JPH0318040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a variable displacement pump.

As a method of controlling the input horsepower of the pump to below a certain value, the shaft horsepower of the pump is determined by the pump discharge pressure p.
Since it is determined by the product PQ of kg/cm ² and the discharge amount cm ³ /sec, it is necessary to perform control so that the condition that PQ=constant is satisfied. To control PQ=constantly, the discharge pressure P (indicated by the horizontal axis in the figure) and the discharge amount Q (indicated by the vertical axis in the figure) are determined along the horsepower curves shown by curves A ₁ and A ₂ in Figure 1. It is preferable to control the relationship between However, in reality, it is difficult to control according to the curves A ₁ , A _{2 ,} etc., so conventionally control is performed using a relationship that approximates these curves. For example, as shown in Japanese Utility Model Application No. 54-110801, two springs are arranged at one end of a spool of a regulator, and the pump discharge pressure is guided to the other end, and one of the two springs is By selecting one spring to a length that causes the spool to deform from the beginning of its stroke, and the other spring to a length that causes the spool to deform from the middle of the spool's stroke, two straight lines as shown by the broken line _B1 in Figure 1 can be created. We obtained an approximate horsepower curve consisting of

In this method of approximation using two straight lines,
Although the objective of controlling the input horsepower of the pump to be below a certain value can be achieved, except for two points where the approximate curve touches the horsepower curve _A1 , the input horsepower of the pump is controlled to be below the allowable horsepower of the prime mover. In other words, there is a drawback that the efficiency of utilization of the prime mover and horsepower decreases accordingly.

As is clear from the horsepower curve in FIG. 1, this rate of reduction in utilization efficiency becomes significantly greater when the input horsepower of the pump is set to a low horsepower (in the case of horsepower curves A ₂ and B ₂ ).

Generally, when two or more pumps are driven by one prime mover, the input horsepower of the own pump is increased or decreased according to the input horsepower of the other pumps, and the total input horsepower is controlled to be less than the output horsepower of the prime mover. If the above-described input horsepower control means based on the approximate curve is used for such control, when the input horsepower of the pump is set to a low horsepower, the control will be performed in a state where the utilization efficiency is significantly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device that allows a pump to work with maximum efficiency while the horsepower is below a certain value.

A further object of the present invention is to provide a control device that can adjust the value of the input horsepower of the pump and obtain maximum utilization efficiency with the adjusted horsepower.

A further object of the present invention is to provide a control device that can finely adjust the set value of input horsepower, taking into account variations in pump efficiency and the like.

The present invention has achieved the above object by providing a regulator for a variable displacement pump, a control flow path connected at one end to an operating pressure source, and having a pressure reducing valve, a first restrictor, and a second restrictor sequentially arranged from the upstream side; a pilot passage that guides the pressure in the control passage between the first restriction and the second restriction to the regulator; and a pressure receiving part that receives the pressure of the upstream flow path of the first throttle at the other end, and the first
A control device for a variable displacement pump, characterized in that the second throttle is configured with a variable throttle that changes the pressure difference before and after the throttle and increases the opening area as the discharge pressure of the variable displacement pump increases. This was achieved by

Furthermore, by adjusting the aperture area of the first diaphragm as a variable diaphragm, the purpose of adjusting the set value of the input horsepower was achieved.

Furthermore, by providing a variable throttle or relief valve in the control flow path downstream of the second throttle, the objective of finely adjusting the set value of the input horsepower was achieved.

The details of the present invention will be explained below based on embodiments shown in the figures.

In FIG. 2, the discharge flow path 2 of the variable displacement pump 1
An actuator (not shown) is connected to via a switching valve 3 or the like. The variable displacement pump 1 is provided with a flow rate control regulator 4 . The flow rate control regulator 4 includes, for example, a servo piston device 5 and a servo valve 6, and is operated by an auxiliary pump 7 used as a regulator operating pressure source. The auxiliary pump 7 can be configured as a fixed displacement pump driven by a common prime mover with the variable displacement pump 1, or it can be a variable displacement pump. Note that the discharge pressure of the variable displacement pump itself may be used as the operating pressure source without providing an auxiliary pump.

Actuation pressure source, e.g. discharge channel 8 of auxiliary pump 7
A first chamber 10 of a cylinder 9 of a servo piston device 5 is connected to the servo valve 6, and a first chamber 10 and a second chamber 11 of the cylinder 9 are connected to the servo valve 6 through passages 12 and 13, respectively.

