Hydraulic system for a construction machine and a method of operating a hydraulic system

Abstract

A hydraulic system of a construction machine, comprising an actuator comprising a piston side chamber and a rod side chamber, a directional control valve (DCV), a first control valve arranged to selectively open or close a connection line fluidly interconnecting a piston side actuator line and a rod side actuator line, a second control valve arranged to selectively open or close the rod side actuator line, and a controller configured to operate at least the DCV, the first control valve and the second control valve, wherein the controller is arranged to control the hydraulic system to one of a slow operating mode and a fast operating mode.

Description

[0001] HYDRAULIC SYSTEM FOR A CONSTRUCTION MACHINE AND A METHOD OF

[0002] OPERATING A HYDRAULIC SYSTEM

[0003] TECHNICAL FIELD

[0004] The present disclosure generally relates to a hydraulic system for a construction machine and a method of operating a hydraulic system in such a construction machine.

[0005] BACKGROUND OF THE INVENTION

[0006] Heavy construction machines such as loaders, excavators, bulldozers etc. commonly use hydraulic systems to actuate machine components such as buckets, booms, drills and many more. Commonly, hydraulic fluid is pumped by one or more pumps and led via fluid lines and valves to actuators. The actuators may be in the form of hydraulic cylinders, e.g., for controlling the extension or retraction of a boom or a bucket. When fluid is passing hydraulic components such as valves, fluid lines or other flow restrictions, energy is lost due to friction and pressure losses. In complex hydraulic systems, this may lead to significant energy losses which have to be compensated for by pumping fluid at higher power in order to achieve a desired actuator speed. These energy losses contribute adversely to the overall efficiency of the construction machine.

[0007] There is a general desire in the industry to decrease energy consumption of construction machines and to increase actuator speeds. Hence, there is a desire for more energyefficient hydraulic systems with decreased internal flow resistances allowing for an increased actuator speed.

[0008] SUMMARY OF THE INVENTION

[0009] A primary object of the present disclosure is to achieve an in at least some aspect improved hydraulic system for a construction machine, and an in at least some aspect improved method for controlling a hydraulic system of a construction machine. In particular, it is an object to provide such a system and method that achieves a faster actuator motion while at the same time being more energy efficient. The above and further objects are solved by the subject matter of the appended independent claims. Further advantageous embodiments can be found in the dependent claims.

[0010] According to a first aspect of the disclosure, at least the primary object is achieved by a hydraulic system of a construction machine, comprising:

[0011] - an actuator, the actuator comprising at least one cylinder and at least one piston with a piston rod, each cylinder comprising a piston side chamber and a rod side chamber,

[0012] - a directional control valve, DCV, wherein the DCV comprises a supply port connected to a fluid supply line, a return port connected to a return line, a first work port connected to the piston side chamber of the actuator via a piston side actuator line and a second work port connected to the rod side chamber of the actuator via a rod side actuator line, wherein the DCV in a first position fluidly connects the supply port with the first work port and the return port with the second work port and in a second position fluidly connects the supply port with the second work port and the return port with the first work port,

[0013] - a first control valve arranged to selectively open or close a connection line fluidly interconnecting the piston side actuator line and the rod side actuator line,

[0014] - a second control valve arranged to selectively open or close the rod side actuator line, and

[0015] - a controller configured to operate at least the DCV, the first control valve and the second control valve.

[0016] The controller is arranged to control the hydraulic system to one of a slow operating mode and a fast operating mode. In the slow operating mode, the controller is arranged to control the first control valve to a closed state and to control the second control valve to an open state.

[0017] In the fast operating mode during extension of the actuator, the controller is arranged to control the first control valve to an open state and the second control valve to a closed state.

[0018] Further, in the fast operating mode during retraction of the actuator, e.g., gravity induced retraction, the controller is arranged to control the first control valve to an open state and to either control the second control valve to a closed state, or to block fluid flow through the fluid supply line.

