Gearbox work

  

(image from: http://hyperlogos.org/files/images/78_large.jpg )

1. What type of gears are used for reverse in a manual gearbox?

the type of gear used for reveres is a normal cross cut toothed gear, this allows the reverse idler gear to be positioned easily with the reverse gears on the output shaft and layshaft without the teeth grinding and stripping.Although the teeth are cross cut, there still is grinding when the three gears meet to mesh as the output shaft will still be spinning, when the reverse idler is pushed in to mesh with the output shaft, there is load as the layshaft is suddenly forced to spin the opposite direction.

2. What type of gears are used for all forward gears in a manual gear box?

With the forward driving gears, helical type are used, this means that the gears are diagonally cut, so that the gear has more surface area to mesh with othee gears other than a cross cut gear. This allows the gears to mesh easily without any whining noise like what the reverse gears make.

3. What is the purpose of a synchromesh unit?

A baulk-ring type of synchromesh unit is commonly used to synchronize the speeds of two gears before engagement. When the synchronizer is assembled, the hub is splined to the main shaft, and the engagement sleeve is splinted to the hub. The syncro ring, with recesses to accommodate the ends of the inserts, is located in each end of the hub, and a conical inner surface faces a matching steel cone on the gear.

(info from: http://moodle.student.cnwl.ac.uk/moodledata_shared/cdx%20etextbook/dswmedia/trans/clutchMan/gearLayOp/baulkring.html )

4. what type of bearings do we find in gearboxes

For the first gear, a caged roller bearing is used, as this gear is a high tension taking gear, the rest of the gears use grooves cut into the output shaft and run on a film of oil. This is because they don’t need to take as much load as 1st gear and are designed to spin at higher rpm’s than 1st gear.

5. Give and explanation of a gear ratio

If there are two gears both the same size with equal amount of teeth meshing, the gearing ratio will be 1:1 (1 to1) if however there are two gears at different sizes, (e.g, the driver gear small than the driven gear) than the ratio will be different. the way to work out ratios is simple as seen bellow:

How to get a gear ratio:

Count the amount of teeth in each gear and record weather it is the driver gear or driven gear like so (note, when you have the fraction of teeth from the input, use that as the start of each equation and multiply it by the other fractions you get from the gears*:

Then go to another set of meshed gears on the layshaft and out put shaft and count their teeth and record whether it is the driver or driven gear as stated above: 

Then multiply the two fractions as seen in the fist picture above: