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AUTOMATIC AIR SUSPENSION

DEPT OF MECH ENGG, SSGMCE SHEGAON Page 01

ABSTRACT

Air ride suspension carries the load on each axle with a pressurized air bag

much like a high pressure balloon. Air ride suspension systems have been incommon use for over forty years and have proven to provide the smoothest and

most shock-free ride of any known vehicle suspension system. Modern air bags areconstructed using the same methods as a tire by using high strength cords which

are then encapsulated in rubber. These units are very durable in service and have a proven life of many years.

In addition to providing extremely smooth ride quality, air ride suspension

also provides other important features. First, the system automatically adjusts air pressure in the air bag so that the trailer always rides at the same height, whether

lightly loaded or heavily loaded. This allows the suspension system to always

provide the maximum usable wheel travel independent of trailer load. In addition,the higher air bag pressure associated with higher trailer loads, automatically provides a stiffer suspension which is exactly what is required for a smooth ride.

The lower air bag pressure for lightly loaded conditions, automatically provides for a softer suspension, thus providing the same ride quality for all trailer loading

conditions. Since each axle is independently supported by its own air bag, the air ride suspension is a truly, fully independent suspension system.

The automatic control of the air bag pressure is accomplished by a solid

state electronic control system specifically designed and packaged for vehicle use.

This system continuously monitors the "ride height" of the trailer suspension andincreases air pressure if the ride height is too low, by turning on an on-board air compressor. The air compressor stops automatically when the proper ride height is

reached. If the ride height is too high, an automatic vent valve vents excess air pressure and stops venting when the proper ride height is reached. All required

electrical power is provided by a 12 volt battery contained in the trailer equipmentcompartment





TABLE OF CONTENTS

CHAPTER

NO.

TITLE PAGE

NO.

1 INTRODUCTION TO AIR SUSPENSION S 01

1.1 Preface 01

1.2 Suspension System1.2.1 Introduction to Suspension System1.2.2 Objective of Suspension System

01

01

03

2 PROBLEM DEFINITION

2.1 General Problems Without Suspension

04

04

2.2 Problems in Spring Suspension 04

3

4

5

LITERATURE REVIEW

3.1 Leaf Spring 3.2 Air Spring 3.3 Air Suspension

BASIC AIR SUSPENSION

4.1 What is an Air Suspension ?4.2 Components of Air Suspension

4.2.1 The Air Supply 4.2.2 Air Bags4.2.3 Height control Valve

4.3 How the Air Suspension Functions?4.4 Advantages

CONCLUSION

05

05

06

07

08

08

0909

10

10

12

13

15

6 REFERENCES 16

II





Chapter-1

INTRODUCTION TO AIR SUSPENSIONS

1.1 Preface

It is important to understand air suspensions because there is a directinteraction between the air suspension and the leveling of a vehicle. In fact, there

are leveling systems available that use the vehicle air suspension to do the

leveling. The HWH Active Air system actually controls the air suspension of a

vehicle while the vehicle is traveling. You must understand the air suspension

before dealing with our systems that are installed on vehicles with an air suspension.

At this time it is important to note that the following discussions are generic innature. There are many different types and manufacturers of air suspensions and

many different ways they are put together. Even different chassis‟s built by the

same manufacturer can be different in some ways. There are different air bag, air tank and valve arrangements. When dealing with suspension issues, it is critical

that you obtain plumbing and wiring diagrams for the specific chassis that you are

working on.

1.2 Suspension system:

1.2.1 Introduction of Suspension system

Suspension is the term given to the system of springs, shock absorbers and

linkages that connects a vehicle to its wheels. Suspension systems serve a dual

purpose — contributing to the car's road holding handling and braking for goodactive safety and driving pleasure, and keeping vehicle occupants comfortable and

reasonably well isolated from road noise, bumps, and vibrations, etc. These goals

are generally at odds, so the tuning of suspensions involves finding the rightcompromise. It is important for the suspension to keep the road wheel in contact

with the road surface as much as possible, because all the forces acting on the

vehicle do so through the contact patches of the tires. The suspension also protectsthe vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.

