EP4321471A1 - Hydraulic system for an industrial truck - Google Patents

Abstract

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

Description

The invention relates to a hydraulic system for an industrial truck with a mast which has at least one extension mast that can be raised and lowered in a stationary mast and a load-carrying device that can be raised and lowered in the extension mast, the hydraulic system having a free-lift cylinder for raising and lowering the load-carrying device and at least one mast lifting cylinder for raising and lowering the extension mast, wherein a control valve device is provided for controlling the lifting operation and the lowering operation of the free lift cylinder and the mast lift cylinder and wherein a mast transition damping device is provided which comprises at least one electrically operated proportional valve.

In industrial trucks with a multiple mast that includes a stationary mast and at least one extension mast, it is known to provide a free lift for the load-carrying means that can be raised and lowered in the extension mast. With the free lift, the load handling device in the extendable mast can be raised without the extendable mast being raised. For this purpose, in known masts, a free-lift cylinder is provided, by means of which the load-carrying means can be raised and lowered in the extension mast, and a mast lifting cylinder is provided, by means of which the extension mast can be raised and lowered in a stationary mast of the mast. The mast lifting cylinder forms a mast lift in which the extension mast is raised and lowered in the standing mast.

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, which lead to loads on the components of the mast and a load picked up.

In order to improve the transition from the free lift to the mast lift and vice versa, it is already known to provide a mast transition damping device which includes at least one electrically operated proportional valve. A generic one Hydraulic system with a mast transition damping device, which includes at least one electrically operated proportional valve, is shown in Figure 3a DE 10 2016 103 256 A1 known.

With the at least one electrically operated proportional valve, the lifting speed or the lowering speed of the free lift cylinder or the mast lift cylinder can be controlled in the area of the transition between the free lift and the mast lift in such a way that an almost gentle/impact-free passage through the mast transition is possible and an almost constant lifting or .Lowering speed is achieved in the transition area between free lift and mast lift.

In the one from Figure 3a DE 10 2016 103 256 A1 In the known mast transition damping device, the electrically operated proportional valves of the mast transition damping device have a basic position designed as a blocking position in the non-controlled, ie de-energized, state, in which no pressure medium can flow out of the free-lift cylinder or the mast-lift cylinder. If a fault in the proportional valves of the mast transition damping device occurs in such a mast transition damping device in lowering operation while lowering a load, for example with a nominal load, the proportional valves are suddenly actuated into the basic position designed as a blocking position, in which the connection of the free lift cylinder and the mast lift cylinder to the container is blocked is. Such a fault in the electrically operated proportional valves can occur in the event of a loss of electrical energy, for example due to a power failure in the electrical control signal of the proportional valves and/or due to a plug of an electrical cable that is connected to an electrical actuating device of the corresponding proportional valve. As a result of the sudden actuation of the proportional valves into the blocking position in the event of such a fault in the proportional valves, the load on the load-carrying device is suddenly stopped and, depending on the previous lowering speed of the load-carrying device and the weight of the load picked up on the load-carrying device, a pulse is introduced into the mast via a pressure peak. Particularly at high lowering speeds of the load-carrying device in the range of greater than 1 m/s, for example 1.2 m/s, in the event of such a fault, for example in the event of an electrical plug being torn off Cable that is connected to the electrical actuation device of the corresponding proportional valve, when lowering the load handler, a large impulse in the form of a pressure peak is introduced into the mast, which can lead to damage to the mechanical structure of the mast and can influence the tilting stability of the industrial truck. Furthermore, after such a fault, in which the proportional valves of the mast transition damping device were actuated into the basic position designed as a blocking position, ie in the de-energized state of the hydraulic system, further lowering of the load is no longer possible.

The present invention is based on the object of providing a hydraulic control system and an industrial truck with a hydraulic control system which is improved with regard to the disadvantages mentioned.

This object is achieved according to the invention in that the proportional valve of the mast transition damping device has a throttle connection which causes a throttled volume flow in the non-controlled state and can be actuated in the direction of a flow position when electrically controlled.

