ANTILOCK BRAKING SYSTEM - PDF document

ANTILOCK BRAKING SYSTEM MODELING AND DEVELPOMENT Vehicle Dynamics (ME5670) Siva Teja Golla (ME14MTECH11025) Harshad Keskar (ME14MTECH11027) Mohini Kale (ME14MTECH11029) Nikhil Mhaske (ME14MTECH11030) Sukanya Joshi (ME14MTECH11037) ANTILOCK BRAKING SYSTEM 1 Indian Institute of Technology, H yderabad INTRODUCTION ANTILOCK BRAKING SYSTEM 2 • Anti - lock braking system (ABS) is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking, preventing the wheels from locking up and avoiding uncontrolled skidding . • ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces . • ABS modulates the brake line pressure independent of the pedal force, to bring the wheel speed back to the slip level range that is necessary for optimal braking performance . PROJECT OUTLINE ANTILOCK BRAKING SYSTEM 3 • Objectives of ABS • Components of ABS • Working of ABS • Mathematical model • System model • Results • Conclusion • References OBJECTIVES OF ABS ANTILOCK BRAKING SYSTEM 4 • To reduce stopping distance 1. The road surface type and conditions can be inferred from the vehicle's braking pressure, wheel slip measurements, and deceleration rate comparisons . 2. The wheel slip is regulated so that the road adhesion coefficient is maximized . By keeping all of the wheels of a vehicle near the maximum friction coefficient, an antilock system can attain maximum fictional force 3. In turn, this strategy leads to the minimization of the vehicle stopping distance . ANTILOCK BRAKING SYSTEM 5 • Stability 1. A locked - up wheel generates a reduced braking force, smaller than the peak value of the available adhesion between tires and road . A locked - up wheel will also lose its capability to sustain any lateral force . This may result in the loss of vehicle stability . 2. The basic purpose of a conventional ABS system is thus to prevent any wheel from locking and to keep the longitudinal slip in an operational range by cycling the braking pressure . ANTILOCK BRAKING SYSTEM 6 • Steerability 1. Good peak frictional force control is necessary in order to achieve satisfactory lateral forces and, therefore, satisfactory steer - ability . 2. If an obstacle appears without warning, emergency braking may not be sufficient . When the wheels are locked, car no longer respond to the driver’s steering intention . 3. With ABS car remains steerable even during emergency braking, and thus the obstacle can be safely avoided. COMPONENTS OF ABS ANTILOCK BRAKING SYSTEM 7 The primary components of the ABS braking system are : • Electronic control unit (ECU) 1. It receives signals from the sensors in the circuit and controls the brake pressure at the road wheels according to the data analysed by the Unit . 2. ECU assists the vehicle operator to prevent wheel lockup by regulating the wheel slip . • Hydraulic control unit or modulator 1. It receives operating signals from the ECU to apply or release the brakes under ABS conditions . 2. It executes the commands using three solenoid valves connected in series with the master cylinder and the brake circuits - one valve for each front wheel hydraulic circuit, and one for both of the rear wheels . Thus brakes can be actuated by controlling hydraulic pressure . ANTILOCK BRAKING SYSTEM 8 • Power booster and master cylinder assembly 1. It is activated when the driver pushes down on the brake pedal . The master cylinder transforms the applied pedal force into hydraulic pressure which is transmitted simultaneously to all four wheels . 