GB2313418A

GB2313418A - Bearing carrier

Info

Publication number: GB2313418A
Application number: GB9709897A
Authority: GB
Inventors: Walter Mehnert; Hans-Hubertus Wolff; Klaus Engel
Original assignee: FER Fahrzeugelektrik GmbH
Current assignee: FER Fahrzeugelektrik GmbH
Priority date: 1996-05-20
Filing date: 1997-05-16
Publication date: 1997-11-26
Also published as: DE19719744A1; GB9709897D0; IT1293096B1; FR2748809A1; ITFI970115A1; ITFI970115A0

Abstract

A bearing arrangement (6) for a shaft (8)), whose angular position is to be tracked for measurement thereof by a rotary pick-up device, is supported in a carrier (1) made of a plastics material which has at least approximately the same coefficient of thermal expansion as the material from which the bearing arrangement is made. The carrier is injection-moulded around the bearing. The plastics material may be reinforced with carbon fibres. The bearing arrangement may be of steel.

Description

Bearing carrier The invention concerns a bearing carrier and more specifically a bearing carrier for a rotary pick-up device.

Typical forms of inductive rotary pick-up or sensor devices as can be found for example in German patent specification No 41 13 745 or German laid-open application (DE-OS) No 41 27 209 include a part or parts which rotate with a rotary shaft to monitor, and a stationary part or parts cooperable with the rotary parts. The parts of the sensor which rotate with the shaft to be monitored and the parts which are arranged stationarily with respect to the shaft must be very accurately positioned and guided relative to each other if a high degree of measuring accuracy and resolution are to be achieved.

In order to ensure that precise positioning and guidance effect, the actual sensor and the shaft to be monitored are already assembled at the manufacturer to constitute a unit, out of the housing of which only the end of the shaft monitored by the sensor projects while a connecting cable for the power supply and for the transmission of the measurement data is taken out of the housing at another location. That unit can then be fixedly mounted at the location of installation by way of suitable mounting devices.

In that respect an essential part is played by the bearing carrier of this unit, which on the one hand is provided with or connected to the above-mentioned mounting devices and which on the other hand is designed to receive a bearing arrangement, by means of which the shaft to be monitored is rotatably mounted and held in the appropriate position.

It is clear that, in order to achieve a high level of measuring accuracy and resolution for the rotary pick-up device, the requirements made in regard to the strength and stability of the bearing carrier and the freedom from play and load-bearing capability of the connection between the bearing carrier and the bearing arrangement must be high, in which respect that connection has to carry both shearing and tensile forces acting in the direction of the longitudinal axis of the shaft and also tilting moments which act transversely to that direction.

In order to be able to satisfy those requirements over as wide as range as possible of temperatures at which such a rotary pick-up device may be used, hitherto both the bearing carrier and also the bearing arrangement were made from steel with a high degree of accuracy, fitted to each other and durably connected together for example by adhesive connections.

Disadvantages with such an arrangement however are the high weight of the bearing carrier made from steel, which amounts to up to 50% of the weight of the overall sensor arrangement, a complicated and expensive post-treatment involving copper-plating and nickel-plating, and the mounting procedure which involves a series of working steps and the automation of which, insofar as it is at all possible, requires a high level of appratus expenditure.

In accordance with the invention there is provided a bearing carrier for a rotary pick-up device, adapted to receive a bearing arrangement for a shaft whose angular position is to be tracked for measurement thereof by the rotary pick-up device, wherein the bearing carrier comprises a plastics material which has at least approximately the same coefficient of thermal expansion as the material from which the bearing arrangement is made, and wherein the bearing carrier is produced in the form of an injection moulding which is connected to the bearing arrangement by being injection-moulded therearound.

Because of the particularly high load-bearing capability of steel, preferably a bearing arrangement consisting of that material is used in conjunction with a plastics material which is reinforced with carbon fibre particles and which enjoys a very high level of strength and the coefficient of thermal expansion of which can be controlled by the proportion of carbon and can preferably be adjusted in a range of between 10 x 10 and 15 x 10 per X, which very well matches the coefficient of thermal expansion of the kinds of steel which are normally used for bearing arrangements of that kind, which is about 12 x 10 per K. At the same time the proportion of carbon provides for good electrical conductivity, which is always wanted.

