JP2000272529A - Steering apparatus for traveling vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent internal pressure from being increased by temperature elevation and expansion of oil in a closed circuit for connecting upper and lower steering cylinders. SOLUTION: Upper steering cylinders 25, 26 in an upper turning body side actuated in response to a handle operation are connected to lower steering cylinders 27, 28 in a traveling body side for changing a wheel steering angle to constitute a closed circuit A, rectilinear restoring force applied to a wheel 18 at the time of traveling is constituted to be transmitted to steering wheel 16 via hydraulic pressure of the closed circuit A and a steering unit 23, and the circuit A is connected to an accumulator 49 with a proviso that the upper steering cylinders 25, 26 are non-actuated conditions so as to release internal pressure of the closed circuit A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering device for a traveling vehicle such as a wheel crane or a wheel shovel that operates wheels of a lower traveling body from a driver's cab of an upper revolving body.

[0002]

2. Description of the Related Art Conventionally, in an upper turning type traveling vehicle provided with an upper turning body, as shown in FIG. 7, a steering unit 1 is arranged on the upper turning body, and steering cylinders 2 and 3 are arranged on the lower running body. A configuration in which the wheel is steered by supplying an amount of hydraulic oil corresponding to the operation amount of the steering wheel 4 from the steering unit 1 to the steering cylinders 2 and 3 via a rotary joint 5 arranged at the center of rotation of the upper swing body. Has taken.

In FIG. 7, reference numeral 6 denotes a steering hydraulic pump driven by an engine. Also, in the figure,
The internal mechanism of the steering unit 1 is schematically represented by the hydraulic symbols of the servo valve 7 and the hydraulic motor 8.

However, according to the above-mentioned prior art, when the vehicle is running, the straight-running restoring force applied to the front wheel by the well-known wheel alignment mechanism is not transmitted to the steering wheel 4 during running, so that the steering wheel is automatically moved to the neutral position (straight-running position). The power to return to does not work.

[0005] That is, the rectilinear restoring force received by the front wheel is applied to the steering cylinders 2 and 3, and the cylinders 2 and 3 try to discharge hydraulic oil toward the steering unit 1. The steering wheel automatically returns to the neutral position after the operation of the steering wheel. In this neutral position, the discharged hydraulic oil is blocked, so that the straight forward restoring force received by the front wheel is not transmitted to the steering wheel 4.

For this reason, the driver has to return the steering wheel 4 to the neutral position by measuring each time after turning the steering wheel 4 and turning the curve.

Therefore, the present inventor has disclosed in Japanese Patent Application No. 9-34527.
In the application of No. 5, etc., an upper turning body of an upper turning type traveling vehicle is provided with an upper steering cylinder, and a lower traveling body is provided with a lower steering cylinder for changing a steering angle of a wheel, and these two cylinders are connected to each other by an oil passage. A technique was proposed in which a closed circuit was configured and the straight-line restoring force received by the wheel during traveling was transmitted to the steering wheel via the hydraulic pressure of the closed circuit and the steering unit.

According to this steering device, since the force is transmitted by the static pressure of the closed circuit, the steering wheel is automatically returned to the neutral position, similarly to a general traveling vehicle such as a truck.

For this reason, although the vehicle is an upper turning type traveling vehicle, the vehicle has excellent straight-line restoring properties, and the steering wheel operation becomes easy. In addition, there is no risk of the vehicle body fluctuating when changing lanes.

[0010]

However, according to this structure, the temperature of the hydraulic oil in the closed circuit rises due to heat generation due to pressure loss at the time of steering operation, heat conduction from the rotary joint and the like, and the oil is closed by expansion. Circuit pressure increases,
Equipment could be damaged.

Accordingly, the present invention provides a steering device for a traveling vehicle which can prevent an increase in internal pressure due to a rise in temperature and expansion of oil in a closed circuit, assuming a configuration in which upper and lower steering cylinders are connected by a closed circuit. Things.

