Visualization of the Contact Condition and Lubricant Flow Between a Seal Ring and a Shaft for Automatic Transmissions

Seal rings are used as shaft seals in automatic transmissions, where they act as a dam to direct pressurized fluid flow to hydraulic circuits. Conventionally, cast-iron seal rings were used, but over the past two decades, this material has been switched to resins like PTFE and PEEK to satisfy performance requirements such as low leakage and low frictional torque. However in using resin seal rings, the shaft sometimes undergoes the so-called three body abrasive wear due to invasion of hard particles, such as wear particles and dust, into the sliding portion between the seal ring and the shaft. To prevent such wear of the shaft, it is important to prevent invasion of hard particles into the sliding portion, and also to promptly discharge hard particles from the sliding portion. We therefore designed a seal ring taking into consideration these needs and investigated its shaft wear reduction effects. We built a test apparatus to observe the contact state of the seal ring face under hydraulic pressure using the LIF method, and clarified the effects of the contact state of the seal ring on shaft wear.