JPH0640055Y2 - Straight traveling control circuit device for hydraulic traveling vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a straight traveling control circuit device for controlling straight traveling of a hydraulic traveling vehicle such as a hydraulic excavator traveling by driving left and right crawlers by a hydraulic motor.

(Prior Art) Conventionally, for example, as a traveling control circuit of a hydraulic excavator,
As shown in the figure, the left and right traveling hydraulic motors a and b for driving the crawlers to the left and right of the hydraulic excavator are connected to the pump circuit e and the tank return circuit f via the direction switching valves c and d, respectively, and Pressure compensation valves g and h are provided between the switching valves c and d and the pump circuit e, respectively, and the higher load pressure of the traveling hydraulic motors a and b is connected to the pump circuit e via the shuttle valve i. There is known one provided with a load sensing system for guiding the discharge amount control device k of the variable displacement pump j.

In this case, when each of the directional control valves c and d is switched to one of the switching positions, the flow rate controlled by the pressure compensation valves g and h flows from the pump j into the traveling hydraulic motors a and b, and the hydraulic excavator operates. By traveling, the higher load pressure of the load pressures of the hydraulic motors a and b is extracted by the shuttle valve i, and the discharge amount of the pump j is controlled according to the magnitude of the extracted load pressure. The pump j is controlled to have a pressure and a flow rate according to the load.

When the hydraulic excavator tries to change the traveling direction to the left or right, for example, when it bends to the right, the stroke of the directional control valve d provided in the hydraulic circuit to the motor b on the right is changed to the stroke of the left directional control valve c. This is done by reducing the flow rate to the traveling hydraulic motor b on the right side, thereby reducing the rotation thereof compared to the traveling hydraulic motor a on the left side.

In the hydraulic excavator having the above hydraulic circuit configuration, the hydraulic motors a and b have the same size, the directional control valves c and d provided in the hydraulic circuits to the hydraulic motors a and b are the same, and the pressure compensating valves g,
If h is also the same, if both switching valves c and d are switched in one direction with the same stroke amount, theoretically the same flow rate flows from the pump circuit e to the motors a and b, and the hydraulic excavator goes straight. Although the vehicle should travel, even if the load pressures of the traveling hydraulic motors are almost the same, the flow rates to the motors a and b should actually be the same due to processing errors of the directional control valves c and d. It was difficult to do, and there were many driving bends.

Therefore, the applicant, as shown in FIG. 2, connects the connection circuits i and j connecting the directional control valves c and d and the pressure compensation valves g and h to each other by the pilot passage 1 so that the traveling of one of the two can be performed. When the load pressure of the hydraulic motor becomes higher than the load pressure of the other traveling hydraulic motor, the flow rate is made to flow from one circuit to the other circuit through the pilot passage k, and the rotational speed of the traveling hydraulic motor having the higher load pressure. The idea was to keep the vehicle going straight by preventing the vehicle from going up.

(Problems to be Solved by the Invention) In the case of the second drawing, the straight traveling of the vehicle is performed by fully switching the respective directional control valves in the same direction. To do so, the stroke of one directional control valve is operated to be smaller than the stroke of the other directional control valve, and the flow rate of passage of the one directional control valve is made smaller than the flow rate of passage of the other directional control valve. There is a need. However, at the time of this direction change, oil flows from the circuit of the other directional control valve into the circuit of the one directional control valve via the pilot passage, so the flow rate passing through the one directional control valve is greatly reduced. In addition, it is necessary to perform an operation to further reduce the stroke, which is inconvenient in operation.

Further, when traveling on a rough land and the road surface where the traveling resistance of the traveling hydraulic motor on one side is large continues for a long time, oil is transferred from the circuit of the traveling hydraulic motor on one side to the circuit of the traveling hydraulic motor on the other side through the pilot passage. Since the parts flow, there is a problem that a larger running bend than the running bend occurs due to a processing error of the directional control valve or the like.

An object of the present invention is to prevent the above-mentioned inconvenience and inconvenience in a straight traveling control circuit equipped with a pilot passage for direct traveling.

(Means for Solving the Problems) In the present invention, a pump circuit to which a variable displacement pump is connected,
To the tank return circuit connected to the tank, connect the left and right traveling hydraulic motors of the hydraulic traveling vehicle via the directional control valves,
A pressure compensating valve is provided between each directional control valve and the pump circuit, and the higher load pressure of each traveling hydraulic motor is guided to the discharge amount control device of the variable displacement pump via a shuttle valve. In this case, each connection circuit connecting each directional control valve and the pressure compensation valve is mutually connected by a pilot passage, and the pilot passage is closed when the pressure difference between the both connection circuits in the pilot passage becomes equal to or higher than the set pressure of the spring. By providing the pilot cutoff valve, the above-mentioned object is achieved.

