{"title":"新型高效无级变速器,适用于中级FWD车辆","authors":"K. Kim","doi":"10.51202/9783181023730-i-271","DOIUrl":null,"url":null,"abstract":"Many kinds of transmissions have been developing and recently electrification is processing rapidly to reduce fuel consumption. Automatic transmission has been developing in multistages to improve fuel economy and power performance. CVT, kinds of transmissions, also need to increase the ratio spread to improve the two performances. Thus CVT has better fuel economy performance through the engine’s optimal operating. So, CVT would be a good solution for fuel economy among the conventional transmissions. The newly developed CVT for FWD vehicles has wider pulley ratio spread than any other competitors. And in spite of wide ratio coverage, CF28 has good competitiveness in the overall length by minimizing the length increase. In spite of reducing transmission length, we had achieved maximum torque capacity, minimum length, highest efficiency, and largest pulley ratio coverage compared to competitors’ middle-class CVTs. Introduction Recently many kinds of transmissions have been continuously developing to increase driving performance and reduce fuel consumption, And to achieve vehicle mount-ability, it necessary to miniaturize the transmission, because the room for transmission gets smaller and smaller. The newly Continuous Variable Transmission(CF28) for the front-wheel-drive vehicle which was recently developed, substantially enlarge the torque capacity based on the current Small-CVT(CF18). Nevertheless, the driving performance has greatly improved through the expansion of ratio span, the competiveness of efficiency, weight and overall length is the best in the same class CVT. The planetary gear was newly designed to reduce the overall length of the transmission and the clutch, hydraulic system, torque converter and oil pump were optimized to improve the efficiency. And the belt & pulley also had been newly designed for the wider ratio span, fewer components, and shorter overall length, lower the weight. In this paper, the new planetary gear, new belt & pulley system, and newly optimized systems for marketability would be described. VDI-Berichte Nr. 2373, 2020 271 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. <Specification Comparison> CF18 (Existing Model) CF28 (New Model) Torque Capacity [kgf.m] 18.3 28 Overall Length [mm] 351 359 Gear Span [UD/OD] 7.0 7.5 Weight [Wet, kg] 73 88 TORQUE-UP, MINIMIZING AND WEIGHT REDUCTION Figure 1 below shows that the CVT for front-wheel (CF18), which is currently in production, has one planetary gear set, one clutch set and one brake set. The newly developed CF28 has been increased only 8mm in overall length despite the fact that the torque capacity was increased by 53% compared to the current mass production CF18. Fig. 1: Cross section of CF18 Fig. 2: schematic of CF18 The following is a description of how we were able to minimize the increase of the overall length and weight. 1. Structure of Planetary gear and Brake To reduce the overall length, it was necessary to change the structure of planetary gear and brake system. Regarding this changes, there are also changes in power flow. The hub of the brake was changed to integrate with carrier rather than the annulus gear. Therefore it was VDI-Berichte Nr. 2373, 2020 272 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. possible to remove the connecting plate of annulus gear and one thrust bearing, and the overall length could be reduced by 6.1mm. The input of power flow was changed from sungear to annulus-gear, and output of power flow was changed from carrier to sun gear. CF18 CF28 Fig. 3: Planetary Gear & Brake 2. Structure of Sheave Connection To reduce the overall length, it was necessary to change the structure of the pulley system. Fixed sheave and movable sheave of CF18 were connected by rollers so that movable sheave can rotate together with fixed sheave and can move through the fixed shave’s axis. But fixed sheave and movable sheave of CF28 were changed to be connected by spline without rollers. Therefore the pulley length could be reduced by 4.2mm. In addition to the overall shortening effect, this change also has an effect on reducing the number of parts and simplification of the assembly process. CF18 CF28 Fig. 4: Fixed Sheave & Movable Sheave VDI-Berichte Nr. 2373, 2020 273 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. 