[0012]

According to a first aspect of the present invention, an upper revolving unit having a driver's cab having a steering wheel is mounted on an upper part of a lower traveling unit having a wheel so as to be pivotable. A traveling vehicle having a steering unit that amplifies the operating force of a steering wheel and transmits the steering force to the wheel has the following configuration.

(I) The upper revolving structure is provided with an upper steering cylinder that operates in response to operation of the handle.

(Ii) The lower traveling body is provided with a lower steering cylinder for changing a steering angle of the wheel.

(Iii) The upper and lower steering cylinders are connected to each other by an oil passage via a rotary joint disposed at the center of rotation of the upper revolving structure to form a closed circuit.

(Iv) The straight-line restoring force received by the wheel during traveling can be transmitted to the steering wheel via the hydraulic pressure of the closed circuit and the steering unit.

(V) A pressure releasing means for releasing the internal pressure of the closed circuit by opening the closed circuit to an external pressure receiving section on condition that the upper steering cylinder is in an inoperative state.

According to a second aspect of the present invention, in the configuration of the first aspect, the closed circuit and the external pressure receiving portion are connected by a pressure relief line as the pressure relief means, and the upper steering cylinder is in a non-operating state to the pressure relief line. A pressure relief valve that switches from the shut-off position to the open position is provided on condition that

According to a third aspect of the present invention, in the configuration of the second aspect, a control means for detecting that the upper steering cylinder is in an inactive state and outputting an operating signal to the pressure relief valve is provided.

According to a fourth aspect of the present invention, in the configuration of the third aspect, an outrigger is provided on the lower traveling body, and the control means includes:
An operation signal is output to the pressure relief valve based on a signal of a switch for operating a vertical cylinder for grounding the outrigger.

According to a fifth aspect of the present invention, in any one of the second to fourth aspects, a neutral return means for applying a force in a direction for returning the handle to the neutral position is provided, and the oil chambers of the upper and lower steering cylinders are provided. A neutral return valve that is operated to switch between a position that communicates with the external pressure receiving portion and a position that shuts off the external pressure receiving portion, wherein the neutral return valve is also used as a pressure relief valve. It is.

According to a sixth aspect of the present invention, in the configuration of the second aspect, as the upper steering cylinder, one of a pair of master cylinders is extended in accordance with the operation direction of the steering wheel.
The master cylinder has an actuator port connected to the lower steering cylinder and a pressure release port connected to the external pressure receiving portion, and is provided with a pressure release port in a neutral state. The actuator port is configured to be connected thereto.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, an accumulator is used as the external pressure receiving portion.

According to the above configuration, the closed circuit is opened to the external pressure receiving portion (the closed circuit is connected to the external pressure receiving portion by the switching operation of the pressure release valve). Excess pressure is released to the outside when the internal pressure rises. For this reason, it is possible to prevent equipment constituting the closed circuit from being damaged.

In addition, since the above-mentioned depressurizing operation is performed on condition that the upper steering cylinder is not operated, there is no possibility that the original steering operation of the steering device is reduced or lost.

In this case, according to the third and fourth aspects,
When it is detected that the upper steering cylinder is in a non-operating state (in claim 4 that the outrigger vertical cylinder is in operation), the depressurizing operation is automatically performed.

According to the fifth aspect of the present invention, the provision of the neutral return means ensures that the steering wheel is returned to the neutral position by the force of the neutral return means during traveling.

In addition, when the neutral position of the steering wheel is displaced by an internal leak generated by each steering cylinder or the rotating joint, the oil chamber of each steering cylinder is communicated with the external pressure receiving portion by operating the neutral return valve. By operating the neutral return means in the state of equal pressure, the steering wheel can be corrected to the neutral position to maintain straight running performance, and the effective stroke of the cylinder (wheel steering angle) can be prevented from decreasing and The turning ability at the time of traveling can be secured.

Since the neutral return valve is also used as a pressure relief valve, the circuit configuration is simplified as compared with the case where a dedicated pressure relief valve is provided.

