[s-cars] Wastegate drawing

[Paul Gailus]

In case this isn't already common knowledge, it looks like there's a
cross-sectional drawing of our wastegate in Fig. 2 of US patent 4,270,356.

http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=4270356

  (hit the "Images" button, and you'll need to have a tiff file viewer)


By the way, I think Dave D could be right about our systems using vacuum
on the bottom of the wastegate diaphragm to keep the wastegate closed
and build more boost.
After all, we've got a great "vacuum cleaner" going on at the inlet of the
compressor, especially when the turbo's wound up. All you need is just a
little bit of restriction from the MAF, air filter, ducts, etc. to get some vacuum.

Consider the following scenario:
1. The flow from the compressor scroll tap is restricted (in the orifice there
and/or in the WGFV itself).
2.  The WGFV tap going to this "vacuum cleaner" is opened by the solenoid
with a duty cycle high enough to flow more than the level of restricted flow
from the compressor tap.

At this point, there's going to be a net air flow coming out of the wastegate
diaphragm assembly, and the pressure there is going to drop below
atmospheric (i.e., a vacuum). This is going to assist the spring in keeping
the wastegate closed, and the boost will build to a higher level.

All this means is that by controlling the flow properly, we've now got bidirectional
control of the wastegate diaphragm with just one WGFV (and without needing to
to also control the top of the wastegate diaphragm).

Paul