Engine controller

An engine controller having a microprocessor for controlling and operating various kinds of electric loads for operating an internal combustion engine in accordance with operating states of various kinds of input sensors for monitoring an operating state-of said internal combustion engine, and the contents of a control program stored to a program memory;

• wherein said various kinds of input sensors include plural exhaust gas sensors;
• each of the exhaust gas sensors has an equivalent voltage source and an equivalent internal resistor connected between a pair of positive and negative terminals;
• a generating voltage Vs of said equivalent voltage source is changed from a minimum value V0 to a maximum value Vm with a theoretical air fuel ratio as a boundary at a predetermined activating temperature;
• a predetermined offset voltage V1 generated by an offset voltage generating circuit is applied to each of the negative terminals of said plural exhaust gas sensors;
• a negative terminal electric potential as a voltage between the negative terminal and a ground circuit is digitally converted through a multi-channel AD converter, and is stored to a RAM memory for arithmetic processing through said microprocessor;
• at least one of a pull-down resistor and a pull-up resistor of high resistance connected to the ground circuit, and a bias resistor of high resistance for giving a predetermined bias electric potential is connected to each of the positive terminals of said plural exhaust gas sensors;
• a positive terminal electric potential as a voltage between the positive terminal and the ground circuit is respectively converted individually digitally through the multi-channel AD converter, and is stored to said RAM memory for arithmetic processing through said microprocessor;
• said program memory includes at least a program as first and second abnormality diagnosing means, and a program as a positive terminal abnormality judgment avoiding means;
• said first abnormality diagnosing means is a means for judging that it is a sky short circuit abnormality for making negative terminal wirings come in mixing contact with an electric power source line, or a ground abnormality for making the negative terminal wirings come in mixing contact with a ground line according to whether a digital converting value D1 of said negative terminal electric potential is excessively large or excessively small with a value proportional to said offset voltage V1 as a reference;
• said second abnormality diagnosing means is a means for judging that it is a sky short circuit abnormality for making positive terminal wirings come in mixing contact with the electric power source line, or a ground abnormality for making the positive terminal wirings come in mixing contact with the ground line according to whether a digital converting value D2 of said positive terminal electric potential is excessively large with a value proportional to an adding value V1+Vm of said offset voltage V1 and a maximum detecting voltage Vm as a reference, or is excessively small with the value proportional to said offset voltage V1 as a reference;
• and said second abnormality diagnosing means judges a disconnection abnormality as said ground abnormality or the sky short circuit abnormality when the disconnection abnormality is generated;
• said microprocessor obtains a digital converting value proportional to a generating voltage Vs of said exhaust gas sensor by a differential arithmetic calculation of the digital converting value D2 of said positive terminal electric potential and the digital converting value D1 of the negative terminal electric potential, and performs abnormality annunciation according to a diagnosing result using said first and second abnormality diagnosing means;
• and
• said positive terminal abnormality judgment avoiding means is a means for judging no ground abnormality of the positive terminal wirings using said second abnormality diagnosing means and considering the differential arithmetic calculation of said microprocessor to be valid when said first abnormality diagnosing means detects the ground abnormality of at least the negative terminal wiring.