WO2007014599A1

WO2007014599A1 - Apparatus for detecting revolutions of a steering shaft

Info

Publication number: WO2007014599A1
Application number: PCT/EP2006/005922
Authority: WO
Inventors: Ekkehart Froehlich; Jens Thom
Original assignee: Valeo Schalter Und Sensoren Gmbh
Priority date: 2005-07-29
Filing date: 2006-06-21
Publication date: 2007-02-08
Also published as: DE102005038516A1

Abstract

The invention relates to an apparatus (2) for detecting revolutions of a steering shaft (8), having a permanent magnet (16, 60), which is coupled to the movement of the steering shaft (8) and describes an annular path (24) when the steering shaft (8) rotates, which annular path passes by a magnetic field sensor (26), which is fixed in position in relation to the permanent magnet (16, 60), wherein the permanent magnet (16, 60) has poles (36, 38; 64, 66), which are opposite one another when viewed within the profile of the annular path (24), and wherein a ferromagnetic element (18, 62) is arranged adjacent to the permanent magnet (16, 60).

Description

Title: Device for detecting revolutions of a steering shaft

description

The invention relates to a device for detecting revolutions of a steering shaft, with a coupled with the movement of the steering shaft permanent magnet which describes an annular path upon rotation of the steering shaft, which passes on a stationary relative to the permanent magnet magnetic field sensor.

Such sensors are based on the Hall effect, which can be used to measure magnetic fields in an existing between the permanent magnet and the magnetic field sensor air gap.

The known Hall sensors are relatively robust and also suitable for applications in which high temperatures can occur. Due to the increasing integration of various components and assemblies in a motor vehicle, however, there is the problem that influence these components or assemblies each other.

On this basis, the present invention is based on the object, a device for the detection of To create revolutions of a steering shaft, with the magnetic interference can be minimized.

This object is achieved in that the permanent magnet seen within the course of the annular path having opposite poles and that adjacent to the permanent magnet, a ferromagnetic element is arranged.

Characterized in that seen along the course of the annular path of the permanent magnet to each other opposite poles, formed between the opposite poles magnetic field lines can be influenced in their course so that they extend from a first pole to an opposite pole, without taking up space and thus the surroundings of the device are magnetically disturbing around the entire magnet.

With the help of the ferromagnetic element, which is arranged adjacent to the permanent magnet, the magnetic field lines can be reduced spatially limited, so that closed magnetic field lines arise. In particular, the magnetic field lines can be returned to a limited extent on one side of the magnet. The magnetic field thus generated is locally limited and thus has a less magnetic influence on the environment of the device. The ferromagnetic element thus has a shielding effect. In addition, the magnetic field generated according to the invention is also relatively dense and thus easy to detect for a magnetic field sensor, in particular for a magnetic field sensor with a unipolar switching characteristic

The ferromagnetic element may be arranged in a plane parallel to the annular path. As a result, a space which is arranged relative to the ferromagnetic element on a side opposite to the permanent magnet side, at least largely freed from magnetic interference.

The ferromagnetic element may also be radially offset relative to the annular track. When the ferromagnetic element is radially inwardly offset, magnetic perturbations in a radially more inwardly offset region can be minimized. When the ferromagnetic element is offset radially outward, magnetic perturbations in a radially outward offset region can be minimized.

The permanent magnet can, in particular on its free side, at least one north pole and at least one south pole exhibit. The permanent magnet thus has at least two mutually opposite poles.

The permanent magnet may have a pole arranged on the outside of the opposite central pole. This embodiment has the advantage that a particularly homogeneous and dense magnetic field is created, which is also evaluable with a magnetic field sensor which generates a digital output value. This embodiment also has the advantage that a locally particularly pronounced magnetic field is created.

