CONTROL SYSTEMS IN AUTOMOBILES

1. Definition of Control System
A control system is a system of devices or set of devices, that manages commands, directs or regulates the behaviour of other device(s) or system(s) to achieve desire results. In other words the definition of control system can be rewritten as a control system is a system, which controls other system. As the human civilization is being modernized day by day the demand of automation is increasing accordingly. Automation highly requires control of devices.
In recent years, control systems plays main role in the development and advancement of modern technology and civilization. Practically every aspects of our day-to-day life is affected less or more by some control system. A bathroom toilet tank, a refrigerator, an air conditioner, a geezer, an automatic iron, an automobile all are control system. These systems are also used in industrial process for more output. We find control system in quality control of products, weapons system, transportation systems, power system, space technology, robotics and many more. The principle of control theory is applicable to engineering and non engineering field both.
1.1 Feature of Control System
The main feature of control system is, there should be a clear mathematical relation between input and output of the system.
1.2 Requirement of Good Control System
Accuracy: Accuracy is the measurement tolerance of the instrument and defines the limits of the errors made when the instrument is used in normal operating conditions. Accuracy can be improved by using feedback elements. To increase accuracy of any control system error detector should be present in control system.
Sensitivity: The parameters of control system are always changing with change in surrounding conditions, internal disturbance or any other parameters. This change can be expressed in terms of sensitivity. Any control system should be insensitive to such parameters but sensitive to input signals only.
Noise: An undesired input signal is known as noise. A good control system should be able to reduce the noise effect for better performance.
Stability: It is an important characteristic of control system. For the bounded input signal, the output must be bounded and if input is zero then output must be zero then such a control system is said to be stable system.
Bandwidth: An operating frequency range decides the bandwidth of control system. Bandwidth should be large as possible for frequency response of good control system.
Speed: It is the time taken by control system to achieve its stable output. A good control system possesses high speed. The transient period for such system is very small.
Oscillation: A small numbers of oscillation or constant oscillation of output tend to system to be stable.
2. Types of Control Systems
There are two main types of control system. They are as follows
1. Open Loop Control System
2. Closed loop control system

1. Control Systems in Automobiles Presented by- Sharath S 01JST16PAE013

2. A control system is a system of devices or set of devices, that manages, commands, directs or regulates the behaviour of other device(s) or system(s) to achieve desire results. Why CS? As the human civilization is being modernized day by day the demand of automation is increasing accordingly. Automation highly requires control of devices. CONTROL SYSTEM

3. Accuracy Sensitivity Noise Stability Bandwidth Speed Oscillation Requirement of Good Control System

4. Open loop control system Closed loop control system Types of control system

5. Open loop control system A control system in which the control action is totally independent of output of the system then it is called  open loop control system . Manual control system is also an open loop control system. Fig - 1 shows the block diagram of open loop control system in which process output is totally independent of controller action.

6. Electric Hand Drier  - Hot air (output) comes out as long as you keep your hand under the machine, irrespective of how much your hand is dried. Automatic Washing Machine  - This machine runs according to the pre-set time irrespective of washing is completed or not. Bread Toaster  - This machine runs as per adjusted time irrespective of toasting is completed or not. Automatic Tea/Coffee Maker  - These machines also function for pre adjusted time only. Timer Based Clothes Drier  - This machine dries wet clothes for pre-adjusted time, it does not matter how much the clothes are dried. Practical Examples of Open Loop Control System

7. Closed loop control system Control system in which the output has an effect on the input quantity in such a manner that the input quantity will adjust itself based on the output generated is called  closed loop control system . In this way closed loop control system is called automatic control system .

