Development of a steer tilt controller for a three wheeled tilting vehicle

A three wheeled tilting vehicle called CLEVER was developed at the University of Bath. The tilt mechanism of this vehicle consisted of two hydraulic actuators that tilted the cabin in response to the driving conditions. Although this system was reliable, it had high power requirements, so a different method was needed. One way in which such a vehicle could be tilted was using the same principle that a motorcycle rider applies to tilt his bike, namely countersteer. This type of tilt control was expected to reduce the power required to lean. First, the vehicle and a basic steer controller were modelled. The simulations showed that the steer controller balanced the vehicle well, but deviated significantly from the intended path. A controller that could combine both the balance and the path following function was required. A good controller for this task is clearly the driver, so a pilot study was launched where the steering inputs of various drivers were measured. This study was carried out using a three wheeled tilting moped. The results of this study showed that the frequency of the steering inputs depended on the driver's experience and the more experienced the driver, the lower the frequency of steer input for a given manoeuvre. The steady state manoeuvre showed that all drivers achieved a lean angle depending on the speed and turning radius in compliance with the theory. The countersteer was difficult to determine, because the drivers shifted their weight to aid the tilting. This indicated that countersteer is dependent on the driver and the driving conditions. However, a correlation between the countersteer and the countersteer rate was found, showing that either little countersteer could be applied for a short time, or a lot of countersteer could be applied for a short time. Another correlation was found between the countersteer rate and the maximum tilt acceleration, where the larger the countersteer rate, the larger the tilt acceleration. Since the tilt acceleration was related to the lateral acceleration, these correlations could aid the development of a steer tilt controller.