Publisher: LuK GmbH & Co. - Schaeffler Group · Torque Converter Clutch projects, LuK fo-cused energy on the entire Torque Converter system. ... quired TCC torque. To fulfil this

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Foreword

Innovations are shaping ourfuture. Experts predict that therewill be more changes in the fieldsof transmission, electronics andsafety of vehicles over the next15 years than there have beenthroughout the past 50 years. Thisdrive for innovation is continuallyproviding manufacturers and sup-pliers with new challenges and isset to significantly alter our worldof mobility.

LuK is embracing these challen-ges. With a wealth of vision andengineering performance, ourengineers are once again provingtheir innovative power.

This volume comprises papersfrom the 7th LuK Symposium andillustrates our view of technicaldevelopments.

We look forward to some intere-sting discussions with you.

Bühl, in April 2002

Helmut Beier

Presidentof the LuK Group

Content

LuK SYMPOSIUM 2002

1 DMFW – Nothing New? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Torque Converter Evolution at LuK . . . . . . . . . . . . . . . . . . . . . . . 15

3 Clutch Release Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4 Internal Crankshaft Damper (ICD). . . . . . . . . . . . . . . . . . . . . . . . . 41

5 Latest Results in the CVT Development. . . . . . . . . . . . . . . . . . . . 51

6 Efficiency-Optimised CVT Clamping System . . . . . . . . . . . . . . . 61

7 500 Nm CVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

8 The Crank-CVT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

9 Demand Based Controllable Pumps. . . . . . . . . . . . . . . . . . . . . . . 99

10 Temperature-controlled Lubricating Oil Pumps Save Fuel . . . 113

11 CO2 Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

12 Components and Assemblies for Transmission Shift Systems135

13 The XSG Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

14 New Opportunities for the Clutch?. . . . . . . . . . . . . . . . . . . . . . . 161

15 Electro-Mechanical Actuators. . . . . . . . . . . . . . . . . . . . . . . . . . . 173

16 Think Systems - Software by LuK. . . . . . . . . . . . . . . . . . . . . . . . 185

17 The Parallel Shift Gearbox PSG . . . . . . . . . . . . . . . . . . . . . . . . . 197

18 Small Starter Generator – Big Impact . . . . . . . . . . . . . . . . . . . . . 211

19 Code Generation for Manufacturing. . . . . . . . . . . . . . . . . . . . . . 225

WESTEV

2 Torque Converter Evolution at LuK . . . . . . . . . . . . . . . . . . . . . . . 15

15LuK SYMPOSIUM 2002

Torque Converter Evolution at LuK

Marc McGrathBruno MüllerEdmund MaucherBhaskar MaratheGeorge Bailey

2

2 Torque Converter Evolution at LuK

16 LuK SYMPOSIUM 2002

IntroductionFor many years, LuK has been recognised asa powertrain specialist with state-of-the-arttorsional vibration isolation technology. Thisexpertise lead LuK into the Toque ConverterClutch and Damper powertrain arena. Follow-ing the successful completion of the firstTorque Converter Clutch projects, LuK fo-cused energy on the entire Torque Convertersystem. LuK has evolved into a premierTorque Converter (TC) and Torque ConverterClutch (TCC) supplier (figure 1). Today, LuKproduces 2.5 Million TCCs and350 Thousand TCs, and as early as 2005 LuKwill produce over 1.5 Million TCs per year.

Fig. 1: LuK Torque Converter Growth

Know How LuK torque converter development is accom-plished through an integrated design ap-proach, incorporating analytical simulation,testing, and optimisation. The TC approachreflects LuK's traditional holistic design anddevelopment technique, enabling problemidentification, creativity and design optimisa-tion before prototypes are built. Commercialtools are not always available to properly per-form the necessary development tasks; insuch cases, LuK develops proprietary tools.

To efficiently develop torque converters, LuKrealised a tool was required to link one-dimen-sional fluid flow, one-dimensional design, two-dimensional torus generation, and three-di-mensional blade architecture. This realisationlead to the birth of LuK’s proprietary. ‘TC De-sign’ program. ‘TC Design’ is capable of col-lectively calculating torque converter perform-ance, torus geometry, blade angles and con-figuration.

As with most LuK tools, ‘TC Design’ featuresa parametric variation feature enabling rapidTC analysis. To complete the developmentprocess, ‘TC Design’ interfaces directly withLuK's commercial 3-D CAD and analysis soft-ware. For example, the exported torus shapeis imported into blade design software, thenthe 3-D blade surface is meshed to accom-modate Computational Fluid Dynamic (CFD)analysis (figure 2). To further analyse the TCperformance, CFD is used to simulate theflows inside the torque converter, providing in-sight into the physics of the fluid dynamic phe-nomena. This insight helps to identify TC op-timisation opportunities.

