Gear train for transferring power to separate shafts spinning at different speeds

Gears

This block represents a gear train for transferring power from one drive shaft to two driven shafts. A combination of simple and bevel gear constraints enable the driven shafts to spin at different speeds, when necessary, and in different directions. One example is an automobile differential, which during a turn enables the inner and outer wheels to spin at different speeds, these depending on the turning radius of each individual wheel.

Any of the shafts can provide the input that drives the remaining two shafts. The differential converts this input into rotation, torque, and power at the driven shafts. The drive gear ratio, which you specify directly in the block dialog box, helps determine the angular velocity of each driven shaft. For more information, see Differential Gear Model

This block is a composite component with three underlying blocks:

The figure shows the connections between the three blocks.

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.

**Crown wheel located**Select the placement of the bevel crown gear with respect to the center-line of the gear assembly. The default is

`To the right of the center-line`

.**Carrier (C) to driveshaft (D) teeth ratio (NC/ND)**Fixed ratio

*g*_{D}of the carrier gear to the longitudinal driveshaft gear. The default is`4`

.

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

**Sun-carrier and driveshaft-casing viscous friction coefficients**Vector of viscous friction coefficients [

*μ*_{S}*μ*_{D}] for the sun-carrier and longitudinal driveshaft-casing 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)`

).

**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.

Differential imposes one kinematic constraint on the three connected axes:

*ω*_{D} =
±(1/2)*g*_{D}(*ω*_{S1} + *ω*_{S2})
,

with the upper (+) or lower (–) sign valid for the differential crown to the right or left, respectively, of the center-line. The three degrees of freedom reduce to two independent degrees of freedom. The gear pairs are (1,2) = (S,S) and (C,D). C is the carrier.

The *sum* of the lateral motions is the transformed
longitudinal motion. The *difference* of side motions *ω*_{S1} – *ω*_{S2} is
independent of the longitudinal motion. The general motion of the
lateral shafts is a superposition of these two independent degrees
of freedom, which have this physical significance:

One degree of freedom (longitudinal) is equivalent to the two lateral shafts rotating at the same angular velocity (

*ω*_{S1}=*ω*_{S2}) and at a fixed ratio with respect to the longitudinal shaft.The other degree of freedom (differential) is equivalent to keeping the longitudinal shaft locked (ω

_{D}= 0) while the lateral shafts rotate with respect to each other in opposite directions (*ω*_{S1}= –*ω*_{S2}).

The torques along the lateral axes, *τ*_{S1} and *τ*_{S2},
are constrained to the longitudinal torque *τ*_{D} in
such a way that the power flows into and out of the gear, less any
power loss *P*_{loss}, sum to
zero:

*ω*_{S1}*τ*_{S1} + *ω*_{S2}*τ*_{S2} + *ω*_{D}*τ*_{D} – *P*_{loss}=
0 .

When the kinematic and power constraints are combined, the ideal case yields:

*g*_{D}*τ*_{D} =
2(*ω*_{S1}*τ*_{S1} + *ω*_{S2}*τ*_{S2})
/ (*ω*_{S1} + *ω*_{S2})
.

Fundamental Sun-Planet Bevel Gear Constraints

In the nonideal case, *τ*_{loss} ≠
0. See Model Gears with Losses.

Gear inertia is assumed negligible.

Gears are treated as rigid components.

Coulomb friction slows down simulation. See Adjust Model Fidelity.

These SimDriveline™ example models contain working examples of differential gears:

Port | Description |
---|---|

D | Rotational conserving port representing the longitudinal driveshaft |

S1 | Rotational conserving port representing one of the sun gears |

S2 | Rotational conserving port representing one of the sun gears |

H | Thermal conserving port for thermal modeling |

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