Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
TOW COUPLING FOR A TRAILER
Document Type and Number:
WIPO Patent Application WO/2001/007274
Kind Code:
A1
Abstract:
A tow coupling for a prime mover and a trailer combination comprises first and second damper units (32,34) reacting between the prime mover and the trailer, and means (54 to 66) for interconnecting the coupling and the braking mechanism of the prime mover such that, until the braking mechanism of the prime mover is actuated, the first and second damper units (32,34) provide a combined, relatively heavy duty damping effect between the prime mover and the trailer, and, on actuation of the braking mechanism of the prime mover, the damping effect of the second damper unit (34) is disconnected whereby damping between the prime mover and the trailer is effected by the first damper unit (32) only and which is chosen to satisfy civilian on-road regulations.

Inventors:
HOLMES GORDON (GB)
Application Number:
PCT/GB2000/002764
Publication Date:
February 01, 2001
Filing Date:
July 18, 2000
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HOLMES GORDON (GB)
International Classes:
B60D1/50; B60T7/20; B60T11/10; B60T13/08; (IPC1-7): B60D1/50; B60T7/20; B60T11/10
Foreign References:
US3682278A1972-08-08
US3796287A1974-03-12
FR2498544A11982-07-30
FR2029595A11970-10-23
US4840256A1989-06-20
US4856621A1989-08-15
Attorney, Agent or Firm:
Sanderson, Michael (Mewburn Ellis York House 23 Kingsway London WC2B 6HP, GB)
Download PDF:
Claims:
CLAIMS
1. A tow coupling for a prime mover and a trailer combination, the coupling comprising a first damper unit (32) reacting between the prime mover and the trailer, characterised by a second damper unit (34) reacting between the prime mover and the trailer, and means (54 to 66) for interconnecting the coupling and the braking mechanism of the prime mover such that, until the braking mechanism of the prime mover is actuated, the first and second damper units (32,34) provide a combined damping effect between the prime mover and the trailer, and, on actuation of the braking mechanism of the prime mover, the damping effect of the second damper unit (34) is disconnected whereby damping between the prime mover and the trailer is effected by the first damper unit (32) only.
2. A coupling as claimed in claim 1 and including an outer cylinder (2) for securing to the trailer and an inner cylinder (6) for securing to the prime mover and guided for linear sliding movement within the outer cylinder (2), the first damper unit comprising a first fluidoperated ram (32) mounted within the inner cylinder (6) and reacting between the inner and outer cylinders (6,2).
3. A coupling as claimed in claim 2 including, within the inner cylinder (6), a fluidoperated piston cylinder assembly (56) the free end of the piston (58) of which is fixed relative to the outer cylinder (2), the second damper unit comprising a second fluid operated ram (34) mounted within the inner cylinder (6) and reacting between the inner cylinder (6) and the cylinder (54) of the pistoncylinder assembly (56), the piston (58) and cylinder (54) of the assembly (56) being locked to prevent relative movement therebetween during normal towing conditions, the assembly being interconnected with the braking mechanism of the prime mover such that, on actuation of said braking mechanism, the pistoncylinder assembly (56) is released to permit substantially unimpeded relative movement between the piston (58) and cylinder (54) thereof.
4. A coupling as claimed in claim 3 in which the cylinder (54) of the pistoncylinder assembly (56) is slidable relative to the inner cylinder (6) whereby, with the pistoncylinder assembly (56) in its locked condition, and on compression of the first and second rams (32,34) as a result of relative movement between the inner and outer cylinders (6,2), the cylinder (54) of the pistoncylinder assembly (56) moves as a unit with the piston (58) thereof and with the pistons (38,42) of the first and second rams (32,34).
5. A coupling as claimed in claim 3 or claim 4 in which the pistoncylinder assembly (56) incorporates a solenoid valve (62) electrically connected with a stop light of the prime mover, the valve (62) being closed under normal towing conditions to maintain the piston cylinder assembly (56) locked, said valve (62) being opened on actuation of the stop light of the prime mover to release the assembly (56) and to permit unrestricted relative movement between the piston (58) and the cylinder (54) of the assembly (56).
Description:
TOW COUPLING FOR A TRAILER TECHNICAL FILED This invention relates to tow couplings for trailers, and more particularly to such couplings capable of accommodating off-road buffeting and oscillations as can occur on rough terrain whilst still being such as to satisfy civilian road regulations.

