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Manual Transmission Mechanism
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Manual Transmission Mechanism

Category: Mechanism
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Manual transmission, simply a gear box has been serving automobiles well from many decades. Even today it is the most popular transmission. Why transmission is required in an automobile? The power generated in the engine flows through the transmission before it reaches the drive wheels. The basic function of the transmission is to control the speed and torque available to the drive wheels at different driving conditions. For example, to up-climb a hill, you need more torque. By reducing the speed of the transmission, you will be able to achieve higher torque for the same power input. Conversely if the torque demand is low we can increase the transmission speed.

Manual transmission works on the simple concept of gear ratio. Transmission changes the gear ratio to make sure you get the optimum power for your engine to the wheels. The standard manual transmission is made up of an engine shaft (input shaft) which comes from the engine, output shaft which goes to the drive wheels, counter shaft which has all the gears. The input shaft turns the counter shaft, which turns all the gears on the output shaft. But all the gears move at different speeds. When the gears aren?t engaged they spin freely from the output shaft because they are not anchored to it.

Only one gear at a time spins the output shaft because of the hubs which are anchored to the output shaft. All the hubs have sleeves. The sleeves slide over the teeth on the gear and anchor them to the hub to drive the output shaft. There are also tiny little teeth. Matching up these tiny little teeth at the edge of our gear with the sleeves? tiny teeth is almost impossible. So between them are the synchronizers which cut the power of the counter shaft, let the wheels drive the output shaft for a change and when we push the synchronizer ring, it gets squeezed against our gear and locks it to the hub, so it is anchored to the output shaft. That?s why when we are shifting the gear, we get the huh-huh sound.

Some manual 5-speed transmissions have minor differences. The big gear which is in mesh with the counter shaft is the first gear. First gear is always gonna be the largest gear in the transmission producing more torque for the back wheel. It has a lot of fast turning force and making one big slow turning force. The slightly small gear next to first gear is second gear. Then goes third and the smallest one is fourth. On most four and five-speed transmissions, fourth gear is what?s called direct drive or one-to-one gear ratio. It means the input and out are turning at the same rate of speed.

The first gear transmission usually have the gear ratio of 3.83:1. This means the input should turn 3.38 times to see the output turn once. That?s nothing but torque. The second gear ratio is 2.062:1, third is 1.4:1 and as mentioned earlier, fourth gear ratio is 1:1.
Fifth gear hidden in the back and it is also called overdrive. First and third are called high gear ratios and fifth is called low gear ratio. In fifth gear one need to turn the shaft only 0.8 times to get the full turn on the output. That?s overdrive which gets much better fuel economy since we are getting power from the forward momentum of the vehicle which don?t need as much power going to engine or wheels. Some six and seven speed cars will have double overdrive for even better fuel economy at those high, higher speeds.
When reverse gear hits, it makes your drive shaft spin the same direction as the counter shaft. Drive shafts attach the wheels. When we shift gears, the wheels are gonna want to spin the counter shaft at a different speed than the engine is trying to spin it. We have to take that power off somewhere, or it will make a grinding sound. We do that using clutch. The clutch has a disc with high friction material on both sides. The engine is actually driving the flywheel and the input shaft to the transmission is mounted to the disc. When the disc is pressed firmly against the flywheel, it catches and can drive the shaft. The clutch is usually squeezed by the springs and attached to a pressure disc and anchored by the pressure plate which gets bolted to the flywheel. Most clutches use three springs. But in performance clutches we can have more and that makes the connection between the disc and the flywheel even stronger and more effective in high torque applications like racing. The diaphragm spring is connected to the pressure disc under the pressure plate. When you hit the clutch it pushes the centre of that diaphragm spring and that pulls up on the springs, which lifts the friction plate off the flywheel. When you let off the clutch panel and re-engage the friction disc, you are gonna bang right into action which we don?t want. We want ease into the movement. So attached to the friction plate there are other plates with coil springs in them. These springs are attached to a hub and that plate is the one that anchors the shaft and that goes to the transmission. Those springs absorb the jolt of re-engaging the friction plate to take a little stress off the other oarts of your drive train. One must try to get one and off the clutch quickly or it might burn out. That happens when the flywheel and the friction plate rub together too much.

Double clutch is clutching twich. Once when you shift into neutral tohit the gas and match the engine revs to the gear you want to go into. Then you hit the clutch a second time to shift into that gear. People always use double clutch when racing, driving big rigs and dunking.

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