[0019] The fast operating mode and the slow operating mode are herein distinguished by the fact that faster extension and retraction of the actuator is enabled in the fast operating mode than in the slow operating mode. In the disclosed hydraulic system, the actuator may selectively be operated in two modes with different speeds both during extension and retraction of the actuator. In the fast operating mode, a fluid connection is created between the rod side chamber and the piston side chamber of the actuator. Hence, parts of the fluid do not have to pass the DCV as would otherwise be necessary but can directly flow between the actuator chambers. Thus, there is much less flow resistance in the fast operating mode compared to the slow operating mode, since there is less fluid flow through the DCV. The actuator can therefore be actuated faster and with less energy losses than in the slow operating mode. The controller may selectively control the actuator to the slow operating mode and the fast operating mode depending on working conditions of the construction machine. In particular, the fast operating mode may be activated upon a request of an operator. The controller may check if the fast operating mode may be activated, and under certain circumstances prohibit the activation of the fast operating mode. An operator may e.g., under certain conditions desire to activate the fast operating mode in order to save time and energy. In other working conditions, the operator may e.g., want to control the actuator with high precision and therefore prefer to operate the actuator in the slow operating mode. The switching between the operating modes may be initiated (desired) by an operator or by an autonomous system or by a remote system.

[0020] Optionally, the hydraulic system may further comprise a pressure compensator in the fluid supply line, wherein, in the fast operating mode during retraction of the actuator, the controller is arranged to control the pressure compensator to a closed state. The pressure compensator is a widely used component in hydraulic systems and enables modulating the flow through the DCV to maintain a substantially constant pressure drop, thus providing a substantially constant flow rate. For the purpose of achieving a fast operating mode during retraction, the pressure compensator may also be used to close the fluid supply line instead of the second control valve . Thus, an alternative way of achieving the fast operating mode during retraction of the actuator is provided which may be useful in case the second control valve cannot be in the closed state for purposes outside of the scope of the disclosure. Further, by using the compensator to block the fluid supply line, components that are already present on common hydraulic systems are used to achieve the fast operating mode during retraction. Optionally, the controller is arranged to control the pressure compensator to the closed state by controlling a pilot valve to an open state, wherein the pilot valve is fluidly connected to the return line, the pressure compensator and the DCV. For this purpose, a load sensing (LS) channel of the DCV is connected to the reservoir.

[0021] Optionally, the controller is configured to selectively control the hydraulic system to the slow operating mode and the fast operating mode both during extension and retraction of the actuator. Hence, extension and retraction may be carried out both in the slow operating mode and in the fast operating mode.

[0022] Optionally, the fluid supply line is fluidly connected to at least one pump. Alternatively, the fluid supply line may be fluidly connected to an external fluid supply or a reservoir capable of providing pressurized hydraulic fluid. Thereby, the hydraulic system can be easily adapted to the circumstances at the construction site.

[0023] Optionally, the return line is fluidly connected to at least one reservoir. Thereby, hydraulic fluid is collected and recycled.

[0024] Optionally, the actuator is arranged to hoist and lower a boom of the construction machine. Thereby, a selective switching between a slow operating mode and a fast operating mode for a boom of a construction machine is achieved.

[0025] Optionally, the actuator is arranged to dump and roll back a bucket arranged on a boom of the construction machine. This enables the selective switching between a slow and a fast operating mode also for a bucket of a construction machine. Of course, the person skilled in the art realizes that the disclosed hydraulic system can be arranged to power any actuator of a construction machine.

[0026] Optionally, the hydraulic system comprises at least one of a first pressure sensor indicative of a piston side pressure and a second pressure sensor indicative of a rod side pressure. The piston side pressure may be measured in the piston side chamber of the actuator, the piston side actuator line or at drilling at the DCV. Analogously, the rod side pressure may be measured in the rod side chamber of the actuator, the rod side actuator line or at drilling at the DCV. Thereby, a smoother and safer control of the actuator is enabled, particularly when switching between the slow operating mode and the fast operating mode.

[0027] Optionally, the controller is configured to activate the fast operating mode in dependence on the piston side pressure and / or the rod side pressure. Since activating the fast operating mode as described above implies that the first control valve is opened in order to fluidly connect the piston side chamber and the rod side chamber of the actuator, a sudden pressure jump occurs to a post activation pressure which is approximately equal to the piston and rod side area ratios of the hydraulic system. If the post activation pressure is too large there is a risk that other parts of the hydraulic system will be negatively affected. For example, a large pressure jump may trigger opening of safety valves or the like, which may lead to pressure loss and unintended actuator movements. This risk is mitigated by activating the fast operation mode in dependence on the piston side pressure and / or rod side pressure.

[0028] Optionally, the controller is configured to predict a post-activation pressure in dependence on the piston side pressure and / or the rod side pressure and to activate the fast operating mode only when the predicted post-activation pressure fulfills a predetermined condition, such as being lower than a threshold pressure. Thereby, too high post activation pressures when activating the fast operating mode are prevented and the risk for unintended actuator movements is decreased.

