Engine knock signal generating apparatus with noise channel inhibiting feedback

• US 4,111,035 A
• Filed: 11/07/1977
• Issued: 09/05/1978
• Est. Priority Date: 11/07/1977
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Hamren, Glen C., West, Gene A.
• Primary Examiner(s): Gill, James J.
• Application Number:
  US05/848,865
• Time in Patent Office: 302 Days
• Field of Search: 73/35
• US Class Current: 73/35.05
• CPC Class Codes: F02P 5/152 dependent on pinking detecting or indicating knocks in internal-combustion engines G01L23/22
• CPC Class Codes: G01H 1/00 Measuring characteristics of vibrations in solids by using direct conduction to the detector G01H9/00, G01H11/00 take precedence
• CPC Class Codes: G01L 23/225 circuit arrangements therefor
• CPC Class Codes: G01N 2291/02872 Pressure
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• CPC Class Codes: G01N 33/2817 using a test engine testing of engines G01M15/00
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A vibration sensor mounted on an internal combustion engine characterized by knock-induced vibrations at a characteristic frequency and by other vibrations is tuned to resonate at substantially the characteristic frequency. A bandpass filter tuned to the characteristic frequency is connected to the vibration sensor output; and the output of the filter is provided to one input of a comparator and to average detector circuitry for generating a unidirectional noise reference signal representing noise at the characteristic frequency, which signal is provided to the other input of the comparator. The knock signal, obtained from the output of the comparator and comprising pulses corresponding to knock-induced peaks of amplitude greater than the unidirectional noise reference signal, is fed back through a low-pass filter to the average detector circuitry in sense to oppose increases in the unidirectional noise reference signal during said knock-induced peaks. The connection of the average detector circuitry to the output of the bandpass filter provides adaptability for mistuned sensors; and the negative feedback to the average detector circuitry reduces the distorting effect, amplified by the bandpass filter, of said knock-induced peaks on the unidirectional noise reference signal, which might otherwise distort the output knock signal.

Claims

1. Apparatus for use with an internal combustion engine having ringing knock-induced vibrations at a characteristic frequency and other vibrations, the apparatus being effective to generate knock signals representing the knock level therein and comprising, in combination:

a vibration sensor mounted on said engine and responsive to both said ringing knock-induced vibrations and said other vibrations to generate a signal;

a bandpass filter having maximum transmission at said characteristic frequency and responsive to the signal from said sensor during a knock-induced ringing vibration to generate a filtered sensor signal having attenuated components at frequencies other than the characteristic frequency compared with those at the characteristic frequency;

average detector means responsive to said bandpass filter for generating from the filtered sensor signal a unidirectional noise reference signal generally proportional to the average unidirectional amplitude of the filtered sensor signal at a higher amplitude than all but the peaks of those components due to knock-induced engine vibrations;

a comparator effective to compare the filtered sensor signal to the unidirectional noise reference signal and to generate knock signals when the filtered sensor output signal exceeds the unidirectional DC noise reference;

low-pass filter means responsive to said knock signals to generate a unidirectional noise reference inhibit signal therefrom;

feedback means connected to apply said unidirectional noise reference inhibit signal to said unidirectional DC noise reference signal generating means in sense to limit the unidirectional noise reference signal when knock signals are generated, whereby the tendency of components due to knock-induced vibrations in the filtered sensor signal to falsely increase the unidirectional noise reference is reduced and the knock signals more accurately represent the level of knock in said engine.

2. The method of detecting knock in an internal combustion engine having ringing, knock-induced vibrations at a characteristic frequency and other vibrations and generating knock signals representing the intensity of such knock, comprising the steps:

sensing the knock-induced and other vibrations and generating a time-varying signal in response thereto;

attenuating components of the time-varying signal not of the characteristic frequency with respect to components at the characteristic frequency to form a filtered time-varying signal;

detecting, averaging and amplifying the filtered time-varying signal to form a unidirectional noise reference signal generally proportional to the average unidirectional amplitude of the filtered time-varying signal at an amplitude higher than all but the peaks of those components due to knock-induced engine vibrations;

comparing the filtered time-varying signal to the unidirectional noise reference signal and generating knock signals when the former exceeds the latter;

low pass filtering the knock signals to form a unidirectional noise reference inhibit signal;

reducing the amplitude of the unidirectional noise reference signal by a proportion of the unidirectional noise reference inhibit signal in feedback to limit the unidirectional noise reference signal when knock signals are generated, whereby the tendency of the unidirectional noise reference signal to rise due to knock-induced vibration components of the filtered time-varying signal is reduced and the knock signals more accurately represent the intensity of knock in the engine.