Hydraulic system for an industrial truck

Abstract

The invention relates to a hydraulic system (1) for a forklift truck with a lifting frame, which has at least one extendable mast that can be raised and lowered in a stationary mast and a load handling device that can be raised and lowered in the extendable mast, wherein the hydraulic system has a free-lift cylinder (10) for raising and lowering the load handling device and at least one mast lift cylinder (11a; 11b) for raising and lowering the extendable mast, wherein a control valve device (15) is provided for controlling the lifting and lowering operation of the free-lift cylinder (10) and the mast lift cylinder (11a; 11b), and wherein a mast transition damping device (35) is provided, which includes at least one electrically actuated proportional valve (36; 37; 37a; 37b).The proportional valve (36; 37; 37a; 37b) of the mast transition damping device (35) has a throttle connection (50) in the uncontrolled state which causes a throttled volume flow and can be actuated in the direction of a flow position (51a) when electrically controlled.

Description

[0001] The invention relates to a hydraulic system for a forklift truck with a lifting frame, which has at least one extendable mast that can be raised and lowered in a stationary mast and a load-handling device that can be raised and lowered in the extendable mast, wherein the hydraulic system has a free-lift cylinder for raising and lowering the load-handling device and at least one mast lift cylinder for raising and lowering the extendable mast, wherein a control valve device is provided for controlling the lifting and lowering operation of the free-lift cylinder and the mast lift cylinder, and wherein a mast transition damping device is provided, which includes at least one electrically actuated proportional valve, wherein the proportional valve of the mast transition damping device can be actuated in the direction of a flow position when electrically actuated.

[0002] In industrial trucks with a multi-lift mast comprising a fixed mast and at least one extension mast, it is known to provide a free lift for the load-handling attachment that can be raised and lowered in the extension mast. This free lift allows the load-handling attachment to be raised in the extension mast without raising the extension mast itself. For this purpose, known lifting masts provide a free lift cylinder by means of which the load-handling attachment can be raised and lowered in the extension mast, and a mast lift cylinder by means of which the extension mast can be raised and lowered within a fixed mast of the lifting mast. The mast lift cylinder constitutes a mast lift, during which the extension mast is raised and lowered within the fixed mast.

[0003] Due to the use of a free-lift cylinder and the mast lift cylinder, shocks occur at the transition from the free lift to the mast lift and vice versa, leading to stresses on the components of the lifting frame and a load being lifted.

[0004] To improve the transition from free stroke to mast stroke and vice versa, it is already known to provide a mast transition damping device comprising at least one electrically actuated proportional valve. A generic hydraulic system with a mast transition damping device comprising at least one electrically actuated proportional valve is known from Figure 3a of DE 10 2016 103 256 A1, which represents the preamble of claim 1.

[0005] With at least one electrically actuated proportional valve, the lifting speed or lowering speed of the free lift cylinder or the mast lift cylinder can be controlled in the area of ​​the transition between free lift and mast lift in such a way that an almost smooth / impact-free passage through the mast transition is enabled and an almost constant lifting or lowering speed is achieved in the transition area between free lift and mast lift.

[0006] In the mast transition damping device known from Figure 3a of DE 10 2016 103 256 A1, the electrically actuated proportional valves of the mast transition damping device have a closed position in the unactuated, i.e., de-energized, state, in which no pressure medium can flow out of the free-lift cylinder or the mast lift cylinder. If a fault occurs in the proportional valves of such a mast transition damping device during lowering operation while lowering a load, for example at rated load, the proportional valves are abruptly actuated into the closed position, in which the connection between the free-lift cylinder and the mast lift cylinder and the reservoir is shut off.Such a fault in electrically actuated proportional valves can occur due to a loss of electrical power, for example, because of a power failure in the electrical control signal to the proportional valves and / or a broken connector on an electrical cable connected to the electrical actuator of the corresponding proportional valve. As a result of the sudden actuation of the proportional valves into the closed position in such a fault, the load on the lifting device is abruptly stopped, and depending on the preceding lowering speed of the lifting device and the weight of the load on the device, a pressure surge is transmitted to the lifting frame.Particularly at high lowering speeds of the load-handling device, exceeding 1 m / s (e.g., 1.2 m / s), a fault such as a broken connector on an electrical cable connected to the electrical actuator of the corresponding proportional valve will introduce a large impulse in the form of a pressure spike into the lifting frame during lowering. This can damage the mechanical structure of the lifting frame and affect the stability of the forklift truck. Furthermore, after such a fault, which causes the proportional valves of the mast transition damping device to be actuated into their locked position (i.e., in a de-energized state of the hydraulic system), further lowering of the load is no longer possible.

[0007] DE 10 2018 119 347 A1 discloses a forklift truck with a hydraulic lifting system and electronic malfunction protection of the lifting system.

[0008] DE 100 21 609 A1 discloses a lifting device for a battery-electrically powered work vehicle.

