GB2257672A - Speed change warning device, eg for vehicle brake lights - Google Patents

Abstract

The device incorporates a modified mercury tilt switch (7) fixed at a predetermined inclination in the line of travel which is part of the brake or acceleration warning circuitry usually incorporating lights, alarms or other communicative devices, eg. rear red brake lights, or integral of a self contained detachable unit with own circuit. Rapid changes of speed cause the mercury (2) to ascend or descend the inclined switch tube (1) thereby switching the warning device on or off. The mercury may bridge a pair of contacts in on/off fashion (upper part of Fig. 1) or move along a resistive loop to form a miniature rheostat (lower part of Fig. 1). The device may be independent or may be used in addition to the usual brake pedal switch so that the brake lights increase in brightness, or additional lights are displayed, under sufficient deceleration. The device may be incorporated into the brake light bulb itself, Fig. 8, Various operating circuits are described. <IMAGE>

Description

SPEED CHANGE WARNING DEVICE This invention relates to speed change warning devices such as lights or alarms.

Motor vehicles and other moving apparatus often need to communicate their change in speed automatically through indicators such as lights. alarms or dials. In particular vehicles used on roads have rear mounted red brake warning lights which are operated by the movement of the brake pedal providing an indirect. inaccurate and somewhat uninformative warning of a reduction in speed. Whether the vehicle is barely changing speed or decelerating as quickly as possible the warning to the vehicles behind is the same. This deficit in information of speed change is particularly hazardous on motorways.

The present invention comprises the incorporation of a modified 'mercury tilt switch '. aligned in the direction of travel, into the speed change warning electrical circuitry of a vehicle (eg. brake lights ) in such a way that the change of speed of the vehicle causes the mercury blob to rise or fall along the fixed. sealed. inclined tube of the switch therebye making, breaking or varying the flow of electrical energy in the circuit. The mercury connects electrical terminals running along the floor of the sealed inclined switch tube.

Several embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 shows two variants of a mercury tilt switch to be fixed at a certain incline to the horizontal.

Figure 2 shows a schematic presentation of a simple electrical circuit incorporating the mercury switch.

Figure 3 schematically illustrates a typical bayonet fitting car brake light bulb into which a deceleration warning switch is incorporated.

Figure 4 shows a schematic plan of one version of a motor vehicles brake warning light circuitry incorporating the proposed device.

Figure 5 shows another version of brake warning light circuitry.

Figure 6 illustrates a self contained battery operated automatic speed change warning light which could be attached to a rear windscreen.

Figure 7 shows a schematic plan of the circuitry used in the unit depicted in figure 6.

Figure 8 depicts a schematic illustration of a car brake warning light bulb with double filaments connected to separate circuits.

Refering to the drawing the essential part of the proposed circuitry is the speed change warning switch 7 which responds to change of speed (ie. acceleration or deceleration ) and is shown in Figure 1 and consists of a hollow tube of insulating material 1 (eg. plastic ) which is sealed at both ends and could contain an inert gas. vacuum or air enviroment in which a blob of mercury 2 is housed.

Two or more electrical connections 4 pass into this container 1 along it's floor ( in relation to gravity ' and form the contacts 3 & 5 for the mercury to bridge in an on/off fashion 3 or in a continuously variable fashion by means of an electrically resistive loop 5 similar to a miniature rheostat. The longitudinal axis of the switch 7 lies in the direction of travel and is inclined at a specific angle to the horizontal axis of the vehicle or unit to which it is fitted.

By way of example the principle will be described in relation to vehicle brake warning lights. In Figure 2 the bold arrow shows the direction of forward travel of a vehicle (eg. car, lorry. train or aircraft ). The switch 7 is inclined at angle 77 to the horizontal. When the speed of the vehicle is constant, accelerating or gently decelerating the mercury 2 remains at the rear. bottom end of the cylinder 1 and the switch 7 is off. When the vehicle decelerates rapidly the mercury 7 will ride forward, up and along the cylinder 1 to bridge the electrical terminals 3 or 5 thus directly connecting the brake warning bulb 8 to the battery 9 causing the bulb to illuminate. When the rate of deceleration reduces the mercury will fall back. down and along the cylinder 1 under the force of gravity disconnecting the terminals.

