WO2012049649A1

WO2012049649A1 - Fail-safe brake system

Info

Publication number: WO2012049649A1
Application number: PCT/IB2011/054530
Authority: WO
Inventors: Paulus Johannes Aucamp
Original assignee: Agricultural And Industrial Mechanisation Group (Proprietary) Limited
Priority date: 2010-10-13
Filing date: 2011-10-13
Publication date: 2012-04-19
Also published as: ZA201108840B

Abstract

The invention concerns a fail-safe brake system for use in combination with a service brake system of a vehicle. The fail-safe brake system includes a high pressure fluid source for supplying fluid to a protection valve though an inlet line to the valve. The inlet line splits into a number of independent circuits which include braking means for braking the vehicle when the system is activated though a network of lines running from the protection valve to the braking means. The system further includes control valves for controlling the activation and deactivation of the fail-safe brake system by controlling the flow of fluid in the circuits. By controlling the fluid flow in the circuits, the activation and deactivation of the braking means are controlled. The fail-safe brake system may be activated and deactivated independently of the service brake system of the vehicle, thereby allowing the braking means to function independently of the service brakes of the vehicle. The invention also concerns a method of activating and deactivating the failsafe brake system.

Description

FAIL-SAFE BRAKE SYSTE

BACKGROUND TO THE INVENTION

This invention relates to a fail-safe brake system. In particular, but not exclusively, this invention relates to a pneumatically operable fail-safe brake system.

Fail-safe brake systems on heavy duty vehicles are well known in the industry. However, there are currently a number of problems associated with these known fail-safe brake systems. In many of these vehicles the fail-safe brake system is not a separate brake system but rather the same brake system as the vehicle's standard service brake system only including additional safety components which must be activated before the service brake system can be deactivated. As a result of incorporating the service brake system into the fail-safe system the two systems cannot operate entirely independently of one another. For example, in the event of a service brake system failure, the fail-safe brake system will also fail. This is a major disadvantage in existing fail-safe brake systems. Another problem currently being experienced with existing fail-safe brake systems is that the system can be bypassed completely or partially by bypassing some of the safety components. In some cases by bypassing a single component the entire fail-safe brake system can be bypassed. Accidents are known to have happened as a result of a driver bypassing safety components in the known brake system.

It is an object of this invention to alleviate at least some of the problems experienced with existing fail-safe brake systems.

It is a further object of this invention to provide a fail-safe brake system that will be a useful alternative to existing fail-safe brake systems.

SUMMARY OF THE INVENTION

According to the invention there is provided a fail-safe brake system for use in combination with a service brake system of a vehicle, the fail-safe brake system including:

a high pressure fluid source for supplying fluid to the fail-safe brake system;

a protection valve splitting a feed line running from the high pressure source into at least two independent fluid flow circuits, one being a primary circuit including braking means for braking the vehicle when the fail-safe brake system is activated and the other being an auxiliary circuit for controlling fluid flow to the primary circuit; and

a control valve located in the auxiliary circuit for controlling the activation and deactivation of the fail-safe brake system;

wherein the fail-safe brake system may be activated and deactivated independently of the service brake system of the vehicle, thereby allowing the braking means to function independently of the service brakes of the vehicle. The system preferably includes four circuits, namely a primary circuit associated with the braking of the rear axle of the vehicle, a secondary circuit associated with the braking of the front axle of the vehicle, a trailer circuit associated with the braking of the trailer axle and an auxiliary circuit in which the control valve is located. In the preferred embodiment the braking means is a disc brake assembly provided at each end of the front and rear axles of the vehicle.

Alternatively, the system may include only two circuits, namely a primary circuit for activating the braking means located in a position such that a braking force is applied to the vehicle's prop-shaft directly when the braking means is activated and an auxiliary circuit in which the control valve is located.

The control valve is preferably manually operable to ensure that an operator must activate the valve manually by following a safety procedure when deactivating the fail-safe system. More preferably, the control valve is a push button valve, an accelerator valve for controlling the fuel supply to the engine of the vehicle or a gear shift control for controlling the shifting of the vehicle's gearbox.

The system may include a number of control valves. Preferably, the system includes a push button valve, an accelerator valve for controlling the fuel supply to the engine of the vehicle and a gear shift control for controlling the shifting of the vehicle's gearbox. The push button valve may be positioned in a line feeding the control valves such that the push button valve must be activated first in order for fluid to flow to the accelerator valve and the shift control.

