Rear Wheel
Rear Wheel
Axle: Keeping the Wheels on the Ground
Axles are the spine of a car’s drive train. They hold the wheels together and, since wheels prop the car up from the ground, bear the full weight of the vehicle. Early axle designs use a single steel shaft to link up the left and right wheels. In this setup, the axle maintains the position of the two wheels relative to one another. As torque flows to the car’s drive train and turns the wheels, the axle keeps tight rein of both wheels and keeps the car from swaggering. A single shaft axle is known to resist a considerable amount of car chassis stress and has high weight capacity. It is commonly used on heavy duty vehicles like trucks and wagons that are usually used to load heavy cargo.
A single shaft axle, however, has its own limitations. Linking up the left and right wheels means that both are going to share one suspension assembly and drive train. When two wheels have a same drive train, both of them turn at the same rate. At cruise speed the limitation of a single shaft axle is tolerable. But, when cornering, the left and right wheels follow different arcs, the one inside the curve smaller than the other. In the event that a car corners and both wheels are rotating at the same rate, the car’s traction on the ground is compromised.
As luxury cars and street sedans have shown, there is more to axle design than its structural features. Marquee brands like the Mercedes-Benz have wheels connected to the car chassis with a split axle. Split axle is basically a reinforced half shaft, usually via enclosing the shaft in a billet, or combining two axles, called tandem axles. Because wheels are supported individually, wheel rotation is determined individually for each of them. This will then result to improved traction when cornering. As an offshoot to the non-inclusion of the single shaft axle in the Mercedes-Benz drive train, the wheels are equipped with an individual suspension setting. Because roads are hardly uniform, wheels with the suspension setting lumped up usually means enduring a bumpy ride. With an individual suspension, each side of the Mercedes-Benz negotiates bumps independently from the rest of the drive train.
Aside from traction and suspension improvement, there are also specialized Mercedes axles that boasts of a capacity to enhance other parts of the drive train like the brake and steering assemblies. Drive axles, commonly known as transaxles, serve as front axle and enhances the Mercedes-Benz steering. Composed of two half axles, transaxles are split axles fitted with differential and universal joints. One of the joints in each of the half axle is a flexible coupling called constant velocity joint, which provides a pivot point for the axle when the car corners. In a rear-wheel drive Mercedes-Benz, a driveshaft to facilitate torque transfer from the engine to the wheels can also be fitted.
As an addition to its use on transmission and steering, the axle can also be incorporated on a Mercedes-Benz brake system that uses engine braking, although this supplemental braking is only needed and used on big vehicles such as sports utility vehicles and limousines. Engine braking utilizes the compression stroke in the combustion process to retard engine speed. When the flywheel compresses the air and fuel mixture in the cylinder heads, one byproduct is heat. This heat, when combustion takes place, is ejected out of the engine and exhausted from the vehicle. When engine slows down, the axle can flow less torque, meaning less rotational force to run the wheels.
About the Author
Dwyane Thomas is a part time cook and full-time auto-enthusiast. This 31-year old Civil and Environmental graduate is a consultant at one of the engineering firms in Pennsylvania.
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The Four Wheel Drive System
I'm sure most of you reading this have heard of the term four-wheel drive, or 4x4, but I will bet some of you don't know what it does, how it works, and why it might benefit you. For a vehicle to be considered to be a four-wheel drive, the engine must be capable of distributing torque to all four wheels. Torque is the power that moves your vehicle. In non four-wheel drive cars and trucks, torque is distributed to either the front or back wheels, while the remaining two wheels are free rolling. In a 4x4, you can either manually engage all four wheels, or it is done for you automatically. Most four-wheel drive owners believe it's a 50/50 distribution of torque, but in most cars, it's more like 65/35.
There are several reasons why one would need a four-wheel drive. All of them have to do with friction. While torque powers the wheels, friction between the tires and the driving surface is what gives you traction, and lets your vehicle move forward. If a vehicle is moving on a muddy surface, there is a lower amount of friction, which causes the tires of a two-wheel drive to spin out, while the vehicle stays in one spot. With a 4x4, the extra torque to all four wheels, instead of just 2 wheels for standard vehicles greatly increases the traction available to the vehicle.
This then provides better friction for the vehicle, ti enable forwward movement. This is also true for wet, snowy, and icy surfaces.
There are different types of four-wheel drive systems, some that require more driver input than others. In a manual four-wheel drive, one has to go outside of the vehicle and lock the hubs. This is a circular type knob located on the front wheels. Once this is done, the vehicle must be put in neutral, and then the control for the four-wheel drive is implemented. IN a "shift on the fly' system, you can engage the four wheel drive while the vehicle is moving, as the hubs are automatically locked. In an automatic four-wheel drive system, the four-wheel drive only works when it is needed, and it requires no driver input. In an all wheel drive system, no driver input is required, and torque is constantly given to all four wheels.
The Audi Quattro is an amazing all wheel drive car that differs from most other vehicles. It has a 40/60 torque distribution, with the bulk of the torque geared towards the rear wheels. This distribution allows the torque from the engine to transfer to the road more efficiently, giving the driver a greater sense of control. It also adjusts to road conditions, and transfers power to the wheels that have the most traction! For instance, if a rear wheel is spinning torque to that wheel is reduced and re-distributed to the other wheels! This allows the driver to have a safer and more confident driving experience.
About the Author
Ed Terran is the pen name for the editor of a
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