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Manual transmissions Engines 101

By Rafael Pérez Vincente

September 4, 2022


[Photo Credit: Universal Technical Institute]

The principle behind a vehicle's transmission is often seen as its ability to attain greater torque (or speed) for the same amount of energy. This phenomenon is attributed to gear ratios and their capacity to effectively differentiate in size to serve different purposes. In 1894, the first chain drive transmission was invented by Emile Levassor and Louis-Rene Panhard. However, this invention was still a primitive design compared to what transmissions are nowadays.

We can imagine transmissions as being a whole set of gears with different ratios that rotate the wheels of the vehicle at different speeds. The gears are loosely placed over the output shaft, which is where the rotational motion goes to the wheels. The engine provides this motion via an input shaft which is connected to a crankshaft that comes out of the engine itself. Additionally, a countershaft is geared directly into the input shaft, which rotates the gears in the output shaft. This countershaft acts as the connector between the input and output shafts, and it delivers rotation to all gears.

In the output shaft, a few more components are needed to make the transmission work. Initially, as the input shaft and the countershaft are rotating the gears from the output shaft at different speeds, a synchronizer ring is needed to match the speed from the output shaft with the speed from the input shaft. Once this is done and the synchronizer and the gear that we´re aiming for are rotating at the same speed, a shift sleeve connected to the output shaft is going to slide into the gear, making it the active gear. Whilst this gear change is happening, the clutch needs to be pressed in order to disengage the engine from the input shaft and make the speed from the gear and the synchronizer the same.

From 1st to 4th gear, their shift sleeves and synchronizers are connected to the output shaft. Connected to the shift sleeves are the shift forks; these are responsible for pushing and moving the sleeve and the synchronizer from one gear to the other via a shift shaft moved by the gearbox.

Some transmissions have extra gears in order to attain more speed: 5th, 6th, or even the 7th gear. These are usually used for racing and are great for vehicles with a great demand for speed and low demand for torque. To understand this, let us talk about the gear ratios in a commercial car. In the first gear, 3.8 rotations of the input shaft are needed to rotate the output shaft one revolution, in the second 2.06, in the third 1.4, in the fourth 1, and in the fifth 0.8. This power delivery system gives the vehicle the ability to have a better fuel economy, better performance, and greater control. The fourth gear is usually known as direct drive, as its ratio is 1:1, and the fifth is called overdrive.


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(Image from Universal Technical institute)

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