GB2037685A - A tractor unit having a fifth wheel for supporting a semi-trailer - Google Patents

Abstract

A tractor unit has a fifth wheel 13 mounted on a trunnion 14, and a road wheel axle 12 coupled to a chassis member 11 of the unit by a resilient device 27; the trunnion being mounted intermediate the ends of a resilient beam 18, the beam having a trailing end 23 mounted on the axle 12 so that loading on the trailing end of the beam is transmitted to the axle; the leading end 21 of the beam being mounted on the chassis member 11 of the unit. <IMAGE>

Description

SPECIFICATION Atractor unit This invention relates to a tractor unit having a fifth wheel for supporting a semi-trailer.

According to a first aspect of the present invention there is provided a tractor unit having a fifth wheel mounted on a trunnion and a road wheel axle coupled to a chassis member of the unit by a resilient device; the trunnion being mounted intermediate the ends of a resilient beam, the beam having a trailing end mounted between the chassis member and the resilient device so that loading on the trailing end of the beam is transmitted through the resilient device to the axle; the leading end of the beam being mounted on the chassis of the unit.

According to a second aspect of the present invention the resilient beam of the first aspect comprises a leaf spring.

According to a third aspect of the present invention the loading end of the resilient beam of any previous aspect is mounted on the chassis by way of a resilient means.

According to a fourth aspect of the present invention the resilient means of the third aspect comprises an air spring.

According to a fifth aspect of the present invention the trunnion of any previous aspect is located relative to the chassis by way of a radius rod.

According to a sixth aspect of the present invention the trunnion of any previous aspect is coupled to the chassis by way of a damper.

According to a seventh aspect of the present invention the resilient device of any previous aspect comprises an axle leaf spring having its ends pivotably connected to the chassis with the axle and beam coupled to the leaf spring at a common position, or separate positions, intermediate the ends of the axle leaf spring.

Exemplary embodiments of the invention will now be described with reference to the accompanying drawings of which Figure 1 and Figure 2 are diagrammatic elevations of the rear end of, respectively, first and second tractor embodiments.

Figure 1 shows chassis member 11 of a tractor with rear axle 12. The tractor has a fifth wheel 13, mounted on trunnion 14, which supports the front of a trailer 15. The trunnion 14 is secured by U-bolts 16 and plate 17 to a leaf spring 18 including a pair of leaves 19,20. The leaf spring 18 has loading end 21 mounted on a slipper bracket 22 secured to chassis member 11. The trailing end of spring 18 is mounted on a slipper bracket 24 which is bolted to axle carrier 25 by way of U-bolts 26. The bolts 26 serve to clamp leaf spring 27 between the slipper bracket 24 and the carrier 25. Front end 28 of spring 27 is pivotably attached to member 11 by bolt 29. Rear end 30 of spring 27 is located by slipper bracket 31 on member 11. Road wheel 32 is mounted on one end of axle 12.

An arrangement of springs similar to springs 18, 27 are provided on a chassis member corresponding to member 11 on the opposite side of the tractor.

Radius rod 33 is centrally pivotted on bracket 34 and has one end connected to trunnion 14 and the other end pivotably connected to damper 35. The damper 35 is anchored by bolt 29 to chassis member 11. An anti-roll bar 36 connects the radius rod 33 and a corresponding radius rod on the opposite side of the tractor.

Figure 2 has a number of components similar in form and function to those shown in Figure 1. As a consequence similar reference numerals are used and description of the components is not repeated.

Trunnion 14 is connected to beam 41 whose leading end 42 is supported by air spring 43 and is laterally located by a compliant mounting 44. The trailing end 44 of beam 41 is mounted on a slipper bracket 45 which is bolted to axle carrier 24. Radius rod 43 has one end connected to trunnion 14 and the other end pivotably connected to bracket 34. The radius rod 43 is connected to a corresponding radius rod on the opposite side of the tractor.