According to the sixth aspect of the present invention, in the master cylinder system in which one master cylinder (upper steering cylinder) operates according to the steering direction to simultaneously operate the lower steering cylinder, a master cylinder in a neutral state, that is, (A) Both master cylinders at the time of non-steering (b) At the time of steering, the internal pressure is released to the outside by the closed circuit communicating with the external pressure receiving part via the inactive master cylinder.

According to the seventh aspect of the present invention, the internal pressure of the closed circuit is released to the accumulator, and when the internal pressure is reduced, the oil is returned to the accumulator. Differently, the refilling of the oil takes place automatically.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

First Embodiment (Refer to FIGS. 1 to 3) FIG. 1 shows an overall schematic configuration of a wheel crane which is an example of an upper turning traveling vehicle to which the present invention is applied.

In the figure, reference numeral 11 denotes a lower traveling body, on which an upper revolving body 12 is mounted via a revolving bearing 13 so as to be rotatable around a vertical axis X.

The upper revolving unit 12 has a telescopic boom 1
4 is provided so that it can be raised and lowered, and the cabin (operator's cab)
A steering wheel 16 is provided in the cabin 15.

On the other hand, in the lower traveling body 11, a front wheel 18 which is a steering wheel in this embodiment is provided at a front portion of a traveling body frame 17, and a rear wheel 19 is provided at a left and right side at a rear portion.

The traveling body frame 17 is provided at its rear end with an engine box 20 in which an engine (not shown) for driving and operating a crane is accommodated. Outriggers 21 are provided to lift and support the body during crane operation.

The outriggers 21 are provided with an outrigger beam (not shown) horizontally extended and stored laterally,
It has a vertical cylinder 21a that expands and contracts vertically, and this vertical cylinder 21a is grounded and lifts and supports the vehicle body.

Further, a rotary joint 22 (shown in FIG. 2) is provided around a vertical axis X which is the center of rotation of the upper revolving unit 12, and the hydraulic pipes on the lower traveling unit 11 side and the upper revolving unit 12 side rotate the hydraulic pipes. The connection is made via the joint 22.

Next, the hydraulic circuit configuration of the steering device will be described with reference to FIG.

A steering unit 23 is disposed on the upper revolving structure side above the rotary joint 22, and a handle shaft 16 a that rotates by operating the handle 16 is connected to an input side of the steering unit 23.

The steering unit 23 is a well-known integral type power steering unit, which operates according to the operation of the steering wheel, and is output as the operation of the link 24.

The steering unit 23 is not limited to the integral type, and another type of steering unit may be used. For example, a booster type (linkage type) may be used.

On the upper revolving structure side, upper left and right steering cylinders 25 and 26 are provided.

The cylinders 25 and 26 are double-acting single-rod cylinders having the same specifications.
R and 26R are connected to the link 24 in a state where they are connected to each other.

On the other hand, lower left and right steering cylinders (double-acting single rod hydraulic cylinders having the same capacity as the upper steering cylinders 25 and 26) 27 and 28 are provided on the lower traveling body side below the rotary joint 22. The rods of the two cylinders 27, 28 are connected to the front left and right wheels 18,
18 knuckle arms 18a, 18a. A tie rod 29 connects the left and right knuckle arms 18a, 18a to each other.

Each of these steering cylinders 25, 2
6, 27 and 28, the rod-side oil chamber 2 of the upper left steering cylinder 25
5b and the head side oil chamber 2 of the right steering cylinder 26
6a is connected by a cylinder cylinder oil passage 30, and the head side oil chamber 2 of the upper left steering cylinder 25
5a and the rod-side oil chamber 2 of the right steering cylinder 26
6b is connected by a cylinder oil passage 31, one cylinder oil passage 30 is connected to a rod-side oil chamber 27b of a lower left steering cylinder 27 and a head-side oil chamber 28a of a lower right steering cylinder 28, and the other cylinder oil passage 31 is Upper and lower connecting oil passages 32 and 33 passing through the rotary joint 22 are connected to a head side oil chamber 27a of the lower left steering cylinder 27 and a rod side oil chamber 28b of the lower right steering cylinder 28, respectively.

