GB2056604A

GB2056604A - Vehicle braking systems

Info

Publication number: GB2056604A
Application number: GB8015151A
Authority: GB
Original assignee: Quinton Hazell Holdings Ltd
Current assignee: Dana UK 1 PLC
Priority date: 1979-05-11
Filing date: 1980-05-07
Publication date: 1981-03-18
Also published as: IT8067735A0; FR2456023A1; DE3017828A1; JPS5617743A

Abstract

A vehicle braking system with fluid controlled brakes has a primary braking circuit 3 operable by the vehicle operator and an auxiliary braking circuit 5 operable in response to movement of a rear detector 18. The auxiliary circuit includes first and second valves 26, 27 in series operable in response to electrical switches 25, 22 controlled respectively by a forward/reverse drive selector 24 and the position of the rear detector 18. <IMAGE>

Description

SPECIFICATION Vehicle braking systems This invention relates to vehicle braking systems and more particularly to such systems where the brake operation is controlled through fluid e.g. air pressure control lines which in turn are controlled by the vehicle operator using a foot pedal and/or hand control for braking the vehicle. It is applicable to self propelled vehicles and to tractor-trailer combinations, tractor semi-trailer units.

Conventional brake systems of this kind operate through a service line which is connected to the operating mechanism of the brake of each braked wheel and is caused to operate by actuation by the vehicle driver operating the foot brake pedal, the pressure in the line being maintained from a fluid tank under pressure. Commonly another line is provided, known as the emergency line, and feeds fluid under pressure to a reservoir which with a tractor/trailer unit isLlocated on the trailer so that if the pressure in the emergency line drops to an unsafe level as by the trailer breaking away from the tractor the brakes are automatically applied. Such systems using a service line and an emergency line form a so-called two-line system.Three-line systems are also known in which an additional secondary brake line is provided and controlled by a further operator control device such as a hand control.

Generally the fluid lines are used to supply fluid at elevated pressure, such as pressurised air. The application of the brakes may be effected by direct application of fluid at elevated pressure or alterna tivelyfluid at elevated pressure may be used to release brakes normally urged towards the on position by spring means.

Known braking systems of this general kind can be applied to a large range of vehicles and are frequently used on load carrying vehicles as well as to trailers coupled to tractors and similar towing vehicles, the trailer brakes being coupled by coiled flexible hollow cable-like tubes to the towing vehicle braking system.When such systems are used with tractor and trailer units the trailer usually has a trailer brake pressure fluid reservoir and the pressure circuit usually includes a relay emergency valve connected to the reservoir so as automatically (a) to apply the trailer brakes when signalled to do so by the service line (b) to apply the trailer brakes when the pressure in the emergency line drops below a certain level for instance, if the trailer becomes disconnected from the tractor, and (c) to maintain the working pressure in the trailer reservoir at the correct level, via the emergency line from the tractor reservoir.

Problems arise in reversing vehicles of the type which usually include such braking systems. When the driver reverses the vehicle he cannot see even through driving mirrors the zone immediately to the rear of his vehicle. Should the drive reverse his vehicle into an obstacle such as a wall or another vehicle, or a loading bay, he will not necessarily become aware of such an impact until considerable damage has occurred to his own vehicle orto the object struck. Where the obstacle is a human being, the person could be seriously hurt before the driver applies his vehicle brakes.

The main object of the invention is to provide an improved vehicle braking system in which the brakes may be applied automatically in the event of an impact at the rear of the vehicle provided the vehicle is not in a forward moving condition.

The invention provides a vehicle braking system comprising a brake mechanism, operable in re sponge to application of fluid at a required pressure, at least one source of fluid at said required pressure and at least two alternative fluid circuits arranged to connect fluid at the required pressure from a source to the brake mechanism, one of said alternative fluid circuits comprising a service line connected to valve means under the control of the vehicle operator and forming part of a primary braking means, and said second fluid circuit being part of an auxiliary braking means operable independently of the primary braking means in response to movement of a movable detector mounted at the rear of the vehicle, said auxiliary braking means including first and second valve means in series in said second circuit operable in response to respective first and second electrical signals to control the connection and release of fluid at the required pressure through the second circuit to and from the brake mechanism, first electrical switch means responsive to a forward/reverse drive selector on the vehicle for use in generating said first electrical signal, and second electrical switch means arranged to respond to the position of said detector at the rear of the vehicle and provide said second electrical signal in dependence on the position of the detector, whereby the auxiliary braking system is arranged to operate the brake mechanism when the said detector is deflected from a normal position by an impact at the rear of the vehicle and at the same time the vehicle drive is in a reversing condition, and release of the auxiliary braking system is effected only when the vehicle drive is released from the reversing condition and the detector is still in said deflected condition.

