DE1272129B - Hydraulic unit, consisting of continuously rotating displacement pumps, the displacement of which is graded according to the power of two of the smallest unit, and a hydraulic drive - Google Patents

Description

Hydraulic unit, consisting of continuously rotating displacement pumps, whose displacement volumes are graded according to the powers of two of the smallest unit, and a hydraulic drive. The invention relates to a hydraulic drive Unit, consisting of continuously rotating displacement pumps, their displacement volume are graded according to powers of two of the smallest unit, and a hydraulic Drive.

In digital control or control loops, the control deviation or the control signal is mostly in coded form and must be used for hydraulic actuators, either as a cylinder for reciprocating motion or as a hydraulic motor for rotating movement are formed in a corresponding flow of hydraulic fluid being transformed.

There are already piston pumps with a steadily steep liquid flow known, which also allow a reversal of the flow direction of the hydraulic fluid. These steep pumps either have a pivotable cylinder body for axial piston pumps or a variable eccentricity of the circular running surface of the piston for Radial piston pumps on. As a result of their kinematically complex structure, these are However, piston pumps which can be steepened in stroke volume are expensive.

They are therefore often replaced by other cheaper positive displacement pumps, z. B. by gear, screw and cell pumps. Because the flow rate = flow rate per unit of time of these simple pumps, however, cannot be changed, the must The flow of liquid is controlled by means of adjusting valves by throttling which generate high heat losses with smaller currents. The pressure increases because of the small opening cross-sections of the steep valve, the largest part must the amount of liquid conveyed by the pumps is blown off via a pressure relief valve will. As the opening cross-section increases, these losses decrease disappears completely when the valve is fully open. But since this state only seldom occurs when running in or moving, this is mainly due to throttling and blowing off most of the expended electrical propulsion energy uselessly consumed and converted into heat, which locally heat the hydraulic fluid strongly can. In order to ensure adequate cooling, there are therefore much larger ones Quantities of liquid required, which often have to be cooled in special coolers, than would be necessary for the pure useful power in the hydraulic circuit.

To at least some adjustment of the amount of liquid delivered To achieve the required, multiple pumps are built in which in one Housing several pumps are arranged next to each other, which automatically when the pressure drops switch on when the flow of liquid required by the control valve is just below Exceeds existing partial flow. But also with the last described, through high effort is a better overall efficiency having pump arrangement the heating of the hydraulic fluid due to the throttling in the control valve itself can not be avoided.

The steep valves also have the major disadvantage that the Desired actuating characteristics (hydraulic fluid flow = f (electrical control current) are difficult to achieve, because only a very precise machining of the valve contours results in similar characteristics. In addition, they are subject to various types of operation Influences from viscosity, temperature, back pressure, etc.

There are also closed pump assemblies known whose Individual pumps operate separate hydraulic circuits via separate control valves where the flows of the individual pumps have different but arbitrary sizes. Furthermore, pump arrangements are known in which a pump with adjustable and a constant displacement pump is equipped; the latter is then for big electricity and small pressure built. It moves the steep piston when it is missing Network force quickly returns to the starting position.

It is also a switching arrangement of multiple positive displacement pumps for stepwise Regulation of the total delivery rate became known, in which the delivery rates of the pumps behave like 1: 3: 9: 27 etc. The suction line like the pressure line of everyone the jointly driven pumps can be optionally connected to the suction line and / or pressure line connectable. This requires both on the suction as on the Print side two valves for each pump. With the known arrangement is a pretty Fine-level control of the delivery rate is possible, but direct control is possible of the individual valves is not possible due to the value of a digital signal. In addition, about half of all stages must be set by a feed pump Part of the amount of liquid conveyed into the pressure line is from at least one further The pump operating as a motor can be fed back into the suction line. Through this the efficiency of the arrangement drops considerably.

The invention aims a hydraulic unit, which the above avoids the disadvantages described.

According to the invention, this is achieved by converting binary-coded Signals in analog quantity values of a hydraulic fluid in each line between each pump and the hydraulic drive a control valve is arranged and the Control valves depending on the individual, each assigned to a pump Establish the line connection for the binary coded signal (for L signals) or interrupt (with 0 signals).

As a simple one. and robust positive displacement pumps are particularly suitable Gear pumps. Rotary lobe or vane pumps can also be used. Are high speeds, no harmonics in the flow rate and low noise if desired, screw pumps are used. Will be very high volumetric efficiency required (95 to 99%), then piston pumps with a constant stroke are used, e.g. B. the very common as motors axial piston arrangements with constant largest Hub.

