WO1994002741A1 - Electromagnetically drivable pump - Google Patents

Abstract

An electromagnetically drivable pump suitable as a pressure supply aggregate for a hydraulic consumer has as driving device a double stroke magnetic system with two exciting windings of identical design arranged next to each other along a common central axis and which coaxially surround an axially movable armature which can be made to move back and forth with the pump piston in step with the alternating current supply of both exciting windings. This pump is designed as a double piston pump (10) with pump pistons (11, 12) and pump chambers (13, 14) of identical design axially arranged on both sides of the armature. The pump pistons (11, 12) have central throughchannels (97, 98) which are permanently in communication with the pump chambers (13, 14) and which are connected to inlet chambers provided in the armature (18) over inlet check valves centrally arranged in the armature (18). The armature input chamber is kept in communication with the hydraulic medium reservoir (104). The central channel (53) within which the armature (18) is movable back and forth is also in communication with the reservoir (104). The frequency and/or the current intensity of the exciting pulses used to alternatively power the exciting windings (22, 23) are adjustable.

Description

Electromagnetically driven pump

description

The invention relates to a magnetically drivable pump as a pressure supply unit for a hydraulic consumer, according to the preamble of patent claim 1.

Such a pump is known from DE 39 33 125.3 AI.

The known pump is designed as a single-piston pump, in which a double-stroke magnet system is provided as the drive system, which comprises two field windings of the same design arranged alongside one another along a central axis. These field windings coaxially surround a movable armature, which can be driven by alternating current supply to the two field windings to the current flow, which is carried out by the pump piston with to-and-fro movements, in the one with a volume increase of a pump chamber linked direction of movement of the piston via an inlet check valve, the pump chamber is filled from the pressure medium reservoir and in the opposite direction of movement of the pump associated with the pumping operation of the pump pressure medium is conveyed via an outlet check valve from the pump chamber to a pressure outlet of the pump. The inlet check valve is at one end of the Housing, the outlet check valve is arranged at the opposite end of the housing. An elongated tube is moved back and forth by means of the armature, in which a check valve, which in turn is designed as a non-return valve, is arranged centrally, which locks in the delivery stroke and opens in the suction stroke. Accordingly, liquid is displaced in the filling stroke via the shut-off valve into the tube section which is arranged pointing towards the outlet valve. During the delivery stroke, liquid also flows in via the inlet valve into the pre-filling space of the tube, which extends up to the shut-off valve, from which liquid is then displaced in the subsequent filling stroke via the opened shut-off valve into the delivery area of the pump.

The known electromagnetically driven pump has at least the following disadvantages due to the structure described so far and the resulting mode of operation:

If the pump works against a high outlet pressure, the armature moves more and more towards the inlet valve, with the result that the tightening forces decrease relatively in the part of the magnet system which is attracting during the delivery stroke due to an associated increase in the air gap. with the result that the performance of the pump decreases. The higher the pressure against which the pump has to work, the lower its efficiency. The relationship between electrical input power and hydraulic delivery power is to a significant extent non-linear.

It is therefore the object of the invention to improve an electromagnetically drivable pump of the type mentioned at the outset in such a way that within a wide range there is a linear relationship between the electrical absorption power and the hydraulic delivery power of the pump and also an operation of the same with high efficiency degree of efficiency can be achieved.

This object is achieved according to the characterizing part of claim 1, according to the basic idea, as follows:

The pump is designed as a double-piston pump with pump pistons and pump chambers of the same design arranged axially on both sides of the armature, the pump chambers being connected to a common pressure outlet via an outlet check valve in each case; the pump pistons have permanently communicating, central through-channels in communication with the pump chambers, which are connected via inlet check valves arranged centrally in the armature to an inlet chamber arranged centrally in the armature, which via at least one radial channel with an outer groove of the armature in communicating connection is formed, which within its axial width is permanently overlapping with the opening cross-section of a radial feed pipe which is connected to the pressure medium storage container, and it is also the central channel within which the armature can be moved back and forth, kept permanently in communicating connection with the storage container. The pump according to the invention designed in this way conveys at least the following advantages:

The symmetrical design of both the double-stroke magnet system and the pump arrangement ensures that the armature in operation of the pump, while its excitation windings are alternately energized in time with an alternating current frequency, always "oscillates" around a central position, which with optimal Exploitation of favorable, small air gap widths in the respective attracting magnet system goes hand in hand. While one part pump is pumping, the other is filled with pressure medium. As a result, the electrical power consumption of the field windings is optimally used for the conversion into hydraulic conveying capacity. Since the armature moves back and forth in a non-pressurized space which is filled with pressure medium - usually lubricating hydraulic oil - the friction losses are also low, and it is also advantageous that it is via the inlet valves and flow paths leading to the pump chambers through the axial longitudinal channels of the pistons are short and can be realized with relatively large cross sections, so that low flow resistances also result in this respect.

In a preferred configuration of a power supply device provided for the operation of the pump, the frequency and / or the current intensity of the current to be alternated The excitation current pulses used by the excitation windings can be adjusted so that the delivery rate of the pump and also its outlet pressure can be controlled in a simple manner by changing these parameters. The pump itself can be designed in a simple manner by suitable selection of the cross-sectional dimensions of the pump pistons and the design possible by suitable design of the double-stroke magnet system for suitable piston strokes at defined delivery rates and output pressures.

It is particularly advantageous if at least one of the pump pistons and one of the excitation windings of the pump are used as a valve body or switching winding of a relief valve designed as a solenoid valve, which, when this winding is excited, connects the pressure output of the pump with its pressure medium storage container when the winding is excited Flow position arrives and otherwise blocks, so that a rapid pressure reduction in a consumer connected to the pump can be brought about by electrical control of this valve. By utilizing the excitation winding of the drive magnet system as a control winding for this relief valve, a simple construction results overall.

Expediently, the excitation winding of the double-stroke magnet system, which is used as the switching winding of the relief valve, is acted upon by a current which is greater than the excitation current strength used for the pumping operation in order to switch on its relief position, the relief position being that of a Pump piston formed valve body of the relief valve is moved to a position in which the piston is a defined distance further away from its basic position assumed in the de-energized state of the excitation windings than in the reversal points of its filling and delivery strokes carried out in pump operation.

