EP0288930B1 - Potentiometer - Google Patents

Abstract

The potentiometer, which is intended to be mounted on heavily vibrating objects such as the engine block of an internal-combustion engine, has an outer housing (10), which is mounted on the object, and an inner housing (20) which is arranged generally in the interior of the outer housing (10). The two housings are connected to one another by means of at least one elastically sprung damping element (27), for example a rubber O-ring, thus, however, being decoupled to the greatest possible extent in vibration terms. <IMAGE>

Description

The invention relates to a potentiometer according to the preamble of claim 1.

The US-PS 3 138 777 shows a linear potentiometer with a housing and a housing cover, which are telescopically displaceable against each other. The housing cover that crosses the outside of the housing is guided on the outside of the housing by means of an additionally provided slide bearing. A flange is attached to the housing with which the potentiometer can be attached to an object. Furthermore, the potentiometer has the usual resistance plate with resistance tracks and electrical connecting wires, which are firmly connected to the housing here. A spring support with sliding contacts that can slide along the resistance path is firmly connected to the housing cover and by means of a slide that penetrates the end wall of the housing cover and is accessible from the outside.

For the watertight sealing of the potentiometer, the housing and the housing cover are connected to each other by a bellows-like, flexible seal that completely protects the slide bearing between the housing cover and housing against the ingress of water.

However, this document does not offer any solutions to the problem of vibration damping. If you flanged this potentiometer to a vibrating object, the resistance plate itself will immediately start to vibrate. Also, the spring carrier, which is guided in the housing via a plastic block 17 and the inner wall of the housing, will also start to vibrate, so that this will result in a failure of the resistance in a short time.

It should also be emphasized that the housing cover only in the actuation direction, i.e. H. is linearly displaceable relative to the housing, but is otherwise coupled in terms of vibration to the housing via the slide bearing 22, so that when the potentiometer is flanged onto a vibrating object, all vibrations are also transmitted to the outer housing.

The US-PS 4 053 865 shows a linear potentiometer, in which a slide is resiliently coupled to the spring support. For this purpose, the spring support has a bore into which an extension of the slide engages, the diameter of the bore being larger than the diameter of the extension. An elastic O-ring and a washer, which is pressed against a stop by the O-ring, provide a coupling between the spring support and the slide, the misalignment can compensate within certain limits. For this it is of course a prerequisite that a front cover, through which the slide protrudes, allows sufficient play for movements of the slide. However, this document also does not help to solve the vibration problem, since there is no vibration decoupling between the potentiometer and its wearing parts when the potentiometer is installed.

The potentiometer according to the present application should u. a. can also be used as a measuring transducer or measuring sensor in control systems in which the position of a movable member is sensed and the potentiometer then emits an electrical output signal proportional to this position. For example, such a potentiometer can sense the position of a throttle valve on an internal combustion engine.

In such cases, the potentiometer is attached to another object, for example directly on the engine block of an internal combustion engine. As a result, the potentiometer also makes all movements and in particular vibrations of this other object. In diesel engines, for example, it was found that a potentiometer flanged directly to the engine block is exposed to accelerations of up to 300 g (g = gravitational acceleration). Due to the inertia of the parts of the potentiometer which are movable relative to one another and in particular the inertia of the grinder, these accelerations cause the grinder to oscillate with respect to the resistance track on the resistance plate, which leads to abrasion of the resistance layer. In tests with conventional potentiometers flanged to a diesel engine, the resistance layer was inside rubbed through from 3 to 4 hours. The potentiometer was then no longer usable.

To solve this problem, attempts have already been made to mount the entire potentiometer in a damped manner with respect to the engine block, for example by screwing it onto the engine block using rubber buffers. Nevertheless, this did not lead to the desired lifespan extension and was sometimes quite complex. The adjustment of the potentiometer was also complex, since the tightening of the fastening screws inevitably deforms the rubber buffers and thus changes the relative position between the potentiometer and the motor block, which necessitates an adjustment; in other words, the electrical output signal of the potentiometer depends on the tightening force of the fastening screws. Sealing the engine block from the potentiometer is also problematic.