According to the invention, the proportional valves of the mast transition damping device in the non-controlled state, ie in the de-energized state, each enable a throttle connection with which a throttled volume flow can flow out of the free-lift cylinder or the mast-lift cylinder. In the case of the proportional valves of the mast transition damping device according to the invention, a fault occurs in the electrically operated proportional valves with a loss of electrical energy, for example due to a power failure of the electrical control signal of the proportional valves and / or due to a plug break in an electrical cable that is connected to an electrical actuating device of the corresponding proportional valve , a throttled volume flow can therefore flow out of the free lift cylinder or the mast lift cylinder via the throttle connection, whereby a sudden stop of the lifting or lowering movement of the load is avoided and damage to the mechanical structure of the mast can be easily avoided and the tilting stability of the Industrial truck is improved. In addition, when the hydraulic system is in a de-energized state, it is possible to further reduce the load, since pressure medium can flow out of the free-lift cylinder and the mast-lift cylinder via the throttle connection when the proportional valves are not activated, ie in the de-energized state.

According to an advantageous embodiment of the invention, in particular the proportional valve is actuated in the non-activated state into a basic position which is provided with the throttle connection. The basic position is therefore designed as a throttle position. The proportional valve of the mast transition damping device is therefore designed as an electrically operated proportional throttle valve. With a de-energized basic position of the proportional valve of the mast transition damping device having a throttle connection, a throttled volume flow can flow out of the free-lift cylinder or the mast-lift cylinder in a simple manner when the proportional valve is not activated, de-energized.

According to an advantageous embodiment of the invention, in particular the proportional valve in the basic position is provided with a throttle opening, in particular a throttle bore. With a throttle opening designed, for example, as a throttle hole, a throttle connection can be easily achieved in the basic position of the proportional valve, by means of which a throttled volume flow can flow out of the free-lift cylinder or the mast-lift cylinder when the proportional valve is not activated and de-energized.

According to an alternative and also advantageous embodiment of the invention, in particular the proportional valve is arranged in a housing, the proportional valve being actuated in the non-controlled state into a basic position, which is designed as a blocking 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, which is formed by a bypass line formed in the housing of the proportional valve and in which a throttle device is arranged, in conjunction with a proportional valve whose basic position is designed as a blocking position, it can be achieved in a simple manner that in the non-controlled, de-energized state of the proportional valve, a throttled volume flow can flow out of the free-lift cylinder or the mast-lift cylinder.

According to an advantageous embodiment of the invention, in particular the free-lift cylinder is connected to the control valve device by means of a first branch line and the at least one mast lift cylinder is connected to the control valve device by means of a second branch line, a first proportional valve of the mast transition damping device being arranged in the first branch line and in the second branch line second proportional valve of the mast transition damping device is arranged. In a hydraulic system with a free-lift cylinder and one or more mast-lift cylinders, two such proportional valves can be used to reduce the pressure medium flow into the free-lift cylinder in a simple manner during lifting operation before the end of the free lift of the free-lift cylinder by activating the proportional valve arranged in the first branch line and the pressure medium flow into the Mast lifting cylinders are initiated by increasing the pressure and in lowering operation before the end of the mast stroke of the mast lifting cylinder by controlling the proportional valve arranged in the second branch line, the pressure medium flow from the mast lifting cylinder cylinder is reduced and the pressure medium flow from the free lifting cylinder is initiated by reducing the pressure, so that a shock-free transition between free lift and Mast lift of the mast can be achieved without loss of speed with little additional construction effort.

According to an advantageous embodiment of the invention, a bypass line is arranged in particular on the first proportional valve, in which a check valve opening in the direction of the control valve device, in particular a check valve, is arranged. With such a check valve it is possible for pressure medium to flow out of the free-lift cylinder during lowering operation during the transition from the mast lift to the free lift without having to control the proportional valve arranged in the first branch line.

According to an advantageous embodiment of the invention, a bypass line is arranged in particular on the second proportional valve, in which a check valve, in particular a check valve, opening in the direction of the at least one mast lifting cylinder is arranged. With such a check valve it is possible for pressure medium to flow into the mast lift cylinder during lifting operation during the transition from the free lift to the mast lift without having to control the proportional valve arranged in the second branch line.

According to an advantageous embodiment of the invention, a mechanical line break protection device is installed in particular on each mast lifting cylinder. The mechanical line break protection device each comprises, in particular, a check valve opening in the direction of the mast lifting cylinder, for example a check valve, and a bypass line with a throttle device arranged in the bypass line. With such a line break protection device on each mast lifting cylinder, the lowering speed of the mast lifting cylinders can be easily limited to permissible values in the event of a fault.

