What is a half axle (driveshaft)
A half axle (or driveshaft) is an element of the vehicle’s chassis that provides the connection between the drive wheel set and the differential. Half axles are mounted on each of the drive wheels.
Types of driveshafts
The drive shaft, depending on its type, can be partially or completely independent of the bending moments acting on it.
The design of the chassis of heavy-duty automotive equipment includes half-axles of the unloaded type. Their structure is represented by a separate part, which is located inside the axle, but the wheel hub with bearings rests on its beam if you need such a bearing unit you can look at it here. The good thing about this design is that the driveshaft is used to transmit torque, but the bearings take on the effects of other forces.
A half-loaded driveshaft is installed on most light-duty and light-duty vehicles. A feature of this design is that its bearing is located between the driveshaft and its housing, with the half axle secured to the wheel hub. The disadvantage of this design is the frequent occurrence of bending forces, negatively affecting the drive shafts in both planes.
In vehicles with front-wheel drive, drive shafts of a different design are used to transmit torque to the wheels, which includes the CV joints and the axle located between them.
Why do half axles fail?
During the operation of a vehicle, all of its running gear elements are constantly under high stress. Drive shafts are no exception to this.
The reasons for the serious stresses that accelerate the wear and tear of the half axles are:
Exposure to constant gravity on the vehicle, resulting in bending moments that adversely affect the body, frame and suspension parts of the auto.
Forces that result from acceleration, movement and braking of the vehicle.
Various loads on the car body, caused by the constant action of the side wind.
The drive shafts are subjected to additional high loads during driving on roads with poor surfaces, which also greatly accelerates their wear.
Failure of a half axle causes the loss of controllability of the vehicle, which is especially unsafe when driving at high speeds. Therefore, constant monitoring of the condition of the driveshafts and proper care of them are extremely important procedures that should not be neglected.
When inspecting the drive axle, special attention should be paid to the half axle bearings. Absence of moisture and dirt on them is the main condition for their long service life.
Peculiarities of driveshaft breakdowns.
At the outset, it should be emphasized that the axle shaft, regardless of its type and the vehicle on which it is installed, is a fairly robust part that almost always functions smoothly, especially on vehicles operated in urban areas. However, it is impossible to completely rule out the occurrence of malfunctions and breakdowns of this element.
Drive shaft bearing failure is often the result of transmission oil leakage caused by the poor condition of the oil seals. This results in additional frictional force, which accelerates the wear of the bearings.
The cause of problems may also be a worn-out dust cover of a CV joint, with both the joint and the half-axle eventually failing.
Prolonged use, aggressive driving style, and continuous driving on bad roads cause damage to the driveshaft. There are cases, when the axle shafts were split into several parts, but, more often, they simply break in the middle.
Unqualified repair works on the chassis and bad quality of half axles may also cause problems.
Axle shafts in the car – what they are and how they work types photo principle of operation
Design and principle of operation of the half axle in the car
The design of the half axle is such that the effect of power transmission will be maximum in any position of the wheels. This design consists of three parts: the external constant velocity joint (CVJ); the shaft; the internal CVJ. The shaft is, roughly speaking, a piece of pipe of a certain length, to which adapters are welded to install the CV joint. To prevent these elements from twisting, they are equipped with special splines.
The shaft is secured with a retaining ring at the end of the adapter, otherwise the shaft can pop out of the C.V. joint when in motion. The drive for the front drive wheel is performed by the external and internal constant velocity joints connected by the half axle. The use of two joints in the drive is caused by the independent suspension of the front wheels. The inner joints are responsible for moving the wheels during vertical suspension strokes, and the outer joints are responsible for turning the wheels relative to the vertical axis, which is a necessity when changing
Main Axle Half Axle Types
Depending on their design, half-axles can be fully or partially unloaded from the bending moments acting on them.
The unloaded semi-axle is particularly suitable for vehicles with a high payload capacity, e.g. buses. This half axle will appear in the drawing as a loose part inside the axle, and will be supported on the axle beam by the wheel hub by means of two bearings. In this design, the half axle transmits torque only, since all the bending force is taken by the bearings.
The semi-loaded axle is, in the vast majority of cases, installed on passenger cars and light trucks. The design of this type of axle half is different in that the bearing is between the axle half and its casing, and the axle half is attached directly to the wheel hub. For this reason, bending moments periodically occur on the shoulder, which act on the half-axle in the vertical and horizontal planes.
On front-wheel-drive vehicles, for the transmission of torque from the gearbox to the wheels, half-axles of a slightly different design are installed. This driveshaft consists of an axle, internal and external CV joints.
Design of the driveshaft of the front-wheel drive vehicle.
Causes of failure of half axles
During the operation of the vehicle, the half axle is constantly working under quite serious loads, among which are:
- bending moment, which occurs due to the force of gravity on the vehicle;
- the tangential reaction that occurs when the vehicle starts to move and brakes;
- lateral force due to vehicle skidding;
- Lateral loads due to strong crosswinds.
Half axles experience almost extreme loads when the vehicle is driven on unpaved roads as well as on broken highways.
Half-axle failure results in complete or partial loss of vehicle handling, so proper, thorough and timely maintenance is essential.
During the operation of the drive axle, you should periodically check the condition of the bearings placed on the half axles. Their longevity can be achieved by providing full protection against penetration of dirt and liquids.
Axle Half Axle Failures
The main failure that most often needs to be repaired is crunchy bearings.
It should be noted that the half axle in most car models is considered a very reliable part, which rarely fails. Especially it concerns the cars working in an urban cycle. But even with them there are problems.
Quite often the cause of early failure of axle shaft bearings is transmission oil leakage, which occurs due to wear of the axle shaft gland. The oil heats up when the car is in motion, flushing out the bearing grease, which increases the internal friction force and destroys the bearings.
In general, bearings are the most common cause of axle half axle failure. Besides being filled with transmission oil, they also break down due to defects of locking rings, and sometimes get jammed due to foreign objects.
A torn CIA duster causes failure of both the entire angular velocity joint and the driveshaft as a whole.
Continuous operation may cause dilatation of axle shaft, up to splines breakage. It is extremely rare, but breakages of half axles with splitting into two parts occur. Most often they break in the middle, near the splines or near the bearing.
Cables of front-wheel drive vehicles often burst, which afterwards is detrimental to joints.
Problems may be caused by accident, prolonged or excessively careless use of the car, unprofessional repair work or low quality of the parts themselves. Repairs are most often accomplished through replacement of the half axle, bearings, or other elements of the mechanism.
Half-discharged and half-discharged axles
Axles are divided into two categories according to their half-axle construction: 1. axles with unloaded half-axles; 2. axles with unloaded half-axles.
Half-discharged half-axles In the half-discharged half-axle arrangement, the half-axle transmits both torque and absorbs transverse loads and vehicle weight. Typically used on passenger cars where the axle load is low. Pros: simpler design; less weight Cons: less loading capacity; if the axle half fails, the wheel is simply separated from the vehicle, with all the ensuing consequences.
Unloaded half axles
In the unloaded half axle arrangement, the half axle transmits only torque and does not absorb transverse loads or the weight of the vehicle. Typically used on trucks where the axle load is high. Advantages: high load capacity; if the axle half is broken, it can be simply removed (if it is a four-wheel drive vehicle, it is possible to continue driving on one axle).