EP0651858B1 - 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

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

Such a pump is known from DE 39 33 125.3 A1.

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 common central axis. These field windings coaxially surround a 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 movement of 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 check valve and pressure medium is conveyed from the pump chamber to a pressure outlet of the pump in the opposite direction of movement of the pump piston associated with the pumping operation 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 check 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 check valve into the tube section which is arranged pointing towards the outlet valve. In the delivery stroke, liquid also flows in via the inlet valve into the prefilling 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 construction 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 due to an associated increase in the air gap in the part of the magnet system which is attracting during the delivery stroke, the tightening forces decrease relatively, with the result that 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.

The object of the invention is therefore to improve an electromagnetically drivable pump of the type mentioned in such a way that within a wide range a linear relationship between the electrical input power and the hydraulic delivery capacity of the pump and also an operation thereof can be achieved with high efficiency.

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; the pump pistons have central through-channels in permanent communication with the pump chambers, which are connected via input check valves arranged centrally in the armature to an input chamber arranged centrally in the armature, which communicates via at least one radial channel with an external groove of the armature, which is within its axial width is permanently overlapping with the opening cross-section of a radial feed pipe which is connected to the pressure medium reservoir, and it is also the central channel within which the armature can be moved back and forth, permanently held 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 is favorable with optimal utilization small air gap widths in the respective attracting magnet system. While one pump is pumping, the other is filled with pressure medium. As a result, the electrical power consumption of the field windings is optimally used to convert it into hydraulic delivery. Since the armature moves back and forth in a non-pressurized space, which is filled with pressure medium - usually lubricable hydraulic oil - the friction losses are also low, with the further advantage that it is via the inlet valves and through the axial longitudinal channels of the pistons leading to the pump chambers are short and can be realized with relatively large cross sections, so that low flow resistances 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 supply to be alternated is the excitation current pulses used adjustable so that by changing these parameters, the delivery rate of the pump and its output pressure can be controlled in a simple manner. 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 outlet 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, reaches a flow position connecting the pressure output of the pump with its pressure medium reservoir, 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 one 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 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 design of the pump according to the invention, in the maximum deflection of a pump piston corresponding to the open position of the relief valve, the outlet valve of the associated pump chamber is pushed open into its position corresponding to the open position of the outlet valve by an axial tappet of the piston of the relief valve, so The relief valve can be designed as a simple 2/2-way valve which, in its open position, connects the pump chamber to the central channel of the magnetizable, ring-cylindrical jacket of the double-stroke magnet system that communicates with the reservoir, this 2/2-way valve The construction of the valve can be realized in a simple manner in that it is arranged in the central bore of the chamber block forming the housing of the relief valve, in which the pump piston forming the valve piston of the relief valve is displaceably guided in a pressure-tight manner nominal groove, which is connected via a relief channel to the central channel communicating with the reservoir and, viewed in the axial direction, between the Pump chamber and the central channel of the double-stroke magnet system is arranged, and that the pump piston has an outer groove communicating via a radial channel with its axial longitudinal channel communicating with the pump chamber communicating connection, which, seen in the axial direction, between the inner groove of the pump chamber block and its die an axially fixed boundary of the central channel forming annular end face is arranged and only overlaps with the inner groove of the pump chamber block when the excitation winding coaxially surrounding the piston is energized with a direct current which is greater than the maximum value of the current with which the excitation windings of the double-stroke magnet system are pulsed during 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 output 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 realized in a structurally simple manner in that it comprises an axially displaceably arranged valve body made of a magnetizable material in the outlet chamber of the respective outlet valve of the pump, which valve body can be urged by energizing a field winding in contact with a valve seat and thereby one of the outlet chamber of the Shuts off the pump to the central channel of the double-stroke magnet system, through the respective chamber block, through the relief channel against the outlet chamber, as long as the field winding is energized.

In a preferred configuration 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 being axial in the outlet chamber slidably guided annular disc is formed, which can be urged against the restoring force of a return spring in contact with the O-ring.

