US3772889A

US3772889A - Servo pump having throttled input

Info

Publication number: US3772889A
Application number: US00153721A
Authority: US
Inventors: R Mason; J Roark
Original assignee: Textron Inc
Current assignee: HR TEXTRON Inc A CORP OF DE
Priority date: 1971-06-16
Filing date: 1971-06-16
Publication date: 1973-11-20
Anticipated expiration: 1990-11-20
Also published as: IT946761B; DE2203212A1; FR2142330A5

Abstract

A fluid flow control system for moving a load positioning member which system utilizes a closed hydraulic system of predetermined capacity including a reservoir. A continuously running fixed displacement pump means having inlet and outlet ports is connected to receive fluid from the reservoir and to transmit the fluid to the load positioning means. Control valve means is disposed to control the amount of fluid flow to the pump means and to direct the flow from the pump means to the load positioning member. Control means is connected to the control valve means to position the control valve means responsive to received signals to properly position the valve means respective to the inlet and outlet ports of the pump means thereby to effect the desired rate of flow. There may be also included make-up valve means between the reservoir and the intake port of the pump means, relief valve means between the output port of the pump means and the reservoir, as well as shut-off valve means responsive to discrepancy in compared signals within the control means of the system for eliminating control of the load positioning member by a particular pump means and control valve means associated therewith.

Description

Ute States 1 1 I 1 3,772,889 Mason et al. [4 1 Nov. 20, 1973 SERVO PUMP HAVING THROTTLE!) INPUT Primary 'Examiner-Edgar W. Geoghegan [75 1" l nv ii'tor's i Richard K. Maia/scams 1111s; Ammeyrmsm" Rbbms John M. Roarli, Canoga Park, both Of Calif.

[57] ABSTRACT V A fluid flow control system for moving a load positioning member which system utilizes a closed hydraulic xiii/Filed! jllllf viii/19951 V system of predetermined capacity including a reser- [21] APPL Nu: 153,721 voir. A continuously running fixed displacement pump means having inlet and outlet ports is connected to receive fluid from the reservoir and to transmit the fluid C5 to the load positioning means. Control valve means is 6 417/295 disposed to control the amount of fluid flow to the [51] Int. Cl. Flsb 15/18 um means and to direct the flow from the pump [58] Field Of Search 60/DIG. 2, 52 R, ans to the load positioning member, Control means 60/53 is connected to the control valve means to position the 411 411 417/295 control valve means responsive to received signals to properly position the valve means respective to the References Cited inlet and outlet ports of the pump means thereby to UNITED STATES PATENTS eflect the desired rate of flow.

2,255,589 9/1941 Johnson 60/97 P There may be also included make-up valve means 2,627,815 2/1953 Bunting 2,584,820 2/1952 Steinhoff..... 2,597,050 5/1952 Audemar 60I907 X between the reservoir and the intake port of the pump 60/475 means, relief valve means between the output port of 60/545 R the pump means and the reservoir, as well as shut-off fig? valve means responsive to discrepancy in compared 3 270 623 9/1966 oamjlii i i alii z 151 RX signals within the control means of the system for 60/52 eliminating control of the load positioning member by 3,282,283 11/1966 Takeda 91/390 x a Particular P p means and 60mm! valve means 3,411,297 11/1968 Hann 60/53 A 1 associated therewith.

3,505,814 4/1970 Beard et al. 60/52 3,270,508 9/1966 Smith et al 3 Claims, 2 Drawing Figures 1 SERVO PUMP HAVING THROTTLED INPUT BACKGROUND OF THE INVENTION The present invention relates to fluid handling systems and particularly to a servo pump, that is, an apparatus for controlling a load positioning member through direct control of the pump.