If, as provided in a preferred configuration of the pump according to the invention, in the maximum deflection of a pump piston corresponding open position of the relief valve, the outlet valve of the associated pump chamber is moved into its open position by an axial tappet of the piston of the relief valve position corresponding to the outlet valve, the relief valve can be designed as a simple 2/2-way valve which, in its open position, connects the pump chamber with the central channel of the master communicating with the reservoir. Connects gnetizable, ring-cylindrical casing of the double solenoid system, this 2/2-way valve can be implemented in a simple manner by constructing a chamber block in the central bore of the relief valve housing, in which the Pump pistons forming the relief valve can be moved in a pressure-tight manner ar is guided, has an arranged inner groove which is connected via a relief channel to the central channel communicating with the storage container and, viewed in the axial direction, between the Pump chamber and the central channel of the Doppelhubmag¬ netsystem is arranged, and that the pump piston ei¬ ne via a radial channel with its axial channel communicating with the pump chamber communicatingly connected external groove, which, seen in the axial direction, between the The inner groove of the pump chamber block and the ring end face forming an axially fixed boundary of the central channel are arranged and only overlap with the inner groove of the pump chamber block when the excitation winding coaxially surrounding the piston is energized with a direct current, the amount of which is greater than the maximum value of the current with which the excitation windings of the double-stroke magnet system are pulsed in pump operation.

For safety reasons, it is also particularly advantageous if a further relief valve designed as a solenoid valve is provided, which connects the pressure outlet of the pump to the pressure medium reservoir in the currentless state of its switching magnet and is otherwise blocked.

Such a valve ensures that the consumer becomes "depressurized" in the event of a power failure, i.e. does not carry out a work stroke, for example, and a situation of potential danger can thereby be avoided.

Such a normally open relief valve can be implemented in a structurally simple manner in that it comprises a valve body which is axially displaceably arranged in the outlet chamber of the respective outlet valve of the pump and consists of a magnetizable material and which can be urged by energizing a field winding in contact with a valve seat and thereby shuts off the discharge channel leading from the outlet chamber of the pump to the central channel of the double-stroke magnet system and passing through the respective chamber block, as long as the field winding is energized.

In a preferred design of the pump, the valve seat of the normally open relief valve is formed by an O-ring which coaxially surrounds the outlet opening on the outlet side of the relief channel, the valve body being provided with a radial flange which can be supported on the O-ring and / or as is formed in the Auslaßkam¬ mer axially displaceably guided washer which can be urged against the restoring force of a return spring in contact with the O-ring.

It goes without saying that, instead of such a design of the relief valve as a seat valve, it is also possible to design the relief valve as a slide valve, as is provided, for example, in a special design for the relief valve which opens when current is supplied to an excitation winding.

Starting from a pump of the type mentioned at the beginning, The object on which the invention is based is also achieved in that the pump is designed as a double-piston pump with pump pistons and pump chambers of the same design arranged axially on both sides of the armature, the pump chambers each having an outlet check valve to a common pressure outlet of the pumps ¬ pe are connected, and that the pump chambers each have individually assigned inlet valves arranged in radial overflow channels, which extend between the pressure medium reservoir and one of the pump chambers, which in turn achieves low flow resistance for filling the pump chambers become.

With this design of the pump, an advantageous structural simplification of the pump is possible in that the inlet valves and outlet valves each associated with one of the pump chambers are integrated in a housing end block which delimits the respective pump chamber in a housing-fixed manner.

Starting from a pump of the type mentioned at the outset, the object on which the invention is based is also achieved in that the pump has two annularly-shaped pump chambers which are movably delimited from one another within a central bore of its housing by an annular flange of the pump piston. and movements of the piston are connected alternately to a common pressure outlet of the pump via an outlet check valve that the piston with push-shaped sections arranged on both sides of the flange is guided so that it can be moved in a pressure-tight manner in bore steps adjoining the central bore, one piston section being connected to the armature of the double-stroke magnet system in a tensile and shear-resistant manner and the other push-button piston section being one axially movable boundary of a compensating chamber communicating with the reservoir forms, and that check valves provided as inlet valves, individually assigned to the pump chambers, which are acted upon by higher pressure in the compensating chamber than in the respective pump chamber in the opening direction and are otherwise blocked, are integrated in the pump piston.

In this type of construction, the overall pump consists of a hydraulic pump module and an electrically controllable drive module, which provides both manufacturing advantages and advantages in terms of a change in design, since, for example, the pump can be converted to a more powerful drive alone Replacement of the drive module is possible.

In a preferred design of such a pump, in which the inlet valves are designed as ball seat valves, the balls of which are arranged in bores of the pump piston and the axes of which run in the direction of the piston displacement movements, the valve seat of the inlet valve is the must open to fill the assigned pump chamber when the piston on the drive side, at the drive end of its bore and the valve seat of the inlet valve that has to open to fill the associated pump chamber when the pump piston is moved towards the compensation chamber, on the end of its valve bore facing this.

This arrangement facilitates the opening of the inlet valves for "sucking in" hydraulic fluid and is therefore expedient if the pump is operated with relatively high armature oscillation frequencies.

The pump according to the invention can be designed by the design of its double-stroke magnet system, the cross-sectional dimensioning of its pistons and the possible specification of its pump frequency within a wide range - the frequency with which the excitation windings of its double-stroke magnet system are alternately energized. and also by the specification or setting of the current strengths of the excitation currents with which the excitation windings are supplied with current, are optimally designed with regard to a large number of different purposes, resulting in a large number of interesting possible uses, a few of which are mentioned below as examples should:

1. Pressure supply unit for actuators of relatively low power, their need-based pressure supply by means of a single - central - pressure supply unit essential for a central pump would require higher performance, but which would only be charged in rare cases according to its performance. Possible uses of this type are, for example, a hydraulic seat adjustment of chairs for medical purposes and / or of motor vehicles, drives for window regulators, sunroofs and the like.

2. Drive energy source for servo systems on motor vehicles, such as servo steering and / or leveling control in motor vehicles, which currently require the use of pumps driven by the vehicle engine and which are "useless" for most of the service life of a vehicle, i.e. must be operated in idle mode.

3. Realization of simple drive-slip control systems which work with activation of the wheel brake of a driven vehicle wheel which tends to spin.

4. Use in the context of an active chassis control, in which hydraulic shock absorbers have to be adapted to dynamically dependent varying values of the wheel load distributions of a vehicle.