http://en.wikipedia.org/wiki/Spring_%28device%29

http://en.wikipedia.org/wiki/Shock_absorber

http://en.wikipedia.org/wiki/Linkage_%28mechanical%29

http://en.wikipedia.org/wiki/Vehicle

http://en.wikipedia.org/wiki/Wheel

http://en.wikipedia.org/wiki/Car_handling

http://en.wikipedia.org/wiki/Brake

http://en.wikipedia.org/wiki/Rear_suspension

http://en.wikipedia.org/wiki/Rear_suspension

http://en.wikipedia.org/wiki/Brake

http://en.wikipedia.org/wiki/Car_handling

http://en.wikipedia.org/wiki/Wheel

http://en.wikipedia.org/wiki/Vehicle

http://en.wikipedia.org/wiki/Linkage_%28mechanical%29

http://en.wikipedia.org/wiki/Shock_absorber

http://en.wikipedia.org/wiki/Spring_%28device%29





Figure 1: Locating Suspension Units

A suspension system comprises springs, shock absorbers and linkages. Thissuspension connects an automobile to its wheels. The suspension systems not only

help in the proper functioning of the car's handling and braking, but also keep

vehicle occupants comfortable and make your drive smooth and pleasant. It also

protects the vehicle from wear and tear. To know about the suspension system, oneneeds to know about the spring rate or suspension rate. Various spring types are

used for different vehicles. In case of heavier suspension loads, the spring rate ishigher and vice versa. Spring rate is measured as a ratio used to measure how

resistant a spring is to being compressed or expanded during the spring's deflection

Besides spring rate, one needs to take in account the wheel rate. Wheel rate is the

effective spring rate when measured at the wheel. It is generally equal to or considerably less than the spring rate.

There are two types of suspension systems- dependent and independent. A

dependent suspension comprises a beam that holds wheels parallel to each other and perpendicular to the axle. An independent suspension helps in the rising and

falling movement of the wheels. There is also a semi-dependent suspension where





the motion of one wheel affects the position of the other but they are not rigidlyattached to each other.

The dependent suspension includes Trailing arms, Satchell link, Panhardrod, Watt's linkage, WOBLink and Mumford linkage. The independent

suspensions includes Swing axle, Sliding pillar, MacPherson strut/Chapman strut,Upper and lower A-arm (double wishbone), multi-link suspension, semi-trailingarm suspension, swinging arm and leaf springs.

1.2.2 Objectives of Suspension system:

1. A suspension system prevents road shocks from being transmitted to thevehicle, its inmates and the automotive components.

2. It helps to protect and safeguard the inmates of the vehicles on sub-

terranean and difficult road terrains.3. The suspension system plays a crucial role in vehicle handling, vehicle

dynamics and adds to the stability of the vehicle while it is running, pitching or rolling.





Chapter 2

PROBLEM DEFINITION

2.1 General Problems without Suspension:

Unspring Weight

Having a large beam connecting the two front wheels results in a lot of mass.

This extra mass really hinders the road holding capability of the suspension

on rough road.

Wheel Movement

Because both wheels are tied together the force acting on each wheel are

directed to the other wheel. Under the load this cause the wheels to„Shimmy‟and decrease the stability of the vehicle in corners

Bad Bump Steer

Because a beam axle makes locating the steering correctly difficult , most

solid axle suspensions suffer from an uncontrollable amount of bump steer .

Again, hindering the performance of the car.

Size

Simply put solid axle are huge and fitting them into a chassis requires an

amount of space practically available.

Ride Quality

Due to the high mass of the axle and the wheels being connected there is not

much ride isolation between the springs and unsprung mass. This results in

rough ride and even worse, compromised road holding capacity.

2.2 Problems in Spring Suspension:

The conventional metal springs faced some drawbacks which were air suspension

system overcomes and so they are preferred and used in more these days. Let's see

some of the plus points of this system.

1) The automatic control devices installed in the vehicle allows making optimumuse of the variable space for deflection of wheel.

2) The height of the automobile remains steady and so the changes in the

alignment of headlamp due to varying loads are restricted.

3) It helps to reduce the load while the vehicle in motion .





Chapter 3

LITERATURE REVIEW

On a summer day in 1904 a young man by the name of William Brush

helped bring about the modern automobile suspension system. Driving his brother Alanson's Crestmobile, Brush was rolling along too fast for the unpaved roads of

the day and went into a curve at 30 mph. The car's right front wheel skittered ontothe dirt shoulder and whammed into a deep rut. Almost at once, the wheel started

to shimmy violently. The undulations of the jarred right front elliptic leaf springhad sent shock waves across the solid I-beam axle to the left side of the vehicle.

