EP1052215B1 - Hydraulic lifting device - Google Patents

Description

The invention relates to a hydraulic lifting device, in particular for battery-powered industrial trucks, according to the preamble of claim 1.

For vehicles equipped with such a hydraulic lifting device ( DE-A1-4416173 ), are usually electrically driven trucks or forklifts, whose operability or duration of the capacity of the battery is determined. In order to extend the operating time of the battery until the next necessary charging, it is known to re-feed the potential energy in the system when the load is raised via an electric motor also operating as a generator into the battery. A hydraulic lifting device with a corresponding energy recovery points an electric motor that drives a pump that promotes hydraulic oil in a lifting operation from a reservoir to the hydraulic lifting cylinder, wherein the adjusting or lifting speed of the hydraulic lifting cylinder is achieved by controlling the rotational speed of the electric motor. In load-lowering mode, the hydraulic oil is conducted by the hydraulic lifting cylinder through a hydraulic motor, which may also be the pump acting in this state as a hydraulic motor. The hydraulic motor drives a generator or working in this state as a generator electric motor, from which by means of a suitable, known per se electrical circuit for energy recovery, the associated battery is charged. It occurs in the lifting operation, the problem that with only slight changes in position of the lift cylinder or its deliberately slow adjustment (slow speed) of the electric motor and thus the pump are operated at a very low speed, which on the one hand an unfavorable efficiency and on the other hand, a high wear of the pump is connected so that their life is reduced.

The invention has for its object to provide a hydraulic lifting device of the type mentioned, in which excessive wear of the pump is reliably avoided even at low and / or slow change in position of the hydraulic lifting cylinder in load lifting operation.

This object is achieved in a hydraulic lifting device of the type mentioned with the features of claim 1. It is provided that the control device in a known manner has a sensor device for detecting the lifting or lowering speed of the lifting cylinder, wherein the speed of the lifting cylinder by means of the speed of the motor is adjustable when the detected stroke speed exceeds a first limit value or the detected lowering speed exceeds a second limit value, and wherein the speed of the lifting cylinder is controllable when falling below the limit values by means of the hydraulic oil volume flow in the supply and return line.

According to the invention, the rotational speed of the electric motor for regulating the lifting or lowering speed of the hydraulic lifting cylinder is used only when the lifting cylinder is adjusted sufficiently quickly or the lifting speed detected by the sensor device determines a predetermined first limiting value V _HG or the lowering speed a predetermined second limiting value exceed v _SH . The two limits may be the same or different and are preferably on the order of 0.1 m / sec. The limit values should be chosen so that the pump at these limits for the speed of the lifting cylinder has a minimum speed in the order of 500 min ^-1. At this or a higher speed, on the one hand, a sufficiently high efficiency is ensured and in particular an excessive wear of the pump is avoided. If the lifting cylinder is adjusted in the lifting operation at a relatively low speed below the specified limits, as is the case for example when starting from the rest position due to inertia and at a selected crawl speed, the speed of the lifting cylinder is not on the speed of the electric motor and thus the pump, but changed over the volume or mass flow of the hydraulic oil flowing in the supply line.

For this purpose, it is provided that the supply line has a branch line, via which in the lifting operation hydraulic oil from the supply line can be branched off and that in the branch line, a flow control valve is arranged, by means of which the hydraulic cylinder supplied hydraulic oil flow is variable. When lifting a load from the rest position of the electric motor and thus the pump is suddenly brought to a preselected minimum speed of for example 500 min ^-1 and at the same time the flow control valve in the branch line is fully opened. The pump delivers the hydraulic oil from the reservoir in the supply line, wherein a considerable part of the hydraulic oil flows through the branch line with the open flow control valve again. When the flow control valve is now gradually closed, the flow rate of hydraulic oil supplied to the hydraulic cylinder in the supply line increases, whereby the lift cylinder is displaced at an increasing speed. If the adjustment of the lifting cylinder should be slower again, the flow control valve is opened accordingly and thus more hydraulic oil discharged via the branch line from the supply, so that the hydraulic cylinder volume flow supplied to the lifting cylinder decreases. In this way, it is ensured that even at very low and / or very slow lifting movements of the lifting cylinder with speeds below the predetermined limit values, the electric motor or the pump are operated with a sufficient minimum speed. If after a complete closing of the flow control valve and thus the branch line, a further increase in the lifting speed of the lifting cylinder is desired, this is achieved by increasing the speed of the pump.

The detection of the lifting or lowering speed of the lifting cylinder by means of the sensor device directly on the lifting cylinder, either by means of a Wegaufnehmersystems the current actual position of the load or the lifting cylinder detected and calculated from taking into account the timing of the speed or the speed can be tapped directly.

