DE19821529A1 - Electrical sliding spring for potentiometric sensors and current-voltage taps, e.g. travel and angle sensors for machines, cars or electronic regulating systems, comprises a sliding contact of vitreous carbon - Google Patents

Abstract

An electrical sliding spring, comprising a sliding contact of vitreous carbon, is new. A sliding spring for electrical tribo-systems in potentiometric sensors and current/voltage taps comprises: (a) a first functional element with an electrical sliding contact of vitreous carbon of defined hardness, the contact being initially shaped during the carbon production process and subsequently being finally shaped according to use; and (b) a second functional element in which mechanical spring force is created separately and is not dependent on the use of metals.

Description

Today's displacement and angle sensors in mechanical engineering, in the automotive sector or in electronic control technology require a high degree of reliability Lifetime stability and precision in the translation of path / angles in electrical signals. Influencing the sensor signals via temperature, Temperature changes, climate or vibrations should be excluded, partially redundant systems are required where security conditions are met have to.

Apart from the highest technologies on an optical or magnetic basis, these systems are today solved potentiometrically because voltage dividers are not sensitive to temperature changes. A potentiometer circuit is shown in Fig. 1 in supervision, in Fig. 2 in cross section.

Here, ( 1 ) mean the external voltage on the test potentiometer ( 2 ). An angle-dependent or path-dependent voltage is fed from the movable wiper spring contact ( 3 ) via a low-resistance contact rail ( 4 ) to a voltage measuring device ( 5 ) as a signal voltage. The signal voltage gives a direct indication of the path / angular position of the loop spring and thus of the size to be measured.

The limits of this technology today are vibrations, which have to be absorbed by a spring system, and noise in the potentiometer signal after a lifespan of several million actuation cycles, which disturbs the further use of the sensor signal. The cause of the noise is the changing contact resistance ( 6 ) between the sliding contacts and the respective sliding track during operation.

The resistance track ( 2 ) or the contact track ( 4 ) today consists of polymeric resistance pastes of high reliability with high tribological capabilities or of cermet pastes. Today silver nickel or multi-finger loop springs made of exotic precious metal alloys are used as grinding spring material.

Fig. 3 shows the sliding spring ( 7 ) with silver nickel or carbon coloid contact as a single contact ( 8 ), whereby the contact points each serve to make contact on the resistance track, and the metal webs ( 9 ) contribute to the achievement of the necessary spring force, ( 10 ) provides Axis for the rotation of the contacts on a circular potentiometer track ( 4 ).

Fig. 4 shows a multi-finger grinding system ( 11 ), the metal holder ( 12 ) serving as an assembly in a housing, the metal webs ( 13 ) to achieve the necessary spring force and the precious metal wires ( 14 ) directly contacting the potentiometer path through the grinding spring represent. The number of parallel precious metal contacts vary between five to 25 and reduce the total contact resistance due to the parallel connection.

Increasing miniaturization has resulted in relatively large pressed ones Rivet contacts or coal pipelines with the much smaller multi-finger contacts Wire thicknesses around 100 microns have been replaced because of the signal fineness and Signal resolution is also determined by the miniaturizability of the loop spring.  

Increasing industrial use has greatly expanded the specified area of application. Compared to control technology in the household, the applicable temperature range has been expanded to -50 ° C / + 150 ° C, as well as vibrations, service life requirements up to over 100 million mechanical cycles or rotary movements, as well as a wide range of chemical environmental influences. Temperature and chemical environmental influences in particular lead to considerable problems when contacting the contact point via the respective microclimate at the contact, as shown in Fig. 5 using an example. Fig. 5 shows the contact resistance between the potentiometer track and the loop spring depending on the loop spring position for a good sensor and for a sensor that cannot be used.

Therefore, the contact material for multiple finger contacts became increasingly noble and more expensive, but can chemical reactions (environmental chemical metal alloy) or chemical deposits (environmental chemistry temperature) and reactions of the Do not prevent microclimate from contact.

Since contact carbon is itself an inert material, the influences mentioned above can occur can be reduced by the choice of special coal according to the invention.  

INVENTION DESCRIPTION

The aim of the invention is the current wiper spring system both in the temperature range (Reducing the reaction microclimate temperature) as well as in the chemical Stability (reduction of the reaction microclimate grinding spring material) significantly improve.

Experiments have shown that by improving the polymer lacquer layer Technology restrictions mentioned above may be reduced, but not sustainable can be improved since chemical reactions on the loop spring and the layer in the Tribosystem, connected with electrical contact, continue to take place.

If the number of fingers of the multi-finger grinding system is reduced, it is reduced the chemical reactivity between the potentiometer path and the Schleifeder existing contact resistance increases because of reduced parallel connection of the wires.

Also an improvement of the tribological system by rounding the contacts or Smoothing the surface does not bring any significant improvement.

