DE10154449A1 - Hydraulic lifting device, in particular for battery-powered industrial trucks, and method for controlling it - Google Patents

Abstract

A hydraulic lifting device, in particular for battery-operated industrial trucks, has a pump which can be driven by an electric motor and by means of which, in the lifting operation, at least one hydraulic hood cylinder is supplied with hydraulic oil from a reservoir via a feed line. The hydraulic oil is returned to the reservoir in load-lowering operation from the lifting cylinder via a return flow line while flowing through the pump that drives the electric motor that operates as a generator. To control the hydraulic lifting device, it is provided that at the beginning of the load-lowering operation, essentially the hydraulic pressure prevailing in the lifting cylinder is built up both in the section of the return flow line located upstream of the pump and in the section downstream of the pump, the pump being operated with an ACTUAL Speed is operated, which is below a speed limit. A proportional pressure relief valve arranged in the return flow line downstream of the pump is only fully opened via a ramp function when the actual speed of the pump is above the speed limit, the electric motor then working as a generator.

Description

The invention relates to a method for controlling a hydraulic lifting device especially for battery powered industrial trucks, one by an electric motor has drivable pump, by means of the lifting operation hydraulic oil from at least one hydraulic lifting cylinder fed to a storage container via a feed line is, the hydraulic oil in the load lowering mode from the Lift cylinder via a return flow line flowing through the driving the electric motor working as a generator Pump is returned to the reservoir. About that In addition, the invention relates to a hydraulic Lifting device in particular for performing the method with a pump driven by an electric motor, by means of which in load lifting operation at least one hydraulic Lift cylinder hydraulic oil from a reservoir via a Feed line can be fed, the hydraulic oil in the Load-lowering operation from the lifting cylinder via a return flow line Flow through the electric motor working as a generator driving pump can be returned to the reservoir is.

Such a hydraulic lifting device is often found with electrically powered industrial trucks or Use forklifts where the operability or -The duration depends essentially on the capacity of the battery is dependent. To the operating time of the battery up to its to extend next necessary charging, it is known that is in the system when the load is raised potential energy via a generator that also works as a generator Partly feed the electric motor back into the battery. A hydraulic lifting device with a corresponding Energy recovery is for example in DE 199 21 629 A1 shown, which has an electric motor that a pump drives the hydraulic oil from a load lifting operation Sucks reservoir through a suction valve and to the hydraulic lifting cylinder promotes. In load lowering mode the hydraulic oil from the hydraulic jack through the pump operating in this state as a hydraulic motor, which is a generator or as in this state Generator working electric motor, from which means a suitable, known electrical circuit the associated battery is charged for energy recovery becomes. The speed of the electric motor becomes Regulation of the lifting or lowering speed of the hydraulic Lift cylinder only used when the lift cylinder is adjusted sufficiently quickly or by means of a Sensor device detected a stroke speed predetermined first limit or the lowering speed overwrite the predetermined second limit value. If the Lift cylinder with a relatively low speed is adjusted below the specified limits, as is for example when starting from the rest position as a result the sluggishness and even with a chosen one Creep speed is the case, the speed of the Lift cylinder does not have the speed of the electric motor and therefore the pump, but via the volume or mass flow of the hydraulic oil flowing in the supply or return line changed. For this purpose, the feed line has a Branch line, on the hydraulic oil in the lifting operation can be branched off from the supply line. The branch line opens downstream in the suction-side section of the feed line of the suction valve, so that the branched amount of Hydraulic oil of the pump is supplied again.

At the positioning times of a hydraulic lifting device of a battery-powered industrial truck or the response times within the position search reduce, it makes sense to use the pump when Let the load movement change direction and not as usual off. However, there is the problem that the pump increased at relatively low speeds Cavitation wear is subject. If the pump is a pump with constant displacement, for example one Vane pump, a spindle pump or one Internal gear pump, the other problem does not arise negligible internal leakage. As a result of the inner Leakage is a safe load or a low one Lowering speed cannot be achieved. If you think about it also takes into account that the pump to avoid of excessive damage with a minimum speed must be operated, this leads together with the inner Leakage to an undefined lowering of the load. The Operating conditions also change depending on of the temperature and which changes over time adjusting wear of the pump.

The invention has for its object a hydraulic Lifting device of the type mentioned and a method for their Creating control at which an excessive Wear of the pump and its internal leakage as far as possible are avoided.