As plastics materials mixed with carbon fibre particles have comparatively little adhesion to smooth surfaces, to ensure that the bearing arrangement is fixed in the bearing carrier in a reliable manner such that the fixing can carry heavy loadings, those two components are positively lockingly connected together, which is possible without involving additional assembly expenditure by virtue of the bearing carrier being injection-moulded around the bearing arrangement.

An important aspect in regard to supporting a shaft which is to be monitored by a rotary pick-up device is that of being able to carry tilting moments which may be very high and which act on the shaft transversely to the axis of rotation thereof, without deformation phenomena and without a reduction in the ease of shaft rotatability. For that purpose the shaft is preferably supported by means of two axially spaced-apart bearings, more particularly ball bearings, the axial spacing of which on the one hand should be as large as possible, but on the other hand can generally only be a fraction of the axial length of each of the two bearings, because of the low structural height which is frequently required for such rotary pick-up devices.

It is therefore usual to provide between the two bearings a spacer ring of suitable thickness, which, in accordance with the state of the art, is of the same outside diameter as or a slightly smaller outside diameter than the two bearings, so that it can be pushed jointly with them into the cylindrical bearing bore extending through a bearing carrier which is also made of steel.

In comparison, in a preferred embodiment of the invention the spacer ring is of a different and in particular larger outside diameter than the two bearings so that it projects radially beyond the peripheral surfaces thereof. When such a bearing arrangement which has been pushed on to the shaft to be mounted and is in a prestressed condition thereon is fitted into the injection moulding mould for the bearing carrier and has the plastics material injection-moulded therearound, then, even if the bearing carrier has end faces aligned flush with the exposed end faces of the two bearings and is thus of the minimum possible axial length in that region.

that configuration provides a positively locking connection between the bearing arrangement and the bearing carrier, which can carry even high forces acting in the direction of the axis of the shaft, as the spacer ring which preferably comprises steel and which is fully embedded with its radially projecting region into the plastics material of the bearing carrier is only loaded in respect of shear by such forces.

If the demands made in terms of that load-bearing capability are lower, the spacer ring may also be of a smaller outside diameter than the two bearings. In the operation of injection-moulding the bearing carrier around the bearing arrangement, the procedure then results in the formation on the bearing carrier of a bead or ridge which projects radially into the interior of the opening extending around the bearing arrangement, which is otherwise cylindrical, the bead or ridge projecting in between the two bearings and securing them to prevent axial displacement.

If plastics materials with an elevated processing temperature are to be used for the operation of injection-moulding the bearing carrier around the bearing arrangement, there is the danger of the bearing grease becoming too hot when the plastics material is directly injection-moulded around the bearings. In such situations, in accordance with an advantageous alternative embodiment of the invention, the bearing arrangement includes a prefereably metal bearing bush in which the bearings can be fitted prior to or after the injection-moulding operation.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 is a view in axial section through a first embodiment of a bearing carrier in which a spacer ring disposed between two bearings of the bearing arrangement projects radially, and Figure 2 is a view in section corresponding to the sectional view in Figure 1 through a further embodiment in which the two bearings are surrounded by a substantially cylindrical bearing bush.

The bearing carriers shown in each of the Figures are each in the form of a substantially radially symmetrical mounting flange.

Referring initially to both of Figures 1 and 2, each of the bearing carriers 1, 1' has a central, substantially cylindrical opening which extends therethrough and in which a bearing arrangement 6, 6' including two ball bearings 3, 4 and a spacer ring 5, 5' is so positioned that the rotary shaft 8 which is mounted in the two bearings 3, 4 and the rotary movement of which is to be tracked for measurement thereof by a sensor (not shown) of a rotary pick-up device extends through the bearing carrier 1, 1' coaxially with respect to the axis of symmetry thereof.

With reference now more specifically to Figure 1 the spacer ring 5 which is included between the two ball bearings 3, 4 that are arranged axially one behind the other is of such an outside diameter that it projects in a radial direction beyond the outer peripheral surfaces of the ball bearings, and thus engages into a peripheral groove in the cylindrical inside surface of the through opening of the bearing carrier 1.

In manufacture of the illustrated arrangement, that peripheral groove is automatically formed by virtue of the fact that the bearing carrier 1 which is reinforced with carbon fibre particles is injectionmoulded around the bearing arrangement 6 which has already been pushed on to the shaft 8 and prestressed in position thereon.