5. Use in metering pumps in the chemical industry which require a sensitive response to desired changes in the delivery rate. Further details and features of the invention result from the following description of special exemplary embodiments with reference to the drawing. Show it:

1 shows an electromagnetically drivable pump according to the invention in section along a radial plane containing the central axis of its double-stroke magnet system, in a scale representation, approximately on a scale of 1.5 / 1,

2 shows details of the pump according to FIG. 1 in a sectional view corresponding to FIG. 1 but enlarged, and

3 is a diagram for explaining the function of the pump shown in FIGS. 1 and 2,

4 shows a further exemplary embodiment of a double-piston pump according to the invention in a representation corresponding to FIG. 1 and

5 shows a third exemplary embodiment of a pump according to the invention which can be driven by means of a double-stroke magnet system in a schematically simplified, greatly enlarged longitudinal sectional view.

The electromagnetically driven device according to the invention shown in FIG. 1, to the details of which reference is expressly made, shown overall with 10 Pump is designed as a double-piston pump with two pump pistons 11 and 12 as well as pump chambers 13 and 14 and outputs 16 'and 16''assigned to them, which are connected to a common pressure output 16 to which a hydraulic consumer, for example as shown, is shown , a linear hydraulic cylinder 17 can be connected.

The two pump pistons 11 and 12 are firmly connected to the armature 18 of a double-stroke magnet system, which is provided as a pump drive and is generally designated 19 and which is arranged so that it can move back and forth centrally between the pump chambers 13 and 14 The longitudinal axis 21 of the pump chambers 13 and 14 is rotationally symmetrical and, seen in the spring-centered neutral position of the armature 18, which the armature 18 assumes when the double-stroke magnet system 19 is de-energized, also symmetrically with respect to the transverse central plane 22 which is perpendicular to the central longitudinal axis 21 is trained.

As a result of alternative excitation of the excitation windings 23 and 24 of the double-stroke magnet system, which are arranged alongside one another along the central longitudinal axis 21, with control currents which can be defined in a defined manner, the armature 18 can be driven to move back and forth in the direction of the central longitudinal axis 21 in a defined manner with different deflection strokes , whereby - at given pressure against which the pump 10 must work, the delivery rate can be set in a defined manner. The excitation windings are wound on the basic form of a cylindrical jacket-shaped bobbin 26 and 27, indicated only by dashed lines, which have outward-facing end flanges 28 and 29 which extend over the radial "thickness" of the excitation windings 23 and 24, whereby the coil formers and their end flanges are made of an electrically insulating plastic material.

The excitation windings 23 and 24 including their coil formers 26 and 27 are, apart from the excitation windings 23 and 24 each individually assigned, radially arranged annular gaps 31 and 32 - otherwise completely - enclosed by an overall ring-cylindrical jacket 33 which is magnetically conductive , ie made of magnetizable soft iron material.

This ring-cylindrical jacket 33 comprises, in the arrangement shown in FIG. 1, symmetrical to the transverse center plane 22 of the pump 10 and coaxial to its central longitudinal axis 21, a radially outer jacket tube 34 which encloses the field windings 23 and 24 on the outside, a radially inner, central jacket tube 36, which bears with its radially outer circumferential surface 37 on mutually adjacent sections of the bobbins 26 and 27 in the field windings 23 and 24 and with its narrow annular end faces 38 and 39 the inner boundaries of the annular gaps 31 and 32 as seen in the axial direction forms two further, radially inner casing tubes 41 and 42, which have conical inner end sections, which have bevel surfaces 43 and 44 which slope obliquely towards the central longitudinal axis 21, which form outer boundaries of the annular gaps 31 and 32 in the axial direction and with their outer, radially extending ones , narrow ring end faces 46 and 47 connect flush to the outer surfaces of annular disk-shaped yoke plates 48 and 49 of the ring-cylindrical jacket 33, which connect the outer magnetically conductive connection between these further jacket pipes 41 and 42 and the outer jacket pipe 34 of the ring-cylindrical one Provide sheath 33 and bear directly against the outer end flanges 29 of the coil bodies 26 and 27, as seen in the axial direction, as well as central, annular disk-shaped yoke plates 51, which provide the space in the axial direction between the inner radial flanges 28 of the coil bodies 26 and 27 fill in and in the central area of the cylindrical ring Jacket 33 convey the magnetically conductive connection between the outer jacket tube 34 and the central inner jacket tube 36.

In the inner jacket tubes 36, 41 and 42 of the magnetizable, ring-cylindrical jacket 33, which are made of magnetically conductive material, a thin-walled tube 52, which is made of antimagnetic stainless steel and is in direct contact with the latter, is inserted, which is flush with its narrow annular end faces outer, radial boundary surfaces of the outer annular disk-shaped yoke plates 48 and 49 of the ring-cylindrical closes magnetizable jacket 33 and forms the radial boundary of a central channel 53, within which the armature 18 of the double-stroke magnet system 19 is slidably mounted to slide back and forth.

In the opposite end sections of the channel 53 delimited by the thin-walled stainless steel tube 52, ring-cylindrical chamber blocks 54 and 56 are inserted in sections, which limit the two valve chambers 13 and 14 of the double-piston pump 10 and are pressure-tight in the end sections of the stainless steel tube 52 are used. The chamber blocks 54 and 56 consist of magnetizable soft iron and are provided with radially outer flanges 57 and 58, which connect flush to the outer surfaces of the outer annular disk-shaped yoke plates 48 and 49 of the ring-cylindrical magnetizable jacket 33. They are held in this position by housing end blocks 59 and 61, which are firmly connected in a manner not shown with the ring-cylindrical jacket 33, which in turn forms part of the housing of the pump 10.

The axial length, measured from the flanges 57 and 58, of the peg-shaped pole cores of the magnetizable sheath 33 forming the field windings 23 and 24 and the armature 18, pointing towards the armature 18 of the double-stroke magnet system 19, forming the sections 54 'and 56' of the chamber blocks 54 and 56, which are fixed to the housing with their radial, inner annular end faces 121 and 122 Form the boundary of the channel space 53, within which the armature 18 can be moved back and forth, is slightly less than the axial extent of the further, radially inner casing tubes 41 and 42 measured up to the conical edges 62 and 63 of the gaps 31 and 32 which bear against the coil formers 26 and 27 of the field windings 23 and 24. These - inner - sections 54 'and 56' of the chamber blocks 54 and 56 are provided with central through bores 64 and 66, in which the pump pistons 11 and 12 projecting as plungers into the pump chambers 13 and 14 are displaceably guided in a pressure-tight manner are. The chamber blocks 54 and 56 have on their flanges 57 and 58 outwardly adjoining outer, peg-shaped sections 54 ″ and 56 ″, which are pressure-tightly received by blind bores 67 and 68 of the housing end blocks 59 and 61, the ones of which Flanges 57 and 58 from the measured axial depth is greater than the correspondingly measured axial expansion of the outer peg-shaped sections 54 ″ and 56 ″ of the chamber blocks 54 and 56, so that through the blind bores 67 and 68 and the outer radial end face ¬ chen 69 and 71 of the outer peg-shaped sections 54 ″ and 56 ″ of the chamber blocks 54 and 56 remain fixedly defined outlet chambers 72 and 73, these outlet chambers 72 and 73 via radial transverse channels 74 and 76 of the housing end blocks with the pressure outputs 16 ' and 16 '' of the pump 10 are communicatively connected. The outer peg-shaped sections 54 ″ and 56 ″ are provided with axial through bores 77 and 78, respectively, which are located between the pump chambers 13 and 14 and the respectively adjacent outlet chamber 72 and 73 extend. The respective outer mouth edges 79 and 81 of these through bores 77 and 78 form the valve seats for outlet check valves 82 and 83 designed as ball seat valves, the valve balls 84 and 86 of which are under axial prestressing valve springs 87 and 88 in System with their associated valve seats 81 and 82 are pushed.

