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The Invention of the Constant Velocity Joint

written by: johnsinit • edited by: Lamar Stonecypher • updated: 2/1/2010

If it weren’t for this Ford engineer, riding in a car could be an unpleasant or even dangerous experience. In 1926 he invented the constant velocity joint, or CV joint. This device allows the outer wheel to steer during turns, at the same time allowing up-down motions of the suspension.

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    Constant Velocity Joint

    Constant Velocity Joints or CV joints are part of the driveline on a front wheel drive or four wheel drive car. The CV joint’s output speed equals the input speed regardless of the angle of the joint. The original version of the CV joint is a ball type joint. It is a flexible joint that allows the wheel on the outside of the turn to steer, and at the same time, it allows the car’s suspension to continue with its up-down motions as the car moves. The CV joint is usually found on the outer end of the driveshaft – joining to the wheels – while the inner drive shaft - connected to the transaxle – usually has a different kind of CV joint called a tripod joint.

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    The Justification

    The reason for using a CV joint on the end of the driveshaft connecting to the wheel is because the outer joint can experience an operating angle of up to 50 degrees when the front wheels are steered. The joint on the inward end, rarely has to operate at more than a 20 degree angle, so a different type of CV joint can be used there.

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    The Inventor

    Not much is known about the life of Alfred Hans Rzeppa. He lived from January 23, 1885 until sometime in January 1965. He worked as an engineer for Ford Motor Company, and arguably his biggest contribution at Ford was his invention of a version of a constant-velocity Joint, or CV joint in 1926. He also improved the design ten years later, in 1936. The details of these inventions can be read in U.S. patents 2,010,899 and 2,046,584, which can be found on the Internet.

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    Constant Velocitiy Joint

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    The Mechanics

    The Rzeppa joint is made with an inner and outer race, which is one rotating piece inside another rotating piece. In the Rzeppa CV joint, six spherical balls are placed between the inner and outer races. The balls are kept in position by holes in a cage assembly that fits between the inner and outer races. The Rzeppa joint is designed so that the balls always bisect the operating angle of the joint.

    If you understand how a bevel gear works, you have a pretty good idea of how a Rzeppa joint works, only instead of angled gear teeth transmitting the torque, the balls push against their tracks in the inner and outer races. This allows the direction of the shaft to be changed with almost constant velocity regardless of the joint angle.

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    Maintenance

    Besides being very flexible, CV joints require little maintenance beyond inspecting the rubber “boot" covering them for cracks. If the boots are cracked, road dirt can get up into the mechanism, causing wear, and if allowed to continue, possible failure of the CV joint.

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    The Alternatives

    A simpler type of joint, called a Universal Joint, is made from two U-shaped hinges close together, oriented at 90 degrees to each other and both connected to a cross shaft or a ball. While this allows good freedom of movement when wheels are steered, with very sharp turning angles, U-Joints can cause the driveline to vibrate. While U-joints are known to be very sturdy, modern CV joints can last just as long if they are properly maintained.

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