Hydraulic system for an industrial truck, in particular reach truck

Abstract

The invention relates to a hydraulic system (1) for a material handling vehicle, in particular a reach truck, wherein the hydraulic system (1) comprises a lifting hydraulic system (2) comprising a main stroke (3) and a free stroke (4), and wherein the hydraulic system (1) comprises a hydraulic pump device (5) configured to supply the main stroke (3) and the free stroke (4) with hydraulic fluid. The hydraulic pump device (5) comprises a first hydraulic pump unit (6) which is connected at a first port (A1) to a reservoir (7) and at a second port (A2) to the main stroke (3), wherein a first connecting line (8) is led from the second port (A2) of the first hydraulic pump unit (6) to the main stroke (3).The hydraulic pump device (5) has a second hydraulic pump unit (10) which is connected at a first connection (A1) to the first connecting line (8) and at a second connection (A2) to the free lift (4), wherein a second connecting line (11) is led from the second connection (A2) of the second hydraulic pump unit (10) to the free lift (4).

Description

[0001] The invention relates to a hydraulic system for a forklift truck, in particular a reach truck, wherein the hydraulic system has a lifting hydraulics comprising a main stroke and a free stroke, and wherein the hydraulic system comprises a hydraulic pump device configured to supply the main stroke and the free stroke with pressure medium.

[0002] Industrial trucks, such as reach trucks, have a hydraulic system with a lifting hydraulic unit that raises and lowers a load in a lifting mast. The lifting hydraulic unit can include a main stroke and a free stroke. The main stroke is designed to raise and lower one or more extension masts of the lifting mast within a fixed mast. The main stroke comprises one or more main lifting cylinders. The free stroke is designed to raise and lower a load-handling attachment, such as a load fork, in the highest extended extension mast. The free stroke comprises one or more free-stroke cylinders. A hydraulic pump is provided to supply the main stroke and the free stroke. In industrial trucks, such as reach trucks, designs are known in which the load-handling attachment can be raised to lifting heights in the range of 15–18 meters.

[0003] A number of requirements are placed on the hydraulic systems of industrial trucks, especially reach trucks.

[0004] The hydraulic system of a forklift truck, in particular a reach truck, whose load handling device can be raised to lifting heights in the range of 15-18m, should enable effective recuperation of the lowering energy of the load when lowering the load.

[0005] The lowering speed of the load-handling device without a load, i.e., the empty load-handling device, should be possible at more than 0.6 m / s, especially during the free stroke. The problem here is that, in known hydraulic systems, the pressure losses from the free-stroke cylinder to the reservoir are too high to achieve a lowering speed of more than 0.6 m / s for the load-handling device without a load.

[0006] In known hydraulic systems, the lowering operation of the load-handling device is controlled by one or more proportional control valves in the lowering path of the free stroke and main stroke. Such proportional control valves in the lowering path of the free stroke and main stroke make the hydraulic system susceptible to contamination.

[0007] In known hydraulic systems, the mast transition between the main stroke and the free stroke is typically poorly damped. This necessitates deceleration of the lifting and lowering movements before and after the transition between the free stroke and the main stroke.

[0008] In known hydraulic systems, the control valves required for the free stroke, main stroke, and auxiliary consumers are arranged in a central valve block and supplied with hydraulic fluid by a single hydraulic pump. This makes the hydraulic system very tunable, as the functions of free stroke, main stroke, and auxiliary consumers influence each other via different viscosities of the hydraulic fluid.

[0009] The present invention is based on the objective of providing a hydraulic system of the type mentioned at the outset, with which one or more of the aforementioned requirements can be implemented in an improved manner.

[0010] This problem is solved according to the invention in that the hydraulic pump device has a first hydraulic pump unit which is connected to a container at a first port and to the main stroke at a second port, wherein a first connecting line is led from the second port of the first hydraulic pump unit to the main stroke, and the hydraulic pump device has a second hydraulic pump unit which is connected to the first connecting line at a first port and to the free stroke at a second port, wherein a second connecting line is led from the second port of the second hydraulic pump unit to the free stroke.

[0011] In the hydraulic system according to the invention, two hydraulic pump units are provided for the lifting hydraulics, which includes the free lift and the main lift, which supply the lifting hydraulics with pressure medium, wherein the first hydraulic pump unit draws pressure medium from the reservoir and delivers it into the hydraulic system, and the second hydraulic pump unit is connected in series with the first hydraulic pump unit and only supplies the partial range of the free lift with pressure medium.

[0012] The hydraulic system according to the invention allows the aforementioned requirements to be implemented in an improved manner.

[0013] According to an advantageous embodiment of the invention, a third connecting line leads from the first connecting line to the first port of the second hydraulic pump unit. A first control valve is arranged in the first connecting line between the second port of the first hydraulic pump unit and the port of the third connecting line. This control valve has a closed position and a flow position, the closed position being designed, in particular, as a check valve opening in the direction of the main stroke. The third connecting line allows the first port of the second hydraulic pump unit to be easily connected to the first connecting line. The lifting and lowering operation of the lifting hydraulics can be easily controlled by the first control valve arranged in the first connecting line.

[0014] According to an advantageous embodiment of the invention, a second control valve is arranged in the second connecting line, which has a closed position and a flow position. The lifting and lowering operation of the free stroke can be easily controlled by the second control valve arranged in the second connecting line.

