EP1252481A1

EP1252481A1 - Linear distance sensor and the use thereof as actuator for motor vehicles

Info

Publication number: EP1252481A1
Application number: EP00983286A
Authority: EP
Inventors: Peter Lohberg
Original assignee: Continental Teves AG and Co OHG
Current assignee: Continental Teves AG and Co OHG
Priority date: 2000-01-13
Filing date: 2000-12-12
Publication date: 2002-10-30
Also published as: US6823725B2; WO2001051893A1; US20030000307A1; JP2003524778A

Abstract

The invention relates to a linear distance sensor for motor vehicles, which comprises a slidable element (4, 5, 7) and a stator (1, 2, 3), said slidable element being provided with a magnetic encoder. Sensor modules that work according to the AMR, GMR or Hall principle are linked with the stator. The slidable element is guided in a bearing (11) that is linked with the stator and that encloses and axially guides the slidable element. The sensor module(s) is/are stationarily linked with the stator. The field-producing device(s) is/are positively linked with the slidable element along the longitudinal axis of the slidable element. The invention further relates to the use of the linear distance sensor for measuring the pedal or lever position in a device for actuating the brakes of a motor vehicle.

Description

Linear displacement sensor and its use as an actuating device for motor vehicles

The invention relates to a linear displacement sensor according to the preamble of claim 1.

It is already known to determine the position and angular velocity of vehicle wheels, for example, using arrangements of magnetically coded disks or rings and magnetic field sensors. For this purpose, the coded disks or rings (so-called encoders) are equipped with permanent magnetic material. A variation of the magnetic field on the encoder is required to perform the position determination by the sensors. This is achieved either by alternating north-south magnetization of the magnetic material along an arc on the encoder, but also by a periodically reduced distance of the magnetic material from the sensor. The magnetic field is then scanned along the circular arc by a magnetic field sensor, which can be, for example, a Hall sensor or a magnetoresistive resistor, in order to determine the wheel position and the angular velocity, for example by counting the signal edges of the sensor signal. The signal generated by the sensor can be amplified and triggered by an electronic circuit mounted in the area of the sensor or integrated in the sensor (active magnetic field sensor). A comparable arrangement is described in WO 95/17680, but also in WO 97/42508 for determining the wheel condition in a motor vehicle.

A high-resolution magnetic displacement sensor emerges from US Pat. No. 4,712,083, which likewise uses the principle of the rotating permanent-magnetic encoder. The encoder is formed by hard magnets arranged at regular intervals from one another, with the magnetic field of all individual magnets is aligned in the direction of movement.

The arrangement described is also exclusively for

Position determination of rotating bodies provided.

DE 196 12 422 uses a displaceable permanent magnet to determine the slider position in a linear potentiometer, the position of which is recognized by means of a stationary gyromagnetic magnetic field sensor. This type of sensor is particularly sensitive to changes in the angle of the magnetic field.

A displacement sensor for determining the position of a throttle valve in a motor vehicle is described in US 5,929,631. Here, a Hall element or, which is preferred, a resistance element that uses the huge magnetoresistive effect (GMR) is used as the magnetic field sensor. The publication also mentions that the arrangement for determining the position can also be used for linear movements in addition to radial movements. The proposed solution is to arrange a large number of magnetic sensors at regular intervals along the route. In one embodiment, an arrangement is shown in which eight GMR sensors are spherically arranged on a rotating cylinder jacket, which run past a rod-shaped permanent magnet which is firmly attached to the inside of the cylinder jacket during rotation. This position determination method is disadvantageous in that a chain or matrix of individual sensors has to be connected to an electronic evaluation circuit. The determination of the position in this way is technically complex and cost-intensive.

An increase in the resolution of magnetic displacement sensors leaves can be achieved according to DE 43 27 047 if, on the one hand, the hard magnets arranged on the encoder are aligned antiparallel and, on the other hand, two magnetic field sensors are used which are arranged slightly offset laterally in the direction of the movement direction. The effect of external interference can be further reduced if several magnetoresistive film resistors are connected together to form Wheatstone bridges. The arrangement described can generally be used for measuring circular or linear changes in position of two objects that are movable relative to one another. However, the document does not provide any suggestions as to how a displacement transducer must be constructed under practical conditions such as those found in motor vehicles.