BACKGROUND Fundamental considerations of road safety require that, when a non-powered road-going vehicle, such as a trailer, is towed behind a powered vehicle, the towed vehicle should itself have a braking system. Otherwise there is a danger of the towed vehicle over-running the towing vehicle when brakes are applied on the latter, thereby resulting in a serious loss of control and possible jack-knifing of the two vehicles.

Whilst such combinations of towing and towed vehicles may take various forms, for example a car towing a trailer, for simplicity in the following description the towing vehicle and its associated braking mechanism will be referred to as'the prime mover'and the towed vehicle with its associated braking mechanism will be referred to as'the trailer'.

Current tow couplings are fitted with an hydraulic or gas damper unit the rating of which is dependent upon the gross weight of the trailer. The damper unit is set such that it retards the inertia-force of the trailer

when the prime mover's brakes are applied, and enables a smooth, progressive braking effect to be applied to the trailer by the trailer brake under civilian road conditions.

As previously mentioned, the damper unit of a tow coupling is set according to the trailer weight and to satisfy EU regulations. Should a combination of prime mover and trailer be used off-road on rough terrain, the combination, and in particular the tow coupling, can be subjected to substantial buffeting and oscillation which can cause serious damage to the damper unit.

Clearly such buffeting could be better withstood if the damper unit of the tow coupling was stiffened, for example by replacing the normal damper unit with a heavy duty unit more capable of withstanding abnormal forces thereon.

However, with such an arrangement, and on return to civilian road conditions, such a heavy duty damper unit would contravene the requirements for the associated trailer under such on-road conditions.

SUMMARY OF THE INVENTION It would be desirable to be able to provide a tow coupling for a prime mover and trailer combination capable of accommodating abnormal forces such as are experienced under off-road conditions whilst still satisfying statutory regulations associated with the trailer under civilian road conditions.

According to the present invention there is

provided a tow coupling for a prime mover and trailer combination, the coupling comprising a first damper unit reacting between the prime mover and the trailer, characterised by a second damper unit reacting between the prime mover and the trailer, and means for interconnecting the coupling and the braking mechanism of the prime mover such that, until the braking mechanism of the prime mover is actuated, the first and second damper units provide a combined damping effect between the prime mover and the trailer, and, on actuation of the braking mechanism of the prime mover, the damping effect of the second damper unit is disconnected whereby damping between the prime mover and the trailer is effected by the first damper unit only.

It will be appreciated that such an arrangement effectively provides heavy duty damping-ie. a combination of the first and second damper units- during conventional towing of the trailer be it on civilian roads or under off-road conditions where the coupling is subjected to abnormal forces, but, as soon as the brakes of the prime mover are actuated, the coupling reverts to a lower damping value which is chosen to satisfy statutory regulations associated with the particular weight of trailer under on-road towing conditions.

In a preferred embodiment of the invention, the coupling includes an outer cylinder for securing to the trailer and an inner cylinder for securing to the prime

mover and guided for linear sliding movement within the outer cylinder, the first damper unit comprising a first fluid-operated ram mounted within the inner cylinder and reacting between the inner and outer cylinders.

Conveniently the coupling includes, within the inner cylinder, a fluid-operated piston-cylinder assembly the free end of the piston of which is fixed relative to the outer cylinder, the second damper unit comprising a second fluid operated ram mounted within the inner cylinder and reacting between the inner cylinder and the cylinder of the piston-cylinder assembly, the piston and cylinder of the assembly being locked to prevent relative movement therebetween during normal towing conditions, the assembly being interconnected with the braking mechanism of the prime mover such that, on actuation of said braking mechanism, the piston-cylinder assembly is released to permit substantially unimpeded relative movement between the piston and cylinder thereof.

Preferably the cylinder of the piston-cylinder assembly is slidable relative to the inner cylinder whereby, with the piston-cylinder assembly in its locked condition, and on compression of the first and second rams as a result of relative movement between the inner and outer cylinders, the cylinder of the piston-cylinder assembly moves as a unit with the piston thereof and with the pistons of the first and second rams.

