WO2006117401A2

WO2006117401A2 - Braking system

Info

Publication number: WO2006117401A2
Application number: PCT/EP2006/062068
Authority: WO
Inventors: Geoffrey Bedding; Nicholas David Bedding
Original assignee: Geoffrey Bedding; Nicholas David Bedding
Priority date: 2005-05-04
Filing date: 2006-05-04
Publication date: 2006-11-09
Also published as: WO2006117401A3; GB0608760D0; GB0509092D0; GB2425811A

Abstract

In a device with one or more movable parts and including a primary hydraulic braking system (1) in communication with, and engageable with, those movable parts, a secondary braking system (4) comprising: means to engage the secondary braking system; means to isolate one or more portions (32) of the primary braking system in communication with one or more movable parts; and means to act on the one or more isolated portions (2) to apply a braking force to the one or more movable parts (3).

Description

BRAKING SYSTEM

The present invention relates to braking systems, in particular to braking systems for machines.

Machines generally include movable parts, and often include the means to cause the parts to move and also to apply a braking force to those moving parts. Automotive vehicles in particular rely heavily on braking systems, and there are many different braking systems available.

Hydraulic brake systems, wherein hydraulic power is used to activate a braking system, were introduced into automotives as an alternative to mechanical brakes.

Operationally, brake systems can be spring or engage, spring return or disengage, and permanent magnet. In spring actuation brakes, a spring is engaged during brake operation and requires power to disengage. Spring return brakes require power to engage, and a spring is used to disengage the brake. Where a permanent magnet is used for brake operation, no electrical power is required for them to operate.

The most common brake systems, friction brakes, operate by friction being caused between contact surfaces transmitting power. Alternatively, toothed contact surface transmitting power without slipping or heat generation, the teeth engaging only when stopped or at low speed, for example speeds of 20rpm or lower. In a non-contact configuration the braking action is provided by a non-contact technology such as magnetic field, eddy currents, etc. Common brake types include band, drum, disc and cone. Band brakes include small metal bands lined with heat and wear resistant friction material, and are the simplest brake configuration. Drum brakes, commonly used on automotive rear wheels, operate by shoes pressing against a spinning surface, called a drum. Cone brakes, comprising a cup and a cone, are lined with heat and wear resistant material, wherein the cone is pressed against the mating cup surface, and are not widely used. Disc brakes comprise brake pads, calliper and rotor. During operation the brake pads are squeezed against the rotor, for which action disc brakes have good heat dissipation properties.

There currently exist hydraulic brakes in the forms of friction, toothed, and non - contact, the relative efficiencies of each being represented by the operating specifications: for example, torque rating (which should equal or exceed application requirements), power (HP), rotary speed, and pressure.

Common features of hydraulic brakes include zero backlash (where there is no play or backlash in the engagement of the load, no load disengagement during a direction reversal); wash down capability (where the brakes are rated for wash down cleaning), and clutch or brake combination (where a clutch and brake are combined). Shaft configuration for hydraulic brakes can be inline, parallel, and right angle. Mounting choices include shaft and flange. Important dimensions to consider include diameter, length, and width.

Callipers form an integral part of many motor vehicle braking systems. They use a hydraulic system to control piston movements by use of, for example, a foot brake system. A brake pedal is connected to pistons in master cylinders and thence by steel tubing with flexible sections to individual cylinders at the wheels, the front and rear hydraulics or other combination being separated. Pressure exerted on the brake pedal is transmitted to the master cylinder which magnifies the force applied. The master cylinder contains a piston that pressurises a network of hydraulic brake lines that lead to each of the vehicle's callipers. The hydraulic pressure this applies in the callipers forces a piston forward which sequentially allows brake pads to be applied to the brake discs, thus bringing the vehicle to a halt and preventing the vehicle from moving further.

