JPS6154361A - Power steering apparatus for car - Google Patents

Abstract

PURPOSE:To improve the steering operation sense by constituting a hydraulic- cylinder driving closed circuit by using a variable-capacity type pump, thus reducing the energy loss. CONSTITUTION:When the operating lever 35 of a pilot control valve 31 is turned rightward by operating a steering wheel, a direction selecting valve 5 is set at left position. Then, the working liquid supplied from a variable-capacity pump 2 flows into the head chamber 14 of a hydraulic cylinder 10 and the rod chamber 15 of a hydraulic cylinder 9 through a flow passage 4, direction selecting valve 5, and a flow passage 13. Further, the liquid returned from the head chamber 10 and the rod chamber 12 returns into the variable-capacity type pump 2 through a flow passage 8, direction selecting valve, and a flow passage 7. Therefore, the hydraulic cylinder 11 extends, and the hydraulic cylinder 9 contracts, and a car is bent at the center connection position.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a power steering device used in a vehicle, particularly a vehicle with a folding body such as a wheel loader.

[Conventional technology]

This type of vehicle with a folding body is equipped with front wheels (71) as shown in FIG. are refractably connected by a pin (751) at approximately the center of the frame, and both ends of a pair of hydraulic cylinders (not shown) are connected to the front frame (72) and the rear frame (74) by pins, respectively. The pressure source is a constant displacement pump (not shown) connected to the engine mounted on the vehicle, and the proportion of the discharge fluid supplied to the hydraulic cylinder and tank side is determined by steering operation of the steering wheel (16). It was controlled by.

This steering valve operation method involves connecting a steering wheel (77) or a manual operation part such as an operating lever to a spool (not shown) of a steering valve (76), as shown in FIG. Link fM L'Y Feedback of vehicle body deflection amount to F781 - Kutsukuiso +1k
There are two types of systems: the feedback linkage system, which is equipped with hands like a steering wheel, and the pilot pressure operation system, which has hands like a steering wheel and an auxiliary operation part, and operates the steering valve using pilot pressure from an Erkuikot pressure source.

To explain the -ψ angle of a power steering device that adopts the feed bank linkage method with reference to Fig. 6, the steering valve (7G) is
) including the feedback mechanism (78)
The steering wheel (77) is brought into contact with the steering wheel (77), and the discharge port of the fixed displacement pump buoy 1) is communicated with the tank (82) at the neutral position shown in the figure. One output port f83) of the steering valve (76) is connected to the head chamber ('86) of the hydraulic cylinder 9 and the rod chamber (decoy) of the other one-pressure cylinder through the flow path 18.1). Other output port (89)
is connected to the head chamber (91) of the hydraulic cylinder 187) and the rod chamber (9) of the hydraulic cylinder by the flow path (90),
In addition, the flow paths (84) and (90) each have a relief valve t9.
3), +94) passageway (95), (!]6
) to the other flow path 1plQ), 1s, ++
K connection, connected.

In this power steering cylinder, when the steering wheel is operated to set the steering valve rI6) to the left position, the hydraulic fluid from the pump (81) is supplied to the steering valve σ0,
It is led to the head chamber 186) of the hydraulic cylinder and the rod chamber 188) of the hydraulic cylinder t87) through the flow path (branch), and the head chamber (9υ and rod chamber (92) are connected to the flow path 1'90), the steering valve. The hydraulic cylinder '87) is connected to the tank f82) through (76) and extends like a hydraulic cylinder.
At the short end, the car body will bend in one direction. If you stop rotating the steering wheel at this point, will you get a fee back? k
tf, the steering valve 76) is in the neutral position.
Return to Δ, port +831. +89) and the discharged liquid from the pump 181) to the tank (82).
As a result, the vehicle body stops in a bent position. Question,
! l17+ This is a relief valve that regulates the maximum discharge pressure from the knee i pump (81).

In the pilot pressure operating type power steering device shown in FIG. 7, the steering valve 'j8) is controlled by the manual pump unit 1199)K. That is, the steering valve 98) and the spool (1
Pilot ports located at both ends of 00 (1001 (+0
2) is manually operated by passage (103), (+oa).
The passage (103) and (+04) are connected to the switching valve (+OS) of (99), and the passage (103) and (+04) are communicated through a passage (107) with a proof p (106) interposed therebetween.

