CN100366490C - power steering - Google Patents

Abstract

The power steering device of the present invention can avoid the generation of residual pressure in the low-pressure side passage when the oil pump is switched between forward and reverse, and avoid deterioration of the control feeling. According to the turning operation of the steering wheel, the reversible oil pump (11) performs hydraulic pressure through the first and second passages (8, 9) relative to the first and second oil pressure chambers (6, 7) of the hydraulic cylinder (1). To the row, thereby controlling the steering wheel. Double discharge passages (13, 14) are provided to relatively discharge the oil pressure in the aforementioned passages to the oil storage tank (12); at the same time, in each discharge passage, according to the first passage and the second The pressure difference in the passage makes the free piston (27) slide, and the aforementioned discharge passages are relatively opened and closed by the poppet valve bodies (25, 26), and the working oil in the passage on the low-pressure side is discharged to the oil storage tank.

Description

power steering

technical field

The present invention relates to, for example, a power steering apparatus for applying a steering force or steering assist by operating an actuating hydraulic cylinder in response to torque input from a steering input device such as a steering of an automobile.

Background technique

As such a conventional power steering device, for example, what is described in Patent Document 1 below is known.

The power steering device has a control shaft installed on the steering wheel, an output shaft connected to the lower end of the control shaft, a rack and a pinion provided at the lower end of the output shaft, connected to the rack and used as an operating hydraulic actuator The operating hydraulic cylinder, through the first passage and the second passage, supplies the operating oil pressure to the reversible oil pump of the left and right first and second operating hydraulic chambers separated by the piston of the operating hydraulic cylinder. , and an electromagnetic switching valve located in the bypass passage connecting the aforementioned first and second passages, and opening and closing the bypass passage.

When the vehicle is running, if the steering wheel is used to perform normal left and right manipulations, the detection mechanism that detects the manipulation torque outputs a channel closing signal to the aforementioned solenoid valve through the control circuit, and at the same time, makes the reversible oil pump rotate forward or reverse, and either side The working oil in the working oil pressure chamber or passage is relatively supplied to the other working oil pressure chamber or passage.

The working oil of the entire closed circuit that fills the working oil pressure chamber or passage of the other side is pressurized by the aforementioned reversible pump; The air bubbles are crushed and the volume of the passage piping is inflated. Therefore, in order to compensate for this volume increase, hydraulic oil is sucked into the passage from the oil storage tank through the check valve, and pressurized by the reversible pump, thereby giving steering assist.

Patent Document 1

Japanese Patent Application Laid-Open No. 59-118569

However, in the aforementioned prior art, the increase in the volume of the passage piping is compensated by the supply from the storage tank, and the hydraulic fluid amounts in the first passage and the second passage are deviated from the compensated hydraulic fluid amounts. Therefore, when the reversible oil pump rotates from the forward direction to the reverse direction to supply working oil to one passage side, since the amount of working oil on the other pressurized passage side exceeds the compensation amount, the other one may The pressure on the passage side will drop, the speed will slow down, and residual pressure will be generated.

Therefore, when the working oil on one passage side is pressurized and the working oil pressure rises, as long as the working oil on one passage side is not pressurized above the residual pressure on the other passage side, steering assist cannot be performed, resulting in Slow power assist and sharp torque changes on the steering wheel may lead to deterioration of the handling feeling.

Contents of the invention

The present invention is proposed in view of the aforementioned technical problems of the conventional power steering device.

The first invention is a power steering device that uses a reversible pump through an oil pressure supply passage composed of a first passage and a second passage in response to an input torque output from a steering input device, compared to a hydraulic pressure supply passage composed of a first passage and a second passage. The first and second hydraulic chambers separated by the cylinder and piston carry out hydraulic supply and discharge, so as to control and steer the wheels. discharge passages, and at the same time, a pair of switching valves are provided in each of the discharge passages, and the pair of switching valves are closed when the internal pressure of one of the first and second passages is increased by the operation of the aforementioned reversible pump. The discharge passage of the high-pressure side passage opens the discharge passage of the low-pressure side passage.

