無級變速器設計【不全】

無級變速器設計【不全】,不全,無級,變速器,設計 12th IFToMM World Congress, Besanon (France), June18-21, 2007 CK-xxx Research and Development of Cone to Cone Type CVT H. Komatsubara* T. Yamazaki S. Kuribayashi Yamagata University Yamagata University Kuribayashi Steamship Yamagata, Japan Yamagata, Japan Tokyo, Japan Abstract 1Traction drive CVT is a low noise and a low vibration. But most of traction drive CVT have complex structure. One of the authors invented a new type of traction drive CVT. As for this new CVT, the structure is simple, and transfer efficiency is high. This new CVT is called Cone to Cone Type CVT(CTC-CVT). The purpose of this research aimed at practical use of CTC-CVT In this report, first the structure and the speed changing mechanism of CTC-CVT is examined. Secondly, the design of CTC-CVT is described. Finally, the mechanical efficiency of power transmission is examined. Keywords: machine element, tribology, lubrication, CVT, traction drive, efficiency I. Introduction In the traction drive, mechanical power is transmitted between two rotors via an elastohydrodynamic lubrication (EHL) oil film. The traction oil intervening between the rotors forms an oil film when it experiences a pressing force, and it transmits mechanical power by the shear force (traction force) of this oil film. The traction drive is low vibration and low noise and has the feature of being able to make up a continuously variable transmission (CVT). For the traction drive type CVT, various structures have been developed. Ring-corn type CVT 1 and kopp type CVT 2 have been applied to industrial machine. Half-toroidal CVT has been practically used for automobiles 3. Power transmission efficiency of this CVT is over 92 % 4. In addition, shaft drive CVT 5 and full-toroidal CVT 6 have been studied. However, the CVT of this traction drive type has a narrow range of reduction ratio and the structure is complex. Thus, Kuribayashi, one of the authors, devised a CVT using cones in the traction drive type CVT, whose structure is simple and from which a high reduction ratio is available7. Figure 1 shows a schematic of the power transmission portion of the devised CVT. Figure 2 shows an exploded perspective view of the power transmission portion. In this CVT, intermediate rolling elements are placed between the input and output shafts to transmit mechanical power. The input and output shafts have a concave conical form, and the intermediate rolling elements have a convex conical form. Because mechanical power is transmitted from cone to cone, this new CVT is *E-mail: hkomatsuyz.yamagata-u.ac.jp E-mail: am01137dipfr.dip.yz.yamagata-u.ac.jp E-mail: a.kotanikuribayashi.co.jp called the cone-to-cone type CVT (CTC-CVT). On the input and output shafts, gears are attached at the shaft end as shown in Figure 2. By attaching the gears, the number of mating parts of the input and output shafts and the rolling elements can be increased. By increasing the number of mating parts of the input and output shafts and the rolling elements, high torque can be transmitted. This study aims at practical development of CTC-CVT which simple structure parts and power transmission efficiency is about 90 %. This time, to know the basic characteristics of the CTC-CVT, one set of input and output shafts and rolling elements was examined without attaching gears at the input and output shaft ends. First the structure and speed-changing mechanism of the CTC-CVT are described. Finally, the design and power transmission efficiency examination of a prototype are presented. Fig. 1. Schematic of CTC-CVT Fig. 2. Exploded perspective view of CTC-CVT 12th IFToMM World Congress, Besanon (France), June18-21, 2007 CK-xxx (a) e=2.0 (b) e=1.0 (c) e=0.5 Fig. 5. Reduction ratio change mechanism of CTC-CVT II. Basic Structure A. Structure of CTC-CVT Figure 3 shows a schematic of the power transmission portion of the CTC-CVT. This CTC-CVT is composed of input and output shafts and an intermediate rolling element inscribed between them. The input and output shafts have a concave conical form, and the intermediate rolling element has a convex conical form. An offset of E is given between the input and output shafts. Traction oil intervenes between the concave cone at the end of each shaft and the convex cone of the intermediate rolling element, and it forms an oil film when a pressing force is applied from the input shaft side. A traction force is produced by the oil film, and the rotation of the input shaft is transmitted to the output shaft via the intermediate rolling element. Speed changes are effected by changing the contact radius of the intermediate rolling element, and the radius change is in turn effected by translating the intermediate rolling element obliquely along the cone angle. B. Speed-changing Mechanism The CTC-CVT changes the speed smoothly by translating the intermediate rolling element obliquely along the cone angle. Figure 4 shows the geometry of the power transmission portion. Letting r1 be the corotation radius of the input shaft, r2 be the corotation radius of the convex cone on the input side, 1 be the angular velocity of the input shaft, and 2 be the angular velocity of the rolling element, then the following relationship is obtained on the input side. 2211rr= (1) Letting r3 be the corotation radius of the convex cone on the output side, r4 be the corotation radius of the output shaft, and 3 be the angular velocity of the output shaft, then the following relationship is obtained on the output side. 3423rr= (2) The reduction ratio, e, is the ratio of the angular velocity of the input shaft to that of the output shaft and is given by the following equation using Equations 1 and 2. 