SNAP CONNECTION SYSTEM

Abstract: In a snap connection system in which a shaft (16) is inserted into a tube (10) to a predetermined position, whereat co-operating surfaces on tube and shaft engage as in a laterally acting wedge, two axially spaced spring loaded balls (12) on one side of the tube urge the shaft into wedging engagement with the tube when in position. During insertion, a further spring loaded ball (13) on the opposite side of the tube adjacent the wedge apex urges the shaft out of wedging engagement with the tube. A detent (17) in shaft (16) accommodates the further ball (13) at the predetermined position, locating the shaft axially and permitting wedging. The balls are biassed by a spring sleeve (11), and a tang (14) thereof locates the sleeve on the tube. The tang may extend to the tube interior to coact with a detent in the shaft so that unclipping is necessary for disassembly. Alternatively, a spring loaded pin extending through sleeve and tube wall may accomplish the same end.

Description: SNAP CONNECTION SYSTEM This invention relates to a system permitting two components to be assembled with an automatic snap connection. It has particular, but not exclusive relevance, to situations where no secondary operations, such as fastening by a nut and bolt, are permissible, for example at any position within a steering column and rack assembly. By suitable design, and taking into account manufacturing tolerances, the system of the invention can enable parts supplied separately by different companies to be easily connected together. According to one aspect of the present invention, there is provided a shaft assembly comprising a tube and a shaft, the shaft being slidable within the tube; characterised by a first means for biassing the tube and the shaft into wedging engagement when the tube and the shaft are in a predetermined axial position; and a second means for biassing the tube and the shaft out of wedging engagement when the tube and the shaft are not in the predetermined position. According to a second aspect of the present invention, there is provided a snap connection system comprising a tube and a shaft for insertion into the tube to a predetermined position; characterised in that the tube and shaft having co-operating surfaces for engagement as a laterally acting wedge when the tube and the shaft are in said predetermined position; at least two axially spaced spring loaded first biassing members being provided in a first axially extending portion of either the tube or the shaft opposite an apex of the wedge and arranged for biassing the shaft into wedging engagement with the tube; and at least one spring loaded biassing member provided in a second axially extending portion of either the tube or the shaft adjacent the wedge apex for urging the shaft out of wedging engagement with the tube, wherein said at least one second biassing member counters the action of the first biassing members, to facilitate insertion of the shaft into the tube, and wherein either the shaft or the tube is provided with at least one detent for accommodating said at least one second biassing member when said predetermined position is reached, thereby to locate the shaft axially thereat and to permit the wedging action to occur under the influence of the first biassing members as a snap connection. Preferably the first and second biassing members are rotatable in a sense facilitating insertion of the shaft into the tube, and withdrawal, for example spring loaded balls. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 illustrates a typical example of the use of the snap connection system, for connecting a steering column to a steering rack; Figure 2 shows a first embodiment of the shaft and tube in diagrammatic longitudinal cross-section, not assembled; Figure 3 shows the tube of Figure 2 in transverse cross-section, taken on line B-B in Figure 2; Figures 4 and 4B show the shaft and tube of Figure 2 assembled in the predetermined position, in diagrammatic longitudinal and transverse cross-section, respectively, the section being on the line A-A; Figure 5 shows a variation in the form of the tube of Figures 2 to 4; Figure 6 shows a second embodiment of the shaft and tube in diagrammatic longitudinal cross-section, not assembled; and Figures 7A and 7B show the assembled tube and shaft of Figure 6 in diagrammatic longitudinal and transverse cross- section, respectively. Figure 1 shows a steering column 1, which includes an intermediate shaft 2 and serves to couple a steering wheel 3 to a steering rack 4. As shown, the intermediate shaft 2 and the steering rack 4 are formed as a shaft and tube (or tube and shaft) and may thus be coupled by an automatic snap connection requiring no ancillary coupling operation(s) . Figures 2 to 4 show a first embodiment in which a tube 10 is provided with an outer spring sleeve 11 which is split at IIA and is shaped and located so as to bias two upper rolling members or balls 12 and a rolling member or lower ball 13 inwardly of the tube, each ball being accommodated within an aperture in the tube wall. A further aperture 14 in the tube wall serves to locate an inwardly directed tang 15 of the spring sleeve 11, formed for example by turning a portion of the end of the sleeve 11, and so prevent axial or rotational displacement of the sleeve 11. The spring sleeve 11 could be of circular (annular) section, as shown, and need not conform to the whole periphery of the tube 10. A shaft 16 for insertion within the tube 10 is provided with an indentation or hole 17 acting as a detent. As shown in the transverse cross-section of Figure 4, the shaft 16 is of V formation providing two mutually inclined lateral wedging surfaces, and its outer surface in the region where wedging is intended to occur closely conforms to the internal surface of the tube 10, which is also of V formation, it being understood that sufficient clearance is provided to enable insertion of the shaft 16 into the tube 10. On insertion of the shaft 16, the lower ball 13 biasses the wedging surfaces away from the tube 10, against the action of the upper balls 12. Without this feature, the wedging action would be increased by the upper balls, and insertion of the shaft would require increased force and generally be more difficult. When the shaft 16 has been inserted to a predetermined position, the lower ball 13 snaps into the detent 17 in the shaft 16, thereby tending positively to locate the shaft 16 axially relative to the tube 10. Such location is reinforced by the biassing action of the upper balls 12, which now act, free of any restraint from the lower ball 13, to wedge shaft and tube together and so increase frictional forces therebetween. This wedging action means that there is no backlash and rattle due to bending forces when the tube and shaft are assembled. If the shaft 16 needs to be inserted a significant distance within the tube 10, an additional lower ball or balls may be provided, axially spaced from the first, with corresponding detents in the shaft. Disassembly is normally possible using a higher force than used during assembly. In Figure 5, the tang 15 is replaced or supplemented by a longer tang or barb 18, which extends into the tube interior and is inclined in the direction of insertion of the shaft 16. The latter is provided with a detent 19 which engages the tang 18 when the shaft is in the predetermined position. In this case, disassembly requires the tube and shaft to be positively undipped. Figures 6 and 7 show a second embodiment which is generally similar to the first, but includes a retention pin 20 which extends through the spring sleeve 11 and a hole in the wall of the tube 10 and which is spring loaded by a spring clip 21. The pin 20 lifts, or is lifted, and the clip flexed, when the shaft in inserted into the tube, and snaps into a hole in the shaft when the predetermined position is reached. Positive withdrawal of the pin 20 may be necessary for disassembly. It will be understood that although the biassing members are shown as balls, and are located on the tube, it would be equally possible for some or all of them to have a different form, e.g. rollers, and to be located on the shaft (with the aperture for the snap location ball formed in the tube) .

