GB2312104A

GB2312104A - Deceleration warning system for a road vehicle

Info

Publication number: GB2312104A
Application number: GB9607412A
Authority: GB
Inventors: Stephen George Watson; Kenneth James Winstanley
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-04-10
Filing date: 1996-04-10
Publication date: 1997-10-15
Also published as: GB9607412D0

Abstract

An externally perceivable signal on a road vehicle is actuated in response to a high rate of deceleration of the vehicle. Deceleration above a threshold level may close an inertia switch 10 thereby energising a set coil 32 of a bistable relay 30 so that contacts 34 of the relay 30 close to energise a further relay 38 whereby the hazard warning lights 13 are activated through a switch 42 of relay 38. The hazard lights 13 remain energised until the normal brake light switch S opens. Opening of the brake light switch S is sensed by a differentiating circuit 46,48 and a diode 50 resulting in an amplification and de-bounce circuit 51 momentarily energising a relay 40 causing momentary energisation of a reset coil 36 of bistable relay 30, such that contacts 34 and 42 open in turn to deenergise the hazard lights 13. The inertia switch 10 may have a mass (20, Fig.2) slidable against the bias of an adjustable spring (26), or an inertial mass (78, Fig.4) adjustably attached to the operating lever (76) of a microswitch (72). In alternatives, one or more indicator lights may be activated instead of the hazard lights 13, the reset coil 36 may be energised by a manually operated switch, and deceleration may be sensed by means responsive to brake fluid pressure or may be calculated electronically from the vehicle speed indicated by the speedometer or by a sensor on a vehicle wheel.

Description

SIGNAL ACTUATING APPARATUS AND SIGNALLING SYSTEM The invention relates to an apparatus for actuating an externally-perceivable-signal providing means of a road vehicle in response to a high rate of vehicle deceleration, and a system for providing, on a road vehicle, an externally-perceivable-signal in response to a high rate of deceleration of the road vehicle.

Brake light systems of road vehicles indicate when a vehicle is being braked, but do not satisfactorily signal whether the vehicle is undergoing rates of deceleration commensurate with normal braking or higher rates of deceleration due to heavy braking, for example in an emergency situation.

In addition to brake light systems, road vehicles generally have manually actuated hazard warning light systems which provide an externally-perceivable-signal, in the form of simultaneous flashing of the vehicle's indicator lights, to warn other road users of hazardous situations.

Although hazard warning light systems can be manually actuated during heavy braking to signal a high rate of deceleration, this inevitably diverts the driver's attention from controlling the vehicle's motion.

According to a first aspect of the invention, there is provided an apparatus for actuating an externallyperceivable-signal providing means of a road vehicle in response to a high rate of vehicle deceleration, comprising means for determining if the vehicle is undergoing a high rate of deceleration and means for actuating the signal providing means responsive to determination by the determining means that the vehicle is undergoing said high rate of deceleration.

According to a second aspect of the invention, there is provided a system for providing on a road vehicle an externally-perceivable-signal in response to a high rate of deceleration of the vehicle, comprising means for determining if the vehicle is undergoing a high rate of deceleration, a signal providing means and means for actuating the signal providing means responsive to determination by the determining means that the vehicle is undergoing said high rate of deceleration.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic representation showing an electrical circuit of an apparatus according to the invention; Figure 2 is a diagrammatic, cross-sectional representation of a deceleration sensor of the apparatus; Figure 3 illustrates the voltage at various points in the circuit as a function of time during braking; and Figure 4 is a diagrammatic representation of an alternative deceleration sensor.

The apparatus comprises a deceleration sensor or inertia sensor 10 and a printed circuit board bearing a circuit, indicated generally at 12 in Figure 1, for actuating the hazard warning light system 13 of a motorised road vehicle in response to detection by the sensor 10 of deceleration exceeding a threshold value. The sensor 10 is mounted on the printed circuit board, as shown diagrammatically in Figure 1.