[0029] Optionally, the actuator acts during extension against a gravitational load, such as by lifting a load. This obviously implies that the actuator is pushed in the retraction direction at least partly by the gravitational load during retraction. This is important since in the fast operating mode, the rod side chamber is not supplied with pressurized hydraulic fluid in retraction direction, but only with fluid from the piston side chamber of the actuator. Hence, retraction in the fast mode relies on a gravitational load pushing the actuator inwards, i.e. in the direction of retraction.

[0030] According to a second aspect of the disclosure, at least the primary object is achieved a construction machine comprising the hydraulic system according to the first aspect.

[0031] Advantages of the second aspect largely correspond to those of the first aspect. According to a third aspect, at least the primary goal is achieved by a method for controlling a hydraulic system of a construction machine, the hydraulic system comprising:

[0032] - an actuator, comprising at least one cylinder and at least one piston with a piston rod, each cylinder comprising a piston side chamber and a rod side chamber,

[0033] - a directional control valve, DCV, wherein the DCV comprises a supply port connected to a fluid supply line, a return port connected to a return line, a first work port connected to the piston side chamber of the actuator via a piston side actuator line and a second work port connected to the rod side chamber of the actuator via a rod side actuator line, wherein the DCV in a first position fluidly connects the supply port with the first work port and the return port with the second work port and in a second position fluidly connects the supply port with the second work port and the return port with the first work port,

[0034] - a first control valve arranged to selectively open or close a connection line fluidly interconnecting the piston side actuator line and the rod side actuator line,

[0035] - a second control valve arranged to selectively open or close the rod side actuator line, and

[0036] -a controller configured to operate at least the DCV, the first control valve and the second control valve.

[0037] The method comprises controlling the hydraulic system to one of a slow operating mode and a fast operating mode. Controlling the hydraulic system to the slow operating mode comprises controlling the first control valve to a closed state and controlling the second control valve to an open state. Controlling the hydraulic system to the fast operating mode, during extension of the actuator, comprises controlling the first control valve to an open state and the second control valve to a closed state. Controlling the hydraulic system to the fast operating mode, during retraction of the actuator, comprises controlling the first control valve to an open state and to either control the second control valve to a closed state, or to block fluid flow through the fluid supply line.

[0038] Advantages and advantageous embodiments of the third aspect largely correspond to those of the first aspect.

[0039] Optionally, the hydraulic system further comprises a pressure compensator in the fluid supply line and the method further comprises: in the fast operating mode during retraction of the actuator, controlling the pressure compensator to a closed state. Optionally, controlling the pressure compensator to a closed state comprises: controlling a pilot valve to an open state, wherein the pilot valve is fluidly connected to the return line, the pressure compensator and the DCV's LS channel.

[0040] Optionally, the hydraulic system comprises at least one of a first pressure sensor indicative of a piston side pressure and a second pressure sensor indicative of a rod side pressure, the method further comprising: activating the fast operating mode in dependence on the piston side pressure and / or the rod side pressure.

[0041] Optionally, the method further comprises: predicting a post-activation pressure in dependence on the piston side pressure and / or the rod side pressure and activating the fast operating mode only when the predicted post-activation pressure fulfills a predetermined condition, such as being lower than a threshold pressure.

[0042] Further advantages and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In the following, the technology disclosed will be described in detail, with reference to exemplifying embodiments and to the enclosed drawings. In the drawings:

[0045] Figs. 1a-1d are side views of an exemplary construction vehicle comprising a boom and a bucket in different working positions.

[0046] Fig. 2a schematically illustrates a hydraulic system in a slow operating mode during actuator extension according to an embodiment of the disclosure.

[0047] Fig. 2b schematically illustrates a hydraulic system in a slow operating mode during actuator retraction according to an embodiment of the disclosure.

[0048] Fig. 2c schematically illustrates a hydraulic system in a fast operating mode during actuator extension according to an embodiment of the disclosure.

[0049] Fig. 2d schematically illustrates a hydraulic system in a fast operating mode during actuator retraction according to an embodiment of the disclosure. Fig. 2e schematically illustrates a hydraulic system in an alternative fast operating mode during actuator retraction according to an embodiment of the disclosure.

[0050] Fig. 3 schematically illustrates a method for controlling an actuator according to an embodiment of the disclosure.

