Dissertation
Using ‘dynamic regenerative braking’ to enhance crash avoidance
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2022
DOI: 10.25820/etd.007774
Abstract
In a vehicle powered by internal combustion (IC) and in some hybrids, there is a significant energy loss when the driver presses the brake pedal. Regenerative braking (RB) is a system that does not use the service brakes of the vehicle. It is typically used in electric and hybrid vehicles to recapture the kinetic energy that would normally be lost while braking as unused heat. In the case of Tesla vehicles, the RB system is triggered as soon as positive pressure starts to be released from the accelerator pedal. The purpose of this thesis is to examine this braking advantage RB provides, understand how it affects driver foot behavior, and find a way to make RB dynamic so that the braking advantage can match the level of danger. A central question not yet examined in the literature is whether regenerative braking provides a kinematic deceleration safety advantage in time and distance over traditional service braking. This research explores three conditions of braking: service braking (SB), low level of regenerative braking, and high level of regenerative braking. Thirty participants took part in a simulator study with a between-subjects study design, allocating 10 participants per condition. The results showed a significant difference between the means of the three conditions for average deceleration of the vehicle in the time interval between the driver releasing the accelerator and pressing the brake for all three events showing RB did provide the drivers with a braking advantage. When events 1 and 2 were combined, there was also significance with maximum brake force.
Vehicles with RB actively decelerate when neither pedal is depressed. We hypothesized that this would result in a difference in driver foot behavior. There were two pieces to explore this potential difference. The first piece was to explore time-based measures. When comparing RB and SB for the time-period from when the driver releases the accelerator pedal, to when the driver presses the brake pedal, the high level of RB was statistically significantly different. The second piece was to code each video to label driver foot behavior based on a set of categories. The 5th category (uncertainty – “wagging foot”) was the only foot behavior appearing in all three conditions (n=2, SB; n=4, low RB; n=6, high RB). The 8th category (brake tap, reposition to throttle, then brake press), only appeared in the high level of RB condition and appeared 9 times (33% rate).
The last piece to explore is how RB can be made dynamic, so that the amount of deceleration imparted by RB changes depending on the environment in front of the user vehicle. For Dynamic RB (DRB) mode 1, upon accelerator pedal release target acceleration must be greater than or equal to the acceleration of the RB level. Since mode 1 assumes the driver will press on the brake pedal, the level of RB does not change once the level is selected at accelerator release. The DRB level is reset when the driver returns their foot to the accelerator pedal in a positive manner. For DRB mode 2, the amount of regenerative braking applied remains dynamic from the time the driver releases the accelerator pedal to when the driver applies the brake pedal.
DRB has to potential to extend the drivers kinematic deceleration advantage by starting the braking process as soon as the driver releases the accelerator pedal in context of the threat ahead, rather than when the driver presses the brake. Another advantage of DRB is it does not take over the braking process by automating it, it simply gives the driver additional assistance. By not automating the braking process, the driver is still in control of the vehicle. Such context-related driver assistance has the potential to further enhance crash avoidance and avoiding crashes altogether or reduce their severity.
Details
- Title: Subtitle
- Using ‘dynamic regenerative braking’ to enhance crash avoidance
- Creators
- Christopher R. M. Rundus
- Contributors
- Daniel V McGehee (Advisor)Geb W Thomas (Committee Member)Chris W Schwarz (Committee Member)Venanzio Cichella (Committee Member)Thomas Schnell (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Industrial Engineering
- Date degree season
- Spring 2022
- DOI
- 10.25820/etd.007774
- Publisher
- University of Iowa
- Number of pages
- x, 114 pages
- Copyright
- Copyright 2022 Christopher R. M. Rundus
- Language
- English
- Date submitted
- 02/03/2022
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 77-85).
- Public Abstract (ETD)
This dissertation focuses on regenerative braking, how human drivers interact with the new braking system, and how to leverage regenerative braking to provide a braking advantage.
The first research question explores the kinematic deceleration advantage that regenerative braking can provide. This research explores three conditions of braking: service braking (SB), low level of regenerative braking, and high level of regenerative braking. It is concluded that the high level of regenerative braking provides a kinematic deceleration advantage.
The second research question explores how driver foot behavior differs between the two braking systems. Drivers using the high level of regenerative braking had longer foot transfer times, and pressed on the brake pedal wth less force. Drivers using the high level of regenerative braking also had a higher rate of foot behaviors that may have indicated uncertainty.
The last piece to explore is how RB can be made dynamic, so that the amount of deceleration imparted by RB changes depending on the environment in front of the user vehicle. Dynamic RB (DRB) is a newly proposed term describing a system that would be able to increase the RB level and therefore augment the braking process depending on the urgency of the traffic conflict and/or roadway context. The adaptive process would take place between throttle release and service brake application. An advantage of DRB is that it adds assistance in the time period between throttle release brake press but does not automate the braking process
- Academic Unit
- Industrial and Systems Engineering
- Record Identifier
- 9984774869202771
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