In the prior art it has been customary in systems utilizing servo pumps that variable displacement pumps be utilized. Such pumps in prior art systems, have been piston pumps operable through the utilization of a variable angle wobble-plate or a vane-type pump utilizing a movable sleeve. In such prior art systems, a plurality of pumps are required and the response thereof has been slow while the power required to operate the same has been quite high. Also the response of the systems utilizing such variable displacement pumps has been limited by the response of the pump.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram illustrating one form of a control system in accordance with the present invention; and

FIG. 2 is a schematic diagram of an alternative embodiment of a system constructed in accordance with the present invention.

SUMMARY OF THE INVENTION A throttling servo pump having a continuously running fixed displacement fluid pump having an inlet port connected to a reservoir of fluid through a flow control valve means normally positioned to throttle said inlet port and means for controlling the positioning of said flow control valve means thereby to direct fluid flow from said pump to position said load positioning means.

DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there is shown a drive motor 11 coupled by a shaft 12 to a wobble-plate 13. Pistons 14 and 15 are connected respectively through swivel joints 16 and 17 to the slanted face 18 of the wobbleplate 13. Thus, as the wobble-plate 13 continuously ro-' tates, the

pistons

14 and 15 are caused to reciprocate. Although only two

pistons

14 and 15 are shown in FIG. 1, it should be expressly understood that any number of pistons may be utilized depending upon the required characteristics of the pump means utilized in a particular application of the invention constructed in accordance with the present description. Such mechanisms as the wobble-plate connected to the pistons are well known in the prior art and, therefore, no detailed description thereof will be provided herein.

As illustrated, the piston 14 reciprocates within a cylinder 19 defining an inlet port 21 and an outlet port 22, while the piston 15 reciprocates within a cylinder 20 which defines an inlet port 23 and an outlet port 24.

The

inlet ports

21 and 23 may be interconnected as illustrated by the conduits and 26, if desired, while the outlet ports 22 and 24 are interconnected as indicated by the

conduits

27 and 28. The

conduits

25 and 26 are each connected to a bore 29 at ports C and

conduits

27 and 28 are each also connected to the bore 29 which will be described in more detail below. Any further included pistons would be similarly constructed and their input and output ports similarly interconnected.

A load 31 is coupled as illustrated by the dashed line 33, to a load positioning means shown generally at 32. The load positioning means 32 may take the form of an actuator having a piston rod 34 coupled to a piston 35 which is positioned within a cylinder 36 divided by the piston 35 into

chambers

37 and 38. A conduit 39 is connected to the chamber 37 and also to the bore 29 at port B while a conduit 41 is connected from the chamber 38 to the bore 29 at port A. A reservoir shown generally at 51 includes a fluid source 52 which is maintained under pressure as illustrated schematically by the piston 52 and spring 54. The reservoir along with the interconnected system parts provides a closed hydraulic system of predetermined capacity. A conduit 55 is connected from the fluid source 52 to the chamber 56 within which the wobble-plate 13 is positioned.

Conduits

57 and 58 are interconnected between the chamber 56 and the bore 29. An additional conduit 59 is also interconnected between the'fluid source 52 and the bore 29.

Check valves, as illustrated by the ball valves, 61 and 62 are provided to close the output ports 22 and 24, during the intake or suction stroke of the

pistons

14 and 15. The ball valve 63 is provided to function as a relief valve thereby to preclude excess pressure being built up by the pump at the output ports 22 and'24 thereof and is connected to function through the conduit 64. I

A control valve means in the form of the spool valve having spaced

lands

71, 72 and 73 thereon is dis-.

83 of the torque motor 82 to one end 84 of the spool 70. Control signals may be applied to the leads 85 of the torque motor 82 to move the armature 83 and thereby move the spool 70 as is well known in the prior art. Therefore, no further description will be given of torque motors or the like. A feedback mechanism as shown generally at 86 may be mounted on the actuator and its moving element connected to the piston rod 34 by the strap 96 thereby providing a signal proportional to the piston rod 34 position. This feedback mechanism 38 may be a Linear Variable Differential Transformer (LVDT) having leads 87 which would be operatively coupled to a demodulator 97 and a servoamplifier 98 through summing point 99. The summation of this feedback signal along with the command signal which is also supplied from there to the summing point 99 result in the error signal which is coupled to the leads 85. This method of generating an error sigal is well known in the prior art.

