Small Starter Generator – Big Impact

Home , Belt (mechanical)

Publisher: LuK GmbH & Co. Industriestrasse 3 • D -77815 Bühl/Baden Telephon +49 (0) 7223 / 941 - 0 • Fax +49 (0) 7223 / 2 69 50 Internet: www.LuK.de Editorial: Ralf Stopp, Christa Siefert Layout: Vera Westermann Layout support: Heike Pinther Print: Konkordia GmbH, Bühl Das Medienunternehmen Printed in Germany

Reprint, also in extracts, without authorisation of the publisher forbidden. Foreword

Innovations are shaping our future. Experts predict that there will be more changes in the fields of transmission, electronics and safety of vehicles over the next 15 years than there have been throughout the past 50 years. This drive for innovation is continually providing manufacturers and sup- pliers with new challenges and is set to significantly alter our world of mobility. LuK is embracing these challenges. With a wealth of vision and engineering performance, our engineers are once again proving their innovative power. Bühl, in April 2002 This volume comprises papers from the 7th LuK Symposium and illustrates our view of technical developments. Helmut Beier We look forward to some intere- President sting discussions with you. of the LuK Group Content

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

LuK SYMPOSIUM 2002 Small Starter Generator – Big Impact

Thomas Pels Dierk Reitz László Mán Bård Vestgård, Kongsberg DevoTek

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Introduction layout is also described as a ‘Crankshaft Start- er Generator (CSG)’ or ‘Integrated Starter As a logical step in the continuing develop- Generator (ISG)’ and is particularly applied in ment of propulsion systems, hybrid drive combination with manual transmissions [4]. trains offer enormous potential for reducing One disadvantage of such a structure is the fuel consumption [1]. However, in addition to limited recuperation potential as a result of environmental aspects, service value comfort drag losses when the combustion engine is and, above all, costs play a crucial role in fu- coasting. ture powertrain concepts. With this in mind, the versions preferred by LuK are those with the 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 opportunities for wide market penetration in the medium term. The first part of the article presents the electrical shift gearbox (ESG), which has the particular advantage of combining the properties of the twin clutch or parallel shift gearbox with the functions of a mild hybrid. The second half presents the starter generator Fig. 1: PSG with Crankshaft Starter Generator in the belt drive (RSG), which offers start-stop functionality with minimum effort. LuK has de- Figure 2 shows a solution with a further clutch veloped a compact two-speed gearbox, which between the E-machine and crankshaft. With extends the application range of the RSG to this configuration, the full potential for regen- high-capacity Otto and Diesel engines. erating energy can be exploited by decoupling the combustion engine when coasting. The Electrical Shift Gearbox (ESG)

Position of the Electrical Machine

The parallel shift gearbox with dry clutches (PSG) offers the ideal basis for a powertrain with high comfort and very good efficiency [3]. To further reduce fuel consumption, the pos- Fig. 2: PSG with three Clutches sibilities for incorporating an electrical machine will be investigated. In addition to the According to simulations for the New European fast, silent start (start-stop), this should also Driving Cycle (NEDC) estimated achievable enable the regeneration of energy from decel- savings are between 15-20% [5]. Moreover, by eration (recuperation) and ‘downsizing’ of the disconnection of the internal combustion engine combustion engine by means of a booster to further reduce fuel consumption, the vehicle function. Figure 1 shows the first attempt at a can be moved pure electrically by the E-ma- direct connection of the E-machine to the chine. In relation to a downsizing of the combus- crankshaft of the combustion engine. Such a tion engine, consumption reductions of approx-

212 LuK SYMPOSIUM 2002 18 Small Starter Generator – Big Impact imately 30% (NEDC) were verified on (built-up) prototypes [6].

The LuK concept goes a step further. As figure 3 shows, it is proposed to integrate the E-machine in the gearbox. In addition to further functional advantages, which will be ex- plored in the next section, this structure offers significant packaging and cost benefits and is described in the following as the electrical shift gearbox (ESG).

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

Fig. 3: Electrical Shift Gearbox

Functions

In order to clearly explain the individual functions of the ESG, both separate gearbox units are shown in parallel (c.f. figure 4). The lower unit contains the odd gears and clutch K1 and is known as gearbox unit 1. Alongside that, gearbox unit 2 consists of the even gears and clutch K2.

