Improved trailer coupling

Abstract

A coupling system (1B) for coupling a towed vehicle to a towing vehicle comprising a pillar (33); a sleeve portion (18) adapted to engage with and disengage from the pillar; a locking plate (2) moving between first and second locking plate positions, wherein in the first locking plate position the locking plate is engaged with the pillar preventing detachment of the sleeve portion , and wherein in the second locking plate position the locking plate is disengaged from the pillar and enables detachment of the sleeve portion ; a pin (4) such that in a first pin position the locking plate is enabled to move to the first locking plate position and in a second pin position the locking plate is restrained in the second locking plate position; and a control shaft (15) for moving the locking plate from the first locking plate position to the second locking plate position. ABSTRACTABSTRACTABSTRACTABSTRACT

Description

PRIORITY CLAIM

[0001] The present application claims priority from Australian provisional Application No. 2025904554, filed on 1 October 2025. The contents of the priority application are hereby incorporated herein by reference. TECHNICAL FIELD

[0002] The present invention relates generally to a coupling device and more particularly relates to couplings or hitches for linking a first vehicle to a second vehicle, such as a trailer, for the purposes of towing the second vehicle over uneven ground where a wide range of articulation between the first vehicle and the second vehicle is required. BACKGROUND

[0003] The commonest form of trailer coupling connects to a conventional towball. Ball-couplings have a cup that is retained on the tow-ball by a tongue engaging the underside of the head of the tow-ball. The tongue is held in the engaged position by a powerful spring. Considerable force is required to retract the tongue sufficiently for the cup to be able to disengage from the tow-ball. The cup is also prone to hanging onto the ball if there is a residual tension or compression between the trailer and the towing vehicle.

[0004] Tow-balls per se only offer a limited range of articulation because the cup runs into the neck of the tow-ball. Additional axes of articulation can be added between the cup and the trailer’s draw-bar. However, such additional axes make it even more difficult to disengage the cup from the tow-ball. One manufacturer produced a coupling where the additional axes of articulation could be temporarily suspended to make it easier to disengage the cup, but this option proved impractical and the product was withdrawn.

[0005] Tow-ball based couplings become noisier as they wear and may fail to securely lock on as a consequence of the wear.

[0006] Pintle ring and hook is another method of coupling. A ring attached to the towed vehicle is fitted over a hook on the towing vehicle. The hook has a latch to retain the ring on it. The large clearances between ring and hook results in high noise levels and impact vibration when changing between accelerating and braking. It is used in the trucking industry and by the military but is generally not acceptable to people towing caravans, horse floats or light trailers.

[0007] There are also a number of different coupling systems that have in common connecting by the manual insertion of a hitching-pin. Difficulties manoeuvring a trailer to obtain accurate alignment for hitching-pin insertion are multiplied if the trailer is too heavy to be manhandled into position, if the trailer has dual axles and also if the wheels are on uneven ground or in sand.

[0008] Some hitching-pin mechanisms incorporate a means to help alignment of the two sides to aid hitching-pin insertion but none of these embodiments can overcome the problem of it being difficult to remove the hitching-pin to uncouple if there is a residual load between the trailer and the towing-vehicle.

[0009] None of the above listed coupling options offer adequate sealing against the ingress of contaminants that can impair proper function or lead to excess wear.

[0010] Then there are couplings which connect to a variety of pillars that have very specific profiles that are dictated in large part by the chosen means of locking onto the pillar.

[0011] The diameter and profile of the head of the pillar influences how easy or difficult it is to get the coupling (female component) to engage on the pillar (male component).

[0012] Secure connection of a trailer to a towing vehicle by any of the coupling means listed so far requires human intervention beyond merely presenting the female component to the male component and lowering of the jockey wheel.

[0013] Some of these non-automatic locking mechanisms do not incorporate an automatic secondary locking mechanism that keeps the coupling securely connected in the event of a mechanical (a spring as an example) failure in the primary locking mechanism.

[0014] It is self-evident that a coupling needs to be in an unlocked state in order for the female component to fully engage on the male component.

[0015] The non-automatic locking mechanisms to a pillar fall into two categories: The first category holds a default unlocked state every time it is uncoupled and requires the operator to remember to manually trigger the locking mechanism after full engagement on the pillar. The second category retains a locked state unless manually held in an unlocked state. This second category has to be manually held open during engagement.

[0016] Both categories are associated with failures to establish a secure connection as a consequence of a human error; not triggering the locking with the former and not opening the locking mechanism with the latter.

[0017] The second category has the advantage of relocking itself if an “inquisitive” person opens the locking mechanism during the owner’s absence. In other words, couplings that require the user to trigger the locking mechanism carry the additional risk of an “inquisitive” person opening the locking mechanism and rendering it unsafe to tow until the owner recognizes the interference and relocks the mechanism. Few owners routinely check their coupling’s status after stopping for a break.

[0018] The safest option would seem to be a fully automatic locking mechanism. Fully automatic locking is defined as one where the mechanism incorporates both a default held-unlocked status whenever it is not engaged with a pillar or dummy pillar plus a means to trigger locking whenever it fully engages on a pillar or dummy pillar.

[0019] The fully automatic option reduces the extent of human intervention required to achieve secure connection to a pillar. However current fully automatic couplings do not exclude the possibility of the user towing with the coupling in a locked state but not fully engaged. Below is the explanation of how this dangerous situation can arise.

[0020] Pillars typically have a circumferential groove in which a locking element, typically a plate or ball bearing(s), engage to ensure secure connection. The groove is typically located toward the top of the pillar which is more accessible for regulating the engagement or release of the locking element.

[0021] If the coupling is presented to the pillar in an already locked state it will be unable to fully engulf the pillar but it may appear to have fully descended especially when viewed from above. The user may then erroneously conclude that the coupling is securely connected because it is both locked and apparently fully engaged.

[0022] When the level of the locking element’s engagement is located high on the pillar the degree of engagement of a locked coupling on the pillar is sufficient for the towing vehicle to tow the trailer until it encounters a road hump that makes it jump off the pillar.

[0023] A fully automatic coupling can be locked when it is assumed to be unlocked either because the hold-open mechanism has developed a fault such as a broken spring or the hold-open mechanism has been prematurely triggered to lock itself e.g. by putting draw-bar-weight scales up into the coupling.

[0024] Because the whole coupling process is usually fully automatic the operator may be lulled into a false sense of security where they fail to recognize that the mechanism is already in the locked state rather than in the expected and required unlocked state.

[0025] There are documented instances of fully automatic couplings disconnecting because of incomplete engagement secondary to the operator erroneously believing the coupling was unlocked when they presented it to the pillar.

[0026] Even with safety chains the consequences of trailer disconnection while towing can be extremely serious and can include causing fatalities.

