JP4737421B2 - Steering assist device - Google Patents

Description

  The present invention relates to a steering assist device provided in a power steering device.

As an electric power steering device, for example, there is a device described in Patent Document 1. In this power steering device, as shown in FIG. 15, a reversible hydraulic pump 50 is driven by an electric motor in accordance with the magnitude and direction of steering torque, and the discharge pressure of the hydraulic pump 50 is supplied to two cylinder chambers of a power cylinder 51. Steering assist is performed by supplying either 51a or 51b. Further, a bypass oil passage 52 that communicates the two cylinder chambers 51a and 51b of the power cylinder 51, a fail-safe valve that opens and closes the bypass oil passage 52, and a spool 54 due to a hydraulic pressure difference between the two cylinder chambers 51a and 51b. And a pressure control valve 55 for connecting the cylinder chambers 51a, 51b on the low pressure side to the reservoir. If it is determined that the steering wheel is turned back, the fail safe valve 53 is temporarily opened for a predetermined time set in advance, thereby suppressing deterioration of the steering wheel when the steering wheel is turned back.
JP 2004-306721 A

However, in the above-described prior art, the steering force largely fluctuates depending on the timing at which the spool 54 of the pressure control valve 55 starts moving when the fail-safe valve that has been opened is closed along with the change in the direction of the discharge pressure of the pump 50 that is determined to be reversal. There is a risk that.
For example, as shown in FIGS. 15A to 15B, when the fail-safe valve is closed before the spool 54 of the pressure control valve 55 is moved, the cylinder chamber (the left side) which has been on the low pressure side until now. The pressure does not rise above the back pressure valve set pressure until the spool 54 (free piston) operates. Then, after the operation in which the spool 54 starts operating, the cylinder pressure on the low pressure side increases at a stretch. If it rises rapidly, pressure fluctuation occurs, that is, the steering force fluctuates. FIG. 16 shows an example of a time chart when the steering force fluctuation (over-assist) occurs at that time.

On the other hand, as shown in FIGS. 17A to 17B, when the fail-safe valve is closed after the spool 54 is operated, the pressure in the low-pressure chamber to which the discharge pressure is supplied from the hydraulic pump 50. May rise at a stretch. If it rises rapidly, pressure fluctuation occurs, that is, the steering force fluctuates. FIG. 18 shows an example of a time chart when the steering force fluctuation occurs at this time.
The present invention has been made by paying attention to the above points, and an object of the present invention is to provide an assist device that can suppress a steering force fluctuation at the time of turning back a steering wheel.

In order to solve the above problems, the present invention includes a power cylinder that is divided into two cylinder chambers by a piston, and a fluid pressure pump that can individually supply fluid pressure to the two cylinder chambers. A steering assist device that assists steering by fluid pressure supplied to a cylinder chamber,
A bypass passage communicating the two cylinder chambers, an opening / closing valve for opening / closing the bypass passage, an opening / closing controller for controlling opening / closing of the opening / closing valve, and a low pressure side cylinder in which a spool is operated by a pressure difference between the two cylinder chambers. A pressure control valve that communicates with the decompression port and decompresses the chamber,
The opening / closing controller synchronizes the transition from opening to closing of the opening / closing valve after the opening of the opening / closing valve with the pressure difference between the two cylinder chambers to the start of operation of the spool of the pressure control valve. It is characterized by taking.

  According to the present invention, even if the bypass passage and the pressure control valve communicating with the two cylinder chambers are provided to suppress the deterioration of the return of the handle at the time of switching, the pressure control valve that reduces the pressure on the low pressure side is reduced. By shutting off the communication between the two cylinder chambers in synchronization with the stop operation, the fluid can be stably supplied to the low-pressure side cylinder chamber in accordance with the steering force. As a result, fluctuations in the steering force when switching the steering direction are reduced. It can be suppressed.

Next, embodiments 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 having a steering assist device according to the present invention.
(Constitution)
First, the structure of the steering apparatus will be described. A steering shaft 2 is connected to the handle 1 and the steering of the handle 1 is transmitted to the rack and pinion 3 via the steering shaft 2, so that the steering rack 4 is moved in accordance with the steering. It is displaced to one side in the width direction, so that the left and right wheels 5 are steered through the tie rods.

