Introduction
The previous normally applies only to the forward gears. The implementation of the reverse gear is usually different, implemented in the following way to reduce the cost of the transmission. Reverse is also a pair of gears: one gear on the countershaft and one on the output shaft. However, whereas all the forward gears are always meshed together, there is a gap between the reverse gears. Moreover, they are both attached to their shafts: neither one rotates freely about the shaft. When reverse is selected a small gear, called an idler gear or reverse idler, is slid between them. The idler has teeth which mesh with both gears, and thus it couples these gears together and reverses the direction of rotation without changing the gear ratio.
Construction And Working
In other words, when reverse gear is selected, it is in fact actual gear teeth that are being meshed, with no aid from a synchronization mechanism. For this reason, the output shaft must not be rotating when reverse is selected: the bike must be stopped. In order that reverse can be selected without grinding even if the input shaft is spinning inertially, there may be a mechanism to stop the input shaft from spinning. The driver brings the vehicle to a stop, and selects reverse. As that selection is made, some mechanism in the transmission stops the input shaft. Both gears are stopped and the idler can be inserted between them. There is a clear description of such a mechanism in the Manual, which refers to it as a "noise reduction system":
Whenever the clutch pedal is depressed to shift into reverse, the mainshaft continues to rotate because of its inertia. The resulting speed difference between mainshaft and reverse idler gear produces gear noise [grinding]. The reverse gear noise reduction system employs a cam plate which was added to the reverse shift holder. When shifting into reverse, the 5th/reverse shift piece, connected to the shift lever, rotates the cam plate. This causes the synchro set to stop the rotating mainshaft.
—A reverse gear implemented this way makes a loud whining sound, which is not normally heard in the forward gears. The teeth on the forward gears of most consumer automobiles are helically cut. When helical gears rotate, there is constant contact between gears, which results in quiet operation. In spite of all forward gears being always meshed, they do not make a sound that can be easily heard above the engine noise. By contrast, most reverse gears are spur gears, meaning that they have straight teeth, in order to allow for the sliding engagement of the idler, which is difficult with helical gears. The teeth of spur gears clatter together when the gears spin, generating a characteristic whine.
Attempting to select reverse while the vehicle is moving forward causes severe gear wear (except in transmissions with synchromesh on the reverse gear). However, most manual transmissions have a many newer six-speed manual transmissions have a collar under the shift knob which must be lifted to engage reverse to also help prevent this.
The spur gear design of reverse gear represents some compromises (less robust, unsynchronized engagement and loud noise) which are acceptable due to the relatively small amount of driving that takes place in reverse. The gearbox of the classic notable example of a gearbox with a helical reverse gear engaged in the same unsynchronized manner as the spur gears described above. Its design allows reverse to share cogs with first gear, and is exceptionally quiet, but results in difficult engagement and unreliable operation. However, many modern transmissions now include a reverse gear synchronizer and helical gearing.
The gearbox provides a selection of gearsfor different driving conditions: standing start, climbing a hill, or cruising on level surfaces. The lower the gear, the slower the road wheels turn in relation to the engine speed.
The constant-mesh gearbox
Construction Of Various Parts:
Gears
Introduction
The previous normally applies only to the forward gears. The implementation of the reverse gear is usually different, implemented in the following way to reduce the cost of the transmission. Reverse is also a pair of gears: one gear on the countershaft and one on the output shaft. However, whereas all the forward gears are always meshed together, there is a gap between the reverse gears. Moreover, they are both attached to their shafts: neither one rotates freely about the shaft. When reverse is selected a small gear, called an idler gear or reverse idler, is slid between them. The idler has teeth which mesh with both gears, and thus it couples these gears together and reverses the direction of rotation without changing the gear ratio.
Construction And Working
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