Each of these steering cylinders 25 to 28
A closed circuit A having a constant pressure is constituted by the oil passages 30, 31, 32, and 33. The static pressure of the closed circuit A transmits the steering wheel operating force to the wheels 18, 18, and The straight-line restoring force received by the steering wheel 18 is transmitted to the steering wheel 16.

That is, when the steering wheel 16 is turned to the right as shown by the arrow in FIG.
3, the rods 25R, 26R of the upper left and right steering cylinders 25, 26 respectively move rightward in the figure.

As a result, hydraulic oil is discharged from the rod-side oil chamber 25b of the upper left steering cylinder 25 and the head-side oil chamber 26a of the right steering cylinder 26 and passes through the oil passages 30 and 32 to the lower left steering cylinder 27. The oil is supplied to the rod-side oil chamber 27b and the head-side oil chamber 28a of the right steering cylinder 28.

As a result, the lower left and right steering cylinders 27 and 28 are operated, and the front left and right wheels 18 and 1 are operated.
8 is steered to the right.

At this time, the lower left steering cylinder 2
Hydraulic oil discharged from the head-side oil chamber 27a of the upper left steering cylinder 25 and the right-side steering of the upper left steering cylinder 25 passes through oil passages 33 and 31. The oil is supplied to the rod-side oil chamber 26 b of the cylinder 26.

On the other hand, when the steering wheel 16 is turned to the left, each part operates in the opposite direction to the above, and the wheels 18 are steered to the left.

After the steering, the straight-line restoring force applied to the wheels 18, 18 is reduced by the lower steering cylinder 27,
From 28, the hydraulic pressure of the closed circuit A is transmitted to the upper steering cylinders 25, 26 and transmitted to the handle 16 via the link 24 and the steering unit 23.

Thus, at the same time that the wheels 18, 18 return to the straight-ahead position, the handle 16 automatically returns to the neutral position (the straight-ahead position).

In this case, each of the upper and lower steering cylinders 25 to 28 has a sliding resistance, and the sum of the sliding resistances of the cylinders is a resistance for returning the steering wheel to a neutral state. However, the steering wheel 16 may not completely return to the neutral position without being transmitted 100%.

Therefore, a configuration is adopted in which the handle 16 is reliably returned to the neutral position by the neutral return cylinder 34 as neutral return means.

The neutral return cylinder 34 is provided with two left and right oil chambers 34a and 34b as shown in an enlarged view in FIG.
5, 36 (hereinafter referred to as left and right oil chambers or free pistons according to the direction of the drawing).

Between the two free pistons 35 and 36,
A head 37a of a headed rod 37 for transmitting a force between the two free pistons 35 and 36 is introduced, and a tip end of the rod 37 is connected to an intermediate portion of the link 24 of the steering unit 23.

In FIG. 3, reference numeral 38 denotes both free pistons 35, 3
Stopper 6 for determining the stop position at the center of the cylinder, 3
Reference numeral 9 denotes an oil chamber formed between the free pistons 35 and 36, and the oil chamber 39 is connected to the tank T via a tank port 40.
And the oil is supplied to and discharged from the oil chamber 39 in accordance with the movement of the free pistons 35 and 36.

Further, neutral return cylinder oil passages 41, 42 are connected to the left and right oil chambers 34a, 34b.

The two neutral return cylinder oil passages 41 and 42
Are connected to a neutral return cylinder line 43 as shown in FIG. 2, and the neutral return cylinder line 43 is connected to a tank line 46 including a check valve 44 and a relief valve 45.
Is connected to the tank T via

In the neutral return cylinder line 43,
Neutral return control valve (electromagnetic switching valve) 47, check valve 48,
An accumulator line 50 including an accumulator 49 is connected in parallel with the tank line 46, and the accumulator 4
9 to the oil chambers 34a, 34b on both sides of the neutral return cylinder 34
(Each hydraulic piston 35, 36) is supplied with the same hydraulic pressure.

On the other hand, the upper steering cylinders 25 and 2
The two cylinder oil passages 30 and 31 connecting the six cylinders 6 are connected to pressure release lines 51 and 52 which also serve as neutral return lines.

