GB2305642A

GB2305642A - Steerable semi-trailer

Info

Publication number: GB2305642A
Application number: GB9519812A
Authority: GB
Inventors: Robert Clive Browning Davis
Original assignee: THOMPSON CARMICHAEL Ltd
Current assignee: THOMPSON CARMICHAEL Ltd
Priority date: 1995-09-29
Filing date: 1995-09-29
Publication date: 1997-04-16
Also published as: GB9519812D0

Abstract

A steerable semi-trailer 1 is connected conventionally to a tractor 2 via a king pin 3. A tandem axle bogie 4 is connected to the underside of the semi-trailer 1 by a turntable 5 arranged to turn about a vertical pivot axis 6 in response to the tractor 2 turning. Bogie/turntable assembly 4,5 is connected to an A-frame assembly 7 (comprising a steering mechanism) by a horizontal pivotal connection 8. A bar 7b is slidable within a tubular section of A-frame 7 and pivotally connected to the back of the tractor 2 to pivot the A-frame and turntable about vertical axis 6 to achieve a limited amount of positive steer for the rear wheels 8. The bar 7b can be disconnected from the back of the tractor and secured under the trailer when steering of the trailer wheels is not desired.

Description

IMPROVEMENTS IN OR RELATING TO SEMI-TRAILERS This invention relates to improvements in or relating to semi-trailers and is more particularly concerned with steering of the semi-trailer.

Problems involved in the steering of semi-trailers around corners are well known and arrangements have been proposed for steering the rear wheels of the trailer in response to movement of the tractor in order to reduce the amount of "cut in" on corners to give a better turning arc that more closely follows the turning arc of the tractor.

It is believed that previously proposed arrangements for steering the rear wheels of a semi-trailer tend to have various disadvantages. There are arrangements for steering the rear axle of a semi-trailer involving a cam and piston system which turns the rear wheels of the semi-trailer in response to the tractor turning. Such systems tend to have a limited turning arc. There are more sophisticated systems comprising levers attached to front and rear axles of the semi-trailer which synchronously push and pull opposite ends of the rear axle in response to directional force from a kingpin turntable. As well as such mechanical steering means, hydraulic steering means have been employed. Such arrangements tend to be rather costly and involve the provision of a turntable at the front of the semi-trailer.In order to fit the turntable at the front of the semi-trailer the centre of gravity has to be raised significantly on the back of the tractor which in itself is undesirable. Additionally, such arrangements may involve hydraulic pipes running along the side of the semi-trailer which can be inconvenient in setting tank settings.

Therefore, such prior proposals tend to be awkward or inconvenient as well as adding significant weight and cost to the semi-trailer. Further, conventional rear wheel steering systems tend to provide a full turning arc which can yield some lack of stability. Overall, it is believed that a generally more simple, cost effective, lighter and more stable arrangement could be provided for steering a semi-trailer. Additionally, there are occasions when such steering of the semi-trailer is not desired, for example when the semi-trailer is reversed or when other vehicles are parked closely alongside and it is believed that current arrangements do not cater for such eventualities.

It is an object of the present invention to at least alleviate the aforementioned, or other, problem with steering of semi-trailers.

According to the present invention there is provided a semi-trailer having a steering mechanism for steering the rear wheels of the semi-trailer, said steering mechanism being connected or connectable between a tractor and the rear wheels of a semi-trailer, said steering mechanism comprising a draw bar which is extendible relative to a receiving member or sleeve of the steering mechanism as the tractor turns a corner, thereby allowing the rear wheels of the semi-trailer to be steered around the corner.

Further according to the present invention there is provided a steering mechanism for the semi-trailer according to the preceding paragraph or the combination of a tractor and semi-trailer in accordance with the preceding paragraph.

Preferably, the steering mechanism is connected to a turntable on which the rear wheels of the semi-trailer are mounted and said mechanism may include a generally A-shaped frame.

Usually, the semi-trailer will be provided with means to disable the steering mechanism, or carry the steering mechanism in an inoperative position, when in use with a tractor, so that the semi-trailer operates as a conventional semi-trailer with fixed axle rear wheels. In one embodiment of the semi-trailer, the steering mechanism may be releasably coupled in an inoperative position to the underside of the semi-trailer, preferably at a location between landing legs of the semi-trailer. The steering mechanism may be pivoted (about a horizontal axis) relative to the rear wheels of the semi-trailer (and relative to said turntable where provided) to enable the steering mechanism to be swung between an operative position (coupled to a tractor) and an inoperative position (coupled to the underside of the semi-trailer).

