Valve System（配气机构）
Inlet Valve Timing（进气配气定时）
If the inlet valve opened at TDC of the intake stroke and closed at BDC of that stroke, it would have a duration of 180°.It would have remained open for half of a complete 360° revolution, or 180°. However, it takes some time for the valve to open to its full position. It also takes time for it to close tightly. Therefore the valve is opened before TDC (BTDC) and closed after BDC (ABDC).
如果进口门在进气行程的上止点打开并且在这次行程的下止点关闭，它将有180°的开度。气门在180°转角内完全打开。然而气门达到全开位置需要一定时间，完全关闭也需要一定时间。因此阀门在上止点(BTDC)之前被打开，在下止点(ABDC)之后关闭。
Exhaust Valve Timing（排气配气定时）
If the exhaust valve opened at BDC at the beginning of the exhaust stroke and closed at TDC at the end of the exhaust stroke, it would have a duration of 180°. But like the inlet valve, the exhaust valve needs time to reach the full-open position, It also needs time to reach the full-closed position. So the exhaust valve opens before BDC and closes after TDC.
如果排气门在排气行程的下止点打开并且在这次行程的上止点关闭，它将有180°的持续。但是像进气门一样，排气门需要时间到达充分打开和关闭的位置。因此排气门在下止点之前打开，在上止点之后关闭。
Valve Overlap（气门重叠）
The intake opens at 17° BTDC and the exhaust closes at 17° ATDC. Thus, for a period of 34°, both of the valves are open: (17° + 17° =34°). This period of time is known as valve overlap. The closing of the exhaust valve laps over the opening of the intake valve. During this time, the first of the new mixture pushes the last of the burned gases out the exhaust valve. Valve overlap is held to a minimum on turbo-charged engines. This prevents the intake charge from being blown out the exhaust.
进气门在上止点前17°打开，排气门在上止点后17°关闭。 因此，有34°的一段时期，两个阀门都是开的：(17°+ 17°= 34°)。这时期被称为气门重叠。排气门的关闭和进气门的开启重叠。在这个时候，新的混合气推动燃烧后的废气从排气门排出。在涡轮增压发动机上气门重叠角被保持在一个最小值。这就防止废气倒流入进气管。
Valve Operation（配气机构）
To coordinate the four-stroke cycle, a group of parts called the valve train opens and closes the valves (moves them down and up, respectively). These valve movements must take place at exactly the right moments. The opening of each valve is controlled by a camshaft.
那些打开和关闭气门的气门传动是为了协调四冲程的工作循环(使他们各自上下移动)。这些阀门运动必须正好在合适的时刻进行。每个阀门的开启由凸轮轴控制。
Overhead camshaft (OHC) valve train（顶置凸轮轴气阀传动）
The cam is an egg-shaped piece of metal on a shaft that rotates in coordination with the crankshaft. The metal shaft, called the camshaft, typically has individual cams for each valve in the engine. As the camshaft rotates, the lobe, or high spot of the cam, pushes against parts connected to the stem of the valve. This action forces the valve to move downward. This action could open an inlet valve for an intake stroke, or open an exhaust valve for an exhaust stroke.
凸轮是一在轴上的蛋形的金属，通过曲轴协调旋转。那金属轴叫凸轮轴，在发动机里的每个气门一般有各自的凸轮。当凸轮轴旋转时，凸轮凸起的或者高点的位置，推动气门座。这行动强迫阀门向下移动。这过程能使进气门在进气行程打开，或者排气门在排气行程打开。
As the camshaft continues to rotate, the high spot moves way from the valve mechanism. As this occurs, valve springs pull the valve tightly closed against its opening, called the valve seat.
因为凸轮轴继续旋转，凸轮轴上的凸起部分离开气门装置。当这发生时，气门弹簧紧紧地关闭气门口，叫做气门座。
Valves in modern car engines are located in the cylinder head at the top of the engine. This is known as an overhead valve (OHV) configuration. In addition, when the camshaft is located over the cylinder head, the arrangement is known as an overhead camshaft (OHC) design. Some high-performance engines have two separate camshafts, one for each set of inlet and exhaust valves. These engines are known as dual overhead camshaft (DOHC) engines.
现代汽车发动机里的阀门位于发动机顶上的汽缸盖。这被称为顶置气门(OHV)结构。另外，当凸轮轴位于汽缸盖上面时，这种方式被称为是顶置凸轮轴(OHC)结构。一些高性能发动机有两个单独的凸轮轴，分别负责开关进气门和排气门。这些发动机被称为双顶置凸轮轴(DOHC)发动机。
Push-rod valve train（推杆气阀传动）
The camshaft also can be located in the lower part of the engine, within the engine block. To transfer the motion of the cam upward to the valve, additional parts are needed.