With articulated vehicles, that is to say tractors coupled to semi-trailers, reasonable ride properties can be obtained with fully laden trailers. However with the tractor only or with an unladen trailer, ride conditions are frequently very poor. This is due to the lack of a sufficient load on the rear springs to give any significant static deflection of the tractor rear springs.

One possible answer to this ride problem is to use an air spring suspension where the static deflection and, so suspension frequency, is undependent of imposed load.

A further answer is to use very low rate steel sprung suspensions. The low rate only partly solves the problem because when unladen, the fifth wheel rides high and makes coupling to a semi-trailer difficult. In addition a reduction in sprung rate leads to a need for anti-roll bars which allow reduction in double wheel (axle) bump rate without reduction in single wheel (roll) rate.

As a consequence ride is improved on rippled surfaces but not on surfaces imposing large axle articulation angles on the tractor.

The present embodiments enable the axle suspension for imposed loads from the trailer to be separated from the axle suspension required to support the unladen tractor. Furthermore they enable braking and driving forces to be more effectively reacted into the tractor frame.

In the case of both embodiments the leaf spring 47 locates the rear axle under driving, braking and cornering conditions. The load imposed on the fifth wheel 13 is divided, in the case of Figure 1, between the loading end 21 and the trailing end 23 of spring 18; and in the case of Figure 2, between the loading end 42 and trailing end 44 of beam 41. In both cases the load on the trailing end passes directly to the rear axle and so through the road wheel to the ground.

The load on the loading end is fed into the frame and is shared between the rear suspension and the unshown front suspension of the tractor.

The embodiment of Figure 2 allows a constant fifth wheel height for all conditions of load and allows the tractor driver to control the fifth wheel height on coupling the tractor to a semi-trailer.

Both embodiments provide a number of advantages: (1) The embodiments can be applied to an existing tractor so that the laden spring periodicity can remain unchanged while the unladen periodicity can be tuned to give the ride characteristic desired.

(2) The total mass of spring material is not significantly changed by applying either embodiment instead of a conventional rear spring. The conventions fifth wheel sub-frame is dispensed with.

A lighter frame sidemember section is possible for the chassis.

(3) Roll stiffness is unchanged and the improved unladen/part laden ride is obtained without the need for a primary anti-roll bar on the tractor suspension.

(4) The "spring fifth wheel" effect is obtained without dive occuring between trailer and tractor on braking.

This last condition is achieved by ensuring that the resultant of the braking force on the fifth wheel and the load reactions there, act along the axis of the radius arm.

While both embodiments show a leaf spring arrangement for the axle similar fifth wheel arrangements could be applied to a tractor equipped with air or coil springs for the axle.

Claims (9)

1. A tractor unit having a fifth wheel mounted on a trunnion and a road wheel axle coupled to a chassis member of the unit by a resilient device; characterised in that the trunnion is mounted intermediate the ends of a resilient beam, the beam has a trailing end mounted between the chassis member and the resilient device so that loading on the trailing end of the beam is transmitted through the resilient device to the axle; and the leading end of the beam is mounted on the chassis of the unit.

2. Atractor unit as claimed in Claim 1 wherein the resilient beam comprises a leaf spring.

3. Atractor unit as claimed in Claim 1 or Claim 2 wherein the leading end of the resilient beam is mounted on the chassis by way of a resilient means.

4. A tractor unit as claimed in Claim 3 wherein the resilient means comprises an air spring.

5. A tractor unit as claimed in any preceding claim wherein the trunnion is located relative to the chassis by way of a radius rod.

6. Atractor unit as claimed in any preceding claim wherein the trunnion is coupled to the chassis by way of a damper.

7. A tractor unit as claimed in any preceding claim wherein the resilient device comprises an axle leaf spring having its ends pivotably connected to the chassis with the axle and beam coupled to the leaf spring at a common position, or separate positions, intermediate the ends of the axle leaf spring.

8. Atractor unit as hereinbefore described with reference to, and as illustrated in, Figure 1 of the accompanying drawing.

9. A tractor unit as herein before described with reference to, and as illustrated in, Figure 2 of the accompanying drawing.