A-arm on:
[Wikipedia]
[Google]
[Amazon]
In automotive suspension, a control arm, also known as an A-arm, is a hinged suspension link between the chassis and the suspension upright or hub that carries the wheel. In simple terms, it governs a wheel's vertical travel, allowing it to move up or down when driving over bumps, into potholes, or otherwise reacting to the irregularities of a road surface. Most control arms form the lower link of a suspension.
The inboard (chassis) end of a control arm is attached by a single pivot, usually a rubber bushing. It can thus control the position of the outboard end in only a single
A control arm may be used to carry the suspension load and transmit them to the spring or shock absorber.
In automotive suspension, a control arm, also known as an A-arm, is a hinged suspension link between the chassis and the suspension upright or hub that carries the wheel. In simple terms, it governs a wheel's vertical travel, allowing it to move up or down when driving over bumps, into potholes, or otherwise reacting to the irregularities of a road surface. Most control arms form the lower link of a suspension.
The inboard (chassis) end of a control arm is attached by a single pivot, usually a rubber bushing. It can thus control the position of the outboard end in only a single degree of freedom
Degrees of freedom (often abbreviated df or DOF) refers to the number of independent variables or parameters of a thermodynamic system. In various scientific fields, the word "freedom" is used to describe the limits to which physical movement or ...
, maintaining the radial distance from the inboard mount. Although not deliberately free to move, the single bushing does not control the arm from moving back and forth; this motion is constrained by a separate link or radius rod
A radius rod (also called a radius arm, torque arm, torque spring, and torsion bar) is a suspension link intended to control wheel motion in the longitudinal (fore-aft) direction. The link is connected (with a rubber or solid bushing) on one en ...
.
This is in contrast to the wishbone, which are triangular and have two widely spaced inboard bearings. These constrain the outboard end of the wishbone from moving back and forth, controlling two degrees of freedom, and without requiring additional links. Certain vehicles -- notably, many Honda
is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan.
Honda has been the world's largest motorcycle manufacturer since 1959, reaching a producti ...
products from the 1990s -- feature what's known as a double wishbone suspension
A double wishbone suspension is an independent suspension design for automobiles using two (occasionally parallel) wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckl ...
. A double wishbone design features both upper and lower control arms that work in tandem with each other to properly locate the wheel. The additional radius rod is then attached to the upper arm.
MacPherson strut
Control arms are most commonly encountered as part of the MacPherson strutindependent front suspension
Independent suspension is any automobile suspension system that allows each wheel on the same axle to move vertically (i.e. reacting to a bump on the road) independently of the others. This is contrasted with a beam axle or deDion axle system in ...
. The control arms are perpendicular
In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It ca ...
to the axis of the vehicle and are termed '' track control arms''. A diagonal ''radius rod'' constrains the strut from moving forward and back.
In MacPherson's original design, an anti-roll bar
An anti-roll bar (roll bar, anti-sway bar, sway bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) whee ...
also acted as the radius rod. This requires the bar to be attached through a ball joint, so as to also provide longitudinal control. In most contemporary designs, still commonly termed MacPherson struts, the radius rod and anti-roll bar are now separate, with the anti-roll bar mounted in a sliding bush.
Spring attachment
A control arm may be used to carry the suspension load and transmit them to the spring or shock absorber. Torsion bar suspension
A torsion bar suspension, also known as a torsion spring suspension, is any vehicle suspension that uses a torsion bar as its main weight-bearing spring. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end term ...
commonly does this, with the outboard end of the torsion bar
A torsion bar suspension, also known as a torsion spring suspension, is any vehicle suspension that uses a torsion bar as its main weight-bearing spring. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end termi ...
attached to the inboard bearing of the control arm..
See also
*Double wishbone suspension
A double wishbone suspension is an independent suspension design for automobiles using two (occasionally parallel) wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckl ...
References
{{Reflist Automotive suspension technologies