Hardy flexible coupling (Autocar Handbook, Ninth edition)

A rag joint refers to certain flexible

joints A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...

(

flexure bearing A flexure bearing is a category of flexure which is engineered to be compliant in one or more angular degrees of freedom. Flexure bearings are often part of compliant mechanisms. Flexure bearings serve much of the same function as conventional b ...

s) found on

automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...

s and other machines. They are typically found on steering column shafts that connect the

steering wheel A steering wheel (also called a driving wheel (UK), a hand wheel, or simply wheel) is a type of steering control in vehicles. Steering wheels are used in most modern land vehicles, including all mass-production automobiles, buses, light and ...

to the

steering Steering is a system of components, linkages, and other parts that allows a driver to control the direction of the vehicle. Introduction The most conventional steering arrangement allows a driver to turn the front wheels of a vehicle using ...

gear input shaft, usually at the steering gear end. They provide a small amount of flex for a steering shaft within a few degrees of the same plane as the steering gear input shaft. It also provides some damping of

vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, suc ...

coming from the steering system, providing some isolation for the steering wheel. This type of joint has also been used on drive shafts. Farm tractors and lawn and garden equipment have often used them in this application, and even some higher-power applications, such as some 1960s race cars, featured them. In automobile and truck prop shaft designs, they have now mostly been replaced by constant-velocity joints or driveshafts with pairs of universal joints or '' giubos''. Rear-wheel drive cars have commonly used a lengthwise propeller shaft with a rubber doughnut joint at the gearbox end (limited movement) and a universal joint at the rear axle (greater movement), or vice versa. This gives articulation where needed, but also stops some of the vibration being transmitted into the body. The joint consists of one or more

doughnut A doughnut or donut () is a type of food made from leavened fried dough. It is popular in many countries and is prepared in various forms as a sweet snack that can be homemade or purchased in bakeries, supermarkets, food stalls, and fran ...

-shaped layers of flat

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, a ...

sheet with reinforcing cords vulcanized in them, similar to a

tire A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...

. In fact, they are cut from used tires. This disc is bolted or

rivet A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the ''tail''. On installation, the rivet is placed in a punched ...

ed to flanges mounted on the ends of the shafts to connect the steering wheel shaft to the steering gear. The ragged cords can be seen on the edge of this piece of rubber, hence the term "rag joint". The bolt holes themselves are often reinforced by steel tubes moulded into the doughnut. The origins of this form of universal joint are from early vehicles that used a disk of thick

leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and ho ...

as a similar flexible joint. These were used into the 1920s. As rubber technology improved (particularly for its resistance to spilled mineral oils), it was possible to replace leather by longer-lasting materials. "Rag joints" were used on some American cars, including GM full size sedans, into the mid 90s. An older vehicle with loose steering or "play in the steering wheel" is often found to have a worn rag joint. One can reach inside the cab and wiggle the steering wheel while watching the rag joint move without the input shaft moving. This condition may cause the vehicle to fail the

vehicle inspection Vehicle inspection is a procedure mandated by national or subnational governments in many countries, in which a vehicle is inspected to ensure that it conforms to regulations governing safety, emissions, or both. Inspection can be required at va ...

, indicating that the worn part needs replacement.

References

{{DEFAULTSORT:Rag Joint Rotating shaft couplings Automotive transmission technologies