Sensor arrangement for a torque and / or angle sensor

Abstract

A sensor arrangement (1) for a torque and / or angle sensor, comprising a tubular segment-shaped magnetic ring (2) which is fastened to a support sleeve (3) via an intermediate element (4), wherein the intermediate element (4) and the magnetic ring (2) are integrally connected to one another via opposing joining surfaces (22, 42), and the intermediate element (4) is formed from a plastic at least in the region of the joining surface (42), wherein the support sleeve (3) is tubular segment-shaped and has a radially outwardly projecting fastening element (31) in one end region, wherein the magnetic ring (2) is designed as a plastic-bonded magnet made of a plastic material filled with magnetic particles, which is integrally connected to the plastic of the intermediate element (4), wherein the intermediate element (4) and the magnetic ring (2) are welded or glued together, characterized by that the fastening element (31) is arranged in an axially form-fitting manner between opposing end faces (21, 41) of the magnetic ring (2) and the intermediate element (4), and a cylindrical-tubular base body of the carrier sleeve (3) is arranged coaxially within the magnetic ring (2) with radial play.

Description

Prior ArtThe invention relates to a transmitter arrangement for a torque and / or angle sensor, which has a tubular-section-shaped magnetic ring which is fastened to a carrier sleeve via an intermediate element, wherein the intermediate element and the magnetic ring are connected to one another in a materially bonded manner via mutually directed joining surfaces, and the intermediate element is formed from a plastic at least in the region of the joining surface, wherein the carrier sleeve is formed in the shape of a tubular section and has a fastening element projecting radially outwards in an end region, wherein the magnetic ring is formed as a plastic-bonded magnet made from a plastic material filled with magnetic particles, which is connected to the plastic of the intermediate element in a materially bonded manner, wherein the intermediate element and the magnetic ring are welded or bonded to one another.In power-assisted steering systems of motor vehicles, the steering torque introduced by the driver via the steering wheel into the steering shaft is detected and an auxiliary torque derived therefrom is coupled into the steering system. The torque is determined by measuring the relative angle of rotation between two sections of the steering shaft coupled via a torsion bar, i.e. the torque-dependent rotation. The relative angle of rotation can be detected by means of a magnetic angle of rotation sensor, in which an encoder element of the type mentioned at the beginning is attached to one section of the steering shaft in a rotationally fixed manner with a coaxial magnetic ring, and a magnetic field sensor arrangement is attached to the other section of the steering shaft, which magnetic field sensor arrangement detects changes in the magnetic field when the magnetic ring is rotated relative to one another and passes them on as a control variable to the power assist control. Moreover, by evaluating the changes in the magnetic field of the magnetic ring relative to the fixed vehicle body, the total amount of the steering angle can be determined.In the prior art, DE 10 2008 047 466 A1 discloses a transmitter arrangement in the form of a magnet assembly. The fastening on a steering shaft is effected by means of a tubular carrier sleeve which is arranged coaxially with respect to the likewise tubular magnetic ring in a rotationally fixed manner. In order to prevent mechanical stresses from being exerted on the magnet ring, for example, during temperature changes from the carrier sleeve, which usually consists of metal, an intermediate element is arranged between the carrier sleeve and the magnet ring, so that the magnet ring is only mechanically coupled to the intermediate element and decoupled from the carrier sleeve. It is proposed here to cast the magnet ring with the intermediate element made of plastic in an injection molding process, so that the magnet ring is connected with the plastic of the intermediate element in a form-fit and / or firmly bonded manner via toothing or undercut geometries.Although the connection in the injection molding process by inserting the magnetic ring into the injection mold is reliable, it is expensive and inflexible from a manufacturing standpoint. This procedure in the prior art is explained by the fact that the ferromagnetic sintered material usually used for the magnetic ring is relatively brittle and accordingly sensitive to mechanical stresses. The positive-locking elements additionally provided in the joining surface on the magnet ring-the aforementioned toothing or undercut geometries-are required due to the material properties of the sintered material with respect to the connection to the plastics intermediate element and mean an additional manufacturing outlay for the