Since several people have asked about how the Short Term Trim strategy works in the EMU Black, below is an excerpt from the help section:
SHORT TERM TRIM STRATEGY
This strategy utilizes a PID controller that corrects the error between the desired Lambda target and the current readings of the probe. It also takes into account the fact that the readings of the WBO probe are delayed due to both the sensor’s reaction time and the time it takes for exhaust gases to reach the probe from the cylinders.
Therefore, an estimate Air flow channel has been introduced, which calculates the amount of air sucked in by the engine per second based on engine parameters.
Parameters
| Parameter | Description |
|---|---|
| Enable | Activates the strategy |
| Rich trim limit | The maximum enrichment of the fuel-air mixture by the short term trim strategy. |
| Lean trim limit | The maximum lean-out of the fuel-air mixture by the short term trim strategy. |
| TPS Limit | Throttle position above which the strategy will be deactivated. |
| Min CLT | Coolant temperature above which the strategy will be activated. |
| Min RPM | he minimum engine RPM above which the strategy will be active. |
| Max RPM | The maximum engine RPM below which the strategy will be active. |
| Min MAP | The minimum MAP value above which the strategy will be active. |
| Max MAP | The maximum MAP value below which the strategy will be active. |
| Transients delay | The time after all events related to ignition/fuel cut (readings from the lambda probe in such situations are unreliable) during which the strategy will be inactive. |
| Max Lambda | The maximum value read from the lambda probe above which the strategy will be inactive. |
PID
The configuration of the PID controller is crucial for the correct operation of the short term trim strategy. Excessive values of the kP and kI coefficients will cause oscillations, while too small values will result in slow controller response.
It is crucial to note that different kP and kI coefficients (smaller) are required for low engine loads compared to high exhaust gas flows. This can be compensated for by using PID kP scale and PID kI scale tables so that, under higher engine load, these values are increased to provide a faster controller response.
| Parameter | Description |
|---|---|
| Proportional gain | The proportional gain of the PID controller. |
| Integral gain | The derivative gain of the PID controller. |
| Integral term limit min | The minimum value of the integral term, preventing PID controller saturation. |
| Integral term limit max | The maximum value of the integral term, preventing PID controller saturation. |
Lambda delay table
The Lambda delay table defines the delay between the change in lambda mixture value and the reading of this change by the lambda sensor. This change results from the sensor’s reaction time, the distance of the lambda sensor from the cylinder head, as well as the amount of exhaust gases flowing. The greater the amount of gases, the faster the exhaust gases reach the sensor, and the shorter the delay in reading by the sensor.
In summary, the largest delay will be at low engine speeds, and the smallest at full engine load at high speeds.
PID kP and kI scale tables
Depending on the engine load (amount of exhaust gases), to achieve the fastest possible fuel dose correction, the PID table kP scale allows for correction of the kP coefficient of the PID controller. In practice, the smallest values of the kP and kI coefficients occur at low exhaust gas flow rates. For higher flow rates, larger values