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Anti-lock Braking System(ABS)

Prepared by:

•Eng.Haitham Shehata Hussein

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Index

What is an Anti-Lock Braking System (ABS)? History of ABS Motivation for ABS Development Overview Principles for ABS Operation ABS Components Overview ABS Components Subaru Impreza ABS Application. How does ABS work? How ABS Work (Video) System Diagram Anti-Lock Brake Types ABS Configurations Design Challenges Advantages & Disadvantages ABS Problems General information Summary Common questions

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What is (ABS)?

Anti-lock braking system (ABS) is an automobile safety system prevent the wheels of a vehicle locking as brake pedal pressure is applied - often suddenly in an emergency or short stopping distance. This enables the driver to have steering control, preventing skidding and loss of traction.

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History of ABS

• 1929 :- ABS was first developed for aircraft by the French automobile and aircraft pioneer Gabriel Voisin, as threshold braking on airplanes is nearly impossible.

• 1936: German company Bosch is awarded a patent an “Apparatus for preventing lock-braking of wheels in a motor vehicle”.

• 1936-: Bosch and Mercedes-Benz partner - R&D into ABS.

• 1972: WABCO partners with Mercedes-Benz developing first ABS for trucks.

• 1978: First production-line installation of ABS into Mercedes and BMW vehicles.

• 1981: 100,000 Bosch ABS installed.• 1985: First ABS installed on US vehicles.

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History of ABS

• 1986: 1M Bosch ABS installed.• 1987: Traction control - in conjunction with

ABS – used on passenger vehicles.• 1989: ABS hydraulic unit combined with

standard hydraulic brake unit• 1992: 10M Bosch ABS installed.• 1995: Electronic Stability - in conjunction with

ABS and TCS - for passenger cars.• 1999: 50M Bosch ABS installed.• 2000: 6 of 10 new cars on the road are ABS

equipped.• 2003: 100M Bosch ABS installed.• Nowadays:- Almost all new cars have ABS.

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Motivation for ABS Development

• Under hard braking, an ideal braking system should:

Provide the shortest stopping distances on all surfaces

Maintain vehicle stability and steer ability.

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Overview

Many different control methods for ABS systems have been developed. These methods differ in their theoretical basis and performance under the changes of road conditions.

ABS Research

Classical Control

Optimal Control

Nonlinear Control

Robust Control

Adaptive Control

Intelligent Control

Figure 1. Sampling of ABS control

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Principles for ABS Operation

When the brake pedal is depressed during driving, the wheel speed decreases and the vehicle speed does as well. The decrease in the vehicle speed, however, is not always proportional to the decrease in the wheel speed. The non-correspondence between the wheel speed and vehicle speed is called “slip” and the magnitude of the slip is expressed by the “slip ratio” which is defined as follows:

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

When the slip ratio is 0%, the vehicle speed corresponds exactly to the wheel speed. When it is 100%, the wheels are completely locking (rotating at a zero speed) while the vehicle is moving.

See Fig 2.

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•The best braking action occurs at 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

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Principles for ABS Operation

• Figure 2 shows the relationship

between braking co-efficient and wheel

slip. It is shown that the slide values for

stopping/traction force are

proportionately higher than the slide

values for cornering/steering force. A

locked-up wheel provides low road

handling force and minimal steering

force.

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Principles for ABS Operation

The main benefit from ABS operation is to maintain directional control of the vehicle during heavy braking in rare circumstances

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ABS Components Overview

Hydraulic unit. Electronic brake control module (EBCM).Two system fuses.Four wheel speed sensors.Interconnecting wiring

The ABS indicatorThe rear drum brake.

(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 (for SUBARU select monitor).(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 (STi).

ABS Components Overview

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ABS Components

• ABS brake system are – Integrated

• An integrated system has the master cylinder and control valve assembly made together.

– Nonintegrated• A nonintegrated has the master

cylinder and control valve assembly made separate.

