Design and Manufacture of an Adaptive Suspension System A Major Qualifying Project Report submitted to the faculty of WORCESTER POLYTECHNIC INSTITUTE This report represents the work of WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review. For more information about the projects program at WPI, please see http://www.wpi.edu/academics/ugradstudies/project-learning.html In partial fulfillment of the requirements for the Degree of Bachelor Science By Michael Gifford, Mechanical Engineering Tanner Landis, Mechanical Engineering Cody Wood, Mechanical Engineering Date April 30, 2015 Professor Cagdas Onal, Advisor Siamak Ghorbani-Faal, Co-Advisor Abstract This project focuses on the design, development, evaluation, and analysis of an adjustable vehicle suspension system. This system is aimed to improve vehicle performance on all terrain conditions from rough to flat surfaces. The proposed design is accomplished through the modification of a double-triangulated four-bar linkage suspension. The modifications allow the upper links of the suspension system to change vertical position on-the-fly, to meet operator preference. The position change alters suspension geometry and therefore the performance characteristics of the vehicle; specifically the anti-squat which impacts vehicle sag and therefore traction. Thus, traction is directly controlled through adjustments to the suspension system. Through video motion analysis of a prototype vehicle before and after the proposed design modifications, we rigorously evaluated the effect of the adjustable suspension system. Future applications of this design are expected to improve the performance characteristics of vehicles of all sizes, ranging from mobile robots to automobiles. In addition to scalability, the advantage of our design is the on-the-fly adaptability, which enables adjustments in suspension performance for the terrain or obstacle being traversed. Authorship This report was a combined effort between all members of our MQP team. Each member evenly contributed to this project and report. 2 | P a g e Acknowledgements Our project team would like to thank all of the following people whose contributions played an important role in the completion of our project: Advisor: Cagdas Onal Co-advisor: Siamak Ghorbani-Faal Thank you to everyone else who helped us throughout this project including the WPI Library Staff, the Rapid Prototyping Team and Ming Luo 3 | P a g e Table of Contents Abstract ........................................................................................................................................... 1 Authorship....................................................................................................................................... 2 Acknowledgements ......................................................................................................................... 3 List of Figures ................................................................................................................................. 7 1.0 Introduction ............................................................................................................................... 9 2.0 Background ............................................................................................................................. 10 2.1 Springs ................................................................................................................................. 10 2.1.1 Leaf Springs .................................................................................................................. 11 2.1.2 Coil Springs .................................................................................................................. 14 2.1.3 Air Springs .................................................................................................................... 15 2.1.4 Torsion Bars ................................................................................................................. 16 2.1.5 Rubber Springs ............................................................................................................. 17 2.1.6 Spring Causes and Effects ............................................................................................ 18 2.2 Shock Dampers ................................................................................................................... 19 2.2.1 Hydraulic Pressure ........................................................................................................ 19 2.2.2 Gas Pressure ................................................................................................................. 19 2.2.3 Air Pressure .................................................................................................................. 20 2.3 Definitions and Scientific Rationale ................................................................................... 21 2.3.1 Anti-squat ..................................................................................................................... 21 2.3.2 Roll-axis........................................................................................................................ 21 2.3.3 Anti-roll bars................................................................................................................. 23 2.3.4 Pinion Angle ................................................................................................................. 25 2.3.5 Center of Gravity .......................................................................................................... 26 2.4 Suspension Systems ............................................................................................................ 27 2.5 Linkage Suspension Systems .............................................................................................. 27 2.5.1 Four Bar Linkage Suspensions ..................................................................................... 27 2.5.2 Current styles of Four Bars ........................................................................................... 28 2.5.3 Advantages vs. Disadvantages ..................................................................................... 30 2.6 Actuators ............................................................................................................................. 31 2.6.1 Hydraulic Actuators ...................................................................................................... 31 4 | P a g e 2.6.2 Pneumatic Actuators ..................................................................................................... 31 2.6.3 Rotational Servomechanisms ....................................................................................... 31 2.7 Specifications for Road Legal Vehicles .............................................................................. 32 2.8 User Interface ...................................................................................................................... 32 2.9 Project Foundation .............................................................................................................. 33 2.9.1 Lab Scale Prototype ...................................................................................................... 33 2.9.2 The Jeep Forward Control ............................................................................................ 33 3.0 Goal Statement ........................................................................................................................ 35 4.0 Methodology ........................................................................................................................... 36 4.1 Determination of 4-Bar Linkage Suspension Degrees of Freedom .................................... 36 4.2 Determination of Anti-Squat ............................................................................................... 36 4.3 Design Constraints .............................................................................................................. 37 4.4 Modeling ............................................................................................................................. 37 4.5 Preliminary Design Options ................................................................................................ 38 4.5.1 Design 1: Coordinate Grid Design ............................................................................... 42 4.5.2 Design 2: Rotational Actuator Design .......................................................................... 43 4.5.3 Design 3: Single Motion Design .................................................................................. 47 4.6 Final Design ........................................................................................................................ 50 4.7 Prototyping .......................................................................................................................... 53 4.8 Test and Analysis ................................................................................................................ 56 4.8.1 Acceleration Test .......................................................................................................... 57 4.8.2 Slope Test ....................................................................................................................