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Research Papers

Causes of Microslip in a Continuously Variable Transmission

[+] Author and Article Information
Songho Kim

 Raytheon UTD, 8350 Alban Road, Springfield, VA 22150songho.kim@alumni.northwestern.edu

Carl Moore

 Department of Mechanical Engineering, Florida A&M University, Tallahassee, FL 32310camoore@eng.fsu.edu

Michael Peshkin

 Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208peshkin@northwestern.edu

J. Edward Colgate

 Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208colgate@northwestern.edu

Spin refers to relative angular motion of the normal of two bodies in contact.

A summary of the internal forces within the CVT can be found in Ref. 7.

Experimental results for other transmission angles also yield little correlation between α and CVT velocity.

J. Mech. Des 130(1), 011010 (Dec 07, 2007) (9 pages) doi:10.1115/1.2803711 History: Received September 02, 2006; Revised February 19, 2007; Published December 07, 2007

The continuously variable transmission (CVT) is a type of transmission that can adopt any arbitrary gear ratio. Whereas typical transmissions utilize toothed gears, the CVT employs a sphere in rolling contact with a set of rollers; loads applied to the CVT are supported across these rolling contacts, resulting in microslips of varying amounts at each contact area. In this paper, we describe the causes of microslips in the CVT and ways to lessen them through an alternative CVT design.

Copyright © 2008 by American Society of Mechanical Engineers
Topics: Rollers
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References

Figures

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Figure 1

Structure of the Arm cobot. The motions of the cobot’s three rotational joints J1, J2, and J3 are related to the cobot’s internal motion as they are connected by three CVTs.

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Figure 2

A CAD model of the CVT. The design of the CVT employs a sphere in rolling contact with four rollers (two drive rollers and two steering rollers).

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Figure 3

The design of the CVT includes a sphere and four rollers. In (a), only the drive rollers are shown and in (b), only the steering rollers are shown.

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Figure 4

Two additional views of the CVT. The orientations of both steering rollers are described by steering angle ϕ.

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Figure 5

The sphere’s instantaneous axis of rotation is described by the CVT angle γ

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Figure 6

Two-dimensional Cartesian coordinate system describing the velocities of the drive rollers

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Figure 7

Two-dimensional Cartesian coordinate system for the CVT with slip

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Figure 8

The pair of drive roller torques τ1 and τ2 can be expressed as the sum of the lateral torque τ⊥ and the parallel torque τ∥

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Figure 9

Lateral slip angle α⊥

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Figure 10

Lateral forces are imparted on the steering rollers by the sphere

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Figure 11

The physical CVT used for experimental testing

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Figure 12

CVT slip angle α versus CVT parallel velocity ω∥ at various CVT loads

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Figure 13

Measured α. CVT loads are between −1Nm and 1Nm in 0.1Nm increments.

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Figure 15

Measured αDR. The drive roller slip angles are plotted against the sphere’s actual transmission angle.

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Figure 16

Modeled αSR. εS=0.0049N−1.

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Figure 17

Modeled αDR. εD=0.0038N−1.

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Figure 18

Modeled α. εS=0.0049N−1, εD=0.0038N−1.

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Figure 19

Suggested design of the box CVT

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Figure 20

Slip angles for the existing CVT

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Figure 21

Slip angles for the box CVT

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