Battery tach

• US 5,004,979 A
• Filed: 03/16/1990
• Issued: 04/02/1991
• Est. Priority Date: 11/03/1987
• Status: Expired due to Term

• Current Assignee: GSLE Subco, LLC (SPX Corporation)
• Original Assignee: Bear Automotive Service Equipment Company (SPX Corporation)
• Inventors: Taghikhani, Majid, Marino, Joseph A., Makhija, Surender K., Puetz, Peter A.
• Primary Examiner(s): Wieder, Kenneth
• Assistant Examiner(s): Regan, Maura K.
• Application Number:
  US07/496,103
• Time in Patent Office: 382 Days
• Field of Search: 324/160, 324/169, 324/170, 324/177, 361/239
• US Class Current: 324/160
• CPC Class Codes: G01P 3/481 of pulse signals

Abstract

A signal representing the RPM of an internal combustion engine is produced by a signal processor connected to the battery of the vehicle. The signal processor derives an electrical signal from the battery which contains signal components produced by operation of the vehicle ignition system, as well as components from a multitude of other sources such as the voltage regulator, fans, air conditioning and other electrical systems of the vehicle. The signal processor filters and signal processes the signal derived from the vehicle battery to produce a signal having a frequency which is related to the RPM of the engine.

Claims

1. A circuit for providing an output signal representative of speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the circuit comprising:

means for deriving directly from the battery an input signal representative of time-varying components in battery current, where battery current is the current flow appearing at a battery terminal;

means for filtering the input signal to produce a filtered signal comprising time-varying components of the input signal having frequencies within a range of frequencies associated with a time-varying signal impressed upon the battery current by operation of the ignition system; and

means for suppressing components in the filtered signal not associated with ignition system operation to produce the output signal as a function of engine speed.

2. The circuit of claim 1 wherein the means for filtering attenuates time-varying components having a frequency outside a range of frequencies normally associated with primary ignition current pulses to extract a first time-varying component related to engine speed.

3. The circuit of claim 2 wherein the means for filtering comprises:

first filter means for attenuating signals with frequencies outside a first range associated with primary ignition current pulses produced by the ignition system when the engine is idling; and

second filter means for attenuating signals with frequencies outside a second range associated with primary ignition current pulses produced by the ignition system when the engine is revving.

4. The circuit of claim 3 wherein the first range is between about 20 Hz and about 50 Hz.

5. The circuit of claim 3 wherein the second range is between about 50 Hz and about 150 Hz.

6. The circuit of claim 2 wherein the means for suppressing comprises:

first and second peak detector means for producing first and second peak detector signals which are a function of positive and negative peak values of the first time-varying component;

first and second comparator means for comparing the first time-varying component with the first and second peak detector signals to produce first and second comparator signals, respectively; and

means for deriving the output signal from the first and second comparator signals.

7. The circuit of claim 1 wherein the means for filtering comprises:

a filter attenuating time-varying components having frequencies outside a range of frequencies normally associated with spark plug ringing to isolate a second time-varying component related to engine speed.

8. The circuit of claim 7 wherein the range of frequencies is greater than about 10 kHz.

9. The circuit of claim 7 wherein the means for suppressing components in the filtered signal comprises:

first and second peak detector means for producing first and second signals as a function of peak values of the second time-varying component, the first and second peak detector means exhibiting different time responses to the second time-varying component; and

comparator means for comparing the first and second signals to produce the output signal.

10. A method of measuring speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the method comprising:

deriving directly from the battery an input signal representative of battery current;

filtering from the input signal representative of battery current, a time-varying signal including components associated with operation of the electrical ignition system, where battery current is current flow appearing at a battery terminal; and

suppressing noise components of the time-varying signal to produce an output signal as a function of engine speed.

11. The method of claim 10 wherein the step of filtering the time-varying signal comprises:

blocking a DC component of a signal measured off the battery;

further filtering AC components of the signal measured off the battery to isolate the time-varying signal.

12. The method of claim 11 wherein the step of further filtering comprises:

attenuating from the signal measured off the battery, signal components having frequencies outside a range associated with primary ignition current pulses.

13. The method of claim 11 wherein the step of further filtering comprises:

attenuating from the signal measured off the battery, signal components having frequencies outside a range associated with ignition burst spark plug ringing.

