EP3689814B1

EP3689814B1 - Hydraulic lifting system

Info

Publication number: EP3689814B1
Application number: EP19155238.9A
Authority: EP
Inventors: Haider KHUDAIR
Original assignee: Toyota Material Handling Manufacturing Sweden AB
Current assignee: Toyota Material Handling Manufacturing Sweden AB
Priority date: 2019-02-04
Filing date: 2019-02-04
Publication date: 2021-11-17
Anticipated expiration: 2039-02-04
Also published as: EP3689814A1

Description

TECHNICAL FIELD

The present disclosure relates to a hydraulic lifting system, a fork-lift truck comprising such a system, and a method for providing such a system to a fork-lift truck.

BACKGROUND ART

Hydraulic lifting systems are commonly used for a plurality of applications such as for industrial equipment and different types of vehicles, wherein fork-lift trucks are a prime example. Hydraulic systems provide a lot of raw force making heavy lifting possible with a tested and reliable technical solution. It is also common to utilize so called one directional hydraulics for lifting machinery and operations, wherein a hydraulic fluid is pumped within the system by means of a motor and a pump when the lifting apparatus is lifted upwards, but wherein a lowering of the apparatus is performed by means of in a controlled manner draining the provided hydraulic fluid from the lifting apparatus and letting said fluid be returned to a hydraulic tank.
Such a solution is beneficial as the motor and pump only needs to be operated for lifting and not for lowering, which saves power and force used. However, potential energy is also lost at a lowering operation, which lost energy is converted to heat within the hydraulic system and its integral parts.
Documents JP 2007 254057 and JP 2010 083672 are examples of relevant prior art as they disclose the preamble of claim 1.

