HYDRAULIC SYSTEM WITH ENERGY RECOVERY

Abstract

A hydraulic system, comprising: a hydraulic pump, a hydraulic load, and an electric machine. The electric machine working as an electric generator and mechanically coupled with said hydraulic pump. A low-pressure fluid tank and a valve assembly comprising one or more valves selectively fluidly connecting the hydraulic load with the low-pressure fluid tank.

Claims

1. A hydraulic system, comprising: a hydraulic pump/motor; a hydraulic load; an electric machine configured to work as an electric generator and mechanically coupled with the hydraulic pump/motor; a low-pressure fluid tank; and a valve assembly comprising one or more valves selectively fluidly connecting the hydraulic load with the low-pressure fluid tank; wherein, when the valve assembly is configured such that when the pressure at the hydraulic load is above a predetermined threshold pressure, the valve assembly fluidly connects the hydraulic load with the hydraulic pump/motor and fluidly disconnects the hydraulic load from the low-pressure fluid tank; wherein, when the pressure at the hydraulic load is below a predetermined threshold pressure, the valve assembly fluidly disconnects the hydraulic load from the hydraulic pump/motor and fluidly connects the hydraulic load with the low-pressure fluid tank, bypassing the hydraulic pump/motor.

2. The hydraulic system according to claim 1, wherein the hydraulic pump/motor is configured to pressurize a hydraulic fluid, wherein the hydraulic load is configured to store energy and to use the stored energy to generate pressure on the hydraulic fluid, wherein the valve assembly includes a first valve subassembly and a second valve subassembly, wherein the first valve subassembly is switchable between a first configuration which is a working configuration and a second configuration which is a relief configuration, wherein the first valve subassembly is fluidly connectable with the low pressure fluid tank through the second valve subassembly, wherein a first exit channel of the second valve subassembly is fluidly connectable with the low pressure fluid tank through a first relief channel and a second exit channel of the second valve subassembly is fluidly connectable with the low pressure fluid tank through a second relief channel, wherein the first relief channel passes through the hydraulic pump/motor in a way that allows the hydraulic fluid to drive the hydraulic pump/motor and the electric machine, wherein the second relief channel bypasses the hydraulic pump/motor, and wherein the second valve subassembly is controllable by the hydraulic pressure at the hydraulic load such as to open the first exit channel and close the second exit channel in case the hydraulic pressure at the hydraulic load is higher than the predetermined threshold pressure and to close the first exit channel and open the second exit channel in case the hydraulic pressure at the hydraulic load is lower than the predetermined threshold pressure.

3. The hydraulic system according to claim 1, wherein the first valve subassembly comprises a solenoid drivable 2-way valve.

4. The hydraulic system according to claim 1, wherein the second valve subassembly comprises one or more pressure-controlled valves, and comprises exclusively pressure-controlled valves.

5. The hydraulic system according to claim 1, wherein the valve assembly comprises a pilot operated valve and a sequence valve both fluidly connectable to the first valve subassembly.

6. The hydraulic system according to claim 1, wherein a first relief channel directly fluidly connects the second valve subassembly with the hydraulic pump/motor.

7. The hydraulic system according to claim 1, wherein a second relief channel fluidly connects the valve assembly with a flow control valve which is fluidly connectable to the low-pressure fluid tank such that the hydraulic fluid is passing from the second valve subassembly through the flow control valve to the low-pressure fluid tank.

8. The hydraulic system according to claim 1, wherein the first relief channel is passing through the hydraulic pump/motor to the low-pressure fluid tank.

9. The hydraulic system according to claim 1, wherein the first relief channel between the hydraulic pump/motor and the second valve subassembly is fluidly connectable to the low-pressure fluid tank by a safety relief valve.

10. The hydraulic system according to claim 1, wherein the hydraulic pump is fluidly connectable with the hydraulic load through a delivery channel which is passing through the first valve subassembly and bypassing the second valve subassembly.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0038] FIG. 1 shows a hydraulic system with a recovery system, wherein the valve assembly is only functionally represented.

[0039] FIG. 2 shows a first concrete implementation of the hydraulic system.

[0040] FIG. 3 shows a second implementation of the hydraulic system.