magnet ring.From EP 1 123 794 B1, it is known to configure the magnet ring as a plastic-bonded magnet, in the form of a plastic part highly filled with magnetic powder. The higher mechanical load capacity of the magnet obtained thereby is to be used for a force-fit and / or form-fit connection to an intermediate element which is connected to the carrier sleeve in a known manner. As already in the aforementioned DE 10 2008 047 466 A1, form-fit elements must likewise be realized, as a result of which a correspondingly high level of production and assembly effort is produced.A sensor arrangement having the features mentioned at the beginning is known from DE 10 2013 015 452 A1. A disadvantage here is that the magnetic ring can be damaged by thermal stresses.In view of the problems explained above, it is an object of the present invention to specify an improved encoder arrangement.SUMMARY OF THE INVENTIONTo solve the aforementioned problems, it is proposed according to the invention that the fastening element is arranged axially in a form-fitting manner between mutually directed end faces of the magnet ring and intermediate element, and a cylindrical-tubular main body of the carrier sleeve is arranged coaxially within the magnet ring with radial play.The magnet ring of a transmitter element according to the invention consists of a composite material in which ferromagnetic magnetic powder-preferably hard ferrite or rare earth magnetic powder-are embedded in a plastic matrix. The magnetic properties are determined by the magnetizable material and the degree of filling, which specifies the proportion by weight of the magnetic powder in relation to the plastic material of the plastic matrix. Because the magnetic particles are bonded adhesively and cohesive in the plastic matrix, advantageous properties of the magnetic ring are obtained, namely a higher mechanical and thermal stability and breaking strength. This circumstance is used, as described in the prior art, for the form-fit and force-fit fixing of the magnet ring.The present invention makes it possible for the first time to considerably simplify the previously complicated attachment of the magnetic ring to the intermediate element by producing a durable cohesive connection between the mutually directed, i.e. mutually abutting, joining surfaces of magnetic ring and intermediate element instead of a positively or non-positively locking connection. In contrast to the prior art, in which complicated combined joining techniques are required for compliance with the predetermined safety standards when fastening the magnetic ring to the carrier sleeve, a particularly reliable, permanently fixed and reliable connection by means of material bonding is made possible according to the invention.The particular advantage of the invention is based on the fact that solid material-bonded connections can only be realized in a sufficiently durable manner if both joining partners-here the magnetic ring and the intermediate element-have materials at least in the region of their joining surfaces which are compatible for a material-bonded connection, i.e. are as well suited as possible. In the invention, this can be realized by selecting the plastic matrix of the magnet ring and the plastic from which the intermediate element is made from plastic materials which are compatible with one another with regard to the parameters which define the strength of a cohesive connection, such as, for example, material-specific adhesion behavior, surface condition, etc. Specifically, in order to realize the invention, the plastic matrix, in which the magnetic material is embedded, is matched accordingly to the plastic from which the intermediate element is manufactured.With regard to a rational production of a transmitter arrangement according to the invention, it is advantageous that the magnetic ring and the intermediate element can be provided individually and are joined together in a materially bonded manner only during the assembly of the carrier sleeve. This enables a lower production outlay and a greater flexibility than in the transmitter arrangements known in the prior art.A particularly preferred embodiment of the invention provides that the plastic of the intermediate element and the plastic material of the magnet ring are thermoplastic polymers compatible with respect to a cohesive connection. Thermoplastic polymers can be adapted to the most varied requirements with regard to their mechanical, thermal and chemical material properties and can be processed well by means of thermal production methods, for example in plastic injection molding. In this way, both the intermediate element and the magnetic ring can be produced cost-effectively as injection molded parts with little effort. In the plastic matrix of the magnetic ring, it is taken into account that a sufficiently high degree of filling with magnetic particles and processing by means of established thermal plastic processing methods such as injection molding, thermoforming and the like is