M.S Ramaiah School of Advanced Studies - Bangalore. Session Objectives

Transcription

1 Suspension Systems, Wheels and Tires Lecture delivered by: Prof. Ashok C.Meti MSRSAS-Bangalore 1 Session Objectives To understand the need for a suspension system Study the various types of springs used in automotive suspension systems To understand the construction and working of Front and Rear suspension systems To get an overview of various developments in the automotive suspension systems 2 1

2 Topics Suspension systems Components of typical suspension systems Electronically controlled suspension systems Wheels and tires 3 Suspension System - Introduction The purpose of the suspension system along with wheels and tires to provide greater handling capabilities as well as increased comfort levels. Suspension refers to the use of front and rear springs to suspend a vehicle s frame, body, engine & power train above the wheels. Sprung-Mass(Weight) Mass(Weight): vehicle s frame, body, engine & power train above the wheels. Unsprung-Mass (Weight): includes wheels and tire, brake assemblies and other structural members not supported by the springs. 4 2

3 sprung mass (body) M s z s suspension spring unsprung mass (wheel, axle) M u tyre stiffness K t suspension damper z u z r The vehicle body must be insulated against road shock. The blue dotted line shows how the vehicle body moves 5 Why need a suspension? Ride comfort Vehicle stability Durability of components Suspension makes owning and driving a car more meaningful! 6 3

4 Ride Comfort 7 The components of a typical suspension System Springs - Absorb shock forces while maintaining i i correct ride height. ht Automotive springs are generally classified by the spring rate (deflection / load) 8 4

5 The springs take care of two fundamental vertical actions: Jounce Occurs when a wheel hits a bump and moves up Rebound Occurs when the wheel hits a dip or hole and moves downward 9 The spring goes back and forth from jounce and rebound Each time the jounce and rebound become smaller This is caused by friction of the spring ss molecular structure and suspension pivot joints A shock absorber is added to each suspension to dampen and stop the motion of the spring quickly 10 5

6 Shock absorbers damp or control motion Conventional shock absorber Gas-charged shock absorber Electronically controlled shock absorber variable shock damping, driver selectable soft, medium and firm settings. MacPherson Struts widely used for independent suspension systems. Effect of damper on wheel oscillations 11 Types of springs Coil springs Linear Rate Spring all linear springs are wound from a steel rod into a cylindrical shape with even spacing between coils Variable Rate (progressive rate) Spring have a consistent wire diameter, are wound in a cylindrical shape and have unequally spaced coils Coil Spring 12 6

7 Leaf springs A Leaf spring assembly Flexing causes a variation in spring length. 13 Torsion Bar The torsion bar is a straight rod of spring steel, rigidly fastened at one end to the vehicle frame or body. The other end attaches to an upper or lower control arm. 14 7

8 As the control arm swings up and down in response to wheel movement, the torsion bar twists to provide spring action. 15 Shock absorbers (Damper*) Damp or control the motion in a vehicle The shock absorbers b are velocity sensitive hydraulic damping devices They work on the principle of fluid displacement on both its compression and extension cycles. A typical car shock has more resistance during its extension cycle than its compression cycle. *US damper 16 8

9 MacPherson Strut A MacPherson strut not only provides ride dampening, it also becomes part of the suspension system. It replaces the upper control arm, upper ball joint and standard shock absorber. In most cases the front springs are also incorporated, making one complete unit model year the Mustang MacPherson struts 18 9

10 Suspension Types Front Suspension Independent Suspension Independent suspensions allow each wheel to move vertically without affecting the opposite wheel. Independent suspension usually operates through heavy-duty coil springs or torsion bars and direct, double acting shock absorbers. 19 Solid Axle Suspension A solid axle is one in which wheels are mounted at either end of a rigid beam so that any movement of one wheel is transmitted to the opposite wheel causing them to steer and camber together Solid axle construction, the axle beam and wheel assemblies are connected to the car by leaf springs and direct or in-direct shock absorber

