齿轮用于大量的机械装置。他们做几件重要的工作，但^重要的是，他们提供了一个齿轮减速机动设备。这是关键的，因为，往往一个小马达旋转速度非常快的设备提供足够的电力，但没有足够的扭矩。比如，电动螺丝刀有一个非常大的齿轮减速，因为它需要大量的扭矩来转动螺钉，但电机只产生少量的扭矩在高速。有了一个齿轮减速，输出速度的转矩增加时，可以减少。
齿轮检测
摆钟工作原理
自行车工作
齿轮的另一件事是调整的方向旋转。比如，在你的车的后轮之间的差，被发送的功率由一个轴运行的车的中心，而差动打开电源90度，将它应用到车轮。
也有很多不同类型的齿轮中的错综复杂。在这篇文章中，我们将了解齿轮究竟是怎么工作的，和我们谈谈你找到各种机械配件的不同类型的齿轮。
在任何齿轮，该比率是由从所述齿轮的中心的接触点的距离来确定。比如，在与两个齿轮的装置，如果一个齿轮是其他的直径的两倍，比例为2:1。
我们可以看看^原始类型的齿轮将木桩伸出车轮。
与这种类型的齿轮的问题是，从每个齿轮的中心的接触点的变化的距离随着齿轮的转动。这意味着，齿轮比变化的齿轮转动时，这意味着输出速度也发生变化。这样在你的车如果您使用的齿轮，这将是不可能维持恒定的速度 - 你会不断地加速和减速。
许多现代齿轮使用一种特殊的称为渐开线齿廓。此配置文件有两个齿轮之间保持恒定的速比非常重要的属性。喜欢上面的挂轮，接触点的移动，但这种运动补偿的渐开线齿轮的齿的形状。有关详细信息，请参阅本节。
现在，让我们来看看一些不同类型的齿轮。
直齿圆柱齿轮的齿轮是^常见的类型。他们有直齿，并且被安装在平行轴。有时候，直齿圆柱齿轮一次创建非常大的齿轮减少。
正齿轮中使用的许多设备，你可以看到所有博闻网的，就像电动螺丝刀，跳舞的怪物，振荡洒水，发条闹钟，洗衣机和干衣机。但你不会找到你的车很多。
这是因为直齿圆柱齿轮可真大。每一个齿轮的齿啮合的齿轮的齿，牙齿的碰撞，而且这种影响会发出声音。这也增加了的齿轮齿上的应力。
为了减少齿轮噪声和应力，大多数在您的汽车的齿轮是螺旋。
螺旋伞齿轮上的齿的齿轮面对的角度切割。当螺旋齿轮系统上的两个齿啮合时，接触的齿的一端开始，并逐渐传播随着齿轮的转动，直到完全啮合的两个齿。
这种渐进式的参与，使操作更平稳，安静比正齿轮斜齿圆柱齿轮。出于这个原因，都使用斜齿轮在几乎所有的汽车变速器。
由于螺旋锥齿轮上的齿的角度，它们创建时，啮合的齿轮上的推力负荷。使用螺旋伞齿轮的设备能够支持这种推力负荷的轴承。
一个有趣的事情关于弧齿锥齿轮的齿的角度，如果是正确的，它们可以被安装在垂直轴的90度的旋转角度，调整。
是有用的，当需要改变的方向的轴的旋转时，锥齿轮。它们通常安装在相隔90度的轴，但可以被设计为工作在其他角度。
伞齿轮上的齿可以是直链，螺旋形或准双曲面。直齿锥齿轮直齿轮齿实际上有同样的问题 - 每个齿啮合，它会影响相应的牙一次。
就像与直齿圆柱齿轮，这个问题的解决方案是曲线的齿轮齿。这些涡旋齿啮合就像螺旋齿：接触在齿轮的一端开始，并逐步在整个齿传播。
在直链和螺旋伞齿轮，轴必须是互相垂直的，但它们也必须在同一平面上。如果你要扩展过去的两轴的齿轮，他们会相交。准双曲面齿轮，另一方面，可以从事与在不同的平面中的轴。
使用此功能在许多汽车的差异。差动装置及输入小齿轮的齿圈是两个准双曲面。这允许输入小齿轮将被安装低于环形齿轮的轴线。图7示出了输入小齿轮啮合的环形齿轮的差动。由于汽车的驱动轴连接到输入小齿轮，这也降低了所述驱动轴。这意味着，所述驱动轴不侵入到乘客车厢的汽车一样多，使得更多房间的人及货物。
蜗轮时使用的大齿轮减速是必要的。这是常见的蜗轮，以减少为20:1，甚至可高达300:1或更大。
很多蜗轮齿轮有一个有趣的属性，没有任何其他的齿轮组：蠕虫可以很容易地转动的齿轮，但不能把齿轮蜗轮。这是因为，在蜗杆的角度是太浅，当齿轮试图旋转它，齿轮和蜗杆之间的摩擦保持蜗杆到位。
此功能是有用的机器，如输送机系统，其中所述锁定功能可以作为为输送机，当电机不转动的制动。另外一个很有趣的用法蜗轮是在托森差速器，一些高性能的轿车和卡车上使用。
使用齿条和小齿轮的齿轮的旋转运动转换成直线运动。这方面的一个很好的例子是很多车的转向系统。方向盘旋转的齿轮相啮合的齿条。当齿轮转动时，它要么向右或向左滑动机架，这取决于哪种方式，你转动滚轮。
也可用于齿轮齿条式齿轮转动旋钮，显示你的体重在一些规模。
行星齿轮组和齿轮比
任何行星齿轮组有三个主要组件：
太阳齿轮
行星齿轮和行星齿轮的载体
环齿轮
这三种组分中的每一个可以是输入，输出，或者可以保持静止。选择哪一块扮演的角色决定的齿轮组的齿轮比。让我们来看看在一个单一的行星齿轮组。
来自我们的传输的行星齿轮组的一个具有72齿的环形齿轮和太阳齿轮30齿。我们可以得到很多不同的齿轮比出这个齿轮。