On the other hand, a manual pump unit j! that moves 1U with low torque and is assisted by pressure fluid from a constant displacement pump (1Oa). l!
When the operating fluid from the pump (+ 08) is guided into the passage (j 03) by operating the switching valve (+ 05) with the steering wheel and setting the switching valve (+ 05) to the right position, for example, this hydraulic fluid passes through the throttle (106) and flows into the passage. (+04), the flow is returned to the tank (82) via the switching valve (+OS), so the pilot pressure generated upstream of the throttle (106) causes the spool (the decoy is in the left position to 9, and the operation from the pump (81) liquid steering valve 198)
, flow path) to the head chamber 186 of the hydraulic cylinder (85).
) and the rod chamber 1g3) of the hydraulic cylinder (87),
Head chamber +9υ and rod chamber f! 12) the flow path 190)
, is connected to the tank (8 force) via the steering valve (98), and the same effect as explained in the conventional device shown in FIG. This is an IJ-F valve that regulates pressure.

[Problem that the invention seeks to solve]

However, the conventional device as described above has the following drawbacks.

1. Whether or not there is a steering operation that causes a large energy loss.', 'The A-system fixed displacement pump (81) is always driven by the engine, and the hydraulic fluid from the pump is constantly sent to the steering valve. ) / When no operation is performed, or when a part of the working fluid is distributed to the hydraulic cylinder to operate the slow steering valve, the entire working fluid from the pump is
Most of that is the steering!・7・Made 9・This contribution is 7ThL, and it is returned to the tank.
゛・Lu′, Neiros is big.

■ When the steering wheel is operated rapidly at the start of the steering operation, the steering valve: ij amount, r; L-B switches to distribute the distribution to the hydraulic cylinders.As a result, the pressure in the hydraulic cylinders suddenly increases and the vehicle body begins to sharply bend, giving the driver a shock and forcing the driver to operate the steering wheel. A bendable car body type like a wheel loader with poor sensation
To hold it in place, it is necessary to apply pressure to the shilling port. Also, the condition of the road surface, jq (uneven, 'j') surface, etc.
There were times when I felt pressure on the port.

In such a case, if you operate the steering so that the pressurized cylinder port communicates with the tank, 1lJn
As hydraulic fluid is discharged from the pressurized 7 cylinder port to the tank W, by, the vehicle body is subjected to sudden steering operations. In addition, at this time, as a result of a larger amount of liquid being discharged to the tank than the amount supplied to the cylinder port, a cavity is formed inside the ring on the side receiving the pressure liquid supply, and the pressure is increased. During the period from when the pressure in the cylinder port is released until the cavity/con on the supply side disappears, a situation occurs in which the vehicle body cannot be steered even though the steering wheel is being operated. In this state, the steering operation would cause the vehicle to sway, resulting in an unpleasant operating sensation, and there were also problems from a safety perspective, such as the cargo collapsing due to bumps.

[Means for solving problems]

In order to solve the above-mentioned problems, in this research, the discharge port and suction port of the unidirectional discharge variable displacement pump are connected to at least one of the head chamber and the rond chamber of the hydraulic pressure/ring for body bending. When a hydraulic pressure/ring percentage operating closed circuit is constructed by reading directly through the directional control valve, the pilot pressure from the pilot pressure command device connected to the steering operation mechanism controls the directional control valve and the variable displacement pump. The discharge flow rate controller ti77 is controlled by 11j (]: Ushida.

[Effect]

Next, the effect will be explained. In the present invention, when the operation part of the steering operation mechanism is operated, pilot pressure corresponding to the direction and amount of operation is taken out from the pilot pressure command device. Variable displacement type; t! Nfuno discharge K quantity ffi The servo piston force flj!18 of the control mechanism is applied, and the hydraulic fluid at a flow rate according to the pilot pressure is sent from the variable displacement pump to one of the hydraulic pressure / su / da through the directional control valve. The liquid flowing into one chamber and returning from the other chamber passes through the directional valve and returns to the variable displacement pump.As a result, the hydraulic sill is expanded or shortened, so that the vehicle does not bend at the point where the vehicle body breaks. K becomes.

