DE102018108303A1 - Method for producing a ring magnet, injection mold, ring magnet and steering torque sensor - Google Patents

Abstract

The invention relates to a method for producing a ring magnet (1) for a steering torque sensor (2) for a motor vehicle (3), comprising the following steps: - providing an injection mold (4) with a substantially annular injection molding cavity (5) which surrounds a central axis (6), the injection molding cavity (5) having a central axis (6) facing peripheral surface (7) with a plurality of segments (8), wherein between adjacent segments (8) in each case an angle (12) is formed, - introducing a plasticized plastic (10) offset with magnetic particles (9) into the injection molding cavity (5), aligning the magnetic particles (9) inside the injection molding cavity (5) by means of a magnetizing device (11) arranged around the injection molding cavity (5), and solidifying of the plasticized plastic (10) .Furthermore, the invention relates to an injection mold (4) for producing a ring magnet (1) for a steering moment sensor (2) for a force tfahrzeug (3), a ring magnet (1) for a steering torque sensor (2) for a motor vehicle (3) and a steering torque sensor (2) for a motor vehicle (3).

Description

The present invention relates to a method for producing a ring magnet for a steering torque sensor for a motor vehicle. Furthermore, the invention relates to an injection mold for producing a ring magnet for a steering torque sensor, a ring magnet for a steering torque sensor for a motor vehicle and a steering torque sensor for a motor vehicle.

Modern motor vehicles often have steering devices in which a steering wheel is coupled via a steering force amplifying device to a steering axle of the motor vehicle. In order to increase the steering force, known power steering devices in particular have an electrical boost device. In generic steering devices continue to be a mechanical coupling of the steering wheel with the steering axle. For detecting a steering torque applied via the steering wheel, such steering devices have a steering torque sensor, which is also referred to as "torque-only sensor" or TOS.

There are steering torque sensors are known which work by utilizing the so-called "Hall effect". Accordingly, for example, an electric current is deflected by an applied magnetic field so that due to the Lorentz force creates an electrical voltage. About the size of this electrical voltage, the strength of the magnetic field can be determined, which in turn is proportional to the applied steering torque. In this way, the steering torque introduced by the steering wheel can be reliably determined.

Known steering moment sensors have a multipole magnetized magnet, in particular a ring magnet, which is usually annular or hollow cylindrical. The individual poles are arranged distributed with alternating magnetic polarity and side by side over the circumference of the ring magnet. Generic ring magnets are for example from the DE 36 89 967 T2 , of the WO 2017/120687 A1 and the DE 25 18 653 known.

Steering torque sensors with such ring magnets have the disadvantage that a magnetic flux in the circumferential direction has a sinusoidal linearity error. This means that an amount of magnetic flux in a central region of a pole has a maximum and decreases to edge regions of the pole to zero. A linearity error in ring magnets has the disadvantage that an accuracy of the determination of the steering torque is thereby reduced.

Various methods are known for reducing the linearity error. Thus, for example, a special, in particular a radial, semi-lateral or the like, magnetization of the ring magnet can be carried out in an injection molding tool in order to magnetize different areas of a pole to different degrees. This can be done for example by means of a special magnetization head or a special arrangement of permanent magnets. In addition, methods are known in which an isotropic magnetic material is used, wherein a magnetization takes place only after removal from the injection molding tool by means of a special Magnetisierkopfes.

Known measures to reduce the linearity error have the disadvantage that they are often very expensive, require a particularly high production cost or are only partially suitable for reducing the linearity error.

It is therefore the object of the present invention to provide a method for producing a ring magnet for a steering torque sensor for a motor vehicle, an injection mold for producing a ring magnet for a steering torque sensor, a ring magnet for a steering torque sensor for a motor vehicle and a steering torque sensor for a motor vehicle, which Disadvantages of the prior art do not have or at least partially not. It is in particular the object of the present invention to provide a method for producing a ring magnet, an injection mold, a ring magnet and a steering torque sensor, which produce or have a reduced linearity error in a simple manner and inexpensively.