此外，锁定任何两个一起的三个组成部分，将锁定整个装置以1:1的齿轮减速。请注意，第一齿轮比上面列出的是减少 - 输出速度比输入速度较慢。第二个是一个过载 - 输出速度是速度比的输入速度。^后再次是减少的，但输出的方向是相反的。还有几个其他的比例，可以得到这个行星齿轮组，但这些都是那些是我们的自动传输有关。您可以尝试这些在下面的动画：
因此，这一个齿轮组，可以制作所有这些不同的齿轮比，而无需任何其他齿轮啮合或脱开。随着这些齿轮组在一行中的两个，我们可以得到四个前进档和一个倒档的我们的传输的需求。在下一节中，我们将会把两套齿轮。
渐开线齿轮配置文件的详细信息
渐开线齿形的齿轮齿，接触点开始接近一个齿轮，当齿轮旋转时，接触点从该齿轮和朝向另一移开。如果你要跟随的接触点，就成了一个齿轮附近开始和结束附近的其他描述的直线。这意味着，接触点的半径变大，齿啮合。
节圆直径是有效的接触直径。由于接触直径不是恒定的，节圆直径是真的平均接触距离。的牙齿开始从事，齿顶对齿接触的底部齿轮的齿内螺纹中径。但是请注意，部分的底部接触齿轮的齿齿顶齿在这一点上是很瘦的。随着齿轮转，接触点向上滑动到^佳的齿轮齿的凸厚部分。这推动了齿顶前面，所以它补偿的接触直径略小。由于牙齿的继续旋转，接触点更加远离移动，外出的节圆直径 - 这个运动补偿，但底齿的档案。的接触点开始滑入底齿的骨感的一部分，从顶部齿轮减去一点点的速度，以补偿增加的直径的接触。^终的结果是，即使不断的接触点的直径改变，速度保持不变。因此，一个渐开线齿轮的齿产生一个恒定的转速比。
Gears are used in tons of mechanical devices. They do several important jobs, but most important, they provide a gear reduction in motorized equipment. This is key because, often, a small motor spinning very fast can provide enough power for a device, but not enough torque. For instance, an electric screwdriver has a very large gear reduction because it needs lots of torque to turn screws, but the motor only produces a small amount of torque at a high speed. With a gear reduction, the output speed can be reduced while the torque is increased.
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Another thing gears do is adjust the direction of rotation. For instance, in the differential between the rear wheels of your car, the power is transmitted by a shaft that runs down the center of the car, and the differential has to turn that power 90 degrees to apply it to the wheels.
There are a lot of intricacies in the different types of gears. In this article, we’ll learn exactly how the teeth on gears work, and we’ll talk about the different types of gears you find in all sorts of mechanical gadgets.
On any gear, the ratio is determined by the distances from the center of the gear to the point of contact. For instance, in a device with two gears, if one gear is twice the diameter of the other, the ratio would be 2:1.
