A manual transmission , also known as a manual gearbox , a standard transmission or colloquially in some countries e. It uses a driver-operated clutch , usually engaged and disengaged by a foot pedal or hand lever, for regulating torque transfer from the engine to the transmission; and a gear selector that can be operated by hand. A conventional 4- or 5-speed manual transmission is often the standard equipment in a modern base model vehicle, with 4-speed being more common in non-passenger vehicles such as pickup trucks and light commercial vehicles.
Higher end vehicles, such as sports cars and luxury cars are often usually equipped with a 6-speed transmission for the base model. Other options include automatic transmissions such as a traditional automatic hydraulic planetary transmission often a manumatic , a semi-automatic transmission , or a continuously variable transmission CVT.
The number of forward gear ratios is often expressed for automatic transmissions as well e. Manual transmissions often feature a driver -operated clutch and a movable gear stick.
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Most automobile manual transmissions allow the driver to select any forward gear ratio "gear" at any time, but some, such as those commonly mounted on motorcycles and some types of racing cars, only allow the driver to select the next-higher or next-lower gear.
This type of transmission is sometimes called a sequential manual transmission. In a manual transmission, the flywheel is attached to the engine's crankshaft and spins along with it. The clutch disc is in between the pressure plate and the flywheel, and is held against the flywheel under pressure from the pressure plate. When the engine is running and the clutch is engaged i. As the clutch pedal is depressed, the throw out bearing is activated, which causes the pressure plate to stop applying pressure to the clutch disk.
This makes the clutch plate stop receiving power from the engine so that the gear can be shifted without damaging the transmission. When the clutch pedal is released, the throw out bearing is deactivated, and the clutch disk is again held against the flywheel, allowing it to start receiving power from the engine.
Manual transmissions are characterized by gear ratios that are selectable by locking selected gear pairs to the output shaft inside the transmission.
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Automatic transmissions that allow the driver to manually select the current gear are called manumatics. A manual-style transmission operated by computer is often called an automated transmission rather than an automatic , even though no distinction between the two terms need be made. Contemporary automobile manual transmissions typically use four to six forward gear ratios and one reverse gear, although consumer automobile manual transmissions have been built with as few as two and as many as seven gears.
Transmissions for heavy trucks and other heavy equipment usually have 8 to 25 gears so the transmission can offer both a wide range of gears and close gear ratios to keep the engine running in the power band.
Operating such transmissions often use the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gears. French inventors Louis-Rene Panhard and Emile Levassor are credited with the development of the first modern manual transmission.
They demonstrated their three-speed transmission in and the basic design is still the starting point for most contemporary manual transmissions. This type of transmission offered multiple gear ratios and, in most cases, reverse.
The gears were typically engaged by sliding them on their shafts hence the phrase shifting gears , which required careful timing and throttle manipulation when shifting, so the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh.
These transmissions are called sliding mesh transmissions or sometimes crash boxes , because of the difficulty in changing gears and the loud grinding sound that often accompanied.
In both types, a particular gear combination can only be engaged when the two parts to engage either gears or clutches are at the same speed. To shift to a higher gear, the transmission is put in neutral and the engine allowed to slow down until the transmission parts for the next gear are at a proper speed to engage. The vehicle also slows while in neutral and that slows other transmission parts, so the time in neutral depends on the grade, wind, and other such factors.
To shift to a lower gear, the transmission is put in neutral and the throttle is used to speed up the engine and thus the relevant transmission parts, to match speeds for engaging the next lower gear.
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For both upshifts and downshifts, the clutch is released engaged while in neutral. Some drivers use the clutch only for starting from a stop, and shifts are done without the clutch. Other drivers will depress disengage the clutch, shift to neutral, then engage the clutch momentarily to force transmission parts to match the engine speed, then depress the clutch again to shift to the next gear, a process called double clutching.
Double clutching is easier to get smooth, as speeds that are close but not quite matched need to speed up or slow down only transmission parts, whereas with the clutch engaged to the engine, mismatched speeds are fighting the rotational inertia and power of the engine. Even though automobile and light truck transmissions are now almost universally synchronized, transmissions for heavy trucks and machinery, motorcycles, and for dedicated racing are usually not.
Non-synchronized transmission designs are used for several reasons. The friction material, such as brass , in synchronizers is more prone to wear and breakage than gears, which are forged steel, and the simplicity of the mechanism improves reliability and reduces cost.
In addition, the process of shifting a non-synchromesh transmission is faster than that of shifting a synchromesh transmission. For racing of production-based transmissions, sometimes half the teeth on the dog clutches are removed to speed the shifting process, at the expense of greater wear. Heavy duty trucks often use unsynchronized transmissions, though military trucks usually have synchronized transmissions, allowing untrained personnel to operate them in emergencies.
In the United States, traffic safety rules refer to non-synchronous transmissions in classes of larger commercial motor vehicles.
In Europe, heavy duty trucks use synchronized gearboxes as standard. Similarly, most modern motorcycles use unsynchronized transmissions: their low gear inertias and higher strengths mean that forcing the gears to alter speed is not damaging, and the pedal operated selector on modern motorcycles, with no neutral position between gears except, commonly, 1st and 2nd , is not conducive to having the long shift time of a synchronized gearbox.
On bikes with a 1-N-2 Most modern manual-transmission vehicles are fitted with a synchronized gear box.
