JPH0414644Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention relates to a drive circuit device for an oil motor that has large load fluctuations, such as an oil motor that drives a generator or a compressor for a refrigerator.

(Prior Art) Conventionally, for example, when a refrigerator is driven by an engine whose rotation speed changes, the engine rotates an oil pump, and the refrigerator is driven by an oil motor that rotates with hydraulic oil discharged from the oil pump. This has been done (for example, Publication of Utility Model Publication No. 10844/1983). One example is as shown in the first diagram, in which a variable displacement hydraulic pump a consisting of a variable displacement piston pump is equipped with a pump displacement control device consisting of two pistons b and c, and an engine e is used to pump the pump. a
When driven, the pump discharges a flow rate controlled by the pump displacement control device d to the discharge circuit g connected to the oil motor f. The oil motor f is rotated by fluid from the discharge circuit g, and rotates the compressor h. The pump capacity control device d operates to reduce the pump capacity of the pump a when pilot pressure from the discharge circuit g acts on the piston c via the pilot valve i, and the pilot valve i moves the piston c into the tank. When the piston c is connected and no pilot pressure acts on the piston c, the pressure of the discharge circuit g and the elasticity of the spring j act on the piston b, which has a smaller area than the piston c, to increase the pump capacity. The pump discharge pressure in front of the orifice l provided in the discharge circuit g is guided to the end face k of the spool of the pilot valve i, and the end face k is applied with a spring m.
The actuator pressure behind the orifice l is guided to the end face n, which has the same area as the orifice l, and the differential pressure between the pump discharge pressure and the actuator pressure is set by the spring m. When the rotational speed of the engine e increases and the pump discharge amount becomes too large, the differential pressure across the orifice l becomes larger than the set force of the spring m, so the spool of the pilot valve i moves and the discharge pressure becomes uniform. The section acts on the piston c, and the pump displacement control device d acts to reduce the pump displacement. Conversely, when the engine speed drops and the pump discharge volume decreases, the differential pressure across the orifice l becomes smaller than the set force of the spring m, so the spool of the pilot valve i is pushed back by the spring m. , the fluid acting on the piston c is discharged to the tank, and the pump displacement control device d increases the discharge amount of the pump a again.

When the pilot valve i operates, the pump a discharges such a flow rate that the pressure difference before and after the orifice l becomes constant, so the load on the oil motor f fluctuates due to changes in the torque of the compressor, etc., or the rotation speed of the engine e changes. Even if the rotation speed changes, constant rotation control of the oil motor f, that is, constant rotation control of the compressor can be performed. With this device, it is also possible to drive a generator with large load fluctuations at a constant rotation speed regardless of load fluctuations.

(Problem to be solved by the invention) In the configuration shown in the first diagram, the oil motor f
When the load on the compressor, etc. is released by the clutch, or when the load fluctuates, the oil motor will overrun due to its own inertia, resulting in cavitation and noise. , the flow rate pushed out from the oil motor f and flowing through the orifice l increases, so
The pilot valve i is switched so as to guide the pressure of the pump discharge circuit g to the piston c, which has the disadvantage that the pump capacity is reduced and the cavitation condition is increased. In addition, when the load is a generator, if an electrical appliance that uses electrical energy obtained from the generator is used intermittently, load fluctuations will occur in the oil motor f. f overruns with its own inertia and the inertia of the generator, causing cavitation, which increases the rotational speed of the oil motor f and the generator, making it difficult to control the generator to an appropriate rotational speed.

In general, it is naturally possible to prevent an oil motor from overrunning by providing a counterbalance valve or a brake valve on the secondary side of the oil motor, but in order to control the rotation speed of the oil motor at a constant level, A separate flow control device is required, even when driving an oil motor in a closed circuit. In other words, if you install a counterbalance valve or a brake valve in the oil motor drive circuit and combine it with a variable displacement hydraulic pump equipped with a pressure and flow rate maintenance control device, overruns can be prevented, but the counterbalance valve A brake valve is required, and a switching valve is required at the oil pump discharge port. In the case of a closed circuit, an owner balance valve is not required, but a boost valve is required separately. Therefore, providing a counterbalance valve or a brake valve to prevent overruns is not only disadvantageous in terms of cost, but also has no merit due to increased installation space and weight.

