GB2484471A - Caravan or trailer braking system having an override associated with a reverse light - Google Patents

Abstract

Caravans and trailers over-run braking systems can be augmented with a second system comprising a compressed air actuator 10 which is activated to apply the drawn vehicle's brakes upon receiving an electrical braking signal from the towing vehicle, preferably from the brake lights. Prior systems act to apply the drawn vehicle's brakes even when the vehicle is reversing. This is overcome by providing means to receive a signal associated with the reverse light of the towing vehicle and in response to a signal from the reversing lamp acts to disengage the second system.

Description

An Improved Braking System for a Caravan or Trailer The present invention relates to an improved braking system for a drawn vehicle, and in particular for a caravan or trailer.

Figure 1 illustrates a caravan chassis C incorporating an over-mn braking system. The system, as illustrated in a simplified form in Figure 2, comprises a towing shaft 1, housed within shroud 1A, which is connected to the tow bar B (not shown in Fig 1) of a tow vehicle by a coupling head 2. Drum brakes 3 are mounted within wheels 4 rotatably mounted to the chassis 10. The drum brakes 3 are connected by cables S to one end of a brake rod 6 by balance bar 8. The brake rod 6 extends towards the front of the chassis C terminating substantially in the vicinity of the towing shaft 1. The front end of the brake rod 6 is pivotally mounted to a first end 7A of a lever 7. The other end 7B of the lever 7 is arranged to abut a free rearward end 2A of the towing shaft 2. Between ends 7A & 7B, the lever is pivotally mounted at 7C to shroud lA.

When the tow vehicle brakes, equal and opposite forces are generated between the lever 7 and towing shaft 1. Because the lever 7 is free to move, it rotates clockwise (as viewed in figure 2) about pivot 7C, drawing brake rod 6 forward. This action is transmitted via the rod 6, through the cables 5 to operate the drum brakes 3 within the wheels 4.

It is often necessary to reverse the caravan whilst it is still hitched to the tow vehicle.

Moving the tow vehicle in reverse, however, mimics the forces which arise during braking, causing lever 7 to rotate and the brakes 3 to engage. In order to prevent the brakes 3 from being applied, the drum brake 3 comprises a mechanism which, in response to the wheel 4 moving in a reverse direction, acts to disengage the brake shoes from the drum. The caravan is then free to travel in the reverse direction, notwithstanding that the brake rod 6 is in a drawn position.

Once the tow and drawn vehicles start to move forward again, the forward motion of wheels 4 acts to move the brake shoes to their normal neutral position. At the same time, lever 7 rotates anti-clockwise back into a non-braking position.

Figure 3 illustrates an improved prior art system in which the brake rod 6 is drawn by an air operated actuator arranged to operate the brake 3 when a brake light of a tow vehicle is activated. The actuator is mounting on a supporting member 13 which is bolted between struts Cl and C2 of chassis C. This system can operate the brakes 3 earlier than the over-run system, improving braking effectiveness, and reducing the likelihood of snaking.

The actuator comprises a bellows having chamber 10 adapted to be filled with compressed air, and a diaphragm 11 which reciprocates within the chamber 10 depending upon the air pressure therein. The diaphragm 11 is connected by a piston 12 to one end of a lever 15. The brake rod 6 is divided into front and back parts 6A, 6B each hinged to the lever such that an outward movement of the diaphragm 11 causes the lever 15 to rotate clockwise about its hinged connection to the front rod 6A. This rotation causes the rear brake rod 6B to be pulled forward to operate the brake 3.

Air is supplied to the chamber 10 through inlet 1OA until predetermined air pressure is reached. Controlling the braking force provided by the actuator is achieved by selecting the predetermined air pressure within the chamber 10. A higher pressure allows the piston 12 to exert a stronger pulling force on the brake rod 6, effecting harder braking.

When the drawn vehicle C is towed in reverse, the over-mn system activates, and the mechanism within wheels 4 reacts to the reverse movement to disengage the brake 3 and relax the brake cables 5 and rod 6. The lever 7, which has already rotated clockwise, does not pull further upon brake rod 6, and so does not operate the brake for the remainder of the reverse movement.

