# Simple Gear

Simple gear of base and follower wheels with adjustable gear ratio, friction losses, and triggered faults

• Library:
• Simscape / Driveline / Gears

## Description

The Simple Gear block represents a gearbox that constrains the connected driveline axes of the base gear, B, and the follower gear, F, to corotate with a fixed ratio that you specify. You choose whether the follower axis rotates in the same or opposite direction as the base axis. If they rotate in the same direction, the angular velocity of the follower, ωF, and the angular velocity of the base, ωB, have the same sign. If they rotate in opposite directions, ωF and ωB have opposite signs.

### Ideal Gear Constraint and Gear Ratio

The kinematic constraint that the Simple Gear block imposes on the two connected axes is

`${r}_{F}{\omega }_{F}={r}_{B}{\omega }_{B}$`

where:

• rF is the radius of the follower gear.

• ωF is the angular velocity of the follower gear.

• rB is the radius of the base gear.

• ωB is the angular velocity of the base gear.

The follower-base gear ratio is

`${g}_{FB}=\frac{{r}_{F}}{{r}_{B}}=\frac{{N}_{F}}{{N}_{B}}$`

where:

• NB is the number of teeth in the base gear.

• NBF is the number of teeth in the follower gear.

Reducing the two degrees of freedom to one independent degree of freedom yields the torque transfer equation

`${g}_{FB}{\tau }_{B}+{\tau }_{F}-{\tau }_{loss}=0$`

where:

• τB is the input torque.

• τF is the output torque.

• τloss is the torque loss due to friction.

For the ideal case, ${\tau }_{loss}=0$.

### Nonideal Gear Constraint and Losses

In the nonideal case, ${\tau }_{loss}\ne 0$. For general considerations on nonideal gear modeling, see Model Gears with Losses.

In a nonideal gear pair (B,F), the angular velocity, gear radii, and gear teeth constraints are unchanged. But the transferred torque and power are reduced by:

• Coulomb friction between teeth surfaces on gears B and F, characterized by efficiency, η

• Viscous coupling of driveshafts with bearings, parametrized by viscous friction coefficients, μ

#### Constant Efficiency

In the constant efficiency case, η is constant, independent of load or power transferred.

In the load-dependent efficiency case, η depends on the load or power transferred across the gears. For either power flow,

`${\tau }_{Coul}={g}_{FB}{\tau }_{idle}+k{\tau }_{F}$`

where:

• τCoul is the Coulomb friction dependent torque.

• k is a proportionality constant.

• τidle is the net torque acting on the input shaft in idle mode.

Efficiency, η, is related to τCoul in the standard, preceding form but becomes dependent on load:

`$\eta =\frac{{\tau }_{F}}{{g}_{FB}{\tau }_{idle}+\left(k+1\right){\tau }_{F}}$`

### Faults

If you enable faults for the block, the efficiency changes in response to one or both of these triggers:

• Simulation time — A fault occurs at a specified time.

• Simulation behavior — A fault occurs in response to an external trigger. Enabling an external fault trigger exposes port T.

If a fault trigger occurs, for the remainder of the simulation, the block uses the faulted efficiency in one of these ways:

• Throughout rotation

• When the rotation angle is within a faulted range that you specify

You can program the block to issue a fault report as a warning or error message.

### Thermal Model

You can model the effects of heat flow and temperature change by selecting a thermal block variant. Selecting a thermal variant:

• Exposes port H, a conserving port in the thermal domain.

• Enables the Thermal mass parameter, which allows you to specify the ability of the component to resist changes in temperature.

• Enables the Initial Temperature parameter, which allows you to set the initial temperature.

To select a thermal variant, right-click the block in your model and, from the context menu, select Simscape > Block choices. Select a variant that includes a thermal port.

## Assumptions

• Gear inertia is assumed negligible.

• Gears are treated as rigid components.

## Ports

### Input

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Physical signal input port for an external fault trigger.

#### Dependencies

To expose the T port:

1. For the Meshing Losses Friction model parameter, select `Constant efficiency` or ```Load-dependent efficiency```.

2. For the Faults Enable faults parameter, select `On`.

3. For the Faults Enable external fault trigger parameter, select `On`.

4. Click or .

For information on related dependencies, see Parameter Dependencies Table.

### Conserving

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Rotational mechanical conserving port associated with the base, or input, shaft.

Rotational mechanical conserving port associated with the follower, or output, shaft.

Thermal port associated with heat flow. Heat flow affects gear temperature, and therefore, power transmission efficiency.

#### Dependencies

The thermal conserving port is optional and is hidden by default. To expose the port, select a variant that includes a thermal port.

