DE20007862U1 - Steering angle measuring system - Google Patents

Description

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PETRI AG
Bahnweg 1

63743 Aschaffenburg

Steering angle measuring system

Description

The invention relates to a steering angle measuring system for determining the steering angle of a steering system in a motor vehicle according to the preamble of claim 1.

From DE 197 58 104 A1, a method and a device for determining the steering angle in a motor vehicle are known by means of a code for determining the angle that is applied over an angular range of 360°, wherein the code and a detector arrangement that scans the code are mounted so that they can rotate relative to one another. The code is formed by a coding ring that is attached to an assembly of the

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Steering system and which has transparent and opaque areas, the arrangement of which defines the code. A photodetector arrangement with at least one light-emitting diode and a photodetector line in the form of a CCD line is used for contactless scanning of the coding ring, with a lens arrangement connected between the coding ring and the CCD line, which focuses the light reflected by the coding ring onto the CCD line.

The steering angle measuring system known from DE 197 58 104 enables a reliable determination of the steering angle in motor vehicles. However, there is the disadvantage that the design of the coding ring known from DE 197 58 104 A1 and the associated photodetector arrangement require a space that limits the possible uses of this steering angle measuring system in a motor vehicle.

The invention is therefore based on the object of creating a steering angle measuring system of the type mentioned at the beginning, which can be produced inexpensively using simple means and is characterized by a small space requirement.

This object is achieved according to the invention by creating a steering angle measuring system with the features of patent claim 1.

It is then provided that the code carrier is a light-permeable material layer arranged on a reflective substrate, into which the code is directly optically burned.

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By burning the code into the code carrier, the effective reflectivity of the substrate behind it (reflectivity of the substrate taking into account the effects of the code carrier, i.e. the reflectivity of the arrangement consisting of substrate and code carrier) is locally influenced, whereby the angle information contained in the code can be read by means of a suitable scanning device.

The design of the code carrier according to the invention is based on the same functional principle as a write-once optical storage disk (WORM: write once read many). In the context of the present invention, the data written onto the code carrier form a code in the form of a measuring graduation, which allows angle determination by means of a suitable scanning device that scans the code carrier without contact.

Writable optical storage disks and the associated writing devices, which use a writing laser to generate short, intense laser pulses in order to vaporize or melt material from a coating on the storage disk at specific points and thus write data onto the storage disk, are manufactured in large quantities. This technology is therefore already sufficiently advanced, which enables the corresponding data storage devices to be manufactured cost-effectively, precisely and reliably. By transferring this technology from a completely different technical field, namely the manufacture of mass storage devices, to measurement technology, the advantages of this technology can be used in steering angle measurement systems.

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It is particularly important that structures with an extension (width) of less than 1 /im can be formed on the code carrier using a writing laser. This means that codes can be generated on very small, ring-shaped code carriers, in particular circular code carriers with a small diameter, which allow angle determination with very high resolution.

This enables, for example, the arrangement of the code carrier designed according to the invention in the steering spindle area of a motor vehicle, where only very little space is available for the installation of an angle measuring system and the diameter of the code carrier is therefore limited to approximately 40 mm.

However, the steering angle measuring system according to the invention has the advantage over the steering angle measuring systems known from the prior art not only that the code carrier itself can be made very compact, but this also applies in the same way to the scanning device by means of which the code carrier is scanned to determine the steering angle. This is because no CCD line with a correspondingly large, associated lens arrangement is required to scan the code carrier provided according to the invention, but rather a simple receiver in the form of a photodiode is sufficient. This receives light that is emitted by a light source of the scanning device, e.g. in the form of a laser diode, in the direction of the reflective substrate provided with the code carrier and is reflected by it. Since the reflection of the light is influenced by the code applied to the code carrier, the position of the scanning device in relation to the

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This means that the scanning device can also be constructed very compactly, whereby the technologies known from the production of mass storage devices can be adopted.

