Home

Spicer® Tire Pressure Control

1. change until you are comfortable with the rate at which they are losing effectiveness Operators should also be instructed to drain the vehicle supply tank from which the system draws its supply completely every night Any water observed coming from the tank while draining deserves to be looked into as a properly working air dryer will not allow water into the air tank during a working day Manual drain valves should be installed which do not require the operator to stand by the truck while the tank is depleted to zero psi as even air from a properly working air System contains sufficient moisture to condense in the tank during overnight drops in ambient temperature For spec ing or service assistance call 1 877 777 5360 or visit our website at www dana com Dana Commercial Vehicle Products Group 3939 Technology Drive d Maumee Ohio USA 43537 DANA SPICER Drivetrain Products www dana com All applications must be approved by the Application Engineering Department Specifications and or design are subject to change without notice or obligation Printed in USA AXSL 0012 12 99
2. get to the tires Air is routed to the tires via air seals which have been installed in the axles Two approaches are used one for non driven axles steers and trailers or tag axles and another for drive axles Air is routed through the center of non driven axles and through a rotary joint which is mounted on the end of the spindle Driven axles utilize a patented air sleeve in conjunction with a special hub Once the air is passed through the hub or hub cap it is connected through the wheel valve to the rim with an air hose It is impor tant to remember that wheels and hubs need to be positioned properly relative to each other to assure proper fit of the hoses to the valve stems Failure to do so may result in stress on the hose or valve stem that can result in air leakage and improper operation If an air line ruptures do lose all of the air in the system The Spicer Tire Pressure Control System utilizes wheel valves to assure that air is not ost from the system in the event of air line breakage Air pressure only exists in the control lines of the system when measuring inflating or deflating the tires Only the hoses between the tires and the wheel valves are normally pressurized Failure of a control ine is sensed by the system and the affected channel is shut down and the operator notified through a service message This depressurized operation also guarantees that tires will not leak down through the air seals while th
3. highway pressure settings Channel Off Hwy Highway Increase Steers 70 90 20 Drives 55 90 35 Trailers 50 90 40 The analysis would be as follows Steer Channel 2x4 5 13 2 X 20 14 7 9 minutes Drive Channel 8x4 5 13 2 X 35 14 7 6 5 minutes Trailer Channel 1 6x4 5 13 2 X 40 147 7 4 minutes Total Time 94654742148 min This analysis is only an approximation It does not take into account several major factors such as compressor efficiency which will change over time or engine speed infla tion time can be improved by downshifting until highway pressures are achieved or numerous minor factors such as atmospher ic variables or the compressibility factor of air It should suffice however to guide one through the task of compressor selection The use of turbo charged compressors can result in inflation times that improve as engine oads are increased only up to the limit of the systems ability to use the air approximately 20 SCFM but this improvement should be weighed against its impact on compressor life and overall vehicle air system design Too much air can be detrimental to system 4 performance as the excessive compressor temperatures generated can result in a higher level of contamination oil blow by and reduced air dryer effectiveness possibly requiring the use of additional means to cool the air such as condensers and heat exchangers How does one diagnose servic
4. mount the wheel valves to provide a neat package for Steer axles Since the hub cap section is not uniform the apparent oil level in the wheel end will vary depending on the position of the hub cap when the vehicle is stopped The addition of oil to the wheel end should always be done through the fill plug in the side of the hub cap not the vent plug in the window since the lines on the window are the appropriate oil level only when the fill plug is at 12 o clock Adding lubricant to the lines with the fill plug in any other position may result in an over filled condition and oil will likely leak past the low pressure vent plug resulting in an unsightly leak Furthermore water or detergent spray should never be directed at the vent plug as it can get past the plug and enter the hub cap contaminating the oil and reducing wheel end life Oil should be exam ined frequently for such contamination and be changed if any oil discoloration is found Many applications for Tire Pressure Control are severe duty applications which demand routine wheel end inspection of bearings on an annual or semi annual basis You should always follow the manufacturers recommen dations for wheel end service Drive Axle Wheel Ends While the addition of air seals into the drive axle hubs does not create any unique requirements for maintenance of the wheel end it does make adherence to current recommended mainte nance practices more important to assur