[0009] EP 0 546 300 A1 discloses an electro-hydraulic control device for load-compensated control of a hydraulic motor.

[0010] The present invention is based on the objective of providing a hydraulic control system and a forklift truck with a hydraulic control system that is improved with regard to the aforementioned disadvantages.

[0011] This problem is solved according to the invention in that the proportional valve of the mast transition damping device has a throttling connection in the uncontrolled state which causes a throttled volume flow and that the hydraulic system has at least two mast lifting cylinders, wherein the free lifting cylinder is connected to the control valve device by means of a first branch line and each mast lifting cylinder is connected to the control valve device by means of a branch line, wherein a proportional valve of the mast transition damping device is arranged in each branch line, wherein a proportional valve is attached to the free lifting cylinder and a proportional valve is attached to each mast lifting cylinder, wherein the proportional valves of the mast transition damping device each have the function of an electrical line break protection device.

[0012] According to the invention, the proportional valves of the mast transition damping device thus enable, in the uncontrolled state (i.e., in the de-energized state), a throttle connection through which a throttled volume flow can escape from the free-lift cylinder or the mast lift cylinder. If a fault occurs in the electrically actuated proportional valves of the mast transition damping device according to the invention, resulting in a loss of electrical energy, for example due to a power failure of the electrical control signal to the proportional valves and / or a broken connector on an electrical cable connected to an electrical actuating device of the corresponding proportional valve, a throttled volume flow can escape from the free-lift cylinder or the mast lift cylinder via the throttle connection, causing an abrupt stop of the lifting or mast lifting operation.Lowering the load is avoided, damage to the mechanical structure of the lifting frame is easily prevented, and the tipping stability of the forklift is improved. Furthermore, when the hydraulic system is de-energized, it is possible to lower the load further because, in the unpowered state (i.e., without power), hydraulic fluid can flow from the free-lift cylinder and the mast lift cylinder through the throttle connection of the proportional valves.

[0013] According to the invention, the free-lift cylinder is connected to the control valve assembly via a first branch line, and each mast lift cylinder is connected to the control valve assembly via a branch line, wherein a proportional valve of the mast transition damping device is arranged in each branch line. In a hydraulic system with one free-lift cylinder and, in particular, at least two mast lift cylinders, such proportional valves, wherein each lift cylinder is assigned a proportional valve, can be used to...In a simple manner, during lifting operation, before the end of a free stroke of the free-stroke cylinder, the pressure medium flow into the free-stroke cylinder is reduced by actuating the proportional valve arranged in the branch line of the free-stroke cylinder, and the pressure medium flow into the mast-stroke cylinder is introduced by increasing the pressure. Similarly, during lowering operation, before the end of a mast-stroke of the mast-stroke cylinder, the pressure medium flow from the mast-stroke cylinders is reduced by actuating the proportional valves arranged in the branch lines of the mast-stroke cylinders, and the pressure medium flow from the free-stroke cylinder is introduced by decreasing the pressure. This allows for a smooth transition between the free stroke and mast stroke of the lifting frame without loss of speed and with minimal additional construction effort.

[0014] According to the invention, a proportional valve is attached to the free-lift cylinder and a proportional valve is attached to each mast lift cylinder, wherein the proportional valves each have the function of an electrical line break protection device.In a hydraulic system where a proportional valve is arranged in each branch line leading to a lifting cylinder, and thus each lifting cylinder is assigned a proportional valve, the function of a mast transition damping and the function of electrical line break protection devices can be easily achieved by attaching the corresponding proportional valves to the free-lift cylinder and to the mast lifting cylinders, since the proportional valve attached to the corresponding lifting cylinder can easily assume the function of a line break protection device in the de-energized state via the throttle connection and can limit the lowering speed of the corresponding lifting cylinder to permissible values.

[0015] According to an advantageous embodiment of the invention, the proportional valve is actuated to a home position in the unactuated state, which is equipped with the throttle connection. The home position is thus designed as a throttle position. The proportional valve of the mast transition damping device is therefore designed as an electrically actuated proportional throttle valve. With a de-energized home position of the proportional valve of the mast transition damping device featuring a throttle connection, a throttled volume flow can easily flow out of the free-stroke cylinder or the mast stroke cylinder in the unactuated, de-energized state of the proportional valve.

[0016] According to an advantageous embodiment of the invention, the proportional valve is provided with a throttle opening, in particular a throttle bore, in its home position. With a throttle opening designed, for example, as a throttle bore, a throttle connection can be easily achieved in the home position of the proportional valve, by means of which a throttled volume flow can escape from the free-stroke cylinder or the mast stroke cylinder when the proportional valve is not actuated and de-energized.