As shown in Figure 2, the deceleration sensor 10 comprises a cylindrical tube 14 which is closed at a first end by an integral end wall 15 and which is formed with a radially inwardly directed annular flange 16 between the end wall 15 and the second end of the tube 14. The tube 14 is made from a non-electrically conductive material. A first electrical contact 17 extends through the wall of the tube 14 approximately midway between the flange 16 and the second end of the tube 14. The contact 17 has, at the inside of the tube, an arcuate surface 18 which is very slightly proud of the inner surface of the tube 14. An annular, second electrical contact 19 partially closes the second end of the tube 14.

An electrically-conductive cylindrical weight 20 lies within the tube 14 and is slidably moveable between a first position, at which the weight 20 abuts the annular flange 16, and a second position, at which the weight 20 abuts the second contact 19. The arcuate surface 18 remains in contact with the weight 20 throughout such movement. The dimensions of the tube 14 and the weight 20, and the materials of the tube 14, the weight 20 and the contact 18 are such that the weight 20 moves within the tube 14 with minimal frictional resistance.

The end wall 15 is provided with a first aperture 22 which allows the ingress and egress of air into the tube 14 as the weight 20 moves within the tube 14. The hole of the annular contact 19 fulfils a similar function.

An adjustment screw 24 extends through and engages with a threaded second aperture provided in the end wall 15. The end of the adjustment screw 24 is connected to one end of a helical spring 26 via a joint 28 which allows relative rotation between the screw 24 and the spring 26. The other end of the helical spring 26 is connected to the weight 20 such that the weight 20 is resiliently biased at the first position.

Hence, the sensor 10 can act as an electrical switch, the weight 20 providing a conductive pathway between the first and second contacts 17,19 when the weight 20 contacts the second contact 19 but not when the weight is in any other position.

The construction of the sensor 10 is such that the weight 20 will make electrical contact with the second contact 19 to establish said conductive pathway provided it experiences a decelerating force exceeding a predetermined threshold value.

The circuit includes a bistable relay 30 having a first coil 32 for moving a switching member M of the relay's switch 34 from a first position (illustrated in Figure 1) to a second position, and a second 36 coil for resetting the switching member M from the second position to the first position. Additionally, the circuit has first and second single coil relays 38,40, each having a switch 42,44 comprising a switching member which is resiliently biased to a first position and which moves to a second position when the respective relay's coil is energised.

The circuit also includes a capacitor 46, a resistor 48, a diode 50 and amplification and debouncing means 51.

The circuit has first and second terminals 52,54 for connection to the positive and negative terminals respectively of a voltage source, which in this embodiment is the vehicle's battery. The circit also has a third terminal 56 for connection to the vehicle's brake light circuit as described below, and a fourth terminal 58 for connection to the vehicle's hazard warning light system 13 as described below.

The first contact 17 of the sensor 10 is connected to the first terminal 52 and the second contact 19 of the sensor 10 is connected to the first coil 32 of the bistable relay 30, which is, in turn, connected to the second terminal 54.

The bistable relay switch 34 and the actuating coil of the first single coil relay 38 are connected in series across terminals 52,54, and the connections to the switch 34 are such that the switch 34 is open when its switching member M is in the first position (as shown in the drawing) and the switch is closed when the switching member M is in the second position.

The switch 44 of the second single coil relay 40 and the second coil 36 of the bistable relay 30 are also connected in series across terminals 52,54 and the connections to switch 44 are such that the switch 44 is open when its actuating coil is de-energised (the position shown in the drawing) and closed when its actuating coil is energised.

The switch 42 of the first single coil relay 38 is connected between the first and fourth terminals 52,58 and the switch 42 is open when its actuating coil is de-energised (the position shown in the drawing) and closed when the associated coil is energised.

The capacitor 46 and the diode 50 are connected together in series between the third terminal 56 and the amplification and de-bouncing means 51 which is, in turn, connected to the actuating coil of the second single coil relay 40. The resistor 48 is connected across the second terminal 54 and the connection between the capacitor 46 and the diode 50, at point 60.

