For sprag clutches to function properly, the sprags must maintain contact with the mating surfaces while in the freewheeling state. That way they can be ready to engage as soon as the relative rotation changes and torque transmission is required.
If the sprags don’t maintain that constant contact, the clutch could slip. If some sprags aren’t in contact but others are, those sprags could experience excessive torque which could cause permanent damage to the clutch.
GMN uses a spring to keep each sprag in contact. There are two different types of springs that have unique operating characteristics:
Meander Spring
The meander spring uses a wire that is bent into a 3D pattern to weave in and out of each individual sprag and around the cage so that the spring pushes between the cage and the toe of the sprag.
That means each sprag has an independent spring force acting on it. Because of the precise spring engagement, clutches with the meander spring are suitable for high indexing applications and are guaranteed to operate at indexing frequencies up to 60 Hz.
Also, sprags that use the meander spring have more surface area because they don’t require the notch that is needed for the Z spring. That means they have a higher torque capacity.
The meander springs produce a slightly higher spring force on the sprags. For applications that are mostly in the freewheeling state, they may not be the best option as they could produce more wear than the sprags that use the Z spring.
Z Spring
The Z spring is a tightly wound coil spring that goes around the outside of every sprag.
The sprags have an angled notch in the middle of the outer surface of the sprags where the spring engages the sprag. That allows the spring to be nested inside the sprag to prevent it from rubbing against the housing bore. In this design, the spring acts on all the sprags together as it tries to push the angle of the sprag notch tangential.
Because the Z spring pushes on all the sprags together, it is not as ideally suited for high indexing applications. However, it is still guaranteed to operate in indexing frequencies up to 10 Hz.
Since the Z spring requires there to be a notch in the outer sprag surface, there is less surface contact area between the sprag and the housing bore. This results in a slightly lower torque capacity.
The Z spring has a slightly lower spring force than the meander spring. It is better suited for applications where the clutch is in the freewheeling state most of the time as it will produce less wear.
Spring Availability in GMN Bearing USA Products
The following GMN product lines are available with either spring style:
- FE 400
- FR, FRN
- FN, FND, FP, FPD
The following GMN product lines are only available with a Z spring:
- FE 400 Z2
- FE 8000
- FK, FKN, FKNN
Interested in GMN Sprag Clutches?
Check out our Sprag Clutch Guide resources below for more information.
- Sprag Clutch 101: What It Is & How It Works
- Sprag Clutch Failure Mechanisms
- Angle of Twist for Sprag Clutch Applications
If you’re interested in using GMN products for your application, send us a quote request below!