[0015] According to an advantageous embodiment of the invention, the hydraulic system has at least one auxiliary consumer, wherein a fourth connecting line leading to the auxiliary consumer is connected to the first connecting line or to the third connecting line. This allows an auxiliary consumer, for example a tilting drive of the lifting frame and / or a side shift of the load-handling device and / or a thrust drive of the lifting frame, to be supplied with hydraulic fluid in a simple manner by the first hydraulic pump unit.

[0016] According to an advantageous embodiment of the invention, a third control valve is arranged in the first connecting line between the connection of the third connecting line and the main stroke, which has a closed position and a flow position. With such a third control valve, the lifting and lowering operation of the main stroke can be easily controlled, and when the third control valve is in the closed position, the at least one auxiliary consumer is supplied with hydraulic fluid by the first hydraulic pump unit.

[0017] According to an advantageous embodiment of the invention, a fourth control valve is arranged in the fourth connecting line, which has a closed position and a flow position. With such a fourth control valve, the supply of pressure medium to the at least one additional consumer can be easily controlled in the flow position.

[0018] According to an advantageous embodiment of the invention, a pressure medium line is provided leading from the second connecting line to the fourth connecting line, in which a first shut-off valve, in particular a check valve, opening towards the fourth connecting line, is arranged. This allows the pressure required for actuating the at least one additional consumer to be generated easily by the second hydraulic pump unit when needed.

[0019] According to an advantageous embodiment of the invention, a second shut-off valve, in particular a check valve, opening towards the auxiliary consumer, is arranged in the fourth connecting line, wherein the pressure medium line between the second shut-off valve and the auxiliary consumer is connected to the fourth connecting line. Such a second shut-off valve ensures in a simple manner that the pressure medium delivered by the second hydraulic pump unit flows to the at least one auxiliary consumer.

[0020] According to an advantageous embodiment of the invention, the first hydraulic pump unit comprises a first hydraulic pump connected to a first electric motor. The first hydraulic pump unit can be operated in pump mode and in motor mode. In pump mode, the first hydraulic pump is driven in a first direction of rotation by the first electric motor, which acts as a motor, and draws hydraulic fluid from the reservoir at the first port and delivers it to the first connecting line at the second port. In motor mode, the first hydraulic pump is driven in a second direction of rotation by the hydraulic fluid present at the second port and drives the first electric motor, which acts as a generator, delivering hydraulic fluid to the first port. The first hydraulic pump thus represents a four-quadrant pump, which, in motor mode, enables the recuperation of the load's energy.

[0021] According to an advantageous embodiment of the invention, the second hydraulic pump unit comprises a second hydraulic pump connected to a second electric motor, wherein the second hydraulic pump unit can be operated in pump mode and in motor mode, wherein in pump mode the second hydraulic pump is driven in a first direction of rotation by the second electric motor operating as a motor and draws hydraulic fluid from the first connecting line at the first connection and delivers it to the second connecting line at the second connection, and wherein in motor mode the second hydraulic pump is driven in a second direction of rotation by the hydraulic fluid present at the second connection and drives the second electric motor operating as a generator and delivers hydraulic fluid to the first connection.The second hydraulic pump is therefore a 4-quadrant pump, which enables recuperation of the load's sinking energy during free stroke in motor operation.

[0022] According to an advantageous embodiment of the invention, an electronic control unit is provided which is configured to control the first electric motor, the second electric motor, the first control valve, and the second control valve. With an electronic control unit that controls the first electric motor, the second electric motor, the first control valve, and the second control valve, the lifting and lowering operation of the free stroke and the main stroke can be easily controlled.

[0023] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the first hydraulic pump unit and the second hydraulic pump unit in pump mode during the lifting operation of the free stroke, such that the flow rate of the second hydraulic pump unit corresponds to the flow rate of the first hydraulic pump unit. During the lifting operation of the free stroke, and thus when lifting a load in the free stroke, both hydraulic pump units are operated in pump mode. The flow rate of both hydraulic pump units is identical. The free stroke is operated at a lifting speed that depends on the flow rate of the hydraulic pump units.

[0024] According to an advantageous embodiment of the invention, the electronic control unit is configured to control the second control valve to the flow position during the lifting operation of the free stroke. This allows the volume flow delivered by the second hydraulic pump unit into the second connecting line to flow to the free stroke for lifting the load.

[0025] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the first hydraulic pump unit and the second hydraulic pump unit in pump mode during lifting operation of the free stroke and additional actuation of the auxiliary consumer, such that the volume flow of the first hydraulic pump unit is greater than the volume flow of the second hydraulic pump unit. To additionally supply the auxiliary consumer with hydraulic fluid when lifting a load in the free stroke, the volume flow of the first hydraulic pump unit is increased such that the second hydraulic pump unit only draws in a portion of the volume flow delivered by the first hydraulic pump unit during lifting operation of the free stroke, thus providing a surplus of fluid for actuation of the auxiliary consumer.

[0026] According to an advantageous embodiment of the invention, an electronic control unit is provided to actuate the fourth control valve, and the electronic control unit is configured to control the second control valve and the fourth control valve to the flow position during the lifting operation of the free stroke and additional actuation of the auxiliary consumer. This allows the lifting operation of the free stroke and the additional actuation of the auxiliary consumer to be controlled in a simple manner.

[0027] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the first hydraulic pump unit and the second hydraulic pump unit simultaneously during the lowering phase of the free lift, such that the flow rate of the second hydraulic pump unit corresponds to the flow rate of the first hydraulic pump unit. Both hydraulic pump units are thus operated in motor mode, with the two electric motors, each acting as a generator, recuperating electrical energy that can be fed into a traction battery of the industrial truck. The free lift is operated at a lowering speed that depends on the flow rate of the hydraulic pump units.