As will be explained further hereinafter, the vehicle brake light switch S is caused to close when the vehicle brake is applied, and the switch is caused to open when the vehicle brake is released. The effect of applying and releasing the vehicle brake is to produce a positive, rectangular wave voltage pulse at terminal 56. The capacitor 46 and resistor 48 form a differentiating circuit which operates on the positive, rectangular wave voltage pulse to produce at the input to diode 50 a positive voltage spike (corresponding to the positive-going edge of the voltage pulse) followed by a negative spike (corresponding to the negative-going edge of the voltage pulse). As shown in the drawing, diode 50 is connected in the reverse-biased configuration and so will only conduct the negative spike, produced when the brake has been released. The amplification and de-bouncing means 51 serves to filter out electrical noise associated with the negative spike (or de-bounce the spike) and to amplify this spike so that the amplified spike is capable of energizing the coil of the single coil relay 40 to cause the associated switch 44 to close momentarily.

The printed circuit board is mounted in a sealed box.

First, second, third and fourth connection leads 62,64,66,68 are soldered or otherwise connected to respective ones of the first, second, third and fourth circuit terminals 52,54,56,58. The leads 62,64,66,68 extend through suitable walls of the box via respective strain-relieved cable grommets mounted in the walls. In this particular embodiment the external ends of the first, third and fourth connection leads 62,66,68 are each conveniently provided with respective Scotchlok (Trade Mark) connectors. The external end of the second connection lead 64 is provided with a ring-tag connector.

Additionally, an aperture is provided in a suitable wall of the box so that the blade of a screwdriver can be inserted into the box and engaged with the adjustment screw 24 for adjustment of the tension of the helical spring 26. A rubber seal is provided for closing the aperture. An arrow is printed on the box indicating the orientation of the sensor 10.

The box is mounted in the vehicle using a bracket and self-tapping screws - the printed arrow being used to orientate the box relative to the vehicle such that the direction of movement of the weight 20 from the first position to the second position corresponds to the forward direction of movement of the vehicle. The Scotchlok (Trade Mark) of the first lead 62 is connected to an electrical cable of the vehicle which, in turn, is connected to the positive terminal of the vehicle's battery via the vehicle's ignition switch such that the voltage of the cable is +12V when the ignition is on and OV when the ignition is off. The ring-tag connector of the second lead 64 is connected to the vehicle's bodywork which, in turn, is connected to the negative terminal of the battery. The Scotchlok (Trade Mark) connector of the third connection lead 66 is connected to any part of the vehicle's brake light circuit which has a voltage of 12V when the vehicle's brake is being applied and the brake lights are illuminated, and is otherwise disconnected from the battery. The Scotchlok (Trade Mark) of the fourth connection lead 68 is connected to the vehicle's hazard warning light system at a cable which is downstream of the manually operated hazard warning light switch and which when energised supplies current to all four of the vehicles's indicator lights. The indicator lights are, in turn, connected to Earth.

In operation, application of the vehicle brake energises the brake light circuit causing the voltage at the third terminal 56 to increase from OV to 12V as shown at X in trace A of Figure 3 (the positive-going edge of the above-mentioned positive, rectangular wave voltage pulse). Simultaneously, the effect of the differentiating circuit formed by capacitor 46 and resistor 48 is to produce the afore-mentioned positive voltage spike, shown at X in trace B of Figure 3. However, flow of current through the coil of the second single coil relay 40 is prevented by the reverse-biased diode 50 and so the positive voltage spike has no material effect.

The decelerating force acting on the weight 20 during braking of the vehicle urges the weight 20 towards the second sensor contact 19. However, the weight 20 will only contact the second sensor contact 19 if the vehicle deceleration exceeds the predetermined threshold value, above which the decelerating force on the weight 20 exceeds the maximum opposing force exertable on the weight 20 by the helical spring 26 (i.e. when the weight 20 abuts the second sensor contact 19). The adjustment screw 24 will have been adjusted during factory assembly such that the weight 20 does not contact the second sensor contact 19 at deceleration rates commensurate with normal braking, but contact occurs at higher deceleration rates, exceeding the threshold value, experienced during heavy braking, for example, in an emergency situation.

Contact between the weight 20 and the second sensor contact 19 completes the conductive pathway of the sensor 10 allowing current to flow through the first actuating coil 32 of the bistable relay 30. This causes the switching member M of the bistable relay to move from the illustrated first position to the second position, causing a current to flow through the coil of the first single coil relay 38. In turn, this causes the switching member of the associated switch 42 to move from the first position to the second position, causing a current to flow from the vehicle battery to each one of the vehicle's indicator lights, causing the indicator lights to flash.

