Fuel Injection Engine - Oxygen Sensor Control
85bmw12GROUP 11 Engine
Bulletin Number 11 03 84 (2034) Page 1 of 3
Montvale, NJ January 1985 Technical Dept.
Subject: 3.5 Liter Fuel Injection Engine with Oxygen Sensor Control
Models: 1985 Series 5, 6, 7
This engine is based on the 3.5 liter ECE engine. The compression ratio was reduced to 8.0:1 by using dished pistons, so that unleaded gasoline can be used. This specific measure has led to an engine power output of 136 kW/182 HP SAE net.
Emission control is achieved through application of a selective catalytic converter (three way catalytic converter), which oxidizes carbon monoxide (CO) and hydrocarbon composites (CnHm) and reduces nitrogen oxide (NOx). These chemical reactions produce the non-poisonous exhaust gas components carbon dioxide (CO2), water or vapor (H2O) and nitrogen (N2).
A new generation of digital engine electronics with oxygen sensor control is applied to have the necessary control and regulation of the fuel/air mixture for production of the stoichiometric fuel/air mixture ratio (14 lbs. air to 1 lb. fuel).
The oxygen sensor has been relocated downstream in the inlet opening of the catalytic converter. This allows a more homogeneous "exhaust mixture" to be sensed by the oxygen sensor. This position also considerably reduces the peak thermal loads so that the sensor only has to be replaced after 50,000 miles.
A so-called adaptive system for fuel/air mixing and emission control is integrated in the new generation of digital motor electronics for the first time.
This new technology makes it possible to correct deviations from the nominal value for injection time (pilot control value).
The control unit receives inputs from various sensors, such as the oxygen sensor, speed and temperature of the engine and these are integrated in the control unit. In addition, switches for idle speed, air conditioner and selected range in automatic transmission cars are processed in the control unit.
The control unit, after comparing input data with programmed data, then gives outputs to supply the engine with the appropriate amount of air and fuel for proper combustion.
During the warm-up phase (up to an operating temperature of 158~F/70~C) the fixed values in the memory are compared with prevailing signals from coolant temperature, engine speed and load, and evaluated for control of fuel injection signals. All of these factors together determine the fuel injection rate during the warm-up phase.
The adaptive pilot control of digital engine electronics mentioned previously is based on continuous comparison of data. These data are compared with the evaluated oxygen values of the sensor in a permanently programmed pilot control graph and constantly keep the memory up to date. The factor, with which the oxygen sensor control must correct the pilot control value, is stored in an intermediate memory. This factor goes immediately to the fuel injection time and extends or shortens this time accordingly. Consequently oxygen sensor control keeps the so-called error adaption time (e.g. the time required by a sensor to detect and correct an erroneous mixture) to a minimum.
Small deviations, such as leakage in engine intake system (leaking oil filler cap or oil dipstick, loose hose clamps on dust cover) are corrected with the adaptive pilot control, so that neither pickup behavior impairment nor poor emission control will occur. The ability of digital engine electronics to carry out corrections has also made the barometer box for altitude correction superfluous, since the adaptive pilot control will, for example, recognize the "thin" air on a high mountain pass (same volume, but less mass) as an excessively "rich mixture" and shorten the fuel injection time accordingly.
Moreover, checking and/or adjusting the idle mixture is no longer necessary during inspections. However, this job is still required for troubleshooting or repairs.
In order to keep the data stored the memory has its own power source. If the source of power for the memory is interrupted (e.g. replacement of battery), new adaptation takes place while running the engine within several minutes. Discharging the battery is not possible, since the memory only requires low mA.
The intermediate memory is always supplied with 12 volts and doesn't lose its up-to-date correction value even after stopping the engine, so that when restarting the engine it is not necessary to have new adaptation.
The adaptive pilot control can be switched off for checking and/or troubleshooting (e.g. defective fuel injector, wrong intake air, etc.) This is accomplished by connecting pin 30 of the digital engine electronics control unit with car ground. As long as this connection is made the memory takes on factor 1 and the oxygen sensor control remains in operation but without influence. Troubleshooting and checking procedures are the same as for all other oxygen sensor controlled engines.
TECHNICAL DATA