Description

According to a first aspect, the present disclosure relates to a system for moving a tool such as a boom, dipper, bucket or hook of a hydraulic machine such as an excavator, crane or forklift.

According to a second aspect, the present disclosure relates to a hydraulic machine such as an excavator, crane or forklift comprising a system according to the first aspect of the present disclosure.

A known hydraulic system for moving a tool such as a boom, dipper, bucket or hook of a hydraulic machine such as an excavator, crane or forklift comprises a diesel engine for driving a hydraulic pump that is arranged for operating a hydraulic cylinder. A drawback of this known system is that it can be improved as regards the energy efficiency.

An objective of the present disclosure is to provide a hydraulic system that has a relative high energy efficiency.

The objective is achieved in that the system according to the first aspect of the present disclosure comprises differential hydraulic cylinders for moving a tool such as a boom, dipper, bucket or hook of a hydraulic machine such as an excavator, crane or forklift.

The system further comprises a first bidirectional hydraulic variable displacement pump, coupled for liquid flow, via a first flow line of said system, to one of a piston rod side and a cylinder base side of a first differential hydraulic cylinder of said differential hydraulic cylinders for operating said first differential hydraulic cylinder. Within the context of the present disclosure operating such a hydraulic cylinder is to be understood as providing and removing a liquid, such as a hydraulic oil, from said hydraulic cylinder for moving a piston rod of the hydraulic cylinder relative to a housing of the hydraulic cylinder. Within the context of the present disclosure, a bidirectional pump is to be understood as a pump that is arranged for pumping a liquid, such as a hydraulic fluid, from a first outlet port of the pump or a second outlet port of the pump while rotating in one direction.

Within the context of the present disclosure, a hydraulic variable displacement pump refers to a hydrostatic pump.

In addition, the system comprises a first generator coupled to said first bidirectional hydraulic variable displacement pump for driving said first bidirectional hydraulic variable displacement pump. The first generator may for instance be provided with an output axle that is mechanically coupled to the first bidirectional hydraulic variable displacement pump. It is noted that due to the provision of the bidirectional pump instead of a bi-rotational pump, there is no need for the first generator to be arranged for driving the output axle thereof in two directions. This is beneficial for realising a system having a relative low complexity and thereby being relatively robust.

A second generator of the system according to the present disclosure is coupled to said first generator and arranged, when said second generator is in a first operational mode, to be driven by said first generator for generating electrical energy, and when said second generator is in a second operational mode, arranged for driving, together with said first generator, said first bidirectional hydraulic variable displacement pump. The first operational mode is beneficial for realising a relative high energy efficiency of the system for instance when the first generator is outputting more power than required for operating the differential hydraulic cylinder. In this instance the surplus of output power may be converted into electrical energy. The second operational mode is beneficial for increasing the power provided to the first bidirectional hydraulic variable displacement pump beyond a level that may be achieved by the first generator. This allows for a first generator having a relative low maximum power output.

The system may further comprise a third bidirectional hydraulic pump, a first bidirectional hydraulic motor and a first tank, wherein said first bidirectional hydraulic variable displacement pump is coupled for liquid flow via said first flow line to said one of said piston rod side and said cylinder base side of said first differential cylinder via said first bidirectional hydraulic motor, wherein said third bidirectional hydraulic pump is arranged to be driven by said first bidirectional hydraulic motor for supplying liquid from said first tank to said first flow line and/or adding liquid to said first tank from said first flow line. This allows for setting a flow rate of liquid in said first flow line to a predetermined range or value for moving the piston rod relative to the piston housing.

It is pointed out that due to the presence of a piston rod at only one side of a piston element that is movable inside the cylinder housing for moving said piston rod, an effective surface of the piston element at the side of the piston rod is smaller than an effective surface of the piston element at the side of the cylinder base. By providing the third bidirectional hydraulic pump, the first bidirectional hydraulic motor and the first tank the velocities of moving the piston rod in and out the cylinder housing may be adapted.

In an embodiment, the system according to the first aspect may comprise a third flow line that couples said first bidirectional hydraulic variable displacement pump for liquid flow to the other of said piston rod side and said cylinder base side of said first differential hydraulic cylinder, wherein said third hydraulic pump is controlled such that a difference of a flow rate of said liquid in said third flow line and a flow rate of said liquid in said first flow line is within a predetermined range, preferably wherein said flow rates are equal.

In an embodiment, the system according to the first aspect of the present disclosure comprises: a second bidirectional hydraulic variable displacement pump coupled for liquid flow, via a second flow line of said system, to one of a piston rod side and a cylinder base side of a second differential hydraulic cylinder of said differential hydraulic cylinders for operating said second differential hydraulic cylinder; wherein said first generator is further coupled to said second bidirectional hydraulic variable displacement pump for driving said second bidirectional hydraulic variable displacement pump and wherein said second generator is arranged, when said second generator is in said second operational mode, for driving, together with said first generator, said first and second bidirectional hydraulic variable displacement pumps.

