US3631393A

US3631393A - Vehicle lamp failure warning system having warning circuit completed when lamp is off

Info

Publication number: US3631393A
Application number: US833404A
Authority: US
Inventors: Allan Bennett
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1968-07-01
Filing date: 1969-06-16
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28
Also published as: DE1933016B2; GB1263711A; DE1933016C3; DE1933016A1; FR2012036A1

Abstract

A lamp failure warning system for a road vehicle has a first lamp circuit which is completed when the lamp is to be illuminated and a second lamp circuit which is completed when the lamp is extinguished but has a resistance sufficiently high to ensure that the lamp is not illuminated. Means is provided sensitive to failure of the lamp when either circuit is completed for giving a warning when the lamp fails.

Description

United States Patent Inventor Allan Bennett Solihull, England Appi. No. 833,404 Filed June 16, 1969 Patented Dec. 28, 1971 Assignee Joseph Lucas Industries Limited Birmingham, England Priority July 1, 1968 Great Britain 31,263/68 VEHICLE LAMP FAILURE WARNING SYSTEM HAVING WARNING CIRCUIT COMPLETED WHEN LAMP IS OFF 2 Claims, 3 Drawing Figs.

US. Cl 340/85, 340/251 Int. Cl 60% 21/00, B60q 1/02 Field 0! Search 340/85, 251

[56] References Cited UNITED STATES PATENTS 3,076,123 1/1963 McDermott 340/251 X 3,271,736 9/1966 Brown 340/251 X 3,408,625 10/1968 Skinner 340/251 X 3,421,157 1/1969 Atkins 340/251 3,428,943 2/1969 Carp et al. 340/251 3,252,157 5/1966 Pabst 340/25] X Primary Examiner-Harold I. Pitts Attorney-Holman & Stern ABSTRACT: A lamp failure warning system for a road vehicle has a first lamp circuit which is completed when the lamp is to be illuminated and a second lamp circuit which is completed when the lamp is extinguished but has a resistance sufficiently high to ensure that the lamp is not illuminated. Means is provided sensitive to failure of the lamp when either circuit is completed for giving a warning when the lamp fails.

PATENTED 05:28 l97| 3631. 393

sum 2 or 2 INVENTOE BY) "1 m ATT was VEHICLE LAMP FAILURE WARNING SYSTEM HAVING WARNING CIRCUIT COMPLETED WHEN LAMP IS OFF This invention relates to lamp failure warning systems.

A lamp failure warning system according to the invention comprises a first lamp circuit which is completed when the lamp is to be illuminated, a second lamp circuit which is completed when the lamp is extinguished and which has a resistance sufficiently high to ensure that the lamp is not illuminated, and means sensitive to failure of the lamp when either the first or the second lamp circuits is completed for giving a warning when the lamp fails.

In the accompanying drawings, FIGS. I and 2 are circuit diagrams illustrating two examples of the invention, as applied to the electrical system of a road vehicle, and FIG. 3 is a circuit diagram showing a modification of FIG. 1.

Referring to FIG. I, the battery 12 of the vehicle has its negative terminal connected to an earthed supply line 14, and its positive terminal connected to a supply line 13 through parallel paths one of which contains the ignition switch II of the vehicle and a resistor 5 in series, and the other of which contains a lighting switch 15. The switch 15 when operated operates simultaneously a second switch 16 controlling the supply of power to a supply line 24, and connected in parallel between the lines 24, I4 are four circuits each containing a diode 6 and a lamp 7 in series. The lamps 7 could, for example, be the side and taillights of the vehicle.

The junction of the diodes 6 and lamps 7 are connected through resistors 8 to the bases of four PNP-transistors 9 the emitters of which are connected to the line 13 and the collectors of which are connected through four resistors 10 to the bases of four NPN transistors 17. The transistors 17 have their emitters connected to the line 14, and their collectors connected through four resistors 18 to the junction of the switch 11 and resistor 5. The collectors of the transistors 17 are further connected through four diodes 19 to the base of an NPN-transistor 20, the emitter of which is connected to the line 14 through a resistor 12, and is also connected to the base of an NPN-transistor 21 having its emitter connected to the line 14. The collectors of the

transistors

20, 21 are connected through a warning lamp 23 to the junction of the resistor 5 and switch 11.

Assuming that the ignition switch 11 is closed, but the switches l5, 16 are open, then a circuit is completed through each of the lamps 7 by way of the resistors 8 and the base emitter paths of the transistor 9 and the resistor 5. The resistances of the four circuits are such that the lamps 7 are not illuminated, but the transistors 9 are all conducting, so that the transistors 17 also conduct. When the switches 15 and I6 are closed, the transistors 9 still conduct, but in this case the current flowing through the diodes 6 to the lamps 7 is sufficient to illuminate them. Thus, when the ignition switch II is closed, the transistors 9 conduct whether the switches 15 and 16 are open or not, but the lamps 7 are only illuminated when the switches 15 and 16 are closed.

As long as all the transistors 17 are conducting, no base current is supplied to the transistor 20, and so the

transistors

20 and 21 are both off. However, when a lamp 7 fails, whether or not that lamp was illuminated, then one of the transistors 9 will cease to conduct, and so the corresponding transistor 17 will also cease to conduct, and current will flow through the switch 11, one of the resistors 18, one of the diodes 19, the base-emitter of the transistor 20 and the base-emitter of the transistor 21 to turn on both

transistors

20, 21 and illuminate the warning lamp 23 to give the required indication.