If the sections of material which form the respectively opposite poles of the permanent magnet are the same size, in a permanent magnet with two poles a point-symmetrical magnetic field and in a permanent magnet with three poles a mirror-symmetrical magnetic field can be created. These symmetries have the advantage that the passage of the permanent magnet on the magnetic field sensor can be detected equally well in both directions of rotation.

The ferromagnetic element is advantageously formed by a ferrous metal sheet. This metal sheet also has a shielding effect, in particular when the metal sheet is formed so that it projects beyond the permanent magnet on all sides. A particularly advantageous embodiment provides that the permanent magnet and the ferromagnetic element are arranged on a common carrier. This arrangement facilitates the accurate positioning of the permanent magnet and the ferromagnetic element to each other. At the same time the unit of carrier, permanent magnet and ferromagnetic element is easy to handle.

When the common carrier is formed of plastic material, the magnetic field formed between the permanent magnet and the magnetic field sensor is not affected. In addition, there are production-related freedoms, so that the permanent magnet and the ferromagnetic element can be injected into the carrier. But it is also possible that the permanent magnet and the ferromagnetic element are glued or welded into the carrier.

If the common carrier is designed as a ring member which is non-rotatably connected to the steering shaft and / or with a torque sensor arranged on the steering shaft, a circular path for the permanent magnet can be generated in a particularly simple manner, thereby ensuring that the permanent magnet with a exact, predetermined distance (air gap) can be passed to the magnetic field sensor. Particular advantages arise when the common carrier is arranged adjacent to a torque sensor, as in this case, Hall sensors can be used for the torque sensor. These are not or only slightly disturbed by the described, shielded course of the magnetic field between the permanent magnet and the magnetic field sensor. The shielding effect is particularly good when the ferromagnetic element is arranged in the axial direction of the steering shaft between the permanent magnet and the torque sensor.

The common carrier can also be part of one

Be torque sensors, so that a unit can be created, which requires only a few parts. In this case, non-influencing Hall sensors or sensors for controlling the steering of a motor vehicle can be used in a small space.

Associated with such a component integration may be that the magnetic field sensor of the device for detecting revolutions of the steering shaft is arranged on or on a circuit board which is at least partially associated with a torque sensor. The invention further relates to various methods for operating a device for detecting revolutions of a steering shaft.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawing, a particularly preferred embodiment is described in detail. The features shown in the drawing and mentioned in the claims and in the description may each be essential to the invention individually or in any combination.

In the drawing show:

Figure 1 is a perspective view of a structural unit of a device for detecting revolutions of a steering shaft and a torque sensor when mounted on a steering shaft;

Figure 2 is a perspective view of a carrier for a permanent magnet and a ferromagnetic element; FIG. 3 shows a magnetic field formed by the permanent magnet and the ferromagnetic element according to FIG. 2;

FIG. 4 shows the magnetic induction generated by the magnetic field according to FIG. 3;

Figure 5 plotted the magnetic induction over different angles of rotation of the steering shaft for different air gaps between the permanent magnet and the magnetic field sensor;

Figure 6 is a view corresponding to Figure 5 for a two-pole magnet. and

FIG. 7 shows a view corresponding to FIG. 3 for the two-pole magnet according to FIG. 6.

In FIG. 1, a device for detecting revolutions of a steering shaft is denoted overall by the reference numeral 2. Adjacent to this device 2, a torque sensor 4 is arranged, wherein the device 2 and the torque sensor 4 form a structural unit 6. This structural unit 6 is mounted on a steering shaft 8, wherein the steering shaft shaft portions 10 and 12, which are rotatable relative to each other. The Shaft sections 10 and 12 are rotatable relative to each other, wherein between the shaft sections 10 and 12 applied torsional force can be detected by the torque sensor 4.

The torque sensor 4 has a housing part, which is designed as an annular support 14, which consists of a plastic material. This is shown in Figure 2, in perspective. The carrier 14 is rotatably connected to the shaft portion 10 and serves, inter alia, to hold components associated with the stator side of the torque sensor 4. On the carrier 14, a permanent magnet 16 and a ferromagnetic element 18 is further arranged. The permanent magnet 16 and the ferromagnetic element 18 are formed in accordance with Figure 2 is substantially cuboid.