The servo valve 6 has a variable sleeve 14 and a spool 15.
A pilot pressure is introduced to one end of the spool 15 through a passage 30, and its pressing force opposes the pressing force of a spring 68 disposed at the other end of the spool.

The piston rod 17 of the servo-piston device 5 is connected to a tilting lever 19 of the variable displacement pump 1. Further, the movable sleeve 14 of the servo valve is connected to the piston rod 17 via a feedback lever 18.

Therefore, when the spool 15 of the servo valve 6 moves in response to fluctuations in pilot pressure, the second chamber 11 of the servo piston device is connected to the pump 7 via the flow path 13.
The piston 16 is actuated by communicating with either the flow path 12 connected to the tank 29 or the tank 29.
At the same time that the tilting lever of the pump is displaced by the operation of the piston 16, the movable sleeve 14 connected to the piston rod 17 via the feedback lever reaches a position where it cuts off communication with the flow path 13, the flow path 12, or the tank 29. The piston 16 is displaced and the operation of the piston 16 is stopped.

That is, the servo valve 6 and the servo piston device displace the tilting lever 19 of the pump in proportion to the pilot pressure, thereby controlling the discharge flow rate.

A discharge passage 8 of the auxiliary pump 7 is connected to a control passage 21 of the control device 20 . The control device 20 includes pressure reducing valves 2 sequentially connected to the control flow path 21 from the upstream side.
2. A first aperture 23 and a second aperture 24 are provided. The pressure reducing valve 22 is the discharge flow path 2 of the variable displacement pump 1.
It has a pilot flow path 25 connected to the first flow path 25 , a first flow path 26 connected to the upstream side of the first throttle 23 , and a second flow path 27 connected to the downstream side of the first throttle 23 .
The differential pressure across the first throttle 23 is changed according to the discharge pressure of the variable displacement pump 1.

The second throttle 24 has a flow path 28 connected to the discharge flow path 2, and is formed as a variable throttle whose opening area changes depending on the discharge pressure of the variable displacement pump 1.

The downstream side of the control flow path 21 of the control device 20 and a part of the sleeve 14 of the servo valve 6 are respectively connected to a tank 29.
It is connected to the.

The control flow path 21 of the control device 20 is connected to the servo valve 6 by an operating flow path 30 at a position between the first throttle 23 and the second throttle 24, and the spool 15 of the servo valve 6 is connected to the first throttle of the control flow path 21. 23 and the second throttle 24 is received as pilot pressure.

In order to maintain the input horsepower of the variable displacement pump 1 at a constant value, the product PQ of the discharge pressure Pd and the discharge amount Q of the variable displacement pump 1 may be made constant as described above.

The opening area of the first diaphragm 23 is A, and the first diaphragm 2
If the upstream pressure of No. 3 is P _x , the downstream pressure P _i , and the flow rate flowing through the control channel 21 is Q _i The following relationship is obtained.

Here, ρ is the fluid density C is a coefficient.

Similarly, if the opening area of the second diaphragm 24 is B, the downstream side is open to the tank, so The following relationship is obtained.

Pilot flow path 25 in the valve body of the pressure reducing valve 22
The volume pressure area for the fluid is a, the first flow path 26
The pressure receiving area for the fluid is b, and the second flow path 27
Let b be the pressure-receiving area for the fluid in the valve body, so that pressure acts on the valve body according to the relationship aPd + bPi = bPx (3).

Also, B=d・Pd…(4) The second aperture 24 is selected so that the following relationship is established.

Here d is a coefficient.

From equations (1) to (3), A ² (a/bPd)=B ² Pi is obtained, and by substituting equation (4), Pi=aA ² /bd ² ·1/Pd (5) is obtained.

From equation (5), in the control device shown in FIG. 2, the discharge pressure Pd of the variable displacement pump 1 and the pressure Pi downstream of the first throttle 23 have a hyperbolic relationship as shown in FIG. In Figure 3, the horizontal axis is Pd and the vertical axis is
Indicates Pi.

The flow rate control regulator 4 has a characteristic as shown in FIG. 4 as Q=KPi (6), where K is a coefficient. In FIG. 4, the horizontal axis shows the pilot pressure Pi, and the vertical axis shows the discharge amount Q of the variable displacement pump 1.

From equations (5) and (6), Pd·Q=KaA ² /bd ² (7), and the result that Pd·Q is constant is obtained. That is, by the control device shown in FIG.
It is possible to control the input of the variable displacement pump so that Pd·Q, that is, the horsepower, is constant.

