i find myself using this more often, for various reasons. i like the driving dynamic of downshifting and it seems to recharge as well as braking. but i'm worried about the stress it might be putting one the cvt. downshifting an auto tranny will ruin them - i know first hand from my vw. so i'm wondering if there is a 'safe' speed for using brake assist? i get no answers from the dealership, but then again, they seem to know little about anything.

 

I run my FEH in "L" all the time. I have been told that the functionality is regulated by software, in the eCVT of the FEH.

 

Pete,

The CVT in the synergy hybrid drive is a simple set of planetary gears that function similarly to the differential in a normal car. The use of the "B" setting when going down a long grade is unlikely to cause excessive wear or damage. It will cause your ICE to work harder so there is a downside there (but minimal). The largest negative is some lost MPG using the "B" option, so that's a reason to minimize its use.

JeffD

 

thks Jeff.
i would never accelerate while in 'B', but rather use it on downgrades and in slowing traffic in lieu of the brakes. the second i need throttle i just put it back into drive- so i think in this instance the ICE isn't working harder and there's no lost mpg. or do you mean it's working harder because of higher revs? the only stress, off throttle, would be to the gears as mentioned, which also has me a little confused. i've seen a planetary gearset on a 4 speed, so exactly how do they make a planetary system that lacks 'shifts'? non hybrid CVT's are belt driven correct?

 

Charles,

Yes the Civc CVT for example uses belts and variable diameter pulleys (I had a 1941 motorcycle that also had a belt driven CVT).

If you want to understand the HSD there is a neat simulation of one (For the older Prius). I have a copy of it at:

http://doctord.dyndns.org:8000/cours...sSimulator.jar

You will need a working Java Interpreter to run it. Get a free one from Sun at:

http://java.sun.com/j2se/1.4.2/download.html

JeffD

 

Can you explain this? I've read elsewhere that it is more fuel efficient to use "B" to slow down rather than the brakes because with the brakes you are losing energy due to heat dissipation from the brake friction. With "B", the energy is getting fed back into the battery.

hihybrid

 

We waste energy in may ways going down hill unless we are recapturing it to recharge the traction battery or allowing the vehicle to gain speed (kinetic energy storage).

If we slow the vehicle down either by using "B" or using the friction brakes (not a light touch as this regenerates energy and recharges the battery - until it is full), we generate heat which is usually waste energy (on a cold day the heat generated by spinning the ICE - pardon the pun - may help keep you, the ICE, and the catalytic warm).

JeffD

 

From all I've gathered about the HSD "B" mode is that it puts less juice back in to battery, using engine compression to slow u down on very steep downhills instead of the electric motors.

Said another way...as u go downhill the battery fills pretty good, up to the 'max' (on-screen it shows all green bars, in reality it's around 80%). So then the friction brakes are used, since the electric motors have no where to put the excess juice, thusly they are not slowing u anymore. So this is where u flick the gear selector into "B" mode and the engine is used to slow things down, instead of the friction brakes. Yet another way this car helps prolong a part (brake shoes)!

It controls the battery charge very tighly, it has a way to lessen brake shoe wear, it saves the air we breathe, it saves a depleting energy source...it's all good.

Love my Prius!

Curt.

 

My personal experience has been that driving in B has no efficiency benefit. It essentially means that your engine will be engaged when slowing down resulting in lower MPG. So if you are driving down a ramp in B, you are saving your brake pads a bit, but its like driving a regular vehicle. In D, your engines will be turned off, batteries will still get charged but you may have to occasionally engage the brakes to prevent acceleration.

The only time I would drive in B is when either the (off)road conditions are not good or if I am driving downhill (at a steep lncline) for several miles where I wouldn't want to overuse my brakes. Hope this helped.

 

My understanding is that when you shift to B, the ICE is turning over to slow the car (and charge the battery), but no fuel is being fed in, so it's not being burned. So it's not really like a regular vehicle. And coasting in D is no guarantee that the ICE has shut down. I often find that after coasting down a long exit ramp to a stop, that the ICE is still running when I stop. It gives me that oh-so-slight shutdown shudder after a few seconds of sitting still.

hihybrid