Motor vehicle display system for indicating the state of motion of the subject vehicle and method of indicating such state

“Display system of a motor vehicle for indicating the state of movement of the vehicle under consideration and method for indicating such state”

This invention relates to a motor vehicle dial system and a method for indicating the state of motion of the vehicle in question. The display system according to the invention allows an observer to gain some sense of the extent of the observed motor vehicle deceleration, for example of the next motor vehicle and to be informed whether the observed motor vehicle is stationary or moving.

Known vehicle display systems include a system that indicates the force applied to the vehicle's brake. Such a system is described in the Road Research Laboratory Report LR287 issued by the UK Ministry of Transport. Report LR287 describes a system comprising a multiple brake light visual display. The number of brake indicator lights that are illuminated on a dial is dependent on the size of the vehicle deceleration. Report LR287 also refers to a brake light operated by a dimmer valve that is activated to indicate a low vehicle deceleration level.

DE 3907714A1 describes an arrangement for indicating the braking of a motor vehicle. The apparatus is designed in such a way that an increase in the number of stop lamps connected in a group is indicative of the braking rate of the vehicle concerned. In this way, the intensity of the stop lamps is controlled to give an indication of the degree of braking of the vehicle. A microprocessor is used to control the actuation of the stop lamps.

According to a first aspect of the invention, a method is provided for indicating the state of motion of the vehicle in question to the next vehicle driver by means of a set of lamps mounted on the vehicle in question and operating to produce a visual display indicative of state of motion to be detected by a vehicle speed measuring device, the method comprising the steps of:

measuring the speed of the vehicle concerned by the operation of the vehicle speed measuring device; characterized in that it determines whether the velocity measurement is less than a reference value and, when so determined, illuminates said lamps in a time dependent sequence to produce an animated visual display indicative of the state of motion as being stationary;

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determining, by operating a distance measuring device of the vehicle mounted on the vehicle concerned, whether said next vehicle is within a predetermined distance behind said vehicle and, when so determined, deactivating said time-dependent sequence and therefore illuminating said lamps in a time-independent manner to produce a static visual display indicative of the state of motion as being stationary.

According to a second aspect of the present invention, there is provided a display system of a motor vehicle for indicating the state of motion of the vehicle to the next vehicle driver, the system comprising:

a set of lamps mounted for use on the vehicle in question and operating to produce a visual display indicative of the state of movement to be detected by a vehicle speed measuring device operating to measure the speed of the vehicle under consideration;

characterized in that it comprises means for comparing the velocity measurement with a reference value;

means for illuminating said lamps in a time dependent sequence in response to said velocity measure which is determined to be less than said reference value, while the sequence produces an animated visual display indicative of the state of motion as being stationary;

a vehicle distance measuring device mounted for use on the subject vehicle and operative to determine whether said next vehicle is within a predetermined distance behind said subject vehicle; and wherein the means for illuminating said lamps are operatively connected to said vehicle distance measuring device such that when said next vehicle is determined to be within said predetermined distance, the time dependent sequence is deactivated and said lamps are therefore illuminated independently of time to produce a static visual display indicative of the state of motion as being stationary.

Preferably the vehicle motion detecting means should comprise a vehicle speed measuring device such as an optical sensor associated with the vehicle speedometer. Alternatively, vehicle speed information generated by an anti-lock braking system may be used as a source of information for vehicle traction sensing means.

Preferably, the indicator may comprise a set of lamps that are

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illuminated and off in a time-dependent manner to indicate that the vehicle is stationary. This animated display may be a predetermined sequence of activating and deactivating the lamps or may be random; if the sequence is predetermined, it may be cyclic. The stationary vehicle display may be disabled after vehicle traction begins. Preferably, the display should remain observable while the vehicle engine is running and the vehicle is stationary until a second vehicle is detected to be a predetermined distance behind the first vehicle using a vehicle distance measuring device. This feature will avoid disturbing the following drivers during idling and stationary traffic.