SUMMARY OF THE INVENTION

Despite prior art there is thus a need to develop an improved hydraulic lifting system, which may alleviate the problem of energy losses within such a system. There is also a need to develop a hydraulic lifting system, which may use other devices coupled to the system while still managing the energy losses within the system. Furthermore, there is a need to develop a fork-lift truck comprising such a hydraulic lifting system. Even further, there is a need to develop a method for providing such a hydraulic lifting system to a fork-lift truck.
An object of the invention is thus to provide an improved hydraulic lifting system, which alleviates the problem of energy losses within such a system. Additional objects are respectively to provide a hydraulic lifting system, which may use other devices coupled to the system while still managing the energy losses within the system, and to provide a fork-lift truck comprising such a device. Furthermore, an object is to provide a method for providing such a hydraulic lifting system to a fork-lift truck.
According to a first aspect a hydraulic lifting system is provided. The hydraulic lifting system comprises a hydraulic circuit, which comprises a feed line and a return line, to which circuit a plurality of components are coupled. The plurality of components comprises: a lifting device, at least one hydraulic auxiliary device, at least one first pump, at least one electric motor for operating the at least one pump, a tank for holding hydraulic fluid, a first control valve, a second control valve, and a control unit, for operating the valves and the at least one electric motor. The first control valve is arranged on the feed line, and being arranged to control a flow of hydraulic fluid through said feed line, which flow is provided to the feed line by means of the pump and the electric motor. A flow through said feed line is directed to the lifting device, which lifting device may perform a lifting operation when provided with said hydraulic fluid. The second control valve is arranged on the return line, and being arranged to re-direct the flow of hydraulic fluid from the feed line to the return line, which leads said hydraulic fluid to the tank. The lifting device performs a lowering operation when the hydraulic fluid is drained therefrom by means of the second control valve. The system further comprises a hydraulic motor, said hydraulic motor may be arranged on the return line, between the second control valve and the tank, wherein the hydraulic motor, when provided with hydraulic fluid from the return line may be arranged to generate mechanical energy to a rotatable axle, and characterized in that the hydraulic lifting system further comprises a third control valve, arranged on the return line and being arranged to control the flow from the lifting device so as to wither be directed to the tank and/or to the hydraulic motor.
This has the advantage that the otherwise not utilized return flow of hydraulic fluid may be used to transform the energy losses of the hydraulic system into useable energy by means of the rotation of the rotatable axle. Furthermore, as the energy transformation is achieved by the hydraulic motor, which is or may be separated from the electric motor and the at least one first pump, said electric motor and first pump may be operated simultaneously as the energy conservation takes place. Thereby the at least one hydraulic auxiliary device may be operated during lowering of the lifting device, which would be impossible if the energy regeneration would be incorporated directly in the first pump or similar. An even further advantage is the rotatable axle may be used so as to operate the hydraulic motor when desired. This may be utilized to assist the flow within the return line by means of creating a suction effect by means of the operated hydraulic motor. If the lifting device is to be lowered with a very low amount of pressure within the lifting device, the draining thereof may not be very fast, and thus the hydraulic motor may be opted to use as a means of speeding up said draining process. This thus allows for a faster lowering operation of the lifting device.
According to an aspect, the rotatable axle may be arranged in selective connection to a generator comprised in the system, which generator is arranged to transform the mechanical energy to electricity when said rotatable axle and said generator are connected.
This has the advantage that the otherwise lost energy of a lowering of the lifting device may be transformed into electricity, which may be provided to the electric motor so as to conserve energy consumption thereof.
According to an aspect, the system may further comprise a battery, which battery is coupled to the generator and being arranged to store electrical energy generated by means of said generator.
This has the advantage that the electricity generated during a lowering operation may be transformed and stored as electrical energy within the battery, and be used at a later point in time.
According to the invention, the system comprises a third control valve, arranged on the return line and being arranged to control the flow from the lifting device so as to either be directed to the tank and/or to the hydraulic motor, preferably said valve is arranged to be able to regulate said flow proportionally in predetermined amounts to the tank and the hydraulic motor.
This has the advantage that the hydraulic motor may be opted to not be operated during a non-optimal lowering operation of the lifting device. If, for example, the flow of hydraulic fluid is very low due to a low pressure within the return line, the hydraulic fluid may not be able to provide enough mechanical energy to the rotatable axle, wherein it may be more beneficial to save the machinery from wear by not having it rotate for such a case. Furthermore, the lowering speed of the lifting device will not risk being further reduced at low load pressure, which risk may occur due to the extra pressure drop caused by the hydraulic motor if the hydraulic fluid is led thereto at low pressure. Also as the flow can be regulated proportionally the amount of energy regenerated can be controlled as desired. For example if the hydraulic function that is to be used during regeneration is not requiring the total amount of energy that can be regenerated.
According to an aspect, the third control valve may be pressure controlled, wherein a pressure detection device is arranged on the return line between the second control valve and the third control valve, wherein the third control valve directs the flow to the hydraulic motor when the pressure exceeds a predetermined value, preferably said pressure detection device is arranged such that the pressure in said return line is directly fed to the pressure control valve.
This has the advantage that the hydraulic motor may be operated within a predetermined and desired working range, which allows for energy conservation/regeneration when efficient to do so, but saves the hydraulic motor from unnecessary wear otherwise, and does not slow down a lowering operation due to a potential pressure drop within the hydraulic motor.