The object of the present invention is therefore to improve the potentiometer of the type mentioned at the outset in such a way that it has a significantly longer service life when it is attached to mechanically vibrating objects and is therefore exposed to high accelerations.

This object is achieved by the features specified in the characterizing part of the patent claim. An advantageous embodiment and development of the invention can be found in the subclaims.

The basic idea of the invention is to no longer decouple the entire potentiometer in terms of vibration from the other object (eg engine block), but only certain parts. These are the parts that are subject to wear. Because the outer case is firm is connected to the other object, the spatial position between the potentiometer and the other object is clearly defined, so that adjustment can be largely eliminated and installation errors avoided. When fastening the potentiometer to the engine block using a rubber buffer as described above, tightening the fastening screws against the force of the rubber buffer also leads to a change in the spatial position between the potentiometer and the engine block and thus to a different adjustment.

With the features of claims 2 to 4, improvements in the damping behavior are obtained in each case, silicone currently providing the best damping behavior.

Claim 5 provides a further improvement in the damping behavior and also a good possibility of precisely aligning the inner and outer housings with one another, which is further improved with the features of claim 6.

Fig. 1:

Einen Längsschnitt des Potentiometers nach der Erfindung;

Fig. 2:

einen Querschnitt längs der Linie C-D der Fig. 1;

Fig. 3:

einen um 90° gegenüber der Schnittebene der Fig. 1 gedrehten Längsschnitt des Potentiometers (Schnitt längs der Linie A-B der Fig. 1);

Fig. 4:

einen Querschnitt längs der Linie E-H der Fig. 3 und

Fig. 5:

einen Querschnitt eines Profiles von bei der Erfindung verwendeten federelastischen Dämpfungselementen.

In the following the invention is explained in more detail using an exemplary embodiment in connection with the drawing; it shows:

Fig. 1:

A longitudinal section of the potentiometer according to the invention;

Fig. 2:

a cross section along the line CD of Fig. 1;

Fig. 3:

a longitudinal section of the potentiometer rotated by 90 ° with respect to the section plane of FIG. 1 (section along the line AB of FIG. 1);

Fig. 4:

a cross section along the line EH of Fig. 3 and

Fig. 5:

a cross section of a profile of spring-elastic damping elements used in the invention.

The exemplary embodiment described is a so-called linear potentiometer, in which the actuating member (which can be actuated from the outside) is displaced in a straight line or linear manner. It is clear to the person skilled in the art that the invention can also be used in the same way for rotary potentiometers and spindle potentiometers.

The potentiometer has an outer housing 10 which is essentially cylindrical and has a flange 11 which projects radially approximately in its center and which has through holes 12 running in the axial direction and having an injected metal bushing 13. By means of these through holes 12, the outer housing 10 can be screwed onto another object.

In the axial direction, the outer housing 10 is open on one side and is closed on the open side by a snap-in cover 14 by snapping this cover behind a latch 16. On the closed side there is a housing base 15 which is integrally connected to the outer housing 10.

Furthermore, as can best be seen from FIGS. 3 and 4, the outer housing 10 has a radially projecting plug socket 18 with three flat plugs 19, which are held at a distance from one another in the plug socket, for example are injected there if the housing and the socket are a plastic injection molded part.

The inner wall of the outer housing - with the exception of the area to which the plug socket 18 connects - is cylindrical. In the outer housing 10, an inner housing 20 is inserted, which extends coaxially to the outer housing 10 and whose outer diameter is smaller than the inner diameter of the outer housing 10, so that an annular space 21 is present between the two housings 10 and 20. This intermediate space enables a certain relative displacement between the inner and outer housing in a radial direction, that is to say perpendicular to the longitudinal axis of the potentiometer. The inner housing 20 is integrally connected on its one end face, which is referred to below as the actuation side, to an essentially cylindrical bearing flange 22, a plain bearing bush 23 being pressed or injected into this bearing flange.

