JPH05256255A - Hydraulic system - Google Patents

Abstract

PURPOSE:To smoothly perform a transfer from minimum displacement operation to maximum displacement operation by starting a pump always from minimum displacement equal to zero, suppressing riseup torque, attaining power saving, omitting a cutoff mechanism of input of clutch or the like, and also surely supplying pressure oil to a control cylinder for increasing displacement at the time of starting cargo handling operation. CONSTITUTION:A cargo handling switching valve 23 and a cargo handling actuator 24 are connected to a delivery passage 17 of a variable displacement swash plate type piston pump 21 through a delivery pipe line 22. A control cylinder 19 is actuated by pressure oil supplied from the delivery pipe line 22 through a control pipe line 25, and a swash plate 11 energized to a minimum displacement position by a reset spring 18 can be press-moved to a maximum displacement position. A variable throttle valve 39, quickly increasing a pressure of control oil to the control pipe line 25 thereafter enlarging the delivery passage 22 at the time of starting cargo handling work, is provided on the halfway of the delivery pipe line 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic system widely used in various industrial machines, industrial vehicles and the like, and more particularly to a hydraulic system including a variable displacement swash plate type piston pump equipped with a swash plate tilt angle adjusting mechanism.

[0002]

2. Description of the Related Art Conventionally, as a swash plate type variable displacement piston pump, one disclosed in Japanese Utility Model Laid-Open No. 60-19776 has been proposed. In this pump, the piston in the cylinder block that rotates integrally with the rotating shaft reciprocates for a distance according to the tilt angle of the swash plate, and the suction port and discharge port on the valve plate that are in sliding contact with the cylinder block. The hydraulic oil is sucked and discharged through the. or,
The tilting angle of the swash plate is always urged by a return spring to a maximum direction, and when a control cylinder for changing the tilting angle of the swash plate is operated by high-pressure hydraulic oil in the discharge passage, the swash plate is moved. Is controlled so as to decrease its inclination angle, and the discharge volume can be adjusted to the minimum volume.

[0003]

However, in the pump having the above-mentioned structure, the return spring is arranged so as to bias the swash plate tilt angle in the increasing direction, and when the operation is stopped, each sliding gap of the cylinder block is increased. Since the discharge system pressure decreases due to the leakage of pressure oil through the control cylinder, the opposing force by the control cylinder disappears and the swash plate remains stationary with the maximum inclination angle due to the elastic force of the return spring. Therefore, there is an unavoidable defect that the starting torque becomes extremely large as a result of the pump being started at the maximum swash plate inclination angle, that is, the maximum capacity during the next operation. Moreover, since the pump cannot obtain the operating hydraulic pressure of the control cylinder, it is impossible to continue the operation of a very small capacity with the swash plate tilt angle kept near 0 °. When there is no load, a clutch mechanism is provided to shut off the input to the pump. There is a need to.

Particularly, in a transmission system of a pump used for a cargo handling device of a specially equipped vehicle such as a dump truck, a transmission shaft and an electromagnetic clutch interposed between a power take-off device (PTO) attached to an automatic transmission and the pump. However, the configuration is complicated and the cost is increased.If the electromagnetic clutch is omitted and the power take-off device is turned on and off to directly control the drive of the pump, the power take-out device is connected and disconnected. Along with this, the range switching of the shift lever must be frequently repeated, and inevitably the operation becomes complicated.

An object of the present invention is to solve the problems existing in the above-mentioned prior art, and to achieve substantial capacity control of the pump in operation by simply turning on / off the switch such as a cargo handling command. Another object of the present invention is to provide a hydraulic system capable of promptly switching the capacity of the pump from the minimum capacity to the maximum capacity during the switching operation from the non-loading state to the loading state with such a configuration.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has a return spring for urging a swash plate in a direction in which the inclination angle of the swash plate is always reduced to reduce the capacity, and the return spring facing the return spring. A variable displacement swash plate type piston pump directly connected to a power supply source, which has a control cylinder for urging in a direction of increasing the tilt angle to increase the displacement, and a discharge pipe connecting a discharge port of the pump and an actuator. Passage, a cargo handling switching valve provided in the middle of the discharge pipeline, a control pipeline that communicates the discharge pipeline and the control chamber of the control cylinder to supply pressure oil to the control cylinder, and the discharge pipeline Is provided in the discharge pipeline downstream of the connection point between the control pipeline and the control pipeline, and is constantly urged by a biasing spring in a direction that reduces the passage area of the discharge pipeline, and Increases the passage area against the elastic force of the biasing spring It is constituted by a variable throttle valve that is pressed in the direction.

