS controller 6 outputs the calculated motor control signal Tr to the electric motor 3c, and outputs the valve control signal Vr to the bypass valve 3b.

  In the power steering device 1, when the driver operates the steering wheel 103 and the steering torque signal Tq is output from the torque sensor 4 in the normal state, the power steering device 1 is opposite to the direction in which steering is assisted based on the steering torque signal Tq. The EPS controller 6 calculates the steering control signal to be sent to the hydraulic pipe and the valve control signal Vr for closing the bypass valve 3b, and the calculation result is output to the electric motor 3c and the bypass valve 3b. Then, the bypass passage 3d is closed, and liquid is fed to the hydraulic pipe opposite to the steering assisting direction, thereby increasing the hydraulic pressure in the power cylinder chamber opposite to the steering assisting direction. A pressure difference is generated between 2L and 2R, a force is generated to push the piston 2a toward the power cylinder chamber side in the direction of assisting steering, and the steering rack 100 is pushed forward toward the power cylinder chamber side in the direction of assisting steering, A steering assist force for turning the steered wheels 101L and 101R in the steering direction is generated.

  Further, the power steering device 1 supplies the liquid to the low pressure side hydraulic pipe when the absolute value of the steering angle of the steered wheels 101L and 101R exceeds a specific steering angle near a predetermined maximum steering angle. The EPS controller 6 calculates the signal and the valve control signal Vr for opening the bypass valve 3b, and outputs the calculation result to the electric motor 3c and the bypass valve 3b. Then, by opening the bypass passage 3d and collecting it in the reservoir 3e, the differential pressure in each of the power cylinder chambers 2L and 2R is gradually lowered, and the liquid pressure is sent to the low-pressure side hydraulic pipe, so that the low-pressure side Increase the hydraulic pressure in the power cylinder chamber, increase the force pushing the piston 2a toward the power cylinder chamber opposite to the direction assisting steering, and decrease the force pushing the piston 2a toward the power cylinder chamber in the direction assisting steering Let Therefore, when the steered wheels 101L and 101R reach the maximum turning angle, the steering assist amount can be sufficiently reduced, and the steered angles of the steered wheels 101L and 101R are limited by the maximum steered angle. The impact caused by the steering assist can be sufficiently reduced.

<Functional configuration of EPS controller>
FIG. 3 is a block diagram showing a functional configuration of the EPS controller 6 of the present embodiment. As shown in FIG. 3, the EPS controller 6 includes a basic assist command value calculation unit 6a, a rack stroke speed calculation unit 6b, a rack end detection unit 6c, a handle turnback detection unit 6d, a rack end detection motor command value calculation unit 6e, A changeover switch 6f, a motor control unit 6g, and a bypass valve control unit 6h are included.

The basic assist command value calculation unit 6a calculates a motor command value Ta for steering assist based on the steering torque signal Tq output from the torque sensor 4 and the vehicle speed signal V output from the vehicle speed sensor 5, and the first 1 motor command value Ta1 is output to the changeover switch 6f.
The rack stroke speed calculation unit 6b calculates the moving speed (rack stroke speed ω) of the piston 2a based on the motor angle signal θf from the electric motor 3c, and the rack stroke speed is detected when the rack end detection unit 6c and the rack end are detected. Output to the motor command value calculator 6e.

  The rack end detection unit 6c indicates whether or not the absolute value of the steering angle of the steered wheels 101L and 101R is equal to or greater than a specific turning angle based on the motor angle signal θf output from the electric motor 3c. The flag Re is set, and the rack end flag Re is output to the rack end detection motor command value calculation unit 6e, the changeover switch 6f, and the bypass valve control unit 6h. Note that the rack end detection flag Re is set to “1” when the absolute value of the steered wheel turning angle is equal to or greater than the specific steering angle, and the rack end detection flag Re is set to “0” when it is smaller than the specific steering angle. "

  The steering wheel return detection unit 6d determines whether or not the steering wheel 103 has been turned back based on the motor angle signal θf output from the electric motor 3c and the steering torque signal Tq output from the torque sensor 4. The steering wheel return flag Rf is set, and the steering wheel return flag Rf is output to the rack end detection motor command value calculation unit 6e, the changeover switch 6f, and the bypass valve control unit 6h. Note that the steering wheel return flag Rf is set to “1” when the steering wheel 103 is turned back by the driver, and the steering wheel return flag Rf is set to “0” when the steering operation is not performed. Reset state.

