Loaded-contact friction between two rotating bodies

Brakes & Detents/Rotational

The Loaded-Contact Rotational Friction block simulates friction between two rotating bodies loaded with a normal force.

The block is implemented as a structural component based on the Fundamental Friction Clutch block. From the locked state, the clutch unlocks if the friction force exceeds the static friction, as defined by the static coefficient of friction and current normal force. For details on how the locking and unlocking are modeled, see the Fundamental Friction Clutch block reference page.

Friction torque is transmitted for normal forces larger than
the **Threshold force** parameter.

B and F are rotational conserving ports associated with the driving and driven shafts, respectively. N is the physical signal terminal through which you import the normal force.

**Force action region**Select how to parameterize the loaded-contact friction. The default is

`Define effective radius`

.`Define effective radius`

— Provide a value for the friction effective radius.**Effective torque radius**Effective radius

*r*_{eff}. Must be greater than zero. The default is`130`

.From the drop-down list, choose units. The default is millimeters (

`mm`

).

`Define annular region`

— Define the friction effective radius in terms of the inside and outside diameters of the friction disk. If you select this option, the panel changes from its default.

**Friction model**Select how to specify the kinetic friction coefficient. The default is

`Fixed kinetic friction coefficient`

.`Fixed kinetic friction coefficient`

— Provide a fixed value for the kinetic friction coefficient.**Kinetic friction coefficient**The kinetic, or Coulomb, friction coefficient. Must be greater than zero. The default is

`0.3`

.

`Table lookup kinetic friction coefficient`

— Define the kinetic friction coefficient by one-dimensional table lookup based on the relative angular velocity between disks. If you select this option, the panel changes from its default.

**Static friction coefficient**The static, or peak, value of the friction coefficient. Must be greater than the kinetic friction coefficient. The default is

`0.35`

.**Velocity tolerance**Relative velocity below which the two surfaces can lock. For the surfaces to lock, the torque across the B and F rotational ports must be less than the product of the effective radius, the static friction coefficient, and the applied normal force. The default is

`0.001`

.From the drop-down list, choose units. The default is radians/second (

`rad/s`

).**Threshold force**The normal force applied to the physical signal port N must exceed the

**Threshold force**parameter value to be applied to the contact. Forces below the**Threshold force**are not applied, and there is consequently no transmitted frictional torque. The default is`1`

.From the drop-down list, choose units. The default is newton (

`N`

).

**Viscous drag torque coefficient**Viscous drag coefficient

*μ*_{visc}for computing the drag torque. The coefficient depends on the type of operating fluid, fluid temperature, and the maximum distance between the disks. The default is`0`

.From the drop-down list, choose units. The default is newton-meters/(radians/second) (

`N*m/(rad/s)`

).

**Initial state**Select the initial condition applied to the Fundamental Friction Clutch state inside the block:

`Locked`

— Rotational ports B and F are initially locked together. This is the default.`Unlocked`

— Rotational ports B and F are initially sliding relative to each other.

The block simulates friction between two rotating bodies loaded with a normal force. When the two rotating bodies are not locked, the friction torque is determined with the following equations:

*τ*_{fr} = *N*· *μ*· *r*_{eff} ·
sign(*ω*) + *τ*_{visc} ,

$${r}_{\text{eff}}=\frac{2}{3}\cdot \frac{{r}_{\text{o}}^{3}-{r}_{\text{i}}^{3}}{{r}_{\text{o}}^{2}-{r}_{\text{i}}^{2}}\text{,}$$

*τ*_{visc} = *μ*_{visc}· *ω* ,

where:

τ_{fr} | Friction torque |

N | Normal force |

μ | Friction coefficient |

r_{eff} | Effective radius |

r_{o} | Disk outside radius |

r_{i} | Disk inside radius |

ω | Relative angular velocity |

τ_{visc} | Viscous drag torque |

μ_{visc} | Viscous drag torque coefficient |

The model does not account for inertia. Add inertia terms externally to the B and F ports as required.

The model computes the torque assuming a uniform distribution of the normal force.

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