Hydraulic system for an industrial truck

Abstract

A hydraulic system (1) for a forklift truck, in particular a battery-electric forklift truck, with a lifting drive (2) for raising and lowering a load-handling attachment, wherein the hydraulic system (1) comprises a first hydraulic pump (5) configured to supply the lifting drive (2) with hydraulic fluid, and a second hydraulic pump (6) which can be engaged by means of a valve assembly (7) to supply the lifting drive (2). The first hydraulic pump (5) and the second hydraulic pump (6) are configured as a dual hydraulic pump unit (10) and the valve assembly (7) is integrated into the dual hydraulic pump unit (10).

Description

[0001] The invention relates to a hydraulic system for an industrial truck, in particular a battery-electrically operated industrial truck, with a lifting drive for raising and lowering a load-carrying device, wherein the hydraulic system has a first hydraulic pump which is designed to supply the lifting drive with pressure medium, and a second hydraulic pump which can be switched on by means of a valve device to supply the lifting drive, wherein the first hydraulic pump and the second hydraulic pump are designed as a hydraulic double pump unit and the valve device is integrated into the hydraulic double pump unit, wherein the hydraulic double pump unit has a housing and the valve device is installed in the housing, wherein a suction channel is formed in the housing, which is connected to a suction connection of the first hydraulic pump and to a suction connection of the second hydraulic pump, a first delivery channel is formed,which is connected to a delivery port of the first hydraulic pump, and a second delivery channel is formed which is connected to a delivery port of the second hydraulic pump.,

[0002] Hydraulic systems of this type are typically used in battery-powered industrial trucks, such as counterbalance forklifts or reach trucks.

[0003] In battery-electric industrial trucks, for example counterbalance forklifts or reach trucks, hydraulic systems are known in which a single hydraulic pump is provided which supplies the lifting drive, with which a load handling device can be raised and lowered, and if necessary other consumers of a working hydraulic system, for example a tilt drive and / or a sideshift drive, with pressure medium.

[0004] The maximum displacement volume of the hydraulic pump, which is driven, for example, by an electric drive motor, is determined by the maximum load pressure of the lifting drive and the power limit of the electric drive motor driving the hydraulic pump.

[0005] For the application of lifting the load handling device without a load, i.e. lifting with a low load pressure, a significantly higher displacement volume of the hydraulic pump could be used than when lifting the load handling device with a nominal load, i.e. lifting with a high load pressure, with the same torque or power curve of the electric drive motor.

[0006] In industrial truck hydraulic systems with a single hydraulic pump that supplies the lift drive with pressurized fluid, an additional increase in the lifting speed of the load-handling device is only possible by increasing the drive speed of the hydraulic pump. However, the lifting speed when lifting without load is limited by the maximum requirements when lifting with a rated load (torque or power limit of the hydraulic pump drive motor), which are determined by the pump size, i.e., the displacement volume of the hydraulic pump, and the maximum output speed of the hydraulic pump.

[0007] However, especially for reach trucks where the lifting drive allows a lifting height of the load handling device of more than 8 m, for example, higher lifting speeds without load are advantageous in order to increase the handling performance of the reach truck. However, due to the power limit of the electric drive motor of the hydraulic pump, the maximum displacement of the hydraulic pump is defined by the maximum load pressure at rated load.

[0008] To achieve higher lifting speeds of the load handling device, hydraulic systems for industrial trucks are already known, in which the hydraulic system comprises two hydraulic pumps. A first hydraulic pump supplies the lifting drive with pressure fluid at all operating points. To achieve higher lifting speeds of the load handling device, a second hydraulic pump is provided, which can be activated as needed to supply the lifting drive via a valve device.

[0009] Such a hydraulic system for an industrial truck with two hydraulic pumps, in which the first hydraulic pump supplies the lifting drive with pressure fluid at all operating points and a second hydraulic pump is activated to supply the lifting drive in order to achieve higher lifting speeds of the load-handling device, is known from DE 198 31 828 B1. In DE 198 31 828 B1, the first hydraulic pump and the second hydraulic pump are formed by two separate hydraulic pump units, resulting in high construction costs. The second hydraulic pump is also connected to the lifting drive via its own connecting line, which further increases the construction costs due to the high piping and assembly costs.

[0010] JP 2001-240390 A discloses a generic hydraulic system having the features of the preamble of patent claim 1.

