JPS6213864A - Anti-cavitation hydraulic circuit for hydrostatic transmission in skid steer loader - Google Patents

Abstract

PURPOSE:To prevent occurrence of cavitation by coupling hydraulic motors each other and supplying oil from the hydraulic pump upon starting of cavitation in the other hydraulic pump. CONSTITUTION:Two hydraulic pumps 2 are connected through a hose 5 with hydraulic motor 6 in a closed circuit. A check valve 11 is arranged at the respective port of said pump 2 to supply working oil from a charge pump 10 through said check valve 11 to the hydraulic pump 2 and the hydraulic motor 6. Excessive working oil will return through a charge relief valve 12 into a tank 13. A control circuit 16 is arranged in the center of respective hose 15 between the hydraulic motors 6. Upon starting of cavitation at any one port side, said circuit 16 is opened by its pressure. Preferably, the control circuit 16 will employ two control valves 21 connected in parallel in reverse direction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hydrostatic transmission (hereinafter referred to as a hydrostatic transmission) used in a skid steer loader (hereinafter referred to as a ``loader'').
It is called rH3Tj by taking the initials of nsmission. ), particularly regarding the prevention of cavitation in the hydraulic circuit of the H8T.

[Prior art] The drive system for the loader equipped with the H3T is based on a method of transmitting energy using hydraulic pressure.The engine drives a variable displacement hydraulic pump, and the hydraulic pressure generated by this hydraulic pump is used to transfer energy to a fixed displacement type. The hydraulic motor rotates to drive the tires. More specifically, as shown in FIG. 3, the output shaft 4 of an engine 3 is directly connected as a rotating shaft to a tandem pump 1 formed by coaxially arranging two axial piston type hydraulic pumps 2. A hydraulic motor 6 is connected to each hydraulic pump 2 via a hose 5 in a closed circuit, and each hydraulic motor 6 is further connected to tires 8 on each side via a final reduction gear 7 such as a chain. By changing the discharge amount and flow direction of the hydraulic pump 2, the rotational speed and rotational direction of the hydraulic motor 6 can be changed, and therefore the rotational speed and rotational direction of the tire 8 can be changed.

By the way, since the hydraulic pump 2 and the hydraulic motor 6 cause internal leakage of hydraulic oil, the main circuit of the H3T is a closed circuit, but a charge circuit is generally provided to compensate for the amount equivalent to the leakage. It is. That is, FIG. 4 shows a typical hydraulic circuit diagram of the H3T according to the conventional technology. It is now possible to replenish only. This charge circuit is provided with a charge relief valve 12 to replenish the leakage amount and return the excess hydraulic oil to the oil tank 13. Note that this charging circuit is generally incorporated into the pump side port block 9 (FIG. 3).

In the hydraulic circuit of the H8T configured in this way, when steering, for example, the rotation speed of the hydraulic motor 6 for driving the right tire is made larger than that of the hydraulic motor 6 for driving the left tire,
When trying to curve the loader to the left, the left tire 8 is dragged by the right tire 8, and the rotation speed of the hydraulic motor 6 for driving the left tire becomes larger than the rotation speed determined by H8T. As a result, the left hydraulic motor 6 causes a pumping action, and due to the pumping action of the hydraulic motor 6, the amount of oil on the side into which hydraulic oil is sucked becomes insufficient, which may cause cavitation.

In order to eliminate this drawback, conventional means have been adopted to increase the set pressure of the charge relief valve 12 to increase the pressure in the main circuit to prevent the occurrence of cavitation.

[Problems to be Solved by the Invention] However, in the conventional technology, there is a pressure drop between the hoses connecting the hydraulic pump and the hydraulic motor, so in order to prevent cavitation on the hydraulic motor side, It is necessary to set the relief valve pressure considerably high, and under normal operating conditions without cavitation,
There is a problem in that the charge pressure becomes unnecessarily high, leading to an increase in oil temperature, which has a negative effect on fuel efficiency, etc.

The purpose of this invention is to eliminate such problems.

[Means for Solving the Problems] According to the present invention, the H3T cavitation prevention hydraulic circuit in the loader uses a control valve that uses a pressure that is likely to cause cavitation as a pilot pressure and opens when one side reaches that pressure. It is characterized in that each of the two ports of one hydraulic motor is communicated with each of the two ports of the other hydraulic motor through a circuit consisting of two circuits connected in parallel in opposite directions. .

