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SI Core Engine Air Mass Flow and Torque Production

A spark-ignition (SI) engine produces torque by controlling the net airflow into the engine using throttle, turbocharger wastegate, and cam-phasing actuators.

While producing torque, the engine must comply with emission standards. To meet the tailpipe emission standards, the ECU operates a three-way-catalyst (TWC) at the stoichiometric air-fuel ratio (AFR).

In addition to emission controls, the ECU:

  • Maximizes torque at middle speeds and high loads by operating rich of stoichiometry.

  • Limits piston crown temperature at high speeds and high loads by running rich of stoichiometry.

Air Mass Flow Models

To calculate engine air mass flow, configure the SI engine to use either of these air mass flow models.

Air Mass Flow ModelDescription
SI Engine Speed-Density Air Mass Flow Model

Uses the speed-density equation to calculate the engine air mass flow, relating the engine air mass flow to the intake manifold pressure and engine speed. Consider using this air mass flow model in engines with fixed valvetrain designs.

SI Engine Dual-Independent Cam Phaser Air Mass Flow Model

To calculate the engine air mass flow, the dual-independent cam phaser model uses:

  • Empirical calibration parameters developed from engine mapping measurements

  • Desktop calibration parameters derived from engine computer-aided design (CAD) data

In contrast to typical embedded air mass flow calculations based on direct air mass flow measurement with an air mass flow (MAF) sensor, this air mass flow model offers:

  • Elimination of MAF sensors in dual cam-phased valvetrain applications

  • Reasonable accuracy with changes in altitude

  • Semiphysical modeling approach

  • Bounded behavior

  • Suitable execution time for electronic control unit (ECU) implementation

  • Systematic development of a relatively small number of calibration parameters

Torque Models

To calculate the brake torque, configure the SI engine to use either of these torque models.

Brake Torque ModelDescription
SI Engine Torque Structure Model

For the structured brake torque calculation, the SI engine uses tables for the inner torque, friction torque, optimal spark, spark efficiency, and lambda efficiency.

If you select Crank angle pressure and torque on the block Torque tab, you can:

  • Simulate advanced closed-loop engine controls in desktop simulations and on HIL bench, based on cylinder pressure recorded from a model or laboratory test as a function of crank angle.

  • Simulate driveline vibrations downstream of the engine due to high-frequency crankshaft torsionals.

  • Simulate engine misfires due to lean operation or spark plug fouling by using the injector pulse width input.

  • Simulate cylinder deactivation effect (closed intake and exhaust valves, no injected fuel) on individual cylinder pressures, mean-value airflow, mean-value torque, and crank-angle-based torque.

  • Simulate the fuel-cut effect on individual cylinder pressure, mean-value torque, and crank-angle-based torque.

SI Engine Simple Torque Model

For the simple brake torque calculation, the SI engine block uses a torque lookup table map that is a function of engine speed and load.

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