Turbocharged Hybrids

[redpoint5]

Originally Posted by Appletank

I'm pretty sure the car is doing that to prevent the battery from maxing out, via wasting energy by spinning the engine with electricity and warming air a bit. You shouldn't be using any fuel in those cases.

It uses fuel and runs the engine at least until reaching a coolant temperature of 130. The car could simply require more brake effort to mechanically waste speed into heat, but instead the car starts up for no reason that has been adequately explained to me.

Engine also comes on above 61 MPH. The trick to bypass that action is to shift to N. It's meant to come on above a certain speed to keep the motors within safe RPM limits, but they built a massively conservative margin in. I've coasted at 75 MPH down a hill without issue.

[Appletank]

Originally Posted by redpoint5

It uses fuel and runs the engine at least until reaching a coolant temperature of 130. The car could simply require more brake effort to mechanically waste speed into heat, but instead the car starts up for no reason that has been adequately explained to me.

Isn't it like, oft repeated wisdom that using your brakes for long downhill stretches risks overheating the brakes and losing braking force altogether? Which is why it is recommended to use engine braking instead. When the Prius's battery is maxed out, it will have to use friction brakes and the car would rather not rely on it for long.

As for why it uses fuel to heat up the coolant, maybe the ECU detects that the engine has stayed off for so long the coolant was cooling off below a threshold, which needs heat to keep the Cat working and lubricant flowing. I dunno without flipping through the readouts with you. I know my car likes keeping the engine on for longer than it need be to get the engine temp to at least 70. It shouldn't need to heat it up to 130 to be hot enough but who knows why Toyota chose that temp.

[Isaac Zachary]

The 2006 Prius seems to kick off the engine at speeds under 25mph. The 2013 Avalon hybrid does it under 45mph. Of course I'd expect a PHEV to have a higher limit.

But the way the car decides when to turn on the engine and when not to is a bit of a pain. I often have to travel down hill on one half of my daily route and then up hill for the second half. So the car starts and warms up going downhill. Then it tries to turn off the engine for the uphill part depleating the HV battery quickly and then needing to run the engine. If there only were a way to keep it in battery mode on the down hill portion then turn on the engine for the uphill portion.

[Appletank]

Originally Posted by Isaac Zachary

If there only were a way to keep it in battery mode on the down hill portion then turn on the engine for the uphill portion.

I think in your case your best option is to find a block heater for your Prius. Your engine starts to get everything up to operating temperature, which is really inconvenient when you're trying to roll downhill. A block heater would let you externally heat everything up before hand and greatly shorten the warmup process. They're generally used to keep engines and batteries warm in below freezing temperatures, but they're a valid choice elsewhere too, if you have a place you can plug in the heater.

If you are willing to get more involved you could also wire in a fuel cutoff switch that you trigger in neutral, the car doesn't seem to care what the engine is doing until put into drive, then it starts complaining about the empty fuel lines.

[Source: hobbit from technofandom]

[redpoint5]

Originally Posted by Appletank

Isn't it like, oft repeated wisdom that using your brakes for long downhill stretches risks overheating the brakes and losing braking force altogether? Which is why it is recommended to use engine braking instead. When the Prius's battery is maxed out, it will have to use friction brakes and the car would rather not rely on it for long.

You misunderstand. I didn't say the engine comes on and then engine brakes. It just comes on and has no effect on the speed. Vehicles in general don't automatically engine break, you have to initiate that.

For context, I've posted this question on PriusChat, where all the diehards and geeks that know everything about a Prius hang out, and nobody's got a clue.

[Isaac Zachary]

Originally Posted by redpoint5

You misunderstand. I didn't say the engine comes on and then engine brakes. It just comes on and has no effect on the speed. Vehicles in general don't automatically engine break, you have to initiate that.

For context, I've posted this question on PriusChat, where all the diehards and geeks that know everything about a Prius hang out, and nobody's got a clue.

And as another Toyota hybrid owner, I can also attest there are times the engine will turn on and won't shut off and I have no clue as to why. Battery temps maybe, with the engine ready to take over for lower potential electric output? I don't know...

[Appletank]

Originally Posted by redpoint5

You misunderstand. I didn't say the engine comes on and then engine brakes. It just comes on and has no effect on the speed. Vehicles in general don't automatically engine break, you have to initiate that.

Technically, as long as the car is not in neutral, or the engine is not disconnected from the transmission in some other way, a car will always engine brake whenever you're not on the throttle. Top gear will have the weakest braking force, increasing as you go down. The light regen while off the throttle in many hybrids is basically simulating engine braking in conventional cars.

Example, let's imagine you're on top of a mountain pass and you are rolling down with gentle pressure on the brake pedal to control the speed. Since you don't need that much braking force, the ECU only uses regen braking to convert kinetic energy into the electricity stored in the battery.

However, after 5 minutes the battery is full and it cannot use regen braking anymore.

Option 1, it replaces regen braking with brake pads. This can work for a short period of time, but you still have another hour of downhill to go, using the brake pads for that long will leave the brake fluid boiling and unusable.

Option 2, the motors waste electrical energy spinning the engine like an air pump in order to get the battery drained enough to continue regen braking, and for the purpose of this thought experiment can do this practically forever.

As long as your requested brake level is constant, the engine spinning up won't result in a noticeable increase in braking force, and you don't burn up the brake pads doing so. Being effectively a CVT the engine can spin at any rate and deliver whatever braking force (wasting 5 kW of battery power to absorb 5 kW from the wheels, etc) is required within reason.

[Hersbird]

Originally Posted by redpoint5

I've gone from empty to fully charged on several occasions in the Prius plug-in, which has just over 3 kWh of usable charge. Coming down from Creator Lake, and coming down from Yosemite. I don't think I can get a full charge coming down from Mt. Hood, which has at least 10 miles of continuous costing/regen.

The annoying thing about the Prius is the engine kicks on for some reason when regen has been going for a long time, or when nearing full charge.

Nice to recover that energy, but the reality is a full charge is like getting an extra 1/5th of a gallon of gasoline.

I wonder if the engine is on but running DFCO? Wouldn't be using any fuel then, just helping slow the car.

My plug in Pacifica would stay off, but I guess I never really tested long regen to the point of full charge. I do know it would do the full battery without ever starting the motor to warm the engine. My Sonata hybrid starts the engine right as you pull away from the curb no matter how much charge or how little throttle you apply. It does seem to warm up pretty quickly, maybe trying to lite the cats off? It will switch to EV mode after only maybe 3 minutes if conditions are right. It's still not showing much water temperature but maybe a little is enough.

The Pacifica went months without ever starting. I finally got that gas refresh point where it wanted to burn the tank. I still only used about 1/4 tank and refilled and that satisfied the nanny.

[Isaac Zachary]

Originally Posted by Appletank

Technically, as long as the car is not in neutral, or the engine is not disconnected from the transmission in some other way,

Technically Toyota hybrids don't have an actual neutral. The engine is always geared to the wheels through the transmission. It's how much torque the second motor/generator creates that determines the torque on the wheels and at the engine.

[redpoint5]

The Prius doesn't DFCO when it starts up do to long periods of regen. It high idles the engine until coolant reaches 130 degrees. It is never running the engine AND engine braking unless you shift to L.

I know all this because I watched coolant temperature, MG1 and MG2 power, closed loop, fuel consumption, among dozes of other things. Plus, you can simply hear the engine high idling and contributing no power to the car or deceleration.