One of the most primitive types of gears we could look at would be a wheel with wooden pegs sticking out of it.
The problem with this type of gear is that the distance from the center of each gear to the point of contact changes as the gears rotate. This means that the gear ratio changes as the gear turns, meaning that the output speed also changes. If you used a gear like this in your car, it would be impossible to maintain a constant speed -- you would be accelerating and decelerating constantly.
Many modern gears use a special tooth profile called an involute. This profile has the very important property of maintaining a constant speed ratio between the two gears. Like the peg wheel above, the contact point moves; but the shape of the involute gear tooth compensates for this movement. See this section for details.
Now let’s take a look at some of the different types of gears.
Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions.
Spur gears are used in many devices that you can see all over HowStuffWorks, like the electric screwdriver, dancing monster, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer. But you won’t find many in your car.
This is because the spur gear can be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth.
To reduce the noise and stress in the gears, most of the gears in your car are helical.
The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement.
This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears. For this reason, helical gears are used in almost all car transmissions.
Because of the angle of the teeth on helical gears, they create a thrust load on the gear when they mesh. Devices that use helical gears have bearings that can support this thrust load.
One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees.
Bevel gears are useful when the direction of a shaft’s rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well.
The teeth on bevel gears can be straight, spiral or hypoid. Straight bevel gear teeth actually have the same problem as straight spur gear teeth -- as each tooth engages, it impacts the corresponding tooth all at once.
Just like with spur gears, the solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical teeth: the contact starts at one end of the gear and progressively spreads across the whole tooth.
On straight and spiral bevel gears, the shafts must be perpendicular to each other, but they must also be in the same plane. If you were to extend the two shafts past the gears, they would intersect. The hypoid gear, on the other hand, can engage with the axes in different planes.
This feature is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows the input pinion to be mounted lower than the axis of the ring gear. Figure 7 shows the input pinion engaging the ring gear of the differential. Since the driveshaft of the car is connected to the input pinion, this also lowers the driveshaft. This means that the driveshaft doesn’t intrude into the passenger compartment of the car as much, making more room for people and cargo.
Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater.
Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm. This is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place.
This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake for the conveyor when the motor is not turning. One other very interesting usage of worm gears is in the Torsen differential, which is used on some high-performance cars and trucks.
Rack and pinion gears are used to convert rotation into linear motion. A perfect example of this is the steering system on many cars. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way you turn the wheel.
Rack and pinion gears are also used in some scales to turn the dial that displays your weight.
Planetary Gearsets & Gear Ratios
Any planetary gearset has three main components:
The sun gear
The planet gears and the planet gears’ carrier
The ring gear
Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset. Let’s take a look at a single planetary gearset.
One of the planetary gearsets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gearset.
Also, locking any two of the three components together will lock up the whole device at a 1:1 gear reduction. Notice that the first gear ratio listed above is a reduction -- the output speed is slower than the input speed. The second is an overdrive -- the output speed is faster than the input speed. The last is a reduction again, but the output direction is reversed. There are several other ratios that can be gotten out of this planetary gear set, but these are the ones that are relevant to our automatic transmission. You can try these out in the animation below:
So this one set of gears can produce all of these different gear ratios without having to engage or disengage any other gears. With two of these gearsets in a row, we can get the four forward gears and one reverse gear our transmission needs. We’ll put the two sets of gears together in the next section.
Details on Involute Gear Profiles
On an involute profile gear tooth, the contact point starts closer to one gear, and as the gear spins, the contact point moves away from that gear and toward the other. If you were to follow the contact point, it would describe a straight line that starts near one gear and ends up near the other. This means that the radius of the contact point gets larger as the teeth engage.
The pitch diameter is the effective contact diameter. Since the contact diameter is not constant, the pitch diameter is really the average contact distance. As the teeth first start to engage, the top gear tooth contacts the bottom gear tooth inside the pitch diameter. But notice that the part of the top gear tooth that contacts the bottom gear tooth is very skinny at this point. As the gears turn, the contact point slides up onto the thicker part of the top gear tooth. This pushes the top gear ahead, so it compensates for the slightly smaller contact diameter. As the teeth continue to rotate, the contact point moves even further away, going outside the pitch diameter -- but the profile of the bottom tooth compensates for this movement. The contact point starts to slide onto the skinny part of the bottom tooth, subtracting a little bit of velocity from the top gear to compensate for the increased diameter of contact. The end result is that even though the contact point diameter changes continually, the speed remains the same. So an involute profile gear tooth produces a constant ratio of rotational speed.
