J2599-Stand-09-2001-Englisch.doc

draft sae j2599 fuel filler pipe assembly design practice to meet low evaporative emission requirements -draftfuel filler pipe assembly design practice to meet low evaporative emission requirementstable of contents page1) scope22) references23) abstract .24) sealability of the filler cap 35) construction of the filler pipe46) sealability of the filler pipe hose.67) sealability of the filler pipe to tank grommet118) emission testing of the pipe assembly.139) electrostatic discharge1510) fuel fill performance. 15.11) fuel filler pipe assembly integrity 1512) flammability. 1513) durability 1514) serviceability.171) scope:this sae recommended practice covers design and evaluation of the entire gasoline filler pipe assembly used on cars and light trucks with respect to compliance with carb (california air resources board) lev ii (meeting or exceeding epa tier 2 and eu stage-5 evaporative emissions requirements). it is limited to an assembly which is joined to the fuel tank using either a hose, quick connect coupling, or a grommet type sealing device. the design practice covers the filler cap, filler pipe, filler pipe assembly to tank hose, and filler pipe assembly to tank grommet or spud. it includes recommendations for design of components and assemblies intended to perform successfully in evaporative emission shed (sealed housing for evaporative determination) tests, based on best practices known at the time of release. 2) references:2.1 sae referencessae j1231sae j1508sae j1692sae j1645sae j1737sae jxxxx (helium leak testing standard)sae jyyyy (micro- s.h.e.d. testing standard)sae jzzzz (gravimetric permeation measurement techniques)sae j30r 6,7,8 (table 7 dimensions and tolerances for sae 30r6, 7, and 8)sae j2027sae j2236 sae j2044sae j2260sae technical paper series 2001-01-0730 estimating real time diurnal (rtd) permeation from constant temperature measurements2.1.1 applicable documentsu/l 746a california exhaust emission standards and test procedures for 2001 and subsequent model passenger cars, light-duty trucks, and medium-duty trucks (6-1-99 proposal)california evaporative emissions standards and test procedures for 2001 and subsequent model motor vehicles (6-1-99 proposal) federal register vol 58/ no 55) 3) abstract:design of clamped hose and elastomeric grommet sealed filler pipe joints is not an exact science; therefore, precise formulas and methods cannot accurately predict performance. however, theoretical and philosophical constructs based on empirical data and industry experience can be used to develop standard practices for evaluating automotive filler neck joining techniques compatible with lev ii evaporative emission demands.beyond the basic functionality of easily allowing the customer to transfer fuel from fuel dispensing nozzles to the fuel tank of the vehicle, four major design considerations of the filler neck assembly are:a) fuel system integrity/crashworthinessb) evaporative emission performance for 15 years / 150,000 milesc) prevent or minimize the buildup of electrostatic chargesd) ease of assembly, with force levels within accepted ergonomic limits.although this recommended practice primarily addresses compliance with evaporative emission regulations, the proposed ranking of these considerations is in the order listed above. fuel system integrity/crashworthiness is the most important concern and is so stated in the environmental regulations governing evaporative emissions.evaporative emission performance is the main topic for this document. because the carb lev-ii regulations for passenger cars have the strictest target (for high volume markets), we will focus on that specific subject here. to satisfy that carb regulation the filler pipe assembly must not add more than its allotted portion of the total hydrocarbon evaporative emission limit when exposed to the prescribed hot soak and diurnal shed test.as with crashworthiness, electrostatic discharge dissipation should not be under-rated based on its ranking. it was given this ranking based on the intent of this emission control oriented design guideline.ease of assembly, is an important design consideration due to increasing emphasis being given to ergonomics if the other requirements have been met there will be some minimum assembly force value that can be achieved. 4) sealability of the filler cap: the filler cap not only provides a seal to the filler neck, but also acts as an air induction device to allow outside air to enter the fuel system in the event that the fuel system pressure is below specification. the cap often also has the ability to act as a pressure relief in the event of an over pressurization of the system. in order to insure that lev ii evaporative emissions demands are met, attention must be paid to the three seals located in the cap, as well as the surface finish of the sealing area of the filler neck. illustration 1 shows the three seals and their corresponding sealing surfaces. these seals and their sealing surfaces must be smooth and free of defects just as the filler pipe hose sealing surfaces must. care must be taken that filler pipes fabricated from welded tubing do not allow weld seam defects in the cap-to-pipe sealing area.emission testing of the fuel filler cap through those areas shown in illustration 1 is accomplished in three stages. first the cap is tested to the defined customer specification with air to verify valve functionality. second the cap is helium