An object of the present invention is to provide a drive device that can prevent overrun and cavitation from occurring due to load fluctuations of an oil motor.

(Means for Solving the Problems) In the present invention, an orifice is interposed in the return circuit returning from the oil motor to the tank, and the pump displacement control device of the variable displacement hydraulic pump that supplies the flow rate to the oil motor is controlled by the pump displacement control device of the variable displacement hydraulic pump that supplies the flow rate to the oil motor. A pilot circuit is provided that guides the discharge pressure to reduce the pump capacity, and when the pressure difference across the orifice exceeds a set value, the pilot circuit is activated to open the pilot circuit and when the pressure difference is below the set value. In order to increase the pump capacity, a pilot valve is interposed to discharge oil from the pump capacity control device into a tank, and a return circuit between the orifice and the oil motor is connected to the primary side of the oil motor via a check valve. By doing so, the above problem was solved.

(Function) When the oil motor is rotated at a constant rotation speed by a variable displacement hydraulic pump, for example, when a refrigerating car compressor is rotated at a constant rotation speed by the oil motor, the clutch between the oil motor and the compressor is disengaged. The oil motor attempts to overrun due to a sudden load reduction, but since an orifice is provided in the return circuit of the oil motor to the tank, back pressure is generated in the fluid flowing out of the oil motor, causing the oil to overrun. Motor overrun can be controlled. If the orifice still cannot prevent overrun, the return circuit between the orifice and the oil motor is connected to the primary side of the oil motor via the check valve. Since the flow rate returns from the return circuit to the primary side of the oil motor, cavitation can be prevented from occurring.

(Embodiment) An embodiment of the present invention will be explained with reference to FIG. 2. In the figure, reference numeral 1 is an oil motor, 2 is a return circuit from the oil motor 1 to the tank 3, and 4 is a return circuit to the return circuit 2. orifice 5 is a variable displacement hydraulic pump equipped with a pump displacement control device 6;
is an engine that drives the pump 5, and 8 is a pump discharge circuit.

The pump displacement control device 6 has the same configuration as the conventional one, and includes a small-diameter control piston 6a to which the pressure of a spring and pump discharge circuit 8 acts, and a large-diameter control piston 6b to which the pressure of the pilot circuit 9 acts. If the force acting on the control piston 6a is greater than the force on the control piston 6b, for example, the tilting of the cylinder block is controlled so that the pump capacity of the pump 5 becomes larger, and vice versa, the force acting on the control piston 6a is When this becomes dominant, the pump capacity is controlled to be reduced.

The pilot circuit 9 is provided with a pilot valve 13 that is switched when the force due to the difference between the pressure in front and the rear of the orifice 4 guided through the circuits 10 and 11 becomes larger than the force set by the spring 12.
When this is switched, the pump discharge pressure from the discharge circuit 8 acts on the control piston 6b via the pilot circuit 9, and control is performed to reduce the pump displacement.

Further, a connection circuit 16 is provided which connects the return circuit 2 between the oil motor 1 and the orifice 4 to the primary side of the oil motor 1. A check valve 15 is provided so that it can be returned to the next side. Reference numeral 14 indicates a compressor of the refrigerating vehicle driven by the oil motor 1. Usually, the compressor 14 is rotated at 1500 to 1800 rpm to obtain the best efficiency.