According to an aspect, the third control valve may be controllable by means of an output signal from the control unit, preferably said control unit receives an input of a detected pressure in the return line for control of the third control valve.
This has the advantage that an operator using the hydraulic lifting system may have a lot more control over the functions of the system as the control unit may be coupled to a user interface, which an operator may use for controlling the individual functions of the system. Also exact control of the regeneration is easy to control. And also it is possible to apply adaptation of the regenerative function depending on what the demand of pressure is required for auxiliary hydraulic functions.
According an aspect, the rotatable axle may be arranged in connection with the first pump and said rotatable axle being arranged to selectively transfer a torque from the hydraulic motor to the first pump, preferably the torque is arranged to be transferred by a clutch, even more preferred said clutch can be controlled such that a predetermined amount of torque can be transferred.
This has the advantage that said torque provided to the first pump may be utilized by said pump so as to operate the pump to some degree without the use of the electric motor. Thus, the first pump may take advantage of this added torque to provide hydraulic fluid to, for example, the hydraulic auxiliary device during a lowering operation of the lifting device, wherein the energy from the lowering of the lifting device is used rather than being lost as internal heat in the system. The electric motor may of course also add more power to the first pump during such a usage, if the torque provided by the hydraulic motor is not large enough to fully operate the first pump for its intended operation. For such a case the electric motor will still be assisted by the provided torque, wherein less energy needs to be used by the electric motor. Also regulation can be more advanced by means of a clutch that allows for a selective amount of torque to be transferred if all torque is not needed by auxiliary hydraulic devices.
According to an aspect, the rotatable axle is further coupled to the at least one electric motor, preferably said motor can be used as a generator, preferably said axle is connected to said electric motor by a clutch, even more preferred said clutch can be controlled such that a predetermined amount of torque can be transferred..
This has the advantage that the electric motor, the first pump, and the hydraulic motor may all be coupled to each other and interact with each other in a seamless manner. The electric motor may also directly operate the hydraulic motor if it is desired to suck the drained hydraulic fluid from the lifting device, without the need for an additional source of power for providing power to the hydraulic motor. Also it is possible to in an advanced way regenerate the energy. In a preferred aspect the electric motor can act as a generator at the same time as the torque generated is partly lead to the motor and partly to the hydraulic pump. Preferably a clutch on the axle provides for this control of a predetermined amount of torque. Thus if a high amount of energy is available to the hydraulic motor, the energy can both generate electric energy by the electric motor/generator and hydraulic pressure by the hydraulic pump.
According to an aspect, the system may further comprises a fourth control valve, arranged on the feed line and being arranged to control a flow from the first pump so as to be directed to the feed line and/or to be re-circulated to the tank.
This has the advantage that a torque may be provided to the first pump from the hydraulic motor, even if the first pump is not to be used at that point in time. The first pump may thus be set to pump even if the flow of hydraulic fluid is not to be used by a device of the system, as such a flow may be re-directed back to the tank by means of the fourth control valve. Furthermore, if a lowering operation provides a torque by means of the hydraulic motor and said torque is used for an auxiliary hydraulic function, wherein the torque is larger than needed for said auxiliary hydraulic function, the fourth control valve may re-direct the resulting excess hydraulic fluid back to the tank, wherein the rotatable axle may rotate at the same speed for both the hydraulic motor and the pump.
According to an aspect, when the at least one hydraulic auxiliary device is arranged on the feed line, between the fourth control valve and the lifting device, and when the at least one hydraulic auxiliary device is operated, the control unit may be arranged to control the fourth control valve, for controlling the flow of hydraulic fluid within the feed line.
This has the advantage that the first pump may be operated to provide a flow of hydraulic fluid to the feed line, wherein the fourth control valve may be used to control said flow and its characteristics to the at least one auxiliary device when it is in need of hydraulic fluid.
According to an aspect, a fork-lift truck is provided. The fork-lift truck may comprise a hydraulic lifting system according to the disclosure, wherein the lifting device of the hydraulic lifting system is the lifting device of the fork-lift truck.
This has the advantage that such a fork-lift truck may be provided with the hydraulic lifting system as defined and explained within the disclosure, wherein the hydraulic lifting system of such a fork-lift truck may utilize all advantages and benefits of the hydraulic lifting system as described herein.
According to an aspect, the hydraulic auxiliary device of the hydraulic lifting system is a hydraulic component of a reach device of the fork-lift truck.
This has the advantage that the reach device of the fork-lift truck may be used to perform a reach operation when the lifting device of the fork-lift truck is being lowered, which is not possible to perform simultaneously with a prior art fork-lift truck using a one directional hydraulic lifting system that uses the pump running in its backwards direction for regeneration, and performs lowering operations for the lifting device solely by draining the hydraulics of said lifting device.
According to an aspect, a method for modifying a fork-lift truck is provided, wherein a hydraulic lifting system according to the disclosure is provided to said fork-lift truck.
This has the advantage that such a fork-lift truck may be provided with an expanded hydraulic lifting system, which may perform more types of operations simultaneously, and conserve energy within the systems of the fork-lift truck. Said fork-lift truck may also be provided with the added benefits of speeding up lowering operations of its lifting device, as has been explained with the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of, as examples, embodiments with reference to the enclosed drawings, in which:

Fig. 1 shows a hydraulic circuit diagram according to an embodiment, not according to the present invention.
Fig. 2 shows a hydraulic circuit diagram according to an embodiment, not according to the present invention.
Fig. 3 shows a hydraulic circuit diagram according to an embodiment.
Fig. 4 shows a hydraulic circuit diagram according to an embodiment.
Fig. 5 shows a hydraulic circuit diagram according to an embodiment, not according to the present invention.
Fig. 6 shows a schematic fork-lift truck comprising a hydraulic lifting system according to an embodiment, and
Fig. 7 shows a flowchart of a method for providing a hydraulic lifting system according to the disclosure to a fork-lift truck.

DETAILED DESCRIPTION

The description of the various features, and modifications thereof, according to the disclosure, will herein be described in more detail with reference to the accompanied drawings. The detailed description with reference to the embodiments depicted are to be viewed as exemplary embodiments comprising a combination of certain features, wherein it should to understood that additional embodiments may be achieved by combining other features into embodiments not depicted herein. The figures are to be viewed as examples and not mutually exclusive combinations. It is thus to be understood that embodiments comprising any of the described feature or a combination of features may be assembled in accordance with the description herein.
Fig. 1 shows a hydraulic circuit diagram not according to the invention. The hydraulic circuit diagram illustrates a hydraulic lifting system 1 according to the disclosure herein. The hydraulic lifting system 1 comprises a hydraulic circuit 3, which comprises a feed line 5 and a return line 7, to which circuit 3 a plurality of components are coupled. The plurality of components comprises: a lifting device 9, at least one hydraulic auxiliary device 11, at least one first pump 13, at least one electric motor 15 for operating the at least one pump 13, a tank 17 for holding hydraulic fluid, a first control valve 19, a second control valve 21, and a control unit (not depicted in the figures for the sake of simplicity), for operating the valves 19, 21 and the at least one electric motor 15. The first control valve 19 is arranged on the feed line 5, and be arranged to control a flow of hydraulic fluid through said feed line 5, which flow is provided to the feed line 5 by means of the first pump 13 and the electric motor 15. A flow through said feed line 5 is directed to the lifting device 9, which lifting device 9 may perform a lifting operation when provided with said hydraulic fluid. The second control valve 21 is arranged on the return line 7, and be arranged to re-direct the flow of hydraulic fluid from the feed line 5 to the return line 7, which leads said hydraulic fluid to the tank 17, wherein the lifting device 9 performs a lowering operation when the hydraulic fluid is drained therefrom by means of the second control valve 21. The basis of hydraulic lifting system 1 is thus to be understood to be similar to a "one-directional" lifting system in which an electric motor is operated for performing lifting operation with a lifting device, whereas the lowering of said lifting device may be performed without operating said motor, and solely control valves in such a hydraulic circuit so as to drain hydraulic fluid from the lifting device to which said fluid was pumped in to perform the lifting operation. The feed line 5 further comprises additional components such as a first check valve 23, arranged between the first control valve 19 and the lifting device 9, so as to force hydraulic fluid to go through the return line after being pumped into the lifting device 9. The at least one hydraulic auxiliary device 11 functions in various manners with regards to the hydraulics and its design, but is herein to be viewed schematically as an additional hydraulic device in general, which is provided with hydraulic fluid from the electric motor 15 and the first pump 13. The at least one hydraulic auxiliary device 11 as depicted in fig. 1 is herein further shown to be provided with an auxiliary control valve 25 so as to control a flow of hydraulic fluid to and from said at least one hydraulic auxiliary device 11.
The system 1 further comprises a hydraulic motor 27, said hydraulic motor 27 is arranged on the return line 7, between the second control valve 21 and the tank 17, wherein the hydraulic motor 27 when provided with hydraulic fluid from the return line 7 is arranged to generate mechanical energy to a rotatable axle 29 . Thereby the energy that would otherwise be lost when the lifting device 9 is lowered may herein be accumulated by means of different manners of utilization of said rotatable axle 29. The hydraulic motor 27 is arranged in an opposite flowing direction compared to the first pump 13, so that the rotatable axle 29 of the hydraulic motor 27 rotates in the same rotational direction, when provided with hydraulic fluid from the return line 7, as a rotational axle of the first pump 13 when said first pump 13 pumps hydraulic fluid from the tank 17 to the feed line 5.
Turning the attention to fig. 2, wherein fig. 2 shows a hydraulic circuit diagram not according to the invention of a hydraulic lifting system 1. The previously mentioned utilization of otherwise lost energy may herein be further delved into. The hydraulic circuit diagram depicted in fig. 2 illustrates a hydraulic lifting system 1, wherein the rotatable axle 29 may be arranged in selective connection to a generator 31 comprised in the system 1, which generator 31 is arranged to transform the mechanical energy to electricity when said rotatable axle 29 and said generator 31 are connected. The rotatable axle 29 may be coupled the generator 31 by means of a first clutch coupling 33, which may, as is depicted in fig. 2, be arranged intermediate the hydraulic motor 27 and the generator 31. The rotatable axle 29 may also be coupled directly into the generator 31, wherein the generator 31 may be provided with an alternative clutch mechanism arranged therein. The rotatable axle 29 may also simply be coupled to the generator 31 directly, wherein the generator 31 may be provided with an option of having said axle 29 roll freely therein, wherein the generator 31 thus does not need to be actively operated due to the rotation of the rotatable axle 29, if desirable. The generator 31 may provide the electric motor 15 with the electricity that it produces, wherein energy consumption may be preserved in said electric motor 15. The electricity may also be provided to other external systems that require and uses electricity, if the hydraulic lifting system 1 is arranged in a device or similar that houses a plurality of such interconnected systems.
