APPARATUS FOR ENGINE COMPRESSION TESTING

• US 3,839,906 A
• Filed: 10/09/1973
• Issued: 10/08/1974
• Est. Priority Date: 10/09/1973
• Status: Expired due to Term

• Current Assignee: Richard Eric Hanson
• Original Assignee: Richard Eric Hanson
• Inventors: Hanson, Richard Eric
• Primary Examiner(s): Myracle, Jerry W.
• Application Number:
  US05/404,802
• Time in Patent Office: 364 Days
• Field of Search: 73/115,117.2,116
• US Class Current: 73/114.23
• CPC Class Codes: G01L 23/085 by measuring fluctuations of starter motor current or of battery voltage battery testing arrangements G01R31/36; testing of electrical installation on transport means G01R31/005; battery testing arrangements G01R31/36

Abstract

An engine compression fault detector includes means for detecting engine cylinder compression peaks from the starter motor current waveform. Each engine peak is compared to a dynamic peak reference which is derived from and related to the maximum cylinder peak of the engine under test. An output circuit provides a missing or low peak indication if the peak reference exceeds any cylinder peak. Overall engine compression evaluation is accomplished by comparing the difference of the average and peak starter current to a predetermined reference signal.

Claims

1. Apparatus for testing engine compression for use with an internal combustion engine having at least two cylinders and said engine having a starter motor and an electrical starter system which supplies starter current to said starter motor during a cranking period, said apparatus comprising, in combination:

means for detecting the starter motor current waveform to provide a compression signal having a time-varying component indicative of the engine cylinder compression cycles;

means for producing a first signal indicative of the average magnitude of the compression signal;

means for producing a second signal related to the maximum peak magnitude of said compression signal;

means for comparing said second signal to said compression signal to provide a first fault signal if the related maximum peak magnitude of the compression signal exceeds the peak magnitude of any one cylinder compression peak;

means for producing a difference signal indicative of the magnitude difference between said first and second signals;

means for providing a reference signal representative of a given magnitude difference between said first and second signals;

means for comparing said difference signal to said reference signal to provide a second fault signal if said given magnitude difference exceeds the magnitude difference between said first and second signals; and

means responsive to at least one of said first and second fault signals for providing a fault indication.

2. The apparatus according to claim 1, including:

means for providing a starting signal indicative of said cranking period; and

delay means responsive to said starting signal for inhibiting said first and second fault signals during a predetermined initial portion of said cranking period.

3. The apparatus according to claim 1, wherein said second signal is derived from said compression signal.

4. The apparatus according to claim 3, wherein the magnitude of said second signal is a predetermined portion of the maximum peak magnitude of said compression signal.

5. The apparatus according to claim 1, including:

means for detecting the cylinder cycles of said engine to provide a speed signal representative thereof; and

means coupled to said means for comparing said second signal to said compression signal and responsive to said speed signal, for comparing said seCond signal to said compression signal only during a portion of each cylinder cycle.

6. The apparatus according to claim 1, wherein said means for producing a difference signal comprises a differential amplifier having first and second inputs respectively coupled to said means for producing said first signal and said means for producing said second signal, said differential amplifier having an output coupled to said means for comparing said difference signal to said reference signal.

7. The apparatus according to claim 6, including divider means coupled to said means for producing said first signal and said means for producing said second signal, said divider means providing a peak reference signal indicative of the difference between said first and second signals, and said peak reference signal being coupled to said means for comparing said second signal to said compression signal, thereby to provide said first fault signal if the magnitude of said peak reference signal exceeds the peak magnitude of any one cylinder compression peak.

8. The apparatus according to claim 1, wherein:

said means for producing said second signal comprises a peak detector having an input coupled to receive said compression signal and said peak detector having an output; and

said means for comparing said second signal to said compression signal comprises a comparator having a first input coupled to the output of said peak detector and said comparator having a second input coupled to receive said compression signal.

9. The apparatus according to claim 3, including a resistive divider coupled between the output of said peak detector and said first input of said comparator, so that said second signal at said first input is a predetermined portion of said maximum peak magnitude of said compression signal.

10. The apparatus according to claim 1, including means for inhibiting engine cylinder combustion during said cranking period.