GB2270288A

GB2270288A - Vehicle accelerometer and display system.

Info

Publication number: GB2270288A
Application number: GB9218608A
Authority: GB
Inventors: Maria Antonio Di
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-09-03
Filing date: 1992-09-03
Publication date: 1994-03-09
Also published as: GB9218608D0

Abstract

An accelerometer determines the acceleration forces acting upon the vehicle. The forces are scaled to indicate their acceptability under normal driving conditions. The representation of the forces is in a form to encourage the driver to develop a smooth driving technique, preferably using an array of coloured LEDs 1, 2, 3 or audible tones to emphasise the different levels of acceptability. The acceleration transducer may be a weighted cantilever bar to which one or more strain gauges are fixed. A level adjustment knob 4 may be provided. <IMAGE>

Description

ACCELEROMETER This invention relates to an accelerometer.

Whilst the speedometer may inform the driver of the speed of the vehicle, no clear or useful information about the accelerating and decelerating forces acting upon the vehicle is provided. An accelerometer acting in real time indicating the magnitude of the accelerating and decelerating forces provides the driver with a useful aid to develop good driving practices.

Harsh or excessive acceleration puts extra strain on the mechanical elements of the vehicle extending from the engine through the gearbox and drive shafts to the tyres. This extra stress on the vehicle components may seriously shorten the life of a component resulting in more frequent replacements than usual. Furthermore, harsh or excessive acceleration is verv inefficient in terms of fuel economy. Not only is energy being expended in accelerating masses unnecessarily, but a large proportion of the fuel remains unburnt under such acceleration.

Similarly, harsh or excessive deceleration (i.e. braking) should also be avoided whenever possible. Here the vehicle's braking system and suspension units are subjected to extra stresses, resulting in increased wear and tear to the brake pads, tyres and shock absorbers. In poor road conditions (i.e. slippery road surfaces), harsh or excessive braking may result in skidding, effectively losing control of the vehicle. In good road conditions, late braking in an harsh or excessive manner increases the likelihood of a rear end shunt due to a following vehicle having less time to react to the rapid deceleration of the vehicle in front.

It is therefore highly desirable from an economic and safety point of view for the driver to develop a smooth driving technique, accelerating in a steady manner within predefined limits while looking sufficiently ahead to anticipate traffic movement so that he may brake well in advance should the need arise, decelerating within predefined limits.

The purpose of this invention is to provide the driver with a real-time indication of the acceleration or deceleration forces acting upon the vehicle, the portrayal of these forces being in such a form as to aid and encourage the driver to minimize these forces by adopting a smooth driving technique.

According to the present invention there is provided an accelerometer comprising of a transducer, an amplifier and a display system, providing a real-time dynamic representation of the acceleration forces experienced by the accelerometer, indicating their acceptability under normal driving conditions.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows the accelerometer in perspective; Figure 2 shows the transducer arrangement; Figure 3 shows a block diagram of the accelerometer.

Referring to figure 1 the accelerometer is a totally selfcontained unit preferably comprising of ten Light Emitting Diodes (LEDs), five green 1, three yellow 2 and two red 3, although other number and/or colour combinations may be used, as well as other types of display systems. These LEDs which may be lit in bar or dot mode are used to display the magnitude of the acceleration or deceleration forces. The LEDs preferably light from left to right with increasing magnitudes of acceleration or deceleration so that small magnitudes cause only the green LEDs to light while larger magnitudes cause the yellow LEDs to light and larger magnitudes still cause the red LEDs to light. The driver is encouraged to accelerate in a smooth manner so that he remains within the green zone.The yellow zone is entered in circumstances where strong acceleration is required such as in an overtaking manoeuvre or pulling away into fast flowing traffic. The red zone should be avoided. If the driver enters this zone he is accelerating excessively and should try to adopt a more restrained approach to acceleration. Similarly during braking he should remain within the green zone indicating a smooth controlled braking manner. Entering the yellow zone indicates harder braking than preferable due to late or unexpected braking. By entering the red zone the driver in braking far to harshly. This is often due to very late braking and represents a failure to read the road. The only legitimate time he should enter the red zone is during an emergency stop.

To aid the driver to read the display, the accelerometer should preferably incorporate a circuit which captures the peak values of the forces and displays them for a period of time after the peaks occurred. The peaks may be displayed together with or without the present values of the forces.

The accelerometer should be firmly attached to the vehicle and zeroed using the adjustment 4 with the vehicle at rest on level ground as inclinations also produce acceleration forces. The accelerometer should preferably incorporate a LED dimming circuit which lowers the brightness of the LEDs at night so not to disturb the driver.

Referring to figure 2 the preferred transducer is one or more strain gauge 5 affixed to a cantilever bar 6 which is securely anchored at one end and has a weight 7 attached to the other.

The bar is mounted in a plane perpendicular to the direction of motion of the vehicle so that acceleration or deceleration forces produce a bending moment which causes the bar to bend about its steady state position. The larger the acceleration or deceleration forces the more the bar bends producing larger deformations of the strain gauge. The resultant change in strain gauge resistance is used to indicate to the magnitude of the forces. To dampen oscillations in the bar the arrangement may be enclosed within a chamber 8 filled with a high viscosity oil 9.

Referring to figure 3 the accelerometer consists of a transducer employed within a wheatstone bridge network. The bridge is balanced using the balancing and zeroing circuitry. If during usage the accelerometer is mounted onto an inclined surface the display may be zeroed using this circuitry. The change in transducer resistance exhibited during acceleration or deceleration causes an imbalance in the bridge and a signal amplifier is used to amplify this imbalance. The output of the signal amplifier is fed into a LED display driver. The driver sequentially lights the LEDs when an increasing voltage is applied to the input. The steps between each LED may represent a linear, log, semi-log or other scale. Logic circuits are employed to select a bar or dot mode of operation. Internal current limiting circuitry within the driver allows the LED array to be connected directly to the driver.Furthermore, a light sensitive diode or similar device is used to control the current through the LEDs so as to minimize the current and therefore the brightness at night.