It is common during reversing movements for the driver to lightly touch the brake pedal. This is enough to activate the brake lights, and so will also operate the actuator. The chamber 10 is filled with compressed air until the predetermined pressure is reached. Because of the linkage has been relaxed by the anti-braking mechanism, the actuator has the effect to further pull rod 6 which, notwithstanding the presence of the anti-braking mechanism, causing the brakes 3 to be re-applied.

The present invention was conceived to overcome this problem.

The invention will now be described by example with reference to the following figures in which: Figure 1 illustrates a caravan chassis having an over-run braking system; Figure 2 is a schematic illustrating, in simplified form, the over run braking system; Figure 3 illustrates a brake system of the prior art, adapted to be installed on the caravan chassis of Figure 1; the system being operative to activate the caravan's brakes when the brake lights of a tow vehicle are activated; Figure 4 illustrates an improved brake system adapted to be installed on the caravan chassis of Figure 1; the system being operative to activate the caravan's brakes when the brake lights of a tow vehicle are activated; and Figure 5 shows schematically, further components of the brake system of Figure 4.

Referring to Fig 4 there is shown an actuator comprising a bellows comprising a chamber 10 having an inlet/outlet 1OA for compressed air. A diaphragm 11 is seated within the chamber at 1 OB and can flex and expand towards or away from the inlet/outlet 1 OA.

A piston 12, secured at one end to the diaphragm, sits partially within the chamber 10, and can reciprocate with the movement of the diaphragm 11. A spring 110 biases the piston 12 and diaphragm 11 towards the inlet/outlet 1 OA.

The actuator is mounted onto a supporting member 13 which traverses the two converging struts Cl, C2 forming a frontward portion of a caravan chassis C. Clamps 14 at each end of the supporting member 13 provide means for attachment to the caravan chassis C. A piston rod 12B, connected at one end to the piston head 12A extends out the chamber 10 and is pivotally mounted 15B to a first end iSA of a pivot bar 15. The second end 1 SC of the pivot bar 15 is pivotally mounted at 1 SD to the supporting member 13 by an adjustable link rod 16. The link rod 16 has a threaded portion 16A which can be used in conjunction with nut I 6B to move end i SC towards or away from supporting member 13.

A first end 17A of a rigid pull plate 17 is pivotally mounted to the pivot bar 15 at a position between iSA and iSC. The pull plate 17 extends towards the back of the caravan C. The distal end 17B comprises an aperture used in conjunction with a clip (not shown) for connection to a length of flexible metal cable 18, which is in turn is connected to a clamp 19. The clamp secures the cable 18 to the brake rod 6 at a position rearward of the pivot bar 15.

Fig S illustrates schematically, components of the system typically housed away from the bellows in a more sheltered place; such as the compartment of the caravan provided for the fuse box and battery.

Compressed air is supplied to the chamber 10 by a compressor 20 via conduit 21.

Operation of the compressor 20 is controlled by control unit 22 which may take the form of a solid state relay and switching unit.

An interface is provided at 23 for receiving the brake signal produced when the brake pedal of a tow vehicle is pressed. Similarly, an interface is provided at 24 to receive the reverse light signal produced when the tow vehicle is put into a reverse gear.

Interfaces 23, 24 typically comprise electrical connectors arranged to be connected, through cabling, to an interface associated with the tow vehicle. The interface of the tow vehicle supplies the caravan with necessary signals for its driving lights to illuminate simultaneously with the lights of the tow vehicle.

Signals received at 23 & 24 are forwarded to the control unit 22. Brake signals received at 23 are also fed to a solenoid operated valve 25 located in conduit 21. The valve 25 reciprocates between a first position and a second position. In the first position the conduit between the compressor 20 and chamber 11 is closed, and a vent 26 in fluid communication to the chamber 11 is open. In the second position the conduit to the compressor 20 is open, and the vent 26 is closed. The solenoid is arranged to move the valve 25 from the first position to the second position upon receiving the brake signal from interface 23.

The compressor 20 is connected to an cxtemal power supply 27, which may be the caravan battery used to power electries within the caravan. In certain circumstances, the power may instead be derived from the tow vehicle, though the former source is usually preferred as it can provide a higher ampage.

The system further comprises an air pressure sensor 28 which senses the air pressure within the conduit 21 and output a signal indicative of the magnitude of the air pressure to the control unit 22.

