Koyo FCB-8 roller clutch and bearing assembly, 8 x 14 x 20 mm

These Koyo FCB drawn cup roller clutch and bearing assemblies are metric series one-way units that allow free rotation in one direction while transmitting torque in the other. They use the same small radial section as drawn cup needle roller bearings, and the needle roller bearing cages on both sides of the clutch carry the radial load and position the shaft in the housing, so no separate support bearings are needed where radial loads are light.

The clutch rollers wedge against precisely formed ramps in the case-hardened drawn cup and lock the cup to the shaft when it rotates in the locking direction. The unit has a glass fibre reinforced nylon cage fitted with stainless steel leaf springs inserted in the cage, with multiple rollers per spring. The stainless steel springs allow higher rates of engagement and give greater spring life, and the nylon cage permits operation at higher temperatures.

The range has 7 sizes with shaft diameters from 8 to 30 mm. Koyo bearings are made by JTEKT Corporation.

Where this product is used

• Indexing, backstopping and overrunning drives
• Office equipment and paper feed rolls
• Paper-towel dispensers and web roll feeds
• Exercise equipment and appliances
• Two-speed gearboxes

Features

• One-way clutch and needle roller bearing assembly in a single drawn cup unit, with a compact radial section
• Stainless steel springs in a glass fibre reinforced nylon cage, multiple rollers per spring
• Torque rating 4.42 to 99.1 N-m and dynamic load rating C 4.22 to 11.5 kN
• Overrun limiting speed 7,300 to 21,000 min-1 with a rotating shaft
• Installed with a simple press fit; no shoulders, keys or snap rings needed
• Operates directly on a hardened shaft

Key specifications

Available sizes

Selecting the right option

Choose the size from the shaft diameter and the torque the clutch must carry, and keep the applied torque, including inertial torque, within the torque rating. Check the housing space against the outside diameter D, the width C and the minimum outside diameter of a steel housing (Z). The load ratings are based on a raceway hardness of at least 58 HRC.

Where radial loads are light, the clutch and bearing assembly can be used without additional support bearings, which reduces overall width, the number of parts and assembly cost. The total dynamic radial load shared by the two needle roller bearing assemblies should not exceed C/3.

The reinforced nylon cage with separate steel springs operates at temperatures up to 120 °C continuously and up to 150 °C intermittently, and the steel spring types have proven dependable at engagement rates up to 6000 or 7000 per minute.

The catalogue also lists the FCBN-K and FCBL-K light series assemblies.

Fitting and use

A drawn cup roller clutch allows free rotation in one direction (overrun) and transmits torque in the opposite direction (lock). The mounted unit engages when the housing is rotated relative to the shaft in the direction of the arrow and the LOCK marking stamped on the cup, so check the orientation before pressing it into the housing.

Press the unit into a through-bored housing with an arbor press or hydraulic ram press, using steady pressure and an installation tool. Never use a hammer or any tool that needs pounding. Chamfer the housing bore (the catalogue suggests 30 degrees) and round the edge where the chamfer meets the bore, because a sharp edge can greatly increase installation forces. Press the unit slightly beyond the chamfer to seat it fully, and never seat it against a shoulder. Shoulders, snap rings, keys and screws are not needed for axial location.

Rotate the shaft in the overrun direction while inserting it, and give the shaft end a large chamfer or rounding. The shaft surface should be 58 HRC or equivalent, with good roundness, taper and surface finish. Use a steel housing: steel is preferred, it is required for high-torque applications to stop the cup expanding radially, and the minimum housing outside diameters given are for steel. If you use a non-steel housing, test the design thoroughly.

Lock-up depends on static friction, so avoid severe vibration or axial movement of the shaft within the clutch, which prevents lock-up. Do not exceed the torque rating, and include the inertial torque of the mechanism as well as the externally applied torque. Test every new application under the expected operating conditions before production.

Oil is the preferred lubricant, and it is necessary for high overrun speeds. Where oil is not practical, the clutches come packed with a soft grease containing mineral oil. Thick grease slows roller engagement and can cause rollers to slip, which can overload the rollers that are engaged. The overrun speed rating is a guide and not an absolute limit.

Each size lists the shaft raceway diameter (S) and the housing bore diameter (H) in the variant specification. Do not inspect a clutch by measuring the outside diameter of the cup directly, because the cup can be slightly out of round until it is pressed into a correctly sized housing. The catalogue inspection method is to press the unit into a ring gage and then check the bore with plug gages.

Related products

Also available from Koyo: the Koyo RCB inch series drawn cup clutch and bearing assembly range.