Hydraulic system

Abstract

The present disclosure relates to a hydraulic system with at least two main control valves and with a hydraulic pilot control system for actuating the main control valves, wherein the hydraulic pilot control system and/or the main control valves are constructed such that the at least two main control valves open one after the other.

Claims

1. A hydraulic system comprising at least first and second main control valves, a pressure reducing valve, and a hydraulic pilot control system for actuating the pressure reducing valve and the first main control valve via a common control pressure, wherein each main control valve includes a spring, and wherein the springs of the main control valves have different spring forces such that the main control valves open in different pressure ranges, and wherein the second main control valve is actuated via an outlet pressure of the pressure reducing valve.

2. The hydraulic system according to claim 1, wherein the first and second main control valves further include different valve rods and/or valve housings to open the first and second main control valves at different strokes.

3. The hydraulic system according to claim 1, wherein at least one of the main control valves is charged with a counterpressure which counteracts the common control pressure.

4. The hydraulic system according to claim 1, wherein at least one of the main control valves is charged with a counter control pressure via a pressure shut-off valve, which counteracts the common control pressure and rises with the common control pressure up to a shut-off pressure.

5. The hydraulic system according to claim 1, wherein the common control pressure is supplied to the first and second main control valves via a common high-pressure supply.

6. The hydraulic system according to claim 1, wherein the common control pressure is supplied via a common variable displacement pump, wherein the variable displacement pump is actuated via a load sensing arrangement.

7. A hydraulically driven implement with the hydraulic system according to claim 1.

8. The hydraulic system of claim 7, wherein the implement is a mobile implement, and wherein the first and second main control valves separately control at least two separate loads.

9. The hydraulic system of claim 7, wherein the implement is a hydraulically driven implement comprising at least two hydraulic pumps for supplying hydraulic pressure for loads of the implement, wherein the at least two main control valves are separately supplied by the first and second hydraulic pumps, and wherein the first and second main control valves supply the same load with hydraulic fluid.

10. The hydraulic system of claim 9, wherein the load that is supplied by the first and second main control valves includes a slewing gear, a traveling gear, or a hydraulic cylinder.

11. The hydraulic system of claim 1, wherein the first and second main control valves control a common load.

12. A hydraulic system comprising: a first main control valve actuating a first load and having a first spring; a second main control valve actuating a second load separate from the first load and having a second spring; and a hydraulic pilot control system for actuating the main control valves via a common control pressure, wherein the first and second springs have different spring forces, and wherein the main control valves have different valve rods and/or valve housings, such that the main control valves open at different strokes due to the different valve rods and/or valve housings and at different control pressures due to the different spring forces, only one after the other.

13. The system of claim 12, wherein the first load is a slewing gear or a traveling gear.

14. The system of claim 13, wherein the second load is a hydraulic cylinder.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a first exemplary embodiment of a hydraulic system according to the present disclosure with main control valves with different spring strengths.

(2) FIG. 2 shows a second exemplary embodiment of a hydraulic system according to the present disclosure with main control valves with differently machined valve rods.

(3) FIG. 3 shows a third exemplary embodiment of a hydraulic system according to the present disclosure with a cascading realized via the pilot control unit.

(4) FIGS. 4a to 4d show four embodiments with different implementations of the cascade control system of the present disclosure with one or more hydraulic pumps and/or one or more loads.

(5) FIG. 5 shows an embodiment of the cascade control system of the present disclosure with more than two main control valves and/or more than two hydraulic pumps.

(6) It should be understood by one skilled in the art that the figures utilize standardized symbols for hydraulic systems, and thus example embodiments may optionally include the detailed features of components as represented.

DETAILED DESCRIPTION

(7) The exemplary embodiments of the present disclosure relate to hydraulic systems comprising at least two main control valves, in particular a multi-circuit load sensing system with downstream summation, which are hydraulically operated under pilot control. According to the present disclosure, there is provided a cascade connection by which the hydraulic control slides used as main control valves are opened in a certain sequence.

(8) The actuation of the system is effected via a common pilot control transmitter 1, in particular a control system via which a certain control pressure is generated for pilot control. The pilot control transmitter for example can be a joystick. The pilot control transmitter 1 can be charged with a constant pilot pressure via a pilot pressure source 15, as it is shown for example in FIG. 3, and reduces the same to the desired control pressure. The constant pilot pressure for example can amount to 35 bar.

(9) Due to its mechanical or hydraulic construction, the hydraulic system according to the present disclosure now allows a cascading of the opening times despite this common actuation. On the one hand, the cascade connection can be realized via different valve springs of the main control valves or via different slide opening starts of the main control valves. There can also be provided a hydraulic cascade pilot control unit, so that the cascade connection is effected via the pilot control. These three alternatives will now again be explained in detail with reference to the exemplary embodiments shown in FIGS. 1 to 3.

(10) FIG. 1 shows two main control valves 2 and 3, which each are charged with the same control pressure of the pilot control transmitter 1 at their control pressure ports 4 and 5. According to the present disclosure, the valve springs 6 and 7 of the two main control slides 2 and 3 are chosen such that, e.g., the spring of the slide 2 responds in a first pressure range and the spring of the slide 3 responds in a second pressure range. For example, the spring 6 of the slide 2 can be chosen such that the same responds in a pressure range between 0 and 20 bar, whereas the spring 7 of the slide 3 responds in the range from 20 to 35 bar. Due to the different valve springs, different opening starts thus are achieved.

