WO2010003801A1

WO2010003801A1 - System for detecting a rotating magnetic field

Info

Publication number: WO2010003801A1
Application number: PCT/EP2009/057628
Authority: WO
Inventors: Rolf Baumann; Steven Andrew Evans; Jochen Geissler; Marcus Meyer; Tilo Koenig
Original assignee: Robert Bosch Gmbh
Priority date: 2008-07-11
Filing date: 2009-06-18
Publication date: 2010-01-14
Also published as: DE102008040360A1

Abstract

A system for detecting a rotating magnetic field comprises a sensor magnet and a magnetic field sensor, wherein the sensor magnet and the magnetic field sensor can perform a rotational movement relative to one another. The sensor magnet has an inner recess, wherein the magnetic field sensor is arranged within an envelope bounding said recess, but at an axial distance from the sensor magnet.

Description

title

Device for detecting a rotating magnetic field

The invention relates to a device for detecting a rotating magnetic field according to the preamble of claim 1.

State of the art

In the use of electric motors for the drive of aggregates or ancillaries in motor vehicles usually the information about the current rotational position of the rotor in the engine plays an important role, for example in drive motors of wipers in motor vehicles, in actuators for transmission or hydraulic systems or in electrical actuatable steering drives. To determine the rotational position devices for detecting a rotating magnetic field are often used, which include a sensor or encoder magnet and a magnetic field sensor for detecting the magnetic field generated by the sensor magnet. The sensor magnet is rotatably connected to the rotor of the electric motor and therefore has the same speed as the rotor. The periodically changing magnetic field of the rotating sensor magnet is detected by the magnetic field sensor, from which the current rotational angle of the rotor can be determined.

For absolute measuring systems, for example for AMR and GMR sensors, two-pole magnetized plates or disks are usually used as sensor magnets, wherein the sensor is arranged at a distance from the magnet surface and detects the rotating magnetic field. The relative position of the sensor Based on the sensor magnet has a significant influence on the strength of the detected signal, since the amplitude of the signal drops sharply with increasing distance to the magnetic surface. The position of the sensor relative to the sensor magnet has a high influence on the quality of the measurement result, so that manufacturing and component tolerances have a relatively strong effect, in particular with a small distance to the magnet. Although increasing the distance to the magnet surface reduces the dependence on tolerances, at the same time the magnetic flux density decreases, so that more sensitive sensors must be used.

Disclosure of the invention

The invention is based on the object, with simple design measures, a device for detecting a rotating magnetic field comprising a sensor magnet and an associated sensor, form so that the sensor signals are less dependent on the position of the sensor relative to the magnet, i. that on the one hand the

Reduce angular errors of the output signal and that on the other hand increases the axial operating range of the sensor system.

This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

The inventive device for detecting a rotating magnetic field is preferably used in electric motors, in particular as a servomotor of an aggregate or accessory in a motor vehicle, for example as a wiper motor in wiper devices, as a window motor or possibly also as a servo motor for transmission or hydraulic systems, in a steering or brake system. The device comprises a donor or

Sensor magnet and an associated magnetic field sensor, wherein the sensor magnet in the application to an electrical Adjusting motor rotatably connected to the rotor and thus has the same speed as the rotor. The magnetic field generated during the rotation of the sensor magnet is detected by the magnetic field sensor and can be used to calculate the rotational angle position or a change in the rotational angular position.

In the device according to the invention, the sensor magnet is at least approximately annular and includes an inner recess at least partially, in which the

Magnetic field lines run between the poles of the magnet; the inner recess forms a magnetic field line space enclosed by the surrounding ring of the sensor magnet. The magnetic field sensor is arranged within an envelope bounded by the inner recess, but at an axial distance from the inner recess. This means that although the sensor is arranged at an axial distance from the magnet, but directly above the inner recess in the magnet, the envelope coincides with the inner wall of the annular sensor magnet, which delimits the inner recess or magnetic field space, but axially projects beyond the inner wall.

The magnetic field lines extend within the inner recess at least approximately parallel to the center plane of the annular sensor magnet. With axial distance to the front of the

Sensor magnets take the field lines of the magnetic field a curved course, which has been shown in the device according to the invention that even at an axial distance from the top of the magnet, a constant flux density can be achieved. Due to the positioning of the sensor within the limited space of the envelope, a reduction of the dependence of the sensor signals is achieved by the center distance, so that on the one hand component and assembly tolerances impact less on the sensor result and on the other hand, the sensors in a much larger Achsabstandsbereich can be used to the magnet. Accordingly, also cheaper - A -

Magnetic materials used and / or smaller sized sensor magnets are used.

As a magnetic field sensor, a GMR sensor (Giant Magneto Resistance) is preferably used. Here, a significant reduction in length can be achieved. In principle, however, is also an application of other magnetic field sensors into consideration, such as AMR sensors (anisotropic magnetoresistive effect).