Fig. 2: TC CFD Analysis

1983 LuK produces the first automatic transmission damper(customer: Ford)

1990 LuK starts developing torque con-verters

1997 LuK begins WT torque converter series production(customer: Allison Transmission)

1998 First LuK torque converter business awarded(customer: GM)

2002 LuK will produce 350 Thousand TCs and 2.5 Million TCCs

2006 LuK will produce 1.5 Million TCs



Fig. 3: Torque Converter Size Reduction

LuK TC development tools yieldTCs with characteristics that werepreviously unthinkable. A recentchallenge was to reduce the TC size,weight and inertia, while simultane-ously flattening the K-Factor curve, andincreasing the engine torque (figure 3).

Furthermore, LuK has developed tools tosimulate the performance of the entire ve-hicle, to estimate changes in fuel economy,NVH, and vehicle performance for variousTC and TCC designs. Perhaps the most fa-mous damper solution is the Turbine Damp-er, which was developed utilising LuK’s TCand TCC tools.

Engine and transmission combinations pos-sess a vibration mode where the turbine iner-tia, transmission inertia and transmission in-put shaft stiffness resonate at the engine com-bustion frequency. Certain vehicles exhibitthis condition at an engine speed and magni-tude which prohibits TCC engagement, due toassociated noise issues, thus degrading fueleconomy. The turbine damper alters the drivetrain natural frequencies, eliminating this par-ticular vibration mode and accordingly provid-ing fuel economy and NVH improvements.These improvements have been recognisedby the automotive industry and the automotivepress (figure 4).

Fig. 4: Turbine Damper on the Road of Success

toruscharacteristic

baseline LuK

weight 15.2 kg 9.7 kg

inertia 0.21 kg · m² 0.12 kg · m²

torus oilvolume 6010 cm³ 2960 cm³

K-Factor 89 89

size 305 mm 280 mm



FutureThe key to LuK’s TC growth has been to addresstoday’s needs, while focusing on tomorrow’schallenges. To continue developing innovativeTC and TCC concepts, global powertrain trendsmust be considered. Future consumers will de-mand more of the same:

� fuel economy

� durability

� performance

� comfort

� cost

Powertrain engineers will approach the con-sumer’s desires quite differently this decade.With respect to TC development, multiple new

powertrain arrangements and themes need tobe considered:

� CVT

� 6-speed stepped automatic

� cylinder shut-off

� starter alternator systems

� increased torque/cylinder

� diesels / direct injection gasoline engines

� lower TCC lock-up speeds

� TC idle disconnect

Building on these trends, LuK has numerouscreative new ideas to address the future chal-lenges. The remainder of this paper will high-light a selection of LuK’s advanced concepts.

Fig. 5: Slipping TCC Theory and Components



Grooved CoverSlipping the TCC is an additional approach tosolving NVH issues. Unlike a damper ap-proach, slipping the TCC provides vibrationisolation by absorbing or filtering the engine’svibrational energy before it excites the pow-ertrain (figure 5). Although slipping implies ef-ficiency reduction, the slipping TCC efficiencyis generally higher than the TC alone. An ad-ditional efficiency gain is achieved by operat-ing the engine at a more favourable fuel con-sumption condition. The undesired energyloss is converted to heat carried away by con-duction and transmission oil convection. It iscritical to reduce the temperature so the fric-tion material or the transmission fluid does notdeteriorate. Deteriorated material and/or oilcan lead to detrimental shudder or TCC con-trol conditions.

Today, LuK has both development and pro-duction experience with two slipping TCC con-cepts, organic facings with cooling groovesand carbon facings (figure 5). The grooved or-ganic facing offers desired friction character-istics and a possible cost advantage, where asthe carbon technology offers improved dura-bility especially for high energy applications.

As the current friction materials wear over life,the cooling flow diminishes degrading thecooling performance. LuK is currently devel-oping the Grooved Cover concept. This con-cept maintains a constant flow over life(figure 6). Since grooves in the cover don’twear, they don’t need to be as deep. There-fore, a greater number of grooves can be usedimproving the friction interface flushing(figure 7). Additionally, the sides of thegrooves in the steel add surface area for heattransfer to the oil via convection. The result isbetter cooling efficiency than a grooved paperTCC with the same flow rate.

