A mess of wires? Don't worry, it's a prototype for
development use only!
As most of you already
realize, our transmission (known as a 4T65e) is electronically controlled by the engine /
transmission computer (PCM - Powertrain Control Module). Shift points, TCC (Torque
Convertor Clutch) lockup, and line pressure are all controlled by the PCM programming.
Fortunately, the factory engineers gave us a choice of a normal shift pattern
and performance shift mode for slightly firmer shifts and more aggressive shift pattern.
This is good, but we've always felt the performance mode didn't quite go far enough
- when we want a firm shift, we want it to hit HARD!
Over the
winter ('98), we've been working on this and determining the best and most
cost effective way to address these issues. We've concluded that there is no easy
way to modify the shift points or shift schedules / patterns, and modifying TCC lockup is
not as simple as it was in previous years due to the introduction of the ECCC
(Electronically Controlled Clutch Capacity) system, where the pressure plate does not
fully lock to the torque convertor cover.
Instead, a special material
is used in the clutch lining that allows a small amount of slippage to constantly occur,
allowing the TCC to be ramped in and out slowly, reducing driveline torsional disturbances
and eliminating TCC shudder or chuggle, two common complaints in the past. However,
it may be possible to increase line pressure to give much firmer shifts!
Shown above is a prototype device that we've been experimenting with to
achieve this goal. No special tools are required for installation and the
transmission is not opened or modified in any way. This device simply plugs into the
existing transmission harness - the harness plug on the transmission end is shown in the
photo to the left. Obviously, this is one of our test units on a bench outside the
vehicle - mounted in the engine compartment this plug is immediately below the throttle
body.
Installation is simply a
matter of unplugging the transmission harness from the transmission, plugging the device
into the transmission, and connecting the harness into the device. The device
interfaces with internal force motors to increase line pressure, thus firming up the
shifts.
So, the question is, how well does it
work? Well, frankly, we're not very happy with this device in its present design and
feel there's still work to be done before we're satisfied. This prototype unit was
intended to vary the TCC application timing as well as regulate line pressure, and in our
opinion, it did not interface well with the new ECCC style clutch, giving very annoying
TCC oscillations. In fact, it was so bad that the wife refused to let us keep the
unit connected as long as she was in the car! After studying the system we
determined it was not feasible to modify the TCC aspects in this manner, so we disabled
this part of the device.
With the TCC modification
circuits disabled, and with only the line pressure circuits active, the device
a bit more driveable and does give a noticeable improvement in shift firmness at part throttle!
Unfortunately, it's really only at WOT (Wide Open Throttle) where we desire a hard
shift, and this unit is still not living up to our expectations at WOT. In fact,
we've requested the option to have a throttle switch input available on the next design
release to only activate under WOT conditions, as the extremely firm part throttle shifts
are getting on the wife's nerves, and frankly, once the novelty wore off, we're finding it
a bit annoying too. So, we still have more work to do, but we expect to have a
satisfactory device soon. We're still consulting with the manufacturer about these
issues and hope they will be able to meet our requirements.
Note that our prototype units have a mess of long wires. Be assured
this is to ease development work only - pictured at left is a typical clean production
unit.
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