GB1568739A - Retention device for a component on a shaft - Google Patents

Description

(54) RETENTION DEVICE FOR A COMPONENT ON A SHAFT (71) We, ROBERT BOSCH GMBH, a German Company, of Postfach 50, 7 Stutt gart 1, Federal Republic of Germany, do whereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be partia31arly described in and by the following statement.

The invention concerns retention devices for preventing axial displacement of components on shafts.

A wn axial retention device comprises a spring nut or disc inclined having segments which are pressed out of the plane of the disc in the opposite direction to which the disc is pressed onto a shaft. Thus, the axial force required for pressing the disc onto the shaft is relatively small, while the force required for removing the disc is relatively large. Of course, when the axial retention device is to be subjected to dynamic stresses, the surface of the shaft has to be roughened to a great extent in order to ensure sufficient resistance to removal of the disc.

Thus, in practice, grooves are cut into the shaft and, in order to prevent the ejection of the spring nut, result in frictional forces which are sufficiently high to meet limited requirements. For reasons of manufacture, the grooves are provided on the shaft in the manner of a screw-thread. This arrangement has the disadvantage that the axial distance between the grooves (pitch) can only be very small since, as has transpired in practice, the "axial accuracy of adjustment" of the spring nut must be less than 0.3 mm. It is a very expensive matter to provide grooves with this degree of precision. A further disadvantage of the known arrangement is that the retention device does not run true, since it aligns itself with the grooves which are produced by the turning operation and which extend in a thread-like manner. Furthermore, a thread groove has the disadvantage that the spring nut engages the wall of the groove correctly in a claw-like manner at only a single point.

This leads to instability with respect to the axial securing of components on the shaft which is unacceptable in the case of high demands. It will be appreciated that other such retention devices are known which do not have these disadvantages but which, on the other hand, are substantially more expensive.

The present invention provides a retention device on a shaft, said device comprising a planar disc which has a central bulge whose apex has a cut-out portion forming at least four radially inwardly directed segments, these segments being arranged diametrically opposite one another in pairs and resiliently engaging associated grooves in the outer surface of the shaft so as to maintain the disc normal to the axis of the shaft, the radially inner ends of a respective pair of segments being axially spaced from those of the next pair of segments by a distance e and the grooves in the shaft being axially spaced apart by a distance 1.5 e.

The device in accordance with the invention, has the advantage that the distance between the grooves on the shaft is greater than the dimension of the axial adjustment tolerance. Thus, the grooves can be manufactured by simple means, even under the conditions of mass production. Furthermore, the disc provided with the segments has the advantage that it engages the shaft reliably at two diagonally opposite locations and thus runs true and precludes instability with respect to its axial position on the shaft.

The grooves are preferably formed as circular, parallel rings by, for example, the method known as "thread rolling". Thus, the disc is securely engaged on the shaft in a claw-like manner and cannot rotate down the shaft in the same manner as a nut is rotated by a screw-thread.

The invention is described further, by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows an axial securing device on the free end of a shaft; Figure 2 shows an enlarged detail of the surface of the shaft and retaining segments, turned in one plane, of a disc of the axial securing device; Figure 3 is a plan view of the disc; Figure 4 is a section taken on the line IV-IV of Figure 3; Figure 5 is a section taken on the line V-V of Figure 3; Figure 6 is a section taken on the line VI-VI of Figure 3; and Figures 7, 8, 9 show three different axial positions of the disc on the outer surface of the shaft, and Figure 10 shows a second embodiment of the surface of a shaft.

Figures 1 to 9 of the drawings show an axial securing device which prevents axial displacement of components on a shaft. The axial securing device comprises a planar disc 2 arranged on a shaft 1. The disc 2 has a central bulge whose apex has a cut-away portion 3 which forms six radially inwardly directed retaining segments 4 located diametrically opposite one another in pairs. The retaining segments 4 engage resiliently in associated grooves 5 in the outer surface of the shaft 1. In the embodiment illustrated in Figure 1, all the grooves 5 form a region located at the free end of the shaft 1. It will be appreciated that, alternatively, the region formed by the grooves 5 may be enclosed by smooth surface regions of the shaft 1 or surface regions thereof which are of some other configuration. It will be appreciated that the external dimension of the shaft, at least at that end from which the disc 2 is slipped onto the shaft, must not be so large that the retaining segments 4 will be plastically deformed when slipping the disc 2 onto the shaft.

The grooves 5 form circular, parallel rings which are calendered in the outer surface of the shaft in a non-cutting manner or which are incorporated therein by means of a chasing tool in a metal-cutting manner. As may be seen particularly in Figure 2, the grooves have a symmetrical, wedge-shaped profile.

The flanks of the grooves are at an angle of approximately 450 to the axis of the shaft 1.

The inner ends of each pair of retaining segments 4 are spaced from the next pair of retaining segments 4' by a distance e measured in the axial direction of the shaft 1. The pair of retaining segments 4' is again spaced from the next pair of retaining segments 4" by the distance e measured in an axial direction (compare particularly Figures 3 to 6). The grooves 5 are spaced apart by the distance 1.5 e which is also measured in the axial direction of the shaft 1 (Figure 2).

As may be seen in Figure 3, the inner ends of the retaining segments 4 are cut out in a ciruular-segment-shaped manner.

The axial securing device which has been described functions in the following manner: Figure 7 shows a first position in which the retaining segment 4,4',4" engage the grooves 5 in the shaft 1. The retaining segments 4" thereby fully engage a groove 5 (Figures 7 to 9 in each case only show one retaining seg ment 4,4',4" having a further retaining segment 4,4',4" located diagonally opposite, wherein, owing to the diagrammatic illustra tion, all the retaining segments 4,4',4" are offset by 600 relative to one another, turned onto the drawing plane, as is shown in Figure 3). Only the inner corners of the retaining segments 4 and 4' in each case engage the next groove 5 contiguous in the axial direction of the shaft 1. Figure 8 shows, viewed in an axial direction, the next possible engagement position of the disc 2 in the grooves 5 of the shaft 1. This second engagement position is axially displaced by 0.5 e relative to the first engagement position shown in Figure 7. In the engagement position illustrated in Figure 8, the inner corners of the retaining segments 4' fully engage a groove 5, while only the inner corners of the retaining segments 4 and 4" engage retaining grooves 5. A third possible engagement position of the disc 2 in the shaft 1 is shown in Figure 9 and is again axially displaced by a value of 0.5 e relative to the engagement position illustrated in Figure 8.

In the engagement position illustrated in Fig ure 9, the retaining segments 4 again fully engage a groove 5, while only the inner corners of the retaining segments 4' and 4" engage a groove 5. When approximately 0.3 mm is chosen for the value e, the distance between the two grooves 5 in the shaft 1 is OA5 mm; the disc 2 can then be fixed on the shaft 1 in axial increments of 0.3 X 0.5 = 0A5 mm. By way of example, this value is commensurate with the conventional manufac turing tolerance when using the axial securing device in fractional horse-power electric motors. In the present instance, the disc 2, which may be made from, for example, a hardened steel, is provided with six retaining segments 4. It will be appreciated that, by using the described principle, two suitable graduations can be obtained with any even numbered pairing.

Basically, there are two possibilities of obtaining the described axial spacing e beween the retaining segments 4,4',4". On the one hand, the diameters D4, D4', D4" of the circularly cut-out inner ends 4,4',4" (Figure 3) of one pair of retaining segments may be different from those of the other pair, wherein the transition radii R4 (Figure 4) from the planar disc 2 into the bulge may be equal in all the retaining segments 4,4',4". On the other hand, the diameters D4 of the inner ends, cut out in a circular-segment-shaped manner, of all the retaining segments 4,4',4" may be of equal size, wherein the transition radii R, R4', R4" from the planar disc into the bulge of one pair of retaining segments 4,4',4" must be different from those of the other pair. When the disc is in its finished state (Figure 3), i.e. after cutting-out and shaping, it will be appreciated that all the diameters D must be of equal size in order to be able to engage the shaft in a claw-like manner.

A second embodiment of grooves 15 in a shaft 10 is illustrated in Figure 10. The grooves 15 have an asymmetrical saw-tooth profile and not a symmetrical saw-tooth profile as in the first embodiment. This sawtooth profile is arranged such that the flanks of the grooves 15 extend, in the pressing-on direction 16 of the disc 2, substantially flatter than the flanks of the grooves 15 extend in the presssing-off direction 17. This has the advantage that the disc 2 can be pressed on in a simpler manner, the axial pressing-off force at the same time being increased.

