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EFI: Electronics for low-emission motor control, part 1

Electronic Fuel Injection (EFI) is a solution that guarantees a low emission as well as a fuel consumption optimization, for small motors that, otherwise, can be very polluting. This fact underlines the importance of trying to find a solution to reduce the impact on the environment of such a type of motors (see Figure 1).

A carbureted small engine with a mechanical governor is quite inefficient and the emissions of such engines are significant. Fuel consumption and emissions of these engines can be reduced by electronic throttle control and retrofitting electronic fuel injection (EFI). The current state of small internal combustion engines (ICE) is that they are often carbureted and generally governors and other methods of control are mechanically achieved. The problem is that a carbureted small engine with a mechanical governor is not very fuel efficient and the emissions of such engines are quite significant. Electronic control for carburetor and ultimately electronic fuel injection (EFI) would reduce emissions and improve fuel economy. [2,4] …  Currently the U.S. standard is stricter for new spark-ignition engines over 225 cc, the maximum permissible Carbon Monoxide (CO) level is 610 g/kWh and Hydrocarbon (HC) + Nitrogen Oxides (NOx) is 8.0 g/kWh and EU levels are 610 g/kWh and 12.1 g/kWh respectively.

In this research it is studied, is it possible to reduce fuel consumption and emissions of carbureted engines by electronic throttle control and by retrofitting electronic fuel injection system. … The primary emissions reducing method tested was electronic fuel injection. …The fuel injection system comprises of fuel supply system, throttle body with fuel injector and electronic control unit (ECU). The ECU controls the injection quantity and injection timing based on sensor outputs. The tested EFI system is controlled by Alpha-N control algorithm. The control algorithm uses throttle position angle and engine rotation speed to read a value from volumetric efficiency (VE) chart to determine the correct fuel delivery.

(Source: International DAAAM Baltic Conference)

Figure 1. A system designed to reduce emissions of a small engine through EFI, and the measured emissions results.

EFI is thus an interesting application of the electronics to reduce pollution, this is the reason for why the STMicroelectronics Company is developing systematic EFI solution based on smart ICs able to realize an effective and optimized ECU (see Figure 2):

Figure 2. A system designed to reduce emissions of a small engine through EFI, and the measured emissions results.
(Source: METHODS FOR REDUCING EMISSIONS OF SMALL INTERNAL COMBUSTION ENGINES by Niinikoski, J.; Ewalds, J.; Heikkinen, E.; Kotilainen, J.; Kääriäinen, M.; Tammi, K.;Kiviluoma, P.; Korhonen, A. & Kuosmanen, P.)

To meet the challenge of offering the required ECU/chipset performance at a competitive price enabling its deployment in large quantities, ST offers a high-integration chipset for an optimized ECU form factor and cost. The backbone of our proposal is the SPC572L64 32-bit Power Architecture MCU and the L9177A peripherals on chip. Specifically designed for small EFI engine management systems, the SPC572L64 includes specific modules such as the GTM (Generic Timer Module) used to lock and track the angular position of the crankshaft and the decimation filter for managing knock sensor signals to ensure accurate injection and ignition timings with a direct effect on engine emission and consumption performance. The L9177A contains all the building blocks for EFI systems from key sensor interfaces and load actuations (solenoids, relays, bulbs, etc.) for diagnostics and networking capabilities.” (Source:

The sensors, whose accuracy and reliability is a key factor for the overall effectiveness of all the EFI solution forms the most interesting part of the system of Fig. 2. Some of these sensors connect to the power supply to sense the feed of the system and to protect the control unit from voltage spikes or noise injected in the power supply lines.

Figure 3 shows the block diagram of a voltage regulator that translates the voltage from the battery of the vehicle 12 V to the 5 V supply voltage, which is the difference of potential needed by the control unit to work properly. A pass diode rectifies the input voltage, which is then filtered by the capacitors and a pass element (a MOS switched on the ON state).

Figure 3. The schematic diagram of a voltage regulator made by STMicroelectronics Company includes a series diode and filter capacitors. (Source:

Part 2 (October 29) will describe more details about the ICs utilized in ECU for EFI solutions.

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