The above problem is solved by the claims. Accordingly, the object is achieved by a method for producing a ring magnet for a steering torque sensor for a motor vehicle according to the independent claim 1, an injection mold for producing a ring magnet for a steering torque sensor according to the independent claim 8, a ring magnet for a steering torque sensor for a motor vehicle according to the independent claim 9 and solved by a steering torque sensor for a motor vehicle according to the independent claim 10.

• - Bereitstellen einer Spritzgussform mit einer im Wesentlichen ringförmigen Spritzgusskavität, welche sich um eine Mittelachse erstreckt, wobei die Spritzgusskavität eine der Mittelachse zugewandte Umfangsfläche mit mehreren Segmenten aufweist, wobei zwischen benachbarten Segmenten jeweils ein Winkel ausgebildet ist,
• - Einbringen eines mit Magnetteilchen versetzten plastifizierten Kunststoffs in die Spritzgusskavität,
• - Ausrichten der Magnetteilchen innerhalb der Spritzgusskavität mittels einer um die Spritzgusskavität herum angeordneten Magnetisiervorrichtung, und
• - Erstarren des plastifizierten Kunststoffs.

According to a first aspect of the invention, the object is achieved by a method for producing a ring magnet for a steering torque sensor for a motor vehicle. The method comprises the following steps:

• - Providing an injection mold with a substantially annular Spritzgusskavität which extends around a central axis, said Spritzgusskavität one of the central axis facing peripheral surface having a plurality of segments, wherein between adjacent segments in each case an angle is formed,
• Introducing a plasticized plastic mixed with magnetic particles into the injection molding cavity,
• Aligning the magnetic particles within the injection molding cavity by means of a magnetizing device arranged around the injection molding cavity, and
• - Solidification of the plasticized plastic.

First, an injection mold for producing the ring magnet is provided. The injection mold has a substantially annular Spritzgusskavität, which is formed in a mold base body of the injection mold. A substantially annular shape is understood according to the invention to mean a shape which, for example, can be enveloped by an annular shell shape and deviates only slightly from this annular shell shape. The injection molding cavity extends around the center axis and has a peripheral surface facing the central axis and a peripheral surface facing away from the center axis. The circumferential surface facing away from the center axis is arranged between the peripheral surface facing the central axis and the central axis. More preferably, the peripheral surface facing away from the central axis has an annular cross-section. The peripheral surface facing the central axis has a cross section with a plurality of sections, wherein an angle is formed between two adjacent sections. These sections may have a convex, concave or straight configuration. Moreover, the Spritzgusskavität is laterally limited by side surfaces. The injection mold preferably has at least two molded parts movable away from one another in order to be able to remove the finished injection molded part from the injection molding cavity of the injection mold.

In the Spritzgusskavität the closed injection mold plasticized plastic is introduced together with magnetic particles. As plastic, a thermoplastic material is preferably used. A plasticized plastic is understood to mean a plastic which, in particular by a corresponding heating, has a flowable state and thus can be adapted to the shape of the injection molding cavity. It is preferably introduced so much plasticized plastic with magnetic particles in the Spritzgusskavität that the Spritzgusskavität is completely filled, so that the ring magnet to be produced has no pores or air pockets. The magnetic particles preferably have a length of less than 1 mm. Preferably, the magnetic particles are formed in powder form. More preferably, the magnetic particles are the same size or at least substantially the same size. It is also preferable that the magnetic particles have a magnetizable material or are formed of a magnetizable material. Furthermore, the magnetic particles are preferably uniformly or at least substantially uniformly mixed with the plasticized plastic.

By means of the magnetizing device, which is arranged around the Spritzgusskavität around, the magnetic particles are aligned. The alignment can also be referred to as magnetizing. The magnetizing device is preferably arranged in the injection mold, surrounding the injection molding cavity in the circumferential direction. Alternatively, the magnetizing device may be arranged on an outer side of the injection mold and surrounding the injection mold. The magnetizing device may have, for example, permanent magnets and / or electromagnets for aligning the magnetic particles. The magnetizing device is designed to selectively magnetize the individual segments of the peripheral surface facing away from the central axis, in particular such that each segment has a defined polarization.