[0027] Most coupling disconnections while on the move are due to operator errors during coupling. Errors include failing to recognize that a fully automatic coupling is not in the unlocked state when presented to the pillar.

[0028] A well designed fully automatic coupling will have a readily observable event occurring during coupling which culminates in a locked state which is readily visually distinguishable from the unlocked state.

[0029] The coupling described in this patent application belongs to the fully automatic pillar category as defined above. The design eliminates the problem of dangerous disconnection from towing with a coupling which is locked but not fully engaged and secured to its pillar. The design achieves this by making it impossible for the coupling to tow when locked and only partially engaged. DISCLOSURE OF THE INVENTION

[0030] In a first aspect, the present invention comprises a coupling system for coupling a towed vehicle to a towing vehicle comprising: a pillar adapted to be mounted to a tow bar tongue of the towing vehicle; a sleeve portion adapted to be mounted to the towed vehicle and adapted to fit over and engage with the pillar and disengage from the pillar; a locking plate adapted to extend through an aperture in the sleeve portion and configured to move between a first locking plate position and a second locking plate position, such that in the first locking plate position the locking plate is engaged with the pillar to prevent detachment of the sleeve portion from the pillar, and such that in the second locking plate position the locking plate is disengaged from the pillar and enables detachment of the sleeve portion from the pillar; a pin extending through the sleeve portion such that in a first pin position the locking plate is enabled to move to the first locking plate position and in a second pin position the locking plate is restrained in the second locking plate position; and a control shaft extending through the sleeve portion adapted to be operated by a user to move the locking plate from the first locking plate position to the second locking plate position.

[0031] The sleeve portion preferably includes a stepped-bore and a skirt and the pillar has a base portion, such that the pillar fits into the stepped-bore and when the sleeve portion is fully engaged with the pillar, the skirt contacts the base portion of the pillar to support the sleeve portion.

[0032] The pillar preferably has a circumferential groove for receiving and retaining the locking plate in the first locking plate position.

[0033] The locking plate can be adapted to be moved to and kept in the first locking plate position under the influence of locking plate biasing componentry.

[0034] According to an embodiment, when the sleeve portion is fully engaged with the pillar, a first end of the pin contacts the base portion of the pillar such that the pin is moved to the first pin position from the second pin position against resistance of a pin biasing member, enabling the locking plate to move to said first locking plate position.

[0035] Preferably, the locking plate includes an opening through which the control shaft extends.

[0036] The control shaft may include a pinion and the locking plate includes a rack located along an edge to the locking plate opening.

[0037] In an embodiment, the control shaft and pinion are adapted to rotate together and the pinion engages with the rack to move the locking plate between the first locking plate position and the second locking plate position.

[0038] In a further embodiment, the control shaft has a first slot positioned in a first orientation and a second slot positioned in a second orientation, the first slot intersecting with the second slot, said second orientation being orthogonal to said first orientation, the coupling system further comprising a retaining member also orthogonal to said first slot, said retaining member when engaged within the first slot enables movement of the control shaft to a first control shaft position under the action of a control shaft biasing member.

[0039] The coupling system may further comprise a primary locked condition and a secondary locked condition, such that the primary locked condition is when the locking plate is in the first locking plate position and the secondary locked condition is when the control shaft is in the first control shaft position and the retaining member is not aligned with the second slot.

[0040] In a further embodiment, when the sleeve portion fully engages with the pillar, the pinion and control shaft rotate through the engagement of the rack with the pinion so that the locking plate moves to the first locking plate position, and the retaining member moves through the second slot until the retaining member reaches the first slot, whereupon the control shaft moves to the first control shaft position.

[0041] When the control shaft is in the first control shaft position, the retaining member is preferably not aligned with the second slot and the control shaft is unable to rotate.

[0042] In an embodiment, when the control shaft is moved to a second control shaft position, the retaining member is aligned with the second slot and the control shaft is able to rotate, whereby such rotation causes the pinion to engage with the rack and move the locking plate to the second locking plate position in which the locking plate is removed from the circumferential groove in the pillar that enables detachment of the sleeve portion from the pillar.

[0043] Preferably, the sleeve portion includes a housing for receiving the locking plate, the pin, the retaining member and the control shaft.

[0044] Preferably, the locking plate has an aperture, said aperture having a recess, said pin adapted to move through the aperture, said aperture recess adapted to receive a head of the pin, and detachment of the sleeve portion from the pillar enables the pin to move to the second pin position in response to the pin biasing member such that the head of the pin is secured in the recess and the locking plate is retained in the second locking plate position.

[0045] The sleeve portion preferably has first and second pivot bolt apertures for respectively receiving a pivot bolt that each connect to a yoke so as to enable the sleeve portion to pivot with respect to the yoke.

[0046] In an embodiment, the sleeve portion aperture through which the locking plate extends is located below an axis through each of the first and pivot bolt second apertures of the sleeve portion, wherein further the distance from the sleeve portion aperture to a bottom of the sleeve portion is less than the distance from an equator of a head of the pillar to a cylindrical column of the pillar.

[0047] In a further embodiment, the pillar has said head, said cylindrical column, a neck between the head and the cylindrical column and a base portion, wherein when the sleeve portion is fully engaged with the pillar the distance between the neck and a face of the base portion that is in contact with the sleeve portion is greater than the distance between the equator of the head and the axis through each of the first and second pivot bolt apertures of the sleeve portion, so that the sleeve portion disengages from the pillar regardless of any residual load between the towing vehicle and the towed vehicle and regardless of the orientation of the towing vehicle and the towed vehicle to each other.

[0048] In an embodiment, if there is inadvertent unlocking of the fully engaged coupling system by a user moving the control shaft to shift the locking plate to the second locking plate position, the primary locked condition and the secondary locked condition are reset automatically when the user releases control of the control shaft.

[0049] In an embodiment, in order to move the locking plate from the second locking plate position to the first locking plate position: the sleeve portion contacts the pillar base portion forcing the pin to move to the first pin position; the locking plate engages with the circumferential groove in the pillar under the action of locking plate biasing componentry; the control shaft is rotated and raised as a result of movement of the locking plate and action of the control shaft biasing member respectively to a first control shaft position.

[0050] In a further embodiment, in order to move the locking plate from the first locking plate position to the second locking plate position: the control shaft is moved from a first control shaft position to a second control shaft position where the control shaft is free to rotate and that, in turn, retracts the locking plate from the circumferential groove of the pillar; the pin thereafter, when the sleeve portion disengages from the pillar, is moved to the second pin position where a head of the pin resides in a recess in the locking plate to retain the locking plate in the second locking plate position.

