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A sway bar (also stabilizer bar, anti-sway bar, roll bar, or anti-roll bar, ARB) is an automobile suspension device. Porsche SE or Porsche ( German, ˈpɔɹʃə is a German manufacturer of automobiles which is majority-owned by the Porsche and Piëch Suspension is the term given to the system of springs, Shock absorbers and linkages that connects a Vehicle to its Wheels Suspension It connects opposite (left/right) wheels together through short lever arms linked by a torsion spring. A torsion spring is a spring that works by torsion or twisting that is a flexible elastic object that stores Mechanical energy when it is twisted A sway bar increases the suspension's roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction. In Mechanics, and Physics, Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed (the The first stabilizer bar patent was awarded to S. L. C. Coleman of Fredericton, New Brunswick on April 22, 1919. Fredericton (pronounced ˈfrɛdrɨktɨn is the capital of the Canadian province of New Brunswick, by virtue of the provincial [1]
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Principles
A sway bar is usually a torsional spring that resists body roll motions. It is usually constructed out of a U-shaped piece of steel that connects to the body at two points, and at the left and right sides of the suspension. If the left and right wheels move together, the bar just rotates about its mounting points and does not bend. If the wheels move relative to each other, the bar is forced to twist.
The bar resists the bending through its stiffness. The stiffness of an anti-roll bar is based on the fourth power of its diameter, the stiffness of the material, the inverse of the length of the lever arms (i. e. , the shorter the lever arm, the stiffer the bar), the geometry of the mounting points, and the rigidity of the bar's mounting points. Some anti-roll bars, particularly those intended for use in auto racing, are adjustable, allowing their stiffness to be altered by increasing or reducing the length of the lever arms. Auto racing (also known as automobile racing, motor racing or car racing) is a Motorsport involving Racing Cars It This permits the roll stiffness to be tuned for different situations without replacing the entire bar. The stiffer the bar, the more force required to move the left and right wheels relative to each other. This increases the amount of force required to make the body roll.
In a turn, the sprung mass of the vehicle's body produces a lateral force at the Center of Mass, proportional to lateral acceleration. In a vehicle with a suspension, such as an Automobile, Motorcycle or a Tank, sprung mass (or sprung weight) is the portion of the Because the cg is usually not on the roll axis, the lateral force creates a moment about the roll axis that tends to roll the body. (The roll axis is a line that joins the front and rear roll centers (SAEJ670e). The moment is called the roll couple.
Roll couple is resisted by the suspension roll stiffness, which is a function of the spring rate of the vehicle's springs and of the anti-roll bars, if any. The use of anti-roll bars allows designers to reduce roll without making the suspension's springs stiffer in the vertical plane, which allows improved body control with less compromise of ride quality. Ride quality refers to the degree of protection offered vehicle occupants from uneven elements in the Road surface or the Terrain if driving Off-road.
One effect of body (frame) lean, for typical suspension geometry, is positive camber of the wheels on the outside of the turn and negative on the inside, which reduces their cornering grip (especially with cross ply tires). Camber angle is the angle made by the Wheel of an automobile specifically it is the angle between the vertical axis of the wheel and the vertical axis of the vehicle when
Anti-roll bars provide two main functions:
The first function is the reduction of body lean. The reduction of body lean is dependent on the total roll stiffness of the vehicle. Increasing the total roll stiffness of a vehicle does not change the steady state total load (weight) transfer from the inside wheels to the outside wheels, it only reduces body lean. The total lateral load transfer is determined by the CG height and track width.
The other function of anti roll bars is to tune the high g / limit understeer behavior of the vehicle. The limit understeer behavior is tuned by changing the proportion of the total roll stiffness that comes from the front and rear axles. Increasing the proportion of roll stiffness at the front will increase the proportion of the total weight transfer that the front axle reacts and decrease the proportion that the rear axle reacts. This will cause the outer front wheel to run at a higher slip angle, and the outer rear wheel to run at a lower slip angle, which is an understeer effect. Increasing the proportion of roll stiffness at the rear axle will have the opposite effect and decrease understeer.
Drawbacks
Because an anti-roll bar connects wheels on the opposite sides of the vehicle together, the bar will transmit the force of one-wheel bumps to the opposite wheel. On rough or broken pavement, anti-roll bars can produce jarring, side-to-side body motions (a "waddling" sensation), which increase in severity with the diameter and stiffness of the sway bars. Excessive roll stiffness, typically achieved by configuring an anti-roll bar too aggressively, will cause the inside wheels to lift off the ground during very hard cornering. This, of course, is only possible if the regular spring rate actually allows the outside wheels to handle the much increased load. This can be used to advantage, in fact many front wheel drive production cars will lift a wheel when cornering hard, in order to overload the other wheel on the axle, so limiting understeer. Understeer is a term for a Car handling condition in which during cornering the circular path of the Vehicle 's motion is of a greater radius than the circle indicated
Some high-priced cars, such as the Range Rover Sport and BMW 7-series, have begun to use "active" anti-roll bars that can be proportionally controlled automatically by a suspension-control computer, reducing body lean in turns while improving rough-road ride quality. A computer is a Machine that manipulates data according to a list of instructions. The first to use this was the Citroen Xantia Activa, a medium sized sedan sold in Europe. The Activa system was an antiroll bar that could be stiffened under the command of the suspension ECU during hard cornering. The car rolled at any time at most 2 degrees. Mercedes S-class ABC system uses another approach, the computer uses sensors to detect lateral load, lateral force, height difference in the suspension strut and uses hydraulic pressure to raise or lower the spring to counter roll. For a complete overview of all S-Class models see Mercedes-Benz S-Class. This system removes the antiroll bar. Most active roll control systems allow a small degree of roll to give a more natural feel.
See also
References
- ^ Mario Theriault, Great Maritime Inventions 1833-1950, Goose Lane Editions, 2001, p. A torsion bar suspension, also known as a Torsion spring suspension or incorrectly torsion beam, is a general term for any Vehicle suspension 69
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