An example of a specific structure of the control device 20 shown in FIG. 2 is shown in FIG. 5.

In FIG. 5, the casing 31 of the control device 20
Inside, there is a control flow path 21 connecting an inlet 32 connected to a discharge flow path 8 of an operating pressure source, for example, an auxiliary pump 7, and an outlet 33 that is a connection port to a conduit connected to a tank 29. is formed. In FIG. 5, the control flow path 21 includes a first path 34, a second path 35, and a third path 3.
6, a fourth passage 37 and a fifth passage 38.
The first passage 34 and the second passage 35 are connected to each other via the pressure reducing valve 22, the third passage 36 is provided with the first throttle 23, and the fourth passage 37 and the fifth passage 38 are arranged with the second throttle. 2
4 are interposed in between.

The pressure reducing valve 22 has a first through hole 39 in the casing 31 that communicates with the first passage 34 and the second passage 35 either directly or via an annular groove. A spool 40 is slidably inserted into the first through hole, and depending on the position of the spool, the opening degree of the constricted portion 41 formed by the land portion 40a of the spool and the first through hole 39 increases or decreases to control the flow. The space between the first passage 34 and the second passage 35 of the passage 21 is opened and closed.

Both ends of the first through-hole 39 are formed as holes 39a and 39b having a larger diameter than the portion that slides and guides the spool 40, into which a first plug part 42 and a second plug part 43 are inserted and fixed, respectively. At the end of the first stopper portion 42 facing the spool 40, stepped first guide holes 45, 45a (small diameter portion ) is bored, and the guide hole 45 and the first piston 4
A first chamber 70 is formed between the stepped portion 4 and the stepped portion 4 .

Similarly, a second guide hole 47 into which a second piston 46 is slidably inserted is bored at the end of the second stopper portion 43 facing the spool 40.
A second chamber 71 is formed between the second piston 7 and the second piston 46 .

The first chamber 70 of the first stopper portion 42 communicates with the second flow path 27 and the working flow path 30 formed in the casing 31 via the annular groove 48 . The second passage 27 is connected to the third passage 36 of the control passage 21 on the downstream side of the first throttle 23, and the working passage 30 is connected to the third passage 36 of the control passage 21.
It is connected to the regulator 4 through the connection port 1.

The second chamber 71 of the second stopper portion 43 is connected to the first flow path 26 via the annular groove 49 . First channel 26
is connected to the first passage 36 on the upstream side of the first throttle 23.

A flow path 50 is formed in the first plug portion 42 and communicates with the pilot flow path 25 in the casing 31, which is connected to the discharge flow path 2 of the variable displacement piston 1. It communicates with the flow path 50. Therefore, the fluid pressure of the pilot passage 25 acts on the end surface of the protruding portion 44a of the first piston 44 inserted into the small diameter portion 45a of the first guide hole.

The pressure-receiving area of the protrusion 44a that receives pressure from the fluid in the pilot flow path 25 is set to the pressure-receiving area a shown in equation (3) above, and the stage of the first piston 44 that receives the pressure of the fluid in the first chamber 70 The pressure receiving area of the attached portion is set to the pressure receiving area b shown in equation (3).

The fluid pressure in the pilot flow path 25 corresponds to the pressure Pd shown in equation (3) since it is connected to the discharge flow path 2 of the variable displacement pump, and the pressure in the second flow path 27 corresponds to the pressure Pd downstream of the first throttle 23. Since it is a pressure, the pressure Pi shown in equation (3)
corresponds to Therefore, the first piston 44 is aPd
The spool 40 is pushed to the right in the figure by the force of +bPi.
By contacting the spool 40, the spool 40 is pushed to the right in the figure.

The pressure receiving area where the end surface of the second piston 46 receives the pressure of the fluid in the second chamber 71 is set to the pressure receiving area b in equation (3). Since the fluid in the second chamber 71 receives pressure on the upstream side of the first throttle 23, the pressure Px in equation (3)
corresponds to Therefore, the second piston is pushed to the left in the figure by the force bPx, and by coming into contact with the spool 40, pushes the spool 40 to the left.
When the spool 40 is stopped, the pressure is balanced, so aPd+bPi=bPx.

The second throttle 24 has a second through hole 51 formed in the casing 31 , and a sleeve 52 is fixed to the second through hole 51 by a third plug portion 53 .

