GB2084408A

GB2084408A - Electromagnetically Actuated, Unidirectional Piston Pump

Info

Publication number: GB2084408A
Application number: GB8126777A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1980-09-08
Filing date: 1981-09-04
Publication date: 1982-04-07
Also published as: DE3033684A1; GB2084408B; FR2489893A1

Abstract

The piston of the pump is constituted by a member (7) of permanently axially magnetised ferromagnetic material of high remanence and coercive force which reciprocates in non-magnetic sleeve (6) between the poles of two coaxial electromagnets (1, 2) each magnetic circuit being closed by a common line of force conducting piece (5) directed radially towards the middle of the piston; and unidirectional flow means (8, 10, 11). Magnetisations and lines of force patterns are discussed (Figures 2-5, not shown). A soft magnetic material disc in the piston homogenises the field therein. Non- magnetic discs at the piston ends prevent magnetic adhesion. Control of the piston movement time characteristic (e.g. linear characteristic) is described w.r.t. Figures 6, 7 (not shown), such as via integration of signal induced in separate winding, or by carrier frequency, inductively, galvomagnetically or optically. <IMAGE>

Description

SPECIFICATION Electromagnetically Actuated, Unidirectional Piston Pump The present invention relates to a unidirectional piston pump having an electromagnetic drive.

Piston pumps having a mechanical drive have been known for a long time. Actuation by steam power was used particularly in mining and in locomotives. Electrical actuation of piston pumps is usually effected indirectly by way of the rotary movement by means of electric motors. There are also pumps having electromagnetically driven oscillating pistons and are known as reciprocating rotor compressors.

In these pumps, the drive power is produced in iron-enclosed systems in that the piston itself, or a ferromagnetic line of force conducting piece, is included in the magnetic circuit and its position influences the magnetic resistance of the magnetic circuit.

Poor efficiency and the high electrical time constant are disadvantages in these compressors.

The high electrical time constant limits the stroke frequency, This constitutes an undesirable limitation for rapid pumping or injection operations when the pumps are used, for example, as injection pumps in motor vehicles.

It is an object of the present invention to provide an electromagnetically actuated pump, which avails these disadvantages and which, moreover, renders it possible to control the speed and position of the piston in accordance with specified time laws.

There is provided by the present invention an electromagnetically actuated, unidirectional piston pump, wherein the piston of which is constituted by a member of ferromagnetic material of high remanence and coercive force, and is permanently axially magnetized and reciprocates in a sleeve of a non-magnetic material between the poles of two coaxially designed electromagnets under the influence of an excitation current, the magnetic circuit in each case being closed by a common line of force conducting piece directed radially towards the middle of the piston; and means are provided to ensure a unidirectional flow through the pump.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a pump of the invention; Figures 2 to 5 are diagrammatic sections illustrating polarities and lines of force disposition in operation of the pump of Figure 1; and Figures 6 and 7 are diagrams of control circuits for operation of the pump of Figure 1.

Referring to Figure 1 , the pump comprises coaxial shell-shaped iron cores 1 and 2 having windings 3 and 4 and a common annular line of force conducting piece 5. A non-magnetic sleeve 6 is inserted between the drilled central poles of the cores 1, 2 and fits into the bore in the conducting piece 5. The cylindrical space thus formed between the pole faces of 1 and 2 is largely filled by a piston 7 manufactured from ferromagnetic material of high remanence and coercive force, such as cobalt samarium, a nonmagnetic valve ball 8 being located in a bore 11 which is provided in the piston 7 and which has a conical seat 10.Alternatively, in the case of a non-bored piston, the cylindrical pump chamber above the piston can be connected to the cylindrical chamber below the piston by way of a passage which extends through the stationary part of the pump and which incorporates a nonreturn valve. A non-return valve in the feed line prevents fluid from flowing back to the source.

Two annular discs 9, made from non-magnetic material, on the end faces of the piston prevent the piston 7 from adhering magnetically to the pole faces of the cores 1 and 2.

Two types of magnetisation, shown diagrammatically in Figures 2 and 3, come under consideration when the piston is to be moved under the influence of excitation currents flowing through the coils 3 and 4. In the first case shown in Figure 2, the piston 7 is continuously magnetised, and the coils are connected such that the pole faces of the electromagnets have the same polarity when voltage is applied. Attraction then occurs at one end of the piston 7 and repulsion occurs at the other end, and a force K results whose direction depends upon the polarity of the voltage source.

An approximate quantitative analysis results in Fo=Fu=C XK for the attractive force when the piston is in its central position, fK representing the flux produced by the magnetised piston, and C representing a constant. The attractive force at the top and the attractive force at the bottom are of equal magnitude and are directed in opposite directions, so that they cancel one another. If an additional flux 05t is then produced by each of the electromagnets, this additional flux is added at one end to the impressed flux of the magnet, while it is subtracted from the flux at the other end.Forces F0X=C (0K+0st)2 FUX=-C (0K4st) are then produced whose resultant is given by F=FoXFUX=4 C XK Xst This force is proportional to the additional flux Xst and also reverses its sign therewith. The factor fK shows that electrical power can be saved by the permanent magnets and, owing to the small additional flux with increased impressed flux, which can be achieved particularly with modern high efficiency magnetic materials, the time constant is also reduced.