2. It provides the power assistance required during braking . • Wheel sensor unit 1. Speed sensors are comprised of a magnet wrapped in a coil and a toothed sensor ring . An electrical field given off by the contact between the magnet and the toothed ring creates a AC voltage . 2. The voltage frequency is directly proportional to the wheel's rotational speed . 3. It monitors the rotational speed of the wheel and transmits this data to the ABS control module . WORKING OF ABS ANTILOCK BRAKING SYSTEM 9 • If a wheel - speed sensor signals a lock up - the ECU sends a current to the hydraulic unit . This energizes the solenoid valve . The action of the valve isolates the brake circuit from the master cylinder . This stops the braking pressure at that wheel from rising, and keeps it constant . It allows wheel velocity to increase and slip to decrease . • When the velocity increases, ECU re - applies the brake pressure to restrict the wheel slip to a particular value . • Hydraulic control unit controls the brake pressure in each wheel cylinder based on the inputs from the system sensor . This in result controls the wheel speed . MATHEMATICAL MODEL ANTILOCK BRAKING SYSTEM 10 • Wheel slip : When the braking action is initiated, a slippage between the tire and the contacted road surface will occur, which make the speed of the vehicle to be different from that of the tire . • The longitudinal slip is defined as ܵ = �ܿ݋ݏ � − � ܴ � �ܿ݋ݏ � The side slip angle is � = ݐܽ݊ − 1 � �೤ � ೣ Force and velocity components on tyre ANTILOCK BRAKING SYSTEM 11 • Vehicle Dynamics According to Newton's second law, the equation of motion of the simplified vehicle can be expressed by , ݉ � � = − � � − � ௔ The road friction force is given by Coulomb law � � = �� The total mass of the quarter vehicle can be written as ݉ � = ݉ ���� + ݉ ௖ 4 Thus, the total normal load cm be expressed by � = ݉ � ݃ − � � � � is the longitudinal weight transfer load due to braking ANTILOCK BRAKING SYSTEM 12 Simulink model for vehicle dynamics ANTILOCK BRAKING SYSTEM 13 • Wheel dynamics According to Newton's second law, the equation of motion at wheel level for the rotational DOF is given by , � � � = − ܶ ௕ + � � ܴ � ANTILOCK BRAKING SYSTEM 14 Simulink model for wheel dynamics SYSTEM MODEL ANTILOCK BRAKING SYSTEM 15 Assumption : Only a linear model was considered and does not include actual road conditions . The system here is modelled only for straight line braking. INPUT PARAMETERS FOR SIMULINK MODEL ANTILOCK BRAKING SYSTEM 16 Gravitational constant ݃ = 32 . 18 ݂ݐ / ݏ 2 Initial velocity of vehicle � 0 = 88 ݂ݐ / ݏ Wheel Radius ܴݎ = 1 . 25 ݂ݐ Mass of vehicle ݉ = 50 lbs Maximum Braking Torque ܶ ௕ ��ೣ = 1500 ݈ܾ݂ ∗ ݂ݐ Hydraulic Lag ܶ� = 0 . 01 ݏ Moment of Inertia � � = 5 ݂ݐ 4 RESULTS ANTILOCK BRAKING SYSTEM 17 VEHICLE SPEED AND WHEEL SPEED (WITHOUT ABS) ANTILOCK BRAKING SYSTEM 18 ANTILOCK BRAKING SYSTEM 19 VEHICLE SPEED AND WHEEL SPEED (WITH ABS) SLIP (WITHOUT ABS) ANTILOCK BRAKING SYSTEM 20 SLIP (WITH ABS) ANTILOCK BRAKING SYSTEM 21 STOPPING DISTANCE (WITHOUT ABS) ANTILOCK BRAKING SYSTEM 22 ANTILOCK BRAKING SYSTEM 23 STOPPING DISTANCE (WITH ABS) CONCLUSION ANTILOCK BRAKING SYSTEM 24 • It is inferred that ABS improves the braking performance. • The stopping distance after using ABS system has considerably reduced. • The error in slip and desired slip is used to manipulate brake pressure in brake cylinder. REFERENCES ANTILOCK BRAKING SYSTEM 25 • Tianku Fu , “Modelling and performance analysis of ABS system with non - linear control”, 2000. • Tobias Eriksson , “Co - simulation of full vehicle model in Adams and anti - lock brake system model in Simulink”, 2014. ANTILOCK BRAKING SYSTEM 26 THANK YOU!