In order to achieve the desired effect of a flow density as constant as possible over a large axial distance between the sensor and sensor magnet, in addition to the basic requirement of the inner, central recess in the magnet further conditions may be met, in particular constructive conditions that contribute to an optimization of the desired effect , For example, a certain ratio of inner diameter to outer diameter of the sensor magnet is predetermined, wherein the ratio is preferably between 0.1 and 0.5. If the ratio is close to the value 0.5, this means that the magnet has a relatively large inner recess in relation to the outer diameter, as a result of which the region in which the sensor can be positioned axially above the magnet is correspondingly increased.

Furthermore, it has proven expedient to equip the sensor magnet with an overall axial height or thickness of 1 mm to about 8 mm. The outer diameter of the sensor magnet is preferably 5 mm to 50 mm.

Furthermore, it is expedient that the radial outer contour and the radial inner contour of the sensor magnet extend at least approximately concentrically with one another. In the case of a circular outer contour thus also the inner contour is circular, accordingly, the enclosing the magnetic field line inner space limiting cylinder shape. Instead of circular contours are also non-circular, concentric outer and inner contours into consideration, for example, angular contours such as square or rectangular. In principle, non-concentric designs are possible.

As a further optimization measure, the transition from the outer contour to an axial end face of the sensor magnet, in particular that side on which the sensor is arranged, be designed symmetrically to the transition from the inner contour to the same axial end face. Furthermore, it is possible to provide a chamfer on the inner contour and / or the outer contour, it being possible to provide both different chamfer angles and the same chamfer angle, for example a chamfer angle of 45 °. In addition, a rounded bevel can also be provided, in particular with a constant radius. The axial height of the chamfer is, based on the total height of the sensor magnet, between 10% and 90%, for example 50% or 60%. In symmetrical design, the radially inner chamfer is the same design as the radially outer chamfer.

Basically comes as an alternative to a symmetrical design, a non-symmetrical design in the formation of radial outer contour and radial inner contour on the side facing the sensor into consideration. For example, the respective axial end side of the sensor magnet in the direction of the inner contour fall straight away, possibly in combination with a straight or rounded bevel in the immediate transition to the inner contour.

According to a further preferred embodiment, it is provided that the magnetic field sensor is arranged along the longitudinal axis of the sensor magnet. Along the axis, the magnetic field lines of the sensor magnet extend at least approximately perpendicular to the axis, whereas with lateral distance from the axis, the magnetic field lines are directed at an angle to the axis. The constant angle of about 90 ° along the axis allows the Position the sensor at different axis positions along the axis, without this being accompanied by a significantly changing flux density. The design of the sensor magnet with inner recess has the advantage that in the case of a deviation of the sensor magnet or sensor position from the longitudinal axis, the generated measurement signal has a smaller angular deviation due to the more homogeneous magnetic field compared to prior art embodiments.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 is a perspective view of a device for detecting a rotating magnetic field, with an annular sensor magnet having a central recess, and a magnetic field sensor, which is arranged at an axial distance along the longitudinal axis of the sensor magnet,

2 shows a section through the annular sensor magnet,

Fig. 3 to 10 different embodiments for the structural design of the sensor magnet.

In the figures, the same components are provided with the same reference numerals.

In Fig. 1, a device 1 for detecting a rotating magnetic field is shown, consisting of an annular

Sensor magnet 2 and a magnetic field sensor 3, which is arranged in the magnetic field of the magnet 2 and is able to sense the magnetic field direction. The magnetic field 5, which emanates from the sensor or encoder magnet 2, extends in a magnetic field line or interior, which is designed as an inner recess 6 of the annular sensor magnet 2, approximately parallel to the median plane of the sensor magnet 2. With axial Distance from the end face of the sensor magnet 2, the magnetic field lines emerge from the sensor magnet and describe, starting from a pole of the bipolar, with north pole N and south pole S designated magnet, an arc in which the magnetic field lines at the second pole again enter the material of the sensor magnet.

At an axial distance a is located above the sensor magnet 2 of the magnetic field sensor 3, which is arranged in particular along the longitudinal axis 4 of the sensor magnet 2. Along the longitudinal axis, the magnetic field lines of the magnetic field 5 also extend approximately parallel to the plane of the sensor magnet. The magnetic field sensor 3 may optionally also be arranged with lateral deviation with respect to the longitudinal axis 4, but it is preferably located within an envelope which is guided through the inner side or contour 8 of the inner recess 6 within the sensor magnet 2 and extends parallel to the axis in the axial direction Longitudinal axis 4 extends.

The magnetic field sensor 3 is in particular a GMR sensor. However, other sensor types are also considered, in particular AMR sensors, TMR sensors, Hall sensors, P-Hall sensors or other sensor types.

For the material of the sensor magnet 2 can be used plastic-bonded magnetic materials containing, for example, ferrite, SmCo or NdFeB. Basically, however, sintered materials made of ferrite, SmCo or NdFeB come into consideration.

