Discussion in 'Gen III 2010+ Prius Fuel Economy' started by Prius42, Jun 19, 2010.
It's the switch over from 24 hr night vision to 24 hr daytime vision Alaska style.
What tool did he use to get those numbers? I want to order one.
No, not Techstream-Lite. The annual subscription for that is a killer and it requires you to drive around with a laptop. While I would be okay with that with specific projects in mind, it wouldn't be something I would do every day.
I'm using a DashDAQ:
DashDAQ from Drew Technologies
Which I've started (but am remiss in updating) talking about in this thread:
It is relatively expensive, but a very nice package. Right now it will display, graph, and log generic OBDII PIDs, the optional GPS (which I have), and a bunch of external devices including a few analog voltage inputs. They are working on the Toyota specific ECUs/PIDs and they signed me up as a beta tester, but only a few work so far. Specifically I have access to ECU 234 (Engine, and ECT) which has about 100 PIDs, ECU 60 (hybrid control) which has 16 PIDs of which very few are interesting, unfortunately, and ECU 61 (also Engine and ECT) with ~60 PIDs many of which overlap with ECU 234. The company is working on enabling more ECUs and I'm waiting on them to release them!
I've had the device for about 2 weeks now and it is a lot of fun. I really like being able to see the data as round gauges, digital readouts (you can easily do 24 at once), and/or a stripchart-like system for looking at the time history of multiple PIDs at once. You can use their standard layouts or there is a layout editor for creating your own gauges and gauge screens. The device runs Linux and has a very nice screen. So far they are totally not interested in making a user configurable "X-gauge like" system, but so far I'm the only person who has ever asked for it. They seem pretty responsive so it might just be a matter of applying group pressure.
So far I really like this unit. The only real drawback is the price, which is high.
Attached is a picture of the unit mounted on my dash with a proclip mount. Unfortunately, it isn't turned on in the picture, which I took for something else, so you can't see how nice the display is. I keep planning on adding a lot of info and screen shots to the thread above but I need to find some extra time somewhere...
The stripcharts I included in my previous post were absolutely trivial to generate. The data file can have many formats, including CSV and is recorded to SDCard. You can read them in excel, but I used a scientific visualization program for Macs called Igor.
Judgeless, this should answer your question too. If you have more questions about this tool, let me know and I'll try to answer them.
So far, in my limited experience, getting descent mileage on my route is just managing the many small hills and the even more abundant crazy drivers. If there is nobody behind me I let the car decelerate going up hills and glide down them and that seems to do well for me. I've gotten as high as 67 mpg (HSI) on my commute when traffic is light. When traffic is heavy I have to maintain speed going up hill and stay well over the speed limit on 2 lane roads, or get run over (or worse, it is DC). In those cases mileage suffers. Still, driving carefully only helps on the margins, in the sense if I drive with a lead foot 10-15 mph over the speed limit, I still seem to get 52-55 on the HSI now that the weather is warmer.
BTW I got a fancy new digital tire pressure gauge for fathers-day and checked what air pressure the dealer put in the tires. It looks like 39 PSI front and rear after 6000 miles.
Sounds like I am doing pretty much the same, but I can't break 56 on the HSI for a tank. Have a 30 mile rt commute with maybe an 800' elevation change over 15 miles. Pretty flat. They just repayed the way and that seems to be helping. At least it sure is quite now.
Shoot for $549, that is not bad. Does the unit have RCA or USB outputs?
Thanks for the info!
G3 Prius spins the ICE at speeds over 46 mph. If you can coast (glide) at 45 or less, you save 2 kW. Since road and air friction at these speeds only takes around 5 kW to overcome, the difference in fuel consumption between 45 and 46 mph is ~ 40%. Assuming 50% ICE and 50% coasting, a 20% MPG improvement might be available to you if the route allows.
This is how I hit MPG in the 70s with my G2 Prius, although I have to travel at a lower speed because my ICE spins at 41 mph. G3 might work well in P&G between 38 and 44 mph.
Good Luck, and nice work!
Hi spiderman. The unit has two USB ports for accessories. I have a GPS connected to one of them. On the back there is a Molex-like connector that has two 0-5V analog inputs and two RS232 ports for more accessories. There is a third USB port that is peripheral-mode, not host-mode which is for plugging the unit into a computer to update its firmware. I'm thinking about using the two analog inputs to monitor the voltage and current from the solar roof, although I may have to add a shunt and an amplifier to get the current. I have to find the energy to take apart the dash, which might take awhile...
I don't have any advice for you about getting better than 56 mpg. You probably know the theory better than I do. You might try just going nuts one day and drive like a real laggard and see if it makes any difference. If it does, at least you will have bounded the problem even if it isn't practical to commute that way.
That's great SageBrush! I knew that the ICE provides some drag when it is spinning but not fueled, but it is nice to see it quantified. I noticed today that the ICE always spins at 1000 RPM when you apply no accelerator above ~46 mph. I believe I read that it does this to keep MG1 from exceeding its max rotation rate. The funny thing is, it is always 1000 RPM regardless of speed. I tried 50, 60, and 70 mph and it was always 1000 +/- 10 rpm. Does it spin faster when the car is at even higher speeds, i.e. what is the "coast" rpm at max -speed (~110 mph)?