[0051] The drawings show diagrammatic, exemplifying embodiments of the present disclosure and are thus not necessarily drawn to scale. It shall be understood that the embodiments shown and described are exemplifying and that the disclosure is not limited to these embodiments. It shall also be noted that some details in the drawings may be exaggerated in order to better describe and illustrate the disclosure. Like reference characters refer to like elements throughout the description, unless expressed otherwise.

[0052] DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

[0053] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

[0054] Figs. 1a-1d 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 a hydraulic system (not shown) comprising one or more actuators such as hydraulic cylinders. Figs. 1a and 1b show the boom 2 in a lowered position and Figs. 1c and 1d 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. 1a and 1c show the bucket 3 in a rolled back position and Fig. 1b shows the bucket 3 in a rolled forward position, whereas Fig. 1d 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, e.g., excavators, demolition machines, drilling machines, forklifts, or tractors. The construction machine 1 comprises one or more hydraulic systems as will be further explained below.

[0055] Fig. 2a schematically illustrates a hydraulic system 100 according to some embodiments of the disclosure. The hydraulic system 100 is here shown in a slow mode during extension of an actuator 10. The actuator 10 comprises at least one cylinder 11, e.g., double-acting cylinder 11. Each cylinder 11 comprises a piston side chamber 13 and a rod side chamber 15. The piston side chamber 13 is connected to a piston side actuator line 14 for supplying or retracting fluid from the piston side chamber 13. Analogously, the rod side chamber 15 is connected to a rod side actuator line 16 for supplying or retracting fluid from the rod side chamber 15. Further, the hydraulic system 100 comprises a directional control valve, DCV, 12. The DCV 12 comprises a supply port P connected to a fluid supply line 31 , a return port T connected to a return line 41. Further, the DCV 12 has a first work port A connected to the piston side chamber 13 of the actuator via the piston side actuator line 14 and a second work port B connected to the rod side chamber 15 of the actuator 10 via the rod side actuator line 16. As illustrated, the DCV 12 has two or more positions, here three, which allow for selectively powering the actuator to extend or retract. In a first position (the left-most position) the DCV 12 fluidly connects the supply port P with the first work port A and the return port T with the second work port B and in a second position (the right-most position) the DCV 12 fluidly connects the supply port P with the second work port B and the return port T with the first work port A. The first and second positions of the DCV are in principle sufficient to control an actuator. However, it is advantageous to equip the DCV 12 with a third position (middle position) in which fluid flow through the DCV 12 is blocked. The first position herein effectuates an extension of the actuator 10, whereas the second position corresponds to retraction of the actuator 10. The third position is used for holding the actuator 10 in a fixed position. The hydraulic system 100 may further comprise a pump 30 connected to the supply line 31 as illustrated. The pump 30 delivers pressurized fluid via the supply line 31 to the supply port (P) of the DCV. As already mentioned, the fluid can be directed towards the piston side chamber 13 or the rod side chamber 15. However, other means of pressurized fluid supply are possible and are encompassed by the disclosure. For example, fluid can be supplied by an external fluid supply or a high-pressure reservoir (not shown in Fig. 2a). Fluid discharged via the return line 41 may be directed to a reservoir 40. In order to avoid cavitation, an anti-cavitation check valve 22 may be disposed in between the rod side actuator line 16 and the return line 41. The features described so far represent well-known means to control the extension and retraction of an actuator by way of a DCV. Based on this, the inventors have realized that a faster actuator motion is possible both during extension and retraction of the actuator 10 by selectively interconnecting the piston side actuator line 14 and the rod side actuator line 16. For this purpose, the hydraulic system 100 comprises an interconnecting line 21 fluidly connecting the piston side actuator line 14 and the rod side actuator line 16 and a first control valve 18 disposed in the interconnecting line 21. The first control valve 18 is arranged to selectively close or open the interconnecting line 21. Further, the hydraulic system 100 comprises a second control valve 19 disposed in the rod side actuator line 16 arranged to selectively allow or block fluid flow therethrough. For improved control, the hydraulic system 100 shown in Fig. 2a comprises at least one first sensor 33 indicative of a piston side pressure Pps, such as a pressure in the piston side chamber 13 and at least one second sensor 34 indicative of a rod side pressure Prs, such as a pressure in the rod side chamber 15. These sensors 33, 34 may be arranged directly in the piston side chamber 13 and / or the rod side chamber 15, respectively. Alternatively, as illustrated in Fig. 2a, the pressure indicating sensors 33, 34 may be arranged to measure a pressure in the piston side actuator line 14 and / or the rod side actuator line 16, respectively. As another option, the pressure indicating sensors 33, 34 may be arranged to measure the piston side pressure Ppsand / or the rod side pressure Prsat suitable drillings of the DCV 12, e.g. a first pressure indicating sensor 33 may be positioned in a drilling of the DCV 12, which drilling has fluid contact with fluid from / to the piston side actuator line 14.

