Types of Suspension Systems

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June 17, 2021

# Vehicle Dynamics

We might have heard many a time about the word �Suspension�. Most of us might know that it is a word related to automobiles and mechanical engineering. In this article, we shall delve deeper into what the term �Suspension� really means and specifically about the various types of suspension. What is a Suspension System?� A vehicle always has a body as well as wheels. In simple terms, a suspension system is a system that connects the body of the vehicle with its wheels. It ensures the smooth relative motion between the body of the vehicle and its wheels. The suspension system consists of various mechanical components that include tires, tire air, springs,�shock absorbers,�and�linkages. The frame and body of a vehicle are attached to the front and rear axle through various types of springs and shock absorbers. This is done to damp, that is, reduce the effects of shocks as a result of traveling on rough or bumpy roads, or humps and uneven roads. The suspension system ensures a more comfortable ride quality in the vehicle and supports increased road-handling efficiency/holding. The Suspension system keeps the wheel in contact with the road with maximum efficiency because it is the contact patches of the tires that come in contact with the reaction forces and ground forces, thus ensuring an overall balance of forces within the vehicle. It is the key system in any vehicle as it protects the vehicle itself, the passengers as well as any cargo or luggage from wear and tear. Traditionally automotive suspension system designs have been compromising between the three conflicting criteria�s namely the road handling, load carrying capacity, and passenger comfort. Parameters like camber, caster angle, and kingpin inclination for better steering qualities are decided based upon the suspension system design. The suspension system of a vehicle is divided into the rear end suspension and front end suspension. Each of them may be of different types and may have different designs. Functions of Suspension System

  1. To maintain proper�steering�geometry.
  2. To safeguard the occupants from road shocks and to provide them with a comfortable ride.
  3. The suspension system prevents the road shocks and additional stresses from being transferred to the vehicle frame.
  4. To provide the required height to body structure as well as bear the torque & braking reaction.
  5. �To keep the vehicle body and frame at the perfect level while traveling over uneven roads.
  6. It also ensures smoothness and stability of the vehicle and passengers when there is sudden lifting or dropping off the front wheel with respect to the rear wheels.
  7. The overall stability of the vehicle is ensured as the vehicle does not bounce or sway, and good road handling is provided while driving, accelerating, cornering, and braking as well as when the vehicle is in pitching or rolling while in motion.

  Requirements for an ideal Suspension System

  1. Minimum deflection is consistent with the required stability.
  2. Comparability with other vehicle components-type, frame wheelbase, steering linkage, and compliant to the proposed vehicle architecture.
  3. Minimum wheel hop.
  4. Low maintenance and operating costs.
  5. Low initial cost.
  6. Minimum weight
  7. Minimum wear.
  8. Adhering to packaging requirements

History of Suspension Systems In ox-drawn carts, the platform swung on Iron chains that were attached to the wheeled frame of the carriage. This type of suspension system remained in place till the 19-th century, with the only modification being the replacement of iron chains by leather straps called thoroughbraces in the 17th century. The thorough brace suspension system has disappeared completely and is not used in any modern automobiles. In the horse and buggy days, the suspension system consisted simply of a beam (axle) that extended across the width of the vehicle. The wheels were mounted to the axle ends in the front, and the axle was rotated at the center to provide steering. The early automobiles used the one?piece axle design but instead of being rotated at the center, it was fix?mounted to the vehicle through springs to provide the cushioning against shocks from the unevenness of roads. The wheels were rotationally mounted at the axle ends to provide steering. By 1750, the first springs, which consisted of thin layers of narrow pieces of strip steel stacked together in an elliptical shape, called the leaf springs came in, used in carriages such as the Landau. Later, leaf springs were replaced by coil springs. In front?engine rear?drive vehicles, the front beam axle was replaced by independently mounted steerable wheels. The wheels were supported by short upper and lower hinged arms holding them perpendicular to the road as did the previous axle beam designs. A coil spring was used to support either the upper or the lower arm to provide dampening. Shock absorbers began to be used to dampen shock loads and also to provide resistance to spring oscillations. Trucks continue to be front?engine, rear?drive vehicles many of which are using beam-type axle suspension systems in both the front and rear. Later it was learned by shortening the upper arm; wheel tilt (camber) could be controlled to prevent edge loading tires while cornering. The power transmitting drive axle in the rear served as the beam?type suspension with dampening provided by either leaf or coil springs as well as shock absorbers. When front?engine front?drive passenger cars were introduced, the upper arm was rotated up and replaced by a member called a �strut� which contained the concentrically mounted spring and shock.��This arrangement provided additional space for transverse-mounted engine/transmission modules and the front driveshaft. This same type of suspension was also used in the rear of many cars. BASIC SUSPENSION SYSTEM COMPONENTS There are three basic types of suspension components: linkages, springs, and shock absorbers.

