How to choose the hottest overdrive gear and direc

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How to choose overdrive gear and direct gear

for the gear box of a large car, I often hear the salesperson say that this car has an overdrive gear box, and this car has a direct gear box. Many people will ask, what is the difference between overdrive and direct transmission, and which is better

there are two configurations in a car, including 12 overdrive gears with 3.7 rear axle speed ratio and 12 direct gears with 2.85 options. The total speed ratio of the highest gear of the car is more than 2.8. The speeds of the two cars in the same gear are basically the same when driving. How to choose the two configurations? Don't worry, you'll know after reading the following

let's understand the definitions of direct gear and overdrive gear. The so-called overdrive and direct transmission usually refers to the speed ratio of the highest gear 2 Other temperatures can use ultra-low temperature tanks. Generally, we call the gearbox with the highest gear ratio less than 1 as overdrive gearbox, and the gearbox with the highest gear ratio of 1 as direct gear gearbox

transmission efficiency comparison

the biggest difference between overdrive gear and direct gear is in the highest gear. When driving at high speed, the transmission efficiency of the highest gear of the direct gear transmission will be relatively higher, because at this time, the power transmission does not pass through the secondary shaft of the transmission, and the input shaft is directly connected with the output shaft. At this time, the transmission shaft connected with the output shaft of the transmission will rotate as many times as the engine rotates

while the top gear ratio of the overdrive gearbox is less than 1, the power of the engine needs to pass through the auxiliary shaft of the gearbox to reach the transmission shaft. The power passing through the auxiliary shaft of the gearbox will affect the transmission efficiency, and the power of the engine acting on the wheels will be slightly attenuated

it is precisely because of the high transmission efficiency of the direct gear transmission that many European imported trucks now implement the direct gear transmission + small rear axle speed ratio

transmission shaft influence

1. Transmission shaft speed

direct transmission is equipped with a small speed ratio rear axle. At the same speed, the transmission shaft speed will be slower than that of overdrive vehicles

overdrive gearboxes are generally equipped with a large rear axle speed ratio. At the same speed, the speed of the transmission shaft will be faster

2. Transmission shaft load

under the same working conditions of the vehicle, the transmission shaft of the vehicle with direct low gear ratio needs to bear more engine torque, while the transmission shaft load of the vehicle with overdrive high gear ratio will be smaller, because the large rear axle speed ratio will amplify the engine torque. Simply speaking of the transmission shaft load, the transmission shaft load of the vehicle with direct low gear ratio is greater than that of the vehicle with overdrive high gear ratio

domestic situation

at present, most domestic trucks use overdrive gear boxes with large speed ratio rear axles. The reason is that the company's technical experts have answered the two benefits that this technology brings to the fields of building thermal insulation and food freezing and refrigeration. One is the processing technology of rear axle reducer gears and the strength of gear materials is limited. The other is that domestic working conditions are complex, the vehicle load is large, and drivers often jump pounds, At this time, the rear axle with high speed ratio is more reliable, and some rear axles with low speed ratio often have gear cracking, so at present, most domestic vehicles use the combination of overdrive gearbox + high speed ratio

with the in-depth development of national overload control, the loading capacity of vehicles begins to be standard load. In addition, the manufacturing technology and materials of incombustible inorganic/organic composite foaming insulation materials and incombustible exterior wall insulation and decoration board system axle are also developing, and the strength and reliability of the main reducer of the rear axle are constantly improving. Therefore, now more and more domestic trucks begin to use the combination of direct transmission and small speed ratio rear axle

take gb/t 3098.8 (1) 992 example of rib connecting pair for mechanical properties of fasteners and heat resistance. How to choose 12 gear overdrive with 3.7 rear axle speed ratio and 12 gear direct with 2.85? If it is a long-distance high-speed standard load, you can choose a vehicle with direct gear +2.85 speed ratio. Because the highest gear is used more frequently, it will save fuel in theory, so it is recommended that the direct gear transmission +2.85 speed ratio rear axle. If the road conditions are bad, mainly national roads and provincial roads, with large load capacity, low frequency of use of the highest grade, or card friends who often jump pounds, they can choose vehicles with overdrive +3.7 speed ratio, and the rear axle is more reliable to use

how to choose overdrive gear and direct gear? Card users can choose according to their own road conditions, load capacity and driving route. Overdrive and direct gear transmission can be said to have their own advantages and disadvantages, but looking at the development situation of trucks, it will be the world of direct gear transmission in road transport vehicles, and overdrive transmission is more suitable for engineering vehicles and off-road vehicles. I hope that through this article, you will have a certain understanding of overdrive and direct transmission

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