xclream

Yesterday as I was coming down a mountain, I have noticed that my car refused to go into EV mode when I try to activate it. The battery indicator was full, and speed was below the required limit. I am not sure why that is, perhaps due to safety, such as the need for engine brake so brakes don't overheat. Engine would stay on most of the time, and occasionally go into EV mode and then engine would start again for no apparently reason (as stated earlier, battery indicator was at full).

It was a very steep, long stretch of road coming down, I think I could have achieve virtually zero-consumption of gas & great mileage if I could have activated the car into EV mode.

Any clues?

jim256

I've always gotten a beep and a message telling me why it would not activate EV (speed, low battery, etc.)--the engine will run to keep the radiator water temp and the catalytic converter at optimal, but other than that you should be able to get EV as long as the speed never gets above 25. However long descents and full battery can cause the engine to run to generate a kind of traditional engine braking. Regenerative braking can't help because the battery is already fully charged. A good discussion here, might help find the answer (Prius Chat) :http://priuschat.com/threads/high-en...wnhill.149421/

TechNut

I know from the Priuses that we have owned that the car has to keep the internal combustion engine at a certain operating temperature. It would start the engine every so often, or after shutting the car off for a bit at the market. I wonder if that is what you are running up against? We haven't had this hybrid on an incline like you described yet so I don't have any personal experience, but I have learned that Toyota hybrids are programmed to do what they need to do so I would be fairly confident there is a reason.

PirelliRC

think of it this way, our hybrid ES does not have a transmission and essentially no gears, like you would find in a combustion engine. It is a CVT. If you were going down an incline, most petrol vehicles will downshift to increase engine braking in order for you to not be on the brakes the whole time. So the reason the system turns on the engine is to take advantage of engine braking. Brake fade is a big safety concern so they must do this. And you are still getting terrific MPG at this point so i wouldnt sweat it too much.

chromedome

The HSD/LHD system has all power sources going through a planetary gear set. I don't think there are any clutches which allow the engine to completely disengage from the system, unlike Honda's setup.

At high speed, MG1 spins backwards to generate electricity and it has an rpm limit, hence the low 112 mph speed limit on the ES. If there's too much charge coming from MG2 through coasting or regen braking, as when going down a steep hill, MG1 spins up the engine to get rid of that excess charge.

Think of the engine as a heat sink in the system. The engine is mechanically spun up and it provides resistance through engine braking, but fuel consumption is minimal with the injectors closed most of the time. It might feel weird compared to normal cars. You can't decouple both MG2 and the engine or you'd have the car coasting down in neutral, with only friction brakes to slow you down.

jollick

Here is a demonstration of the Toyota Hybrid System, a good 30 minute tutorial. Weber State University (WSU) - Automotive Technology Department - Transmission Lab. A comparison and demonstration of the 3rd Generation Toyota Hybrid Transaxles used in the 2010-2013 Prius family (P410, P510), 2006 - 2013 Highlander HV family (P310, P313), and 2007-2012 Camry HV family (P311, P314)


There is a clutch disc plate. A very interesting video.

lamikela1

Actually the ES350 does the same thing on steep downhills. It took me by surprise the first time mine did this as I did not expect it. I only noticed this while in EVO mode and not in Normal or Sport. Also only while using the cruise control. If the car could not maintain the correct set speed it would downshift and go to a lower gear to slow down. Once it reached the set speed again it upshifted and resumed normal operation. I could never duplicate this in the other modes.

SLH

Over a period of many years, many thousands of drivers have crashed their cars (and thousands have died) by going downhill badly. Most thought that their brakes could keep them at a safe speed all the way down the mountain. But mechanical brakes heat up when they are used, and they fail when they get too hot. Driving schools and experience drivers teach us to use use "engine braking" on long/steep downhill runs, to save the brakes....

The new hybrid cars first use the regeneration to fill the battery. Then they warm up the brakes a little. But finally, they use engine braking, by putting the transmission into a configuration where the motion of the wheels turns the engine. The smart computers on these new cars do this for us, instead of depending on drivers to be educated or experienced enough.

I pray that you never experience brake failure while going down a mountain. It is one of the least pleasurable of all possible driving experiences.

FiOSDave

Does the emergency brake help, in any situation?

Mike728

It's called a "parking" brake, so it only helps when the car is parked.

Arty101

The parking brake will work but only for short distances and slow. The lining isn't meant for anything long or fast. I'd use engine braking and then the emergency parking brake if your brakes fail. The brakes from an older pool car failured on me once on a fairly steep hill, and engine braking and the parking brakes managed to stop the car. As SLH says, thank goodness it wasn't the mountains.

mcomer

The Parking Brake is a very light duty drum style brake built inside the rear disc brake rotor. As brake fade and failure is related to the heat created by the friction of continued brake application by the disc calipers, this will be affected as well. Better than Fred Flintstone draggin' his feet but the name says it all, holds the cars weight while parking to eliminate the burden on the parking pawl in the transmission that engages when in "Park".
While on the ES it is still activated with a foot pedal, the new NX follows the design of the GS and LS by reducing the operation to a button. So much for Rockford type "handbrake turns"!!

FiOSDave

I used to do that quite often when driving my 1964 MG Midget in Gymkhanas! Back in those days, it was called an emergency brake!
Of course, the Midget was so light, it would stop it rather quickly!


And thank you to all who responded!


Dave

Arty101

I also think back in the day, people use to use their hand brakes to cause the rear wheels to cut loose and cause oversteer for some 'excitement'.