Anti-lock Braking System and it’s

Shaheem TMReg. No. 90012064

DOI , CUSAT

Advancements

Overview

Introduction What is ABS Timeline of ABS Motivation for development Simple hydraulic braking system Principles of ABS Components Working Types Advancements Advantages & Disadvantages summary

Introduction

Conventional braking system - Wheel lockup Reduces steering ability - vehicle slides out of control

Anti-lock Braking system (ABS) – Driver can break hard- No locking of wheels

What is ABS ? Anti-lock braking system (ABS) - automobile safety

system Prevent wheel locking Skidding wheel - less traction than a Non-skidding wheel Anti-lock brakes benefit

Can stop faster Steer while you stop

Preventing skiddingMaintain traction

Timeline

1929 : ABS first developed for aircraft by the French automobile developer Gabriel Voisin 1936: German company Bosch patented “Apparatus for preventing lock-braking of wheels in a motor vehicle”1936-: Bosch and Mercedes-Benz partner - R&D into ABS1972: WABCO partners with Mercedes-Benz developing ABS for trucks1978: First production-line ABS into Mercedes and BMW vehicles1981: 100,000 Bosch ABS installed1985: First ABS installed on US vehicles

1986: 1M Bosch ABS installed.1987: Traction control - with ABS 1989: ABS hydraulic unit combined with standard hydraulic brake unit1992: 10M Bosch ABS installed1995: Electronic Stability - with ABS and TCS - for passenger cars1999: 50M Bosch ABS installed2000: 6 of 10 new cars on the road are ABS equipped2003: 100M Bosch ABS installedPresent: Almost all new cars have ABS

More features – ESP – EBD – Cruise control – Auto Brake Assist

Motivation for ABS development

Under hard braking – Ideal system should

Provide the shortest stopping distances on all surfaces

Maintain vehicle stability and steer ability.

Comparison

Simple Hydraulic Braking system

Consists of

Master cylinder Four wheel cylinders

Simple Hydraulic Braking system

Brakes Applied

Pistons pushes

fluid from

Master cylinder

Fluid pushes pistons

of wheel

cylinders

Brake shoes

pushed out

Wheels get

locked

Vehicle stops

Principles of ABS When brakes applied- vehicle speed comes down Decrease in vehicle speed not always proportional to decrease in wheel speed Non-correspondence - Slip Magnitude measured as Slip ratio

Slip ratio = [(Vehicle speed – Wheel speed)/Vehicle speed ]× 100%

When Slip ratio = 0% : Vehicle speed corresponds exactly to wheel speedSlip ratio = 100% : Wheels locked - vehicle moves

Best braking action between 10-20%.

If vehicle speed and wheel speed is the same wheel slippage is 0%

A lock-up wheel will have a wheel slippage of 100%

(A) Slip ratio (B) Coefficient of friction between tire and road surface

(1) Icy road(2) Asphalt-paved road(3) Control range by ABS

Pressure Modulation in ABS

Release and reapply of the brake pedal – avoid locking of wheels - avoid the skidding

Antilock braking system does the same Brakes applied - pressure is quickly applied & released at the wheels - pressure

modulation Pressure modulation prevent the wheel locking ABS modulate the pressure 15 times per seconds ABS precisely controls the slip rate of wheels - ensure maximum grip force from

the tyre - ensures maneuverability and stability

ABS Components Overview

1.Hydraulic Unit2.Electronic Brake Control Module [EBCM]3.Four wheel speed sensors4.Interconnecting wiring5.ABS indicator

ABS Components Overview(1) ABS control module and hydraulic control unit (ABSCM & H/U)(2) Two-way connector(3) Diagnosis connector(4) ABS warning light(5) Data link connector(6) Transmission control module (AT models only)(7) Tone wheels(8) ABS wheel speed sensor(9) Wheel cylinder(10) G sensor(11) Stop light switch(12) Master cylinder(13) Brake & EBD warning light(14) Lateral G sensor