It is therefore an object of the present invention to propose a linear displacement sensor for motor vehicles which offers maximum reliability with high displacement resolution under practical conditions such as corrosion, wear, dirt, extreme heat and extreme cold.

This object is achieved by a linear displacement sensor according to claim 1.

According to the invention, a linear displacement sensor with an integrated magnetically active component for, for example, mechanical actuation devices of brake devices is described. The invention is based, inter alia, on the idea of using the mechanics of the actuating device at the same time as mechanics of non-contact linear displacement sensors, which are to depict the driver's actuation request either weighted proportionally or path-dependent. The magnetic field of the encoder is measured or detected by one or more magnetic field sensors. The magnetic field is either completely or only partially detected by the magnetic field sensor, whereby a partial detection of the magnetic field is understood in the sense of the invention if not all of the measured variables, such as field strength and direction of the field vector, describe the magnetic field by the sensor module or sensors but, for example, only the field strength and two direction coordinates of the field vector in the xy plane of a suitably chosen coordinate system.

The sensor module according to the invention contains at least one magnetic field sensitive sensor and possibly an electronic circuit for further processing of the sensor signal. The invention can be carried out with magnetic field sensitive sensors which operate according to the XMR principle, preferably the AMR, the GMR principle, or the Hall principle. The AMR principle is understood when the sensor uses the anisotropic magnetoresistive effect. Corresponding sensors are known, for example, from S. Mengel, “Technology Analysis Magnetism Volume 2: XMR Technologies”, Section 2.2, pages 18 to 20, VDI Technology Center Physical Technologies, Düsseldorf, 1997.

The GMR principle is understood when the sensor element uses the "Giant Magnetoresisitive Effect". The Hall principle is understood when the sensor uses the Hall effect.

Preferably only sensors are used that work according to the AMR principle.

In a preferred embodiment, the linear displacement sensor according to the invention is characterized in that the Sensor module contains a bridge circuit made of magnetic field sensors, the main plane of which is aligned parallel to the surface normal and to the longitudinal axis of the displaceable element.

In the sense of the present invention, the surface normal of the displaceable element is understood to mean a direction vector which is perpendicular to the surface of the displaceable element.

If, for example, the displaceable element is in the form of a rod with a circular cross section, the surface normal corresponds to the radius vector of the rod.

In a second preferred embodiment, the main plane of at least one sensor module with a bridge circuit is oriented perpendicular to the surface normal of the displaceable element.

It is particularly preferred if both of the sensor variants mentioned above are implemented in the linear displacement sensor according to the invention. With this functional principle, different magnetic field components of a magnetic encoder track are used and the field strength pattern of the encoder track is converted into different signals.

The output signal or the output signals of the magnetic sensors, which contain the information about the movement, are preferably provided in electrical form at the output. This signal can be processed by one or more sensor circuits and made available, for example, in digitized form at the output of the sensor circuit.

The means of generating the permanent magnetic field line Course 33 is also referred to in the literature as an encoder. It comprises, for example, either a permanent magnetic material which has been magnetized alternately along its longitudinal axis or at least two magnetized permanent magnetic materials arranged in series which modulate the course of the magnetic field through different orientation or magnetization strength of the magnetic material. For example, bi- or multipolar permanent magnets can be used. Encoders are preferably used which comprise a homogeneous magnetic material which has been magnetized in accordance with the desired magnetic field line course.

The permanent magnetic material is oriented in particular anti-parallel with respect to the magnetic north-south direction.

The permanently magnetic material is, for example, permanently magnetized ceramic material, e.g. anisotropic barium ferrite magnets are used, preferably plastic-bonded ferrite material. Particularly preferably, a plastic-bonded magnetic material that can be used according to the invention can be a material that e.g. for the production of magnetized wheel bearing seals. This wheel bearing material is known per se and is used, for example, by the companies C. Freudenberg, Weinheim (DE), SNR, Annecy (FR), FAG Kugelfischer, Schweinfurt (DE).

To improve the magnetic properties of the field generating agent, an iron yoke can be provided on the back. An iron yoke can preferably be dispensed with when using permanently magnetized ceramic material, and it is the case with plastic-bound materials however expedient to provide a magnetic iron yoke. The iron yoke advantageously consists of magnetically highly conductive iron material which, in the case of rod-shaped or linear bodies, is deposited in the field generating means and, which is particularly preferred, forms a firm bond with it.

