EP1331199B1 - Control system, especially for use in hydraulic lifting devices - Google Patents

Abstract

The control device includes a pressure scale (32) connected to the return line (26) of a hydraulic hoisting mechanism (10). An unblocking mechanism (44) moves the pressure scale to a control position during the lowering of a load to allow the controlled flow of fluid through the return line, or to the blocking position to block the fluid flow through the return line during the failure of a throttle valve.

Description

The invention relates to a control device, in particular for use in hydraulically operated lifting devices for raising and lowering loads, with a connected to a return line of the lifting device, electrically controllable throttle valve and a pressure compensator, which is provided with at least one blocking and a control position and which cooperates with an unlocking device.

A pertinent hydraulic control device is known from DE 44 23 644 C2. The known hydraulic control device is intended for use in the area of lifting devices, in particular for lifting masts of forklifts, having a feed pump connected to a reservoir for hydraulic fluid as a pressure supply and connected to a return line control piston which acts as a pressure compensator, and in which the return line is connected to the reservoir. The control piston has an inlet which is connected in the conveying direction of the pump behind a check valve to a pump connecting to the lifting conveyor line and which is connected via a control line to a connecting line between the pump and the check valve, that the control piston is formed in the lowering direction as a discharge pressure balance and in the stroke direction as a circulation pressure balance. The control piston is loaded by a spring to the opposing acting a biasing spring is arranged, which is taken over its spring force interconnection of a control piston as an open pressure balance on the one hand in the idle state without external action a passage position, and as a closed pressure balance on the other is taken in the resting state without external action, a blocking position, pretends. The control arrangement is designed in the lowering direction of the lifting device as a two-way - current regulator and in the stroke direction as a three-way current regulator. For a switching of the control piston from the function as a discharge pressure balance in the function as a circulation pressure balance, an evaluation of a pressure difference in the region of the check valve is made. Furthermore, a metering orifice designed as a throttle valve is arranged between the control piston and the lifting device, and the throttle valve itself forms a two-way valve.

High demands are placed on the lowering function of forklift trucks today. Thus, in addition to the so-called. "Stacker leaks" a load-independent limitation of the maximum speed, high sinking speeds are possible even with an empty fork and a sensitive metering of the lowering speed itself. The lowering function in modern trucks is often used as a seat valve with a constant opening behavior and series-connected constant Volumetric flow controller or designed as a slide valve with discharge pressure compensator, wherein seat and slide valve are increasingly electrically proportional actuated.

In these electrically operated systems, the standard EN 1175, Part 1 or 2 (Safety of industrial trucks-Electrical requirements, General requirements for industrial trucks with battery electric Drive or internal combustion engine) that in the event of an error, the load movement can be stopped anyway.

An obvious way to meet this requirement would be to use an additional series-connected valve; However, this would significantly reduce the lowering speed with empty fork, which is not wanted.

If in the above-mentioned known hydraulic control device according to DE 44 23 644 C2 a lowering of the load carried out, the discharge pressure balance is held in its open position and the return line establishes a fluid-conducting connection between the lifting device and the fluid reservoir in the form of the tank. Although then a blocking or switching unit is connected in front of the pressure balance in the return line. However, if there is a failure during the lowering operation in the associated locking unit, for example in the form of an escapement, the fluid-carrying path is essentially switched through to a throttle point and, in particular, a lifting device under load can unintentionally move downwards, which entails considerable security risks , so that the standard EN 1175-1 and 2 is not met in the known solution.

From DE 196 22 763 A1 a valve arrangement is known, in whose housing a spring-loaded in the closing direction valve body is arranged. The pertinent valve body controls the flow through a fluid channel whose input can be connected to a constant-displacement pump and whose outlet can be connected to a tank. On the not acted upon by the pump pressure side of the valve body is a control chamber. Between the fluid channel and the control chamber, a throttle is arranged. A switching valve connects in its rest position the control chamber with the Tank and interrupts this connection in his working position. A switchable abutment for the spring increases in the working position of the switching valve, the bias of the spring relative to the rest position of the valve. To simplify the valve arrangement, the valve body and the slide of the switching valve are arranged in a common bore, wherein a spring is guided between the valve body and the slide. The slide of the switching valve is used at least at interrupted connection between the control chamber and the tank as an abutment for the spring. In the pertinent embodiment, the valve assembly, in particular as a relief valve for a supplied by a constant pump consumer used, for example in the form of a conventional forklift, the known hydraulic valve assembly in addition to an operating state "hold" for the fork, the operating conditions "lifting slowly" and "Lifting fast", as well as "lowering slowly" and "lowering fast" allows. Although high lowering speeds for an empty fork are possible with this known solution, it can also come here during the lowering of the associated locking unit to a failure, for example in the form of an inhibition, with the disadvantage already described, that in particular a standing under load lifting device (fork ) can move unintentionally downwards, which leads to considerable security risks.
Based on this prior art, the invention has the object, while maintaining the advantages of the known solution, namely to provide a compact constructive control device at low manufacturing costs available, which allows a high lowering speed with empty fork in normal operation, so to further improve in that even in the event of an accident, the safety is significantly increased and there can not be an undesired lowering of the lifting device with or without load. This object is achieved by a hydraulic control device with the features of claim 1 in its entirety.

Characterized in that according to the characterizing part of claim 1, the pressure balance in its normal position, the return line blocks that by controlling the unblocking the pressure compensator when lowering the load assumes its control position and dass.bei a failure of the throttle valve by means of the unbolting the pressure compensator in its locked position brought is or in case of failure of the pressure balance, the throttle valve assumes its blocking position, the actual load holding function by two series-connected closed hydraulic actuators, which are individually controlled electrically realized. As a result, both a hydraulic and an electrical redundancy of the load-holding function is given. Due to the redundant arrangement, the lowering movement is stopped automatically and safely even if one of the two electric or one of the two hydraulic actuators of pressure compensator and throttle valve fails.

The throttle valve is closed in the normal position and is electrically driven preferably via a proportional pressure control valve. The pressure compensator is designed as a discharge pressure balance so that it also remains closed in the normal position and occupies the open control position only when pressing the lowering function. The pressure compensator piston is held in the normal position by a spring in the blocking position. Only by controlling an unblocking device via a directional control valve with pending lowering signal is the unlocking of the piston and the pressure compensator can regulate. If, for example, the piston of the throttle valve then remains in the open position in the event of an error after switching off the lowering signal, the load movement is stopped by closing the pressure compensator (fail-safe position). Since in the control device according to the invention can be dispensed with an additional series-connected valve, on the one hand, the solution according to the invention can be implemented inexpensively and, secondly, the lowering speed when lowering without load is not unnecessarily reduced by an additional flow resistance.

With the redundant safety concept, the standard EN 1175 Part 1 or 2 is then met, and in the event of a fault, the load movement can be stopped in any case.

In a preferred embodiment of the control device according to the invention, the unblocking device is a Entsperrzylinder with an energy storage, preferably in the form of a compression spring, which seeks to keep the pressure balance in its locked position, wherein a pressure supply via a switch-engageable counteracts with its fluid pressure of the pertinent force direction of the unlocking. The unlocking device is thus able to push the pressure compensator in the direction of its blocking position via its force accumulator and to hold it securely in this blocking position. Preferably, the Entsperrzylinder and the pressure compensator are mechanically coupled to each other via an actuating piston of the unlocking cylinder.

In a further preferred embodiment of the control device according to the invention, a control line is connected to the return line between the lifting device and the throttle, which passes the pending hydraulic pressure as a control signal to the pressure compensator, wherein by means of a tap line of the upcoming hydraulic pressure between the throttle valve and pressure compensator as another control signal the opposite Direction of action is passed to the pressure compensator. As a result, a current control function is achieved.

Fig.1

in der Art eines Schaltplanes die wesentlichen Komponenten für eine Senkfunktion bei einer Hubvorrichtung mit Lastkompensation und redundant wirkender Sicherheitseinrichtung;

Fig.2,3,4 und 5

einen Ventilblock mit den relevanten Ventilkomponenten zur Realisierung einer Schaltvorrichtung nach der Fig.1, und zwar in Normalstellung, Regelstellung, Fail-Safe-Stellung sowie beim Senken ohne Last.

In the following the control device according to the invention will be explained in more detail with reference to the drawing. This show in principle and not to scale representation of the

Fig.1

in the form of a circuit diagram, the essential components for a lowering function in a lifting device with load compensation and redundant safety device;

Fig.2,3,4 and 5

a valve block with the relevant valve components for the realization of a switching device according to the Fig.1, in normal position, control position, fail-safe position and when lowering without load.

1 shows in the manner of a circuit diagram an embodiment of the hydraulic control device, wherein the structural components shown there are shown only insofar as they relate to the lowering function for a hydraulically operating lifting device 10 with a load compensation and a redundant safety switching device. The lifting device 10 is constructed in the manner of a hydraulic working cylinder with a working piston 12 and an actuating rod 14. The actuating rod 14 is connected at its one free end to the working piston 12 and at its other free end with a load receiving device 16, for example, with a piece goods 18 is loaded as a load. Furthermore, the working piston 12 within the cylinder housing divides this into a piston chamber 20 and a rod space 22. The lifting device 10 is intended represent a mast from a forklift truck; However, it could well consist of a hydraulically operated Aufzugeinrichtung od. Like. Exist, with several lifting devices 10 in apparent successive series or series arrangement could trigger one or more lifting operations (not shown).

