JPH02261902A - Variable circuit of discharge capacity of pump in clossed center load sensing system - Google Patents

Abstract

PURPOSE:To improve minute operability by changing a pump discharge capacity by way of making variable the additional force used for changing over a change-over valve which works by a pump discharge pressure, and actuator load pressure and an additional force of a spring and others. CONSTITUTION:In the case of normal work, when a change-over valve 7 is changed over from N to L or M, discharge pressure of a pump 2 becomes higher by the pressing force of a spring 15 connected to a regulator 16 than the load pressure of an actuator 3 because of a restrictor 20 so that the change- over pressure of a valve 13 is controlled. Additionally, when a ficon curve is made variable, a valve 18 is changed over with an instruction 19, hydraulic pressure from a pump 17 is supplied to the regulator 16, the pressing force of a valve 13 is lowered by way of changing the mounting length of the spring 15 and the flow from the pump 2 to the actuator 3 so that the ficon curve changes from (e) to (f). Consequently, it is possible to improve minute operability.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a variable pump discharge volume circuit in a closed center load sensing system, and particularly to a single pump system used in construction machinery such as a bassinet. The present invention relates to an improvement in a pump discharge volume variable circuit suitable for application to.

(Prior Art) Conventionally, in a construction machine such as a snow bell, two pumps 53 and 54 for a hydraulic power source are driven via P and 7,052 disposed in an engine 51, and a working machine is operated. actuators such as packets, arm pooms and rotations55.56
．． Two switching valves 5960 to switch oil pressure to 5758
(hereinafter referred to as 2 pumps and 2 pulps) and separate piping 6
The circuit shown in FIG. 8, connected by 1.62, is mainly used. Recently, in addition to this, two pumps71.7
No. 7 connects the hydraulic pressure from No. 2 to one switching valve 73 (hereinafter referred to as two pumps and one pulp) through pipes 74 and 75.
The circuit shown in the figure is used. In this case, the switching valve 7
3 uses a closed center system, and the two pumps 7172 have a discharge volume of each pump set to a load pressure p.
A load sensing system 80 is used to make the flow variable, and the flow control pulp 81 is switched to change the discharge amount of one pump 72.

(Invention tries to solve! l! II) However,
In the conventional 2-pump 2-valve system described above, the two pumps are P,
T. 0 (Fig. 8) or in tandem (Fig. 7), each of which is connected to a separate 211 switching valve by piping, which makes the structure complex and takes up space. There is a problem that it is widely used and the price is high.The two pump one pulp shown in Fig. 7 has the same problem as above because there are two pumps, and in terms of performance, the first O
There is a problem with the diagram.

■ In the range of throttling (stroke □ flow rate characteristics) of the switching valve stroke A (stroke of one lever), even when switching from 2 pumps to 1 pump, the fine control curve (A) of the flow rate flowing to the actuator will be different from the stroke. It is constant and cannot be changed.

■ Even if the flow control pulp is changed and the discharge amount is reduced to one pump, the maximum flow rate will decrease from (B) to (C), but the problem in item 0 will not be resolved.

Furthermore, in order to simplify the structure, reduce the price, and narrow the space, it is sufficient to use one pump per pulp, but the required flow rate for the maximum discharge amount of the pump is If the speed is small, there is a problem that even if the rotation of the pump is lowered by the engine or the like, the rotation speed (d) (maximum speed of the actuator) does not change as shown in FIG. 11, resulting in a discrepancy with the sensation.

The present invention has focused on the above-mentioned conventional problems, and aims to provide 11,111 channels of pump discharge volume in a closed center load sensing system that can vary the fine control curve and pump discharge volume even for one pump and one pulp. .