[0011] US 2008 / 152513 A1 discloses a hydraulic circuit that enables energy recovery of a lifting cylinder.

[0012] A hydraulic system of an industrial truck is known from DE 10 2011 053 958 A1.

[0013] CN 103 950 870 B discloses a forklift hydraulic system with energy recovery and dual pump oil supply functions.

[0014] The present invention is based on the object of providing a hydraulic system for an industrial truck of the type mentioned above which has a lower construction cost.

[0015] This object is achieved according to the invention in that the second conveying channel is connected to the first conveying channel within the housing.

[0016] According to the invention, the two hydraulic pumps thus form a hydraulic double pump unit, into which the valve device, by means of which the second hydraulic pump can be switched on to supply the lifting drive, is integrated and thus installed.

[0017] Combining the two hydraulic pumps into a hydraulic double pump unit results in a particularly reduced construction effort. The integration and thus installation of the valve assembly into the hydraulic double pump unit leads to a further reduction in construction effort, as the second hydraulic pump does not require a separate connecting line to connect to the lifting drive, thus eliminating the piping effort for the second hydraulic pump and the lifting drive, as well as the associated assembly effort.

[0018] According to the invention, the hydraulic double pump unit has a housing, and the valve device is built into the housing. This allows for simple installation and thus easy integration of the valve device into the hydraulic double pump unit.

[0019] According to the invention, a suction channel is formed in the housing, which is connected to a suction port of the first hydraulic pump and to a suction port of the second hydraulic pump, a first delivery channel is formed, which is connected to a delivery port of the first hydraulic pump, and a second delivery channel is formed, which is connected to a delivery port of the second hydraulic pump and to the first delivery channel. The suction ports of the two hydraulic pumps can preferably be easily connected to a container for supplying pressure medium using the suction channel in the housing. The lifting drive can preferably be easily connected to the first delivery channel, which is connected to the delivery port of the first hydraulic pump, and to the second delivery channel, which is connected to the delivery port of the second hydraulic pump, by means of a connecting line.

[0020] According to an advantageous embodiment of the invention, the valve device preferably has an on-position in which the delivery connection of the second hydraulic pump is connected to the first delivery channel, and a off-position in which the delivery connection of the second hydraulic pump is connected to the suction channel. In the off-position, by connecting the delivery connection of the second hydraulic pump to the suction channel, the second hydraulic pump can be easily short-circuited to the suction channel or a container connected thereto. In the on-position, by connecting the delivery connection of the second hydraulic pump to the first delivery channel, the second hydraulic pump can be switched on to supply the lifting drive and increase the lifting speed of the load-handling device.

[0021] According to an advantageous embodiment of the invention, the valve device preferably has a check valve, in particular a spring-loaded check valve, arranged in the second delivery channel and opening in the direction of the first delivery channel, and a control valve device arranged in a connecting channel connecting the second delivery channel to the suction channel. The check valve can be used, in particular, to easily control the connection of the delivery connection of the second hydraulic pump to the first delivery channel. The control valve device, which is arranged in the connecting channel connecting the second delivery channel to the suction channel, can be used, in particular, to easily control the connection of the delivery connection of the second hydraulic pump to the suction channel.

[0022] According to an advantageous embodiment of the invention, the control valve device preferably has a blocking position forming the connected position and a flow position forming the disconnected position. In the blocking position of the control valve device, the connection between the delivery port of the second hydraulic pump and the suction channel is preferably blocked. This preferably allows the delivery port of the second hydraulic pump to be connected to the first delivery channel via the opening check valve. In the flow position of the control valve device, the connection between the delivery port of the second hydraulic pump and the suction channel can preferably be established in a simple manner.

[0023] According to an alternative and equally advantageous embodiment of the invention, the valve device preferably comprises a control valve device arranged in the second delivery channel and connected to a connecting channel connected to the suction channel. Such a control valve device can preferably be used to easily control the connection of the delivery port of the second hydraulic pump to the first delivery channel and the connection of the delivery port of the second hydraulic pump to the suction channel.

[0024] According to an advantageous embodiment of the invention, the control valve device preferably has a first control position forming the connected position, in which the second delivery channel is open and the connection between the second delivery channel and the connecting channel is blocked, and a second control position forming the switched-off position, in which the second delivery channel is connected to the connecting channel and the connection between the second delivery channel and the first delivery channel is blocked. In the first control position, the connection between the delivery connection of the second hydraulic pump and the first delivery channel for the connected position can be established in particular in a simple manner. In the second switching position, the connection between the delivery connection of the second hydraulic pump and the suction channel for the switched-off position can be established in particular.

