JP2000247247A - Power steering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a power steering for a front two-axle vehicle to be controllable in steering even during the stop of an engine-driven pump and to simplify device structure, miniaturize the device and to reduce cost. SOLUTION: This power steering is provided with a front power cylinder 6 and a rear power cylinder 7 for controlling steering of front and rear steered wheels 2, 3 of a front two-axle vehicle. A pump steering means 30 for normally connecting a main pump driven by an engine of the vehicle, to a control valve 15 and connecting a sub-pump driven by a means other than the engine, in a short-circulated state to the tank 12, 13 side is provided between the main pump 10 and sub-pump 11, and the control valve 15 for selecting a passage of fluid pressure from each pump by the steering operation of a steering wheel. An actuator selecting means 40 is provided to select a passage to the front power cylinder 6 or rear power cylinder 27 to feed fluid pressure from the control valve 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device used for a vehicle having a pair of front and rear steering wheels (hereinafter referred to as "steering wheels"), that is, a so-called front two-axle vehicle.

[0002]

2. Description of the Related Art Among large vehicles such as large trailers, large trucks, etc., there is known a so-called front two-axle vehicle in which a pair of steered wheels are arranged in front of and behind a vehicle. In such a front two-axle vehicle, generally, a power steering device that applies a steering assist force to each steering link mechanism in order to perform steering control of two front and rear pairs of steered wheels by steering operation of a steering wheel. Is generally provided. Such a conventional power steering device for a front two-axle vehicle is disclosed in, for example, JP-A-55-148652 and JP-B-61-14034.

Conventionally, this type of power steering apparatus includes, for example, an integral type power steering (with a built-in power cylinder) for turning the front steered wheels via a front steered link mechanism, and a rear steered wheel connected to the rear. A power cylinder for turning the vehicle via a steering link mechanism.

[0004] Fluid pressure from a pump driven by a vehicle engine is selectively supplied to these power cylinders through a control valve that switches a flow path by a steering operation of a steering handle. A steering assist force is applied to each of the steering link mechanisms, and the front and rear steered wheels are steered in a required state. Of course,
A steering link mechanism that steers the front and rear steered wheels is mechanically connected to operate in conjunction with a steering operation of a steering wheel.

[0005]

However, in the conventional power steering apparatus described above, the front and rear steered wheels are steered and controlled by respective power cylinders by the fluid pressure from one engine driven pump. Therefore, the following problems may be caused.

In other words, if the engine-driven pump breaks down or the hydraulic piping from the pump is damaged and fluid pressure cannot be supplied to each power cylinder, manual steering of the steering wheel is performed. It is necessary to steer the front and rear steered wheels only by the steering operation, and a heavy steering force is required, so that a quick steering operation cannot be performed and a heavy burden is imposed on a steering operator.

For this reason, in the conventional power steering device,
In addition to the engine-driven pump, for example, a sub-pump that uses axle rotation as a drive source is provided, and fluid pressure is supplied from the sub-pump to a rear power cylinder for steering rear steering wheels to perform steering. A system in which the steering force is reduced by using the assisting force is proposed in, for example, Japanese Patent Publication No. 62-22 / 1987.

However, in such a conventional power steering apparatus, a control for switching a flow path on the rear side for supplying fluid pressure from the sub-pump to a power cylinder on the rear side in accordance with a steering operation of a steering handle. Requires a valve. Further, during running of the vehicle, the sub-pump and the control valve are operated only when, for example, the output of the power cylinder on the main side is insufficient and the steering resistance of the steering wheel is increased, so that it is necessary to cut more than usual. It is necessary to adopt a structure.

Therefore, such a structure has a problem that the number of components of the entire apparatus is large, the structure is complicated, and the cost is high, for example, two fluid pressure circuits are additionally provided. Further, in such a structure, it is necessary to position the control valves of the respective systems so that the straight traveling state of the vehicle is at the neutral position, which is a problem in terms of workability during assembly.