It is understood 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, the object on which the invention is based is also achieved in that the pump has two annular chamber-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 which move in time with the reciprocating movements of the piston are connected alternately to a common pressure outlet of the pump via an outlet check valve that the piston with plunger-shaped sections arranged on both sides of the flange is guided in a pressure-tight manner in bore stages adjoining the central bore, one piston section being connected to the armature of the double-stroke magnet system in a pull-and-push-proof manner and the other plunger-shaped piston section having an axially movable limitation with the Storage container communicating connected compensation chamber, and that provided as inlet valves, individually assigned to the pump chambers check valves, which are acted upon by higher pressure in the compensation chamber than in the respective pump chamber in the opening direction and otherwise blocked, are integrated in the pump piston.

In this design, the overall pump consists of a hydraulic pump module and an electrically controllable drive module, which brings both manufacturing advantages and design changes, because, for example, the pump can be converted to a more powerful drive simply by replacing the drive module is.

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, the axes of which extend in the direction of the piston displacement movements, the valve seat of the inlet valve is that which opens to fill the assigned pump chamber must when the piston is on the drive side moves towards the drive-side 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 which this end of its valve bore is arranged.

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.

• 1. Druckversorgungsaggregat für Stellantriebe relativ geringer Leistung, deren bedarfsgerechte Druckversorgung mittels eines einzigen - zentralen - Druckversorgungsaggregats eine zentrale Pumpe wesentlich höherer Leistung erfordern würde, die aber nur in seltenen Fällen entsprechend ihrer Leistungsfähigkeit belastet würde. Einsatzmöglichkeiten dieser Art sind beispielsweise eine hydraulische Sitzverstellung von Stühlen für medizinische Zwecke und/oder von Kraftfahrzeugen, Antriebe von Fensterhebern, Schiebedächern und dergleichen.
• 2. Antriebs-Energiequelle für Servo-Systeme an Kraftfahrzeugen wie eine Servo-Lenkung und/oder eine Nivauregulierung bei Kraftfahrzeugen, die derzeit den Einsatz vom Fahrzeugmotor angetriebener Pumpen erfordern, die den größten Teil der Einsatz-Zeit eines Fahrzeuges "nutzlos" d.h. im Leerlauf betrieben werden müssen.
• 3. Realisierung einfacher Antriebs-Schlupf-Regelungssysteme die mit Aktivierung der Radbremse eines zum Durchdrehen neigenden angetriebenen Fahrzeugrades arbeiten.
• 4. Einsatz im Rahmen einer aktiven Fahrwerksregelung, bei der hydraulische Stoßdämpfer an dynamisch bedingte variierende Werte der Radlastverteilungen eines Fahrzeuges angepaßt werden müssen.
• 5. Einsatz bei Dosierpumpen in der chemischen Industrie, die ein sensibles Ansprechverhalten auf erwünschte Änderungen der Förderleistung erfordern.

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 wide limits - the frequency with which the excitation windings of its double-stroke magnet system are alternately energized - and also by the specification or The setting of the current strengths of the excitation currents with which the excitation windings are energized can be optimally designed with regard to a large number of different purposes, which results in a large number of interesting possible uses, of which a few should be mentioned as examples below:

• 1. Pressure supply unit for actuators of relatively low power, their need-based pressure supply by means of a single - central - pressure supply unit, a central pump essential would require higher performance, but which would only rarely be charged 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 a power steering and / or a level control in motor vehicles, which currently require the use of motor-driven pumps, the majority of the time of use of a vehicle "useless" ie idle must be operated.
• 3. Realization of simple traction control systems that work by activating the wheel brake of a propelled vehicle wheel that tends to spin.
• 4. Use in the context of an active chassis control, in which hydraulic shock absorbers have to be adapted to dynamically 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.