(Means for Solving the Problems) In order to achieve the above object, a first invention according to the present invention provides a load sensing system in which the discharge volume of a closed center switching valve and a pump of at least 1fl1 or more is made variable depending on the load pressure. In construction machinery equipped with the system, the pump's discharge volume is changed by varying the pump's discharge pressure, the load pressure of the actuator, and the additional force used to switch the switching valve operated by the additional force of a spring or the like. In the second invention, the fine control curve is made variable within the range of throttling of the switching valve, and in the third invention, the discharge volume of the pump is changed in accordance with the rotational speed of the engine.

(Function) According to the above configuration, even in one pump of the pump discharge volume variable circuit in the closed center load sensing system, the flow rate flowing to the actuator is equal to the stroke within the range of the fine control curve with respect to the stroke of the operating lever. However, it is variable, allowing for fine control when you want to move it a little. In addition, even at the maximum discharge rate of a single pump, the discharge rate can be varied according to engine fluctuations, so even if the actuator has a small required flow rate compared to the maximum discharge rate of the pump, the pump can be rotated by the engine etc. When the rotation speed is lowered, the turning speed changes accordingly, matching human senses and making the machine easier to use. Furthermore, since one pump and one pulp can be used, the structure can be simplified, the space can be narrowed, and the price can be reduced.

(Example) Hereinafter, an example of a variable pump discharge volume circuit in a closed center load sensing system according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows a first embodiment, in which a variable displacement pump 2 (hereinafter referred to as pump 2) is driven by the power of an engine or the like +111.
and a closed-center stack-type switching valve 7.8 that switches hydraulic pressure to actuators 34 for the boom, arm, packet, and swivel device (not shown) that operate the work equipment.
are connected to the variable displacement pump 2 via piping 9 and to the tank 11 via piping 10. The pump 2 has a regular regulator 12 that makes the discharge volume of the pump variable.The pump 2 is connected to a regular regulator 12 that makes the discharge volume of the pump variable. It is connected to the piping 9 and receives the discharge pressure Pp of the pump 2, and the discharge volume Qp of the pump 2! It's in control. The valve 13 has three points and two positions (E and F positions), and the control method is the discharge pressure of the pump 2 acting on one end (a) of the valve, and each actuator 3.4 acting on the other end (b). A regulator 16 is connected to the spring 15, and the installation length of the spring 15 is changed by receiving hydraulic pressure from a pump 17 via a valve 18. This makes the pressing force variable. A spring 16a is built into the regulator 16 and is contracted by hydraulic pressure from the pump 17. The valve 18 is operated by a command 19 from a changeover switch (not shown) provided near the driver's seat. The switching valve 78 has pipes 9a and 9 connected in parallel to the pipe 9 from the pump 2.
b is connected, and piping 3a, 3b is connected to the actuator 3 of the boom, and actuator 4 of the swing device is connected to the actuator 3 of the boom.
Pipes 4a and 4b are connected to the pipes 4a and 4b. The switching valve 7.8 has three positions; in the neutral position N, the pump port is closed, and in the switching position %M, it is throttled by a variable throttle 20 of a throttling provided on the spool, etc.
Further, at the switching values IL and M, the throttle 20 has a constant area and is connected to the check valve 21 through the port R at each position.The check valves 21 and 22 are connected by the biloft pipe 23a23b, Pilot tube 24
The piping 3a, 3b, 4 of each actuator 3.4 via
pressure reducing valves 25a, 25b inserted in the circuits to a, 4b,
26a and 26b. Further, the switching valve 7.8 is switched in response to a pressure command from a pilot proportional pressure valve or the like by operating a lever provided near the driver's seat (not shown). In this example, hydraulic pressure is used, but electrical commands may also be used.Also, at the switching position M, the area of the aperture 20 may not be constant but may be a variable maximum value.