  The steering device having the above configuration is equipped with a steering assist device for assisting steering. The steering assist device includes a power cylinder 6, a hydraulic pump 7 as a fluid pressure pump, a motor 8 that drives the hydraulic pump 7, a torque sensor 9 that detects a steering torque Tq input to the steering shaft 2, and a torque sensor 9. A controller 10 is provided for controlling the motor 8 based on the detected steering torque Tq.

  The power cylinder 6 is disposed with its axis directed in the same direction as the steering rack 4, and a piston 6 a that divides the cylinder tube into two cylinder chambers 6 b and 6 c is coupled to the steering rack 4. The two cylinder chambers 6b and 6c of the power cylinder 6 are connected to the hydraulic pump 7 via first and second communication passages 11 and 12, respectively. The hydraulic pump 7 is a circumscribed gear pump 7 that is driven by a motor 8. The hydraulic oil discharge direction is changed by changing the forward / reverse rotation direction, and the first or second communication passages 11, 12 are passed through. The hydraulic oil is supplied to one of the cylinder chambers 6b and 6c through a reversible type.

  The two communication paths 11 and 12 communicate with each other through a bypass path 13, and a fail-safe valve 14 as an on-off valve is interposed in the middle of the bypass path 13. The failsafe valve 14 is an electromagnetic valve that opens and closes according to a command from the controller 10. The fail-safe valve 14 is normally open and is open when no command is supplied.

  Further, a bypass valve 15 as a pressure control valve is disposed on the power cylinder 6 side of the two communication paths 11 and 12 with respect to the bypass path 13. As shown in FIGS. 2 and 3, the bypass valve 15 is formed in series on the left and right sides, and the left and right switching valve portions 15A and 15B for switching communication / closure between the communication passages 11 and 12 and the reservoir tank 17, A free piston portion 15C is disposed between the switching valve portions 15A and 15B and controls the relative operating positions of the valve bodies 18 and 19 of the left and right switching valve portions 15A and 15B. The left and right valve bodies 18 and 19 and the free piston 20 constitute a spool.

  Each of the left and right switching valve portions 15A and 15B has two sets of input ports 23 and discharge ports 24 corresponding to the left and right communication passages 11 and 12, and is formed into a cylindrical sleeve. Are connected to corresponding communication passages 11 and 12, and a discharge port 24 is connected to a drain tank via a check valve 26. The valve bodies 18 and 19 disposed in the sleeve are urged toward the free piston 20 (center side) by a spring 21 disposed in a back pressure chamber formed on the bottom side of the sleeve, and the pump 7 In the non-operating state, the discharge port 24 is closed by being held in a neutral position. In addition, the pressure in the corresponding communication passages 11 and 12 is introduced into each of the back pressure chambers as a back pressure.

  The free piston 20 is composed of a piston body 20a that divides the inside of the sleeve, and left and right rods 20b and 20c that protrude from the piston body 20a to the left and right and that can contact the valve bodies 18 and 19 that face the tip portions. It is disposed between the left and right valve bodies 18 and 19. Each input port 23 opens into the left and right pressure receiving chambers 30 and 31 of the piston main body 20a (sealed space between the piston main body 20a and the valve main bodies 18 and 19). , 31 is introduced with the pressure of the communication passages 11, 12. As a result, the free piston 20 is moved in one of the left and right directions (axial direction) in accordance with the differential pressure between the communication passages 11 and 12, that is, the differential pressure between the two cylinder chambers 6b and 6c. . In a state where there is a differential pressure, the discharge port 24 is opened by moving it to the other back pressure chamber side against the spring force of the spring 21 corresponding to one of the valve bodies 18 and 19, and the discharge port 24 and the input port. By making 23 the communication state, the corresponding communication passages 11 and 12 are made to communicate with the reservoir tank 17 through the check valve 26.

