world's number spring....table ofcontents pleasenote theinformation contained in this...

World's Number 1AirSpring.

TABLE OF CONTENTS

PLEASE NOTE

The information contained in this publicationis intended to provide a general guide to thecharacteristics and applications of these prod-ucts. The material, herein, was develol0edthrough engineering design and development,testing and actual applications and is believedto be reliable and accurate. However, Firestonemakes no warranty, express or implied, of thisinformation. Anyone making use of this materialdoes so at his own risk and assumes all liabilityresulting from such use. It is suggested that com-petent professional assistance be employed forspecific applications.

1 Advantages

2 Terms Air Springs &Suspensions

3 Types OfAir Springs

4 How To Use TheProduct Data Sheets

Application Considerations

6 Basic Principles(Derivation of Formulas)

7 Sample Calculations-Air Springs & Suspensions

8 Sample CalculaUons:Using A Personal Computer

9 Warranty Considerations

23

33

37

49

63

71

HISTORY

In the early 1930's, the Firestone Tireand Rubber Company began experimentsto develop the potential of pneumaticsprings.Between 1935 and 1939, several makes

of U.S. automobiles were equipped withair springs and extensively tested to provethe potential of automotive air suspensionsystems. They were never put into pro-duction, however, because significantdevelopments in steel spring design gavean improved ride at much lower cost thanthe air spring system at that time.

In 1938, the country's largest manufac-turer of motor coaches became interestedin using air springs on a new design busthey were developing. Working withFirestone engineers, the first busses weretested in 1944 and the inherent ride supe-riority of air suspensions was clearlydocumented.

In the early 1950's, after several yearsof intensive product development, the airsprung bus finally went into production.That was the beginning of the Airide(R) airspring success story.The success of air springs in bus appli-

cations spurred new interest in truck andtrailer applications as well as industrialshock and vibration isolation uses. Con-sequently, almost all of the busses, mostof the Class 8 trucks and many of thetrailers on the road today now ride on airsprings, and significant advances inthedesign of control systems have openedthe door to automotive applications aswell.

TERMS AIR SPRINGS& SUSPENSIONS

PRESSURE 8 PROCESS TERMS

Absolute Pressure. The pressure in avessel located in a complete vacuum.Usually determined by adding 14.7 to thegauge pressure. Absolute pressuregauge pressure + atmospheric pressure.

Adiabatic Process. All the calculationvariables, volume, pressure, and tem-perature, change without any heattransfer (not often a real life situation).

Atmospheric Pressure. The averageatmospheric air pressure measured atsea level. Normally accepted to be 14.7pounds per square inch (psi).

Constant Volume With AirflowProcess. Volume and temperature con-stant, pressure changes. This conditionapplies when load is added or removedfrom above the air spring over a periodof time.

Gauge Pressure. Gas or liquid pressurein a vessel, which is higher than atmo-spheric pressure. Usually measured by aBourdon tube gauge in pounds persquare inch (psi).

Polytropic Process. All the calculationvariables, volume, pressure, and tem-

perature, change with heat transfer tothe air spring structure. To account forthis, air spring dynamic operation is calcu-lated by the use of what is known as thepolytropic exponent (n). n 1.38 is the9enerally accepted value for air springs.

AIR SPRING COMPONENT TERMS

Bead. A part of the flexible member thatlocks the cord structure to an inside rein-forcing metal ring and provides a meansof sealing the joint between the flexiblemember and the adjacent structure.

Bead Plate. A metal plate closing the topend of the flexible member. It is attachedto the flexible member by crimping. It hasstuds, blind nuts, brackets, or pins to fa-cilitate its attachment to the vehicle struc-ture. A means of supplying air to the as-sembly is provided as a separate fitting orin combination with an attachment stud.Convoluted type springs incorporate asecond bead plate on the bottom to createan air tight unit and to provide a means offastening the unit to the suspension.

Bead Ring. A metal ring incorporating ashaped cross-section that grips the beadof the flexible member and provides ameans of attaching and sealing the beadto a plate or other structure.

Bumper. Usually, these are made ofrubber, plastic, or rubber and fabricmaterials. They are used to support thevehicle when there is no air in the airsprings, when the vehicle is not in use,or when there is a system failure on theroad. They will also, to some degree,cushion the shock of very severe axleforce inputs to prevent damage to boththe Airide(R) spring assembly and to thevehicle.

Clamp Ring. A metal band placed nearthe end of a beadless flexible member. Itis swaged tightly in place to secure thebeadless flexible member to the upperend cap and piston.

Flexible Member. The fabric-reinforcedrubber component of the air springassembly.

Lower End Closure. Usually a metalcup-shaped component used to close offand seal the lower end of reversible sleevetype air springs. It is frequently molded tothe flexible member. It generally has ablind nut which allows it to be secured tothe piston and/or lower mounting surfaceby the use of a long bolt. Larger diameterend closures may have mtfltiple studs al-lowing them to be bolted directly to thepiston.

Piston. A metal or plastic component ofthe air spring assembly usually placed atthe lower end of the flexible member andused to both support and provide a sur-face for the flexible member to roll on.It also provides a means for attaching theassembly to the mounting surface. Pis-tons with tailored contours may be usedto obtain air spring characteristics tomeet special performance requirements.

Upper End Cap. A plastic or metal com-ponent containing an air entrance anda means of fastening or positioning theair spring assembly to the adjacentmounting surface. The air entrance maybe combined with a mounting stud.

Assembly. This includes the flexiblemember, which may include an end clo-sure, upper bead plate, piston, or lowerbead plate with an internal bumper. Seeillustration on page 11.

Assembly Volume. The internal workingair volume, exclusive of any externalworking volume.

Bumper Volume. The space taken upinside the air spring assembly by thebumper. See Bumper Volume Chart onpage 36.

Compression Stroke (Jounce). Thereduction in heioht from the normal de-

sion heioht of the sprino as it cycles indynamic operation.

Curb Load. The normal minimum staticload the air spring is expected to support.It is a zero payload condition, but includesthat portion of the unloaded vehicle thatis supported by the axle. It is this axleload divided by the number of air springsworking with the axle and adjusted ac-cording to any lever arm ratio incorpo-rated in the suspension.

Design Load. This is the normal maxi-mum static load the air spring suspensionis expected to support. It is the rated axleload divided by the number of air springsworking with the axle and adjusted ac-cording to any suspension lever arm ratioincorporated.

Design Height. The overall height of theair spring as selected from the character-istics chart design position range. The airspring selected should provide for ad-equate jounce and rebound travel for theproposed suspension. The design heightwould be the starting position for calcu-lating the spring and suspension dynamiccharacteristics.

Dynamic Force. The instantaneous sup-porting force developed by the air springduring vehicle motion. It is this constantlychanging force that creates the springrate, suspension rate, and in combinationwith the normal vehicle load on thespring, creates the suspension system'snatural frequency.

