Suspension - INFORMATIONAL

[sakuraguy]

Suspension - INFORMATIONAL


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 handling and braking for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations. These goals are generally at odds, so the tuning of suspensions involves finding the right compromise. 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.

Spring rate
This may vary with deflection. For active suspensions, it may depend on other things. The softer the springs, the more important the other requirements are. Spring rate is often a compromise between comfort and handling, but when other things are compromised instead, as in the 1960s Lotus Elan, both may be achieved.

Spring rates typically have units of lbf/in. or N/mm. An example of a linear spring rate is 500 lbf/in. For every inch the spring is compressed, it exerts 500 lbf. A non-linear spring rate (typically increasing) is one that the force exerted increasess exponentially. For example, the first inch exerts 500 lbf, the second inch exerts an additional 550 lbf, the third inch exerts another 600 lbf.

Travel
Bottoming or lifting a wheel can cause serious control problems or directly cause damage. "Bottoming" can be either the suspension, tires, fenders, etc. running out of space to move or the body or other components of the car hitting the road. The control problems caused by lifting a wheel are less severe if the wheel lifts when the spring reaches its unloaded shape than they are if travel is limited by contact of suspension members.

Damping
This may also vary, intentionally or unintentionally. Like spring rate, the optimal damping for comfort may be less than for control.

Damping controls the body movement of the car. An undamped car will oscillate up and down. With proper damping levels, the car will settle back to a normal state in a minimal amount of time

Camber control
Camber changes with wheel travel and with body roll. A tire wears and brakes best perpendicular to the road. Depending on the tire, it may hold the road best at a slightly different angle. Small changes in camber, front and rear, are used to tune handling.

Roll Center Height
This is important to body roll and to relative weight transfer, front and rear. It may affect tendency to rollover. All other things being equal the end of the car with the higher roll center will have more weight transfer and therefore more slip in a turn. However, the roll moment distribution in most cars is set more by the antiroll bars than the RCH.

Flexibility and vibration modes of the suspension elements
In modern cars, the flexibility is mainly in the rubber bushings.

Isolation from high frequency shock
For most purposes, the weight of the suspension components is unimportant, but at high frequencies, caused by road surface roughness, the parts isolated by rubber bushings act as a multistage filter to suppress noise and vibration better than can be done with only the tires and springs. (The springs work mainly in the vertical direction.)

Contribution to unsprung weight and total weight
These are usually small, except that the suspension is related to whether the brakes and differential(s) are sprung.

Space occupied
Designs differ as to how much space they take up and where it is located.

Force distribution
The suspension attachment must match the frame design in geometry, strength and rigidity.

Air resistance (Drag)
Currently this is signficant only on racing cars (e.g. Formula One), but may become important on production cars in order to improve aerodynamics and thus fuel efficiency.

Cost
Production methods improve, but cost is always a factor. The continued use of the solid rear axle, with unsprung differential, especially on heavy vehicles, seems to be the most obvious example.


Springs and dampers
All suspensions use springs to absorb impacts and dampers (or shock absorbers) to control spring motions. A number of different types of each have been used:


Passive, Semi Active, and Active Suspensions
Traditional springs and dampers are referred to as passive suspensions. If the suspension is externally controlled then it is a semi-active or active suspension.

Semi-active suspensions include devices such as air springs and switchable shock absorbers, various self-levelling solutions, as well as systems like Hydropneumatic, Hydrolastic, and Hydragas suspensions. Delphi currently sells shock absorbers filled with a magneto-rheological fluid, whose viscousity can be changed electromagnetically, thereby giving variable control without switching valves, which is faster and thus more effective, along with being cheaper. An Australian company, Kinetic, is having (as of 2005) some success with various semi-active systems, which provide adjustable roll control and damping, by using cross linked shock absorbers, and other methods. They have now been bought out by Tenneco and Alcorn.

