Motorcycle (Quarter-Car) Suspension Simulation

MECE 4333 - Vehicle Systems Modeling and ControlThe University of Texas - Pan American

July 17, 2006

Introduction

You have been asked to model the response of the front suspension of a motorcycle (refer to Figure1). Themodel will later be used to design a active suspension component. The model should be able to accommodatea realistic range of frequency inputs from the road surface.The motorcycle suspension is being designedfor a dual-purpose motorcycle that will be used on- and off-road. It will be a touring bike primarily targetedat customers that like to travel on their motorcycle but wishto take it off-road occasionally to exploresand dunes, logging trails, creek beds, etc. A range of spring constants and damping coefficients have bedetermined and are provided below. However, because the motorcycle will be dual purpose and will use atire with some off-road capability, there is some concern asto how the tire wall stiffness and air pressurewill affect the performance. A tire with specified parameters has be chosen for the preliminary design (seekt

andbt below). Thus, you should model the front suspension dynamics with and with out the tire complianceand damping.

Problem

You must numerically explore the range of possible designs and provide the customer some feedback thatwill help him/her select appropriate springs and shock absorbers. The customer has specified that the allow-able spring rate and damping constant ranges are 2000-8000 N/m and 20-80 N-s/m, respectively. Remember

Figure 1: Photorealistic view of front suspension of the motorcycle.

1

that the bike will be dual purpose and must have reasonable off-road ability. Some pertinent parameters areprovided below.

Parameter Value DescriptionWs 500 lb Motorcycle weight w/o driverWus 100 lb Front suspension unsprung weightF/R 45/55 Front/Rear weight distributionkt 80 kN/m Tire wall stiffnessbt 100 N-s/m Tire damping constant

You must model the system in MATLAB/Simulink using several spring rate/damper constant options.You must determine what the best combination of spring rate and damper constant is for this dual purposeapplication. To do so, you will need to simulate the responsefor the range of spring rates and damperconstants. Additionally, you will have to numerically experiment with a variety of road/terrain profile inputs.You must derive these inputs yourself, one for a reasonable road surface and another for an off-road surface.Your simulations should account for the weight of an averagedriver (remember that the weight distributionfront to rear is 40/60).

Tasks

Complete the following tasks:

1. Derive appropriate profiles to represent the road and off-road terrain surfaces. Within your report,provide 2-D plots of these profiles with labels. Also, In yourreport describe how you came up withthese profiles.

2. Assume that the motorcycle is traveling at a constant velocity of your choice (you must qualify thischoice for each surface profile), and program the profile intoSimulink as the input to your system.

3. Simulate the response of the motorcycle front suspensionfor numerous combinations of spring ratesand damper constants within the ranges specified above usingeach of the surface profiles as inputs.Within your report provide plots of several of these responses including plots for your recommendedspring/damper combination. Be sure to discuss the results and describe how you chose your finaldesign.

4. Submit a report detailing your results and final design. Follow the organization provided by theReport Templatewhich you can download from the classWeb site.

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 Simulinkblock diagrams used to create the plots. You should also include plots of results. Some of these plots shouldappear within the body of the report and the rest can be placedin the appendix. You will graded on theneatness and organization of your scripts, block diagrams,and plots. Use good programming practices likeproviding comments within the scripts. Rule of thumb on plots: the reader (or client) should be able to

2

easily decipher what the plot represents (i.e. use labels and legends and organize the data in an appropriatemanner). You will also be graded on the completeness of the results provided whether within the body ofthe report or within the appendix.

Variable PercentageNeatness 10Organization 20Completness 70

Report

You must submit a report using theReport Templatementioned above. Be sure to follow the recommenda-tions mentioned within the template. For instance, figures should have captions and should appear within thewidth of the column. You will be graded on neatness, creativity, and completeness. Make your documentlook professional. Credit will be given to those that spend extra effort devising realistic road or off-roadsurface profiles. Keep in mind that you are describing your results to a client, so be sure to provide sufficientevidence to support your final design. Make sure that the client can follow along how you came to a finaldecision.

Variable PercentageCreativity 20Neatness 10Organization 20Completness 50

3