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Toyota has developed a new full time 4WD system, called “EC-HYMATIC” or Electronically Controlled - HYdraulic Multi-plate clutch Active Traction 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, a 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 4WD system, EC-HYMATIC, considerably improves handling characteristics, traction performance and stability of a 4WD vehicle.

Recently in the world, many modifications and improvements have been taking place in automatic transmission fluid (ATF) in order to get more excellent performance and durability of automatic transmission. The most important criterion for the improvement of ATF is a superior friction characteristic. To consider the performance of ATF, we have investigated the correlation of criteria between actual vehicle tests and bench-scale tests (e.g. SAE#2 Friction Test). And it was proved that conventional criteria and test methods for bench-scale tests were not enough to give best prediction of actual vehicle performance especially for shift quality, anti-shudder performance and static torque capacity which were regarded as of major importance for the development. Based on the findings, we have considered new criteria and test methods for the frictional characteristics, and specific requirements for ATF have been proposed from the standpoint of actual vehicle performance.