JP2001055153A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To steer a power steering device even when an engine driving type pump is stopped, to simplify the structure of the device, to reduce the size and cost of the device, and to prevent pressure loss during operation. SOLUTION: This device includes a main pump P1, a sub-pump P2, and a power cylinder for feeding pressure fluid from each pump through a passage switching control valve to steer a steering wheel. Further, the device includes a main-sub switching spool valve 20 for feeding pressure fluid of at least one of the main pump and the sub-pump to the control valve, and circulating return fluid to at least one of a main tank T1 and a sub-tank T2. Pressure fluid from the main pump is introduced as pilot pressure to one end of the spool valve 20, and a compression coil spring 34 is provided on the other end thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steering a pair of left and right steering wheels (hereinafter referred to as "steering wheels") in various vehicles such as large vehicles such as large trailers and large trucks. The present invention relates to a power steering device provided with a power cylinder for causing a power steering.

[0002]

2. Description of the Related Art In a power steering apparatus of this kind, a main pump and a sub-pump are used as a fluid pressure source for a power cylinder for generating a steering assist force, and two systems of pressure fluid supply systems are switched from each pump. A structure provided with a switching valve having a spool for performing the operation is disclosed in, for example, Japanese Patent Application Laid-Open No. 50-32374.

In the initial state, the conventional switching valve is maintained in a state in which the pressure fluid from the main pump and the pressure fluid from the sub-pump are supplied to a hydraulic pressure consuming part (control valve or power cylinder). During the normal operation when the flow rate of the pressurized fluid from the pump reaches a certain amount or more, only the pressurized fluid from the main pump is supplied by the spool valve that operates by the fluid pressure difference before and after the throttle, and the sub pump is connected to the tank. To operate the sub-pump in a no-load state.

[0004] When the flow rate of the pressure fluid from the main pump decreases and drops below a certain amount, the operation of the spool enables the operation of the hydraulic pressure consuming part by the supply of the pressure fluid from the sub-pump. And

That is, the switching valve has a spool which is operated by a fluid pressure difference before and after a throttle portion provided in the supply passage of the pressure fluid from the main pump,
When the spool is operated, the connection path from the connection portion of the pressurized fluid from the sub-pump provided in a part of the spool in the axial direction to the hydraulic pressure consumption portion is closed.

[0006]

In the conventional power steering apparatus as described above, a spool for switching between a main pump and a sub-pump is provided before and after a throttle section provided in the middle of a supply path of a pressure fluid from the main pump. Since the operation is performed by the fluid pressure difference, it is inevitable that a power loss occurs in driving the pump due to a pressure drop generated in the throttle portion.

In the above-described conventional apparatus, the pressure fluid from the sub-pump or the pressure fluid from the main pump when the spool is actuated merges with the supply path of the pressure fluid to the hydraulic pressure consuming portion via the check valve. Therefore, power loss due to the pressure drop when passing through the check valve cannot be avoided.

Further, in the above-described conventional apparatus, during normal operation, until the pressure fluid from the main pump reaches a constant flow rate and the spool operates, the supply system of the pressure fluid from the sub-pump consumes hydraulic pressure. Section will be connected to the supply system of the pressure fluid to the section. Then, in this state, the sub-pump is operated in a loaded state, so that power loss occurs at this point.

In addition, in the above-described conventional example, when switching to return the spool of the valve, the movement of the spool is restricted due to the structure in which the supply passage is provided in the spool, and the pressure from the main pump is reduced. Even when the flow rate of the fluid becomes insufficient, the valve may not return, and at this time, the flow of the pressurized fluid from the main pump may be stopped.

Further, in the above-mentioned conventional example, even if the supply flow rate from the main pump is insufficient, the supply of the pressurized fluid from the sub-pump may not be performed depending on the operation state of the spool. It is desirable to take some measures that can be taken.

