Obviously intended for Mark Kovalsky… But I thought everyone else might share my curiosity.

When the light turns green and I mash the gas pedal to the floor with my 415 cu inch V10, I have a (slight) understanding that the transmission oil pump provides hydraulic pressure which mechanically squeezes the bands/clutches to apply the torque… Correct so far?

Anyway my question is about shifting – Regarding that split-second moment between gears – where does all of that engine power go? Does the computer magically release the throttle for me for that moment?

On a manual transmission vehicle, obviously we lift off the gas and then reapply after shift.

Mark, after you answer, I want to ask you if your answer is different when comparing the throttle-by-wire system compared to standard older vehicle that has a throttle cable. Thanks in advance!

 

Interesting question...

I bet the short answer is the power goes to heat.

 

It's my understanding that there's always some "overlap" in gear changes where the current gear and the next are applying or releasing. Many of the shift reprogramming kits shorten that overlap for a "sportier experience".

 

Correct. Except that bands are pretty much a thing of the past. It's pretty much all clutches now.

An automatic is different. It is never between gears. All gears are in mesh at all times. Different clutches apply and release to hold different parts of the planetary gearset to create different ratios.

Up until the 90's there was no mechanism to lower engine torque during the shift. The engine just continued to do what it was doing, and the transmission pulled the engine speed down due to the added load of the next higher gear.

In the 90's software was developed that retarded the engine spark during a portion of the shift. This reduced the torque the engine produced, making it easier for the transmission to pull the engine speed down. A side benefit is that the shift times came down (this is the time that the clutches slip during a shift. Even on manual transmissions you slip the clutch when launching.) This made the shifts feel faster and crisper, without adding any harsh feel. Those of us who's job performance was based mostly on how shifts felt LOVED this new software! People thought I was a genius. I wasn't, I didn't invent this, I just followed directions on how to make it work. And it sure worked!

Not when I want to go fast I don't! My right foot stays planted on the floor, the left kicks the clutch pedal to the floor and releases, while the right hand moves the shifter as fast as it can. I haven't done much of that since I was MUCH younger and had a '73 Montego GT with a 351CJ and a Toploader four speed.

It has changed with drive by wire. Now the throttle plate opening can be reduced as well as retarding spark. There was no way to control the throttle plate during a shift with a cable system.

 

Very very interesting.

The part that intrigued me most was regarding the milliseconds of clutch slippage. (And the fact that bands aren't used any more). So there is some "waste" during "gear changes". By your descriptions it seems infantecimal (sp?)

 

Infinitesimal according to my dictionary. Not that I can spell it, either.

Typical shift times had always been about 500 milliseconds. Not all of that was slip time, this was from commanding the shift until the ratio change was completed. This took into account time for the solenoid armature to move, pressure to reach the shift valve, time for the shift valve to move, time for pressure to reach the clutch, time for the clutch to stroke, and THEN the slip time started.

With good design, and eliminating shift valves, the 5R110W had a 400 millisecond shift time.

There will always be waste during a shift. As a clutch applies there is slippage for a short duration. This creates heat, and heat only is created in a transmission from waste energy.

Reducing the engine torque during a shift reduces the energy waste during a shift. A byproduct of this strategy is that clutches last longer. I don't think that was anticipated by the people that developed this strategy. Those of us in Transmission Engineering saw that as the main benefit, the shift quality improvement was an added bonus.