The control valves can be used as solenoid valves in a manner known per se be designed and control the individual place values of the binary-coded signal the magnets directly or via amplifiers. However, the control valves can also by a fluid depending on the individual values of the coded signal, which can represent a control deviation or a control signal can be actuated.

Is one of the displacement pumps controlled by the individual priority values blocked by the hydraulic drive, so the liquid it delivers is in a manner known per se through a special opening of the blocking control valve conveyed back into the storage container.

The z. B. submitted by a reader, the individual values electrical signals corresponding to the coded number can be very weak. You can z. B. amplify electronically and with the amplified signals Then actuate the control valves immediately. An electronic amplification of the signals however, it can often be omitted if the control valves are equipped with a hydraulic system known per se Are equipped with pilot control.

Particularly exact analog values are obtained if the drive speed is the pumping is rigid. Such a rigid speed behavior show aggregates, from self-starting electrical synchronous motors whose speed only depends on the Frequency of the supply voltage depends, and from volumetrically high-quality pumps, namely consist of piston pumps with a constant stroke. For high-quality control loops pressure losses and elasticities in the lines should also be eliminated as far as possible will. It is therefore particularly beneficial here to use the displacement pumps together with the associated control valves in the hydraulic fluid container to unite. There are then also those when a pump is blocked and a return is carried out resulting small losses are kept even smaller. With oil as hydraulic fluid The drive motor and pumps could even be in the oil of the storage container with low power run so that seals are omitted. But with greater performance it is better the drive motor z. B. to be attached with a vertical shaft outside the oil; there the permanent loss of the motor is slightly greater than the loss of the pumps and valves can be and the minimum amount of oil increases.

The invention has numerous advantages. So are with relative few pumps any number of output stages with a fixed interval possible. Through this depending on the control deviation, the manipulated variable receives as many values as they are given by the number of places of the digital signals. Expensive Adjusting pumps and difficulties with valve characteristics are eliminated, and on the valves no longer need major requirements in terms of their machining accuracy because they only have to open completely and close completely. the individual pumps and thus the analog output values of the total flow rate without a special digital-to-analog converter depending on the individual values of a digital signal controlled directly or possibly via an amplifier will. The valve passages only need to be designed for the slightest pressure drop which can therefore be smaller than the smallest in the usual position valves. This also keeps the losses very small.

This extreme reduction in all throttle losses in the hydraulic circuit the amount of hydraulic fluid can also be reduced to a minimum. The control characteristic of the actuator according to the invention is a step-shaped (analog-quantized) Proportional characteristic, the number of stages of which depends on the number of pumps. The steps in practice wear out due to the leakage oil in the simple fixed displacement pumps mentioned, because the volumetric efficiency at the nominal flow rate is around 90% here; if necessary can use the smallest pressure accumulator, e.g. B. rubber hoses, have a balancing effect. It can fast-acting pressure relief valves are also used for the pressure peaks that before pressure accumulators have the advantage that they are up to the cutting off of the pressure peaks maintain the rigid wall of the control loop, which means high control accuracy Condition is.

In the drawing, the invention is illustrated by means of exemplary embodiments explained in more detail. FIG. 1 shows a closed circuit with three individual ones Pumps and an actuating cylinder; F i g. 2 an open circuit with four pumps and a hydraulic motor.