In a development of the invention, provision is made for a flow regulator valve to be arranged in the return line, by means of which the volume flow of the hydraulic oil recirculated from the hydraulic cylinder into the reservoir can be changed. When lowering the lifting cylinder or the load with low lowering speeds, the speed change is achieved solely by changing the flow area of the flow control valve and thus the volume or mass flow of the hydraulic cylinder derived from the lifting cylinder. The hydraulic oil flowing in the return line also flows through a hydraulic motor or the pump acting as a hydraulic motor in this state, the electric motor rotating in idling. If the lowering speed reaches a value above the predetermined limit, the change in the lowering speed can be achieved by controlling the electric motor to a certain speed, whereby a counter-torque is generated, with such a lowering speed ensures that the speed of the pump and thus of the electric motor above the device-specific minimum speed of, for example, 500 min ^-1 . In this case, the conditional by the raised load potential energy of the entire system is converted by the acting as a generator electric motor into electrical energy and supplied to the battery.

Although individual flow control valves may each be provided for the supply line and the return line, in a preferred embodiment of the invention it is provided that the line section of the return line having the flow control valve part simultaneously is the branch line, so that the flow control valve is effective both in raising and lowering the hydraulic lift cylinder in the aforementioned manner.

In load-lowering mode, the hydraulic oil flowing back to the reservoir drives a hydraulic motor. This may be formed independently of the pump, but alternatively it is also possible that the pump operates in load-lowering operation as a hydraulic motor.

Preferably, the line arrangement is provided so that the pump is flowed through in the same direction of the hydraulic oil both in load lifting operation and in the same direction and thus always rotates in the same direction of rotation, wherein it is preferably provided that the electric motor in both operating states in the same Direction turns. In this way, the design effort can be kept low. In addition, due to the same direction of rotation of the motor both in load lifting operation and in load-lowering operation, the reaction times are significantly reduced when changing the direction of movement, whereby a more accurate positioning is possible.

In order to ensure the maintenance of a struck stroke position and to prevent falling of the hydraulic lifting cylinder or the load in case of failure of the system or in case of power failure, a check valve is biased in the return line, which is biased in the blocking position. In case of power failure, the check valve and the flow control valve close automatically and thus prevent that hydraulic oil from the hydraulic cylinder flows back into the reservoir. It is provided in particular that the check valve is disposed near the flow control valve. In case of failure of the engine control during the lowering process, the holding function by the check valve and the flow control valve ensured in two-channel manner.

Further details and features of the invention will become apparent from the following description of an embodiment with reference to the drawing, wherein the single figure shows a circuit diagram of a hydraulic lifting device according to the invention.

A hydraulic lifting device 10 shown in the figure comprises a reservoir 11 for hydraulic oil, which is connected to two hydraulic lifting cylinders 13 via a feed line L1 consisting of several sections L1.1, L1.2 and L1.3. The indications "upstream" and "downstream" used refer to an oil flow from the reservoir 11 to the lifting cylinders 13, i. in the feeding direction for the lifting operation.

In the first section L1.1 of the supply line L1, a first check valve 12 is arranged, which is an oil flow in the feed direction, i. to the lifting cylinders 13 permits and prevents backflow.

Downstream of the first check valve 12, a hydraulic pump P is arranged, which can be driven by means of an electric motor M, which receives energy from a battery, not shown, via a power connection 21. From the pump P leads a leakage line L3 back into the reservoir 11th

Downstream of the pump P, a second section L1.2 of the supply line L1 connects, which leads to a check valve 15 which is adjustable between an open position in which a flow in both directions is possible, and a blocking position, in which only one oil flow in the feed direction, ie to the lifting cylinders 13, possible and a return flow is prevented. The check valve 15 is biased in a mechanical manner, for example by means of a spring in a blocking position, which it automatically assumes in case of power failure.

Between the pump P and the check valve 15, there is arranged a second check valve 14, which also provides only an oil flow in the feed direction, i. to the lifting cylinders 13 permits and prevents backflow.

Connected to the check valve 15 is a third section L1.3 of the supply line L1, which branches at its downstream end into two connecting lines L4.1 and L4.2, which each lead to one of the hydraulic lifting cylinders 13.

In the third section L1.3 of the supply line L1 branches off a discharge line L5, which has a normally closed valve 17 and returns to the reservoir 11.

Between the second check valve 14 and the check valve 15 branches off from the second section L1.2 of the supply line L1 from a branch line L2, in which a flow control valve 16 is arranged and between the first check valve 12 and the pump P in the first section L1.1 the supply line L1 opens.

