JPH0794821B2 - Fluid control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is used in construction machinery and the like, in which a variable displacement pump and a fixed displacement control pump are driven by an engine, and variable by the fluid discharged from the control pump. The present invention relates to a fluid control device that controls a discharge amount control unit of a displacement pump to control a discharge amount of a variable displacement pump.

<Prior Art> Conventionally, there is a fluid control device of this type as shown in FIG. 4 (Japanese Utility Model Publication No. 52-6769). In this fluid control device, a variable displacement pump 2 and a fixed displacement control pump 3 are interlocked with an engine 1, the variable displacement pump 2 and a hydraulic motor 5 are connected by a main line 4, and the variable displacement pump 2 is connected. The swash plate control cylinder 7 for controlling the swash plate 6 and the control pump 3 are connected by a control line 9 provided with a servo valve 8 in the middle.

Then, in a state where the rotation speed of the engine 1 is maintained at the rated rotation speed (the rotation speed close to the maximum rotation speed above idling),
By controlling the inclination of the swash plate 6 of the variable displacement pump 2 by the servo valve 8 via the swash plate control cylinder 7, the discharge amount per one rotation of the variable displacement pump 2 is controlled,
The rotational speed of the hydraulic motor 5 is variably controlled.

<Problems to be Solved by the Invention> However, in the above-described conventional fluid control device, the variable displacement is performed by changing the inclination of the swash plate 6 by the servo valve 8 in a state where the rotation speed of the engine 1 is always maintained at the rated rotation speed. Shape pump 2
Therefore, even if the swash plate 6 of the variable displacement pump 2 is returned to the neutral position and the discharge amount is substantially zero, the engine 1 is rotating at the rated speed. However, there is a problem that the fuel consumption of the engine 1 increases and power loss is large.

Further, in the above-described conventional fluid control device, the discharge amount is controlled by changing the inclination of the swash plate 6 of the variable displacement pump 2 while controlling the rotation speed of the engine 1 to always be a constant value. Therefore, the number of revolutions of the engine 1 and the inclination of the swash plate 6 must be individually controlled, which complicates the operation, complicates the structure, and raises the cost.

Therefore, an object of the present invention is to correlate the number of revolutions of the engine with the discharge amount per one revolution of the variable displacement pump to control only the number of revolutions of the engine so that the number of revolutions of the engine can be increased. By increasing the discharge amount per revolution of the variable displacement pump and increasing the engine speed only when necessary, power loss can be reduced, and the displacement of the variable displacement pump can be controlled only by controlling the engine speed. An object of the present invention is to provide a fluid device which can be increased or decreased in quantity, easy to operate, simple in structure and low in cost.

<Means for Solving Problems> In order to achieve the above object, the fluid control device of the present invention is
As illustrated in FIG. 1, the variable displacement pump 12 having a structure in which the discharge amount is increased as the fluid pressure introduced to the discharge amount control cylinders 22 and 23 connected to the variable control element 21 is increased.
And a fixed displacement type control pump 13 are interlocked with the engine 11, and a sequence valve 37 that opens at a set pressure is provided on a control line 26 that guides the fluid pressure of the control pump 13 to the discharge amount control cylinders 22 and 23. On the other hand, it is characterized in that a throttle 39 is provided on a branch line 41 branching from the control line 26 between the sequence valve 37 and the control pump 13 to the tank.

<Operation> When the number of revolutions of the engine 11 is increased, the discharge amount of the control pump 13 per unit time is increased, so that the branch line 41
The pressure on the upstream side of the throttle 39 increases. Then, when the pressure on the upstream side of the throttle 39 becomes equal to or higher than the set pressure of the sequence valve 37, the sequence valve 37 opens and the fluid discharged from the control pump 13 causes the discharge control cylinders 22, 23 of the variable displacement pump 12 to flow.
As shown by the solid line in FIG. 2, the variable displacement pump 12 starts to discharge the flow rate. Then, since the pressure on the upstream side of the throttle 39 increases as the rotation speed of the engine 11 increases, the discharge amount of the variable displacement pump 12 increases as the rotation speed of the engine 11 increases.

