Through several experiences on the development of high performance 4-valve engines for sporty passenger cars, Toyota has found another way to apply its benefits for standard engines. The main benefits are, high volumetric efficiency, low friction loss and fast burn by a central spark plug; all of which are no doubt available for standard engines as well. At the same time Toyota notices that careful attention should be paid to the idea of making the engine torque curve higher in the low and middle speed ranges instead of only high horsepower in the high speed range.
As a result of numerous schematic studies including 3-valve layouts, three important factors such as 4-valve combustion chamber having a narrow valve angle, a valve gear composed of double camshafts and direct acting tappet with ‘no’ hydraulic valve lash adjuster were finally selected. This combustion chamber gives a compact cylinder head similar to that of a SOHC. With regard to camshaft driving, one camshaft is driven by a cogged belt from the crankshaft which engages the other with the gear. Gear noise caused by troublesome fluctuating torque between two camshafts is eliminated by a special zero-backlash mechanism.
The 3S-FE, 2-liter. 4-valve engine accorded with this concept has achieved 5.1% torque and 18.6% horsepower gains compared with the original engine, the 2S-E, 2-liter 2-valve. Furthermore, this new engine has some positive features to reduce noise and vibration in order to appeal to the senses of drivers, for example, a torsional and bending damper pulley on the crankshaft is used.
This paper describes the story on the development of the state-of-the-art standard engine concept.