3. Optimize the Packaging Condition To improve the packaging condition on vehicle, packaging analysis had been completed with various vehicles. So, it was necessary for CF28 to optimize external designs of transmission. Design of Housing parts and external devices had been more optimized to improve the mount ability on middle class vehicles. As a result CF28 has a good competitiveness compared to competitors’ middle class CVT.(Fig. 5) According to In-Diff. distance, CF28 has two option to satisfy the mount-ability on various vehicles(189mm/204mm). Especially 189mm of In-Diff. distance is difficult condition for constructing internal parts in middle class CVT. This is about 8mm smaller than the competitor’s middle class CVT. Fig. 5: Package Layout Fig. 6: Comparison of Packaging Condition EFFICIENCY IMPROVEMENT Needless to say, the transmission efficiency is more important than ever in accordance with the recent fuel efficiency regulations. VDI-Berichte Nr. 2373, 2020 274 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. The front-wheel CVT(CF18), which is currently in production, boasts the world’s highest level of CVT efficiency. Likewise CF28 has significantly improved efficiency compared to competitor’s middle-class CVT. 1. Oil Pump Oil pump was one of the biggest losses in the transmissions using hydraulic control and We could improve transmission efficiency through optimization of capacity and minimized drive losses. The oil pump of CF28 is vane type, which is able to reduce drive torque loss by maximum 9% in comparison to gear-type pump. It allowed an improvement of 0.4% in CVT efficiency. Fig. 7: Comparison of Drive Torque 2. Chain Belt Chain belt is also important item to improve the efficiency dramatically. The chain was also applied to the CF18 and had been proved to be very efficient compared to the push belt. Chain belt of CF28 has better efficiency of 5% in under-drive area, 3% in over-drive area than push belt of CF28 in same CVT assembly. As a result, chain belt has better efficiency of 1.9% than push belt, It also appeared with a fuel economy difference of 1.2% on vehicle test. It is due to the fact that the chain has less friction loss than the belt. Chain Belt Push Belt Fig. 8: Variator of CVT Pulley VDI-Berichte Nr. 2373, 2020 275 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. Fig. 9: Efficiency Test in CVT Assembly 3. Separating Spring Separating springs were applied to reverse brake system to improve the efficiency while driving forward. Because when CVT operates driving forward, the drag torque must be occurred on disk set of reverse brake. Forward clutch does not need separating spring because forward clutch is engaged in step “D” position and drag torque is not generated. These springs are assembled between the disk set, and help the brake’s each disk to maintain same clearance. This prevents the drag torque loss from increasing because the disk is positioned to one side. Reverse Brake Disk set Separating Spring Fig. 10: Separating Spring in Brake VDI-Berichte Nr. 2373, 2020 276 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. 4. Wider Pulley Ratio Span Ratio span is one of the important performance indicators of transmission. Wider ratio coverage improves fuel economy in the high ratio region and acceleration in the low ratio region. In the high ratio region, the engine speed is lowered to improve fuel efficiency. In the low ratio region, the engine torque is multiplied to improve the acceleration performance. Fig. 11: Wider Pulley Ratio To increase the pulley ratio width, the distance between two pulleys‘ axes was also increased by 5%. And system analysis had been done to secure stiffness under the worst use conditions, to optimize sheaves in terms of weight reduction. Primary Pulley Secondary Pulley Fig. 12: Pulley Strength by CAE Analysis VDI-Berichte Nr. 2373, 2020 277 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. Fig. 13: Pulley Deformation by CAE Analysis COST REDUCTION In modern rimes, the competition of the transmissions on the price and efficiency is getting overheated. The cost reduction technologies had also been applied to lower the material cost, and then to improve the marketability of CF28. The price competitiveness of CF28 also reached the world's highest level in the middle class vehicles’ CVTs which is currently in production. 