The two pressure relief lines 51 and 52 are connected to the accumulator line 50 via pressure relief valves 53 and 54 which also switch and operate between the open position A and the shutoff position B, respectively, and also serve as neutral return valves. I have.

The pressure relief valves 53 and 54 are connected to the cabin 1 shown in FIG.
While being operated by the neutral return switch 55 provided in the inside 5, it is also operated by the controller 56 together with the neutral return control valve 47.

The controller 56 is an extension switch 57 for extending the outrigger vertical cylinder 21a of FIG. 1, which is one of the signals indicating that the steering is not being performed (the upper steering cylinders 25 and 26 are not operating). Alternatively, when the reduction switch 58 for reducing the size is operated, the switching signal is output to the neutral return control valve 47 and both the pressure release valves 53 and 54 based on this switch signal.

As a result, during non-steering, the neutral return control valve 47 is moved from the open position A to the shut-off position B in FIG.
3, 54 are respectively switched from the blocking position B to the opening position A in the figure.

In FIG. 2, 59 and 60 are both pressure relief valves 53 and 5.
4 is a check valve provided in parallel with 4, 61 is a hydraulic pump for steering as a hydraulic source of the steering unit 23, 62 is provided in an oil passage connecting the pump 61 and the tank T to both the pump and tank ports of the steering unit 23. A flow divider 63, an oil replenishment hydraulic pump for replenishing oil to the closed circuit A and the like via an oil replenishment line 64 as required, and an oil replenishment valve 65 for opening and closing the oil replenishment line 64 (electromagnetic switching) And 66 are relief valves for setting the discharge pressure of the oil replenishing hydraulic pump 63, and 67 are relief valves for setting the discharge pressure of the steering unit hydraulic pump 61.

Next, the operation of the steering device will be described.

I. Automatic neutral return operation after steering The depressurizing valves (neutral return valves) 53 and 54 are normally at the illustrated shut-off position B, and in this state, the closed circuit A is closed to the outside.

When the neutral return cylinder 34 is not steered, the oil chambers 34a, 34b on both sides have substantially the same pressure, and the rod head 37a is pushed by the free pistons 35, 35 on both sides to be located at the center of the cylinder.

When the steering is performed in this state, the cylinder 34 is pushed to the left or right in the drawing by the output of the link 24, and a pressure difference is generated between the oil chambers 34a and 34b on both sides of the cylinder.

At this time, the thrust of the neutral return cylinder 34 causes a resistance to the output of the steering unit 23, but there is no problem if the output of the steering unit is made sufficiently large.

After steering, as described above, the wheels 18, 1
8 is transmitted to the link 24 of the steering unit 23 at the same time as the neutral return cylinder 3
4 tries to return to the neutral position, and this cylinder return force is applied to the link 24 together with the rectilinear restoring force.

The cylinder returning force is set to be larger than the sum of the sliding resistances of the steering cylinders 25 to 28, and the steering wheel 16 is reliably returned to the neutral position by the total returning force.

Even when the thrust of the neutral return cylinder 34 is set to be smaller than the sum of the sliding resistances of the steering cylinders 25 to 28, the neutral return cylinder 34 assists the return of the handle 16 to the neutral position. Needless to say, the handle 16 returns well.

In this way, after steering, the steering wheel 16 is reliably returned to the neutral position, and the desired straight running performance can be secured.

On the other hand, the amount of oil decreases in the closed circuit A due to internal leaks at the steering cylinders 25 to 28 and the rotary joint 22.
The neutral position is shifted from the straight position. In other words, the return position of the steering wheel 16 after steering is accurate to the neutral position (wheel 1
8, 18), and not only the straight running performance is impaired, but also the effective stroke of the steering cylinders 25 to 28 is shortened, and the inherent turning ability of the crane during running is reduced.

Then, when necessary, the handle 16 is neutralized as follows.

II. Neutral position correction action The neutral pressure release valve (neutral return valve) is operated by operating the neutral return switch 55 with the wheels 18 and 18 visually adjusted to the straight traveling position.
Activate 53 and 54 to switch from the blocking position (b) to the opening position (a).

