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This suspension system will fulfil their task by allow the forces to be distributed when the wheels are rotating on the ground, complying with design specification in every load state. Also we have the geometric variation of the body position from the trim which is caused by the static and quasi static forces, these three coordinates of the centre of gravity and three angles of the body reference system which is yaw, pitch and angle. These three angles are included under the vehicle static. The main work of suspension is to absorb the shocks and irregularities that are transferred to the body, this is accomplished by the damping systems.
Normally it is possible that the tyre alone can isolate the shocks that are coming from the road, but this can only be accomplished when the vehicle is driven at a smooth road and at very low speed. Because tyres damping properties are not good enough to handle the road shocks, that is why we have suspension system, this allows the wheels to rotate freely, very safe and comfortable for driving.
The basic different types of suspension systems are available today. These are semi Independent, dependant and independent suspension (Genta & Morello, 2009, p. 153).
Front Wheel Drive Diagram
According to May, 2005, p. 470 state that, when we speak about suspension we have to include the terms sprung and unsprung weight. Sprung mass indicates as the weight of the vehicle that is supported by the springs including the frame, body and everything attached to them including the parts of the suspension and unsprung mass refers as the weight of the suspension components such as the wheels, tyres and brakes on which the springs rest, or all the parts of the suspension that are not supported by the springs
The independent suspension
As the name suggest the wheels in this system are attached independently, and this helps to reduce the impact that is transferred to the other wheel when the vehicle travels through road irregularities. This system involves McPherson strut, double wishbone and multilink.
The strut contains shock absorber and spring is located by a ball joint, which is built in to the end of the suspension arm while the rubber mounting is moulded at the other end. This is one of the few reasons that make the suspension parts of this system work freely and it makes this by far the most common type of suspension in the market today.
(3D auto.com, 2006).
The negative part is it is required more solid chassis or sub frame structure, the slight change in wheel track causes the tyre to scrub during the bouncing of one wheel and the alignment of the steering geometry is critical and needs more attention (Crankshaft).
Independent suspension system
This system usually connects the two wheels that are paralleled to each other on the same rigid straight and perpendicular axle, because all mechanical linkage work together, this can affect the movement of the other wheel when the vehicle road shocks or irregularities occur. Due to its ruggedness, this system is mostly often used on heavy truck, SUVs and rear wheel drive cars (Blue Ribbon Motoring LLC, 2010).
Dependent suspension system
Semi independent suspensions:
This systems utilizes a cross member that joins the two trailing arms. Regardless of the solid connection with the cross member and the trailing arms, the cross member will always twist with each up and down movement of the wheels. This twisting activity will give semi independent movement as well as stabilizer effect. The purpose of this suspension is to limit the body displacement to a minimum. This helps to increase the vehicle stability.
Suspensions system can also be classified as passive or active.
Passive suspension system involves shock absorber and spring. These two elements are passive because they cannot add energy to this type of suspension system and passive suspension is the one that receives the energy from sources like engine which affects the body motion. This limits the motion close to its static equilibrium (Genta & Morello, 2009, p.358).
The following diagrams are examples of passive and active suspension:
Passive suspension system
Active suspension system
These are basically heavy wound steel wire used to support the weight of the vehicle as well as to absorb energy from road shocks or vibration between the road and the vehicle body. Springs usually located between control arms and chassis or around McPherson strut. They can be conical or spiral wound, constant rate or uneven rate, changeable pitch spacing and variable wire thickness. Coil springs can be customised and also be used in different variations and arrangement in the suspension system (Ciulla, 2002).
When the vehicle travels through road shocks, the energy is given to the spring that is deflected, the spring creates an oscillating motion that results affects the handling and comfortability of the car. To stop this, damping members (shock absorbers) are installed. They are designed to store this oscillation energy and let the spring to return to its natural state. Few different types of shock absorbers are available today. These are hydraulic, lever type and telescopic direct acting type (Hillier, 1991, p. 364)
This type of spring is mainly used in the heavy and commercial vehicles. It is made up of one or more flat leaves or bent toughened steel or plates of composite material that are attached at the ends to the vehicle under body. It connects the vehicle frame to the axle by using the U bolt that secures the metal plates that rest against the leaf springs. The U bolt also keeps the spring level against the axle, this helps to stop the vehicle from shaking under the load when driving.
It has a hook end that makes it flexible when the road shocks and vibration occur. The leaf spring shape allows them to flex and absorb bumps. This type of spring is very reliable and strong in carrying heavy loads, they also help in spreading the load on all over the chassis while the coil spring just transmit it to a single point (Spring-makers-resource.net).
These are usually metal bars which act as a spring and can also be moved about its axis through twisting. The main job is to resist the torque placed on the vehicle by twist it along its axis. This torque is created by the force when the vehicle is moving, once the torque has been counteracted, it normally returns to its natural state. This provides the resistance level to the forces that are generated by the movement of the vehicle.