This task is carried out with regard to the method Control of a hydraulic lifting device solved in that at the beginning of the load-lowering operation both in the upstream of the Pump located section of the return line as well downstream portion of the return line essentially the hydraulic in the lifting cylinder Pressure is built up, the pump with a ACTUAL speed is operated below one Speed limit is, and that a downstream in the return line Pump arranged proportional pressure relief valve only then essentially via a ramp function is fully opened when the actual speed of the pump is above the speed limit, with the Electric motor then works as a generator.

The invention is based on the basic idea, the inner one To minimize leakage of the pump by using both outputs the pump has the same hydraulic pressure to operate is brought, whereby even when the pump is stopped (zero Speed) excluded the internal leakage and accordingly the internal cavitation wear is avoided. The Fine control or regulation of small Lowering speeds of the load can be achieved by a correspondingly low Pump speed can be reached, which then like a pure volumetric dosing system works. Because the pressure difference Δp on the pump and its flow Q in this state are minimal, only a very small one arises Power consumption. If the actual speed of the pump at Load-lowering operation exceeds the speed limit value, the energy Recovery mode activated, in which the proportional Pressure relief valve, which is downstream of the pump in the Return line is arranged, is fully open and the electric motor works as a generator; Hydromotor working pump is driven.

To make a gentle start when lowering Achieving movement start is a further development of the invention provided that the pressure in the return line at the beginning of the load lowering operation by means of a proportional Pressure control valve, which is arranged upstream of the pump a ramp function on the prevailing in the lifting cylinder hydraulic pressure is brought.

To prevent excessive wear on the pump, this is preferably never below during load lifting operation operated at a predetermined minimum speed. In addition, made sure that the pump in the lifting operation over a pressureless start starts. This is according to the invention achieved in that the pump at the beginning of Load lifting operation the hydraulic oil over a branch line returns to the storage tank without pressure, like the actual Pump speed below the speed limit lies, and that the branch line by means of a valve is closed as soon as the actual speed of the pump is above of the speed limit. At the speed limit it is preferably the specified one Minimum pump speed.

Regarding the hydraulic lifting device, the above said task solved in that a first Pressure transducer is provided, which prevails in the lifting cylinder hydraulic pressure detects that a second pressure sensor is provided, which is the input pressure of the pump detects that in the return line upstream of the pump proportional pressure control valve is arranged that a Control device is provided, by means of which input pressure of the pump by controlling the Pressure control valve depending on the pressure transducers measured pressure values at the prevailing in the lifting cylinder hydraulic pressure is adjustable, and that downstream of the Pump in the return line is proportional Pressure relief valve is arranged, being about the proportional Pressure control valve to raise, hold or lower the load constant speed and direction of rotation of the pump is possible.

Further details and features of the invention and in particular the hydraulic lifting device are from the following description of an embodiment below Reference to the drawing can be seen, the only one Figure is a schematic diagram of an inventive hydraulic lifting device shows.

A hydraulic lifting device 10 shown in the figure comprises a reservoir 11 for hydraulic oil, which is connected to two hydraulic lifting cylinders 12 via a supply line L1 consisting of several sections and subsequent connecting lines L4.1 and L4.2. The information "upstream" and "downstream" used in the following refer to an oil flow from the reservoir 11 to the lifting cylinders 12 , ie in the feed direction for the lifting operation.

The feed line L1 is made up of several line sections. A first section L1.1 leads from the reservoir 11 to a hydraulic pump P which can be driven by means of an electric motor M which, in a manner not shown, draws energy from a battery via a motor control unit. A leakage line L7 (shown in dashed lines) can lead back from the pump P into the reservoir 11 . In the first section L1.1 of the feed line L1, which represents the suction-side section of the pump P, a suction valve NSV, which is designed as a check valve, is arranged, which allows an oil flow in the feed direction, ie from the reservoir 11 to the pump P, and prevents a backflow.

Downstream of the pump P, there is a second section L1.2 of the feed line L1, which leads to a first seat valve SV1, which is adjustable between an open position in which a flow in both directions is possible and a blocking position in which an oil flow in the feed direction, that is to say to the lifting cylinders 12 . The first seat valve SV1 is biased by a spring into the blocking position, which it automatically assumes in the event of a power failure.

