Automobiles widely use piston-type internal combustion engines, which have a relatively small range of torque and speed variation. However, complex operating conditions require vehicles to have traction and speed that can vary over a considerable range. To resolve this contradiction, a transmission is installed in the drivetrain. As a major component of the drivetrain, the transmission's input shaft receives the engine's output torque and speed, and through changes in the gear ratios of the transmission gear set, adapts to changing driving conditions and coordinates with the engine's operation, resulting in better vehicle power and fuel economy. Synchronous Transmissions In asynchronous transmissions, when shifting using engagement sleeves, the circumferential speeds of the corresponding internal and external splines on the engagement sleeves and engagement rings of the two gears to be engaged must be equal (synchronized) for smooth engagement. If gears are forced to engage when the two teeth are not synchronized, impact and noise will occur between the teeth, affecting their service life and even causing breakage. Therefore, to prevent spline impact during shifting in a synchronized transmission, a complex operation is required, which must be completed quickly and correctly within a short time. This can easily cause fatigue even for highly skilled drivers. Therefore, measures were required in the transmission structure to ensure smooth gear shifting while simplifying operation and reducing driver workload. Synchronizers were developed to meet these requirements. After years of effort, synchronizers have been added to various types of truck transmissions, making gear shifting in trucks similar to that in passenger cars. The timing of gear shifts is easier to control, but the principle of synchronizing the internal and external splines during shifting remains the same; the synchronization is now achieved by the synchronizer instead of the driver. This requires a certain amount of shifting force and time. Drivers often overlook this adjustment process and time. Even after shifting, the significant speed difference between the engine and transmission input shafts results in a large impact force when the driver releases the clutch, leading to a high synchronizer failure rate—over 70% of transmission repairs are due to synchronizer damage caused by improper driver operation. This damage is often overlooked. While synchronizers have brought convenience to drivers, they have also created challenges for maintenance personnel. For many years, researchers have been studying how to extend the lifespan of transmission synchronizers and how to improve shifting methods for easier driver operation. Numerous synchronizers and shifting systems have been developed, but for various reasons, no breakthroughs have been achieved. With the continuous development of computer technology, the decrease in hardware costs, and the widespread use of mobile network technology in automobiles, computer-controlled intelligent shifting systems were developed in the 1990s. The emergence of this system made the current automatic control synchronizerless shifting system a reality. The working principle of the intelligent shift synchronizerless transmission is as follows: the intelligent shift synchronizerless transmission is controlled by a computer, and the process is completed by controlling the cylinders through solenoid valves. Sensors measure the rotational speed of the main shaft, the speed of the intermediate shaft, and the engine's output torque, etc. The computer calculates the shifting timing, comprehensively determines the gear to be shifted, and automatically completes the shift without moving the clutch pedal. The transmission structure is basically the same as a traditional mechanical transmission. In the synchronizerless transmission, the speed of the main shaft and the coordination between the gears are achieved through the electrical control of the motor and the transmission. The reduction of the transmission gears is achieved through the transmission brake on the intermediate shaft of the transmission. Currently, only electro-pneumatic controlled fully automatic shifting mechanical transmissions are equipped with synchronizerless shifting mechanisms. A fully automatic mechanical transmission for heavy-duty trucks with electro-hydraulic control, featuring an optional synchronizerless shifting mechanism, is about to be launched. Synchronizerless Transmission Shifting Braking When shifting from a lower gear to a higher gear, the speed of the gear being shifted must decrease, and the intermediate shaft must also decrease in speed. This decrease in intermediate shaft speed synchronizes the engaging gear ring and the inner and outer splines of the engaging gear sleeve on the gear being shifted, achieving the shifting purpose. The reduction in intermediate shaft speed is accomplished through the braking action of an intermediate shaft reducer mounted at the front end of the intermediate shaft. The intermediate shaft reducer friction plates (see Figure 1) consist of two pieces: one fixed to one end of the intermediate shaft and the other fixed to a sliding piston. The piston is relatively fixed to the transmission housing and cannot rotate, only allowing axial movement. Axial movement brings the two friction plates into contact, generating braking force to reduce the intermediate shaft speed. Intermediate shaft braking only works when shifting from a lower gear to a higher gear. Conversely, when shifting from a higher gear to a lower gear, the speed of the gear being shifted must increase, and the intermediate shaft must also increase in speed. This increase in intermediate shaft speed synchronizes the engaging gear ring and the inner and outer splines of the engaging gear sleeve, achieving the shifting purpose. The intermediate shaft speed is increased by increasing the engine speed. No intermediate shaft braking device is needed during this shifting process. Shifting process of a non-synchronized transmission: 1. Upshifting operation, taking shifting from 1st gear to 2nd gear as an example (see Figure 2). (1) Reduce engine torque (MR engine control system). (2) Clutch disengagement (KB clutch control system/KR clutch control device). (3) 1st gear disengagement (GS transmission control module). (4) Intermediate shaft reducer braking system deceleration (GS transmission control module/gate cylinder 5th valve). (5) Shift to 2nd gear (GS transmission control module). (6) Clutch engagement (KB clutch control system/KR clutch control device). (7) Reinstate engine torque (MR engine control system). 2. Downshifting operation, taking shifting from 4th gear to 3rd gear. (1) Reduce engine torque (MR engine control system). (2) Clutch disengagement (KB clutch control system/KR clutch control device). (3) 4th gear disengagement (GS transmission control module). (4) Clutch engagement (KR clutch control system/KR clutch control device). (5) Increase engine speed (MR engine control system). (6) Shift to 3rd gear. (7) Increase engine torque again according to load and speed (MR engine control system).