The system may further comprise a fourth bidirectional hydraulic pump, a second bidirectional hydraulic motor and a second tank, wherein said second bidirectional hydraulic variable displacement pump is coupled for liquid flow via said second flow line to said one of said piston rod side and said cylinder base side of said second differential cylinder via said second bidirectional hydraulic motor, wherein said fourth bidirectional hydraulic pump is arranged to be driven by said second bidirectional hydraulic motor for supplying liquid from said second tank to said second flow line and/or adding liquid to said second tank from said second flow line.

In an embodiment, the system according to the first aspect may comprise a fourth flow line that couples said second bidirectional hydraulic variable displacement pump for liquid flow to the other of said piston rod side and said cylinder base side of said second differential hydraulic cylinder, wherein said fourth bidirectional hydraulic pump is controlled such that a difference of a flow rate of said liquid in said fourth flow line and a flow rate of said liquid in said second flow line is within a predetermined range, preferably wherein said flow rates are equal.

It is advantageous, if said first and/or second bidirectional hydraulic variable displacement pumps are coupled to said second generator and wherein said second generator is further arranged, when said second generator is in a third operational mode, to be driven by said first and/or second bidirectional hydraulic variable displacement pumps for generating electrical energy. The third operational mode is beneficial for realising a relative high energy efficiency of the system.

It is beneficial if one of said third hydraulic pump and said first bidirectional hydraulic motor has a variable displacement. This is beneficial for setting a flow rate of liquid in said first flow line to a predetermined range or value for moving the piston rod relative to the piston housing.

It is beneficial if one of said fourth bidirectional hydraulic pump and said second bidirectional hydraulic motor has a variable displacement. This is beneficial for setting a flow rate of liquid in said second flow line to a predetermined range or value for moving the piston rod relative to the piston housing.

In an embodiment of the system according to the first aspect, said first bidirectional hydraulic variable displacement pump is coupled for liquid flow, by said first flow line, with said piston rod side of said first differential hydraulic cylinder via said first bidirectional hydraulic motor. This is beneficial for realizing a system that is intended for use in an application wherein the tool exerts a relative large force on the piston rod when the piston rod is moved away from the cylinder base.

In an embodiment of the system according to the first aspect, said first bidirectional hydraulic variable displacement pump is coupled for liquid flow, by said first flow line, with said cylinder base rod side of said first differential hydraulic cylinder via said first bidirectional hydraulic motor. This is beneficial for realizing a system that is intended for use in an application wherein the tool exerts a relative large force on the piston rod when the piston rod is moved towards the cylinder base.

In an embodiment of the system according to the first aspect, said third hydraulic pump is arranged for supplying liquid from said first tank in a section of said first flow line between said first bidirectional hydraulic motor and said first bidirectional hydraulic variable displacement pump and/or wherein said third hydraulic pump is arranged for adding liquid to said first tank from said section of said first flow line.

It is advantageous if, said system further comprises a fifth hydraulic pump, wherein said fifth hydraulic pump is arranged for maintaining a pressure of said liquid in said first flow line within a predetermined range, by supplying liquid from said first tank or a further tank of said system to said first flow line.

In this regard, it is beneficial if said fifth hydraulic pump has a variable displacement and/or is unidirectional. In an embodiment of the system according to the first aspect, said fifth hydraulic pump is arranged for maintaining a pressure in said first flow line in a range of 20 to 30 barg, preferably 25 barg.

In this regard, it is beneficial if the fifth hydraulic pump is arranged for further maintaining a pressure in said second, third and/or fourth flow line in a range of 20 to 30 barg, preferably 25 barg.

In a yet further embodiment of the system according to the present disclosure, the fifth hydraulic pump is arranged for maintaining a pressure in all flow lines for hydraulic fluid in a range of 20 to 30 barg, preferably 25 barg.

It is beneficial if, said system further comprises a load detector for detecting a load factor of said first generator and a control unit, communicatively coupled to said load detector, wherein said control unit is arranged for bringing said second generator in said first operational mode or said second operational mode taking into account a load factor detected by said load detector.

Preferably, said system further comprises a storage unit arranged for storing electrical energy generated, when in said first operational mode or third operational mode, by said second generator and supplying electrical energy, when said second generator is in said second operational mode.

In this regard, it is beneficial if said second generator is in said first operational mode when the first generator is outputting more power than required for operating the differential hydraulic cylinder and a ratio of an actual charge of the storage unit and a maximum charge capacity of the storage unit is lower than a predetermined amount, preferably lower than 0.9, more preferably lower than 0.75. In other words, when the amount of electric charge stored in the storage unit drops below the predetermined amount while the first generator is outputting more power than required, the storage unit is charged by the second generator. Should the amount of electric charge be larger than the predetermined amount, the second generator will not charge the storage unit. It is advantageous if said first generator comprises an internal combustion engine, preferably a diesel engine.