For example, a hydropneumatic Citroën will "know" how far off the ground the car is supposed to be and constantly reset to achieve that level, regardless of load. It will not instantly compensate for body roll due to cornering however. Citroën's system adds about 1% to the cost of the car versus passive steel springs.

Fully active suspensions use electronic monitoring of vehicle conditions, coupled with the means to impact vehicle suspension and behavior in real time to directly control the motion of the car. Lotus Cars developed several prototypes, and introduced them to F1, where they have been fairly effective, but have now been banned. Nissan introduced a low bandwidth active suspension in circa 1990 as an option that added an extra 20% to the price of luxury models. Citroën has also developed several active suspension models (see Hydractive).

A recently publicised fully-active system from Bose Corporation uses linear electric motors, ie solenoids, in place of hydraulic or pneumatic actuators that have generally been used up until recently.

Springs
Leaf spring - AKA Hotchkiss, Cart, or semi-elliptical spring
Torsion beam suspension
Coil spring
Rubber bushing
Air spring


Dampers or shock absorbers
The shock absorbers damp out the, otherwise resonant, motions of a vehicle up and down on its springs. They also must damp out much of the wheel bounce when the unsprung weight of a wheel, hub, axle and sometimes brakes and differential bounces up and down on the springiness of a tire. The "corduroy" bumps found on dirt roads are caused by this wheel bounce. These bumps are more common on US dirt roads, where solid rear axles are common, than they are in e.g. French dirt roads, where unsprung weight tends to be low and suspensions well damped.


Suspension types
Suspension systems can be broadly classified into two subgroups - dependent and independent. These terms refer to the ability of opposite wheels to move independently of each other.

A dependent suspension normally has a live axle (a simple beam or 'cart' axle) that holds wheels parallel to each other and perpendicular to the axle. When the camber of one wheel changes, the camber of the opposite wheel changes in the same way.

An independent suspension allows wheels to rise and fall on their own without affecting the opposite wheel. Suspensions with other devices, such as anti-roll bars that link the wheels in some way are still classed as independent.

A third type is a semi-dependent suspension. In this case, jointed axles are used, on drive wheels, but the wheels are connected with a solid member, most often a deDion axle. This differs from "dependent" mainly in unsprung weight.

Interconnected suspensions (mechanically interconnected, such as anti-roll bars; and hydraulically or pneumatically interconnected, e.g., SAE 2005-01-3593, SAE 2003-01-0312) have also been used to achieve a better compromise among vertical, roll and pitch properties.


Dependent suspensions
Dependent systems may be differentiated by the system of linkages used to locate them, both longitudinally and transversely. Often both functions are combined in a set of linkages.

Examples of location linkages include:

-Trailing arms
-Satchell link
-Panhard rod
-Watts linkage
-Inboard
-WOBLink
-Mumford linkage
-Leaf springs used for location (transverse or longitudinal)
-Fully elliptical springs usually need supplementary location links and are no longer in common use
-Longitudinal semi-elliptical springs used to be common and still are used on some -US cars and on trucks. They have the advantage that the spring rate can easily be made progressive (non-linear)
-A single transverse leaf spring for both front wheels and/or both back wheels, supporting solid axles was used by Ford Motor Company, before and soon after World War II, even on expensive models. It had the advantages of simplicity and low unsprung weight (compared to other solid axle designs), as well as the other advantages of solid axles.
-In a front engine rear drive vehicle, dependent rear suspension is either "live axle" or deDion axle, depending on whether or not the differential is carried on the axle. Live axle is simpler but the unsprung weight contributes to wheel bounce.

Because it assures constant camber, dependent (and semi-independent) suspension is most common on vehicles that need to cary large loads, as a proportion of the vehicle weight, that have relatively soft springs and that do not (for cost and simplicity reasons) use active suspensions. However the use of dependent front suspension has become limited to a few trucks.

 

[sakuraguy]

MacPherson strut

http://img124.imageshack.us/img124/9575/400pxmcphersonstrutdk5.jpg

The MacPherson strut is a type of car suspension system widely used in modern vehicles, named after Earl S. MacPherson who developed the design. The first car to feature MacPherson struts was the 1949 Ford Vedette,[1] and it was also adopted in the 1951 Ford Consul and later Zephyr. It can be used for both front and rear suspensions, but is usually found at the front, where it provides a steering pivot (kingpin) as well as a suspension mounting for the wheel. Rear struts of a similar design are properly called Chapman struts.

It consists of a small subframe (an A–arm) or a substantial link stabilized by a secondary link which provides a bottom mounting point for the hub or axle of the wheel. This subframe provides both lateral and longitudinal location of the wheel. The upper part of the hub is rigidly fixed to the inner part of the strut proper, the outer part of which extends upwards directly to a mounting in the body shell of the vehicle. This type of suspension is only used with monocoque (unitary) body construction since the upper mounting can be a reinforced portion of the inner wheel well. The strut will usually carry both the coil spring on which the body is suspended and the shock absorber, which is usually in the form of a cartridge mounted within the strut. The strut also usually has a steering arm built into the lower inner portion. The whole assembly is very simple and can be preassembled into a unit; also by eliminating the upper control arm, it allows for more width in the engine bay, which is useful for smaller cars, particularly with transverse oriented engines such as most front wheel drive vehicles have. For those reasons, it has become almost ubiquitous with manufacturers.

In addition to its simplicity and low manufacturing cost, it has few real vices with respect to handling, although a little geometric analysis shows that it cannot allow vertical movement of the wheel without some degree of either camber angle change, sideways movement, or both. It is not generally considered to give as good handling as A arms (wishbones), perhaps because it allows the engineers less freedom to choose camber change and roll center. The wheel tends to lean with the body, leading to understeer. Another drawback is that it tends to transmit noise and vibration from the road directly into the body shell, giving higher noise levels and a "harsh" feeling to the ride compared with systems such as double wishbones, requiring manufacturers to add extra noise reduction or cancellation and isolation mechanisms. Also, because of its greater size and robustness and greater degree of attachment to the vehicle structure, when the internal seals of the shock absorber portion wear out replacement is relatively expensive compared to replacing a simple shock absorber. However, despite the stated drawbacks the strut setup is still used on high performance cars such as the Ford Mustang, Porsche 911, all BMWs and several Mercedes-Benz models.

 

[sakuraguy]

Chapman Strut


A Chapman strut is an automobile suspension device. Being a strut, it is designed to act as both a shock absorber (with an integrated coil spring) and a wheel location device. That is, it is designed to resist lateral forces. Chapman struts are the term for such a device when used on rear wheels, while the very similar MacPherson strut is used in front. (See MacPherson strut for more information.)

The Chapman strut was named after Colin Chapman, the famed Lotus founder and engineer, and was first used on the Lotus 12.

 

[sakuraguy]

Swing Axle

http://img450.imageshack.us/img450/1280/swingaxlediagrampv2.gif


A swing axle suspension is a simple type of independent suspension used in automobiles. Swing axles have universal joints connecting the driveshafts to the differential, which is attached to the chassis. They do not have universal joints at the wheels - the wheels are always perpendicular to the driveshafts. Swing axle suspensions traditionally used leaf springs and shock absorbers. Pre 1967 Volkswagens used torsion bars as their spring.

This type of suspension was considered better than the more typical solid axle for two reasons:

It reduced unsprung weight since the differential is mounted to the chassis
It eliminates sympathetic camber changes on opposite wheels
However, there are a number of shortcomings to this arrangement:

A great amount of single-wheel camber change is experienced since the wheel is always perpendicular to the driveshaft
"Jacking" on suspension unloading (or rebound) causes negative camber changes on both sides
Reduction in cornering forces due to change in camber can lead to oversteer instability.
These problems were evident on Volkswagen up until 1967 and others.