[Function] In the cavitation prevention hydraulic circuit according to the present invention as described above, when one hydraulic motor side is about to cause cavitation, the control valve between the hydraulic motors opens and takes in hydraulic oil from the other hydraulic motor side to prevent cavitation. It is designed to prevent

[Example] Hereinafter, together with the drawings, the H8T in the loader according to the present invention will be explained.
A preferred embodiment of the hydraulic circuit will be described in detail.

Note that the same or equivalent parts as in the conventional configuration will be described using the same reference numerals.

FIG. 1 shows a hydraulic circuit diagram of an embodiment of the present invention, in which, as in the conventional case, two axial piston-type hydraulic pressures arranged coaxially are provided with rotational force by an engine (not shown). Pumps 2 are connected to left and right hydraulic motors 6 by hoses 5 in a closed circuit, respectively. A check valve 11 is provided at each port of the hydraulic pump 2, and the charge pump 10 compensates for hydraulic oil leaked from the hydraulic pump 2 and the hydraulic motor 6 via the check valve 11. . The remaining hydraulic oil after replenishing the leakage amount passes through the charge relief valve 12 and is transferred to the oil tank 13.
It is now back to .

Further, one of the two ports of the hydraulic motor 6 is connected to one port of the opposing hydraulic motor 6 by a hose 15, and the remaining ports are also connected to each other by the hose 15. A control circuit 16 is interposed in the center of each hose 15 between the hydraulic motors 6 . This control circuit 16
The control circuit 16 is configured so that when cavitation is about to occur on either side of the port, the pressure opens the control circuit 16.There are various types of control circuits 16, but the second control circuit 16 As clearly shown in the figure, when the pressure in the pilot pipe 18 branched from the pipe line 17 on one side decreases, the spool 20 is sucked against the tensile force of the spring 19 and the open valve is opened. A control circuit 16 is constructed by using two control valves 21 and connecting them in opposite directions and in parallel, as shown in Fig. 1.
is suitable. In addition, in FIG. 2, the reference numeral 22 is a drain pipe.

In such a configuration, to describe the operation of the cavitation prevention hydraulic circuit according to the present invention, when the loader moves straight, that is, when the rotation speed of both the left and right hydraulic motors 6 is the same,
Since there is no large pressure drop on either side of the hydraulic motors 6, all control valves 21 are closed and each hydraulic motor 6 operates independently.

Furthermore, when the rotation speed of the left and right hydraulic motors 6 is changed in order to make the loader curve or skid, the lower rotation side hydraulic motor 6 causes a pumping action, as explained in the prior art section. Due to this pump action, the amount of oil on the port side that sucks hydraulic oil becomes insufficient and cavitation is likely to occur, but one of the control valves 21 opens in response to the pressure at that time, and the hydraulic motor 6 on the high rotation side Since a sufficient amount of oil is supplied to the port, a portion of the oil flows into the cavitation side, thereby preventing cavitation on the port side.

[Effects of the Invention] As described above, according to the present invention, since the charging circuit was conventionally provided only on the hydraulic pump side,
In order to prevent cavitation on the hydraulic motor side, it was necessary to increase the pressure in the main circuit between the hydraulic pump and the hydraulic motor, but if the hydraulic motors are connected and one is about to cause cavitation, the other By making it possible to replenish hydraulic oil from the hydraulic pump side, cavitation can be prevented without increasing the pressure in the main circuit. Therefore, since it is possible to keep the set pressure of the main circuit low, problems such as deterioration of fuel efficiency due to increase in oil temperature are eliminated, and the performance of the H3T can be improved.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram of an embodiment of the present invention, FIG. 2 is a detailed diagram of a control valve provided in the hydraulic circuit of FIG. 1, FIG. 3 is a schematic explanatory diagram of a drive device by H8T, In Figure 0, which is a hydraulic circuit diagram of the conventional H8T, 2: Hydraulic pump, 3: Engine, 5.15: Hose, 6: Hydraulic motor, 8 tires,
16: Control circuit 21: Control valve

Claims (1)

[Claims] The skid is equipped with two sets of hydrostatic transmissions, each consisting of a variable displacement hydraulic pump driven by an engine and a fixed displacement hydraulic motor connected in a closed circuit, each to independently drive the left and right tires. In a steer loader, one hydraulic motor is connected via a circuit consisting of two control valves connected in opposite directions and in parallel, with the pressure that is likely to cause cavitation being used as pilot pressure, and one side of which opens when the pressure reaches that pressure. Each of the two ports in the hydraulic motor is communicated with each of the two ports in the other hydraulic motor, and when one hydraulic motor side is about to cause cavitation, the control valve opens and takes in hydraulic oil from the other hydraulic motor side. A cavitation prevention hydraulic circuit for a hydrostatic transmission that prevents cavitation.