Conventionally, vehicles include a handbrake system in addition to the hydraulic braking system and, in contrast to the hydraulic braking system, the handbrake system is mechanical rather than hydraulic. The handbrake system includes a handle, engageable by the driver, and is attached by a cable to the conventional handbrake unit within the rear braking system. The conventional handbrake unit includes a cam adjacent the or each rear wheel which, on engagement of the handbrake, moves against a piston which is thereby forced against one brake pad to prevent the car from moving. The piston applies the inner pad first and then, through the design of the floating callipers, pushes the calliper body until the outer pad comes into contact with the disc causing a pinching motion. This applies direct pressure on one side of the disc and indirectly on the other via the floating body of the calliper. A ratchet system is also required in this system to compensate for brake pad wear.

This conventional handbrake system is safe for use on, for example, vehicles such as conventional automobiles, where the weight of the engine is situated at the front of the vehicle, however in some cases such handbrakes are less suitable. For example in some cars the bulk of the vehicle weight is positioned towards the rear of the vehicle rendering the mechanical handbrake less effective.

The present invention provides, according to a first aspect, in a device with one or more movable parts and including a primary hydraulic braking system in communication with, and engageable with, those movable parts, a secondary braking system comprising means to engage the secondary braking system; means to isolate one or more portions of the primary braking system in communication with one or more movable parts; and means to act on the one or more isolated portions to apply a braking force to the one or more movable parts.

The above and other aspects of the present invention will now be described by way of example only with the aid of the accompanying drawings in which:

Figure 1 shows a diagrammatic view of a portion of the braking system according to a first embodiment with the handbrake system in its non-engaged position, Figure 2 illustrates the braking system of Figure 1 with the handbrake in an engaged position, Figure 3 shows a diagrammatic view of the braking system of Figure 1 including the handbrake and calliper,

Figure 4 shows a diagrammatic view of a portion of the braking system according to a second embodiment, with the handbrake system in a non-engaged position, Figure 5 shows the system of Figure 4 with the handbrake system in an engaged position,

Figure 6 shows a diagrammatic view of the braking system of Figure 4 including the handbrake system and calliper, and

Figure 7 shows a diagrammatic view of the braking system of Figure 5 including the handbrake system and calliper.

Figure 8 shows a plan view of a portion of the braking system at a calliper according to a second embodiment, with multiple pistons.

Figure 9(a)-(c) shows an inlet seal.

Figure 10 shows the arrangement of Figure 8 with the inlet seal of Figure 9 in position.

A first embodiment of the present invention will now be described. With reference to Figure 1, point (1) is the main fluid inlet. The main fluid inlet is part of the conventional hydraulic braking system of a vehicle and connects brake components at a wheel of the vehicle with the brake pedal (not shown). Fluid in the hydraulic braking system is in fluid communication with the slave cylinder compression chamber 2 via main fluid inlet 1. A compressive force is applied to the brake fluid in chamber (2) as the brake pedal of the vehicle is pressed forcing fluid into the calliper and slave cylinder compression chamber 2. The compressive force acting on fluid in the chamber 2 forces piston A (3) into the brake pads at the wheel (not shown), which in turn are forced into contact with the brake disc (not shown). This procedure is common to foot braking.

In the non-engaged position of Figure 1 brake fluid can flow from the main fluid inlet 1 into the slave cylinder compression chamber 2 through main fluid inlet opening 32.

Pressure exerted on and removed from the brake pedal (not shown) urges fluid into and out of the calliper and the slave cylinder compression chamber 2, affecting the pressure of the fluid in the chamber and thereby engaging and disengaging the brake in a conventional manner. As can be seen in Figure 1 the handbrake activating arm 12 is in a non-engaged position (4), and the handbrake is not engaged. In this position the braking system acts conventionally, in that the pressure in the calliper and chamber 2, and thus the braking performance, is directly related to the pressure on the brake pedal (not shown) itself.

Both Figures 1 and 2 show, in addition to the components of a conventional braking system already described, components of the handbrake system of a first embodiment of the present invention. These components include a first piston 7, a second piston 8, a first spring 10 positioned between first and second pistons, a second spring 22 in the slave cylinder compression chamber, between the first piston 7 and piston 3, an 'O' ring 9 and seal 11, for example a conventional lip seal.