Swing axles were supplanted by deDion axles in the late 1960s, though live axles remained the most common. Most rear suspensions have been replaced by more modern independent suspensions in recent years, and both swing and deDion types are virtually unused today.

The First Production (1960-1964) Chevrolet Corvair used this design. The alleged unsafe behaviour of the Corvair was described in detail by Ralph Nader in his book "Unsafe At Any Speed". Second Production Corvairs (1965-1969) used a true independent rear suspension system.

 

[sakuraguy]

Trailing Arm

A trailing-arm suspension is an automobile suspension design in which one or more arms (or "links") are connected between (and perpendicular to) the axle and the chassis. Simple trailing-arm designs in live axle setups often use just two or three links and a Panhard rod to locate the wheel laterally.

A semi-trailing arm suspension is an independent rear suspension system for automobiles in which each wheel hub is located only by a large, roughly triangular arm that pivots at two points. Viewed from the top, the line formed by the two pivots is somewhere between parallel and perpendicular to the car's longitudinal axis; it is generally parallel to the ground.

Trailing-arm and multilink suspension designs are much more commonly used for the rear wheels of a vehicle where they can allow for a flatter floor and more cargo room. Many small vehicles feature a MacPherson strut front suspension and trailing-arm rear axle.

 

[sakuraguy]

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. 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 loads along their own length, in tension and compression, but not in bending. Some multi-links do use a swing arm 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.

http://img370.imageshack.us/img370/319/200px5linkm3drearhi9.gifhttp://img124.imageshack.us/img124/1442/200px5linkm3dtopof7.gif


Plan view
The arms have to control toe/steer and lateral compliance. This needs a pair of arms longitudinally separated.

Front view
The arms have to control camber, particularly the way that the camber changes as the wheel moves up (into jounce, or bump) and down into rebound or droop.

Side view
The arms have to react traction and braking loads, usually accomplished via a longitudinal link. They also have to control caster. 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.

Advantages of multi-link suspension
In its simplest form the multi-link suspension is orthogonal - that is, it is possible to alter one parameter in the suspension at a time, without affecting anything else.

This is in direct contrast to say 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 will allow the vehicle to flex more, this means simply that the suspension will be able to move more easily to conform to the varying angles of off roading. This being said, multi-link equipped vehicles are ideally suited for sports such as rock crawling, and desert racing. A side note to the use of multi-link suspension use in desert racing, the use of a good sway bar is needed to counter body roll.

Disadvantages of multi-link suspension
It is difficult to optimise the geometry without a full 3d analysis, and compliance effects are important.

 

[sakuraguy]

Double Wishbone Suspension

In automobiles, a double wishbone suspension is an independent suspension design using two parallel wishbone-shaped arms to locate the wheel. Each wishbone (or arm) has two mounting positions 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 many more.


The double wishbone suspension is also often referred to as double 'A' arm or short long arm (SLA) suspension. It is commonly used in sports cars, luxury cars and light trucks.

A very similar arrangement, often using a single arm, is the A-arm suspension.

The suspension consists of a pair of upper and lower lateral arms, roughly horizontal and of similar length. The upper arm is usually slightly shorter to induce more negative camber on the outside wheel as the vehicle body rolls in a turn. Between the arms there is a knuckle with a spindle or hub which carries the wheel bearing and wheel. Knuckles with an integral spindle usually do not allow the wheel to be driven. A bolt on hub design is commonly used if the wheel is to be driven.

In order to resist fore-aft loads such as acceleration and braking, the arms need two bushings or ball joints at the body.

At the knuckle end, single ball joints can be used, in which case the steering loads have to be taken via a steering arm, and the wishbones look A- or L-shaped. An L-shaped arm is generally preferred on passenger vehicles because it allows a better compromise of handling and comfort to be tuned in. The bushing in line with the wheel can be kept relatively stiff to effectively handle cornering loads while the offline joint can be softer to allow the wheel to recess under fore aft impact loads. For a rear suspension a pair of joints can be used at both ends of the arm, making them more H-shaped in plan view.