As shown in FIG. 4, the controller 10 includes a normal assist unit 10 </ b> A, a turn-back determination unit 10 </ b> B, a spool operation determination unit 10 </ b> C, and a fail safe valve drive unit 10 </ b> D.
The normal assist unit 10 </ b> A calculates an assist direction and an assist force based on the vehicle speed V input from a vehicle speed sensor (not shown) and the steering torque Tq from the torque sensor 9, and outputs the assist command value to the motor 8. Specifically, the discharge side of the pump 7 is selected according to the direction of the steering torque Tq, and the rotation direction and torque of the motor 8 are controlled so that the discharge pressure is proportional to the steering torque Tq.

  The turn-back determination unit 10B detects whether the handle 1 is turned back. When turning back is detected, the turn-back determination flag Re is turned on. Alternatively, switchback detection is output to the feel safe valve drive unit 10D and the spool operation determination unit 10C. For example, when the direction of the steering torque Tq is reversed, it is determined that the switch is turned back, or when the steering torque Tq is zero and the direction of the motor 8 rotation angle ω is changed.

When the switching determination flag Re is turned on, the spool operation determination unit 10C operates to determine whether or not the spool starts to operate and to detect the operation of the spool (determined by the movement of the free piston 20 in this embodiment). Then, the spool operation flag Fm is turned on. The detection of the operation of the spool may directly detect the movement of the spool itself. Alternatively, the operation of the spool may be estimated and detected from the difference in pressure between the two cylinder chambers 6b and 6c. For example, it may be detected that the spool starts operating when the pressure difference between the two cylinder chambers 6b and 6c having the pressure difference becomes zero.
When power is supplied to the controller 10, such as when the ignition is turned on, the fail safe valve drive unit 10D supplies a close command to the fail safe valve 14 to normally close the fail safe valve 14.

Next, processing at the time of switching in the failsafe valve driving unit 10D will be described with reference to FIG. First, when it is detected in step S10 that the switching determination flag Re is turned on, in step S20, a drive-off command, that is, an open command is supplied to the fail safe valve 14, and the process proceeds to step S30.
In step S30, when it is detected from the spool operation determination unit 10C that the spool operation flag Fm is turned on, the process proceeds to step S40, and a drive-on command, that is, a close command is supplied to the fail safe valve 14 so as to be in the closed state.
Here, the switching determination flag Re and the spool operation flag Fm are turned off in synchronization with, for example, outputting the closing command to the fail safe valve.

(Operation)
In the power steering device having the steering assist device having the above-described configuration, the failsafe valve 14 is normally closed when the system is operating normally, and the steering torque Tq of the steering wheel 1 and Depending on the direction, hydraulic oil is supplied to one of the two cylinder chambers 6b and 6c to be on the high pressure side, and the other chamber is on the low pressure side.

  When the handle 1 is in the neutral position, such as when the vehicle is traveling straight ahead, the oil pump 7 is in an inoperative state. In this case, since a pressure difference does not occur in the two communication passages 11 and 12, the left and right valve bodies 18 and 19 are maintained in the neutral position via the free piston 20 by the spring force of each spring 21. The left and right valve bodies 18 and 19 are in a state in which the discharge port 24 is closed.

  When the steering wheel 1 is steered, for example, in the right direction from the neutral position, the oil pump 7 is driven forward, for example, via the motor 8 by the control current, as shown in FIG. It is discharged into the single communication path 12. Most of the hydraulic fluid in the first communication passage 12 flows into the first cylinder chamber 6 c through the back pressure chamber, and part of it flows into the first pressure receiving chamber 30. As a result, the first pressure receiving chamber 30 becomes high pressure and the second pressure receiving chamber 31 becomes low pressure, so that the free piston 20 slides in the direction of the second valve body 18 (left direction in FIG. 3). The second valve body is retracted toward the back pressure chamber against the spring force of the spring 21. Although the discharge port of the first pressure receiving chamber 30 is kept closed, the second pressure receiving chamber 31 side is opened, and a part of the hydraulic oil in the second communication passage 11 is quickly transferred to the reservoir through the check valve. Discharged. Thus, the steering assist force that assists the movement of the rack 4 by decreasing the pressure in the second cylinder chamber 6b (left side in FIG. 5) and increasing the pressure in the first cylinder chamber 6c (right side in FIG. 6). Is generated in the power cylinder 6.

