Vehicle dynamics ppt shiva

A brief analysis on vehicle dynamics.

1. VEHICLE DYNAMICS,TOOLS AND TECHNIQUE TO ASSES VEHICLE DYNAMICS PRESENTED BY SHIVANAND S.R. NO.: 575/16 ROLL NO: 3604540010 TO Mr. R.K.AMBIKESH ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING HARCOURT BUTLER TECHNICAL UNIVERSITY KANPUR, 208002

2. CONTE N TS 1.INT R O D U C T I ON 2.. ASPECTS OF VEHICLE DYNAMICS 3. WEIGHT TRANSFER 4. POWER AND TORQUE CHARACTERISTICS OF VEHICLE 5. ENGINE POWER OUTPUT 6. AUTOMOTIVE RESISTANCES AND PROPULSIVE POWER 7. MEASUREMENT OF THE TEST VEHICLES 8. CO N C L USIONS 10.R E FERE N CES

3. 1. INTR O DUC T ION VEHICLE DYNAMICS   - It is the study of how the vehicle will react to driver inputs on a given road. Vehicle dynamics is a part of engineering primarily based on classical mechanics . Vehicles Wheels Motion Self-powered Dynamics Greek “DYNAMIS” power Vehicle Ride and Handling Ride is associated with comfort and grip Handling is associated with path following Driving task has two components: Command and control

4. 2 . ASPECTS OF VEHICLE DYNAMICS Some attributes or aspects of vehicle dynamics are purely  dynamic. These include: Body flex Body roll Bump Steer Bundorf analysis Directional stability Understeer, oversteer Pitch Roll Yaw Noise, vibration, and harshness Ride quality Speed wobble Weight transfer and load transfer

5. BODY FLEX  Body flex is a lack of rigidity in a motor vehicle's chassis. It is often something to be avoided by  car manufacturers  as higher levels of body flex is a sign of structural weakness, and means that the vehicle's  suspension cannot work as efficiently . 2. BODY ROLL  Body roll is the load transfer of a vehicle towards the outside of a turn. When a vehicle is fitted with a suspension package, it works to keep the wheels or tracks in contact with the road, providing grip for the driver of the vehicle to control its direction . 3. BUMP STEER  Bump steer or roll steer is the term for the tendency of the wheel of a car to steer itself as it moves through the suspension stroke. It is typically measured in degrees of steer per metre of upwards motion or degrees per foot.

6. 4 . BUNDORF ANALYSIS A  Bundorf analysis is a measure of the characteristics of a vehicle that govern its  understeer balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration . 5. DIRECTIONAL STABILITY   Directional stability is stability of a moving body or vehicle about an axis which is perpendicular to its direction of motion. Stability of a vehicle concerns itself with the tendency of a vehicle to return to its original direction in relation to the oncoming medium (water, air, road surface, etc.) when disturbed (rotated) away from that original direction. 6. UNDERSTEER AND OVERSTEER  Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than the amount commanded by the driver.

7. Figure 2. Understeer Figure 1. Oversteer

8. 7. PITCH Pitch is the front-and-rear motion of a car about an axis that extends from the left to right of a vehicle and trough the centre of gravity, or transverse (side-to-side) Y - axis. Pitch is typically taken to be positive (+) for upward movement of the vehicle nose and negative (-) for downward movement of the vehicle nose. 8. ROLL The rolling moment acts about the longitudinal axis and is produced by that side wind forces it has only minor influence on the vehicle stability depending on the suspension system. Figure 3. Pitching, Rolling, Yawing

9. 9 . YAW Angular oscillation of the vehicle about the vertical axis is called yawing. It is the vertical movement of the complete vehicle body so the complete body rises up and down and known as Bouncing. 10. NOISE, VIBRATION, AND HARSHNESS   Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, harshness is a subjective quality, and is measured either via "jury" evaluations. 11. RIDE QUALITY   Ride quality refers to a vehicle's effectiveness in insulating the occupants from undulations in the road surface (e.g., bumps or corrugations). A vehicle with good ride quality provides a comfort for the driver and passengers . 12. SPEED WOBBLE Wobble, shimmy, tank-slapper, speed wobble, and even death wobble are all words and phrases used to describe a quick (4–10 Hz) oscillation of primarily just the steerable wheel(s) of a vehicle.