In the above-described conventional apparatus, it is necessary to arrange the rear control valve in the power steering main body side by side with the front control valve in the axial direction of the input shaft on the steering wheel side. ,
Enlargement of the entire device, especially the power steering main body, is inevitable. When such a power steering main body becomes large, a problem arises from the viewpoint of a space for assembling into a vehicle, and it is desired to take some measures to eliminate such a problem.

The present invention has been made in view of such circumstances, and is intended to be used when an engine-driven pump of a vehicle is stopped due to a failure or the like and a supply pipe for supplying fluid pressure from the pump is damaged. Power steering that enables steering control of front and rear steered wheels of a front two-axle vehicle, has a reduced number of components, simplifies the structure, and can reduce the size and cost of the entire device. The aim is to obtain a device.

[0012]

In order to meet such an object, a power steering apparatus according to a first aspect of the present invention is provided for steering a pair of front and rear steered wheels of a front two-axle vehicle. In the power steering apparatus, a main pump driven by a vehicle engine, a sub-pump driven by drive means other than the engine, and a flow path switching of fluid pressure from each pump by a steering operation to a steering wheel. A control valve to perform, a front-side power cylinder that controls turning of a front-side steered wheel by a steering assist force obtained by a fluid pressure switched by the control valve, and a steering assist force obtained by a fluid pressure switched by the control valve. A rear power cylinder that controls the steering of the rear steered wheels,
Pump switching means for switching between the main pump and the sub-pump to supply fluid pressure to the control valve, and switching the fluid pressure from the control valve to the front power cylinder and the rear power cylinder. , An actuator switching means for selectively feeding a sheet is provided.

In the power steering apparatus according to a second aspect of the present invention, in the first aspect, the pump switching means is disposed between the main pump and the sub-pump and the control valve to control one of the pumps. It is characterized in that it is configured to be connected to a valve and short-circuit the other pump to the tank side.

According to a third aspect of the present invention, in the power steering apparatus according to the first or second aspect, the rear power cylinder is operated as a main actuator together with the front power cylinder by fluid pressure from the main pump. And a second cylinder operated as a sub-actuator by the fluid pressure from the sub-pump.

According to a fourth aspect of the present invention, in the power steering apparatus according to the third aspect, the actuator switching means is disposed between the control valve and the main actuator and the sub-actuator, and the control valve is connected to any one of the control actuator and the main actuator. When connected to one of the actuators, the left and right chambers of the cylinder constituting the other actuator are short-circuited.

According to a fifth aspect of the present invention, in the power steering apparatus according to the first, second, third, or fourth aspect, the pump switching means and the actuator switching means include a fluid from the main pump. The switching operation is performed using the pressure as a pilot pressure.

According to the present invention, when the engine-driven main pump is operating normally, the pump switching means supplies the fluid pressure from the main pump to the flow path switching control valve. Fluid pressure is supplied from the control valve to a main actuator including a first cylinder of a front power cylinder and a first cylinder of a rear power cylinder in accordance with a steering operation of a steering wheel. Is assisted with a required steering assist force. At this time, the fluid pressure from the sub-pump is supplied to the tank via the pump switching means, and the sub-pump enters a no-load operation state.

According to the present invention, when the main pump driven by the engine breaks down or the piping for supplying fluid pressure from the pump is damaged, the pump switching means connects the sub-pump to the control valve. At the same time, the fluid pressure supplied from the sub-pump to the control valve is supplied to the second cylinder of the rear power cylinder as a sub-actuator as a sub-actuator by the switching operation of the actuator switching means, so that the rear steering wheel is steered. can do. Further, with the steering operation of the steering wheel and the steering operation of the rear steered wheels, the front steered wheels are also steered, and required steering can be performed.

[0019]

1 to 5 show one embodiment of a power steering apparatus according to the present invention. In these figures, the reference numeral 1 indicates a power steering device used for a front two-axle vehicle. As shown in FIGS. 1 and 5, the power steering device 1 is not shown in its entirety, but is provided front and rear at a front portion of a vehicle body (a front end portion of a body chassis frame) of a large vehicle. The steering assist force at the time of turning each pair of the steered wheels 2 and 3 in accordance with the steering operation of the steering wheel 4 is changed by the front and rear steering link systems (the drag links 2a and 3 in FIG. 5).
a and only the knuckle arms 2b and 3b).

Reference numeral 5 denotes an integral type power steering body which has been widely known. As shown in FIG. 5, an input shaft (stub shaft) 7 connected to a steering shaft 4a from the steering handle 4 is disposed on the main body 5, and the main body 5 is provided with a main body 5 as shown in FIG. A front power cylinder 6 for turning the front steered wheels 2. Here, a case of a ball screw type power steering is shown.

Reference numeral 8 denotes a sector gear, which is an output shaft of the front power cylinder 6, and reference numeral 9 denotes a pitman arm for transmitting the rotation of the sector gear 8 to the front steering wheel 2 via the drag link 2a and the knuckle arm 2b.

Reference numeral 10 denotes an engine-driven main pump driven by a vehicle engine (not shown). Reference numeral 11 denotes a drive source other than the engine, for example, a sub-pump driven by rotation of an axle or rotation of an electric motor. Pump 1
Numerals 0 and 11 draw fluid (hydraulic oil) from tanks 12 and 13 and discharge the fluid at a required fluid pressure. The fluid pressure (oil pressure) from these pumps 10 and 11 is supplied to a flow path switching control valve 15 provided in the main body 5 through a pump switching means 30 described later.

As shown in FIG. 3, inside the steering body 5, there is formed a mechanism which is conventionally widely known as a ball screw type power steering. Explaining this, reference numerals 16 and 17 in FIG. 3 denote valve housings which also serve as the steering body and the valve cover for closing the opening end of the steering body 5 described above. In the internal space formed by these, there is provided a piston 18 having a rack tooth meshing with the sector gear 8 to move forward and backward in the axial direction with the steering operation of a steering handle (not shown). Two pressure chambers (left and right chambers) 6a and 6b are formed before and after the piston 18.
The left and right chambers 6a and 6b constitute a front power cylinder 6.

When the piston 18 operates, a rack formed on the side of the piston 18 meshes with the sector gear 8 to rotate the shaft of the sector gear 8. This rotation is transmitted to the front steered wheels 2 via a pitman arm 9 (see FIG. 5) constituting the steering mechanism, thereby performing steering.

The stub shaft 7 which rotates by the steering operation of the steering handle 4 is supported through the valve housing 17, and one end of the stub shaft 7 faces the piston 18 at the tip end thereof via a ball screw mechanism 19. The connected worm shaft 20 is arranged coaxially. Reference numeral 21 denotes a torsion bar which is disposed coaxially in the shafts 7, 20 and both ends of which are integrally connected to the respective shafts 7, 20. Due to the twist of the torsion bar 21, the stub shaft 7 and the worm shaft 20 rotate relatively, and the rotary control valve 15 is operated.

The control valve 15 is provided at the inner end of the stub shaft 7 so as to rotate integrally therewith, and has a rotor 15a having a plurality of valve grooves on its outer periphery.
A sleeve 15b provided integrally with the worm shaft 20 and having a plurality of valve grooves on an inner periphery thereof; The control valve 15 operates by the relative rotation of the rotor 15a and the sleeve 15b to perform a switching operation of the hydraulic flow path, and pressurizes the hydraulic oil from the pump 10 or 11 by the steering operation of the steering handle 4 to perform the switching operation. The power is selectively supplied to the left and right chambers 6a, 6b of the front power cylinder 6,
The piston 18 that applies the steering assist force to the steered wheels is moved in the steering direction.

The specific structure and operating state of the rotary control valve 15 described above, and the movement of the piston 18 during steering, and the sector gear 8 is rotated by this movement, so that the front steered wheels 2 move in a required direction. Since the turning operation is widely known, a detailed description thereof will be omitted.

In FIG. 5, reference numeral 25 denotes a driven lever having one end pivotally supported on a side portion of the chassis frame. The driven lever 25 is connected to the pitman arm 8 by a connecting rod 26, and interlocks with the movement of the pitman arm 8. It is configured to swing. This driven lever 25
The other end is the drag link 3a, the knuckle arm 3b
Through the rear steering wheel 3.

