How much does Hybrid really contribute to mileage?

That is what I think, but it would probably be a real dog, but I think it would get even better highway mileage and you would have to leave the ECVT. Probably be really bad in the hills / mountains, and city mileage would suffer.

 

This should be straight forward... take the
Corolla 1.8l w/automatic:
132 hp @ 6000 rpm; 128 lb.-ft. @ 4400 rpm, combined FE: 30
Prius
134 hp @ 5200 rpm, 105 lb.-ft. @ 4000 rpm, combined FE: 50

So if you overlook the differences in transmissions it is obvious to me the hybrid system contributes a great deal. I think the big advantage is is the engine is off when it is not needed.

Perhaps I am over simplifying the question.? I do that a lot.

 

There's a real simple comparison. Compare the Prius to the non-hybrid Prius, it's easy.

There's a non-hybrid Prius ? Yep there has been all along, right there hiding in plain sight.

The Prius is a smallish, 5 door hatchback with a 1.8L ICE tuned to the Atkinson cycle, plus two e-motors ( MG1 and MG2 ), a battery pack and an ECVT in place of a traditional transmission.

What Toyota vehicle is also a smallish, 5 door hatchback with a 1.8L ICE tuned to the Otto cycle...without the hybrid equipment..but including a traditional transmission? It's the Matrix, the non-hybrid Prius.

Matrix combined EPA number is 28 mpg, 25 City / 31 Highway
Prius combined EPA number is 50 mpg, 51 City / 48 Highway

The rest is easy. BTW these increases in fuel economy are pretty consistent with all four of the major hybrid systems; HSD, IMA, Ford and the GM 2-Mode. Essentially what the hybrid systems do is to improve the fuel usage of the basic ICE-only systems by about 40% on average.

Matrix uses 35.7 gal to drive 1000 miles.
Prius uses 20.0 gal to drive 1000 miles, a 44% improvement.

 

Matrix 1.8L AT...

 

Silly me... why didn't I think of the Matrix?

 

If only it were that simple. All sorts of other things enter into this. Aerodynamics for one, especially on the Prius.

 

Correct. And I believe the hypothetical posed by the OP presumes that the Prius would keep its Atkinson cycle, shutting off at stops, etc. Imho, the only way the battery/hybrid aspect actually improves mileage is in recovering kinetic energy during regenerative braking. Beyond that, the Prius is in fact just a really efficient ICE vehicle, as far as I can see. So in my mind, the question boils down to how much energy would be lost due to friction braking in the absence of the battery and regeneration capability? Ladies and Gentlemen... start your napkins!

 

Base Matrix is 7% lighter than the base Prius as well. Gets complicated in a hurry.

 

There is a non-hybrid Civic and a hybrid Civic, find the FE ratio and apply it to the Prius.
City 26 Hwy 34 Comb 29 vs. City 40 Hwy 45 Comb 42 = 69% as good, so I would expect 34.5 combined for a non hybrid Prius (Postus?)

(You could use the Camry, hybrid vs non-hybrid, but the Civic is a closer weight match)

 

Actually the hybrid Camry to the regular Camry or the hybrid Ford Fusion to the regular are both better because the Civic is a mild hybrid. You don't want to eliminate the weight difference of the hybrid batteries, a non hybrid Prius would not have a HV battery and the associated weight.

 

Actually no - the hybrid system with its eCVT allows the engine speed to be adjusted to much lower RPM during highway cruise than a conventional transmission to allow the ICE to be more efficient

A mechanical CVT (e.g. as on some Nissan cars) could also improve things but without the battery the engine would have to larger to provide adequate power and so not have as good fuel consumption.

Note that the Prius has better freeway fuel consumption than ANY other car being sold today - it can get around 60mpg @60mph.

kevin

 

How much is the electrical part of the hybrid system contributing to the fuel economy at > 60 mph?

 

This question illustrates the fundamental problem with this thread: the very nature of the HSD used on the Prius prevents an apples to apples comparison of efficiency with and without the hybrid components.

The Prius drive system, the HSD, requires the electrical parts at all speeds. Part of the power is routed mechanically, and part goes from the ICE to MG1 to MG2. At low speeds and power levels you can drive with all electrical, but at no time will it run only from the ICE.

To answer this posters question, you could take out the HSD and directly couple the ICE to the drive wheels. This would produce your best possible efficiency, but would require your Prius to be towed up to speed and released, and then continue to drive only at that "sweet spot" speed.

Tom

 

From what I read, the ICE is directly connected to the PSD on the planet ring, right? So in theory, the car could run solely from the ICE, right? And let see the engine produces something around 98hp.
So the question than is how much more efficient is the Atkinson over the standard cycle engine?

 

To answer this question requires the 2ZR-FE Brake Specific Fuel Consumption chart, and I haven't seen one anywhere. Here's a set of BSFC charts for various vehicles.

Typically an Otto-cycle engine achieves about 25% efficiency at peak efficiency - 2ZR-FXE achieves about 37%. However, drivers generally don't drive at peak efficiency; although more of the fuel consumed is converted into useful work, more fuel is being consumed at this higher engine speed than at the lower speeds. The chart shows how much fuel is consumed to produce 1kW of useful work for one hour, but it doesn't show a raw amount of fuel consumed per engine revolution. While the fuel consumed per unit of power may be less for a higher engine speed, there's still more fuel going through the engine per second because it's revolving more quickly.

