GB2344387A

GB2344387A - An inertia braking system for a trailer

Info

Publication number: GB2344387A
Application number: GB9824850A
Authority: GB
Inventors: Philip Andrew Hanson
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-11-13
Filing date: 1998-11-13
Publication date: 2000-06-07
Also published as: GB9824850D0

Abstract

An inertia braking system for a trailer includes an overrun control device operatively connected to the trailer wheel brakes and adapted to effect trailer braking upon braking of the towing vehicle, and means for manually or automatically selectively inhibiting, at least partially, the braking effect of the overrun control device. As illustrated, in addition to overrun control damper 14, the system includes a supplementary damper 32 and associated telescopic strut 34. When used off-road, hydraulic cylinder 30 repeatedly engages axle beam 24 to incrementally charge strut 34, via a one-way valve 38, so that the supplementary damper then operates to increase the effective damping of the overrun control device. During normal highway usage, the hydraulic cylinder is not operated, so that the strut is uncharged and the supplementary damper is inactive. Fluid returns to reservoir 40 via a bleed valve 42. Alternatively, a single damper (44, Fig.5) charged by cylinder 30 may be used.

Description

IMPROVEMENTS IN AND RELATING TO TRAILER BRAKING The present invention relates to an improved inertia braking system for trailers and other towed vehicles which is particularly, though not exclusively, applicable to the use of said trailers/towed vehicles"off-road".

Conventional inertia braking systems typically comprise a hydraulic damper installed inside the towing member (which slides in a housing), the damper being attached to the towing member and the housing. Braking of the towing vehicle causes application of the trailer wheel brakes, via the inertia operated"overrun brake control"damper and associated lever connected to the trailer wheel brakes.

Trailers and other towed vehicles over a certain size and/or weight are required by law to have such a system, and the inertial braking systems in use on trailers in the EC have to meet performance requirements which are sensitive and ideal for normal highway use.

However, should the trailer be used off-road (particularly at speeds higher than a crawl), the sensitivity of the EC conforming inertia braking system results in unwanted, repeated applications of the trailer brakes. This excessive frequency of braking is disadvantageous, causing a number of technical problems, including damage to the towing equipment, generation of high temperatures at the brakes, and premature failure of the overrun brake control damper. The severity of the effects of these problems range from driver fatigue to potentially disastrous incidents such as failure of the trailer coupling or brakes.

The aim of the present invention is therefore to provide an improved inertia braking system for a trailer (which term is to be interpreted as including any towed vehicle) which overcomes the aforementioned and other disadvantages, and which is particularly suitable for off-road applications.

According to a first aspect of the present invention there is provided an improved inertia braking system for a trailer, the system including a overrun control device operatively connected to the trailer wheel brakes and adapted to effect trailer brakes upon braking of the towing vehicle, wherein the system is provided with means for selectively inhibiting, at least partially, the braking effect of the overrun control device.

The selective inhibition may be implemented manually, but it is prefered that this would happen automatically, for example upon encountering rough"off-road"conditions. Thus, the system is preferably provided with sensor means for determining such conditions, according to a predetermined (fixed or variable) threshold, and effecting inhibition of the braking system accordingly.

Preferably, the system is provided (in addition to the usual overrun control damper), with a supplementary damper and associated telescopic strut, the latter acting to nullify the effect of the supplementary damper during normal highway usage.

The supplementary damper is, as described in the previous paragraph, inactive under normal road conditions. However by means of the strategic positioning of at least one displacement measurement device, which is preferably a hydraulic cylinder, within or associated with the trailer suspension, the supplementary damper can be activated. The supplementary damper then operates to increase the effective damping of the primary overrun control device.

In a hydraulically operated system, this would conveniently be achieved by arranging for the activation of the hydraulic cylinder to cause fluid to be displaced towards the telescopic strut which, once fully charged, effectively becomes a solid strut.