Referring now to Figure 2, the handbrake activating arm 12 is shown in an engaged position (5), rotated in an anticlockwise direction about pivot point 20 in relation to its position in Figure 1, creating pressure at point 6 on second piston 8. As a result second piston 8 is pushed towards first piston 7 which is in turn pushed into the slave cylinder compression chamber 2 increasing pressure in the calliper and in chamber 2. Consequently piston A (3) is forced, as before, into the brake pads which come into contact with the brake disc, thus working to the same principle as standard hydraulic brake systems.

As the handbrake mechanism is engaged, and the first and second pistons 7 and 8 are forced further into chamber 2, seal 11 around first piston 7 passes across main fluid inlet opening 32 providing a barrier inhibiting passage of brake fluid between the main fluid inlet 1 and the calliper and slave cylinder compression chamber 2, and retaining the brake fluid in the calliper and slave cylinder compression chamber 2. As seen in Figure 2, 'O' ring 9 encircles first piston 7 ensuring that fluid flowing through main fluid inlet opening 32 cannot pass through to the handbrake mechanism including second piston 8 and handbrake activating arm 12. The brake fluid trapped in the slave cylinder compression chamber 2 is subject to a compressive force by action of the handbrake activating arm 12, and as described in relation to the conventional hydraulic braking system forces the piston A (3) outwards, applying the brake pads to the disc, and preventing the vehicle from moving. By this means the callipers' hydraulic system is isolated from that of the master cylinder and brake pedal.

Between first piston 7 and second piston 8 there is provided a preloaded spring 10. As discussed, engaging the handbrake forces first 7 and second 8 pistons into the calliper and slave cylinder compression chamber 2 increasing the pressure in the calliper and chamber. In addition, second piston 8 moves towards first piston 7 against the action of the spring 10. During this process, for example when the pressure in the calliper and slave cylinder compression chamber reaches a predetermined pressure, the preloaded spring (10) starts to contract and store energy. On full engagement of the handbrake, second piston 8 is pushed fully into first piston 7 against the action of the spring 10, contracting the spring 10. As the braking system cools to the ambient temperature the discs, pads and brake fluid all contract. As this happens tension in the spring 10 is released, forcing first piston 7 further into chamber 2, maintaining a constant pressure to piston A (3), ensuring the brakes remain engaged and at a constant pressure.

As discussed, seal 11, provided around first piston 7, provides a barrier between the slave cylinder compression chamber 2 and the main fluid inlet 1 when the handbrake mechanism is engaged. The seal provides for fluid to enter the slave cylinder compression chamber 2 through the main fluid inlet opening 32 only when pressure at the main fluid inlet opening 32 is greater than the pressure in the chamber 2. The seal 11 thereby ensures that the brake pedal of the main braking system still works when the handbrake is engaged. This is important in the event that the handbrake is partly engaged and can only act to slow the vehicle and not prevent movement of the vehicle. With the handbrake partly engaged, first 7 and second 8 pistons are positioned as shown in Figure 2, such that piston 7 and seal 11 blocks the main fluid inlet opening 32 thereby blocking entry for hydraulic fluid from the main braking system into the slave cylinder compression chamber 2. 'O' ring 9 prevents access of hydraulic fluid to the second piston 8 and activating arm 12. However, as the seal 11 allows fluid into the slave cylinder compression chamber 2 when pressure at the main fluid inlet opening 32 exceeds the pressure in the chamber 2, the footbrake will remain useable when the handbrake is partly engaged and can act to prevent movement of the vehicle.

When the foot brake is lifted the seal 11 will conventionally allow fluid to leave the calliper until pressure in the slave cylinder compression chamber returns to the pressure of the partially engaged handbrake alone.

The braking system includes a groove 15 extending from the main fluid inlet opening 32 to the 'O '-ring 9. Fluid from the main fluid inlet 1 enters this groove but is prevented from reaching the piston 8 and activating arm 12 by 'O' ring 9. Due to the presence of groove 15 brake fluid can always enter behind the seal 11, regardless of the position of the seal, and the seal will operate as described.