  1. LINKAGES - The linkages attach at only two points. The body or frame of the vehicle would�be one of the points which will be connected to the other point, knuckle, upright, axle, or another link. The linkages are the bars and brackets that support the wheels, springs, and shock absorbers.Links with different shapes are used for the different types of suspension systems. They vary from straight bars to forged, cast, or stamped metal shapes that best fit to support the springs, shocks, and wheels onto vehicle frames or body structures.

The simplest linkage is a straight bar that connects one wheel to the other on the opposite side of the vehicle. Others can be intricately shaped so as to connect springs, shock absorbers, and wheels to vehicles

  1. SPRINGS: Springs cushion the vehicle by dampening shock loads from bumps, holes, and irregularities in the road. Shock absorbers use hydraulic pistons and cylinders to cushion the vehicle too, from shock loads. They also serve to dampen spring oscillations, thus bring the vehicle back to a neutral position soon after being shock-loaded by a road obstruction.

There are three different spring types that are used in suspension systems: coil, leaf, and torsion bar. Torsion bars involve the twist of a long bar to provide a spring rate to dampen car shock loading. Torsion bars mount across the bottom portion of a vehicle and are more difficult to package than the other type of springs. Coil springs are merely wound torsion bars. They are commonly used because they are compact, easily mounted, and have excellent endurance life properties. Leaf springs are long thin members that are loaded in bending. They are used as an assembly being comprised of several layers of thin metal to obtain the correct spring rate. Leaf springs serve as both the damping member and the linkage. A leaf spring is a slender�arc-shaped length of�spring steel of a�rectangular cross-section. In the most common configuration, the center of the arc provides a location for the�axle, while loops formed at either end provide for attaching to the vehicle chassis. For very heavy vehicles, a leaf spring can be made from several leaves stacked on top of each other in several layers, often with progressively shorter leaves. The modern development of leaf springs involves examples like the 2016 Volvo XC90, which has a transverse leaf spring in high-tech composite materials, similar to the latest Chevrolet Corvette. This means a straight leaf spring that is tightly secured to the chassis and the ends of the spring bolted to the wheel suspension, to allow the spring to work independently on each wheel. This means the suspension is smaller, flatter, and lighter than the traditional setup.

  1. SHOCK ABSORBERS: Shock absorbers use a piston and cylinder along with adjustable valves to control the flow of hydraulic fluid to set the damping force in both the retract (jounce) and extend (rebound) positions. Shock absorbers are set to retract under a lower force than to extend. This action absorbs road bump forces and dampens spring oscillations resulting in better vehicle ride and control.

