Adaptive fuzzy iterative control strategy for the wet-clutch filling of automatic transmission Shuhan Wanga,b, Yanjing Liua,b, Zhuo Wangd, Peng Donga,b,⇑, Yunjiang Chenga,b, Xiangyang Xua,b, Peter Tenbergec aDepartment of Automotive Engineering, School of Transportation Science and Engineering, Beihang University, Beijing 100191, PR China bBeijing Key Laboratory for High-efficient Power Transmission and System Control of New Energy Resource Vehicle, Beihang University, Beijing 100191 , PR China cInstitute of Industrial and Automotive Drivetrains, Ruhr-University Bochum, Bochum 44801, Germany dInner Mongolia First Machinery Group Co., Ltd, Baotou 014030, PR China article info Article history: Received 10 May 2018Received in revised form 26 March 2019Accepted 3 May 2019Available online 11 May 2019 Keywords: Wet clutchClutch fill controlFuzzy logic Adaptive control Iterationabstract In the gear shifting processes of an automatic transmission (AT), fast and smooth transi- tions between different gears without drivetrain jerking are always expected, which leads to a desire for high-quality clutch-to-clutch shifts. The accurate and effective filling controlof clutches is the base for achieving desirable clutch-to-clutch shifts. This study focuses on developing an adaptive fuzzy iterative control strategy for the filling process of wet clutches in ATs. Firstly, a specific structure and dynamic characteristics of the wet clutchactuating system is analyzed to assist in the designing of control strategies. Afterwards, three types of deviations that usually occur in the filling process, named as speed drop, clutch tie-up and engine flare respectively, are defined and analyzed according to theirdifferent characteristics. The adaptive control strategy is then developed to realize thereduction of the deviations. The concrete adjustment performed by the control strategy is based on the features of the previous deviations during the adaptive iteration. Moreover, a double-input-and-double-output fuzzy logic controller (DIDO-FLC) is designedand introduced in the control strategy, which can adjust the fast filling time and the max- imum fast filling pressure of the clutch simultaneously. In order to validate the proposed strategy, the results of vehicle test are presented, which demonstrate that the deviationsare effectively diminished and the shifting quality is obviously improved. /C2112019 Elsevier Ltd. All rights reserved. 1. Introduction Automatic transmissions, as a kind of widely equipped stepped multi-speed transmissions in the automotive industry, usually utilize clutches to transfer torque at various speed ratios [1]. On account of the stringent vehicle emission standards and the increasing concern for fuel economy, there are a prevalent tendency for ATs to have more speeds in recent years, which leads to a frequent use of clutches in the gear shifting process of daily driving [2,3] . Wet clutches are the mechanisms used to transmit torque by means of wet friction. They are widely utilized to selectively engage gear elements under the various working conditions of ATs [4]. The gear shifting can be implemented as a clutch-to- https://doi.org/10.1016/j.ymssp.2019.05.008 0888-3270/ /C2112019 Elsevier Ltd. All rights reserved.⇑Corresponding author at: Department of Automotive Engineering, School of Transportation Science and Engineering, Beihang University, Beijing 100191, PR China. E-mail address: dongpengbeihang@163.com (P. Dong).Mechanical Systems and Signal Processing 130 (2019) 164–182 Contents lists available at ScienceDirect Mechanical Systems and Signal Processing journal homepage: www.else vier.com/locate/ymssp Nomenclature Ac area of the control pressure side Afb area of the feedback pressure side Ain(xs) input area for hydraulic oil related to the spool position Aout(xs)output area for hydraulic oil related to the spool position Ap pressure-bearing area of the piston Api cross-sectional area of the pipe connected to the pressure chamber A*