Technical Field

[0001] The present disclosure relates generally to a hydraulic system for a construction machine and a method of recovering energy in such a construction machine.

Background

[0002] In the field of heavy machinery designed for performing construction work, earthwork and mining, hydraulic machines such as excavators, loaders etc. are commonly used. Hydraulic fluid is pumped in a hydraulic system with fluid lines and valves to actuators including hydraulic cylinders and motors e.g., for hoisting/lowering a boom and rollback/dumping a bucket connected to the boom. During hoisting, the elevated boom and bucket, including any load therein, gains potential energy. During lowering of the boom, this potential energy is converted to heat as the hydraulic fluid is evacuated from the hydraulic cylinders and returned to a tank. The energy consumption of construction machine could be reduced by recovering the potential energy of the boom/bucket.

[0003] In order to recover energy, the hydraulic system requires additional components such as fluid lines and control valves to redirect the return fluid, either to an accumulator for storage or for generation of electrical energy via the pump/motor. This redirection of hydraulic fluid is often complicated and leads to energy losses through leakage, pressure losses and/or energy conversion. Hence there is a need to develop hydraulic systems which are less complicated and more efficient to prevent energy losses.

Summary of Invention

[0004] An objective of the present disclosure is therefore to provide an improved hydraulic system to solve the problems identified above.

[0005] According to a first aspect of the present disclosure, there is provided a hydraulic system for a construction machine, the hydraulic system comprising: a first actuator system comprising a first actuator and a first directional control valve, DCV. The first DCV comprises a supply port connected to a supply line, a return port connected to a return line, a first work port arranged in fluid communication with a piston side of the first actuator through a piston side actuator line, and a second work port arranged in fluid communication with a rod side of the first actuator through a rod side actuator line. The hydraulic system further comprises a pump arranged to supply hydraulic fluid to the first DCV through the supply line; a reservoir arranged to receive hydraulic fluid from the first DCV through the return line; and a controller configured to operate the pump and the first DCV. The first DCV is operable to selectively bring the pump in fluid communication with the first actuator system through the supply line and to selectively bring the first actuator system in fluid communication with the reservoir through the return line, to power the first actuator. The first DCV is operable to direct a return flow of hydraulic fluid from the first actuator system through the supply line to operate a hydraulic function in the hydraulic system separate from the first actuator.

[0006] By means of the bidirectional capability of the first DCV, the present disclosure provides an improved solution for recovering energy by directing the return flow of hydraulic fluid through the supply line to directly power a hydraulic function different from the first actuator. Hence, the need for redirection via additional control valves and fluid lines is obviated, thereby reducing the complexity of the hydraulic system and facilitating mounting on the construction machine. At the same time, energy losses are reduced since the pressure in the return flow of hydraulic fluid may be used directly to operate another hydraulic function in the hydraulic system separate from the first actuator without conversion to another energy form. Examples of hydraulic functions include actuators for movement of other components of the construction machine, or the construction machine as a whole.

[0007] In one embodiment, the first DCV may comprise a first pressure compensator. The first pressure compensator enables modulating the flow of hydraulic fluid through the first DCV to maintain a substantially constant pressure drop, thus providing a substantially constant flow rate.

[0008] In one embodiment, the first actuator may comprise at least one hydraulic boom cylinder, arranged to hoist and lower a boom of the construction machine. With the present solution, it is possible to recover energy during lowering of the boom.

[0009] In one embodiment, the hydraulic system may further comprise a first control valve interconnecting the piston side and rod side actuator lines and a second control valve arranged in the rod side actuator line, each of the first and second control valves being operable to selectively direct hydraulic fluid therethrough. By means of the control valves, the present solution enables redirecting a portion of the return flow of hydraulic from the piston side to the rod side of the first actuator. This is ideal in a first operating scenario with high pressure and corresponding low flow of hydraulic fluid. Conversely, in a second operating scenario with low pressure and corresponding high flow of hydraulic fluid, the control valves may be operated such that the return flow of hydraulic from the piston side of the first actuator is directed to the first DCV and the supply line, and the rod side of the first actuator is brought in fluid communication with the reservoir for refilling.

