US3556150A - Electro hydraulic servovalve - Google Patents

Abstract

An electrohydraulic servovalve including a signal responsive torque motor having at least one high energy permanent magnet providing a magnetic flux field. A flux field shunt is affixed to the magnet to compensate for the effects of temperature on servovalve operating characteristics to ensure a consistent hydraulic output function in relation to a given input signal over a wide range of operating temperatures.

Description

United States Patent I Inventor Donald A. King Camarillo, Calif.

Appl. No. 823,877

Filed May 12, 1969 Patented Jan. 19, 1971 Assignee Borg Warner Corporation Chicago, II]. a corporation of Delaware ELECTRO HYDRAULIC SERVOVALVE 8 Claims, 5 Drawing Figs.

US. Cl. l37/625.4, 1 37/625.62; 335/217, 335/236- Int. Cl ..Fl6lt 31/04, H02k 33/ 12 Field ofSearch ..137/625.65,

625.62, 625.4; 335/217, 236; 310/36, 29, (Inquired), 214, 216

[56] References Cited 3 UNITED STATES PATENTS 1,632,609 6/1927 Lee 335/217 2,720,603 [0/1955 Mitchell et a1. 335/2 1 7X 2,961,002 1 1/ 1960 Gordon 137/625'.62 3,154,728 10/1964 Bordenet... 335l236X 3,194,998 6/1965 Marfut 335/217X 3,415,283 12/1968 Trbovich et a1 l37/625.62

Primary Examiner-M. Cary Nelson Assistant Examiner-R. B. Rothman Attomeys-Donald W. Banner, Lyle S. Motley, C. G. Stallings and William S. Mc Curry ABSTRACT: An electrohydraulic servbvalve including a signal responsive torque motor having at least one high energy permanent magnet providing a magnetic flux field. A flux field shunt is affixed to the magnet to compensate for the effects of temperature onservovalve operating characteristics to ensure a consistent hydraulic outputfunction in relation to a giveninput signal over a wide range of operating temperatures.

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ATTORNEY I 1,-ELECTRQ'HYDRAULICSERVOV-ALVE BAcxoRouND or Tl-IEINVENTION The invention relates to electrohydraulic servovalves. More I particularly, it relates to electrohydraulic-'servovalves having means to compensate for: the effects of temperature on servovalve operating characteristics. Electrohydraulic servovalves are used to'translate' a low energy electrical-input .to a high energy hydraulic output. Servovalv'es in many applications are exposed to a-widerange of operating temperatures. Under such conditions, it is typical to experience a gradual degradationin servovalve output at any given electrical input asoperating temperature increases. .This

phenomenon is attributedto a'grean'extent to the thermal characteristics of the high energy permanent magnets commonly used in these devices. f

, The effect of temperature on the remanence of a permanent magnet manifestsitselfin two different ways: 1 l.-The nonreversible effect; and

2.The-reversibleeffect.;.- L 1 'Theformerproduce's "a loss in the remanentflux' density, which when certaintemperature extremes "are encountered cannot be restored. "This 'nonreversible effect can be eliminated by the simple expedient of. cycling the magnet several times throughttheant'icipatedrange before finally adjustingitsoperatingflux density. I v

The reversible effect cannot be eliminated, however, and servovalve. operating characteristics are affected by the degradation of the magnetic fluxgfield astemperatureim creases.

Ina servovalvepincreased operating temperature not only affects themag'ne tic characteristics of thetorque motor, but also produces significant changes in-valve orificeand pumping characteristics due to mechanical thermal expansion.

It is essential .to reliable servovalve performance to minimize the variations ino'utput signal in relation to varying temperature conditions. It has beendetermined that. compensation fortheefi'ects of temperature oh'thevarious operating characteristics may be providedbycontrol of the flux density of the permanent magnets/forming part of the servovalve torque motor. lnthis way, asingle compensationmeansovercomes the undesirable variations in' operatin'g characteristics of theservovalveeomponents.

1 Accordin'gly,:i,t is thejprincipal object 6:- the .presentinvention to providean electrohydraulic servovalve which includes means for compensating for the effects of temperature upon all of the operating variables affected by changesin'operating temperature to produce a consistent hydraulic output function in relation to given electrical, input'command.

, SUMMARY OF THE INVENTION Very generally, the electrohydraulic servovalve of the present invention includes atorque motor responsive to an electrical input signal to control an hydraulic output function.