The present invention has been made in view of such circumstances, and can be applied to a case where an engine-driven pump of a vehicle is stopped due to a failure or the like, or a supply pipe of a pressurized fluid from the pump is damaged. , The left and right steering wheels can be steered, the number of components is small, the structure is simple, the size of the entire device can be reduced and the cost can be reduced. It is an object of the present invention to obtain a power steering device capable of improving fuel efficiency by the use of a power steering device.

[0012]

According to a first aspect of the present invention, there is provided a power steering apparatus comprising: a main pump and a sub-pump; A power cylinder that steers the steered wheels by feeding through a flow path switching control valve by steering.
A main / sub switching spool valve for supplying a pressure fluid of at least one of the main pump and the sub pump to the control valve, and returning a return fluid from the control valve to at least one of the main tank and the sub tank. Is provided.

According to the present invention (invention of claim 1), during a normal operation in which a main pump such as an engine-driven type is operating, the pressure fluid from the main pump is supplied to the main pump.
The fluid is supplied from the flow path switching control valve to the power cylinder via the sub switching spool valve. Accordingly, the left and right steered wheels are assisted and turned by the required steering assist force.

On the other hand, when the main pump breaks down or the pressure fluid supply piping from the pump is damaged, the main / sub switching spool valve connects the sub pump to the control valve, and the sub pump turns off. The pressure fluid supplied to the control valve is supplied to the power cylinder.

According to a second aspect of the present invention, there is provided a power steering device comprising:
2. A spool according to claim 1, wherein one end of a spool constituting the spool valve is connected to a pilot pressure passage for using a pressure fluid supplied from the main pump as a pilot pressure, and the other end is urged to the one end side. It is characterized in that a force means is provided.

According to the present invention (invention of claim 2), when the pressure fluid is supplied from the main pump, the spool is moved to the other end by the pilot pressure by the pressure fluid, and the pressure fluid disappears. Then, the spool is moved to one end side by the urging force of the urging means.

According to a third aspect of the present invention, there is provided a power steering device comprising:
The short-circuit passage according to claim 1 or 2, wherein the spool constituting the spool valve is provided with a short-circuit path for connecting the sub-pump to the sub-tank during a normal operation and bringing the sub-pump into a short-circuit state.

According to the present invention (invention of claim 3), when the flow rate of the pressurized fluid from the main pump is sufficient, the sub-pump is connected to the sub-tank via the spool valve to be in a short circuit state. And the sub-pump is in a no-load state.

According to a fourth aspect of the present invention, there is provided a power steering device comprising:
The pressure fluid from the main pump is supplied to the control valve during normal operation to the spool constituting the spool valve according to claim 1 or 2, and a flow rate of the pressure fluid from the main pump decreases. ,
A flow path for switching a flow path for feeding the pressure fluid from the sub-pump to the control valve, and returning a return fluid from the control valve to the main tank during normal operation, and a flow rate of the pressure fluid from the main pump. And a flow path for switching a flow path for returning to the sub-tank when the flow rate decreases.

According to the present invention (claim 4), when the flow rate of the pressure fluid from the main pump decreases due to the movement of the spool of the spool valve for switching between the main and sub, the pressure fluid from the sub pump is joined. And the supply of the pressurized fluid from the sub-pump ensures the supply flow rate to the power cylinder via the control valve and the return fluid from the control valve to the main tank and the sub-tank. In this case, the flow of the return fluid from the power cylinder through the control valve is secured, and the steered wheels can be steered.

[0021]

1 to 5 show one embodiment of a power steering apparatus according to the present invention. In these figures, what is indicated by reference numeral 1 in FIGS. 1 and 2 is an integral type power steering main body 1 widely known in the related art in a power steering apparatus. As shown in FIG. 2, the power steering body 1 has an input shaft (stub shaft) 2 connected to a steering shaft (both not shown) from a steering handle. And a power cylinder 3 for turning the right steering wheel via a steering link mechanism (not shown).
In this embodiment, a case of a ball screw type power steering will be described.

