Independent suspension is any
automobile
A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...
suspension
Suspension or suspended may refer to:
Science and engineering
* Suspension (topology), in mathematics
* Suspension (dynamical systems), in mathematics
* Suspension of a ring, in mathematics
* Suspension (chemistry), small solid particles suspend ...
system that allows each wheel on the same
axle
An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
to move vertically (i.e. reacting to a bump on the road) independently of the others. This is contrasted with a
beam axle
A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have als ...
or
deDion axle
De Dion rear axle
A de Dion tube is a form of non- independent automobile suspension. It is a considerable improvement over the swing axle, Hotchkiss drive, or live axle. Because it plays no part in transmitting power to the drive wheels, it ...
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
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 ...
or other such mechanisms. The anti-roll bar ties the left and right suspension spring rates together but does not tie their motion together.
Most modern vehicles have independent front suspension (IFS). Many vehicles also have an independent rear suspension (IRS). IRS, as the name implies, has the rear wheels independently sprung. A fully independent suspension has an independent suspension on all wheels. Some early independent systems used
swing axle
A swing axle is a simple type of independent (rear wheel) suspension designed and patented by Edmund Rumpler in 1903. This was a revolutionary invention in automotive suspension, allowing driven (powered) wheels to follow uneven road surfaces ...
s, but modern systems use
Chapman or
MacPherson strut
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, and is named for American automotive engineer Ear ...
s,
trailing arm
A (semi) trailing-arm suspension, sometimes referred to as (semi) trailing-link is a vehicle axle or wheel suspension design in which one or more horizontal arms (or "links"), perpendicular to and forward of the axle, are connecting the axle or ...
s,
multilink, or
wishbones.
Independent suspension typically offers better
ride quality
Ride quality refers to a vehicle's effectiveness in insulating the occupants from undulations in the road surface (e.g., bumps or corrugations).
A vehicle with good ride quality provides a comfort for the driver and passengers.
Importance
Good r ...
and
handling characteristics, due to lower ''unsprung weight'' and the ability of each wheel to address the road undisturbed by activities of the other wheel on the vehicle. Independent suspension requires additional engineering effort and expense in development versus a beam or live axle arrangement. A very complex IRS solution can also result in higher manufacturing costs.
The key reason for lower unsprung weight relative to a live axle design is that, for driven wheels, the
differential unit does not form part of the
unsprung elements of the suspension system. Instead, it is either bolted directly to the vehicle's
chassis
A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...
or more commonly to a
subframe
A subframe is a structural component of a vehicle, such as an automobile or an aircraft, that uses a discrete, separate structure within a larger body-on-frame or unit body to carry certain components, such as the engine, drivetrain, or suspen ...
.
The relative movement between the wheels and the differential is achieved through the use of swinging driveshafts connected via
universal joints (U joints), analogous to the
constant-velocity (CV) joints used in
front-wheel-drive
Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional lon ...
vehicles.
Independent suspension
Suspension
Suspension is the only component that separates the driver and/or passenger from the ground. The suspension in a vehicle helps absorb harshness in the road. There are many systems and designs that do this, such as independent suspension.
Advantages
This system provides many advantages over other suspension systems. For example, in solid axle suspension systems, when one wheel hits a bump, it affects both wheels. This will compromise traction, smoothness of the ride, and could also cause a dangerous wheel shimmy when moving at high speeds. With independent suspension systems, the bump primarily affects only the contacted wheel. This offers many advantages such as greater ride comfort, better traction, and safer, more stable vehicles on the road.
Types
Double wishbone suspension
In automobiles, a double wishbone suspension is an independent suspension design 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 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
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 design of steering an ...
,
caster angle
250px, θ is the caster angle, the red line is the pivot line, and the grey area is the tire.
250px, Front suspension of a race car, the caster angle is formed by the line between upper and lower ball joint.
The caster angle or castor angle is t ...
,
toe pattern,
roll center
The roll center of a vehicle is the notional point at which the cornering forces in the suspension are reacted to the vehicle body.
There are two definitions of roll center. The most commonly used is the geometric (or kinematic) roll center, wher ...
height,
scrub radius
The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. It can be positive, negative or zero.
The kingpin axis also known as steerin ...
, scuff and more.
Multi-link suspension
A multi-link suspension is a type of vehicle suspension design typically used in independent suspensions, using three or more lateral arms, and one or more longitudinal arms. A wider definition considers any independent suspensions having three control links or more multi-link suspensions. These arms do not have to be of equal length, and may be angled away from their "obvious" direction. It was first introduced in the late 1960s on the Mercedes-Benz C111 prototype and put into production later on their W201 and W124 series.
