US 3744243 A
An electro hydraulic control system wherein the capacity of a variable pump is automatically controlled in response to the pressure in the conduits which couple the pump to a fluid driven motor. Signals commensurate with pressure are generated and fed back to a control signal generating means which adjusts pump capacity via a servovalve.
Description (OCR text may contain errors)
Elted States Patent 1 1 Faisandier 1 1 July 10, 1973 1 1 CONTROL SYSTEM  inventor: Jacques J. Faisandier, Chatillon sous Bagneux, France  Assignee: Societe DApplications Des Machines Matrices, Issy les Moulineaux, France  Filed: Jan. 4, 1971  Appl. No.: 103,476
 Foreign Application Priority Data Jan, 9, 1970 France 7000970 52] us. 01 ..60/431, 417/212, 60/451, 60/452 51 1111. C1. FlSb 15/18 58 Field of Search 60/53 R, 53 GC, 52 vs,
 References Cited UNITED STATES PATENTS Maurer 60/52 VS 6/1965 Gauthier et a1. 60/53 R 11/1970 Long et a1 60/52 VS FOREIGN PATENTS OR APPLICATIONS 412,816 3/1922 Gennany 60/52 VS Primary ExaminerEdgar W. Geoghegan Attorney-Fishman and Van Kirk 5 7 ABSTRACT An electro hydraulic control system wherein the capacity of a variable pump is automatically controlled in response to the pressure in the conduits which couple the pump to a fluid driven motor. Signals commensurate with pressure are generated and fed back to a control signal generating means which adjusts pump capacity via a servovalve.
8 Claims, 5 Drawing Figures PATENTEB JUL 1 0197s saw 1 or 2 PATENIED JUL 1 0197s sum 2 0F 2 CONTROL SYSTEM BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates to electro-hydraulic controls. More specifically, the present invention is directed to the control of hydraulic machinery and especially to machinery of the type employing a variable delivery pump and associated motor. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
(2) Description of the Prior Art While not limited thereto in its utility, the present invention is particularly well suited for safely controlling the operation of a fixed cylinder capacity hydraulic motor having a variable delivery pump associated therewith. In the usual instance, the cylinder capacity of the pump is regulated or adjusted by an auxiliary power cylinder which is, in turn, controlled by an electrically operated servovalve. Power for the solenoid of the servovalve will typically be provided by an electronic control amplifier.
In cases where the speed of the hydraulic motor is the parameter which is to be controlled the inputs to the control amplifier will typically comprise a command signal and a feedback signal commensurate with pump speed. The speed signal may be provided by means such as a tachometer driven directly by the hydraulic motor or by sensing a pump operating parameter commensurate with motor speed.
In situations where the output shaft position of the motor is the parameter to be controlled, a comparator synchro may be operatively connected to the motor and the voltage developed by the synchro will be compared with a command voltage to generate an error signal which is fed to the control amplifier.
The above, briefly described prior art speed and position controls operate satisfactorily only if the resisting torque of the hydraulic motor does not exceed the systern design value. In order to enhance flexibility and provide a margin of safety, it has been proposed to incorporate valve means which permits by-passing of the motor when the pressure differential thereacross exceeds the critical or design value. Systems employing such by-pass valve, however, have a number of disadvantages. First, in the event of prolonged operation with, for example, excessive load on the hydraulic motor, the oil contained in the pump and by-pass circuit will become heated. As is well known, overheating of the oil in an hydraulic circuit may result in burning or otherwise damaging vital parts of the pump and motor as well as effecting the qualitites of the hydraulic fluid itself. A second disadvantage of such by-pass safety systems is that energy is wasted under conditions where the design pressure differential is exceeded. Thusly, obviously a more powerful prime mover' is required for driving the variable pump and would be necessary if it were possible for the capacity of pump to be adjusted at all times so that the critical pressure differential was not exceeded.
