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Boost Control: Open Loop vs Closed loop

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Open Loop vs Closed loop

02.04

00:00 - When we're using an ECU to control a specific parameter on the engine, we have the option of using open loop or closed loop control.
00:09 I briefly mention the term, closed loop, in the PID module, but now I will discuss what the terms open loop and closed loop mean.
00:18 Open loop is the simplest system to configure and tune so we'll deal with this first.
00:24 In an open loop control system, the ECU will operate an output, such as the boost control solenoid at a set duty cycle.
00:34 In this sort of system, there is no feedback to tell the ECU whether the boost pressure is higher or lower than our target.
00:41 An irrespective of the actual boost pressure, the ECU will keep providing the same duty cycle to the solenoid.
00:49 The result is that we may see the boost pressure very slightly from our target, based on engine load or atmospheric conditions.
00:58 This defeats some of the advantages that electronic boost control can offer, but to see these advantages, we need to use closed loop control.
01:08 Closed loop control will look at the current boost pressure as well as our desired boost target.
01:15 Any time the measured boost pressure doesn't match the target, there will be an error and the ECU will use a PID controlled algorithm to actively alter the duty cycle being supplied to the waste gate solenoid, in order to reduce the error to zero.
01:31 Closed loop control has the ability to provide more stable and consistent boost levels, as atmospheric conditions change or engine load and exhaust temperature change.
01:43 This can give superior results but also requires more work from the tuner in order to optimise the PID control settings and achieve stable boost.