In addition, by operating the operating part of the steering operation mechanism in the opposite direction to the front direction, the discharge flow rate of the directional control valve and the variable displacement 11'f type pump (if the servo piston of the variable displacement pump is controlled, the discharge direction of the variable displacement pump can be changed. remains unchanged, but since the directional control valve is switched in the opposite direction to the front, the direction of the hydraulic fluid flowing into the hydraulic cylinder changes, and the direction in which the vehicle bends is reversed from the front.

When the operating portion of the steering operating mechanism is returned to the neutral position, the pilot pressure from the pilot pressure command device becomes approximately flat.

As a result, the directional control valve returns to the neutral position (i), cuts off the hydraulic cylinder from the variable displacement pump and the tank, and forms a closed circuit with the variable displacement pump. Since the pump displacement of the control mechanism is minimized, the minimum flow rate of the working fluid will circulate in the closed circuit.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings. In Fig. 1, a unidirectional discharge variable displacement pump (2) equipped with a regulator (1) serving as a discharge flow rate control mechanism connects a discharge port (3) to a directional control valve (5) through a flow path (4). It is connected to the pump port P, and the suction port (6) is connected to the tank port T of the directional control valve (5) by a flow path (7). One output port A of the directional control valve (5) is connected to the head chamber 00) of the hydraulic cylinder (9) and the rond chamber f12) of the hydraulic cylinder (old) through a flow path (8), and Output capo) B is connected to the head chamber (1, υ and the rond chamber of the hydraulic cylinder (9) + 15) of the overnight pressure cylinder 0υ by the flow path (13).
When the directional control valve (5) is in the neutral position shown in the figure, the directional control valve (5) forms a closed circuit with the channels (4), (7) and the pump (2), and the directional control valve (5) When the pump (2) assumes either the left or right functional position, the pump (2) is in the flow path (/J),
(7), the directional switching valve (5), the flow path (8), (131) and the hydraulic cylinder (9), tlυ constitute a closed circuit.

The regulator (1) is connected to the rotating portion of the pump (2) via a tilting lever (16), and has a large diameter portion 11 at one end.
7) into the liquid chamber (18), and a servo piston (22) facing the liquid chamber (11) to which the servo pressure of the small diameter part (1! lj full-time servo pump (20) is led) at the other end. , a sleeve +231 connected to this servo piston via a tilting lever (16) and a spool slidably connected to the sleeve +1) are connected to control the port of the night room (18). It has a servo fPt25+, the pilot valve 1-+261 of this servo valve is connected to the outlet port of the shuttle valve (28) by a passage (27), and the both ports of the Noya Nottle valve (2 (to) are connected to the passage [29).

+, 30) connects the pilot port 155) at both ends of the spool of the directional control valve (5) with the passage f61),
+62+ and pilot control valve c
31) is connected to the inlet port of the pressure reducing valve Cf1J and i33+.

Pilot control il' by pilot pressure command device: 1
斤T31+ is a steering operation pus 1'ih link (
3. Operation lever G35) connected to 1) and this 41''
? ! The two pressure reducing valves 34 are in contact with the operating levers via springs C37).

133), then operate the steering wheel (shallow groove steering wheel) and tilt the operating lever (for example, from the neutral position to the right), the pressure reducing valve C is pushed by the three lever springs (36) and the servo is activated. The passage (38) connected to the pump (20) is connected to the passage (29).
+, and a pilot pressure proportional to the operating angle of the operating lever C, 351 is taken out to the passage (29).

On the other hand, each of the flow paths fs)+1131 has a relief valve 1'! ')1t (40) is provided, and its secondary passage fi
The channels (131, 112) are connected to the channels g3, +31. Selectively connects to the tank (・17) via the pressure switching valve (・1, 1 nof valve +, i61). Also, the flow path (=l), (7) is connected to a pair of opposing checks. valve 118
1.149) is connected by a passageway 501 with an interposed valve, and the area between the check valves of the passageway (50) limits the hydraulic pressure from the servo pump (20) l) The secondary side of the IJ-fusho 51) A relief valve (3) is connected to the passageway (52) and downstream of this passageway for setting the boost pressure. A regulating relief valve (54) is provided.

