GB2083718A - Car lights on indicator - Google Patents

Abstract

A motor vehicle electrical system includes a device AD1, for warning that the vehicle's lamps (Input T2) have been left on when the ignition (Input T1 is switched off. The warning device which comprises NAND gate IC1 and monostable IC2, can be deactivated by switching the ignition back on, or by switching the lamps off. A facility is provided whereby it is possible to switch the lamps off to deactivate the device and the back on for use as parking lights without the warning device being reactivated. <IMAGE>

Description

SPECIFICATION Motor vehicle electrical systems This invention relates to motor vehicle electrical systems, and in particular to those having a lamp or lamps.

Hitherto, a problem not infrequently met by motorists has been that of leaving vehicle lights on when the vehicle is not in use. This typically occurs when the lights have been switched on during daylight in conditions of poorvisibilty, and results in a waste of energy derived from the vehicle's battery which is sometimes left in such a low state of charge that the vehicle's engine cannot be re-started.

According to the invention, there is provided a motor vehicle electrical system including a voltage source, a switchable lamp powered by said voltage source, a master switch which when switched off stops the vehicle's motor, and a warning device which is activated when said lamp is on and said master switch is switched from on to off.

Thus when the vehicle's lamps are on and the driver makes ready to leave the vehicle, a warning is provided of the lamps' condition upon his switching off the master switch, which typically the engine's ignition switch.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a circuit diagram of a part of a motor vehicle electrical system in accordance with the invention; and Figure 2 is a diagram showing phase relationships and voltage levels at points in the circuit of Figure 1.

The Figure 1 shows a circuit diagram of that part of the electrical system which is concerned with actuation of a warning device ADl,the remainder of the system being conventional and therefore not shown.

The circuit includes two integrated circuit building blocks: I.C. lisa quad nand gate, similar two C.M.O.S.

4011, and l.C. 2 is a mono-stable of a similar type to C.M.O.S. 4098. The system is for use on a 12 volt negative earth vehicle. The supply for the circuit is taken via terminal T3, which is connected directly to a voltage source comprising the vehicle's battery.

Connections are taken: to the vehicle's chassis earth via terminal T4, to the lamp circuit via terminal T2, and to the ignition/master switch via terminal T1.

The mono-stable l.C.2. has two inputs controlling its action: 1. The trigger input, which will run the mono-stable as the potential changes from zero volts to a higher voltage (positive edge trigger), on its input.

2. The reset input. If this input is held low, the mono-stable will not operate. When this input is high (the same potential as terminal T3), the mono-stable will respond to the change in voltage on the trigger input.

Resistors R1 and R2 form a potential divider, with zener diode D1 being a voltage limiting device. D1 will also protect the input to gate 'A' from negative poiarity spikes that may occur at terminal T2.

Terminal T1 has more protection because the ignition circuit on a spark-ignited engine is prone to various transient potentials in both the positive and negative directions.

Zener diode D2 is a high voltage spike protector (typically rated at 18 volts) and also a reverse polarity spike protector.

Afuse may be connected between the earth point for the device on the vehicle's chassis, and terminal T4. This fuse will protect the circuit if excess current flows in D2.

Resistors R3 and R4form a potential divider, and zener diode D5 limits the input voltage to gate 'C'.

Capacitor C1, diode D3 and resistor R3 form a smoothing circuit, so that when the ignition/master switch is turned to the 'off' position, any voltage spikes produced as the engine runs on for a short time will not affect the operation of the unit.

Diodes D4 and D6, together with resistor R5, form a simple OR gate. Resistor R6 and capacitor C2 delay the rising potential from the output of gate 'A' for approximately 1 ms, which is long enough for the reset input of the mono-stable to reach the same potential as terminal T3 before the mono-stable is triggered.

The audible warning device AD1 is an electronic buzzer but could be an electronic circuit that will create a tone to be reproduced through a suitable transducer, e.g. moving coil loudspeaker, piezoelectric transducer or any other suitable device.