[0010] In one embodiment, the hydraulic system may further comprise a pressure sensor arranged to measure a pressure in the supply line and at least one pressure sensor arranged to measure a piston side and/or rod side pressure in the first actuator, wherein the controller is configured to operate the first DCV to direct hydraulic fluid from the supply line to the first actuator system only if the pressure in the supply line is higher than the piston side or rod side pressure in the first actuator. By measuring the pressure in the pump gallery and the cylinder chambers of the first actuator and controlling operation of the first DCV accordingly, a check valve functionality is achieved.

[0011] In one embodiment, said hydraulic function may comprise a second actuator system comprising a second actuator and a second DCV, the second DCV being operable to selectively bring the second actuator system in fluid communication with the supply line and the return line, to power the second actuator. By powering the second actuator by means of the hydraulic pressure of the return flow of hydraulic fluid in the supply line, the potential energy in the hydraulic system may be recovered whilst minimising energy losses from energy conversion.

[0012] In one embodiment, the second actuator may comprise a hydraulic bucket cylinder arranged to dump and roll back a bucket arranged on a boom of the construction machine. The present solution provides an efficient recovery of potential energy by rolling back the bucket, e.g. as a natural response to lowering of a boom.

[0013] In one embodiment, said hydraulic function comprises an accumulator connected to the supply line and/or an electric motor/generator connected to the pump and arranged to recover energy from a return flow of hydraulic fluid in the supply line. In cases where the amount of recoverable potential energy is higher than what is required to power a further hydraulic actuator, the remaining energy may be stored as pressurised hydraulic fluid in the accumulator or converted to electrical energy by the generator.

[0014] In a second aspect of the present disclosure, there is provided a construction machine comprising a boom and a hydraulic system according to the first aspect. The present solution enables reduced energy consumption in a construction machine compared to conventional hydraulic systems.

[0015] In a third aspect of the present disclosure, there is provided a method for recovering energy in a hydraulic system of a construction machine. The hydraulic system comprises a first actuator system comprising a first actuator and a first directional control valve, DCV. The first DCV comprises a supply port connected to a supply line, a return port connected to a return line, a first work port arranged in fluid communication with a piston side of the first actuator through a piston side actuator line, and a second work port arranged in fluid communication with a rod side of the first actuator through a rod side actuator line; a pump arranged to supply hydraulic fluid to the first DCV through the supply line. The hydraulic system further comprises a reservoir arranged to receive hydraulic fluid from the first DCV through the return line; and a controller configured to operate the pump and the first DCV. The first DCV is operable to selectively bring the pump in fluid communication with the first actuator system through the supply line and to selectively bring the first actuator system in fluid communication with the reservoir through the return line, to power the first actuator.

[0016] The method comprises the steps of: operating the pump and the first DCV to direct hydraulic fluid to the piston side of the first actuator to power the first actuator in a first direction; ceasing operation of the pump to allow the first actuator to move in a second direction, opposite the first direction, thereby discharging hydraulic fluid from the piston side of the first actuator through the piston side actuator line; directing a return flow of hydraulic fluid from the first actuator system through the supply line to operate a hydraulic function in the hydraulic system separate from the first actuator. [0017] In one embodiment, the first actuator may comprise at least one hydraulic boom cylinder, and wherein the first and second directions correspond to hoisting and lowering, respectively, of a boom of the construction machine.

[0018] In one embodiment, the method may further comprise: measuring a pressure in the supply line; measuring a piston side and/or rod side pressure in the at least one hydraulic boom cylinder; and operating the pump and the first DCV to direct hydraulic fluid from the supply line to the first actuator system only if the pressure in the supply line is higher than the piston side or rod side pressure in the at least one hydraulic boom cylinder.

