Car Suspensions Why important • power generated by a engine is useless if the driver can't control the car • Car suspension job : – to maximize the friction between the tires and the road surface – to provide steering stability with good handling – to ensure the comfort of the passengers

Double-wishbone suspension

Vehicle Dynamics • imperfections roads apply forces to the wheels • road bumps causes the wheel move up - down perpendicular • wheel experience vertical acceleration

Vehicle Dynamics Vehicle Dynamics • Without suspension, all wheel's vertical • study of the forces on moving car called energy is transferred to the frame “vehicle dynamics” -- 2 characteristic • the wheels lose contact with the road – Ride - ability to smooth out bumpy road • the wheels slam back into the road – Handling - ability to safely accelerate, brake and corner • Suspension will absorb the energy of the vertically accelerated wheel • described in 3 principles - road isolation, road holding and cornering Road Isolation Road Holding Definition Goal Solution Keep tires in contact Minimize the Definition Goal Solution The degree of with the ground, transfer weight maintains contact (because the friction from side to with the road between the tires side and front to Absorb energy from surface in various and the road affects back, (cause to ability to absorb or Allow vehicle body road bumps and types of directional ability to steer, reduces the isolate road to ride dissipate it without changes brake and tire's grip on the shock from the undisturbed while causing undue accelerate) road) passenger traveling over compartment rough roads. oscillation in the vehicle. Example: The weight of a car will shift from the rear tires to the front tires during braking called "dive." The opposite effect, the weight transfer from the front tires to the back during acceleration called "squat"

Cornering Suspension as part of Chassis Definition Goal Solution Minimize body roll, which Transfer weight occurs as centrifugal force during Ability to travel pushes outward on a cornering from a curved center of gravity (CG) while the high side of path cornering, raising one side the vehicle to of the vehicle and lowering the low side the opposite side

major systems in vehicle major systems in vehicle • Frame - structural, load-carrying • Steering system - mechanism that component that supports the car's enables the driver to guide and direct engine and body, which are in turn the vehicle supported by the suspension • Tires and wheels - components that • Suspension system - setup that make vehicle motion possible by way of supports weight, absorbs and dampens grip and/or friction with the road shock and helps maintain tire contact three components of any suspension: Coil Springs • springs • most common type • dampers made by heavy-duty • anti-sway bars. torsion bar coiled around an axis. Coil springs compress and expand to absorb the motion of the wheels

Leaf springs • several layers of metal bound together to act as a single unit. mostly used in trucks and heavy-duty vehicles

Torsion bars • use the twisting properties of a steel bar to provide coil-spring-like performance

• One end of a bar is anchored to the vehicle frame -- the other end to a wishbone, which acts like a lever that moves perpendicular

• When the wheel hits a bump, vertical motion is transferred to the wishbone -- then, through the levering action. Torsion bar then twists along its axis to provide the spring force Air springs • consist of a cylindrical chamber of air positioned between the wheel and the car's body • use the compressive qualities of air to absorb wheel vibrations

Springs: Sprung and Unsprung Mass • sprung mass -- mass of the vehicle • Stiffness -- how the sprung mass supported on the springs responds while car is being driven • unsprung mass -- loosely defined as • Loosely sprung cars : prone to dive and the mass between the road and the squat during braking and acceleration – suspension springs body tend to roll during cornering • Tightly sprung cars : less forgiving on bumpy roads, but minimize body motion • springs absorb energy, but not dissipating it -- require dampers

Dampers: Shock Absorbers • controls unwanted spring motion through a process known as dampening • Shock absorbers reduce magnitude of vibration by turning kinetic energy of suspension movement into heat energy Dampers: Struts and Anti-sway Bars • strut -- shock absorber mounted inside a coil spring • perform two jobs: dampening function like shock absorbers, and structural support for the vehicle suspension

Dampers: Anti-sway Bars • anti-roll bars -- used along with shock absorbers or struts to give additional stability

Suspension Types: Front • Front suspension - dependent systems – rigid front axle that connects the front wheels • Front Suspension - Independent Systems – allowed to move independently McPherson strut • combines shock absorber and coil spring into a single unit • more compact and lighter suspension system that used for front-wheel drive vehicles

Double wishbone suspension systems • several different configurations with wishbone-shaped arms • mounting positions one at frame and one at wheel • Each wishbone bears a shock absorber and a coil spring to absorb vibrations • help minimize roll or sway and provide for a more consistent steering feel

Coil Spring type 1 Coil Spring type 2 • wheel spindles are supported by • lower arm be replaced an upper and with a single solid arm lower 'A' shaped – as control arm arm • the lower arm • load-bearing capability carries most of the almost entirely to the load upper arm and the spring mounts Multi-link suspension • as the spindle turns for steering, it alters the geometry of the suspension by torquing all four suspension arms • gives even better road-holding properties • the spring (red) is separate from the shock absorber

Rear suspension - dependant Trailing-arm suspension systems • arm is joined at the front to the chassis, allowing the rear to swing up and down • Solid-axle, leaf-spring • twin-trailing-arm work on exactly same as the double wishbones

Solid-axle, coil-spring Beam Axle • diagonal bar prevent side-to- side movement in the beam

• front wheel drive cars 4-Bar Hydrolastic Suspension • rear end housing is always perpendicular to the ground • lateral stability by diagonal bar

Hydropneumatic Suspension The Future of Car Suspensions • uses linear electromagnetic motor (LEM) at each wheel • not limited by inertia of fluid-based dampers • Amplifiers provide electricity to motors drive power to regenerated with each compression

BOSE LEM system • LEM extend and compress much greater speed, eliminate all vibrations in passenger cabin • counteract the body motion while accelerating, braking and cornering