GB2180417A - Vehicle brake light circuits - Google Patents

Abstract

A control circuit includes a pair of normally-closed relay contacts 14 arranged in the current path from the brake light switch (connected at 13) to vehicle brake lights (connected at 11). The relay RL is controlled by a 555 oscillator IC1 energised by the operation of the vehicle foot brake, or hand brake, or hazard warning lights (connected at 12), or an independent switch. A delay circuit including a capacitor C2, resistors R4 and RV2 and transistor TR1 is arranged to inhibit operation of the oscillator for a pre-set period following actuation of one the energising switches. The brake lights are on continuously during the delay period and are then caused to flash until either the ignition switch is turned off or the energising switch is released. A driver warning light LED is energised whenever the brake lights are energised; alternatively, or additionally, an audible warning may be given. A circuit including a thyristor Thy1 and a transistor TR2 minimises electrical interference on opening and closing of contacts 14, the brake lights being energised via a resistor R9 when contacts 14 are open. <IMAGE>

Description

SPECIFICATION Brake light circuits This invention relates to apparatus for use in a motor vehicle, in conjunction with the brake light circuit thereof.

It is a legal requirement in most countries that motor vehicles be fitted with brake lights-that is to say, at least one red light mounted on the vehicle to face rearwardly, which light is illuminated whenever the principal brake of the vehicle is applied. Most vehicles in fact have two or more such brake lights, all of which are controlled by a single electrical switch appropriately mounted so that whenever the foot brake of the vehicle is applied, the switch is closed and current is supplied to the brake lights. In most vehicles, the current supply is further controlled by the master electrical switch (usually referred to as the "ignition switch") of the vehicle, so as to prevent inadvertent electrical drain for example when the engine is turned off.

Most modern passenger cars are further fitted with an electrical switch associated with the hand brake, which switch is closed whenever the hand brake is applied, but which is used solely to control the supply of current to a warning lamp in the passenger compartment, to remind a driver to release the hand brake before setting-off. The hand brake switch is not normally connected to the brake lights of the vehicle and consequently following drivers are not given any warning by the brake lights should the vehicle be stationary in an unexpected place, with the hand brake applied but with the foot brake released.

In order to give a warning to other drivers that a vehicle has stopped in an unexpected or dangerous position, all modern vehicles are fitted with so-called "hazard warning" circuitry which in effect serves to cause all four turnindicator lights to be flashed simultaneously.

However, the activation of the hazard warning requires a deliberate action on behalf of the driver and experience shows that drivers tend not to activate the hazard warning until some considerable time after the vehicle has been stationary-and only then if the driver anticipates the vehicle remaining so for a further considerable period. Also, since the front turnindicator lights are flashed as well as the rear turn-indicator lights, this may cause a distraction for example when in a slowly-moving or stationary traffic queue and there is advantage only in warning following drivers.

It is a principal object of the present invention to provide apparatus which may be installed in a motor vehicle so as to make it more obvious to other following road users that the vehicle is likely to present a hazard.

Accordingly therefore, in its broadest aspect this invention provides apparatus for use on a motor vehicle having at least one brake light circuit including a rearwardly facing brake light and a brake light switch arranged for operation on application of the brakes so as to supply current to the brake light, which apparatus includes switch means configured for insertion in the brake light current path and arranged upon operation repeatedly to interrupt the current path to the brake light, the apparatus having means to sense the actuation of a control switch and being arranged thereafter to cause repeated interruption of the current path to the brake light.

The apparatus may be connected to the electrical circuitry of a vehicle to sense the actuation of any one or more of an independent electrical switch, the switch associated with the hazard lights circuitry, the brake lights switch and a switch associated with the vehicle hand brake. In the two first-mentioned case , operation of the apparatus occurs only when deliberately initiated by the vehicle driver, but it is greatly advantageous for the apparatus automatically to operate in hazardous circumstances. To allow this to occur, it is preferred for the apparatus to be adapted to operate whenever the brakes have been applied for longer than a pre-set period so as thereafter automatically to cause the brake light to flash on and off.

