Start of Mass Production of the First Ball Screw for Electric-Powered Actuators Used On Automated Manual Transmissions(AMTs)

NTN has begun mass production of ball screws for use in electric-powered actuators used to change gears in Automated Manual Transmissions (AMTs) mounted on trucks. By changing from mechanical to electric power, it is possible to reduce part count to about one-third the count for air-pressure or hydraulic systems. In the case of electric-powered systems, use of the NTN ball screw realizes a major reduction in frictional losses, thus contributing to improved economy on the vehicle.

Recent years have witnessed mechanical automation of manual transmissions on vehicles and mounting of AMTs to improve economy and ease the burden on the driver. With conventional AMTs, air pressure or hydraulic pressure is used as the axial actuation force. However, these systems require hydraulic pumps, piping and other parts, thus leading to higher costs.

Even among electric powered devices, those devices using worm gears and sliding screws suffer from considerable friction and reduced efficiency. This results in such problems as insufficient actuation power and slow response.

The NTN ball screw solves those problems. Instead of using worm gears and sliding screws for the actuator, use is made of ball screws with their minimum friction resistance. This reduces the energy transfer loss to a figure of only about 10% (the same loss is about 60% for worm gears and slip screws). This in turn makes it possible to considerably reduce consumed electric power. In order to make it possible to locate NTN ball screws in transmission sections with limited space, a spinning top method is used for the ball rotation method to realize a more compact system. In addition, in response to the punishing load conditions of the transmission, the load distribution of the ball rotation section can be evenly distributed for an ideal internal design and outstanding durability.

In addition, NTN is presently developing ball screw units for electric powered actuators for use in different applications , such as brakes and control devices in engines, where this new technology can be applied. We now plan to extend use of this technology to different fields.

Advantages of an electric powered actuator using the NTN ball screw

• About one-third the part count (compared to air-system AMTs)
• Compact size

Features of the NTN Ball Screw

• Less friction loss for higher efficiency
  (Has a friction mechanism in which a ball screw turns so that the energy transfer loss is reduced to just 10%)
• The spinning top method is used for the ball screw rotation method. Compared to the conventional return tube method, it is possible to achieve a more compact size with a 20% reduction in nut diameter.
• Improved durability with optimization of internal design such as load distribution in the ball rotation section (about 3 times compared to conventional equipment from NTN)

Applications

Electric-powered actuators for motor vehicles

External View Upper screw: For shifting Lower screw: For selecting