[0019] In one embodiment, the hydraulic system may further comprise a first control valve interconnecting the piston side and rod side actuator lines and a second control valve arranged in the rod side actuator line, each of the first and second control valves being operable to selectively direct hydraulic fluid therethrough, the method comprising: in a first operating scenario, opening the first control valve and closing the second control valve to direct a portion of the return flow of hydraulic fluid from the piston side actuator line to the rod side actuator line; and in a second operating scenario, closing the first control valve and opening the second control valve to bring the rod side of the at least one hydraulic boom cylinder in fluid communication with the reservoir.

[0020] In one embodiment, said hydraulic function may comprise a second actuator system comprising a second actuator and a second DCV, the second DCV being operable to selectively bring the second actuator system in fluid communication with the supply line and the return line, to power the second actuator, the method comprising: operating the second DCV to direct the return flow of hydraulic fluid from the supply line to the second actuator system to power the second actuator in a first direction in response to movement of the first actuator in the second direction.

[0021] In one embodiment, the second actuator may comprise a hydraulic bucket cylinder arranged to dump and roll back a bucket arranged on a boom of the construction machine, wherein powering the hydraulic bucket cylinder in the first direction corresponds to rolling back the bucket. [0022] In one embodiment, said hydraulic function may comprise an accumulator connected to the supply line and/or an electric motor/generator connected to the pump, the method comprising: directing the return flow of hydraulic fluid to the accumulator for storage and/or to the pump to drive the electric motor/generator to generate electrical energy.

Brief Description of Drawings

[0023] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:

Figs, la-ld are side views of an exemplary construction vehicle comprising a boom and a bucket showing different working positions.

Fig. 2 is a schematic view of a hydraulic system according to one embodiment of the present disclosure in a first operation scenario.

Fig. 3 is a schematic view of a hydraulic system according to one embodiment of the present disclosure in a second operation scenario.

Fig. 4 is a schematic view of a hydraulic system according to one embodiment of the present disclosure.

Detailed Description

[0024] In the following, a detailed description of a hydraulic system according to the present disclosure is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of ‘including’, ‘comprising’, or ‘having’ and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms ‘mounted’, ‘connected’, ‘supported’, and ‘coupled’ and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, ‘connected’ and ‘coupled’ are not restricted to physical or mechanical connections or couplings.

[0025] In the context of the present disclosure, the term ‘flow path’ should be understood as the way or course followed by a fluid through the hydraulic system. A flow path does not necessarily constitute a physical structure of the hydraulic system, the term instead being used as a general description of how the fluid flows through the hydraulic system. A flow path may be defined by an internal passage in the hydraulic system or any component thereof which delimits the boundaries of the flow path and thereby constitutes a physical structure of the hydraulic system. An internal passage may in turn be subdivided into one or more sections, thus comprising conduits, channels, bores and/or openings which together form the internal passage.

[0026] Figs, la-ld are side views of a construction machine 1 in the form of a loader, e.g., used in underground mining or tunnelling, also known as an LHD (load, haul, dump) loader. The loader comprises a boom 2 which may be hoisted and lowered by means of one or more actuators such as hydraulic cylinders. Figs, la and lb show the boom 2 in a lowered position and Figs. 1c and Id show the boom 2 in an elevated position. A bucket 3 is mounted on the boom 2 and may be operated to roll back or dump by means of one or more actuators such as hydraulic cylinders. Figs, la and 1c show the bucket 3 in a rolled back position and Fig. lb shows the bucket 3 in a rolled forward position, whereas Fig. Id shows the bucket 3 in a dumping position. It is understood that the present disclosure is not limited to loaders used underground, but may encompass other types of construction machines comprising a boom and including hydraulic systems for operating various load implements such as steering, swinging, lifting etc. of the construction machine. Examples of other construction machines encompassed by the present disclosure include excavators. The construction machine 1 comprises a hydraulic system as will be further explained below.

[0027] Referring now to Fig. 2, there is shown a schematic view of a hydraulic system for a construction machine 1 according to the present disclosure. The hydraulic system comprises a first actuator system 10 with a first actuator 11 and a first directional control valve, DCV 12. The first actuator system 10 is connected to a pump 30 through a supply line 31 and to a reservoir 40 through a return line 41. The pump 30 is arranged to supply pressurised hydraulic fluid to the first actuator system 10 through the supply line 31 via the first DCV 12 to power the first actuator 11.

