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. You can easily add and remove backlash, faults, and thermal effects.

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:

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

Backlash

You can incorporate the effects of backlash in your model. Backlash is the excess space between a gear tooth and the mating gear teeth. Increasing the backlash compensates for lowering manufacturing tolerances and allows the free motion of lubricants in the gears to prevent jamming. However, excess backlash can cause premature wear on your system components and can affect measurements that rely on gear position. The block applies backlash for start-ups and reversals.

You can set Backlash model to:

• No backlash — The block ignores the effects of backlash.

• Spring-damper — The block uses a Translational Hard Stop implementation to simulate backlash similar to a spring and damper in parallel.

• Instantaneous impulse — The block locks the gears in contact while the relative backlash velocity remains below the Static Contact Threshold parameter. The block unlocks the gears when the contact force changes direction.

This option is suitable for HIL simulation.

When you set Backlash model to Spring-damper or Instantaneous impulse, the block relates gear rotation to linear backlash as:

${v}_{Tooth}={r}_{B}{\omega }_{B}-\beta {r}_{F}{\omega }_{F},$

where:

• vTooth is the relative linear velocity of the gear tooth.

• rB is the Base (B) gear radius parameter associated with the base gear.

• rF is the follower gear radius, where rF = NF/NB·rB, and the Follower (F) to base (B) teeth ratio (NF/NB) parameter represents NF/NB.

• ωB and ωF are the angular velocities of the base and follower gears, respectively.

• β is the gear direction sign. When you set:

• Output shaft rotates to In same direction as input shaft, β = 1.

• Output shaft rotates to In opposite direction as input shaft, β = -1.

The block treats the meshing gear tooth as a position, xTooth, with respect to the linear backlash, Backlash, where -1/2·Backlash < xTooth < 1/2·Backlash. Backlash is equivalent to the Linear backlash parameter. The Initial offset parameter is equivalent to the initial position of xTooth.

When you set Backlash model to Instantaneous impulse, the hard stop can incorporate a nonzero value for the Coefficient of restitution parameter, e, into the momentum balance equation. During a collision,

$e=\frac{{v}_{Backlash,t-}}{{v}_{Backlash,t+}},$

where t- and t+ are the instants before and after the collision, respectively. The block asserts 0 < e < 1. For more information, see State Reset Modeling. Simscape™ logs the mode state of the gear as the intermediate M.

StateValue
M = 0Disengaged
M = 1Forwards engaged with xtooth = 1/2·Backlash
M = -1Backwards engaged with xtooth = -1/2·Backlash

The hard stop simulates static contact at the bounds. The gears lock when a collision occurs and |vTooth| < vtol, such that vTooth = 0. Here, vtol is equivalent to the Static Contact Threshold parameter.

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 enabling the optional thermal port. To enable the port, set Friction model to Temperature-dependent efficiency.

Additionally, you can choose to model efficiency that varies with loading and temperature by setting Friction model to Temperature and load-dependent efficiency. 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.

Variables

Use the Variables settings to set the priority and initial target values for the block variables before simulating. For more information, see Set Priority and Initial Target for Block Variables.

Assumptions

• Gear inertia is assumed to be negligible.

• Gears are treated as rigid components.

Ports

Input

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Physical signal input port for an external fault trigger.

Dependencies

To enable the T port:

1. On the Meshing Losses tab, set Friction model to Constant efficiency, Load-dependent efficiency, Temperature-dependent efficiency, or Temperature and load-dependent efficiency.

2. On the Faults tab:

• Set Enable faults to On.

• Set Enable external fault trigger to On.

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

Dependencies

To enable this port, on the Meshing Losses tab set Friction model to either:

• Temperature-dependent efficiency

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.

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.

• 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. Torque transfer is determined from user-supplied data for gear efficiency and temperature.

• Temperature and 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. Torque transfer efficiency is determined from user-supplied data for gear loading and temperature.

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

Dependencies

To enable this parameter, 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

To enable this parameter, 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

To enable this parameter, set Friction model to Load-dependent efficiency.

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

Dependencies

To enable this parameter, 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

To enable this parameter, 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

To enable this parameter, set Friction model to Load-dependent efficiency.

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

To enable this parameter, set Friction model to either:

• Temperature-dependent efficiency

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

To enable this parameter, 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

To enable this parameter, 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

To enable this parameter, 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

To enable this parameter, 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

To enable this parameter, set Friction model to Temperature and load-dependent efficiency.