The shape of the field generating means is similar to that of a thin-walled tube, a narrow, flat ruler or that of a round rod, for example. Field generating means are preferably used in the form of flat rulers with a spherical or trapezoidal profile, or round bars with iron core filling.

The axially leading bearing is preferably designed such that the area of the field generating means is at least partially sealed by the bearing itself. In this case, additional sealing means in the area of the bearing can be dispensed with. It is particularly advantageous if the sealing agent itself also takes on the function of storage.

The displaceable element preferably comprises a shaft, an actuating element mechanically connected to the shaft and a force transmission means, so that when the actuation element is actuated by means of an external force which acts on the force transmission means, the shaft and thus the field generating means are essentially free of tension. and / or compressive forces can be axially displaced.

The displaceable element can be of any cross-sectional shape and is either solid or has an axial recess, as is present, for example, in the case of a tubular object. The displaceable element is preferably a profile tube. According to the invention, the term “profile tube” is understood to mean a conventional tube with any cross-section, for example round, oval, square, square with rounded corners or polygonal.

The shaft 7 can be formed in one piece or consist of several individual parts. The connection of the shaft with the actuating element is designed so that the shaft is moved with the rod in a precise location. For example, the shaft can be screwed to the actuating element.

The cross-sectional shape of the shaft preferably corresponds essentially to that of a profile tube defined above, wherein the shaft can additionally be hollow or solid. However, the shaft particularly preferably has an axial opening, as is typical for profile tubes.

The force transmission means for transmitting an external force to the actuating means is used, for example, to transmit the force of a brake pedal to the brake cylinder. The actuating means is preferably a direct connection to the actuating rod of the brake cylinder or in particular this rod itself. The force transmission means must essentially be designed for forces in the direction of the brake release, ie in the direction of the actuating rod, but can, which is preferred, Transfer forces even under tensile loads. The force transmission means can be a rigid or movable connection to the brake pedal; this is preferably a movable connection. The force transmission means is, for example, a ball joint, a needle bearing or a cone camp .

The arrangement according to the invention for measuring linear paths advantageously has a particularly low hysteresis.

A redundant arrangement according to the invention means arrangements which are either fully redundant, partially redundant or also contain two or more redundant systems, so that in the event of a failure or malfunction of a sensor or a sensor circuit, a duplicate element has the function of the failed or faulty element or detects its malfunction and, if necessary, reports it to a monitoring device.

The resolution of the linear displacement sensor essentially depends on the nature of the sensor and that of the field generating means (encoder). For example, the change in the magnetic field along the encoder (encoder track) can be varied depending on the requirements by the distance between the individual magnets.

According to the invention, linear path-dependent magnetic encodings of the encoder track can be used, but also non-linear magnetic encodings. However, multi-track codes can also be used, but preferably single-track codes are used, in particular linear single-track codes.

Another possibility is to design the magnetic encodings in such a way that, in cooperation with suitable sensors, an analog path resolution, which is much finer in comparison to a quantized path resolution, can be realized. is settled. In practice, however, it is expedient to generate a quantization by periodically repeating a magnetization pattern, so that a signal quantized with respect to the path is present as the output signal of the magnetic sensor.

The invention also relates to the use of the linear displacement sensor described above for measuring the pedal or lever position in an actuating device for braking motor vehicles.

The linear displacement transducer according to the invention can preferably also be used for piston shafts, actuating rods, throttle valves and hydraulic pistons in motor vehicles.

Further advantageous embodiments of the invention result from the following description of the figures.

