Half Car Suspension Model Report 672v6q

Vehicle Suspension Modeling MECE 4333 - Vehicle Systems Modeling and Control The University of Texas - Pan American August 7, 2006

Introduction You are asked to model the response of a vehicle to a series of road inputs using the half-car suspension model. Parameters are provided below in Table 1 for a generic sedan. However, you can earn bonus credit if you use suspension parameters and vehicle mass and rotational inertia parameters for a vehicle of your choice (preferably the vehicle you simulated for the previous two projects). Note that because a half-car suspension model is used, the spring and damping constants are the effective quantities for the combined front and rear axles. For example, the front suspension spring stiffness, k f s , given below is the stiffness for both the front driver-side and front enger side suspensions (i.e. k f s = k f sd + k f sp where k f sd and k f sp and the driver- and enger-side spring constants at the front end). Thus, published data for spring stiffness and damping constant are for each individual spring and shock absorber and not for the combined front or rear suspensions. To facilitate your simulations, make the following assumptions: • The vehicle drives at a constant velocity; • The road surface is a repeated oscillation; and • The road provile can be reasonably represented by piece-wise linear approximations.

Problem You will derive 3 scenarios for road profiles that the vehicle will drive over. You must provide x-y plots of these profiles within your report and describe in detail the scenarios your are simulating. Include a description of the general geometry of the repeated road input and describe the circumstances under which the vehicle is driving over these inputs providing information like the approximate velocity. Scenarios should be realistic. A Simulink block diagram and sample MATLAB scripts are provided at the course website: • HalfCarSuspensionModel02.mdl – Simulink block diagram, • HalfCarSuspensionTimeResponse.m – main MATLAB script to simulate responses, • SpeedBumps.m – function to generate road profile for “Speed Bumps” scenario from class notes, and • HighwayWarningTrack.m – function to generate road profile for “Highway Warning Track” scenario from class notes.

1

Parameter kft bft m f us kfs bfs Ic ms krs brs mrus krt brt L Lf Lr

Value 200 kN/m 125 N-s/m 100 kg 30 kN/m 750 N-s/m 2704 kg-m2 1700 kg 20 kN/m 750 N-s/m 80 kg 200 kN/m 125 N-s/m 2.7 m 1.1 m 1.6 m

Description front tire stiffness font tire damping front suspension unsprung mass front suspension stiffness font suspension damping pitch rotational inertia vehicle sprung mass rear suspension stiffness rear suspension damping rear suspension unsprung mass rear tire stiffness rear tire damping wheel base length from center of mass to rear axle length from center of mass to front axle

Table 1: Generic sedan vehicle parameters.

V ms, Ic krs yrus yroad(x-L)

Lr

yc

Lf x

brs

kfs

mrus krt

bfs mfus

brt

kft L

Figure 1: Half-car suspension model schematic.

2

bft

yfus yroad(x)

Tasks Complete the following tasks: 1. Derive 3 road input scenarios. 2. Describe each scenario providing general geometry of the road profile including x-y plots, vehicle velocity, and a description of the “real-life” circumstance the scenario is supposed to simulate. 3. Simulate the response of the vehicle to the 3 scenarios. For each scenario, provide 3 separate plots that show (1) the vehicle responses, (2) the suspension responses, and (3) the tire responses. 4. Analyze the results for the 3 scenarios. For each explain which of the 3 subsystems (i.e. vehicle dynamics, suspension dynamics, or tire dynamics) is most active and why.

Grading You will be graded separately on the numerical simulations and the report.

Simulations For the simulations, you must submit as a an appendix to your report all the MATLAB scripts and Simulink block diagrams used to create the plots. You should also include plots of results. Some of these plots should appear within the body of the report and the rest can be placed in the appendix. You will graded on the neatness and organization of your scripts, block diagrams, and plots. Use good programming practices like providing comments within the scripts. Rule of thumb on plots: the reader should be able to easily decipher what the plot represents (i.e. use labels and legends and organize the data in an appropriate manner). You will also be graded on the completeness of the results provided whether within the body of the report or within the appendix. Variable Neatness Organization Completeness

Percentage 10 20 70

Report You must submit a report using the Report Template mentioned above. Be sure to follow the recommendations mentioned within the template. For instance, figures should have captions and should appear within the width of the column. You will be graded on neatness, creativity, and completeness. Make your document look professional. Credit will be given to those that spend extra effort devising realistic road or off-road surface profiles. Keep in mind that you are describing your results to a client, so be sure to provide sufficient evidence to your final design. Make sure that the client can follow along how you came to a final decision. Variable Creativity Neatness Organization Completeness

3

Percentage 20 10 20 50