GB2109873A - Improvements in or relating to pumps - Google Patents

Abstract

A pump comprises a piston 130 which is made of magnetic material and can undergo reciprocatory movement in a chamber formed in a bobbin 112. Coils 114, 115 are wound on the bobbin 112 and are arranged to be energised alternately to cause the piston to reciprocate in the chamber. The piston defines a fluid flow passage through which fluid can flow via a flow control device 150. When the piston 130 moves in one direction fluid is drawn into the chamber through an inlet 140 and when the piston moves in the opposite direction the fluid can flow via the flow control device 150 for discharge through an outlet 148 during a subsequent stroke of a piston. The pump can be mounted to form part of the piston of an actuator. <IMAGE>

Description

SPECIFICATION Improvements in or relating to pumps This invention relates to pumps. In particular it relates to pumps of the type in which a piston which can reciprocate within a cylinder or chamber to cause fluid to flow from an inlet to an outlet. A feature of the present invention is the provision of a pump which can be constructed in a very compact form.

According to the present invention there is provided a pump comprising a piston which includes or carries magnetic material and which is arranged so that it can undergo reciprocatory movement within a chamber, means for producing a magnetic field the direction of which altemates to cause the piston to reciprocate within the chamber, an inlet for fluid to said chamber, said piston defining a fluid flow passage through which fluid can flow from said inlet through a one way fluid control device, said fluid flow passage being in communication with an outlet for the pump, the arrangement being such that as the piston moves in one direction fluid is drawn in through said inlet and as the piston moves in the opposite direction said fluid can flow through said one way fluid flow control device for discharge during a subsequent stroke of the piston, said means for producing the magnetic field including a pair of coils and means for supplying an alternating current to said coils such that one coil is energised during the positive portion of the alternating cycle and the other coil is energised during the negative portion of the alternating cycle, said current supply to said coils including diodes arranged to pass only the positive portion of the alternating cycle to the one coil and the negative portion to the other coil.

The inlet of the pump and the output of the pump may be arranged coaxially with the chamber and piston. Either or both of the inlet and outlets may include valve means for controlling flow of fluid therethrough.

According to another aspect of the present invention there is provided an actuator including an actuating member which can be moved to cause operation of a device such as a valve, and means for moving the actuating member comprising a pump which is arranged to pump hydraulic fluid into a variable capacity chamber, said pump being mounted so that it forms part of said actuating member and can pump fluid into said variable capacity chamber to cause the actuating member to move.

The invention will be described now by way of example only with particular reference to the accompanying drawing. In the drawings: Figure 1 is an axial section through one embodiment of a pump in accordance with the present invention; Figure 2 is an axial section through another embodiment of a pump constructed in accordance with the present invention, Figure 3 is an axial section through a valve actuator incorporating a pump in accordance with the present invention, and Figures 4 and 5 show two arrangements for feeding current to the coils of the pump of Figure 3.

Referring to Figure 1 an hydraulic pump has a casing 10 which includes a tubular part 11 with circular end plates 1 2 and 14. Each end plate 1 2 has a central circular aperture which receives an end projection of one of two cylindrical pieces of magnetic materials 1 5, 16. Each piece of magnetic material has an inner end surface 17, 18 which is generally conical in form, the end faces being spaced axially to define therebetween a chamber 1 9. Each cylindrical member also has an axial through bore 21,22. The through bore 21 constitutes an inlet for the pump whilst the bore 22 receives a tubular member 23 which projects into the chamber 1 9 and terminates in a rod like part 24.The rod like part 24 has threaded onto the external surface thereof a tubular member 25 having axial bores 26 at one end of each of which is a one way valve arrangement 27. The tubular member 23 at its junction with the rod like part 24 has radial through apertures 28. The opposite end of the tubular member 23 terminates against a valve 30 which is normally biassed to a closed position by a spring 31 which extends between a valve member 32 and the tubular bushing 33 which is screwed into the end portion of the magnetic part 16.