Immediately behind the first seat valve SV1 is a first check valve RV1, which only allows an oil flow in the feed direction, ie to the lifting cylinders 12, and prevents a backflow.

From the second section L1.2 of the supply line L1, a pressure line L _DA4 branches off between the pump P and the first seat valve SV1, which leads to a fourth pressure sensor DA4, by means of which the pressure prevailing in the second section L1.2 of the supply line L1 is detected can.

A branch line L6 branches off from the second section L1.2 of the supply line L1 between the pump P and the pressure line L _DA4 , in which a proportional pressure relief valve PDBV is arranged and which opens into the reservoir 11 .

The first seat valve SV1 is followed by a third section L1.3 of the supply line L1, which branches at its downstream end into the two connecting lines L4.1 and L4.2, each of which leads to one of the hydraulic lifting cylinders 12 . A further pressure line L _DA1 branches off from the connecting line L4.2 and leads to a first pressure sensor DA1, by means of which the pressure prevailing in the connecting line L4.2 and thus the load pressure can be detected.

One branches in the third section L1.3 of the feed line L1 Return line L2, which also consists of several Sections L2.1, L2.2 and L2.3 exist. A first section L2.1 the return line L2 leads from the third section L1.3 the supply line L1 to a second seat valve SV2, the between an open position in which a flow in both Directions is possible, and a locking position adjustable is in which an oil flow is blocked in both directions is. The second seat valve SV2 is in by means of a spring the locking position biased.

A second section L2.2 of the return line L2 runs from the second seat valve SV2 to a proportional pressure control valve PDRV. A further pressure line L _DA3 branches off from the second section L2.2 of the return line L2, which leads to a third pressure sensor DA3, by means of which the pressure prevailing in the second section L2.2 of the return line L2 can be detected. A bypass line L5 leads from the proportional pressure control valve PDRV to the second section L1.2 of the supply line L1. The bypass line L5 opens into the second section L1.2 of the supply line L1 between the pressure line L _DA4 and the first seat valve SV1. In addition, a third section L2.3 of the return line L2 leads from the proportional pressure control valve PDRV to the suction-side first section L1.1 of the supply line L1 and opens into this between the suction valve NSV and the pump P. Close to the mouth of the third section L2.3 of the return line L2 in the first section L1.1 of the supply line L1 branches off from the third section L2.3 of the return line L2 a further pressure line L _DA2 , which leads to a pressure sensor DA2, by means of which the prevailing in the vicinity of the inlet of the pump P. Pressure can be detected.

Parallel to the first sections of the return line L2 a bypass line L3 runs at one end together with the first section L2.1 of the return line L2 in the third section L1.3 of the feed line L1 and with their other end in the third section L2.3 of the Return line L2 opens. In the bypass line L3 is a third seat valve SV3 arranged between a Open position in which there is a flow in both directions is possible, and a locking position is adjustable in which is an oil flow in the return direction, d. H. of the third section L1.3 of the feed line L1 to the third Section L2.3 of the return line L2 is prevented. The third seat valve SV3 is in a spring Pre-locked position. Immediately after the third Seat valve SV3 is a second check valve RV2 arranged that a flow in the return direction, d. H. of the third section L1.3 of the feed line L1 to the third Section L2.3 of the return line L2 permits and a Prevents flow in the opposite direction.

The hydraulic oil can flow back from the lifting cylinders 12 into the reservoir 11 via a path which is referred to in its entirety as the return flow line. The return flow line comprises the connecting lines L4.1 and L4.2, part of the third section L1.3 of the supply line L1, the return line L2, the bypass line L3, parts of the first and second sections L1.1 and L1.2 of the supply line L1 including the flow through the pump P and the branch line L6.

The different operating modes of the hydraulic lifting device 10 are explained in detail below.

In load lifting operation, ie for lifting the lifting cylinders 12 , the hydraulic oil from the reservoir 11 must be conveyed through the supply line L1 into the corresponding chambers of the lifting cylinders 12 . Starting from a standstill of the lifting cylinders 12 , the proportional pressure relief valve PDBV in the branch line L6 and the first seat valve SV1 in the feed line L1 are opened, while the second seat valve SV2 and the third seat valve SV3 are closed. The electric motor M is brought to a minimum speed with the pump P via an adjustable ramp function. The hydraulic oil sucked in by the pump P from the reservoir 11 through the suction valve NSV and the first section L1.1 of the supply line L1 and delivered via the further second section L1.2 occurs in this state, that is to say generally for a fraction of a second, on account of the fully open proportional pressure relief valve PDBV completely into the branch line L6 and is discharged without pressure into the reservoir 11 .

