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The active tilting system was implemented by adding an additional degree of freedom (DOF) at the connection between the front tires and the front independent suspension. The additional DOF, which is modeled as a revolute joint, allows the wheel to rotate about the vehicle body fixed x-axis.

Active tilting system modeled for three-wheeled city vehicle

Megacities were in mind when a team of researchers from the University of Waterloo undertook a study on an active tilting system for a three-wheeled personal vehicle. The idea was that a compact vehicle with a narrow track and tilting capability would be a good solution to the megacity problems of congestion and limited parking availability.

Among the big challenges of a narrow-track vehicle is stability. Vehicles such as Toyota’s concept i-Road three-wheeler (two wheels in front, one in back) have a track and wheelbase about half that of a conventional car. (The i-Road has an active tilting system of its own that changes the wheel’s camber angle.)

Active tilting has been studied not only by some automakers, but by independent researchers as well. The University of Waterloo researchers believe the effects of tilting systems on three-wheelers’ maneuverability and safety in different driving conditions have not been fully analyzed.

For their specific objectives, the researchers’ goal was to demonstrate better maneuverability of their tilting system compared to a base vehicle with no tilting functionality. They implemented a model in Maplesoft’s MapleSim multidomain symbolic simulation environment for comparison of system performance at different speeds and front-wheel steering angles.

There were three main simulation inputs to the tilting: the vehicle’s longitudinal speed, the front wheel’s steering angle, and the desired yaw rate. The three inputs were modeled using a ramp profile, and it was assumed that the steering and desired yaw rate inputs had the same signal parameters, such as the ramp duration and time offset, but with a different magnitude. In reality, the two inputs are not be perfectly matched due to delays in the active tilting and steering systems. Also, the steering and tilting inputs are activated after certain period when the vehicle’s vertical motions are in a steady state. The aerodynamics, gradient, and rolling resistance forces were not included in the simulations.

The active tilting system improved the vehicle’s maneuverability for the all sets of vehicle longitudinal speeds and steering angles, and the effect was more significant at the higher vehicle longitudinal speeds. For example, when the vehicle was travelling at 45 km/h (28 mph) and made a turn by changing the front steering angle to 4°, the difference between the tilting vehicle and non-tilting vehicle’s turning circle’s diameter was 9.5 m (31 ft). However, when the vehicle was travelling at 20 km/h (12 mph) and made a turn by changing the front wheel steering angle to 17°, the difference in the turning circle’s diameter was only 2.1 m (6.9 ft).

The researchers' work is part of an international collaborative effort on “Personal Electric Vehicle Design and Control” consisting of researchers from: the Systems Design Engineering Department, University of Waterloo, Canada; Automotive Engineering Institute, Technical University of Darmstadt, Germany; and Mechanical and Aerospace Engineering department, State University of New York at Buffalo, USA.

This article is based on SAE International technical paper 2014-01-0087, “Improving Stability of a Narrow Track Personal Electric Vehicle Using an Active Tilting System,” by Shinhoon Kim (a master's student who led the research), John McPhee, and Nasser Lashgarian Azad of the University of Waterloo. The paper will be presented at the SAE 2014 World Congress on April 9 as part of the “Vehicle Dynamics, Stability and Control” technical session planned by the SAE Vehicle Dynamics Committee / Automobile Chassis Activity; Motorsports Engineering Committee / Motorsports Engineering Activity, and organized by David A. Finch of Raetech Corp.; W. Riley Garrott of the U.S. National Highway Traffic Safety Administration; Paul Grygier (retired-U.S. NHTSA); Mark Heitz; Gary J. Heydinger of SEA, Ltd.; Raymond Leto of TotalSim LLC; David R. Mikesell of Ohio Northern University; Michael Royce; M. Kamel Salaani of Transportation Research Center Inc.; and Amandeep Singh of U.S. Army TARDEC.

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