(11) Alternatively or in addition, in one of the slides (in FIG. 1 the slide 3) a pressure source or corresponding circuit 9 can be provided, which charges the same with a counterpressure. The same effect thereby is achieved as by the mechanical amplification of the spring strength of the slide 3. Via the counter control pressure port 8, the valve 3 is charged with a counter control pressure from the circuit 9, wherein the counterpressure advantageously is constant.

(12) The same spring strength thereby can be used as in the slide 2, which now is amplified via the pressure source 9, since the counterpressure adds up to the spring pressure. For example, the spring strength for the valve 3 likewise can lie between 0 and 20 bar and be amplified by 10 bar from the pressure source 9.

(13) In the variant shown in FIG. 2, the opening starts of the main slides 2 and 3 are, however, mechanically fixed differently on the valve rods 10 and 11. Depending on the manufacturer of the basic slide, this can be effected in the form of grooves or holes. As a result, a cascade connection can be established by slide hardware without corresponding switching logic.

(14) As shown in FIG. 2, both pistons 10 and 11 have the same stroke 12, but the piston of the main control valve 2 already opens after a short distance, whereas the piston of the main control valve 3 only opens later by the stroke 13. In the exemplary embodiment, this is achieved in that the groove 14 on the valve rod 11 of the main control valve 3 is shorter than the groove 14 on the valve rod 10 of the main control valve 2, and thus will only connect the pressure supply P with the opening A or A leading to the load at a larger stroke. As noted, the pressure supply P may be provided via a common variable displacement pump P for driving the at least two loads, such as first load (load 1) and second, separate, load (load 2), wherein the variable displacement pump is actuated via a load sensing arrangement LS. The box illustrating load 1 may represent a first gear of a boom, such as a slewing gear or traveling gear, or a hydraulic cylinder of a boom. Likewise, with regard to load 2.

(15) In this exemplary embodiment, the valve springs 6 and 7 also can be designed identically, so that the different opening starts solely are effected by the mechanical design of the valve rods. Alternatively, this might also be effected by a different mechanical design of the valve housings.

(16) In the variant shown in FIG. 3, the cascade connection however is realized via a corresponding design of the pilot control valve unit. In particular, the main control slides 2 and 3 thus can be used unchanged. In FIG. 3, two different variants in turn are combined, which can however also be used individually.

(17) On the one hand, a pressure reducing valve 16 can be provided, which is charged with the constant pilot pressure from the pilot pressure source 15. The pressure reducing valve 16 is charged with the control pressure 17 of the pilot control transmitter 1 and has a certain pressure ratio x, so that at the pressure outlet 18 of the pressure reducing valve 16 x times the control pressure 17 is applied. The first main control valve 2 is charged with the actual control pressure 17, the second main control valve 3 with the changed control pressure 18 of the pressure reducing valve. Thus, x times the control pressure specified by the control transmitter acts on the pressure port 5 of the main control valve 3, whereas the simple control pressure specified at the control transmitter 1 acts on the piston pressure port 4 of the main control valve 2.

(18) Alternatively or in addition, a pressure shut-off valve 19 can be provided, which is charged with the control pressure from the pilot pressure transmitter 1 and has a defined shut-off pressure. Via the pressure from the pressure shut-off valve 19, a counterpressure is exerted on the pressure port 4 of the main control valve 2. As long as the control pressure lies below the shut-off pressure of the shut-off valve 19, the same pressure acts on both sides a and b of the main control valve 2, so that the same stops in the neutral position. When the control pressure specified at the control transmitter 1 now is increased above the shut-off pressure set at the pressure shut-off valve 19, the pressure at the pressure port 4 will only be increased on the a side, whereas on the b side the pressure set in the shut-off valve 19 remains the same, so that the pressure port 4 now likewise is deflected via the pressure difference between a and b.

(19) As shown in FIG. 3, both variants can also be combined, so that the one valve is charged with counterpressure via the pressure shut-off valve, whereas the other valve is actuated via the pressure reducing valve.

(20) In the case of several valves it would also be conceivable to use several pressure reducing valves with different pressure ratio and/or several pressure shut-off valves with different shut-off pressures.

(21) Furthermore, in the case of two main control valves the pressure for both main control valves also might each be applied via pressure reducing valves with different pressure ratio or via pressure shut-off valves with different shut-off pressure.

(22) FIGS. 4a to 4d show four embodiments showing different implementations of the cascade control system of the present invention with one or more hydraulic pumps and/or one or more loads. In FIG. 4a, the two main control valves 2 and 3 are connected entirely in parallel, are supplied by a common hydraulic pump 30 and control the same load 40. In FIG. 4b, the two main control valves 2 and 3 are connected in parallel with respect to the pump side and are supplied by a common hydraulic pump 30, but control separate loads 41 and 42. In FIG. 4c, the two main control valves 2 and 3 are connected in parallel with respect to the load side and control the same load 40, but are separately supplied by separate hydraulic pumps 31 and 32. In FIG. 4d, the two main control valves 2 and 3 are neither connected in parallel with respect to the pump side, nor with respect to the load side. They are separately supplied by separate hydraulic pumps 31 and 32 and control separate loads 41 and 42. FIG. 5 shows an embodiment where more than two main control valves are used. The main control valves 50 to 53 are separately supplied by separate hydraulic pumps 31 to 34, but control the same load 40.

(23) In an embodiment, the hydraulic system is constructed such that the more than two main control valves 50 to 53 open and close in a predefined sequence.

(24) In particular with a high-pressure supply of a multi-circuit system via a load sensing control with downstream summation, the present disclosure allows to hydraulically operate the main control valves under pilot control and nevertheless achieve a cascade connection.

(25) Hydraulic systems according to the present disclosure in particular can be employed in mobile working machines, such as in a hydraulic excavator.