1. Single Pinion Planetary Gear In the case of two-step CVT, simple compound planetary gear set is required, which increases the burden of material cost. But CF28 can shift only by Belt & Pulley; CF28 only needs one planetary gear set for step “forward” and “backward”. To save the material cost and weight, single pinion planetary gear has been applied. The material cost of single pinion type could be reduced by about 27% compared to double pinion typ","PeriodicalId":244804,"journal":{"name":"Dritev – Drivetrain for Vehicles 2020","volume":"87 1","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"New high efficiency CVT for middle class FWD vehicle\",\"authors\":\"K. Kim\",\"doi\":\"10.51202/9783181023730-i-271\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Many kinds of transmissions have been developing and recently electrification is processing rapidly to reduce fuel consumption. Automatic transmission has been developing in multistages to improve fuel economy and power performance. CVT, kinds of transmissions, also need to increase the ratio spread to improve the two performances. Thus CVT has better fuel economy performance through the engine’s optimal operating. So, CVT would be a good solution for fuel economy among the conventional transmissions. The newly developed CVT for FWD vehicles has wider pulley ratio spread than any other competitors. And in spite of wide ratio coverage, CF28 has good competitiveness in the overall length by minimizing the length increase. In spite of reducing transmission length, we had achieved maximum torque capacity, minimum length, highest efficiency, and largest pulley ratio coverage compared to competitors’ middle-class CVTs. Introduction Recently many kinds of transmissions have been continuously developing to increase driving performance and reduce fuel consumption, And to achieve vehicle mount-ability, it necessary to miniaturize the transmission, because the room for transmission gets smaller and smaller. The newly Continuous Variable Transmission(CF28) for the front-wheel-drive vehicle which was recently developed, substantially enlarge the torque capacity based on the current Small-CVT(CF18). Nevertheless, the driving performance has greatly improved through the expansion of ratio span, the competiveness of efficiency, weight and overall length is the best in the same class CVT. The planetary gear was newly designed to reduce the overall length of the transmission and the clutch, hydraulic system, torque converter and oil pump were optimized to improve the efficiency. And the belt & pulley also had been newly designed for the wider ratio span, fewer components, and shorter overall length, lower the weight. In this paper, the new planetary gear, new belt & pulley system, and newly optimized systems for marketability would be described. VDI-Berichte Nr. 2373, 2020 271 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. <Specification Comparison> CF18 (Existing Model) CF28 (New Model) Torque Capacity [kgf.m] 18.3 28 Overall Length [mm] 351 359 Gear Span [UD/OD] 7.0 7.5 Weight [Wet, kg] 73 88 TORQUE-UP, MINIMIZING AND WEIGHT REDUCTION Figure 1 below shows that the CVT for front-wheel (CF18), which is currently in production, has one planetary gear set, one clutch set and one brake set. The newly developed CF28 has been increased only 8mm in overall length despite the fact that the torque capacity was increased by 53% compared to the current mass production CF18. Fig. 1: Cross section of CF18 Fig. 2: schematic of CF18 The following is a description of how we were able to minimize the increase of the overall length and weight. 