The device 1 is preferably used for position detection of the rotor of an electric motor. For this purpose, the sensor magnet 2 is rotatably connected to the rotor of the electric motor, whereas the magnetic field sensor 3 is arranged fixed to the housing. But it is also possible a reverse arrangement in which the

Magnetic field sensor fixed to the rotor and the sensor or encoder magnet is fixed to the housing. In Fig. 2, the sensor magnet 2 is shown in section. The overall height or thickness is denoted by h, the inner diameter of the inner recess 6 by d, the outer diameter of the outer contour 7 with D. On the sensor side facing the sensor magnet 2 in the region of the outer contour 7 and in the region of the inner contour. 8 in each case a chamfer 9 or 10, which assumes an angle α or β relative to the longitudinal axis 4 or a parallel to the longitudinal axis. In the embodiment, the angles α and ß are equal, they are about 45 °. In principle, however, different angles α and β for the chamfer 9 or 10 on the outer contour 7 or the inner contour 8 come into consideration.

The axial height of the chamfers 9 and 10 is denoted by c. The axial height c of the chamfers 9 and 10 is between 10% and 90% of the total axial height h of the sensor magnet. In the exemplary embodiment, c is about 60% of h.

The ratio d to D of inner diameter d to outer diameter D is preferably between 0.1 and 0.7. In absolute terms, the outer diameter D is advantageously 5 mm to 50 mm, the total axial height h is 1 mm to 8 mm.

In the figures 3 to 10 different embodiments for the sensor magnet 2 are shown.

In Fig. 3, the sensor magnet 2 is designed as a cylindrical ring with a continuous cylindrical outer contour 7 and inner contour 8 in the region of the inner recess 6.

According to Fig. 4, the outer contour 7 is cylindrical, the inner contour 8 has a chamfer 10. The envelope through the inner contour 8 can either be placed in the region of the cylindrical portion through the inner contour 8 or, according to an alternative embodiment, by the transition between the chamfer 10 and the end face of the sensor magnet 2, the mounted in the Condition facing the magnetic field sensor; in the latter case, the chamfer is enclosed by the envelope.

In Fig. 5, only one chamfer 9 is provided in the region of the outer contour 7, whereas the inner contour 8 is cylindrical and without chamfer.

In the embodiment according to FIG. 6, both a chamfer 9 in the region of the outer contour 7 and a chamfer 10 in the region of the inner contour 8 are provided; This embodiment corresponds to that of FIG. 2.

In Fig. 7, a chamfer is also provided on the inside and the outside, wherein the transition of the chamfer 10 is formed rounded in the region of the inner contour to the cylindrical portion of the inner contour.

Figures 8 and 9 substantially correspond to the embodiment of FIG. 7, but with increasing rounding in the transition between the cylindrical inner contour of the chamfer 10th

In the embodiment of FIG. 10, the chamfer 10 extends radially outward until reaching the outer chamfer 9, which is associated with the outer contour 7.

Claims

claims

1. A device for detecting a rotating magnetic field (5), comprising a sensor magnet (2) and a magnetic field sensor (3) for detecting the magnetic field generated by the sensor magnet (2), wherein the sensor magnet (2) and the magnetic field sensor (3) relative to each other can perform a rotational movement, characterized in that the sensor magnet (2) has an inner recess (6), wherein the magnetic field sensor (3) within an inner recess (6) limiting envelope, but at an axial distance to the sensor magnet (2) is arranged.

2. Device according to claim 1, characterized in that the sensor magnet (2) is at least approximately annular and an inner recess (6) at least partially encloses

3. Device according to claim 1 or 2, characterized in that the radial outer contour (7) and the radial inner contour (8) of the sensor magnet (2) extend at least approximately concentric.

4. Device according to one of claims 1 to 3, characterized in that the ratio (d / D) of inner diameter (d) to outer diameter (D) of the sensor magnet (2) is between 0.1 and 0.7.

5. Device according to one of claims 1 to 4, characterized in that the outer contour (7) and / or the inner contour (8) of the sensor magnet (2) with a chamfer (9, 10) is provided, wherein the axial height (c ) of the chamfer (9, 10) is between 10% and 90% of the total axial height (h) of the sensor magnet (2).

6. Device according to one of claims 1 to 5, characterized in that the outer diameter (D) of the sensor magnet (2) is 5 mm to 50 mm.

7. Device according to one of claims 1 to 6, characterized in that the total axial height (h) of the sensor magnet (2) is 1 mm to 8 mm.

8. Device according to one of claims 1 to 7, characterized in that the transition from the radial outer contour (7) to an axial end face of the sensor magnet (2) is symmetrical to the transition from the radial inner contour (8) to the axial end face.

9. Device according to one of claims 1 to 8, characterized in that the transition from the inner contour (8) to an axial end face of the sensor magnet (2) is provided with a radius.

10. Device according to one of claims 1 to 9, characterized in that the sensor (3) zugewanden and opposite sides of the sensor magnet (2) are not parallel, so that over the radius of the sensor magnet (2) forms a variable wall thickness, which decreases towards the longitudinal axis.

11. Device according to one of claims 1 to 10, characterized in that the magnetic field sensor (3) is a GMR sensor.

12. Device according to one of claims 1 to 11, characterized in that the magnetic field sensor (3) is arranged at least approximately along the longitudinal axis (4) of the sensor magnet (2).

13. Electric motor, in particular electric DC motor with a device according to one of claims 1 to 12, wherein the sensor magnet (2) is rotatably connected to the rotor of the electric motor.