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. Control arms play a crucial role in the suspension system of a vehicle. They help to keep the wheels aligned and maintain proper tire contact with the road, which is essential for safety and stability. [1]
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, 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. [2]
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 products from the 1990s -- feature what's known as a double wishbone suspension. 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.
Control arms are most commonly encountered as part of the MacPherson strut independent front suspension. The control arms are perpendicular to the axis of the vehicle and are termed track control arms. A diagonal radius rod constrains the strut from moving forward and back. [2] [3]
In MacPherson's original design, an anti-roll bar 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.
A control arm may be used to carry the suspension load and transmit them to the spring or shock absorber. [4] Torsion bar suspension commonly does this, with the outboard end of the torsion bar attached to the inboard bearing of the control arm.
Camber angle is one of the angles made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of a wheel and the vertical axis of the vehicle when viewed from the front or rear. It is used in the creation of steering and suspension. If the top of the wheel is further out than the bottom, it is called positive camber; if the bottom of the wheel is further out than the top, it is called negative camber.
The MacPherson strut is a type of automotive suspension system that uses the top of a telescopic damper as the upper steering pivot. It is widely used in the front suspension of modern vehicles. The name comes from American automotive engineer Earle S. MacPherson, who invented and developed the design.
A strut is a structural component commonly found in engineering, aeronautics, architecture and anatomy. Struts generally work by resisting longitudinal compression, but they may also serve in tension.
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 terminates in a lever, the torsion key, mounted perpendicular to the bar, that is attached to a suspension arm, a spindle, or the axle. Vertical motion of the wheel causes the bar to twist around its axis and is resisted by the bar's torsion resistance. The effective spring rate of the bar is determined by its length, cross section, shape, material, and manufacturing process.
Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.
Independent suspension is any automobile suspension system that allows each wheel on the same axle to move vertically independently of the others. This is contrasted with a beam axle or deDion axle system in which the wheels are linked. "Independent" refers to the motion or path of movement of the wheels or suspension. It is common for the left and right sides of the suspension to be connected with anti-roll bars or other such mechanisms. The anti-roll bar ties the left and right suspension spring rates together but does not tie their motion together.
A double wishbone suspension is an independent suspension design for automobiles using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as camber angle, caster angle, toe pattern, roll center height, scrub radius, scuff, and more.
A trailing-arm suspension, also referred to as trailing-link, is a form of vehicle suspension. In a motor vehicle it places one or more horizontal arms perpendicular to and forward of the axle on the chassis or unibody, which are connected to the axle or wheels with pivot joint(s). These are typically used on the rear axle or wheels of vehicles, but also found in both front and main landing gear of aircraft.
The Chapman strut is a design of independent rear suspension used for light cars, particularly sports and racing cars. It takes its name from, and is best known for its use by, Colin Chapman of Lotus.
A swing axle is a simple type of independent suspension designed and patented by Edmund Rumpler in 1903 for the rear axle of rear wheel drive vehicles. This was a revolutionary invention in automotive suspension, allowing driven (powered) wheels to follow uneven road surfaces independently, thus enabling the vehicle's wheels to maintain better road contact and holding; plus each wheel's reduced unsprung weight means their movements have less impact on the vehicle as a whole. The first automotive application was the Rumpler Tropfenwagen, another early example was the 1923 Tatra 11 later followed by the Mercedes 130H/150H/170H, the Standard Superior, the pre-facelift Volkswagen Beetle and most of its derivatives, the Chevrolet Corvair, and the roll-over prone M151 jeep amongst others.
An anti-roll bar is an automobile suspension part that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It links opposite front or rear wheels to a torsion spring using short lever arms for anchors. This increases the suspension's roll stiffness—its resistance to roll in turns.
A strut bar, strut brace, or strut tower brace (STB) is an automotive suspension accessory on a monocoque or unibody chassis to provide extra stiffness between the strut towers.
A radius rod is a suspension link intended to control wheel motion in the longitudinal (fore-aft) direction. The link is connected on one end to the wheel carrier or axle, on the other to the chassis or unibody of the vehicle. Radius rods are typically mounted ahead of the wheel. In that position they resist dive under braking forces and wheel hop under acceleration.
In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles, and are used on virtually every automobile made. They bionically resemble the ball-and-socket joints found in most tetrapod animals.
A dual ball joint suspension uses a pair of arms, one in tension, one in compression, to replace a wishbone, in a MacPherson or SLA suspension. The outer end of each arm terminates in a ball joint, hence the name.
Automotive suspension design is an aspect of automotive engineering, concerned with designing the suspension for cars and trucks. Suspension design for other vehicles is similar, though the process may not be as well established.
Jaguar's independent rear suspension (IRS) unit has been a common component of a number of Jaguar production cars since 1961, passing through two major changes of configuration up to 2006 and last used in the Jaguar XK8 and Aston Martin DB7. This article concentrates on the first generation Jaguar IRS, which firmly established the marque's reputation for suspension sophistication, combining as it did smooth ride with excellent roadholding and low levels of noise, vibration, and harshness (NVH). The two generations overlap in time due to their being used in both full size and sports models that were updated at different times.
In automotive suspensions, a suspension link, control link or link is a suspension member, that attaches at only two points. One point being the body or frame of the vehicle and the other point attaching to the knuckle, upright, axle or another link. The link pivots on either a bushing or a ball joint at each attachment point. A link differs from a control arm because it can only control one of the degrees of freedom by itself.
Dual-pivot steering geometry is a geometric arrangement of linkages in the steering of a car designed to reduce or eliminate scrub radius by moving the pivot point of the king pin outboard, in order to improve steering precision and straight line stability.
Pull-rod suspension and push-rod suspension refer to a specialised type of automotive suspension system which is largely based on a double-wishbone system, incorporating elements of the commonly used MacPherson strut.