I've always downshifted all my vehicles for the braking effect.
My pet refernce about this was that I never used my brakes
except to stop. This includes all I've driven with automatic transmissions.
Never had any transmission problems. Haven't read anything in the HCH-II
manuals about downshifting. Other vehicles I've driven listed the maximum
RPM's or maximum speed for shifting down to a given gear.

Can this be a positive for FE in certain situations?

How about the effects on the CVT?

Ken

 

As per my own experience, the only time downshifting on HCH-II has a measurable benefit is during extreme cold weather. Especially when the regenerative brakes do not work while the car is cold. By downshifting we can had a substancial charge to the battery pack which otherwise would be wasted.

While managing the State of Charge during the summer is a necessity for great FE, the extreme winter poses several special challenges in addition to the already bad fuel economy. The greatest is the battery management always wanting to always keep the battery fully charged. If we don't help it then the engine is going to be diverting load more frequently to the charge process making the FE even worse.

Anyhow, downshifting our CVT's is not considered a bad thing at all when done smoothly and within reason. Violent and stressful downshifts are definitely not good in the long run as it can lead to accellerated wear of the CVT belt & the forward clutch.
I personally avoid doing it as frequently as I did in a vehicle with a manual transmission. Instead I do it solely when the regen braking is not working.

Cheers;

MSantos

 

I do it at times. I've never had an auto shift down at a speed that would over-rev the engine. It's programmed in, even in the old cars, by means of hydralic pressure schemes. The CVT doesn't hold back all that good though

 

My advice is...don't do it!

The only reason that you would use "downshifting" to slow down would be to conserve your brakes.

Fair enough except...in the HCH-II stage one of braking is performed by the electric motor acting as generator ie. it's a brake! Heavier braking will bring in the mechanical brakes.

So you already have a way of braking without using your mechanical brakes AND...it puts power back into the battery pack.

So don't waste all that kenetic energy. That's the whole idea of a Hybrid after all!

 

I downshift at opportune times. For instance, if I come over a hill and there is a stop light at the bottom - the light has just turned green, but there is a line of cars waiting to get started. I like to downshift in those conditions, because the car seems to slow more smoothly and quickly than with the brakes. I also seem to get more regen out of the downshift than I do with the brakes, as metioned earlier. If I'm approaching the last car in line and it hasn't started to move yet, I'll of course apply the brakes, but I'll also leave the car in 'S' and ease it in. That way, if I happen to get below 7 mph before the car in front of me gets going, I don't have to worry about an autostop, followed by a jerky start (and less FE, since the stop will be less than 6 seconds). As soon as the last car in line is moving, I'll shift back to 'D' and accellerate.

I'll also downshift at times if I'm taking a corner a little fast in an effort to conserve momentum. The downshift does, of course, slow me down more, but it gives me a much better control around the corner. As I come out of the turn I'll upshift and accellerate.

I also have been using MSANTOS' suggestion of downshifting when the engine is cold for better SOC management. Don't know exactly why it regens in S when it won't in D, but I just report 'em, I don't explain 'em.

 

If you want to have a positive effect on your MPG avoid getting up to a speed you have to brake from.

The best hybrids can only recover 30% of the kinetic energy.
That means you waste 70% of it.

If you avoid braking your waste 0% of it.

 

Hi toast64 (Bill),

I agree with you 100% right down to the way you take corners.
I've been doing it that way for 58 years w/o the hybrid incentive.
Driving a hybrid just makes it that much more fun ... immediately seeing the result it produces on the dashboard display.

In regard to downshifting when it is cold, I suspect the software is programmed to
prevent regen until a certain temperature is reached. The increase in RPM's must be
enough to override this provision. I would also think that the amount of regen would increase due to the increase in RPM's whenever this occurs, whether hot or cold. This
is only my best guess - perhaps someone else has another idea on this?

Galileo

 

OK, what's better then: light regen braking with the pedal and the tranny in "D" on long hills or putting it in "S" and letting the CVT do the braking?

Antictodally, I would say that putting it in "S" builds charge faster. However, (as I noticed for the first time yesterday) "S" doesn't do a ****ed thing when your battery is full. I was on a ~1000 foot vertical downhill canyon carver with speeds in the 20mph range and got about half way down before "S" stopped slowing me down. At that point, I had to use the real brakes to keep my speed in check because I wasn't getting any regen with the brake pedal either (obviously).

 

That is a good point.

That is a characteristic of the system that I always thought could be better documented in the user's manual. As some of us already know, the regen system will simply dis-engage for any of the following reasons:
-to avoid a temperature build-up in the stator motor
-manage charge delivery to a cold battery pack
-manage charge delivery to a hot battery pack
-avoid overcharging a battery pack
-system's operational fault or discrepancy

Obviously, while going downhill for a while you triggered at least one of these conditions. Yes, it could have been the 4th condition but it could also have been the 1st.

Since the regen system is inherently dynamic this means that we cannot
depend on it as a primary source of forward braking. Also, because of its design the system cannot simply discard the generated energy and must widthdraw its influence altogether. Clearly, it can be dangerous if we depend on it regularly for braking as it may cut off un-expectadely.

As most will agree, we should use primarily the brake pedal for braking power - at least as a best practice, if not for safety reasons.


Cheers;

MSantos

 

I don't think it's a good idea to downshift to S when the engine and batteries are cold. You don't get any regen right after a cold start because the HCH is programmed not to overload the batteries in such conditions. Forcing regen probably shortens the battery life.

When you take your foot off the gas pedal the engine quickly goes into valves-shut mode which keeps engine drag to a minimum. Even in S gear, engine drag is very small when the valves are shut off. So if your SOC is full, shifting down won't give much engine braking power.

What S gear does when the SOC isn't full is induce a more aggressive regen to simulate engine braking. You can get pretty much the same effect by pressing your foot on the brake pedal just enough to get eight green bars of regen. I use S anyway sometimes when going downhill, for covenience, to avoid holding my foot on the brake. But I don't believe it has any extra regen benefit.