Publisher: LuK GmbH & Co. - Schaeffler Group · PDF fileForeword Innovations are shaping our future. Experts predict that there will be more changes in the fields of transmission,

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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

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

211LuK SYMPOSIUM 2002

Small Starter Generator – Big Impact

Thomas PelsDierk ReitzLászló MánBård Vestgård, Kongsberg DevoTek

18

18 Small Starter Generator – Big Impact

212 LuK SYMPOSIUM 2002

IntroductionAs a logical step in the continuing develop-ment of propulsion systems, hybrid drivetrains offer enormous potential for reducingfuel consumption [1]. However, in addition toenvironmental aspects, service value comfortand, above all, costs play a crucial role in fu-ture powertrain concepts. With this in mind,the versions preferred by LuK are those withthe best cost-to-benefit ratio. [2].

Two systems are presented in this paper,which, for their respective applications, repre-sent, in LuK’s estimation, the greatest oppor-tunities for wide market penetration in the me-dium term. The first part of the article presentsthe electrical shift gearbox (ESG), which hasthe particular advantage of combining theproperties of the twin clutch or parallel shiftgearbox with the functions of a mild hybrid.The second half presents the starter generatorin the belt drive (RSG), which offers start-stopfunctionality with minimum effort. LuK has de-veloped a compact two-speed gearbox, whichextends the application range of the RSG tohigh-capacity Otto and Diesel engines.

The Electrical Shift Gearbox (ESG)

Position of the Electrical MachineThe parallel shift gearbox with dry clutches(PSG) offers the ideal basis for a powertrainwith high comfort and very good efficiency [3].To further reduce fuel consumption, the pos-sibilities for incorporating an electrical ma-chine will be investigated. In addition to thefast, silent start (start-stop), this should alsoenable the regeneration of energy from decel-eration (recuperation) and ‘downsizing’ of thecombustion engine by means of a boosterfunction. Figure 1 shows the first attempt at adirect connection of the E-machine to thecrankshaft of the combustion engine. Such a

layout is also described as a ‘Crankshaft Start-er Generator (CSG)’ or ‘Integrated StarterGenerator (ISG)’ and is particularly applied incombination with manual transmissions [4].One disadvantage of such a structure is thelimited recuperation potential as a result ofdrag losses when the combustion engine iscoasting.

Fig. 1: PSG with Crankshaft Starter Generator

Figure 2 shows a solution with a further clutchbetween the E-machine and crankshaft. Withthis configuration, the full potential for regen-erating energy can be exploited by decouplingthe combustion engine when coasting.

Fig. 2: PSG with three Clutches

According to simulations for the New EuropeanDriving Cycle (NEDC) estimated achievablesavings are between 15-20% [5]. Moreover, bydisconnection of the internal combustion engineto further reduce fuel consumption, the vehiclecan be moved pure electrically by the E-ma-chine. In relation to a downsizing of the combus-tion engine, consumption reductions of approx-



imately 30% (NEDC) were verified on (built-up)prototypes [6].

The LuK concept goes a step further. Asfigure 3 shows, it is proposed to integrate theE-machine in the gearbox. In addition to fur-ther functional advantages, which will be ex-plored in the next section, this structure offerssignificant packaging and cost benefits and isdescribed in the following as the electrical shiftgearbox (ESG).

Fig. 3: Electrical Shift Gearbox

FunctionsIn order to clearly explain the individual func-tions of the ESG, both separate gearbox unitsare shown in parallel (c.f. figure 4). The lowerunit contains the odd gears and clutch K1 andis known as gearbox unit 1. Alongside that,gearbox unit 2 consists of the even gears andclutch K2.

Driving with the Combustion En-gineDuring operation in gearbox unit 2 the startergenerator (SG) is directly linked to the com-bustion engine via clutch K2. Figure 4 showsan example of driving in 4th gear with gener-ator function. Reversing the torque directionon the E-machine results in a booster function.

According to the shift strategy in gearboxunit 2, during operation in an odd gear, eitheran even gear is pre-selected or a neutral po-sition is selected. If gearbox unit 2 is in neutral,

Fig. 4: Driving in Gearbox Unit 2 - Generator Operation

Fig. 5: Driving in 5th Gear with Gearbox Unit 2 in Neutral

then clutch K2 is closed to transfer generatortorque (figure 5). With a pre-selected gear, theE-machine is driven via the engaged gear - asdescribed in figure 6. A booster function canagain be performed by reversing the torque di-rection on the electrical machine.



