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Close-ratio
A close-ratio transmission describes a motor vehicle transmission with a smaller than average difference between the gear ratios. They are most often used on sports cars in order to keep the engine in the power band. There is no industry standard as to what constitutes a close-ratio transmission, a transmission that one manufacturer terms close-ratio may not necessarily be considered close-ratioed by another manufacturer. Generally speaking, the more gears a transmission has, the closer they are together. A continuously variable transmission has a near infinite "number" of gear ratios, which implies an infinitely close-ratio between gears. However, with no specific gear ratios, it would not be considered a close-ratioed transmission. Comparison with ordinary transmission This table compares the ratios of three Porsche 911 vehicles from 1967 to 1971, the first being the standard 901/75 transmission, the second being the 901/76 transmission denoted "For hill climbs", and the third bei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gear Ratio
A gear train is a mechanical system formed by mounting gears on a frame so the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing a smooth transmission of rotation from one gear to the next. Features of gears and gear trains include: * The gear ratio of the pitch circles of mating gears defines the speed ratio and the mechanical advantage of the gear set. * A planetary gear train provides high gear reduction in a compact package. * It is possible to design gear teeth for gears that are non-circular, yet still transmit torque smoothly. * The speed ratios of chain and belt drives are computed in the same way as gear ratios. See bicycle gearing. The transmission of rotation between contacting toothed wheels can be traced back to the Antikythera mechanism of Greece and the south-pointing chariot of China. Illustrations by the Renaissance scientist Georgius Agricola show gear trains with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmission (mechanics)
Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differential, and final drive shafts. In the United States the term is sometimes used in casual speech to refer more specifically to the gearbox alone, and detailed usage differs. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and where different rotational speeds and torques are adapted. Often, a transmission has multiple gear ratios (or simply "gears") with the ability to switch between them as the speed varies. This switching may be done manually (by the operator) or automatically (by a control unit). Directional (forward and reverse) control may also be provided. Single-ratio transmissions also exist, which simply cha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Engine Efficiency
Engine efficiency of thermal engines is the relationship between the total energy contained in the fuel, and the amount of energy used to perform useful work. There are two classifications of thermal engines- #Internal combustion (gasoline, diesel and gas turbine-Brayton cycle engines) and # External combustion engines ( steam piston, steam turbine, and the Stirling cycle engine). Each of these engines has thermal efficiency characteristics that are unique to it. Engine efficiency, transmission design, and tire design all contribute to a vehicle's fuel efficiency. Mathematical definition The efficiency of an engine is defined as ratio of the useful work done to the heat provided. : \eta = \frac = \frac where, Q_1 is the heat absorbed and Q_1-Q_2 is the work done. Please note that the term work done relates to the power delivered at the clutch or at the driveshaft. This means the friction and other losses are subtracted from the work done by thermodynamic expansion. Thus an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Automatic Transmission
An automatic transmission (sometimes abbreviated to auto or AT) is a multi-speed transmission used in internal combustion engine-based motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions. It typically includes a transmission, axle, and differential in one integrated assembly, thus technically becoming a transaxle. The most common type of automatic transmission is the hydraulic automatic, which uses a planetary gearset, hydraulic controls, and a torque converter. Other types of automatic transmissions include continuously variable transmissions (CVT), automated manual transmissions (AMT), and dual-clutch transmissions (DCT). An electronic automatic transmission (EAT) may also be called an electronically controlled transmission (ECT), or electronic automatic transaxle (EATX). A hydraulic automatic transmission may also colloquially called a " slushbox" or simply a "torque converter", although the latter term c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Manual Transmission
A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission (mechanics), transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch (which is usually a foot pedal for cars or a hand lever for motorcycles). Early automobiles used ''sliding-mesh'' manual transmissions with up to three forward gear ratios. Since the 1950s, ''constant-mesh'' manual transmissions have become increasingly commonplace and the number of forward ratios has increased to 5-speed and 6-speed manual transmissions for current vehicles. The alternative to a manual transmission is an automatic transmission; common types of automatic transmissions are the Automatic transmission#Hydraulic automatic transmissions, hydraulic automatic transmission (AT), and the continuously variable transmissio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Overdrive (mechanics)
Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption, lower noise, and lower wear. The term is ambiguous. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is ''over-geared'', and cannot reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning at higher RPM. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. The point of maximum power is somewhat lower than the absolute maximum RPM to which the engine is limited, the " redline" RPM. A car's speed is limited by the power required to drive it against air resistance, which increases with speed. At the maximum possible speed, the engine is running at its point of maximum power, or ''power peak'', and the car is traveling at the speed where air resistance equals that max ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drivetrain
A drivetrain (also frequently spelled as drive train or sometimes drive-train) is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components of a motor vehicle that deliver power to the drive wheels. This excludes the engine or motor that generates the power. In marine applications, the drive shaft will drive a propeller, thruster, or waterjet rather than a drive axle, while the actual engine might be similar to an automotive engine. Other machinery, equipment and vehicles may also use a drivetrain to deliver power from the engine(s) to the driven components. In contrast, the powertrain is considered to include both the engine and/or motor(s) as well as the drivetrain. Function The function of the drivetrain is to couple the engine that produces the power to the driving wheels that use this mechanical power to rotate the axle. This connection involves physically linking the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Overdrive (mechanics)
Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption, lower noise, and lower wear. The term is ambiguous. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is ''over-geared'', and cannot reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning at higher RPM. The power produced by an engine increases with the engine's RPM to a maximum, then falls away. The point of maximum power is somewhat lower than the absolute maximum RPM to which the engine is limited, the " redline" RPM. A car's speed is limited by the power required to drive it against air resistance, which increases with speed. At the maximum possible speed, the engine is running at its point of maximum power, or ''power peak'', and the car is traveling at the speed where air resistance equals that max ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sports Car
A sports car is a car designed with an emphasis on dynamic performance, such as handling, acceleration, top speed, the thrill of driving and racing capability. Sports cars originated in Europe in the early 1900s and are currently produced by many manufacturers around the world. Definition Definitions of sports cars often relate to how the car design is optimised for dynamic performance, without any specific minimum requirements; both a Triumph Spitfire and Ferrari 488 Pista can be considered sports cars, despite vastly different levels of performance. Broader definitions of sports cars include cars "in which performance takes precedence over carrying capacity", or that emphasise the "thrill of driving" or are marketed "using the excitement of speed and the glamour of the (race)track" However, other people have more specific definitions, such as "must be a two-seater or a 2+2 seater" or a car with two seats only. In the United Kingdom, early recorded usage of the "sports car" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Automotive Transmission
Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differential, and final drive shafts. In the United States the term is sometimes used in casual speech to refer more specifically to the gearbox alone, and detailed usage differs. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and where different rotational speeds and torques are adapted. Often, a transmission has multiple gear ratios (or simply "gears") with the ability to switch between them as the speed varies. This switching may be done manually (by the operator) or automatically (by a control unit). Directional (forward and reverse) control may also be provided. Single-ratio transmissions also exist, which simply chan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geometric Mean
In mathematics, the geometric mean is a mean or average which indicates a central tendency of a set of numbers by using the product of their values (as opposed to the arithmetic mean which uses their sum). The geometric mean is defined as the th root of the product of numbers, i.e., for a set of numbers , the geometric mean is defined as :\left(\prod_^n a_i\right)^\frac = \sqrt /math> or, equivalently, as the arithmetic mean in logscale: :\exp For instance, the geometric mean of two numbers, say 2 and 8, is just the square root of their product, that is, \sqrt = 4. As another example, the geometric mean of the three numbers 4, 1, and 1/32 is the cube root of their product (1/8), which is 1/2, that is, \sqrt = 1/2. The geometric mean applies only to positive numbers. The geometric mean is often used for a set of numbers whose values are meant to be multiplied together or are exponential in nature, such as a set of growth figures: values of the human population or inter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