SUMMARY OF THE INVENTION The present invention overcomes the above, briefly discussed and other deficiencies and disadvantages of the prior art by providing a novel and improved electro-hydraulic control. In accordance with one embodiment of the invention a pressure sensor is inserted in each of the hydraulic lines which couple the variable capacity pump to the associated motor. These pressure sensors, which preferably are of the threshold type, provide or generate feedback voltages which are returned to the electronic circuitry which generates the control signal for the pump servovalve solenoid. A parameter commensurate with pump cylinder'capacity is also sensed and a signal proportional thereto may also be fed back to the input of the control signal generating circuitry. The feedback signals and a command signal are combined in the servovalve control circuitry and a valve control signal is generated which will appropriately vary pump cylinder capacity if the pressure in one or the other of the fluid supply lines between the pump and motor exceeds a predetermined critical value.
To summarize the preceeding, the present invention develops a feedback signal proportional to pressure for the purpose of power limitation of the hydraulic control circuit. Performance of the invention may be enhanced if the pump is driven by an electric motor selected on the basis of minimum power requirements. In such a case, since the maximum pressure in the hydraulic circuit must decrease when the rate of delivery in.- creases, the product of pump power and capacity will be a constant. The return of a signal commensurate with the product of power and capacity as an input to the servovalve control amplifier will result in a reduction in motor speed if the product exceeds the critical or design value.
Alternatively, by employing an electric motor to drive the variable cylinder capacity pump and taking advantage of the characteristic of the motor to absorb current in proportion to the output torque developed, another control scheme maybe derived. Since the current or power requirements of the motor will generally be known, pump drive motor current may be sensed as the regulating variable and employed in the same manner as hydraulic loop pressure to generate a signal which will be employed to reduce the speed of the motor when a critical value of pump drive motor current, and thus load on the hydraulic motor, is exceeded.
BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous other objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the various figures and in which: i
FIG. 1 is a schematic diagram of a first embodiment of the present invention;
FIG. 2 is a schematic diagram of a second embodiment of the invention, the embodiment of FIG. 2 being a modification of the FIG. 1 embodiment;
FIG. 3 is a schematic diagram of a third embodiment of the present invention, the embodiment of FIG. 3 employing an alternating current motor to drive the hydraulic pump;
FIG. 4 is a schematic diagram of a modification of the embodiment of FIG. 3, the embodiment of FIG. 4 employing a direct current motor; and
FIG. 5 is a schematic diagram of a further embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIG. 1, a hydraulic motor is indicated at 1. Motor 1 is supplied with driving fluid from a variable capacity pump 2. The means by which the capacity of pump 2 may be varied is indicated schematically by lever 3 which forms an angle a with a reference direction.
The control of the capacity of pump 2; that is, the positioning of lever 3; is accomplished by means of a double-acting cylinder indicated schematically at 4. The position of the piston in cylinder 4 is controlled by a solenoid operated servovalve S. The solenoid of valve 5 being indicated at 6. Control current for solenoid 6 is provided by amplifier 7 and delivered to the solenoid via conductor 8'.
Control amplifier 7 has a plurality of input signals applied thereto. A command signal, for example as developed across a potentiometer, is applied to conductor 8 thence delivered to amplifier 7. Feedback voltages, de veloped in the manner to be described below, are applied to junctions 10 and 20 and thence delivered to the input of amplifier 7.
The wiper arm of a potentiometer 9 is mechanically coupled to the lever 3 and thus a signal commensurate with the capacity of pump 2 is developed and fed back to amplifier 7 via junction 10. Signals commensurate with the pressure in hydraulic lines 12 and 13, which complete the fluid circuit between the motor 1 and pump 2, are also generated and delivered, in the manner to be described below, to the input of amplifier 7 via junction 20.
The pressure in hydraulic lines 12 and 13 is sensed by pickup devices 14 and 15 respectively. Pressure sensors 14 and 15, which will preferably be threshold type pickups, are well known in the art and will not be described herein. The movable pistons of pickup units 14 and 15 are mechanically connected to the wiper arms of respective potentiometers 16 and 17 and, by means of positioning the wiper arms, will cause the generation of signals commensurate with pressure which are ap plied to conductors I8 and 19, respectively. If deemed necessary or desirable, suitable filter circuits 18' and 19 may be connected in lines 18 and 19 for enhancing the desired control action. The pressure signals appearing at the outputs of filters 18' and 19' are applied to junction 20 and thence to the input of amplifier 7.
