The Pioneering “4-Stroke”
介绍雅马哈发动机技术背后的故事。
“超级越野赛”是一种在美国出生且极具娱乐性的越野摩托车比赛，在专门准备的体育场内举行。球迷们的欢呼声从看台上传来，他们惊奇地注视着从巨大的跳跃中飞过空中的车手，并在这项运动特有的许多具有挑战性的倾斜转弯中燃烧。极短的进近导致陡峭的跳跃，以及在急速离开之前快速导航，需要快速加速；这就是二冲程发动机的轻量化和爆发力真正出众的地方。直到 1997 年，250cc 2 冲程机器在重量轻、功率和驱动力之间的出色平衡使它们成为赛道上最快的，并且 2 冲程在 Supercross 网格中占据主导地位。然而，随着对更环保机器的推动和更严格的排放标准的实施，四冲程量产摩托车已成为经销商展厅的主流。预测四冲程浪潮也将很快进入越野摩托车世界，雅马哈很快就着手开发四冲程越野摩托车。
结果是 YZM400F 雅马哈工厂机器(#1)的诞生。在拉斯维加斯 1997 年 AMA Supercross 赛季的最后一轮比赛中，它赢得了比赛，这标志着 4 冲程机器在 Supercross 赛事中首次获胜。雅马哈还将其 4 冲程技术应用于开发 YZ400F 量产越野摩托车，并于 1998 年将其投放市场，并立即改变了全球越野摩托车的面貌。如今，四冲程已成为全球顶级摩托车越野赛的主流选择。毫无疑问，开启了 4 冲程越野摩托车时代的是拉斯维加斯那令人难以置信的夜晚，以及雅马哈为将 4 冲程带入泥土而承担的巨大挑战。
5-Valve Technology to Achieve Rapid Combustion
The development aim for the factory-spec YZM400F was performance potential on par with the 2-stroke YZ250 but in an even lighter package. To achieve this goal, Yamaha applied its technology and expertise garnered in motorcycle engine development and automobile racing (#2) in the 1980s and 1990s and began development of a unique DOHC 5-valve single-cylinder engine. The engine used the same cylinder head design as an F1 engine and was lightweight, tipping the scales at only 500 grams more than that of the YZ250. The 5-valve layout made it easier to give the combustion chamber a lens-like form and also made it easier to achieve a high compression ratio. The resulting rapid combustion produced a lot of power and achieved the team’s goal. The area around the cylinder head also had a compact design, leading to a smaller overall chassis size. Furthermore, the wide powerband unique to a 4-stroke gave riders the added advantage of not needing to shift as frequently.
Incidentally, motorcycles were not the only place Yamaha took its 4-stroke challenge. The YZF-R1 (#3) supersport bike was released during the same period as the YZ400F, and its 1,000cc 20-valve (five valves per cylinder) engine was transplanted into the FX140 (#4) in 2002, creating the world’s first 4-stroke personal watercraft. In 2003, the same engine was used to power Yamaha’s first 4-stroke snowmobile, the RX-1 (#5).