In the second case shown in Figure 3, the two halves of the piston 7 are magnetised in opposite directions, so that the end faces of the piston have the same polarity. The coils 3, 4 of the electromagnets 1, 2 are connected such that the pole faces of the electromagnets have opposite polarities when a control current is flowing. Here also, the control flux at one end of the magnet is added to the impressed inherent flux, while it is subtracted from the inherent flux at the other end.

Thus, a force proportional to the control flux is again produced when the piston is in its central position.

The relative permeability is only slightly greater than 1 in the new high-coercive magnet materials. Thus, the lines of force characteristic which is illustrated in Figure 4, and in which an inhomogeneous additional field exists within the permanent magnet, is formed between the poles of the electromagnets 1, 2 and the annular lines of force conducting piece. The resultant force is thereby decreased compared with an homogeneous field. The field in the permanent magnet piston can be homogenized by inserting a disc of soft magnetic material into the piston, so that the drive force which can be obtained is increased. This is illustrated diagrammatically in Figure 5. The line of the magnetic induction enter the disc, shown by hatching, radially from the lines of force conducting piece 5.The lines of magnetic induction exit axially from the disc and then, disregarding a certain amount of straying which is not taken into account in Figure 5, permeate the permanent magnet cylindrical pieces 13 and 14 also in a substantially axial direction, so that they enter the pole faces of the electromagnets 1, 2 normally as before.

The linear dependence of the drive force of the piston upon the current, particularly the possible reversal of the direction of the force, renders it possible to control the time characteristic of the movement of the piston by a prescribed current characteristic. Thus, for example, a linear characteristic with respect to time can be enforced by a regulating operation in which the speed of the piston is maintained constant. A suitable signal for the speed is the voltage induced by the moving magnetic piston. This voltage can be extracted by means of equivalent circuits and can be used as an input signal for a circuit for controlling the coil current, as is indicated in Figure 6. The excitation current flows into the windings 3 and 4 of the electromagnets by way of the control device 1 5 and the extraction circuit 16.The signal wi5t for the instantaneous speed of the piston is formed in 16. The device 1 5 is controlled by the difference between Wist and the desired value of the speed w50llB Alternatively, it is possible to obtain the signal wl5t with a separate winding in which the movement of the magnetized piston induces a speed-proportional voltage.

A position signal is produced if this signal is electrically integrated. A desired position can be assumed by feeding back the signal, in accordance with Figure 7, into the control device 1 5 for the excitation current. In the selected embodiment, the sensor winding 1 7 is provided for this purpose and controls the integrator 1 8 and supplies the position signal siSt indirectly by way of the integrator 1 8. After the desired value 5soli of the desired value of the position has been subtracted, the signal is applied to the control device 1 5 which, for example, can be in the form of a PD regulator, and thus affects the excitation current. It is thereby possible to set a specific swept volume of the pump, selectively in the forward flow or return flow. Alternatively, instead; of measuring the position by integrating the speed signal, the position can be measured with other means of length measuring technique, such as by carrier frequency, inductively, galvanomagnetically, or optically.

Claims

1. An electro-magnetically actuated, unidirectional piston pump, wherein the piston of which is constituted by a member of ferromagnetic material of high remanence and coercive force, and is permanently axially magnetized and reciprocates in a sleeve of nonmagnetic material between the poles of two coaxially designed electromagnets under the influence of an excitation current, the magnetic circuit in each case being closed by a common line of force conducting piece directed radially towards the middle of the piston; and means are provided to ensure a unidirectional flow through the pump.

2. A pump according to claim 1, wherein said means comprise an axial through bore in said piston and a non-return valve located therein.

3. A pump according to claim 1, wherein said means comprise a passage in the pump body connecting the input and output sides of the piston, and a non-return valve located in said passage.

4. A pump according to claim 1, 2 or 3, wherein the ferromagnetic material of the piston is cobalt samarium.

5. A pump as claimed in any of claims 1 to 4, wherein the piston is continuously axially magnetised in one direction, and the windings of the two electromagnets are connected such that two poles of like polarity are produced opposite the end faces of the piston when a current is flowing.

6. A pump as claimed in any of claims 1 to 4, wherein the piston has two halves which are axially magnetised in opposite directions, two unlike poles being located frontally opposite the said halves when the electromagnets are energised.

7. A pump as claimed in any of claims 1 to 6, wherein a disc of soft magnetic material is inserted in the centre of the piston.

8. A pump according to claim 7, wherein said disc is located within the annular lines of force conducting piece to permit better utilisation of the permanent magnetic material.

9. A piston pump as claimed in any of claims 1 to 8, wherein the current flowing through the coils of the electromagnets is controlled by means of an electronic circuit in a manner which produces a desired course of the movement of the piston.

1 0. A piston pump as claimed in claim 9, wherein the input variable of the electronic circuit is a voltage which is induced in the windings by the movement of the magnet and which is indicative of the instantaneous speed of the magnet.

1 A piston pump as claimed in claim 10, wherein a separate winding is provided for producing the piston speed signal.

12. A piston pump as claimed in claim 10 or 11, wherein the speed signal is converted by electrical integration to a position signal which is used to control the piston stroke.

1 3. An electromagnetically actuated, unidirectional piston pump, substantially as hereinbefore described with reference to the accompanying drawings.