[0028] According to an advantageous embodiment of the invention, an electronic control device is configured to control the first control valve and the second control valve to the flow position during the lowering operation of the free stroke. This allows the volume flow exiting the free stroke during lowering operation to flow into the reservoir in a simple manner, with the energy of the lowering process being recuperated by the motor operation of the two hydraulic pump units.

[0029] According to an advantageous embodiment of the invention, an electronic control unit is configured to operate the first hydraulic pump unit and the second hydraulic pump unit in motor mode during the lowering operation of the free stroke and additional actuation of the auxiliary consumer, such that the flow rate of the first hydraulic pump unit is lower than the flow rate of the second hydraulic pump unit. To additionally supply the auxiliary consumer with hydraulic fluid when lowering a load in the free stroke, the flow rate of the first hydraulic pump unit is reduced so that the second hydraulic pump unit provides a surplus during the lowering operation of the free stroke, which is available for actuating the auxiliary consumer.

[0030] According to an advantageous embodiment of the invention, the electronic control unit is provided to actuate the fourth control valve, and the electronic control unit is configured to control the first control valve, the second control valve, and the fourth control valve to the flow position during the lowering operation of the free stroke and additional actuation of the auxiliary consumer. This allows the volume flow exiting the free stroke during the lowering operation to flow into the container in a simple manner, and the excess to flow to the auxiliary consumer for its actuation.

[0031] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the first hydraulic pump unit in pump mode during the lifting operation of the main stroke. This allows the main stroke to be supplied with hydraulic fluid from the first hydraulic pump unit in a simple manner, with the main stroke being operated at a lifting speed that depends on the flow rate of the first hydraulic pump unit.

[0032] According to an advantageous embodiment of the invention, the electronic control unit is provided to actuate the third control valve, and the electronic control unit is configured to control the third control valve to the flow position during the lifting operation of the main stroke. This allows the volume flow delivered by the first hydraulic pump unit into the first connecting line to flow to the main stroke for lifting the load.

[0033] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the first hydraulic pump unit in pump mode during lifting operation of the main stroke and additional actuation of the auxiliary consumer. Preferably, the volume flow delivered by the first hydraulic pump unit is controlled such that it corresponds to the sum of the demand of the main stroke and the demand of the auxiliary consumer.

[0034] According to an advantageous embodiment of the invention, the electronic control unit is provided to actuate the third and fourth control valves, and the electronic control unit is configured to control the third and fourth control valves to the flow position during lifting operation of the main stroke and additional actuation of the auxiliary consumer. This allows the volume flow delivered by the first hydraulic pump unit to easily flow to the main stroke and the auxiliary consumer.

[0035] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the first hydraulic pump unit in motor mode during the lowering phase of the main stroke. The first hydraulic pump unit is thus operated in motor mode, in which the first electric motor, functioning as a generator, recuperates electrical energy that can be fed into a traction battery of the industrial truck. The main stroke is performed at a lowering speed that depends on the flow rate of the first hydraulic pump unit.

[0036] According to an advantageous embodiment of the invention, the electronic control unit is provided to actuate the third control valve, and the electronic control unit is configured to actuate the first control valve and the third control valve to the flow position during the lowering operation of the main stroke. This allows the volume flow exiting the main stroke during the lowering operation to flow into the reservoir in a simple manner, with the energy of the lowering process being recuperated by the motor operation of the first hydraulic pump unit.

[0037] According to an advantageous embodiment of the invention, the electronic control unit is configured to control the third control valve and the fourth control valve to the flow position during the lowering operation of the main stroke and additional actuation of the auxiliary consumer. This makes it possible to easily ensure that the volume flow exiting the main stroke during lowering operation is available to supply the auxiliary consumer.

[0038] According to an advantageous embodiment of the invention, the electronic control unit is configured to operate the second hydraulic pump unit in pump mode during the lowering operation of the main stroke and additional actuation of the auxiliary consumer. If the pressure of the volume flow exiting the main stroke during lowering operation is insufficient to actuate the auxiliary consumer, the pressure can be easily increased by operating the second hydraulic pump unit to ensure the auxiliary consumer is actuated.

[0039] The invention further relates to a forklift truck, in particular a reach truck, with a hydraulic system described above.

[0040] The invention has a number of advantages.

[0041] The hydraulic system according to the invention makes it possible to easily achieve lifting and lowering speeds in the main stroke and in the free stroke of greater than 0.6m / s, preferably greater than 1m / s.

[0042] In the hydraulic system according to the invention, the lowering speed in the free stroke and in the main stroke is no longer adjusted by mechanical throttling at corresponding control directional control valves, but can be controlled by the volume flow of the two hydraulic pump units, for example the rotational speed of the first and second pumps. This makes it possible to control the lowering speed independently of viscosity.

[0043] In the hydraulic system according to the invention, the lifting operation of the main stroke and the lifting operation of the free stroke can be carried out simultaneously.

[0044] In the hydraulic system according to the invention, the position of the fork carriage in the extension mast can be calculated from the volume pumped or absorbed by the second pump.

[0045] The hydraulic system according to the invention offers high energy efficiency through the recuperation of sink energy during the sinking operation of the free stroke and main stroke. This allows for lower temperatures of the hydraulic fluid in the hydraulic system, thereby reducing the cooling capacity required for the hydraulic fluid.

