NEWS
Take a look at the heavy truck "double intermediate shaft" gearbox.
▎Where did the double intermediate shaft come from?
Before 1960s, the main structure of automobile gearbox was single intermediate shaft. With the improvement of expressway network in western developed countries, freight cars begin to develop towards large-scale, high-speed and specialization. With the increasing power of the engine, designers hope to increase the bearing capacity of the transmission on the one hand, and don't want the axial size of the transmission to become larger on the other hand, which is self-contradictory, so the double intermediate transmission came into being.
In the 1960s, Eaton pioneered the Fuller double countershaft gearbox, which was patented in 1965, and soon became popular among American heavy vehicles. By the 1980s, the double countershaft gearbox almost monopolized the American market of transmission for heavy vehicles.
At the same time, as China entered the reform and opening-up, the society urgently needed heavy truck technology products with large load and fast driving speed. In 1984, Faster introduced Fuller double intermediate shaft transmission technology and began to produce double intermediate shaft transmission, which kicked off the popularization of double intermediate shafts in China.
For more than 40 years, domestic freight trucks have been developing towards high power. In order to better meet the requirements of vehicle dynamic performance and economy, heavy-duty transmission is also developing towards multi-gears, large speed ratio and small step difference. In the tide of the times, the double intermediate shaft transmission surpassed the single intermediate shaft transmission and gradually became the mainstream configuration of our heavy trucks.
▎What are the characteristics of double intermediate shafts?
Double-shaft transmission has two identical intermediate shafts, which are symmetrically arranged, so that the power transmitted from the main shaft to the intermediate shaft is divided. The intermediate shaft and the bearings and gears on it only bear half of the total power; The force transmitted from the intermediate shaft to the main shaft is equal in magnitude and opposite in direction, so the main shaft only bears torque, not bending moment, which improves the stress situation of the main shaft and bearing, and greatly improves the reliability and durability of the transmission.
When designing a double countershaft transmission, it can reduce the center distance and the diameters of gears, narrow the width of gears and reduce the diameters of shafts, thus shortening the axial size and reducing the weight of the transmission. The shorter axial size is beneficial to realize the design of multi-gear and small step difference, while the lighter transmission weight is beneficial to light weight and improve the economy of the whole vehicle.
Because the main shaft will not bend and deform, it can also avoid the damage caused by gear meshing, effectively reduce the noise of gear meshing of the transmission, and comprehensively prolong the service life of the transmission.
gear shaft
▎gear shaft
Gear shaft refers to a mechanical part that supports rotating parts and rotates with them to transmit motion, torque or bending moment. Generally, it is a round metal rod, and each section can have different diameters. The rotating parts of the machine are mounted on the shaft.
▎basic content
According to the different shapes of axes, shafts can be divided into crankshaft and straight shaft. According to the bearing condition of the shaft, it can be divided into: ① Rotating shaft, which bears both bending moment and torque when working, is the most common shaft in machinery, such as shafts in various reducers, etc. (2) Mandrels, which are used to support rotating parts to bear bending moment without transmitting torque. Some mandrels rotate, such as the shafts of railway vehicles, while others do not, such as the shafts supporting pulleys, etc. (3) The transmission shaft is mainly used to transmit torque without bearing bending moment, such as the long optical axis in the crane moving mechanism and the driving shaft of the automobile, etc. In the design, the application of gear shafts is generally nothing more than the following situations: 1. Gear shafts are generally pinion gears (gears with few teeth) 2. Gear shafts are generally at high speed (that is, at low torque level) 3. Gear shafts are rarely used as sliding gears with variable speed, and are generally fixed-running gears. First, because they are at high speed, their high speed is not suitable for sliding speed change. 4. Gear shaft is a combination of shaft and gear. However, when designing, it is necessary to try to shorten the length of the shaft. If it is too long, it is not conducive to the machining of the upper gear hobbing machine. Secondly, if the shaft is supported too long, it will become thicker and increase the mechanical strength (such as rigidity, deflection, bending resistance, etc.).
How to judge gears and shafts
▎How to judge when designing gears and shafts?
For steel gears with very small diameter, if the distance E from the tooth root circle to the bottom of the keyway is less than 2mt (MT is the end modulus) when it is a cylindrical gear, if E is less than e<1.6m calculated according to the size of the small end of the gear when it is a bevel gear, the gear and the shaft should be integrated into a gear shaft. If the E value exceeds the above size, it is reasonable to manufacture the gear separately from the shaft.