EP0254252B1 - Rotary potentiometer, in particular for use as an angular position sensor for the rotary positioning of a shaft - Google Patents

Description

The invention relates to a rotary potentiometer according to the preamble of claim 1. Such rotary potentiometers are commercially available in a wide variety of designs, with the spring support usually being mounted in the housing with as little play as possible. If such a rotary potentiometer is to be used as a rotary position sensor, for example for the angular position of a shaft, the problem arises that the axis of rotation of the rotary potentiometer is not always aligned with the central axis of the shaft. There can be a so-called There is a "center offset" of the two axes. These two axes can also be tilted towards each other. This is unsatisfactory in mechanical and electrical terms. Mechanically, this easily leads to destruction. From an electrical point of view, there may be deviations in linearity and hysteresis. Of course, this is unacceptable for many applications. An example of an application is the scanning of the position of the throttle valve of an internal combustion engine, wherein a measurement signal for the control of the ignition timing and / or the injection timing and the injection quantity is to be generated for a fuel injection.

The object of the invention is therefore to improve the rotary potentiometer of the type mentioned in such a way that it provides excellent linearity of its electrical output signals in relation to the rotary position over a long service life, even if the axis of rotation of the potentiometer is not the main axis of the potentiometer actuating shaft is aligned.

This object is achieved by the features specified in the characterizing part of patent claim 1. Advantageous refinements and developments of the invention can be found in the subclaims.

The following advantages were achieved with a rotary potentiometer according to the invention:
The service life was satisfactory, ie with 10⁶ rotary movements over the entire angular range, there were no damage or deviations in the electrical Values on; the characteristic of the rotary potentiometer was linear with a tolerance of +/- 2% over the entire angular range. The reproducibility was better than 0.3% and the voltage hysteresis was less than 1.5%. Furthermore, the torque was uniformly linear over the entire rotation range.

Fig. 1:

Einen Schnitt des Drehpotentiometers (längs der Linie A-F der Fig. 3);

Fig. 2:

Eine weitere Schnittansicht des Drehpotentiometers;

Fig. 3:

Eine teilweise aufgeschnittene Draufsicht des Potentiometers, gesehen von der Drehbetätigungsseite her;

Fig. 4:

Einen weiteren Schnitt des Drehpotentiometers wobei einige Teile (Widerstandsplatte und Lagerbuchse) fortgelassen sind;

Fig. 5:

Eine Draufsicht des bei dem Drehpotentiometers verwendeten Federträgers, gesehen von der Drehbetätigungsseite her;

Fig. 6:

Einen Querschnitt des Federträgers der Fig. 5;

Fig. 7:

Eine Seitenansicht des Federträgers der Fig. 5;

Fig. 8:

Einen Teilschnitt längs der Linie E-F der Fig. 5;

Fig. 9:

Einen Querschnitt des bei dem Drehpotentiometer verwendeten Käfigs, der die Widerstandsplatte gegenüber dem Gehäuse hält und zentriert;

Fig. 10:

Eine vergrößerte Einzelheit X der Fig. 9;

Fig. 11:

Einen Querschnitt der bei der Erfindung verwendeten Lagerbuchse;

Fig. 12:

Eine Seitenansicht der Lagerbuchse;

Fig. 13:

Eine Draufsicht auf die Lagerbuchse; und

Fig. 14:

Eine Seitenansicht des Federträgers mit an ihm befestigter Schleiferfeder.

The invention is explained in detail below using an exemplary embodiment in conjunction with the drawing. It shows :

Fig. 1:

A section of the rotary potentiometer (along the line AF of Fig. 3);

Fig. 2:

Another sectional view of the rotary potentiometer;

Fig. 3:

A partially cutaway top view of the potentiometer, seen from the rotary actuation side;

Fig. 4:

Another section of the rotary potentiometer with some parts (resistance plate and bearing bush) omitted;

Fig. 5:

A plan view of the spring support used in the rotary potentiometer, seen from the rotary actuation side;

Fig. 6:

A cross section of the spring support of Fig. 5;

Fig. 7:

A side view of the spring support of Fig. 5;

Fig. 8:

A partial section along the line EF of Fig. 5;

Fig. 9:

A cross section of the cage used in the rotary potentiometer that holds and centers the resistance plate against the housing;

Fig. 10:

An enlarged detail X of FIG. 9;

Fig. 11:

A cross section of the bearing bush used in the invention;

Fig. 12:

A side view of the bearing bush;

Fig. 13:

A top view of the bearing bush; and

Fig. 14:

A side view of the spring support with the wiper spring attached to it.

It should be noted that different scales were used in the individual drawings.

The rotary potentiometer has a housing 1, which is closed with a cover 2 with an integrated plug plate. A resistance plate 3 is fixedly held in the housing, on which a spring support 4 is rotatably and oscillatingly mounted, specifically via a metal bearing bush 5, which in turn is held free of play by a bearing bush holder 6, the bearing bush holder 6 being free of play in an opening of the resistance support 3 is held. A wiper spring 7 is attached to the spring carrier 4, which is designed here as a brush wiper spring and with two Brushes 57 is in sliding electrical contact with resistance tracks applied to the resistance plate. The resistance carrier 3 is fixedly centered and held in a recess of the housing 1 by means of a “cage” 8, this cage 8 also serving as a support for a torsion spring 9 which is fastened at one end to the spring carrier 4. The potentiometer is biased into an end position by this torsion spring 9. In the exemplary embodiment, three plugs 10 are soldered onto the resistance carrier 3. These plugs are in electrical connection with the mentioned resistance tracks. They protrude through the resistance carrier 3 and are soldered to the side facing the wiper spring 7. The cover 2 is fastened to the housing 1 by means of rivets 11, a cavity between the cover and the side of the resistance carrier 3 facing it being completely filled with a sealing compound 12, so that the resistance carrier 3 is encapsulated in a watertight manner with respect to the cover 2.

The housing 1 has on its actuation side (bottom in FIG. 1) a central through opening 13 through which an actuation shaft (not shown) can engage in a blind bore 14 of the spring support 4. Said actuating shaft is connected to a rotating part, the rotational position of which is to be detected by the rotary potentiometer according to the invention. For example, this is the pivot axis of the throttle valve of an internal combustion engine, the opening position of which is to be detected. The rotary potentiometer is then flanged to the internal combustion engine by means of screws projecting through fastening openings 15. In practice, it is not always ensured that the main or rotational axis 16 of the rotary potentiometer is exactly aligned with the central axis of the rotary actuating shaft. Rather, these two axes can have a so-called center offset and / or be at an angle to one another. This leads to inaccuracies or linearity errors of the potentiometer in relation to the rotary position of the rotary driver. Furthermore, excessive stresses on the rotary potentiometer can occur which lead to its destruction.

In order to avoid these problems, the spring support 4 is mounted such that it oscillates with respect to the resistance support 3, so that the axis of rotation of the spring support can oscillate or wobble with respect to the main axis of rotation 16. On the other hand, the spring support 4 is held practically immovable in relation to the resistance support 3 in the axial direction (only the axial play required for the pendulum movement is present), with the result that the pressing force of the wiper spring 7 relative to the resistance support 3 only changes even when the spring support 4 swings out to the side changes minimally, so that the electrical contact resistance between the resistance tracks and the wiper spring is constant within very narrow limits. This is further favored by the relatively large length of the arms of the wiper spring.

The oscillating mounting is obtained by a flexible bearing pin 17, which is integrally formed here on the spring support 4. The flexibility of the bearing pin 17 is obtained by the fact that it has slots 18 which run in the axial direction and are offset in the radial direction. Through these slots 18, the bearing pin 17 can be resiliently radially deformed, so that, as a result, the spring support can oscillate relative to the rigid bearing bush 5.

