Misfire diagnosis apparatus for an internal combustion engine

Claim 1

In a misfire diagnosis apparatus for an internal combustion engine with a crankshaft for outputting power and a camshaft for actuating valves having, a crank plate connected to said crankshaft for indicating a crank angle, a crank angle sensor for detecting said crank angle of said crankshaft and for generating a crank angle signal, a cam plate connected to said camshaft for indicating a cam position, a cam angle sensor for detecting said cam position of said camshaft and for producing a cam angle signal, and control means responsive to said crank angle and said cam angle for controlling an ignition timing of said engine, an improvement in the apparatus which comprises: a plurality of even numbers of slits provided on a periphery of said crank plate for indicating said crank angle, said slits being diametrically and symmetrically arranged on said periphery and each pair of said slits being spaced apart by at least three different specific angles; a plurality of cam slits provided on a periphery of said cam plate and spaced angularly apart at a predetermined angle on said periphery for indicating said cam position; momentum change rate calculating means for comparing a momentum of a section in which no work is done by previous combustion and a momentum of a section in which no work is done by present combustion, thereby to calculate a momentum change rate of a cylinder at a combustion stroke held between the sections; momentum change rate comparing means for reading out an average momentum change rate learning value corresponding to operating conditions from an average momentum change rate learning value map of the pertinent combustion stroke cylinder, and for comparing said momentum change rate with said average momentum change rate learning value; discriminating means responsive to said crank angle signal and said cam angle signal for discriminating a cylinder number at a combustion stroke and for producing a cylinder number signal; misfire judging means responsive to an acceleration signal, said cylinder number signal, said crank angle signal and said cam angle signal for comparing a compared result of said comparing means with a misfire judgement level corresponding to said operating conditions read out from a misfire judgement level map of said pertinent combustion stroke cylinder, thereby to judge a misfire state every cylinder and to generate a misfire signal; average momentum change rate learning value setting means for setting an average momentum change rate learning value on the basis of a momentum change rate of said pertinent combustion stroke cylinder in normal state and the first-mentioned average momentum change rate learning value, and for updating said first-mentioned average momentum change rate learning value stored in the operating region of said average momentum change rate learning value map of said pertinent combustion stroke cylinder; and warning means responsive to said misfire signal for storing a number of said misfire corresponding to said cylinder number and for indicating a malfuction of said internal combustion engine.