(References: https://www.cedengineering.com/userfiles/Automotive%20Suspension%20Systems.pdf, https://en.wikipedia.org/wiki/Leaf_spring ) Difference between rear suspension and front suspension A vehicle is something that is used for the very purpose of moving and hence, merely designing it such that it has a balanced front-to-rear weight distribution when it is still, is not even close to enough. The whole balance and mathematical calculations of the vehicle must be done for when the vehicle is in motion, when it accelerates, decelerates, and changes directions. The front and rear suspensions have entirely different functions under different circumstances. In a rear-wheel-drive car, rear suspension handles the �squatting� of the car as it accelerates, managing the traction of the rear tires against the ground. At the same time, the front suspension tries to maximize the front wheels� ability to steer, even though they�re losing traction. Conversely, when you decelerate, the rear tires keep the back of the car following the front, while the front suspension works with the brakes and the Anti-lock braking system (ABS) to keep the front wheels rolling and steering. But basically, the job of the suspension is, at any given moment, to keep the three other wheels as firmly on the ground as possible. A four-wheel-drive (4WD/AWD) vehicle needs suspension for both the front wheels and rear wheels, but a two-wheel-drive vehicle can have a very different configuration for front and rear wheels. Four-wheel drive�often has suspensions that are similar for both the front and rear wheels For�front-wheel-drivecars, the rear suspension has few constraints, and a variety of beam axles�and�independent suspensions, whereas, for�rear-wheel-drivecars, the rear suspension has many constraints and independent suspension. The front end suspension is more complicated than the rear end suspension because the front wheels not only move up and down with respect to the car frame but also swing at various angles to the car frame for steering. In order to permit the front wheels to swing to one side or the other for steering, each wheel is ported on a spindle which is part of the steering knuckle. The steering knuckle is then supported through ball joints, by upper and lower control arms which are attached to the car frame. Types of Front End and Rear End Suspension Systems

  1. Front End Suspension System
    1. Rigid axle front suspension.
    2. Independent front suspension
      1. Twin I-Beam Suspension System
      2. Single I-Beam Front Suspension System
      3. Independent Front End Suspension Using Torsion Bar
      4. Parallelogram Type Independent Front Suspension
      5. Struck and Link Type Suspension System
      6. Trailing Arm Independent Front Suspension
      7. Sliding Types Suspension System
      8. Vertical Guide Suspension System
    3. Rear End Suspension System
    4. Longitudinal and Transverse Leaf Spring Rear End Suspension
    5. Coil spring rear end suspension
    6. De Dion Tube
    7. Independent Type Coil Spring Rear End Suspensions

Front End Suspensions The Front End Suspensions May Be of Two Types

  1. Rigid axle front suspension.
  2. Independent front suspension

 

  1. Rigid Axle Front Suspension

This type of suspension was used throughout the world, due to its simple design before the introduction of independent front wheel suspension. It may use either two longitudinal leaf springs or a transverse spring, usually in conjunction with shock absorbers. These assemblies are mounted similar to rear leaf spring suspensions. The spring assembly consists of several curved metal strips, stacked on each other and clamped together and is in turn attached to the front axle by �U� bolts.

  1. Independent Front Suspension

In this type of suspension, each front wheel is independently and separately supported by a coil, torsion bar, or leaf spring. Most of the commercial passenger cars today, use the independent front suspension and the coil spring system is the most common type used. Types of Independent Front Suspension

  1. Twin I-Beam Suspension System

This type of suspension is used for front-drive axles in four-wheel-driveFordF-Series�trucks and�sport utility vehicles. Each front wheel is supported at the end by a separate I beam and hence provides a greater deal of flexibility. Pivots are used to attach the ends of the I-beams to the frame. Radius-arms are used to attach the wheel ends of the two I-beams to the frame. This helps prevent backward motion of the forward movement of the wheels.

  1. Single I-Beam Front Suspension System

The Single I-beam Front Suspension System is different from the Twin I-beam Suspension System in that, in Single I-beam Front Suspension System, the I-beam has a hole in each end through which a kingpin is assembled to hold the steering knuckle in place. Each end of the I-beam is supported by a leaf spring. This kind of suspension is used in larger vehicles. 3. Independent Front End Suspension Using Torsion Bar Independent torsion bar suspension takes effect on each wheel rather than the entire axle. One end of the torsion bar is firmly attached to the chassis, while the other end is attached to the respective wheel axle, which can move freely. The suspension helps absorb shock by causing the lower arm to twist the torsion bar. The arm returns to normal when the wheels are no longer under stress.

