Rag joint
Encyclopedia
A rag joint refers to certain flexible joints
(flexure bearing
s) found on automobile
s. They are typically found on steering
shafts that connect the steering wheel
to the steering 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
coming from the steering system, providing some isolation for the steering wheel.
This type of joint was also used on drive shafts of 1960s race cars, later being replaced by the constant-velocity joint
or driveshafts with pairs of universal joint
. 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). This gives articulation where needed, but also stops some of the vibration being transmitted into the body.
The joint consists of a piece of doughnut
shaped rubber
with reinforcing cords vulcanized in it, similar to a tire
. This disc is bolted or rivet
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
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 the leather by something longer-lasting.
An older vehicle with loose steering or "play in the steering wheel" is often found to have a worn out 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 is unnacceptable and needs to be replaced.
Kinematic pair
A kinematic pair is a connection between two bodies that imposes constraints on their relative movement. Franz Reuleaux introduced the kinematic pair as a new approach to the study of machines that provided an advance over the notion of elements consisting of simple machines.Hartenberg & Denavit...
(flexure bearing
Flexure bearing
A flexure bearing is a bearing which allows motion by bending a load element.A typical flexure bearing is just one part, joining two other parts. For example, a hinge may be made by attaching a long strip of a flexible element to a door and to the door frame...
s) found on automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s. They are typically found on steering
Steering
Steering is the term applied to the collection of components, linkages, etc. which will allow a vessel or vehicle to follow the desired course...
shafts that connect the steering wheel
Steering wheel
A steering wheel is a type of steering control in vehicles and vessels ....
to the steering 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
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
coming from the steering system, providing some isolation for the steering wheel.
This type of joint was also used on drive shafts of 1960s race cars, later being replaced by the constant-velocity joint
Constant-velocity joint
Constant-velocity joints allow a drive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive and all wheel drive cars...
or driveshafts with pairs of universal joint
Universal joint
A universal joint, universal coupling, U joint, Cardan joint, Hardy-Spicer joint, or Hooke's joint is a joint or coupling in a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion...
. 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). This gives articulation where needed, but also stops some of the vibration being transmitted into the body.
The joint consists of a piece of doughnut
Doughnut
A doughnut or donut is a fried dough food and is popular in many countries and prepared in various forms as a sweet snack that can be homemade or purchased in bakeries, supermarkets, food stalls, and franchised specialty outlets...
shaped rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
with reinforcing cords vulcanized in it, similar to a tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
. This disc is bolted or rivet
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 the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole, and the tail is upset, or bucked A rivet...
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
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
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 the leather by something longer-lasting.
An older vehicle with loose steering or "play in the steering wheel" is often found to have a worn out 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 is unnacceptable and needs to be replaced.