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Center for Transportation Studies
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Patrick Starr, Lee Alexander, graduate student Samuel Kidane, and Rajesh Rajamani during construction of the experimental vehicle.

"Development and Evaluation of a Novel Traffic Friendly Commuter Vehicle"

Presentation by Rajesh Rajamani, Dept. of Mechanical Engineering

October 10, 2006

As traffic congestion continues to worsen in metropolitan areas, researchers are looking for new ways to increase the carrying capacity of urban freeway systems. Researchers at the University of Minnesota’s Department of Mechanical Engineering think their design for a narrow commuter vehicle could help solve congestion problems by fitting twice as many individual vehicles into the width of a single regular lane. The three-wheeled vehicle incorporates a novel computer-controlled stability system, allowing it to turn without tipping at highway speeds despite its short axle width and upright seating position.

Associate professor Rajesh Rajamani, a member of the research team, gave a presentation on the development of the prototype vehicle at an Advanced Transportation Technologies Seminar October 10, 2006. The project was led by research fellow Lee Alexander, and included  professor Patrick Starr and graduate students Jesse Gohl and Samuel Kidane. A research report on the project was also published by the Intelligent Transportation Systems Institute.

In his presentation, Rajamani highlighted the challenge of developing a control system that would tilt the vehicle like a motorcycle automatically in response to steering input from the driver, thereby counteracting the centripetal force that would otherwise tend to destabilize a relatively tall, narrow vehicle when turning. The problem of automatic tilt control is further complicated by the need to operate seamlessly at both low speeds (in city traffic) and at high speeds (on the freeway).

One of the main innovations in the vehicle control system lies in how it handles tilting and turning, based on a dynamic model of vehicle movement developed by the researchers. Rather than interpreting steering input directly as a request to change direction and then deriving the proper degree of tilt to maintain stability, the system treats a movement of the steering control as a request to tilt the vehicle. Once the tilt is accomplished, the change in direction follows automatically.

Solving these problems required the researchers to develop a “steer-by-wire” control system that relies entirely on computer-controlled servomotors to guide the vehicle, instead of a direct mechanical connection between the steering control and the wheels. The computerized system is able to control tilt by counter-steering—steering slightly opposite the direction of a desired turn—causing the vehicle to lean into the turn and change direction smoothly. While this may seem counter-intuitive, a similar technique is used unconsciously by cyclists as they lean into turns.

The final project report presents a detailed explanation of the dynamic model and the mathematical simulations used to develop and test it, along with a description of the experimental test vehicle and its implementation of the control system. “Development of a Novel Tilt-Controlled Narrow Commuter Vehicle” (CTS 06-05) is available from the CTS Web site. Additional information on the project is available on the project page.