1. Structure of Planetary gear and Brake To reduce the overall length, it was necessary to change the structure of planetary gear and brake system. Regarding this changes, there are also changes in power flow. The hub of the brake was changed to integrate with carrier rather than the annulus gear. Therefore it was VDI-Berichte Nr. 2373, 2020 272 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. possible to remove the connecting plate of annulus gear and one thrust bearing, and the overall length could be reduced by 6.1mm. The input of power flow was changed from sungear to annulus-gear, and output of power flow was changed from carrier to sun gear. CF18 CF28 Fig. 3: Planetary Gear & Brake 2. Structure of Sheave Connection To reduce the overall length, it was necessary to change the structure of the pulley system. Fixed sheave and movable sheave of CF18 were connected by rollers so that movable sheave can rotate together with fixed sheave and can move through the fixed shave’s axis. But fixed sheave and movable sheave of CF28 were changed to be connected by spline without rollers. Therefore the pulley length could be reduced by 4.2mm. In addition to the overall shortening effect, this change also has an effect on reducing the number of parts and simplification of the assembly process. CF18 CF28 Fig. 4: Fixed Sheave & Movable Sheave VDI-Berichte Nr. 2373, 2020 273 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. 3. Optimize the Packaging Condition To improve the packaging condition on vehicle, packaging analysis had been completed with various vehicles. So, it was necessary for CF28 to optimize external designs of transmission. Design of Housing parts and external devices had been more optimized to improve the mount ability on middle class vehicles. As a result CF28 has a good competitiveness compared to competitors’ middle class CVT.(Fig. 5) According to In-Diff. distance, CF28 has two option to satisfy the mount-ability on various vehicles(189mm/204mm). Especially 189mm of In-Diff. distance is difficult condition for constructing internal parts in middle class CVT. This is about 8mm smaller than the competitor’s middle class CVT. Fig. 5: Package Layout Fig. 6: Comparison of Packaging Condition EFFICIENCY IMPROVEMENT Needless to say, the transmission efficiency is more important than ever in accordance with the recent fuel efficiency regulations. VDI-Berichte Nr. 2373, 2020 274 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. The front-wheel CVT(CF18), which is currently in production, boasts the world’s highest level of CVT efficiency. Likewise CF28 has significantly improved efficiency compared to competitor’s middle-class CVT. 1. Oil Pump Oil pump was one of the biggest losses in the transmissions using hydraulic control and We could improve transmission efficiency through optimization of capacity and minimized drive losses. The oil pump of CF28 is vane type, which is able to reduce drive torque loss by maximum 9% in comparison to gear-type pump. It allowed an improvement of 0.4% in CVT efficiency. Fig. 7: Comparison of Drive Torque 2. Chain Belt Chain belt is also important item to improve the efficiency dramatically. The chain was also applied to the CF18 and had been proved to be very efficient compared to the push belt. Chain belt of CF28 has better efficiency of 5% in under-drive area, 3% in over-drive area than push belt of CF28 in same CVT assembly. As a result, chain belt has better efficiency of 1.9% than push belt, It also appeared with a fuel economy difference of 1.2% on vehicle test. It is due to the fact that the chain has less friction loss than the belt. Chain Belt Push Belt Fig. 8: Variator of CVT Pulley VDI-Berichte Nr. 2373, 2020 275 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. Fig. 9: Efficiency Test in CVT Assembly 3. Separating Spring Separating springs were applied to reverse brake system to improve the efficiency while driving forward. Because when CVT operates driving forward, the drag torque must be occurred on disk set of reverse brake. Forward clutch does not need separating spring because forward clutch is engaged in step “D” position and drag torque is not generated. These springs are assembled between the disk set, and help the brake’s each disk to maintain same clearance. This prevents the drag torque loss from increasing because the disk is positioned to one side. Reverse Brake Disk set Separating Spring Fig. 10: Separating Spring in Brake VDI-Berichte Nr. 2373, 2020 276 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. 