The main components of an automotive electronic control system include the electronic control unit (ECU), sensors, and actuators.
1. Electronic Control Unit
The ECU is the "brain" of the automotive electronic control system. It comprehensively analyses and processes the electrical signals from various sensors and the feedback signals from some actuators, providing reference voltage to the sensors and outputting control signals to the actuators, enabling them to operate as required by the control objectives.
The software is integrated and stored within the ECU, with the core being a microprocessor. This microprocessor typically uses a single-chip microcomputer, which facilitates easy function expansion and higher control precision. It is utilised in electronic control systems for data acquisition, computational processing, output control, system monitoring, and self-diagnosis. Most ECUs have similar circuit structures, with the primary variations in control functions depending on the developed software and the changes in input and output modules, tailored to the specific functions of the electronic control system.
2. Sensors
Sensors are the "eyes" and "ears" of the automotive electronic control system. They convert various physical parameters of the vehicle’s working conditions and states into electrical signals and transmit them to the ECU. The sensors used in automotive electronic control systems can be categorised into various types based on their working principles and the forms of output signals, such as pulse sensors, potentiometer sensors, thermistor sensors, and contact switch sensors.
3. Actuators
Actuators are the "hands" and "feet" of the automotive electronic control system. The ECU controls the actuators to manage the objects being controlled. The actuators respond quickly to the control signals outputted by the ECU, ensuring the controlled objects operate in the desired state.
For example, the fuel injector. The ECU determines the fuel injection quantity. It controls the injector's needle valve, deciding the opening duration (injection pulse time). The fuel injection quantity is a set value stored in the ECU, pre-determined based on the engine’s conditions, which are determined by the engine speed and intake volume.
Basic Principles of Automotive Electronic Control Systems
A series of instruction programs are pre-stored in the ECU's program memory. These instructions are fixed during the design and manufacturing stages. The input signals to the ECU come from various sensors in the control system.
When the ECU is operational, it receives signals from sensors distributed throughout the vehicle, compares this input information with the "standard parameters" stored in memory, and based on the results, controls the actuators to take appropriate actions.
1. Engine Control System
1.1 Electronic Fuel Injection System
The electronic fuel injection system of a petrol engine can be divided into two main parts: the air supply system and the fuel supply system. The air supply system provides clean air to the engine and controls the intake volume according to the engine conditions. The fuel supply system provides the engine with accurately measured fuel.
In the engine’s electronic fuel injection system (EFI), the ECU primarily determines the basic fuel injection quantity based on the intake volume. It then adjusts the fuel injection quantity based on signals from sensors such as the coolant temperature sensor and the throttle position sensor. This ensures the engine receives the optimal air-fuel mixture under various operating conditions, improving engine performance, fuel economy, and emissions. In addition to fuel injection control, the electronic fuel injection system also includes injection timing control, fuel cut-off control, and fuel pump control.
1.2 Electronic Ignition System
The main function of the electronic ignition system (ESA) is to control the ignition advance angle. This system determines the optimal ignition advance angle to ignite the air-fuel mixture based on signals from various sensors, improving the engine's combustion process, thereby enhancing engine performance, fuel economy, and reducing emissions. The electronic ignition system also has functions for controlling the ignition timing and preventing engine knocking.
The electronic ignition system typically comprises sensors, the ECU, ignition coils, spark plugs, and ignition fault alarms. It generates a spark under high voltage to ignite the compressed mixture in the cylinder at the optimal timing, based on signals from various sensors, controlled by the engine ECU.
1.3 Idle Control System
The idle control system (ISC) is an auxiliary control system for the engine. Its function is to control the engine's intake volume through the idle control valve under idle conditions, based on the coolant temperature, air conditioning compressor status, and transmission gear engagement, ensuring the engine operates at the optimal idle speed.
1.4 Emission Control System
The emission control system electronically controls the engine's emission control devices. Emission control includes exhaust gas recirculation (EGR) control, evaporative emission canister purge control, oxygen sensor and air-fuel ratio closed-loop control, and secondary air injection control.
1.5 Intake Control System
The intake control system adjusts the engine's intake volume based on the engine speed and load changes to improve charging efficiency, enhancing engine performance.
1.6 Turbocharging Control System
The turbocharging control system manages the operation of the engine's turbocharging device. In vehicles equipped with exhaust turbochargers, the ECU controls the turbocharging device based on the intake manifold pressure, regulating the turbocharging intensity.