In front view the suspension is a 4-bar link, and it is easy to work out the camber gain (see camber angle) etc., for a given set of bush locations.

The various bushes do not have to be on horizontal axes, parallel to the vehicle centre line. If they are set at an angle then antidive and antisquat can be dialled in.

The advantage of a double wishbone suspension is that it is fairly easy to work out the effect of moving each joint, so you can tune the kinematics of the suspension easily and optimize wheel motion. It is also easy to work out the loads that different parts will be subjected to which allows more optimized lightweight parts to be designed.

The disadvantage is that it is slightly more complex than other systems like a MacPherson strut.

SLAs are very common on front suspensions for larger cars, Pickups and SUV's and double wishbones are very common at both ends of racing cars.

Prior to the dominance of front wheel drive in the 1980s, many everyday cars used double-wishbone front suspension systems, or a variation on it. Since that time, the MacPherson strut has become almost ubiquitous, as it is simpler and cheaper to manufacture. Double-wishbones are usually considered to have superior dynamic characteristics, load handling capability and are still found on higher performance vehicles.

 

[sakuraguy]

Shock Absorber


A shock absorber in common parlance (or damper in technical use) is a mechanical device designed to smooth out or damp a sudden shock impulse and dissipate kinetic energy. It is analogous to a resistor in an electric RLC circuit.

http://img124.imageshack.us/img124/3583/gasdampermovri2.gif

Explanation
Shock absorbers must absorb or dissipate energy. One design consideration, when designing or choosing a shock absorber is where that energy will go. In most dashpots, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid will heat up. In air cylinders, the hot air is usually exhausted to the atmosphere. In other types of dashpots, such as electromagnetic ones, the dissipated energy can be stored and used later.

Description
Pneumatic and hydraulic shock absorbers commonly take the form of a cylinder with a sliding piston inside. The cylinder is filled with a fluid, such as hydraulic fluid or air. This fluid filled piston/cylinder combination is a dashpot.

Applications
Shock absorbers are an important part of automobile suspensions, aircraft landing gear, and the supports for many industrial machines. Large shock absorbers have also been used in architecture and civil engineering to reduce the susceptibility of structures to earthquake damage and resonance.

Vehicles suspension
In a vehicle, it reduces the effect of travelling over rough ground. Without shock absorbers, the vehicle would have a bouncing ride, as energy is stored in the spring and then released to the vehicle, possibly exceeding the allowed range of suspension movement. Control of excessive suspension movement without shock absorption requires stiffer (higher rate) springs, which would in turn give a harsh ride. Shock absorbers allow the use of soft (lower rate) springs while controlling the rate of suspension movement in response to bumps. They also, along with hysteresis in the tire itself, damp the motion of the unsprung weight up and down on the springiness of the tire. Since the tire is not as soft as the springs, effective wheel bounce damping may require stiffer shocks than would be ideal for the vehicle motion alone.

Spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars can be used in torsional shocks as well. Ideal springs alone, however, are not shock absorbers as springs only store and do not dissipate or absorb energy. Vehicles typically employ both springs or torsion bars as well as hydraulic shock absorbers. In this combination, "shock absorber" is reserved specifically for the hydraulic piston that absorbs and dissipates vibration.

Structures
Applied to a structure such as a building or bridge it may be part of a seismic retrofit or as part of new, earthquake resistant construction. In this application it allows yet restrains motion and absorbs resonant energy, which can cause excessive motion and eventual structural failure.

Types of shock absorbers
There are several commonly-used approaches to shock absorption:

-Hysteresis of structural material, for example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent, by the hysteresis of their springs and frames.