When the rate of deceleration falls below the threshold value the weight 20 will move away from the second sensor contact 19. However, the switching member M of the bistable relay 30 will remain in the second, closed position so that the first single coil relay 38 and the indicator lights remain energised. This situation is maintained until the brake is released, whereupon the voltage at the third terminal 56 decreases from 12V to OV as shown at Y in track A of Figure 3 (the negative-going edge of the afore-mentioned positive, rectangular wave voltage pulse). Simultaneously, the effect of the differentiating circuit formed by the capacitor 46 and resistor 48 is to produce the afore-mentioned negative voltage spike, shown at Y in trace B of Figure 3. This pulse is conducted by the diode 50, and, after debouncing and amplification by the means 51, energises the coil of the second single coil relay 40 thereby causing the switching member of the associated switch 44 to move from the first position to the second position before returning to the first position. This, in turn, momentarily energises the second coil 36 of the bistable relay 30 causing the switching member M of the bistable relay 30 to reset. This causes the coil of the first single coil relay 38 to become de-energised, whereupon the switching member of the associated switch 42 returns to the first position de-energising the vehicle's hazard warning light system.

It will be appreciated that the apparatus described above may be varied. For example, other deceleration sensors may be used in place of the sensor 10 described above. An alternative deceleration sensor 70 is shown in Figure 4.

The deceleration sensor or inertia sensor 70 comprises a low-torque microswitch 72 having a rotatable control 74 to which is attached an actuating arm 76 such that rotation of the arm 76 around the control 74 turns the control 74.

The microswitch 72 has a pair of terminals (not shown) connected by a circuit which is open or closed depending on the rotational position of the control 74. When the deceleration sensor 10 is replaced by the deceleration sensor 70, one of the microswitch terminals is connected to the first terminal 52 of the circuit 12 and the other microswitch terminal is connected to the first coil 32 of the bistable relay 30. A suitable microswitch is sold by ........... under Stock No. 339-207.

A weight 78 is attached to the arm 76 such that its position along the arm 76 can be adjusted.

The microswitch 72 is fixed within the sealed box by two screws 80 such that the arm 76 is free to move. One end of a spring 82 is attached to the arm 76. The other end of the spring 82 is attached to a swivel 86 which, in turn, is attached to an adjustment screw 84 in threaded engagement with a fixed bracket 88. The arrangement is such that the spring 82 exerts a force on the arm 76 which produces a rotational moment on the control 74 urging the control 74 to rotate such that that arm 76 moves towards the bracket 88. The arm 76 is prevented from reaching the bracket 88 as the rotation of the control 74 is limited by a stop mechanism (not shown) within the microswitch 72.

The force exerted on the arm 76 by the spring 82 can be adjusted by rotating the adjusting screw 84.

The position of the arm 76 shown in Figure 4 corresponds to the above-mentioned limit of rotation of the control 74 and in this position the circuit connecting the two microswitch terminals is open. When the arm 76 rotates against the force exerted by the spring 82 (anticlockwise in the orientation shown in Figure 4), the control 74 passes through a switching position causing the circuit connecting the microswitch terminals to close.

In use, deceleration of the vehicle produces a decelerative force on the weight 78 which in turn produces a rotational moment on the control 74. The components of the deceleration sensor 70 are orientated such that the decelerative moment on the control 74 opposes the moment produced by the spring 82, and if the former exceeds the latter the arm 76 will move away from the bracket 88.

The arm 76 and control 74 will only rotate through the above-mentioned switching position (thereby closing the circuit connecting the microswitch terminals) if the decelerative moment exceeds the moment produced by the spring when the control is at the switching position. The position of the weight 78 along the arm 76 and the position of the adjustment screw 84 will have been preset so that rotation through the switching position only occurs when the vehicle's deceleration exceeds the predetermined threshold value.

The closing of the circuit connecting the microswitch terminals causes a current to flow through the first coil 32 of the bistable relay 30 which in turn actuates the hazard warning light system as described above.

Alternatively, instead of using a deceleration sensor or inertia sensor 10,70 which detects deceleration directly, a deceleration determining means which calculates the vehicle's deceleration from the vehicle's speed may be used. In this case, the deceleration determining means may include means for determining the vehicle's speed.