FIG. 2 shows an alternative arrangement which is suitable for use with a positive earth system. The battery 41 of the vehicle has its positive, earthed, terminal connected to a supply line 43 and its negative terminal connected to a supply line 44. One side of the lamp 25 to be monitored is connected to the line 43, and its other side is connected to the line 44 through a diode 26 and the switch 27 controlling the lamp, the junction of the lamp 25 and diode 26 being connected through a resistor 28 at the base of an NPN-transistor 29, the emitter of which is connected to the line 44 through the ignition switch 42 and the collector of which is connected through a resistor 31 to the line 43. The collector of the transistor 29 is also connected through a diode 32 to the base of an NPN- transistor 34 having its emitter connected to the base of an NPN-transistor 33, the emitter of which is connected to the line 44, through the switch 42. The collectors of the transistors 33 and 34 are connected through a warning lamp 35 to the line 43.

In operation, assuming that the switch 37 is open and the ignition switch 42 is closed, current flows through the warning lamp 25 and the resistor 28 turns the transistor 29 on, but the current flowingthrough the lamp 25 is insufficient to illuminate it. When the switch 27 is closed, the lamp 25 is illuminated, and the transistor 29 is still held on. Thus, as long as the lamp 25 is operating satisfactorily, the transistor 29 prevents current from flowing through the diode 32. However, when the lamp fails, whether or not the switch 27 is open, the transistor 29 is turned off and current flows through the resistor 31 and diode 32 to turn on transistors 34 and 33, so that the warning lamp 35 is illuminated.

It will be noted that in FIG. I the lamp switch I5, 16 is a double switch, and the resistor 5 is employed, whereas in FIG. 2 a single lamp switch 27 is used and there is no equivalent to the resistor 5. The reason for this is that in FIG. 1 the low-gain PNP-transistor 9 require a low valve for resistors 8 in order that insufficient base drive can be supplied to saturate them. In order to prevent excessive power dissipation with the lighting switch open, the resistor 5 is incorporated to increase the base-emitter resistance of each of the transistors 9. It is then necessary to use the two-part lighting switch l5, 16 to isolate the line 24 from the line 13 when the switches l5, 16 are open. This problem does not arise in FIG. 2, where the transistors 29 equivalent to the transistors 9 in FIG. 1 are NPN-transistors which have higher gains.

In systems where it is inconvenient to use a double switch 15, I6, the modification shown in FIG. 3 can be used. In FIG. 3, only the circuit associated with one lamp 7 is shown, and it will be seen that compared with FIG. I the part 16 of the switch 15, 16 is omitted, with the diode 6 having its anode connected through the switch 15 directly to the positive battery terminal. The resistor 5 is also omitted, so that the switch 11 completes a direct connection to the line 13. Each transistor 9 is now replaced by a pair of transistors 9a and 9b. The transistor has its base connected to the resistor 8 and its emitter connected to the line 13, while its collector is connected to the base of the transistor 9b, the collector of which is connected to the line 13 and the emitter of which is connected to the resistor 10. The transistors 90 and 9b form an effective high-gain PNP-combination, and using this arrangement the resistor 8 can be chosen so that the circuit operates satisfactorily without the necessity of the resistor 5, and the consequent requirement for a double switch 15, 16.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

I. A lamp failure warning system comprising a first lamp circuit which is completed when the lamp is to be illuminated, a second lamp circuit which is completed when the lamp is extinguished, and which has a resistance sufficiently high to ensure that the lamp is not illuminated, said first lamp circuit when completed increasing the current flow in the lamp to illuminate the lamp, and a second lamp circuit remaining completed when the first lamp circuit is completed, and means operable by said second lamp circuit and sensitive to failure of the lamp when either the first or second lamp circuits is completed for giving a warning when the lamp falls.

2. A lamp failure warning system for a road vehicle, comprising a series circuit connected across the battery of the vehicle and including a lighting switch, a diode and a lamp, a second circuit connected across the vehicle b ttery and including the ignition switch of the vehicle, the emitter-base path of a transistor, a resistor and said lamp, said second circuit being completed when the ignition switch is closed to cause the transistor to conduct but the current flowing through the lamp being insufi'rcient to energize it until the lighting switch is closed, and means operable by the collector current of said transistor for giving a warning when the baseemitter current of said transistor is broken by failure of said lamp. 5

Claims

1. A lamp failure warning system comprising a first lamp circuit which is completed when the lamp is to be illuminated, a second lamp circuit which is completed when the lamp is extinguished, and which has a resistance sufficiently high to ensure that the lamp is not illuminated, said first lamp circuit when completed increasing the current flow in the lamp to illuminate the lamp, and a second lamp circuit remaining completed when the first lamp circuit is completed, and means operable by said second lamp circuit and sensitive to failure of the lamp when either the first or second lamp circuits is completed for giving a warning when the lamp fails.

2. A lamp failure warning system for a road vehicle, comprising a series circuit connected across the battery of the vehicle and including a lighting switch, a diode and a lamp, a second circuit connected across the vehicle battery and including the ignition switch of the vehicle, the emitter-base path of a transistor, a resistor and said lamp, said second circuit being completed when the ignition switch is closed to cause the transistor to conduct but the current flowing through the lamp being insufficient to energize it until the lighting switch is closed, and means operable by the collector current of said transistor for giving a warning when the base-emitter current of said transistor is broken by failure of said lamp.