possible. The plastic material of the intermediate element preferably has a similar or identical polymer matrix to the magnetic ring. This achieves the effect that a particularly secure cohesive connection can be produced by means of thermal joining techniques, with a material structure which passes homogeneously through the joint, i.e. in which the plastic in the joint has identical material properties as within the joining partners. A cohesive connection by means of adhesive bonding can likewise be realized in a particularly secure and durable manner in that the adhesive used can be optimally adapted to the one plastic material used jointly for the magnetic ring and intermediate element, or to the compatible and thus similar plastic materials. This ensures a firm and secure adhesion to the joining surfaces of the magnetic ring and intermediate element.As thermoplastic polymers, use can be made, for example, of polyamides (PA), polypropylenes (PP), polyphenylene sulfides (PPS) or other thermoplastic plastics.Advantageously, the intermediate element and / or the magnetic ring is formed as an injection-molded part. Production by plastic injection molding can be effected efficiently with the required properties. The magnetic ring can alternatively be designed as a pressed part, wherein a higher filling degree with magnetic particles can be realized.The plastic material from which the magnetic ring is made is preferably highly filled with magnetic particles, preferably with a filling degree of between 80% and 97% based on the mass. For production by injection molding, the range of 84%-94% is particularly suitable, up to 97% in a molded part.The intermediate element and the magnetic ring are welded, preferably ultrasonic welded. During the welding, the plastic material is thermally locally melted in the region of both joining surfaces and brought into contact with one another, so that a homogeneously continuous material structure is formed during the solidification of the melt. Friction welding methods, generally referred to interchangeably here as ultrasonic welding, are particularly well suited for the material-bonded connection of plastic parts. In this case, vibrations are coupled into the joint via a welding punch, during ultrasonic welding via a so-called sonotrode, wherein the joint surfaces locally melt and are connected to one another as a result of the internal molecular and boundary surface friction which arises. After solidification, the magnetic ring and the intermediate element together form a one-piece component which can no longer be separated in a non-destructive manner by the material-bonded or here materially bonded connection of the involved plastics. Alternatively to ultrasonic welding, welding by means of a laser beam can also be used.To improve the ultrasonic welding, it is furthermore advantageous that welding material reservoirs protruding relative to the joining surface are formed on the intermediate element and / or on the magnetic ring. These are also referred to as welding preparations and can be formed by ribs or projections which are formed on the respective joining surface of the joining partner or partners. When the joining surfaces are brought together, the weld preparations first come into contact with one another, melt and fill the joining gap in a materially integral manner. This ensures the quality of the weld within relatively large dimensional tolerances.An alternative configuration of the materially bonded connection provides that the intermediate element and the magnetic ring are bonded to one another. The bonding takes place by means of an adhesive which adheres as optimally as possible to the plastic material of both the magnet ring and the intermediate element. In the invention, this can be achieved by using compatible plastics which have identical or at least very similar adhesion properties with respect to a cohesive connection by means of the adhesive. In a manner known per se, the adhesive can be applied to one or both joining surfaces, which are subsequently brought into contact. The mounting of the magnet ring and the intermediate element together with the carrier sleeve can be effected efficiently in this way.Preferably, the magnetic ring is connected on a substantially axial end face to an axial end face of the intermediate element. In this case, an annular or circular ring segment-shaped joining surface can be formed on an end face of the substantially tube-section-shaped magnetic ring, which surface corresponds to a corresponding joining surface on the intermediate element.For the relative alignment or fixing, positive locking elements can be arranged on the magnetic ring and / or the intermediate element in the region of the joining surfaces. The form-fit elements can have, for example, mutually corresponding projections and depressions which engage one another when the joining surfaces are joined together. Alternatively, it is conceivable to insert positioning pins in a form-fitting manner through corresponding openings