Effective Area. The actual working areaperpendicular to the output force of thespring. It is not the diameter of the spring.This working area, when multiplied by thegauge pressure in the spring, producesthe correct output force. Conversely, di-viding the measured output force of thespring by the measured internal gaugepressure obtains the correct effective area.In many cases, this is the only practicalway to obtain it.

Extension Stroke (Rebound). The in-crease in height from the normal designheight of the spring as it cycles in dynamicoperation.

Reservoir Volume. Any working air vol-ume located externally from the air springassembly, but functioning with the spring.

SUSPENSION RELATED TERMS

Height Sensor. An electronic devicethat senses the position of a suspensionor other mechanical device. The outputsignal from this device is sent to a controlcircuit which then exhausts or adds air tothe air spring through a solenoid valve.

Leveling Valve. A pneumatic valve thatsenses the distance between the vehicleframe and the axle via a mechanical link-age which adds or exhausts air pressureto maintain a constant vehicle height.

Sprung Mass Natural Frequency. Thespeed of vertical oscillations of the sus-pended vehicle sprung mass. Can be ex-pressed in cycles per minute (cpm) orcycles per second (hertz).

Sprung Mass (Weight). That partof the vehicle structure and cargo that issupported by the suspension.

Unsprung Mass. That part of the sus-pension that is not supported by thespring (e.g., trailing arm, axle & wheels,air spring, etc.).

OUTER COVER

An air spring is a carefully designedrubber and fabric flexible member whichcontains a column of compressed air. Theflexible member itself does not provideforce or support load; these functions areperformed by the column of air.

Firestone air springs are highly engi-neered elastomeric flexible memberswith specifically designed metal endclosures. The standard two-ply versionis made up of four layers:

(R) Inner Liner. An inner liner ofcalendered rubber.

Frst Ply. One ply of fabric-reinforced rubber with the cordsat a specific bias angle.

Second Ply. A second ply of fabric-reinforced rubber with the same biasangle laid opposite that of the first ply.

Outer Cover. An outer cover ofcalendered rubber.

Although the two-ply air spring is stan-dard, many of our air springs are alsoavailable in fourJply rated constructionfor use at higher pressures.Each air spring's flexible member is

identified by a style number, which ismolded in during the curing (vulcaniza-tion) process. Examples would be 16, 22,313, 1T15M-6, etc. Ths identfies only therubber/fabric flexible member.., not thecomplete assembly.

10

IEVERSIBLE SLEEVE STYLE AIR SPRINGWITH CRIMPED BEAD PLATE

Stud. Mounting stud. Usually1/2"-13 UNC.

M Combination Stud. Combination3/4"-16 UNF mounting stud withNPT internal air entrance.

Bead Plate. 9 gauge (.49") carbonsteel, plated for corrosion resistance.Permanently crimped to the flexiblemember to form an airtight assemblywhich allows for leak testing before theunit leaves the factory.

B Flexible Member. Wall gauge isapproximately .25 inches. See page 9 fordetailed information.- Bumper (Optional). An internal de-vice to prevent damage to the air springduring times when no air is in thesystem.

U End Closure. This is made of steeland is permanently molded to the flexiblemember (except for 1T19 series airsprings).

1 Piston. May be made of aluminum,steel, or engineered composites. Thethreaded holes in the piston are used tosecure the assembly to the mountingsurface.

Piston Bolt. Attaches the piston tothe flexible member end closure. Formounting, a long bolt may be used com-ing up through the mounting surface andattaching to the end closure. Or, a shortbolt may be used to attach the piston tothe end closure.

SERVICE ASSEMBLY

On Firestone's reversible sleeve styleAiride(R) air springs, the flexible member,with cured-in end closure and bead plate,is a separate sealed unit. This unit iscalled a Service Assembly, and may bepurchased without the piston as an eco-nomical replacement for existing airsprings in truck and trailer suspensions.

NOTE: There are several different mounting options avail-able for most air springs. Therefore, always specify boththe style number and the complete Assembly Order Num-ber (AON). For example, T15M-6, Assembly OrderNumber W01-358-9082. Both numbers are published onthe Product Data Sheets for individual air springs.

12

Bead Plate. 9 gauge (.149") carbonsteel. Plated for corrosion resistance.Permanently crimped to the flexiblemember to form an airtight assemblywhich allows for leak testing before theunit leaves the factory.

0 Fleble Member. Wall gauge isapproximately .25 inches. See page 9 fordetailed information.

Bumper (Optional). An internaldevice to prevent damage to the airspring during times when no air is inthe system.

Flush Air Inlet. 1/4" NPT is standard.3/4" NPT is also available for most parts.

|3

Blind Nut. 3/8"-16 UNC thread x 5/8"deep (two or four per plate, dependingupon the part size). Used for mountingthe part.

D Girdle Hoop. A solid steel ring orstranded wire ring cured to the flexiblemember between the convolutions.

NOTE: There are several different mounting options avail-able for most air springs. Therefore, always specify boththe style number and the complete Assembly Order Num-ber (AON). For example, Style #22, Assembly OrderNumber W01-358-7410. Both numbers are published onthe Product Data Sheets for individual air springs.

14

The larger convoluted parts are avail-able with bead rings or permanently at-tached plates called, "rolled plates."Rolled plate assemblies may offer an ad-vantage over the bead ring parts becauseinstallation is much easier (they attachthe same way as the bead plate parts).When installing the rolled plate parts, a

backup plate as large in diameter as thebead plate must be used. This plateshould be a minimum of 1/2" thick.The blind nut and air entrance loca-

tions of rolled plate assemblies are avail-able from Firestone.

Ar Inlet. 3/4" NPT is standard.

l Blind Nut. 1/2"-13 UNC thread x 3/4"deep is standard.

B Upper Bead Plate. 6-gauge (. 194')carbon steel, plated for corrosion resis-tance. Permanently attached to the flex-ible member with a clamp ring (D) toform an airtight assembly. Allows forleak testing before the assembly leavesthe factory.

Clamp Ring. This ring is crimped tothe bead plate to permanently attach it tothe flexible member. It is also plated forrust protection.

Girdle Hoop. Solid steel type curedto the flexible member between theconvolutions

Fllexible Member. Wall gauge is ap-proximately .25 inches (see page 9 forconstruction).

Lower Bead Plate. Usually the sameas the upper bead plate, except withoutthe air inlet.

16

Mounting Plate. Not included. Seepage 21 for material, machining recom-mendations and installation instructions.

D Bead Ring Bolt. May be one of fourvarieties included with air springassemblies. See chart on page 21.

17

Nuts & Lock Washers. Includedwith air spring assembly.

Flexible Member. Wall gauge isapproximately .25 inches.

D Girdle Hoop. Wire wound typeshown, molded into the flexible member.

Bead Rng. Steel countersunk typeshown. May also be of a second stampedsteel variety or made of aluminum (seepage 2:l).

The flexible member is available sepa-rately as a replacement on convolutedbead ring assembfies.

REVERSIBLE SLEEVE AIR SPRINGSBEAD RING ASSEMBLIES

Mounting Plate. Not included. Seepage 21 for material, machining recom-mendations and installation instructions.

D Bead Ring Bolt. May be one of fourvarieties included with the air spring as-sembly (see chart on page 21).

Nuts & Lock Washers. Includedwith air spring assembly.

Flexible Member. Wall gauge is ap-proximately .25 inches.

' End Closure. This is made of steeland is permanently molded into the flex-ible member (except for the 1T19 style airspring).

D Piston. May be made of aluminum,steel, or engineered composites. Thethreaded holes in the piston are used tosecure the assembly to the mountingsurface.

Bead Ring. Steel countersunk typeshown. May also be of a second stampedsteel variety or made of aluminum. (Seepage 21).

The flexible member with cured-inend closure is available separately as areplacement.

20

STEEL BUTTON HEADBEAD RING

STEEL COUNTER SUNKBEAD RING

ALUMINUM RIBBED NECKBEAD RING

ALUMINUM ALLEN HEADBEAD RING

Standard Bolt Length (in)17/8

Standard Effective Length (in)1,28

Standard Order Number(bolt only)

W01-358-3607

Thread%6-24UNF

Tightening Torque (ft-lb)17 to 22

Standard Bolt Length (in)1%

Standard Effective Length (in)1.22

Standard Order Number(bolt only)

W01-358-3625

Thread%6-24UNF

Tightening Torque (ft-lb)17 to 22

Length

Supplies r- LengthPate

Optional Shoer LengthRibbed Neck Bolt

J Use 1/4"Cap Screws

cluded)

Custom_erSupplies Plate

Optional Bolt Length (in)Standard Bolt Length (in)1% (il/4)

Standard Effective Length (in) Optional Effective Length (in)1.28 (.66)

Standard Order Number Optional Order Number(bolt only) (bolt only)

W01-358-3620 (W01-358-3618)

ThreadThread%-24UNF %-24 UNF

Tightening Torque (ft-lb)Tightening Torque (ft-lb)28 to 32 28 to 32

WITH BEAD RINGS

When using bead rings, you will needto fabricate your own mounting plates.Hot or cold rolled steel provides satisfac-tory mounting surfaces with finishes of250 micro inches, if machined in a circu-lar fashion, or 32 micro inches whenground (side-to-side). The thickness of

mounting plates depends upon the appli-cation. The plates must be strong enoughand backed by structural members to pre-vent bowing of the plates when subjectedto the forces or loads involved. The flex-ible member provides its own seal, so "O"rings or other sealants are not required.

iNSTALLATION

Follow this technique for assembling abead ring style flexible member to themounting plate:

Insert the bolts into the bead ring,which has already been attached to theflexible member.

2Slip all of the bolts, which protrude

through the bead ring, into the matingholes of the mounting plate and attachthe lock washers and nuts. Finger tightenall nuts to produce a uniform gap be-tween the bead ring and mounting plateall the way around. The bolts will bepulled into place by the action of tighten-ing the nuts. When using aluminum beadrings, it may be necessary to lightly tapthe ribbed neck bolts with a small ham-mer to engage the splined portion intothe bead ring.

3Make certain that the flexible member

bead is properly seated under the beadring. Please note that uniform successivetightening of the nuts is important to seatthe rubber bead properly to the mountingplate around its full circumference.

4Tighten all nuts one turn each, moving

around the circle until continuous contactis made between the bead ring andmounting plate.

5Torque all nuts to the torque specifica-

tions shown in the chart on the previouspage, going at least two complete turnsaround the bolt circle.

NOTE: Consult Firestone for proper selection of beadring type.

22

1T15M-11

The part description is shown in theupper right hand corner. The standardpiston is used unless noted below thepart description.

D Bead plate diameter.

Bead plate mounting arrangementand air inlet location and size.

Alignment: the relationship of thebead plate mounting to the pistonmounting.

D Maximum rubber part diameter at100 psig and minimum height.

Piston body diameter.

Bumper and reference number.

"B" dimension. The distance from themounting surface to the rubber loop at100 psig.

Mounting arrangement of thepiston's threaded holes or stud(s).

Piston base diameter.

The last four digits of the AssemblyOrder Number, W01-358-9320.

H Approximate weight of the assembly.

Piston height.

STATIC DATARecommended Design PositionStalic Pressure 10-100 Psig

The Maximum Rebound Height isthe maximum extended position of theair spring before the flexible member isput in tension. Some means of prevent-ing the suspension extending the airspring past this height must be providedto prevent damage to the air spring.Shock absorbers are typically used, how-ever chains, straps, and positive stopsmay also be used.

D The Design Position Range showsthe recommended operating range ofstatic heights. This range is 16 to 20inches for the 1T15M-11, as shown onthe chart. Use outside this range may bepossible, however, Firestone should beconsulted.

The Constant Pressure Curve is theLoad trace obtained as the part is com-pressed from the maximum height to theminimum height while maintaining aregulated constant pressure in the part.A series of constant pressure curves, 20psig through 120 psig are shown at 20psi increments. The 120 psig curve isshown for reference only, as most partsare limited to static design pressure of100 psig.

l The Volume Curve is a plot of thedata points obtained by measuring thevolume of exhausted liquid as the part iscompressed from maximum to minimumheight while maintaining a regulatedpressure of 100 psig in the air spring.(This is the volume without a bumper).

The Shaded Area (24" to 28") on theleft side of the chart is a range of heightsin which the air spring is not normallyused except during unloading as the axlegoes in rebound. Do not use in ths rangeof heights for applying a force.

The number, B-0689, is the TestRequest Reference Number.

100 Psig DataHeight Load Volume B-Dim(In) (Lbs) (Cu In) (In)

Dynamic Characteristics at Various Design Heights

Pressure Rate Natural FrequencyHeight(In) (Lbs) (Psig) (Lbs/In)

Dynamic Load vs Deflection

APPLICATIONCONSIDERATIONS

Obtaining the maximum performanceand life from Airide(R) air springs requiresproper application.

AIR SPRING CHOICE CONSIDERATIONS

The air spring design height should bekept within the recommended range toget optimum performance and durability.Select a spring that carries the suspen-sion rated load in the range of 80-90 psig.This gives you an air spring that has theoptimum characteristics for your applica-tion (i.e., natural frequency, size, cost,etc.). The compressed height of the airspring in the suspension must not be lessthan the minimum height of the airspring chosen, as shown on the ProductData Sheet.

Conversely, the extended height of theair spring in the suspension must not begreater than the maximum extendedheight of the air spring chosen (refer tothe Product Data Sheet).

INSTALLATION CONCERNS (CONVOLUTEDAIR SPRIHGS)

To achieve the maximum lifting force,and produce a minimum of horizontalforces, convoluted air springs should bepositioned at the normal design height

with the centers of both bead platesaligned. The bead plates can be angledso that a good relationship betweencompression and extension travel canbe achieved with appropriate bumpercontact.The maximum extended height shouldnever be exceeded. Under normalconditions, the included angle be-tween the bead plates should not begreater than 20 however withFirestone's approval, angles of up to30 may be acceptable on some mod-els.

Reversible sleeve air springs in-corporating internal bumpers shouldhave the bead plate and piston parallelwithin 3 to 5 at bumper contactheight. Normally, the piston is angledat the design position so that a goodrelationship between compressed andextended travel can be achieved.

Reversible sleeve air springs whichdo not have an internal bumper mayhave the piston angled to allow fullcompression stroke without the flex-ible member being pinched betweenthe piston and the bead plate.

Flexible membermust not rubagainst itself

Reversible sleeve type air springs may stroke through an arc,but care must be taken to prevent the flexible member fromrubbing internally against itself where it rolls over the piston.

Plastic pistons should normally be fullysupported over the entire base surface.Exceptions should be reviewed byFrestone.Metal pistons used with 1T15 size or

smaller assemblies may be mounted on aflat beam surface at least three incheswide which extends the full diameter ofthe piston base.Bead plates should be supported by a

back-up plate the size of the bead plate.Under certain circumstances, the beadplate may be supported by a minimumthree-inch wide beam. These mountingsshould also be reviewed by Firestone.

If a single long fastening bolt is used toclamp the air spring end closure and thepiston to the trailing arm, it should begrade 5 or above, and tightened accord-ing to the appropriate value shown in thechart on page 35. If the piston is tippedmore than 5 degrees, some means shouldbe provided to locate the piston.

34

:ASTENER ''IGHTENINGSPECIFICATIONS

Description Size

Bead ring nuts onbolts

5/16-24

Bead ring boltsand nuts

3/8-24

Bolts in blind nutsin bead plates

3/8-16

End of adapterstuds in blind nut

3/8-16

Nut on end ofadapter studs

1/2-13

Studs on bead platesor blind nuts

1/2-13 or1/2-20

Bolt to attach pistonbase to lowermounting surface

1/2-13

Nut on air entrance 3/4-16stud

NPT air supply fitting 1/4 & up

Nut on end closure 3/4-10lower mounting

Torque(Ib-ft)

17-22

28-32

15-20

15-20

25-30

25-30

25-30

40-45

17-22

45-50

OPERATIONAl. CAUTIONS

Air spring failure can be caused by avariety of situations, including internal orexternal rubbing, excessive heat andoverextension. For further details, referto Section 9, Warranty Considerations.Bead plates are normally fully sup-

ported, however, mounting the beadplate directly to the frame raft, or othermounting surface with less than fullsupport, may be possible.

The normal ambient operating tem-perature range for standard vehicular airsprings is -65F to +135F.

UMPERS

In general, bumpers are used to sup-port the vehicle weight to preventdamage to the flexible member duringtimes when no air is in the system. Theyare also used as stops when the axle israised by a lift unit. In applications thatrequire frequent bumper contact, consultFirestone.

35

Nurnr

3073

313631473155315731593162

320932853294335033863404360436913777

4457

45184519

49647725

48.58.8

28.570.393.0

41.0

40.4

65.3

43.4

33.919.7

9.4

34.637.7

11.3

31.048.022.128.21.6

32.2

CAUTION: Contact Firestone for specificbumper applications

36

BASIC PRINCIPLES

iNTRODUCTION

The fundamental concept of an airspring is a mass of air under pressure ina vessel arranged so that the pressureexerts a force. The amount of static forcedeveloped by the air spring is dependenton the internal pressure and the size andconfiguration of the vessel. The vessel isdefined in this manual as the Airide(R)

spring by Firestone or air spring.Dynamic force is the result of internal

pressure changes and air spring effectivearea changes as height decreases (com-presses) or increases (extends).The amount of pressure change for a

stroke depends on volume changecompared to total volume at equilibriumposition. For the convoluted type, effectivearea change for a stroke depends onwhere in the total travel range the motiontakes place. For the reversible sleeve type,the shape of the piston, size of the pistonrelated to the flexible member diameter,and cord angle built into the flexible mem-ber all have an influence on effective area.The effective area can be arrived at by

taking the longitudinal static forcedeveloped at a specified assembly heightand dividing this force by the internalpressure (psig) existing in the air springat that height. This method is used todevelop the static effective areas used indynamic rate and frequency calculations.

EFFECTIVE AREA

Effective area is the load carrying areaof the air spring. Its diameter is deter-mined by the distance between thecenters of the radius of curvature of theair spring loop. The loop always approxi-mates a circle because the internal airpressure is acting uniformly in all direc-tions, so that only the area inside thecenters is vertically effective. For aconvoluted air spring, the effective areaincreases in compression and decreaseson extension. For a reversible sleeve airspring, the effective area is constantwhile operating on the straight side ofthe piston, increases when working onthe flare of the piston in compression,and decreases when the rubber part liftsoff the piston in extension.When a vehicle having air springs in its........

suspension is at rest, and then load isadded or removed, the height controlvalve operates to add or remove suffi-cient air in the air spring to maintain theset air spring overall height. This then in-creases or decreases the pressure in theair spring the amount needed to providethe required lifting force to match thecurrent downward force created by thenew load condition, and equilibrium isagain reached.

" EFFECTIVE

DIAMETER

+

EFFECTIVEDIAMETER

EFFECTIVE 1DIAMETER

Convoluted Reversible SleeveAir Spring Air SpringChange In Change in

Effective Diameter Effective Diameter

Effective areaLoad

Pressure

Load (supporting force) Pressure x Area

38

SPECIAL CNANG|S O SAT|

Non-flowprocess, specific heats as-sumed constant. Subscripts 1 and 2 referto the initial and final states, respectively.

P Absolute PressureT Absolute TemperatureV Total Volume

Constant Volume (Isochoric)

This is an unattainable process due tothe nature of the flexible member, how-ever, at static conditions, the change inpressure may be calculated for a changein temperature.

U Constant Pressure (Isobaric)

Dynamically, the only way to maintainconstant pressure is in combinationwith infinite volume and is generallynot useful.

Constant Temperature (Isothermal)

P VP V

This requires very slow movements notnormally applicable to air spring operation.

Q Reversible Adiabatic (Isentropic)

PVk pava

This is defined as a process with noheat transferred to or from the workingfluid. This is a theoretical process notattainable with pneumatic springs,however, for rapid deflections, it isclosely approached, k=1.404 for air.

