DE10357146A1 - Angular displacement and or torque measurement device, especially for a motor vehicle, comprises capacitors with moving capacitor plates attached to the steering column so that they move relative to fixed capacitor plates - Google Patents

Abstract

Sensor device comprises first (2) and second (5) capacitors, with each capacitor having at least a moving capacitor plate (3, 6) and at least a fixed capacitor plate (4, 7). The moving capacitor plates are mounted on a rotating shaft (8), in particular the steering column. As the steering column rotates the capacitance of the capacitors varies.

Description

The The present invention relates to a sensor device for angular and / or torque detection and in particular an angle and / or torque sensor for vehicles.

sensors for recording angles and / or torques are from the State of the art in diverse Embodiments known and are often used in vehicles. Known sensors use capacitive, inductive, transit time or optical measuring methods. For An application of such sensors in vehicles are very high Requirements regarding a thermal and mechanical load capacity of the sensor and an unrestricted Functionality over as possible the entire lifetime of vehicles at the lowest possible Costs. When using optical sensors lies the main problem is that in case of signs of pollution in the optical path or a creeping blindness of the detectors the functionality no longer exists. The use of inductive measuring principles for sensors is in a promotion too inaccurate after a high-precision angular resolution. Measurement principles, which exploit the duration of ultrasound signals are very expensive and consuming to manufacture and thus for mass production for use not suitable in vehicles. For capacitive measuring principles are especially the relative humidity, which is a change of the electricity constant of the Air causes and thus the capacity between the capacitor plates influenced, and the temperature fluctuations, especially the size and the distance affected by the capacitor plates, for accurate signal evaluation problematic. Therefore, so far in the automotive sector mainly optical Angle sensors used.

Advantages of invention

The inventive sensor device with the features of claim 1, in contrast, the Take advantage of using an angle measurement up to almost 720 ° the capacitive measuring principle allows. According to the invention here are Absolute angle measurements of 720 ° -X ° possible, where the angle X through the width of the capacitor plates used is determined. The width of the capacitor plates can be such chosen be that the angle X is about 10 °, so an absolute angle measurement of well over 700 ° absolute angle is possible. According to the invention this is achieved in that the sensor device has a first and a having second capacitor. Both capacitors point each at least one movable and a fixed capacitor plate on. The movable capacitor plates are rotatable on one mounted shaft whose rotation angle is to be measured. The fixed and / or movable capacitor plates have it has a shape such that the capacitance of the capacitors changes with a rotation of the shaft. The double arrangement of the capacitors thus enables a measurement of a Absolute angle of significantly above 700 °, without the sensor device has a complex counting device. there is the sensor device according to the invention very inexpensive in a mass production manufacturable and very sturdy, so easy to use in Vehicles possible is.

The under claims have preferred developments of the invention to the subject.

Around a particularly simple evaluation of the capacitive measurement signals to enable is the shape of the fixed and / or movable capacitor plates chosen asymmetrically. Particularly preferred are the capacitor plates of the first capacitor mirrored to the capacitor plates of the second capacitor arranged and rotated by 180 ° arranged to each other. In this case, the capacitor plates of the first and second capacitor the same outer shape.

Preferably the capacitive capacitor plate of the capacitors has a worm shape, wherein the movable capacitor plate is perpendicular to the axis of the shaft is arranged. According to one Particularly preferred embodiment of the invention is the screw shape the movable capacitor plate thereby formed such that the Snail shape starts at a point on the shaft and a steady slope along the shaft. Preferably, the starting point and the end point of the snail on a line through the center point the wave and a distance from the starting point to the end point the line preferably corresponds to twice the radius of the shaft.

A Contacting of the movable capacitor plates of the sensor device preferably takes place via the wave. As a result, a particularly cost-effective construction can be achieved.

According to another preferred embodiment of the present invention, the movable capacitor plates are placed on the circumference of the shaft, so that the movable capacitor plates practically form an additional jacket to the shaft. The length of the movable capacitor plates in the axial direction of the shaft is different at each point of the shaft circumference. Beson Preferably, the length of the movable capacitor plates in the axial direction of the shaft changes with a constant pitch. In this embodiment, the shaft is preferably made of a non-conductive material or over the shaft is a cylindrical sleeve made of a non-conductive material.

