DE20220388U1 - Device for measurement of the torque applied to a shaft, e.g. a motor vehicle steering wheel shaft, has a flux concentrator that enables a magnetic field sensor to be securely positioned so that it is insensitive to tolerances - Google Patents

Abstract

Device for determining the torque between two shaft sections that move relative to each other, comprises a multipolar magnetic ring (24) arranged around the first shaft section (14) and a stator support (30) with two stator elements (26, 32) fixed to the second shaft section (12). Each stator has axially extending fingers equally distributed around its circumference. The fingers (34, 36) form holes between themselves with the fingers of each section linked by a flux ring. A magnetic flied sensor (44) has flux concentrators between the flux rings of the stator elements.

Description

S:\IB5DUP\DUPAMM\2C0211\382 6090IDE-20C30S23.doc

Applicant:

Valeo switches and sensors

Stuttgarter Strasse 119

74321 Bietigheim-Bissingen

General power of attorney: 4.3.5.-No.306/99AV

38260901EN 04.04.2003

STE/HAT

Title: Device for determining a torque exerted on a shaft

Description

The invention relates to a device for determining a torque exerted on a shaft, wherein the shaft has a first shaft section and a second shaft section and the two shaft sections can be rotated relative to one another, with a multipole magnet ring surrounding the first shaft section and connected to it and a stator holder fastened to the second shaft section, wherein two stator elements are fastened to the stator holder and each stator element has fingers projecting in the axial direction, which are evenly distributed over at least part of the

Umfar.gs are arranged distributed and have gaps between them, wherein the fingers of each stator element are connected to one another via a magnetic flux ring, the magnetic flux rings are spaced apart from one another and a magnetic field sensor is arranged between the magnetic flux rings, wherein at least one magnetic flux concentrator is assigned to the magnetic field sensor.

US 4,984,474 discloses a torque sensor which is essentially formed by one or more magnetic rings and two stator elements, which, however, have a small number of poles. The small number of poles has the disadvantage that a ripple is modulated onto the signal measured by the sensor when the steering shaft rotates, which can only be compensated for by suitable electronic addition of two signals offset by half a pole width or by completely ring-shaped flux collecting rings. Furthermore, a torque sensor constructed in this way is relatively sensitive and susceptible to interference, since the magnetic flux concentrator is mounted radially outside the stators. Furthermore, such a construction is very sensitive to concentricity tolerances. Finally, the stators have spacers which are formed by separate rings, which makes the construction relatively complex.

From FR 2,821,668 Al a device is known in which the sensor consists of a discretely constructed multipole magnet ring and two nested

soft magnetic stators. These stators have finger-shaped structures on the radial inside, which scan the magnetic poles, and an annular gap on the radial outside, in which a stationary magnetic field sensor is located.

The pole pitch must be chosen relatively roughly due to the discrete design of the magnetic wheel (pole width 20°), which results in an equally large linearity range, but this is not fully utilized because the range of the angle to be measured is only about ± 3° to 5° due to the required rigidity of the torsion system. The magnetic flux cannot be utilized optimally because the air gap forming the magnetic return path is the same over the entire circumference, so that the magnetic flux is distributed over a large area and is therefore relatively small at the location of the magnetic field sensor.

Based on FR 2,821,668 A1, the invention is based on the object of providing a torque sensor with which a stronger signal can be generated without great technical effort. However, the magnetic sensor should be robust and insensitive to the vibrations that occur in motor vehicles.

This object is achieved according to the invention with a device of the type mentioned above in that the

Magnetic flux concentrator is provided between the magnetic flux rings.

The arrangement of the magnetic flux concentrator has the significant advantage that the magnetic field sensor is arranged in a protected manner. The magnetic flux concentrator receives a much stronger signal, which can be used as a direct measure of the torque without the need for complex evaluation. A further advantage is that the structure according to the invention is insensitive to mechanical tolerances, since the magnetic flux concentrator is located inside the stator.

