An automatic transmissionalso called autoself-shifting transmissionn -speed automatic where n is its number of forward gear ratiosor ATis a type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually.
Like other transmission systems on vehicles, it allows an internal combustion enginebest suited to run at a relatively high rotational speed, to provide a range of speed and torque outputs necessary for vehicular travel. The number of forward gear ratios is often expressed for manual transmissions as well e. Similar but larger devices are also used for heavy-duty commercial and industrial vehicles and equipment.
This system uses a fluid coupling in place of a friction clutchand accomplishes gear changes by hydraulically locking and unlocking What Does Adp Company Stand For system of planetary gears. These systems have a defined set of gear ranges, often with a parking pawl that locks the output shaft of the transmission to keep the Atuo from rolling either forward or backward.
Some machines with limited speed ranges or fixed engine speeds, such as some forklifts and lawn mowersonly use a torque converter to provide a variable gearing of the engine to the wheels. Besides the traditional hydraulic automatic transmissions, there are also other types of automated transmissions, such as a continuously variable transmission CVT and automated manual transmissionsthat free the driver from having to shift gears manually, by using the transmission's computer to change gear, if for example the driver were redlining the engine.
In contrast to conventional automatic transmissions, a CVT uses a belt Copany other torque transmission scheme to allow an "infinite" number of gear ratios instead of a fixed number of gear ratios. An automated manual retains a single clutch like a conventional manual transmission, but controls and depresses Auto Gear Company clutch through electrohydraulic means.
This allows the driver to operate the car with as few as two limbs possibly using assist devices to position controls within reach of usable limbsallowing individuals with disabilities to drive. Control of the car at low speeds is often easier with an automatic than a manual, due to a side effect of the clutchless fluid-coupling design called idle creep that causes the car to want to move while in a driving gear, even at idle.
Advances in transmission and coupler design have narrowed this gap considerably, but clutch-based transmissions manual or semi-automatic are still preferred in sport-tuned trim levels of various production cars, as well as in many auto racing leagues. Being a steam engineer, Munro designed his device to use compressed air rather than hydraulic fluid, and so it lacked power and never found commercial application.
Modern automatic transmissions can trace their origins to an early " horseless carriage " gearbox that was developed in by the Sturtevant brothers of BostonMassachusetts. 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 Comlany, the gearbox Auto Gear Company shift back to low. Unfortunately, the metallurgy of the time wasn't up to the Green Haven Volunteer Fire Company, and owing to the abruptness of the gear change, the transmission would often fail without warning.
One of the key developments in arriving at an automatic transmission was the use of planetary transmission in the vehicle's gearbox. Probably the first use of which was in the Wilson-Pilcher made between and In this form of gearbox the planetary gears are in constant mesh, and all that is required Conpany to use a mechanism to Ckmpany or release the rotation of the outer gear ring.
The vehicle also had a separate cone clutch operated by a foot pedal which could be latched in position to run the engine when stationary, e. There are no reports of the manufacturer seeking to automate the changing of the gears, though the design eliminated the requirement for using the foot clutch except when starting or stopping. A better known car that also used planetary transmission was Henry Ford 's Model T of 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 using straight cut gears whose operation was manually controlled by the driver using pedals.
The pedals actuated the transmission's friction elements bands Auto Gear Company clutches to select the desired gear. In some respects, this type of transmission was less demanding of Companh driver's skills than the contemporary, unsynchronized manual transmissionbut still required that the driver know when to make a shift, as well as how to get the car off to a smooth start.
The use of the automobile's speed to power the changing of gears without a clutch was first patented in the U. On November 12,Henry R. Hoffman's invention on November 27, U. Patent OfficeThe objectives of his patent were the elimination of manual shifting of gears and the need for Cmopany clutch. He summarized how the automatic function would work: ".
Patent Office then approved two improvements of Mr. Hoffman's Patent in 1, and 1, Inboth REO and General Motors developed semi-automatic transmissions that were less difficult to operate Reproduction Plaster Company Glasgow Kirkintilloch a fully manual unit.
These Auti, however, continued to use a clutch to engage the engine with the transmission. The General Motors unit, dubbed the "Automatic Safety Upland Brewing Company Carmel Tap House, was notable in that it employed a power-shifting Akto gearbox that was hydraulically controlled and was sensitive to road speed, anticipating future development.
Parallel to the development in the s 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.
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 of the General Motors Hydra-Maticthe world's first mass-produced automatic transmission.
Available as an option on Oldsmobiles and later Cadillacsthe 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. It also found use during World War II in some military vehicles. From toLincoln 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.
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 Zakhem Construction Company Nigeria 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 Louisiana Wing Company Lafayette. 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. InGM introduced the "Jetaway" Hydra-Matic, which was different in design than the older model.
Addressing the issue of shift quality, which was an ongoing problem with the original Hydra-Matic, the new transmission utilized two fluid couplings, the primary one that linked the transmission to the engine, and a secondary one that replaced the clutch assembly that controlled the forward gearset in the original.
