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INNOVATIONS IN SUSPENSION
SYSTEMS
Suhas.Rao.Shyam.K
Need of a Suspension
• Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels.
• Serve a dual purpose – contributing to the car's handling and passenger comfort.
• Protects the vehicle itself and any cargo or luggage from damage and wear.
Functions of a Suspension System
• Maintains correct vehicle ride height. • Reduces the effect of shock forces.• Maintains correct wheel alignment.• Supports vehicle weight.• Keeps the tyres in contact with the road.• Controls the vehicle's direction of travel.• Provides comfort by damping all external forces.
Requirements of a Suspension System
• Minimum deflection consistent with required stability.• It should be of low initial cost.• It should be of minimum weight.• It should have low maintenance and low operating cost.• Minimum and even tyre wear.
Types of suspension systems
Semi-dependentsuspension
Independent suspension
Dependent suspension
Outline
• Normal Terrain suspensions.• Uneven Terrain suspensions.• Applications.• Conclusion.
Normal Terrain Suspension systems: 1. Coil Spring: Coil springs often find its application with independent suspension. Coil springs are superior to leaf springs as far as the energy storage is concerned. 2. Leaf Spring: Internal friction provides damping. Prone to weaken over time.
Normal Terrain Suspension systems: 3. Telescopic shock absorber: When the relative motion between the automobile frame and the driving axle occurs due to vibration, the oil flows from one cavity to another cavity, due to which the friction between the hole walls and the oil forms the damping force thus effectively restricting the movement of external forces.
4. Torsion bar: One end is attached to the frame and the other to the lower control arm. The bar resists twisting action and acts like a conventional spring.
Normal Terrain Suspension systems: 5. Hydrolastic Suspension: In this system a displacer unit is connected at each of the four wheels. In the displacer unit rubber is used as a spring where as fluid is used as damping medium. All the displacer units are interconnected. When the piston moves up due to the movement of the wheel, the fluid flows up through the damper valve. The fluid under pressure above the valve compresses the rubber thereby effectively damping the force.
6. Hydragas Suspension: With Hydragas, the rubber spring is removed completely. The fluid still exists but above the fluid but now there is a separating membrane or diaphragm, and above that is a cylinder or sphere which is charged with nitrogen gas. The nitrogen section is what has become the spring and damping unit whilst the fluid is still free to run from the front to the rear units and back.
Normal Terrain Suspension systems: 7. Solid Axle Beam: Just as it sounds, in the beam axle setupboth of the rear wheels are connected to each other by a solid axle.New developments in springs, roll bars, and shocks have kept the solid axle practical for some applications. They are nearly universally used in heavy-duty trucks and most light and mediumduty pickup trucks, SUVs, and vans also use a beam axle, at least inthe rear. Beam axles have an important advantage for off-road applications
8. Trailing Link Suspension: This suspension design uses a set of arms located ahead of the wheels to support the unsprung mass. In essence the wheel “trails” the suspension links. Hence the name. This is an older system not used so much any more because of the space it takes up.
Normal Terrain Suspension systems: 9. Wishbone Suspension: This is commonly referred to as a “double wishbone” suspension as the A shaped control arms resemble a wishbone. The spring is placed between the lower wishbone and the underside of the cross-member. The vehicle weight is transmitted from the body and the cross-member to the coil spring through which it goes to the lower wishbone member. A shock absorber is placed inside the coil spring and is attached to the cross-member and to lower wishbone member.
Normal Terrain Suspension systems: 10. Macpherson Strut: This strut based system, where the spring/shock directly connects the steering knuckle to the chassis and acts as a link in the suspension, offers a simple and compact suspension package. Today most small cars will use this type of suspension because it is cheap, has good ride qualities, and has the compact dimensions necessary for front wheel drive cars.
Normal Terrain Suspension systems: 11. Air Suspension: Air Suspension is a type of vehicle suspension powered by an electric or engine driven air pump or compressor. This compressor pumps the air into a flexible bellows, usually made from textile-reinforced rubber. This in turn inflates the bellows, and raises the chassis from the axle.
12. Magnetic Suspension: Magnetic ride control uses a system known as magneto rheological technology for suspension damping. Each absorber is filled with a polymer liquid containing many small magnetic particles. An electric charge is sent to the liquid in the absorber hence solidifying the polymer mixture resulting in constriction of movement of the oil through orifices.
Normal Terrain Suspension systems: 13. Bose Suspension: The Bose suspension system includes a linear electromagnetic motor and power amplifier at each wheel, and a set of control algorithms. When electrical power is applied to the coils in the motor, the motor retracts and extends, creating motion between the wheel & car body. The power amplifier delivers electrical power to the motor in response to signals from the control algorithms. The Bose suspension demonstrates the ability to combine in one automobile a much smoother ride than any luxury sedan and less roll and pitch than any sports car.
Normal Terrain Suspension systems: 14. Active Body control: In the ABC system, a computer detects body movement from sensors located throughout the vehicle, and controls the action of the active suspension with the use of hydraulic servo mechanisms. Almost instantaneously, the servo regulated suspension generates counter forces to body lean, dive and squat during various driving manoeuvres.
Normal Terrain Suspension systems: 15. Hydraulic Roll control: The DRC system (known as Dynamic Ride Control - DRC - by Audi) is a pure mechanical damping system which monitors road conditions and cornering forces, and adjusts the suspension accordingly. Both shock absorbers on the same side of the vehicle are connected with the diagonally opposed dampers on the other side, each by means of one central valve. By connecting diagonally opposed shock absorbers vehicle pitching and diagonal chassis movements are minimised. The result is that the car is more stable at high speeds, as well as offering greater ride comfort at any speed. Other advantages include: better handling, less tyre wear, lower maintenance costs, preventing any tendency for over-steer and improved cornering ability.