The above-mentioned prestressing effect is achieved by the two inner bearing races 10, 11 being urged in an axial direction towards each other after insertion of the shaft 8. That results in a bearing arrangement which is prestressed in an O-shape.

In the injection moulding procedure with which the bearing carrier 1 is produced, a plurality of arresting or mounting pins 14 of which only two are shown in Figure 1 are simultaneously injected into the bearing carrier 1. The pins 14 extend parallel to the axis of rotation of the shaft 8 and project with a substantial part of their length beyond the end face of the bearing carrier 1, which faces upwardly in the Figure. They serve to hold in a defined position the parts (not shown) of the rotary pick-up device which do not rotate with the shaft 8. The ends of the mounting pins 14, which are embedded into the plastics material of the bearing carrier 1, can be provided with an end thickening or grooving or knurling (not shown) to produce a positively locking connection.

As can further be seen from Figure 1, the end face of the bearing carrier 1, beyond which the mounting pins 14 project, has an edge bead or ridge 15 which projects in the axial direction and which extends over the entire periphery thereof and whose cylindrical inside surface serves for receiving with a precise fit a measuring chamber 18 of which part is shown at 18 in Figure 1 and which belongs to the measuring portion of the rotary pick-up device (not shown). Figure 1 shows the part of the measuring chamber 18, which is connected to the bearing carrier 4 which serves as a bottom for the housing of the pick-up device. Fitted on to the cylindrical outside surface of the edge bead or ridge 15 is a housing cap 17 which encloses the rotary pick-up device and of which also only the part immediately adjacent to the bearing carrier 1 is shown.

The end face of the bearing carrier 1, which faces towards the interior of the housing and beyond which the mounting pins 14 project, is covered by an electrically conductive plate 20 which preferably comprises metal and which has a central opening 21 through which the shaft 8 projects inwardly. The diameter of that central opening 21 is approximately equal to the inside diameter of the outer bearing race 23 of the ball bearing 3 so that the plate 20 projects with its inside edge beyond the through opening in the bearing carrier 1, which accommodates the bearing arrangement, and it thus contributes to fixing the bearing arrangement in place in the bearing carrier.

The plate 20 is anchored in the bearing carrier 1 by virtue of the fact that the plate 20 has peripherally spaced, radial projections 25 of which only one is shown in Figure 1. Those projections 25 extend through the edge bead or ridge 15 to such an extent that they are exposed with their peripheral edges at the cylindrical outside surface of the bead or ridge 15 and as a result can come into electrically conductive engagement with the housing cap 17 which is fitted on to the assembly.

In that way the plate 20 is positively lockingly connected to the bearing carrier 1 and, with the cap 17 which also comprises an electrically and magnetically conductive material, forms a Faraday cage which screens the interior of the housing, in which the rotary pick-up device is disposed, from interference fields.

It will be seen from the foregoing description that, prior to the operation of injection moulding the bearing carrier 1, the plate 20 is also positioned jointly with the bearing arrangement 6 in the injection moulding mould for the bearing cararier 1, and is connected thereto by being injection-moulded therearound.

Looking now at Figure 2 the spacer ring 5' between the two bearings 3, 4 is of the same outside diameter as them and is enclosed with them jointly by an axially extending, substantially cylindrical bearing bush 28 which comprises metal and into which the two bearings 3, 4 and the spacer ring 5' can be fitted either prior to or after the injection moulding operation.

The bearing bush 28 affords the advantage that it makes it possible to use plastics materials with relatively high injection moulding temperatures for the injection moulding procedure, because, due to its thermal capcity, it prevents overheating of the grease of the bearings 3, 4 which are already fitted into it prior to the injection moulding operation.

If the bearings 3, 4 and the spacer ring 5' are already fitted into the bearing bush 28 before the operation of injection-moulding the plastics material around the bearing bush 28, then, as shown in Figure 2, the plastics material injection-moulded therearound can at least partially embrace not only the end face of the bearing bush 28 which is the lower end face in Figure 2 but also the corresponding end face of the bearing 4, and can thus additionally fix the bearing 4.

