ACTIVE SUSPENSION SYSTEM BY VIJAYKUMAR R. SACHANE

SEMINAR TOPIC

Introduction to SUSPENSION SYSTEM 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 braking.

Protects the vehicle itself and any cargo or luggage from damage and wear

In suspension systems, usually two most important features are expected to be improved – disturbance absorbing (i.e. passenger comfort) and attenuation of the disturbance transfer to the road (i.e. car handling).

WHAT IS AN ACTIVE SUSPENSION SYSTEM The Active or adaptive suspension is an

automotive technology that controls the vertical movement of the wheels with an onboard system rather than the movement being determined entirely by the road surface.

It has two main functionalities, one is to isolate the vehicle body with its passengers from external disturbance inputs which mainly come from irregular road surfaces.

The other is to maintain a firm contact between the road and the tyres to provide guidance along the track.

The basic function of the vehicle suspension is to provide comfort to passengers, maximize the friction between the tyres and the road surface and provide steering stability with good handling. In active suspension systems, it employs springs as the main form of support, however the dampers can usually be controlled. A active suspension has the ability to change the damping characteristics of the shock absorbers without any use of actuators.

SUSPENSION SYSTEM – LAY OUT

IMPORTANT PROPERTIES

Spring rate The spring rate (or suspension rate) is a component in

setting the vehicle's ride height or its location in the suspension stroke. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke).

Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the vehicle from the road.

Vehicles that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate close to the upper limit for that vehicle's weight.

DAMPING

Damping is the control of motion or oscillation, as seen with the use of hydraulic gates and valves in a vehicles shock absorber. This may also vary, intentionally or unintentionally. Like spring rate, the optimal damping for comfort may be less than for control.

ROLL CENTER HEIGHT This is important to body roll and to front to rear

roll stiffness distribution. However, the roll stiffness distribution in most cars is set more by the antiroll bars than the RCH. The height of the roll center is related to the amount of jacking forces experienced.

VIBRATION MODES OF THE SUSPENSION ELEMENTS SUSPENSION SPRINGS

Suspension Springs are the suspension system's primary line of defense.

These variables within the surface of the street or the backcountry road send force up through the wheels. . The suspension spring's task is to absorb this power and carry your wheels back to a condition of equilibrium. You will find several standard types of Suspension Springs used on contemporary vehicles: Leaf Springs, Coil Springs, Torsion Bars, and Air Springs. 

SUSPENSION BUSHINGS

Suspension Bushings connect your expensive suspension components together, serve as protective seals to connection points, and are vital to how they function.

They make a perfect connection between the different parts of your suspension system.  This results in perfect suspension alignment and drastically better handling. 

SHOCK ABSORBERS (DAMPERS)

It is a device that controls unwanted spring motion through a process known as dampering.  Shock Absorbers slow down and reduce the magnitude of vibratory motions by turning energy of suspension movement into energy that can be dissipated through hydraulics.  A Shock Absorber is placed between the frame of the car or truck and the wheels.

WORKING OF ACTIVE SUSPENSION SYSTEM

The active suspension can be arranged in series OR parallel combination with the passive suspension such as spring

The sensor is attached at the top cover to measure the motion of the suspension system. 

It uses one or more sensors that can generate sensor signals to indicate the motion.

Then it is coupled to controller having processor. It receives the signal & generates control

signals.The control signals are transmitted to amplifier

that drives active suspension element. 

Sensors And Controller

Roll on Corners

Some productions vehicles with active

Suspension

Mitsubishi Galant-  "Dynamic ECS", world’s first production semi-active electronically controlled suspension system(1987) BMW M3 - "BOGE adjustable damping" system(1989)

 Infiniti Q45 - "Full-Active Suspension (FAS)", world's first production fully active suspension system(1990)  Lexus GS-  Active Stabilizer Suspension System(2007)

DIFFERENCE BETWEEN ACTIVE & PASSIVE SUSPENSION SYSTEM

Let us consider the work of passive vibration isolation system by the example of a suspension bracket of the automobile. In any suspension bracket there are elastic elements, which soften pushes and impacts of the road. Other not less important element of a suspension bracket is the shock-absorber -- the device which is intended to terminate excited the oscillation. Many drivers think that shock-absorbers is only the means to maintain comfort. Actually functions of this element of a suspension bracket are directly connected to maintenance of contact of a wheel with road, i.e. with controllability of the automobile and traffic safety. 

First animation shows that too hard suspension system of a car results in throwing of the car on unevenness of the road, while too soft suspension system will swing the car, which results in lost of the contact between the wheels and the road.

In second animation active vibration isolation system among the spring there is feedback circuit which consists of a piezoelectric accelerometer, an analog control circuit, and an electromagnetic transducer. The spring supports the weight of the table top and the device which is mounted on the table. The motion of the table top is detected by a highly sensitive piezoelectric accelerometer consisting of a mass resting on a piezoelectric disc and covered by a housing.

MATHEMATICAL MODEL OF ACTIVE SUSPENSION SYSTEM The model can be used for determining

the adjustable arm’s angle for which the system produces a required force.

The trailing arm joins the unsprung mass (wheel unit) to the sprung mass (the car body) and provides a connection to the primary spring and damper. The adjustable arm defines the position at which the secondary spring is attached to the suspension system.

Where

For small suspension deflections, it is assumed that the point at which the secondary spring is attached to the suspension system moves along a circular trajectory Where

ADVANTAGES Improved Steering, Handling and BrakingIn a rigid suspension, if one wheel jogs or bounces, the entire axle tilts, causing the opposing wheel to tip in or out at the top, no longer rolling straight ahead, an effect called "bump steer".Rigid axles are also less responsive on turns and vehicles carrying heavy loads are subject to instability called "shimmy", caused by forces translated across the axle from wheel to wheel. During hard braking, solid beam suspension can cause the front of the vehicle to nose dive and twist. Independent front suspension (IFS) corrects or vastly improves all of these effects by allowing wheels on the same axle to respond independently to driving conditions.

Ride QualityRide quality is a concern that has evolved with our culture's increasing dependency on automobiles for recreational and commuter travel. Overall ride quality, or how comfortable a car feels to ride in or drive, is measured by a combination of factors, including noise and vibration, the translation of bumpy road surface to passengers, the smoothness of the car's steering and how well a car handles and corners.Active suspension system solves some of these problems by de-coupling the front wheels, improving overall stability and creating isolation between the suspension and the vehicle chassis.

Size and Fuel EfficiencyIt is difficult to beat a solid axle for strength and simplicity, but the price of that strength is size and mass. For heavy duty vehicles and the solid steel cruisers of the 1940s and 1950s, a rigid axle made good design sense. As passenger vehicles have gotten smaller and more performance-oriented, heavy, bulky, rigid axles are no longer practical, particularly because heavier vehicles burn more fuel. Independent front suspensions have evolved with modern car materials, creating lighter, more flexible and responsive vehicles.

DISADVANTAGES

Need for a large external power source

Complex control algorithms

Complex closed-loop control systems.

Requirement of fast-acting devices

Increased cost

In the case of active suspension system, as in any other innovations of automotive technology, today's innovation is tomorrow's standard feature. Inspite of its high initial cost, let us expect to see them in the Indian roads soon. The trickle-down effect will take some time, but it'll happen and when such a time comes we can expect much lesser accidents, less fatalities and more comfort in driving the roads.

Conclusion

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