or recesses in the magnetic ring and in the intermediate element. This makes it possible to ensure optimum relative positioning during the mounting of the magnetic ring on the intermediate element. After the assembly of the materially bonded connection, the positioning pins can be removed again or remain in the component.The carrier sleeve is designed in the form of a tube section and has a fastening element projecting radially outwards in an end region. The fastening element can be designed in the manner of a flange, with a continuously encircling collar or flange ring on the outside, or with a plurality of projections or flange segments projecting radially outwards from the pipe section. The flange ring or the flange segments can be connected to the intermediate element, for example via a cohesive and / or positive connection. The fastening element can be arranged at the end face or at a distance from the end.Play is present in the radial direction, so that a thermal expansion of the carrier sleeve, which is typically made of metal, preferably of steel, does not transmit any stresses to the magnetic ring.DESCRIPTION OF THE DRAWINGSAdvantageous embodiments of the invention are explained in more detail below with reference to the drawings. In detail, the following show: FIG. 1 shows a transmitter arrangement according to the invention in a perspective view, FIG. 2 shows a longitudinal section through the transmitter arrangement according to FIG. 1, FIG. 3 is an exploded view of the transmitter arrangement according to FIG. 1 , FIG. 4 shows a longitudinal section as in FIG. 2 through the elements of the transmitter arrangement before assembly, FIG. 5 shows a detailed view of the sectional representation from FIG. 2.Embodiments of the InventionIn the various figures, identical parts are always provided with the same reference numerals and are therefore generally also designated or mentioned only once in each case.FIG. 1 shows a perspective view of a transmitter arrangement 1 according to the invention at an angle to the longitudinal axis A. This is formed by a magnet ring 2 and a carrier sleeve 3 which is attached to the magnet ring 2 via a substantially annular intermediate element 4.The intermediate element 4 has an annular basic shape and has a joining surface 42 on its axial end face 41 directed against the magnetic ring 2. The intermediate element 4 is formed from plastic, preferably as an injection molded part made from a first thermoplastic.The magnetic ring 2 has the basic shape of a cylindrical tube section with an axial end face 21 directed against the intermediate element 4, on which a joining surface 22 is formed, which corresponds to the joining surface 42 of the intermediate element 4. The magnet ring 1 is designed as a plastic-bonded magnet, made of a plastic material highly filled with magnetic powder. The plastic material is preferably likewise a thermoplastic, in the plastic matrix of which the ferromagnetic magnetic particles of the magnetic powder are embedded.According to the invention, the plastic material from which the intermediate element 4 is formed and the plastic material that forms the plastic matrix of the magnetic ring 2 are compatible with one another with respect to a cohesive connection, here preferably a thermal weld. It is conceivable that the first and second plastic material are formed from an identical polymer, for example polyamide (PA), polypropylene (PP), polyphenylene sulfide (PPS) or other, or at least from similar, compatible polymer materials, which enable a cohesive connection in the melt for thermal weldability, or are compatible with respect to their surface properties with respect to a cohesive connection by means of an adhesive introduced between the joining surfaces 22 and 42.The carrier sleeve 3 has a cylindrical-tubular base body made of metal, preferably made of steel, which is arranged coaxially within the magnet ring 2 with radial play and has, at its end facing the intermediate element 4, a radially outwardly projecting, annularly encircling flange 31, which forms a fastening element of the carrier sleeve 3. One axial end face 32 of the flange 31 is directed axially toward the intermediate element 4, and the other axial end face 33 toward the magnetic ring 2.To produce a transmitter arrangement 1, the magnet ring 2, the intermediate element 4 and the carrier sleeve 3 are provided and moved relative to one another in the axial direction from the pre-assembly position shown in FIGS. 3 and 4, wherein the flange 31 of the carrier sleeve 3 is positioned axially between the magnet ring 2 and the intermediate element 4, as shown in FIG. 2.From the enlarged illustration in FIG. 5, it can be seen that the intermediate element 4 has an axial recess radially inside the joining surface 42, in which recess the flange 31 of the carrier sleeve 3 is received as illustrated. A one-piece composite component is formed by a cohesive connection of the intermediate element 4 to the magnetic ring 2 on the joining surfaces 22 and 