Abstract
Automatic control schemes for spark ignited engines achieving optimal raw emissions require precise actuation of the fuel injectors, the ignition, the electronic throttle, etc.
Inherently, the microprocessor of the electronic control unit runs in a time based mode whereas the engine running at variable speed operates stroke by stroke, i.e., in a crank angle based mode. This necessitates a precise timing of the control commands for fuel and spark (and maybe of additional features). For variable engine speeds, this task is demanding. And it can be very time-consuming if the synchronization is realized via interrupts, particularly at high engine speeds.
For spark timing, the control variables are usually defined by the spark timing expressed in crank angle before top dead center and by the dwell angle. For fuel injection, the control variables are usually defined by the start of the injection pulse expressed in a value for the crank angle and by the (time) duration of the injection pulse.
When the engine undergoes severe transients w.r. to load and/or engine speed, it is not sufficient to define the duration of the injection pulse prior to its start. Rather, changing the duration of the injection pulse while it is running is highly desirable. This means, the pulse should be shortened, i.e., aborted prematurely, or prolonged, even if this means that a second injection pulse has to be started because the originally commanded pulse has already ended.
In order to investigate the potential of such highly flexible actuation schemes, a VLSI chip has been designed, realized, and tested using the technology of field programmable gate arrays (FPGA). The chip has the following features:
{nThe start of a pulse (for fuel or spark) is always a value for the crank angle.
{nThe duration of a pulse can be expressed either as an increase in crank angle (typical for spark timing) or as a time duration (typical for fuel injection).
{nThe length of a pulse can be modified on the fly, i.e., even after it has started.
{nProlonging a pulse (for fuel) can result in a second (or third, etc.) pulse when the first (or previous) pulse has already come to completion.
{nPredefined pulse trains are feasible. They are adaptable in the above-mentioned way.
{nProcessing of the signals of the encoder for the crank angle is done on chip.
{nAll of the real-time information which the chip holds can be read by the microprocessor of the electronic engine control module at any time. - This includes the information about the instantaneous engine speed.
In order to minimize the hand-shaking efforts between the chip and the electronic control unit, an architecture of a dualported-random-access-memory has been implemented.