A spool 55 is slidably inserted into the sleeve 52 and has a throttle opening formed as an annular groove 54 with a tapered surface. The sleeve 52 has a first annular recessed chamber 56 communicating with the fourth passage 37 of the control passage 21 of the casing 31 and a second annular recessed chamber 57 communicating with the fifth passage 38 on its inner peripheral surface. First annular recessed chamber 56 and second annular recessed chamber 57
can be completely shut off by the spool 55, and can be communicated with by the diaphragm opening 54 by moving the spool 55 in the axial direction. Since the aperture opening is formed so that its opening area gradually changes depending on the position of the spool 55 in the axial direction, the area between the fourth path 37 and the fifth path 38 changes depending on the movement position of the spool 55. The amount of aperture is variable.

A flow path 58 is formed in the third plug portion 53 and is connected to the discharge flow path 2 of the variable displacement pump via the flow path 50 of the first plug portion 42 and the flow path 28 in the casing 31. The fluid in passage 58 exerts a force on spool 55, either directly or through piston 59, pushing it to the right in the figure. The spool 55 has a third stopper portion 53.
A spring 61 is attached via a spring seat 60 to the end face opposite to the
is seated, and the other end of the spring 61 is held down by a spring holder 62. The spring retainer 62 is slidably guided into the third through hole 51. The position of the spring presser 62 is adjusted by an adjustment screw 64 screwed onto one side of a cover plate 63 fixed to the casing 31, and the initial tension of the spring 61 is adjusted. The adjusting screw 64 is locked in the adjusted position by a nut 65.

The spool 55 of the second throttle 24 receives the force of the discharge pressure Pb from one side and the force of the spring 61 from the opposite side, so that under the action of the adjusted force of the spring 61, the spool 55 moves, and the aperture area changes. In the figure, when the discharge pressure Pd increases, the spool 55 moves to the right in the figure, and the aperture opening area changes to gradually increase. The diaphragm aperture area B is set so that B=dPd as shown in equation (4).

The operation in the example shown in FIGS. 2 and 5 will be explained.

When the discharge pressure Pd of the variable displacement pump 1 increases, the pressure acting on the protrusion 44a of the first piston of the pressure reducing valve 22 and the pressure acting on one end of the spool 55 of the second throttle 24 increase, so that the spool 22 and the spool 55 Move to the right of the diagram. Second aperture 24
Since the opening area of .pi. increases, the fluid pressure in the fourth passage 37 decreases, and the pressure Pi acting on the first piston 44 of the pressure reducing valve 22 decreases according to equation (5). Due to the decrease in the operating pressure Pi, the spool 15 of the servo valve 6 moves to the right in FIG.
The piston 16 moves to the right and the tilting lever 19 is moved in the direction of decreasing the tilting angle. That is, the discharge amount of the variable displacement pump 1 is reduced. As the tilting lever 19 moves, the sleeve 14 is moved, and when the spool 15 and sleeve 14 return to their neutral position, the piston 16 stops and the tilting lever 19 is held at that position.

On the other hand, in the pressure reducing valve 22, the movement of the spool 40 opens the space between the first passage 34 and the second passage 35 of the control passage 21, and the fluid flows into the third passage 36, so that the amount of inflow on the upstream side of the first throttle 23 is increases and the pressure Px
increases, the operating pressure against the second piston 46 rises, and the spool 40 is pushed back to the left in the figure.
The spool 40 stops when the operating pressures at both ends are balanced. At this time, the opening area of the diaphragm portion 41 connecting the first path 34 and the second path 35 has a limited value.

When the discharge pressure Pd decreases, the spool 55 and the spool 40 move in the opposite direction, and the second throttle 24
As the opening area B decreases, the operating pressure Pi increases,
Push the spool 15 of the servo valve 6 to the left in the figure. As a result, the servo piston 16 of the servo piston device 5 moves to the left in the figure, and the tilting lever 19 moves in the direction of increasing the discharge amount.

On the other hand, the spool 40 of the pressure reducing valve 22 moves to the left in the figure, and the opening area of the throttle part 41 between the first passage 34 and the second passage 35 of the control flow passage 21 decreases, so that the first
The pressure on the upstream side of the throttle 23 decreases, and the spool 40
is pushed back to the right and returns to its initial position.

With the embodiments shown in FIGS. 2 and 5, it is possible to perform control approximately along a predetermined hyperbola instead of approximating it to a hyperbola as in the past, and constant horsepower control can now be carried out with maximum efficiency.

