What Is An Axle? Types Of Axles - SKengineers

 

WHAT IS AN AXLE?

An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type axle is referred to as a spindle.

Types Of Axle -

Axles come in three standard types -

Rear axle -

This axle is responsible for the power supply to the drive wheels. It comes in two halves, called half-waves, which are connected by the differential. In most cases, the rear axles are under tension, meaning that they rotate with the vehicle’s wheels.

Front axle -

This axle is located in the front of the vehicle and is responsible for assisting in steering and processing bumps on uneven road surfaces. They consist of four main parts: the beam, the swivel pin, the tie rod and the stub axle. The front axles must be as robust as possible. That is why they are usually made of carbon steel or nickel steel.

Stub Axle -

Stub axles are attached to the vehicle’s front wheels, with kingpins connecting these axles to the front axle.

Types Of Rear Axle -

Not all rear axles are the same, as the support and mounting methods there are three types of rear axles -

Semi-floating axle -

This rear axle connects the wheel to the flange on the outside of the axle shaft and holds it securely. One bearing supports the axle shaft and the other is in the axle housing. Since it has two bearings, a semi-floating axle must be larger than the other options to produce the same torque. Semi-floating axles are used for automobiles, SUVs, and medium-sized trucks, Pickups with half a ton and low power.

Full-floating axle -

As the name suggests, thanks to two bearings, this type of axle effectively floats in place and maintains its position. It only transmits the drive torque. Fully floating axles are best for larger vehicles, e.g. heavy trucks. Some medium-sized trucks with larger towing capacity or those with all-wheel drive can also benefit from fully floating axles.

Three-quarter floating axis -

It is more complex than the semi-floating axle and also more reliable. It helps in maintain wheel alignment and handles side thrust and driving torque.

Live Axles -

Live axles are used to transmit power throughout the component. They are responsible for driving the wheels that they are attached to. Despite being designed as a moving part, some live axles may also be used to support the weight of the vehicle. When examining a front wheel drivetrain, live axles are responsible for steering the vehicle. Depending on the vehicle, some may utilize a live rear axle that is also responsible for steering.

The most common type of passenger vehicles contain live axles only in the rear of the assembly, while in a four-wheel drive vehicle, both the front and rear axles are live. Six-wheel drive vehicles contain three axles which are all live axles.

Dead Axles -

Dead Axles are used solely as a support for part of the vehicle while providing a mounting for the vehicle's wheel assembly. Typically, dead axles are found in the front area of commercial trucks and truck-tractors. Almost all common passenger vehicles lack a front axle, as they utilize independent front-wheel suspensions. It is uncommon for a commercial vehicle to rely on a dead axle.

A dead axle is technically not included in the parts that make up a drivetrain and does not have a differential attached to it, as it is a free rotating axle that is only utilized when there is a large amount of weight placed on it. They mount wheels, bearings and even gears in some drive axle setups.

Dead axles remain in sync with the drivetrain itself and are crucial for commercial vehicles that utilize them. Despite not transferring power like live axles do, their importance lies with their responsibility to carry the wheel itself.

 Axle Housing -

Axle housing cases are manufactured in either a one-piece or split construction. An axle housing with a split design is commonly referred to as "banjo housing" by many, as they bear resemblance to a banjo instrument. Both the front and rear openings of the axle housing are provided in the center housing. The differential carrier closes the front opening, while a spherical cover plate covers the rear opening.

It is responsible for carrying the weight of a vehicle and is typically an extremely heavy component. Heavy-duty trucks and truck-trailers possess axle housing that is heavier than the housing found in common commercial vehicles, as they are designed to transport heavy weight.

The axle housing in light-duty trucks may be a combination of cast iron and cast steel tube. The differential and final drive cases are generally a cast and machined unit, while the axle housing itself is welded or extruded steel tubing.

There are several components that may be welded into the axle housing itself, such as: mounting flanges, braking plates, spring mounting plates and any accessory units that a mechanic or driver may want to install into the housing. These components are typically replacement or upgrade seals or plates that that are installed by a third-party.

