GB2396142A

GB2396142A - Tractor linkage mechanism for a positive steer trailer

Info

Publication number: GB2396142A
Application number: GB0228975A
Authority: GB
Inventors: Kevin William Raven; Paul Anthony Raven
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-12-11
Filing date: 2002-12-11
Publication date: 2004-06-16
Also published as: GB0228975D0

Abstract

A mechanism for linking a positive steer trailer 6 with a fifth wheel 11 of a tractor unit 2 comprises a chassis member 19, a downwardly extending king pin 10 for fifth wheel engagement, a steering actuator for turning steerable trailer wheels 12, and an engagement feature (18 see fig 3) for engaging with a fifth wheel entrance channel 30. The king pin 10 is fixed to the trailer chassis member 19 whilst the engagement feature (18 see fig 3) is free to rotate about the king pin 10 for conveying rotary motion from the fifth wheel 11 to the steering actuator, which may include a hydraulic linkage or alternatively a first pivot arm 34 connected by a rod 51 to a second pivot arm 71, acting via further rods 53,153,54,154 on a third pivot arm 75 preferably to turn the rear wheels 12 of the trailer by an angle less than the steering angle of the tractor unit.

Description

al 1 - 23961 42

Tractor Linkage Mechanism for a Positive Steer Trailer The present invention relates to trailers, both extendible trailers and trailers of fixed length, that may connected and 5 disconnected to a tractor unit by a fifth-wheel coupling mechanism, and in particular to positive steer trailers having steerable wheels and a steering linkage mechanism for linking the trailer with a fifth-wheel of a tractor unit.

10 There are many different types of road-going transport trailers for connection to a tractor unit. The most common type of connection between a tractor unit and a trailer is the so-called "fifth-wheel" mechanism, in which a rear portion of the tractor has on an upper surface a rearwards 15 facing clasp mechanism that engages and disengages with a downwards facing king pin in a forwards portion of the trailer. Trailers come in many lengths, but it is common for long 20 trailers to be up to 13.7 m (45 feet) in length in Europe or 17.4 m (57 feet) in the USA. Such long trailers may also be rated according to national law to carry heavy loads up to 50 tonnes gross, including the weight of the trailer. In order to help spread the load and lessen wear and tear on the 25 public highway, trailers often have multiple axles, -with two or four tyres on each axle. Three axle trailers are common in the United Kingdom and Continental Europe.

Another way to spread the load exerted on the roadway when 30 carrying a heavy load is to use an extendible trailer in its lengthened conf Duration. This is done even when carrying a short but heavy load, for example a 6.1 m (20 cot) ISO 3733a2 :2 c=-. Her 2002

i Container having a 40 tonne weight.

While a tractor-trailer unit may have _decuate manoeuvrability on a motorway, or other main highway, 5 problems arise when a driver has to steer the tractor-crailer unit around tight corners, or otherwise manoeuvre in a confined space. First, the turning circle of the tractor-

trailer will be greater with increasing length. Second, the trailer will tend to pivot about on one axle and set of 10 wheels, with wheels on other axles scraping sideways on the road surface. Such wear on Lyres is referred to as "tyre scrub". On a three axle "'railer, Lyre scrub can reduce Lyre life by a factor of three. A full size trailer may have 12 Lyres, each of which costs in the United Kingdom between ú200 15 and E300. A commercial hau'ier covering typical mileage may have to replace these Lyres after one year's usage. The problem of Lyre scrub may Therefore result in an additional operating cost to the haulier of between ú1600 and:400 per trailer per year.

One solution to the turning circle problem is to use an articulated trailer, but such trailers have a poorer stability, particularly in high winds, than non-arculated trailers. Furthermore, some long loads may not be capable of 25 being carried using an articulated trailer. Although tyre scrub will be reduced, the problem will not in genera' be eliminated. Another solution is to use what are known in the inc._stry as "positive steer" trailers. Positive steer trailers have a tractor linkage mechanism that engages with he tractor fifth-wheel. As the angle between the trailer and tractor *'33a2 : -:e._e- 2002

- 3 unit changes, the linkage mechanism turns at least one axle in the same direction as the turn of the tractor's front wheels. If the trailer has multiple axles, all may be linked to turn positively. However, it is more common for just one 5 axle to be turned and for the driver to raise temporarily the other axles, for example by means of an air suspension system. Examples of commercially available positive steer trailers 10 are those manufactured by Tridec B.V. of Son, Holland (see http://www.tridec. nl), and those manufactured by Muldoon Transport Systems Ltd of Dungannon, United Kingdom (see http://www.muldoon._om and patent document WO98/21082). Such trailers use a conventional downward extending king pin to 15 make a connection with the tractor fifth-wheel. The king pin is supported in the centre of a circular turntable, which is rotatable about an axis extending along the length of the king pin. The turntable has a captive engagement feature that locates with a tapered entrance channel in the fifth-wheel 20 for guiding the king pin to the clasp mechanism within the fifth-wheel. The turntable is itself supported around its periphery by a circular ring or track. Bearings are provided in the supporting ring in order to provide smooth movement of the turntable and to transfer the weight of the trailer down 25 to the fifth-wheel mechanism and the tractor unit.

