890526 Toyota EC-HYMATIC — A New Full Time * System for Automatic Transmission Shinya Nakamura, Masakazu Ishikawa, and Teruo Akashi Toyota Motor Corp. Takao Taniguchi and Fumitomo Yokoyama Aisin AW Co., Ltd. ABSTRACT Toyota has developed a new full time 4 WD system, called " EC-HYMATIC" or .Electronically .Controlled - HYdraulic _Multi-plate clutch .Active Xrac,tion intelligent Control. This system permits an automatic torque transfer, depending on driving conditions, for front and rear wheels under control of the speed difference between the two. The system developed consists of a center differential^ speed difference control clutch system employing multi- plate clutch, and a gear set for rear axle drive. The speed difference control clutch system is controlled by a unique electro-hydraulic system using a microcomputer. An extensive use of computer simulations and vehicle test and evaluation has successfully developed an appropriate control strategy for the clutch system. The new JlWD system, EC-HYMATIC, considerably improves handling characteristics, traction performance and stability of a HWD vehicle. IN RECENT YEARS, more and more UWD system has been accepted for use for not only off-road vehicles but passenger cars. Such an increaced application of the MWD system is aimed at further improving traction performance and handling characteristics of a high performance vehicles and those of an ordinary performance vehicle in its driving on a slippery road. To meet specification requirements and marketing concept of respective iiWD vehicles, various approaches including use of the center differential and the viscous coupling have been taken for development of an appropriate HWD system. In pursuit of an ideal UWD system development, Toyota Moter Corporation, in cooperation with Aisin AW Co.,Ltd., has introduced a new full time ilHD system under an extensive use of simulations and vehicle test and evaluation. This new system , using a speed difference control mechanism, with a multi-plate clutch installed, enables an optimum control on ilWD vehicles. This paper will discuss the concept, structure, control system and vehicle test results of the new EC-HYMATIC system. CONCEPT AND BASIC STRUCTURE CONCEPT OF THE NEW FULL TIME ilWD SYSTEM - The following three items constitute the concept of the new 4WD system ; (1) A IlWD system that makes optimum control on traction performance, handling characteristics, tight cornering brake and other vehicle requirements. (2) A iiWD system that optimizes applications for each category from ordinary to high performance vehicles. (3) A ilWD system that upgrades in coordination with other vehicle control systems including ABS. The analysis on the foregoing concept is detailed as follows. BENEFIT OF THE CENTER DIFFERENTIAL - In case of the operating vehicle with the rigid itWD system, the front wheels are in the condition of braking and the rear in the condition of traction by the effect of the synchronized rotation 23 Downloaded from SAE International by University of Birmingham, Sunday, August 19, 2018of f case whee hea v tigh mak i con t can dist rear the corn cent turn shou diff whee The tr ac foil Sf = ront , the Is p y lo t co ng s rary abso ribu whe wi nd erin er d ing Alt Id b eren Is o slip t i on OHS : and torq r o vid ad , a rneri moot h , the rb th te th els c up t g bra if f er of th hough e con ce be ccurs rati cond rear ue d es t nd a ng ^ tur cen e sp e to onst orqu ke d enti e ve thi side twee eve os o i tio wheels. In this ifference of these he drive train with a t the same time the rake should occur, ning difficult. On the ter differential AWD eed difference and rque to the front and antly. As a result, e and the tight o not occur, and the al iiWD rearizes smooth hicle. s is a known fact, what red is that t