In the axial direction, the bearing journal 17 is held relative to the bearing bush 5 by two radially outwardly projecting projections 19 and 20. The collar 19 arranged at the free end of the bearing pin 17 can be pressed radially inward due to the slots 18, so that the bearing pin 17 can be inserted into the bearing bush 5 without problems and snaps or locks there. This insertion is facilitated by a chamfer 21 at the free end of the journal. The lower collar 20 acts in the other direction opposite the opposite end face of the bearing bushing 5. Due to the spring force of the wiper spring 7, the spring support 4 is pushed away by the resistance support 3 to such an extent that the collar 19 of the bearing pin 17 abuts the corresponding end face of the bearing bushing 5 . As can be seen in Fig. 1, there is only a very slight play in the axial direction between the collar 20 and the corresponding end face of the bearing bush 5. This slight play is required to allow the pendulum movement of the journal 17.

In the illustrated embodiment, the bearing bush 5 is made of metal for reasons of low wear. In order to be able to easily mount this bearing bush on the resistance carrier 3, it is inserted into the bearing bush holder 6 and locked there in the axial direction between two radially inwardly projecting edges 22 and 23 of the bearing bush holder 6 (cf. FIG. 11). The bearing bush holder 6 is off elastic material such as plastic. The bearing bush holder 6 is in turn snapped into an opening of the resistance carrier 3 and also by means of two axially spaced edges 24 and 25. The spacing between these two edges 24 and 25 corresponds to the thickness or material thickness of the resistance carrier 3 said opening of the resistance carrier 3 can be inserted, it has on its outside radially protruding projections 26 which are inclined in the axial direction and are elastic in themselves, so that the bearing bush holder 6 can be snapped into the resistance carrier 3. The exact shape of these projections 26 can be seen in FIGS. 11, 12 and 13. The projections are arranged mirror-symmetrically in pairs and approximately crescent-shaped in plan view (FIG. 13). In order to obtain a better clamping effect, the edges 25 of the projections 26 pointing in the direction of the resistance support 3 are slightly inclined, as a result of which a certain wedge effect is obtained. In order to continue to ensure a good insertion of the bearing bush holder 6 into the opening of the resistance carrier 3, the outer circumference of the upper part of the bearing bush holder 6 is designed to be slightly tapered, which is expressed in the angle (FIG. 12). With this arrangement described, the bearing bush is absolutely fixed and free of play on the resistance carrier 3.

So that in the normal position the spring support 4 is aligned centrally to the main axis 16 of the housing and, in addition to the permitted rotating and oscillating movement, does not undergo any further displacements, the resistance support 3 must be firmly and correctly aligned relative to the housing 1 be kept. For this purpose and to facilitate assembly, the resistance carrier 3 is held in the cage 8 (housing insert). This cage 8 (see also FIGS. 2, 4 and 9) is adapted to the shape of the resistance carrier 3 with regard to the contour of its outer wall. The upper edge 27 of its outer wall 28 serves as a support for the resistance carrier 3. To hold and clamp the resistance carrier 3, several spring arms 29 are provided on the outer wall 28 of the cage 8, which protrude beyond the upper edge 27 and with their inwardly facing surface a limitation for form a displacement of the resistance carrier 3. In addition, the spring arms 29 have projections 30 projecting outward beyond the contour of the outer wall 28 (cf. in particular FIG. 10). A central recess of the housing 1, on the other hand, is very precisely adapted to the outer contour of the outer wall 28, so that when the cage 8 is inserted into this central recess of the housing 1, the spring arms 29 are pressed inwards, as a result of which they are pressed against the end face of the resistance carrier 3 and tighten it tight. (see FIGS. 1 and 2). An additional securing of the resistance carrier 3 in the cage 8, which is already effective during assembly, is also obtained in that the spring arms 29 have inwardly pointing projections 31 (see FIG. 10), behind which the resistance carrier 3 engages.

So that the cage 8 is centered even more precisely in the housing 1, the spring arms 29 have additional, outwardly projecting ribs 32 (see FIG. 10) which are guided in correspondingly shaped recesses 33 in the housing 1. These ribs can also (different from the representation of FIGS. 9 and 10) except for the Reach down the bottom of the cage and thus practically be projections of the outer wall 28 of the cage.

