Posted: August 15th, 2022

Differential and Rear Drive Axle Technology

Differential and Rear Drive Axle Technology
A drive axle is an integral assembly containing mechanical components used to deliver power from the vehicle’s engine to the wheels (Tata). The driveshaft connects the engine and wheels and has a differential axle technology installed to aid effective wheel spin and turn. A differential has mechanisms installed to allow the left and right wheel to turn differently at different speeds while transferring power to both wheels. The power generated inside the engine is transferred through a pinion gear which turns a ring gear. The ring gear then is attached to a spider gear that performs two types of rotations, one along with the ring gear, while it can also rotate within its axis. The spider gear then meshes to two side gears connected to the left and right wheels.
When vehicles move on a straight path, the spider gear only moves along with the ring gear but not within its axis. However, when the vehicle is turning left or right, the spider gear performs both sets of rotation. The spider gear spins in the direction of the turn to allow the wheel covering a longer distance to move faster through a higher spin ratio. Loaded vehicles can have more than one spider gear, which moves in different directions to ensure consistent wheel spin. Differential axle technology also provides speed reduction at pinion gear assembly. This is done when the vehicle is moving at a higher gear ration and results in torque multiplication. A mechanism also referred to as gear reduction. The reduction is calculated by dividing the number of teeth on the large gear by the number of teeth on the small gear (Granby). The other function of a differential is turning the power flow by 90 degrees. Since engine rpm is higher than wheel rpm, the differential acts as a speed reducing device.
Most modern cars are manufactured with a front-wheel-drive system; hence the differential is located at the front tires. However, cars manufactured before 1980 used rear-wheel drive. Currently, rear-wheel-drive vehicles are usually those that need more horsepower due to higher loads, such as big trucks or law enforcement pursuit vehicles. Rear axles are usually induction hardened for increased strength. Rear-axle designs include semi-floating, three-quarter floating, and full floating. Semi-floating axles are installed in passenger vehicles where the shaft and the housing support the vehicle’s weight. On the other hand, the three-quarter floating axle is used in light trucks where the vehicle’s weight is transferred to the axle casing. Finally, the full-floating axle is used in heavy-duty trucks where the axle housings support the vehicle’s weight.
One major drawback of the differential and rear-drive technology is the inability of the differential to balance power flow when the wheels are on surfaces with different traction. The differential sends more power to the wheel experiencing difficulty. As a result, the wheel on a good surface cannot move as effectively to propel the car into better terrain. This is usually noticeable when driving a two-wheel-drive through mud or smooth sand. If the driver fails to balance the car well, the vehicle ends up stuck on one side. To combat this problem, engineers have come up with limited-slip differentials to aid two-wheel drive vehicles. Limited slip differentials provide more driving force to the wheel with traction when one wheel begins to slip. However, four-wheel-drive vehicles are still more reliable when it comes to navigating rugged and tough terrains due to both front and rear differentials.
References
Granby, John. Sciencing.Com, 2017, https://sciencing.com/calculate-reduction-ratio-6602288.html.
Tata, Robert P. Cedengineering.Com, 2012, https://www.cedengineering.com/userfiles/Passenger%20Car%20Drive%20Axle%20Technology.pdf.

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