TECHNICAL FIELD

The present invention relates to an engine misfire detection device and method for detecting a misfire in an engine.

BACKGROUND ART

PTL 1 discloses a device for detecting a misfire in an engine. The engine misfire detection device disclosed in PTL 1 executes air-fuel ratio F/B control based on a wide and linear air-fuel ratio signal in proportion to the oxygen concentration of exhaust gas discharged from an engine and detects a misfire in the engine in accordance with an air-fuel ratio AF during the control. Specifically, the detected air-fuel ratio is compared with a predetermined misfire determination value set in advance on the air-fuel ratio lean side, and the occurrence of the misfire is determined when the air-fuel ratio is leaner than the misfire determination value.

CITATION LIST

Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No. 2014-234814

SUMMARY OF INVENTION

Technical Problem

The rotation speed of the engine, the air-fuel ratio, and the like fluctuate with vehicle operation states. A crankshaft is connected to a vehicle wheel, and thus fluctuations occur with the traveling resistance (traveling load) that is received from a step or the like during vehicle traveling on a rough road. Accordingly, it needs to be determined whether a decline in engine rotation speed and a decline in air-fuel ratio are attributable to a misfire or traveling resistance, and there is a possibility of wrong detection.

The present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a device and method for detecting a misfire in an engine that enable high-accuracy engine misfire detection.

Solution to Problem

An engine misfire detection device according to the present invention for achieving the above object includes a supercharger rotation speed measurement unit measuring a rotation speed of a supercharger, a misfire index calculation unit calculating a misfire index from a degree of change in the rotation speed of the supercharger measured by the supercharger rotation speed measurement unit, and a misfire determination unit determining a misfire in an engine when the misfire index calculated by the misfire index calculation unit exceeds a pre-set determination value.

Accordingly, once the supercharger rotation speed measurement unit measures the rotation speed of the supercharger and the misfire index calculation unit calculates the misfire index from the degree of change in the rotation speed of the supercharger, the misfire determination unit determines a misfire in the engine when the misfire index exceeds the pre-set determination value, and thus a misfire in the engine is determined from the degree of change in the rotation speed of the supercharger. The rotation speed of the supercharger hardly fluctuates with vehicle operation states, and thus it is possible to detect a misfire in the engine with high accuracy.

In the engine misfire detection device according to the present invention, the misfire index calculation unit calculates the misfire index based on the degree of change in the rotation speed of the supercharger at a top dead center position of a piston entailed by crankshaft rotation.

Accordingly, if the engine undergoes no misfire when the piston is at the top dead center position, an in-cylinder pressure is at its maximum and rotation of a turbine rotated by exhaust gas from that cylinder also rises. Therefore, a misfire in the engine can be determined with high accuracy by a misfire in the engine being determined based on the degree of change in the rotation speed of the supercharger at this time.

In the engine misfire detection device according to the present invention, the misfire index calculation unit regards a decrease rate of the rotation speed of the supercharger at the top dead center position as the misfire index.

Accordingly, a misfire in the engine can be clearly determined by a misfire in the engine being determined based on the decrease rate of the rotation speed of the supercharger.

In the engine misfire detection device according to the present invention, the misfire index calculation unit calculates a decrease rate of the rotation speed of the supercharger at the top dead center position and regards a deviation of the decrease rate of the rotation speed of the supercharger as the misfire index.

Accordingly, a misfire in the engine can be clearly determined by a misfire in the engine being determined based on the deviation of the decrease rate of the rotation speed of the supercharger.

In the engine misfire detection device according to the present invention, a crank angle measurement unit measuring a crank angle is provided and the misfire determination unit specifies a misfiring cylinder based on the crank angle measured by the crank angle measurement unit when the misfire in the engine is determined.

Accordingly, the misfiring cylinder is specified based on the crank angle when the misfire in the engine is determined, and thus the misfiring cylinder can be detected with high accuracy.

An engine misfire detection method according to the present invention includes a step of measuring a rotation speed of a supercharger, a step of calculating a misfire index from a degree of change in the rotation speed of the supercharger, and a step of determining a misfire in an engine when the misfire index exceeds a pre-set determination value.

The rotation speed of the supercharger hardly fluctuates with vehicle operation states, and thus it is possible to detect a misfire in the engine with high accuracy.

Advantageous Effects of Invention

According to the device and method for detecting a misfire in an engine of the present invention, an engine misfire can be detected with high accuracy.