[0046] The hydraulic system according to the invention has significantly reduced flow resistances to the lifting cylinders of the free stroke and the main stroke compared to a hydraulic system of the prior art with one or more proportional control valves.

[0047] In the hydraulic system according to the invention, a smooth or gentle mast transition between free lift and main lift can be easily achieved, since the retraction speed or the extension speed between the lifting cylinders of the free lift and the main lift can be controlled via the volume flows of the two hydraulic pump units.

[0048] In the hydraulic system according to the invention, the extension sequence of the lifting cylinders for the free stroke and the main stroke can also be easily determined. The diameters of the lifting cylinders for the free stroke and the main stroke can thus be selected independently of each other.

[0049] Further advantages and details of the invention are explained in more detail by way of example using the embodiment shown in the schematic figure.

[0050] In the Figur 1 Figure 1 shows a hydraulic circuit diagram of a hydraulic system according to the invention for a forklift truck, for example a reach truck.

[0051] The hydraulic system 1 has a lifting hydraulic system 2, which comprises a main stroke 3 and a free stroke 4. In the illustrated embodiment, the main stroke 3 has two main stroke cylinders 3a, 3b. In the illustrated embodiment, the free stroke 4 has a single free stroke cylinder 4a.

[0052] The main lift 3 is designed to raise or lower one or more extension masts in a fixed mast within a lifting frame of the industrial truck (not shown in detail). The free lift 4 is designed to raise and lower a load-handling device, for example, a load fork, in the highest extended extension mast.

[0053] The hydraulic system 1 has a hydraulic pump device 5 which is designed to supply the main stroke 3 and the free stroke 4 with hydraulic fluid.

[0054] The hydraulic pump device 5 comprises a first hydraulic pump unit 6, which is connected to a reservoir 7 at a first port A1 and to the main stroke 3 at a second port A2. For this purpose, a first connecting line 8 leading to the main stroke 3 is connected to the second port A2 of the first hydraulic pump unit 6.

[0055] The hydraulic pump device 5 has a second hydraulic pump unit 10, which is connected to the first connecting line 8 at a first port A1 and to the free stroke 4 at a second port A2. For this purpose, a second connecting line 11 leading to the free stroke 4 is connected to the second port A2 of the second hydraulic pump unit 10.

[0056] A third connecting line 15 is provided to connect the first connection A1 of the second hydraulic pump unit 10 with the first connecting line 8, which leads from the first connecting line 8 to the first connection A1 of the second hydraulic pump unit 10.

[0057] In A first control valve 20 is arranged between the second connection A2 of the first hydraulic pump unit 6 and the connection of the third connection line 15 of the first connecting line 8. The first control valve 20 has a closed position 20a and a flow position 20b. In the illustrated embodiment, the closed position 20a is designed as a check valve opening in the direction of the main stroke 3.

[0058] The first control valve 20 is actuated into the closed position 20a by means of a spring device 21. The first control valve 20 can be actuated into the open position 20b by means of an electrical actuating device 22, for example a solenoid.

[0059] In the second connecting line 11 a second control valve 25 is arranged, which has a blocking position 25a and a flow position 25b.

[0060] The second control valve 25 is actuated into the closed position 25a by means of a spring device 26. The second control valve 25 can be actuated into the open position 25b by means of an electrical actuating device 27, for example a solenoid.

[0061] The hydraulic system 1 has at least one auxiliary consumer 30, wherein a fourth connecting line 31 leading to the auxiliary consumer 30 is connected to the third connecting line 15. The at least one auxiliary consumer 30 can be configured, for example, as a tilting drive of the lifting frame and / or as a side shifter of the load-handling device and / or as a thrust drive of the lifting frame.

[0062] In the first connecting line 8, a third control valve 35 is arranged between the connection of the third connecting line 15 and the main stroke 3, which has a blocking position 35a and a flow position 35b.

[0063] The third control valve 35 is actuated into the closed position 35a by means of a spring device 36. The third control valve 35 can be actuated into the open position 35b by means of an electrical actuating device 37, for example a solenoid.

[0064] In the fourth connecting line 31 leading to the at least one additional consumer 30, a fourth control valve 40 is arranged, which has a blocking position 40a and a flow position 40b.

[0065] The fourth control valve 40 is actuated into the closed position 40a by means of a spring device 41. The fourth control valve 40 can be actuated into the open position 40b by means of an electrical actuating device 42, for example a solenoid.

[0066] In hydraulic system 1, a pressure medium line 50 is provided, leading from the second connecting line 11 to the fourth connecting line 31. In A first shut-off valve 51, opening towards the fourth connecting line 31, is arranged in the pressure medium line 50. In the illustrated embodiment, the first shut-off valve 51 is designed as a check valve 52 opening towards the fourth connecting line 31.

[0067] A second shut-off valve 55, opening towards the additional consumer 30, is arranged in the fourth connecting line 31. In the illustrated embodiment, the second shut-off valve 55 is designed as a check valve 56 opening towards the further consumer 30.

[0068] The pressure medium line 50 is connected to the fourth connecting line 31 between the second shut-off valve 55 and the auxiliary consumer 30. The fourth control valve 40 is located in the fourth connecting line 31 between the connection of the pressure medium line 50 and the auxiliary consumer 30.

[0069] The first hydraulic pump unit 6 comprises a first hydraulic pump 6b which is driven by a first electric motor 6a. In the illustrated embodiment, the first hydraulic pump 6b has a constant displacement volume.

[0070] The first hydraulic pump unit 6 can be operated in pump mode and in motor mode.

