Introduction

This book is not intended to be exclusively of interest to automotive engineers, either in training or in post, although they have formed the majority of the readership of previous editions. It is intended to be of assistance to those involved not only with the actual testing of engines, powertrains and vehicles, but also with all aspects of projects that involve the design, planning, building, and major modernization of engine and powertrain test facilities.

We are today (2011) at a significant break in the continuity of automotive engine and powertrain development. Such is the degree of system integration within the modern vehicle, marine, and generating machinery installations that the word "engine" is now frequently replaced in the automotive industries by the more general term "powertrain".

So, while much of this book is concerned with the design, construction, and use of facilities that test internal combustion engines, the boundaries of what exactly constitutes the primary automotive IC power source is becoming increasingly indistinct as hybridization, integration of electrical drives, and fuel cell systems are developed.

The unit under test (UUT) in most cells today, running automotive engines, has to either include actual or simulated vehicle parts and controllers, not previously thought of as engine components. This volume covers the testing of these evolving powertrain technologies, including transmission modules, in so far as they affect the design and use of automotive test facilities.

Drivers' perception of their vehicle's performance and its drivability is now determined less by its mechanical properties and more by the various software models residing in control systems interposed between the driver and the vehicle's actuating hardware. Most drivers are unaware of the degree to which their vehicles have become "drive by wire", making them, the driver, more of a vehicle commander than a controller. In the latter role the human uses the vehicle controls, including the accelerator pedal, to communicate his or her intention, but it is the engine control unit (ECU), calibrated and mapped in the test cell, that determines how and if the intention is carried out. In the lifetime of this volume this trend will develop to the point, perhaps, where driver behavior is regionally constrained.

Twenty years ago drivability attributes were largely the direct result of the mechanical configuration of the powertrain and vehicle. Drivability and performance would be tuned by changing that configuration, but today it is the test engineers and software developers that select and enforce, through control "maps", the powertrain and vehicle characteristics.

In all but motor sport applications the primary criteria for the selected performance maps are those of meeting the requirements of legislative tests, and only secondarily the needs of user profiles within their target market.

Both US and European legislation is now requiring the installation, in new light vehicles, of vehicle stability systems that, in a predetermined set of circumstances, judge that the driver is about to lose control or, in conditions that are outside a pre-programmed norm, intervenes and, depending on one's view, either takes over powertrain control and attempts to "correct" the driver's actions, or assists the driver to keep a conventional model of vehicle control.

A potential problem with these manufacturer-specific, driver assistance systems is their performance in abnormal conditions, such as deep snow or corrugated sand, when drivers, few of whom ever read the vehicle user manual, may be unaware of how or if the systems should be switched on or off.

Similarly, on-board diagnostic (OBD) systems are becoming mandatory worldwide but their capabilities and roles are far exceeding the legislatively required OBD-11 monitoring of the performance of the exhaust emission control system. Such systems have the potential to cause considerable problems to the test engineer rigging and running any part of an automotive powertrain in the test cell (see Chapter 11).

The task of powertrain and vehicle control system optimization known as powertrain and vehicle calibration has led to the development of a key new role of the engine test cell, a generation of specially trained engineers, test techniques, and specialized software tools.

The task of the automotive calibration engineer is to optimize the performance of the engine and its transmission for a range of vehicle models and drivers, within the constraints of a range of legislation. While engines can be optimized against legislation in the test cell, provided they are fitted with their vehicle exhaust systems, vehicle optimization is not such a precise process. Vehicle optimization requires both human and terrain interfaces, which introduces another layer of integration to the powertrain engineer. The same "world engine" may need to satisfy the quite different requirements of, for example, a German in Bavaria and an American in Denver, which means much powertrain calibration work is specific to a vehicle model defined by chosen national terrain and driver profiles.

This raises the subject of drivability, how it is specified and tested. In this book the author has, rather too wordily, defined drivability as follows:

For a vehicle to have good drivability requires that any driver and passengers, providing they are within the user group for which the vehicle was designed, should feel safe and confident, through all their physical senses, that the vehicle's reactions to any driver input, during all driving situations, are commensurate to that input, immediate, yet sufficiently damped and, above all, predictable.

Testing this drivability requirement in an engine or powertrain test bed is difficult, yet the development work done therein can greatly affect the character of the resulting vehicle(s); therefore, the engine test engineer must not work in organizational or developmental isolation from the user groups.

A proxy for drivability of IC engine-powered vehicles that is currently used is a set of constraints on the rate of change of state of engine actuators. Thus, within the vehicle's regions of operation covered by emission legislation, "smoothness" of powertrain actuator operation may be equated with acceptable drivability.

The coming generation of electric vehicles will have drivability characteristics almost entirely determined by their control systems and the storage capacity of their batteries. The whole responsibility for specification, development, and testing this "artificial" control and drivability model, for every combination of vehicle and driver type, will fall upon the automotive engineer.

Most drivability testing known to the author is based on a combination of subjective judgment and/or statistically compiled software models based on data from instrumented vehicles; this area of modeling and testing will be an interesting and demanding area of development in the coming years.

Fortunately for both the author and readers of this book, those laws of chemistry and thermodynamics relevant to the internal combustion engine and its associated plant have not been subject to change since the publication of the first edition over 17 years ago. This means that, with the exception of clarifications based on reader feedback, the text within chapters dealing with the basic physics of test facility design has remained little changed since the third edition.

Unfortunately for us all, the laws made by man have not remained unchanging over the lifetime of any one of the previous editions. The evolution of these laws continues to modify both the physical layout of automotive test cells and the working life of many automotive test engineers. Where possible, this volume gives references or links to sources of up-to-date information concerning worldwide legislation.

Legislation both drives and distorts development. This is as true of tax legislation as it is for safety or exhaust emission legislation. A concentration on CO2 emission, enforced via tax in the UK, has distorted both the development of engines and their test regimes. Legislation avoidance strategies tend to be developed, such as those that allow vehicles to meet "drive-by" noise tests at legislative dictated accelerations but to automatically bypass some silencing (muffling) components at higher accelerations.

From many site visits and discussions with managers and engineers, it has been noticeable to the author that the latest generation of both test facility users and the commissioning staff of the test instrumentation tend to be specialists, trained and highly competent in the digital technologies. In this increasingly software-dependent world of automotive engineering, this expertise is vital, but it can be lacking in an appreciation of the mechanics, physics, and established best practices of powertrain test processes and facility requirements. Narrowing specialization, in the author's recent experience, has led to operational problems in both specification and operation of test facilities, so no apology is offered for repeating in this edition some fundamental advice based on experience. Many of the recommendations based on experience within this book have stories behind them worthy of a quite different type of volume.

All test engineers live in a world that is increasingly dominated by digital technology and legal, objective, audited "box-ticking" requirements, yet the outcome of most automotive testing remains stubbornly analog and...