After some exhaustive research and testing here in Auburn Hills, we have
concluded that the main issue with COP Ignition systems is the inductive
coupling of primary switching noise ( >10**7 A/sec) to everything in the
engine compartment and to body sheet metal.
Briefly, wiring design is often done by the wiring vendor for minimum
number of different part numbers in the assembly plant and minimum
material content. This often leads to a situation that causes the
switched primary circuit to be a large loop, encompassing much of the
engine compartment. This causes a fairly high efficiency coupling mode
especially to the inside surface of body sheet metal. Since the net
current in the panels must add up to zero, an opposite current is induced
on the outside surface. This current gives rise to a normal
(perpendicular to the surface) electric field that, in turn, couples very
efficiently to our antennas!
The best was we have found to remedy this is to route the
ignition-switched-battery, which supplies the COP (and, incidentally,
injector) switching pulses to a large, low inductance (stacked film) 0.5uF
capacitor located AT THE GROUND POINT for the high-speed switches (the
engine controller ground); then rerouting the feed to the engine IN THE
HARNESS containing the switched side of the coils and injectors.
This operation provides a near zero area loop for these nasty noise
currents, thus minimizing coupling to the rest of the world. This is
usually enough to cure AM Broadcast reception issues. It may not be
sufficient for the high sensitivity HF SSB receiver. Additional measures,
such as a high u (type 77 or J) ferrite common mode choke on the engine
harness, where it leaves the engine for the controller (when mounted on
the body) keeps both primary and secondary and injector garbage on the
engine where it belongs (No, you can't get rid of it; you still need to
make sparks.). In extreme cases, an RC snubber may need to be installed
in parallel with each coil primary. The snubber needs to be the complex
conjugate impedance of the coil primary (220 ohms and 0.033uF comes to
mind for one of our COPs).
These remedies, while they are invasive, will not adversely affect
critical engine control systems (emissions, driveability and fuel economy)
IF implemented exactly as described.
Try Bytemark.com for high initial permeability ferrites and ferrite
technical information.
Bill Gilmore WB8FPQ
Electromagnetic Compatibility Engineer
Core EMC, Electrical/Electronic Engineering
Powertrain Component EMC / SRT & HEV Platform EMC
(248) 576-5813
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|