[0051] In a second aspect, the present invention comprises a connection arrangement between a towed vehicle and a towing vehicle comprising the coupling system of at least the first aspect and further comprising: a connector connected to the towed vehicle and including an anchor, a yoke connected to the anchor, the yoke also connected to the sleeve portion of the coupling system; a tow bar tongue connected to the towing vehicle and connected to the pillar; the sleeve portion being free to rotate about a longitudinal axis of the pillar when the sleeve portion engages with the pillar. [0051A] The coupling system may further comprise O-ring seals to seal against ingress of contaminants to the coupling system when the sleeve portion is engaged with the pillar, including a dummy pillar.

[0052] Securely engaging and disengaging the coupling from the pillar is as follows:

[0053] The coupling’s biasing means ensure that when it is not engaged with either a pillar or a dummy pillar a pin, termed a hold-open pin, is keeping the locking-plate in the second unlocked position whereby the sleeve portion is free to fully engage a pillar.

[0054] When a jockey wheel is lowered and the sleeve portion has fully engaged on the pillar, the hold-open pin comes into contact with a base portion of the pillar and is displaced upward thereby freeing the locking-plate to move to the first locked position under the influence of the locking-plate’s biasing componentry.

[0055] The movement of the locking-plate with its rack from the second unlocked position to the first locked position drives the engaged pinion gear to rotate the control-shaft such that the retaining member in the horizontal-groove / slot comes to lie above the vertical-groove / slot thereby allowing the control-shaft’s biasing member to raise the control-shaft to where it will no longer be able to rotate; the coupling or sleeve portion is now locked onto the pillar and also secondarily locked.

[0056] Uncoupling requires the reverse sequence: pushing down the controlshaft so that the horizontal-groove / slot aligns with the retaining member, using the lever to rotate the control-shaft such that the pinion gear’s engagement on the locking-plate’s rack retracts the locking-plate to the second unlocked position, using the jockey wheel to lift the sleeve portion free of the pillar which allows the hold-open pin to resume its locking of the locking-plate in the second unlocked position.

[0057] The fully automatic locking mechanism herein disclosed represents an important advance over all the coupling designs where achieving a secure connection requires human intervention beyond merely presenting the trailer and the towing-vehicle components to each other.

[0058] In addition, this automatic locking mechanism eliminates the possibility of towing a trailer that is presumed to be securely connected because the coupling is in a locked state but is in fact not securely connected because of incomplete engagement of the trailer and the towing-vehicle components.

[0059] In addition, this invention has automatic secondary locking which protects against rogue uncoupling from failure of the biasing means that establishes primary locking. Some couplings do not have any secondary locking mechanism, in some the secondary locking is not automatic and in others the secondary locking presents a means to temporarily prop the primary locking open. The latter practice is very dangerous as it predisposes to towing with the coupling totally unlocked.

[0060] A further advantage of this invention is the complete sealing against the ingress of contaminants to the articulation between the pillar and the sleeve portion as well as all of the moving components controlling the locking mechanism. Other systems offer no means or less reliable means for keeping the coupling free of contaminants that can impair proper function or lead to excess wear.

[0061] This new mechanism, as described herein, has the additional advantage of requiring minimal force from a user to operate the lever and control-shaft that unlocks the coupling.

[0062] The new mechanism also offers a means to readily adjust the friction restraining free rotation of the sleeve portion on a third axis in order to keep the uncoupled sleeve portion in a desired orientation against gravity. The latter facilitates a “backing into” coupling technique. This is where a lone driver, with the aid of a reversing camera, can back the pillar’s head into the mouth of the sleeve portion which is oriented toward the incoming pillar head. The sleeve portion then rolls over the head of the pillar and the driver can readily tell from the camera view when he has backed far enough to get out and lower the sleeve portion to full engagement.

[0063] Optimizing the profile of the neck of the pillar to ensure the sleeve portion smoothly aligns with and then descends onto the pillar is a further improvement only made possible by this invention moving the usual location of a coupling’s locking mechanism away from engagement with the head of a tow-ball or pillar to engagement lowdown on the column of a pillar

[0064] With this invention when the sleeve portion is fully engaged on the pillar the vertical distance from the neck of the pillar down to the top face of the base portion of the pillar is greater than the vertical distance from the equator of the head of the pillar to the third axis that extends between the first and second apertures of the sleeve portion, used to receive bolts to connect the sleeve portion to the yoke of the connector. Consequently, this mechanism once unlocked will always disengage smoothly regardless of any residual load between the first towing vehicle and the second towed vehicle and regardless of the orientation of the vehicles to each other. The reason is that the third axis is above the equator of the head at the stage of uncoupling where the sleeve portion disengages the column and becomes free to rotate off the head in the direction of the residual load. This is a major advantage over any tow-ball based coupling where the cup wants to hook under the head and interfere with smooth release. This “hooking under” phenomena is even more troublesome with tow-ball based couplings that incorporate additional axes of rotation to improve their range of articulation.

[0065] With this invention there is no need for the operator to have their hand anywhere near the coupling at any stage where unanticipated movement of the first towing vehicle relative to the second towed vehicle could lead to a hand injury. This is because nothing needs to be held during the coupling process while during uncoupling the lever operating the unlocking mechanism only has to be held in the unlocked position until the hold-open pin has reengaged. The reengagement of the hold-open pin occurs well before the sleeve portion has let go of the pillar.

[0066] A further advantage of the design is that it does not need an expensive coupling-specific lock as it can be secured with an off the shelf padlock locking the dummy pillar inside the sleeve portion.

[0067] Further or alternative embodiments of the invention may be disclosed herein or may otherwise become apparent to the person skilled in the art through the disclosure herein. These and other embodiments are considered to fall within the scope and object of the invention. DESCRIPTION OF FIGURES

