DE2057457A1 - Electro-hydraulic drive - Google Patents

Description

The invention is concerned with electro-hydraulic drives with a hydraulic control circuit, which one with a Motor, preferably a hydraulic motor with generally fixed cylinder capacity, connected pump with variable delivery rate having, wherein the changes in the cylinder content can be controlled by incoming signals via an input circuit.

The variable delivery rate of the pump - or better, its cylinder hold - Is controlled by means of an auxiliary actuator, which is in turn controlled by a servo valve, the electromagnetic coil of which is controlled by an electronic amplifier, usually a transistor amplifier.

There are generally several at the input of this amplifier Tensions on. In the event that it is a speed

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control, the voltages are usually provided by a control signal and one roughly proportional to the speed Voltage generated when the variable displacement pump rotates at approximately constant speed.

But there are also known devices in which a feedback signal comes from a tachometer generator driven by the hydraulic motor.

In the case of position control, a synchro-comparator is generally attached to the hydraulic motor and that of The voltage supplied to it with the control or target voltage. The error signal determined in this way is then fed to the amplifier.

Such an arrangement works in a satisfactory manner with the exception of the case that the moment of resistance of the hydraulic motor has just exceeded the value for which the entire arrangement was intended. To remedy this deficiency, was already proposed to install a valve, preferably with double security, which serve as a bypass for the motor can when the pressure difference reaches the critical value.

This system, which makes it possible to avoid excess pressures, has two points Defects on;

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The first iat to see that in the event of one being too long continuous work (the load is too high for the hydraulic motor, for example) in the pump and the bypass circuit The oil contained is heated, so that there is a risk that it ignites and parts of the essential for the function Pump destroyed. The second deficiency is in the loss of energy that occurs to see. This requires the use of a drive motor for the pump, which is more powerful than it would be necessary if one could regulate the delivery rate of the pump at any moment in such a way that never the dangerous or critical pressure is exceeded.

With the invention, which deals with this problem for the first time, an elegant and safe solution is found Proposed problem, which is that the input circuit is acted upon with a feedback signal, which proportional to one derived from the hydraulic control circuit Pressure is. According to a preferred embodiment it is provided that in each line of the hydraulic control circuit a transmitter, preferably a threshold transmitter, is switched on, which converts the pressure changes into electrical voltage changes, which are used as the input circuit for the changes of the cylinder content are fed back in such a circuit that the cylinder

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content-determining variable, for example the angle oc, with respect to its absolute value decreases when the pressure in one of the lines exceeds a predetermined value.

Briefly speaking, the invention can thus be seen in the fact that it involves the application of a feedback or reaction, which is proportional to the pressure, is to limit the control output.

This facility can be conveniently improved if the electric drive motor of the pump is calculated as precisely as possible.

Under these conditions it is necessary for the maximum pressure to decrease while the flow rate increases, since the output of the pump is proportional to PxQ (pressure multiplied by the flow rate), which means that the product P χ cylinder content, i.e. P- oc , is kept constant by feeding this product in a feedback circuit or as a counter variable to the input of the amplifier in such a way that the speed decreases when P-oiden exceeds the critical value.

The invention can be practiced in other ways, for example when the variable cylinder capacity pump is driven by an electric motor.

ORJGINAL INSPECTED 109829 / 1Π37

An electric motor powered by direct or alternating current can be, has the characteristic property that it is variable as a function of the torque output Absorbs current strength, and it is generally known the current strength, which must not be exceeded.

One can therefore use the absorbed current intensity as a controlled variable use which is equivalent to the pressure used in the aforementioned embodiment, with the aim of increasing the speed of the hydraulic motor when the critical current is exceeded.

Further features, details and advantages of the invention emerge from the following description of preferred embodiments management examples based on the drawing. Here i

1 shows a circuit diagram of a first embodiment of a drive according to the invention;

Pig. FIG. 2 shows a circuit diagram which is improved compared to FIG Embodiment;

3 shows a scheme for a second implementation option the idea of the invention;

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FIG. 4 shows a modification of the embodiment according to FIG Use of direct current and

Fig. 5 shows a further embodiment, which is intended for the case is that the pump does not only rotate in one direction.

In the diagram of FIG. 1, 1 denotes the hydraulic motor and 2 denotes the pump with variable cylinder content. the Control of the cylinder content is indicated symbolically by the lever 3, which has an angle c < with a starting position. includes. The movements of the lever 3 are controlled by the double servomotor 4, which in turn is controlled via a servo valve 5. The coil 6 of this electric valve 5 is over an electronic amplifier 7 is fed.

) l The control voltages arriving at 8 and the feedback voltages or signals arriving at 10 and 20 are fed to the amplifier 7 via the line 8 ¹ . The position of the lever 3 is sensed via the potentiometer 9 and the voltage obtained at 10 is fed back to the input side of the amplifier 7.

To each of the lines 12 and 13, which form the circuit in which the hydraulic motor 1 and the pump 2 are switched on,

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is one of the two transmitters or sensors 14 and 15 »at which are preferably threshold transducers connected. These donors are not described in detail, as they are well known. These transmitters 14 and 15 each supply a voltage via the potentiometers 16 and 17, which acts as a feedback signal via lines 18 and 19 at 20 to the input side of the amplifier 7 "is performed".

With a bypass valve is referred to, which works, if the pressure difference between lines 12 and 13 is critical Assumes value.

From the above description it can be seen that the control signals arriving via the line 8 are superimposed by two counter signals, one of which, supplied at 20, is proportional to the pressure, while the other, supplied at 10, corresponds to the speed. ^{A network or electrical pilter 18 1} or 19 'is provided in each of the lines 18 and 19, which are principally RC circuits which are intended to improve the quality of the suppression of the servomechanism. Such filters are nowadays generally part of the state of the art in such devices.

