The Heart Of Any CV-Joint – The Cage

Constant velocity (CV) joints play an essential function in the cars, shifting energy from power transmission system to the wheels. As an integral part of the drivetrain system, the CV joint is responsible for accommodating the dynamic movement of the suspension while maintaining a consistent rotational velocity, thereby enhancing driving performance, comfort and overall vehicle reliability.

The CV joint operates by utilizing a set of specially designed balls and an inner and outer housing that enable it to accommodate both angular and rotational movement. This design is particularly important for vehicles with front-wheel drive (FWD) and all-wheel drive (AWD) configurations, where the front wheels are both responsible for steering and transmitting power. CV joints allow for seamless power delivery even as the wheels turn and move up and down, ensuring that the engine’s power is efficiently transmitted to the road surface.

One of the key benefits of the CV joint is its ability to maintain a constant velocity as power is transmitted through different angles. This is particularly important during turns, as the inner wheel needs to travel a shorter distance than the outer wheel. Without a CV joint, the drivetrain would experience binding, resulting in excessive wear on the components and an uncomfortable driving experience.

To guarantee the clean and green operation of these joints, fundamental is the role of a small component called “cage”. The CV joint cage holds the balls (or rollers) in place, allowing for the smooth transfer of torque from the driveshaft to the wheels while accommodating the rotational movement of the joint. When the CV joint rotates, the balls move around inside the cage: the cage prevents the balls from rubbing against each other, which can cause damage and affect the performance of the CV joint.

In this article the role of CV joint cages, their importance and the way they contribute to the general overall performance of a vehicle will be analysed.

A Constant Velocity (CV) joint cage is a vital component of the drivetrain system in vehicles equipped with front-wheel drive or all-wheel drive. The accurate geometrical precision of the cage in all its dimensions together with proper metallurgical properties (both in terms of fibres flow and of heat treatment quality and consistency) are important parameters that can make the difference in the quality of the car driving experience and in the life of the whole cv-joint itself.

For instance, an excessive clearance of the cage with the ring and/or with the steel balls will cause rough and inconsistent power transmission, arriving in the worst cases to generate even tedious clicking noises, often more noticeable when turning in one direction over the other.

A poorer resistance to wear and to fatigue of the cage (for example due to “not continuous fibres flow” caused by usage of tubes + turning technology instead of bars + forging process in the cage manufacturing process) can cause the premature damage of the cage, so generating vibrations coming from the front end of the vehicle, especially during acceleration. These vibrations are usually felt in the steering wheel or the floorboard and may increase in intensity as the vehicle’s speed increases. The vibrations are the results of imbalance in the CV joint cage, causing it to vibrate during operation.

Other effect of damaged cage on the performance of the CV-joint is the exit of the grease from the contact area between balls and rings. The final effect is a reduction of lubrication effect, an increase of friction and a bigger exposure of the joint to external contamination: all the above causes generate a negative loop, so further increasing wear and damages of cage.

In general, a damaged CV-joint cage can compromise the safety in driving. In fact, it can cause difficulty in steering, such as stiffness or resistance when turning. The lack of smooth power transfer and increased clearance in the joint can make challenging to steer the vehicle accurately, potentially compromising the control and safety on the road.

In addition to its role in maintaining a constant velocity during turns, the CV joint also contributes to minimizing torque steer, a phenomenon often encountered in high-powered front-wheel-drive vehicles. Torque steer is the tendency of the vehicle to pull to one side under hard acceleration and it occurs due to uneven distribution of torque between the two front wheels. The design of the CV joint (and especially of its cage) helps mitigate this issue by allowing each wheel to move independently, reducing the effects of torque steer and providing a more controlled driving experience.

In effect, the design of the cage determines its ability to distribute and manage the forces and stresses experienced during operation. A well-designed CV joint cage should evenly distribute the load on the balls, preventing excessive stress on any specific area. This reduces the risk of premature wear or failure. In the commonly used design named “window or pocket design”, the windows hold the balls in place, allowing for a larger contact area between the cage and the balls so distributing the load more effectively: this design helps to minimize friction and wear, resulting in improved durability and performance. The number of windows affects the smoothness of rotation and the distribution of forces. Cages with a higher number of windows tend to offer better performance due to improved load distribution and reduced friction. However, a higher number of windows may also increase the complexity and manufacturing cost of the cage.

The material used for the cage must possess specific characteristics such as strength, hardness, and wear resistance to withstand the demanding operating conditions. Such properties may be duly reinforced through accurate specific heat treatment.

Steel is the most commonly used material for CV joint cages due to its excellent strength and durability. High-grade steel alloys, such as chrome-molybdenum steel, are often employed to enhance the cage’s performance. These alloys provide superior strength and hardness, allowing the cage to withstand the high rotational speeds and heavy loads associated with CV joint operation.

In addition to steel, some other materials like polymers or composite materials can be used. These alternative materials offer advantages like reduced weight, improved corrosion resistance and reduced friction. However, their implementation is typically limited to specific applications or performance requirements.

From the above considerations it is clear how the CV-joint cages cannot be considered as commodity product but as a high-added value technological component that can make the difference in assuring comfortable proper driving experience to the car driver, besides the relative safety. Cheaper options may have a shorter lifespan due to inferior materials and construction lower precision.

The crucial features of the cages to achieve the above superior performances are many: the geometrical perfection of all the dimensions of the cage will assure the correct clearance in the joint between cage, rings and balls; the consistent surface heat treatment (even through special processes like nitriding or carbo-nitriding) and hardness will guarantee the resistance to wear and fatigue even in the toughest environmental conditions (e.g., high temperatures, dusty conditions, off-roading or rough terrains).

The ICT cages for CV-joints guarantees a smoother and longer life in the application, achieving well more than the mileage of standard joints. Their higher precision allows to minimize power losses, to maximize torque transfer to the wheels, which is especially crucial for vehicles with demanding performance requirements, and to contribute to a quieter and smoother driving experience.

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[Courtesy: ICT]