On the contrary, when the rotational speed of the engine 11 is decreased, due to the hysteresis of the discharge amount control cylinders 22 and 23 of the variable displacement pump 12, the solid line at the time of increasing the rotational speed of the engine 11 is not traced, and FIG. As shown by the broken line in the figure, the discharge amount decreases, but when the pressure falls below the set pressure of the sequence valve 37, the sequence valve 37 closes, and the discharge amount control cylinders 22 and 23 of the variable displacement pump 12 upstream of the throttle 39. Pressure is not guided. Therefore, the discharge amount of the variable displacement pump 12 returns to zero.
Therefore, the point at which the discharge of the variable displacement pump 12 is started is the engine even in the direction of increasing the rotation speed of the engine 11.
When the fluid device is used in a vehicle or the like, the feel of the accelerator pedal is improved, the operability of the vehicle is improved, and the vehicle operation is improved. It can be solved that it is difficult to stop.

<Example> Hereinafter, the present invention will be described in detail with reference to illustrated examples.

As shown in FIG. 1, the engine 11 has a variable displacement pump 12
And a fixed displacement type control pump 13 are directly connected and linked. The variable displacement pump 12 is connected to a hydraulic motor 15 for traveling the vehicle as an actuator by main lines 16 and 17 to form a closed circuit.

The swash plate control cylinders 22 and 23 also serve as discharge amount control cylinders for controlling the tilt angle of the swash plate 21 of the variable displacement pump 12.
It is connected to the control pump 13 via control lines 26, 27, 28 having a switching valve 25 in the middle. The variable displacement pump 12 can discharge fluid in both directions by tilting the swash plate 21 in both directions from the neutral position. Further, in the variable displacement pump 12, when the differential pressure between the fluid pressure applied to the swash plate control cylinder 22 and the fluid pressure applied to the swash plate control cylinder 23 becomes a certain pressure or more, the swash plate 21 tilts by a certain angle or more. , Begins to discharge fluid, and the swash plate 21 increases as the pressure difference increases.
The inclination angle is increased and the discharge amount is increased.

The discharge port of the control pump 13 and the pump port P of the switching valve 25
The differential pressure between the front and rear is, for example, 2 kg / cm ^{2 in} the control line 26 between
A sequence valve 37 that opens with a branch line 41 that branches to a tank 38 from between the sequence valve 37 and the control pump 13 is provided.
A throttle 39 and a relief valve 40 are sequentially installed from the upstream side.
To the branch line 41 between the throttle 39 and the relief valve 40, the main lines 16 and 17 are connected via check valves 42 and 43,
Fluid is supplied to the main lines 16 and 17 at the set pressure of the relief valve 40. That is, the control pump 13 supplies the fluid for controlling the discharge amount of the variable displacement pump 12 and charges the main lines 16 and 17 with the fluid when the amount of the fluid in the main lines 16 and 17 is insufficient. Have the function to Further, the branch line 41 between the throttle 39 and the relief valve 40 and the tank port T of the switching valve 25 are connected by a return line 46 having a throttle valve 45 with check in the middle.

In addition, the pump port P of the sequence valve 37 and the switching valve 25
Between the control line 26 and the return line 46, a sequence valve that opens at a differential pressure of 2 kg / cm ² or more, for example, 4 kg / cm ²
51 is connected by a branch line 53 having a variable aperture 52,
Further, they are also connected by a branch line 56 having a variable aperture 55 in the middle. Furthermore, the load port of the switching valve 25
A and B are connected to swash plate control cylinders 23 and 22 by control lines 27 and 28, respectively. Further, the control line 27 and the control line 28 are normally connected by a line 59 having a variable throttle 57 that is fully closed and has the same function as a clutch.

Incidentally, 61 is a filter provided in the suction line of the control pump, and 62 is a cooler.

The fluid device configured as described above operates as follows.