Additionally, vents or valves are installed on top of the housing to prevent pressure from building up, which develops from heat within the housing. Heat is produced from normal operation of the vehicle, and these vents or valves release the heat. If the pressure is not released from the housing, it may force the axle lubricant to move past the rear wheel oil seals and damage the vehicle's brake linings. Despite allowing air to pass through the housing, these vents prevent debris and dirt from entering.

Types Of Front Axle -

There are vehicles have two main types of front axle -

Dead Front Axle -

These axles stay in place and don’t rotate with the wheels. Most dead front axles and differentials have housings that prevent them from coming into contact with water or dirt.

Live Front Axle -

Unlike dead front axles, live front axles deliver driving power from the gearbox to the front wheels.

Types Of Stub Axle -

As The Engineers Post explains, there are four types of stub axle -

Elliot -

This type uses a kingpin, a yoke, and a cotter to connect to the front axle.

Reverse Elliot -

This type has the opposite arrangement of a standard Elliot stub axle.

Lamoine -

This stub axle type has an L-shaped spindle instead of a yoke-type hinge.

Reverse Lamoine -

It has the opposite layout of a standard Lamoine stub axle.

Terminology -

On cars and trucks, several senses of the word axle occur in casual usage, referring to the shaft itself, its housing, or simply any transverse pair of wheels. Strictly speaking, a shaft which rotates with the wheel, being either bolted or splined in fixed relation to it, is called an axle or axle shaft. However, in looser usage, an entire assembly including the surrounding axle housing (typically a casting) is also called an axle.

An even broader (somewhat figurative) sense of the word refers to every pair of parallel wheels on opposite sides of a vehicle, regardless of their mechanical connection to each other and to the vehicle frame or body. Thus, transverse pairs of wheels in an independent suspension may be called an axle in some contexts. This very loose definition of "axle" is often used in assessing toll roads or vehicle taxes, and is taken as a rough proxy for the overall weight-bearing capacity of a vehicle, and its potential for causing wear or damage to roadway surfaces.

Structural features and design -

A straight axle is a single rigid shaft connecting a wheel on the left side of the vehicle to a wheel on the right side. The axis of rotation fixed by the axle is common to both wheels. Such a design can keep the wheel positions steady under heavy stress, and can therefore support heavy loads. Straight axles are used on trains (that is, locomotives and railway wagons), for the rear axles of commercial trucks, and on heavy duty off-road vehicles. The axle can optionally be protected and further reinforced by enclosing the length of the axle in a housing.

In split-axle designs, the wheel on each side is attached to a separate shaft. Modern passenger cars have split drive axles. In some designs, this allows independent suspension of the left and right wheels, and therefore a smoother ride. Even when the suspension is not independent, split axles permit the use of a differential, allowing the left and right drive wheels to be driven at different speeds as the automobile turns, improving traction and extending tire life.

 A tandem axle is a group of two or more axles situated close together. Truck designs use such a configuration to provide a greater weight capacity than a single axle. Semi trailers usually have a tandem axle at the rear.

Axles are typically made from SAE grade 41xx steel or SAE grade 10xx steel. SAE grade 41xx steel is commonly known as "chrome-molybdenum steel" (or "chrome-moly") while SAE grade 10xx steel is known as "carbon steel". The primary differences between the two are that chrome-moly steel is significantly more resistant to bending or breaking, and is very difficult to weld with tools normally found outside a professional welding shop.

How Many Axles Does A Car Have?

The number of axles in a car depends on the type of vehicle. In most cases, cars have two axles to turn the wheels. Larger vehicles that carry more passengers and have more wheels can have more axles.

It’s easy to identify the number of axles your car or other vehicle has. Just look at your car from the side and then count the pairs of tires. Most cars have a total of four tires or two sets of tires, one in the front and one in the rear. Two sets of tires correspond to two axles.