The piston-cylinder assembly may incorporate a

solenoid valve electrically connected with a stop light of the prime mover, the valve being closed under normal towing conditions to maintain the piston-cylinder assembly locked, said valve being opened on actuation of the stop light of the prime mover to release the assembly and to permit unrestricted relative movement between the piston and the cylinder of the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view from above, partly in longitudinal horizontal section, of a tow coupling according to the invention; Fig. 2 is a side view, partly in longitudinal vertical section, of the coupling of Fig. 1, and Fig. 3 is a rear end view, partly in transverse vertical section, of the coupling of Fig. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the illustrated tow coupling comprises an outer cylinder 2 mounted on a frame 4, for example by welding, the frame 4 being rigidly secured to a trailer (not shown) for example by bolts, the cylinder 2 and frame 4 typically being of heavy duty steel.

Slidably mounted within the outer cylinder 2 is an inner cylinder 6 guided by bearings 8 of nylon or the like. One end of the inner cylinder 6 comprises a coupling member 10 for attachment to the rear of a prime mover.

A securing disc 12 of substantial thickness is

mounted in the open end of the inner cylinder 6 remote from the coupling member 10 and is fixed relative to the outer cylinder 2 by means of a pin 14 extending through the outer cylinder 2, through opposed axial slots 16 formed in the inner cylinder 6 and through a bore in the disc 12.

Figs. 1 and 2 show the inner cylinder 6 fully extended to the right as viewed in the drawings relative to the outer cylinder 2, which position is determined by abutment of the ends of the slots 16 nearest the open end of the inner cylinder 6 with the pin 14.

A flexible bellows 18 reacts between, to seal, the ends of the inner and outer cylinders 6,2 adjacent the coupling member 10, the fully retracted position of the inner cylinder 6 within the outer cylinder 2 being determined by abutment of an annular shoulder 20 on the inner cylinder 6 with the end face 22 of the outer cylinder 2. In this position of the inner cylinder 6, the other ends of the slots 16 lie adjacent to, but just spaced from, the pin 14.

The free end of the inner cylinder 6 is closed by an end cap 24 which is screwed into the cylinder 6 and is used to adjust the desired pre-load on the coupling as will be detailed below, a washer 26 of rubber or the like reacting between the cap 24 and the disc 12.

The cap 24 carries an adjusting bolt 28 and a lock nut 30, the head of the bolt 28 reacting with, to actuate, the lever arm (not shown) of a braking

mechanism for the trailer.

Mounted within the inner cylinder 6 are a pair of damper units 32,34, which may be hydraulically or gas actuated, and which are conveniently of the same rating.

The first damper unit 32 comprises a cylinder 36 and a piston 38, while the second damper unit 34, which extends parallel with the first unit 32, comprises a cylinder 40 and a piston 42.

The two cylinders 36,40 are connected together and to the inner cylinder 6 by means of a pin 44 extending through the three cylinders 6,36,40 as clearly seen in Fig. 1 and whereby the cylinders 36,40 move with the inner cylinder 6.

The free end of the piston 38 of the damper unit 32 is secured to the fixed disc 12 and is locked thereto by a lock nut 46, whereby said piston is effectively secured to the outer cylinder 2, and the damper unit 32 reacts between the inner and outer cylinders 6,2.

A linear bearing assembly generally referenced 48 is mounted within the inner cylinder 6. The assembly 48 comprises a lower section 50 bolted or otherwise securely attached to the inner wall of the cylinder 6, and an upper section 52 mounted on the lower section 50 to be slidable therealong.

Bolted to the upper section 52 of the bearing 48 is the cylinder 54 of an hydraulic piston-cylinder assembly indicated generally at 56 and also including a piston 58 extending from the cylinder 54.

The free end of the piston 58 is secured to the disc 12, and is locked thereto by a lock nut 60, thereby effectively attaching the piston 58 to the fixed outer cylinder 2.

An hydraulic valve 62 for the assembly 56 is mounted on the cylinder 54, as is a solenoid-operated control switch 64 for the valve 62, an electric cable 66 feeding from the switch 64 through a protective covering 68 housed in a channel in the wall of the inner cylinder 6, through a watertight connector 70 in the wall of the outer cylinder 2 and thence through a protective shroud 72. The cable 66 is connected to the brake lighting circuit of the prime mover to which the trailer is coupled by the coupling member 10.