As will now become apparent, the lands 71 and 72 of the spool 70 divide the bore 29 into a chamber 91 to which the output ports of the various piston cylinders of the pump means is connected. The lands 71 and 73, as well as the land 73 and one end of the bore 29 provide a chamber 92 to which the reservoir is connected Operation of the system in accordance with the present invention would occur under one of two conditions.

The first of these is if an input command singal is applied to the summing point 99; the other condition would be if a feedback signal is applied to the summing point 99. Obviously, a combination of the two signals may be applied. In any event an error signal is generated and applied to the torque motor 82 for purposes of discussion, assume that in either event the piston 35 is to move downwardly as viewed in FIG. 1.

If a command signal is being applied to cause the downward movement of the piston 35, the spool 70 is moved toward the right proportional to the command signal thereby connecting the flow port B to the chamber 91 and thereby the output of the pump means, while the flow port A and the flow port C are connected to the reservoir. Under these circumstances the input port of the pump is connected to the reservoir through the chamber 56 and conduit 55 and during'the intake stroke of the pistons would thereby receive hydraulic fluid. This fluid must flow through port C. The

pressure drop across port C is the difference between the reservoir pressure and the vapor pressure of the fluid. Since both of these pressures are constant. The area of port C is a function of the displacement of spool 70. The flow of the piston(s) is therefore a direct function of the displacement of spool 70. This fluid is then pumped through the flow port B and to the chamber 37 of the actuator 32. As the piston moves downwardly the hydraulic fluid in the chamber 38 moves through the conduit 41 and through the flow port A into the reservoir through chamber 92, conduit 58, chamber 56 and conduit 55. When the piston 35 reaches the commanded position, as determined by the feedback means 86, the spool 70 again returns to the position shown in FIG. 1 thereby blocking flow ports A, B, and C. The rate at which the actuator 32 moves depends on the displacement of the spool 70 as previously described.

Assuming now that the load is attempting to move the piston 35 in a downward direction, a feedback signal is generated by the feedback means 86 thereby causing the spool 70 to move toward the left as viewed in FIG. 1. Under, these circumstances flow port A is connected to the chamber 91 and thereby the output port of the pump means, while the flow ports B and C are connected to the reservoir. Under these circumstances, the pistons of the pump means on their intake strokes receive fluid from the reservoir through port C as previously described except that it receives its fluid from chamber 92 and conduit 58 and pistons 19 and pump this fluid through the output ports of the pump to the chamber 38 of the actuator 32 thereby returning the piston to the proper position and resisting attempted further movement of the piston by the forces applied by the load 31. During this operation it should be noted that additional fluid is pumped into a fixed volume thereby causing an increase in pressure. As soon as this attempted movement has been properly resisted by creating a higher differential pressure across the piston 35 of the actuator 32, the spool 70 is returned to the position illustrated in FIG. 1 thereby again closing the flow ports A, B and C.

From the foregoing description it can now be seen that the delivery of hydraulic fluid by the pump is controlled by throttling the inlet port of the pump and permitting the same to be opened only during the time a flow demand is created by the load positioning apparatus such as the actuator 32.

Referring now to FIG. 2, there is illustrated a servopump control system which operates in accordance with the principles of the system illustrated in FIG. 1

and above described. Many of the features of the system shown in FIG. 2 are identical to those shown in FIG. 1 and, therefore, will not be discussed in detail below. However, where similar fixtures to those shown in FIG. 1 are discussed, the same reference numberals will be used. Only those portions of the system which are different will be described below.

