1. Diesel engine characteristics make the maximum torque range too short
Compared with gasoline engines of the same level, diesel engines have obvious torque advantages, higher thermal efficiency, and more rugged and durable, thus becoming the preferred power for commercial vehicles, even tanks and ships. However, the maximum speed and torque range of diesel engine is not as good as that of gasoline engine.
Take trucks as an example. The maximum torque range of almost all diesel engines is very small, no matter Benz or Volvo, Cummins, Weichai or Xichai.
For example, Dongkang's Z14NS6B520 has a book parameter of 520 horsepower of 2500 Nm, and the maximum torque range is 1000-1500 rpm;
Volvo D16G750750 horsepower 3550 Nm torque, the maximum torque range is 1050-1400 rpm.
For passenger cars, BMW's B58B30C engine has a 3.0T displacement of 340 horsepower and 450 Nm of torque, but the maximum torque range can be from 1500 rpm to 5200 rpm.
2. The speed is not enough to make up
With such a small range of torque and speed, more gears must be equipped for the truck in order to achieve the best dynamic performance within the speed limit of the regulations.
The more gears, the better the engine can output at different speeds and different road conditions. This is why light trucks start to use small 8 gears.
On the other hand, there are more and more gears for passenger cars from the previous 4AT to the current 8AT, 9AT and even 10AT. The same is true.
3. The more gears, the wider the gear ratio, the more fuel saving
In order to highlight the fuel saving performance of the product, the manufacturer will try to make the engine work in the economic speed range as much as possible. For example, when starting, overtaking, and going uphill, select different low gears according to different road conditions, while at the high speed stage, try to select overdrive or direct gear according to the combination of the rear gear ratio and the rear axle gear ratio.
4. Multi-gear design can take full account of vehicle ride
The truck engine has large power and torque, while the speed range is small. If the transmission gear is too small, the impact of the vehicle when shifting will be large, and the burden and wear of the clutch will be increased. The denser gear ratio will make the shift smoother. But at the same time, the disadvantage is that it needs to shift frequently at different speeds.
5. Why do many drivers shift gears?
Multiple gears means that the driver needs to step on the clutch and shift gears several times from starting to cruising. For trucks that are in the climbing stage or heavy load, basically no driver jumps to shift gears.
However, in some cars that are not particularly heavy, there is little demand for power, and many drivers are willing to jump and shift gears. In this way, a car with 16 gears can shift to the rear gear after 8 times. The right hand and left foot can save some energy, and it will be much easier after the day.
6. The era of AMT is the era of less mistakes
The times are advancing, and the manual gear that has been used for decades will gradually be replaced by the automatic gear. Admittedly, at present, the automatic transmission is a little expensive, but it has incomparable advantages in being easier, more fuel-saving, more durable. Take the most widely used AMT transmission of trucks.
7. Save time and effort
No left foot clutch, right hand shift. According to the survey of Jianghuai Automobile Group, urban logistics vehicles need to shift 10-13 times per kilometer. According to the driving mileage of urban vehicles of 100 kilometers per day, drivers need to shift about 1300 times. Automatic transmission vehicles can greatly reduce the labor intensity of drivers.
8. Avoid incorrect operation
Novice drivers and bad driving habits have a great impact on the service life of the clutch, which may lead to early scrapping of the clutch, or even vehicle failure. Automatic transmission vehicles can avoid misoperation, extend the service life of vehicles and reduce the requirements for drivers.
In summary, more gears can improve the power, fuel economy and shift smoothness of the truck. However, the more gears, the better. Too many gears will lead to frequent gear changes, resulting in power interruption and increasing the driver's operating difficulty. Therefore, there is no best choice, only the most suitable one.
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