Apparatus for detecting a start of an engine for a motor vehicle
This is a continuation of application Ser. No. 453,154, filed Dec. 27, 1982, which was abandoned upon the filing hereof. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus for detecting a starting state of an engine, and more particularly to an apparatus for detecting the starting state of the engine at an inspection line of a factory and the like. 
     At the inspection line of the factory and the like, if an inspector starts an engine by mistake during inspection of a motor vehicle and the motor vehicle starts running, an inspection apparatus and the motor vehicle to be inspected may be damaged or the inspectors may be injured. 
     To prevent the occurence of the above accidents due to the careless operation of the inspector, a stopper may be used for the motor vehicle which prevents the motor vehicle from running even in response to the start of the engine. 
     However, the above-mentioned stopper may not be able to be used for all types of motor vehicles due to its structual difficulties, and an automatic type stopper requires a large number of instruments and so forth. Therefore, the prevention of the above-described accidents is still, in most part, depending on intensive care by the inspector. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an apparatus for detecting a start of an engine, in which the starting state of the engine can be accurately detected. 
     According to the present invention, a sensor senses a change over time of the magnetic flux around a starter motor or a wire connecting the starter motor to a battery. The sensor outputs a voltage signal, which varies in response to the change of the magnetic flux corresponding to the change over time of the current flowing to the starter motor, to a judging device. In the judging device, the voltage signal is compared with a reference voltage value to output a detecting signal indicating that the engine is started. 
     Since a current flowing to the starter motor is abruptly varied when the starter motor is started and stopped, the sensor detects the variation of the magnetic flux in response to the variation of the current at each start or stop. Accordingly, the judging device outputs two detecting signals indicating the start and stop of the engine respectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram showing an embodiment according to the present invention; 
     FIG. 2 is a circuit diagram illustrating in detail each element shown in FIG. 1; 
     FIG. 3A is a time chart illustrating the operation signal of the starter motor; 
     FIG. 3B is a time chart illustrating the change over time of the current flowing to the starter motor from the battery; and 
     FIG. 3C is a time chart illustrating the detecting signal outputted from the monostable multivibrator. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, numeral 2 denotes a motor vehicle having an internal combustion engine which is started by a starter motor connected to a battery via a wire. A sensor 4 for sensing a magnetic flux outputs a voltage signal corresponding to a change with time of a current flowing to the starter motor from the battery. The sensor 4 is connected to a judging device 6, which includes an amplifier 8, a comparator 10, a monostable multivibrator 12 and an output terminal 14. The judging device outputs a detecting signal indicating that the starter motor is started and stopped. The sensor 4 and the judging device 6 are provided separately from the motor vehicle. More specifically, when the apparatus according to the present invention is used for inspection, the sensor 4 is placed around the starter motor or the wire connecting the starter motor to the battery, and after the inspection the sensor 4 is detached from the motor vehicle. 
     Referring to FIG. 2, the sensor 4 includes a coil 20 detecting the magnetic flux which varies in response to the change of the current flowing to the starter motor from the battery. One end of the coil 20 is connected to an input terminal of the amplifier 8 and the other end thereof is connected to a ground. 
     The amplifier 8 includes an integrated circuit (operational-amplifier) IC, resistors R 1 , R 2 , R 3  and R 4  and condensers C 1  and C 2 . An output terminal of the amplifier 8 is connected to an input terminal of the comparator 10 which includes an integrated circuit (voltage comparator) IC, a resistor R 5  and a variable resistor VR 1 . 
     An output terminal of the comparator 10 is connected to an input terminal of the monostable multivibrator 12 which includes an integrated circuit (precision timer) IC 3 , resistors R 6  and R 7  and condensers C 3  and C 4 . An output terminal of the multivibrator 12 is connected to an external output terminal 14 of the judging device 6. 
     The terminal No. 7 of the integrated circuit IC 1  and the terminals No. 8 of the integrated circuts IC 2  and IC 3  are connected to a voltage supply, respectively, and the terminals No. 4 of the integrated circuits IC 1  and IC 2  and the terminal No. 1 of the integrated circuit IC 3  are connected to ground. 
     The following table gives the manufacturer and the manufacturer&#39;s part number for the integrated circuits in this apparatus. 
     
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Reference No.                                                             
             Part No.  Manufacturer                                       
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IC.sub.1     CA 3130   RCA Corporation                                    
IC.sub.2     LM 311    National Semiconductor                             
                       Corporation                                        
IC.sub.3     SN 72555  National Semiconductor                             
                       Corporation                                        
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     With reference to FIGS. 3A, 3B and 3C, operation of the preferred embodiment of the apparatus described above according to the present invention will be provided below. 
     When the starter motor is started at time point t 1  as shown in FIG. 3A, the current flowing through the wire to the starter motor from the battery varies from zero to several hundreds of amps and results in variation of the magnetic flux around the starter motor and the wire. This in turn energizes the coil 20 of the sensor 4 so that a variation in coil voltage results in response to that of the magnetic flux. 
     The voltage signal thus generated in the coil 20 is fed to the amplifier 8 so that the voltage signal is amplified to a desired amplitude. FIG. 3B shows the waveform of the amplified voltage signal which is outputted from the amplifier 10. 
     The amplified voltage signal is fed to the comparator 10 for comparison with a reference voltage V 1  as shown in FIG. 3B set by the variable resistor VR 1 . The variable resistor VR 1  is adjusted so that the amplitude of the reference voltage V 1  is more than that of ignition noise (shown at C) in voltage superposed on the amplified voltage signal fed from the amplifier 8. 
     When the amplitude of the amplified voltage signal is more than that of the reference voltage V 1 , that is, when the starter motor is started at the time point t 1 , the comparator 10 outputs a pulse signal to the monostable multivibrator 12. Upon receiving the pulse signal from the comparator 10 the multivibrator 12 is triggered by the trailing edge of the received pulse signal to produce the detecting signal a, which indicates that the starter motor has started, for a metastable time period of the multivibrator 12 as shown in FIG. 3C. The detecting signal a thus produced is received by the external output terminal 14 from which the detecting signal a is fed to external warning equipment 16, for example, a warning lamp or a warning buzzer and the like which lets the inspector know of the start of the engine. 
     After the starter motor has started, since the current of several tens of amps flowing to the starter motor does not substantially vary, a voltage signal greater than the reference voltage V 1  in value is not outputted from the amplifier 8. Consequently, when the current of several tens of amps flowing to the starter motor is interrupted at a time point t 2  to stop the starter motor, the large amplitude of the coil voltage is induced in the coil 20 and forms a waveform of the voltage signal as shown FIG. 3B at time point t 2 . When the voltage signal thus produced and exceeding the reference voltage in value is fed to the comparator 10, the comparator 10 outputs a pulse signal which is fed to the multivibrator 12. The trailing edge of this pulse signal in turn triggers the multivibrator 12 to output the detecting signal b, which indicates that the starter motor is stopped at the time point t 2 , for the metastable time period of the multivibrator 12 as shown FIG. 3C. The detecting signal b is also received by the external output terminal 14 for the same purpose described above. 
     The apparatus described above can be applied to a diesel engine wherein no ignition noise is produced because there is no ignition plug. Therefore, in the case of the application of the present invention to the diesel engine, the judging device 6 is relatively simplified as compared with a gasoline engine.