JPH11351203A - Hydraulic drive circuit device for working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic drive circuit device for a working vehicle which reduces the discharge quantity of a variable displacement hydraulic pump directly coupled with an engine for traveling a vehicle without generating, any pressure loss of discharge fluid, and can be manufactured lightweight at a low cost. SOLUTION: In a hydraulic drive circuit device in which an orifice 5 and a hydraulic pilot operation type center bypass control valve 6 are interposed in a discharge circuit 3 continuous to a tank 4 from a variable displacement hydraulic pump 2 directly coupled with an engine 1 for traveling, the pressure before and behind the orifice 5 is lead to a discharge quantity control device 8 of the hydraulic pump through a signal line to control the increase/decrease of the discharge quantity of the pump, a sequence valve 14 is provided in the discharge circuit, and a pressure reducing valve 16 is interposed in the hydraulic pilot circuit, a solenoid control valve 19 to selectively introduce the pressure in the downstream or the tank pressure to a signal line 7b is provided. A second solenoid control valve to lead the secondary pressure of the pressure reducing valve 16 to a spring chamber of the sequence valve 14 may be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive circuit device for driving work equipment of a work vehicle such as a refuse collection vehicle.

[0002]

2. Description of the Related Art Heretofore, in a working vehicle equipped with several working devices such as a dust scraping plate and a dump cylinder, these working devices are hydraulically driven.
The drive hydraulic pressure is also obtained from a variable displacement hydraulic pump directly connected to a traveling engine of a work vehicle.
An example of a hydraulic drive circuit in which a variable displacement hydraulic pump of a conventional garbage truck is directly connected to an engine is as shown in FIG. 1, and a variable displacement hydraulic pump b which is directly connected to a traveling engine a and driven to rotate. To the discharge circuit d connected to the tank c,
An orifice e and four hydraulic pilot operated center bypass switching valves f for driving various work equipment are interposed, and the pressure before and after the orifice e is discharged from the hydraulic pump b via a signal line g. The discharge amount control device h is guided to the discharge amount control device h to operate the discharge amount control device h to increase or decrease the discharge amount of the pump, and a sequence valve i is provided in the discharge circuit d between the center bypass switching valve f and the orifice e. It is known that the pilot pressure of the switching pilot circuit j of the switching valve f is secured by using a solenoid valve k for shutting off the discharge circuit d when the vehicle is not working or the vehicle is running, and a discharge circuit d. A large-diameter safety valve 1 is provided to remove the flow rate to the tank. m is a circuit safety valve.

[0003] The discharge amount control device h is a known device which controls the discharge amount to be constant even if the pump rotation speed increases and decreases. The servo selection valve n and the orifice e operate by a pressure difference before and after the orifice e. e, a servo opening / closing valve o that operates at a pressure in front of the pump e. When the pump rotation speed increases and the discharge amount increases beyond a predetermined amount and the pressure difference increases, the servo selection valve n moves to move the orifice e. The forward pressure is guided to the displacement control cylinder p via the servo open / close valve o, and the displacement of the pump is reduced by extending the cylinder p against the spring of the other displacement control cylinder q to reduce the pump displacement. To a predetermined amount. When the pump rotation speed decreases and the discharge amount decreases below a predetermined amount and the pressure difference decreases, the servo selection valve n moves to discharge the fluid in the displacement control cylinder p to the tank, and the other displacement control. The pump capacity is reduced by the spring of the cylinder q so as to increase, and the discharge amount is increased to a predetermined amount. When the pressure of the discharge circuit d becomes equal to or higher than the set pressure, the servo open / close valve o moves against the spring to guide the pressure of the discharge circuit d to the displacement control cylinder p. Reduce to capacity.

[0004]

What is shown in FIG. 1 is
A variable displacement hydraulic pump b is directly connected to the traveling engine a. For example, when the work vehicle is traveling at high speed, the hydraulic pump b also rotates at high speed and a large amount of hydraulic oil is discharged to the discharge circuit d. When the working equipment is not operated and the discharge amount passes through the center bypass switching valve f and is discharged to the tank c, the hydraulic oil generates heat, which is not preferable. Therefore, the discharge circuit d is shut off by the solenoid valve k during traveling. And the capacity control device h
Is controlled to be the minimum discharge amount to reduce heat generation. However, the solenoid valve k has a discharge circuit d
Need a large thing that can pass without limiting the flow rate of
Since a safety valve 1 for absorbing the surge pressure generated at the time of the switching is also required, the cost is high and the weight is increased. Further, the solenoid valve k provided in the discharge circuit d
Since a passage resistance is given to the fluid flowing through the discharge circuit d, a pressure loss occurs when the working equipment is operated, which is not preferable.

It is conceivable to connect the hydraulic pump b to the engine a via a clutch and disengage the clutch while the work vehicle is running. However, the clutch is expensive and its maintenance is not easy.