In F ir g. 1 drives an electric motor 1, usually a three-phase squirrel-cage rotor or in the case of very high-quality controls or regulations, its speed is rigid compliant synchronous motor, the three pumps 3, 4, 5 and the auxiliary pump via the shaft 2 6 at. The pumps 3, 4, 5, 6 are so-called "Fixed displacement pumps" that have an almost constant displacement volume per revolution. The pump 5 promotes the unit amount, the pump 4 twice the unit amount and the pump 3 four times the amount Unit quantity. The pumps have only one delivery direction and can be used in the same Also work as a motor. They suck over from the storage container 7 the suction lines 8, 9, 10, 11 their liquid (z. B. oil) and press them over the return lines 12,13,14 when the pumps are short-circuited back into the reservoir 7 back. As a result, the pump circuits are always full of well-cooled flowing fluid Oil filled and therefore free of air pockets. The auxiliary pump 6 has the return line 15, through which the oil runs back when the pressure relief valve 16 responds. The control valves 17, 18, 19 for the pumps 3, 4, 5 each have a blocking position (0) and one Open position (L). In the blocking position, the pump lines 20, 21 are the Pump 3, lines 22, 23 of pump 4 and lines 24, 25 of pump 5 via lines 8, 12 and 9, 13 and 10, 14, d. H. i.e. via the container liquid, shorted. The main lines 26, 27 and 28, 29 and 30, 31 are in the blocking position locked. In the open position (position L), in which a closed circuit prevails, the following lines are connected to each other: 20 with 26, 21 with 27 for Pump 3, 22 with 28, 23 with 29 for pump 4, 24 with 30, 25 with 31 for pump 5. The Lines 26, 28, 30 flow in line 32, lines 27, 29, 31 in Line 33 together. The valves 17, 18, 19 are actuated by the springs 34, 35, 36 in the locked position (0) is pressed. The reversing valve137 is used to reverse the flow directions. Its actuation takes place in a similar manner, namely by the spring 38, although it has no locking position (0). Under the influence of the spring 38, the oil flows into the drawn direction, which is called positive (+). In this positive The directional position is therefore the line 32 with the line 39 and the line 33 connected to line 40.

The lines 39, 40 are at the two ends of the working cylinder 41 connected, in which the piston 42 moves a piston rod. The double-acting Cylinder 41 has a double-sided piston rod, i. H. with the same piston area for Zinc and clockwise rotation drawn. Of course, cylinders with one-sided Piston rod are used, but then the speed is in one direction smaller by the reduction of the piston area due to the cross-section of the piston rod. Instead of the cylinder, as shown in FIG. 2 shows hydraulic motors with constant Displacement per revolution, so-called "constant motors", for two directions of rotation be used. The closed cycle of FIG. 1 requires a priming pump with non-return valve to container 7 for refilling the small amount of leakage oil. Therefor the auxiliary pump 6 can be used. Since this is in the short circuit of the pumps of any air pockets, cleaned oil is then mixed with the circulation oil and improved in terms of air inclusions, the refill effect of the Replace auxiliary pump 6 with a very small memory (not shown) on the Line 20, since no transition from position 0 to position L by corresponding Displacement of the control edges is filled. This displacement causes z. B. when the pump 3 is switched on in the hydraulic circuit, the line 12 takes a few milliseconds earlier than line 8 is shut off. The small memory can be omitted entirely if the connection of line 8 via 21, 20 with line 26 for a few milliseconds is established after the connection between line 20 and line 12 has already been interrupted was.

With low requirements, e.g. B. for actuators for simple timing chains, simple electromagnetic valves that operate with an actuating power of 50 to 100 watts have a proper time of 50 to 100 ms. With higher quality actuators for electrohydraulic control loops with digital measurement, on the other hand, must, especially when transistors are used in the electrical pilot control, as is the case today in digital systems it is the rule to use considerably smaller tax payments of z. B. a maximum of 3 watts suffice. In addition, the valve operating times must be reduced to at least 20 to 30 ms, if possible 10 to 20 ms between electrical signaling and end of the adjustment movement. The additional hydraulic ones meet these conditions Pilot controls 44, 45, 46, 47, the pump valves 17, 18, 19 and the reversing valve Press 37: The associated control lines 48, 49, 50, 51 are disconnected from the lines 52 and 53 fed through the pump line 54 of the auxiliary pump 6. The small pressure accumulator 55 permits the control performance when the valves are operated for a short time considerably to increase over the average power of the auxiliary pump 6. The pressure relief valve 16 blows only when the maximum permitted boost pressure of the pressure accumulator is exceeded. Instead of the pressure relief valve 16, a pressure-dependent bypass valve can be used in order to preserve the smallest losses. The arrows drawn in the control lines 48, 49, 50, 51 indicate the direction of the control fluid, with only in the Line 53 can occur in both directions. Because only with her both flows Charging current of the accumulator as well as the discharge current through. For the sake of simplicity the unpressurized control currents with their lines to the container 7 are not especially drawn.

