Cruise control operated pulse and glide

Some of us over in GreenHybrid are planning to do some comparative testing of pulse and glide versus steady-state speed. The first problem is coming up with a reproducible, pulse and glide protocol. The following pulse and glide protocol eliminates the 'foot feather' so we can get consistent, reproducible results:

1. Start at 43 mph on cruise control
2. Pull back cruise control to 'suspend' speed control
3. At 40 mph, put car in "N" for a ballistics glide
4. At 25 mph, put car in "D" and resume cruise control
5. When car reaches 43 mph, GOTO first step

This is a 25-43 mph, pulse and glide cycle, the maximum speed range that can easily be supported by the cruise control. Cruise control 'turns off' at 23 mph so the 25 mph low end avoids having to reset it each time. The acceleration from 25 mph to 43 mph will always follow the the built-in cruise control profile. The "D" mode coasting from 43 mph to 40 mph will trigger the ICE to stop. The ballistics glide from 40 mph to 25 mph will achieve a uniform, minimum drag coast without special effort.

The only drawback of this protocol is going down a grade in "N" violates many state driving codes. However, like traveling 5 mph over the speed limit, this is not a big deal in most jurisdictions and enforcement risks are a different problem.

There are several variations of this protocol:

• 25-43 -- maximum P&G speed range
• 25-38
• 25-33 -- minimum P&G speed range and minimum speed
• 30-43
• 30-38
• 35-43 -- minimum P&G speed range and maximum speed

This will let us develop a performance model that should allow us to compare P&G to an identical, steady-state speed over the same course in the same conditions.

I did some practice runs this afternoon and this is what they look like:



This was on an access road that was not terribly level but enough to get an idea of the equivalent, steady-state mph, 33-34 mph. Last year I was able to plot some steady-state speed runs:


For this test, I'll run a combination of pulse and glide and constant speed runs.

Bob Wilson

 

<div class='quotetop'>QUOTE(nark @ May 5 2007, 04:12 PM) [snapback]436141[/snapback]</div>

Opps! Will do but it may not happen right away. Give me a day or so:

Y-axis - Miles Per Gallon
X-axis - Speed in Miles Per Hour

Bob Wilson

 

<div class='quotetop'>QUOTE(efusco @ May 5 2007, 04:21 PM) [snapback]436144[/snapback]</div>

I found that once we've reached the cruise control speed, pulling back to trigger 'ICE off' takes a second or so and I need to move my right hand from the cruise control stalk to the shifter. With a little practice, I can be ready to shift into "N" just as 40 mph shows up on the display. I had tried using 41 mph in one case, the ICE didn't shutdown before the car was in "N". In this mode with the car in "N", the ICE continues to run until put back into "D." For me, it is a question of squeezing in two manual steps and I'm comfortable with a 43 mph to 40 mph interval.

<div class='quotetop'>QUOTE(efusco @ May 5 2007, 04:21 PM) [snapback]436144[/snapback]</div>

In engineering testing, I like to minimize all other variables. I have no doubt that there may be special cases but I need a baseline first. Then we can investigate things like 'terrain driving' and other effects. But if I'm investigating these special cases, expect to see them taken one at a time using a methodology that can be easily (relatively easily) repeated by anyone.

Actually we can compare Friday and Saturday practice sessions. The difference is Friday used an access road with about a +/- 5m change in elevations and the Saturday session used a route with +/- 1m difference:





BTW, I'll be sharing my raw data along with a spreadsheet with formulas and small samples. The source data will consist of time stamps with millisecond resolution:

1. MG1 rpm and MG1 torque in one sample
2. MG2 rpm and torque in one sample
3. battery current
4. MG2 torque and rpm in one sample
5. MG1 torque and rpm in one sample
6. fuel injector time in milliseconds

Each cycle takes a little over 1 second.

Bob Wilson

 

Preliminary data using 25-43 PNG and 34 mph CC:
Direction,Temp,Style,MFD MPG,Distance
S,73,CC,73.9,2.6
N,73,CC,84.8,2.6
S,73,PnG,77.8,2.1
N,73,PnG,94.1,2.2
S,73,PnG,84.9,2.1
N,77,PnG,93.0,2.6
S,77,CC,76.5,2.6
N,77,CC,90.2,2.6
S,77,CC,70.0,2.6
N,77,PnG,90.3,2.7

Averaging all five samples:
88.0 - PnG (+11%)
79.1 - CC

Averaging the middle three samples:
87.0 - PnG (+12%)
77.1 - CC

I've recorded the data with a Graham scanner and will do a detailed energy analysis later. However, I'm not happy with the variations in results:


Of the samples, I'll start my detailed analysis with the best and the worst of PnG and CC. This will hopefully give insight to improving the protocol. A cursory look at the data suggests the north bound tests did better than the south bound tests but the relative performance ratios look to be about the same.

Bob Wilson

 

<div class='quotetop'>QUOTE(thebrattygurl @ May 6 2007, 10:57 PM) [snapback]436662[/snapback]</div>

Scoop them back in because I think I've figure out a fix to the data variability. With Pulse and Glide, I have a great deal of operator input so I can ensure complete cycles. However, with cruise control, there is a cycle of ICE on/off that I have no control. I'm hoping my Graham data provides enough detail that I can adjust for complete ICE on/off cycles. But there is another fix.

I can use the 'forced charge' to put the battery in the same state at the beginning of each run. This will give both Pulse and Glide and steady-state cruise control the same 'boost'. The overall numbers will be unreasonably high but I can document that with a warning. But the main thing is I should achieve groups of results closer together so we can compare the differences.

The risk is my 2.5 mile test course may be too short. Even at 34 mph, a fully charged battery may run for such a large portion that I don't get a full cycle. My only alternative is a stretch of about 15 miles west of Decatur that looks to be fairly flat. It is a divided highway and I can drive it safely with blinkers.

The ultimate answer is a closed, flat track but I'm concerned about fees. If the speeds were slower, I could use some of the large parking lots and I may try one or two just for grins. Most of these lots are posted at 25 mph so 34 mph is a little too obvious but we'll see.

Bob Wilson

 

Here are the first five samples showing:
<blockquote>CC - south 73.9 MPG
CC - north 84.8 MPG
PnG - south 77.8 MPG
PnG - north 94.1 MPG
PnG - south 84.9 MPG</blockquote>




This are the last five samples showing:
<blockquote>PnG - north 93.0 MPG
CC - south 76.5 MPG
CC - north 90.2 MPG
CC - south 70.0 MPG
PnG - north 90.3 MPG</blockquote>




One unexpected result using cruse control for 34 mph was how little time the ICE was off and the vehicle sustained speed on just battery power. Although the transaxle operated in "energy recirculate" mode, there was not enough battery energy to "stealth" mode on battery power. The accumulated ICE run time led to the lower CC MPG. This is a good strategy for battery life, avoiding charge/discharge, but not so good for low fuel efficiency.

This also suggests 'great expectations' for higher battery energy are unlikely to be realized in practice. It may be that the battery is really there to handle short term energy demands and operating the transaxle.

There are more details to look at but this gives a big picture of what is going on at 34 mph CC and 25-43 PnG.

Bob Wilson