Driveline Actuation

About Torques, Forces, and Motion

From the torques and forces applied to driveline inertias and masses, a Simscape™ Driveline™ simulation determines the resulting motion from the driveline component connections and defining equations. However, a simulation can also accept motions imposed on a driveline and solve for the torques and forces to produce those motions. In general, a driveline simulation is a mixture of these two requirements, solving dynamics both forward (torque and force to motion) and inverse (motion to torque and force). Imposing motions and applying torques and forces to a driveline are together forms of mechanical actuation.

This section describes how to actuate drivelines with torques, forces, and motions, as well as how to set motion initial conditions. All of these actuation types (except for initial conditions) require physical signal inputs to define time-varying functions that carry physical units.

Torque-Force Actuation and Motion Actuation Are Complementary and Mutually Exclusive

In all cases, you should exercise care as you apply a mixture of actuation types to a driveline and its degrees of freedom (DoFs). The complete effect of the actuation types must be such that:

  • Driveline DoFs actuated by torques and forces are not also subject to motion actuation. (They can be subject to motion initial condition settings.)

  • Driveline DoFs actuated by motions are not also subject to torque or force actuation.

For a Simscape Driveline model to simulate nontrivial motion, torque and motion actuation types complement one another exactly to account consistently for the motion of all the DoFs. If this criterion is not satisfied, one of these outcomes results:

  • The motion of the driveline is trivial, staying in its initial motion state for the entire simulation.

  • The actuation types are inconsistent with each other, and the simulation stops with an error.

  • The actuation types leave the driveline motion underdetermined or overdetermined, and the simulation stops with an error.

For more about driveline simulation errors, see Driveline Simulation Errors.

Actuate a Driveline with Torques and Forces

You can apply a torque to a rotational driveshaft, or a force to a translational driveshaft, in the following ways:

  • Directly, with an Ideal Torque Source or Ideal Force Source block.

  • Indirectly, with a dynamic element that generates torque or force. Such blocks include torque converters, clutches and clutch-like elements, and engines.

A torque or force source accepts a physical signal input and originates, from its mechanical conserving port, a mechanical connection line carrying that torque or force.

The Simscape Driveline simulation solves for the motion of the spinning or sliding driveshaft, given the torque or force that it is subject to. Therefore you cannot also subject that same driveshaft to motion actuation.

    Note:   A driveline actuated by a torque must have a nonzero inertia, represented by one or more connected Inertia blocks. A torque-actuated driveline without any inertia experiences a singular acceleration. (The analogous restriction holds for force actuation, masses, and Mass blocks.) In this case, the Simscape Driveline simulation stops with an error.

Actuate a Driveline with Motions

You can apply a motion to a driveshaft directly, with an Ideal Angular Velocity Source or Ideal Translational Velocity Source block.

A motion source accepts a physical signal input and originates, from its mechanical conserving port, a mechanical connection line spinning or sliding with the specified motion.

The Simscape Driveline simulation solves for the torque or force carried by the spinning or sliding driveshaft, given its motion. Therefore you cannot also subject that same driveshaft to torque or force actuation.

Set Initial Conditions of Driveline Motion

When driveline simulation starts, the complete driveline determines the initial motion of all driveshafts by a combination of constraints, motion sources, and initial condition settings. You set the initial conditions for the rotational and translational motion of inertias and masses in their respective Inertia and Mass blocks. The block default for initial velocities is zero (no initial motion).

For more information about constraints and degrees of freedom, see Driveline Degrees of Freedom.

    Note:   Ensure that whatever initial conditions you impose on the Inertia and Mass blocks in your driveline are consistent with all of the driveline's constraints and motion sources. If an inconsistency occurs, Simscape Driveline simulation stops with an error at model initialization.

Resolving Undetermined Motions in Complex Gears

A simple gear has two ports and imposes one constraint between them, leaving one independent DoF. Once one port is connected to a driveshaft, the motion of the other port's driveshaft is determined.

A complex gear has three or more ports and imposes one or more constraints among them. A complex gear can have any number of independent DoFs, including none.

If a simulation apportions the initial motions of a complex gear in an unsatisfactory way, determine how you want the overall initial motion divided up and enforce that division by setting initial conditions on the connected Inertia and Mass blocks.

However you divide the initial motion among the gear shafts, ensure that this division is consistent with all constraints in your driveline, as well as any motion sources.

For more information about complex gears, see Basic Motion, Torque, and Force Modeling.

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