Description of the carburetor Pierburg 2BE «Ecotronic» (BMW 5 Series E12)

Carburetor 2BE, developed by Pierburg (carburetor with auxiliary elements) and Bosch (controller and sensor for incoming air temperature), equipped with an electronic control system "Ecotronic". In general, the system, which received the same name, consists of a simplified carburetor, servo drives, sensors and a controller.

The use of a carburetor with electronic mixture control allows maintaining an optimal fuel-air mixture (with a stoichiometric ratio of 14.7:1) and optimal filling of cylinders in various engine operating modes, increase fuel efficiency and reduce the content of harmful impurities in exhaust gases, improve vehicle operating conditions, increase the reliability of the fuel system, and facilitate maintenance and diagnostics. In the event of failure of the electronic control system, the 2BE carburetor begins to operate as a conventional carburetor. The Ecotronic system performs the following functions.

Enrichment of the combustible mixture during engine start-up, warm-up and acceleration

During a cold start, during warming up and acceleration of the engine, enrichment of the combustible mixture is required. It is carried out depending on the crankshaft speed, the position of the throttle valve of the 1st chamber, the duration of engine operation after a cold start, the temperature of the coolant and the opening speed of the throttle valve of the 1st chamber. Based on this information, the controller determines the required degree of enrichment of the combustible mixture and issues a corresponding control signal to the servo drive of the air damper. During acceleration, the air damper briefly moves in the closing direction. The moment of closing, its duration and the algorithm for reopening the air damper are determined by the controller depending on the operating parameters.

Controlling the amount of combustible mixture at start-up and at fast idle speed

The amount of combustible mixture required for reliable engine starting and simultaneous transition to accelerated idle mode is determined by means of the 1st chamber throttle valve servo drive depending on the coolant temperature and crankshaft speed. After the first excess of the specified idle mode, cylinder filling is controlled by regulating the engine idle speed.

Engine idle speed control

The idle speed mode is regulated independently of such parameters that usually influence it as the degree of engine running-in (values of friction moment), the temperature of the incoming air and the atmospheric pressure, and are constantly maintained at a given level.

For these purposes, the measured crankshaft speed is continuously compared with the set value stored in the controller's memory. If the idle speed deviates from the nominal value, the position of the throttle valve of the 1st chamber is adjusted by the servo drive in accordance with the proportional-integral control algorithm. The control of the regulation is selected in such a way that the idle speed is regulated over the entire temperature range. This means that the nominal value of the idle speed is adjusted depending on the coolant temperature.

Stopping fuel supply when the engine speed drops and when the engine stops

When closing the carburetor throttle valve, the fuel supply must be turned off.

To do this, the forced idle system (FIS) interrupts the fuel supply to the carburetor by completely closing the throttle valve of the first chamber when the engine speed exceeds a certain value. Fuel supply to the carburetor is resumed as a result of the simultaneous action of the servo drives of the throttle valve of the first chamber and the air damper when the crankshaft speed decreases to a certain threshold. This avoids interruptions in engine operation when the combustion process of the combustible mixture is resumed.

The original version is on the portal: BMWman