  This paper addresses the co-optimization of speed and gearshift control for
battery electric vehicles using short-range traffic information. To achieve
greater electric motor efficiency, a multi-speed transmission is employed,
whose control involves discrete-valued gearshift signals. To overcome the
computational difficulties in solving the integrated speed-and-gearshift
optimal control problem that involves both continuous and discrete-valued
optimization variables, we propose a hierarchical procedure to decompose the
integrated hybrid problem into purely continuous and discrete sub-problems,
each of which can be efficiently solved. We show, by simulations in various
driving scenarios, that the co-optimization of speed and gearshift control
using our proposed hierarchical procedure can achieve greater energy efficiency
than other typical approaches.