A first solenoid coil 40 is located in the annular space between the tubular housing part 11 and the magnetic member 1 5 whilst a second solenoid coil 41 is located in the annular space between the tubular housing part 11 and the magnetic member 1 6. An alternating current can be supplied to each coil by way of diodes 44, 45 which are so arranged that one of the coils is arranged to receive only the positive part of an alternating current cycle whilst the other coil is arranged to receive only the negative part. Thus the coils 40 and 41 are energised alternately. The magnetic circuits are so arranged that when one of the coils is energised the magnetic field so produced exerts a force in a first axial direction of the pump whilst when the other coil is energised the magnetic force is in the opposite direction.

A piston 50 which is made of magnetic material is mounted so that it can move back and forth within the chamber 19. The piston has a tubular part 51 at one end of which is an inwardly directed annular flange 52 the inner surface of which contacts the exterior of the tubular member 23. At its other end the internal surface of the tubular part 51 is threaded to receive a tubular part 55 which carries a non-return valve 56. The non-return valve 56 is designed to allow fluid flow from the chamber 1 9 into the cavity 60 defined within the tubular part 51 of the piston 50. The outer periphery of the piston 50 has axially extending grooves indicated at 65 which allow the piston to move through fluid contained within the chamber 19.

In operation of the pump an alternating current of 50 c/s is supplied to the coils 40 and 41 by way of the diodes 44, 45. During the positive half cycle of the alternating current one of the coils 40, 41 is energised and during the negative half cycle the other coil is energised. This results in the production of a magnetic field within the chamber 1 9 the effect of which is to produce a magnetic force in one direction for that half of the alternating current cycle and a magnetic force in the opposite direction for the other half of the alternating current cycle. Thus the piston 50 which is made of magnetic material is caused to move back and forth within the chamber 19 in response to the changes in the direction of the magnetic force.Considering the situation when the piston 50 moves from a position in which it is in contact with the end face 1 7 of the magnetic member 1 5 fluid is sucked in behind the piston through the inlet 21. On the return stroke of the piston this fluid then enters the cavity 60 within the tubular piston by way of the non-return valve 56. On the next stroke the fluid which has entered the cavity within the piston is expelled by way of valves 27 and bores 28 to the interior of the tubular member 23. Subsequently the fluid exits by way of valve 32 to the outlet of the pump which is constituted by the bushing 33.

The present pump can be constructed in a very compact form and produces a relatively high output. The pump can be used without the need for inlet and outlet valves although the efficiency is improved by using inlet and outlet valves. As shown in Figure 1 the inlet valve is a conventional plate valve 32 although as an alternative an 0ring valve of the form shown in the inset of Figure 1 can be used. This comprises an O-ring 65 located within a circumferential groove in the end of the tubular part 23. The O-ring normally seals radial apertures 66 formed in the tubular part 21 but can expand in response to fluid pressure to allow the fluid to pass to the outlet of the pump.

When the pressure is relieved the O-ring 65 can then contract to seal the apertures.

Figure 2 shows a modification of the pump of Figure 1. In this modification the inlet to the chamber is by way of a radial extending port 81.

The pump shown in Figure 2 has two outlets extending coaxiaily with the pump housing The piston is arranged to move in a reciprocal fashion in the manner described with reference to Figure 1 and outputs to the outlets are provided on alternate strokes of the piston.

Referring now to Figure 3 there is shown an embodiment of the invention in which the hydraulic pump forms part of the actuating member of a valve actuator. The hydraulic pump is mounted in the end region of the actuator housing 100 between a thrust member 101 and the end face 102 of the housing 100 which includes a cylindrical projecting portion 103. The pump assembly is supported within a cup shaped member 104 which is mounted coaxially with the actuator housing 100. The closed end 1 05 of the cup shaped member 104 carries a solenoid valve assembly 106 which is located within the cylindrical portion 103. The portion of the actuator housing accommodating the valve assembly is sealed by means of a rubber bladder 108.

The pump assembly comprises an outer tubular member 111 which is slidably mounted in the cup shaped member 104. The tubular member 111 accommodates a one piece metal bobbin 112 which is made of magnetic material.

The bobbin is shaped to define two annular chambers each of which accommodates one of two axially spaced solenoid coils 114, 1 55. In particular it will be noted that the bobbin is profiled at regions identified by reference numeral 118 for a reason to be described later. The bobbin 112 has an axial through bore which accommodates a piston assembly 130 made of magnetisable material. The wall of the bore is formed with a step at 11 9. Two of the profiled portions 11 8 are formed with through apertures 120 which communicate with the through bore.