WHAT WE CLAIM IS: 1. A retention device on a shaft, said device comprising a planar disc which has a central bulge whose apex has a cut-out portion forming at least four radially inwardly directed segments, these segments being arranged diametrically opposite one another in pairs and resillently engaging associated grooves in the outer surface of the shaft so as to maintain the disc normal to the axis of the shaft, the radially inner ends of a respective pair of segments being axially spaced from those of the next pair of segments by a distance e and the grooves in the shaft being axially spaced apart by a distance 1.5 e.

2. A retention device as claimed in claim 1, in which the grooves form circular, parallel rings about the shaft.

3. A retention device as claimed in claim 1 or 2, in which the grooves are situated at the free end of the shaft.

4. A retention device as claimed in claim 1 or 2, in which the grooves are disposed between two regions of the shaft which are profiled differently from the grooved part of the shaft and which are preferably smooth.

5. A retention device as claimed in any preceding claim, in which the grooves are symmetrical in transverse cross-section.

6. A retention device as claimed in one of the claims 1 to 4, in which the grooves have a saw-tooth-like profile.

7. A retention device as claimed in claim 1, in which the radially inner ends of the segments are arcuate.

8. A retention device as claimed in claim 7, in which the arcuate portions of the ends of each pair of segments have a diameter that is different from those of the other pairs, and in which the radii of curvature at the feet of the segments are of equal size for all the segments.

9. A retention device as claimed in claim 7, in which the arcuate portions of the ends of each pair of segments have a diameter equal to the diameters of the other pairs, and in which the radii of curvature at the feet of the segments are equal for the two segments in each pair but differ for segments in different pairs.

10. A retention device constructed and arranged substantially as herein particularly described with reference to and as illustrated in Figs. 1 to 9 or Figs. 1 to 9 when modified by Fig. 10 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. 4,4',4" must be different from those of the other pair. When the disc is in its finished state (Figure 3), i.e. after cutting-out and shaping, it will be appreciated that all the diameters D must be of equal size in order to be able to engage the shaft in a claw-like manner. A second embodiment of grooves 15 in a shaft 10 is illustrated in Figure 10. The grooves 15 have an asymmetrical saw-tooth profile and not a symmetrical saw-tooth profile as in the first embodiment. This sawtooth profile is arranged such that the flanks of the grooves 15 extend, in the pressing-on direction 16 of the disc 2, substantially flatter than the flanks of the grooves 15 extend in the presssing-off direction 17. This has the advantage that the disc 2 can be pressed on in a simpler manner, the axial pressing-off force at the same time being increased. WHAT WE CLAIM IS:

1. A retention device on a shaft, said device comprising a planar disc which has a central bulge whose apex has a cut-out portion forming at least four radially inwardly directed segments, these segments being arranged diametrically opposite one another in pairs and resillently engaging associated grooves in the outer surface of the shaft so as to maintain the disc normal to the axis of the shaft, the radially inner ends of a respective pair of segments being axially spaced from those of the next pair of segments by a distance e and the grooves in the shaft being axially spaced apart by a distance 1.5 e.

2. A retention device as claimed in claim 1, in which the grooves form circular, parallel rings about the shaft.

3. A retention device as claimed in claim 1 or 2, in which the grooves are situated at the free end of the shaft.

4. A retention device as claimed in claim 1 or 2, in which the grooves are disposed between two regions of the shaft which are profiled differently from the grooved part of the shaft and which are preferably smooth.

5. A retention device as claimed in any preceding claim, in which the grooves are symmetrical in transverse cross-section.

6. A retention device as claimed in one of the claims 1 to 4, in which the grooves have a saw-tooth-like profile.

7. A retention device as claimed in claim 1, in which the radially inner ends of the segments are arcuate.

8. A retention device as claimed in claim 7, in which the arcuate portions of the ends of each pair of segments have a diameter that is different from those of the other pairs, and in which the radii of curvature at the feet of the segments are of equal size for all the segments.

9. A retention device as claimed in claim 7, in which the arcuate portions of the ends of each pair of segments have a diameter equal to the diameters of the other pairs, and in which the radii of curvature at the feet of the segments are equal for the two segments in each pair but differ for segments in different pairs.

10. A retention device constructed and arranged substantially as herein particularly described with reference to and as illustrated in Figs. 1 to 9 or Figs. 1 to 9 when modified by Fig. 10 of the accompanying drawings.