The hydraulic lifting system 1 may also further comprise a battery 35, which battery 35 may be coupled to the generator 31 and be arranged to store electrical energy generated by means of said generator 31. The battery 35 is depicted in fig. 2, however it should be mentioned that it may not be arranged therein without deviating from the scope of protection as defined herein. Thus, the generator 31 may be arranged in the system 1 without a battery 35 coupled thereto, even if both said components are depicted in the mentioned fig. 2.
The generator 31 may also further comprise an integrated second electric motor 37, wherein the generator 31 and said second electric motor 37 may be used for different circumstances. The generator 31 may be used to transform the mechanical energy of the rotatable axle 29 so as to generate electricity when the lifting device 9 is lowered, as described. But the second electric motor 37 may also be used to rotate the rotatable axle 29 if a lowering operation of the lifting device 9 is slow due to a low internal pressure within the lifting device 9. If such a situation occurs, which may arise if the lifting device 9 has performed a lifting operation with a low load thereon, wherein the internal pressure may be low as a result, the hydraulic motor 27 may be used to suck hydraulic fluid through the return line 7, and thus speed up the draining of hydraulic fluid via the return line 7, and in turn also speed up the lowering of the lifting device 9.
Fig. 3 shows a hydraulic circuit diagram according to the invention. The hydraulic circuit diagram depicted in fig. 3 illustrates a hydraulic lifting system 1, wherein said system 1 further comprises a third control valve 39, arranged on the return line 7 and being arranged to control the flow of hydraulic fluid from the lifting device 9 so as to either be directed to the tank 17 or to the hydraulic motor 27. This is preferably made possible in a proportional manner, such that the desired ratio between fluid to the tank and to the hydraulic motor 27 can be precisely controlled. The third control valve 39 may herein be controllable by means of an output signal from the control unit, which output signal thus control the state of the third control valve 39 and which way it will lead the hydraulic fluid passing there through. A pressure detecting device 45 may be arranged to the hydraulic circuit 3, and is in fig. 3 shown to be arranged on the feed line 5, between the lifting device 9 and the second control valve 21, wherein said pressure detection device 45 may detect the pressure of both the feed line 5 and at least part of the return line 7 (depending on the state of the second control valve 21). Said detected pressure may be used as an input to the control unit so as to control the third control valve 39. The return line 7 may further comprise a pressure compensator 47 to regulate the flow therein, arranged on the return line 7 between the second control valve 21 and the third control valve 39, as shown in fig. 4. The pressure compensator 47 may further be connected to the feed line 5, so as to be controlled by the pilot pressure of the feed line 5.
The hydraulic lifting system 1 may further, as depicted in fig. 3, be coupled in such a manner that the rotatable axle 29 may be arranged in connection with the first pump 13 and said rotatable axle 29 being arranged to selectively transfer a torque from the hydraulic motor 27 to the first pump 13. Thus, if a lowering operation if performed with the lifting device 9, and the first pump 13 is simultaneously to be used to provide hydraulic to the at least one hydraulic auxiliary device 11, the third control valve 39 may be set to steer the hydraulic fluid towards the hydraulic motor 27, through line 7b, which hydraulic motor 27 in turn may provide its generated torque to the first pump 13, by means of the rotatable axle 29 being arranged in connection with the first pump 13. If the torque transferred from the hydraulic motor 27 to the first pump 13 is enough to provide the hydraulic auxiliary device 11 with enough pressure to perform its operation, energy consumption will be lowered by a large margin as the electric motor 15 does not need to be operated at all. If the torque provided is not enough to fully provide the hydraulic auxiliary device 11 with its needed pressure, energy consumption may still be lowered to some extent as the electric motor 15 may provide the remainder of the needed power to the first pump 13, wherein said remainder of provided energy will be lower than if the electric motor 15 would be the only device providing the energy needed for the operation of the hydraulic auxiliary device 11. It is preferred that the third control valve 39 is a valve that can be precisely controlled, such that if the regenerated energy exceeds the energy needed by the electric motor, a proportional amount of hydraulic fluid could be returned directly to the tank 17 through line 7a, and consequently the remainder is lead through line 7b.
