Would double battery = double mileage?

[dcb]

my main concern about that is I don't know the limitations of the mini-scan or if it is relying on the cpu, since both are a bundle of variables (a big part of software is variables) would rather go to the source, i.e. is there a hall sensor on the mg1 and mg2 leads and batt leads? and where do they figure engine watts? Not expecting you to jump into that compared to the ease of a plug in scanner, just painfully aware of the limitations of trusting what a computer is telling you about a sensor.

But understanding we don't know what the software/system is doing (i.e. if it is just measuring mg1 and batt and deducing mg2 or something) then we don't really understand the data.

[bwilson4web]

Originally Posted by dcb

my main concern about that is I don't know the limitations of the mini-scan or if it is relying on the cpu, since both are a bundle of variables (a big part of software is variables) would rather go to the source, i.e. is there a hall sensor on the mg1 and mg2 leads and batt leads?

Let me try and answer what I think is being asked:

• "the cpu" - the miniscanner has a microprocessor that issues and read OBD commands to the car computers. It uses the 10.5k BAUD, ISO-9141 interface using KWP2000 (variable packet length) via the K and L line pins. In this respect, it is nearly identical to the ScanGauge II. But Scangauge owners have to program XGAUGEs to retrieve engineering data. Graham Davies went to considerable effort to reverse engineer the NHW11 Prius protocol and make sure he returned engineering units. So far, operational data has matched the vehicle specs.
• "the source" - are kilowatts of variable 240-330V AC, three-phase signals, variable traction battery voltages in the 240-330V DC range along with other Hall, magnetic, and potentiometer sources. All of the hazardous electrical power sources are well protected including safety interlocks and thus difficult to reach without risking breaching the automotive safety systems. It isn't impossible to add instrumentation taps to the sources but some of them are located in the engine compartment of a running car, not a trivial task. I had started that process when a used, Graham miniscanner became available.

Originally Posted by dcb

and where do they figure engine watts?

The raw data is loaded into a spreadsheet and converted to watts using standard engineering formula:

• watts = volts * amps
• watts = k * rpm * torque
• transaxle gear geometry - if you know two of ICE, MG1, and MG2 rpm, the third can be derived based upon the fixed gear teeth ratio
• fuel flow = mass air flow / 14.7

I intend to provide the raw data as part of a spreadsheet with all of the constants and formulas.

Originally Posted by dcb

. . . Not expecting you to jump into that compared to the ease of a plug in scanner, just painfully aware of the limitations of trusting what a computer is telling you about a sensor.

I'm used to it:

• ~15 years - network engineer
• ~5 years - network operations
• ~5 years - architect for automated test system
• ~15 years - operating system programmer

What about you?

Originally Posted by dcb

. . . But understanding we don't know what the software/system is doing (i.e. if it is just measuring mg1 and batt and deducing mg2 or something) then we don't really understand the data.

I have only had a Prius to study since October 2005, to understand what is going on, and I'm still learning. For example, I had never considered measuring the electrical path efficiency by using the ratio of MG1 and MG2 watts. In the past, I just used an approximation 92% efficiency for MG1::MG2 energy flow and had a rule of thumb, 92% * 92% ~= 85%. So I knew the professor's lecture notes of "70%" were dreadfully wrong. I have seen similar reports by hybrid skeptics which is quite common in EU 'papers' dismissive of the Prius. BTW, my 92% was an approximation that came from the Oak Ridge papers cited earlier.

Remember the old saying,"Aerodynamically a bumblebee can't fly." That is how so many hybrid skeptics fail by taking one piece of information without looking at the system as a whole. It is like declaring a circuit to be inefficient because it has a resistor.

Bob Wilson

[IamIan]

Originally Posted by bwilson4web

It is the integrated system of ICE and transaxle that gives the Prius unmatched efficiency.

'unmatched efficiency'....????

In what specific limited context are you thinking of?

Unmatched I think goes too far ... the context will matter of course ... different designs are stronger or weaker in different contexts ... but unmatched ? ... that is too open ended ... and I know of several contexts that there are other more efficient systems than the Prius system.

