Multi-link suspension
Overview
 

A multi-link suspension is a type of vehicle suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...

 design typically used in independent suspension
Independent suspension
Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically independently of each other. This is contrasted with a beam axle, live axle or deDion axle system in which the wheels are linked – movement on one side affects...

s, using three or more lateral arms, and one or more longitudinal arms.
A wider definition considers any independent suspensions having 3 control arms or more multi-link suspensions.

These arms do not have to be of equal length, and may be angled away from their 'obvious' direction.

Typically each arm has a spherical joint (ball joint) or rubber bushing at each end.
Encyclopedia
Multi-link rear suspension of the 5-link type
rear view
top view

A multi-link suspension is a type of vehicle suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...

 design typically used in independent suspension
Independent suspension
Independent suspension is a broad term for any automobile suspension system that allows each wheel on the same axle to move vertically independently of each other. This is contrasted with a beam axle, live axle or deDion axle system in which the wheels are linked – movement on one side affects...

s, using three or more lateral arms, and one or more longitudinal arms.
A wider definition considers any independent suspensions having 3 control arms or more multi-link suspensions.

These arms do not have to be of equal length, and may be angled away from their 'obvious' direction.

Typically each arm has a spherical joint (ball joint) or rubber bushing at each end. Consequently they react to loads along their own length, in tension and compression, but not in bending. Some multi-links do use a trailing arm
Trailing arm
thumb|220px|Trailing arm rear suspension of [[Front-engine, front-wheel drive layout|FF]] carsA trailing-arm suspension is an automobile suspension design in which one or more arms are connected between the axle and the chassis. It is usually used on rear axles...

 or wishbone, which has two bushings at one end.

On a front suspension one of the lateral arms is replaced by the tie-rod, which connects the rack or steering box to the wheel hub.

In order to simplify understanding it is usual to consider the function of the arms in each of three orthogonal planes.

Solid Axle Configuration

For a solid axle vehicle the multi link suspension provides control of the axle during suspension cycling and to locate the axle under the vehicle. The most common is the 4 link with panhard bar. This is found in many cars and pickup trucks. The 4 link is also used heavily in off road racing and drag racing. The 4 link for a solid axle has a few variations such as the triangulated 4 link and double triangulated 4 link. Although common in off-road vehicles these are not commonly found on the street.

Plan view

The arms have to control toe
Toe (automotive)
In automotive engineering, toe, also known as tracking, is the symmetric angle that each wheel makes with the longitudinal axis of the vehicle, as a function of static geometry, and kinematic and compliant effects. This can be contrasted with steer, which is the antisymmetric angle, i.e. both...

/steer and lateral compliance. This needs a pair of arms longitudinally separated.

Front view

Independent Suspension

The arms have to control camber
Camber angle
thumb|100px|From the front of the car, a right wheel with a negative camber angleCamber angle is the angle made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of the wheels used for steering and the vertical axis of the vehicle when viewed from the front or...

, particularly the way that the camber changes as the wheel moves up (into jounce, or bump) and down into rebound or droop.

Solid Axle Suspension

In a solid axle suspension the upper arms may have an angle of at least 45 degrees between them, to prevent the axle from moving from side to side while allowing the axle to articulate and move freely up and down.

Side view

Independent Suspension

The arms have to react traction and braking loads, usually accomplished via a longitudinal link. They also have to control caster
Caster angle
thumb|250px|θ is the caster angle, the red line is the pivot line, and the grey area is the tire.Caster angle or castor angle is the angular displacement from the vertical axis of the suspension of a steered wheel in a car, bicycle or other vehicle, measured in the longitudinal direction...

. Note that brake torques also have to be reacted - either by a second longitudinal link, or by rotating the hub, which forces the lateral arms out of plane, so allowing them to react 'spin' forces, or by rigidly fixing the longitudinal link to the hub.

Solid Axle Suspension

For a solid axle the lower arms control forward and backward motion, the upper arms control forward and backward rotation. This rotation is present under acceleration and braking.

Advantages of multi-link suspension

Benefit of independent suspension

Multi-link suspension allows the auto designer the ability to incorporate both good ride
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. A car with very good ride quality is also a comfortable car to ride in. Cars which disturb vehicle occupants with major or minor road...

 and good handling
Car handling
Automobile handling and vehicle handling are descriptions of the way wheeled vehicles perform transverse to their direction of motion, particularly during cornering and swerving. It also includes their stability when moving at rest. Handling and braking are the major components of a vehicle's...

 in the same vehicle.

In its simplest form, multi-link suspension is orthogonal—i.e., it is possible to alter one parameter in the suspension at a time, without affecting anything else. This is in direct contrast to a double wishbone suspension, where moving a hardpoint or changing a bushing compliance will affect two or more parameters.

Advantages also extend to off-road driving. A multi-link suspension allows the vehicle to flex more; this means simply that the suspension is able to move more easily to conform to the varying angles of off-road driving. Multi-link-equipped vehicles are ideally suited for sports such as desert racing. In desert racing, the use of a good sway bar
Sway bar
A sway bar or anti-roll bar or stabilizer bar is a part of an automobile suspension that helps reduce the roll of a vehicle that is induced by cornering or road irregularities. It connects opposite wheels together through short lever arms linked by a torsion spring...

 is needed to counter body roll.

Benefits of solid-axle multi-link suspension

The benefit of the triangulated and double-triangulated arrangement is that they do not need a panhard bar. The benefits of this are increased articulation and potential ease of installation. The multi-link for solid axle offers a benefit over the independent multi-link in that it is significantly cheaper and much less complex to build.

Disadvantages of multi-link suspension

Multilink suspension is costly and complex.
It is also difficult to tune the geometry without a full 3D computer aided design analysis. Compliance under load can have an important effect and must be checked using a multibody simulation software.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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