This invention relates to a vehicle steering column incorporating an adjustable reach facility.

An adjustable reach facility is one which permits the steering column to be moved in an axial direction relative to itself so as to move the steering wheel to a position to suit the comfort of the driver. In order to achieve this, the steering column includes two parts which can slide relatively to one another.

According to the present invention, there is provided a vehicle steering column having a coupling between two portions of the steering column, which coupling incorporates a means for providing preloaded torque resistance to inhibit transmission of rotational backlash through the steering - column, characterised in that the coupling comprises a torsion bush having first, second and third zones contiguous with each other, the first and second zones being connected by the third zone and the first and second zones being angularly offset one from the other.

One of the two parts can be a tube or hollow shaft, whilst the other of the two parts can be a hollow or solid shaft. With this arrangement, the torsion bush can be partially fitted inside one end of the hollow tube or shaft and another part of the torsion bush is fitted over one end of the other part.

The degree of angular offset or twist depends on the functional requirement but is preferably 1 to 5° from the

longitudinal axis through a fixed zone pre erably still 2° from the longitudinal axis through the fixed zone.

The shafts may be of any shape suitable to be coupled together by the coupling means so that rotational backlash does not occur and the coupling means is under constant torque. The shafts may be substantially rectangular in shape with curved shorter ends, the coupling means being dimensioned to couple together the shafts. The shafts may also be substantially triangular in shape with the coupling means dimensioned to couple together the shafts.

The degree of twist of the coupling means is termed the spring rate of the proposed torsion and is calculated from the following basic formula:-

θ = TL JG

θ = Angle of twist per unit length T = Applied torque L = Length of bush J = Polar moment of inertia G = Shear modulus of elasticity.

For different configurations made in similar materials the Polar moment of inertia is the only parameter which changes, i.e J = bh (h ² + b ² ) for rectangle.

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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 whic :-

Figure 1 is a diagrammatic perspective view of part of a vehicle steering column incorporating an adjustable reach facility and coupling means according to one embodiment,

Figure 2 is a diagrammatic perspective view of an inner element shown in Figure 1 and showing more completely the construction of a coupling means shown in Figure 1,

Figure 3 is a view taken in the direction of the arrow B in Figure 2,

Figure 4 is a cross-sectional view of Figure 2 along the line C-C,

Figure 5 is a perspective view of an inner means and showing more completely the construction of a coupling means according to another embodiment, and

Figure 6 is a perspective view of an inner means and showing more completely the construction of a coupling means according to a further embodiment.

With reference to the drawings there is shown part of a vehicle steering column incorporating an adjustable reach facility 1 and a coupling means in the form of a torsion bush 3.

The adjustable reach facility 1 comprises hollow shaft 5, shaft 4 and the torsion bush 3. A zone.19 of the bush 3 is mounted in one end of the hollow outer shaft 5. The solid inner shaft 4 has one. end slidably mountable within the bush 3 so that it can be .moved in an axial direction relative to the shaft 5.

The outer shaft 5 is made of steel and is substantially rectangular in cross-section with curved shorter ends 6 and 7 and flat side walls 8 and 9 on both its outer and inner surfaces 1Q and 11 respectively. The shaft 5 has an expanded portion at the one end so as to accommodate the inner shaft 4 and the torsion bush 3.

The inner shaft 4 has a substantially rectangular cross-section with curved shorter ends 12 and 14 and flat side walls 15 and 16 and is dimensioned so as to be slidably mountable within the torsion bush 3 and the shaft 5. The inner shaft 4 is the product of a cylinder originally having a diameter of 19 mm which was cut away to form the flat side walls 12 and 14 spaced 14 mm apart.

Specifically with reference to Figures 2 and 3 the torsion bush 3 is hollow and comprises first, second and third zones 18, 19 and 20 which are shown to be constructed continuously with one another, with the first and second zones 18 and 19 being connected by the third zone 20. The first and second zones 18 and 19 are arranged so that the longitudinal axis through the first zone 18 is offset by 2° from the longitudinal axis through the second zone 19, the longitudinal axis for the second zone being along the line D-D. Both the inner and outer surfaces of the first and second zones 18 and 19 have a substantially rectangular cross-section with curved shorter ends 21 and 22 and the flat side walls 23 and 24. The third zone 20 forms a cut-away section 17 enabling the first and second zones 18 and 19 to flex relative to each other.

The torsion bush 3 is arranged to couple together the inner and outer shafts 4 and 5 and its second zone 19 is mounted in the expanded portion of the outer shaft 5. The first

zone 18 and connecting, third zone 20 extend outwardly of the expanded portion over the one end of the inner shaft 4.

With reference to Figure 2 the shaft 4 shown, in phantom, is mounted within the torsion bush 3. The change in alignment of the first zone 18, relative to the second zone 19 for the vehicle steering column in its assembled form, is indicated by broken lines and shows that in order for the shaft 4 to be mounted within the torsion bush 3 the first zone 18 must be flexed so that its longitudinal axis is along the line D-D corresponding with the longitudinal axis of the second zone 19. The dimension of the third zone 20 determines the degree of flex that can occur between the first and second zones 18 and 19. Therefore when the vehicle steering column is in its assembled form the torsion bush 3 is under constant torque which construction prevents rotational backlash of the inner and outer shafts 4 and 5.

This arrangement therefore has the advantage that the torsion bush 3 absorbs any rotational backlash between the inner and outer shafts 4 and 5 whilst maintaining the facility to transmit torque through the shafts 4 and 5.

In another embodiment, the inner shaft 4 may be a hollow shaft.

With reference to Figure 5 there is shown another embodiment wherein an inner solid tube 30 is slidably mounted within a coupling means 31. The tube 30 is substantially triangular in cross-section having three equilateral sides 32, 33 and 34.

The coupling means 31 has first, second and third zones 35, 36 and 37, the first and second zones 35 and 36 being connected by the cut away third zone 37. The first and second zones 35 and 36 are twisted relative to each other. The second zone 36 of the coupling means 31 is fixed to one end of an outer tube (not shown) .

With reference to Figure 6 there is shown a further embodiment wherein an inner solid tube 40 is slidably mounted within a coupling means 41. The tube 40 is substantially square in cross-section having sides 42, 43, 44 and 45.

The coupling means 41 has first, second and third zones 46, 47 and 48, the first and second zones 46 and 47 being connected by the cut away third zone 48. The first and second zones 46 and 47 are twisted relative to each other.

The second zone 47 of the coupling means 41 is fixed to one end of an outer tube (not shown) .