This invention relates to an articulated vehicle of the type described in our Published European Patent Application No. EP-A2-0112712.

Such an articulated vehicle comprises: a front sub-chassis and a rear sub-chassis having at least one drive axle; a main chassis pivotally supported by each sub-chassis; an engine mounted on one of the sub-chassis; a mechanism for communicating constant velocity power between the sub-chassis, the mechanism comprising an intermediate shaft which extends substantially along the centre-line of the main chassis when the centre-lines of the sub-chassis and the main chassis are aligned, the ends of the intermediate shaft being provided with universal joints connected respectively to a front shaft extending substantially along the centre-line of the front sub-chassis and a rear shaft extending substantially along the centre-line of the rear sub-chassis; steering means for causing the front sub-chassis to pivot relative to the main chassis; and control means for controlling pivoting of the rear sub-chassis relative to the main chassis in dependence on the pivoting of the front sub-chassis.

In the vehicle described in EP-A2-0112712, the universal joints are substantially equidistant from the respective pivot axes of the sub-chassis and pivoting of the two sub-chassis in relation to the main chassis is controlled in such a manner that, during turning, the

angle between the centre-lines of the two sub-chassis and the centre-line of the main chassis are equal and opposite, thereby ensuring that trouble-free functioning of the shaft arrangement so that constant velocity power is communicated between the sub-chassis.

The design of vehicle described in the above mentioned European Patent Application brings a number of ^' advantages, which are described in that application. However, since the control of the pivoting of the rear sub-chassis is derived from the steering of the front sub-chassis, there is a problem in ensuring that the control means has sufficient power to turn the rear sub-chassis and in particular to return it to straight-ahead travel after turning of the vehicle; in particular, there are difficulties in complying with the normal requirement that, if the steering wheel is released during ^* turning, the vehicle should either continue turning on the same radius or straighten up. What is therefore desired ^" is a vehicle of the above mentioned type which overcomes this problem without sacrificing the advantages of the vehicle described in our earlier European Patent Application.

Furthermore, we have now found that in some circumstances it is desirable to allow a trailer (main chassis) to cut in to a limited extent during turning, this having the advantage of extending the practical overhang behind the rear wheels (rear sub-chassis)

Accordingly, in the present invention the control means controls pivoting of the rear sub-chassis in such a manner that, during turning, the centre-lines of the two sub-chassis intersect each other at a point whose locus is nearer to the pivot axis of the front sub-chassis than to the pivot axis of the rear sub-chassis, and the

universal joints of the intermediate shaft are positioned such that they are equidistant from the said point of intersection.

This arrangement ensures that, although the intermediate shaft does not remain parallel with the centre-line of the main chassis during turning, the angle between the front shaft and the intermediate shaft is always equal and opposite to the angle between.the rear shaft and the intermediate shaft, thereby ensuring trouble-free functioning of the shaft arrangement so that constant velocity power is communicated between the sub-chassis. An important advantage is that, since the locus of the point of intersection of the front sub-chassis centre-line and the rear sub-chassis centre-line is nearer to the front- pivot axis t-ha to the rear pivot axis, the angle between the rear sub-chassis centre-line and the main chassis centre-line, during .turning, is less than the angle between the front sub-chassis centre-line and the main chassis centre-line; consequently, the power required to pivot the rear sub-chassis is reduced in relation to that required to pivot the front sub-chassis.

Any convenient control means may be used for controlling the pivoting of the rear sub-chassis, whether mechanical means, hydraulic means, electrical means, or a combination of means. In particular, any of the means- described in our earlier European Patent Application may be used.

The invention will be described further with reference to the accompanying drawing, in which:

Figure 1 is a schematic plan view of the propeller shafts and wheels of an articulated vehicle in accordance with the invention; and

Figure 2 is a similar view of another vehicle in accordance with the invention.

The vehicles illustrated are of the types described in our published European Patent Application No. EP-A2-0112712, to which the reader is referred for the details of construction, which are not described below.

The vehicle illustrated in Figure 1 comprises a standard or special highway tractor or leading unit with three axles, the rear two of which are driven. A trailing unit or trailer with two driven axles can rotate about a so-called fifth wheel coupling comprising a transverse pivot and a turntable mounted on the chassis of the tractor, constituting a first sub-chassis having a centre line 1'. The trailer chassis constitutes-the main chassis of the vehicle and has a centre-line 2'. Attached to the rear of the trailer chassis is a turntable whose lower section is attached to a second sub-chassis which carries the trailer axles and which has a centre-line 6'.