[0068] Embodiments of the present invention will now be described, by way of example only, in relation to figures, wherein: Figure 1 is a perspective view of a connection arrangement between a towing vehicle and a towed vehicle with a connector component of the towed vehicle shown separate from a tow bar tongue of the towing vehicle, the connector having a sleeve portion and the tow bar tongue having a pillar attached thereto, the pillar and the sleeve portion forming a coupling system; Figure 2 is an exploded perspective view of component parts of the coupling system and associated connector and tow bar tongue; Figure 3 shows side, end and top views of the pillar and sleeve portion engaged and sectional views along line C-C and D-D; Figure 4_illustrates a side view of the pillar and a sectional side view of the pillar along line A-A; Figure 5_shows perspective, top and end views of the locking-plate and a sectional view taken along line E-E; Figure 6 shows two perspectives views of the control-shaft and a perspective view of a knob used to rotate and handle the control-shaft; Figure 7 is a perspective cut-away view of the sleeve portion’s locking-plate, pin and control-shaft, with the locking-plate in a first locking position engaged with the pillar; Figure 8 illustrates a perspective view, a rear view and a sectional view along line A-A of the coupling system with the sleeve portion engaged and locked to the pillar and the locking-plate in a first locking position engaged with the pillar; Figure 9 illustrates a rear view and sectional view along line F-F in which the locking-plate is retracted to a second locking-plate position in which the coupling system is in an unlocked state and the sleeve portion removed from the pillar; Figure 10 shows various views, including side and sectional views of a pivot bolt used to connect the sleeve portion to a yoke of the connector; and Figure 11 shows perspective and side views of a dummy pillar and a perspective view of a dummy pillar cover, when the coupling system in not in use. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0069] Referring to Figure 1, there is shown a connector 1A and a tow-bar tongue 1 that enable a coupling system 1B to couple a towed vehicle (not shown) and a towing vehicle (not shown). The tow-bar tongue 1 of the towing vehicle has a pillar 33 mounted and connected to the tongue 1. The coupling system 1B includes the pillar 33 and a sleeve portion 18, which is adapted to be mounted to the towed vehicle and adapted to fit over and engage with the pillar 33 and disengage from the pillar 33. In the following description the term “front” applies to being nearer to the towing vehicle to which the tongue 1 is attached. The term “rear” applies to being further away from the towing vehicle.

[0070] The connector 1A is comprised of an anchor 13 and a yoke 10.A sleeve portion 18 is connected to the yoke 10 and engages with and locks onto the pillar 33. The yoke 10 has a first arm 10A, a second arm 10B and a web 10C that connects to each of the arms 10A, 10B and is connected to anchor 13. The sleeve portion 18 is connected to each of the arms 10A, 10B through respective yoke pivot bolts 7.

[0071] A knob 41 on a lever 19 opens the automatic locking mechanism of the coupling system 1B by means described in subsequent figures.

[0072] Referring to Figure 2, the anchor 13 is attached to a trailer’s draw-bar by bolts (parts being mounting bolts 30, washers 31 and nuts 32) or by other means that would be obvious to those skilled in the art. The anchor 13 has a front (first) bush 28 and a rear (second) bush 29 that support a longitudinal-shaft 11 which is fixed to the web 10C of yoke 10. The longitudinal-shaft 11 is retained within the anchor 13 by a castle-nut 12 and a castle-nut roll-pin 27. The longitudinal-shaft 11 is free to rotate in the anchor 13 on a second axis 68.

[0073] The pillar 33 and the location of its associated tow pillar O-ring 25 are described in Figure 4.

[0074] The sleeve portion 18 is suspended within the yoke 10 on two yoke pivotbolts 7. The yoke 10 has bushes 9 to allow the sleeve portion 18 to rotate around a third axis 69.

[0075] The sleeve portion 18 can engage and rotate around the pillar 33 on a first axis 70, which is a longitudinal axis through the pillar 33. When the connector 1A is connected to the pillar 33, through the sleeve portion 18, the axes 68, 69 and 70 intersect at a common point and the axes 68, 69 and 70 are mutually at right angles to each other. The three axes 68, 69 and 70 provide an unlimited range of articulation between a trailer / towed vehicle and a towing vehicle (neither object illustrated).

[0076] The coupling system 1B also includes a locking-plate 2 adapted to extend through an aperture or slot 60 in the sleeve portion 18 and is configured to move between a first locking-plate position (shown in Figure 8) and a second locking-plate position (shown in Figure 9). In the first locking-plate position the locking-plate 2 is engaged with the pillar 33 to prevent detachment of the sleeve portion 18 from the pillar 33. In the second locking-plate position the lockingplate 2 is disengaged from the pillar 33 and enables detachment of the sleeve portion 18 from the pillar 33. The position of the locking-plate 2 within the aperture or slot 60, for receiving the locking-plate 2, (see Figure 3) in the sleeve portion 18 dictates whether the sleeve portion 18 is locked onto or engaged with the pillar 33 or is free to disengage from pillar 33. Components 4, being a pin and specifically a hold-open pin and 4A (a head of the pin 4), 6 (a spring for the pin 4), 17 (locking-plate biasing componentry in the form of springs for the lockingplate 2), 15 (control-shaft) and 22 (a biasing member for the control-shaft 15) control the position of the locking-plate 2. The locking-plate 2 is adapted to be moved to and kept in the first locking-plate position under the influence or force of the locking-plate biasing componentry 17. Refer to Figure 5, Figure 6, Figure 7, Figure 8 and Figure 9 for a description of the features and functions of these components. Refer to Figure 7, Figure 8 and Figure 9 for a description of the functions of components 3 (retention plate), 3A (screws), 5 (grub screw) and 20 (retaining member).

[0077] Refer to Figure 10 for a description of the yoke pivot-bolt 7, pivot-bolt-washer 16, yoke friction O-ring 21 and screw 8.

[0078] Referring to Figure 3, the sleeve portion 18 has a stepped (central) bore 52 for the tow pillar 33, dimensioned to engage on the pillar 33, whereby the pillar fits into the stepped bore 52. The skirt 18A is the lower part of the sleeve portion 18 that abuts a pillar base portion 37 (see Figure 4) of an engaged pillar 33. Thus, when the sleeve portion 18 is fully engaged with the pillar 33, the skirt 18A contacts the base portion 37 to support the sleeve portion 18.

[0079] Level D on the sleeve portion 18 (see Figure 8) is defined as the level where the larger diameter bore 52A (Figure 9) of central bore 52 diameter to accommodate the pillar’s base portion 37 changes to the lesser diameter bore 52B of central bore 52 to accommodate the pillar’s column 36 (see Figure 4).

[0080] Two pivot bolt apertures or stepped bores 61 of the sleeve portion 18 together with respective bores 10D and 10E having bushes 9 in arms 10A, 10B of yoke 10 each accept a yoke-pivot bolt 7 in order to connect the yoke 10 to the sleeve portion 18, which enables the sleeve portion 18 to pivot with respect to the yoke 10. The first and second pivot bolt apertures or stepped bores 61 are located on opposite sides of the sleeve portion 18. The yoke-pivot bolts 7 provide a third axis for rotation 69.

[0081] Level E on the sleeve portion 18 is defined as being at the level of the third axis 69 extending between the first and second bores 10D and 10E in arms 10A, 10B of yoke 10.

[0082] The locking-plate aperture or slot 60 passes through the sleeve housing 18B of sleeve portion 18 and through the sleeve portion 18 to the stepped central-bore 52. A retention plate recess 58 on the back of the housing 18B is dimensioned to accept retention-plate 3 which is retained in position by screws 3A (see Figure 2). The housing 18B and sleeve portion 18 are adapted to receive the locking-plate 2, the pin 4, retaining member 20, in the form of a pin, and the control-shaft 15 as detailed below. The locking-plate aperture 60 through which the locking-plate 2 moves is located below an axis 69 through each of the first and second pivot bolt apertures 61 of the sleeve portion 18, wherein further the distance from the locking-plate aperture 60 to a bottom 18C of the sleeve portion 18 is less than the distance from an equator 34A of a head 34 of the pillar 33 to a cylindrical column 36 of the pillar 33 (see Figure 4).