An important application of the steering angle measuring system according to the invention is to transmit the angular position of the steering wheel to the braking system so that during a braking process the individual vehicle wheels can be braked in a targeted manner depending on the angular position of the steering wheel.

In order to optically burn the code onto the code carrier using a writing laser or the like, material can be evaporated at certain points on the translucent material layer forming the code carrier. This creates marks on the code carrier in the form of elevations and depressions, with the elevations corresponding to those places on the code carrier where no material was evaporated, while the depressions correspond to those places where material was removed. The elevations and depressions influence the reflectivity of the substrate coated with the code carrier, so that the code can be easily scanned optically.

Alternatively, the code can also be generated by using laser pulses to selectively melt the translucent material layer arranged on the reflective substrate that serves as the code carrier. After the laser pulse has died down, the melted material cools down very quickly and solidifies in an amorphous form.

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This also influences the reflectivity of the substrate behind it, which in turn enables optical scanning.

The reflective substrate can be formed by a reflective surface of the steering system itself, on which the material layer forming the code carrier is applied. For this purpose, a corresponding material layer, e.g. an Azu color layer commonly used in writable disk storage devices, is applied, in particular vapor-deposited, to a suitable ring-shaped component of the steering system.

Alternatively, the reflective substrate can also be formed by a reflective surface of a separate, ring-shaped base body, on which the material layer forming the code carrier is applied and which is attached to an assembly of the steering system. The substrate can in particular have a gold or silver reflective layer.

The code can be formed, for example, by a so-called bar code, in which marks in the form of lines burned into the code carrier extend either transversely to the circumferential direction of the code carrier (as is common practice with angle measuring systems with bar codes) or in the circumferential direction of the code carrier (as is the case with the pits of compact discs). To form a code, the width or length of the lines or the distance between adjacent lines can be varied. On the other hand, a digital code can also be formed in which, for example, all the lines are identical and it only depends on whether a line is present at certain points.

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is present or not. Bars can be considered to be those places on the code carrier where material has been evaporated or melted to form a bar.

Using a bar code or other code forms, an absolute angle measuring system can be created in a simple manner by forming different code words on the code carrier, each of which represents a defined angle range on the code carrier and which are arranged one behind the other along the circumference of the code carrier.

Since the marks burned into the code carrier as bits of the digital code (e.g. in the form of bars) can have an extension of less than 1 μπλ along the circumference of the code carrier, code words with an extension in the order of 0.01 mm along the circumference of the code carrier can be formed.

Therefore, with a very simple absolute code constructed by stringing together different code words, angular resolutions of a fraction of a degree can be easily achieved even with very small code carriers (with a correspondingly small diameter of e.g. 40 mm). If the maximum possible resolution is not even aimed for due to the small spatial extent of the code words, the assigned code word can be repeated several times within the respective angular range - e.g. angular ranges of 1° each with a resolution of 1°. If, for example, an angular range of 1° on the code carrier has an extension of 1 mm along the circumference of the code carrier, but the individual code words

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only an extension of 0.1 mm each, it would be possible to repeat the corresponding code word ten times within each individual code area.

The greater the desired resolution, the more different code words must be provided and the greater the complexity of the individual code words, e.g. in terms of the number of bits the code words consist of.

The particular advantage of the solution according to the invention is evident when an absolute code is formed from a large number of different code words arranged next to one another, since the extent of the individual code words along the circumference of the code carrier determines the maximum possible angular resolution and the extent of these individual code words is minimized according to the invention. Of course, the solution according to the invention can also be used for relative codes with a periodic sequence of identical marks.

In a preferred embodiment of the invention, the code has at least two code tracks running next to each other along the circumference of the code carrier and containing the same angle information, whereby the code tracks arranged next to each other can in particular be identical. By determining the angle by scanning two or more code tracks, each containing the same angle information, tolerances of the angle measuring system, in particular a radial offset within the arrangement, can be compensated. The individual code tracks can run either circularly or spirally on a circular code carrier.

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It is only important that the code carrier contains angle information over the entire angle range of interest, usually 360°.

