WO2001042045A1

WO2001042045A1 - Deceleration warning system

Info

Publication number: WO2001042045A1
Application number: PCT/GB2000/004713
Authority: WO
Inventors: Lloyd Kingsley Newman; Michael Dunlop Young
Original assignee: YOUNGKING Pty Ltd
Current assignee: YOUNGKING Pty Ltd
Priority date: 1999-12-11
Filing date: 2000-12-11
Publication date: 2001-06-14
Anticipated expiration: 2002-06-11

Abstract

There is described a deceleration warning system for installation in a road vehicle. The deceleration warning system emits a rearwardly-directed warning light in response to a sensed deceleration of the vehicle. The deceleration warning system can also emit a warning light when the vehicle braking system is operated above a predetermined operating level. Also described is a collision warning system for a vehicle wherein a warning light is emitted in response to the rate of change of distance between the vehicle and another object, when the rate of change of distance is above a predetermined level.

Description

Deceleration Warning System

This invention relates to deceleration warning systems, and relates more particularly but not exclusively to deceleration warning systems adapted for road vehicles to give visual warning to drivers of following vehicles that a road vehicle fitted with a deceleration warning system in accordance with the invention is undergoing deceleration, and preferably when the deceleration is in excess of a predetermined level of deceleration.

Conventional road vehicles are usually fitted with a vehicle brake system which includes warning system compiled to the vehicles brake system wherein the actuation of the vehicle brake closes an electrical switch to energise one or more rear-facing lights to emit red light towards following vehicles, thereby to warn the drivers (or riders) of following vehicles that braking has commenced, without waiting for visual observation that an inter-vehicle gap has suddenly started to reduce. However, such conventional brake light systems do not distinguish between minimal braking and strong braking. This gives rise (for example) to the situation where frequent speed adjustment in heavy traffic results in frequent minor applications of brakes, and consequent frequent illumination of brake lights, which tend to detract attention from an initially indistinguishable emergency braking until it is too late to avoid colliding with the vehicle in front.

According to a first aspect of the present invention, there is provided a deceleration warning system for installation on a road vehicle, the deceleration warning system comprising deceleration sensing means for sensing deceleration of the vehicle, and light emitting means responsive to sensed deceleration of the vehicle to emit a rearwardly-directed deceleration warning light.

Preferably, the road vehicle has a braking system comprising braking means and brake light means functioning upon operation of the braking means to emit a brake warning light, said rearwardly-directed deceleration warning light augmenting or otherwise modifying the brake warning light.

Preferably, the light emitting means is responsive only to deceleration above a predetermined level of deceleration. Preferably, the deceleration sensing means includes an accelerometer .

Preferably, the deceleration sensing means includes a radar system to give a deceleration output signal.

Preferably, the radar system utilises the Doppler effect to measure the speed of the vehicle and give said deceleration output signal.

Preferably, the deceleration sensing means includes means for deriving a deceleration output signal from a control signal being representative of vehicle speed or rate of change of vehicle speed, the control signal being derived from a signal representative, directly or indirectly, of the speed of rotation of one or more of the wheels of the vehicle.

Preferably, the control signal is derived from one or more of: a vehicle anti-lock braking system; a vehicle stability control system; a vehicle traction control system.

Preferably, the system includes an electrical or electronic control circuit for controlling the light emitting means.

Preferably, the control circuit is computer controlled and/or forms part of a computerised control unit. Preferably, the control circuit includes a pulse generator which is capable of emitting an electrical pulse representative of the rate of deceleration.

Preferably, the electrical pulse is input to the light emitting means to cause the light emitting means to pulse on and off at a rate proportional to the rate of deceleration.

Preferably, the light emitting means is in a first state when the vehicle is decelerating and the deceleration is below a predetermined level of deceleration, and is in a second state when the vehicle is decelerating and the deceleration is above said predetermined level of deceleration.

Preferably, the light emitting means emits no light when in the first state, and emits a pulsed light when in the second state.

