How do gearboxes

The gears are mounted on shafts, which are supported by and rotate via rolling element bearings. The gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed. Gearboxes are used in many applications including machine tools, industrial equipment, conveyors, and really any rotary motion power transmission application that requires changes to torque and speed requirements.

Most of the motion industry makes no differentiation between the terms gearhead and gearbox. But in a few contexts, the term gearbox specifically refers to housed gearing as described above while the more general term gearhead refers to assemblies otherwise open gearing that installs within some existing machine frame. The latter are targeted to compact or battery-powered mobile designs necessitating especially tight integration and omission of extra subcomponents.

They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The teeth on bevel gears can be straight , spiral or hypoid. Straight bevel gear teeth actually have the same problem as straight spur gear teeth -- as each tooth engages, it impacts the corresponding tooth all at once. Just as with spur gears, the solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical teeth: the contact starts at one end of the gear and progressively spreads across the whole tooth.

On straight and spiral bevel gears, the shafts must be perpendicular to each other, but they must also be in the same plane. If you were to extend the two shafts past the gears, they would intersect. The hypoid gear , on the other hand, can engage with the axes in different planes. This feature is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows the input pinion to be mounted lower than the axis of the ring gear.

Figure 7 shows the input pinion engaging the ring gear of the differential. Since the driveshaft of the car is connected to the input pinion, this also lowers the driveshaft.

This means that the driveshaft doesn't intrude into the passenger compartment of the car as much, making more room for people and cargo.

Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of , and even up to or greater. Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place.

This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor is not turning. One other very interesting usage of worm gears is in the Torsen differential , which is used on some high-performance cars and trucks. Rack and pinion gears are used to convert rotation into linear motion. A perfect example of this is the steering system on many cars. The steering wheel rotates a gear which engages the rack.

As the gear turns, it slides the rack either to the right or left, depending on which way you turn the wheel. Rack and pinion gears are also used in some scales to turn the dial that displays your weight.

Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset.

Let's take a look at a single planetary gearset. One of the planetary gearsets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gearset.

Also, locking any two of the three components together will lock up the whole device at a gear reduction. Notice that the first gear ratio listed above is a reduction -- the output speed is slower than the input speed. The second is an overdrive -- the output speed is faster than the input speed. The last is a reduction again, but the output direction is reversed. When the driver selects a gear, matching cone-shaped friction surfaces on the hub and the gear transmit drive, from the turning gear through the hub to the shaft, synchronising the speeds of the two shafts.

With further movement of the gear lever, the ring moves along the hub for a short distance, until its teeth mesh with bevelled dog teeth on the side of the gear, so that splined hub and gear are locked together. Modern designs also include a baulk ring, interposed between the friction surfaces.

The baulk ring also has dog teeth; it is made of softer metal and is a looser fit on the shaft than the hub. The baulk ring must be located precisely on the side of the hub, by means of lugs or 'fingers', before its teeth will line up with those on the ring. In the time it takes to locate itself, the speeds of the shafts have been synchronised, so that the driver cannot make any teeth clash, and the synchromesh is said to be 'unbeatable'.

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