Chassis System Chassis is the systems between the

Chassis System • Chassis is the systems between the body and the road and includes frame/sub-frame, suspension (front and rear), steering system, brake system, wheels and tires • The scope of suspension design is the choice of basic geometry for optimum wheel location, the mounting of suspension members to the body (including the use of sub-frames), the springing medium, and the provision of damping of vertical wheel movement • The scope of steering design is the optimization of front suspension geometry for steering, the choice of steering system, the provision of power assistance, the satisfaction of safety requirements • The scope of brake system design is the choice of friction system, the design of the operating linkage, the provision of servo assistance, the satisfaction of safety requirements, the provision of anti-lock braking and other enhancements such as emergency brake assist. • The choice of wheel and tire size, choice of wheel material and tire configuration, choice of spare wheel configuration or “run flat” technology

Suspension System Requirements • Allow each wheel to move vertically to provide ride comfort, while constraining its movement in other directions to maintain stability and control. Vertical wheel movement from the datum position compresses a spring keeping wheel movement within limits, although bump and rebound stops are provided should the limit – normally set by the space constraints of body design – be reached. A damper ensures that the subsequent spring movement (an oscillation) is quickly reduced to zero. • The other most important secondary aim of suspension design is to keep all four wheels as nearly upright as possible at all times, not only when traveling across uneven surfaces but also when the body rolls during cornering. A conventional car tire delivers optimum grip for cornering, braking and accelerating when it is upright. In practice it is impossible to achieve this ideal constraint without resorting to extremely costly and space-consuming measures, and current suspension systems are in most cases concerned to approach it as nearly as possible. • In some cases, as with the use of trailing arms at the rear of frontdriven cars, the inevitable camber change and reduced grip during cornering is exploited as a means of reducing understeer – but overall cornering grip is also sacrificed as a result.

Suspension System Requirements • • • Another important requirement is that the weight of the unsprung mass i. e. wheel, tire, hub and suspension assembly at the “road” end of the spring, should be as low as possible. The lower the weight is relative to the weight of the body (the lower the ratio of unsprung to sprung mass), the less the body will react to any wheel movement, and the better the tire will be maintained in contact with the road surface, to the benefit of both ride comfort and road holding The task of the suspension linkage which attaches each wheel to the vehicle body is to keep the wheel as nearly upright as possible in all circumstances (zero camber angle) and pointing in the desired direction (nominally parallel to the vehicle centre line, except when the front wheels are being steered), regardless of the unevenness of the road surface which causes the wheels to move vertically, and of the attitude of the vehicle body which may move in pitch, roll, and heave (pure vertical movement) according to the forces acting at its centre of gravity. The importance of keeping the wheels as nearly vertical as possible is that this gives the tires the best chance to operate efficiently, with minimum rolling resistance. Many competition cars deliberately run positive (topinwards) camber to achieve maximum cornering grip but the rate of tire wear and the additional rolling resistance when running in a straight line are unacceptable in most road-going cars.

Primary Functions of Suspension • • Support vehicle weight. Keep the tires in contact with the road. Control vehicle’s direction of travel Maintain correct wheel alignment, important in vehicle handling • Reduce effect of shock loads with the use of springs, dampers and bushings • Maintain correct vehicle ride height

Types of Front Suspension Type Usage Cost and Package Control Weight Mc. Pherson Strut Small FWD Cars Light & Not Compact expensive Ok SLA or Double Luxury Heavier & Wishbone Cars expensive Not compact Good Solid Axle with Heavy Leaf Springs Trucks Compact Minimum Heavy & not expensive

Mc. Pherson Strut Suspension Top Mount Bump Stopper Spring Strut Rubber boot Lock Nut Link Camber Bolt Wheel Mounting Bolt Stabilizer Bar Wheel Cap Rubber Bushes Drive Shaft / Spindle Wheel Bearing Lower Link Tyre Wheel Rim Brake Disc Heat Shield for Ball Joint (To protect from Brake Disc heat) Lower Ball Joint

Features of Mc. Pherson Strut §Upper control arm in double wishbone is eliminated §Provides anchoring of tie rod on knuckle §Combines the following parts into one assembly to provide wheel control ØSpring Seats ØSprings, Bump stoppers ØRebound Stopper ØLink for mounting Stabilizer Bar ØLower the Forces on BIW-Mountings §Provide Better Space at the side to mount transverse Engine & Gear box §Better Space for Front Crash Members & Crumple zones

