Sealed Movement Sensor

The invention relates to sensors for the measurement of mechanical variables of movement, in particular to an angle-of-rotation sensor for automotive vehicle brake units furnished with traction slip control system and/or to be used for vehicle steering control systems and for vehicle chassis control systems.

Sensors having the function of rate-of-revolutions sensors are explained, for example, in the series of publications by Messrs. Robert Bosch GmbH, "PKW-Bremsanlagen mit ABS" (Passenger Car Brake Units with Anti-lock System), first edition of September 1989, page 20. These rate-of-revolution sensors operate by the induction principle. The housing is either fabricated from a stainless steel casing or of plastics material, a chisel pole or a rhombic pole as the assembly position of the sensor may be and projecting from the housing being directed to an impulse wheel fixed to the wheel hub. The pole stud is furnished with a permanent magnet within the housing which as an essential component of the measuring element generates a magnetic field and of the induction of a voltage within the coil winding positioned on the pole stud as soon as there is a rotation of the impulse wheel.

The rate-of-revolutions sensors described above have, however, the disadvantage that special provisions are required in order to ensure a smooth functioning which must, among others, protect the sensor against mud and moisture. This includes the greasing of the sensor and the exact adjustment of the gap between the impulse wheel and the sensor. In addition, the relatively insufficient miniaturization and the comparatively heavy weight of the prior-art sensors contrasts with the requirement of an optimum integratability.

It is, therefore, the object of the invention to create a sensor of the kind mentioned above which is distinguished by a particular suitability for miniaturization, by a great versatility and integratability and which, without being sensitive to mud and splash water, ensures a signal processing at any time, without particular adjusting procedures and corrosion protecting measures being required.

According to the invention, this object is achieved by a process for the manufacture of such a sensor.

The embodiments of the invention are enunciated which will be illustrated and explained in more detail in the following in conjunction with the further features and advantages of the invention, making reference to several accompanying drawings (FIGS. 1 to 3).

FIG. 1 shows an arrangement of the travel sensor with the impulse wheel at the wheel bearing;

FIG. 2 shows an upscaled part-section of the measuring device integrated in the travel sensor; and

FIG. 3 shows a sectional representation of the measuring element in FIG. 2.

FIG. 1 shows in a diagrammatic sketch a rotor 11 fabricated from a light-gauge sheet-steel stamping which is fixed as an impulse generator to the rotating part of the wheel bearing housing 12. In the illustration shown, said rotor 11 is furnished with a plurality of magnetic pole pairs 13 which are uniformly distributed over the circumference (so-called external magnetization) and which are fixed onto the rotor 11 configurated in the shape of a sectional disc member in a positive locking-type engagement and/or in a frictional locking engagement. The cross-sectional profile of the rotor 11 is centered at the internal collar 14 of the wheel hub and is cranked z-shape in the direction of the wheel bearing in such a manner that the internal radius of the rotor 11 ends at the wheel bearing sealing ring 15. The carrier housing 4 which is configurated in the shape of an injection moulding simultaneously overlaps the collar 14 of the wheel hub, so that any penetration of splash water and mud between the rotor 11 and the measuring device is virtually excluded. This section of the carrier housing 4 is configurated as a protecting cap 10 for this purpose which when positioned at the driven vehicle axle as shown in the drawing is designed as a cover disc being penetrated, for example, by a wheel axle or by a driving shaft 16.

In lieu of a rotor being furnished with pairs of magnetic poles a conventional toothed rim may be used as well. However, in that case it will be necessary to accommodate a permanent magnet within the sensor housing (so-called internal magnetization), which may, indeed, lead to an increase of the overall space requirements of the sensor.

FIG. 2 shows the functionally and constructionally relevant elements of the sensor. The measuring element chamber 2 accommodating the measuring element 1 is formed by the two-part housing 3, one part of which being pluggable into the other, the one housing half being designed as a cup 6 and the other housing half as a cover 7 allowing to be pressed in and reaching down to the cup bottom. Advantageously, said cup 6 is configurated in the shape of a thin-walled, non-ferromagnetic, deep-drawn metal element. In particular, the use of austenitic stainless steel is suited for this purpose for reasons of corrosion-resistance. Cover 7 is made of a high-strength plastic material with elevated melting point, for example of thermoset plastic. Through openings are provided in the cover 7 which are intended for the electric connections 5 coming from the measuring element 1, and from the IC module 8. The cartridge so constituted by the housing halves 6, 7, by the measuring element 1 accommodated therein and by the IC-type switching circuit is surrounded by the carrier housing 4.

Said carrier housing 4 is preferably fabricated by injection-coating of the two-part housing 3 with plastic material, the cover 7 absorbing the injection-coating pressure and preventing the penetration of plastic material into the measuring element chamber 2. A bus bar inserted in said plastic material establishes the electric connection between the connections of the IC and the peripheral plug-type connector. An additional protection against the penetration of water in the direction of the electric connections 5 of the IC module or semiconductor 8 is ensured by the sealing 9 which is pressed into the annular groove at the cup 6. The measuring element chamber 2 may, for example, be filled with silicon in order that the measuring element 1 and its IC module 8 are retained in the cup 6 without movement.

Beyond the advantages of the sensor which have already been mentioned and which regard its compactness, its lack of sensitivity to splash water and to mud, the described two-part housing 3 in the shape of the illustrated cartridge affords a universal application, independently of the structural requirements of the carrier housing 4.

Reference is now made to FIG. 3 which shows a top view of the two housing halves 3, which are formed by the cup 6 and by the cover 7, together with the measuring element 1 which may, for example, be configurated as a Hall element for application of the Hall effect, and with the IC module 8 being arranged spacially on top. Said measuring element 1 and said IC module 8 are superimposed the way of plate-shaped layers and are interconnected through conductor foils 17 being configurated as film hinges. On account of the special incorporating requirements the housing slightly differs from the circular housing shape, which becomes noticeable from the lateral flattening. In addition, the rectangular electric connections 5 are visible which are configurated in the shape of contact studs and which lead through the carrier housing 4.