[0028] To that end, the first DCV 12 comprises a supply port P connected to a supply line 31, a return port T connected to a return line 41, a first work port A arranged in fluid communication with a piston side 13 of the first actuator through a piston side actuator line 14, and a second work port B arranged in fluid communication with a rod side 15 of the first actuator 11 through a rod side actuator line 16. The first DCV 12 may comprise a spool arranged inside a manifold or housing which is mechanically, electrically, pneumatically or hydraulically operated, e.g., by means of electromechanical solenoids. The spool comprises lands and grooves formed thereon to block or permit flow of hydraulic fluid through the DCV, depending on the position of the spool.

[0029] The first DCV 12 is operable to selectively bring the pump 30 in fluid communication with the first actuator system 10 through the supply line 31 and to selectively bring the first actuator system 10 in fluid communication with the reservoir 40 through the return line 41, to power the first actuator 11. More specifically, the first DCV 12 may be operable between a closed position (illustrated by the middle box in Fig. 2), a first working position (illustrated by the left box in Fig. 2) in which the supply port P is interconnected with the first work port A and the second work port B is interconnected with the return port T, and a second working position (illustrated by the right box in Fig. 2) in which the supply port P is interconnected with the second work port B and the first work port A is interconnected with the return port T. Sliding movement of the spool allows for controlling the position of the lands and grooves and vary the degree of opening in a continuous stepless manner, from fully closed to fully open as well as partially open, thereby controlling the flow of hydraulic fluid through the first DCV 12.

[0030] The hydraulic system further comprises a controller 50 arranged to operate the pump 30 and the first DCV 12. In order to power a first action of the first actuator 11, the first DCV 12 is brought to the first working position such that hydraulic fluid is supplied from the pump 30 through the supply line 31 and the piston side actuator line 14 to the piston side 13 of the first actuator 11. Thereby, the first actuator 11 is displaced in a first direction, e.g. upwards as illustrated by the arrows. At the same time, the rod side 15 of the first actuator 11 is placed in fluid communication with the reservoir 40 through the rod side actuator line 16 and the return line 41 such that hydraulic fluid displaced by the upwards movement of the first actuator 11 is directed to the reservoir 40.

[0031] Conversely, a second action by the first actuator 11, opposite the first action as illustrated by the downward arrows in Fig. 3, is powered by bringing the first DCV 12 to the second working position, whereby hydraulic fluid is supplied to the rod side 15 and evacuated from the piston side 13. In one embodiment, the first actuator 11 may comprise one or more hydraulic boom cylinders arranged to move the boom 2 of the construction machine 1. The first action then corresponds to hoisting of the boom 2 and the second action corresponds to lowering of the boom 2.

[0032] Instead of actively powering the first actuator 11 to perform the second action, i.e., lowering the boom 2, the hydraulic system according to the present disclosure is configured to allow the boom 2 to be lowered by means of an own weight fall due to gravity, as will be explained with reference to Figs. 4-6. The potential energy of the boom 2 gained by hoisting may then be recovered by utilizing the increase in hydraulic pressure on the piston side 13 of the first actuator 11. To that end, the first DCV 12 is operable to direct a return flow of hydraulic fluid from the first actuator system 10 through the supply line 31 to operate a hydraulic function in the hydraulic system separate from the first actuator 11. As such, the first DCV 12 is bidirectional, i.e., capable of directing flow in both directions. More specifically, the controller 50 is configured to cease operation of the pump 30 to lower the flow out from the pump 30 into the supply line 31, and to operate the first DCV 12 to the first working position to initiate a controlled own weight fall of the boom 2. This enables a return flow of hydraulic fluid from the piston side 13 of the first actuator 11 through the piston side actuator line 14, which is then directed through the first DCV 12 between the first work port A and the supply port P to the supply line 31.