[0017] According to an alternative and equally advantageous embodiment of the invention, the proportional valve is arranged in a housing, wherein the proportional valve, in its unactuated state, is actuated into a home position configured as a closed position, and the throttle connection is formed by a bypass line formed in the housing of the proportional valve, in which a throttle device is arranged. With a throttle connection formed by a bypass line formed in the housing of the proportional valve, in which a throttle device is arranged, it can be easily achieved, in conjunction with a proportional valve whose home position is configured as a closed position, that a throttled volume flow can escape from the free-stroke cylinder or the mast stroke cylinder in the unactuated, de-energized state of the proportional valve.

[0018] The invention further relates to a forklift truck with a hydraulic system according to the invention.

[0019] The invention has a number of advantages.

[0020] With the proportional valves of the mast transition damping device according to the invention, the mast transition between free lift and mast lift can be traversed without speed reduction in both lifting and lowering operation of the load handling device, thereby enabling a high throughput of the industrial truck.

[0021] With the proportional valves of the mast transition damping device according to the invention, the full mechanical stroke of the free-lift cylinder and the mast lift cylinder(s) can be utilized.

[0022] In the event of a power loss, for example due to a broken connector, the movement of the load-handling device is not abruptly stopped thanks to the throttle connection of the proportional valves in the mast transition damping device. This results in less stress on the lifting mast and a reduced risk of the forklift tipping over.

[0023] In the event of an energy loss, for example due to a broken plug, an emergency lowering of the load is possible due to the throttling connection of the proportional valves of the mast transition damping device, for example with the help of a suitable device on the control valve assembly.

[0024] When the proportional valves of the mast transition damping device are designed as an electrical line break safety device, in the event of a fault, the proportional valves can be returned to their initial position via a time-controlled movement (ramp). This prevents a sudden reduction in the load's speed.

[0025] When the proportional valves of the mast transition damping device are designed as an electrical line break protection device, the proportional valves of the mast transition damping device are always in their default position when unactuated and de-energized, and thus the line break protection device is always engaged or active. This provides increased safety for the industrial truck.

[0026] The proportional valves of the mast transition damping device according to the invention also make it possible to design the free-lift cylinder with a smaller piston diameter, thereby enabling a higher speed when lifting and lowering.

[0027] Further advantages and details of the invention are explained in more detail, for example, with reference to the exemplary embodiments shown in the schematic figures. Here, Figure 1 shows a schematic circuit diagram of an embodiment of a hydraulic system, Figure 2 shows a schematic circuit diagram of an embodiment of a hydraulic system according to the invention, Figure 3 shows a schematic circuit diagram of a further embodiment of a hydraulic system and Figure 4 shows a schematic circuit diagram of a further embodiment of a hydraulic system according to the invention.

[0028] In the Figures 1 to 4Each figure shows a schematic diagram of the hydraulic system 1 of a forklift truck (not shown in detail). Identical components are identified by the same reference numbers.

[0029] The industrial truck has a lifting frame (not shown in detail) on which a load-handling device is mounted and can be raised and lowered. The load-handling device consists, in particular, of a lifting carriage that is vertically movable on a lifting frame, to which, for example, a load fork formed by fork tines is attached as an attachment.

[0030] The lifting frame consists in particular of a mast and at least one extension mast which is arranged on the mast in a way that can be raised and lowered, and on which the load-handling device is arranged in a way that can be raised and lowered.

[0031] The lifting frame has at least two lifting stages. For raising and lowering the load-handling device relative to the extension mast, the hydraulic system includes a free-lift cylinder 10. The free-lift cylinder 10 constitutes a first lifting stage (free lift). For raising and lowering the load-handling device, a flexible traction element (not shown in detail), for example, a lifting chain, is provided. This chain is attached at one end to the lifting carriage, guided over a pulley on the extendable piston rod of the free-lift cylinder 10, and attached at one end to the extension mast. For raising and lowering the extension mast relative to the base mast, the hydraulic system 1 includes at least one mast lifting cylinder 11a, 11b. The mast lifting cylinder 11a, 11b constitutes a second lifting stage (mast lift). In the illustrated embodiments, two mast lifting cylinders 11a, 11b are provided.

[0032] A control valve device 15 is provided for controlling the lifting and lowering operation of the free-lift cylinder 10 and the mast lift cylinders 11a, 11b.

[0033] In the illustrated embodiments, the control valve assembly 15 is designed as a proportional valve with intermediate throttling positions, comprising a closed position 15a (neutral position), a lifting position 15b, and a lowering position 15c. For this purpose, the control valve assembly 15 is connected to a delivery line 16 of a pump 17, which draws pressure medium from a container 19 via a suction line 18, to a container line 20 leading to the container 19, and to a consumer line 21, which is connected to the free-lift cylinder 10 and the mast lift cylinders 11a and 11b.

[0034] In the closed position 15a of the control valve assembly 15, the connection between the consumer line 21 and the delivery line 16 and the reservoir line 20 is shut off. In the lifting position 15b of the control valve assembly 15, the delivery line 16 is connected to the consumer line 21. In the lowering position 15c of the control valve assembly 15, the consumer line 21 is connected to the reservoir line 20.