For example, one or more sensors could be fitted to one or more of the vehicle's wheels (preferably non-driven wheels) for determining the vehicle's speed. The sensor or sensors would pass signals representative of the vehicle's speed to an electronic processing unit, which would calculate the vehicle's deceleration and detect deceleration rates exceeding the predetermined threshold value.

Alternatively, the deceleration determining means may make use of the vehicle's existing speedometer system. In this case, the determining means would include an electronic processing unit and means for linking the processing unit to the vehicle's speedometer system. Signals corresponding to the vehicle's speed would be passed via the linking means from the vehicle's speedometer system to the processing means. As before, the processing unit would calculate the vehicle's deceleration and detect rates of deceleration exceeding the predetermined threshold value.

It is not necessary to use either an inertia sensor 10,70 or means for calculating the vehicle's deceleration from the vehicle's speed as described above. Other means may be used to determine if the vehicle is undergoing a high rate of deceleration. For example, the apparatus may use a pressure transducer incorporated into the vehicle's brake master cylinder hydraulic output pipe. This transducer would link into an electronic sensing system, which would monitor the brake line pressure for sharp exceedance of a predetermined pressure level. The emphasis may be placed on the short pressure rise-time, as gradual braking with a heavy application right at the end, may not activate the system in time to give sufficient warning to following drivers. A motion sensor (e.g.

mercury switch) and logic, may be included to prevent false triggering of the hazard warning light system whilst the vehicle is at standstill, for example if a driver is holding down the brake pedal too hard at traffic lights.

The apparatus may also be modified in a number of other ways.

For example, instead of completing a pathway for current to flow from the battery to the hazard warning light system, the apparatus may complete a pathway from the hazard warning light system to Earth.

The hazard warning light system in some vehicles is actuated by providing a circuit between two contacts of the system. In this case the apparatus would include "go" and "return" leads for separate connection to respective ones of the contacts. The "go" and "return" leads would be connected to the switch 42 of the first single coil relay 38 such that the switch 42 opens and closes a circuit between the two contacts.

Instead of actuating the hazard warning light system, the apparatus may be adapted for actuating any other externally-perceivable-signal providing means.

Instead of including a single lead 68 for energising the hazard warning light system the apparatus may include one or more leads for directly energising one or more of the vehicle's indicator lights. In this case, a desired number of the indicator lights may be actuated.

De-energisation of the vehicle's hazard warning light system, after heavy braking, need not be triggered by release of the vehicle's brake, as described above, but instead could be triggered manually by the driver. In this case, the second single coil relay 40 would be replaced by a manually operable switch such that the manually operable switch was connected between the first terminal 52 and the second coil 36 of the bistable relay 30. The third connection lead 66, the third terminal 56, the capacitor 46, the diode 50, the amplification and de-bouncing means 51 and the resistor 48 would, in this case, be dispensed with. In operation, the manually operable switch would normally be in an open position so that the second coil 36 of the bistable relay 30 remained de-energized. Braking causing vehicle deceleration above the predetermined threshold value would energise the vehicle's hazard warning light system, as described above. De-energisation of the warning system would be achieved, generally after the vehicle had come to a standstill, by the driver operating the manually operable switch to momentarily close the switch. This would momentarily energise the second coil 36 of the bistable relay 30 and consequently de-energise the hazard warning system, as described above.

Additionally, although the apparatus described above makes use of the vehicle's battery to power the vehicle's hazard warning light system, a system may be provided comprising a deceleration sensor and a circuit as described above, and further including an externally-perceivable-signal providing means. In this case deceleration exceeding the threshold value would result in actuation of the externally-perceivable-signal providing means of the system. Such a system may be connected to the vehicle's battery or may include an independent power source.

Claims

1. Apparatus for actuating an externally-perceivablesignal providing means of a road vehicle in response to a high rate of vehicle deceleration, comprising means for determining if the vehicle is undergoing a high rate of deceleration and means for actuating the signal providing means responsive to determination by the determining means that the vehicle is undergoing said high rate of deceleration.

2. Apparatus according to claim 1, wherein said high rate of deceleration is a rate of deceleration exceeding a threshold value.

