Air/fuel ratio detecting apparatus, and method of detecting normal and abnormal conditions of the sensor

A method of detecting normal and abnormal conditions of the air/fuel ratio sensor, which comprises the steps of:

• (a) determining if all cylinders are being injected, the predetermined number of cylinders are being injected, or all of the cylinders are stopped injecting;
• (b) calculating a correction coefficient from the following equation in accordance with the result of the determinations;
• ##EQU4## where V.sub.1 =the detection voltage V.sub.i when all cylinders are being injected,
• V.sub.2 =the detection voltage V.sub.i when the predetermined number of cylinders are being injected,
• V.sub.3 =the voltage V.sub.i when all cylinders are stopped injecting,
• (c) comparing an obsolete value of :
• A-K :
• with a predetermined value of .alpha. determined on the basis of linearity of the output characteristics of the air/fuel ratio sensor where K is the ratio of the number of all the cylinders to the predetermined number of cylinders;
• and
• (d) determining occurrence of an abnormal condition of the air/fuel ratio sensor in accordance with the result of the comparison.

A method of detecting normal and abnormal conditions of an air/fuel ratio sensor, which comprises the steps of:

• (a) determining if a deceleration flag is set at "1";
• (b) determining if a correction flag is set at "1" in accordance with the result of said first determination;
• (c) determining if all of cylinders in question are being injected in accordance with the result of said second determination after detecting an all cylinder injected condition;
• (d) setting a first read-in completion flag (4RF) to "1";
• (e) maintaining the above condition, i.e., all cylinder injected condition,
• (f) adjusting the air/fuel ratio to a constant value;
• and
• (g) detecting a detection voltage (V.sub.i) from a pump current detecting circuit.

An air/fuel ratio sensor detecting apparatus which comprises:

• (a) deceleration condition determining means for determining the deceleration condition of an engine;
• (b) an air/fuel sensor for detecting air/fuel ratio of exhaust gas of the engine;
• (c) means for changing the number of fuel injection cylinders to be injected during deceleration;
• (d) setting-up means for setting up a supply air/fuel ratio of each cylinder to a predetermined value;
• (e) coefficient calculating means for calculating a coefficient A in accordance with the following equation;
• and ##EQU6## where V.sub.1 =detection voltage (V.sub.i) from the pump current detection circuit when all cylinders are being injected,
• V.sub.2 =the detection voltage of the pump current detection circuit when the predetermined number of cylinders are being injected,
• V.sub.3 =the detection voltage of the detection circuit when all of the cylinders are stopped injecting;
• and
• (f) determining means for determining normal/abnormal conditions of the air/fuel ratio sensor in accordance with the coefficient A, thus, calculated.