LDRLMX 3.100 (Calculation of LDR Maximum Cylinder Charge rlmax)

See the funktionsrahmen for the following diagrams:

ldrlmx-main LDRLMX function definition

ldrlmx-fldrrx

ldrlmx-sstb

ldrlmx-set

ldrlmx-rlmx-w

ldrlmx-tsel

ldrlmx-frxta-w

ldrlmx-hierarchy

ldrlmx-initialise

LDRLMX 3.100 Function Description

The function LDRLMX calculates the allowed maximum cylinder charge.

In the main path, the maximum charge value dependent on engine speed is given by the characteristic LDRXN. This can be corrected, if necessary, through intervention of the workshop tester.

For this purpose, an additive overboost increase (drlmaxo, delta maximum cylinder charge during overboost) is applied via the knock-control intervention.

On the rlmx path, a multiplicative correction is applied via the characteristic field KFTARX as a function of engine speed and intake air temperature.

Subsequently, there is an intervention via the sub-function FLDRRX as a function of the average ignition angle retardation in knock control (wkrma). This function consists of two parts, a quasi-steady state long-term component (permanent RAM) which takes the fuel octane rating into account, and a dynamic short-term component to take all other perturbations into account. The low pass of the long-term component is active only above a speed-dependent load threshold RLKRLDA that is representative for fuel adaption. The characteristic field KFFLLDE sets the steady-state reduction.

The low pass of the short-term component works with the difference of the filtered long-term average value (wkrmstat) and the actual average value (wkrma). To avoid conflicting interventions from both the aforementioned components, the minimum difference is limited to zero.

The associated drawdown value is determined by KFFSLDE.

The overboost path is corrected separately, by a dependence on the sum of both low-pass outputs (wkrmsu) and the speed of the associated drawdown is determined via KFFLDEO.

The time constants of the two components are each separated into predetermined up-regulating and down-regulating speed dependencies.

Further on down the main pathway, the maximum cylinder charge is limited by an external pressure dependency to avoid overloading the turbocharger at high altitudes.

This limit (maximum compressor pressure ratio) which is engine speed and tsel (tans/tumc)-dependent is determined via KFLDHBN, by multiplying the external pressure by the maximum absolute pressure and then using pirg_w and fupsrl_w to convert to a cylinder charge level.

When an ambient temperature sensor is present, the map KFLDHBN is addressed with the ambient temperature through the system constant SY_TFUMG and CWRLMX = 1 and to the instrument cluster via CAN. If no ambient temperature sensor is available or CWRLMX = 0, the map KFLDHBN is addressed with tans.

Via the system constants SY_TFMO, SY_GGGTS the oil temperature (toel) or the cooling water temperature from the instrument cluster (tmki) are read by sensors, whose signal is evaluated in functions %GGTOL or %GGGTS. If the respective variables are available via the CAN (tolc or tmkic) then switching to the CAN-variables will occur or, in case of failure, to surrogate values​​.

If a system failure is detected, an additional engine speed dependent (pressure) limitation (LDPBN) comes into force, which is analogous to the altitude limitation on the cylinder charge level. Switching back only occurs when resetting the tripping fault and in idle mode (B_ll).

In the overboost condition (E_ldo) an engine speed dependent limit (LDORXN) is switched in so that both the engine and the turbocharger adequately protected. Switching back also occurs only when resetting the error (E_ldo) and in idle-mode (B_ll).

LDRLMX 3.100 Application Notes

LDRXN: It must be ensured that even at speeds below the turbocharger response speed meaningful rlmax-values ​​(about 10% above the value of throttle plate at full open test bench) can be specified. Above the turbocharger response speed, the regular allowable and desired rlmax values ​​are defined in this characteristic.

LDORXN: maximum allowable cylinder charge, such that there is sufficient protection by an appropriately strong throttling of the throttle and turbocharger. (Remove the wastegate pressure hose during application!)

LDPBN: pressure relief in case of diagnosis (sudden torque drop should be no larger than about 15%).

KFLDHBN: Firstly, in the compressor performance map, acquire the regular full load line at speed sample points ​​ of KFLDHBN as well as the maximum pressure ratio line (due to the surge limit, maximum turbocharger-speed or prohibited areas of poor efficiency) to define the operational limit.

Then one carries on the height gradients from the normal full load line starting, at any engine speed, up to an operating limit.

This increases with increasing altitude (decreasing ambient pressure) of the volume flow rate and the pressure ratio with 1013/ambient pressure.

This new intersection then defines the maximum pressure ratio for KFLDHBN at the respective engine speed.

Attention! It must be ensured through appropriate application of RLKRLDA and LDRXN that the operating range of the long-time filter (rl > RLKRLDA) can always be reached! Otherwise, it might happen that a very large decrease will be locked in the long-term component itself and no new adaptation can take place.

All other values ​​are highly dependent on the project.

Basic data input

ATTENTION applicators, these data are extremely project-specific and must be verified in each project application! Please note carefully or risk engine damage! In order to achieve the same functionality as in LDRLMX 3.70 in the absence of CAN message from the instrument cluster, note the following.

LDRXN: 140%

LDORXN: 15%

LDPBN: 1500 mbar

KFLDHBN: from low engine speed 1.9 to medium engine speed (2500 rpm) constant 2.5

FKRXTOL: 1.0 (1.0 does not limit the boost pressure control)

KFFKRXTM: 1.0 (1.0 does not limit the boost pressure control)

KFFLDEO: 1.0 (1.0 does not limit the boost pressure control)

KFFSLDE: 1.0 (1.0 does not limit the boost pressure control)

KFFLLDE: 1.0 (1.0 does not limit the boost pressure control)

KFFWLLDE: 1.0 (1.0 does not limit the boost pressure control)

KFTARX: data values of 1.0 below IAT of 75°C. Data values linearly reduced from 1.0 to 0.8 between 75°C and 120°C)

KFTARXZK: about 10% less than KFTARX

LDRXNZK: about 15% less than LDRXN

RLKRLDA: ca. 0.6 x LDRXN (the greatest possible relative load reduction must be greater than the value from RLKRLDA otherwise there will be a risk of dead lock!)

TLKRLDAB: ca. 3-5 seconds

TLKRLDAU: ca. 5-7 seconds

TSKRLDAB: 1-2 seconds

TSKRLDAU: 2-4 seconds

CWRLMX: 1 (Addressing of KFLDHBN via ambient temperature in instrument cluster (tumc)).

CWRLMX: 0 (Addressing of KFLDHBN via intake air temperature (tans)).

Abbreviations