Abstract:
In an indicating lamp circuit wherein a plurality of indicating lamps are each connected in series with a plurality of switches which respond to the operating condition of a motor car, each lamp is energized by a power source through a switch adapted to close only when an engine for driving the motor car stops. Upon energization faulty lamps are not illuminated so that their faulty condition is automatically detected when the engine is not in operation.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus for detecting fault of indicating lamps, especially those used in motor cars. 
     In a motor car a plurality of lamps are used to indicate the operating conditions of various portions, and faults such as the breakage of the filaments of the lamps should be supervised constantly. 
     Heretobefore, one or more check switches have been provided for merely checking indicating lamps so that it has been necessary to operate such check switches in order to detect that one of the lamps is faulty. Accordingly, it is more or less troublesome to operate check switches. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide improved indicating lamp circuit for detecting faults in any one of a plurality of indicating lamps provided on a motor car, which is simple in construction but automatically detects faulty indicating lamps. 
     Another object of the present invention is to provide an improved indicating lamp circuit capable of detecting faulty indicating lamps while the motor car is not running but permitting the indicating lamps to display various operating conditions of the motor car when it is in operation. 
     Another object of the present invention is to provide a lamp indicating circuit in which the indicating lamps may be simultaneously tested to determine which lamps are fault-free and which are faulty. 
     According to the present invention there is provided an indicating lamp circuit for detecting the fault of a plurality of indicating lamps of a motor car or vehicle of the type comprising a plurality of switches responsive to various operating conditions of the motor car, a plurality of indicating lamps connected in series with respective switches, means for connecting terminals of the indicating lamps to one pole of an electrical source or supply, characterized in that there are provided a common conductor, switch means connected between the common conductor and the other pole of the source, said switch means being closed when an engine of the motor car stops its operation, and a plurality of diodes connected between the common conductor and the remaining terminals of the respective indicating lamps. The switch means, common conductor and diodes comprise means for automatically detecting faulty indicating lamps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIGS. 1 to 4 inclusive are circuit diagrams illustrating various embodiments of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the embodiment shown in FIG. 1, indicating lamps L 1  and L&#39; 1  are connected in series with respective sensor switches such as SW 2  and SW&#39; 2  and an ignition switch SW 1  is connected between one terminal of a battery BY and the indicating lamps L 1  and L&#39; 1 . The ignition switch SW 2  comprises means for applying the battery BY voltage to the series combinations of lamps and sensor switches. The otherterminal of the battery and sensor switches SW 2  and SW&#39; 2  are grounded. The electrical ground to which the battery and switches are connected constitutes means defining an electrically conductive path between the grounded battery terminal and the grounded switches. An oil pressure switch SW 3  and an oil pressure indicating lamp L 2  are connected in series across the battery BY through the ignition switch SW 1 . Respective indicating lamps L 1  and L&#39; 1  are connected by the diodes D 1 , D 2  to the junction between the oil pressure switch SW 3  and the oil pressure indicating lamp L 2 . The oil pressure switch SW 3  is opened while the engine of the motor car or vehicle is operating but is closed when the engine stops. 
     In operation, when the ignition switch SW 1  is closed and the engine isnot operating, the oil pressure switch SW 3  is closed so that various indicating lamps L 1 , L&#39; 1  and L 2  are lighted through diodes D 1  and D 2  and the oil pressure switch SW 3 . Accordingly, fault of any lamp can be detected at a glance because faulty lamps would not illuminated. 
     During operation of the engine, since the oil pressure switch SW 3  is opened, all indicating lamps will not be lighted until associated sensor switches SW 2 , SW&#39; 2  operate. 
     As described above, by providing a circuit including diodes between the oilpressure switch and indicating lamps it is possible to readily determine whether the indicating lamps are faulty or not while the engine is stopped. Thus, the oil pressure switch SW 3  also functions as a lamp-checking switch and is operable to simultaneously energize all of thelamps to indicate which lamps are fault-free. 
     In the embodiment shown in FIG. 2, in the common grounding circuit for checking indicating lamps, that is, in the circuit including the diodes D 1  and D 2  is arranged a relay switch of a relay RY 1  which is closed when the charging lamp L 3  of a voltage regulator (not shown) is lighted. Namely, a switch SW 4  connected in series with the charging lamp L 3  of the voltage regulator is closed as long as the engine and hence the generator of the motor car is not operating and, accordingly, charging lamp L 3  is lighted when ignition switch SW 1  is closed. At the same time the relay RY 1  is also energized to close its switch. Since, accordingly, the oil pressure switch SW 3  is also closed when the engine is stopped, the grounding circuits for respective indicating lamps are estblished thus enabling a determination of faulty indicating lamps in the same manner as in FIG. 1. 
     When the engine is started the oil pressure switch is opened and the voltage of the generator builds up so that switch SW 4  associated withthe voltage regulator of generator is opened. As a consequence relay RY 1  is de-energized to open the grounding circuit for the indicating lamps L 1  and L&#39; 1 . 
     With this embodiment even when either one of the oil pressure switch SW 3  or the charging lamp switch SW 4  is ON due to some condition during the operating of the engine any one of the indicating lamps L 1 and L&#39; 1  will not be lighted but these lamps are lighted only when sensor switches SW 2  and SW&#39; 2  associated therewith are operated. When both switches SW 3  and SW 4  are closed at the same time lampsL 1  and L&#39; 1  will be lighted. It is, however, to be noted that simultaneous fault of both switches SW 3  and SW 4  hardly takes place. 
     In another modification shown in FIG. 3, the oil pressure switch SW 3  showin in FIG. 1 is substituted by a relay RY 2  responsive to the voltage of the neutral voltage mode of a polyphase alternating current generator AL which is used to charge the battery BY through a rectifier arrangement. 
     While the engine is not operating, the neutral voltage of the alternator ALis zero so that the contact of the normally closed relay RY 2  is actuated thus closing the grounding circuit for the indicating lamps L 1  and L&#39; 1 . However, when the engine is operated and as the neutral voltage is generated (the neutral) voltage is equal to about one half of the terminal voltage of the alternator) the relay switch of relay RY 2  is opened thus opening the grounding circuit for the indicating lamps L 1  and L&#39; 1 . Thus, this embodiment operates in the same manner as that shown in FIG. 1. 
     In still another embodiment of this invention shown in FIG. 4, the relay RY 1  shown in FIG. 2 is substituted by a relay RY 2  operated by the neutral voltage of a polyphase alternator AL. The operation of this embodiment is identical to that at the embodiment shown in FIG. 2. 
     According to this invention, any special operation for checking for faults of a plurality of indicating lamps is performed automatically at the time of starting the engine. After starting of engine a check circuit, that is,the grounding circuit, is interrupted automatically and respective indicating lamps are lighted in response to the closure of sensor switchesassociated therewith. Thus, the invention contributes greatly to the safe running of the motor car and make needless troublesome checking operations.