As the tractor steers to left or right of the trailer via its front steering axles so that the tractor sub-chassis centre-line 1' rotates through a given angle α in relation to the main chassis centre-line 2' about the pivot axes 27 of the front turntable, the trailer sub-chassis centre-line 6' is rotated about the pivot axes 30 of the rear turntable to an opposite but smaller angle β in relation to the main chassis centre-line 2' by suitable control means. Such control means can comprise tension rods connecting the front and rear sub-chassis or telescopic members mounted parallel to the respective centre-lines 1' and 6' and pivoted to a bearing which slides on a transverse guide member, as described in the above-mentioned European Patent Application.

The engine and transmission are mounted on the front sub-chassis and are connected both to the tractor drive axles and the trailer drive axles. Cardan shafts are arranged so as to impart constant velocity into the trailer axles at any degree of turn, as described below.

During turning, the sub-chassis centre-lines 1' and 6' intersect at a point 61 whose locus 62 crosses' to the main chassis centre-line 2 ' at a point 63. The ratio between the distance from the point 63 to the axes 27 and the distance between the point 63 and the axes 30 is approximately 0.6. The locus 62 is a circular arc of large radius and can, in practical terms, be approximated tσ a straight line.

A front Cardan shaft 18 extending along the front sub-chassis centre-line 1' is connected to an intermediate Cardan shaft 20 which is, in turn, connected to a rear Cardan shaft 21 extending along the rear sub-chassis centre-line 6'. The distance L_ " between the front Hookes joint of the intermediate shaft 20 and the point of intersection 61 of the sub-chassis axes l ¹ and 6' is arranged to be equal to the distance L_ between its rear Hookes joint 20b and the said point of- intersection 61. From this it follows that the angles C and D between the axes of the shaft 20 and the respective axes of the shafts 18 and 21 are equal.

In the drawing, the lines 64 and 66 are perpendicular to the respective centre-lines 1' and 6', and the line 67 is perpendicular to the centre-line 2". A and B represent the angles between the line 67 and the lines 64 and 66 respectively. Accordingly;

C + D = α + β = A + B.

The ratio of the distance between the Hookes joints 20a and 20b when the centre-lines l',2', and 6 ¹ are aligned is made large enough to allow sufficient telescoping of the intermediate shaft 20 to enable it to length during steering from the central to the maximum steering angle.

In the case in which the control means comprises a transverse guide member, as described above, this member will be arranged directly above the locus 62. ^" As described in the above-mentioned European Patent Application, the control means may be assisted by a hydraulic ram.

In the articulated vehicle illustrated in Figure 2 the tractor sub-chassis 1 is connected to the main chassis 2 by a pivot 41, defining the pivot axis 27. The rear sub-chassis 6 carries the main chassis 2 by wa of a turntable 5, defining the pivot axis 30.

The engine transmission (not shown) is connected to a transfer box 46 whose output shaft (extendingalong the front sub-chassis centre-line 1') drives, on the one hand, the intermediate shaft 20 and, on the other hand, a Cardan shaft 47 from which drive is transmitted at constant velocity to each of the two front drive axles 48. The shaft 20 is connected to a rear Cardan shaft 49 mounted on the rear sub-chassis 6, from which drive is transmitted at constant velocity to the two rear drive axles 51.

Steering is obtained by turning the whole of the tractor about the axis 27 by means of hydraulic rams 52 acting between the sub-chassis 1 and the main-chassis 2, and at the same time turning the rear sub-chassis 6 through a smaller, opposite angle by means of hydraulic rams 53 between it and the main chassis 2. In the

position shown, the angle α between the axes 1' and 2' is 25° and the angle β between the,axes 6' and 2' is 20°. The relative pivoting of the sub-chassis 1,6 is controlled with the aid of a pivotal connection 54 between them, comprising a bracket 56 rigidly fixed on the sub-chassis 1 and a bracket 57 rigidly fixed on an axially slidable member 58 mounted on the sub-chassis 6. The brackets 56,57 are connected by a vertical pivot pin 59 whose pivot axis 61 coincides with the point of intersection of the centre-lines l',6'.

It will be noted that the locus of the axis 61 during turning is an arc of a circle centred on the axis 27 and is nearer to the axis 27 than to the axis 30. In the embodiment illustrated the said locus also crosses the centre-line 2 ' at a point which is nearer the axis 27 than the axis 30; it may, however, be permissible in some circumstances for this point to be half-way between the axes 27,30.

In this case it is the shaft 49 which telescopes during turning, being made sufficiently long for this purpose, while the length of the intermediate shaft 20 remains substantially unchanged (e.g. a change of about 30 mm), with its Hookes joints 20a,20b equidistant from the axis 61.

Various modifications may be made within the scope of the invention, as described in the above-mentioned European Patent Application.