In FIG. 2, reference numeral 4 denotes a sector gear which is an output shaft of the power cylinder 3. Although not shown, the rotation of the sector gear 4 is a pair of left and right provided at the front of the vehicle body from a pitman arm via a drag link and a knuckle arm. , And the steering wheel is turned in accordance with the steering operation.

1 and 3, reference numeral P1 denotes an engine-driven main pump driven by a vehicle engine (not shown), and P2 is driven by a drive source other than the engine, for example, rotation of an axle or rotation of an electric motor. These pumps P1 and P2 draw fluid (hydraulic oil) from tanks T1 and T2 and discharge the fluid at a required fluid pressure. Fluid pressure (oil pressure) from these pumps P1 and P2 is supplied to a flow path switching control valve 10 provided in the main body 1 via a main / sub switching spool valve 20 described later.

As shown in FIG. 2, a mechanism widely known as a conventional ball screw type power steering is formed inside the steering main body 1. To explain this, reference numerals 5 and 6 in FIG. 2 denote valve housings which also serve as the steering body and the valve cover for closing the opening end side of the steering body 1 described above. A piston 7 having rack teeth that moves forward and backward in the axial direction with a steering operation of a steering handle (not shown) and that meshes with the sector gear 4 is provided in an internal space formed by these components. Two pressure chambers (left and right cylinder chambers) 8a and 8b are formed before and after the piston 7, and the left and right cylinder chambers 8a and 8b constitute the power cylinder 3.

When the piston 7 operates, the rack formed on the side of the piston 7 meshes with the sector gear 4,
The shaft of the sector gear 4 is rotated. This rotation is transmitted to the steered wheels via a pitman arm (not shown) constituting the steering mechanism, thereby performing steering.

A stub shaft 2 which is rotated by a steering operation of a steering handle is penetrated through the valve housing 6, and one end of the stub shaft 2 faces the inside of the piston 7 via a ball screw mechanism 9. The worm shaft 11 is disposed coaxially. Reference numeral 12 denotes a torsion bar which is coaxially disposed in the shafts 2 and 11 and has both ends integrally connected to the shafts 2 and 11 respectively. Further, a rotary control valve 10 is provided, which is activated by the relative rotation of the stub shaft 2 and the worm shaft 11 by the torsion bar 12.

The control valve 10 is provided at the inner end of the stub shaft 2 so as to rotate integrally therewith, and has a rotor 13 having a plurality of valve grooves on its outer periphery, and is provided integrally with the worm shaft 11. And a sleeve 14 having a plurality of valve grooves on the inner periphery. The control valve 10 includes a rotor 13 and a sleeve 1.
The hydraulic cylinder is operated by relative rotation with the hydraulic cylinder 4 to perform a switching operation of a hydraulic flow path, and pressurized oil from the pump P1 or P2 is turned to the left of the power cylinder 3 by a steering operation of a steering handle.
The piston 7 that selectively supplies the right chambers 8a and 8b and applies a steering assist force to the steered wheels is moved in the steering direction.

The specific structure and operating state of the above-mentioned rotary control valve 10, the movement of the piston 7 during steering, and the movement of the sector gear 4 by this movement cause the steered wheels to be steered in the required direction. Since the operation is widely known, a detailed description thereof will be omitted.

According to the present invention, in the power steering apparatus having the above-described structure, a main pump P1 driven by a vehicle engine, a sub-pump P2 driven by drive means other than the engine, and steering of the steering handle. A control valve 10 that switches the flow path of the pressure fluid from each of the pumps P1 and P2 by a steering operation, and a power cylinder 3 that steers the steered wheels by a steering assist force obtained by the pressure fluid switched by the control valve 10. Have.

A spool valve 20 for switching between main and sub is provided in the fluid pressure passage from the main pump P1 and sub-pump P2 to the control valve 10. As shown in FIGS. 1 and 2, the spool valve 20 is provided inside a valve body 21 fixed to a part of the valve housing 6 constituting the power steering main body 1 with bolts or the like.

