anyone knows what is THE BIG SCIENCE behind HSD cutting off at 42mph? well, not completely, but ICE kicks in.

i am really curious, why do we have to lose all the idling ICE gas $$, when we are simply rolling down the frway or hill? what is it that just MUST HAVE ICE ON to roll at speeds over 42mph? doing nothing but wasting idle gas?

esp here, in Pacific NW, where we have abundance of long downhills that are just screaming to roll down with no engine.

why, or why??

 

I also live in PNW (Seattle). When I go >40mph on a downhill, the ICE on my Camry shuts off. Are you on "B" mode when you go downhill? If you are on "D", the ICE should shut off unless one of these are true: the ICE hasn't warmed up yet; the SOC is low; your heater/AC is on and not in "ECO" mode and the temp setting is more than 10 degrees different from the ambient temps; or you're on "B" mode.

 

The ICE starts turning at 42 MPH to prevent the MG (the one controlling the HSD) from going over it's rpm limit. The gas supply is shut off when you don't need power so stop worrying.

JeffD

 

falls along my further observation lines today.
i turned display from consumption to energy. it appears that engine does not operate when in "free roll" mode. mpg gauge handle sits at 60mpg.

interesting.

kinda screwy in my situation, as my speedometer is 4 miles off and that 42 mph limit is, actually, 38. yet, she still bumps out of E mode at 42 on speedo.

well, as far as that engine is REALLY off and NOT USING GAS FOR IDLING, i'll do just that - stop worrying.

btw, he-he, rolling down the hill in N shows much better overall mpg on consumption display, than rolling in D mode.

gods, I am missing tachometer in this car!!

thanks, guys!!

 

OK, here's the science:

However, from equation 1 in The Power Split Device, we know that MG1 spins backwards 2.6 times faster than the ring gear and MG2 spin forwards. This situation isn't safe when the car is travelling at high speed. At 42 m.p.h. and above, keeping the planet carrier still would result in MG1 spinning backwards at more that 6500 r.p.m. So that this doesn't happen, the computer configures MG1 as a generator and begins to draw off power. The generator drag created prevents MG1 from overspinning and instead the planet carrier begins to turn forwards. By spinning the planet carrier and the ICE at 1000 r.p.m., MG1 is protected at speeds of up to 65 m.p.h. At higher speeds, the planet carrier and ICE must spin faster. The electrical power produced by MG1 in this process can be used to charge the battery.

 

well, i had my scangauge finally hooked up to TCH.

it may be different with longer drives, but as of 1.5 mile to my son's house and back, even though energy screen shows that ICE is off, and mpg gauge flattens at 60mpg, engine still works. anywhere between 1200 to over 600 rpms. I humbly do not believe that this is possible with gas supply shut off to the engine.

now, like i said - this was 2 short trips today. it may be different after longer drive and thorough warm up.

i'll report tomorrow, as i take to work.

 

The two electric motors working together will keep the ICE spinning. Even with no fuel being injected. This usually happens at higher speeds when coasting.

Whenever the ICE is stopped and needs to start, the two motors spin the ICE up from 0 to "idle" speed, then inject fuel. Much smoother than a "normal" car...

 

no, i understand that. it is quite weird. looking at the energy monitor, with engine appearing to be shut off, rpms stay up. all at a sudden, without any change in speed or else, rpms will go to 0, which is - car is rolling, but engine is not spinning. or working.

like i said, i am not jumping to any conclusions. it needs to be warmed up well. also, i am curious, how does it know rpms? probably off one of the sensors, but which one?

if the motors engage ICE and cause rpms to show, then rpms should go up as car rolls down the hill, right? quite opposite was observed, rpms rightfully go down, as it logically should, as load on engine(working off gas) reduces, right?

ok, let me do a few days of driving around with scangauge connected to it. before we get into any deep discussions on this. not many here have a tool allowing to monitor a lot of information otherwise not available, so let me do some snooping.

 

Get a ScanGuage (A $160 OBD2 scanner with a real-time display). It will display RPM as well as three other parameters (out of many choices) while driving.

JeffD

 

jeffd, you read my last 2 posts, didn't you?