Page 199 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Suzuki Motor Corporation 181

Further, the fuel tank is communicated with the intake passage of the throttle body by a
passage for evaporated fuel. A bypass passage communicates with the intake passage and
bypasses the intake throttle valve. An idle air amount control valve is provided in the bypass
passage for controlling flow there through. When it is necessary to adjust idle rotational speed
at start up of the engine, at high temperature, and due to an increase in electrical load and the
like, the idle air amount control valve opens or closes the bypass passage, thereby increasing or
decreasing the air amount and stabilizing the idle rotational speed.
The air flow meter, first to fourth fuel injection valves, idle air amount control valve, and air
amount control valve for power steering are connected to a control section serving as a control
means. A crank angle sensor, a distributor, an opening degree sensor of the intake throttle
valve, a knock sensor, a water temperature sensor, and a vehicle velocity sensor are connected
to the control section, respectively. The distributor is connected to the control section through
an ignition coil and a power unit for ignition.
An upstream oxygen sensor 1 serving to detect oxygen concentration as an exhaust component
value is provided on the upstream side of the catalytic converter and a downstream oxygen
sensor 2 provided on the downstream side of the catalytic converter are connected to the
control section. The control section executes what is called a dual oxygen feedback control in a
manner such that fuel supply amounts to the first to fourth fuel injection valves of the internal
combustion engine are controlled.

The aidfuel ratio is first feedback controlled to a value in a stationary operating range of the
internal combustion engine by a first detection signal from the upstream oxygen sensor 1, the
aidfuel ratio is open controlled in case of an accelerating/decelerating operation other than the
stationary operating range of the internal combustion engine, and when the second feedback
control performing conditions are satisfied, the aidfuel ratio is second feedback controlled by a
second detection signal from the downstream oxygen sensor 2, and in cases other than the
second feedback control performing conditions, the aidfuel ratio is open controlled.

Patent disclosure JP6081635 (1 994) comprises two methods.
1) The first method judges deterioration of the catalytic converter by the calculated area ratio
of the output signals of the upstream and downstream oxygen sensors. The signals are
measured within a specific time interval starting at the fuel reset time after fuel cut during
deceleration. The areas are calculated by integrating the signals in time.
2) The second method judges deterioration of the catalytic converter by measuring the
duration of response time from the fuel cut ending time until the time when the judgment
voltage outputted from the two oxygen sensors exceeds a specified judgment voltage.

The method of JP6200811 (1994) comprises the following steps:
I) checking whether deterioration judging conditions are accomplished and in case they do
2) calculating a standard comparison value from a) the measured delay times of the upstream
and downstream sensors during a ricMean variation of the engine aidfuel ratio during
feedback-control and b) the feedback correcting amount