On the operating regime of metal pushing V-belt CVT under steady-state microslip conditions

1
On the operating regime of metal pushing V-belt
CVT under steady-state microslip conditions
2004 International CVT Congress, CA, USA
SAE 2004-34-2851

• Nilabh Srivastava
• Imtiaz Haque
• Department of Mechanical Engineering
• Clemson University
• September 24, 2004

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Presentation Outline

• Introduction to CVT (Continuously Variable
  Transmission)
• Research Objective
• Literature Review
• Model Development
• Results
• Conclusion
• Future Work Recommendations

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Introduction
Metal belt structure
Metal V-belt CVT
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Research Objective
Research Focus

• Develop model to capture dynamic interactions in
  a metal V-belt CVT under
• steady state microslip conditions
• Study the influence of loading conditions
  (torque and forces) on belt slip
• Study belt slip behavior under microslip
  conditions i.e. due to gap between
• belt elements
• Investigate operating regime of the CVT for
  efficient torque transmission (i.e.
• meeting the load requirements)
• Predict torque transmitting capacity of the CVT

Research Support US ARMY TACOM
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Literature Review

• Related to Slip models Operating Regime
• Gerbert, G., Belt Slip A unified approach,
  ASME J. of Mechanical Design, Vol. 118, 1996
• Sun, D. C., Performance analysis of a variable
  speed-ratio metal V-belt drive, Transactions of
  ASME, Mechanisms, Transmission, and Automotive
  Design, 110, 1988
• Micklem, J. D.. et al, Modeling of the steel
  pushing V-belt continuously variable
  transmission,Proceedings Inst. Of Mech. Eng.,
  Vol. 208, 1994
• Carbone, G., et al, Theoretical Model Of Metal
  V-Belt Drives During Ratio Changing Speed, ASME
  Journal of Mechanical Design, Vol. 123, 2000
• Kobayashi D., Mabuchi Y., Katoh Y., A Study on
  the Torque Capacity of a Metal Pushing V-Belt for
  CVTs, SAE Paper 980822, Transmission and
  Driveline Systems Symposium, 1998
• Srivastava,N., Haque, I., On the transient
  dynamics of a metal pushing V-belt CVT at high
  speeds, International J. of Vehicle Design,
  (accepted March 2004)
• Srivastava,N., Blouin, V., Haque, I., Using
  Genetic Algorithms to identify initial operating
  conditions for a transient CVT model, 2004 ASME
  IMECE, Nov 13-19, 2004 (accepted)

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Model Development
Assumptions

• The pulleys are rigid and there is no
  misalignment between them
• Elements and bands are treated as a continuous
  belt
• The center of mass of the element and that of
  the band pack coincide
• Belt length is constant
• Impending slip conditions exist at all contact
  surfaces
• Bending and torsional stiffness of the belt are
  neglected
• The element dimensions are small in comparison
  to the pulley radii
• The total gap between the elements is
  distributed uniformly in the region of zero or
  very low compression in the belt

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Model Development
Free Body Diagrams
TdT
T
Driven Band pack
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Model Development
Free Body Diagrams
Driven Element
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Model Development
Free Body Diagrams
Forces of belt element on DRIVEN pulley

• Free body diagrams of the two pulleys yield
  torque equations

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Model Development
Elemental Gap and Slip
Redistribution of elemental gap

• Belt microslip is defined on the basis of mean
  gap Kobayashi,1998

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Results
Simulation Parameters
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Results
Belt Compressive Force Profile
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Results
Transmission ratio vs. Driver axial Force (5 Nm)
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Results
Transmission ratio vs. Driver axial Force (30 Nm)
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Results
Transmission ratio vs. Maximum Load Torque
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Results
Driver side belt slip vs. Driver axial force
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Results
Driver side belt slip vs. Driven axial force
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Results
Driver side belt slip vs. Input Torque
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Conclusions

• Dynamic interactions were noted under steady
  state microslip conditions
• Belt slip was calculated on the basis of gap
  redistribution
• Belt slip is influenced by loading conditions of
  torques and forces
• Operating regime could be identified for a given
  CVT configuration and specified loading
  conditions, under the assumption of microslip and
  quasi-static variation in transmission ratio
• Increasing torque on one of the pulleys increases
  slip on that pulley, provided loading conditions
  on the other pulley are kept constant
• Increasing axial force on one of the pulleys
  reduces slip on that pulley, provided loading
  conditions on the other pulley are kept constant
• Maximum transmittable torque can be estimated
  just before the belt undergoes gross slip

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Future Work Recommendations

• Belt can undergo both macro and micro slip, so
  the operating regime should be estimated by
  taking inertial effects into account besides the
  loading effects Srivastava,N., Blouin, V.,
  Haque, I., Using Genetic Algorithms to identify
  initial operating conditions for a transient CVT
  model, 2004 ASME IMECE, Nov 13-19, 2004
  (accepted)
• Belt slip is not only influenced by loading
  conditions of torques and forces, but also by
  inertial effects gt The assumption of constant
  sliding angle over the pulley wrap is violated at
  high speed variations - Srivastava,N., Haque, I.,
  On the transient dynamics of a metal pushing
  V-belt CVT at high speeds, International J. of
  Vehicle Design, (accepted March 2004)
• The friction between individual bands in the band
  pack have been neglected. However, it is presumed
  that it will not significantly cause shifts in
  the operating regime of the CVT. Kim H., Lee J.,
  Analysis of Belt Behavior and Slip
  Characteristics for a Metal V-belt CVT,
  Mechanism Machine Theory,1994
• Friction between the surfaces can also be modeled
  using elastohydrodynamic lubrication theory
• Flexural effects have been neglected. However, at
  high speeds and under high loading conditions,
  the pulley sheaves can undergo flexural
  vibrations, thereby, influencing operating regime
  of the CVT
• Real-world experiments need to be run on a CVT
  for verifying the consistency of operating regime
  obtained from the simulation model. However, the
  results of the model are in consonance with those
  obtained under conditions of no-load (i.e.
  Kobayashi,D., SAE Paper 980822, 1998)