In a preferred form a vehicle display system comprises all prior aspects of the invention. The vehicle display system having vehicle deceleration detecting means, vehicle motion detecting means, an indicator and a vehicle proximity detector are all operatively interconnected to produce a signal indicating the size of the vehicle deceleration. vehicle and if the vehicle is stationary. The vehicle proximity detector works to alter the indicator signal and thereby minimize any annoying effect caused by the indicator signal on observers in nearby vehicles.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 shows four schematic representations A through D of a dial according to the invention;

Fig. 2 shows five schematic representations A through E of the display shown in Fig. 1 used to indicate that a vehicle is stationary;

Fig. 3 is a schematic electronic circuit diagram of a display system according to the invention that generates the display sequences shown in Figs. 1 to 2;

Fig. 4 is a schematic block diagram further showing wiring details of the system shown in Fig. 3;

Fig. 5 shows an example of accelerometer connections as part of the electronic circuitry used to control a dial system according to the invention;

Fig. 6 further shows wiring details of part of bar graph controller

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60 680 418 / ΡΤ of the circuit shown in Fig. 3;

Fig. 7 shows a cross-sectional side elevation of the speed sensor and part of the dial system opto switch according to the invention;

Fig. 8 gives electrical details of the opto switch shown in Fig. 7 and connected to the circuitry shown in Figs. 3 and 4;

parts A through H of Fig. 9 show various elevation drawings of the mechanical components of the opto switch shown in Fig. 7;

Fig. 10 shows details of part of the proximity sensor electrical connectors shown in Figs. 3 and 4;

Fig. 11 shows a time sequence of pulses for various component parts of the proximity sensor shown in Figs. 3, 4, 11 and 12;

Fig. 12 shows the wiring of part of two monostable proximity sensor devices shown as part of Figs. 3 and 4; and Fig. 13 shows the wiring of the monostable logic board as partially shown in Fig. 12.

In a preferred embodiment a motor vehicle display system 1 according to the invention comprises a set 2 of eight lights 10 to 17 which would normally be displayed as red lights in a horizontal set. Figs. IA to D show a progressive increase in the number of lights that are illuminated depending on the size of the vehicle deceleration. Lights are represented as “on” in the drawings by attenuation of light compared to “off” which is indicated by a black rectangle. Fig. 1A shows central lights 10 and 11 while Fig. 1D shows all eight lights 10 to 17 illuminated.

The display may include a different number of lamps, for example, lights 10 and 11 could preferably be replaced by a single unit. The dial would then comprise seven lights but it should certainly also be possible to have nine or eleven lights. Although rectangular lights are shown here it is also possible to have lights of different shapes. The lights may be of different colors although red or amber lights are preferred.

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The light assembly 2 may be carried in the rear of a vehicle as well as in the standard light position of the high level brake in the rear window of a motor car, for example. The lights are rearward facing and located so that they are readily visible to an observer, for example the driver of a motor vehicle traveling or positioned behind the motor vehicle on which the lighting display is mounted. The lights 10 to 17 are illuminated in pairs from center pair 10 and 11 outwards to outer pair 16 and 17 during a progressive brake warning (PBW) display. As the vehicle slows down the deceleration is indicated by a number of lights that are illuminated. Soft deceleration causes lights 10 and 11 to illuminate, while slightly stiffer braking and therefore greater deceleration causes lights 12 and 13 to be illuminated beyond lights 10 and 11 as shown in Fig. 1B. The firm retardation of the vehicle caused for example by the firm depression of the brake pedal is discovered by the vehicle display system 1 and causes additional lights to be activated. Thus lights 14 and 15 are illuminated in addition to lights 10 to 13 to indicate a relatively large vehicle deceleration as shown in Fig. 1C. To show a faster reduction in vehicle speed all eight lights are illuminated including outer pair 16 and 17 as shown in Fig. ID.