In such prior art positive steer systems, an engagement

feature locates and engages with the entrance channel to the fifth-wheel so that when the angle of the tractor unit 30 changes with respect to that of the trailer, the engagement feature causes the turntable to rotate. A mechanical or hydraulic linkage then transfers this rotational polio. to a 3 33a2 : 2 He -e--e - 2002

- 4 rear axle steering mechanism, so that when the tractor turns in one direction, one or more of the tractor axles are turned cooperatively to reduce the tractor-trailer turning circle and to reduce or eliminate Lyre scrub.

While such known positive steer systems provide a solution to the problems of excessive wheel scrub and large turning circle, such systems have not been universally adopted by trailer manufacturers or customers. Prior art sys ems add a

10 considerable amount of weight to the trailer itself, which will correspondingly reduce the net weight which may be carried by the trailer according to national laws. For example, one prior art positive steer mechanism adds in total

800 kg to the weight of the trailer. In addition, prior art

15 systems add significantly to the purchase cost of a trailer, and may need additional servicing to keep the ifth-wheel linkage mechanism fully operational.

It is an objec of the present invention to provide a more 20 convenient tractor linkage mechanism for a positive steer trailer. Accordingly, the invention provides linkage mechanism for linking a post ve steer trailer with a fifth-;;neel of a 25 tractor unit, cvmcrising at least one trailer chassis member, a downwardly extending king pin for engagement w th said fifth-wheel, a steering actuator for turning steerable trailer wheels, and an engagement feature for engaging with a fifth-wheel entrance channel for said king pin,;;:-erein the 30 king pin is st_ -Sally fixed to said trailer chassis member, and the engaged_-- feature is free to rotate abou the static king pin for c -.-,-eying rotary motion from the fi in-wheel to 3733a2 :_ee:--e 2002

- 5 the steering actuator to turn said steerable trailer wheels.

This arrangement provides several potential benefits. First, the forces carried through the king pin can be transferred 5 directly to chassis section frame members, without for example being transferred through any intervening bearings or other movable parts. The king pin may be statically fixed to a transverse chassis member, for example by being bolted or otherwise connected directly to a plate that extends fully 10 between a pair of a longitudinally extending load-bearing frame members. In contrast, the movable parts of the linkage mechanism bear no weight from the trailer or its load, and only need to transmit the forces needed to activate the steering actuator to turn the steerable wheels.

This allows a considerable reduction in mechanical complexity, weight and manufacturing cost as compared with prior art steering linkage mechanisms that require the king

pin to be mounted on a turntable.

The potential reduction in weight also allows a corresponding increase in net load which may be carried by the trailer.

The reduction in mechanical complexity makes i. easier to 25 retro-fit a non-steerable trailer.

When the chassis member to which the king pin is s atically affixed consists of or comprises a plate, this place may have an aperture in which the engagement feature is Free to move 30 as the engagement feature rotates about the king pen. In a preferred embodiment of the invention, the aper re in the plate is an annu an aperture extending over an an_ of up to 3733a2 :-. e:^e- 002

- 6 180 . Also in a preferred embodiment, the steering actuator is connected to the engagement feature at an arm which moves 5 under the action of the engagement feature when the engagement feature rotates about the king pin.

Because the plate may be used as a rub plate on which the front section of the trailer sides when being connected and 10 disconnected with a tractor unit, it is preferred if the arm is pivotably connected to a chassis member above the plate.

This chassis member may, for example, be a transverse beam or transverse load bearing frame member. The plate may then extend at a lower level than the arm.

Such a chassis member may, in any event, be required for structural purposes, for example serving as transverse bracing for longitudinal frame members. This support for the arm may therefore not introduce any additional weight to the 20 structure of the trailer.

In a preferred embodiment of the invention, the arm is pivotally connected to at least one chassis member, and pivots under the action of the engagement feature when the 25 engagement feature rotates about the king pin.

The arm may have an elongate slot in which the engagement feature moves when the engagement feature rotates about the king pin. Such a slot can be useful in defining the location 30 of the engagement feature with respect to the rest of the steering linkage mechanism.

3733a2 :2:ecer._e'.002

- 7 It will normally be the case that the king pin lies on a longitudinal centre line of the trailer. The engagement feature may then be midway along the length of the slot when the engagement feature also lies on a longitudinal centre 5 line of the trailer.