When the ignition switch is 'on' and the lamps are on, terminals T1 and T2 are at the same potential as terminal T3. The output of l.C.1 gate 'C' will then be at zero volts (logic level 0, low), as will be the output of gate 'A' and gate 'B'.

When the potential is removed from terminal T1 only, by turning the ignition/master switch to the 'off' position, the output of gate 'C' goes high, allowing the mono-stable to be triggered. At the same time, gate 'A' output goes high (point V). This rising edge is delayed by the action of resistor R6 and capacitor C2.

The warning device can be disabled by returning the ignition/master switch to the 'on' position. This action connects T1 to the same potential as T3; therefore, gate 'C' output goes low, thus disabling the mono-stable, and silencing the alarm.

Again, when the potential is removed from T1, and the audible device is sounding, it may also be silenced by removing the potential from terminal T2, that is, turning off the vehicle's lamps. This action will cause the output of gate 'B' to go high. This potential, in turn, is passed to gate 'C' via diode D6, diode D4 being reversed biased, to return gate 'C' output low, taking the mono-stable reset input low, disabling the mono-stable and silencing the audible device.

With terminal T1 open circuit or at a potential of zero volts, it is possible to apply a potential to terminal T2, turn the lamps 'on', without activating the mono-stable and audible warning device. This is because the output of gate 'A' is permanently high, thus not affecting the mono-stable trigger input.

A diagram of phase relationships and voltage levels is shown in Figure 2.

Thus, the device will generate an audible tone, for a pre-determined length of time, when the lamps on a vehicle are 'on' and the ignition/master switch is turned to the 'off' position. The tone can be silenced by any one of three actions before the predetermined time has elapsed: 1. Returning the ignition/master switch to the 'on' or 'run' position; 2. Switching the lamp switch to the 'off' position; 3. Switching the lamp switch 'off' and 'on' will silence the tone, but leave the lamps 'on' for parking.

This is the cancel feature.

It will be appreciated that the circuit could be modified from the form illustrated and still perform the functions in accordance with the invention.

Again, the audible warning device could be replaced or supplemented by a visual display, although this could more easily escape attention under typical conditions in which the lights are left on by mistake unless it was made particularly clear.

Claims (13)

1. A motor vehicle electrical system including a voltage source, a switchable lamp powered by said voltage source, a master switch which when switched off stops the vehicle's motor, and a warning device which is activated when said lamp is on and said master switch is switched from on to off.

2. An electrical system as claimed in claim 1, wherein said warning device is arranged to operate, when activated, for a predetermined period.

3. An electrical system as claimed in claim 1 or 2, wherein said warning device is deactivated immediately by switching said lamp off.

4. An electrical system as claimed in claim 1,2 or 3, wherein said warning device will remain deactivated when said lamp is switched on again after the lamp has been switched off to deactivate the warning device.

5. An electrical system as claimed in any one of claims 1 to 4, wherein said warning device is deactivated immediately by switching said master switch on.

6. An electrical system as claimed in any preceding claim, wherein said warning device remains inactive when said master switch is off and said lamp is switched from off to on.

7. An electrical system as claimed in any preceding claim, wherein operation of said warning device is controlled by an electronic circuit including a NAND gate which receives inputs from the lamp circuit and the master switch, the output from said NAND gate being used to activate the warning device.

8. An electrical system as claimed in claim 7, including means to inhibit operation of said warning device when said master switch is on.

9. An electrical system as claimed in claim 7 or 8, including means for delaying receipt by said warning device of outputs from said NAND gate.

10. An electrical system as claimed in claim 7,8 or 9, wherein output from said NAND gate is used to trigger a mono-stablecontrolling operation of said warning device.

11. An electrical system as claimed in claim 7 and 9, wherein said master switch controls a reset on said mono-stable to inhibit operation of the warning device whenever the master switch is on.

12. An electrical system as claimed in any preceding claim, wherein sajd warning device produces an audible warning.

13. An electrical system substantially as herein efore described with reference to the accompanying drawings.