A history of Engine Management Systems according to DENSO

Before Electronic Control Units (ECUs) were adapted into car engines, ignition timing, air-fuel mixture and idle speed were mechanically set and controlled by simple mechanical or pneumatic systems – for example by compressed air or gas.

The Electronic Control System (EMS), an electronically controlled unit which operates a car’s engine, began to use an ECU around 30 years ago. ECUs are now used by every OEM, controlling a series of actuators on an internal combustion engine to ensure optimal engine performance at all times, improving the performance, economy and reliability of cars.

Within the EMS, various types of sensors detect the operating condition of the engine transmitting information to the engine ECU. The ECU then processes the information and controls the operation of the actuators in order to operate the engine at optimal conditions. Engine speed, for example is controlled by the EMS which regulates fuel injection function and ignition timing, instead of having a throttle plate that restricts the incoming air supply.

On some recent cars, the engine ECU is connected to other ECUs through an onboard LAN (Local Area Network). The data of other ECUs, such as the operating condition of the air conditioner, is also utilised to operate the engine at optimal conditions.

Back in 1971, mechanical systems started to be replaced by fuel injection paired with simple ECUs. The fuel injection control ECU consisted of analogue circuits, which continued to be used until 1975.

Due to the emissions regulation that took effect in 1975 and subsequent years, the internal elements of the ECU were organised into integrated circuits and an air-fuel ratio feedback control system was added as one of the EMS’ aimed at achieving high precision and reliability.

With the use of microprocessors in 1980, the EMS was completely revamped with the addition of ignition timing control, idle speed control, and diagnosis functions. In 1984, the lean-burn engine came into being, and in 1996, the direct injection system engine was made practical.

The methods for detecting the intake air volume, which forms the basis of fuel injection control, have also changed with the times. In the beginning, a speed density system known as ‘D-Jetronic’ was adopted. This detected the intake manifold pressure in the form of signals picked up by a vacuum sensor, as a means of indirectly detecting the intake air volume.

After 1975, emissions regulation began to take effect, meaning that D-Jetronic was replaced by a mass flow system known as ‘L-Jetronic’, which used a mechanical airflow metre to directly and precisely detect the intake air volume.

The advent of microprocessors later on accelerated the use of semi-conductors in vacuum sensors, which enabled a high-precision detection of intake air volume with DJetronic, and resulted in the use of D-Jetronic. More recently, L-Jetronic, which uses a compact hot-wire type airflow meter, is in the mainstream.

As for DENSO, it developed the world’s first Exhaust Gas Recirculation (EGR) Valve in 2014, integrating an air intake throttle valve and an EGR valve, which helps to make diesel engine emissions cleaner at half the size of conventional models.

DENSO also launched the world’s first plug-in type Mass Air Flow metre inserted into the intake pipe wall, reducing the size and weight and aiding installation, as well as being the first to introduce quantitative measurement to its Lambda Sensors, enabling them to sense both if the air/fuel mixture is too lean or too rich, and by how much.

Today, DENSO’s EMS products are fitted as original equipment in many of the world’s leading vehicle marques.