The piston-cylinder assembly 56, the valve 62 and the switch 64 comprise a unitary construction mounted on the upper section 52 of the linear bearing 48.

A support plate 74 is secured to the cylinder 54 of the assembly 56, the free end of the piston 42 of the damper unit 34 being attached to the support plate 74 and locked thereto by a lock nut 76.

Grease nipples 78 are provided in the outer cylinder 2 to enable lubrication of the bearings 8.

The described tow coupling operates as follows.

The end cap 24 is screwed into the inner cylinder 6 to engage the disc 12 by way of the washer 26 to apply the desired pre-load to the piston-cylinder assembly 56 and to the damper units 32,34, the cap 24 being retained

in its operative position by a grub screw 80 projecting from the inner cylinder 6 into a groove in the end cap 24.

The bolt 28 and lock nut 30 are adjusted to determine the desired setting of the lever arm of the trailer's braking mechanism.

During normal towing of the trailer, the hydraulic valve 62 is closed, which serves to lock the piston 58 of the assembly 56 relative to the cylinder 54 thereof.

Thus the assembly 56 is fixed relative to the outer cylinder 2, thereby, by way of the plate 74, fixing the piston 42 of the damper unit 34 relative to the outer cylinder, the piston 38 of the damper unit also being fixed relative to the outer cylinder 2 by its connection to the disc 12.

It will thus be appreciated that, on relative sliding movement between the inner and outer cylinders 6,2, the cylinders 36,40 of the damper units 32,34, which are arranged to move with the inner cylinder 6, move relative to the associated pistons 38,42 to create a damping effect which is a combination of the effects provided by the units 32,34, and the brakes on the trailer are actuated dependent upon the extent of the relative movement to which the braking lever (not shown) is subjected by the bolt 28.

Such heavy duty damping, although also provided in on-road conditions, is particularly advantageous under rough off-road conditions and can readily absorb the

buffeting and oscillations to which the tow coupling is subjected under such conditions.

During such damping, it will be understood that there is relative movement between the outer cylinder together with its attached components, and the inner cylinder and its attached components.

The piston-cylinder assembly 56, which is rigid under such conditions, is effectively attached to the outer cylinder 2 through the connection of the piston 58 to the disc 12, the movement of the inner cylinder 6 relative to the outer cylinder 2, and therefore to the assembly 56, being accommodated by relative sliding movement between the upper and lower sections 52,50 of the linear bearing 48.

On braking of the prime mover, whether under on- road or off-road conditions, the solenoid switch 64 is actuated as a result of actuation of the brake lighting system of the prime mover, this switch 64 serving to actuate hydraulic control valve 62.

This valve 62, once opened, allows unrestricted fluid flow within the assembly 56, whereby the piston 58 can move substantially unrestricted within the cylinder 54.

Such a condition of the assembly 56 eliminates the damping effect of the unit 34, as the plate 72, and therefore the piston 58, is no longer fixed relative to the outer cylinder 2.

Thus only the damper unit 32 is operating to apply

the correct damping force for the weight of trailer and according to official requirements for on-road conditions, the trailer brakes being applied in dependence upon movement of the bolt 28.

Once braking of the prime mover is terminated, the switch 64 closes the valve 62 whereby hydraulic fluid within the assembly 56 free-flows within the cylinder 54 to the opposite side of the piston to return the assembly 56 to its locked condition.

Thus there is provided a tow coupling between a trailer and a prime mover so arranged that, when towing on civilian road or over rough terrain, or when using only the engine and gears of the prime mover to retard the trailer's speed as during a steep decline, and when both the damper units operate to retard the weight of the trailer, the unit comprising the piston-cylinder assembly 56, hydraulic valve 62 and solenoid switch 64 slides along the lower section 50 of the linear bearing 48, and the trailer's brakes are applied without the prime mover's brakes being applied.

As soon as the brakes on the prime mover are applied, damping of the coupling is effected by a single damper unit, and the trailer brakes are applied conventionally.

The precise construction of the coupling may vary from that described and illustrated without departing from the scope of the appended claims. In particular, the means by which the effect of the second damper unit

is eliminated from the coupling on actuation of the prime mover brakes may be other than a hydraulic piston- cylinder assembly under the control of a solenoid actuated valve.

Other modifications and variations will be apparent to those skilled in the art.