Since the present implementation fll has the above-mentioned configuration, in FIG. 1, when the steering wheel (not shown) is operated and the operating lever U5 of the pilot control valve example is tilted to the right, the pressure reducing valve lever is moved. When activated, the passages (38) and (29) communicate with each other, and the pilot pressure proportional to the operating angle of the operating lever increases the passage +2.
115G
) communicates with the tank 17) via the passage (G2), (30) and the pressure reducing valve (33), so the direction switching 2p(5)t
'! Take the left position. On the other hand, the pilot pressure flowing in from the passage (29) is 1 yen (2 yen to 1 yen).
Afterwards, it is supplied to the pilot port 126) of the servo valve (25). To this pilot pressure, l) servo valve (25
) assumes the left position, the liquid chamber ++5tVi tank (,17
), the servo piston t22) moves to the right to increase the pump rotation angle, and the pump discharge flow rate increases. At that time, the sleeve +2:3) that interlocks with the servo piston (22) moves to the right, and when the through hole of this sleeve is blocked by the spool 0/D, the C chamber (18) is blocked and the servo piston (22) moves to the right. ) stops moving to the right, and the pump discharge flow rate becomes constant.

The working fluid from the variable displacement pump (2) passes through the flow path (4), the left-position directional control valve (5), and the flow path (13), and then reaches the head chamber (1.υ and direct pressure cylinder (9
) flows to the rondo chamber +151, and the return liquid 9 from the head chamber 00) and the rondo chamber (12) flows through the flow path (8) and the directional control valve (5
), the flow path (7) is returned to the variable displacement pump (2) with a diameter of 1. The revised cylinder (lυ) is extended, the hydraulic cylinder (9) is held in place, and the single stroke is bent at its central connection point.

In addition, the vehicle body deflection in the opposite direction is caused by the pilot control valve 13.
1) Operate the operating lever 1115) to the left/same position 1i;
This is done by doing 1. In other words, in this case, Bosanben (
33) is activated to connect the passage +:+S+ with (30), and the pilot pressure taken out to the passage (30) is transferred to the passage fG2.
+ to the pilot port 15G of the directional valve (5)
The pilot port (55) is 1m long! Gl)
, 12! ], 1 pressure valve t3L'l and tank (4
7), the directional control valve (5) is switched to the right position. On the other hand, the pilot pressure flowing into the servo valve (28) from the passage (30) passes through the passage (27).
25), the servo valve (25) and the servo valve (22) move one step like the front and back, and the working fluid from the pump (2) flows through the flow path (51), the right (\r via the directional control valve (5) that takes the position, and the flow path (8) (
The liquid flowing to the head chamber (10) of the hydraulic cylinder (9) and the rond chamber (121) of the hydraulic cylinder (1'D) returns to the n1 head chamber q/υ and the liquid chamber (15), respectively. Since the flow flows through the directional control valve (5) and the flow path (7) to the variable displacement pump (2), the pressure cylinder (9) expands overnight, the hydraulic cylinder 0υ shortens, and the vehicle body moves forward. It is refracted in the opposite direction.

1, switching valve f, 15) is the flow path (B), fl:! The excess flow rate in the closed circuit is discharged to the tank ID by switching the low pressure side flow path of the tank 1.1 to the tank 1.17) via the relief valve f and I61. In addition, to replenish the leakage from the pump (2), use the servo pump +201, 'Noleaf valve f51), and check valve (18) from the tank.
) or (, +9+).This allows the fluid in the closed passage and the fluid in the tank to circulate, and the vehicle body to reduce the force 1.
Liquid for i-folding, King cylinder f91. It absorbs the increase/decrease in the amount α in the i:i4 circuit caused by the difference in the amount of expansion/contraction of iυ.

Next, when the steering wheel is operated to return the operating lever ': I51 to the neutral position, the output port of the previously operating pressure reducing valve will now communicate with the tank passageway (57), and the directional control valve (57) will be moved to the neutral position.
) returns to the neutral position with both pilots (55) l r, +6) at the same pressure, and the servo valve (25) spring 1133
) is pushed to the right position, and the liquid chambers t18) and (2I) communicate with each other, and the servo piston -/f22) moves to the left to minimize the amount of pump tilting. Therefore, the minimum flow rate of the working fluid from the pump (2) circulates in the closed circuit connecting the pump 1'2) and the directional control valve (5). On the other hand, hydraulic cylinder +91
．． til+ is stopped because the supply of hydraulic fluid from the pump is cut off by the directional control valve (5) and the pump is closed.