leak tested using an appropriate hard vacuum or accumulation test method to verify seal integrity. finally the cap/neck assembly is micro shed tested.the test setup includes a fuel reservoir with drain/fill port capability of venting fuel vapor outside of shed during testing, and a representative or actual production fill pipe. the components of the system must be constructed with the fuel filler cap being at the highest point on the fuel reservoir in the shed. the recommended test fuel for preconditioning and testing is carb certified fuel and the preconditioning is done at a constant temperature of 40 c in a vapor environment for 21 days or until stabilization occurs. it is recommended to use a one hour constant temperature micro shed test at various time intervals to prove stabilization has been achieved. once stabilization has been proven, evaporative emissions are measured during a carb 24-hour diurnal shed test needs to be conducted and data taken for report out. cap to filler pipe seal areacap to filler pipe sealpressure relief seal (optional) outside air induction seal illustration 1fuel filler cap 5) construction of the filler pipe:the inner-diameter of the fuel fill pipe must be designed in such a way as to provide a liquid seal at 4-10 gallon per minute rate during the vehicle fueling process, while optimizing vapor management. the liquid seal prevents fuel vapors from escaping the fill neck assembly and being discharged to the atmosphere during refueling. vapor entrainment during fueling must also be a consideration. ingestion of excessive amounts of atmospheric air can reduce the effectiveness of the orvr (on board refueling vapor recovery) system.the filler pipe may be made of metallic or polymeric material. it may be a one-piece tube or an assembly as shown in illustration 2. permeation (see section 8) through the tube wall would not be an emission concern when a metallic filler pipe is employed, but must be considered when using a polymeric design. leakage is a concern at each joint of the assembly (see illustration 2) as well as at the filler pipe to hose and hose to tank spud joints. refueling emissions standards did not change for lev ii, and have been successfully met with various “l(fā)iquid seal” and “mechanical seal” designs. this technology is well established, and thus will not be included as part of this standard.evaporative emissions from a capped fuel filler can come from leaks between different components, and permeation through the materials used. there are a number of construction options for fuel fillers, but to achieve the best evaporative emission performance, it is preferable to minimize the number of leak paths and use the lowest permeation materials that still support the other functional requirements.the following sections provide evaporative emissions considerations for various fuel filler pipe construction options that may be specified for use on lev ii applications. assembly fmeas (failure mode and effect analysis) and design validation plans should address these points. helium leak detection (using pressures representative of what the component sees in-use) is a convenient method of quickly identifying any leak paths. mini- or micro-shed testing is the most effective way to measure the effect of both permeation and leak paths, but accurate data requires proper conditioning with fuel, which can take hundreds of hours for low permeation materials. for materials with known permeation rates at in-use conditions, an approximation of the components performance can be calculated using the exposed surface area and the length of the permeation path.5.1 metal fuel fillers (coated steel, stainless steel or aluminum) are typically zero-permeation, but may exhibit leak paths from rough surface finish (i.e. weld seam, tooling marks, coating flaws), corrosion or poor joints. forming the full length of the main tube from a single metal tube is preferred. coatings at the cap sealing surface must be robust against the chipping or scratching by pump nozzles during refueling that may create leak and corrosion concerns.5.2 plastic fuel fillers (multilayer blow-molded, or extruded/injection molded combinations) have some measurable permeation rate, so minimizing the fuel-exposed area is strongly recommended. although corrosion is typically not an issue, they carry over the requirements for smooth surface finish at sealing areas, and leak-free joints.5.3 fuel cap retainers may be integral with the tube forming the fuel filler, or a separate component. forming the means of cap retention (the “thread”) and the cap sealing surface in the expanded end of the tube is ideal because it minimizes the leak and permeation paths. separate retainers may be welded, crimped or snap-fit into place. the weld of a welded retainer (plastic or metal) that seals to the cap is a potential leak path. assemblies using crimped or snap-fit retainers require an elastomeric seal, which is itself a permeation and potential leak path. further, if the retainer itself is of a material permeable to hydrocarbons, its contribution must also be considered in the performance of the fuel filler assembly.5.4 recirculation tubes may be incorporated as a part of some lev ii fuel fillers to minimize the amount of fuel vapor the orvr system must contain, or as a means of including the fuel filler and cap during obd (on board diagnostics) ii leak tests. if not an integral part of the primary fuel filler tube, the