The above-mentioned front steered wheels 2 and rear steered wheels 3 are configured to turn in conjunction with each other with an optimum ratio in accordance with their positional relationship. Although not shown, the left and right front steered wheels 2 and the left and right rear steered wheels 3 are connected to each other by a tie rod arm and a tie rod (not shown).

Reference numeral 27 denotes a rear power cylinder having one end connected to the other end of the driven lever 25 and the other end connected to a side portion of the vehicle body chassis frame.

The rear power cylinder 27 includes a first cylinder 28 that operates by the fluid pressure from the main pump 10 and a second cylinder 29 that operates by the fluid pressure from the sub-pump 11. In addition, 27 in FIG.
a is a piston rod of the rear power cylinder 27;
a, 28b are the left and right chambers of the first cylinder 28, 29a,
Reference numeral 29b denotes left and right chambers of the second cylinder 29.

According to the present invention, as a power steering device used for the front two-axle vehicle described above, a main pump 10 driven by a vehicle engine, a sub-pump 11 driven by drive means other than the engine, A control valve 15 for switching the flow path of the fluid pressure from each of the pumps 10 and 11 by a steering operation on the steering wheel 4, and the front steering wheel 2 is steered by a steering assist force obtained by the fluid pressure switched by the control valve 15. The vehicle includes a front power cylinder 6 for steering control, and a rear power cylinder 27 for steering control of the rear steering wheel 3 by a steering assist force obtained by the fluid pressure switched by the control valve 15.

A pump switching means 30 for switching to one of the main pump 10 and the sub-pump 11 and supplying fluid pressure to the control valve 15 is provided, and a fluid pressure from the control valve 15 is supplied to the front side power supply. Cylinder 6, rear power cylinder 27
Actuator switching means 40 for selectively feeding by switching the flow path to the actuator.

The pump switching means 30 is disposed between the main pump 10 and the sub-pump 11 and the control valve 15, and when one of the pumps (the main pump 10) is connected to the control valve 15, Pump (sub-pump 11) is connected to the tank side to cause a short circuit.

This will be described in detail with reference to FIGS. 1 and 2. The pump switching means 30 is constituted by a spool valve 31 which performs switching operation by using the fluid pressure from the main pump 10 as a pilot pressure. In FIG. 1, a pump switching valve is used. The spool valve 31 includes a spool 32 that slides in a valve hole 30b formed in the body 30a. Fluid pressure from the main pump 10 is guided to the right end of the spool 32 in the drawing through a pilot passage 33 provided in the body 30a, while drain (tank pressure) is guided to the other end and the spool 32 is moved to one end. Is provided with a compression coil spring 34 that urges the compression coil spring 34.

2A and 2B, PM is a connection port from the main pump 10, and PS is a sub-pump 11
, The connection port to the tank 12, TM
TS is a connection port to the tank 13. IN is a feed port for feeding fluid pressure from one of the pumps 10 and 11 to the control valve 15, and OUT is a return port for returning oil from the control valve 15 to the tank side. .

In the normal state shown in FIG. 2A, the pressure oil from the main pump 10 moves the spool 32 to the left,
At this time, the connection port PM is connected to the feed port IN by an annular groove 35 provided in the spool 32. The port TM reaching the tank 12 is connected to the return port OUT via an annular groove 37 provided in the spool 32. 37a is a drain passage portion. In this state, the path from the sub-pump 11 is connected to the port TS returning from the port PS to the tank 13 via the path 36 in the spool 32, and is in a short-circuit state.

On the other hand, FIG. 2B shows a state in which the main pump 10 side has failed for some reason and supply of pressure oil has stopped. At this time, the spool 32 moves to the right in the drawing, and the port PS from the sub-pump 11 is connected to the port IN to the control valve 15 by the annular groove 3 of the spool 32.
5 are connected. The return port OUT is connected to the port TS to the tank 13 via the annular groove 37. Further, in this state, the port PM on the main pump 10 side and the port TS to the tank 12 are in a shut-off state.

