Boost controller: Difference between revisions

Revision as of 22:41, 21 January 2019

Revision as of 00:07, 30 June 2019

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=== Control details ===

[[Image:4portsolenoid.jpg|thumb|220px|A 4-port pneumatic solenoid installed to control a dual port wastegate controlled by a single [[Pulse-width modulation|PWM]] [[PID controller|PID]] controller]]

Control for the solenoids and stepper motors can be either [[PID controller|closed loop]] or [[open loop]]. Closed loop systems rely on [[Feedback loop|feedback]] from a [[Manifold Absolute Pressure sensor|manifold pressure sensor]] to meet a predetermined boost pressure. Open loop systems have a predetermined control output where control output is merely based on other inputs such as throttle angle and/or engine [[Revolutions per minute|RPM]]. Open loop specifically leaves out a desired boost level, while closed loop attempts to target a specific level of boost pressure. Since open loop systems do not modify control levels based on MAP sensor, differing boost pressure levels may be reached based on outside variables such as weather conditions or engine coolant temperature. For this reason, systems that do not feature closed loop operation are not as widespread.

Boost controllers often use pulse width modulation (PWM) techniques to bleed off boost pressure on its way to the reference port on the wastegate actuator diaphragm in order to (on occasion ) under report boost pressure in such a way that the wastegate permits a turbocharger to build more boost pressure in the intake than it normally could. In effect, a boost-control solenoid valve lies to the wastegate under the [[engine control unit]]´s (ECU) control. The boost control solenoid contains a needle valve that can open and close very quickly. By varying the [[pulse width]] to the solenoid, the solenoid valve can be commanded to be open a certain percentage of the time. This effectively alters the flow rate of air pressure through the valve, changing the rate at which air bleeds out of the T in the manifold pressure reference line to the wastegate. This effectively changes the air pressure as seen by the wastegate actuator diaphragm. Solenoids may require small diameter restrictors be installed in the air control lines to limit airflow and even out the on/off nature of their operation.