Preferably said first and second valve means are connected in series in said second circuit, said first valve means providing an exhaust outlet and being connected on the side of the second valve means remote from the brake mechanism. In this way, once the brakes have been applied by operation of the auxiliary braking means, the fluid pressure in the second fluid circuit between the second valve means and the brake mechanism can only be connected to exhaust through the second valve means while this remains in an open condition. To remain in the open condition an electrical signal is required from the second electrical switch means corresponding to the detector at the rear of the vehicle remaining in a deflected condition due to an impact.

This provides a valuable safety feature in that if the vehicle is inadvertently reversed into an object, the auxiliary braking means will automatically apply the brakes. If the driver then selects a forward drive the brakes will be released permitting forward movement provided the detector at the rear of the vehicle was still deflected by the impact at the time of selecting the forward drive. If therefore the driver has reversed against a solid object such as a wall or loading bay, he is able to drive forwards away from the obstruction without descending from the driving position of the vehicle.If however he has engaged a readily deflectable object such as a person.the initial impact with the detector at the rear of the vehicle will apply the brakes but the action of the knocking the person down will permit the detector at the rear of the vehicle to resume its normal position thereby changing the state of the second electrical switch means and preventing change in fluid pressure applied to the brake mechanism through the second valve means. The brakes will thereby remain applied despite selecting a forward driving condition for the vehicle. This can only be overcome by the driver descending from the cab and walking to the rear of the vehicle to inspect the damage caused. He may then manually operate the deflector away from its normal position to reactivate the second switch means and thereby release the brakes through the second valve means.Thereafter the vehicle can be driven away.

Preferably the first and second valve means comprise solenoid valves each connected in an electrical circuit incorporating the associated electrical switch means. Commonly heavy vehicles operate with braking systems actuated byfluid pressure which is elevated with respect to atmospheric pressure and the present invention is particularly applicable to such vehicle braking systems where pressurised fluid is supplied from a source of pressurised fluid through said two alternative fluid circuits to the brake mechanism.

The vehicle braking system may incorporate additional fluid pressure circuits in addition to the aforesaid two fluid circuits.

In one preferred arrangement the brake mechanism is arranged to receive pressurised fluid from a source of pressurised fluid through a relay emergency valve. In such an arrangement said service line is arranged to supply pressurised fluid to the relay emergency valve in order to operate the brake mechanism in response to actuation of said valve means under the control of the vehicle operator. In such an arrangement it is preferred that said fluid circuit is connected to said relay emergency valve by means of a changeover valve device to which said service line is also connected. In this way the changeover valve may operate in response to fluid pressure in eitherthe service line or the second fluid circuit so as to connect whichever of said circuits is pressurised to the relay emergency valve and to isolate the other.

Preferably said changeover valve means comprises a shuttle valve.

Preferably a fluid storage reservoir is provided between said first and second valve means and said shuttle valve so as to maintain the brake mechanism in an on condition once the auxiliary braking means has been actuated to apply the brakes.

In a particularly convenient arrangement said first and second valve means and the shuttle valve are mounted on a common mounting member said mounting member providing the reservoir.

The vehicle braking system may comprise a multi-line fluid actuated brake system such as for example a two-line or a three-line system.

Preferably said second electrical switch means comprises a microswitch together with an actuator mechanically linked to said detector.

Preferably said actuator comprises a cam device arranged to rotate with movement of said detector.

Preferably said detector comprises a bumper bar mounted on one or more arms arranged to pivot about a horizontal axis. Preferably said bumper bar is biased to a normal position and incorporates an energy absorbing device for absorbing the energy any impact which may deflect the bumper bar from the normal position.

Preferably said microswitch forming part of the second electrical switch means is mounted adjacent a flexible diaphragm forming part of a wall of a sealed enclosure for the switch means. Preferably said flexible diaphragm includes a thin flexible plate arranged to abut said cam member.

The system of the invention may be wholly on the vehicle when it is a self-propelled vehicle. Where the self-propelled vehicle is a tractor towing a trailer with brakes for its road wheels, the system may be divided into two parts, one including the vehicle speed ratio control and the driver operated valve and pressure protection valve when used and the other part containing the remainder of the actuating parts of the system.