The hydraulic output function is variable in response to the input signal. The servovalve includes a-torque motor having at least one permanent magnet to establish aflux'field. A magnetic shunt'is affixed to the permanent magnet which produces an inverse characteristicof gain in'relation to increasingtemperature to compensate-for the'effects of temperature upon the servovalve operating parameters including loss of magnetization, mechanical and thermal expansion, orifice characteristics, and pumping effects,

The compensator is affixed tothe magnet in contact with the maximum potential portions of the magnet and is shaped I to provide maximum contact with the magnet to provide optimum compensating efficiency. 'At low temperature,a portion of the magnetic flux field produced by the magnet is bypassed through the compensator. As temperature increases,

the efficiency of the compensator, because of its inherent.

characteristic of inverse gain, is reduced. As temperature increases, an increased proportion of magnetic flux is released into the active magneticeircuit to compensate for the overall degradation of the available flux field as well as the other operating variables affected by the increased temperature.

More particular objects and advantages of the present invention will become apparentin' connection with the following description having reference to theaccomp'anying drawings.

DESCRlPTlON OF THE DRAWlNGS FIG. 1 is a sectional elevationalview in partial schematic of an electrohydraulic servovalve illustrative of principles of the l l't'fsent-inv'ention.

FIG. 2 isaside elevational sectional view of the apparatus of FIG. l talten generally along the line 2-2 of that FIG.

FIG. '3 is a perspective view of a portion of the apparatus of FIG. 1 illustrating a torque motor permanent magnet and attach'e d compensator. a

FIG. 4 is a diagrammatic view of a portion of the apparatus of FIG. 1 illustrating conditions existing at low temperature. FIG. 5 is a diagrammatic view of a portion of the apparatus of FIG. 1 illustrating conditions existing at high temperature.

" DETAILED-DESCRIPTION i I Referringspecifically to the drawings, there is illustrated an facing, spaced apart relation.

A pair f orifice elements 21 are'dispos ed withinthe valve body and define fixed orifices '22 spaced outwardly of the noz- .zles' in adirection away from the vertical passage 17. Passages '25 provide fluid communication between the orifices 22 and the nozzles 19. V

Hydraulic fluid under pressure in the order of magnitudeof 3,000 psi. is applied to theiservovalveby a hydraulic supply pump (not shown). This fluid enters'the valve body and is 'divided' intoa pair of inlet or supplyjpassages 27. This fluid passes 4 through the nozzles 22 into the passages 25. Each passage 25 is in communication with an output passage 29.

These passages are, in turn, connected to the actuator 15 and fluid, flow through the outlet passages. accomplishes the desired movementof the actuator in-response to the input signal. The passages 25 are additionally in communication with the sump of the supply pump through the nozzles 19 and the vertical passages 17.

Disposed within the vertical passage 17 is a flapper 31. The flapper includes a support ring 33 secured to the valve body 13 in fluid tight relation. This support ring is provided with a flexible diaphragm (not shown) which provides a flexible, fluid tight seal between the valve body 13 and the torque motor 11. I The portion of the flapper 31 extending into the vertical passage includesa flattened end portion 35 disposed between the nozzles 19 in juxtaposed, spaced apart relation to the nozzle openings. The flapper further includes a portion 37 extend- 7 ing into the torque .motor 11 which includes an integrally formed transverse armature 39 of magnetic material which forms the armature of the torque motor 11.

The passages 29 communicate hydraulic output of the servovalve to the actuator 15 through passages or conduits 41. The actuator 15 includes a hollow cylinder 43 within which is disposed a reciprocable piston 45. The piston is secured to an output shaft 47 which extends outwardly of the cylinder and is connected to a mechanical linkage, and imparts movement to the linkage in response to the servovalve operation.

direction. Conversely theflow of fluid through the other of the passages 29 and conduit 41 into the cylinder 43 causes movement of the piston 45 and output shaft 47 in the opposite direction. In this way, movement of the mechanical linkage may be readily accomplished in response to the hydraulic flow in the servovalve.

The torque motor 11 is secured to the main valve body 13 in overlying relation to the flapper 31. A cover member 49 surrounds the torque motor.

