GB1571769A

GB1571769A - Electromagnetic acuator

Info

Publication number: GB1571769A
Application number: GB18147/78A
Authority: GB
Original assignee: Voith Getriebe KG
Current assignee: Voith Getriebe KG
Priority date: 1977-05-10
Filing date: 1978-05-08
Publication date: 1980-07-16
Also published as: DE2720877A1; DE2720877B2; FR2390817A1; NL186661C; AT367560B; NL7804987A; IT7868054A0; IT7853298V0; ATA271578A; JPS617002B2; IT1159665B; FR2390817B1; NL186661B; DE2720877C3; JPS5412456A

Description

(54) ELECTROMAGNETIC ACTUATOR (71) We, VOITH GETKIEBE KG, of Alexanderstrasse 2, D-7920 Heidenheim, Germany (Fed. Rep.) a German Company, do hereby dedare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described, in and by the following statement:- The invention relates to an electromagnetic actuator including a regulating device.

An electromagnet with an associated regulating device is known from the German Auslegeschrift 2019 345, (corresponding British Patent Specification 1 324445). The prior art also discloses an electromagnet (German Offenlegungsschrift 23 39 592) which can have a regulating device in accordance with the previously-mentioned German Auslegeschrift and a final control element connected to the plunger armature and extending through the polepiece to transmit the armature operating force to the valve member of a delivery valve or itself forming the valve member.This arrangement, in which the device to be actuated (for example a valve) is combined with the electromagnet so that the valve adjoins the casing of the electromagnet in the region of the polepiece, is preferred to the arrangement according to the German Auslegeschrift 20 19 345, Figure 2, in which the valve is attached to the electromagnet on the end opposite to the polepiece, namely because it is more advantageous to allow the armature operating force to act by applying thrust (and not by applying tension).

It is the object of the invention to arrange the regulating device of the electromagnet so that it is protected in the best possible way and so that the conductors which carry the measured value are as short as possible.

It was hitherto not possible to solve this problem satisfactorily.

Initially the regulating device was disposed separately of the electromagnet in a well protected place which was not readily accessible to everyone, for example within a control cabinet. This called for the provision of a relatively large number of electric conductors between the regulating device and the electromagnet, as a rule four conductors for measuring the magnetic field strength and two conductors for supplying the energizing current.

The disadvantage of this arrangement is due particularly to the risk of falsification of the measured value because the measuring conductors are very long.

Attempts have therefore also been made to dispose the regulating device directly laterally of the casing of the electromagnet. The previously mentioned conductors could be substantially shortened by this procedure because they had to be instaled merely within the casing of the electromagnet. This arrangement however was not satisfactory because the regulating device was less well protected against external effects (for example risk resulting from shocks or moisture) and was accessible to everyone in an undesirable manner. Furthermore, the mlanufactur,ing costs for the electromagnet are higher because an additional casing part, arranged on the side, had to be provided for the regulating device.

According to the present invention there is provided an electromagnetic actuator comprising a plunger armature, a regulating device for adjusting the armature operating force in accordance with an electric reference variable as set point independently of the position of the plunger armature over the armature excursion distance by measurement of the magnetic induction as a measured variable and by varying the energizing current accordingly, a magnetisable casing, a polepiece which attracts the plunger armature when the electromagnet is energized, and a final control element, associated with the plunger armature and extending through the polepiece for the purpose of transmitting the armature operating force to a device which is to be actuated, the regulating device being installed in the casing of the electromagnet in the region of the outer endface of the polepiece.

Accordingly the regulating device is no longer attached laterally to the casing shell of the electromagnet but is associated with one of the end faces of the casing, namely the endface on which the polepiece is disposed. In other words: the regulating device is arranged in an unusual manner at the place at which the final control element connected to the plunger armature is brought out from the electromagnet. If the valve is an electromagnetically influenced pressure regulating valve - as is frequently the case - the electromagnet casing merges at this place with a valve casing or both casings adjoin each other at that place.

The proposal to arrange the regulating device at the very endface which is already "occupied" therefore initially met criticism.

Above all, it was held that there is a risk that the operation of the regulating device together with its sensitive electronic components could be impaired by heat emitted on the one hand by the electromagnet and on the other hand by the Bowing medium in the case of a pressure regulating valve. There were also fears of the risk that the flow medium cold reach the electronic components and that the place available on the above-mentioned endface would in any case be very confined and would be further restricted in the control part by the final control element extending therethrough.

However, it will be appreciated that it is advantageous that the conductors for measuring the magnetic field strength and for supplying the energizing current could again be substantially shortened. These conductors need only extend through a single component, namely the polepiece. Advantageously a Hall generator is used for measuring the magnetic field strength and is conveniently disposed on the internal endface of the polepiece. It is therefore situated closely adjacent to the regulating device so that the very low Hall voltage is not falsified by any interference signals on its passage to the regulating device. A substantial improvement is achieved in this respect, even when compared with the arrangement of the regulating device laterally on the casing shell of the electromagnet.