In a further development, a magnetic flux concentrator is arranged between the magnetic field sensor and each magnetic flux ring. This means that the magnetic flux between the magnetic flux ring and the magnetic field sensor always runs via a magnetic flux concentrator.

In order to obtain an optimal amplification of the signal, the magnetic flux concentrator extends adjacent to the magnetic flux ring over a section in its circumferential direction. The magnetic flux concentrator is advantageously adapted to the curvature of the magnetic flux ring. In order to keep the resistance in the air gap forming the return as low as possible, a very narrow gap is provided between the magnetic flux concentrator and the magnetic flux ring.

Air gap is present. The advantage here is that the magnetic field sensor works without contact and yet has a low resistance in the return path.

In one embodiment, the air gap runs in a surface extending in the circumferential direction. In another embodiment, the air gap runs in a surface extending in the radial direction, i.e. in a radial plane. In the first case, the magnetic field sensor is inserted axially into the stator and in the second embodiment, it is inserted radially.

Preferably, the magnetic flux concentrator has a section adjacent to the magnetic flux ring and a section adjacent to the magnetic field sensor. In this way, the magnetic flux concentrator can extend both into the immediate vicinity of the magnetic flux ring and into the immediate vicinity of the magnetic field sensor.

In a special embodiment, the sections are arranged in planes or surfaces that are offset from one another or at an angle to one another. In this way, the magnetic flux is optimally directed and guided by the magnetic flux rings in the direction of the magnetic field sensor. The two sections are connected to one another via a bend.

In order to ensure optimal use of the entire field, namely in terms of field strength, angle measuring range,

To obtain the required number of poles and so on, the section adjacent to the magnetic flux ring is wider than the width of a finger, in particular it is twice as wide. For redundancy, at least two independent magnetic field sensors are provided. The flux concentrators then have two bends. The flux concentrator is designed in a certain length to obtain greater sensitivity and to average out any signal ripple.

Simple assembly and precise allocation to one another is achieved by arranging the magnetic flux concentrator(s) and the magnetic field sensor in a common holder and/or sensor housing. This holder is used to position both the magnetic field sensor and the magnetic flux concentrators relative to one another and to fix them within the stator, while also protecting them against environmental influences.

Further advantages, features and details of the invention emerge from the subclaims and the following description, in which two particularly preferred embodiments are described in detail with reference to the drawing. The features shown in the drawing and mentioned in the claims and in the description can each be essential to the invention individually or in any combination.

In the drawing show:

Figure 1 is a perspective view of the torque sensor according to the invention arranged on a shaft, partially in section;

Figure 2 is a sectional view in the direction of arrow II in Figure 1;

Figure 3 is a schematic representation of the relative positions of the magnetic ring and the stator without any torque acting on the shaft (Figure 3a) and with torque applied (Figure 3b);

Figure 4 shows a longitudinal section through a second embodiment of the torque sensor according to the invention;

Figure 5 is an enlarged representation of detail V according to Figure 4;

Figure 6 shows a section VI-VI according to Figure 5; Figure 7 shows a section VII-VII according to Figure 5; and

Figure 8 is a schematic representation of the relative positions of the magnetic ring and the stator without any torque acting on the shaft (Figure 8a) and with applied torque (Figure 8b).

Figure 1 shows a steering shaft of a motor vehicle, designated as a whole by 10, of which two shaft sections 12 and 14 can be seen. The two shaft sections 12 and 14 are connected to one another via a torsion bar spring 16, so that their free, mutually facing ends 18 and 20 are rotated relative to one another when a torque is applied to the steering shaft 10. A magnetic ring holder 22 is attached to the end 20 of the shaft section 14, which carries a multipole magnetic ring, designated as a whole by 24. This magnetic ring 24 surrounds the steering shaft 10 with a radial distance, so that a stator element 26 can engage between the magnetic ring 24 and the steering shaft 10.