The fixed spring 22 in chamber 2 applies pressure to the pistons 7, 8 and A(3) ensuring that as the hydraulic mechanism is disengaged the pistons return to their non-engaged position, as shown in Figure 1.

Figure 3 shows an overview of the braking system of a wheel of a vehicle including the calliper 33 and secondary braking system according to the first embodiment shown in Figures 1 and 2. As the fluid in the slave cylinder compression chamber 2 is placed under increased pressure by pressure on the brake pedal (not shown) forcing fluid through main fluid inlet opening 32, or by engagement of the handbrake forcing piston 7 into chamber 2, piston 3 moves to engage the brake and brake fluid via calliper portion 33, also urges piston 34 to engage the brake. Figures 4 to 7 show, in addition to the components of a conventional braking system already described, a second embodiment of the present invention. As discussed in relation to the first embodiment, the main braking system of the vehicle (not shown) is in fluid communication with the calliper and slave cylinder compression chamber 2 via main fluid inlet 1, such that pressure on a vehicle brake pedal forces brake fluid through the main fluid inlet opening 32 into chamber 2. As also disclosed above, the compressive force on fluid in the chamber 2 forces pistons 3, 34 into brake pads of the wheel (not shown), which in turn are forced into contact with brake disc (not shown).

Referring now to Figures 4 and 5, handbrake activating arm 12 is shown in non- engaged and engaged orientations; respectively. The handbrake activating arm 12 is pivotable between the two orientations about a pivot point 20 responsive to a handbrake (not shown), and is connected to the handbrake by a cable or other conventional means (not shown).

Figure 4 shows a surface 21 of the activating arm 12 in contact with a base portion 23 of second piston 8, first piston 7 positioned adjacent piston 8 with a spring or springs 10 provided therebetween. As in the first embodiment 'O' ring 9 encircles first piston 7 and ensures that fluid flowing through the main fluid inlet opening 32 cannot pass through to second piston 8 and handbrake activating arm 12. A second 'O' ring 24 is provided around the piston 7 to provide a further seal.

As also shown in Figures 5-7, in the second embodiment the main fluid inlet 1 further includes a one-way value 25, comprising a one-way fluid inlet 26, a valve chamber 28, a seal 27 and also a spring 29. One-way valve 25 is conventional and permits fluid to flow one way through the valve when the pressure on the valve in the direction of flow exceeds a predetermined value.

Figure 4 further shows cap 30, conventionally attached within the braking system, which holds in position the slave cylinder compression chamber spring 22 and valve chamber spring 29. Cap 30 includes openings 35, ensuring that the chamber 2 and valve chamber 28 remain in fluid communication with pistons 3 and 34 calliper portion 33 (see Figures 6 and 7). As already disclosed in relation to the spring 10, the chamber spring 22 compresses as the handbrake arm 12 moves to its engaged position and pressure in the respective chambers increase.

Figure 5 shows the embodiment of Figure 4 with the handbrake -activating arm 12 in an engaged position. From the position shown in Figure 4 the handbrake activating arm 12 has rotated in a clockwise direction about pivot point 20 to the position shown in Figure 5, resulting in surface 21 of the activating arm acting on base portion 23 of second piston 8 urging second piston 8 towards first piston 7, causing spring 10 to compress and urging first piston 7 into the slave cylinder compression chamber 2.

As first piston 7 moves into the chamber 2 'O' ring 24 provides a barrier between main fluid inlet opening 32 and chamber 2, to fluid passing out of the chamber 2 into the main fluid inlet 1, and to fluid passing from the main braking system into the chamber 2. As in the first embodiment, 'O' ring 9 ensures that fluid in the main fluid inlet 1 cannot pass through second piston 8 and handbrake activating arm 12. By this means the hydraulic system at the calliper is isolated from that of the master cylinder and brake pedal when the handbrake is engaged, and pressure on the fluid in the calliper and slave cylinder compression chamber 2 is increased by engagement of the handbrake causing the brakes to act and prevent movement of the vehicle.