  From this state, when the handle 1 is turned back to the left and steered leftward, the oil pump 7 rotates in reverse via the motor 8 and, contrary to the above, the hydraulic fluid on the first communication path 12 side on the high pressure side. Is sucked and discharged to the second communication passage 11 on the low pressure side and supplied to the second cylinder chamber 6b side through the back pressure chamber 31. However, since the valve body 18 of the second switching valve portion 15A is in the open state, the hydraulic oil discharged to the second communication passage 11 is discharged to the reservoir.

  When the switchover is detected, the fail-safe valve 14 is opened and the high pressure side first communication passage 12 and the low pressure side second communication passage 11 communicate with each other through the bypass passage 13. The difference between the two cylinder chambers 6b, 6c when the hydraulic oil flows into the second communication passage 11 side through the bypass passage 13 and assists the pressure increase on the second communication passage 11 side and the steering torque Tq is reversed. Pressure release time is shortened.

  When the pressure difference in the two communication passages 11 and 12 becomes zero, as shown in FIG. 7, the free piston 20 starts to operate on the first switching valve portion 15B side (the right side in FIG. 3). The valve main body 18 of the second switching valve portion 15A moves in the closing direction, and at this time, the fail safe valve 14 is closed in synchronization with the start of the operation of the free piston 20 to be discharged into the second communication passage 11. The hydraulic fluid is supplied to the second cylinder chamber 6b as it operates in the closing direction of the valve body 18 of the second switching valve portion 15A.

As described above, when the pressures of the two cylinder chambers 6b and 6c become equal at the time of switching, the amount of increase in hydraulic pressure to the second cylinder chamber 6b is closed by closing the fail-safe valve 14 in synchronization with the start of operation of the free piston 20. As a result, the fluctuation of the hydraulic pressure in the second cylinder chamber 6b when the fail-safe valve 14 is closed can be kept small.
FIG. 8 shows an example of a time chart at that time. In FIG. 8, the broken line shows the behavior in the conventional case.

  The free piston 20 starts to operate, that is, the valve body 18 of the second switching valve portion 15A closes the discharge port 24 to close the fail-safe valve. As the discharge port 24 is closed, the pressure in the second cylinder chamber 6b increases, so that fluctuations in pressure when the fail-safe valve is closed can be suppressed to a small level, that is, occurrence of large fluctuations in steering force can be suppressed. . That is, at the time of turning, the direction of the assist force can be changed in a short time, and sudden torque fluctuations at the steering wheel 1 are prevented, and a good steering feeling can be obtained.

(Second Embodiment)
Next, a second embodiment will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the part similar to the said embodiment.
(Constitution)
The basic configuration of the present embodiment is the same as that of the first embodiment, except that the fail-save valve that is opened may be closed even before the free piston 20 is activated during the turning-back process. .

In this embodiment, the process at the time of switching in the fail safe valve drive unit 10D is performed as shown in FIG. The difference from the first embodiment is that when it is determined in step S40 that the spool operation flag Fm is off, the process proceeds to step S50.
In step S50, it is determined whether or not the high-pressure side cylinder pressure is less than the back pressure valve set pressure. If it is determined that the pressure is less than the back pressure valve set pressure, the process proceeds to step S30. The process proceeds to step S40 and the fail safe valve is changed to closed.
Other configurations are the same as those in the first embodiment.

(Function and effect)
FIG. 10 shows a time chart example of the present embodiment.
In the present embodiment, when it is determined that the switchover is made, the fail-safe valve is opened, the two cylinder chambers 6b and 6c are brought into communication, and the high-pressure side hydraulic fluid moves to the low-pressure side, so that the high-pressure side cylinder pressure is reduced. As the pressure drops, the cylinder pressure on the low pressure side increases. Furthermore, the discharge direction of the pump 7 is changed to the low pressure side.

