NSK has announced that its equity affiliate, NSK-Warner K.K., has developed a pawl-type one-way clutch for automobile powertrains.

The new one-way clutch is applicable to the lubricant-free environment connecting the engine and transaxle in a hybrid system. It functions to prevent reverse rotation of the engine when a two-motor hybrid car is operating as an EV. In addition, when the engine is running, it reduces drag torque by 90% when idle running, contributing to improved fuel economy. NSK expects global annual sales of this product to reach JPY2bn (US$18bn) by 2022.

Development background
Recent years have seen tighter fuel economy regulations, global improvements in fuel economy due to regulations in each country, and the introduction of new energy vehicles (EVs and PHVs). Efforts have been made to reduce the amount of lubricating oil and drag torque* in order to improve the fuel economy in vehicle power trains. This trend created the need for a one-way clutch that could be used in a lubricant-free environment and could reduce drag torque during idle running. Conventional sprag-type and roller-type one-way clutches require lubrication, and since they transmit power by friction, reducing their size and drag torque was an issue.

NWC has developed a pawl-type one-way clutch that functions as a mechanical clutch with a new configuration that can be used without lubrication and that reduces drag torque while idle running.

Product features

  • Suitable for lubricant-free environments
    • The clutch is applicable to a lubricant-free environment because it uses pawls that do not touch the inner ring when idle running, and the component parts such as the pawls and inner and outer rings are coated with solid lubricant.
  • Reduced drag torque during idle running
    • Drag torque has been reduced by 90% compared with conventional products by disengaging the pawls using centrifugal force with the speed of rotation set during idle running, eliminating contact between the pawls and inner ring and using the clutch in a lubricant-free environment.
  • Smaller, lighter weight
    • The new clutch achieves 2.5 times greater torque capacity but at a lighter weight than one-way clutches that use the conventional structure, which conveys torque through friction.
  • Reduced backlash (rattling)
    • Backlash, which was one of the problems with ratchet-type (pawl-type) clutches, has been reduced substantially by changing the phase of engagement between pawls.

Product Benefits
This product maximises the EV performance of PHVs and contributes to improved fuel consumption.