  1. Parallelogram Type Independent Front Suspension

The upper arm, lower arm, and stub axle are connected in the shape of a parallelogram. It consists of an upper arm/link and lower arm/link which attaches to, and are connected by the stub axle carrier or steering knuckle. The lower arm is generally larger than the upper arm and they may not be parallel. This arrangement maintains the track width as the wheels rise and fall and so minimizes tire wear caused by the wheel scrubbing sideways.

  1. Strut and Link Type Suspension System / Mac Pherson System

In this type of suspension system, the loading points are widely spaced. The normal top link is replaced by a flexible mounting, and the telescopic damper acts as the kingpin. That is, it uses the top of a telescopic damper as the upper steering pivot. It has a slight rolling action and absorbs shocks easily.

  1. Trailing Arm Independent Front Suspension

A�trailing-arm suspension, also known as�trailing-link�is a�vehicle suspension�design in which one or more arms or links are connected between the�axle�and a pivot point which is located on the�chassis�of the vehicle. It is typically used on the rear axle of a motor vehicle. This kind of suspension maintains a constant track and wheel attitude with a slight change in wheelbase and caster angle. A coil spring is attached to the trailing arm which itself is attached to the shaft carrying the wheel hub. When the wheel moves up and down, it winds and unwinds the spring. A torsion bar has also been used in certain designs in place of the coil springs.

  1. Sliding Types Suspension System

A sliding pillar�suspension is a type of�independent front suspension�for light cars. The�stub axle�and wheel assembly are attached to a vertical pillar or�kingpin. The stub axle can move up and down as well as rotate in the frame members. Track, wheel attitude, and wheelbase remain unchanged throughout the rise and fall of the wheel.

  1. Vertical Guide Suspension System

In the vertical guide suspension system, the kingpin is attached directly to the cross member of the frame. It can slide up and down, thus compressing and expanding the springs. The track wheelbase and wheel attitude remain unchanged, but the system has decreased stability.

  1. Coil Spring Front Suspension

There are 3 types of coil spring front suspension. In the first type, the coil spring is located between the upper and lower control arms. The lower control arm has one point of attachment to the car frame. In the second type, the coil spring is located between the upper and lower control arms. The lower control arms have two points to the attachment to the car frame. In the third type, the coil spring is between the upper control arm and spring tower or housing that is part of front-end sheet metal work.

  1. Rear End Suspension System
    1. Longitudinal and Transverse Leaf Spring Rear End Suspension

Longitudinal leaf spring and coil spring rear end suspensions are widely used in modern vehicles. Transverse leaf spring rear end suspension is used in conjunction with the Hotchkiss drive, the leaf springs must be made strong and resilient enough to transmit the driving thrust and torque to resist sideways, in addition, to hold the spring weight of the body. The spring weight is kept as less as possible, in order to improve the side of the vehicle. Because the springs do not generally support the wheels, rims, tires, brakes, and rear axles, the weight of these parts is called the spring weight. The spring is clamped to the rear-axle housing by U-bolts, its every end is pivoted to the frame, by means of eyes formed in the ends of the longest leaf. One end of the longleaf is secured to the front hanger by a bolt and the other end to the rear hanger by spring shackles. Both the hangers are bolted to the frame. The spring elongates in compression and shortens in expansion. This change in length of the spring is compensated by a shackle. At the middle position of the spring length, the rebound clips are placed. They are loose enough to permit the leaves to slide on the other and tight enough to permit the leaves together when the spring rebounds. The spring eyes are usually provided with bushings or some anti-friction material, such as bronze or rubber.

