| About the SSL |
| Personnel |
| Facilities |
| Projects |
| Internals |
| Data and Publications |
| Friends of the SSL |
| Directions |
| Contact Us |
| Current Events |
University of Maryland Three-Dimensional Sprags and Rollers
Sprag and roller clutches are two types of overrunning clutches that automatically engage to transmit torque by relative rotation in one direction and automatically disengage for overrunning by relative motion in the other direction. They are used in rotating mechanical systems when torque must be transmitted in one direction only or where the driven member is to be permitted to "overrun" the driver
Sprag clutches have a cylindrical outer and inner race and a series of specially contoured and processed sprags. The inner and outer races are concentric and the sprags are installed in the annular space between them as shown in Figure 1. Each sprag is designed with a geometry that makes its two diagonals of different length. One direction of relative rotation between the races causes the sprags to rotate so that the longest diagonal is in contact with the two races. The length of this diagonal is greater than the annular distance between the races, so the sprags are wedged between the races, providing a solid connection for transmission of torque. Relative rotation between the races in the opposite direction causes the sprags to rotate so that the shortest diagonal is in contact with the two races. Its effective length is such that the clutch is disengaged and free to overrun.
Figure 1 ¥ Traditional "Two-Dimensional (2-D)" Sprag and Races
Roller clutches have one race that provides a cylindrical race surface and a second race that has a series of wedge-shaped friction surfaces spaced about its circumference. The rollers are installed between these concentric races at the wedge-shaped friction surfaces. Engagement and disengagement are determined by the direction of relative rotation. Relative rotation in one direction causes the rollers to roll up the wedge surface, engaging the clutch, wedging the rollers between the races, and providing a solid link for transmission of torque. Rotation in the other direction causes the roller to roll down the wedge surface, disengaging the clutch for overrunning.
NASA/Goddard Space Flight Center (GSFC)
has developed and
patented
an innovative three-dimensional (3-D) sprag that replaces the concentric, cylindrical surfaces of the inner and outer races with grooves into which the tapered periphery of the 3-D sprag fits as shown in Figure 2.
Figure 2 ¥ NASA/GSFC 3-D Sprag and Races
The 3-D sprags were originally developed as a robotic joint brake for NASA/GSFC robotic activity and their benefits over the traditional 2-D sprags and rollers are:
Additional information on sprags can be found in:
Three-dimensional roller locking sprags have spun off many patents.
| EVA Wrench Home | 3-D Sprags and Rollers | Commercial 3-D Roller Wrench | EVA 3-D Roller Wrench |
| Publications | Awards | Personnel | Applications |
| Sprag Resources | Contacts |
| SSL Home | About SSL | Personnel | Facilities |
| Projects | Internals | Publications | Friends |
| Directions | Contact Us | Current Events |