In orderthatthe invention may be more fully understood a braking system in accordance there with will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows diagrammatically a vehicle braking system in accordance with the invention, Figure 2 shows the system mounted on a vehicle trailer, Figure 3 shows on an enlarged scale part of the system, and Figure 4 shows on an enlarged scale another part of the system.

Figure 1 shows a vehicle braking system for a tractor-trailer combination with parts to the left of the line 1 being mounted on the tractor and parts to the right of the line 1 being mounted on the trailer.

The braking system includes primary braking means marked 2 which include two fluid pressure lines, a service line 3 and an emergency line 4. An auxiliary braking circuit 5 is also provided as well as an independent secondary line 6 operated by a hand control valve located in the driver's cab. The service' line 3 is connected to a valve 7 operated by the vehicle driver from his driving seat and the valve is normally operated by the vehicle brake foot pedal.

The valve 7 has an inlet connected to a source of pressurised air on the tractor unit. The service line 3 is connected through a flexible connection 8 at the junction of the tractor and trailer. On the trailer unit the service line 3 is connected through a shuttle valve 9 and fluid pipe 10 to a relay emergency valve 11. The relay emergency valve 11 is in turn connected to a source of fluid under pressure shown as a reservoir 12.

The emergency line 4 is connected on the tractor to a tractor reservoir of pressurised fluid through a pressure protection valve 13 arranged to prevent loss of pressure from the tractor reservoir should the coupling to the trailer be disconnected or broken.

The line 4 is again connected through a flexible coupling 8 to the relay emergency valve 11.

The brake mechanism in this case is a conventional air operated brake cylinder one of which is shown at 14. It will of course be understood that a number of brake cylinders are provided depending on the number of wheels to be braked and each is connected by a line 15 to the relay emergency valve 11.

The secondary line 6 is connected through a flexible coupling 8 directly to the brake cylinder 14.

The arrangement shown in Figure 1 and consisting of the lines 3, 4 and 6 from athree-line brake system which operate in a conventional manner. When the foot pedal is operated to open the valve 7 and allow pressure to pass through the service line 3, the valve 9 allows the pressure to be applied to the relay emergency valve 11 which in turn releases pressure from the reservoir 12 to the brake cylinder 14 through the line 15. The emergency line 4 supplies pressure through the valve 13 from the tractor reservoir and through the relay emergency valve 11 to the reservoir 12. Should the pressure in the line 4 drop below an acceptable level the relay emergency valve causes pressure from the reservoir 12 to be applied through the lines 15 to the brake cylinders so as to apply the brakes.

In accordance with the invention this particular embodiment includes an auxiliary braking means operable independently of the primary braking means in response to movement of a movable detector located at the rear of the trailer. As is shown in Figures 1 and 2, the rear detector is provided in the form of a horizontal bumper bar 17 extending horizontally across the rear of the vehicle and mounted rigidly on arms 18 pivotally mounted at their upper ends on horizontal pins 19. In this way the bumper bar 17 projects downwardly below the chassis of the trailer and will cause to move in a clockwise direction as seen in Figures 1 and 2 should the vehicle be reversed into an obstacle. The bar 17 and arms 18 are urged into a normal rest position by a spring 20 (see Figure 2) and an energy absorbing shock absorber unit 21 is provided to absorb energy on any impact at the rear of the vehicle.As seen in Figure 1 the upper end of the arm 18 is arranged to operate an electrical switch unit 22 the function of which will be described below.

The tractor unit has a forwardireverse drive selector normally in the form of a gear lever marked 24.

This is arranged to operate a further electrical switch 25.

The auxiliary braking means is provided by the line 5 which is connected to the shuttle valve 9. The line 5 includes a first solenoid valve 26 and a second solenoid valve 27 connected in series in the line 5.

The second solenoid valve 27 includes an actuating coil 28 connected in series with the switch 22, which forms a second switch means, which is in turn connected through a flexible coupling to the tractor to a power supply line 29. The power supply line 29 is also connected through the switch 25 to an actuating coil 30 of the first solenoid valve 26. The solenoid valve 26 is connected by a fluid pressure line 31 to the reservoir 12 and also to an exhaust port 32. The valve 27 is connected to the shuttle valve 9 by a section of fluid line marked 33 which has sufficient capacity to act as a further reservoir.

In normal operation, the shuttle valve 9 takes up a position which disconnects the line 5 from the line 10 leading to the relay emergency valve 11. It does however permit connection between the sevice line 3 and the line 10. In this way the primary braking system can operate in the conventional manner.