Then, the closed circuit A is connected to the accumulator 4
9, the left and right upper steering cylinders 25,
The oil chambers 25a, 25b, 26a, 26b of 26 are adjusted to the accumulator set pressure, and the upper steering cylinders 25, 26 and the handle 16 are returned to the neutral position by the thrust of the neutral return cylinder 34.

The lower steering cylinders 27, 2
8 is neutral when the wheels 18, 18 are adjusted to the neutral position.

Thus, the deviation of the steering wheel 16 from the neutral position can be corrected, and the straight running performance and the original effective stroke of the steering cylinders 25 to 28 can be secured.

According to the above-described position correcting method, the neutral position of the upper steering cylinders 25 and 26 may be left unclear, and sensors for detecting the neutral position of the cylinder are not required.

III. Depressurizing action Heat generated by pressure loss during steering operation, rotating joint 2
Since the temperature of the oil in the closed circuit A may increase due to heat conduction from the engine 2 and the internal pressure may increase, the pressure is released as follows during non-steering without affecting the steering operation.

When the expansion switch 57 or the reduction switch 58 for the outrigger vertical cylinder 21a shown in FIG. 1 is operated, the pressure relief valves 53 and 54 are switched to the open position a by a switching signal from the controller 56.

Thus, the closed circuit A is communicated with the accumulator 49 and the oil chambers 2 of the left and right upper steering cylinders 25 and 26 are operated in the same manner as in the neutral position correcting operation.
5a, 25b, 26a, and 26b communicate with the accumulator 49, and when the internal pressure of the closed circuit A is higher than the accumulator set pressure, the pressure corresponding to the differential pressure is released to the accumulator 49.

At this time, when the neutral return control valve 47 is switched to the shut-off position B, the neutral return cylinder 34
Is disconnected from the accumulator 49 and the cylinder 34
Is locked inoperative.

Thus, when pressure is released in a state where the upper and lower steering cylinders 25, 26, 27, 28 are not neutral, only the upper steering cylinders 25, 26 become neutral due to the operation of the neutral return cylinder 34. Is prevented.

In this way, during non-steering, the pressure relief function of the closed circuit A is automatically performed without disturbing the original steering function, and damage to the equipment due to an increase in internal pressure is prevented.

In this embodiment, the depressurizing action is performed based on the operation of the extension / reduction switches 57 and 58 for the outrigger vertical cylinder. However, other signals indicating the non-steering state, such as parking The depressurizing action may be performed based on a signal indicating that the brake has been applied.

Second Embodiment (See FIGS. 4 to 6) Only differences from the first embodiment will be described.

In the second embodiment, a master cylinder system, that is, a pair of master cylinders 67 and 68 as an upper steering cylinder is provided. In the system in which the cylinders 27 and 28 are simultaneously operated, the pressure of the closed circuit A is released in a neutral state of the master cylinder.

As shown in FIGS. 4 and 5, the left and right steering master cylinders 67, 68
7R and 68R have fan-shaped connecting links 69 with pins 7
0, 70 and the long holes 71, 71, the output of the steering unit 23 during steering, the link 24,
The signal is transmitted to one of the master cylinders 67 or 68 via the connecting link 69, the elongated hole 71, and the pin 70, and the cylinder 67 or 68 operates only in the reduction direction. In FIG. 5, 6
9a is a rotation center axis of the connecting link 69.

As shown in FIG. 6, the master cylinders 67 and 68 are connected to an actuator port AP connected to the lower steering cylinders 27 and 28 and an accumulator 49 (not shown in FIG. 4). It has a connected tank port TP, and both ports AP and TP communicate with each other in a neutral state (when not operating).

The tank ports TP, TP of the master cylinders 67, 68 are connected to each other by a communication oil passage 72, and the communication oil passage 72 is connected to the accumulator line 50 (accumulator 49) by a pressure release line 73. .

When the cylinder 67 or 68 is contracted, the check valve 74 shown in FIG.
a, 68a is sent to the lower steering cylinders 27, 28 from the actuator port AP. As a result, the cylinders 27 and 28 are extended or contracted to steer.

