GB2137420A

GB2137420A - Electromagnetically-operated adjusting means

Info

Publication number: GB2137420A
Application number: GB08407891A
Authority: GB
Inventors: Franz Pischinger; Peter Kreuter
Original assignee: Fev Forsch Energietech Verbr
Current assignee: Fev Forsch Energietech Verbr
Priority date: 1983-03-28
Filing date: 1984-03-27
Publication date: 1984-10-03
Also published as: FR2543651B1; DE3311250C2; JPS59211203A; JPH0377646B2; IT1177615B; BR8401405A; IT8447934A0; GB8407891D0; IT8447934A1; FR2543651A1; GB2137420B; DE3311250A1

Abstract

An electromagnetically-operated adjusting means for the valves of displacement machines, comprises an oscillatory spring-mass system 12-20 which can be held by electromagnets (1,2) in each of two end positions of maximum oscillation deflection so that at least two discrete switching positions are achieved. The electromagnets and their armature(s) 17 are designed as part of a damping means and, at the same time, at least one of the electromagnets, by the use of one or more hydraulically-operated length-equalizing elements (21), are connected to a housing (7) or to a valve stem (12) in such a manner that the distance between a valve seat and the pole faces of the electromagnet or electromagnets is matched to the distance between the valve seat and the pole face or faces of the armature so that the armature approaches the electromagnet and the valve approaches the seat in a similarly damped manner. <IMAGE>

Description

SPECIFICATION Electromagnetically-operated adjusting means The invention concerns electromagneticallyoperated adjusting means (as used, for example, to operate valves in machines such as reciprocatingpiston internal combustion engines, pumps and other displacement machines) wherein a springmass system can be held by electromagnets in each of two end positions of maximum oscillation deflection so that at least two discrete switching positions are obtained and wherein the period of dwell in the switching positions can be controlled by energizing the electromagnets over any required period.

Adjusting means of this kind must be set very accurately if manufacturing tolerances, thermal expansion and wear arse not to lead to malfunctioning which can occur if control elements actuated by the adjusting means do not all occupy their functionfulfilling switching positions, e.g., if a valve is not correctly positioned on its seat, and if the actuating mechanism, such as an armature, is misplaced on an electromagnet.

With this consideration in mind, it is proposed in DE-PS 23 35 150 that play should be established within the transmission members between the actuating mechanism and the valve, so that, in the closing position, the armature will bear against the electromagnet and, at the same time, the valve will lie on its seat. The impact of the armature on the electromagnet is absorbed by disc springs which are compressed towards the end of each stroke. In DE-OS 30 24 109 it is proposed that a resilient connection between a valve spindle and an armature should provide for the necessary length equalization, and at the same time a certain degree of damping of the impact of the armature on the magnet is achieved.

In order to avoid high mechanical loads at contact faces and to prevent noise and bounce when components, moved relatively to each other, abut one another, electromagnets are used in conjunction with components which, during the entire movement or only part thereof, bring out pneumatic damping by varying an enclosed volume of gas. In such an arrangement, use is generally made of special additional components which are not directly associated with the electromagnet. For the purpose of performing their function, these additional components are directly or indirectly connected to the appropriate components of the electromagnet so that they are able to damp down the movement of the components of the electromagnet relatively to each other in the required portions of the movement.

German Patent Specification No. 1,055,091 illustrates a form of electromagnet having additional damping means. Therein the function of the damping means is taken over by a bellows which is firmly connected to the armature and which, towards the end of the movement, is compressed by encountering stops so that the enclosed air is compressed and discharged through an opening with the result that the required damping action takes place towards the end of the movement.

This method of achieving damping by the use of additional components involves additional cost because of the presence of the damping means and of the transmission members for effecting the movement and for immobilizing the parts involved.

The aim of the present invention is to damp down the impact when the armature encounters the magnet and, at the same time, when the actuated control element moves into one or more switching positions, and to ensure that each position is occupied in a precise manner. In addition, the invention aims at reducing the cost of the construction, the space required and the number of movable parts, as well as achieving operational reliability by enabling precise setting of the adjusting means, particularly as regards the end positions of the movable parts, to be carried out automatically.