39

Polytropic

PVn- Constant

This process usually represents actualexpansion and compression curves forpressures up to a few hundred pounds.By giving "n" different values and assum-ing specific heats constant, the precedingchanges may be made special cases ofthe polytropic change. Thus for:

n I, PV Const. (Isothermal)n- k, pvk= Const. (Isentropic)n-- 0, P Const. (Constant Pressure)n- 0% V Const. (Constant Volume)

The principal formulas for air compres-sion up to a few hundred pounds pres-sure where lnk are:

and

T2 (VI/n-1(n-1)

T -) P )

During air spring dynamic operation,the pressure, volume and temperaturechange instantaneously. The air springflexible member structure also changesdepending upon the specific configura-tion. As a result, air springs operate in therange lnk, however, a generallyacceptable value for "n" is 1.38 for normalvehicle operation.

Note: Shadow boxesJare used to designate important formulas.

40

E

o"5 : Lc

L ALek

',- Ahe- Ahc-'e L

Extension Compression

Deflection

Rate is the slope of the tangent at theequilibrium position. For small incrementsof deflection, rate equals the load changeper unit deflection.

(The slope of the chord line through Lcand Le is parallel to the tangent at L forsmall deflections.)

U K (Lc- Le)/(Ahc + Ahe)Where:

K Rate (Load per unit deflection)

L Load at compression travel

Le Load at extension travel

Ahc Height change, compression

Ahe Height change, extension

U L Po (A)L Po (AD

Where:Pg Gauge Pressure at LPge Gauge Pressure at LeA Effective area at LcAe Effective area at Le

setting Ahc Ahe- .5 inch

U K- Po(A)- Poe(Ae)

D Po -Pa-14.7Poe Pae-- 14.7

Where:

P Absolute Pressure at LcPe Absolute Pressure at Le14.7 Atmospheric Pressure

!i now using the polytropic gas law andn- 1.38

41

Where:

Pal Absolute pressure atequilibrium position

V Volume atequilibrium position

V Volume at LcV Volume at L

substitutingD in a

Pge PalkTT -14.7

now substitute in

Il K Pgc(Ac)- Pe(Ae)

Then, grouping terms, this becomes the general rate formula for air springs.

.38

Ae/TTe 14.7(A Ae)

ATURAE. REQU|NCY

Since the air spring has a variable rateand essentially a constant frequency, it ishelpful to calculate the natural frequencywhen evaluating characteristics.When considering a single-degree-of-

freedom system (undamped), the classicaldefinition of frequency s as follows:

Note: The period of free vibration (which is the reciprocalof frequency,) is the same as the period of a mathematicalpendulum, tle length of which is equal to the static deflec-tion of the spring under the action of load W.

f_co ands02= K2 m

Where:

f Frequency, cycles per secondc0 Circular frequency,

radians per secondK Rate, pounds per inchm- Mass, pound seconds

per inch

Then:

Also.Wg

Where-

W- Weight, poundsg Acceleration of gravity,

386 inches per second

Substituting:

cpm

cpm

This is normally rounded to.

Where.

K- RateW- Weight (load)

Also since:W

de (effective deflection)K

188= cpm I

43

Effective deflection (dE) has no physicalsignificance, however, has mathematicalmeaning. It is defined as load divided byrate and is graphically explained below.

Variable Rate Spring

Load DeflectionCurve

Tangent

Deflection

Loadde

Rate

Load- Rate x de

Note: For a constant rate spring, de and the deflectionfrom free height are equal.

vs. the spring located fore or aft of thewheel. Note the distance to the spring isalways 'A" whether located forward or aftof the axle.

Schematic representation of a trailingarm suspension:

Wheel Spring1111///I// ZZ4/l/ll//

Lw Ls

Where:

Lever Arm Ratio LAR

LAR- Distance to spring ADistance to wheel B

And:

SPRING MASS SYSTEMWITH LEVER ARM

The rate and frequency at the wheel(axle) are the same as that of the springonly if the centerline of the spring islocated on the centerline of the wheel.The following is a derivation of the rateand frequency relationship at the wheel

I Rate at spring

Ls Load at spring

Zs Deflection at spring

For an equivalent spring at the wheel:

Kw Rate at wheel

L Load at wheel

Zw Deflection at wheel

T| R|IT|ONSH|P

Balancing moments about the pivot

U LA- LwB

LW

Also.

Load Rate x de

LwLAR

Solving for Kw

Lw

D L KZ

substitutingU in D

Solving for Lw

So.

Kw

FREQUENCY R|T|ONSH|P

And:

cpm

D fw 188 cpm

from the natural frequency derivation where

f Frequency at spring

fw Frequency at wheelAlso:

LsA- LwB fromu

Solving for Ls

now using Kw-Ks - from

and substitute in D

Lx B

Or':

now substitute fs from

fw fs(LAR)So"

F'ecen, w- F,'equen tin xLA/ /,46

Polytropic Gas Law

Dynamic Air Spring Rate

K Pal Ac Ae "J[4 7(Ac Ae)

Natural Frequency

Lever Arm Considerations

LAR_Distancetospring_A /

Rate at wheel Rate at sprin x (LA)

Frequency at wheel Frequency at spring x (LAR)I/ /

SAMPLE CALCULATIONS:AiR SPRINGS & SUSPENSIONS

CA[.CUET|NG DYNAH|C

AND :REQUENCY

The dynamic rate of an air spring overa plus and minus 1/ inch stroke iscalculated using Formula 8 on page 42,substituting values as follows:

Where.

K Rate (lb/in)

Pal- Absolute pressure (psia) atdesign positionGauge pressure (psig) at designposition plus 14.7- Pgl / 14.7

Effective area (ins) at design positionLoad (lb) / Pressure (lb/ins)

Ac Effective area (ins) at 1/ff inchbelow design positionLoad (lb) / Pressure (lb/ins)

Ae- Effective area (ins) at / inchabove design positionLoad (lb) / Pressure (lb/ins)

V1 Internal volume atdesign position (in

Vc Internal volume at / inchbelow design position (in

Ve Internal volume at /ff inch abovedesign position (in

For example, find the air spring rateof the 1T15M-11, W01-358-9320 at an18 inch design height and a load of7000 pounds. See the Product DataSheet for the necessary information.

The effective area on the 100 psig curve iscalculated:

A1-Load 7146 71.46 in

Pressure 100

Also calculate A andA.

A 7146 71.46 in100

7146A 71.46 in

100

Then calculate the pressure at7000 pounds:

700097.96 psig

71.46

49

Then calculate the rate:

K-Pal Ac c -Ae) -14.7(Ac-Ae)

-71.46 -14.7(71 46-71 46)1170.2 1244.46

K 677 lb/in

Now calculate the frequency:

f-188K-1881677W 7000

f- 58.5 cpm

Note: These are the same values shown in theDynamic Characteristics Chart on the Product Data Sheetat 18 inches and 7000 pounds.