However, when the reverse driving condition has been selected by the unit 24, the first switch 25 is actuated to provide a first electrical signal to the first solenoid valve 26 causing the valve to open. This permits fluid pressure from the reservoir 12 to pass through the line 31 to the solenoid valve 27. The valve 27 is normally closed. Should the vehicle be reversed into an obstacle or there be other impact on the bumper bar 17 while the vehicle is in a reverse drive condition, movement of the bumper bar 17 operates the second switch 22 to supply current to the solenoid valve 27 and cause the valve to open.

Pressure in the line 33 then causes the shuttle valve 9 to change overto a position at which the service line 3 is isolated from the relay emergency valve 11 and the auxiliary braking line 5 is connected through the valve 9 and line 10 to the relay emergency valve.

This immediately causes pressure from the reservoir 12 to be applied through the valve 11 and line 15 to the brake cylinders 14.

If therefore the driver should reverse the vehicle into a wall or loading bay or alternatively hit an obstacle such as a parked vehicle or a person, the brakes will be applied immediately to bring the vehicle to a halt. If the driver then attempts to drive forwards away from the obstacle he would move the drive selector 24 to a forward drive condition thereby changing the switch 25 to caust the first solenoid valve 26 to isolate the supply of air pressure from the line 31 to the solenoid valve 27. If the bumper bar 17 remains in the deflected condition due to the obstacle continuing to hold the bumper bar against its bias then the switch 22 remains operated so as to keep the solenoid valve 27 in the open condition.

This allows air pressure from the brake cylinders to pass back through the shuttle valve 9 and through the pipe 33, through the valves 27 and 26 to the exhaust port 32 thereby releasing the brakes. The driver can then drive forwards. If however the obstacle has been displaced by the reverse movement of the vehicle so that the bar 17 has been allowed to reverse to its normal position, as will be the case should a pedestrian be knocked over, the return movement of the bar 17 operates the switch 22 so as to close the solenoid valve 27. This prevents release of air pressure from the brake cylinders due to the air pressure trapped in the reservoir formed by the pipe 33 between the valve 27 and the relay emergency valve 11. This continues to supply air pressure from the reservoir 12 through the line 15 to the brake cylinders 14 so that the brakes remain applied and the vehicle cannot be drive forwardly.

The driver must then dismount from the cab and go to the rear of the vehicle in order to inspect the situation. He can then manually deflect the bar 17 so as to reoperate the switch 32 and thereby open the valve 27 causing a release in pressure applied through the line 10 to the relay emergency valve 11 so that the brakes are then released.

The rear detector provided by the bumper bar 17 may be of the type shown in US Patent 3913963.

Although in Figure 1 the first solenoid valve 26 is shown connected by the pipe 31 directly to the reservoir 12, the pipe 31 may alternatively be connected to other points should they form a more ready source of fluid under pressure. For example, the pipe 31 may alternatively be connected directly to a further port on the relay emergency valve 11.

The above described system is suitable for use with a two-line system or a three-line system and may be used with spring brake actuators. In such a case the fluid pressure is used to release the brakes from an on position caused by spring operation. It will of course be appreciated that the braking system may be mounted wholly on a single vehicle which incorporates the drive unit and the bumper bar 17.

Should the bumper bar 17 become jammed in a forward deflector position due to for example a very heavy impact with an obstruction then the brakes will be applied by the auxiliary braking system but they will be released when the vehicle is put into a forward gear so that the vehicle may still be driven forward normally. As the brakes will then be applied whenever reverse gear is selected there is an incentive to repair the bumper mechanism to regain full use of the safety feature A preferred construction for the auxiliary braking means is shown in Figures 2,3 and 4. As shown in Figure 3, the two solenoid valves 26 and 27 are mounted in an enclosed weather-proof casing 40 which in turn is mounted on a mounting chamber 41 having a hollow interior providing an internal reservoir of sufficient volumetric capacity for that previously described for the line 33.The shuttle valve 9 is also mounted directly on the hollow housing 41 so that the two valves 26 and 27 and shuttle valve 29 form a single unit 42 which may be located art a convenient position under the trailer chassis as shown in Figure 2.

As shown in Figure 3 theelectrical connections to the solenoid valves 26 and 27 pass through a weather-proof grommet 43 and the fluid pressure line 31 passes through a similar weather-proof grommet 44. The shuttle valve 9 and casing 40 are bolted to opposite ends of the housing 41 and additional fastenings (not shown) may be formed directly between the shuttle valve 9 and casing 40.