Immediately after the pump P is started, the proportional pressure relief valve PDBV and the proportional pressure control valve PDRV are closed, as a result of which the pressure in the supply line L1 increases. If it is determined by means of the pressure sensor DA4 that the pressure in the supply line L1 has reached the load levitation pressure which is determined by means of the pressure sensor DA1, the speed control of the pump P is released and the oil is supplied through the supply line L1 and the connecting lines L4.1 and L4.2 conveyed to the lifting cylinders 12 so that they are raised. The speed determined in this way, at which the speed control is enabled, is saved each time and is permitted as the minimum speed N _min when braking the lifting movement.

When braking the lifting movement, the steps in carried out in reverse order. The speed of the pump P is set to the constant, minimum permitted value Nmin set, which ensure the conditions p (DA4) = p (DA1) must, d. H. the speed must be at least so high that it cover the oil losses while still maintaining the levitation pressure can generate. This ensures that the Pump is not operated in a speed range in which lubrication of the pump is not ensured.

If the desired height position has been missed in the automatic operation of the lifting device or if a user initiates the so-called levitation method (= slow adjustment) via a selection button, the pump P will continue to be operated at a predetermined minimum speed M _V (> N _min ), the seat valve SV2 of the return line L2 opened and the lifting or lowering movement determined via the proportional pressure control valve PDRV. If the command is given to the proportional pressure control valve PDRV via the current supply to generate a pressure greater than the levitation pressure, the load is raised. The oil supply from the pump P to the lifting cylinders 12 via the bypass line L5 and the proportional pressure control valve PDRV is opened and the drainage of the oil from the lifting cylinder 12 into the third section 2.3 of the return line L2 and thus to the suction side of the pump P is at the proportional pressure control valve PDRV closed.

When the proportional pressure regulator valve PDRV is commanded to generate a pressure lower than the load floating pressure, the load is slowly lowered despite the pump P continuing to run. The oil supply from the pump P to the lifting cylinders 12 via the bypass line L5 and the proportional pressure control valve PDRV is closed thereon and the discharge of the oil from the lifting cylinders 12 via the return line L2 to the suction side of the pump P is opened at the proportional pressure control valve PDRV. The remaining amount of oil is fed from the pump P via the branch line L6 and the proportional pressure relief valve PDBV to the reservoir 11 .

If the pressure on the pressure sensor DA3 and the pressure on the pressure sensor DA1 are the same, the load is held in position. Since you go through the state of posture during the transition from lifting to lowering and vice versa, this movement can also be compared to a hovering process. It should be noted that the pressure limiting or pressure regulating valves themselves cannot regulate a volume and the maximum lifting or lowering speed of the lifting cylinders 12 is limited solely by the pump speed.

In the load lowering mode, ie the lowering of the lifting cylinders 12 , the hydraulic oil must be returned from the lifting cylinders 12 to the reservoir 11 . For this purpose, the proportional pressure relief valve PDBV and the proportional pressure control valve PDRV are adjusted slightly below the load levitation pressure detected by the pressure transducer DA1, ie p (DA4) = p (DA3) ≤ p (DA1). The electric motor M is kept regulated at zero speed and the seat valve SV2 is opened. The flow of the proportional pressure control valve PDRV is then reduced via an adjustable ramp. As a result, there is an increase in pressure in the return line L2 and also on the input side of the pump P, which is detected by the pressure sensor DA2. A pressure equalization takes place through the pump P to such an extent that the preset pressure also prevails in the branch line L6 upstream of the proportional pressure relief valve PDBV. As soon as the pressure sensor DA2 has determined the preprogrammed value of the pressure increase, the speed control of the pump is activated and the seat valve SV3 is opened. Since the oil can only flow to the reservoir 11 via the proportional pressure relief valve PDBV preset to the load levitation pressure, the pressure at both pump connections is approximately the same. The pump will thus act like a fine metering device, the internal leakage being zero and small lowering speeds of the lifting cylinders now being able to be regulated via a relatively low speed, since the risk of cavitation wear is excluded.

As soon as the pump reaches the specified minimum speed the pressure on the proportional one Pressure relief valve PDBV via an adjustable ramp function up to its minimum is reduced and the electric motor M starts in Generator operation to work by passing through the pump is driven.

