Hello all, I have a tiny question. After I bought my prius last week and search on the net about its specs, I found that there is something weird in the engine. Prius gasoline engine (2ZR-FXE) with 1800 CC displacement produces 98 HP and 140 N.M, and the whole hybrid system produces 134 HP. Comparing to the same size corolla engine (2ZR-FE) with 1800 CC displacement produces 132 HP and 170 N.M. The difference between the two gasoline engine is the corolla engine produces 34 HP than the gasoline engine in prius, also it produces more tourque. The question is, why would Toyota use a less power engine with same displacement in prius, why they didn’t use the same corolla engine in prius to produce more power from the hybrid system? My Best Regards, Emad
The corolla is an otto cycle while the prius is an atkinson cycle. Search those terms for a better understanding of Toyota's choices.
The goal of the Prius is not high power. It is economy, more MPG. It is a delicate balance which they pull off quite well.
The Atkinson cycle engine in the Prius converts 40% of the energy into motion, the rest becomes heat. The Otto cycle in the Corolla converts 25% of the energy into motion, the rest becomes heat. If you do not care about MPG, the Otto cycle engine would bolt right in.
Along the same lines as above, the Prius engine scores 50 MPG on the U.S. scale, while the Corolla engine scores only 31 to 32 MPG in a smaller, lighter car.
Those two engines are very similar, except the valve timing (and electrically vs. belt-driven water pump and compressor). BUT ... Is the Corolla version as susceptible to excessive oil consumption and clogging of its EGR system after it accumulates a few miles?
Also, never equate CC with HP. HP is the product of how a motor works as a whole. Displacement (CC) is just a measurement of how much combustion space a motor employs. Motorcycles "tweak" HP output all the time by tuning the fuel map, intake and exhaust systems. A less restrictive exhaust system can massively boost HP output.
CC is a particularly bad way to look at an Atkinson cycle engine as the intake valves do not close near bottom dead center, but about 1/3 of the way up the cylinder, so the captured fuel/air is a much smaller number of CCs than the full stroke measured. This is why the Prius engine has a 'compression' ratio (actually it expansion ratio) of 13:1 but runs on regular gas and acts like its compression ratio is 8:1 (because that is all the air it trapped)
The Atkinson Cycle has a great many issues that make the Otto cycle more appealing to Manufacturers. Low HP per CC Low torque at low RPMs Limited RPM range As designed by Toyota, the 50 to 80 HP electric motor hides many of these issues. An electric motor produces maximum torque at 0 RPMs Electric HP needs less build up time, it seems stronger because you did not wait for it. Infinite gear ratios hide the limited RPM range in normal use. Proponents of a Diesel hybrid, do not factor in the differences needed to mask the weaknesses of a Diesel which are not the same. Diesels tend to really hate start-stop, A theoretical M/G1 will need to be MUCH bigger to start a Diesel over and over. Diesels change RPM very slowly. You are going to need to be able to change the speed of M/G2 not lock it to wheel speed like the Prius. Most 'real' Diesel Hybrids run the engine at a fixed speed to make electricity (and perhaps charge a battery) and propel the vehicle entirely with motors.
The Atkinson Cycle works well with a steady load and speed. The Otto Cycle does much better over a range of load and speed needed for the automotive use. The short compression, long expansion of the Atkinson Cycle means that more power to obtained per unit of fuel and so is much more efficient. To work in an automotive application it needs to be augmented by the electric motor.
Except that it isn't augmented in the 3rd generation much, unless you're whipping it hard. That's why battery charge level normally does not drop significantly when I climb long hills. Instead of relying on energy from the battery to make up for the low engine torque, the system uses more engine revolutions than would be necessary to get up the hill with most Otto-cycle cars---even modestly powered ones. That strategy can be noisy, but is better in the long run than unnecessarily exercising the battery to accomplish the same result.
I suspect that in this situation that there is not much change in the SOC is because MG1 is generating the electricity to be used by MG2 to augment the ICE and may have surplus to feed to the battery. (The energy screen should show this.)
And what is supplying MG1 with the energy to generate electricity? The ICE. If the ICE would not do that, it could rev less.
When I'm doing 80 in my Prius on the freeway? I keep seeing new Corolla's blowing by me! And Honda Fit's... it's like I'm standing still... at 80. It's crazy.
But then you won't get up the hill, unless the battery supplies sufficient energy to MG2. That wouldn't be good.
That's understandable. Most Prius owners are interested in conserving fuel (not necessarily at 80 mph though), but drivers of non hybrids are normally not so MPG conscious. In some areas speed limits are simply recommended speeds so let her rip!
