Copyright © 2009 SAE International ABSTRACT In this paper, we will focus on a systematic reasoning to obtain a suited test bench for covering the verification of a complete set of embedded electronics functional specification of a hybrid powertrain. The HIL (Hardware In the Loop) test bench enables the control unit environment in real time to be simulated and their closed loop behavior in wished situations to be studied. Based on control unit and system specifications, the method describes how to define the HIL platform in terms of hardware interface and internal behavior (models). INTRODUCTION Current requirements of ecology and mobility are at the basis of the project development of hybrid powertains. Among others, the Volvo Group is investigating a parallel hybrid powertrain solution for its buses, trucks and refuse vehicles. This new technology involves new embedded electronics hardware for the control of the complete driveline and requires same level of software controller verification [1]. That is why a particular attention must be paid in specifying adapted tools to ensure the maximum quality of control strategies. These strategies are implemented in several embedded ECU (Electronic Control Units), whose behavior has to be first checked aside at ECU level and then jointly at system level. The systematic reas oning that we pres ent in this paper wants to give a rigorous approach to develop any HIL platform for verification purpose [2]. It is based on the specifications of an electronic system to test. In the context of hybrid software system, we will show with one example in the shape of one Trucks Hybrid parallel specific electronic feature on how the implementation of this verification method has lead to the development of well sized simulation models. Then the result of a representative ECU validation will be presented. Based on this result, we will finally conclude with an evaluation of the efficiency of this method. I - HYBRID TRUCKS AND ELECTRONIC ARCHITECTURE In this part, we will present what are the impacts linked to the development of a hybrid commercial vehicle on the powertrain electronic system. 1 - HYBRID COMMERCIAL VEHICLE A commercial vehicle is mainly used for dedicated and repetitive applications. This leads to a large number of variants. To handle them and to minimize the number of hardware solutions, software parameter settings are preferred. Besides, a similar application can be optimized from different points of view depending of the wished features. The defin ition of these features is dependant of the equilibrium between three actors: the manufacturer, the driver and the owner of the vehicle. We can quote quality, safety, security, profitability, performance, comfort, price, noise, reliability, fuel consumption, public image, friendly usage, maintenance… Thereby, the software management should allow specific settings to enhance any of these features. The hybrid technology offers new opportunities of optimization, since a new actuator, the electric motor, is available on the powertrain. It makes possible to get a better equilibrium between coupled phenomenons. Furthermore, new functions can be achieved: electric mode (zero emission or sile nt mode), electric power take-off, braking regeneration, stop and go, electric boost, auxiliaries’ electrification. All these advantages make thus attractive this hybrid architecture. However, it needs a more powerful cooling system for the new components (electric machine, powe r electronics and battery); although battery technology is evolving incessantly, it remains quite limited compared to fossil fuel storage in term of specific energy; the hardware system reliability is quite unkn own since the market is still new especially for commercial vehicles; finally, the added product cost will need to be compensated for through a subsequent fuel consumption reduction to secure a return on investment.