REPUBLIQUE DU CAMEROUN REPUBLIC OF CAMEROON PAIX-TRAVAIL-PATRIE PEACE-WORK-FATHERLAND ------------------------------------ ------------------------------------ UNIVERSITE DE BAMENDA UNIVERSITY OF BAMENDA ------------------------- ------------------------- INSTITUT NATIONAL SUPERIEUR NATIONAL HIGHER POLYTECHNIC POLYTECHNIQUE INSTITUTE BAMBILI-BAMENDA BAMBILI-BAMENDA ------------------------ ------------------------ FAX: 33 36 36 94 P.O.BOX. 39 BAMENDA TEL : 33 36 36 94 AUTOMOBILE ENGINEERING (MECE3206) EXPOSE COURSE INSTRUCTOR: Engr. N. Flevis A STUDENT NAME: DJIOMO NGOUNOU DELVNE MATRICULE: UBa21E0132 ACADEMIC YEAR 2023/2023 A continuously variable transmission CVT A continuously variable transmission in a vehicle senses the accelerator input with engine load and get shifted to the desired speed or torque gear ratio automatically, in other words we can say that a cvt transmission is one of the simplest types of automatic transmission that provides continuous uninterrupted power within a specified range of speed and torque ratios. COMPONENTS OF CVT: 1. Clutches I. Primary clutch The primary clutch is an advanced form of centrifugal clutch and is typically mounted to the output end of the engine crankshaft. II. Secondary clutch The secondary clutch is mounted to the input shaft of the transmission, transaxle, or the like. In modern CVT systems such as those used in recreational vehicles, the secondary clutch has two functions: as a “slave” to the primary clutch and to provide a torque sensing element. 2. Pulleys ; In Cvt pulleys play an important role as the conical shape pulleys integrated over input and output shafts are the reason for continuously variable transmission’s continuous n-number of speed and gear ratios, due to the different cross section of these conical pulleys multiple torque and speed ratios are obtained. 1. Fixed input pulleyIt is a conical pulley mounted over the input shaft (on the right-hand side), this pulley does not move (too and fro) over the shaft but rotates with the input shaft, usually fixed pulley is smaller in size. 2. Fixed output pulley It same as fixed input pulley but unlike fixed input shaft this shaft is placed on the left-hand side over the output shaft. 3. Feeding input pulley or sheaveIt is the type of conical pulley which is mounted over the input shaft and have inner splines meshed with the shaft splines in such a fashion that it can move (too and fro) as well as rotates with the input shaft. the too and fro moment of this shaft over the input shaft make it possible to shift gear ratios. 4. Feeding output pulley or sheave Same as moving input pulley but unlike moving input shaft, this shaft is placed on the right-hand side over the output shaft. 3.Shafts : Same as manual transmission type 2 shafts are needed by Cvt transmission to transfer power from engine to the final drive that are Input shaftOutput shaft- 4.Belt or Chain; The belt in most CVT systems is a heavy duty “V-belt” which is V-shaped in cross section. They are made of rubber components reinforced with Kevlar and other materials to enhance durability. HOW CVT WORKS? The transmission has the ability to change continuously by using an infinite number of gear ratios between maximum and minimum values. To facilitate different gear ratios, the working diameters of the two main pulleys in the transmission need to be altered. While the pulley that is connected to the engine is called the input pulley, the one that is connected to the drive wheels is called the output pulley. One side of the pulley is fixed while the other side is movable. This movement is facilitated by a hydraulic cylinder which can change the space between the two sides of the pulley. When the pulley halves come closer to each other, the belt that runs between them goes higher on the pulley, thereby increasing the diameter of the pulley. TORQUE RATIOS Torque ratios are achieved when the v-belt rotates at the lower cross section of the input pulleys and at the greater cross section of the output pulley. SPEED RATIOS: And speed ratios are achieved when v-belt rotates at the higher cross section of the input pulley and lower cross-section of the output pulley. Advantages • Better fuel consumption than a regular automatic transmission as the CVT is able to keep the car in its optimum power range regardless of speed • There is improved acceleration due to the lower power loss experienced • Stepless transmission • It has the ability to allow the engine to rev almost immediately which delivers maximum torque. • Provides a smoother ride than automatic transmission Disadvantages • Higher cost • Belt-driven CVTs (VDP system) have a limited amount of torque, however the technology is constantly being improved. • Transmitting motion by friction causes greater wear • Require special oil and other materials Introduction to Epicyclic Gear Train Introduction: Epicyclic gearing also called as planetary gearing. It is a gear system that consists of one or more outer gear (planet gear) rotating about a central (sun gear). The planet gear are mounted on a moveable arm (carrier) which itself may rotate relative to the sun gear. Epicyclic gearing systems may also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears. Figure show an example of epicyclic gearing. It is used to increase output speed. The planet gear carrier is driven by an input torque. The sun gear provides the output torque, while the ring gear is fixed. Parts Of Epicyclic Gear train Gear ratio: The gear ratio in an epicyclic gearing system can be different by the design of the gear teeth and the ways of input rotation to the gear. Epicyclic Gearbox Parts : The three basic components of the epicyclic gear are: 1. Sun: The central gear 2. Planet carrier: Holds one or more peripheral planet gears, of the same size, meshed with the sun gear 3. Annulus