Don't get me wrong... the Prius system has it's benefits ... but I think you went to far... and left it too open ended ... as it is , left that open ended ... the statement is incorrect... I think you need to add some qualifiers / limitations to make it correct.

[bwilson4web]

Originally Posted by IamIan

. . . I know of several contexts that there are other more efficient systems than the Prius system. . .

Examples?

Bob Wilson

[IamIan]

Originally Posted by bwilson4web

Examples?

Sure ... I'll break it down into a general example of what I am referring to ... there are other examples of course for different contexts ... and there are millions of potential contexts , thousands of different vehicles can be explored ... I have no intention of going through all of them... it would take years.

First I would like to make it clear I do think the Prius design is a good one ... but no one design is the best at everything ... context always matters ... My impression on the Prius design intent is to minimize low efficiency , not maximize high efficiency.

Steady State Contexts: ( Easiest )
There are several system designs with higher peak ICE efficiencies than the Prius ICE ... as I recall the Prius BSFC it tops out around ~220g/kwh ... under ideal conditions ... which is good compared to some ... but not the best... there are ICE's with better.

If the vehicle operating context allows for steady state operating conditions that are close enough to the ICE's peak operating efficiency point ... this peak operating point of the ICE dominates the available mechanical energy efficiency from the fuel to move the vehicle with.

The transmission between the available Mechanical energy and applied mechanical energy has it's operating efficiency limits ... the Prius has a good transmission ... better than some ... but I doubt it is the most efficient transmission ever made ... because there are other transmissions that already operate at high efficiencies ... in addition to conventional transmission losses the synergy drive also adds apposing generator action in the power split planetary gear set ... there is not a large margin of improvement even available , even for those it is better than... this gives us a maximum amount of applied to the wheels mechanical energy per unit of fuel.

The net vehicle design also results in a minimum amount of energy for vehicle to move at any given speed or any given distance ... The Prius uses less energy to move than many vehicles ... but it is not the best ... there are several that use less... the Honda Gen-1 Insight for example at a steady ~50MPH needs ~27% less mechanical energy per mile to move than a Prius does.

Energy Out / Energy In = Vehicle net system % Efficiency.

A variety of vehicles in this steady state context can result in greater vehicle net system % Efficiency.. weather it be from lower amount of energy to move ... or from a greater amount of applied mechanical energy per unit of fuel.

In order for the Prius system to beat the system efficiency potential of the Gen-1 Honda Insight the ICE would have to operate at more than ~27% better ... and the Prius ICE peak efficiency is not 27% better.

It doesn't have to be just the Gen-1 Insight ... there are other ICEs that have higher peak efficiencies than Prius ICEs ... and there are other vehicles that use less energy energy to move than the Prius... and I suspect other transmissions that have equal or greater efficiency ... etc.

- - - - - -

We can also look at some of the other components ... Battery Cycle Efficiency ... Inverter operating efficiency ... Motor operating efficiency ... etc ...

The Prius system is good ... It's motor is good ... but no one motor is the most efficient motor under all contexts ... design compromises are part of the real world ... it's Inverter is good ... but it is not the most efficient inverter ever made under all context ... it's batteries are good , but not the most efficient ever made under all context ... etc.... etc...

It is a good system ... but 'unmatched' ... that is too open ended and goes to far ... unless you add more qualifiers or limitations ... as is , it is just an incorrect statement.

[Frank Lee]

....^... yesh....

[bwilson4web]

Kinda of a long route to just one example:

Originally Posted by IamIan

. . . the Honda Gen-1 Insight for example . . .

So let's see how it stands. Looking at payload passenger and cargo cubic feet mile per gallon:
Fuel Economy

• 2,151 = (36+6.5)*50.6 :: 2001 Insight (compact, auto), 7 vehicles
• 2,856 = (36+6.5)*67.2 :: 2004 Insight (compact, manual), 4 vehicles
• 4,585 = (89+12)*45.4 :: 2003 Prius (compact, auto), 25 vehicles
• 5,684 = (94+22)*49.0 :: 2010 Prius (midsize, auto), 149 vehicles

36 ft. cu. estimated using 2003, compact Prius cabin scaled by 2/5 seats.
6.5 ft. cu. reported by Edmunds as a 5 ft{3} and 1.5 ft{3} space.
I prefer user reported mileage, real-world drivers.

