GB2551313A

GB2551313A - Over-run braking mechanism

Info

Publication number: GB2551313A
Application number: GB1609534.1A
Authority: GB
Inventors: George Williams Stephen
Original assignee: Tbd (owen Holland) Ltd
Current assignee: Tbd (owen Holland) Ltd
Priority date: 2016-05-31
Filing date: 2016-05-31
Publication date: 2017-12-20
Anticipated expiration: 2036-05-31
Also published as: GB2553636A; GB2553636B; GB2551313B; GB201710239D0; GB201609534D0

Abstract

An over-run brake has a housing 15 for coupling to a trailer has a stop fixed to the housing with an aperture through which a bar 20 slides with a first end acting on a brake lever 25, a resilient compression member 35 reacting against the first end of the bar and the stop 17, and a compression spring 30 reacting against a second end of the bar and the stop 17. A metal washer and nylon pad 23 can slide with the bar, and a rubber bush used instead of a spring as the resilient compression member. The bar can be a pivoted tow bar or draw bar mounted on a turntable (11, fig 2), with gusset plates (160, figs 4-6) to resist bending when contact a towing vehicle. The trailer can be a dolly or bogie with rollers (7, fig 1) for aircraft luggage, with snatching damped when in a train.

Description

OVER-RUN BRAKING MECHANISM

FIELD OF THE INVENTION

[0001] The present invention relates to an over-run braking mechanism, a draw bar comprising the over-run braking mechanism and a trailer or dolly comprising the draw bar.

BACKGROUND OF THE INVENTION

[0002] Over-run or surge braking mechanisms are commonly fitted to towed trailers, and use the motion of the trailer relative to the towing vehicle to automatically actuate the trailer brakes. As the towing vehicle brakes and slows down, the inertia of the trailer continues forward toward (or over-running) the towing vehicle. The over-run brake mechanism comprises a bar attached to the towing vehicle, which slides within a housing. The bar acts on a brake lever, which in turn applies the trailer brakes to slow the trailer. The sliding action of the bar can be controlled by a spring.

[0003] Controlling the speed of the trailer with respect to the speed of the towing vehicle in this way can lead to undesired effects, as the braking action of the trailer responds to the towing vehicle speed but not necessarily in a smooth or optimally synchronised manner. As the over-run braking mechanism actuates the brakes, the trailer is moving faster than the towing vehicle and so the trailer brakes are sharply applied. This has the effect of slowing the trailer quickly, at which point the brakes may be released and the trailer is then moving more slowly than the towing vehicle. The towing vehicle then sharply accelerates the trailer, and this results in the trailer travelling at a higher speed than the towing vehicle, the trailer brakes are sharply applied again, and the cycle continues. Travelling up and down an incline, or reversing, presents further challenges.

[0004] This situation is particularly exacerbated where a single towing vehicle may be towing multiple trailers connected to each other in a train, such as a number of container dollies carrying luggage at an airport. In this situation, the sub-optimal cycle of braking between potentially long trains of dollies results in jolting and jarring, or 'snatching', between adjacent dollies. Frequent heavy braking leads to overloading of the draw bar spring and high maintenance costs. Any pivoting motion between the draw bar and the housing also results in lateral movement between adjacent dollies and hence snaking of the dolly train, which increases towards the end of the train. This presents a combination of safety and maintenance issues. The towing vehicle becomes difficult to drive, and the risk of jack-knifing occurs where the container dollies bind with other dollies whilst snaking or the draw bar is snagged. The train of dollies also operates with high noise levels as a result of the snatching and snaking motion.

SUMMARY OF THE INVENTION

[0005] A first aspect of the invention provides an over-run braking mechanism for a trailer, the mechanism comprising a housing for coupling to a trailer, a bar slidable with respect the housing, and having a first end arranged to act on a brake lever and a second end opposite the first end, a stop fixed to the housing and having an aperture through which the bar extends, a compression spring which reacts against the second end of the bar and the stop, and a resilient compression damper which reacts against the first end of the bar and the stop.

[0006] A second aspect of the invention provides a draw bar for a trailer and having the over-run braking mechanism according to the first aspect.

[0007] A third aspect of the invention provides a trailer having the over-run braking mechanism of the first aspect or the draw bar of the second aspect.