Around additionally for angle measurement nor a torque measurement with the sensor device according to the invention possible The sensor device preferably comprises a third one and a fourth capacitor, which is also disposed on the shaft are. It is between the first and the second capacitor and the third and fourth condenser arranged a torsion bar. Preferably, the first and second capacitors are on the shaft arranged redundantly. A torque can be detected by detecting a temporally different reacting of the capacitor pairs on the right and the left of the torsion bar are detected, the size of the signal is measured by the occurring maximum capacitance difference and From this a torque value can be determined.

Around to enable a particularly easy readability of the measuring signals the capacitors of the sensor device are arranged such that in the starting point of the measurement a maximum or a minimum capacity the capacitors is obtained. The starting point for a steering angle sensor would be present for example, the neutral position of the steering wheel.

Around a insensitivity of erfindungsσemäßen sensor device against external influences such e.g. Temperature fluctuations, fluctuations in air humidity, change the distance of the capacitor plates due to a temperature change etc., a reference capacitor is preferably provided, which is immediate, i. in the same climatic space, adjacent is arranged to the capacitors of the sensor device. The reference capacitor has a plate thickness as the capacitors of the sensor device on. Thereby can for example, by a difference signal evaluation of the signals of the measuring capacitor with fixed reference capacitances become. Preferably, the capacitance of the reference capacitor the same or greater than the maximum capacity the measuring capacitors. Furthermore, it should be noted that when using the sensor device according to the invention as a torque sensor for each capacitor pair provided a separate reference capacitor can be. Preferably, the reference capacitors are in a closed housing arranged with the capacitors of the sensor device.

The inventive sensor device is particularly preferred in vehicles and particularly advantageous used as steering angle sensor. In this case, the sensor device according to the invention also for direct steering systems, such as so-called "steer-by-wire" systems are suitable, which with very little Steering lock work.

drawing

following The present invention is based on preferred embodiments described in conjunction with the drawing. In the drawing is:

1 FIG. 2 shows a schematic side view of a sensor device for detecting a rotation angle according to a first exemplary embodiment of the invention, FIG.

2 a side view of one on the in 1 shown shaft mounted movable capacitor plate of the first capacitor,

3 a side view of one on the in 1 shown shaft mounted movable capacitor plate of the second capacitor,

4 a representation of the variable capacitor plate of 2 with relative sizes,

5 a schematic sectional view of the sensor device of 1 .

6 a diagram showing the capacities as a function of the rotation angle of the shaft,

7 a diagram showing the differential capacitance of the capacitors on the shaft to fixed reference capacitors over the rotation angle of the shaft,

8th 1 is a schematic side view of a sensor device according to a second embodiment for detecting a rotation angle and a torque,

9 a schematic side view of a sensor device according to a third embodiment of the invention, and

10 a schematic view of a sensor device according to a fourth embodiment of the invention.

description the embodiments

The following is with reference to the 1 to 7 a sensor device 1 according to a first embodiment of the present invention.

As in 1 shown, comprises the sensor device according to the invention 1 a first capacitor 2 and a second capacitor 5 , The first capacitor 2 consists of several movable capacitor plates 3 and several fixed capacitor plates 4 , More precisely, there is the first capacitor 2 in this embodiment, five movable capacitor plates 3 and five fixed capacitor plates 4 , For better clarity are in 1 not all capacitor plates labeled. A movable capacitor plate 3 is in 2 shown in side view. How out 2 is apparent, is the movable capacitor plate 3 formed in the form of a worm and on a shaft 8th whose rotation angle is to be determined attached. The worm shape of the movable capacitor plate 3 starts at a point B on the shaft and ends at a point F (cf. 4 ).