[0035] In the illustrated embodiments, the control valve assembly 15 is arranged in a control directional control valve block 22.

[0036] The control valve device 15 can, for example, be electrically actuated by means of an electronic control device 25.

[0037] Alternatively, the control valve assembly 15 can have a separate lifting valve for controlling the lifting operation of the load-handling device and a separate lowering valve for controlling the lowering operation of the load-handling device.

[0038] The free-lift cylinder 10 and the mast lift cylinders 11a, 11b are in the Figures 1 to 4 designed such that in lifting operation of the load handling device the free lift cylinder 10 extends first and then the mast lift cylinders 11a, 11b extend and in lowering operation of the load handling device the mast lift cylinders 11a, 11b retract first and then the free lift cylinder 10 retracts.

[0039] The hydraulic system 1 of the Figures 1 to 4 further features a mast transition damping device 35, which includes at least one electrically actuated proportional valve.

[0040] In the Figure 1The free-lift cylinder 10 is connected to the control valve assembly 15 by means of a first branch line 30 branching off from the consumer line 21, and the at least one mast lift cylinder 11a, 11b is connected to the control valve assembly 15 by means of a second branch line 31 branching off from the consumer line 21. The branch line 31 is connected to the mast lift cylinder 11a by means of a first connecting line 31a and to the mast lift cylinder 11b by means of a first connecting line 31b.

[0041] In the Figure 1 The mast transition damping device 35 has two electrically actuated proportional valves 36, 37, wherein the first proportional valve 36 is arranged in the first branch line 30 and the second proportional valve 37 is arranged in the second branch line 31.

[0042] A bypass line 40 is arranged on the first proportional valve 36, in which a shut-off valve 41, in particular a check valve, opening in the direction of the control valve device 15, is arranged.

[0043] A bypass line 42 is arranged on the second proportional valve 37, in which a shut-off valve 43, in particular a check valve, opening in the direction of the mast lifting cylinders 11a, 11b, is arranged.

[0044] In the Figure 1 The proportional valves 36, 37 of the mast transition damping device 35 are arranged with the bypass lines 40, 42 and the shut-off valves 41, 43 arranged therein in a valve block 45 of the mast transition damping device 35.

[0045] In the Figure 1Each mast lifting cylinder 11a, 11b is equipped with a mechanical line rupture protection device 60a, 60b. The line rupture protection device 60a attached to the mast lifting cylinder 11a comprises a shut-off valve 62a, for example a check valve, opening towards the mast lifting cylinder 11a, and a bypass line 63a with a throttle device 64a arranged in the bypass line 63a. The line rupture protection device 60b attached to the mast lifting cylinder 11b comprises a shut-off valve 62b, for example a check valve, opening towards the mast lifting cylinder 11b, and a bypass line 63b with a throttle device 64b arranged in the bypass line 63b.

[0046] In the Figure 1Furthermore, a mechanical line rupture protection valve device 60c is attached to the free-lift cylinder 10. The line rupture protection device 60c attached to the free-lift cylinder 10 comprises a shut-off valve 62c, for example a check valve, which opens in the direction of the free-lift cylinder 10, and a bypass line 63c with a throttling device 64c arranged in the bypass line 63c.

[0047] The electrically actuated proportional valve 36 or 37 of the mast transition damping device 35 has a throttling connection 50 in the unactuated state which causes a throttled volume flow and can be actuated in the direction of a flow position 51a when electrically actuated.

[0048] In the Figure 1In the unactuated state, the proportional valve 36 or 37 is actuated to a basic position 51b, which is equipped with the throttle connection 50. The throttle connection 50 is formed, for example, by a throttle opening 52, such as a throttle bore, which is effective in the basic position 51b. The basic position 51b is thus designed as a throttle position.

[0049] The proportional valve 36 or 37 is each actuated into the home position 51b by a spring device 55 and can be actuated in the direction of the flow position 51a by means of an electrical actuating device 56, for example a proportional solenoid. The actuating devices 56 are connected to the electronic control unit 25 for control purposes.

[0050] The hydraulic system 1 of the Figure 1The mast transition damping device 35, formed by the two electrically actuated proportional valves 36, 37, is thus combined with mechanical line break protection devices 60a, 60b, 60c on the free lift cylinder 10 and on the mast lift cylinders 11a, 11b.

[0051] The electronic control unit 25 is located in the Figures 1 to 4 with a sensor device not shown in detail, for example a stroke height sensor or a stroke height switch, in conjunction with which the mast transition area between the free lift and the mast lift can be determined.

[0052] The hydraulic system 1 of the Figure 1 It works as follows.