Other ways to indicate progressive deceleration could be to vary the relative sizes of the light pairs, for example by increasing the size of the lights 12 and 13 compared to the inner pair 10 and 11 and so on, so that that outer pair 16 and 17 would be the largest. This is used to increase the apparent “growth” effect of the dial by emphasizing faster vehicle deceleration and its increasing proximity to vehicles in the rear. Alternatively, each pair of lights could be of a different color, shade or intensity compared to other pairs of lights. For example, different shades of amber could be used from a light shade to inner pair 10 and 11 and darkening to outer pair 16 and 17, or possibly outer pair 16 and 17 could be red. An additional method would be to vary the relative intensity of the light pairs so that the outer pair 16 and 17 could be brighter than the inner pair 10 and 11. A combination of these parameters could be used on a PBW display and the light indicator could also be described. a stationary vehicle.

The lights could themselves include electro-luminescent bulbs that radiate light through translucent and colored filters. Alternatively, reflective lights could be used having phosphorescent targets: this can reduce the dazzle effect of the dial. Other forms of light source are considered such as light emitting diodes, for example. The display may also comprise a control which allows it to be

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ΕΡ0 680 418 / ΡΤ the intensity of the global dial varies, for example, allowing the adjustment of a bright day to night setting.

Operation of the deceleration light sequence may be independent of the vehicle's braking system and mainly dependent on the vehicle's absolute deceleration unless lights 10 and 11 can be illuminated when the vehicle's brake pedal is depressed regardless of Actual deceleration caused. Thus the initial indication of the indicator light is similar to the known brake light indicator, such as the single central brake light mounted for use on some motor vehicles. In a preferred form, however, the initial deceleration is independent of either the vehicle's brake or accelerator controls. This may not always be possible since certain national laws may require that the first lights only be illuminated when the brake pedal is depressed.

An advantage of a dial system according to the present invention is that it can be mounted on a vehicle during manufacture or alternatively later make minor modifications to a vehicle so that a retrofit unit or assembly could be made available to the vehicle. Aftermarket. This is possible as long as the deceleration can be detected by an accelerometer (described later) that is independent of any existing vehicle components.

The dial system can be used to generate a dial indicative of a stopping vehicle. This particular arrangement is called a stationary vehicle indicator (VSI). The dial can be animated or static. An animated visual display sequence is shown schematically in Fig. 2A to D by way of example. In this case, six of the eight lights in set 2 are illuminated continuously and the light pairs are deactivated sequentially. Thus, in figure 2A lights 10 and 11 are deactivated while lights 12 to 17 are illuminated, and in figure 25 lights 12 and 13 are deactivated while the rest of the display is illuminated. Figs. 2C and D show lights 14 and 15 off and 16 and 17 off respectively while the rest is illuminated. This sequence may be cyclically operated while the vehicle is, for example, stationary and has a repetition period of about 1 second. The dynamic animated effect is helpful in attracting drivers' attention on subsequent vehicles. The effect of the animated display is such that it is intended to indicate that the associated vehicle is stationary and not just braking, this should be evident on the display and / or sequence and therefore several different sequences of numbers can be used. .

The animated sequence of the stationary vehicle indicator may be inhibited when the

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60 680 418 / seguinte next vehicle is within a certain distance behind the vehicle carrying dial system 1. This has the beneficial effect of preventing boredom or hypnotization of subsequent vehicle occupants, for example when in dense traffic or when stopped at the traffic control lights. An indication that the vehicle is stationary may still be made by holding the outer pair of lights 16 and 17 in a continuously lit mode as shown in Fig. 2E. This in itself has the added benefit of avoiding further interpretation by the driver of the next vehicle that the vehicle ahead is about to accelerate. Alternatively, the illumination intensity of lights 10 to 17 may be reduced when the next vehicle is a predetermined distance behind. This has the advantage of keeping the same dial while the vehicle is stationary, thus avoiding any confusion from the next vehicle driver. Lights 10 to 17 can be dimmed by simply dividing the voltage across the lamps when a proximity sensor, described later, gives a signal indicating the proximity of a vehicle to the rear. It is evident that the "stationary vehicle indicator" dial should be terminated when the vehicle begins to move, so it is appropriate for display system 1 to include a vehicle motion detector (described in detail later) that functions to detect if the vehicle is moving.