4. Wider Pulley Ratio Span Ratio span is one of the important performance indicators of transmission. Wider ratio coverage improves fuel economy in the high ratio region and acceleration in the low ratio region. In the high ratio region, the engine speed is lowered to improve fuel efficiency. In the low ratio region, the engine torque is multiplied to improve the acceleration performance. Fig. 11: Wider Pulley Ratio To increase the pulley ratio width, the distance between two pulleys‘ axes was also increased by 5%. And system analysis had been done to secure stiffness under the worst use conditions, to optimize sheaves in terms of weight reduction. Primary Pulley Secondary Pulley Fig. 12: Pulley Strength by CAE Analysis VDI-Berichte Nr. 2373, 2020 277 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. Fig. 13: Pulley Deformation by CAE Analysis COST REDUCTION In modern rimes, the competition of the transmissions on the price and efficiency is getting overheated. The cost reduction technologies had also been applied to lower the material cost, and then to improve the marketability of CF28. The price competitiveness of CF28 also reached the world's highest level in the middle class vehicles’ CVTs which is currently in production. 1. Single Pinion Planetary Gear In the case of two-step CVT, simple compound planetary gear set is required, which increases the burden of material cost. But CF28 can shift only by Belt & Pulley; CF28 only needs one planetary gear set for step “forward” and “backward”. To save the material cost and weight, single pinion planetary gear has been applied. The material cost of single pinion type could be reduced by about 27% compared to double pinion typ\",\"PeriodicalId\":244804,\"journal\":{\"name\":\"Dritev – Drivetrain for Vehicles 2020\",\"volume\":\"87 1\",\"pages\":\"0\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"1900-01-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Dritev – Drivetrain for Vehicles 2020\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.51202/9783181023730-i-271\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Dritev – Drivetrain for Vehicles 2020","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.51202/9783181023730-i-271","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
摘要
因此,与竞争对手的中产级CVT相比,CF28具有较好的竞争力。5)根据In-DiffCF28有两种选择,以满足不同车辆的安装能力(189毫米/204毫米)。尤其是189mm的调差。距离是中档无级变速器内部部件构造的困难条件。这比竞争对手的中产级CVT小约8毫米。图5:包装布局图6:包装工况效率改进对比根据最近的燃油效率法规,传动效率比以往任何时候都更加重要。VDI-Berichte no . 2373, 2020 274 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39。Das Erstellen和Weitergeben von Kopien dieses pdf第一晚zulässig。目前正在生产的前轮CVT(CF18)具有世界最高水平的CVT效率。同样,与竞争对手的中产阶级CVT相比,CF28的效率显著提高。1. 油泵是液压控制传动系统中损耗最大的部件之一,通过优化容量,减少传动损耗,可以提高传动效率。CF28油泵为叶片式,与齿轮式油泵相比,最大可减少9%的驱动扭矩损失。它使CVT效率提高了0.4%。图7:驱动转矩对比链带也是显著提高效率的重要项目。链条也应用于CF18,并已被证明是非常有效的相比,推带。在相同的CVT总成中,CF28链带的下驱动区效率为5%,上驱动区效率为3%。结果表明,链条带的效率比推动带高1.9%,在整车试验中也出现了1.2%的燃油经济性差异。这是由于链条的摩擦损失比皮带小。图8:CVT皮带轮VDI-Berichte编号2373,2020 275 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39。Das Erstellen和Weitergeben von Kopien dieses pdf第一晚zulässig。图9:CVT总成效率测试将分离弹簧应用于倒车制动系统,提高了倒车时的行驶效率。因为当无级变速器正行驶时,阻力扭矩必须发生在倒车制动器盘组上。前向离合器不需要分离弹簧,因为前向离合器啮合在步长“D”位置,不产生拖拽力矩。这些弹簧组装在盘组之间,并帮助制动器的每个盘保持相同的间隙。这可以防止阻力扭矩损失增加,因为磁盘被定位到一侧。图10:制动盘分离弹簧VDI-Berichte编号2373,2020 276 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39。Das Erstellen和Weitergeben von Kopien dieses pdf第一晚zulässig。4. 传动比跨距是变速器的重要性能指标之一。更宽的比率覆盖范围提高了高比率区域的燃油经济性和低比率区域的加速性能。在高比区域,降低发动机转速以提高燃油效率。在低速比区域,发动机扭矩成倍增加,以提高加速性能。图11:更宽的皮带轮比为了增加皮带轮比宽度,两个皮带轮轴线之间的距离也增加了5%。并进行了系统分析,以确保在最恶劣的使用条件下的刚度,并在减轻重量方面优化轮轴。图12:滑轮强度CAE分析VDI-Berichte Nr. 2373, 2020 277 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39。Das Erstellen和Weitergeben von Kopien dieses pdf第一晚zulässig。图13:CAE分析的皮带轮变形降低成本现代,变速器在价格和效率上的竞争日趋激烈。降低成本的技术也被应用于降低材料成本,从而提高CF28的适销性。CF28的价格竞争力也达到了目前正在生产的中档车型cvt的世界最高水平。1. 单小齿轮行星齿轮对于两级无级变速器,需要简单的复合行星齿轮组,增加了材料成本负担。但CF28只能通过皮带轮换挡;CF28只需要一个行星齿轮来“前进”和“后退”。为了节省材料成本和重量,采用了单小齿轮行星齿轮。与双小齿轮相比,单小齿轮的材料成本可降低约27%
New high efficiency CVT for middle class FWD vehicle
