Tachometer based on electrical ripple and calibrated by mechanical engine signals

Abstract

The tachometer includes a microphone for disposition next to the exhaust of the vehicle and an accelerometer for disposition adjacent to its engine. A selected one of the outputs is connected to an ADC which provides digital samples to a central processing unit. Also, the ripple from the battery is sampled and provided to the CPU. The CPU calculates a constant representing the relationship of the frequencies of the ripple samples and the mechanical samples and responds to the ripple samples and the constant to provide output signals corresponding to the speed of the engine. The speed is displayed.

What is claimed is:  
     
       1. A tachometer for determining the speed of the engine in a vehicle that includes a battery-operated electrical system which produces a DC voltage having a ripple thereon, the engine producing mechanical oscillations during operation, the tachometer comprising: 
       a first input circuit for coupling to the electrical system for providing first signals representative of the frequency of the ripple,  
       a second input circuit for coupling to the engine for providing second signals representative of the frequency of the mechanical oscillations, and  
       a processing circuit coupled to said first and second input circuits and operating under stored program control for calculating a constant representing the relationship of the frequencies of the first and second signals and for responding to said first signals and the constant to provide third signals corresponding to the speed of the engine  ( a )  to collect simultaneously a first predetermined number of ripple samples from the first signal and a second predetermined number of mechanical samples from the second signal,  ( b )  to calculate the frequency of the mechanical samples to provide a mechanical frequency,  ( c )  to store the mechanical frequency,  ( d )  to repeat the previous two steps a third predetermined number of times,  ( e )  to provide a representative mechanical frequency from the stored mechanical frequencies,  ( f )  to calculate the frequency of the ripple samples,  ( g )  to calculate the ratio of the representative mechanical frequency to the ripple sample frequency,  ( h )  to store such ratio,  ( i )  to repeat the three previous steps a fourth predetermined number of times, and  ( j )  to identify a representative ratio which becomes a constant, and  ( k )  to provide third signals corresponding to the speed of the engine as a function of the constant and the frequency of the ripple.    
     
     
       2. The tachometer of  claim 1 , wherein said constant is calculated while the engine is idling. 
     
     
       3. The tachometer of  claim 1 , wherein said second input circuit includes a microphone for disposition next to the exhaust of the vehicle. 
     
     
       4. The tachometer of  claim 1 , wherein said processing circuit includes a multiplexer coupled to said first and second means  input circuits. 
     
     
       5. The tachometer of  claim 1 , wherein said first input circuit includes a bandpass filter. 
     
     
       6. The tachometer of  claim 5 , wherein the bandpass of said bandpass filter is about 500 to 10,000 Hz. 
     
     
       7. The tachometer of  claim 6 , wherein said second input circuit includes a bandpass filter. 
     
     
       8. The tachometer of  claim 7 , wherein the bandpass of said bandpass filter is about 5 to 150 Hz. 
     
     
       9. The tachometer of  claim 1 , and further comprising a display coupled to said processing circuit to display the speed of the engine. 
     
     
       10. A tachometer for determining the speed of the engine in a vehicle that includes a battery-operated electrical system which produces a DC voltage having a ripple thereon, the engine producing mechanical oscillations during operation, the tachometer comprising: a first input circuit for coupling to the electrical system for providing first signals representative of the frequency of the ripple, 
       a second input circuit for coupling to the engine for providing second signals representative of the frequency of the mechanical oscillations, an analog-to-digital converter coupled to said first and second means to provide ripple samples in response to the first signals and mechanical samples in response to the second signals,  
       and a central processing unit coupled to said analog-to-digital converter and operating under stored program control for calculating a constant representing the relationship of the frequencies of the ripple samples and the mechanical samples and for responding to said ripple samples and the constant to provide output signals corresponding to the speed of the engine.  
     
     
       11. The tachometer of claim  10   1 , wherein said central  processing unit  circuit determines the frequencies of said ripple samples and said mechanical samples by Fast Fourier Transformation. 
     
     
       12. The tachometer of  claim 10 , wherein said central processing unit is programmed: to collect simultaneously a first predetermined number of ripple samples and a second predetermined number of mechanical samples, to calculate the frequency of the mechanical samples to provide a mechanical frequency, to store the mechanical frequency, to repeat the previous two steps a third predetermined number of times, to provide a representative mechanical frequency, to calculate the frequency of the ripple samples, to calculate the ratio of the representative mechanical frequency to the ripple sample frequency, to store each such ratio, to repeat the previous two steps a fourth predetermined number of times and to identify a representative ratio which becomes said constant. 
     