Subsequently, the plasticized plastic, in particular by cooling, solidified. Preferably, the solidification is such that the magnetic particles are fixed in the aligned position by the solidified plastic. For this purpose, it may be provided that the alignment is carried out by means of the magnetizing device until complete solidification of the plasticized plastic. Subsequently, the injection mold can be opened and the finished ring magnet can be removed from the injection molding cavity.

An inventive method for producing a ring magnet for a steering torque sensor for a motor vehicle over conventional methods has the advantage that with simple means and in a cost-effective manner, a ring magnet can be produced having an outer peripheral surface with a non-circular, in particular polygonal, cross-section and thus has no or at least a significantly reduced linearity error.

According to a preferred development of the invention, it may be provided in a method that an injection mold is used in which the peripheral surface of the injection molding cavity facing the central axis has segments of uniform design. The uniformly shaped segments have the same shape and preferably the same size. More preferably, an equally large angle is formed between all adjacent segments. A cross section of the circumferential surface facing the central axis is preferably in accordance with a uniform design Polygon formed. This has the advantage that a ring magnet with a particularly small linearity error can be produced in a simple manner and inexpensively.

It is inventively preferred that an injection mold is used, wherein each segment of the central axis facing peripheral surface is plate-shaped, wherein adjacent segments are arranged at a predefined angle to each other. In the context of the invention, a plate-shaped design is understood to mean a design having a flat, in particular non-curved, surface. A cross section of the central axis facing peripheral surface is thus formed according to a polygon. The use of such an injection mold has the advantage that with simple means and cost, a ring magnet with a particularly small linearity error can be produced.

More preferably, an injection mold is used, in which the central axis facing circumferential surface of the injection molding cavity has sixteen juxtaposed segments. In this way, for example, a ring magnet can be produced which has eight segments with a first magnetic pole and eight segments with a second magnetic pole opposite the first magnetic pole. Such a ring magnet is particularly suitable for the production of a steering torque sensor.

In a particularly preferred embodiment of the invention may be provided in a method that are used as magnetic particles ferrite magnets. Ferrite magnets are also referred to as FE magnets. The ferrite magnets are preferably provided as FE powder. Ferrite magnets are available inexpensively, have a good magnetizability and are therefore particularly suitable for the cost-effective production of ring magnets.

Preferably, a permanent magnet magnetizer is used, the permanent magnets comprising a rare earth material. Permanent magnets have the advantage that a targeted and reproducible orientation of the magnetic particles is improved. By means of rare-earth material, permanent magnets with a particularly high and permanent magnetic flux density can be produced in an advantageous manner. The orientation of the magnetic particles can thus be further improved in an advantageous manner.

It can be inventively provided that the magnetic particles are aligned such that magnetic particles of adjacent magnetic segments of the ring magnet have an opposite orientation. Preferably, the magnetic particles are aligned such that magnetic particles associated with a first magnetic segment are aligned in accordance with a magnetic north pole and magnetic particles of a second magnetic segment adjacent to the first magnetic segment according to a south magnetic pole. The magnetic poles of the ring magnet thus have radially away from the central axis. In this way, a ring magnet can be produced, which has a particularly low linearity deviation and is particularly suitable for a steering torque sensor.

According to a second aspect of the invention, the object is achieved by an injection mold for producing a ring magnet for a steering torque sensor for a motor vehicle. The injection mold has a mold base body and an injection molding cavity formed in the mold base body, which extends around a center axis of the injection molding cavity. According to the invention, the injection mold is designed for carrying out a method according to the invention.

The injection mold has a substantially annular Spritzgusskavität, which is formed in a mold base body of the injection mold. A substantially annular shape is understood according to the invention to mean a shape which, for example, can be enveloped by an annular shell shape and deviates only slightly from this annular shell shape. The injection molding cavity extends around the center axis and has a peripheral surface facing the central axis and a peripheral surface facing away from the center axis. The circumferential surface facing away from the center axis is arranged between the peripheral surface facing the central axis and the central axis. More preferably, the peripheral surface facing away from the central axis has an annular cross-section. The peripheral surface facing the central axis has a cross section with a plurality of sections, wherein an angle is formed between two adjacent sections. These sections may have a convex, concave or straight configuration. Moreover, the Spritzgusskavität is laterally limited by side surfaces. The injection mold preferably has at least two molded parts movable away from one another in order to be able to remove the finished injection molded part from the injection molding cavity of the injection mold.

In the described injection mold for producing a ring magnet for a steering torque sensor for a motor vehicle, all the advantages that have already been described for a method for producing a ring magnet for a steering torque sensor for a motor vehicle according to the first aspect of the invention. Accordingly, the injection mold according to the invention compared to conventional injection molds the advantage that with simple means and in a cost effective manner, a ring magnet can be produced, which has an outer peripheral surface with a non-circular, in particular polygonal, cross-section and thus no or at least a significantly reduced linearity error.

According to a third aspect of the invention, the object is achieved by a ring magnet for a steering torque sensor for a motor vehicle. The ring magnet has a substantially annular base body extending around a central axis, the base body having magnetic particles embedded in a plastic, and wherein the base body has an outer peripheral surface facing away from the central axis and extending in the circumferential direction of the ring magnet. According to the invention, the outer circumferential surface has a plurality of magnet segments, wherein an angle is formed between two adjacent magnet segments. Magnetic particles of adjacent magnet segments are different, in particular oppositely magnetically oriented. The ring magnet according to the invention is preferably produced according to a method according to the invention.

The magnet segments of the outer peripheral surface of the ring magnet according to the invention are preferably plate-shaped and / or uniform and / or of equal size. Between the adjacent magnet segments, an equally large angle is preferably formed in each case. Preferably, the outer peripheral surface of the ring magnet has a, in particular regular, polygonal cross section. The ring magnet has a, in particular thermoplastic, plastic. Furthermore, the ring magnet has aligned magnetic particles which are embedded in the plastic. The magnetic particles preferably have a length of less than 1 mm. The magnetic particles are aligned such that adjacent magnetic segments are formed as opposite magnetic poles. The magnetic poles of the ring magnet are remote in the radial direction from the central axis.

In the case of the ring magnet according to the invention for a steering torque sensor for a motor vehicle, all the advantages already result from a method for producing a ring magnet for a steering torque sensor for a motor vehicle according to the first aspect of the invention and to an injection mold for producing a ring magnet for a steering torque sensor for a motor vehicle have been described according to the second aspect of the invention. Accordingly, the ring magnet according to the invention over conventional ring magnet has the advantage that it can be produced by simple means and in a cost-effective manner, and an outer peripheral surface having a non-circular, in particular polygonal, cross-section and thus no or at least a significantly reduced linearity error.

According to a fourth aspect of the invention, the object is achieved by a steering torque sensor for a motor vehicle. According to the invention, the steering torque sensor has a ring magnet according to the invention.

In the steering torque sensor for a motor vehicle according to the invention, all the advantages that already result from a method for producing a ring magnet for a steering torque sensor for a motor vehicle according to the first aspect of the invention, to an injection mold for producing a ring magnet for a steering torque sensor for a motor vehicle according to the second Aspect of the invention and to a ring magnet for a steering torque sensor for a motor vehicle according to the third aspect of the invention have been described. Accordingly, the steering torque sensor according to the invention over conventional steering torque sensors has the advantage that it can be produced by simple means and in a cost-effective manner, and a ring magnet having an outer peripheral surface with a non-circular, in particular polygonal, cross-section with no or at least a significantly reduced linearity error having.

• 1 in einem Ablaufdiagramm eine bevorzugte Ausführungsform des erfindungsgemäßen Verfahrens,
• 2 in einer Schnittdarstellung eine bevorzugte Ausführungsform einer erfindungsgemäßen Spritzgussform,
• 3 in einer Seitenansicht eine bevorzugte Ausführungsform eines erfindungsgemäßen Ringmagneten, und
• 4 in einer Seitenansicht ein Kraftfahrzeug mit einem erfindungsgemäßen Lenkmomentsensor.