[0056] Analogously, a second pressure indicating sensor 34 may be positioned in a drilling of the DCV 12, which drilling has fluid contact with fluid from / to the rod side actuator line 16.

[0057] A controller 50 is configured to control the DCV 12, the first control valve 18 and the second control valve 19 to achieve different operation modes, namely a slow operating mode and a fast operating mode both during extension and retraction of the actuator 10. The controller 50 is also arranged to receive sensor inputs, such as pressure values from the pressure indicating sensors 33, 34. The controller 50 is also configured to control the pump 30. In some embodiments explained below, the controller 50 may be configured to control a pilot valve 20, which pilot valve 20 is in fluid contact with a spring 23 of a pressure compensator 17, the return line 41 and the DCV 12. More particularly, the DCV has a load sensing (LS) channel which is in fluid contact with the spring chamber 23 of the compensator 17 and with the return line 41. The pilot valve 20 is arranged in between the compensator spring chamber 23 and the return line 41. When the pressure on the compensator spring chamber is low, i.e. when the pilot valve 20 is controlled to an open state, the pressure on line 31 acts on the compensator and pushes towards the spring to close compensator 17 to block fluid flow through the supply line 31. To block flow totally there is spring 23 setting amount of pressure required on the line 31. Thus, some smaller amounts of flow might occur in certain situations.

[0058] The controller 50 and associated methods are now described with reference to figs. 2a- 2e. Arrows indicate the flow directions in the respective lines.

[0059] Fig. 2a illustrates the hydraulic system 100 in the slow operating mode during extension of the actuator 10. Here, the DCV 12 is in the first position, thus directing fluid towards the piston side chamber 13, and, at the same time directing fluid from the rod side chamber 15 towards the reservoir 40. In the slow operating mode, the first control valve 18 is in a closed state and the second control valve 19 is in an open state.

[0060] Analogously, Fig. 2b illustrates the hydraulic system 100 in the slow operating mode during retraction of the actuator 10. Here, the DCV 12 is in the second position, thus directing fluid from the piston side chamber 13 towards the reservoir 40. Since the gravitational force of the load acts to retract the actuator 10, retraction may be performed by simply letting fluid drain from the piston side chamber 13 to the reservoir 40. The pump 30 may thereby be used for other purposes, such as for pressurizing a different hydraulic system or auxiliary systems of the construction machine. For this purpose, the pilot control valve 20 is controlled to an open state (as illustrated in fig. 2b), such that the compensator 17 blocks the fluid supply line 31 when the pressure on 31 exceeds the compensator spring setting. Hence, in this case, fluid is targeted to be sucked from the reservoir 40 via the anti-cavitation valve 22 as much as possible. Thus, in this case, retraction is effectuated by using as small flow from the pump 30 as possible.

[0061] Alternatively, a retraction solely actuated by gravitational forces of the load may also be effectuated by shutting down the pump 30 or controlling the pump 30 to a lower pump flow. In this case the compensator may be maintained in the open state (not shown in fig. 2b). Shutting off the pump may decrease energy consumption of the hydraulic system In another alternative not shown in fig. 2b, the pump 30 may be operated to pressurize the rod side chamber 15 by maintaining a relatively high pump flow and maintaining the compensator 17 in the open state. In this alternative, the actuator 10 is pushed in the retractive direction both by the gravitational force of the load acting on the actuator 10 and by the pressure in the rod side chamber 15. This alternative is useful when gravitational forces are not enough for a desired actuator retraction.