5. port which connects it to the tire These filters are intended to trap contaminants contained in the tire and prevent them from entering the wheel valves and should be changed at any time the tire is removed either for rotation or replacement Service technicians must be careful not to damage the filter by installing adjustable fittings too deeply into the tire port To do so will crush the filter and possibly tear it Instructions in the service manual should be followed closely Care must also be taken to prevent contaminant entry any time control air lines are disconnected Trailer couplings are especially critical as they may frequently be disconnected with the trailer For this reason Spicer recommends the use of an in line air filter in the trailer line to prevent contamina tion from entering the coupling and traveling to the trailer wheel valves It is also important to blow any debris from hoses tubing and fittings when servicing the vehicle Instances have been encountered wherein hose slivers from the initial installation have been trapped in the system causing problems later What is the minimum temperature for operation The Spicer Tire Pressure Control System has been developed using the same industry standards for operation to 40 degrees as most vehicle components Operation at tem peratures below that is possible however some service codes may be encountered under extremely cold conditions which may
6. Second the system monitors itself to assure that deflation can proceed reliably and deflation may be delayed while the system assures that all deflation parameters are properly met Finally to assure that tire pressures are balanced following a deflation sequence Spicer Tire Pressure Controls are programmed to go through a short reinflation period to bring all pressures within the proper limits Inflation times are affected by even more factors primarily related to overall tire volume and compressor output The Spicer Tire Pressure Control System has been designed to work on a wide range of trucks and truck configurations and as such will work with most any compressor output presuming the compressor is in good operating condition The issue of inflation time requirements deserves some discussion Over the past ten years numerous test results have been docu mented which show that the use of on board controls to adjust tire pressures does not reduce tire life Tire manufacturers have suggested that tire durability will not be compromised as long as inflation capability is Sufficient to inflate tires to 75 of the rec ommended cold highway pressure within 15 minutes of achieving highway speed and 100 in 25 minutes This guideline can lead the person spec ing the vehicle to an approxi mation of required compressor capacity using the simple analysis below Dana urges those who are considering the use of Tire Pressure Control t
7. Spicer Tire Pressure Control Questions and Answers About Reduced Pressure Operation and Spicer Tire Pressure Control Is the use of reduced tire pressures approved by the tire manufacturers The tire manufacturers have approved operation at reduced pressures when lim iting the vehicle speeds Their industry group The Tire and Rim Association T amp RA has published guidelines which outline the tire sizes loads and pressures to apply this technology While major manufacturers have monitored or taken part in numerous studies to determine the safety and efficacy of reduced pressure operation most tire distributors are either unaware of the work or are inexperienced in applying the guidelines Over time and with increasing popularity of tire pressure controlling systems the awareness of the tire industry in the field will grow Does low pressure work only in sand How about mud clay snow and ice Reduced tire pressure enhances the mobility of vehicles through two different mechanisms flotation and traction In both cases it is the longer footprint asso ciated with reduced pressure operation that brings about the improvement A steel belted radial tire does not increase the width of the rubber in contact with the ground as frequently thought To understand the concept of flotation as it relates to land vehicles one should consider the similarity to a water borne vessel Just as a loaded ship displaces water and p
8. b cap using a rotary joint on non driven axles to simplify installation and improve reliability Introduction of diagnostic tools using either industry standard devices or personal computers simplifying troubleshooting and repair Publication of troubleshooting and service manuals as well as driver instructions and in cab aids to improve driver understanding of systems Wheel valve design improvements to increase system reliability with longer trailer combinations and reduce sensitivity to control system leaks Pneumatic controls design changes to reduce sensitivity to control system leaks ntroduction of new steer axle products up to 14 600 Ibs capacity to improve routing of air to steer wheel ends Does Spicer TPCS fit Meritor drives Which ones How about others Spicer drive axle air seal hardware was developed to fit on the Spicer R spindle configuration Dana uses this spindle on sin gle axles between 21 000 and 26 000 Ibs capacity and on tandems from 40 000 through 52 000 Ibs capacity The R config uration meets industry standards for fitment of wheel end hardware hubs bearings seals etc however individual axle manufacturers have latitude outside of the specific dimen sions for the bearings and the seals to accommodate manufacturing processes and other considerations Historically the Meritor R configuration has differed from the Spicer configuration specifi cally in th