If plastics materials involving still higher temperatures are to be used for the injection moulding procedure, the plastics material is firstly injection-moulded around the empty bearing bush 28 and the bearings 3, 4 with the shaft 8 and the spacer ring 5' are inserted after the material has cooled down. In that case, unlike the situation shown in Figure 2, the through opening 29 in the material injection-moulded around the assembly must be of the same inside diameter as the bearing bush 28 so that the two bearings 3, 4 can be inserted from the mutually opposite ends in order to produce the O-shaped prestressing effect already referred to above.

It will further be seen from Figure 2 that the bearing bush 28 which comprises metal, at its end which is the upper end in Figure 2, has a radial flange 20' which performs the same function as the plate 20 described with reference to Figure 1. The radial flange 20' is of a comparatively large axial thickness in order to increase the abovementioned thermal capacity of the bearing bush 28.

A further particularity of the embodiment of Figure 2 is that in this case the mounting pins 14' comprise the same plastics material as the bearing carrier 1' and are produced jointly therewith in the injection moulding operation.

This embodiment of Figure 2 also has an edge bead or ridge 15' which embraces an axially projecting rim 30 of the flange 20' of the bearing bush 28. The opening 31 which is surrounded by the edge bead or ridge 15' has a frustoconical inside surface which enlarges outwardly, starting from the cylindrical inside surface of the rim 30.

That arrangement affords the advantage that the bearing bush 28 with its flange 28' and the rim 30 can be very accurately produced as a turned component and thus permits insertion with an even greater accuracy of fit of the measuring chamber which is shown at 18 in Figure 1 but which is not shown in Figure 2.

In both the embodiments of Figures 1 and 2 the bearing carrier 1, 1' can serve at the same time as a mounting flange for the entire rotary pick-up device. For that purpose, it has mounting bores 36 which extend from the outer end face in parallel relationship with the shaft 8 and which are provided with a female screwthread. Only one of the mounting bores 16 is shown in each of Figures 1 and 2.

If the respective edge bead or ridge 15, 15' is disregarded, each of the bearing carriers 1, 1' is of an axial length which is substantially equal to the axial length of the bearing arrangement 6, 6', which in turn results from the axial length of the two ball bearings 3, 4 and the thicknesses of the spacer rings 5, 5' and the plate 20 or the rim 30. That arrangement therefore provides a minimal axial structural length which could not be achieved if the outwardly disposed ball bearing end faces were to have plastics material injection-moulded therearound, to provide a positively locking connection.

In situations of use in which particularly high levels of requirement do not have to be made in regard to screening of the rotary pick-up device and its electronic systems, the electrical conductivity of the plasticss material used to make the bearing carrier 1, 1' is sufficient so that the embodiment shown in Figure 1 can omit the plate 20 and the axial length involved can be reduced to the minimum value which is governed by the bearing geometry.

As an alternative to a radially projecting spacer ring 5, in this variant it is also possible to use a spacer ring which is of a markedly smaller outside diameter than the outer races of the ball bearings 3, 4.

In that case the bearing arrangement is then prevented from axial displacement by an inwardly projecting plastics bead which is automatically produced when the plastics material is injection moulded around the bearing arrangement.

As is indicated by the outer edge line of the ball bearing 4, which is shown by a line of greater emphasis in Figures 1 and 2, the outer race 23 of that ball bearing 4 has a chamfer at the outside edge of its end face so that when the plastics material is injection moulded around the bearing carrier 1, a small inwardly projecting edge portion is formed, which also contributes to fixing the bearing arrangement.

It will be noted that the above-described bearing carriers according to the invention makes use of the fact that inexpensive injectionmouldable plasticss are available on the market, which after processing thereof have a high degree of strength and whose coefficient of thermal expansion is in the same range as or is equal to that of the material used for the bearings.

That provides that the high level of accuracy of fit between the bearing arrangement and the bearing carrier, which is achieved in manufacture by virtue of the bearing carrier being injection-moulded around the bearing arrangement remains unchanged over a wide temperature range and fluctuations in ambient temperature do not result either in the fit of the bearing arrangement in the bearing carrier becoming loose or in the production of clamping or jamming forces wich could adversely affect easy rotatability of the shaft in the bearing arrangement.