The armature 18 of the double-stroke magnet system 19, which is made of magnetizable soft iron, for the explanation of which reference should also be made to the detailed illustration in FIG. 2, is designed in its basic form as a thick-walled tube, within which two are provided by a central partition 89 a total of pot-shaped depressions 91 and 92, which extend over the major part of the length of the armature 18 and are open towards the chamber blocks 54 and 56, are delimited from one another into which the pump pistons 11 and 12 have flange-shaped inner end sections 93 and 94 the intermediate wall 89 adjoining each other and to the casing sections 96 'and 96''of the tube 96 of the armature 18 which delimit the recesses 91 and 92 radially on the outside are then mechanically fixed and pressure-tight. The pump pistons 11 and 12 have central longitudinal channels 97 and 98 which are in communication with the respective pump chamber 13 and 14, respectively. The intermediate wall 89 is provided with a central, axial through-bore 99 which, via radial transverse channels 101, which open into an outer annular groove 102 of the anchor tube 96, Ren clear cross section in any possible position of the armature 18 is in overlap with the cross section of a pressure medium supply pipe 103 radially crossing the magnetizable jacket 33 between the field windings 23 and 24, is held in communicating connection with the pressure medium storage container 104. The channel 53, within which the armature 18 is arranged so as to be able to be moved back and forth, is via outer longitudinal grooves 105 of the outer tube 96 of the armature 18, which extend from its central outer annular groove 102 and into the sections arranged on both sides of the armature of the central channel 53 open, held in communicating connection with the storage container 104 and therefore filled with pressure medium. Within the flange-shaped end sections 93 and 94 of the valve pistons 11 and 12, radially delimited valve chambers 106 and 107 are formed by step-widened end sections 97 'and 98' of the central longitudinal channels 97 and 98 of the pump pistons 11 and 12, into which the Central through bore 99 of the intermediate wall 89 of the armature 18, each with a chamfer surface 108 or 109 that widens conically towards the valve chambers 106 and 107. These conical chamfer surfaces 108 and 109 form seating surfaces for the valve balls 111 'and 112' each of a check valve used as an inlet valve 111 or 112 for filling the pump chambers 13 and 14, these valve balls 111 'and 112' passing through A weakly pre-tensioned valve spring 113 and 114, respectively, which settle on the valve chambers 106 and 107 against the regions of the longitudinal channels 97 and 98 which are smaller in cross section Support ring shoulders 116 and 117, and be pressed into the sealing contact with valve seat surfaces 108 and 109, respectively. "Weakly preloaded" valve spring is intended to mean that the valve balls 111 'and 112' lift off their valve seat surface 108 or 109 when the pressure in the respective pump chamber 13 or 14 is increased by a small amount, eg is 0.2 bar lower than the pressure prevailing in the pressure medium reservoir 104, as a rule the atmospheric ambient pressure.

By return springs 118 and 119, the annular groove-shaped areas of the cup-shaped recesses 91 and. Which are delimited over the major part of their length by the radially outside through the jacket sections 96 'and 96' 'of the anchor tube 96 and radially inside by the valve pistons 11 and 12 92 of the armature 18 are received and are supported in the axial direction on the one hand on the flange-shaped end sections 93 and 94 of the pump pistons 11 and 12 and on the other hand on the inner annular end faces 121 and 122 of the chamber blocks 54 and 56 arranged opposite each other the armature 18 of the double-stroke magnet system 19 is pushed into the spring-centered basic position shown in FIG. 1, in which its plane of symmetry coincides with the transverse center plane 22 of the pump 10 or its exciter winding arrangement 23, 24.

In operation of the double-piston pump 10 explained so far, its excitation windings 23 and 24 are alternately acted upon by current pulses, as a result of which the armature 18 is driven to reciprocate movements taking place in the rhythm of the alternating excitation of the two excitation windings 23 and 24, and the two "sub-pumps", each by a piston 11 or 12, the pump chamber 13 or 14 receiving the latter the associated inlet valves 111 and 112 and outlet valves 82 and 83 are formed, alternately performing their delivery or filling stroke, one of the two pumps operating in delivery mode, whereby a constant, only slightly pulsating pressure medium flow for consumption cher 17 is achieved.

For an explanation of design principles, on the basis of which the double-piston pump 10 can be structurally optimized with regard to defined specific uses, reference is now also made to the diagram in FIG. 3, which, depending on the excitation current intensity, qualitatively defines the parameters as parameters Depends on the magnetic force K _M acting on the armature 18 on the position of the armature 18 within the ring-cylindrical magnetizable jacket 33 of the double-stroke magnet system 19.

The abscissa in the diagram is the axial distance of the one, as shown in FIGS. 1 and 3, the left magnetically active surface 123 of the armature 18 from the inner annular end face 121 of the "left" pole core arranged axially opposite it, which through the axially inner pin-shaped extension 54 'of the left chamber block 54 is formed, applied and dinate the amount of the magnetic attractive force acting between the ring-cylindrical, magnetizable jacket 33 and the armature 18 when the left excitation winding 23 is energized.

In this diagram, the possible values of the magnetic attraction force are represented by a first curve 124, which result when the excitation winding 23 is acted upon by an excitation current of the - relatively low - current intensity I ₀ , and thereby the armature 18 extends as far as Contact of its magnetically effective ring end face 123 against a radial stop face 126 of a so-called “anti-adhesive plate” 127 that faces it and is formed, for example, as a thin-walled plastic plate and onto the inner, magnetically effective ring end face 121 of the extension 54 through the inner pin-shaped extension 'of the left valve chamber block 54 formed pole core is applied, which is to prevent the magnetizable armature 18 from coming into direct contact with the magnetizable pole core and being able to "stick" to it due to magnetic remanence effects.

