Difference between revisions of "LAMBTS 2.120 (Lambda for Component Protection)"

Revision as of 09:45, 11 September 2011

See the funktionsrahmen for the following diagrams:

lambts main

lambts enable (Enabling conditions for Lambda-component protection and enabling through factor ftbts_w)

lambts lambtszw (Component protection due to changes in ignition angle)

lambts initialisation

Purpose:

Protection of components (exhaust manifold, turbocharger, etc.) through mixture enrichment.

Principle:

An excessively high exhaust gas temperature can be lowered by enriching the air-fuel mixture. Through this enrichment, more fuel enters the cylinder than would be required for stoichiometric combustion of the fuel. The unburned fuel vaporises on the cylinder walls and cools them which decreases the exhaust gas temperature.

LAMBTS: Overview

Target lambda can be enriched via the map KFLBTS which depends on the engine speed (nmot) and relative cylinder charge (rl). The enrichment is only effective when a modelled temperature tabgm_w, tkatm_w, tikatm_w or twistm_w in the sub-function LAMBTSENABLE exceeds its applicable threshold and the delay time TDLAMBTS + TVLBTS has expired. The system constant SY_ATMST defines whether twistm_w from the function %ATMST is available and the system constant SY_ATMLA defines whether twilam_w from the function %ATMLA is available.

The map KFLBTS describes the necessary steady-state enrichment, while the processes of the temperature model describe the dynamic state. This avoids early enrichment through a spike to a steady-state critical operating point.

The temperature hysteresis DTBTS or DTWISBTS prevents periodic switching on and off of the enrichment, if enrichment is set at a temperature below the cut-in temperature.

For projects with stereo exhaust systems, where the difference between the exhaust temperatures of the two cylinder banks at the same operating point can be very large, component protection can be applied separately to both cylinder banks via the maps KFLBTS and KFLBTS2 if the system constant SY_STERBTS = true.

A deterioration in ignition angle efficiency leads to an increase in exhaust gas temperature but this deterioration can be counteracted with a mixture enrichment (see sub-function DLAMBTSZW). The actual ignition angle is calculated from the ignition angle efficiency (etazwg), the basic ignition angle (zwgru) and the average ignition angle efficiency (etazwim). The difference of etazwg and etazwim results in the degradation efficiency (detazwbs). An additive enrichment depending on detazwbs can now be done via the map KFDLBTS. The enrichment can be reduced or eliminated in desired areas by means of the characteristic KFFDLBTS which is a function of engine speed and relative cylinder charge. Also, this enrichment is only effective when a modelled exhaust temperature exceeds its corresponding threshold.

The critical component temperatures can be exceeded for a brief time TVLBTS. First, however, the time TDLAMBTS must have expired. The low-pass filter ZDLBTS provides the option of smoothing an otherwise abrupt change in enrichment upon reaching a critical component temperature.

MEAN: Averaging the Efficiencies at the Actual Ignition Angle

Here is an averaging over 10 ms increments of the present ignition angle efficiencies over a 100 ms increments.

LAMBTS 2.120 Application Notes

Requirements:

- Application of the basic ignition angle (see %ZWGRU)

- Steady-state lambda - basic adaptation

- Application of knock control

- Application of the exhaust temperature model (see %ATM), including lambda-path and ignition angle path

- Installation of a temperature sensor on the protected region of the exhaust system (e.g. exhaust manifold or catalytic converter)

Codewort LAMBTS

Note 1

If Bit 2 value = 1 then tabgkrm_w wird is used as the critical temperature

If Bit 2 value = 0 then tabgm_w w is used as the critical temperature

Note 2

If Bit 1 value = 1 then updating dlambts for transmission intervention applies

If Bit 1 value = 0 then dlambts for gear intervention is frozen

Note 3

If Bit 0 value = 1 then updating dlambts for dashpot applies

If Bit 0 value = 0 then dlambts for dashpot is frozen

Switch on only when system constant SY_TURBO is active

Example: Updating dlambts for dashpot and transmission protection frozen

CWLAMBTS Bit 0 = 1 and CWLAMBTS Bit 1 = 1

CWLAMBTS = 2⁰ + 2¹ = 1 + 2 = 3

Presetting of parameters (function inactive!)

