Path Following Performance of Narrow Tilting Vehicles Equipped With Active Steering

Abstract

Narrow Tilting Vehicles offer an opportunity to reduce both traffic congestion and carbon emissions by having a small road footprint, low weight, and a small frontal area. Their narrow width requires that they tilt into corners to maintain stability; this may be achieved by means of an automated tilting system. Automated tilt control systems can be classed as Steering Tilt Control (STC) in which active control of the front wheel steer angle is used to maintain stability, Direct Tilt Control (DTC) in which some form of actuator is used to exert a moment between the tilting part(s) of the vehicle and a non-tilting base, or a combination of the two (SDTC). Combined SDTC systems have the potential to offer improved performance as, unlike STC systems, they are effective at low speeds whilst offering superior transient roll stability to DTC systems. However, alterations to the front wheel steer angle made by STC and SDTC systems may result in unwanted deviations from the driver’s intended path. This paper uses multi-body simulations of a three-wheeled Narrow Tilting Vehicle performing an emergency lane change manoeuvre to show that the path followed by a SDTC equipped vehicle in response to a given series of steer inputs differs significantly from that followed by a DTC equipped vehicle. It is also shown that by using a revised series of steer inputs, a vehicle equipped with SDTC is able to successfully follow a similar path to one equipped with DTC, and that the roll stability of the vehicle is not unduly compromised. Finally, the influence of higher DTC system gains on the SDTC system is considered. It is shown that the result is a small improvement in the vehicle’s path following response at the expense of a small reduction in vehicle roll stability.