9. disappear when either the component warms up under use or from increasing ambient temperatures These may include codes related to temperature induced leakages as extremely cold temperatures will cause materials to shrink and reduce the effective ness of sealing Dana recommends that the pneumatic control unit be placed in the cab herever cold weather is encountered so that cab heat can assist in warming the unit to enable operation While system operation is possible at low emperatures the primary reason for prob lems at temperatures below freezing is not with the system components but with the effectiveness and maintenance of air drying equipment Extremely cold air has very little moisture in it while warm air can hold tremendous amounts In fact at 80 F 27 C atmospheric air can hold almost 50 times more water than at 13 F 25 C Failure to monitor and maintain the air system during warmer months will result in entrained moisture in the air tanks and sys tem components that are certain to cause problems as temperatures fall Failure to rou tinely drain air tanks can result in whole water passing from the tanks through the system and even into the tires where it can inhibit the systems ability to deflate even at tempera tures of 65 F 18 C Although the Spicer System minimizes the possibility of con densed water in the controls and the tires whole water can only be controlled by posi tiv
10. e items for TPCS The Spicer TPCS wiring harness includes a connector which meets industry standard requirements for connection to modern diagnostic tools The interface is fully compatible with other vehicle systems to also allow connection through a central OEM supplied connector interface Both hand held tools such as those from MPSI and personal computers may be used Use of a personal computer requires the purchase of a serial interface connector such as Kent Moore part umber J38351 or B amp B Electronics part number 232ESAER to make the connection By plugging the tool connector into the TPCS diagnostic connector the technician can do a complete diagnostic analysis of the system including retrieval of historic service codes Diagnostic software discs are available for System users at no charge from Dana Spicer Heavy Axle and Brake Division How does the Spicer System detect tire imbalances and low tires The Spicer Tire Pressure Control System uses sophisticated microcomputer technolo gy and has extraordinary capability to analyze information Dana engineers have developed algorithms for the System which critically evaluate many details of operation Much of this evaluation is done in the short period of time between initiation of a pressure check or selection of a new pressure mode and the decision to proceed with a change of pressure The System evaluates the pneumatic signa ture from the time of t
11. e the best life from the seals Wheel bearing adjustment is just as important to good air seal life as it is to good oil seal life Improper adjustment allows excessive play and runout in the seal and results in reduced seal performance Always follow the recommended practices of the axle supplier and The Maintenance Council of the American Trucking Associations to assure Satisfactory performance It is very important that seals which are performing properly not be disturbed unnecessarily during routine maintenance for brakes or other wheel end repairs The wheel end equipment utilizes an outboard mounted brake drum design so that brake repairs can be made without disturbing the hub Removal of the wheels with the hub and brake drum as a unit is not recommended and may necessi tate replacement of all seals both air and oil Even if these seals are to be replaced proper installation will be extremely difficult with the wheels and drums attached to the hub with a higher likelinood of damage to the seal The specification of hub piloted wheel designs allows the removal of dual wheels with only ten fasteners avoiding the additional labor requirements of older stud piloted designs Removal and replacement of drive axle hubs will also demand addition of lube through the hub lube fill hole to assure sufficient wheel end lubrication to the inner bearing This lubrication must be added after the axle shafts but before the w