Show it

1 shows an example of a linear displacement sensor which can be used in an actuating device for braking motor vehicles for detecting the position of the pedal position,

2 shows another example of a linear displacement sensor according to FIG. 1 with two sensor modules (S, SC, S ', SC'),

3 shows a schematic representation of the field line course along the surface of an encoder in the axial direction together with differently oriented sensor modules and a graphic representation of the output signal of these sensor modules, 4 examples of field generating means that can be used according to the invention without magnetic yoke a and with yoke b for insertion into a recess of the displaceable element,

5 examples of field generating means which can be used according to the invention without inference (a) and with inference (b) for insertion into a bore or an axial opening of the displaceable element,

6 further, also schematically illustrated examples of shafts 7 according to the invention together with insertable or used field generating means 9, 9 ', 9' ',

7 examples in a schematic representation for combinations of sensors and field generating means according to the invention with a representation of the sensor electronics and an example of an output signal generated by the sensor electronics when the field generating means moves in the direction of the axis of movement BA around the deflection x,

8 shows schematic representations of examples of sensor / encoder combinations according to the invention with alignment of the sensor plane perpendicular to the surface normal r of the displaceable element,

9a shows an example of a combination of a combination of sensor and encoder according to the invention, in which the sensor plane is parallel to the surface normal r and perpendicular to the direction of movement X a shaft 7 is aligned,

9b shows an example according to the invention of a shaft with two inserted field generating means,

9c shows an example of a shaft according to the invention with two field generating means in a schematic representation, wherein an encoder does not extend over the full length of the encoder and

Fig. 9d an inventive example in a schematic

Representation of a tubular shaft with a radially symmetrical field generating means which is pushed into the interior of the tube.

Figure 1 shows the detail of an actuator, e.g. an actuating device for brakes, with the essential machine elements, in which the magnetically active components mentioned are integrated and with which they form the arrangement or device according to the invention. These are a stator 1, 2, 3 and an actuating element 4, which is a rod, for example, which are displaced back and forth by the distance x during the actuating or resetting process. In this example, the actuating element 4 is actuated by an external force acting on the actuating element, for example via an additional rod

5 acts, operated, both rods via a ball joint

6 are mechanically coupled. The rod 4 is mechanically connected to a shaft 7, wherein the rod 4 and the shaft 7 can also be made from a common piece. In the example, the shaft is designed as a tube. The production from one piece and partial training as a tube is particularly preferred. In this case only the tubular stucco is called a shaft. It is also possible to use a continuous rod 4 according to the invention, which houses the encoder or encoders. The cross section of the rod 4 and the shaft 7 and the opening cross section of the stator 1, 2, 3, which comprises the rod, are preferably circular, but this is not absolutely necessary. For example, cross sections can also be used which are square, triangular or trapezoidal or dovetail-shaped. The stator is preferably a composite of several housing parts, but can also be made in one piece. The sensor carrier 2, in or on which the sensors S are advantageously embedded, clipped, screwed or positively clamped with associated integrated circuits for signal processing SC, is connected in a fixed manner to the housing part 1. The sensor carrier is preferably also a holder for a plug 8 or, alternatively, for a cable, for forwarding sensory signals S (x), which map the displacement x, to electronics processing the signals. Housing part 1 and sensor carrier 2 are preferably connected to one another in a rotationally secure manner. In the example, sensor carrier 2 is pressed onto housing part 1 via a resilient cap 3. But it is also possible that the sensor carrier 2 is screwed to the housing part 1, glued or pressed with another resilient holding mechanism. It is particularly advantageous if a means is provided which provides protection against rotation of the sensor carrier in relation to the housing part.

The arrangement according to the invention is protected against dirt, wetness (corrosion), iron-containing particles, small parts, etc. For this purpose, in the area of the shaft between the housing and the rod 5 there is a sealing means 10, which in the example a rubber sleeve is provided. A rod-side seal 11 also provides protection against dirt.

FIG. 1 shows a particularly preferred variant with regard to the shaft / field generating means (encoder). A tubular encoder (see FIG. 5, types 28a to 33a and 28b to 33b) is inserted into a tubular, thin-walled shaft 7. An iron yoke can also be used advantageously here. This has the advantage that there are no magnetic attraction forces on particles on the inside of the tubular encoder. With the circular design, the encoder is mechanically protected and the shaft can be guided through a pressure-loaded seal.

FIG. 2 shows a linear displacement transducer that largely corresponds to FIG. 1. In contrast to Figure 1, the arrangement is simply redundant. In sensor carrier 2 there are two sensors S, S ', each with sensor circuits SC, SC' assigned to the sensor. Two encoders 9 and 9 'are embedded in the shaft. The position-synchronous signals Sl (x) and S2 (x) are generated by the interaction of the encoder, sensor and sensor circuit.

