Clutch

Friction clutch; the normalized normal force f_n (0…1) engages it.

  • signal
  • rotational
  • Modelica Standard Library
  • 3 ports
  • 3 parameters
BlockClutchKindclutchLibraryRotational

Description

A friction clutch between two flanges, pressed together by a normal force set through the fn input. While slipping it transmits a friction torque proportional to the normal force; once the relative speed reaches zero the flanges lock until the transmitted torque exceeds the static limit.

The sliding friction coefficient is fixed at μ = 0.5 for all slip speeds. Stuck and sliding phases are switched by solver events.

Example

Clutch, backlash, and rotational sources A clutch that locks, gear backlash, a spring-damper coupling, and a load that steps its torque.

100 rad/s at 0.1 sDriveClose at 0.5 sClutchDriven 1 kg·m²Driven speedω ref 10 sin 2πtSpeed sourceBacklash 0.1 radInertia 0.01Speed behind backlash0.5 N·mTorque sourceCouplingInertia 0.02, damping 0.05Coupled speed0.4 N·mShaft loadLoad speed
In Gradara, select a Clutch block and press F1, then choose Open example. It opens as a new model in My models, ready to run.

Also in this example:ConstantMechanical loadStepInertia & loadSpeed sensorSine waveSpring-damperBacklashInertia (ideal)Torque sourceConstant torqueSpeed sourceSpeed sensor (ideal)

Ports

Inputs 1

  • fnf_normalizedsignal

    Normalized normal force, nominally 0 to 1; fn = fn_max · f_normalized. At zero or below, the clutch is open and transmits no torque.

Conserving terminals 2

  • aflange_arotational

    Flange a. Receives −τ.

  • bflange_brotational

    Flange b. Receives τ, the friction torque.

Parameters

  • Maximum normal forcefn_max1000 N

    ≥ 0

    Normal force at f_normalized = 1, in newtons. Zero or positive.

  • Geometry constantcgeo1

    Geometry constant, in meters, converting force times friction coefficient into torque. For N friction interfaces with inner and outer radii rᵢ and rₒ, cgeo = N · (rₒ + rᵢ)/2.

  • Stiction peakpeak1.1

    ≥ 1

    Ratio of the maximum static torque to the sliding torque at zero slip. At least 1.

Equations

Modelica
fn = fn_max · f_normalized
ω_rel = d(flange_b.phi − flange_a.phi)/dt
Sliding (ω_rel ≠ 0): τ = sign(ω_rel) · μ · cgeo · fn, with μ = 0.5
Stuck (ω_rel = 0): τ follows from the torque balance while |τ| ≤ peak · μ · cgeo · fn
Open (fn ≤ 0): τ = 0
flange_b.tau = τ, flange_a.tau = −τ

Implementation

Modelica Standard Library 4.1.0Modelica.Mechanics.Rotational.Components.Clutch
MSL documentation

Assumptions and limitations

  • The friction coefficient cannot be changed and does not vary with slip speed or temperature.
  • f_normalized is not limited; values above 1 give more than fn_max.
  • Rigid when stuck: no torsional compliance in the plates.

Tips

  • Drive fn from a Ramp or a rate-limited signal for a smooth engagement.

See also

Select a block in Gradara and press F1 to open its page offline.