Fig. 6: Grooved Cover Cooling

Fig. 7: Comparison of Cover and Facing Grooves



Speed Dependent CoolingFor driving comfort, it is advantageous to en-gage the TCC at high differential speed and/ortorque levels, requiring the TCC to dissipatelarge power amounts. For this scenario, it isbeneficial to increase the cooling flow relativeto power. Unfortunately, with today's produc-tion concepts, the flow is dependent on the re-quired TCC torque. To fulfil this need, LuK isdeveloping an innovative concept (figure 8).The concept links the cooling flow to the TCCslip speed or relative engine/transmissionspeed. The increased flow is achieved bytransferring oil from the apply pressure side topiston chambers and then to the release pres-sure side.

Fig. 8: Power Dependent Cooling TCC Concept

The cooling flow or oil transfer rate is depend-ent on the relative speed between the TC cov-er (engine) and the TCC piston (transmis-sion). Since TCC torque capacity is defined byapply pressure, the amount of oil transferredfrom one side to the other side is maintainedproportional to the torque. Accordingly, thecooling flow varies relative to power levels.

Multifunction Torque ConverterIt is possible to further minimise losses asso-ciated within the torque converter. To maxim-ise efficiency the TCC should remain engagedas much as possible, yet, powertrain naturalfrequencies often limit TCC operation to high-er engine speeds. In manual transmission ve-hicles, this limitation is overcome with a dualmass flywheel designed to lower these naturalfrequencies, allowing lower operating speeds.

When a vehicle is stopped at traffic lights, thetorque converter is pumping fluid but no usefulwork is being done. Some manufacturers shiftthe transmission into neutral by opening aclutch in the transmission. To move the vehi-cle, the clutch must be reengaged quickly,which requires the freewheeling transmissioncomponents to come to an abrupt stop(figure 9). This must be done carefully or therewill be a bump when the clutch engages, sim-ilar to what is felt when a transmission is shift-ed into drive.

LuK has devised two- and three-pass Multi-Function Torque Converter (MFTC) con-cepts to

1. lower powertrain natural frequencies, and

2. provide an idle disconnect function.



Fig. 9: Benefit of Idle Disconnect in the TC

A cross-section of a two-pass concept isshown in figure 10. A second clutch, an im-

peller clutch, has been introduced betweenthe cover and impeller (or TC pump). The TCC

release pressure (channel 2 in figure 10) isfed between the input shaft and stator shaft,and the TCC apply pressure (channel 1 in

figure 10) is fed between the pump hub andstator shaft. At stops both pressures are kept

high, therefore no torque is transmitted to theimpeller and the converter drag is eliminated.

When the driver releases the brake, the TCC

apply side is open and the release pressureapplies the impeller clutch, which is designed

for adequate torque capacity while maintain-ing cooling flow (figure 11). The engagement

is invisible to the operator, because only therelatively small impeller inertia is accelerated

instead of decelerating the turbine and trans-mission components.

To lock the TCC, apply pressure pushes be-

tween the impeller and cover and the impellerslides toward the turbine (figure 12). Thetorque now flows from the cover, through the

damper, through the TCC, and to the inputshaft. The cover inertia is fixed to the engine,

and the impeller and turbine are fixed to theinput shaft, moving the impeller inertia from

the engine into the powertrain thereby lower-ing its natural frequency. Idle resonance and

start-up/shut-off noise issues are completelyavoided with this concept.



Fig. 10: Multi-Function Torque Converter (Idle Disconnect Mode)

Fig. 11: Multi-Function Torque Converter (Torque Converter Mode)

Fig. 12: Multi-Function Torque Converter (TCC Lock-up Mode)



Torque Reverse ConverterTo provide reverse motion, a continuous var-iable transmission (CVT) requires a planetarygear set with two clutch packs. Vehicle launchis achieved via a start up element. This canbe a fluid coupling or a torque converter. Boththe start up element and the reverse gear ar-rangement are only employed during limitedvehicle operations, launch and backing. Un-fortunately, a considerable portion of the CVTcost is consumed by the planetary gear setand the start up element. To reduce the cost,LuK’s idea is to combine the two auxiliary func-tions into one structural element.

In the forward operation, the TC stator redi-rects the turbine exiting fluid into the impeller,enabling torque multiplication. The redirectionattempts to rotate the stator in the opposingdirection as compared to the turbine and im-peller. The stator counter rotation is restrictedvia its connection to the transmission case.

Connecting the stator to the transmissioninput shaft would propel the vehicle backward.To achieve the required reverse torque, torquemultiplication can be regained by connectingthe turbine to the transmission case.