Preferably, the light emitting means emits a steady light when in the first state, and emits a pulsed light when in the second state.

Preferably, the deceleration warning light is emitted only during operation of vehicle braking means of the road vehicle.

According to a second aspect of the present invention, there is provided a deceleration warning system for installation on a road vehicle, the deceleration warning system comprising means for sensing operation of the braking system of the vehicle and light emitting means responsive to sensed operation of the braking system above a predetermined operating level to emit a rearwardly-directed deceleration warning light.

Preferably, the braking system is a foot pedal operated braking system and wherein the operating level is determined by the operating pressure applied to the foot pedal.

Preferably, the road vehicle has a braking system comprising braking means and brake light means functioning upon operation of the foot pedal to emit a brake warning light, said rearwardly-directed deceleration warning light augmenting or otherwise modifying the brake warning light.

Preferably, the control circuit is computer controlled and/or forms part of a computerised control unit.

Preferably, the control circuit includes a pulse generator which is capable of emitting an electrical pulse representative of the operating pressure. Preferably, the electrical pulse is input to the light emitting means to cause the light emitting means to pulse on and off at a rate proportional to the operating pressure.

Preferably, the light emitting means is in a first state when the foot pedal is operated and the operating pressure is below a predetermined level of pressure, and is in a second state when the foot pedal is operated and the operating pressure is above said predetermined level of pressure.

According to a third aspect of the present invention, there is provided a collision warning system for installation on a road vehicle, the collision warning system comprising means for detecting the rate of change of distance between the vehicle and a reference object and light emitting means responsive to sensed rate of change of distance to emit a collision warning light.

Preferably, the reference object is another vehicle. Preferably, the other vehicle is to the front or to the rear of the road vehicle.

Preferably, the reference object is a stationary object.

Preferably, the collision warning light is a rearwardly-directed collision warning light.

Preferably, the collision warning light is installed within sight of the vehicle driver.

Preferably, the system includes a deceleration warning system as claimed in Claims 1 to 26.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings wherein:

Fig 1A is a block schematic diagram of a first embodiment of the invention; Figs IB-IE depict electrical and mechanical signals associated with operation of the first embodiment; Fig 2A-2D depict electrical and mechanical signals associated with operation of a modified form of the first embodiment; Fig 3 is a block schematic diagram of part of a second embodiment of the invention; Fig 4 is a block schematic diagram of part of a third embodiment of the invention; Fig 5A is a simplified diagram of part of a fourth embodiment of the invention; Fig 5B is a block schematic diagram of the fourth embodiment; Fig 6A is a simplified diagram of part of a fifth embodiment of the invention; Fig 6B depicts an electrical signal associated with operation of the fifth embodiment; Fig 6C is a block schematic diagram of the fifth embodiment; Fig 7 is a block schematic diagram of a sixth embodiment of the invention; and Fig 8 is a block schematic diagram of a seventh embodiment of the invention.

Referring first to Fig 1A, a first embodiment 10 of the deceleration warning system in accordance with the invention is fitted to a conventional road vehicle (not shown) .

The fundamental concept of the invention is to provide a visual warning to following drivers when the vehicle speed reduces at a significant rate. This concept can be implemented by the performance of three functions:

1 Determination of the rate of reduction of vehicle speed. 2 Processing of deceleration data to determine what visual warning, if any, should be given. 3 Implementing the visual warning such as by providing power to a flashing brake light.

The aim of the warning system 10 is to alert following drivers when the vehicle slows down rapidly, requiring a response from the following driver to avert a collision or other undesirable consequence.

Rapid slowing of the vehicle can be detected by monitoring the rate of change of vehicle speed with regard to time. This is also termed the magnitude of deceleration of the vehicle. Speed is the rate of change of distance with respect to time. It thus follows that if vehicle distance travelled measurements are available, the rate of change of distance can be evaluated to determine speed, of which, in turn, the rate of change can be found to determine deceleration.