Even before the pressures of the two cylinder chambers 6b and 6c coincide with each other and the movement of the free piston 20 starts, the fail-safe valve 14 is closed when the high-pressure side cylinder pressure becomes equal to or lower than the back pressure valve set pressure. Here, before the operation of the free piston 20 is started, when the high pressure side cylinder pressure is equal to or lower than the back pressure valve set pressure, the low pressure side cylinder pressure is less than the back pressure valve set pressure. That is, even if the failsafe valve is closed, the cylinder pressure on the low pressure side is lower than the back pressure valve setting pressure, so it continues to rise even before the free piston 20 moves, and the cylinder pressure on the low pressure side is set to the back pressure valve setting. By operating the free piston 20 in a state lower than the pressure, it is possible to suppress a rapid increase in the cylinder pressure on the low pressure side after the operation of the free piston 20, thereby suppressing steering fluctuation.
Other operations and effects are the same as in the above embodiment.

(Third embodiment)
Next, a third embodiment will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the part similar to the said embodiment.
(Constitution)
The basic configuration of this embodiment is the same as that of the above embodiment, but the processing at the time of switching in the failsafe valve driving unit 10D is slightly different as shown in FIG. That is, the difference is that the fail-save valve that is opened may be closed during the turning-back process even before the free piston 20 is actuated.

In the processing at the time of switching in the failsafe valve drive unit 10D in the present embodiment, as shown in FIG. 11, the processing of step S60 is performed after the failsafe valve is opened in step S20 when switching is detected. Different.
In step S60, it is determined whether or not the high-pressure side cylinder pressure is less than a predetermined pressure, for example, the back pressure valve set pressure or less. If it is determined that the pressure is less than the predetermined pressure, the process proceeds to step S70. Moves to step S30.

Here, the predetermined pressure is an upper limit value of the high-pressure side cylinder pressure at the time of switching, in which the low-pressure side cylinder pressure at the start of the operation of the free piston 20 is estimated to be less than the back pressure valve set pressure.
In step S70, it is determined whether or not the rotation of the motor 8 has been reversed, that is, whether or not the discharge direction of the pump 7 has been changed. If it is determined that the change has been made, the process proceeds to step S40 and the fail safe valve 14 is closed.
Other configurations are the same as those in the above embodiment. Moreover, you may perform the process of step S50 (refer FIG. 9) in 2nd Embodiment.

(Function and effect)
FIG. 12 shows a time chart example of the present embodiment.
In this embodiment, when the cylinder pressure on the high pressure side when the handle 1 is turned back is less than a predetermined pressure, the fail-safe valve 14 that is opened is implemented in synchronization with the discharge of the pump 7 switching to the low pressure side. .
Even if the fail safe valve 14 is closed before the operation of the free piston 20, the low pressure side cylinder pressure when the fail safe valve 14 is closed is at least a back pressure valve set pressure lower than the high pressure side cylinder pressure when the handle 1 is turned back. Since it becomes possible to make it less than, it is suppressed that a pressure rises rapidly after free piston 20 operation | movement, and a steering force fluctuation | variation is suppressed.

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the part similar to the said embodiment.
(Constitution)
Although the basic configuration of the present embodiment is the same as that of the third embodiment, the processing at the time of switching in the failsafe valve driving unit 10D is slightly different as shown in FIG.

In the process at the time of switching in the fail safe valve driving unit 10D in the present embodiment, as shown in FIG. 12, the process of step S80 is performed instead of step S60 in FIG.
In step S80, it is determined whether or not the vehicle speed at the time of switching is greater than or equal to a predetermined vehicle speed. If it is determined that the vehicle speed is greater than or equal to the predetermined vehicle speed, the process proceeds to step S70.
Other configurations are the same as those of the third embodiment. Further, the process of step S60 (see FIG. 11) in the third embodiment may be performed in combination.

(Function and effect)
FIG. 14 shows a time chart example of the present embodiment.
In this embodiment, when it is determined that the vehicle speed when the handle 1 is turned back is equal to or higher than the predetermined vehicle speed, the open fail-safe valve 14 is implemented in synchronization with the discharge of the pump 7 being switched to the low pressure side.
When the vehicle speed is high, the steering force required for turning is low. Therefore, when the vehicle speed is high, the vehicle speed of the high-pressure side cylinder pressure at the time of turning is lower than when the vehicle speed is low.

