Device for detecting a rotational angle of a rotatable part

A device for detecting a rotational angle of a rotatable part, e.g., a steering wheel, includes at least one magnet, at least one sensor which detects the magnetic field of the magnet, at least one housing in which the sensor and/or the magnet is/are movably situated relative to one another, and at least one printed circuit board which is contacted in an electrically conductive manner by at least one connecting element of the sensor. The printed circuit board has at least one interface or a connector plug from which the output signal of the sensor or an output signal derived therefrom is relayed to an evaluation unit which ascertains the absolute position of the rotational angle as a function of the output signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for detecting a rotational angle of a rotatable part.

2. Description of Related Art

A generic system for contactless detection of a rotational angle of a rotatable element is known from published German patent application document DE 195 43 562 A1. In order to easily detect the absolute rotational position of the rotatable element, the sensor system is made up of at least two sensor elements, and is situated relative to the rotatable element in such a way that in any rotational position, the field lines emanating from the rotatable element extend transversely with respect to the sensor structures specified by the direction of a current in the sensor elements. Using various electronic evaluation devices, the directional components of the field lines may be evaluated for ascertaining the rotational position by evaluating the phase position between input signals and output signals of the particular sensor elements. Either sinusoidal or square alternating voltages or direct current voltages are supplied as input signals.

An object of the present invention is to further simplify the device for detecting a rotational angle.

BRIEF SUMMARY OF THE INVENTION

The device according to the present invention for detecting a rotational angle of a rotatable part has the advantage over the related art that, due to the relative detection of the rotational angle, it is not necessary to spatially integrate internal evaluation units, for example microcontrollers, etc., directly into the sensor in order to compute an absolute steering angle. A more compact installation space may also be achieved in this way. Corresponding subsequent steps such as calibration of the sensor during fabrication in the manufacturing plant are dispensed with. This results in lower manufacturing and assembly costs. Compared to sensors having optical measuring elements, the device according to the present invention is very robust, since the relatively rapid loss of its accuracy or function due to the possible penetration of contaminants no longer occurs.

In one advantageous refinement, a further sensor is provided for detecting the magnetic field of the magnet, the sensor being situated at a distance from the first sensor in such a way that an output signal results which is phase-shifted with respect to the output signal of the other sensor. In addition to the relative change in position, it is then also possible to detect the direction of rotation. By placing further sensors around the magnet, the resolution may also be increased without the need to make extensive changes to the measuring principle or design. For this purpose it is necessary to provide only one linkage means, preferably on the printed circuit board, which links the two output signals to an output signal having higher resolution by using logical operations (AND and OR gates). This involves little complexity. On the other hand, it is necessary to relay only one output signal to the evaluation unit, thus reducing the cabling complexity.

In one advantageous refinement, a device is provided, preferably on the printed circuit board, for shifting the signal level of at least one output signal of a sensor. It is particularly advantageous to select the signal levels of the sensors in such a way that in normal operation they differ from the voltage levels of the supply voltage or ground. A malfunction in the sensor may be deduced in a particularly simple manner solely on the basis of the signal level. For this purpose it is particularly advantageous to provide an error recognition unit in the evaluation unit which, on the basis of the signal level of at least one of the output signals, recognizes whether an error is present in one of the sensors.

In one advantageous refinement it is provided that at least one connecting element of the sensor has at least one bending region. This bending region is used in particular to compensate for voltages, for example as the result of thermal stress. The mechanical stability of the system may be further increased in this way. In one advantageous refinement, a connecting element of the sensor has at least one further bending region. In this way the connecting element for the electrical contacting may be attached to the printed circuit board in a suitable manner, for example by soldering. The device may thus be manufactured more easily, while at the same time the mechanical strength is increased.

In one advantageous refinement, at least one retaining element is provided for absorbing mechanical stresses which act on the sensor. The retaining element is designed in the form of ribs on the housing or on a part connected to the housing. This retaining element absorbs mechanical forces which act on the sensor, thus allowing the robustness of the device to be further increased. In addition, the sensor or its connecting elements may be fixed to the housing by melting the retaining ribs, for example by hot caulking or laser action, which further increases the strength.