From the second section L1.2 of the supply line L1 branches off between the pump P and the second check valve 14 from a bypass line L6, in which a pressure relief valve 19 is arranged and which opens into the discharge line L5 between the valve 17 and the reservoir 11. From the bypass line L6 branches a likewise opening into the discharge line L5 bypass line L7, in which a further check valve 18 is arranged. This further check valve 18 is between a Open position in which a flow in both directions is possible, and a blocking position adjustable, in which only a flow from the drain line L5 to the second section L1.2 of the supply line L1 is possible and a flow in the opposite direction is prevented.

The two lifting cylinders 13 are each associated with a sensor device 20 shown only schematically, which detects the current position of the lifting cylinder 13 or the load and a corresponding control signal to a processing unit, in which the lifting or lowering speed of the lifting cylinder is calculated.

• Im Lasthebebetrieb, d.h. zum Anheben der Hubzylinder 13 muß Hydrauliköl aus dem Vorratsbehälter 11 durch die Zuführleitung L1 in die entsprechende Kammer der Hubzylinder 13 gefördert werden. Ausgehend von einem Stillstand der Hubzylinder 13 wird das Stromreglerventil 16 in der Zweigleitung L2 vollständig geöffnet und gleichzeitig wird der Elektromotor M mit der Pumpe P auf eine Mindestdrehzahl von 500 min^-1 gebracht. Das von der Pumpe P aus dem Vorratsbehälter 11 über den ersten Abschnitt L1.1 der Zuführleitung L1 angesaugte und über den weiterführenden zweiten Abschnitt L1.2 geförderte Hydrauliköl wird in diesem Zustand vollständig oder zumindest annähernd vollständig über die Zweigleitung L2 aufgrund des vollständig geöffneten Stromreglerventils 16 in einen stromauf der Pumpe P liegenden Bereich der Zuführleitung L1 zurückgeführt. Anschließend wird das Stromreglerventil 16 allmählich geschlossen, wodurch ein zunehmender Anteil des von der Pumpe P geförderten Volumenstroms an Hydrauliköl durch den dritten Abschnitt L1.3 der Zuführleitung und die Verbindungsleitungen L4.1 und L4.2 zu den Hubzylindern 13 gelangt, wodurch diese zunächst langsam und dann mit zunehmender Geschwindigkeit angehoben werden. Eine Erhöhung der Hubgeschwindigkeit wird durch eine Verringerung des Durchflußquerschnittes des Stromreglerventils 16 und die damit verbundene Erhöhung des Volumenstroms an Hydrauliköl zu den Hubzylindern 13 erreicht. Entsprechend kann die Hubgeschwindigkeit verringert werden, indem der Strömungsquerschnitt des Stromreglerventils vergrößert und somit der Volumenstrom an Hydrauliköl zu den Hubzylindern verringert wird. Die auf diese Weise einzustellende maximale Hubgeschwindigkeit wird bei vollständigem Schließen des Stromreglerventils 16 erreicht. Wenn eine weitere Erhöhung der Hubgeschwindigkeit der Hubzylinder 13 gewünscht ist, kann diese über eine Erhöhung der Drehzahl des Elektromotors M und somit der Pumpe P erreicht werden.

In the following, different modes of operation of the lifting device 10 are explained:

• In lifting operation, ie for lifting the lifting cylinder 13 hydraulic oil must be conveyed from the reservoir 11 through the supply line L1 into the corresponding chamber of the lifting cylinder 13. Starting from a standstill of the lifting cylinder 13, the flow control valve 16 is completely opened in the branch line L2 and at the same time the electric motor M is brought with the pump P to a minimum speed of 500 min ^-1 . The hydraulic oil drawn by the pump P from the reservoir 11 via the first section L1.1 of the supply line L1 and conveyed via the continuing second section L1.2 in this state is completely or at least approximately completely via the branch line L2 due to the fully opened flow control valve 16 returned to a lying upstream of the pump P area of the supply line L1. Subsequently, the flow control valve 16 is gradually closed, whereby an increasing proportion of the pumped by the pump P volume flow of hydraulic oil through the third section of the supply line L1.3 and the connecting lines L4.1 and L4.2 to the lifting cylinders 13, whereby they are initially raised slowly and then with increasing speed. An increase in the lifting speed is achieved by reducing the flow area of the flow control valve 16 and the associated increase in the volume flow of hydraulic oil to the lifting cylinders 13. Accordingly, the stroke speed can be reduced by increasing the flow area of the flow control valve and thus reducing the volume flow of hydraulic oil to the lift cylinders. The maximum stroke speed to be set in this way is achieved when the flow control valve 16 is completely closed. If a further increase in the lifting speed of the lifting cylinder 13 is desired, this can be achieved by increasing the rotational speed of the electric motor M and thus of the pump P.