By means of a second curve 128 and a third curve 129 of the diagram, for possible, but higher excitation currents of, for example, 1.5 I ₀ and 2 I ₀ associated excitation states of the left excitation winding 23, the possible values of the between the armature 18 and the annular cylindrical magnetizable jacket 33 represents effective attractive forces. The 3, curve curves 124, 128 and 129 are only for the region of particular interest between the spring-centered basic position of the armature 18, which is marked in the diagram by the dashed plane 131 of its magnetically active ring face 123 and the abutment surface 126 of the anti-adhesive plate 127, the course plane 132 of which is also shown in dashed lines in the diagram in FIG. 3.

For the exemplary embodiment of the pump 10 selected for explanation, it is assumed that, seen in the basic position of the armature 18, the axial distance of the running plane 131 of its magnetically effective end face 123 from the inner end face 121 of the pole core or the stop face 126 of the anti-adhesive plate 127 is greater than their structurally predetermined distance from the radial plane 133 marked by the narrow free annular end face 62 'of the conical edge section 62 of the conical tube 41.

In this configuration, while the armature 18 moves in the direction of the arrow 134 toward the cone tube 41 of the ring jacket 33 which is magnetized when the field winding 23 is energized, the magnetic attraction force acting between the latter and the armature 18 initially increases, depending on the current intensity of the Excitation current along the rising branches 124 ', 128' or 129 'of the curves 124 and 128 or 129. In the position of the armature 18 in which its magnetically effective end face 123 runs in the radial plane 133 marked by the free end face 62 'of the cone tube 41, a relative maximum 124 ″ or 128 ″ or 129 ″ of the attractive force is achieved, which with a minimal width of the “air” gap is linked between the free end face 62 'of the cone tube 41 and the magnetically active end face 123 of the armature 18 and thus also with a minimum of the magnetic resistance between the conical region of the cone tube 41 and the armature 18. This magnetic "transition" resistance increases again when the armature 18 moves further in the direction of the arrow 134 toward the pole core, where a decrease in the magnetic attractive force is associated, which is shown in the diagram in FIG. 3 is represented by the falling branches 124 '", 128''' and 129 '" of the curve 124 and 128 and 129. This decrease, which is due to the fact that the magnetic resistance between the conical region 62 of the conical tube 41 and the armature 18 increases again until, in a radial plane 134, the same value of the magnetic resistance between the conical region 62, 62 ' of the conical tube 41 and the armature 18, on the one hand, and between this and the inner annular end face 121 of the pole core 54 ', on the other hand, corresponds to a relative minimum 124 ″ or 128 ″ or 129 ″ of the magnetic attraction is traversed, after which, 121, the magnetic attraction force between it and the anchor 18 again rises sharply with further approach of the armature to the pole core 54 ', as indicated by the anstei¬ constricting branches 124 ^v, 128 ^v and 129 ^v of the progress curves 124 and 128 or 129, until finally, when the armature 18 has reached the contact position of its magnetically active ring end face 123 with the stop face 126 of the anti-adhesive plate 127, absolute maximum values 124 ^VI or 128 ^VI or 129 ^{VI of} the magneti¬ attraction force are reached, which correspond to the minimum value of the magnetic resistance between the pole core 54 ', 121 and the armature 18 and the amount of which is significantly higher than the relative maximum values 124'', 128 "and 129", the minimum value of the magneti¬ cal resistance between the conical region 62 of the conical tube 41 and the armature 18 correspond.

The force / displacement characteristic field formed by the curve 124, 128 and 129 of the diagram in FIG. 3 shows immediately that the mechanical configuration of the double-stroke magnet system 19 shown in solid lines is favorable if the pump 10 has a relative high delivery capacity - delivery volume per stroke - should have, but can work at a comparatively low output pressure level. It is then expedient to utilize a movement stroke of the armature 18 in which its magnetically active end face 123 reaches the radial plane 133 marked by the free ring end face 62 'of the conical region 62 of the conical tube 41. The movement stroke H- ^ which results for the periodic pumping operation then corresponds to the double value 2 hL of the deflection h- ^ which the armature 18 experiences in the introductory phase of a pumping operation in which it is marked by the plane 131 Basic position moved into the radial plane 133, which is marked by the free annular end face 62 'of the conical tube 41. After the execution of this introductory stroke, the magnetic ring end face 123 of the armature moves periodically back and forth between the radial plane 133 and the radial plane 136 seen from this, as illustrated in the lower part of FIG. 3 by a sinusoidal movement curve 135.

"The delivery volume Q related to the unit of time, which is due to the relationship:

Q = F _A -2H • n

in which F _A denotes the effective cross-sectional area of the pump pistons 11 and 12, H the piston stroke in the steady operating state and N the frequency of the alternating energization of the excitation windings is H because of the large amount - * L of the piston stroke is also particularly high.

If, on the other hand, the pump 10 is to be able to deliver a high output pressure, a mechanical configuration of the double-stroke magnet system is advantageous in that the spring-centered basic position for the armature 18 is the position in which the radial plane 131 of its magnetically effective annular end face 123 coincides with the radial plane 133 marked by the free annular end face 62 'of the conical region 62 of the conical tube 41 and is used for the pumping A region "symmetrical" with respect to this radial plane 133 is used, which is delimited in FIG. 3 by the radial planes 137 and 138 "parallel" to the radial plane 133, between which the magnetic attraction between the magnetizable ring jacket 33 and the armature 18 is approximately constant and corresponds almost to the maximum values 124 "and 128" or 129 "of the characteristic curves 124, 128 and 129, the magnetic attraction forces generally increasing with increasing excitation current. The decisive factor for the steady state of operation The value H _{2 of} the filling and delivery strokes of the armature 18 is, however, significantly lower compared to the case in which the pump 10 can work with a moderate outlet pressure, an increase in the delivery rate in the high pressure operation of the pump 10 however, at least in a limited but interesting area by increasing the frequency n of the alternating energization of the excitation windings 23 and 24 d double stroke magnet system 19 is possible.

