Decoding an alternator output signal

Abstract

An engine diagnostic system is provided that enables a service technician to evaluate engine cylinder contribution to output power. The service technician couples one or more signal leads to the vehicle's battery, alternator, or accessory receptacle (e.g., cigarette lighter receptacle) to provide an alternator output signal to a signal analyzer. The signal analyzer processes the alternator output signal to generate an engine signature, which represents engine cylinder contribution to engine output power.

1 - 42 . (canceled)  
   
   
       43 . A signal processing system for generating indexed engine data, the system comprising: 
 a computing device including a communications interface and a processor;    wherein the communications interface is configured to receive an alternator output signal and the processor is configured to decode the alternator output signal to generate the indexed engine data.    
   
   
       44 - 48 . (canceled)  
   
   
       49 . The signal processing system of  claim 43 , wherein the processor is configured to demodulate the alternator output signal and index the demodulated alternator output signal to generate the indexed engine data.  
   
   
       50 . The signal processing system of  claim 43 , wherein the processor is configured to: 
 obtain a diode ripple signal from the alternator output signal;    detect a first zero crossing of a diode tone;    signal a counter when the first zero crossing is detected;    detect a second zero crossing of the diode tone; and    store the value of the counter responsive to detecting the second zero crossing.    
   
   
       51 . The signal processing system of  claim 50 , wherein the processor is further configured to produce the indexed engine data based on the stored value of the counter.  
   
   
       52 . The signal processing system of  claim 51 , wherein a time base of the indexed engine data is independent of an engine RPM and a diode ripple tone frequency.  
   
   
       53 . The signal processing system of  claim 49 , wherein the processor is configured to perform an angle demodulation on the alternator output signal.  
   
   
       54 . The signal processing system of  claim 53 , wherein the processor is configured to: 
 obtain a diode ripple signal from the alternator output signal;    sample the ripple signal to generate a diode ripple data stream;    filter the diode ripple data stream to generate a diode tone; and    perform the angle demodulation on the diode tone to obtain a phase demodulated signal.    
   
   
       55 . The signal processing system of  claim 54 , wherein the processor is further configured to perform the angle demodulation on the diode tone by calculating an arctangent of the diode tone to produce a phase signal, and differentiating the phase signal to yield the phase demodulated signal.  
   
   
       56 . The signal processing system of  claim 54 , wherein the processor is configured to condition the diode ripple data stream to adjust dynamic range before sampling the ripple signal to generate a diode ripple data stream.  
   
   
       57 . The signal processing system of  claim 53 , wherein the processor is further configured to perform the angle demodulation on the alternator output signal by calculating an arctangent of the alternator output signal to produce a phase signal, and differentiating the phase signal to yield a phase demodulated signal.  
   
   
       58 . A method for generating indexed engine data, the method comprising: 
 receiving an alternator output signal; and    decoding the alternator output signal to generate the indexed engine data.    
   
   
       59 . The method of  claim 58 , comprising: 
 demodulating the alternator output signal; and    indexing the demodulated alternator output signal to generate the indexed engine data.    
   
   
       60 . The method of  claim 58 , comprising: 
 obtaining a diode ripple signal from the alternator output signal;    detecting a first zero crossing of a diode tone;    signaling a counter when the first zero crossing is detected;    detecting a second zero crossing of the diode tone; and    storing the value of the counter responsive to detecting the second zero crossing.    
   
   
       61 . The method of  claim 60 , comprising producing the indexed engine data based on the stored value of the counter.  
   
   
       62 . The method of  claim 61 , wherein a time base of the indexed engine data is independent of an engine RPM and a diode ripple tone frequency.  
   
   
       63 . The method of  claim 59 , comprising performing an angle demodulation on the alternator output signal.  
   
   
       64 . The method of  claim 63 , comprising: 
 obtaining a diode ripple signal from the alternator output signal;    sampling the ripple signal to generate a diode ripple data stream;    filtering the diode ripple data stream to generate a diode tone; and    performing the angle demodulation on the diode tone to obtain a phase demodulated signal.    
   
   
       65 . The method of  claim 64 , wherein performing the angle demodulation on the diode tone comprises: 
 calculating an arctangent of the diode tone to produce a phase signal; and    differentiating the phase signal to yield the phase demodulated signal.    
   
   
       66 . The method of  claim 64 , comprising conditioning the diode ripple data stream to adjust dynamic range before sampling the ripple signal to generate a diode ripple data stream.  
   
   
       67 . The method of  claim 63 , wherein performing the angle demodulation on the alternator output signal comprises: 
 calculating an arctangent of the alternator output signal to produce a phase signal; and    differentiating the phase signal to yield a phase demodulated signal.