4 and 5 show further field generating means according to the invention. Variants 17a to 39a are encoders without iron yoke 281.282 and variants 17b to 39b with iron yoke 281.282. In the case of tubular encoders, the iron yoke is a thin inner tube without an air gap to the magnetic material. This tube can preferably also be a mechanical support for particularly thin-walled tubes. In the case of a rod-shaped encoder, the iron yoke is a wire-shaped iron core. According to the invention, the encoders can be provided with the examples of magnetization patterns listed below:

A magnetic encoder period (shown in

Sub-images 18a, 18b, 33a, 33b, 34a, 34b), several magnetic equidistant encoder periods

(shown in partial images 17a, 17b, 25a, 25b, 26a,

26b, 27a, 27b, 28a, 35b), Several magnetic non-equidistant encoder periods

(shown in partial images 19a, 19b, 32a, 32b, 39a, 39b), multi-track magnetic rulers (shown in

Parts 20a, 20b),

Single linear magnetic slope periods

(shown in sub-images 21a, 21b), Multiple linear magnetic slope periods

(shown in sub-images 22a, 22b), individual non-linear magnetic slope periods

(shown in sub-images 24a, 24b), multiple non-linear magnetic slope periods

(shown in partial images 23a, 23b), helical lines with single linear magnetic

Slope period (shown in partial images

29a, 29b, 36a, 36b), screw line with several linear magnetic

Gradient periods (shown in partial images

30a, 30b, 37a, 37b), screw line with several non-linear magnetic

Slope periods (shown ^' in partial images

31a, 31b, 38a, 38b). Examples of encoder shafts are shown in FIG. The material of the shaft 7 should have the lowest possible magnetic conductivity, which is the case, for example, with magnetically non-conductive steel or hard aluminum. The encoders 9, 9 ', 9''can be embedded in different regions 74, 75 of the shaft body. Partial image a) of FIG. 6 shows a tubular shaft 7, in the outer jacket 72 of which a linear encoder 9 is embedded. The ruler shown is one of the type 25a according to FIG. 4. This has a trapezoidal profile and is therefore captively connected to the shaft, provided that the recess 74 is also shaped in a trapezoidal manner. Rulers with a rectangular profile (FIG. 4, for example type 17a) can also be embedded in the outer jacket. When integrated in the outer jacket, it is particularly advantageous to provide the encoders with iron yoke. Partial image b) of FIG. 6 shows a further tubular shaft, in the inner jacket of which several encoders of different lengths are embedded. This variant is advantageous if the shaft is guided through a pressure-loaded seal.

Partial picture c) shows a further tubular shaft, in the wall of which holes 92, 93 'are embedded, into which the encoders rod-shaped encoders can be inserted. In this case, the encoder is advantageously mechanically completely protected and the shaft can be guided through a pressure-loaded seal.

Partial image d) shows another shaft, which can be designed as a very thin-walled tube in comparison to the embodiment in partial image e), while the wall thickness is locally reinforced to accommodate the bores.

Partial image e) of FIG. 6 shows another shaft with the special feature that the bores of the wall are eccentrically are guided, wherein the diameter of the holes is larger than the wall thickness of the shaft. This offers the advantage that encoders (for example types 34a to 39a and 34b to 39b) with a relatively large diameter and correspondingly higher magnetic field strength can be used captively. This is the case, for example, if the radius and the remaining wall thickness remaining after the bore are smaller than the wall thickness of the shaft.

FIG. 3 shows sensor arrangements with different orientation of the sensors with respect to the shaft. The encoder 9 generates a periodic field line course 33 in the longitudinal direction of the encoder. The field line course can also be called an encoder track. The field line course shown is characteristic of magnetic material with zones 31, 32 of a homogeneous magnetic material, for example a ferrite, which are magnetized alternately in the north / south pole orientation. The encoder track expands into the image plane. In the first variant shown in the left partial image of the figure, AMR sensors are connected to form a bridge circuit 13, the sensors all coming to lie in a common plane 131. The plane in the left partial image is oriented perpendicular to the encoder plane, ie parallel to the surface normal of the displaceable element, and parallel to the direction of movement or to the longitudinal axis of the displaceable element. In addition, the lamella structure of the sensors is preferably oriented perpendicular or parallel to the surface normal in this orientation. If this structure is moved in the direction X along the encoder track, the vector of the magnetic field strength rotates through the bridge plane and the bridge produces an output signal with two signal periods 14 per encoder period λ. This effect is hereinafter referred to as the 2α effect. - 1 !

