# Matching Quality Detection System of Synchronizer Ring and Cone
## 1 Introduction  
The friction elements used in modern automotive transmission come in many forms, the performance of which has a direct influence on the power, economy, and reliability of cars [1]. In order to best meet specific operating conditions, in addition to the use of a multi-plate friction clutch [2], a cone friction synchronizer is also widely used in automotive transmission and has become a key component [3]. The synchronizer is used for gear-shifting. In shifting, the engine optimal speed might be lost. So for optimal performance of transmission systems, it is important to increase the quality of the synchronizer [4], which can avoid the impact of meshing at different speeds, make shifting fast and accurate, easy to operate, and can greatly improve the life expectancy of the transmission [5]. Its performance is important for cutting down noise, reducing the shift force [6] and shifting time, which are key indicators to measure the quality of shifting [7]. The friction elements actually used in a gearbox must have specific functions, and be combined with an appropriate medium in an optimal way in order to enable a synchronizer to operate continuously throughout the life cycle. The common structures of synchronizers include the inertia type, supercharged type, etc., but the working principle is basically the same. They all rely on the friction principle to synchronize the synchronizer ring and cone, where the rotational speeds are different, to achieve smooth shifting [8]. Taking the inertia type synchronizer as an example, its structural composition is shown in Figure 1. The main components are the sliding sleeve, synchronizer rings [9], cones, and the positioning pin. The synchronization process of the synchronizer consists of three steps [10], and as shown in Figure 2, where 1 indicates the positioning pin, 2 indicates the sliding sleeve, 3 indicates the synchronizer ring, and 4 indicates the cone. (1) Step1, as shown in Figure 2A, the sliding sleeve begins to move axially under force \(F\) of the slider, leaving the intermediate position. At the same time, the positioning pin is deflected, and the synchronization ring is pushed so that it can be in contact with the cone. When the friction surfaces come into contact with each other, because of the different angular velocity of the cone and the sliding sleeve, the locking surface is contacted at this time, and the sliding sleeve is prevented from moving in the shifting direction due to the axial force. \(\Delta\omega\) is the difference of rotational speed between the sleeve and cone. (2) Step2, as shown in Figure 2B, the force of the cylinder acting on the sliding sleeve continues to act on the friction surface. Due to the action of friction torque, the rotational speeds of the sliding sleeve and the cone are gradually closer until they become the same, which means \(\Delta\omega=0\);  
(3) Step3, as shown in Figure 2C, after \(\Delta\omega=0\) the friction torque does not exist, but the axial force still acts on the locking element. Then, the locked state is released, the combined teeth of the sliding sleeve and the cone are engaged, and the synchronization process ends. Figure 1: Composition of an inertia type synchronizer (1 st and 2 nd gear). Figure 2: Synchronization process of the synchronizer. (**A**) Step 1, (**B**) Step 2, (**C**)Step 3. Friction is critical in the use of the synchronizer. As shown in Figure 3, friction between the synchronizing ring and the cone is determined by positive pressure \(F\), friction angle \(\alpha\), and friction coefficient \(\mu\)[11]. If positive pressure \(F\) is determined, when the synchronizing ring is deformed friction angle \(\alpha\) and friction coefficient \(\mu\) will change which will result in a change of friction. It can be seen that the performance of the synchronizer has a strong relationship with the friction torque, so it is directly dependent on the matching degree between the contact cone surfaces.