The dynamic performance of narrow actively tilting vehicles

The major advantage of a motorcycle with respect to a passenger car is the possibility of the driver to tilt during cornering and thereby maintaining stability whereas a passenger car will suffer from the risk of capsizing at high speed. This observation has motivated recently various manufacturers to develop new concepts of narrow vehicles that are able to tilt like a motorcycle but offer the comfort of a passenger car, allowing further downsizing of vehicles enabling higher fuel efficiency. As a result, there seems to arise a whole new class of vehicles, which cannot be compared, to either passenger cars or motorcycles, with typical examples such as the Ford Gyron and the GM Lean Machine. More recent examples are the Daimler Benz Life Jet and the Carver of Brink Dynamics. This paper includes a mathematical treatment of the dynamic behaviour of such vehicles, denoted here as a Narrow Tilting Vehicle (NTV). The analysis is based on a vehicle concept consisting of three main rigid bodies, a front assembly (front fork), a mid-assembly (passenger cabin) and a two-wheeled rear-assembly (engine, rear part of chassis including rear suspension, wheels, etc.). Important criteria for the designer are a stable behaviour and, on the other hand, a smooth, responsive cornering performance. As it turns out, various eigenmodes related to yaw, steering and roll behaviour of the vehicle are working against each other in this respect. Obviously, many vehicle design parameters play an important role where which have a major impact on the vehicle behaviour. One might distinguish the overall dimensions, mass distribution, front-fork geometry, tyre characteristics, suspension layout, the tilting controller design, etc. Due to the large variety in parameter-combinations, sensitivity regarding one single parameter always depends on the selected reference case for the remaining parameters, and therefore cannot be extrapolated easily to reach its optimal value. In the paper, the design parameters having a major impact on the vehicle performance are identified. The impact of parameter modifications on the vehicle stability and handling performance is discussed on the basis of mathematical analysis, and interpreted in physical terms (supported by numerical analysis and experimental results). That means that, finally, tendencies in changes in vehicle performance can be and resulting in general guidelines for the design of this new class of vehicles.