In order to further reduce the friction torque and reduce oil leakage, NTN has developed a V-shaped lubricating groove sealing ring for automobile transmission, which reduces the friction torque by 60% compared with the conventional sealing ring. Various resin sealing rings with an outer diameter of 15 to 60 mm are used in automobile transmissions (automatic transmissions, continuously variable transmissions, etc.). To achieve low fuel consumption in vehicles, these seals require low friction torque and low oil leakage. In response to this requirement, NTN developed a polyetheretherketone (PEEK) resin low-friction torque seal with a V-shaped lubricating groove (Figure 1) and started mass production. Figure 1 Low friction torque seal The number and shape of the V-shaped lubricating grooves were optimized through fluid analysis and tests to further reduce the torque of the low friction torque seal. This paper presents the results of fluid analysis validation of torque reduction for low friction torque seals. 1. The function and application of the sealing ring The sealing ring is installed between the relatively moving shaft and the casing in the oil pressure circuit of the transmission to play a sealing role. When the sealing ring slides, the oil pressure of the sealing oil pushes the sealing ring to the inner surface of the housing and the side wall of the shaft groove, and maintains the pressure inside the oil pressure circuit. The sealing ring needs to have low friction torque, low oil leakage and high wear resistance. When the friction torque is reduced, the transmission efficiency is increased for higher energy efficiency. Reducing oil spills makes hydraulic pumps more efficient and smaller, making them more energy efficient. In order to maintain low friction torque and low oil leakage operation, and to achieve a long service life, the seal ring needs to be resistant to wear while preventing wear of the seal ring sliding fitting. The application of an NTN conventional seal with a rectangular cross-section is shown in Figure 2. Since the contact area between the sealing ring and the side wall of the shaft groove is smaller than the contact area between the sealing ring and the inner surface of the casing, when the shaft or the casing rotates, the sliding resistance of the side wall of the shaft groove is small, and the sealing ring slides on the side wall of the shaft groove. The sealing ring is in surface contact with the side wall of the shaft groove, so there is less oil leakage. Figure 2 Application of sealing ring 2. Low friction torque sealing ring 2.1 Features By setting the V-shaped lubrication groove on the surface of the sealing ring sliding on the side wall of the shaft groove, the low friction torque and low oil leakage of the low friction torque sealing ring are realized. The sealing ring is made of BEAREEPK5301 material made of PEEK resin with special additives. There is an injection-molded V-shaped lubricating groove on the side, and the shape of the butt step is complex. Oil leakage at the butt step is reduced by the complex shape of the butt step. Compared with NTN conventional products, low friction torque seals have the following characteristics: 1) friction torque reduction up to 60%; 2) 1/10 wear rate; 3) comparable low oil leakage. 2.2 Comparison of the shapes of the lubrication grooves 2.2.1 Friction torque measurement results The schematic diagram of the test equipment is shown in Figure 3. The friction torque is measured by applying oil pressure through the circulating oil between the two seal rings installed on the shaft groove and rotating the housing. Table 1 Test sealing ring Note: The outer diameter of the sealing ring is 50 mm, the thickness is 1.6 mm, and the width is 1.5 mm. Figure 3 Schematic diagram of the test equipment The relationship between oil pressure and friction torque is shown in Figure 4. Divide the measured friction torque of 2 sealing rings by 2 to obtain the friction torque of 1 sealing ring. The friction torque of the sealing ring with V-shaped lubricating groove is 60%~70% lower than that of the non-lubricating groove sealing ring (regular product of NTN), and 20% lower than that of the sealing ring with square lubricating groove. 2.2.2 Results of fluid analysis The reason for the decrease in friction torque is considered to be that the application of the V-shaped lubrication groove reduces the contact area between the seal ring and the sidewall of the shaft groove and improves the lubrication of the sliding surface. The difference in friction torque between the two shapes of lubricating grooves is attributed to the difference in lubrication conditions. Fluid analysis confirmed this. The analysis results of the fluid region model of a lubrication groove are shown in Figure 5. When a V-shaped lubricating groove is used, the oil film pressure at one end of the lubricating groove is high due to hydrodynamic effects. The axial force generated by the oil film pressure is in the opposite direction to the force that presses the seal ring against the side wall of the shaft groove by the oil pressure, so the oil pressure can be reduced. It is also assumed that due to the pressure difference, oil flows from the ends of the lubricating grooves to the sliding surfaces between the lubricating grooves, helping to reduce the friction torque. On the other hand, the high oil film pressure observed in the V-shaped lubricating groove was not observed in the square lubricating groove. Fig.4 Relationship between oil pressure and friction torqueFig.5 Oil film pressure distribution on sliding surface 3. Verification of reducing friction torque by optimizing V-shaped lubricating groove 3.1 Fluid analysis conditions Frictional torque measurement results and oil film pressure distribution on sliding surface The force at the end of the lubricating groove is opposite to the force that reduces the friction torque due to the oil film pressure (oil film reaction force). The greater the oil film reaction force, the lower the friction torque. Therefore, it can be considered that the greater the number of V-shaped lubricating grooves and the wider the width, the greater the oil film reaction force. Fluid analysis confirmed this. The definition of the length, width, depth, angle and spacing of the V-shaped lubrication groove of the sealing ring for analysis is shown in Figure 6. The size of the sealing ring is: outer diameter 44 mm, thickness 2 mm, width 2.3 mm. Model the fluid region of 1 V-shaped lubricating groove of the seal ring based on fluid analysis,The oil film reaction force of one lubricating groove is obtained by integrating the oil film pressure caused by the hydrodynamic effect. The product of this force and the number of grooves was defined as the oil film reaction force of one seal, and comparisons were made under different conditions. It should be noted that, compared with the oil film pressure of the V-shaped lubricating groove, the oil film pressure in the contact area between the side of the seal ring and the side wall of the shaft groove is very small and can be ignored.