In one advantageous refinement, at least one pocket or recess is provided in the housing for accommodating the sensor. The sensor may be precisely positioned in this way, in particular when even further sensors are to be situated relative to one another with high precision in order to achieve a defined phase shift of their output signals. The sensor is preferably situated in such a way that it senses a magnetic field of the magnet which extends essentially parallel to the rotational axis of the rotatable part. The installation height of the device may be kept low in this way. In one advantageous refinement, at least one fastening means is provided in the housing for connecting the printed circuit board to the housing. The printed circuit board may be precisely positioned in this way. For fastening the housing to the printed circuit board, the fastening means preferably has a thermally deformable design, for example with the aid of hot caulking. Thus, the fastening process might be carried out together with the retaining ribs in only one operation. In one advantageous refinement, at least one rivet connection is provided as the fastening means. This rivet connection is used in particular for absorbing forces which act on the printed circuit board, for example forces introduced via the connector plug. The stability and robustness of the system are thus further increased.

In one advantageous refinement, the integrated component formed from the hub and the magnet is produced by extrusion coating the magnet using plastic. In this way even further, more complex geometries may be easily achieved in this component.

It is particularly advantageous for the magnet to have an essentially L-shaped cross section. The hub may thus be integrated together with the magnet, resulting in greater strength for producing an integrated component.

In one advantageous refinement, the hub has at least one carrier for transmitting a rotational motion of the rotatable part, preferably a steering column. A component or a recess which extends in the radial direction toward the rotational axis of the rotatable part is provided as the carrier. The integrated component might be installed from the top or the bottom, depending on the configuration of the housing, without having to adapt the housing to different installation spaces. For the same components, this increases the flexibility of the system.

In one advantageous refinement the hub has at least one bearing surface, which is preferably oriented perpendicular to the rotational axis, for rotatably supporting the hub in the housing. At least one bearing surface of the hub is preferably made of a wear-resistant material. The bearing surfaces may thus be selected independently of the geometry of the magnet in such a way that an optimal solution results with regard to the interplay with the housing (fit, tolerances, ease of installation, etc.). In addition, more complex structures may be implemented for the hub. The hub is advantageously made of the same material as the magnet, preferably plastic or a fully magnetizable material. The manufacture of the component may be further simplified in this way.

In one advantageous refinement, the hub and/or the magnet cooperate(s) with a fixing element for fixing to the housing. It is particularly advantageous when the fixing element allows a motion of the magnet or of the hub in the direction of rotation, but prevents a motion parallel to the rotational axis in the installed state. The fixing element has a movable or elastic design, preferably as a snap hook, and/or is connected to the housing or to the hub.

A snap hook which fixes the hub in both the axial and radial directions is particularly suitable as a fixing element. However, after the installation process the snap hooks are free of force or tension, so that they do not limit the mobility of the hub or the magnet with respect to the housing. The number of snap hooks is advantageously selected in such a way that the hub is still reliably fixed even if a hook fails, for example due to breakage. For example, five snap hooks are uniformly distributed around the circumference of the hub to achieve this functionality. The operational reliability of the device may be further increased in this way. In addition, due to the snap hook, a cover for axially fixing the hub is unnecessary, so that components may be spared.

DETAILED DESCRIPTION OF THE INVENTION

A magnet10is situated in the upper, outer circumferential region of an annular or hollow cylindrical hub16, thus forming an integrated component17. Magnet10is designed as a multipole magnet, as illustrated inFIG. 2, which shows magnet10in the top view. To improve the connection of magnet10to hub16, a projection is provided at the bottom of magnet10which in this region extends slightly farther in the direction of rotational axis18of hub16than in the upper region thereof. Hub16and magnet10are engaged with, for example, a steering column or another part which is connected to the steering wheel. The part which rotates during the steering motion, for example the steering column, is connected via a carrier32to hub16, which is situated in device8for detecting the rotational angle. The rotational motion of the part is thus transmitted directly to hub16. Hub16contains magnet10, which is designed as a multipole magnet. The magnet bears north poles12and south poles14which are distributed in alternation over its circumference. Thus, during rotation of the steering column, multipole magnet10co-rotates at the same angular velocity. This provides the option of placing a sensor20at a certain location in the measurable range of the magnetic field which provides measured values which are a function of the magnetic field direction at that location, or which may be deduced from same. For this purpose a Hall sensor might be used as sensor20, which emits a binary signal depending on whether its sensitive range is predominantly in the area of influence of a north pole12or of a south pole14. It is important that sensor20and magnet10are movably situated relative to one another. The sensor might also be designed as a Reed contact which modifies its output signal as a function of the magnetic field.