Several methods by which vehicle speed or its rate of change can be determined are described below, firstly with reference to Fig 1A.

An accelerometer 12 mounted on the vehicle with its sensitive axis aligned fore/aft could be used to sense vehicle deceleration. This would typically be communicated to interfacing devices by means of an electric signal (as subsequently detailed in Figs 1B- ID) . The accelerometer 12 may be dedicated to the warning system function or it may also be utilised for other vehicle systems such as airbag deployment control or vehicle navigation. It is quite likely that some vehicles are already fitted with a suitable accelerometer for systems such as these.

The output of the accelerometer 12 is coupled by a signal lead 14 to a Schmitt trigger 16 which serves to mitigate jittering and render more stable the output of the accelerometer 12. The output of the Schmitt trigger 16 is coupled by a signal lead 18 to a multivibrator 20 whose operation is initiated and maintained by the presence of a signal on the lead 18. The multivibrator 20 operates at a fixed pulse repetition rate, and with a fixed mark/space ratio. The output of the multivibrator 20 is coupled by a power lead 22 to a rear-facing warning light (or group of lights) 24. The light (s) 24 are mounted in a laterally central position (in contrast to conventional side-mounted brake lights) and flash in synchronism with the output of the multivibrator 20 (as described below with reference to Fig IC) . Alternatively, the lights could be mounted with or formed integrally with, the side mount brake lights.

Fig IB schematically depicts the sustained energisation of the conventional brake lights (vertical axis) with respect to time (horizontal axis) during an application of the vehicle brakes. On the same scale as Fig IB, Fig IC depicts the intermittent energisation of the warning light 24. Fig ID depicts the brake pedal force, and Fig IE depicts the consequential deceleration rate of the vehicle. It is to be particularly noted that the accelerometer 12 is such as to produce an output on lead 14 (leading to a binary "1" or "enable" signal on lead 18) only when vehicle deceleration reaches a first predetermined level of deceleration, at which point the warning light 24 starts flashing (Fig IC) . When the deceleration of the vehicle subsequently falls below a second predetermined level of deceleration, the signal on lead 18 switches to binary "0" or "disable", so terminating flashing of the warning light 24. The multivibrator 20 may be such as to complete a pulse of standard duration even if the multivibrator is disabled during a light- energising pulse, so as to avoid a short flash and potential confusion for following drivers. The second predetermined level of deceleration is lower than the first predetermined level of deceleration in order to provide the deceleration warning system 10 with requisite hysteresis and certainty of functional switching.

Figs 2A-2D describe a modification of the system 10 (as detailed above with reference to Figs 1A-1E) . When the conventional brake light comes on at the commencement of braking (Fig 2A) the warning light 24 comes on at the same time, and stays on continuously until the brake pedal force (Fig 2C) and the consequent deceleration (Fig 2D) rise above the first predetermined level of deceleration, at which point the modified warning system causes the light 24 to flash as before (compare Fig 2B with Fig IC)

The drawback of the use of an accelerometer is that it cannot distinguish between deceleration associated with speed changes and the acceleration due to the earth's gravitational field. This becomes a problem when the axis of the accelerometer is not perpendicular to the gravitational field, ie when travelling up or down hill. High pass filtering can be used in an attempt to minimise the influence, however, this still results in an imperfect sensing system. Confirming that the sensed deceleration is caused at least partially by braking, and not entirely by travelling downhill can be achieved by also sensing brake pedal actuation. One possible design concept would operate such that on detecting deceleration above the threshold the warning would only be activated if the brake pedal is being depressed, as will now be detailed with reference to Fig 3.

The circuit shown in Fig 3 modifies the function of the system 10 (Fig 1A) between the signal lead 18 and the multivibrator 20. The Fig 3 modification consists of a two-input AND gate 30 having one input fed by the signal lead 18, while the other input is fed by a signal taken from the output lead 32 of the brake pedal switch 3A, ie the same signal as energises the conventional brake lights (eg as in Figs IB and 2A) . The output 36 from the AND gate 30 controls the multivibrator 20 (omitted from Fig 3) in place of the signal on the lead 18.