According to the invention, this aim is achieved, in adjusting means of the construction described in the opening paragraph of this Specification, by use of electromagnets and armatures which are designed as part of a damping means while, at the same time, at least one of the electromagnets, by the use of one or more hydraulically-operated length-equalization elements, is connected to a housing or valve in such a manner that the distance between a valve seat and the pole faces of the electromagnet or electromagnets is matched with the distance between the valve seat and the pole face or faces of the armature so that the armature approaches the electromagnet and the valve approaches the seat in a similarly damped manner.

Due to the fact that the valve or other control element approaches its seat in practically the same manner as the armature approaches the electromagnet or electromagnets, the required positioning aimed at by the invention is achieved so that manufacturing tolerances, thermal expansion and wear are offset.

The advantages achieved by means of the invention result, in particular, from the fact that all the movable parts of the adjusting means move without impact into their switching positions so that noise is largely avoided and mechanical loading is considerably reduced. A further advantage is that the damping function is achieved within the space present in the electromagnet(s) and, at the same time, the cost of the components for achieving the damping function can be reduced. Furthermore, setting of the adjusting means is unnecessary either during assembly or servicing During operation, changes in the lengths of the actuated adjusting members or of the adjusting means as a result of thermal expansion are automatically offset.

Examples of adjusting means in accordance with the invention are shown in the drawings, in which: Figure 1 shows, in longitudinal section, a first form of construction in accordance with the invention; Figures 2-4 are similar illustrations of further embodiments; Figures 5and 6 illustrate preferred forms of lengthequalization elements; Figures 7and 8 are illustrations of parts of preferred forms of electromagnetic setting means; and Figures 9and 10 show details of further forms of length-equalization elements.

Figure 1 shows, by way of example, electromagnetically-operated adjusting means comprising electromagnets 1 and 2 and their coils 3 and 4, as well as covers 5 and 6 for the coils. The electromagnet 2 is firmly connected to a housing 7, while electromagnet 1, together with a pneumatic biasing device formed by a cylinder 8 and a piston 9, is guided in the housing 7 so as to execute axial movements between stops 10 and 11. The stem 12 of a valve is guided in a valve guide 13 which is solidly connected to the housing 7. A spring 14 acts on the valve in a conventional manner by way of a spring washer 15 and valve cotters 16. By way of a centering disc 20, an armature 17 mounted on a guide 18 is connected in a mechanically positive manner to the end of the stem 12 of the valve by means of a spring 19 which is supported on the piston 9 of the biasing device.The positioning of the electromagnet 1 together with the biasing device is achieved by a length-equalizing element 21 which acts in both directions. The length-equalizing element 21 is firmly secured to the housing by means of a screw 22, and a flange 23 of a vertically-displaceable piston 24 is connected to the electromagnet 1 through a collet 25 and the cylinder 8 so that the changes in length of the setting means are transmitted to the length-equalizing element.

The shape-locking mounting of the length-equalizing element permits the transmission of compressive forces as well as tensile forces.

Figure 2 shows electromagnetically-operated adjusting means with a length-equalizing element 26, acting in one direction only, for positioning the electromagnet 1. The length-equalizing element 26 is fitted in a cylindrical recess in the cylinder 8 of the biasing device and is held by a cover 27. The mechanically positive method of mounting permits the transmission of only compressive forces.

Figure 3 shows electromagnetically-operated adjusting means with a length-equalizing element 28 which acts in both directions. Here the lengthequalizing element 28 is screwed tightly onto the valve stem 12. The piston flange 23 of the lengthequalizing element 28 is secured by means of a box nut 29 and by way of a guide sleeve 30 to the armature 17 in such a manner as to be displaceable relatively to the valve stem.

Figure 4 shows an electromagnetically-operated adjusting means with a length-equalizing element 28 which, by way of the cover 31, is connected in a mechanically positive manner to the guide sleeve 30 and the valve stem 12 so that only compressive forces can be transmitted.

