JPH0432246B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic circuit for construction machinery such as a hydraulic excavator or a hydraulic crane, and particularly to a hydraulic circuit suitable for a cooling circuit for hydraulic oil.

[Prior art] The appropriate temperature for the hydraulic oil in the hydraulic circuit of construction machinery is approximately 40 to 60°C, although it depends on the type of oil. This can cause damage to the overall functionality of hydraulic equipment, such as increased breakage and leakage, deterioration of hydraulic fluid, and aging of seals in various parts. As a countermeasure for this, conventionally, an oil cooler has been provided to constantly cool the hydraulic oil and adjust the temperature so as not to exceed an appropriate temperature.

However, on the other hand, if the oil cooler cools the oil too much and the temperature drops below the appropriate temperature, the viscosity of the hydraulic oil will increase, making it difficult to start the engine.
Frictional resistance within equipment and piping increases, causing pressure loss and speed reduction.

A hydraulic hydraulic circuit for a conventional construction machine will be described with reference to FIG. 2, taking a hydraulic excavator circuit for a hydraulic excavator as an example. In the figure, reference numeral 1 denotes a hydraulic pump driven by a prime mover 3, which supplies hydraulic fluid discharged through a control valve 5 to a plurality of actuators such as a hydraulic cylinder 7. When the spool of the control valve 5 is in the neutral position, return oil from the hydraulic cylinder 7, etc. corresponding to the discharge amount from the hydraulic pump 1 and the operation amount of the control valve 5 is passed through the control valve 5 to the oil cooler 8.
After being cooled, it is returned to the tank 9. 2
A hydraulic pump is installed in parallel with the hydraulic pump 1, and is connected to another actuator (not shown) via a control valve 6. 4 is a fan for cooling the oil cooler 8 which is directly connected to the prime mover 3, and 10 is a relief valve for the oil cooler 8. 11 is a variable displacement pump for the swing motor 14, which includes hydraulic pumps 1 and 2;
It is arranged in parallel with the motor 3 and is driven by the prime mover 3. The variable displacement pump 11 is attached to a regulator 12,
By operating the regulator 12, the amount of hydraulic oil discharged becomes variable. Reference numeral 13 denotes a swing control valve equipped with a center bypass, which supplies the swing motor 14 with hydraulic oil discharged from the variable displacement pump 11 in accordance with the amount of operation of the control valve. Then, the returned oil and the amount discharged from the variable displacement pump 11 when the spool of the swing control valve 13 is in the neutral state passes through the oil cooler 8 via the swing control valve 13 and is returned to the tank 9 after being cooled. It will be done. A hydraulic pilot pump 15 for generating pilot pressure is installed in parallel with the variable displacement pump 11, and its discharge oil is supplied to a pilot switching valve 16 that controls the swing control valve 13. A shuttle valve 17 is provided between the pilot switching valve 16 and the swing control valve 13.
Only when the rotation motor 14 is switched between the forward and reverse directions to drive the swing motor 14, pressure oil with a pressure commensurate with the amount of operation of the pilot switching valve 16 is guided to the regulator 12 via the shuttle valve 17.
The discharge amount of the variable displacement pump 11 is increased. 22 is a hydraulic pilot pump 15
It is a relief valve.

[Problems to be Solved by the Invention] In the conventional working hydraulic circuit having the above configuration, the hydraulic cylinder is adjusted to match the discharge amount from the hydraulic pump 1 and the operation amount of the control valve 5 when the spool of the control valve 5 is in the neutral position. The return oil from 7 etc. is cooled by the oil cooler 8 and returns to the tank 9, and
Similarly, the return oil from the swing motor 14 and the discharge amount from the variable displacement pump 11 when the spool of the swing control valve 13 is in the neutral state are also returned to the tank 9 after being cooled by the oil cooler 8. In this way, the hydraulic oil is constantly cooled, and the cooling is performed regardless of the temperature of the hydraulic oil.

Therefore, even if the temperature of the hydraulic oil is lower than a predetermined temperature and does not require cooling, cooling continues, and the temperature drops below the appropriate temperature, increasing the viscosity of the hydraulic oil and impairing engine startability. In addition to worsening the temperature and increasing the resistance inside the equipment and piping, there are also problems such as wasting energy and time to raise the hydraulic oil to an appropriate temperature.

