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Boost Control

The MS3 Firmware has two algorithms for controlling boost:

In addition to the algorithm selection, there are several other settings that must be properly configured in order to use the boost control feature. The full boost control settings dialog can be found below:

Image boostsettings

Boost Control Common Settings

This section covers settings that are used by both the open-loop and closed-loop control algorithms.

Additional Closed-loop settings

Enabling the closed-loop boost control algorithm enables the following additional settings:

Miscellaneous Boost Control Configuration

This section covers all remaining boost control settings.

Overboost Protection

Overboost protection works similarly to a rev-limiter, except that it can stop engine operation when boost exceeds a user-set limit. In addition, use of the overboost protection feature is required when using the closed-loop boost control algorithm.

The following settings affect the operation of overboost protection:

Other Boost Control Settings

The following settings remain:

Closed-loop Tuning Tips

This section reviews some tips for tuning closed-loop boost control. Tuning closed-loop boost control should be done in two steps:

  1. Tune open-loop boost control - In order to make sure that you have the proper polarity set for your valve, and to get a feel for the boost that certain duty cycles yield, it is recommended that open loop boost control is tuned first.
  2. Set Up Overboost Protection - The closed-loop boost control code uses the maximum boost set in Overboost Protection for some of its internal calculations. This was done purposely so that during the tuning process for boost control, if the settings wildly incorrect, boost will still not climb any higher than the Overboost Protection allows it.
  3. Tune Proportional-Integral-Derivative (PID) gains - The PID gains are the main controls for how quickly the boost will reach the target, and how close it will remain to the target through the RPM range. Steps for tuning this can be found below.

Tuning open-loop boost control

Open-loop boost control tuning is very simple. The main tuning table appears below:

Image openloopboost

Notice that areas which should have low boost have higher duties. This is because a higher duty should correspond with a more opened wastegate, which should correspond roughly to lower boost. If while tuning open-loop boost, higher duty results in higher boost and closed-loop boost control will eventually be used, toggle the Output Polarity setting to the opposite of its current setting.

To tune the actual boost levels, just adjust the duty table so that boost reaches the desired level at each point in the table.

Use open-loop boost control to try out different frequency settings and find the settings that work the best for the particular solenoid being used.

Setting up Overboost Protection

The boost control settings dialog contains the Overboost Protection settings. Setting this ups very similar to setting up a rev-limiter. Choose from Fuel Cut or Spark cut or Both. If the engine being tuned is still equipped with a catalytic converter, spark cut should not be used.

The maximum boost should be set up a few kPa higher than the maximum target boost will be in the closed-loop boost target table. Hysteresis should be set so that MAP jitter does not cause it to alternate rapidly between on and off.

Tuning Closed-loop boost control

The first step for tuning Closed-loop boost control is to set the desired targets in the Boost Control Target table. Typically lower throttle positions will have lower boost targets:

Image closedloopboost

Typically, the defaults for the following settings can be used:

The next step after setting up the target table and supporting settings is to tune the PID gains:

  1. Set Integral and Differential Gains to 0% - To make tuning the Proportional gain easier, set the Integral and Differential gains to 0%.
  2. Set Proportional gain to 100% and slowly lower - While tuning Proportional gain, higher numbers mean slower boost climb and lower final boost. For safety, start with a very high gain (100% should be sufficient). Find the RPM that typically spools quickly, and fully and quickly depress the accelerator. Note how much boost is reached. If boost overshoots the target dramatically, increase the Proportional gain. Otherwise, reduce the Proportional gain and try again. Do this until boost reaches the target with a small amount of overshoot.
  3. Tune the Integral Gain - The next step after the target is reached consistently is to tune the Integral gain. Starting from the RPM used to tune the P-gain, fully depress the accelerator and watch the boost as the engine climbs through the RPM range. As the engine accelerates through the rev range, the boost will probably creep away from the target. Keep increasing the I gain until the controller adequately maintains the target with minimal oscillation. It may be necessary to increase the P gain a bit after tuning the I gain since the two gains tend to counteract each other.
  4. tune the Derivative Gain - Increase the D gain until the overshoot is minimized. Care must be taken when increasing the D gain as too much D gain can over-dampen the effects of the P and I gains.

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