[0007]

According to the present invention, by taking the above means, when the actuator is at rest, even if the pump is driven, there is almost no pressure increase in the discharge pipe line directly connected to the oil tank, and the control cylinder does not substantially function. The swash plate replaces the clutch (off) function by keeping the minimum tilt angle (about 0.1 to 4 °) equal to zero capacity. Further, in this state, the variable throttle valve is in a state where the passage area of the discharge pipe is held by the biasing spring at a position where the throttle is maximized.

When oil supply to the actuator is started by operating the cargo handling switching valve from this state, the pressure in the discharge pipe line rises based on the operating load, and the pressure oil is supplied to the control cylinder via the control pipe line. Then, the movement of the control piston is promoted, and the swash plate is biased in the direction of increasing the inclination angle. At this time,
Since the passage area of the discharge pipeline is throttled by the variable throttle valve, the hydraulic pressure of the discharge pipeline upstream of the variable throttle valve increases rapidly, and therefore the control hydraulic pressure from the control pipeline to the control chamber of the control cylinder increases. However, the pump quickly and surely rises from the minimum capacity equal to zero, and when the swash plate reaches the maximum inclination angle, the pump is rapidly shifted to the steady operation of the maximum capacity.

In this steady operation state, the pressure of the hydraulic oil flowing in the discharge pipe line rises according to the cargo handling load, and the momentum due to the increase in the flow rate also acts.
The variable throttle valve is moved in the direction of increasing the area of the discharge conduit against the elastic force of the biasing spring, and does not hinder the supply of hydraulic oil in the steady operation state.

Further, when the work such as cargo handling is completed and the oil supply to the actuator is substantially stopped, the pressure in the discharge pipe line is reduced and the inner peripheral surface of the control cylinder and the outer peripheral surface of the control piston slide. Along with the leakage of pressure oil through the gap and the leakage of pressure oil from the reflux orifice or the like provided in the control cylinder, the control pressure in the control cylinder that was biased in the direction of increasing the swash plate inclination angle decreases, As a result, the swash plate, which is bent by the elastic force of the return spring, is gradually displaced toward the inclination angle reducing side, and the pump is shifted to the minimum capacity equal to zero while continuing the operation. At the same time, the biasing spring moves the variable throttle valve in the direction of increasing the throttle amount.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic system embodying the present invention will be described below with reference to FIGS.

FIG. 1 shows the construction of a hydraulic system in which the present invention is applied to an industrial vehicle. As a variable displacement hydraulic pump 21 driven by an engine E, a swash plate type piston pump is used. This piston pump will be described with reference to FIG. 5. The front housing 2 is joined and fixed to the front (left) end surface of the center housing 1,
A rear end cover 3 is joined and fixed to a rear (right) end surface of the center housing 1, and an operating space 4 is formed inside them. A rotating shaft 5 is supported by a bearing 6 between the opposed end walls of the front housing 2 and the end cover 3, and is directly rotated by an engine E or the like by a power take-out device (PTO) (not shown) connected to the outer end of the rotating shaft 5. It is supposed to be done.

A cylinder block 8 is attached to the rotary shaft 5.
Are connected by a spline for synchronous rotation,
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 accommodated 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 10 from the suction port 14, and the hydraulic oil in the cylinder bore 10 is discharged from the discharge port 15. A suction passage 16 and a discharge passage 17 that 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 tilt angle (about 0.1 to 4 °) equal to zero capacity.
It is biased in the direction of displacement to the minimum capacity position. The rear end cover 3 has a control cylinder 19
Is supported in a cantilever manner, and a control piston 20 is housed in the cylinder 19 so as to be capable of reciprocating in the same direction as the rotating shaft 5, and its tip end surface pushes a sphere moored to a part of the swash plate 11. The piston 1 is moved by pushing the tilt angle of the swash plate 11 in a direction to increase the tilt angle against the elastic force of the return spring 18.
The stroke 2 can be changed to adjust the discharge volume. Accordingly, since the control chamber 19a in the control cylinder 19 is at atmospheric pressure when the hydraulic circuit is stopped, the elastic force of the return spring 18 causes the swash plate 11 to have a minimum displacement position where the inclination angle becomes minimum in FIG. Urged to hold.

Further, as shown in FIG. 1, a cargo handling switching valve 23 is connected to the discharge passage 17 of the variable displacement type swash plate type piston pump 21 configured as described above through a discharge pipe line 22. The cargo handling switching valve 23 includes a cargo handling actuator 24.
Are connected. The suction passage 16 and the cargo handling switching valve 23 are connected to the oil tank T.