Another function of the cage 8 is to hold the torsion spring 9. For this purpose, the cage has an inner, cylindrical sleeve 34 (FIG. 9) which is at a distance from the cylindrical part 35 of the outer wall 28 and which does not extend in the axial direction up to Top edge 27 extends. The torsion spring 9 is inserted into the intermediate space thus formed. With a radially outwardly projecting arm, the torsion spring 9 is supported between two ribs 37 and 38, these ribs adjoining the cylindrical part 35 with a passage opening for the arm 36 of the spring 9. (Fig. 4). Another, axially extending arm 39 of the torsion spring 9 engages in a recess 52 provided on the outer circumference of the spring carrier 4 and thus prestresses the spring carrier in the direction of rotation in one direction.

The upper edge of the sleeve 34 of the cage 8 finally serves as a stop for the pendulum movement of the spring support, which can best be seen from FIGS. 1 and 2.

In order to obtain a defined "zero position" of the spring support 4 with respect to the housing, the spring support 4 has one or two rotation limit stops 40 on its outer circumference, which cooperate with corresponding stops 41 in the central through opening of the housing 1. Furthermore, these stops can also serve as a stop for limiting the range of rotation of the spring support 4.

3, 5 and 6, the connection of a driver shaft to the spring support will now be explained. The spring support 4 has opposite to the through opening 13 of the housing 1, a blind hole 42, in which two driver webs 43 and 44, starting from the cylindrical inner wall of the Sackboh tion 42 protrude. The side surfaces 45, 46, 47 and 48 of the driver webs are inclined with respect to the central axis of rotation 16 (see the angle 49 in FIG. 6). In the exemplary embodiment in FIG. 3, the driver shaft (not shown) rotates the spring support 4 counterclockwise (see Arrows in Fig. 3) so flat driver surfaces of the driver shaft come to rest on the side surfaces 46 and 48. Since these "contact surfaces" are undercut from above, it is ensured that there is always a line contact between the driver shaft and the contact surfaces 46 and 48 even with a center offset between the axis of rotation 16 and the center axis of the driver shaft and also when the driver shaft is inclined is. As a result, synchronism between the rotary driver and the spring carrier 4 is ensured even in these two possible error states. This avoids the synchronism error between the input and output shafts known from universal joints. If the carrier webs 43 and 44 are approximately considered as three-sided prisms, the edges of the prism are inclined at an acute angle 49 (FIG. 6) with respect to one of the planes which is formed by a base side of the prism and the axis of rotation 16 Inclination angles of the contact surfaces 46 and 48 are inclined in opposite directions. 3 and 5, both contact surfaces 46 and 48 are thus "undercut". If you extend the tops of the contact surfaces 46 and 48 with an imaginary straight line, it can be seen that these two lines do not go through the central axis 16, but run past it at a distance. The distance between these two lines corresponds approximately to the thickness of the screwdriver-like extension of the drive shaft. The angle of inclination 49 mentioned is of the order of 3 °. The side surfaces 45 and 47 opposite the contact surfaces 46 and 48 are also inclined here in a corresponding manner. In the view of FIG. 3 they are not undercut, ie they are visible in the view of FIG. 3.

The spring support 4 shown in FIGS. 5 to 8 is designed with respect to the direction of rotation shown in FIG. 3 for the other direction of rotation, ie it is rotated clockwise in the direction seen from the actuating shaft. Accordingly, the surfaces 45 and 46 or 47 and 48 are interchanged with respect to FIG. 3. In Fig. 5 it can also be seen that protrusions 50 and 51 are provided on the inwardly facing wall of the blind bore 42 immediately in front of the contact surfaces 46 and 48 of the driver webs 43 and 44, which act as run-on surfaces for the "blade" of the rotary driver serve. These projections 50 and 51 lie directly opposite one another and, as a result, ensure that the spring support is tilted when the drive shaft is inclined or is deflected in an oscillating manner in the bearing bush. The radially inward-facing surfaces of the projections 50 and 51 are also "undercut", ie the thickness of the projections decreases from the opening side towards the inside. The angle between these surfaces and the central axis is also approximately 3 °. Fig. 6 can also be seen that the blind hole 42 is widened somewhat conically towards its opening in order to permit the wobbling movement of the spring carrier with respect to the driving shaft.