The exact proportions are detailed in 4 shown. The worm shape starts here on the shaft 8th at point B and passes over the points C, D, E and F once around the circumference of the shaft 8th , In this case, the screw increases, starting from the point B, with a constant slope. As in 4 As shown, the worm widened in point C, starting from a center M of the shaft 8th , 0.5 times a radius A of the shaft 8th , At point D, the worm widened to the length of radius A, at point E the worm widened to 1.5 times the radius A and at point F the worm reached 2 times the radius A.

How out 1 combined with 5 is apparent, are the first capacitor 2 and the second capacitor 5 mirrored to each other on the shaft 8th arranged and rotated by 180 ° on the shaft. Furthermore, the fixed capacitor plates 4 respectively. 7 formed by thin rods. A contacting of the movable capacitor plates 3 and 6 takes place over the shaft 8th and a connection line 9 , Thus, the fixed capacitor plates 4 and 7 , as in 1 shown formed from a plurality of individual bars, which are interconnected via an upper common connecting element, so that they have a substantially comb-like shape. Between the fixed capacitor plates are each on the shaft 8th fixed movable capacitor plates 3 . 6 arranged. The number of fixed and movable capacitor plates of the first and second capacitors are the same and determine the measurable maximum and minimum capacitance. The width of the fixed capacitor plates 4 and 7 determines the maximum measurable definite absolute angle. If the width of the fixed capacitor plate theoretically goes to zero, an absolute angle of plus / minus 360 °, ie, in the sum of an angle of 720 °, can be measured. Because the fixed capacitor plates 4 and 7 however, must have a certain width, the actual measurable absolute angle is slightly smaller than 720 °.

The function of the sensor device according to the invention of the first embodiment is as follows: As in 5 shown, the respective coverage of the fixed and variable capacitor plates is the cause of the capacitance of the respective capacitor. When the wave 8th with the attachable movable capacitor plates 3 respectively. 6 turns, the capacitance of the first and second capacitors changes, the capacitance change being proportional to the rotation angle of the shaft 8th is. Thus, in an evaluation unit based on the changes in the capacitance or on the basis of a comparison of the actual capacitance of the capacitors with stored reference values of the capacitance, the rotation angle of the shaft 8th be determined.

6 shows the changes of the capacity according to a change of a steering angle of the shaft 8th , Because the two capacitors 2 and 5 mirrored and rotated by 180 ° on the shaft 8th are arranged, arise in 6 two mirrored gradients of capacity. Here, the curve drawn in dashed lines is the capacitance curve C1 of the first capacitor 2 and the solid line, the capacitance curve C2 of the second capacitor 5 , In order to obtain the most accurate measurement result, preferably the angle of the shaft 8th measured only with a capacitor. Here, the fast capacitance change of a capacitor near the zero value of the angle gives the decision criterion for measuring an angle in the positive direction by the first sensor 2 with the capacity curve C1, which here in 1 is shown in dashed lines, since this is the angle 0 to + 360 ° -X ° a capacity change without change of sign exists. With a rotation of the shaft 8th in the negative direction, the measurement signal C2 of the second capacitor is correspondingly 5 used, which also has no sign change over a range of 0 to -360 ° + X °. Here, the size X ° is dependent on the aforementioned thickness of the fixed capacitor plates, and the thinner the fixed capacitor plates, the smaller the amount of the angle of X becomes. That is, the angle of rotation is basically measured with two capacitors and the different rise of the traces close The zero point of the measurement serves as a plausibility check and to determine only one measuring curve with which the angle is measured. The rise of the measuring straight can be evaluated with an evaluation ASIC.

As in 7 A determination of the angle of rotation can also be determined on the basis of a signal image of the difference between the variable capacitances and the fixed capacitances of the capacitors.

The following is with reference to 8th a sensor device 1 according to a second embodiment of the present invention. Identical or functionally identical parts are denoted by the same reference numerals as in the first embodiment.

As in 8th shown includes the sensor device 1 practically a double arrangement of in 1 shown sensor device. More precise is a wave 8th through a torsion bar 10 divided into two shaft halves, wherein on the first half of the shaft, a first capacitor 2 and a second capacitor 5 are arranged according to the first embodiment, and on the second shaft half are a third capacitor 2 ' and a fourth capacitor 5 ' arranged. Thus, the two pairs of capacitors 2 . 5 and 2 ' . 5 ' in the same way on the shaft 8th and between them the torsion bar 10 arranged.