[0062] Referring to Fig. 2c, the fast operating mode during extension is explained. As before, the DCV 12 is in its first position, thereby controlling the actuator 10 to extend. In order to achieve a faster and energy-efficient extension of the actuator 10, the controller 50 is operable to selectively open the first control valve 18, which is disposed in the connecting line 21. This enables the fluid expelled from the rod side chamber 15 to flow directly to the piston side chamber 13, see arrows in Fig. 2c indicating the flow directions in this mode. The second control valve 19 is at the same time controlled to the closed state, thereby preventing fluid from rod side chamber 15 to flow towards the reservoir 40. The fluid now directly flowing from the rod side chamber 15 to the piston side chamber 13, would otherwise have to pass the DCV 12, which imposes a flow restriction associated with pressure losses and speed decrease. Therefore, the actuator motion is faster in the fast operating mode than in the slow operating mode and energy losses are decreased.

[0063] Retraction in the fast operating mode can be performed in two different ways. These alternatives are illustrated in Figs. 2d and 2e, respectively. In both alternatives, the DCV 12 is in its second position so as to cause the actuator 10 to retract. Also, in both alternatives the first control valve 18 is controlled to the open state, allowing fluid expelled from piston side chamber 13 to flow to the rod side chamber 15. Since the rod is taking up a part of the rod side chamber 15, not all fluid expelled from the piston side chamber 13 flows towards the rod side chamber 15. Instead, parts of the fluid flow towards the DCV 12 and to the reservoir 40. In order to block the flow to or from the supply line 31 , either the second control valve 19 may be controlled to closed state, as depicted in Fig. 2d, or the supply line 31 is blocked using the compensator 17, as depicted in Fig. 2e. The compensator 17 has a spring chamber 23 which is fluidly connected to the return line 41 and the DCV 12. A pilot valve 20 is arranged between the return line 41 and the compensator 17. In the fast operating mode during retraction, the pilot valve 20 may now be controlled to an open state, which results in a lower pressure on the compensator spring chamber, thereby closing the compensator 17 for fluid flow therethrough. In other words, the two alternative embodiments for the fast operating mode during retraction differ in where the flow is blocked, i.e. either in the rod side actuator line 16 as depicted in Fig. 2d or in the fluid supply line 31 as depicted in Fig. 2e. In the fast operating mode during retraction, the rod side chamber 15 cannot be pressurized by the pump 30. Here, the retraction is always actuated by the gravitational force of the load acting on the actuator 10. In case of very small loads on the actuator 10, this may lead to comparably low actuator speeds as compared to the slow mode when pressurizing the piston side chamber 15. Here, the term “fast operating mode” is to be interpreted in comparison with the slow operating mode when the rod side chamber 15 is not pressurized from pump. However, when the compensator 17 is used to close the fluid supply line 31 , pressurized fluid can still be provided by the pump 30 to the compensator 17 if the pressure in the compensator 17 falls too low.

[0064] A method for controlling a hydraulic system 100 of a construction machine as described above is illustrated in Fig. 3. The method comprises the following actions:

[0065] Action S1 : controlling the hydraulic system 100 to one of a slow operating mode and a fast operating mode.

[0066] During both retraction and extension of the actuator 10, controlling the hydraulic system 100 to the slow operating mode comprises an action S2 of controlling the first control valve 18 to a closed state and controlling the second control valve 19 to an open state.

[0067] During extension of the actuator 10, controlling the hydraulic system 100 to the fast operating mode comprises an action S3a of controlling the first control valve 18 to an open state and the second control valve 19 to a closed state.

[0068] During retraction of the actuator 10, controlling the hydraulic system 100 to the fast operating mode comprises an action S3b of controlling the first control valve 18 to an open state and to either control the second control valve 19 to a closed state, or to block fluid flow through the fluid supply line 31.

[0069] As mentioned above, the control method performed by the controller 50 achieves an operation of the hydraulic control system in two speed modes, i.e., the slow operating mode and the fast operating mode, both during extension and during retraction of the actuator. As illustrated in Fig. 3, the method may further comprise the following optional actions:

[0070] Action S3c: In the fast operating mode during retraction of the actuator 10, controlling the pressure compensator 17 to a closed state. Controlling the pressure compensator 17 to a closed state may comprise controlling the pilot valve 20 to an open state, wherein the pilot valve 20 is fluidly connected to the return line 41 , the pressure compensator 17 and the DCV's 12 LS (load sensing) channel.

[0071] Thereby, the fluid supply line 31 is blocked instead of the rod side actuator line 16. Blocking the fluid supply line 31 using the pressure compensator 17 has the advantage that already present components can be used, since a pressure compensator 17 is common on most construction machines. Further, using the compensator 17 the pump 40 can still be used to supply additional pressure in case of low pressure in the supply line 31.