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ABS Components

• ABS systems consist of 4 primary components:1- ABS Controller; the brains of the system.  ABS Controllers are a computer that reads the inputs and then controls the system to keep the wheels from locking up and skidding.

2- ABS Speed Sensors; there are generally one on each wheel (sometimes they are located on the differential). It detects a change in acceleration in the longitudinal direction of the vehicle and outputs it to the ABSCM as a voltage signal.

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ABS Components

3- ABS Modulator/Valves; some system have separate valves for each wheel with a modulator to control them.  Other systems they are combined.  In either case they work with the controller and the pump to add or release pressure from the individual wheels brakes to control the braking.

4- ABS Pumps; since the ABS modulator/valves can release pressure from the individual wheels brakes there needs to be a way to restore the pressure when required.  That is what the ABS pumps job is. When the pump is cycling, the driver may experience a slight pedal vibration.  This cycling is happening many times per second and this slight vibration is natural.

(1) ABS control module and hydraulic control unit

(2) ABS control module section(3) Valve relay(4) Motor relay(5) Motor(6) Front left inlet solenoid valve(7) Front left outlet solenoid valve (8) Front right inlet solenoid valve(9) Front right outlet solenoid

valve(10)Rear left inlet solenoid valve(11)Rear left outlet solenoid valve(12)Rear right inlet solenoid valve(13)Rear right outlet solenoid

valve

(14)Automatic transmission control Module

(15) Diagnosis connector

Subaru Impreza ABS Application.

(16) Data link connector(17) ABS warning light(18) Stop light switch(19) Stop light(20) G sensor(21) Front left ABS wheel speed sensor(22) Front right ABS wheel speed sensor(23) Rear left ABS wheel speed sensor(24) Rear right ABS wheel speed sensor(25) IGN(26) Battery(27) Brake warning light(28) Parking brake warning light(29) Brake fluid level switch(30) Lateral G sensor (STi)(31) Driver-controllable center differential control unit

Subaru Impreza ABS Application.

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How does ABS work?

Figure 3. ABS Operating Diagram

We will discuss how one of the simpler system works.

Sensors at each of the four wheels sense the rotation of the wheel. Too much brake application wheel stop rotating Sensors ECU releases brake line pressure wheel turns

again. then ECU applies pressure again stops the rotation of the wheel

releases it again and so onNB: This releasing and re-application or pulsing of brake

pressure happens 20-30 times per second or more. This keeps the wheel just at the limit before locking up and

skidding no matter ABS system can maintain extremely high static pressure and must be

disabled before attempting repairs.

How does ABS work? Simplicity

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How ABS Work (Video)

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How does ABS work? Solenoid Valve

• Solenoid Valve Assembly:

Is a pair of valves that can:

A. Increase pressure

B. Hold pressure steady

C. Decrease pressure

How does ABS work? Solenoid Valve

During pressure increase mode of operation fluid is allowed to flow through both solenoids to the brake caliper

Solenoid 1

Pressure increase

Solenoid 2

Pressure decrease/Vent solenoid

Brake line under pressure

Brake fluid line not under pressure

A. Increase pressure

During Pressure Hold mode of operation both solenoids are closed and no additional fluid is allowed to flow to brake calipers.

Solenoid 1

Pressure increase

Solenoid 2

Pressure decrease/Vent

B. Hold pressure steady

How does ABS work? Solenoid Valve

During Pressure Vent mode the pressure increase solenoid is closed. The Vent solenoid opens allowing fluid to vent into an accumulator chamber

Solenoid 1

Pressure increase

Solenoid 2

Pressure decrease/Vent

C. Decrease pressure

How does ABS work? Solenoid Valve

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System Diagram

• Figure 4. ABS Block Diagram

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ABS Types

• ABS brakes are either 1 Channel3 Channel4 Channel

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ABS Types

One-channel, one-sensor ABS

This system is commonly found on

pickup trucks with rear-wheel

ABS. It has one valve, which

controls both rear wheels, and

one speed sensor, located in the

rear axle.