[0008] Advantageously, the over-run braking mechanism of the first aspect provides a simple, low cost and low maintenance design suitable for high usage environments. Additionally, the solution is purely mechanical and avoids the cost or maintenance commitment of a much more expensive and complicated system, for example a pneumatic or hydraulic over-run braking system. The compression damper ensures the braking operation of the trailer is effectively controlled such that oscillation of the compression spring is damped. Issues with snatching and snaking of the attached trailer or trailers is obviated. Brake operation is smoothed and hence ease of use by the operator and associated noise levels are reduced.

[0009] The compression damper may be a compression spring or a bush. The bush may comprise any low cost compressible material, such as a rubber bush or steel spring.

[0010] A trailer is a towed vehicle usually an unpowered vehicle designed for connection to a towing vehicle. The towing vehicle may be a tug, tractor, truck or other vehicle with strong traction power capable of pulling or towing one or more trailers attached in tandem behind the towing vehicle. The towed vehicle or trailer may be a dolly. The dolly may be a bogie. A dolly in its most basic form is a mobile platform. The dolly may be a container dolly adapted for use in ground transportation at an airport, for example to carry luggage to and from an aircraft for loading or unloading.

[0011] A draw bar is also known as a tow bar. The second end of the bar may have a towing eye for coupling to a hitch of towing vehicle or another trailer. The second end of the bar may alternatively have any other suitable tow hitch.

[0012] The housing is connected to a pivot for pivotal connection to a chassis of the trailer.

[0013] A further aspect of the invention provides a draw bar with a gusset plate extending from the draw bar housing. The gusset plate may be shaped to provide one or more contact points which make contact with a towing vehicle or trailer when the draw bar is at a maximum articulation angle. The draw bar may be combined with any other aspect of the invention above.

[0014] The housing may be arranged such that it makes no direct contact with the towing vehicle or trailer at the maximum articulation angle. The housing may have a longitudinal axis, the gusset plate may extend laterally from the longitudinal axis. The gusset plate may include one or more reinforcement portions. The reinforcement portion may be located generally at the one or more contact points.

[0015] The contact point may be a contact zone. The gusset plate provides surfaces of first contact with either vehicle to which the draw bar is attached. This prevents the contact with the container dolly or tug being directly through the draw bar housing.

Advantageously, the gusset plate may be shaped to minimise point loading at potential contact points or zones and to reduce the bending moment on the components within the draw bar. The gusset plate shape also may have one or more narrow or recessed portions, these portions may accommodate the shape of the adjacent vehicle in order to allow a tight turning radius.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the invention will now be described with reference to the accompanying drawings, in which: [0017] Figure 1 is a perspective view of a container dolly with a draw bar according to an embodiment of the invention, [0018] Figure 2 is a plan view of the container dolly and draw bar of Figure 1, [0019] Figure 3 is a cross section through the draw bar of Figures 1 and 2, taken through line A-A in Figure 2, showing an over-run braking mechanism according to an embodiment of the invention, [0020] Figure 4 is a perspective view of a draw bar according to a further embodiment of the invention, [0021] Figure 5 is a view from below the draw bar, showing the draw bar of Figure 4 attached at one end to a towing vehicle via the tow eye, and [0022] Figure 6 is a view from below the draw bar, showing the draw bar of Figure 4 mounted at one end to a container dolly, and attached via the tow eye at the opposing end to a further container dolly. DETAILED DESCRIPTION OF EMBODIMENT(S) [0023] Figures 1 and 2 show a draw bar 1 attached at one end to a container dolly 5. The opposing end of the draw bar 1 attaches to a towing vehicle (not shown). The towing vehicle may be a powered vehicle with or without a driver, i.e. the towing vehicle may be the front or lead vehicle of the towing train of vehicles. Alternatively, the towing vehicle may be a further container dolly 5, such that the draw bar 1 is located attached to vehicles in the central part of a train of towed vehicles. In this embodiment the towed vehicles are container dollies, however any kind of towable vehicle or trailer may be used.