A system as shown in FIG. 2 is designed so as to be operable in a redundant control system having a plurality of control channels at least one of which is connected to position a load. Such redundant control system utilizing such apparatus as shut-off valves, engage valves and hydraulic logic to ascertain failure of a particular channel is well known in the art, and reference in any detailed description will, therefore, not be made herein. For example, and for more detailed information with respect to redundant control systems reference should be made to U.S. Pat. Nos. 3,391,611, 3,338,138 and 3,385,171. Therefore, as a result of the foregoing references no detailed description will be made of the shut-off valve, reset piston, start solenoid, or the other control channels except during a general operational description of the system shown in FIG. 2.

One feature of the system shown in FIG. 2 which is not present in FIG. 1 is the utilization of a make-up valve 101 which includes a spool 102 having

areas

103 and 104 disposed in isolated chambers of the bore 105 within which the spool 102 is permitted to move. The area 103 is connected to the chamber 37 of the actuator by means of the conduit 106 while the area 104 is connected to chamber 38 by the conduit 107. Also disposed within the bore 105 is a spring 108 which exerts a continuous foce on the spool 102 urging it in an upward direction as viewed in FIG. 2. During the time that the combined pressure in the

chambers

37 and 38 exerted against the

areas

103 and 104 equals a predetermined force which is greater than the force of the spring 108, the make-up valve remains in the position illustrated. In the position illustrated, a port 109 is maintained closed by the spool 102. The port 109 is connected by the conduit 1 11 to the chamber'56 which is connected to the reservoir 51. If the force generated by the spring 108 overcomes the force generated by the pressures from the

chambers

37 and 38 and the makeup valve is permitted to open the port 109, communication is established with the reservoir 51 through the conduit 112 which is connected to the intake port of the pump means.

Another difference of the system shown in FIG. 2 as compared to that in FIG. I is that the

chambers

37 and 38 of the actuator are connected to chambers 115 and 116 of the bore 117 in which the control spool 118 reciprocates. The flow ports D and E are normally blocked by the

lands

121 and 122 of the spool 118 respectively. As is illustrated, the flow ports D and E are directly connected to the output and input ports of the pump means respectively.

It can therefore be seen that in the event the spool 118 is moved toward the left as shown in FIG. 2, the output of the pump means is connected to the flow port D and fluid is caused to flow under pressure to the chamber 37 of the actuator. At the same time the flow port E is connected to the input port of the pump and to the chamber 38 of the actuator. Thus, the fluid being supplied to the chamber 37 of the actuator is being supplied by the fluid present in the chamber 38 of the actuator. The foregoing, of course, assumes that the makeup valve remains in the position shown in FIG. 2. In the event a shortage of fluid as required develops, the pressure appearing in the chamber 38 drops below a predetermined minimum thus permitting the make-up valve to open and supply additional fluid from the reservoir to the input of the pump means.

Alternatively, if the spool 18 is moved toward the right as viewed in FIG. 2, the flow'port D is connected to the chamber 38 of the actuator and to the output of the pump while the flow port E, the input to the pump, is connected to the chamber 37 of the actuator with results similar to those above described.

In addition to the foregoing an additional feature of the system shown in FIG. 2 is the mechanism whereby a discrepancy in the signal being applied for control purposes may be detected thereby indicating a malfunction in the control channel. Such is accomplished by providing a monitor torque motor 120 which has an identical signal applied thereto as is applied to the torque motor 82 for control purposes. However, the armature of the torque motor 120 is connected to a monitor spool which reciprocates within a bore 129 provided in the control spool 118. As is shown, reservoir 51 is connected by the conduit 123 to a port 124 in the spool 118 which port is normally blocked by the land 125 of the monitor spool. A conduit 126 connects system pressure, the output port of the pump means, through a restriction orifice 127 to a chamber 128. In the event of a discrepancy occurring, the monitor spool and control spool will move differently thereby connecting reservoir to the conduit 126 and thus will actuate the shut-off valve thereby eliminating control of the actuator by the pump shown in FIG. 2. Under these circumstances, control of the positioning of the actuator and thereby a load that would be connected thereto would be transferred to other control channels as described in the above referred to United States Patents.