Therefore, according to this invention, if the steering wheel is turned in one direction, the reversible pump works, for example, hydraulic pressure is supplied to the first passage side, and the switching valve closes the discharge passage on the first passage side while opening the second passage side. The discharge passage is connected to the oil storage tank. As a result, almost all of the operating hydraulic pressure on the side of the second passage and the second operating hydraulic chamber is supplied to the first operating hydraulic chamber by the reversible pump through the first passage, and part of the operating hydraulic pressure is supplied to the first operating hydraulic chamber by the side of the second passage. Drain passage quickly drains to reservoir.

Therefore, the speed of pressure drop on the second passage side is accelerated, and generation of residual pressure can be prevented. As a result, the steering assist can be quickly performed, and sudden torque fluctuations can be prevented from occurring at the steering wheel, and a good steering feel can be obtained.

The second invention is characterized in that the switching valve is disposed between the double discharge passages, and relatively opens and closes the respective discharge passages based on the pressure difference between the first passage and the second passage.

According to this invention, since the operation of the switching valve is mechanically performed by the pressure difference between the two passages instead of an electrical method, it is expected to simplify the control and structure for switching and suppress the increase in cost.

The third invention is characterized in that a valve body for opening and closing each of the discharge passages of the switching valve is constituted by a poppet valve body.

According to this invention, since the valve body is formed as a poppet valve body, it is possible to prevent the valve body from being locked due to so-called dirt such as metal powder, and to ensure stable operation.

The fourth invention is characterized in that: the above-mentioned poppet valve bodies are slidably accommodated in a pair of valve holes, and have a sealing portion that separates the valve holes into a first chamber and a second chamber, that is, a back pressure chamber; The aforementioned first chamber communicates with the aforementioned oil pressure supply passage and the oil storage tank, and the switching operation of the poppet valve controls the connection/blocking of the aforementioned oil pressure supply passage and the oil storage tank; the aforementioned second chamber communicates with the aforementioned oil pressure supply passage, On the second chamber side of the poppet valve, there is a pressure receiving surface on which the poppet valve is energized toward the first chamber by the oil pressure supplied from the reversible pump.

According to this invention, since the first chamber connected to the oil storage tank is separated by the sealing part, and the pressure receiving surface of the poppet valve facing the direction of the first chamber is opposite to the oil pressure supplied by the reversible pump. Two chambers, so the pressure difference acting on the front and back of the poppet valve can really cut off the communication between the oil pressure supply passage and the oil storage tank.

The fifth invention is characterized in that each of the poppet valves in the fourth invention has an elastic member in the second chamber that energizes the poppet valve toward the first chamber.

According to this invention, since the position of the poppet valve in the valve hole can be specified when the oil pressure does not act on the poppet valve, the switching valve can be freely set as a normally closed valve or a normally open valve. In addition, even when the oil pressure acting on the poppet valve front pressure is relatively small, since the elastic member energizes the poppet valve toward the first chamber, the communication between the oil pressure supply passage and the oil storage tank can be blocked reliably.

The sixth invention is characterized in that the power steering device of the aforementioned fifth invention has a connecting passage connecting the first chambers of the pair of valve holes to each other, and a free piston slidably provided in the connecting passage; The free piston moves axially through the pressure difference between the first passage and the second passage, and controls the opening and closing of the poppet valve.

According to this invention, since the free piston blocks the oil pressure communication in the valve hole, the oil pressure on the high pressure side can be prevented from leaking to the low pressure side, and the poppet valve on the low pressure side can be surely opened.

A seventh invention is characterized in that the free piston in the sixth invention has a crimping portion that opens the valve by crimping the poppet valve.

According to this invention, since the crimping portion is directly pressed against the poppet valve to open the valve, compared with opening the valve only by oil pressure, the poppet valve can be surely opened.

The eighth invention is characterized in that the crimping portion in the seventh invention is in contact with the poppet valves on both sides when the reversible pump is not in operation.

