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Title:
VEHICLE BRAKING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2021/001795
Kind Code:
A1
Abstract:
This invention concerns a vehicle braking system (10). The system includes at least one service brake (12.1, 12.2) and pressurising means (16) for providing pressurised fluid for controlling actuation of the brake between its disengaged and engaged positions. The system may include a relay valve (22) located between the pressurising means (16) and the brake for controlling operation of the brake. The system may also include a pressure sensing device (46) for automatically actuating a failsafe brake (50.1, 50.2) of the vehicle upon detection of a pressure differential in the system.

Inventors:
GIEZING CHRISTIAAN PETRUS (ZA)
EDER LANCE (ZA)
Application Number:
IB2020/056287
Publication Date:
January 07, 2021
Filing Date:
July 03, 2020
Export Citation:
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Assignee:
COMPACTION TECH PROPRIETARY LIMITED (ZA)
International Classes:
B60T13/14; B60T13/22; B60T17/22
Foreign References:
US6418716B12002-07-16
US5330259A1994-07-19
US3617096A1971-11-02
Attorney, Agent or Firm:
SPOOR & FISHER et al. (ZA)
Download PDF:
Claims:
CLAIMS

1 . A vehicle braking system including:

at least one brake which is operable between a first, disengaged position, wherein the brake is disengaged from a braking element, and a second, engaged position, wherein the brake is engaged with the braking element;

pressurising means for providing pressurised fluid to the at least one brake for controlling actuation of the brake between its disengaged and engaged positions;

a relay valve located between the pressurising means and the at least one brake, wherein the relay valve is operable between a first, inactive configuration, wherein the flow path between the pressurising means and the brake is wholly obstructed and the brake is in the disengaged position, and a second, active configuration, wherein the flow path between the pressurising means and the brake is either partially or wholly unobstructed such that the brake is actuated into the engaged position; and

actuating means for actuating the relay valve between its inactive and active configurations when, in use, the actuating means exerts a force on the relay valve.

2. A vehicle braking system according to claim 1 , including two separate, and distinct, hydraulic sub-systems between the actuating means and the at least one brake.

3. A vehicle braking system according to either claim 1 or 2, wherein the relay valve is positioned to break direct flow communication between the actuating means and the at least one brake such that the actuating means does not directly operate the brake between its disengaged and engaged positions.

4. A vehicle braking system according to claim 3, wherein the force exerted on the relay valve by the actuating means determines the degree by which the flow path between the pressurising means and the brake is obstructed.

5. A vehicle braking system according to any one of claims 1 to 4, including at least one failsafe brake which is operable between a first, disengaged position, wherein the failsafe brake is disengaged from a braking element, and a second, engaged position, wherein the failsafe brake is engaged with the braking element.

6. A vehicle braking system according to claim 5, wherein the pressurising means provides pressurised fluid to the at least one failsafe brake in order to maintain the failsafe brake in its disengaged position.

7. A vehicle braking system according to either claim 4 or 5, including a pressure sensing device configured to detect a pressure drop in a fluid line feeding the at least one brake.

8. A vehicle braking system according to claim 7, including front and rear service brakes, wherein the actuation means is in fluid connection with the front service brakes through a first fluid line and in fluid connection with the rear service brakes through a second fluid line, and wherein the pressure sensing device is connected between the first and second fluid lines so as to sense a pressure differential between the first and second fluid lines.

9. A vehicle braking system according to claim 8, wherein the actuating means includes a brake pedal configured to be actuated by the driver of the vehicle and a master cylinder carrying a piston which is actuated by the brake pedal such that when, in use, the brake pedal is depressed, hydraulic fluid in the master cylinder flows the first line to the front service brakes and through the second line to the relay valve, and wherein the pressure sensing device is configured to detect a drop in pressure in the master cylinder.

10. A vehicle braking system according to any one of claims 7 to 9, wherein the pressure sensing device comprises a bias valve that is actuated automatically upon detection of a pressure differential.

1 1 . A vehicle braking system according to claim 10, wherein the bias valve comprises a normally closed limit switch such that an electrical circuit between the switch and the pressurising means is normally closed and switches to an open position automatically upon detection of a pressure differential by the bias valve.

12. A vehicle braking system including:

at least one brake which is operable between a first, disengaged position, wherein the brake is disengaged from a braking element, and a second, engaged position, wherein the brake is engaged with the braking element;

actuating means for actuating the at least one brake between its disengaged and engaged positions, wherein the actuating means is in fluid connection with the at least one brake through a fluid line;

a pressure sensing device configured to detect a change in pressure in the fluid line;

at least one failsafe brake which is operable between a first, disengaged position, wherein the failsafe brake is disengaged from a braking element, and a second, engaged position, wherein the failsafe brake is engaged with the braking element; and

pressurising means which is configured to actuate the at least one failsafe brake between its disengaged and engaged positions;

wherein the pressure sensing device is connected to the pressurising means such that, in use, when a change in pressure in the fluid line is detected the pressurising means is automatically actuated to operate the at least one failsafe brake from its disengaged position into its engaged position.

13. A vehicle braking system according to claim 12, wherein the pressure sensing device comprises a bias valve which is automatically actuated upon detection of a pressure differential.

14. A vehicle braking system according to claim 13, wherein the pressure sensing device comprises a normally closed limit switch such that an electrical circuit between the switch and the pressurising means is normally closed and switches to an open position automatically upon detection of a pressure differential by the bias valve.

15. A vehicle braking system according to any one of claims 12 to 14, wherein including front and rear service brakes, wherein the actuation means is in fluid connection with the front service brakes through a first fluid line and in fluid connection with the rear service brakes through a second fluid line, and wherein the pressure sensing device is connected between the first and second fluid lines so as to sense a pressure differential between the first and second fluid lines.

16. A vehicle braking system according to claim 15, wherein the actuating means includes a brake pedal configured to be actuated by the driver of the vehicle and a master cylinder carrying a piston which is actuated by the brake pedal, such that when, in use, the brake pedal is depressed, the fluid in the master cylinder flows through the first and second fluid lines to the front and rear brakes, and wherein the pressure sensing device is configured to detect a drop in pressure in the master cylinder.

17. A vehicle braking system according to claim , including a relay valve located between the pressurising means and the at least one brake, wherein the relay valve is operable between a first, inactive configuration, wherein the flow path between the pressurising means and the at least one brake is wholly obstructed and the brake is in the disengaged position, and a second, active configuration, wherein the flow path between the pressurising means and the at least one brake is either partially or wholly unobstructed such that the brake is actuated into the engaged position, and wherein the relay valve is actuated between its inactive and active configurations when, in use, the actuating means exerts a force on the relay valve.

18. A vehicle braking system according to claim 1 7, including two separate, and distinct, fluid sub-systems between the actuating means and the at least one brake.

19. A vehicle braking system according to either claim 1 7 or 18, wherein the relay valve is positioned to break direct flow communication between the actuating means and the at least one service brake such that the actuating means does not directly operate the at last one brake between its disengaged and engaged positions.

20. A vehicle braking system according to claim 19, wherein the force exerted on the relay valve by the actuating means determines the degree by which the flow path between the pressurising means and the at least one brake is obstructed.

21 . A method of activating a failsafe brake of a vehicle, the method including:

detecting a pressure differential in a braking system of the vehicle;

automatically engaging the failsafe brake upon detecting the pressure differential by breaking an electrical circuit between the braking system of the vehicle and pressuring means that retains the failsafe brake in a normally disengaged position.

22. A method according to claim 21 , wherein the step of detecting a pressure differential in the system includes using biasing valve and detecting bias between a first fluid line feeding front service brakes of the vehicle and a second fluid line feeding rear service brakes of the vehicle.

23. A method according to claim 22, wherein the step of automatically engaging the failsafe brakes includes switching a normally closed switch to its open position upon detecting bias between the first and second fluid lines.