Creative connections within the torqueconverter interchanging the transmissioninput shaft and transmission case connec-tions will provide both forward and reversevehicle operations.

A four-element torque converter is utilised toindependently control forward and reversecharacteristics. Three elements of the torqueconverter are active in forward mode(figure 13). In the reverse mode, all four ele-ments are active (figure 14).

LuK’s Torque Reverse Converter (TRC) con-cept realises the required start-up and reversefunction in a single unit. This configuration notonly reduces cost, it saves crucial space aswell.

Fig. 13: Torque Reverse Converter(Forward Operation)

Fig. 14: Torque Reverse Converter(Reverse Operation)



Starter Alternator Torque Converter

LuK has been involved with the developmentof starter alternator systems since the early1980s. The advantages of starter alternatorSystems are increased electrical power andreduced fuel consumption, providing bothcomfort and economy.

Fig. 15: Starter Alternator Solutions

Combining a starter alternator with a TCequipped drive train places new demands onthe torque converter design, and offers theability to disconnect the engine from the TCand starter alternator while maintaining con-tinuous transmission pump operation. Thesedemands are required to foster inertia startsand brake regeneration.

LuK is focusing on TC solutions that meet the previously mentioned demands. LuK is de-veloping several torque converter starter al-ternator arrangements in conjunction with various starter alternator suppliers (figure 15).

LuK’s future advanced development effortsare concentrating on possible configurationswith the multifunction-torque-converter wherethe demands can be fulfilled without requiringextra parts (figure 16).

Fig. 16: MFTC Starter Alternator Concept



SummaryAt LuK, the design and development of torqueconverters is achieved through an integrateddesign approach, incorporating analyticalsimulation, testing, and optimisation. This ap-proach is a systematic design and develop-ment process that uses several analyticaltools. Where commercial software was notavailable to perform the necessary tasks, pro-grams were developed internally. This proc-ess was intended to optimise and improve de-signs, but it also allows for identification ofproblem areas before prototypes are built.This results in high-efficiency optimum torqueconverter designs.

The torque converter clutch (TCC) and damp-er are integral parts of the torque converter,and LuK has similar analytical tools to designthese components and predict their perform-ance. LuK’s 20 years of experience results ina perfect marriage between the TCC andtorque converter performance. Tools havebeen developed to predict powertrain torsion-al vibrations, so that damper characteristicscan be optimised. TCC thermal models arebuilt so that cooling concepts can be designedwhich allow continuous slipping of the clutchto isolate vibrations.

In addition, LuK has developed inhouse soft-ware to simulate the performance of the entirevehicle. Changes in fuel economy and vehicleperformance for various torque converter de-signs can be predicted before a prototype ve-hicle is even made.

Another benefit of this integrated design anddevelopment approach is that innovative so-lutions that may otherwise be overlooked,such as improved TCC cooling for slipping ap-plications, unique TCC damper configura-tions, and TC systems such as the multifunc-

tion, reverse gear, and starter-alternatortorque converters, become apparent.

LuK is presently working on the following in-novative torque converter concepts:

� TCCs with grooved covers instead ofgrooved facings to increase interface cool-ing in slipping systems

� Slip dependent cooling to increase the vol-ume of cooling flow as the power generatedby the slipping TCC increases

� Multi-Function Torque Converter as a com-bination of a dual-mass flywheel and atorque converter

� Torque converter incorporating reverse gear

� Torque converters for starter alternator sys-tems

References[1] Middlemann, V.; Wagner, U: The

Torque Converter as a System, 6th LuKSymposium 1998.

[2] Jürgens, G.: Transmission Systems: AComparitive View, 5th LuK Symposium1994.

[3] Middlemann, V.; Gundlapalli, R.;Halene, C.; Marathe, B.: Developmentof Axially-Squashed Torque Convertersfor Newer Automatic Transmissions,2000 ASME International Fluids Engi-neering Division Annual Summer Meet-ing, June 11-15, 2000, Boston, MA,FEDSM2000-11326.

[4] Kozarekar, S.; Maucher, E.;Marathe, B.: Analysis of 3-ElementTorque Converter as Reverse Gear,2000 ASME International Fluids Engi-neering Division Annual Summer Meet-ing, June 11-15, 2000, Boston, MA,FEDSM2000-11327.

Documents

Publisher: LuK GmbH & Co. - Schaeffler Group · Torque Converter Clutch projects, LuK fo-cused energy on the entire Torque Converter system. ... quired TCC torque. To fulfil this