  1. Coil Spring Rear End Suspension

The typical rear coil spring suspension uses two lower control arms to control the wheelbase, and one or more upper control arms to control side motion and axle rotation. This type of suspension is often found in rear-wheel drive vehicles and is always used in conjunction with torque tube, torque reaction link, or torque rod drive. Therefore the coil springs are not subjected to driving thrust or twist. Stabilizers and radius rods are also used which relieve the coil springs of all stresses except those acting in a vertical direction. The stabilizer prevents excessive roll or sideways when the car is concerning. The radius rod keeps the rear axle and frame in lateral alignment. The coil springs are seated in pan-shaped brackets with spring seats attached to the rear axle.

  1. De-Dion Tube

The rigid De-Dion tube is located longitudinally by two parallel links and laterally by a watt linkage. It uses a universal joint at both the wheel hubs and differential�and uses a solid tubular beam to hold the opposite wheels in parallel. The tube maintains the track at a constant width. It is a beam axle suspension, according to the suspension geometry, and is not directly connected to the chassis�nor is it intended to flex. De-Dion suspension is not an independent suspension because a tubular axle connects and supports both wheels. It plays no part in transmitting power to the drive wheels, it is sometimes called a "dead axle". (Reference: https://en.wikipedia.org/wiki/De_Dion_tube )

  1. Independent Type Coil Spring Rear End Suspensions

A rear-end suspension using the radius arm is an example of Independent Type Coil Spring Rear End Suspensions In traverse leaf spring rear end suspension, a single transverse spring is used. Such springs are mounted in an inverted position parallel to and above the rear axle and each end is shaken to the axle. The transverse rear springs are always used in combination with torque-tube drive, and hence they do not carry the driving thrust and torque. DEPENDENT, INDEPENDENT, AND SEMI-INDEPENDENT SUSPENSIONS Suspension systems can be broadly classified into two subgroups: dependent and independent. These groups are made based on the criteria of to what degree the opposite wheels of a vehicle can move independently of each other. A�dependent suspension holds wheels parallel to each other and perpendicular to the axle through a�beam�(a simple 'cart' axle) or a (driven)�live axle. It has a solid axle that goes across the width of the frame. The opposite wheels are dependent on each other, that is, they work as a single team. The change in direction of one of the wheels affects the opposite wheel simultaneously. This makes a dependent suspension ideal for vehicles on rough terrain with harsh topography and is the primary type of suspension used in rear-wheel-drive automobiles, and�SUVs. Independent suspension allows each wheel to move on its own without affecting the position of the opposite wheel. Any jarring is contained to one side or wheel. There are different types of independent suspension systems�in modern cars like MacPherson strut/Chapman strut, Upper and lower�A-arm�(double wishbone), Multi-link suspension, etc. Semi-dependent suspension is another type of suspension. In this case, the motion of one wheel does affect the position of the other, but they are not rigidly attached. The twist-beam�rear suspension is an example of a semi-dependent suspension system. In semi-independent suspensions, the wheels of an axle can move relative to one another, as in an independent suspension, but the position of one wheel affects the position and attitude of the other wheel. This effect is achieved through the twisting or deflecting of suspension parts under load.   PASSIVE, SEMI-ACTIVE, ACTIVE, and INTERCONNECTED SUSPENSIONS