Figure 5 shows a length-equalizing element acting in one direction only. The hydraulic lengthequalizing element comprises a cylindrical component 32 and a piston component 33 which are interconnected in a gas-tight and liquid-tight manner by a bellows 34 arranged between them so that liquid cannot escape and harmful substances cannot penetrate. The outer surface 35 of the piston component 33 and the inner surface of the cylinder component 32 slide one upon the other and are designed to act both as guide and seal faces. A pressure chamber 36 within the two components 32 and 33 is sealed off from a leakage space 37 and from a liquid reservoir 38 by a thin-walled extension 39 of the lower edge of the piston. Leakage fluid is able to flow back, through an opening 40 formed in the piston wall, into the liquid reservoir 38.A gas-filled bellows 41 forming a pressure reservoir and a volume-equalizing element is contained within the reservoir 38 and is solidly connected to the upper end-face of the piston 33. The lower part or base of the piston comprises a machine-turned part 42 accommodating a discharge bore 43 and a springloaded non-return valve 44. A spring cage 45, on which is supported a spring 46 which closes a bore 47 by means of a ball 48, is centrally located on the lower surface of the base 42 of the piston and is held against it in a mechanically positive manner by a spring 49. The upper end-face 50 of the cylinder acts as an endstop for compressing the length-equalizing element to the greatest possible extent. Above the sealing extension 39, the piston component 33 has an annular channel 51 which communicates with the leakage space 37 by way of a connecting duct 52.

Figure 6 illustrates a length-equalizing element which acts in both directions. This element comprises a piston 24, acting in both directions, and two cylinder components 53 and 54 which are rigidly interconnected by way of spacers 55. The piston 24 is connected in a gas-tight and liquid-tight manner to the cylinder components 53 and 54 by two bellows 56 and 57 so that liquid cannot escape and harmful substances cannot penetrate. The surfaces 58 and 59 which slide upon one another are designed both as slide faces and sealing faces. The ends 60 and 61 of the piston, together with the cylinder components 53 and 54, enclose liquid chambers 62 and 63 the contents of which are able to flow into a liquid reservoir 66 by way of overflow bores 64 and 65.

Sealing lips 67 and 68 formed by thin-walled extension of the piston wall prevent the liquid from flowing away through the seal gaps 58 and 59 into the leakage spaces 69 and 70. The sealing action is reinforced by annular channels 71 and 72 which communicate with the leakage spaces 69 and 70 by way of discharge channels 73 and 74.

A small but unavoidable quantity of leakage liquid is able to flow back into the liquid chamber through retu m4low openings 75 and 76. The base 61 of the cylinder accommodates a non-return valve 77 the spring cage 78 of which is connected in a mechanically positive manner to the base of the piston by a spring 79. A spring 60 in the fluid chamber 62 is supported on the cylinder component 53 and the upper end 60 of the piston.

Figure 7 shows a portion of magnetically-operated adjusting means comprising an electromagnet 1, an armature 17, a helical spring 19 and a coil cover 5.

Annular elements 82 and 83 of non-magnetic resilient material are connected in a gas-tight manner to the electromagnet 1. The compressed gas is able to escape through the blow-off opening 84 so that the armature 17 can engage in a shock-free manner.

Figure 8 likewise illustrates a portion of electromagnetically-operated adjusting means. A space for an enclosed volume of gas is not fully closed off; instead, specific gaps, through which the compress ed gas is able to flow away, are formed by special configurations of the armature 17, the sleeve 85, the electromagnet 1 and the centering disc 20.

Further forms of the end zone of the piston are illustrated on a larger scale in Figures 9 and 10.

These are described in the following explanation of the mode of operation of the various lengthequalizing elements (acting in one or both directions) and their use in electromagnetically-operated adjusting means.

When an external force acts on the lengthequalizing element shown in Figure 5, then, even with small differences between the distances of travel of the piston component 33 and the cylinder component 32, a high pressure is set up in the liquid chamber 36 so that the sealing lip 39 at the lower edge of the piston is pressed against the cylinder wall with the result that the liquid chamber 36 is closed off almost completely against the seal faces 35.

Even when rapid changes in load occur, the hydraulic fluid located between the guide faces can be rapidly carried away through an annular channel 51 and a connecting channel 54 so that the pressure difference necessary for applying the sealing lip 39 is automatically brought about. Since the non-return valve 44 also moves into its blocking position and only very small quantities of hydraulic fluid are able to flow from the pressure chamber 36 into the liquid reservoir 38 by way of the discharge bore 43, changes in distance of travel resulting from the effect of force are possible only to a very slight extent.

