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Bonded piston seals (BPSs) which consist of metal ring and rubber lips are used as hydraulic pistons for Automatic Transmission (AT) or Continuously Variable Transmission (CVT). While engaging clutches, BPSs preserve the hydraulic pressure, therefore it is necessary to endure number of cyclic pressure through the life. This paper describes a reliable design method of BPSs with taking account of the influence of residual stress on the fatigue limit of the metal ring. A new plastic-elastic analysis model considering Bauschinger effect is applied in order to estimate the residual stress, which generates due to metal forming process. Validation for calculated residual stress is done by X-ray diffract meter. A proofed BPS design calculated with this new FEM model shows longer fatigue life than conventional design.

A new valve stem seal design has been developed to achieve superior control of the oil flow rate to valve guide. This design exhibits increased performance in the control of the oil flow rate under high pressures of the inlet or exhaust port and under high valve stem eccentricity. The recent demands of stable function, minimized oil consumption, and more efficient emission controls are achieved by this new design.

NBR (acrylonitrile butadiene rubber) has been used for the oil seal equipped on a power steering. However, lack of heat resistance was occasionally observed for NBR, with the recent trend of customer's demand for increasing the life of oil seals in high temperature environmental condition. We developed an oil seal with H-NBR material, which could exhibit the superior performance in the heat resistance; however, it had a weak point in low temperature environment. We have developed HNBR1, the new H-NBR, which has been improved in the performance for low temperature [1]. HNBR1 has been applied for power steering seals as the rubber material, which has superior heat resistance, cold resistance and oil resistance.