Next, the operation of the above embodiment will be explained. In the case of normal work in which the changeover switch is not activated, for example when operating the boom, the changeover valve 7 is moved from the neutral position N to the changeover position or to the M position by operating the control lever provided near the driver's seat. 20 (Aperture area Zm
d), the discharge pressure Pp of the pump 2 is higher than the load pressure of the boom, that is, the pressure Pa of the piping 3a, 3b of the actuator 3 of the boom, by a predetermined amount of pressure Pc. That is, P p −P a + P c
---(1), the predetermined amount of pressure Pc is set by the pressing force of the spring 15 connected to the regulator 16, and the pressure of the throttle 20 is set to the predetermined amount of pressure Pc by the discharge capacity Qp of the pump 2. The switching pressure of valve 13 is controlled. In other words, Qp-CXZX p -a- Qp=CXZXrgo rτ -----(2), and the flow rate to the actuator is determined by the area Z of the restrictor 20 and the valve 13.
is determined by the square root of the switching pressure Pc. Therefore, the flow rate to the actuator 3.4 is determined according to the area 2 which is variable depending on the stroke of the spool etc. of the switching valve 7, and the discharge capacity Qp of the pump 2 increases or decreases accordingly.At this time, the connection is made to the port with the actuator. Check valve 2
1 to the actuator 3, but since the pressures P1 and 22 acting on the pressure reducing valve 25a are almost equal, the pressure resistance at the pressure reducing valve 253 is only a small resistance due to the spring 25c. Also, boom and M
IIl! When I is opened, the switching valves 7.8 are both in the switching position, or they are switched to M, and 0 flows into the boom and the actuator 11 times through the throttle of each switching valve 7.8 and the piping. At this time, if the load pressure P3 of the swing side is smaller than that of the boom, the boom load pressure Pa
passes through the check valve 21, and the check valve 22 compares the boom load pressure Pa with the swing load IEPs.Since the boom load IEPa is higher, it passes through the check valve 22, and the pump 2 Pressure reducing valves 25a, 25b, 26a, 26b guided to the valve 13 and connected to each actuator
guided by. Although the pressure reducing valve of the boom flows with little resistance as described above, the pressure reducing valve of the swing performs a large pressure reduction Psa, and becomes the predetermined load pressure Ps for the swing.

That is, P P # P s + P c + P a a
--(3) The discharge capacity Qp of the pump 2 is controlled by the switching pressure of the valve 13 so that the flow rate flowing through the spool areas Z7 and Z8 of the switching valve 7.8 becomes a predetermined pressure Pc.

Next, when making the fine control curve variable, the valve 18 is switched in response to a command 19 from the changeover switch, and the hydraulic pressure from the pump 17 is supplied to the rectifier 1 notor 16 via the valve 18.

This hydraulic pressure is used to deflect the spring 16a in the regulator 16, and the length of the spring 15 connected to the regulator 16 is changed to reduce the pressing force on the valve 13. It is reduced to 6 P ca.

As a result, in the case of work in which the changeover switch is activated,
For example, when operating the boom, if the switching valve 7 is switched from the neutral position N to the switching position or M by operating a lever provided near the driver's seat, the spool etc. will move up to the zero point of the operating lever stroke as shown in Fig. Since the area of the orifice 2G provided at , the flow rate to the actuator is determined by the area Z of the throttle 20 and the square root of the switching pressure Pc of the valve 13 and decreases from Qp to Qpa. Similarly, at stroke W point or higher, the maximum discharge capacity of the pump 2 becomes Qp.
The value decreases from max to Qpamax, and the fine control curve shifts from (E) to (E). This transition is caused by valve 13
It can be made variable by changing the pressing force.

FIG. 3 shows an overall configuration diagram of the second embodiment, and the same parts as in the first embodiment are denoted by the same reference numerals, and the explanation thereof will be omitted. A regulator 16 is connected to the spring 15, and receives hydraulic pressure from a pump 17 via a pressure regulator valve 31 to apply pressure to the spring 1.
The attachment of No. 5 makes the pressing force variable by gradually changing the length in proportion to the pressure. The pressure proportional valve 31 receives a command signal 3 from a changeover switch (not shown) provided near the driver's seat.
2, and the command signal 32 is activated by the engine 33.
It fluctuates in accordance with the rotation of a rotation sensor 34 disposed at.