  1. Passive Suspensions

Traditional springs and dampers are referred to as passive suspensions. The passive suspension system is the most commonly used type of suspension system, to control the dynamics of a vehicle�s vertical motion as well as spinning (pitch) and tilting (roll). The term �Passive� indicates that the suspension elements cannot provide energy to the suspension system. The passive suspension system limits the motion of the body and wheel by limiting their relative velocities to a rate that gives the required ride comfort.� This is achieved by using some type of damping element placed between the body and the wheels of the vehicle, such as a hydraulic shock absorber. Leaf spring, Torsion bar suspension, and Coil spring are examples of passive suspension systems. 2. Semi-Active Suspensions Semi-active systems only change the viscous damping coefficient of the shock absorber and do not add energy to the suspension system. They require less energy to function and are less expensive. Among semi-active control devices, magneto-rheological (MR) dampers are particularly interesting because of the high damping force they can produce with low power requirements (being possible to operate with batteries), simple mechanical design, and low production costs. Semi-active suspensions include devices, such as air springs�and switchable shock absorbers, various�self-leveling solutions, as well as systems, like hydropneumatic, hydrolastic, and hydra gas suspensions. 3. Active Suspensions An active suspension uses an onboard system to control the vertical movement of the vehicle's wheels relative to the chassis or vehicle body rather than the passive suspension provided by large springs where the movement is determined entirely by the road surface. Active suspensions are divided into two classes: real active suspensions, and adaptive or semi-active suspensions. While adaptive suspensions only vary shock absorber�firmness to match changing road or dynamic conditions, active suspensions use some type of�actuator�to raise and lower the chassis independently at each wheel. These technologies allow car manufacturers to achieve a greater degree of�ride quality�and�car handling�by keeping the tires perpendicular to the road in corners, allowing better�traction�and control. An onboard computer detects body movement from sensors throughout the vehicle and, using that data, controls the action of the active and semi-active suspensions. The system virtually eliminates�body roll�and pitch variation in many driving situations including�cornering,�accelerating, and�braking. Interconnected suspension, unlike semi-active/active suspensions, could easily passively decouple different vehicle vibration modes. They provide greater freedom to specify independently bounce, pitch, roll, and warp dynamics than conventional (passive) suspension arrangements. Interconnections can be realized by various means, such as mechanical, hydraulic, and pneumatic. Anti-roll bars are one of the typical examples of mechanical interconnections, while it has been stated, that fluidic interconnections offer greater potential and flexibility in improving both the stiffness and damping properties. OTHER COMMON TYPES OF SUSPENSION SYSTEMS

  1. Live axle with a Watt�s link
  1. Swing axle
  1. Double wishbone suspension

 

  1. Live axle with a Watt�s link

A live axle�is a type of beam axle in which the shaft also transmits power to the wheels. It houses the vehicle's differential inside the�axle casing�itself and is connected to the wheels by rigid half-shafts. The entire�axle�moves as one, so if a left wheel drops into a pothole, the right wheel moves upward in response. The differential being the center point of the�axle, the drive shafts protrude from either side and drive each wheel. In a Watt's linkage, also known as the�parallel linkage, the central moving point of the linkage is constrained to travel on a nearly straight line. It allows the axle of a vehicle to travel vertically while preventing sideways motion. It is a good compromise between the toughness of a solid axle and the ultimate dynamics of independent suspension.

  1. Swing axle

A�swing axle�is an independent (rear wheel) suspension.� Some automobile rear swing axles have�universal joints�connecting the�driveshafts�to the�differential, which is attached to the�chassis. Swing axles do not have universal joints at the wheels as the wheels are always perpendicular to the drive shafts. Thus, the design is not suitable for a car's front wheels, which require steering motion. Swing axle suspensions conventionally used�leaf springs�and�shock absorbers. It was also used in aircrafts before the 1910s.

  1. Double wishbone suspension

In automobiles, a double-wishbone suspension is an�independentsuspension�design using two wishbone-shaped arms (sometimes parallel) 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 careful control of the motion of the wheel throughout suspension travel, controlling parameters such as�camber angle,�caster angle,�toe�pattern,�roll center height, and�scrub radius. The more the double-wishbone suspension is compressed, the more negative camber is introduced, due to the use of unequal-length control arms. A double-wishbone suspension system maintains a better tire contact patch with the road.   (References: http://iosrjournals.org/iosr-jmce/papers/vol13-issue4/Version-1/A1304010106.pdf https://en.wikipedia.org/wiki/Car_suspension https://www.researchgate.net/publication/245391162_Interconnected_vehicle_suspension https://www.theengineerspost.com/types-of-suspension-system/ https://www.carsguide.com.au/car-advice/whats-a-watts-linkage-34480 https://en.wikipedia.org/wiki/Swing_axle )        

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