GTR Idle Control

The GTR has a Closed Loop Idle control system that uses a target RPM to derive an Airflow target which is corrected in closed loop. The two functions (target RPM and Closed Loop Control) can be split into Idle RPM target, Idle Airflow target and Idle Ignition timing control. There are many limits and adjustments that are applied to each of these functions. There are many diagram in this document and which use the following symbols.

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Note: If The Maps or Logging parameters are not available for your CAL ID in the latest version of ProECU or RaceROM patch please contact support@ecutek.com and we will get them added as soon as possible.

GTR Idle control in Short

Idle control in the GTR is quite complex but when split into the controlling influences

1. Feed forward (steady state corrections) based on known triggers (like headlights and A.C.)

2. Feed back corrections based on Idle RPM error

In principle you can set the target RPM and then adjust the base airflow with all accessories off at operating temperature etc to give you as small an integral value as possible, then you can tune the dead band values for integral correction to keep idle steady.

Once it holds steady you can introduce the feedforward corrections like electrical loads power steering and A.C. and check that the values don’t create to much integral correction. You can also tune the Dashpot maps and below idle extra air.

Once this is complete you should be able to let is all cool down and check the cold starting and idle warm up characteristics are satisfactory and adjust if necessary. If you have large than standard throttle bodies you may want to change the “Idle Open Area Conversion Factor“ to suit the increase in throttle area.

Specific details on the idle functions are as follows.

Idle RPM Target

Idle Control starts with a base target RPM which sets a base target airflow and goes through multiple corrections to arrive at a final target airflow which then gets converted into a throttle open area and then a throttle angle.

The Idle RPM target is set as per below and then passed through to the idle airflow function to set airflow targets and make airflow corrections.

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The Start UP Idle RPM target corr. is defined as follows, with short and long post start phases targeting slightly higher RPM by increasing the idle target in the target map by a set percentage. These maps can be tuned if you want to try improve the after start properties on big build cars.

The output of these calculation’s are then fed into the idle air flow demand maps

Idle Airflow Target

The overview of the Idle Airflow Control functions are as shown below.

In the above diagram the idle airflow components are split into the following categories

• Airflow and throttle

• Cat Warm Up

• Dashpot

• Electrical Load Compensation

• Power Steering Compensation

• Idle Stability

• Closed Loop Control

• Idle Up (after start)

The base target is the idle airflow target map which outputs the base amount of idle airflow required by the car, it then has the idle airflow for coolant temperature addition added straight onto it.

These values should be close to what you are seeing with a stable idle so cars with big cams might need adjusting.

The first Addition to the Idle Airflow is the electrical Load correction this accounts for the extra torque used by the alternator, head lights and defog system. Electrical load corrections are simple 1D map additions and are selected and applied to the base calibration and then limited for maximum addition.

Then the AC Correction is calculated using the aircon pressure sensor and the multipliers and offsets, there is a dead band applied to the AC correction to ensure that small corrections are ignored. It is then converted into and idle target dependant airflow amount with an addition factor if required added on to the final correction.

Then the radiator Fan Correction maps are applied based on the radiator fan duty settings

The Power Steering Correction amount is calculated using the 1D values and the measured power steering pressure and then added to the main airflow amount

Then the integral Feedback amount is calculated using the idle RPM error and the feedback gains. This idle airflow amount is also used in the calculation of the learnt idle airflow stored in EEPROM

The Cat Warmup Adjustment factor is calculated as per the function and then added to the main airflow calculation. From the testing performed in house these maps never appears to be referenced.

If the RPM is below the target Idle amount there is an additional correction amount added to the main calculation much like the Dashpot function.

To compensate for a fast drop in RPM the ECU runs the dashpot airflow system to deliver a slightly higher airflow to introduce a little more torque when approaching the idle target to stop the RPM undershooting. This consist to two separate function of which it chooses the largest value and then adds it to the main idle airflow amount. The first dashpot function is a single value added at a specific time (left of image below) the second is a combination of the base map using RPM Ramp rate as an input that fades out over time using the reduction rate.

There is a limit applied to the airflow amount at this point to protect against high negative manifold pressures sucking oil from the sump into the manifold. This comes in the form of the “Min Target Airflow for Idle (neg press)” map.

After this limit is applied corrections are added to this airflow value for after start, throttle leakage, coolant temperature, AIT and stored learning value, as per below

The after start corrections to the target RPM and the target airflow are defined as follows, using post start timers and set correction values that decay until closed loop idle is started

The Final Airflow target derived from this series of functions is then converted into a throttle angle using the current engine speed and engine volume to develop a required throttle flow percentage, which then translates to an open area and throttle angle via the TPS maps. The translation from airflow to throttle angle should not need to be changed, if bigger throttles are employed the TPS maps should be rescaled to suit the change in open area.

After the final idle airflow requirement is calculated it is converted into an open area using the Idle Open Area Conv Factor which is then limited by the Idle Throttle Open Area Limit map plus the Idle Throttle Limit RPM compensation.

The final open area is added to the current requested throttle open area and converted to a desired throttle angle base using the TPS maps the throttle angle base is then used as the minimum throttle angle and all values are calculated between this minimum and full open. This is why depending on the logging parameter you may see the throttle angle slowly drop as RPM goes up, if you look at the TPS voltage it stays flat at WOT however the open angle calculated decreases as the idle open area / position amount calculated has increased.

Idle Ignition Timing Control

Idle Ignition timing is derived from a separate function but uses some of the calculated outputs from the idle airflow as corrections. The ignition timing for idle uses a base target with some corrections and then uses proportional and integral feedback to account for instantaneous changes in torque and better control idle.

The start of idle ignition timing begins using the appropriate Idle Ignition timing map then the corrections for lean burn etc and first Idle retard for cat warm up.

The correction value is calculated in airflow and converted to ignition referencing the Idle MBT values and the torque available vs ignition retard maps which are used in other functions for determining offsets to base ignition timing. The Final correction factor is calculated as per below

To calculate the base and correction amounts the following function utilising the maps list (plus others that are not added as they are not active). It starts with the output of the target idle airflow for drive or neutral and is corrected for all of the loads, it includes the feed forward values which use the initial value to give an immediate increase in airflow when an action is taken and reduction rates to feed the timing back out and use the idle airflow to recover the torque

Idle ignition feedback (and feed forward) is calculated using the RPM error (final target - current RPM) and multiplying it by the prop and integral factors. As standard it appears that the ignition integral is not active except on start and before closed loop fueling is active. The Proportional ignition values are added depending on the normal or start operation the Integral for ignition is turned off normally.

These values can be adjusted to try and improve idle stability and low speed drivability. There are logging parameters to assist in tuning these and all of the 2D maps and selected 1D maps have been added for Live tuning, If there are any questions please contact support@ecutek.com.