Run-Flats forpeople Mover Systems F.R. Grimaldi Hutchinson Industries, 460 Southhard Street,

Transcription

1 Run-Flats forpeople Mover Systems F.R. Grimaldi Hutchinson Industries, 460 Southhard Street, infl, net Abstract Run-Flat systems are mounted within a pneumatic tire and are designed to allow the vehicle, on to which the tire is fitted, the ability to continue operation at a reduced speed For people mover systems this prevents disruption of service and damage to the guideway and provides the convenience of being able to repair the tire at the central maintenance facility and, most importantly, it provides passenger safety. Different types of flat prevention products and Run-Flat systems are available These include, tires with foam or polyurethanefill,solid press-on tires and the various central support Run-Flat systems made from aluminum, rubber or a elastomer composite. The advantages and disadvantages of each type are discussed in this paper. 1 Introduction Hutchinson S.A. is the sponsor of this paper. Hutchinson is an affiliate of Total Petroleum, with its European headquarters outside of Paris and its USA headquarters in Trenton, NJ.. Hutchinson produces a broad array of products for the worldwide automotive industry Among the products that it produces are several variations of a device, genetically referred to as a central support Run-Flat system Simply stated, it may be described as a solid wheel that is placed within a pneumatic tire. Its purpose is to allow the tire to function, on a limited basis, if the tire should loose its air due to minor damage Run-Flats are an item that will hopefully never be used but are there for valuable protection should the need occur. The various Run- Flat system designs currently available are the subject of this paper These three primary points will be expanded upon: The advantages of pneumatic tires for people mover systems # Advantages of having a Run-Flat installed into the vehicle's tires The types of Run-Flat devices designed to cope with a damaged and deflated tire and the advantages and disadvantages of each

2 512 Urban Transport and the Environment for the 21st Century 2 Pneumatic Tires For People Mover Systems The name "People Mover Systems" covers many types of public transit systems. These include light rail, operator controlled and automated people movers (APM) of both the straddle and suspended types, usually called monorails, as well as personal rapid transit (PRT) vehicles. If wheels, rather than magnetic levitation, are chosen to support and to transport the vehicles then there are only two choices: steel wheels or pneumatic rubber tires. Steel wheels become thefirstchoice when: the loads are high (greater than-8,500 kg per wheel) speeds are high (greater than -120 km/hr, with exceptions) Steel wheels offer the distinct advantage of being able to perform their function at the extreme levels of load and speed. That is to say that they will allow a very heavy train to travel at a very fast speed to a very distant destination with little or no concern about the ability of the steel wheels to perform. However, there is a price to pay... the high cost of the track bed the need for both a primary and a secondary suspension the high cost of the wheel bogie Passenger discomfort due to the noise of the steel wheels rolling over steel track and the squeal associated with braking require long headways due to poor wheel-to-track traction Pneumatic tires are usually thefirstchoice when the extremes of load and speed are not required. This would be the case with the smaller suspended or straddle types of APMs or PRTs. These smaller systems are designed to alleviate traffic congestion in major cities or to provide convenience for people at airports, amusement parks, and other high populous sites. Pneumatic tires offer the following advantages: smooth ride low initial cost low noise levels low replacement cost better traction for faster acceleration and deceleration But they do have a major disadvantage... THEY DO GO FLAT III

3 Urban Transport and the Environment for the 21st Century Advantages of Run-Flats With a well designed Run-Flat system installed in the vehicle's tires, the people mover system will be able to utilize all of the benefits of an air filled pneumatic tire. At the same time, it will be able to cope with the consequences and inconveniences of a deflated tire. The advantages applicable to all Run-Flat systems are: enhanced passenger safety and comfort allow the transport of people to a safe location for debarkation in the event of a tire deflation between stations prevention of a system shutdown in the event of a tire deflation and allows the vehicle to continue operation at a reduced speed minimizes damage to the vehicle and guideway and allows emergency tire repairs to be performed at the central maintenance facility tire pressure monitors, if included in the system, will eliminate regular scheduled pressure checks and warn of an impending tire deflation due to a minor damage 4 Solid and Filled Tires, Run-Flat Devices, and Pressure Monitors There are two categories of devices that will either eliminate tire deflations or allow a damaged and deflated tire to operate. These are: 4.1 Solids 4.11 pneumatic tire with foam or gel fill 4.12 solid press-on tires 4.2 Central Support Run-Flats used with airfilledtires 4.21 metallic central support system (fixed) - made bymichelin 4.22 rubber central support system (fixed) - made byhutchinson 4.23 composite central support system (rotates) - made by Hutchinson Although solid tires provide certain advantages (discussed below) there is an inherent problem with high heat generation. This limits their usefulness to light loads and slow speeds or to only intermittent high load and speed conditions. Airfilledpneumatic tires used with a central support Run-Flat system do not loose their performance capabilities. Being airfilledthey operate at the cooler design temperatures. 4.3 Pressure Monitors (see description below)