In another embodiment, the animated display may change to a static display of unchanged intensity when a vehicle in the rear is detected by the proximity sensor. The static dial may for example be a linear array of amber triangular lights. In another form the VSI signal may be generated by the same lights used for the PBW signal, where in the latter case the lights are red rectangles, for example, and in the previous case the lights change to amber triangles, for example when the vehicle stops.

The electronic circuitry used to control the light display is shown in Figs. 3 and 4. The circuit diagram is schematic but can be seen to generate a logic sequence dependent on several inputs that activate the light display shown in Figs. 1 and 2.

The vehicle display system 1 shown comprises the set 2 of eight lights 10 to 17 which are 12V 5W (or 21W) lamps, for example. The traditional red brake light is generated in the usual way using a translucent red filter. Light pairs 10e 11, 12 and 13, 14e 15e 16e 17 are connected to power transistors 20, 21, 22 and 23, respectively. Each lamp is connected to a + 12V DC source and is illuminated when the relevant power transistor is opened to ground. As long as the lamps are connected in pairs as shown, only one input to the transistor is required.

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60 680 418 / ΡΤ relevant 20 to 23 to illuminate or deactivate each pair of lamps.

The combined display effect of progressive brake warning and stationary vehicle indication is generated in this example using the circuitry shown to open and close transistors 20 to 23 between lamps and ground. The circuit includes a + 12V DC power supply (not shown) and a regulating circuit 30 which generates a + 5V output. The accelerometer unit 32 and 33 is a piezoresistive seismic mass type accelerometer arranged on a Wheatstone bridge with integral control and temperature compensation as shown in Fig. 5. This provides an output signal proportional to vehicle acceleration (or deceleration) that It is supplied to variable resistor 52 and whose signal is independent of the mechanical brake system actuated by the brake pedal and thus allows for cases such as skidding. The throttle unit 32 and 33 is excited by a + 12V output that is powered by a DC-DC converter 70. The converter 70 may be a 750 mW encapsulated miniature device that provides a + and 12V power to the signal amplifier 71 The converter 70 is completely reverse polarity protected and each of the input and output lines are decoupled using electrolytic capacitors (not shown). Amplifier 71 comprises a Wheatstone bridge 72 (as for example that described in Radio Spares data sheet 8155 issued November 1987). Amplifier 71 may be an out-of-current article or modified such that amplifier 71 in a specific form has a gain of 250 and zero adjustment for a ± 6.7V output. Gain and zero adjustment are set to values ​​compatible with the accelerometer. The accelerometer 32 may for example be an Entran EGD-240-10. The voltage gauge amplifier 71 is used to raise the signal level from 10 mV / g to a level compatible with bar graph control 36 which should be 2.5 V / g in this specific example. This device as a whole has the advantages of a fixed state (DC) response, miniature size, robustness, low cost and ease of application.

The analog accelerometer output passes through a 10 KOhm variable register to a bar graph controller 36 which is an LM3914 device, for example as shown in Fig. 6. The gain and deviation variation of the amplifier output signal 33 together with the variation of potentiometer 52 can be used to change the input voltage of controller 36 to any given vehicle deceleration. In this example, controller 36 has a linear output relative to the input signal. Thus, the number of lights illuminated by the progressive brake warning system may be selected at four levels representative of the vehicle deceleration from 0 O5g to O 2g, O 2g to O 4g, O 4g to O 6g, and 0.6g and above for example.

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These bands are determined by way of example and may be varied to suit the type of dial used. The lower limit level that causes the first deceleration light to come on is preferably set to a level such that simply changing the shift does not turn on the light but should preferably allow a signal to be generated when the driver is deliberately decelerating, but smoothly. , for example by reducing the pressure on the accelerator pedal. Moreover, the increment of the levels need not be uniform, as is approximately the case in the above example, and could vary nonlinearly as exponentially.