The elongate slot may extend in a horizontal plane. The engagement feature then extends downwardly from the slot along an axis parallel to an axis of the king pin.

One way in which the slot may help to retain the engagement feature within the slot is if the slot has a capture feature.

For example, the engagement feature has a flange, and the capture feature is a rebate that extends along the length of 15 the slot and which engages with the flange to help retain the engagement feature within the slot.

The steering actuator may either comprise a direct mechanical linkage, such as at least one elongate component, for example 20 a push/pull rod, for transferring the relative rotational motion of the rifth-wheel longitudinally along the length of the trailer. Alternatively, the steering actuator may include an indirect mechanical linkage such as pair of hydraulic actuators linked by a hydraulic line.

Also according to the inven ion, there is provided a positive steer trailer, comprising a downwardly extending king pin for engagement with a fifth-wheel of a tractor unit, steerable trailer wheels, a steering actuator for turning said 30 steerable tra- en wheels, and an engagement feature for engaging with a fifth-wheel entrance channel for said king pin, wherein t:e king pin is statically fixed to at least one 333a2 :,:ec, ,_,er 200

- 8 trailer chassis member, and the engagement feature is free to rotate about the static king pin for conveying rotary motion from the fifthwheel to the steering actuator to turn said steerable trailer wheels.

The positive steer trailer may be an extendible trailer comprising a forwards chassis section that has the king pin and engagement feature, and a rearwards bogie section that has the steerable wheels. The sections are then relatively 10 movable between extended and retracted positions at which positions the chassis and bogie sections may be secured into engagement with each other. The steering actuator accommodates the relative movement of the chassis section and bogie section so that rotary motion from the fifth-wheel is 15 conveyed to the steering actuator to turn the steerable trailer wheels when the trailer sections are engaged at extended and retracted positions.

If the steering actuator is an all-mechanical actuator formed 20 of a plurality of rigid elongate components for transferring rotational motion for the fifth-wheel longitudinally along the length of the trailer, the trailer additionally comprises means by which the elongate components may be selectively engaged and disengaged when the trailer is secured in 25 extended and retracted positions in order to accommodate the relative movement of the chassis section and bogie section as these sections are moved between extended and retracted positions. 30 If, on the other hand, the steering actuator includes a hydraulic linkage, the linkage may comprise a first hydraulic actuator in the chassis section linked to the engagement 33a2 : J ece.. me - 2002

feature, a second hydraulic actuator in the bogie section linked to the steerable wheels, and a hydraulic line between these two hydraulic actuators for transmitting hydraulic energy between the actuators. The hydraulic line can then be 5 arranged to accommodate the relative movement of the chassis section and bogie section as these sections are moved between extended and retracted positions.

The invention further provides a tractor-trailer unit, 10 comprising a tractor unit having steerable front wheels and a fifth-wheel coupling and a positive steer trailer having: a downwardly extending king pin, said king pin being engaged by the fifth-wheel to link the trailer to the tractor unit; steerable trailer wheels; a steering actuator for turning 15 said steerable trailer wheels) and an engagement feature that is engaged with a fifth-wheel entrance channel for said king pin, wherein the king pin is statically fixed to at least one trailer chassis member, and the engagement feature is free to rotate about the static king pin to convey rotary motion from 20 the fifth-wheel to the steering actuator to turn said steerable trailer wheels in cooperation with said steerable front wheels.

The invention will now be described in more detail, by way of 25 example only and with reference to the accompanying drawings, in which: Figure 1 is a plan view of a tractor-traier unit, comprising a tractor unit having steerable front wheels 30 and a fifth-wheel coupling and an extendible positive steer trai er according to the invention, showing the trailer in a retracted configuration and tee tractor 33a2 :::ece-.-e- 2002

- 10 unit turning right with a rearmost pair of s eerable trailer wheels turning cooperatively also to the right; Figure 2 is a plan view of the positive steer trailer of 5 Figure 1, shown with a fifth-wheel engagement feature and the steerable rear trailer wheels in a sraight ahead orientation; Figure 3 is a cross-sectional side view of the positive 10 steer trailer, taken along lines III-III of Figure 2; Figure 4 is a cross-sectional side view of the positive steer trailer, taken along lines IV-IV of Figure 2 15 Figure 5 is a simplified plan view of the post. he steer trailer s milar to that of Figure 1, but with the trailer in an extended configuration, show- with a fifth-wheel engagement feature and the steerable rear trailer wheels in a left turn orientation; Figure 5A is an enlarged fragmentary plan vies of a portion of Figure 5, showing a fifth-wheel coup ing and engagement mechanism and in the steering ac ator a first pivoting arm to which is pivotably confected a 25 forwardmost push/pull rod; Figure 5B is an enlarged fragmentary plan --ew of a portion of -igure 5, showing a converter member that downwardly converts the rotational motion c- he fifth 30 wheel for turning the steerable trailer wheels at a reduced angle; 3733a2 ::-.:errbe! 2002