12. e tire management businesses in 1999 Over 35 000 systems have been provided since 1987 to numerous military and and commercial programs These systems are fielded worldwide and were proven in Operation Desert Storm as a vital element of tactical wheeled vehicle mobility Several important features account for the success of the product among them Depressurized control line strategy which extends seal life eliminates tire leakdown when parked and provides fail safe operating capability Speed sensing to assure that tires are not operated continuously at cross country pressures when traveling at highway speeds Simple push button operation using pre set terrain based pressure modes Electronic pressure supply sensing to assure proper integration with brake and other on board air systems The Spicer Tire Pressure Control System was introduced to the commercial market in 1994 It is presently available from Kenworth Western Star Volvo Mack and Peterbilt Dana continues to work toward wider availability of the system Tire Pressure Control was created by building on the same technology used successfully in the military systems The following list represents some of the many enhancements that have been integrated into the commercial version Multiple channel operation allowing the independent control of pressures on steer drive and trailer tires Integration of the wheel valve into the hu
13. e vehicle is parked even for extended periods How do the wheel valves work Can they malfunction The wheel valve is an essential part of the Spicer System which improves overall sys tem safety and reliability by allowing control lines to be depressurized unless actually inflating deflating or measuring tire pres sures It is an extremely simple device con sisting of spring loaded diaphragms biased against seats to contain air to the wheel end In the absence of a control signal the springs act against the diaphragms and seats to close the valve Positive pressure signals are used to measure and inflate tires negative pres sures are used to deflate As a result of the simple design the wheel valves possess an inherent high reliability even in the environment of a truck air system In fact similar diaphragm and spring con cepts are used in most of the valves used in a trucks today because of their high reliability and ability to tolerate wide temperature ranges and some level of contamination The biggest difference between the Spicer Tire Pressure Control System and other systems used on the truck is in the volume of air used Since inflating tires uses a large volume of air possibilities of contamination are greater Contamination is the largest single reason for wheel valve malfunction Measures must be taken to prevent contamination from entering the system Each wheel valve includes a filter in the
14. e width of the outer bearing journal It is Dana Corporations understanding that the spindle configuration of the Meritor prod uct was changed in 1999 to accommodate the hardware required to equip their axles with Spicer TPCS The hardware will also fit on spindles from some other axle manufac turers We have found that Mack tandems of 38 000 Ibs and 50 000 Ibs will accept the hardware without modification however their 44 000 Ib axles will not Dana will review axle spindle geometry from other manufactur ers at their request if they provide the necessary drawing information What pressure range can the system control pressures to The Spicer System can reduce pressures to as low as 25 psi and inflate to 90 psi Practically speaking 90 psi is the max cold tire pressure setting because of the air system limitations on most vehicles where the compressor Cut in is set to 90 psi It must be noted that although the cold setting is limited to 90 psi Spicer Tire Pressure Control allows unlimited pressure rises resulting from heat generated in the tire This is essential in that systems which do not allow unlimited pressure rises should rightfully have their pressures programmed to hot pressures which can be 15 higher than cold Tire pressures beyond 90 psi can be achieved however since the source pressure is very close to the tire pressure actual inflation will be extremely slow To say that any system can deliver pres
15. echnology to work closely with their tire supplier to obtain the informa tion needed about tire volumes and operating pressures as well as suggested inflation times for their application In simple terms inflation time can be approximated by dividing the internal volume of the tires by the compressor output and multiplying the result by the amount of the desired pressure increase In order for this to work however all terms must have compati ble units tire volume in cubic feet ft compressor output in standard cubic feet per minute SCFM and pressure increase in atmospheres atm Atmospheres can be found by dividing the pressure increase in psi by 14 7 A formula for this can be expressed as Volume ft Output SCFM X Pressure Increase psi 14 7 psi Time min Since the Spicer Tire Pressure Control System allows the independent control of pressures on steer drive and trailer tire groups the times must be calculated for each of the channels and added together for a total time For example lets presume a typical 18 wheel tractor trailer combination with two tires on the steer channel and eight each on the drive and trailer axle groups an internal tire volume of 4 5 ff for each tire and a compressor output of 13 2 SCFM Typically compressor output is rated at a nominal engine output speed such as 1250 RPM Furthermore lets presume the following pressure increases between the off highway and
