474 IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, VOL. 15, NO. 3, MAY 2007 Control of Integrated Powertrain With Electronic Throttle and Automatic Transmission Daekyun Kim, Huei Peng, Shushan Bai, and Joel M. Maguire Abstract—A process to design the control strategy for a vehicle can be used to realize and integrate features such as idle speed with electronic throttle control (ETC) and automatic transmission control, cruise control, adaptive cruise control, traction control, is proposed in this paper. The driver’s accelerator pedal position etc. In this paper, we investigate an integrated powertrain con- is interpreted as a power request, which is to be satisfied by co- ordinating the transmission gear shift and the throttle opening in trol feature, which coordinates the control of transmission (gear an optimal fashion. The dynamic programming (DP) technique is shifting) and engine (throttle). The design goal is to satisfy the used to obtain the optimal gear shift and throttle opening which driver’s power demand while optimizing fuel economy. maximizes fuel economy while satisfying the power demand. The For modern powertrain systems equipped with ETC, many optimal results at different power levels are then combined to form studies explored the possible advantage of controlling the a gear map and a throttle map which governs the operation of the integrated powertrain. A control architecture concept is presented throttle opening angle during a gear shift. In [3], Ge et al. where the relationship between the accelerator pedal position and present a control algorithm to minimize the reduction in ve- the power demand level can be adjusted according to the prefer- hicle performance and deterioration of shift quality due to the ence of the vehicle performance target. Simulation, vehicle test, sudden change of the gear ratio. Using a closed-loop control and dynamometer test results show that the proposed integrated scheme, the throttle opening is adjusted during the shift to powertrain control scheme produces power consistently and im- proves fuel efficiency compared with conventional powertrain con- reduce the speed difference between the synchronized gears in trol schemes. the gearbox and the speed difference between the driving and the driven plates of the clutch. Minowa et al. [4] interpreted the Index Terms—Automatic transmission, dynamic programming (DP), electronic throttle control, gear shift map, integrated power- accelerator pedal position as a drive shaft torque demand. The train control. throttle opening can then be controlled to compensate for the torque reduction caused by the selection of the gear shift timing for minimum fuel consumption. The method was found to be I. INTRODUCTION promising in improving fuel economy and acceleration feel. Yasuoka et al. [5] presented an integrated control algorithm N conventional vehicles powered by gasoline engines, the for a powertrain system with ETC and continuously variable I accelerator pedal actuated by the driver is mechanically transmission (CVT). Target engine torque and target CVT linked to the engine throttle which regulates the airflow to the ratio to achieve the demanded drive torque with optimum fuel intake manifold. When the driver holds the accelerator pedal economy is determined based on the gear ratio map and drive constant, the power and torque generated by the engine will torque demand. Moreover, to improve the torque response change with engine speed, and thus, the driver needs to vary during a transient, the engine torque is used to compensate for the pedal position to obtain constant torque (acceleration) or the lag in inertia torque and the gear ratio change response. power from the engine. Since each powertrain has its own Sakaguchi et al. [6] asserts that to improve fuel efficiency the torque/power characteristics, drivers bear the responsibility to entire powertrain, including engine and transmission, need to adapt to the powertrain, instead of the other way around. The be considered rather than just focusing on the engine. For a mechanical linkage between accelerator pedal to the throttle vehicle equipped with CVT, an algorithm to calculate the en- is replaced by an electronic connection, commonly known as gine torque and CVT ratio combinations achieving the highest electronic throttle control (ETC) [1], [2] in modern vehicles. overall efficiency for the powertrain is developed. ETC provides flexibility between the pedal to throttle mapping When an advanced powertrain is equipped with electronic and, thus, a new design degree-of-freedom. For example, it throttle, the accelerator pedal is no longer linked with the engine throttle plate. Therefore, the detected pedal motion needs to be Manuscript received October 30, 2006; revised January 8, 2007. Manuscript interpreted as a driver demand, typically either as a torque de- received in final form January 25, 2007. Recommended by Associate Editor K. mand or a power demand. In this