In Figures 2. & 5 the switch 17 represents the standard type of spring loaded contact switch which operates the brake light 8 in response to brake pedal 15 depression by foot 16. One arrangement is that the switch 17 continues to operate the brake pedal light 8 through a resistor 6 producing one intensity of light but when switch 7 operates conjointly with rapid deceleration the direct contact produces a brighter intensity of light and a second more imminent warning of braking and danger.

An alternative arrangement as shown in Figure 4 involves two separate brake warning lights which could be of different colours or shapes ( eg. red & purple ) with the proposed device 7 being directly and constantly connected to the battery 9 and bulb 8 giving warning of sudden deceleration even if the brake pedal is not depressed, this automatic warning being useful in crash or mechanical failure situations.

If the rheostatic version 5 of the speed change warning switch 7 is used in the above examples the brightness of the brake light 8 will vary upto a fixed maximum according to the degree of deceleration.

In Figure 3 a novel application of the rheostatic version of switch 7 is shown incorporating it into a 'thinking' brake light bulb. Using bayonet fittings 13 the bulb can only be fixed into it's holder one way ensuring the switch 7 is inclined at the correct angle. assuming the bulb holder is mounted horizontally ( as it is in most vehicles ). This arrangement allows easy application of the proposed device without alteration to existing vehicle circuitry.

NB. In Figures 3 & 8 the following components of standard brake warning bulbs are shown: bulb glass 10. bulb filament 11, earth or negative connection/metal casing 12 and positive central terminal 14.

An alternative version of the thinking ' brake light bulb shown in Figure 8 could involve the use of two seperate light filaments in the same bulb. one being connected 22 in the conventional way to the spring loaded contact switch 17 operated by brake pedal depression. the other filament being connected through the speed change warning switch 7 to a live contact 23 of the ignition circuit. This double filament arrangement would entail alteration to existing brake warning light bulb holders to provide the dual central positive terminals.

A further example of a speed change warning light is shown in figures 6 & 7. This is an independent unit incorporating it's own small battery 9 connected through speed change warning switch 7 to warning bulb 8 mounted in a reflector dish 21 contained in it's own casing 18. The unit casing 18 is attached to a windscreen by an adhesive lip 19 and the correct inclination of the switch 7 in relation to gravity is obtained by turning the dial 20 to align the dial arrow as required. Such a device could he fitted to car rear windscreens and would compensate for the different slope angles of these screens.

Any or all of these applications could easily be adapted to warn of rapid acceleration by reversing the tilt of the speed change warning switch 7 in the examples given noting the direction of travel is left to right of the page in the examples.

It should be noted that the sensitivity of the speed change warning switch 7 will be affected by the inclination of the surface on which the vehicle is traveling. As regards a brake warning device it will be more sensitive going downhill and less sensitive uphill which is a useful feature. An advantage in using mercury as the electrical bridge in the switch 7 is the 'all or nothing ' effect this element tends to have as regards its movement and it's ability to envelope the electrical terminals minimizing arcing and wear at any one point of electrical contact therefore improving reliability.

Claims (7)

1) A speed change warning device which incorporates a fixed, inclined. modified mercury tilt switch aligned in the direction of travel of the vehicle to which it is attached and serves as part of the speed change warning device electrical circuitry. such as rear mounted brake lights. in such a way that the change of speed of the vehicle causes the mercury blob of the switch to rise or fall along the floor of the fixed, sealed. inclined tube of the switch therebye making, breaking or varying the flow of electricity across the switch connections and hence in the speed change warning circuitry.

2) A speed change warning device as claimed in claim 1 such that the inner electrical terminals of the mercury switch run along the floor of the mercury switch casing.

3) A speed change warning device as claimed in claim 1 or claim 2 wherein the inner electrical terminals of the mercury switch form a continuous loop of eiectrically resistive material such that movement of the mercury dramatically alters the electrical resistance measured across the external terminals of the switch.

4) A speed change warning device as claimed in claim 3 wherein the mercury switch and/or resistors are incorporated into the circuit of and structure of a standard sized light bulb. eg. a vehicle brake warning light bulb.

51 A speed change warning device as claimed in claim 3 or claim 4 wherein an independent light unit incorporating light bulb, reflector, means of attachment, independent power supply and mercury switch with adjustable inclination can be fixed to any useful vantage position such as a rear windscreen.

6) A speed change warning device as claimed in claim 1 or claim 5 which uses a different coloured warning light than red when the mercury switch operates.

7) A speed change warning device substantially as described herein with reference to Figures 1 to 8 of the accompanying drawing.