A gearbox in a car is a process of conveying the energy from one piece of equipment to another. It is used to amplify the torque, while reducing the speed. The torque is the power that is generated through twisting and bending of a solid material. This terminology is always used in place of the transmission. Since it is located at the junction of a power shaft, a gearbox is mostly used to create a right angle amend in direction. Each unit serves for a particular purpose with the gear ratio being designed to give a certain level of the required force. The ratio is always fixed, and it cannot be modified at any time once the gearbox is created. The only appropriate and possible changes that can take place are the adjustments that allow the speed of a shaft to increase, correspondingly reducing the speed of transmission (Nice, 2010).
Background of Gearbox Components
The earliest automobiles (gearboxes) offered a manual transmission. They applied the same principle of today’s stick-shift vehicles, which include cars like Ford Model T. Such cars used a two forward gears and a single reverse attached to the engine through a series of pedals. As car traffic grew larger and worse, engineers started to look for the ways of making a car that would shift its gear to another automatically. Various designers spent many years perfecting the current automatic transmission. This development in cars was followed by a close succession in 1941, when Chrysler introduced the “fluid Drive”. This is a semi-automatic transmission that still had a clutch pedal. The fluid pedal allowed a driver to start out without the use of a clutch since the electronic overdrive would kick in automatically. Although this happened, drivers had to use the clutch to change between “high” and “low” gears (Kohara Gear Industry Co., 2003).
It can be argued that the automatic transmission, with its ease of use and simplicity, gave up the automobile to the people, hence fulfilling the wishes and promises of President Hoover Herbert. The automatic gearbox broadened the vistas of an increasing mobile labour force, fed the flow of migration to suburb areas, and welcomed women back into the economy after the war. The automatic transmission achieved this by offering “no muss, no fuss” kind of shifting. This is because there were no more engine racing or lugging, or a missed shift gates. All that was needed was to press the gas and the vehicle would do the rest.
The Functioning of a Gearbox
There are three types of transmission in an automobile machine. These include: the manual, continuously variable and automatic ones. A vehicle that is manually transmitted gives the best examples of a simple gearbox. In both the continuously variable and automatic transmissions, gearboxes are in a closed system, and they require a very minimal human interaction. The manual transmission exists in two dissimilar systems. They include the constant mesh and the sliding mesh. The sliding mesh system utilizes straight cut spur gears. These are gears that spin without restraint and need a manipulation from a driver in order to synchronize the changeover from one speed to the other. The driver is expected to coordinate the revolutions of the engine to the required road speed. In case the transaction between the gears is not correctly timed, the gears crush and create a loud grinding sound as the teeth smash together. The constant mesh system is a diagonally cut helical or double helical gear sets that are lastingly meshed together. The synchronized rings or friction cones are added to the gears in order to create a transition that is smoother, when gears are being changed. This kind of transmission is generally found in theagricultural equipment or racing cars (Memmer, 2009).
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In a sliding mesh gearbox, there is a neutral position. This is whereby the engine is on motion, but the clutch is engaged and the clutch gears are drives the counter drive gear. In this case, the rotational direction of a counter shaft is opposite to the shaft of the clutch. In this state, the first, second and the third gears are free. The main transmission does not rotate, and the wheels are not in motion. The advantage of a constant mesh gear over others is that it does not wear and tear and any possibility of disengaging or engaging gears does not occur. It is essential to understand that the transmission system of a car is the processes that involve transmitting the engine power to the wheels by the use of a transfer clutch and gear mechanisms. The transmission system consists of gear mechanisms and clutch.
Components of a Gearbox
The answer to the modern automatic transmission is with the help of a torque converter. The torque converter takes the place of a clutch in the manual transmission. This is the direct descendant of the earlier component known as a fluid coupling. A torque converter gives the benefit of reproducing the turning power that is provided by the engine. This component connects to the motor by a metal rod called the transmission shaft, also known as an input shaft, which is fitted next to the engine crankshaft, but it does not touch it. It is crucial to understand that there is no direct connection between the transmission (gearbox) and the engine. However, the engine turns the transmission via a process that is known as the hydraulic coupling. A torque converter has several components that facilitate multiplying the expected power (Naunheimer, Bertche, Ryborz, & Novak, 2011).