The angle of rotation is calculated as in the first embodiment by determining the change in capacitance, wherein in the second embodiment, theoretically from the four capacitors 2 . 5 . 2 ' . 5 ' can be selected. Furthermore, in the sensor device 1 According to the second embodiment, the torque of the shaft can be determined by a time-varying reaction of the capacitor pairs 2 and 5 on the one hand and the capacitor pairs 2 ' and 5 ' on the other hand. The size of the signal can be measured by the respective maximum capacity difference reached and interpreted in a torque value.

The following is with reference to 9 a sensor device 1 according to a third embodiment of the present invention. Identical or functionally identical parts are again denoted by the same reference numerals as in the first and second embodiments.

How out 9 is apparent, is the sensor device 1 according to the third embodiment is formed substantially like that of the second embodiment, and thus can both the rotation angle and the torque of the shaft 8th determine. In contrast to the second embodiment, in the third embodiment, the shaft with the two double-arranged capacitor pairs 2 . 5 . 2 ' . 5 ' in a housing 11 arranged. The wave 8th is at a first camp 12 and a second camp 13 stored in the housing wall. Furthermore, in the housing, a first reference capacitor 14 and a second reference capacitor 15 arranged.

By the arrangement of the sensor device 1 in a housing 11 On the one hand, negative external influences such as moisture, dirt and, for the most part, heat radiation can be prevented. Furthermore, this allows the sensor device 1 surrounding housing substantially the same external conditions for all capacitors of the sensor device. Furthermore, by the arrangement of the two reference capacitors 14 and 15 Capacitance fluctuations of the capacitors 2 . 5 . 2 ' . 5 ' , which are caused for example due to temperature changes or changes in humidity and thus the dielectric constant, are compensated. This is achieved by measuring the difference between a reference capacitor and a measuring capacitor during signal evaluation. The reference capacitors have an equal or greater capacity than the maximum capacity of the screw capacitors. The reference capacitors are made of the same material as the screw capacitors and have the same plate spacing as the screw capacitors. Since only the capacitance difference between the reference capacitor and the measuring capacitor is thus always measured, external influences which have an effect on the capacitances of the capacitors can be compensated for.

Hereinafter, a sensor device 1 according to a fourth embodiment with reference to 10 described.

The sensor device 1 has a similar structure as in 1 shown sensor device of the first embodiment. In contrast to the first embodiment, the capacitors of the sensor device 1 However, constructed differently according to the fourth embodiment. As in 10 shown are on a wave 8th a first capacitor 22 and a second capacitor 25 arranged. The first capacitor 22 includes a movable capacitor plate 23 which on the shaft 8th is attached, and a fixed capacitor plate 24 , The movable capacitor plate 23 is on the circumference of the shaft 8th applied and points in the axial direction XX of the shaft 8th over the shaft circumference a different length. As a result, the capacitance of the capacitors changes depending on the respective rotational position of the shaft 8th , In the unrolled state is the movable capacitor plate 23 thus essentially triangular. Next, as described in the first embodiment, a second capacitor 25 mirrored and rotated by 180 ° to the first capacitor 22 arranged. The second capacitor 25 also includes a movable capacitor plate 26 , which rest on the circumferential mantle of the shaft 8th is placed on top and a fixed capacitor plate 27 , Here is the second capacitor 25 such to the first capacitor 22 arranged that the second capacitor has there its minimum value, where the first capacitor 22 has its maximum value (cf. 10 ). The wave 8th is further made of an electrically non-conductive material and a contacting of the located on the shaft movable capacitor plates 23 and 26 takes place via a conductive inner core 16 respectively. 17 (see. 10 ).

The sensor device 1 according to the fourth embodiment can also determine only the rotation angle. However, it is of course also conceivable that, as in the second and third embodiments, four capacitors constructed in this way are arranged in the form of two pairs of capacitors and between the two pairs of capacitors, a torsion bar is arranged to determine the torque of the shaft can. Furthermore, as in the third embodiment, it is also possible for the capacitors to be arranged in a housing and for one or more reference capacitors to be provided for external influences on the sensor device 1 to eliminate.