[0024] The container dolly 5 has a chassis 6 onto which a load is placed, for example luggage to be loaded or unloaded from an aircraft as part of a ground transportation system at an airport. The chassis 6 comprises an upper platform having radiused corners. A plurality of spaced apart rollers or inverted castors 7 is arranged on the surface of the chassis 6. In this embodiment, the rollers 7 are located in rows extending transversely across the chassis 6, illustrated generally perpendicular to the longitudinal axis of the container dolly. The longitudinal axis is in the direction of travel of the container dolly 5. The rows of rollers 7 are arranged generally spaced apart and in parallel to each other and distributed along the longitudinal axis of the container dolly 5, so as to extend over the top surface of the chassis 6. In alternative embodiments, the rollers 7 could be placed in any arrangement and in any orientation or array of orientations covering part or the majority of the surface of the chassis 6. The rollers 7 allow luggage to be easily manoeuvred on to and off the container dolly 5. A central set of plates 7A provide a walkway for operators to work on and around the sides of the container dolly 5.

[0025] The container dolly 5 has four wheels 10 located generally at each corner of the platform. At least some of the wheels comprise brakes. The rear, non-steered wheels are braked. In alternative arrangements, the container dolly may have only two wheels, or more than four wheels. All wheels may be braked, or either of the front or the rear wheels may be braked. In multi axle trailers, any combination of wheels or wheel sets located on axles may be braked. Equally steering may be applied to any combination or none of the wheels. A tow hitch 14 is located at the rear of the container dolly 5, to enable further vehicles or container dollies 5 to be attached and so assemble a train of towed vehicles or dollies 5.

[0026] Referring to Figure 2, the draw bar 1 is pivotally mounted to the container dolly 5 at a first end via a turntable 11. Alternatively, an Ackermann steering system could be used. The turntable 11 enables the draw bar 1 and front axle carrying the two front wheels to rotate as the vehicle in front turns through an angle. The draw bar 1 is mounted to the turntable 11 via a fixture arrangement. The draw bar 1 is able to rotate by around sixty degrees clockwise and sixty degrees anti-clockwise relative to a central longitudinal axis 13 of the container dolly 5 to which the draw bar 1 is mounted. The opposing end of the draw bar 1 has a tow eye 12, the tow eye 12 locating to the tow 14 hitch on the vehicle or container dolly in front. The draw bar 1 also includes a flexible barrier hoop 8 located generally between the first end of the draw bar 1 towards the mounting point to the turntable and the tow eye end. The flexible barrier hoop 8 is made of a hard plastic and is designed as a safety feature to prevent an operator or any other person from stepping over the draw bar 1 whilst attached between container dollies 5 and/or a towing vehicle.

[0027] The draw bar 1 comprises a housing 15 attached at the first end to the container dolly 5. The first end comprises a pivot P shown in Figure 2, the pivot providing pivotal connection to the chassis 6. The draw bar 1 is able to pivot vertically for ease of attachment to the vehicle in front. Small gusset plates 4 are located between the housing 15 and the pivot location, forming a triangular brace between the housing and the pivot assembly. In addition, the action of raising the drawbar 1 or lowering the draw bar 1 above/below towing height also leads to the container dolly 5 brakes being activated. This is a safety feature to ensure that the brakes are applied in circumstances where, if released, the container dolly 5 could move off in an uncontrolled fashion. For example, if the container dolly 5 becomes detached from the towing vehicle whilst towing, the draw bar will drop to the ground, or when the draw bar is manually manoeuvred in to raised position for storage. In either case, the brakes application prevents the container dolly 5 from 'run away'.

[0028] Figure 3 provides a cross-sectional view through the draw bar housing 15 according to arrows A-A in Figure 2. The housing 15 is a square section steel tube. The housing comprises a mild steel generally square section tube. In alternative embodiments, any generally rigid material could be used, whether metal, plastic or composite. The housing may be cylindrical rather than square in section, or indeed be formed in any hollow section. The housing has a lifting handle 9 and the draw bar 1 has a hinged attachment to the turntable 11 at the first end, in order that the draw bar 1 can be lifted vertically by hand and attached to a vehicle via the tow eye 12.

[0029] A bar 20 is slidably located within the housing 15. The draw bar is a cylindrical steel shaft, and in alternative embodiments could be formed in any suitably rigid material and be of any cross-section capable of sliding axially within the housing 15. A first end of the bar 20 is located to the tow eye 12. As shown in Figure 3, an opposing, second end of the bar 20 abuts a contact 22 comprising a washer arrangement located on a brake lever 25. As the draw bar slides axially within the housing 15, the brake lever 25 pivots around a fixed axis 27. When the vehicle in front brakes and slows down, the bar 20 slides axially further into the housing 15 towards the brake lever 25. Alternatively, the housing 15 slides further over the bar 20, as the container dolly 5 being towed moves forward towards the vehicle in front which is braking and slowing. The brake lever 25 is thus rotated about fixed axis 27 so as to pull on the brake rod 28 and actuate the brakes at the wheels 7 of the container dolly 5.

