無段自動變速箱（Continuously Variable Transmission, CVT）& 齒輪比,終傳比,輪胎尺吋跟速度之間的關係

有V型橡膠帶式、金屬帶式、多盤式、鋼球式、滾輪轉盤式等多種構造，大都利用金屬帶和可變半徑的滾輪 (尚未撰寫)”>傳輸動力。透過主動滾輪與被動滾輪半徑的變化，達到齒輪比的變化。理論上這種傳動方式的效率很高，不過必須建立在能負荷所傳遞的動力的情況下。由於是利用鋼帶與滾輪之間的摩擦力傳遞動力，所以鋼帶及滾輪的工作情況十分苛刻。為了有效傳遞動力，鋼帶與滾輪之間不允許打滑，而且原本產生的熱能已經很多，如果再打滑恐怕將會造內部機件的燒毀或嚴重耗損。而為了增加靜摩擦力，最直接的方式就是增加鋼帶與滾輪之間的壓力。但摩擦力增加了，動力傳輸的耗損也會增加，無形中還是增加了油耗。並且鋼帶的強度也是一大重點。所以CVT變速箱縱然有舒適、效率高等等優點。缺點就是目前一般的CVT變速箱不能承受較大的扭力。不然就是要用較高的油耗作補償。

Advantages

CVTs can compensate for changing vehicle speeds, allowing the engine speed to remain at its level of peak efficiency. This improves fuel economy and by effect, exhaust emissions.

CVTs operate smoothly since there are no gear changes which cause sudden jerks.

Very few problems have been reported with the CVT transmission, lowering the cost of ownership.

There are 25% fewer moving parts to a CVT transmission.

They are also cheaper, but still expensive to repair.

The fluids do not have to be changed as often as in an automatic transmission.

Disadvantages

CVTs operate smoothly and efficiently, without spending energy to jerk the car during a shift. This can give a perception of low power, because many drivers expect a jerk when they begin to move the vehicle. However, the expected jerk of a non-CVT can be emulated by CVT control software, thus eliminating this marketing problem.

Since the CVT keeps the engine turning at constant RPM over a wide range of vehicle speeds, pressing on the accelerator pedal will make the car move faster but doesn’t change the sound coming from the engine as much as a conventional automatic transmission gear-shift. This confuses some drivers and, again, leads to an impression of a lack of power. This can be considered a disadvantage if the driver desires to hear the engine change tone.

CVT torque-handling capability is limited by the strength of their transmission medium (usually a belt or chain), and by their ability to withstand friction wear between torque source and transmission medium (in friction-driven CVTs). CVTs in production prior to 2005 are predominantly belt- or chain-driven and therefore typically limited to low-powered cars and other light-duty applications. Units using advanced lubricants, however, have been proven to support any amount of torque in production vehicles, including that used for buses, heavy trucks, and earth-moving equipment.

source: http://en.wikipedia.org/wiki/Continuously_variable_transmission

齒輪比,終傳比,輪胎呎吋跟速度之間的關係
玩車的朋友常常看到這幾個字眼。一般的汽車會註明齒輪比數據
例如 BMW的 M3 ( E46 ) 的齒輪比跟終傳比如下：
1st : 4.227
2nd: 2.528
3rd: 1.669
4th: 1.226
5th: 1.000
6th: 0.828
final: 3.746
一至六就是變速箱各檔的齒輪比，final就是差速器的終傳比。

齒輪比是用「多少比一」來表示，” 3 ” 就是引擎轉一圈，透過齒輪轉換後就只剩1/3圈，數字越大，表示引擎的轉速會被轉換成更慢的速度，等於一就是跟引擎轉速一樣，小於一則會得到高於引擎的轉速。引擎動力在傳到輪胎之前必須經過變速箱內的齒輪組與差速器的齒輪組作兩次減速，才能將引擎每分鐘高達數千轉的轉速降至到輪胎能在地面行走的適當速度。
假設M3配置的輪胎周長為2公尺= 0.002公里，當M3以四檔 5000rpm行駛時，我們可以算出：
速度 = 5000 (引擎每分鐘轉數) / 1.226 (四檔齒輪比) / 3.746 ( 終傳比 ) *0.002(輪胎周長 ) * 60 (一小時分鐘數 ) =130.6 km/h，約時速130公里。

這裡可知齒輪比與終傳比及輪胎尺吋是掌控速度的一大關鍵，不過在同一台車上，追求極速或是加速的齒輪比調整剛好是兩個極端，極速越高，通常得付出加速差的代價，反之加速越快，也會造成極速降低的現象，最理想的調整是因應不同賽道環境去調整齒輪比跟終傳比，盡量讓賽車在各種賽道上都能發揮最佳表現。

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