JPS61122336A - Hydraulic circuit for running for construction vehicle - Google Patents

Abstract

PURPOSE:To enable to perform slow running suitable to a crane work, by providing a control device which detects control and non-control of only the running switching valve of a valve group and regulates the discharge flow rate of a variable volume pump according to a running speed. CONSTITUTION:Variable volume pumps 1a and 1b feed pressure oil to valve groups 14a and 14b having running control valves 15a and 15b, respectively. Meanwhile, based on an instruction from a controller 22, regulators 3a and 3b of hydraulic pumps 1a and 1b are controlled. The controller 22 controls ON-OFF of control of a running control valve 15 and ON-OFF of control of other control valves, and inputs a signal detected by means of which discharge voltages of the two pumps are detected by sensors 18, 19, and 21, and an ON- OFF signal from a speed selecting switch 20. The controller, when a vehicle is running and other control is not effected, controls the discharge flow rate of the two pumps 1 depending upon a running speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a hydraulic circuit for running a construction vehicle such as a hydraulic excavator or a crane.

[Background of the invention]

A conventional hydraulic circuit for driving a construction vehicle is shown in FIG.

la and Lb are variable displacement pumps, 2 is a pilot pump,
3a, 3b are regulators, 4a, 4b are pistons that control the tilt angles of variable displacement pumps la, lb, 5a, sb
l 6a and 6b are solenoid valves.

7a, 7b, 8a, 8b are flow paths; 9a, 9b are tilting angle sensors that detect the tilting angle of the variable displacement pumps la, lb;
0 is a flow path connected to the pilot pump 2, 11 is a pilot relief valve that determines the maximum pressure of the flow path, 12 is a tank, 13a and L3h are fixed capacity travel motors, 14a
, 14b is a control valve, and 15a, 15b are travel switching valves.

16a and 16b are discharge pipes of the variable displacement pumps la and Ib; 17 is a main relief valve that determines the maximum pressure of the discharge pipes 16a and 16b; and 21a.

21b is a sensor that detects the discharge pressure of the discharge pipes 16a, 16b, and 22 is a controller that controls the electromagnetic valves 5a, 5b, 6a, 6b using the sensors 21a, 21b as input signals.

In this way, the conventional driving system includes the tilt angle sensor 9a,
9b and discharge pressure sensors 21a and 21b, the tilt angle and discharge pressure are input signals, and the solenoid valves 5a and sbl 6a+
The output of the variable displacement pumps 1a and 1b was controlled via the pump 6b in accordance with the engine horsepower.

For this reason, even when loading and unloading from a trailer or when working with a crane, the speed may increase due to the balance between pressure and flow rate. Traveling speed had to be limited by setting the lever to half-position, which required skill in operation. Also, in order to set the operating lever to the half position, use the energy, )V'l-1I15''''''''8 pa.

In order to solve this problem, a traveling hydraulic circuit is known that uses a variable displacement motor for traveling, as shown in FIG.

In FIG. 4, 23a and 23b are regulators, 24
25 is a pipe, 25 is a switching valve, 2G is a pipe for supplying pilot pressure to the switching valve 25, 27a+27b is a variable displacement motor, and other components are the same as in FIG. 3.

Pressure from the pilot pump 2 is applied to regulators 23a and 23b via a switching valve 25.

Controls the tilt angle of variable displacement motors 27a and 27b. This changes the running speed, and the running force is small at high speeds and becomes large at low speeds. For this reason,
If a sufficient running traction force is applied at high speeds, the running traction force becomes too large at low speeds, making it easy to damage the vehicle body. Furthermore, if the traction force was set to a level that would not damage the car body at low speeds, the traction force would be too small at high speeds, resulting in a lack of pitching ability.

Therefore, even with this arrangement, there is a problem in that it is difficult to control the running speed to a state suitable for the work when changes in running force are taken into account.

[Purpose of the invention]

Book J! ! The object of the present invention is to provide a hydraulic circuit for running a construction vehicle that can easily control the running speed to a speed suitable for work.

[Summary of the invention]

The present invention detects the state in which only the travel switching valve of the control valve is used, and changes the discharge flow rate of the variable displacement pump according to the travel speed at this time, for example, changing the discharge flow rate in a low speed state to a high speed state. It is characterized in that the discharge flow rate is controlled to be less than the maximum discharge flow rate.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 18 is a travel switching valve 15a.

+5b is a sensor that detects that it is operated; 19 is a control valve 14a other than travel switching valves 15a and 15b;
, 14b is a sensor for detecting the operation of another operating valve, and 2o is a travel speed selection switch. Other same reference numerals as in FIG. 3 indicate equivalent parts.