Accordingly, even if the fail safe valve 14 is closed before the operation of the free piston 20, the cylinder pressure on the low pressure side when the fail safe valve 14 is closed can be made lower than the back pressure valve set pressure. Later, a sudden rise in pressure is suppressed, and a fluctuation in steering force is suppressed.
The predetermined vehicle speed may be set to a vehicle speed value at which the high-pressure side cylinder pressure becomes, for example, the back pressure valve set pressure.

It is a system configuration figure concerning an embodiment based on the present invention. It is a figure which shows the hydraulic circuit which concerns on embodiment based on this invention. It is a key map showing a fail safe valve concerning an embodiment based on the present invention. It is a figure which shows the structure of the controller which concerns on embodiment based on this invention. It is a figure which shows the process of the fail safe valve drive part which concerns on 1st Embodiment based on this invention. It is a figure explaining the operation | movement at the time of the normal steering which concerns on embodiment based on this invention. It is a figure which shows the operation state at the time of the switching which concerns on 1st Embodiment based on this invention. It is a figure which shows the example of a time chart which concerns on 1st Embodiment based on this invention. It is a figure which shows the process of the fail safe valve drive part which concerns on 2nd Embodiment based on this invention. It is a figure which shows the example of a time chart which concerns on 2nd Embodiment based on this invention. It is a figure which shows the process of the fail safe valve drive part which concerns on 3rd Embodiment based on this invention. It is a figure which shows the example of a time chart which concerns on 3rd Embodiment based on this invention. It is a figure which shows the process of the fail safe valve drive part which concerns on 4th Embodiment based on this invention. It is a figure which shows the example of a time chart which concerns on 4th Embodiment based on this invention. It is a figure which shows the conventional operation | movement. It is a time chart which shows the conventional problem. It is a figure which shows the conventional operation | movement. It is a time chart which shows the conventional problem.

Explanation of symbols

6 Power cylinders 6b and 6c Cylinder chamber 7 Pump 8 Motor 10 Controller 10A Normal assist unit 10B Switchback determination unit 10C Spool operation determination unit 10D Fail safe valve drive units 11 and 12 Communication path 13 Bypass path 14 Fail safe valve (open / close valve)
15 Bypass valve (pressure control valve)
18, 19 Valve body (spool)
20 Free piston (spool)

Claims (6)

A power cylinder divided into two cylinder chambers by a piston and a fluid pressure pump capable of individually supplying fluid pressure to the two cylinder chambers are provided, and steering is assisted by the fluid pressure supplied to the two cylinder chambers. A steering assist device,
A bypass passage communicating the two cylinder chambers, an opening / closing valve for opening / closing the bypass passage, an opening / closing controller for controlling opening / closing of the opening / closing valve, and a low pressure side cylinder in which a spool is operated by a pressure difference between the two cylinder chambers. A pressure control valve that communicates with the decompression port and decompresses the chamber,
The opening / closing controller synchronizes the transition from opening to closing of the opening / closing valve after the opening of the opening / closing valve with the pressure difference between the two cylinder chambers to the start of operation of the spool of the pressure control valve. A steering assist device characterized by being performed.   2. The steering assist device according to claim 1, wherein the start of operation of the spool is determined based on a difference in pressure between the two cylinder chambers.   The open / close controller changes the open / close valve to open when it detects turning of the handle, and changes the open / close valve to open when it determines that the spool has started to operate. The steering assist device according to claim 2.   When the pressure in the cylinder chamber on the high pressure side is less than the back pressure valve set pressure of the pressure control valve, the open / close controller opens the open / close valve even before determining that the spool has started operating. The steering assist device according to claim 3, wherein the steering assist device is changed to closed.   When the opening / closing controller determines that the pressure in the cylinder chamber on the high pressure side is less than the predetermined pressure, the spool starts operating when the supply of the working fluid by the fluid pressure pump is changed to the cylinder chamber side on the low pressure side. The steering assist device according to claim 3 or 4, wherein the open / close valve is changed to a closed state even before the determination.   When the opening / closing controller determines that the vehicle speed at the time of turning the steering wheel is equal to or higher than a predetermined vehicle speed, it determines that the spool has started to operate when the supply of the working fluid by the fluid pressure pump is changed to the cylinder chamber side on the low pressure side. The steering assist device according to any one of claims 3 to 5, wherein the open / close valve is changed to closed even before the operation.

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