JPH0235164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an open circuit hydraulic drive device for driving a hydraulic actuator such as a hydraulic cylinder, and is suitable for a hydraulic working machine such as a hydraulic excavator.

Hydraulic excavators and the like require warming up in cold weather in order to obtain a hydraulic oil viscosity suitable for work.

Conventionally, when the weather is cold, an operator manually switches the center bypass type directional control valve to make it inoperable, either by setting the hydraulic cylinder to the end of its stroke or, if the hydraulic motor is using some type of restraint, to the inoperable state. As a result, the pressure in the main circuit increases to the set pressure of the relief valve, and the relief valve operates. Pressure oil from the hydraulic pump is discharged into the tank via the relief valve, and the power loss at that time causes the temperature of the hydraulic oil in the main circuit to rise and warm up. During this time, the operator must hold the operating lever in the switching position, which is very cumbersome. Also, it is not possible to use this time to perform other start-up inspections.

In addition, in order to reduce the relief loss in the relief valve during normal operation, this type of hydraulic drive device is equipped with a variable displacement hydraulic pump, and the pump is equipped with a variable displacement hydraulic pump that prevents the discharge pressure from exceeding a predetermined set pressure. Some devices are equipped with a control device that controls the discharge capacity, so-called pressure cut-off control, but when warming up this device, the relief loss power consumed to raise the hydraulic oil temperature is small, so warming up is necessary. Problems may occur such as a longer turn-up time or the temperature of the hydraulic oil not reaching the required value.

The object of the present invention is to be able to warm up the hydraulic oil in the same way even for pressure cut-off control without requiring the operator's hands during warming up, and to do so by changing the main circuit. It is an object of the present invention to provide a hydraulic drive device having a warming-up function that can be warmed up without having to do so.

In order to achieve the above object, the present invention provides a hydraulic drive device including a hydraulic pump, a center bypass type directional control valve, and a hydraulic actuator to which pressure oil of the hydraulic pump is supplied by the center bypass type directional control valve. warm-up command means for outputting a command signal for setting the center bypass type directional control valve to an opening degree selected from among an opening degree that fully closes its center bypass portion and an opening degree in the vicinity thereof; The present invention is characterized in that a pilot pressure supply means is provided for supplying a pilot pressure corresponding to the command signal to one pilot port of the center bypass type directional control valve when the signal is output.

In the above configuration, when a command signal is output from the warm-up command means in cold weather, pilot pressure corresponding to the command signal is supplied from the pilot pressure supply means to one pilot port of the center bypass type directional control valve. As a result, the center bypass portion of the center bypass type directional control valve is throttled. Restriction amount (opening degree) of this center bypass section
is arbitrarily selected by the warming-up command means depending on whether or not the configuration is such that pressure cut-off control is implemented, and whether or not warm-up is performed by the relief valve even in a configuration where pressure cut-off control is not implemented. . If the opening degree of the center bypass section is less than fully closed, warming up is performed by the center bypass section.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 1 shows an embodiment of the invention. This embodiment performs pressure cutoff control. A variable displacement hydraulic pump 1 is connected to a hydraulic cylinder 3 via a center bypass directional valve 2 by an open circuit. The center bypass type directional switching valve 2 communicates the center bypass part 4 with the tank 5 in the neutral position, and gradually narrows the opening area of the center bypass part 4 while being switched to the switching position, and also reduces the supply to the hydraulic cylinder 3. Increase the flow rate, and at the complete switching position, fully close the center bypass section 4,
Supply the full flow rate to the hydraulic cylinder 3. The relief valve 6 sets the maximum value of the discharge pressure of the variable displacement hydraulic pump 1. The pilot valves 7a and 7b generate a pilot pressure signal according to the amount of operation of the operating lever 8, and switch the center bypass type directional switching valve 2. The hydraulic pressure source 9 supplies control hydraulic pressure. The servo valve 10, the cut-off valve 11 and the servo cylinder 12 constitute a pressure cut-off control device. The servo valve 10 changes the discharge capacity of the variable displacement hydraulic pump 1, the cut-off valve 11 operates when the discharge pressure of the variable displacement hydraulic pump 1 reaches a predetermined set pressure, and reduces the discharge capacity.
The servo cylinder 12 drives a variable displacement mechanism 13 such as a swash plate of the variable displacement hydraulic pump 1, and transmits its operation amount to the servo valve 1 via a link 14.
It feeds back to 0.