[0083] A horizontal-bore 57 accepts a retaining member 20 (see Figures 2 and 7) which is held captive by the secured retention-plate 3 (see Figures 2 and 7).

[0084] A (vertical) stepped bore 54 for the pin 4 passes down through the sleeve portion 18 and enters the stepped-bore 52 at the level of the skirt 18A. The top of the stepped-bore 54 has a threaded bore 55 to accept a grub-screw 5. An access-hole 59 passes through any part of the sleeve portion 18 that lies vertically above the stepped-bore 54. The pin 4, is located in the stepped bore 54 and is pushed down by a pin biasing member, in the form of spring 6, that is retained by a grub-screw 5 engaged in the threaded bore 55.

[0085] A (vertical) stepped bore 56 adapted to receive control-shaft 15 passes down through housing 18B of the sleeve portion 18. The control-shaft 15 is located in the stepped-bore 56 and is retained in position by the retaining member 20 (see Figures 2 and 7).

[0086] The control-shaft 15 can move up and down in the stepped-bore 56 to an extent limited by the engagement of the retaining member 20 in a first slot or groove 44 of the control-shaft 15 which has a first orientation, being vertical (see Figure 6). A control-shaft biasing member in the form of spring 22 is positioned below the control-shaft 15 (see Figures 2 and 7) and is biased to push the controlshaft 15 upward.

[0087] The control-shaft 15 can rotate about its longitudinal axis to an extent limited by the engagement of a retaining member 20 in a second slot or groove 45 of the control-shaft 15 which has a second orientation, being horizontal, and orthogonal to the first orientation of the first slot or groove 44. (see Figure 6). The first and second slots 44, 45 are co-located in the sense that retaining member 20 is able to move between the slots 44, 45 as the control-shaft 15 moves between a first control-shaft position, in which the retaining member 20 is positioned in first slot 44 orthogonal to the longitudinal axis of the first slot 44, and a second control-shaft position, in which the retaining member 20 is positioned in second slot 45. The retaining member 20, when engaged within the first slot 44, enables movement of the control-shaft 15 to the first control-shaft position under the action of the control-shaft biasing member 22.

[0088] Rotation of the control-shaft 15 occurs in response to locking-plate biasing componentry, in the form of springs 17, (see Figures 2 and 7) moving the rack 51 on the locking-plate 2 (see Figure 5) against the pinion 43 on the controlshaft 15 (see Figures 6 and 7). The biasing of the locking-plate 2 position by the springs 17 can be overridden by an opposing force applied to the lever 19 on the control-shaft 15 (see Figures 1 and 6).

[0089] Referring to Figure 4, The pillar 33 is a single element with the following zones from the top of the pillar 33 down to the base of the pillar 33: a head 34, a neck 35, a cylindrical column 36, a base portion 37 and a threaded shank 38. The neck 35 is between the head 34 and the cylindrical column 36. The spring washer 24 and tow pillar nut 23 secure the pillar 33 to a tow-bar tongue 1 using the threaded shank 38.

[0090] The pillar 33 has a circumferential groove 39 located low down on the column 36 that the locking-plate 2 engages in to lock the sleeve portion 18 onto the pillar 33 whereby the locking-plate 2 is locked in the first locking-plate position within the groove 39.

[0091] All downward forces (draw-bar weight) on the sleeve portion 18 are born by the top weight-bearing face 37A of the base portion 37. The base portion 37 has an O-ring groove 40 for the tow pillar O-ring 25.

[0092] The head 34 is part of a sphere the equator 34A of which is located at Level A (see Figure 8). Level B is defined as being the level at which the neck 35 transitions to being the cylindrical column 36. Level C is defined as being at the top-face 37A of the base portion 37.

[0093] The head 34 and the column 36 have the same diameter. When the sleeve portion 18 descends over the head 34 it may initially be out of alignment with the column 36. With progressive descent the internal surface of the sleeve portion central-bore 52 contacts the neck 35. The sleeve portion 18 is then forced into alignment with the pillar 33 provided the downward force at the intersection of axes 68 and 69 is located inside the circumference of a theoretical upward extension of the column 36. The sleeve portion 18 descends smoothly onto the column 36 when it is fully aligned to the pillar 33. If at presentation of the centralbore 52 to the head 34 the intersection of axes 68 and 69 is located outside a theoretical upward extension of the column 36 the sleeve portion 18 will tilt further out of alignment with the pillar 33 and be unable to descend to full engagement.

[0094] Referring to Figure 5, The locking-plate 2 is able to slide back and forth within the aperture or slot 60 in the sleeve portion 18. The position of the lockingplate 2 within the aperture or slot 60 is determined by the influence of the springs 17, the position of the pin 4 and the position of the control-shaft 15.

[0095] The front end of the locking-plate 2, opposite to where the springs 17 are located, can locate into the circumferential groove 39 in the pillar 33 and is curved-to provide maximum engagement in the groove 39 when the locking-plate 2 is in the first locked position. The springs 17 protrude from bores / spring cavities 49 in the back end of the locking-plate 2. An opening 50 in the locking-plate 2, and through which the control-shaft 15 extends, has a rack 51 along one of the edges or side walls of the opening 50. The rack 51 engages with a pinion 43 on the control-shaft 15 (see Figure 6). Thus, the control-shaft 15 and pinion 43 are adapted to rotate together and the pinion 43 engages with the rack 51 to move the locking-plate 2 between the first locking-plate position and the second lockingplate position. An aperture 47 in the locking-plate 2 allows the shaft of the pin 4 to pass through. How far the locking-plate 2 can slide forward and back in the aperture or slot 60 in the sleeve portion 18 is determined by the length of the aperture 47. At the front end of the aperture 47 there is a recess 48 that the head 4A of the pin 4 can engage with and be retained in. Detachment of the sleeve portion 18 from the pillar 33 enables the pin 4 to move to the second pin position in response to the pin biasing member 6 such that the head 4A of the pin 4 is secured in the recess 48 and the locking-plate 2 is retained in the second locking-plate position.

[0096] Referring to Figure 6, at an upper end of the control-shaft 15 is a lever 19 with a knob 41. The lower end of control-shaft 15 has the pinion (gear) 43. Above the level of the pinion gear 43 the control-shaft 15 has a vertical-groove (first slot) 44 that at its upper end is confluent or intersects with a horizontalgroove (second slot) 45. The first slot 44 is positioned in a first orientation (vertical) and a second slot 45 positioned in a second orientation (horizontal), the first slot 44 intersecting with the second slot 45 and the second orientation being orthogonal to said first orientation. Above the level of the horizontal-groove 45 there is an O-ring groove 42 for a control-shaft O-ring 26.

