Bosch D-Jetronic WAS: What SU stands for

[Chris Rhodin]

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>From memory...  The inputs are intake air temp., manifold pressure, =
coolant temp., throttle motion (more later), and distributer contacts.  =
That's what I remember.  I used to have a book, if I find it I'll send =
corrections.  The throttle sensor didn't sense position it sensed motion =
by dragging a brush down a "ladder" of contacts, this info was used to =
simulate an accelerator pump.  The manifold pressure sensor was two =
bellows stacked to move the LVDT core, one of the bellows was sealed and =
provided altitude compensation, the other was piped to the plenum to =
measure the pressure there.  An LVDT (Linear Variable Differential =
Transformer) is three non-overlapping coils wrapped down the length of a =
tube with a moving core in the tube.  An AC signal is driven into the =
primary and the core position can be read off the secondaries.  I don't =
know the electronics required to drive and read an LVDT off the top of =
my head, but I do know they don't have the drift and linearity problems =
of other sensors (available in the late sixties).

I popped the top off the computer once and found nothing but transistors =
and passive components (there may have been an op-amp in a TO-5 package =
too).  There were a number of resistors mounted on standoffs, apparently =
you calibrated by changing these parts.  Based on components I saw I =
would say it was equivalent to the recent 555 circuit with some =
additional inputs.  A one-shot triggered by the distributor whose period =
was controlled through some analog sensors.

The fuel injectors (one per port) looked just like the ones on my 1986 =
Mustang.  The big difference is the old Bosch injectors used a short =
hose to connect to the fuel rail.

Chris Rhodin
chris at notav8.com

----------
From: 	mrvette
Sent: 	Wednesday, July 08, 1998 16:29
To: 	diy_efi at efi332.eng.ohio-state.edu
Subject: 	Re: What SU stands for

just how complicated was this analogue computer?  what inputs did it =
use?  was
it based on silicon technology?  use chips?   what is an LVDT?  same as =
a MAP
sensor? did it have fuel injecters like what we see today?  GENE

Chris Rhodin wrote:
>=20
> My 1972 Renault R-17 had Bosch D-Jetronic fuel injection in it.  This =
was an all electronic (with the exception of the thermo-time switch) =
system that I've seen in VWs from the late-sixties.  It used an LVDT to =
measure the manifold pressure and an analog computer to set the pulse =
width, the distributor had an extra set of contacts that provided timing =
information to the computer.  By the mid-seventies Bosch had moved away =
from the electronic systems in favor of the mechanical CIS systems.
>=20
> As far as I know this is the earliest all electronic FI produced in =
volume (emphasis on volume).
>=20
> Chris
>=20


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