# US 7,746,079 B2 · Ion current detecting apparatus for internal combustion engine

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- Number: US 7,746,079 B2
- Document ID: US7746079B2
- Status: Granted
- Kind: B2
- Application number: 11/632,928
- Filed: 2005-08-09
- Published: 2008-02-07
- Granted: 2010-06-29
- Earliest claimed: 2004-08-09
- Assignees: Diamond Electric Mfg. Co., Ltd.
- Inventors: Yoshiyuki Fukumura; Mitsuhiro Izumi; Shinobu Sugisaki; Tsutomu Kusuhara
- Web page: https://patentgrep.com/patent/US7746079B2

## CPC

- F02D 35/021: {using an ionic current sensor}
- F02P 17/12: Testing characteristics of the spark, ignition voltage or current (testing of sparking plugs H01T13/60)
- G01L 23/221: {for detecting or indicating knocks in internal combustion engines}
- F02D: CONTROLLING COMBUSTION ENGINES (vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed B60K31/00; conjoint control of vehicle sub-units of different type or different function, road vehicle drive control systems for purposes other than the control of a single sub-unit B60W)
- F02P: IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES ({anti-pollution means for internal-combustion engines F02B17/00}; specially adapted for rotary-piston or oscillating-piston engines F02B53/12; {ignition of gas turbine plants F02C7/26; ignition of jet propulsion plants F02K9/95; starting of combustion engines F02N9/00}; ignition of combustion apparatus in general, glowing plugs F23Q; measuring of physical variables in general G01; controlling in general G05; data processing in general G06; electrical components in general see Section H; {ignition coils H01F38/12}; sparking plugs H01T13/00)
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)

## Abstract

An ion current detecting apparatus includes a capacitor C that is charged as a spark plug 3 discharges, a Zener diode ZD that limits a maximum voltage of the capacitor C while charging, a detection resistor R2 through which a discharge current of the capacitor C flows, and a comparator circuit 5 that compares a current value of the detection resistor R2 with a predetermined value. A charge quantity Q of the capacitor C at discharge start is set so that, as a consequence of a discharging operation of the capacitor C, discharge duration required until the current value of the detection resistor R2 falls below the predetermined value becomes longer than time duration in which the ion current generated by fuel combustion in the engine combustion chamber lasts. The ion current detecting apparatus automatically detects degradation in an insulation resistance in the spark plug, ensuring normal operation in engine control.

## Claims

### Claim 1

An ion current detecting apparatus for an internal combustion engine, comprising:
a capacitor that is charged as a spark plug discharges;
a voltage limiting element that limits a maximum voltage of the capacitor while charging;
a detection resistor through which a discharge current of the capacitor flows; and
a comparator circuit that compares a current value of the detection resistor with a predetermined value,
wherein a stage prior to the comparator circuit is provided with an amplifying element including an inverting input terminal, a non-inverting input terminal, and an output terminal, and
the comparator circuit compares a voltage value of the output terminal of the amplifying element with a fixed reference voltage value, and
wherein the amplifying element is connected with an input resistor provided between the capacitor and the inverting input terminal, and a feedback resistor provided between the inverting input terminal and the output terminal, and
the feedback resistor functions as the detection resistor wherein
degradation of an insulation resistance in an ion current path through which an ion current flows is determined either by:
providing a prohibiting step in which fuel supply to a combustion chamber of an internal combustion engine is prohibited, and determining an output from the comparator circuit in the prohibiting step, or
setting a charge quantity of the capacitor at discharge start so that, as a consequence of a discharging operation of the capacitor, discharge duration required until the current value of the detection resistor falls below the predetermined value becomes longer than time duration in which the ion current generated by fuel combustion in the combustion chamber in the internal combustion engine lasts.

### Claim 2 (depends on 1)

The ion current detecting apparatus according to claim 1, wherein as a consequence of a comparison operation by the comparator circuit in the prohibiting step, the insulation resistance in the ion current path is determined to be degraded if the current value of the detection resistor exceeds the predetermined value.

### Claim 3 (depends on 2)

The ion current detecting apparatus according to claim 2, wherein the prohibiting step is provided at a starting time of the internal combustion engine.

### Claim 4 (depends on 1)

The ion current detecting apparatus for an internal combustion engine according to claim 1, wherein the comparator circuit detects time duration in which the current value of the detection resistor is maintained at a higher level than the predetermined value, and the degradation of the insulation resistance in the ion current path is determined based on the detected time duration.

### Claim 5 (depends on 1)

The ion current detecting apparatus for an internal combustion engine according to claim 1, wherein while the comparator circuit detects time duration in which the current value of the detection resistor is maintained at a higher level than the predetermined value, the degradation of the insulation resistance in the ion current path is determined based on the current value of the detection resistor during the detected time duration.

### Claim 6 (depends on 5)

The ion current detecting apparatus for an internal combustion engine according to claim 5, wherein the degradation of the insulation resistance in the ion current path is determined based on a value of current integration of the detection resistor during the time duration.

### Claim 7 (depends on 1)

The ion current detecting apparatus for an internal combustion engine according to claim 1, wherein since a time measured from the capacitor discharge start until an ending time of an emission varies depending on a number of rotations (rpm) of the engine, the apparatus is adapted to employ a value for the ending time of the emission when the number of rotations of the engine is at a minimum number of rotations.

### Claim 8 (depends on 1)

The ion current detecting apparatus for an internal combustion engine according to claim 1, wherein the voltage limiting element is a Zener diode connected in parallel with the capacitor.

### Claim 9 (depends on 7)

The ion current detecting apparatus for an internal combustion engine according to claim 7, wherein the charge quantity is set to be no less than 2.5 μC.