Fig. 1

Eine erfindungsgemäße elektromagnetisch antreibbare Pumpe im Schnitt längs einer die zentrale Achse ihres Doppelhub-Magnetsystems enthaltenden Radialebene, in maßstäblicher Darstellung, etwa im Maßstab 1,5/1,

Fig. 2

Einzelheiten der Pumpe gemäß Fig. 1 in einer der Darstellung der Fig. 1 entsprechenden, jedoch vergrößerten Schnittdarstellung und

Fig. 3

ein Diagramm zur Erläuterung der Funktion der in den Fig. 1 und 2 dargestellten Pumpe und

Fig. 4

ein weiteres Ausführungsbeispiel einer erfindungsgemäßen mittels eines Doppelhub-Magnetsystems antreibbaren Pumpe in schematisch vereinfachter, stark vergrößerter Längsschnitt-Darstellung.

Further details and features of the invention result from the following description of special exemplary embodiments with reference to the drawing. Show it:

Fig. 1

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, for example on a scale of 1.5 / 1,

Fig. 2

Details of the pump according to FIG. 1 in a sectional view corresponding to FIG. 1 but enlarged and

Fig. 3

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

Fig. 4

a further 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 illustration.

The electromagnetically driven device according to the invention shown in FIG. 1, to the details of which reference is expressly made, generally designated 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 outlet 16 to which a hydraulic consumer, for example as shown, a linear hydraulic cylinder 17 can be connected.

The two pump pistons 11 and 12 are fixedly 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 14 is rotationally symmetrical and, seen in the spring-centered neutral position of the armature 18, which it occupies in the de-energized state of the double-stroke magnet system 19, is also symmetrical with respect to the transverse central plane 22 which is perpendicular to the central longitudinal axis 21.

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 various reciprocating movements in the direction of the central longitudinal axis 21 in a defined manner, thereby - at predetermined pressure against which the pump 10 must work, the delivery rate is adjustable.