3. Apparatus according to claim 1 or claim 2, wherein the determining means is an inertia sensor.

4. Apparatus according to claim 3, when dependent on claim 2, wherein the inertia sensor comprises a moveable member resiliently biased to a first position so as to require a force to be exerted on the member to move the member to a second position, said determination to which said actuation is responsive comprising movement of the member to the second position due to the decelerating force on the member.

5. Apparatus according to claim 4, wherein the resilient bias is effected by adjustable means, adjustment of the biasing means altering the magnitude of the force required to move the member from the first position to the second position whereby to adjust the threshold value.

6. Apparatus according to claim 4 or claim 5, wherein the inertia sensor includes an electrical switch, movement of the member to the second position causing switching of the switch, said switching causing the actuating means to actuate the signal providing means.

7. Apparatus according to claim 1 or claim 2, wherein the determining means comprises processing means for calculating the rate of vehicle deceleration from signals representative of the vehicle's speed.

8. Apparatus according to claim 7, wherein the determining means comprises means for determining the vehicle's speed, said speed determining means generating said signals representative of the vehicle's speed.

9. Apparatus according to claim 7 or claim 8, when claim 7 is dependent on claim 2, wherein the determining means includes an electrical switch and is adapted for switching of the switch if the vehicle undergoes deceleration exceeding the threshold value, said switching causing the actuating means to actuate the signal providing means.

10. Apparatus according to claim 1 or claim 2, wherein the determining means is adapted to measure the value of a parameter of the vehicle's braking system, said parameter being indicative of vehicle deceleration, and said actuating means being arranged to actuate the signal providing means in dependence on the value measured by the determining means.

11. Apparatus according to claim 10, wherein said parameter is brake fluid pressure.

12. Apparatus according to claim 10 or claim 11, when claim 10 is dependent on claim 2, wherein the determining means includes an electrical switch, switching of the switch being dependent on the value and causing said actuation.

13. Apparatus according to any preceding claim, wherein the actuating means includes a first switching circuit switchable between first and second states in which the signal providing means is respectively de-energized and energized.

14. An apparatus according to claim 13, wherein the actuating means includes resetting means for switching the first switching circuit from said second, energized state to said first, de-energized state.

15. An apparatus as claimed in claim 14, wherein the resetting means is connectable to the vehicle brake light circuit and is operable to switch the switching circuit from said second to said first state in response to an output from said vehicle brake light circuit indicating that the vehicle brake has been released.

16. An apparatus as claimed in claim 15, wherein the resetting means includes a differentiation circuit for differentiating said output, and a second switching circuit for switching said first switching circuit from said second state to said first state in response to the differentiated output from the vehicle brake light circuit.

17. Apparatus according to claim 14, wherein the resetting means includes a resetting circuit including a manually operable switch, the resetting circuit being connected to the first switching circuit for switching the first switching circuit from said second state to said first state on operation of said manually operable switch.

18. An apparatus as claimed in any one of claims 13 to 17, wherein the said first switching circuit includes a bistable relay.

19. Apparatus according to any one of claims 13 to 18, when dependent on any one of claims 6, 9 and 12, wherein said switching of the electrical switch causes switching of the first switching circuit from the first state to the second state.

20. Apparatus according to any one of claims 13 to 19, wherein the first switching circuit includes a first terminal for electrical connection to a voltage source of the vehicle and a second terminal for electrical connection to the signal providing means, the first switching circuit providing an electrical connection between said first and second terminals while the first switching circuit is in the second state.

21. Apparatus according to any one of claims 13 to 19 wherein the first switching circuit includes a first terminal for electrical connection to earth and a second terminal for electrical connection to the signal providing means, the first switching circuit providing an electrical connection between said first and second terminals while the first switching circuit is in the second state.

22. Apparatus according to any one of claim 13 to 19, wherein the first switching circuit includes first and second terminals for separate electrical connection to the signal providing means, the switching circuit providing an electrical connection between said first and second terminals while the switching circuit is in the second state.

23. Apparatus according to claim 18 or any claim dependent thereon, wherein the switching circuit includes a further relay.

24. Apparatus according to claim 23, when dependent on any one of claims 20 to 22, wherein the further relay disconnects the first and second terminals when the first switching circuit is in the first state and connects the first and second terminals when the first switching circuit is in the second state.