We claim: 1. A syttem for supplying fluid under pressure to an actuator comprising:

pump means having an inlet and an outlet; an actuator; a reservoir of said fluid; control valve means connected between said pump means and said actuator and normally blocking fluid flow between said reservoir and said pump inlet and between said actuator and said pump outlet; signal responsive means connected to move said control valve means to provide direct fluid communication between said pump inlet and outlet and said actuator, said pump means transferring fluid from one part of said actuator to a different part thereof thereby to position said actuator; a conduit means interconnecting said reservoir and 5 said pump means inlet;

make-up valve means connected in said conduit means for maintaining said conduit means normally closed; and pressure sensitive means connected to said actuator and to said make-up valve means to actuate saidmake-up valve means and interconnect said reser-- voir to said pump inlet when the pressure at said actuator is at a predetermined level. 2. A throttling pump load positioning apparatus comprising:

a continuously running fixed displacement fluid pump means having inlet and outlet ports; a reservoir of fluid; conduit means connecting said inlet ports to said reservoir;

flow control valve means in said conduit means connected to control the flow of fluid from said reservoir to said inlet parts, said flow control valve means normally blocking flow between said reservoir and said inlet ports;

means for controlling said flow control valve means to permit fluid flow between said reservoir and said inlet ports; &.

load positioning means connected to said outlet ports; and feedback means responsive to fluid flow and/or pressure demands of said load positioning means connected between said load positioning a means and said means for controlling said valve means.

3. A throttling pump load positioning apparatus comprising:

a continuously running fixed displacement fluid pump means having inlet and outlet ports;

a reservoir of fluid;

inlet conduit means connecting said inlet ports to said reservoir;

load positioning means connected to said outlet ports;

flow control spool valve means in said inlet conduit means connected to control the flow of fluid from said reservoir to said inlet ports, said spool valve having lands thereon normally blocking said pump inlet and outlet ports from communication with said reservoir and said load positioning means respectively and;

means for controlling said flow control valve means to permit fluid flow between said reservoir and said inlet ports.

Claims

1. A syttem for supplying fluid under pressure to an actuator comprising: pump means having an inlet and an outlet; an actuator; a reservoir of said fluid; control valve means connected between said pump means and said actuator and normally blocking fluid flow between said reservoir and said pump inlet and between said actuator and said pump outlet; signal responsive means connected to move said control valve means to provide direct fluid communication between said pump inlet and outlet and said actuator, said pump means transferring fluid from one part of said actuator to a different part thereof thereby to position said actuator; a conduit means interconnecting said reservoir and said pump means inlet; make-up valve means connected in said conduit means for maintaining said conduit means normally closed; and pressure sensitive means connected to said actuator and to said make-up valve means to actuate said-make-up valve means and interconnect said reservoir to said pump inlet when the pressure at said actuator is at a predetermined level.

2. A throttling pump load positioning apparatus comprising: a continuously running fixed displacement fluid pump means having inlet and outlet ports; a reservoir of fluid; conduit means connecting said inlet ports to said reservoir; flow control valve means in said conduit means connected to control the flow of fluid from said reservoir to said inlet parts, said flow control valve means normally blocking flow between said reservoir and said inlet ports; means for controlling said flow control valve means to permit fluid flow between said reservoir and said inlet ports; & load positioning means connected to said outlet ports; and feedback means responsive to fluid flow and/or pressure demands of said load positioning means connected between said load positioning means and said means for controlling said valve means.

3. A throttling pump load positioning apparatus comprising: a continuously running fixed displacement fluid pump means having inlet and outlet ports; a reservoir of fluid; inlet conduit means connecting said inlet ports to saiD reservoir; load positioning means connected to said outlet ports; flow control spool valve means in said inlet conduit means connected to control the flow of fluid from said reservoir to said inlet ports, said spool valve having lands thereon normally blocking said pump inlet and outlet ports from communication with said reservoir and said load positioning means respectively and; means for controlling said flow control valve means to permit fluid flow between said reservoir and said inlet ports.