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, the bobbins 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 internally arranged annular gaps 31 and 32 - otherwise completely - enclosed by an overall annular cylindrical jacket 33 which is magnetically conductive, i.e. 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 rests with its radially outer circumferential surface 37 on adjacent sections of the bobbins 26 and 27 of both field windings 23 and 24 and with its narrow annular end faces 38 and 39 forms the inner boundaries of the annular gaps 31 and 32 as seen in the axial direction, two more, radially inner casing tubes 41 and 42, which have conical inner end sections, which have chamfer surfaces 43 and 44 that slope obliquely towards the central longitudinal axis 21, that form outer boundaries of the annular gaps 31 and 32 in the axial direction, and with their outer, radially running, 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 mediate the outer magnetically conductive connection between these further jacket tubes 41 and 42 and the outer jacket tube 34 of the ring-cylindrical jacket 33 and directly to the outside seen in the axial direction End flanges 29 of the bobbin 26 and 27 abut, as well as central, annular disk-shaped yoke plates 51, which fill the space in the axial direction between the inner radial flanges 28 of the bobbin 26 and 27 and in the central region of the ring-cylindrical jacket 33 the magnetis ch convey 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 in direct contact with the latter and is made of antimagnetic stainless steel, is inserted, which, with its narrow annular end faces, is flush with the outer, radial boundary surfaces of the outer annular disk-shaped yoke plates 48 and 49 of the annular 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, sections of ring-shaped cylindrical blocks 54 and 56 are inserted, which delimit the two valve chambers 13 and 14 of the double-piston pump 10 and are inserted pressure-tightly into the mentioned end sections of the stainless steel tube 52. 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 ring-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 to the annular 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 sections 54 'and 56' of the chamber blocks 54 and 56 which form the pole cores of the magnetizable jacket 33 surrounding the field windings 23 and 24 and the armature 18 and which point towards the armature 18 of the double-stroke magnet system 19 56, which with its radial, inner ring end faces 121 and 122 is fixed to the housing 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 abut 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 holes 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. 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 flanges 57 and 58 of which from the measured axial depth is greater than the correspondingly measured axial extension 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 faces 69 and 71 of the outer peg-shaped sections 54 "and 56 "of the chamber blocks 54 and 56 are fixedly delimited outlet chambers 72 and 73, these outlet chambers 72 and 73 being communicatively connected to the pressure outlets 16 'and 16" of the pump 10 via radial transverse channels 74 and 76 of the housing end blocks. The outer pin-shaped sections 54 " and 56 "are provided with axial through holes 77 and 78, which are between de n 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 in contact with their associated valve seats 81 by valve springs 87 and 88, respectively, which are under axial preload or 82 will be 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, in its basic form, designed as a thick-walled tube, within which a total of two are formed by a central intermediate wall 89 Over the largest part of the length of the armature 18, cup-shaped depressions 91 and 92 which are open towards the chamber blocks 54 and 56 are delimited from one another, into which the pump pistons 11 and 12 with flange-shaped inner end sections 93 and 94 are adjacent to the intermediate wall 89 and to the the recesses 91 and 92, the radially outer boundary jacket portions 96 'and 96 "of the tube 96 of the armature 18 are then inserted mechanically firmly and pressure-tight. The pump pistons 11 and 12 have central longitudinal channels 97 and 98, respectively, with the respective pump chamber 13 and 14 are in communicating connection. The intermediate wall 89 is connected to a central one , Axial through bore 99, which via radial transverse channels 101, which open into an outer annular groove 102 of the anchor tube 96, the 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 which radially traverses 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 the central outer annular groove 102 and into the sections of the central one arranged on both sides of the armature Channel 53 open, held in communication with the reservoir 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 armature 18 opens with a chamfer surface 108 or 109, which widens conically towards valve chambers 106 and 107. These conical chamfer surfaces 108 and 109 form seating surfaces for the valve balls 111 'and 112' each as 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' each having a weakly preloaded valve spring 113 or 114, which settle on the valve chambers 106 and 107 against the areas of the longitudinal channels 97 and 98 which are smaller in cross section Support ring shoulders 116 and 117, and be pressed into sealing contact with valve seat surfaces 108 and 109. "Weakly preloaded" valve spring is intended to mean that the valve balls 111 'and 112' lift off their valve seat surfaces 108 and 109 when the pressure in the respective pump chamber 13 or 14 is lower by a small amount, for example by 0.2 bar is 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 92 of the armature 18, which are delimited over the major part of their length by the radially outer regions of the cup-shaped recesses 91 and 92 of the armature 18 delimited radially on the outside by the jacket sections 96 'and 96 "of the armature tube 96 and radially on the inside by the valve pistons 11 and 12 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 ring 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 inserted into the in 1, spring-centered basic position, 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 applied with current pulses, which causes the armature 18 is driven to reciprocating movements occurring in time with 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 and the associated one 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 steady, only slightly pulsating pressure medium flow to the consumer 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 different specific uses, reference is now also made to the diagram of FIG. 3, which, depending on the excitation current as a parameter, qualitatively determines the dependence on the armature 18 acting magnetic force K _M from 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 this, which through the axially inner peg-shaped Extension 54 'of the left chamber block 54 is formed, plotted and as the ordinate 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 strength I ₀ and the armature 18 thereby remains magnetically active Moves the annular end face 123 on a radial stop face 126 of a so-called “anti-adhesive plate” 127 facing this, which is formed, for example, as a thin-walled plastic plate and onto the inner, magnetically effective annular end face 121 of the inner pin-shaped extension 54 ′ of the left valve chamber block 54 Pole core is applied, which is intended to prevent the magnetizable armature 18 from coming into direct contact with the magnetizable pole core and from being able to "stick" to it due to magnetic remanence effects.

A second course curve 128 and a third course curve 129 of the diagram provide the possible values of the between the armature 18 and the ring-cylindrical magnetisable for corresponding, but higher excitation currents of, for example, 1.5 I ₀ and 2 I ₀ associated excitation states of the left excitation winding 23 Sheath 33 represents effective attractions. The 3, curve curves 124, 128 and 129 are only for the area of particular interest between the spring-centered basic position of the armature 18, which is marked in the diagram by the dashed curve plane 131 of its magnetically active ring face 123 and the stop face 126 of the Anti-adhesive plate 127 is drawn, the level of which 132 is also shown in dashed lines in the diagram of FIG. 3.