ABS components

ABS systems are Integrated

Non- integrated

ABS components

ABS has four Primary Components

ABS Controller ABS Speed Sensors

ABS Modulator/Valves ABS Pumps

Working of ABS

Under normal braking

Brakes applied No current flow from ECU to hydraulic unit Solenoid valves not energized – brake master cylinder pressure

reaches wheels Vehicles stops ABS not involved - Still ECU monitors each wheel for lock- up

Working of ABS

When wheel lock-up sensed

Wheel sensors senses a wheel lock-up ECU sends a current to hydraulic unit The solenoid valve gets energised Valve isolates the brake circuit from master cylinder Stops the braking pressure at wheel rising – kept it constant

Working of ABS

Still wheel deceleration is rapid

ECU sends larger current to hydraulic unit Armature of Hydraulic unit moves faster Opens a passage : Brake circuit – Master cylinder Pressure in brake caliper reduced

Working of ABS

When wheel is accelerated again

ECU stops current to Hydraulic unit De-energises the solenoid valve Pressure is build up The cycle repeats several times in a second Vehicle stops safely

Working of solenoid valve in ABS

It has 3 modes

Increase pressure Hold pressure

Decrease pressure

Solenoid 1

Pressure increase

Solenoid 2

Pressure decrease/Vent solenoid

Brake line under pressure

Brake fluid line not under pressure

Increase pressure

Solenoid 1

Pressure increase

Solenoid 2

Pressure decrease/Vent

Pressure hold

Solenoid 1

Pressure increase

Solenoid 2

Pressure decrease/Vent

Pressure decrease

Types of ABS

Three types

Four channel – Four sensor ABS Three channel – Three sensor ABS One channel – One sensor ABS

Advancements

Automatic Stability Control / Electronic Stability Control (Program) - ESP

Automatic Traction Control - ATC

Automatic Stability Control / Electronic Stability Program - ESP

Components

Yaw rate sensorESP hydraulic control unit

Steering angle sensorG sensor

Wheel speed sensorsECU

Operation

Under normal driving

ESC works in background- monitors steering & vehicle direction Determines intended direction – steering angle sensor

Determines vehicle’s actual direction- yaw sensor- wheel speed sensors Compares the obtained data

Operation

When detects a loss of steering control

Detects – Understeer or Oversteer ESC estimates direction of speed

Applies brakes to individual wheels asymmetrically Create torque about vehicle’s vertical axis- oppose skid

Brings vehicle back to control Additional operation – reduces engine power, operate transmission

Oversteer Understeer

Automatic Traction Control - ATC

Apply brakes when drive wheel attempts to spin and lose traction A secondary function of ESP

Activated when throttle input & engine torque is mismatched to road surface conditions

Automatic Traction Control - ATC

ATC intervention consists of the following

Brake force applied to one or more wheels Reduction or suppression of spark sequence to one or more cylinders

Reduction of fuel supply to one or more cylinders Closing the throttle

Components of traction control

The main hardware for traction control and ABS are same Wheel sensors

ECU ATC valve

Advantages of ABS

Reduce the stopping distance. Steer while the brakes are firmly applied.

Maintain directional stability and control over steering during braking. Safe and effective.

Automatically changes the brake fluid pressure at each wheel to maintain optimum brake performance.

ABS absorbs the unwanted turbulence shock waves.

Disadvantages of ABS

Increased braking distances under some limited circumstances cost

Maintenance cost of a car equipped with ABS is more System damage

Summary

The antilock braking system controls braking force by controlling the

hydraulic pressure of the braking system, so that the wheels do not lock

during braking.

The antilock braking system prevents wheels locking or skidding, no matter

how hard brakes are applied, or how slippery the road surface. Steering stays

under control and stopping distances are generally reduced.

References

[1] “Effectiveness of ABS and vehicle stability control systems”(PDF). Royal Automobile Club of Victoria. April 2004.[2] “Non-skid braking” Flight International. 30 October 1953. pp. 587–588.[3] “Chrysler Imperial Sure Brake system description”. ImperialClub.org[4] "Electronic Stability Control (ESC)" . nhtsa.gov[5] Heibing, Bernd (2011), Chassis Handbook Springer, ISBN9783834897893[5] "Speed With Style", Cycle World, June 1992, ISSN0011-4286