Fig 4 shows a variation of the Fig 3 arrangement, in which a two-input AND gate 40 is placed downstream of the multivibrator 20 (ie on the output side of the multivibrator 20), with an interposed inverting buffer 42. As with the Fig 3 arrangement, in the Fig 4 variation the other input of the AND gate 40 is fed with the output 32 of the brake pedal switch 34. The output 44 from the AND gate 40 directly controls the warning light 24 (omitted from Fig 4) . The inverting buffer 42 ensures that the brake light is on when the threshold is not yet reached but the brake pedal is depressed.

While the embodiments so far described with reference to Figs 1A-4 use an accelerometer, other forms of deceleration sensor are possible, as will now be described.

A tilt switch when inclined at an angle to the vertical such that fore/aft deceleration of adequate magnitude caused it to switch is acting as an accelerometer with a built in threshold detector/switch. Instead of providing an analogue output it is effectively a binary digital output. It retains the disadvantage in not being able to discriminate between deceleration associated with speed changes and the acceleration due to the earth's gravitational field. Thus a tilt switch (not shown) could take the place of the accelerometer 12 and Schmitt trigger 16 shown in Figure 1A.

Vehicle speed can alternatively be sensed by directly measuring ground speed. This would typically be done by the use of a radar beam and the doppler concept, although other techniques are also available. Such a radar system may be readily incorporated in collision avoidance systems already fitted to some vehicles which use radar distance sensing. A doppler radar speed measuring system 50 is schematically depicted in Fig 5A. The speed measurement is converted to deceleration measurement by the circuit arrangement depicted in Fig 5B.

Referring to Fig 5B, the doppler radar speed measuring system 50 produces a speed-dependent output signal on output lead 52 which serves as input to signal differentiation 54. Since reducing ground speed directly equates to vehicle deceleration, a signal on the differentiator output lead 56 is a deceleration signal equivalent to the accelerometer output signal on lead 14 in the first embodiment 10 (Fig 1A) , except that in the arrangement of Figs 5A & 5B, the initial measurement is of true ground speed and is quite independent of spurious accelerometer signals arising from the vehicle being on an ascending or descending route (eg in mountainous territory) . The output signal from differentiator 54 is processed in a Schmitt trigger 16 and a multivibrator 20 (which serve the same function as the Schmitt trigger 16 and the multivibrator 20 of Fig 1A) to drive the warning light 24.

The arrangement of Fig 5B can optionally be modified in the same manner as the warning system 10 of Fig 1A was optionally modified as described with reference to Figs 2A-2D,or Fig 3, or Fig 4.

Further variations in means for sensing vehicle deceleration are possible, and another such variation will now be described with reference to Figs 6A-6C.

Modern vehicles already typically sense speed or distance travelled. This data is used for items such as the speedometer and the odometer but also for functions such as automatic transmission control. These signals can readily also be utilised for calculation of rate of change of speed for the warning system, using electronic hardware and/or software (Fig 6C) . The signals are commonly in the form of a square wave pulse train 60 (Fig 6B) as they are typically generated by a slotted rotor 62 passing a magnetic proximity sensor 64 (Fig 6A) . The frequency of the pulse train is proportional to speed, while pulse count is proportional to distance travelled. The rate of change of frequency is proportional to acceleration. The pulse train 60 (Fig 6B) which is the output of the sensor 64 (Fig 6A) has its frequency (pulse repetition rate) converted to a frequency-dependent analogue signal 66 by a frequency-to-voltage converter 68 (Fig 6C) . The remainder of the embodiment shown in Fig 6C corresponds in structure and function to the downstream parts of the embodiment of Fig 5B, and accordingly these parts of Figs 6C are identified with like reference numerals. For details of the function of Fig 6C, reference should be made to the functional description of Fig 5B.

