TRANSMISSION OPERATION

 

In general, the transmission refers to the entire system that transmits torque and power from the engine to the wheels. This system is therefore located between the engine and the drive wheels of the vehicle. In addition to its role of transmitting engine torque to the wheels, it has other crucial functions:

Distribute power between the two or four drive wheels according to their speed, and even when this differs from one wheel to the other;

Adjust the driving power according to the speed, accelerations and decelerations of the vehicle.

The transmission consists of the flywheel, the clutch, the gearbox, the differential or self-locking axle and the drive shafts.

THE FLYWHEEL AND THE CLUTCH

These two parts are closely linked. They connect the engine to the gearbox and thus allow the torque and engine power to be conveyed to the gearbox. Depending on the position of the clutch pedal, the flywheel and the clutch can be joined or separated. When they are joined, energy flows from the engine to the gearbox. On the contrary, when they are disjoint, there is no transmission of engine torque. The driver can thus shift into gear or stop the vehicle to go into neutral. 

THE GEARBOX

Its role is to coordinate between the rotational speed of the engine, transmitted via the flywheel and the clutch, and the rotational speed of the wheels. The gearbox is therefore the element which makes it possible to adjust the engine torque according to the driving conditions. For example, when starting or climbing a steep grade, your vehicle will need a lot of torque. The gearbox delivers this torque to the drive wheels.

DRIVESHAFTS

The transmission shafts are directly attached to the drive wheels, which they drive when they are rotated by the self-locking axle. By this rotational movement transmitted to them, the drive wheels then drive the vehicle.

THE DIFFERENT TYPES OF TRANSMISSION

There are 3 types of transmission: traction, rear-wheel drive and all-wheel drive.

TRACTION: FRONT TRANSMISSION

Traction is the most common type of transmission used on today's automobiles. The two front wheels are driven and each is driven by a half-shaft.

There are two possible configurations of the front transmission: with a longitudinal (perpendicular to the motor axis) or transverse (parallel to the motor axis) powertrain. The latter is more recent and much more compact. In addition, it has the advantage of offering better road holding.

The traction system offers several advantages:

The vehicle has very good traction in all conditions, including on snow or slippery surfaces. It therefore offers better safety in winter.

All components involved in the transmission are located in one place, which allows the system to take up little space. This space saving benefits the passenger compartment of the vehicle.

This is the system with the best transmission efficiency. It therefore consumes less fuel.

The main disadvantage of traction is the risk of the two front wheels slipping when starting or accelerating at low gears. This risk increases in winter, on snow or ice.

THE PROPULSION: REAR TRANSMISSION

In this configuration, the two rear wheels are driven. The front wheels still steer the vehicle, but the rear wheels are there to propel it. This type of transmission is found a lot on vans or heavier premium vehicles.

Three configurations are possible in a rear drivetrain, and each has advantages and disadvantages.

REAR ENGINE

On some rear-wheel-drive vehicles, the engine and transmission are located at the extreme rear of the vehicle, behind the axle of the wheels. This so-called “cantilever” configuration is quite common at Porsche. It has several advantages:

Traction is reinforced at the rear, which allows better performance on start-up and during acceleration.

The entire powertrain is concentrated at the rear, which saves space and gives the vehicle better roominess.

This configuration facilitates cornering and makes driving pleasant on winding roads.

But the cantilever motor also has disadvantages:

Since the rear axle is heavier, it will have a greater tendency to drag the vehicle. On a slippery road or in the snow, the risks of spinning are therefore higher.

As the front of the vehicle is lighter, it is more sensitive to side winds or low steering inputs. Driving in a straight line at high speed is therefore more difficult to maintain.