Unit 4 Ttw.pptx

UNIT-IV BRAKES & WHEELS Drum brakes & Disc brakes Construction and Working and its Types, Front and Rear brake links layouts. Brake actuation mechanism. Spoked wheel, cast wheel, Disc wheel & its merits and demerits. Tyres and tubes Construction & its Types. Steering geometry Mohsin Ahmed.A AUTOMOBILE ENGINEERING ASSISTANT PROFESSOR

Braking System • Brakes are employed to stop or slow down the speed of vehicle. • When brake applied to wheel braking force is created that force oppose the speed of wheel or rotation of force

Braking requirement • • • •

The vehicle must stop in smallest distance. It must act suddenly in emergency. It must have strong braking force. It must neither slip nor kid the vehicle And less heat production. • It must operate on least effort

Types of brakes: • • • • • • • • • • • • • • •

Breaks are divided into seven types as per there uses, functionality, locations etc. 1) On the basis of purpose saved. a) Main brake. b) Parking brake. 2) On the basis of location. a) Wheel mounted. b) Transmission mounted. 3) On the basis of drivers ergonomics. a) Foot brake. b) Hand brake. 4) On the basis of actuating. a) Mechanical brake. b)Hydraulic brake. c) Air brake. d)Electric brake.

Types of brakes-contd • • • • • • • • • •

5) On the basis of construction. a) Drum brake. b)Disc brake. 6) On the basis of application of brake efforts. a)Manual brake. b)Power brake. c)Power assisted. 7) On the basis of action of brake shoes. a)Internal expanding brake. b)External contracting brake.

Drum brake

Typical drum brake parts

Drum Brake

mechanical Drum brake • In the mechanical Drum brake system such as in two-wheeler & auto rickshaw, the brake shoes are actuated by a cam, which is attached to the brake linkage & pedal. • When the brake pedal is pressed, the cam turns; causing the brake shoes to expand outwards and rub against the drum.

mechanical Drum brake • The friction between the brake linings and the drum causes the drum to stop rotating, thereby the wheel to stop. • When, the brake pedal is released, the retracting springs bring the brake shoes back to their original position, causing a gap between them and the drum and to again spin it freely.

Drum brake hydraluic

hydraulic Drum brake • The hydraulic Drum brake system such as in cars is a bit superior to mechanical one and the cam is replaced by the hydraulic wheel cylinder. • In hydraulic system, instead of cam, the wheel cylinder’s pistons push the brake shoes outwards. • The brake shoes are mounted on the anchor plate or braking plate, which holds the brakes system parts together and on to the car’s axle.

hydraulic Drum brake • When the brake pedal is pressed, the oil in the brake master cylinder multiplies the hydraulic force sent to the wheel cylinders; causing its pistons to push outwards. • The pistons, in turn, cause the brake shoes to expand and rub against the drum. • The friction between the brake linings and the drum causes the drum to stop rotating, thereby the wheel to stop.

Pneumatic assisted Drum brake • The third type – pneumatic assisted Drum brake system; actuated by air-pressure, which works on the same principle of that of mechanical Drum brake system. • It is also operated by a bigger size cam or the ‘S’ shaped cam and is popularly known as the “S-Cam” brake system. • However, the cam is turned with the help of a pneumatic piston, which is actuated by high-pressure compressed air. • This type of drum brake system is used mostly in the medium to heavy commercial vehicles.

Advantages of Drum brake system • • • •

Simple design and parts Easy & cheaper to manufacture Low maintenance cost Comparatively longer life

Disadvantages of Drum Brake system • Low braking force compared to Discs • Gets faded when applied for prolonged time • The brake shoe lining made of asbestos is harmful to humans • When wet, the braking grip reduces considerably • Non-asbestos linings catch moisture, causing Drum brakes to grab suddenly

Disc brake • Disc brake system is widely used on front wheels in mid-range two wheeler such as – commuter & sports bikes. • The Disc brake system is used on the front wheels of most hatchback cars, entry level sedans & MUVs; whereas, it is also widely used on both front & rear wheels of high end cars in combination with hydraulic / vacuum brake actuating systems.