Fig. 6: Driving in 5th Gear with Pre-Selected 4th Gear

Electrical Start-Up/Driving

It is possible to drive purely by means of elec-tricity with suitably large electrical power fromthe E-machine and battery. For this, bothclutches remain open and, depending on thespeed and load, together with the efficiencymap, the torque is fed over the 2nd, 4th or6th gear to the wheels (figure 7).

Kinetic Energy Regeneration (Re-cuperation)In order to achieve efficient usage of energyfrom deceleration, the combustion engine isdecoupled from the drive train when coasting.The E-machine, which builds up generatortorque according to speed, brake pedal posi-tion and optimum gear ratio, takes over decel-eration of the vehicle and converts the kineticenergy into electrical energy (figure 8).

By integrating the air-conditioning compres-sor into gearbox unit 2 as per figure 9, the ki-netic energy of the vehicle can also be directlyused to produce cooling energy. Hence if pow-er demand of the electrical consumers is low,intermediate storage in the battery, which is af-fected by efficiency, is avoided. Provided thatthe air-conditioning system (A/C) has in-creased storage capacity, e.g. through a larg-er evaporator unit, refrigerant is cooled for lat-er use during standstill.

If a suitable refrigerant such as CO2 is used,the air-conditioning system can also produceheat [7]. In addition to benefits in energyalongside the direct production of cooling en-ergy during recuperation, the system showspromise for heat management in the hybridvehicle.

Fig. 7: Electrical Driving Fig. 8: Recuperation



This particularly applies to modern combus-tion engines with direct-injection, fully variablevalve timing and similar, which, due to their lowpart-load consumption’s, are partly already re-lying on auxiliary heaters today.

Stationary Air-ConditioningIn future vehicles, stationary or pre-air-condi-tioning will be considered to increase comfort.Moreover, adequate air-conditioning is re-quired during the standstill phases of the com-bustion engine in start-stop operation. How-ever, in LuK’s opinion, the electrically drivensystems currently being investigated to satisfythese requirements have some drawbacks.Firstly, an E-machine with a mechanical poweroutput of approx. 2 - 5 kW must be installed.In addition the starter generator including thepower electronics for electrical supply of thecompressor drive has to be correspondinglylarger. Altogether, in addition to a disadvan-tage in terms of weight, it leads to considera-ble costs for electrical components. Further-more, in view of the repeated energy conver-sion compared with a conventional system, itresults in disadvantages in terms of energy [8].

On the ESG the air-conditioning compressoris connected to the E-machine via the conven-tional magnetic clutch. In normal driving, thepower is provided mechanically by the com-

bustion engine via gearbox input shaft 2. Dur-ing a standstill phase, the starter generatorcan electrically drive the air-conditioning com-pressor in neutral position of gearbox unit 2and with an opened clutch K2, as illustratedin figure 10.

Cold Start

In addition to reduce the required maximumtorque of the electrical machine, ensuring thepower output of the battery as small as pos-sible is the main goal to optimise cold startingbehaviour [9]. The conventional starter satis-fies this requirement through a high gear ratiobetween the rotor shaft and flywheel.Figure 11 illustrates the fundamental advan-tages resulting from this gear ratio, wherebya 1.9 l DI-Diesel engine is used as an exam-ple. Firstly it results in an increased inertia(when referring to the crankshaft) comparedto a crankshaft starter generator, by which thespeed fluctuations during start-up are signifi-cantly reduced. By keeping to a minimumspeed necessary for a safe start-up (here:80 1/min), this produces lower average start-ing speeds and thus reduced mechanicalstarting power. Furthermore, the E-machineruns in a speed range of significantly higherefficiency by the gear ratio, through which the

Fig. 9: Recuperation Including Air-Conditioning System

Fig. 10: Stationary Air-Conditioning



Fig. 11: Cold Start Performance – System Comparison Conventional Starter / ESG / CSG

electrical power absorbed from the batterycan again be reduced.

Two potential solutions are presented for de-signing a cold start gear ratio to the ESG. Theintegration of the E-machine into the gearboxenables two existing gears to be used as acold start gear ratio. Figure 12 shows thetorque flow from the starter generator to thecombustion engine via a combination of twogear wheels of the gearbox.

