Lighter weight, smaller size, more power, more functionality, better performance, longer life, higher energy efficiency, reduced CO2 emissions and lower overall costs – this is a major trend in today’s transmission manufacturing, just like in other areas such as automotive engineering. Thrust washers are an important part of the transmission. Since they separate the different gears, they are subject to large axial forces and extremely high friction loads. The compact design of the housing, high pressure (P) and high speed (V) increase the oil temperature. Wear-resistant materials such as polyimide (PI) and polyamide-imide (PAI) cannot meet these extremely demanding requirements. The high-performance polymer PEEK has a good performance in thrust washers and is therefore a mature alternative to PI, PAI and metal materials.

Meeting demanding requirements: Today’s automatic transmissions must transmit torques of more than 500Nm in vehicles and more than 2000Nm in trucks. To meet noise and performance requirements, helical gears are used in automatic transmissions. The resulting axial forces must be absorbed by the thrust washers. At 6500 rpm, the axial forces in vehicles can typically reach 3000N. Depending on the diameter of the thrust washer, the resulting PV peaks can be as high as 50-70MPam/s when lubricated with oil. To improve fuel economy, gearboxes are becoming lighter and more compact, with higher transmission ratios. This results in less free space and can lead to poor lubrication. Today’s automatic transmissions have to be supplied with sufficient lubrication in any driving situation via a complex system of oil channels and hollow shafts. The oil sump temperature can reach 150°C and even higher in the torque converter area. Thrust washers made of PEEK high-performance polymers are increasingly being used in many automatic transmissions due to their numerous advantages over metals, providing built-in safety.

Customized material modification: Originally developed for thrust bearings, PEEK5600LF30 was later added as a premium wear-resistant solution with PEEK5600CF30 polymer to meet the increasing requirements of thrust washer applications. Like PEEK5600LF30, the PEEK5600CF30 series meets these extremely high requirements and has good dry-running properties even without oil lubrication. It also offers additional performance advantages and is PTFE-free. In tribological systems with very high speeds, the composite material forms an intermediate film layer on the counter-friction surfaces, which significantly reduces the friction coefficient and wear rate. This typical effect of polymer materials has been confirmed by numerous dry and wet tribological studies. Compared with PI and PAI polymers, the PEEK5600CF30 series has a lower wear rate, a lower and more stable friction coefficient, reduced friction surface temperatures, and a higher compressive strength.

application

Flywheel: Thrust washers made of PEEK high-performance polymer fulfill two different functions in dual-mass flywheels. They act as vibration dampers between the engine and the transmission, separating two objects that vibrate relative to each other and sealing the system from the surroundings. For an exact match of the system, the coefficient of friction must remain constant over the entire service life at 120°C. Likewise, vibrating motion places high demands on the friction properties of this anti-wear modified PEEK polymer.

Planetary gears: PEEK polymers have been used for thrust washers in planetary gears in bus automatic transmissions for decades. In this application, the ability to withstand up to 1,800Nm of torque during stop-start operations is more critical than high speeds throughout a service life of more than 500,000km. In addition to good emergency running properties, the low wear rate and good oil resistance of anti-wear modified PEEK polymers also play an important role.

Continuously variable automatic transmission: In addition to flywheels, thrust washers are finding new uses, including continuously variable transmissions (CVTs), dual clutch transmissions (DCTs) and multi-step automatic transmissions. Speeds of up to 10,000 rpm and system pressures of 25 bar place high demands on the wear resistance of the materials used. PEEK high-performance polymer materials, with their excellent overall performance and the ability to be injection molded without the costly post-processing process of PAI, will continue to develop new uses as a material choice for transmission thrust washers, helping engineers find more economical and effective solutions.