Further, the discharge passage 17 and the control chamber 19a of the control cylinder 19 are communicated with each other by a control pipe 25 provided in the end cover 3, and a pressure control valve 26 is interposed in the middle thereof to control from the discharge pipe 22. The amount of control oil supplied to the chamber 19a is controlled. This pressure control valve 26
2, has a spool 27 reciprocally accommodated in a spool chamber 3a provided in the end cover 3, and the control conduit 25 can be opened by an annular groove 28 formed on the outer periphery of the spool 27. Has become. Also, spool 2
The large-diameter portion 29 formed on the outer periphery of the control valve 7 allows the control conduit 25 to be closed continuously. Further, the back pressure chamber 30 formed by the right end surface of the spool 27 and the spool chamber 3a is connected to a control conduit 25 on the downstream side of the spool 27 by a communication passage 31.

The rear end cover 3 has a spool chamber 3
A lid 32 for sealing a is screwed, and a spring 33 is interposed between the lid 32 and a spring receiving plate 34 connected to one end surface of the spool 27, and always biases the spool 27 to the open circuit position. ing. The spool 27 is operated by the control pressure P _C introduced into the back pressure chamber 30 from the control pipe 25 through the communication passage 31 and the elastic force of the counter spring 33, and the control pressure P _C is set to a set value. When it exceeds the control pressure, the spool 27 continuously reduces and closes the opening of the control pipe 25, and the control pressure P
_It regulates the upper limit of _C. 1 and 5, reference numeral 2a is a stopper that regulates the maximum tilt angle of the swash plate 11.

As shown in FIG. 1, the discharge conduit 22 has a discharge conduit 22 at the time of switching from the unloaded condition to the loaded condition.
A variable throttle valve 39 for interposing a high hydraulic pressure from the control line 25 to the control chamber 19a of the control cylinder 19 is interposed so as to efficiently increase the initial pressure inside. An example of the variable throttle valve 39 will be described with reference to FIG. 3. A casing 40 is joined and fixed to the side surface of the rear end cover 3 in correspondence with the discharge passage 17, and the discharge passage 40a has an end portion of the discharge pipe 22. Are connected. A spool 42 is accommodated in a housing chamber 40b formed in the lower portion of the casing 40 so as to be capable of reciprocating in the vertical direction so as to increase or decrease the passage area of the discharge passage 40a. It is urged upward so that the area is minimum). Further, a spline protrusion 42a extending in the vertical direction is formed on the outer peripheral surface of the spool 42, and is accommodated movably only in the vertical direction along a spline groove 40c formed in the accommodating chamber 40b. Further, an inclined surface 42b for pressure reception, which is directed toward the discharge passage 17, is formed at the tip of the spline-fitted spool 42.

Next, the operation of the vehicle hydraulic system configured as described above will be described. As shown in FIG. 1, when the actuator 24 in which the cargo handling switching valve 23 is switched to the non-cargo handling position is at rest (non-cargo handling), even if the pump 21 is driven together with the engine E, the discharge pipe line 22 directly connected to the oil tank T is provided. The rise of the discharge pressure P _d is low. This pressure is set to the set pressure P ₁ during non-loading shown in FIG. 6, that is, because the cargo handling switching valve 23 provided in the discharge conduit 22 is actuated, the pressure is maintained at several atmospheric pressure even during non-loading. Further, in this non-loading state, although the spool 27 of the pressure control valve 26 maintains the normal position (open position) by the elastic force of the spring 33, it is lower than the set pressure P ₁ during non-loading shown in FIG. Since it is lower than the set pressure P ₂ of the control pressure P _C required for switching from the high non-cargo handling to the cargo handling state, the control cylinder 19 does not substantially function, and the swash plate 11 has zero capacity due to the elastic force of the return spring 18. The clutch (off) function is replaced by maintaining the minimum tilt angle (0.1 to 4 °) equal to. Therefore, the starting torque of the pump 21 is small,
It consumes less power.

When the loading 24 of the actuator 24 is started by operating the cargo handling switching valve 23 in this state, the discharge pressure P _d in the discharge conduit 22 rises based on the operating load, and at the same time, via the control conduit 25. Since the control pressure P _C supplied to the control cylinder 19 also increases, the control piston 20 moves forward against the elastic force of the return spring 18 to urge the swash plate to increase its tilt angle. That is, the pump 21 rises from the minimum capacity equal to zero, and when the control pressure P _C (= P _d ) reaches the switching set value P ₂ , the swash plate 11 shifts to the steady operation with the maximum tilt angle, that is, the maximum capacity, and the cargo handling work is performed. Done.

