不同种类引擎的平滑解释

[蓝魔]

http://www.e31.net/engines_e.html

The Inline-Four Engine

Now things get complicated. Although it seems that a four cylinder engine is free of vibration, it is not.
An inline four engine fires every 180° which means that always two pistons are in the same position and move in the same direction. Because of the symmetrical arrangement there is no end-to-end vibration as with the three cylinder engine (piston 1 and 4 plus 2 and 3 are pairs).
Thre problem is the vertival movement. At first glance it seems that the forces generated by the first piston are cancelled by the second and the forces of the third are cancelled by the fourth. But that is not the case!
As you can see in the picture, pistons which are moving up, are moving at different speeds than pistons that are moving down. So there are vibrations again which have to be cancelled by balancer shafts.

The crankshaft of an inline four engine.
Frontal view of crankshaft.

Forces generated by pistons and rods which are moving up and
down do not cancel themselves but result in 'second order forces'.

[蓝魔]

The V6 is a special kind of V-engine. It is normally the case that two pistons, one for the left and one for the right cylinder bank, share a crank pin. In a V6 the crank pins have to be splitted and shifted in order to avoid vibration between banks.
There are two kinds of V6 engines with different V-angles in use, 60° and 90°. The 90°-V6 has a 30° crank pin shift (see picture), the 60°-V6 60° shift.
Just as the three cylinder engines, a V6 generates end-to-end vibration, so a balancer shaft is needed. Thus V6-engines are inferior to inline six engines concerning smoothness, despite having the same number of cylinders.
So why use V engines? Although twice as much camshafts are needed, the higher friction, the lack of smoothness and the higher production cost, the V6 uses much less space, which helps saving costs in other places and allows front wheel drive (which saves further costs).

Crankshaft of a 90°-V6 with 30° pin shift.
Frontal view of crankshaft.

[蓝魔]

As you can see an inline six engine consists basically of two mirrored three cylinder engines. That results in two sorts of vibrations (around cylinder #2 and #5) which cancel themselves. So there isn't even end-to-end vibration.
Because the crankshaft is identical to the one of a three cylinder, only twice as long and with twice as much pistons, here as well is no change of the center of gravity and no forces are generated, neither horizontal nor vertical ones. That is the reason why inline six cylinder engines run so smoothly.

The crankshaft of an inline six engine.
Frontal view of crankshaft.

[蓝魔]

There are two types of V8s which differ by crankshaft. The V-angle is always 90°. The two types are called cross-plane (crank pins at a 90° angle) and flat-plane (crank pins at 180°). V8 engines have the advantage of not being in need of split crank pins in order to avoid vibrations between cylinder banks.
With a cross-plane V8, however, the last cylinder is not in the same position as the first, so there is end-to-end vibration again. That can be solved by adding counterweights to the crankshaft which cancel the forced created by the pistons. That is possible only in a V-engine with a V-angle of 90° and without splitted crank pins. These counterweights, fitted to an inline engine, would move to the side when the piston moves up or down and therefore generate additional vibration. But in a 90° V-engine there are pistons on the same crank pin which move exactly into the opposite directions of the counterweights (because of the bank angle) and their forces can be cancelled. Cross-plane V8s are therefore running quite smooth but because of the heavier crankshaft they are not as revvy.
Flat-plane V8 engines do not have those problems. They are also more responsive because of less rotational inertia. That increases maximum rpm and top-end power. In addition the crank case can be smaller which lowers the center of gravity.
But why are the flat-plane engines used in sports cars only if there are so many advantages? That's because of the crankshaft itself, the disadvantage of the flat-plane type. As you can see, the arrangement of crank pins is identical to a four cylinder engine which means there are also vibrations, only stronger, as basically two inline-four engines are running simultaneously. In sports cars those vibrations are reduced by using very lightweight pistons and connecting rods. That is of course expensive and because ride quality isn't too important either, the rough characteristics (compared to a cross-plane) are tolerated. Because of the crankshaft, the sound of such an engine is the one of two four cylinder engines. A (typical american) cross-plane burbling cannot be achieved.

[蓝魔]

The V12 is said to be the most sophisticated engine design, being free of vibrations and running smoothly. But so does an inline six. Now what is the difference between those two concepts concerning smoothness, as even the crankshafts look alike?
Let us return to the one-cylinder. It was said there, that an engine's power delivery occurs in 'jerks', every time a combustion takes place. And that is the secret of a V12: the smoothness is increased by more combustions per crankshaft revolution.