Basically, a design of the double-piston pump 10, as explained with reference to FIGS. 1 to 3, to a high output pressure is also possible in that the stroke range, also associated with high magnetic attraction forces, is used in the diagram in FIG. 3, within which the steeply rising branches 124 ^v , 128 ^v and 129 ^{v of} the force / displacement characteristic curves 124, 128 and 129 run insofar as these characteristic curves correspond to amounts of magnetic attraction force which are higher than the relative maxima 124 ", 128" and / or 129 "which arise for the radial plane 133, which is marked by the narrow annular end face 62 'of the conical tube 41. However, the output bridge that can be reached with such a design of the pump 10 would not be, at least not appreciably higher than with a design of the pump on the stroke range delimited by the radial planes 137 and 138, since the maximum output pressure of the pump 10 in any case by the minimum value of the usable attraction force is limited, which - in the steady state - can be reached when the armature 18 takes its greatest distance from the pole core face 121 of the respectively attracting pole core.

In the double-piston pump 10, one of its left pistons 11, as shown in FIG. 1, is also formed as a valve body of a slide valve, designated overall by 140, which is energized by one current, which in turn is left-hand in FIG. 1, with a current which is higher than the maximum current with which the excitation windings 23 and 24 are alternately energized in pumping operation can be controlled into an open position in which the outlet valve 82 is also pushed open by the pump piston 11 and pressure medium from the consumer 17 via the open outlet valve 82, the Pump chamber 13, the central channel 97 of the left pump piston 11, a radial channel 141 communicating with it, which opens into a circumferential groove 142 of the pump piston 11, as well as an inner groove 143 of the left chamber block 54 which can be overlapped therewith and one this with the central channel 53 of the double stroke Relief channel 144 connecting the magnet system 19 can flow out to the storage container 104. The circumferential groove

142 of the pump piston 11 is between the inner annular end face 121 of the chamber block 54 and its inner groove

143 arranged in such a way that it cannot overlap with this inner groove 143 in normal pumping operation, but only when the left excitation winding 23 is supplied with a direct current of sufficient current and thus the valve piston 11 has a greater deflection to the pole core 54 ' experienced as in pump operation. The inlet valve 82 is then opened by means of a plunger 146 which continues the pump piston 11 axially and which lifts the valve ball 84 of the outlet valve 82 from its seat 79. The excitation winding 23 is used in this way as a switching magnet for the relief solenoid valve 140. If necessary, an additional excitation winding (not shown) can be provided to actuate the valve 140.

Furthermore, a relief valve 147, which is also designed as a solenoid valve, is provided, which has its own field winding 148, which is arranged within the housing end block 61 on the right in FIG. 1, which is supplied with direct current in normal pumping operation and thereby has an annular disk-shaped material made of magnetizable material Valve body 149, which is guided axially displaceably in the blind bore 68 of the right housing end block 61, pulls into sealing contact with an O-ring 151, which surrounds the blind bore-side mouth opening 152 of a relief channel 153, which extends within the right chamber block 56 between the central channel 53 of the double lifting magnet system 19 and the blind hole 68 of the right housing end block 61. When the current supply to the further field winding 148 ceases, be it due to the switching off of the pump 10 or due to a power failure, the annular disc 149 is lifted from its sealing seat on the O-ring 151 by the action of a return spring 154 and thereby the consumer 17 relieved via the discharge channel 153 and the central channel 53 to the pressure medium reservoir 104.

4, to the details of which reference is now made, a double piston pump 20 is explained as a further exemplary embodiment, which is functionally analogous to the pump according to FIG. 1 and is largely identical to the latter in terms of the double-stroke magnet system provided for the drive.

To the extent that elements of pumps 10 and 20 according to FIGS. 1 and 4 are given the same reference numerals, this should include a reference to the structural and functional equality or analogy of such elements and, insofar as such elements with reference to FIG 4 are not specifically mentioned, mean the reference to the relevant parts of the description of FIG. 1, so that the explanation of the exemplary embodiment according to FIG. 4 can be restricted to its design differing from the exemplary embodiment according to FIG. In contrast to this, in the double-piston pump 20 according to FIG. 1, its inlet valves 111 ″ and 112 ″ corresponding to the inlet valves 111 and 112 functionally and hydraulically and “geometrically” are directly between the pressure medium reservoir 104 and the two pump chambers 13 and 14 arranged in order to keep the radial overflow channels 156 and 157 between the reservoir 104 and the pump chambers 13 and 14 as short as possible.

According to this direct assignment of the inlet valves 111 "and 112" to the pump chambers 13 and 14, the pump pistons 11 'and 12', which extend in the axial direction on both sides of the armature 18, are designed as solid, circular-cylindrical rods which are designed as Project plunger into pump chambers 13 and 14. The design of the armature 18 and the double-stroke magnet system 19 are completely analogous to the exemplary embodiment according to FIG. 1. The inlet valves 111 'and 112' and the outlet valves 82 and 83 each individually assigned to the pump chambers 13 and 14 are each integrated in a housing end block 59 'and 61'. In the case of the pump 20 too, the central channel 53, in which the armature 18 is arranged such that it can be moved back and forth in the axial direction, communicates with the pressure medium reservoir 104 via the external axial grooves 105 of the armature 18 and the radial transverse channel 101 .

Also with the double-piston pump 20 according to FIG. 1 Relief valves corresponding to the relief valves 140 and / or 147 of the exemplary embodiment according to FIG. 1, not shown for the sake of simplicity, may be provided functionally.

To explain a third exemplary embodiment of a pump 30 driven by a double-stroke magnet system, reference is now made to FIG.

In the case of this electromagnetically drivable pump 30, its hydraulic functional part 30 ', the actual "pump" on the one hand, and the drive element 161 on the other hand, which consists of the double-stroke magnet system with an axially reciprocating oscillating armature, are function elements that are in themselves uniform trained which can be mechanically coupled to one another in such a way that the piston of the pump 30 ', designated overall by 162, also carries out the oscillating movements of the armature of the drive element 161, which is not shown for the sake of simplicity. The fastening and coupling elements in this regard are not shown for the sake of simplicity and can be implemented using conventional constructional means.

For the drive element 161, with regard to the design of the double-stroke magnet system, in particular the arrangement of the excitation windings, the design of the air gaps and the magnetically conductive jacket, and the arrangement of return springs, which are the spring-centered basic position of the armature - and the piston 162 - determine the pump 30 ', assuming a structure, as explained in principle by means of FIGS. 1 and 4, to which reference is made in this regard.

The further explanation of the exemplary embodiment according to FIG. 3 can therefore be restricted to its hydraulic pump unit 30 '.

