JPH05340403A - Hydraulic system - Google Patents

Abstract

PURPOSE:To control the revolution of a hydraulic motor almost constantly by controlling an oil quantity to be fed to the hydraulic motor to a proper one even if a temperature of oil being discharged out of a hydraulic pump is varied to some extent. CONSTITUTION:A fixed displacement hydraulic motor 23 is connected to a variable displacement, hydraulic pump 21 via a main oil passage 22 and, in turn, a compressor 24 is connected to this motor 23. In addition, the main oil passage 22 and a capacity controlling cylinder 19 of the pump 21 are interconnected to each other by a control passage 25. In succession, each hydraulic pressure in front and in the rear of a throttle 28 interposed in a main oil passage 22A downstream of the motor 23 is made to act on a capacity control valve 26 through both first and second pilot oil passages P1 and P2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic system for a vehicle equipped with an air conditioning compressor.

[0002]

2. Description of the Related Art A conventional hydraulic system shown in FIG. 6 has been proposed. In this system, a constant displacement hydraulic motor 43 is connected to a discharge port of a variable displacement hydraulic pump 41 rotated by an engine or the like via a main oil passage 42. A compressor 44 of a cooling device is connected to the output shaft of the hydraulic motor 43. Variable displacement hydraulic pump 41
Is provided with a control cylinder 46 that constitutes a pump discharge capacity control mechanism 45. Further, the hydraulic motor 43
The oil pressure before and after the throttle 48 interposed in the main oil passage 42 on the upstream side of the valve acts on the control cylinder 46 through the pilot oil passages 49 and 50 and the capacity control valve 47. Then, when the rotation speed of the hydraulic pump 41 changes due to the fluctuation of the engine rotation speed, the amount of oil supplied to the constant displacement hydraulic motor 43 is controlled to be substantially constant, and the rotation speed of the compressor 44 is controlled to be constant. Is becoming

[0003]

In the above hydraulic system, since the throttle 48 is provided in the main oil passage 42 between the hydraulic pump 41 and the motor 43, the kinematic viscosity of the oil increases as the temperature of the oil rises. Due to the decrease, the volumetric efficiency of the hydraulic motor 43 decreases. That is, when the temperature of the oil supplied to the hydraulic motor 43 rises, the amount of oil leaked from the drain passage 51 provided for protecting the motor 43 to the oil tank increases, and the discharge flow rate of the hydraulic pump 41 becomes constant. Even if there is, the actual rotation speed of the hydraulic motor 43 decreases. For this reason, the rotation speed of the compressor 44 by the hydraulic motor 43 fluctuates as the oil temperature fluctuates, the cooling capacity also fluctuates, and stable air conditioning operation cannot be performed.

An object of the present invention is to solve the above problems existing in the prior art and to control the amount of oil supplied to the hydraulic motor to an appropriate amount even if the temperature of the oil discharged from the hydraulic pump fluctuates. An object of the present invention is to provide a hydraulic system capable of controlling the rotational speeds of a hydraulic motor and a compressor to be substantially constant.

[0005]

Therefore, according to the present invention,
A variable displacement hydraulic pump having a pressure sensitive displacement variable mechanism,
A constant displacement hydraulic motor interposed on the main oil passage of the variable displacement hydraulic pump, a compressor for a cooling device rotated by the constant displacement hydraulic motor, and a main oil passage on the upstream side of the hydraulic motor, A control passage that communicates with the control chamber of the pressure-sensitive displacement control mechanism and supplies a control hydraulic pressure from the main oil passage to the control chamber; and a control hydraulic pressure that is interposed on the control passage and is supplied to the control chamber. A displacement control valve is provided for controlling the discharge displacement of the hydraulic pump to be substantially constant by adjustment.

Further, the capacity control valve is provided corresponding to the valve body for opening and closing the control passage, and the first and the second for adjusting the opening degree of the control passage by the valve body. A pressure sensing chamber, a throttle interposed in the main oil passage on the downstream side of the hydraulic motor, and first and second pilots for guiding the hydraulic pressure before and after the throttle to the first and second pressure sensing chambers. And an oil passage.

[0007]

According to the present invention, when the variable displacement hydraulic pump is operated and oil is supplied from the main oil passage to the hydraulic motor, the hydraulic motor is rotated and the compressor is driven. The oil discharged from the hydraulic motor is returned from the main oil passage to the oil tank through the throttle. The hydraulic pressure before and after the throttle acts on the first and second pressure-sensitive chambers of the displacement control valve through the first and second pilot oil passages, the opening of the control passage by the valve body is adjusted, and the displacement control mechanism is controlled. The hydraulic pressure to the chamber is adjusted, the discharge capacity of the hydraulic pump is controlled to be substantially constant, and the rotation speed of the compressor is controlled to be constant.