50

The curves on the Dynamic Load vs.Deflection Chart (Section 4) can be calcu-lated using the formulas developed inSection 6. It is helpful to construct a tableof values as shown below.

Static EffectiveHeight Load Volume Area

(in) (lb) (cu in) (sq in)

Line 21

Absolute Gauge DynamicPressure Pressure Load(psia) (psig) (Ib)

OrS

Line

Line D "15

The 1T15M-11 on an M-9 piston is usedfor this example (W01-358-9320).Refer to that Product Data Sheet.

Conditions selected:Air spring load 4000 lbDesign height 18 inches

Find:Dynamic load at + 3 inch compressionDynamic load at- 3 inch extension

Line U is the selected design condition.

Line D is the data for 3 inch compression.

Line D is the data for 3 inch extension.

Note: For loads between constant pressure curves,calculate the effective area By using the load onthe closest constant pressure curve. Then calculatethe pressure By dividing the design load By theeffective area.

Line H entries are determined as follows (Design).

Static Load, This value is obtained on the closest constant pressure curve,60 psig in this case, at the 18 inch design height. Refer to the Static LoadDeflection Curve.

L- 4200

Volume, This value is taken from the 100 psig Data Table at 18 inch height

V1 1207.89 cu in

Effective Area, Calculated at 60 psig and 18 inch height.

Load 420070 in

Pressure 60

Gauge Pressure, The Design Load divided by the effective area.

L 4000j1 57.14 psig

A 70

Absolute Pressure, Gauge pressure / 14.7.

Pal Pgl + 14.7 57.14 + 14.7 71.84 psia

Dynamic Load at point 1, equals the Design Load 4000 lb.

Enter these values in the data chart constructed.

52

Now calculate the values for Line D (3 inch compression):

Static Load, From the 60 psig constant pressure curve and 15 inch design height.

L- 4200 lb

Volume, From the 100 psig Data Table at 15 inch height.

V2 981.62 cu in

Effective Area, At 60 psig and 15 inch height.Load 4200

A2 70 inPressure 60

Absolute Pressure, Use the polytropic gas law.

P2-PI -71.84 9-B-P2 95.65 psia

Gauge Pressure, Absolute pressure- 14.7.

P, Pa 14.7 95.65 14.7 80.94 psig

Dynamic Load, Effective area x pressure.

DL2 P, x A- 80.94 x 70- 5666 lb

G's, The ratio of Dynamic Load to Design Load.

DL2 5666G 1.42

L 4000

Enter these values in the data chart constructed.

Now calculate the values for Line D (3 inch extension):

Static Load, From the 60 psig constant pressure curve and 21 inch design height.

L- 4000 lb

Volume, From the 100 psig Data Table and 21 inch height.

V:- 1419.72 cu in

Effective Area, At 60 psig and 21 inch height.

Load 4000A3 66.67

Pressure 60

Absolute Pressure, Use the polytropic gas law.

(Vl/nV3 / 1207"89 ]138

P P, z-:-. 71.84 57.48 psia1419.72

Gauge Pressure, Absolute pressure- 14.7.

P. P- 14.7 57.48- 14.7 42.78 psig

Dynamic Load, Effective area x pressure.

DL P., x A, 42.78 x 70 2852 lb

G's, The ratio of Dynamic Load to Design Load.

DL 2852G .71

L 4000

A plot of the dynamic load points vs.height will give the curve shown on theProduct Data Sheet, Dynamic Load vs.Deflection Chart with a starting point of18 inch height and 60 psig.

The completed table of values is shown below.

Static EffectiveHeight Load Volume Area

(in) (Ib) (cu in) (sq in)

AbsolutePressure(psia)

GaugePressure(psig)

DynamicLoad(Ib)

Line Q 21 4000 1419.72 66.67 57.48 42.78 2852

Line D 18 4200 1207.89 70 71.84 57.14 4000

Line Q 15 4200 981.62 70 95.65 80.94 5666

a's

0.71

1.0

1.42

55

TRAILING ARM SUSPENSIONCALCULAT|ONS

The trailing arm design is a common truck andtrailer air suspension. The air spring does not carrythe same load that is applied at the wheel (axle). Theformulas developed in Section 6 are used.One method of obtaining a trial suspension

design follows for a 20,000 lb axle, using a 1T15M-6reversible sleeve air spring at 13 inch height.Determine the necessary trailing arm ratio needed

to support the axle design load within the air springmaximum allowed static pressure of 100 psig whichcreates a lifting force of 7,045 lb at a 13 inch height.See Product Data Sheet (W01-358-9082).

FRAME /

( WHEEL

Assume an unsprung weight of 800 lb

Load at wheel Lw (20,000- 800) + 2 9600 lb.

Lw 9600LARLs 7045

1.36 using the M-6 at 100 psig

For this example a 90 psig operating pressure will be used.

Lw 9600LARLs 6340

---1.52 using the M-6 at 90 psig

Note, the 6340 lb at 90 psig is calculated by multiplying the pressure ratiotimes the load at 100 psig, or:

90100--x 7045- 6340 lb

56

Now using the maximum OD of theM-6, 12.6 inches, and an assumed axlediameter of 5 inches plus a minimumclearance of one inch, calculate thedimension "C" shown in the illustrationon page 56:

C (1/2 x OD air spring / 1/2 x axle diameter) / clearance

--/- /1-9.8inch2 2

Calculating dimension "C" in thismanner places the air spring as close tothe axle as possible, which provides-thelowest rate and frequency at the wheel(with the air spring aft of the axle).

Now calculate dimensions "A" and "B"with LAR- 1.52 and C -9.8.

LAR-A-1.52-B/C-B/9"8B B B

1.52B- B- 9.8

9.8B 18.85 inch.52

Then determine A.

A- B / C 18.85 / 9.8- 28.65 inch

Note that with a given "B" dimension(e.g., 21 inches) determined by otherfactors, proceed as follows:

ALAR 1.52

B

A- 1.52 B 1.52 x 21 31.9

Then check for clearance at the axle:

C A- B- 31.9- 21 10.9 which is greater than 9.8

The following is now known for thesample situation:

20,000 lb axle rating

Load at wheel 9600 lb

Load at the spring 6340 lb

LAR- 1.52

Distance from pivot to spring 28.65 inch

Distance from pivot to axle- 18.85 inch

Design height 13 inch

58

The system characteristics may now becalculated using the preceding resultswith data from the Product Data Sheet1T15M-6 (W01-358-9082).