Power transistors 20 and 23 are required to illuminate lamps 10 to 17 by generating a high output from the relevant OR ports 40 to 43. Transistor input 20, which controls central lamps 10 and 11, is connected to the OR port. 40. The default input for OR port 40 is low since the + 5V supply passes through a resistor and an inverter 44.

Inverter 44 output is high when controller 36 allows PI tip to take input to low inverter 44. Similarly, controller 36 gives high output to inverters 45, 46 and 47 by enabling tips P2, P3 and P4 respectively. Thus, in the case of mild deceleration detected by accelerometer 32, controller 36 only forces PI to generate a low input to inverter 44. A high input signal at OR port 40 causes a high input at the input base of transistor 20 which thus illuminates lights 10 and 11.

Figs. 3 and 4 also show how, using device 80, a brake pedal signal can be used to illuminate the central pair of lights 10 and 11 whenever the brake pedal is depressed. This could be used to indicate a very slight deceleration below the preset limit of the progressive brake warning system.

The stationary vehicle indication display described with reference to Fig. 2 may be made using the opto switch 34 and the circuitry shown in Figs. 3, 4 and 8 which comprise a vehicle motion detector that measures vehicle speed, although for the stationary vehicle indication display it is only essential to know whether the vehicle is stationary or moving.

Information that the vehicle is stationary can be obtained using a toothed opto-sensor 34 attached to the rear of a vehicle speedometer (not shown). The speedometer control cable rotates a toothed disk 91 housed in a nylon 95 cover. The toothed disk 91 is applied to a spindle 94 which is placed in series between the speedometer and the cable. Opto-switch 34 includes an LED 92 and a photodiode 93. As the spindle rotates, the light

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The infrared LED 92 ΕΡ0 680 418 / é is alternately dimmed and can then focus on photo diode 93. The integrated circuitry filters the output of photo diode 93 to produce a clean square wave TTL (Transistor / Logic Transistor) compatible with frequency of which is proportional to vehicle speed.

The opto-switch output signal 34 is applied to the RC (resistor / capacitor) mains 100 shown in Fig. 3. When the signal is high (+ 12V) the small 0.1 microfarad capacitor charges quickly through the first resistor. 10 kilo-ohms. As the signal voltage drops to zero, the current stored in the small capacitor discharges through the path of the smallest resistance, in this case through the diode and the relatively large 100 microF capacitor. Even without a voltage applied through the capacitor, the load is lost through the 10 kilo-ohms resistor as it cannot pass back through the diode. Assured that the square wave frequency is low enough, the charge on the 100 microF capacitor will almost completely dissipate before being charged again. The voltage seen by the positive terminal of comparator 25 (such as device 339 for example) will be virtually zero with small peaks around 12mV as each load packet is applied to it. As the frequency increases the small capacitor pumps smaller amounts of charge to the large capacitor, increasing the potential in it and thus the voltage at the comparator terminal 25. At this point the frequency is such that the charge does not have enough time to completely dissipate through the second resistor, so that the charge on the large capacitor increases with each amount of charge sent to it. After several cycles the system will reach equilibrium and a fixed voltage will be present at the positive terminal of the comparator, increasing the voltage proportionally with the vehicle speed.

Comparator 25 has a reference voltage set by voltage divider 53 applied to its negative input. When the positive terminal is below the reference voltage the comparator output 25 is held high by the 5V pull. Above the reference voltage comparator 25 pulls its output to ground. The components in the RC 100 grid and the reference voltage are adjusted so that the transition occurs at very low speed of the almost stationary vehicle. A binary signal is then available to the control system indicating “stationary vehicle” (logic 1) or “non-stationary vehicle” (logic 0).

The mechanical components of the opto-switch device are shown in Figs. 9A through H. In which case Fig. 9A shows an end elevation from the cable side and Fig. 9B is a sectional side elevation along the axis AA of housing 95A. Fig. 9C shows an end elevation from the end of the speedometer and Fig. 9D is a

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60 680 418 / ΡΤ sectional side elevation by the axis BB of the housing part 95B. Fig. 9E shows a side elevation of the spindle 94, while Fig. 9F is an end elevation thereof. Fig. 9G is an end elevation of the toothed disc 91 and Fig. 9H is a view of a clamp used to complete the assembly.

