Signal conditioning circuit for vehicle diagnostic system

• US 3,961,239 A
• Filed: 03/26/1975
• Issued: 06/01/1976
• Est. Priority Date: 03/26/1975
• Status: Expired due to Term

• Current Assignee: Clean Air Technologies Inc.
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Lach, Richard F.
• Primary Examiner(s): Corcoran, Robert J.
• Application Number:
  US05/562,388
• Time in Patent Office: 433 Days
• Field of Search: 324/15, 324/16 R, 324/16 T, 324/16 S, 73/116, 73/117.3, 73/118, 307/247 A, 307/268, 307/261, 307/234
• US Class Current: 324/384
• CPC Class Codes: F02P 17/06 using a stroboscopic lamp
• CPC Class Codes: G01M 15/044 by monitoring power, e.g. by operating the engine with one of the ignitions interrupted; by using acceleration tests
• CPC Class Codes: G01P 3/4802 by using electronic circuits in general

Abstract

The rpm, dwell and timing of an internal combustion engine are measured by starting and stopping a digital counter on the leading edge of pulse waveforms generated either within the engine or by a timing light. To measure rpm and dwell only the low coil signal is used. For rpm measurement, the counter is started when the ignition points open, and stopped upon the next opening of the points. To measure dwell the counter is started by the opening of the points and stopped when the points close, the resultant count being the inverse of dwell, and this count is subtracted from the rpm count to obtain dwell. Timing is measured by starting the counter upon the firing of the number one cylinder, and providing an additional signal delayed in time as a function of the distributor advance to stop the counter. The count in the counter is converted to rpm, dwell or timing by either analog or digital techniques. A high energy ignition adapter circuit prevents triggering of the counter by a false indication of the opening of the points due to a waveform peculiar to low coil signals produced in vehicles using high energy ignition systems. A timing light delay circuit having a variable delay is incorporated with the timing light to produce the delayed signal proportional to distributor advance, the delay being adjustable within two selectable ranges. By measuring and displaying the computed dwell for each cylinder in sequence, distributor mechanical wear associated with shaft bearings and drive gears may be detected. Power contribution and dynamic relative compression for each cylinder may be measured by using the counter to measure the time that the points are open, and the time that the points are closed, for each cylinder in sequence, and displaying the measurements.

Claims

1. In a diagnostic system for a motor vehicle having an internal combustion engine, said engine having an ignition system for selectively supplying a series of spark voltage pulses to a plurality of spark ignition devices, said voltage pulses exhibiting ringing and large voltage excursions, the improvement of a signal conditioning circuit for said voltage pulses comprising

a transistor having an emitter, a base and a collector,

means for biasing the base of said transistor so that said transistor is normally nonconductive,

a capacitor connected to the collector of said transistor,

a source of voltage connected to the collector of said transistor and to said capacitor, said capacitor being charged by said voltage source when said transistor is nonconductive,

a comparator having first and second input terminals and an ouput terminal,

means connecting said voltage source to the first input terminal of said comparator, and connecting said capacitor to the second input terminal of said comparator, said comparator producing a first voltage output at the output terminal thereof when said capacitor is discharged, and producing a second voltage output at the output terminal thereof when said capacitor is charged to a predetermined voltage level,

means connecting said series of spark voltage pulses to the base junction of said transistor to cause conduction thereof, said capacitor discharging through said conducting transistor,

output circuit means connected to the output terminal of said comparator, said output circuit means producing an output signal in the form of a square wave having a leading edge occurring simultaneously with the leading edge of said spark voltage pulses, and having a trailing edge delayed in time from the trailing edge of said spark voltage pulses by a fixed time constant as a function of the charging rate of said capacitor,

and ignition adapter circuit means connected in series between said ignition system and the base junction of said transistor for preventing conduction of said transistor until said spark voltage pulses attain a preselected voltage magnitude.

2. A signal conditioning circuit as in claim 1 in which said ignition adapter circuit means includes a forward biased diode and a reverse biased Zener diode connected in series.

3. A signal conditioning circuit as in claim 1 and including switch means for bypassing said ignition adapter circuit means.