In the diagram on the right, the common level of the bridge circuit is aligned parallel to the encoder level, i.e. perpendicular to the surface normal of the displaceable element. If the displaceable element is moved in the direction X along the encoder track, only a partial vector of the magnetic field strength acts on the bridge layer, so that an output signal with only one signal period 16 per encoder period λ is produced. This effect is hereinafter referred to as the lα effect. Both effects can be implemented in specific sensor elements that are either designed to detect a direction of movement or to recognize no direction of movement. When using the 2α effect, the sensor elements contain in particular two bridges rotated by 45 °, which provide SIN / COS signals from which the direction of movement can be derived using known methods. With the lα effect, the spatial phase shift of the bridge branches compared to the encoder period λ is used to detect the direction of movement.

A particularly simple arrangement is obtained when only one of the sensor bridges from FIG. 3 is used. In this case, however, the possibility of detecting the direction of movement must be dispensed with.

If sensors based on the 2α effect are used, a high path resolution can be achieved in particular if known interpolation networks are connected in series which quantize the encoder period λ and thus the path x in fine detail.

Examples of sensor / encoder combinations with high spatial resolution are shown in FIG. 7. The sensors shown work according to the AMR principle and use the principle of the 2α effect. The combination is in drawing a of a sensor 40 with a downstream electronic network 41 is shown. The network is used for interpolation and signal processing. The network and the sensor are preferably integrated in a common sensor module A. The network is built internally so that an interpolation factor with a value of at least (λ / 8) / Δx is used, where Δx corresponds to the smallest resolvable path increment. In partial image a, the sensor plane of the sensor 40 is aligned in the direction of the direction of movement X and in the direction of the surface normal of the encoder, so that the field vector of the generated magnetic field rotates periodically through the plane of the AMR layer in the encoder used.

According to drawing b, sensor module A provides a binary signal as a sign for the direction of movement and at a distance

Δx an incremental signal pulse train V * (n * Δx).

In partial image c and d of FIG. 7, examples of sensor / encoder combinations are shown which differ from the embodiment shown in partial image a with regard to the orientation of the sensor plane. In contrast to partial image a, the sensor plane is oriented perpendicular to the direction of movement X here. The encoders of type 29a or 31a shown here generate a magnetic field that rotates through the plane of the AMR layer in the same way as partial image a.

The sensors 40 are connected to a module for signal processing SC, so that a location-dependent signal S (x) is produced which corresponds to that of sensor A in its effect.

In Figure 8, examples of sensor / encoder combinations are shown that use the AMR principle according to the lα effect work. However, they generate different output signals on the same encoder.

Part a shows a sensor module B in combination with an encoder of type 21a. If sensor module B is moved in the positive or negative X direction, the sensor reacts either with an increase or a decrease in the output signal depending on the direction. The analog signal can be quantized almost arbitrarily by an analog-digital converter in order to achieve a high path resolution. Sub-image b of FIG. 8 shows a sensor module C in combination with an encoder of the type 17a. The output signal of the module is a pulse sequence, the sequence of which corresponds to the number of scanned poles of the encoder. A bit sequence with additional information is imprinted between the pulses using the pulse pauses that are not required. It makes sense to design the additional information so that the direction of movement of the encoder can be derived from it.

Sub-picture c shows an exemplary embodiment with two sensor modules of type D (reference symbols D1 and D2). However, type B sensor assemblies can be used as well

(Reference symbols B1 and B2). A suitable encoder is, for example, type 17a. The blocks Dl (or Bl) and D2

(or B2) are mutually offset by half a pole width and generate two mutually orthogonal signals. When using two type B sensor modules, SIN or COS signals are generated. The output signal can be converted into a high-resolution quantized location signal with directional information in accordance with the manner described above in FIG. 8 (2α sensor). When two type D sensors are used, square-wave signals are generated, from which the directional information can also be derived in an analog manner. However, the reachable local resolution of the total path limited to the number of poles.