A potential problem is that if brakes lock during heavy braking these signals can indicate zero speed during this period, which may result in the warning system failing to function as desired. The fitment of anti-lock or ABS braking systems will eliminate this problem. The fitment of ABS also present a new possibility for vehicle speed sensing. These systems typically also generate a pulse train as described above from each wheel, which could be employed separately or combined in some way to determine deceleration. This option promises to be the most cost-effective as it is most likely to be able to utilise existing vehicle systems.

Some general requirements of deceleration warning systems will now be discussed. A key requirement for any signal from which deceleration is derived is that it does not introduce significant delay. It is imperative that the warning commences almost immediately on threshold deceleration being reached. The rate at which acceleration calculations can be updated if a pulse train as described above is used is of the order of half a pulse period at best. It is thus necessary that the pulse frequency, even at low speeds is sufficiently high to render this delay acceptable.

There are many different forms a visual warning can take, and many ways of modulating these to implement different warning levels. The first option is whether the light comes on at a steady state when the brake is applied and whilst deceleration level is low. This assumes that the warning light is separate from the conventional tail brake lamps. It may be possible that the warning light is integrated with these. Alternatively the warning light could take the place of the centre "eye level" brake light.

The possibilities include: • flashing brake light at fixed flash rate and mark space ratio (light steady until threshold deceleration level is reached, so giving a total of two warning levels) . • flashing brake light at fixed flash rate and mark space ratio (light off until threshold deceleration level is reached to give a more immediate warning effect since the first flash is "on" , not "off") . • flashing brake light at varying flash rate and/or varying mark space ratio to simulate varying intensity. • light with varying intensity • light that changes in shape or size.

For systems where the warning light does not vary in intensity it is merely necessary to determine when the threshold deceleration level has been reached. To prevent "flickering" operation in some circumstances it is then necessary to compare deceleration levels against some lower threshold at which the warning is turned off.

If the warning level is modulated in some way it is necessary to continuously monitor deceleration level and control the warning in accordance with this level. The most logical scheme would be to increase the warning level (flash rate, intensity) in direct proportion to the amount by which the threshold level has been exceeded. Other, non-linier, functions could of course also be implemented. Once again, some lower threshold should be set for turn-off.

As discussed above there are many options both for sensing deceleration and for producing a visual warning. There are thus many combinations of these options that can be implemented in a design. Some of the more likely design concepts were summarised in Figs 1A-6C, and other embodiments of the invention will now be described with reference to Figs 7 and 8.

Referring now to Fig 7, this is a block schematic diagram of a further embodiment 70 of a deceleration warning system in accordance with the invention, in the form of an electric circuit which serves to illuminate deceleration warning lights whether or not the brakes are applied. (Components of the circuit 70 which correspond to components of earlier embodiments are given the same reference numerals) .

Upon activation of the vehicle brake switch 34 the electrical circuit 70 senses the deceleration rate of the vehicle by way of the accelerometer 12 generating a signal 14 once a preset value of deceleration has been reached or exceeded. Normally the rate will be about 0.5g, where "g" is acceleration due to gravity.

This signal 14 is fed to a level detector 72 which serves to detect a preset value of deceleration. The output 74 from the level detector 72 is coupled to a monostable latching device 76.

The latching device 76 has means to maintain the signal generated by the accelerometer 12 for a prescribed duration enabling the circuit 70 to remain electrically energised until a cycle of a series of flashes of a deceleration warning light have been completed. In this embodiment, the deceleration warning light 24 is an array of light emitting diodes (whose current- limiting resistors are omitted from Fig 7) .

The flashing rate of the array of light emitting diodes 24 is controlled by the multivibrator 20 (as in previous embodiments) .

The multivibrator 20 determines the cycle of the series of flashes of the array of light emitting diodes 24 according to the signal generated by deceleration sensing accelerometer 12 and the flashing rate is proportional to the rate of deceleration.

For example when the deceleration exceeds 0.5g for about ten milliseconds, the series of light emitting diodes cyclically illuminate in even cycles of "off" and "on" at a rate of about six flashes per second for a period lasting longer than six seconds.