4 514 Urban Transport and the Environment for the 21st Century 5 General Descriptions 5.1 Foam or Gel Fill This protection method utilizes a standard pneumatic tire in which the air is replaced with a foam polymer or a polyurethane gel material. Both products are designed to prevent a tire deflation. These materials have found some limited success when used with guide or steer tires, but are generally unsuccessful with load tires. Figure 1 Advantages maintenance free not affected by minor damage Foam or Gel Fill Disadvantages high heat generation limiting load and speed capabilities negatively affects ride comfort non-transferable from tire to tire, and therefore expensive over time w/ new tire replacements heavy weight requires special equipment for installation 5.2 Solid Press-on Tires Solid press-on tires, designed with an appropriate rubber or polyurethane compound, are proving to be suitable for the guide wheel position in certain monorail applications. If the average loads are low and the peak loads are of short duration, the solid tire may prove to be a successful and low cost substitute for pneumatic tires. New designs are under development that will allow solid and pneumatic tires to be interchangeable on a given hub and wheel bogie without major vehicle redesign. Figure 2

5 Urban Transport and the Environment for the 21st Century 515 # # Advantages low cost relative to all other systems (tire & wheel included) maintenance free not affected by minor damage Solid Press-on Tires Disadvantages high heat generation limiting load and speed capabilities negatively affects ride comfort 5.3 Metallic Central Support Run-Flat - Fixed Figure 3 This design utilizes an aluminum alloy metallic insert that is roughly in the shape of a rolled "I" beam. It fits in a rubber channel, at its base, is centered and spans the distance between the beads. It is a fixed design that is clamped to and rotates synchronously with the wheel. Metallic Central Support Run-Flat - Fixed Advantages does not affect ride, handling or wear characteristics of the tire transferable from tire to tire durable reusable (within limits) a proven design Disadvantages requires special take-apart wheels very expensive when price of wheel and Run-Flat is considered as a single unit sold as an proprietary assembly only design not easily adaptable to production change (e.g. not able to customize diameter to control ride height in deflated mode) difficult to install requires lubricant to promote slippage between tire interior and Run-Flat, (see note following 5.5 Composite Run- Flat below)

6 516 Urban Transport and the Environment for the 21st Century 5.4 Rubber Central Support System - Fixed Figure 4 This design material is rubber which is shaped to fit a specific tire and wheel combination. The width at the base is greater than the distance between the beads, thus creating an interference fit that locks the Run-Flat to the tire and wheel. It rotates at the same speed as the wheel in the deflated mode. The rubber Run-Flat was originally designed for military vehicles in which the requirements for runflat performance are demanding and crucial The rubber Run-Flat performs well and may surpass the load, distance or speed capabilities of the other designs Rubber Central Support System - Fixed Advantages does not affectride,handling or wear characteristics of the tire design is adaptable to production changes (e.g. able to customize diameter to control ride height in deflated mode) can be mounted on standard flat base and take-apart rims low to moderately priced when fitted on standard flat base or take-apart rims may be used with all tire and wheel brands transferable from tire to tire reusable (within limits) durable easy to install with special tools a proven design with many years of successful military service one piece design w/o metal connectors Disadvantages special tools are required for mounting requires lubricant to promote slippage between tire interior and Run-Flat.