[0053] To lift the load-handling device, with the control valve assembly 15 actuated in the lifting position 15b, hydraulic fluid is conveyed from the control valve assembly 15 into the consumer line 21 to the valve block 45 of the mast transition damping device 35. The proportional valve 36 of the mast transition damping device 35 is actuated by the control unit 25 into the flow position 51a, so that hydraulic fluid flows via the proportional valve 36 (actuated in flow position 51a) and the branch line 30 into the free-lift cylinder 10. Due to the area ratio of the free-lift cylinder 10 to the mast lift cylinders 11a and 11b, no hydraulic fluid initially flows through the shut-off valve 43 into the mast lift cylinders 11a and 11b.As soon as the free-lift cylinder 10 approaches the mast transition area, which is detected by the control unit 25 via the sensor device, the electronic control unit 25 begins to actuate the proportional valve 36 into the basic position 51b, which is designed as a throttle position. As a result, the volume flow upstream of the proportional valve 36 is dammed up to such an extent that pressure medium flows from the control valve device 15 into the mast lift cylinders 11a, 11b via the opening shut-off valve 43.

[0054] To lower the load-handling device, with the control valve assembly 15 actuated in the lowering position 15c, hydraulic fluid from the mast lifting cylinders 11a, 11b is fed via the branch line 31 into the valve block 45 of the mast transition damping device 35. The proportional valve 37 of the mast transition damping device 35 is actuated by the control unit 25 into the flow position 51a, so that hydraulic fluid flows via the proportional valve 37, actuated in flow position 51a, into the consumer line 21 and via the control valve assembly 15, actuated in the lowering position 15c, to the reservoir 19. Due to the area ratio of the free-lift cylinder 10 to the mast lifting cylinders 11a, 11b, no hydraulic fluid initially flows from the free-lift cylinder 10 via the shut-off valve 41 to the control valve assembly 15.As soon as the mast lift cylinders 11a, 11b approach the mast transition area, which is detected by the control unit 25 via the sensor device, the electronic control unit 15 begins to actuate the proportional valve 37 into the basic position 51b, which is designed as a throttle position. As a result, the volume flow upstream of the proportional valve 37 is dammed up to such an extent that pressure medium flows from the free lift cylinder 10 to the control valve device 15 via the opening shut-off valve 41.

[0055] In the Figure 2The free-lift cylinder 10 is connected to the control valve assembly 15 by means of a first branch line 30 branching off from the consumer line 21, the first mast lift cylinder 11a is connected to the control valve assembly 15 by means of a second branch line 31a branching off from the consumer line 21, and the second mast lift cylinder 11b is connected to the control valve assembly 15 by means of a third branch line 31b branching off from the consumer line 21.

[0056] In the Figure 2The mast transition damping device 35 has three electrically actuated proportional valves 36, 37a, 37b, wherein one proportional valve 36, 37a, 37b of the mast transition damping device 35 is arranged in each branch line 30, 31a, 31b. The first proportional valve 36 is arranged in the first branch line 30, the second proportional valve 37a is arranged in the second branch line 31a, and the third proportional valve 37b is arranged in the third branch line 31b.

[0057] The proportional valve 36 is mounted on the free-lift cylinder 10, wherein the proportional valve 36 of the mast transition damping device 35 also functions as an electrical line break protection device 60c of the free-lift cylinder 10. The proportional valve 37a is mounted on the mast lift cylinder 11a, wherein the proportional valve 37a of the mast transition damping device 35 also functions as an electrical line break protection device 60a of the mast lift cylinder 11a. The proportional valve 37b is mounted on the mast lift cylinder 11b, wherein the proportional valve 37b of the mast transition damping device 35 also functions as an electrical line break protection device 60b of the mast lift cylinder 11b.

[0058] The electrically actuated proportional valves 36, 37a, 37b of the mast transition damping device 35 each have a throttling connection 50 in the unactuated state which causes a throttled volume flow and can be actuated in the direction of a flow position 51a when electrically actuated.

[0059] In the Figure 2 The proportional valves 36, 37a, 37b are each actuated in the unactuated state to a basic position 51b, which is provided with the throttle connection 50. The throttle connection 50 is formed, for example, by a throttle opening 52, such as a throttle bore, which is effective in the basic position 51b. The basic position 51b is thus designed as a throttle position.

[0060] The proportional valves 36, 37a, 37b are each actuated into the home position 51b by a spring device 55 and can be actuated in the direction of the flow position 51a by means of an electrical actuating device 56, for example a proportional solenoid. The actuating devices 56 are connected to the electronic control unit 25 for control purposes.

[0061] The hydraulic system 1 of the Figure 2 thus exhibits one of the three electrically actuated proportional valves 36, 37a, 37b formed

[0062] Mast transition damping device 35 in combination with electrical line break protection devices 60a, 60b, 60c on the free lift cylinder 10 and on the mast lift cylinders 11a, 11b, wherein the proportional valves 36, 37a, 37b of the mast transition damping device 35 attached to the corresponding lift cylinders each have the function of a line break protection device 60a, 60b, 60c.

