Automatic and Manual Transmission - Report Example

Running Head: AUTOMATIC AND MANUAL TRANSMISSION Automatic and Manual Transmission Name Institution PART a CONTINUOUS VARIABLE TRANSMISSION This is a type of transmission where the transmission can be able to change concurrently at some continuous range of different gear ratios. The flexibility of the system allows the input shaft to be kept at a constant angular velocity. Where low torque requirements are needed the belt type will provide a simple solution. History of evolution of continuous variable transmission (CVT) IN 1490 Leonardo da Vinci came up with the idea of continuous transmission of power. In 1879 Milton Reeves developed a variable transmission unit for a simple saw milling machine which he later used it in his first car. A v twin engine was developed for a motor cycle in 1910 which was later improved by the British to a multi gear system motorcycle using continuous variable transmission. A British made cyclo car was introduced to the market using the CVT technology for power transmission. George Constantinesco then invented Constantinesco vehicle which were a very efficient engine using the continuous variable transmission in 1926. In 1950 a more automatic version of the car was produced by  Hub van Doorne the Variomatic, car. The main aim of this invention was to come up with a more efficient affordable car for use by the people (Oskar & Young, 1965). In 1965 there was introduction of the first ever garden tractors which were using continuous variable transmission in there system. The two models were the 875 tractors and the 1075 garden tractors. In 1974 the first ever motorcycle using rubber belt for power transmission in the continuous variable transmission was developed. In 1987 the Subaru Company produced there first brand Subaru cars using the continuous variable transmission. This was alongside the ford and Nissan companies who became the first companies to produce a vehicle using a steel belt in the continuous variable transmission. 1992 Nissan improved the CVT by coming up with their own which could allow higher torque level due to the inclusion of a torque converter system. 1996 the first ever heavy torque tractor was introduced that used hydrostatics in the continuous variable transmission allowing working at high torque levels. 2000 Audi Company introduced the first continuous variable transmission using a chain drive as the power transmitter. By 2010 there was a lot of improvement on the continuo’s variable transmission system for instance the using of hydraulic converters for CVT that allowed hydraulic friction rather than the mechanical friction system improving efficiency by minimizing frictional loses. Distinguishing features between CVT and conventional automatic transmission Fuel efficiency CVT allow the engine only to operate within the most efficient range with the help of a clutch whereas in automatic transmission uses a torque converter which acts as the fluid coupling providing an inefficient connection between engine and wheels. Gear shifting In automatic transmission the change in gears is done by a control unit whereas in continuous variable transmission it’s done the aid of the clutch system. Advantages of continuous variable transmission over manual and automatic transmission They have a better fuel consumption compared automatic transmission as the engine is always maintained at the optimal power range regardless of the speed its moving There are lower power loses therefore the speed acceleration are very high compared to automatic transmission. The ride on the continuous variable transmission is smooth compared to the automatic transmission vehicles There is minimal efficiency loses in the continuous variable transmission s compared to the automatic transmission It easily adapts to the varying conditions or nature of the road alongside with the proportional power demands giving a more suitable ride to the user Due to the well controlled engine speed there is lees air pollution from the engine and related green house gases emission (Janiszewski, 1988). Disadvantages of continuous variable transmission It has got high initial and maintaining costs Continuously varying transmission with belt have limited amount of torque that can be transmitted at a given period There is likely hood of greater wear and tear losses caused by the related frictional loses during power transmission Limitation of continuous variable transmission and solution Limitation It gives room to the engine to operate at any desired speed leading to higher noise levels from the engine that make it uncomfortable for some of the users. Solution This can be minimized by the use of a proper cladding material in the transmission system to reduce the noise levels to acceptable levels. PART B ASSESSMENT STRUCTURE PROJECT INTRODUCTION Transmission system There are four main types of transmission systems :manual transmission system, semi automatic transmission system continuously variable transmission and the automatic transmission system. Manual transmission system In this kind of system all the gears are selected manually by the operator with help of a gear Selecting mechanism and clutch. Working principle Fly wheel of the engine is connected to the engine crank shaft tapping motion from it. The clutch disk is usual pressed on the flywheel surface by a pressure plate. If the clutch pedal is pressed the clutch disk is engaged allowing the flywheel to tap motion from the crank shaft thereby transmitting power to the wheels. Depressing the clutch relieves pressure being applied to the flywheel so no power is transmitted. The gears are chosen by interlocking the paired gears to the output shaft. Stages in manual power transmission system a. Clutch at full depression The clutch disk is not into contact with the fly wheel therefore there is no power transmission from engine to the wheels b. Clutch slips Gives time to the engine to gradually make adjustments of its speed relative to the newly engaged gear this is between full depressing and releasing of the clutch c. Clutch fully released Clutch pressed the flywheel fully full power transmission from the crankshaft to the wheels of the vehicle Automatic transmission Mainly consist of an Epicyclic gear planetary gear and a torque converter. One or more gear are in rotator motion relative to a central gearing this allows for a smaller sized gearbox that can easily manage different torque speed ratios. Stages of automatic transmission a. Pack it provides a lock to the transmission system preventing the vehicle from moving b. Reverse gives the car the ability to move backward through movement of gear in the opposite direction to the forward c. Neutral ensure there is no transmission by providing disconnection from the flywheel d. Low gives lower speed to navigate on hilly areas e. Drive permits selecting of