7 Urban Transport and the Environment for the 21st Century Composite Central Support System -Rotates Figure 5 This design concept is unique in the fact that it can be fitted on low cost standard production tubeless wheels. It features a roller and a runner design in which the runner clamps to the rim and allows the roller to rotate independently of the wheel and tire. This system and other composite nonrotating types are used on high security vehicles such as armored cars, VIP limousines and on people mover systems. This system offers the best combination of benefits for general use with people mover systems. Composite Central Support System - Rotates Advantages May be mounted on nearly all standard drop center or flat base rims inexpensive when the Run-Flat and wheel are considered as a single unit design is easily adaptable to production changes (e.g. able to customize diameter to control ride height in deflated mode) does not affect ride, handling or wear characteristics of the tire may be used with all tire and wheel brands durable transferable from tire to tire reusable (within limits) may be installed with std. tools does not require any additional lubricant in the tire a proven design with many years of successful service Disadvantages moderately difficult to install training required for mounting

8 518 Urban Transport and the Environment for the 21st Century te: How does a Run-Flat work? In normal tire operation (inflated mode) the distance covered by one tire revolution is determined by the tire's circumference. In the deflated mode it is the "Run-Flat's circumference which determines the distance covered. Being smaller, the distance is less. However, the tire's circumference is fixed as is the distance it will travel in one revolution. Here-in lays the challenge! Without corrective measures the high level of frictional heat would quickly destroy the tire. The roller/runner design addresses this challenge by allowing the roller to operate independently of the fixed runner and, while in the deflated mode, at the same circumferential speed as the tire. Frictional heat at the interface is dramatically reduced. The fixed metallic and rubber designs utilizes a high temperature lubricant that is placed at the interface of the Run-Flat and the crown of the tire. This lubricant allows the Run-Flat to slide on the tire's crown thereby reducing friction and tire destroying heat. Some History... Run-Flat systems were originally developed for military tactical vehicles for both the USA and NATO forces. The consequences of a tire deflation in a military scenario can be life threating. A need for a system that would allow the vehicle, its load and its passengers, the ability to escape to a safe location is mandatory. Hutchinson took up this challenge and became the technology leader with the introduction of the VPPV and later the VFI rubber Run-flats. These systems meet the stringent Finabel performance requirements and the US Army requirement of 30 miles at 30 MPH. The experience and knowledge gained with the military has led to the development of Run-Flat systems for people mover systems and other vehicles in which the ability to continued operation with a deflated tire is crucial to the safety of the vehicle's occupants. The development and marketing of Run-Flat products is controlled by Hutchinson - USA.

9 Table 1 Parameter Is a special wheel required? Can Run-Flat be customized to control ride height in a deflated mode, to fit specific tires/wheels and meet varying runflat performance requirements? Transferable from tire to tire? Reusable? Changes operating temperature or ride & handling characteristics of tire? Requires special tools? Installation difficulty? Is additional lubricant required? Price including wheel? Summary of Advantages and Disadvantages Foam or Gel Fill Difficult Moderate (costs reoccur w/ new tire) Solid presson tire Very Low assembly price Metallic Run-Flat Moderate Very High Rubber Run-Flat (may use w/.flat base & std. takeapart rims) Easy w/spc. tools Moderate (w/ standard flat base wheel Composite Run-Flat (may use w/ std. drop center & flat base rims) Moderate Low cr P e* P ts P t* CL o> tfl e o e* CD 3 t* CD N> c/> r-*-

10 520 Urban Transport and the Environment for the 21st Century 6 Pressure Monitors Pressure monitors will provide significant benefits for the operators of people mover systems. A pressure monitor, unlike a low pressure warning device, continuously monitors tire air pressure as well as the temperature of the contained air. Transmitters that are located within the tire send information to a receiver that is generally mounted within the vehicle. The receiver may be interfaced with a central computer thus providing the information in the most useful format. In a effort to conserve battery power the signal is transmitted at vehicle speed of 16 km/hr or greater. Under these conditions the useful battery life is projected to last 160,000 km. With this information, the operator will benefit in the following ways: eliminates, or at least reduces, regular tire pressure maintenance warns of an impending deflation that is the result of minor tire damage thus allowing repair and the likely prevention of a total tire destruction by maintaining correct tire pressure the tire's life is extended with correct pressure the tire's rolling resistance is reduced thus reducing the vehicle's propulsive power consumption increases the useful life of the Run-Flat system te: Pressure Monitors and Low Pressure Warning Systems are available through Hutchinson and other manufactures.