The pilot cutoff valve includes a spool slidably provided in a valve casing, springs provided at both ends of the spool for holding a neutral position of the spool, and both ends of the spool facing each other. The pressure of each connecting circuit connecting the directional switching valve and the pressure compensating valve introduced so as to act,
And a flow passage formed on the spool for opening the pilot passage at a neutral position of the spool.

(Operation) If the directional control valves are switched by the same stroke,
Pressure oil is supplied to the left and right traveling hydraulic motors from the pump circuit under the control of the pressure compensation valve, and the discharge amount of the variable displacement hydraulic pump is controlled according to the higher load pressure of each traveling hydraulic motor. If there is a cause that obstructs the straight traveling of the hydraulic traveling vehicle, such as the flow rate to one traveling hydraulic motor increases due to the processing error of the directional control valve etc. The flow rate flows from the higher hydraulic circuit to the lower connecting circuit via the pilot passage that connects the switching valve and the connecting circuit connecting the pressure compensating valve to each other. As a result, the traveling hydraulic motor of the hydraulic circuit with the higher pressure is The number of revolutions does not increase, and it is possible to automatically prevent the curve of straight traveling.

When the hydraulic traveling vehicle is turned to the left or right, it is operated so that the stroke of one of the directional control valves is shortened to reduce the flow rate of passage therethrough. When the pressure in the connecting circuit connecting the pressure compensating valve of the above and the pressure in the connecting circuit connecting the other directional control valve and the pressure compensating valve in front of it differ by more than a set value, the pilot passage connecting both connecting circuits will The provided pilot cutoff valve operates so as to close the pilot passage, and since the small flow rate of the flow of the one directional control valve is maintained, the vehicle changes its direction as it is and corrects the stroke of the one directional control valve. No need, easy operation.

Further, when the pressure of the traveling hydraulic motor on one side becomes higher than a certain value and becomes higher than the pressure of the traveling hydraulic motor on the other side, the pilot passage is automatically closed, so that a large traveling bend in the state where the traveling resistance on one side is large. Can be prevented.

(Embodiment) An embodiment of the present invention will be described with reference to FIG. 3, in which reference numeral (1) indicates a pump circuit to which a variable displacement pump (2) is connected, and (3) indicates a tank (4). The connected tank return circuits, (5) and (6), are traveling hydraulic motors that drive the left and right crawlers and wheels of a hydraulic traveling vehicle such as a hydraulic excavator.

The left and right traveling hydraulic motors (5) and (6) for driving the left and right crawlers are directional switching valves (10) and (11) provided with a forward rotation position (7), a stop position (8), and a reverse rotation position (9). Are connected in parallel to the pump circuit (1) and the tank return circuit (3) through the respective directional control valves (10) and (11) to the forward rotation position (7) or the reverse rotation position (9). Traveling hydraulic motors (5) (6) from the pump circuit (1) in proportion to the distance
A type in which the flow rate to the is reduced is used. For each circuit that connects each directional control valve (10) (11) and the pump circuit (1), the area of the flow path (15) is set according to the pressure difference across the directional control valve (10) (11). Pressure compensating valves (12) (13) each having a compensator spool (14) for changing are provided respectively, and the directional control valves (10) (11) are applied to the traveling hydraulic motors (5) (6) regardless of their load pressures. ) The constant flow rate is supplied according to the stroke. In addition, the one with the higher load pressure of each traveling hydraulic motor (5) (6) is connected to the shuttle valve (1
It is extracted by 6) and led to the discharge amount control device (17) of the variable displacement pump (2), and the extracted load pressure and direction switching valve (1
0) A load sensing system in which the discharge amount control device (17) operates so that the pump (2) discharges only the flow amount determined by (11) is configured.

Connecting circuits (18) (19) connecting the directional control valves (10) (11) and the pressure compensating valves (12) (13) are connected to each other by a pilot passage (20), and the directional control valves (10) are connected. When the vehicle travels straight ahead by operating (11) with the same stroke, if there is a difference in the load pressure of each traveling hydraulic motor due to a machining error of the directional control valve, etc., the pilot passage (2
The pressure oil is circulated between the connection circuits (18) and (19) via the (0) so that the straight traveling state is maintained.

With the above configuration, when the direction of the vehicle is changed, the flow of the connection circuit (18) to the traveling hydraulic motor (5) of the series is reduced by slightly returning the stroke of the direction changeover valve (10). In this case, the flow rate of the connection circuit (18) does not decrease as a result of the flow rate flowing from the other connection circuit (19) through the pilot passage (20),
Further, an operation for returning the stroke of the direction switching valve (10) may be required. Further, in a traveling state in which the load pressure of one traveling hydraulic motor is significantly increased, a large bend in traveling occurs, which is not preferable.

Therefore, in the present invention, the pilot passage valve (20) closes the pilot passage (20) when its pressure exceeds the set pressure of the springs (21) (21).
Is provided to improve the operability for changing direction and prevent a large bend when traveling with a high load pressure applied to one traveling hydraulic motor.