With this configuration, start-up gear ratios be-tween 2.5 and 7 can be achieved, accordingto the selection of the gear wheel pairing. Dur-ing the start-up process the vehicle outputshaft must be decoupled. As the example infigure 13 shows, this can be done via a mod-ified dog clutch, which connects gear wheels2 and 5 in the cold start position as an addi-tional position and simultaneously decouplesthe output shaft (figure 13c). However, decou-pling is generally also possible using a neutralposition of other shift elements, e.g. through

a neutral gear shift in the transfer gear of a4-wheel drive vehicle.

The shifting of an axially movable gear wheelto the flywheel provides a second version ofa cold start gear ratio. This is explained inchapter The ESG Prototype in more detail.

Fig. 12: Cold Start with Combination of two Gears



Fig. 13: Modified Dog Clutch

a) Neutral b) 2nd Gear Engaged c) Cold Start Position

Warm Start

Warm start occurs in the neutral position of

gearbox unit 2 via clutch K2 to the combustionengine. To reduce the time until the vehiclestarts up, a creeping torque can be fed to theoutput shaft during the start-up process viaclutch K1 and engaged 1st gear (figure 14).Due to the additional gear ratio, the cold start

requirements on the E-machine are reducedas shown in figure 11. The torque required forquick acceleration of the combustion engineafter a stop phase is therefore a determiningfactor in the system. This results in a compar-atively compact starter generator design and

a very low rotor inertia. This is of crucial im-portance for maintaining short synchronisa-tion times in Gearbox Unit 2.

Fig. 14: Warm Start in Start-Stop Operation

a)

b)

c)



The ESG Prototype

By building up a vehicle, LuK wants to showthat it is possible to achieve the functions ofthe drive train concept described in the previ-ous section, without adversely affecting thecomfort of the standard transmission. In par-ticular, it is the synchronisation of gearboxunit 2 and the dynamic coupling / decouplingof the combustion engine to facilitate the re-cuperation operation that are at the forefrontof the development.

The test vehicle is a passenger car from thelower medium-class size with a 1.3 l DI-Dieselengine and a 5-speed PSG with dry clutches.The 42 V starter generator is positioned indriving direction in front of the gearbox with theaxle in parallel to the gearbox input shaft. Theconnection occurs via an intermediate gear tothe gear wheel of the 4th gear with a ratio of0.84. The air-conditioning compressor is fixedto the E-machine housing and is driven with

a gear ratio of 1 by the rotor shaft by a V-ribbedbelt. Figure 15 shows the general view of thedrive train with the orientation in the enginecompartment. Fixation of the E-machine to thegearbox is done via a modified gearbox brack-et. Additional reinforcement is achieved by thebolting of the seal face between the gearboxcasing and intermediate gear, as shown infigure 16.

In order to exploit the benefits of a cold startgear ratio as described, the E-machine is di-rectly connected to the flywheel of the crank-shaft in the test vehicle during cold starting.Figure 17 shows the principle, which is similarto a conventional starter mechanism. A gearwheel, movable in an axial direction by a so-lenoid mounted on the extended motor shaft,can be engaged in the starter ring gear. Theoptimised layout of the E-machine means thatan axle base between gearbox input shaft androtor shaft can be achieved, which enables acold start ratio of 3.5.

Fig. 15: General View of the Drive Train



Fig. 16: View of ESG Components

Fig. 17: Connection of the E-Machine to the Flywheel for the Cold Start

Starter Generator in the Belt Drive (RSG)

Operating PrincipleThe great potential for reducing fuel consump-tion through the increased functionality of theESG requires extensive intervention in thedrive train. This includes complex measuresin the design of control units and software tointegrate an energy management system. Iffunctions are reduced to the start-stop oper-ation, the belt driven starter generator be-comes an attractive solution [5, 10, 11]. Thisconcept enables the use of tried and testedcomponents with minimum changes on the

existing auxiliary drive [12]. Furthermore, therelatively low starting power enables the useof traditional 12 V lead-acid batteries, possiblyin AGM technology (Absorptive Glass Matt).The RSG can be combined with all gearboxeswithout the need for modifications to the drivetrain. Consequently, the application requiresconsiderably lower development effort in com-parison with all other starter generator sys-tems.

Figure 18 shows a schematic drawing of theRSG system operating principle in the startmode. It shows that the gear ratio of the V-ribbed belt (2.5 ... 3) on Diesel engines andlarger Otto engines is not sufficient for safestarting, especially at low temperatures. Forthis reason, LuK has developed a compacttwo-speed gearbox, which enables a higheroverall ratio (e.g. 6…7) for starting.