The above-described bearing carriers thus fulfil the necessary requirements in terms of load-bearing capability and precision together with a substantial reduction in weight, and easier and less expensive mounting can be achieved. The bearing carriers permit a bearing arrangement to be securely and accurately fitted therein while also ensuring satisfactory functioning of the bearing arrangement.

It will be appreciated that the above-described embodiments of the invention have been set forth solely by way of example and illustration thereof and that various other modifications and alterations may be made therein without thereby departing from the scope of the invention as defined by the appended claims.

Claims

1. A bearing carrier for a rotary pick-up device, adapted to receive a bearing arrangement for a shaft whose angular position is to be tracked for measurement thereof by the rotary pick-up device, wherein the bearing carrier comprises a plastics material which has at least approximately the same coefficient of thermal expansion as the material from which the bearing arrangement is made, and wherein the bearing carrier is produced in the form of an injection moulding which is connected to the bearing arrangement by being injection-moulded therearound.

2. A bearing carrier as set forth in claim 1 wherein the bearing arrangement comprises steel and the coefficient of thermal expansion of the plastics material used for the bearing carrier is in the range of 10 x 10-6 to 15 x 10-6 per K.

3. A bearing carrier as set forth in claim 1 or claim 2 wherein the bearing arrangement and the bearing carrier are positively lockingly connected together.

4. A bearing carrier as set forth in claim 1, claim 2 or claim 3 the bearing arrangement includes first and second bearings which are arranged one behind the other in the axial direction of the bearing arrangement and a spacer ring between the bearings.

5. A bearing carrier as set forth in claim 4 wherein the outside diameter of the spacer ring markedly differs from that of the bearings.

6. A bearing carrier as set forth in claim 5 wherein the spacer ring is of a markedly larger outside diameter than the bearings.

7. A bearing carrier as set forth in claim 4 wherein the bearing arrangement includes a bearing bush in which the bearings can be fitted.

8. A bearing carrier as set forth in any one of the preceding claims which is of a substantially rotationally symmetrical configuration such that its axis of symmetry coincides with the longitudinal axis of the shaft to be supported therein.

9. A bearing carrier as set forth in any one of the preceding claims which constitutes a flange-like bottom of a housing for accommodating the rotary pick-up device and has mounting pins which are parallel to its axis of symmetry and projecting beyond one of its ends, for holding parts of the rotary pick-up device which are stationary with respect to the shaft.

10. A bearing carrier as set forth in claim 9 wherein the mounting pins comprise steel, they are injection-moulded in place in the operation of injection moulding the bearing carrier, and they have a knurling configuration to produce a positively locking connection in the region of their ends which are embedded in the bearing carrier.

11. A bearing carrier as set forth in claim 9 wherein the mounting pins are produced integrally with the bearing carrier in the operation of injection moulding the bearing carrier.

12. A bearing carrier as set forth in any one of claims 9 to 11 including an electrically conductive housing cap which is fitted on to the bearing carrier, and a substantially plate-shaped, electrically and magnetically conductive screening element which is also injection-moulded. into the bearing carrier and which substantially covers over the surface of the end beyond which the mounting pins project, the screening element in the assembled condition being electrically conductively connected to said cap.

13. A bearing carrier as set forth in claim 12 wherein the screening element is enclosed by an edge bead of the bearing carrier but passes radially through same in at least one angular segment region to such an extent that it is exposed at the peripheral outward side of the edge bead and can there come into electrically and magnetically conducting engagement with the inside surface of the housing cap which is fitted on over the edge bead.

14. A bearing carrier as set forth in claim 12 wherein the bearing arrangement includes a bearing bush and bearings fitted in the bearing bush, and the screening element is formed by a substantially radially extending flange which is integrally connected to the bearing bush.

15. A bearing carrier as set forth in any one of the preceding claims wherein the bearing arrangement includes first and second bearings, and the bearings are ball bearings each having at least an inner race and prestressed in such a way that after introduction of the shaft to be supported into the inner bearing races they are urged towards each other in the axial direction.

16. A bearing carrier as set forth in any one of the preceding claims which is made from a plastics material of good electrical conductivity.

17. A bearing carrier as set forth in any one of the preceding claims which is made from a plastics material reinforced with carbon fibre particles.

18. A bearing carrier substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawing.

19. A support bearing assembly for a rotary pick-up device, including a bearing carrier as set forth in any one of the preceding claims.