Both the permanent magnet 16 and the ferromagnetic element 18 may, however, also extend along a circular arc, in particular adapted to the annular course of the carrier 14.

When the steering shaft 8 is moved in directions of rotation indicated by 22a and 22b, the permanent magnet 16 moves along a circular path 24 schematically indicated in FIG. 4. The ferromagnetic element 18 moves in a plane parallel to the web 24. The permanent magnet 16 can be passed with a corresponding rotational position of the steering shaft 8 to a stationary magnetic field sensor 26, wherein between the permanent magnet 16 and the magnetic field sensor 26, an air gap is formed. The magnetic field sensor 26 is arranged on a circuit board 28, which is also associated with the torque sensor 4. The circuit board 28 has a second magnetic field sensor 30, which is assigned to the torque sensor 4.

The carrier 14 is formed substantially rotationally symmetrical and has an annular bead 32, with which the carrier 14 is rotatably connected to the shaft portion 10 of the steering shaft 8. From the bead 32 extends radially outwardly an annular disc 34, in which the permanent magnet 16 and the ferromagnetic element 18 are injected. In Figure 2, the carrier 14 is shown cut in a portion of the annular disc 34 to make the shape of the permanent magnet 16 and the ferromagnetic element 18 more visible.

The permanent magnet 16 has according to Figure 3 a total of three poles and that is a central north pole 36 and two outside south poles 38. The outside south poles 38 have the same length together as the central north pole 36. The permanent magnet 16 and the ferromagnetic elements 18 are arranged in parallel planes. In this case, the ferromagnetic element 18 extends in its plane beyond the outer sides of the permanent magnet 16 addition, which is particularly well visible in Figure 4.

The magnetic field generated by the described structure of permanent magnet 16 and ferromagnetic element 18 is shown in Figure 3 based on magnetic field lines. The magnetic field has main field lines 40 which extend arcuately from the north pole 36 back to one of the south poles 38, pass therethrough and are returned via the ferromagnetic element 18. The magnetic field also has adjacent field lines 42, which extend approximately laterally adjacent to the south poles 38. As a result of the described arrangement, the magnetic field lines 40 and 42 extend outside the material of the permanent magnet 16 and of the ferromagnetic element 18 only in a region which, viewed from the ferromagnetic element 18, faces the permanent magnet 16. As a result, the rear region in which the torque sensor 4 is arranged can be freed of interfering magnetic field influences, so that the function of the magnetic field sensor 30 is not impaired. If, as shown in FIG. 4, the permanent magnet 16 is moved along the annular path indicated by 24 and is guided past the magnetic field sensor 26, a magnetic induction is produced. The field strength detected by the magnetic field sensor is shown in FIG. In this case, the north pole 36 is associated with a magnetic induction 44, and the south poles 38 each have an opposite magnetic induction 46. The magnetic inductions 44 and 46 have local maxima, which are assigned to the centers of the respective poles 36 and 38.

FIG. 5 shows a diagram in which the Tesla values of the magnetic inductions 44 and 46 are plotted over different angles of rotation of the steering shaft 8. The magnetic inductions 44 and 46 cause the magnetic field sensor 26 to produce an output signal 48 whose value is 0 or 1.