-Dry friction as used in wheel brakes, but using disks (classically made of leather) at the pivot of a lever, with friction forced by springs. Used in early automobiles such as the Ford Model T, up through some British cars of the 1940s. Although now considered obsolete, an advantage of this system is its mechanical simplicity; the degree of damping can be easily adjusted by tightening or loosening the screw clamping the disks, and it can be easily rebuilt with simple hand tools. A disadvantage is that the damping force tends not to increase with the speed of the vertical motion.

-Fluid friction, for example the flow of fluid through a narrow orifice (hydraulics), constitute the vast majority of automotive shock absorbers. An advantage of this type is that using special internal valving the absorber may be made relatively soft to compression (allowing a soft response to a bump) and relatively stiff to extension, controlling "jounce", which is the vehicle response to energy stored in the springs; similarly, a series of valves controlled by springs can change the degree of stiffness according to the velocity of the impact or rebound. Specialized shock absorbers for racing purposes may allow the front end of a dragster to rise with minimal resistance under acceleration, then strongly resist letting it settle, thereby maintaining a desirable rearward weight distribution for enhanced traction. Some shock absorbers allow tuning of the ride via control of the valve by a manual adjustment provided at the shock absorber. In more expensive vehicles the valves may be remotely adjustable, offering the driver control of the ride at will while the vehicle is operated. The ultimate control is provided by dynamic valve control via computer in response to sensors, giving both a smooth ride and a firm suspension when needed. Many shock absorbers contain compressed nitrogen, to reduce the tendency for the oil to foam under heavy use. Foaming temporarily reduces the damping ability of the unit. In very heavy duty units used for racing and/or off-road use, there may even be a secondary cylinder connected to the shock absorber to act as a reservoir for the oil and pressurized gas.

-Compression of a gas, for example pneumatic shock absorbers, which can act like springs as the air pressure is building to resist the force on it. Once the air pressure reaches the necessary maximum, air dashpots will act like hydraulic dashpots. In aircraft landing gear air dashpots may be combined with hydraulic dampening to reduce bounce. Such struts are called "oleo" struts (combining oil and air).

-Magnetic effects. Eddy current dampers are dashpots that are constructed out of a large magnet inside of a non-magnetic, electically conductive tube. Furthermore, many modern hybrid automobiles have regenerative braking, which uses a reversed electric motor to dampen and eventually stop the motion of the car.

-Inertial resistance to acceleration, for example the Citroën 2CV has an additional pair of rear shock absorbers that damp wheel bounce with no external moving parts. The energy is absorbed by hydraulic fluid friction, but their operation depends on the inertia of an internal weight. These are essentially small versions of the tuned mass dampers used on tall buildings.

-Composite hydropneumatic devices which combine in a single device spring action, shock absorption, and often also ride-height control, as in some models of the Citroën automobile.

-Conventional shock absorbers combined with composite pneumatic springs with which allow ride height adjustment or even ride height control, seen in some large trucks and luxury sedans such as certain Lincoln automobiles. Ride height control is especially desirable in highway vehicles intended for occasional rough road use, as a means of improving handling and reducing aerodynamic drag by lowering the vehicle when operating on improved high speed roads.

-The effect of a shock absorber at high (sound) frequencies is usually limited by using a compressible gas as the working fluid and/or mounting it with rubber bushings.

 

[sakuraguy]

STRUT & STRUT BAR


An automotive suspension strut combines the primary function of a shock absorber (as a damper), with the ability to support sideways loads not along its axis of compression, somewhat similar to a sliding pillar suspension, thus eliminating the need for an upper suspension arm. This means that a strut must have a more rugged design, with mounting points near its middle for attachment of such loads.

http://img370.imageshack.us/img370/4306/800pxstrutbaroj3.jpg

A strut bar or strut brace is a mostly aftermarket car suspension accessory used in conjunction with MacPherson struts on monocoque or unibody chassis to provide extra strength between the strut towers.