According to an advantageous embodiment of the invention, a mechanical line break protection device is installed in particular on the free-lift cylinder. The mechanical line break protection device includes in particular a check valve opening in the direction of the free-lift cylinder, for example a check valve, and a bypass line with a throttle device arranged in the bypass line. With such a line break protection device on the free-lift cylinder, the lowering speed of the free-lift cylinder can be limited to permissible values in a simple manner in the event of a fault.

According to an advantageous embodiment of the invention, in particular the first proportional valve is mounted on the free-lift cylinder and has the function of an electrical line break protection device. By attaching the first proportional valve according to the invention to the free-lift cylinder, the function of a mast transition damping and the function of an electrical line break protection device can be achieved in a simple manner with the first proportional valve, since the first proportional valve attached to the free-lift cylinder functions in a simple manner in the de-energized state through the throttle connection a line break protection device can take over and can limit the lowering speed of the free-lift cylinder to permissible values.

According to an alternative and also advantageous embodiment of the invention, the free-lift cylinder in particular is connected to the by means of a first branch line Control valve device connected and each mast lifting cylinder connected to the control valve device by means of a branch line, a proportional valve of the mast transition damping device being arranged in each branch line. In a hydraulic system with a free-lift cylinder and in particular at least two mast-lift cylinders, such proportional valves, with each lifting cylinder being assigned a proportional valve, can be used to easily control the pressure medium flow in lifting operation before the end of a free lift of the free-lift cylinder by controlling the proportional valve arranged in the branch line of the free-lift cylinder the free lift cylinder are reduced and the pressure medium flow is introduced into the mast lift cylinder by increasing the pressure and in lowering operation before the end of a mast stroke of the mast lift cylinder the pressure medium flow from the mast lift cylinders is reduced by controlling the proportional valves arranged in the branch lines of the mast lift cylinders and the pressure medium flow from the free lift cylinder is initiated by pressure reduction so that a smooth transition between the free lift and the mast lift of the mast can be achieved without loss of speed and with little additional construction effort.

According to an advantageous embodiment of the invention, a proportional valve is installed in particular on the free-lift cylinder and/or a proportional valve is installed on each mast-lift cylinder, the proportional valves each having the function of an electrical line break protection device. In a hydraulic system in which a proportional valve is arranged in each branch line leading to a lifting cylinder and a proportional valve is therefore assigned to each lifting cylinder, the corresponding proportional valves can be easily connected to the proportional valves by attaching the corresponding proportional valves to the free-lift cylinder and/or to the mast-lift cylinder Function of a mast transition damping and the function of electrical line break protection devices can be achieved, since the proportional valve attached to the corresponding lifting cylinder can easily take over the function of a line break protection device in the de-energized state through the throttle connection and can limit the lowering speed of the corresponding lifting cylinder to permissible values.

The invention further relates to an industrial truck with a hydraulic system according to the invention.

The invention has a number of advantages.

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 passed through without reducing the speed in both lifting and lowering operation of the load-carrying device, whereby a high handling capacity of the industrial truck can be achieved.

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 or cylinders can be utilized.

In the event of a loss of energy, for example as a result of a plug being torn off, the movement of the load-carrying device is not suddenly stopped due to the throttle connection of the proportional valves of the mast transition damping device. This leads to a lower load on the mast and a reduced risk of the truck tipping over.

In the event of a loss of energy, for example as a result of a plug being torn off, an emergency lowering of the load is possible due to the throttle connection of the proportional valves of the mast transition damping device, for example with the aid of a suitable device on the control valve device.

When the proportional valves of the mast transition damping device are designed as an electrical line break protection device, in the event of a fault, the proportional valves can be brought into the basic position via a time-controlled movement (ramp). This avoids a sudden reduction in the speed of the load.

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 the basic position in the unactuated, de-energized state and therefore the line break protection device is always engaged or active. This offers increased safety for the industrial truck.

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, which enables a higher speed when lifting and lowering.

Figur 1

einen schematischen Schaltplan einer ersten Ausführungsform eines erfindungsgemäßen hydraulischen Systems,

Figur 2

einen schematischen Schaltplan einer zweiten Ausführungsform eines erfindungsgemäßen hydraulischen Systems,

Figur 3

einen schematischen Schaltplan einer dritten Ausführungsform eines erfindungsgemäßen hydraulischen Systems und

Figur 4

einen schematischen Schaltplan einer vierten Ausführungsform eines erfindungsgemäßen hydraulischen Systems.