A part of the valve body 21 is provided with first and second pump ports 22 and 23 to which the main pump P1 and the sub-pump P2 are connected. The control valve 10 and the spool valve 20 are connected to each other. Return ports 24, 25 for returning the return oil of the pressure oil flowing back to the main tank T1 and the sub tank T2.
Is provided.

In this embodiment, the valve body 21 having the above-described spool valve 20 is integrally provided on the side of the valve housing 6 of the power steering body 1 of the power steering apparatus. Since it can be attached to a portion where there is little restriction on space, it is advantageous in reducing the size and size of the entire device. Further, in the structure integrally assembled to the steering body 1, the passages (26, 27) in the body 21 and the passages (16, 17) in the valve housing 6 can be directly connected. This is advantageous in practical use as compared with the pipe connection, and has the advantage that the reliability as a fail mechanism is increased.

In FIGS. 1 and 2, reference numerals 26 and 27 denote passages formed so as to open to the joint surface of the valve body 21 with the valve housing 6, and these are pump P
1, a passage 26 for feeding the pressure fluid from P2 to the control valve 10, and a return passage 27 for returning the return oil from the control valve 10 to the tanks T1, T2. In FIG. 1, reference numerals 16 and 17 denote passage holes serving as a P port and a T port of the control valve 10 formed on the valve housing 6 side to which the passages 26 and 27 are connected.
Reference numerals a and 27a denote O-rings for sealing.

With such a structure, the main pump P
1. Connecting the switching spool valve 20 for switching the sub-pump P2 to the passage holes 16 and 17 serving as the P port and the T port from the flow path switching control valve 10 in the power steering body 1 of the power steering device. Because it can be installed directly without using piping,
The number of parts in the entire apparatus is small, assembly can be performed easily, a structure that does not take up mounting space can be achieved, and there is no problem of liquid leakage.

As shown in FIGS. 1 and 2, the main and sub switching spool valve 20 is provided with a valve body 21.
And a spool 32 held movably in the axial direction within a valve hole 31 formed in the valve hole 31. Reference numeral 33 denotes a plug for closing the open end of the valve hole 31, and reference numeral 34 denotes a compression coil spring as urging means for urging the spool 32 to an initial position (the right end side in FIG. 1).

In the spool valve 20, a pilot passage 3 branched from a part of the first pump port 22 connected to the main pump P1 is provided in the right end chamber 35.
6 is connected, and the fluid pressure of the pressurized fluid from the main pump P1 is introduced as pilot pressure. On the other hand, in the chamber 37 on the left end side of the spool valve 20, the first or second tank port 24, 25 has a passage 3 formed in the spool 32.
8 and is at tank pressure. This room 37
The tank is connected to the main tank T1 or the sub tank T2 via the passage 38 in accordance with the movement of the spool 32, and is always at the tank pressure.

Therefore, the spool 32 is in the state shown in FIG. 1 or FIG. 4 in a state where the fluid pressure equal to or higher than the predetermined pressure is supplied from the main pump P1. On the other hand, when the fluid pressure decreases, the spool 32 gradually moves to the right in FIG. 1, and when the supply of the fluid pressure is stopped, as shown in FIGS. 5 (a state moved to the right end side in the figure).

In the drawing, reference numerals 42, 43, 44 and 45 are formed on the inner peripheral wall of the valve hole 31 so as to be displaced in the axial direction, and the first and second pump ports 22 and 23, the first and second tanks are formed. An annular groove to which ports 24 and 25 are connected;
Reference numerals 6 and 47 denote annular grooves formed on the outer periphery of the spool 32 so as to face the opening ends of the passages 26 and 27 connected to the passage holes 16 and 17 serving as the pump port and the tank port of the control valve 10 to the valve hole 31. It is.

Reference numerals 48 and 49 denote two annular grooves formed on the outer periphery of the spool 32.
The annular groove 43 corresponding to the second pump port 23 when the spool 32 is in the state shown in FIGS.
Is formed at a position communicating with the annular groove 45 corresponding to the tank port 25. These annular grooves 48 and 49 are connected by a short-circuit passage 50 formed inside the spool 32.

