|
U of M College of Engineering Control Seminar Series Sponsored by Ford Motor Company, General Motors, and Whirlpool |
Minimizing impacts in Electromagnetic Valve
Actuators
Kathy Peterson
University of
Michigan
Mechanical
Engineering Department
In an effort to improve the
performance of the standard internal combustion (IC) engine, electromagnetic
valve actuators (EVAs) have been proposed as a solution to achieve variable
valve timing (VVT). By replacing
the camshaft commonly found in most automotive engines, EVAs decouple the
motion of the engine valves from the crankshaft. In doing so, they allow for
VVT which research has shown can significantly improve torque, fuel economy,
and emissions. Unfortunately, EVAs suffer from excessively loud impacts between
their moving components that prevent them from begin commercially viable.
Application of control theory to
EVAs is hindered by non-negligible electrical dynamics and nonlinearities in
the magnetic subsystems. To ensure fast transition times, stiff springs are
required to increase the bandwidth
of the mechanical components of the system. To counteract the stiff springs, numerous turns are required
in the magnetic coils resulting in a large inductance and thus a relatively low
bandwidth electrical subsystem.
Therefore the common simplifying
assumption of current control is no longer valid. The non-negligible electrical dynamics
introduce further complications due to nonlinearities in the magnetic force and
gap reluctance. At large gaps the
magnetic force is very weak and at small gaps back-EMF effects become
significant resulting in poor control authority.
This presentation discusses
various nonlinear control techniques used to minimize the impacts associated
with the operation of EVAs.
Through a combination of Lyapunov based control and extremum seeking
control the impacts are reduced from approximately 1 m/s to 0.1 m/s. To
stabilize the system and account for the nonlinearities present in the
dynamics, the universal stabilizing feedback proposed by E.D. Sontag is
used. A discrete extremum seeking
controller is then used to exploit the repetitive nature of the system to
improve performance. As the valves
open/close several thousand times per minute, the extremum seeking control uses
information from previous valve events to select a control Lyapunov function
on-line to minimize the impacts from one valve event to the next.
It is hoped that the control
solutions presented here will find further application in other areas such as;
collision avoidance in active magnetic bearings, operation of electrostatic
actuators in telescopes, fine
position control of fuel injectors and drug delivery systems, self-tuning of discrete repetitive
tasks such as spark timing in IC engines, and telecommunications relays.
3:30 – 4:30 p.m.