It will be appreciated that this preferred form of the apparatus of this invention is intended to improve road safety, by automatically giving road users following a vehicle fitted with the preferred form of the apparatus a warning should the brakes of the vehicle be maintained applied for more than a pre-determined period. This warning is given by causing the or each brake light to flash on and off, after an initial period where the or each brake light just remains continuously lit.

Said pre-set period during which the brake lights operate normally preferably is less than 30 seconds and advantageously is approximately 6 seconds. Such a value will allow most normal driving to be performed without the brake lights commencing to flash under the control of the apparatus, but should the vehicle be stopped or slowed down for a longer period, the brake lights will automatically commence flashing. The pre-set period may be adjustable, by means of a suitable control disposed for operation by the driver, so that he may alter said pre-set period dependent upon the particular driving conditions encountered.For example, if the driver is caught in a slow-moving queue of near-stationary traffic, then a relatively long pre-set period may be desirable, but on the other hand when driving on a motorway or other trunk road at relatively high speeds, it may be preferable to seiect a much shorter pre-set period.

As mentioned, in addition to the apparatus being arranged for connection to the brake light switch, it may also be used on a vehicle having a driver warning light for the hand brake, in which case the apparatus may be connected to the hand brake warning light switch, so that should the hand brake be applied whilst the master electrical switch (the ignition switch) be on, the brake lights initially will be turned on but following the expiry of said pre-determined period, the brake lights will start to flash on and off, until either the hand brake is released or the ignition switch is turned off.

In order that the apparatus of this invention may operate in a "fail-safe" manner, it is preferred for the switch means of the apparatus to comprise a pair of normally-closed relay contacts which are arranged in series with the current path for the brake lights, so that the opening of the contacts interrupts the current path. The operation of the relay is controlled by the apparatus of this invention, but should the apparatus fail in any way, the relay contacts will remain closed. This will ensure current flow to the brake lights, whenever the brake light switch is closed. Provided however that the apparatus is functioning normally, that current path will be interrupted on opening the relay contacts, when the relay is energised.

To this end, the apparatus may include an integrated timer circuit, connected to operate as a low frequency oscillator but with a delay circuit to inhibit the operation thereof for said pre-set period.

The apparatus of this invention may be arranged to provide a driver with an indication of the actuation of the circuit. For example, a driver indicator light may be illuminated whenever the brake lights also are illuminated, in a similar manner to that employed with the turnindicators; in this way, a driver will be able to observe whether the brake lights are lit continuously, or are being flashed by the apparatus of this invention. As an alternative, or in addition, to such an indicator light, an audible warning may be given, for example just when the brake lights are being flashed.

By way of example only, one specific embodiment of this invention will now be described in detaii, reference being made to the accompanying drawing which is the circuit diagram of apparatus of this invention intended for fitting to a motor vehicle, in the brake light circuit thereof.

The embodiment of apparatus of this invention described in the following is constructed as a self-contained unit intended either for retro-fitting to an existing vehicle, or for incorporation in the electrical circuitry of a vehicle, when the vehicle is being constructed. The unit may be substantially in the form of a closed box (not shown) but having four externallyaccessible terminals 10 to 13 inclusive.

The fitting of such a unit to an existing vehicle will now be described.

Terminal 10 is connected to the vehicle chassis, so as to provide an earth return path for the electronic circuitry within the unit. The wire leading from the vehicle brake light switch to the brake lights themselves is removed from the switch and is connected instead to terminal 11. A wire is used to link terminal 12 to the hazard warning lights flasher unit output terminal, and a further wire is used to connect terminal 13 to the brake light switch terminal from which the brake light wire has been removed.

Within the unit, electronic circuitry is arranged so that when current is supplied to terminal 13 from the brake light switch (presuming the vehicle ignition switch is on), the brake lights will be illuminated via normally closed contacts 14 of relay RL--and this will hold good even should the electronic circuitry otherwise fail. Equally, whenever the hazard warning lights are energised, so too will be the brake lights via the same contacts 14.