According to this invention, when the reversible pump is in the non-working state, the crimping part does not abut the poppet valves on both sides, and the poppet will not be opened after the free piston works until the crimping part abuts the poppet valve. When the reversible pump is in a non-working state and the crimping part is in contact with the poppet valves on both sides, if the free piston moves with the help of oil pressure, the poppet valve can be opened immediately, thus improving the poppet valve. Response performance. In addition, when the reversible pump is not working, since the free piston is located in the middle position, the free piston does not deviate to any side, so the same control response speed can also be obtained.

A ninth invention is characterized in that, in the power steering device of the seventh invention, a pair of elastic members are provided between the free piston and the pair of poppet valves.

According to this invention, since the free piston is in the center position when the reversible pump is not working, the free piston does not deviate to any side, so the left and right control response speeds can be the same.

The tenth invention is characterized in that, in the poppet valve according to the fourth invention, the switching portion for controlling the connection/blocking of the hydraulic supply passage and the oil storage tank is formed in a conical shape.

According to this invention, the poppet valve can be prevented from being locked because it is difficult for foreign matters such as dirt to enter the switching portion.

The eleventh invention is characterized in that, in the power steering apparatus of the fourth invention, the first chamber communicates with the discharge path of the oil storage tank, and the two first chambers communicate with each other on the upstream side of the oil storage tank.

According to this invention, since the working oil discharged from the first chamber on one side is directly supplied to the first chamber on the other side, the first chamber on the other side does not need to suck the working oil from the oil storage tank, and the left and right first chambers The oil flow between them is good. Therefore, the handling feeling when the reversible pump is not in operation can be improved.

The twelfth invention is characterized in that, in the power steering device of the fourth invention, the second chamber has a pair of openings, and the opening on one side communicates with the oil pressure supply passage on the side of the reversible pump; The opening on one side communicates with the hydraulic pressure supply circuit on the hydraulic cylinder side.

According to this invention, since the hydraulic pressure of the hydraulic supply passage can be supplied to the second chamber without providing a branch passage from the hydraulic supply passage, the structure of the device can be simplified.

A thirteenth invention is characterized in that, in the power steering device of the first invention, the switching valve opens the discharge passages on both sides when the reversible pump is in a non-operating state.

According to this invention, when the reversible pump is in the non-working state, that is, in the straight-forward state, the two hydraulic chambers of the hydraulic cylinder and the oil pressure in the oil storage tank are the same, and the control feeling becomes natural. In addition, since no residual pressure remains in the hydraulic pressure supply passage, it is possible to avoid a state where the steering is energized to either the left or the right.

A fourteenth invention is characterized in that, in the power steering apparatus of the first invention, the switching valve closes the discharge passages on both sides when the reversible pump is in a non-operating state. According to this invention, when the reversible pump is in a non-operating state, the discharge passages on both sides are opened, and during the period until the switching valve on the pressurizing side is closed, the operation responds due to oil pressure leaking from the switching valve to the oil storage tank. The performance is reduced; and when the reversible pump is in a non-working state, if the discharge passages on both sides are closed, since there is no oil pressure on the pressurized side to leak to the oil storage tank, the response performance of the control will not be reduced.

Description of drawings

FIG. 1 is a schematic diagram showing a hydraulic cylinder and a hydraulic circuit provided by the first embodiment of the present invention.

Fig. 2 is a schematic diagram showing the operation of this embodiment.

Fig. 3 is a schematic diagram showing the operation of this embodiment.

Fig. 4 is a longitudinal sectional view showing a switching valve according to a second embodiment of the present invention.

Fig. 5 is a longitudinal sectional view showing a switching valve according to a third embodiment of the present invention.

Detailed ways

Embodiments of the power steering device of the present invention will be described in detail below based on the drawings.