In wheatstone bridge networks the polarity of the imbalance potential depends on whether there is an increase or decrease in the transducer resistance. Acceleration and deceleration forces would therefore lead to opposite polarities of imbalance potential. However by adopting a switchable arrangement to the bridge supply voltage a constant polarity is maintained in the imbalance potential. This allows both acceleration or deceleration to be displayed by directly amplifying the imbalance potential. To achieve this, the signal amplifier has a dead band region about the zero forces position. When the unit is within this region a threshold detector enables an oscillator. The oscillator is used to clock a flip-flop which in turn controls the switching of the bridge supply voltage. Thus the bridge supply voltage is continually changing direction when the unit is within the dead band region. If a large enough imbalance potential of the correct polarity appears at the signal amplifier the threshold detector disables the oscillator and the bridge supply voltage is maintained across the bridge in a direction determined by the state of the flip-flop.

In normal circumstances, it is acceptable for vehicles to slow down at a faster rate than to speed up (i.e. to undergo larger deceleration forces before entering the yellow or red zones than acceleration forces). The magnitude of the imbalance potential appearing at the signal amplifier inputs is a function of the bridge supply voltage. Therefore by using a lower bridge supply voltage for deceleration than acceleration a lower output voltage is obtained, or in other words, greater deceleration forces are required to achieved the same output. Alternatively, the correct scaling of the forces as related to the coloured zones is achieved by amplifying the imbalance potential less when generated by a deceleration force than when generated by an acceleration force.The bridge supply voltages need to be as stable as possible therefore they should preferably be amplifications of a reference voltage. The overall amplification of the imbalance potentials may be selectable to correspond more closely to particular types of vehicles.

The preferred method of capturing the peak values of the forces is to connect a diode, capacitor arrangement to the output of the signal amplifier so that the capacitor captures the peak output voltage values. The peak value is compared to present value by a voltage comparator which triggers a monostable when the present value falls below the peak value. The monostable is used to trigger the discharge of the capacitor thereby controlling the peaks display time. Fast switching of the LED driver input between the present value and the peak value results in both values being displayed concurrently.

Although not shown in this embodiment the accelerometer may incorporate a sound generating system which may be used with or without the LEDs. Different tones may be used to indicate the different magnitudes of the acceleration and deceleration forces.

Claims

1 An accelerometer comprising of a transducer, an amplifier and a display system, providing a real-time dynamic representation of the acceleration forces experienced by the accelerometer, indicating their acceptability under normal driving conditions.

2 An accelerometer as claimed in Claim 1, wherein both positive and negative acceleration forces are displayed, suitably scaled to their respective acceptability.

3 An accelerometer as claimed in Claims 1 or 2, wherein the peak values in acceleration forces (positive and/or negative) are displayed, together with or without the present values, for a period of time after they occurred.

4 An accelerometer as claimed in Claim 3, wherein a diode, capacitor arrangement is used to capture the peak output voltage values, the peak value compared to the present value by a voltage comparator, which triggers a monostable when the present value falls below the peak value, the monostable being used to trigger the discharge of the capacitor. If desired, present values may be displayed together with the peak values by fast switching of the LED driver input between the present value and the peak value.

5 An accelerometer as claimed in any preceding claim, wherein the transducer is employed within a wheatstone bridge network, the bridge balancing circuit providing the accelerometer zeroing facility.

6 An accelerometer as claimed in Claim 5, wherein the transducer comprises of one or more strain gauges attached to a weighted cantilever bar provided with or without damping.

7 An accelerometer as claimed in Claim 5 or 6, wherein the wheatstone bridge supply voltage is of switchable polarity to maintain a constant imbalance voltage polarity.

8 An accelerometer as claimed in Claim 7, wherein the imbalance voltage is monitored by a threshold detector, the detector being used to enable an oscillator, the oscillator being used to clock a flip-flop, the flip-flop outputs controlling the switching of the bridge supply voltage.

9 An accelerometer as claimed in Claims 5, 6, 7 or 8, wherein the wheatstone bridge supply voltage is of switchable magnitude to provide a scaling factor to the imbalance voltage.

10 An accelerometer as claimed in Claims 5, 6, 7 or 8, wherein the imbalance voltage in amplified less if produced by a deceleration force than if produced by an acceleration force to provide the correct scaling of the output voltage.

11 An accelerometer as claimed in any preceding claim, wherein the display system comprises of a LED driver and an array of Light Emitting Diodes (LEDs) in any number and/or colour combination, or other suitable display system.

12 An accelerometer as claimed in Claim 11, wherein the LED driver lights the LEDs in bar or dot mode, the steps between each LED representing a linear, log, semi-log or other scale.

13 An accelerometer as claimed in Claim 11 or 12, wherein a light sensitive diode or similar device is used to control the current through the LEDs so as to minimize the current and therefore the brightness at night.

14 An accelerometer as claimed in any preceding claim, wherein the overall amplification of the acceleration forces (positive and/or negative) is selectable to suit different types of vehicle.

15 An accelerometer as claimed in any preceding claim, wherein the accelerometer incorporates a sound generating system, used with or without the LEDs, so that different tones are generated to indicate the different magnitudes of the acceleration and deceleration forces.

16 An accelerometer substantially described herein with reference to Figures 1-3 of the accompanying drawings.