paper, the accelerator pedal po- Butts. This work was supported by General Motors Powertrain. sition is interpreted as a request for power for two reasons. First, D. Kim was with the Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2121 USA. He is now with Research and De- the definition of an “ideal powertrain” is a power source that pro- velopment and Strategic Planning, General Motors, Warren, MI 48090-9055 duces power in a reliable way. The other is that according to a USA (e-mail: [email protected]). study by Vahabzadeh et al. [7], engine power was found to be H. Peng is with the Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2121 USA (e-mail: [email protected]). the best physical measurable parameter representing the driver’s S. Bai is with the General Motors Powertrain, Ypsilanti, MI 48197-0935 USA demand. (e-mail: [email protected]). In this paper, we will develop throttle/gear maps that satisfy J. M. Maguire is with the General Motors Powertrain, Pontiac, MI 48340- 2920 USA (e-mail: [email protected]). driver’s power demand, and in the meantime, achieve optimal Digital Object Identifier 10.1109/TCST.2007.894641 fuel economy. First, a vehicle model that is accurate enough 1063-6536/$25.00 © 2007 IEEE KIM et al.: CONTROL OF INTEGRATED POWERTRAIN WITH ELECTRONIC THROTTLE AND AUTOMATIC TRANSMISSION 475 to emulate a target vehicle is created. The model includes submodels for an engine, a torque converter, a transmission gear box, and the tire/vehicle dynamics. The model is vali- dated against a wide open throttle field test data in addition to the EPA fuel economy cycle tests. The simulation model is then simplified to obtain a control design model for the dynamic programming (DP) process, with all the state and input variables discretized into manageable numbers of grid points. Vehicle launch at selected constant pedal positions (i.e., constant power request) are used as the maneuvers for our opti- mization process. A DP problem with fuel economy and power Fig. 1. Vehicle simulation model in SIMULINK blocks. production error as the cost function was then solved for each of these maneuvers. The optimal inputs (throttle opening and TABLE I gear shift) are obtained for each maneuver at constant power VEHICLE PARAMETERS request. Results from all the power levels are then combined to form a throttle map and a gear map. The obtained throttle map and gear map are implemented in the vehicle simulation model and are tested for fuel economy by running the EPA fuel economy cycle. Finally, the maps are implemented in the test vehicle and are evaluated for fuel economy, performance, and comfort. II. VEHICLE SIMULATION MODEL In this section, the simulation model of the target vehicle system is described. This model will be used to test fuel economy and drivability of the powertrain control strategies. It will also serve as the basis for the model of the DP optimization. The model needs to be accurate enough to emulate the behavior of the target vehicle yet possess minimal complexity. The model is composed of two main components: the powertrain and the tire/vehicle body. The powertrain is further divided into three subcomponents: the engine, the torque converter, and the transmission gearbox. The powertrain is subdivided in this manner to anticipate future modifications of these subcompo- nents into various different component systems such as engines with variable cylinder activation technology, diesel engines, six-speed ATs, CVTs, etc. The math-based optimization pro- cedure established in this study is not confined to powertrain systems with conventional subcomponents but is meant as the backbone for control design of general powertrains. For the tire/vehicle body, only the longitudinal dynamics is considered since, in general, fuel economy and drivability of a vehicle are measured only in regards to the longitudinal motion of the vehicle. The vehicle model is structured in the Matlab/SIMULINK environment, as shown in Fig. 1. The target vehicle for this study is a two-wheel drive production pickup truck with a 5.3-L V8 engine equipped with ETC and a four-speed AT. Parameters of Fig. 2. (a) Engine torque map. (b) Engine fuel rate map. the truck are shown in Table I. A. Engine torque converter pump torque, is the pump spin loss, and The engine angular speed is calculated from the engine is the accessories loss torque. The engine torque is obtained rotational dynamics from a steady-state map [see Fig. 2(a)] which is a function of throttle opening and . The torque converter pump torque is (1) calculated from (3) shown in Section II-B. The pump loss is based on engine speed and throttle opening. The accessories where and are the rotational inertia of the engine and the loss torque is only dependent on the engine speed. The fuel con- torque converter pump, and are the engine torque and the sumption of the vehicle is calculated using a steady-state map 476 IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, VOL.