[0025] According to an advantageous embodiment of the invention, the control valve device can preferably be designed as a switching valve or as a proportional valve.

[0026] According to an advantageous embodiment of the invention, the control valve device is preferably electrically actuated by means of an electrical actuating device, in particular by means of a magnet. With an electrical actuating device, the control valve device can be easily actuated between the connected position and the disconnected position.

[0027] According to an advantageous embodiment of the invention, an electronic control device is preferably provided, which is connected on the input side to an operating element and on the output side to the valve device for controlling the valve device. The electronic control device is designed such that the valve device is controlled depending on the actuation of the operating element. This allows the valve device to be easily actuated into the connected or disconnected position by an operator of the industrial truck depending on the actuation of the operating element, for example, a lever or button.

[0028] According to an advantageous embodiment of the invention, the electronic control device is preferably designed such that when the control element is actuated, the valve device is actuated into the connected position or the deactivated position, and when the control element is not actuated, the valve device is actuated into the deactivated position or the connected position. By actuating the control element, for example, an operator of the industrial truck can easily activate the connected position to request a higher lifting speed of the lifting drive.

[0029] According to an advantageous embodiment of the invention, an electronic control device is preferably provided, which is connected on the input side to a sensor device that detects the load pressure of the lifting drive and on the output side to the valve device for controlling the latter. The electronic control device is designed such that the valve device is controlled as a function of the load pressure of the lifting drive. This allows, in particular, the valve device to be easily actuated into the connected or disconnected position depending on the current load pressure of the lifting drive.

[0030] According to an advantageous embodiment of the invention, the electronic control device is preferably designed such that the valve device is actuated to the connected position when the load pressure of the lifting drive is below a limit load pressure, and is actuated to the disconnected position when the load pressure of the lifting drive is above the limit load pressure. This makes it particularly easy to ensure that the second hydraulic pump is activated during lifting without a load or during lifting in the partial load range, in order to achieve a higher lifting speed of the load-handling device during lifting without a load or during lifting in the partial load range.

[0031] According to an advantageous embodiment of the invention, the first hydraulic pump and the second hydraulic pump are preferably driven by a common drive motor, in particular an electric motor. Since the second hydraulic pump can be switched on and off as needed, in particular by means of a valve device, both hydraulic pumps can be driven by a common drive motor, thereby further reducing the construction complexity of the hydraulic system.

[0032] The invention has a number of advantages.

[0033] By switching on the second hydraulic pump, for example when the load pressure during lifting is below the limit load pressure, significantly higher lifting speeds of the load handling device can be achieved at partial load or without load with a much smaller size of the drive motor driving the hydraulic pumps.

[0034] The invention further enables downsizing of the drive motor driving the hydraulic pumps, since when lifting with nominal load and thus high load pressure of the lifting drive, the pump volume is reduced by switching off the second hydraulic pump.

[0035] By shutting off the second hydraulic pump when the drive motor is switched on, high starting speeds of the first hydraulic pump can be achieved. This can ensure a long service life for bearings, such as plain bearings, in the hydraulic pumps.

[0036] Furthermore, costs are optimized because the integration of the valve device into the hydraulic double pump unit eliminates the piping effort of the second hydraulic pump with the lifting drive and the associated assembly effort.

[0037] In conjunction with a control element that can be actuated by an operator of the industrial truck, for example a lever or button, which is to be actuated in addition to a control element that controls the lifting operation, for example a joystick, the operator can actively initiate a boost function with an increased lifting speed in the lifting operation of the lifting drive by additionally actuating the control element.

[0038] The invention also makes it possible to easily create a variation between a standard industrial truck with a single hydraulic pump and a performance industrial truck with a hydraulic system according to the invention with a hydraulic double pump unit, since these variants can be easily created in the industrial trucks by two pump variants, namely a single pump and a hydraulic double pump unit according to the invention, without further changes or adaptations in the hydraulic system of the industrial trucks.

[0039] Further advantages and details of the invention are explained in more detail by way of example with reference to the embodiments shown in the schematic figures. Figure 1 shows a circuit diagram of a first embodiment of the invention, Figure 2 shows a variant of the first embodiment according to the Figure 1 and Figure 3 shows a circuit diagram of a second embodiment of the invention.