The arrangement of the switch 22 is shown more fully in Figure 4, the switch 22 comprises a microswitch mounted within a weather-proof housing 45.

The housing 45 has an eccentric mounting unit 46 to allow simple adjustment of the precise positioning of the switch unit on the trailer chassis. The switch had an actuating projection 47 which lies closely adjacent a flexible diaphragm 48 covering an aperture in one wall of the housing 45. The diaphragm 48 incorporates a stainless steel flexible plate which engages a rotary cam 49 coupled to the arm 18 so that pivotal movement of the arm 18 causes rotation of the cam 49 which bears against the diaphragm 48 and causes actuation of the switch 22 by depressing the projection 47. In this way the switch unit forms a totally enclosed weather-proof unit which is simply adjusted in position so as to provide sensitive and accurate response to the slightest movement of the bumper 17. Due to the sealed natureofthe mounting actuation of the switch is independent of the effect of exposure to weather conditions.

It has been found that the above described system in which the application of fluid pressure through the auxiliary braking system is controlled by two solenoid valves in series each controlled by electrical signals provides a particularly advantageous and reliable system. Furthermore the system is very easily fitted to standard tractor and trailer constructions. Commonly the gearbox for a tractor unit has provision for an electrical switch to be engaged by reverse gear selection, for example for operation of reversing lights and consequently the switch 25 can very simply be fitted to a standard gearbox arrangement.

The invention is not limited to the details of the foregoing example.

Claims

1. A vehicle braking system comprising a brake mechanism operable in response to application of fluid at a required pressure, at least one source of fluid at said required pressure, and at least two alternative fluid circuits arranged to connect fluid at the required pressure from a source to the brake mechanism, one of said alternative fluid circuits comprising a service line connected to valve means under the control of the vehicle operator and forming part of a primary braking means, and said second fluid circuit being part of an auxiliary braking means operable independently of the primary braking means in response to movement of a movable detector mounted at the rear of the vehicle, said auxiliary braking means including first and second valve means in series in said second circuit operable in response to respective first and second electrical signals to control the connection and release of fluid at the required pressure through the second circuit to and from the brake mechanism, first electrical switch means responsive to a forward/reverse drive selector on the vehicle for use in generating said first electrical signal, and second electrical switch means arranged to respond to the position of said detector at the rear of the vehicle and provide said second electrical signal in dependence on the position of the detector, whereby the auxiliary braking system is arranged to operate the brake mechanism when the said detector is deflected from a normal position by an impact at the rear of the vehicle and at the same time the vehicle drive is in a reversing condition, and release of the auxiliary braking system is effected only when the vehicle drive is released from the reversing condition and the detector is still in said deflected condition.

2. Avehicle braking system according to claim 1 in which said first and second valve means are connected in series in said second circuit, said first valve means providing an exhaust port and being connected on the side of the second valve means remote from the brake mechanism.

3. A vehicle braking system according to claim 1 or claim 2 in which the first and second valve means comprise solenoid valves each connected in an electrical circuit incorporating an associated electrical switch means.

4. A vehicle braking system according to any one of the preceding claims in which the said service line and said second fluid circuit are connected by a changeover valve device which is operable to permit either one or the other to connect fluid of the required pressure to operate the brakes.

5. A vehicle braking system according to claim 4 in which said changeover valve and the first and second valve means are connected together as a unit.

6. Avehicle braking system according to claim 5 in which the changeover valve and the first and second valve means are mounted on a common housing having a hollow interior providing a reservoir of pressurised fluid to maintain the brakes in an on condition while release of air pressure through said first and second valves is prevented.

7. A vehicle braking system according to any one of the preceding claims in which said second electrical switch means comprises a microswitch mounted in an enclosed chamber adjacent the detector at the rear of the vehicle.

8. Avehicle braking system according to claim 7 in which the microswitch is mounted adjacent a flexible diaphragm against which a cam responsive to movement of the detector is arranged to act.

9. A vehicle braking system according to claim 8 in which said detector comprises a horizontal bar arranged to be pivotally mounted adjacent the rear of the vehicle and said cam comprises a rotary cam arranged to rotate on pivotal movement of the bar.

10. A vehicle braking system according to any one of the preceding claims in which said detector adjacent the rear of the vehicle comprises-a bumper bar incorporating energy absorbing means to absorb energy on impact at the rear of the vehicle.

11. A vehicle braking system substantially as hereinbefore described with reference to the accompanying drawings.