Advantages are also achieved for manu- facturing because auxiliary supports for the above-mentioned conductors are omitted; instead these conductors can be directly sol dered, for example on a circuit board which supports the regulating device. Furthermore, the manufacture of the casing is simpler and less expensive than in the arrangement in which the regulating device is disposed in a lateral box which must be closed by an additional lid.

Moreover tests with an electromagnetic actuator constructed in accordance with the invention indicated that the temperature which occurs in the region of the regulating device is only approximately 10 higher than the temperature which was previously measured when the regulating device was disposed on the casing shell of the electromagnet.

Preferably, the casing of the electromagnet is combined in the region of the polepiece with the device which is to be actuated, said regulating device being disposed between the polepiece and the device which is to be actuated.

In this case the regulating device is completely inaccessible for as long as the entire system comprising the electromagnet is in operation.

This could also be expressed by saying that the regulating device between the electromagnet and the device to be actuated (for example pressure regulating valve control element with mechanical dynamic balance or the like) is "concealed". Since the electromagnet is flange-mounted by means od its polepiece endface to the device which is to be actuated it follows that the device also forms the closing lid which would otherwise be required at this place of the electromagnet.

If hydraulic fluid ingresses from a pressure regulating valve into the regulating device this will generally be harmless for the components thereof. However, as a precaution a plastics material can be cast into the space of the casing which remains after installation of the regulating device. This provided additional protection for the electronic components of the regulating device. Conveniently the interior of a connecting socket (for leading in electrical conductors) can also be fitted with cast plastics material). This solves the problem of sealing the said connecting socket in a particularly simple manner.

Conveniently, a bearing neck, is integrally formed on the polepiece for supporting the final control element and extends through the circuit board. This ensures that the two supports for the plunger armature and the final control element are situated at a substantial distance from each other - despite the circuit board, which supports the regulating device, being arranged directly on the external endface of the polepiece - without the need for increasing the overall length of the electromagnet.

Such a long distance between the abovementioned supports is important to ensure a supporting action which is substantially free of friction; jamming is thus avoided.

One embodiment of the invention is des cribbed hereinbelow by reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through an electrically controlled pressure regulating valve; Figure 2 is a cross-section along the line 11-11 of Figure 1.

The illustrated electrically controlled pressure regulating valve is designed for converting an electrical quantity (control variable) into an analog hydraulic variable. Briefly, it is a hydraulic signal transducer.

The apparatus comprises a valve casing 10 with a central bore 11 for a valve spool 12, also an inlet 13, an outlet 14, a discharge 15 and a leakage oil discharge 16. As shown symbolically a delivery branch 8 of a pump 7 can be connected to the inlet 13 and a duct which supplies the regulated pressure (i.e. the hydraulic output variable) to a load 5 can be connected to the outlet 14. The outlet 14 com- municates via ports 17 with one endface 18 of the spool 12. A rod 20, which forms the final control element of an electromagnet, referenced in its entirety with the numeral 9, bears against the opposite endface 19 of the spool 12.

The electromagnet 9 substantially comprises a magnet casing 21, a magnet ooil 22, a polepiece 23, a connecting socket 24 for an electric plug connection 25 (for supplying an electric control variable and for supplying energy), also a movable plunger armature 26 in which the above-mentioned rod 20 is screw-mounted.

A bearing neck 27 with a plain bearing inserted therein and a bore 28, also having a plain bearing disposed therein, on the lefthand end of the magnet housing 21 is provided for supporting the rod 20 with the plunger armature 26.

A circuit board 30 for a regulating device is attached to the polepiece 23 in the space between said polepieces 23 and the valve casing 10. The regulating device is provided to maintain the armature operating force at a constant value which can be defined by the reference variable (set point) the armature operating force being independent ob the position of the plunger armature 26 over the armature excursion distance or stroke. The magnetic induction which occurs between the polepiece 23 and the plunger armature 26 is the controlled con dition (measured variable) and is measured at that place by a Hall generator 31. The latter is connected by means od four conductors (two measuring conductors, two control conductors) to the circuit board 30. Only one of the four conductors is indicated at 32.The armature operating force is adjusted by varying the energizing current (conductor 33) which flows through the magnet coil 22.

The electric components of the regulating device disposed on the circuit board 30 are indicated in the drawing at 34, 35 and 36. The conductors which extend from the plug connection 25 to the circuit board 30 are designated with the numeral 37. The magnet coil 22, the polepiece 23 and the circuit board 30 are located in the axial direction by means d a circlip 38. The circuit board 30 is a circular disc through the centre of which projects the bearing neck 27 for reasons of space saving (in order to achieve a short overall length).