For the exemplary embodiment of the pump 10 selected for the explanation, it is assumed that, seen in the basic position of the armature 18, the axial distance of the course 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 is the 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 towards 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 it and the armature 18 initially increases, depending on the current intensity of the excitation current 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 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 between the free end face 62 'of the conical tube 41 and the magnetically effective end face 123 of the armature 18 and thus also with a minimum of the magnetic resistance between the conical region of the conical tube 41 and the armature 18. This magnetic "transition" resistance increases when the armature 18 moved further in the direction of arrow 134 towards the pole core, which is accompanied by a decrease in the magnetic attraction, which in the diagram of FIG. 3 is caused by the falling branches 124 ″ ″, 128 ″ ″ and 129 ″ ″ of the profile curves 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 again increases until in a radial plane 134, which corresponds to the same value of the magnetic resistance between the conical area 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, a relative minimum 124 ″ ″ or 128 ″ ″ or 129 ″ ″ of the magnetic attraction force is passed through, after which, when the armature approaches the pole core 54 ′, 121, the magnetic attraction force between it and the armature 18 rises steeply again, as a result of the rising branches 124 ^V , 128 ^V and 129 ^{V of} the curve 124 and 128 or 129 represents, until finally, when the armature 18 has reached the contact position of its magnetically effective 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 magnetic attraction force have been reached, which correspond to the minimum value of the magnetic resistance between the pole core 54 ', 121 and the armature 18 and are significantly higher in magnitude than the relative maximum values 124 ", 128" and 129 ", the minimum value of the magnetic resistance between the conical region 62 of the Cone tube 41 and the anchor 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 when the pump 10 has a relatively high delivery rate - Delivery volume per stroke - should have, but can work at a comparatively low outlet 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 cone tube 41. The movement stroke H ₁ that results for the periodic pumping operation then corresponds to twice the value 2 h _{1 of} the deflection h ₁ that 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.

gegeben ist, in welcher mit F_A die wirksame Querschnittsfläche der Pumpenkolben 11 und 12, mit H der Kolbenhub im eingeschwungenen Betriebszustand und mit n die Frequenz der alternierenden Bestromung der Erregerwicklungen bezeichnet sind, ist dann wegen des großen Betrages H₁ des Kolbenhubes ebenfalls besonders hoch.The delivery volume Q̇ related to the time unit, which is determined by the relationship: $$\dot{\text{Q}}{\text{= F}}_{\text{A}}\text{· 2H · n}$$

is given, 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 then also particularly high because of the large amount H _{1 of} the piston stroke .

On the other hand, if 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 active ring face 123 with the through the free annular end face 62 'of the conical area 62 of the conical tube 41 marked radial plane 133 coincides and for the pump area an area "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 force between the magnetizable ring jacket 33 and the armature 18 is approximately constant and almost corresponds 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 value H _{2 of} the filling and delivery strokes of the The armature 18 is, however, significantly smaller compared to the case in which the pump 10 can work with a moderate outlet pressure, however an increase in the delivery rate in the high pressure operation of the pump 10 is, at least in a limited, nevertheless interesting area, by increasing the frequency n the alternating energization of the excitation windings 23 and 24 of the double-stroke magnet system 19 may resembled.

Basically, a design of the double-piston pump 10, as explained with reference to FIGS. 1 to 3, for a high outlet pressure is also possible in that in the diagram of FIG. 3 the stroke range, also associated with high magnetic attraction forces, is used, 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 that are higher than the relative maxima 124 ", 128" and / or 129 " arise for the radial plane 133, which is marked by the narrow annular end face 62 'of the conical tube 41. The output bridge achievable with such a design of the pump 10 would not, however, at least not significantly higher than with a design of the pump on the stroke range limited 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 Attractive force is limited, which - in the steady state - can be reached when the armature 18 takes its greatest distance from the pole core end face 121 of the respectively attracting pole core.