Driving with the Combustion En- gine During operation in gearbox unit 2 the starter generator (SG) is directly linked to the combustion engine via clutch K2. Figure 4 shows Fig. 5: Driving in 5th Gear with Gearbox Unit 2 in Neutral an example of driving in 4th gear with generator function. Reversing the torque direction on the E-machine results in a booster function. then clutch K2 is closed to transfer generator torque (figure 5). With a pre-selected gear, the According to the shift strategy in gearbox E-machine is driven via the engaged gear - as unit 2, during operation in an odd gear, either described in figure 6. A booster function can an even gear is pre-selected or a neutral po- again be performed by reversing the torque di- sition is selected. If gearbox unit 2 is in neutral, rection on the electrical machine.

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Kinetic Energy Regeneration (Re- cuperation) In order to achieve efficient usage of energy from deceleration, the combustion engine is decoupled from the drive train when coasting. The E-machine, which builds up generator torque according to speed, brake pedal position and optimum gear ratio, takes over deceleration of the vehicle and converts the kinetic energy into electrical energy (figure 8).

By integrating the air-conditioning compressor into gearbox unit 2 as per figure 9, the kinetic energy of the vehicle can also be directly used to produce cooling energy. Hence if power demand of the electrical consumers is low, intermediate storage in the battery, which is af- fected by efficiency, is avoided. Provided that Fig. 6: Driving in 5th Gear with th the air-conditioning system (A/C) has in- Pre-Selected 4 Gear creased storage capacity, e.g. through a larger evaporator unit, refrigerant is cooled for lat- Electrical Start-Up/Driving er use during standstill. If a suitable refrigerant such as CO is used, It is possible to drive purely by means of elec- 2 the air-conditioning system can also produce tricity with suitably large electrical power from heat [7]. In addition to benefits in energy the E-machine and battery. For this, both alongside the direct production of cooling en- clutches remain open and, depending on the ergy during recuperation, the system shows speed and load, together with the efficiency nd th promise for heat management in the hybrid map, the torque is fed over the 2 , 4 or vehicle. 6th gear to the wheels (figure 7).

Fig. 7: Electrical Driving Fig. 8: Recuperation

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Fig. 9: Recuperation Including Fig. 10: Stationary Air-Conditioning Air-Conditioning System

This particularly applies to modern combus- bustion engine via gearbox input shaft 2. Dur- tion engines with direct-injection, fully variable ing a standstill phase, the starter generator valve timing and similar, which, due to their low can electrically drive the air-conditioning com- part-load consumption’s, are partly already re- pressor in neutral position of gearbox unit 2 lying on auxiliary heaters today. and with an opened clutch K2, as illustrated in figure 10. Stationary Air-Conditioning In future vehicles, stationary or pre-air-condi- Cold Start tioning will be considered to increase comfort. Moreover, adequate air-conditioning is re- In addition to reduce the required maximum quired during the standstill phases of the com- torque of the electrical machine, ensuring the bustion engine in start-stop operation. How- power output of the battery as small as pos- ever, in LuK’s opinion, the electrically driven sible is the main goal to optimise cold starting systems currently being investigated to satisfy behaviour [9]. The conventional starter satis- these requirements have some drawbacks. fies this requirement through a high gear ratio Firstly, an E-machine with a mechanical power between the rotor shaft and flywheel. output of approx. 2 - 5 kW must be installed. Figure 11 illustrates the fundamental advan- In addition the starter generator including the tages resulting from this gear ratio, whereby power electronics for electrical supply of the a 1.9 l DI-Diesel engine is used as an exam- compressor drive has to be correspondingly ple. Firstly it results in an increased inertia larger. Altogether, in addition to a disadvan- (when referring to the crankshaft) compared tage in terms of weight, it leads to considera- to a crankshaft starter generator, by which the ble costs for electrical components. Further- speed fluctuations during start-up are signifi- more, in view of the repeated energy conver- cantly reduced. By keeping to a minimum sion compared with a conventional system, it speed necessary for a safe start-up (here: results in disadvantages in terms of energy [8]. 80 1/min), this produces lower average start- On the ESG the air-conditioning compressor ing speeds and thus reduced mechanical is connected to the E-machine via the conven- starting power. Furthermore, the E-machine tional magnetic clutch. In normal driving, the runs in a speed range of significantly higher power is provided mechanically by the com- efficiency by the gear ratio, through which the

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

electrical power absorbed from the battery a neutral gear shift in the transfer gear of a can again be reduced. 4-wheel drive vehicle.