The described embodiments are preferably used in vehicles and in particular in steering. The sensor devices according to the invention 1 are arranged between the steering wheel and the steering gear. Furthermore, the illustrated embodiments of the sensor device 1 particularly well used in direct steering systems, especially in steer-by-wire systems with little steering lock. In such "steer-by-wire" systems, in particular, an absolute angle of 700 ° is sufficient, since the steering movement of the steering wheel is transmitted electronically to the steering axis, so that in particular a so-called revolution counting system can be dispensed with. This has great cost advantages.

Claims (13)

Sensor device comprising a first capacitor ( 2 ; 22 ) and a second capacitor ( 5 ; 25 ), wherein the first capacitor has at least one movable capacitor plate ( 3 ; 23 ) and a fixed capacitor plate ( 4 ; 24 ) and the second capacitor comprises at least one movable capacitor plate ( 6 ; 26 ) and a fixed capacitor plate ( 7 ; 27 ), and wherein the movable capacitor plates on a rotatably mounted shaft ( 8th ), wherein the fixed and / or movable capacitor plates have a shape such that the capacitance of the capacitors ( 2 . 5 ; 22 . 25 ) upon rotation of the shaft ( 8th ) changes. Sensor device according to claim 1, characterized in that that the shape of the fixed and / or movable capacitor plates is asymmetric. Sensor device according to claim 2, characterized in that the capacitor plates ( 3 . 4 ) of the first capacitor ( 2 ) mirror-inverted and rotated by 180 ° to the capacitor plates ( 6 . 7 ) of the second capacitor ( 5 ) are arranged. Sensor device according to one of the preceding claims, characterized in that the fixed capacitor plates ( 4 . 7 ; 24 . 27 ) have a rod-like shape. Sensor device according to one of the preceding claims, characterized in that the movable capacitor plates ( 3 . 6 ) have a helical shape and perpendicular to the axis (XX) of the shaft ( 8th ) are arranged. Sensor device according to claim 5, characterized in that a starting point (B) and an end point (F) of the spiral-shaped movable capacitor plate on a line through a center (M) of the shaft ( 8th ) lie. Sensor device according to claim 6, characterized in that that a distance from the starting point (B) to the end point (F) along the Line through the center corresponds to twice the radius (A) of the shaft. Sensor device according to one of claims 1 to 3, characterized in that the movable capacitor plates ( 23 . 26 ) on the circumference of the shaft ( 8th ), wherein the length of the movable capacitor plates ( 23 . 26 ) in the axial direction (XX) of the shaft ( 8th ) at each point along the circumference of the shaft ( 8th ) is different. Sensor device according to claim 8, characterized in that the length of the movable capacitor plates ( 23 . 26 ) in the axial direction (XX) of the shaft ( 8th ) changes with a constant slope. Sensor device according to claim 8 or 9, characterized in that the shaft ( 8th ) from egg nem electrically non-conductive material is manufactured and a contacting of the movable capacitor plates ( 23 . 26 ) via conductive cores ( 16 . 17 ) takes place in the shaft. Sensor device according to one of the preceding claims, characterized by a third capacitor ( 2 ' ) and a fourth capacitor ( 5 ' ), which on the shaft ( 8th ), wherein between the first and second capacitors ( 2 . 5 ) and the third and fourth capacitors ( 2 ' . 5 ' ) a torsion bar ( 10 ) is arranged. Sensor device according to one of the preceding Claims, characterized in that the capacitors of the sensor device are arranged such that in an initial state of the shaft the capacitors have either their maximum capacity or their minimum capacity. Sensor device according to one of the preceding claims, characterized by a reference capacitor ( 14 . 15 ), which immediately adjacent to the capacitors ( 2 . 5 . 2 ' . 5 ' ) of the sensor device is arranged to determine a reference capacitance immediately adjacent to the sensor device.