CVT, regenerative braking and....

[My2cents]

......driving in the mountains. When descending a mountain do you "downshift" the CVT, use the brakes (regenerative braking) or a combination of both?

[rjent]

Use "L" as much as possible. Low give you the maximum braking without friction as you can get. Just remember, it doesn't take long to recharge a hybrid's battery, so when the battery is charged back up, your engine will come on to brake with compression.

[mwr]

......driving in the mountains. When descending a mountain do you "downshift" the CVT, use the brakes (regenerative braking) or a combination of both?

If the battery isn't fully charged, i don't think it matters how you do it since applying the brakes (gently, not hard) wouldn't use the friction brakes but instead only regenerative. After the battery is fully charged, the only way I've found to brake with control over the speed is to set CC for a low speed and then regulate the speed with the accelerator. Seemed strange at first but I soon got the hang of it.

Edited March 25, 2016 by mwr

[md13ffhguy]

Use "L" as much as possible. Low give you the maximum braking without friction as you can get. Just remember, it doesn't take long to recharge a hybrid's battery, so when the battery is charged back up, your engine will come on to brake with compression.

Why not just engage the Grade Assist button?

[mwr]

Why not just engage the Grade Assist button?

I find I have no control over the "strength" of Grade Assist; it just does what it does which often isn't what I want.

[Barsoom]

I found that descent assist was useful on short steep hills, but on longer mountain range descents the HVB filled up and the engine began racing. I then switched it off and used regular braking. For the record, this was on HWY 17 across the Santa Cruz Mountains coming back into San Jose, CA.

[mwr]

I found that descent assist was useful on short steep hills, but on longer mountain range descents the HVB filled up and the engine began racing. I then switched it off and used regular braking. For the record, this was on HWY 17 across the Santa Cruz Mountains coming back into San Jose, CA.

That's exactly what happens with descent assist or using CC set to a low speed. But that "racing" engine provides engine braking, just as in conventional cars when using lower gears to provide engine braking. I prefer that to using friction brakes in downhill mountain driving.

[lolder]

Use the engine braking on long downhills. It doesn't hurt it and uses no fuel.

[aschulz261]

It is a little disconcerting listening to the engine screaming on a downhill, but as the above post states, it uses no fuel. it happens all the time here coming down the mountain. i usually turn on the AC to max cold and turn on the the rear defrost to "burn off" as much electricity as i can.

 

it does seem counter productive seeing 2000 rpm on the uphill segment and 4000 on the downhill segment, but i see ~20mpg going up and infinite coming down.

Edited March 30, 2016 by aschulz261

[Griswald]

Use the engine braking on long downhills. It doesn't hurt it and uses no fuel.

Any time the engine is running, it is burning fuel.

[Waldo]

Any time the engine is running, it is burning fuel.

 

That was true about 30 years ago, but not any more.

[lolder]

When the HVB becomes full going down a long hill, the transmission automatically uses the ICE for "compression" braking. It uses no fuel in this manner. It's a very clever way of avoiding mechanical brake use. Trucks use it all the time.

[Griswald]

That was true about 30 years ago, but not any more.

Ohhh, so you have a 1986 hybrid? Funny, but my fathers 2016 Subaru is running during engine breaking and thus using fuel. But its not 30 years old, so...

[Texasota]

Ohhh, so you have a 1986 hybrid? Funny, but my fathers 2016 Subaru is running during engine breaking and thus using fuel. But its not 30 years old, so...

What these guys are saying is true and maybe the term "running" is misleading in this case. The crankshaft of the ICE is turning and the pistons are going up and down but no fuel is being injected into the cylinders and no combustion is occurring. The ICE is simply being used as an air compressor resulting in a braking effect when going down hill. This is not peculiar to only hybrids. My Ford Focus had the same capability.

[md13ffhguy]

Any time the engine is running, it is burning fuel.

I think what was meant about Grade Assist operation, was that the engine is engaged or turning, not necessarily "running," per se. While the sound it makes might be disconcerting, I believe it to be normal for this car. Of course, my passengers always think there's something going wrong... Edited March 31, 2016 by md13ffhguy

[Waldo]

Ohhh, so you have a 1986 hybrid? Funny, but my fathers 2016 Subaru is running during engine breaking and thus using fuel. But its not 30 years old, so...

 

As Texasota mentioned, just because the engine is spinning does not mean the fuel injectors are opening. It's called Decel Fuel Shut-off and fuel injected engines have been using it for about 30 years. Here are some links confirming that Subaru has been using it for a while:

 

http://www.subaruforester.org/vbulletin/f107/deceleration-fuel-cutoff-58243/

 

http://forums.nasioc.com/forums/showthread.php?t=2184765

 

 

BTW if your father's Subaru engine is breaking, he has bigger things to worry about than the fuel consumption ;)

[My2cents]

Thanks for all the responses. Looks like the grade assist button does the job. Also found this on a CMAX website:

 

http://fordcmaxenergiforum.com/topic/1305-grade-assist-discussion/

[mwr]

My issue withthe grade assist is that we have no control over it, meaning no control over the speed of the car as it goes downhill. It just does what it does.

[aschulz261]

For me, the grade assist attempts to maintain the speed that the car was at when the deceleration started. If you let off the throttle at 60 mph, it tries to maintain 60. If you let off the throttle at 30 mph, it tries to maintain 30. There isn't anything to set or adjust, just let off the throttle and it will try to maintain the speed you were just doing.

 

There is a limit to the grade assit though. If you exceed the amount of energy the generator is capable of putting back in the battery OR the battery becomes full, the engine braking will take over.

 

Decel Fuel Cut Off is one of the many reasons fuel injected engines get better fuel economy than a carburetor. It is a specific mode of operation that relies on various parameters to be in play. Engine load, rpm, vehicle speed, manifold vacuum, and throttle position. Low engine load, high manifold vacuum, low throttle position means a the vehicle is decelerating and it shuts off the fuel and just lets the engine spin.

[My2cents]

Found this informative video from Ford: https://m.youtube.com/watch?v=k2_bk8ZO53E