Fundamentals of Vehicle Dynamics and Modeling, 1 by Bruce P Minaker

Fundamentals of Vehicle Dynamics and Modelling

A Textbook for Engineers with Illustrations and Examples

Bruce P.Minaker

University ofWindsor
ON, CA

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Preface

This is my first attempt at writing a book. After many years of effort, I realize now that I was unprepared for such a task when I began, but I did it in the hopes that some of you may find it useful. What prompted this foray into the textbook market? Over many years of university teaching, I have found many texts on this topic and others that, while providing good relevant coverage, add much more content than necessary. I believe that this level of breadth is not in the reader's best interest, with many left overwhelmed by the prospect of mastering so much material, and eventually resigning themselves to never finishing. It is intimidating for a student to contemplate absorbing over a thousand pages in a twelve‐week semester.

My objective was to produce a book that is suitable for a single‐semester senior undergraduate or early graduate level mechanical engineering course, perhaps in a program with some focus on automotive engineering. It assumes that the student has some foundation in mathematics, particularly linear algebra and differential equations, and basic rigid body dynamics. The book does not aim to be a complete reference, but rather to give a solid foundation while generating enthusiasm in the student reader. I have found vehicle dynamics to be a most intellectually rewarding topic, and if I can share some of that with my readers, then I have accomplished my goal.

The book opens with some brief general discussion of the topic, and follows with an introduction to tire modelling. It includes material on longitudinal dynamics, lateral dynamics, and vertical dynamics. I have included many of the classic models that first drew me in, problems small enough to solve by hand on paper, without the use of a computer. This leads into some larger problems, tied to my work on automatic generation of the equations of motion of multibody systems, and its application to vehicle dynamics. The text concludes with a chapter expanding the necessary mathematical background for those readers who may require it.

I would like the reader to come away with answers to the three following questions: First, what are the concepts and tools used to generate a mathematical model of vehicle motion? Next, what are the fundamental vehicle ride and handling behaviours that we can predict from well‐established models? Finally, how has the arrival of multibody dynamics and computer aided engineering changed what we can do now? Hopefully, this will remove some of the mystery behind many of the software tools used in industry today, and how they generate at their results.

Astute readers may notice what seems like an odd combination of British and American English styles in the text. This stems from my education in and use of Canadian English. You can expect ‘‐our’ rather than ‘‐or’, but ‘‐ize’ instead of ‘‐ise’. In any instance where there was flexibililty in spelling, punctuation or grammar, I have tried to emulate those pre‐war vintage textbooks that I enjoy collecting.

Bruce P. Minaker

Windsor, Ontario, Canada

List of Symbols

A mathematical style consistent with formatting standards is used wherever possible throughout the text. This has proven to be surprisingly difficult, as the symbols that have typically been associated with certain quantities tend to be inconsistent between fields, or overlapping. As a result, a few concessions and stylistic choices have been made, e.g., the character images has been used to indicate a damping matrix, in place of the more commonly used images, as the latter is also used in the standard state space form. The lowercase images is still used to indicate a damping coefficient in the scalar case.

Upright characters indicate a mathematical constant (images, images, images), italics are used to indicate a quantity is a mathematical variable, (images, images), and boldface is used to indicate a vector quantity, (images, images). Lowercase characters are chosen wherever possible, with the exception of matrices, which are always set in bold upright uppercase (images, images). When the appropriate lowercase character is already in use, an uppercase character may be substituted. Historically, certain quantities (e.g., scalar components of force and moment vectors) have been set in uppercase; these choices are maintained when appropriate. No distinction is made between Latin and Greek characters when formatting; the traditional Greek characters are maintained for several quantities. Multicharacter names are avoided, to eliminate confusion with products of variables. Note that these rules are also applied to subscripts, i.e., if a quantity is marked with an italic subscript, that subscript is itself a variable. An upright subscript indicates a specific named instance of the variable. Any character modified with a dot above indicates the time derivative of that quantity (images, images). A vector modified with a circumflex indicates a unit vector (images). The standard basis vectors are images, images, and images. A vector modified with a tilde indicates the skew symmetric matrix of the vector (images). A pair of vertical bars around a character is used to indicate the absolute value of a scalar, the magnitude of a vector or a complex number, or the amplitude of a time varying sinusoid (images, images). The transpose of a matrix or a vector is indicated using a prime (images). Column vectors may be presented as a row by using transpose notation for the space savings offered.