For enhanced safety, a by-pass valve 21 may be connected between lines 12 and 13. By-pass valve 21 is normally closed and will open when the difference in pressure between lines 12 and 13 attains a predetermined critical value.
From the preceding description it may be seen that feedback signals proportional to speed, as developed at potentiometer 9, and commensurate with pressure, as developed at potentiometers 16 and 17, are superimposed on the command signal delivered to the control system via conductor 8. Amplifier 7 will combine the command and feedback signals to develop a control signal which is applied to solenoid 6. The control signal applied to solenoid 6 will cause servo valve 5 to effect control over the capacity of pump 2 via cylinder 4 and lever 3. The control action is such that any increase in the pressure differential across motor 1 above the design value, or an excess pressure in either of conduits 12 or 13, will result in a decrease in the cylinde capacity of pump 2.
Considering now the embodiment of FIG. 2, the disclosed control system is the same as that abovediscussed with relation to FIG. 1 with the exception of the addition of potentiometer 22. The wiper arm of potentiometer 22 is operatively connected to lever 3 and thus a second signal commensurate with the angle a is developed. The potentiometer 22 is shunt-fed from conductor 13 and thus a voltage commensurate with the pressure in hydraulic line 12 is applied across the potentiometer. A signal on the wiper arm 23 of potentiometer 22 will, accordingly, be a voltage which is proportional to Pa This signal is delivered via conductor 25 to a voltage sensitive threshold device 26. Device 26 will be adjustable so as to provide an output signal to amplifier 27 when the critical value of the product P a is exceeded. Amplifier 27 may also perform a filtering function and additional threshold devices 28 and 29 and associated amplifiers 30 and 31 may be inserted in conductors 18 and 19 in place of filters 18' and 19'.
The embodiment of FIG. 3 operates with a unidirectional motor driven by pump 2. Pump 2 is, in turn, driven by a three-phase, alternating current motor 32. One of the supply lines 33 for three-phase motor 32 is provided with acurrent transformer 34. The current induced in the secondary winding of transformer 34 is sensed by a threshold device 35. The output of device 35 is applied to preamplifier 36.
The output of the preamplifier 36 may be applied to a rectifier device 38' and the output of rectifier 38 will be passed through a filter and limiter circuit 38". The output of filter 38" will be a voltage commensurate with the current being drawn by driving motor 32 and this voltage will be combined, at junction 39, with the command signal 38. The combined signals from junction point 39 are delivered, via junction 41, to power amplifier 37 which is equivalent to amplifier 7 of the embodiment of FIGS. 1 and 2. Amplifier 37 provides control current for the solenoid operated servovalve 40. A feedback signal commensurate with the angle a of lever 3 is also applied to the input of amplifier 37 via junction 41. It will be understood that the portions of the hydraulic circuit downstream of the servovalve 40 will be identical to those circuit elements which are downstream of servovalve 5 of the FIG. 1 embodiment with the exception that the pressure sensors 14 and 15 may be omitted.
The embodiment of FIG. 4 is similar to that of FIG. 3 with the exception that alternating current motor 32 has been replaced by a direct current motor 42. Since it is not possible to employ a current transformer, such as transformer 3d of FIG. 3, with d.c. motor 42, amplifier 43 is employed to sense the current drawn by motor 42. It is to be understood that there are numerous commercially available devices which may be employed to sense the current being drawn by dc. motor.
42. The output of amplifier 43 is applied to a threshold device 44 and, if necessary, thereafter to a modulator 44'. The output of device 44 or modulator 44 is combined with the command signal 38 and thereafter ap plied to power amplifier 37. The feedback signal a is also applied to amplifier 37 via junction 41.
As previously noted, the embodiments of FIGS. 3 and 4 may be employed only with a unidirectional motor. Restated, if pump 2 is allowed to rotate in both directions, the reduction of speed which would be produced for rotation in one direction would provide a signal which would result in an increase of speed when the pump was rotated in the opposite direction. This, of course, is precisely that opposite result from that which is desired.
