Engine Management System

Engine Management System

The Engine Control Module (ECM) controls the engine management system. The system consists of an ECM and a number of sensing and actuating devices. The sensors supply the ECM with input signals, which relate to engine operating conditions and driver requirements. The ECM uses calibrated data-tables and maps to evaluate the sensor information. The ECM then uses the results to command an appropriate response from the actuating devices. The system provides the necessary engine control accuracy and adaptability to:
- Minimize exhaust emissions and fuel consumption.
- Provide optimum driver control under all conditions.
- Minimize evaporative fuel emissions.
- Provide system diagnostics when malfunctions occur.

In addition to these functions the ECM also interfaces with other vehicle systems through the Controller Area Network (CAN) communications network.

The 32-bit ECM is at the center of the system and provides the overall control. Its functions are listed below, each of which are dependent on the engine and vehicle state at any moment of time and driver requirements.

- Starting: Ensures that conditions are safe to crank the engine.
- Engine: Controls the rate of air and fuel flow into the cylinders; adjusts the intake manifold volume; controls the ignition and intake camshaft timing.
- Fuel supply: Controls the operation of the fuel pumps and the EVAP canister purge valve.
- Cooling: Controls the engine cooling fans.
- Battery: Optimizes the battery charging conditions.
- Air Conditioning (A/C) and screen heater: Controls the speed of the engine when these additional loads are added, also disables the A/C when it is beneficial to reduce the load on the engine.
- Speed control: Provides the option to maintain a fixed vehicle speed without driver intervention.
- Robustness: Maintains engine running condition under intermittent or permanent single point failures on any sensors or actuators fitted to the system, and records Diagnostic Trouble Codes (DTCs) of these failures for system diagnosis.
- Diagnosis: Notifies the driver when a system malfunction occurs and records data for system diagnosis.

Fuel Injection
The ECM controls one injector per cylinder in sequential operation. The size of the injector used is so that stoichiometric control is possible at minimum load with allowance for EVAP canister purge valve correction, and at maximum load to provide sufficient fuel flow at all engine speeds. The timing of injector firing, relative to intake valve closing, during normal starting and running conditions is optimized to provide the best compromise between emissions and performance, time to first-ignition and smooth engine operation at start-up, for all engine conditions at all temperatures. The mass of fuel per-injection is derived from a calculation based on a ratiometric match to the metered airflow.

The ECM is capable of adapting to fuel system tolerances and engine internal wear under all operating conditions. The ECM continually monitors the differential pressure between the fuel rail and plenum, and uses this value to calculate the injector pulse width with the required mass of fuel per-injection. The ECM also continually monitors the temperature of the fuel being injected into the engine and provides compensation for the changing flow characteristics of the fuel system at different temperatures. By monitoring the battery supply voltage the ECM can ensure that the fuel supply to the engine is unaffected by voltage fluctuation.

Ignition
The system uses one ignition coil per-cylinder. A base ignition map is provided so that the engine can be optimized for emissions, fuel economy, performance and avoidance of cylinder knock throughout its speed and load range. Ignition timing during starting is used during engine cranking and under speed modes to provide the best compromise between emissions, time to first ignition and smooth engine operation at start up, at all temperatures. Provision is made to compensate for the effect of changing air intake temperature on the combustion detonation limit. The system contains the necessary hardware for the detection of combustion knock within the engine cylinders; the ECM uses this information to gradually adjust the ignition timing until the combustion knock is at a safe and inaudible level.

Variable Valve Timing (Normally Aspirated Engines)
The ECM controls the fully variable phase change system, which acts on the intake camshafts. The target positions of both camshafts are optimized to provide the best compromise between performance, refinement, fuel economy and emissions. During transient operation, the rate of change of the Camshaft Position (CMP) is controlled to optimize drivability. Operation of the Variable Valve Timing (VVT) will be restricted if environmental conditions exist that could affect normal operation of the VVT, for example very low ambient temperatures. Provision is made to ensure that the intake camshafts are restrained in the retard position during engine start. The ECM will also detect a variable valve timing mechanical malfunction, and act to compensate for the malfunction.

Variable Air Intake System (V6 Engines)
The ECM controls two intake manifold tuning valves. Each valve is a two positional device; the switching point of the valve is dependant on engine speed and a definable change in engine performance. The valve switching points are optimized for maximum torque in the wide-open Throttle Position (TP).

Exhaust Gas Recirculation (V8 Engines)
The ECM controls the flow of exhaust gases to reduce oxides of nitrogen in emissions by re-circulating metered amounts of exhaust gas into the intake of the engine. This lowers the combustion temperature, limiting the formation of nitrogen oxides. The Exhaust Gas Recirculation (EGR) flow is optimized for fuel economy, emissions and drivability for all engine-operating conditions.

Electronic Throttle Control
The electronic throttle controls the airflow into the engine under closed loop feedback control of the ECM. The correct throttle disc position is calculated as a function of driver demand and of the engine's momentary operating mode. A fail safe system is incorporated that complies with legislative requirements, including mechanical limp-home operation.

Idle Speed Control
Idle speed is dependent on Engine Coolant Temperature (ECT) and gear selection (neutral or drive). Idle speed is optimized for combustion stability, idle quality, Idle Speed Control (ISC) capability and fuel economy at all operating conditions. Compensations to the idle speed will be made for conditions, such as variable ambient air temperature, to increase idle speed to satisfy charging system requirements.

Vehicle Speed Control
The engine management system incorporates a speed control system. This enables the driver to set a speed, and control and maintain the speed of the vehicle without having to operate the accelerator pedal. The speed control switches are momentary action switches, mounted on the steering wheel. The function of the switches is organized so that a function relating to a switch of higher priority always overrides a function relating to a lower priority switch. The switch priority is:
1. Cancel
2. Set
3. Resume