In such a structure, the spool valve 20 operates as shown in FIG. 1 and FIG. 3 (specifically, FIG. 4 and FIG. 5), and controls the pressure fluid from the main pump P1 and the sub-pump P2 by the control valve. 10 and the fluid on the return side is appropriately returned to the main pump T1 and the sub-tank T2, so that the supply amount required by the power cylinder 3 is ensured, and an appropriate steering assist force is always provided. It is configured to obtain.

This will be described in detail with reference to FIGS. 1, 2, 4 and 5. The spool valve 20, which switches the supply system from the main pump P1 and the sub-pump P2, starts the operation of the main pump P1 and releases the pressure fluid. 1 and 4 at the time when the supply is started. At this time, depending on the position of the spool 32, the pressure fluid from the main pump P1 is sent from the annular groove 42 to the control valve 10 through the supply-side passage 26 via the annular groove 46. On the other hand, the return-side passage 27 is connected from the annular groove 47 to the main tank T1 through the annular groove 44, and a return-side flow path is secured.

At this time, the sub-pump P2 reaches the annular groove 45 from the annular groove 43 through the annular groove 48 on the spool 32, the short-circuit passage 50, and the annular groove 49, and is connected to the sub-tank T2. Has become. Therefore, the sub-pump P2 is operated in a no-load state.

In the spool valve 20 described above, the communicating portion between the annular groove 43 on the sub-pump P2 side and the annular groove 48 on the short-circuit passage 50 side is denoted by A, as shown in FIG.
The communicating portion between the annular groove 43 on the second side and the annular groove 46 on the pump port P side is B, the communicating portion between the annular groove 42 on the main pump P1 side and the annular groove 46 on the pump port P side is C, and the sub tank T2 side D is the communicating portion between the annular groove 45 of the sub-tank T2 and the annular groove 49 of the sub-tank T2, and E is the communicating portion between the annular groove 45 on the sub-tank T2 side and the annular groove 47 on the tank port T side. Assuming that the communicating portion between the annular groove 44 and the annular groove 47 on the tank port T side is F, the open / closed state of these A to F has the relationship shown in Table 1 below as the spool 32 moves. .

[0044]

[Table 1]

Here, in Table 1, the closed state is indicated by "x".
Further, in each of the operation states (1) to (3), important portions of the states at the communication portions A to F for securing or blocking the flow of the pressure fluid are indicated by bold letters.

As is apparent from Table 1 and FIG. 4, when the main pump P1 is normally driven and discharges the pressurized fluid, the communication portions A, C, D and F are connected to the spool valve 20. Open, otherwise closed. Therefore, in this state, the pressurized fluid is supplied from the main pump P1 and the return side is the main tank T1.
1, the power cylinder 3 is appropriately operated by the control valve 10 in accordance with the operation of the steering wheel, and a steering assist force in a required state can be obtained. Moreover, at this time, the communication parts A and D are open in FIG. 4, the sub-pump P2 and the sub-tank T2 are short-circuited, and there is no load, so that the power loss is reduced.

In the normal state described above, when the flow rate of the pressure fluid from the main pump P1 decreases and the pilot pressure acting on the chamber 35 decreases, the spool 32 changes from the state of FIG. 4 to the state of FIG. To the right side in the figure. These states will be described with reference to Table 1 below. As the supply from the main pump P1 via the communication section C decreases, the communication section B gradually opens to allow the sub pump P
Feeding of the pressure fluid from 2 is started. Note that the above-described state is instantaneous, and the state immediately changes to the state immediately after.

At this time, the main pump P includes a point in time when the pressure fluids from the two pumps P1 and P2 merge and flow.
Switching from 1 to the sub-pump P2. In this state, the short-circuit state between the sub-pump P2 and the sub-tank T2 is released by gradually closing the communication portions A and D.

As shown in Table 1, the return fluid from the power cylinder 3 is returned to the sub-tank T2 from the return path to the main tank T1 via the return path joined to both tanks T1 and T2. It will be switched to the road.

