Grooved splined shaft with overmoulding

1. A shaft having a splined portion which comprises a first set of teeth with each tooth spaced radially at intervals about a first outer circumferential region of the shaft and a second set of teeth comprising an equal number of teeth to the first set that are also spaced radially at the same regular intervals about a second outer circumferential region of the shaft that is offset axially from the first region, with at least one tooth of the first set of teeth aligned with a corresponding tooth of the second set to form a pair in which the two teeth of the pair together form an elongate spline; and wherein the first tooth and second tooth of each elongate spline are separated from each other in a direction parallel to the axis of the shaft by a groove that terminates at each end by a shoulder forming an end of a respective tooth, wherein each shoulder is tapered in a direction normal to an axis of the shaft and in that an overmolding is provided that comprises a portion that covers the teeth that is continuous with a portion that extends into the groove, an outer face of the overmolding defining a plurality of teeth that each correspond to a respective underlying tooth of the shaft;

wherein all of the first and second teeth are aligned in pairs to form elongate splines, and wherein the groove that spaces a pair of teeth of one spline is located at a different axial position along the shaft from the grooves that separate the teeth of the immediately adjacent splines.

2. The shaft according to claim 1 in which at least one of the tapered shoulders comprises a first portion that extends from a tip of the tooth for a first distance along the shaft that reduces in distance from the axis of the shaft, a second portion that extends for a second distance along the shaft that reduces in distance from the axis at points that are further from the tooth, and a connecting region that joins the first and second portions.

3. The shaft according to claim 2 in which the connecting region comprises an abrupt step or a region that tapers at a greater rate than the first and second portions.

4. The shaft according to claim 2 in which the first portion, and/or the second portion, taper linearly.

5. The shaft according to claim 1 in which all the first and second teeth are aligned in pairs to form elongate splines, in which the groove between each pair of teeth forming a spline comprises a part of a single continuous land that extends around a complete circumference of the shaft.

6. The shaft according to claim 1 in which the grooves between splines are located at one of two different axial positions to form a staggered pattern around the circumference of the shaft whereby a pair of teeth with a groove in the first axial position are neighboured by pairs of teeth with a groove in the second axial position.

7. The shaft according to claim 1 in which the splined portion is made of metal and the overmolding comprises a plastic material or an elastomer.

8. The shaft according to claim 1 in which the overmolding is shaped so that the region of overmolding that covers the groove or grooves has the same outer profile as the region that covers the teeth, defining a continuous elongate spline shape from one end of the overmolding to the other.