In view of the problems of the prior art described above, the present invention provides a hydraulic circuit for construction machinery that can increase or decrease the amount of cooling of hydraulic oil depending on the temperature of the hydraulic oil and maintain the temperature of the hydraulic oil appropriately. The purpose is to

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a hydraulic pump that drives an actuator via a control valve;
A variable displacement pump that drives the swing motor via a swing control valve, a hydraulic pilot pump that supplies pressure oil to a pilot switching valve that controls the swing control valve, and a regulator of the variable displacement pump that controls the pilot switching valve. In the operating hydraulic circuit of construction machinery, which is equipped with a pilot circuit that transmits the output pressure of the valve and connects the tank port of the swing control valve to the tank via an oil cooler, an electromagnetic circuit that connects the input port to the hydraulic pilot pump A valve and an oil temperature detection means for outputting a signal to switch the solenoid valve from a closed position to an open position when the hydraulic oil temperature is higher than a preset temperature, one input port is connected to the pilot circuit, and the other is connected to the pilot circuit. The output port of the solenoid valve is connected to the input port of the pump, and the shuttle valve is provided with the regulator of the variable displacement pump connected to the output port.

[Function] With the above configuration, when the temperature of the hydraulic oil is below a preset temperature, the solenoid valve is in the closed position by a signal from the oil temperature detection means, and the regulator of the variable displacement pump is closed. The pilot pressure signal output from the pilot switching valve that controls the swing control valve is transmitted through one input port and output port of the shuttle valve, and the discharge amount of the variable displacement pump is adjusted according to the pilot pressure signal. increases or decreases. This discharged hydraulic oil is guided from the tank port of the swing control valve to the oil cooler.
After being cooled in an oil cooler, it is returned to the tank.

When the temperature of the hydraulic oil is above a preset temperature, the solenoid valve is switched to the open position by a signal from the oil temperature detection means, and the pilot pressure output from the pilot switching valve that controls the swing control valve is The signal is transmitted to one input port of the shuttle valve, the hydraulic signal from the solenoid valve is transmitted to the other input port,
The larger of these signals is transmitted to the regulator of the variable displacement pump via the output port, and the discharge amount of the variable displacement pump is always adjusted according to the pilot pressure signal at least according to the output signal from the solenoid valve. Increases beyond the preset value. This discharged hydraulic oil is led to the oil cooler from the tank port of the swing control valve, cooled by the oil cooler, and then returned to the tank.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. In the figure, the same reference numerals as in FIG. 2 indicate the same things.

In the figure, 18 is an oil temperature detector installed in the tank 9 that detects a preset temperature of the hydraulic oil, and the oil temperature detected by the oil temperature detector 18 is connected electrically. The signal from the amplifier 19 is sent to the solenoid valve 20 whose input port is connected to the hydraulic pilot pump 15. In this case, the solenoid valve 20 operates in conjunction with the detected oil temperature, and when it receives an oil temperature signal that exceeds a preset temperature, it is switched from a closed state to an open state, and the solenoid valve 20 is switched from a closed state to an open state, and the preset temperature is When the oil temperature signal drops further, the open state is switched to the closed state. 21 is a shuttle valve, one input port of which is connected to a pilot circuit (the output port of the shuttle valve 17 in the figure) that transmits the output pressure of the pilot switching valve 16 to the regulator 12, and the other input port of the solenoid valve 20. Connect the output port of the The output port of the shuttle valve 21 is connected to the regulator 12.

With this circuit configuration, the operation of the regulator 12 is performed by using pressure oil from the pilot circuit and the solenoid valve 2.
This is done through the shuttle valve 21 which outputs pressure oil with a higher pressure than the pressure oil from 0. When the oil temperature exceeds a preset temperature, an oil temperature signal from the oil temperature detector 18 causes the solenoid valve 20 to open as shown. For this reason, the hydraulic pilot pump 15 is operated not only when the swing motor 14 is being driven but also when it is not being driven.
The discharge pressure oil is led to the regulator 12 via the shuttle valve 21, and the discharge amount of the variable displacement pump 11 is increased.