1342322131rrrre= (3) If the corotation radii, r1 and r4, of the input and output shafts are equal, the following equation is obtained. 32rre = (4) If the convex cone is translated, the corotation radii r2 and r3 of the intermediate rolling element at the points of contact respectively with the input and output shafts change. As shown in Figure 5(a), the reduction ratio is 2.0 if the length of r2 is twice the length of r3. It is 1.0 if the length of r2 is equal to the length of r3 (Figure 5(b). Likewise, the reduction ratio is 0.5 if the length of r2 is half the length of r3 (Figure 5(c). Thus, when the corotation radii of the intermediate rolling element change, the reduction ratio changes according to Equations 3 and 4. Fig. 3. Schematic of power transmission portion Fig. 4. Geometrical parameters of CTC-CVT III. Design of CTC-CVT Prototype To verify the operation and performance of the CTC-CVT, a CTC-CVT prototype was designed. Figure 6 shows a sectional view of the designed CTC-CVT. Table 1 shows the specifications for the designed CTC-CVT prototype. As a design condition, a motor with a rated capacity of 15 kw and a rotational speed of 1500 rpm was used as the input power source. The design was done on the design concept of attaining a prototype with high power transmission efficiency. For changing the speed, a mechanism to translate the r2=2r3 r2=r3 r2=r3/2 12th IFToMM World Congress, Besanon (France), June18-21, 2007 CK-xxx Fig. 6. Schematic view of CTC-CVT intermediate rolling element along the cone angle by turning a handle was used. Figure 7 shows a schematic of the transmission mechanism. A case supports the intermediate rolling element, and a slider is attached to the case. A groove is cut in the frame at the same angle as the convex cone. A handle is attached on the top of the case, and turning the handle translates the case along the groove and can effect stepless speed changes. The pressure force necessary for the traction drive is given by the loading cam on the input shaft side. The loading cam is a device to produce a pressing force according to the input torque. For the bearings on the input and output shafts, a duplex angular bearing and roller bearing are used. The bearings of the CTC-CVT experience radial and thrust loads. These bearings are used as a combination that can carry these loads and cause little power loss at the bearings. The CVT was designed so that the duplex angular bearing will carry radial and thrust loads and the roller bearing will carry a large radial load. The distance between the bearings was decided in consideration of the allowable angle and efficiency of the bearings. For the lubrication of the various parts of the CVT, forced lubrication using a CVT lubrication hydraulic unit (pump, filter, cooler and tank) was used, and this unit is installed separately from the CVT prototype. Labyrinth seals are used, in consideration of the power loss by the sealing devices. Fig. 7. Schematic of Transmission Mechanism Output Torque T2 (Nm) 95.5 Reduction ratio e 0.5 - 2.0 Input speed N1 (min-1) 1500 Output speed N2 (min-1) 750 - 3000 Cone angle (deg) 46 Contact radius r1，r4 (mm) 46 Offset E (mm) 13 TABLE I. Design specification of CTC-CVT IV. Examination of Power Transmission Efficiency Power transmission efficiency is most important as performance of the transmission and an examination about this was performed. The power loss by the traction drive type CVT includes the loss by the support bearing, the loss occurring at the contact surface of the power transmission portion, the loss by agitation of traction oil and the loss by oil seals and other sealing devices. The prototype fabricated this time employs forced lubrication, which sprays traction oil onto the CVT by the external hydraulic unit. Thus it is thought that there is no power loss by agitation of traction oil. Because labyrinth seals are used for the sealing devices, it is considered that there is no power loss by the sealing devices. Therefore, the loss by the support bearing and the loss at the contact surface of the power transmission portion were examined. A. Effect of Bearing Loss By the pressure force from the loading cam, a radial load acts on the roller bearing on the input and output shafts, and radial and thrust loads occur on the duplex