In this embodiment, as shown in FIG. 3, the discharge passage 40a near the downstream side of the control pipe 25 is provided with the variable throttle valve 39 for reducing the passage area of the discharge passage 40a in the non-loading state. When the cargo handling state is switched to the cargo handling state, the hydraulic pressure P _d in the discharge passage 17 sharply increases as shown in FIG. Therefore, the control pressure P _C acting on the control cylinder 19 also quickly reaches the switching set pressure P ₂ , and the swash plate 11 quickly moves from the minimum capacity position (non-loading state) to the maximum capacity position (loading state). And it can be reliably switched.

The amount Q of oil flowing through the discharge pipe line 22 in the non-load handling state shown in FIG.
It is obtained by multiplying _min by the idle speed n and dividing by 1000.

[0023]

[Equation 1] Q = (V _min × n) / 1000 Once the oil amount Q in the above formula is determined, the discharge pressure P _d is determined from the internal volume of the discharge passage 17, and this discharge pressure P _d is the control line 2
5 is supplied into the control chamber 19a of the control cylinder 19 and acts on the control piston 20 as a control oil pressure P _C.
Thus, the spring 43 for biasing the spool 42 in order to obtain the control piston 20 can be set control pressure P _C required for Susumudo as set pressure P _2, the set pressure P ₂ in a short time The elastic force of is set.

Further, when the swash plate 11 is switched to the maximum capacity position as shown in FIG. 5, the discharge amount becomes a large flow rate Q'as shown in FIG. 4, and this large flow rate Q'is changed.
9 acts on the spool 42, so that the spool 42 is retracted into the accommodation chamber 40b against the spring 43, and a sufficient discharge passage area is secured.

Next, the action of the pressure oil acting on the spool 42 will be described in detail. In FIG. 3, the mass flow rate of oil (Q × γ, where γ is the specific gravity of the oil) is the spool 42 per unit time. The force that hits the inclined surface 42b of the above acts as a load F. That is, the inclined surface 42b of the spool 42
A load F (= S × P _d ) obtained by multiplying the projected area S in the direction of oil flow by the pressure P _d acts on this. The load F is a component force f _a of the inclined surface 42b in the same direction and the normal direction, f _b, and the elastic force of the component force f _C spring 43 in the axial direction of the spool 42 about the component force f _b of which Spool 4 against
It becomes the force to push 2. This component force f _C does not act as a force to push the spool 42 in the retracted direction in the non-loading state, and after the pump 21 shifts to the loading state with the maximum capacity, the discharge pressure is P _{d as} shown in FIG. To P _d ′,
When the load F increases to F ′ and the component force f _C that pushes the spool 42 in the axial direction also increases to f _C ′, the spool 42 starts to retract while compressing the spring 43.

In the hydraulic system described above, the pipe volume of the discharge pipe line 22 is much larger than the discharge amount in the pump minimum capacity state. Therefore, if the variable throttle valve 39 is not used, as shown in FIG. As shown by the two-dot chain line, the time until the control pressure P _C reaches the set pressure P ₂ of several atmospheres becomes longer, or in some cases it is maintained even if the control pressure is insufficient or the control piston 20 is operated. As a result, there is a problem that the tilt angle of the swash plate 11 cannot be moved and held in the maximum capacity state. However, in this embodiment, the above problem can be solved by a simple configuration.

Further, in the cargo handling state, the discharge pressure P _d is further increased as shown in FIG. 6 due to the increase of the discharge flow rate of the pump 21 and the increase of the operating load of the actuator 24 which are influenced by the rotation speed of the engine E. When the control pressure P _{C applied} to the control cylinder 19 exceeds the set value P ₃ , the balance between the control pressure P _C applied via the communication passage 31 and the elastic force of the counter spring 33 is lost, and The spool 27 of the pressure control valve 26, which has been held in the normal position (open position) up to this time, continuously reduces its opening degree, and eventually operates to completely cut off the oil supply to the control cylinder 19 via the control line 25. Therefore, the upper limit of the control pressure P _C in the control cylinder 19 is reliably regulated, and unnecessary overload on the swash plate 11 and the like is skillfully avoided.