Advantages of Mc. Pherson Strut • Advantages Disadvantages 1. Combination of several parts into one assembly 1. Less favorable kinematic 2. Upper transverse link replaced by top mount 2. Forces & vibrations transferred to 3. Occupies less space characteristics inner wheel-arch panel which is relatively elastic 1. Transverse engine mounting possible 3. Difficult to insulate against road 2. More space for front crumple zone 4. Friction between piston rod & noise guide impairs the springing effect 5. Critical to package [Gaps between Tyre & damper, Springs & Wheelarch] 6. Ground Clearance critical

Double Wishbone Suspension Tyre Stabilizer Bar Top Mount Upper Control Arm Upper Ball Joint Brake-Rod Rubber Bushes Brake Disc Steering Gear Knuckle Lower Link Tie Rod Lower Ball Joint Spring& Damper Wheel Mounting Bolt

Features of SLA or Double Wishbone §Has 2 control arms (upper & lower) connected to the steering knuckle by ball joints (UBJ & LBJ) §Upper control arm in double wishbone is shorter than lower arm which helps control the camber angle to desired level during body roll §Spring, shock and anti-roll bar are attached to LCA §Steering arm is attached to the knuckle

Advantages of Double Wishbone Suspension • Advantages • Disadvantages 1. Kinematics can be controlled easily 1. More complex than Mc. Pherson Strut 2. Provides good camber compensation during vertical movement 2. Short spindle SLAs tends to require stiffer bushings at the body, as the braking and cornering forces are higher. Also they tend to have poorer kingpin geometry, due to the difficulty of packaging the upper ball joint and the brakes inside the wheel. 3. Pitching movements can be balanced i. e anti-dive, anti-squat possible 4. Toe-in, Camber & Track change can be controlled optimally due to variety of control parameters 3. Long spindle SLAs tend to have better kingpin geometry, but the proximity of the spindle to the tire restricts fitting oversized tires, or snow chains. The location of the upper ball joint may have styling implications in the design of the sheetmetal above it.

Front Suspension Parts ARB Sub-frame Steering Tie-rods Subframe Knuckle Strut / Damper Suspension Bush Lower Link Spring Tyre Ball Joint Corner Module Wheel rim Drive Shaft / Bearing

Types of Rear Suspension Type Usage Cost and Package Control Weight Twist Beam Small FWD Cars Multi-Link Luxury Heavier & Cars expensive Not compact Good Hotchkiss Trucks Compact Minimum Light & Not Compact expensive Heavy & not expensive Ok

Twist Beam Rear Suspension E D E Welded Rigid Connection S T P D B S TA CB TA : Trailing Arms CB : Cross Beam B : Pivot Bushes S : Coil Spring D : Dampers E : Top Mount T : Torsion bar P : Panhard Rod P

Features of Twist Beam Suspension §Very compact package §Inexpensive to manufacture, assemble/disassemble. §Eliminates several parts: control arms, anti-roll-bar, etc. §Twist axle acts as a anti-roll-bar §High stresses in the welds

Advantages of a Twist Beam Suspension • Advantages • Disadvantages 1. Whole axle easy to assemble & dismantle 1. Exhibits compliance Oversteer 2. Requires very little space, easy to package spare tire, fuel tank, etc. 2. Torsion & Shear stress in Cross member 3. Spring-Damper assembly is easy to fit. 4. Control Arms & Rods are eliminated. 5. Wheel to Spring Damper ratio favorable. 6. Less unsprung mass 7. Cross member acts as a anti-roll-bar 8. Negligible toe-in & track change 9. Low camber change under lateral forces. tendency 3. High stress in weld seams

Twist Beam Rear Suspension Parts Packaging Unitized Bearing Twist Beam Module Suspension Bush Tyre Strut / Damper Drum Spring Drum Brake Wheel rim

3 -Link Rear Suspension Top Mount Coil Spring Damper Sub-frame Transverse Links Longitudinal Link Pivot Bushings

3 -Link Rear Suspension Parts Subframe with Multilink Suspension Unitized Bearing Multi-Link Suspension Bush Strut / Multi-Link Suspension Damper Drum Spring Drum Brake Tyre

Features of 3 -Link Rear Suspension §Relatively expensive §Requires more space §Easier to control wheel movement with 3 links §Longitudinal link picks up longitudinal loads §Transverse links pick up lateral loads