[蓝魔]

In boxer engines the pistons are not aligned upright or in V-shape, but lie horizontally opposed. This type of engine not only achieves an extraordinary low center of gravity but also runs perfectly smooth and free of vibrations - regardless of number of cylinders.
As you can see in the following picture, a pair of pistons are not only always in the same position but also move with the same speed - only into different directions so that all vibrations are cancelled.

A boxer-engine runs always smoothly.

[ldwlx]

好！

[蓝魔]

那个链接还有一篇文章写的不错，是关于扭力和马力的关系：
http://www.e31.net/torque_e.html

扭力说白了，就是平时我们感到的推背的力量。这个力量拿来加速，或者拿来拖东西，或者维持车上坡等等。

而马力是感觉不到的，马力只是扭力乘以转速的一个乘积。只要扭力一样，引擎在 2000rpm 发力，和在 6000rpm 发力，对加速或者拖东西毫无区别。

关键问题就是，引擎的转速有限，必须通过不停的换更高档，才能让车越来越快。不难理解，两个引擎，假如输出扭力一样的话，哪个引擎能在同一个档位内输出扭力持续的转速越高，哪辆车就加速更快。

这是因为能持续到更高转速的引擎，必然比另一个引擎能推迟升挡。而一旦升档，输出到轮子上的扭力，必然因为齿轮比下降了，而大大降低，比能继续持续的引擎的加速力量下降。

而马力正是扭力乘以转速的，也就是说扭力持续到越高的转速，马力就越大，车的总体加速越快。

所以如果大家都只需要开 20-30km/h，或者同一个档位内加速的话，马力就毫无意义。

这也就是为什么扭力范围宽广的引擎，虽然没感到加速推背感有多强，但是速度上去的很快，原因就是它能持续的范围更长更广，自然就不知不觉的速度上去了。


------------------


我刚学车的时候，跟别人玩红灯起步的时候，我就发现了这个现象。

跟小 civic 玩起步，大家一起冲出去，车身并排，谁也快不过谁，我想，对方真快啊，估计我赢不了。

然后，眼看转速到了 5200rpm，大家还是并排，谁也没有优势的时候，突然听到小 civic 换挡，瞬间没了加速。我大喜，趁它换挡，我继续地板油门，一直扯到 7000rpm，迅速把它拉开好几个车身的位置。然后换二档，再加速，然后就彻底把它远远抛在后面。

这时即使我们都在二档，就算输出的扭力差不多，也由于之前已经比它快了一截速度，就算同时加速，也会由于速度差，把它越拉越远。

所以，drag start，如果双方扭力差不多，或者就算对方扭力比你强，看起来起步加速快，不要慌张，还要看谁能持续加速的更长，而后来居上。

[siminzxu]

扭力说白就是力,马力是功率.只有力可以产生加速度,跟车马力有关,扭力是个曲线,比较复杂可以计算的.

我想速度快后,扭力主要是克服越来越大的摩擦力,用于加速的力就少了,这时候你有更多多余的力加速就好.

[siminzxu]

根据能量守衡定理也可以解释,速度越快,单位时间跑的距离也大,功就越大,但无论如何都不可能超过车自己的马力.

[笑熬漿糊]

说白了，就看jetta的引擎就可以了，如果要更快什么的，就看傲地的了。

[已吻封笺]

作者: 笑熬漿糊

说白了，就看jetta的引擎就可以了，如果要更快什么的，就看傲地的了。

您能不能把签名改一下呀

————擎傲世之龍碼 從混沌中明清澈
————驾捷达之灵气 从熬弟中找平衡

横批：捷达元帅

[笑熬漿糊]

作者: 已吻封笺

您能不能把签名改一下呀

————擎傲世之龍碼 從混沌中明清澈
————驾捷达之灵气 从熬弟中找平衡

横批：捷达元帅

其实保时捷911更快，还稳，开个200以上过海边的弯路跟玩一样。

[已吻封笺]

作者: 笑熬漿糊

其实保时捷911更快，还稳，开个200以上过海边的弯路跟玩一样。

靠，熬弟啊六什么的，以前常开，还有些发言权，才敢跟偶像少谈，介宝石姐，咱末摸过呀介搭不上话儿呀

[蓝魔]

作者: siminzxu

扭力说白就是力,马力是功率.只有力可以产生加速度,跟车马力有关,扭力是个曲线,比较复杂可以计算的.

我想速度快后,扭力主要是克服越来越大的摩擦力,用于加速的力就少了,这时候你有更多多余的力加速就好.

