Device for controlling multiple hydraulic actuators

Abstract: A device for controlling multiple hydraulic actuators to protect a system from an overpressure caused by increasing the load on an individual actuator. By controlling the supply of hydraulic fluid to a pair of cylinders (18,20) each associated with a pilot valve (25,34,45) so that each cylinder always has enough fluid pressure to operate, the device of the present invention prevents the shutdown of the device caused by too much fluid going to the actuator operating at the maximum pressure. Thus all actuators continue to operate even if one is overpressured.

Description: The present invention relates to a device for controlling multiple hydraulic actuators and, more particularly, to a device for controlling multiple hydraulic actuators to protect a system from an overpressure caused by increasing the load on an individual actuator. The present invention can be applied, for example, to such a system as a power shovel that operates such multiple actuators as a spin motor, a boom cylinder, an arm cylinder, a bucket cylinder, and a driving motor. In the prior art, described below with reference to Figure 1, the drain pressure of a variable drain pump is controlled by the maximum load pressure in any one of a plurality of actuators. The prior art has drawbacks as follows. In the prior art device of Figure 1, when the variable orifice of one of a pair of switching valves sets a minimum value and the variable orifice of the other switching valve sets a maximum value, the cylinder attached to the other switching valve makes a full stroke, causing the load to increase. The increased load triggers an overload relief valve associated with that cylinder. Because the power (or Q x P, where Q is a quantity of fluid and P is pressure) remains constant, the amount of fluid drained by the variable drain pump has to decrease, as shown by the curve in Figure 2. Therefore the supply of fluid decreases to that switching valve set at the minimum value. In the worst case, the fluid supply drops so low that the cylinder stops altogether, thereby stopping all the actuators. An object of the present invention is to provide a device for controlling multiple actuators that overcomes the drawbacks of the prior art device. A further object of the present invention is to provide a device for controlling multiple actuators where the fluid drained from the variable drain pump is not lost, so that all actuators can continue to work even when their load pressure rises. Briefly stated, the present invention provides a device for controlling multiple hydraulic actuators to protect a system from an overpressure caused by increasing the load on an individual actuator. By controlling the supply of hydraulic fluid to a pair of cylinders each associated with a pilot valve so that each cylinder always has enough fluid pressure to operate, the device of the present invention prevents the shutdown of the device caused by too much fluid going to the actuator operating at the maximum pressure. Thus, all actuators continue to operate even if one is overpressured. According to the present invention, a load sensing active hydraulic control device comprises a tank for containing hydraulic fluid, a plurality of actuators, a pump connecting to said plurality of actuators and to said tank, said pump being effective for pumping said hydraulic fluid, each of said plurality of actuators having at least one directional switching valves respectively, said directional switching valves being connected in parallel, each of said switching valves having at least one pilot chamber and a pair of variable orifices, said variable orifices being open an amount responsive to a pressure in said at least one pilot chamber, a pressure compensating valve being connected to said variable orifices whereby a pressure difference is maintained between a load pressure on one of said actuators and a pressure downstream of said variable orifices, and means provided for controlling the output of said pump according to the highest load pressure of any of said plurality of actuators characterised in that at least one switching pilot valve is connected downstream of said switching valves to at least one of the fluid lines whereby a maximum pressure is fixed for said plurality of actuators, whereby, when said load pressure rises to a pressure sufficient to actuate said at least one switching pilot valve, said at least one pilot chamber is connected to said tank. The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which:- FIGURE 1 is a circuit diagram of the control device of the prior art; FIGURE 2 is a graph showing the relationship of P (pressure) to Q (quantity of fluid) in a variable drain pump; and FIGURE 3 is a circuit diagram of the control device of the present invention. In the various Figures of the drawings, like parts are identified by