On the other hand, the oil discharged from the cylinders 27 and 28 flows into the accumulator 49 via the master cylinder 67 or 68 in a neutral (non-operating) state.

Thus, both master cylinders 67, 6
8 oil chambers 67a, 68a and lower steering cylinder 2
The closed circuit A connecting the first and second cylinders 7 and 28 is in communication with the accumulator 49 through one of the master cylinders 67 or 68 even when the steering is not performed. When ascending, the excess pressure is released to the accumulator 49 via the inactive master cylinder.

The oil chambers of the master cylinders 67 and 68 are connected to each other by a communication oil passage 75. The communication oil passage 75 is provided with a neutral return valve 76 that switches between the open position a and the shutoff position b. Have been. 77 is the neutral return valve 7
6 is a neutral return switch for operating 6.

According to the configuration of the second embodiment employing the master cylinder system, since the master cylinders 67 and 68 serving as the upper steering cylinders function as pressure relief valves, it is not necessary to add a separate pressure relief valve. As shown in the figure, only one neutral return valve 74 is required.
Since the neutral return control valve 47 of the embodiment is not required, the hydraulic circuit configuration is simplified.

Since the depressurizing operation is performed not only during non-traveling as in the first embodiment, but also during traveling through the inactive master cylinder 67 or 68, the internal pressure rise is prevented. It can be prevented more reliably.

Incidentally, the steering wheel 16 may be mechanically returned to the neutral state by using a spring or the like instead of the hydraulic cylinder as the neutral return means.

Further, the neutral return means does not necessarily need to completely return the steering wheel 16 to the neutral state when the vehicle travels, and may return the neutral state to a range where the vehicle does not interfere with the travel (a state close to the complete neutral state). Good.

[0106]

As described above, according to the present invention, a closed circuit connecting the upper and lower steering cylinders is opened to the external pressure receiving section on condition that the upper steering cylinder is inactive. According to the configuration described above, the closed circuit is connected to the external pressure receiving part by the switching operation of the pressure relief valve), so that when the internal pressure of the closed circuit rises, excess pressure is released to the outside to prevent damage to the equipment in the closed circuit. Can be.

Further, since the above-mentioned depressurizing operation is performed on condition that the upper steering cylinder is not operated, there is no possibility that the original steering operation of the steering device is reduced or lost.

In this case, according to the third and fourth aspects of the present invention,
When it is detected that the upper steering cylinder is in a non-operating state (in claim 4 that the outrigger vertical cylinder is in operation), the depressurizing operation is automatically performed.

On the other hand, according to the fifth aspect of the present invention, the provision of the neutral return means ensures that the steering wheel is returned to the neutral position by the force of the neutral return means during traveling.

In addition, when the neutral position of the steering wheel is displaced by an internal leak generated by each steering cylinder or the rotating joint, the oil chamber of each steering cylinder is communicated with the external pressure receiving portion by operating the neutral return valve. By operating the neutral return means in the state of equal pressure, the steering wheel can be corrected to the neutral position to maintain straight running performance, and the effective stroke of the cylinder (wheel steering angle) can be prevented from decreasing and The turning ability at the time of traveling can be secured.

Further, since the neutral return valve is also used as a pressure relief valve, the circuit configuration is simplified as compared with the case where a dedicated pressure relief valve is provided.

According to the invention of claim 6, in the master cylinder system in which one master cylinder (upper steering cylinder) operates according to the steering direction and simultaneously operates the lower steering cylinder, a master cylinder in a neutral state, that is, (A) Both master cylinders at the time of non-steering (b) At the time of steering, the internal pressure is released to the outside by the closed circuit communicating with the external pressure receiving part via the inactive master cylinder.

According to the seventh aspect of the present invention, the internal pressure of the closed circuit is released to the accumulator, and when the internal pressure is reduced, the oil is returned to the accumulator. In contrast, the oil replenishment action is automatic.

[Brief description of the drawings]

FIG. 1 is a side view of a wheel crane to which the present invention is applied.