or Ring Gear: An outer ring with inward-facing teeth that mesh with the planet gear or gears In many epicyclic gearing systems, among the three basic components, one component is held stationary; one component is input, provide power to the system and last component is output, receive the power from the system. The ratio of input rotation to output rotation is dependent upon the number of teeth in each gear, and upon which component is held stationary. Epicyclic Gearbox Diagram : Working of epicyclic gearbox: First gear ratio: This provide high torque ratios to the vehicle which helps the vehicle to move from its initial state and is obtained by fixing the annular gear which in turn causes the planet carrier to rotate with the power supplied to the sun gear. Second gear ratio: This provides high-speed ratios to the vehicle which helps the vehicle to attain higher speed during a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier the driven member and annular the driving member in order to achieve high-speed ratios. Reverse gear ratio: This gear reverses the direction of the output shaft which in turn reverses the direction of the vehicle, this gear is achieved by fixing the planet gear carrier which in turn makes the annular gear the driven member and the sun gear the driver member. Note- More speed or torque ratios can be achieved by increasing the number of planet and sun gear in epicyclic gearbox. Advantages of Epicyclic Gearbox: High reduction ratios Compact and lightweight with high torque transmission High radial loads on the output shaft It is quieter in operation Uniform distribution of load over all gears having greater tooth contact. Disadvantages of planetary gear systems • Complexity • Efficiency calculations are difficult Hydramatic Transmission HYDRAMATIC TRANSMISSION is classified as fully automatic transmissions. The epicyclic gearboxes contain three or four speeds, a reverse gear, and oiloperated brakes and clutches. A governor controls the transmission by adjusting the oil pressure in response to the car’s speed. Hydramatic drive doesn’t need a clutch pedal to engage/disengage from engine, unlike other transmission systems. Rear Unit ;The Rear unit is composed of multiple parts. These include an internal gear, drum, brake band assembly, sun gear, main shaft, planet cage, and output shaft. The drum and brake band assembly have the function of maintaining the internal gear in reduction mode. The main shaft, on the other hand, propels the sun gear and serves as the primary driving member. When the internal gear is stationary, the planet cage serves as the driven member. Reverse Unit ;The Reverse Unit comprises three main parts: sun gear, planet cage, and internal gear with external and internal teeth. The planet cage, on the other hand, splines to both the output shaft and the internal gear. To keep the internal gear stationary, the anchor pin engages with the external teeth. Meanwhile, the sun gear and planet cage work together to reverse the output shaft’s direction. First Gear | Hydramatic Transmission Locking the sun gear of the front unit allows for the transfer of power from the flywheel to the torus cover. From there, the power transfers to the planet cage. Afterward, the cage rotates around the stationary sun gear at a reduced speed. It then transfers power to the driving of the fluid flywheel via the front section of the intermediate shaft. The power transfer process begins with the main shaft, which transfers power from the driven torus to the sun gear of the rear unit. From there, the sun gear rotates around the planet pinions that drive the output shaft. The combined gear ratio of the two gear sets is the product of their gear ratios. Specifically, the gear ratio in the internal gear and sun gear of the front unit is 67:30, while that of the rear unit is 67:41. Second Gear To shift to second gear, release the front band and engage the front clutch to put the front unit in direct drive. As a result, power is transmit from the flywheel to the torus cover, and then to the locked front unit. Once the front unit is in direct drive, power flows directly from the front section of the intermediate shaft to the fluid flywheel. Finally, the rear unit carries the power to the output shaft, resulting in the vehicle moving in second gear. It is worth noting that the gear ratio for the second gear is 2.63:1, thereby allowing the vehicle to achieve an optimal balance between speed and torque. Third Gear ;To shift to third gear, release the clutch and apply the front band to shift into reduction. To shift back, release the front band and engage the rear clutch. This locks the front unit while connecting the rear unit in direct drive. Power flows from the flywheel to the front unit, then to the rear unit, and finally to the output shaft. The gear ratio for the third speed is 1:45:1. Fourth Gear ;To obtain the fourth gear, lock the clutch and release the band in the front unit-shifting it into direct drive and BEARING the rear unit into direct drive. The flywheel powers the locked front unit, intermediate shaft, rear unit, and output shaft. Reverse Gear ;The reverse unit does not transmit power while in any of the forward speeds. To engage reverse, shift the selector lever to the reverse position, which will shift the front unit into reduction. Then release the rear band and clutch and secure the gear by engaging the anchor pin in the external teeth of the reverse internal gear.The gear ratio in reverse is 4:30:1. Hydramatic Transmission Parts Hydramatic Transmission Advantages 1. 2. 3. 4. This technology reduces fuel consumption. The use of planetary gearing results in less wear and tear on the vehicle. This driving system helps to minimize driver fatigue. The absence of a gear lever or clutch pedal makes this system particularly user-friendly.
