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Synthesis_of_an_8-speed_AT_for_hybrid_drives 8AT混合动力变速箱.pdf

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SYNTHESIS_OF_AN_8 SPEED_AT_FOR_HYBRID_DRIVES AT 混合 动力 变速箱
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SYNTHESIS OF AN EIGHT-SPEED AUTOMATIC TRANSMISSION FOR HYBRID DRIVES IAV develops future transmission generations by using computer-aided synthesis programs. The new eight- speed planetary automatic transmission for transverse applications results from a total solution amount of 1.6 billion transmission variants. The derivable modular transmission system comprises a conventional trans - mission as well as a mild and a full hybrid version. It offers numerous advantages in comparison with current systems regarding speed number, hybrid functions, efficiency, size and costs. 16 COVER STORY TRANSMISSIONS06I2010 Volume 10 MORE RATIO RANGE The vehicle transmission harbors major potential for meeting the challenges exhaust gas and fuel consumption. Wide ratio ranges with a high number of well- stepped speeds ensure efficient coverage of the combustion-engine map and deliver plenty of traction. Manual transmissions currently providing a maximum of six speeds and ratio ranges up to ? total≈ 6 will in future hardly be in a position to satisfy these goals. Further ratio steps reduce the driving comfort as a result of the greater amount of gear-shifting effort they involve and the risk of overburdening the driver becomes greater which is why theoretical fuel savings are not necessarily achieved in real operation. Fully automatic transmissions are better suited to providing driving comfort from a large number of ratio steps. Present-day dual-clutch transmissions offer as many as seven speeds and ratio ranges of ? total≈ 6.5. Even higher numbers of ? total≈ 7 are possi- ble with planetary automatic transmissions with up to eight ratios. As a result of the more exacting design-space restrictions in vehicles with front-transverse engines, map converters of this type are only mass-pro- duced with a maximum of six speeds and a ratio range of up to ? total≈ 6. At present, round 80 % of all passenger cars worldwide are powered by front, trans- versally installed combustion engines. It is expected that with production figures rising, this percentage will increase over the next few years. This means that from the aspect of reducing fleet consumption, the signifi- cance of fully automatic, front-transverse transmissions with a greater number of speeds is set to grow. Dual-clutch transmis- sions, particularly those operated electrome- chanically, permit marginally better con- sumption over planetary automatic trans- missions which, in turn, are more compact in design, more cost-effective to make and also provide better driveaway dynamics and shift strategies with greater flexibility [1]. It is for this reason that the following analyses focus on planetary automatic transmissions for front-transverse applications. With planetary automatic transmissions, the traditional approach to providing addi- tionally required ratio steps is to use fur- ther mechanical transmission components, such as gear sets or shift elements. Although this has an adverse effect on costs, weight and size, the trade-off can be resolved by means of innovative gear structures that employ the limited number of transmission components for more speeds. 1 shows the key aspects develop- ers are aiming to optimize, such as achiev- ing high levels of efficiency, low drag losses and less loads on mechanical com- ponents. Hybridizing the conventional powertrain produces the means for realiz- ing many demands as a result of the addi- tional degree of freedom it offers on the energy-management side. Intelligent mod- ular systems made up of conventional and hybrid transmission variants reduce devel- opment and production costs. The conventional and predominantly intuitive search for new gear structures is less suitable for taking account of these complex challenges. The abundance of DIPL.-ING. ERIK SCHNEIDER is Head of Hardware Development for Transmission and Hybrid Systems at IAV GmbH in Chemnitz (Germany). DIPL.-ING. J?RG MüLLER is Manager of the Transmission and Hybrid System Concepts and Synthesis Team at IAV GmbH in Chemnitz (Germany). DIPL.-ING. MIRKO LEESCH is Development Engineer in the Transmission and Hybrid System Concepts and Synthesis Team at IAV GmbH in Chemnitz (Germany). DIPL.