Investigation of Performance Differences and Control Synthesis for Servo Controlled and Vacuum Actuated Wastegates

Paper #:
  • 2017-01-0592

Published:
  • 2017-03-28
Abstract:
Turbocharging plays an important role in the downsizing of engines. Model based approaches for boost control is increasing the demand for controlling the wastegate flow more accurately. In todays’ cars the wastegate is usually controlled only with a duty cycle and with no position feedback. Because of this a constant duty cycle can give different wastegate positions depending on the engine operating point. Currently the most frequently used feedback in todays’ cars is the boost pressure which is the controller reference. This means that there is a large time constant from actuation command to the effect in boost pressure which can impair dynamic performance. In this paper the performance of an electrical controlled vacuum actuated wastegate also named as vacuum wastegate is compared to an electrical servo-controlled wastegate also named electric wastegate. Their performances are investigated with the two actuators installed on a turbocharged inline four gasoline engine in an engine test bench. Furthermore, different control synthesis designs for these different actuators are investigated. A state-feedback controller with standard models for the electric wastegate is described and implemented which gives a position controlled wastegate. A main difference between vacuum and electric wastegate is that the latter has a position sensor. To make an extended comparison between the solutions the vacuum wastegate is also equipped with a position sensor and controller using standard control design methods. The controllers are implemented and compared in both a simulation environment and evaluated in an engine test stand. In addition, for the electric wastegate both soft landing and tightening features are also implemented and investigated, their aim is to improve the lifetime and behavior at or near the closed position.
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