Whenever current is fed to terminal 11, through the relay contacts 14, a light emitting diode LED is also energised through resistor R10, to indicate functioning of the brake lights.

A circuit including a thyristor THY1, a transistor TR2, and resistors R6-R9 as well as diodes D5 and D6 is provided to minimise electrical interference on opening and closing of the relay contacts 14, by ensuring that when the relay contacts are opened, the brake lights are still supplied with current through a 12Q resistor R9 and thyristor THY1.

A known design of integrated electronic timer, IC1, type No. 555, is provided to control the supply of current through the coil of the relay RL. The timer circuit is connected as an oscillator, so that output terminal 3 is alternately made high and low; when low, current will flow through the coil of relay RL, so opening the contacts 14. The duty cycie of the oscillator may be adjusted using variable resistor RV 1.

Following the supply of power to terminal 13, operation of the timer is inhibited until capacitor C2 has been charged via resistors R4 and RV2. When however the voltage at the' junction between capacitor C2 and resistor R4 has risen sufficiently to enable transistor TRI to conduct, then the timer may commence oscillation so alternately opening and closing the relay contacts 14. The period of delay, prior to the timer operating, may be adjusted using variable resistor RV2.

If the circuit described above is to operate also should the hand brake be applied and provided the ignition switch of the vehicle is turned on, then a further terminal (not shown) may be provided, connected by a diode to the junction of diodes D1 and D2; the further terminal should be connected to the output side of the hand brake warning light switch.

Claims (14)

1. Apparatus for use on a motor vehicle having at least one brake light circuit including a rearwardly facing brake light and a brake light switch arranged for operation on application of the brakes so as to supply current to the brake light, which apparatus includes switch means configured for insertion in the brake light current path and arranged upon operation repeatedly to interrupt the current path to the brake light, the apparatus having means to sense the actuation of a control switch and being arranged thereafter to cause repeated interruption of the current path to the brake light.

2. Apparatus according to claim 1, wherein said control switch the actuation of which the apparatus senses is the hazard lights switch of the vehicle.

3. Apparatus according to claim 1 or claim 2, wherein said control switch the actuation of which the apparatus senses is said brake light switch.

4. Apparatus according to any of claims 1 to 3, wherein the apparatus is adapted for use on a vehicle having a driver warning light for the hand brake, said control switch the actuation of which the apparatus senses is a switch associated with the hand brake of the vehicle which switch is actuated whenever the handbrake is applied.

5. Apparatus according to claim 3 or claim 4, wherein the apparatus is adapted to allow normal brake light operation under the control of the brake light switch upon initial application of the brakes, but, for as long as the brakes remain operated following the expiry of a pre-set period after the application thereof, the apparatus operates repeatedly to interrupt the current path to the brake light so causing the brake light to flash on and off.

6. Apparatus according to claim 5, wherein said pre-set period during which the brake light operates normally is less than 30 seconds.

7. Apparatus according to claim 2, wherein said pre-set period is substantially 6 seconds.

8. Apparatus according to claim 1, wherein said pre-set period is adjustable, by means of a suitable control disposed for operation by the vehicle driver.

9. Apparatus according to any of the preceding claims, wherein said switch means comprises a pair of normally-closed relay contacts which are arranged in series with the current path for the brake lights, so that the opening of the contacts interrupts the current path.

10. Apparatus according to claim 9, wherein an electronic circuit is provided including an integrated timer circuit connected to operate as a low frequency oscillator but with a delay circuit to inhibit the operation thereof for said pre-set period, the timer circuit output controlling the relay contacts.

11. Apparatus according to any of the preceding claims, wherein the apparatus is configured to provide a vehicle driver with an indication of the actuation of the circuit.

12. Apparatus according to claim 11, wherein a driver indicator light is provided, which light is illuminated whenever the brake lights also are illuminated.

13. Apparatus for use on a motor vehicle having at least one brake light circuit which apparatus is arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A motor vehicle having at least one brake light circuit and whenever fitted with apparatus according to any of the preceding claims.