Documentation

Capabilities of Simscape Driveline Software

What Simscape Driveline Software Contains

Simscape™ Driveline™ software is a set of block libraries in the Simulink® environment and based on Simscape software. You connect Simscape Driveline blocks to normal Simulink blocks through Simscape physical signal blocks that define physical units.

The blocks in the Simscape Driveline library and the related mechanical blocks in the Simscape Foundation library are the elements to model driveline systems. These systems consist of one or more inertias and masses, rotating about or translating along one or more axes, constrained to rotate or translate together by gears, which transfer torque and forces to different parts of the driveline. You can represent drivelines with components organized into hierarchical subsystems, as in any Simulink model. You can:

  • Constrain motion with gears.

  • Add complex dynamic elements such as clutches, clutch-like elements, and other couplings.

  • Represent such vehicle components as bodies and tires.

  • Actuate bodies with torques, forces, and motions.

  • Integrate the Newtonian rotational and translational dynamics, then measure the resulting motions.

Relation to Simscape Software

To model and simulate physical systems, Simscape Driveline models use such Simscape technologies as nondirectional physical connections and conserving ports, physical signals carrying physical units, custom component modeling, specialized solvers, and data logging.

The Simscape mechanical rotational and translational domains form the basis of the Simscape Driveline block libraries and models. The Simscape Foundation library (Simscape) includes physical signal blocks (Simscape); and basic mechanical blocks (Simscape) representing inertia, mass, and simple mechanical couplings. It also includes motion, torque, and force sources and sensors.

For more about modeling and simulating in the Simscape environment, see the Simscapedocumentation.

Physical Connections, Mechanical Conserving Ports, and Physical Signals

On Simscape Driveline blocks, the mechanical conserving ports anchor physical connection lines that, in this domain, represent mechanical axes. These axes are either rotation axes along which torque is transferred and around which inertias rotate, or translation axes along which force is transferred and along which masses translate.

Certain blocks defined in Simscape domains also require input or output signals that carry physical units, or physical signals. Simscape physical signal lines and ports represent and connect physical signals with units. Conversion blocks allow you to convert dimensionless Simulink signals to Simscape physical signals, and back.

Model Driveline Systems

Simscape Driveline software extends Simulink and Simscape software with blocks to model driveline components and properties, represent drivelines as physical networks, and to solve the equations of motion.

To build and run a Simscape Driveline model representation of a driveline:

  1. Specify rotational inertia or translational mass for each body. Connect the bodies with physical connection lines representing driveline axes at mechanical conserving ports.

    If needed, ground the driveline to one or more mechanical references fixed in space.

  2. Constrain the driveline axes to rotate or translate together by connecting them with gears. Gears impose static constraints on driveline motions and transfer torques and forces at fixed ratios.

  3. As necessary, add dynamic elements that transfer torque, force, and motion among driveline axes in a nonstatic way. These elements include internal torque-generating components such as damped springs, clutches, clutch-like elements, transmissions, and torque converters. You can also construct and connect your own dynamic elements.

    Similarly, add dynamic sources and environmental interactions, such as engines, vehicle bodies, and tires.

  4. Set up mechanical sources and sensors to initiate and record body motions, and to apply external torques and forces to the driveline.

  5. Connect the Simscape Solver Configuration to the driveline, then configure it. Start the simulation, calling the Simulink and Simscape solvers to find the motions of the system. Display and analyze the motion.

Model Inertias and Gears

Simscape Driveline software defines a driveline as a collection of rotating and translating bodies, defined by their rotational inertias and translational masses. Rotational and translational degrees of freedom (DoFs) originate on inertias and masses, but are carried by physical connection lines. Directly connecting one body to another constrains both bodies to rotate at the same angular or linear velocity. A torque or force applied to one body is applied to both. You can also ground driveline axes to mechanical references that do not move and that represent infinite effective inertia or mass.

Note

All Simscape Driveline DoFs are absolute in an implicit global coordinate system at rest, but are measured and used in a relative way, between one component and another. To measure regarding the global rest frame, ground sensors or other components with mechanical reference blocks.

In a real driveline, the bodies can also be connected indirectly by gears that couple driveline axes. The gears constrain the axes to rotate together. These gears can be simple or complex and can couple two or more axes. The gears have two roles:

  • Constraining the connected axes to rotate or translate together at velocities in fixed ratio or ratios.

  • Transferring the torques or forces flowing along one or more axes to other axes, also in fixed ratio or ratios.

Model Dynamic Driveline Elements

To create more realistic driveline models, you elaborate on simple drivelines consisting of inertias, masses, and gears. You add complex mechanical elements that generate torques and forces internally within the driveline, between one axis and another. Certain Simscape Driveline blocks encapsulate as subsystems entire models of complex driveline elements:

  • Load-dependent loss models of nonideal gears.

  • Clutches and clutch-like elements that model the locking and unlocking of pairs of driveline axes by applying kinetic and static friction

  • Vehicle component models that represent engines, tires, and vehicle bodies

  • Specialized torque and force models, such as torque converters, hard stops, and damped spring-like torsion

Model Custom Driveline Elements

The blocks provided in the Simscape Foundation library can serve as starting points for developing variant or entirely new models to simulate the same components. You can also study masked subsystems by looking under their masks. If necessary, break the link between the block and the library before modifying it, and then create your own version. Or, create your own new blocks using Simscape Driveline and Simscape components, or with the Simscape language.

For more information on specialized driveline components, see Specialized and Customized Driveline Components.

Actuate and Sense Motion

Simscape motion sources and sensors are the blocks that you use to insert and extract basic kinematic and dynamic information:

  • Source blocks impart motion to driveline axes and impose externally defined torques and forces on the bodies of a driveline.

  • Sensor blocks measure the motions of, and the torques and forces transferred along, the axes of a driveline system.

Source inputs and sensor outputs (Simscape) are physical signals that carry units.

Simulate and Analyze Motion

Once you specify all the rotational inertias and translational masses of the bodies and interconnect the bodies with gears and other driveline elements, the dynamic problem of finding the system motion is solvable. To finish a driveline model and prepare it for simulation, you connect the driveline to the Simscape solver. This solver defines certain aspects of the simulation and integrates the Newtonian dynamics for the system, applying all internal and external torques and constraints to find the motions of the bodies.

Once your model is ready for simulation, run it and analyze its motions, torques, and forces.

Inverse Dynamics — Trimming and Linearization

You typically do not know the torques and forces necessary to produce a given set of motions. By motion-actuating your driveline with motion sources and measuring the resulting torques and forces, you can find the torques and forces required to produce specified motions. This technique inverts the canonical approach to dynamics, which consists of finding motions from torques and forces.

A special case of inverse dynamics is trimming. This technique involves searching for steady-state motions of the bodies, when their accelerations and the torques and forces they experience vanish. Using the specialized tools in Simscape and Simulink, you can perturb such a steady motion state slightly to find how the system responds to small disturbances. The response indicates the system stability and suitability for controllers.

Generating Code — Real-Time and Hardware-in-the-Loop Simulation

Simscape Driveline software is compatible with Simulink Acceleration modes, Simulink Coder™, and Simulink Real-Time™ software. With these products, you can generate code versions of the models that you originally create in Simulink with block diagrams, enhancing simulation speed and model portability. A common application of generated code is defining real-time and hardware-in-the-loop simulations.

The presence of clutches in a driveline model induces locking-unlocking iterations and dynamic discontinuities. These discontinuities place certain restrictions on code generation. For more information about these restrictions, see Driveline Simulation Performance and Simscape Driveline Limitations.

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