the same reference numerals. Referring to Figure 1, in the prior art a variable drain pump 1 is connected to two ports 5 associated respectively with a first directional switching valve 3 and a second directional switching valve 4 through a high pressure fluid line 2. Two pairs of pilot chambers 3a, 3b and 4a, 4b are respectively attached to opposite sides of the respective switching valves 3 and 4 and are coupled to pilot operating valves V1 and V2 whereby pilot operation valves V1 and V2 control an output pilot pressure. Switching valves 3 and 4 are normally in a neutral position and ports 5,5 are closed (as illustrated). Switching valves 3 and 4 are each provided with a pair of variable orifices 6, 6'. Placing either of switching valves 3 or 4 in either a left or a right position by operation of pilot valves V1, V2 opens the pair of variable orifices 6, 6' associated with that valve. The opening of the pair of variable orifices 6, 6' is proportional to the setting of the valve. Downstream of the each pair of variable orifices 6, 6' is a pressure compensating valve 8 connected to its respective valve 3, 4 through a check valve 7. Each of switching valves 3 and 4 also has a supply port 9 that is connected to the downstream side of pressure compensating valve 8. Supply ports 9, 9 are closed when switching valves 3 and 4 are at a neutral position illustrated in Figure 1. Moving switching valves 3, 4 to either a left or a right position couples supply ports 9, 9 with either one of a pair of actuator ports 10, 11 and connects the other actuator port with a tank fluid line 12. A load detecting port 13, 13 of each switching valve 3 and 4 is connected with tank fluid line 12 when switching valves 3 and 4 are in a neutral position. When switching valves 3 and 4 are switched either left or right, each load detecting port 13 is connected to the actuator port 10, 11 with the higher pressure. Each pair of actuator ports 10 and 11 of switching valves 3 and 4 is connected respectively to respective ends of a pair of cylinders or actuators 19 and 20 through a pair of fluid lines 17 and 18 to which a respective overload relief valve 21, 22 is connected. Pressure compensating valves 8, 8 equalize the respective pressures on the upstream side of check valves 7, 7 to that of pilot chambers 8a, 8a and the respective pressures of load detecting ports 13, 13 to that of pilot chambers 8b, 8b. A shuttle valve 14 transfers to pilot chamber 8b the highest pressure of any one among the actuators controlled by switching valves 3 and 4. Pressure compensating valve 8 operates at the pressure of the lower of the pair of variable orifices 6, 6', that is at a fixed rate higher than the maximum load pressure from one of the actuators 19, 20. The maximum load pressure chosen by shuttle valve 14 is transferred to a pilot chamber 15a of a control valve 15, and a pilot chamber 15b has the pressure of high pressure fluid line 2 or the pressure of variable drain pump 1. The difference between the pressure of variable drain pump 1 and the maximum load pressure actuates control valve 15. Control valve 15 operates control cylinder 16, which runs at constant power, to keep the pressure from variable drain pump 1 at a fixed rate higher than the maximum load pressure. In the above arrangement, pilot operating valves V1 and V2 supply a pilot pressure to either pilot chambers 3a, 3b of switching valve 3 or pilot chambers 4a, 4b of switching valve 4. For example, the pilot pressure from pilot chamber 3b shifts switching valves 3 to the right position. Similarly, the pilot pressure from pilot chamber 4b shifts switching valve 4 to the right position. As switching valves 3 and 4 change their settings, the opening of the pair of variable orifices 6, 6' also changes and variable drain pump 1 supplies amounts of fluid under pressure that correspond to the ratio of each pair of variable orifices. When the fluid is supplied to bottom chambers 19a and 20a of actuator cylinders 19 and 20 or to one of the individual actuator cylinders, the fluid in top cylinder chambers 19b, 20b returns to tank fluid line 12 through switching valves 3 and 4. Control cylinder 16 controls the quantity of fluid supplied from pump 1 according to the maximum load pressure required at any one or more of the actuators 19, 20. Referring to figure 2, variable drain pump 1 depends on the product of a pressure P and a quantity of fluid Q, which product is fixed. Thus, the higher the maximum load pressure, the less the amount of fluid drained from variable drain pump 1. The amount drained corresponds to the ratio of the pair of variable orifices 6, 6' of either switching valve 3 or switching valve 4. As the above description makes clear, since the drain pressure of variable drain pump 1 is controlled by the maximum load pressure on multiple actuators, a difficulty can arise in its operation. When either of the pair