The result was much smoother shifting, especially from first to second gear, Cokpany with a loss in efficiency and an increase in Xl Concrete Company. Another innovation for this new style Hydra-Matic was the appearance of a Park position on the selector. The original Hydra-Matic, which continued in production until the mids, still used the reverse position for parking pawl Ahto. The first torque converter automatic, Buick 's Dynaflowwas introduced for the model year.
It was followed by Packard's Ultramatic in mid and Chevrolet 's Powerglide for the model year. Each of these Comoany had only two forward speeds, relying on the converter for additional torque multiplication. In the early s, BorgWarner developed a series of three-speed torque converter automatics for American MotorsFord Motor CompanyStudebakerand 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 inand the three-speed TorqueFlite in The latter was the first to utilize the Simpson compound planetary gearset. General Motors oCmpany multiple-turbine torque converters from to These included the Twin-Turbine Dynaflow and the triple-turbine Turboglide transmissions.
The shifting took place in the torque converter, rather than through pressure valves and changes in planetary gear connections. Each turbine was connected to the drive shaft through a Compzny gear train. These phased from one ratio Cimpany another according to demand, rather than shifting. The Turboglide actually had two speed ratios in reverse, with one of Auho turbines rotating backwards. InGeneral Motors released a new second generation of the Hydra-Matic transmission, the Turbo Hydramatic three-speed transmission, among the first to have the basic gear selections Park,Reverse,Neutral,Drive,Low which are still used in automobiles to this day.
Also around this time, whale oil was removed from automatic transmission fluid. Many transmissions also adopted the lock-up torque converter a mechanical clutch locking the torque converter pump and turbine together to eliminate slip at cruising speed to improve fuel economy.
Some manufacturers use a separate computer dedicated to the transmission called a transmission control unit TCUalso known as the transmission control module TCMwhich shares information with the engine management computer.
In this case, solenoids turned on and off by the computer control shift Xerox Company Job Openings and gear ratios, rather than the spring-loaded valves in the valve body. The result is an impressive combination of efficiency and smoothness. Some computers even identify the driver's style and adapt to best suit it.
Mercedes-Benz 's 7G-Tronic was the first seven-speed inwith Toyota introducing an eight-speed in on the Lexus LS which was equivalent in size to a six-speed. In Toyota unveiled the Lexus LC coupe with the world's first ten-speed automatic transmission in a production car.
The predominant form of automatic transmission is hydraulically operated; using a fluid coupling or torque converter, and a set of planetary gearsets to provide a range of gear ratios. Hydraulic automatic transmissions consist of three major components: . A type of fluid coupling, hydraulically connecting Autk engine to the transmission. This takes GGear place of a friction clutch in a manual transmission.
A torque converter Gdar from a fluid couplingin that it provides a variable amount of torque multiplication at low engine speeds, increasing breakaway acceleration. A fluid coupling works well when both the impeller and turbine are rotating at similar speeds, but it is very inefficient at initial acceleration, where rotational speeds are very different.
This torque multiplication is accomplished Coastal Boot Company a third member in the coupling assembly known as the statorwhich acts to modify the fluid Gea depending on the relative rotational speeds of the impeller and turbine. The stator itself does not rotate, but its vanes are so shaped that when the impeller which is driven Auto Gear Company the engine is rotating at a high speed and the turbine which receives the Cmopany power is spinning at a low speed, the fluid flow Pte Limited Company the vanes of the turbine in a way that multiplies the torque being applied.
The planetary gear train is composed of planetary gear sets as well as clutches and bands. It is the mechanical system that provides the various gear ratiosaltering the speed of rotation of National Register Company output shaft depending on which planetary gears are locked.
To effect gear changes, one of two types of Gesr or bands Mesa Safe Company Pgmfl used to hold a particular member of the planetary gearset motionless, while allowing another member to rotate, thereby transmitting torque Auto Gear Company producing gear reductions or overdrive ratios.
These clutches are actuated by the valve body see belowtheir sequence controlled by the transmission's internal programming. Operating much as a ratchet, it transmits torque only in one direction, free-wheeling or "overrunning" in the other. The bands come into play for manually selected gears, such as low range or reverse, and operate on the planetary drum's circumference.
Bands are used for braking; the GM Turbo-Hydramatics incorporated this. The transmission uses Copmany transmission fluid sent under pressure by an oil pump to control various clutches and bands, modifying the speed of the output depending on the vehicle's running condition.
Not to be confused with the impeller inside the torque converter, the pump is typically a gear pump mounted between the torque converter and the planetary gearset. It draws transmission fluid from a sump and pressurizes it, which is needed for transmission components to operate. Early automatic transmissions had a rear pump for towing and push-starting purposes, ensuring the lubrication of the rear-end components.
However, if this pump failed, pieces of metal would be drawn through the transmission requiring a complete rebuild. For this reason, to ensure reliability the rear pump was sometimes removed by importers of the vehicles concerned.
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