The system may also include a hand brake control valve associated with the vehicle's hand brake and a brake pedal valve associated with the vehicle's brake pedal, wherein both the hand brake valve and the brake pedal valve form part of the primary circuit so that the fail-safe brake system cannot be deactivated without first activating both the hand brake and brake pedal valves.

Preferably, fluid flow in the auxiliary circuit is automatically cut off if the pressure in the line feeding the control valve or control valves drops below a predetermined minimum pressure.

The system may be a pneumatic system with the high pressure source being a compressor which supplies the system with pressurised air. Preferably, the system includes a release valve which is located in the feed line running from air compressor, the release valve regulating the pressure in the system by exhausting air to the atmosphere when the pressure is above a maximum pressure or charging the system if the pressure is below a minimum pressure.

According to another aspect of the invention there is provided a method of deactivating a fail-safe brake system, the method including the steps of pressurising a feed line of the system, activating a control valve, activating a hand brake valve associated with the hand brake of the vehicle, and activating a brake pedal valve associated with the brake pedal of the vehicle.

The control valve is preferably activated prior to the hand brake valve, thereby ensuring that the braking force applied as a result of the hand brake of the vehicle cannot be released without the control valve being activated first. The control valve may further be manually activated.

The method may also include the steps of activating an accelerator valve for controlling the fuel supply to the engine of the vehicle and activating a gear shift control for controlling the shifting of the vehicle's gearbox. The control valve is preferably activated prior to activating the accelerator valve and the gear shift control, thereby ensuring that vehicle is inoperable prior to deactivating the control valve. Preferably, the fluid flow in a line supplying the control valve is automatically cut off if the pressure in the line drops below a predetermined minimum pressure, thereby activating the fail-safe brake system.

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 diagrammatic representation of a fail-safe brake system according to the invention; and

Figure 2 shows a perspective view of braking means of the fail-brake system of Figure 1.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Figure 1 shows a diagrammatic representation of a fail-brake system 10 according to the invention for use in combination with an existing service brake system of a vehicle (not shown). Although used in combination the fail-safe brake system 10 may be activated and deactivated entirely independently from the service brake system of the vehicle. The embodiment of the invention illustrated in the figures is for use on a heavy duty vehicle such as a truck, hauler, grader or any other heavy duty vehicle. However, it will be appreciated that alternative embodiments of the invention could easily be fitted to other vehicles including light duty vehicles.

The system 10 includes a high pressure fluid source 12 for supplying fluid to a number of independent circuits which in use feed braking means 14 for braking the vehicle. In the illustrated embodiment the braking means 14 is in the form of disc brake assemblies provided at each end of the vehicle's front and rear axles. From Figure 1 it can be seen that the vehicle has four wheels with disc brakes 14.1 and 14.2 located at the ends of the front axle and disc brakes 14.3 and 14.4 located at the ends of the rear axle of the vehicle.

Each disc brake assembly 14 is fitted to an existing trumpet housing assembly located at each end of the axles. Figure 2 shows a perspective view of the disk brake assembly 14 fitted to the trumpet housing assembly. In this figure it can be seen that the disc brake assembly includes a brake disc 16 and a booster 18 which in use assists in applying a braking force on a calliper 20. A person skilled in the art of brake systems will be familiar with the functioning of a disc brake assembly and it will accordingly not be discussed in detail.

Returning to Figure 1 , it can be seen that the high pressure fluid source 12, which in the preferred embodiment is an air compressor run from the vehicle's engine, feeds a release valve 22 though line 24. In the system 10 the release valve 22 controls the maximum pressure in line 24 and, as a result, the system. The release valve 22 will in use exhaust to the atmosphere or charge the system depending on the pressure in the system. From the release valve 22 air is supplied to a protection valve 26. It is at the protection valve where line 24 splits into four independent air flow circuits which are fed through lines 28, 30, 32 and 34 respectively. Apart from regulating the air flow between the different circuits the protection valve 26 also protects the different circuits so that each of the circuits stays separate without any flow of air occurring between them.