[0040] In the Figures 1 to 3 identical components are provided with the same reference numbers.

[0041] In the Figures 1 to 3 a hydraulic system 1 of an industrial truck, for example a battery-electric industrial truck, is shown.

[0042] The hydraulic system 1 has a lifting drive 2 for raising and lowering a load-handling device (not shown in detail), for example, a load fork comprising forks. In the illustrated embodiment, the lifting drive 2 has one or more lifting cylinders 3.

[0043] The hydraulic system 1 has a first hydraulic pump 5, which supplies the lifting drive 2 with pressure medium, and a second hydraulic pump 6, which can be switched on by means of a valve device 7 to supply the lifting drive 2.

[0044] A common drive motor 8 is provided to drive the first hydraulic pump 5 and the second hydraulic pump 6. In the illustrated embodiment, the drive motor 8 is designed as an electric motor.

[0045] The first hydraulic pump 5 and the second hydraulic pump 6 are designed as a hydraulic double pump unit 10. The valve device 7 is integrated into the hydraulic double pump unit 10 and thus installed.

[0046] For this purpose, the hydraulic double pump unit 10 has a housing 11 into which the valve device 7 is installed.

[0047] The first hydraulic pump 5 has a suction port S1 and a discharge port P1. Accordingly, the second hydraulic pump 6 has a suction port S2 and a discharge port P2.

[0048] Formed in the housing 11 of the hydraulic double pump unit 10 is a suction channel 12, which is connected to the suction port S1 of the first hydraulic pump 5 and to the suction port S2 of the second hydraulic pump 6. The suction channel 12 is also connected to a reservoir 13, for example, via a reservoir line 14 connected to the suction channel 12, from which the two hydraulic pumps 5, 6 draw pressure fluid.

[0049] Formed in the housing 11 of the hydraulic double pump unit 10 is a first delivery channel 20, which is connected to the delivery port P1 of the first hydraulic pump 5. A connecting line 21 is connected to the first delivery channel 20 and connects the first delivery channel 20 to a directional control valve block 22 of the hydraulic system 1. The lifting cylinder 3 is connected to the directional control valve block 22 by means of a further connecting line 23. The directional control valve block 22 is provided with a control directional control valve device (not shown in detail), with which the lifting and lowering operation of the lifting drive 2 can be controlled. During the lifting operation of the lifting drive 2, the first delivery channel 20 is connected to the connecting line 23 by means of the control directional control valve device. During the lowering operation of the lifting drive 2, the connecting line 23 is connected to the container 13 by means of the control directional control valve device.

[0050] It is understood that further hydraulic consumers can be connected to the directional control valve block 22 and controlled by means of corresponding control directional control valve devices, for example a tilt drive of the load-handling device and / or a side shift of the load-handling device.

[0051] Furthermore, a second delivery channel 30 is formed in the housing 11 of the hydraulic double pump unit 10, which is connected to the delivery port P2 of the second hydraulic pump 6. The second delivery channel 30 is also connected to the first delivery channel 20 within the housing 11.

[0052] The Figures 1 to 3 The valve device 7 shown has a connection position in which the delivery connection P2 of the second hydraulic pump 6 is connected to the first delivery channel 20, and a connection position in which the delivery connection P2 of the second hydraulic pump 6 is connected to the suction channel 12.

[0053] In the examples of the Figures 1 and 2 the valve device 7 has a check valve 40 arranged in the second conveying channel 30, which opens towards the first conveying channel 20. In illustrated embodiments of the Figures 1 and 2 The check valve 40 is designed as a spring-loaded check valve. The valve device 7 of the Figures 1 and 2 further comprises a control valve device 45, which is arranged in a connecting channel 46 connecting the second delivery channel 30 to the suction channel 12. The connecting channel 46 is connected to the second delivery channel 30 between the delivery port P2 and the check valve 40 and leads to the suction channel 12.

[0054] The control valve device 45 is in the illustrated embodiments of the Figures 1 and 2designed as a two-port two-position valve and has a blocking position 45a forming the connection position and a flow position 45b forming the cut-off position.

[0055] The control valve device 45 is in the Figure 1 The embodiment shown is designed as a switching valve.

[0056] The control valve device 45 is in the Figure 2 The embodiment shown is designed as a proportional valve that throttles in intermediate positions.