Reference to the accompanying drawings, the invention is explained in more detail below. Each show schematically:

• 1 in a flow chart a preferred embodiment of the method according to the invention,
• 2 in a sectional view, a preferred embodiment of an injection mold according to the invention,
• 3 in a side view a preferred embodiment of a ring magnet according to the invention, and
• 4 in a side view of a motor vehicle with a steering torque sensor according to the invention.

Elements with the same function and mode of action are in the 1 to 4 each provided with the same reference numerals.

In 1 a preferred embodiment of the method according to the invention is shown schematically in a flowchart. In a first process step 100 becomes an injection mold 4 (see. 2 ) having a substantially annular Spritzgusskavität 5 (see. 2 ) provided. The injection molding cavity 5 extends around one central axis 6 (see. 2 ). Furthermore, the Spritzgusskavität 5 the injection mold 4 one of the central axis 6 facing peripheral surface 7 (see. 2 ) with several segments 8th (see. 2 ), where between adjacent segments 8th one angle each 12 (see. 2 ) is trained. In a second process step 200 becomes a plasticized plastic 10 (see. 3 ) in the Spritzgusskavität 5 introduced, in particular by means of an injection molding device. In the plasticized plastic 10 are magnetic particles 9 (see. 3 ) arranged. In a third process step 300 be the inside of the injection mold cavity 5 arranged magnetic particles 9 by means of a around the Spritzgusskavität 5 Magnetizer arranged around 11 (see. 2 ). In this way, each one segment 8th associated magnetic particles 9 aligned such that they form a magnetic pole, either a south pole or a north pole. magnetic 9 , which neighboring segments 8th are assigned are magnetized such that they form a different magnetic pole. In a fourth process step 400 becomes the plasticized plastic 10 solidified, especially by cooling. Cooling may be passive by exposure to ambient temperature or actively by exposure to a cooling medium such as air, in particular cooled air. Subsequently, the finished ring magnet 1 from the injection molding cavity 4 removable. This is the injection mold 4 preferably apparently.

2 shows a preferred embodiment of an injection mold according to the invention 4 schematically in a sectional view. The injection mold 4 has a mold body 14 with a first half of the mold 17 and a second mold half 18 on. The injection mold 4 is shown in a closed state. To open the injection mold 4 are the first half of the mold 17 and the second half of the mold 18 away from each other. In the mold body 14 is an injection molding cavity 5 formed, wherein a first part of the Spritzgusskavität 5 in the first half of the mold 17 and a second part of the injection molding cavity 5 in the second half of the mold 18 is trained. The injection molding cavity 5 has a substantially annular cross-section and is about a central axis 6 trained around. One of the middle axis 6 facing peripheral surface 7 has several segments 8th on, being between two adjacent segments 8th an angle 12 is trained. The middle axis 6 facing peripheral surface 7 thus has a polygonal cross section. To the injection molding cavity 5 around is a magnetizer 11 for aligning in the injection molding cavity 5 arranged magnetic particles 9 arranged.

In 3 is a preferred embodiment of a ring magnet according to the invention 1 schematically shown in a side view. The ring magnet 1 has a basic body 15 with a substantially annular cross-section which extends around a central axis 6 extends. An outer peripheral surface 16 of the ring magnet 1 , which from the central axis 6 facing away, has a plurality of plate-shaped magnetic segments 13 on, which are arranged side by side. Between adjacent magnet segments 13 is each an angle 12 educated. Thus, the ring magnet 1 on the outer peripheral surface 16 polygonal trained. The main body 15 has a plastic 10 in which aligned magnetic particles 9 are arranged. The magnetic particles 9 are aligned so that the magnet segments 13 are each formed as a magnetic pole. There are adjacent magnet segments 13 designed as different magnetic poles. Due to the plate-shaped design of the magnet segments 13 points the ring magnet 1 a particularly low linearity deviation and is thus for use in a steering torque sensor 2 (see. 4 ) for a motor vehicle 3 (see. 4 ) particularly suitable. The ring magnet according to the invention 1 is preferably according to a method of the invention, in particular using an injection mold according to the invention 4 , produced.