As mentioned above the system 10 includes four independent circuits. The first circuit, which is associated with line 28, is a primary circuit which in use brakes the rear axle. The second circuit, which is associated with line 30, is a secondary circuit which in use brakes the front axle while the third circuit, which is associated with line 32, is a trailer circuit which in use brakes the trailer axle if a trailer is connected to the fail-safe brake system 10. The fourth circuit, which is associated with line 34, is an auxiliary or control circuit which includes a number of control valves which are generally indicated by the reference numeral 38 and discussed in detail below. Returning to the primary, secondary and trailer circuits it can be seen from Figure 1 that these circuits include reservoirs 36.1, 36.2 and 36.3 respectively. Air is allowed to accumulate in the reservoirs for use at the disc brakes 14 or trailer brakes (not shown).

The control valves 38 are used to ensure that the vehicle is only fully operable while the fail-safe brake system 10 is completely deactivated. In the illustrated embodiment the control valves 38 include a gear shift control 40, an accelerator air throttle valve 42 and a valve 44 which only allows air to pass through it once it has been activated. In the illustrated embodiment the control valves 38 are manually operable to ensure that the driver of the vehicle has to deactivate the fail-safe system by following a safety procedure. The valve 44 is for example a push button valve which only allows the flow of air towards the gear shift control 40 and accelerator valve 42 once the button has been pressed. Therefore, the valve 44 is positioned first in the air flow line 34 of the auxiliary circuit so that air is prevented from flowing to either the gear shift control 40 or accelerator valve 42 before activation of the valve 44. It should be clear that the gear shift control 40 only allows the vehicle's gearbox to shift gears when a required air pressure is present in its feeding line 40.1. In turn, the accelerator valve 42 controls the air flow in line 34 towards a booster 46 located on the vehicle's fuel pump (not shown). This is done in order to control the engine's revolutions and accordingly the speed at which the vehicle is travelling. If the air pressure in line 34 is inadequate as a result of for example an air supply shutdown, the accelerator valve 42 stops operation of the engine.

The push button valve 44 can furthermore only be activated while the pressure in line 34 is at a required minimum pressure. In other words, air supply to the system is cut off below the required minimum pressure. In the preferred embodiment the minimum pressure is preferably between about 3 and 6 bar, more preferably between 4 and 5 bar and most preferably about 4.7 bar. Should the air pressure drop to below the required minimum pressure, i.e. 4.7 bar, at any time the valve 44 will automatically shut down. This will result in the accelerator valve 42 preventing air flow to the booster 48 in order to stop operation so that the engine is allowed to idle only, the gear shift control shifting the gearbox to neutral and emergency brakes (not shown) being activated so that the vehicle is brought to a standstill. Once the emergency brakes have been activated, the vehicle cannot be moved without first deactivating the fail-safe brake system again.

The fail-safe brake system 10 also includes brake pedal valve 48, associated with the vehicle's brake pedal, and a hand brake valve 50, associated with the vehicle's hand brake, for controlling air flow in the primary, secondary and trailer circuits. As shown in Figure 1 the brake pedal valve 48 is located so that both the primary and secondary circuits pass through it, thereby ensuring that operation of the brake pedal valve controls activation of the disc brakes 14 on both the front and rear axles. In the primary circuit, air is allowed to flow from line 28 towards the brake pedal valve 48 via line 52. While no pressure is applied to the brake pedal of the vehicle air is prevented from passing though the valve 48 and deactivating the disc brakes 14.3 and 14.4. As soon as pressure is applied to the brake pedal, the brake pedal valve 48 is activated and air is allowed to flow through the valve towards a rear axle valve 56 which in turn controls air flow to the rear disc brakes 14.3 and 14.4 through lines 58 and 60 respectively. The rear valve 56 is also fed by line 28 connecting the reservoir 36.1 to the rear valve directly. Similarly to the rear brakes 14.3 and 14.4, the front brakes 14.1 and 14.2 are also connected to the brake pedal valve 48 so that activation of the brake pedal valve in use allows air to flow to the front brakes via lines 62 and 64. Therefore, pressure has to be applied to the brake pedal in order for the air flow to reach the front and rear brakes via brake pedal valve 48. This means that the fail-safe brake system 10 cannot be deactivated without the operator applying pressure on the brake pedal of the vehicle. A further safety feature of the fail-safe brake system 10 is that air supply to the front and rear disc brakes 14 are also controlled by the hand brake valve 50. From Figure 1 it can be seen that the hand brake valve 50 is fed by line 66 which is connected to line 34 at a location downward of the push button valve 44. As a result, air flow only reaches the hand brake valve 50 after activation of the push button valve 44. In its closed position, i.e. when the vehicle's hand brake is activated, air is prevented from passing through the hand brake valve 50 and into the auxiliary and trailer circuits. This prevents air from reaching the front brakes 14.1 and 14.2 and rear brakes 14.3 and 14.4 via lines 68 and 70 respectively. When the hand brake valve 50 is in its open position, i.e. the vehicle's hand brake is deactivated, air is allowed to flow to the front, rear and trailer brakes to deactivate them.

The hand brake valve 50 further controls air flow to a spring brake actuator (not shown) which in turn controls the emergency brakes of the vehicle. Should the air supply to the spring brake actuator be shut off by activation of the hand brake valve 50, the emergency brakes will automatically be applied. A skilled person will be well aware that when applying emergency brakes on a heavy duty vehicle, the brakes must be applied gradually in order to prevent serious damage to the vehicle. As a result, whenever the emergency brakes are applied they are applied gradually, thereby preventing catastrophic failure.

Turning now to the trailer circuit, it can be seen from Figure 1 that the line 32 supplies air to a trailer control valve 72 which controls air supply to trailer brakes (not shown) via couplings 74. The trailer control valve 72 is connected to the brake pedal valve 48 via lines 76 and 78 and to the hand brake valve 50 via line 80. As a result the trailer circuit is directly linked to the primary, secondary and auxiliary circuits so that air supply to the trailer control valve 72 may be controlled by the brake pedal valve 48 and hand brake valve 50. In other words, the trailer brakes can only be deactivated once the front and rear brakes 14 of the vehicle as well as the vehicle's hand brake have been deactivated. The trailer control valve 72 further controls emergency brakes on the trailer in that as soon as the air supply to the trailer fails, a spring brake actuator (not shown) automatically applies the emergency brakes on the trailer. Similarly to the vehicle's emergency brakes, the trailer's emergency brakes are applied gradually to prevent catastrophic failure.

The method of deactivating the fail-safe brake system 10 will now be described in greater detail. In order for a driver to operate the vehicle there are a number of procedural steps that need to be followed. Once the vehicle has been started, air pressure will build up in line 34. When the pressure reaches the required minimum pressure of 4.7 bar, the push button valve 44 in line 34 can be activated to allow air supply to the gear control 40, accelerator valve 42 and hand brake valve 50. To deactivate the fail-safe brake system 10 the hand brake valve 50 must be activated by releasing the vehicle's hand brake. Accordingly it should be clear that the fail-safe system 10 can only be deactivated once both the brake pedal valve 48 and hand brake valve 50 are charged i.e. at the required working pressure. With both valves 48 and 50 charged the vehicle's gearbox can be put into gear. Up to this stage the gearbox is in neutral, thus preventing any torque from being transmitted to the vehicle's wheels. Only after the above procedure has been followed can the vehicle be driven by applying a force on the accelerator pedal.

In an alternative embodiment of the invention not shown in the drawings, the fail-safe brake system 10 is used on light duty vehicles. In this embodiment of the invention there is no need to install additional disc brakes on the wheels of the vehicles as in the case of heavy duty vehicles. The reason for this is that the weight of the light duty vehicle allows the braking force to be applied directly to the prop-shaft of the vehicle without the risk of shearing a shear sleeve in the gearbox as the case in heavy duty vehicles. In this embodiment a disc brake assembly (not shown) is installed in a position wherein upon activation thereof it applies a braking force to the prop-shaft directly. Accordingly, three of the disc brake assemblies 14 which are used in the first embodiment may be dispensed with. ln this embodiment for light duty vehicles a spring brake actuator (not shown) for actuating the disc brake on the prop-shaft is also installed. The spring brake actuator is configured to be spring actuated and vacuum deactivated. In other words, the spring force is used to apply the brake while the vacuum works to release it. In use, as soon as the vehicle is started a vacuum starts building up in the system. Once the spring force has been overcome by the vacuum in the system, the spring is released to - release the brake. The opposite also applies in that as soon as the vacuum disappears the spring actuator applies the brake to activate the fail-safe brake system.

It must further be understood that in the second embodiment two of the circuits may be dispensed with so that the fail-safe brake system 10 includes a primary circuit which controls the brake on the prop-shaft and an auxiliary circuit which provides the fail-safe aspects of the invention as explained above with reference to the first embodiment.