FIG. 5 shows further courses of magnetic inductions 50 and 52. These inductions are compared with the magnetic Inductions 44 and 46 associated with smaller air gaps between the permanent magnet 16 and magnetic field sensor 26, so that the local maxima of the magnetic Inductions 50 and 52 are more pronounced. Regardless of the choice of the air gap, the course of the magnetic induction 44 and 46 intersect with the Runs 50 and 52 in areas that are associated with approximately a rotation angle of the steering shaft 8 of -5 ° and + 5 °. In this case, the exact angular positions are determined by the position of the pole transitions between the north pole 36 and the south poles 38. It is therefore advantageous to adapt the switching thresholds of the magnetic field sensor 26 to these crossing regions, so that the changeover between the values 0 and 1 occurs when the switching threshold 54 designated 54 is exceeded or undershot. As a result, a tolerant to sensor deviations that affect the air gap, tolerant sensor arrangement can be created.

Due to the three-pole design of the permanent magnet 16, the courses of the magnetic inductions 44, 46, 50 and 52 are such that the transition from a negative magnetic induction (eg 46) to a positive magnetic induction (eg 44) with a comparatively steep gradient accompanied. As a result, the switching thresholds 54 are assigned to a very small angular range, as a result of which the values of the output signal 48 can change precisely and reproducibly between 0 and 1.

The magnetic field sensor 26 may have some hysteresis despite the described steep gradient. This means that the magnetic field sensor 26 when exceeded a first switching threshold of "0" to "1" and when a second switching threshold falls below the value of the hysteresis is less than the value of the first switching threshold, again provides an output signal "0". For the described example it follows that the switching point for the change from "0" to "1" is associated with a rotation angle which is -5.3 ° (see reference numeral 72 in FIG. 5). When the output signal 48 changes from the value "1" to "0", the magnitude of this value is assigned to an angle of rotation which is, for example, 5.4 °, ie in absolute value, due to the fact that the second switching threshold is slightly lower than the first switching threshold is slightly larger (see reference numeral 74 in Figure 5). Since this difference in the position of the switching points is reproducible, an exact reference point (reference point or "index center", reference numeral 76) can be created with the aid of the mean value of the switching points and a correction of the hysteresis can optionally be carried out using additionally available information about the direction of rotation of the steering shaft 8 ,

In particular, when the switching thresholds 54 are not at the level of the crossing regions, the width between the switching points 72 and 74 depends on the air gap between the permanent magnet 16 and the magnetic field sensor 26. The position of the index center 76 is, however, from this air gap independent and can be used as an exact reference position.

If the index center 76 is known, tolerances of the overall lengths of the centric pole 36 of the permanent magnet 16 can be computed by means of an evaluation unit. In a corresponding manner, rotational angle tolerances can be compensated, which result during assembly of the carrier 14 on the steering shaft 8.

FIG. 6 shows the course of a magnetic induction 56 for a two-pole magnet shown in FIG. 7, again plotted over the angle of rotation of the steering shaft 8. In a region adjacent to 0 °, the profile has a local minimum and, subsequently, a steep flank which leads to leading to a local maximum. The magnetic induction is point symmetric about a zero crossing designated 58. The magnetic induction 56 generated by means of the two-pole permanent magnet 60 shown in FIG. 7 can be evaluated, for example, by a linear magnetic field sensor which outputs an output signal proportional to the magnetic induction. In this case, the zero crossing 58 corresponds to a reference position, which can be determined precisely by the fact that the described edge in the region of the zero crossing 58 is very steep. According to FIG. 7, the permanent magnet 60 is arranged adjacent and parallel to a ferromagnetic element 62. The permanent magnet 60 has a south pole 64 and a north pole 66, each occupying half of the material of the permanent magnet 60. By the permanent magnet 60, a magnetic field is generated having 68 designated main field lines, which lead from the north pole 66 to the south pole 64 and via the ferromagnetic element 62 back to the north pole. Furthermore, the magnetic field has side-field lines 70 arranged laterally. The permanent magnet 60 and the ferromagnetic element 62 may be arranged in the carrier 14 instead of the permanent magnet 16 and the ferromagnetic element 18 (see FIG. 2).