[0072] The method may further comprise an action S1a of activating the fast operating mode in dependence on the piston side pressure Ppsand / or the rod side pressure Prs. Further, the controller 50 may be configured to allow or prohibit activation of the fast operating mode in dependence on the piston side pressure Ppsand / or the rod side pressure Prs.

[0073] This is particularly important for safety reasons, since a too high pressure in the piston side chamber 13 may lead to unintentional actuator motion upon opening the first control valve 18, since a too high pressure jump may activate safety valves, such as shock valves, of the hydraulic system. For example, the controller may decide if the fast operating mode may be activated by comparing the piston side pressure Ppsand / or the rod side pressure Prs to a pressure threshold. Alternatively, a difference, a quote, or any other function of the piston side pressure Ppsand rod side pressure Prsmay be computed and compared to a suitable threshold value.

[0074] The method may further, or alternatively, comprise an action of predicting a postactivation pressure in dependence on the piston side pressure Ppsand / or the rod side pressure Prs and activating S1 b the fast operating mode only when the predicted postactivation pressure fulfills a predetermined condition, such as being lower than a threshold pressure.

[0075] After the first control valve 18 is opened, the piston side pressure and the rod side pressure are approximately equal. The predicted post-activation pressure corresponds to the predicted pressure after the first control valve 18 is opened in the piston / rod side of the hydraulic system 100, e.g. in the piston side chamber 13 or the rod side chamber 15, the piston side actuator line 14 or the rod side actuator line 16. For example, the predicted post activation pressure should be below a threshold pressure before activation of the fast operating mode is allowed. The threshold pressure may be chosen to correspond to the activation pressure of safety valves of the hydraulic system 100. For example, a limit for the resulting pressure may be 400 bar or 250 bar. However, the choice of the threshold pressure for the post activation pressure may depend on the size of the hydraulic system, safety valves or other properties of the hydraulic system 100.

[0076] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1. A hydraulic system (100) of a construction machine (1), comprising: an actuator (10), comprising at least one cylinder (11) and at least one piston with a piston rod, each cylinder (11) comprising a piston side chamber (13) and a rod side chamber (15), a directional control valve (12), DCV, wherein the DCV (12) comprises a supply port (P) connected to a fluid supply line (31), a return port (T) connected to a return line (41), a first work port (A) connected to the piston side chamber (13) of the actuator via a piston side actuator line (14) and a second work port (B) connected to the rod side chamber (15) of the actuator (10) via a rod side actuator line (16), wherein the DCV (12) in a first position fluidly connects the supply port (P) with the first work port (A) and the return port (T) with the second work port (B) and in a second position fluidly connects the supply port (P) with the second work port (B) and the return port (T) with the first work port (A), a first control valve (18) arranged to selectively open or close a connection line (21) fluidly interconnecting the piston side actuator line (14) and the rod side actuator line (16), a second control valve (19) arranged to selectively open or close the rod side actuator line (16), and a controller (50) configured to operate at least the DCV (12), the first control valve (18) and the second control valve (19), wherein the controller (50) is arranged to control the hydraulic system (100) to one of a slow operating mode and a fast operating mode, wherein in the slow operating mode, the controller (50) is arranged to control the first control valve (18) to a closed state and to control the second control valve (19) to an open state, and wherein in the fast operating mode during extension of the actuator (10), the controller (50) is arranged to control the first control valve (18) to an open state and the second control valve (19) to a closed state, and wherein in the fast operating mode during retraction of the actuator (10), the controller (50) is configured to control the first control valve (18) to an openstate and to either control the second control valve (19) to a closed state, or to block fluid flow through the fluid supply line (31).

2. The hydraulic system (100) according to claim 1, further comprising a pressure compensator (17) in the fluid supply line (31), wherein, in the fast operating mode during retraction of the actuator (10), the controller (50) is arranged to control the pressure compensator (17) to a closed state.

3. The hydraulic system (100) according to claim 2, wherein the controller (50) is arranged to control the pressure compensator (17) to the closed state by controlling a pilot valve (20) to an open state, wherein the plot valve (20) is fluidly connected to the return line (41), the pressure compensator (17) and the DCV (12).

4. The hydraulic system (100) according to any one of the preceding claims, wherein the controller (50) is configured to selectively control the hydraulic system (100) to the slow operating mode and the fast operating mode both during extension and retraction of the actuator (10).

5. The hydraulic system (100) according to any one of the preceding claims, wherein the fluid supply line (31) is fluidly connected to at least one pump (30).