In such a return side, both tanks T
1, since the switching between the main and the sub is performed after passing through the return state to T2, the return-side flow volume can be secured as necessary and sufficiently, so that the operation on the power cylinder 3 side is not hindered. Absent. Here, the above-mentioned state is for securing the return-side flow path in the process of closing the communication path F, and the switching from the state to the state is performed instantaneously. In the state shown in FIGS. 3 and 5, the main pump P1
The supply path on the side and the return path to the main tank T1 are completely closed, and the supply path from the sub-pump P2 and the return path to the sub-tank T2 are secured.

The spool valve 2 for switching the main and sub pumps P1 and P2 of the power steering device 1 as described above.
0, when the hydraulic pressure of the pressure fluid on the main pump P1 side is operated as the pilot pressure, the main and sub pumps are not simply switched with the movement of the spool 32, but the main pump P1 and the sub pump P
2. A state is provided in which the main tank T1 and the sub-tank T2 respectively communicate with the pump port P and the tank port T of the control valve 10 at the same time. Therefore, the supply amount and the return amount of the pressure fluid during the switching of the spool valve 20 do not become insufficient, and the pumps P1, P2,
The required supply amount and return amount are obtained between the tanks T1 and T2 and the power cylinder 3, and the steering assist force by the power cylinder 3 can be appropriately generated.

In other words, according to the present invention, by using the above-mentioned switching spool valve 20, the supply of the pressurized fluid from the main pump P1 to any one of the power cylinders 3 via the control valve 10 at all times. The pressure fluid is supplied to the cylinder chambers 8a and 8b, and the other chamber is connected to the main tank T1, so that a required steering assist force can be obtained and the steering operation can be easily performed. If the flow rate of the pressurized fluid from the main pump P1 decreases, the switching spool valve 20 is operated by the reduction of the pilot pressure to switch between the feed system and the recirculation system, and the sub pump P2 changes the state. Steering can be easily performed by the pressurized fluid.

The present invention is not limited to the structure described in the above embodiment, and it goes without saying that the shape, structure, etc. of each part can be appropriately modified or changed. For example, a main pump P1 is used as a hydraulic source for operating a power steering body 1 of a power steering device for steering a steered wheel, and a pump driven by an automobile engine is used as a hydraulic source. A pump driven by rotation of an axle or an electric motor is referred to as a sub-pump P2.
Has been described, but the present invention is not limited to this.
For example, the main pump P1 and the sub-pump P2 may both be driven by an electric motor.

Needless to say, the sub-pump P2 is not limited to the axle drive system or the electric drive system using an electric motor as described above, but may be any one that can be driven by an appropriate drive source other than the engine. Further, in the above-described embodiment, the case where the main tank T1 and the sub-tank T2 are separately provided on the return side of the pressure fluid has been described, but these may be configured by a common tank.

In the above-described embodiment, the case where the power steering main body 1 is of a ball screw type has been described. However, the present invention is not limited to this, and the rack and pinion type and other types of power steering structures can be used. It may be.

[0056]

As described above, according to the power steering apparatus of the present invention, only the main pump is normally connected to the control valve by the spool valve for switching between the main and the sub. Can be supplied to the power cylinder through the flow path switching control valve to generate the required steering assist force.
The steered wheels can be steered in a required state in accordance with the steering operation of the steering wheel. In addition, at this time, the sub-pump is connected to the tank side and is operated under no load, so that no power loss occurs.

Further, according to the present invention, the pressure fluid from the main pump is supplied through the throttle portion, and the pressure fluid from the sub-pump is supplied through the check valve as in the conventional device. Therefore, there is no possibility that the presence of the switching valve causes power loss.

According to the present invention, for example, when the engine-driven main pump breaks down or the pressure fluid supply piping from the pump is damaged, the pressure fluid of the main pump is changed to the pilot pressure. The spool valve is instantaneously switched, the sub-pump is connected to the control valve, and the pressure fluid from this sub-pump can be supplied to the power cylinder via the control valve. Can be steered.