10. 3 . WEIGHT TRANSFER Mechanism Of weight transfer The mechanism (cause) of fractional weight transfer may be understood by the free body diagram showing forces and moments acting on a vehicle at the time of braking. From mechanics it is known that when a body is accelerated in a straight path, the inertia force IF acts on its centre of gravity (C.G.) and whose magnitude is given by When brakes are applied, the forces IF and F R form an anticlockwise couple whose tendency is to cause overturning effect on the vehicle. The magnitude of this overturning couple is given by However, the vehicle is not going to overturn due to a righting couple produced on the establishment of forces Q between the wheels and the ground .The directions of Q on front and rear wheels are such so as to cause clockwise moment of righting couple whose magnitude is  

11. Continued …….. Where L is the wheelbase of the vehicle. Its consequence is to increase the perpendicular reaction between front wheels and the ground by an amount equal to Q, and to decrease it between the rear wheels and the ground by the same amount. Initially the weight of the vehicle is shared equally by each wheel. In a 4-wheeler, it is W/4 which now becomes, W/4+Q on front wheels, and W/4-Q on rear wheels.   Figure 4. Forces and moments to explain as to why a part of weight is transferred on braking

12. 3.POWER AND TORQUE CHARACTERISTICS OF AUTOMOBILE

13. 4. ENGINE POWER OUTPUT Following types of powers are being quoted with reference to engines. 1 . Indicated power (IP) 2. Brake power (BP) 3. Frictional power (FP) 4. Taxable horsepower (THP) 5. Drawbar power (DHP) INDICATED POWER The power developed inside the cylinder by combustion of gases is called indicated horsepower. An indicating device an oscilloscope is used to determine IP .  

14. 2. BRAKE POWER The power available at the crankshaft (for onward transmission to drive the vehicle) is called the brake power. Rating of automotive engines is done m terms of BP. Brake power can be measured by dynamometer. where N is in rpm and T in kgf -m. If N is in rps and T in Nm, then 4500 will be replaced by 1000 and power will be kW. Then it will be calculated by, 3. FRICTION POWER Loss of power due to friction occurs at many places inside the engine despite proper lubrication. One of the major causes of this loss is friction between piston-rings and the cylinder. It normally accounts for about 75% of all frictional losses in the engine. FP = IP - BP  

15. 4. TAXABLE HORSEPOWER It is also used to categorize engines on a uniform basis. To illustrate, we consider a race event of auto vehicles in which all types of vehicles ranging from mopeds, scooters, motorcycles, cars etc. are the participants. Question arises whether all these vehicles should run together, or they be grouped in different categories. 5. DRAWBAR HORSEPOWER A larger proportion of brake horsepower goes waste in overcoming various resistances in a moving vehicle. Rest of the Power is utilized to propel the vehicle. This power which is utilized to propel the vehicle is known as drawbar horsepower (DHP). DHP = BHP - RESISTANCES  

16. 5. AUTOMOTIVE RESISTANCES AND PROPULSIVE POWER The brake horsepower available at the crankshaft of an automotive engine is not fully utilized to Speed up the vehicle much of it goes waste to overcome various resistances which are given as under. 1. Road resistances: (a) Rolling resistance (b) Frictional resistances 2. Road gradient resistance 3. Air (or wind) resistance 4. Accelerating resistance 1. (a) Rolling Resistance It mainly occurs due to the deformation of road and tyre, and dissipation of energy through impact. The rolling resistance depends upon,

17. Mass of the vehicle Material of the road surface such as; asphalt, macadam, gravel, clay, wood or sand. Nature (quality) of the road surface such as poor, good, dry or wet. Material of the tyres Inflation of the tyres The rolling resistance R, can be expressed by , R r = C r mg where C r is rolling resistance constant and m is mass of the vehicle. The value of C r , depends upon the condition of tyre and road surfaces in contact. The rolling resistance may also be determined empirically by the following formula which includes the effect of velocity V of the auto vehicle . R r = (0.0112 + 0.00006V) mg Continued ……..

18. A comparison equations shows that the rolling resistance constant is related with the vehicle’s velocity as C r = 0.0112 + 0.00006V 1.(b) Frictional resistances Another kind of road resistance is frictional resistance that includes resistance due to transmission losses also. Such losses are owing to Lower gear efficiencies in first, second, and top gears. Churning of oil in gearbox and the rear axle system. Adhesion of tyre which is about 65% of the total losses in chassis. The frictional resistance R can be approximated by R f =132.5 + 50.5 m Continued……..

19. 2 . Road gradient resistance Slope (Gradient) of the road has considerable effect on the resistance to motion of the vehicle. The gradient resistance depends upon mass of the vehicle slope of the Road on which vehicle is moving The road gradient resistance R g is expressed by R g = mg   Figure 6. Gradeability of vehicle

20. 3. Air (or wind) resistance The air resistance faced by an automobile depends upon Speed of the vehicle Size and shape of the vehicle Speed of moving air Direction of wind with respect to direction of the vehicles motion R a is expressed by :- R a = C a A V 2 Figure 7. Effect of speed on Air resistance

21. 6 . TRACTIVE RESISTANCE AND PROPELLING POWER The sum of the resistances discussed earlier is known as the tractive resistance RT and is considered at the axle of the vehicle. Thus R t = R r + R f + R g + R a + R acc here R acc is the accelerating work required to be done at the axle.   (N-km/hr ) therefore required power is obtained as : if the efficiency of transmission between the engine crankshaft and the driving axle is η  