In the double-piston pump 10, one of the pistons 11 on the left, as shown in FIG. 1, is also designed as a valve body of a slide valve, designated 140 as a whole, which is supplied with current that is higher than the maximum by energizing the one excitation winding 23, which in turn is in accordance with FIG Current with which the excitation windings 23 and 24 are alternately energized in the 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, and an inner groove 143 of the left chamber block 54 which can be overlapped therewith and one with the central channel 53 of the double stroke Magnet system 19 connecting relief channel 144 can flow out to the reservoir 104. The circumferential groove 142 of the pump piston 11 is arranged between the inner annular end face 121 of the chamber block 54 and its inner groove 143 in such a way that it cannot overlap with this inner groove 143 in normal pumping operation, but only if the left excitation winding 23 is more adequate with a direct current Current is energized and thereby the valve piston 11 experiences a greater deflection towards the pole core 54 'than 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 right housing end block 61 according to FIG. 1 and which is supplied with direct current in normal pumping operation, and thereby has an annular disk-shaped valve body 149 made of magnetizable material 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 energization of the further field winding 148 stops, 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 the consumer 17 thereby relieves the relief duct 153 and the central duct 53 to the pressure medium reservoir 104.

To explain a second exemplary embodiment of a pump 30 driven by means of a double stroke magnet system, reference is now made to FIG. 4.

In 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 designed as functional elements that are uniform in each case, 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 is the spring-centered basic position of the armature - and the piston 162 - determine the pump 30 ', assuming a structure as explained in principle with reference to FIG. 1, to which reference is made in this regard.

The further explanation of the exemplary embodiment according to FIG. 4 can therefore be restricted to its hydraulic pump unit 30 '.

Seen along the central longitudinal axis 163 of the pump element, which also forms the central longitudinal axis of the drive unit 161, the housing of the pump unit 30 ', designated overall by 164, has a first bore step 166, which forms the radial delimitation of a compensation chamber 167, which on one side is formed by an end end wall 168 is completed and in permanent communication with the pressure medium reservoir 169.

This first bore step 166 is followed by a second radial annular shoulder 171, followed by a second, smaller diameter with the first coaxial bore step 172, in which the piston 162 is guided so as to be pressure-tightly displaceable with a plunger-shaped piston section 173 as shown in FIG. 4. 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. In this third bore step 176, the piston 162 is guided in a pressure-tight manner with a central, radial piston flange 177. This third, central one Bore step 176 connects via a third radial shoulder 178 to a fourth bore step 179, 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 in a pressure-tight manner with a "right", second tappet-shaped section 181, which is located within a drive-side chamber 180 of the pump element housing 164, the radial boundary of which is formed by a fifth bore stage 182 with a larger diameter, and to the fourth bore step 179 in turn connects via a radial annular shoulder 183, to which the armature of the drive unit 161 is connected in a tensile 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, which corresponds to the spring-centered basic position of the armature of the double-stroke magnet system 161, the latter can carry out the same piston strokes in the direction of the arrow 187 - to the left - and in the direction of the arrow 188 - to the right. 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, which is shown as a check valve. Due to the enlargement of the left pump chamber 184, which is accompanied by the volume reduction, the right pump chamber 186 receives pressure medium from the compensating chamber 167 via an inlet valve 192, which is also associated with this and is also shown as a check valve and is integrated in the pump piston 162.

If the piston 162 moves in the direction of the arrow 188 - to the right -, pressure is correspondingly built up in the right-hand pump chamber 186, which is provided via a second outlet valve 193, again shown as a check valve, at the pressure outlet 191 of the pump 30 ', while at the same time pressure medium flows from the compensation 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 is favored 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 192 assigned to the right 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 in the compensation chamber 167.

Even if the tappet-shaped sections 173 and 181 of the piston 162 have relatively large diameters D ₁ 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 those for the maximum achievable output pressure relevant ring end faces 202 and 203 of the central piston flange 177 can be kept very small in that the diameter D _{2 of} this piston flange 177 and the central bore step 176 is selected only slightly larger than the diameter D _{1 of} the tappet-shaped piston sections 173 and 181.