The small flow of leakage fluid which cannot be completely avoided passes through the bore 40 into the reservoir 38 which is large enough to accommodate all of the fluid displaced from the pressure chamber 36 since the volume of gas in the bellows 41 is correspondingly compressed. When the lengthequalizing element is relieved of load, the spring 49 offsets differences in length by moving the piston 33 out of the cylinder 32 to such an extent that equilibrium with the applied external forces is established. The now-opening non-return valve 44 and a slight excess pressure in the reservoir 38 bring about a rapid exchange of fluid and, therefore, rapid occupation of the new position determined by the balancing of forces. The maximum deflection of the length-equalizing element is determined by the greatest possible elongation of the bellows 34.

Torque introduced from the exterior is taken up by the bellows 34. To keep this load small, at least one endface 53 is so formed that the applied forces cannot develop great torque.

The mode of operation of the length-equalizing element illustrated in Figure 6 is dependent upon the direction of the applied external force. If, by way of the flange 23, an external force applied to the piston 24 is initiated in the direction of the cylinder component 54, then, even when the differences between the distances of travel of the piston 24 and the cylinder component 54 are small, high pressure develops in the pressure chamber 63 and this presses the sealing lip 39 against the cylinder wall so that the chamber 63 is closed off almost completely at the sealing faces 59.Since, in addition, the non-return valve 77, because of the pressure obtaining in the pressure chamber 63, prevents flow of fluid into the reservoir 66, the fluid can escape from the chamber 63 only by way of the overflow bore 64, so that controlled downward movement of the piston 24 into the cylinder component 54 is possible by a suitable layout and form of the overflow bore 64. The sealing action of the sealing lip 68 is intensified by means of an annular channel 72 since the fluid contained in the sealing gap 59 is rapidly carried away through a discharge channel 74 so that the pressure difference necessary for the sealing action of the sealing lip is automatically established even when rapid changes in load occur The small stream of leakage fluid which unavoidably occurs is able to flow back into the liquid reservoir 66 through the return-flow opening 76.During movement of the piston 24 towards the cylinder component 54, fluid can discharge from the reservoir 66 into the pressure chamber 62 through the overflow bore 65. The reservoir contains a gas-filled bellows 81 for offsetting fluctuations in pressure and volume. If a force acts in the described manner on the equalizing element, only slight differences in distance of travel occur in dependence upon the applied external force and upon time.

If the action of the force is reversed, i.e., if the piston moves into the cylinder component 53, then the overflow bore 65 in the upper end 60 of the piston permits rapid flow of the fluid from the pressure chamber 62 into the reservoir 66 so that the pressure in the pressure chamber 62 rises only slightly. However, the pressure is sufficient to cause the sealing gaps to be closed off so that downward movement of the piston can be controlled by way of the discharge opening. The non-return valve 77 in the base 61 of the piston opens and therefore permits fluid to be exchanged between the reservoir 66 and the pressure chamber 63. During this loading ofthe equalizing element, relatively great chambers in distance travelled occur in dependence upon the applied external force and upon time.

Figure 1 illustrates electromagnetically-operated adjusting means having a length-equalizing element 21 which acts in both directions. During operation of the equipment, the length-equalizing element 21 positions the electromagnet 1 so that the changes in length which occur between the pole faces of the armature 17 and the disc of the valve 12 correspond to the distance between the pole faces of the electromagnets 1 and the valve seat. For this purpose, the equalizing element 21 is fitted in such a way that the pressure chamber 63 is located at the top in the Figure 1 arrangement.

During the time in which the electromagnet is switched off, the greater force of the spring 19, compared with that of the spring 79, causes the electromagnet 1, together with the biasing device, to move upwards relatively to the housing 7, and the fluid is discharged from the pressure chamber 63 by way of the overflow bore 64 in metered amounts.

When the electromagnet 1 is switched on again and upon approach of the armature 17, the electromagnetic forces overcome those of the spring 19 so that the electromagnet 1, together with the biasing device, is drawn into contact with the armature 17, the valve 12 being located in the seat by the force of the spring 14. the downward movement of the electromagnet 1,together with the biasing device, is promoted by the then-open non-return valve 17 and the overflow bore 65 designed to inhibit flow, and by the greater force of the spring 79 compared with that of the spring 80. The required timing of the positioning procedure can be set by appropriate construction of the non-return valve 77, the overflow bores 64 and 65, and the springs 79 and 80.