The temperature detector 15 detects the temperature of the hydraulic oil in a predetermined portion in the main circuit (for example, in the discharge side conduit of the variable displacement hydraulic pump 1). Warming up control circuit 1
6 becomes operational by turning on switch 17,
When the temperature detector 15 detects a hydraulic oil temperature below a predetermined temperature required for warming up, it receives this as a warming up command and gives a control signal at a predetermined level to the electromagnetic proportional control valve 18. . The electromagnetic proportional control valve 18 generates a pilot pressure signal of a predetermined level from the control hydraulic pressure of the hydraulic power source 9, outputs it to the center bypass type directional control valve 2, and maintains it at a predetermined opening position. 19 is a shuttle valve.

The opening area a of the center bypass portion 4 of the normal center bypass type directional control valve 2 changes depending on the displacement of the directional control valve, as shown in FIG. Also,
At that time, the discharge pressure p of the variable displacement hydraulic pump 1
changes as shown in FIG. 2 when the hydraulic cylinder 3 reaches the stroke end and becomes inoperable. That is, as the directional valve displacement increases, the opening area a of the center bypass portion 4 becomes narrower, the discharge pressure p increases, and the directional valve displacement increases beyond point A. Then, the set pressure of the cut-off valve 11 is reached, and thereafter it is kept constant.

In this embodiment, the pilot pressure signal level of the electromagnetic proportional control valve 18 is set so that the directional control valve displacement is determined at point B immediately before reaching the set pressure of the cut-off valve 11.

When the switch 17 is turned on and the hydraulic oil temperature at that time is below the predetermined temperature required for warming up, the warming up control circuit 16 operates and a pilot pressure signal of a predetermined level is sent from the electromagnetic proportional control valve 18 to the center bypass type. It is input to the directional switching valve 2, and the displacement at point B is given. By this,
All the pressure oil from the variable displacement hydraulic pump 1 flows into the center bypass section 4, which is narrowed to a predetermined small opening area, and the discharge pressure at that time does not reach the set pressure of the cut-off valve 11, and the power consumption of the prime mover is the highest. Since the pressure is maintained at the required pressure, a considerable amount of power loss occurs in the center bypass section 4, and this power loss is converted into heat, raising the temperature of the hydraulic oil.

According to this embodiment, if the switch 17 is a manual switch, the warm-up operation is performed by simply operating the switch first, and if the switch 17 is an automatic switch, no operation is required to perform the warming-up operation. Therefore, the operator can use this time to perform other pre-work inspections. Further, since the relief valve 6 does not relieve, noise can be reduced and wear and tear on the parts of the relief valve 6 can be reduced. Furthermore, warming up can be performed without making any changes to the main circuit.

In the illustrated embodiment, the warming-up control circuit 16 and the electromagnetic proportional control valve 18 constitute an example of the warming-up means of the present invention.

Instead of the temperature detector 15, a warming-up termination command switch operated by an operator may be provided.

Instead of the pilot valves 7a and 7b, two electromagnetic proportional control valves may be provided, and an electric signal proportional to the operational input may be applied to these electromagnetic proportional control valves to generate a pilot pressure signal. Further, the center bypass type directional control valve 2 may be operated by an electro-hydraulic servo valve.

It is also possible to easily take a safety measure in which the fact that the hydraulic cylinder 3 is near the stroke end is detected by a sensor or the like, and the warming-up operation is performed only in this case.

When the present invention is applied to a hydraulic drive device in which pressure cut-off control is not performed, the directional control valve displacement, that is, the opening position shown in FIG. 2, may be set to a point closer to the right than point A. good. Furthermore, if the center bypass section 4 is set to the complete switching position where it is fully closed, a power loss occurs due to relief in the relief valve 6, and the hydraulic oil is warmed up.

As explained above, according to the present invention, the warming-up means for maintaining the center bypass type directional control valve at a predetermined opening position by a warming-up command is provided, and the opening degree position of the center bypass type directional control valve is Since it is automatically controlled without manual operation, the warm-up of the hydraulic oil can be performed in the same way for pressure cut-off control without requiring the operator's hand during warming-up. be able to. Moreover, no changes are required to the main circuit.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a characteristic diagram of a center bypass type directional control valve according to an embodiment of the present invention. 1... Variable displacement hydraulic pump, 2... Center bypass type directional valve, 3... Hydraulic cylinder, 4...
Center bypass section, 6... Relief valve, 15...
Temperature detector, 16...warming-up control circuit, 18...electromagnetic proportional control valve.

Claims (1)

[Claims] 1. In a hydraulic drive device comprising a hydraulic pump, a center bypass type directional control valve, and a hydraulic actuator to which pressure oil of the hydraulic pump is supplied by the center bypass type directional control valve, the center bypass type directional control valve is warming-up command means for outputting a command signal to set the center bypass portion to a fully closed opening degree and a selected opening degree among the opening degrees in the vicinity thereof; 1. A hydraulic drive device equipped with a warming-up function, characterized in that a pilot pressure supply means is provided to one pilot port of a switching valve to supply a pilot pressure according to the command signal.