14. A circuit generating a tachometric output signal derived from electrical signals occurring in an electrical system for an internal combustion engine, the electrical system including a battery and an ignition system, the circuit comprising:

means for deriving directly from the battery an input signal representative of time-varying components in battery current, where battery current is the current flow appearing at a battery terminal;

filtering means for attenuating components of the input signal having frequencies outside a predetermined range to produce a filtered signal; and

means for suppressing noise in the filtered signal to produce the tachometric output signal.

15. A electronic tachometer responsive to signals occurring in an electrical system of an internal combustion engine, wherein the electrical system includes a battery and an ignition system which includes at least a first spark plug, the tachometer comprising:

means for deriving an input signal representative of time-varying components in battery current appearing at a battery terminal;

a first signal processing path for generating a first tachometric output signal from time-varying components of the input signal associated with primary switching current in the ignition system;

a second signal processing path for generating a second tachometric output signal from time-varying components of the input signal associated with ignition burst spark plug ringing; and

means for selecting between the first and second tachometric output signals; and

means responsive to the selected tachometric output signal for displaying engine rotational speed.

16. The tachometer of claim 15, wherein the first signal path comprises:

filtering means for attenuating components of the input signal having frequencies outside a plurality of predetermined frequency ranges and producing filtered signals associated with each frequency range;

means for selecting a filtered signal; and

a noise suppression stage including,

means for generating set and reset signals in response to transitions of the selected filtered signal exceeding threshold levels, and

a bistable device responsive to the set and reset signals for producing the first tachometric output signal.

17. The tachometer of claim 15, wherein the second signal path comprises:

filtering means for attenuating components of the input signal having frequencies outside a predetermined frequency range and producing a filtered signal; and

a spark plug ring detect stage operating on the filtered signal to eliminate signal noise, the spark plug ring detect stage including,

a fast peak detector operating on the filtered signal;

a slow peak detector operating on the filtered signal; and

means for comparing outputs of the fast and slow peak detectors for producing the second tachometric output signal.

18. The tachometer of claim 16, wherein the means for generating set and reset signals in the noise suppression stage further include:

a positive peak detector responsive to the selected filtered signal for generating a positive threshold level signal;

a negative peak detector responsive to the selected filtered signal for generating a negative threshold level signal;

a first comparator generating the reset signal in response to the selected filtered signal exceeding the positive threshold level signal; and

a second comparator generating the set signal in response to the selected filtered signal exceeding the negative threshold level signal.

19. The tachometer of claim 18, wherein the positive peak detector and negative peak detector generate positive and negative threshold level signals which vary as a function of a fraction of a weighted average of recent positive and negative going transitions of the selected filtered signal.

20. The tachometer of claim 19, wherein the filtering means of the first signal processing path include:

a first filtering circuit path producing a first filtered signal in which the time-varying components of the input signal below 20 Hz and above 50 Hz have been attenuated; and

a second filtering circuit path producing a second filtered signal in which the time-varying components of the signal below 50 Hz and above 150 Hz have been attenuated.

21. The tachometer of claim 20, and further comprising means for selecting between first and second filtered signals from the first or second filtering circuit path depending upon which range the instant measured frequency of the tachometric output signal lies.

22. The tachometer as set forth in claim 21, wherein the means for selecting between first and second filtered signals exhibit hysteresis to avoid hunting.

23. A electronic tachometer operating on signals occurring in an electrical system for an internal combustion engine, wherein the electrical system includes a battery and an ignition system which includes at least a first spark plug, the tachometer comprising:

input terminals for connection to positive and negative terminals of the battery for developing an input signal representative of time-varying components in battery current;

a first signal processing path for generating a first tachometric output signal from components of the input signal associated with primary switching current, the first signal processing path including,

filtering means for attenuating components of the input signal having frequencies outside predetermined frequency ranges and producing filtered signals associated with each frequency range;

means for selecting a filtered signal; and

a noise suppression stage including,

means for generating set and reset signals in response to transitions of the selected filtered signal exceeding threshold levels, and

a bistable device responsive to the set and reset signals for producing a first tachometric output signal;

a second signal processing path for generating a second tachometric output signal from components of the signal associated with ignition burst spark plug ringing, the second signal processing path comprising,

filtering means for attenuating components of the input signal having frequencies outside a predetermined frequency range and producing a filtered signal; and

a spark plug ring detect stage operating on the filtered signal, the ring detect stage including,

a fast peak detector operating on the filtered signal,

a sloe peak detector operating on the filtered signal, and

means for comparing outputs of the fast and slow peak detectors for producing the tachometric output signal;

means for selecting between the first and second tachometric output signals; and

means responsive to the selected tachometric output signal for displaying engine rotational speed.