8. Examples of Automotive Closed-loop Control Systems Control System Indirectly c o nt r ol l ed variable Directly c o nt r ol l ed variable Manipulated variable Sensor Actuator Fuel injection system Air-fuel ratio Exhaust oxygen content Quality of injection fuel Zirconia or Titania based electro- chemical Fuel injector Knock control Knock Knock sensor output Ignition timing Piezo-electric accelerometer Ignition coil switch. Transistor Anti-lock braking system Wheelslip limit Wheelspeed Brake time pressure Magnetic reluctance ABS solenoid valve

9. Comparison of Open Loop And Closed Loop Control System

10. ECU (based on Micro Computers) Battery Analogue signals e.g. t r a n s d u c er signals Digital signals e.g. switch states Power supply regulator Analogue to digital converter and multiplexer Input i nt er f acing Micro- c om p u t er Output circuitry Motors Solenoids Lamps, LED’s etc.

11. Electronic fuel injection (EFI) Allows precise and fast control of fuel injected By control of the ‘on-time’ period of the solenoid operated injectors (Spray nozzle) and plunger. Delivery pipe fuel pressure is maintained constant by a fuel pressure regulator Opening and closing times of between 0.5 and 1 ms. Engine operating speed of 6000 rpm (10 ms revolution time) Injector on-time can be controlled between 1 and 10 ms.

12. Power driver application Multi-point or sequential fuel injection, with one fuel injector near the intake valve (or valves) of each cylinder. At a device level, a fuel injector ic package Provides the high solenoid drive current required Incorporates both over-voltage and short-circuit protection, Fault reporting diagnostic routines also included

13. Two types of EFI System - 1. Speed-density EFI Inlet manifold absolute pressure (MAP) sensor has an important role Fuel injection opening period or pulse width is related directly to the mass of air flowing into the engine as fuel-air ratio must be maintained constant in steady-state operation And the mass of air-flow is related to the manifold absolute pressure by the equation where V d is the displacement of the cylinder, n v is the volumetric efficiency or the fraction of V d actually filled on each stroke, [= f(speed)] p i is manifold absolute pressure, R is a constant and T i is the intake air temperature. a m R T i  V d n v P i

14. 2. Mass air-flow EFI Direct measurement of the quantity of air drawn into the engine (using an air-flow sensor (AFS)). Simple flap-type, Hot-wire and Direct measurement is better than feed-forward control In speed density EFI (Factors like variation in volumetric efficiency, engine displacement due to speed and internal deposits need to be taken care of ). Both of these forms of EFI may be improved Exhaust gas oxygen sensor for closed-loop control of the air–fuel ratio. If engine is to be controlled precisely air–fuel ratio must be controlled to within 1%. Only possible with closed-loop control,

15. Closed-loop control of air–fuel ratio The objective of low exhaust-gas emission levels Maintain the air–fuel ratio at 14.7:1 [ stoichiometrically / chemically perfect] Three-way catalytic converters to control emission

16. In a closed loop system the fuel injection period computed by air intake measurement is modified Based on measured E xhaust G as O xygen (EGO) content. injection period modification factor between 0.8 and 1.2. EGO tells whether  < 1 or  > 1 Closed loop system has a limit cycle frequency between 0.5 to 2 Hz Pollutant emission as a function of relative air–fuel ratio, l (Chowanietz, 1995)

17. Electronic clutch control To relieve pressing of clutch during gear change Throttle cable of accelerator pedal replaced by closed loop control system Accelerator pedal position sensor and servomotor Connected to an ECU for the gear change process

18. Block Diagram of an Automatic Clutch and Throttle system Control of clutch engagement and disengagement Improved safety Prevention of engine starting when in gear Inappropriate gear change Throttle motor Electronic control unit Hydraulic power unit and solenoid control valve (operation clutch release lever) Clutch release lever position sensor Throttle servo system Throttle position f eedback Accelerator pedal position sensor Gear lever load switch Gear position sensor Gearbox input shaft speed sensor Engine speed sensor Clutch release cylinder pressure Solenoid control signal

19. Integration of Transmission and Engine Fuel injection and ignition t imi n g Throttle position sensor Throttle idle switch Selector lever position sensor Hold mode switch Stoplight switch Overdrive inhibit switch Automatic transmission fluid temperature sensor Torque converter output speed Vehicle speed Engine r.p.m. Atmospheric pressure sensor E n gine c o n t r ol unit S ole n oi d valve control Handshake signals between ECUs Transmission control unit W a t er thermosensor Th r o t tle po si tion sensor Knock sensor Airflow sensor Intake air thermo se n sor Engine r.p.m. signal Engine Transmission During gear change up transmission ECU signals the engine management ECU cut off fuel injection and Signals TECU to allow gear change During gear change down TECU energizes signals E-ECU Changes ignition timing a few degrees to reduce engine torque, Signals TECU to allow gear change In the end both systems return to independent operation.