Between the lifting device 10 and a fluid reservoir 24 (tank), a valve block designated as a whole by 28 is connected in a return line 26. The valve block 28 in this case has a connection A for the connection of the lifting device 10 and a connection T for the connection of the fluid reservoir 24. Furthermore, the valve control block 28 has a connection point P for pressure supply, for example in the form of a hydraulic pump 30, the with its suction side to the fluid reservoir 24 is also connected. The pressure supply could also be done internally via the hydraulic circuit of the forklift.

The valve block 28 has a connected to the return line 26 pressure compensator 32, which is also referred to with discharge pressure balance on. The pressure compensator 32 is shown in its unactuated normal position 34 in FIG. 1, in which it blocks the return line 26 from the fluid reservoir 24. In addition to this normal or blocking position 34, the pressure compensator 32 has a control position 36 with throttle function. On its one side actuation with pressure control spring 40, the pressure compensator 32 is connected to a tap line 42 which is connected in the return line 26 between the throttle and pressure compensator 32. The pressure compensator 32 cooperates with an unlocking device 44, which is constructed in the manner of an unlocking cylinder with a piston rod part 46, which via an energy store 48 in the form of a compression spring, the pressure compensator 32 in its normal or to keep blocking position 34. The energy accumulator 48 is arranged in the piston chamber 50, in particular in the form of a piston ring space, the unlocking cylinder and the rod annulus 52 of the unlocking cylinder is connected via a fluid-conducting connection line 54 to the output X of a switching device 56 in the form of a custom-built 3/2-way valve. Furthermore, the switching device 56 is connected via the terminal P to the pressure supply 30. According to the illustration of Figure 1, the switching device 56 is shown in its blocking the connection of connecting line 54 with the pressure supply 30, wherein in the pertinent blocking position, the connecting line 54 is connected via the drain line 58 to the return line 26 and thus to the fluid Storage container 24.

Furthermore, in the return line 26 between the lifting device 10 and pressure compensator 32, a throttle valve 60 is connected, which consists of a 2/2-way proportional slide valve with a pilot unit 62 which is permanently connected via a direct connection 64 to the pressure supply 30. 1, the pilot unit 62, which is formed in the manner of a proportional pressure regulating valve, is connected to the fluid reservoir 24, and on its output side Y, the pilot unit 62 is in driving connection with the operating side of the throttle valve 60 In the normal position of the control device shown in Figures 1 and 2, therefore, the pressure compensator 32 is held in its locked position, which is ensured at no pressure in the line 54 that the unlocking device 44 brings the pressure compensator 32 in its locked position. When the connecting line 54 is held without pressure, the energy storage 48 can relax and pushes the piston rod part 46 with the result that the pressure compensator 32 reaches the normal or blocking position 34. The existing residual stress the energy storage 48 is sufficient in any case, reliable in any operating situation to bring the pressure compensator piston 68 in its blocking position. Thus, a first safety step is already fulfilled and so ensured that in case of failure not accidentally the pressure compensator 32 remains in its open position 38 or control position 36.

Between the lifting device 10 and the throttle valve 60, a control line 66 is connected to the connection point Z, which passes on the pending hydraulic pressure as a control signal to the pressure compensator 32. If the throttle valve 60 remains in its closed position shown in FIG. 1, the volume flow displaced from the piston chamber 20 when the load 18 is lowered would be picked up at the connection point Z and passed on to the control line 66, which then acts in the same effective direction as the energy store 48 would then seek to hold the pressure compensator 32 in its blocking position 34 or to bring it to.

The individual switching and valve functions for the lowering function according to FIG. 1 will now be explained in greater detail below with reference to FIG. In this case, the same components, as they are reproduced in the circuit diagram in Figure 1, reproduced in Fig.2ff with the same reference numerals. The statements made so far also apply to the following representations.

FIG. 2 firstly shows the normal position of the lowering function, as represented in the circuit diagram in FIG. The discharge pressure compensator 32 is shown in its normal or blocking position 34, in which the tank connection T is decoupled from the return line 26. The unlocking device 44 is with its piston rod part 46 in abutment with the control piston 68 of the Pressure compensator 32 and the energy storage in the form of the compression spring 48 is relaxed to a predeterminable residual stress. The throttle valve 60 with the Wegeschieberkolben 70 is in operative connection with the pilot unit 61, wherein the terminal A is separated via the return line 26 from the tank port T.