Two potential solutions are presented for de- The shifting of an axially movable gear wheel to the flywheel provides a second version of signing a cold start gear ratio to the ESG. The a cold start gear ratio. This is explained in integration of the E-machine into the gearbox chapter The ESG Prototype in more detail. enables two existing gears to be used as a cold start gear ratio. Figure 12 shows the torque flow from the starter generator to the combustion engine via a combination of two gear wheels of the gearbox.

With this configuration, start-up gear ratios between 2.5 and 7 can be achieved, according to the selection of the gear wheel pairing. Dur- ing the start-up process the vehicle output shaft must be decoupled. As the example in figure 13 shows, this can be done via a modified dog clutch, which connects gear wheels 2 and 5 in the cold start position as an additional position and simultaneously decouples the output shaft (figure 13c). However, decoupling is generally also possible using a neutral Fig. 12: Cold Start with Combination of position of other shift elements, e.g. through two Gears

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a) Warm Start

Warm start occurs in the neutral position of gearbox unit 2 via clutch K2 to the combustion engine. To reduce the time until the vehicle starts up, a creeping torque can be fed to the output shaft during the start-up process via clutch K1 and engaged 1st gear (figure 14). Due to the additional gear ratio, the cold start requirements on the E-machine are reduced as shown in figure 11. The torque required for b) quick acceleration of the combustion engine after a stop phase is therefore a determining factor in the system. This results in a comparatively compact starter generator design and a very low rotor inertia. This is of crucial im- portance for maintaining short synchronisation times in Gearbox Unit 2.

Fig. 13: Modified Dog Clutch a) Neutral b) 2nd Gear Engaged c) Cold Start Position Fig. 14: Warm Start in Start-Stop Operation

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The ESG Prototype a gear ratio of 1 by the rotor shaft by a V-ribbed belt. Figure 15 shows the general view of the drive train with the orientation in the engine By building up a vehicle, LuK wants to show compartment. Fixation of the E-machine to the that it is possible to achieve the functions of gearbox is done via a modified gearbox brack- the drive train concept described in the previ- et. Additional reinforcement is achieved by the ous section, without adversely affecting the bolting of the seal face between the gearbox comfort of the standard transmission. In particular, it is the synchronisation of gearbox casing and intermediate gear, as shown in unit 2 and the dynamic coupling / decoupling figure 16. of the combustion engine to facilitate the recuperation operation that are at the forefront In order to exploit the benefits of a cold start of the development. gear ratio as described, the E-machine is directly connected to the flywheel of the crank- The test vehicle is a passenger car from the shaft in the test vehicle during cold starting. lower medium-class size with a 1.3 l DI-Diesel Figure 17 shows the principle, which is similar engine and a 5-speed PSG with dry clutches. to a conventional starter mechanism. A gear The 42 V starter generator is positioned in wheel, movable in an axial direction by a so- driving direction in front of the gearbox with the lenoid mounted on the extended motor shaft, axle in parallel to the gearbox input shaft. The can be engaged in the starter ring gear. The connection occurs via an intermediate gear to optimised layout of the E-machine means that the gear wheel of the 4th gear with a ratio of an axle base between gearbox input shaft and 0.84. The air-conditioning compressor is fixed rotor shaft can be achieved, which enables a to the E-machine housing and is driven with cold start ratio of 3.5.

Fig. 15: General View of the Drive Train

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existing auxiliary drive [12]. Furthermore, the relatively low starting power enables the use of traditional 12 V lead-acid batteries, possibly in AGM technology (Absorptive Glass Matt). The RSG can be combined with all gearboxes without the need for modifications to the drive train. Consequently, the application requires considerably lower development effort in comparison with all other starter generator systems.

Figure 18 shows a schematic drawing of the RSG system operating principle in the start mode. It shows that the gear ratio of the V- ribbed belt (2.5 ... 3) on Diesel engines and Fig. 16: View of ESG Components larger Otto engines is not sufficient for safe starting, especially at low temperatures. For this reason, LuK has developed a compact two-speed gearbox, which enables a higher overall ratio (e.g. 6…7) for starting.

