SI Engine Torque Structure Model

The spark-ignition (SI) engine implements a simplified version of the SI engine torque structure calculation used in a Bosch Engine Management System (EMS). For the torque structure estimation calculation, the block requires calibration tables for:

  • Inner torque — Maximum torque potential of the engine at a given speed and load

  • Friction torque — Torque losses due to friction

  • Optimal spark — Spark advance for optimal inner torque

  • Spark efficiency — Torque loss due to spark retard from optimal

  • Lambda efficiency — Torque loss due to lambda change from optimal

  • Pumping torque — Torque loss due to pumping

The tables available with Powertrain Blockset™ were developed with the Model-Based Calibration Toolbox™.

Lookup TableUsed to DeterminePlot

Inner torque, fTqinr

Tqinr=fTqinr(L,N)

The inner torque lookup table, fTqinr, is a function of engine speed and engine load, Tqinr=fTqinr(L,N), where:

  • Tqinr is inner torque based on gross indicated mean effective pressure, in N·m.

  • L is engine load at arbitrary cam phaser angles, corrected for final steady-state cam phaser angles, dimensionless.

  • N is engine speed, in rpm.

Friction torque, fTfric

Tfric=fTfric(L,N)

The friction torque lookup table, fTfric, is a function of engine speed and engine load, Tfric=fTfric(L,N), where:

  • Tfric is friction torque offset to inner torque, in N·m.

  • L is engine load at arbitrary cam phaser angles, corrected for final steady-state cam phaser angles, dimensionless.

  • N is engine speed, in rpm.

Pumping torque, ƒTpump

TpumpTpump(L,N)

The pumping torque lookup table, ƒTpump, is a function of engine speed and injected fuel mass, TpumpTpump(L,N), where:

  • Tpump is pumping torque, in N·m.

  • L is engine load, as a normalized cylinder air mass, dimensionless.

  • N is engine speed, in rpm.

Optimal spark, fSAopt

SAopt=fSAopt(L,N)

The optimal spark lookup table, fSAopt, is a function of engine speed and engine load, SAopt=fSAopt(L,N), where:

  • SAopt is optimal spark advance timing for maximum inner torque at stoichiometric air-fuel ratio (AFR), in deg.

  • L is engine load at arbitrary cam phaser angles, corrected for final steady-state cam phaser angles, dimensionless.

  • N is engine speed, in rpm.

Spark efficiency, fMsa

Msa=fMsa(ΔSA)ΔSA=SAoptSA

The spark efficiency lookup table, fMsa, is a function of the spark retard from optimal

Msa=fMsa(ΔSA)ΔSA=SAoptSA

where:

  • Msa is the spark retard efficiency multiplier, dimensionless.

  • ΔSAis the spark retard timing distance from optimal spark advance, in deg.

Lambda efficiency, fMλ

Mλ=fMλ(λ)

The lambda efficiency lookup table, fMλ, is a function of lambda, Mλ=fMλ(λ), where:

  • Mλ is the lambda multiplier on inner torque to account for the air-fuel ratio (AFR) effect, dimensionless.

  • λ is lambda, AFR normalized to stoichiometric fuel AFR, dimensionless.

The engine brake torque is a based on inner torque with lambda efficiency, spark retard efficiency multipliers, pumping torque, and a friction torque offset

Tbrake=MλMsaTqinrTfricTpump

To account for thermal effects, the torque structure model corrects the friction torque calculation as a function of coolant temperature.

Tfric=MfricfTfric(L,N)Mfric=ffric,temp(Tcoolant)

The pumping torque is a function of engine speed and engine speed.

Tpump=fTpump(L,N)

SAopt

Optimal spark advance timing for maximum inner torque at stoichiometric air-fuel ratio (AFR)

ΔSA

Spark retard timing distance from optimal spark advance

SA

Spark advance timing

L

Engine load at arbitrary cam phaser angles, corrected for final steady-state cam phaser angles

N

Engine speed

Mλ

Lambda multiplier on inner torque to account for the AFR effect

λ

Lambda, AFR normalized to stoichiometric fuel AFR

Msa

Spark retard efficiency multiplier

fMsa

Spark efficiency lookup table to account for torque loss due to spark retard from optimal

fTfric

Friction torque lookup table to account for torque losses due to friction

fMλ

Lambda efficiency lookup table to account for torque loss due to lambda change from optimal

fSAopt

Optimal spark lookup table, for maximum inner torque as a function of engine speed and load

fTqinr

Inner torque lookup table, for maximum torque potential of the engine at a given speed and load

Tbrake

Engine brake torque after accounting for spark advance, AFR, and friction effects

Tfric

Friction torque offset to inner torque

Tqinr

Inner torque based on gross indicated mean effective pressure

Tpump

Pumping torque

Mfric

Friction torque modifier

Tcoolant

Coolant temperature

References

[1] Gerhardt, J., Hönninger, H., and Bischof, H., A New Approach to Functional and Software Structure for Engine Management Systems – BOSCH ME7. SAE Technical Paper 980801, 1998.

See Also

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