Ae

7045100

7O5OIO0

7042100

70.45 in. (at 13 inch height)

70.5 in (at 1_2.5 inch height)

70.42 in (at 13.5 inch height)

Va 917.41 cu in (at 13 inch height)

Vc 879.31 cu in (at 12.5 inch height)

Ve 955.30 cu in (at 13.5 inch height)

Now calculate the pressure at the13 inch height:

634090 psig

70.45

Air Spring Rate:

Ks 104.7 [74.75- 66.591

Ks 854.35 1.176 853.2 lb/in

Air Spring Frequency:

fs-188K--5-W 1881853"26340 68.97 cpm

6O

Wheel Rate:

K,,, K, (LAR)

853.2 (1.52)2= 1971 lb/in

Wheel Frequency:

f,, f, (LAR) /e

/e68.97 (1.52) 85 cpm

Other factors that must be consideredinclude, but are not limited to:(R) Maximum extension(R) Minimum height(R) Stroke at the axle

61

SAMPLECALCULATIONSUSING A P|RSONAI

COMPUTER

Carmel,

piston

Design Height

(ib) (psig) (lb/in)

59.59.

(Sample File STATSPL.WKI)

NSTRUCTONS

In this example you will calculate thestatic rate and frequency of the ITI5M-11(W01-358-9320) reversible sleeve style airspring on an M-9 piston at an 18 inchdesign height.

U Load *Lotus i-2-3 or file compatiblespreadsheet.

Load the file named STATCALC.WKLfrom the disk provided. Save the file witha new name (for example MIDH18) on aseparate data disk.

Enter the information:

Date (Label.)Part Number (Label)Test Request # (Label)Design Height (Value)Bumper Volume (Value)Bumper Number (Label)Load start (Value)Load increment (Value)

63

*Lotus 1-2-3 is registered trademark of Lotus Development Corp.

D Enter the areas (sq in) andvolumes (cu in):

(R) A1 is the effective area at thedesign height.

(R) Ac is the effective area at 1/2 inchbelow design height.

(R) Ae s the effective area at 1/2 nchabove design height.

(R) VI s the internal volume at thedesign height.

(R) Vc is the volume at I/2 nch belowthe design height.

(R) Ve is the volume at 1/2 nch abovethe design height.

Note: All entries are values. If a bumper is used, subtractthe bumper volume from V1, Vc, and Ve. Refer to theBumper Volume Chart on page 36.

The pressure, rate and frequencyare automatically calculated for the loadsselected.

Save the File with the new file nameselected in Step 2.

64

piston

(ib) (psig) (ib/in)

spring

(Sample File WHFRQSPL.WK1)

NSTRUCTIONS

In this example you will calculate thewheel frequency of the 1T15M-11(W01-358-9320) reversible sleeve styleair spring on an M-9 piston at an 18 inchdesign position.

B Load *Lotus 1-2-3 or file compatiblespreadsheet.

Load the file named WHFREQ.WKfrom the disk provided. Save the file witha new name (for example MllWFREQ)on a separate data disk.

D Enter the information:

Date (Label)Part Number (Label)Test Request # (Label)Design Height (Value)Bumper Volume (Value)Bumper Number (Label)


65

D Enter the areas (sq in) and volumes(cu in):

(R) A1 is the effective area at thedesign height.(R) Ac is the effective area at 1/2 inchbelow the design height.(R) Ae is the effective area at 1/2 inchabove the design height.(R) V1 is the internal volume at thedesign height.(R) Vc is the volume at 1/2 inch belowthe design height.(R) Ve is the volume at 1/2 inch abovethe design height.

Note: All entries are values. If a bum]aer is used, subtractthe bumper volume from V1, Vc, and Ve. Refer to theBumper Volume Chart on page 36.

Enter four air spring loads that mightbe of interest to you. The air spring pres-sure, rate, and frequency are automati-cally calculated for the loads you selected.

Enter the suspension dimensions.Dimension A is the distance from thepivot to the spring center line. DimensionB is the distance from the pivot to theaxle center line.

The lever arm ratio, its square andsquare root are calculated and used inthe calculations for loads, rates and fre-quencies.

D The air spring loads, rates and fre-quencies are repeated.

The wheel (axle) loads, rates, and fre-quencies are calculated. Change theloads in step 5 to obtain any desiredwheel loads.

Save the file with the new name youselected in Step 2.

66

piston

Design HeightDesign

DynamicHeight psig psig

(in) (ib) in) in) (psia) (psig)

design

(Sample File DYNSPLI.WK1)

INSTRUCTIONS

In this example you will calculate thedynamic load for the 1T15M-11358-9320) reversible sleeve style airspring on an M-9 piston at an 18 inchdesign position and a load of

spreadsheet.

from the disk provided. Save the file witha new name (for example,on a separate data disk.

Date (Label)Part Number (Label)Test Request # (Label)Design Height (Value)Design Load (Value)Pressure (Which con- (Value)stant pressure curve used)


67

Ateach height, enter the load fromthe constant pressure curve closest to thedesign load. Take this information fromthe Product Data Sheet. In this example,the design load selected was that at 100psig. In general, volume data is availableonly at 100 psig, and is used for all loads.Enter the volume data from the 100 psigstatic data chart on the Product DataSheet at each height. Subtract thebumper volume if applicable.

The following are automaticallycalculated at each height:

Air spring effective area (sq in)Air spring absolute pressure (psia)Air spring gauge pressure (psig)Air spring dynamic load (lb)G's for compression heights (a ratioof dynamic load to design load)

A dynamic load vs. height plot willgive the results of the Dynamic Load vs.Deflection Chart on the 1T15M-11 DataSheet, part number 9320.

Save the file with the new file nameselected in Step 2.

68

piston

Design HeightDesign

DynamicHeight psig psig

(in) in) in) (psia) (psig) (ib)

-2.0

design

(Sample File DYNSPL2.WK1)

DYNAMIC LOAD

INSTRUCTIONS

In this example you will calculate thedynamic load for the 1T15M-11 (WO1-358-9320) reversible sleeve style airspring on an M-9 piston at an 18 inchdesign position and a load of 4,000 lb.

U Load *Lotus 1-2-3 or file compatiblespreadsheet.

Load the file named DYNAMIC.WK1from the disk provided. Save the file witha new name (for example, M11DYN2) ona separate data disk.

Enter the information:

Date (Label)Part Number (Label)Test Request # (Label)Design Height (Value)Design Load (Value)Pressure (Which con- (Value)stant pressure curve used)


69

D At each height, enter the load fromthe constant pressure curve closest to thedesign load. Take this information fromthe Product Data Sheet. In this example,the design load of 4,000 lb is closest tothe 60 psig curve. In general, volume datais available only at 100 psig and is usedfor all loads. Enter the volume data fromthe 100 psig static data chart on theProduct Data Sheet at each height.Subtract the bumper volume ifapplicable.

The following are automaticallycalculated at each height:

Air spring effective area (sq in)Air spring absolute pressure (psia)Air spring gauge pressure (psig)Air spring dynamic load (lb)G's for compression heights (a ratioof dynamic load to design load)

A dynamic load vs height plot willgive the results of the Dynamic Load vs.Deflection Chart on the 1T15M-11 DataSheet, part number 9320.

