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Constant-velocity joint
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Constant-velocity joint
A constant-velocity joint (also called a CV joint and homokinetic joint) is a mechanical coupling which allows the shafts to rotate freely (without an appreciable increase in friction or backlash) and compensates for the angle between the two shafts, within a certain range, to maintain the same velocity.
A common use of CV joints is in front-wheel drive vehicles, where they are used to transfer the engine's power to the wheels, even as the angle of the driveshaft varies due to the operation of the steering and suspension.
The predecessor to the constant-velocity joint was the universal joint (also called a Cardan joint) which was invented by Gerolamo Cardano in the 16th century. A short-coming of the universal joint is that the rotational speed of the output shaft fluctuates despite the rotational speed of the input shaft being constant. This fluctuation causes unwanted vibration in the system and increases as the angle between the two shafts increases. A constant-velocity joint does not have this fluctuation in output speed and therefore does not possess this unwanted vibration. Also, although universal joints are simple to produce and can withstand large forces, universal joints often become "notchy" and difficult to rotate as the angle of operation increases.
The first type of constant-velocity joint was the Double Hooke's (Double Cardan) Joint which was invented by Robert Hooke in the 17th century. This design uses two universal joints connected by a shaft and offset by 90 degrees thereby cancelling out the speed variations inherent in each individual joint.
Many other types of constant-velocity joints have been invented since then.
Double Cardan Joints are similar to Hooke's use of two universal joints except that the length of the intermediate shaft is shortened leaving only the yokes; this effectively allows the two Hooke's joints to be mounted back to back. DCJs are typically used in steering columns, as they eliminate the need to correctly phase the universal joints at the ends of the intermediate shaft (IS), which eases packaging of the IS around the other components in the engine bay of the car. They are also used to replace Rzeppa style constant-velocity joints in applications where high articulation angles, or impulsive torque loads are common, such as the driveshafts and halfshafts of rugged four-wheel drive vehicles.
To be truly constant-velocity, Double Cardan joints require a centering element that will maintain equal angles between the driven and driving shafts. This centering device requires additional torque to accelerate the internals of the joint and does generate some additional vibration at higher speeds.
The Tracta joint works on the principle of the double tongue and groove joint. It comprises only four individual parts: the two forks (a.k.a. yokes, one driving and one driven) and the two semi-spherical sliding pieces (one called male or spigot swivel and another called female or slotted swivel) which interlock in a floating (movable) connection. Each yoke jaw engages a circular groove formed on the intermediate members. Both intermediate members are coupled together in turn by a swivel tongue and grooved joint. When the input and output shafts are inclined at some working angle to each other, the driving intermediate member accelerates and decelerates during each revolution. Since the central tongue and groove joint are a quarter of a revolution out of phase with the yoke jaws, the corresponding speed fluctuation of the driven intermediate and output jaw members exactly counteracts and neutralizes the speed variation of the input half member. Thus the output speed change is identical to that of the input drive, providing constant velocity rotation.
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Constant-velocity joint
A constant-velocity joint (also called a CV joint and homokinetic joint) is a mechanical coupling which allows the shafts to rotate freely (without an appreciable increase in friction or backlash) and compensates for the angle between the two shafts, within a certain range, to maintain the same velocity.
A common use of CV joints is in front-wheel drive vehicles, where they are used to transfer the engine's power to the wheels, even as the angle of the driveshaft varies due to the operation of the steering and suspension.
The predecessor to the constant-velocity joint was the universal joint (also called a Cardan joint) which was invented by Gerolamo Cardano in the 16th century. A short-coming of the universal joint is that the rotational speed of the output shaft fluctuates despite the rotational speed of the input shaft being constant. This fluctuation causes unwanted vibration in the system and increases as the angle between the two shafts increases. A constant-velocity joint does not have this fluctuation in output speed and therefore does not possess this unwanted vibration. Also, although universal joints are simple to produce and can withstand large forces, universal joints often become "notchy" and difficult to rotate as the angle of operation increases.
The first type of constant-velocity joint was the Double Hooke's (Double Cardan) Joint which was invented by Robert Hooke in the 17th century. This design uses two universal joints connected by a shaft and offset by 90 degrees thereby cancelling out the speed variations inherent in each individual joint.
Many other types of constant-velocity joints have been invented since then.
Double Cardan Joints are similar to Hooke's use of two universal joints except that the length of the intermediate shaft is shortened leaving only the yokes; this effectively allows the two Hooke's joints to be mounted back to back. DCJs are typically used in steering columns, as they eliminate the need to correctly phase the universal joints at the ends of the intermediate shaft (IS), which eases packaging of the IS around the other components in the engine bay of the car. They are also used to replace Rzeppa style constant-velocity joints in applications where high articulation angles, or impulsive torque loads are common, such as the driveshafts and halfshafts of rugged four-wheel drive vehicles.
To be truly constant-velocity, Double Cardan joints require a centering element that will maintain equal angles between the driven and driving shafts. This centering device requires additional torque to accelerate the internals of the joint and does generate some additional vibration at higher speeds.
The Tracta joint works on the principle of the double tongue and groove joint. It comprises only four individual parts: the two forks (a.k.a. yokes, one driving and one driven) and the two semi-spherical sliding pieces (one called male or spigot swivel and another called female or slotted swivel) which interlock in a floating (movable) connection. Each yoke jaw engages a circular groove formed on the intermediate members. Both intermediate members are coupled together in turn by a swivel tongue and grooved joint. When the input and output shafts are inclined at some working angle to each other, the driving intermediate member accelerates and decelerates during each revolution. Since the central tongue and groove joint are a quarter of a revolution out of phase with the yoke jaws, the corresponding speed fluctuation of the driven intermediate and output jaw members exactly counteracts and neutralizes the speed variation of the input half member. Thus the output speed change is identical to that of the input drive, providing constant velocity rotation.
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