Claims (11)

1. Electromagnetically drivable pump (10) by way of pressure-supply unit for a hydraulic consumer installation equipped with a two-stroke magnet system (19) by way of driving device for a reciprocating pump, said magnet system comprising two identically designed field coils (23, 24) arranged next to one another along a common central axis (21), said field coils coaxially encompassing an axially moveable armature (18) capable of being driven by alternately supplying current to the two field coils (23, 24) so as to induce reciprocating movements in phase with this supply of current and executed also by the plunger of the pump, whereby in the direction of plunger movement associated with an increase in the volume of a pump chamber the pump chamber is filled via an admission valve from the pressure-medium storage reservoir (104) and in the opposite direction of pump-plunger movement pressure medium is fed via a discharge valve from the pump chamber to a pressure outlet (16) of the pump (10), characterised by the following features:

   a) the pump is conceived as a twin-plunger pump (10) having pump plungers (11, 12) axially arranged on either side of the armature (18) and firmly connected to the latter and pump chambers (13, 14) of identical design, said pump chambers (13, 14) being connected, via one outlet check valve (82, 83) each, to a common pressure outlet (16) of the pump (10);

   b) the pump plungers (11, 12) comprise central through ducts (97, 98) permanently communicating with the pump chambers (13, 14), said through-ducts being connected, via inlet check valves (111, 112) centrally arranged within the armature (18), to an inlet chamber (99) provided within the armature (18), said armature communicating, via at least one radial duct (101), with an external groove (102) of the armature (18), said groove being so designed as to permanently overlap within its axial width the opening cross-section of a radial feed duct (103) communicating with the pressure-medium storage reservoir (104).

   c) a central duct (53), within which the armature (18) is so arranged as to slide therein in reciprocating manner, also communicates with the storage reservoir (104).
2. Pump according to Claim 1, characterised in that the frequency and/or the current intensity of the excitation current impulses used for alternately supplying current to the excitation coils (22, 23) is adjustable.
3. Pump according to Claim 1 or Claim 2, characterised in that at least one of the plungers (11 and/or 12) of the pump and one of the excitation coils (23 and/or 24) serve by way of valve body and switching coil of a relief valve (140) in the form of a solenoid, said relief valve being switched, whenever current is supplied to said excitation coil (23 and/or 24), to a through-flow position in which the pressure outlet (16) of the pump (10) communicates with the pressure-medium storage reservoir (104) of said pump and is otherwise closed.
4. Pump according to Claim 3, characterised in that the excitation coil (23) of the two-stroke magnet system serving by way of switching coil for the relief valve (140) is capable of being excited, with a view to switching to the relief position of said valve (140), by a current having an intensity which is higher than the intensity of the excitation current used for operating the pump and in that the relief position of the relief valve (140) is attained at a deflection stroke of the pump plunger (11) constituting the valve body that is greater than the filling and compression strokes executed in the course of operating the pump.
5. Pump according to Claim 4, characterised in that in the open position of the relief valve (140) corresponding to the maximal deflection stroke of the plunger (11) the admission valve (82) of the associated pump chamber (13) is pushed to its open position by an axial actuator (146) of the pump plunger constituting the valve body of the relief valve (140) and in that the relief valve (140) is designed as a 2/2-way valve which in its open position connects the pump chamber (13) to the central duct (53) communicating with the storage reservoir (104) and pertaining to the magnetisable annular cylindrical jacket (33) of the two-stroke magnet system (19), so as to cause said pump chamber to communicate with said central duct.
6. Pump according to Claim 5, characterised in that the relief valve (140) comprises an internal groove provided within the central bore (64) of the chamber block (54) constituting the housing of the relief valve and in which the pump plunger (11) constituting the valve body of the relief valve (140) is capable of sliding in pressure-tight manner, said internal groove being connected via a relief duct (144) to the central duct (53) communicating with the storage reservoir (104) and, viewed in the axial direction, being arranged between the pump chamber (13) and the central duct of the two-stroke magnet system (19) and in that the pump plunger (11) comprises an external groove (142) which communicates via a radial duct (141) with its axial longitudinal duct (97) that communicates with the pump chamber (13), said external groove, viewed in the axial direction, being arranged between the internal groove (143) of the chamber block (54) and an annular front surface (121) pertaining to said chamber block and constituting one boundary of the central duct (53), said boundary being firmly connected to the housing in the axial direction, and overlapping the internal groove (143) of the valve chamber block (54) only when the excitation coil (23) coaxially surrounding the plunger (11) is supplied with a direct current, the intensity of which is distinctly greater than the intensity of the current impulses used for the alternating stroke control of the armature (18).
7. Pump according to one of Claims 1 to 6, characterised in that a relief valve (147) in the form of a solenoid is provided, which in the no-current state of its switching magnet (148) releases the relief path (153) connecting the pressure outlet (16) of the pump (10) with its storage reservoir (104) while keeping it closed at any other time.
8. Pump according to Claim 7, characterised in that the relief valve (147) opening in the no-current state comprises a valve body (149) made from magnetisable material and arranged in axially slidable manner within the outlet chamber (72 or 73) of one of the outlet valves (82 or 83) of the pump (10), said valve body being capable of being pressed into contact with a valve seat when a field coil (148) is supplied with current and as a result keeps the relief duct (153) leading from the outlet chamber (72 or 73) of the pump to its central duct (53) and passing through the respective chamber block (54 or 56) closed in relation to the outlet chamber (72 or 73) as long as the field coil (148) is supplied with current.
9. Pump according to Claim 7, characterised in that the valve seat of the relief valve (147) opening in the no-current state is constituted by an O-ring (151) surrounding the relief-duct outlet aperture on the outlet-chamber side and in that the valve body (149) is provided with a radial flange capable of being supported by the O-ring (151) and/or is designed as an annular disc which is capable of axially sliding within the outlet chamber (71 or 73), it being possible to press said flange or disc, in opposition to the restoring force of a restoring spring (154), into contact with the O-ring (151).
10. Electromagnetically drivable pump (30) by way of pressure-supply unit for a hydraulic consumer installation equipped with a two-stroke magnet system by way of driving device for a reciprocating pump, said magnet system comprising two identically designed field coils arranged next to one another along a common central axis, said field coils coaxially encompassing an axially moveable armature capable of being driven by alternately supplying current to the two field coils so as to induce reciprocating movements in phase with this supply of current and executed also by the pump plunger (162), whereby in the direction of plunger movement associated with an increase in the volume of a pump chamber the pump chamber is filled via an admission valve from the pressure-medium storage reservoir and in the opposite direction of pump-plunger movement pressure medium is fed via a discharge valve from the pump chamber to a pressure outlet (191) of the pump, characterised by the following features:

    a) the pump (30) comprises within a central bore stage (176) of its housing (164) two annular pump chambers (184 and 186) which are moveably delimited in relation to one another by an annular flange (177) of the pump plunger (162), said pump chambers being connected to a common pressure outlet (191) of the pump (30') so as to alternate in phase with the reciprocating movements of the plunger (162) via a corresponding output check valve (189 and 193, respectively):

    b) the plunger (162) is guided by means of sections (173 and 181) in the form of slides arranged on either side of the flange (177) in pressure-tight moveable manner into bore stages (172 and 179) adjoining the central bore stage (176), one plunger section (181) being connected to the armature of the two-stroke magnet system in a manner resistant to both tension and thrust and the other plunger section (173) in the form of a slide constituting an axially mobile boundary of a compensating chamber (162) pertaining to the pump section (30') and communicating with the storage reservoir (169);

    c) check valves individually associated with the pump chambers (184 and 186) and serving by way of admission valves (192 and 194) are structurally integrated within the pump plunger (162), said check valves being induced to open when the pressure in the compensating chamber (167) is higher than in the given pump chamber (184 or 186) and are otherwise closed.
11. Electromagnetically drivable pump in accordance with Claim 10, whereby the admission valves (192, 194) are designed as ball-type seat valves, the balls (196) of which are arranged within bores (197, 198) of the pump plunger (162) and the axes of said bores extend in the direction of plunger movement, characterised in that the valve seat (199) of that admission valve (194) which has to open whenever the plunger (162) moves to the drive side in order to fill the associated pump chamber (184) is arranged at that end of its bore (198) which is on the drive side while the valve seat (201) of that admission valve (192) which has to open whenever the pump plunger (162) is moved towards the compensating chamber (167) in order to fill the associated pump chamber (186) is arranged at that end of the valve bore (197) which faces said compensating chamber (167).

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