Using only one sensor20would allow the relative rotational angle of the steering column to be ascertained, but not the direction of rotation. Therefore, a further sensor22is provided which is placed at a defined distance from first sensor20so that a certain shift β of the two output signals21,23of the two sensors20,22, respectively, results. It may be deduced on the basis of the time sequence of signal edges21,23whether the steering wheel, i.e., the steering column, is rotated in the clockwise or counterclockwise direction. Sensors20,22have been situated farther radially outward relative to magnet10so that they detect the magnetic field of the magnet in the radial orientation.

In order to supply sensors20,22with the necessary operating voltage and to provide their output signals21,23to the requesting systems, for example a control unit58of an electronic stability program, electronic components are required. These electronic components are mounted on a printed circuit board26and electrically connected. Additional functions, such as for changing the voltage level, may be implemented at that location if necessary.

Hub16, magnet10, sensors20,22, and printed circuit board26are accommodated in a housing28, which via an integrated connector plug30allows connection to the power and communication network of the motor vehicle. Housing28also carries out other functions, for example supporting hub16together with magnet10, axial fixing using fixing elements36, or further attachment functions of sensors20,22via retaining elements50, to be discussed below.

In principle it would also be possible to measure the field of magnet10in the axial direction relative to rotational axis18. Sensors20,22would then need to be situated above or below magnet10, not lateral to same, in order to detect the magnetic field of the sensor in the axial direction.

A key aspect of device8according to the present invention for detecting a rotational angle is the integration of magnet10into hub16. This might be achieved, for example, by extrusion coating of magnet10using plastic. By a suitable selection of the material, the resulting combined component of magnet10and hub16may be designed in such a way that wear-free or wear-resistant support of hub16in housing28is achieved. The suitable selection of the material of hub16also depends on the material of housing28; examples of possible suitable materials are polyamide (PA12) and polybutylene terephthalate (PBT).

As is apparent fromFIG. 9, bearing surfaces34, which cooperate with corresponding counterbearing surfaces of housing28, may be selected independently of the geometry of magnet10in such a way that an optimal solution may be found with regard to the interplay with housing28(fit, tolerances, ease of installation). The bearing for housing28is formed by two bearing surfaces34whose cross sections are perpendicular to one another, as a result of which hub16is aligned relative to rotational axis18in the axial and radial directions. A third bearing surface34at the upper edge of the outer circumference of hub16cooperates with fixing element36, described below. It is also provided that at least one carrier32is integrated into hub16. Two types of carriers32are shown inFIGS. 7 and 8as examples. In the first type, a recess which is outwardly oriented in the radial direction is provided at the inner side of hub16, in which a complementary projection of a rotatable part, for example the steering column, is able to engage. In the second type, a further carrier32is provided which has a projection which is oriented from the inner side of hub16toward rotational axis18and which cooperates with a corresponding recess in the rotatable part.

The combined module made up of hub16and magnet10is particularly advantageous, since more complex geometries may also be implemented at hub16, for example elastically resilient snap hooks. A connection with housing28may be established using such snap hooks. Alternatively, the same material used for multipole magnet10might also be used for hub16, thus simplifying production of the component. For example, the hub might then be produced as a component with the aid of an injection molding process. Another alternative is to design hub16as a component having symmetrical bearing points, as the result of which integrated magnet10would be centrally situated.

For attaching device8for detecting a rotational angle to the movable part such as the steering column, for example, carrier elements32are always necessary, which are mounted on one side of hub16. If it is then necessary for space reasons to install housing28in the inverted position, for example because connector plug30is oriented in the opposite direction, it is only necessary to likewise install hub16of device8in the inverted position. Thus, two variants of the same device are provided without changing hub16or magnet10. These options are shown inFIGS. 10 and 11, in both cases hub16being oriented in the same way regardless of the position of connector plug30.