FIG. 2 shows one embodiment in which different pilot pressure command devices may be used. In this embodiment, as a pilot pressure command device, the manual pump tilting amount is assisted by a part of the hydraulic fluid from the servo pump (20) and oscillates with low torque).
158), and the pilot pressure from this manual pump unit 1581 controls the two servo valves of the regulator (1) and the directional control valve (5). In other words, it is operated by the steering wheel. Passage connected to the output port of the manual port/control valve (58) 59) +291. t: lOi / Yano Toru 7F + 28
The inlet port of No. 1 is connected to the pilot bow (261) of the servo valve (25) through the passage +27), and the outlet port of the Yanotl valve (28) is connected to the pilot bow (261) of the servo valve (25) through the passage +27).
) is connected to the tank (!17) through the aperture (60).
do. Father, passage t29), f:30) is passage +61
1. ! 62) to pilot port of directional valve (5)! 5! li), i, 56).

Therefore, if the manual pump unit ei8) '0 is operated with the steering wheel and the switching valve (59) is placed in the left position j1, for example, the s61. F.

The operation speed of the 11 flow meter is related to the operating speed of the valve, and the emergency valve (59), passage (391,7 ginotle valve) 28) 1,
γ passes through 1) 0) and returns to tack (11), so
A pilot pressure is generated that is approximately proportional to the operating speed of the steering wheel.This pilot pressure is transferred to the pilot port f5 of the directional control valve (5) via the ! led to it, pilot port 1
5G) is connected to the tank (first time) via the passage [i21.001, OFF] history valve ii)]) and the ri/ri passage +57), so the directional control valve (5) switches to the position =, and the flow path (4) and (1
3) and the flow channel (connecting the sword and (8). On the other hand, the crest (+
The pilot pressure generated upstream of jO) passes through the passage (2η) to the pilot port i:lI;l of the servo valve (25).
VC is also set at 4I゛λ, and this pilot pressure is applied to the setting spring (6
3), the liquid chamber (18) communicates with the tank (4η) and the servo piston (221 moves to the right, increasing the amount of pump tilting,
At that time, sleeve C interlocked with servo piston/(22)
;3) moves to the right, and when the through hole (not shown) of this sleeve is closed by the spool (21), the liquid chamber (18) is blocked and the servo biston (122) stops moving to the right. When the setting spring (63) is moved, the overnight chambers (21) and (18) are communicated, and the servo piston (22) moves to the left, reducing the amount of pump tilting. When the switching valve (59) is placed directly in the neutral position, the pilot ports of the directional switching valve (5) and the servo valve (25) are cut off from the pilot pressure supply and are connected to the control valve (17) via the throttle (60). Since the pilot pressure becomes approximately zero, the directional control valve (5) returns to the neutral position. Also, since the servo valve I25) takes the left position, the servo piston y+221
moves to the left and reaches stroke ☆::IK', where the pump #t:I quantity becomes minimum.

Next, operate the steering wheel to set the switching valve (59) to the position [I'f
f, the hydraulic fluid proportional to the operating speed of the steering wheel passes through the passage (30), the shuttle valve B25), and the throttle 160) and returns to the tank t, +7), so the throttle fGO)
A pilot pressure similar to that described above is generated upstream of. This pilot pressure is led to the pilot port t56) of the directional control valve (5) through the passage (62), and the pilot port f551 is connected to the 1 m path (61+, f20+, directional control valve +59).
＋, via tank passage 157) in the evening (17)
m, the directional control valve (5) is turned to the left f, Z 1. =/,
, take. On the other hand, the pilot pressure generated upstream of e') (Go) is also transferred to the pilot port 1261 of the servo valve (25) through the passage.
) switches to the position 16, the liquid chamber (18) becomes the tank (1α), the servo piston 7 (22) moves to the right, the pump rotation amount increases, and the pump discharge amount increases.

Other structures and functions are similar to those shown in FIG.

Note that the regulator of the present invention is not limited to that shown in FIGS. 1 and 2. Appropriately use a known item, for example, a forward lever as shown in Fig. 3 (161K Piston rod J6 of piston type single-acting linter (ti-1))
A spring (67) may be inserted into the rond chamber (6G) to introduce a pilot pressure proportional to the operating angle of the steering wheel into the head chamber (68).

〔Effect of the invention〕

As explained above, in the present invention, when there is no steering operation, the discharge flow rate from the variable displacement pump is the minimum, and the discharge flow rate of the variable displacement pump is the same as the pilot pressure. Since the pilot pressure is approximately proportional to the change in steering operation, the pump discharge fluid can be used effectively, and energy loss in the steering system is extremely small.