If now the pressure compensator 32 occupy their control position 36 shown in FIG. 2, a lowering signal is given via a corresponding actuating device, such as a joy stick (not shown), and the switching device 56 is activated simultaneously and automatically, the pressure supply 30 being pressurized during operation is connected to the connecting line 54. The fluid pressure of the pressure supply 30 then penetrates into the rod annulus 52 of the unlocking device 44 and pushes the piston rod part 46 in the direction of the Fig.1 seen to the right against the action of the energy storage 48 in the corresponding housing parts. But then comes the control position 36 of the pressure compensator 32 in the fluid-conducting connection position between the piston chamber 20 and the fluid reservoir 24 via the return line 26. In the direct connection 64 for actuating the pilot control unit 62 (proportional pressure control valve) such a pressure exists in that the further pilot control unit 61 can be actuated and the directional spool piston 70, viewed in the direction of view of FIGS. 2 and 3, is moved out of its position closing the return line 26 into the throttle position 72. In the pertinent switching position of Figure 3 is then a continuous, uniform lowering of the load receiving device 16 under the load 18. Depending on the load situation, the pending lowering is automatically nachregelbar by itself, so that regardless of the load 18 is a substantially constant lowering speed can be maintained depending on manual specification. The lowering speed is then independent of the load 18 only dependent on the throttle position of the way spool 70.

If a fault would now occur, the load device 16 could be lowered in an uncontrolled manner with its load 18 in the control position according to FIG. However, if the switching device 56 is no longer activated, this assumes their blocking position shown in Figure 1 and the connecting line 54 to the unlocking device 44 is held without pressure. In this case, in turn pushes the energy storage 48, the piston rod unit 46 and brings the pressure compensator 32 in its normal or blocking position 34. Should this lead to a malfunction, for example, the switching device 56 should remain in its switched-position or the pressure compensator 32 is an inhibition have, then still a shutdown via the throttle valve 60 is possible, which would assume its blocking position 63 shown in Figure 1 under the influence of its actuating spring. If there is a malfunction in the region of the throttle valve 60, for example in the form of an escapement, the pressure compensator 32 is in any case able, via its mechanical unlocking cylinder unit 44, to interrupt the lowering function directly. The pertinent interruption position is shown in Figure 4, in which the control piston 68, the connection between the return line 26 and junction T to the fluid reservoir 24 safely interrupts.

If the pressure compensator 32, as shown in Figure 5, spent in a position "lowering without load", both the control piston 68 and the directional spool 70 is connected in an open passage position or in a throttle position, so that such to achieve a fast lowering function controlled. This takes place automatically when the load pressure is less than the control pressure.

The current controller according to the invention with redundant stop function (Fail-Safe) thus allows a load-independent specification of the speed and a high lowering speed even when the fork is empty and at the same time sensitively metering the lowering speed.

Claims (7)

1. Control device, especially for use with hydraulic lifting means (10) for the lifting and lowering of loads, with an electrically controllable throttle valve (60) that can be connected with a return line (26) of the lifting means (10) as well as with pressure scales (32), equipped with at least one blocking (34) and one control position (36) and co-operating with an unblocking means (44), whereby the pressure scales (32) block the return line (26) in their normal position, characterised in that the pressure scales (32) take up their control position during the lowering of the load by controlling the unblocking means (44), and in that the pressure scales (32) can be moved into their blocking position (34) by means of the unblocking unit (44) when the throttle valve (60) fails, and in that the throttle valve (60) takes up its blocked position (63) during a failure of the pressure scales (32), so that the lowering movement is safely and automatically stopped even when one of the two electric, or one of the two hydraulic members of the pressure scales and the throttle valve fails.
2. Control device according to Claim 1, characterised in that the unblocking means (44) takes the form of an unblocking cylinder with an energy store (48), preferably in the form of a pressure spring that attempts to hold the pressure scales (32) in their blocked position (34), and in that a pressure supply can be switched on via an additional switching means (56) and acts against the said force direction of the unblocking means (44) with its fluid pressure.
3. Control device according to Claim 2, characterised in that the unblocking cylinder and the pressure scales (32) are mechanically coupled with each other via an activating piston (46) of the unblocking cylinder.
4. Control device according to Claim 2 or 3, characterised in that the additional switching means (56) consists of a 3/2-way valve.
5. Control device according to one of the Claims 1 to 4, characterised in that the throttle valve (60) can be controlled and evenly adjusted via a proportional pressure regulating valve (62), the same being permanently connected to a pressure supply via a direct connection (64).
6. Control device according to one of the Claims 1 to 5, characterised in that a control line (66) is connected to the return line (26) between the lifting means (10) and the throttle valve (60), the same transmitting the incoming hydraulic pressure in the form of a control signal to the pressure scales (32), and in that the incoming hydraulic pressure between the throttle valve (60) and the pressure scales (32) is transmitted to the pressure scales (32) via a take-off line (42) in the form of an additional control signal with opposite effect.
7. Control device according to Claim 5, characterised in that the pressure scales (32), the unblocking means (44), the throttle valve (60), and the pressure regulating valve (62) take the form of one single construction component in the form of a valve block (26).

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