Figure 2 shows corresponding electromagnetically-operated adjusting means with an equalizing element 26 which acts in one direction only and is so fitted that the pressure chamber 26 is disposed at the top in the Figure 2 arrangement. When the electromagnet 1 is switched off, the piston component 33, depending upon the fluid which has flowed from the pressure chamber 36 into the cylinder component by way of the discharge bore 43, moves downwards because of the greater force of the spring 19 compared with that of the spring 49, so that the electromagnet 1, together with the biasing device, is upwardly displaced. If the electromagnet is switched on again, no forces can be transmitted to it by the equalization element.By means of the spring 49, the length difference which has occurred is quickly cancelled out since the non-return valve opens, so that rapid overflow of the fluid from the reservoir 38 into the pressure chamber 36 takes place.

Figure 3 shows electromagnetically-operated adjusting means having a length-equalization element 28 acting in both directions. In contrast to the adjusting means illustrated in Figures 1 and 2, the length-equalization element 28 equalizes the distance between the pole faces of the armature and the valve disc with the distance between the pole faces of the electromagnet and the valve seat. The lengthequalizing element is so fitted that the pressure chamber 63 is disposed at the bottom in the Figure 3 arrangement.

If the electromagnetic 1 is switched off and the electromagnet 2 is switched in, the spring 19 accelerates the valve 12 and the length-equalizing element 28 brings them into the switching position in which the valve is open and holds them in that position since the armature 17 is held in the open position by the electromagnet 2, with the result that the position of the piston 24 in relation to the electromagnet 2 is set. The accelerating force of the spring 19, which acts on the valve by way of the length-equalizing element 28, is opposed by the inertia of the valve and the force of the spring 14. Since the non-return valve 77 is in its blocking position, only slight quantities of oil flow from the pressure chamber 63 by way of the discharge bore 64 into the fluid reservoir 66 so that only very small relative movements between the armature 17 and the valve 12 are possible.With the result that the valve opens in the required manner. By means of the arrangements described in Figues 7 and 8, the armature reaches the stop of the electromagnet 2 in a shock-free manner, and the inertia of the valve is opposed by only slight resistance to flow of the oil by way of the non-return valve 77 which does not block in this direction so that the movement of the valve 12 exceeds the maximum stroke possible when the armature 17 and the valve 12 are rigidly connected.

During the length of time in which the armature is held by the electromagnet 2, the tensioned spring 14 then acts on the length-equalizing element 28 through the spring disc 15, the valve cotters 16 and the valve 12, so that, with the non-return valve 77 now blocking flow, only small quantities of oil flow from the pressure chamber 63 through the returnflow bore 64 and into the reservoir 66, and the spring 14 thus returns the valve to a position close to that occurring when the armature and the valve are rigidly connected. If the electromagnet 2 is now switched off and the electromagnet 1 is switched in, the spring 14 brings the valve together with the length-equalizing element 28 into the Figure 3 switching position, and the valve is held in this position by the electromagnet 1.By means of an appropriate arrangement of the overflow bore 64, both the valve 12 and the armature 17 are damped almost simultaneously and brought respectively against the valve seat and the electromagnet 1. In the illustrated switching position, force flows between the electromagnet and the spring 19 by way of the armature 17, the centering sleeve 20 and the piston 9, and the armature is pulled up by the flow-promoting form of the overflow bore 65 and by the non-return valve 77 against a lower flow resistance. The mechanically positive connection between the armature 17 and the guide sleeve 31 is achieved by the greater force of the spring 79 compared with that of the spring 80, the spring 79 being braced against the valve 12 which is held in its seat because of the greater force of the spring 14 compared with that of the spring 79.Thus, the axial changes in length of the valve which occur during operation of the equipment can be compensated.

Figure 4 shows an electromagnetically-operated adjusting means having a length-equalizing element acting in one direction only. This element 29 performs the same function as the length-equalizing element 28 described in connection with Figure 3.

The length-equalizing element 29 is so fitted that the pressure chamber 36 is disposed at the bottom in the Figure 4 arrangement.

The opening action proceeds in the same way as described above in connection with the lengthequalizing element 28. Changes in length occurring during actuation of the adjusting means and leading to elongation of the length-equalizing element 29 cannot be prevented or influenced, since tensile forces cannot be transmitted by the element 29.

These differences in length are cancelled out by the spring 49 within the length-equalizing element 29.