Further advantages and details of the invention are explained in more detail, for example, using the exemplary embodiments shown in the schematic figures. This shows

Figure 1

a schematic circuit diagram of a first embodiment of a hydraulic system according to the invention,

Figure 2

a schematic circuit diagram of a second embodiment of a hydraulic system according to the invention,

Figure 3

a schematic circuit diagram of a third embodiment of a hydraulic system according to the invention and

Figure 4

a schematic circuit diagram of a fourth embodiment of a hydraulic system according to the invention.

In the Figures 1 to 4 A schematic structure of a hydraulic system 1 of an industrial truck of an industrial truck (not shown in detail) is shown. The same components are provided with the same reference numbers.

The industrial truck has a lifting frame, not shown, on which a load-carrying device can be raised and lowered. The load-carrying device consists in particular of a lifting carriage that can be moved vertically on a mast and to which, for example, a load fork formed by fork arms is attached as an attachment.

The mast consists in particular of a standing mast and at least one extension mast which can be raised and lowered on the standing mast and on which the load-carrying means is arranged such that it can be raised and lowered.

The mast has at least two lifting stages. The hydraulic system has a free-lift cylinder 10 for raising and lowering the load-carrying device relative to the extension mast. The free-lift cylinder 10 forms a first lifting stage (free lift). For raising and lowering the load-carrying means, in particular a flexible traction means (not shown), for example a lifting chain, is provided, which is attached to the lifting carriage with a first end, is guided via a deflection roller on the extendable piston rod of the free-lift cylinder 10 and with a second end attached to the extension mast. To raise and lower the extension mast relative to the stationary mast, the hydraulic system 1 has at least one mast lifting cylinder 11a, 11b. The mast lifting cylinder 11a, 11b forms a second lifting stage (mast lifting). In the exemplary embodiments shown, two mast lifting cylinders 11a, 11b are provided.

A control valve device 15 is provided to control the lifting operation and the lowering operation of the free lift cylinder 10 and the mast lift cylinders 11a, 11b.

In the exemplary embodiments shown, the control valve device 15 is designed as a proportional valve throttling in intermediate positions with a blocking position 15a designed as a neutral position, a lifting position 15b and a lowering position 15c. For this purpose, the control valve device 15 is connected to a delivery line 16 of a pump 17, which sucks pressure medium from a container 19 by means of a suction line 18, to a container line 20 led 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 , 11b is connected.

In the blocking position 15a of the control valve device 15, the connection of the consumer line 21 to the delivery line 16 and the container line 20 is blocked. In the lifting position 15b of the control valve device 15, the delivery line 16 is connected to the consumer line 21. In the lowered position 15c of the control valve device 15, the consumer line 21 is connected to the container line 20.

The control valve device 15 is arranged in a control directional valve block 22 in the exemplary embodiments shown.

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

Alternatively, the control valve device 15 may have a separate lifting valve for controlling the lifting operation of the load-carrying device and a separate lowering valve for controlling the lowering operation of the load-carrying device.

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

The hydraulic system 1 of the Figures 1 to 4 further has a mast transition damping device 35, which includes at least one electrically operated proportional valve.

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

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

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

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

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

In the Figure 1 A mechanical line break protection device 60a, 60b is installed on each mast lifting cylinder 11a, 11b. The line break protection device 60a mounted on the mast lifting cylinder 11a comprises a check valve 62a which opens in the direction of the mast lifting cylinder 11a, for example a check valve, and a bypass line 63a with a throttle device 64a arranged in the bypass line 63a. The line break protection device 60b mounted on the mast lifting cylinder 11b comprises a check valve 62b which opens in the direction of the mast lifting cylinder 11b, for example a check valve, and a bypass line 63b with a throttle device 64b arranged in the bypass line 63b.

In the Figure 1 A mechanical line break safety valve device 60c is also attached to the free-lift cylinder 10. The line break protection device 60c mounted on the free-lift cylinder 10 includes a check valve 62c that opens in the direction of the free-lift cylinder 10, for example a check valve, and a bypass line 63c with a throttle device 64c arranged in the bypass line 63c.