A scanning device is provided for optical scanning of the code, which has a transmitter, e.g. in the form of a laser diode, and a receiver, e.g. in the form of a photodiode. The transmitter emits radiation to the substrate coated with the code carrier, which reaches the receiver after reflection from this substrate. The code applied to the translucent code carrier influences the reflection of the light on the substrate, which leads to a characteristic radiation image on the photo receiver, which is evaluated by an evaluation device (evaluation electronics) downstream of the receiver to determine the current steering angle.

According to a variant of the invention, the code is scanned by means of the scanning device in the radial direction with respect to the axis of rotation of the two assemblies that can rotate relative to one another. The scanning can take place both on the inner diameter and on the outer diameter of the ring-shaped code carrier.

According to another variant of the invention, the code is scanned by means of the scanning device in the axial direction with respect to the axis of rotation of the two mutually rotatable assemblies.

It is possible to attach the code carrier or the scanning device directly to the steering wheel and to assign the other of these two components to a module that is fixed with respect to the steering wheel. According to a preferred

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In this embodiment, the code carrier is arranged on the steering wheel and the scanning device on the steering column or steering spindle cover or on a turn signal switch.

Alternatively, an additional structural unit consisting of a rotor and a stator can be attached to the steering system, which are rotated against each other when the steering system is actuated in accordance with the movement of the steering wheel, wherein the code carrier on the one hand and the scanning device on the other hand are each assigned to one of the two functional elements, rotor or stator.

The rotor and the stator can simultaneously form a housing for the steering angle measuring system, which protects the code carrier and the scanning device. The rotor is attached to the steering wheel or the steering column, for example, and the stator to a component that is fixed in relation to the steering wheel or the steering column, e.g. the steering column cover. Before installation in the steering system, the rotor and the stator are preferably temporarily locked together.

With regard to further possible geometric arrangements of the code on the one hand and the scanning device on the other hand, reference is made to DE 197 58 104 A1, which relates to a different type of steering angle measuring system, but the arrangement of the code or the individual code tracks and the associated scanning device can be transferred to the present technical solution.

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The rotor can, for example, be made as an injection-molded part made of PC and designed to be reflective, either by using a reflective material or by coating it with a reflective material. The code carrier is then applied to this, e.g. in the form of a translucent varnish, into which the marks required to form the code are then burned.

Further advantages of the invention will become clear from the following description of embodiments with reference to the figures.

Show it:
Fig. 1 -

a cross-section through a steering angle measuring system which is arranged in a housing consisting of a rotor and a stator and in which a code of the steering angle measuring system is scanned axially;

Fig.2

a modification of the embodiment of Fig. 1, in which the code is scanned radially;

Figures 3a
and 3b -

a further embodiment of a scanning device with which the code from Figures 1 and 2 can be scanned;

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Fig. 4a and
and 4b -

an embodiment of a code carrier with two different variants of a code burned into it;

Figures 5a
and 5b -

a representation of a steering angle measuring system consisting of a code carrier arranged on a steering wheel skeleton with a burned-in code and a scanning device arranged on a steering column switch for scanning the code.

Figure 1 shows a cross section through a rotor 10 and a stator 20, which form a housing for a steering angle measuring system for determining the steering angle in a motor vehicle.

The rotor 10 is attached to a rotating assembly of the steering system of the motor vehicle, e.g. to the steering wheel, via locking elements 16 (one of which is shown as an example in Fig. 1), and the stator 20 is connected to a stationary assembly of the steering system, e.g. to a steering column or steering spindle cover, via further locking elements 26 (one of which is shown as an example in Fig. 1). The rotor 10 and the stator 20 can be rotated relative to one another about an axis of rotation A, so that when the steering wheel rotates, they rotate relative to one another in accordance with this movement.