The torque motor includes a pair of permanent magnets 53 supported in vertically disposed spaced apart relation between a pair of generally horizontal pole pieces 55. The magnets are horizontally elongated and have poles or maximum potential portions in contact with the pole pieces.

As seen in FIG. 1 the pole pieces include upwardly and downwardly directed end portions 57 terminating in closely spaced relation defining working air gaps associated with opposite ends of the armature 39 of the flapper 31. The pole pieces direct the flux field established by the permanent magnets across the gaps between the facing end portions and \thereby establish a concentrated magnetic field associated with the flapper armature (see F [68.4 and The torque motor 11 additionally includes a pair of electrical coils 59 and 61. Each coil is disposed in surrounding relation to a portion of the armature 39 on opposite sides of the flapper. These coils are connected to a source of electrical input signal (not shown) which established an electromagnetic flux f eld.

Opposite ends of the armature 39 are each subjected to two magnetic flux fields, one established by the permanent magnets and concentrated upon the armature ends by the pole pieces 55 and one established by electrical coils 59 and 61. By controlling the current flow to each coil, a differential flux is produced which will cause movement of the armature in either the clockwise or counterclockwise direction. This will in turn cause a corresponding movement of the flattened end portion 35 of the flapper toward one of the nozzles 19 and away from the other progressively inhibiting flow through one nozzle opening and progressively increasing flow through the other. Inhibiting flow through one nozzle causes a corresponding increase in the flow through the associated outlet passage 29 in conduit 41 into the actuator cylinder 43. An increase in flow through the opposite nozzle causes flow from the cylinder 43 through the opposite conduit.4l in passage 29 into the passage 25 and through the nozzle opening to the sump. This action causes movement of the piston 45 and output shaft 47 in one direction or the other, depending upon the direction of movement of the flattened end portion 35. Equalization of the current flow in the coils 59 and 61 returns the flapper flattened end portion 35 to the neutral position resulting in an equal flow through each nozzle opening. At that point movement of the piston 45 is terminated. I

In accordance with the present invention and as best seen in FIG. 3, compensating means are provided in the torque motor to ensure consistent hydraulic output in relation to a given input signal command. The compensating means includes a pair of shunts 63 secured to the permanent magnets 53 which provide the initial or constant flux field of the torque motor 1 l The shunt 63 is essentially rectangular in shape and it includes opposite end portions 65 which are deformed slightly in a direction toward the magnet to which it is affixed to insure intimate contact with the end portions of the shunt with the areas of maximum potential of the magnet.

In the illustrated embodiment the shunts 63 are secured to the permanent magnets 53 by a spot weld 67 intermediate the poles of the magnet in the area of minimum potential. It must be appreciated that any suitable means for fastening the compensator may be utilized so long as intimate direct contact between the compensator and the magnet in the areas ofmaximum potential of the magnet is achieved.

The compensator is formed of any suitable permeable material such as, for example, nickel-iron alloy which has a high permeability and low temperature and suffers a loss of permeability as temperature increases, thus reducing its ability to divert magnetic flux.

FIGS. 4 and 5 illustrate the operation of the compensators 63. While in the illustrated embodiment one such compensator 63 is attached to each one of the permanent magnets 53, it must be appreciated that in certain applications only one compensator attached to one magnet need be used without in any way departing from the scope of the invention.

As illustrated, the compensators or shunts 63 attached to the magnets 53 present a high permeability path between the areas of maximum potential of the magnets at low operating temperatures. As a result the compensators bypass or divert a relatively large amount of magnetic flux from the pole pieces 55 and consequently from the working air gap between the pole piece end portions 57. This arrangement establishes the maximum flux field provided by the permanent magnetsto which the end portions of the armature 39 are subjected. As the temperature of the servovalve increases the magnetic field of the permanent magnets 53 inherently decreases. Simultaneously the permeability of the shunt or compensator 63 also decreases and is therefore less effective to bypass flux from the pole pieces 55 and working air gap between the end portions 57 of the pole pieces.

By selecting shunts of proper size and shape the-flux across the working air gap may be maintained at a constant value and the servovalve can thus deliver a constant output regardless of the operating temperatures experienced. The shunt is sized to not only compensate for the degredation of the magnetic field of the permanent magnets 53 in relation to increasing temperature, but also is sized to compensate for the variation in other operating characteristics of the valve such as orifice characteristics, mechanical thermal expansion and pumping effects. Thus by utilizing a single compensating arrangement the effects of temperature upon all servovalve components is minimized and consistent output in response to the given input signal is assured throughout a wide range of operating temperatures.