[0071] In pump operation, the first hydraulic pump 6b is driven in a first direction of rotation by the first electric motor 6a, which operates as a motor, and draws pressure medium from the reservoir 7 at the first connection A1 and delivers the pressure medium at the second connection A2 into the first connecting line 8.

[0072] In motor operation, the first hydraulic pump 6b is driven in a second direction of rotation, opposite to the first, by the hydraulic fluid present and flowing in at the second port A2, and drives the first electric motor 6a, which operates as a generator. In motor operation, the first hydraulic pump 6b pumps hydraulic fluid flowing out of the first port A1 into the reservoir 7.

[0073] The second hydraulic pump unit 10 has a second hydraulic pump 10b which is driven by a second electric motor 10a. In the illustrated embodiment, the second hydraulic pump 10b has a constant displacement volume.

[0074] The second hydraulic pump unit 10 can be operated in pump mode and in motor mode.

[0075] In pump operation, the second hydraulic pump 10b is driven in a first direction of rotation by the second electric motor 10a, which operates as a motor, and draws pressure medium from the first connecting line 8 at the first connection A1 and delivers the pressure medium to the second connecting line 11 at the second connection A2.

[0076] In motor operation, the second hydraulic pump 10b is driven in a second direction of rotation, opposite to the first, by the hydraulic fluid present and flowing into the second port A2, and drives the second electric motor 10a, which operates as a generator. In motor operation, the second hydraulic pump 10b delivers the hydraulic fluid to the first port A1 and thus into the third connecting line 15.

[0077] A pressure relief valve 60 is connected to the first connecting line 8, and its outlet is connected to the reservoir 7. The pressure relief valve 60 is designed to limit the maximum operating pressure of the hydraulic system 1 to a defined level.

[0078] Hydraulic system 1 includes an electronic control unit 70, which is configured to control the first electric motor 6a, the second electric motor 6b, the first control valve 20, and the second control valve 25. The electronic control unit 70 is further configured to control the third control valve 35 and the fourth control valve 40. For this purpose, the electronic control unit 70 is connected to the electrical actuators 22, 27, 37, 42 of the control valves 20, 25, 35, 40.

[0079] The electronic control unit 70 is connected in a manner not shown in detail to operating elements, for example one or more joysticks, with which an operator can specify the lifting operation of the free lift 4 and the main lift 3 as well as the lowering operation of the free lift 4 and the main lift 3 and can specify the operation of at least one additional consumer 30.

[0080] The electronic control unit 70 is designed to operate the first hydraulic pump unit 6 and the second hydraulic pump unit 10 in pump mode during lifting operation of the free stroke 4, and thus when lifting a load within the free stroke 4, such that the flow rate of the second hydraulic pump unit 10 corresponds to the flow rate of the first hydraulic pump unit 6. The electric motors 10a and 6a are driven by the electronic control unit 70 at such a speed that the second hydraulic pump 10b rotates at such a speed that the flow rate of both hydraulic pumps 6b and 10b is identical.

[0081] During the lifting operation of the free lift 4, the electronic control unit 70 actuates the second control valve 25 to the flow position 25b. The first control valve 20 is not actuated and is in the closed position 20a. The third control valve 35 is not actuated and is in the closed position 35a. The fourth control valve 40 is not actuated and is in the closed position 40a.

[0082] The hydraulic pump 6b, operating in pump mode, draws hydraulic fluid from the reservoir 7 and, in the closed position 20a of the first control valve 20, delivers the hydraulic fluid via the opening check valve into the first connecting line 8 and to the first port A1 of the hydraulic pump 10b. In pump mode, the hydraulic pump 10b delivers the hydraulic fluid from the first port A1 to the second port A2 and thus into the second connecting line 11 and, via the control valve 25, which is set to the flow position 25a, to the free stroke cylinder 4. This causes the free stroke cylinder 4a to extend according to the flow rate delivered by the hydraulic pump 10b. The extension speed of the free stroke cylinder 4 is controlled by the electronic control unit 70 via the rotational speed of the electric motors 6a and 10a.

[0083] If, during the lifting operation of the free lift 4, the auxiliary consumer 30 is also activated, the speed of the electric motor 6a, and thus of the hydraulic pump 6b operating in pump mode, is increased by the electronic control unit 70 such that the flow rate of the first hydraulic pump unit 6 is greater than the flow rate of the second hydraulic pump unit 10. The speed of the electric motor 6a, and thus of the hydraulic pump 6b operating in pump mode, is increased in such a way that the hydraulic pump 10b operating in pump mode only draws in a portion of the flow rate of the first hydraulic pump 6b. As a result, the first hydraulic pump 6b provides an excess flow rate, exceeding the requirements of the free lift 4, to supply the auxiliary consumer 30, which is adapted to the requirements of the auxiliary consumer 30.

[0084] The electronic control unit 70 actuates the fourth control valve 40 to the flow position 40b to actuate the auxiliary consumer 30, so that the excess volume flow of the first hydraulic pump 6b flows via the opening second shut-off valve 55 and the fourth control valve 40, which is set to the flow position 40b, to the auxiliary consumer 30 for its actuation.

[0085] The electronic control unit 70 is designed to operate the first hydraulic pump unit 6 in motor operation and the second hydraulic pump unit 10 in motor operation during the lowering operation of the free stroke 4 and thus when lowering a load within the free stroke 4, such that the volume flow of the second hydraulic pump unit 10 corresponds to the volume flow of the first hydraulic pump unit 6.