This stator element 26 is part of a stator, designated overall by 28, which is attached to a stator holder 30. This stator holder 30 is in turn attached to the free end 18 of the shaft section 12. A second stator element 32 is located radially opposite the first stator element 26 and, like the first stator element 26, is held and securely positioned by the stator holder 30. Fingers 34 and 36 protrude downwards from both stator elements 26 and 32, which hold the magnetic ring 24 between them. The two stator elements 26 and 32 are made of soft magnetic material.

Furthermore, it can be seen in Figure 1 that the free upper ends 38 and 40 of the two stator elements 26 and 32 form a gap 42. A magnetic field sensor 44 is arranged in this gap 42 and is located directly

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which can be clearly seen from Figure 2. The fingers 34 and 36 each protrude from a magnetic flux ring 46 and 43, which bring together the magnetic flux induced in the fingers 34 and 36 and direct it in the direction of the magnetic field sensor 44.

From Figure 2 it is clearly visible that a first magnetic flux concentrator 56 is arranged on the magnetic field sensor 44, which lies between the magnetic field sensor 44 and the magnetic flux ring 46. A second magnetic flux concentrator 58 is arranged between the magnetic field sensor 44 and the magnetic flux ring 48. The two magnetic flux concentrators 56 and 58 each have a section 60 and 62, which are adjacent to the magnetic flux rings 46 and 48. Between the two sections 60 and 62 there is a section 64, which is adjacent to the magnetic field sensor 44. The sections 60 and 62 each merge into the section 64 via a bend. When the flux concentrators 56 and 58 are manufactured as sintered parts, the middle section 64 is not bent, but the sections 60 and 62 facing the magnetic flux ring 46 and 48 are continuous, and only on the side facing the magnetic field sensor 44 is there a hump that forms the section 64. Adjacent to the sections 60 and 62 there is a small air gap 42 that separates them from the magnetic flux rings 46 and 48, which is clearly shown for the second embodiment in Figure 7. The two magnetic flux concentrators 56 and 58 and the magnetic field sensor 44 are in a common

Housing and can be inserted in the axial direction between the two magnetic flux rings 46 and 43 into the stator 28.

Figures 3a and 3b show the position of the individual fingers 34 and 36 with respect to the poles 50 and 52 of the magnetic ring 24. It can also be seen that the fingers 34 and 36 are radially opposite one another.

In Figure 3a, no torque is applied to the steering shaft 10, so that Figure 3a shows the rest or neutral state. It is clearly visible that the fingers 34 and 36 are opposite the transitions 54 between the poles 50 and 52. For reasons of symmetry, the stator elements 26 and 32 remain magnetically neutral overall; this means that no magnetic field is formed in the air gap 42.

If a torque is applied to the steering shaft 10, the two ends 38 and 40 of the two shaft sections 12 and 14 rotate against each other, which is shown in Figure 3b. The fingers 34 and 36 are now opposite one of the poles 50 and 52 (in Figure 3b, the pole 50). The radially inner fingers 34 are opposite the north poles, for example, and the radially outer fingers 36 are opposite the south poles. Consequently, the inner stator element 26 is magnetized to a north pole and the outer stator element 32 to a south pole. The gap 42 delimited by the ends 38 and 40, which is formed over the entire circumference, represents the magnetic

Conclusion: The magnetic field sensor 44, which is fixedly attached to the housing 63 of the steering shaft 10, shown in Figure 4, for example, dips its sensitive surface into this gap 42 and measures the strength of the magnetic induction via the magnetic flux concentrators 56 and 58, which is a direct measure of the magnitude of the torque. The strength of the magnetic induction is also constant over the entire circumference of the gap 42 at a constant torque. This means that the steering shaft 10 with the magnetic ring 24 and the stator 28 can be rotated unhindered. The sensor 44 works completely contactlessly.

With negative torque, the direction of the relative rotation changes so that the fingers 34 are opposite the poles 52. This reverses the polarities in the stator elements 26 and 32.

