The Mechanical Diode® Company
Technology Introduction

Brief Overview Of Conventional Technology
Sprag & Roller ClutchCurrently, two types of overrunning clutches predominate - the prag clutch and roller ramp clutch. These devices Rely on a wedging action to lock-up, which means sprags and races must endure extremely high radial stresses to transmit even a moderate amount of tangential force, or useful torque. As a result, these clutches must be made from expensive, high quality bearing steel which has been hardened to withstand the forces generated by the wedging action.

In additional, conventional one-way clutches offer limited functionality and greatly reduced load capacity in applications with very-high overrun speeds, high engagement speeds, and vibration - all of which are present to some degree in most automotive environments.

All of these factors combine to make conventional one-way clutches the weakest link in automatic transmissions.

Sprag & Roller Ramp Clutches
Brief Overview of Mechanical Diode Operation
MD Strut The Mechanical Diode is a high-resolution planar ratchet which uses low-mass rectangular struts instead of ratchet pawls. The struts are positioned between a plate with pockets for the retracted struts and a second plate with notches for strut engagement. The struts have a very high ratio of contact area to mass, yet are slim enough to achieve full engagement with only 15 degrees of pivot. The struts' low mass, rectangular construction, and lengthwise pivoting axis give them a very low moment of rotational inertia. This - together with the small actuation angle - allows a relatively small spring to almost instantaneously move the strut into locking position. The position of the strut asses (radially, in a planar fashion) renders strut actuation insensitive to centrifugal force. During even moderate overrun speeds, the struts "fly" on a layer of oil.

Planar Delivery Of Force for Strong, Reliable Operation
The Mechanical Diode's planar strut arrangement and 15 degree strut engagement angle allow it to transfer force in a more direct fashion - thereby avoiding the trap of using "extreme radial forces to transfer even moderate amounts of torque" which afflicts conventional one-way clutches.

In fact, the MD utilizes more than 93% of the strut's compressive strength to transfer torque. Parasitic (axial) forces are relatively small - especially when compared with friction-actuated one-way clutches, where the contact angle is typically 83 degrees and 99% of the compressive load is directed radially. In wedging-action clutches, both sprag loading and hoop stress are very high, and these parts must be manufactured from expensive, high-quality steel.

By contrast, the MD generates lower parasitic forces, so it's typically smaller and lighter than wedging-action one-way clutches.

MD Strut RotationTorque Comparisons Chart

Single-Strut Positive Engagement vs. Load Sharing
Instead of sharing enormous radial loads among many sprags or rollers, the Mechanical Diode works by engaging a single strut at lock-up, a design made possible by its planar transfer of force and the large load bearing surface offered by each strut.

MD Carrier Plate Since only one strut engages at a time, precise - and expensive - machining isn't needed to ensure the simultaneous engagement of many parts. In sprag-type clutches, a failure to engage all load-bearing surfaces simultaneously can quickly lead to catastrophic failure of the device.

For positive engagement, the MD's struts use angled load bearing surfaces, so the force of engagement automatically forces the strut into a fully engaged position.

And due to the positive locking nature of its components, the MD suffers no torsional windup.

The absence of torsional windup and the low actuation angle of the Mechanical Diode - typically 15 degrees - results in excellent engagement resolution, which minimizes engagement impact and prolongs component life.

Long Overrun Life
With the MD, the load-bearing surfaces of the components never come into contact during overrun - any incidental contact is between surfaces which don't mate during engagement.

And, even at moderate overrunning speeds, the struts remain in their pockets and "fly" on a layer of oil - never coming into contact with the notch plate at all. The higher the overrun speed, the more pronounced this effect becomes. This allows the MD to overrun at very high speeds, and affords a long overrun life.

Manufacturing Advantages
Typically, the Mechanical Diode can be manufactured more economically than conventional clutches - a result of two main factors.

First, the MD generates few radial stresses, so the struts and "races" can be made from less expensive materials. This allows manufacturing techniques such as powdered metal molding and fine blanking to be used.

Secondly, the MD engages only one strut at a time, so precise machining - mandatory when the load is to be shared among many elements - isn't required. This further reduces costs.

In fact, due to the smaller size and form factor of the MD, drop-in replacements for existing friction-locking one-way clutches can be easily designed and afford ably manufactured.

Versatile, Reliable, Affordable - Even Under Adverse Conditions.
Mechanical Diode offers extreme reliability in all types of automotive environments, especially those where high torque, vibration, or high overrunning speeds decrease the effectiveness of wedging-type one-way clutches.

In addition, its smaller form factor and typically lower cost of manufacture make it an excellent tool for automotive manufacturers who are striving to improve product reliability while holding the line on costs.

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