This type of telescopically adjustable shaft is prior known from Patent publication EP 0,449, 194 Al, wherein a tube with a smaller outer diameter is capable of sliding within a larger diameter casing. A sleeve element can be rotated for clamping the inner surface of a frictional locking ring against the outer surface of the inner tube. A problem with this type of telescopic system is the difficulty to create such a major frictional gripping force which would be sufficient e. g. in a skiing, skating or Nordic walking pole application, wherein the shaft is subjected to major axial loads. The frictional gripping force can be enhanced by decreasing the angle of wedge, but the angle of wedge cannot be decreased beyond the limit at which the conical faces grip

each other in such a way that the frictional locking ring is not able to re- expand when the grip is released.

It is an object of the present invention to provide a sleeve joint for a telescopically adjustable shaft, which is capable of providing a more effective friction grip and a highly convenient use.

According to the present invention, this object is accomplished in such a way that at least two frictional locking rings are axially in succession and between the same is at least one clamping collar, having its both ends provided with internal conical end faces which draw away or diverge from each other when approaching the outer surface of the clamping collar.

An advantage of the invention is that the joint is sufficiently sturdy for stressing the shaft with a substantial axial load. The inventive telescopic shaft, along with its sleeve joint, finds a particularly suitable application in the lengthwise adjustment of skiing, skating and Nordic walking poles. The sturdiness and user-friendliness of the joint enables use of the shaft also as a tool handle. The shaft can be used for example as a broomstick or a mop handle. Whatever accessory is employed at the end of the shaft, it can be replaced whenever necessary. For example, the shaft element of a ski pole, which includes a snow ring and a spike member, can be replaced with a shaft element which carries the resilient tip of a Nordic walking pole. Moreover, the inventive shaft takes very little space in storage or transportation. In addition, the adjustment of a shaft length is stepless.

The shaft material may comprise a composite material, i. e. resin-bonded reinforcement fibers, such as carbon and/or glass fibers. Another suitable material for the shaft or pole is a metal. The sleeve joint has its sleeves made of a hard, injection-moulding plastic.

Preferred embodiments of the invention are disclosed in the non- independent claims.

The invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 shows a sleeve joint for a telescopic shaft in an exploded view.

Fig. 2 shows axonometrically an exploded view.

Fig. 3 shows a sleeve joint in a split-up axonometric view.

Fig. 1 shows schematically a shaft, which is telescopically adjustable by means of a sleeve joint and which is indicated by reference numeral 1.

Depending on a particular application, the number of joints is typically 1-3 per shaft 1. In the region of a sleeve joint, the shaft 1 consists of an outer casing 2 and an inner tubing 3, the latter being pushed inside the outer casing 2.

Fig. 1 illustrates a first sleeve section 4 and a second sleeve section 20 constituting a sleeve joint. The first sleeve section 4 of a sleeve joint is permanently secured at its top portion 5 around the end of the larger diameter tube or outer casing 2, for example by injection moulding.

The first sleeve section 10 has the cylindrical outer surface of its base portion 7 provided with its male thread 6. On the other hand, the second sleeve section 20 has the inner surface of one of its ends provided with a female thread 22, the first sleeve section 10 and the second sleeve section 20 being engaged with each other by means of the discussed threads 6 and 22.

The first sleeve section 4 has its base portion 7 terminating in a planar annular surface 8, which penetrates into a cylindrical space 24 in the second sleeve section 20.

The inner tubing 3 has its outer diameter (see fig. 3) designed to enable its sliding movement within the outer casing 2 and the first and second sleeve sections 4 and 20 constituting a sleeve joint. Therefore, the sleeve sections 4 and 20 have their bottom portions provided with regions 6a and 21 of the smallest inner diameter, which correspond to the outer diameter of the inner tubing 3 with a running fit.

