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INTRODUCTION
The name "Tiptronic" was created by Porsche, who made the first such transmission, but it also can refer to similar transmission systems from other manufacturers, tiptronic transmission is the latest innovation in the field of automatic power transmission systems, which combines the both worlds of transmissions, manual and automatic. A tiptronic transmission is an automatic transmission that can be controlled like a manual transmission. In a standard automatic transmission, a computer selects which gear the car should operate in, but a tiptronic transmission gives this control to the driver.
The purpose of the tiptronic transmission system is to give the driver more control of the car's performance and approximate the feel of a manual transmission while keeping the car as easy to drive as an automatic. Car makers had attempted to design a manual transmission that performed like an automatic, but the tiptronic approach was more successful.
A tiptronic is a type of automatic transmission that allows driver flexibility and control by adopting some of the advantages of a manual transmission. A tiptronic gearbox allows the driver to override the automatic mode for better control of performance. This system allows the car to operate as a sports car when on the open road, or to be driven as an automatic in congested traffic or built up urban areas.
2. LITERATURATURE SURVEY
2.1. CONVENTIONAL MANUAL AND AUTOMATIC TRANSMISSIONS
In Europe the manual transmission (MT) has always been very popular, 80% people like manual transmission and 20% people like automatic transmission because manual transmission is more comfortable then automatic transmission. Despite all Predictions that the automatic transmission (AT) would get a bigger market share, like in the US and Japan because of its higher comfort. Reasons for this are that the manual transmission benefits from its high efficiency, low weight and costs and optimal space economy. Another important aspect is that Europeans prefer choosing the gears manually, in other words remain in control. This situation has led to developments in the field of manual transmissions. MT developers have been trying to make the MT more comfortable, like an AT. But at the same time it should maintain and further improve the advantages it has over the AT. On the other hand the developments of the AT are focused on giving the driver more control over the transmission and improve its disadvantages, low efficiency, low space economy, high weight and costs.
This exercise is primarily aimed at discussing developments in the area of manual gearboxes. But since a lot of these developments are aimed at closing the gap between automatic and manual gearboxes, a brief description of automatic and semi-automatic transmissions is made here as well. In the following paragraphs the most recent innovations in the MT area, which are available on the market, are shortly summarized. Prior to that brief descriptions of the conventional MT and AT are presented for a better understanding.
2.2 MANUAL TRANSMISSION
A layout of a standard drive train, engine longitudinally in the front and rear wheels driven, with manual transmission is shown in fig. 2.2. The MT can be disconnected from the engine using a clutch. This is required to make shifting and synchronization of the gears possible without transmitting engine torque. This is also one of the biggest disadvantages of the MT the interruption of the torque flow during shifts.
A mechanical page link between the clutch pedal and the clutch enables opening and closing of the clutch. Another mechanical page link between the shifter in the vehicle sinterior and the transmission enables the driver to shift gears in any chosen sequence. A differential distributes the torque flow to the driven wheels.
The layout of the gems from a MT and its position in the vehicle depend on the available build space, which wheels (rear, front or four wheel drive) are driven and the position of the engine. The number of stages of the transmission and for the number of ratio steps making up the individual gears determines in which category a geared transmission can be placed. A stage refers to a gear pair, or the power flow from one shaft to another. Difference is made between single, two and multi-stage transmissions. In a single-stage MT the power flow enters the MT at the input shaft and is transmitted directly to the output shaft by one gear pair. In a two-stage MT a third shaft called counter- or lay shaft is added. The power flow now is transmitted from the input to the output shaft via the counter-lay shaft. Two gear pairs are involved in this. If three or more gear pairs are used to transmit the engine torque the MT is called a multi-stage MT.
This connects the drive train to the engine. When the driver wants the car to start moving, they can select the appropriate gear according to the speed of the car. When braking is required, a manual gearbox makes engine braking possible. By changing down gears, the driver slows the engine. Lower gears are used for speeding up or slowing down, higher gears are used when cruising at speed; engine revs drop and less fuel is consumed.
Manual gearboxes are generally cheaper, lighter, give better performance and have more fuel efficiency than an automatic
2.3 AUTOMATIC TRANSMISSION
Modern automatic transmissions can trace their origins to an early "horselesscarriage" gearbox that was developed in 1904 by the Sturtevant brothers of Boston, Massachusetts. This unit had two forward speeds, the ratio change being brought about by flyweights that were driven by the engine. At higher engine speeds, high gear was engaged. As the vehicle slowed down and engine RPM decreased, the gearbox would shift back to low. Unfortunately, the metallurgy of the time wasn't up to the task, and owing to the abruptness of the gear change, the transmission would often fail without warning.
The next significant phase in the automatic transmission's development occurred in 1908 with the introduction of Henry Ford's remarkable Model T. The Model T, in addition to being cheap and reliable by the standards of the day, featured a simple, two speed plus reverse planetary transmission whose operation was manually controlled by the driver using foot pedals. The pedals actuated the transmission's friction elements (bands and clutches) to select the desired gear. In some respects, this type of transmission was less demanding of the driver's skills than the contemporary, unsynchronized manual transmission, but still required that the driver know when to make a shift, as well as how to get the car off to a smooth start.
Parallel to the development in the 1930s of an automatically-shifting gearbox was Chrysler's work on adapting the fluid coupling to automotive use. Invented early in the 20th century, the fluid coupling was the answer to the question of how to avoid stalling the engine when the vehicle was stopped with the transmission in gear. Ironically, Chrysler itself never used the fluid coupling with any of its automatic transmissions, but did use it in conjunction with a hybrid manual transmission called "Fluid Drive" (the similar Hy-Drive used a torque converter). These developments in automatic gearbox and fluid coupling technology eventually culminated in the introduction in 1939 of the General Motors Hydra-Matic, the world's first mass-produced automatic transmission.