The rotatable axle 29 may further be coupled to the at least one electric motor 15, as well as the first pump 13. That is, the rotatable 29 axle may be a single axle connecting the electric motor 15, the first pump 13 and the hydraulic motor 27 to each other. The couplings between said different components may then further comprise clutches or similar mechanics, so as to control which part that will be affected by the rotation of the rotatable axle 27, or they may individually be opted to rotate without any work being needed at the time, wherein the rotatable axle 29 may roll freely within a device without said axle 29 being made to activate its intended function within said device. As the rotational direction of the three devices 13, 15, 27 may be the same when said devices 13, 15, 27 are operated for their primary purposes, the axle may in an efficient manner connect said devices 13, 15, 27 to interact with each other.
The hydraulic lifting system 1 may further comprise a fourth control valve 41, arranged on the feed line 5 and being arranged to control a flow from the first pump 13 so as to either be directed to the feed line 5 or to be re-circulated to the tank 17. The fourth control valve 41 may thus be configured to achieve the above stated functionality. If the lifting device 9 is lowered and provides hydraulic fluid to the hydraulic motor 27, which in turn provides a torque to the first pump 13, the first pump 13 may actively work as a pump and is thus to transfer hydraulic fluid from the tank 17 to the feed line 5. The fourth control valve 41 may in such a case re-direct said hydraulic fluid back to the tank 17, through line 5a instead wherein the downstream portions of the feed line 5 are not subjected to an increased internal pressure build-up as a result. This may be utilized for example if an auxiliary hydraulic device 11 is to be used, but wherein said device needs a lesser amount of hydraulic fluid than provided to the feed line 5. The fourth control valve 41 may thus function as a controlling and/or safety feature to avoid pressure build-up and to regulate hydraulic fluid within the system 1. Another safety feature may be added in the form of a pressure controlled valve 43, arranged on the feed line 5, between the fourth control valve 41 and the first control valve 19, wherein when the internal pressure within the feed line 5 surpasses a predetermined value, said pressure controlled valve 43 may open automatically and drain the feed line 5 by means of re-directing hydraulic fluid within the feed line 5 back to the tank 17.
The hydraulic lifting system 1 may comprise a hydraulic auxiliary device 11 as stated, wherein the control unit of the system 1 may further be configured to utilize the fourth control valve 41 as a control valve for said hydraulic auxiliary device 11. When the at least one hydraulic auxiliary device 11 is arranged on the feed line 5, between the fourth control valve 41 and the lifting device 9, and when the at least one hydraulic auxiliary device 11 is operated, the control unit may be arranged to control the fourth control valve 41, for controlling the flow of hydraulic fluid therein to the hydraulic auxiliary device 11 via the feed line 5.
Fig. 4 shows a hydraulic circuit diagram according to an embodiment. The hydraulic circuit diagram depicted in fig. 4 illustrates a hydraulic lifting system 1, similar to the one depicted in fig. 3. There are however some differences that will be described herein. The hydraulic lifting system 1 according to fig. 4, comprises a third control valve 39, wherein said third control valve 39 may be pressure controlled, wherein a pressure detection device 45 is arranged on the return line 7 between the second control valve 21 and the third control valve 39, wherein the third control valve 39 directs the flow to the hydraulic motor 27, through line 7b, when the pressure exceeds a predetermined value. Thus a pressure is communicated through a line 45a, that controls the third control valve 39. The advantages from this feature has been described previously within the disclosure and should thus be obvious. The return line 7 may further comprise a pressure compensator 47 to regulate the flow, arranged on the return line 7 between the second control valve 21 and the third control valve 39, as shown in fig. 4. The pressure compensator 47 may further be connected to the feed line 5, so as to be controlled by the pilot pressure of said feed line 5. It is preferred that the third control valve 39 is a valve that can be precisely controlled, such that if the regenerated energy exceeds the energy needed by the electric motor, a proportional amount of hydraulic fluid could be returned directly to the tank 17 through line 7a, and consequently the remainder is lead through line 7b. In this case this is controlled by the pressure in the line 45a.
Fig. 5 shows a hydraulic circuit diagram not according to the invention. The hydraulic circuit diagram depicted in fig. 5 illustrates a hydraulic lifting system 1 of an alternative embodiment. The embodiment depicted in fig. 5 may comprise the basis of the hydraulic lifting system 1 as described previously, and in parts be similar to the hydraulic lifting system as described with reference to fig. 1 in that it comprises a first and a second control valve 19, 21, arranged on the feed line 5 and the return line 7 respectively. The embodiment according to fig. 5 does however not comprise the third or the fourth control valves, but instead solves the functionality of said two valves in an alternative manner. The hydraulic motor 27 arranged on the return line 7 is herein configured to always provide a torque to the rotatable axle 29, but the coupling of the axle 29 is herein shown to be connected to the electric motor 15, comprising a second clutch coupling 49 coupled intermediate there between. The hydraulic motor 27 may thus rotate the rotatable axle 29 as soon as the lifting device 9 is drained via the return line 7 when a lowering operation thereof is performed. The second clutch coupling 49 may however be controlled to either transfer the torque provided from the hydraulic motor 27 or not, depending on the state of said first clutch coupling 49. It should be understood that the coupling can be arranged such that it only partly transfers the torque as generated as