Top Speed on the Electric Motor?

34 MPH is the limit of EV-button induced, absolutley no gas-engine spin, truly 'golf-cart' mode.

42 MPH is the upper limit of non-EV button speed, then the gas engine actually spins (but may not be combusting, not contributing to forward propulsion).

I've been near 60 MPH with nothing but the orange arrows showing "battery only". I'm still a bit unclear what is happening then. Engine is obviously turning, but would appear (no "engine red arrows") not to be contributing to forward motion...would that then be a limit to the electric motor RPM (MG2?)

Suffice it to say, it's an amazing car which does amazing things, never before seen in a mass-produced automobile. Yes, I'm still thrilled to drive this car.

 

Above the 42 MPH (66 kmPH) speed when in "electric only" mode (not EV mode) the engine is spun but no fuel is injected. The MFD doesn't report this, but the Canview or Scangauge II shows the engine spinning. This is to ensure you don't over-spin MG1. Its' RPM is proportional to wheel speed and inversely proportional to engine RPM. At 60 MPH when coasting the ICE only turns around 950 RPM (I forget the exact number), whereas true "fuel use idle", such as at warm-up or the beginning of coast, is around 1250 RPM. Once the system decides to "shut off" the ICE the RPM drops to the 950 value.

 

Does it matter?

 

when the ice is shutoff the engine stil runs? at 950..

 

Yes, at above 42 MPH on the MFD you'll see no power coming from the ICE but it is still reving around 1,000 RPM. If you press the accelerator very lightly, Prius can maintain speed (or gain speed on down hills) just on the battery power alone while keeping the ICE reving and consuming no fuel. This mode is known as stealth. I like to call it Civic Hybrid full hybrid wannabe EV mode.

 

Its pretty easy to see "warp stealth" mode under the right conditions. Most common time I see it is long gradual downhill freeway. The type that needs just a little gas to keep up speed. Often in this condition the engine is running and battery is charging since you hardly need any power to the wheels. When the battery gets up to 1 or 2 bars from the top you should be able to do the usual glide shuffle on the gas (let it all the way up then depress lightly) and get into this high speed electric only (ice spinning but not running) mode. Depending on the hill you can often keep this up for a very long time as the power usage is very light. I've been able to get this to happen at 75mph, so I'm not sure if there is an upper limit? If the battery gets up to 1 bar from the top or completely full you may even see the car drop into this mode automatically. I've actually noticed it happen a few times with the cruise control on.

rob

 

I have had all electric and no power use (Super Stealth) at 115km /hr and it is all made possible by that magical little PSD.

The following link that I found on another thread shows the PSD and has a burst on how it works and has a neat little slider to set up your own scenarios.

Toyota Prius - Power Split Device

I think that will explain what you need to know.

 

Good links and explanations above. I'll take a crack at a simple explanation:

In the Prius, unlike a conventional car, nothing is ever disengaged, but the PSD (essentially a differential) allows any one component to stand still while the other two are moving. Thus if the engine is standing still while the car is moving forward, MG1 must spin backwards. The faster the car goes, with the engine not spinning, the faster MG1 must spin backwards to compensate. Since every electric motor has a speed above which it will be damaged, even if it is not powered, MG1 cannot be allowed to spin too fast. If the car is going faster than 42 mph and the engine is not spinning, MG1 would be turning too fast. So to protect the MG1, the computer starts the engine spinning in order to slow down MG1.

Normally at this point the computer will start the engine and run it in the normal manner. But if the SOC of the traction battery is very high, and the power demand is very small, it will sometimes spin the engine without drawing power from it. The MFD shows the engine not providing power, though CAN-View (and perhaps Scan Gauge) will show that it is spinning. Some folks use the term "super stealth" to refer to the condition when the engine is spinning but not providing power. I consider the term inappropriate because it suggests "quieter than quiet" which is not what's happening. In normal driving you will see this condition only rarely. But it can happen at any speed the car can go. I never saw it when I lived in flat North Dakota, and saw it for the first time when driving over the mountains, on the descent.

As noted above, if you initiate EV mode using the EV switch, the car will issue an EV Deny when you reach 34 mph, and then either start the engine (the most common outcome) or go into into electric mode on its own. I've never seen an explanation for why 34 mph is the cut-off for EV mode, when 42 mph is the usual cut-off for regular electric mode.

I believe that the so-called "super stealth" does not normally occur as the result of exceeding 42 mph while in so-called "stealth" mode. More often you are driving, with the engine running, and if conditions are right the engine may shut down but continue to spin because your speed is over 42 mph.

 

According to "the nomograph" (how many here remember that from the old days of Prius? sigh), the 42 mph limit arose from the 6500 rpm limit of MG1. In the 2004 and newer Prius, that MG1 speed limit was increased to 10,000 rpm, but the software was not changed to allow faster EV.