FIG. 2 is a hydraulic circuit configuration diagram of the steering device according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a neutral return cylinder used in the same device.

FIG. 4 is a hydraulic circuit configuration diagram of a steering device according to a second embodiment of the present invention.

FIG. 5 is a front view showing a connection portion between a steering unit and a master cylinder (upper steering cylinder) in the same device.

FIG. 6 is a sectional view of a master cylinder used in the device.

FIG. 7 is a hydraulic circuit configuration diagram of a conventional steering device.

[Explanation of symbols]

Reference Signs List 16 Steering wheel 18, 18 Front wheel to be steered 23 Steering unit 25, 26 Upper steering cylinder 27, 28 Lower steering cylinder A Closed circuit 30 to 33 Oil path constituting closed circuit 22 Rotary joint 34 Neutral return as neutral return means Cylinders 51, 52 Depressurizing lines 53, 54 constituting depressurizing means Depressurizing valves 49 also serving as neutral return valves 49 Accumulators as external pressure receiving parts 56 Controllers for depressurizing 57, 58 Steering cylinders are inactive Outrigger vertical cylinder extension / reduction switch indicating 67, 68 Master cylinder as upper steering cylinder PA Actuator port of master cylinder PT Same tank port (pressure release port) 73 Pressure release line

Claims (7)

[Claims] 1. An upper part of a lower traveling body having wheels,
A traveling vehicle having a steering unit on which an upper revolving superstructure having a driver's cab having a steering wheel is rotatably mounted, and having a steering unit for amplifying the operating force of the steering wheel and transmitting the amplified operating force to the wheels, is provided with the following configuration. A steering device for a traveling vehicle, comprising: (i) The upper revolving superstructure is provided with an upper steering cylinder that operates according to the operation of the handle. (ii) The lower traveling body is provided with a lower steering cylinder that changes a steering angle of the wheel. (iii) The upper and lower steering cylinders are connected to each other by an oil passage via a rotary joint disposed at the center of rotation of the upper revolving structure to form a closed circuit. (iv) The straight-line restoring force received by the wheel during traveling can be transmitted to the steering wheel via the hydraulic pressure of the closed circuit and the steering unit. (v) Provided is a pressure release means for releasing the internal pressure of the closed circuit by opening the closed circuit to an external pressure receiving section on condition that the upper steering cylinder is in an inoperative state. 2. A pressure release means, wherein a closed circuit and an external pressure receiving portion are connected by a pressure release line, and the pressure release line is moved from a shut-off position to an open position on condition that the upper steering cylinder is in a non-operating state. The steering apparatus for a traveling vehicle according to claim 1, further comprising a pressure relief valve that switches. 3. The steering apparatus for a traveling vehicle according to claim 2, further comprising control means for detecting that the upper steering cylinder is in an inoperative state and outputting an operation signal to the pressure relief valve. 4. An outrigger is provided on the undercarriage, and the control means is configured to output an operation signal to the pressure relief valve based on a signal of a switch for operating a vertical cylinder for grounding the outrigger. The steering apparatus for a traveling vehicle according to claim 3, wherein: 5. A neutral return means for applying a force in a direction for returning the steering wheel to the neutral position, and shuts off a position at which the oil chambers of the upper and lower steering cylinders communicate with the external pressure receiving portion and the external pressure receiving portion. 5. A neutral return valve which is operated to switch between the neutral return position and the neutral return valve, and wherein the neutral return valve is also configured as a pressure relief valve. Steering device for traveling vehicles. 6. An upper steering cylinder is provided with a pair of master cylinders, one of which extends and contracts only in one direction in accordance with an operation direction of a steering wheel, and the master cylinder is connected to the lower steering cylinder. 3. The traveling vehicle according to claim 2, further comprising an actuator port connected to the external pressure receiving portion and a pressure release port connected to the external pressure receiving portion, wherein the pressure release port and the actuator port are connected in a neutral state. Steering device. 7. The steering apparatus for a traveling vehicle according to claim 1, wherein an accumulator is used as the external pressure receiving section.