OVERVIEW OF AUTOMOTIVE CONTROL SYSTEM

The automobile is rapidly becoming a complex electromechanical system due in a part to advance in computing and sensing technologies as well as advances in estimation and control theory .

Vehicles have onboard computing system to coordinate several control functions. Example: control function associated with Engine and Transmission, traction control etc..

Types of control function:

Power train controlVehicle controlBody control

Basic concepts and Terminologies:

Power train control:

It consist of engine and transmission control system.

It also includes fuel injection control, carburetor control, Anti knock control etc..

The goal of engine control system is to ensure that an engine operates at near-optimal conditions at all times.

Electronic transmission control is used primarily in automatic transmissions.

It determines the optimal shift point for the torque convertor and lock up operation point based on the throttle angle and vehicle speed measurement.

ECU controls both engine and transmission.

Four wheel drive system are used 1. To obtain the optimal torque transmission ratio(depends on vehicle forward velocity)2. In breaking and acceleration.3. Between the front and rear wheels.

Vehicle control systems:

It include suspension control, steering control, cruise control, braking control (e.g antilock brake system) and traction control.

These system improve various vehicle functions including response, steering stability, ride, and handling: many were introduced in recent decades or are currently being developed.

Body control:

It includes Automatic air conditioning , electronic meters, multi instrument displays, energy control systems, security systems, communication systems, door-lock systems, power windows, and rear-obstacle detection.

The intent of these systems is to increase driving comfort and convenience and to improve the value of the automobile.

These features often are perceived immediately by drivers as a benefit and typically are introduced first in luxury vehicles.

Air fuel Ratio control:

The Air fuel ratio is the control variable and it is controlled by fuel injection at each cylinder.

A mass air flow sensor is used and fuel injector is the actuator.

Current system use an EGO sensor for air fuel ratio control.

EGR control:

The control variable is the EGR rate, the EGR control valve is the actuator, and the engine temperature and speed measurement are used to compute the proper EGR rate.

The drawbacks of EGR includes increased HC emission, deteriorated fuel economy, and combustion instaility at idle or low engine speed and or when engine is cold.

Spark timing Control:

Spark timing control is adjusted to affect engine- torque output.

The response is usually faster than throttle angle manipulations.

It also is used to affect emission and fuel economy and to minimize engine knock.

Electronic transmission control:

The hydraulic pressure and solenoid status can be controlled for fuel economy and comfort.

The shift point typically is regulated based on two measurements: vehicle speed and manifold absolute pressure(MAP) or throttle angle.

Idle speed control:

The purpose of the idle speed control function is to maintain idle speed in the presence of load disturbance as well as to minimize speed for reduced fuel consumption and emission

An idle speed controller typically measures the idle speed adjusts the airflow rate using either the throttle or an idle speed control valve.

Controlled variable

Control input

Control algorithm

Sensors and Actuators

Fuel control Air fuel ratio Injected fuel Smith predictor Airflow, EGO, fuel injector

EGR control EGR rate EGR valve opening Optimal control Valve position, EGR valve

Spark timing control

Spark timing Primary current Rule-based, optimal control

Crank angle, Vibration

Idle speed control Idle speed Air flow rate PI, linear quadratic regulator

Engine speed, Idle speed control valve, throttle

Cruise control Vehicle speed Airflow rate PI, adaptive PI Vehicle speed, throttle

Transmission Gear ratio Pressure, current Rule Based Vehicle speed, MAP

All wheel drive, four wheel drive

Torque distribution Pressure, current Rule based, P, PI,PID

Engine speed, Steering angle, control valve.

Four wheel steering

Wheel angle Stepper motor Feed forward, PI Vehicle speed, wheel angle, stepper motor

ABS Slip ratio Pressure, current Rule based, sliding mode

Vehicle speed, wheel speed, control valve.

Control system:

The control system with single loop with a single input/ single output (SISO) system, which attempts to control only one variable.

An electronic control system includes many controlled variables, actuators, and sensors in fact they are multi input / multi output (MIMO) control system.

Control structures and Algorithms:

Air Fuel Ratio Control:

Conversion Efficiency of two way catalytic converter:

EGR Control:

Spark Timing Control:

Vehicle communication Networks:

Vehicle communication networks provide the infrastructure to exchange information among vehicle electronic units.

These electronic units are not only actuator and sensor components with network capabilities but also ECUs such as the engine controller.

A slower and less expensive network system such as the local International network(LIN)

For safety and vehicle performance, critical information exchange high speed communicatiion network protocols such as the Controller Area Network(CAN).

For critical safety features such as X-by-wire applications, guaranteed delivery of the information within specified time boundaries is required.

To satisfy the strict communication requirements, design features such as multiple physical routes and software based message priorities are considered.

Vehicle supervisory control:

With additional performance requirements for morden vehicles, the relative amount of supervisory- control software compared to the total amount is increasing.

The combination of this trend with the desire to maximize the requirements and computing resource allocation requirements and modularity for cost- reduction purpose means that supervisory control algorithms are distributed to subsystem controllers and rely on vehicle communication networks and external information inputs.

Modularizing the design of components in such a networked control system to make them swappable can reduce development time, calibration costs, and maintenance and other costs