GB2113635A - Trailer - Google Patents

Abstract

A trailer comprises a load platform on a frame (11) supported near to its rear end on a pair of wheels (14). Near to its front end, the frame is connected by a universal ball joint (20, 21) with a towing frame (15) having at one end a towing eye (16) and at the opposite end a pair of wheels (17). The frame (15) may be provided with a plurality of longitudinally spaced sockets (21) for selectively receiving the ball (20). Ring parts (23) may be released to allow disconnection of the towing frame (15) from the load platform frame (11). The ball joint (20, 21) may be replaced by a thrust bearing having rollers confined between two circular races. <IMAGE>

Description

SPECIFICATION Trailer This invention relates to a trailer of the kind comprising a load carrying structure, a towing structure, a first set of wheels mounted on the load carrying structure adjacent to a rear of the trailer, a second set of wheels mounted on the towing structure and a joint structure which connects the load carrying structure and the towing structure in such a manner that relative pivoting about an upright axis can occur for steering of the trailer. Usually, each set of wheels comprises one pair of wheels only but references herein to a pair of wheels are to be taken to include references to a set of more than two wheels.

An example of a trailer of the kind referred to is described in British Patent Specification No. 1,529,977. The joint structure of this known example of trailer includes an intermediate member which can pivot relative to the towing structure about an axis which is generally upright in use and can also pivot relative to the load carrying structure about an axis which is always perpendicular to both a longitudinal centreline of the load carrying structure and the upright pivot axis. The joint structure is designed to prevent pivoting of the load carrying structure relative to the towing structure about an axis which is parallel to the longitudinal centreline of the towing structure.Provided that the generally upright pivot axis is maintained exactly vertical, a front part of the load carrying structure is maintained horizontal even when the centre of gravity of a load borne by the trailer is spaced considerably from the longitudinal centreline of the load carrying structure, and the towing frame is turned about the upright pivot axis relative to the load carrying structure.

The trailer described in the aforesaid published Specification has a number of disadvantages. If, when the four wheels of the trailer are rolling in the same direction, one of these wheels rises or falls relative to the other wheels, the load carrying structure is twisted about an axis parallel to its longitudinal centreline. The published Specification indicates that the load carrying structure is designed to have a low torsional rigidity about this axis.

However, a large degree of twisting will tend to damage the load carrying structure. Twisting of the load carrying structure will also occur if, when the trailer is being towed around a corner, one pair of wheels is rolling in a direction different from that in which the other pair of wheels is rolling and the connection between the trailer and a towing vehicle either rises or falls relative to the trailer wheels. Twisting would be particularly excessive if the trailer is unhitched from the towing vehicle whilst the axis of rotation of the first pair of wheels is perpendicular to the axis of rotation of the second pair of wheels and the towing eye or the like of the trailer is permitted to descend to the ground.

According to the present invention, the joint structure of a trailer of the kind described is arranged to allow relative pivotal movement of the load carrying structure and towing structure about three mutually orthogonal axes and the towing structure includes a first part of a releasable coupling, which part, during towing of the trailer is engaged by a second part of the coupling on a tractor, and which first part is separated from the second part of the coupling when the trailer is separated from the tractor and wherein the first coupling part is adapted to define, in conjunction with the second coupling part, a yaw axis.With this arrangement, limited rocking of the towing structure about an axis of rotation of the second pair of wheels does not cause twisting of the load carrying structure, even when the axis of rotation of one pair of wheels is substantially perpendicular to the axis of rotation of the other pair of wheels.

By the yaw axis, we mean an axis which is generally upright when the trailer is being towed and about which relative angular movement of the tractor and trailer occurs, when the tractor is driven around a corner.

The preferred joint structure includes a ball joint. Alternatively, the joint structure may include a Hooke's joint and means for accommodating relative pivoting about an axis which is perpendicular to the pivot axes of the Hooke's joint. Inevitably, relative pivoting movement about at least one of the three mutually perpendicular axes must be limited but the joint structure may be adapted to allow unlimited pivoting movement about another of the axes.

If required, means may be provided for limiting relative pivotal movement of the load carrying structure relative to the towing structure about an axis parallel to a longitudinal centreline of the load carrying structure to a range of pivotal movement which is sufficiently large to accommodate all pivoting expected to occur during normal use of the trailer.

The joint structure may be adapted to permit separation of the load carrying structure from the towing structure.

Two examples of trailers embodying the invention will now be described, with reference to the accompanying drawings, wherein: Figure 1 shows diagrammatically a perspective view of a trailer, and and adjacent part of a tractor, a load carrying structure being separated from a towing structure of the trailer for ease of illustration.