This set the entire front of the car to vibrating furiously. Brush was caught

unawares and lost control. The car crashed through a barbed-wire fence, hit a ditchand overturned in a cow pasture.

Several hours later young William 'fessed up to Alanson, whose demeanor switched from stern to thoughtful, since he was trying to design a better car. That

car, dubbed the Brush Two-Seat Runabout, finally appeared in 1906. It featured arevolutionary suspension system that incorporated two innovations never before

assembled together: front coil springs and devices at each wheel that dampenedspring bounce -- shock absorbers -- mounted on a flexible hickory axle.

Some European car makers had tried coil springs, with Gottlieb Daimler in

Germany being the leading exponent. However, most manufacturers stood fast

with leaf springs. They were less costly, and by simply adding leaves or changingthe shape from full elliptic to three-quarter or half elliptic, the spring could bemade to support varying weights.

Leaf Spring

Leaf springs in one form or another have been used since the Romans

suspended a two-wheeled vehicle called a Pilentum on elastic wooden poles. Thefirst steel spring put on a vehicle was a single flat plate installed on carriages bythe French in the 18th century.

The venerable leaf spring, which some manufacturers still use in rear suspensions today, was invented by Obadiah Elliot of London in 1804. He simply

piled one steel plate on top of another, pinned them together and shackled each endto a carriage.





The coil spring is not a spring chicken, either. The first patent for such a

spring (British patent No. 792) was issued to R. Tredwell in 1763. The mainadvantage of coil springs was that they did not have to be spread apart andlubricated periodically to keep them from squeaking, as leaf springs did.

Figure 2 :Model T Ford leaf spring

Henry Ford's 1908 Model T Ford featured old-fashioned leaf springs with a noveltwist -- he used only one spring at each axle, mounted transversely, instead of one

at each wheel. Ford's adaptation of high-strength vanadium steel from a French

racing car allowed him to save weight and cut costs in many areas of the Model Twithout compromising its durability.

With the exception of a car here and there, independent coil spring frontsuspension remained in limbo for 25 years after the introduction of the Brush

Runabout. Then suddenly in 1934, General Motors, Chrysler, Hudson, and othersreintroduced coil spring front suspension, this time with each wheel sprung

independently. In that year, most cars started using hydraulic shock absorbers and balloon (low-pressure) tires. Coupling a solid front axle with shock absorbers and

these tires really aggravated front end shimmy. Suspending each wheel

individually lessened the effects of spring bounce.

3.2 Air Spring

Air springs combine spring and shock absorbing action in one unit and were

often used without metal springs. The first one was developed by Cowey Motor Works of Great Britain in 1909. It was a cylinder that could be filled with air from





a bicycle pump through a valve in the upper part of the housing. The lower half of

the cylinder contained a diaphragm made of rubber and cord which, because it wassurrounded by air, acted like a pneumatic tire. Its main problem was that it oftenlost air.

The newest air spring, developed by Goodyear, is found on some late-modelLincolns. Like the ones that have preceded them, these ride-on-air units are morecostly than conventional springs and hydraulic shock absorbers.

3.3 Air Suspension

Air suspension, which Lincoln ballyhooed for some models in 1984 wasintroduced in 1909 by the Cowey Motor Works of Great Britain. It did not work well because it leaked.

Figure 3: Stout-Scarab

The first practical air suspension was developed by Firestone in 1933 for anexperimental car called the Stout-Scarab. This was a rear-engined vehicle that used

four rubberized bellows in place of conventional springs. Air was supplied bysmall compressors attached to each bellow. As you might imagine, the air bagsuspension was an expensive setup -- still is, in fact.

The first automobile to use torsion bar suspension was the 1921 Leyland.

Most of the credit for the wide acceptance of torsion bars in Europe goes to Dr.Ferdinand Porsche who made it standard on most of his cars, beginning with the1933 Volkswagen prototypes. By 1954, 21 makes of European cars were equipped

with torsion bars.