速度快了以后，阻力会增大，但这不是主要原因。

主要原因是速度上去后，超出了引擎转速，上档后，齿轮比下降，扭力到轮子上的就越来越小。

起步或者低速时的加速快，是因为档位低，等你加速到超出转速范围了，必然要上档，所以加速会下降。

[busrel]

作者: 蓝魔

那个链接还有一篇文章写的不错，是关于扭力和马力的关系：
http://www.e31.net/torque_e.html

扭力说白了，就是平时我们感到的推背的力量。这个力量拿来加速，或者拿来拖东西，或者维持车上坡等等。

而马力是感觉不到的，马力只是扭力乘以转速的一个乘积。只要扭力一样，...

你这个说法是不对的。。。。 F=MA只能适用于连续做功的理想状态，发动机是非连续做功的。所以必须用马力来衡量。计算发动机做功需要用积分了，要积分所有发力的点火扭力。你感受的推背感是在单位时间内扭力的总和，简称马力。

F=MA在现实世界是几乎不存在的，即使电动马达这种连续扭力的玩意，也有磁铁转南北极那一瞬间不做功的空隙。这也就是为啥F=MA只能在高中的物理课本出现。

[蓝魔]

作者: busrel

你这个说法是不对的。。。。 F=MA只能适用于连续做功的理想状态，发动机是非连续做功的。所以必须用马力来衡量。计算发动机做功需要用积分了，要积分所有发力的点火扭力。你感受的推背感是在单位时间内扭力的总和，简称马力。

F=MA在现实世界是几乎不存在的，即使电动马达这种连续扭力的玩意，也有磁铁转南...

我认为不对。马力是扭力乘以转速，同样的扭力在任何转速下推背感都是一样的。Dyno 上测出来的扭力，符合实际推背感一致。推背感就是扭力，或者说是很短时间内的扭力，这个跟转速无关。

推背感的总和，才是扭力曲线相对引擎转速的积分，这个就是扭力曲线底下的总面积，取决于加速的快慢，而不是任何扭力或者马力峰值能表现出来的。

[busrel]

作者: 蓝魔

我认为不对。马力是扭力乘以转速，同样的扭力在任何转速下推背感都是一样的。Dyno 上测出来的扭力，符合实际推背感一致。推背感就是扭力，或者说是很短时间内的扭力，这个跟转速无关。

我不知道你说的推背感是指什么,如果是指加速感的话那么一定是马力,要说感受的力....我不认为你能通过座椅感受出点火瞬间的那个力,而且那个力是随着转速的提高而变小的.

[蓝魔]

作者: busrel

我不知道你说的推背感是指什么,如果是指加速感的话那么一定是马力,要说感受的力....我不认为你能通过座椅感受出点火瞬间的那个力,而且那个力是随着转速的提高而变小的.

推背感就是 torque，就是油门到底时，引擎输送到轮子上的力。

这个力抵消了车的阻力后，就是拿来加速的，符合 F=ma。

这个力也可以拿来拖东西，因为拖东西加大了阻力，而且需要加速的质量上升，所以扭力大的车，能拖动更重的东西，否则额外的扭力被拖的东西克服了，车就无法加速或者起步了。

不知道你有没有把你的车送到 dynamometer 上测量，或者调试 ECU，我说的 torque 是在 dynamometer 上测量出来的。具体方法就是车轮开上类似滚筒的东西，然后油门到底，同时加大滚筒内部的阻力，直到油门全开时，引擎不再加速，这个阻力就是引擎油门全开时额外的力量，也就是平时加速的推背力。测量整个 torque curve，就是重复上述方法，但是停留在每个转速上。

这个 torque 不一定随着转速提高而下降，往往时先提高，再下降，有些车还会忽高忽低，或者只是一个 bell curve，这些都不理想。最理想的就是很平的 torque，一直持续到高转速，实际的感觉就是车能维持加速的时间很长，而不只是降档或者起步时窜出去一下。

[busrel]

作者: 蓝魔

推背感就是 torque，就是油门到底时，引擎输送到轮子上的力。

这个力抵消了车的阻力后，就是拿来加速的，符合 F=ma。

这个力也可以拿来拖东西，因为拖东西加大了阻力，而且需要加速的质量上升，所以扭力大的车，能拖动更重的东西，否则额外的扭力被拖的东西克服了，车就无法加速或者起步了。

不知道你...

我再重复一遍（最后一遍）现实世界中，F=ma不成立,物理要重修啊。