Figure 5C is an enlarged fragmentary plan view of a portion of Figure 5, showing two disengaged first couplings on left and right sides of a forwards chassis section, which when the trailer is in a r_.racted 5 configuration may be engaged and disengaged with matching second couplings in a rearwards bogie section to selectively engage and disengage push/pull rods in the two sections; 10 Figure 5D is an enlarged fragmentary plan view of a portion of Figure 5, showing two engaged pairs of couplings on opposite left and right sides of the trailer, each formed from a third coupling in the chassis section and the second coupling in the bogie 15 section, which serve to turn the rear steerable wheels in response to rotational movement of the:-wheel and engagement feature when the trailer -s in an extended configuration; 20 Figure 6 is a side view of the trailer of Figure 5, with the steering actuator shown in phantom outline; Figure 7 is a perspective fragmentary view rm above and to one side of the fifth-wheel coup_-ng and 25 engagement mechanism and first pivoting arm similar to that of Figure 5A, but shown in the str--_h - ahead orientation; Figures 8, 9 and 10 are, respectively, perspec -ve, plan 30 and side views of the first pivoting arm of F-_-e 7; Figure 11 s a cross-sectional view t.rcgh the 333a2 :: We e-.r* 2002

- 12 fifth-wheel coupling and engagement mechanism and first pivoting arm of Figure 7, taken in the direction of line XI-XI of r igure 9; 5 Figure 12 is a perspective fragmentary view from above and to one side of the right hand third coupling and second coupling of Figure 5D, shown engaged when the trailer is in the extended configuration) 10 Figure 13 is a fragmentary side view of the right hand first coupling of Figure 5C, when engaged with the right hand third coupling of Figure 5D when the trailer is in the retracted configuration; 15 Figure 1: and 15 are fragmentary transverse cross sectional views of the paired right hand first and second couplings, taken along line A-A of Figure 13, shown respectively disengaged and engaged) 20 Figure 16 is a fragmentary perspective view from below and to one side of the paired right hand first and second couplings of Figure 13; and Figure 17 is a fragmentary perspective view from above 25 and to one side of a push/pull steering linkage to the steerable set of rear trailer wheels.

Figure 1 is a plan view of a tractor-trailer unit 1 according to the inver ion, comprising a tractor unit 2 having 30 steerable frog wheels 4 and an extendible positive steer trailer 6. The trailer 6 has a forwards chassis section and a rearwards belie section 9. The chassis section q has in a 3 3 3a2 : 2 Feces. e' ^002

- 13 frontmost portion a downwardly extending king pin 10 by which the trailer 6 may be engaged and disengaged with a fifth-

wheel mechanism 11 in a central rearmost portion of the tractor unit 2 above traction wheels 3. Figure 1 shows the 5 tractor-trailer unit 1 turning right with a rearmost pair of steerable trailer wheels 12 turning cooperatively also to the right. The trailer also has two forwards sets of non-

steerable wheels 13, which may be lifted by a conventional air suspension system 35 when not in use. The steerable 10 wheels 12 have a conventional non-lifting air suspension system 17. Each trailer wheel 12,13 is covered by a semicircular plastic guard 27 to reduce wheel spray in wet conditions. 15 The illustrated trailer 6 is a skeletal trailer with a number of ISO standard twist-lock container mounts 5 for carrying ISO Containers with lengths of 6.1 m (20 feet), 9.1 m (30 feet), 12.2 m (40 feet) and 13.7 m (45 feet).

20 Referring now also to Figures 2 to 4, the trailer 6 is an extendible trailer, with the chassis section 8 being slideably connected to the bogie section 9. Each section has a pair of longitudinal load-bearing frame members 22,122;23,123 the, slide relative to one another when the 25 trailer 6 is extended or retracted. Figures 1 to 4 show the trailer 6 secured in a retracted configuration, by means of a known fifth-whee-type pin and clasp mechanism of the type described in patent document GB 2,298, 399 A, the contents of which are hereby incorporated by reference. As llustrated, 30 an upwardly extending pin 14 in the bogie section 9 is captured by a first rearwardly facing clasp 15 in the chassis section 8. When -he trailer is to be extended, t.e first 3733a2 :?:e.-.=er 00-

clasp 15 disengages with the pin 14 thus allowing the tractor unit 2 to pull the chassis section 8 forwards, until a second forwards facing clasp 16 engages with the pin 14, as shown in Figure 6. Although not illustrated, the trailer 6 includes 5 sensors and actuators in the clasp mechanisms 15,16 that cooperate with a brake circuit to permit automatic extension and retraction of the trailer, as described more fully in patent document WO 99/05002, the contents of which are hereby incorporated by reference.