[0033] Energy is then recovered by using this return flow of hydraulic fluid to operate the separate hydraulic function in the hydraulic system. Steps in a corresponding method for recovering energy in the hydraulic system as described herein above are carried out as follows. First, the pump 30 and the first DCV 12 are operated (by means of the controller 50) to direct hydraulic fluid to the piston side 13 of the first actuator 11 to power the first actuator 11 in a first direction, e.g. hoisting upwards. The operation of the pump 30 is then ceased to allow the first actuator 11 to move in a second direction, opposite the first direction, e.g. downwards, thereby discharging hydraulic fluid from the piston side 13 of the first actuator 11 through the piston side actuator line 14. The resulting return flow of hydraulic fluid from the first actuator system 10 is then directed through the supply line 31 to operate a hydraulic function in the hydraulic system separate from the first actuator 11.

[0034] In one embodiment, the separate hydraulic function comprises a second actuator system 20 comprising a second actuator 21 and a second DCV 22, the second DCV being operable to selectively bring the second actuator system in fluid communication with the supply line 31 and the return line 41, to power the second actuator 21. The second DCV 22 may be similar to the first DCV 12 as described above having first and second work ports, a supply port and a return port, and may be operated between a closed position and first and second working positions to direct flow of hydraulic fluid to and from the second actuator 21 and thereby power the latter. During normal operation, hydraulic fluid is supplied to the second actuator system 20 from the pump 30 and returned to the reservoir 40, similar to the first actuator system. In the case of energy recovery, the hydraulic fluid is instead supplied from the first actuator system 10 as a return flow of hydraulic fluid through the supply line 31. The second DCV 22 is then operated to direct the return flow of hydraulic fluid from the supply line 31 to the second actuator system 20 to power the second actuator 21 in a first direction in response to movement of the first actuator 11 in the second direction.

[0035] In one embodiment, the first DCV 12 may comprise a first pressure compensator 17 which may be arranged in the supply line 31 between the pump 30 and the supply port A of the first DCV 12. Such an arrangement with the first pressure compensator 17 upstream of the first DCV 12 (during normal operation) is known as precompensation. It is also foreseen to provide a post-compensation arrangement with the first pressure compensator 17 downstream of the first DCV 12. The first pressure compensator 17 comprises two pilot passage or load sensing (LS) channels (indicated by the hatched lines in Figs. 2-6) for measuring the pressure drop across the first DCV 12. In operation, the first pressure compensator 17 is configured to open or close to substantially maintain the differential pressure across the first DCV 12, and thereby modulate the flow rate. Similar to the first DCV 12, the first pressure compensator 17 is bidirectional as indicated by the arrows inside the box in Figs. 2-6 to allow fluid flow in both directions. Return flow of hydraulic fluid during energy recovery is not modulated by the first pressure compensator 17. Additionally, the second DCV 22 may comprise a second pressure compensator 27 operating in a similar manner to the first pressure compensator 17 with the difference that the second pressure compensator 27 comprises a check valve such that flow is only permitted in the direction from the supply line 31 to the second actuator system 20.

[0036] In one embodiment, the second actuator 21 comprises one or more hydraulic bucket cylinders arranged to move the bucket 3 arranged on the boom 2 of the construction machine 1. The first action then corresponds to rolling the bucket 3 back and the second action corresponds to rolling the bucket 3 forward, i.e. dumping the bucket 3. In a common operating situation, after emptying the contents of the bucket 3 in an elevated position of the boom 2, roll back of the bucket 3 is performed concomitantly with lowering of the boom 2 to avoid the lip of the bucket 3 from touching the ground. When driving the construction machine 1, it is also desirable that the bucket lip is visible to the operator to avoid collisions. By means of the hydraulic system according to the present disclosure, energy may be recovered by directing the return flow of hydraulic fluid from the piston side 13 of the hydraulic boom cylinder(s) to the piston side of the hydraulic bucket cylinder. Thus, the energy consumption of the construction machine 1 is reduced.

Additionally, by providing a bidirectional DCV, the existing supply line 31 may be utilized for the return flow of hydraulic fluid, thereby obviating the need for additional control valves and fluid lines.