24. A method according to any one of claims 21 to 23, wherein the step of detecting a pressure differential in the fluid braking system includes detecting a pressure differential between fluid lines feeding front services brakes and rear service brakes of the vehicles.

25. A method according to any one of claims 21 to 24, wherein the step of detecting a pressure differential in the braking system includes detecting a drop in pressure in a master cylinder in fluid communication with a brake pedal of the vehicle.

Description:
VEHICLE BRAKING SYSTEM

BACKGROUND TO THE INVENTION

This invention relates to a vehicle braking system . In particular, but not exclusively, the invention relates to a vehicle braking system that eliminates the requirement for an intensifier and/or for monitoring brake service pressure.

Vehicle braking systems typically include a master cylinder which is in flow communication with the service brakes of the vehicle. In use, a driver of the vehicle typically depresses a brake pedal which actuates a piston in the master cylinder. This, in turn, compresses the hydraulic fluid such that the service brakes engage their associated brake discs or drums. An intensifier may also be located in the fluid line between the master cylinder and the service brakes in order to assist in the braking process. The intensifier may be necessary to increase the volume of fluid provided by the brake pedal to an operating volume that is sufficient to engage the service brakes. Where an intensifier is used, the direct flow communication between the master cylinder and the service brakes is broken. As a result, a first closed hydraulic circuit or system exists between the master cylinder and the intensifier, and a second closed hydraulic circuit or system exists between the intensifier and the service brakes.

It is known that regular bleeding of the hydraulic fluid in the second closed hydraulic system, between the intensifier and the service brakes, is required to ensure the longevity of the service brakes. Typically, the hydraulic fluid is bled from the hydraulic line and replaced with fresh fluid. Once the system has been bled, a small amount of hydraulic fluid, also known as drag, needs to be removed in order to take into account the effects of heat generation during operation of the braking system . Typically, the heat build-up causes the expansion of the hydraulic fluid in the closed system . If the drag is not removed or if insufficient drag is removed, the expansion of the hydraulic fluid may cause the service brakes to engage their brake discs or drums without the driver of the vehicle depressing the brake pedal. This reduces the longevity of the service brakes, increases maintenance costs and could lead to the service brakes burning out.

The inclusion of the intensifier makes the bleeding of the service brakes a more complex and labour intensive exercise. As mentioned above, the bleeding process is an important process from a maintenance and longevity perspective and should be performed at frequent intervals. However, due to the complexity and difficulty involved in the bleeding process, maintenance is often either insufficiently or incorrectly carried out or entirely neglected, which results in reduced service brake life.

Vehicles, such as mining vehicles, for example LDV’s (light driving vehicles), are often fitted with failsafe brakes which are configured to be employed in the event that the service brakes fail. Failures in the braking system typically occur when the hydraulic lines suppling the front and rear brakes or the master cylinder supplying the brakes with hydraulic fluid fail. Presently, in the event of such a failure, the driver of the vehicle has to engage an emergency switch or button in order to activate the failsafe brakes. Alternatively, the driver may switch off the ignition of the vehicle or open the door of the vehicle in order to activate the failsafe brakes.

Some vehicles include a pressure differential valve which is configured to pick up any pressure differential between the hydraulic lines supplying the front brakes and the hydraulic lines supplying the service brakes. In these known systems, when a pressure drop is detected, a switch is engaged and the driver is made aware of the pressure drop, usually by means of an emergency light located on the dashboard of the vehicle. Once the driver becomes aware of the pressure drop, the emergency switch is engaged manually by the driver so as to activate the failsafe brake.

Any failure of a vehicle’s braking system may lead to serious or even fatal injuries and this is of particular concern in respect of mining vehicles operating in and around mining operations. A significant disadvantage of the known vehicle braking systems is that there is a delay between detecting a failure of the service brakes or the master cylinder and engaging the failsafe brakes. In many instances it takes the driver a while to notice the warning light indicating the failure, after which the driver still has to activate the emergency switch to engage the failsafe brakes. During the time that it takes the driver to notice the failure and engage the failsafe brakes the vehicle may move a significant distance, which may cause serious or fatal injuries to the driver and/or other personnel.