[0057] The control valve device 45 is in the Figure 1 illustrated embodiment can be actuated electrically by means of an electrical actuating device 50, for example by means of a magnet, in particular a switching magnet. In the illustrated embodiment of the Figure 1the control valve device 45 can be actuated by means of a spring 51 in the direction of the blocking position 45a and by means of the electrical actuating device 50 in the direction of the flow position 45b.

[0058] The control valve device 45 is in the Figure 2 illustrated embodiment can be actuated electrically by means of an electrical actuating device 50, for example by means of a magnet, in particular a proportional magnet. In the illustrated embodiment of the Figure 2 the control valve device 45 can be actuated by means of the spring 51 in the direction of the flow position 45b and by means of the electrical actuating device 50 in the direction of the blocking position 45a.

[0059] In the embodiment of the Figure 3 the valve device 7 has a control valve device 60 which is arranged in the second conveying channel 30 and is connected to a connecting channel 61 connected to the suction channel 12.

[0060] In the illustrated embodiment, the control valve device 60 is designed as a three-port two-position valve which is connected at a first port A1 to the section of the second delivery channel 30 connected to the delivery port P2 of the second hydraulic pump 6, at a second port A2 to the section of the second delivery channel 30 connected to the first delivery channel 20 and at a third port A3 to the connecting channel 61.

[0061] The control valve device 60 has a first control position 60a forming the connected position, in which the first port A1 is connected to the second port A2 and the third port A3 is blocked. In the control position 60a, the second conveying channel 30 is thus open and the connection between the second conveying channel 30 and the connecting channel 61 is blocked. The control valve device 60 has a second control position 60b forming the disconnected position, in which the first port A1 is connected to the third port A3 and the second port A2 is blocked. In the control position 60b, the second conveying channel 30 is connected to the connecting channel 61 and the connection between the second conveying channel 30 and the first conveying channel 20 is blocked.

[0062] The control valve device 60 is in the Figure 3In the illustrated embodiment, the control valve device 60 is designed as a proportional valve that throttles in intermediate positions. Alternatively, the control valve device 60 can be designed as a switching valve.

[0063] The control valve device 60 is in the Figure 3 In the illustrated embodiment, the control valve device 60 can be actuated electrically by means of an electrical actuating device 70, for example by means of a magnet, in particular a proportional magnet. In the illustrated embodiment, the control valve device 60 can be actuated by means of a spring 71 in the direction of the first control position 60a and by means of the electrical actuating device 50 in the direction of the second control position 60b. Alternatively, the control valve device 60 can be actuated by means of the spring 71 in the direction of the second control position 60b and by means of the electrical actuating device 70 in the direction of the first control position 60a.

[0064] To operate the control valve device 45 of the Figures 1 , 2 or the control valve device 60 of the Figure 3 An electronic control device 80 is provided in the valve device 7 formed therein, which is connected on the input side to a sensor device 81 that detects the load pressure of the lifting drive 2 present in the connecting line 23, and on the output side to the actuating device 50 or 70. The electronic control device 80 is designed such that the control valve device 45 or 60 of the control valve device 7 is controlled as a function of the load pressure of the lifting drive 2.

[0065] The electronic control device 80 is designed such that the valve device 7 is actuated into the connected position when the load pressure of the lifting drive 2 is below a limit load pressure and is actuated into the disconnected position when the load pressure of the lifting drive 2 is above the limit load pressure.

[0066] In the Figures 1 and 2 For this purpose, the control valve device 45 is controlled by the control device 80 in the lifting operation of the lifting drive 2 when the load pressure of the lifting drive 2 is below the limit load pressure and is switched on by the control device 80 in the lifting operation of the lifting drive 2 when the load pressure of the lifting drive 2 is below the limit load pressure and is switched off by the control device 80 in the lifting operation of the lifting drive 2 when the load pressure of the lifting drive 2 is above the limit load pressure and is switched off by the control device 80 in the flow position 45b.

[0067] In the Figure 3For this purpose, the control valve device 60 is controlled by the control device 80 in the lifting operation of the lifting drive 2 when the load pressure of the lifting drive 2 is below the limit load pressure and is controlled by the control device 80 in the lifting operation of the lifting drive 2 when the load pressure of the lifting drive 2 is below the limit load pressure and is controlled by the control device 80 in the lifting operation of the lifting drive 2 when the load pressure of the lifting drive 2 is above the limit load pressure and is controlled by the sensor device 81 in the second control position 60b which is the switch-off position.