In FIG. 3, the spool valve 31 constituting the pump switching means 30 described above is connected to the periphery of the valve housing 17 in the steering body 5 provided with the front power cylinder 6 for turning the front steered wheels 2. It is attached using part of the direction. According to such a configuration, in the integral type steering main body 5, the pump switching means 30 can be attached by effectively utilizing the periphery of the valve housing 17 in which a dead space is generated in the periphery. There is an advantage that the number of components of the steering device can be reduced and piping of each part can be omitted, so that the entire device can be reduced in size and cost can be reduced.

The actuator switching means 40 is disposed between the control valve 15 and the front power cylinder 6 and the rear power cylinder 27, as shown in FIGS. 1 and 4 (a) and 4 (b). .

When the first cylinder 28 of the front power cylinder 6 and the rear power cylinder 27 as the main actuator 50 is connected to the control valve 15, the second cylinder of the rear power cylinder 27 as the sub-actuator 51 Left and right chambers 29 of cylinder 29
It is configured such that a short circuit is caused by communicating a and 29b.

The second side of the rear power cylinder 27
When the cylinder 29 (sub-actuator 51) is connected to the control valve 15, the first cylinder 2 of the front power cylinder 6 and the rear power cylinder 27
The left and right chambers 28a and 28b of FIG. 8 are connected to each other so as to be short-circuited.

4A and 4B, reference numeral 40a denotes a body, 40b denotes a valve hole, and a spool 42 constituting a spool valve 41 is slidably disposed in the valve hole 40b. ing. At one end of the spool 42, hydraulic pressure from the main pump 10 is introduced as pilot pressure. A compression coil spring 43 is disposed at the other end of the spool 42, and a drain (tank pressure) is introduced.

Here, C1 and C2 switch the flow path of the pressure oil from the control valve 15 in accordance with the steering operation of the steering handle 4, so that one port is an introduction passage and the other port is a return passage. It is. Also, C1i, C2i
Is an integral type (front side) power cylinder 6 as a main actuator 50 and its left and right chambers 6
Ports for feeding or recirculating pressurized oil to the left and right chambers 28a, 28b of the first cylinder 28 of the rear power cylinder 27 via a, 6b.

C1c and C2c are ports connected to the left and right chambers 29a and 29b of the second cylinder 29 of the rear power cylinder 27 constituting the sub-actuator 51.

The actuator switching valve as the actuator switching means 40 is normally in the state shown in FIG. 4A. At this time, the spool is controlled so that the pressure oil from the control valve 15 is supplied to the main actuator 50 and recirculated. Forty-two annular grooves 44 and 45 are formed. In the state shown in FIG. 4B, the sub-actuator 51 is connected to the control valve 15.

In the drawing, reference numerals 46 and 47 denote communication passages formed in the spool 42. In the state of FIG. 4A, the ports C1c and C2c on the sub-actuator 51 side are connected and short-circuited. . 4B, the ports C1i and C2 on the main actuator 50 side
i is short-circuited. Thus, the control valve 15
Short-circuiting the actuator not connected to the
The left and right chambers of the corresponding cylinder are communicated to give no resistance to the piston rods connected to the front and rear steered wheels 2 and 3,
This is to prevent a so-called hydraulic lock state from occurring.

FIG. 4A shows a normal operation state in which the supply of the pressure oil from the main pump 10 is performed. At this time, the first of the front power cylinder 6 and the rear power cylinder 27 as the main actuator 50 is shown. By supplying the pressure oil to the cylinder 28, the front and rear steered wheels 2, 3 are steered and controlled in a required direction.

FIG. 4B shows a case where the supply of the pressure oil from the main pump 10 is stopped. At this time, the main actuator 50 side is in a short-circuit state. Therefore, the rear steering wheel 3 is steered by the supply of the pressure oil to the second cylinder 29 of the rear power cylinder 27 as the sub-actuator 51, and the front steering wheel is caused by this and the steering wheel operation. 2 can also be steered.