The electrically actuated proportional valve 36 or 37 of the mast transition damping device 35 has, in the non-controlled state, a throttle connection 50 which causes a throttled volume flow and can be actuated in the direction of a flow position 51a when electrically actuated.

In the Figure 1 the proportional valve 36 or 37 is actuated in the non-controlled state into a basic position 51b, which is provided with the throttle connection 50. The throttle connection 50 is, for example, one that acts in the basic position 51b Throttle opening 52, for example a throttle bore, is formed. The basic position 51b is therefore designed as a throttle position.

The proportional valve 36 or 37 is each actuated by a spring device 55 into the basic position 51b 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 devices 56 are connected to the electronic control device 25 for control purposes.

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

The electronic control device 25 is in the Figures 1 to 4 with a sensor device, not shown, for example a lifting height sensor or a lifting height switch, with which the mast transition area between the free lift and the mast lift can be determined.

The hydraulic system 1 of the Figure 1 works as follows.

To lift the load-carrying device, with the control valve device 15 being actuated into the lifting position 15b, pressure medium is conveyed from the control valve device 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 device 25 into the flow position 51a, so that pressure medium flows into the free-lift cylinder 10 via the proportional valve 36 actuated into the flow position 51a and the branch line 30. Due to the area ratio of the free-lift cylinder 10 to the mast-lift cylinders 11a, 11b, no pressure medium initially flows via the check 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 device 25 using the sensor device, the electronic control device 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 in front of the proportional valve 36 increases accumulated so that pressure medium flows from the control valve device 15 into the mast lifting cylinders 11a, 11b via the opening check valve 43.

To lower the load-carrying device, with the control valve device 15 being actuated into the lowering position 15c, pressure medium is fed from the mast lifting cylinders 11a, 11b 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 device 25 into the flow position 51a, so that pressure medium flows out to the container 19 via the proportional valve 37 actuated in the flow position 51a into the consumer line 21 and via the control valve device 15 actuated into the lowering position 15c. Due to the area ratio of the free-lift cylinder 10 to the mast-lift cylinders 11a, 11b, initially no pressure medium flows from the free-lift cylinder 10 via the check valve 41 to the control valve device 15. As soon as the mast-lift cylinders 11a, 11b approach the mast transition area, which is detected by the control device 25 using the sensor device , the electronic control device 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 in front of the proportional valve 37 is accumulated to such an extent that pressure medium flows from the free-lift cylinder 10 to the control valve device 15 via the opening check valve 41.

In the Figure 2 the free lift cylinder 10 is connected to the control valve device 15 by means of a first branch line 30 branching off from the consumer line 21, the first mast lifting cylinder 11a is connected to the control valve device 15 by means of a second branch line 31a branching off from the consumer line 21 and the second mast lifting cylinder 11b is connected by means of a third, Branch line 31b branching off from consumer line 21 is connected to control valve device 15

In the Figure 2 the mast transition damping device 35 has three electrically actuated proportional valves 36, 37a, 37b, with a proportional valve 36, 37a, 37b of the mast transition damping device 35 being 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 in the second branch line 31a arranged and the third proportional valve 37b arranged in the third branch line 31b.

The proportional valve 36 is attached 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. The proportional valve 37a is attached to the mast lifting cylinder 11a, with the proportional valve 37a of the mast transition damping device 35 continuing to have the function of an electrical line break protection device 60a of the mast lifting cylinder 11a. The proportional valve 37b is attached to the mast lifting cylinder 11b, with the proportional valve 37b of the mast transition damping device 35 continuing to have the function of an electrical line break protection device 60b of the mast lifting cylinder 11b.

In the non-controlled state, the electrically actuated proportional valves 36, 37a, 37b of the mast transition damping device 35 each have a throttle connection 50 which causes a throttled volume flow and can be actuated in the direction of a flow position 51a when electrically actuated.

In the Figure 2 the proportional valve 36, 37a, 37b is actuated in the non-controlled state into 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 acting in the basic position 51b, for example a throttle bore. The basic position 51b is therefore designed as a throttle position.

The proportional valve 36, 37a, 37b is each actuated by a spring device 55 into the basic position 51b 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 devices 56 are connected to the electronic control device 25 for control purposes.