When the brake pedal of the tow vehicle is depressed, it causes a signal to be sent to the brake light of the tow vehicle, and through an electrical interface associated with of the tow bar, to the brake lights of the caravan. This signal is also received at 23.

The brake signal is applied to the solenoid valve 25 which in response moves the valve to the second position establishing a fluid connection between the compressor and the chamber 10.

The brake signal is also received by the control unit 22 which, in response, turns on the compressor 20. Air from the compressor 20 passes, through the conduit 21, to the chamber 10. The increased pressure within chamber 10 flexes the diaphragm against bias 110 pushing piston 12 out of the chamber 10.

Piston 12 acts against the pivot bar 15 causing it to rotate clockwise as viewed in Figure 4 about hinged connection 1 SD. This movement translates as a pulling action on pull bar 17. The force is transmitted through cable 18 and clamp 19 to pull the brake rod 6 towards the front of the caravan C so as to activate the brake 3.

When a specified air pressure is reached, a signal from sensor 28 is received by control 22 which switches off compressor 20. Whilst the brake pedal remains depressed, pressurised air is still retained within the chamber 11 by virtue of the non retum valve 29. Should the pressure subsequently drop, e.g. because diaphragm and piston 12 have moved outwardly, the control unit will restart the compressor 20 until the specified pressure is reached again.

Upon release of the brake pedal, the absence of a brake light signal causes the control 22 to turn off the compressor 20. Solenoid valve 25 reverts to its first position allowing pressurised air within the chamber to be expelled through vent 26. Bias spring 110 causes diaphragm 11 and piston 12 to withdrawn, and lever 15 to rotate anti-clockwise. Brake rod 6 is no longer subjected to a pulling force through cable 18, and so brake 3 disengages.

The pressure required to activate switch 22 is selected depending upon the braking force required. A pressure is chosen which provides sufficient breaking without locking the brakes 3. Whilst the brake pedal remains depressed, the brake will remain in operation.

When the tow vehicle is put into reverse, a signal from interface 24 is received by the control unit 22. For as long as this signal is received, the control unit 22 will not turn on the compressor 20, even if the brake light signal from interface 23 is also received.

In order to prevent damage to the compressor 20 caused by repeated or constant use, the system may also comprise a thermal sensor 30 which senses the temperature of the compressor 20 and outputs a signal indicative thereof to control unit 22. When the sensed temperature is above a pre-determined safe operation limit, the control unit 22 will shut down the compressor 20.

Various modifications to the afore-described example may be made without departing from the scope of the claimed invention. For example the actuator in the above example operates using compressed air as this makes it relatively cheap and simple manufacture. It is also a simple means of providing a graduated braking force.

However, it is possible for other systems to be used. For example the system may use other gases or fluids. Alternatively, the actuator may be driven mechanically or electrically/magnetically; e.g. through use of a solenoid.

Clamps are a preferred means of attachment to the brake rod, and the supporting member to the chassis, because it enables the system to be easily retro-fitted to pre-assembled caravans, and to be moved between caravans if required. Nevertheless, alternative attachment means could be employed such as welding.

The brake system may instead of being attached to the brake rod, be attached to other parts of the brake linkage, e.g. cables, lever or balance bar.

Many variations may be made to the arrangement of the control unit. For example, the pressure sensor may not feed directly to the control unit 22, but instead, be formed as a separate unit incorporating an electronic switch. The sensor/switch unit may be arranged between the interface 23 and the control unit 22 to control the application of the signal between the two. For example, it can be arranged to prevent the brake signal from reaching the control unit 22 once a specific pressure within the braking chamber has been reached, thereby causing the control unit 22 to turn off the compressor 20.

Claims (3)

1. -10 -Claims 1. A braking system for a drawn vehicle comprising a brake connected to a linkage; the braking system comprising an actuator arranged to draw the linkage to activate the brake when a brake light of a tow vehicle is activated; characterised in that the system comprises means to switch off or disengage the actuator when a reverse light of the tow vehicle is activated.
2. 2. A braking system according to claim 1 comprising a compressed air actuator, a pump to supply compressed air to the actuator to draw the linkage, and means to switch the pump off when the reverse light of the tow the vehicle is activated.
3. 3. A drawn vehicle comprising a brake connected to a linkage, having the braking system of claim 1 or 2.