The advantage is that the pole pitch of the magnetic ring 24 can be selected relatively finely, so that the linearity range almost coincides with the angle ranges to be measured. This results in a larger output signal for the same torque compared to the state of the art, which is equivalent to a better signal-to-noise ratio. Since the magnetic ring is made of a plastic-bonded magnetic material, it can be manufactured more cheaply and more precisely. Due to the large distance between the fingers 34 in relation to the air gap 42

and 3 6 there is no competing shunt and the magnetic field lines concentrate optimally on the magnetic flux concentrators 56 and 58. This also increases the output signal. Since the magnetic field sensor 44 is arranged in the axial direction in the gap 42, assembly is made easier because the magnetic field sensor 44 can be attached directly to a holder which is pushed onto the shaft 10 in the axial direction and is centered by it. This results in small assembly tolerances.

Figure 4 shows a longitudinal section through a second embodiment of the invention, wherein identical or equivalent components are designated by identical reference numerals. The magnetic ring, which is surrounded by the stator 28, is attached to the end 18 of the shaft section 14. This stator 28 is in turn attached to the end 20 of the shaft section 12 via the stator holder 30. The structure of the stator 28 essentially corresponds to that described in FR 2,821,668 A1, so that the stator 28 has two stator elements 26 and 32. These stator elements 26 and 32 are bent essentially in an L-shape, wherein one L-leg is formed by the magnetic flux ring 46 or 48 and the other L-leg is formed by the fingers 34 or 36. The fingers 34 and 36 are shown, for example, in Figures 6 and 8.

Between the two magnetic flux rings 46 and 48, as clearly shown in Figure 5, the magnetic field sensor 44

which in turn is housed in the sensor housing 65. Next to the magnetic field sensor 44 are the two magnetic flux concentrators 56 and 58, which with their section 64 lie directly against the magnetic field sensor 44.

Figure 6 shows the magnetic flux concentrator 56 in longitudinal section and it can be seen that the section 64 merges into the two sections 60 and 62. Overall, the magnetic flux concentrator 56 is curved and follows the curvature of the magnetic flux ring 46. It can also be seen that the two sections 60 and 62 essentially cover two fingers 36 of the magnetic flux ring 46, whereby the magnetic flux induced in these two fingers 36 is concentrated and fed to the magnetic field sensor 44. The flux concentrator 56 or 58 can also be straight. The length is not correlated with the number of fingers 36 covered. The flux collected by the fingers 34 and 36 is distributed over the circumference by the magnetic flux rings 46 and 48 and the flux concentrators 56 and 58 specifically direct the flux back via the magnetic field sensor 44.

The design of the two magnetic flux concentrators 56 and 58 can be clearly seen from Figure 7, in particular the course of the sections 60, 62 and 64, and it is clearly visible that the sections 64 are adjacent to the magnetic field sensor 44 and the sections 60 and 62 are directly adjacent to the magnetic flux rings 46 and 48, whereby between

between sections 60 and 62 and the magnetic flux rings 4, 6 and 48 there is only a small air gap 42.

In Figure 8a, as in Figure 3a, the neutral position is shown, in which no torque is applied to the steering shaft 10. In this position, the individual fingers 34 and 36 are exactly in the middle of the respective transitions 54 between the poles 50 and 52. For reasons of symmetry, the stator elements 26 and 32 and thus also the magnetic flux rings 46 and 48 remain magnetically neutral. This means that no magnetic field is formed in the air gap 42.

In Figure 8b, a torque is exerted on the steering shaft 10 so that the magnetic ring 24 and the stator 28 rotate relative to one another. The fingers 34 and 36 are now opposite the south poles 50 and the north poles 52, respectively. A magnetic flux is now induced in the stator elements 26 and 32, which is transferred to the magnetic field sensor 44 via the magnetic flux rings 46 and 48 and the magnetic flux concentrators 56 and 58. The same advantages are achieved as in the first embodiment. The magnetic field sensor 44 is mounted together with its sensor housing 66 in the radial direction, which can be seen in Figure 4. This sensor housing 66 is fixed by a housing 68, with the steering shaft 10 being decoupled from the housing 68 via pivot bearings 70.