The opto-switch device is given by way of example only and it is considered that the stationary vehicle indication display may be enabled using input data for any form of stationary detection such as an electronic speedometer or anti-braking system. -blocking (ABS). With respect to the latter it is possible to modify the present ABS components normally used to provide the information required by the display system in both its PBW and VSI functions. Anti-lock braking systems typically comprise a device attached to a wheel hub whose device rotates with the wheel to provide an electronic signal proportional to the wheel rotation rate, for example using an electromagnetic inductive technique. For ABS purposes it is only required to know if the wheel locks. However, for the purpose of the present display system, more information about vehicle speed is required for deceleration to be calculated. Therefore, modification of the inductive device of the ABS may be carried out to provide appropriate information discussed later in the output signal of the device.

In the VSI system described herein, a square wave generator 37 triggers a counter 38 which is for example a 74161 device. Using AND ports 24a and 24b, only when the comparator 25 and oscillator 37 outputs are high and the proximity sensor 60 (described later) is low, and the clock input for counter 38 is high. While the vehicle is stationary the counting ratio is determined by oscillator 37 which can be configured to generate a specific time interval between switching display signals shown in Figs. 2A to D.

Counter 38 generates a binary output from 0 to 4 which is supplied to multiplexer 39, which is for example a 74138 device. Multiplexer generates high and low outputs at tips M1, M2, M3 and M4 depending on the input signal from counter 38 The tips M1, M2, M3 and M4 are connected to an input terminal of AND gates 48, 49, 59 and 51 respectively. The other input to AND gates 48 to 51 is taken from comparator output 25 and proximity sensor 60 at port 24a, which is thus the output signal that activates the stationary vehicle animated display.

The outputs of AND gates 48 to 51 are connected to an input of OR gates 40 to 43 previously described with respect to the progressive brake warning displays. When

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ΕΡ0 680 418 / ΡΤ the vehicle is stopped the input to OR ports 40 to 43 of inverters 44 to 47 will be low as there is no change in speed to generate an accelerometer 32 output signal. So when any of the OR 40 ports inputs 43 of the AND gates 48 to 51 get high, the relevant pair of lamps is illuminated. The animated cyclic display described with reference to Fig. 2 is effected by the timing of oscillator 37 and the switching sequence generated by multiplexer 39. The display sequence can easily be varied by changing these components or, in fact, by configuring the electrical circuit differently, for example by wiring individual lamps rather than by wiring pairs.

Completion of the stationary vehicle animated display can be achieved in a number of ways such as for example using the proximity sensor 60 shown in Figs. 3, 4, 10, 11 and 12. A variety of devices may be used such as infrared, optical, microwave or radar systems, however, an ultrasonic device is described herein provided, inter alia, that it is considered easy to be proof. of time and have small dimensions and low cost. The ultrasonic transducer 61 may be a small 26 Khz transducer (e.g. 25 mm) with a maximum range of 9 m when used for example with a small directional cone. Proximity sensor 60 includes a remote range module 62 which controls transducer 61 and filters its output. Module 62 provides a digital lockout output titled C in Fig. 11. As the transducer is depressed the lock is switched low. It stays low until the first echo is received by what it switches upwards. It remains high until it is pressed down again at the beginning of the next pressure pulse (A in Fig. 11). If the object is out of range of sensor 60 (more than 9m in this example), then the lock is not switched upward by the feedback echo. In the event that the trigger shifts the lock up momentarily and then down again, the pulse width being similar to that of the shot in approximately 180 microseconds, as shown in Fig. 11. The duration of the close low pulse provides a means for calculate the distance to an object, in this case a vehicle in the rear.