Reference is now made also to Figure 5, 5A-D and 6, in which for clarity container mounts 5 have been omitted, as have spray guards 27 above the non-steerable trailer wheels 13.

The extendible trailer 6 has a positive steer mechanism that 15 is driven by a fifth-wheel engagement feature 18 which extends downwardly in a direction parallel with the king pin 10. The king pin lies on a longitudinal central axis 80 of the trailer 6. When the trailer steerable wheels 12 are in the straight-ahead orientation, the engagement feature 18 20 also lies on the longitudinal central axis 80.

As shown most clearly in Figure 7, the king pin 10 is affixed to a plate 19, which extends transversely between the pair of chassis section longitudinal frame members 22,122, by means 25 of a circular flange 20 and a ring of bolts 21. This is a conventional arrangement for trailers having no wheel steering. The King pin 10 is therefore neither free to move nor rotate.

30 With regard now also to Figures 8-11, the engagement feature 18 extends dowr.vards through an annular aperture 26 in the transverse plate 19. The aperture 26 extends over an arc of 33a2 :::e Abe-:2002

- 15 180 which is cen ered on the king pin 10 and bisected by the longitudinal axis. As viewed in a forwards facing direction, the aperture 26 has left and right portions 26',26" each of which curves outwards and forwards to subtend an angle of 5 90 .

As shown in Figure 11, the aperture 26 has clearance for a circular crosssection middle portion 28 of the engagement feature 18, so that the engagement feature 18 may slide 10 freely in the aperture 26. Only a forwards wedge-shaped lower portion 29 of the engagement feature 18 extends below the transverse plate 19 to the level of the fifth-wheel 11.

A trailer 6 will be connected to a tractor unit 2 only when 15 the steerable wheels 12 are in the straight-ahead orientation, and so when the king pin 10 slots into an entrance channel 30 of the fifth-wheel 11, the wedge-shaped lower portion 29 of the engagement feature 18 slots in the channel 30 behind the king pin 10.

The wedge-shaped portion 29 is shaped so that there will normally be some clearance with right or left side walls 31,32 of the entrance channel 30. When the tractor 2 begins to turn left or right, the wedge-shaped portion 29 will come 25 into positive contact with the right or left side walls 31,32, causing the engagement feature 18 to move along the left or right por ions 26', 26" of the annular aperture 26.

The engagement -ature 18 is connected to the rest of the 30 steering actuator at a first pivot arm 34 by means of a straight slot 36 -n the arm 34 into which the middle portion 28 of the encage..ent feature 18 passes. This middle portion 3733a2 :.':e^e-.-e- 2002

- 16 28 is bounded on a lower side by a first retention feature in the form of a circular flange 38 that contacts s lower surface 39 of the transverse plate 19 around the edges of the annular aperture 26. The middle portion 28 is bounded on an 5 upper side by a second retention feature in the form of a circular head 40 that is seated in a matching rebate 41 that extends fully around the periphery of the annular aperture 26. 10 The first pivot arm 34 is pivotably mounted midway along the length of the arm 34 at a central pivot 42 to the underside of a transverse chassis member 44 that extends fully between the longitudinal frame members 22,122. The first pivo arm 34 is therefore between the transverse chassis member 44 and the 15 transverse plate 19. The pivot 42 lies on the lane tudinal axis 80 and includes a pin 43 that extends downwardly through a central circular aperture 45 in the transverse chassis member 44. A square cap 46 extends around the pin 4_ and is welded to the transverse member 44 to secure the pin 43 to 20 the member 44. The pin extends inside a low friction nylon bushing 46 inside a cup 47 that is welded to an upper surface 48 of the first pivot arm 34. A lower surface of the first pivot arm 34 is covered across its full extent by a low friction nylon skin 49. Apart from the annular aver Are 26, 25 the plate 19 extends fully underneath the first pivot arm 34.

Together, the nylon bushing 46 and skin 49 allow ^e first pivot arm 34 to pivot smoothly on the pin 43 ant an upper surface 50 of the transverse plate 19.

30 As explained above, relative rotational movemen of the fifth-wheel 11 and the trailer 6 causes the ca ses the engagement feature 18 to move along left or rich port-one :, 33a2 :-:er:=e.002

- 17 26',26" of the annular aperture 26 and the in doing so, the engagement feature 18 is also caused to slide along left or right portions 36', 36" of the elongate slot 36 of the first pivot arm 34, causing the first pivot arm 34 to pivot about 5 the pin 43.