The junction between the bobbin 112 and the cup shaped member 104 is sealed by means of an annular seal 123. The end wall 126 of the bobbin is recessed at 128 to define a chamber 129 between the bobbin and the end of the cup shaped member 104.

The outer tubular part 111 is cut away at 125 so that the interior thereof can communicate with the annular chamber formed between the cup shaped part 104 and the rubber seal 108.

Additionally the bobbin has radially extending cut away portions which are indicated at 126 and 127.

The piston assembly 1 30 comprises a first piston part 131 which has a first tubular portion 132 and a second thicker walled tubular portion 133. The tubular portion 132 is arranged so that it can slide within a tubular sleeve 135 which is fixed within the through bore of the bobbin between a shoulder 136 on the bore wall and a castellated boss 138 screwed into the end portion of the bobbin 112. An inlet plate valve 140 is located in an axial through aperture of the castellated boss 1 38 adjacent the end of the sleeve 1 35. The larger diameter portion 133 of the piston part 131 can slide axially within a chamber defined between the step 11 9 and the inner end face of the sleeve 135. The larger diameter portion 1 33 has axial through bores 134.

The second part of the piston assembly 130 comprises a tubular member 144 which is located partially within the tubular portion 133 and partially within a sleeve 145 which is sealed within the axial through bore of the bobbin by means of seal 136. The tubular part 144 can slide axially with the other piston part 131. The sleeve 145 is secured within the bobbin bore by a tubular washer 146 which is screwed into the bore. The through aperture of the washer 146 accommodates an outlet plate valve 1 48.

Within a central portion of the bore of the piston assembly 1 30 there is disposed a valve member in the form of a ball 150. The ball can move between a step 151 formed on the first piston part and a series of angularly spaced projections 1 52 formed on the internal surface of the second piston part.

The solenoid valve assembly 106 has a valve member 1 60 which is normally held by means of a spring 161 in a position in which it does not restrict flow of fluid through a bore 1 62 of a bushing 1 63 extending through the end face 105 of the cup shaped member 104. The bushing 1 63 is disposed adjacent the outlet end of the sleeve 145.

Electrical energy for the solenoid valve 106 and the solenoid coils 114, 11 5 can be supplied via a cable 170 which extends into the chamber containing the valve assembly through a port assembly 1 71.

The annular space 1 72 between the cup shaped member 104 and the seal 108 contains hydraulic fluid such as oil.

It will be noted that the thrust member 101 is screwed to the end of the bobbin 112 by means of screws 1 75. A plate 1 78 is sandwiched between the seal and the end face of the bobbin.

The plate 178 is bent at its end portions 179 to provide a support for the rubber seal 108 where it folds over at 179.

The thrust member 101 is profiled (in a manner not shown) to conform with the profiled surface of the end face of the piston 1 80 of the actuator.

The co-operating profiled portions prevent the thrust member from rotating relative to the piston 180 and thus, because the thrust member 101 is screwed to the bobbin 112, the pump assembly is prevented from rotating within the housing 100.

In operation of the pump, an alternating current of 50 cycles per second is supplied to the coils 114,115 by way of the cable 170. The alternating current is supplied by way of diodes as described with reference to Figure 1 so that during the positive half cycle of the alternating current one of the coils 114, 11 5 is energised whilst during the negative half cycle the other coil is energised. This results in the production of a magnetic field within the region of the piston assembly 130, the effect of which is to produce a magnetic force in one direction for one half of the alternating current cycle and a magnetic force in the opposite direction for the other half of the alternating current cycle.Thus the piston assembly 1 30 is caused to move back and forth within the chamber defined between the step 11 9 and the end face of the sleeve 135. Considering the situation when the piston assembly 1 30 moves from a position in which the portion 131 is in contact with the end face of the sleeve 135, i.e.

from left to right in Figure 3, fluid is sucked in behind the piston assembly through the inlet valve 140. Fluid is drawn from the annular reservoir 1 72 through the cut away portions 1 25 and 1 27 and past the castellations on the castellated boss 138. During this movement of the piston assembly, the valve member in the form of the ball 1 50 seats against the valve seat consisting of the step 1 51 so that the fluid within the bore of the tubular part 144 is forced out through the outlet vlave 148. Provided the solenoid valve 106 has been actuated so that the member 160 closes the bore 162, the fluid is pumped into the chamber 1 29 between the end face of the bobbin 11 2 and the end face of the cup shaped part 104.The bores 134 are provided to assist movement of the piston assembly through fluid between the step 11 9 and the inner end face of the sleeve 135.

