PowerPoint Presentation

Vehicle dynamicsParts of Vehicle DynamicsAerodynamicsGeometry analysis: SteeringBody and tire specific : Suspension, Braking.Power generation and travel components : Engine and TransmissionBasic chassis modeling

Facets of Vehicle DynamicsAnalysis of primary forces acting on the tires.Performance of vehicle tested : Accelerating ,Braking , Cornering and Ride.Method and reason of application of forces affecting above parameters.Preparing model to enact close to reality conditions and predict vehicle behaviour in realistic manner, hence study response of vehicle to the above parameters.

Coordinate Systems

Origin is at the CG(right hand orthogonal coordinate system)Motion described by the velocities (forward, lateral, vertical, roll, pitch and yaw).X- forward and longitudinalY-lateral out right side of the vehicleZ-downward with respect to the vehiclep -Roll velocity about the X-axisq -Pitch velocity about the Y-axisr Yaw velocity about the Z-axis

Coordinate Systems Contd.

Earth Fixed Coordinate System:X- forward travelY- travel to the rightZ vertical travel(positive downward)- Heading angle Course angle side slip angle(angle between x axis and the vehicle velocity vector)Forces acting on the car

Common forces acting on a vehicle are shown in this figure

Note the aerodynamic drag force and the traction forces acting.These are the only forces having play in the cars longitudinal movement.Crash TestingFrontal-impact tests: These are usually impacts upon a solidconcretewall at a specified speed, but can also be vehicle-vehicle tests.Side-impacttests: these forms of accidents have a very significant likelihood of fatality, as cars do not have a significantcrumple zoneto absorb the impact forces before an occupant is injured.

Roll-overtests: which tests a car's ability (specifically thepillarsholding the roof) to support itself in a dynamic impact. More recently dynamic rollover tests have been proposed as opposed to static crush testing.Computer model: Because of the cost of full-scale crash tests, engineers often run manysimulated crash testsusing computer models to refine their vehicle or barrier designs before conducting live tests.

Crash testing for SAE cars is very important. Generally computer model testing of the car is done due to lack of funds. An impact attenuator is fitted in front of the car to reduce impact on crashing.

What does Weight Transfer Do?Anytime the car's direction changes through braking, accelerating, or cornering, each tire will experience a gain or loss of mechanical downforce.This weight transfer has significant impact on traction.By reducing the loss of load on the unloaded tires, we retain the traction they can provide.

Vehicle Weight DistributionAdding weight to the car increases the work the tire must do, and improves grip.Balancing the weight evenly in the car provides an even distribution for balanced response to dynamic changes.Intentionally biasing the weight distribution to a specific side or quarter of the car might be advantageous for the net results of grip under dynamic conditions.TractionLoad transfer causes the availabletractionat all four wheels to vary as the car brakes, accelerates, or turns. This bias to one pair of tires doing more "work" than the other pair results in a net loss of total available traction.During positive acceleration when the engine power is driving two or fewer wheels.The most powerful cars are almost neverfront wheel drive, as the acceleration itself causes the front wheels' traction to decrease. This is why sports cars usually have eitherrear wheel driveorall wheel driveIn the all wheel drive case, the power tends to be biased toward the rear wheels under normal conditions.

Wheel SpinAwheelspinoccurs when the force delivered to the tire tread exceeds that of available tread-to-surface friction and one or more tires lose traction.Wheelspin can also occur when changing gears while the vehicle is in motion, as the inertia of the engine and flywheel rotating at a higher rate than the next highest gear tries to bring the input shaft of the transmission to the same speed.During AccelerationWhen you accelerate, the weight of the car is thrown backwards. This causes the rear suspension to compress slightly and increases the available grip at the rear tyres.

During BrakingCars can brake much harder than they can accelerate. Weight transfers under braking are thus more likely to affect the balance of the car

During CorneringIt's important to consider sideways weight transfers when cornering. If you turn into a corner progressively rather than 'chucking it in', this will transfer the weight to the outside wheels in a gradual manner.

Take a front engined rear wheel drive car as an example and throw it into a corner hard while accelerating gently. Diagram 4 below shows the levels of grip at each wheel. The size of the circle indicates the total level of grip at each wheel, the larger the circle the more grip is available. Green represents how much of the available grip is being used by cornering, orange by acceleration or braking.

Front and Rear Wheel DriveRear-wheel drive offers better initial acceleration than does FWD when a quick start is of the essence. That's because weight is transferred to the rear of the car upon accelerating, thus boosting traction.

RWD also permits expert drivers to use various techniques to slide the rear end around corners, which is a skill most useful in racing.