Backlash

Backlash option. You can select:

• No backlash — The block ignores the effects of backlash.

• Spring-damper — The block uses a hard stop implementation to simulate backlash.

• Instantaneous impulse — The block locks the gears in contact while the relative backlash velocity remains below the Static Contact Threshold parameter. The block unlocks the gears when the contact force changes direction.

This option is suitable for HIL simulation.

Translational distance that a gear tooth can travel between meshing teeth.

Dependencies

To enable this parameter, set Backlash to Spring-damper or Instantaneous impulse.

Initial translational position of the gear tooth with respect to the amount of backlash you specify in the Linear backlash parameter. Specify a position, xTooth, that meets the condition -1/2·Backlash < xTooth < 1/2·Backlash, where Backlash is equivalent to the value that you specify for the Linear backlash parameter.

Dependencies

To enable this parameter, set Backlash to Spring-damper or Instantaneous impulse.

Base gear distance from the center to the meshing point on the gear tooth.

Dependencies

To enable this parameter, set Backlash to Spring-damper or Instantaneous impulse.

Stiffness and rebound options for the hard stop model. You can choose from these options:

• Stiffness and damping applied smoothly through transition region, damped rebound

• Full stiffness and damping applied at bounds, undamped rebound

• Full stiffness and damping applied at bounds, damped rebound

Dependencies

To enable this parameter, set Backlash to Spring-damper.

Distance where the block gradually applies effects of stiffness and damping. When you set Hard stop model to Stiffness and damping applied smoothly through transition region, damped rebound, the block smoothly transitions the onset of stiffness and damping as the hard stop approaches full stiffness.

Dependencies

To enable this parameter, set:

• Backlash to Spring-damper.

• Hard stop model to Stiffness and damping applied smoothly through transition region, damped rebound.

Effective translational spring stiffness of the gear collision.

Dependencies

To enable this parameter, set Backlash to Spring-damper.

Effective translational damping of the gear collision.

Dependencies

To enable this parameter, set Backlash to Spring-damper.

Loss of translational kinetic energy during collisions. A value of 0 represents an inelastic collision, and a value of 1 represents a perfectly elastic collision where the gear retains all kinetic energy. The default of 0 is equivalent to simulating gear torque when the gears are in contact, and removing torque when the gear changes direction and the tooth travels the backlash distance.

Dependencies

To enable this parameter, set Backlash to Instantaneous impulse.

Velocity, vtol, below which the gear tooth becomes locked with the meshing teeth. The block sets vTooth = 0 when |vTooth| < vtol.

Dependencies

To enable this parameter, set Backlash to Instantaneous impulse.

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

The Faults tab is not visible when you set Friction model to No meshing losses - Suitable for HIL simulation.

Enable externally or temporally triggered faults.

Dependencies

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

Efficiency when a fault is triggered.

Dependencies

This parameter is not visible when either:

• On the Meshing Losses tab, Friction model is set to No meshing losses - Suitable for HIL simulation.

• Enable faults is set to Off.

Option to enable an externally triggered fault.

Dependencies

This parameter is not visible when either:

• On the Meshing Losses tab, Friction model is set to No meshing losses - Suitable for HIL simulation.

• Enable faults is set 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 either:

• On the Meshing Losses tab, Friction model is set to No meshing losses - Suitable for HIL simulation.

• Enable faults is set to Off.

Simulation time that triggers a temporal fault.

Dependencies

This parameter is not visible when either:

• On the Meshing Losses tab, Friction model is set to No meshing losses - Suitable for HIL simulation.

• Enable faults is set to On and Enable temporal fault trigger is set 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 either:

• On the Meshing Losses tab, Friction model is set to No meshing losses - Suitable for HIL simulation.

• Enable faults is set to Off.

Reporting preference for the fault condition.

Dependencies

This parameter is not visible when either:

• On the Meshing Losses tab, Friction model is set to No meshing losses - Suitable for HIL simulation.

• Enable faults is set 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

To enable this parameter, set Friction model to either:

• Temperature-dependent efficiency

Temperature at simulation start.

Dependencies

To enable this parameter, set Friction model to either:

• Temperature-dependent efficiency

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Extended Capabilities

C/C++ Code GenerationGenerate C and C++ code using Simulink® Coder™.

Introduced in R2011a

Simscape Driveline Documentation 