1、 STD-ALMA SbFTMLO-ENGL L99b Ob87575 0004939 328 m 96FTMlO Scuffing Resistance of Vehicle -1 ransrnission tiears by: Dr. F.J. Joachim and Dr. H.F. Collenberg ZF Friedrichschafen AG TECHNICAL PAPER Scuffing Resistance of Vehicle Iiansmission Gears Dr. FJ. Joachim and Dr. H.F. Collenberg, ZF Friedrichs
2、chafen AG Tbe statements and opinions contained herein arc those of the author and should not be construed as an officiai action or opinion of the American Gear Manufactwm Association. Abstract in many transmission types, the lubricant fulnus other funciions apart from lubricating the gearing, for e
3、xample in friction elements (synchroniztr unit, clutch) in vehicle transmissions, or as a hydrauiic fluid (torque converter, retarder, steering system). The modem trends are now high contact ratio gearing as well as the use of low viscosity lubricants to duce chuming losses. Therefore, at the gear d
4、esigfi and lubricant additive stages, compromises are now necessas, which require the most precise information possible on scufnng It will be demonstrated that the normal test procedures for determining scufnng resistance are not suitable for lubricant ciassifcation for vehicle trammsa *om (GL4and G
5、L5). By reducing the tooth width as well as doubling the speh, the scuffing test to DIN 51354 sandards was increased in severiy to such an extent, that the parameters necessary for transmission dimensioning could be determined for even higher scuffing resistant oils. The oil data necessary for suffc
6、ient scuffing resistaace wiii be shown for different t * ondesigntypes. Withinthe scop of lifetime oil nUs, attention should be paid to oil aging processts. The.profile and tooth trace of gears on modem transmissi . ons are nowadays comcted, almost without exception, to compensate for load-related d
7、eformation and production discrepancies. in the current calculation procedures these corrections, which tend to increase scufnng resistance, are not considered to an adequate extent. A process is being presented, in which scrifnng resiStance is caicuiated for every point on the tooth flank, based on
8、 the “flash tmperature method“, and taking ail variations and corrections into account. It will be demonstrated with practical examples,that,asearlyasthedcSignstage,thismethodcanbeusedtodetectflankareasatrisk,and toeiiminatethemwitb a specific correction design. of the gwing and lubricant. Copyright
9、 O 1996 American Gear Manufacturers Association 1500 Kmg Street, Suite 201 Alexandria, Viia, 22314 October, 1996 ISBN: 1-55589-677-4 STD-AGMA SbFTMLO-ENGL L77b Obi37575 OODq94L Tb SCUFFING RESISTANCE OF VEHICLE TRANSMISSON CEARf3 F.J. Joachim, H.F. Collenberg ZF Friedrichshafen AG 1 Introduction The
10、 following essay describes new test and calculation procedures for defining the scuffing load capacity of gears in vehicle transmissions. The standard test for defining the scuffing load capacity of lubricants . as per DIN 51354 /8/ only allows differentiation between uninhibited (without anti wear
11、additives) and lowly-inhibited oils (MI-GL 2 and GU) up to damage load level 12. More highly-inhibited lubricants as per MI-GL4 and GL-5, which are also used in vehicle transmissions, reach damage load levels above 12 and can therefore no longer be differentiated. To enable classification of such lu
12、bricants also, proposals were put forward to make the tests more severe as part of internal investigations. Based on these investigations, the FVA (Forschungsvereinigung Antriebstechnik = German Research Association of Transmission Technology) developed a more severe scuffing test as part of a resea
13、rch program. The differences between this and the standard tests will be outlined and explained. Generally, procedures as per DIN 3990 /1/ and IS0 TR 13989 are used for checking scuffing load capacity calculations. As a supplement to this, a procedure which also considers profile and tooth trace cor
14、rections will be outlined. 2 Requirements for transmission lubricants The lubricant is an important design component and must be considered as early as the transmission configuration and design. phase. The main functions of the lubricant are to minimize friction and wear on sliding and rolling compo
15、nents, dissipate heat and protect against corrosion. Using an automatic transmission from a passenger car as an example, Fig. 1 shows the numerous transmission components whose function and lifetime directly depend on the lubricant. In such cases, there has to he compromise in order to fulfill often
16、 contradictory criteria such as load-bearing capacity, resistance to temperature and ageing, cold- ._ - -. - Cean Seais Thrust washers Bearings slip rings Pinstic parts ) Frcmheelr Shaft-hub Bores / valves ) Multi-discclutches Lubricant conncetions Fig. I: Lubricant injbenced components in an automa
17、tic trcrnsmssion shift characteristics, efficiency, friction characteristics, costs, availability, etc. The “lubricant-transmission component“ matrix outlines the main failure critena, Table 1. Possible tooth flank damages such as scuffing, pitting, micropitting and wear are substantially influenced