11 Front Independent Suspensions Double A-Arm Suspension 21 MacPhersion Strut Suspension 22 11

12 Control Rod Suspension Torsion Bar Suspension 23 Rear Axle Suspension Solid Axle-Hotchkiss Drive Four Link Suspension 24 12

13 Anti-Roll Bar Also called an anti-sway bar, this device connects the left and right suspensions together and anchors to the vehicle frame. Typically used at the front and rear of the vehicle, the anti-roll bar is commonly used to adjust the handling balance of the vehicle and limit the amount of sway or body roll during cornering. 25 Adaptive Suspension Use electronic shock absorbers with variable valving and some uses variable air springs. Electronic sensors monitor factors such as Vehicle height, Vehicle speed Steering angle Braking force Door position Shock damping status Engine vacuum status Throttle position Ignition switching The controller analyze all the inputs and switch the suspension in to a preset operating mode matching the existing conditions. These systems work in fully automatic mode and driver selectable mode 26 13

14 Electronic Air Suspension System 27 Active Suspension Some of the advanced adaptive suspensions systems are called Active Suspension systems. This configuration i refers to those controlled by double-acting hydraulic cylinders or solenoids(actuator) that are mounted on each wheel. Each actuator maintains a sort of hydraulic equilibrium with others to carry the vehicle weight, while maintaining the desired body attitude. It also serves as its own shock absorber, eliminating the need for yet another suspension component

15 Bose Suspension System The linear electromagnetic motor is used as a telescoping suspension strut A torsion bar connected to one end of the lower arm supports the weight of the vehicle. The wheel damper keeps the tire from bouncing and losing contact with the road. The motors, mounted on each wheel, receive input from sensors throughout the vehicle and react to bumps and potholes instantaneously, using downward force to extend the wheel into potholes while keeping the car level. As the wheel move back up onto the road, the suspension recaptures nearly all the energy expended. The system also improves handling, and comfort during different driving conditions. 29 Wheels Wheels are made of either stamped or pressed steel discs riveted or welded together. They are also available in the form of aluminum or magnesium rims that are die-cast or forged. Magnesium wheels are commonly referred to as mag wheels though made up of aluminum alloy Aluminum wheels are lighter compared to pressed steel wheels 30 15

16 At the center of the wheel, tapered mounting holes are provided that help center the wheel with the hub Wheel size is designated by rim width and rim diameter Rim width is determined by measuring the rim between the flanges Rim diameter is measured across the bead seating areas from the top to bottom of the wheel 31 Tires Tires and wheel assemblies provide the only connection between the road and vehicle. Modern tires require increased attention to achieve their full potential of extended service and correct ride control

17 Tires: The primary purpose of tires is to provide traction. They also help the suspension absorb road shocks. In addition to providing good traction, tires also designed to carry weight of the vehicle. They must perform under a variety of conditions such as Wet or dry road Paved with asphalt, concrete or gravel There might be NO road at all! The car may be moving slow or fast on straight or on curved roads. Going up the hill or going down the hill The friction created between the road and the rolling tire gives traction. The tire must have sufficient traction as well as provide least rolling resistance 33 The pneumatic tires are of two types. Tube type Tubeless type The tires have 3 basic type of construction: Bias Ply Belted Bias Ply Radial Ply* 34 17

18 There are tire designs that contain up to 200 raw materials as well as a complex architecture t of steel belts, textile til plies and computer designed tread patterns. The tires will have different tread designs to provide different capabilities to the tire. The common tread pattern categories: Symmetrical Asymmetrical Unidirectional 35 Aquaplaning / hydroplaning 36 18

19 Tire Rating and designations

20 Michelin Tweels "Tweel" concept - a word made up of the combination o of Tire eand Wheel It is actually an assembly of four pieces bonded together: the hub, a polyurethane spoke section, a "shear band" surrounding the spokes, and the tread band - the rubber layer that wraps around the circumference and touches the road. 39 Summary The need for a suspension system in an automobile has been explained Various types of springs used in automotive suspension systems have been discussed Construction and working of Front and Rear suspension systems have been explained An overview of various developments in the automotive suspension systems have been given 40 20