[0097] A through hole 77 in the control-shaft 15 permits the attachment of a padlock (not illustrated). The level of the hole 77 is such that it is only accessible when the control-shaft 15 is in the up (first control-shaft) position associated with the mechanism being locked. With a padlock in place the control-shaft 15 cannot be pushed down into a second control-shaft position and the sleeve portion 18 cannot be separated from a dummy-pillar 73 or pillar 33 held within the central bore 52 of the sleeve portion 18.

[0098] Referring to Figure 7, The numbered components have already been described in Figures 1-6. This cut-away view illustrates the locking-plate 2 engaged in the circumferential groove 39 to secure the sleeve portion 18 and the connector 1A to the pillar 33. The pin 4 extending through the sleeve portion 18 is in a first pin position where the locking-plate 2 is enabled to move to the first locking-plate position. The pin 4 is in a second pin position where the lockingplate is restrained in the second locking-plate position. The control-shaft 15 extending through the sleeve portion 18 is adapted to be operated by a user to move the locking-plate 2 from the first locking-plate position to the second locking-plate position. The shaft of the pin 4 is in the up position (first pin position) whereby the head 4A of the pin 4 has disengaged from the recess 48 which in turn has allowed the locking-plate 2 to move under the influence of the springs 17 to engage the circumferential groove 39. The inward movement of the rack 51 has driven the pinion 43 to rotate to the position where the retaining member 20 is aligned with the vertical-groove (first slot) 44 which in turn allows the control-shaft 15 to pop-up to the first control-shaft position under the influence of the spring 22.

[0099] Referring to Figure 8, The nature of the numbered components has been provided in the descriptions of preceding Figures 1-7. In the three drawings of Figure 8 the sleeve portion 18 has fully engaged the pillar 33 and the automatic double locking mechanism that secures the sleeve portion 18 to the pillar 33 has been triggered to automatically double lock the sleeve portion 18 to the pillar 33.

[00100] The two drawings on the right side of Figure 8 are included to define the position of the cross-section A-A which is drawn to a different scale in the drawing on the left side of Figure 8.

[00101] When the sleeve portion 18 is fully engaged on the pillar 33 the Level D (as defined in paragraph 0058) of the sleeve portion 18 coincides with the Level C (as defined in paragraph 0070) of the pillar 33.

[00102] When the sleeve portion 18 is fully engaged on the pillar 33 the distance from Level E (as defined in paragraph 0060) to Level A (as defined in paragraph 0070) is defined as X and the distance from Level D to Level B (as defined in paragraph 0070) is defined as Y. A design requirement for this coupling is that the distance Y must be greater than the distance X as only this geometry ensures smooth disengagement regardless of any load in any direction between the trailer and the towing-vehicle. Thus, when the sleeve portion 18 is fully engaged with the pillar 33, the distance between the neck 35 and a face 37A of the base portion 37 that is in contact with the sleeve portion 18 is greater than the distance between the equator 34A of the head 34 and the axis 69 through each of the first and second pivot bolt apertures 61 of the sleeve portion 18, so that the sleeve portion 18 disengages from the pillar 33 regardless of any residual load between the towing vehicle and the towed vehicle and regardless of the orientation of the towing vehicle and the towed vehicle to each other.

[00103] Referring to the cross-section drawing in Figure 8, the shaft of the pin 4 has been displaced upwards to the first pin position from the second pin position, against the resistance of a pin biasing member in the form of spring 6, by contact with the top-face 37A of the base portion 37. Thus, when the sleeve portion 18 is fully engaged with the pillar 33, a first end 4B of pin 4 contacts the base portion 37 of pillar 33 such that the pin 4 is moved up to the first pin position where it is disengaged from the recess 48 in the locking-plate 2, which enables the biasing componentry or springs 17 to push the locking-plate 2 from the second locking-plate position to the first locking-plate position where locking-plate 2 is in full engagement with the circumferential groove 39 in the pillar 33. This sequence is referred to as automatic primary locking.

[00104] The pinion 43 on the control-shaft 15 is permanently engaged with the rack 51 on the locking-plate 2 and therefore rotates as the locking-plate 2 slides across to full engagement with the circumferential groove 39 in the pillar 33. As a consequence of this rotation, the retaining member 20 becomes aligned with the first slot or vertical-groove 44 in the control-shaft 15. In turn the controlshaft 15 is forced to pop up to the first control-shaft position under the influence of the control-shaft biasing member or spring 22. When the control-shaft 15 is popped up, the retaining member 20 no longer aligns with the second slot or horizontal-groove 45 in the control-shaft 15, thereby denying disengagement of the locking-plate 2 from the circumferential groove 39 in the pillar 33 until such time as the control-shaft 15 is manually pushed back down to the second controlshaft position. This sequence is referred to as automatic secondary locking because in the event of the springs 17 failing, the locking-plate 2 will remain fully engaged in the circumferential groove 39. A secondary locked condition is therefore when the control-shaft 15 is in the first control-shaft position and the retaining member 20 is not aligned with the second slot 45 and the control-shaft 15 is unable to rotate.

[00105] Thus, when the sleeve portion 18 fully engages with the pillar 33, the pinion 43 and control-shaft 15 rotate through the engagement of the rack 51 with the pinion 43 so that the locking-plate 2 moves to the first locking-plate position, and the retaining member 20 moves through the second slot 45 until the retaining member 20 reaches the first slot 44, whereupon the control-shaft 15 moves to the first control-shaft position. This entire sequence is referred to as automatic double locking.

[00106] If an “inquisitive” individual unlocks the locking mechanism in the owner’s absence, the automatic primary locking and secondary locking will relock as soon as the individual lets go of the knob 41. Thus, if there is inadvertent unlocking of the fully engaged coupling system by a user moving the control-shaft 15 to shift the locking-plate 2 to the second locking-plate position, the primary locked condition and the secondary locked condition are reset automatically when the user releases control of the knob 41 and the control-shaft 15.

[00107] There is an O-ring 25 on the pillar’s base portion 37 which seals against the interior wall of the stepped-bore 52 in the region of the skirt 18A; at a level below the lower end of the hold-open pin’s stepped-bore 54.

[00108] The control-shaft 15 is also fitted with an O-ring 26 that seals against the interior walls of the stepped-bore 56 for the control-shaft 15.

[00109] Accordingly, all internal moving components in the coupling mechanism are protected against the ingress of contaminants that might impair their proper operation, preferably through the use of O-ring seals.