Disc brake • Disc brake got its name from the circularshaped plate or disc or rotor; onto which the disc brake parts are mounted. A conventional Disc Brake system consists of a brake disc, two fiction pads and brake calliper. In the Disc brake system; the friction pads apply grip on the external surface of disc to perform braking

Disc brake • . The disc brake consists of: – A circular disc made of – cast iron in cars and steel in two-wheeler – A caliper assembly consisting of hydraulic pistons – A pair of brake pads (one each on the either sides) – Bleed screw

Disc brake

Disc brake

Single piston • In the single piston design such as in two-wheelers, the brake pads are actuated by a single piston, which is attached to the brake calliper. • When the brake lever is pressed, the brake oil pushes the piston causing the brake pads to contract and rub against the disc. • The friction between the brake pads and the disc causes the disc to stop rotating, thereby the wheel to stop. • When, the brake lever is released, the brake pads retract to their original position, causing a gap between them and the disc and to again spin it freely.

Twin Piston • The twin piston design such as in cars is almost identical to single piston one, except for the piston, which are two in numbers. • In this system, the twin pistons push the brake pads to apply brake. • The brake pads are mounted in the calliper, which holds the brakes system parts together.

Twin Piston • When the brake pedal is pressed, the oil in the brake master cylinder multiplies the hydraulic force sent to the callipers; causing its piston to contract. • The pistons, in turn, cause the brake pads to contract and rub against the disc. • The friction between the brake pads and the disc causes it to stop rotating, thereby the wheel to stop.

Twin caliper • The third type – Twin caliper system; actuated by two callipers, which works on the same principle of that of single caliper brake system. In this design, there are two calipers instead of one. This type of system is used more commonly in high speed cars. This system provides more effective braking.

Twin caliper

Ventilated Discs • Modern vehicles are fitted with ventilated discs. When you apply brakes, the kinetic energy of the vehicle is converted to heat due to the friction between the brake pads and the disc. Ventilated discs have passages or an air vent that helps pass air through the disc and provides cooling & prevents brake fading.

Advantages of Disc brake system • • • • •

No adjustment required Better stopping performance Fade-free braking in all conditions Can check wear without dismantling the unit Easy & quick to replacement of pads as compared to Drum brakes

Disadvantages of Disc Brake system • High braking force needed compared to Drum brake • Low life of brake pads compared to brake shoes • Need separate hand-brake mechanism when fitted to rear wheels

Mechanically Operated System

Hydraulically Operated System

Pneumatically Operated System • Nowadays both low and high pressure air brake systems are fitted in vehicles, but most light category vehicles use only air to boost the effort applied by the driver. • A full compressed-air braking system, is normally used in heavy vehicles, but is too expensive, bulky and heavy for light vehicles. Some light trucks in the 3 ton category incorporate a partcompressed-air system called air/hydraulic (air over hydraulic). • This air system combined with a hydraulically operated arrangement reduces the maximum pedal pressure to a comfortable limit. • Now a days it is common to use a disc-type brake with a vacuum servo as standard equipment in many cars. • This device utilizes manifold depression, or ‘vacuum’ produced by an engine-driven pump, to assist the driver in the application of the brake.

Brake Layout

Disc Wheel

Schematic of Disc Wheel

Spoke Wheels • The spoke wheels are consisted of a steel rim and spokes that are made up of both steel and other metals. • The spokes are attached to the hub where the brake drum or the disc brake situates, the other extreme end of the spoke is screwed with nipples on the circular steel rim. • The whole structure makes a sturdy yet flexible wheel base for the rubber tyre.