Selecting a thermal variant enables thermal parameters. For more information, see Parameter Dependencies Table.

## Parameters

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### Parameter Dependencies Table

The table shows how the visibility of some Meshing Losses parameters and Faults parameters depend on the thermal model and the option that you choose for other parameters. To learn how to read the table, see Parameter Dependencies.

Default Model — For nonthermal models, thermal port H is not visible.Thermal Model — For thermal models, thermal port H is visible.
Meshing LossesMeshing Losses

Friction model — Choose ```No meshing losses - Suitable for HIL simulation```, ```Constant efficiency```, or ```Load-dependent efficiency```

Friction model — Choose ```Temperature-dependent efficiency``` or ```Temperature and load-dependent efficiency```

No meshing losses - Suitable for HIL simulationConstant efficiencyLoad-dependent efficiencyTemperature-dependent efficiencyTemperature and load-dependent efficiency

Efficiency

Input shaft torque at no load

Temperature

Temperature

Follower power threshold

Nominal output torque

Efficiency

Efficiency at nominal output torque

Follower power threshold

Efficiency matrix

Follower angular velocity threshold

Follower angular velocity threshold

FaultsFaults

Enable faults — Choose `Off` or `On`

OffOn

Faulted efficiency

Enable external fault trigger — Choose `Off` or `On`. Selecting `On` makes thermal port T visible.

Enable temporal fault trigger — Choose `Off` or `On`

OffOn

Simulation time for fault event

Faulted angle range

Reporting when fault occurs — Choose `None`, or `Warning`, or `Error`

### Main

Fixed ratio gFB of the follower axis to the base axis. The gear ratio must be strictly positive.

Direction of motion of the follower (output) driveshaft relative to the motion of the base (input) driveshaft.

### Meshing Losses

Meshing losses parameters depend on the thermal model. For more information, see Parameter Dependencies Table.

#### Default (Nonthermal) Meshing Losses Parameters

Friction models at various precision levels for estimating power losses due to meshing.

• ```No meshing losses - Suitable for HIL simulation``` — Neglect friction between gear cogs. Meshing is ideal.

• `Constant efficiency` — Reduce torque transfer by a constant efficiency factor. This factor falls in the range 0 < η ≤ 1 and is independent from load.

• `Load-dependent efficiency` — Reduce torque transfer by a variable efficiency factor. This factor falls in the range 0 < η < 1 and varies with the torque load.

#### Dependencies

This parameter is visible when you choose a thermal model. This parameter affects the visibility of other Meshing Losses parameters and Faults parameters.

Torque transfer efficiency, η, between base and follower shafts. Efficiency is inversely proportional to the meshing power losses.

#### Dependencies

This parameter is visible when you choose a nonthermal model and set Friction model to ```Constant efficiency```.

Absolute value of the follower shaft power above which the full efficiency factor is in effect. Below this value, a hyperbolic tangent function smooths the efficiency factor to 1, lowering the efficiency losses to 0 when no power is transmitted.

As a guideline, the power threshold should be lower than the expected power transmitted during simulation. Higher values might cause the block to underestimate efficiency losses. Very low values tend to raise the computational cost of simulation.

#### Dependencies

This parameter is visible when you choose a nonthermal model and set Friction model to ```Constant efficiency```.

Net torque,τidle, acting on the input shaft in idle mode, that is, when torque transfer to the output shaft equals zero. For nonzero values, the power input in idle mode completely dissipates due to meshing losses.

#### Dependencies

This parameter is visible when you choose a nonthermal model and set Friction model to `Load-dependent efficiency`.

Output torque, τF, at which to normalize the load-dependent efficiency.

#### Dependencies

This parameter is visible when you choose a nonthermal model and set Friction model to `Load-dependent efficiency`.

Torque transfer efficiency, η, at the nominal output torque. Larger efficiency values correspond to greater torque transfer between the input and output shafts.

#### Dependencies

This parameter is visible when you choose a nonthermal model and set Friction model to `Load-dependent efficiency`.

Absolute value of the follower shaft angular velocity above which the full efficiency factor is in effect, ωF. Below this value, a hyperbolic tangent function smooths the efficiency factor to one, lowering the efficiency losses to zero when at rest.

As a guideline, the angular velocity threshold should be lower than the expected angular velocity during simulation. Higher values might cause the block to underestimate efficiency losses. Very low values tend to raise the computational cost of simulation.

#### Dependencies

This parameter is visible when you choose a nonthermal model and set Friction model to `Load-dependent efficiency`.

#### Thermal Model Meshing Losses Parameters

Friction models at various precision levels for estimating power losses due to meshing. The block incorporates temperature dependencies and can incorporate load dependencies.