Isolation of the chamber 2 from the main fluid inlet 1 in response to engagement of the handbrake provides for the handbraking system to utilise the hydraulic fluid of the main braking system, however, a consequence is that full or partial engagement of the handbrake provides a barrier inhibiting passage of fluid between the main braking system, the slave cylinder compression chamber 2, and the calliper portion 33 via the main fluid inlet opening 32, in response to pressure on the brake pedal. Pressure on the brake pedal increases pressure in the main fluid inlet 1, and with the provision of the barrier between the chamber 2 and the main fluid inlet 1 due to the full or partial engagement of the handbrake, this pressure will result in fluid entering the chamber 2 via the one-way valve 25 when the pressure in the main fluid inlet 1 exceeds a predetermined value. Therefore partial engagement of the handbrake does not prevent the footbrake from having a braking effect.

Figure 6 shows the braking system at a wheel of a vehicle, with the main fluid inlet 1 in fluid communication with the slave cylinder compression chamber 2 and calliper portion 33, such that pressure on a brake pedal (not shown), or engagement of the handbrake (not shown), will cause piston 3 and, via the calliper portion 33, the further piston 34, to engage the brake pads (not shown) and the disc brakes (not shown) of the vehicle.

Figure 7 shows the arrangement of Figure 6 with the handbrake -activating arm 12 in an engaged position. The main fluid inlet opening 32 is blocked by first piston 7 and 'O' ring 24, and 'O' ring 9 further prevents brake fluid reaching the second piston 8 and activating arm 12. Engaging the brake pedal of the main braking system increases pressure in the main fluid inlet 1 and when this pressure exceeds a predetermined value fluid enters one way valve 25 and thereby slave cylinder compression chamber 2 and calliper portion 33.

Figure 8 shows the arrangement of the second embodiment with further pistons 50, 51. Multi-piston braking systems are known, and the features of the present invention may be used with vehicles including 2, 4, 6 or more pistons in which advantageously it is contemplated that the handbrake portions may be used with only one of the pistons. Figure 8 shows this feature with the second embodiment only, however it is contemplated that the arrangement of the first embodiment is also suitable for a multi- piston system. Hydraulic braking systems can lose fluid from many parts of the braking system, and such a loss can reduce the effectiveness of the braking. In the present case loss of fluid would impact the effectiveness of both the main brakes and the secondary, or hand, brake. There is therefore provided, in the main fluid inlet, an inlet seal, 40, shown in Figures 9 (a)-(c), and in Figure 10 in relation to the second embodiment of the present invention. The seal is also useable in the first embodiment of the invention.

As can be seen in Figure 10 the main fluid inlet 1 narrows as it approaches main fluid inlet opening 32, and the inlet seal 40 is positioned adjacent this narrow portion held in place by a weak seal spring 42. The seal is V-shaped with an opening 43 at the point of the V and a shoulder 45 which abuts the narrowing section 41 of the inlet wall, the shoulder 45 holding the seal in place. Fluid passes through the seal opening

43 to enter the slave cylinder compression chamber from main fluid inlet 1, and the shape of the seal prevents fluid from passing from the slave cylinder compression chamber into the main braking system past the inlet seal 40. The weak spring 42 holds the inlet seal 40 in place by the inlet but is sufficiently weak that pressure from within the slave cylinder compression chamber 2 will push the seal away from the narrowing portion of the inlet permitting fluid to pass around the seal and into the main braking system.

Loss of hydraulic fluid from the primary braking system will result in a loss of pressure in the main fluid inlet 1 so that fluid will flow from the slave cylinder compression chamber into the main fluid inlet past inlet seal 40. The spring 42 is sufficiently strong that when pressure of fluid in the chamber 2 falls to a predetermined value the spring 42 will urge the seal 40 against the narrowing portion 41 of the inlet 1, thereby preventing further fluid loss from the chamber. The handbrake will then be useable even thought the primary braking system fails.