Figure 2 shows diagrammatically a side elevation of a further trailer, a part of the load carrying structure of the further trailer being omitted.

The trailer shown in Fig. 1 comprises a load carrying structure 10 and a towing structure 9 which are releasably connected together by a joint structure. The load carrying structure 10 includes a rectangular frame 11 supporting a load platform 1 2 and itself supported near to a rear end of the trailer on an axle 1 3 carrying a pair of rear wheels 14 of the trailer. The wheels 14 have a common axis of rotation which is fixed with respect to the frame 11, although springs may be interposed between the axle and the frame, if required.

The towing structure comprises an elongated frame 1 5 having rigidly mounted at one end a towing eye 1 6 which, when the trailer is towed by a tractor, engages a towing hook 26 of the tractor and is releasably retained thereon by an abutment 27 on the tractor. A front pair of wheels 1 7 are carried on a rigid axle 1 8 for rotation about a front wheel axis 1 9. An end portion of the frame 1 5 which is remote from the towing eye is secured to the axle 1 8. If required, springs may be interposed between the frame 1 5 and the axle 1 8.

The towing hook 1 6 and towing eye 1 6 collectively define a yaw axis 28 about which limited angular movement of the frame 1 5 relative to the tractor can occur during towing.

Limited relative movement of the frame 1 6 and tractor about a roll axis 29 and about a pitch axis 30 is also permitted by the coupling constituted by the hook 9 and eye 1 6. The relative angular movement about the pitch axis and about the roll axis which are expected to occur during use are small, relative to the relative movement about the yaw axis which may occur. It will be noted that the hook 1 6 is positioned at an apex of the frame 1 5 so that there is clearance for large angular movements about the yaw axis.

The joint structure comprises a ball 20 and a socket 21 in which the ball is normally disposed. The socket 21 is provided in the frame 1 5 at a position lying between the axle 18 and the towing eye 1 6. The ratio of the distance from the centre of the socket to the axis 1 9 to the distance from the centre of the socket to the centre of the eye 1 6 is selected according to the proportion of the downward load transmitted through the ball 20 in use which is required to be applied to the towing vehicle.The frame 1 5 may be provided with a plurality of sockets for receiving the ball 20 selectively, these sockets being spaced apart from one another longitudinally of the frame 1 5. One of these sockets, or the sole socket, may be disposed directly above the axis 1 9 so that no substantial downward load is applied to the towing vehicle.

Alternatively, a body defining the socket 21 may be releasable from the frame 15, the frame being adapted to receive this body in a selected one of a plurality of alternative positions. This arrangement also enables the ratio of the distance from the centre of the socket to the axis 1 9 to the distance from the centre of the socket to the centre of the eye 1 6 to be adjusted.

The ball 20 is secured on the frame 11 by means of a stem 22 having an upper end portion fixed in the frame, extending downwardly from the frame and having the ball at its lower end. The ball is rigid with the frame 11. In the example illustrated, the stem 22 is spaced somewhat rearwardly from the front edge of the load platform 12, the degree of overhang of the load platform with respect to the stem 22 being selected according to the required distribution of load between the ball 20 and the rear wheels 14. It will be understood that the ball transmits downward load from the frame 11 to the frame 1 5 and also transmits traction forces from the frame 1 5 to the frame 11.

Releasable clamping means is provided for retaining the ball 20 in the socket 21. The clamping means may be in the form of a diametrically split ring 23 secured by bolts to that part of the frame 1 5 in which the socket is formed. If the ring parts 23 are released from the frame, the ball can be withdrawn from the socket to disconnect the load carrying structure from the towing structure. Thus, a single towing structure can be used successively with a plurality of load carrying structures. In this case, the load carrying structures would be provided with means for temporarily supporting the front end of the structure in the absence of the towing structure. Alternative forms of clamping means may be provided to permit the ball to be released quickly and easily from the socket.

Instead of releasing the ball from the socket, the body which defines the socket may be released from the towing structure or the ball may be released from the load carrying structure to permit separation of the load carrying structure from the towing structure.

The joint structure allows relative pivoting movement of the load carrying structure 10 and towing structure 9 about three mutually orthogonal axes which intersect at the centre of the ball 20. Thus, even when the towing frame 1 5 is turned about an upright axis relative to the load platform 12, the towing eye 1 6 can be raised and lowered without subjecting the frame 11 to torsional stress.