The scheme of Figure 2 is essentially the same as that of the figure

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1 match. However, it is completed by a second potentiometer 22, the movable arm 23 of which is common with the arm 3 is moved. The potentiometer 22 is supplied with a voltage via a branch of the line 18 and consequently which is proportional to the pressure. The potentiometer 22 will thus supply a voltage which is proportional to the product P'Oc, which is given at 24 via line 25 to the input of the amplifier.

A device 26 responding to a specific threshold value is provided in line 25, this threshold value corresponds to the critical product P-α. This device 26 is followed by a filter amplifier 27. In each of the Lines 18 and 19 is also a device 28 or 29 that responds to a threshold value, possibly with one Amplifier and filter, switched on, each device being followed by an amplifier 30 and 31, respectively.

In the embodiment according to FIG. 3, it is assumed that the hydraulic motor only rotates in one direction. It is only the pump operating with a variable delivery rate and its electric drive motor 32 are shown. The motor 32 is fed with three-phase electricity, for example drawn from the network. In one of the phases 33 there is a current transformer and a limiter 35 is provided, which the desired amperage

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adjusts and an amplifier 36 in front of the input to the main amplifier 37 is connected downstream.

A possibly provided phase rectifier or demodulator modulator is dotted, depending on the type of control selected signal with filter or limiter 38 ". The control signal arrives at 38. At 39, the input circuit the signal supplied by the amplifier 36 is supplied in the opposite connection. The amplifier 37 corresponds to the amplifier 7 according to FIG 1. The servo valve connected downstream of the amplifier 37 is denoted by 40. The entire part of the assembly that goes to the servovalve . 40 is connected downstream is not shown. He is according to the part Figure 1 is identical, which supplies the variable proportional to the angle α, the counter or feedback variable at 41 is supplied to the input side of the amplifier 37.

In the embodiment according to FIG. 4, the motor 32 according to FIG. 3 is replaced by a direct current motor 42. In this case it is not possible to use a current transformer that satisfactorily converts the various currents (power and signals). This separation can, however, by means of an amplifier 43 with a floating mass or one Modulator 44 'or further by means of a photocell or other equivalent device. At 44 it is again denotes a device responsive to a threshold value. Otherwise the execution example differs

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of FIG. 4 not that of FIG. 3.

When the rotation of the pump and accordingly the one driving it Motor takes place in two opposite directions, the embodiments according to Figures 3 and 4 are not sufficient, since the resulting reduction in speed in one direction of rotation does not also occur in the other direction of rotation, "Instead, an increase in speed is to be expected there, which corresponds exactly to the opposite of the desired effect.

In Figure 5, a possible modification of the embodiments of Figures 3 and 4 is now shown, which a new mode of operation enables, in particular eliminates the difficulties mentioned above.

In FIG. 5, the filter amplifier 36 of FIG. 3 is again shown as the limiter 35, the part in front of the limiter 35 not being changed. Behind the amplifier 36, the line through which arrives the signal of acoustic feedback or counter, a switching or polarity reversal is divided into two arms 45,46, so that thanks to the electrical switchover ^Λ ters A <possible. The changeover switch 47 is in the position shown when it is positive, in the other position when it is negative. The switchover can easily be achieved if one or two electrical contacts (not shown) are switched on in the line serving for the return of the signal corresponding to the angle at 41

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are energized via the one or more coils of the relay 47 can be. But it is also possible to construct the changeover switch 47 by means of semiconductors.

At the output of the amplifier 56 is a device schematically at 48 shown, which is intended to limit the size of the counteraction or counter-tension. This facility can, for example, from a Zener diode. Or another be formed equivalent element, which is able to limit the amplitude of the counter voltage, so that, if too great a current surge occurs, the speed does not reverse too quickly, and that as a result the entire Arrangement does not come to oscillate around the speed 0.

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Claims (7)

20S7457 claims 1.} Electro-hydraulic drive with a hydraulic control circuit, which has a variable flow rate pump connected to a motor, the changes in the cylinder content being caused by signals arriving via an input circuit are controllable, characterized in that the input circuit has a feedback signal applied to it, which is proportional to a pressure derived from the hydraulic control circuit. 2. Drive according to claim 1, characterized in that a transmitter in each line of the hydraulic control circuit preferably a threshold value transmitter is switched on, which converts the pressure changes into electrical voltage changes, which to the input circuit for the signals controlling the changes in the cylinder content in such a Circuit that the variable determining the cylinder content decreases with respect to its absolute value, when the pressure in one of the lines exceeds a predetermined value. 3. Drive according to claim 1 and 2, characterized in that 109829/1037 -. 13 - the input circuit has a feedback signal applied to it, which is the product of the pressure in the Lines and a size indicating the cylinder content is proportional * 4. Drive according to claim 31 characterized by two potentiometers, whose tapping elements are mechanically coupled, with a potentiometer being one of the. the cylinder content outputting a proportional voltage, while the other potentiometer with one of the encoders output electrical voltage is applied. 5. Drive according to one or more of the preceding claims, in which the pump by means of an electric motor is driven, characterized in that the input circuit is proportional to the load on the electric motor Feedback signal is applied. 6. Drive according to claim 5, wherein the electric motor is fed with reversible direct current, characterized in that that the circle serving to supply the feedback signal subdivides, one automatically in one of the two partial circles controlled reversing device provided and these two circles are automatically interchangeable. 109829 / 10.37 2US / A57 7. Drive according to claim 5 or 6, characterized in that
that a voltage limiter is switched on in the circuit used to supply the feedback signal. 109829/1037 ORIGINAL INSPECTED Blank page