22. 7. MEASUREMENT OF THE TEST VEHICLES 7.1. BENCH TESTS 7.1.1. LOCATION OF CENTRE OF GRAVITY The location of centre of gravity of the test vehicle is determined in a longitudinal, lateral and vertical direction. Below, the longitudinal direction is called the x coordinate, the lateral direction y coordinate and the vertical direction z coordinate. The location of centre of gravity in the x and y directions is determined by measuring the four wheel loads by means of wheel-load scales, onto which the vehicle is placed. Alongside the overall weight of the vehicle determined in this way, the position of the centre of gravity in an x and y direction can be calculated with the known wheel base and track width variables by production of torque equilibria. The height of the centre of gravity is determined by weight displacement when lifting an axle. In this process, the brakes are released and the transmission is in neutral, through which the wheels can be freely turned. The efficiency lines of the axle loads pass through the wheel centre lines. To detect the axle load of the axle which has not been lifted, two wheel-load scales are used.

23. As a function of the inclination of the vehicle, the axle loads on the front and rear axle change. The height h of the centre of gravity above the level passing through the front and rear wheel centre line can be calculated via the torque equilibrium around the rear wheel centre line from the difference of the axle loads and the angle of inclination of the vehicle in question: Figure 8. Measurement f the vehicle’s centre-of-gravity height h cog

24. 7.1.2. MOMENT OF INERTIA The  moment of inertia, otherwise known as the angular mass or rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis; similar to how mass determines the force needed for a desired  acceleration . It depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rotation rate. Now that the location of centre of gravity is known, the moments of inertia (MOI) around the longitudinal, lateral and vertical axes can be measured. This is done by the vehicle oscillating around the corresponding axes at the centre of gravity of the vehicle against springs of a known stiffness. By measurement of the oscillation time T, the moments of inertia can be calculated with known spring stiffness. To determine the moments of inertia around the lateral axis of the vehicle, the vehicle is placed on a cutting line transverse to the direction of travel. The cutting line is aligned in such a way that the centre of gravity of the vehicle in a horizontal position of the vehicle is vertically above the cutting line. In the longitudinal direction of the vehicle, springs on which the vehicle supports itself via the auxiliary frame are clamped in at identical distances.

25. Continued …….. Euler's theorem is used to calculate the moment of inertia of the vehicle/frame unit around the cutting line axis from the frequency of the oscillations of this system: By subtracting Θ y ,Frame from the overall moment of inertia around the cutting line Θ y , total, the moment of inertia of the vehicle alone around the cutting line axis. Θ y,Veh = Θ y,total – Θ y,Frame The second item having an influence on the moment of inertia around the lateral axis is the so-called “Steiner ratio” of the vehicle. Θ y,CoG = Θ y,Veh - m Veh ∆h 2 y,Veh

26. 7.2. BRAKE FORCE DISTRIBUTION These measurements are done on the “ABS test bench” of the ika . The ABS test bench has four sets of rollers driven independently of one another onto which the vehicle is placed. Thanks to a movable frame for the rollers for the rear axle, the test bench can be adjusted to various wheel bases. All four wheels are driven evenly via the rollers with a speed corresponding to a traction of 6.5 kph . The reaction torque and thus the effective brake power up to a maximum of 5 kN are measured by a force transmitter interposed between the drive unit support and the frame. A detection roller measures the actual wheel speed in order to switch the test bench off automatically in the event of excessive slip between the rollers and the wheel. A principal diagram of the ABS test bench is shown in Fig ure . Figure 11. ABS test-bench

27. 7.3. DRIVING TESTS Table 3. Driving test instruments

28. 8. CONCLUSION 1. Enhance vehicle steerability and stability Steerability is enhanced in normal driving condition. Braking is involved only when the vehicle tends to instability 2. Precise steering control requires understanding of interaction between tyre and road. Treated as disturbance to be cancelled out. 3. Vehicle state estimation uses interaction between tire and road as source of information. Seen by observer as force that govern vehicle’s motion. 4. Vehicle dynamics are important to enable a good overall design of such a complex product as a vehicle intended for mass production at affordable cost for the customers.  

29. 9. REFRENCES K.M. Gupta, “Automobile Engineering” by Umesh Publications, Third Edition, Page no. 78-84, 87-90,. R.S. Khurmi , J.K. Gupta, “ Theory Of Machines” by S. Chand Publications, Third Edition Page no. 253-255. K.M. Moeed , “Automobile Engineering” by Katson Publications, Revised Edition 2016, Page no. 63-64. J. J. Uicker ; G. R. Pennock ; J. E. Shigley (2003). Theory of Machines and Mechanisms (3rd ed.). New York: Oxford University Press.  ISBN   9780195155983 . Marion, JB; Thornton, ST (1995). Classical dynamics of particles & systems (4th ed.). Thomson.  ISBN   0-03-097302-3 .

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