When driving multiple variable displacement pumps with one prime mover, if the required horsepower decreases due to load fluctuations of one or several pumps, increase the input horsepower of the other pumps to keep the overall input horsepower constant. It can be controlled and used with maximum efficiency. To this end, it is convenient to use a variable opening area diaphragm as shown in FIG. 6 for the first diaphragm 23 in the embodiments of FIGS. 2 and 5. By making the first diaphragm 23 variable, the area A in equation (7) becomes variable and PdQ
The value of , that is, the input horsepower can be changed. The first throttle 23 can be manually adjusted, or it can be changed mechanically according to the input torque or discharge pressure of another pump using conventionally known techniques. be.

A second throttle 24 in the control flow path 21 of the control device
A relief valve 66 as shown in FIG. 7 or a third throttle 67 which is a variable throttle as shown in FIG.
By connecting (Pd-α) ² /Pd(Q-β)=Ka/bd ²・A ² ...(8) it is possible to adjust the constants α and β shown in Figure 2, Figure 5 or PQ according to the embodiment shown in Figure 6
= Constant In a controllable device with approximately constant input horsepower, even if the horsepower value deviates from the set value due to problems such as pump efficiency, it becomes possible to correct the error. In general, problems with pump efficiency and leakage in the flow path system occur when the value of Pi in Figure 3 is relatively different from the conditions set. For example, due to pump efficiency, etc. teeth
In the case where only Pio has a constantly decreasing value, Fig. 7,
Relief valve 66 or third throttle 67 in FIG.
Adjust to increase only Pio. As a result, α and β in the eighth equation are adjusted, and even if there is a decrease due to pump efficiency, PdQ can be obtained as a predetermined value.

According to the present invention, the discharge amount can be controlled according to changes in the variable displacement pump discharge pressure using a simple control device consisting of a combination of two throttles and a pressure reducing valve, with a constant relationship of PQ=constant, compared to the conventional linear approximation. This makes it possible to use the full capacity of the prime mover without wasting any play in the capacity of the prime mover depending on the conditions.

By making both of the two throttles variable, it is possible to adjust the input horsepower of the variable displacement pump, making it possible to drive efficiently with any input horsepower. Even in certain cases, the overall input horsepower remains constant and all pumps can be operated efficiently.

Furthermore, by simply adding a third variable throttle to the control device, even if the input horsepower is lower than the theoretical input horsepower due to pump efficiency, etc., the flow rate control regulator of the variable displacement pump can be operated at the theoretical operating pressure, enabling accurate control. did.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a curve showing the relationship between discharge pressure and flow rate when the input horsepower is constant, and a conventional control curve that approximates it, and FIG. 2 is a control circuit diagram using the control device according to the present invention. , FIG. 3 is a diagram showing the relationship between the discharge pressure of the variable displacement pump and the operating pressure for the flow rate control regulator in the control device according to the present invention, and FIG. 4 is a diagram showing the relationship between the operation pressure in the flow rate control regulator and the discharge amount of the variable displacement pump. 5 is a sectional view showing an example of the specific structure of the control device in the embodiment of FIG. 2, and FIG.
A circuit diagram of the control device part showing a modification in which the first throttle of the example shown in the figure is changed to a variable throttle. Figure 7 shows a relief valve in the example shown in Figure 6, and Figure 8 shows a modification in which a variable throttle is additionally installed. It is a circuit diagram. 1...Variable capacity pump, 2...Discharge channel, 4...
...Flow rate control regulator, 7...Auxiliary pump (operating pressure source), 20...Control device, 21...Control flow path,
22...Pressure reducing valve, 23...First throttle, 24...Second throttle, 66...Relief valve, 67...Variable throttle.

Claims (1)

[Scope of Claims] 1. A regulator for a variable displacement pump; A control channel having one end connected to an operating pressure source and having a pressure reducing valve, a first throttle, and a second throttle sequentially arranged from the upstream side; a pilot passage that guides the pressure in the control passage between the throttle and the second throttle to the regulator, and the pressure reducing valve connects the discharge pressure of the variable displacement pump to one end of the spool and the flow passage downstream of the first throttle. and a pressure receiving part at the other end that receives the pressure of the flow path upstream of the first throttle, and the pressure before and after the first throttle according to the discharge pressure of the variable displacement pump. A control device for a variable displacement pump, characterized in that the second throttle is configured to change the difference and increase the opening area as the discharge pressure of the variable displacement pump increases. 2. The control device for a variable displacement pump according to claim 1, wherein the first throttle is formed as a variable throttle. 3. The control device for a variable displacement pump according to claim 1, wherein a relief valve or a variable throttle is disposed downstream of the second throttle in the control flow path.