The hydraulic system 1 of the Figure 2 thus has one formed by the three electrically operated proportional valves 36, 37a, 37b 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, the proportional valves 36, 37a, 37b of the mast transition damping device 35 mounted on the corresponding lifting cylinders each having the function of a line break protection device 60a, 60 b, 60c.

The hydraulic system 1 of the Figure 2 works as follows.

To lift the load-carrying device, with the control valve device 15 being actuated into the lifting position 15b, pressure medium is conveyed from the control valve device 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 device 25 into the flow position 51a, so that pressure medium flows into the free-lift cylinder 10 via the proportional valve 36 actuated into the flow position 51a and the branch line 30. Due to the area ratio of the free-lift cylinder 10 to the mast-lift cylinders 11a, 11b, no pressure medium 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 device 25 by means of the sensor device, the electronic control device 25 begins to actuate the proportional valve 36 into the basic position 51b designed as a throttle position and to actuate the proportional valves 37a, 37b into the flow position 51a . As a result, the volume flow in front of the proportional valve 36 is accumulated to such an extent that pressure medium flows from the control valve device 15 into the mast lifting cylinders 11a, 11b via the proportional valves 37a, 37b actuated in the direction of the flow position 51a.

To lower the load-carrying means, with the control valve device 15 being actuated into the lowering position 15c, the control device 25 actuates the proportional valves 37a, 37b into the flow position 51a, whereby pressure medium from the mast lifting cylinders 11a, 11b into the Consumer line 21 and flows out to the container 19 via the control valve device 15 actuated in the lowering position 15c. Due to the area ratio of the free-lift cylinder 10 to the mast-lift cylinders 11a, 11b, no pressure medium initially flows from the free-lift cylinder 10, even in the basic position 51b located proportional valve 36 to the control valve device 15. As soon as the mast lifting cylinders 11a, 11b approach the mast transition area, which is recognized by the control device 25 by means of the sensor device, the electronic control device 15 begins to actuate the proportional valves 37a, 37b into the basic position 51b designed as a throttle position and to actuate the proportional valve 36 into the flow position 51a. As a result, the volume flow in front of the proportional valves 37a, 37b is accumulated to such an extent that the pressure in the consumer line 21 increasingly decreases, so that increasingly more pressure medium flows from the free-stroke cylinder 10 to the control valve device 15 via the proportional valve 36 which is opened into the flow position 51a .

The electrically operated proportional valves 36, 37a, 37b of Figure 2 continue to have the function of the line break protection devices 60a, 60b, 60c. If the load-carrying device is not raised or lowered and the proportional valves 36, 37a, 37b are not activated, the proportional valves 36, 37a, 37b are in the basic position 51b, which is designed as a throttle position. This corresponds to the condition of a collapsed line break protection device. In the event of a line break, the lowering speed of the load-carrying means is limited to a permissible value by means of the throttle connection 50 of the proportional valve 36, 37a, 37b which is effective in the basic position 51b.

If a deviation or an error, for example a line break, is detected by the control device 25 during a lifting or lowering process of the load-carrying device, the control device 25 controls the proportional valves 36, 37a, 37b into the basic position 51b designed as a throttle position. This ensures that the lowering speed of the load-carrying means is limited to a permissible value by means of the throttle connection 50 effective in the basic position 51b.

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

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

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

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

In the Figure 3 is analogous to Figure 1 A mechanical line break protection device 60a, 60b is installed on each mast lifting cylinder 11a, 11b. The line break protection device 60a mounted on the mast lifting cylinder 11a comprises a check valve 62a which opens in the direction of the mast lifting cylinder 11a, for example a check valve, and a bypass line 63a with a throttle device 64a arranged in the bypass line 63a. The line break protection device 60b mounted on the mast lifting cylinder 11b comprises a check valve 62b which opens in the direction of the mast lifting cylinder 11b, for example a check valve, and a bypass line 63b with a throttle device 64b arranged in the bypass line 63b.

The electrically actuated proportional valve 36 or 37 of the mast transition damping device 35 has, in the non-controlled state, a throttle connection 50 which causes a throttled volume flow and can be actuated in the direction of a flow position 51a when electrically actuated.

In the Figure 3 the proportional valve 36 or 37 is actuated in the non-controlled state into 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 acting in the basic position 51b, for example a throttle bore. The basic position 51b is therefore designed as a throttle position.

