JPS625935Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a cooling circuit for a hydraulically driven vehicle in which a part of the hydraulic pressure in a closed circuit is cooled by an oil cooler provided in a working machine hydraulic circuit.

Conventionally, the hydraulic circuit of a hydraulically driven vehicle has a closed circuit that connects a variable pump driven by the power of an engine, etc. and a hydraulic motor linked to the drive wheels. A small-capacity charge pump is installed for replenishment, and an oil cooler is installed in the middle of the pipeline that drains oil leaked from the variable pump and motor into the tank to prevent the oil temperature from rising in the closed circuit. It is prevented. Also, considering the power loss, it is preferable for the amount of oil supplied by the charge pump to be small, but if the capacity of the charge pump is made too small, oil leakage from the variable pump and motor will be reduced, and the amount of oil flowing through the oil cooler will be reduced. As a result, the efficiency of the oil cooler decreases, resulting in the need for a larger oil cooler, which takes up more space and is more expensive.

This idea was made with the aim of improving this problem.The oil leaked from the variable pump or motor is circulated in the oil cooler installed in the hydraulic circuit of the work machine, and is cooled together with the oil flowing in the hydraulic circuit of the work machine. The present invention provides a cooling circuit for a hydraulically driven vehicle in which the oil in the closed circuit can be sufficiently cooled even with a small oil cooler.

This invention will be described in detail below with reference to an illustrated embodiment. In the figure, 1 is a power source such as an engine mounted on a hydraulic drive vehicle (not shown), and 2 is a variable pump driven by the power source 1.
A closed circuit 4 is connected between the hydraulic motor 3 and the hydraulic motor 3 which is interlocked with a drive wheel (not shown). Further, reference numeral 5 denotes a charge pump, which supplies oil that is insufficient due to leakage from the variable pump 2 and hydraulic motor 3 to the closed circuit 4, and also supplies oil that has leaked from the variable pump 2 and the hydraulic motor 3 to a drain pipe 12. It is introduced into the cooler bypass valve 6. The cooler bypass valve 6 is installed upstream of the oil cooler 8 provided in the return pipe line 7a of the work machine hydraulic circuit 7, and separates the return oil from the work machine hydraulic circuit 7 from the variable pump 2 and the hydraulic motor 3. It has a merging position a where leaked oil is merged and flows into the oil cooler 8, and a bypass position b where the merged oil is drained into the tank via the bypass pipe line 10, and the merging position a includes: An orifice 9 is provided in the return line 7 to generate a pilot pressure for switching the cooler bypass valve 6 from position a to position b. In other words, when the return flow rate from the work machine hydraulic circuit 7 is large, a portion of the return flow rate is transferred to the oil cooler 8.
In addition to allowing the oil to drain directly from the orifice 9 to the tank 11 without passing through it, when the oil temperature is low and the pressure loss due to the oil cooler 8 is large, the cooler bypass valve 6 is used to take advantage of the increase in pressure in the return pipe 7a.
is switched from the confluence position a to the bypass position b, so that most of the oil is drained into the tank 11 without passing through the oil cooler 8.

As described in detail above, this invention includes a cooler 8 in the return line 7a of the work machine hydraulic circuit 7, and a throttle 9 for generating pilot pressure in the cooler bypass valve 6.
are installed in parallel, the hydraulic pump 2 and the hydraulic motor 3
The amount of charge from the charge pump 5 is reduced by letting the oil leaked from the case flow into the upstream side of the cooler 8, so that the leaked oil is cooled in the oil cooler 8 together with the return oil from the work machine hydraulic circuit 7. Small oil cooler 8
This makes it possible to sufficiently cool the oil flowing through the closed circuit 4, and since there is no need to separately provide an oil cooler for the closed circuit 4, no installation space is required, which is also economical.

[Brief explanation of the drawing]

The drawing is a circuit diagram showing an embodiment of this invention. 1 is a power source, 2 is a variable pump, 3 is a hydraulic motor, 4 is a closed circuit, 6 is a bypass valve, 7 is a working machine hydraulic circuit, 7a is a return pipe, and 8 is an oil cooler.

Claims (1)

[Scope of utility model registration request] In a hydraulically driven vehicle equipped with a drive circuit and a work machine hydraulic circuit 7 in which a variable pump 2 driven by a power source 1 and a hydraulic motor 3 interlocked with a drive wheel are connected by a closed circuit 4, the work machine hydraulic circuit is A cooler 8 and a throttle 9 for generating pilot pressure for the cooler bypass valve 6 are provided in parallel in the return pipe 7a of the pump 7, and oil leaked from the cases of the hydraulic pump 2 and the hydraulic motor 3 flows upstream of the cooler. A cooling circuit for a hydraulically driven vehicle characterized by: