NSK Develops Long Life Piston Shafts for Automatic Transmissions

NSK developed a planetary gear mechanism for an automatic transmission (AT) and the like, and a pinion shaft having a longer life than the original product. It can be fixed to the bracket of the planetary gear mechanism and used as the rotation shaft of each pinion. This product can improve the efficiency of various gearboxes such as AT, HEV (Hybrid), and Continuously Variable Transmission (CVT).

In order to improve fuel efficiency, automotive manufacturers require smaller and lighter gearbox bearings. In addition, most bearings for gearboxes reduce the frictional resistance due to the stirring resistance and reduce the viscosity of the AT lubricant. If the HEV travels with the motor, the operation of the oil pump is stopped, and the use environment is severe. In order to reduce the impact of variable speeds and improve the power transmission efficiency, AT is moving toward multi-level development. Therefore, the rotational speed requirements for transmission bearings are also increasing.

The pinion shaft developed this time replaced the material from the original high carbon high chromium steel SUJ2 with NSK's independently developed medium carbon high chromium steel "SHX3" to improve the fatigue resistance. Heat treatment from the general steps, namely carbonitriding, high-frequency quenching, tempering was changed to a dedicated heat treatment, eliminating the quenching process. Reduced bending caused by thermal deformation reduces damage caused by bending. With these effects, a long life of 2.5 times or more is achieved. When the design life is the same, it can be reduced or reduced by 20% compared with the original.

Since the required minimum oil amount is reduced from 100 ml/min of the original product to 50 ml/min by half, the oil pump can also be reduced, thereby reducing the loss. In addition, the maximum operating temperature is increased from 120°C below the original product to less than 150°C, so it can also be used when the lubrication conditions are severe and at high rotational speeds. In addition, by changing the bearing supporting the pinion shaft to the CageAnd Roller type, the maximum speed of the support is 3 times more than that of the full-roller type of 12,000 rpm, that is, 38,000 rpm.