[0041] FIGS. 1-3 are shown approximately to scale.

DETAILED DESCRIPTION

[0042] FIG. 1 schematically shows a hydraulic load 2 with a piston 2a in a cylinder 2b which may be actuated by a pressurized hydraulic or work fluid. It is understood that in alternative embodiments the hydraulic load 2 may comprise a hydraulic motor, for example. For actuating the load 2, a hydraulic pump/motor 1 may generate high-pressurized hydraulic fluid which is delivered to the load 2 through a delivery channel 13 and partially through a relief channel 9b. The hydraulic pump/motor 1 is fluidly connected to the load 2 through the delivery channel 13. The delivery of pressurized hydraulic fluid from the pump/motor 1 to the load 2 is controlled by a first valve subassembly 5a of a valve assembly 5. The delivery channel 13 may bypass a second valve subassembly 5b, which is explained in more detail below. When the pump/motor 1 delivers pressurized hydraulic fluid to the load 2, the load 2 is actuated. For example, in a fork lifter the load 2 may be used to lift a weight. When the weight has been lifted, the first valve subassembly 5a may be used to fluidly disconnect load 2 from the pump/motor 1 and the weight may be held in the same position until a relief channel 9b, 10b is opened and the pressurized work fluid may flow from the load 2 through the relief channels to a low-pressure fluid tank 4.

[0043] The first valve subassembly 5a is fluidly connected with the second valve subassembly 5b. The second valve subassembly 5b has one or more hydraulic valves which are configured such that a first fluid exit 9a of the second valve subassembly 5b is opened if or when the pressure value on the load side of the second valve subassembly 5b is above a threshold value p*. In this case, the second exit channel 10a is closed at the same time.

[0044] The hydraulic fluid then flows through a first relief channel 9b, which may, in a part of its length, be identical to the delivery channel 13, to the hydraulic pump/motor 1 and further to the low-pressure fluid tank 4, thereby driving the hydraulic pump/motor 1. The hydraulic pump/motor 1 is mechanically coupled to the electrical machine 3 which may in this case act as a generator and generate electric energy. The electric energy may then be fed into a converter 14. The converter 14 may convert the electric energy to DC electric energy, for example, and may feed it into an energy storage device such as a battery 15.

[0045] The converter 14 may at the same time act as the control and energy source for a second electric motor 16. For example, the second electric motor 16 may be used to propel a vehicle comprising the hydraulic system, such as a fork lifter. This way, the battery 15 and the converter 14 may be used for control and as an energy source for both electric machines 3, 16. The second electric motor 16 may in a braking phase also act as a generator and feed energy into the battery 15.

[0046] If or when the pressure value at the load side of the second valve subassembly 5b is below the threshold p*, the first exit channel 9a is closed and the second exit channel 10a is opened such that the hydraulic fluid may be delivered directly from the second valve subassembly 5b through a second relief channel 10b to the fluid tank 4.

[0047] Using the modes of operation illustrated in FIG. 1, it is possible to guarantee that hydraulic fluid may flow from the load 2 to the low-pressure tank 4 in an appropriate time with an appropriate speed and that at the same time, if or when the pressure at the load 2 is sufficient, the hydraulic fluid may pass through the hydraulic pump/motor 1 and drive the hydraulic pump/motor 1. The hydraulic pump/motor may then drive a generator in order to recover energy and convert it into electric energy that may be stored in an energy storage such as an electric battery.

[0048] FIG. 2 shows a further embodiment of the hydraulic system explained with respect to FIG. 1. In the embodiment depicted in FIG. 2 the valve assembly 5 comprises three valves, a solenoid-actuated valve 6 which is driven by an electric signal and which selectively fluidly connects the hydraulic load 2 either with the hydraulic pump/motor 1 or with the valves 7, 8 of the second valve subassembly 5b. The valve 7 is a sequence valve which fluidly connects its entrance channel 17 to its exit channel 9a if or when the pressure at its entrance channel 17 is higher than p*. In this case, the valve 7 opens so that hydraulic fluid may pass through the valve 7 to the hydraulic pump/motor 1.