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

Starter Generator in the Belt Drive (RSG) Fig. 18: Operating Principle - Start Mode

Operating Principle

The great potential for reducing fuel consumption through the increased functionality of the ESG requires extensive intervention in the drive train. This includes complex measures in the design of control units and software to integrate an energy management system. If functions are reduced to the start-stop operation, the belt driven starter generator be- comes an attractive solution [5, 10, 11]. This concept enables the use of tried and tested components with minimum changes on the Fig. 19: Operating Principle - Generator Mode

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After the first ignition, the combustion engine drives 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 a two-speed gearbox is always required, cannot be defined precisely due to the many different E-machines being developed. The belt layout also has a considerable effect on the achiev- Fig. 21: Torque Flow in Planetary Gear Set on able gear ratios of the specific accessory Running Combustion Engine drives. LuK assumes that two-speed gearboxes are used on RSG systems for Otto engines O1.8 l displacement and for Diesel engines from around 1.4l cylinder capacity. These ref- During start-up torque is transferred from the erence values apply to a system with a nom- electrical machine via the belt to the pulley. inal voltage of 14V. On more powerful 42V- The torque is fed over the sun gear linked to systems the application range without a two- the belt pulley into the planetary gear set. At speed gearbox is naturally extended. In view of the functions (and costs!), such applications the same time the ring gear is joined via a are more likely to be categorised as mild or soft (start-up) free wheel to the crankcase. The hybrids [13]. torque on the internal ring gear is thus added to the torque that is fed and is transferred via Figures 20 and 21 show the essential gearbox the planet carrier to the crankshaft. Depend- components and clarify the torque flows during on the design, the starting gear ratio of this ing the states of start and generator operation. gearbox is between 2.5 and 3.5. As soon as the combustion engine starts to deliver torque, the start-up free wheel is overtaken until, fi- nally, all planetary gear components rotate at the same speed. Then the second one-way clutch, which is now transferring combustion engine torque from the planet carrier direct to the sun gear, i.e. with gear ratio 1, engages. This second free wheel decouples all accessories from the cyclic irregularities of the combustion engine in generator operation and is thus described as an auxiliary free wheel. Figure 22 represents measurement results from the auxiliary free wheel on the combustion engine test rig with a 1.9 l DI Diesel engine Fig. 20: Torque Flow in Planetary Gear Set during the Start Process under load.

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In addition to providing a high gear ratio for the this example the damper mass is connected start operation and decoupling the accesso- to the crankshaft via a rubber ring. Figure 24 ries, the gearbox also takes on the function of shows a layout with damper as a separately a crankshaft damper, which many engines designed component. The gearbox is con- need at the free crankshaft end for reducing nected to the crankshaft of the combustion en- torsional vibrations. For this, the required gine via a central screw. damper mass is connected to the planet carrier, either by a rubber spring or by using spe- Due to the short time duration of speed differ- cial helical compression springs, depending ences in the gearbox, only small demands are on the design. If steel compression springs are made on the lubrication of the components. A used, this enables the natural frequency to be maintenance-free grease fill will satisfy these tuned precisely, thus allowing the use of rela- requirements and also offers benefits for the tively small damper masses. Given the varied selection of low-cost, low-friction seals. packaging space proportions, it can, however, make sense to keep the crankshaft damper, By using a simple actuator, the gearbox gains which is sometimes designed as a separate additional functionality. The fixation of the in- component, as an independent unit. Such a ternal ring gear to the crankcase is controlled version is presented among other items in the next section. by the actuator. This happens by interrupting the torque flow to the casing bracket with a so- lenoid. For that reason the starter generator, in motor operation, can drive accessories with a crankshaft at standstill. This is an interesting option, especially when viewed alongside stationary air-conditioning.