6. The hydraulic system (100) according to any one of the preceding claims, wherein the return line (41) is fluidly connected to at least one reservoir (40).

7. The hydraulic system (100) according to any one of the preceding claims, wherein the actuator (10) is arranged to hoist and lower a boom (2) of the construction machine (1).

8. The hydraulic system (100) according to any one of the preceding claims, wherein the actuator (10) is arranged to dump and roll back a bucket (3) arranged on a boom (2) of the construction machine (1).

9. The hydraulic system (100) according to any one of the preceding claims, comprising at least one of a first pressure sensor (33) indicative of a piston sidepressure Ppsand a second pressure sensor (34) indicative of a rod side pressure10. The hydraulic system (100) according to claim 9, wherein the controller (50) is configured to activate the fast operating mode in dependence on the piston side pressure Ppsand / or the rod side pressure Prs.

11. The hydraulic system (100) according to any one of claims 9 or 10, wherein the controller is configured to predict a post-activation pressure in dependence on the piston side pressure and / or the rod side pressure and to activate the fast operating mode only when the predicted post-activation pressure fulfills a predetermined condition, such as being lower than a threshold pressure.

12. The hydraulic system (100) according to any one of the preceding claims, wherein the actuator (10) during extension acts against a gravitational load, such as by lifting a load.

13. A construction machine comprising the hydraulic system (100) according to any one of the preceding claims.

14. A method for controlling a hydraulic system (100) of a construction machine, the hydraulic system (100) comprising- an actuator (10), comprising at least one cylinder (11) and at least one piston with a piston rod, each cylinder (11) comprising a piston side chamber (13) and a rod side chamber (15),- a directional control valve (12), DCV, wherein the DCV (12) comprises a supply port (P) connected to a fluid supply line (31), a return port (T) connected to a return line (41), a first work port (A) connected to the piston side chamber (13) of the actuator via a piston side actuator line (14) and a second work port (B) connected to the rod side chamber (15) of the actuator (10) via a rod side actuator line (16), wherein the DCV (12) in a first position fluidly connects the supply port (P) with the first work port (A) and the return port (T) with the second work port (B) and in a second position fluidlyconnects the supply port (P) with the second work port (B) and the return port (T) with the first work port (A),- a first control valve (18) arranged to selectively open or close a connection line (21) fluidly interconnecting the piston side actuator line (14) and the rod side actuator line (16),- a second control valve (19) arranged to selectively open or close the rod side actuator line (16), and-a controller (50) configured to operate at least the DCV (12), the first control valve (18) and the second control valve (19), the method comprising controlling (S1) the hydraulic system (100) to one of a slow operating mode and a fast operating mode, wherein controlling the hydraulic system (100) to the slow operating mode comprises controlling (S2) the first control valve (18) to a closed state and controlling the second control valve (19) to an open state, and wherein controlling the hydraulic system (100) to the fast operating mode, during extension of the actuator (10), comprises controlling (S3a) the first control valve (18) to an open state and the second control valve (19) to a closed state, and wherein controlling the hydraulic system (100) to the fast operating mode, during retraction of the actuator (10), comprises controlling (S3b) the first control valve (18) to an open state and to either control the second control valve (19) to a closed state, or to block fluid flow through the fluid supply line (31).

15. The method according to claim 14, wherein the hydraulic system (100) further comprises a pressure compensator (17) in the fluid supply line (31), the method further comprising, in the fast operating mode during retraction of the actuator (10), controlling (S3c) the pressure compensator (17) to a closed state.

16. The method according to claim 15, wherein controlling the pressure compensator (17) to a closed state comprises controlling a pilot valve (20) to an open state, wherein the pilot valve (20) is fluidly connected to the return line (41), the pressure compensator (17) and the DCV (12).

17. The method according to claim 14-16, wherein the hydraulic system (100) further comprises at least one of a first pressure sensor (33) indicative of a piston side pressure Ppsand a second pressure sensor (34) indicative of a rod side pressure Prs, the method further comprising, activating (S1a) the fast operating mode in dependence on the piston side pressure Ppsand / or the rod side pressure Prs.

18. The method according to claim 17, further comprising, predicting a post-activation pressure in dependence on the piston side pressure and / or the rod side pressure and activating (S1b) the fast operating mode only when the predicted post-activation pressure fulfills a predetermined condition, such as being lower than a threshold pressure.