16. eel relative to the hub to assure that the new wheel is installed in proper position to reconnect the hoses when complete Prior to removing the tire he must disconnect the air lines and plug or cap them if the tire is still pressurized as there are no valve cores in the stem of a TPCS controlled wheel A smooth 6 jawed locking plier or other tool may be used to temporarily crimp the hose After putting the new tire in position the hoses must be replaced and properly restrained to prevent damage While inflating following comple tion of a tire change the system may display a check tire icon indicating that air in one tire is lower than others on the channel This indication should clear after the system is used to inflate the tires Is the system reliable in sandy and or dusty environments The Spicer Tire Pressure Control System uses many of the same operating principles of the Spicer Central Tire Inflation System which was so successful in Operation Desert Storm Over 5 000 systems were fielded in that effort without any reported failures The desert terrain of Saudi Arabia and Kuwait and Iraq represents some of the harshest conditions in the world The commercial sys tem has been tested across the United States in wide ranging environments for over 1 5 million miles prior to production What is the maintenance impact of adding a system to my truck Several items should be looked at from a maintenance per
17. ely draining all water which has condensed from the tanks Proper preventative mainte nance demands draining all tanks to zero pressure whenever the truck is to be left unused for an extended period Does a standard truck air compressor satisfy the requirements for TPC Air compressor output capacity requirements are determined by factors such as the total internal volume of the tires being controlled and the pressure range over which one is operating the tires While in some cases a manufacturer s standard compressor may be appropriate it will not be in others Specifying too much air capacity can also be harmful by causing additional heat which results in oil consumption that will contami nate the system Owners dealers and manu facturers will need to consider the application when specifying the compressor Manufacturers will also need to work with compressor and air dryer suppliers to assure the factory installed air system will meet the needs of the user Compressor and dryer manufacturers may have established specific installation requirements for the use of their products with high air usage systems such as Spicer Tire Pressure Control Is it more difficult to change tires on a TPCS equipped truck Tire changes on a TPCS equipped truck will require additional steps which although not difficult will add to the amount of work required The technician will need to take care and note or mark the location of the wh
18. es above governor cut in come at the expense of high brake reserve pressures Dana considers high vehicle brak ing reserve pressures an essential element of vehicle safety and therefore prefers to use the margins between governor cut in and cut out to assure maintenance of these reserve pressure levels Dana feels that any strategy which reduces the average braking reserve levels or substantially increases the time required to achieve those levels violates the intent and spirit of regulations such as FMVSS 121 How long does it take for inflation and deflation Any discussion of inflation and deflation times must consider many factors such as tire volumes pressure settings and compres Sor capacities to adequately address the issue One must also distinguish between the time required to change the pressure in a given group of tires and the time required for a system to signal that a pressure changing operation has been completed For example the Spicer Tire Pressure Control System can through its wheel valve reduce the pressure in a 11R24 5 dual set from 90 psi to 45 psi a 3 atmosphere reduc tion in approximately 2 minutes but the sys tem may indicate that the operation has not been completed for more than three minutes Several factors may influence this time First the system checks to assure that brake pres sure reserves are maintained and may sus pend operations which change pressures to give this first priority
19. essure checks to 15 seconds and thereby use the system to keep the tire inflated If the tire damage is sig nificant the system will not be able to keep up with the leak and a 9P or 10 P code may result In this event the vehicle may require immediate tire repair It is important to note that tire damage is not always readily visible and that operators should use care in deter mining the extent of tire damage The only reliable way to determine which tire is low is to use a pressure gage and inspect any tire which measures low Frequently out of balance tire pressure con ditions occur on start up after the vehicle has been idle for extended periods such as weekends as a result of slow leaks in the tire and wheel assembly The system can help to identify these leaks early enough that the observant owner can have small leaks repaired before they become larger leaks which force downtime and limit retreadability It must also be noted that pneumatic control system leakage can mimic the pneumatic signature for an 11P code and result in false arms In this case the operator can use run flat to proceed however the system should be serviced as soon as possible since leaks will always get worse over time and eventually cause additional service messages and make diagnosis and repair more difficult The use of service diagnostic tools will greatly simpli fy the identification and repair of leaks o How does the air