24. A electronic tachometer operating on signals occurring in an electrical system for an internal combustion engine, wherein the electrical system includes a battery and an ignition system, the tachometer comprising:

means for deriving an input signal representative of time-varying components in battery current;

a signal processing path for generating a tachometric output signal from components of the input signal associated with primary switching current, the signal processing path including,

filtering means for attenuating components of the input signal having frequencies outside predetermined frequency ranges and producing filtered signals associated with each frequency range;

means for selecting between filtered signals; and

a noise suppression stage including,

means for generating set and reset signals in response to transitions of the selected filtered signal exceeding threshold levels, and

a bistable device responsive to the set and reset signals for producing a first tachometric output signal; and

means for displaying engine rotational speed in response to a tachometric signal.

25. A electronic tachometer operating on signals occurring in an electrical system for an internal combustion engine, wherein the electrical system includes a battery and an ignition system which includes at least a first spark plug, the tachometer comprising:

means for deriving an input signal representative of time-varying components in battery current;

a signal processing path for generating a tachometric output signal from components of the input signal associated with spark plug ringing, the signal processing path comprising,

filtering means for attenuating components of the representative signal having frequencies outside a predetermined frequency range and producing a filtered signal; and

a spark plug ring detect stage operating on the filtered signal, the ring detect stage including;

a fast peak detector operating on the filtered signal;

a slow peak detector operating on the filtered signal; and

means for comparing outputs of the fast and slow peak detectors for producing the tachometric output signal;

means for displaying engine rotational speed in response to a tachometric signal.

26. A circuit for providing a tachometric output signal representative of speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the circuit comprising:

first connector means for making direct and continuous electrical connection to a positive terminal of the battery;

a second connector means for making direct and continuous electrical connection to a negative terminal of the battery;

means connected to the first and second connector means for deriving an electrical signal from the battery which includes DC and AC components;

means for removing the DC component from the electrical signal;

means for processing the AC components of the electrical signal to select one of the AC components which is representative of operation of the ignition system and which changes as a function of engine speed; and

means for producing the tachometric output signal as a function of the AC component selected.

27. A circuit for providing a tachometric output signal representative of speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the circuit comprising:

means for making direct and continuous electrical connection to positive and negative terminals of the battery to derive from the battery a multi-component electrical signal appearing across the positive and negative terminals, wherein the electrical signal contains DC and AC components;

means for separating from the multi-component electrical signal an AC signal component produced by primary switching current of the ignition system; and

means for producing the tachometric output signal as a function of the AC signal component produced by primary switching current of the ignition system.

28. A circuit for providing a tachometric output signal representative of speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the circuit comprising:

means for making direct and continuous electrical connection to positive and negative terminals of the battery to derive from the battery a multi-component electrical signal appearing across the positive and negative terminals, wherein the electrical signal contains DC and AC components;

means for separating from the multi-component signal an AC signal component produced by spark plug ringing in the ignition system; and

means for producing the tachometric output signal as a function of the AC signal component produced by spark plug ringing in the ignition system.

29. A circuit for providing an output signal representative of speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the circuit comprising:

means for deriving an input signal representative of time-varying components in battery current, where battery current is the current flow appearing at a battery terminal;

means for filtering the input signal to produce a filtered signal comprising time-varying components of the input signal having frequencies within a range of frequencies associated with a time-varying signal impressed upon the battery current by operation of the ignition system, wherein the means for filtering attenuates time-varying components having a frequency outside a range of frequencies normally associated with primary ignition current pulses to extract a first time-varying component related to engine speed and wherein the means for filtering comprises;

first filter means for attenuating signals with frequencies outside a first range associated with primary ignition current pulses produced by the ignition system when the engine is idling;

second filter means for attenuating signals with frequencies outside a second range associated with primary ignition current pulses produced by the ignition system when the engine is revving;

means for selecting a signal from one of the first and second filter means as a function of engine speed; and

means for suppressing components in the filtered signal not associated with ignition system operation to produce the output signal as a function of engine speed.