Additionally, in general, the time required for variable displacement pumps to reach their maximum discharge flow rate from deafness is approximately 0.3 seconds. The rate of change in the discharge flow rate can be easily changed by changing the capacity of the hydraulic cylinder, etc., so compared to the conventional system, which used a steerer puff valve to switch the working fluid from a fixed displacement pump, the amount of pressure applied to the hydraulic cylinder is reduced. The amount of feed can be increased slowly, so there is less noise at the start of steering operation. Therefore, it is possible to prevent the sudden start of vehicle body bending seen in the prior art, and to provide the driver with a favorable steering operation feeling.

In addition, the discharge port of the pressurized hydraulic cylinder communicates with the suction side port of the variable displacement pump when the directional valve functions, and its pressure is lower than the pressure in the discharge channel of the variable displacement pump. Since the communication with the tank is cut off by the switching valve (15) until the discharge flow rate of the variable displacement pump is reached, the counterflow flow rate is pressurized by the suction flow meter 1, which corresponds to the discharge flow rate of the variable displacement pump, and the flow rate is increased from the discharge port of the hydraulic cylinder. be discharged. Therefore, no cavities are generated in the discharge side flow path of the variable displacement pump, and the steering operation does not cause the vehicle body to wobble.

In the present invention, a variable displacement pump with unidirectional discharge is used, and the direction of vehicle bending is controlled by a directional control valve, but instead of this, a variable displacement pump with bidirectional discharge is used. It is also conceivable that the direction of bending of the vehicle body be configured to control the discharge direction of the variable displacement pump by switching. However, when changing the bending direction from left to right or vice versa during car body bending, it is necessary to control the port/bump transmission part from normal to reverse or from reverse to positive with a bidirectional discharge variable displacement pump. As mentioned above, if the rate of change in the discharge flow rate of the variable displacement pump is slowed down to reduce the /:I torque at the start of steering operation, the discharge direction can also be switched between forward and reverse.
However, there is also a delay in switching. On the other hand,
The variable displacement pump according to the present invention has a one-way discharge, so it can be quickly adjusted using a directional control valve. Also, the same left and 1 stop of the 411 body refraction are also the switching of the directional control valve; Therefore, it is possible for a variable displacement pump to maintain a certain discharge flow rate even when the steering wheel is not operated. can be started and stopped.

As explained in detail above, for the present invention, a variable displacement pump is used to connect the α-pressure cylinder M operating closed circuit ((h
By creating an open-circuit configuration using a conventional fixed displacement pump, the power steering system of a vehicle can be
1 pressure point is lIr7r, and in addition, a variable displacement pump with one-way discharge is used, and the steering direction is changed by a directional control valve [I'4, so the discharge flow rate change of the variable displacement pump is It is possible to prevent problems caused by slow speed and achieve quick response speed.

[Brief explanation of the drawing]

1 and 2 are hydraulic circuit diagrams showing embodiments of the present invention, FIG. 3 is a diagram of another embodiment of a discharge flow rate control mechanism of a variable displacement pump, and FIG. 4 is a plan view of a vehicle with a folding body. 5 is a perspective view showing an example of a steering valve operating mechanism, and FIGS. 6 and 7 are hydraulic circuit diagrams of a conventionally installed system. DESCRIPTION OF SYMBOLS 1...Regulator, 2...One-way discharge variable displacement pump, 5...Directional switching valve, 9, 11...Liquid pressure/su/da, 10.14...Head chamber, 12. 15... Rondo room, 22 units≠4... Servo piston, 31... Pilot control valve, 58... Manual pump unit, 77...
・Steering wheel, 78・Link+S t+4゜Representative patent attorney
Tai 1) Ken 3 Fig. 4 Fig. 5/l: 5 Link Gigou

Claims (1)

[Claims] The discharge port and suction port of a variable displacement pump with unidirectional discharge are connected to the head chamber and rod chamber of at least one hydraulic cylinder for bending the vehicle body via a directional control valve to form a closed circuit for driving the hydraulic cylinder. A power steering device for a vehicle, characterized in that the directional control valve and the discharge flow rate control mechanism of the variable displacement pump are controlled by pilot pressure from a pilot pressure command device to which a steering operation mechanism is connected. .