Friction models at various precision levels for estimating power losses due to meshing.

• ```Temperature-dependent efficiency``` — Reduce torque transfer by a constant efficiency factor that is dependent on temperature but does not consider the gear load. This factor falls in the range 0 < η ≤ 1 and is independent from load.

• `Load-dependent efficiency` — Reduce torque transfer by a variable efficiency factor that is dependent on temperature and load. This factor falls in the range 0 < η < 1 and varies with the torque load.

#### Dependencies

This parameter is visible when you choose a thermal model. This parameter affects the visibility of other Meshing Losses parameters.

Array of temperatures used to construct an efficiency lookup table. The array values must increase from left to right. The temperature array must be the same size as the efficiency array in temperature-dependent models. The array must be the same size as a single row of the efficiency matrix in temperature and load dependent models.

#### Dependencies

This parameter is visible for thermal models.

Array of efficiencies used to construct a 1-D temperature-efficiency lookup table for temperature-dependent efficiency models. The array values are the efficiencies at the temperatures in the Temperature array. The number of elements must be the same as the number of elements in the Temperature array.

#### Dependencies

This parameter is visible for thermal models when you set Friction model to ```Temperature-dependent efficiency```.

Absolute value of the follower shaft power above which the full efficiency factor is in effect, pF. Below this value, a hyperbolic tangent function smooths the efficiency factor to 1, lowering the efficiency losses to 0 when no power is transmitted.

As a guideline, the power threshold should be lower than the expected power transmitted during simulation. Higher values might cause the block to underestimate efficiency losses. Very low values tend to raise the computational cost of simulation.

#### Dependencies

This parameter is visible for thermal models when you set Friction model to ```Temperature-dependent efficiency```.

Array of base-gear loads used to construct a 2-D temperature load efficiency lookup table for temperature and load dependent efficiency models. The array values must increase left to right. The load array must be the same size as a single column of the efficiency matrix.

#### Dependencies

This parameter is visible when you choose a thermal model and set Friction model to ```Temperature and load-dependent efficiency```.

Matrix of component efficiencies used to construct a 2-D temperature load efficiency lookup table. The matrix elements are the efficiencies at the temperatures given by the Temperature array and at the loads given by the Load at base gear array.

The number of rows must be the same as the number of elements in the Temperature array. The number of columns must be the same as the number of elements in the Load at base gear array.

#### Dependencies

This parameter is visible when you choose a thermal model and set Friction model to ```Temperature and load-dependent efficiency```.

Absolute value of the follower shaft angular velocity above which the full efficiency factor is in effect, ωF. Below this value, a hyperbolic tangent function smooths the efficiency factor to one, lowering the efficiency losses to zero when at rest.

As a guideline, the angular velocity threshold should be lower than the expected angular velocity during simulation. Higher values might cause the block to underestimate efficiency losses. Very low values tend to raise the computational cost of simulation.

#### Dependencies

This parameter is visible when you choose a thermal model and set Friction model to ```Temperature and load-dependent efficiency```.

### Viscous Losses

Two-element array with the viscous friction coefficients in effect at the base and follower shafts. To neglect viscous losses, use the default setting, `[0, 0]`.

### Faults

For nonthermal models, Faults parameters are not visible when you set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation```.

Enable externally or temporally triggered faults.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation```. This parameter affects the visibility of other Faults parameters.

Efficiency when a fault is triggered.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation``` or when you set the Enable faults parameter to `off`.

Option to enable an externally triggered fault.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation``` or when you set the Enable faults parameter to `off`. When you select `on` for this parameter, the T port is exposed.

Option to enable a temporally triggered fault.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation``` or when you set the Enable faults parameter to `off`. When you select `on` for this parameter, the Simulation time for fault event parameter becomes visible.

Simulation time that triggers a temporal fault.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation```, or when you set the Enable faults parameter to `on` and set the Enable temporal fault trigger parameter to `off`.

Rotational angle range for the faulted efficiency. For a value or multiples of 2π rad, the faulted efficiency is applicable throughout rotation.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation``` or when you set the Enable faults parameter to `off`.

Reporting preference for the fault condition.

#### Dependencies

This parameter is not visible when you choose a nonthermal model and set the Meshing Losses Friction model parameter to ```No meshing losses - Suitable for HIL simulation``` or when you set the Enable faults parameter to `off`.

### Thermal Port

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.

#### Dependencies

Selecting a thermal block variant for the Block choice parameter makes this parameter visible.

Temperature at simulation start.

#### Dependencies

Selecting a thermal block variant for the Block choice parameter makes this parameter visible.

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