In use, the hydraulic brakes of a vehicle may be applied conventionally by actuating a braking foot pedal or other means. According to the present invention a handbrake is provided which also uses the hydraulic braking system, and the handbrake may be used to prevent a vehicle's motion, and maintain it at rest.

Engaging the handbrake causes the handbrake activating arm 12 to rotate about pivot point 20 towards second piston 8 and, by action of the surface 21 of the activating arm against the base 23 of second piston 8, urges second piston 8 against the action of the spring or springs 10 towards first piston 7.

As well as compressing the spring 10, movement of the second piston 8 urges the first piston 7 into the slave cylinder compression chamber 2 compressing the slave cylinder compression chamber spring 22 against the cap 30, and also applying a compressive force on fluid within the chamber 2. The compressive force on the fluid in the chamber 2 forces fluid through openings 35 in the cap 30, urging the piston 3 against the brake pads (not shown) and also forcing fluid into the calliper portion 33 to act on piston 34, thereby applying a braking force and preventing further motion of the vehicle.

Further movement of the vehicle is therefore discouraged by action of the engaged handbrake. While the handbrake is engaged, first piston 7 and seal 11 in the first embodiment, or first piston 7 and 'O' ring 24 in the second embodiment, provide a barrier to entry of fluid into the chamber 2 through the main fluid inlet opening 32, thereby isolating the hydraulic system at the calliper from the main braking system. Therefore when the handbrake is engaged, there is provided a barrier to entry of fluid into the chamber 2 via main fluid inlet opening 32 following pressure exerted on the, for example, footbrake of the vehicle. Disengaging the handbrake results in the first 7 and second 8 pistons returning to the non-engaged positions of Figures 1 and 4, assisted by spring 22, releasing pressure in the chamber 2 and removing the barrier between chamber 2 and the main fluid inlet opening 32, such that pressure on the footbrake will once again result in access to the slave cylinder compression chamber 2 via main fluid inlet opening 32. Following engagement of the handbrake, as the temperature of the components of the braking system approaches the ambient temperature, the components may contract, releasing tension in springs 10 and 22, urging first piston 7 further into chamber 2 and maintaining a constant pressure on piston A ensuring that the brakes remain engaged at a constant pressure.

Partial engagement of the handbrake will cause a drag on the motion of the vehicle, but may not be sufficient to prevent motion entirely. A barrier is provided, in both embodiments, against passage of fluid between the main fluid inlet 1 and the slave cylinder compression chamber 2, but the arrangement of the seal 11 of the first embodiment or one-way valve 25 of the second embodiment permits entry of fluid into the chamber 2 in response to pressure on the brake pedal. Thus the main braking system can be engaged to effect a braking action on the vehicle when the handbrake is fully or partially engaged.

Pressure exerted on the brake pedal when the handbrake is fully or partially engaged will result in fluid from the main fluid inlet 1 entering the slave cylinder compression chamber 2 through the seal 11 of the first embodiment or one-way valve 25 of the second embodiment when pressure in the main fluid inlet exceeds a predetermined value.

Pressure on the footbrake when the handbrake is partially engaged will therefore, above a predetermined pressure, permit utilisation of the main braking system via the brake pedal.

As can be understood, the handbrake of the present invention is fully self-adjusting, by means of the springs 10, 22.

The present invention is not restricted to the details of the foregoing embodiments, for example it is contemplated that the present invention will apply to all kinds of suitable brakes and not just the disc brakes disclosed in the first and second embodiments. In addition, the activating arm may move clockwise or anticlockwise about pivot point 20 when the handbrake is engaged, and alternative, for example alternating conventional means for urging second piston 8 into first piston 7 are also contemplated. The seal provide by the 'O' rings 9 and 24, and the resilient means provided by springs 10, 22 and 29 may also be provided by other means. Also the cap 30 with openings 35 may be replaced by other means to retain the springs 22 and 29 in place while ensuring fluid communication between chamber 2 and calliper portion 33. The inlet seal 40 may have any shape which will provide for the seal to be retained in the inlet 1 and allow fluid to pass through, and may not have a shoulder which abuts a narrow portion of the inlet, and the inlet itself may not have a narrow portion.

