The Fuel Injector Story - Part 2: The Origins Of Electronic Fuel Injection

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DESCRIPTION
In 1957 Bendix would introduce the first electronic fuel injection system, the Bendix Electrojector. In Bendix’s system, fuel at a constant pressure of 1.3 Bar or 20psi, was supplied by a non-metering electric fuel pump to electrically actuated solenoid fuel injectors, located within the intake manifold and aimed at the each intake valve. The engine's distributor was modified to incorporate a second rotor and set of contacts known as the trigger selector unit.

This unit was used to electrically tie the injector of the firing piston to the control electronics, allowing the system to match both the rotational speed and piston timing of the engine in a manner similar to the ignition system. What made the Electrojector system remarkable for its day, was how it controlled fuel flow. Each injector was metered by pulse width modulation, where the "open-time" or duty cycle was determined by a pulse width. Metering was accomplished through an analog electronic modulator unit that modified the injector pulse width primarily using sensors that measured intake manifold pressure and air temperature.

The vacuum created within the intake manifold directly corresponded to the air flow into the engine. Ultimately, the sophistication of Bendix’s system became its downfall as it proved to be far too unreliable for vehicle use.

RISE OF JETRONIC
In 1965, Bosch had licensed the patents for the problematic Bendix Electrojector system and introduced their first electronic fuel injection system, called Jetronic, in the autumn of 1967 on the Volkswagen 1600 LE and TLE. It operated in a similar manner, utilizing solenoid injectors, a constant-pressure common fuel rail and a distributor based injector selection system.

RETURN TO MECHANICAL
The K-Jetronic system, fundamentally, was similar to GM’s mechanical Rochester Ramjet System described in Part 1. From there, this metered fuel was then distributed to spring-loaded check valve injector nozzles located at each cylinder. What made K-Jetronic unique was how it metered fuel. A secondary mechanism known as a control pressure regulator simultaneously adjusted the operating fuel pressure of the air-metering system to better match the operating state of the engine.

LAMBDA SENSORS
With the introduction of legislation that restricted automotive exhaust emissions in the late 1960s, fuel injection would now become a critical tool in meeting these new requirements. It was soon realized that fuel-injection was the most effective method to easily and consistently maintain the ratios needed for catalytic converters. Because this target window was so narrow, an oxygen or lambda sensor would be placed within the exhaust stream, creating a closed-loop feedback system.

TRANSITION TO DIGITAL
Bosch’s would extend the inline electromechanical flow control technique first used on its lambda sensor variants to it’s KE-Jetronic system, transitioning fuel metering further to electronic control. Ultimately a fully electronic system would be embraced with the introduction of L-Jetronic in 1974.

DIGITAL FUEL INJECTION
They were initially employed in a limited manner alongside analog and mechanical systems, for fuel metering control, both in carburetors and mechanical fuel injection, and for ignition control. Finally, by 1979, the first fully digital engine management fuel injection system, called Motronic, would be introduced by Bosch. Much like it’s electronic analog counterpart, these systems all use an engine control unit to vary the duty cycle of solenoid fuel injectors, fed by constant fuel pressure, to meter fuel. However, unlike analog and mechanical systems, digital ECUs convert sensor signals to a digital value and indirectly determine the ideal injector duty-cycle for a given engine state, completely in software.

. Most modern digital fuel injection systems employ some combination of manifold pressure sensing, vane based volume flow sensing, or mass flow sensing as the basis for their air-sensing strategy. Air mass flow sensing in particular was introduced during the 1980s.

Engine ignition would also integrate into these rapidly evolving management systems. Engine knock sensing would also be integrated, allowing software to constantly adapt ignition timing based on engine operating conditions and fuel properties. By the mid 1990s, microprocessor based electronic fuel injection became a standard of the automotive industry.

Engine management systems were now tasked with operating variable camshaft timing and duration mechanisms, forced induction, variable length intake tracks, throttle by wire and various emissions control devices.

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