Vehicle Dynamics and Chassis System MEC 4674

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIAEND OF SEMESTER EXAMINATIONSEMESTER I, 2014/2015 SESSIONKULLIYYAH OF ENGINEERING

Programme : Mechanical-Automotive Engineering Level of Study : UG4Time : 9.00am -12.00 noon Date : 5 JAN 2015Duration : 3 hrs Section : 1 Course Code : MEC 4674Course title : Vehicle Dynamics and Chassis System

INSTRUCTION(S) TO CANDIDATESDO NOT OPEN UNTIL YOU ARE ASKED TO DO SO

This question paper has EIGHT (8) printed pages (including cover page and Appendix) with SIX (6) Questions. Total marks : 100. This examination is worth of 50% of the total assessment. Answer any FIVE (5) questions from SIX (6)

Any form of cheating or attempt to cheat is a serious offence which may lead to dismissal.

Q.1 [20 marks](a) Define the suspension system. Explain how suspension system contributes on vehicle stability during braking and acceleration. (5 marks)(b) Figure Q1(b) shows a two-degrees-of-freedom quarter car model. Formulate the equation of motion to estimate the undamped natural frequency in Hz of the sprung and unsprung masses. (5 marks)

Figure Q1(c) The sprung parts of a passenger car weigh 11.12 kN and the unsprung parts weight 890 N. The combined stiffness of the suspension springs is 45.53 kN/m and that of the tires is 525.35 kN/m. (i) Determine the two natural frequencies of the bounce motions of the sprung and unsprung masses. (5 marks)(ii) Calculate the amplitudes of the sprung and unsprung parts if the car travels at a speed of 48 km/h over a road of a sine wave form with a wavelength of 9.15 m and amplitude of 5 cm.(5 marks)

Q.2 [20 marks](a) Define vehicle traction force. Explain the ways to improve the vehicle stability both in turning and braking conditions.(4 marks)(b) A vehicle of weight 20 kN is travelling on a dry asphalt pavement with a coefficient of road adhesion 0.45, tire tangential stiffness 3906 kN/m, vehicle ground contact pressure 110.3 kN/m2, tyre width is 0.20 m and longitudinal strain of tire in compression 0.02. (i) Find the longitudinal tractive force of the vehicle per unit contact length of the tire just at the starting over the asphalt.(2 marks)(ii) Find the tire contact length if the ratio of the contact length of the tire () is 0.85.(2 marks)(iii) Find the traction force due to the sliding and adhesion(4 marks)(iv) Find the power requirement of the vehicle for the traveling speed of 90 km/h.(2 marks)(v) Estimate the vehicle ground contact pressure and power requirement if 50 kg payload is added to the vehicle. Use the estimated tire contact length in (ii).(4 marks)

Q.3 [20 marks](a) Define the vehicle translation and rotational motion during turning. Explain the dynamic parameters of the steering system. (7 marks) (b) Explain how power steering system shows in Figure Q3(b) assists the driver to change the vehicle direction. (5 marks)

Figure Q3(b)(c) A sports car weighs of 9.919 kN and has a wheelbase of 2.26 m. The centre of gravity (CG) is located 1.22 m behind the front axle. The cornering stiffness of each front tire is 58.62 kN/rad and that of each rear tire is 71.36 kN/rad. The steering gear ratio is 20:1. (i) Determine the vehicle handling characteristics. (2 marks)(ii) What would happen to the steady-state handling characteristics of the vehicle, if the cornering stiffness of the tire is interchanged and CG of the vehicle is located 1.04 m behind of the front wheel? (3 marks)(iii) Determine the steady state yaw velocity gain and lateral acceleration of the vehicle. (3 marks)

Q.4 [20 Marks](a) Define the vehicle slippage. If the vehicle speed is m/s, wheel radius Rw m and rotational speed is rad/sec, find the slippage of the vehicle during braking mathematically. (3 marks)(b) Explain how you can convert a conventional braking system has shown in Figure Q4(b) into an electro-mechanical braking system.(6 marks)

Figure Q4(b)

(c) A vehicles braking system is operated with a disk braking system. The experimental results showed that the braking capacity of the vehicle is 2944 Nm. The position of the braking pad from the center of the wheel: R0 = 0.2875 m, Ri = 0.20 m, and angular position, =400. The actuating force is applied on the brake pad by means of a hydraulic cylinder with a piston diameter of 0.038m. If the safety factor of the braking system and the frictional coefficient of the braking pad material are considered to be 1.21 and 0.37 respectively, determine, (i) the actuating force (4 marks)(ii) the hydraulic pressure that is needed at the brake pad (4 marks)(iii) the maximum contact pressure. (3 marks)

Q.5 [20 marks]1. Figure Q5(a) shows the subsystem of a rear driven vehicular driveline. Develop the basic mathematical model to compute the torque for the engine, transmission, final drive and drive wheel (12 marks)

Figure Q5(a)

1. A passenger car weighs 12.45 kN, including the four tires. Each of the tires has an effective diameter of 67 cm and a radius of gyration of 27.9 cm, weighs 222.4 N. The engine develops 44.8 kW at 4000 rpm, and the equivalent weight of the rotating parts of driveline at engine speed is 444.8 N with a radius of gyration of 10 cm. The transmission efficiency is 88% and the total reduction ratio of the driveline in the second gear is 7.56:1. The vehicle has frontal area of 1.67 m2 and the aerodynamic drag coefficient is 0.45. The average coefficient of rolling resistance is 0.015. Calculate the,(i) Vehicle total motion resistance(3 marks)(ii) Vehicle acceleration(2 marks)(iii) vehicle traction force(3 marks)

Q.6 [20 marks](a) Define track vehicle steerability. Derive the equation that can be used to justify the tracked vehicle steerability over the soil surface. Consider for tracked vehicle: wheelbase L, tracked width B and weight W and soil surface: cohesiveness c, internal frictional angle , rolling motion resistance coefficient fr and ground bearing capacity P.(4 marks)(b) A hybrid air-cushion tracked vehicle of weight 1.7 kN is designed for operating on swamp terrain which have a bearing capacity of 7 kN/m2. The vehicle parameters were optimized as follows: ground contact length, 0.54 m, width, 0.12 m and tread, 0.4 m. The terrain parameters are given as cohesiveness 1.37kN/m2 and internal friction angle 260, if the vehicle coefficient of rolling and lateral motion resistance is considered as 0.15 and 0.5 respectively, determine the,(i) steerability of the vehicle over the specified terrain (3 marks)(ii) traction force of the vehicle for the outer and inner track. (3 marks)(iii) power requirement of the vehicle if the vehicle turning speed is 6 km/h. Consider the traction force of the track which will contribute on vehicle turning. (3 marks) (c) A wheel vehicles braking system is operated with a disk braking system. The experimental result showed that the braking capacity of the vehicle is 2944 Nm. The position of the braking pad from the centre of the wheel: outer radius 0.2875 m, inner radius 0.20 m, and angular position 400. The actuating force is applied on the brake pad by means of a hydraulic cylinder with a piston diameter of 0.038m. If the safety factor of the braking system and the frictional coefficient of the braking pad material are considered to be 1.21 and 0.37 respectively, determine, (i) the actuating force (4 marks) (ii) the hydraulic pressure needed at the brake pad (3 marks)

APPENDIX

Helping formulae:

Suspension system

For amplitude, where, Z1= amplitude of sprung part in m, z0=amplitude of the road in m,

7