[0063] The hydraulic system 1 of the Figure 2 It works as follows.

[0064] To lift the load-handling device, with the control valve assembly 15 actuated in the lifting position 15b, hydraulic fluid is pumped from the control valve assembly 15 into the consumer line 21 and into the branch lines 30, 31a, 31b connected to the consumer line 21. The proportional valve 36 of the mast transition damping device 35 is actuated by the control unit 25 into the flow position 51a, so that hydraulic fluid flows via the proportional valve 36 (actuated in flow position 51a) and the branch line 30 into the free-lift cylinder 10. Due to the area ratio of the free-lift cylinder 10 to the mast lift cylinders 11a, 11b, no hydraulic fluid initially flows into the mast lift cylinders 11a, 11b.As soon as the free-lift cylinder 10 approaches the mast transition area, which is detected by the control unit 25 via the sensor device, the electronic control unit 25 begins to actuate the proportional valve 36 into the basic position 51b, which is configured as a throttle position, and to actuate the proportional valves 37a and 37b each into the flow position 51a. As a result, the volume flow upstream of the proportional valve 36 is dammed up to such an extent that hydraulic fluid flows from the control valve device 15 into the mast lift cylinders 11a and 11b via the proportional valves 37a and 37b, which are actuated in the direction of the flow position 51a.

[0065] To lower the load-handling device, with the control valve assembly 15 actuated in the lowering position 15c, the proportional valves 37a and 37b are each actuated to the flow position 51a by the control unit 25, causing hydraulic fluid to flow from the mast lift cylinders 11a and 11b through the open proportional valves 37a and 37b into the consumer line 21 and, via the control valve assembly 15 actuated in the lowering position 15c, to the reservoir 19. Due to the area ratio of the free lift cylinder 10 to the mast lift cylinders 11a and 11b, no hydraulic fluid initially flows from the free lift cylinder 10 and the proportional valve 36, which is in the home position 51b, to the control valve assembly 15.As soon as the mast lift cylinders 11a, 11b approach the mast transition area, which is detected by the control unit 25 via the sensor device, the electronic control unit 15 begins to actuate the proportional valves 37a, 37b into the basic position 51b (designed as a throttle position) and actuate the proportional valve 36 into the flow position 51a. As a result, the volume flow upstream of the proportional valves 37a, 37b is dammed up to such an extent that the pressure in the consumer line 21 decreases progressively, so that an increasing amount of hydraulic fluid flows from the free lift cylinder 10 to the control valve device 15 via the proportional valve 36, which is now open to the flow position 51a.

[0066] The electrically operated proportional valves 36, 37a, 37b of the Figure 2The proportional valves 36, 37a, 37b continue to function as line rupture protection devices 60a, 60b, 60c. If no lifting or lowering operation of the load-handling device is performed and the proportional valves 36, 37a, 37b are not actuated, the proportional valves 36, 37a, 37b are in their default position 51b, which is configured as a throttle position. This corresponds to the state of a collapsed line rupture protection device. In the event of a line rupture, the lowering speed of the load-handling device is thus limited to a permissible value by means of the throttle connection 50 of the proportional valves 36, 37a, 37b, which is effective in the default position 51b.

[0067] If a deviation or fault, such as a line break, is detected by the control unit 25 during a lifting or lowering operation of the load-handling device, the control unit 25 controls the proportional valves 36, 37a, 37b each to the basic position 51b, which is designed as a throttle position. This ensures that the lowering speed of the load-handling device is limited to a permissible value by means of the throttle connection 50 effective in the basic position 51b.

[0068] In the Figure 3 is analogous to Figure 1The free-lift cylinder 10 is connected to the control valve assembly 15 by means of a first branch line 30 branching off from the consumer line 21, and the at least one mast lift cylinder 11a, 11b is connected to the control valve assembly 15 by means of a second branch line 31 branching off from the consumer line 21. The branch line 31 is connected to the mast lift cylinder 11a by means of a first connecting line 31a and to the mast lift cylinder 11b by means of a first connecting line 31b.

[0069] In the Figure 3 The mast transition damping device 35 has two electrically actuated proportional valves 36, 37, wherein the first proportional valve 36 is arranged in the first branch line 30 and the second proportional valve 37 is arranged in the second branch line 31.

[0070] The proportional valve 36 is analogous to the Figure 2attached to the free-lift cylinder 10, wherein the proportional valve 36 of the mast transition damping device 35 continues to have the function of an electrical line break protection device 60c of the free-lift cylinder 10.

[0071] The second proportional valve 37 is analogous to the Figure 1 a bypass line 42 is arranged in which a shut-off valve 43, in particular a check valve, opening in the direction of the mast lifting cylinders 11a, 11b, is arranged.