Further according to the present invention there is provided a semi-trailer having one or more of the following features (a) A steering mechanism connected to a rear wheel bogie mounted on a turntable at the rear of the semi trailer, said mechanism being connected or connectable to a tractor, (b) the steering mechanism of claim (a) being selectively coupled to a tractor in an operative position or to the semi-trailer in an inoperative, stowage position yielding fixed axle semi-trailer operation, (c) a steering mechanism as claimed in (a) and/or (b) which has an A-frame or draw bar assembly, (d) a steering mechanism as in (c) which has a portion pivotally connected relative to the turntable (about a horizontal axis) to enable said portion to pivot between operative and stowage positions.

Further advantageous features of the present invention will be evident from the following description and drawings.

An embodiment of a semi-trailer in accordance with the present invention will now be described by way of example only, with reference to the following, much simplified, generally schematic drawings, in which: FIGURE 1 shows a side view of a tractor and semi-trailer in accordance with the present invention; FIGURE 2 shows an underneath view of the tractor and semi trailer as shown in FIGURE 1, and FIGURES 3 to 5 show arc paths taken by various vehicles, whilst FIGURE 6 shows the arc path that may be provided by a semitrailer in accordance with the present invention.

Referring to FIGURES 1 and 2 of the drawings, a semitrailer 1 is connected conventionally to a tractor 2 via king pin or fifth wheel connection 3 in known manner. The general form of the semi-trailer 1 and the tractor 2 are well known and so have only been reproduced schematically in FIGURES 1 and 2 of the drawings. Conventional semitrailers are usually fitted with a rear fixed bogie that may be of the double or tandem axle type. However, in accordance with the present invention, the tandem axle bogie 4 is connected to the underside of the semi-trailer 1 by means of a turntable 5 arranged to turn about vertical pivot axis 6 in response to the tractor 2 turning a corner in a manner yet to be described.

The bogie/turntable assembly 4,5 is pivotally connected at the front thereof to an A-frame assembly 7 (comprising a steering mechanism) by means of horizontal pivotal connection 8. The form of A-frame assembly 7 shown in Figure 2 varies slightly from Figure 1, since Figure 2 does not actually show a pivotal connection 8. However, Figure 2 shows in chain dotted lines the position at which the pivotal connection 8 would be located relative to the semi-trailer. To conform with Figure 1 the A-frame assembly 7 would in practice be shorter than that shown in Figure 2 so that axis 8 would coincide with the widest part of the A-frame.The A-frame assembly has a central, square section tube 7a which slidably receives an inner tube or draw bar 7b (having an outer cross section corresponding with the inner cross-section of tube 7a) which is pivotally connected at one end thereof to the rear of the tractor 2 at pivot connection 9. The pivot connection 9 may be constituted by a simple towing hook (not shown) located on the rear cross member (not shown) of a standard tractor that couples with an eye on the front of tube 7b. Once again the general format of the draw bar A-frame assembly 7 will be known for different applications and thus is not shown in detail in the FIGURES of the drawings.

The main difference in the present invention is that the A-frame assembly 7 is connected to the rear wheels of a semi-trailer 1 as well as being connected to the tractor 2 in such a manner that a limited amount of positive steer can be achieved for the rear wheels of a semi-trailer 1 which may significantly reduce the amount of "cut-in" on corners more particularly when compared with the conventional, fixed bogie semi-trailer of the same type or even with much shorter length fixed bogie semi-trailers.

It will be evident from the FIGURES of the drawings that as the tractor 2 turns around a corner it will swing about the vertical axis 3a provided by the king pin 3 and as the back of the tractor swings out it will displace the pivotal axis 9 laterally causing the A-frame assembly 7 to swing about the vertical pivotal axis 6 of the turntable 5 together with the wheels of the bogie 4 thereby inducing an element of positive steer into the trailer bogie. If the tractor 2 was adapted so that the pivotal connection 9 (towing hook) were carried artificially far back then the tractor and semi-trailer could steer a near perfect path with the trailer bogie wheels closely following the wheel path of the tractor wheels.However, usually only a limited degree of positive steer is required because there can be an inherent significant loss of stability in full positive steering of semi-trailer bogies.