The above serves only as an example and it would be envisaged that deceleration could also be detected at intervals of less than 0.2g over a range of at least 0.2g to 0.8g with cycles of illumination varying according to deceleration, the frequency of flashes being from 2 to 20 per second for a duration in the range of 4 to 20 seconds.

Compared to the previous embodiments, the circuit 70 additionally comprises a further inverting buffer 78 whose input is the output 32 of the brake light switch 34. Thus the output 80 of the inverting buffer 78 is "high" when the switch 34 is open, ie when the vehicle is not currently being braked by driver actuation of the vehicle braking system. The buffer output 80 is combined with the multivibrator output 22 in a further two-input AND gate 82 to provide, "flashing" output 84 when the brake light switch 34 is open.

As in the embodiment of Fig 4, the circuit 70 includes a "flashing" signal 44 when deceleration is sensed simultaneously with the brake light switch 34 being closed (signifying driver braking) .

The signals 44 and 54 are combined in a two-input OR gate 86 whose output 88 provides a "flashing" signal whether the brake light switch 34 is open or closed.

Thus, line 44 provides no signal if the brake pedal is not operated; provides a constant on-signal for the brake lights when the break pedal is operated and deceleration is below the preset threshold; and provides a pulsed on-signal for the brake lights when the brake pedal is operated and deceleration is above a preset level.

Also, line 84 provides no signal when the brake pedal is operated (irrespective or deceleration); and provides a pulsed on-signal when deceleration is above the preset level and the brake pedal is not operated.

The output 88 controls a warning light driver circuit 24D (including the afore-mentioned current-limiting resistors) whose output directly drives the warning lights 24.

Referring now to Fig 8, there is shown a further embodiment 90 of a deceleration warning system for use on a vehicle, the system 90 having a brake pedal 91 which is connected to a conventional wheel braking system (not shown or described) and also connected to a pressure sensitive switch 92. A signal from the pressure sensitive switch 92 is input to a brake light control system 93 (other inputs may also be made as is described later) . The brake light control system 93 generates an output dependent on the inputs, the output being fed into a number of brake lights 94 such that the intensity and/or brightness of the brake lights 94 is dependent upon the output of the brake light control system 93. In use, the pressure sensitive switch 92 not only detects when the brake pedal 91 is pressed but also the speed and force with which it is pressed. The pressure sensitive switch 92 generates a signal dependent upon the speed and force with which the brake pedal 91 is pressed. This signal is input into the brake light control system 93. Other signals may be input into the brake light control system 93 from sensors which detect other factors such as the outside light conditions or the speed and deceleration of the vehicle. For example, a speed and/or acceleration sensor 95 and an outside condition sensor 96 can be incorporated into the braking system and input to the brake light control system 93.

The brake light control system 93 uses these inputs to determine the most effective intensity and/or brightness of the brake lights 94 and generates an output signal which causes the brake lights 94 to function with the desired level of intensity and/or brightness. For example, if the brake light control system 93 receives an input from the pressure sensitive switch 92 indicating that the brake pedal 91 is being pressed quickly and with force, the brake light control system 93 will process from this input that the vehicle is slowing down quickly and may be coming to a sudden stop. In order to indicate to the other drivers, the brake light control system 93 causes the brake lights 94 to increase in brightness. In an alternative example, if the brake light control system 93 detects from the pressure sensitive switch 92 or the speed/deceleration input that the vehicle has come to a complete stop, the brake light 94 may be caused to flash or change colour.

The signal from the sensor detecting the outside light conditions can be used by the brake light control system 93 to adjust the intensity and/or brightness of the brake lights 94 dependent upon how bright the outside light levels are. For example, at night the brightness of the brake lights 94 adjusts such that the lamps are not so bright as to dazzle the drivers behind the vehicle. However, were the driver to drive through a brightly lit tunnel, the brightness of the brake lights 94 may be increased to allow the brake lights 94 to be seen clearly in the bright tunnel .