The permanent magnets 16 and 18 and their ferromagnetic elements 18 and 62 can also be arranged on the radially outer circumference of the annular disc 34, so that the permanent magnet 16 and the permanent magnet 60 faces radially outward and the ferromagnetic element 18 and 62 in the radial direction inside is arranged. The associated magnetic field sensor 26 can then be positioned in the radial direction outside and in alignment with the permanent magnet 16 or 60.

Claims

claims

1. A device (2) for detecting revolutions of a steering shaft (8), with a with the movement of the steering shaft (8) coupled to the permanent magnet (16, 60), upon rotation of the steering shaft (8) has an annular path

(24), which passes on a relative to the permanent magnet (16, 60) fixed magnetic field sensor (26), characterized in that the permanent magnet (16, 60) within the course of the annular path (24) seen mutually opposite poles (36, 38, 64, 66) and that adjacent to the permanent magnet (16, 60) a ferromagnetic element (18, 62) is arranged.

2. Device (2) according to claim 1, characterized in that the permanent magnet (16, 60) at least one north pole (36, 66) and at least one south pole (38, 64).

3. Device (2) according to claim 1 or 2, characterized in that the permanent magnet (16, 60) has a pole (38) arranged on the outside opposite the central pole (36).

4. Device (2) according to at least one of the preceding claims, characterized in that the material portions which respectively form opposite poles (36, 38; 64, 66) of the permanent magnet (16, 60) are of equal size.

5. Device (2) according to at least one of the preceding claims, characterized in that the ferromagnetic element (18, 62) is formed by a ferrous metal sheet.

6. Device (2) according to at least one of the preceding claims, characterized in that the permanent magnet (16, 60) and the ferromagnetic element (18, 62) are arranged on a common carrier (14).

7. Device (2) according to claim 6, characterized in that the common carrier (14) is formed from plastic material.

8. Device (2) according to claim 6 or 7, characterized in that the permanent magnet (16, 60) and the ferromagnetic element (18, 62) injected into the carrier (14), glued or welded.

9. Device (2) according to at least one of claims 6 to 8, characterized in that the common carrier (14) is designed as a ring member, the non-rotatably connected to the steering shaft (8) and / or with a the steering shaft (8) arranged torque sensor (4) is connected.

10. Device (2) according to at least one of claims 6 to 9, characterized in that the common carrier (14) is arranged adjacent to a torque sensor (4).

11. Device (2) according to at least one of claims 6 to 10, characterized in that the common carrier (14) is part of a torque sensor (4).

12. Device (2) according to at least one of the preceding claims, characterized in that the ferromagnetic element (18, 62) in the axial direction of the steering shaft (8) between the permanent magnet (16, 60) and a torque sensor (4) is arranged.

13. Device (2) according to at least one of the preceding claims, characterized in that the magnetic field sensor (26) of the device (2) for detecting revolutions of the steering shaft on or on a circuit board (28) is arranged, at least partially the torque sensor ( 4) is assigned.

14. Device (2) according to at least one of the preceding claims, characterized in that the ferromagnetic element (18, 62) in a to annular path (24) is arranged parallel plane.

15. Device (2) according to at least one of the preceding claims, characterized in that the ferromagnetic element (18, 62) is arranged radially offset relative to the annular path (24).

16. A method for operating a device (2) according to at least one of the preceding claims, characterized in that for determining the position of the permanent magnet (16, 60) relative to the magnetic field sensor (26) by a mutually opposite poles (36, 38; 64, 66) of the permanent magnet (16, 60) caused gradient of the magnetic field sensor (26) detected magnetic field strength is taken into account.

17. The method according to claim 16, characterized in that when exceeding a predetermined limit, the gradient, a switching point (72, 74) is assigned.

18. The method according to claim 17, characterized in that two mutually adjacent switching points (72, 74) are determined that a reference point (76) is determined, which is located centrally between the switching points (72, 74) and that the reference point (76) of a Reference position of the permanent magnet (16, 60) relative to the magnetic field sensor (62) corresponds.