Many kinds of transmissions have been developing and recently electrification is processing rapidly to reduce fuel consumption. Automatic transmission has been developing in multistages to improve fuel economy and power performance. CVT, kinds of transmissions, also need to increase the ratio spread to improve the two performances. Thus CVT has better fuel economy performance through the engine’s optimal operating. So, CVT would be a good solution for fuel economy among the conventional transmissions. The newly developed CVT for FWD vehicles has wider pulley ratio spread than any other competitors. And in spite of wide ratio coverage, CF28 has good competitiveness in the overall length by minimizing the length increase. In spite of reducing transmission length, we had achieved maximum torque capacity, minimum length, highest efficiency, and largest pulley ratio coverage compared to competitors’ middle-class CVTs. Introduction Recently many kinds of transmissions have been continuously developing to increase driving performance and reduce fuel consumption, And to achieve vehicle mount-ability, it necessary to miniaturize the transmission, because the room for transmission gets smaller and smaller. The newly Continuous Variable Transmission(CF28) for the front-wheel-drive vehicle which was recently developed, substantially enlarge the torque capacity based on the current Small-CVT(CF18). Nevertheless, the driving performance has greatly improved through the expansion of ratio span, the competiveness of efficiency, weight and overall length is the best in the same class CVT. The planetary gear was newly designed to reduce the overall length of the transmission and the clutch, hydraulic system, torque converter and oil pump were optimized to improve the efficiency. And the belt & pulley also had been newly designed for the wider ratio span, fewer components, and shorter overall length, lower the weight. In this paper, the new planetary gear, new belt & pulley system, and newly optimized systems for marketability would be described. VDI-Berichte Nr. 2373, 2020 271 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. CF18 (Existing Model) CF28 (New Model) Torque Capacity [kgf.m] 18.3 28 Overall Length [mm] 351 359 Gear Span [UD/OD] 7.0 7.5 Weight [Wet, kg] 73 88 TORQUE-UP, MINIMIZING AND WEIGHT REDUCTION Figure 1 below shows that the CVT for front-wheel (CF18), which is currently in production, has one planetary gear set, one clutch set and one brake set. The newly developed CF28 has been increased only 8mm in overall length despite the fact that the torque capacity was increased by 53% compared to the current mass production CF18. Fig. 1: Cross section of CF18 Fig. 2: schematic of CF18 The following is a description of how we were able to minimize the increase of the overall length and weight. 1. Structure of Planetary gear and Brake To reduce the overall length, it was necessary to change the structure of planetary gear and brake system. Regarding this changes, there are also changes in power flow. The hub of the brake was changed to integrate with carrier rather than the annulus gear. Therefore it was VDI-Berichte Nr. 2373, 2020 272 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. possible to remove the connecting plate of annulus gear and one thrust bearing, and the overall length could be reduced by 6.1mm. The input of power flow was changed from sungear to annulus-gear, and output of power flow was changed from carrier to sun gear. CF18 CF28 Fig. 3: Planetary Gear & Brake 2. Structure of Sheave Connection To reduce the overall length, it was necessary to change the structure of the pulley system. Fixed sheave and movable sheave of CF18 were connected by rollers so that movable sheave can rotate together with fixed sheave and can move through the fixed shave’s axis. But fixed sheave and movable sheave of CF28 were changed to be connected by spline without rollers. Therefore the pulley length could be reduced by 4.2mm. In addition to the overall shortening effect, this change also has an effect on reducing the number of parts and simplification of the assembly process. CF18 CF28 Fig. 4: Fixed Sheave & Movable Sheave VDI-Berichte Nr. 2373, 2020 273 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. 3. Optimize the Packaging Condition To improve the packaging condition on vehicle, packaging analysis had been completed with various vehicles. So, it was necessary for CF28 to optimize external designs of transmission. Design of Housing parts and external devices had been more optimized to improve the mount ability on middle class vehicles. As a result CF28 has a good competitiveness compared to competitors’ middle class CVT.