Fig. 1 shows the first embodiment of the present invention, which mainly describes the hydraulic cylinder 1 and the hydraulic circuit 2 of the power steering device. As a general situation of the device, it consists of the following parts: In the steering wheel shown, the rack and pinion provided on the output shaft connected to the lower end of the steering shaft of the steering wheel are provided on the lower end side of the output shaft and are used to detect the steering torque of the steering wheel and the road surface input force from the left and right front wheels. The detecting device is the aforementioned hydraulic cylinder 1 connected to the aforementioned rack, and a hydraulic circuit 2 that discharges operating hydraulic pressure to the hydraulic cylinder 1 .

In the hydraulic cylinder 1, a piston rod 4 connected to the rack is inserted into a cylindrical cylinder portion 3 extending in the vehicle body width direction, and a piston sliding in the cylindrical cylinder portion 3 is fixed to the piston rod 4. 5. In addition, in the cylindrical cylinder portion 3 , the piston 5 is partitioned into left and right first hydraulic chambers 6 and second hydraulic chambers 7 .

The aforementioned hydraulic circuit 2 has: a pair of first and second passages 8, 9 connected to the aforementioned hydraulic chambers 6, 7 at one end, connected to the other end of the two passages 8, 9 and driven by a pump motor 10 A reversible oil pump 11 of its positive and negative rotation is respectively connected to the aforementioned first and second passages 8, 9 and midway, and its downstream ends are connected to the first and second discharge passages 13 and 14 of the oil storage tank 12, and are set Between the double discharge passages 13 and 14, according to the pressure difference in the passages 8 and 9, the switching valve 15 that switches the respective discharge passages 13 and 14 relatively and switches to the communication with the oil storage tank 12, in the aforementioned first, On the upstream side of the second passages 8, 9, the compensating hydraulic oil is supplied to the first and second oil storage tanks 18, 19 of the respective passages 8, 9 through the compensation passages 16, 17, respectively.

The pump motor 10 controls the rotation, stop, forward and reverse rotation of the oil pump 11 based on the detection signal output from the detection device and the control current from the electronic controller not shown in the figure.

The above-mentioned double discharge passages 13, 14 are connected to the discharge passage 20 communicating with the oil storage tank 12 at the joints at their respective downstream ends; 12 check valve 21.

The aforementioned switching valve 15 has a pair of valve holes 22 a , 22 b , valve bodies 23 , 24 , a pair of poppet valve bodies 25 , 26 , and a free piston 27 . The pair of valve holes 22a, 22b are formed in series across the aforementioned first and second passages 8, 9, respectively, and communicate with the aforementioned discharge passages 13, 14 at the central side communicating with each other; The cylindrical shape with one end sealed is fixed inside the aforementioned valve holes 22a, 22b; the pair of poppet valve bodies 25, 26 are freely slidably arranged inside the aforementioned two valve bodies 23, 24. The pressure difference of the two passages 8, 9 relatively switches the aforementioned discharge passages 13, 14; the free piston 27 can be freely slid in the direction of each poppet valve body 25, 26, that is, it can be freely slid in the axial direction. The sliding hole 22c between the aforementioned two valve holes 22a, 22b controls the relative actuation positions of the aforementioned poppet valve bodies 25, 26.

The aforementioned poppet valve bodies 25, 26 are disposed in series in each of the valve bodies 23, 24, and are formed into stepped cylindrical shapes, and are mainly composed of valve portions 25a, 26a and large-diameter rear end portions 25b, 26b. . The opposite front end surfaces of the valve parts 25a, 26a are generally conical; the rear end parts 25b, 26b with large diameters receive the aforementioned passages 8 from the back pressure chambers 30, 31 at the bottom sides of the valve bodies 23, 24. , The operating oil pressure in 9. Also, abutment shafts 25c, 26c abutting against both end surfaces of the central shaft 27a of the free piston 27 are integrally provided at the opposite front ends of the respective valve parts 25a, 26a.

Each poppet valve body 25, 26 is energized in the direction of the aforementioned free piston 27 by the elastic force of the coil springs 28, 29 elastically installed between the bottom surface of the valve body 23, 24 and the rear end portion 25b, 26b. In the non-operating state, the neutral position is maintained. In this state, each valve part 25a, 26a is seated on the seat surface of the front end of the valve body 23, 24 to form a so-called normally closed type that closes each discharge passage 13, 14.