Advantages of 3 -Link Rear Suspension • Advantages • Disadvantages 1. Pitching movements can be balanced 1. Costly as compared to twist beam and i. e 100% anti-dive, anti-squat possible other suspensions due to increased number of components, links, bushings & 2. Toe-in, camber, track change can be controlled optimally due to variety of control parameters bearings 2. Higher production & assembly costs 3. Higher degree of tolerance control required to maintain geometry

Hotchkiss Rear Suspension

Hotchkiss Rear Suspension Tyre Conventional Leaf Spring Parabolic Leaf Spring Wheel rim Hotchkiss Suspension U Bolt Hotchkiss Suspension Shackle Suspension Bush ARB Bush

Features of Hotchkiss Rear Suspension §Simple in design §High weight §Easy to assemble §Provides good pay load carrying capacity §Robust in design

Advantages of Hotchkiss Rear Suspension • Advantages • Disadvantages 1. Simple with very few parts 1. High weight of suspension i. e high 2. Easy to manufacture & assemble 3. Robust design 4. High load carrying capacity unsprung mass. 2. Occupies More Space than other suspension types

Wheel Movements Controlled by Suspension • • • Jounce & Rebound Roll Toe in/Toe out Left or Right Steer Camber Spin

Axle/Vehicle Jounce & Rebound z Rear View y At Ride Height Spring Compression In Jounce z y Spring Extension At Ride Height In Rebound

Axle/Vehicle Roll z Rear View y At Ride Height Spring Compression Axle Roll z y At Ride Height Spring Compression Body Roll

Wheel Camber z y Wheels with no Camber Wheels with Camber Rear View

Wheel Toe in/Toe out x Top View y Wheel Toe-in Wheel Toe-out

Wheel Steer x Top View y Wheel RH Steer Wheel LH Steer

Suspension Geometry in Wheel Jounce Note: Wheel Assembly In Jounce 1) 2) 3) Upper Ball Joint 4) Upper Control Arm 5) Wheel Assembly Ride Height Lower Ball Joint Lower Control Arm Body Pivot Wheel at original position (pink) Wheel in jounce (blue) Original control arms (solid) Control arms in jounce (dotted) Note wheel camber z y Rear View

Suspension Geometry in Wheel Rebound Note: Wheel Assembly In Jounce Upper Ball Joint Upper Control Arm Wheel Assembly Ride Height Lower Ball Joint Lower Control Arm 1) 2) 3) 4) 5) Wheel at original position (pink) Wheel in jounce (blue) Original control arms (solid) Control arms in jounce (dotted) Note wheel camber z Body Pivot y Rear View

Steering Geometry Error in Wheel Jounce Note: z Rear View y Steering arm Ball joint 1) 2) 3) 4) 5) Wheel at original position (pink) Wheel in jounce (blue) Original tie rod (solid) Tie rod in jounce (dotted) Note geometry error New path for steering arm ball joint New position for body ball joint Tie Rod Ideal path for steering arm ball joint Ideal Location for body ball joint

Steering Geometry Error in Wheel Jounce z Ball joint Pulled out Ball joint Pulled in Short Tie Rod Path y Steering arm ball joint at jounce Steering arm ball joint at ride height Long Tie Rod Path Center for Short tie rod Ideal center for tie rod on body Center for long tie rod Ideal path Rear View

Steering Geometry Error in Wheel Jounce z y Ball joint Pulled out Steering arm ball joint at jounce New Path Center above Ideal jounce New Tie Rod Rear View Ideal Tie Rod Steering arm ball joint at ride height Ideal center for tie rod on body Ideal path

Steering Geometry Errors Position of Tie Road to Body Joint Steering Arm Ball Joint Steering Geometry Position Error At ideal center On ideal path None Inboard towards wheel Pulled in towards body in jounce or rebound Toe-in (link ahead ) Toe -out (link behind) Outboard towards body Pulled out towards body in jounce or rebound Toe-in (link behind) Toe-out (link ahead) Below ideal center Pulled out jounce and pulled in in rebound right steer (behind) left steer (ahead) in roll Above ideal center Pulled in in jounce and pulled out in rebound right steer (ahead) left steer (behind) in roll

Suspension Roll Center • Roll center is defined as a location at which lateral forces developed by the wheels are transferred to the sprung mass • Each suspension has a roll center • Lateral forces can be applied to the sprung mass at the roll center without causing suspension roll • Each suspension has a roll axis about which un-sprung mass rolls when a pure moment is applied • Vehicle roll axis is the line joining the roll centers of the front and rear suspensions