[0086] During the lowering operation of the free stroke 4, the electronic control unit 70 opens the first control valve 20 to the flow position 20b and the second control valve 25 to the flow position 25b. The third control valve 35 is not opened and is in the closed position 35a. The fourth control valve 40 is not opened and is in the closed position 40a.

[0087] The hydraulic fluid flowing from the free-lift cylinder 4b during lowering operation flows via the second control valve 25, which is set to flow position 25b, to port A2 of the motor-driven hydraulic pump 10b. The pump is driven by the outflowing hydraulic fluid and drives the electric motor 10a, which operates as a generator. The hydraulic fluid flowing from hydraulic pump 10b at port A1 flows via the first control valve 20, which is set to flow position 20b, to port A2 of the motor-driven hydraulic pump 6b. The pump is driven by the outflowing hydraulic fluid and drives the electric motor 6a, which operates as a generator. The hydraulic fluid flowing from hydraulic pump 6b at port A1 flows back into the reservoir 7. Thus, during the lowering operation of the free lift 4, the energy from the lowering process is recuperated by the generator operation of the electric motors 6a and 10a during motor operation of the two hydraulic units 6 and 10.The retraction speed of the free-lift cylinder 4 is controlled by the electronic control unit 70 via the speed of the electric motors 6a, 10a.

[0088] If, during the lowering operation of the free stroke 4, an additional auxiliary consumer 30 is activated, the electronic control unit 70 reduces the speed of the motor-driven hydraulic pump 6b by appropriately controlling the electric motor 6a, such that the flow rate of the first hydraulic pump unit 6 is smaller than the flow rate of the second hydraulic pump unit 10. The speed of the electric motor 6a, and thus of the motor-driven hydraulic pump 6b, is reduced to such an extent that the motor-driven hydraulic pump 6b only draws in a portion of the flow rate of the second hydraulic pump 10b. This results in the second hydraulic pump 10b, operating in motor mode, providing an excess flow rate in the second connecting line 15 to supply the auxiliary consumer 30, which is adapted to the demand of the auxiliary consumer 30.

[0089] The electronic control unit 70 actuates the fourth control valve 40 to the flow position 40b to actuate the auxiliary consumer 30, so that the excess volume flow of the second hydraulic pump 10b flows via the opening second shut-off valve 55 and the fourth control valve 40, which is set to the flow position 40b, to the auxiliary consumer 30 for its actuation.

[0090] The electronic control unit 70 is designed to operate the first hydraulic pump unit 6 in pump mode during the lifting operation of the main stroke 3, thus when lifting a load within the main stroke 3.

[0091] During the lifting operation of the main stroke 3, the electronic control unit 70 opens the third control valve 35 to the flow position 35b. The first control valve 20 is not activated and is in the closed position 20a. The second control valve 25 is not activated and is in the closed position 25a. The fourth control valve 40 is not activated and is in the closed position 40a. The second hydraulic pump unit 10 is not operated during the lifting operation of the main stroke 3.

[0092] The hydraulic pump 6b, operating in pump mode, draws hydraulic fluid from the reservoir 7 and, in the closed position 20a of the first control valve 20, delivers the hydraulic fluid via the opening check valve into the first connecting line 8 and, via the third control valve 35, which is set to the flow position 35b, to the main stroke 3, thereby extending the main stroke cylinders 3a, 3b according to the flow rate delivered by the hydraulic pump 6b. The extension speed of the main stroke cylinders 3a, 3b is controlled by the electronic control unit 70 via the speed of the electric motor 6a.

[0093] If, during the lifting operation of the main stroke 3, the additional consumer 30 is also activated, the electronic control unit 70 increases the speed of the hydraulic pump 6b, which is operated in pump mode, by appropriately controlling the electric motor 6a, such that the first hydraulic pump 6b provides an excess volume flow to supply the additional consumer 30, which is adapted to the requirements of the additional consumer 30, exceeding the requirements of the main stroke 4.

[0094] The electronic control unit 71 opens the fourth control valve 40 to the flow position 40b to actuate the auxiliary consumer 30, so that the excess volume flow of the first hydraulic pump 6b flows via the opening second shut-off valve 55 and the fourth control valve 40, which is opened to the flow position 40b, to the auxiliary consumer 30 to actuate it.

[0095] The electronic control unit 70 is designed to operate the first hydraulic pump unit 6 in motor operation during the lowering operation of the main stroke 3.

[0096] During the lowering phase of the main stroke 3, the electronic control unit 70 opens the first control valve 20 to the flow position 20b and the third control valve 35 to the flow position 35b. The second control valve 25 is not opened and is in the closed position 25a. The fourth control valve 40 is not opened and is in the closed position 40a.

[0097] The hydraulic fluid flowing from the main lifting cylinders 3a, 3b during lowering operation flows via the third control valve 35, which is opened to flow position 35b, and via the first control valve 20, which is opened to flow position 20b, to port A2 of the hydraulic pump 6b, which is operated in motor mode. The pump is driven by the outgoing hydraulic fluid and drives the electric motor 6a, which operates as a generator. The hydraulic fluid flowing from the hydraulic pump 6b at port A1 flows back into the reservoir 7. During the lowering operation of the main lifting cylinder 3, the energy from the lowering operation is thus recuperated by the generator operation of the electric motor 6a in motor mode of the hydraulic unit 6. The retraction speed of the main lifting cylinders 3a, 3b is controlled by the electronic control unit 70 via the speed of the electric motor 6a.