Another special characteristic of device8is the attachment of hub16to housing28, which is carried out with the aid of fixing elements36. To prevent hub16together with magnet10from moving out of housing28in the axial direction, the hub and magnet must be fixed in the axial direction. For this purpose fixing elements36are provided, which preferably are designed as snap hooks or clips. For these fixing elements36it is important that on the one hand they allow motion of hub16about rotational axis18, but on the other hand they prevent displacement, with a defined play, in the axial direction. Fixing elements36surround hub16in a circle. When hub16is inserted into housing28, counterforces which occur when fixing elements36are bent away must first be overcome. If hub16has reached its end position, fixing elements36spring back over the hub, so that fixing elements36are completely free of force or tension. Hub16is thus able to rotate without generating undesired friction on fixing elements36. Fixing elements36are selected with regard to their number and placement in such a way that hub16is secured over more than half of its circumference, whereby, even if a fixing element36fails, the axial fixation is maintained. In addition, as a result of this approach there is no need for a cover, which otherwise would be necessary for securing hub16, and there is likewise no need for fastening means such as screws or rivets, for example, required for this purpose.

One example of a geometric configuration of a fixing element36with respect to hub16is shown inFIG. 12. Fixing element36is directly or indirectly connected to housing28. For installation, hub16is inserted into housing28from above, and via the bevel pushes the tip of snap hook36outward. In the end position, hub16then rests on the countersurface of housing28. Snap hook36then springs back and counteracts axial displacement of hub16. Fixing element36is situated at a radial distance from the outer side of hub16and magnet10. The bottom side of snap hook36cooperates with the exterior top side of hub16, which is designated as bearing surface34in the top right side ofFIG. 9.

Instead of snap hooks having a defined geometry as possible fixing elements36, elastically supported fixing elements36might be used. The “spring” and “secure” functions may also be distributed over more than one element. Alternatively, it would be possible to mount fixing elements36not on hub16or housing28, but, rather, on an additional component used for mutually connecting hub16and housing28. Fixing elements36might also be situated on the outer side of hub16and elastically engage in corresponding recesses in housing28.

Sensors20,22are made up of a housing40and multiple connecting elements42, via which the signals of the electronic components inside housing40are guided. Sensors20,22must be situated in housing28in a fixedly defined position relative to one another and to magnet10. For this purpose, pockets41are provided in housing28which are matched to the outer contour of housing40and allow defined positioning. Such pockets41are shown inFIGS. 19 and 20. Connecting elements42of sensors20,22are bent by approximately 90 degrees (reference numeral43) in order to electrically contact radially oriented sensors20,22with printed circuit board26. Sensors20,22are preferably designed as so-called through hole technology (THT) components, and are used in the same way as a surface mounted technology (SMT) component. This allows measurement of the magnetic field of magnet10perpendicular to the orientation of the usable surfaces of printed circuit board26. In addition, further bending regions44,46of connecting elements42are provided.

As shown inFIG. 13, after housing40is fixed and connecting elements42are soldered to printed circuit board26, a first bending region44is used to compensate for voltages which may result, for example due to alternating thermal load during operation. A second bending region46is connected thereto, via which connecting elements42are guided to printed circuit board26in such a way that the bending region is wetted with solder in the most effective manner possible and may thus be electrically and mechanically connected to printed circuit board26in a contacting area48. In the exemplary embodiment according toFIG. 13, this results in an essentially S-shaped curve of connecting elements42.

The exemplary embodiment according toFIG. 14also includes a first bending region44in order to guide connecting elements42into the contacting areas, essentially parallel to the surface of printed circuit board26.