The major disadvantage of the torsion bar is it cannot provide the progressive spring rate while the progressive torsion bars have a tendency to crack when the diameter of the bar changes (CDX Online eTextbook).
Anti roll bar/Sway bar/Stabiliser:
This is fitted underneath the front and rear of the vehicle, connected at the lower control arm. They operate together with shock absorbers/struts to provide the vehicle with at most stability as well as body roll and improve cornering traction. When the wheels move at different angles from the other, an anti sway bar helps it in maintaining the balance and stability in case of a bad movement or a sway of the vehicle. It can also help in reducing over steer or under steer when the correct anti roll bars are chosen. They are fitted tightly and tend to give a bumpy ride as it transfers force direct to the other wheel. The tighter it is the safer the vehicle is from rolling (Turnfast.com, 2008).
The air spring is designed to provide a vibration free and a smooth ride with a preset constant frame height. It also helps to reduce the spring oscillation so that the steering control is not compromised. It can work as a mechanical leaf type spring or used with them. The air spring system helps to reduce the road shock transfer to the chassis, cargo and the driver. In addition to that it can be easily adjusted according to the load and road conditions by using a height control valve. Other major components used in this system are pressure regulator, air lines and air springs.
Zero stability to dampen suspension oscillation is the main disadvantage of this system and shock absorber is used to overcome this (Bennet, 2007, p. 268).
These are the linkage between the vehicle, springs, struts and shock absorbers. They tend to provide the movement point of the vehicle as well as avoiding metal to metal contact between the body and the suspension links. They are designed to be soft enough to maintain the alignments settings that help in maintaining steering control and allow the adequate rotational movement. Bushes are usually fitted where ever there is a metal to metal contact. However, the main disadvantage is, it is wearing out after some time and thus need to be replaced and it can be expensive and hard job depends on the types of bushes or where they are going to be fitted (Autolign).
Common locations of vehicle bushes.
The main job for the ball joint is to enable the suspension to move on any angle or rotating the coupling that is usually the interface between knuckle and a control arm in a vehicle suspension. It performs as the pivot point between the suspension and the tyre and this helps in improving the performance (TRW Automotive, 2010).
This is normally connects the body chassis to the suspension of the vehicle.
COMMON SUSPENSION SYSTEM TYPES:
This normally connected at the front of the chassis, it allows the rear to move up and down. Two of these become double trailing systems arm and usually work precisely the same as the double wishbone. The arms of this system can be seen from the side of the chassis, travel back equivalent to it. However it takes a lot of room underneath but it doesnââ‚¬â„¢t experience the side to side scrubbing setback as the double wishbone systems (Longhurst, 2010).
Trailing arm car suspension
This type of suspension is the further development of double wishbone, the higher transverse link is replaced by a pivot point on the wheel house panel, that takes the end of the piston road and the coil spring, this create the forces from all directions to be concentrated at this point and this causes a bending stress in the piston road. When this happens, a normal rod diameter in shock absorber must be increased by at least 18mm from 11 mm, this will avoid the detrimental elastic camber and camber exchanges. The parts of this system are usually combined into one assembly while its negative point is it takes a lot of room underneath the car (Reimpell, Stoll & Betzler, 2001, p. 10).
This is an independently system, usually the wheel is directed by a pair of triangulated wishbones and track road. The lower wishbone is connected to the strut and this offers the vertical support. The sporty set up design of this system is due to its generous through loading width and a low height. This has a beneficial effect on for motion drive, the transmission of high active forces and road-holding. It also provides camber control that gives a better handling. The negative point is it can engage a space and expensive to design (Volkswagen Canada, 2010)
This is originated from the double wishbone, the suspension links use more than three lateral arms and more than one longitudinal arms, and these can be in various length and the angle can be away from their natural directions. The arms are normally connected by spherical joint or bushing at each end and this stopping them from bending, it also allows them to work in tension and compression. The pivots in this suspension are designed to allow the spindle to turn for the steering and change the geometry of the suspension by provide torque in all suspension arms. Different car manufactures have different designs. The main positive aspect is this system lets the vehicle to flex more, better handling because of the multi links while the negative part is it is more expensive to design and manufacture due to its complexity (Raiciu, 2009)
Transverse leaf spring:
This system was used during the old days, it involves leaf spring and independent double wishbone together. The leaf spring is connected at each end of the lower wishbone and is mounted across the vehicle. A sub frame in the middle of the car is connected by the centre of the spring and each of the shock absorbers is mounted at each side of the lower wishbones (Longhurst, 2010)
Transverse leaf spring suspension
Solid-axle: leaf spring
This provides an easy way of placing and mounting the hub and wheel units. Along with coil or leaf springs can create an effective non independent suspension system. The drive is transferred through the final drive unit and axles to the wheels, and this situation causes the axle to become a live axle. The torque reaction which is caused by a vehicle when it accelerates, causing a housing of the axle to spin in the opposite of the wheel rotation. During braking, a similar result can occur but with the twisting result in the way of wheel rotation. This can cause the twisting of the leaf spring and this can result in obstructing with the suspension motion ((CDX Online eTextbook).
Transverse leaf spring suspension
Solid-axle: coil spring
This system has replaced leaf springs because they are lighter and have less unsprung weight that provides a comfortable ride but they cannot hold the axle in line. It is mainly used in the rear wheel drive vehicles. It is normally comes with one or more control arms and two lower control arms that manage the side movement and axle motion. The track bar may be needed when one upper arm is used, this connects the vehicle from one end to the other end. In reducing the vibration, rubber bushing can be used as the suspension travels through road irregularities. The track bar is not required when two upper arms are used (Monroe technology driven safety, 2008)
The rear coil spring suspension is a variation of the rear leaf spring suspension often found in rear-
Solid axle coil spring suspension diagram
In this suspension the pair of front two wheels are connected to each other using a solid axle. This results in no camber loss from body roll because the wheels are always perpendicular to the road. It is also very simple structure since it doesnââ‚¬â„¢t contain many parts, it is very strong and can be very useful in carrying bigger loads. The disadvantages of this suspension is, it is too big thus gives a lot of mass and takes a lot of space, since it is a dependent suspension the force from one wheel can be transmitted to the other wheel and this can result in an uncomfortable ride and reducing the vehicle stability in cornering (Lowry, 2004)
This was originally invented by Citroen. The system compresses a gas rather than a fluid. The hydraulic fluid normally provide levelling and damping while the gas becomes a spring. Sometime this system can be driven using an engine driven pump that causes the hydraulic system to be pressurised and this assists it in levelling on the different height, jack assisting and stop the body roll. Fully powered braking system and power steering can also be available. The rear and front unit contains hydrolastic displacers, a small bore pipe is used to interconnect these displacers, and each displacer incorporates a rubber spring. The pipes, rubber, and fluid that are featured in this system always act as a damping system. The rubber springs are to keep the car level and freed from any tendency pitch. It can perform this without hinder the complete range of activity on any suspension and this provides the soft ride. The negative points are, it can be expensive to fix or replace it and sometime it does require a very well trained person to deal with (Marsh, 2001).
This type of suspension is commonly used in Audi A4. It contains aluminium materials that are used to reduce an unsprung weight to the minimum. The differential in this system is moved to the front and the clutch to the rear, and the front axle has been repositioned 154 mm farther forward. Optimisation of axle-load distribution is achieved by relocating the car battery in the boot. By having additional differential at the rear, weight distribution is even better balanced. These vehicles will be more responsive and will take less effort to guide and position, resulting in better handling and very low under steer and gives good traction when cornering
(Audi AG, 2007)
ELECTRONIC AND ACTIVE SUSPENSIONS
This type of suspension is operated by the computer, which collects the data from different sensors such as how fast the vehicle is turning, speed of the wheels rotation, pitch, roll and height information. A simple system only involves maintaining the height level of the vehicle whereas, the four wheel height adjustment system can improves ground clearance when off road and minimises aerodynamic drag and economical fuel consumption.
Suspension systems that are electronically controlled tend to be more expensive and are usually found in high performance and luxury cars.
Active suspension systems are the most recent developments that involve microprocessing. This varies the orifice size of the restrictor valve in a hydraulic suspension or shock absorber which causes the effective spring rate to change, lateral force, load, acceleration, or a driver preference vehicle speed can be control inputs for the processor (
Electromagnetic suspension that combines a passive spring with a brushless tubular permanent magnet actuator. During cornering and braking this system gives more safety and stability by presenting a pitch and an active roll. It can also eliminate the road shocks by due to the measurements, static and dynamic specifications of the actuator are developed. The fulfilling of the thermal and volume specifications can be completed by using a slot less external-magnet tubular actuator (http://alexandria.tue.nl/openaccess/Metis230153.pdf)
(Koji, Masaharu, Takaaaki, 2006)
INTEGRATED KINETIC TM H2 CES SYSTEM:
This system is an interconnected passive reactive system that controls damping and reducing high roll and articulation stiffness. The tyre load optimisation improves performance. This is achieved by replacing four double-acting hydraulic cylinders each with two integrated CES damper valves on antiroll bars and shock absorbers. An automatic pressure maintenance unit (APMU), and a pair of accumulators with valves and interconnected hydraulic lines. The flow is restricted by the two CES valves in each corner, this allows the better performance and good handling. In addition to that, the CES damper valves are electronically controlled by the intelligent control algorithms in order to allow the wheel motions and a body control (Tenneco).