[0072] In the Figure 3 is analogous to Figure 1Each mast lifting cylinder 11a, 11b is fitted with a mechanical line rupture protection device 60a, 60b. The line rupture protection device 60a fitted to the mast lifting cylinder 11a comprises a shut-off valve 62a, for example a check valve, opening towards the mast lifting cylinder 11a, and a bypass line 63a with a throttle device 64a arranged in the bypass line 63a. The line rupture protection device 60b fitted to the mast lifting cylinder 11b comprises a shut-off valve 62b, for example a check valve, opening towards the mast lifting cylinder 11b, and a bypass line 63b with a throttle device 64b arranged in the bypass line 63b.

[0073] The electrically actuated proportional valve 36 or 37 of the mast transition damping device 35 has a throttling connection 50 in the unactuated state which causes a throttled volume flow and can be actuated in the direction of a flow position 51a when electrically actuated.

[0074] In the Figure 3 In the unactuated state, the proportional valve 36 or 37 is actuated to a basic position 51b, which is equipped with the throttle connection 50. The throttle connection 50 is formed, for example, by a throttle opening 52, such as a throttle bore, which is effective in the basic position 51b. The basic position 51b is thus designed as a throttle position.

[0075] The proportional valve 36 or 37 is each actuated into the home position 51b by a spring device 55 and can be actuated in the direction of the flow position 51a by means of an electrical actuating device 56, for example a proportional solenoid. The actuating device 56 is connected to the electronic control unit 25 for control purposes.

[0076] The hydraulic system 1 of the Figure 3 The device thus features a mast transition damping device 35 formed by the two electrically actuated proportional valves 36, 37 in combination with the mechanical line break protection devices 60a, 60b on the mast lifting cylinders 11a, 11b and with the electrical line break protection device 60c on the free lifting cylinder 10.

[0077] The hydraulic system 1 of the Figure 3 It works as follows.

[0078] To lift the load-handling device, with the control valve assembly 15 actuated in the lifting position 15b, hydraulic fluid is conveyed from the control valve assembly 15 into the consumer line 21 and the branch lines 30, 31. The proportional valve 36 of the mast transition damping device 35, located on the free-lift cylinder 10, is actuated by the control unit 25 into the flow position 51a, so that hydraulic fluid flows via the proportional valve 36 (actuated in flow position 51a) and the branch line 30 into the free-lift cylinder 10. Due to the area ratio of the free-lift cylinder 10 to the mast lift cylinders 11a, 11b, no hydraulic fluid initially flows through the shut-off valve 43 into the mast lift cylinders 11a, 11b.As soon as the free-lift cylinder 10 approaches the mast transition area, which is detected by the control unit 25 via the sensor device, the electronic control unit 25 begins to actuate the proportional valve 36 arranged on the free-lift cylinder 10 into the basic position 51b, which is designed as a throttle position. As a result, the volume flow upstream of the proportional valve 36 is dammed up to such an extent that pressure medium flows from the control valve device 15 into the mast lift cylinders 11a, 11b via the opening shut-off valve 43.

[0079] To lower the load-handling device, with the control valve assembly 15 actuated in the lowering position 15c, the proportional valve 37 is actuated by the control unit 25 in the flow position 51a, causing hydraulic fluid to flow from the mast lift cylinders 11a, 11b via the open proportional valve 37 into the consumer line 21 and via the control valve assembly 15, actuated in the lowering position 15c, to the reservoir 19. Due to the area ratio of the free lift cylinder 10 to the mast lift cylinders 11a, 11b, no hydraulic fluid initially flows from the free lift cylinder 10 and the proportional valve 36, which is mounted on the free lift cylinder 10 and is in its home position 51b, to the control valve assembly 15.As soon as the mast lift cylinders 11a, 11b approach the mast transition area, which is detected by the control unit 25 via the sensor device, the electronic control unit 15 begins to actuate the proportional valve 37 into the basic position 51b, which is configured as a throttle position, and to actuate the proportional valve 36 mounted on the free lift cylinder 10 into the flow position 51a. As a result, the volume flow upstream of the proportional valve 37 is dammed up to such an extent that the pressure in the consumer line 21 decreases progressively, so that an increasing amount of hydraulic fluid flows from the free lift cylinder 10 to the control valve device 15 via the proportional valve 36, which is now open to the flow position 51a.

[0080] In the Figure 4 is a variant of Figure 2 depicted.

[0081] In the Figure 4The proportional valves 36, 37a, 37b each have a housing 70 in which the corresponding proportional valve 36, 37a, 37b is installed. In the unactuated state, the proportional valve 36, 37a, 37b is actuated to a basic position 51b, which is configured as a closed position. The throttle connection 50 of the proportional valve 36, 37a, 37b is formed by a bypass line 71 located in the housing 70 of the corresponding proportional valve 36, 37a, 37b, in which a throttle device 72 is arranged.