It is an object of this invention to alleviate at least some of the problems experienced with existing vehicle braking systems, and in particular the problems experienced with the servicing of braking systems and/or the failsafe brakes of braking systems.

It is a further object of this invention to provide a vehicle braking system that will be a useful alternative to existing braking systems. It is a further object of this invention to provide a vehicle braking system that will be a useful alternative to existing vehicle braking systems, particularly of mining vehicles.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided a vehicle braking system including:

at least one brake which is operable between a first, disengaged position, wherein the brake is disengaged from a braking element, and a second, engaged position, wherein the brake is engaged with the braking element;

pressurising means for providing pressurised fluid to the at least one brake for controlling actuation of the brake between its disengaged and engaged positions;

a relay valve located between the pressurising means and the at least one brake, wherein the relay valve is operable between a first, inactive configuration, wherein the flow path between the pressurising means and the at least one brake is wholly obstructed and the brake is in the disengaged position, and a second, active configuration, wherein the flow path between the pressurising means and the at least one brake is either partially or wholly unobstructed such that the brake is actuated into the engaged position; and

actuating means for actuating the relay valve between its inactive and active configurations when, in use, the actuating means exerts a force on the relay valve.

The system may be a hydraulic system.

The system preferably includes two separate, and distinct, fluidic sub systems between the actuating means and the at least one brake. The relay valve may be positioned to break direct flow communication between the actuating means and the at least one service brake such that the actuating means does not directly operate the at least one brake between its disengaged and engaged positions.

There is provided for the force exerted on the relay valve by the actuating means to determine the degree by which the flow path between the pressurising means and the at least one brake is obstructed.

The system may include at least one failsafe brake which is operable between a first, disengaged position, wherein the brake is disengaged from a braking element, and a second, engaged position, wherein the brake is engaged with the braking element.

The pressurising means preferably provides pressurised fluid to the at least one failsafe brake in order to maintain the failsafe brake in its disengaged position.

The system may include a pressure sensing device configured to detect a pressure drop in a fluid line feeding the at least one brake.

The system may further include front and rear service brakes, wherein the actuation means is in fluid connection with the front service brakes through a first fluid line and in fluid connection with the rear service brakes through a second fluid line, and wherein the pressure sensing device is connected between the first and second fluid lines so as to sense a pressure differential between the first and second fluid lines.

The actuating means may include a brake pedal configured to be actuated by the driver of the vehicle and a master cylinder carrying a piston which is actuated by the brake pedal such that when, in use, the brake pedal is depressed, fluid in the master cylinder flows the first line to the front service brakes and through the second line to the relay valve, and wherein the pressure sensing device is configured to detect a drop in pressure in the master cylinder. The pressure sensing device may comprise a bias valve that is actuated automatically upon detection of a pressure differential. The bias valve comprises a normally closed limit switch such that an electrical circuit between the switch and the pressurising means is normally closed and switches to an open position automatically upon detection of a pressure differential by the bias valve.

In accordance with a second aspect of the invention there is provided a vehicle braking system including:

at least one brake which is operable between a first, disengaged position, wherein the brake is disengaged from a braking element, and a second, engaged position, wherein the brake is engaged with the braking element;

actuating means for actuating the at least one brake between its disengaged and engaged positions, wherein the actuating means is in fluid connection with the at least one brake through a fluid line;

a pressure sensing device configured to detect a change in pressure in the fluid line;

at least one failsafe brake which is operable between a first, disengaged position, wherein the brake is disengaged from a braking element, and a second, engaged position, wherein the brake is engaged with the braking element; and

pressurising means which is configured to actuate the at least one failsafe brake between its disengaged and engaged positions;

wherein the pressure sensing device is connected to the pressurising means such that, in use, when a change in pressure in the fluid line is detected the pressurising means is automatically actuated to operate the at least one failsafe brake from its disengaged position into its engaged position.