Further, according to the present invention, the temperature of the oil supplied to the hydraulic motor fluctuates during the operation of the hydraulic system, and the fluctuation of the kinematic viscosity thereof fluctuates the amount of oil leaked from the protective drain passage of the hydraulic motor. Even if the hydraulic pressure before and after the throttle based on the amount of oil actually discharged from the outlet of the hydraulic motor is applied to the first and second pressure sensitive chambers of the displacement control valve to control the displacement of the hydraulic pump, Also, the number of revolutions of the compressor can be controlled to be constant regardless of the temperature fluctuation of the oil.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment embodying the present invention will now be described with reference to FIG.
~ It demonstrates based on FIG. As shown in FIG. 3, the front housing 2 is joined and fixed to the front (left) end surface of the center housing 1 of the variable displacement swash plate type hydraulic pump used in this hydraulic system, and the rear (right) of the center housing 1 is fixed.
A rear end cover 3 is joined and fixed to the end surface, and a crank chamber 4 is formed inside them. A rotary shaft 5 is supported between bearings 6 and 7 between the opposed end walls of the front housing 2 and the end cover 3, and is used as a power supply source by a power take-out device (PTO) (not shown) connected to the outer ends of the rotary shaft 5. It is designed to be directly rotated by the engine E, etc.

A cylinder block 8 is attached to the rotary shaft 5.
Are connected by a spline so that they can rotate synchronously,
A plurality of cylinder bores 9 are formed in the cylinder block 8 in parallel with the rotary shaft 5. A piston 12 moored to a swash plate 11 via a shoe 10 is housed in each of the cylinder bores 9 so as to be capable of reciprocating. or,
A cylinder bore 9 in a cylinder block 8 that rotates integrally with the rotating shaft 5 is alternately communicated with an arc-shaped suction port 14 and discharge port 15 that are provided through the valve plate 13 and have an arc shape. As a result, the hydraulic oil is sucked into the cylinder bore 9 from the suction port 14, and the hydraulic oil in the cylinder bore 9 is discharged from the discharge port 15. A suction passage 16 and a discharge passage 17 which communicate with the suction port 14 and the discharge port 15 are formed in the rear end cover 3.

Due to the return spring 18, the swash plate 11 always has a minimum inclination angle (about 0.1 to 4 °) equal to zero capacity.
It is biased in the direction of displacement to the minimum capacity position. A control cylinder 19 which constitutes a pressure-sensitive capacity variable mechanism is cantileveredly supported on the rear end cover 3, and a control piston 20 is reciprocally movable in the cylinder 19 in parallel with the rotary shaft 5 in the same direction. It is housed. The tip surface of the control piston 20 pushes the swash plate 11 to move it.
The stroke of the piston 12 is changed and the discharge capacity is adjusted by pushing the tilt angle of the piston in a direction in which it increases against the elastic force of the return spring 18. Therefore, since the control chamber 19a in the control cylinder 19 is at atmospheric pressure when the hydraulic circuit is stopped, the swash plate 11 is at the minimum displacement position in FIG. Urged to hold. Reference numeral 2a is a stopper that regulates the maximum tilt angle of the swash plate 11.

Next, the construction of the entire hydraulic system using the minimum displacement start-up type piston pump 21 constructed as described above will be explained with reference to FIG. In the discharge passage 17 of the piston pump 21, a protective drain passage 23a is provided via a main oil passage 22.
Is connected to a constant capacity oil motor 23. A compressor 24 of a cooling device is connected to an output shaft of the motor 23.

The main oil passage 22 and the control chamber 19a of the control cylinder 19 are connected by a control passage 25. A capacity control valve 26 is connected in the middle of the control passage 25.

A casing 27 for accommodating the capacity control valve 26 is joined and fixed to a side surface of the rear end cover 3 as shown in FIG. A discharge passage 27a connected to the discharge passage 17 is formed in the casing 27. Further, the discharge passage 27a and the control chamber 19a are communicated with each other by the control passage 25, and the capacity control valve 2
6 is interposed.