The side opposite the actuating side of the inner housing 20 is closed by an insertable cover 24. The surface of this cover 24 facing outwards in the axial direction is arranged at a distance from the surface of the housing base 15 pointing inwards, so that the inner housing 20 can also be relatively displaced in the axial direction relative to the outer housing 10. In a corresponding manner, a corresponding axial distance 26 is also present on the actuating side between the cover 14 of the outer housing and a connecting web 25 which connects the cylindrical part of the inner housing to the bearing flange 22. In the area of the two end faces of the inner housing, a spring-elastic damping element 27 or 27 'is now provided, which in The illustrated embodiment is an O-ring that holds the inner housing 20 relative to the outer housing 10. In order to obtain a clear fixation in the axial and radial directions, the inner housing 20 has a right-angled step 28 on the connecting web 25 (FIG. 1), so that the O-ring 27 both on a radially outwardly facing surface and on a surface this is right-angled in the axial direction. In the same way, the cover 24 has a step 29, the surface of which faces in the axial direction is just flush with the end face of the inner housing 20. So that the O-ring 27 'there is also at two mutually perpendicular surfaces of the lid 24 or outer housing 20. Furthermore, the O-ring 27 is located on the actuating side on the one hand on the radially inwardly facing wall of the outer housing 10 and on the axially facing surface of the cover 14, so that the outer housing 20 (including the cover 14) also perpendicular contact surfaces with the O -Ring 27 has. Finally, the same also applies to the O-ring 27 ', which bears against the radially inwardly facing surface of the outer housing 10 and the axially inwardly facing surface of the housing base 15.

The two resilient damping elements 27 and 27 'fix on the one hand the inner housing 20 in the outer housing 10 and on the other hand allow due to their resilient properties a certain relative displacement between the inner and outer housing, whereby they strongly dampen vibrations or shocks that act on the outer housing due to their material properties , so that the inner housing is only very weakly influenced by such vibrations or shocks.

Since the spring-elastic damping elements also have the greatest possible distance from one another in the axial direction of the inner housing, the greatest possible clamping length is obtained and thus the best possible vibration damping of the inner housing.

An actuating member 30 is mounted in the inner housing, which here consists of a slide 31 and a spring support 32. The slide is designed here as a cylindrical component and guided in the plain bearing bush 23. The spring support 32 is attached to one end of the slider. It carries one or more wiper springs 33 which are in contact with their free end on predetermined tracks of a resistance plate 40 and slide along these tracks when the spring carrier is moved. In the specific exemplary embodiment, the spring support is prestressed in one direction by means of compression springs 34. These compression springs are supported on the one hand on the inner housing or here specifically on a pin 35 'on the cover 24 of the inner housing and on the other hand on the spring support, where they are guided by pins 35. As can best be seen from FIG. 2, the spring support 32 is also guided in the inner housing 20 such that it cannot rotate, in grooves 36 running parallel to the axial direction, in which laterally projecting arms 37 of the spring support 32 are guided, the compression spring 34 also being in these grooves are led.

The already mentioned resistance plate 40 is also fastened in the inner housing 20 and here carries resistance tracks 41, along which the wiper spring 33 can slide. These resistance tracks are connected to connection tabs 42, which are also attached to the resistance plate 40 and are designed here as contact springs, since they are only pressed with spring force against the ends of the resistance tracks.

As shown in Fig. 3, these terminal lugs 42 are inserted through the resistance plate 40 and then bent over so that they run with a section parallel to the resistance plate. At their end they are then again bent essentially at right angles from the resistance plate and formed into a clamp 43. The necessary electrical connection between the terminal lug 42 and the associated tab 19 is made via a flexible strand 44, which is laid in an S-shape. For good electrical connection, the strand 44 is soldered to the connecting lug 42 and to the tab 19 at soldering points 45 and 46. Since soldered strands at the transition area to the soldering point are not mechanically very strong and break particularly with mechanical vibrations, the strand 44 is still mechanically clamped in the area of its two ends, on the one hand by the clamp 43 on the connecting lug 42 and on the other hand by another Terminal 47 on the socket 18. The socket 18 is rigidly connected to the outer housing 10, while the resistance plate 40 and thus the terminal lug 42 is rigidly connected to the inner housing 20, so that the strand 44 vibrates or between the two relative to each other moving housings 10 and 20 lies. On the one hand, it must of course not form a mechanical vibration coupling, which is achieved through its mechanical flexibility and its laying in an S-shape. On the other hand, however, it must of course be connected at its two ends as firmly as possible to the component assigned in each case, so that the potentiometer does not fail due to the wire breaking.