The proportional valve 36 or 37 is each actuated by a spring device 55 into the basic position 51b 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 electronic control device 25 for control purposes.

The hydraulic system 1 of the Figure 3 thus has a mast transition damping device 35 formed by the two electrically operated 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 lift cylinder 10.

The hydraulic system 1 of the Figure 3 works as follows.

To lift the load-carrying device, with the control valve device 15 being actuated into the lifting position 15b, pressure medium is conveyed from the control valve device 15 into the consumer line 21 and the branch lines 30, 31. The proportional valve 36 of the mast transition damping device 35 arranged on the free-lift cylinder 10 is actuated by the control device 25 into the flow position 51a, so that pressure medium flows into the free-lift cylinder 10 via the proportional valve 36 actuated in the flow position 51a and the branch line 30. Due to the area ratio of the free-lift cylinder 10 to the mast-lift cylinders 11a, 11b, no pressure medium initially flows via the check 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 device 25 by means of the sensor device, the electronic control device 25 begins to actuate the proportional valve 36 arranged on the free-lift cylinder 10 into the basic position 51b designed as a throttle position. As a result, the volume flow in front of the proportional valve 36 is accumulated to such an extent that pressure medium flows from the control valve device 15 into the mast lifting cylinders 11a, 11b via the opening check valve 43.

To lower the load-carrying device, with the control valve device 15 being actuated into the lowering position 15c, the control device 25 actuates the proportional valve 37 into the flow position 51a, whereby pressure medium from the mast lifting cylinders 11a, 11b via the opened proportional valve 37 into the consumer line 21 and via the Control valve device 15 actuated in the lowering position 15c flows out to the container 19. Due to the area ratio of the free-lift cylinder 10 to the mast-lift cylinders 11a, 11b, no pressure medium initially flows from the free-lift cylinder 10 and the proportional valve 36, which is in the basic position 51b and is mounted on the free-lift cylinder 10, flows to the control valve device 15. As soon as the mast-lift cylinders 11a, 11b approach the mast transition area, which is recognized by the control device 25 by means of the sensor device, the electronic control device 15 begins to actuate the proportional valve 37 into the basic position 51b designed as a throttle position and to actuate the proportional valve 36 attached to the free-lift cylinder 10 into the flow position 51a. As a result, the volume flow in front of the proportional valves 37 is accumulated to such an extent that the pressure in the consumer line 21 increasingly decreases, so that increasingly more pressure medium flows from the free-stroke cylinder 10 to the control valve device 15 via the proportional valve 36 which is opened into the flow position 51a.

In the Figure 4 is a variant of the Figure 2 shown.

In the Figure 4 the proportional valves 36, 37a, 37b each have a housing 70 in which the corresponding proportional valve 36, 37a, 37b is installed. The proportional valve 36, 37a, 37b is actuated in the non-activated state into a basic position 51b, which is designed as a blocking position. The throttle connection 50 of the proportional valve 36, 37a, 37b is each formed by a bypass line 71 formed in the housing 70 of the corresponding proportional valve 36, 37a, 37b, in which a throttle device 72 is arranged.

The proportional valve 36, 37a, 37b of Figure 4 is actuated by a spring device 55 into the basic position 51b 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 device 25 for control.

From the control device 25 are 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 in the lifting operation of the load-carrying device during the mast transition from the free lift to the mast lift and in the lowering operation of the load-carrying device during the mast transition from the mast lift to the free lift, there is a uniform movement of the load-carrying device without a change in speed or shocks in the Mast transition is achieved.

During lifting operation, the volume flow into the free-lift cylinder 10 in the mast transition area is increasingly throttled by appropriately controlling the proportional valve 36 of the mast transition damping device 35, whereby a continuous decrease in the extension speed of the free-lift cylinder 10 is achieved. The proportional valves 37a, 37b are each actuated into the flow position 51a. The dynamic pressure that increases due to throttling leads to a continuously faster extension of the mast lifting cylinders 11a, 11b. The overlapping movement of the free lift cylinder 10 and the mast lift cylinders 11a, 11b is preferably carried out in such a way that the lifting speed of the load remains constant in the mast transition area.