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The stator 20, which is rotationally symmetrical with respect to the axis of rotation A, forms a base part of the housing accommodating the steering angle measuring system, with a rear wall 21 of the stator 20, provided with a recess 21a, forming the bottom of the housing and the side wall 22 of the stator 20 forming part of the side wall of the housing. Two rotationally symmetrical webs 23, 24, which run essentially parallel to the side wall 22, protrude perpendicularly from the rear wall 21 of the stator 20. One of these webs (23) is arranged directly next to the side wall 22 and forms with it a receptacle which is essentially U-shaped in cross section. The second web 24 is offset from the first-mentioned web 23 towards the axis of rotation A of the stator 20.

The rotor 10, which is also rotationally symmetrical with respect to the axis of rotation A, forms a cover that can be placed on the stator 20 and is rotatably mounted in it, so that the rotor 10 and stator 20 form a housing for accommodating the steering angle measuring system. A rear wall 11 of the rotor 10, provided with a recess 11a, forms the upper cover surface of the housing and the side wall 12 of the rotor forms a component of the side wall of the housing. In addition to the side wall 12 of the rotor 10, a web 13 of rotationally symmetrical design extends parallel to the side wall 12, which projects perpendicularly from the rear wall and which, together with the side wall 12, forms a receptacle that is essentially U-shaped in cross section.

The two U-shaped receptacles 12, 13 and 22, 23 of the rotor 10 on the one hand and the stator 20 on the other hand

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interlock with their legs and thus form an essentially closed side wall of the housing that houses the steering angle measuring system.

A laser diode 6 with electrical connections 7 is arranged in a receptacle 25 in the rear wall 21 of the stator 20 as an essential component of the scanning device 5 of the steering angle measuring system, which can emit laser beams parallel to the axis of rotation A (axial) towards the rear wall 11 of the rotor 10. In the radiation area of the laser diode 6, a circular, reflective substrate 2 extends on the rotor 10 over the entire angle of 360°, which is attached to the rear wall 11 of the rotor 10 opposite the laser diode 6 and is provided with a code carrier 1. The code carrier 1 preferably consists of a translucent color layer, e.g. a bluish Azu color layer, which is applied to the substrate 2 and has a code in the form of a measuring graduation which allows the angle of rotation of the rotor 10 with respect to the stator 20 and thus the steering angle of the motor vehicle to be determined.

The code carrier 1 can have a large number of elevations and depressions arranged next to one another along the circumference of the code carrier, from which different code words arranged next to one another are formed, each of which represents a specific angular range of the rotor 10. These elevations and depressions can be formed on the code carrier by evaporating material at certain points on the code carrier 1, creating depressions with respect to which the areas with non-evaporated material act as elevations. These elevations and depressions influence the reflection of the light emitted by the

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Laser diode 6 radiates light onto the reflective substrate 2 and thus acts as marks of a code applied to the code carrier 1.

The light reflected by the substrate 2 forms a light-dark pattern on a photodiode serving as a receiver (and not shown in Fig. 1), which is characteristic of the angular range of the rotor 10 scanned by the laser diode 6, since each angular range is assigned a characteristic code on the code carrier 1.

With reference to Fig. 1, it should also be noted that locking elements 27 are provided on the stator 10, which engage in the recess 11a of the rear wall 11 of the rotor 10 and via which the rotor 10 and the stator 20 can be locked together to form a housing before installation in the steering system.

Fig. 2 shows a modification of the embodiment of Fig. 1, the essential difference being that here the scanning of the code by means of the laser diode 6 takes place radially with respect to the axis of rotation A.

For this purpose, a receptacle 25 for the laser diode 6 is formed in the radially inwardly offset web 24 of the stator 20, from which the laser diode 6 radiates radially in the direction of the web 13 arranged next to the side wall 12 of the stator 10. The substrate 2 coated with the code carrier 1 runs in a ring shape along the entire circumference of the rotor 10 on this web 13.

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With regard to the further technical features of the arrangement shown in Fig. 2, reference is made to the above description of Fig. 1; identical components are provided with identical reference numerals in these two figures.

