Auto Enginuity comes with a utility called "Speed Tracer" that tries to report different vehicle parameters including rolling drag, ICE performance and MPG. But the initial MPG report was disappointing: We know that slowing down often peaks the MPG as the engine turns off. Worse, this report lacks details about what is going on. This evening, I re-ran a warm-up test with an improved protocol and recorded the generic, engineering data: The engineering data: Coolant temperature - values on the right axis Engine rpm - values on the left axis Vehicle speed - values on the right axis MAF airflow - values on the right axis Commanded EGR setting - values on the right axis Catalyst temperature - values on the left axis, note that the initial values before the ICE started were excessive so I substituted coolant temperature. Thereafter, it reported consistent data. Looking closer at the vehicle warm-up reveals something unexpected: What is interesting is that after the coolant temperature reaches 70C, a critical temperature in the NHW11/NHW20, we suddenly see cooled Exhaust Gas Recirculation coming in whenever the ICE is running. The MAF flow should still be an excellent indicator for fuel consumption since it is upstream of the cooled exhaust input. You'll also notice the initial engine operation is at a constant rpm and not tied to energy needed for gentle acceleration. This data looks promising ... and accurate. Regardless, I like the data quality and it looks like I'll be able to remap MPG vs MPH much easier. ROUTE: http://maps.google.com/maps?f=d&sou...03096&sspn=0.270521,0.510178&ie=UTF8&t=p&z=12 Bob Wilson
I think EGR activation is expected. I see it used to control the Cat temp. Whenever ICE RPM spiked, EGR was activated to lower exhaust temp and prevent fuel enrichment. EGR and EHR worked very well. The coolant and Cat temp climbed up and then leveled off.
Just found a really juicy piece of information from Dan Yerace, Toyota North America senior principal powertrain design engineer. Source
Thanks! Every piece of information adds to our understanding. BTW, I added a Google link showing the test route for this data. I traveled down one river valley make a left turn around the end of the ridge and traveled back up another. The altitude changes: ~600 ft - start ~634 ft - end ~638 ft - highest point found on route ~575 ft - lowest point found on route Bob Wilson
Another chart when I tested use of "N" to minimize warm-up fuel costs. Result, no evidence that shifting to "N" saves a dram of gas: One interesting aspect is the ICE speeds up, even when in "N", as the speed increased during the initial hill roll-down. In spite of this, the MAF reported fuel consumption simply rolled down as the ICE warmed up. This chart also shows engine auto-stop happens once the coolant reaches 40C. Bob Wilson
It is great to see the coolant temp increases when the ICE is in use. The coolant temp increased by 52 deg C (64 -> 158 deg F) in about 9 minutes. That's about 10 deg F every minute. Your average speed looks to be around 15 mph. We can establish city driving warm up during the Spring increases 10 deg F per minute. Can you start up and jump on the highway? I'd like to see how much faster the warm up with the engine at different load.
This is my NHW11 warm-up route and profile. I wanted to compare and contrast how my 2003 Prius warms up versus the 2010 using the same route and protocol. I've uploaded the excel spreadsheets to "Prius Technical Stuff" forum since that area includes a lot of the 'gray beards.' I like PriusChat but they have this quota that I have to be careful about. Feel free to download the spreadsheets and look at other interesting data. To some extent, my opportunities for highway speeds are limited by the local roads. The best I can do is about 50-55 mph about 0.5 miles from the house and it still has traffic lights. Bob Wilson
Bob, The graph in post #7 is from NHW11? The ZVW30 label in the top right of the graph mislead me. I did not get the spreadsheet but went with the ZVW30 graph from your first post. A rough calculation shows gen3 Prius warms up about 20 deg F per minute, twice faster than gen1 Prius!
It is my wife's ZVW30. Both graphs posted are ZVW30. The first set came from a route that goes to 50 mph versus the last one that follows my NHW11, warm-up route. I just recorded the warm-up data for our NHW11 but in 80F weather. I'll reformat the graphs for nominal 640 width and plot the NHW11 data so we can compare and contrast. Bob Wilson
Here is my NHW11 warm-up route and protocol. The key is use of "N" to the maximum extent possible. I've also run my wife's ZVW30 using the same route and protocol: NHW11 ZVW30 Bob Wilson
The NHW11 test started in the afternoon at 81F. An opportunistic capture. The ZVW30 was at about 4:00 AM, closer to 60F. Still, the pattern is clear. I have a thermistor hack for my NHW11 and when I have it installed, the engine follows the ZVW30 profile. When the 1.5L engine reaches 40C, it spoofs the thermistor to 70C allows auto-stop and Stage-4 to start sooner. But I had pulled it out because I really didn't know what other 'bad effects' it might have including on emissions. Now I see it makes the 1.5L engine follow the same warm-up profile as the ZVW30 so it is going back in, permanently. Bob Wilson
Charts and graphs! Graphs and Charts! Just give it to me in plain english. Is the yearling going to live? Should I plant the crops early? Yes, I'm an idiot...but you lost me after "Hi".
We have a a small but steep hill climb: What I found interesting is the EGR enables on the backside of the hill when it went into lean mode. The EGR kept the catalytic convert temperature flat instead of letting it rise from the lean mixture. I'm going to replicate the hill climb on a taller, longer and faster hill. Bob Wilson
I repeated the hill climb using Brindley Mountain and was surprised at the results: What I found is the EGR works right up to about 3,500 rpm. Thereafter, the EGR backs off, the catalytic converter temperature rises but the car has more than enough power to climb the 8% grade hill. Once the engine speed drops below 3,500, the EGR kicks in and the catalytic converter soon cools off. It also looks like something above 1,500 rpm has some effect on EGR operation but there is not enough data to tell, yet. Since the EGR is used to run a leaner mixture, this becomes an upper threshold speed for fuel efficient operation based upon mixture. Driving by rpm would be a sweet trick for cross-country and hill driving. Alternatively, just drive by catalytic converter temperature. Bob Wilson
I started looking at the correlation between ICE rpm, EGR %, Catalytic converter temperature, and MAF flow: So it looks like the most efficient ICE operating range is a maximum of 3,000-3,500 rpm. Above this ICE power range, there is not enough EGR to handle keeping the catalytic converter in a relatively low temperature range. What we don't have is a good mapping of MPH to ICE rpm. Bob Wilson
Bob, The Brake Specific Fuel Consumption map indicates clearly that the car deliberately goes from best economy to best power at 3,650rpm: This is done to improve acceleration times, and you can see the change from the NHW20 (on the left) which kept torque approximately constant. The shape of the curve above 4,000rpm follows the Wide-Open-Throttle line. The most efficient engine output in terms of power output per unit flow of fuel input is from about 1,200 to 3,000rpm, but that's with the engine on a test bench rather than attached to the transaxle. It may be that transaxle efficiency is poorer below 3,000rpm.
I think we're seeing the same thing in the Auto Enginuity data. The 3,000-3,500 rpm band is the boundary of peak EGR and a transition from minimum catalytic converter temperatures to something higher. As a general rule, the hotter the exhaust, the more energy lost out the tail pipe. I just didn't have enough data points around 3,650 rpm to detect any patterns. Bob Wilson