The details of the pilot cutoff valve (22) are as shown in the fourth illustration, and the ports (23) (2) connected to the pilot passage (20) are shown.
Spool (25) slidably in a valve housing (24) equipped with 3)
Are provided, the springs (21) and (21) are applied to both ends of the spool (25) to maintain the neutral position, and the connection circuits (18) and (19) are connected via the ports (23) and (23). A groove or a through hole which is introduced so that the pressures act in opposition to each other and allows the ports (23) (23) to communicate with the spool (25) at its neutral position to open the pilot passage (20). A flow passage (27) consisting of

To explain the operation, operate both directional control valves (10) and (11) by the same stroke to put them in the forward rotation position (7), and rotate the traveling hydraulic motors (5) and (6) to make the vehicle go straight. Although the vehicle is in a running state, if the pressure of the connection circuit (19) of one hydraulic motor (6) increases due to a processing error of each directional control valve (10) (11), etc., the pilot passage (20) is passed through. The oil flows to the connection circuit (18) of the other hydraulic motor (5), which reduces the flow rate to the one hydraulic motor (6), reducing its rotational speed and maintaining the straight traveling state. .

When changing the direction of the vehicle to the right, for example, the stroke of the directional control valve (11) to the traveling hydraulic motor (6) on the right side is made smaller than the stroke of the directional control valve (10), and the flow rate of the connection circuit (19) is reduced. Is smaller than the flow rate of the connection circuit (18), but if the pressure difference between the circuit (19) and the circuit (18) becomes equal to or higher than the set pressure of the spring (21), the pilot shutoff valve (22) Since the spool (25) slides to close the pilot passage (20), the flow rate in the circuit (19) is kept low, and the direction can be smoothly changed to the left.

Further, even when a large load pressure is continuously generated in the traveling hydraulic motor on one side during rough land traveling, the pilot cutoff valve (22) automatically closes the pilot passage (20).
The maneuverability is improved without causing a larger running bend than the running bend due to a processing error of the directional control valve or the like.

The setting of the spring (21) of the pilot shut-off valve (22) is arbitrary, the spool (2 at a pressure differential of a few tens of kg / cm ²
It is preferable to set 5) to close the passage (20).

(Effects of the Invention) As described above, in the present invention, the pressure compensating valve is provided in front of each directional control valve that controls the left and right traveling hydraulic motors of the hydraulic traveling vehicle, and the variable displacement pump is controlled by the pressure in front of the directional switching valve. In a straight-ahead control circuit device having a configuration for controlling the discharge amount, and a connecting circuit connecting each directional switching valve and a pressure compensating valve to each other through a pilot passage, in the pilot passage,
Since the pilot cutoff valve is provided to close the pilot passage when the pressure difference between the connection circuits becomes equal to or higher than the set pressure, the operation when changing the direction of the vehicle is facilitated, and a large load pressure is applied to the traveling hydraulic motor on one side. This has the effect of preventing large running bends in the running state that occurs.

[Brief description of drawings]

FIG. 1 is a hydraulic drive circuit diagram of a conventional hydraulic traveling vehicle, FIG. 2 is a diagram of a hydraulic drive circuit improved from the conventional example shown in FIG. 1, and FIG. 3 is a circuit diagram of an embodiment of the present invention. The figure is a cross-sectional view of an example of a pilot shutoff valve. (1) ... Pump circuit, (2) ... Variable displacement pump (3) ... Tank return circuit (4) ... Tank, (5) (6) ... Travel hydraulic motor (10) (11) ... Direction switching valve, (12) ) (13)… Pressure compensation valve (16)… Shuttle valve, (17)… Discharge rate control device (18) (19)… Connection circuit, (20)… Pilot passage (21) (21)… Spring, (22) )… Pilot shutoff valve (24)… Valve housing, (25)… Spool (27)… Flow passage

Claims (2)

[Scope of utility model registration request] 1. A pump circuit to which a variable displacement pump is connected,
To the tank return circuit connected to the tank, connect the left and right traveling hydraulic motors of the hydraulic traveling vehicle via the directional control valves,
A pressure compensating valve is provided between each directional switching valve and the pump circuit so that the higher load pressure of each traveling hydraulic motor is guided to the discharge amount control device of the variable displacement pump via the shuttle valve. In this case, each connection circuit connecting each directional control valve and the pressure compensation valve is mutually connected by a pilot passage, and the pilot passage is closed when the pressure difference between the both connection circuits in the pilot passage becomes equal to or higher than the set pressure of the spring. A straight traveling control circuit device for a hydraulic traveling vehicle, which is provided with a pilot shutoff valve. 2. The pilot shutoff valve includes a spool slidably provided in a valve casing, springs provided at both ends of the spool for holding a neutral position of the spool, and both ends of the spool. Pressure of each connection circuit connecting each of the directional control valves and the pressure compensating valve introduced so as to oppose each other, and a flow for opening the pilot passage at the neutral position of the spool formed on the spool. The straight traveling control circuit device in the hydraulic traveling vehicle according to claim 1, further comprising: a road.