how does a gear box work?

Answer 1

In mechanics, a transmission, (also called a "Standard" or "Manual" transmission) or gearbox is the system of gears and/or the hydraulic system (called variously "Hydrodynamic" or "Fluid" or "Automatic" transmission) that transmits mechanical power from a prime mover— such as an engine or electric motor—to some form of useful output device, normally rotary in form, and generally at a reduced rate of angular speed but at a higher motive torque (power).

Generally, transmissions will provide a significant speed-power conversion known as gear reduction (in speed) to a higher torque (rotational force or power). In motor vehicle transportation, a vehicle transmission may provide many different speed-power ratios known colloquially as 'gears' or 'speeds', and possibly several variant speeds in reverse direction as well— Tractors and large trucks especially may have a dozen or more forward 'gears' which vary from a crawling speed at high torque to high speed at low torque where the only torque needed with a load coasting along at a given speed are that small additional energy (force) needed to overcome ongoing friction and other road losses such as climbing a grade. When the torque needed to surmount a grade is insufficient at a higher rotational speed, the gearbox is shifted into a lower gear to provide more power, as was needed when initially accelerating said vehicle to the desired road speed. Gearing has much in common with the mechanics and mechanical factors present in pulley systems. One trades distance (numbers o rotations) for increased force.

Early transmissions (gearboxes) included right-angle drives and other gearing in windmills, horse-powered devices, and steam engines, mainly in support of pumping, milling, and hoisting. Most modern gearboxes will either reduce an unsuitable high speed and low torque of the prime mover output shaft to a more useable lower speed with higher torque, or do the opposite and provide a mechanical advantage (i.e increase in torque) to allow higher forces to be generated. However, some of the simplest gearboxes merely change the physical direction in which power is transmitted.

Many systems, such as typical automobile transmissions, include the ability to select one of several different gear ratios. In this case, most of the gear ratios (simply called "gears") are used to slow down the output speed of the engine and increase torque. However, the highest gear(s) may be an "overdrive" type that increases the output speed.


[edit] Manual transmission
Main article: manual transmission
Manual transmissions come in two basic types: a simple unsynchronized system where gears are spinning freely and must be synchronized by the operator to avoid noisy and damaging "gear clash", and synchronized systems that will automatically "mesh" while changing gears. The former type is only used on some rally cars and heavy-duty trucks nowadays.

Manual transmissions dominate the car market outside of North America. They are cheaper, lighter, usually give better performance, and fuel efficiency (although the latest sophisticated automatic transmissions may yield results slightly closer to the ones yielded by manual transmissions), and it is customary for new drivers to learn, and be tested, on a car with a manual gearchange. In Japan, Germany, the UK, Ireland, Sweden and France at least, a test pass using an automatic car does not entitle the driver to use a manual car on the public road unless a second manual test is taken. In most of the other European nations like Italy and the Netherlands, obtaining a driver's license is only possible by passing a driver's test driving a car with manual transmission.[citation needed] Manual transmissions are much more common than automatic transmissions in Asia & Europe.


[edit] Automatic transmission
Main article: automatic transmission
Most modern North American cars have an automatic transmission that will select an appropriate gear ratio without any operator intervention. They primarily use hydraulics to select gears, depending on pressure exerted by fluid within the transmission assembly. Rather than using a clutch to engage the transmission, a torque converter is put in between the engine and transmission. It is possible for the driver to control the number of gears in use or select reverse, though precise control of which gear is in use is usually not possible.

Automatic transmissions are easy to use. In the past, automatic transmissions of this type have had a number of problems; they were complex and expensive, sometimes had reliability problems (which sometimes caused more expenses in repair), have often been less fuel-efficient than their manual counterparts and their shift time was slower than a manual making them uncompetitive for racing. With the advancement of modern automatic transmissions this has changed. With computer technology, considerable effort has been put into designing gearboxes based on the simpler manual systems that use electronically-controlled actuators to shift gears and manipulate the clutch, resolving many of the drawbacks of a hydraulic automatic transmission.

Automatic transmissions have always been extremely popular in the United States, where perhaps 19 of 20 new cars are sold with them (many vehicles are not available with manual gearboxes anymore). In Europe automatic transmissions are gaining popularity as well.

Attempts to improve the fuel efficiency of automatic transmissions include the use of torque converters which lock-up beyond a certain speed eliminating power loss, and overdrive gears which automatically actuate above certain speeds; in older transmissions both technologies could sometimes become intrusive, when conditions are such that they repeatedly cut in and out as speed and such load factors as grade or wind vary slightly. Current computerized transmissions possess very complex programming to both maximize fuel efficiency and eliminate any intrusiveness.

For certain applications, the slippage inherent in automatic transmissions can be advantageous; for instance, in drag racing, the automatic transmission allows the car to be stopped with the engine at a high rpm (the "stall speed") to allow for a very quick launch when the brakes are released; in fact, a common modification is to increase the stall speed of the transmission. This is even more advantageous for turbocharged engines, where the turbocharger needs to be kept spinning at high rpm by a large flow of exhaust in order to keep the boost pressure up and eliminate the turbo lag that occurs when the engine is idling and the throttle is suddenly opened.


[edit] Semi-automatic transmission
Main article: semi-automatic transmission
The creation of computer control also allowed for a sort of half-breed transmission where the car handles manipulation of the clutch automatically, but the driver can still select the gear manually if desired. This is sometimes called "clutchless manual". Many of these transmissions allow the driver to give full control to the computer.

There are some specific types of this transmission, including Tiptronic, Geartronic, and Direct-Shift Gearbox.

There are also sequential transmissions which use the rotation of a drum to switch gears

Answer 2

It wouldn't be unrealistic for the clutch to need replacing at this mileage, this would be the most common cause of your symptoms, if a drive shaft goes you wont move at all, equally if the gearbox goes you wont move or you will lose specific gears. High revs with a low speed indicate imminent clutch failure, so avoid using the car until this is resolves as a badly slipping clutch can get very hot and even shatter doing damage to other components such as the bell housing. Good news is it doesn't sound like the gearbox, bad news is a clutch is a servicable item so don't expect one under warranty. Hope this helps!

Answer 3

a gear box holds the gears together

Answer 4

Here are a few links to shed some light on what a transmission does and how it works.

Good question.

Answer 5

A gearbox changes the force/direction of movement.

Answer 6

it changes the speed of rotation of the shaft or changes the direction; or changes the axis on which the shaft rotates. or all of the above