Upward and downward movement of one wheel of the trailer relative to the other wheels can occur also without subjecting the frame 11 to torsional stress. It will be noted that relative pivoting of the load carrying structure and towing structure about an axis 24 parallel to a longitudinal centreline of the load carrying structure is limited, when the axle 1 8 is parallel to the axle 13, by engagement of the frame 11 with one or other of the wheels 1 7.

Additional means for limiting relative pivotal movement about the axis 24 may be provided. Such additional means may comprise pads or rollers carried on the frame 11 at positions spaced from the upright axis 25 and engageable with upwardly facing surfaces of the frame 1 5. Such means would be effective to limit pivoting about the axis 24 even when the axle 18 is perpendicular to the axle 1 3. It will be understood that the pads or rollers may be carried on the frame 1 5 to engage downwardly facing surfaces of the frame 11.

Certain parts of the trailer illustrated in Fig.

2 correspond to parts hereinbefore described with reference to Fig. 1. In Fig. 2, such corresponding parts are indicated by like reference numerals with the prefix 1 and the preceding description is deemed to apply, except for the differences hereinafter mentioned.

The trailer shown in Fig. 2 does not include a load platform mounted directly on the frame 111. The frame 111 is adapted to support a tipping body (not shown) arranged generally in a known manner. The frame 111 includes a goose-neck 1 26 to which the stem 1 22 is secured. As compared with the stem 22, the stem 122 is relatively short. There is below the goose-neck sufficient clearance to enable the front wheels 11 7 to pass beneath the goose-neck.

The towing eye 11 6 is not welded directly to the frame 11 5. The towing eye is welded to a draw bar 1 27 connected by a pivot pin 1 28 with the frame 11 5 at the front end thereof. The draw bar can thus pivot upwardly and downwardly about an axis which is parallel to the front wheel axis 11 9. In order that downwardly directed load can be applied to the towing vehicle through the draw bar 127, there is operatively interposed between the draw bar and the frame 11 5 a pair of springs 1 29 which may be formed of an elastomer.

The springs 1 29 are disposed one adjacent to each side of the frame 11 5 and rest on an upwardly facing surface of that frame. Plates 1 30 which rest on the springs are connected by rods 131 with an end portion of the draw bar 127 underlying the springs. When the towing eye 11 6 is raised relative to the frame 115, the rods 1 31 are subjected to tension and the springs 129 are compressed. Upward pivoting of the towing eye relative to the frame 11 5 is thereby limited but the springs can yield resiliently when downwardly directed shock loads are exerted on the frame 11 5 from the frame 111. This reduces the application of shock loads to the towing vehicle.

Whilst we prefer to mount the ball on the load carrying structure and'provide the socket in the towing structure, the joint structure may be inverted, if required.

There may be substituted for the ball joint a thrust bearing having rollers confined between two circular races, the bearing being arranged to accommodate angular movement about a substantially upright axis by rolling of the rollers between the races and being arranged to accommodate relatively limited movement about any axis in a generally horizontal plane by relative movement of the races away from each other at one side of the bearing. A rollerthrust bearing may be used for this purpose, preferably a bearing in which the track of each race on which the rollers run is of a part-spherical form. In a case where this form of bearing is provided and the load carrying structure is required to be separable from the towing structure, it would be necessary for the bearing to be detachable from one or other of these structures.

Whilst the example of trailer illustrated in the drawing comprises a single pair of rear wheels and a single pair of front wheels, it will be understood that a larger number of front wheels and/or rear wheels may be provided, these being mounted on one rear axle and one front axle or mounted on tandem rear axles and/or tandem front axles.

Claims (6)

1. A trailer comprising a load carrying structure, a towing structure, a first pair of wheels mounted on the load carrying structure adjacent to a rear of the trailer and a second pair of wheels mounted on the towing structure, wherein the towing structure and the load carrying structure are connected together by a joint structure which allows relative pivoting movement of the load carrying structure and the towing structure about three mutually orthogonal axes and wherein the towing structure includes a first part of a releasable coupling, which part, during towing of the trailer, is engaged by a second part of the coupling on a tractor and which first part is separated from the second part of the coupling when the tractor is separated from the trailer, and wherein the first coupling part is adapted to define, in conjunction with the second coupling part, a yaw axis.

2. A trailer according to Claim 1 wherein the joint structure comprises a ball joint.

3. A trailer according to Claim 1 or Claim 2 wherein the joint structure is adapted to be released to permit separation of the load carrying structure from the towing structure.

4. A trailer substantially as herein described with reference to and as shown in Fig.

1 of the accompanying drawings.

5. A trailer according to Claim 4 modified substantially as herein described with reference to and as shown in Fig. 2 of the accompanying drawings.

6. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.