FIGS. 9a to 9d show further examples of encoder / sensor combinations.

The shaft 7 shown in FIG. 9a with an inserted encoder 9 (type 21a) is combined with a 2α sensor 40. Its output signal is fed to an electronic circuit SC, which generates the signal S (x).

Figure 9b shows a shaft 7 with two inserted encoders 9,9 'of type 17a. They are type A sensor assemblies that produce high-resolution signals. These signals are then processed in a further electronic circuit SC3. This circuit monitors the function of both sensor modules according to known redundancy principles and generates the signal S (χ), which may have been cleaned of interference, at the output.

FIG. 9c shows a shaft 7 with two encoders of the types 17a and 18a with different lengths. Encoder type 17a is combined with a high-resolution sensor module of type A and encoder type 18a with a sensor module D with low spatial resolution. In the local area in which both sensor modules are in the area of the respectively assigned encoder (redundancy area), the sensor signals are processed in a further electronic circuit SC3 in a manner known per se according to redundancy principles to form an output signal S (x).

The exemplary embodiment in FIG. 9d shows a tubular shaft with an inserted, also tubular encoder, the encoder having an iron yoke of type 28b. In connection with several sensors, redundant operation is particularly easy in this way. Two similar types with high spatial resolution come as sensors 40. solution, and as sensor D a type with a comparatively low spatial resolution is used. Here too, the sensors 40 with the circuits SCI and SC2 form sensor assemblies of type A. All three sensor signals are processed in an electronic circuit SC3 according to redundancy principles known per se to form an output signal S (x). The cylindrically symmetrical shape of the encoder shaft is particularly favorable here, since the sensors can be arranged at any angle on the circumference of the shaft. Due to the iron yoke, no iron particles can stick to the interior of the shaft.

The type 28b encoder used consists of a plastic-bonded magnetic material.

The sensors or sensor modules which can be used according to the invention are predominantly commercially available. Examples of commercial sensors and sensor assemblies are listed below:

Angle sensor LK28, IMO Wetzlar (2α) Angle sensor LK15, IMO Wetzlar (2α) AMR bridge KMZB34, Philips Hamburg (lα) ASIC UA1272, Philips Hamburg (lα) Active wheel sensor OH223, Philips Hamburg (lα) Active wheel sensor OH243, Philips Hamburg ( lα) Active wheel sensor OH191, Philips Hamburg (lα) Active wheel sensor OH203, Philips Hamburg (lα)

All listed lα types are offered with a uniform housing shape and have a 2-wire connection. The output signal is provided in the form of a current signal. Some size specifications for the exemplary embodiments are specified below:

^■ Thickness of the magnetic layer of the encoder:

> = 1mm (preferably 0.2 to 4 mm)

• Length of an encoder:

54 mm (preferably 10 to 100 mm)

Example for the realization of a high resolution in the range of approx. Δx = 0.1 mm:

• Air gap (encoder / sensor element): about 2 mm

(preferably greater than about 0.5 and less than about 5 mm)

• polar period λ:

6 mm (preferably less than or equal to 6 mm)

^{■ Sensor} element:

Angle sensor LK28, IMO, Wetzlar (2α)

• Network:

8-way interpolation network type 601.3028.02, IMO, Wetzlar

Example for the implementation of a resolution in the range of about Δx = 2.0 mm:

Air gap (encoder / sensor element):

2 mm (preferably about 0.5 to about 2.5 mm) pole period λ:

4 mm (preferably 0.5 to 5 mm) sensor element:

Active wheel speed sensor OH223, PHILIPS Hamburg (lα)

Claims

claims

1. Linear displacement transducer for motor vehicles with at least one axially displaceable, one-part or multi-part composed element (4,5,7) and a stator (1,2,3), one or more field generating means (9,9 ') in the displaceable element a permanently present, modulated magnetic field line course (33) and / or modulated magnetic field strength are arranged, and the field generating means or have along their longitudinal axis at least one permanent magnetic material with a modulated field line course and / or with a modulated field strength (31, 32), and with the stator one or more sensor modules are connected in a fixed position, the at least one magnetic field sensor

(S, S ') and possibly one or more sensor circuits (SC, SC) and which convert the magnetic field line course in whole or in part into further processable output signals and the magnetic field sensors either according to the AMR principle, the GMR principle or the Hall principle work, characterized in that the displaceable element is guided by a bearing (11) connected to the stator, which at least partially encompasses the displaceable element and thereby guides axially that the sensor module or sensors are connected to the stator in a stationary manner and that along the longitudinal axis of the displaceable element or the field generating means are positively connected to the displaceable element.