The controller 22 in FIG.
The discharge flow rate shown in FIG. 2 can be selectively controlled between the first curve A and the first curve by the signal . In other words, when the sensor 18 detects that the travel switching valves 15a and 15b are used, and the sensor 19 detects that the other operation valves are not used, the speed selection switch 20 is switched to the low speed side. When the speed is switched to the high speed side, the characteristic shown by the curve A in FIG. 2 is obtained.

In other situations, that is, when the travel selector valves +5a and 15b and other operating valves are used, or when only the operating valves other than the travel selector valve are used.

The maximum discharge flow rate becomes curve A in FIG. 2, and the maximum discharge flow rate is obtained.

These relationships are summarized in the table below. O in the same table
N indicates the usage status of the valve according to the sensor signal as shown in Figure 2. When only the travel switching valves 15a and 15b are used and the high speed state is in use, the discharge flow rate Q is maximum, so the travel is performed according to the discharge flow rate. speed is obtained, while the 5 travel selector valves 15a, 1
When only 5b is used and the speed is low, the discharge flow rate Q is limited, so the traveling speed can be kept low. Therefore, by switching the speed selection switch 20 according to the type of work, either the high speed state or the low speed state can be easily selected.

A variable displacement pump la adjusts this discharge flow rate.

The tilt angle of lb is controlled by the controller 22.

The discharge pressure of variable displacement pumps Ia and lb is measured by sensors 21a,
21b, and the controller 22 calculates the tilt angle according to this detected pressure. If the calculated tilt angle is larger than the actual tilt angle, the controller 22
From the solenoid valve 6a.

A signal is sent to 6b, and the flow paths 8a and 8b are connected to the tank 11°,
ゎ7 e”A h”/ 4 a, 4 b tt
"FL'fl□ Increase the tilting angle of the displacement pump la, 11). On the other hand, if the calculated tilting angle is smaller than the actual tilting angle, the controller 22 increases the tilting angle of the solenoid valve 5a.

A signal is given to channel 5b, and channels 7a, 7b and channels 8a, s
In both cases, the calculated tilting angles of the variable displacement pumps La and lb are reduced by communicating between the pistons 4a and 4b and driving the pistons 4a and 4b upward due to the difference in the received pressure applied to the pistons 4a and 4b. When the angle matches the actual tilt angle, each solenoid valve 5a.

5b, 5a, and sb return to their original positions.

In the above-described embodiment, the sensors 18 and 19 are of electric type, but they may be of hydraulic type as long as they are means for detecting the predetermined usage status of the valve. Further, the control of the discharge flow rate of the variable displacement pump is not limited to the illustrated configuration, and various control devices can be used.

Further, although the speed selection switch is used to change between two speeds, high speed and low speed, it is also possible to use a potentiometer to continuously change the speed.

According to the embodiment configured in this way, the discharge flow rate Q of the pump can be reduced, so that the travel switching valves 15a,
Fine operations using the 15b can also be easily performed. Further, the energy loss at this time can be reduced, and since the output at this time does not become large, there will be no inconvenience such as damage to the main body.

〔Effect of the invention〕

As explained above, the present invention provides a
The detection means detects that only the travel switching valve is being used, and the discharge flow rate of the variable displacement pump is adjusted according to the travel speed at this time. Since there are several control bags E to be adjusted, the traveling speed can be easily controlled to a speed suitable for the work, and therefore, it is easily possible to reduce the traveling speed and work slowly when working with a crane.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram of a traveling hydraulic circuit for a construction vehicle according to an embodiment of the present invention, FIG. 2 is a discharge flow characteristic diagram when the traveling speed changes according to FIG. 1, and FIGS. 3 and 4 are 1 shows different hydraulic circuits for driving a conventional construction vehicle. 1a+1b...--variable displacement pump, 3a, 3b-
...Regulator, 5a, 5b, 6a, 6b...
...Solenoid valve, 13a, l3b-travel motor, t4a+14b...control valve,
15a, 15b... Travel switching valve, 18. L9・
...Sensor, 2o...Speed selection switch, 22...Controller. Case 1 Diagram 2 Eker P

Claims (1)

[Scope of Claims] 1. The travel switching valve described above is used in a hydraulic circuit for traveling of a construction vehicle configured to give a discharge flow rate from a variable displacement pump to a control valve having a travel switching valve and other operating valves. and a control device for controlling the discharge flow rate of the variable displacement pump in accordance with the traveling speed when the detection means detects the state in which the operating valve is not used. A hydraulic circuit for driving construction vehicles featuring: 2. In the device according to claim 1, the control device limits the discharge flow rate of the variable displacement pump in the above state and when traveling at low speed, and limits the discharge flow rate of the variable displacement pump in other conditions. A hydraulic circuit for driving a construction vehicle, which is characterized by controlling the flow rate to a maximum.