Automatic Engine Braking (with an auto trans)

[LesGrandsPieds]

I'm intrested in engine braking. I watched this little flash thing Honda has about their new cars where they automatically sense acceleration when you aren't pressing on the gas and automatically downshift to keep your speed constant. This ends up helping you maintain a constant speed down hills. I thought it was pretty interesting. It's called Grade Logic Control, watch it for yourself, it's pretty cool. You might have to press the play button.

I think my sister's Toyota might have a feature very similar to this.

Has anyone else noted this technology in other cars? Which ones? And does this technology cause a downshift when the brakes are applied?

Seems like automatic engine braking in an car with an automatic transmission could easily be implemented with some good programming. It also seems like it would be idea for engines with VVT, since adjusting the timing of the valves can increase or decrease the engine's drag.

[alkemist]

I never heard about this on full auto trannys

But you can make the car brake for itself in cruise mode or if you have tiptronic you would lower the gear yourself.

[BlueFusion6851]

Some cars do a downshift when you are close to completely stopping. If I want to slow down or maintain speed I just slap my gear selecter into 3 or 2.

[beyondloadedSE]

The Ford Fusion im leasing does this.

[curtis73]

Auto trannys DO have engine braking, just not as much as a manual because the Torque converter works best in the forward direction. The grade logic control simply increases the engine braking by selecting a lower gear which raises RPMs and has a more favorable torque ratio.

The same thing can be done with any automatic by just dropping it down a gear. It may stress a transmission that was not designed with all that downshifting in mind, but no transmission should die from a few downshifts.

I also have to think that the main reason for things like grade logic control in small cars is to save brakes. Well, brake pads cost $15 per set. A tranny rebuild costs about $1500. Thanks, I'll continue to brake going downhill.

Grade logic control is a great addition to heavier trucks that do a lot of towing. In that case there are possibilities that brakes could overheat and fade making a runaway truck with 15,000 lbs behind it.

[drdisque]

part of it is if you are on an extreme slope and stab the brakes and say hit a rock or something, you could easily flip over, that won't happen if your car slows you down enough that you won't have to stab the brake.

[stick99]

From the looks of the video, it seems like Honda is taking care of all the guess work of driving up and down hills. For people who understand cars and know how to drive well, they will naturally downshift (turn the overdrive off for auto trannies) in order to have to power to make it up a hill. Honda has programed the computers automaticly turn off overdrive when needed. As for downhill downshifting, there are arguements saying it's both good and bad. Honda seems to think its good and has programed the computers to do it for you.

[boarder_punk]

Most auto trannys use a seperate band internally so that the driver can manually choose gears, thus the 3 2 1 markings on your gear selector. This band generally has the same thickness (although it may have a smaller surface area) of friction material as the normal forward band, and in most trannys is designed for engine braking. Also, when this band is applied it should be holding completely, not slipping, so also not wearing its friction surface; when brakes are applied they slip (unless the wheels are locked up), so they wear more quickly than they would if they didn't slip.