[0068] In the switching position of the valve device 7 of the Figures 1 to 3 This allows an increased lifting speed of the load handling device to be achieved.

[0069] Alternatively or additionally, the electronic control device 80 can be connected on the input side to an operating element 85, for example a lever or button, which can be actuated by the operator of the industrial truck, and on the output side to the actuating device 50 or 70, wherein the electronic control device 80 is designed such that the control valve device 45 or 60 of the valve device 7 is controlled depending on the actuation of the operating element 85.

[0070] The electronic control device 80 is designed, for example, such that when the operating element 85 is actuated, the valve device 7 is actuated into the switched-on position and when the operating element is not actuated, the valve device 7 is actuated into the switched-off position.

[0071] In the Figures 1 and 2For this purpose, the control valve device 45 is controlled by the control device 80 in the lifting operation of the lifting drive 2 with the additionally actuated control element 85 into the blocking position 45a forming the switching-on position and by the control device 80 in the lifting operation of the lifting drive 2 with the additionally actuated control element 85 into the flow position 45b forming the switching-off position.

[0072] In the Figure 3 For this purpose, the control valve device 60 is controlled by the control device 80 in the lifting operation of the lifting drive 2 with the additionally actuated control element 85 into the first control position 60a forming the switch-on position and by the control device 80 in the lifting operation of the lifting drive 2 with the additionally actuated control element 85 into the second control position 60b forming the switch-off position.

[0073] The operator can thus actively change the switching position of the valve device 7 of the Figures 1 to 3 and thereby call up an increased lifting speed of the load handling device.

[0074] Alternatively, the electronic control device 80 can be designed such that when the operating element 85 is actuated, the valve device 7 is actuated into the switch-off position and when the operating element is not actuated, the valve device 7 is actuated into the switch-on position.

[0075] In the hydraulic system 1 according to the invention, the valve device 7 is integrated into the hydraulic double pump unit 10. The second hydraulic pump 6 is switched on or off depending on the load pressure during lifting operation of the lifting drive 2, sensed by the sensor device 81 on the connecting line 23 leading to the lifting drive 2. Alternatively or additionally, the second hydraulic pump 6 can be switched on or off depending on the actuation of the control element 85.

[0076] In the hydraulic system 1 according to the invention, the volume flow of the second hydraulic pump 6 is short-circuited directly to the suction channel 12 of the two hydraulic pumps 5, 6 within the housing, provided it is not required and the valve device 7 is in the shut-off position. In the hydraulic system 1 according to the invention, the volume flow of the second hydraulic pump 6 is conveyed directly into the first delivery channel 20 within the housing, provided it is required to increase the lifting speed of the load-handling device and the valve device 7 is in the switched-on position. The second hydraulic pump 6 therefore requires no external hoses or piping.

[0077] If the load pressure of the lifting drive 2 during lifting operation is below the defined limit load pressure, for example 100 bar, the second hydraulic pump 6 can be in the blocking position 45a of the control valve device 45 of the Figures 1 , 2or in the first control position 60a of the control valve device 60 of the Figure 3 This allows very high lifting speeds of the load-carrying device to be achieved with or without partial load. If the load pressure of the lifting drive 2 during lifting operation exceeds the defined limit load pressure and thus the pump torque of the two hydraulic pumps 5, 6 exceeds the maximum torque or the maximum power of the drive motor 8, the second hydraulic pump 6 is switched on by actuating the control valve device 45 of the Figures 1 , 2 into the flow position 45b or the control valve device 60 of the Figure 3 into the second control position 60b to the suction channel 12 and thus to the container 13. Thus, in lifting operation, when the load pressure of the lifting drive 2 is above the defined limit load pressure, only the first hydraulic pump 5 acts to lift the load-carrying device. The check valve 40 of the Figures 1 , 2This prevents a short circuit between the first hydraulic pump 5 and the tank 13.

[0078] The invention is not limited to the Figures 1 to 3 illustrated embodiments.

[0079] In the Figure 1 the control valve device 45 can alternatively be designed as a proportional valve.

[0080] In the Figure 2 the control valve device 45 can alternatively be designed as a switching valve.

[0081] In the Figure 3 the control valve device 60 can alternatively be designed as a switching valve.