[0082] The proportional valve 36, 37a, 37b of the Figure 4 Each is actuated into the home position 51b by a spring device 55 and can be actuated in the direction of the flow position 51a by means of an electrical actuating device 56, for example a proportional magnet. The actuating device 56 is connected to the electrical control unit 25 for control purposes.

[0083] The control unit 25 is used in the Figures 1 to 4 the corresponding proportional valves 36, 37a, 37b of the mast transition damping device 35 are controlled in such a way that, during the lifting operation of the load-handling device, a uniform movement of the load-handling device is achieved during the mast transition from the free lift to the mast lift, and during the lowering operation of the load-handling device, a uniform movement of the load-handling device is achieved without a change in speed or shocks in the mast transition.

[0084] During lifting operation, the volume flow into the free-lift cylinder 10 in the mast transition area is progressively throttled by appropriately controlling the proportional valve 36 of the mast transition damping device 35, thereby achieving a continuous decrease in the extension speed of the free-lift cylinder 10. The proportional valves 37a, 37b are each actuated in the flow position 51a. The increasing dynamic pressure resulting from the throttling leads to a continuously faster extension of the mast lift cylinders 11a, 11b. The overlapping movement of the free-lift cylinder 10 and the mast lift cylinders 11a, 11b is preferably designed such that the lifting speed of the load remains constant in the mast transition area.

[0085] During lowering operation, the volume flow from the mast lifting cylinders 11a, 11b in the mast transition area is progressively throttled by appropriately controlling the proportional valves 37a, 37b in the basic position 51b of the mast transition damping device 35, thereby achieving a continuous decrease in the retraction speed of the mast lifting cylinders 11a, 11b. The proportional valve 36 is actuated in the flow position 51a. The pressure reduction in the consumer line 31 due to the throttling leads to a continuously faster retraction of the free lifting cylinder 10. The overlapping movement of the free lifting cylinder 10 and the mast lifting cylinders 11a, 11b is preferably designed such that the lowering speed of the load in the mast transition area remains constant.

[0086] Due to the mast transition damping, the free lift cylinder 10 and the mast lift cylinders 11a, 11b move into their mechanical end position at a very low speed in both lifting and lowering operations.

Claims

1. Hydraulic system (1) for an industrial truck with a lifting framework which has at least one extension mast, raisable and lowerable in a stationary mast, and has a load-bearing means, raisable and lowerable in the extension mast, wherein the hydraulic system has a free-lift cylinder (10) for raising and lowering the load-bearing means and has at least one mast lift cylinder (11a; 11b) for raising and lowering the extension mast, wherein provision is made of a control valve device (15) for controlling the raising operation and the lowering operation of the free-lift cylinder (10) and of the mast lift cylinder (11a; 11b), and wherein provision is made of a mast transition damping device (35) which comprises at least one electrically actuated proportional valve (36; 37; 37a; 37b), wherein the proportional valve (36; 37; 37a; 37b) of the mast transition damping device (35) is actuatable in the direction of a flow position (51a) when activated electrically, wherein the free-lift cylinder (10) is connected to the control valve device (15) by means of a first branch line (30), wherein a proportional valve (36) is mounted on the free-lift cylinder (10), characterized in that, in the non-activated state, the proportional valve (36; 37; 37a; 37b) of the mast transition damping device (35) has a throttle connection (50) which gives rise to a throttled volume flow, and in that the hydraulic system (1) has at least two mast lift cylinders (11a, 11b), wherein each mast lift cylinder (11a; 11b) is connected to the control valve device (15) by means of a further branch line (31a; 31b), wherein a proportional valve (36; 37a; 37b) of the mast transition damping device (35) is arranged in each branch line (30; 31a; 31b), wherein a proportional valve (37a; 37b) is mounted on each mast lift cylinder (11a; 11b), wherein the proportional valves (36; 37a; 37b) of the mast transition damping device (35) each have the function of an electrical line break protection device (60a; 60b; 60c).

2. Hydraulic system according to Claim 1, characterized in that, in the non-activated state, the proportional valve (36; 37; 37a; 37b) is actuated into a basic position (51b), which is provided with the throttle connection (50).

3. Hydraulic system according to Claim 2, characterized in that, in the basic position (51b), the proportional valve (36; 37; 37a; 37b) is provided with a throttle opening (52), in particular a throttle bore.

4. Hydraulic system according to Claim 1, characterized in that the proportional valve (36; 37; 37a; 37b) is arranged in a housing (70), wherein, in the non-activated state, the proportional valve (36; 37; 37a; 37b) is actuated into a basic position (51b) which is configured as a blocking position, and the throttle connection (50) is formed by a bypass line (71) which is formed in the housing (70) of the proportional valve (36; 37; 37a; 37b) and in which a throttle device (72) is arranged.

5. Industrial truck having a hydraulic system (1) according to one of the preceding claims.

Images