With a MacPherson strut suspension system where the spring and shock absorber are combined in the one suspension unit, the entire vertical suspension load is transmitted to the top of the vehicle's strut tower, unlike a double wishbone suspension where the spring and shock absorber may share the load separately. In general terms, a strut tower in a monocoque chassis is a reinforced portion of the inner wheel well and is not necessarily directly connected to the main chassis rails. For this reason there is inherent flex within the strut towers relative to the chassis rails.

A strut bar is designed to reduce this strut tower flex by tying two parallel strut towers together. This transmits the load of each strut tower during cornering via tension and compression of the strut bar which shares the load between both towers and reduces chassis flex.

A direct result of this is improved chassis rigidity (similar to that gained from a lower tie bar); hence, the understeer is reduced, tire wear improved and metal fatigue is greatly reduced in the strut tower area. Following the aftermarket's lead, some manufacturers have started fitting strut bars to performance models, including the NISSAN Skyline R34 and the HOLDEN VY II Commodore, as standard equipment.

 

[sakuraguy]

Torsion Beam Suspension


Torsion beam suspension, also known as a torsion bar or torsion spring suspension, is a vehicle suspension system. One end of a long metal bar is attached firmly to the vehicle chassis; the opposite end terminates in a lever, mounted perpendicular to the bar, that is attached to the axle of the suspension arm or wishbone. Vertical motion of the wheel causes the bar to rotate along its axis and are resisted by the bar's torsion resistance. The effective spring rate of the bar is determined by its length and diameter.

The main advantages of torsion beam suspension are durability, easy adjustability of ride height, and small profile along the width of the vehicle. It provides a longer travel than leaf spring systems, and takes up less of the vehicle's interior volume compared to coil springs. A major disadvantage is that torsion bars, unlike coil springs, usually cannot provide a progressive spring rate, forcing designers to compromise between ride quality and handling ability - progressive torsion bars are available, but at the expense of durability since they have a tendency to crack where the diameter of the bar changes. In most torsion bar systems, especially Chrysler's, ride height (and therefore many handling features) may be adjusted by bolts which connect the torsion bars to the steering knuckles and require nothing more than crawling under the car with a wrench in hand. In most cars which use this type of suspension, swapping torsion bars for those with a different spring rate is usually an extremely easy task.

Some vehicles use torsion bars to provide automatic leveling, using a motor to tighten the bars to provide greater resistance to load and, in some cases (depending on the speed with which the motors can act), to respond to changes in road conditions.

The system was applied to many new armoured fighting vehicle designs during the Second World War. It was used extensively in European cars as well as by Packard in the 1950s. The Packard used torsion bars at both front and rear, and interconnected the front and rear systems to improve ride quality. The most famous passenger-car application was the Chrysler system used beginning with the 1957 model year, although Chrysler's "Torsion-Aire" suspension was only for the front; the same basic system was maintained until the 1981 introduction of the K-car. Light-duty Dodge trucks however continue to use torsion bars on their front suspension.

General Motors has used torsion bars since 1966, starting with the E-platform vehicles (Oldsmobile Toronado, Cadillac Eldorado), 4 wheel drive S-10 pickups, and since 1988, full size trucks (GMT400, GMT800, and GMT900 series).

Some front-wheel drive automobiles use a type of torsion bar rear suspension, sometimes called a twist-beam system, in which the rear wheels are carried on trailing arms connected by a laterally mounted torsion beam. The torsion beam functions both as wheel-locating arm and as an anti-roll bar to resist lateral motion of the wheels as the body leans in turns. Its advantages are that it is inexpensive to manufacture and install, and engages a minimum amount of interior volume, leaving more space for the carriage of passengers, cargo, and other components. Because the torsion bar acts in the lateral plane, not vertically, the twist-beam axle cannot provide ride-height adjustment, and it suffers the same handling limitations as any other beam axle suspension. Twist-beam rear suspensions were pioneered on the Volkswagen Golf in the early 1970s, and remain common on compact cars and minivans.

 

[sakuraguy]

End.


Regards,

SakuraGuy
Zerotohundred.Com