I also wondered how your 2 kW of engine drag compared to what I measured with the cars ICE absolute-Torque PID. I assume this is some sort of load cell on the camshaft, but I have no idea how it is really implemented. Anyway I measure the drag torque of the non-fueled ICE at 10-11 ft-lb.
Taking the higher number which is what it usually reports, and converting to SI units, this is 14.9 N-m. Now we need to convert to power. Energy is torque through an angle, and power is energy/time so in SI-units
power (kW) = torque*2*pi*rotation_speed
= (torque (N-m) * 2*PI * RPM)/6e4
= 1.56 kW
Which is pretty close to your 2 kW. Since I can measure ICE torque and rpm, I can make a new gauge to give me ICE power! Excellent...
When I have watched rpm with a ScanGauge II in my G2 Prius, rpm does increase with coasting speed, although I think it is stepwise. The 2 kw drag number came from Prius wizard Hobbit testing his G2 Prius.
Your results just sound like a nice improvement in G3, although I also do not know how your torque is being measured and have no idea how accurate it is.
I guess that's the apples/oranges thing coming into play. I am new to my 2008 Prius....about 3 weeks. I have adjusted my driving drastically based on what I've read here in the forum. I am close to 50mpg (49.4) on this tank at around 270 miles. My commute is very mixed roads, suburban, then state route w/lots of stop lights ...then about 10 miles of normal 45-55mph roads. Lots of hills which help on the way and hurt on the way home. I have had my air on constantly as well due to the mid 90 weather and humidity. I live outside Philly so Maryland is probably pretty similar driving. I envy 60mpg as I doubt I'll ever see that with my normal driving. The warm up cycle was something I wasn't aware of till I really started watching so I see the quick trips to the store are not helpful at all. I was taking quick hops a lot early just to drive my new car ....but now I see the wisdom in combining trips instead of running to the store for a quick item etc. It seems 49-50mpg is going to be about the best for my normal driving but that's in my Gen II. I do see some in my car doing much better but I can't figure out how w/out holding up traffic. Since my last car was only getting 19mpg and required Premium ...this is a homerun for me at any rate. Is there a major difference in mileage between the Gen III and II??
I haven't yet seen anything but 1000 rpm for the coasting ICE at 50,60,70 mph. I'll try 80 next week and log the whole thing. I'm also seeing the coasting torque vary between 9-11 ft-lbs. I'm going to try and get some deterministic numbers from the logs to see if the G3 actually has lower ICE coasting drag than the G2. This is all modulo the accuracy of the torque PID in the G3. Do you have a link to how hobbit measured this for the G2 or which search term to use to find it? Thanks!
I wouldn't worry about it all that much, after all getting a practical 50 mpg is, you know, fantastic. Trying for higher mileage and figuring out how the car works, is just something to do with a new toy on an otherwise very monotonous commute. It seems more constructive than the nutcases weaving in and out of traffic to get to work 30 seconds sooner.
Laughed out loud at that "nutcase" comment. I must admit I was one of those nuts not long ago and this car has certainly mellowed me out. I have noticed that many of the people flying by me at 80mph end up only one or two cars ahead at the next road work lane closure or stoplight. I listen to my music and as you say carefully watch my display to manipulate the throttle for best gas mileage, all the while happily tooling down the road while my wallet doesn't take a beating nor the environment. Works pretty well.
Well what's the new EPA rating for the Gen 2? 48mpg isn't it? You're already ahead. It really depends on the area you live. I remember a few years back, those getting 60mpg+ were mostly those in the southern states (except EFusco and Tony). The rest of us had to content with "only" 50-55 mpg. But as more and more folks got into the Prius, we started seeing higher mileage being attained elsewhere and I'm thinking if those ppl can get 60+mpg in the Gen 2, they can probably touch 65 or even 70mpg in the new one.
I'm already beating my old Prius' average even though I'm living in a colder climate.
Excellent job! You are my hero...seriously, I have struggled to get to 51mpg's. I need to go back to the drawing board and see what I'm doing wrong.
Well said. It happened to me this morning as a Ford F-350 was riding my bumper, then flew by me. I cruised to the red light and guess who was sitting there on my left side...the F-350. Nutcases never win!:rockon:
I recommend these articles by Hobbit:
Sweet spot refinement
The first article discusses the benefits of using the ICE in its highest efficiency mode or not at all, i.e. the basis of pulse-and-glide. This means, essentially keeping the ICE at around 15 kW output (20 HP). (See the engine efficiency graph and explanatory text in the article). The GIII seems to have a larger power range where the engine ECU keeps the ICE at peak efficiency starting around 12 kW up to just over 30. Still the idea is to keep the ICE at the lower end of this range but not below it. If you run the engine at too low a power output you may burn less fuel but you aren't getting much for it, and your fuel efficiency suffers.