After assembling all components of the electromagnet 9 and of the regulating device 30 to 36 and after installing the conductors 37 but prior to attachment of the valve casing 10 the space between the circuit board 30 and the valve casing 10 including the interior of the connecting socket 24 is filled with a plastics casting compound 39. It is convenient to select a plastics substance which remains relatively soft and can be readily removed when required.

An air gap remains around the rod 20 so that movement thereof is not obstracted.

WHAT WE CLAIM IS: 1. An electromagnetic actuator comprising a plunger armature a regulating device for adjusting the armature operating force in accordance with an electric reference variable as set point independently of the position of the plunger armature over the armature excursion distance by measurement of the magnetic induction as a measured variable and by varying the energizing current accordingly, a magnetisible casing, a polepiece which attracts the plunger armature when the electromagnet is energized, and a final control element, associated with the plunger armature and extending through the polepiece for the purpose of transmitting the armature operating force to a device which is to be actuated, the regulating device being installed in the casing od the electromagnet in the region of the outer endface of the polepiece.

2. An electromagnetic actuator as claimed in claim 1 wherein the casing is combined in the region of the polepiece with the device which is to be actuated, said regulating device being disposed between the polepiece and the device which is to be actuated.

3. An electromagnetic actuator as claimed in claim 1 or claim 2, wherein a circuit board which supports the regulating device is disposed on the outer endface of the polepiece in the casing.

4. An electromagnetic actuator as claimed in claim 3, wherein the space disposed between the circuit board and the device which is to be actuated is at least partially filled with a plastics casting substance.

5. An electromagnetic actuator as claimed in claim 4, wherein the casing is provided in the region ob the polepiece with a connecting socket for the introduction of electrical conductors, the connecting socket together with said space being filled with a plastics casting substance.

6. An electromagnetic actuator as claimed in any of claims 3 to 5, wherein a bearing neck is integrally formed on the polepiece for supporting the final control element and extends through the circuit board.

7. An electromagnetic actuator substantially as herein described with reference to and as shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. which supplies the regulated pressure (i.e. the hydraulic output variable) to a load 5 can be connected to the outlet 14. The outlet 14 com- municates via ports 17 with one endface 18 of the spool 12. A rod 20, which forms the final control element of an electromagnet, referenced in its entirety with the numeral 9, bears against the opposite endface 19 of the spool 12. The electromagnet 9 substantially comprises a magnet casing 21, a magnet ooil 22, a polepiece 23, a connecting socket 24 for an electric plug connection 25 (for supplying an electric control variable and for supplying energy), also a movable plunger armature 26 in which the above-mentioned rod 20 is screw-mounted. A bearing neck 27 with a plain bearing inserted therein and a bore 28, also having a plain bearing disposed therein, on the lefthand end of the magnet housing 21 is provided for supporting the rod 20 with the plunger armature 26. A circuit board 30 for a regulating device is attached to the polepiece 23 in the space between said polepieces 23 and the valve casing 10. The regulating device is provided to maintain the armature operating force at a constant value which can be defined by the reference variable (set point) the armature operating force being independent ob the position of the plunger armature 26 over the armature excursion distance or stroke. The magnetic induction which occurs between the polepiece 23 and the plunger armature 26 is the controlled con dition (measured variable) and is measured at that place by a Hall generator 31. The latter is connected by means od four conductors (two measuring conductors, two control conductors) to the circuit board 30. Only one of the four conductors is indicated at 32.The armature operating force is adjusted by varying the energizing current (conductor 33) which flows through the magnet coil 22. The electric components of the regulating device disposed on the circuit board 30 are indicated in the drawing at 34, 35 and 36. The conductors which extend from the plug connection 25 to the circuit board 30 are designated with the numeral 37. The magnet coil 22, the polepiece 23 and the circuit board 30 are located in the axial direction by means d a circlip 38. The circuit board 30 is a circular disc through the centre of which projects the bearing neck 27 for reasons of space saving (in order to achieve a short overall length). After assembling all components of the electromagnet 9 and of the regulating device 30 to 36 and after installing the conductors 37 but prior to attachment of the valve casing 10 the space between the circuit board 30 and the valve casing 10 including the interior of the connecting socket 24 is filled with a plastics casting compound 39. It is convenient to select a plastics substance which remains relatively soft and can be readily removed when required. An air gap remains around the rod 20 so that movement thereof is not obstracted. WHAT WE CLAIM IS:

1. An electromagnetic actuator comprising a plunger armature a regulating device for adjusting the armature operating force in accordance with an electric reference variable as set point independently of the position of the plunger armature over the armature excursion distance by measurement of the magnetic induction as a measured variable and by varying the energizing current accordingly, a magnetisible casing, a polepiece which attracts the plunger armature when the electromagnet is energized, and a final control element, associated with the plunger armature and extending through the polepiece for the purpose of transmitting the armature operating force to a device which is to be actuated, the regulating device being installed in the casing od the electromagnet in the region of the outer endface of the polepiece.