Therefore, according to the present invention, the two pumps, the main and the sub, and the spool valve for switching the feeding system stop the engine-driven pump of the vehicle due to a failure or the like, or pressurized fluid from the pump. Even when the supply pipe is damaged, the left and right steering wheels can be steered, and the number of components is small, the structure is simple, and the size and cost are reduced despite the device structure. Also, there is no wasteful horsepower consumption, and the fuel efficiency can be improved by reducing the flow rate.

Further, according to the present invention, when the spool valve is operated for switching, for example, when switching from the main pump to the sub-pump, the pressure fluid from the sub-pump is supplied through the state of supplying the pressure fluid from both the main pump and the sub-pump. Since it is provided with a flow path for switching the flow path for feeding the control valve to the control valve, or for switching the flow path for returning the return fluid from the control valve to both the main tank and the sub tank to the sub tank through a state of being returned, The flow rate of the pressure fluid to the power cylinder via the control valve and the flow path of the return fluid are always and sufficiently secured, and the steered wheels can be steered in a required state.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a power steering apparatus according to the present invention, and is an end view of a power steering main body section in which a switching spool valve portion as a main part is sectioned.

FIG. 2 is a side sectional view of a power steering main body in FIG. 1;

FIG. 3 is an end view of the power steering main body showing a state in which the switching spool valve of FIG. 1 is switched from a main side to a sub side.

FIG. 4 is an enlarged sectional view of a switching spool valve which is a main part of FIG.

FIG. 5 is a cross-sectional view when the spool valve is switched from the state of FIG. 4 to a state corresponding to FIG. 3 described above.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power steering main body part of a power steering device, 2 ... Input shaft (stub shaft), 3 ... Power cylinder, 4 ... Output shaft (sector gear), 5 ... Steering body, 6 ... Valve housing, 7 ... Piston, 8a, 8b: left and right cylinder chambers, 10: control valve for switching flow paths, 1
DESCRIPTION OF SYMBOLS 1 ... Worm shaft, 13 ... Rotor, 14 ... Sleeve, 16, 17 ... Passage, 20 ... Spool valve for switching main and sub, 21 ... Valve body, 22, 23 ... First and second pump ports, 24, 25 ... first and second return ports, 26, 27 ... passages, 31 ... valve holes, 32 ...
Spool, 33 plug, 34 compression coil spring (biasing means), 35 chamber, 36 pilot passage, 37 chamber
38 passage, 50 short circuit passage, P1 main pump, P
2. Sub pump, T1 main tank, T2 sub tank.

Claims (4)

[Claims] A power pump that steers steered wheels by feeding a pressure fluid from each of the pumps through a flow path switching control valve by steering steering of a steering handle. In the power steering device provided with, while supplying the pressure fluid of at least one of the main pump and the sub-pump to the control valve, returning fluid from the control valve to at least one of the main tank and the sub-tank A power steering device comprising a main and sub switching spool valve for recirculation. 2. The power steering apparatus according to claim 1, wherein a pilot pressure passage for using a pressure fluid supplied from the main pump as a pilot pressure is connected to one end of a spool constituting the spool valve. A power steering device comprising an urging means for urging the spool toward one end at one end. 3. The power steering apparatus according to claim 1, wherein a short-circuit passage for connecting the sub-pump to the sub-tank during a normal operation and providing a short-circuit state is provided in a spool constituting the spool valve. A power steering device, characterized in that: 4. The power steering apparatus according to claim 1, wherein a pressure fluid from the main pump is supplied to the control valve during normal operation to a spool constituting the spool valve. When the flow rate of the pressure fluid from the main pump decreases, the flow path for switching the flow path for supplying the pressure fluid from the sub-pump to the control valve, and the return fluid from the control valve during normal operation to the main tank. And a flow path for switching a flow path for returning to the sub-tank when the flow rate of the pressure fluid from the main pump decreases.