The 2nd article tells you how to operate the ICE at peak efficiency using the HSI. The HSI appears to be, essentially, an ICE power output meter above the center line. As Hobbit points out, 15 kW is about where the HSI bar graph is equal with the right edge of the "ECO" indicator.
My new DashDaq will read out ICE engine torque directly from the engine ECU (234). This coupled with the engine RPM, available from the generic OBDII PIDs, gives a direct way of measuring ICE power output (power = torque*rpm). I programmed this into my DashDAQ and made a gauge for it:
The gauges on this page are (left to right) ICE power (kW), ICE torque (ft-lbs) and RPM. The digital gauges under the analog gauges are Batt SOC, coolant temp, and instantaneous Fuel economy.
This is really helpful since I can roughly calibrate the HSI display, and I have something with tick-marks which is a lot easier to read and control accurately than the HSI.
So, the HSI is approximately an ICE power output meter although it is not very linear. At cruising speed, I measure the HSI vs actual power output as: the center line (where the ICE is almost certain to kick on) is about 10 kW, the right edge of the "ECO" label (as reported by Hobbit) is at ~15 kW, the dividing line to the "power" area is at ~25 kW, and the right edge of the power area is at about 45 kW. These are all approximate since it is a bit of a drag to look at two spatially separated gauges at once. If I could log the HSI like I can the DashDaq signals then I could do this more exactly and also see if the HSI is really a power output meter or whether these correlations vary somewhat with speed, for example. At least at cruising speed (40-60 mph) these values appear fairly stable at +/- 10% or so.
Keeping the ICE at 15 kW (right edge of "ECO" symbol), as hobbit points out, does accelerate the car well above 60 mph on the straight-and-level. It will also keep above 55 mph going up a slow incline. If you try to maintain this power output, you will probably build up too much speed, which is fine because then you take your foot off the accelerator and then nudge it into glide (around 1/4" showing on the HSI, using the traction battery to counter-act the unfueled engine drag). Slow down a few mph and repeat.
I started off having a pretty awful tank this time around. I was in stop-and-go long enough to deplete the traction battery and run the ICE for a long period of time at nearly a stand-still. It was 99F and really humid, so the AC was running full-steam. Fuel economy was terrible. I've been playing with using 15 kW as a target point for two days and the HSI now says 61 mpg at ~250 miles. Now I'm having a reasonably good tank. I'm also not babying the car as much as I was during my last tank but keeping at 60+ on the highway. The point is not to go slow, but to keep the car from running the ICE at low efficiency. You actually need to run the ICE a bit harder than just watching the instantaneous fuel economy meter might indicate which will build up some speed, and then turn the ICE off for awhile. Your average mpg will be better than trying to keep the HSI around the center line.
The hypermilers here are probably all laughing at me by now (since they know all of this), but this is really coming full circle in my understanding of how to operate this car. I also really like the DashDaq for letting me see a lot of the data that makes this a reality for me. It really is a nice toy.
Finally I'm really sorry to Hobbit for poorly paraphrasing his excellent articles. Read-them, they are well written.
Finally here is a link to a few of the other DashDaq displays I've put together to monitor and log many parameters at once (sorry about the poor quality iPhone pics):
Sorry if this is a dumb question. I'm brand new to my 2010 Prius, and am trying to get mileage like yours. How do you know when your friction brakes are being used?
First I want to thank you for the write-up. I had not heard of the DashDaq before. At $700, it is a little pricy since I already have a nuvi GPS but I can see where many would find value. I keep looking at my GPS and wishing it also recorded vehicle data.
One thing I was curious about:
I've done similar things with a Graham scanner, recording the data for later analysis. Combined with injector timing or MAF data, I've been able to make a BSFC chart.
Their web page reports:
Do you know if these are coming from an actual torque sensor in the engine or perhaps some kind of 'table lookup?'
The reason I ask is in the case of the NHW11, I use MG1 torque and divide by 28% to get the engine torque. However, due to sampling errors, I can get 'impossible' values during transients. For example, the Graham scanner samples at ~100 ms. for each value but the engine state can change much faster so the product of the rpm and torque are coming from different sample times. Do you see 'impossible' power values during power changes?
Another reasons for seeing variance is the existence of what used to be called 'heretical mode' or Toyota calls energy recirculate mode. The power split device normally flows power from ICE to drive at lower speeds but at higher speeds, from drive to ICE to force lower rpm, high torque drive.
Any idea of the data sampling rate with our ZVW30 Prius?
Have you considered plotting fuel per power vs. RPM? This should give a BSFC chart to compare with the Toyota papers. It also gives 'field' values which again helps map out performance. A typical BSFC chart is done with a dynometer using an engine test stand with the throttle wide open. In the 'real world', there are partial throttle conditions these BSFC charts don't address very well.
Thanks again, nice write-up.
I have my first 10 tanks now, HSI =61mpg avg, Pump says 59 mpg avg. Got one tank at 65 mpg HSI . Avg speeds 40 mph, little AC, no cruise, 44 psi, ECO mode, mixed driving, lots of hills. Use all the tricks documented here.
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