  When the rack end is detected, the motor command value calculation unit 6e includes a first motor command value Ta1 output from the basic assist command value calculation unit 6a, a rack stroke speed ω output from the rack stroke speed calculation unit 6b, and a rack end detection unit 6c. By the steering assist when the turning angle of the steered wheels 101L, 101R is limited to the maximum turning angle based on the rack end flag Re output from the steering wheel return flag Rf output from the steering wheel return detection unit 6d. A second motor command value Ta2 for reducing the generated impact is calculated, and a motor command calculation process (described later) for outputting the calculation result (second motor command value Ta2) to the changeover switch 6f is executed. In the motor operation calculation process, a bypass valve closing command for closing the bypass passage 3d or a bypass valve opening command for opening the bypass valve 3b is output to the bypass valve control unit 6h.

  The changeover switch 6f is a first motor output from the basic assist command value calculation unit 6a based on the rack end flag Re output from the rack end detection unit 6c and the return flag Rf output from the handle return detection unit 6d. Either the command value Ta1 or the second motor command value Ta2 output from the motor command value calculation unit 6e at the time of rack end detection is output to the motor control unit 6g. Specifically, when the rack end detection flag Re is “0”, or when both the rack end detection flag Re and the turnover flag Rf are “1”, the first motor command value Ta1 is output. Further, when the rack end detection flag Re is “1” and switching is performed and the flag Re is “0”, the second motor command value Ta2 is output.

The motor control unit 6g is configured to supply a current (motor control signal Tr) for driving the oil pump 3a in accordance with the motor angle signal θf (first motor command value Ta1 or second motor command value Ta2) output from the changeover switch 6f. Is output to the electric motor 3c.
The bypass valve control unit 6h includes a rack end flag Re output from the rack end detection unit 6c, a handle return flag Rf output from the handle return detection unit 6d, and a bypass output from the rack end detection motor command value calculation unit 6e. A valve control signal Vr for controlling the opening / closing operation based on the valve closing command or the bypass valve opening command is output to the bypass valve 3b.

<Operation of motor command value calculation unit at rack end detection>
Next, motor command calculation processing executed by the rack end detection motor command value calculation unit 6e will be described with reference to the flowchart of FIG. This motor command calculation process is executed every time a predetermined time (for example, 10 msec.) Elapses. As shown in FIG. 4, first, in step S101, the motor command calculation process is output from the rack end detector 6c. The rack end detection flag Re and the rack stroke speed ω output from the rack stroke speed calculation unit 6b are acquired.

Next, the process proceeds to step S102, and it is determined whether or not the rack stroke speed ω acquired in step S101 is larger than a predetermined maximum rack speed maxsp. If it is greater than the maximum rack speed maxsp (Yes), the process proceeds to step S105, and if it is equal to or less than the maximum rack speed maxsp (No), the process proceeds to step S101.
In step S101, a bypass valve closing command is output to the bypass valve control unit 6h.

Next, the process proceeds to step S104, the second motor command value Ta2 (= 0) for stopping the electric motor 3c is output to the changeover switch 6f, and this calculation process is terminated.
On the other hand, in the step S105, it is determined whether or not the rack end detection flag Re acquired in the step S101 is set to “1” (the absolute value of the steered wheel turning angle is equal to or greater than a specific turning angle). judge. When the set state is “1” (Yes), the process proceeds to step S106. When the reset state is “0” (No), the process proceeds to step S101.

In step S106, it is determined whether or not the handle return flag Rf output from the handle return detection unit 6d is set to “1” (whether a return operation has been performed). When the set state is “1” (Yes), the process proceeds to step S101. When the reset state is “0” (No), the process proceeds to step S107.
In step S107, a bypass valve opening command is output to the bypass valve control unit 6h.
Next, the process proceeds to step S108, and the second motor command value Ta2 (= CurrentTyp (constant)) for driving the electric motor 3c to be fed to the hydraulic pipe on the low pressure side is output to the changeover switch 6f. The process proceeds to step S105.