Along the central longitudinal axis 163 of the pump element, which is also the central longitudinal axis of the drive unit

161 forms, seen, the housing of the pump unit 30 ', designated overall by 164, has a first bore step 166 which forms the radial boundary of an equalizing chamber 167 which is closed on one side by an end end wall 168 and is permanently communicating connection with the pressure medium reservoir 169.

This first bore step 166 is adjoined via a first radial annular shoulder 171 by a second diameter, which is smaller with the first coaxial bore step 172, in which the piston 162 has a piston section 173 on the left as shown in FIG. 5 is guided in a pressure-tight manner. This second bore step 172 merges via a second radial annular shoulder 174 into a third, central bore step 176, which in turn has a somewhat larger diameter. The piston is in this third bore step 176

162 with a central, radial piston flange 177 guided in a pressure-tight manner. This third, central one Bore step 176 adjoins a fourth bore step 179 via a third radial shoulder 178, the diameter of which corresponds to that of the second bore step 172, which extends between the first bore step 166 and the central bore step 176. In the fourth bore stage 179, the piston 162 is guided so as to be pressure-tightly displaceable with a "right", second push-shaped section 181, which is formed within a drive-side chamber of the pump element housing 164, the radial boundary of which is formed by a fifth bore stage 182 again having a larger diameter the fourth bore step 179 in turn connects via a radial ring shoulder 183, with which the armature of the drive unit 161 is connected in a tension-resistant and shear-resistant manner.

Within the central bore step 176, a left, annular pump chamber 184 and a right, also annular pump chamber 186 are axially movably delimited by the central piston flange 177 of the pump piston 162, the axial boundaries of which are fixed to the housing and are formed by the central annular shoulders 174 and 178.

From the basic position of the piston 162 corresponding to the spring-centered basic position of the armature of the double-stroke magnet system 161, the latter can have the same piston strokes in the direction of arrow 187 - to the left - and in the direction of arrow 188 - to the right - To run. If the piston 162 experiences a displacement in the direction of the arrow 187, then Pressure is built up in the left-hand pump chamber 184 and made available at the pressure outlet 191 of the pump 30 'via a first outlet valve 189 shown as a check valve. Due to the enlargement of the left pump chamber 184, which is accompanied by a reduction in volume, the right pump chamber 186 receives pressure medium from the compensating chamber 167 via an inlet valve 192 which is associated with the same and also represented as a check valve and which is integrated in the pump piston 162.

If the piston 162 moves in the direction of the arrow 188 — to the right — pressure is built up accordingly in the right-hand pump chamber 186, which pressure is made available at the pressure outlet 191 of the pump 30 ′ via a second outlet valve 193, again shown as a check valve , while at the same time pressure medium flows out of the equalizing chamber 167 via a now opening, second inlet valve 194, which is also shown as a check valve integrated in the pump piston 162, into the enlarging left pump chamber 184.

The valve balls 196 of the inlet valves 192 and 194 are arranged in bores 197 and 198 of the piston 162, the central axes of which run parallel to the central axis 163 of the pump element 30 '. The conical valve seat 199 of the inlet valve 194, which is assigned to the left pump chamber 184, is located to the right of its valve ball 198, so that its inertia opens of the valve favors when the pump element 30 'is operated at high frequency and the piston 162 moves to the right, ie executes the filling stroke for the left pump chamber 184. Accordingly, the inlet valve 194 assigned to the right-hand pump chamber 186 is also arranged such that its valve seat 201 is arranged to the left of the valve ball 196, the opening of this valve 194 also being promoted by the inertia of the hydraulic fluid located in the compensating chamber 167 .

Even if the ram-shaped sections 173 and 181 of the piston 162 have relatively large diameters D ^ and thus correspondingly large cross-sectional areas, the pump element 30 'can also be designed for high output pressures with relatively low drive powers or forces, since the ring end faces 201 and 202 of the central piston flange 177 which are decisive for the maximum achievable outlet pressure can be kept very small by choosing the diameter D _{2 of} this piston flange 177 and the central bore step 176 to be only slightly larger than the diameter DL of the ram-shaped piston sections 173 and 181.