Thus, when on the highway the towing vehicle and trailer with the inertial braking system of the present invention operates conventionally as the additional damper is inactive and the sensitivity of the system is equivalent to EC requirements, whereas on going"off-road", the hydraulic cylinder detects displacement (in the generally vertical direction) above a pre-determined threshold due to rough ground conditions and activates the supplementary damper resulting in reduced trailer braking which would otherwise be detrimental during off-road use.

Alternatively, the same inhibitory effect can be achieved without the use of a supplementary damper/telescopic strut arrangement, and in this alternative embodiment of the invention there is only a single damper which is switchable between high and low damping values. The hydraulic cylinder would then be connected to the single damper and acts to change its damping characteristics according to the degree of displacement detected.

The threshold level referred to above is determined primarily by positioning of the hydraulic cylinder, preferably with a clearance close to or above the level of displacement met by the trailer suspension under normal highway conditions.

Conveniently, there are a number of such hydraulic cylinders disposed at various positions on the trailer, the net effect of these being to"average out"the displacement to avoid the supplementary damper being inadvertently activated whilst on the highway.

In the first mentioned ("telescopic strut") embodiment, since the system may require several cycles of suspension displacement to fully charge the telescopic strut, a nonreturn valve is preferably included in the hydraulic line to enable incremental (cumulative) charging. Also, a relief valve is preferably included to avoid over-charging of the strut, and so that the system can automatically return to the conventional braking action appropriate to normal highway usage means are conveniently provided to cancel the strut pressure quickly and effectively upon returning to the road (which may either be a time delay dumping of the strut fluid, or other means).

Other additional features of the"telescopic strut" embodiment include an oil reservoir (which may be shared with the brake system) to facilitate installation and servicing, a strut manual override to enable selection of the"off-road" mode of operation should the normal road-going damper fail.

According to a second aspect of the present invention there is provided a trailer incorporating an improved braking system according to the sixth paragraph hereof.

According to a third aspect of the present invention there is provided a method of improving an existing inertia braking system of a trailer, the system including a overrun control device operatively connected to the trailer wheel brakes and adapted to effect trailer brakes upon braking of the towing vehicle, the method including provided the system with means for selectively inhibiting, at least partially, the braking effect of the overrun control device.

Embodiments of the present invention will now be described, by way of example only, and contrasted with the prior art, with reference to the accompanying drawings, in which: Figure 1 illustrates the general layout of a conventional trailer overrun control device, Figure 2 illustrates an overrun braked trailer, Figure 3 illustrates the hydraulic cylinder installation, Figure 4 illustrates the first embodiment of the invention, Figure 5 illustrates the second embodiment of the invention, and Figure 6 is a schematic drawing of the hydraulics layout of the system according to the present invention.

Referring to the drawings, a conventional inertia braking system 10 (i. e overrun control device) for a trailer comprises a lever 12 connected to the trailer wheel brakes, and a damper 14 which is usually installed inside the towing member 13 (see solid lines in Fig 1) but may also be installed above, beside or under the towing member (see broken lines for one alternative position).

A trailer 16 generally comprises a payload 18, an overrun control device 10 mounted on drawbar 22, the payload 18 being supported by two or more road wheels 20 mounted on axle 24 by means of one or more suspension members 26.

According to the invention, the normal operation of the braking device 10 is inhibited by fitting a hydraulic cylinder 30 between the axle and the payload, at such a clearance height x above the axle that movement of the axle under normal road conditions would not affect the cylinder and hence the braking system (see Figure 3).

However, upon encountering"off-road"conditions axle movement will increase considerably, the axle beam 24 will impinge upon hydraulic cylinder 30 with consequent inhibitory (de-sensitising) effect on the braking system, as will be described in more detail hereinafter.