20. Powertrain Control System Also includes Exhaust gas recirculation system (circulating exhaust into intake to reduce max combustion temp, and hence NO x ) Controlled by powertrain ECU Engine temp , load, speed Evaporative Emission Control System (to circulate fuel vapour into intake and prevent leakage into atmosphere)

21. Chassis Control Systems Anti Lock Braking system Electronic Damping Control system Power Assisted Steering System Traction Control Systems

22. Anti-lock braking systems (ABS) The vehicle skids, the wheels lock and driving stability is lost so the vehicle cannot be steered; The braking distance increases due to skidding; The tyres may burst due to excessive friction and forces being concentrated at the points where the locked wheels are in contact with the road surface;

23. Antiskid braking system (ABS) All electronic signals come to the electronic controller (ECU) The ECU controls the hydraulic modulator To control the Brake line pressure in Brake master cylinder

24. Wheel-speed and braking pressure during ABS-controlled braking If wheel decelerates beyond a certain level, curtail brake pressure (1) If wheel decelerates further, reduce brake pressure further (2) If wheel accelerates, increase brake pressure (3)

25. Traction control systems Prevent drive wheels from wheel spinning during starting or – Accelerating on A wet or icy surface. Avoid reduction of either steering response in front- wheel-drive (fwd) / vehicle stability on rear-wheel- drive ( rwd ) vehicles. Tcs operates- To maximize adhesion to the road surface during Acceleration Same sensors as in ABS The actuation uses fuel, ignition and driven wheel braking action

26. Curve recognition or cornering detection also affects the control strategy for TCS. This strategy employs the difference in wheel speeds of the non-driven wheel speeds as a basis for reductions in the slip setpoint to enhance stability in curves. High vehicle speeds and low acceleration requirements on low coefficient of adhesion surfaces imply a control strategy of progressively lower slip threshold setpoints as the vehicle speed increases, gives maximum lateral adhesion on the surface.

27. Electronic damping control The primary function of a shock absorber control vehicle movement against roll during turning and pitch during acceleration or braking. Requires hard suspension secondary role To prevent vehicle vibration caused by a poor road surface. Requires a soft suspension Electronic damping control (EDC) used to attain these twin objectives altering the characteristics of spring and oil-filled damper arrangement difficult and expensive Simple option - Suspensions with at least three settings; ‘soft’, ’medium’ and ‘firm’ OR electronically controlled suspension systems using air, nitrogen gas and hydraulic oil as a suspension agent.

28. Longitudinal acceleration Measured directly using an acceleration sensor, or Inferred from brake system pressure and throttle opening angle. Used to control pitching during acceleration / Braking Lateral forces Inferred by the rate at which the steering Wheel is being turned and the vehicle speed. Used by the ecu to prevent rolling. The actuators are dampers fitted with two on-off fluid control solenoids used to select one of four different damper settings (normal, soft, super-soft and firm). Driver can choose sport or smooth ride Mode. In sport mode soft or super-soft damper settings excluded Result in a harder but more stable ride. Electronically controlled damping system

29. Electric PAS Input to the rack and pinion steering System is from a motor/reduction gearbox Motor torque is applied directly to either the pinion gear shaft or to the rack shaft. The steering effort range is greater than with hydraulic systems, Installations are cheaper and reliable. Power is only consumed when steering wheel moves, (unlike hydraulic system) A torque sensor on the column shaft The electric motor coupled to the worm wheel mechanism through a reduction gearbox. The load torque t l on the steering colum is the load presented by the worm mechanism and the rack and pinion assembly to which it is attached.

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