The pressure sensing device may comprise a bias valve which is automatically actuated upon detection of a pressure differential. The pressure sensing device may comprise a normally closed limit switch such that an electrical circuit between the switch and the pressurising means is normally closed and switches to an open position automatically upon detection of a pressure differential by the bias valve.

The system include front and rear service brakes, wherein the actuation means is in fluid connection with the front service brakes through a first fluid line and in fluid connection with the rear service brakes through a second fluid line, and wherein the pressure sensing device is connected between the first and second fluid lines so as to sense a pressure differential between the first and second fluid lines.

The actuating means includes a brake pedal configured to be actuated by the driver of the vehicle and a master cylinder carrying a piston which is actuated by the brake pedal, such that when, in use, the brake pedal is depressed, the fluid in the master cylinder flows through the first and second fluid lines to the front and rear brakes, and wherein the pressure sensing device is configured to detect a drop in pressure in the master cylinder.

The system may further include a relay valve located between the pressurising means and the at least one brake, wherein the relay valve is operable between a first, inactive configuration, wherein the flow path between the pressurising means and the at least one brake is wholly obstructed and the brake is in the disengaged position, and a second, active configuration, wherein the flow path between the pressurising means and the at least one brake is either partially or wholly unobstructed such that the brake is actuated into the engaged position, and wherein the relay valve is actuated between its inactive and active configurations when, in use, the actuating means exerts a force on the relay valve.

The system preferably includes two separate, and distinct, fluidic sub systems between the actuating means and the at least one at least one brake. The relay valve is preferably positioned to break direct flow communication between the actuating means and the at least one service brake such that the actuating means does not directly operate the at least one brake between its disengaged and engaged positions.

The force exerted on the relay valve by the actuating means preferably determines the degree by which the flow path between the pressurising means and the at least one brake is obstructed.

In accordance with another aspect of the invention there is provided a method of activating the failsafe brake of a vehicle, the method including: detecting a pressure differential in a braking system of the vehicle; automatically engaging the failsafe brake upon detecting the pressure differential by breaking an electrical circuit between the braking system of the vehicle and pressuring means that retains the failsafe brake in a normally disengaged position.

The step of detecting a pressure differential in the system may include using biasing valve and detecting bias between a first fluid line feeding front service brakes of the vehicle and a second fluid line feeding rear service brakes of the vehicle.

The step of automatically engaging the failsafe brakes may inlcude switching a normally closed switch to its open position upon detecting bias between the first and second fluid lines.

The step of detecting a pressure differential in the braking system may include detecting a pressure differential between fluid lines feeding front services brakes and rear service brakes of the vehicles.

The step of detecting a pressure differential in the braking system may include detecting a drop in pressure in a master cylinder in fluid communication with a brake pedal of the vehicle BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic view of a first embodiment of a vehicle brake system in accordance with the invention;

Figure 2 shows a schematic view of a second embodiment of a vehicle braking system in accordance with the invention; and

Figure 3 shows a schematic view of a third embodiment of a vehicle braking system in accordance with the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including", "comprising", or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted", "connected", and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings and are thus intended to include direct connections between two members without any other members interposed therebetween and indirect connections between members in which one or more other members are interposed therebetween. Further, "connected" is not restricted to physical or mechanical connections or couplings. Additionally, the words "lower", "upper", "upward", "down" and "downward" designate directions in the drawings to which reference is made. The terminology includes the words specifically mentioned above, derivatives thereof, and words or similar import. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term“include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of a vehicle braking system in accordance with the invention is generally indicated by reference numeral 10.

In this description the vehicle braking system 10 is descried as a braking system for a mining vehicle. Although it is envisaged that the system 10 will be particularly useful for use on a mining vehicle it is envisaged that the system 10 could be used on vehicles other than mining vehicles. It should therefore be understood that the invention is not limited to the use on mining vehicles but could be used on other vehicles across different industries.