In the exemplary embodiment described, the inner housing 20 and all functional components such as resistance plate 40, wiper support 32 and slide 31 arranged in the inner housing are vibrationally decoupled from the outer housing 10. When installing the potentiometer on another object, e.g. on an engine block, of course, care must be taken to ensure that the vibrations of the engine block via the actuating member and here in particular the slide 31 are not coupled back onto the inner housing and the parts located there. For this purpose, the coupling or connection between the slide 31 and a part of this other object must also be carried out in terms of vibration. For this purpose, for example, a magnetic coupling can be provided, which at least transmits at least high-frequency vibrations or movements with strong acceleration or with a strong change in acceleration (jerk) to the slide 31 in a damped manner. In the embodiment shown, the slider 31 is to sense the position of a component due to its axial position. If this component is itself a rod, it is sufficient for a correct connection if the ends of the slide 31 and the rod touch each other, but can be moved in the radial direction (with respect to the axis of the slide 31). This already provides a vibration decoupling in the radial direction. Furthermore, it will be ensured that the above-mentioned rod is in turn vibration-damped.

An even better vibration decoupling between the inner and outer housing or an even better damping is obtained if instead of the O-rings 27 or 27 'rubber and in particular silicone rings are used, which have the cross-sectional shape of FIG. 5, namely form a square with rounded corners 50 and concave (inward) side walls 51. Such rings are commercially available and are sold, for example, under the registered trademark "Quad-Ring" by the company BUSAK + LUYKEN.

Claims (8)

1. A potentiometer comprising

   - a housing having housing parts which are displaceable relative to one another and which are joined together by an elastic element (27, 27'),

   - a flange (11) attached to the housing for securing the potentiometer to another object, such as an engine block of a combustion engine for instance,

   - an actuating element (30) which is movable relative to the housing,

   - a resistance plate (40) held in the housing,

   - a slider (33) which is coupled with the actuating element (30) and upon the movement thereof slides along a defined path (41) on the resistance plate (40), and

   - comprising several electrical connections (19), of which one is electrically connected to the slider and of which at least one other is electrically connected to the defined path,
   characterised

   - in that the housing parts are designed as an exterior housing (10) and an interior housing (20) arranged inside the exterior housing (10),

   - in that the interior housing (20) is mounted inside the exterior housing (10) so as to be vibration-damped by means of at least one spring-elastic damping element (27, 27'),

   - in that the flange (11) and the electrical connections are fixedly attached to the exterior housing (10), and

   - in that the resistance plate (40) and the actuating element (30) are held on the interior housing (20).
2. A potentiometer according to claim 1, characterised in that the spring-elastic damping element is an O-ring (27, 27').
3. A potentiometer according to claim 1, characterised in that the spring-elastic damping element (27, 27') is a ring, the cross-section of which is in the shape of a square with rounded corners (50) and concave-shaped sides (51).
4. A potentiometer according to one of claims 1 to 3, characterised in that the spring-elastic damping element (27, 27') is made of rubber, silicone or some other spring-elastic synthetic material.
5. A potentiometer according to one of claims 1 to 4, characterised in that there are provided between the interior and the exterior housing (20, 10) two spring-elastic damping elements (27, 27') which are in each case arranged between the two end edges of the interior housing (20) and the inside corners of the exterior housing (10) facing them.
6. A potentiometer according to claim 5, characterised in that the interior housing (20) has on its two end edges respective steps (28, 29) to accommodate and guide the spring-elastic damping element (27, 27').
7. A potentiometer according to one of claims 1 to 6, characterised in that the electrical connections between the connections (flat-pin plug 19) and the defined path (resistance path 41) or the slider (brush spring 33) are created by means of a multi-stranded cable (44) which is soldered on at both ends, and in that one end of the multi-stranded cable (44) is mechanically clamped to the resistance plate (40) and the other end of the multi-stranded cable (44) is mechanically clamped to the exterior housing (20) or to a plug socket (18) joined therewith by means of clamps (43, 47).
8. A potentiometer according to one of claims 1 to 7, characterised in that the actuating element (30) is connected, vibration-damped, to a part of the other object which is to be attached.

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