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In this embodiment, the magnetic field sensor 44 is also arranged in a protected manner and is easy to install, and the signal has no ripple due to the magnetic flux concentrators 56 and 58. The signal generated by the magnetic field sensor 44 corresponds directly to the applied torque.

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Claims (13)

1. Device for determining a torque exerted on a shaft ( 10 ), wherein the shaft ( 10 ) has a first shaft section ( 14 ) and a second shaft section ( 12 ) and the two shaft sections ( 12 and 14 ) can be rotated relative to one another, with a multipole magnet ring ( 24 ) surrounding the first shaft section ( 14 ) and connected thereto and a stator holder ( 30 ) fastened to the second shaft section ( 12 ), wherein two stator elements ( 26 , 32 ) are fastened to the stator holder ( 30 ) and each stator element ( 26 , 32 ) has fingers ( 34 , 36 ) projecting in the axial direction, which are arranged evenly distributed over at least part of the circumference and have gaps between them, wherein the fingers ( 34 , 36 ) of each stator element ( 26 , 32 ) are connected to one another via a magnetic flux ring ( 46 , 48 ), the magnetic flux rings ( 46 , 48 ) are spaced apart from one another and a magnetic field sensor ( 44 ) is arranged between the magnetic flux rings ( 46 , 48 ), wherein at least one magnetic flux concentrator ( 56 , 58 ) is assigned to the magnetic field sensor ( 44 ), characterized in that the magnetic flux concentrator ( 56 , 58 ) is provided between the magnetic flux rings ( 46 , 48 ). 2. Device according to one of the preceding claims, characterized in that a magnetic flux concentrator ( 56 , 58 ) is arranged between the magnetic field sensor ( 44 ) and each magnetic flux ring ( 46 , 48 ). 3. Device according to one of the preceding claims, characterized in that the magnetic flux concentrator ( 56 , 58 ) extends adjacent to the magnetic flux ring ( 46 , 48 ) over a portion of its circumference. 4. Device according to one of the preceding claims, characterized in that the magnetic flux concentrator ( 56 , 58 ) is adapted to the curvature of the magnetic flux ring ( 46 , 48 ). 5. Device according to one of the preceding claims, characterized in that a narrow air gap ( 42 ) is present between the magnetic flux concentrator ( 56 , 58 ) and the magnetic flux ring ( 46 , 48 ). 6. Device according to claim 5, characterized in that the air gap ( 42 ) extends in a surface extending in the circumferential direction. 7. Device according to claim 5, characterized in that the air gap ( 42 ) extends in a surface (radial plane) extending in the radial direction. 8. Device according to one of the preceding claims, characterized in that the magnetic flux concentrator ( 56 , 58 ) has a section ( 60 , 62 ) adjacent to the magnetic flux ring ( 46 , 48 ) and a section ( 64 ) adjacent to the magnetic field sensor ( 44 ). 9. Device according to claim 8, characterized in that the sections ( 60 , 62 , 64 ) are arranged in planes or surfaces which are offset from one another or at an angle to one another. 10. Device according to claim 8 or 9, characterized in that the sections ( 60 , 62 , 64 ) merge into one another via an offset. 11. Device according to one of claims 8 to 10, characterized in that the section ( 60 , 62 ) adjacent to the magnetic flux ring ( 46 , 48 ) is wider than the width of a finger ( 34 , 36 ), in particular is twice as wide. 12. Device according to one of claims 8 to 11, characterized in that the magnetic flux concentrator(s) ( 56 , 58 ) and the magnetic field sensor ( 44 ) are arranged in a common holder ( 68 ) and/or sensor housing ( 66 ). 13. Device according to one of the preceding claims, characterized in that the magnetic flux concentrator ( 56 , 58 ) extends over at least one area which corresponds to the width of two adjacent fingers ( 34 , 36 ) of a stator element ( 26 , 32 ).