Experiments with coal pipelines or coloid contacts have shown that in the tribosystem the coal compacts are both too soft - which is caused by smearing coal a change in the value of the potentiometer track - as well as that of the coal pellets because of their size, the scanning fineness of miniaturized potentiometer tracks reduced compared to today's requirements.

According to the invention, the requirements can only be met in the context of a micro / electromechanical process chain using a special dissolve high temperature carbon.

Here "green coal" is used, (a not fully hardened material) that only under further temperature treatment in a dense, high temperature stable Coal of sufficient hardness greater than 100 HV with amorphous structure and sufficient good conductivity converts, so-called glass coal.

In terms of process technology, "green coal" offers the additional advantage that Manufacturing process of "green coal" all known technologies such as casting, Pressing, spraying, but also lamination or extrusion.

The resulting multiple benefits of "green coal" in plate, bar or In this preliminary stage, the shape of the profile can also be known today micromechanical work steps such as sawing, punching and drilling mechanically or using a laser in the design as a benefit or in the individual part structure.  

Only a closing temperature treatment leads the "green coal" into the final coal condition, with a volume loss of approx. 100 percent occurs, which further reduces the carbon contact in size.

Fig. 6 shows an example of the process steps that can be used and the use of coal as a contact according to the invention.

Fig. 6a shows the "green coal" ( 15 ) after production in the plan either as a plate ( 16 ) or as a web or conductor 17 ).

Fig. 6b shows the "green coal" in cross-section, whereby notches ( 18 ) or constrictions and constrictions ( 19 ) are used.

Fig. 6c shows a section of the "green coal" ( 20 ) after mechanical processing or structuring by laser as a preliminary stage for a continuous carbon loop spring contact.

Fig. 6d shows several contact carbons ( 21 ) connected, for example two contact carbon points / potentiometer layer are used ( 22 ) are, for example, surveys that are planned to position the acting spring forces. For this purpose, beads ( 23 ) can also be used as an alternative.

Fig. 6e shows an example that round or pointed shapes are also possible.

Fig. 7 shows the structure of the proposed new wiper system using examples, but not by way of limitation.

Fig. 7a shows a vertically resilient system in a recess ( 24 ) in a molded part ( 25 ), the spring force being generated from rubber-elastic material 26 ) which is embedded in the molded part. The carbon contact ( 27 ) can, but need not, correspond to a shape from 6c to 6e.

Fig. 7b shows a leaf spring system ( 28 ) in a molded part ( 29 ), the spring force being generated by an injected spring plate ( 30 ). ( 31 ) represents the carbon grinding spring, ( 32 ) the spring support as a whole and ( 33 ) the axis guide for an angle sensor.

Fig. 7c shows a metal leaf spring system ( 34 ) into which the carbon contact ( 35 ) has been clipped. The metal spring ( 36 ) can be designed torsionally by a spring bar, but also by two or more spring bars in a torsion-damped manner.

The spring forces can also be sprayed from a resilient Polymer material directly together with the spring support or from resilient Metal inserts are made. Since the coal bridge is already in Carbon loop spring system is included, the additional electrical connection two contact points are eliminated. It is therefore not a resilient, electrically conductive Metal more for the electrical bridge connection of the non-resilient electrical Contacts necessary.

Claims (14)

1. Material, construction and manufacture of a loop spring for electrical tribosystems in potentiometric sensors and current collectors of the type that in a first functional element, the electrical sliding contact made of glassy carbon defined hardness is produced individually or in combination, with a provisional Shaping already taken into account in the coal manufacturing process, the final one Shaping from one benefit takes place only in the final stage, and in a second Functional element the mechanical spring force is created separately and no longer is bound to the use of metals, 2. the first functional element from at least one carbon contact per lane exists, the carbon contacts of different tracks directly conductive are interconnected. 3. the carbon contacts according to claim 2 and the connecting elements of this one and consist of the same material. 4. the hardness of the coal according to claim 1 to 3 by the burning conditions in The Vickers hardness can be adjusted from 100 to 400 HV. 5. the shape of the carbon contacts according to claim 2 and 3 process engineering Casting, spraying, pressing, punching, milling, turning etc. from "green coal" getting produced. 6. The coal according to claim 1 to 5 individually or as a panel or panel or benefit profile can be burned. 7. the coherent carbon contacts according to claim 2 to 6 beads and Have holding bars on which spring forces can act. 8. the shape of the carbon contacts according to claim 6 at the contact point by the Final work step (for example separating) can be set. 9. single or several coherent carbon contact points per grinding track for the carbon contacts according to claim 2 and 3 are produced. 10. The functional element spring force can be designed as a leaf spring or compression spring can. 11. the functional element spring force according to claim 10 against Torsional vibrations and vibrations can be optimized by a spring network can. 12. the functional element spring force according to claim 10 both from a conductive, as can also be made from an insulating material. 13. The functional element spring force according to claim 10-12 in a cage integrated with the coal, 14. The functional element coal according to claim 2 to 9 and the functional element Spring force according to claim 9-12 connected by clipping, gluing or soldering can be.