To read a BSFC chart: the engine speed is along the bottom, and the load along the side. To work out how much fuel will be consumed, know that one gram of gasoline contains about 12.33Wh of energy (one kg has 44.4MJ so one gram has 44.4kJ, 1 kWh being equal to 3,600kJ). Therefore, to work out efficiency, multiply the fuel amount given in grams by 12.33 and divide that into 1000. For the Prius, peak is 220g/kWh so the efficiency is 1000/(12.33 x 220) = 1000/2712.6 = 0.3686 or 36.9%. For diesels, use 12.61 as diesel has more energy per unit mass (45.4MJ/kg). The Volkswagen 2.0L TDI 196g/kWh is about 40.4%.

The engine speed on most cars, with a number of fixed gear ratios, is governed by the current gear ratio and the wheel speed - as you accelerate the engine speed has to rise. To keep a constant speed, the engine torque has to be balanced with the road demand (if it were producing more torque than required to just balance, it would accelerate, if less, it would slow) so you go across the chart to find the engine speed, then down the chart to meet torque. As you can see, engines get less efficient as demand drops, with the sweet spot being at about 80%, above which again there's less efficiency towards 100%, fully-open throttle (called Wide Open Throttle or WOT). The outer line on the chart represents the limits of what the engine can do in terms of torque versus engine speed.

On a CVT, the car has the choice of controlling throttle or speed to produce a certain amount of torque. (The torque at the axle is basically the force required to overcome the losses, multiplied by the radius of the wheel plus tyre. Power is just that force multiplied by the engine speed. You can get more power either by creating a greater force at the same engine speed, or the same force at a higher engine speed.) The 'Basic Operating Line' you see on the Prius charts is the line that the Prius tries to follow - as you can see, on Gen 3, aiming at about 80-85% throttle over 1,000rpm up to 3,650rpm, then opening the throttle right up over 3,650rpm, the assumption being that if you're flooring it, you need as much power as it can give, damn the efficiency. Gen 2 would never open up completely.

The Prius eCVT differs from a conventional CVT in that there is no slippage, and no clutch or fluid converter, so those sources of loss are eliminated. It's not perfect - multiple conversions from kinetic to electrical energy, back to kinetic, cause some loss - but in general, more efficient than a conventional CVT and at the most efficient point, at least as good as a manual.

The Prius can do a lot of magical things but it can't defeat physics - it can't slow the engine below 1,000rpm or it will stall. Even then, the barely-open throttle settings use a lot of fuel for little benefit. That's where the hybrid system comes into play at low speed - it shuts down the engine and runs electrically for a while, amortizing the cost of running the engine over multiple stop/start cycles. Instead of producing only 20Nm of torque, half-open, it can produce 40Nm of torque and absorb 20Nm in the generator to recharge the battery. There are losses in discharging and recharging, but they outweigh the losses involved in running the engine at low demand levels.

You can't run the Prius just from the ICE as it doesn't have enough torque, at minimum revs, to actually move the car from rest. It would just stall. In order to move off, regular cars need a slipping clutch or a fluid converter to allow the engine to rev faster than the wheel speed, divided by the gear ratios, allows, and they require multiple gear ratios to multiply up the torque, and divide the revs. Prius just uses 400-odd lb*ft of torque from MG2, which it can achieve at zero revs.

It's still not over at highway speeds, because to accelerate on a conventional car, you have to open the throttle a bit, or to decelerate, close it a bit, in each case moving outside the most efficient band. There are a lot of tiny accelerations and decelerations going on as the terrain changes. The hybrid can absorb these slight changes using the battery and motors, so it doesn't need to change the engine speed away from the average power demand, keeping it locked into an efficient speed and load. Big changes would cause a lot of discharging and recharging, which outweigh decreases in efficiency, so most acceleration, as the driver sees it, is done by changing engine demand and speed. The fuel is cut completely when you brake, and the engine stops spinning completely below 42mph (Gen 2) or 46mph (Gen 3). This isn't possible in a conventional car as the engine has to keep spinning even if the fuel is cut, unless you pull in the clutch or shift to neutral. (It would be possible to 'bump start' the engine but it might not be as smooth as the Prius manages.)

Ultimately, though, the Prius is still a gasoline-powered car and its efficiency at core is down to an efficient engine; the hybrid system allows that engine to be used most efficiently, and allows an engine sized for average demand to be used without sacrificing acceleration performance.

 

Precisely. The Prius without it's battery and e-motors is useless. The Atkinson cycle ICE would never be able to be sold for real world usage in a Prius. Flintstone-mobile comes to mind.

If one says, well put the Otto cycle engine in the Prius...then it becomes a Matrix.

 

No, The MG2 motor HAS to turn if the wheels turn, and always turns in a direct ratio to wheel rotation. The ICE powers the planetary ring which only pushes the outer ring if it meets resistance from the Sun ring, MG1.

The Prius DOES have a mode where neither MG2 or MG1 provide or generate electricity, it is Labeled 'N' and not much happens in N.

 

For city driving the huge advantage is to get EV boost for accelerating from a dead stop. This is the most costly transaction for an ICE to do on a non-hybrid in terms of fuel economy. I noticed the 2010 uses electric far more efficiently than the 2008 when accelerating from a dead stop. It is relatively cheap in terms of power when using a battery. When using gas it is very expensive.