That site is interesting, one thing it doesn't talk about is the electric draw of the electric motors though. If I remember right MG1 is the larger drive motor while MG2 is the starter/alternator/smaller one. Like if I set the ICE to 1100 rpm, it requires MG2 to run at 1500rpm to keep MG1 at 0 rpm which ends up being 26mph.
If I re adjust the figures to get something logical for 55mph while keeping the ICE at 1100 rpm, it has to turn MG1 at -4500 rpm and MG2 has to spin at 3250. I'm pretty sure at those figures it would have to be heavily using the battery since I'm pretty sure the ICE doesn't have enough hp at 1100 rpm to make the car go 55mph. I don't have a tach/scan gauge to validate, but it sounds more like 1500-1800 rpm in cruise. Bringing up the ICE rpm allows the MG1 and MG2 rpm's to be lower.
For the actual control, I'm not sure if the computer is doing the math on the fly for the given load, but I suspect it's more likely using lookup tables like the fuel map tables and the computer is tuned via that table to give desirable results. My guess would be the table route which goes back to the idea of if you increase the tire size, it will be like going up hill for what the computer sees, or going against a higher wind speed. Pretty sure that would mean the throttle is pressed more, but you'd be going at a slow mph according to the computer than what the real speed is.
Really not 100% sure what the overall effect would be. I think using a scan gauge to monitor rpm and such, swapping tires out and seeing the effect is about the only way to really know for sure. The whole system is a bit counter intuitive compared to a normal car.
For the BSFC graph, that's exactly what I figured the bold line was for, but thanks for clearing that up. Seems like the target for take offs would be to target the lower end of the gray zone to be in the most efficient range. I suspect there's a point in the gray blob that's more ideal than the rest, but maybe the effect isn't isn't to really measure.
I've been looking around on google maps for a good area for a test section of road. There's two main options that I know has very little traffic, one is 2 miles, the other is 2.5 miles. I'll have to keep poking around, I'd like to find around a 5 mile stretch of road and do steady state mph vs mpg for my car in mostly stock form since I think that will give the best base line vs basing it on take to tank fill ups. If I understand things right, the displayed mpg figures don't get calibrated at all, so it should be a consistent reading I would think. I'm used to my corolla where the best mpg I could possibly get from the car was around 45mph (40mph was best but hard to keep it from down shifting on small hills and such). The prius on the other hand I'm not super sure what the best travel speed is. I've seen people say there's a sweet spot around 57mph and another said something like 62mph. From the tiny bit I've played around, it looks like 45mph gets much better mpg than 55mph and is likely how people can hit 50mpg+ with this generation of prius. It's really crazy how consistent the numbers are on this car though, like you can just about predict the average travel speed purely from the mpg figure from what I've been seeing so far. Of course modded cars throws that logic out the window a bit.
If putting larger tires on the prius makes everything else the same besides the extra spinning mass, then I suspect the only room for mpg increase would be smaller tires or narrower tires and it's main effect would be stop and go traffic which isn't what I'm doing. I'd dare to say if the same 1.5L engine was paired up to a normal manual transmission, I could get as good of mpg with a little work keeping the engine rpm in the right ranges, at least for constant speed cruising. The CVT setup is a neat concept though, seems like it's a very reliable way to design a transmission too.
For gen2 vs gen3 hybrid batteries, I just searched it a bit, sounds like they are the same internally for the main battery modules, same voltage and number of cells so same capacity. Google's first result that gives the instant answer in results gave the wrong figures. It's a per-release post before the 2010 came out, so I guess maybe there was a rumor of a 1.6kwh battery that was incorrect or something.
NiMh is 1.2v per cell, what you're calling a cell is actually a "module" as one site put it. There's 6 cells per module, 28 modules (from your post but pretty sure that's right), so 168 total cells or a nominal voltage of 201.6v. I don't know NiMh batteries too well, but I've done quite a lot of reading up on Lithium Ion and similar tech batteries. 3.6v nominal voltage, 4.2v is fully charged, and around 3v is fully discharged. Here's a Lithium Ion discharge chart. 1C is 1x capacity of draw, so if it's 2200mah rated cell, then 1C is 2.2 amp draw. Lithium Ion does really well at low and high discharge rates, but lower should give more capacity as less heat is generated. I've hread NiMh does very well with high amp draws and Toyota designed these batteries to sit between something like 40% and 80% state of charge so the battery will last an extremely long time. I suspect the NiMh batteries last longer than the Lithium Ion versions even though that's the latest and "greatest" tech. I've read that charging NiMh is a little more tricky, I don't remember why though. I was looking for "cheap" batteries to use for backup power sort of like a power wall. Eventually I'd like to get solar panels and go effectively off the grid. If I read my power bill right, the only fee I'd have to pay to stay connected is $7/mo just to have the access to the power lines. There's always going to be maintenance and such, so it probably wouldn't be a bad idea to stay hooked up just for the "backup" power if/when my main power doesn't come from the grid. The prices have jumped up a lot lately before the fuel price increase so it might be quite economical for DIY solar installs. Good figure in my mind is 10% ROI, or 10 years to break even. Lead acid batteries taken care of well generally lasts for 10 years and batteries are a major % of the initial cost. Kind of getting side tracked, but someone might find it interesting at least.
Also I ran over your math, you got it all right, 1.3104kwh to be exact. Seems like most people round to 1.3kwh though.
I find it interesting that the electric motors in the 2nd gen prius can make around a max 60kw of power (80hp), but the battery pack max output I think I read was 36kw or 48hp. Still quite impressive, about 27.5C discharge rate. The highest output Lithium Ion cells that I'm aware of (for tool batteries) are max output of 40C.