In lowering operation, the volume flow from the mast lifting cylinders 11a, 11b in the mast transition area is increasingly throttled by appropriately controlling the proportional valves 37a, 37b in the basic position 51b of the mast transition damping device 35, whereby a continuous decrease in the retraction speed of the mast lifting cylinders 11a, 11b is achieved. The proportional valve 36 is actuated into the flow position 51a. The reducing pressure in the consumer line 31 due to throttling leads to a continuously faster retraction of the free-lift cylinder 10. The overlapping movement of the free-lift cylinder 10 and the mast-lift cylinders 11a, 11b is preferably designed in such a way that the lowering speed of the load in the mast transition area remains constant.

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

Claims (13)

Hydraulic system (1) for an industrial truck with a lifting mast, which has at least one extension mast that can be raised and lowered in a stationary mast and a load-carrying device that can be raised and lowered in the extension mast, the hydraulic system having a free-lift cylinder (10) for raising and lowering the load-carrying device and at least a mast lifting cylinder (11a; 11b) for raising and lowering the extension mast, a control valve device (15) being provided for controlling the lifting operation and the lowering operation of the free-lift cylinder (10) and the mast lifting cylinder (11a; 11b), and wherein a mast transition damping device (35) is provided, which comprises at least one electrically operated proportional valve (36; 37; 37a; 37b), characterized in that the proportional valve (36; 37; 37a; 37b) of the mast transition damping device (35) in the non-controlled state has a throttle connection which causes a throttled volume flow (50) and can be actuated in the direction of a flow position (51a) when electrically controlled. Hydraulic system according to claim 1, characterized in that the proportional valve (36; 37; 37a; 37b) is actuated in the non-activated state into a basic position (51b) which is provided with the throttle connection (50). Hydraulic system according to claim 2, characterized in that the proportional valve (36; 37; 37a; 37b) is provided with a throttle opening (52), in particular a throttle bore, in the basic position (51b). Hydraulic system according to claim 1, characterized in that the proportional valve (36; 37; 37a; 37b) is arranged in a housing (70), the proportional valve (36; 37; 37a; 37b) being in a basic position (36; 37; 37a; 37b) when not activated. 51b), which is designed as a blocking position, and the throttle connection (50) is formed by a bypass line (71) formed in the housing (70) of the proportional valve (36; 37; 37a; 37b), in which a throttle device (72) is arranged. Hydraulic system according to one of claims 1 to 4, characterized in that the free-lift cylinder (10) is connected to the control valve device (15) by means of a first branch line (30) and the at least one mast-lift cylinder (11a; 11b) by means of a second branch line (31 ) is connected to the control valve device (15), a first proportional valve (36) of the mast transition damping device (35) being arranged in the first branch line (30) and a second proportional valve (37) of the mast transition damping device (35) being arranged in the second branch line (31). is arranged. Hydraulic system according to claim 5, characterized in that a bypass line (40) is arranged on the first proportional valve (36), in which a check valve (41) opening in the direction of the control valve device (15), in particular a check valve, is arranged. Hydraulic system according to claim 5 or 6, characterized in that a bypass line (42) is arranged on the second proportional valve (37), in which a check valve (43), in particular a check valve (43), which opens in the direction of the at least one mast lifting cylinder (11a; 11b). Check valve is arranged. Hydraulic system according to one of claims 1 to 7, characterized in that a mechanical line break protection device (60a; 60b) is mounted on each mast lifting cylinder (11a; 11b). Hydraulic system according to one of claims 1 to 8, characterized in that a mechanical line break protection device (60c) is installed on the free-lift cylinder (10). Hydraulic system according to claim 9, characterized in that the first proportional valve (36) is mounted on the free-lift cylinder (10) and has the function of an electrical line break protection device (60c). Hydraulic system according to one of claims 1 to 4, characterized in that the free-lift cylinder (10) is connected to the control valve device (15) by means of a first branch line (30) and each mast-lift cylinder (11a; 11b) by means of a branch line (31a; 31b) with the control valve device (15) is connected, with a proportional valve (36; 37a; 37b) of the mast transition damping device (35) being arranged in each branch line (30; 31a; 31b). Hydraulic system according to claim 11, characterized in that a proportional valve (36) is mounted on the free-lift cylinder (10) and/or a proportional valve (37a; 37b) is mounted on each mast lifting cylinder (11a; 11b), the proportional valves (36; 37a; 37b) each have the function of an electrical line break protection device (60a; 60b; 60c). Industrial truck with a hydraulic system (1) according to one of the preceding claims.

Images