When the operation of the cargo-handling changeover valve 23 stops the oil supply to the actuator 24 after finishing the work such as cargo-handling,
With the drop of the discharge pressure P _d based on the release of the operating load,
The pressure control valve 26 is held in the original open position by the spring 33, and the control pressure P _C in the control chamber 19a that has been biased in the direction to increase the discharge pressure P _d and the swash plate inclination angle is as shown in FIG. It suddenly drops to over the switching setting pressure P ₂ to the non-cargo handling setting pressure P ₁ ,
The swash plate 11 which is bent by the elastic force of the return spring 18 is displaced toward the inclination angle reducing side, and the pump 21 shifts to the minimum capacity equal to zero while continuing the operation.

By the way, in the above cargo handling state,
The control pressure P _C in the control cylinder 19 is controlled by the pressure control valve 26.
Since the upper limit value of P is the set pressure P ₃ , the control pressure P _C is rapidly lowered during the switching operation from the cargo handling to the non-cargo handling state, and the response of the capacity switching is improved. When the pressure control valve 26 is omitted, the control pressure P _C becomes high as well as the discharge pressure P _d , so this high pressure leaks out to the set pressure P
_It takes longer to decrease to ₂ or less.

The present invention is not limited to the above embodiment, but can be embodied as follows. (1) As shown in FIG. 7, while accommodating the spool 44 having the throttle passage 44a inside the casing 40,
The spool 43 is always rotated in the direction in which the throttle amount is maximized.
The discharge passage 40a on the upstream side of the spool 44 and the pressure chamber 46 provided in the lower portion of the spool 44 are connected by the communication passage 45. Also in the case of this embodiment, at the time of switching from the non-cargo handling to the cargo handling state, the pressure P _{C of the} control oil supplied to the control conduit 35 can be quickly raised to perform the switching operation promptly and surely. Since the oil flows freely in the state where the throttle passage 44a corresponds to the discharge passage 40a during the cargo handling, the pressure loss can be suppressed.

(2) As shown in FIG. 8, a plate-shaped throttle valve 4
7 should always be urged by the spring 48 to a position where the throttle amount is maximized. (3) In the above embodiment, the pressure control valve 26 is replaced by the pump 21.
It was installed in the rear end cover 3 of the
Be configured separately from 1.

[0032]

As described in detail above, according to the present invention, since the substantial pump operation (discharge) is always started from the minimum capacity equal to zero, the start-up torque is small, the power saving and the extreme load are performed. In addition to suppressing fluctuations, the capacity under no load can be maintained at the minimum capacity equal to zero, so the input disconnecting mechanism such as the clutch can be omitted, and the switching operation from the non-loading state to the loading state can be performed quickly and reliably. be able to.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram in a non-loading state, which schematically illustrates a part of an embodiment of a hydraulic system according to the present invention.

FIG. 2 is a sectional view showing an example of a pressure control valve.

FIG. 3 is a sectional view showing an example of a variable throttle valve in a maximum throttle state.

FIG. 4 is a sectional view showing an example of a variable throttle valve in a minimum throttle state.

FIG. 5 is a vertical sectional view of a swash plate type variable displacement piston pump.

FIG. 6 is a graph showing the relationship between non-cargo handling and cargo handling operation time, and discharge pressure and control pressure.

FIG. 7 is a cross-sectional view showing another example of the variable throttle valve.

FIG. 8 is a sectional view showing another example of the variable throttle valve.

[Explanation of symbols]

11 swash plate, 18 return spring, 19 control cylinder, 1
9a control room, 21 variable displacement swash plate type piston pump,
22 discharge pipe, 23 cargo switching valve, 24 actuator, 25 control pipe, 26 pressure control valve, 27 spool, 30 back pressure chamber, 31 communication passage, 33 spring, 39 variable throttle valve, 42, 44 spool, 43, 48 Energizing spring, P _C control pressure, P ₁ non-loading setting pressure, P ₂ non-loading and switching setting pressure, E engine.

Claims (1)

[Claims] 1. A return spring for constantly reducing the tilt angle of a swash plate so as to reduce the capacity, and a return spring facing the return spring for increasing the tilt angle of the swash plate so as to increase the capacity. A variable displacement swash plate type piston pump having a control cylinder and directly connected to a power supply source, a discharge pipe line connecting a discharge port of the pump and an actuator, and a cargo handling switching provided in the middle of the discharge pipe line. A valve, a control pipeline for communicating pressure oil to the control cylinder by communicating the discharge pipeline with the control chamber of the control cylinder, and a discharge pipeline downstream of a connection point between the discharge pipeline and the control pipeline. Is provided in the passage and is always urged by the urging spring in a direction to reduce the passage area of the discharge pipeline, and the passage area is resisted against the elastic force of the urging spring by increasing the oil pressure flowing through the discharge pipeline. Hydraulic system consisting of a variable throttle valve that is pressed in an increasing direction .