Lockup Torque Converter
Since the single connection between the two sides of a torque converter is a fluid connection, it is estimated that there is a little slippage of about 2% to 8%. In order to increase the gas mileage and the efficiency, the modern automatic gearboxes have a lockup clutch, also known as a torque converter clutch. As the speed of a car increases to almost 40 miles per hour, the extremely pressurized gearbox fluid is transmitted through a transmission shaft activating the clutch piston. The metal pin then locks the turbine to the impeller causing an effect of bypassing the torque converter. This instance remains like that for some time, hence slowing the car to a speed less than 40 miles per hour. At that point, the clutch piston unfastens, and the torque converter goes in again.
Planetary Gear Sets
The planetary gear set is composed of different sized gears. They are known as planetary, because they are in a circular shape and revolve around a single central gear that is called a sun gear. The system has three elements, namely the sun gear; pistons, drum and planet carrier; and ring gear and a drum. In the first gear, the planetary gear that lies on the front is engaged, hence locking the input shaft. At this point, the gear ratio is 2:46:1, which makes the car start accelerating. On a high gear, the ratio is 1:1, and all the planetary members are locked to one another and the output shaft. On the other hand, in a reverse mode, the high clutch and the reverse are applied. In this scenario, the input shaft is locked to the reverse and a high clutch drum, sun gear and input shell. In this state, the gear ratio is 2:17:1.
Servo Pistons, Bands and Clutches
Some vehicles use a multiple disc clutch operation. In such a setting, a series of fiction discs are put between steel plates. The clutch has a return spring and a piston. This composition is called a clutch pack. When some fluid pressure is applied to the pack, the piston engages, hence locking the assembly and driving wheels. When the pressure discharges, the piston unfastens, and the wheels stop moving. Other cars that use transmission bands use a flexible ring that is fit around the outside of the clutch. This enhances by tightening and engaging the gears, and hence loosening to release them. This method of transmission uses a servo piston to deactivate and activate the bands. The gearbox is connected to the wheels through an output shaft. This meshes to the axles in different ways, depending on the design of the car. The gearbox then turns the output shaft, which correspondently spins the axles making the wheels to run. Many current front-wheel drive vehicles use the transaxle assembly, which in return saves weight, hence increasing the mileage and space. The transaxle has the axles and transmission in a single unit that is attached to the engine (Wongthianchai, 2007).
Materials Used to Manufacture Gears
The materials that are used to make gears highly depend on the services and strength conditions such as noise or wear. The gears may be manufactured from non metallic materials or metallic ones. Gears that are metallic with cut teeth are commercially obtained from steel, bronze and iron. The non metallic materials that make gears, for instance, rawhide, synthetic resins, such as nylon, are used to reduce the unnecessary noise. In most cases, the cast iron is used to make gears due to its good wearing properties, ease of production, and excellent ability of a machine, when it comes to manufacturing of complicated shapes by the use of a casting method. On the other hand, steel is used to make high strength gears. Steel can be composed of alloy steel or carbon steel. The gears made from steel are usually heated and treated in order to combine the hardness and toughness property of teeth. Lastly, the phosphor bronze is used to make worms gears in order to reduce the wear and tear of wears, which could be excessive with steel or cast iron.
Manufacturing of gears requires many processing operations in a chronological stages, depending on the material, types of gears and the desired quality. The first stage is performing the blank with or without teeth. In this stage, the casting procedure takes place. Gear blanks and gears with teeth, which require little finishing and machining, are manufactured. By the use of sand casting, blanks that are of large iron gears, and which require few pieces are produced. The blank is then prepared in appropriate teeth and dimensions by machining the cast perform. Secondly, gears can be manufactured by rolling. For instance, the helical or straight teeth or an external steel gears that are of medium diameter are generated by cold rolling. Rolling impact high accuracy and surface integrity is employed for high quality and productivity. On the other hand, large size gears are manufactured by hot rolling and finished via machining (Gurgenci, 2001).
Environmental impact of Gearbox Materials
As much as the automatic transmission has become common around the world, vehicles are involved in various problems that cause effects that are not environmentally friendly. For instance, poor shift feel, accelerated wear and tear of friction components in a gearbox and transmission shudder contribute towards creating the non-friendly fuel economy. The oil absorption and topographic parameter are associated with the anti-shudder performance. A material that is porous has a quicker and better absorption of oil than materials that have smooth surfaces. Therefore, it is pivotal to create gearboxes with materials that are porous in order to save fuel and reduce the waste emission of unused gas.
