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Sprag Clutches
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Catalog excerpts

Sprag Clutches - 2

SPRAG TYPE ONE-WAY CLUTCHES for AutomobilesWith the recent improvements of automobiles in performance and comfort, demand for higher performance and functions in auto- matic transmissions has increased.KOYO has been producing highly-reliable sprag type one-wayclutches for automatic transmission with superior torque trans- mission performance by employing the latest analysis techniques and machining technologies.Inner and outer rings for one-way clutches are specially fabricatedto comply with customer's specific requirements and ensure maxi- mum performance. This brochure covers dimensions...

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Sprag Clutches - 3

1.1 Functions1.2 Structure 1.3 Nomenclature1.4 Designation1.5 Principle of Torque Transmission 1.6 Strut Angle 2. Rated Torque and Drag Torque > 2.1 Rated Torque2.2 Required Rated Torque2.3 Drag Torque2.4 Types of Sprags 2.5 Sprag Selection > 2 3. Mounting and Design of Inner and Outer Rings 223 344 3.1 Support of Radial Load3.2 Axial Mounting3.3 Materials and Hardness of Inner and Outer Rings3.4 Sectional Height of Inner and Outer Rings 3.5 Chamfering of Inner and Outer Rings3.6 Precision of Inner and Outer Rings 5 4. Lubrication 55 666 4.1 Lubricant4.2 Lubrication Method 5. Mounting 7 5.1...

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Sprag Clutches - 5

1.3 Nomenclature ˔ Sprag ˔ Drag clip > Mates between inner and outer rings to transmit torque. High-carbon chromium steel is drawn and heat-treated to obtain 60 HRC or more hardness. Several pieces are provided on the outer diameter surfaceof the cage.The drag clip secures the cage against the outer ring by aspring action in order to synchronize movement of the cagewith the outer ring for positive and prompt engagement of thesprags.The clip is made of stainless steel plate. ˔ Cage > Arranges sprags equally on the circumference for uniformtorque transmission. The cage is made of heat-treated...

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Sprag Clutches - 6

1.5 Principle of Torque Transmission The sprags are arranged equally on the circumferencebetween the inner and outer rings by the cage and are constantly in contact with the inner and outer rings by springforce. Since the sprags are larger than the space between the inner and outer rings, they are arranged at an angle to the raceway surfaces of the inner and outer rings. The sprag surfaces in contact with the inner and outersurfaces are shaped such that the sprag height appears to increase when the sprags rotate around their centers (Fig.1.5). When the outer ring rotates counterclockwise as...

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Sprag Clutches - 7

When the required endurance performance of the clutch is10 Ћ and tan Ќ are excessively small, the load on thecontacting surfaces becomes large, thus decreasing torque transmission capability. Since Ћ Ћ with tan is always greater than Ќ exceed the friction coefficient Ќ , tan Ћ is smaller than Ж of therespective contacting surfaces, the sprags slip and fail to engage hence transmitting no torque. When tan Ж The sprag type one-way clutch is designed to transmittorque by friction between the contacting surfaces of the sprag with the inner ring and the outer ring. If tan for torque...

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Sprag Clutches - 9

3.1 Support of Radial Load 3.2 Axial Mounting Since the sprag type one-way clutch cannot radial load,required the rolling bearing or plane bearing to support the radial load (Fig. 3.1). Mounting width of the sprag type one-way clutch shall beset to W f dimension or more as shown in the dimensionaltable. Use the retaining plates similar to that shown in Fig. 3.3 to retain the one-way clutch in the axial direction and to hold the lubricant. Ensure a clearance between retaining plate andinner ring of 0.5 to 2mm. > Outer ringSprag Inner ringRolling bearing W f )RetainingplateRetainingplate...

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Sprag Clutches - 10

3.5 Chamfering of Inner and Outer Rings Chamfer of approx. 1 to 2 mm in length and 30 ˃ in anglemust be made at the ends of the raceway of the inner andouter rings to facilitate assembly of the one-way clutch (Fig.3.6). 3.4 Sectional Height of Inner and Outer Rings Radial load is applied to the inner and outer rings of thesprag type one-way clutch by sprag engagement. Since tensile stress occurs on the external diametersurface of the outer ring in the circumferential direction, theouter ring must have sufficient tensile strength. Set the sectional height of the inner and outer rings as...

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Sprag Clutches - 11

Appropriate lubricant and adequate supply are vital toensure maximum performance of the sprag type one-wayclutch. If a continuous oil groove as shown in Fig. 4.1 cannot beprovided due to the mechanical structure of the inner-ring-rotating clutch, an oil sump must be provided on the internaldiameter surface of the inner ring as shown in Fig. 4.2 to ensure sufficient oil quantity. 4.1 Lubricant Lubricant must be carefully selected since it determinesfriction coefficient of the sprag with the inner or outer ring andinfluences torque transmission performance. In general, automatic transmission...

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Sprag Clutches - 12

5.3 Simultaneous Mounting to Outer and Inner Rings To mount the one-way clutch on the inner and outer rings atthe same time, use a jig as shown in Fig. 5.3 and rotate theinner or outer ring in the freewheeling direction during assembly. > Since the sprag type one-way clutch is a high precisionmechanism, ensure that it is free from dirt, rust, and damage. Handle with care. Mishandling may deform the cage, ordislodge the sprags. Mount the end bearings on each side before and after assembly of the one-way clutch. After mounting in a transmission, check that engagementand drag directions are...

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Sprag Clutches - 13

6.2 Roll-over Excessive popping may cause sprags to become stuck inthe pockets of the cage, known as pop-out. Roll-over is a phenomenon in which sprags fall beyond theengagement position toward the opposite side due to exces- sively high torque. This subjects the raceway surfaces of theinner and outer rings to excessive force, causing deepbrinelling. > Engagement direction Inner ringRolled-over sprag Engaging spragOuter ring The causes of popping are described below. Fig. 6.4 Roll-over of One-way ClutchFig. 6.2 One-way Clutch in Pop-out State > ˔ Inappropriate lubricant lowers the friction...

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Sprag Clutches - 14

KOYO conducts various evaluation tests to confirm theperformance of sprag type one-way clutches upon request. The evaluation tests include those listed below. Table 7.1 shows operating conditions required for perfor-mance evaluation and selection of one-way clutches. For reference to performance evaluation and selection, use Table 7.1. > ʦ kN ʧɹ Roll-over torque ˔ Rated torque Loading torque is gradually increased to determine the threshold torque at which roll-over occurs in sprags. > Loading torque ˔ Constant torque is repeatedly loaded to determine the durability of the one-way clutch. >...

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