A first rearwardly extending linking push/pull rod 51 is connected via a ball mount 61 above the left portion 36' of the elongate slot 36, so that when the first pivot arm 34 is 10 moved by the engagement feature 18, the first linking push/pull rod 51 is pushed backwards or pulled forwards.

The first linking push/pull rod 51 is connected to a second pivot arm 71 at a ball joint 62 at a right hand end 71" of 15 the second pivot arm 71. The second pivot arm 71 is connected to a second transverse chassis member 74 at a pivot joint 72 in a similar manner to that described above for the first pivot arm 34. Because the first linking push/pull rod 51 is connected to the first pivot arm 34 at a point with lower 20 radius than the connection to the second pivot arm 71, the second pivot arm 71 moves through a small arc than the first pivot arm 34.

A pair of similar rearwardly extending push/pull rods 53,153 25 are connected to right and left portions 71", 71' of the second pivot arm 71 at ball joints 63,163 which are radially inside the ball joint 62 on the right portion 71" co which the first linking rod push/pull 51 is connected. Therefore, the movement of the pair of push/pull rods 53,153 is further 30 reduced as compared with the movement of the first p vat arm 34. The second pivot arm 71 and associated ball joints 62,63,163 therefore act as a converter member that downwardly 33a2 :e:e:.-_e- 2002

- 18 converts the rotational motion of the fifth-wheel 11 for turning the steerable trailer wheels 12 at a reduced angle a.

The result is that when the engagement feature 18 is turned through 90 , the rear trailer wheels 12 are turned through an 5 angle = 28 .

Each of the pair of push/pull rods 53,153 extends rearwardly along opposite sides of the trailer longitudinal axis 80 to similar first couplings 91,191 to which the push/pull rods 10 53,153 are connected by similar ball joints 64,164. Because the components in the steering actuator rearwards of the second pivot arm 71 are duplicated on opposite sides of the trailer longitudinal axis 80, with one side pushing whilst the other side pulls, only components on the right side will 15 be further described in detail. However, components on the left side which correspond with those on the right side will be denoted in the drawings with reference numerals incremented by 100.

20 The first coupling 91 is pivotably mounted at a pivot 65 which has a vertical axis to the longitudinal frame member 22 via a bracket 92 that extends laterally inwards of the longitudinal frame member 22. The first coupling 91 has a vertically oriented cylinder 93 having open upper andlower 25 ends 94,95. The cylinder 93 pivots about the bracket pivot 65 under the push/pu2l action of the push/pull rod 53.

When the trailer 6 is in the retracted configuration, then as shown in Figures 13-16, the first coupling 91 in the chassis 30 section 8 is oopcsite and directly above a second coupling 81 in the bogie section 9. The second coupling 81 is pivotably mounted at a pivot 66 having a vertical axis to the bogie 3733a2 : e-e31te. 2002

r section longitudinal frame member 23 via a bracket 82 that extends laterally inwards of the longitudinal frame member 23. The second coupling 81 has a vertically oriented piston 83 driven by an air-driven pneumatic actuator 84.

Both of the first pair of couplings 81,91 are therefore laterally inside and adjacent to respective longitudinal frame members 23,22.

10 Although not shown in the drawings for clarity each such actuator 84 is connected via control valves to the same trailer air supply used in the suspension and braking systems. The couplings 15,16 are similarly activated via control valves and air supply lines. The air valves and 15 brakes are all controlled centrally by a trailer control system (not illustrated) which receives signals from activation sensors at each clasp and coupling to activate trailer brakes and clasp and coupling control valves in order to sequence and control the extension and retraction of the 20 trailer 6.

The piston 83 has a chamfered upper tip 85, and the cylinder lower end 95 has an outwardly tapered opening 96 to aid insertion of the piston 83 into the cylinder 93 in the event 25 that these are not perfectly aligned. In addition, the first coupling 91 has a capture feature centered on the c-vot 65 in the form of an annular arc-shaped groove 97 in a lower surface 98 of the first coupling 91 the: extends symmetrically either side of the tapered cylinder cgening 96.

30 This groove is shown in phantom outline in Fig C. In the event that the p stow 83 is misaligned with the cylinder 93, the piston will --serf upwardly in the groove 97 and then be 3 33a2 :- Ice.. Her 2002

- 20 captured by the cylinder 93 as soon as the cylinder 93 comes into alignment with the piston 83.

When, as shown in Figure 15, the piston 83 is engaged within 5 the cylinder 93, the piston 83 pivots about the bracket pivot 66 under the push/pull action of the push/pull rod 53.

As shown in Figure 17, another rearmost push/pull rod 54 extends rearwardly from the second coupling 81 at a ball 10 joint 67 towards a third pivot arm 75 at which the rearmost push/pull rod 54 is connected by a ball joint 68. When the rearmost push/pull rod 54 is moved forwards and backwards via the engaged first and second couplings 91,81, the third pivot arm 75 rotates a turntable 76 to which the steerable rear 15 wheels 12 are mounted, thereby turning the rear wheels 12.

