Page 502 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 1 5. 1 Modelling and assembly of the full vehicle

Table 15.1-4 A portion of an MSC.ADAMS command file showing the implementation of differential equations to retrieve and use integral and
derivative terms for a state variable

Alternatively, the preview vector can be adjusted for ‘model’ the driver needs in order to retain control in
body slip angle before it is used if oscilliatory behaviour is what would otherwise become stressful circumstances of
to be avoided. The length of the preview vector must be non-linear vehicle behaviour and multiple requirements
adjusted with speed if reasonably consistent behaviour is for control – typically vehicle orientation (body slip
to be produced. For ‘normal’ driving this type of model angle) and velocity (path control). Useful learning occurs
can produce acceptably plausible results but for ma- on low grip environments that can be readily transferred
noeuvres such as the ISO 3888 Lane Change the be- across to high grip. In low grip environments, the ex-
haviour becomes unacceptably oscilliatory particularly treme non-linearity of response of the vehicle can be
after the manoeuvre. explored at low speeds and with low stress levels,
An alternative method, used by the authors with some allowing the driver to piece together a model to be used
success for a variety of extreme manoeuvres, is to focus within their own heads; it is then a matter of practice to
on the behaviour of the front axle. This model fits with transfer the lessons to a high grip environment. The same
one of the author’s (Harty) experience of driving at or concepts can be used to explore the behaviour of a driver
near the handling limit, particularly on surfaces such as model within a multibody system environment such as
snow where large body slip angles highlight the mecha- MSC.ADAMS.
nisms used in the driver’s mind. High performance The formulation used is described below. All sub-
driving coaches rightly concentrate on the use of a scripts x and y are in the vehicle reference frame. The

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