[0030] In order to control the axial sliding action of the bar 20 and housing 15, a compression spring arrangement is provided within the housing 15, as will now be described.

[0031] A portion of the bar 20 is slidably located within the housing 15. At or near the point of maximum extension of the bar 20 from the housing 15, the draw bar 15 has a shoulder 22 on which a metal washer and nylon pad arrangement 23 is located (hereafter termed washer arrangement). The shoulder 22 and washer arrangement 23 slide axially with the bar 20 and locate the bar 20 within the housing 15. The housing 15 has a stop 17 fixed rigidly to the housing 15, and located partway along a length of the housing 15. The stop 17 extends radially between the housing 15 and the bar 20. The bar 20 passes through and is supported by the stop 17. Figure 3 shows the stop bolted through the housing 15 wall. A number of alternative fixing means well known in the art is possible. A compression spring 30 is contained between the shoulder 22 and washer arrangement 23 at one end, and one axial face 18 of the stop 17. In this embodiment, the compression spring 30 is a coil spring, and a portion of the bar 20 passes through the compression spring 30. The compression spring 30 is the main spring serving to control and damp the action of the bar 20 as the bar 20 slides axially to operate the brake lever 25. The compression spring 30 has a spring rating sufficient to provide a resilient urging force against the sliding action of the bar 20, in order to provide a controlled operation of the brake lever 25.

[0032] A castellated nut 21 and split spin is located near the second end of the bar 20. A secondary compression member, in this embodiment a compression spring or 'snatch' spring 35, is located between a second axial face 19 of the stop 17 and the castellated nut 21. The snatch spring 35 in this embodiment is also a coil spring, having a stiffer spring rating than the main compression spring 30. The snatch spring 35 acts to attenuate the shock loading of the main compression spring 30 as the bar 20 returns to an axial position where the brake lever 25 is not being operated. When the brake lever 25 is not under actuation by the bar 20, i.e. no braking force is being applied to the trailer, the snatch spring 35 is not under significant compression. Under braking action and with the main compression spring 30 compressed, there may therefore be a gap between the snatch spring 35 and the second axial face 19 of the stop 17 and/or the castellated nut 21 and the spring 35 is unloaded.

[0033] The secondary compression member 35 provides a resilient urging force in the generally opposing direction to the main compression spring. Thus, the mechanism now operates without sudden braking and releasing of the brakes. When the towing vehicle or container dolly in front brakes and slows, the bar 20 slides relative to the housing 15 and activates the brake lever 25. The relative motion between bar 20 and housing 15 is damped by the main compression spring 30, which provides a resilient urging force against the sliding action, the spring rating dictating the resistance and hence level of control. As the container dolly or trailer slows to the speed of the vehicle or dolly in front, the brakes release. If the release is due to rapid acceleration of the towing vehicle or trailer, the secondary compression member 35 attenuates any shock load on the draw bar or trailer.

[0034] A compressible bush could provide the secondary, compression action in alternative embodiments. The bush could be made of any suitable material, for example rubber.

[0035] Figure 4 shows an alternative embodiment of the draw bar 100. The draw bar 100 comprises a set of profiled gusset plates 160 located on either side of the housing 150. These contrast with the draw bar 1 shown in the embodiment of Figure 2, which has no gusset plates. During manoeuvring or in tight turning scenarios, the towing vehicle or the container dolly 5 may contact the housing, exerting an excessive bending moment at contact points along the draw bar 1 and causing damage to the draw bar 1. The gusset plates 160 on the draw bar 100 shown in Figures 4 to 6 are designed to prevent direct contact of either the towing vehicle or the container dolly 5 with the housing 150. Figures 5 and 6 are views from underneath the draw bar assembly, looking up at the draw bar 100.

