Design and Control of Fully Flexible Valve Actuation Systems for Internal Combustion Engines

 

Student: Pradeep Gillella

 

Project Introduction:

The motivation to improve fuel efficiency and reduce emissions of the internal combustion engine comes from the dwindling oil reserves and the increased concerns about climate change. A key step towards realizing these improvements is to introduce flexibilities into the fundamental subsystems used for air and fuel management. Traditional air management systems use camshaft based mechanisms to actuate the intake/exhaust valves and have very little or no flexibility.
The benefits offered by fully flexible valve actuation motivate the development of electronically controlled “Camless valve actuation systems”. Research in this area during the past two decades has lead to the development of several concepts. The widespread deployment of such systems has been impeded by the stringent performance requirements to ensure reliable operation, i.e.,

  • Large magnitude of actuator force is required to overcome the inertia and spring forces to achieve the required acceleration of the engine valve.
  • The direction of the forces needs to change rapidly to be able to operate the engine valve at high speeds (50 Hz @ 6000 RPM)
  • Precise control of the forces is required for accurate positioning of the engine valve to avoid collisions with the piston and control of the valve seating
  • In addition to the performance requirements, the overall cost and complexity of the system needs to be minimized to facilitate the mass production of these systems.

 

Current Research
In this research, we propose to address the problem from two perspectives.

Approach 1
A design-based solution capable of achieving fully flexible operation using simple and inexpensive components has been developed.

1

 

2

 

  • System capable of fully flexible operation i.e., Variable lift, variable timing, variable duration and seating control
  • All the flexibilities are achieved using two-state valves which make the system suitable for mass production
  • Valve trajectory is controlled by a hydro-mechanical internal feedback system, which has very high bandwidth and can thus ensure precise control at high speeds.

A key component in the hydro-mechanical internal feedback mechanism is currently being redesigned to improve the performance and robustness of the system.  A model based design procedure using optimization via dynamic programming and computational fluid dynamic analysis has been developed and shown to deliver the required improvements.

Approach 2
This approach is aimed at ensuring precise valve profile tracking during engine speed variations as shown in (b).  The valve profile shown in (a) during the engine speed transients is aperiodic in the time domain as shown in (c). Sampling the entire control system in the crank angle domain recovers the periodicity in the signal as shown in (d). However, this makes the plant model (actuator dynamics) to be time-varying. The application of the newly developed “Time-varying Internal Model based controller” for this tracking control problem is currently under investigation.

3

  • A framework for extending the TV-IM controller to higher order systems has been developed and validated using simulations.
  • The development of a robust stabilizer to aid in the experimental implementation of the controller is currently in progress.

 

The validation of the rotational angle domain control can also motivate similar approaches to other engine subsystems as well as general rotational machinery.

 

Reference:

  1. Gillella, P. and Sun, Z., “Design, Modeling and Control of a Camless Valve Actuation System with Internal Feedback”, IEEE Transactions on Mechatronics, Vol. 16, No.3, pp.527-539, June, 2011.
  2. Gillella, P. and Sun, Z., “Transient Control of a Camless Valve Actuation System Using a Time-Varying Repetitive Controller”, Proceedings of the 2010 Dynamic Systems and Control Conference, Boston, MA, DSCC2010-4149, September, 2010.