When the temperature inside the freezer reaches a predetermined temperature, the compressor 14 is disconnected from the oil motor 1 by the clutch, and as a result, the load on the oil motor 1 is greatly reduced. When the rotational speed of the engine 7 increases due to a reduction in load and the flow rate of the pump discharge circuit 8 increases, the differential pressure across the orifice 4 increases as in the case of the conventional example shown in FIG. The pilot valve 13 operates to cause the pump displacement control device 6 to perform a control operation to reduce the pump displacement, and the flow rate is maintained such that the pressure difference across the orifice 4 balances the force of the spring 12 of the pilot valve 13, that is, the set constant value. Reduce pump capacity until flow rate is reached. However, if the load fluctuates rapidly, the rotation speed cannot be maintained constant simply by controlling the pump capacity due to the inertia of the oil motor 1 itself, resulting in overrun of the oil motor 1 and cavitation. .

In the case of the present invention, the occurrence of such overrun and cavitation conditions is prevented in the following manner. That is, in the overrun state, the flow rate discharged from the oil motor 1 increases, but even if the flow rate is to be increased, the orifice 4 is provided in the return circuit 2 and the passage resistance is increased, so the oil motor 1 The back pressure increases and applies a braking action to the oil motor 1, and at the same time the differential pressure across the orifice 4 increases, so the pilot valve 13 causes the pump displacement control device 6 to reduce the pump flow rate to suppress the increase in differential pressure. As a result, overrun of the oil motor 1 can be suppressed and the rotation speed can be maintained at a constant speed. Also, if the load on the oil motor 1 decreases greatly, the orifice 4
It is thought that the resistance of the motor 1 is insufficient, resulting in an overrun to some extent, but even if an overrun occurs, if the cavitation state occurs, that is, the pressure on the primary side of the motor 1 becomes lower than the pressure in front of the orifice 4 of the return circuit 2, the connection will be interrupted. The check valve 15 of the circuit 16 is opened to prevent cavitation from occurring. Also, at this time, the differential pressure across the orifice 4 increases due to the overrun condition, so the pilot valve 13 guides the pump discharge pressure to the piston 6b of the pump displacement control device 6 to try to control the pump displacement to the minimum. However, since the pump discharge pressure is approximately zero and the force to actuate the piston 6b is weak, the pump displacement control device 6 operates to maximize the pump displacement using the spring of the other piston 6a, so the pump discharge amount increases. This reduces the occurrence of cavitation.

(Effects of the invention) As described above, according to the invention, in the oil motor drive circuit where load fluctuations are large, an orifice is installed in the return circuit from the oil motor to the tank to operate the pilot valve that controls the pump displacement. Since the orifice is arranged to provide back pressure to the oil motor to prevent its overrun, the return circuit between the orifice and the oil motor can be connected to one of the oil motors via a check valve. Since it is connected to the next side, cavitation can be prevented even if the orifice cannot prevent overrun, and its configuration is simple and inexpensive to manufacture, and it can control the rotation speed of the oil motor at a constant speed. It has the effect of not interfering with

[Brief explanation of drawings]

FIG. 1 is a diagram of a conventional example, and FIG. 2 is a diagram of an embodiment of the present invention. 1...Oil motor, 2...Return circuit, 3...
Tank, 4... Orifice, 5... Variable displacement hydraulic pump, 6... Pump capacity control device, 9... Pilot circuit, 13... Pilot valve, 15...
Check valve.

Claims (1)

[Scope of utility model registration request] A pilot circuit is provided in which an orifice is interposed in the return circuit returning from the oil motor to the tank, and the discharge pressure of the pump is guided to the pump displacement control device of the variable displacement hydraulic pump that supplies flow to the oil motor to reduce the pump displacement. The pump displacement control device operates to open the pilot circuit when the pressure difference before and after the orifice exceeds a set value, and to increase the pump capacity when the pressure difference is less than the set value. A drive circuit device for an oil motor subject to large load fluctuations, comprising a pilot valve for discharging oil into a tank, and a return circuit between the orifice and the oil motor connected to the primary side of the oil motor via a check valve.