Although the fail-safe brake system 10 has been described above as a pneumatic system, it should be clear that a fluid other than air could be used without departing from the principles of the invention. It should further be clear that although the system 10 has been described as a fail-safe brake system, it could also be used merely as an auxiliary system on a vehicle.

Claims

1. A fail-safe brake system for use in combination with a service brake system of a vehicle, the fail-safe brake system including:

a high pressure fluid source for supplying fluid to the fail-safe brake system;

wherein the fail-safe brake system may be activated and deactivated independently of the service brake system of the vehicle, thereby allowing the braking means to function independently of the service brakes of the vehicle.

2. A fail-safe brake system according to claim 1 , wherein the system includes four circuits, namely a primary circuit associated with the braking of the rear axle of the vehicle, a secondary circuit associated with the braking of the front axle of the vehicle, a trailer circuit associated with the braking of the trailer axle and an auxiliary circuit in which the control valve is located.

3. A fail-safe brake system according to claim 2, wherein the braking means is a disc brake assembly provided at each end of the front and rear axles of the vehicle.

4. A fail-safe brake system according to claim 1 , wherein the system includes two circuits, namely a primary circuit for activating the braking means located in a position such that a braking force is applied to the vehicle's prop-shaft directly when the braking means is activated and an auxiliary circuit in which the control valve is located.

5. A fail-safe brake system according to any one of the preceding claims, wherein the control valve is manually operable to ensure that an operator must activate the valve manually by following a safety procedure when deactivating the fail-safe system.

6. A fail-safe brake system according to claim 5, wherein the control valve is a push button valve, an accelerator valve for controlling the fuel supply to the engine of the vehicle or a gear shift control for controlling the shifting of the vehicle's gearbox.

7. A fail-safe brake system according to any one of the preceding claims, wherein the system includes a number of control valves.

8. A fail-safe brake system according to claim 7, wherein the control valves include a push button valve, an accelerator valve for controlling the fuel supply to the engine of the vehicle and a gear shift control for controlling the shifting of the vehicle's gearbox.

9. A fail-safe brake system according to claim 8, wherein the push button valve is positioned in a line feeding the control valves such that the push button valve must be activated first in order for fluid to flow to the accelerator valve and the shift control.

10. A fail-safe brake system according to any of the preceding claims, wherein the system includes a hand brake control valve associated with the vehicle's hand brake and a brake pedal valve associated with the vehicle's brake pedal, wherein both the hand brake valve and the brake pedal valve form part of the primary circuit so that the fail-safe brake system cannot be deactivated without first activating both the hand brake and brake pedal valves.

11. A fail-safe brake system according to any one of the preceding claims, wherein fluid flow in the auxiliary circuit is automatically cut off if the pressure in the line feeding the control valve or control valves drops below a predetermined minimum pressure, thereby activating the failsafe brake system.

12. A fail-safe brake system according to any one of the preceding claims, wherein the system is a pneumatic system with the high pressure source being a compressor which supplies the system with pressurised air.

13. A fail-safe brake system according to claim 12, wherein a release valve is located in the feed line running from air compressor, the release valve regulating the pressure in the system by exhausting air to the atmosphere when the pressure is above a maximum pressure or charging the system if the pressure is below a minimum pressure.

14. A method of deactivating a fail-safe brake system, the method including the steps of pressurising a feed line of the system, activating a control valve, activating a hand brake valve associated with the hand brake of the vehicle, and activating a brake pedal valve associated with the brake pedal of the vehicle.

15. Method according to claim 14, wherein the control valve is activated prior to the hand brake valve, thereby ensuring that the braking force applied as a result of the hand brake of the vehicle cannot be released without the control valve being activated first.

16. Method according to claim 15, wherein the control valve is manually activated.

17. Method according to either claim 14 to 16, including the steps of activating an accelerator valve for controlling the fuel supply to the engine of the vehicle and activating a gear shift control for controlling the shifting of the vehicle's gearbox.

18. Method according to claim 19, wherein the control valve is activated prior to activating the accelerator valve and the gear shift control, thereby ensuring that vehicle is inoperable prior to deactivating the control valve.

19. Method according to any one of claims 14 to 18, wherein fluid flow in a line supplying the control valve is automatically cut off if the pressure in the line drops below a predetermined minimum pressure.

20. Method according to any one of claims 14 to 19, wherein the fail-safe brake system is a brake system according to any one of claims 1 to 13.