[0049] The valve 7 is hydraulically controlled and driven by the pressure at its entrance channel 17. The second valve subassembly further comprises a pilot-operated valve 8 which opens if or when the pressure at its entrance channel 18 is lower than the pressure p*. In this case, the valve 8 allows hydraulic fluid to pass through its exit channel 10a and through the second relief channel 10b to the low-pressure fluid tank 4. If or when or as soon as the pressure at the entrance channel 18 is above p*, the valve 8 closes. Valve 8, too, is controlled and operated using hydraulic pressure.

[0050] The exit channel 10a of the valve 8 is fluidly connected with the second relief channel 10b, which passes through a flow control valve 11. The flow control valve 11 is controlled by hydraulic pressure and compensates pressure variations and changes in order to guarantee a constant fluid flow.

[0051] The hydraulic pump/motor 1 is fluidly connected with the second valve subassembly 7, 8 via the first relief channel 9b. The first relief channel 9b is partially identical with the delivery channel 13 which is used to deliver high-pressurized fluid from the hydraulic pump/motor 1 to the load 2. The delivery channel 13 passes through the solenoid-actuated valve 6. The delivery channel or the solenoid-actuated valve 6 contains a check valve 19, 20 (FIG. 3). The check valve 19, 20 is configured to allow pressurized fluid to be delivered to the hydraulic load 2 through the check valve 19, 20, and to block the flow of hydraulic fluid from the load 2 towards the hydraulic pump/motor 1.

[0052] The sequence valve 7 and the pilot-operated valve 8 are fluidly connected to one another at their entrance channels 17, 18. The valves 7, 8 and are further connected to a fluid port or exit channel of the solenoid-actuated valve 6. The exit channel 9a of the sequence valve 7 is fluidly connected with the hydraulic pump/motor 1 and with the safety relief valve 12. The exit channel 10a of the pilot-operated valve 8 is fluidly connected with the flow control valve 11. The hydraulic load 2 is fluidly connected with an entrance channel of the solenoid-actuated valve 6.

[0053] FIG. 3 shows a variation of the embodiment depicted in FIG. 2.

[0054] In the embodiment shown in FIG. 3, the exit channel 19 of the solenoid-actuated valve 6 is fluidly connected or directly fluidly connected with the entrance channels 17, 18 of the sequence valve 7 and the pilot-operated valve 8. The exit channel 19 is further fluidly connected with to hydraulic pump/motor 1 through a check valve 20. The check valve 20 is configured to allow hydraulic fluid to flow through the check valve 20 from the hydraulic pump/motor 1 towards the hydraulic load 2, and blocks the flow of hydraulic through the check valve 20 from the hydraulic load 2 towards the hydraulic pump/motor 1. If or when the load 2 is relieved by opening the valve 6, hydraulic fluid under pressure may flow from the load 2 to the valves 7, 8 at the same time. The fluid path toward the hydraulic pump/motor 1 is blocked by the check valves 19, 20. The valves 7, 8 open according to the pressure valve regime described above so that the pressurized fluid from the load 2 either flows through the hydraulic pump/motor 1 if or when the pressure is high enough to exceed the value p*, or it flows through the valve 8 and the flow control valve 11 directly to the low-pressure fluid tank 4, thereby bypassing the hydraulic pump/motor 1.

[0055] The presently proposed hydraulic system may be used to recover hydraulic or hydrostatic energy from or via a hydraulic load, and to convert it to electric energy which may subsequently be stored in a storage device such as a battery. At the same time, it can be guaranteed that the pressure and/or speed of hydraulic fluid flowing from the hydraulic load to the low-pressure fluid tank is sufficient to allow the load to be relieved and the energy to be recovered fast enough, such as within a predetermined amount of time. For example, in a fork lifter, it can be guaranteed that the fork is lowered fast enough. The embodiments disclosed herein require few control means. The control means used are mostly based on hydraulically driven controls.

[0056] FIGS. 1-3 show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example.

[0057] It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. Moreover, unless explicitly stated to the contrary, the terms “first,” “second,” “third,” and the like are not intended to denote any order, position, quantity, or importance, but rather are used merely as labels to distinguish one element from another. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

[0058] As used herein, the term “approximately” is construed to mean plus or minus five percent of the range unless otherwise specified.

[0059] The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.