4 shows a motor vehicle 3 with a steering torque sensor according to the invention 2 schematically in a side view. The car 2 has a steering system 19 on, which is indicated only schematically in this illustration. The steering system 19 is as an active steering system 19 designed so that a steering of the motor vehicle 3 is relieved for a driver. For determining a driver's steering wheel via an unillustrated steering wheel of the steering system 19 applied steering torque has the steering system 19 a steering torque sensor according to the invention 2 on, which is indicated only schematically in this figure.

LIST OF REFERENCE NUMBERS

1

ring magnet

2

Steering torque sensor

3

motor vehicle

4

injection mold

5

Spritzgusskavität

6

central axis

7

facing peripheral surface

8th

segment

9

magnetic

10

plastic

11

magnetizing

12

angle

13

magnetic segment

14

Form body

15

body

16

outer peripheral surface

17

first half of the mold

18

second mold half

19

steering system

100

first process step

200

second process step

300

third process step

400

fourth process step

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 3689967 T2 [0004]
• WO 2017/120687 A1 [0004]
• DE 2518653 [0004]

Claims (10)

Method for producing a ring magnet (1) for a steering torque sensor (2) for a motor vehicle (3), comprising the following steps: - Providing an injection mold (4) having a substantially annular Spritzgusskavität (5) which extends around a central axis (6), said Spritzgusskavität (5) one of the central axis (6) facing peripheral surface (7) with a plurality of segments (8) having an angle (12) between adjacent segments (8), Introducing a plasticized plastic (10) offset with magnetic particles (9) into the injection molding cavity (5), - Aligning the magnetic particles (9) within the Spritzgusskavität (5) by means of a about the Spritzgusskavität (5) arranged around magnetizing device (11), and - Solidification of the plasticized plastic (10). Method according to Claim 1 , characterized in that an injection mold (4) is used, wherein the said central axis (6) facing peripheral surface (7) of the Spritzgusskavität (5) has uniformly shaped segments (8). Method according to Claim 1 or 2 , characterized in that an injection mold (4) is used, wherein each segment (8) of the central axis (6) facing peripheral surface (7) is plate-shaped, wherein adjacent segments (8) arranged at a predefined angle (12) to each other are. Method according to one of the preceding claims, characterized in that an injection mold (4) is used, wherein the peripheral surface (7) of the injection molding cavity (5) facing the center axis (6) has sixteen juxtaposed segments (8). Method according to one of the preceding claims, characterized in that ferrite magnets are used as magnetic particles (9). Method according to one of the preceding claims, characterized in that a magnetizing device (11) is used with permanent magnets, wherein the permanent magnets comprise a rare earth material. Method according to one of the preceding claims, characterized in that the magnetic particles (10) are aligned such that magnetic particles (10) of adjacent magnetic segments (13) of the ring magnet (1) have an opposite orientation. Injection mold (4) for producing a ring magnet (1) for a steering torque sensor (2) for a motor vehicle (3), comprising a mold base body (14) and an injection molding cavity (5) formed in the mold base body (14), which surrounds a central axis ( 6) of the injection molding cavity (5), characterized in that the injection mold (4) for carrying out a method according to one of Claims 1 to 7 is trained. Ring magnet (1) for a steering torque sensor (2) for a motor vehicle (3), comprising a substantially annular base body (15) extending around a central axis (6), the base body (15) embedding magnetic particles embedded in a plastic material (10) (9), and wherein the base body (15) facing away from the central axis (6), in the circumferential direction of the ring magnet (1) extending outer peripheral surface (16), characterized in that the outer peripheral surface (16) a plurality of magnetic segments (13), wherein between two adjacent magnet segments (16) an angle (12) is formed, wherein magnetic particles (9) of adjacent magnetic segments (13) are oriented differently magnetically, and wherein the ring magnet (1) in particular according to a method according to one of Claims 1 to 7 is made. Steering torque sensor (2) for a motor vehicle (3), characterized in that the steering torque sensor (2) a ring magnet (1) according to Claim 9 having.

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