Transmission gears are always in mesh and rotating, but gears on one shaft can freely rotate or be locked to the shaft. The locking mechanism for a gear consists of a collar or dog collar on the shaft which is able to slide sideways so that teeth or dogs on its inner surface bridge two circular rings with teeth on their outer circumference: one attached to the gear, one to the shaft hub.
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When the rings are bridged by the collar, that particular gear is rotationally locked to the shaft and determines the output speed of the transmission. The gearshift lever manipulates the collars using a set of linkages , so arranged so that one collar may be permitted to lock only one gear at any one time; when "shifting gears", the locking collar from one gear is disengaged before that of another is engaged. One collar often serves for two gears; sliding in one direction selects one transmission speed, in the other direction selects another.
In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged the collar initially applies a force to a cone-shaped brass clutch attached to the gear, which brings the speeds to match prior to the collar locking into place.
The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings also called blocker rings or baulk rings.
The synchro ring rotates slightly due to the frictional torque from the cone clutch. In this position, the dog clutch is prevented from engaging. The brass clutch ring gradually causes parts to spin at the same speed. When they do spin the same speed, there is no more torque from the cone clutch and the dog clutch is allowed to fall into engagement. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed.
The modern cone system was developed by Porsche and introduced in the Porsche ; cone synchronisers were called Porsche-type for many years after this. In the early s, only the second-third shift was synchromesh in most vehicles, requiring only a single synchro and a simple linkage; drivers' manuals in vehicles suggested that if the driver needed to shift from second to first, it was best to come to a complete stop then shift into first and start up again.
With continuing sophistication of mechanical development, fully synchromesh transmissions with three speeds, then four, and then five, became universal by the s.
Many modern manual-transmission vehicles, especially sports cars, now offer six speeds. The Porsche offers a seven-speed manual transmission, with the seventh gear intended for cruising—the top speed being attained on sixth. Reverse gear is usually not synchromesh, as there is only one reverse gear in the normal automotive transmission and changing gears into reverse while moving is not required—and often highly undesirable, particularly at high forward speed.
Additionally, the usual method of providing reverse, with an idler gear sliding into place to bridge what would otherwise be two mismatched forward gears, is necessarily similar to the operation of a crash box.
Among the vehicles that have synchromesh in reverse are the — Ford Contour and Mercury Mystique, '00—'05 Chevrolet Cavalier, Mercedes 2. Like other transmissions, a manual transmission has several shafts with various gears and other components attached to them. Typically, a rear-wheel-drive transmission has three shafts: an input shaft, a countershaft and an output shaft.
The countershaft is sometimes called a layshaft. In a rear-wheel-drive transmission, the input and output shaft lie along the same line, and may in fact be combined into a single shaft within the transmission. This single shaft is called a mainshaft. The input and output ends of this combined shaft rotate independently, at different speeds, which is possible because one piece slides into a hollow bore in the other piece, where it is supported by a bearing.
Sometimes the term mainshaft refers to just the input shaft or just the output shaft, rather than the entire assembly. In many transmissions the input and output components of the mainshaft can be locked together to create a gear ratio, causing the power flow to bypass the countershaft.
The mainshaft then behaves like a single, solid shaft: a situation referred to as direct drive. Even in transmissions that do not feature direct drive, it's an advantage for the input and output to lie along the same line, because this reduces the amount of torsion that the transmission case has to bear.
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Under one possible design, the transmission's input shaft has just one pinion gear, which drives the countershaft. Along the countershaft are mounted gears of various sizes, which rotate when the input shaft rotates. These gears correspond to the forward speeds and reverse. Each of the forward gears on the countershaft is permanently meshed with a corresponding gear on the output shaft.
However, these driven gears are not rigidly attached to the output shaft: although the shaft runs through them, they spin independently of it, which is made possible by bearings in their hubs.
Reverse is typically implemented differently; see the section on Reverse. Most front-wheel-drive transmissions for transverse engine mounting are designed differently. For one thing, they have an integral final drive and differential. For another, they usually have only two shafts; input and countershaft, sometimes called input and output.
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The input shaft runs the whole length of the gearbox, and there is no separate input pinion. Front-wheel and rear-wheel-drive transmissions operate similarly. When the transmission is put in neutral and the clutch is disengaged, the input shaft, clutch disk and countershaft can continue to rotate under their own inertia. In this state, the engine, the input shaft and clutch, and the output shaft all rotate independently. Among many different types of clutches, a dog clutch provides non-slip coupling of two rotating members.
It is not suited to intentional slipping, in contrast with the foot-operated friction clutch of a manual-transmission vehicle. The gear selector does not engage or disengage the actual gear teeth which are permanently meshed. Rather, the action of the gear selector is to lock one of the freely spinning gears to the shaft that runs through its hub.
The shaft then spins together with that gear. The output shaft's speed relative to the countershaft is determined by the ratio of the two gears: the one permanently attached to the countershaft, and that gear's mate which is now locked to the output shaft.
Locking the output shaft with a gear is achieved by means of a dog clutch selector. The dog clutch is a sliding selector mechanism which is splined to the output shaft, meaning that its hub has teeth that fit into slots splines on the shaft, forcing that shaft to rotate with it.
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However, the splines allow the selector to move back and forth on the shaft, which happens when it is pushed by a selector fork that is linked to the gear lever. The fork does not rotate, so it is attached to a collar bearing on the selector. The selector is typically symmetric: it slides between two gears and has a synchromesh and teeth on each side in order to lock either gear to the shaft.