Spoke Wheels

Why Spoke Wheels • On a motorcycle the tyre is a first contact point with the tarmac, hence if we start sequencing the parts come into play while absorbing the shocks, it is the tyres that comes first, whose rubber absorbs the shock first then it is the wheel. • And in case of spoke wheels the flexible property of it plays important role in absorbing shocks next to the rubber of the tyres. • It is then the actual shock absorber takes the charge and effectively absorbs the shocks.

alloy wheel • The alloy wheels are made up of light weight metal alloys mainly aluminum or magnesium, the process involved in making the alloy wheels is majorly casting, where the extremely hot molten alloy is poured into ready-made cast of the wheel and after cooling down the raw wheel is extracted from the casting mold and then after finishing it is ready for use.

• For strength and durability there is another method used for making the alloy wheels and it is "Forging" which is used for making more durable alloy wheels for race spec super sportbikes. • The process starts with a solid metal piece which is pressed by a hydraulic pressing machine at very high temperature to make a compressed round piece of that metal, which is further sent to the CNC machine to cut the extra metal from that circular piece of metal and finally there comes a forged alloy wheel which is several times stronger than the cast alloy wheel used in our commuter motorcycles.

Why Alloy Wheels? • Alloy wheels are made up of light weight metal therefore the final product is lighter than the spoke wheel which is made up of steel rim. • The reduction of weight caused by the alloy wheels make significant difference in cut throat competition in racing bikes and they add into the fuel efficiency of the commuter bikes as well. • At high to very high speeds the solid alloy wheels provide great stability as compare to the spoke wheels which are not that stable at high speeds due to its flexible nature, which comes from the spokes of the wheel.

Rim Sizes & Designations • To ensure correct fit between a tyre and rim, all manufacturers ofwheels and tyres comply with standard dimensions, as recommended by automotive manufactures. • The width of the rim is the distance across the rim flanges, at the bead seat. • Its diameter is the distanceacross the centre of the rim from bead seat to bead seat.

• The shape of well-based rims is provided by a letter code, such as J, K, JJ and KK. The width of the rim and the diameter is traditionally in inches. A rim designated 7 JJ by 14 would refer to a rim measuring 7 inches across the rim flanges and 14 inches in diameter from bead seat to bead seat, with the profile conforming to a JJcode

• The tyre must be an exact fit on the rim, to fulfil a number of functions. It ensures that the narrow contact area between the beads of the tyre and the rim will seal the air in a tubeless tyre. It transfers all the forces between the tyre and the wheel, without slipping or chafing. It ensures the friction between the tyre and the rim prevents the tyre turning on the rim.

Cross-Ply Tyres

• Two types of tyre construction are common cross-ply and radial ply. The cross-ply tyre is the older form. It is also called a bias-ply or conventional tyre. • It is constructed of 2 or more plies or layers of textile casing cords, positioned diagonally from bead to bead. • The rubber-encased cords run at an angle of between 30 and 38degrees to the centreline, with each cord wrapped around the beads. • A latticed criss-crossed structure is formed, with alternate layers crossing over each other and laid with the cord angles in opposite directions.

• This provides a strong, stable casing, with relatively stiff sidewalls. • However during cornering, stiff sidewalls can distort the tread and partially lifting it off the road surface. This reduces the friction between the road and the tyre. Stiff sidewalls can also make tyresrun at a high temperature. • This is because, as the tyre rotates, thecords in the plies flex over each other, causing friction and heat. • A tyre that overheats can wear prematurely.

Radial Ply Tyres

• Radial ply tyres have much more flexible sidewalls due to their construction. They use 2 or more layers of casing plies, with the cord loops running radially from bead to bead. The sidewalls are more flexible because the casing cords do not cross over each other. However, a belt of 2 or more bracing layers must be placed under the tread. • The cords of the bracing layers maybe of fabric, or of steel and are placed at 12, to 15 degrees to the circumference line. • This forms triangles where the belt cords cross over the radial cords. • The stiff bracing layer links the cord loops together to give fore and aft stability, when accelerating, or braking and it prevents any movement of the cords during cornering. • The cord plies flex and deform only in the area above the road contact patch.