18、 by the properties of the lubricant. Viscosity, molecular structure and additives determine either the lubricant film thickness or the friction factor and, consequently, the surface stress. A particularly important factor with regard to scuffing load capacity is the chemical-physical interaction bet
19、ween the lubricant and the surface, which influences the material properties around marginal zone Fia. 2 STD-AGHA SbFTMLO-ENGL 19Sb m Ob87575 00049q2 712 Cam Anti-friction k8rings, frcewbeelr O O. O (0) O O O. Plane bearings, thrnst washen, guide slecva O. O O Tab. 1: Inemctive nrahir lubricant tran
20、musSon elements Sra1i.g clemcnfs Phstic pam (cage) Bores, v8iver Effect of iubricant O O O O. Hydrodyi. Inbriuaon Libriait (bib rpced) I Bound8ry mixed friction hycr Fig. 2: Effd of iubncanz on flank stress and strength 3 Risk of scuffing: today intensive analyses coupled with the development of tes
21、t and calculation procedures /1,2,3,8/) resulted in the development of lubricants with a scuffing load capacity sufficient for the intended transmission applications. However, new trends in Vehicle transmission development require even greater consideration of scuffing load capacity. The following d
22、evelopments have resulted in an increased risk of scuffing in manual and automatic transmissions: the use oflow-viscosity lubricants (Am to improve cold shift characteristics, the use of fill for life lubricants which resist high temperatures /5/, reduced oil levels introduced to reduce splash losse
23、s, the use of extra-depth gearing to reduce noise levels, the omission of coatings (e.g. phosphating) to save costs or for environmental reasons. The oocurrence of scuffing damage has already been dealt with in a number of publications (e. 1 2; 1 4; 1 6; I Dip lubrication Split lubrication I Time/lo
24、adrtige min I 45 I 15 I 7.5 I Temperatire Pinion face width mm Gear ince width mm I Driver -I pinion I Tub. 2: Test conatiom uccording TGL 26890 DO/ ZF carried out its own investigations to determine the influence of the following with a more severe test: speed, load, oil temperature, drive directio
25、n, operating time, lubricant .grade, tooth profile, tooth width, tooth flank roughness. The effects of these influences can be seen in Table 3. By increasing the circumferential speed from 8.3 m/s to 16.6 m/s and reducing the pinion tooth width from 20 mm to 10 mm, a test including about 4 more dama
26、ge load levels is possible. This makes classification of GL-4 oils possible Fig. 4. Fig. 5 shows test results with two different oils. The lifetime oil evaluated as having a damage load level 12 in the standard test as per DIN 51354 was evaluated as damage load level 10 in the more severe test. The
27、damage patterns from the standard test and more severe scuffing test are almost comparable. However, in the more severe test there was increased wear on the test pinion root due to the increased specific load. The calculated scuffing temperature can be used to compare the standard test with the more
28、 stringent test, Fig. 6. According to this calculation, it is possible to include up to 6 more damage load levels in the test. Influence U Doubling speed Load Start temperature Change of driver Time per lord stage Lubrication mode (without scsrity) Tooth profile Half facc width increased surface rou
29、ghness Increase of 2 1 - 2 - - 2 1-2 not prrcticrble Tgb. 3: Posdies to increase the severity of the stonM scumng test acc. DIN 5354 t I FZCn/8.3/90 I A116.9/90/10 I TCL26890 I DIN 51354 kverc test Fig. 4: Ckificaton of severe scuffing test AlOI16,6lYOi compured to API specification GL-1 to 5 _ t 14
30、1 Fig. 5: Test results of DIN 51354 compared fo severe scumng test I I II - LiibriC8tbn Oil tnnpmrure from lord stage 4 at the Stlrt dercb load stage OC -I O dip lubrication system 90f3 - Seventest . Stindud test A/16.9/90/10 FZC Al.3190 DIN 51354 Fig. 6: Comparison between standard test A/8,3190 an
31、d severe test AIOI16,6190/ by means of integral temperature 43 Standardization of a more severe scuffing test Based on the above results, Shell AG and ZF Friedrichshafen AG initated an FVA investigation program to be carried out at the FZG (Forschungsstelle fr Zahnrder und Getriebe: Research Center
32、for Gears and Transmission Construction at Munich Technical University). As part of the systematic investigations, the object was to develop a more severe scuffing test which could be standardized. The newlydeveloped test procedure is described in FVA information sheet no. 243 /91 and is available t
33、o all companies. The major changes as compared to the previous standard test are summarized in Table 4. These include reducing the tooth width to 10 mm, increasing circumferential speed to 16.6 m/s and changing the drive direction from the pinion to the wheel. mim 15 75 Raining time per lord slage T
