World’s 1st Production Selectable One-Way Clutches for Automatic Transmissions.

World’s 1st Production Selectable One-Way Clutches for Automatic Transmissions.

Five Controllable Mechanical Diodes (CMDs) launching with three different customers.

Means Industries is launching five mass production Controllable Mechanical Diodes (CMDs) with three different customers. This is the first time Means’ CMD technology will be integrated with its successful Mechanical Diode (MD) technology, and the first selectable one-way clutches (SOWCs) to be used in high-volume powertrain applications. While these applications differ in design, the CMDs function similarly, decrease packaging space, reduce mass by eliminating components, and provide a system cost savings. Unlike other one-way clutches, CMDs can also use lightweight materials, such as aluminum, to transmit torque which leads to further mass reduction. CMDs are easily integrated into powerflows and highly configurable. Overall, Means CMDs are proven to facilitate improved fuel economy and reduced CO2 emissions.

Means currently manufactures its version of a one-way clutch (OWC) called the Mechanical Diode (MD). Similar to sprag and roller OWCs, MDs transmit torque when rotated in one direction and freewheel in the opposite direction. MDs are used in automatic transmissions to provide smooth 1st to 2nd gear shifts. To transmit torque in 1st gear, the MD uses locking elements called struts which passively engage by rotating the MD in the lock direction. When 2nd gear is commanded, the MD freewheels in the opposite direction, as the struts cannot transmit torque. The ability to smoothly transition from transmitting torque to freewheeling contributes to satisfactory shifting. Often, a low/reverse (L/R) clutch pack, which primarily transmits torque in reverse and low gear, is found adjacent to the MD. Simultaneously engaging the MD and L/R clutch pack creates a brake, which prevents rotation in either direction and is necessary for specific gear ratios to be achieved in a given powerflow.

After several successful MD product launches, Means began developing the Controllable Mechanical Diode (CMD).The CMD eliminates the need for the L/R clutch pack by having the ability to transmit torque in reverse and 1st gear. To accomplish this, a second set of locking elements (commonly referred to as reverse struts) are added to the basic MD architecture. The reverse struts are controllable and lock in the opposite direction to that of the passive struts (commonly called forward struts). The reverse struts can be turned on (uncovered) or off (covered) as needed. Commonly, this is done by a hydraulic actuation system which can be integrated into the CMD or transmission valve body. By engaging both the forward and reverse struts, the CMD functions as a brake which is similar to simultaneously engaging the MD and L/R clutch pack.

The primary advantages of incorporating a CMD into a transmission include reduced spin loss resulting in improved fuel economy, decreased packaging size and mass, and systems cost savings.

The L/R clutch pack is a large spin loss contributor because it is disengaged (open) for most of the transmission’s operation. The CMD primarily reduces spin loss by replacing the L/R clutch pack with the controllable reverse strut set. The reverse struts are off (covered) during freewheel, which allows the CMD to provide similar spin loss performance to that of the MD. Additional spin loss gains are achieved by integrating oil management features into CMD assembly.

Additionally, eliminating the L/R clutch pack negates the need for a backing plate, apply piston, piston return spring, and all necessary secondary machining to the transmission case. Removing the components not only reduces packaging space and mass, but it also leads to a system cost savings.

Unlike conventional roller and sprag OWCs, Means’ MDs and CMDs can use aluminum components to transmit torque because of the way engagement forces are reacted. Benefits are also realized through component integration, reductions in mass, decreases in rotating inertia, and the ability to incorporate complex part geometry.

To learn more about CMDs and Means’ technology, please visit for more information.

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