Additionally, by keeping part of the drivetrain in the rear, RWD cars usually have weight distribution closer to the optimal 50 percent front/50 percent rear than can be achieved with a FWD system: Equal weight distribution improves a vehicle's overall balance and handling.The Downside of Front-Wheel DriveDespite its practical advantages, front-wheel drive has several performance disadvantages. Some exhibit a characteristic called "torque steer," in which unequal power application to one of the front wheels causes the vehicle to pull to one side or another under heavy acceleration.A FWD vehicle's turning radius can often be greater than the same vehicle with RWD. That's because cramming all that powertrain and drivetrain equipment under the hood doesn't leave enough room for the front wheels to be turned as sharply as in a rear-wheel-drive application.FWD systems also tend to wear out faster than the less-complex RWD systems. Further, the lifespan of front tires can be compromised because so much weight is placed on them and they have to handle all of the acceleration and steering forces as well as much of the braking.

Ups and Downs of RWDPerformance goes up: When you punch the accelerator pedal in a rear-wheel-drive vehicle, the weight transfers to the rear end, just where you want it during acceleration. This leaves the front wheels to focus on directing the vehicle. RWD has its own disadvantages. RWD cars require a driveshaft and to accommodate it, they have that space-robbing interior hump down the middle of the passenger cabin. They also need a rear differential to make the 90-degree turn necessary to transfer engine power from drive shaft to the rear wheels. These components add extra cost and weight to a vehicle while robbing horsepower and making RWD cars generally less fuel-efficient than front-wheel-drive vehicles.Rear-wheel drive also is more challenging in inclement weather. Without the aid of traction control, a RWD car can more easily end up on somebody's front lawn or stuck in a ditch. Fortunately, traction control is standard on most cars and trucks today.

The High and Low 4WDMost 4WD systems have low and high ranges that can be selected by the driver, usually with an electronic switch.Whether electronic or mechanical, the 4WD's low setting provides even greater torque for pulling or climbing in an off-road environment. The setting's low gearing also makes it easier to descend steep slopes on unstable surfaces without using and burning up the brakes.The 4WD's high setting is the default setting and is useful for slippery on-road situations, such as packed snow or ice or loose sand or gravel.

Other terminologies

OW Front Track widthWB - WheelbaseCornering

Vehicle is assumed to turn around a center and above is the actual geometry of the front and the rear tires .Tire slip characteristics

Under cornering conditions tire develops a lateral force and also a lateral slip. The angle between direction of heading and direction of travel is known as slip angle.

Various forces are needed to be considered while designing a vehicle.Cornering characteristics are very important to study, speed of the cars depends upon the lateral force generated by the vehicle.Various departments like steering, chassis and suspension must work out a model to create the most comfortable ride and handling features.RideTerm commonly used in reference to tactile and visual vibrations produced during the driving of the car.Major objective of the teams is to reduce the decibel level of the noises generated during the drive.There are two sources of excitation of noises: Road Roughness and On-board issues(Tire assembly, engine and driveline components.

Power Train

Various Types of chassisLadder ChassisTubular Space FrameMonocoqueUltra Light Steel Auto Body (ULSAB) monocoque.BackboneGlass fibreAluminium Space frame

Ladder Chassis

Earliest Chassis , used till the 60s.indicated by its name, looks like a ladder - two longitudinal railsinterconnected by several lateral and cross braces.

Advantages: easy and cheap to buildDisadvantages:2 D Structure ; hence low torsional RigidityMost SUVs, Classic carsTubular Space Frame

TVR Tuscan3 Dimensional design using tubes.Tubular space framechassis employs dozens of circular-section tubes position in different directions to providemechanical strength against forces from anywhere.Advantage: Very strong in any directionDisadvantage: Very complex, costly and time consuming to be built.Impossible for robotised productionWho use it ? All Ferrari before the 360M, Lamborghini DiabloMonocoque

Monocoque is a one-piece structure which defines the overall shape of the car.Advantages:low production cost and suitability to robotised production.Another advantage is space efficiency.Disadvantages:very heavy, Pressed sheet metal is not as strong as metal tubes orextruded metalThe rigidity-to-weight ratio is also the lowest among all kinds of chassis bar the ancient ladder chassis.Glass Fibre Body

Advantages:It is lighter than steel and aluminium, easy to be shaped and rust-proof.Cheap, needs only a pair of hands

Disadvantages:Higher tolerance in dimensions leads tobigger assembly gaps can be seen. This is usually perceived as lower visual quality compare with steel monocoque.ChassisFSAE style cars require skeletal frame(steel tubular) chassis.Major parts include bulkhead, roll hoops, cockpit, engine and differential compartments.

Solidworks modeling and ansys simulation lets us create this model use in our car.