[00110] Referring to Figure 9, the nature of the numbered components has been provided in the descriptions of preceding Figures 1-8. In these two Figure 9 drawings there is no pillar 33 engaged in the sleeve portion 18.

[00111] The Figure 9 cross-section drawing is the same as in Figure 8 except the coupling system has been manually unlocked and the pillar 33 has been disengaged. The coupling is now in a status where it can accept and automatically double lock onto pillar 33 that is fully inserted into the stepped bore 52.

[00112] Unlocking the coupling system 1B, that is, to move the locking-plate 2 from the first locking-plate position to the second locking-plate position, involves first pushing or moving the control-shaft 15 down against its spring 22 from its first control-shaft position into the second control-shaft position where the controlshaft 15 is free to rotate and that, in turn, retracts the locking-plate 2 from the circumferential groove 39 of the pillar 33. Specifically, the retaining member 20 moves from first slot 44, aligns with the second slot 45 and moves into the horizontal second slot 45. The lever 19 is then used to rotate the locking-shaft 15 clockwise as viewed from above. The rotation of the pinion 43 which is engaged on the rack 51 in turn retracts the locking-plate 2 into the second locking-plate position away from the circumferential groove 39 to the degree where no part of the locking-plate 2 lies within the stepped central-bore 52. The sleeve portion 18 is then free to be raised on or detached from the pillar 33. The lever 19 only needs to be held in the unlocked position until the sleeve portion 18 is raised sufficiently for the head 4A of the pin 4 to engage with and be retained in the recess 48 in the locking-plate 2. The pin 4 is now in the second pin position and the lockingplate 2 is retained in the second locking-plate position. The engagement of the head 4A of the pin 4 in the recess 48 occurs well before the sleeve portion 18 is high enough to allow the trailer to separate from the towing vehicle. Thus the operator’s hands are well clear of the coupling at the moment of full separation.

[00113] Not all operators appreciate that especially on sloping or uneven ground a trailer may move toward or away from the towing vehicle when a coupling is released. Such movement causes the sleeve portion 18 to rotate within the yoke 10 on the third axis 69 which in turn can result in an injured hand if the operator is still holding onto the lever 19 at the moment of complete and sometimes sudden separation.

[00114] Referring to Figure 10, the perspective view illustrates a pivot-bolt 7 with a head 71. The inner part of the pivot-bolt 7, called a body engagement segment 63, engages in the pivot-hole 61 in the sleeve portion 18. The outer part of the pivot-bolt 7, called a bush engagement segment 64, articulates with the bush 9 in the yoke arms 10A and 10B. The outer end of the pivot-bolt 7 has a raised dog 66.

[00115] The washer 16 has straight groove 67 and a circular washer O-ring groove 65 on its inner face. The dog 66 on the end of the pivot bolt 7 engages in the washer groove 67 and stops the washer 16 from rotating on the pivot bolt 7. The depth of the groove 67 is greater than the height of the dog 66.

[00116] The section B-B drawing in Figure 10 illustrates a central countersunk-hole 53 through the full thickness of the washer 16 and a threaded bore 62 in the outer part 64 of the pivot-bolt 7.

[00117] The section C-C drawing in Figure 10 illustrates pivot-bolt 7, washer 16 and screw 8 suspending the sleeve portion 18 in the yoke 10 to provide the third axis of rotation 69 on the bushes 9 press-fitted into the yoke arms 10A and 10B.

[00118] The pivot-bolts 7 are a press-fit to the pivot-holes 61 in the sleeve portion 18 and this method of fitting stops the pivot-bolts 7 from being able to rotate in the pivot-holes 61.

[00119] The O-ring 21 in the groove 65 is compressed between the outer face of the yoke 10 and the washer 16. The degree of compression is regulated by the tensioning of the screw 8. Dimensions are such that the desired degree of compression is achievable before the washer 16 contacts the pivot-bolt 7. The compressed O-ring 21 restricts the otherwise free rotation of the sleeve portion 18 on the third axis 69 sufficiently for the sleeve portion 18 to retain a selected orientation against the influence of gravity.

[00120] Referring to Figure 11, the pillar 33 is kept free of contaminants by attaching the tow pillar-cover 72 when the sleeve portion 18 is not engaged on the pillar 33. The pillar-cover 72 compresses the O-ring 25 and this stops it from falling off the pillar 33.

[00121] The dummy-pillar 73 has the same profile as the pillar 33 from the middle of the column 36 downwards and has a knob 76 in place of the shank 38. The O-ring groove 74 is fitted with an O-ring 75 for the dummy pillar 73.

[00122] The dummy-pillar 73 is inserted into the central-bore 52 whenever the sleeve portion 18 is not connected to the pillar 33. The automatic double locking mechanism triggered by the sleeve portion 18 fully engaging a pillar 33 is similarly triggered when the dummy-pillar 73 is fully inserted into the central-bore 52.

[00123] For security the dummy-pillar 73 can be locked inside the sleeve portion 18 by locking a padlock (not illustrated) across the padlock-hole 77 in the control-shaft 15 (see Figure 8). This is because the padlock blocks the controlshaft 15 from being pushed down and then rotated to release the locking-plate 2 retaining the dummy-pillar 73.

[00124] The dummy-pillar 73 can be stored inside the pillar cover 72 when the sleeve portion 18 is connected to the pillar 33.

[00125] When the dummy-pillar 73 and pillar-cover 72 are used according to instruction there is no risk of contamination of either the pillar 33, the wall of the central-bore 52 or locking mechanism (parts 2, 6, 4, 4A, 15, 17 and 22) with material that could impair the reliable functioning of the locking mechanism or predispose to excessive ware.

[00126] While the invention has been described with reference to preferred embodiments above, it will be appreciated by those skilled in the art that it is not limited to those embodiments, but may be embodied in many other forms, variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, components and / or devices referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[00127] In this specification, unless the context clearly indicates otherwise, the word “comprising” is not intended to have the exclusive meaning of the word such as “consisting only of”, but rather has the non-exclusive meaning, in the sense of “including at least”. The same applies, with corresponding grammatical changes, to other forms of the word such as “comprise”, etc.

[00128] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

[00129] Any promises made in the present document should be understood to relate to some embodiments of the invention, and are not intended to be promises made about the invention in all embodiments. Where there are promises that are deemed to apply to all embodiments of the invention, the applicant / patentee reserves the right to later delete them from the description and they do not rely on these promises for the acceptance or subsequent grant of a patent in any country.