34、ub. 4: Comparison between s 8 test runs; average failure load stigr K, = 9.0 - - - _ _. -. . . . Tab. 5: Example for the shock test procedure and dculation of avemge lua stage ace. 19i It is planned to check the suitability of the more severe scuffing test /9/ by carrying out a national and internat
35、ional pooled test. If the results of this test are positive, it will be possible to standardize the procedure. It must be assumed that the more stringent test will increasingly replace the standard test, as the new procedure can be used to check all lubricant specifications using narrow test gears o
36、nly. The test gears shall be produced by ZF Friedrichshafen AG (as are all FZG test gears) and may be requested from the dealers. The level of resistance against scuffing can be calculated as per DIN 399o/Section 5 Ill. An IS0 working group is currently preparing IS0 TR 13989. A draft version is due
37、 to be published in late 1996. The details of the DIN standard and IS0 Technical Report for scuffing calculations on spur gears differ only slightly. The basis is identical, both offering the option of flash temperature or integral temperature methods. The following examples of scuffing load capacit
38、y are calculated according to the integral temperature method (DIN 3Y90). 5.1 Automatic transmissions The required compromises in lubricant composition, as described in section 2, prohibit high concentrations of what are known as “extreme pressure additives“ (EP) in automatic transmissions for comme
39、rcial vehides and passenger cars. These additives provide effective prevention against scuffing. Checks on calculations made on the gear sets in a modem automatic transmission for passenger cars reveal that damage load level 12 mu1 be retained as per DIN 51354 in order to assure scuffing resistance
40、1.5 . 2.0 in the planet gear sets and therefore reliably prevent scuffing,Fig.7. - STD-AGMA SbFTMLO-ENGL L77b = Ob87575 OOOq745 b2L . .1 C gear -_ 4th gear 3rd gear I 2nd gear I ist gear t 2s 1 I ATF: Load stage I2 acc. DIN 51354 I 1.0 J I I 8 1 O0 125 150 Oil tempentire /“CI a Epicyclic 1 - - - Int
41、ermediate drive - Epicyclic 2 -a - Final drive Fig. 7: Calculated scuffing resistance for automatic tmnstnissions for cars However, the spur gear sets in transmissions for front or all wheel drive vehicles must be investigated more precisely. High circumferential speeds caused by larger center dista
42、nces as well as the inclusion of extra-depth gearing to ensure reduced noise levels sometimes lead to a theoretical level of scuffing resistance which is below 1.5. In such cases, the gearing corrections must also be optimized with regard to scuffing in order to guarantee problem-free operation, see
43、. section 6. 5.2 Manual transmissions Oils from MI classification GL-4 are traditionally prescribed for manual transmissions. These lubricants largely exceed the application limits of conventional scufing tests. Therefore, an exact calculation of scuffing load capacity was not possible nor necessary
44、 as scuffing damage was not a problem in these transmissions. GL-4 oils also reached damage load level 12 in the more severe scuffing test described in section 4.2. Safe levels of scuffing resistance ( 2.5) were even calculated for heavy duty manual transmissions for tnicks, Fig. 8. The desired aim
45、of extending oil change intervals in ZF-ECOSPLIT transmissions for heavy duty trucks also led to the development of new lubricants which, even today, allow oil change intervals of 300,000 km under certain conditions. The more severe scuffing test and more exact calculation methods were used to show
46、that oils with damage load level 10 in the more severe scuffing test are sufficient even for heaviest of applications, meaning it was possible to reduce specifications for the development of the new oils Fig. 8. These results also proved to be of assistance for development of the ZF-INTARDER, a hydr
47、aulic brake integrated iii the transmission. The omission of the GL-4 requirments mtint it was possible to produce a shared oil circuit for the transmission and intarder. Low-viscosity oils with low scuffing load capacity are often used in manual transmissions for passenger cars, pickups and light c
48、ommercial vehicles in order to reduce splash losses and optimize shifting. One of the prerequisites for this is exact calculation and experimental checking of pitting and scuffing load capacity as shown -1 = Fill for life oil 0 CL4 Load stage 12 Load stage IO Fig. 8: Calculated scuffing resisunce fo
49、r manual shifled heavy huck transmission: comparison jll for life oil versus GL 4 Oil - in Fig. 9. Initiai tests on a production version transmission revealed scuffing damage in gears 1, 2 and 3. By optimizing the tooth tip relief, it was possible to obtain sufficent swffing load capacity and release the transmission. I ATF: Load stage 10 acc. DIN 51354 I “ I Ist gear I 2ndgear I 3rdgear I a Tcstng Truck Track Truck overload normal wad mountain wad mountain wad increased * Scuffing failure tip relief Fig. 9: Scufing resistance of manual
