BGSRM 17.10 (Cylinder Charge Detection, Intake Manifold Model)

BGSRM 17.10 Function Description

See the funktionsrahmen for the following diagrams:

bgsrm-bgsrm Function overview

bgsrm-bps

bgsrm-brl Calculation of the fresh and residual gas filling of the cylinders

bgsrm-brfges Calculating total cylinder charge

bgsrm-bpirg

bgsrm-bpirg1

bgsrm-pirg

bgsrm-rlsu

Function Description

The aim of the function:

The intake manifold model calculates the fresh gas filling of the combustion chamber from the air mass flow into the intake manifold.

Description:

An integrator emulates the storage characteristic of the intake manifold. It integrates, with the integrator coefficient KISRM, the relative difference between the inlet relative air fill rlroh_w and the outlet relative air fill rl_w and supplies, after correction with the intake manifold temperature via ftsr and the standard pressure 1013 mbar, the fresh gas partial pressure in the intake manifold.

This integrator is calculated in real time. This makes it possible to describe the increase in pumping capacity with increasing engine speed without parameter change.

External exhaust gas recirculation is taken into account by adding the partial pressure of residual gas psagr_w in the intake manifold (see module BGAGR). As a result there is now a measurable quantity available, namely the intake manifold pressure ps_w, that can be used to compare with the model in the application phase.

The partial pressure of fresh gas in the intake manifold is now limited to a maximum value such that the overall pressure in the intake manifold ps_w does not increase beyond psmx_w, and also so that in the MAF meter reverse flow range, the intake manifold pressure never oscillates to large values; thus the fresh gas filling rl_w is indirectly limited by the intake manifold pressure model.

During load variations-UT, an approximate pressure balance exists between the intake manifold and cylinder which means that there is also a linear relationship between cylinder filling and the intake manifold. Additionally, there is still the residual gas in the cylinder which must be described, since exhaust gas remains in the cylinder after the end of the exhaust event and a part of this residual gas temporarily flows back into the intake manifold, but is then sucked in again.

The camshaft overlap angle wnwue is characteristic of the crank angle, during which both inlet and also exhaust valves are opened and is thus a (nonlinear) measure of the average cross-sectional area, which represents an available flow of exhaust gas from the exhaust tract into the intake manifold. Since the exhaust gas mass throughput also depends on the transit time, engine speed must also be used as an input variable to describe the effect.

Hence it follows that there is a linear rl_w - ps_w connection with offset KFPIRG (as a function of engine speed and camshaft overlap angle) and gradient KFPSURL (as a function of engine speed and camshaft overlap angle).

Since the residual gas component pirg and the gradient fupsrl are dependent on the intake manifold changeover, the intake manifold position switches over as required by the corresponding map. To obtain fupsrl no abrupt changes in the residual gas component pirg and the gradient fupsrl, they are filtered by a lowpass filter with time constant ZVTPRGSU.

Exhaust gas pressure decreases with decreasing ambient pressure and therefore the residual gas component in the cylinder, therefore the offset pirg_w corrected with the altitude factor fho_w. For the slope fupsrl_w, a correction takes place according to the combustion chamber temperature ftbr.

With external exhaust gas recirculation, the conversion of intake manifold pressure to cylinder filling supplies all of the air filling the cylinder rfges_w including the EGR component. The component part of residual gas filling of the cylinders rfagr_w is obtained from the ratio of residual gas partial pressures in the intake manifold psagr_w to intake manifold pressure ps_w. The remaining filling part describes the fresh gas filling of the cylinders rl_w.

rl_w is the key parameter for incorporating all the filling-dependent effects and is the basic variable for pilot control of the fuel injection.

The extracted fresh gas mass flow rate mlw is obtained from the product of rl_w, speed and the conversion factor umsrln_w.

In contrast to previous tl-filter applications, the time constant of the relative load-transient effect is no longer explicitly applied via a characteristic curve, but this is implicit in the equilibrium of the intake manifold pressure models and the (predictable) value of KISRM. The value for KISRM is also switched depending on the intake manifold setting.

Application Notes

Requirements:

"- Conversion for air mass flow rate applied in rl (see function BGMSZS)"

"- Applied temperature compensation (see function BGTEMPK)"

Application tools:

for intake manifold pressure model equilibrium conditions:

"- Slow manifold pressure measurement in the collector'

dynamic comparison of intake manifold pressure with the intake manifold pressure model for measurement:

"- Throttle plate actuator"

"- Fast-measurement in the intake manifold collector (sensor time constant <10 ms, sampling rate <4 ms)"

Default values for the parameters:

"- Maximum allowable ratio manifold pressure/pressure before throttle”

FPVMXN = 1.20

"- In the cylinder internal residual gas partial pressure KFPRG"

50 mbar at the smallest wnwue, 300 mbar at largest wnwue small, with increasing engine speed is less

"- Gradient rl (ps) characteristic KFURL"

0.105%/mbar at the smallest wnwue, 0.142%/mbar at the largest wnwue, with increasing speed is less

"- Gradient of intake manifold pressure integrator KISRM"

KISRM = zkorr/[(Vs/VH) x z]

where

z is the number of cylinders (4 – 8)

VH is the total stroke volume of all the cylinders (i.e. engine displacement)

Vs is the intake volume from throttle plate through to the inlet valves, typically 1.5 to 3.0 x VH

zkorr is a correction factor for numerical stability: 0.90 when z = 4, 0.92 when z = 5, 0.95 when z = 6 or 1.00 when z > 6.

e.g. if z = 4 with Vs/VH = 2.2, KISRM = 0.1023

Switching off the Function:

"- From the intake manifold dynamics emulation: KISRM = 1.0"

Procedure:

"- Steady state for each engine speed nmot and camshaft overlap angle wnwue"

At about 4 to 5 points of relative load rl, determine measured intake manifold pressure, calculate a straight line through these points, then determine the intake manifold pressure offset KFPRG (at rl = 0) and KFURL from the gradient of the line.

"- After steady-state application of the intake manifold pressure model takes place, throttle plate jumps should be (e.g. rl = 26% to 60%)"

and comparing intake manifold pressures measured by the fast intake manifold pressure sensor with intake manifold pressures emulated in the ECU ps_w, the dynamic correctness of the air-filling model must be proven. Existing small deviations can possibly be corrected through minor changes in KISRM; but the intake manifold pressure dynamics and thus the rl-dynamics should be described satisfactorily with the calculated value of KISRM.

Affected functions:

All functions that use the charge signal rl, almost all!

Abbreviations