Chapter-4

BASIC AIR SUSPENSION

4.1 What is an air suspension?

„The air suspension system is an air-operated, microprocessor controlled

suspension system. This system replaces the conventional coil spring suspension

and provides automatic front and rear load leveling. The 4 air springs, made of

rubber and plastic, support the vehicle load at the front and rear wheels‟.An air suspension supports the vehicle on the axles with an arrangement of air

bags instead of some type of steel spring, leaf or coil, or some type of torsion

spring arrangement. The air bags are sometimes referred to as air springs or bellows. Suspensions that have steel or torsion springs that are supplemented by

the use of air bags are not considered air suspensions. There are combinationsystems that have both air and steel springs. Usually the air suspension components

are used on the rear of the vehicle.

Figure 2: Advanced Air Suspension

Depending on the situation, this type of air suspension will probably have to bedealt with for leveling purposes. Normally, the air suspension is just one part of the

air system on the vehicle. Most (but not all) vehicle with an air suspension alsohave air brakes along with other equipment that

may be operated with air. Any of these other systems can cause problems with the





air suspension. Other air systems including the brake systems in general, will not

be discussed in this school. It is important to understand that on vehicles with air systems, especially with air brakes, manufacturers must follow specific regulations

when designing their air systems. The brake system will always be the main

concern for the air system. There will be safety features installed in the system thatmake the brake system the main priority for the air system.

4.2 Components of the air suspension

An air suspension has three basic components. The air supply, the air bags and

the height control valves. As stated before, there are many different types of thesecomponents and different arrangements of how these components are used. In the

following section, we will discuss several different arrangements of thesecomponents but this is by no means a complete discussion of all of the possible

arrangements.

Figure:3: Components of air suspension

4.2.1 The air supply.

The air supply is engine air compressor, the air tanks, air valves and air

lines. The engine air compressor supplies air for every piece of air equipment onthe vehicle. The maximum pressure supplied by the compressor varies. For many

years, the air supply was maintained around 120 to 125 psi but on some newer,





larger vehicles this has been increased to 135 psi. There will be dash gauges that

will supply system pressure information but all vehicles have what we refer to as a“pop off valve”. You can hear the valve “pop off” when the system reaches the

maximum air pressure.

The air supply is maintained through an arrangement of air tanks. Air tank arrangement is one thing that varies greatly between different air systems. I haveseen systems with one tank that has primary and secondary compartments built in,

and systems with some type of main, secondary or auxiliary tank for everycomponent of the system, as many as 10 to 12 different tanks. The terminology for

these tanks varies greatly also. There are primary tanks, secondary tanks, wettanks, auxiliary tanks, front brake tanks, rear brake tanks and ping tanks to name

some of them. No mater how many there are or what they are called, they all do basically the same thing, they store air for the different systems on the vehicle.

4.2.2 Air bags

Air bags are simply a rubber bladder that holds air. Air bags are also referredto as air springs or bellows. The air bags are located between the frame of the

vehicle and the vehicle axles. Air bags are rated for weight and pressure capacities.Air bag placement and arrangements vary amongst chassis manufacturers. At the

very least, there will be one air bag for each side of each axle in the vehicle. Therecan be two air bags for each side of the axles but I have never seen a tag axle with

more that one bag per side. Some manufacturers use two air bags for each side of the drive axle and some use two air bags for each side of the drive and front axles.

Space between air bags for side to side placement also varies. Some place the air bags outboard as far as they can and some have the bags closer together. When two

bags per side are used, one will be in front of the axle and the other behind theaxle. Again, spacing can vary. Most air bags will have some device such as a cone

that keeps the air bag from being crushed or damaged when fully deflated.

Inflating air bags is limited to the available air pressure to the suspension system.This is why the relief setting of the engine air compressor should not be changed.

4.2.3 Height control valves

The height control valves (HCV from now on) are kind of the brains of thesystem. They dictate how much air is in the air bags. This dictates the height the

vehicle sits at, thus, Height Control Valve. Most HCVs are mechanical valves butelectronic HCVs are available. The HCV is mounted to the frame of the vehicle.





Figure 3:Air Bag System

An L shaped linkage attaches the HCV to the axle. As the axle moves up and downin relationship to the frame, the linkage moves the valve or electronic mechanism.

With mechanical valves, there is an air line from the air supply to the HCV. Thereis an air line from the HCV to the air bag or bags+ that it controls. The HCV also

has an exhaust port. When the connecting linkage moves up, the HCV connects theair supply to the air bag(s), inflating the bag(s). When the connecting linkage

moves down, the HCV connects the air bag(s) to the exhaust port, deflating the

bag(s). This controls the height of the vehicle.