[0036] Figure 5 shows the part of the draw bar 100 attached to the rear of a towing vehicle 102 via a tow hitch 14. The draw bar 100 is angled relative to the towing vehicle 102, such as may occur in a tight reverse turning scenario. Without gusset plates 160, the edge of the towing vehicle 102 would contact the draw bar 100 with the potential for damage to the draw bar housing 150. The gusset plates 160 have contact zones A arranged to be the potential points or areas of contact with the towing vehicle 102. The contact zones A prevent damage of the draw bar housing 150 by minimising point loading at potential contact zones and reducing the bending moment on the components within the draw bar 100. The addition of gusset plates 160 to the housing 150 of the draw bar 100 strengthens the draw bar housing 150.

[0037] Figure 6 shows the draw bar 100 mounted to a first container dolly 5 and attached to the rear of a second container dolly 5 A via a tow hitch 14. The comer of the container dolly 5 A to which the draw bar 100 is attached via the tow eye 12, is contacting the gusset plate 160. In circumstances where the central longitudinal axis 50 of the first container dolly 5 is at an acute angle (less than 90 degrees) to a central axis 50A of the second container dolly 5A, there is the potential for damage to the drawbar housing 150 on contact with the second container dolly 5A. This situation is only likely to occur when the vehicles are being reversed. The container dolly 5 A potentially contacts the draw bar 100 at contact zone A and also contact zone B. The gusset plates 160 provide the contact with the container dolly 5 A instead of contact being directly through the draw bar housing 150. The gusset plates 160 are shaped to minimise point loading at potential contact zones and to reduce the bending moment on the components within the draw bar. The narrowing of the profile at point C allows the container dolly 5A to locate with the draw bar 100 to provide a tight turning radius. The maximum articulation angle in the further embodiment of the draw bar 100 is maintained relative to the embodiment of the draw bar 1 in Figures 1 and 2. That is to say that the gusset plates 160 do not restrict the maximum articulation angle when compared to the maximum articulation angle of a draw bar 1 having the small gusset plates 4 shown in Figure 2. The wider portions of the gusset plate 160 at points A and B also ensure that the tow eye and the bar 200 are held in position and away from the container dolly 5 A, avoiding undue loading at the tow eye 12.

[0038] The gusset plates 160 have reinforcing plates 54 located at particular contact zones (shown at zones A and B in figures 5 and 6) in order to increase the surface area of contact points and hence provide additional strength to the gusset plates 160.

[0039] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. An over-run braking mechanism for a trailer, the mechanism comprising a housing for coupling to a trailer, a bar slidable with respect the housing, and having a first end arranged to act on a brake lever and a second end opposite the first end, a stop fixed to the housing and having an aperture through which the bar extends, a compression spring which reacts against the second end of the bar and the stop, and a resilient compression member which reacts against the first end of the bar and the stop.

2. An over-run braking mechanism according to claim 1, wherein the compression member is a compression spring.

3. An over-run braking mechanism according to claim 1, wherein the compression member is a bush.

4. A draw bar for a trailer and having the over-run braking mechanism according to any preceding claim.

5. A draw bar according to any preceding claim, wherein the second end of the bar has a towing eye for coupling to a hitch of towing vehicle or another trailer.

6. A draw bar according to any of claims 4 to 5, wherein the housing is connected to a pivot for pivotal connection to a chassis of the trailer.

7. A draw bar according to any of claims 4 to 6, further comprising a gusset plate extending from the housing.

8. A draw bar according to claim 7, wherein the gusset plate is shaped to provide one or more contact points which make contact with a towing vehicle or trailer when the draw bar is at a maximum articulation angle.

9. A draw bar according to claim 7 or claim 8, wherein housing is arranged such that it makes no direct contact with the towing vehicle or trailer at the maximum articulation angle.

10. A draw bar according to any of claims 7 to 9, wherein the housing has a longitudinal axis, the gusset plate extends laterally from the longitudinal axis.

11. A draw bar according to any of claims 7 to 10, wherein the gusset plate includes one or more reinforcement portions.

12. A draw bar according to claim 11, wherein the reinforcement portion is located generally at the one or more contact points.

13. A trailer having the over-run braking mechanism or the draw bar of any preceding claim.

14. A trailer according to claim 13, wherein the trailer is a dolly.

15. A trailer according to claim 14, wherein the dolly is adapted for use in ground transportation at an airport.

16. An over-run braking mechanism as substantially herein described with reference to the accompanying drawings.

17. A draw bar as substantially herein described with reference to the accompanying drawings.

18. A trailer as substantially herein described with reference to the accompanying drawings.