The control magnets 56, 57, 58, 59 have small powers because of the hydraulic pilot control, z. B. 3 watts each, and for the sake of clarity are only shown with their symbols without the associated electrical circuit. The counter springs 34, 35, 36, 38 push their valves into the right switching position when the control magnets are de-energized. Control magnet 58 of the pump 5, the z. B. 11 / min promotes is controlled depending on the last place value of a binary-coded number. Control magnet 57 of pump 4 delivering 21 / min from the penultimate place value and control magnet 56 of pump 3 delivering 41 / min from the first place value of a three-digit coded number in the example. Is z. B. the coded signal L 0 L, which corresponds to the decadic value 5, before the pumps 3 and 5 are opened, which deliver into the pressure line 1 + 4 = 51 / min. With three pumps, seven delivery levels (1 + 2 + 4 = 71 / min) and one blocking level (01 / min) can be set. A total of 16 stages can be achieved with four pumps, 32 stages with five pumps, etc. The control magnet 59 only passes on the ± symbol; which is contained, for example, in a punched tape. It is operated in such a way that there is a positive conveying direction when the control magnet 59 is switched off and the spring 58 acts, and a negative conveying direction is generated; when it is on.

The individual flow rates of pumps 3, 4, 5 and their total flow for the working cylinder 41 form a closed circuit as far as the pumps are switched on. The pumps 3, 4, 5 therefore do not have to move in their conveying direction can only push the circular current, but can also be pushed by it, when the piston 42 is displaced by an external force. This is for example however, with a rotating constant motor, as shown in FIG. 2 is shown, the case with winch drives, when the winch is under a pulling load, the drive energy So comes from the outside and has to be released again for the purpose of braking from the circuit. When the pumps 3, 4; 5 can also be operated as motors then drive them For example, the asynchronous motor1 is used as a generator via its synchronous speed. It then becomes an asynchronous generator and prevents it if its breakdown torque is correct is designed, a noticeable increase in the pump speed above the rated speed. The load is therefore lowered at an approximately constant speed.

In the locked position of the overall arrangement, for example in the case of a winch drive, a holding brake is applied, which is released in all other positions 1 to 7 is that a special, not shown control valve the release cylinder of this Holding brake with the auxiliary pump 6 connects. The pressure accumulator 55 then serves at the same time for quick release of the holding brake. Basically, however, is in the circuit the F i g. 1 already contain the effect of a holding brake, since the one described above Zero position blocks the working cylinder 41 or the fixed-displacement motor with the oil circuit. Because of the high volumetric efficiency of the hydraulic servomotors a holding brake is practically carried out by this measure alone, see above that the special holding brake is a pure safety brake that is only used for Hold or for the one-off interception of the lowering load in the event of a defect in the hydraulic circuit must be designed.

In Fig. 2 shows a so-called open hydraulic circuit, which is possible with controls when the hydraulic motor does not have any pulling forces or must process torques, so with-; for example with an actuator great friction. With control loops, e.g. B. with copying "controls", which in reality Represent position controls, the full range can be used for a short time in the event of a negative control deviation Counterforce or part of it on the piston; ken. Furthermore, in FIG. 2 drawn a pump combination that has four pumps instead of three pumps. The auxiliary pump, which only needs to deliver the control oil here has been omitted for the sake of clarity. It is built with the same structure as in Fig. 1, i.e. with a pressure relief valve and pressure accumulator, at the beginning of the line 60 in FIG. 2 connected.

The motor 61 drives the pumps 63, 64, 65 and 66 via the shaft 62. The smallest pump 66 is again designed for the unit of the flow rate, the pump 65 for twice, the pump 64 for four times and the pump 63 for eight times this unit flow of the pump 66. The dual-stage flow rates of these four pumps are symbolically larger the diameter of the symbol. In the case of an open circuit, pumps can be used that only have one delivery direction and cannot be used as hydraulic motors. The open circuit therefore does not allow any back work and can therefore, in contrast to the closed circuit of FIG. 1 not even with certain controls, e.g. B. be used with winches to brake pulling loads. The pumps suck the liquid from the container 71 via the suction lines 67, 68, 69; 70 at. The line sections 72, 73, 74, 75 going from the pumps lead to the control valves 76, 77, 78 and 79. In the blocking position (0) of these control valves, all of the pumped oil is returned to the container via the lines 80, 81, 82 71 promoted back.

The four pumps 63, 64, 65, 66 result in 1 -f- 2 + 4 + 8 = 15 positions for the flow rate of all pumps. With the zero position there is a total of 16 positions. Here, too, the valve 83 controls the flow of oil that has flowed into the collecting line 88 via the lines 84, 85, 86, 87. In the positive position (+), the line 91 is connected to the line 88. Motor 92 is again a constant motor, that is to say a hydraulic motor with a constant displacement volume per revolution.

