Re: [DML] Automaitc Transmission Shifting

[mike.griese@xxxxxxxxxxxxxxxx]

You want to shift just past the point where the car makes maximum
horsepower.  This is usually several hundred rpm before redline.  
Shifting at 2500 rpm is considered to be a short-shift.  When I'm
pushing my car, I tend to shift around 5800 rpm.  

Automatic transmissions are different in that you have a torque 
converter between the flywheel and gearbox.  Instead of a 
mechanically actuated clutch to disconnect the gearbox from 
the engine when you shift, you have a fluid coupling that matches
the engine rpm with the rpm of the input shaft of the gearbox.
There are shift characteristics specific to the converter - stuff like 
stall speed, etc. that are dependent on the way the converter is 
designed, the shear characteristics of the automatic transmission 
fluid, the clutch bands, etc.  The shift quality of an automatic 
tends to lean toward smooth shifts rather than maximum acceleration,
so the parameters of the components are selected for that rather 
than high rpm shifts.  A practiced driver with good mechanical 
sensitivity can shift quickly and smoothly at high rpm.  Basically, 
this means you really can't choose the same rpm as a shift point as 
a manual transmission, and I'm not sure if there is enough 
information available about the torque converter to determine
an upper rpm limit for a shift point.

--
Mike


-------------- Original message from "Steve" <p2freak@xxxxxxxxx>: -------------- 


> Group, 
> 
> Want to pick your brains here, especially the mechanical types. 
> 
> Suppose I have a field programmable transmission governor/computer. 
> Goal: Want to get max acceleration (0-60 mph). 
> 
> What shift points do I set the computer to up shift? 2500 engine RPM, 
> 2100 RPM? Do I need to look at the RPM torque graph to figure this out? 
> 
> On my Toyota automatic transmission, the shift point seems to be 
> around 2500 to 3000 RPM. How is it that with stick shift, the driver 
> red lines engine before shifting (at least in Hollywood movies anyway)? 
> 
> Thanks a bunch. 
> 
> 
> Steve 
> VIN#04421 

[Non-text portions of this message have been removed]



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