The digital close signal is used to regulate a monostable device 63, such as a dual adjustable 74123, for example, operating at high. The lockout output is fixed at + 5V as a high logic state and when it is firmly switched ON by module 62 the lockout output is pushed to ground, low logic; otherwise the output is logical high. Thus the closing output is compatible with logic 5V TTL in control box 3. The total output is applied to an input “A” of the first monostable 63 as shown in Fig. 12. Each time the transducer is triggered the closing edge of the lock sets the high monostable as shown in trace D of Fig. 11. The monostable timing circuit is calibrated so that it regulates monostable 63 after a

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0.018s period which corresponds to a range of approximately 3m from the transducer. A total of 6m is traversed by the sound at 330m / 's. The duration of the PRR pulse repetition rate is set at 0.06s (this is greater than the time equivalent to the sound path length) in this example. Monostable 63 should be a DM74LS123 device, for example, where the delay Tw - 0.37 CxRx such that for Cl = 10 microfarads and RI = 10 kiloOhm variable and R2 - 2.2 kilo-Ohm as shown in Fig. . 12, Tw = 0.008 to 0.0452s giving a range of 1.34 to 7.45 meters. Delay selection Tw = 0.018s is therefore given only as an example for vehicle detection up to approximately 3 meters from transducer 61.

The digital closure output of module 62 and the mono-stable output 63 are coupled using an AND logic gate. The output of this port thus gives a high logic state if a car is detected within the specified range, three meters in this example, as shown in dash E of Fig. 11. This pulse signal is fed to input “B” of a second mono device. -stable 64, again a 74123 device, for example. The device 64 delay period is set to approximately 110% of the PRR duration.

Thus, as long as one car is within range (3m in this example) the output of the second monostable 64 remains high. If the next vehicle moves out of range then the monostable 64 is not reactivated and falls back down after 0.066s (110% of PRR duration) and remains low until a vehicle is again detected within range. . Then a binary signal exits the proximity sensor 60 indicating vehicles less than 3m behind (logical high) or vehicle or vehicles larger than 3m behind (logical low). This is shown by the trace F in Fig. 11.

Proximity sensor output 60 is reversed and supplied to an AND port 24a which also has input for comparator output 25. If the vehicle is stopped and there is no vehicle within range of sensor 60, then both inputs to door 24a will be high and the animated display is activated as previously described.

Proximity sensor output 60 is also provided to AND port 24C to which comparator output 25 is also applied. If the vehicle is stationary and there is a vehicle within the predefined range then both inputs to the AND 24C port will be high and the outer pair of lights 16 and 17 will be illuminated until the vehicle behind moves out. of range, or as is apparently more likely, the vehicle with the dial system 1 begins to move, in which case the stationary vehicle indicator is deactivated entirely.

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It is also considered that while an accelerometer 32 and opto-switch 34 are used in this example, it is possible to make use of a vehicle anti-lock braking system (ABS) and the speed sensor rotates it in a speed dial system. according to the invention. It is possible to continuously measure the speed of a vehicle from this source (or indeed any independent vehicle speed measuring device) and thereby calculate acceleration using a time reference. It will then be possible to use this source to control the described logic circuit precisely to illuminate and deactivate lamps 10 to 17 according to the sequence described with respect to Figs. 1 and

2. This technique has the benefit of substantially utilizing an already assembled system to generate relevant vehicle information independent of the braking system itself. It can therefore be readily incorporated during construction and has the advantage of reducing the cost of the dial system itself. However, as previously described, some modification of the currently available ABS devices may be required to specifically improve the signal generated using such a device. In particular it may be necessary to increase the sampling rate of the ABS device to provide a signal of sufficient variability to allow predefined deceleration / acceleration bands to be distinguished. In a preferred form of the present display system, input information should be derived from ABS devices connected to diagonally opposed wheels in a vehicle. Additionally, the ABS device and a time reference system as described could justly be used to provide a signal to a display that is indicative of the vehicle moving at constant speed or accelerating. The display for the latter may comprise for example a set of green lights, depending on the number of which are activated by the size of the acceleration.