20. he wheel valve opening pulse to the time of the actual pressure read ing During this period approximately two seconds the pneumatic response of the System is compared to acceptable responses stored in the memory of the controller If the response merely indicates that the pressure of a given channel is low inflation will be initiat ed If the response indicates that pressure is higher than that requested a deflation will be commanded Other responses may indicate something less than acceptable readiness for the change of tire pressure and trigger a service code so the driver can evaluate how best to proceed The signature analysis technique allows the system to detect if one tire is significantly out of balance from the others in the same axle group Parameters for the low tire detection have been established to trigger the check tire icon when the pressure in one wheel end of a channel group is approximately 50 or less than the others in the group Since such a loss of pressure could have occurred over the 5 to 15 minute pressure check inter val a substantial tire leak could be indicated and therefore the driver may also see an 11 P code indicated after the completion of a pres sure changing sequence The driver should physically inspect the tires on the affected axle group for possible leaks or damage before proceeding If a tire puncture is found the driver may select the run flat key to reduce the interval of tire pr
21. heels are installed Vehicle Air System A final area demanding additional maintenance attention is the vehi cle air system including the compressor and the dryer The adjustment of tire pressures requires the use of far more air than normal where air is used primarily for braking Increases in both compressor duty cycle percent on time and continuous on time make the load on the air system far more severe and demanding of special attention As the actual air system impact is strongly dependent on the application i e how fre quently the tire pressure system is being used to adjust pressures it is not possible to predict with certainty how often a particular fleet or owner will need to service the com pressor and air dryer but it is essential for users to determine a maintenance cycle that works for their application While getting acquainted with the use of Tire Pressure Control in your operation you should pay particular attention to the air dryer to determine a proper service interval for you Initially a daily look at the discharge from the dryer will tell you if the system is working properly Oil or any discharge other than water is cause for investigation and correc tion Maintenance personnel should also be checking air dryer cartridges and the air supply tank for signs of contamination monthly until the first replacement is necessary and then checking cartridges at an interval half way to the period of the first
22. in their opera tion Manual reduction of tire pressure and reduced speed operation until tires can be re inflated will allow most users to prove the benefits to themselves with a minimal invest ment in time or money It should also be Stated that the use of reduced tire pressure will not prevent one from ever becoming stuck again especially when you consider the prospects that you will be operating in places where you may not have been previous to using lower pressures How are tire pressure settings developed Tire pressures have been developed to pro vide the sidewall deflections appropriate for various tire sizes Of course one must remember that reduced operating speeds are required to use these reduced pressures Generally tire manufacturers specify on high way tire pressures to achieve sidewall deflec tions of 10 13 These pressures allow operating speeds up the tire design limit Off highway deflections are typically 20 22 and limit vehicle speeds to 35 mph Emergency pressure settings may go to 30 deflection with a typical speed limit of 10 mph The vehicle owner should always select tire pressures with the assistance of their tire supplier The Tire and Rim Association has developed reduced pressure and speed charts to assist in selection of tire pressures When did Dana start making tire inflation systems Dana is the world s leading provider of central tire inflation systems having acquired th