of variable orifices 6, 6' of switching valve 3 is set to a minimum value and either of the pair of variable orifices 6, 6' of switching valve 4 is set to a maximum value, cylinder 20 makes a full stroke. The load increases so that either overload relief valve 21 or overload relief valve 22, connected to respective sides of piston in cylinder 20, opens. The amount of fluid that drains from variable drain pump 1 decreases, according to the curve of Figure 2, since the amount of power is fixed. Therefore the supply of fluid to switching valve 3 is reduced, and, in the worst case, cylinder 19 comes to a complete stop. Referring to the present invention illustrated in Figure 3, the majority of the fluid control device and its circuitry and mode of operation is identical with that of Figure 1, as will be apparent from a comparison of Figures 1 and 3. However, the pilot chamber 4b of the switching valve 4 is connected to a pilot valve 25 through a pilot line 24 that continues after the valve 25 to tank T. Pilot valve 25 is biassed to its illustrated closed position by a spring 26 at one side. A pilot chamber 27 at its opposite side is coupled to the fluid line 18 from actuator cylinder 20 so that both have the same pressure. Hence, pilot valve 25 is opened when the pressure in fluid line 18, i.e. the load pressure of the cylinder 20, opens an overload relief valve 22. The connection of pilot chamber 4b of switching valve 4 to tank T is controlled by switching pilot valve 25. Normally, pilot line 24, which contains an orifice 28, is closed. Pilot line 24 is also connected to the pilot operation valve V2 through an orifice 29. If one of the variable orifices 6, 6' of switching valve 3 is opened to the minimum setting, then the pair of variable orifices 6, 6' of switching valve 4 is opened to the maximum. A full stroke of cylinder 20 raises the pressure in fluid line 18 and opens pilot valve 25 and as a result, pilot chamber 4b of switching valve 4 makes a connection with tank T. The pressure in both the pilot line 24 and fluid line 18 is decreased, and switching valve 4 therefore returns to a neutral position, thereby reducing the opening of the pair of variable orifices 6, 6'. As a result, the amount of fluid flowing to cylinder 20 is decreased. For example, when the opening of one of the pair of variable orifices 6, 6' of switching valve 4 becomes less than the opening of the pair of variable orifices 6, 6' of switching valve 3, the amount of fluid from variable drain pump 1 is decreased in proportion to the ratio of the two levels, so that fluid under pressure is supplied to fluid cylinder 19 connected to switching valve 3. As illustrated, pilot valve 25 is connected only to bottom chamber 20a of cylinder 20. Pilot valve 25 may also connect to a single fluid line 17 or to both fluid lines 17 and 18. Even though the load pressure of cylinder 20 increases almost to the pressure setting of overload relief valve 23, cylinder 19 will not stop. It will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Claims: A load sensing active hydraulic control device which comprises a tank for containing hydraulic fluid, a plurality of actuators (19,20), a pump (1) connecting to said plurality of actuators (19,20) and to said tank, said pump (1) being effective for pumping said hydraulic fluid, each of said plurality of actuators (19,20) having at least one directional switching valves (3,4) respectively, said directional switching valves (3,4) being connected in parallel, each of said switching valves (3,4) having at least one pilot chamber (3a,3b,4a,4b) and a pair of variable orifices (6,6'), said variable orifices (6,6') being open an amount responsive to pressure in said at least one pilot chamber (3a,3b,4a,4b), a pressure compensating valve (8) being connected to said variable orifices (6,6') whereby a pressure difference is maintained between a load pressure on one of said actuators (19,20) and a pressure downstream of said variable orifices (6,6'), and means (15,16) provided for controlling the output of said pump (1) according to the highest load pressure of any of said plurality of actuators (19,20) characterised in that at least one switching pilot valve (25) is connected downstream of said switching valves (3,4) to at least one of the fluid lines (17,18) whereby a maximum pressure is fixed for said plurality of actuators (19,20), whereby, when said load pressure rises to a pressure sufficient to actuate said at least one switching pilot valve (25), said at least one pilot chamber (3a, 3b,4a,4b) is connected to said tank.

Inventors: HASEGAWA YOSHIMI, KOIWAI HIDESHI, NAITO HISATO, NISHIUMI KENICHI, YONEKUBO YOSHITAKE, HASEGAWA, YOSHIMI, KOIWAI, HIDESHI, NAITO, HISATO, NISHIUMI, KENICHI, YONEKUBO, YOSHITAKE
Applicants: KAYABA INDUSTRY CO LTD, KAYABA INDUSTRY CO., LTD.
Application year: 1992
Main classification: F15B11
IPC codes: F15B11, E02F9