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ABS Types

Three-channel, three-sensor ABS

This scheme, commonly found on pickup

trucks with four-wheel ABS, has a speed

sensor and a valve for each of the front

wheels, with one valve and one sensor

for both rear wheels. The speed sensor

for the rear wheels is located in the rear

axle.

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ABS Types

Four-channel, four-sensor ABS

This is the best scheme. There is a

speed sensor on all four wheels and a

separate valve for all four wheels.

With this setup, the controller

monitors each wheel individually to

make sure it is achieving maximum

braking force.

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Configurations of ABS Types

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ABS Configurations

Figure 5. Depending on the ABS application, there

are several typical layouts.

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Design Challenges

ABS control is highly nonlinear control problem due to the complicated relationship between its components and parameters. The research that has been carried out in ABS control systems covers a broad range of issues and challenges. Many different control methods for ABS have been developed and research on improved control methods is continuing. Most of these approaches require system models, and some of them cannot achieve satisfactory performance under the changes of various road conditions. While soft computing methods like Fuzzy control doesn’t need a precise model. A brief idea of how soft computing is employed in ABS control is given.

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Design Challenges

Fuzzy control :Is Intelligent control systems can be used in ABS control to emulate the qualitative aspects of human knowledge with several advantages such as robustness, universal approximation theorem and rule-based algorithms.

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Advantages & Disadvantages

• Advantages:

1. It allows the driver to maintain directional stability and control over steering during braking

2. Safe and effective

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

4. ABS absorbs the unwanted turbulence shock waves and modulates the pulses thus permitting the wheel to continue turning under maximum braking pressure

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Advantages & Disadvantages

• Disadvantages1. Stop Times - Anti-lock brakes are

made to provide for surer braking in slippery conditions. However, some drivers report that they find the stopping distances for regular conditions are lengthened by their ABS system, either because there may be errors in the system, or because noise of the ABS may contribute to the driver not braking at the same rate.

2. Delicate Systems - It's easy to cause a problem in an ABS system by messing around with the brakes. Problems include disorientation of the ABS system, where a compensating brake sensor causes the vehicle to shudder, make loud noise or generally brake worse.

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Advantages & Disadvantages

3. Cost - An ABS can be expensive to maintain. Expensive sensors on each wheel can cost hundreds of dollars to fix if they get out of calibration or develop other problems. For some, this is a big reason to decline an ABS in a vehicle.

4. System damage - A variety of factors can cause the system to be less effective, and can present with everything from shuddering of the vehicle to loud noises while trying to stop

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ABS Problems

Problems with ABS

The sensors on the wheels might get contaminated by metallic dust. When this condition occurs the sensors become less efficient in picking up problems. In modern ABS systems, two more sensors are added to help:

wheel angle sensor,

gyroscopic sensor

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ABS Problems

The idea behind this is that when the gyroscopic sensor detects that the car’s direction is not the same as what the wheel sensor reports, the ABS software will cut in to brake the necessary wheel in order to help the car go the direction the driver intends.

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General information.

Statistics show that approximately 40 % of

automobile accidents are due to skidding.

Skidding , vehicle instability, steer inability and

long distance stopping, These problems

commonly occur on vehicle with conventional

brake system which can be avoided by adding

devices called ABS.

If there is an ABS failure, the system will revert

to normal brake operation. Normally the ABS

warning light will turn on and let the driver

know there is a fault.

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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.

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Common Questions

oWhat is ABS?

oWhy is that important?

oHow do I know whether my vehicle has ABS?

oWill I notice anything when the ABS is working or not?

oDoes ABS change the way I should use the brakes?

oHow does ABS work?

oDo cars with ABS stop more quickly than cars without?

oAre all antilock systems the same?

oHow can I familiarize myself with ABS?

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Thanks for your

attention