Double Wishbone Suspension System(10bme1065)

TOPIC:DOUBLE WISHBONE SUSPENSION

BY NIKHIL GUPTA(10BME1065)

ASSIGNMENT 3

Suspension system is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. It is basically cushioned for a

passenger protects the luggage or any cargo and also itself from damage and wear.

DOUBLE WISHBONE SUSPENSION

INTRODUCTION

The main role of suspension system is as follows:1. Supports the weight of vehicle.2. Provides smoother ride for the driver and passengers

i.e. acts as cushion.3. Protects your vehicle from damage and wear.4. Plays a critical role in maintaining self-driving

conditions.5. Keeps the wheels pressed firmly to the ground for

traction. 6. Isolates the body from road shocks and vibrations

which would otherwise be transferred to the passengers and load.

ROLE OF SUSPENSION SYSTEM

Sprung mass : - Sprung mass (weight) refers to vehicle parts supported on the suspension system, such as the body, frame, engine, the internal components, passengers, and cargo. Unsprung mass :- Unsprung mass refers to the components that follow the road contours, such as wheels, tires, brake assemblies, and any part of the steering and suspension not supported by the springs.

DEFINITIONS OFSPRUNG &UNSPRUNG MASS

Principle Definition Goal Solution

Road isolation

The vehicles ability to absorb or isolate road

shocks from passengers’

compartment.

Allow the vehicles body to ride

undisturbed while travelling through

rough roads.

Absorb energy from road bumps and

dissipate it without causing undue

oscillation in the vehicle.

Road holding

The degree to which the car maintains

contact with the road surface in various

types of directional changes and in a

straight line.

Keeps the tiers in contact with the

ground because it is the

Friction between the ground and tiers are

that effects the vehicle ability to steer , accelerate

and brake.

Minimize the transfer of vehicle’s weight from side to side and from front

to back as this transfer of weight

reduces tiers grip on the ground.

Cornering

The ability of the vehicle to travel on

curved path.

Minimizes body roll which happens when

the car pushes outwards due to the

center of gravity while cornering.

Transfers the weight of the vehicle from

high side of the vehicle to the lower

side.

GOALS OF SUSPENSION SYSTEM

The variety of independent systems is greater and includes:• Sliding pillar• Swing axle• MacPherson strut/Chapman strut• Upper and lower A-arm (double wishbone)• Multi-link suspension• Semi-trailing arm suspension• Swinging arm• Leaf springs

TYPES OF SUSPENSIONS

The double-wishbone suspension, also known as an A-arm suspension, is another common type of front independent suspension.While there are several different possible configurations, this design typically uses two wishbone-shaped arms to locate the wheel. Each wishbone, which has two mounting positions to the frame and one at the wheel, bears a shock absorber and a coil spring to absorb vibrations. Double-wishbone suspensions allow for more control over the camber angle of the wheel, which describes the degree to which the wheels tilt in and out. They also help minimize roll or sway and provide for a more consistent steering feel. Because of these characteristics, the double-wishbone suspension is common on the front wheels of larger cars.

DOUBLE WISHBONE SUSPENSION SYSTEM

PARTS OF DOUBLE WISHBONE SUSPENSION

Coil springs: this is the most common type of spring and is, in essence, heavy-duty torsion bar coiled around an axis. Coil springs compress and expand to absorb the motion of the wheel. Dampers (shock absorbers): unless a damping structure is present, a car spring will extend and release the energy it absorbs from a bump at an uncontrolled rate. The spring will continue to bounce at its natural frequency until all the energy is used up. A suspension built on spring alone would make for an extremely bouncy ride and, depending on the terrain, an uncontrolled car.

Enter the shock absorber, or scrubber, a device that controls unwanted spring motion through a process known as dampening. Shock absorbers slow down and reduce the magnitude of vibratory motions by turning the kinetic energy of suspension movement into heat energy that can be dissipated through hydraulic fluid.

The dampers are basically an oil pump placed between the lower arm and the chassis frame. In a twin tube design, one of the most common types of shock absorbers, the upper mount is connected to a piston rod, which in turn is connected to a piston, which in turn sits in the tube filled with hydraulic fluid. The inner tube is known as the pressure tube, and the outer tube is known as the reserve tube. The reserve tube stores excess hydraulic fluid.

1. Camber To let the wheel bring all those forces and torque on the road it has to be kept in constant contact with the road. This means that under ideal circumstances a wheel is always perpendicular to the road. Tilting in corners or on bumps minimizes the area of the wheel in contact with the road so this is not desired. This tilting of the wheel is called camber. In an ideal situation the camber angle of the wheel is always zero degrees. In reality the camber angle changes with the up and down movement of the suspension. Also body roll affects the camber angle. Often cars have a light Positive camber angle under no load conditions to make up for the compression of the suspension and rubber bushes. When normally loaded the camber angle becomes zero. More on camber in the under steer/over steer section. This angle is one of the most important in the suspension system.

Factors affecting the suspension system

THE FOLLOWING PICTURE SHOWS THE CAMBER ANGLE

2. Caster & Kingpin Inclination (KPI) To offer enough feel to the steering and to get a self-returning action the suspension can be set up to achieve this by carefully choosing the caster angle and kingpin inclination angle. You can get a very strong self-centring effect if the tyre footprint trails the steering axes. As shown here in the wheel of a handcart and the same principle as used in our car. The angle between the steering axis and a line from wheel centre to the ground is called the caster angle. The bigger the angle the stronger the self-centring action. If the angle is negative the steering is very light and very nervous. Another way to get a selfcentring action is by creating a steering offset. (3. In the figure to the right). This can be created if the projected KPI angle doesn't align with the footprint center of the tier. The wheel forces will try to pull the center of contact patch of the front wheels forward, thus the wheel will rotate about the point of the kingpin axle projected to the ground.

The steer momentum is the product of distance 3. And the wheel force. Increasing the inclination angle will decrease the self-centering steering effect. Also notice that the steering effort here is changing with the amount of power supplied to the wheels. So for front wheel drives reducing steering effort by altering the KPI is not a very elegant solution. So why not increase the KPI so that distance 3. is zero? Well with increasing KPI also the lateral forces on the cars increase thus making it more

3. Toe-in & Toe-out Toe-in and toe-out is the angle that the wheels deviate from the driving direction. It is used because the driving force and road resistance tends to squeeze the rubbers in the suspension. By giving the car a toe-in or toe-out setting the wheels are in a straight line when driving. The rear wheels seldom have toe-in or toe-out. The front wheels of a rear wheel driven car mostly have toe-in. Toe-out is used in front wheel driven cars because the driving force tends to turn the wheel inwards. The kingpin inclination also plays a (minor) role in how much toe-in or toe-out is needed. The less kingpin inclination the more steering momentum is generated pulling the wheel inwards thus more toe-out is also needed to compensate.

TOE IN AND TOE OUT ANGLE