If the HCV is electronic, as the linkage moves, the sensors in the HCV sendinformation to an electronic control. These controls will open or close air solenoid

valves as needed to inflate or deflate the bags. There are two basic styles of mechanical HCVs, the instant response valve (IR valve) and the delay valve. These

names are accurate descriptions of how the valves react. The IR valve will start toinflate or deflate the air bags as soon as the valve activating lever moves. The

delay valve has a slight delay when the activating lever moves before inflating or deflating the air bags. The number and arrangement of HCVs used on a suspension





Figure 4: Height Control Valve

varies a little. There are normally three HCVs used on a suspension. Either there isone for the front axle and two for the rear, (most common arrangement) or someuse two on the front axle and one on the rear. A few chassis have been done with

one HCV for each side of the front and rear axles, a total of four, but this wouldnot be very common. Vehicles with a tag axle use regulated air or tie the tag air

bags to the driver air bags to control the tag air bags. Although it may be done, Iknow of no one using HCVs to control the tag axle air bags.

4.3 How the air suspension functions

The vehicle is supported on the frame with an arrangement of airbags. The vehicleair system, engine air compressor, tanks, lines, etc., supplies air to the height

control valves (HCV) mounted to the frame of the vehicle. The height controlvalves are connected to the air bags with an air line. The linkage which connects

the HCVs to the axles rotates the HCV valving as it moves up and down. Whenweight is added to the vehicle or transferred through the suspension of the vehicle,

the air in the air bag(s) is compressed, the frame moves closer to the axle. Thisforces the HCV linkage up. As the linkage moves up, the valving of the HCV

connects the air supply to the air bag(s). The added pressure and volume inflates

the air bag(s), causing the frame to move away from the axle. As the frame moves

back to the proper ride height, the HCV linkage moves to the neutral position. Thismoves the valving away from the air supply and locks the air in the air bag to

maintain the proper ride height. As weight is removed from the vehicle or thesuspension shifts weight away, the existing pressure in the air bag(s) can push the

frame away from the axle. The HCV linkage is pulled down. This connects the air bag(s) to the HCV exhaust port. As air is exhausted from the air bag(s), the frame





lowers back down towards the axle. As the linkage moves up to the neutral

position, the exhaust port is closed and the air is again locked in the air bag(s),maintaining proper ride height. These three drawings show a schematic example of

the height control valve in the neutral position, inflate position and deflate or

exhaust position.

Figure 5 : Working Of HCV

4.4 ADVANTAGES

Excellent Suspension and driving comfort

Fully automatic Level Control Lifting and lowering function

Easy to service





Figure: 7 Actual Working Air Suspension





Chapter-8

CONCLUSION

Air suspension is today mainly feature for luxury vehicle . It offers a lot of feature for compact class. Cost or price level will be more attractive. Integration &smart design is key. The Air Suspension System has ability to change the load

carrying capacity simply by changing the air pressure. From the whole discussion in air suspension system, I observe that the

system is like a white blood cell .As white blood cell provides energy to our bodyto fight against diseases or viruses which try to destroy or try to decrease our life

,in the similar way air suspension system provides the energy to a vehicle to protect itself from damaging, increasing life of the vehicle ,increases the handing ,

increases comfort of passengers and many more.

So, according to me if you remove the suspension system, then you feel likein bull- cart in Audi , Mercedes types luxurious cars. The only difference is speed.So, the scope of Air Suspension System is Too Bright.





REFERENCE

[1]. "Air Suspension Explained." Online. 17 August 2004. Available:

www.lincolnmarkviii.org/suspension/asexplained.htm[2]. “Air Suspension, Part I.” Online. 31 August 2004. Available:

http://www.rodandcustommagazine.com/howto/4923/

[3]. “The New Wave of Shock Absorbers” Online Article. 1 July 2004

Author: Jacques Gordon Available:http://www.motorage.com/motorage/article/articleDetail.jsp?id=110152

[4]. "Magneshocks..Future Of Shock Absorbers Is Here Today!" Online. 16August 2004. Available: www.magneshocks.com

[5]. "Cadillac.com - ESV -Stability Enhancement System." Online. 17 August2004.Available:www.cadillac.com/cadillacjsp/models/featureDynamic.jsp?model=esv&

feature=stabilitrak

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