Braking or stopping the lowering movement takes place in according to the reverse order.

Instead of pressure control via the pressure control valve PDRV, a speed control using a fine proportional flow controller for small amounts of oil and high resolution in differential flow methods can also be used for the levitation method. The fine proportional flow controller can open with its one connection between the second seat valve SV2 and the proportional pressure control valve PDRV in the second section L2.2 of the return line L2 and with the other connection to the section of the bypass line located behind the second check valve RV2 and thus facing the pump P. L3 must be connected. The lifting, lowering or hovering of the load can be determined via the difference between the pump delivery quantity Q _P and the discharge quantity Q _PSR via the fine proportional flow controller. If the pump delivery rate Q _{P is} greater than the discharge rate Q _{PSR of} the fine proportional flow controller, the load is raised. If the pump delivery rate Q _{P is} less than the discharge rate Q _{PSR of} the fine proportional flow controller, the load is slowly lowered. If the two quantities Q _P and Q _{PSR are the} same, the load is held in position. The amount of oil can either be regulated using the fine proportional flow controller or varied accordingly using the pump speed.

Claims (5)

1. Method for controlling a hydraulic lifting device, in particular for battery-powered industrial trucks, which has a pump (P) which can be driven by an electric motor (M), by means of which at least one hydraulic lifting cylinder ( 12 ) hydraulic oil from a reservoir ( 11 ) via a feed line (in load lifting operation) L1) is supplied, with the hydraulic oil in load-lowering operation from the lifting cylinder ( 12 ) via a return flow line (L2, L3, L1.2, L6) while flowing through the pump (P) driving the electric motor (M) working as a generator into the reservoir ( 11 ) is returned, characterized in that at the beginning of the load-lowering operation both in the upstream of the pump (P) section (L2.3) of the return flow line and in the downstream section of the pump (P) (L1.2) of the return flow line essentially the hydraulic pressure prevailing in the lifting cylinder ( 12 ) is built up, the pump being operated at an ACTUAL speed, which is below a speed limit value, and that a proportional pressure relief valve (PDBV) arranged in the return flow line downstream of the pump (P) is only essentially fully opened via a ramp function when the actual speed of the pump is above the speed limit value, the electric motor (M) then works as a generator. 2. The method according to claim 1, characterized in that the pressure in the return line at the beginning of the load-lowering operation by means of a proportional pressure control valve (PDRV), which is arranged upstream of the pump (P), via a ramp function on the hydraulic prevailing in the lifting cylinder ( 12 ) Pressure is brought. 3. The method according to claim 1 or 2, characterized in that the pump (P) at the beginning of the lifting operation, the hydraulic oil as long as a branch line (L6) in the reservoir ( 11 ) returns as the actual speed of the pump below the speed - Limit value lies, and that the branch line (L6) is closed by means of a valve (PDBV) as soon as the actual speed of the pump (P) is above the speed limit value. 4. The method according to any one of claims 1 to 3, characterized characterized in that the speed limit of The minimum speed of the pump (P) corresponds. 5. Hydraulic lifting device, in particular for carrying out the method according to one of claims 1 to 4, with a pump (P) which can be driven by an electric motor (M) by means of the at least one hydraulic lifting cylinder ( 12 ) in a load lifting operation, hydraulic oil from a reservoir ( 11 ) via a Feed line (L1) can be supplied, the hydraulic oil in load-lowering operation from the lifting cylinder ( 12 ) via a return flow line (L2, L3, L1.2, L6) while flowing through the pump (P) driving the electric motor (M), which operates as a generator Reservoir ( 11 ) can be returned, characterized in that a first pressure sensor (DA1) is provided which detects the hydraulic pressure prevailing in the lifting cylinder ( 12 ), and that a proportional pressure control valve (PDRV) is arranged in the return flow line upstream of the pump (P) that a second pressure transducer (DA2) is provided which detects the inlet pressure of the pump (P), that a control device Seal is provided, by means of which the input-side pressure of the pump can be adapted to the hydraulic pressure prevailing in the lifting cylinder ( 12 ) by controlling the pressure control valve (PDRV) as a function of the pressure values measured by the pressure transducers (DA1, DA2), and that downstream of the pump (P) a proportional pressure relief valve (PDBV) is arranged in the return flow line.