Why would the 1.8L Engine only be 100HP

Yum, a sport hatchback with the 1.8L Lexus hybrid ... coming in less than one year ... check it out. Independent rear suspension, fun to drive, etc...

Lexus CT 200h Future Hybrid Vehicle

 

Totally agree ... ever since gas prices really peaked 2 years ago (and likely before that) ... American boob tube marketing has been so sneaky to only quote highway MPG's, high limit MPG's.

My car is a daily driver for commuting, store, etc... I care about the average fuel economy as measured at the pump.

 

I forgot to mention that increasing the ICE power also requires MG1 to be larger and a more powerful inverter. The ratio is roughly 3.5 to 1, ICE to MG1 power. A larger MG1 increases the peak inverter and traction battery power.

Bob Wilson

 

Why is that? Is it related to the torque ratio of the PSD?

 

Yes. The PSD splits the power between a mechanical path and an electrical path. Using a more powerful engine requires a more powerful electrical path for that portion of the power.

Tom

 

When I want fuel economy, I take the white car. When I go to the track, I take the black car.

 

Just a precision: the Atkinson cycle in the Prius has a 13:1 expansion ratio, not compression ratio. The ratio is changed by reducing the compression cycle.

Not sure about your equation for effective size... The gas still burns in a 1.8L of volume.

 

I didn't realize that color made such a difference. I'm glad I bought a black Prius.

Tom

 

Yes but it doesn't compress 1.8 liters. Some of the charge is blown back out the intake valves at the beginning of the compression stroke. This is not about achieving the best horsepower per pound or per cubic inch. It's all about using the lowest fuel amount per horsepower (hour).
"Souping up" these engines is exactly the wrong approach.

 

A traditional Otto cycle engine takes in a volume of air about equal to its displacement. At wide open throttle, this air and fuel mass is a coarse indicator of the potential engine power, useful for initial comparison of different engines.

An Atkinson cycle engine of the same displacement consumes a smaller volume of intake air and fuel per stroke, therefore limiting its potential power. The other poster's equation simply relates the Prius engine to the size of a more commonplace Otto cycle engine consuming the same amount of air and fuel per stroke.

The comparison is not exact, because the two engines don't have the same efficiency. But it is still a useful guide.

 

Hi fuzzy1,

This is tricky to think about. The intake stroke is the same in both engines as the displacement is the same. That is, the Prius Atkison engine is not a "stroker" (engine with same block but longer con-rods) version of the Echo/Corolla (gen 2/gen 3) Otto engine. So, to obtain the 13:1 expansion ratio, the head is a high compression head, and the exhaust valves open later.

With the purely high-compression head (actually high expansion head - high compression head is a term from the 60's/70's hot rodding) approach the Atkinson compression stroke has closed valve displacement that is lower than the Otto. The high-compression head is closer to the top of the piston, but the change in overall gas volume is not that great, and the efficive compressed gas volume is more dramatically effected by intake valve closing time.

Another way to make the Atkinson engine would be to go with the same head, and make the engine a stroker - which would increase the displacement rating.

Its hard to say which way these things were done in the Prius without comparing the parts.

 

The original way to make an Atkinson Cycle engine, and still the only "real" Atkinson engine, is to use a complex crankshaft arrangement that allows all four cycles of the engine to occur with each rotation of the crankshaft. Because of mechanics of this linkage, it is possible but not necessary for an Atkinson Cycle engine to have differing compression and power strokes. Saying that again, just so everyone understands this, it is not necessary for an Atkinson Cycle engine to have a longer expansion stroke than compression.

This brings up the question of why you would use an Atkinson Cycle if the strokes are the same. The answer is that the Atkinson Cycle engine was developed to get around the patent on the Otto Cycle engine. It was nothing more than a rule beater to avoid paying royalty fees. The happy accident is that it did allow for differing strokes, and eventually people realized that there was some benefit to this.

On modern engines, people use the term "Atkinson Cycle" to refer to a modified Otto Cycle engine where valve timing is used to effectively create a longer expansion stroke. It's not really an Atkinson Cycle at all, but that's how we now use it. The old patent beating crankshaft system has gone the way of the dinosaurs.

Tom

 

That's kind of what I have always wondered...except I would rather have a 98HP electric motor, and an 80HP gasoline engine.

 

And where would your 100 hp of electric power come from?

At least 20 hp would need to come from a battery (100-80 hp from the ICE). Would you be willing to pay the price for a big enough battery to supply such power for sustained durations? And when the battery would be empty, would you agree to drive a 80 HP car with a total car weight higher than the current Prius (you would have more battery, hence more weight)?

In the case of the current Prius, the ICE (peak 98 hp / 73 hp) provides ~2/3 torque to the wheels and ~1/3 to a generator (max output of 42 kW) that passes electrical power back to the main motor (80 hp / 60 kW). All together, they provide 134 hp / 100 kW.

 

This is a most interesting thread, and I have enjoyed reading all the post. With no technical knowledge ... I think Toyota has done a terrific job of balancing many complex engineering challenges, and producing a remarkable vehicle.

I am always amused (and amazed) whenever someone writes about performance mods, and turbo-charging the Prius. It reminds me of when I was a teen and installed glaspack mufflers. An Uncle said that Detroit spent a fortune making cars quiet ... Toyota spent a fortune making the Prius what it is: economical, comfortable, dependable, and for the most part, problem free.

Years ago I owned a car with a 4 cylinder 2 L engine. I installed headers, shaved the head, raised the compression, installed dual side draft Weber carbs, and installed a 3/4 race camshaft. Yes, it would run run like a V8 .... but it was noisy, idled rough, and was a gas hog. Twice I broke the fibre overhead cam belt because of the heavy springs on the valves. Neither occurred at a convenient time or place.

 

Noise and Power is a testosterone thing.

 

He's currently in 3rd place in points at that drag strip in the "tuner" class. He also got some positive attention at his previous autocross.

 

Not nearly as much as aerodynamic drag reductions:

• variable cooling air inlet - this gives a solid mileage improvement at all temperatures
• air dam and side skirts - reduces under car drag and improves traction
• air gap seals - around the doors
• improved rear taper - recover more air energy from the rear
• wheel well covers - reduces air spilling into side streams and air entrapped in wheels
• moon wheel covers - reduces air entrapped in wheels

The 1.8L engine and transmission are already quite efficient at high power levels and simply reducing the drag pays much higher dividends.

We already are modifying our hybrids and the list is much longer and larger than playing with just the engine. The impact of adding a turbo to the 1.8L engine has yet to make a lot of sense. Still, experimentation is good.

One option you might consider is an electric driven compressor. You'll need to tap the traction battery power but this offers a number of significant improvements:

• no exhaust modifications - much simpler plumbing
• zero power, compression - compressed air available as the engine spins up, much like a regular super charger
• complete computer control - boost can be adjusted as needed to fit an optimum engine operating state
• flexible location - an electric driven compressor can fit just about anywhere since the only pipe feeds the intake manifold

Pure speculation, but you might pickup an air conditioner compressor and see if it could drive a roots-style compressor. You should have enough power to achieve a respectable boost yet still have control over its operation. Best of all, short pipe to air intake.

Bob Wilson