I remember ten years ago, around 2010, most cars had AN transmissions that were still 4-speed, and at that time, they were good cars with 6AT. But nowadays there are more and more AT gearboxes, 8AT, 9AT and even 10AT. Some people have questions: design so many gears, can they be used if they are not on the high speed? Today we will talk about this topic.
<h1 class="pgc-h-arrow-right" data-track="10" >8AT adds two more high-end bits to the 6AT? </h1>
Some people think that the 8AT is to continue to add two high-end positions to the 6AT, but this is not the case, because it does not make any sense to change the performance of the transmission. For example, 6AT used to run 120 in 6 gears, the engine speed was 2200 rpm, and after adding two high gears, it was possible to use 7 gears to run 120 engine speeds of 2000, and 120 engines to run 1800 with 8 gears, but this did not make much sense, because the two additional high grades may not be used at all in daily driving. And in terms of 6AT performance, coping with 120 per hour is more than enough, adding two high-end positions in vain has no real significance. Improving the performance of gears with high daily usage is more important. It's like building an embankment, with a focus on reinforcing low places, not high ones. In fact, the two gears with more than 8AT are equivalent to being disassembled and installed between the various gears.
<h1 class="pgc-h-arrow-right" data-track="35" > so can the 8AT car use the highest grade if it does not run at high speed? </h1>
I think for 8AT for the probability of using the highest gear in daily driving is not large, the above figure is a car equipped with an 8AT gearbox, according to the transmission system parameters calculated out of the speed and engine speed corresponding to the table, you can see that when the speed reaches 80 km / h, the corresponding engine speed of 8 gears is 1210 rpm, theoretically speaking, it can be used to 8 gears at this time. But the engine output torque at this speed is not very large, and the 8-speed transmission ratio is small, the torque amplification is very small, if you use 8 gears to drive, the power reserve will be very small, it is likely to be slightly sloped or slightly step on the throttle gearbox will immediately downshift, basically can only be used occasionally in the downhill section or at a uniform speed.
But this does not mean that 8AT is redundant, let's talk about the benefits of 8AT two more gears:
<h1 class="pgc-h-arrow-right" data-track="13" >1, improve the power of daily driving</h1>
For example, an 8AT gearbox, the final speed ratio of 1 gear is 14.1, that is to say, 1 gear can amplify the engine torque by 14.1 times, while the final speed ratio of the 6AT gearbox 1 gear of the same specification is 11.4, which can only be enlarged by 11.4 times, and as can be seen from the above figure, the overall speed ratio of the new 8AT from 1 gear to 6 gear is smaller than the previous 6AT, so the overall power performance will be better than 6AT.
<h1 class="pgc-h-arrow-right" data-track="14" >2, increase the torque converter lock range, better power, lower fuel consumption</h1>
The above figure is a schematic diagram of the principle of a torque converter, the pump wheel of the torque converter rotates with the engine, throws the transmission oil out, impacts the turbine blades, and transmits the power to the gearbox through the turbine. However, this transmission method is not a hard connection, there is slippage, the transmission efficiency is not high, so the later engineers set up a set of clutches between the shell of the torque converter and the turbine, in a specific case, the clutch can lock the shell of the torque converter and the turbine together, so that a hard connection is formed between the engine and the gearbox, and the transmission efficiency is greatly improved, which is the locking of the torque converter.
However, the early 6AT transmission torque converter locking range is limited, and the torque converter cannot be locked under many working conditions, so there is no advantage in fuel consumption. On the one hand, the 8AT increases the number of gears, and the connection between each gear is more close and smooth, on the other hand, it is optimized on some hardware, which can improve the locking range of the hydraulic torque converter of the new gearbox and improve fuel consumption and power feeling. The disadvantage is that some of the conformity is sacrificed.
<h1 class="pgc-h-arrow-right" data-track="18" >3, reduce high-speed cruising speed, save fuel</h1>
I have driven a small displacement manual transmission car to run at high speed, this car 5 gear run 120 when the engine speed is 3000 rpm, this speed of the power is already very good, acceleration, climbing, overtaking are enough. However, the problem of even speed driving and downhill sections on flat roads comes out: uniform driving does not require too much power, especially on downhill roads, if the engine brake force is too large if the throttle is released and sliding, the faster the car slides. Taxiing in neutral gear does not meet safe driving regulations. Driving on the accelerator is too high engine speed, it feels wasteful. Because of the downhill road, there is no need for too much driving force, at this time, if you can have one more high grade, you can reduce the engine speed, and it will be more fuel-efficient when going downhill.
The 8AT also has this consideration, the 8AT top gear shift ratio is smaller, so the engine speed can be further reduced when driving in the highest gear if the conditions are suitable at the same speed. For example, at a speed of 120 km / h on the high speed, the downhill section of the 6AT still has to use 6 gears and 2200 rpm, while the 8AT can be driven in 8 gears at this time, and the engine speed is only 1800 rpm, which can further reduce fuel consumption.
The most important thing is that the upgrade from 6AT to 8AT does not require additional gear sets, the number of planetary gear sets of 6AT is enough to match 8 gears, only need to change the clutch system and gear gear ratio, so the extra gears will not lead to an increase in the size and weight of the gearbox. The manual gearbox wants to increase the gear must increase the gear and gear shift device, will certainly increase the friction and weight, usually used not much, but waste.
Although the current sales of pure electric vehicles are gradually increasing, the status of fuel vehicles in the short term cannot be completely replaced, and the 6AT gearbox will be gradually eliminated in the future, replaced by more gear AT gearboxes.