Antilock braking system (ABS)

To elevate English language capability for automotive engineering, and survey is extra about knowledge related to automobile,we are students in DHOT2 class,in Ho Chi Minh university of industry. We introduce to Teacher and every peoples about our essay, with topic : Antilock braking system.

Anti-lock braking system

(ABS)

I. Preamble.

To elevate English language capability for automotive

engineering, and survey is extra about knowledge related

to automobile,we are students in DHOT2 class,in Ho Chi

Minh university of industry We introduce to Teacher

and every peoples about our essay, with topic : Anti-lock

braking system

Although, we tried to perfect our esay but our knowledge

are finite So we do not escape faults, hope Teacher help

II. Contents.

1 Introduction.

Anti-block braking system is a system on motor vehicles which prevents the wheels from locking while braking An anti-locking

braking system allows the driver to maintain steering control under heavy braking by preventing a skid and allowing the wheel to continue

to forward roll and create lateral control, as directed by driver steering inputs Most commonly, braking distances are shortened

Disadvantages of the system include increased braking distances under rather rare circumstances and the creation of a "false sense of security" among drivers who do not understand the operation and limitations of ABS

Since it came into widespread use in production cars, ABS has made considerable progress Recent versions not only handle the ABS

function itself (i.e preventing wheel locking) but also traction control,

brake assist, and electronic stability control, amongst others

Anti-lock braking systems were first developed for aircraft in 1929 by the French automobile and aircraft pioneer Gabriel Voisin, as threshold braking an airplane is nearly impossible

Anti-Lock Brake Types:

Four-channel, four-sensor ABS, Three-channel, three-sensor ABS, Two-channel, two -sensor ABS, One-channel, one-sensor ABS

2 Constitution of anti-lock braking system

The Antilock Braking System (ABS) consists of a conventional hydraulic brake system plus antilock components.

a draulic unit

The hydraulic unit with the attached EBCM is located between the surge tank and the fire wall on the right side of the vehicle The basic hydraulic unit configuration consists of return pump motor, return pump, four isolation valves, four dump valves, two Low Pressure Accumulators (LPA), two High Pressure Attenuators (HPA)

The hydraulic unit controls hydraulic pressure to thefront calipers and rear wheel cylinders by modulating

hydraulicpressure to prevent wheel

lockup

b antilock components.

Antilock components include an

electronic brake control module

(EBCM), two system fuses,four wheel

speed sensors (one at each wheel), interconnecting wiring, the ABS indicator, and the rear drum brake…

Isolation valve

Dump Valve

Low pressure accumulator

High Pressure Attenuator

Return Pump Motor

3 Operating principle.

Compression stroke: the pump is filled via the inlet ball seat, then the motor eccentric rotates moving the piston to displace the fluid After the pressure build-up closes the inlet valve the piston displacement increases the pressure until the outlet ball opens The outlet

pressurewill continue to increase for the rest of the piston stroke Return Stroke: The piston retracts, forced by its spring, as the motor eccentric returns to its low end position

The pressure at the inlet side of the outlet ball then decreases due to the displaced volume and the pressure difference across this ball holds

it closed.The pressure at the outlet side of the inlet ball seat,which is

set to open at a certain pressure level also decreases until this valve opens With the outlet ball closed, the pump is filled with additional fluid from the low pressure accumulator

The pressure will continue until a stall point is reached and

compression of the piston cannot generate enough differential

pressure anymore to open the outlet ball seat

The ABS equipment may also be used to implement traction control

on acceleration of the vehicle If, when accelerating, the tire loses traction with the ground, the ABS controller can detect the situation and take suitable action so that traction is regained Manufacturers often offer this as a separately priced option even hough the

infrastructure is largely shared with ABS More sophisticated versions

of this can also control throttle levels and brakes simultaneously

4. wheel speed sensors and rings.

Front wheel speed sensors are installed to the front

knuckle and rear wheel speed sensors are installed to

the backing plate

Wheel speed sensors are no

serviceable And the air

cap is not adjusted Front

wheel speed sensor ring is

pressed onto the drive axle

shaft Each ring contains 40

equally spaced teeth

Exercise care during

service procedures

to avoid prying or

contacting this ring

Excessive

contact may cause damage

to one or more teeth

Rear wheel speed sensor

rings are incorporated into

the HUB drum

III Discussion.

1.sign and selection of components.

Given the required reliability it is illustrative to see the choices made

in the design of the ABS system Proper functioning of the ABS

system is considered of the utmost importance, for safeguarding both the passengers and people outside of the car The system is therefore

built with some redundancy, and is designed to monitor its own

working and report failures The entire ABS system is considered to

be a hard real-time system, while the subsystem that controls the self diagnosis is considered soft real-time As stated above, the general working of the ABS system consists of an electronic unit, also known

as ECU (electronic control unit), which collects data from the sensors and drives the hydraulic control unit, or HCU, mainly consisting of the valves that regulate the braking pressure for the wheels

The sensors measure the position of the tires, and are generally placed on the wheel-axis The sensor should be robust and

maintenance free, not to endanger its proper working, for example an

inductive sensor These position measurements are then processed by the ECU to calculate the wheel-spin.The hydraulic control unit is generally located right next to the ECU (or the other way around), and consists of a number of valves that control the pressure in the braking circuits All these valves are placed closely together and packed in a solid block This makes for a very simple layout, and is thus very robust