The vehicle braking system 10 includes a at least one brake, particularly two rear service brakes 12.1 , 12.2 mounted on the vehicle. The service brakes 12.1 , 12.2 are operable between a first, disengaged position wherein the brakes 12.1 , 12.2 are disengaged from braking elements in the form of brake discs or drums 14.1 , 14.2, for example, and a second, engaged position wherein the brakes 12.1 , 12.2 are engaged with the brake discs or drums 14.1 , 14.2. The braking system 10 further includes pressurising means 16 for providing pressurised fluid to the service brakes 12.1 , 12.2 in order to actuate the brakes 12.1 , 12.2 between their disengaged and engaged positions. The system 10 may be a hydraulic system and it is envisaged that the pressurising means 16 could be in the form of a hydraulic power pack with an accumulator 18 and emergency dump valve 20.

The braking system 10 further includes a relay valve 22. The relay valve 22 is located between the power pack 16 and the service brakes 12.1 , 12.2. The relay valve 22 is configured to be actuated between a first, inactive configuration, wherein the flow path between the power pack 16 and the service brakes 12.1 , 12.2 is wholly obstructed, and a second, active configuration, wherein the flow path between the power pack 16 and the service brakes 12.1 , 12.2 is either partially or wholly unobstructed. In the first, inactive configuration of the relay valve 22 the service brakes 12.1 , 12.2 are in their disengaged position while in the second, active configuration the service brakes 12.1 , 12.2 are actuated into their engaged positions. The relay vale 22 is therefore used to operate the service brakes 12.1 , 12.2 between their disengaged and engaged positions. The power pack 16 is in flow communication with the relay valve 22 via hydraulic line 24. A second hydraulic line 26 then connects the relay valve 22 with the service brakes 12.1 , 12.2. The relay valve 22 provides flow communication between the hydraulic lines 24, 26 when in its active configuration.

The braking system 10 includes actuating means 28, preferably comprising a brake pedal 30 and master cylinder 32, to actuate the relay valve 22 between its inactive and active configurations. The relay valve 22 is actuated by a force being exerted on the relay valve 22. When the brake pedal 30 is depressed, a piston within the master cylinder 32 displaces hydraulic fluid out of the master cylinder and to the relay valve 22 via hydraulic line 34. The displaced hydraulic fluid then typically exerts a force on a valve element of the relay valve 22 which momentarily, or as long as the force is maintained, actuates the relay valve from its inactive configuration into its active configuration, wherein hydraulic fluid is directed from the power pack 16 to the service brakes 12. When the brake pedal 30 is released, the pressure of the hydraulic fluid on the valve element of the relay valve 22 is released and the relay valve 22 returns to its inactive configuration. Once the flow path between the power pack 16 and the service brakes 12.1 , 12.2 is once again wholly obstructed, an exhaust port 36 of the relay valve 22 opens to allow the hydraulic fluid in the service brake chambers to be dumped.

In the illustrated embodiment of the system 10, the actuating means 28 also actuates front service brakes 38.1 , 38.1 of the vehicle, which may be disc brakes for example. Similar to the service brakes 12.1 , 12.2, the front service brakes 38.1 , 38.2 are operable between disengaged and engaged positions. The master cylinder 32 is in flow communication with the front service brakes via hydraulic line 40. In this configuration, the actuating means 28 also actuates the front disc brakes 38.1 , 38.2 of the vehicle between their disengaged and engaged positions.

From Figure 1 it should be understood that the baking system 10 defines a first hydraulic system or circuit 42 for providing hydraulic fluid to the service brakes 12.1 , 12.2 and a second hydraulic system 44 for providing hydraulic fluid to the service brakes 38.1 , 38.1 . A pressure sensing device 46 for sensing or detecting a change in the pressure within the first and second hydraulic systems 42, 44, in particular in the hydraulic lines 34 and 40 that feed hydraulic fluid to the service brakes 12.1 , 12.2 and the front service brakes 38.1 , 38.2.