MacPherson strut
This is the most common, widely used front suspension system in cars today. It is a very simple and effective design that uses a strut-type spring and shock absorber that work as a team that will pivot on a single ball joint. This system was popularized in British Fords in the 1950s, then adopted by BMW (1962) and Porsche (1963). Later, this space-efficient system became widespread with the growing popularity of front-wheel drive vehicles.
One problem with this system is that once the spring or the top plate becomes worn, the driver of a car with this system may hear a loud "clonk" noise at full lock (i.e. steering wheel turned to the extreme left or extreme right positions), as the strut's spring jumps back into place. This noise is often confused with CV-joint knock.
Transverse leaf-spring
Several independent suspension designs have featured transverse leaf springs. Most applications used multi-leaf steel springs, although more recent designs have used fiber reinforced plastic (FRP, typically fibers are fiberglass) springs. In addition to spring type (multi-leaf steel, FRP), a distinction can be drawn between systems where the spring also acts as a locating link and those where the spring only acts as a spring member.
The
AC Cobra
The AC Cobra, sold in the United States as the Shelby Cobra and AC Shelby Cobra, is a sports car manufactured by British company AC Cars, with a Ford V8 engine. It was produced intermittently in both the United Kingdom and later the United ...
is an example of a transverse, multi-leaf steel spring suspension that uses the leaf spring as the upper suspension arm. Alternatively, the
1963 Corvette's rear suspension is an example where the transverse leaf spring is used only as a ride spring. In both examples, the leaf spring is centrally mounted, preventing displacement of the wheel on one side from affecting the wheel on the other side.
In 1981, General Motors pioneered the use of a FRP plastic transverse leaf spring on the
third-generation Corvette. As in the examples above, the spring used a single, central mount which isolated the left and right movements. The FRP spring reduced weight and eliminated the inner leaf friction as compared to the multi-leaf metal spring which was standard on the car.
Rather than centrally mounting the transverse leaf spring and thus isolating the left and right sides of the springs, some manufacturers, starting with
Fiat
Fiat Automobiles S.p.A. (, , ; originally FIAT, it, Fabbrica Italiana Automobili di Torino, lit=Italian Automobiles Factory of Turin) is an Italian automobile manufacturer, formerly part of Fiat Chrysler Automobiles, and since 2021 a subsidiary ...
used two widely spaced spring mounts. This was first used on the front of the 1955
Fiat 600
The Fiat 600 ( it, Seicento, ) is a rear-engine, water-cooled city car, manufactured and marketed by Fiat Automobiles, Fiat from 1955 to 1969 — offered in two-door fastback sedan and four-door Multipla mini MPV body styles.
Measuring only ...
and later at the rear on the
Fiat 128. The spring is allowed to pivot inside of the mounts which allows the displacement of the spring on one side to affect the other side. This mechanical communication between the left and right sides of the suspension results in an effect similar to that of 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) wheels ...
.
Chevrolet Corvettes, starting with the 4th generation in 1984 have combined the
dual pivot mounts with FRP leaf springs.
The transverse leaf spring is not used as commonly as it was earlier. It is very rare on modern cars, the Corvette and a few Volvo models being examples.
In the past it was more widely used in many
Triumphs
''Triumphs'' (Italian language, Italian: ''I Trionfi'') is a 14th-century Italian series of poems, written by Petrarch in the Tuscan language. The poem evokes the Roman triumph, Roman ceremony of triumph, where victorious generals and their armies ...
. The
Herald
A herald, or a herald of arms, is an officer of arms, ranking between pursuivant and king of arms. The title is commonly applied more broadly to all officers of arms.
Heralds were originally messengers sent by monarchs or noblemen to ...
,
Vitesse,
Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft used by the Royal Air Force and other Allied countries before, during, and after World War II. Many variants of the Spitfire were built, from the Mk 1 to the Rolls-Royce Griff ...
, and
GT6 all used a rear transverse leaf spring, as well as the 1995-98
Volvo 960/S90/V90 and a rare Swedish sports car incorporating the Volvo 960 rear suspension called the
JC Indigo.
Note that this type of suspension should not be confused with earlier, rigid axle applications such as those used on
early Ford cars.
References
# Arvinmertitor Inc. "Independent Suspension for Off-highway Use." LexisNexis Academic.
# "independent suspension." Dictionary.com's 21st Century Lexicon. Dictionary.com, LLC. 14 Nov. 2011.
External links
{{Automotive handling
Automotive suspension technologies