CAO WENJING

A Pulse-and-Glide (PnG) strategy, which periodically switches the operating modes of the powertrain between the engine driving mode(pulse mode) and the glide mode, is proven to be effective in improving fuel economy in a single traveling scenario by a past research. It’s found that, when using PnG strategy, switching the operating point of the engine between the minimum Brake Specific Fuel Consumption (BSFC) points and the idling point can contribute in improving fuel economy in car-following scenario. However, the following factors about PnG are still not clear: 1)what are the optimal values of the initial vehicle speed, the duration of the pulse mode and the engine power during the pulse mode for fuel efficiency; 2)whether these values depend on the driving scenarios. In this paper, an optimization problem is formulated to find the optimal PnG pattern in a single traveling scenario for fuel economy. Under the assumption that the engine works at a constant operating point during the pulse mode, it is found that the most fuel-efficient engine operating point during the pulse mode is not the minimum BSFC point, but an operating point with a lower torque and a lower rotation speed.

Assuming that the engine can be stopped while decelerating and stopping, a method to improve fuel efficiency by optimizing the vehicle speed pattern and clutch solution engagement timing, engine operating point, gear ratio, engine on / off timing, etc. was studied. It was found that depending on the driving conditions, it is effective to increase the vehicle speed before stopping after coasting with the engine off.

This paper proposes a two-stage hierarchy control system with model predictive control (MPC) for connected parallel HEVs with available traffic information. In the first stage, a coordination of on-ramp merging problem using MPC is presented to optimize the merging point and trajectory for cooperative merging. After formulating the merging problem into a nonlinear optimization problem, a continuous/GMRES method is used to generate the real-time vehicle acceleration for two considered HEVs running on main road and merging road, respectively. The real-time acceleration action is used to calculate the torque demand for the dynamic system of the second stage. In the second stage, an energy management strategy (EMS) for powertrain control that optimizes the torque-split and gear ratio simultaneously is composed to improve fuel efficiency. The formulated nonlinear optimization problem is solved by sequential quadratic programming (SQP) method under the same receding horizon. The simulation results demonstrate that the vehicles can merge cooperatively and smoothly with a reasonable torque distribution and gear shift schedule.

To reduce drivers’ mental load and traffic congestion caused by merging maneuver, a merging trajectory generation method aiming for practical automatic driving was proposed in a past research by the authors. In this paper, the robustness of the merging trajectory generation method against sensor noises that contaminate the state variables is enhanced. The robustness was enabled by adding dummy optimization variables that relax the constraints of variables expressed by equations and barrier functions. The stage costs composed by these introduced variables were designed to generate safe and smooth merging maneuver. Effectiveness of the proposed method for a typical case was observed in the simulation results. To check if the proposed method works well under different initial conditions, 116 initial conditions were generated randomly. The proposed method solved all the cases of merging problem, while the conventional method failed in 80% of the cases.

This paper has proposed a gap selection and path generation method during merging maneuver of automobile. In this method the merging problem of one merging vehicle and multiple main lane vehicles is formulated using a model predictive control method. Lanes of a motor way are approximated with proposed smooth lines. Assuming that the main lane vehicles run on the centerline of the main lane, an appropriate path of the merging vehicle can be simply designed and modified according to the motions of the main lane vehicles. To generate mild merging, accelerations of all the relevant vehicles are constrained. Effectiveness of the proposed method is validated by computer simulations of the merging maneuvers of one merging vehicle and two main lane vehicles in different conditions. An example of actual cooperative merging maneuver is generated by the proposed method. Further the collision avoidance ability and the initial condition dependent property of the proposed method are tested.