25. Apparatus according to any preceding claim wherein the signal providing means is the hazard warning light system of a vehicle.

26. Apparatus according to any one of claims 1 to 19 including a power source.

27. System for providing on a road vehicle an externallyperceivable-signal in response to a high rate of deceleration of the vehicle, comprising means for determining if the vehicle is undergoing a high rate of deceleration, a signal providing means and means for actuating the signal providing means responsive to determination by the determining means that the vehicle is undergoing said high rate of deceleration.

28. System according to claim 27, wherein said high rate of deceleration is a rate of deceleration exceeding a threshold value.

29. System according to claim 27 or claim 28, wherein the determining means is an inertia sensor.

30. System according to claim 29, when claim 29 is dependent on claim 28, wherein the inertia sensor comprises a moveable member resiliently biased to a first position so as to require a force to be exerted on the member to move the member to a second position1 said determination to which said actuation is responsive comprising movement of the member to the second position due to the decelerating force on the member.

31. System according to claim 30, wherein the resilient bias is effected by adjustable means, adjustment of the biasing means altering the magnitude of the force required to move the member from the first position to the second position whereby to adjust the threshold value.

32. System according to claim 30 or claim 31, wherein the inertia sensor includes an electrical switch, movement of the member to the second position causing switching of the switch, said switching causing the actuating means to actuate the signal providing means.

33. System according to claim 27 or claim 28, wherein the determining means comprises processing means for calculating the rate of vehicle deceleration from signals representative of the vehicle's speed.

34. System according to claim 33, wherein the determining means comprises means for determining the vehicle's speed, said speed determining means generating said signals representative of the vehicle's speed.

35. System according to claim 33 or claim 34, when claim 33 is dependent on claim 28, wherein the determining means includes an electrical switch and is adapted for switching of the switch if the vehicle undergoes deceleration exceeding the threshold value, said switching causing the actuating means to actuate the signal providing means.

36. System according to claim 27 or claim 28, wherein the determining means is adapted to measure the value of a parameter of the vehicle's braking system, said parameter being indicative of vehicle deceleration, and said actuating means being arranged to actuate the signal providing means in dependence on the value measured by the determining means.

37. System according to claim 36, wherein said parameter is brake fluid pressure.

38. System according to claim 36 or claim 37, when claim 36 is dependent on claim 28, wherein the determining means includes an electrical switch, switching of the switch being dependent on the value and causing said actuation.

39. System according to any one of claims 27 to 38, wherein the actuating means includes a first switching circuit switchable between first and second states in which the signal providing means is respectively de-energized and energized.

40. System according to claim 39, wherein the actuating means includes resetting means for switching the first switching circuit from said second, energized state to said first, de-energized state.

41. System according to claim 40, wherein the resetting means is connectable to the vehicle brake light circuit and is operable to switch the switching circuit from said second to said first state in response to an output from said vehicle brake light circuit indicating that the vehicle brake has been released.

42. System according to claim 41, wherein the resetting means includes a differentiation circuit for differentiating said output, and a second switching circuit for switching said first switching circuit from said second state to said first state in response to the differentiated output from the vehicle brake light circuit.

43. System according to claim 40, wherein the resetting means includes a resetting circuit including a manually operable switch, the resetting circuit being connected to the first switching circuit for switching the first switching circuit from said second state to said first state on operation of said manually operable switch.

44. System according to any one of claims 39 to 43, wherein the said first switching circuit includes a bistable relay

45. System according to any one of claims 39 to 44, when dependent on any one of claims 32, 35 or 38, wherein said switching of the electrical switch causes switching of the first switching circuit from the first state to the second state.

46. System according to any one of claims 27 to 45, further including a power source.

47. System according to any one of claims 27 to 46, wherein the signal providing means comprises one or more road vehicle indicator lights.

48. Apparatus for actuating an externally-perceivablesignal providing system of a road vehicle in response to a high rate of vehicle deceleration, substantially as hereinbefore described with reference to the accompanying drawings.

49. System for providing on a road vehicle an externallyperceivable-signal in response to a high rate of deceleration of the road vehicle, substantially as hereinbefore described with reference to the accompanying drawings.