The actuator switching means 40
As shown in FIG.
Similar to the spool valve 31 constituting the pump switching means 30 described above, in the steering body 5 provided with the front power cylinder 6 for turning the front steered wheels 2, a part of the valve housing 17 in the circumferential direction is used. It is attached. According to such a configuration, the actuator switching means 40 can be additionally provided in the integral type steering body 5 by effectively utilizing the periphery of the valve housing 17 having a dead space around the integral steering body 5. There is an advantage that the number of components of the picking device is reduced and piping of each part is omitted, so that the entire device can be reduced in size and cost.

In other words, the power steering body 5
In this case, the dead space can be effectively used, the size of the device can be reduced, the number of components in the entire device can be reduced, and the cost including manufacturing cost and assembly cost can be reduced.

Therefore, in the power steering device 1 having the above-described structure, even if one of the fluid pressure supply sources (the main pump 10, the fluid pressure supply path, etc.) fails due to the failure of the pump 10, the breakage of the supply path, or the like. Even if it does, by supplying the fluid pressure from the other fluid pressure supply source (sub-pump 11) using the pump switching means 30, any of the front and rear steered wheels 2, 3 is sent to the steering wheel 4. The steering control can be appropriately performed in accordance with the steering request.

In the power steering apparatus 1 described above, the two pumps 10 and 11 and the one control valve 15 for switching the flow path, the steering assist force for turning the front and rear steered wheels 2 and 3 are used. The two power assist systems constituted by the main actuator 50 (the first cylinder 28 of the front power cylinder 6 and the rear power cylinder 27) and the sub-actuator 51 (the second cylinder 29 of the rear power cylinder 27) It is possible to easily switch and use the pump switching means 30 and the actuator switching means 40 comprising a simple switching valve, and the number of components is small, the structure is simple, and the cost can be reduced. Further, since there is only one control valve 15 for switching the flow path, there is no problem of troublesome positioning at the neutral position which is necessary when two control valves are arranged side by side as in the related art.

The present invention is not limited to the structure described in the above embodiment, and it goes without saying that the shape, structure and the like of each part can be appropriately modified or changed. For example, a hydraulic source for operating the power steering device 1 for controlling the steering of the front steered wheels 2 is constituted by a pump 10 driven by an automobile engine, and the hydraulic pressure to an auxiliary power cylinder is supplied to an axle of the automobile or an electric motor. Although the pump 11 is driven by the rotation of the motor, it is not limited to this. In particular, the sub-pump 11 serving as a hydraulic pressure source for the auxiliary power cylinder (the second cylinder 29 of the rear power cylinder 27)
The driving method is not limited to the axle driving method described above or an electric driving method using an electric motor or the like, but may be any driving method using an appropriate driving source other than the engine.

Further, in the above-described embodiment, the case where the power steering main body 5 is of a ball screw type has been described. However, the present invention is not limited to this, and the power steering body 5 may be of a rack and pinion type or any other type of power steering structure. It may be.

[0056]

As described above, according to the power steering apparatus according to the present invention, when the engine-driven main pump breaks down or the piping for supplying fluid pressure from the pump is damaged, etc. The pump switching means connects the sub-pump to the control valve, and supplies the fluid pressure supplied from the sub-pump to the control valve to the sub-actuator (the second cylinder of the rear power cylinder) by the switching operation of the actuator switching means. By actuating this, a steering assist force is applied to control the steering of the rear steered wheels. Further, with the steering operation of the steering wheel and the steering operation of the rear steered wheels, the front steered wheels are also steered and required steering can be performed.

According to the power steering apparatus according to the present invention, two pumps and one control valve for switching the flow path, and a steering assist force for steering the front and rear steering wheels are provided. Obtain main actuator (first cylinder of front power cylinder and rear power cylinder), sub-actuator (second cylinder of rear power cylinder)
Can be easily switched and used by the pump switching means including a simple switching valve and the actuator switching means, the number of components is small, the structure is simple, and the cost can be reduced. There is an advantage.

Further, according to the present invention, when the engine-driven main pump is operating normally, the fluid pressure is transmitted to the main actuator (the front power cylinder and the front power cylinder) through the pump switching means and the flow path switching control valve. The front and rear steered wheels can be steered in response to a steering operation, but at this time, they are driven by something other than the engine (for example, axle rotation or an electric motor). Since the sub-pump is short-circuited to the tank side, the sub-pump is in a so-called no-load operation state, and is excellent in energy efficiency.