Now these numbers may seem strange until you translate them into a specific example. So imagine you have four parking lots filled each with the above make and model of cars but empty gas tanks. You have 100 people each with a suitcase who need to be moved 100 miles in the next three hours including loading and fueling (aka., the Katrina evacuation) but there is just 50 gallons of gas (everyone brings just 0.5 gallon of gas.)

Which car(s) do you use?

1. 2001 Insight - requires 50 vehicles to burn 1.98 gallons each or 99.0 gallons
2. 2004 Insight - requires 50 vehicles to burn 1.49 gallons each or 74.5 gallons
3. 2003 Prius - requires 20 vehicles to burn 2.20 gallons each or 44.0 gallons (plus 4 Insights or 2 Prius or 6 gallons spare)
4. 2010 Prius - requires 20 vehicles to burn 2.04 gallons each or 40.8 gallons (plus 6 Insights or 4 Prius or 9 gallons spare)

Efficiency ~= output / input :: (passenger + cargo ft{3}) * miles / gallon

Bob Wilson

ps. It might be fun to model the Leaf with generators that need to charge them up for 100 miles.

[Frank Lee]

Not if you have 1 person + some stuff/vehicle cuz they're all going different places at different times.

[jamesqf]

Originally Posted by bwilson4web

So let's see how it stands. Looking at payload passenger and cargo cubic feet mile per gallon:

Except that that's more than a little misleading: a 747 configured for max passenger capacity can get over 100 mpg, but it's hardly efficient for one passenger. Rail can do even better, 400-500 passenger-mpg, but again hardly efficient with one passenger.

I wonder, though, about the relative efficiency of Insight vs Prius. Prius has all those motors & gears going into its drive, which would seem to present the potential for some friction losses &c. Insight just has a regular gearbox with the electric motor bolted to a fixed shaft, so no additional mechanical losses above what a standard transmission would incur.

[bwilson4web]

Originally Posted by jamesqf

Except that that's more than a little misleading: a 747 configured for max passenger capacity can get over 100 mpg, but it's hardly efficient for one passenger. Rail can do even better, 400-500 passenger-mpg, but again hardly efficient with one passenger.

I would be more impressed if you had bothered to post an example:

On the flight to Dallas/Fort Worth, I asked the flight crew on each leg how much fuel and how many seats. I used the Huntsville to Dallas distance via Google Maps for the distance and wall-clock time. So I was able to calculate my miles per gallon for the trip and the elapsed, net speed, including the plane change in Atlanta.

Where is your data?

I'm sorry but this is an especially weak, 'special pleadings' to make to someone who lives in Huntsville AL. We just had the latest 'airline closing our Huntsville operation' to our local airport. So every time I pay for my own flight, I find the best price from either Nashville, TN, two hours away, or Birmingham, AL, two hours away. I'm very much aware of load factors and the impact upon flight routes from direct, personal experience.

Originally Posted by jamesqf

I wonder, though, about the relative efficiency of Insight vs Prius. . . .

Excellent point, let's look at the respective specifications:

• weight - 1,865 lbs vs 2,765 lbs
• cross-section - (66.7 x 53.3) vs (66.7 x 57.6)
• coefficient of drag - rear wheel well covers vs. nothing:
  
  
  

Lower weight is lower rolling resistance. Smaller cross-section is lower drag for the same coefficient of drag. Closer to laminar airfoil, lower drag for same cross section. As for vehicle drag, ask the owner of the Honda with a 0.10 coefficient of drag:

Originally Posted by Frank Lee

Not if you have 1 person + some stuff/vehicle cuz they're all going different places at different times.

Ok, based upon your specs, here is your next car:

Of course this is unfair but it shows the where this argument leads to.

In reality, I'm a great believer in "the right tool for the right job" but sometimes you get a tool a little larger to deal with outsized loads . . . like groceries or taking co-workers somewhere. But I also have co-workers who commute on motorcycle (except when it rains or icy or snow or too cold or too hot.)

Bob Wilson