In an alternative embodiment, the brake light 94 comprises a number of lamps, each lamp activating in turn as the pressure applied to brake pedal 91 increases.

In a further alternative embodiment, the brake light 94 comprises a number of flashing lamps. The rate of flashing is dependent upon the pressure applied to the brake pedal 91 such that as the pressure applied to the brake pedal 91 increases, the rate of flashing of the lamps increases. The lamp can also operate continuously if a specified amount of pressure is applied, for example, if the vehicle comes to a sudden stop.

Thus there has been described a system that warns following vehicles of a high rate reduction of vehicle speed. Fundamentally the system aims to warn the following driver of the rapid narrowing of the distance between vehicles. This may occur due to a speed increase of the following vehicle, speed decrease of the leading vehicle, or both. An alternative concept is thus to measure this distance or its rate of change and provide a warning if it decreases at a significant rate. The threshold rate could be varied with speed, using a lower rate at a higher speed due to the increased stopping distance at speed. The system could also warn if the following distance is too small (with regard to stopping distance) for the vehicle speed. The following distance could be measured directly by any range finding type of technology such as ultrasonic ranging, radar and lidar.

While the invention has been described and schematically illustrated in the context of vehicles such as conventional passenger-carrying cars (eg as shown in Fig 5A) , the invention is applicable to all forms of road vehicles, whether passenger-carrying or freight-carrying, and whatever the number of wheels, eg cars, lorries, buses, motorbikes, etc. The invention is also applicable to off-road vehicles.

While certain modifications and variations have been described above, the invention is not restricted thereto, and other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended claims.

For example, the various functions of the electronic and electrical circuitry could be performed by a computer, computer based or micro-processor based system. Also, with a view to mitigating any potential difficulty associated with delays in providing and reading the pulse trains it is possible to use control system techniques to pre-empt the reaching of the threshold. This can be implemented by monitoring the rate of change of deceleration and use this parameter to predict that the threshold will be reached within a defined time period. This would permit implementation of the warning before the threshold is reached. Employing such a predictive technique will result in a more liable and more useful system.

Claims

1. A deceleration warning system for installation on a road vehicle, the deceleration warning system comprising deceleration sensing means for sensing deceleration of the vehicle, and light emitting means responsive to sensed deceleration of the vehicle to emit a rearwardly-directed deceleration warning light.

2. A deceleration warning system as claimed in Claim 1, wherein the road vehicle has a braking system comprising braking means and brake light means functioning upon operation of the braking means to emit a brake warning light, said rearwardly- directed deceleration warning light augmenting or otherwise modifying the brake warning light.

3. A deceleration warning system as claimed in either one of the preceding claims, wherein the light emitting means is responsive only to deceleration above a predetermined level of deceleration.

4. A deceleration warning system as claimed in any one of the preceding claims, wherein the deceleration sensing means includes an accelerometer.

5. A deceleration warning system as claimed in any one of claims 1 to 3 , wherein the deceleration sensing means includes a radar system to give a deceleration output signal.

6. A deceleration warning system as claimed in Claim 5, wherein the radar system utilises the Doppler effect to measure the speed of the vehicle and give said deceleration output signal.

7. A deceleration warning system as claimed in any one of claims 1 to 3 , wherein the deceleration sensing means includes means for deriving a deceleration output signal from a control signal being representative of vehicle speed or rate of change of vehicle speed, the control signal being derived from a signal representative, directly or indirectly, of the speed of rotation of one or more of the wheels of the vehicle.

8. A deceleration warning system as claimed in Claim 7, wherein the control signal is derived from one or more of: a vehicle anti-lock braking system; a vehicle stability control system; a vehicle traction control system.

9. A deceleration warning system as claimed in any one of the preceding claims, wherein the system includes an electrical or electronic control circuit for controlling the light emitting means.

10. A deceleration warning system as claimed in Claim 9, wherein the control circuit is computer controlled and/or forms part of a computerised control unit.