It is envisaged that the pressure sensing device 46 could be in the form of a proportioning valve or bias valve. The bias valve 46 is fitted in the lines 34 and 40 at a position between the master cylinder 32 and the service brakes 12.1 , 12.2 and 38.1 , 38.2 respectively. In use, upon detection of a pressure differential between the first 42 and second 44 hydraulic systems, the bias valve 46 is automatically activated. The bias valve 46 has a switch 48 is designed to be switched between an open and a closed position upon detecting any bias in the lines 34 and 40. In the preferred embodiment of the system 10, the switch 48 is a normally closed switch such that, upon detection of a bias in the lines 34 and 40, is automatically switched to its open position. In use, when the pressure in the hydraulic line 34 in the first hydraulic system 42, the pressure in the hydraulic line 40 in the second hydraulic system 44, or the pressure in the master cylinder 32 drops, the bias valve 46 will detect the bias, which in turn automatically actuates the switch 48 from its closed to its open position. More about the operation of the switch 48 is said below.

The braking system 10 also includes at least one failsafe brake, preferably two failsafe brakes 50.1 , 50.2. The failsafe brakes 50.1 , 50.2 are preferably spring applied, hydraulic release failsafe brakes. The brakes 50.1 , 50.2 are again operable between a first, disengaged position wherein a hold off pressure acts on the brakes 50.1 , 50.2 such that they are disengaged from braking elements in the form of a brake discs or drums, for example, and a second, engaged position wherein the hold off pressure is released and the brakes 50.1 , 50.2 are engaged with the brake discs or drums. In the illustrated system 10, the braking elements 14.2, 14.2 on which the service brakes 12.1 , 12.2 act are the same braking elements on which the failsafe brakes 50.1 , 50.2 act. However, this is not essential to the invention and the failsafe brakes 50.1 , 50.2 could engage different braking elements.

The hold off pressure maintaining the failsafe brakes 50.1 , 50.2 in their disengaged positions is provided by the power pack 16. The power pack 1 6 supplies continuous pressure to the failsafe brakes 50.1 , 50.2 via hydraulic line 52 in order to keep them disengaged from the braking elements 14.1 , 14.2. In use, the failsafe brakes 50.1 , 50.2 are typically engaged when the pressure sensing device 46 detects a bias between the pressure in lines 34 and 40 resulting from a drop in pressure. This detection of the pressure differential actuates the switch 48 move from its closed to its open position. The switch 48 is connected to the power pack 16 through a normally closed electrical circuit 54 such that activation of the switch breaks the circuit. By breaking the circuit, a solenoid in the power pack 16 deactivates the emergency dump valve 20 thereby releasing the hold off pressure acting on the failsafe brakes 50.1 , 50.2. This allows the failsafe brakes 50.1 , 50.2 to engage the brake discs or drums 14.1 , 14.2 as a result of their spring bias. Upon release of the pressure, the failsafe brakes 50.1 , 50.2 are automatically moved from their released to their engaged positions to engage their respective brake discs or drums 14.1 , 14.2. The system 10 of the invention therefore eliminates the need to engage the failsafe brakes 50.1 , 50.2 manually when the driver notices a drop in pressure.

It is envisaged that the system 10 will include a safety feature that, after activation of the failsafe brakes 50.1 , 50.2, require an inspection of the system by an authorised person, such as a certified technician for example, in order to disengage the failsafe brakes. This safety feature therefore ensures that the braking system 10 is in a fully operational condition before allowing the system 10, and in particular the switch 48, to be reset. In other words, this safety features prevents the failsafe brakes 50.1 , 50.2 from being disengaged while the system 10 is defective.

In the system 10 only the service brakes 12.1 , 12.2 of the vehicle are actuated via the relay valve 22. The service brakes 38.1 , 38.2 and the failsafe brakes 50.1 , 50.1 bypass the relay valve 22. The service brakes 38.1 , 38.2 are actuated by the master cylinder 32 while the failsafe brakes 50.1 , 50.2 are acquitted by the pressuring sensing device 46.

From the above description of the system 10 it should be clear that a significant advantage of the system is that the failsafe brakes 50.1 , 50.2 are automatically activated in the event of a hydraulic failure in the system. As a result, the delays in applying the failsafe brakes of the known braking systems are eliminated, thereby reducing braking distances and preventing uncontrolled movement of the vehicle in the case of a hydraulic failure.