Fig. 1 illustrates also one preferred configuration for socket-like frictional gripping elements 100 in a partial cross-section, and fig. 2 shows the same in an axonometric view. The frictional gripping elements 100 are preferably made of a resilient, rather hard plastic or the like material, such as polyurethane. The frictional gripping elements 100 comprise a number of axially successive socket components 9,10, 11. According to the exemplary embodiment, these include two actual frictional locking rings 10, which have their preferably cylindrical inner faces establish an actual locking grip with the inner tubing 3. In addition, the frictional gripping elements 100 include a clamping collar 11 set between the actual frictional locking rings 10, as well as clamping collars 9 mounted on the ends of the actual frictional locking rings 10. The end surface of these end clamping collars 9, directed away from the frictional locking rings 10, constitutes a planar annular surface 9a.

The actual frictional locking rings 10 are provided with a lengthwise slot 10c, which is provided for allowing a radial contraction for the actual frictional locking rings 10. Radial contraction occurs as the clamping collar components 9,11 bear against each other with end faces 9b, lla and 11b thereof, which are in the shape of conical surface segments, and with a force of sufficient magnitude. The frictional locking rings 10 have conical faces 10a and 10b

approaching each other when progressing towards the outer surface of the ring 10. The clamping collar components 9 and 10 have complementary conical faces 9b and 11a, llb, which draw away from each when progressing towards the outer surface of the clamping collar 9,10. Both ends of the clamping collar 11 set between the frictional locking rings 10 are provided with conical end faces 11a, llb, which draw away from each other when progressing towards the outer side of the clamping collar 10. Each component of the frictional gripping means 100 has a cylindrical inner surface 9c, 10d, llc, having an inner diameter which corresponds to the smaller inner diameters 6a and 21 of the sleeve sections 4 and 20, whereby the inner tubing 3 can be passed through the frictional gripping socket 100 with a respective running fit. The conical end faces of the sockets 9,10, 11 form an angle of less than 45°, preferably an angle of about 25°-40°, with respect to the axial direction. The second sleeve section 20 has the end of its cylindrical space 24 designed as an annular lip or shoulder 23, which has also an extension formed by the smaller inner diameter zone 21 of the second sleeve section 20. It is illustrated in fig. 3 that the frictional gripping elements 100 have the first end clamping collar 9 thereof bearing by way of its annular surface 9a against the annular lip 23 of the sleeve section 20. The other components of the frictional gripping means 100 are in a bearing relationship as an axial extension of this first end clamping collar 9, as already described above. Hence, the frictional locking ring 10 surrounds the inner tubing 3 extended through the second sleeve section 20. Thus, the frictional gripping means 100 have the other end thereof consisting of a second, similar end clamping collar 9 and it bears by way of its annular surface 9a against a planar annular surface 8 of the first sleeve section 4.

In the process of coupling the sleeve sections 4 and 20 with each other, the threaded joint 6,22 is initially rotated no further than to such an extent that the frictional gripping elements 100 do not clamp axially against each other.

This is followed by adjusting a position of the inner tubing 3 relative to the

outer casing 2 as desired. Next, the sleeve sections 10 and 20 are rotated further relative to each other for coupling the same with each other in a final locking position by means of the threads 6 and 22. Thus, the second end clamping collar 9, bearing against the end 8 of the first sleeve section 4, applies contraction on other components of the frictional gripping means 100, the actual contractible components 10 of the frictional gripping means 100 contracting in a radial direction, as can be appreciated from fig. 3. As a result of this, a frictional locking grip is established between an inner wall 10d of the actual locking ring and the outer wall of the inner tubing 3. The inner tubing 3 is securely clamped by this grip in a desired position relative to the outer casing. Naturally, the inner tubing 3 must extend in a sufficient degree beyond the frictional gripping elements 100, preferably to a depth inside the outer casing sufficient to prevent breaking or buckling or some other such failure of the shaft 1 over the joint region.

In order to provide a sufficient gripping area, the frictional locking rings 10 have an axial length which preferably exceeds its diameter. If necessary, the gripping area can be varied by varying the axial length of the frictional locking rings 10.

The diameter of the shaft 1 transforms to what is conical in the axial direction. One or more of the individual tubular elements can also be slightly conical. Hence, dimensions for both sleeve joints of the shaft 1, such as, for example, diameters for the threads 6 and 22 and a diameter for the frictional gripping elements 100, may also vary according to the diameter of the pole 1.