Alternatives are possible. Thus, 90-degree bend43in the vicinity of housing40might be dispensed with when it is necessary to detect the magnetic field in the axial direction instead of in the radial direction, as described. 90-degree bend43might also be replaced by a different angle. Alternatively, first bending region44might be dispensed with, as illustrated inFIG. 15, if this is necessary for relevant reasons, for example cost or feasibility. Alternatively, second bending region46might also be dispensed with, and the contacting with printed circuit board26might be achieved in a manner other than soldering, for example using a mechanical snap-in plug which is already mounted on printed circuit board26and into which connecting elements42are inserted. Similar embodiments are illustrated inFIGS. 14 and 16. Second bending region46might likewise be dispensed with if this is necessary due to the selected soldering process or for other reasons, in order to guide connecting elements42in a straight line to the end (FIGS. 14,16). Optionally, a third bending region47for the two outer connecting elements42might be provided in order to increase the distance between connecting elements42, if this is necessary due to the selected soldering process or for other reasons. In another variant according toFIG. 18, the two outer connecting elements42are bent outwardly in a third bending region47, and after a 90-degree bend43extend essentially parallel to the surface of printed circuit board26, and via first bending region44undergo a V- or U-shaped bend, and then once again extend essentially parallel to the surface of the printed circuit board until step-shaped second bending region46once again aligns contacting areas48parallel to printed circuit board26in the immediate vicinity thereof for suitable contacting. In principle, other sensor elements20,22might also be bent in this way if they are to be used in the sensor, such as Reed contact sensors, for example.

Sensor20,22according toFIG. 14is situated in pocket41in housing28, and is connected in an electrically conductive manner to printed circuit board26via contact regions48(FIGS. 19,20). To further improve the fastening of sensor elements20,22to housing28, rib-shaped retaining elements50are preferably provided on housing28which are matched to the outer geometries of connecting elements42. This is because during use of device8for detecting a rotational angle, forces occur which may act on connecting elements42of sensor20,22. The soldered connection would have to absorb these forces, which might adversely affect its service life if the forces were not absorbed at another location. Alternatively, housing40of sensor20,22might also be stressed in such a way that connecting elements42in or on housing28might be damaged, for example by being broken off. For this reason, so-called caulking ribs50are provided on housing48, along connecting elements42, as retaining elements. When sensor20,22is inserted into pocket41in housing28, connecting elements42are first passed between ribs50, thus being guided and allowing better matching of connecting elements42and printed circuit board contacting areas. For the hot caulking, the plastic is then locally melted to ribs50, and as the result of application of force, using a punch, for example, connecting elements42are fixed by the solidifying plastic. The material is thus able to absorb the above-mentioned forces, so that there is little or no stress on the soldered connection or housing40of sensor20,22. InFIG. 20, corresponding ribs50are shown prior to melting. Alternatively, it might be provided that the material of ribs50is melted not by hot caulking, but with the aid of some other method, for example laser action. In another alternative embodiment it is possible not to melt material, but instead to fix the legs to housing28in another way, for example using an adhesive or other mechanical components. Alternatively, the fixing function might be achieved using an additional component which is mounted on housing28.

In the perspective view according toFIG. 21, housing28is illustrated together with printed circuit board26, but without integrated part17. Printed circuit board26may be fastened to housing28via two pins51. These pins51are part of housing28, and are thus made of the same material as the housing. Printed circuit board26is pressed into housing28in order to be fastened via these pins51. Printed circuit board26is correctly positioned in this way. The height of pins51is preferably designed in such a way that sufficient material is available to make use of this additional material for fastening printed circuit board26via hot caulking. The corresponding curved shape of the pins after deformation, preferably by hot caulking, is denoted in each case by reference numeral52. A rivet connection53is also provided which in particular absorbs forces which occur at connector plug30and are transmitted to printed circuit board26.

Rivets53are preferably made of metal. In addition, the annular bearing surface of housing28for supporting hub16on lower bearing surfaces34thereof is seen particularly well in this view.

The perspective view according toFIG. 22shows in an overall view all components previously described. Hub16together with integrated magnet10, which in this view is not visible, is rotatably supported in housing28via fixing elements36and corresponding bearing surfaces34. Displacement in the axial direction of hub16is not possible, since the bottom side of snap hooks36together with top side of hub16counteracts axial displacement. Recess32at the inner side of hub16is visible, which cooperates as a carrier32with a steering column (not shown). Four sensors20,22, for example, are distributed in the circumferential direction, and detect the magnetic field of magnet10in the radial direction and optionally send appropriate output signals via connecting elements42to other components of printed circuit board26, not specified in greater detail. The resolution of device8might be further increased by using additional sensors which are suitably positioned. On the other hand, for this purpose a third and fourth sensor might be used whose two output signals are provided to a different system, for example one pair having adjusted voltage levels, and the other pair without adjustment.