The aforementioned free piston 27 slides to the left and right in the figure according to the pressure difference between the aforementioned passages 8, 9, that is, according to the pressure difference between each passage 8, 9 and the pressure chamber 32, 33 formed in the middle of each discharge passage 13, 14, Overcoming the elastic force of the opposite coil springs 28, 29, either poppet valve body 25, 26 is relatively switched and slid forward and backward.

In addition, in the middle of the above-mentioned compensation passages 16 and 17, there are first and second one-way valves that allow the operating oil in the first and second oil storage tanks 18 and 19 to flow into the passages 8 and 9 only. 34, 35.

Furthermore, in the suction passage 36 of the oil pump 11, there is provided a check valve 37 that allows only the working oil from the oil storage tank 12 to flow into the oil pump 11 direction.

Next, the function of this embodiment will be described. First, when the vehicle is running straight ahead, the driver does not turn the steering wheel but maintains a neutral state, the electronic controller does not output control current to the pump motor 10, and the oil pump 11 is in a non-operating state. In this case, as shown in FIG. 1, since there is no pressure difference in each passage 8, 9, each poppet valve body 25, 26 maintains the neutral position through the free piston 27 by the elastic force of each coil spring 28, 29. . Therefore, each valve part 25a, 26a is seated on each seat surface, and it is the state which closed each discharge passage 13,14.

Then, if the steering wheel is turned to the right, the control current from the electronic controller passes through the pump motor 10, for example, to drive the oil pump 11 to rotate forward. Under the action of the pump, as shown in Figure 2, the operating oil in the second passage 9 is sucked and discharged into the first passage 8, and then most of the operating oil in the first passage 8 passes through the back pressure chamber 30 flows into the first hydraulic chamber 6 , and part of it flows into the first pressure receiving chamber 32 through the first discharge passage 13 . At the same time, the operating oil in the first oil storage tank 18 also flows into the first passage 8 and the first operating oil pressure chamber 6 through the oil pump 11 to make up for the shortage.

Thus, the first pressure receiving chamber 32 becomes high pressure, and at the same time, the second pressure receiving chamber 33 becomes low pressure. Because of this, as shown in the figure, the free piston 27 slides toward the second poppet valve body 26 (to the left), Overcoming the elastic force of the coil spring 29 , the second poppet valve body 26 retreats toward the back pressure chamber 31 . At the same time, leave the first poppet valve body 25 .

Therefore, the first discharge passage 13 maintains the closed state, and the second discharge passage 14 opens the side of the pressure receiving chamber 33, and a part of the operating oil in the second passage 9 is quickly discharged to the reservoir through the check valve 21 as indicated by the arrow. In the fuel tank 12. Therefore, the pressure drop speed on the side of the second passage 9 is accelerated, and generation of residual pressure is prevented.

On the other hand, if the steering wheel is returned to the original state from the rightward turning operation state, and then the leftward turning operation is performed, the oil pump 11 is reversed by the electronic controller through the pump motor 10 .

Therefore, as shown in FIG. 3 , contrary to the foregoing, the operating oil on the side of the first passage 8 and the operating oil in the second oil storage tank 19 are discharged into the second passage 9 and supplied to the second passage through the back pressure chamber 31 . Oil pressure chamber 7.

Therefore, the internal pressure of the first pressure receiving chamber 32 decreases, while the internal pressure of the second pressure receiving chamber 33 increases, the free piston 27 slides to the right as shown in the figure, and overcomes the elastic force of the coil spring 28 to make the first poppet valve The body 25 retreats toward the back pressure chamber 30, and at the same time, leaves the second poppet valve body 26.

As a result, the second discharge passage 14 is closed, while the first discharge passage 13 is opened to the first pressure receiving chamber 32 side, and a part of the working oil in the first passage 8, as indicated by the arrow, passes through the check valve 21 rapidly. Drain into the oil storage tank 12. Therefore, the speed of pressure drop on the side of the first passage 8 is accelerated, and generation of residual pressure can be prevented in the same manner as described above.