a whole, or in any desired amount of this torque. Furthermore, the system 1 may comprise a third clutch coupling 51, arranged between the electric motor 15 and the first pump 13, wherein the torque from the hydraulic motor 27, the electric motor 15, or both, may be selectively controlled by means of the second and third clutch couplings 49, 51, in any amount. The two clutch coupling 49, 51 may thus control the system land all its functions with regards to the lifting device 9, regenerative functionality when draining said lifting device 9, and any present hydraulic auxiliary devices 11 comprised therein. It is also shown in fig. 5 that the hydraulic lifting system 1 as depicted herein comprises two hydraulic auxiliary devices 11, which is fully possible without deviating from the scope of protection defined within the disclosure. The hydraulic lifting system 1 may comprise an even larger plurality of hydraulic auxiliary devices 11 as well. It should also be mentioned that any such present hydraulic auxiliary device 11 may be designed with a plurality of valves or other hydraulic components, but for the sake of simplicity they are herein merely broadly described as general hydraulic auxiliary devices 11, wherein their specifics do not matter for the sake of the hydraulic lifting system 1 as explained herein. Thus it should be understood that the hydraulic lifting system 1 can be controlled very precisely. An input of generated energy from return line 7 can partly or completely be regenerated into input torque to the electric motor 15 through control of clutch 49, the electric motor can in turn either transfer the torque further to the hydraulic pump 13 in full or partly by means of control of the clutch 51. From this it can be understood that if needed, the motor 15 can operate as a generator and turn torque into electric energy. Or the electric motor 15 can operate as a motor but with an electric input that is lower than the demand for the pump, and the remainder received mechanically from the torque of the hydraulic motor 27 delivered through clutch 49 to the electric motor 15. Thus it is possible to regenerate energy through the return line 7 and the hydraulic motor 27 and at the same time run the electric motor 15 for providing torque through the clutch 51 to the pump 13, but reduce the electric energy needed for this operation with the energy regenerated by the hydraulic motor 27. Also the electric motor 13 can function as a generator if there are a surplus of energy available as torque from the hydraulic motor 27. Then the hydraulic motor 27 can both mechanically provide torque to the electric motor 15 as a generator and also torque to the pump 13.
Fig. 6 shows a schematic fork-lift truck 53 comprising a hydraulic lifting system 1 according to an embodiment. The fork-lift truck 53 may be any type of fork-lift truck 53 comprising a lifting system that uses hydraulics, and wherein the hydraulic lifting system comprises at least one hydraulic auxiliary device within the hydraulic circuit of said hydraulic system. The lifting device 9 of the hydraulic lifting system 1 is thus, as should be obvious, the lifting device 9 of the fork-lift truck 53. The hydraulic lifting system 1 according to the disclosure herein may thus utilize and take advantage of the otherwise lost energy that is provided to the return line 7 of the system 1 when the lifting device 9 of the fork-lift truck 53 is lowered by means of draining the lifting device 9 via the return line 7 of the hydraulic system 1. Said energy may be conserved, transformed, stored and/or re-directed within the system so as to utilize it simultaneously as the lifting device 9 is lowered, or at a later point in time if stored.
In particular, and as an example, the fork-lift truck 53 may comprise a hydraulic lifting system 1 according to the disclosure, wherein the hydraulic auxiliary device 11 of the hydraulic lifting system 1 is a hydraulic component of a reach device 54 of the fork-lift truck 53. By means of the inventive concept of the hydraulic lifting system 1 as explained throughout the disclosure, said reach device 54 may thus be used at the same time as the lifting device 9 of the fork-lift truck 53 is being lowered, and with a lower energy consumption than if the system 1 did not comprise the various features as described herein. The reach device may thus perform a reach movement, e g. by moving a mast in horizontal direction together with the fork of the fork-lift truck 53 under the described conditions herein.
Fig. 7 shows a flowchart of a method for providing a hydraulic lifting system 1 according to the disclosure to a fork-lift truck 53. Said method may be performed as part of a maintenance of the fork-lift truck 53, or an upgrade thereof, if the fork-lift truck 53 prior to such a maintenance operation comprises a one-directional lift/drain system according to prior art. The method may be performed by adding the relevant components according to the hydraulic lifting system as described with reference to figs. 1-5, at an original feed line and return line respectively. The method may also be performed by providing the hydraulic lifting system 1 in its entirety to a fork-lift truck 53, regardless of its initial state.
The foregoing description of the embodiments has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the embodiments to the variations described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate principles and practical applications, and to thereby enable one skilled in the arts to understand the invention in terms of its various embodiments and with the various modifications that are applicable to its intended use. The components and features specified above may, within the framework of the disclosure, be combined between different embodiments specified. Thus, all individual as described herein may be combined in various additional embodiments not shown or explained within the scope of the invention as defined by the appended claims, as long as it would not be logically contradictive to do so.