Fig. 18: Operating Principle - Start Mode

Fig. 19: Operating Principle - Generator Mode



After the first ignition, the combustion enginedrives the generator in the traditional way(figure 19). If a two-speed gearbox is used,then it shifts automatically into ratio 1.

The RSG Gearbox

A particular capacity limit, where the use of atwo-speed gearbox is always required, cannotbe defined precisely due to the many differentE-machines being developed. The belt layoutalso has a considerable effect on the achiev-able gear ratios of the specific accessorydrives. LuK assumes that two-speed gearbox-es are used on RSG systems for Otto engines�1.8 l displacement and for Diesel enginesfrom around 1.4l cylinder capacity. These ref-erence values apply to a system with a nom-inal voltage of 14V. On more powerful 42V-systems the application range without a two-speed gearbox is naturally extended. In viewof the functions (and costs!), such applicationsare more likely to be categorised as mild or softhybrids [13].

Figures 20 and 21 show the essential gearboxcomponents and clarify the torque flows dur-ing the states of start and generator operation.

Fig. 20: Torque Flow in Planetary Gear Set during the Start Process

Fig. 21: Torque Flow in Planetary Gear Set on Running Combustion Engine

During start-up torque is transferred from theelectrical machine via the belt to the pulley.The torque is fed over the sun gear linked tothe belt pulley into the planetary gear set. Atthe same time the ring gear is joined via a(start-up) free wheel to the crankcase. Thetorque on the internal ring gear is thus addedto the torque that is fed and is transferred viathe planet carrier to the crankshaft. Depend-ing on the design, the starting gear ratio of thisgearbox is between 2.5 and 3.5. As soon asthe combustion engine starts to deliver torque,the start-up free wheel is overtaken until, fi-nally, all planetary gear components rotate atthe same speed. Then the second one-wayclutch, which is now transferring combustionengine torque from the planet carrier direct tothe sun gear, i.e. with gear ratio 1, engages.This second free wheel decouples all acces-sories from the cyclic irregularities of the com-bustion engine in generator operation and isthus described as an auxiliary free wheel.Figure 22 represents measurement resultsfrom the auxiliary free wheel on the combus-tion engine test rig with a 1.9 l DI Diesel engineunder load.



In addition to providing a high gear ratio for thestart operation and decoupling the accesso-ries, the gearbox also takes on the function ofa crankshaft damper, which many enginesneed at the free crankshaft end for reducingtorsional vibrations. For this, the requireddamper mass is connected to the planet car-rier, either by a rubber spring or by using spe-cial helical compression springs, dependingon the design. If steel compression springs areused, this enables the natural frequency to betuned precisely, thus allowing the use of rela-tively small damper masses. Given the variedpackaging space proportions, it can, however,make sense to keep the crankshaft damper,which is sometimes designed as a separatecomponent, as an independent unit. Such aversion is presented among other items in thenext section.

Fig. 22: Decoupling of Accessory Drive (Measurement)

LuK Gearbox Variants

As described in the previous section, the gear-box can be positioned on the crankshaft or al-ternatively on the rotor shaft of the generator.The basic difference in these is that the inte-gration of the gearbox into the crankshaft pul-ley permits the use of a V-ribbed belt due tothe lower force level in the belt. Both versionshave been built at LuK in different variationsand examined on test rigs and in vehicles.Figure 23 shows a sectional illustration of agearbox with integrated crankshaft damper. In

this example the damper mass is connectedto the crankshaft via a rubber ring. Figure 24shows a layout with damper as a separatelydesigned component. The gearbox is con-nected to the crankshaft of the combustion en-gine via a central screw.

Due to the short time duration of speed differ-ences in the gearbox, only small demands aremade on the lubrication of the components. Amaintenance-free grease fill will satisfy theserequirements and also offers benefits for theselection of low-cost, low-friction seals.

By using a simple actuator, the gearbox gainsadditional functionality. The fixation of the in-ternal ring gear to the crankcase is controlledby the actuator. This happens by interruptingthe torque flow to the casing bracket with a so-lenoid. For that reason the starter generator,in motor operation, can drive accessories witha crankshaft at standstill. This is an interestingoption, especially when viewed alongside sta-tionary air-conditioning.

