Vehicle Dynamic Opportunities in Electrified Vehicles for Active Safety Interventions

Licentiate thesis, 2015

Although the sales of electrified vehicles is growing, studies indicate that the growth is inadequate to sufficiently reduce CO2 emissions and mitigate global warming. Some form of added incentive is needed to drive electrified vehicle sales. On the other hand, there is an increased need for traffic safety due to the adoption of ambitious goals such as the Vision Zero. This thesis attempts to identify vehicle dynamic opportunities to improve vehicle safety that are enhanced or enabled by electrified drivetrains, thereby offering an opportunity to add value to electrified vehicles and make them more attractive to consumers. As an example of a low hanging fruit, the possibility of accelerating an electrified lead vehicle to mitigate the consequences of, or prevent being struck from behind was investigated. A hypothetical Autonomous Emergency Acceleration (AEA) system (analogous to the Automatic Emergency Braking (AEB) system) was envisioned and the safety benefit due to the same was estimated. It was found that the AEA system offers significant opportunities for preventing or reducing injuries in rear-end collisions. The possibility of using propulsion to improve safety in an obstacle avoidance scenario in the presence of oncoming traffic was also investigated. In order to better understand the manoeuvre kinematics, a large number of these cases with varying scenario parameters were investigated in an optimal control framework. Analysis of the results showed that, in this scenario, the obstacle length and the ratio of oncoming vehicle to host vehicle velocities were the two most important parameters which determined the extent of benefit that can be achieved with propulsion. Based on this insight, more detailed investigations were then done for fewer, but more extreme cases of the scenario to estimate the safety benefit due to propulsion both with restricted and unrestricted steering. Results showed that while significant benefit can be achieved due to propulsion even with unrestricted steering, its benefit is amplified when the steering is restricted. Finally, simple closed loop wheel force controllers for lateral control were implemented in simulation. Investigations using the same showed that when performing lateral control alone in this scenario, it is beneficial to be able to do so without slowing the vehicle down which can be done with an electrified drivetrain. In summary, several vehicle dynamic opportunities for improving safety using electrified drivetrains were identified. Detailed investigations of select cases showed that significant safety benefit stands to be gained by appropriate control of electrified drivetrains in the accident scenarios. Consequently, a strong opportunity is seen for adding safety related value to electrified vehicles at little to no extra cost.