• There are no heavy plies to distort and flexing of the thin casing generates little heat, which is easily dispersed. • A radial ply tyre runs cooler than a comparable cross-ply tyre and this increase tread life. • A radial tyre has less rolling resistance as it moves over the road surface.

Tubeless tyres

Tubeless tyres • Tubeless tires are pneumatic tires that do not require a separate butyl rubber inner tube. • Traditional designs of pneumatic tires required a separate inner tube which could fail for a number of reasons, such as: incorrect tire fitment, or friction between the tire wall and inner tube generating excess heat causing a blowout. Tubeless tire technology does away with the need for an inner tube thereby increasing safety. • In a tubeless tire, the tire, which has an inner lining of impermeable halobutyl, and the rim of the wheel form an airtight seal, with the valve being directly mounted on the rim.

Tube and tubeless tires comparison

• If a tubeless tire gets punctured, air escapes only through the hole, leading to a gentle deflation of the tire. Conversely, an inner tube could potentially burst like a balloon, leading to a rapid deflation of the tire which could result in sudden loss of control of the vehicle. A liquid tire sealant can be added to tubeless tires to prevent deflation.

STEERING GEOMETRY The term "steering geometry" (also known as "front-end geometry") refers to the angular Relationship between suspension and steering parts, front wheels, and the road surface. Because alignment deals with angles and affects steering, the method of describing alignment measurements is called steering geometry.

There are five steering geometry angles : Camber Caster king pin inclination Toe in & Toe-out on turns

Camber: Camber angle is the angle between

the vertical line and centre line of the tyre when viewed from the front of the vehicle.  Camber angle is positive when this is outward. This happens when wheels are further apart at top than at bottom. On the contrary, camber angle is negative when angle is inward. This happens when wheels are further apart at bottom than at top.  The camber, should not be more than 2 degree, because this causes uneven or more tyre wear on one side than on other side.

Caster:Caster angle is the tilt of king pin centre line towards front of back from the vertical line. It is the angle between the vertical line and king pin centre line in the wheel plane when looked from side.

King pin inclination It is the angle between king pin centre line

and vertical line when seen from the front of . the vehicle. d It is also called steering axle inclination ort King pin inclination and caster are use to improve directional stability in cars. ee steering eff  This is also used to reduce • when steering a stationary it reduces tyre wear.  This inclination varies from 4 to 8 degr

TOE IN & TOE OUT  In automotive engineering, toe also known as tracking.  This can be contrasted with steer, which is the anti

symmetric angle, i.e. both wheels point to the left orright, in parallel (roughly).

 Positive toe, or toe in, is the front of the wheel pointingin

towards the centerline of the vehicle

 Negative toe, or toeout, is the front of the wheel pointing

away from the centerline of the vehicle.

ACKERMANN STEERING GEOMETRY  Ackermann steering geometry is a geometric arrangement of linkages in the

steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of differentradii.  Modern cars do not use pureAckermann steering partly because it ignores

important dynamic and compliant effects.  The use of such geometry helps reduce tyre temperatures during high-speed

cornering but compromises performance in low speed maneuvers.  The intention of Ackermann geometry is to avoid the need for tyre to slip

sideways when following the path around a curve.  As the rear wheels are fixed, this centre point must be on a line extended from

the rear axle.  Intersecting the axes of the front wheels on this line as well requires that the

inside front wheel is turned, when steering, through a greater angle than the outside wheel .

Ackerman – Truck Steering System Straight ahead

Right turn

Left turn

Car Steering Systems Rack and pinion Steering arm

Gearbox

Rack Tire rod

Tire rod Gearbox

Idler arm

Relay link

Steering arm Pitman arm

Truck Steering Systems

Tire rod Steering arm Gearbox Pitman arm Drag link