angular bearing. Due to these loads, a torque loss occurs at each bearing. This torque loss is expressed as kinetic friction torque, Mt. The kinetic friction torque, Mt, occurring at each bearing is expressed by the following equation: vltMMM+= (5) where Ml is the load term and Mv is the velocity term. 12th IFToMM World Congress, Besanon (France), June18-21, 2007 CK-xxx B. Effect of Spin Around the normal to the contact surface of the power transmission portion, relative rotary motion of the oil film occurs in the elliptic contact area, and this motion is called spin. The traction oil is heated by this spin, increasing the slippage and reducing the shear force. The loss due to the spin was theoretically found by an analytical method by using the elastoplastic model of Johnson and Tevaarwerk 8 and taking into account the oils shear force reduction accompanying the heating. C. Power Transmission Efficiency The power transmission efficiency P can be expressed by the following equation using the speed transmission efficiency S and torque transmission efficiency T. TSP= (6) The speed transmission efficiency represents the relationship of the actual rotational speed to the rotational speed of the ideal transmission free from slippage under point contact condition. The speed transmission efficiency can be found theoretically from the slippage rate (creep) on the input and output sides. The creep can be found from the traction curve as the magnitude of creep for the set traction coefficient. The traction curve represents the relationship between creep and traction coefficient. The traction coefficient represents the ratio of the traction force to the normal force, which is the normal component of the pressure force acting on the intermediate rolling element. Figure 8 shows the traction curve of the CTC-CVT for the design specifications given in Table 1. The temperature of the traction oil was taken at 60 C. The torque transmission efficiency represents the relationship of the actually transmitted torque to the ideally transmitted torque free from slippage under point contact condition. The torque transmission efficiency can be found from the loss at each bearing and the loss due to spin. Figure 9 shows the calculated power transmission efficiency versus input torque for reduction ratios of 2.0, 1.0 and 0.5. The power transmission efficiency decreases as the input torque increases. The power transmission efficiency also decreases as the reduction ratio decreases, that is, the output speed is increased. The torque loss at the bearings increases as the input torque increases. When the output speed is increased, a torque loss occurs at the bearings. Moreover, the surface pressure in the contact area becomes large and the slippage increases, so the power loss becomes large. The power transmission efficiency was 93% at a reduction ratio of 2.0 for the design specifications given in Table 1. V. Conclusion (1) Aiming at practical development of a CTC-CVT which is a continuously variable transmission using cones, we designed a prototype and examined its power transmission efficiency. (2) We found the bearing loss and spin loss in the traction area, which contribute to a reduction of power transmission efficiency. As a result, the calculated efficiency of the designed CTC-CVT is 93%. The CTC-CVT designed this time is now in the process of fabrication, and we will do a trial run to measure the efficiency and compare it with the theoretical value. 00.020.040.060.080.10123456 Creep Cr%Traction coefficient e=2.0e=1.0e=0.5 Fig. 8. Traction curve of CTC-CVT 7075808590951000102030405060708090 100 110 120Input torqueNmPower transmission efficiency%e=2.0e=1.0e=0.5 Fig. 9. Power transmission efficiency of CTC-CVT References 1 Okamura and Kashiwabara, Development of Transmission by 3K-Type CVT (1st Report, Design of Transmission), Trans. JSME, Series C 57-538, (1991), 288-293. 2 FRANK NAJLEPSZY, Traction Drives Roll up Impressive Gains, MACHINE DESIGN, 57-25, (1985), 68-75 3 Machida, Hata, Nakano and Tanaka, Half-Troidal Traction Drive Continuously Variable Transmission for Automobile Propulsion Systems (Traction Drive Materials, Transmission Design and Efficiency) Trans. JSME, Series C 59-560, (1993), 1154-1160. 4 Imanishi, Machida, Tanaka, A Study on a Toroidal CVT for Automotive Use, Proceedings of the Machine Design and Tribology Division Meeting In JSME (IMPT-100), (1997), 531-536 5 Yamanaka, Igari and Inoue Study of Shaft Drive Continuously Variable Transmission (1st Report, Analysis of Mechanism and Prototype), Trans. JSME, Series C 70-692, (1993), 1154-1160. 6 Misada, Oono, Transmission Efficiency and Power Capacity Analysis of Infinity Variable Transmission Variator, Koyo Engineering Journal No.168, (2005), 46-49 7 Kuribayashi, Continuously Variable Transmission, Japanese Patent Public Disclosure No. 2001-173745, Japan Patent Office. 8 Johnson, K. L. and Tevaarwerk, J. L., Shear behaviour of elastohydrodynamic, Proc. R. Soc. Lond, A.356, (1977), 215-236.