11. A deceleration warning system as claimed in either one of claims 9 or 10, wherein the control circuit includes a pulse generator which is capable of emitting an electrical pulse representative of the rate of deceleration.

12. A deceleration warning system as claimed in Claim 11, wherein the electrical pulse is input to the light emitting means to cause the light emitting means to pulse on and off at a rate proportional to the rate of deceleration.

13. A deceleration warning system as claimed in any one of the preceding claims, wherein the light emitting means is in a first state when the vehicle is decelerating and the deceleration is below a predetermined level of deceleration, and is in a second state when the vehicle is decelerating and the deceleration is above said predetermined level of deceleration.

14. A deceleration warning system as claimed in Claim 13, wherein the light emitting means emits no light when in the first state, and emits a pulsed light when in the second state.

15. A deceleration warning system as claimed in Claim 13, wherein the light emitting means emits a steady light when in the first state, and emits a pulsed light when in the second state.

16. A deceleration warning system as claimed in any one of the preceding claims, wherein the deceleration warning light is emitted only during operation of vehicle braking means of the road vehicle.

17. A deceleration warning system for installation on a road vehicle, the deceleration warning system comprising means for sensing operation of the braking system of the vehicle and light emitting means responsive to sensed operation of the braking system above a predetermined operating level to emit a rearwardly-directed deceleration warning light.

18. A deceleration warning system as claimed in Claim 17, wherein the braking system is a foot pedal operated braking system and wherein the operating level is determined by the operating pressure applied to the foot pedal.

19. A deceleration warning system as claimed either one of Claims 17 or 18, wherein the road vehicle has a braking system comprising braking means and brake light means functioning upon operation of the foot pedal to emit a brake warning light, said rearwardly-directed deceleration warning light augmenting or otherwise modifying the brake warning light.

20. A deceleration warning system as claimed in any one of Claims 17 to 20, wherein the system includes an electrical or electronic control circuit for controlling the light emitting means.

21. A deceleration warning system as claimed in Claim 20, wherein the control circuit is computer controlled and/or forms part of a computerised control unit.

22. A deceleration warning system as claimed in either one of Claims 20 or 21, wherein the control circuit includes a pulse generator which is capable of emitting an electrical pulse representative of the operating pressure.

23. A deceleration warning system as claimed in Claim 22, wherein the electrical pulse is input to the light emitting means to cause the light emitting means to pulse on and off at a rate proportional to the operating pressure.

24. A deceleration warning system as claimed in any one of Claims 17 to 23, wherein the light emitting means is in a first state when the foot pedal is operated and the operating pressure is below a predetermined level of pressure, and is in a second state when the foot pedal is operated and the operating pressure is above said predetermined level of pressure.

25. A deceleration warning system as claimed in Claim 24, wherein the light emitting means emits no light when in the first state, and emits a pulsed light when in the second state.

26. A deceleration warning system as claimed in Claim 24, wherein the light emitting means emits a steady light when in the first state, and emits a pulsed light when in the second state.

27. A collision warning system for installation on a road vehicle, the collision warning system comprising means for detecting the rate of change of distance between the vehicle and a reference object and light emitting means responsive to sensed rate of change of distance to emit a collision warning light.

28. A collision warning system as claimed in Claim 27, wherein the reference object is another vehicle.

29. A collision warning system as claimed in Claim 28, wherein the other vehicle is to the front or to the rear of the road vehicle.

30. A collision warning system as claimed in any one of Claims 27 to 29, wherein the reference object is a stationary object.

31. A collision warning system as claimed in any one of Claims 27 to 30, wherein the collision warning light is a rearwardly-directed collision warning light.

32. A collision warning system as claimed in any one of Claims 27 to 30, wherein the collision warning light is installed within sight of the vehicle driver .

33. A collision warning system as claimed in any one of Claims 27 to 32, wherein the system includes a deceleration warning system as claimed in Claims 1 to 26.