The change in the lifting speed of the lifting cylinder 13, which takes place either via a control of the flow control valve 16 for the purpose of changing the Durchflußquerschnittes or by driving the Elektromotr for the purpose of changing the speed is carried out as a function of the current stroke speed, which is detected by the sensor devices 20. If the current lifting speed is below a predetermined limit value v _HG , the change in the lifting speed is effected solely by driving the current regulator valve. If the current stroke speed is above the limit v _HG, changing the lifting speed is carried out solely by driving the electric motor M, it being ensured in this state that the rotational speed of the electric motor M is above a minimum speed, for example, 500 min. ¹

In the load lowering operation, ie the lowering of the lifting cylinder 13, the hydraulic oil must be returned from the lifting cylinders in the reservoir 11. For this purpose, the check valve 15 and the flow control valve 16 are opened. The hydraulic oil can then flow from the lifting cylinders 13 via the connecting lines L4.1 and L4.2, the third section L1.3 of the supply line L1 and through the check valve 15 in the branch line L2, wherein it flows through the flow control valve 16 and in the first Section L1.1 of the supply line L1 flows. At a direct backflow into the reservoir 11, the hydraulic oil is prevented by the first check valve 12. The hydraulic oil then flows through the pump P, which can operate as a hydraulic motor in this state, and enters the bypass line L6 and from there via the bypass line L7 and the opened further shut-off valve 18 into the supply line 11 leading to the reservoir 11 L5. At low lowering speeds of the lifting cylinder 13, which are detected by the sensor devices 20, the return flow of the hydraulic oil is achieved solely by driving the flow control valve 16 in the branch line L2. The electric motor, which is driven by acting as a hydraulic motor, by the hydraulic oil in the same direction as in the lifting operation flowed through pump P, thereby operates at idle, so that the hydraulic oil is introduced without pressure into the reservoir 11. A change in the lowering speed can be achieved by changing the flow area of the flow control valve 16. Upon complete opening of the flow regulating valve 16, the pump P and the motor M to rotate at a speed corresponding to the minimum speed, for example 500 min. ¹ The associated lowering speed of the lifting cylinder 13 corresponds to the limit v _SG .

If a greater lowering speed is desired, the change is made by controlling the speed of the electric motor M for generating a counter-torque, wherein the pump P flowing through and driving hydraulic oil drives the acting as a generator in this state electric motor, wherein an excess of energy is removed at the electric motor M and fed via the power connector, 21 in the battery.

Claims (8)

1. A hydraulic lifting device, in particular for battery-driven fork lift trucks, with a pump (P) that can be driven by an electric motor (M), by means of which pump hydraulic oil can be supplied from a storage tank (11) via a feed pipe (L1, L4.1, L4.2) in the load lifting operation to at least one hydraulic lifting cylinder (13), wherein the hydraulic oil can, during the load lowering operation, be returned to the storage tank (11) from the lifting cylinder (13) via a return pipe (L4.1, L4.2, L1.3, L2, L1.1, L1.2, L6, L7, L5) flowing through a hydraulic motor (P) driving the electric motor (M) operating as a generator, and with a control device for varying the lifting and lowering speed of the lifting cylinder (13), wherein the control device has a sensor device (20) for recording the lifting and lowering speed of the lifting cylinder 13, wherein the speed of the lifting cylinder (13) can be regulated by means of the speed of the motor (M) when the recorded lifting speed exceeds a first limit value v_HG or the recorded lowering speed exceeds a second limit value v_SG, and wherein the speed of the lifting cylinder (13) can be regulated by means of the volumetric hydraulic oil flows in the feed and return pipes when it drops below the limit values, characterised in that the feed pipe has a branch pipe (L2) via which, during the load lifting operation, hydraulic oil can be branched off from the feed pipe, and in that a flow control valve (16) is arranged in the branch pipe, by means of which valve the volumetric hydraulic oil flow fed to the hydraulic cylinder (13) can be varied.
2. The lifting device according to Claim 1, characterised in that a flow control valve (16) is arranged in the return pipe, by means of which valve the volume flow of the hydraulic oil returned from the hydraulic cylinder (13) to the storage tank (11) can be varied.
3. The lifting device according to Claim 2, characterised in that the pipe section (L2) of the return pipe having the flow control valve (16) is at the same time part of the branch pipe.
4. The lifting device according to any one of Claims 1 to 3, characterised in that the pump (P) operates as a hydraulic motor in the load lowering region.
5. The lifting device according to any one of Claims 1 to 4, characterised in that the hydraulic oil flows through the pump (P) in the same direction both in the load lifting and load lowering operations.
6. The lifting device according to any one of Claims 1 to 5, characterised in that the electric motor (M) rotates ion the same direction both ion the load lifting region and in the load lowering operation.
7. The lifting device according to any one of Claims 1 to 6, characterised in that a shutoff valve (15) preloaded into the shutoff position is arranged in the return pipe.
8. The lifting device according to Claim 7, characterised in that the shutoff valve (15) is arranged close to the flow control valve (16).

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