In Figure 4, a first embodiment of an improved braking system 28 according to the invention is shown, in which the usual on-highway damper 14 is underslung, and a supplementary damper 32 for off-highway use is fitted within the towing member, in association with a chargeable telescopic strut to which the lever 12' (which is connected to the trailer brakes) is connected. As can be seen in Figure 6, the hydraulic cylinder is connected, within the hydraulic circuit, via line 31 to the telescopic strut 34, whereby each displacement of cylinder 30 (due to axle movement) charges strut 34 incrementally, until it is fully charged and becomes effectively a solid strut. Whilst in the uncharged condition (i. e normal road usage) this strut (which has a stroke equal to or greater than the stroke of the overrun control device 28 and the dampers 32 and 14) telescopes in and out to effectively nullify the supplementary damper 32, whereas once fully charged the supplementary damper 32 is brought into play, effectively desensitising the trailer overrun brake system to such a level as to make towing of the trailer possible without damage to the braking system or towing coupling parts.

To allow incremental charging of strut 34, which acts as a collapsible extension strut of supplementary damper 32, a non-return valve 38 is fitted within line 31. A pressure limiter 36 is also fitted in line 31, to avoid excessive pressure building up, and a hydraulic reservoir 40 is disposed between return lines 33,41 and the cylinder 30.

A bleed valve 42 in return line 41 allows the fluid displaced into strut 34 during charging to be drained back into reservoir 40.

The dampers 14 and 32 for on and off-highway conditions, respectively, may be integrated into one switchable unit, in which case the axle mounted hydraulic cylinder 30 would initiate the switching of off-road mode of operation.

In Figure 5 an alternative (and simpler) embodiment of the invention is illustrated, in which a single damper 44 has high and low damping values and is switchable between the two -in this case the hydraulic cylinder 30 would be connected to the single damper 44 to effect the change of damping values.

Claims

CLAIMS 1. An inertia braking system for a trailer, the system including a overrun control device operatively connected to the trailer wheel brakes and adapted to effect trailer brakes upon braking of the towing vehicle, wherein the system is provided with means for selectively inhibiting, at least partially, the braking effect of the overrun control device.
2. A system as claimed in claim 1 wherein selective inhibition is implemented manually or automatically.
3. A system as claimed in claim 2 wherein the inhibition is implemented automatically upon encountering rough"off-road"conditions.
4. A system as claimed in claim 3 provided with sensor means for determining rough conditions, according to a predetermined (fixed or variable) threshold, and effecting inhibition of the braking system accordingly.
5. A system as claimed in any of claims 1 to 4 wherein the system is provided (in addition to the usual overrun control damper), with a supplementary damper and associated telescopic strut, the latter acting to nullify the effect of the supplementary damper during normal highway usage.
6. A system as claimed in any of claims 1 to 5 wherein the supplementary damper is activated by means of the strategic positioning of at least one displacement measurement device, which is preferably a hydraulic cylinder, within or associated with the trailer suspension, which then operates to increase the effective damping of the primary overrun control device.
7. A system as claimed in claim 6 being hydraulically operated and wherein the activation of the hydraulic cylinder causes fluid to be displaced towards the telescopic strut which, once fully charged, effectively becomes a solid strut.
8. A system as claimed in claim 6 wherein there is only a single damper which is switchable between high and low damping values and the hydraulic cylinder is connected to the single damper and acts to change its damping characteristics according to the degree of displacement detected.
9. A system as claimed in claim 8 wherein the threshold level is determined primarily by positioning of the hydraulic cylinder, preferably with a clearance close to or above the level of displacement met by the trailer suspension under normal highway conditions.
10. A system as claimed in any of claims 6 to 9 wherein there are a number of such hydraulic cylinders disposed at various positions on the trailer, the net effect of these being to"average out"the displacement to avoid the supplementary damper being inadvertently activated whilst on the highway.
11. A trailer incorporating an improved braking system according to any of claims 1 to 10.
12. A method of improving an existing inertia braking system of a trailer, the system including a overrun control device operatively connected to the trailer wheel brakes and adapted to effect trailer brakes upon braking of the towing vehicle, the method including provided the system with means for selectively inhibiting, at least partially, the braking effect of the overrun control device.