Now, in order to move the vehicle forward, the switching valve 25 is switched to the right symbol position, and the throttle valve 57 for bypass, which has the same function as the clutch, is fully closed. Then, when the accelerator pedal of the engine 11 is depressed to increase the rotation speed of the engine 11, the discharge flow rate of the control pump 13 that is linked to the engine 11 increases. The fluid discharged from the control pump 13 passes through the throttle 39 of the branch line 41, pushes the relief valve 40 open, and is discharged to the tank. When the main lines 16 and 17 are not filled with oil, the check lines 42 and 43 are used to supply oil to the main lines 16 and 17. The charge pressure for replenishing oil to the main lines 16 and 17 is the set pressure of the relief valve 40. The engine 11 has a low rotation speed and the control pump 13 has a small discharge amount, and the differential pressure before and after the throttle 39 of the branch line 41 is 2 kg / cm.
² or less, i.e. sequence valve 3 in control line 26
When the pressure difference before and after 7 is 2 kg or less and the sequence valve 37 is closed, the swash plate control cylinders 22 and 23 have branch lines 56
The same fluid pressure in the return line 46 (the set pressure of the relief valve 40) is guided by, the swash plate 21 does not tilt, the variable displacement pump 12 idles, and does not discharge fluid. In addition, the engine
When the rotation speed of 11 increases and the discharge flow rate from the control pump 13 increases, the differential pressure between the primary side and the secondary side of the sequence valve 37 increases.
When the pressure exceeds ² kg / cm ² , the sequence valve 37 is opened and the discharge fluid from the control pump 13 starts to be supplied to the downstream side thereof.
Then, the fluid of the control line 26 flows out to the return line 46 via the variable throttle 55 of the branch line 56. The pressure Pa on the primary side of the variable throttle 55 is guided to the swash plate control cylinder 23, and the pressure Pb on the secondary side is guided to the swash plate control cylinder 22. The variable displacement pump 12 does not discharge oil until the pressure, that is, the control pressure (Pa-Pb), reaches a value for inclining the swash plate 21. Further, the rotation speed of the engine 11 increases and the control pump 13
Input rotation speed increases and the control pressure (Pa-
When Pb) becomes a certain value or more and reaches a value for tilting the swash plate 21, the swash plate 21 tilts and the variable displacement pump 12 starts discharging fluid to the main line 16. In this manner, when the variable displacement pump 12 discharges oil and the sequence valve 51 is closed, the discharge amount of the variable displacement pump 12 varies depending on the input rotation speed of the control pump 13. Especially the engine 11
That is, the rate of increase of the control pressure (Pa-Pb) with respect to the input rotation speed of the control pump 13 depends on the opening areas of the throttle 39 and the variable throttle 55. Therefore, the rate of increase can be changed by adjusting the opening degree of the variable throttle 55, and as a result, the discharge amount of the variable displacement pump 12 with respect to the input rotation speed of the control pump 13 can be adjusted.

Further, the rotation speed of the engine 11 increases, and the control pressure (Pa-Pb) causes the differential pressure (4 kg / Pa) before and after the sequence valve 51.
cm ² ) and above, sequence valve 5 in branch line 53
1 will be opened and the fluid in control line 26 will be bypassed to the tank from return line 46 through variable throttle 52 in branch line 53. At this time, the control pressure (Pa-Pb) with respect to the change of the input speed of the control pump 13 is the throttle 39
And the total aperture area of the variable diaphragm 52 and the variable diaphragm 55. Further, the rotation speed of the engine 11 that discharges the maximum flow rate in which the swash plate 21 is tilted by the maximum angle is adjusted by adjusting the opening degree of the variable throttle 52 that operates after the sequence valve 51 is opened.

On the other hand, when the rotational speed of the engine 11 decreases and the differential pressure (Pa-Pb) before and after the throttle 39 becomes 2 kg or less for opening the sequence valve 37, the sequence valve 37 is closed and the swash plate control is performed. Fluids having the same pressure are introduced into the cylinders 23 and 22, and the swash plate 21 immediately returns to the neutral position, and the discharge amount becomes zero. In this way, the action of the sequence valve 37 causes the discharge start point and the discharge stop point of the variable displacement pump 12 to match the rotation speed of the engine 11, so that the hysteresis is eliminated.

In order to more clearly explain the above operation, a state in which the variable throttle 52 and the sequence valve 51 are selectively operated will be described with reference to FIGS.