In this way, when the steering wheel is turned left and right, the internal pressure of the passages 8 and 9 which become the low pressure can be quickly reduced, and the steering wheel can be quickly assisted, which can prevent the steering wheel from suddenly changing torque, thereby obtaining good performance. operational sense.

In addition, since the work of the aforementioned poppet valve bodies 25, 26 is controlled by the pressure difference of the first and second passages 8, 9, that is, the pressure difference of the pressure receiving chambers 32, 33, it is not related to the electric valves using solenoid valves and the like. Compared with the device, it is expected to simplify the control; at the same time, because it is a simple mechanical structure, it is easy to manufacture and can limit the increase in cost.

In addition, since the front end faces of the valve portions 25a, 26a are constituted by a pair of conical (inclined) poppet valve bodies 25, 26, for example, it is difficult for foreign matter such as dirt to enter, so each valve portion 25a, 26a can be prevented from being damaged. Lock-up phenomenon.

Fig. 4 shows a second embodiment of the present invention in which the configuration of the switching valve 15 is changed to a so-called normally open type.

That is, the axial length of the central shaft 27a of the free piston 27 is set to be extended by a predetermined amount in the left and right directions, and the poppet valve bodies 25, 26 are arranged slightly offset toward the respective back pressure chambers 30, 31.

Therefore, when the steering wheel is turned left and right, as in the first embodiment, the free piston 27 slides left and right according to the pressure difference in the first and second passages 8, 9, and the poppet valve body 25, 26 opens one side. The discharge passages 13 and 14 can prevent the generation of residual pressure, and naturally can play the same role and effect as described above; in the neutral state where the steering wheel is not rotated, the free piston 27 remains in the left and right neutral positions, and each valve body 25a, 26a Leaving the seat surface, the respective discharge passages 13, 14 are opened. Therefore, the mutual communication state of each discharge passage 13, 14 can be ensured.

Fig. 5 shows the third embodiment, with the normally open switching valve 15 of the second embodiment as the basic structure, between the two sides of the free piston 27 and the poppet valve bodies 25, 26, coil springs 37, 38.

Thus, as in this embodiment, each poppet valve body 25, 26 is forcibly kept in a neutral position by the relative elastic force of the aforementioned coil springs 37, 38 and the coil springs 28, 29 in each back pressure chamber 30, 31, Therefore, when the oil pump 11 is not in operation, each of the discharge passages 13 and 14 can be forcibly opened. According to this, manual steering can be ensured when the pump is locked, and a fail-safe function can be obtained.

As for technical ideas other than the content of the invention that can be grasped from the foregoing embodiments, they are as described in (a), (b) below.

(a) In the power steering device according to the second invention, the switching valve has a pair of valve holes, a pair of valve bodies, and a free piston. The pair of valve holes are respectively formed across the aforementioned first and second passages, and connect the aforementioned discharge passages to the central side that communicates with each other; the pair of valve bodies are freely slidably arranged inside the aforementioned two valve holes, based on The pressure difference of the aforementioned first and second passages relatively switches the aforementioned discharge passages; the free piston is freely slidable in the direction of each valve body and is set in the communication hole connecting the two aforementioned valve holes in the center, and through the aforementioned discharge passages. The passage senses the pressure difference of each passage to control the actuating position of each valve body.

According to this invention, since the switching valve is entirely mechanically constructed, compared with the high-priced electromagnetic type, it can naturally limit the increase in cost; in particular, the free piston directly senses the pressure difference of each passage, and with the sliding of the free piston, it can be controlled. The actuation position of each valve body, therefore, the overall structure is simplified, and good actuation control of the aforementioned valve bodies can be obtained.

(b) In the power steering device according to any one of the first to third inventions, the downstream sides of the discharge passages are connected to each other, and the switching valve is opened when the reversible pump is not in operation. , Connecting two discharge passages to form a normally open type.