Figures 7 and 8 illustrate forms of impactabsorbing means for electromagnetically-operated setting means. The armature 17 moves, initially unrestrictedly, towards the electromagnet 1 until the resilient sealing rings 82 and 83 contact the armature 17 and thus a chamber is formed by the pole face of the armature 17, the pole face of the electromagnet 1 and the coil 5, in which chamber a volume of gas is tightly enclosed. Following the moment when contact is made, movement is influenced by the compression of the included gas so that the armature 17 encounters the electromagnet 1 in a shockfree manner. The sealing rings are so designed and arranged that, substantially, they perform a sealing but not a damping function.

In the arrangement illustrated in Figure 8 the damping volume of gas is not completely tightly enclosed but is so formed by a special configuration of the armature 17, the sleeve 85 and the centering disc 20 that, when the armature 17 approaches the electromagnet 1, gaps of diminishing width are formed which progressively inhibit the discharge of the compressed gas as closer approach takes place.

The herein described impact-damping means for electromagnetically-operated adjusting systems is principally suitable for damping the impact of moved components on the pole faces in the case of all electromagnets, relays or similar devices wherein one or more components, moved at right angles to the pole faces, can be brought into or held in one or more positions by electromagnetic or other forces.

If the length-equalizing element of Figures 5 and 6 are incorporated in electromagnetically-operated adjusting means as illustrated in Figures 3 and 4, the length-equalizing elements are subjected to considerable acceleration. In order to ensure operational reliability in such applications, special forms of the non-return valve may be necessary. Figures 9 and 10 illustrate, on a larger scale, forms of the end zone of the piston which are suitable for these applications.

The non-return valve shown in Figure 9 comprises a ball 86 which is acted upon by a spring 87 biased by a plug 88 and which is so arranged that the direction of movement of the non-return valve lies at right angles to the line of action of the acceleration of the valve-clearance equalizing element so that uncontrolled opening of the non-return valve, due to slight effects on the acceleration force on the ball, can be avoided.

The non-return valve shown in Figure 9 comprises a ball 86 which is acted upon by a spring 87 biased by a plug 88 and which is so arranged that the direction of movement of the non-return valve lies at right angles to the line of action of the acceleration of the valve-clearance equalizing element so that uncontrolled opening of the non-return valve, due to slight effects of the acceleration force on the ball, can be avoided.

Figure 10 illustrates an acceleration-neutralizing form of non-return valve. This valve, comprising a ball 89 connected to a guide 90 by way of a cylindrical component 91 and a cylindrical spindle 92, is loaded by a spring 93 braced against a plug 94 and closes off a liquid reservoir 95 from a pressure chamber 96. The components of the non-return valve are of such dimensions that, upon acceleration of the valve-clearance equalizing element which occurs mainly at right angles to the direction of movement of the non-return valve, the moment of mass inertia of the spindle 92 equates with the moment of mass inertia of the ball 89 and the component 91 in relation to the guide 90 so that acceleration of the non-return valve at the valve seat causes no reaction forces. Because of the provision of a connecting passage 98, the same level of pressure always obtains in the valve chamber 97 as in the pressure chamber 96.

Claims

1. Electromagnetically-operated adjusting means for the valves or other control elements of displacement machines, comprising an oscillatory spring-mass system which can be held by electromagnets in each of two end positions of maximum oscillation deflection so that at least two discrete switching positions are achieved, in which the electromagnets and their armature(s) are designed as part of a damping means and, at the same time, at least one of the electromagnets, by the use of one or more hydraulically-operated length-equalization elements, is connected to a housing of the adjusting means in such a manner that the distance between a valve seat and the pole faces of the electromagnet or electromagnets is matched to the distance between the valve seat and the pole face or faces of the armature so that the armature approaches the electromagnet and the valve approaches the seat in a similarly damped manner.

2. Electromagnetically-operated adjusting means for the valves or other control elements of displacement machines, comprising an oscillatory spring-mass system which can be held by electromagnets in each of two end positions of maximum oscillation deflection so that at least two discrete switching positions are achieved, in which the electromagnets and their armature(s) are designed as part of a damping means and, at the same time, at least one of the electromagnets, by the use of one or more hydraulically-operated length-equalization elements, is connected to a valve in such a manner that the distance between a valve seat and the pole faces of the electromagnet or electromagnets is matched to the distance between the valve seat and the pole face or faces of the armature so that the armature approaches the electromagnet and the valve approaches the seat in a similarly damped manner.