1.7 Cruise Control System
The cruise control system allows the driver to set a cruise control mode, enabling the ECU to automatically control the engine based on vehicle operating conditions and environmental information, maintaining a constant vehicle speed.
1.8 Warning and Reminder System
The ECU controls various indicators and alarm devices. If a fault occurs in the control system (such as an oxygen sensor failure or high fuel tank temperature), the warning system immediately signals to alert the driver.
1.9 Self-Diagnosis and Alarm System
In the engine control system, the ECU is equipped with a self-diagnosis and alarm system to monitor the operation of various parts of the control system. When the ECU detects fault signals from sensors or actuators, it lights up the "CHECK ENGINE" light on the dashboard to alert the driver of an engine fault. Simultaneously, the system stores the fault information in the memory as fault codes to assist maintenance personnel in identifying the fault type and scope.
1.10 Failure Protection and Emergency Backup System
When a sensor or sensor circuit fails, the failure protection system automatically operates based on pre-set reference signal values to keep the engine running. For instance, if the coolant temperature sensor circuit fails, inputting an unrealistic temperature signal to the ECU, the failure protection system will control the engine based on a standard signal to prevent improper air-fuel mixtures. If the ECU doesn't receive the ignition controller's confirmation signal, the failure protection system stops fuel injection to prevent unburned fuel from entering the cylinder.
When the control system computer fails, the emergency backup system (backup integrated circuit) takes over, forcing the engine to operate in a basic mode to prevent the vehicle from stalling. The emergency backup system can only maintain the engine's basic functions and cannot ensure optimal engine performance.
2. Transmission Control System
The electronic hydraulic automatic transmission is formed by adding an electronic control system to the hydraulic transmission. It monitors the vehicle and engine operating conditions through sensors and switches, converting this information into electrical signals input to the electronic control unit. The electronic control unit, based on these signals, controls the shift valves of the hydraulic control unit through solenoids, thus controlling the shifting moments and gear changes to achieve automatic transmission.
The electronic hydraulic automatic transmission converts parameters such as engine speed, throttle opening, vehicle speed, engine coolant temperature, and automatic transmission fluid temperature into electrical signals through various sensors and inputs them to the computer. The computer, based on these signals and set shifting rules, sends electronic control signals to the shift solenoids and hydraulic solenoids. These solenoids then convert the electronic signals into hydraulic control signals, and the control valves in the valve body control the actions of the shifting actuators, thus achieving automatic shifting.
3. Chassis and Body Control System
3.1 ABC Body Control System
The ABC body control system includes suspension damping devices installed between the wheels and the body. An air spring, installed in the airbox, and a hydraulic cylinder manage the suspension system. The coil spring supports the wheel side through an elastic disc connected to the shock absorber and the body side through a movable axis, with additional force acting on the suspension controlled by the hydraulic cylinder's pressure oil.
ABC Body Control System Components:
A1p13 - Multifunction display
B22/7 - Left rear height sensor
B24/6 - Right rear body acceleration sensor
N72/1s3 - Comfort/sport switch
B4/5 - ABC pressure sensor
B22/8 - Left front height sensor
B24/12 - ABC lateral acceleration sensor
S9/1 - Brake light switch
B22/1 - Left rear piston travel sensor
B22/9 - Right front height sensor
B24/14 - ABC longitudinal acceleration sensor
X11/4 - Diagnostic connector
B22/4 - Left front piston travel sensor
B22/10 - Right rear height sensor
B40/1 - ABC oil temperature sensor
Y36/1 - Front axle distribution valve unit
B22/5 - Right front piston travel sensor
B24/3 - Left front body acceleration sensor
N51/2 - ABC control computer
Y36/2 - Rear axle distribution valve unit
B22/6 - Right rear piston travel sensor
B24/4 - Right front body acceleration sensor
N72/1s2 - Height control switch
Y86/1 - ABC throttle valve
3.2 DSC Body Dynamic Control System
BMW's DSC body dynamic control system integrates the ASC automatic stability control system and the traction control system. It controls the wheel slip status by selectively braking the driving wheels to stabilise the vehicle. On slippery surfaces like snow, desert, or gravel, the driver can activate the DTC mode with a button, enhancing the vehicle's