SUMMARY OF THE INVENTION The present invention provides a hydraulic drive circuit device for a working vehicle which can reduce the discharge amount of a variable displacement hydraulic pump directly connected to a vehicle running engine without causing pressure loss in a discharge fluid, and which can be manufactured at a light weight and at a low cost. It is intended to do so.

[0007]

According to the present invention, there is provided a hydraulic pilot-operated hydraulic pump for hydraulically driving an orifice and working equipment in a discharge circuit of a variable displacement hydraulic pump which is driven directly connected to a traveling engine of a working vehicle. The center bypass switch valve is interposed, and the pressure before and after the orifice is guided to the discharge amount control device of the hydraulic pump via a signal line to operate the discharge amount control device, thereby increasing or decreasing the discharge amount. A sequence valve for securing a pilot pressure of a switching pilot circuit of the switching valve is provided in a discharge circuit between the center bypass switching valve and the orifice, and a pressure reducing valve for regulating an upper limit of the pressure of the circuit is provided in the pilot circuit. In the interposed hydraulic drive circuit device, select the rear pressure or tank pressure to a signal line that guides the pressure behind the orifice to the discharge amount control device. By providing a solenoid control valve for incoming and so as to achieve the above object. The discharge amount control device includes a servo selection valve and a servo opening / closing valve for controlling the introduction and removal of the pressure of the discharge circuit to the displacement control cylinder of the variable displacement hydraulic pump. The front and rear pressures and the spring force act, and the servo open / close valve can be constituted by a spring and the pressure of a discharge circuit in front of the orifice acts. Further, the above object can also be achieved by a configuration in which a second solenoid switching valve for guiding the secondary pressure of the pressure reducing valve to the spring chamber of the sequence valve is provided.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a garbage truck will be described with reference to the drawings. In FIG. 2, reference numeral 1 denotes a traveling engine of a work vehicle, and 2 denotes a direct connection to the engine 1. Reference numeral 3 denotes a discharge circuit of the hydraulic pump 2 connected to the tank 4. In the discharge circuit 3, an orifice 5 and four hydraulic pilot operated center bypass switching valves 6a, 6b, 6c, 6d are interposed. Each switching valve is connected by pipes to working equipment of the refuse collection vehicle such as a scraping plate, a dump cylinder, a trash input lock, and the like, and these apparatuses are hydraulically driven by the switching operation.

The pressure before and after the orifice 5 of the discharge circuit 3 is guided to the discharge amount control device 8 of the hydraulic pump 2 via signal lines 7a and 7b, so that the difference between the pressures becomes constant. The discharge amount control device 8 controls the pump displacement of the hydraulic pump 2 so that the flow rate flowing through the hydraulic pump 2 becomes constant. The structure of the discharge amount control device 8 is the same as that of the prior art. The servo selection valve 9 in which the pressure before and after the orifice 5 acts on both ends of the spool, and the pressure in front of the orifice 5 is a spring force. A servo opening / closing valve 10 which operates when the pressure becomes larger than the predetermined value. The engine rotation speed increases to increase the discharge amount, and the difference between the pressures before and after the orifice 5 is determined by the converted pressure of the setting spring of the servo selection valve 9. Is larger, the servo selection valve 9 moves from the position shown in the figure to guide the pressure in front of the orifice 5 to the displacement control cylinder 12,
The cylinder 12 expands the other displacement control cylinder 13 while compressing its spring, and reduces the pump displacement until a predetermined pressure difference is obtained. And
When the difference between the pressures before and after the discharge amount becomes equal to the converted pressure of the set spring, the servo selection valve 9 returns to the illustrated position. Actually, the selection valve 9 repeats the above movement and return to control the discharge amount to be constant. In addition, the pressure of the discharge circuit 3 increases due to an increase in load or the like.
When the pressure exceeds the spring-equivalent pressure, the on-off valve 10 moves from the position shown in the drawing against the spring, and introduces the pressure of the discharge circuit 3 into the displacement control cylinder 12 so that the amount corresponding to the pressure is increased. And reduce the discharge amount.

The orifice 5 and the center bypass switching valve 6
a each of the center bypass switching valves 6
The switching pilot circuit 15 is provided with a sequence valve 14 for extracting the hydraulic pilot pressure of the above, and the switching pilot circuit 15 is provided with a pressure reducing valve 16 for regulating the upper limit of the pressure. 17 is a circuit safety valve. Each center bypass switching valve 6 is of a well-known spool type having two solenoids 18, and when one of the solenoids 18 is excited, the pressure of the pilot circuit 15 is reduced by the switching valve 6.
And the switching operation is performed.

