Engineering Forum INTRODUCTION TO ELECTRONIC ENGINE CONTROL SYSTEMS

Electronic Control Systems Operation
Nowadays, most of the machines use electronic controlled engines which are power efficient and consume less fuel rather than normal conventional engines. Also, these electronic engines meet environmental requirements of exhaust emission.

These engines have an ECU, Electronic Control Unit, which will collect all the information from engine operation systems, the same as with conventional engines. It is like a human brain which controls the body. It acts as the brain of the engine and it controls the engine operating systems. As the human brain receives information from eyes, ears and hands etc, the ECU incorporates sensors to know engine operation condition such as ambient air temperature, charge air temperature, coolant temperature, oil temperature and engine rpm etc. Operating software, like a reasonable thinking in the human brain, is installed in the ECU to control engine operations according to the information from the sensors. So, without the ECU the engine will not operate, and without sensors the ECU cannot control the engines.

The ECU needs many sensors to know engine condition and it uses “Temperature Sensors” to know coolant temperature, charge air temperature and oil temperature, and “Pressure Sensors” to know charge air pressures, fuel pressures and oil pressures. Now the ECU knows temperatures and pressures of engine operating systems, but not yet the engine rpm nor piston position in the cylinder to inject fuel into the cylinder at the correct firing order.

Piston position depends on the rotation of crankshaft, and firing order depends on the rotation of camshaft. In which case a sensor is installed over the camshaft timing gear to know which cylinder is at TDC with compression stroke to inject fuel into the cylinder. This sensor is called “Camshaft Position Sensor”, and it tells the ECU which cylinder is at TDC with compression stroke to inject fuel. In this way it detects which cylinder is ready to fire at TDC. And then a sensor is installed over the crankshaft or over the flywheel on some engines to count engine rpm and this sensor is called “Crankshaft Speed Sensor”. Both of these sensors are also called “Speed Sensors” because they also count engine rpm.

In the Electronic Engine Control System, fuel system is electronically controlled so that each cylinder can be separately controlled. For this reason, Electronic Unit Injection Pumps or Electronic Unit Injectors are used for each cylinder. The pumps are mechanically actuated by the camshaft and electronically controlled by the ECU.




Volvo D6D Engines and D7D Engines use Electronic Unit Injection Pumps. Electronic Unit Injection Pumps have solenoid-operated valves and pumping action and high pressure are due to the upward movement of the plunger in the unit pump body. The plunger is pushed upward by the cam lobe on the camshaft. High pressure fuel is injected into the cylinder from the nozzle. The ECU controls the fuel injection by energizing or de-energizing the solenoid valve to start or stop the injection into the cylinders.

Volvo D12C Engine of EC460B Excavator uses Electronic Unit Injectors. Unit Injector is a combination of a pump and a nozzle. Unit Injectors are placed directly above the cylinders and this system needs overhead camshaft. Unit injectors have solenoid-operated valves and pumping action and high pressure are due to the downward movement of the plunger in the injector body. The plunger is pushed downward by the cam lobe on the camshaft. So the fuel injection is controlled by energizing or de-energizing the solenoid valve in the pump to start or stop injection into the cylinder.
In this way, the electronic control system operates the engine by controlling the Electronic Unit Injectors to deliver fuel according to a given set of engine conditions, in precise amounts, and at a precise time in relation to piston position. In order to achieve this, the control system performs the following functions:

• Constantly monitor engine operating conditions
• Precisely determines piston position
• Deliver optimum amount of fuel for a given set of operating conditions
• Deliver fuel at optimum piston position
• Provide multiple control modes
• Perform self-diagnosis

In coming up issues: “How the ECU performs during Engine Starting Mode and Engine Running Mode” will be explained.
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