The ever inflating oil prices that are driven by the slow depletion of oil deposits around the world, along with the massive global warming issues caused by the emission of carbon dioxide, the environmental saving awareness and energy saving have taken a global apprehension. The tendency of green energy industry has taken charge in developing and designing of environmental friendly vehicles. This has brought in development of electric vehicles, which focus on zero pollution emission and low consumption of energy. The other benefit of an electric vehicle is based on the power performance in the system of transmission or the gearbox. The gearbox has a different gear ratio, and the scope of performance of the motor can be raised with a big torque and low speed with a high speed of rotation. This way, an electric vehicle with a gearbox has a better road load confrontation performance, as compared to a vehicle with a single ratio box. This is because an electric vehicle can reduce the requirements of power for the motor and enhance the performance of the car. Therefore, an efficient gearbox (transmission) serves as a better way to increase the performance of a vehicle that is electrically controlled (Banker, 1996).
The technology that is used by the gear shift control of a gearbox depends on whether it is manually transmitted or not. For a manual transmission, the gear shifting process is realized by pushing a shift lever behind the steering wheel or on the floor of the carriage to different stalls, hence pulling a steel cable connecting it to the shift lever. Such technology for a gearbox is purely mechanical and manual, which hence fails to satisfy the diversified and new car space requirements and design of an innovative control gear shift. The traditional manual gearbox at most times causes noise pollution. It is estimated that accuracy of gears and assembly cause the highest level of noise pollution. It is, therefore, significant to maintain a highly accurate gearbox, which is well assembled. There are other various factors that contribute to the noise produced by gears. For instance, the design of a vehicle contributes 35%, fabrication – 30%, and the assembly contributes 15 % of noise production from a gearbox. However, the quietness of gearbox while in operation is a specific demand for many drivers. Therefore, highly precision gears, which have a better finish for the tooth surface, are highly recommended. Thus, helical gears are the most effective for reducing the noise when compared with other gears such as spur. Additionally, plastic gears are quiet, although the strength is low.
Advancement of Materials
Performance, economy, low emissions, and reliability are the modern demands that have to be met by designers and engineers. Advanced materials are one of the main elements for producing a gearbox in order to improve a long and medium reliability. In fact, materials, which are currently used by modern designers and engineers, cause limitations and stringent conditions, hence creating a certain limitation for implementing new solutions. There are many researches that are being carried in order to increase the efficiency of transmission. The first aim is to develop materials that are resistant to high temperatures. Temperature levels have increased over recent years, whereas certain thresholds cannot be conquered as a result of structural limits of the materials available, for instance, iron casts. Additionally, the weight reduction affects the efficiency of a gearbox (Lawcock, Buckley-Golder, & Sarafinchan, 1999).
With the mentioned factors, designers are developing advanced materials in order to improve the efficiency and increase the structural resistance of a gearbox. This means that the gearbox will be durable and reliable, while its weight will be reduced. The materials that are used for manufacturing a gearbox are magnesium and aluminum. However, the current development of a new-generation alloy will bring about an increase of operating under high temperatures. It is also wise to have protective coats on the materials used in order to increase their operation under high temperatures. Composite materials that have metallic matrixes are also crucial in reducing the weight of gearbox components. In case of an iron cast, it is essential to coat and galvanize the gearbox in order to improve the performance. Avio Aero is committed to the development of advanced materials and implementation of new architectures to improve the efficiency of transmission. There is a universal consensus that the requirement is to develop completely new materials instead of improving the existing ones. This will imply a true revolution in manufacturing of gearboxes (Sun & Hebbale, 2005).
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There is no doubt that gearboxes are used in many areas, except in cars. However, gearbox plays a vital role in transmitting the power from the engine to the wheels. The research paper has successfully discussed the roles that a gearbox plays in a car, and the components that make it up. The various components work together in order to ensure that the gearbox works effectively. The environmental concern on the effects that a gearbox has and the materials used is also discussed in the paper. The paper also focused on the environmental concern and the development that are in place in order to rectify the situation. Various and consistent processes which are in place in ensuring that a gearbox is well manufactured are also discussed in detail. Lastly, it is important to note that a manual and automatic transmission in vehicles has been discussed, bringing out the different roles that a gearbox plays. As a result of completing this research paper, the full functioning, manufacturing and environmental concerns of a gearbox have been efficiently covered.