Although the above construction is not particularly different from the conventional hydraulic drive circuit device for a work vehicle equipped with a variable displacement hydraulic pump directly connected to the engine, in the present invention, the discharge amount control device 8 is provided with the orifice. A solenoid switching valve 19 for selectively introducing the rear pressure or the tank pressure is provided in the signal line 7b for guiding the pressure behind the fifth valve 5. With this configuration, while the work vehicle is traveling, the solenoid switching valve 1
9 is operated to guide the tank pressure to the signal line 7b and to switch one of the center bypass switching valves 6 to the switching position to generate a high load pressure in the discharge circuit 3. In opposition to the switching position, the pressure of the discharge circuit 3 in front of the orifice 5 is introduced into the displacement control cylinder 12, so that the pump displacement is reduced to a minimum. In the case of a refuse collection vehicle, it is preferable to select a center bypass switching valve 6a for driving a lock cylinder working device that consumes no flow as the center bypass switching valve 6 to be switched. Since the solenoid switching valve 19 is provided on the signal line 7b having a small flow rate, a surge pressure hardly occurs at the time of the switching, there is no need to provide a safety valve for preventing surge pressure, and the flow rate is small. Therefore, a small and light one for small flow rate can be used. Whether the signal line 7b is connected to the tank by excitation or demagnetization of the solenoid of the solenoid switching valve 19 can be arbitrarily determined by usability.

In the above-mentioned example, the center bypass switching valve 6a is operated to generate a pressure for guiding the pressure into the displacement control cylinder 12 in the discharge circuit 3. However, each center bypass switching valve 6 includes a sequence valve 14, a pressure reducing valve 16, and a circuit. In the case of a configuration provided as a unit together with necessary devices such as the safety valve 17, FIG.
As shown in the figure, the spring chamber 14a of the sequence valve 14
Is provided with a second solenoid switching valve 20 for guiding the secondary pressure or tank pressure of the pressure reducing valve 16, and when the tank pressure is introduced into the signal line 7 b by the solenoid switching valve 19, the switching valve 20 is also switched so that the sequence valve is switched. The discharge circuit 3 may be operated to shut off the discharge circuit 3 to generate a high pressure to be guided into the displacement control cylinder 12. In this case, the switching valve 20 only controls the transmission of the pressure of the pilot circuit 15 through which only a small flow rate flows, so that the same small and light valve as the solenoid switching valve 19 can be used.

[0013]

As described above, according to the present invention, a hydraulic drive circuit for a work vehicle in which an orifice for detecting a differential pressure and a center bypass switching valve are provided in a discharge circuit of a variable displacement hydraulic pump directly connected to a traveling engine. In the apparatus, a solenoid switching valve is provided in a signal line for guiding the pressure behind the orifice to the discharge amount control device of the hydraulic pump, and the pressure behind or the tank pressure is selectively introduced into the signal line by switching. Therefore, while the work vehicle is running, the discharge amount from the hydraulic pump can be reduced by switching the solenoid switching valve and the center bypass switching valve, thereby reducing the heat generation of the hydraulic oil and the power loss of the engine. The structure is simpler and lighter than connecting the engine and the hydraulic pump by a clutch. Is also possible to control the sequence valves by operating the Rinisetsu valve, the switching valve is the same effect as the dealt with in a small size is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram of a conventional hydraulic drive circuit device for a work vehicle.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

1 traveling engine, 2 variable displacement hydraulic pumps, 3
Discharge circuit, 4 tanks, 5 orifices, 6.6a-6
b ・ 6c ・ 6d Center bypass switching valve, 7a ・ 7b
Signal line, 8 discharge amount control device, 14 sequence valve, 15 switching pilot circuit, 16 pressure reducing valve, 19
Solenoid switching valve, 20 switching valve,

Claims (3)

[Claims] An orifice and a hydraulic-pilot-operated center bypass for hydraulically driving work equipment are provided in a discharge circuit connected to a tank from a variable displacement hydraulic pump which is directly connected to a traveling engine of a work vehicle. The switching valve is interposed, and the pressure before and after the orifice is guided to the discharge amount control device of the hydraulic pump through a signal line, and the discharge amount control device is operated at the pressure to increase or decrease the discharge amount of the pump. A sequence valve for securing a pilot pressure of a switching pilot circuit of the switching valve is provided in a discharge circuit between the bypass switching valve and the orifice, and a pressure reducing valve for regulating an upper limit of the pressure of the circuit is provided in the pilot circuit. In the hydraulic drive circuit device, the pressure or the tank pressure is selectively introduced into a signal line for guiding the pressure behind the orifice to the discharge amount control device. Hydraulic drive circuit system for a working vehicle, characterized in that a solenoid selector valve. 2. The discharge control device according to claim 1, wherein said discharge control device comprises a servo selection valve and a servo open / close valve for controlling the introduction and elimination of the pressure of said discharge circuit to a displacement control cylinder of said variable displacement hydraulic pump. 2. The work vehicle according to claim 1, wherein a pressure and a spring force before and after the orifice act on the spring, and the servo open / close valve is a spring and a pressure of a discharge circuit in front of the orifice act on the servo open / close valve. Hydraulic drive circuit device. 3. The hydraulic drive circuit device for a work vehicle according to claim 1, wherein a second solenoid switching valve for guiding a secondary pressure of the pressure reducing valve is provided in a spring chamber of the sequence valve.