Driveline Simulation Errors

Fix Driveline Modeling and Simulation Errors

A variety of errors can cause your Simscape™ Driveline™ simulation to stop before completion. Some of these errors arise from nonphysical configurations of the driveline.

Correct Overconstrained and Conflicting Degrees of Freedom

Analyzing and counting the driveline degrees of freedom (DoFs) are essential to fixing one type of simulation error. For information about degrees of freedom, see Driveline Degrees of Freedom.

To run successfully, your driveline simulation must have a positive number of independent DoFs, from the start to the end of the simulation. Furthermore, the model DoFs must not conflict with each other.

If you encounter a simulation error where the driveline cannot move, check whether the number NDoF of independent DoFs is positive, and whether the DoFs do not conflict with each other.

Checking the Number of DoFs

If NDoF is not positive:

  • Remove one or more constraining blocks, such as Gears, Clutches or clutch-like elements, and Mechanical Rotational References.

  • Remove one or more Ideal Angular Velocity Source blocks.

Try one or both of these steps repeatedly until you locate the origin or origins of the simulation failure and make NDoF positive.

Checking the Consistency of DoFs

Consider also whether two or more DoFs are in conflict. For example, check whether two velocity sources are trying to move a single DoF in two different ways. Such a configuration creates a motion conflict and leads to a simulation error.

Correct Clutch and Transmission Errors

Faulty clutch and transmission configurations generate many driveline motion failures and usually arise from DoF conflicts and errors. Clutches impose conditional or dynamic constraints.

To avoid or solve such problems, pay close attention to the collective state of your clutches, including clutches occurring inside transmission subsystems. The key to avoiding errors with transmissions is to work out and implement a complete and consistent clutch schedule.

Common mistakes include:

  • Locking too many clutches simultaneously, leading to redundant dynamic constraints and overconstrained (not enough) DoFs.

  • Locking conflicts among clutches, leading to nonredundant but still conflicting constraints.

    Example: Locking one clutch locks one driveline axis to another. You could also lock the first driveline axis simultaneously to a third axis with another clutch. If the second and third axes cannot turn at the same velocity, these DoFs are in conflict.

  • Locking too few clutches simultaneously. This error does not overconstrain DoFs or put them in conflict. However, it puts a transmission into a neutral state where it cannot transmit any torque or motion.

For information about adjusting simulation for clutches, see Optimize Simulation of Clutches and Gears, Clutches, and Transmissions.

Correct Inconsistent Initial Conditions

Like motion sources, initial conditions can cause motion conflicts. Unlike motion sources, they do not impose constraints or remove DoFs from the driveline, because they act only at the start of the simulation. However, under certain circumstances, initial conditions can cause errors when you start the simulation:

  • Initial conditions conflict with one another.

    Example: You couple two driveline axes through a Gear with a gear ratio of 2. The base axis must spin twice as fast as the follower, in the same direction. If you actuate the base with a velocity source, and the follower is connected to an inertia with initial velocity not set to half the initial base velocity, the simulation stops with an error.

  • Initial conditions conflict with motion sources. When the simulation starts, the signal controlling a velocity source acting on an axis and the initial velocity value specified on an Inertia or a Mass attached to that axis must agree. Analogous requirements hold for velocities transformed by gear couplings.

Regardless of how you set the initial conditions of your driveline axes, the complete set of initial conditions must be consistent with itself. Driveline connection lines satisfying angular velocity constraints (for example, branched lines, or lines in closed loops) must have the same initial angular velocities.

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