Available as an option on 1940 Oldsmobiles and later Cadillacs, the Hydra-Matic combined a fluid coupling with three hydraulically-controlled planetary gearsets to produce four forward speeds plus reverse. The transmission was sensitive to engine throttle position and road speed, producing fully automatic up- and down-shifting that varied according to operating conditions.
The Hydra-Matic was subsequently adopted by Cadillac and Pontiac, and was sold to various other automakers, including Bentley, Hudson, Kaiser, Nash, and Rolls-Royce. It also found use during World War II in some military vehicles. From 1950-1954, Lincoln cars were also available with the Hydra-Matic. Mercedes-Benz subsequently devised a four-speed fluid coupling transmission that was similar in principle to the Hydra-Matic, but of a different design.
Interestingly, the original Hydra-Matic incorporated two features which are widely emulated in today's transmissions. The Hydra-Matic's ratio spread through the four gears produced excellent "step off" and acceleration in first, good spacing of intermediate gears, and the effect of an overdrive in fourth, by virtue of the low numerical rear axle ratio used in the vehicles of the time. In addition, in third and fourth gear, the fluid coupling only handled a portion of the engine's torque, resulting in a high degree of efficiency. In this respect, the transmission's behavior was similar to modern units incorporating a lock-up torque converter.
The first torque converter automatic, Buick's Dynaflow, was introduced for the 1948 model year. It was followed by Packard's Ultramatic in mid-1949 and Chevrolet's Powerglide for the 1950 model year. Each of these transmissions had only two forward speeds, relying on the converter for additional torque multiplication. In the early 1950s, BorgWarner developed a series of three-speed torque converter automatics for American Motors, Ford Motor Company, Studebaker, and several other manufacturers in the US and other countries. Chrysler was late in developing its own true automatic, introducing the two-speed torque converter PowerFlite in 1953, and the three-speed TorqueFlite in 1956. The latter was the first to utilize the Simpson compound planetary gearse.
In fig. 2.3 a layout of a standard drivetrain with an automatic transmission is shown. The first difference between a MT and AT equipped drivetrain is the connection of the transmission with the engine. In the case of a conventional AT a torque converter is used to realize this. The second difference is that in a conventional AT the gear steps are defined within planetary gear sets by using brakes and wet clutches. The planetary gear sets are positioned in an axial arrangemen.
Due to the torque converter and the transmission braked planetary gear sets the AT can make shifts without power interruption. The brakes and clutches within the AT are hydraulically controlled, an engine driven pump supplies the hydraulic oil. This oil pump, the oil cooler, wet clutches and the torque converter are the principal components that reduce the efficiency of the AT compared to the MT.
The AT has some advantages over the MT. It enables faster and 'smarter' shifting than the average driver. And therefore some AT drivers realize lower fuel consumptions than with a MT, despite the lower AT efficiency. Reduced driver stress, which leads to improved road safety and ride comfort are also benefits over the MT. Because the torque converter is responsible for a part of the change in transmission ratio, an AT theoretically requires fewer gear steps than a MT.
An automatic transmission is a gearbox that can change gears without use of a driver operated clutch. Instead, the vehicle relies on a torque converter which is placed between the engine and transmission. Automatics are easier to use than manuals, and are fast gaining popularity. Initially automatics had many drawbacks to them, but advancements in technology have enabled a more sophisticated automatic transmission to emerge, bringing them closer to a manual in fuel efficiency and performance.
The energy efficiency of automatic transmission has increased with the introduction of the torque converter lock-up clutch, which practically eliminates fluid losses when engaged. Modern automatic transmission also minimize energy usage and complexity, by minimizing the amount of shifting logic that is done hydraulically. Typically, control of the transmission has been transferred to computerized control systems which do not use fluid pressure for shift logic or actuation of clutching mechanisms.
2.4 TRANSMISSION SEMI-AUTOMATIC TRANSMISSIONS
In the last few years, car manufacturers have attempted to make the AT more popular by providing the driver with more control. This led to an automatic gearbox with the possibility to select gears sequentially by hand, the so-called semi-automatic. The first large car manufacturer that made this optionally available was Porsche, with its tiptronic system introduced in 1990 on the Porsche 911.
Based on an AT with torque converter it offers, besides the conventional automatic mode, a manual override allowing the driver to shift. The system is not faster or more efficient than a conventional automatic, but it provides more involvement for the driver. The system does not involve large changes to the transmission itself. The shifter system has to be changed as well as the control software that makes the shifts. Porsche, ZF and Bosch cooperatively developed tiptronic. Other car manufacturers followed soon with their own systems or licensed the tiptronic system from Porsche. The semi-automatic gearbox keeps all the other disadvantages of a normal automatic compared to a MT. That is, low efficiency, large installation space and high weight and manufacturing cost.
Many modern semi-automatic transmissions can operate in the same manner as a conventional type of automatic transmission by allowing the transmission's computer to automatically change gear, if for example the driver was redlining the engine. Despite superficial similarity, manumatics differ significantly in internal operation and driver's "feel" from semi-automatic transmissions. A manumatic, like a standard automatic transmission, uses a torque converter instead of clutch to manage the page link between the engine and transmission - and therefore the roadwheels, though a manumatic has the ability to command shifts manually which is not found on a regular automatic.