As will be evident from FIGURES 1 and 2 of the drawings, the A-frame assembly 7 extends between landing legs 10 of the semi-trailer 1 and the pivotal connection 9 provides a releasable coupling such that the A-frame assembly 7 can be disconnected from the tractor unit 2 in order to allow the semi-trailer to operate in a conventional unsteered manner. Thus, once the A-frame assembly 7 has been uncoupled from the tractor 2 (by pivoting the A-frame about horizontal axis 8) it is envisaged that the draw bar 7b can be retained in an appropriate position to the underside of the semi-trailer 1 (the draw bar eye, where provided, could be hooked onto an appropriate hook in a central position) within the semitrailer structure, typically by providing a mounting or cradle for the eye in the centre of the landing leg subframe (not shown).Advantageously, for ease of operation, it is envisaged that the A-frame assembly 7 could be disconnected from the tractor 2 in the aforedescribed manner and secured to the underside of the semi-trailer in order to allow the semi-trailer 1 to operate in a conventional manner more particularly when it is desired to reverse the semi-trailer owing to the difficulties often encountered in reversing rear wheel steerable semitrailers. Also, a driver may be comfortable with a conventional operation semi-trailer in situations where vehicle access is generally good or unrestricted.

Additionally, it may be that the tractor 2 being utilised with the semi-trailer 1 has not been adapted for connection to the A-frame assembly 7. Thus, the semi-trailer 1 could still be used with such a tractor albeit in a generally conventional manner.

Thus, the aforedescribed embodiment of the present invention provides a semi-trailer for selected use as a conventional fixed semi-trailer and as a positive steer or self-tracking rear wheel semi-trailer for use with an adapted tractor.

In order to demonstrate the expected effectiveness of the present invention FIGURES 3 to 5 show the turning arcs of some other vehicles whilst FIGURE 6 shows the improved turning arc associated with semi-trailer with positive rear wheel steering in accordance with the present invention.

It is to be understood that the scope of the present invention is not to be unduly limited by a particular choice of terminology and that a specific term may be replaced or supplemented by any equivalent or generic term.

Further it is to be understood that individual features, method or functions related to the semi-trailer, tractor, steering mechanism or parts thereof alone or in combination might be individually patentably inventive. The singular may include the plural or vice versa.

Claims

1. A semi-trailer having a steering mechanism for steering the rear wheels of the semi-trailer, said steering mechanism being connected or connectable between a tractor and the rear wheels of a semi-trailer, said steering mechanism comprising a draw bar which is extendible relative to a receiving member or sleeve of the steering mechanism as the tractor turns a corner, thereby allowing the rear wheels of the semi-trailer to be steered around the corner.

2. A semi-trailer as claimed in Claim 1 in which the steering mechanism is connected to a turntable on which the rear wheels of the semi-trailer are mounted.

3. A semi-trailer as claimed in Claim 1 or Claim 2 in which the steering mechanism includes a generally A-shaped frame.

4. A semi-trailer as claimed in any one of the preceding claims in which the semi-trailer is provided with means to disable the steering mechanism, or carry the steering mechanism in an inoperative position.

5. A semi-trailer as claimed in Claim 4 in which the steering mechanism can be releasably coupled in an inoperative position to the underside of the semi-trailer.

6. A semi-trailer as claimed in Claim 5 in which the semi-trailer can be releasably coupled in said manner at a location between landing legs of the semi-trailer.

7. A semi-trailer as claimed in Claim 6 in which the steering mechanism can be pivoted relative to the rear wheels of the semi-trailer (and relative to said turntable where provided).

8. A semi-trailer as claimed in Claim 7 in which the steering mechanism is pivotable about a horizontal axis.

9. A semi-trailer substantially as herein described with reference to FIGURES 1,2 and 6 of the accompanying drawings.

10. A semi-trailer having one or more of the following features (a) A steering mechanism connected to a rear wheel bogie mounted on a turntable at the rear of the semi trailer, said mechanism being connected or connectable to a tractor, (b) the steering mechanism of claim (a) being selectively coupled to a tractor in an operative position or to the semi-trailer in an inoperative, stowage position yielding fixed axle semi-trailer operation, (c) a steering mechanism as claimed in (a) and/or (b) which has an A-frame or draw bar assembly, (d) a steering mechanism as in (c) which has a portion pivotally connected relative to the turntable (about a horizontal axis) to enable said portion to pivot between operative and stowage positions.