In a specific example of an electrohydraulic servovalve of the type described a range of operating temperatures from between 20 F. to 320 F. was experienced. It was determined that the servovalve experienced an average gain, that is, change in hydraulic output function in relation to a given electrical input command in the order of l0percent at 320 F. and+5 percent at 20 F. as referenced to the gain experienced at a temperature of F. This gain was attributable to the variations in magnetic, hydraulic and mechanical characteristics of the servovalve in relation to variations in operating temperature. Since the compensator produces an inverse gain curve that is, it experiences a reduction in the ability to bypass magnetic flux as temperature increases, attachment ofthe magnet shunt to the permanent magnets result in the establishment of a constant hydraulic output function in response to a given electrical input signal over the entire operating range. A compensator of generally rectangular shape formed of Carpenter (Registered Trademark) 032 alloy of a metal thickness of .020 inch was determined to provide the necessary compensating capabilities. One such compensator was attached to each of the permanent magnets of the servovalve. The compensator was formed of rectangular shape to ensure that sufficient contact area between the compensator and the maximum potential portions of the magnet was provided. In this regard a contact area extending from the polarity extremes of the magnet to 25 percent of the distance to its neutral magnetic zone was provided.

As can be seen an electrohydraulic servovalve has been provided which produces a consistent hydraulic output function in relation to a given input signal over a wide range of operat- '5 ing temperatures. The compensator accommodates variations in magnetic, hydraulic and mechanical characteristics of the valve in relation to variations in temperature.

Various features of the invention have been particularly shown and described. However, it must be appreciated that various modifications may be made without departing from the scope of the invention.

lclaim: v

1. An electrohydraulic servovalve including a main valve body defining a divided fluid path, a pair of nozzles disposed in spaced apart facing relation, each one of said nozzles being in fluid communication with a separate portion of said fluid path, a flapper having an end portion positioned intermediate said nozzles and movable toward and away from each said nozzle to control the flow of fluid in each portion of said divided flow path, said flapper including an opposite end defining an armature, and a torque motor secured to said valve body to effect movement of said flapper, said torque motor including at least one permanent magnet to provide a permanent magnet flux field acting upon said armature, and at least one electric coil responsive to an electrical input signal to provide a variable flux field acting upon said armature to vary the position of said flapper, said torque motor including at least one compensating shunt made of permeable material affixed to said permanent magnet in contact therewith to bypass a portion of said permanent magnet flux field at low temperature and being responsive to temperature to reduce the amount of flux bypassed as temperature increases.

2. An electrohydraulic servovalve as claimed in claim 1 wherein said compensating shunt is in contact with said permanent magnet at the maximum potential portion of said mag net.

3. An electrohydraulic servovalve as claimed in claim 2 wherein said compensating shunt is generally rectangular and includes opposite end portions deformed slightly in a direction toward said magnet and wherein said shunt is affixed to said magnet with said deformed end portions thereof in contact with the maximum potential portions of said magnet.

4. An electrohydraulic servovalve as claimed in claim 1 wherein said torque motor includes a pair of permanent magnets disposed in spaced apart relation, a pair of pole pieces of magnetic material contacting said magnets at the maximum potential portions thereof, said pole pieces including opposite end portions disposed in facing spaced relation defining air gaps therebetween and a portion of said armature of said flapper is disposed in said air gap, said torque motor further including a pair of said electrical coils each one of said coils surrounding a portion of said armature adjacent said portions thereof disposed in one of said air gaps, and a pair of said compensating shunts, each one of which is affixed to one of said permanent magnets.

5. A torque motor for an electrohydraulic servovalve having a flapper movable to control the flow of fluid therethrough including an armature, said torque motor including at least one permanent magnet to provide a permanent magnet flux field acting upon the armature and at least one electric coil responsive to an electrical input signal to provide a variable flux field acting upon the armature, said torque motor including at least one compensating shunt made of permeable material affixed to said permanent magnet in contact therewith to bypass a portion of said permanent magnet flux field at low temperature and being responsive to temperature to reduce the amount of flux bypassed as temperature increases. 1

6. A torque motor as claimed in claim 5 wherein said compensating shunt is in contact with said permanent magnet at the maximum potential portions of said magnet.