The first and second couplings 91,91 are automatically disengaged by the trailer control system at the same time as the pin 14 is disengaged from the rearwards facing clasp 15.

20 The driver then pulls the tractor unit 2 forwards to extend the trailer 6, and when the pin 14 enters and is automatically engaged with the forwards facing clasp 16, the second coupling 81 in the bogie section has travelled rearwards to come into opposite vertical alignment with a 25 third coupling 91'. The third coupling 91' is of similar arrangement and construction to the first coupling 9:, and is therefore denoted in the drawings with the same reference numerals primed.

30 The third coupling 91' engages with the second coopt ng 81 in the same manner as described above in relation to he first coupling 91, and so will not be described again in c_ ail.

333a2 2 -ce.-.=e- 3002

As shown in Figures 1 and 5, a rearmost push/pull rod 55 of the chassis section extends between the first and third couplings 91,91', at which points this push/pull road is 5 connected to the couplings 91,91' by corresponding ball joints 70,69. When the first coupling 91 is pivotably moved as described above, this then causes a corresponding pivoting movement in the third coupling 91', which is then transferred to the second coupling 81 and thence to the third pivot arm 10 75 to turn the steerable trailer wheels 12 as described above. When the trailer 6 is to be retracted, the process of disengaging the forwards clasp 16 and pin 14 is simultaneous 15 with the disengagement of the third and second couplings 91', 81, whereupon the trailer 6 can be moved to the retracted position. In response to the rearwards facing clasp 15 engaging with pin 14, the second coupling 81 is made by the trailer control system to engage with the first coupling 91.

It should be noted that although the illustrated embodiment shows the elongate slot 36 in the first arm 34 to be straight. It may alternatively be possible to use a curved elongate slot, for example if the engagement feature 18 is 25 free to move somewhat in the longitudinal direction along the length of the entrance channel 30 to the ffth-wheel mechanism 11. Th-s could be useful to introduce a non-linear relationship between the rotation of the engagemer feature 18 and the turning of the steerable trailer wheels i2.

Although the nvention has been described above in terms of a skeletal trailer for carrying containerized leads, the 3 7 3 3 a 2 Cecebe r 2 O O '

- 22 invention is applicable to all other types of trailer, for example, flatbed trailers, curtain-sided trailers, and trailer with fold down or removable side panels.

5 The extendible positive steer trailer described above provides useful benefits, in terms of reduced Lyre scrub, and reduced turning circle, and also maintains the benefits of an extendible trailer. The positive steer mechanism is mechanically independent of the king pin, and as a result is 10 mechanically simpler, cheaper and lighted to manufacture than a positive steer trailer which uses a pivoting turntable or other pivoting mechanism centered and supported on or around the king pin.

3733a2 :0:-^e.-.-e- 2002

Claims

- 23 Claims:

1. A linkage mechanism for linking a positive steer trailer with a fifthwheel of a tractor unit, comprising at least one 5 trailer chassis member, a downwardly extending king pin for engagement with said fifth-wheel, a steering actuator for turning steerable trailer wheels, and an engagement feature for engaging with a fifth-wheel entrance channel for said king pin, wherein the king pin is statically fixed to said 10 trailer chassis member, and the engagement feature is free to rotate about the static king pin for conveying rotary motion from the fifth-wheel to the steering actuator to turn said steerable trailer wheels.

15 2. A linkage mechanism as claimed in Claim 1, in which the king pin is statically fixed to a transverse chassis member.

3. A linkage mechanism as claimed in Claim 2, in which said transverse chassis member consists of or comprises a plate, 20 said plate having an aperture in which the engagement feature is free to move as the engagement feature rotates about the king pin.

4. A linkage mechanism as claimed in Claim 3, in which the 25 aperture in the plate is an annular aperture extending over an arc of up to 180 .

5. A linkage mechanism as claimed in any preceding claim, in which the steering actuator is connected to the engagement 30 feature at an arm which moves under the action of the engagement feature when the engagement feature rotates about the king pin.

3733a2 10 December 2002

- 24 6. A linkage mechanism as claimed in Claim 5, when appendant from Claim 3 or Claim 4, in which the plate extends underneath the arm.

5 7. A linkage mechanism as claimed in Claim 6, in which the arm is pivotably connected to a chassis member above the plate. 8. A linkage mechanism as claimed in any of Claims 5 to 7, 10 in which the arm is pivotably connected to at least one chassis member, and pivots under the action of the engagement feature when the engagement feature rotates about the king pin. 15 9. A linkage mechanism as claimed in Claim 7 or Claim 8, in which the arm has an elongate slot in which the engagement feature moves when the engagement feature rotates about the king pin.

