气门结构演示图

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OHV engine design

 OHV means OverHead Valve - an engine design where the camshaft is installed inside the engine block and valves are operated through lifters, pushrods and rocker arms (an OHV engine also known as "Pushrod" engine). Although an OHV design is a bit outdated, it has been successfully used for decades. An OHV engine is very simple, has more compact size and proven to be durable.
Downsides: it\'s difficult to precisely control the valve timing at high rpm due to higher inertia caused by larger amount of valve train components (lifter-pushrod-rocker arm). Also it\'s very difficult to install more than 2 valves per cylinder or implement some latest technologies such as Variable Valve Timing - something that could be easily done in a DOHC engine.

OHC or SOHC engine——我们的4G18就是类似这结构，不过是16气门，每缸4气门

 OHC in general means OverHead Cam while SOHC means Single OverHead Cam.
In the SOHC engine the camshaft is installed in the cylinder head and valves are operated either by the rocker arms or directly through the lifters (as in the picture).
The advantage is that valves are operated almost directly by the camshaft - easy to achieve the perfect timing at high rpm. Also it\'s possible to install three or four valves per cylinder
The disadvantage - an OHC engine requires a timing belt or chain with related components - more complex and more expensive design.

DOHC or Twin cam engine

 DOHC or Double OverHead Cam - the setup used in many today\'s cars. Since it\'s possible to install multiple valves per cylinder and place intake valves on the opposite side from exhaust vales, DOHC engine can "breath" better meaning that it can produce more horsepowers with smaller engine volume. Compare: The 3.5-liter V6 DOHC engine of 2003 Nissan Pathfinder has 240 h.p, similar to 245 h.p of the 5.9-liter V8 OHV engine of 2003 Dodge Durango.
Pros: High efficiency, possible to install multiple valves per cylinder and adopt variable timing.
Cons: More complex and more expensive design.

以下是引用62306230在2006-7-16 16:23:47的发言：
老石啊，够射精的标准了没

看不懂啊～ 你的因各历史真的这么好吗？

还好吧，这些还不算太难懂啦呵呵

我看到不认识的子查金山啊呵呵

楼主翻译好了再让大家共享吧！一劳永逸呀！！！！！！！！！

用了金山快译,原文如下:

OHV 引擎设计
 OHV 意谓在头上的活瓣 -引擎凸轮桥被安装进里面引擎的设计阻塞，而且活瓣经过举起的人， pushrods 和摇杆双臂被操作。 (一个 OHV 引擎也以～闻名 "Pushrod" 引擎) 虽然 OHV 设计是一一点点旧式的,它有成功的被用长达十年。 一个 OHV 引擎非常简单, 有比较紧凑的大小和证明持久。
缺点: 它是困难精确的在是由於被比较大量的活瓣火车成份引起的比较高的惯性高转/每分控制活瓣时间安排的。 (举起的人-pushrod- 摇杆手臂) 它也是非常困难安装超过 每圆筒 2个活瓣或工具例如  可变的活瓣时间安排的一些最新技术的 - 某物可能是容易地在一个 DOHC 引擎中做。

OHC 或 SOHC 引擎——我们的 4G18就是类似这结构，不过是 16 气门，每缸 4 气门
 OHC 大体上方法在头上的凸轮而 SOHC 意谓单顶置的凸轮。
在 SOHC 引擎中，凸轮桥被安装在圆筒中头，而且活瓣被操作或被摇杆武装或直接的经过举起的人.(当做在照片中)
利益是活瓣被凸轮桥几乎直接的操作 - 容易的在高转/每分达成完美的时间安排。 它也是可能安装每圆筒三或四个活瓣的
缺点 - 一个 OHC 引擎用～需要时间安排带子或链相关的成份 - 较多的合成物和比较贵的设计。

DOHC 或双顶置的凸轮引擎
 DOHC 或两倍的在头上的凸轮 - 在许多今天的汽车中被用的装备。因为它是可能安装来自排气谷的相反边上的每圆筒多样的活瓣和地方吸入活瓣的,DOHC 引擎罐子 "呼吸" 比较意义它能用～生产较多的马力比较小的引擎体积。 比较: 2003 日产探险者的 3.5 个公升的 V6 DOHC 引擎有 240 h.p, 类似 5.9 个公升的 V8 OHV 引擎的 245 h.p 2003 避开 Durango。
职业者: 高的效率, 可能的安装每圆筒多样的活瓣而且采用可变的时间安排。
精读: 较多的合成物和比较贵的设计。

哈哈翻译还是还是基本看的懂的呵呵