-ING. RICO RESCH is Development Engineer in the Transmission and Hybrid System Concepts and Synthesis Team at IAV GmbH in Chemnitz (Germany). AUTHORS 1 Key aspects and demands on a vehicle transmissions with each optimization aim 17potential solutions also harbors a high risk of overlooking significantly better transmis- sions. Instead, increasing use is being made of systematic syntheses that examine all realizable combinations of transmission topologies on a computerized basis [2]. IA V presents here the methodology behind such synthesis programs for creat- ing new transmission generations with favorable properties for conventional and hybrid drives. By way of example, the potential of this approach is demonstrated on the basis of a new hybrid eight-speed planetary automatic transmission for front-transverse applications. PRINCIPLE OF SYSTEMATICALLY TRANSMISSIONS SYNTHESIS Before synthesis can commence, it is neces- sary to define the demands that are placed on the new transmission for any type of powertrain, for example in passenger cars, commercial vehicles or railway applications. The following properties provide the input data for the synthesis program:: demanded series of ratios: necessary power shifts: maximum number of components for the available package: position of input and output: maximum loads: hybrid functionalities. Using the example of planetary automatic transmissions 2 on the left illustrates the principle followed by IA V-made synthesis software, this being divided into two pro- gram parts. The first program part initially generates all possible combinations of con- ventional transmission variants on the basis of the input data. The computer calculates all of the mathematically coded planetary gear set topologies as well as shift-element configurations, combining these to create gear structures that are then tested with graph-theoretical algorithms in relation to actually being able to implement the design. Only appropriate options are then examined for their maximum number of speeds. Once this has been done, the gear-set ratios for the gear structures offering a sufficiently high number of speeds are optimized in such a way that the demanded series of ratios is achieved in the best possible way while taking into account the necessary power shifts. By way of option, the algo- rithm also allows for additional secondary conditions, such as the achievement of high levels of tooth efficiency or low loads on the components. ② illustrates at the top right the tremendous solution diversity this syn- thesis step offers. Even as few as three plan- etary gear sets with five and six shift ele- ments result in the program investigating some 1.6 billion gear structures. With four planetary gear sets, the number of solutions found rises to 1091 billion codings. The second program part of the program performs a benefit analysis to examine and evaluate all of the generated gear structures in relation to their conventional properties, such as number of parts, series of ratios, shift logic, torque and speed loads on components, levels of efficiency and drag losses. The software also investigates the feasibility of implementing the demanded hybrid functionalities, such as starting the combustion engine, all-electric driving, boosting and recuperation capability as well as infinitely variable electrical power- split driving ranges. For this purpose, the synthesis program takes into account all of the options for integrating one or more electric motors in the transmission. The weightings and limit values for the various criteria can be matched extremely accu- rately to the specific application, leaving only transmissions with the best conven- tional and hybrid properties in the final set of solutions. This is then presented in a ranking list. ② shows at the bottom right the typical procedure for preparing the results in this way, with each point repre- senting a newly synthesized transmission. Individual search areas are characterized by different component configurations. These transmissions that best meet the overall requirements are of major significance to the subsequent development process. MODULAR SYSTEM OF THE NEW PLANETARY AUTOMATIC TRANSMISSION The potential offered by systematically synthesizing transmissions in the way presented is now illustrated on the basis of a generated transmission system. The aim of developing the new eight-speed plane- tary automatic transmission for front-trans- verse applications is to arrive at significant advantages over the state of the art. Pro- viding two additional forward speeds with- out further gear sets and shift elements, improving overall efficiency as well as permitting parallel hybrid modes that also offer the best possible level of efficiency are the main boundary conditions. Electric propulsion obviates the need for any mechanical reverse speed. In addition to this, the gear-set topology is to form the basis for a variable modular system. The results of synthesis is the gear-set structure of a mild hybrid planetary auto- matic transmission presented in 3 on the left with the associated shift logic shown in tabular form in 4 . Using just three simple minus planetary gear sets, two brakes and three clutches, it is possible to produce eight well-stepped forward speeds with a 2 Sequence and solution variety of the systematic transmission synthesis COVER STORY TRANSMISSIONS 1806I2010 Volume 10 high ratio range of, for example, ? total= 7.6 by selectively engaging three shift elements. Both configurations illustrate