Documentation

Ring-Planet

Planetary gear set of carrier, planet, and ring wheels with adjustable gear ratio and friction losses

Library

Gears/Planetary Subcomponents

Description

The Ring-Planet gear block represents a set of carrier, planet, and ring gear wheels. The planet is connected to and rotates with respect to the carrier. The planet and ring corotate with a fixed gear ratio that you specify. A ring-planet and a sun-planet gear are basic elements of a planetary gear set. For model details, see Ring-Planet Gear Model.

The block models the effects of heat flow and temperature change through an optional thermal port. To expose the thermal port, right-click the block and select Simscape > Block choices > Show thermal port. Exposing the thermal port causes new parameters specific to thermal modeling to appear in the block dialog box.

Dialog Box and Parameters

Main

Ring (R) to planet (P) teeth ratio (NR/NP)

Ratio gRP of the ring gear wheel radius to the planet gear wheel radius. This gear ratio must be strictly greater than 1. The default value is 2.

Meshing Losses

Parameters for meshing losses vary with the block variant chosen—one with a thermal port for thermal modeling and one without it.

 Without Thermal Port

 With Thermal Port

Viscous Losses

Planet-carrier viscous friction coefficient

Viscous friction coefficient μP for the planet-carrier gear motion. The default is 0.

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

Thermal Port

Thermal mass

Thermal energy required to change the component temperature by a single degree. The greater the thermal mass, the more resistant the component is to temperature change. The default value is 50 J/K.

Initial temperature

Component temperature at the start of simulation. The initial temperature influences the starting meshing or friction losses by altering the component efficiency according to an efficiency vector that you specify. The default value is 300 K.

Ring-Planet Gear Model

Ideal Gear Constraints and Gear Ratios

Ring-Planet imposes one kinematic and one geometric constraint on the three connected axes:

rRωR = rCωC + rPωP , rR = rC + rP .

The ring-planet gear ratio gRP = rR/rP = NR/NP. N is the number of teeth on each gear. In terms of this ratio, the key kinematic constraint is:

gRPωR = ωP + (gRP – 1)ωC .

The three degrees of freedom reduce to two independent degrees of freedom. The gear pair is (1,2) = (P,R).

    Warning   The ring-planet gear ratio gRP must be strictly greater than one.

The torque transfer is:

gRPτP + τRτloss = 0 ,

with τloss = 0 in the ideal case.

Nonideal Gear Constraints and Losses

In the nonideal case, τloss ≠ 0. See Model Gears with Losses.

Limitations

  • Gear inertia is assumed negligible.

  • Gears are treated as rigid components.

  • Coulomb friction slows down simulation. See Adjust Model Fidelity.

Ports

PortDescription
CRotational conserving port representing the planet carrier
PRotational conserving port representing the planet gear
RRotational conserving port representing the ring gear
HThermal conserving port for thermal modeling

Example

The sdl_epicyclic_gearboxsdl_epicyclic_gearbox example model uses two Ring-Planet gears to model a nonideal epicyclic gear set.

Was this topic helpful?