[0098] If, during the lowering operation of the main stroke 3, the auxiliary consumer 30 is also actuated, the electronic control unit 70 opens the fourth control valve 40 to the flow position 40b. This allows the hydraulic fluid flowing from the main stroke cylinders 3a, 3b during lowering operation to flow to the auxiliary consumer 30 for actuation via the opening second shut-off valve 55 and the fourth control valve 40, which is open to the flow position 40b.

[0099] Should the pressure of the hydraulic fluid flowing from the main lifting cylinders 3a, 3b during lowering operation be insufficient to actuate the auxiliary consumer 30, the electronic control unit 70 operates the second hydraulic pump unit 10 in pump mode. The hydraulic pump 10b of the second hydraulic pump unit 10, operating in pump mode, draws in the hydraulic fluid flowing from the main lifting cylinders 3a, 3b during lowering operation at port A1 and delivers it at port A2 into the hydraulic fluid line 50. The hydraulic fluid delivered and pressurized by the hydraulic pump 10b then flows through the opening check valve 51 in the hydraulic fluid line 50 and the fourth control valve 40, which is set to flow position 40b, to actuate the auxiliary consumer 30.

[0100] In the illustrated embodiment, the control valves 20, 25, 35, 40 are designed as switching valves.

[0101] The invention is not limited to the embodiment shown.

[0102] Alternatively, the control valve 20 or the control valve 25 or the control valve 35 or the control valve 40 can be designed as a proportional valve.

[0103] Alternatively, no additional consumer 30 may be provided, which eliminates the need for the fourth control valve 40.

Claims

1. Hydraulic system (1) for a forklift truck, in particular a reach truck, wherein the hydraulic system (1) has a lifting hydraulics (2) comprising a main stroke (3) and a free stroke (4), and wherein the hydraulic system (1) comprises a hydraulic pump device (5) configured to supply the main stroke (3) and the free stroke (4) with hydraulic fluid, characterized by the fact thatthe hydraulic pump device (5) comprises a first hydraulic pump unit (6) which is connected at a first port (A1) to a reservoir (7) and at a second port (A2) to the main stroke (3), wherein a first connecting line (8) is led from the second port (A2) of the first hydraulic pump unit (6) to the main stroke (3), and the hydraulic pump device (5) comprises a second hydraulic pump unit (10) which is connected at a first port (A1) to the first connecting line (8) and at a second port (A2) to the free stroke (4), wherein a second connecting line (11) is led from the second port (A2) of the second hydraulic pump unit (10) to the free stroke (4).

2. Hydraulic system (1) according to claim 1, characterized by the fact thata third connecting line (15) is led from the first connecting line (8) to the first connection (A1) of the second hydraulic pump unit (10), wherein a first control valve (20) is arranged in the first connecting line (8) between the second connection (A2) of the first hydraulic pump unit (6) and the connection of the third connecting line (15), which has a closed position (20a) and a flow position (20b), wherein in particular the closed position (20a) is designed as a check valve opening in the direction of the main stroke (3).

3. Hydraulic system (1) according to claim 1 or 2, characterized by the fact that in the second connecting line (11) a second control valve (25) is arranged, which has a blocking position (25a) and a flow position (25b).

4. Hydraulic system (1) according to one of claims 1 to 3, characterized by the fact thatthe hydraulic system (1) has at least one additional consumer (30), wherein a fourth connecting line (31) leading to the additional consumer (30) is connected to the first connecting line (8) or to the third connecting line (15).

5. Hydraulic system (1) according to any one of claims 1 to 4, characterized by the fact that In the first connecting line (8) between the connection of the third connecting line (15) and the main stroke (3) a third control valve (35) is arranged, which has a blocking position (35a) and a flow position (35b).

6. Hydraulic system (1) according to claim 4 of claim 5, characterized by the fact that in the fourth connecting line (31) a fourth control valve (40) is arranged, which has a blocking position (40a) and a flow position (40b).

7. Hydraulic system (1) according to any one of claims 4 to 6, characterized by the fact thatA pressure medium line (50) is provided leading from the second connecting line (11) to the fourth connecting line (31), in which a first shut-off valve (51), in particular a check valve (52), opening in the direction of the fourth connecting line (31), is arranged.

8. Hydraulic system (1) according to claim 7, characterized by the fact that In the fourth connecting line (31) a second shut-off valve (55), in particular a check valve (56) opening towards the auxiliary consumer (30), is arranged, wherein the pressure medium line (50) between the second shut-off valve (55) and the auxiliary consumer (30) is connected to the fourth connecting line (31).

9. Hydraulic system (1) according to any one of claims 1 to 8, characterized by the fact thatThe first hydraulic pump unit (6) comprises a first hydraulic pump (6b) which is in drive connection with a first electric motor (6a), wherein the first hydraulic pump unit (6) can be operated in pump mode and in motor mode, wherein in pump mode the first hydraulic pump (6b) is driven in a first direction of rotation by the first electric motor (6a) operating as a motor and draws hydraulic fluid from the reservoir (7) at the first port (A1) and delivers it to the first connecting line (8) at the second port (A2), and wherein in motor mode the first hydraulic pump (6b) is driven in a second direction of rotation by the hydraulic fluid present at the second port (A2) and drives the first electric motor (6a) operating as a generator and delivers hydraulic fluid to the first port (A1).