2. Linear displacement transducer according to claim 1, characterized in that the positive connection is established by at least one of the following steps:

- fitting an elongated field generating means (73) in a recess (74) on the surface (72) of the displaceable element,

Using a profile tube with an axial recess (76) and with an inner surface (72), and fitting an elongated field generating means (73) into a further recess (75) provided on the inner surface (72),

- Inserting a field generating means (9, 9 ') into a bore (92, 93, 92', 93 ') arranged in the area of the casing (71) of the displaceable element and parallel to the main axis of the displaceable element

- Use of a profile tube with an axial recess (76), with an axial recess (76) and with an outer jacket region of the profile tube (71), and producing a ring fit, in which the field generating means (91) is pushed into the displaceable element, whereby for All steps apply that the surface of the displaceable element (72) is essentially free of elevations and depressions.

3. Linear displacement sensor according to claim 1 or 2, characterized in that the magnetic field sensors work according to the AMR principle.

4. Linear displacement sensor according to at least one of claims 1 to 3, characterized in that the displaceable element comprises a shaft (7) which carries the field generating means, an actuating element (4) mechanically connected to the shaft and a force transmission means (6), so that when the actuating element (4) is actuated by means of an external force which acts on the force transmission means, the shaft and thus the field generating means are essentially free of tension and / or Compressive forces is axially displaced.

5. Linear displacement sensor according to at least one of claims 1 to 4, characterized in that a magnetic yoke (281, 282) is integrated in the shaft.

6. Linear displacement sensor according to at least one of claims 1 to 5, characterized in that sealing means (10, 11) are present which protect the field generating means against contamination and corrosion.

7. Linear displacement sensor according to claim 6, characterized in that the sealing means (10, 11) comprise bellows, rubber sleeves (10) and sliding seals (11).

8. Linear displacement sensor according to at least one of claims 1 to 7, characterized in that the fixed connection between the sensor module / s and stator is carried out by a sensor carrier (2) which is part of the stator and is mechanically detachably connected to it.

9. Linear displacement sensor according to at least one of claims 1 to 8, characterized in that a redundant function is ensured by arranging at least two magnetic field sensors in the linear displacement sensor, the magnetic field sensors either tapping the magnetic field of a common field generating means or some or all sensors the magnetic field of one tap each field generating means specifically assigned to a magnetic field sensor.

10. Linear displacement transducer according to claim 9, characterized in that a first magnetic field sensor is offset relative to a second magnetic field sensor in the axial direction by up to a magnetic field period, so that the output signal of the second magnetic field sensor is phase-shifted from the output signal of the first magnetic field sensor.

11. Linear displacement transducer according to claim 9 or 10, characterized in that at least one magnetic field sensor is present, which has a lower resolving power compared to another magnetic field sensor present in the arrangement.

12. Linear displacement sensor according to at least one of claims 4 to 11, characterized in that the shaft (7) is a cylindrical tube, the permanent magnetic material (91) has the shape of a cylindrical tube, the magnetic field being radially symmetrical along the longitudinal axis of the magnetic material is (28a, 28b) and the permanent magnetic material is pushed into the axial recess (76) of the shaft.

13. Linear displacement sensor according to at least one of claims 1 to 12, characterized in that at least one sensor module contains a bridge circuit made of magnetic field sensors (13), the main plane (131) of which is aligned parallel to the surface normal (r) and the longitudinal axis (X) of the displaceable element is.

14. Linear displacement sensor according to at least one of claims 1 to 10, characterized in that at least one sensor module is a bridge circuit made of magnetic sensors (15) contains, whose main plane (151) is oriented perpendicular to the surface normal (r) of the displaceable element.

15. Use of the linear displacement sensor according to at least one of claims 1 to 14 for measuring the pedal or lever position in an actuating device for braking motor vehicles.