The block in designed to simulate a bevel clutch connecting two rotating bodies. The block allows you to simulate a friction disk package with an arbitrary number of contact surfaces. The torque transfer may be applied in both directions (bidirectional) or in a predetermined (from one port to another). In the second case, torque will be transmitted only if the angular speed at the transmitting port is greater than or equal to the angular speed at the receiving port.
The block uses a model of contact sliding friction of two surfaces under the action of a pressing force. The relative slip speed ω in rad/s is determined by the formula:
where ωB, ωF – angular speeds at ports "B" and "F", respectively, rad/s
Defining the friction curve is possible in two ways: the Stribeck curve and the tabulated curve.
Stribek curve
When using this method, the Stribeck friction curve [1] and viscous friction (Figure 1) are used to determine the friction torque.
Figure 1. Dependence of friction torque on relative speed
The friction torque is determined by the formula:
where:
TB and TF – torques applied to ports "B" and "F", respectively, Nm
Tbrk – breakaway friction torque, Nm
Tc – dry (coulomb) friction torque, Nm
ωth – breakaway angular speed, rad/s
C – damp ratio, s/rad
Fr – coefficient of internal friction, Nm·s/rad
Friction torques Tbrk and Tc are calculated depending on the value of the pressing force according to the formulas:
where:
P – pressing force, N
N – number of contact surfaces
D – wear factor of friction surfaces valued from 1 to 0, where 1 corresponds to zero wear
μ – breakaway friction factor
μs – dry (coulomb) friction factor
Reff – effective radius of the disk in meters which is set explicitly or calculated by the formula:
where:
Ro – outer disk radius, m
Ri – inner disk radius, m
α – bevel angle, rad
Tabulated curve
Using this method the friction factor is defined by interpolating a given table. If the slip speed exceeds the value specified in the table, extrapolation is not carried out.
The friction torque is determined by the formula:
where μ(|ω|) – friction factor value obtained as a result of interpolation.
Inputs
Name
Description
Connection line type
N
Number of contact surfaces
Mathematical
V
Port for connecting the drive shaft (base)
Rotary mechanics
F
Port for connecting the driven shaft (following)
Rotary mechanics
Outputs
None.
Properties
Name
Parameter
Description
By default
Data type
Type of torque transmission
Dir
Type of torque transmission The possible values are: "Bidirectional", "Port B to Port F", "Port F to Port B"
The threshold value of the angular speed below which the value of the friction force is reduced to achieve the stability of the numerical solution. The property is available when selecting the model defining method as "Stribek curve"
Effective disk radius. Changing the property is only possible when choosing the method of disk geometry defining as the "Effective radius", otherwise the property is displayed in the "Read-only" mode and is for reference only