Fig. 22: Decoupling of Accessory Drive (Measurement)

LuK Gearbox Variants

As described in the previous section, the gearbox can be positioned on the crankshaft or al- ternatively on the rotor shaft of the generator. The basic difference in these is that the integration of the gearbox into the crankshaft pulley permits the use of a V-ribbed belt due to the lower force level in the belt. Both versions have been built at LuK in different variations and examined on test rigs and in vehicles. Figure 23 shows a sectional illustration of a Fig. 23: Gearbox with Integrated Crankshaft gearbox with integrated crankshaft damper. In Damper

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The belt driven starter generator is characterized by the following features: ; Reduced fuel consumption due to Start-Stop of the internal combustion engine ; Low development effort, easy application ; Connection to combustion engine independent of drive train ; Very low system costs, especially when 14 V system is used ; No additional weight ; Convenient packaging proportions By using the described two-speed gearbox, a lower belt ratio can also be realized. In addition to providing significant relief of the belt and tensioning system, this leads to further consumption benefits through better operating points of the generator and reduced iner- Fig. 24: Gearbox with Separate Crankshaft Damper tias. LuK also sees additional benefits in the vibrational decoupling of the auxiliary drive through the free wheel functionality and the Summary optional neutral position of the gearbox for the electrical drive of air-conditioning compres- The ESG is characterized by the following features: sor, water- and powersteering pump on a stationary combustion engine. ; Very low fuel consumption due to Starter generators and hybrid drive train are – Start-Stop operation of the internal the appropriate means for significantly reduc- combustion engine ing fuel consumption in future vehicles. Both – Recuperation with a decoupled com- of the systems presented here have the po- bustion engine tential to make a considerable contribution to – Integration of the air-conditioning in the reducing the much discussed anthropoge- powertrain management system nous CO2 emissions in accordance with leg- islative requirements. ; Shift comfort the same as the basic gearbox without an E-machine ; (Mild) hybrid as add-on solution with electrical power up to 30 kW, depending on requirements ; Comparatively low costs due to reduced demands on electrical components ; Optimum dimensions of E-machine and power electronics ; Increased functionality (electrical driving, booster function, stationary air-conditioning)

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References ciency, 10th Aachen Colloquium Auto- mobil and Engine Technology 2001. [1] Weiss, M.; Heywood, J.; Drake, E.; [7] Kuhn, P.; Graz, M.; Obrist, F.; Schafer, A.; AuYeung, F.: ON THE Parsch, W.; Rinne, F.: Kohlendioxid- ROAD IN 2020 – A life-cycle analysis of R744 als Kältemittel in Fahrzeug-Kli- new automobile technologies, Energy maanlagen, ATZ 103 Nr. 12, 2001. Laboratory MIT Cambridge 2000. [8] Morgenstern, S.: Endenergieverbrauch [2] Reik, W.: Mögliche Anordnungen des von Kältemittelkompressoren im Pkw, Startergenerators im Antriebsstrang. Haus der Technik Tagung ‘Nebenaggre- LuK Fachtagung ‘E-Maschine im An- gate im Fahrzeug’ 2001. triebsstrang’ 1999. [9] Höcker, J.; Richter, G.: Development [3] Berger, R.; Meinhard, R.; Bünder, C.: trends for future car batteries, VDI- The Parallel Shift Gearbox PSG – Twin Berichte Nr. 1418, 1998. Clutch Gearbox with Dry Clutches, 7th LuK Symposium 2002. [10] Bischof, H.; Bork, M.; Schenk, R.: Start- ergenerator: System, Funktion, Kompo- [4] Koch, A.; Lehmann, J.; Probst, G.; nenten, LuK Fachtagung ‘E-Maschine Schäfer, H.: The Integrated Starter- im Antriebsstrang’ 1999. Generator as Part of the Powertrain Management, 9th Aachen Colloquium [11] Pels, T.; Mán, L.: Strukturen für Starter- Automobil and Engine Technology generatoren, Haus der Technik Tagung 2000. ‘Nebenaggregate im Fahrzeug’ 2001. [5] Reik, W.; Pels, T.; Reitz, D.: Strukturen [12] Duhr, J.; Farah, P.; Schoester, L.: für Startergeneratoren und Hybrid- Stop/Start Function: The Clawpole Ma- antriebe - Integrierter Startergenerator chine - a good alternative to the ISG, (ISG), Hrsg. Schäfer, H., expert Verlag Haus der Technik Tagung ‘Energies- 2000. peicher- und Generatorsysteme für Kraftfahrzeuge’ 2000. [6] Mesiti, D.; Rovera, G.; Tamburro, A.; Umberti, M.: Minimal Hybrid Configura- [13] N. N.: Mild hybrid set for production, tion Using an Automatic Dual Clutch European Automotive Design Septem- Gearbox for Matching Comfort and Effi- ber 2001, p. 86.

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