[0037] Referring now to Figs. 4 and 5, two different pressure and flow scenarios during energy recovery are illustrated. The first actuator system 10 is here provided with a first control valve 18 which interconnects the piston side actuator line 14 and the rod side actuator line 16, and a second control valve 19 arranged in the rod side actuator line 16. The second control valve 19 is arranged between the first DCV 12 and the connection point between the first control valve 18 and the rod side actuator line 16. Each of the first and second control valves is operable to selectively direct hydraulic fluid therethrough.

[0038] In Fig. 4, when a large force is required to operate the separate hydraulic function, a high pressure is generated in the return flow of hydraulic fluid leading to a corresponding low flow. In such a case, the first control valve 18 is opened and the second control valve is closed such that a portion of the return flow of hydraulic fluid from the piston side 13 of the first actuator 11 is directed from the piston side actuator line 14 to the rod side actuator line 16 and further to the rod side 15 of the first actuator 11.

[0039] In Fig. 5 on the other hand, when only a small force is required to operate the separate hydraulic function, a low pressure is generated in the return flow of hydraulic fluid leading to a corresponding high flow. In such a case, the first control valve 18 is closed and the second control valve 19 is opened such that the return flow of hydraulic fluid from the piston side 13 of the first actuator 11 is directed from the piston side actuator line 14 to the first work port A of the first DCV 12 and further to the supply line 31, whereas the rod side 15 is placed in fluid communication with the reservoir 40 through the second work port B of the first DCV 12 and the return line 41. In both the above cases, hydraulic fluid to refill the rod side 15 of the first actuator 11 is taken from the source which requires the least amount of energy required to ensure optimal operation and reduce energy consumption.

[0040] Furthermore, the hydraulic system may comprise pressure sensors to measure the pressure at various points in the hydraulic system, including a first pressure sensor 32 arranged to measure the pressure in the supply line 31 (i.e. pump gallery), a second pressure sensor 33 arranged to measure a piston side pressure in the first actuator 11, and a third pressure sensor 34 arranged to measure a rod side pressure in the first actuator 11 (i.e. the respective cylinder chambers). The controller 50 is connected to the pressure sensors 32-34 to receive pressure measurements therefrom. Further, the controller 50 is configured to operate the first DCV 12 in dependence of the sensed pressures. More specifically, during normal operation the first DCV 12 is operated to direct hydraulic fluid from the supply line 31 to the first actuator system 10 only if the pressure in the supply line is higher than the piston side or rod side pressure in the first actuator 11. Conversely, if the pressure in the supply line 31 is lower than the piston side or rod side pressure in the first actuator 11, the first DCV 12 is operated to block flow of hydraulic fluid from the supply line 31 to the first actuator system 10. Thus, by means of the pressure sensors 32-34 and the controller 50, the first DCV 12 is operated to act as a check valve to prevent unwanted reverse flow of hydraulic fluid. Further pressure sensors (not shown) may be provided to measure pressure in the second actuator system 20, for instance at the LS channel of the second pressure compensator 27 and/or at the work ports of the second DCV 22.

[0041] Similarly, during energy recovery the return flow of hydraulic fluid from the first actuator system 10 to the supply line 31 is only permitted when the piston side pressure in the first actuator 11 exceeds the pressure in the supply line 31.

[0042] In case the energy to be recovered from the first actuator 11 exceeds the required energy to operate the second actuator 21, the return flow of hydraulic fluid may be utilized to operate other hydraulic functions in the construction machine 1 such as e.g. steering, swinging or lifting as indicated by the connection at the bottom right of Fig. 6. Alternatively or additionally, the return flow of hydraulic fluid may be directed to an accumulator 60 connected to the supply line 31 for storage and/or an electric motor/generator 70 connected to the pump 30 to generate electrical energy which may be stored in a battery (not shown).

[0043] Embodiments of a hydraulic system according to the present disclosure has been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0044] All the described alternative embodiments above or parts of an embodiment can be freely combined without departing from the inventive idea as long as the combination is not contradictory.