Claims

1. A coupling system for coupling a towed vehicle to a towing vehicle comprising:a pillar adapted to be mounted to a tow bar tongue of the towing vehicle;a sleeve portion adapted to be mounted to the towed vehicle and adapted to fit over and engage with the pillar and disengage from the pillar;a locking plate adapted to extend through an aperture in the sleeve portion and configured to move between a first locking plate position and a second locking plate position, such that in said first locking plate position the locking plate is engaged with said pillar to prevent detachment of the sleeve portion from the pillar, and such that in said second locking plate position the locking plate is disengaged from said pillar and enables detachment of the sleeve portion from the pillar;a pin extending through the sleeve portion such that in a first pin position the locking plate is enabled to move to said first locking plate position and in a second pin position the locking plate is restrained in the second locking plate position; anda control shaft extending through the sleeve portion adapted to be operated by a user to move the locking plate from said first locking plate position to said second locking plate position.

2. The coupling system according to claim 1 wherein the sleeve portion includes a stepped-bore and a skirt and the pillar has a base portion, such that the pillar fits into the stepped-bore and when the sleeve portion is fully engaged with the pillar, the skirt contacts the base portion of the pillar to support the sleeve portion.

3. The coupling system according to claim 2 wherein the pillar has a circumferential groove for receiving and retaining the locking plate in the first locking plate position.

4. The coupling system according to any one of the previous claims wherein the locking plate is adapted to be moved to and kept in the first locking plate position under the influence of locking plate biasing componentry.

5. The coupling system according to claim 2 wherein when the sleeve portion is fully engaged with the pillar, a first end of the pin contacts the base portion of the pillar such that the pin is moved to the first pin position from the second pin position against resistance of a pin biasing member, enabling the locking plate to move to said first locking plate position.

6. The coupling system according to claim 3 wherein the locking plate includes an opening through which the control shaft extends.

7. The coupling system according to claim 6 wherein the control shaft includes a pinion and the locking plate includes a rack located along an edge to the locking plate opening.

8. The coupling system according to claim 7 wherein the control shaft and pinion are adapted to rotate together and the pinion engages with the rack to move the locking plate between the first locking plate position and the second locking plate position.

9. The coupling system according to claim 8 wherein the control shaft has a first slot positioned in a first orientation and a second slot positioned in a second orientation, the first slot intersecting with the second slot, said second orientation being orthogonal to said first orientation, the coupling system further comprising a retaining member also orthogonal to said first slot, said retaining member when engaged within the first slot enables movement of the control shaft to a first control shaft position under the action of a control shaft biasing member.

10. The coupling system according to claim 9 further comprising a primary locked condition and a secondary locked condition, such that the primary locked condition is when the locking plate is in the first locking plate position and the secondary locked condition is when the control shaft is in the first control shaft position and the retaining member is not aligned with the second slot.

11. The coupling system according to claim 9 or claim 10 wherein when the sleeve portion fully engages with the pillar, the pinion and control shaft rotate through the engagement of the rack with the pinion so that the locking plate moves to the first locking plate position, and the retaining member moves through the second slot until the retaining member reaches the first slot, whereupon the control shaft moves to the first control shaft position.

12. The coupling system according to claim 11 wherein when the control shaft is in the first control shaft position, the retaining member is not aligned with the second slot and the control shaft is unable to rotate.

13. The coupling system according to claim 12 wherein when the control shaft is moved to a second control shaft position, the retaining member is aligned with the second slot and the control shaft is able to rotate, whereby such rotation causes the pinion to engage with the rack and move the locking plate to the second locking plate position in which the locking plate is removed from the circumferential groove in the pillar that enables detachment of the sleeve portion from the pillar.

14. The coupling system according to any one of the claims 9 to 13 wherein the sleeve portion includes a housing for receiving the locking plate, the pin, the retaining member and the control shaft.

15. The coupling system according to claim 5 wherein the locking plate has an aperture, said aperture having a recess, said pin adapted to move through the aperture, said aperture recess adapted to receive a head of the pin, and detachment of the sleeve portion from the pillar enables the pin to move to the second pin position in response to the pin biasing member such that the head of the pin is secured in the recess and the locking plate is retained in the second locking plate position.

16. The coupling system according to any one of the previous claims wherein the sleeve portion has first and second pivot bolt apertures for respectively receiving a pivot bolt that each connect to a yoke so as to enable the sleeve portion to pivot with respect to the yoke.

17. The coupling system according to claim 16 wherein the sleeve portion aperture through which the locking plate extends is located below an axis through each of the first and pivot bolt second apertures of the sleeve portion, wherein further the distance from the sleeve portion aperture to a bottom of the sleeve portion is less than the distance from an equator of a head of the pillar to a cylindrical column of the pillar.

18. The coupling system according to claim 17 wherein the pillar has said head, said cylindrical column, a neck between the head and the cylindrical column and a base portion, wherein when the sleeve portion is fully engaged with the pillar the distance between the neck and a face of the base portion that is in contact with the sleeve portion is greater than the distance between the equator of the head and the axis through each of the first and second pivot bolt apertures of the sleeve portion, so that the sleeve portion disengages from the pillar regardless of any residual load between the towing vehicle and the towed vehicle and regardless of the orientation of the towing vehicle and the towed vehicle to each other.

19. The coupling system according to claim 10 wherein if there is inadvertent unlocking of the fully engaged coupling system by a user moving the control shaft to shift the locking plate to the second locking plate position, the primary locked condition and the secondary locked condition are reset automatically when the user releases control of the control shaft.

20. The coupling system according to claim 9 wherein in order to move the locking plate from the second locking plate position to the first locking plate position:the sleeve portion contacts the pillar base portion forcing the pin to move to the first pin position;the locking plate engages with the circumferential groove in the pillar under the action of locking plate biasing componentry;the control shaft is rotated and raised as a result of movement of the locking plate and action of the control shaft biasing member respectively to a first control shaft position.

21. The coupling system according to claim 3 wherein in order to move the locking plate from the first locking plate position to the second locking plate position:the control shaft is moved from a first control shaft position to a second control shaft position where the control shaft is free to rotate and that, in turn, retracts the locking plate from the circumferential groove of the pillar;the pin thereafter, when the sleeve portion disengages from the pillar, is moved to the second pin position where a head of the pin resides in a recess in the locking plate to retain the locking plate in the second locking plate position.

22. The coupling system according to any one of the previous claims further comprising O-ring seals to seal against ingress of contaminants to the coupling system when the sleeve portion is engaged with the pillar, including a dummy pillar.

23. A connection arrangement between a towed vehicle and a towing vehicle comprising the coupling system of any one of claims 1 to 22 and further comprising:a connector connected to the towed vehicle and including an anchor, a yoke connected to the anchor, the yoke also connected to the sleeve portion of the coupling system;a tow bar tongue connected to the towing vehicle and connected to the pillar;the sleeve portion being free to rotate about a longitudinal axis of the pillar when the sleeve portion engages with the pillar.

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