Now, if the temperature of the hydraulic oil is above a preset temperature, the solenoid valve 20 is switched to the open position as shown in FIG. The pilot signal output from the pilot switching valve 16 to be controlled is
The hydraulic pressure signal is transmitted to one input port of the shuttle valve 21 via the shuttle valve 17, while the hydraulic pressure signal from the solenoid valve 20 is transmitted to the other input port of the shuttle valve 21. The larger pressure signal among these is transmitted to the regulator 12 of the variable displacement pump 11 via the output port of the shuttle valve 21,
The discharge amount of the variable displacement pump 11 is increased in accordance with the pilot pressure signal. This increased discharged hydraulic oil is guided from the tank port of the swing control valve 13 to the oil cooler 8, cooled by an amount corresponding to the increased discharge amount, and returned to the tank 9 with the oil temperature gradually lowered.

If the cooling continues and the oil temperature sensor 18 detects an oil temperature signal lower than a preset temperature, there is no longer a need for cooling with the increased discharge amount, and the oil temperature increases. Detector 18
The solenoid valve 20 is switched to the closed position by a signal from the solenoid valve 20. Therefore, only the pilot pressure signal output from the pilot switching valve 16 when the swing motor 14 is driven is sent to the regulator 12 from the shuttle valve 1.
7 and one input port and output port of the shuttle valve 21, and the pilot pressure signal is transmitted to the variable displacement pump 11 depending on the magnitude of the pilot pressure signal.
Increase or decrease the discharge amount. This discharged hydraulic oil is
The oil is guided from the tank port of the swing control valve 13 to the oil cooler 8 and returned to the tank 9.

As mentioned above, variable displacement pumps for swinging are the most likely to cause a rise in the temperature of the hydraulic oil, in other words, due to the large inertial load, the drive pressure reaches the relief valve setting value during acceleration and deceleration, causing pressure oil relief. 11, it is possible to control not only the discharge amount when the swing control valve 13 is operated, but also the discharge amount of the variable displacement pump 11 to the increasing side according to the preset temperature of the hydraulic oil. Since the discharge amount is cooled by the oil cooler 8, the amount of hydraulic oil that can be cooled can be controlled according to the temperature rise, and the temperature of the hydraulic oil in the tank 9 can always be maintained within a predetermined range. Therefore, in addition to improving engine startability, it is also possible to connect the oil discharged from the hydraulic pump 1 directly from the control valve 5 to the tank 9.
High surge pressure generated in the cylinder 7 etc. due to flow resistance of the oil cooler and damage to the oil cooler due to the surge pressure can also be prevented.

[Effects of the Invention] As explained above, the present invention has the effect of increasing or decreasing the amount of cooling of the hydraulic oil depending on the temperature of the hydraulic oil and maintaining the temperature of the hydraulic oil appropriately.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a working hydraulic circuit of a construction machine according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of an operating hydraulic circuit in a conventional hydraulic excavator. DESCRIPTION OF SYMBOLS 1, 2... Hydraulic pump, 5, 6... Control valve, 7... Hydraulic cylinder, 8... Oil cooler, 11... Variable displacement pump, 12... Regulator, 13... Control valve for swing, 14... Swing motor, 15... Hydraulic pressure Pilot pump, 16... Pilot switching valve, 17, 21...
Shuttle valve, 18...Oil temperature detector, 20...Solenoid valve.

Claims (1)

[Claims] 1 A hydraulic pump that drives an actuator via a control valve, a variable displacement pump that drives a swing motor via a swing control valve, and a hydraulic pilot that supplies pressure oil to a pilot switching valve that controls the swing control valve. The working hydraulic pressure of construction machinery is equipped with a pump and a pilot circuit that transmits the output pressure of the pilot switching valve to the regulator of the variable displacement pump, and the tank port of the swing control valve is connected to the tank via an oil cooler. The circuit includes a solenoid valve whose input port is connected to a hydraulic pilot pump, and an oil temperature detection means that outputs a signal to switch the solenoid valve from the closed position to the open position when the hydraulic oil temperature exceeds a preset temperature. , characterized in that a shuttle valve is provided in which the pilot circuit is connected to one input port, the output port of the solenoid valve is connected to the other input port, and the regulator of the variable displacement pump is connected to the output port. Hydraulic circuit for construction machinery.