(Fig. 5) According to In-Diff. distance, CF28 has two option to satisfy the mount-ability on various vehicles(189mm/204mm). Especially 189mm of In-Diff. distance is difficult condition for constructing internal parts in middle class CVT. This is about 8mm smaller than the competitor’s middle class CVT. Fig. 5: Package Layout Fig. 6: Comparison of Packaging Condition EFFICIENCY IMPROVEMENT Needless to say, the transmission efficiency is more important than ever in accordance with the recent fuel efficiency regulations. VDI-Berichte Nr. 2373, 2020 274 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. The front-wheel CVT(CF18), which is currently in production, boasts the world’s highest level of CVT efficiency. Likewise CF28 has significantly improved efficiency compared to competitor’s middle-class CVT. 1. Oil Pump Oil pump was one of the biggest losses in the transmissions using hydraulic control and We could improve transmission efficiency through optimization of capacity and minimized drive losses. The oil pump of CF28 is vane type, which is able to reduce drive torque loss by maximum 9% in comparison to gear-type pump. It allowed an improvement of 0.4% in CVT efficiency. Fig. 7: Comparison of Drive Torque 2. Chain Belt Chain belt is also important item to improve the efficiency dramatically. The chain was also applied to the CF18 and had been proved to be very efficient compared to the push belt. Chain belt of CF28 has better efficiency of 5% in under-drive area, 3% in over-drive area than push belt of CF28 in same CVT assembly. As a result, chain belt has better efficiency of 1.9% than push belt, It also appeared with a fuel economy difference of 1.2% on vehicle test. It is due to the fact that the chain has less friction loss than the belt. Chain Belt Push Belt Fig. 8: Variator of CVT Pulley VDI-Berichte Nr. 2373, 2020 275 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. Fig. 9: Efficiency Test in CVT Assembly 3. Separating Spring Separating springs were applied to reverse brake system to improve the efficiency while driving forward. Because when CVT operates driving forward, the drag torque must be occurred on disk set of reverse brake. Forward clutch does not need separating spring because forward clutch is engaged in step “D” position and drag torque is not generated. These springs are assembled between the disk set, and help the brake’s each disk to maintain same clearance. This prevents the drag torque loss from increasing because the disk is positioned to one side. Reverse Brake Disk set Separating Spring Fig. 10: Separating Spring in Brake VDI-Berichte Nr. 2373, 2020 276 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. 4. Wider Pulley Ratio Span Ratio span is one of the important performance indicators of transmission. Wider ratio coverage improves fuel economy in the high ratio region and acceleration in the low ratio region. In the high ratio region, the engine speed is lowered to improve fuel efficiency. In the low ratio region, the engine torque is multiplied to improve the acceleration performance. Fig. 11: Wider Pulley Ratio To increase the pulley ratio width, the distance between two pulleys‘ axes was also increased by 5%. And system analysis had been done to secure stiffness under the worst use conditions, to optimize sheaves in terms of weight reduction. Primary Pulley Secondary Pulley Fig. 12: Pulley Strength by CAE Analysis VDI-Berichte Nr. 2373, 2020 277 https://doi.org/10.51202/9783181023730-I-271 Generiert durch IP '54.70.40.11', am 29.09.2021, 19:39:39. Das Erstellen und Weitergeben von Kopien dieses PDFs ist nicht zulässig. Fig. 13: Pulley Deformation by CAE Analysis COST REDUCTION In modern rimes, the competition of the transmissions on the price and efficiency is getting overheated. The cost reduction technologies had also been applied to lower the material cost, and then to improve the marketability of CF28. The price competitiveness of CF28 also reached the world's highest level in the middle class vehicles’ CVTs which is currently in production. 1. Single Pinion Planetary Gear In the case of two-step CVT, simple compound planetary gear set is required, which increases the burden of material cost. But CF28 can shift only by Belt & Pulley; CF28 only needs one planetary gear set for step “forward” and “backward”. To save the material cost and weight, single pinion planetary gear has been applied. The material cost of single pinion type could be reduced by about 27% compared to double pinion typ