Variable preload ball drive

• US 4,617,838 A
• Filed: 04/06/1984
• Issued: 10/21/1986
• Est. Priority Date: 04/06/1984
• Status: Expired due to Fees

• Current Assignee: Nastec, Inc.
• Original Assignee: Nastec, Inc.
• Inventors: Anderson, William J.
• Primary Examiner(s): Dorner, Kenneth J.
• Assistant Examiner(s): Novais, David
• Application Number:
  US06/597,609
• Time in Patent Office: 928 Days
• Field of Search: 74/798, 74/198, 74/202, 74/206, 74/796
• US Class Current: 475/195
• CPC Class Codes: F16H 13/08 with balls or with rollers acting in a similar manner

Abstract

A traction ball drive of the type having torque ball driven split inner races drivingly connected to an output shaft wherein a plurality of preload balls retained in variable depth arcuate grooves formed the opposed annular surfaces of one of the inner races and a pre-load ring, slidably keyed to the output shaft and resiliently loaded by a disk spring, provide preloading on the torque balls with the preload balls traversing the grooves responsive to torque variations to establish the required dynamic loading between the inner races and the torque balls.

Claims

1. A fixed ratio ball drive having first and second relatively rotatable shafts, each shaft operating as either an input or output shaft, a pair of concentric annular race nembers, one of said race members being fixed against rotation and defining a unitary, axially undivided raceway, the other of said race members defining a spaced facing raceway, a plurality of torque balls retained in said raceways, a drive member connected to said first shaft having means circumferentially spacing and drivingly engaging said torque balls, both of said raceways having a radius of curvature greater than said torque ball radius, said other race member consisting of first and second race rings relatively axially movable along said second shaft to compressively radially engage the torque balls at a predetermined substantially fixed contact angle, the first race ring being fixedly rotatably connected to said second shaft, the second race ring being rotatable with and axially slidable relative to said second shaft;

a preload ring carried and driven by said second shaft, said preload ring being axially spaced from and axially shiftable relative to said second race ring;

a circumferentially spaced series of circumferentially extending opposed ramp surfaces formed in opposed axial surfaces of said rings, said ramp surface being inclined at a predetermined angle relative to the radial plane of said rings;

preload balls retained between said opposed ramp surfaces establishing rolling axial driving engagement between said rings between said ramp surfaces;

spring means operative between said preload ring and said second shaft exerting an axial force on said second race ring through said preload ring and preload balls toward siad first race ring to create a frictional force between said raceways and said torque balls just sufficient to transmit minimum expected torque demands on said drive;

said predetermined angle of inclination being related to said preload balls such that an applied greater than minimum torque demand on said drive, when transmitted to said preload ring as driven by said second shaft, results in rolling movement of said preload balls between said ramp surfaces; and

,

said rolling movement of said preload balls providing an additional axial force in proportion to said applied torque which, with said spring force, provides a combined axial force to increase the friction between said torque balls and said raceways to a level which is sufficient to maintain rolling driving engagement therebetween at said substantially fixed contact angle.

2. The ball drive as recited in claim 1 wherein said ramp surfaces are defined by a plurality of arcuate grooves in said opposing axial surfaces of the second race ring and said preload ring.

3. The ball drive as recited in claim 2 wherein said grooves are disposed in a constant diamter circumferential series.

4. The ball drive as recited in claim 3 wherein said ramp surfaces bear a constant axial inclination.

5. The ball drive as recited in claim 4 wherein each groove comprises a pair of oppositely extending ramp surfaces.

6. The ball drive as recited in claim 1 wherein said spring means is a disc spring.

7. The ball drive as recited in claim 6 wherein said disc spring is fully compressed to exert a predetermined axial force.

8. The ball drive as recited in claim 7 wherein said predetermined axial force is less than about 20 percent of said combined axial force.