CCAS 3381 CCAS 3381 AUTOMOTIVE SKILL IAUTOMOTIVE SKILL I

SUSPENSION &

STEERING SYSTEM

OBJECTIVESOBJECTIVESTo understand

the operational principles and basic mechanisms of suspension & steering systems

Lecture – 1 hourWorkshop – 1 hour

Double-wishbone suspension on Honda Accord 2005 Coupe

SUSPENSION SYSTEM (1)SUSPENSION SYSTEM (1) Power of a car is

useless if car cannot be controlled

Car suspension:

–maximizes friction between tires and road surface

– provide steering stability with good handling

– ensure the comfort of the passengers

SUSPENSION SYSTEM (2)SUSPENSION SYSTEM (2) Vehicle dynamics

– Ride - car's ability to smooth out bumpy road – Handling - car's ability to safely accelerate, brake &

corner Road isolation - allow vehicle body to ride

undisturbed while traveling over rough roads Road holding - keep tires in contact with ground

(friction between tires and road affects a vehicle's ability to steer, brake & accelerate)

Cornering - minimize body roll

SUSPENSION SYSTEM (3)SUSPENSION SYSTEM (3) Frame - structural, load-

carrying component supporting car's engine & body (supported by suspension )

Suspension system - setup supporting weight, absorbing & dampening shock & helps maintaining tire contact

Steering system - mechanism enabling driver to guide & direct vehicle

Tires & wheels - components making vehicle motion possible by way of grip &/or friction with road

SUSPENSION SYSTEM (4)SUSPENSION SYSTEM (4)Springs:

–Coil springs

–Leaf spring

–Torsion bars

–Air springs Sprung mass &

unsprung mass

SUSPENSION SYSTEM (5)SUSPENSION SYSTEM (5) Sprung mass - mass of the vehicle supported

on the springs Unsprung mass - mass between the road and

the suspension springs

–Stiffness of springs affects how sprung mass responds while the car is being driven

– Loosely sprung cars versus tightly sprung cars - balance passenger comfort with handling is a complex task

SUSPENSION SYSTEM (6)SUSPENSION SYSTEM (6)Shock absorbers -

controls unwanted spring motion through dampening

–compression cycle

–extension cycle

SUSPENSION SYSTEM (7)SUSPENSION SYSTEM (7) Struts and Anti-sway Bars

– Strut: shock absorber inside a coil spring

provide dampening functionprovide structural support for the vehicle

suspensioncritical safety feature - worn shocks & struts

allow excessive sway reducing tire grip, handling & braking performance

– Anti-sway or anti-roll barsgive moving stability creates a more level ride & reduces vehicle

sway

Common strut design

Anti-sway bars

SUSPENSION SYSTEM (8)SUSPENSION SYSTEM (8) Dependent front suspension -

rigid front axle connecting the front wheels

Independent system - front wheels are allowed to move independently (MacPherson strut, double wishbone)

Double-wishbone suspension on

Honda Accord 2005 Coupe

Double-wishbone allows for more control over camber angle of the wheel (degree to which the wheels tilt in and out) & they also help minimize roll or sway and provide for a more consistent steering feel.

SUSPENSION SYSTEM (9)SUSPENSION SYSTEM (9) Dependent rear suspension - solid axle

connects the rear wheels Independent rear suspension system –

both rear wheels are mounted & sprung individuallyBose® Suspension Front Module

SUSPENSION SYSTEM (10)SUSPENSION SYSTEM (10)

SUSPENSION SYSTEM (11)SUSPENSION SYSTEM (11)

STEERING SYSTEM (1)STEERING SYSTEM (1) During turning your front

wheels are not pointing in the same direction

Geometry of steering linkage makes the inside wheel turn more than the outside wheel

STEERING SYSTEM (2)STEERING SYSTEM (2)

Rack-and-pinion steering

–most common– converts steering wheel rotation to linear– provides gear reduction to turn wheels

A steering wheel rotates 360o causing wheels turning 20o has steering ratio of 360/ 20 = 18:1

Variable-ratio steering Power Rack-and-pinion

STEERING SYSTEM (3)STEERING SYSTEM (3) Recirculating-ball

steering

–Used on many trucks and SUVs today

– contains a worm gear Power steering in a

recirculating-ball system works similarly to a rack-and-pinion system

STEERING SYSTEM (4)STEERING SYSTEM (4) Power Steering

– Rotary-vane pump driven by car's engine via a belt and pulley - amount of flow provided by the pump depends on the car's engine speed (pressure-relief valve)

– Rotary valvesenses steering wheel force – assist driver only when necessary like during parking

STEERING SYSTEM (5)STEERING SYSTEM (5)Today’s steering system runs

constantly, pumping fluid all the time (wastes)

– "drive-by-wire" system (like joysticks)

–General Motors concept car (Hy-wire)

STEERING SYSTEM (6)STEERING SYSTEM (6)

WHAT COULD GO WRONG (1)WHAT COULD GO WRONG (1) Worn & loose ball joints causing suspension

noise (typically a "clunking" sound when hitting a bump)

Bent wheel (shimmy on steering wheel & sideway movement of wheel)

Leaked shock absorbers (realignment after strut change)

Shocks too soft Worn shocks (sway, dip, bounce) Loose steering wheel (> 0.25”) – tie rod ends,

rack, wheel bearing) Power steering ‘morning sickness’ – worn

steering rack

WHAT COULD GO WRONG (2)WHAT COULD GO WRONG (2)Steering wheel jerks to one side upon

hitting bump – misalignment in chassis & bent steering arm

Car pulled to one side – wheel misalignment (camber, toe-in), tire pressure, mismatched tires, sagging spring, dragging brake, unreleased parking brake, uneven load)

Unbalanced tires – static & dynamicMost problems affecting the suspension

and steering system develop gradually as a result of wear. Watch for the following warning signs.

WHAT COULD GO WRONG (3)WHAT COULD GO WRONG (3)There’s too much play (free movement)

in the steering wheel. With power steering, there should be virtually no play in the wheel. In a manual system, there should be no more than 2 inches of play.

The steering wheel vibrates or is difficult to turn.

The front end of the car wobbles or shimmies.

The car bumps as you turn the wheel while driving on a smooth road.

WHAT COULD GO WRONG (4)WHAT COULD GO WRONG (4)The car pulls to one side as you drive.The car bounces too much after hitting a

bump.Tread wear on the front tires is uneven.

THE ENDTHE ENDIQ + EQ + SQ = TQ*