Claims: CLAIMS ; 1. A shaft assembly comprising a tube (10) and a shaft (16), the shaft (16) being slidable within the tube (10); characterised by a first means (12) for biassing the tube and the shaft into wedging engagement when the tube and the shaft are in a predetermined axial position; and a second means (13) for biassing the tube and the shaft out of wedging engagement when the tube and the shaft are not in the predetermined position. 2. A shaft assembly according to claim 1, wherein the firεt and second biassing means (12, 13) bias the tube and the shaft in a direction transverse to an axis common to the tube and the shaft. 3. A shaft assembly according to claim 1 or 2, wherein the tube (10) and the shaft (16) have complementary interengaging wedge shaped surfaces. 4. A shaft assembly according to claim 1, 2 or 3, wherein the first means for biassing comprises a plurality of axially spaced apart spring loaded first rolling members (12) . 5. A shaft assembly according to any one of the preceding claims, wherein the second means for biassing comprises at least one spring loaded second rolling member (13) . 6. A shaft assembly according to claim 5, further comprising a detent provided in the shaft (10) or tube (16) for accommodating said at least one second rolling member (13) when the tube and the shaft are in said predetermined position. 7. A shaft assembly according to any one of the preceding claims, wherein said second means (13) is positioned to transversely oppose said first means (12) . 8. A shaft assembly according to any one of the preceding claims and further comprising a spring sleeve (11) mounted externally on the tube (10) . 9. A shaft assembly according to claim 8, wherein the tube (10) has an aperture (14) therein and the spring sleeve (11) has an inwardly extending tang (15) engaging the tube aperture. 10. A shaft assembly according to claim 8, wherein the shaft (16) has an aperture (19) therein and the tang (18) engaging the shaft aperture (19) when the tube (10) and the shaft (16) are in the predetermined position. 11. A shaft assembly according to claim 8, wherein the spring sleeve (11) and the tube (10) each have a hole therethrough and the shaft has an aperture therein, there being a spring loaded pin (20) mounted about the spring sleeve (11) , the pin (20) extending through the spring sleeve hole and the tube hole and when the tube (10) and the shaft (16) are in the predetermined position, the pin extending into the shaft aperture. 12. A snap connection system comprising a tube (10) and a shaft (16) for insertion into the tube to a predetermined position; characterised in that the tube (10) and shaft (16) having co-operating surfaces for engagement as a laterally acting wedge when the tube and the shaft are in said predetermined position; at least two axially spaced spring loaded first biassing members (12) being provided in a first axially extending portion of either the tube (10) or the βhaft (16) opposite an apex of the wedge and arranged for biassing the shaft into wedging engagement with the tube; and at least one spring loaded biassing member (13) provided in a second axially extending portion of either the tube or the shaft adjacent the wedge apex for urging the shaft out of wedging engagement with the tube, wherein said at least one second biassing member (13) counters the action of the first biassing members (12) , to facilitate insertion of the shaft into the tube, and wherein either the shaft or the tube is provided with at least one detent for accommodating said at least one second biassing member (13) when said predetermined position is reached, thereby to locate the shaft (16) axially thereat and to permit the wedging action to occur under the influence of the first biassing members (12) as a snap connection. 13. A vehicle steering column incorporating a shaft assembly according to any one of claims 1 to 11 or a snap connection system according to claim 12.

Inventors: BAYNES IAN DAVID, HANCOCK MICHAEL THOMAS, BAYNES, IAN, DAVID, HANCOCK, MICHAEL, THOMAS
Applicants: NASTECH EUROP LTD, NASTECH EUROPE LIMITED
Application year: 1996
Main classification: B62D1
IPC codes: B62D1, F16B7, F16D1