Of course, in the embodiment shown in Fig. 2, the arrangement of the laser diode 6 on the one hand and of the substrate 2 and the code carrier 1 on the other hand can be spatially swapped by arranging the laser diode 6 radially further outward with respect to the substrate 2 and the code carrier 1.

In both embodiments, it is also easily possible to arrange the laser diode 6 on the rotor and the substrate 2 with the code carrier 1 on the stator. In addition, the substrate 2 does not necessarily have to be a separate ring-shaped component attached to the rotor 10 or stator 20, but the code carrier 1 could also be applied directly to the rotor 10 or the stator 20 if the corresponding wall of the rotor or stator reflects sufficiently.

Figures 3a and 3b show a modification of the scanning device 5 which can be used in the embodiments according to Figures 1 and 2 for scanning the code carrier 1 arranged on the substrate 2. Figure 3b shows a plan view of the scanning device 5 shown in cross section in Figure 3a together with the code carrier 1 and the holder 25.

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The scanning device 5 according to Figures 3a and 3b comprises a laser diode 6, by means of which a laser beam can be generated which is reflected by the substrate 2 coated with the code carrier 1, and a photodiode arrangement 8 which receives the reflected laser beam. The photodiode arrangement 8 arranged next to the laser diode 6 here comprises several individual sensor elements. Instead, however, a photodiode with only a single sensor element can also be used as a receiver for the reflected laser beam. When using several sensor elements, complete code words of the code carrier 1 can be detected simultaneously. In the other case, the information of the code carrier 1 corresponding to a complete code word is read in one after the other and recognized by the associated evaluation unit as a code word.

In principle, a CCD line can also be used as a receiver for the reflected laser beam, although this involves increased effort and space requirements.

Fig. 4a shows a plan view of a circular ring-shaped code carrier 1 which is applied as a coating to a corresponding circular ring-shaped substrate and into which a code 3, 4 is burned in accordance with the detailed illustration in Fig. 4b. Fig. 4b shows in particular that the data 3 and 4, which form a code word or a specific section of the code, can be burned into the code carrier 1 next to one another both along the circumference (at position 3) and in the radial direction (at position 4).

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Figures 5a and 5b show a further embodiment of a steering angle measuring system according to the invention, in which the code carrier 1 with the associated substrate 2 is arranged directly on the steering wheel 110 and in which the associated scanning device with a laser diode 6 and a photodiode arrangement 8 is provided on a cover surface 122 of a steering column switch 120.

The steering wheel 110 shown in cross section in Fig. 5a comprises a steering wheel hub 111, via which the steering wheel 110 can be connected in a rotationally fixed manner to a steering column or steering spindle 109 (Fig. 5b), a steering wheel skeleton 112, a casing 113 of the steering wheel skeleton 112, a contact carrier 115 spring-connected to the steering wheel skeleton 112 for triggering a horn function or the like, and an airbag module 116, indicated by dashed lines, arranged in the central steering wheel area. If a driver exerts a force on the cover of the airbag module 116, this is transferred to the contact carrier 115, causing it to move towards the steering wheel skeleton 112 and the horn function to be triggered.

Concentrically to the hub 111 of the steering wheel 110, a circular substrate 2 is arranged on the steering wheel skeleton 112, which is coated with a code carrier 1. The code carrier 1 is oriented in such a way that it can be scanned by means of a scanning device 5 arranged on the steering spindle side (see Fig. 5b).

In Fig. 5b, a steering column switch 120 is shown in perspective, which has a housing 121 that is arranged in a rotationally fixed manner within the motor vehicle, e.g. by fastening in the area of the dashboard. In its base

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surface 122, the housing 121 has an opening 123 through which the steering column 109 projects into the interior of the housing 121. In its cover surface 124 opposite the bottom surface 122 and facing the steering wheel 110, the housing has a recess 125 through which the hub 111 of the steering wheel 110 (see Fig. 5a) can be placed onto the steering column 109 in a rotationally fixed manner.