how easy it is to adapt the series of ratios to different requirements. The high driveaway ratio provides the capability of driving off in first gear with one internal shift element. Com- bustion-engine power is transferred extremely economically as a result of high levels of tooth efficiency and low engine speeds, keeping drag losses low in only ever two open shift elements and in the bearings. The large number of possible power shifts forms the basis for flexible driving strategies. The electric motor is integrated by means of an additional ratio 3 Construction set system of the eight-speed automatic transmission   order your own JOT-IST- subscription! Two issues p.a. print-/ e-magazine: 69,– €  per e-mail barbara.brueckbauer@ springer.com  per fax +49(0)61 1.78 78-440 International Surface Technology www.jot-ober? aeche.de 100040_55x240_4c.indd 1 12.02.2010 10:47:34 4 Shift logic of the eight-speed automatic transmission 1 stVariation 2 ndVariationShift element engagedShift element engaged for operation with combustion engine Stationary ratios P1 –3.16 –3.16 P2 –3.32 –3.32 P3 –2.02 –2.02 Additional ratios S1 –0.99 –0.995 S2 –1.10 –1.00 CD 1.67… 2.22 1.67… 2.22 Speed Brake Clutch Ratio Ratio Structure A B C D E F G Conventional + Mild hybrid + Full hybrid 1 4.63 5.09 2 2.92 2.90 3 1.92 1.81 4 1.31 1.20 5 1.07 1.01 6 0.85 0.82 7 0.74 0.73 8 0.68 0.67 Conventional R –3.3 –3.63 Mild hybrid Start ICE 1.67… 2.22 1.67… 2.22 1 E 7.72 … 10.28 8.48 … 11.31 2 E 4.87… 6.48 4.83 … 6.44 Full hybrid Start GN ∞ … 2.92 ∞ … 2.90 Step 1.59 1.52 1.47 1.23 1.26 1.15 1.10 ? total 6.9 1.59 Step 1.75 1.60 1.51 1.19 1.22 1.13 1.08 ? total 7.6 1.75 19stage to the input shaft. The resultant torque multiplication permits comfortable combustion-engine starting and dynamic electric operation in both directions of travel with an electric motor smaller than a crankshaft starter generator. The higher engine speed also makes it possible to exploit maximum electrical power output during boost and recuperation cycles, even when driving in an economical style at low combustion-engine speeds. The clutch on the input side decouples the combustion engine during electric propulsion and starts the primary engine without repercussions while the vehicle is in motion. Further transmission variants can be derived from this gear-set topology with only minor component modifications. For a conventional planetary automatic trans- mission (③ , center), a mechanical reverse speed is supplemented by a third brake. The use of a hydrodynamic converter as a drive- off element is a conceivable option. The full-hybrid derivative (③ , right) with a fur- ther sun gear shaft on the output planetary gear set provides comfortable, infinitely var- iable, electrical power-split driving ranges with low levels of electric actuation power at the two electric motors. Continuously variable start-off from neutral can be used for both directions of travel and replaces a conventional drive-off element. Modular systems of this type can be used in future to help reduce manufacturing costs as they permit a high level of component sharing. DESIGN OF A MILD-HYBRID PLANETARY AUTOMATIC TRANSMISSION Selected design details of the eight-speed planetary automatic transmission for a mild hybrid are described in the following as a way of permitting better assessment of the synthesized gear set structure (③ , left). The gear structure is extended by an addi- tional reverse-speed brake to ensure a rep- resentative comparison with today‘s con- ventional transmission generations. A typi- cal front-mounted transverse combustion engine with a maximum torque of 350 Nm and maximum speed of 6000 rpm provides the platform. With the hybrid transmis- sion, it is necessary to consider the addi- tional typical load profiles for the electric motor which has a maximum torque of 75 Nm and a maximum power of 12.5 kW . All of the clutches and brakes as well as two of the planetary gear sets are positioned on the main drive shaft, 5 . T o realize all power shifts, the shift elements are of disk- type design. T o reduce axial length, the third planetary gear set is positioned on the intermediate shaft and connected by means of two spur-gear sets. The output gear set to the differential has a ratio of 3.56. In combi- nation with the second option for configur- ing the gear-set ratio shown in ④ , plenty of drive-off traction can be provided with inter- nal shift elements which is why there is no need for any hydrodynamic converter, also saving space. All planetary gear sets are extremely compact on account of the favorable sta- tionary gear ratios. As a result of higher levels of torque, it is necessary to make the third planetary gear set just slightly more solid by using an additional fifth planetary gear. The permanent-magnet excited syn- chronous motor is positioned close to the intermediate shaft. Use of the chain drive allows easy adjustment of ratio to the input shaft and prov
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