In the enlarged sectional view of FIG. 8 it can be seen that the projections 51 (or 50) are rounded in the direction of the opening of the blind bore 42 (reference number 53) to facilitate insertion of the driver shaft.

Finally, it can be seen from FIGS. 6 and 7 that the spring support has fastening projections 54 running parallel to the bearing pin 17 for fastening the wiper spring 7. As can be seen from FIGS. 4 and 14, the wiper spring has corresponding openings through which the fastening projections 54 protrude. With a snap ring 55 which engages behind a collar of the fastening projections 54, the wiper spring is then held on the spring carrier.

Claims (12)

1. Rotary potentiometer, in particular for use as a rotary position sensor for the rotary position of a shaft, having

   - a housing (1)

   - a resistor carrier (3) held therein

   - a spring carrier (4) rotatably mounted in the housing (1)

   - a brush spring (7) which is secured to the spring carrier (4) and which is in brushing electrical contact with a resistor layer of the resistor carrier (3), and

   - means for coupling the shaft to the spring carrier (4),

   characterized in that the spring carrier (4) is additionally mounted to oscillate with respect to the resistor carrier (3) such that its axis of rotation (16) can adopt an acute angle with respect to a vertical on the resistor carrier (3).
2. Rotary potentiometer according to Claim 1, characterized in that the spring carrier (4) has a flexible bearing journal (17) arranged centrally with respect to the axis of rotation (16) of the spring carrier (4).
3. Rotary potentiometer according to Claim 2, characterized in that the flexible bearing journal (17) is held in a rigid bearing bush (5) which for its part is secured to the resistor carrier (3).
4. Rotary potentiometer according to Claim 3, characterized in that the bearing journal (17) is held in the bearing bush (5) non-displaceably (with low play) in the axial direction.
5. Rotary potentiometer according to one of Claims 2 to 4, characterized in that the bearing journal (17) has axially running slots (18).
6. Rotary potentiometer according to Claim 4 or 5, characterized in that the bearing journal (17) has at its free end a radially jutting projection (19) which is latched into the end side of the bearing bush (5).
7. Rotary potentiometer according to one of Claims 1 to 6, characterized in that the spring carrier (4) has on its side opposite the rotary journal (17) a blind bore (42) into which entrainment webs (43, 44) project, the entrainment webs (43, 44) having undercut bearing surfaces (46, 48) such that entrainment surfaces of the shaft bear against the bearing surfaces (46, 48) even in the event of a centre offset of the shaft with respect to the axis of rotation (16) of the spring carrier (4) and/or in the event of the axis of the shaft being tilted with respect to the axis of rotation.
8. Rotary potentiometer according to Claim 7, characterized in that the entrainment webs (43, 44) have approximately the shape of a three-sided prism, and in that the edges of the prism are inclined at an acute angle with respect to a plane enclosing a base side of the prism and the axis of rotation (16).
9. Rotary potentiometer according to Claim 8, characterized in that, directly adjoining the bearing surfaces (46, 48) of the entrainment webs (43, 44), the blind bore has radially inwardly projecting projections (50, 51), whereof the radial extent is smaller than that of the entrainment webs, and in that these projections (50, 51) are also undercut.
10. Rotary potentiometer according to Claim 9, characterized in that the acute angle of the edges of the prisms is in the order of magnitude of 3°.
11. Rotary potentiometer according to one of Claims 1 to 10, characterized in that the resistor carrier (3) holding the bearing bush (5) for the spring carrier (4) is held in a housing insert (cage 8) which is tensioned by spring arms (29) which are bent when the cage (8) is pushed into the housing (1).
12. Rotary potentiometer according to one of Claims 1 to 11, characterized in that the spring carrier (4) has a radius-shaped chamfer (56) whereof the radius goes out from the theoretical centring point or oscillating point of the bearing journal (17).

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