I Save the file with the new file nameselected in Step 2.

70

WARRANTYCONSIDERATIONS

iNTRODUCTiON

Firestone air springs are designed toprovide years and thousands of milesof trouble-free service. The durabilityof Firestone air springs is such that theywill often outlast other maintenanceitems on your suspension, such as bush-ings, shocks, leveling valves orregulators.

Airide(R) springs by Firestone are*warranted to be free of material defectsand/or workmanship for various periodsof time, depending upon the application.Replacements may be provided by theoriginal suspension manufacturer, manu-facturer's representative or dealer, or byany Firestone air spring distributor. Alllabor and incidental costs associated withreplacing the defective air spring are theresponsibility of the purchaser, or enduser.

Firestone Industrial Products Companyoffers a complete line of Airide springs,with replacement springs available forvirtually every vehicular air suspensionsystem.

Since each individual air spring is closelyexamined and pressure tested at thefactory, the vast majority of prematurefailures and consequent warranty returnsare found not to be defective, but fail be-cause of abuse caused by other problemsassociated wth the suspension.Before you nstall a new ar sprng, you

should carefully examine the old one todetermine what caused t to fail. if t wasdue to a defect in the suspension system,,then the new air sprng will also fail un-less you correct the problem.The information that follows was

developed to illustrate the types offailures that may occur, and to assist youin determining the cause and correctiveaction required.

71

*Complete warranty information may be obtained from anyFirestone Airide air spring distributor by calling 1-800-247-4337.

Most air spring failures are caused bya lack of suspension maintenance orimproper application. This is a guide tocommon failures that are not coveredby warranty.

Appearance Or Condition

Off-center bumper contact

Same as bottoming out or abrasion(See pages 74 and 75)

Possible Causes

Worn bushing

Improper installation

72

LOOSE GIRDLE HOOP


Flexible member distorted and girdlehoop torn loose

Possible Causes

Running at extended positions withlow air pressure

73

BOTTOMING OUT

Appearance or Condition

Bead plate concave

Internal bumper loose

Hole in girdle hoop area (convoluted)

Hole in bead plate junction area

Leaking around blind nuts

Possible Causes

Broken or defective shock absorber

Defective leveling valve

Overloaded vehicle

Pressure regulator set too low

Wrong air spring (too tall)

74


Hole rubbed into side of flexible member

Hole in flexible member area that rolls overpiston (reversible sleeve style air springs)

Possible Causes

Structural interference such as:

broken shock misalignmentloose air line worn bushings

No air pressure (reversible sleeve style)

Foreign material (sand, rocks, etc.)

Wrong air spring

75

CiRCUMFERENTiAL CUTS


Flexible member cut in circle at bead platejunction

Flexible member cut in circle at piston junction(reversible sleeve style)

Possible Causes

High pressure, fully extended forlong periods of time

Impact in compressed position

76

OVER-EXTENSION


Bead plate convex, especially around blindnuts or studs

Flexible member separated from bead plate

Leaking at blind nuts or studs

Leaking at end closure (reversible sleeve type)

Loose girdle hoop on convoluted style

Possible Causes

Broken or wrong shock absorber

Defective leveling valve

Ride position too high

Defective upper stop (lift)

Wrong air spring (too short)

77

PREVENTIVE MAINTENANCECHECKLIST

The following items should be checkedwhen the vehicle is in for periodicmaintenance.

WARNING: Never attempt to service an airsuspension with the air springs inflated.

Inspect the O.D. of the air spring.Check for signs of irregular wear or heatcracking.

2Inspect air lines to make sure contact

doesn't exist between the air line and theO.D. of the air spring. Air lines can rub ahole in an air spring very quickly.

3Check to see that there is sufficient

clearance around the complete circum-ference of the air spring while it is at itsmaximum diameter.

4Inspect the O.D. of the piston for

buildup of foreign materials. (On areversible sleeve style air spring, thepiston is the bottom component ofthe air spring).

5Correct ride height should be

maintained. All vehicles with air springshave a specified ride height establishedby the O.E.M. manufacturer. This height,which is found in your service manual,should be maintained within 1/4". Thisdimension can be checked with thevehicle loaded or empty.

6Leveling valves (or height control

valves) play a large part in ensuring thatthe total air spring system works asrequired. Clean, inspect and replace,if necessary.

7Make sure you have the proper shock

absorbers and check for leakinghydraulic oil and worn or broken endconnectors. If a broken shock is found,replace it immediately. The shockabsorber will normally limit the reboundof an air spring and keep it fromoverextending.

8Check the tightness of all mounting

hardware (nuts and bolts). If loose,re-torque to the manufacturer'sspecifications. Do not over-tighten.

78

CLEANING

APPROVED METHODS

Approved cleaning media are soap andwater, methyl alcohol, ethyl alcohol andisopropyl alcohol.

NON-APPROVED METHODS

Non-approved cleaning mediainclude all organic solvents, open flames,abrasives and direct pressurized steamcleaning.

PLEASE NOTE: The total inspection process of the airsprings on your vehicle can be performed in a matterof minutes. If any of the conditions described on theprevious page exists, please take corrective action toensure that your air springs will perform properly. Itwill save you both time and money in the long run.

79

SUGGESTED READING

SAE Information Report, First Edition, June 1988, SAE HS 1576, Manual forIncorporating Pneumatic Springs in Vehicle Suspension Designs (Warrendale, PA:Society of Automotive Engineers, Inc., 1988).

Thomas D. Gillespie, Fundamentals of Vehicle Dynamics (Warrendale, PA: Society ofAutomotive Engineers, Inc., 1992).

Robert K. Vierck, Vibration Analysis, 2nd ed. (New York: Harper & Row, 1979).

HISTORY

In the early 1930's, the Firestone Tireand Rubber Company began experimentsto develop the potential of pneumaticsprings.Between 1935 and 1939, several makes

of U.S. automobiles were equipped withair springs and extensively tested to provethe potential of automotive air suspensionsystems. They were never put into pro-duction, however, because significantdevelopments in steel spring design gavean improved ride at much lower cost thanthe ar spring system at that time.

In 1938, the country's largest manufac-turer of motor coaches became interestedin using air springs on a new design busthey were developing. Working withFirestone engineers, the first busses weretested in 1944 and the inherent ride supe-riority of air suspensions was clearlydocumented.

In the early 1950"s, after several yearsof intensive product development, the airsprung bus finally went into production.That was the beginning of the Airide(R) airspring success story.The success of air springs in bus appl-

cations spurred new interest n truck andtrailer applications as well as ndustralshock and vbrafion solaton uses. Con-sequently, almost all of the busses, mostof the Class 8 trucks and many of thetrailers on the road today now rde on arsprings, and sgnficant advances n thedesign of control systems have openedthe door to automotive applications aswell.

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