     
       13. The tachometer of claim  12   1 , wherein the steps of calculating the mechanical sample frequency and the ripple sample frequency are by Fast Fourier Transformation. 
     
     
       14. The tachometer of claim  12   1 , wherein the first predetermined number is 10,000, the second predetermined number is 256, the third predetermined number is 128 and the fourth predetermined number is between 108 and 128. 
     
     
       15. The tachometer of claim  12   1 , wherein the representative mechanical frequency is the average of the mechanical frequencies. 
     
     
       16. The tachometer of claim  12   1 , wherein the representative ratio is the most frequently appearing of the ratios. 
     
     
       17. The tachometer of claim  10   1 , and further comprising a keyboard to supply information to the central processing unit. 
     
     
       18. The tachometer of  claim 10  and further comprising a display coupled to said central processing unit to display the speed of the engine. 
     
     
       19. A tachometer for determining the speed of the engine in a vehicle that includes a battery-operated electrical system which produces a DC voltage having a ripple thereon, the engine producing mechanical oscillations during operation, the tachometer comprising: 
       a first input circuit for coupling to the electrical system for providing first signals representative of the frequency of the ripple;  
       a second input circuit for coupling to the engine for providing second signals representative of the frequency of the mechanical oscillations; and  
       a central processing unit coupled to said input circuits and operating under stored program control for (a) calculating the frequency of the ripple, (b) calculating the frequency of the mechanical oscillations to provide a mechanical frequency and storing the calculated mechanical frequency and repeating this calculation and storage step a predetermined number of times, (c) averaging the calculated and stored mechanical frequencies to provide a representative mechanical frequency, (d) calculating a constant representing the relationship of the frequency of the ripple and the representative mechanical frequency, and (e) responding to the constant and the frequency of the ripple to provide output signals corresponding to the speed of the engine.  
     
     
       20. A tachometer for determining the speed of the engine in a vehicle that includes a battery-operated electrical system which produces a DC voltage having a ripple thereon, the engine producing mechanical oscillations during operation, the tachometer comprising: 
       a first input circuit for coupling to the electrical system for providing first signals representative of the frequency of the ripple;  
       a second input circuit for coupling to the engine for providing second signals representative of the frequency of the mechanical oscillations; and  
       a central processing unit coupled to said input circuits and operating under stored program control for (a) calculating the frequency of the ripple, (b) calculating the frequency of the mechanical oscillations to provide a mechanical frequency, (c) calculating the ratio of the mechanical frequency to the frequency of the ripple and storing the ratio and repeating this calculation and storage step a predetermined number of times to identify a representative ratio which becomes a constant, and (d) responding to the constant and the frequency of the ripple to provide output signals corresponding to the speed of the engine.  
     
     
       21. The tachometer of  claim 19 , wherein the constant is calculated while the engine is idling. 
     
     
       22. The tachometer of  claim 19 , wherein the second input circuit includes a microphone for disposition next to the exhaust of the vehicle. 
     
     
       23. The tachometer of  claim 19 , wherein the processing unit includes a multiplexer coupled to the first and second input circuits. 
     
     
       24. The tachometer of  claim 19 , wherein each of the first and second input circuits includes a bandpass filter. 
     
     
       25. The tachometer of  claim 19 , and further comprising a display coupled to the processing unit to display the speed of the engine. 
     
     
       26. The tachometer of  claim 19 , wherein the central processing unit calculates the frequency of the ripple and the frequency of the mechanical oscillations by Fast Fourier Transformation. 
     
     
       27. The tachometer of  claim 20 , wherein the constant is calculated while the engine is idling. 
     
     
       28. The tachometer of  claim 20 , wherein the second input circuit includes a microphone for disposition next to the exhaust of the vehicle. 
     
     
       29. The tachometer of  claim 20 , wherein the processing unit includes a multiplexer coupled to the first and second input circuits. 
     
     
       30. The tachometer of  claim 20 , wherein each of the first and second input circuits includes a bandpass filter. 
     
     
       31. The tachometer of  claim 20 , and further comprising a display coupled to the processing unit to display the speed of the engine. 
     
     
       32. The tachometer of  claim 20 , wherein the central processing unit calculates the frequency of the ripple and the frequency of the mechanical oscillations by Fast Fourier Transformation. 
     
     
       33. The tachometer of  claim 20 , and further comprising a keyboard to supply information to the central processing unit.