Further, according to the present invention, when one actuator is connected to the control valve by the actuator switching means, the left of the other actuator is connected to the control valve.
Since the right ventricle can be connected, the side disconnected by the actuator switching means is short-circuited, and there is no possibility of causing a so-called hydraulic lock state when the rear steered wheels are steered.

[Brief description of the drawings]

FIG. 1 shows one embodiment of a power steering apparatus according to the present invention, and is for explaining an outline of an entire system when a pair of front and rear steered wheels of a front two-axle wheel is steered and controlled. FIG.

FIGS. 2A and 2B are enlarged views showing a pump switching unit in FIG. 1, wherein FIG.
FIG. 4 is a diagram showing a state when a failure occurs on the main pump side.

FIG. 3 is a cross-sectional view of a main part of an integral type power steering main body including a flow path switching control valve and a front power cylinder for steering-controlling a front steering wheel in FIG. 1;

FIGS. 4A and 4B are enlarged views showing the actuator switching means in FIG. 1, in which FIG. 4A shows a state during a normal operation, and FIG. 4B shows a state when a failure occurs on the main pump side. is there.

FIG. 5 is a schematic diagram for explaining some components of a steering system in a front two-axle vehicle to which the power steering device according to the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Power steering device for front two-axle vehicles, 2 ... Front steering wheel (front steering wheel), 3 ... Rear steering wheel (rear steering wheel), 4 ... Steering handle, 4a ... Steering shaft, 5 Steering body, 6 Front power cylinder, 6a, 6b
Left and right chambers, 7: input shaft (stub shaft), 8: sector gear, 9: pitman arm, 10: engine-driven main pump, 11: non-engine driven sub-pump, 12, 13 ... tank, 15 ... Flow path switching control valve, 16: steering body, 17: valve housing, 18: piston, 19: ball screw mechanism,
20 worm shaft, 25 driven lever, 27 rear power cylinder, 28 first cylinder, 28a, 2
8b: left and right chambers, 29: second cylinder, 29a, 29
b: left and right chambers, 30: pump switching means, 31: spool valve, 32: spool, 40: actuator switching means, 41: spool valve, 42: spool, 50
... Main actuator, 51 ... Sub actuator.

Claims (5)

[Claims] 1. A power steering device for turning a pair of front and rear steered wheels of a front two-axle wheel, comprising: a main pump driven by an engine of a vehicle; and driving means other than the engine. A sub-pump driven by a steering valve, a control valve for switching a flow path of fluid pressure from each pump by a steering operation to a steering handle, and a front side by a steering assist force obtained by the fluid pressure switched by the control valve. A front power cylinder for steering control of the steered wheels, and a rear power cylinder for steering control of the rear steered wheels by a steering assist force obtained by a fluid pressure switched by the control valve, wherein the main pump Pump switching means for switching to one of the sub-pumps and supplying fluid pressure to the control valve; Power steering apparatus characterized by a fluid pressure provided actuator switching means for selectively fed by switching the flow path to the front power cylinder, rear power cylinder from trawl valve. 2. The power steering apparatus according to claim 1, wherein the pump switching means is disposed between the main pump and the sub-pump and the control valve, and connects one of the pumps to the control valve. And the other pump is short-circuited to the tank side. 3. The power steering apparatus according to claim 1, wherein the rear power cylinder is operated as a main actuator together with the front power cylinder by a fluid pressure from the main pump. A power steering apparatus comprising: a cylinder; and a second cylinder that is operated as a sub-actuator by a fluid pressure from the sub-pump. 4. The power steering apparatus according to claim 3, wherein the actuator switching means is disposed between the control valve, the main actuator, and the sub-actuator, and connects the control valve to one of the actuators. A power steering device characterized in that when connected, the left and right chambers of a cylinder constituting the other actuator are short-circuited. 5. The power steering apparatus according to claim 1, wherein the pump switching means and the actuator switching means are arranged such that:
A power steering apparatus wherein the fluid pressure from the main pump is switched and used as a pilot pressure.