A determining device for determining a failure in an engine cylinder of an internal combustion engine, comprising a variation detecting unit for sequentially detecting a variation in an engine speed between a first engine speed detected by an engine speed detecting unit during a combustion process at a first engine cylinder and a second engine speed detected by the engine speed detecting unit during a combustion process at a second engine cylinder immediately preceding the first engine cylinder with respect to an ignition sequence of all of the engine cylinders, a first determining unit for determining that a misfire has occurred when the variation in the engine speed detected by the variation detecting unit is larger than a predetermined first variation in the engine speed, a second determining unit for determining that a failure has occurred in an engine cylinder when a frequency at which the first determining unit determines that a misfire has occurred is larger than a predetermined frequency, and a value control unit for increasing at least one of the predetermined first variation in the engine speed and the predetermined frequency in accordance with an increase in the engine load detected by the engine load detecting unit.
In a misfire detecting device for an internal combustion engine, a crank angle detector detects the crank angle of the engine, a speed detector detects the speed of the engine from the crank angle thus detected, a load detector detects the load of the engine from the speed thus detected; and a misfire detector detects the misfire rate of the engine from the load thus detected, and outputs a misfire detection signal when the misfire rate thus detected exceeds a misfire rate determining value set according to a certain amount of load.
In a method of detecting misfires in a gasoline internal combustion engine, the angular velocities of rotation of the engine detected by an angular velocity sensor are calculated over a period of time, and when the difference between the average value of the angular velocities of rotation and the maximum or minimum value thereof is equal to or larger than a predetermined threshold value, the occurrence of misfires is determined. The threshold value is changed according to the operating conditions of the engine such as engine speed or load. Thus, in the method, most suitable, threshold values are set over wide ranges spanning from low speed to high speed, and from light load to heavy load. The abnormal rotation of the engine due to misfires can thereby be with high accuracy.
In a misfire detecting apparatus for a multicylinder internal combustion engine, a rotational signal outputting unit outputs a rotary signal at every predetermined rotary angle, and a tentative misfire decision unit tentatively decides, on the basis of the rotary signal, whether or not misfire has occurred in each cylinders of the engine. A tentative misfire number counting unit counts the number of tentative misfires decided for respective cylinders, and a counting result storage unit stores the counting results. After a given number of tentative misfire decisions have been made, it is decided that misfire has actually occurred, only if the counting result, for a part of the cylinders, among the counting results for respective cylinders stored in the counting result storage unit is larger than a predetermined number.
A method is provided for recognizing erratic combustion in a multicylinder internal combustion engine by using a time measuring device to measure successive time periods which a crankshaft needs to rotate through predetermined angles during operating strokes of successive cylinders. The method includes determining a static component by using a calculating device to subtract a time period of the next cylinder in an ignition order from the time period of a cylinder to be examined. The static component is multiplied with a standardizing factor by using the calculating device. A dynamic component is determined by using the calculating device to subtract a time period of a next cylinder in the ignition order from a time period of a preceding cylinder in the ignition order, and a dynamic component is negated. A change component for a lack of smoothness value is formed, the lack of smoothness value is multiplied with a weighting factor to form a weighted value, and the weighted value is set equal to zero if the weighted value is negative. A sliding average is formed from the weighted value in a sliding averaging process. A lack of smoothness value is determined from addition of the static component, the dynamic component, and the sliding average. A combustion misfire is recognized if the smoothness value falls below a given limit value.
A misfiring detecting device comprising a sensor for detecting the angular velocity of the crankshaft. The elapsed time required for the crankshaft to rotate by a certain crank angle is detected at the time of combustion at each cylinder. The difference .DELTA.T.sub.n (=T.sub.n -T.sub.n-2) of the elapsed time T between cylinders with explosion strokes one interval apart is found and it is judged that a misfire has occurred when the difference .DELTA.T.sub.n has exceeded a set value K.sub.1 and also the pattern of change of the elapsed time (.DELTA.TC) has become the pattern of change of the time of a misfire.
