This component models a **one-way clutch**, i.e., a
component with two flanges where friction is present between the
two flanges and these flanges are pressed together via a normal
force. These flanges may be sliding with respect to each other.

A one-way-clutch is an element where a clutch is connected
in parallel to a free wheel. This special element is provided,
because such a parallel connection introduces an ambiguity into the
model (the constraint torques are not uniquely defined when both
elements are stuck) and this element resolves it by introducing
**one** constraint torque only instead of two
constraints.

Note, initial values have to be chosen for the model such that the relative speed of the one-way-clutch ≥ 0. Otherwise, the configuration is physically not possible and an error occurs.

The normal force fn has to be provided as input signal f_normalized in a normalized form (0 ≤ f_normalized ≤ 1), fn = fn_max * f_normalized, where fn_max has to be provided as parameter.

The friction in the clutch is modeled in the following way. When the relative angular velocity is positive, the friction torque is a function of the velocity dependent friction coefficient mue(w_rel), of the normal force fn, and of a geometry constant cgeo which takes into account the geometry of the device and the assumptions on the friction distributions:

frictional_torque =cgeo*mue(w_rel) *fn

Typical values of coefficients of friction:

dry operation :mue= 0.2 .. 0.4 operating in oil:mue= 0.05 .. 0.1

The geometry constant is calculated - under the assumption of a uniform rate of wear at the friction surfaces - in the following way:

cgeo=N*(r0+ri)/2

where **ri** is the inner radius,
**ro** is the outer radius and **N**
is the number of friction interfaces,

The positive part of the friction characteristic
**mue**(w_rel), w_rel >= 0, is defined
via table mue_pos (first column = w_rel, second column = mue).
Currently, only linear interpolation in the table is supported.

When the relative angular velocity w_rel becomes zero, the elements connected by the friction element become stuck, i.e., the relative angle remains constant. In this phase the friction torque is calculated from a torque balance due to the requirement that the relative acceleration shall be zero. The elements begin to slide when the friction torque exceeds a threshold value, called the maximum static friction torque, computed via:

frictional_torque =peak*cgeo*mue(w_rel=0) *fn, (peak>= 1)

This procedure is implemented in a "clean" way by state events and leads to continuous/discrete systems of equations if friction elements are dynamically coupled. The method is described in (see also a short sketch in UsersGuide.ModelingOfFriction):

- Otter M., Elmqvist H., and Mattsson S.E. (1999):
**Hybrid Modeling in Modelica based on the Synchronous Data Flow Principle**. CACSD'99, Aug. 22.-26, Hawaii.

See also the discussion State Selection in the User's Guide of the Rotational library.

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