23. of 6096 have been demonstrated solely through the reduction of tire pressures on a vehicle in a 6x4 configuration When reduced tire pressure is combined with all wheel drive improvements of over 10096 are readily achievable The combination of improved flotation and traction results in the possibility of tremendous improvements in overall mobility While these improvements are most striking in coarse grained soils such as sand improvements are also measur able on other soils such as clay and muskeg In simplest terms if operation of a vehicle results in surface penetration by the tires reduced tire pressures and the resulting improved flotation may help If the surface is hard but slippery reduced pressures should not have a significant effect since friction is the dominant limiter to mobility Uneven terrain should also be consid ered Reduction in tire pressure will result in a loss of ground clearance If operating in areas with deep ruts high center crowns or sharp break overs this can become an important issue It can also be noted how ever that higher nominal speed capability stemming from the improved ride and control when traveling cross country at reduced pressures may allow the operator to traverse some obstacles that could not be crossed at lower speeds Customers should be reminded that one need not actually install a tire pressure adjustment system on their vehicle to determine if reduced pressures will work
24. spective when using vehicles equipped with Spicer Tire Pressure Control Wheel Valve Filters The first item is the wheel valve filters Filters are included in each wheel valve in the air connection to the tire hose This filter traps debris from the tire and helps to assure reliable wheel valve opera tion Even tires which were clean during mounting have been found to have loose debris in them after many hours of operation and it is important that this debris not get into the wheel valve Dana recommends that these filters be changed whenever tires are rotated or replaced Since it is difficult to determine how long it takes for this tire dirt to develop your application may demand more frequent changing Tires which deflate to uneven pres sures within the same axle group would be a reason to look at changing the filters Non driven Wheel End Lubrication Another item is the area of wheel end lubrication for non driven wheel ends such as steers and trailers In order to deliver air to a tire a system must route air through the wheel end via a rotary joint inside the hub cap If air were to leak from this rotary joint and pres surize the wheel end the main inboard oil seal could be damaged or displaced The Spicer Tire Pressure Control System utilizes a special plug in the center of the hub cap window which vents easily to make build up of pressure in the wheel end unlikely and the hub cap itself has been designed to
25. sures higher than 90 psi without consideration of this fact is somewhat misleading Realistically higher tire pressures will require that the truck air system pressure be increased to 145 150 psi and that pressure reducing devices be installed for vehicle braking and other systems Another detail which is important to note involves the physics of moisture control Spicer Tire Pressure Controls utilize an oper ating regime which minimizes the possibility of moisture accumulating in the tires by forcing all of the air to be compressed to a level higher than that to which the tires will be inflated Since all of the air going to the tires will be less than this peak pressure it will be even dryer than when it left the on board air dryer since it has been expanded Such a regime is critical for proper long term system operating reliability and keeping moisture out of the tires where it can have long term consequences Systems which do not use such a regime may appear to be working when they are not as they do not signal inability to change pressures to the operator Finally the issue of safety cannot be ignored The design of Dana s Tire Pressure Control demands that vehicle air brake reservoirs be brought to a high pressure level before any tire pressure checking or changing operation be allowed to begin not merely the minimum governor cut in level Other systems may be programmable to allow higher tire pressure settings but pressur
26. ushes a discernible bow wave in front of it a truck on a soft surface displaces the sand or soil and is forced to run essentially uphill as it moves a wave of sand in front of it By lengthening the footprint the force exert ed by the vehicle on the ground surface measured in pounds per square inch psi can be significantly reduced This reduction results in a lesser penetration of the surface by the tire similar to the reduction in draft of a ship as its load is diminished or the reduced penetration in snow of a person wearing snowshoes This improved flotation allows the vehicle to move about the surface with less disturbance to it A discussion of traction needs to consid er the difference between traction and friction Although friction is independent of area traction is very dependent on area A surface with limited friction will demonstrate tire slippage with much less effect on the surface the tire is slipping relative to the surface Limited traction will show wheel slippage but with resulting surface disturbance as the thrust generated by the tire overcomes the rr lt fana gt SPICER Drivetrain Products ability of the soil to resist it Since a longer footprint results in a more favor able distribution of shear forces in the surface the soil is less likely to be displaced by the torque of the rotating tire and increased traction results Traction increases as measured by drawbar pull

Spicer® Tire Pressure Control

Contents

Download Pdf Manuals

Related Search

Related Contents

Spicer&reg; Tire Pressure Control

Contents

Download Pdf Manuals

Related Search

Related Contents

Spicer® Tire Pressure Control