Claims

1. Hydraulic system (1) for an industrial truck, in particular a battery-powered industrial truck, with a lifting drive (2) for lifting and lowering a load pickup means, wherein the hydraulic system (1) has a first hydraulic pump (5), which is configured to supply the lifting drive (2) with pressure medium, and a second hydraulic pump (6), which can be activated by means of a valve device (7) for supplying the lifting drive (2), wherein the first hydraulic pump (5) and the second hydraulic pump (6) are configured as a hydraulic double pump assembly (10) and the valve device (7) is integrated into the hydraulic double pump assembly (10), wherein the hydraulic double pump assembly (10) has a housing (11) and the valve device (7) is installed in the housing (11), wherein, in the housing (11), an intake channel (12) is configured, which is connected to an intake port (S1) of the first hydraulic pump (5) and to an intake port (S2) of the second hydraulic pump (6), a first delivery channel (20) is configured, which is connected to a delivery port (P1) of the first hydraulic pump (5), and a second delivery channel (30) is configured, which is connected to a delivery port (P2) of the second hydraulic pump (6), characterized in that the second delivery channel (30) is connected to the first delivery channel (20) inside the housing (11).

2. Hydraulic system according to Claim 1, characterized in that the valve device (7) has an activation position, in which the delivery port (P2) of the second hydraulic pump (6) is connected to the first delivery channel (20), and has a deactivation position, in which the delivery port (P2) of the second hydraulic pump (6) is connected to the intake channel (12).

3. Hydraulic system according to Claim 1 or 2, characterized in that the valve device (7) has a check valve (40), which is arranged in the second delivery channel (30) and opens in the direction of the first delivery channel (20), in particular a spring-loaded check valve, and a control valve device (45), which is arranged in a connecting channel (46) connecting the second delivery channel (30) to the intake channel (12).

4. Hydraulic system according to Claim 3, characterized in that the control valve device (45) has a blocking position (45a), which forms the activation position, and a throughflow position (45b), which forms the deactivation position.

5. Hydraulic system according to Claim 1 or 2, characterized in that the valve device (7) has a control valve device (60), which is arranged in the second delivery channel (30) and is connected to a connecting channel (61) connected to the intake channel (12).

6. Hydraulic system according to Claim 4, characterized in that the control valve device (60) has a first control position (60a), which forms the activation position and in which the second delivery channel (30) is open and the connection of the second delivery channel (30) to the connecting channel (61) is shut off, and a second control position (60b), which forms the deactivation position and in which the second delivery channel (30) is connected to the connecting channel (61) and the connection of the second delivery channel (30) to the first delivery channel (20) is shut off.

7. Hydraulic system according to any of Claims 3 to 6, characterized in that the control valve device (45; 60) is configured as a switching valve or as a proportional valve.

8. Hydraulic system according to any of Claims 3 to 7, characterized in that the control valve device (45; 60) can be electrically actuated by means of an electrical actuating device (50; 70), in particular by means of a magnet.

9. Hydraulic system according to any of Claims 1 to 8, characterized in that an electronic control device (80) is provided, which is connected at the input end to an operator control element (85) and at the output end to the valve device (7) in order to activate it, wherein the electronic control device (80) is configured in such a way that the valve device (7) is controlled depending on the actuation of the operator control element (85).

10. Hydraulic system according to Claim 9, characterized in that the electronic control device (80) is configured in such a way that, when the operator control element (85) is actuated, the valve device (7) is actuated to the activation position or to the deactivation position and, when the operator control element (85) is not actuated, the valve device (7) is actuated to the deactivation position or to the activation position.

11. Hydraulic system according to any of Claims 1 to 10, characterized in that an electronic control device (80) is provided, which is connected at the input end to a sensor device (81) detecting the load pressure of the lifting drive (2) and at the output end to the valve device (7) in order to activate it, wherein the electronic control device (80) is configured in such a way that the valve device (7) is controlled depending on the load pressure of the lifting drive (2).

12. Hydraulic system according to Claim 11, characterized in that the electronic control device (80) is configured in such a way that the valve device (7) is actuated to the activation position at a load pressure of the lifting drive (2) below a limit load pressure and is actuated to the deactivation position at a load pressure of the lifting drive (2) above the limit load pressure.

13. Hydraulic system according to any of Claims 1 to 12, characterized in that the first hydraulic pump (5) and the second hydraulic pump (6) are driven by a common drive motor (8), in particular an electric motor.

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