In the negative position (-) of the valve 83, the line 89 is with 88 and the line 90 connected to 91, so that now with unchanged conveying direction the hydraulic motor 92 runs in the opposite direction from the pumps. As the return lines 90 run directly into the container 71, there is still a zero position of the reversing valve 83 is necessary, which is represented symbolically in the middle field. Because of these three Positions + 0 - the reversing valve 83 has two control magnets 93; 94 with the to it associated hydraulic pilot controls 95, 96, which via the control lines 97, 98 are connected to the common control line 99. The springs 100 and 101 guarantee the zero position when the two control magnets 93, 94 are switched off are, d. That is, the springs 100 and 101 are mutually connected in their action and hold the zero position with corresponding pre-tensioning against each other. The other control valves 76, 77, 78, 79 are simpler than in the open circuit in Fig. 1. Your springs 102, 103, 104, 105 switch the associated pumps 63, 64, 65, 66 back onto the container 71. Upon actuation of the control magnets 106, 107; 108, 109 by means of the hydraulic pilot controls 110, 111, 112, 113, the individual Pumps 63, 64, 65, 66 are connected to the collecting line 88.

The control of the individual pumps via the valves as a function of a binary-coded number is basically already in the example F i g. 1 treated.

As already stated, the open cycle has the disadvantage that no work back on the electric motor 61 is possible. But he has the big one Advantage that the circulating amounts of oil always run through the container 71 and thereby can give off their heat loss ala the larger amount of oil. Also don't kick Leakage oil losses. The heat loss is compared to the throttle and blow-off method of the usual hydraulic control circuits, especially when the Pumps 63, 64, 65, 66 and their control valves 76, 77, 78, 79 in one block can be assembled directly above the storage container. In the example of the F i G. 1 there is an open circuit for the pumps, which are in the respective positions are not involved in the useful flow. Because of the strong reduction in heat loss by the invention, these temporary open circuits are sufficient for the discharge of the total oil heat.

Claims (9)

Claims: 1. Hydraulic unit, consisting of permanently circulating displacement pumps, the displacement of which according to powers of two of the smallest unit, and a hydraulic drive, d u r c h g e k e n n -z e i c h n e t that for converting binary-coded signals into analog ones Quantities of hydraulic fluid in each line between each pump (3 to 5, 63 to 66) and the hydraulic drive (41, 92) a control valve (17 to 19, 76 to 79) is arranged, and the control valves depending on the individual, The line connection of the binary-coded signal assigned to a pump in each case Establish (with an L signal) or interrupt (with a 0 signal). 2. Hydraulic unit according to claim 1, characterized in that the control valves (17 to 19, 76 to 79) are designed in a manner known per se as solenoid valves, and the individual Place values of the binary-coded signal directly or via amplifier the magnets (56 to 58, 106 to 109). 3. Hydraulic unit according to claim 1, characterized characterized in that the control valves depending on the individual values of the binary-coded signal can be actuated by an F1uid. 4. Hydraulic Unit according to Claim 2 or 3, characterized in that one of the hydraulic Drive shut off displacement pump in a known manner the promoted Hydraulic fluid is returned directly to the reservoir (71). 5. Hydraulic Unit according to Claim 1 or the following, characterized in that the one connection the displacement pumps with the hydraulic drive producing or interrupting Control valves (17 to 19, 76 to 79) a hydraulic pilot control known per se (44 to 46, 110 to 113). 6. Hydraulic unit according to claim 1 or following, characterized in that the positive displacement pumps by a preferably self-starting synchronous motor (1, 61) are driven. 7. Hydraulic power unit according to claim 1 or the following, characterized in that the displacement pumps together with the associated control valves with the reservoir (7, 71) of the Hydraulic fluid are structurally combined. B. Hydraulic unit according to claim 7, characterized in that the displacement pumps (3 to 5, 63 to 66) when using of hydraulic oil together with the drive motor (1, 61) in the C51 of the reservoir (71) are operated. 9. Hydraulic unit according to claim 1 or the following, characterized in that when the connection is restored between one locked displacement pump and the hydraulic drive (41, 92) in the locked position line (12 to 14) conveying the hydraulic fluid to the reservoir (7, 71) due to the associated control valve a little earlier than that of the hydraulic drive leading line (26, 28, 30) is closed. Considered publications: German Auslegesehrift No. 1004 483.