Another significant advantage of the braking system 10 of the invention is that there is no longer a need to include an intensifier in the system . The maintenance and servicing procedures are therefore simplified significantly. As a result, the service life of the brakes is improved which, in turn, leads to reduced operational and maintenance costs. It is also envisaged that failure rates will be reduced due to the improvements in the servicing of the braking system 10 obtained as a result of the invention. These advantages are achieved by, amongst others, eliminating the need for the actuating means 28 to actuate the service brakes 12.1 , 12.2 directly. Instead, the actuating means 28 is in direct flow communication with the relay valve 22, which allows the service brakes 12.1 , 12.2 to be actuated by the power pack 16. As a result, two separate, and distinct, hydraulic sub-systems exist between the actuating means 28 and the service brakes 12.1 , 12.2. The relay valve 22 acts as the interface between the two sub-systems. From Figure 1 it should be understood that the first system 42 consists of the two sub-systems. Due to the nature of the external hydraulic pressure supply from the power pack 16 in combination with the relay valve 22, it is not necessary to remove the drag from the hydraulic system when bleeding the hydraulic fluid from the line 26 that is in direct fluid communication with the brakes 12.1 , 12.2. Furthermore, the use of external or independent pressurising means 16 also provides higher service pressure to the service brakes 12.1 , 12.2.

The embodiment of the braking system 10 described above comprises both the relay valve 22 and the pressure sensing device 46, thereby providing both the servicing related advantages and the failsafe braking advantages of the invention. However, the invention is not limited to the inclusion of the combination of the relay valve 22 and the pressure sensing device 46. In other words, these two components are optional.

A second embodiment of the braking system that excludes the pressure sensing device 46 is shown in Figure 2. In this figure the non-limiting example of the vehicle braking system in accordance with the invention is generally indicated by reference numeral 1 10. Again, like numerals indicate like features.

The braking system 1 10 is substantially similar to the braking system 10 and, accordingly, only the most significant differences will be described. Due to the exclusion of the pressure sensing device 46 the failsafe brakes 50.1 , 50.2 are not engaged automatically in the event of a pressure drop. Instead, the failsafe brakes 50.1 , 50.2 are typically engaged when the driver of the vehicle becomes aware of a loss of pressure in the service brake hydraulic line 34, in the front disc brake hydraulic line 40 or in the master cylinder 32 and thereafter activates an emergency switch (not shown). Activation of the emergency switch causes a solenoid to be actuated in the power pack 16 that deactivates the emergency dump valve 20 thereby releasing the hold off pressure acting on the failsafe brakes 50.1 , 50.2.

A third embodiment of the braking system that excludes the relay valve 22 is shown in Figure 3. In this figure the non-limiting example of the vehicle braking system in accordance with the invention is generally indicated by reference numeral 210. Again, like numerals indicate like features.

The braking system 210 is substantially similar to the braking system 10 and, accordingly, only the most significant differences will be described. As a result of the exclusion of the relay valve 22 the actuation means 28 actuates the service brakes 12.1 , 12.2 directly. When the brake pedal 30 is depressed it actuates the piston within the master cylinder 32 which displaces hydraulic fluid out of the master cylinder and to the service brakes 12.1 , 12.2 via hydraulic line 34. An intensifier 156 may be located in the hydraulic line 34 to increase the volume of hydraulic fluid being delivered to the service brakes 12.1 , 12.2.

In this third embodiment of the braking system 210, the failsafe brakes 50.1 , 50.2 are automatically actuated as described with reference to the first embodiment of the braking system 10.

It will be appreciated that the above description only includes some embodiments of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention. It is easily understood from the present application that the particular features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. In this way, the description of the present invention and the related figures are not provided to limit the scope of the invention but simply represent selected embodiments.

The skilled person will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless otherwise expressed or it is evident that these characteristics are incompatible. Also, the technical characteristics described in a given embodiment can be isolated from the other characteristics of this embodiment unless otherwise expressed.