Investigating the Handling Response of UH-BEV21 Vehicle Using vsim in MATLAB

The design of the vehicle’s platform allows the location of the battery pack to be moved forwards or backwards resulting in a +/- 5% shift of weight bias. The precise location of the battery pack has yet to be determined. Considering a stable handling requirement for the UH-BEV21 vehicle, the front to rear weight bias is a key aim of this investigation.

Setting Up the Vehicle Simulation

As previously discussed, the vehicle simulation program has been created to run in the MATLAB environment. You have free access to a fully licenced versions of this software which you can access by logging into the MathWorks website. Once logged in, you can download a copy of this software for use on your own computer. Please note vsim has not been developed to run using the online version of the software, therefore please do not use vsim using Matlab online. The alternative to installing Matlab on your own PC is to use the UH remote desktop application. Please note that whilst this assignment requires the use of MATLAB, a detailed knowledge of programming using this software is not required. The focus of this assignment is the use of the simulation software and the interpretation of the data generated.  

The baseline vehicle model available in vsim is called UH_BEV21. The latest release of vsim is “vsim97” and can be downloaded from the assignment briefing area. It is recommended to save a copy of the vsim97 folder on your UH Onedrive.  

Before running vsim, ensure that the vsim97 folder is selected as the current folder in Matlab. The program will fail to load otherwise. Enter vsim97 in the Command Window to start the program. From the Simulation Options available, select Skid-Pan Test (Fast Program, based on Steady-State analysis) – (SkidPan SS).

In the Skid-Pan Test simulation program, choose the vehicle file by clicking Load Vehicle, select UH BEV21. Change the radius of turn to 33 metres. Change the default friction constant to 0.8. To load the tyre file, select Pacejka 89 – Hemingway coefficients, select the 245/35 ZR 18 file for both the front and rear tyres.

The car data file contains a number of user definable variables, the supplied model represents the baseline UH BEV21 vehicle and can be used as supplied for the first part of the assignment. If changes are made to the variables, you must either select Update All Data Only or Update All Data and Save File for the change to have effect when the simulation is next run. If the former option is used, it is possible to revert to the previous configuration.

Deliverables

Deliverables

In Chapter 4 of this assignment brief you will find four questions, which will lead you in a logical fashion through the investigation. Please answer each question in turn taking care to address all the points raised in each question.

Please simply provide answers to the questions. There is no requirement in this assignment to adhere to normal technical report style i.e. abstracts, conclusions etc are not required, although the use of a normal technical writing style is required. Questions 1 to 3 should be no longer the 400 words each. Question 4 should be no longer than 600 words. Citations from external sources should be used as required and referenced in a consistent manner.

Marks will be given for the quality of the technical analysis and discussion of the simulated data and the way you present your arguments. You are encouraged to use figures displaying data generated using the model where appropriate. You will also be graded on the quality of your figures. It is acceptable for figures to be made using either MATLAB’s built in graphing tool or using a spreadsheet. Please do not present screenshots of traces from MATLAB. Hand drawn graphs are also not acceptable.

Report Format and structure – visual presentation, legibility and layout.

Language used – standard of writing (grammar, spelling & punctuation). Fluency, conciseness and effectiveness of communicating ideas.

Technical content - Quality of analysis, depth and appropriateness. Quality of conclusions.

Use of MATLAB, presentation of graphs, diagrams and proper reference citations

Report Format and structure – visual presentation, legibility and layout.

Language used – standard of writing (grammar, spelling & punctuation). Fluency, conciseness and effectiveness of communicating ideas.

Technical content - Quality of analysis, depth and appropriateness. Quality of conclusions and proper reference citations.

Standard University Lateness penalties will apply, see P.1 of this assignment briefing sheet for details

The Questions

Question 1 – Determination of the Handling Response of the Baseline Car

i.Determine the Ackermann steer angle for the UH-BEV21 on a circular skid pad following a 33m radius turn. Assume the vehicle centre line tracks a 33m radius.

ii.After running the skid pad simulation, present a graph of front wheel steer angle in degrees versus lateral acceleration. You will need to calculate the lateral acceleration from the vehicle’s speed and radius of turn.

iii.Determine the ideal yaw rate of the vehicle at the limiting speed of the skid pad test. This corresponds to the yaw rate a neutral handling car would possess.  

iv.Compare the steady state yaw rate of the prototype vehicle at its limiting speed to that of the ideal vehicle.

v.Using your answers from parts i – iv, explain the nature of the handling behaviour of the prototype vehicle is and if the limit behaviour is appropriate for a production road car.

Question 2 – Review of Vehicle Design Specification With Respect to Vehicle Handling

i.From Page 1 of the Chassis input data in the vsim car file, discuss what you believe to be the key reasons that explain the vehicle handling traits seen in the baseline setup examined in question 1. Your answer should make reference to the stability margin and design influences that affect handling balance.

ii.Considering the baseline vehicle handling balance and recalling that the vehicle’s platform allows the location of the battery pack to be moved forwards or backwards resulting in a +/- 5% shift of weight bias, state with justification what the revised front percentage weight bias should be to increase (i.e. make positive) the vehicle’s understeer gradient.

Question 3 – Investigating the Impact of Change to Weight Bias

Using your answer from Question 2 ii) answer the following:

i.Present a graph of front wheel steer angle in degrees versus lateral acceleration for both the baseline configuration and the new vehicle configuration. Discuss the new results and how they compare to the response at the limit for a neutral handling vehicle.  

ii.Compare the steady state yaw rate of the new configuration vehicle at its limiting speed to that of the baseline and the ideal vehicle.

iii.From the results seen in Questions 3 i – ii) explain what the handling behaviour of the new vehicle configuration is and if the handling balance is appropriate for a production road car.

Question 4 – Investigating the Impact of Design Influences on Handling Balance

The UH-BEV21 design team are keen to further promote an increased understeer gradient. You are to recommend design changes that can be implemented to increase the vehicle’s understeer gradient. You are to validate your recommendations by presenting new skid pad test results following further skid pad testing using the vsim software. You must include graphical results in your answer to back up your findings. Finally, you are to present an updated UH-BEV21 Vehicle Design Specification table, highlighting any changes from the baseline specification.