To improve the connection of sensor elements20,22to printed circuit board26, on the one hand appropriate bending regions44,46,47are provided in particular to compensate for thermal voltages. On the other hand, retaining elements50are also provided which absorb mechanical forces which act on sensor elements20,22or their connecting elements42. As described, these retaining elements might be designed as ribs50.

As a further key aspect of device8for detecting a rotational angle of a rotatable part, instead of an absolute measurement, which is otherwise customary, a relative measurement of the motion of a steering column is provided. Only a single sensor is necessary for this purpose. In addition to the relative rotational angle of the steering column, the direction of this rotation may also be detected as the result of providing two sensors20,22. When the steering wheel rotates, pulsed output signals are generated, as is apparent in the signal curves according toFIG. 23. By using appropriate AND or OR gates, as shown in linkage56, the two output signals21,23may be combined into a single pulsed output signal54. When the steering wheel rotates, the appropriate signal sequences are generated which may be associated with a rotational angle on the basis of defined characteristics. The number of pulses is therefore directly proportional to the angle by which the steering wheel moves. With the aid of a downstream evaluation unit60which is separate from device8for detecting a rotational angle, the absolute angle may be ascertained with sufficient accuracy and communicated to the requesting systems, such as a control unit58, for example. An algorithm is also necessary, via which the neutral position of the steering wheel is to be ascertained to allow initialization of the relative detection. This algorithm is likewise executed in evaluation unit60. This algorithm is known to one skilled in the art, and is not further discussed below. Thus, in present device8only the output signals of sensors20,22, which are designed as binary signals as a function of the type of magnetic field, or signal54which is linked therefrom, is/are transmitted to control unit58. Only at that location is the absolute position of the steering wheel ascertained in a microcontroller60, as an example of an evaluation unit.

Control unit58or microcontroller60also has an appropriate interface to device8. The absolute steering angle information ascertained in microcontroller60may optionally be relayed via a bus system64to further control units, not described in greater detail. Additional sensors66may be integrated into control unit58, the values from which are also required by microcontroller60, for example for computing appropriate control variables for an electronic stability program in a motor vehicle. Wheel speed signals of further wheel speed sensors66are also delivered to control unit58, as likewise shown as an example inFIG. 24.

Device8for detecting a rotational angle represents a safety-relevant component in the vehicle, for which reason emitted signals21,23must be checked for correctness. For this purpose electronic components are mounted on printed circuit board26which shift the binary output signals of sensors20,22to offset levels. Instead of, for example, 5 V and 0 V (as a typical pull-up voltage and ground potential, respectively), the signals are converted to 4.5 V and 0.5 V. If a short circuit on the supply voltage or ground is then present in sensor20,22, these variables are also output by sensor20,22, i.e., in the referenced error case, 5 V and 0 V. The downstream system, for example microcontroller60, is able to immediately recognize that an error is present in device8, since the signal levels differ from the expected signal levels. For this purpose, microcontroller60compares the output signals of sensors21,23which are modified by the above-mentioned electronic components, or optionally linked output signal54, to corresponding limiting values, and in the event of a positive or negative deviation recognizes an error of sensor20,22. This might also be achieved using a current signal.

Linkage56on printed circuit board26, previously explained with reference toFIG. 23, must also be provided for achieving higher resolution. A new output signal54is thus generated which allows a higher resolution of the rotational motion of the steering wheel.

The described device for detecting a rotational angle may be used for numerous applications. It is particularly suited for detecting a steering angle. The steering angle is already necessary in a number of vehicle functions, for example the electronic stability program, adaptive cruise control, Park Pilot, driver fitness monitoring, active front steering, all-wheel steering, adaptive lighting control, or electrohydraulic steering. However, the use is not limited thereto.