42, wherein the flange 31 of the carrier sleeve 3 is held in an axially positively locking manner in the now axially covered recess. In this case, no material or form-fitting connection is produced between the carrier sleeve 3 and the magnet ring 2, so that the transmission of mechanical stresses, for example due to different thermal expansion, from the metallic carrier sleeve 3 to the magnet ring 2 is ruled out.The material-bonded connection between the axially mutually adjoining joining surfaces 22 and 42 can be produced by a thermal welding method, preferably by friction or ultrasonic welding. For this purpose, the magnetic ring 2 is axially supported, while a welding punch 5, preferably a sonotrode 5 of an ultrasonic welding device, is pressed axially from the outside, i.e. from the free end side in the region of the joining surface 42, axially against the intermediate element 4, as indicated in FIG. 5 by the arrow. In this case, the joining surface 42 is pressed against the corresponding joining surface 22 on the magnetic ring 2 and vibrational energy is coupled in, as a result of which the joining surfaces 22 and 42 are heated and partially melted.The joining surface 22 of the magnetic ring 2 has an axially projecting projection 23, which in the embodiment shown is formed as a circumferential rib with a cutting-edge-shaped cross section.As a result, a welding material reservoir is provided, which is already melted at the beginning of the welding when the projection 23 first comes into contact with the joining surface 42. The molten or at least pasty plastic distributes itself in the joining gap between the joining surfaces 22 and 42, wherein in the boundary surface region a diffusion or mixing of the plastic materials of the magnetic ring 2 and the carrier sleeve 4 occurs.In the region of the joining surface 42, a form-fit element 44 can likewise be formed in the form of an axially projecting, annularly encircling rib. This can engage in a corresponding depression 24 in the joining surface 22. As a result, the intermediate element 4 can be easily positioned relative to the magnetic ring 2.After the end of the ultrasonic excitation, the plastic solidifies in the joining region, so that a cohesive connection is produced and a one-piece composite component made of plastic is formed from the intermediate element 4 and the magnetic ring 2. In the radial recess delimited by the recess 43 and the end face 21, the flange 31 is fixed in a form-fitting manner with respect to the axial direction.Alternatively, a liquid or pasty adhesive can be introduced between the joining surfaces 22 and 42 which is optimally adapted to the plastic materials of the magnetic ring 2 and the intermediate element 4 with regard to a cohesive connection.

Claims

Transmitter arrangement (1) for a torque and / or angle sensor, which has a tubular-section-shaped magnetic ring (2) which is fastened to a carrier sleeve (3) via an intermediate element (4), wherein the intermediate element (4) and the magnetic ring (2) are connected to one another in a materially integral manner via mutually directed joining surfaces (22, 42), and the intermediate element (4) is formed from a plastic at least in the region of the joining surface (42), wherein the carrier sleeve (3) is formed in the shape of a tubular section and has a fastening element (31) projecting radially outwards in an end region, wherein the magnetic ring (2) is formed as a plastic-bonded magnet from a plastic material filled with magnetic particles, which is connected to the plastic of the intermediate element (4) in a materially integral manner, wherein the intermediate element (4) and the magnetic ring (2) are welded or bonded to one another, characterized in that, the fastening element (31) is arranged axially form-lockingly between mutually directed end faces (21, 41) of the magnetic ring (2) and intermediate element (4), and a cylindrical-tubular main body of the carrier sleeve (3) is arranged coaxially within the magnetic ring (2) with radial play.Transmitter arrangement according to Claim 1, characterized in that the plastic of the intermediate element (4) and the plastic material of the magnetic ring (2) are thermoplastic polymers which are compatible with respect to a cohesive connection.Transmitter arrangement according to Claim 1, characterized in that the intermediate element (4) and / or the magnetic ring (2) is designed as an injection-moulded part.Transmitter arrangement according to Claim 1, characterized in that the magnetic ring (2) is designed as a pressing part.Transmitter arrangement according to Claim 1, characterized in that the plastic material of the magnetic ring (2) is highly filled with magnetic particles, with a filling degree of between 80% and 97% based on the mass.Transmitter arrangement according to Claim 1, characterized in that the magnetic ring (2) is connected on a substantially axial end face (21) to an axial end face (41) of the intermediate element (4).

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