10. Hydraulic system (1) according to any one of claims 1 to 9, characterized by the fact thatThe second hydraulic pump unit (10) comprises a second hydraulic pump (10b) which is in drive connection with a second electric motor (10a), wherein the second hydraulic pump unit (10) can be operated in pump mode and in motor mode, wherein in pump mode the second hydraulic pump (10b) is driven in a first direction of rotation by the second electric motor (10a) operating as a motor and draws hydraulic fluid from the first connecting line (8) at the first connection (A1) and delivers it to the second connecting line (11) at the second connection (A2), and wherein in motor mode the second hydraulic pump (10b) is driven in a second direction of rotation by the hydraulic fluid present at the second connection (A2) and drives the second electric motor (10a) operating as a generator and delivers hydraulic fluid to the first connection (A1).

11. Hydraulic system (1) according to any one of claims 1 to 10, characterized by the fact thatan electronic control device (70) is provided which is configured to control the first electric motor (6a) of the first hydraulic pump unit (6), the second electric motor (10a) of the second hydraulic pump unit (10), the first control valve (20) and the second control valve (25).

12. Hydraulic system (1) according to claim 11, characterized by the fact that the electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in pump mode and the second hydraulic pump unit (10) in pump mode during the lifting operation of the free lift (4), such that the volume flow of the second hydraulic pump unit (10) corresponds to the volume flow of the first hydraulic pump unit (6).

13. Hydraulic system (1) according to claim 12, characterized by the fact that the electronic control device (70) is designed to control the second control valve (25) to the flow position (25b) during the lifting operation of the free lift (4).

14. Hydraulic system (1) according to one of claims 11 to 13, characterized by the fact that the electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in pump mode and the second hydraulic pump unit (10) in pump mode during the lifting operation of the free lift (4) and additional actuation of the auxiliary consumer (30), such that the volume flow of the first hydraulic pump unit (6) is greater than the volume flow of the second hydraulic pump unit (10).

15. Hydraulic system (1) according to claim 14, characterized by the fact that the electronic control device (70) is provided to control the fourth control valve (40), and the electronic control device (70) is designed to control the second control valve (25) to the flow position (25b) and the fourth control valve (40) to the flow position (40b) during lifting operation of the free lift (4) and additional actuation of the auxiliary consumer (30).

16. Hydraulic system (1) according to any one of claims 11 to 15, characterized by the fact that the electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in motor operation and the second hydraulic pump unit (10) in motor operation during the lowering operation of the free stroke (4), such that the volume flow of the second hydraulic pump unit (10) corresponds to the volume flow of the first hydraulic pump unit (6).

17. Hydraulic system (1) according to claim 16, characterized by the fact that the electronic control device (70) is designed to control the first control valve (20) to the flow position (20b) and the second control valve (25) to the flow position (25b) during the lowering operation (4) of the free stroke.

18. Hydraulic system (1) according to any one of claims 11 to 17, characterized by the fact thatthe electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in motor operation and the second hydraulic pump unit (10) in motor operation during the lowering operation of the free stroke (4) and additional actuation of the auxiliary consumer (30), such that the volume flow of the first hydraulic pump unit (6) is smaller than the volume flow of the second hydraulic pump unit (10).

19. Hydraulic system (1) according to claim 18, characterized by the fact that the electronic control device (70) is provided to control the fourth control valve (40), and the electronic control device (70) is designed to control the first control valve (20) to the flow position (20b), the second control valve (25) to the flow position (25b) and the fourth control valve (40) to the flow position (40b) during lowering operation of the free stroke (4) and additional actuation of the auxiliary consumer (30).

20. Hydraulic system (1) according to any one of claims 11 to 19, characterized by the fact that the electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in pump mode during the lifting operation of the main stroke (3).

21. Hydraulic system (1) according to claim 20, characterized by the fact that the electronic control device (70) is provided to control the third control valve (35), and the electronic control device (71) is designed to control the third control valve (35) to the flow position (35b) during the lifting operation of the main stroke (3).

22. Hydraulic system (1) according to one of claims 11 to 21, characterized by the fact that the electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in pump mode during lifting operation of the main lift (3) and additional actuation of the auxiliary consumer (30).

23. Hydraulic system (1) according to claim 22, characterized by the fact thatthe electronic control device (70) is provided to control the third control valve (35) and the fourth control valve (40), and the electronic control device (70) is designed to control the third control valve (35) to the flow position (35b) and the fourth control valve (40) to the flow position (40b) during lifting operation of the main stroke (3) and additional actuation of the auxiliary consumer (30).

24. Hydraulic system (1) according to one of claims 11 to 23, characterized by the fact that the electronic control unit (70) is designed to operate the first hydraulic pump unit (6) in motor operation during the lowering operation of the main stroke (3).

25. Hydraulic system (1) according to claim 24, characterized by the fact thatthe electronic control device (70) is provided to control the third control valve (35), and the electronic control device (70) is designed to control the first control valve (20) to the flow position (20b) and the third control valve (35) to the flow position (35b) during the lowering operation of the main stroke (3).

26. Hydraulic system (1) according to any one of claims 11 to 25, characterized by the fact that the electronic control unit (70) is designed to control the third control valve (35) to the flow position (35b) and the fourth control valve (40) to the flow position (42b) during lowering operation of the main stroke (3) and additional actuation of the auxiliary consumer (30).

27. Hydraulic system (1) according to claim 26, characterized by the fact thatthe electronic control unit (70) is designed to operate the second hydraulic pump unit (10) in pump mode during the lowering operation of the main stroke (3) and additional actuation of the auxiliary consumer (30).

28. Industrial truck, in particular reach truck, with a hydraulic system (1) according to one of the preceding claims.

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