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Modelling Slip- and Creepmode Shift Speed Characteristics of a Pushbelt Type Continuously Variable Transmission
Technical Paper
2004-40-0003
Sector:
Language:
English
Abstract
Historically slip in a CVT was regarded as destructive. The
reason for this was that slip was not controllable and since it is
unstable always resulted in damage to the variator. Recent
publications suggest that limited amounts of slip in a pushbelt
type variator can be allowed [6]. This opens the door to other
strategies for lowering the powerconsumption of CVT's. Not only
can slip be used for optimizing variator efficiency [1], actuation
efficiency can also be greatly improved. If the safety margin is
eliminated, the clamping force can be reduced by more than 25%.
This can be directly translated into a 25% decrease in actuation
power. Shifting behaviour is also influenced by slip [3]. This
effect can be used to greatly reduce the power needed for fast
shifting during emergency stopping, tip-shifting and kickdown
actions. Using this strategy the force needed for shifting is
reduced, and with it the power needed from the actuation system is
reduced.
This has not only effects on the power consumed by the actuation
system of the CVT, which is by itself a significant factor in the
variator efficiency, but also has some implications on the design
of the CVT. If actuation forces are smaller, the actuation system
can be smaller and cheaper, and the CVT itself will be lighter.
Furthermore, other actuation systems than hydraulics can be
considered, for example electromechanical actuation, to further
enhance the controllability and efficiency of the actuation system.
In this paper measurements are shown for shifting behavior of the
CVT and a relation will be given with slip in the system. The
results are used to model the transient behavior of the CVT.