According to the second aspect, the present disclosure relates to a hydraulic machine such as an excavator, crane or forklift comprising a system according to the first aspect of the present disclosure for moving a tool of said hydraulic machine.

Embodiments of the system according to the first aspect of the present disclosure presented previously correspond to or are similar to embodiments of the hydraulic machine according to the second aspect of the present disclosure.

Effects of the system according to the first aspect of the present disclosure presented previously correspond to or are similar to effects of the hydraulic machine according to the second aspect of the present disclosure.

It is advantageous if said hydraulic machine is a forklift a container handler. Preferably, said container handler is arranged for handling containers according to ISO 668:2020.

In this regard, it is beneficial if said forklift or container handler is provided with a system wherein said first and/or second bidirectional hydraulic variable displacement pumps are coupled to said second generator and wherein said second generator is further arranged, when said second generator is in a third operational mode, to be driven by said first and/or second bidirectional hydraulic variable displacement pumps for generating electrical energy. This is attractive for recovering a part of the energy provided, by the first generator or provided by the first and second generator together, during lifting a load such as a container when lowering the load.

The present disclosure will now be explained by means of a description of an embodiment of a system in accordance to the first aspect, and a hydraulic machine according to the second aspect, in which reference is made to the following schematic figures, in which: Fig. 1 a schematic overview of a system according to the first aspect of the present disclosure is shown;

Fig. 2 elements of a system according to the first aspect of the present disclosure are shown;

Fig. 3 elements of another system according to the first aspect of the present disclosure are shown;

Fig. 4 elements of a further system according to the first aspect of the present disclosure are shown;

Fig. 5 elements of yet another system according to the first aspect of the present disclosure are shown;

Fig. 6 a hydraulic machine according to the second aspect of the present disclosure is shown.

The system 1 comprises multiple differential hydraulic cylinders 3, 5, 7, 9, for moving a tool such as a boom, dipper, bucket or hook of a hydraulic machine such as an excavator or a crane.

The system 1 further comprises a first bidirectional hydraulic variable displacement pump 11 for operating first differential hydraulic cylinders 3, 5 of the differential hydraulic cylinders 3, 5, 7, 9. The first bidirectional hydraulic variable displacement pump 11 is coupled, for liquid flow, via a first flow line 25 to a piston rod side 27 of the first differential hydraulic cylinder 3, 5 and via a third flow line 39 to a cylinder base side 37 of the first differential hydraulic cylinder 3, 5. Both the first flow line 25 and the third flow line 39 are coupled via a pilot operated check valve 34, wherein the pilot operated check valve 34 is pilot to open, to the respective cylinder base side 37 and the piston rod side 27 of the first differential hydraulic cylinder 3, 5, for blocking liquid flow from the first differential hydraulic cylinder 3, 5 back into the first flow line 25 and/or the third flow line 39. The valve 34 is further arranged for completely blocking the flow from the first flow line 25 and/or the third flow line 39 into the first differential hydraulic cylinder 3, 5, for example when the system 1 is not operational.

The system 1 furthermore comprises a second bidirectional hydraulic variable displacement pump 13 for operating second differential hydraulic cylinders 7, 9 of the differential hydraulic cylinders 3, 5, 7, 9. The second bidirectional hydraulic variable displacement pump 13 is coupled, for liquid flow, via a second flow line 31 and via a further pilot operated check valve (not shown), wherein the further pilot operated check valve is pilot to open, to a piston rod side of the second differential hydraulic cylinder 7, 9 and via a fourth flow line 40 and via the further check valve to a cylinder base side 37 of the second differential hydraulic cylinder 7, 9.

A first generator 15, which comprises an internal combustion engine, is coupled to the first bidirectional hydraulic variable displacement pump 11 and the second bidirectional hydraulic variable displacement pump 13 for driving the first bidirectional hydraulic variable displacement pump 11 and the second bidirectional hydraulic variable displacement pump 13.

A second generator 17 is coupled to the first generator 15 as well to the first and second bidirectional hydraulic variable displacement pumps 11 , 13. When the second generator 17 is in a first operational mode, the second generator 17 is driven by the first generator 15 for generating electrical energy. When the second generator 17 is in a second operational mode, the second generator 17 is arranged for driving, together with the first generator 15, the first and second bidirectional hydraulic variable displacement pump 11 ,13. When the second generator 17 is in a third operational mode, the second generator 17 is driven by the first and/or second bidirectional hydraulic variable displacement pump 11 , 13 for generating electrical energy.