The Toyota-version, bigger-battery, rechargeable PHEVs get a software reflash that allows them to EV up to approximately 62 mph, which is approximately the "real limit". I reckon one has to be pretty tight with Toyota to get their hands on that reflash. I certainly don't know how to get it!

Since Toyota's R&D on the MGs and planetary gearsets is certainly continuing, and since those devices are not dying in the field at horrifying rates, I anticipate that we might see e.g. 12,000 rpm spin limits, and proportionate increases in EV-only speeds in future Prius. Ma Toyota still holds a few cards, in the face of potential competition from GM and Tesla, etc. It will be fun to see how all this plays out.

 

On the contrary! Since all the energy for the car ultimately comes from gas, you actually save gas by driving in a manner that minimizes the use of the electric motor. Situations where EV mode is more efficient are relatively limited.

Again, you are mistaken. It is more efficient to accelerate using the gas engine, and use electric-only mode only for steady-speed driving on flat or downhill roads. The reason for this is that all the electricity drawn from the battery must be replaced later by running the gas engine. Electric mode is more efficient when the SOC is high and the power demand is very low. Under these conditions the car will cut off the engine.

Lower-than-expected MPG are due to the unrealistic EPA testing procedures, though under ideal driving conditions and with the right technique, people (including some PriusChatters) have exceeded the EPA figures.

 

You have probably noticed that even if the car is warmed up fully and the battery is fully charged, the car will still use the ICE under more than turtle acceleration. In this case it's to protect the battery from too much current discharge, which can damage it. The system can run the ICE, generate electricity (MG1), and feed that as well as current from the battery (in moderation) to power the electric motor (MG2) if that's the programmed "best method". Or it can just switch to ICE propulsion aided by electric from the battery (MG2). This is why it doesn't use electric only most of the time. It's limited by the battery current capability. I suspect this limit will be raised by the plug-in Prius due out this fall (fleet only), due to the double battery pack. I wonder if they will put in two battery pack fans?

 

I really hope that is true. I wonder how many seconds will elapse between the time the code hits the service site (in support of the initial phev release) and when someone first tries to reflash their standard Prius with it... My guess is not very many

Rob

 

How would you flash a Prius? You'd need the THHT, and at that price it's not likely anyone would be jumping at a reflash. You can't just plug in your laptop to a Prius! Perhaps a friendly dealer, but I doubt they would be interested unless Toyota sanctioned it. Iphone bricks are one thing, Prius bricks are quite another!

 

Please tell me where you think all that electricity comes from?

The biggest single fuel saver in a Prius is the Atkinson Cycle engine. This engine achieves up to double the efficiency of a normal Otto-cycle engine. Why don't we see Atkinson Cycle engines in all cars? Because this engine has a very low power to size ration, the very same engine but lacking the Atkinson cycle (offset crank, very high compression ratio and retarded inlet valve timing) achieves only a combined cycle consumption of 6.1L/100km in a much lighter Yaris but it produces 80kW of power and 141Nm of torque, the poor little Prius engine only makes 57kW and 115Nm but coupled with HSD achieves a combined cycle of 4.4L/10km. How can the Prius get by with such a gutless engine? Enter HSD!

HSD main contribution to economy is to keep the Atkinson cycle engine in its most efficient load and RPM range while the HSD can use power stored in the battery to boost the power to the wheels giving acceptable acceleration. It also boosts acceleration from stationary when the ICE isn't able to produce any torque the electric motors are at their best. As a bonus the HSD is used to capture some of the energy normally wasted during braking which is stored for later use.

Yes, using a light or trailing throttle will use less energy in any car, only the Prius shows you a switch to electric and 0 fuel consumption during this faze, what it doesn't show is you use a little more fuel when the ICE starts to replace the charge into the batteries.

Other fuel saving design features are the low aero drag, (lowest of any 4 door sedan) low rolling resistance tyres, minimised frontal area, (ever wonder why the roof has a low section through the middle?) weight reduction, (alloy panels) and climate control.

 

Better question, what's the average % breakdown of electrical generation from:
* ICE Charging
* Regenerative Braking
* Coasting/Downhill Driving

PS: I know you're right about this, and ICE charging probably makes up a vast majority of the battery charge. I'm just curious how much on average is gained from braking or downhill driving.

 

I should have just posted, see Daniel's post.
I have made a pretty big edit to my last post.

BigJay, 100% of the energy used to propel the vehicle comes from petrol and is converted to kinetic energy by the ICE. From there some of that kinetic energy is converted to electrical energy then some of that stored as chemical energy for later use while the rest is used immediately to propel the car.

The percentage of energy recaptured from the wheels to generated by the ICE driving the HSD generator is dependant on terrain. I suspect and this is just a guess, it ranges from <1% on flat ground and if you are a careful driver who minimises braking up to maybe 5% in hilly terrain and careless driving.

Avoiding regen will boost fuel economy.