<Specific operation of power steering device>
Next, the operation of the power steering apparatus of the present embodiment will be described based on specific conditions.
First, it is assumed that the driver steers the steering wheel 103 in the left direction at high speed. Then, as shown at less than time t1 in FIG. 5, when the absolute value of the steering angle of the steered wheels 101L, 101R is smaller than the specific turning angle, the rack end flag Re is “0” in the rack end detection unit 6c. The steering wheel return detection unit 6d sets the steering wheel return flag Rf to “0”, and these flags Re and Rf are output to the rack end detection motor command value calculation unit 6e. The basic assist command value calculation unit 6a calculates a first motor command value Ta1 for steering assist, and outputs the first motor command value Ta1 to the changeover switch 6f.

  At that time, when the motor command calculation processing is executed by the rack end detection motor command value calculation unit 6e, as shown in FIG. 4, first, in step S101, the rack end detection flag Re “1” and The rack stroke speed ω is acquired, the determination in step S102 is “Yes”, the determination in step S105 is “No”, a bypass valve closing command is output to the bypass valve control unit 6h in step S101, and in step S104, After the second motor command value Ta2 (= 0) is output to the changeover switch 6f, this calculation process is terminated.

  As shown in FIG. 2, when the steering wheel 103 is steered and the steering rack 100 is stroked to the right side by the bypass valve control unit 6h, the bypass valve 3b is closed, and the first motor command value is set by the changeover switch 6f. Ta1 is output to the motor control unit 6g, and the motor control unit 6g outputs a motor control signal Tr for driving the oil pump 3a to the electric motor 3c according to the first motor command value Ta1. Then, the oil pump 3a supplies liquid to the left hydraulic pipe 3L (opposite to the steering assisting direction), thereby increasing the hydraulic pressure in the left power cylinder chamber 2L, and the difference between the power cylinder chambers 2L and 2R. A pressure is generated, and a force is generated to push the piston 2a toward the right power cylinder chamber 2R (the direction in which steering is assisted), and the steering rack 100 is pushed forward toward the right power cylinder chamber 2R, causing the steered wheels 101L and 101R to move. Steering assist for turning in the steering direction is performed.

Further, while the assist is turned back, the absolute value of the steering angle of the steered wheels 101L and 101R is determined to be a specific turning by the rack stroke speed ω faster than the maximum rack speed maxsp as shown at time t1 in FIG. If the angle is exceeded, the rack end detection unit 6c sets the rack end flag Re to “1” and outputs the rack end detection time motor command value calculation unit 6e.
Further, when the motor command calculation processing is executed by the rack end detection motor command value calculation unit 6e, as shown in FIG. 4, the determination in step S102 is “Yes” through step S101, and step S105. In step S106, the bypass valve opening command is output to the bypass valve control unit 6h. In step S108, the second motor command value Ta2 (= CurrentTyp ( Is output to the changeover switch 6f, the process proceeds to step S105.

Then, the bypass valve control unit 6h opens the bypass valve 3b as shown in time t2 of FIG. 5 and FIG. 6, and the oil as the working fluid is collected in the reservoir 3e, whereby the left power cylinder chamber The differential pressure between 2L and the right power cylinder chamber 2R is gradually decreased, and the second motor command value Ta2 is output to the motor control unit 6g by the changeover switch 6f, and the second motor command value Ta2 is output by the motor control unit 6g. Accordingly, a motor control signal Tr for driving the oil pump 3a is output to the electric motor 3c. Then, the oil pump 3a supplies liquid to the hydraulic pipe 3R on the right side (direction side assisting steering (low pressure side)), whereby the hydraulic pressure in the right power cylinder chamber 2R is increased, and the left power cylinder chamber 2L side (steering) The force pushing the piston 2a to the opposite side (high pressure side) to the direction of assisting is increased, and the force pushing the piston 2a to the right power cylinder chamber 2R side (direction side assisting steering (low pressure side)) is reduced. . Therefore, the steering assist amount is reduced until the steered wheels 101L and 101R reach the maximum turning angle, and as a result, the steered angles of the steered wheels 101L and 101R are limited by the maximum steered angle. Sometimes the impact that occurs is made small enough.
On the other hand, if the driver turns the steering wheel 103 after the turning angle reaches the maximum turning angle, the turning flag detection unit 6d sets the turning flag Rf to “1” and the motor command value at the time of rack end detection. It is output to the calculation unit 6e.
When the motor command calculation process is executed by the rack end detection motor command value calculation unit 6e, as shown in FIG. 4, the determination of step S106 is “Yes” through steps S101 to S105. In step S101, a bypass valve closing command is output to the bypass valve control unit 6h, and in step S104, the second motor command value Ta2 (= 0) is output to the changeover switch 6f, and then the calculation process is terminated. .

