While the number of roadways is expected to remain approximately the same, the number of vehicles on the road is expected to quadruple to three billion by 2050. This could lead to problems such as negative environmental impacts, fossil fuel shortage, traffic congestion, and parking space limitations. Electric urban vehicles can be a potential solution due to their environment-friendly image. They can operate at a higher efficiency while lowering energy consumption and greenhouse gas emission. Their smaller sizes allow them to travel on bike lanes or on lane-split roads, making it possible to navigate in cluttered areas and park in unconventional spaces. Although the benefits of urban vehicles are significant, their popularization is still in its infancy.
The overall goal of this project is to develop new technologies, specifically for electric urban vehicles to improve the performance, safety, stability, and price competitiveness for their popularization in urban areas.
Together with the corresponding research, the main undertaken tasks include:
- Development of an integrated in-wheel system
- Drive-by-wire system
- Integrated vehicle safety/stability system
- Prototyping, testing and evaluation
An integrated in-wheel system (IIWS) based on a modular design around the geometric boundaries of a conventional wheel is being developed.
This presents a corner module to simplify vehicle design and assembly, while reducing the costs.
This IIWS is comprised of multiple components, including:
- Drive (electric motor)
- Active camber
- Steering systems
The IIWS assures safe and optimal vehicle performance.
It allows for torque vectoring and active steering which increases directional stability control. Furthermore, direct rollover stability control is possible through vehicle track and wheel lateral force control.
In drive-by-wire systems, the traditional throttle, steering, and brake systems are replaced with electronically controlled systems. Throttle-by-wire has already replaced cable systems in many current vehicles and has improved engine efficiency while reducing vehicle emissions. Furthermore, the drive-by-wire devices will free up additional space to improve the interior layout. Despite all of these benefits, the failure of these systems can pose a safety concern. The reliability in most cases can be achieved through redundancy by housing independent steering and braking systems for the vehicles. In addition, electronic and control redundancy for the braking and steering systems at the vehicle control level are being considered.
Due to their narrower track width and smaller wheels, urban vehicles are more prone to rollover and directional instability. The proposed integrated in-wheel system with an independent motor, steering system, and active camber will enable unprecedented control of the vehicle's directional and rollover stability.
When combined with an integrated vehicle control system the stability of urban vehicles can be increased to that of conventional larger passenger vehicles. To further enhance the stability, a near autonomous driving assistance sensory system can be integrated to keep track of moving pedestrians, bicycles, etc. that are in the immediate vicinity of the vehicle.
It will also plan routes based on traffic data and the limited urban vehicles' capabilities.
For evaluating and testing the technologies developed in this project and bringing them closer to reality, two-seater urban vehicle prototypes are being designed and fabricated. In the selection of a configuration for the prototypes, manufacturability, safety, vehicle dynamics and stability, passenger comfort, weight of the vehicle, and associated costs will be considered.
As mentioned above, the track width ratio of urban vehicles results in decreased stability. To address this issue, an active tilting mechanism is modeled in MapleSim for a three-wheel urban vehicle. This tilting mechanism intends to allow relative rotation between the carbody and the chassis, gaining lateral forces from changes in side slip angles and camber angles of the tires to increase stability. The MapleSim results for different tilting angles are shown below where the maximum allowed tilting angles are found to be 45 degrees.
This model is also used to study the cornering performance. Vehicle turning radiuses at the given speed but with different leaning angles are studied. The trajectories shown below demonstrates that tilting do help to reduce the turning diameter. The bigger the tilting angle and the higher the speed, the effect is more obvious. While non-tilting conditions show that the normal force at the inner wheel drops about 50% during cornering, the normal force when a tilt angle of 45 degrees is applied remains almost unchanged in steady state. Hence, tilting movement help to increase vehicle stability shown by a smaller load transfer ratio index.