Planetary gear train with stepped planet gear set
Gears
This block represents a planetary gear train with composite planet gears. Each composite planet gear is a pair of rigidly connected and longitudinally arranged gears of different radii. One of the two gears engages the centrally located sun gear while the other engages the outer ring gear.
Compound Planetary Gear
The block models the compound planetary gear as a structural component based on Sun-Planet and Ring-Planet Simscape™ Driveline™ blocks. The figure shows the block diagram of this structural component.
To increase the fidelity of the gear model, you can specify properties such as gear inertia, meshing losses, and viscous losses. By default, gear inertia and viscous losses are assumed negligible. The block enables you to specify the inertias of the internal planet gears only. To model the inertias of the carrier, sun, and ring gears, connect Simscape Inertia blocks to ports C, S, and R.
You can model the effects of heat flow and temperature change through an optional thermal conserving port. By default, the thermal port is hidden. To expose the thermal port, right-click the block in your model and, from the context menu, select Simscape > Block choices. Specify the associated thermal parameters for the component.
Fixed ratio g_{RP} of
the ring gear to the planet gear. The gear ratio must be strictly
greater than 1. The default is 2
.
Fixed ratio g_{PS} of
the planet gear to the sun gear. The gear ratio must be strictly positive.
The default is 1
.
Parameters for meshing losses vary with the block variant chosen—one with a thermal port for thermal modeling and one without it.
Vector of viscous friction coefficients [μ_{S} μ_{P}]
for the sun-carrier and planet-carrier gear motions, respectively.
The default is [0 0]
.
From the drop-down list, choose units. The default is newton-meters/(radians/second)
(N*m/(rad/s)
).
Moment of inertia of the combined planet gears. This value must
be positive or zero. Enter 0
to ignore gear inertia.
The default value is 0
kg*m^2.
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.
Component temperature at the start of simulation. The initial
temperature alters the component efficiency according to an efficiency
vector that you specify, affecting the starting meshing or friction
losses. The default value is 300
K.
Compound Planetary Gear imposes two kinematic and two geometric constraints on the three connected axes and the fourth, internal wheel (planet):
r_{C}ω_{C} = r_{S}ω_{S}+ r_{P1}ω_{P} , r_{C} = r_{S} + r_{P1} ,
r_{R}ω_{R} = r_{C}ω_{C}+ r_{P2}ω_{P} , r_{R} = r_{C} + r_{P2} .
The ring-planet gear ratio g_{RP} = r_{R}/r_{P2} = N_{R}/N_{P2} and the planet-sun gear ratio g_{PS} = r_{P1}/r_{S} = N_{P1}/N_{S}. N is the number of teeth on each gear. In terms of these ratios, the key kinematic constraint is:
(1 + g_{RP}·g_{PS})ω_{C} = ω_{S} + g_{RP}·g_{PS}ω_{R} .
The four degrees of freedom reduce to two independent degrees of freedom. The gear pairs are (1,2) = (P2,R) and (S,P1).
Warning The gear ratio g_{RP} must be strictly greater than one. |
The torque transfers are:
g_{RP}τ_{P2} + τ_{R} – τ_{loss}(P2,R) = 0 , g_{PS}τ_{S} + τ_{P1} – τ_{loss}(S,P1) = 0 ,
with τ_{loss} = 0 in the ideal case.
In the nonideal case, τ_{loss} ≠ 0. See Model Gears with Losses.
Gears are assumed rigid.
Coulomb friction slows down simulation. See Adjust Model Fidelity.
Port | Description |
---|---|
C | Rotational conserving port representing the planet gear carrier |
R | Rotational conserving port representing the ring gear |
S | Rotational conserving port representing the sun gear |
H | Thermal conserving port for thermal modeling |