3. Adjusting means according to claim 1 or claim 2, in which the hydraulic length-equalization element is sealed off from a pressure chamber in a gas-tight and liquid-tight manner and contains a liquid reser voirfortopping up the length-equalizing pressure chamber.

4. Adjusting means according to claim 3, in which the liquid reservoir is provided in the hollow piston component of a piston-and-cylinder unit having a piston component and a cylinder component.

5. Adjusting means according to claim 4, in which the faces of the cylinder component and piston component which slide on each other guide the two components relatively to each other and form a seal.

6. Adjusting means according to claim 4 or claim 5, in which the outer edge of the base of the piston component has a cylindrical extension the outside diameter of which corresponds to that of the piston component and which, under the operating pressure of the hydraulic liquid, expands to such an extent in the pressure chamber that it moves into firm contact with the cylinder surface and thus seals off the pressure chamber.

7. Adjusting means according to any one of claims 3 - 6, in which a gas-filled pressure reservoir is provided in the liquid reservoir so as to keep the pressure in the liquid reservoir substantially constant.

8. Adjusting means according to any one of claims 4 - 7, in which a bellows serving to close off the piston-and-cylinder unit in a gas-tight and liquidtight manner is so dimensioned that it has a mechanical strength sufficient to keep the elongation of the hydraulic equalization element within permitted limits and for it not to be damaged by any torque which may occur between the cylinder component and the piston component.

9. Adjusting means according to any one of claims 3 - 8, in which the pressure chamber is connected to the liquid reservoir by way of a discharge bore.

10. Adjusting means according to any one of claims 3 - 9, in which the hydraulic liquid can flow rapidly from the liquid reservoir into the pressure chamber by way of a non-return valve.

11. Adjusting means according to any one of claims 3 - 10, in which the fluid leaked from the seal can flow back into the liquid reservoir through an opening in the piston component.

12. Adjusting means according to any one of claims 6 - 11, in which, to provide the pressure difference necessary for applying pressure to the c Zlindrical extension when rapid changes in load occur, an annular channel above the thin cylindrical extension communicates with the liquid reservoir so that liquid discharges rapidly from the seal and the pressure at the rear of the cylindrical extension is this rapidly reduced.

13. Adjusting means according to any one of claims 4 - 12, in which an end face of the cylinder component and/or of the piston component is so formed that bracing forces are taken up by a central bracing face having a small outside diameter.

14. Adjusting means according to any one of claims 10 - 13., in which the non-return valve is so arranged in the base of the piston component that the direction of movement of the non-return valve does not coincide with the main acceleration direction ofthe length-equalizing element.

15. Adjusting means according to any one of claims 10 - 14, in which the non-return valve is arranged in the base of the piston component in such a manner that no forces are applied to the sealing faces between the valve and the valve seat as the result of acceleration of the valve-clearance equalization element.

16. Adjusting means according to any preceding claim, in which the components of one or more electromagnets are so shaped that at least the components of the pole faces which are at right angles to the direction of movement form parts of a chamber which encloses the effective volume of a pneumatic damping means.

17. Adjusting means according to any preceding claim, in which parts of the electromagnet or electromagnets which move relatively to each other are so formed that a volume of gas is enclosed over all or part of the distance of movement.

18. Adjusting means according to any preceding claim, in which the faces of the damping chamber which lie parallel to the direction of movement are formed by parallel or substantially parallel surfaces of components, so that, in this zone, the damping chamber is formed by parallel or substantially parallel pairs of surfaces.

19. Adjusting means according to any preceding claim, in which the faces of the damping chamber which are parallel to the direction of movement are made of solid or resilient materials.

20. Adjusting means according to any preceding claim, in which the seals constituted by the pairs of faces parallel to the direction of movement, form, depending upon the stroke, different shapes and sizes of cross-sectional faces for the discharge of the enclosed gas.

21. Adjusting means according to any preceding claim, in which the faces parallel to the direction of movement are made of resilient material so that sealing of the gas chamber is achieved.

22. Adjusting means according to any preceding claim, in which fixed unchanging discharge openings are provided in all the components enclosing the gas chamber.

23. Adjusting means according to any preceding claim, in which fixed unchanging discharge openings are provided in components which slide on other components over the distance of movement, so that the discharge openings acquire different shapes and sizes depending upon the stroke.

24. Adjusting means according to claim 1 or claim 2 substantially as described herein with reference to any Figure of the accompanying drawings.