Enrichment through switching off the lambda target value: KFLBTS = 1.0 (all engine speeds & all relative cylinder charges)

Critical exhaust gas temperature: TABGBTS = 900°C

Critical temperature near the catalytic converter: TKATBTS = 900°C

Critical temperature in the catalytic converter: TIKATBTS = 900°C

Critical cylinder head temperature: TWISTBTS = 200°C

Critical turbocharger temperature: TWILABTS = 950°C

Temperature hysteresis for component protection: DTBTS = 20°C

Temperature hysteresis for cylinder head temperature: DTWISBTS = 10°C

Temperature hysteresis for turbocharger turbine temperature: DTWISBTS = 20°C

Enrichment through switching off delta lambda target value: KFDLBTS = 0.0 (for all detazwbs)

Low-pass for deactivating enrichment: ZLBTS = 0.1 s

Low-pass for deactivating delta-enrichment: ZDLBTS = 0.1 s

Time delay for enabling component protection deactivation: TDLAMBTS = 0.0 s (only effective prior to ignition).

Time delay for deactivating enrichment: TVLBTS = 0.0 s

Weighting factor for normalizing the delta lambda target value: KFFDLBTS = 1.0 (alle nmot, alle rl)

Component protection factor depending on tabgm_w: FBSTABGM = 1.0 (alle tabgm_w)

SY_ATMST = 0, when %ATMST is not available

SY_ATMLA = 0, when %ATMLA is not available

Procedure:

1.) Application of Steady-state Enrichment

- A temperature sensor is installed to measure the actual temperature at the thermal critical point.

- Enrichment independent enabling of the exhaust gas temperature model: TKATBTS = TIKATBTS = TABGBTS = TWISTBTS = 20°C for example.

- Enrichment path through ignition angle intervention switched off: e.g. KFDLBTS = 0.0 (all detazwbs)

- Knock control is enabled through the application of the characteristic KFLBTS by measuring the exhaust gas temperature at each operating point and where necessary by enrichment (KFLBTS values ​​<1) on a non-critical limiting value.

2.) Application of Enrichment through Ignition Angle Adjustment

In the application of the enrichment through ignition angle adjustment, steady-state enrichment via KFLBTS must be active.

Application of the enrichment map KFDLBTS:

- Set the ignition angle application without engine torque intervention condition (B_zwappl): CWMDAPP [bit 0] to be equal to 1

- Approach the operating point at which the largest overall enrichment was necessary in the map KFLBTS.

- Through ZWAPPL gradually retard the ignition angle and make enrichments for high exhaust gas temperature via KFDLBTS.

The characteristic field KFDLBTS should remain unchanged for the further application.

The characteristic field KFFDLBTS must be applied at the maximum latest ignition angle position (e.g. through ZWAPPL):

- Approach all operating points of KFFDLBTS and control exhaust temperature. Correct the enrichment.

3.) Application of the Temperature Threshold Values TABGBTS, TKATBTS, TIKATBTS, TWISTBTS

TABGBTS, tabgm and tabgkrm or refer to a location close to the lambda probe or exhaust manifold.

TKATBTS and tkatm refer to a location near the catalytic converter.

TIKATBTS and tikatm refer to a location in the catalytic converter.

TWISTBTS and twistm refer to the cylinder head. If SY_ATMST = 0 twistm does not exist in the project.

All thresholds are applied only when all components must be protected. If a component is not critical, the corresponding threshold is set to the maximum possible value.

- Double-check application of the exhaust temperature model, including the lambda and ignition angle paths.

- If the actual measured temperature reaches the critical component temperature, the modelled temperature must be transferred to the corresponding threshold value. Possible errors in the exhaust gas temperature model can be found by again in the emerging thresholds TABGBTS, TKATBTS, and TIKATBTS TWISTBTS.

- The choice of values for the temperature thresholds TABGBTS, TKATBTS, TIKATBTS and TWISTBTS must be checked “dynamically”. I.e. enrichment should not be used too late with a jump from a thermally non-critical to a thermally critical region, otherwise the component temperature will overshoot. In this case, a lower value for the corresponding threshold temperature should be selected.

- The temperature hysteresis DTBTS or DTWISBTS should be sufficiently large that the enrichment does not periodically turn on and off.

- A dead time TDLAMBTS > 0 s is permissible only in those projects in which a steady-state component critical temperature can be exceeded without damage on a one-off basis (total time that B_tatmbts is active), But normally, however TDLAMBTS = 0.0 s.

- A dead time TVLBTS > 0 s is permissible only in such projects in which a steady-state critical component temperature can be exceeded for brief periods any number of times with no damage. But normally, however, TVLBTS = 0.0 s.

- A delay with the time constants ZLBTS or ZDLBTS is only useful for projects where abrupt enrichment leads to a noticeable jump in torque. A delay in the enrichment will result in overshooting of the temperature components. If the overshoot is not tolerable, enrichment must be enabled from a lower component temperature.

Affected Functions:

%LAMKO via lambts_w