FIG. 5 illustrates a modification which may be made to the embodiments of FIGS. 3 and 4 in order to permit operation of the pump and its driving motor in either direction. Thus, considering simultaneously FIGS. 3 and 5, the current transformer 34 and other circuit elements upstream of threshold device 35 of FIG. 3 have not been depicted in FIG. 5 since such circuit elements are in no way modified. In the embodiment of FIG. 5, the output of preamplifier 36 is delivered to parallel circuits 45 and 46. An inverter circuit is included in circuit 46 and a relay means 47 is employed to connect the appropriate one of the two parallel circuits to amplifier 36. The relay 47 will be in the position shown if a is positive and in the opposite position if a is negative. The change over or operation of switch 47 is achieved by providing, along the line which supplies the feedback proportional to a to junction 41, contacts (not illustrated) which are adapted to excite the coil or coils of the relay 47. It is, of course, to be observed that relay 47 may be replaced by an electronic switch of a type well known in the art.
It is further to be noted that the output of amplifier 36 is also applied to a voltage limiter device indicated schematically at 48. Device 48 may, for example, comprise a Zoner diode or any equivalent device capable of limiting the amplitude of the feedback so that, if there is too large a current impulse, the speed is not reversed too rapidly and consequently the system will not start to hunt around the zero speed.
While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been shown by way of illustration and not limitation.
What is claimed is:
1. Apparatus for exercising control over a fluid driven system, said fluid driven system including a variable capacity pump coupled to a motor by conduit means and actuator means connected to the pump for adjusting the capacity thereof, said control apparatus comprising:
means for sensing the pressure in said conduit means and for generating electrical signal commensurate therewith;
control signal generating means responsive to electrical signals applied thereto for generating actuator means electrical control signals when one of said signals commensurate with pressure exceeds a predetermined value;
means coupled to the actuator means and responsive to said electrical control signals for converting said control signals to motion of the actuator means whereby the pump cylinder capacity will be decreased if the predetennined pressure value is exceeded;
means applying electrical command signals as an input to said control signal generating means; and means for feeding back said signals commensurate with pressure to an input of said control signal generating means. 2. The apparatus of claim 1 further comprising: means for generating a signal commensurate with pump capacity;
5 means for multiplying said pump capacity signal by an electrical signal commensurate with pressure in said conduit means; and
means for delivering the signal provided by said multiplying means to said control signal generating means.
3. The apparatus of claim 1 wherein said pump and motor are connected by a pair of conduits and wherein said pressure sensing means comprises:
a pressure sensor operatively associated with each of said conduits, said sensors including piston means positioned in relation to conduit pressure; and transducer means mechanically connected to each of said sensor piston means for generating electrical signals commensurate with conduit pressure.
4. The apparatus of claim 2 wherein said pump and motor are connected by a pair of conduits and wherein said pressure sensing means comprises:
a pressure sensor operatively associated with each of said conduits, said sensors including piston means positioned in relation to conduit pressure; and
transducer means mechanically connected to each of said sensor piston means for generating electrical signals commensurate with conduit pressure.
5. The apparatus of claim 4 wherein said multiplying means comprises:
potentiometer means having its wiper arm mechanically coupled to said control signal generating means; and v means applying the signal generated by one of said transducer means across said potentiometer means.
6. Apparatus for exercising control over a fluid driven system, said fluid driven system including a variable capacity pump coupled to a motor by conduit means and actuator means connected to the pump for adjusting the capacity thereof, said system further including an electric power prime mover for the pump, said control apparatus comprising:
means for sensing the current drawn by said electric motor and for providing a signal commensurate therewith, said signal commensurate with current being indicative of the pressure in said conduit means; and
50 means responsive to said signal commensurate with motor current for controlling the .pump actuator means.
7. The apparatus of claim 6 wherein said electric motor is a direct current motor and wherein said control apparatus further comprises:
means connected between said current sensing means and said actuator controlling means for delivering a signal of proper polarity to said controlling means regardless of direction of rotation of 0 said electric motor.
8. The apparatus of claim 6 further comprising: voltage limiter means connected to said current sensing means for limiting the magnitude of the signals applied to the actuator controlling means.
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