As shown in FIG. 4, a spool 29 as a valve element is accommodated in the spool accommodating chamber 27b of the casing 27 so as to be linearly movable back and forth. The spool 29 is formed with first and second large diameter portions 29a and 29b, and an annular groove 29c is formed between the large diameter portions. A first pressure sensing chamber R1 is formed on the left side of the spool accommodating chamber 27b, and the pressure sensing chamber R1 is located upstream of the throttle 28 interposed in the main oil passage 22A downstream of the constant displacement hydraulic motor 23. It is connected to the main oil passage 22A via a first pilot oil passage P1. Further, a second pressure sensing chamber R2 is formed on the right side of the spool accommodating chamber 27b, and the spool 2 is formed inside the second pressure sensing chamber R2.
A spring 30 for biasing 9 is interposed. This spring 30
As a result, the spool 29 is urged in the direction of opening the control passage 25 and closing the drain passage 33. The second pressure sensing chamber R2 communicates with the main oil passage 22A on the downstream side of the throttle 28 via the second pilot oil passage P2.

In this embodiment, the discharge capacity of the pump 21 will be described later by causing the differential pressure across the throttle 28 to act on the first and second pressure sensitive chambers R1 and R2 of the capacity control valve 26. It is controlled so as to be constant.

As shown in FIG. 1, the control passage 25 has an open circuit port 3 for supplying pressure oil to the capacity control valve 26.
1a and a drain port 31b are provided with a switchable electromagnetic switching valve 31. The switching valve 31 is switched by an air conditioner switch 32.

Although not shown in this embodiment, an oil filter, an oil cooler, a high pressure cut switch and the like are provided. Next, the operation of the hydraulic system configured as described above will be described.

Now, when the minimum displacement start-up type piston pump 21 is stopped, the pressure in the main oil passages 22 and 22A has dropped to the atmospheric pressure. Therefore, as shown in FIGS. The inclination angle of is minimized by the return spring 18. The spool 29 of the capacity control valve 26 is held by a spring 30 at a position where the control passage 25 is opened. Further, the air conditioner switch 32 is turned off and the electromagnetic switching valve 31
Is held by the drain port 31b, the communication between the control chamber 19a of the control cylinder 19 and the main oil passage 22 is cut off.

When the pump 21 is started by the engine E in this state, the amount of oil sent to the main oil passage 22 of the pump 21 becomes the minimum capacity which is almost zero. Since this small amount of pressure oil is returned to the oil tank T from the drain port 31b of the electromagnetic switching valve 31, the hydraulic motor 23 does not rotate and the compressor 24 is in a stopped state.

Here, the air conditioner switch 32 is turned on and the electromagnetic switching valve 31 is opened as shown in FIG.
When switched to a, the displacement control valve 26 is opened, so the discharge pressure oil in the main oil passage 22 that has risen to the minimum capacity acts on the control chamber 19a of the control cylinder 19 through the control passage 25. Then, the tilt angle of the swash plate 11 is increased by the control piston 20 in FIG. 3, and the discharge capacity of the pump 21 is increased as shown in FIG.

A hydraulic pressure corresponding to the amount of oil actually discharged from the hydraulic motor 23 is generated in the main oil passage 22A before and after the throttle 28 on the downstream side of the motor 23. This hydraulic pressure is passed through the first and second pilot oil passages P1 and P2 to the first and second pilot oil passages.
Of the pressure sensitive chambers R1 and R2. Therefore, the capacity control valve 2
The spool 29 of No. 6 is moved and adjusted to a position in which the differential pressure acting on the front and rear thereof and the biasing force of the spring 30 are balanced.
The opening degree of the control passage 25 is adjusted. That is, the pump 2
When the discharge amount of 1 increases and the differential pressure increases, the pressure of the first pressure sensing chamber R1 in FIG. Since the hydraulic pressure is reduced, the inclination angle of the swash plate 11 is reduced and the discharge capacity of the pump 21 is reduced. On the contrary, when the pump discharge capacity decreases and the differential pressure decreases, the spool 29 increases the opening of the control passage 25 and increases the control hydraulic pressure acting on the control cylinder 19 in FIG. The angle is increased and the discharge capacity of the pump is increased. By repeating this operation, the oil amount to the hydraulic motor 23 is controlled to be substantially constant, and the rotation speed of the compressor 24 is maintained constant.

At this time, even if the temperature of the oil supplied to the hydraulic motor 23 fluctuates and the amount of oil leaked from the protective drain passage 23a of the hydraulic motor 23 fluctuates due to the fluctuation of the kinematic viscosity, the hydraulic motor 23 also fluctuates. Since the hydraulic pressure around the throttle 28 based on the amount of oil actually discharged from the outlet of the hydraulic pump 21 is applied to the first and second pressure sensitive chambers R1 and R2 of the displacement control valve 26 to control the displacement of the hydraulic pump 21, The rotation speeds of the motor 23 and the compressor 24 can be controlled to be constant irrespective of oil temperature fluctuations.

Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, a variable displacement hydraulic pump 35 that is activated at maximum capacity is used as a hydraulic pump, and an electromagnetic clutch 36 is interposed between the pump 35 and the engine E. Further, the electromagnetic switching valve 3 of the first embodiment
1, the air conditioner switch 32 is connected to the electromagnetic clutch 36. Further, the capacity control valve 37
As the spring 29, the spool 29 is always held in the drain passage 33 by the spring 30 and is held in the closed position of the control passage 25.

Therefore, when the electromagnetic clutch 36 is turned on by the air conditioner switch 32 and the hydraulic pump 35 is started by the engine E at the maximum capacity, the oil discharged from the pump 35 is sent to the hydraulic motor 23 and The motor is rotated and the compressor 24 is started. Also, the hydraulic motor 23
The oil discharged from the main oil passage 22A is returned to the oil tank T through the throttle 28. At this time, the pressure before and after the throttle 28 is applied to the capacity control valve 37 by the first and second pilot oil passages P1,
It acts on the first and second pressure sensitive chambers R1 and R2 through P2, the amount of oil discharged from the pump 35 is adjusted according to the differential pressure, and the amount of oil discharged from the pump 35 is controlled to be constant.

Also in this second embodiment, since the throttle 28 is provided in the main oil passage 22A on the downstream side of the motor 23, the proper amount of oil required to rotate the hydraulic motor 23 constant even if the temperature of the oil fluctuates. Can be controlled.

The present invention is not limited to the above embodiment, but can be embodied as follows. (1) Instead of the control cylinder 19, for example, a bellows type pressure-sensitive variable capacity mechanism (not shown) is used.

(2) In the above embodiment, the spool 29 is biased by the spring 30 in the direction to open or close the control passage 25. However, the spring 30 is omitted and the spool 29 is moved to the first position.
And a diaphragm (not shown) operated by the pressure of the second pressure sensitive chambers R1 and R2.

[0029]

As described in detail above, according to the present invention, even if the temperature of the oil discharged from the hydraulic pump fluctuates, the amount of oil supplied to the hydraulic motor is controlled to a proper amount and the rotational speed of the hydraulic motor is controlled. Can be controlled to be substantially constant, fluctuations in the rotation of the compressor can be suppressed, and the cooling capacity can be stabilized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an air conditioner stopped state of a hydraulic system according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an air conditioner operating state of the hydraulic system.

FIG. 3 is a sectional view of a variable displacement hydraulic pump.

FIG. 4 is a sectional view showing an open state of the capacity control valve.

FIG. 5 is a hydraulic circuit diagram showing an air conditioner stop state according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional hydraulic system.

[Explanation of symbols]

11 Swash Plate, 17 Discharge Path, 19 Control Cylinder Constituting Pressure Sensitive Capacity Variable Mechanism, 19a Control Chamber, 20 Control Piston 21, 35 Variable Capacity Hydraulic Pump, 22
Main oil passage, 22A Main oil passage downstream of hydraulic motor, 23
Constant displacement hydraulic motor, 23a protective drain passage, 24
Compressor, 25 control passages, 26 capacity control valve, 28
Throttle, 29 Spool as valve body, R1 first pressure sensing chamber, R2 second pressure sensing chamber, P1 first pilot oil passage, P2
Second pilot oil passage, T oil tank.

Claims (1)

[Claims] 1. A variable displacement hydraulic pump having a pressure sensitive variable displacement mechanism, a constant displacement hydraulic motor interposed on a main oil passage of the variable displacement hydraulic pump, and rotated by the constant displacement hydraulic motor. A control for connecting a compressor for a cooling device, a main oil passage on the upstream side of the hydraulic motor, and a control chamber of the pressure-sensitive capacity variable mechanism to supply control hydraulic pressure from the main oil passage to the control chamber. A passage, and a displacement control valve interposed on the control passage and adjusting the control oil pressure to the control chamber to control the discharge displacement of the hydraulic pump to be substantially constant. A valve body that opens and closes, first and second pressure-sensitive chambers that are provided corresponding to the valve body and that adjust the opening of the control passage by the valve body, and main oil on the downstream side of the hydraulic motor. The throttle interposed in the road and the hydraulic pressure before and after this throttle Serial first and second first and second for guiding creel into the pressure sensitive chamber of the hydraulic system is constituted by a pilot oil passage.