Fig. 23: Gearbox with Integrated Crankshaft Damper



Fig. 24: Gearbox with Separate Crankshaft Damper

SummaryThe ESG is characterized by the following fea-tures:

� Very low fuel consumption due to

– Start-Stop operation of the internalcombustion engine

– Recuperation with a decoupled com-bustion engine

– Integration of the air-conditioning in thepowertrain management system

� Shift comfort the same as the basic gearboxwithout an E-machine

� (Mild) hybrid as add-on solution with electri-cal power up to 30 kW, depending on re-quirements

� Comparatively low costs due to reduced de-mands on electrical components

� Optimum dimensions of E-machine andpower electronics

� Increased functionality (electrical driving,booster function, stationary air-conditioning)

The belt driven starter generator is character-ized by the following features:

� Reduced fuel consumption due to Start-Stopof the internal combustion engine

� Low development effort, easy application

� Connection to combustion engine inde-pendent of drive train

� Very low system costs, especially when14 V system is used

� No additional weight

� Convenient packaging proportions

By using the described two-speed gearbox, alower belt ratio can also be realized. In addi-tion to providing significant relief of the beltand tensioning system, this leads to furtherconsumption benefits through better operat-ing points of the generator and reduced iner-tias. LuK also sees additional benefits in thevibrational decoupling of the auxiliary drivethrough the free wheel functionality and theoptional neutral position of the gearbox for theelectrical drive of air-conditioning compres-sor, water- and powersteering pump on a sta-tionary combustion engine.

Starter generators and hybrid drive train arethe appropriate means for significantly reduc-ing fuel consumption in future vehicles. Bothof the systems presented here have the po-tential to make a considerable contribution toreducing the much discussed anthropoge-nous CO2 emissions in accordance with leg-islative requirements.



References[1] Weiss, M.; Heywood, J.; Drake, E.;

Schafer, A.; AuYeung, F.: ON THEROAD IN 2020 – A life-cycle analysis ofnew automobile technologies, EnergyLaboratory MIT Cambridge 2000.

[2] Reik, W.: Mögliche Anordnungen desStartergenerators im Antriebsstrang.LuK Fachtagung ‘E-Maschine im An-triebsstrang’ 1999.

[3] Berger, R.; Meinhard, R.; Bünder, C.:The Parallel Shift Gearbox PSG – TwinClutch Gearbox with Dry Clutches,7th LuK Symposium 2002.

[4] Koch, A.; Lehmann, J.; Probst, G.;Schäfer, H.: The Integrated Starter-Generator as Part of the PowertrainManagement, 9th Aachen ColloquiumAutomobil and Engine Technology2000.

[5] Reik, W.; Pels, T.; Reitz, D.: Strukturenfür Startergeneratoren und Hybrid-antriebe - Integrierter Startergenerator(ISG), Hrsg. Schäfer, H., expert Verlag2000.

[6] Mesiti, D.; Rovera, G.; Tamburro, A.;Umberti, M.: Minimal Hybrid Configura-tion Using an Automatic Dual ClutchGearbox for Matching Comfort and Effi-

ciency, 10th Aachen Colloquium Auto-mobil and Engine Technology 2001.

[7] Kuhn, P.; Graz, M.; Obrist, F.;Parsch, W.; Rinne, F.: Kohlendioxid-R744 als Kältemittel in Fahrzeug-Kli-maanlagen, ATZ 103 Nr. 12, 2001.

[8] Morgenstern, S.: Endenergieverbrauchvon Kältemittelkompressoren im Pkw,Haus der Technik Tagung ‘Nebenaggre-gate im Fahrzeug’ 2001.

[9] Höcker, J.; Richter, G.: Developmenttrends for future car batteries, VDI-Berichte Nr. 1418, 1998.

[10] Bischof, H.; Bork, M.; Schenk, R.: Start-ergenerator: System, Funktion, Kompo-nenten, LuK Fachtagung ‘E-Maschineim Antriebsstrang’ 1999.

[11] Pels, T.; Mán, L.: Strukturen für Starter-generatoren, Haus der Technik Tagung‘Nebenaggregate im Fahrzeug’ 2001.

[12] Duhr, J.; Farah, P.; Schoester, L.:Stop/Start Function: The Clawpole Ma-chine - a good alternative to the ISG,Haus der Technik Tagung ‘Energies-peicher- und Generatorsysteme fürKraftfahrzeuge’ 2000.

[13] N. N.: Mild hybrid set for production,European Automotive Design Septem-ber 2001, p. 86.

Publisher: LuK GmbH & Co. - Schaeffler Group · PDF fileForeword Innovations are shaping our future. Experts predict that there will be more changes in the fields of transmission,

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