In the first and third operational mode, the generated electrical energy is stored in a storage unit 41 if a ratio of an actual charge of the storage unit 41 and a maximum charge capacity of the storage unit 41 is lower than 0.75. In case the second generator 17 is in the second operational mode, the stored electrical energy is supplied to the first and second bidirectional hydraulic variable displacement pumps 11 , 13.

A load detector 43 is arranged for detecting a load factor of the first generator 15 and a control unit 35, communicatively coupled to the load detector 43, arranged for bringing the second generator 17 in the first operational mode or the second operational mode taking into account a load factor detected by the load detector 43.

The system 1 furthermore comprises a third bidirectional hydraulic pump 19, a first bidirectional hydraulic motor 21 and a first tank 23. The hydraulic motor 21 is coupled in the first flow line 25, wherein the third bidirectional hydraulic pump 19 is arranged to be driven by the first bidirectional hydraulic motor 21 for supplying liquid from the tank 23 in a section of the first flow line 25 between the first bidirectional hydraulic motor 21 and the first bidirectional hydraulic variable displacement pump 11 and/or adding liquid to the tank 23 from the section of the first flow line 25. The third hydraulic pump 19 is controlled such that a flow rate of the liquid in the third flow line 39 and a flow rate of the liquid in the first flow line 25 are preferably equal.

The system 1 additionally comprises a fifth hydraulic pump 29 and a further tank 33. The fifth hydraulic pump 29 has a variable displacement. Upstream from the first bidirectional hydraulic motor 21 , the fifth hydraulic pump 29 is coupled via a check valve 36 to an upstream section of the first flow line 25. Downstream from the first bidirectional hydraulic motor 21 , the fifth hydraulic pump 29 is coupled via a further check valve 38 to a downstream section of the first flow line 25. The fifth hydraulic pump 29 is furthermore coupled via a yet further check valve 40 to the third flow line 39. The fifth hydraulic pump 29 is arranged for maintaining a pressure of the liquid in the first flow line 25 and the third flow line 39 within a predetermined range of 20 to 30 barg, by supplying liquid from the further tank 33 to the first flow line 25 and the third flow line 39. In an embodiment of the system 1 , the first tank 23 and the further tank 33 may be one and the same tank. In other words the further tank 33 may be a part of the first tank 23.

Fig. 2 and Fig. 3 disclose elements of different embodiments of the system 1 according to the first aspect of the present disclosure as described above, in which Fig. 2 discloses the third bidirectional hydraulic pump 19 with a variable displacement and Fig.3 discloses the first bidirectional hydraulic motor 21 with a variable displacement. Fig. 4 discloses elements of a yet further embodiment of system 1 according to the first aspect of the present disclosure, in which the first bidirectional hydraulic motor 21 is included in the third flow line 39, wherein the third bidirectional hydraulic pump 19 is arranged to be driven by the first bidirectional hydraulic motor 21 for supplying liquid from the tank 23 in a section of the third flow line 39 between the first bidirectional hydraulic motor 21 and the first bidirectional hydraulic variable displacement pump 11 and/or adding liquid to the tank 23 from the section of the third flow line 39, such that the flow rates in both flow lines 25, 39 are preferably equal. In this embodiment, the fifth hydraulic pump 29 is coupled via a check valve 36 to the first flow line 25. Upstream from the first bidirectional hydraulic motor 21 , the fifth hydraulic pump 29 is coupled via a further check valve 38 to an upstream section of the third flow line 39. Downstream from the first bidirectional hydraulic motor 21 , the fifth hydraulic pump 29 is coupled via a yet further check valve 40 to a downstream section of the third flow line 39.

The embodiments shown in Fig. 2, 3 and 4 described previously, can equivalently be applied to the part of system 1 comprising the second bidirectional hydraulic variable displacement pump 13, coupled via the second and fourth flow lines 31 , 40 to the second differential hydraulic cylinders 7, 9.

Fig. 5 discloses elements of yet another system according to the first aspect of the present disclosure, wherein the system 1 comprises additional bidirectional hydraulic variable displacement pump 12, 14 and 16 for operating an additional set of differential hydraulic cylinders. The first and second generator 15, 17 are coupled to the bidirectional hydraulic variable displacement pumps 11 , 12, 13, 14. When the second generator 17 is in a second operational mode, the second generator 17 is arranged for driving, together with the first generator 15, the bidirectional hydraulic variable displacement pump 11 , 12, 13, 14. When the second generator 17 is in a third operational mode, the second generator 17 is driven by the one or more of the bidirectional hydraulic variable displacement pumps 11 , 12, 13, 14 for generating electrical energy, which is stored storage unit 41.

Fig. 6 discloses a forklift 101 comprising a moving a tool 105 and the system 1 according to the first aspect of the present disclosure for moving a tool 105 of the forklift and for recovering a part of the energy provided during lifting a load such as a container when lowering the load.