Mechanism and Machine Theory 137 (2019) 67–82 Contents lists available at ScienceDirect Mechanism and Machine Theory journal homepage: www.elsevier.com/locate/mechmachtheory Research paper Optimal design of power matching for wheel loader based on power reflux hydraulic transmission system Yingzhe Kan a , Dongye Sun a , ∗, Yong Luo b , Ke Ma a , Junren Shi a a State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing 40 0 044, China b Key Laboratory of Advanced Manufacturing Technology for Automobile Parts. Ministry of Education, Chongqing University of Technology, Chongqing, 40 0 054, China a r t i c l e i n f o Article history: Received 28 December 2018 Revised 3 March 2019 Accepted 11 March 2019 Keywords: Wheel loader Power reflux hydraulic transmission system Power matching Optimized design a b s t r a c t The traditional hydraulic transmission system for wheel loaders is inefficient and, in power matching, prevents improvement in performance during spading and transport. This paper proposes a power reflux hydraulic transmission system (PRHTS) with a ca- pacity adjustment device, which retains both flexible transmission and the advantages of the low-speed high-torque characteristics while improving transmission efficiency, and the capacity adjustment device can meet the requirements for the capacity factor of the hydraulic transmission system during spading and transport. Based on numerical calculations and an analysis of the basic characteristics of the proposed PRHTS, a method for the optimal design of power matching systems for wheel loaders is proposed. The results for matching show that compared with traditional hydraulic transmission systems, the proposed method increases the range of the high-efficiency working area ( η≥75%) during transport by 384 r ·min –1 , enhances average efficiency during transport by 10.99%, reduces the average working fuel consumption rate by 10.61 g ·(kW ·h) –1 , and increases the average output power by 36.72 kW while ensuring the original power performance and fuel economy of the wheel loader during spading. ©2 0 1 9 Published by Elsevier Ltd. 1. Introduction Wheel loaders often operate in harsh working environments where the external load is variable. Therefore, the torque converter (TC) is often used as a flexible device to connect the engine and the shifting device. However, due to transmis- sion efficiency characteristics of the TC, the efficiency of a traditional automatic transmission is unexceptional. Thus, it is important to improve efficiency and reduce energy consumption [1,2] . The lock-up TC uses a lock-up clutch between the pump impeller and the turbine to convert the hydraulic transmission of the TC into a mechanical transmission to improve efficiency [3,4] . However, it loses both the advantages of the low-speed high-torque characteristics and the flexibility of the transmission system. Owing to complex and unpredictable changes in the external load on the wheel loader, the impact of the transmission system is enhanced, and the comfort of the driver and service life of the transmission system are reduced. To solve this problem, researchers have developed a power split transmission system that combines hydraulic transmission with mechanical transmission to improve the efficiency of transmission [5,6] . However, system increases in torque at low speeds are small. Therefore, the automatic adaptability of the wheel loader to variable external load deteriorates. ∗Corresponding author. E-mail address: dysun@cqu.edu.cn (D. Sun). https://doi.org/10.1016/j.mechmachtheory.2019.03.020 0094-114X/© 2019 Published by Elsevier Ltd. 68 Y. Kan, D. Sun and Y. Luo et al. / Mechanism and Machine Theory 137 (2019) 67–82 Nomenclature PRH