On the return stroke of the piston assembly from its position against the step 11 9, the valve member 151 sits against the projections 152 so that fluid which was drawn in during the previous stroke can move past the valve member 1 50 and into the bore of the tubular portion 114. During this movement of the piston assembly the inlet valve 140 closes so that fluid cannot escape therefrom. Also because of the volume of the space on the inlet side of the valve member 1 50 is approximately twice the volume on the outlet side some fluid is forced out through the outlet valve 148 during this stroke also. Thus the pump will pump fluid through the outlet valve 1 48 on all strokes of the piston assembly 1 30.

The cycle described above is repeated for as long as an alternating current is supplied to the solenoids 114, 11 5. It will be appreciated that as fluid is pumped into the chamber 129 between the end face of the bobbin 12 and the end of the cup shaped member 104 that the whole pump assembly will be caused to move axially relative to the cup shaped member 104 from right to left as shown in Figure 3. Because the pump is connected to the piston 1 80 of the actuator, the piston will be caused to move axially a corresponding amount so that the valve associated with the actuator is operated in a manner which will be apparent to those skilled in the art.The degree of movement of the piston can be controlled by seiecting the time for which alternating current is supplied to the solenoid coils 114, 11 5. Potentiometers can be provided in the cylinder assembly for feeding back signals indicative of the piston position. These signals can be used in a manner which will be apparent to those skilled in the art to control operation of the pump. The folds 179 on the rubber bladder 108 are provided to allow the bladder to expand with movement of the pump assembly.

An important feature of the present arrangement is the fact that the pump assembly forms part of the actuating piston of the actuator.

This is made possible by the very compact arrangement of the pump assembly. In the embodiment illustrated in Figure 3 a conventional pneumatically operated cylinder assembly has been replaced by the pump assembly together with the reservoir 1 72 and seal 108.

The profiled portions 11 8 provided on the bobbin 112 are designed to maximise the magnetic flux flowing through the piston assembly. The ports 120 allow fluid to flow from the chamber within which the piston 1 30 moves through the cut away portion 126 to the annular reservoir containing the hydraulic fluid. This fluid carries away heat from the coils and thus acts as a cooling means for the coils. The use of a one piece bobbin ensures alignment of the pump armature and pistons and reduces air gaps in the magnetic circuit to a minimum.

When it is desired to return the pump assembly and piston to its original position the solenoid valve 106 can be opened to allow the hydraulic fluid which has been pumped into the chamber between the bobbin and the end of the cup shaped member to flow out through the bore 162, through a passage 1 85 and into the annular reservoir 1 72 of hydraulic fluid. The piston will automatically move back to its initial position shown in Figure 3 under the influence of a spring (not shown). The solenoid valve also acts as a relief valve during pumping since it will allow fluid to bleed therethrough when the pressure exerted by the pump reaches a given value.

It will be seen from Figure 3 that the piston assembly 130 makes use of differential area pistons. This allows the pump armature cylinders and pistons to be manufactured to a convenient size compatible with forces produced by the solenoids. The use of differential area pistons gives the pump flexibility because the dimensions of the piston portions 131, 144 and the sleeves -135,145 to be carefully selected to suit the application.

The arrangement shown in Figure 3 has a triple oil seal to atmosphere. The seals concerned are shown at 136, 123 and 108. Any leakage past the seal 1 36 is passed to the reservoir 172 which is bounded by the bladder seal 1 08. If the bladder fails leakage is contained by a seal on the actuator piston 180.

The pump and actuator assembly can be used for operating linear and rotary valves in a "fail safe" manner Operation in one direction is against the bias of a spring which is compressed by the piston to automatically operate in the opposite direction. In the event of electrical failure the solenoid valve 106 opens and the actuator piston 1 80 and valve are returned to the safe position by the spring.

Two arrangements for feeding current to the coils 114, 11 5 are shown in Figures 4 and 5.