Claims

Claims 1. Electromagnetically drivable pump as a pressure supply unit for a hydraulic consumer, which has a double-stroke magnet system as the drive device for a piston pump, which comprises two field windings of the same design, which are arranged along a common central axis and which are coaxial surround an axially movable armature, which can be driven by alternating energization of the two field windings to reciprocating movements carried out by the pump piston in time with this energization, in one direction of movement of the piston linked to an increase in volume of a pump chamber The pump chamber is filled from the pressure medium reservoir via an inlet valve and pressure medium is conveyed in the opposite direction of movement of the pump piston via an outlet valve from the pump chamber to a pressure outlet of the pump, characterized by the following features: a) The pump is designed as a double-piston pump (10) with pump pistons (11, 12) and pump chambers (13, 14) of the same design arranged axially on both sides of the armature, the pump chambers (13, 14) each having an outlet Check valve (82, 83) are connected to a common pressure outlet (16) of the pump (10); b) The pump pistons (11, 12) have central through-channels (97, 98) which are permanently in communication with the pump chambers (13, 14) and which are connected via inlet check valves arranged centrally in the armature (18) ( 111, 112) are connected to an input chamber (99) provided in the armature (18), which communicates via at least one radial channel (101) with an external groove (102) of the armature (18) which is permanent within its axial width is designed to overlap with the opening cross section of a radial inlet channel (103), which communicates with the pressure medium reservoir (104); c) The central channel (53), within which the armature (18) can be moved back and forth, is also in communication with the storage container (104). 2. Pump according to claim 1, characterized in that the frequency and / or the current intensity of the excitation windings used for the alternating energization of the excitation windings (22, 23) is adjustable. 3. Pump according to claim 1 or claim 2, characterized ge indicates that at least one of the pistons (11 and / or 12) of the pump and one of the excitation windings (23 and / or 24) as a valve body and switching winding as a Solenoid valve designed ent load valve (140) are used which, when this excitation winding (23 and / or 24) is energized, reaches a flow position connecting the pressure outlet (16) of the pump (10) with its pressure medium reservoir (104) and is otherwise blocked . 4. Pump according to claim 3, characterized in that the excitation winding (23) used as switching winding of the relief valve (140) of the double-stroke magnetic system for switching the relief position of this valve (140) can be excited with a current, the strength of which is greater is than the excitation current strength used for the pumping operation, and that the relief position of the relief valve (140) is reached with a greater deflection stroke of the pump piston (11) forming the valve body than the filling and pressure strokes carried out in pumping operation. 5. Pump according to claim 4, characterized in that in the maximum deflection stroke of the piston (11) corresponding open position of the relief valve (140), the inlet valve (82) of the associated pump chamber (13) by an axial plunger (146) of the the valve body of the relief valve (140) forming the pump piston is pushed open into its open position, and that the relief valve (140) is designed as a 2/2-way valve which in its open position has the pump chamber (13) with the central channel (53) of the magnetizing, which communicates with the storage container (104) baren, ring-cylindrical jacket (33) of the double-stroke magnet system (19) communicatingly connects. Pump according to Claim 5, characterized in that the relief valve (140) has a pump piston (11) in the central bore (64) of the chamber block (54) forming the housing of the relief valve in which the pump piston forming the valve body of the relief valve (140) ) is guided so as to be displaceable in a pressure-tight manner, has an arranged inner groove which, via a relief channel (144), communicates with the central channel communicating with the reservoir (104) (53) is connected and, viewed in the axial direction, is arranged between the pump chamber (13) and the central channel of the double-stroke magnet system (19), and that the pump piston (11) has a radial channel (141) with it. has its axial longitudinal channel (97) communicating with the pump chamber (13) in communicating connection external groove (142), seen in the axial direction, between the inner groove (143) of the chamber block (54) and the ring end face (121) which forms an axially fixed boundary of the central channel (53) and is in overlap with the inner groove (143) of the valve chamber block (54) only when the piston ( 11) coaxially surrounding excitation winding (23) is supplied with a direct current, the amount of which is significantly greater than the current intensity of the current pulses used for alternating stroke control of the armature (18). Pump according to one of claims 1 to 6, characterized in that a relief valve (147) designed as a solenoid valve is provided which, when its switching magnet (148) is de-energized, has a pressure output (16) of the pump (10) with its valve Releases the reservoir (104) connecting relief path (153) and otherwise keeps locked. Pump according to claim 7, characterized in that the normally open relief valve (147) is arranged in the outlet chamber (72 or 73) of one of the outlet valves (82 or 83) of the pump (10) and is axially displaceable and made of magnetizable material ¬ standing valve body (149), which can be urged by energizing a field winding (148) in contact with a valve seat and thereby leading from the outlet chamber (72 or 73) of the pump to its central channel (53), the respective cam ¬ merblock (54 or 56) passing through relief channel (153) against the outlet chamber (72 or 73) blocked as long as the field winding (148) is energized. Pump according to claim 7, characterized in that the valve seat of the normally open relief valve (147) is formed by an O-ring (151) which surrounds the outlet opening of the relief channel on the outlet side, and in that the valve body (149) also a radial flange that can be supported on the O-ring (151) and / or as in the outlet chamber (71 or 72) is designed to be axially displaceably guided and can be urged against the restoring force of a restoring spring (154) in contact with the O-ring (151). 10. Electromagnetically drivable pump as a pressure supply unit for a hydraulic consumer, which as a drive device for a piston pump has a double-stroke magnet system which comprises two field windings of the same design arranged along a common central axis, which are coaxial surround an axially movable armature, which can be driven by alternating energization of the two field windings to reciprocating movements carried out by the pump piston in time with this energization, in one direction of movement of the piston linked to an increase in volume of a pump chamber The pump chamber is filled from the pressure medium reservoir via an inlet valve and pressure medium is conveyed in the opposite direction of movement of the pump piston via an outlet valve from the pump chamber to a pressure outlet of the pump, characterized in that the pump is a double Oil piston pump (20) with pump pistons (11 ', 12') arranged axially on both sides of the armature and pump chambers (13, 14) of the same design is formed, the pump chambers (13, 14) each having an outlet check valve (82 , 83) to a common pressure outlet (16) of the pump (20) are connected and that the pump chambers (13, 14) each have individually assigned inlet valves (111 ", 112") in radial overflow channels (156, 157) which are located between the pressure medium reservoir (104) and one of the pump chambers extend (13 or 14). 11. Pump according to claim 10, characterized in that the respective one of the pump chambers (13 or 14) assigned inlet valves (111 ", 112") and Auslaßven¬ tile (82, 83) in each one of the pump chamber (13 or 14) housing-terminating housing end block (59 'or 61') are integrated. 12. Electromagnetically drivable pump as a pressure supply unit for a hydraulic consumer, which has a double-stroke magnet system as the drive device for a piston pump, which comprises two field lines of the same design arranged alongside one another along a common central axis, which coaxially surround an axially movable armature, which can be driven by alternating energization of the two field windings to reciprocating movements carried out by the pump piston with the reciprocation of this energization, in the one direction of movement linked to an increase in volume of a pump chamber the piston is filled via an inlet valve from the pressure medium reservoir and is pumped in the opposite direction of movement of the pump. penkolbens pressure medium is conveyed via an outlet valve from the pump chamber to a pressure outlet of the pump, characterized by the following features a) the pump (30) has two annular chamber-shaped pump chambers (184 and 186) which are delimited relative to one another within a central bore step (176) of their housing (164) by an annular flange (177) of the pump piston (162), which are clocked the reciprocating movements of the piston (162) are alternately connected to a common pressure outlet (191) of the pump (30 ') via an outlet check valve (189 or 193); b) the piston (162) with push-shaped sections (173 and 181) arranged on both sides of the flange (177) is guided in a pressure-tight manner in bore steps (172 and 179) adjoining the central bore step (177), the one piston section (181 ) is connected to the armature of the double-stroke magnet system in a tensile and shear-proof manner and the other push-rod-shaped piston section (173) has an axially movable limitation of an equalizing chamber (162) of the pump element that communicates with the reservoir (169). 30 ') forms; c) provided as inlet valves (192 and 194), the Pump chambers (184 and 186) individually assigned check valves, which are acted upon by higher pressure in the compensation chamber (167) than in the respective pump chamber (184 or 186) in the opening direction and are otherwise blocked, are structurally integrated in the pump piston (162). 13. Electromagnetically driven pump according to claim 12, wherein the inlet valves are designed as ball seat valves, the balls of which are arranged in bores of the pump piston, the axes of which extend in the direction of the piston displacement movements, characterized in that the valve seat (199) of the inlet valve (194) which must open to fill the associated pump chamber (184) when the piston (162) moves towards the drive side, at the drive end of its bore (198) and the valve seat (201) of the inlet valve (192) which is used to fill the assigned pump chamber (186) must open when the pump piston (162) is displaced towards the compensation chamber (167) on which this end of the valve bore (197) facing it is arranged.