In the cover surface 124 of the housing 121, a scanning device 5 is also arranged in such a way that the code carrier 1 can be scanned with it to determine the steering angle (i.e. to determine the angular position of the steering wheel 110 with respect to the steering column switch 120). The scanning device 5 consists of a laser diode 6 and a photodiode arrangement 8, as shown in Fig. 3b.

The steering column switch 120 accommodates switch levers 126, such as turn signal switches, with which various electrical functions of a motor vehicle can be triggered.

Claims (15)

1. Steering angle measuring system for determining the steering angle of a steering system in a motor vehicle with a ring-shaped code carrier which has a code in the form of an angular division, and a scanning device for scanning the code, the code carrier and the scanning device each being assigned to one of two mutually rotatable assemblies of the steering system, characterized in that a light-permeable material layer arranged on a reflective substrate ( 2 ) is provided as the code carrier ( 1 ), into which the code ( 3 , 4 ) is optically burned. 2. Steering angle measuring system according to claim 1, characterized in that material has been evaporated at specific points on the code carrier ( 1 ) to form the code ( 3 , 4 ). 3. Steering angle measuring system according to claim 1, characterized in that material has been melted at certain points on the code carrier ( 1 ) to form the code ( 3 , 4 ). 4. Steering angle measuring system according to one of the preceding claims, characterized in that the reflective substrate ( 2 ) is formed by a reflective surface of the steering system, on which the material layer forming the code carrier ( 1 ) is applied. 5. Steering angle measuring system according to one of claims 1 to 3, characterized in that the reflective substrate ( 2 ) is formed by a reflective surface of an annular base body on which the material layer forming the code carrier ( 1 ) is applied and which can be fastened to an assembly of the steering system. 6. Steering angle measuring system according to one of the preceding claims, characterized in that the code is designed as a bar code. 7. Steering angle measuring system according to one of the preceding claims, characterized in that the code ( 3 , 4 ) comprises a plurality of different code words, each of which represents a defined angle range on the code carrier ( 1 ) and which are arranged one behind the other along the circumference of the code carrier ( 1 ). 8. Steering angle measuring system according to one of the preceding claims, characterized in that the code has at least two code tracks with matching angle information running alongside one another along the circumference of the code carrier ( 1 ). 9. Steering angle measuring system according to one of the preceding claims, characterized in that the code ( 3 , 4 ) is optically scanned by means of the scanning device ( 5 ). 10. Steering angle measuring system according to claim 9, characterized in that the scanning device ( 5 ) has a transmitter ( 6 ), in particular in the form of a laser diode, and a receiver ( 8 ), in particular in the form of a photodiode arrangement. 11. Steering angle measuring system according to one of the preceding claims, characterized in that the code ( 3 , 4 ) is scanned by means of the scanning device ( 5 ) in the radial direction with respect to the axis of rotation (A) of the two mutually rotatable assemblies ( 10 , 20 ). 12. Steering angle measuring system according to one of the preceding claims, characterized in that the code ( 3 , 4 ) is scanned by means of the scanning device ( 5 ) in the axial direction with respect to the axis of rotation (A) of the two mutually rotatable assemblies ( 10 , 20 ). 13. Steering angle measuring system according to one of the preceding claims, characterized in that the code carrier ( 1 ) or the scanning device ( 5 ) is arranged on the steering wheel ( 110 ). 14. Steering angle measuring system according to claim 13, characterized in that the code carrier ( 1 ) is arranged on the steering wheel ( 110 ) and the scanning device ( 5 ) is arranged on a steering column or steering spindle cover or a steering column switch ( 120 ). 15. Steering angle measuring system according to one of claims 1 to 12, characterized in that an additional structural unit consisting of a rotor ( 10 ) and a stator ( 20 ) is attached to the steering system, which are rotated relative to one another when the steering system is actuated in accordance with the movement of the steering wheel, and that the code carrier ( 1 ) on the one hand and the scanning device ( 5 ) on the other hand are each assigned to one of the two functional elements rotor ( 10 ) and stator ( 20 ) respectively.