Abstract For the purpose of reducing fuel consumption, a hybrid heavy duty truck was considered. Generally, HV (Hybrid Vehicle)'s energy is regenerated from deceleration energy in urban area. Hybrid heavy duty truck's energy is regenerated from potential energy on highway. Under this circumstance, some portion of energy may not be accumulated, because capacity of HV battery is limited. In order to maximize accumulating energy in the next descent, HV battery's energy shall be adequately reduced beforehand. This can be achieved by optimizing motor assist torque considering road's altitude and gradient. In this paper, performance of the algorithm is discussed. 1. Introduction To reduce fuel consumption, more precisely, maximizing HV system's performance, an HV system for heavy duty trucks was assessed( 1). Previously, in order to reduce fuel consumption for conventional heavy duty truck, cooperating with GPS(2) and optimized cruise control system was proposed( 3). It controls engine torque; and choosing suitable gear which is based on road gradient. However, hybrid heavy duty truck has different problem, which is required big size battery capacity to accumulate all of the available energy. Therefore, it is difficult to use previous algorithm for hybrid heavy duty truck. In addition, in systems for passenger vehicles and light duty trucks, which operate primarily in urban areas, energy is mainly regenerated through deceleration. Conversely, in heavy duty trucks which primarily drive long distances on highways, energy is mainly regenerated through highway descents. This requires developing a control algorithm from a different standpoint than for passenger vehicles.Current control algorithm faced the issue that, due to battery capacity limitations, some of the energy accumulated in long descents is lost. Focusing on that point this research developed control algorithm that enhanced energy efficiency by anticipating road altitude and gradient and applying appropriate motor assist in climbs, thereby maximize battery depletion and increasing the amount of energy that can be accumulated in the subsequent descent. This paper reports on the observed effects. 2. HV Systems for Heavy Duty Trucks 2.1. Approaches to Energy Regeneration Systems for passenger vehicles and light duty trucks, which operate primarily in urban areas, accumulate energy during deceleration and use it to provide some of the required torque at motor start or during acceleration, thereby reducing fuel consumption. By contrast, heavy duty trucks, which primarily drive long distances on highways, decelerate less frequently than passenger vehicles, reducing the quantity of accumulated energy. In highway descents with steep gradients, maintaining a stable speed becomes difficult and drivers make use of the engine brake and retarder to keep vehicle speed stable. This causes the kinetic energy of the truck to be lost as thermal energy. If that energy can be accumulated, temporarily stored in the battery as electrical energy, and used by the motor to assist in providing torque during climbs, reducing fuel consumption is possible. 2.2. Structure of the System Figure 1 shows the diagram of the system built for this research. The motor is set behind the transmission, on the same axis as the propeller shaft. By doing so motor speed becomes independent of engine speed or transmission gear Development of Road's Gradient Anticipatory Algorithm for Hybrid Heavy Duty Truck2014-01-2377 Published 09/30/2014 Hiroyuki Ishizaka Hino Motors, Ltd. Kazuo Tanaka, Motoyasu Tanaka, and Yusuke Tanaka The University of Electro-Communications CITATION: Ishizaka, H., Tanaka, K., Tanaka, M., and Tanaka, Y., "Development of Road's Gradient Anticipatory Algorithm for Hybrid Heavy Duty Truck," SAE Technical Paper 2014-01-2377, 2014, doi:10.4271/2014-01-2377. Copyright © 2014 SAE InternationalDownloaded from SAE International by Birmingham City Univ, Tuesday, August