a range of gears for the vehicle DISCUSSION Types of manual transmission Non Synchronous transmission Sliding mesh: Engagement of the gears is done by sliding them on the shaft where proper timing and throttle manipulation was necessary during the shifting. . Spur gears are arranged to mesh with each other to provide a change in speed or direction. In constant mesh the gears are in contact whole time while in synchronous mesh only in contact during engaging. During shifting to either the higher or lower gear the clutch is released and engagement done in neutral. Constant mesh transmission has parallel shafts with gears in constant mesh. In the collar shift version. Shifting is accomplished by locking free-running gears to their shafts with sliding collars. In the synchromesh version, gears can be selected without clashing by synchronizing the speeds of mating gears before they engage. Synchronous transmission The gears during motion are rotating and meshed but the only difference is that gears on either shaft can freely rotate or be locked to that shaft. A dog collar is the mechanism used to attach the gear to the shaft when required providing the locking mechanism. The collars are controlled by linkages that ensure only one gear is locked at any given time allowing for power transmission Types of automatic transmission a. Epicyclic gear box High torque frictional clutches are normally used allowing for gear engagement rather than splinned shifting collars. During movement of the engine shifting is done simultaneously there is no need to disengage the clutch. It’s very expensive and uneconomical in terms of efficiency. Planetary gear is made of sun gear smaller planet gears and a carrier gear . In this system al the gears are usually in constant mesh with each other. The planets gears have freedom to free turn on the spindles during a single Epicyclic train. Where either gear reduction action or reversal can be easily done. b. Torque Convertor Allows the transmission of mechanical power instead of a clutch. The prime mover is responsible for the rotation of the driving turbine which id the pump. The movement of the impellor allows both the linear and rotator motion of the hydraulic fluid. The pump directs the hydraulic fluid towards the direction of the turbine blades. Difference in angular velocities at the input and output causes net force acting towards the output of the turbine generating torque allowing rotator motion in same direction as the pump. The fluid moves in one direction that can be visible difference between the angular velocities of input and output may result a net centripetal force (Kluger & Long, 1999). Material selection on various components of a gearbox Synchro hub and sleeve are made of steel. The block ring the part that rubs on the gear to change its speed is made of softer material i.e. brass to minimize frictional wear. Comparison between manual and automatic clutch systems A Clutch is a mechanical component used during engagement of the flywheel allowing power from the engine to the wheels Advantages Manual clutch 1. It allows more engine power transmission as it has more precise gear transmission shifts 2. It gives the operator a better engine control compared to the automatic one 3. It allows the driver to push start the car on a dead battery Disadvantages 1. Difficult in operating in heavy traffic 2. High maintenance cost due to tear and wear Advantages of automatic clutch transmission 1. Minimum wear and tear low maintenance cost 2. Can be easily operated in heavy traffic Disadvantage 1. In case of dead battery unless its charged the engine won’t start 2. Limited engine control of the operator Essential features of a good clutch: (i) It should have good ability of taking load without dragging and chattering. (ii) It should have higher capacity to transmit maximum power without slipping. (iii) Friction surface should be highly resistant to heat effect. The control by hand lever or pedal lever should be easy Limitation planetary gear box and how it can be improved Requires a lot of lubrication because of the increased number of gears which also are complex and inaccessible incase of damage to one of them. They should be made in such a way that one can easily access the various components in case of breakdown allowing easier repair. Limitation constant mesh gear box and how it can be improved Lower efficiency because of the high number of mesh teeth in the system for power transmission this can be rectified by minimizing the number of gear teeth which are constantly being meshed at any given time. Limitation sliding mesh gear box and how it can be improved Shorter life span compared to constant mesh gearbox because of the sliding action this can be minimized by using more resistant material such as hardened steel or carst iron for the bevel gears used (Kluger & Long, 1999). Modern design transmission With the current designs in transmission the engine can be able to change the gears on its own to various gear ratios free the driver from such duties. Hydraulic transmission system is one of the popular ones where fluid coupling performs the function as the frictional clutch in a manual transmission system. This reduces the frictional loses experienced allowing more power, torque and speed transmission levels at an economical value. As a result the modern automatic transmission edges out the manual. For heavy machines that have a limited speeding capability torque converters are used for varying the gearing to the wheels. CONCLUSION Transmission is a speed reducing mechanism, equipped with several gears. The simplest transmissions, often called gearboxes, provide gear reduction sometimes in conjunction with a right-angle change in direction of the shaft. There are four main types of transmission the manual semi automatic, automatic and the continuously varying transmission system. Either of the transmission system has its own advantages and disadvantages even though the automatic system is on the upper edge compared to the rest from the economical point of view. The choice of type of transmission may also be subjective to the preference of the driver. References Oskar, W., & Young, R. E. (1965). U.S. Patent No. 3,167,970. Washington, DC: U.S. Patent and Trademark Office. Kluger, M. A., & Long, D. M. (1999). An overview of current automatic, manual and continuously variable transmission efficiencies and their projected future improvements (No. 1999-01-1259). SAE Technical Paper. Janiszewski, G. K. (1988). U.S. Patent No. 4,738,149. Washington, DC: U.S. Patent and Trademark Office. Shinar, D., Meir, M., & Ben-Shoham, I. (1998). How automatic is manual gear shifting?. Human Factors: The Journal of the Human Factors and Ergonomics Society, 40(4), 647-654. Simancik, C. D., & Zemke, K. M. (1980). U.S. Patent No. 4,235,123. Washington, DC: U.S. Patent and Trademark Office. Read More