In the above configuration, the operation will be explained next. fj4
For example, when you want to slow down the rotation of a pump with a small required flow rate compared to the maximum discharge amount of the pump, such as the power (h bell ml!!1), for turning, etc., the rotational speed of the engine 33 is controlled by a signal from an accelerator pedal (not shown) At the same time, the pressure proportional valve 3 is lowered by the command signal 32 from the rotation sensor 34 disposed in the engine 33 by operating the changeover switch.
Switch 1. The command signal is sent to engine 3 as shown in Figure 4.
It is varied in accordance with the variation in the rotational speed of No. 3. The pressure proportional valve 31 responds to the command signal 32 to
By changing the pressure Ppi, the spring 15
The switching pressure Pc of the regulator 16 is changed as shown in Fig. 6 by gradually changing the length in proportion to the pressure.The switching pressure PC of the regulator 16 changes the discharge capacity (or The discharge flow rate to the actuator similarly varies according to variations in the rotational speed of the engine 33.

In the above embodiment, the command signal is varied linearly in proportion to the engine variation, but it may be varied in a quadratic, tertiary, or other continuous manner using a normal contraler.

(Effects of the Invention) As explained above, according to the present invention, the variable circuit for the discharge volume of the pump in the closed center load sensing system has a circuit that makes the fine control curve and maximum discharge volume variable even in one pump. Therefore, even within the fine control curve range for the lever stroke, the flow rate flowing to the actuator can be varied with respect to the stroke, and the discharge amount of one pump can also be varied.
l [Improve productivity. Furthermore, even if the required flow rate is small compared to the pump's maximum discharge rate, if the pump rotation is lowered by an engine or the like, the rotation speed will change accordingly to match human sensation, making the machine easier to use. In addition, since one pump of pulp can be produced, the structure is simple, the space can be narrowed, and the price can be reduced.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram showing the first practical example of a pump discharge volume variable circuit in a closed center load sensing system according to the present invention f142 Fig. 142 shows the relationship between the stroke of the spool and the flow rate to the actuator according to the present invention figure. FIG. 3 is an overall configuration diagram showing a second embodiment of a pump discharge volume variable circuit in a closed center load sensing system according to the present invention. FIG. 4 is a diagram showing the relationship between engine rotational speed and command signal voltage. FIG. 5 is a diagram showing the relationship between engine rotational speed and pressure on the regierator. FIG. 6 is a diagram showing the relationship between engine rotational speed and regierator switching pressure. FIG. 7 is a diagram showing the relationship between engine rotational speed and pump discharge capacity. Figure 18 is an overall configuration diagram of a conventional two-pump, two-valve hydraulic circuit. FIG. 9 is an overall configuration diagram of a pump discharge volume variable circuit in a conventional closed center load sensing system. FIG. 10 is a diagram showing the relationship between the stroke of the spool and the flow rate to the actuator in the circuit shown in FIG. 9. 111th! ! ! I is a diagram showing the relationship between the engine rotation speed and the maximum speed of the actuator in the circuit shown in FIG. 9. 12.16 ・−・ Regulator 13・・・・
- Receiver regulator valve 15...Spring 21.22...Check valve 25a, 25b, 26a, 26b - Pressure reducing valve

Claims (3)

[Claims] (1) In construction machinery equipped with at least one closed center switching valve and a load sensing system that varies the pump discharge volume depending on the load pressure, the pump discharge pressure, the actuator load pressure, and the additional force of the spring, etc. A variable pump discharge volume circuit in a closed center load sensing system, characterized in that the pump discharge volume is varied by varying the additional force used to switch a switching valve operated by the pump. (2) A variable pump discharge volume circuit in a closed center load sensing system according to claim 1, wherein the fine control curve is variable within the range of throttling of the switching valve. (3) The circuit for variable displacement of the pump in the closed center load sensing system according to claim 1 or 2, characterized in that the displacement of the pump is changed according to the rotational speed of the engine.