Patent ID: 6054859
Filing Date: 2000-04-25
Classification: F02P

Abstract:
A combustion state detecting apparatus for an internal combustion engine, comprising:an ignition coil unit generating a firing voltage at a high voltage output terminal;high-voltage supply circuitry connected to at least two spark plugs;biasing means for applying a bias voltage, via said high-voltage supply circuitry, to said at least two spark plugs;bias voltage protection means for preventing said bias voltage from discharging through said ignition coil unit, said bias voltage protection means being connected in series between said high voltage output terminal and said high-voltage supply circuitry;ion current detecting means for detecting, as an ion current, ions generated in succession to discharging of said at least two spark plugs upon application of said firing voltage, said ion current being a current which flows through said at least two spark plugs under said bias voltage; andan electronic control unit for detecting said combustion state, in an engine cylinder provided with said at least two spark plugs, on the basis of said ion current;said internal combustion engine including a plurality of cylinders each provided with a respective one of a plurality of spark plugs, said plurality of spark plugs including said at least one spark plug;said ignition coil unit including a primary winding having one end connected to a power supply source, and a secondary winding electromagnetically coupled to said primary winding;a power transistor, connected to said primary winding of said ignition coil, and responsive to an ignition signal to turn on/off a primary current flowing through said primary winding;means for inducing said firing voltage in said secondary winding upon interruption of said primary current;said high-voltage supply circuitry including:a distributor having a center electrode connected to said bias voltage protection means, anda plurality of peripheral electrodes disposed around said center electrode, each with a gap in opposition thereto;said plurality of spark plugs being connected to said peripheral electrodes in correspondence to said cylinders, respectively;said biasing means including a plurality of high-voltage diodes each respectively connected to a corresponding one of said plurality of spark plugs, each of said plurality of high-voltage diodes being connected so that said bias voltage to each of said plurality of spark plugs has the same polarity as said firing voltage;said electronic control unit generating said ignition signal based on operating state information of said internal combustion engine and detects combustion state within each of said engine cylinders on the basis of the relevant ion current detection signal; andsaid bias voltage protection means comprising a bias voltage protection diode,wherein said bias voltage protection means further comprises a resistor connected in series, said resistor connected between said high voltage output terminal and said bias voltage protection diode.