Since the dirt road is right at the start/end of my trips I don't see that effect much. Of course the first couple miles the mpg is pretty horrible since it's recharging the battery. It would be interesting to dig up the right numbers to calculate how good or bad driving purely in electric mode is. A while back I took some real world figures of people testing the prius as a generator (1kw load on the 12v system) using an inverter and accounting for the inverter losses and fuel used, it was very comparable to to the large backup diesel generators that are for power backup during peak grid usage which are generally loaded at the ideal amount for the best power output per unit of fuel burnt (80% load of capacity or so if I remember right). It's insanely more efficient than a 5hp 5kw generator, I think it was 2-3 times more efficient than a Honda 1500w generator at max efficient load.
Anyway, I suspect we need charge vs discharge efficiency of the NiMh cells, inverter efficency, ICE (at the ideal load), MG1/MG2 efficiency for generating and discharging. There's a lot of steps there, so I suspect the 66% figure from before is probably a good estimation.
Some googling around I found something that looks good. They basically say 100% efficiency for charging, 80% for discharging, average that to 90% for easier math.
NiMH Charge and Energy Efficiency ยท AA Cycler
This is a real interesting chart that came up while searching for other numbers. Looks like under ideal conditions, the motor/inverter combo can hit 95% efficiency, the low end is 65%, but it looks like most of the area is around 90%. 90% is a pretty solid number when calculating efficiencies of electronics if they are designed well, I was expecting 90% for the motors, and 90% for the inverter (90% of 90% is 81% overall).
https://www.researchgate.net/figure/...fig3_346897527
Using those numbers and assuming a 90% for electric motor + inverter, that leaves us to the ICE efficiency (thermo efficiency). First google result says mine is about 37%, same site says your's should be 38%.
https://www.greencarcongress.com/201...-20110411.html
1 gallon of 87 octane gas holds roughly 33.7kwh worth of energy. 37% drops it down to 12.496kwh (12.806kwh for 38%) for the output of the ICE as mechanical work to the electric motor(s) for charging. 90% is 11.222kwh into the battery and 80% drop from the discharge of the battery 8.98kwh back to the electric motor to move the car 90% again 8.08kwh. Overall efficiency 23.98% Ignoring the engine's number since either case the engine is making the power to move the car or charge the battery... we get round trip efficiency of power going into the battery and back out at 64.8%. That's really close to the 66% figure before (whoever did the math probably used the 95% figure instead of 90% for the inverter/motors).
Now for the real interesting question... the prius engine is roughly 37% efficient but clearly that's under ideal conditions, just how much does it drop when it's in the warm up phase. I'd assume while the engine is warming up, it should be using the battery as much as possible until the engine is warm enough to have a high enough efficiency to be worth while recharging the battery back up.
https://www.anl.gov/article/plugin-h...ing-efficiency
Looks like a room temp engine (22C or 72F) uses roughly 25% more fuel than fully warmed up. Pretty interesting study, looks like for the exact engine, it takes quite a long time for the oil to come up to temp. On the Toyota Camry, there's a heat exchanger on the oil filter to the engine coolant, I guess that design is to help with quicker warmups of the oil to give better mpg.
So 25% more fuel used (or 25% lower thermal efficiency for the engine, so 27.75%) vs let's call it 65% efficiency of a fully warmed up engine charging and discharging the battery for the mechanical work which works out to be about 24% efficiency overall.
Lot of numbers thrown around and such, but if I didn't mess up anywhere, a cold engine is still more efficient than charging and discharging the battery for electric only mode by almost 4% (purely theory based). Once the engine is fully warmed up, it's 13% less efficient. In other words, if this math is all right, driving the last 1/4 mile on engine power would be more efficient than on electric by quite a bit, so pulse and glide would probably make massive improvements for that short leg of the trip, another way to trick the engine into running would be to turn the HVAC system on and make it demand the engine to be on. AC would be less than ideal but I suspect that's the easiest way to get the engine to stay on for a bit.
There's some small numbers I'm missing in all of this, the steady state average mpg for say 10mph, 20mph, 30mph on a trip long enough to run on the battery out of charge or use some trick to force the car to drive under engine power. If the mpg is bad enough, maybe at those low speeds it's more efficient to go the battery charge route and the ideal thing to do is to actually drive faster. Nice and counter intuitive again lol.
It's been a while, but based on my experience with my Corolla, it did quite well at low loads. 45mph was roughly the best mpg, 35mph it gave very good numbers still compared to the 45mph number. I didn't drive it under 35 very often so I don't recall how much the mpg dropped at lower speeds. I know when it was cold started from my parent's house, I always targeted hitting a reasonable mpg figured by the first corner (1/2 mile down the road, slightly down hill). It's been a long time since I did that, I think it was around 45mph I'd get the car up to then coast in neutral till the stop sign and I could hit 35mpg+ on the scan gauge. 25% of 45mpg is 33.75mpg, so I guess I was targeting about the same efficiency as my normal driving but with a cold engine (25% less FE). Really crazy how all of these numbers are working out so well.
Anyway, all of this math and thought experiments gives me some ideas. Of course low hanging fruit first, fix the front end of the car up, get the rear strut fixed (might lower mpg since it will sit higher), grill block(s). Belly pan should be a good item too, basically try to insulate the engine so it warms up faster, but not restrict air flow too much so the radiator can still do it's job, hood seal helped a ton on my corolla to keep heat in the engine for longer. Seems like the most gains on a prius are more engine/trans/heat related than the really easy areo stuff.