凸轮轴也装在发动机底部的气缸体内。为了将凸轮的运动传给气门需要一些附属装置。
In this arrangement, the cam lobes push against round metal cylinders called cam follower. As the lobe of the cam comes up under the cam follower, it pushes the cam follower upward (away from the camshaft). The cam follower rides against a push rod, which pushes against a rocker arm. The rocker arm pivots on a shaft through its center. As one side of the rocker arm moves up, the other side moves down, just like a seesaw. The downward-moving side of the rocker arm pushes on the valve stem to open the valve.
在这种布置中，凸轮凸角推动凸轮挺杆。当凸轮的凸角在凸轮挺杆下出现时，它推动凸轮挺杆向上运动(离开凸轮轴)。凸轮挺杆推动控制摇臂的推杆。摇臂以通过它的中心为轴而旋转。当摇臂的一侧上升，其另一侧下降，正如一块跷跷板一样。摇臂向下移动的那一边推动气门杆以打开气门。
Because a push-rod valve train has additional parts, it is more difficult to run at high speeds. Push-rod engines typically run at slower speeds and, consequently, produce less horsepower than overhead-camshaft designs of equal size. (Remember, power is the rate at which work is done.)
因为推杆气阀传动有另外的部分，所以很难以高速运转。推杆发动机一般在低速运转，从而产生比相同大小的顶置凸轮轴较少功率。(记住，功率反映了工作能力。)
Valve Clearance（气门间隙）
When the engine runs in compression stroke and power stroke, the valves must close tightly on their seats to produce a gas-tight seal and thus prevent the gases escaping from the combustion chamber. If the valves do not close fully the engine will not develop full power. Also the valve heads will be liable to be burnt by the passing hot gases, and there is the likelihood of the piston crown touching an open valve, which can seriously damage the engine.
当发动机处于压缩行程和做功行程时，阀门必须紧紧地关闭以产生一个不透气的气封，以防止气体逃离燃烧室。如果阀门不完全关闭，发动机将不能发挥全部动力。此外气门头易于被通过的热气体燃烧，这有可能使活塞频繁冲击打开的气门，使发动机严重损坏。
So that the valves can close fully some clearance is needed in the operating mechanism. This means that the operating mechanism must be able to move sufficiently far enough away from the valve to allow the valves to be fully closed against its seat by the valve spring. However, if the clearance is set too great this will cause a light metallic tapping noise.
所以阀门能完全关闭，气门间隙在操作机构内是必须的。这意味着操作机构必须离阀门足够远以允许阀门通过气门弹簧使其完全关闭。但是，如果间隙太大，将引起金属轻敲的噪音。
Camshaft Drive Mechanism（凸轮轴驱动机构）
Each cam must revolve once during the four-stroke cycle to open a valve. A cycle, remember, corresponds with two revolutions of the crankshaft. Therefore, the camshaft must revolve at exactly half the speed of the crankshaft. This is accomplished with a 2:1 great ratio. A gear connected to the camshaft has twice the number of teeth as a gear connected to the crankshaft. The gears are linked in one of three ways:
在四行程循环时，每凸轮必须旋转打开一阀门。记住，一个循环相当于曲轴旋转两次。因此，凸轮轴必须以曲轴正好一半的速度旋转。这用2：1的传动比完成。齿轮连接到凸轮轴的齿数是齿轮连接到曲轴的两倍。齿轮连结有三种方式：
（1）Belt drive（皮带传动）
A cog-type belt can be used. Such belts are made of synthetic rubber and reinforced with internal steel or fiberglass strands. The belts have teeth, or slotted spaces to engage and drive teeth on gear wheels. A belt typically is used on engines with overhead-cam valve trains.
齿型带能被使用。这样的带是由合成橡胶做成并且用内部的钢或者玻璃纤维绞合加强。皮带上有齿，或者槽以啮合并且驱动传动齿轮上的齿。皮带一般与顶置凸轮阀门传动一起被用在发动机上。
（2）Chain drive（链传动）
On some engines, a metal chain is used to connect the crankshaft and camshaft gears. Most push-rod engines and some OHC engines have chains.
在一些发动机上，金属链被用来连结曲轴和凸轮轴齿轮。大多数推杆发动机和一些顶置凸轮轴发动机都有链。
（3）Gear drive（齿轮传动）
The camshaft and crankshaft gears can be connected directly, or meshed. This type of operating linkage commonly is used on older six-cylinder, inline engines.
凸轮轴和曲轴齿轮可能被直接连结，或者相啮合。这类操作联动通常被用在更老的六气缸，直列发动机上。
A camshaft driven by a chain or belt turns in the same direction as the crankshaft. But a camshaft driven directly by the crankshaft gear turns in the opposite direction. Timing belts are used because they cost less than chains and operate more quietly. A typical timing belt is made of neoprene (synthetic rubber) reinforced with fiberglass.
凸轮轴被链或者带驱动，使其朝着曲轴相同的方向转动。但是凸轮轴被曲轴齿轮直接驱动，其将在相反方向上转动。正时皮带被使用，因为他们花费少于链子，而且噪音少。一条典型的正时皮带由用玻璃纤维加强的氯丁橡胶(合成橡胶)做成的。