7. A torque motor as claimed in claim 6 wherein said compensating shunt is generally rectangular and includes opposite end portions deformed slightly in a direction toward said magnet and wherein said shunt is affixed to said magnet with said deformed end portions thereof in contact with the maximum potential portions of said magnet.

8. A torque motor as claimed in claim 5 wherein said torque motor includes a pair of permanent magnets disposed in spaced apart relation, a pair of pole pieces of magnetic material contacting said magnets at the maximum potential portions thereof, said pole pieces including opposite end portions disposed in facing spaced relation defining air gaps therebetween and a portion of said armature of said flapper is disposed in each said air gap, said torque motor further including a pair of said electrical coils each one of said coils surrounding a portion of said armature adjacent said portions thereof disposed in one of said air gaps, and a pair of said compensating shunts, each one of which is affixed to one of said permanent magnets.

Claims (8)

1. An electrohydraulic servovalve including a main valve body defining a divided fluid path, a pair of nozzles disposed in spaced apart facing relation, each one of said nozzles being in fluid communication with a separate portion of said fluid path, a flapper having an end portion positioned intermediate said nozzles and movable toward and away from each said nozzle to control the flow of fluid in each portion of said divided flow path, said flapper including an opposite end defining an armature, and a torque motor secured to said valve body to effect movement of said flapper, said torque motor including at least one permanent magnet to provide a permanent magnet flux field acting upon said armature, and at least one electric coil responsive to an electrical input signal to provide a variable flux field acting upon said armature to vary the position of said flapper, said torque motor including at least one compensating shunt made of permeable material affixed to said permanent magnet in contact therewith to bypass a portion of said permanent magnet flux field at low temperature and being responsive to temperature to reduce the amount of flux bypassed as temperature increases.

2. An electrohydraulic servovalve as claimed in claim 1 wherein said compensating shunt is in contact with said permanent magnet at the maximum potential portion of said magnet.

3. An electrohydraulic servovalve as claimed in claim 2 wherein said compensating shunt is generally rectangular and includes opposite end portions deformed slightly in a direction toward said magnet and wherein said shunt is affixed to said magnet with said deformed end portions thereof in contact with the maximum potential portions of said magnet.

4. An electrohydraulic servovalve as claimed in claim 1 wherein said torque motor includes a pair of permanent magnets disposed in spaced apart relation, a pair of pole pieces of magnetic material contacting said magnets at the maximum potential portions thereof, said pole pieces including opposite end portions disposed in facing spaced relation defining air gaps therebetween and a portion of said armature of said flapper iS disposed in said air gap, said torque motor further including a pair of said electrical coils each one of said coils surrounding a portion of said armature adjacent said portions thereof disposed in one of said air gaps, and a pair of said compensating shunts, each one of which is affixed to one of said permanent magnets.

5. A torque motor for an electrohydraulic servovalve having a flapper movable to control the flow of fluid therethrough including an armature, said torque motor including at least one permanent magnet to provide a permanent magnet flux field acting upon the armature and at least one electric coil responsive to an electrical input signal to provide a variable flux field acting upon the armature, said torque motor including at least one compensating shunt made of permeable material affixed to said permanent magnet in contact therewith to bypass a portion of said permanent magnet flux field at low temperature and being responsive to temperature to reduce the amount of flux bypassed as temperature increases.

6. A torque motor as claimed in claim 5 wherein said compensating shunt is in contact with said permanent magnet at the maximum potential portions of said magnet.

7. A torque motor as claimed in claim 6 wherein said compensating shunt is generally rectangular and includes opposite end portions deformed slightly in a direction toward said magnet and wherein said shunt is affixed to said magnet with said deformed end portions thereof in contact with the maximum potential portions of said magnet.

8. A torque motor as claimed in claim 5 wherein said torque motor includes a pair of permanent magnets disposed in spaced apart relation, a pair of pole pieces of magnetic material contacting said magnets at the maximum potential portions thereof, said pole pieces including opposite end portions disposed in facing spaced relation defining air gaps therebetween and a portion of said armature of said flapper is disposed in each said air gap, said torque motor further including a pair of said electrical coils each one of said coils surrounding a portion of said armature adjacent said portions thereof disposed in one of said air gaps, and a pair of said compensating shunts, each one of which is affixed to one of said permanent magnets.

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