Disable Regeneration

Put your Prius in neutral, but not over 42 MPH in a gen 2 (risk over reving the HSD). The neutral limit in a Gen3 is a bit faster.

JeffD

 

So for your situation, mikesR, no. 73 MPH is too fast to risk shifting to neutral. Practice feathering the accelerator or live with it.

 

Just lift your foot off the gas and let the car slow itself down, and charge the HV battery! I have the same situation, it's about a 5 mile downhill slope that I basically run for free! Now, up the hill sucks!, but I still manage a 48 MPG tank! If I were more of a flatlander, my numbers would be higher. You could also drop it in to "B" Mode, that will help slow you down!
At the bottom of the hill, my HV battery is usually Green! Embrace the Regen, it is your friend!

 

Are the down hills over charging your HV battery? Hybrids are the only cars that can turn gravity into free energy. Why would you wanna disable it? Going down the grapevine, my HV battery would be fully charged 1/3 way down the hill. After I got to the bottom of the hill, I can milk that regenned electricity for about 3 miles before the ICE supplying power to the wheel. When the HV battery is full, you'll get above average mileage in the 60's, even at highway speed. If the HV battery is low, you'll get way below average mileage in the 30's and low 40's

 

Wait, can you really hurt the HSD system by shifting into neutral at speeds over 42mph?

I've done it before at speeds of 80mph going down a hill! D: Oh lord.

I thought the system would do what it had to do to keep the motor / generators happy but wouldn't let any power go to the wheels?

 

I use my right foot to disable regen.

 

Huh? I have always understood that if the car is already above the transition limit (42 mph for Gen2, 46 for Gen3), then the engine is already spinning and will protect the HSD. So shifting at 73 should be fine.

The known risk mechanism is shifting to neutral below this transition speed when the ICE is not spinning, then allowing the car to roll downhill to a speed significantly above this transition speed. MG1 could overspeed because, in neutral, the ECU cannot spin up the ICE to protect it.

During the runaway Toyota fiasco, Sikes was advised by 911 dispatch to shift to neutral while his car was flying at 80-90 mph, a move he refused to perform. And we agreed here that such a shift would be correct in a true runaway. And I tried it myself numerous times at regular highway speed.

Am I misremembering or misinterpreting something here?

 

No, you can't. The risk comes from shifting to N while the ICE is stationary, and then accelerating to speeds above 42 mph. It's not a likely scenario, since you need a really big hill, but it is possible.

At speeds above the transition speed (around 42 mph), the ICE is already spinning, so it keeps spinning. At speeds below the transition, the ICE might not be spinning. If it isn't spinning, it can't start in N, so it can't protect MG1 from overspeed if you accelerate down a big hill.

Tom

 

Shifting into "N" above 42 MPG will cause the engine to idle (receive fuel injection), so it might actually hurt fuel economy.

Feathering the accelerator to achieve full glide (no arrows) is difficult above 42 MPH, since the ICE is always spinning anyway, but it can be done.

 

On HSD only "true" regen at lower speeds "my" understanding. I am unsure "why" any1 would "shift" or "drop" into different cvt transmission gear while in drive(forward motion) at "high" speed.

Use "B" for descending hill, moutain,and incline....

I "trust" my defensive driving and brakes so if you are driving next to me and I see you lose control I now know why..........if you go high speed gear change...

If your doing 65+mph you may not be so concerned about "prius" performance or "mpg" and more worried about law enforcement and local speed limits...... "73"mph??

 

On down hill what does your SG2 SOC% read?

 

At the bottom of the hill, or slightly there after, the MFD battery goes Full Green! The Scan Gauge reported SOC at 82%....

 

Regen works at all speeds. I'm not sure what you mean by "true" regen. You seem to like scare quotes.

But only if the hill is long and steep enough to charge the HV battery to the high limit before reaching the bottom.

It's okay to use B in other situations, but it will generally hurt mileage.

This is just a tad bit alarmist. The Prius never really changes gears, and it never really shifts into Neutral. Shifting gears in the Prius is not a control risk, other than taking one hand from the steering wheel.

Once again, a bit over the top. The maximum posted speed limit in many states is 75 mph.

Tom

 

That is negative for this state 70mph limit......daytime only and with "rush" hour lucky to see 50mph
Oh and you may want to read up on "regen" a tad

 

I agree, this is quite annoying.

*goes back to lurking*

 

Since I have a commute that consists of a long steep grade and high speeds I think I can answer this easily.

To reduce the drag of regen simply lift off the throttle completely then reapply slight pressure on the throttle until the arrows on the MFD switch to show energy going from the motors to the wheels and nothing coming from the engine. You will use a little energy from the HV battery to maintain this state but you can coast/glide much further this way than you would be able to do if regen was engaged. In this state your are getting infinite mpg (9999 on the Scangauge). Since you are using a little HV it's not a perfectly free lunch but it's close.

You want your screen to look like this when gliding above 42mph. Thanks to sandman for the pic.


At some point you may run SOC down to 57.5% or less and at which point the engine will turn on to recharge the HV battery and bring SOC back above 57.5%. At this point mpg will drop to 150mpg or so assuming you are still just coasting with little throttle applied. You can either stay in this mode or shift into neutral if the hill is long enough to still benefit from a longer glide. In neutral you will not be able to regen and SOC will continue to drop albeit slowly BUT your mpg will be in the 300s instead of 125-150. I generally only use neutral glides for short periods on my commute and even then only occasionally. As qbee42 stated above, you are not going to hurt the car by shifting to neutral at high speeds.

 

I'll get right on that.



Tom

 

In many areas of the country that have large hills/mountains with highways on them, 70mph+ is not an uncommon speed to travel. Prius mpg performance is enhanced if one allows the car to accelerate as fast as the slope will carry them rather than use regen, engine braking (B mode), or brakes to slow them down. It's simple physics really. The further one can travel with the engine off (using zero fuel) and propelled by kinetic energy the better mpg one will achieve.

My commute has just such a hill. I've had years to toy with different techniques for max mpg while traveling downhill.

Multiply elevation by 10. 1,200ft ASL. Total distance approx. 47miles