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IMA in Action

One of the things I noticed while we had the Accord Hybrid was that NOBODY ELSE will notice that it's any different from a normal Accord. This is quite a departure from driving something like the Prius, which practically shouts "LOOK AT ME!!! I'M AN ECO-GEEK!!!" or "OUTTA MY WAY!!! I'M HEADING TO A TREKKIE CONVENTION!!", provoking stares, swiveling heads, finger pointing, lewd hand gestures, etc... For many people, the Accord Hybrid's invisibility is a GOOD thing. Regardless of how exciting it looks (or doesn't), it's quite a pleasure to drive. How many other 5-passenger, normal looking cars do you know of that can zing from 0 RPM to 60mph in right around 7 seconds? And what's more impressive is that this Accord does it with very little drama - the Accord's gas V6 is already one of the world's best V6s on the road, and obviously having the instant services of up to an additional 100lb-ft of peak torque on tap only helps. This car is not astonishingly quicker than a normal Accord V6, and unfortunately we were unable to run any side by side comparisons, but it certainly has more zest overall, even with taller ratios in the automatic gearbox.

Since Honda's IMA technology does not permit the vehicle to run exclusively under electric power, it is often categorized as a "mild" hybrid system. This label doesn't always sit well with Honda PR folks, but the Accord Hybrid is probably one of the "mildest" of "mild hybrids" now available.

Much of the time in normal driving the "charge/assist" gauge will show little to no activity and the battery level barely seems to fluctuate. On the other hand, the "ECO" light (which illuminates during cylinder deactivation) cycles rather frequently. Contrast this IMA activity to the Civic Hybrid, whose IMA-related dashboard updates flash with a frequency rivaled only by a video game. Also, the Civic Hybrid's state of battery charge is much more dynamic than the Accord Hybrid's. This is most likely because the electric motor assist of the Civic Hybrid's IMA system contributes a larger proportion of the vehicle's propulsion than the Accord Hybrid's.

The Accord's IMA system takes a path to efficiency that seems to be geared more towards preserving kinetic energy and enabling the VCM to operate as much as possible. For example, take the case where you are cruising along on the freeway and you have to brake lightly for a merging car. While at a steady cruising speed (so long as it's below approximately 82mph), the engine will most likely be engaging VCM's 3-cylinder mode. Now when you tap the brakes to slow for the merging vehicle, the IMA system will use its regenerative braking mode to "make a deposit" into your "energy account" (battery pack). Once you're clear of the impediment, you can gently resume your speed and if you're easy on the throttle the IMA will "withdraw" the stored energy from your "energy account", applying electrical assist to help resume your original speed while (hopefully) maintaining VCM's 3-cylinder mode. The idea is to minimize the impact on fuel economy of such interruptions. The actual impact of such an incident may seem insignificant, but considering how many times you have to change your speed on a typical road trip, the net savings could be quite significant.

The Accord IMA's system is 95.2% efficient at generating electricity from braking and is able to convert the stored electrical energy back to motive energy at an efficiency of 97.5%, so in theory, every time you're forced to relinquish some of that hard-earned kinetic energy, you're potentially getting a 92.8% rebate on the energy that would have otherwise been disippated as heat.

Even at a steady state cruising speed, you will see the IMA and VCM systems working in concert to maximize efficiency. As the road changes elevation and even with minor variations in wind conditions, the load on the drivetrain will fluctuate. As the load demands increase, the IMA system will attempt to serve these increased demands to maintain 3-cylinder operation for as long as possible. For most load fluctuations, the IMA assist is adequate, but in more extreme cases, the VCM will instantly and transparently shift to 6-cylinder mode until the load demands settle back to a state allowing for the more efficient 3-cylinder mode of operation. Again, this may seem like a minor contribution, but the net effect is fairly significant.

Obviously in extreme cases, such as when you romp the throttle, all eighteen or so bars of "assist" will illuminate and maximum available thrust will immediately be delivered to the front tires. But unless you're ripping down a dragstrip, you will rarely leave the hammer down for even as long as 10 seconds (you're guaranteed supralegal speeds if you DO). As such, you very likely won't see the the battery level dip at all during such a romp. Even after a full afternoon of repeated 0-60 runs we only saw the level dip down one notch to three bars of charge. The "normal" charge state of the battery remained on 4 bars for most of the time we had the car, though on one extended tenderfooted drive I managed to get it to register 5 bars (which may or may not have been "full" - it appeared there was space for one more bar on the battery gauge, but we never saw it illuminated)

While driving the car, you cannot feel or hear the IMA or VCM systems as they operate. The only real indication is the multi-function display on the gauge cluster. The VCM is very difficult to detect - more difficult to detect than the VCM on the '05 Odyssey, which is itself very difficult to detect. For a while, I was convinced that I could detect the Accord's VCM operation, but in "blind tests" I turned out to be guessing wrong more often than correctly. So in short, the impact on normal driving is virtually nil.

Due to scheduling constraints surrounding our road test, unfortunately we were unable to carry out any sort of "scientific" testing of the Accord Hybrid's fuel economy performance. The best we can do is provide a few scenarios and data points. Our first drive in the car was about 60 miles and involved a good 40 miles of torturous stop and go Friday afternoon Atlanta traffic. The trip computer reported an average of about 23.5mpg. I later made another trip of similar length, this time in much more favorable traffic conditions and observed a little over 34mpg. The roads were a mixture of 2 lane country highway, freeway, and about 10 miles of surface streets. During our 0-60 testing and photography sessions, we saw the trip computer briefly plunge below 17mpg.

Continue to the next page to view the first published dyno tests of the '05 Accord Hybrid.

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Subject Thread Originator Replies Last Post
  Why the i-VTEC
NSXman 1
  What octane gas for the dyno?
AZCivic 1
  Any word on VCM for all V6 engines
NSXman 0
  The No-Sunroof Hybrid conspiracy.
rkn 0
  wood trim
  The Civic Hybrid was not overlooked IMO
uhhhh 1
  it's not fair.
MugenDX 0
  It would be nice to have the Dyno comparison for low revs
danielgr 3
  Hybrid coupe? (accord or civic)
onefasthuman 1
  Why does the engine look so screwed up in the vid
uhhhh 2
  Hearing VCM operation in the Dyno is normal
danielgr 0
  Engine cut-off system
aznstuart 1
  Oil, Vespa, PR and TORQUEmada
TonyEX 0
  DVD in console???
  Dyno Comparison
  Navi DVD ROM
02TL 0
  nice write up
Dren 0
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