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 Table	Used to Determine	Plot
Inner torque, $f_{T q i n r}$	$T q_{i n r} = f_{T q i n r} (L, N)$	The inner torque lookup table, $f_{T q i n r}$ , is a function of engine speed and engine load, $T q_{i n r} = f_{T q i n r} (L, N)$ , where: $T q_{i n r}$ 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, $f_{T f r i c}$	$T_{f r i c} = f_{T f r i c} (L, N)$	The friction torque lookup table, $f_{T f r i c}$ , is a function of engine speed and engine load, $T_{f r i c} = f_{T f r i c} (L, N)$ , where: $T_{f r i c}$ 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, ƒ_Tpump	`T_pump=ƒ_Tpump(L,N)`	The pumping torque lookup table, ƒ_Tpump, is a function of engine load and engine speed, `T_pump=ƒ_Tpump(L,N)`, where: T_pump 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, $f_{S A o p t}$	$S A_{o p t} = f_{S A o p t} (L, N)$	The optimal spark lookup table, $f_{S A o p t}$ , is a function of engine speed and engine load, $S A_{o p t} = f_{S A o p t} (L, N)$ , where: SA_opt 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, $f_{M s a}$	$\begin{array}{l} M_{s a} = f_{M s a} (Δ S A) \\ Δ S A = S A_{o p t} - S A \end{array}$	The spark efficiency lookup table, $f_{M s a}$ , is a function of the spark retard from optimal $\begin{array}{l} M_{s a} = f_{M s a} (Δ S A) \\ Δ S A = S A_{o p t} - S A \end{array}$ where: $M_{s a}$ is the spark retard efficiency multiplier, dimensionless. $Δ S A$ is the spark retard timing distance from optimal spark advance, in deg.
Lambda efficiency, $f_{M λ}$	$M_{λ} = f_{M λ} (λ)$	The lambda efficiency lookup table, $f_{M λ}$ , is a function of lambda, $M_{λ} = f_{M λ} (λ)$ , where: $M_{λ}$ 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

$T_{b r a k e} = M_{λ} M_{s a} T q_{i n r} - T_{f r i c} - T_{p u m p}$

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

$\begin{array}{l} T_{f r i c} = M_{f r i c} f_{T f r i c} (L, N) \\ M_{f r i c} = f_{f r i c, t e m p} (T_{c o o l a n t}) \end{array}$

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

$T_{p u m p} = f_{T p u m p} (L, N)$

$S A_{o p t}$	Optimal spark advance timing for maximum inner torque at stoichiometric air-fuel ratio (AFR)
$Δ S A$	Spark retard timing distance from optimal spark advance
$S A$	Spark advance timing
$L$	Engine load at arbitrary cam phaser angles, corrected for final steady-state cam phaser angles
N	Engine speed
$M_{λ}$	Lambda multiplier on inner torque to account for the AFR effect
$λ$	Lambda, AFR normalized to stoichiometric fuel AFR
$M_{s a}$	Spark retard efficiency multiplier
$f_{M s a}$	Spark efficiency lookup table to account for torque loss due to spark retard from optimal
$f_{T f r i c}$	Friction torque lookup table to account for torque losses due to friction
$f_{M λ}$	Lambda efficiency lookup table to account for torque loss due to lambda change from optimal
$f_{S A o p t}$	Optimal spark lookup table, for maximum inner torque as a function of engine speed and load
$f_{T q i n r}$	Inner torque lookup table, for maximum torque potential of the engine at a given speed and load
$T_{b r a k e}$	Engine brake torque after accounting for spark advance, AFR, and friction effects
$T_{f r i c}$	Friction torque offset to inner torque
$T q_{i n r}$	Inner torque based on gross indicated mean effective pressure
T_pump	Pumping torque
M_fric	Friction torque modifier
T_coolant	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.

SI Engine Torque Structure Model

References

See Also

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