In FIG. 2, the throttle 39 of the branch line 41 and the sequence valve 37 of the control line 26 are made to function, but the variable throttle 52 of the other branch line 53 is fully closed to eliminate the function of the branch line 53. The characteristic is shown in a state where the variable diaphragm 55 of 56 is fully closed and the function of the branch line 56 is lost. In this case, the input rotational speed N at which the variable displacement pump 12 starts discharging can be reliably set by the set pressure of the sequence valve 37, and the variable displacement pump 12 can be increased in accordance with the increase in the rotational speed of the engine 11. When the discharge amount is increased and the rotation speed of the engine 11 is decreased to decrease the discharge amount of the variable displacement pump 12, even if there is hysteresis in the middle as shown by the broken line in FIG. When the control valve (Pa-Pb) is zero and the input rotation speed N is below a certain value, the discharge amount is immediately released. Indicates that there is no hysteresis in the input rotation speed at which the discharge amount becomes zero.

In addition to the configuration shown in FIG. 2, FIG. 3 shows the characteristic curve of the input rotation speed N and the discharge amount Q having an inflection point T by making the sequence valve 51 and the variable throttle 52 of the branch line 53 function. It is a thing.

In the above embodiment, the control pump 13 also serves as a charge pump that replenishes oil to the main lines 16 and 17, but the control pump and charge pump functions may be separated and a separate charge pump may be provided. Further, in the above embodiment, the branch line 41 is provided with the relief valve 40, and the main lines 16 and 17 are provided.
Although the oil is charged to the tank, the relief valve 40 may be removed when the oil is not replenished. Also, only one swash plate control cylinder may be used. Further, the main line may be an open circuit.

<Advantages of the Invention> As is apparent from the above, according to the present invention, the variable displacement pump and the fixed displacement control pump are linked to the engine, and the discharge port of the control pump and the discharge amount control of the variable displacement pump are controlled. The cylinder is connected by a control line having a sequence valve, and a throttle is provided in the branch line that branches from the sequence valve and the control pump to the tank, so that the pressure of the control line increases as the engine speed increases. Can be increased to increase the discharge amount per revolution of the variable displacement pump in accordance with the increase in the engine revolution speed. Therefore, the per displacement of the variable displacement pump can be controlled by controlling only the engine revolution speed. It is possible to variably control the discharge amount of the engine, and it is not necessary to constantly drive the engine at the rated speed, which reduces the fuel consumption rate and reduces power loss. You can do it. Further, since the discharge amount per one rotation of the variable displacement pump can be controlled by controlling only the engine speed, there is no need to individually control the engine and the variable displacement pump as in the conventional case, and the operation can be performed. It is simple, the structure is simple, and the cost can be reduced.

Further, according to the present invention, a sequence valve is provided in the control line, and when the pressure in the control line becomes higher than the pressure for opening the sequence valve, the fluid pressure is guided to the discharge amount control cylinder of the variable displacement pump. Since the variable displacement pump discharges the fluid, in the direction of increasing the engine speed, the variable displacement pump discharges the fluid from the time the sequence valve opens and the engine speed decreases. The variable displacement pump does not discharge the fluid from the time when the sequence valve is closed in the direction to allow the variable displacement pump to discharge from the engine.
When used in a vehicle or the like, the operability is extremely improved.

[Brief description of drawings]

FIG. 1 is a fluid circuit diagram of an embodiment of the present invention, FIGS. 2 and 3 are characteristic diagrams of a fluid device of the present invention, and FIG. 4 is a circuit diagram of a conventional fluid control device. 11 …… Engine, 12 …… Variable displacement pump, 13 …… Control pump, 15 …… Hydraulic motor, 16,17 …… Main line, 2
1 …… Swash plate, 22,23 …… Swash plate control cylinder, 26,27,28 ……
Control line, 37,51 …… Sequence valve, 39 …… Throttle, 40
...... Relief valve, 41,53,56 …… Branching line, 52,55,57…
… Variable aperture.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-51-149630 (JP, A) JP-A-63-214562 (JP, A) West German patent publication 2008078 (DE, A)

Claims (1)

[Claims] 1. A variable displacement pump (12) having a structure for increasing the discharge amount as the fluid pressure introduced into a discharge control cylinder (22, 23) connected to a variable control element (21) increases.
And the fixed displacement type control pump (13) are linked to the engine (11), and set in the control line (26) that guides the fluid pressure of the control pump (13) to the discharge amount control cylinders (22, 23). While a sequence valve (37) that opens with pressure is installed, the control line (26) between the sequence valve (37) and the control pump (13) is throttled to a branch line (41) that branches to a tank. A fluid control device provided with (39).