  As shown in FIG. 8, when the steering wheel 103 is turned back and the steering rack 100 is stroked from the right side to the left side by the bypass valve control unit 6h, the bypass valve 3b is closed, and the changeover switch 6f causes the first motor to be closed. The command value Ta1 is output to the motor control unit 6g, and the motor control unit 6g outputs a motor control signal Tr for driving the oil pump 3a according to the first motor command value Ta1 to the electric motor 3c. Then, the oil pump 3a supplies the fluid to the right hydraulic pipe 3R (opposite to the steering assisting direction), thereby increasing the hydraulic pressure in the right power cylinder chamber 2R, and the difference between the power cylinder chambers 2L and 2R. Pressure is generated, and a force is generated to push the piston 2a toward the left power cylinder chamber 2L (the direction in which steering is assisted). The steering rack 100 is pushed forward toward the left power cylinder chamber 2L, and the steering wheels 101L and 101R are moved. Steering assist for turning in the steering direction is performed. That is, the driving state of the electric motor 3c is restored, and the normal steering assist is smoothly restored.

  Thus, in the power steering device 1 of the present embodiment, when the absolute value of the steering angle of the steered wheels 101L and 101R exceeds a specific angle near the maximum turning angle, the bypass valve 3b is opened. At the same time, the oil pump 3a is driven so as to supply the liquid to the power cylinder chamber on the low pressure side (the power cylinder chamber on the opposite side of the power cylinder that has been supplied so far). Therefore, when the steering angle of the steered wheels 101L and 101R is near the maximum steering angle, the hydraulic pressure in the power cylinder chamber on the low pressure side is increased and the force pushing the piston 2a toward the power cylinder chamber side on the high pressure side is increased. Can do. Therefore, by actively pushing out (pulling out) the fluid in the high-pressure side power cylinder chamber, the differential pressure between the cylinder chambers, that is, the steering assist force can be sufficiently reduced in a short time. As a result, as shown in FIG. 5, the steering assist amount can be sufficiently reduced until the steered wheels 101L and 101R reach the maximum turning angle, even if the turning speed is high. The impact generated when the steered angles of the steered wheels 101L and 101R are limited by the maximum steered angle can be sufficiently reduced.

Further, when the turning speed becomes zero, all the hydraulic pressures of the cylinder chambers 2L and 2R can be collected in the reservoir 3e, and the generation of steering assist can be stopped. As a result, the steering force by the driver is reduced. In addition, it is possible to prevent a shock from being generated by unnecessary assist torque.
Further, when the driver turns the steering wheel 103 back, the bypass valve 3b is closed, and steering assist according to the steering torque and the vehicle speed is performed. Therefore, when the steering wheel 103 is turned back, the driver can steer with a small steering torque, and can smoothly perform the turning operation.

  In the present embodiment, an example is shown in which the bypass valve 3b is immediately closed when the turning operation of the steering wheel 103 is detected, but the present invention is not limited to this. For example, the bypass valve 3b may be gradually closed after the switching operation is detected, so that a shock due to a sudden rise in steering assist can be prevented.

Second Embodiment
Next, a second embodiment of the power steering device of the present invention will be described with reference to the drawings.
In the second embodiment, when the absolute value of the steering angle of the steered wheels 101L and 101R exceeds a specific angle, the amount of liquid fed to the power cylinder chamber on the low pressure side increases as the rack stroke speed ω increases. This is different from the first embodiment.
Specifically, as shown in FIG. 9, in the second embodiment, steps S201 to S204 are used instead of step S108 in FIG.