joint of the recirculation tube to the primary fuel filler tube must be considered a potential leak path. at the opposite end, there are many alternatives for connecting the recirculation tube to the rest of the vapor system. typical connections may include a male end form for a quick connector (reference sae j2044), or a male end form for a tube or hose (reference section 6 of this standard). if a tube or hose is incorporated as part of the fuel filler assembly, its permeation rate and fuel-exposed area must be considered in the performance of the fuel filler assembly. any defective joint is a potential leak pathvapor recirculation tube(optional)sealing area flatness and finish (no radial leak paths) to accomplish adequate sealing energy and consistency filler pipecap thread formed into funnel or in insert. thread insert must form a leak proof assembly sealing area illustration 2filler neck6) sealability of the filler pipe hose; at their root, all elastomerically sealed joints are compression seals. in the case of hose connections the compression is achieved through dimensional interference between the hose and the pipe, and the force added by a hose clamp.6.1 interference:interference of the inside diameter of the hose (hose id illustration 3) to the sealing surface (tube dia. illustration 3) of the fitting is one of the most important criteria in designing a sealing system. there is a direct relationship between hose to fitting interference, including that of the barb, and push-on force. the relationship between interference and push-on will also change with hose material, reinforcement type, and construction. worst-case tolerance stack-ups should always have at least a line-to-line fit between the inner hose diameter and the tube diameter of the fitting. installation effort requirements should never compromise this hose to fitting fit. clearance fits of any magnitude can lead to leaks. the greater the hose to fitting interference (provided the joint can be assembled, and the elastic limits of the bulk hose are not exceeded), the better the probability of a sealed joint. interference is calculated as shown in the following equationexpression :(tube o d hose i d)/hose i d) x 100n o s e d ia 1mm l e s s t h a n m i n i d o f h o s etube d iab a r b h g th o s e i d n o s h a r p e d g e m a xrecommended r a d = 1 / 4 o f b a r b h g t .5 r a d1 4 d e g t yp end form hoseillustration 3 fitting design and hose fitnominal hose i d mmnominal barb hgt. mm*nominal tube od mmnominal hose radial elongation %hose to fittinginterference %14.814.414%2.9%16.816.413%2.5%19.919.511%2.6%251.425.614%2.4%321.432.811%2.5%381.639.011%2.6%* barb heights are based on sae j1231 and are recommended practice. pull off loads will dictate required final barb height.6.2 fitting surface shape and finish:the finish and shape of the mating surfaces of the fitting and the hose is a critical characteristic in the sealing design. the more consistent the sealing surface, the better the chance the joint has to seal (see fitting roundness section 6.3). finish recommendations follow.6.2.1 surface finishthe recommended surface finish for best sealing performance is as follows:a) has an rms (root mean square) value equal to or less than 30 micronsb) the roughness lay must always be perpendicular to the axis of the fitting c) no longitudinal flaws that exceed the roughness limit are permitted on the barb of the fittingd) any flaws on the shank of the fitting that form a continuous leak path must be considered detrimental to sealing.e) circumferential roughness or flaw usually do not contribute to leaks and may be allowed.note: all above comments concerning surface finish apply to both coated and uncoated fittingstypical flaw or scratchroughness (height)( direction of predominant surface pattern)axial direction of fittinglay roughness is to be measured circumferentially in order to detect and rate longitudinal defectsfitting30 micronsillustration 4fitting surface finish6.3 fitting roundness:parting lines and weld seams can be direct leak paths. larger parting lines have a higher probability of causing a joint leak than joints with smaller, faintly visible parting lines. depressions or crevices below the contact surface may also cause leaks. mismatch of dies or molds may also cause a leak path either directly, or as a result of scoring the i d of the hose during assembly. for this recommended practice, parting lines, flash and mismatch are considered flaws and must be smaller than the surface roughness specifications. furthermore, these flaws, if present, must not form a continuous leak pathfittingleak path caused by mismatch ordepressionhosehose clampillustration 5mismatch6.4 sealing length: longer sealing lengths provide a more robust design and assembly process. if the sealing length is not long enough, there is a greater potential that the clamp will be mis-positioned. in production settings, where accurate placement of the clamp cannot be guaranteed (assuming loose assembly), there is a greater possibility that the clamp will be placed either on the bead of the fitting or the hose stop. if the clamp is not perpendicular to the pipe axis, a leak may develop.minimum interference should beline to line (see illustration 3)barb to clamp .75 hose idbarb to hose end 10 mm hose id 1.5 x id idealmin. engagement3.003.00clamp skewness should not exceed 3 deg.illustration 6assembly recommendations6.5 clamping requirements: as a reference for cl