Manual Transmission

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Manual Transmission

            The first transmission invented was the manual transmission system. A manual transmission, also known as a manual gearbox or standard transmission (informally, a "manual", "stick shift", "straight shift", or "straight drive") is a type of transmission used in motor vehicle applications. It generally uses a driver-operated clutch, typically operated by a pedal or lever, for regulating torque transfer from the internal combustion engine to the transmission, and a gear-shift, either operated by hand (as in a car) or by foot (as on a motorcycle).

             In a manual transmission, the driver needs to disengage the clutch to disconnect the power from the engine first, select the target gear, and engage the clutch again to perform the gear change.


Components of Manual Transmission

The diagram below shows a very simple two-speed transmission in neutral:

            The green shaft comes from the engine through the clutch. The green shaft and green gear are connected as a single unit. (The clutch is a device that lets you connect and disconnect the engine and the transmission. When you push in the clutch pedal, the engine and the transmission are disconnected so the engine can run even if the car is standing still. When you release the clutch pedal, the engine and the green shaft are directly connected to one another. The green shaft and gear turn at the same rpm as the engine.)

            The red shaft and gears are called the layshaft. These are also connected as a single piece, so all of the gears on the layshaft and the layshaft itself spin as one unit. The green shaft and the red shaft are directly connected through their meshed gears so that if the green shaft is spinning, so is the red shaft. In this way, the layshaft receives its power directly from the engine whenever the clutch is engaged.

            The yellow shaft is a splined shaft that connects directly to the drive shaft through the differential to the drive wheels of the car. If the wheels are spinning, the yellow shaft is spinning.

 

            The blue gears ride on bearings, so they spin on the yellow shaft. If the engine is off but the car is coasting, the yellow shaft can turn inside the blue gears while the blue gears and the layshaft are motionless.

            The purpose of the collar is to connect one of the two blue gears to the yellow drive shaft. The collar is connected, through the splines, directly to the yellow shaft and spins with the yellow shaft. However, the collar can slide left or right along the yellow shaft to engage either of the blue gears. Teeth on the collar called dog teeth, fit into holes on the sides of the blue gears to engage them.

Working of Manual Transmission

            When the gear selector fork is shifted into first gear, the collar engages the blue gear on the right:


            In this picture, the green shaft from the engine turns the layshaft, which turns the blue gear on the right. This gear transmits its energy through the collar to drive the yellow drive shaft. Meanwhile, the blue gear on the left is turning, but it is freewheeling on its bearing so it has no effect on the yellow shaft.

Five-Speed Manual Transmission:

            The five-speed manual transmission is fairly standard on cars today. Internally, it looks something like this:


            There are three forks controlled by three rods that are engaged by the shift lever.  The shift lever has a rotation point in the middle. When you push the knob forward to engage first gear, you are actually pulling the rod and fork for first gear back.

            When you move the shifter left and right you are engaging different forks (and therefore different collars). Moving the knob forward and backward moves the collar to engage one of the gears.

Idler Gear or Reverse Gear:

            The idler gear is a small gear (purple) and is slid between red and blue gear. At all times, the blue reverse gear in this diagram is turning in a direction opposite to all of the other blue gears. The idler has teeth that mesh with both gears, and thus it couples these gears together and reverses the direction of rotation without changing the gear ratio.

 


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