In addition, this 2nd Embodiment includes many structures equivalent to the structure of the said 1st Embodiment, attaches | subjects an equivalent code | symbol to an equivalent structure, and abbreviate | omits the detailed description.
In step S201, the rack stroke speed ω output from the rack stroke speed calculator 6b is acquired, and then the process proceeds to step S203.
In step S202, the third motor command value Tx used for calculating the second motor command value Ta2 is calculated according to the control map of FIG. 10 based on the rack stroke speed ω obtained in step S201, and then the step S203. Migrate to

The control map of FIG. 10 is configured such that the absolute value of the third motor command value Tx increases linearly as the absolute value of the rack stroke speed ω increases.
In step S203, based on the rack stroke speed ω acquired in step S201, a first motor gain Ge1 used for calculating the second motor command value Ta2 is calculated according to the control map of FIG. Transition.

  The control map of FIG. 11 shows the absolute value of the rack stroke speed ω in a region where the rack stroke speed ω is smaller than a predetermined rack speed threshold value ωth (speed at which the impact generated at the rack end can be sufficiently reduced). The first motor gain Ge1 increases linearly, and the first motor gain Ge1 is set to a relatively large constant value in a region larger than the rack speed threshold ωth.

In step S204, the third motor command value Tx calculated in step S202 is multiplied by the first motor gain Ge1 calculated in step S203, and the result of the multiplication is set as a second motor command value Ta2 to the changeover switch 6f. Output.
As described above, in the power steering apparatus 1 of the present embodiment, the third motor command value Tx is calculated so that the liquid feed amount to the power cylinder chamber on the low pressure side increases as the rack stroke speed ω increases. I made it. Therefore, as the turning speed increases, the hydraulic pressure in the low-pressure side power cylinder chamber increases, and the force pushing the piston 2a toward the power cylinder chamber opposite to the steering assist direction can be increased. Even if the speed is faster, the impact generated when the turning angle is limited by the maximum turning angle can be sufficiently reduced.

  Also, as shown at time t2 in FIG. 12, when the rack stroke speed ω becomes equal to or less than the rack speed threshold value ωth, the amount of liquid fed to the low-pressure side power cylinder chamber decreases as the rack stroke speed ω decreases. In addition, the first motor gain Ge1 is calculated. Therefore, when the rack stroke speed ω can be sufficiently decelerated after the absolute value of the steering angle exceeds the specific steering angle, unnecessary motor driving can be suppressed and motor heating can be prevented.

<Third Embodiment>
Next, a third embodiment of the power steering apparatus of the present invention will be described with reference to the drawings.
In the third embodiment, when the absolute value of the steering angle of the steered wheels 101L and 101R exceeds a specific angle, the driving of the oil pump 3a is stopped when the steering torque by the driver decreases. However, this is different from the second embodiment.
Specifically, as shown in FIG. 13, in the third embodiment, step S301 is used instead of step S201 of FIG. 9, and steps S302 and S303 are used instead of step S204.

In addition, this 3rd Embodiment includes many structures equivalent to the structure of the said 2nd Embodiment, attaches | subjects an equivalent code | symbol to an equivalent structure, and abbreviate | omits the detailed description.
In step S301, the rack stroke speed ω output from the rack stroke speed calculator 6b and the steering torque signal Tq output from the torque sensor 4 are acquired, and then the process proceeds to step S202.
In step S302, based on the steering torque signal Tq acquired in step S301, a second motor gain Ge2 used for calculating the second motor command value Ta2 is calculated according to the control map of FIG. Transition.

In the control map of FIG. 14, in a region where the steering torque indicated by the steering torque signal Tq is equal to or smaller than a predetermined steering torque threshold Tqth, the second motor gain Ge2 is “0”, and the steering torque signal Tq is the steering torque threshold. In a region larger than Tqth, the second motor gain Ge2 is configured to be “1”.
In step S303, the third motor command value Tx calculated in step S202 is multiplied by the first motor gain Ge1 calculated in step S203 and the second motor gain Ge2 calculated in step S302. The multiplication result is output to the changeover switch 6f as the second motor command value Ta2.

  As described above, in the power steering device 1 of the present embodiment, as shown at time t3 in FIG. 15, when the steering torque indicated by the steering torque signal Tq becomes equal to or less than the steering torque threshold value Tqth, the second motor command value Ta2 Is set to "0" (so that the oil pump 3a stops), the second motor gain Ge2 is set to "0". Therefore, when the steering torque is small, such as when the hand is released from the steering wheel 103 or when the steering wheel is lightly held, unnecessary motor driving can be suppressed and motor heating can be prevented.

As described above, in the above embodiment, the EPS controller 6 in FIG. 1, the rack end detection motor command value calculation unit 6e in FIG. 3, steps S105, S107 and S108 in FIG. 4, steps S202 to S204 in FIG. 13 steps S202, S203, S301 to S303 constitute the assist steering control means described in the claims.
The power steering device 1 of the present invention is not limited to the contents of the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

It is a lineblock diagram showing one embodiment of a power steering device of the present invention. It is a principal part enlarged view which expands and shows the structure of the pump unit of FIG. It is a block diagram which shows the functionality of the EPS controller of FIG. It is a flowchart which shows a motor command calculation process. It is a time chart for demonstrating operation | movement of 1st Embodiment. It is explanatory drawing for demonstrating operation | movement of 1st Embodiment. It is a time chart for demonstrating operation | movement of 1st Embodiment. It is explanatory drawing for demonstrating operation | movement of 1st Embodiment. It is a flowchart which shows the motor command calculation process of 2nd Embodiment. It is a control map used in motor command calculation processing. It is a control map used in motor command calculation processing. It is a time chart for demonstrating operation | movement of 2nd Embodiment. It is a flowchart which shows the motor command calculation process of 3rd Embodiment. It is a control map used in motor command calculation processing. It is a time chart for demonstrating operation | movement of 3rd Embodiment.

Explanation of symbols

1 is a power steering device, 2 is a power steering mechanism, 2a is a piston, 2b is a power cylinder, 2L is a left power cylinder chamber, 2R is a right power cylinder chamber, 3a is an oil pump, 3b is a bypass valve, 3c is an electric motor, 3d is a bypass path, 3e is a reservoir, 3R is a right hydraulic pipe, 3L is a left hydraulic pipe, 4 is a torque sensor, 5 is a vehicle speed sensor, 6 is an EPS controller, 6a is a basic assist command value calculation unit, and 6b is a rack stroke speed. Calculation unit, 6c is rack end detection unit, 6d is steering wheel turnback detection unit, 6e is rack end detection motor command value calculation unit, 6f is changeover switch, 6g is motor control unit, 6h is bypass valve control unit, 100 is steering Rack, 101L and 101R are steered wheels, 102 is a steering shaft, 103 is a steering wheel

Claims (5)

A power cylinder that is connected to a steering rack and that is movable in the left-right direction and is divided into two left and right chambers, a pump that feeds liquid into one of the two left and right chambers, and the pump that is based on a driver's handle operation state An assist steering control means for performing steering assist of the driver by controlling the driving of the vehicle, a bypass path communicating between the left and right two chambers, and a bypass valve capable of opening and closing the bypass path,
The assist steering control means opens the bypass valve when the steered wheel is near the maximum turning angle and drives the pump so that liquid is fed to the power cylinder chamber on the low pressure side. A power steering apparatus characterized in that steering time control is executed.   The assist steering control means drives the pump so that the liquid feed amount to the power cylinder chamber on the low pressure side increases as the stroke speed of the piston increases during the maximum turning control. The power steering device according to claim 1.   In the maximum steering control, the assist steering control means gradually decreases the amount of liquid fed to the low-pressure side power cylinder chamber according to a decrease in the stroke speed when the stroke speed of the piston becomes a predetermined value or less. The power steering apparatus according to claim 1 or 2, wherein the power steering apparatus is made small.   4. The assist steering control unit according to claim 1, wherein the assist steering control unit stops driving the pump when the steering torque applied to the steering wheel is equal to or less than a predetermined value during the maximum turning control. The power steering device according to item.   2. The assist steering control unit, when the steering operation direction is reversed during the maximum turning control, closes the bypass valve and restarts the steering assist of the driver. 5. The power steering device according to claim 4.

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