According to this invention, when the vehicle is going straight and the steering wheel is in a neutral state, since the double discharge passages are in a connected state, manual steering can also be ensured when the pump is locked, and a fail-safe function can be obtained.

The present invention is not limited to the configurations of the foregoing embodiments. For example, the free piston 27 may not be used, and the rear end portions 25b, 26b of the poppet valves 25, 26 may be changed to sense the internal pressure of the back pressure chambers 30, 31. The pressure area and the pressure receiving area of the valve body 25a, 26a which senses the internal pressure of each pressure receiving chamber 32, 33 directly make each poppet valve body 25, 26 operate by the pressure difference.

Claims (14)

1. A power steering device, the power steering device, according to the input torque output from the steering input device, is separated from the hydraulic cylinder piston by a reversible pump through an oil pressure supply passage composed of a first passage and a second passage. The formed first and second hydraulic chambers carry out hydraulic supply and discharge, so as to control and steer the wheels, which are characterized in that: A double discharge passage is provided to discharge the hydraulic oil in the first passage and the second passage to the oil storage tank, and at the same time, a pair of switching valves are provided in each discharge passage, and the pair of switching valves are connected to the reversible pump. When the internal pressure of one of the first and second passages is increased by operation, the discharge passage of the high-pressure side passage is closed, and the discharge passage of the low-pressure side passage is opened. 2. The power steering device according to claim 1, wherein the switching valve is disposed between the double discharge passages, and is configured to relatively open and close the respective discharge passages according to the pressure difference between the first passage and the second passage. path. 3. The power steering apparatus according to claim 2, wherein said switching valve comprises a poppet valve body for opening and closing each of said discharge passages. 4. The power steering device according to claim 3, characterized in that: The aforementioned poppet valve bodies can be freely slidably accommodated in a pair of valve holes, and have a sealing portion that separates the valve holes into a first chamber and a second chamber, that is, a back pressure chamber; The aforementioned first chamber communicates with the aforementioned oil pressure supply passage and the oil storage tank, and the switching operation of the poppet valve body controls and switches the connection/blocking of the aforementioned oil pressure supply passage and the oil storage tank; The second chamber is connected to the oil pressure supply passage, and there is a pressure receiving surface on the side of the second chamber of the poppet valve body where the oil pressure supplied by the reversible pump energizes the poppet valve body toward the first chamber. . 5. The power steering device according to claim 4, wherein each of the poppet valve bodies has an elastic member in the second chamber that energizes the poppet valve body toward the first chamber. 6. The power steering device according to claim 5, further comprising a connecting passage connecting the first chambers of the pair of valve holes to each other, and a free piston slidably provided in the connecting passage; The free piston moves axially through the pressure difference between the first passage and the second passage, and controls the opening and closing of the poppet valve body. 7. The power steering device according to claim 6, wherein said free piston has a pressure contact portion for opening the valve by pressure contact with said poppet valve body. 8. The power steering device according to claim 7, wherein the crimping portion abuts against the poppet valve bodies on both sides when the reversible pump is in a non-operating state. 9. The power steering device according to claim 7, wherein a pair of elastic members are provided between the free piston and the pair of poppet valve bodies. 10. The power steering apparatus according to claim 4, wherein the poppet valve body is formed in a conical shape as a switching portion for controlling connection/blocking of the oil pressure supply passage and the oil storage tank. 11. The power steering system according to claim 4, wherein the first chamber communicates with the discharge passage of the oil storage tank, and the two first chambers communicate with each other on the upstream side of the oil storage tank. 12. The power steering device according to claim 4, wherein the second chamber has a pair of openings, and the opening on one side communicates with the hydraulic pressure supply passage on the side of the reversible pump; The opening part communicates with the hydraulic pressure supply circuit on the hydraulic cylinder side. 13. The power steering apparatus according to claim 1, wherein said switching valve opens said discharge passages on both sides when said reversible pump is in a non-operating state. 14. The power steering apparatus according to claim 1, wherein said switching valve closes said discharge passages on both sides when said reversible pump is in a non-operating state.

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