20 10. A linkage mechanism as claimed in Claim 9, in which the king pin lies on a longitudinal centre line of the trailer, the engagement feature being midway along the length of the slot when the engagement feature also lies on a longitudinal centre line of the trailer.

11. A linkage mechanism as claimed in Claim 9 or Claim 10, in which the arm is pivotably connected to a chassis member midway along the length of the arm.

30 12. A linkage mechanism as claimed in any of Claims 9 to 11, in which the elongate slot is straight.

3733a2 10 December 2002

- 25 13. A linkage mechanism as claimed in any of Claims 9 to 11, in which the elongate slot is curved.

14. A linkage mechanism as claimed in any of Claims 9 to 13, 5 in which the slot extends in a horizontal plane, the engagement feature extending downwardly from the slot along an axis parallel to an axis of the king pin.

15. A linkage mechanism as claimed in any of Claims 9 to 14, 10 in which the slot has a capture feature which helps to retain the engagement feature within the slot.

16. A linkage mechanism as claimed in Claim 15, in which the engagement feature has a flange, and the capture feature is a 15 rebate that extends along the length of the slot and which engages with said flange to help retain the engagement feature within the slot.

17. A linkage mechanism as claimed in any of claims 5 to 16, 20 in which the steering actuator includes at least one push/pull rod for translating movement of the arm to steerable wheels.

18. A positive steer trailer, comprising a downwardly 25 extending king pin for engagement with a fifth-wheel of a tractor unit, steerable trailer wheels, a steering actuator for turning said steerable trailer wheels, and an engagement feature for engaging with a fifth-wheel entrance channel for said king pin, wherein the king pin is statically fixed to at 30 least one trailer chassis member, and the engagement feature is free to rotate about the static king pin for conveying rotary motion from the fifth-wheel to the steering actuator 37 33a2 10 December 2002

to turn said steerable trailer wheels.

19. A positive steer trailer as claimed in Claim 18, in which the trailer is an extendible trailer comprising a 5 forwards chassis section, said forwards section having the king pin and engagement feature, and a rearwards bogie section, said rearwards section having the steerable wheels, said sections being relatively movable between extended and retracted positions at which positions said sections may be 10 secured into engagement with each other, wherein the steering actuator accommodates said relative movement of the chassis section and bogie section so that rotary motion from the fifth-wheel is conveyed to the steering actuator to turn said steerable trailer wheels when said trailer sections are 15 engaged at extended and retracted positions.

20. A positive steer trailer as claimed in Claim 19, in which the steering actuator is an all-mechanical actuator formed of a plurality of rigid elongate components for 20 transferring said motion longitudinally along the length of the trailer, the trailer additionally comprising means by which said components may be selectively engaged and disengaged when the trailer is secured in said extended and retracted positions in order to accommodate said relative 25 movement of the chassis section and bogie section.

21. A positive steer trailer as claimed in Claim 19, in which the steering actuator includes a hydraulic linkage, said linkage comprising a first hydraulic actuator in the 30 chassis section linked to the engagement feature, a second hydraulic actuator in the bogie section linked to the steerable wheels, and a hydraulic line between said first and 37 33a2 10 December 2002

- 27 second hydraulic actuators for transmitting hydraulic energy between said actuators, wherein said hydraulic line accommodates said relative movement of the chassis section and bogie section.

22. A tractor-trailer unit, comprising a tractor unit having steerable front wheels and a fifth-wheel coupling and a positive steer trailer having: a downwardly extending king pin, said king pin being engaged by the fifth-wheel to link 10 the trailer to the tractor unit; steerable trailer wheels; a steering actuator for turning said steerable trailer wheels; and an engagement feature that is engaged with a fifth-wheel entrance channel for said king pin, wherein the king pin is statically fixed to at least one trailer chassis member, and 15 the engagement feature is free to rotate about the static king pin to convey rotary motion from the fifth-wheel to the steering actuator to turn said steerable trailer wheels in cooperation with said steerable front wheels.

20 23. A linkage mechanism for linking a positive steer trailer with a fifth-wheel of a tractor unit, substantially as herein described, with reference to or as shown in the accompanying drawings. 25 24. A positive steer trailer with a linkage mechanism for linking the trailer with a fifth-wheel of a tractor unit, substantially as herein described, with reference to or as shown in the accompanying drawings.

30 25. A tractor-trailer unit, comprising a tractor unit and a positive steer trailer with a linkage mechanism for linking the trailer with a fifth-wheel of a tractor unit, 3733a2 10 December 2002

- 28 substantially as herein described, with reference to or as shown in the accompanying drawings.

3733a2 10 December 2002