A Study On Unsprung Mass with In-Wheel Motors – Myths and Realities

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Abstract: A Study On Unsprung Mass

It has long been widely accepted that unsprung mass is an important parameter in ride and
handling behaviour. In a wide-ranging study connected to feasibility studies for in-wheel motors,
some specific and detailed measures for the sizes of the effects in play have been taken – and the
reality is something of a surprise compared to what “everybody knows”. Subjective, Objective and
Predictive measures of ride & handling suggest that the modern development toolbox is easily
capable of restoring dynamic performance and that the opportunities afforded by in-wheel motors
in terms of packaging and vehicle dynamics control are of substantial interest to the vehicle
dynamics community.

A Study On Unsprung Mass – Content

The studies were carried out using numerical models and real physical vehicles. Primary concerns with the addition of hub motors centre on:

i) degraded roadholding

ii) degraded ride comfort

In evaluating vehicle performance, it is unwise to become obsessive about a single measure. Instead it is good practice to consider a so-called “balanced scorecard” with a number of different indicators. These indicators can be expressed using numerical measures, whether formed from predictive modelling, measured data or subjective review in-vehicle with an expert assessor.

Ground vehicle dynamic performance can be broadly split into:

– ride: the ability of the vehicle to absorb disturbances

– refinement: the ability of the vehicle to attenuate noise and vibration

– active safety: the ability to stop and steer in emergency situations

– driveability: the response of the vehicle to the controls – steering, braking and drive – in normal situations.

Exercises were carried out using subjective assessment, objective measurements and predictive analysis to review the impact on dynamic performance with increased unsprung mass.