Claims

A hydraulic lifting system (1) comprising a hydraulic circuit (3), which comprises a feed line (5) and a return line (7), to which circuit (3) a plurality of components are coupled, the plurality of components comprises:
a lifting device (9),

at least one hydraulic auxiliary device (11),

at least one first pump (13),

at least one electric motor (15) for operating the at least one pump (13),

a tank (17) for holding hydraulic fluid,

a first control valve (19),

a second control valve (21), and

a control unit, for operating the valves (19, 21) and the at least one electric motor (15),

wherein the first control valve (19) is arranged on the feed line (5), and being arranged to control a flow of hydraulic fluid through said feed line (5), which flow is provided to the feed line (5) by means of the pump (13) and the electric motor (15), wherein a flow through said feed line (5) is directed to the lifting device (9), which lifting device (9) performs a lifting operation when provided with hydraulic fluid,

and wherein the second control valve (21) is arranged on the return line (7), and being arranged to re-direct the flow of hydraulic fluid from the feed line (5) to the return line (7), which leads said hydraulic fluid to the tank (17), wherein the lifting device (9) performs a lowering operation when the hydraulic fluid is drained therefrom by means of the second control valve (21),

wherein the system (1) further comprises a hydraulic motor (27), said hydraulic motor (27) being arranged on the return line (7), between the second control valve (21) and the tank (17), wherein the hydraulic motor (27) when provided with hydraulic fluid from the return line (7) is arranged to generate mechanical energy to a rotatable axle (29), characterized in that the hydraulic lifting system (1) further comprises a third control valve (39), arranged on the return line (7) and being arranged to control the flow from the lifting device (9) so as to either be directed to the tank (17) and/or to the hydraulic motor (27).
The hydraulic lifting system (1) according to claim 1, wherein the rotatable axle (29) is arranged in selective connection to a generator (31) comprised in the system (1), which generator (31) is arranged to transform the mechanical energy to electricity when said rotatable axle (29) and said generator (31) are connected.
The hydraulic lifting system (1) according to claim 2, further comprising a battery (35), which battery (35) is coupled to the generator (31) and being arranged to store electrical energy generated by means of said generator (31).
The hydraulic lifting system according to claim 1, wherein said valve (39) is arranged to be able to regulate said flow proportionally in predetermined amounts to the tank (17) and the hydraulic motor (27).
The hydraulic lifting system (1) according to claim 1 or 4, wherein the third control valve (39) is pressure controlled, wherein a pressure detection device (45) is arranged on the return line (7) between the second control valve (21) and the third control valve (39), wherein the third control valve (39) directs the flow to the hydraulic motor (27) when the pressure exceeds a predetermined value.
The hydraulic lifting system (1) according to claim 1 or 4, wherein the third control valve (39) is controllable by means of an output signal from the control unit, preferably said control unit receives an input of a detected pressure in the return line (7) for control of the third control valve (39).
The hydraulic lifting system (1) according to any of the preceding claims, wherein the rotatable axle (29) is arranged in connection with the first pump (13) and said rotatable axle (29) being arranged to selectively transfer a torque from the hydraulic motor (27) to the first pump (13), preferably the torque is arranged to be transferred by a clutch (49), even more preferred said clutch can be controlled such that a predetermined amount of torque can be transferred.
The hydraulic lifting system according to claim 7, wherein the rotatable axle (29) is further coupled to the at least one electric motor (15), preferably said electric motor (15) can also be used as a generator, preferably said axle (29) is connected to said electric motor (15) by a clutch (51), even more preferred said clutch can be controlled such that a predetermined amount of torque can be transferred.
The hydraulic lifting system (1) according to claim 1 or claim 4, wherein it further comprises a fourth control valve (41), arranged on the feed line (5) and being arranged to control a flow from the first pump (13) so as to be directed to the feed line (5) and/or to be re-circulated to the tank (17).
The hydraulic lifting system (1) according to claim 9, wherein when the at least one hydraulic auxiliary device (11) is arranged on the feed line (5), between the fourth control valve (41) and the lifting device (9), and when the at least one hydraulic auxiliary device (11) is operated, the control unit is arranged to control the fourth control valve (41), for controlling the flow of hydraulic fluid within the feed line (5).
A fork-lift truck (53) comprising a hydraulic lifting system (1) according to any of claims 1-10, wherein the lifting device (9) of the lifting system (9) is the lifting device (9) of the fork-lift truck.
The fork-lift truck (53) according to claim 11, wherein the hydraulic auxiliary device (11) of the lifting system (1) is a hydraulic component of a reach device of the fork-lift truck (53).
Method for modifying a fork-lift truck, characterized in that a hydraulic system (1) according to any of the claims 1-10 is provided to a fork-lift truck (53).