In 1976, the Society of Automotive Engineers (SAE) published standard J670e, establishing a convention for terminology and notation for vehicle dynamics. In 1991, the International Organization for Standardization (ISO) published a vehicle dynamics vocabulary, ISO 8855. The SAE J670e and ISO 8855 standards are incompatible in several aspects, the most notable being the axis systems defined in the two documents. The SAE standard utilizes an axis system based on aeronautical practice, with the images axis positive forward, the images axis positive to the driver's right, and the images axis positive down. The ISO standard utilizes an axis system with the images axis positive forward, the images axis positive to the driver's left, and the images axis positive up. In this text, the SAE standard and the corresponding historical aeronautical notation will be used in the discussion of the vehicle models in Chapters 3, 4, and 5, as they were developed well before 1991. In Chapter 6, an ISO‐style axis system will be used when discussing a modern multibody dynamics approach.

Scalar symbols

Symbol Description
images longitudinal distance from mass centre to front axle
images longitudinal distance from mass centre to rear axle
images damping coefficient, or tire cornering coefficient
images drag coefficient
images arbitrary constant coefficient
images arbitrary constant coefficient
images longitudinal distance from mass centre to trailer hitch
images longitudinal distance from trailer mass centre to trailer hitch
images force, or arbitrary function
images gravitational acceleration
images longitudinal distance from trailer mass centre to trailer axle, or time step
images centre of mass height
images counter increment
images spring stiffness
Symbol Description
images pitch radius of gyration
images yaw radius of gyration
images length
images mass
images counter end, or dimension
images angular velocity, images axis direction
images angular velocity, images axis direction
images angular velocity, images axis direction
images eigenvalue, or exponent coefficient
images time, or track width
images linear velocity, images axis direction
images linear velocity, images axis direction
images linear velocity, images axis direction
images location, images axis direction
images location, images axis direction
images location, images axis direction
images centre of mass
images roll moment of inertia
images pitch moment of inertia
images yaw moment of inertia
images frontal area
images moment, images axis direction
images moment, images axis direction
images moment, images axis direction
images power
images cornering radius
images time step size, discrete time
images force, images axis direction
images force, images axis direction
images force, images axis direction

Vector or matrix symbols

Symbol Description
images acceleration vector
images force vector
images moment vector
images location and orientation vector
images radius vector
images spin vector
images input signal
images unit vector
images linear and angular velocity vector
images state vector, location vector, eigenvector
images output vector
images vertical location vector
images system matrix
images input matrix
images output matrix
images feedthrough matrix
images descriptor matrix
images input force matrix
images input rate force matrix, or transfer function matrix
images deflection Jacobian matrix
images identity matrix
images inertia matrix
images constraint Jacobian matrix
images stiffness matrix
images damping matrix
images mass matrix
images transformation matrix
images rotation matrix
images angular velocity transformation matrix
images orthogonal complement matrix
images orthogonal complement matrix
images velocity matrix

Greek symbols

Symbol Description
images tire slip angle
images body slip angle
images trailer sway angle
images steer angle
images camber angle
images damping ratio
images efficiency
images pitch angle
images friction gradient
images wavelength
images coefficient of friction
images jacking force angle
images density
images real component of eigenvalue, or tire slip ratio
images time constant
images roll angle, or phase angle
images yaw angle
images imaginary component of eigenvalue, or angular frequency
images angular acceleration vector
images elastic deflection vector
images angular position vector
images Lagrange multiplier
images linear velocity vector
images constraint equation vector
images angular velocity vector