Referring to Figure 4 an alternating current source is connected to the terminals L, N. The terminals L, N are connected to the coils 114, 11 5 by way of diodes 200, 201. The arrangement is such that during one half of the alternating current cycle (Figure 4A) current is supplied to the coil 114 and during the other half (Figure 4B) it is supplied to the coil 11 5. The direction of current flow is shown by arrows 203 and the magnetic circuit by arrows 204. Figures 5A and 5B show a similar arrangement the main difference being that in the Figure 5 arrangement the current flows through the coils in opposite directions during opposite half cycles whilst in Figure 4 it is in the same direction. With both arrangements the piston 1 30 is caused to oscillate but in the -Figure 5 arrangement the magnetic poles at the moving part reverse at the end of each half cycle. This has the effect of lowering the thrust available whilst at the same time reducing the current flowing through the windings. The use of iron with a low hysteresis would also reduce this effect.

Claims (11)

Claims

1. A pump comprising a piston which includes or carries magnetic material and which is arranged so that it can undergo reciprocatory movement within a chamber, means for producing a magnetic field the direction of which alternates to cause the piston to reciprocate within the chamber, an inlet for fluid to said chamber, said piston defining a fluid flow passage through which fluid can flow from said inlet through a one way fluid control device, said fluid flow passage being in communication with an outlet for the pump, the arrangement being such that as the piston moves in one direction fluid is drawn in through said inlet and as the piston moves in the opposite direction said fluid can flow through said one way flow control device for discharge during a subsequent stroke of the piston, said means for producing the magnetic field including a pair of coils and means for supplying an alternating current to said coils such that one coil is energised during the positive portion of the alternating cycle and the other coil is energised during the negative portion of the alternating cycle, said current supply to said coils including diodes arranged to pass only the positive portion of the alternating cycle to the one coil and the negative portion to the other coil.

2. A pump as claimed in claim 1 wherein the the inlet of the pump and the outlet of the pump are arranged coaxially with the chamber and piston.

3. A pump as claimed in claim 1 or claim 2 wherein either or both of the inlet and outlets includes valve means for controlling flow of fluid therethrough.

4. A pump as claimed in any one of claims 1 to 3 wherein said two coils are wound in axially spaced relationship on a one piece bobbin, the piston assembly being located in an axial through bore of the bobbin.

5. A pump as claimed in any preceding claim wherein said piston comprises two generally tubular members arranged to provide a differential area piston and the flow control device comprises a ball disposed in the piston bore.

6. An actuator including an actuating member which can be moved to cause operation of a device such as a valve, and means for moving the actuating member comprising a pump which is arranged to pump hydraulic fluid into a variable capacity chamber, said pump being mounted so that it forms part of said actuating member and can pump fluid into said variable capacity chamber to cause the actuating member to move.

7. An actuator which includes an actuating member which can be moved to cause operation of a device such as a valve, and means for moving the actuating member comprising a pump including a piston which includes or carries magnetic material and which is arranged so that it can undergo reciprocatory movement within a chamber, means for producing a magnetic field the direction of which alternates to cause the piston to reciprocate within the chamber, an inlet for fluid to said chamber, said piston defining a fluid flow passage through which fluid can flow from said inlet through a one way fluid control device, said fluid flow passage being in communication with an outlet for the pump, the arrangement being such that as the piston moves in one direction fluid is drawn in through said inlet and as the piston moves in the opposite direction said fluid can flow through said one way fluid flow control device for discharge during a subsequent stroke of the piston, the pump being mounted such that it forms part of said actuating member and being arranged to pump fluid into a variable capacity chamber to cause said actuating member to move.

8. An actuator including an actuating member which can be moved to cause operation of a device such as a valve, and means for moving the actuating member comprising a pump as claimed in any one of claims 1 to 5, the pump being mounted such that it forms part of said actuating member and being arranged to pump fluid into a variable capacity chamber to cause said actuating member to move.

9. An actuator as claimed in any one of claims 6 to 8 wherein movement of said actuating member is arranged to take place against the action of biassing means.

10. A pump substantially as hereinbefore described with reference to and as shown in any one of Figures 1 to 3 of the accompanying drawings.

11. An actuator substantially as hereinbefore described with reference to and as shown in Figure 3 of the accompanying drawings.