Claims

CLAIMS:

1. In a device with one or more movable parts and including a primary hydraulic braking system in communication with, and engageable with, those movable parts, a secondary braking system comprising: means to engage the secondary braking system; means to isolate one or more portions of the primary braking system in communication with one or more movable parts; means to act on the one or more isolated portions to apply a braking force to the one or more movable parts.

2. A device according to claim 1 wherein the device is a vehicle and a movable part is a wheel of the vehicle.

3. A device according to claim 1 or claim 2 wherein each isolated portion includes a slave cylinder compression chamber.

4. A device according to claim 3 wherein the means to act on the one or more slave system compression chambers comprises at least one piston adjacent the chamber, the piston movable between a first position with the secondary braking system not engaged and a second position with the secondary braking system engaged, the piston in the second position applying a compressive force on hydraulic fluid in the chamber thereby applying the braking force.

5. A device according to claim 4 wherein the chamber communicates with the primary braking system by means of a main fluid inlet, and the means to isolate the chamber from the primary braking system comprises providing a barrier between the main fluid inlet and the chamber.

6. A device according to claim 5 wherein the barrier comprises the piston or, if more than one piston, the piston nearest the chamber, when displaced from its first unengaged position, and further isolating means.

7. A device according to claim 6 wherein the further isolating means comprises a seal around the piston, or the nearest piston, the seal permitting hydraulic fluid from the primary braking system to enter the chamber only when hydraulic pressure in the main fluid inlet is greater than hydraulic pressure in the chamber.

8. A device according to claim 6 wherein the further means comprises an 'O' ring around the nearest piston.

9. A device according to claim 8 wherein a one-way valve is positioned in the main fluid inlet, the one-way valve permitting hydraulic fluid to enter the chamber from the primary braking system dependent on hydraulic pressure in the main fluid inlet exceeding a predetermined pressure.

10. A device according to claim 9 wherein the one-way valve further includes a spring.

11. A device according to any one of claims 4 to 10 wherein the secondary braking system iurther includes an 'O' ring around the piston or, if there is more than one piston, around the piston furthest away from the chamber.

12. A device according to claim 11 wherein the means to engage the secondary braking system comprises a handbrake handle.

13. A device according to claim 12 wherein the means to act includes a handbrake activating arm connectable to the handbrake handle.

14. A device according to claim 4, wherein there are two pistons and a spring separates the first and second pistons.

15. A device according to claim 14 wherein as the two pistons are urged into the slave cylinder compression chamber, the second piston is urged towards the first piston against the action of the spring.

16. A device according to claim 15 wherein when the handbrake is engaged, the spring acts to maintain a braking force when the temperature of the braking system approaches the ambient temperature.

17. A device according to claim 16 wherein when the handbrake is engaged, the spring acts to maintain a braking force when the brake components become worn.

18. A device according to claim 15 wherein the slave cylinder compression chamber includes a spring.

19. A device according to claim 14 wherein the handbrake activating arm is movable between a first position with the handbrake not engaged and a second position with the handbrake engaged, responsive the handbrake handle, the arrangement being such that movement of the arm from the first to the second position urges the pistons into the slave cylinder compression chamber.

20. A device according to claim 15 wherein as the two pistons are urged into the slave cylinder compression chamber the chamber spring is compressed between the at least one piston and a piston of the primary hydraulic braking system.

21. A device according to claim 5 wherein the main fluid inlet includes an inlet seal, the inlet seal permitting fluid to flow through the main fluid inlet towards the main fluid inlet opening.

22. A device according to claim 21 wherein the seal is held resiliency in position such that flow from the slave cylinder compression chamber and into the main fluid inlet is resisted by the seal unless pressure in the flow direction exceeds a predetermined value.

23. A vehicle including the secondary braking system of the preceding claims.

24. A machine including the secondary braking system of the preceding claims.

25. A braking system including the secondary braking system of the present invention.

26. A device substantially as herein described with reference to the accompanying drawings.