The central control unit generally consists of two microcontrollers, both active simultaneously, to add some redundancy to the system These two microcontrollers interact, and check each other's proper working These microcontrollers are also chosen to be

power-efficient, to avoid heating of the controller which would reduce

durability The software that runs in the ECU has a number of

functions Most notably, the algorithms that drive the HCU as a

function of the inputs, or control the brakes depending on the recorded wheel spin This is the obvious main task of the entire ABS-system Apart from this, the software also needs to process the incoming information, e.g the signals from the sensors There is also some software that constantly tests each component of the ABS system for its proper working Some software for interfacing with an external source to run a complete diagnosis is also added As mentioned before the ABS system is considered hard real-time The control algorithms,

and the signal processing software, certainly fall in this category, and get a higher priority than the diagnosis and the testing software The requirement for the system to be hard real-time can therefore be

reduced to stating that the software should be hard real-time The required calculations to drive the HCU have to be done in time

Choosing a microcontroller that can operate fast enough is therefore the key, preferably with a large margin The system is then limited by the dynamic ability of the valves and the communication, the latter being noticeably faster The control system is thus comfortably fast enough, and is limited by the valves

2 How does ABS work?

ABS uses wheel speed sensors to determine if one or more wheels are trying to lock up during braking If a wheel tries to lock up, a series of hydraulic valves limit or reduce the braking on that wheel This prevents skidding and allows you to maintain steering control

3 Why do we want or need this.

In a recent Canadian Automobile Association survey of some 1700 members, 66% correctly associated ABS with vehicle stability in an emergency, and 53% correctly stated that ABS allows the driver to steer while braking.Since the ABS will not allow the tire to stop

rotating, you can brake and steer at the same time The braking and steering ability of the vehicle is limited by the amount of traction the tire can generate

If you demand steering while braking, the 100% of traction that the tire can generate will be divided between both tasks For example, if you require 50% for steering then there is 50% of available traction left for braking If you require 10% for steering then there is 90% left for braking Be aware that 100% traction on a dry road is a great deal more traction than 100% traction on ice! Therefore, your vehicle is

unable to steer and brake as well on a slippery surface as it can on a dry road

4.Which vehicles have antilock braking systems, and which ones don’t ?

The Department of Transportation requires that ABS be on: Air-braked truck tractors built on or after March 1, 1997 Other air-Air-braked vehicles (trucks, buses, trailers and converter dollies) built on or after March 1, 1998 Hydraulically-braked trucks and buses with a gross vehicle weight rating of 10,000 lbs or more built on or after March 1,

1999 Many commercial vehicles built before these dates have been voluntarily equipped with ABS

IV Conclusion.

A 2003 Australian study[1] by Monash University Accident Research Centre found that ABS:

← Reduced the risk of multiple vehicle crashes by 18 percent

← Reduced the risk of run-off-road crashes by 35 percent

On high-traction surfaces such as bitumen, or concrete many (though not all) ABS-equipped cars are able to attain braking distances better (i.e shorter) than those that would be easily possible without the benefit of ABS Even an alert, skilled driver without ABS would find

it difficult, even through the use of techniques like threshold braking,

to match or improve on the performance of a typical driver with an ABS-equipped vehicle, in real world conditions ABS reduces chances

of crashing, and/or the severity of impact The recommended

technique for non-expert drivers in an ABS-equipped car, in a typical full-braking emergency, is to press the brake pedal as firmly as

possible and, where appropriate, to steer around obstructions In such situations, ABS will significantly reduce the chances of a skid and subsequent loss of control

In gravel and deep snow, ABS tends to increase braking distances

On these surfaces, locked wheels dig in and stop the vehicle more quickly ABS prevents this from occurring Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock The primary benefit of ABS on such surfaces is to increase the ability of the driver to

maintain control of the car rather than go into a skid — though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice On a very slippery surface such as sheet ice

or gravel it is possible to lock multiple wheels at once, and this can defeat ABS (which relies on detecting individual wheels skidding) Availability of ABS relieves most drivers from learning threshold braking But part of the answer is that on heavy snow, locked wheels can be useful because they gather up a "wedge" of snow which helps

to slow the vehicle ABS allows this wedge to clear every time the wheels are unlocked The same can apply on sand in some conditions

A June 1999 NHTSA study found that ABS increased stopping

distances on loose gravel by an average of 22 percent [1]

According to the NHTSA,

"ABS works with your regular braking system by automatically

pumping them In vehicles not equipped with ABS, the driver has to manually pump the brakes to prevent wheel lockup In vehicles

equipped with ABS, your foot should remain firmly planted on the brake pedal, while ABS pumps the brakes for you so you can

concentrate on steering to safety."

When activated, some earlier ABS systems caused the brake pedal

to pulse noticeably As most drivers rarely or never brake hard enough

to cause brake lock-up, and a significant number rarely bother to read the car's manual, this may not be discovered until an emergency When drivers do encounter an emergency that causes them to brake hard and thus encounter this pulsing for the first time, many are

believed to reduce pedal pressure and thus lengthen braking distances,

contributing to a higher level of accidents than the superior emergency stopping capabilities of ABS would otherwise promise Some

manufacturers have therefore implemented a brake assist system that determines that the driver is attempting a "panic stop" and the system automatically increases braking force where not enough pressure is applied Nevertheless, ABS significantly improves safety and control for drivers in most on-road situations

[1] Nguyen Tuan Hung, Meng – Technical English for Automive Engineering – September, 2007.

[2] Quang Huy – Auto Engine and Body Repair -

Communication and Transport publisher – May, 2005.

[3]documents from Internet: website: www.dtdauto.com

Part 1

Preamble 1 Part 2

Contents 8 Part 3

Discussion 11 Part 4

Conclusion 13 References 14