Uneven Terrain Suspension systems: 1. Radius Arm Setup: The radius arm design uses two arms that run parallel to the frame. They mount to a perch on the frame and solidly to the axle housing and allow the axle to pivot up and down. A track bar runs from the frame to the axle perpendicular to the radius arms to keep the axle centred on the frame.
2. Parallel and Triangulated Four Link: Instead of a radius arm with a fixed mount on the axle, it uses an upper and lower link on each side with pivots on both ends. As the axle cycles up and down, the links allow it to maintain the same relationship with the ground and the caster angle remains constant. Another four link design is the triangulated four link. The parallel four link needs a track bar to locate the axle side to side. With a triangulated four link design, if the links are mounted at great enough angles, a track bar is not needed. The greater the angles, the more the links will resist side to side movement.
Uneven Terrain Suspension systems: 3. Ford Twin Traction Beam: Ford has an independent suspension design that is part solid axle and part independent suspension – the Ford Twin Traction Beam or TTB. The TTB is similar to a solid axle except the drive axles and housing pivot in the centre. The two wheel drive version is called the twin I-beam. It may look strange but TTB is very strong due to the length of the beams. It spreads the stresses out and has a much better shock ratio than A-arms.
Uneven Terrain Suspension systems: 4. Rocker-Bogie Suspension: The rocker-bogie design has no springs or stub axles for each wheel, allowing the rover to climb over obstacles, such as rocks, that are up to twice the wheel's diameter in size while keeping all six wheels on the ground. As with any suspension system, the tilt stability is limited by the height of the centre of gravity. . Based on the centre of mass, the system can withstand a tilt of at least 45 degrees in any direction without overturning. The system is designed to be used at slow speed of around 4cms per second (3.9 in/s) so as to minimize dynamic shocks and consequential damage to the vehicle when surmounting sizable obstacles. During each wheel's traversal of the obstacle, forward progress of the vehicle is slowed or completely halted. This is not an issue for the operational speeds at which these vehicles have been operated to date.
4. Rocker-Bogie Suspension: In order to go over a vertical obstacle face, the front wheels are forced against the obstacle by the center and rear wheels. The rotation of the front wheel then lifts the front of the vehicle up and over the obstacle. The middle wheel is then pressed against the obstacle by the rear wheels and pulled against the obstacle by the front until it is lifted up and over. Finally, the rear wheel is pulled over the obstacle by the front two wheels. During each wheel's traversal of the obstacle, forward progress of the vehicle is slowed or completely halted. This is not an issue for the operational speeds at which these vehicles have been operated to date.
4. Rocker-bogie suspension: Operating mechanisms. 1) Differential Gearbox: Two gears connect to the two rockers and the third (middle) gear connects to the body.
2) Differential Bar: The middle of the bar is connected to the body with a pivot and the two ends are connected to the two rockers through some short links.
Uneven terrain suspension systems: 5. Multilink Suspension: The multi-link rear suspension is an innovative construction. Three transverse links and one longitudinal link per wheel (four-link principle) each absorb different forces. This means that longitudinal and transverse dynamics can be configured precisely and almost independently of each other, achieving maximum directional stability and comfort. Only small modifications need to be made to the structure of the multi-link rear suspension for it to be suitable for use on front-wheel drive models as well as four-wheel drive cars. The links are configured to ensure that the camber angle of the wheel remains unchanged during suspension movement. ‘Toe’ and ‘caster’ dimensions are also controlled by the links.
Applications of linear motion bogie: 1) Adapting to terrain parameters, there are different possibilities for rover suspension like LBS. Spring and damper application to double lambda suspension good solution for high-speed off-road vehicles
Applications of linear motion bogie: 2) The possibility to implement Rocker-Bogie suspension in Front Loading Vehicles: The main problem associated with current suspension systems installed in heavy loading vehicles rovers (including those with active and semi active suspension systems) is their slow speed of motion which derail the rhythm to absorb the shocks generated by wheels which remain the result of two factors. First, in order to pass over obstacles the vehicle must be geared down significantly to allow for enough torque to raise the mass of the vehicle. Consequently, this reduces overall speed which cannot be tolerated in the case of heavy loading vehicles. Second, if the vehicle is travelling at a high speed and encounters an obstacle (height greater than 10 percent of wheel radius), there will be a large shock transmitted through the chassis which could damage the suspension or topple down the entire vehicle. That is why current heavy loading vehicles travel at a velocity of 10cm/s through uneven terrain.
Applications of linear motion bogie:
3) As an amphibious vehicle: Design of mechanical system on land that contains the features of water vehicle. The wheel should be retracted to enhance the stability of vehicle while it in water mode. Retractable wheels are designed to increase vehicle speed when manoeuvring on the water's surface. If the wheels are deployed, the water flow under the surface of the vehicle will be blocked and distracted by the wheel. The wheel will disturb the water flow path causing a high pressure before the wheel and low pressure after it. In a post- disaster relief, the road surfaces become uneven and rough. It will disrupt the mobile stability and movement. The intelligently designed wheel suspension allows the vehicle to traverse over very uneven or rough terrain and even climb over obstacles.
Conclusion: This article covers the suspension trends in the modern world. It can be seen that Independent suspensions have been given primarily more importance than any other suspension system. This is because of the high degree of comfort provided by the independent motion of the wheels when passing over an obstacle. But Bose suspension has proven itself as a winner in both fields of comfort and performance. But when it comes to off-road vehicles the good old solid axle and Twin I beam has been preferred over other types. The motive of this study is to understand mechanical design and the advantages of Linear Bogie system in order to find suitability to implement it in conventional loading vehicles to enhance their efficiency and also to cut down the maintenance related expenses of conventional suspension systems.
