Ugh, what exactly is Super Highway Mode (SHM)??

I think it was a CleanMPG thread where I found out about shm... but I have a scangauge.

I think you can hit it without a sg... I use it at secondary road speeds...50 mph ish. Get up to 55 or so then back off a bit. I find it won't quite hold my speed unless it's a slight downhill or downwind. If you're looking at the consumption screen you should see a jump to something like 70mpg. If it jumps higher you may have gone ev instead. You may have to hold the go pedal steady for a couple of seconds for this to kick in.

It doesn't quite hold my speed often, so I use the terrain and pulse on the uphills and shm on downs and flats.

IGN is the ignition timing... I presume degrees before top dead centre, but that's a guess on my part... it's just an indicator for me since shm kicks in at 14 on that gauge.

 

I guess of the three given terms, "state" is closest, though "technique" is vital to achieve the state.

Let's see if we can make this simple. It is where at near-highway speeds the ICE is running under load but very near the threshold where it becomes unloaded and runs inefficiently. If one accepts that the SHM pioneers' criterion of IGN 14 (more on that in a minute) identifies this sweet spot, added instrumentation such as ScanGauge is essential.

Still, you can try it by following BAllanJ's advice: get up to 55 MPH (that's about the max on level terrain due to the higher wind resistance at higher speed) and back off on the go-pedal until just before the ICE cuts off. If you're even in the ballpark, you will still see energy flow on the Energy screen from the ICE to the wheels, and your instantaneous MPG will be at about 1.5 x speed or higher. I've seen iMPG as high as 90-100+ under the right conditions. You'll also see energy flow constantly flickering into and out of the battery. Once you've hit it, assuming level terrain and no significant wind, you'll very gradually lose speed, perhaps going a couple of miles before having to accelerate back up to 55. The acceleration is done under moderate load, indicated by IGN values of 17 or 18. You repeat this process for as long as safety, terrain, and traffic tolerate. Therefore it's cyclical like P&G, though there is no gliding.

It requires a reasonably good state of charge on the hybrid battery (6 blue bars or better). It's pretty much for rural travel only with extended segments uninterrupted by traffic, lights, or stop signs. It's not for interstate highway travel because of the slow speeds. Fairly level terrain is essential except perhaps for slight downhills where it can be used as BAllanJ describes. There is not really enough power to push the car up even a modest uphill, and too much downslope results in acceleration. With such a downhill you're probably better off using "warp stealth" (a good search should turn up discussions on that).

Let's see if this non-mechanic can explain (subject to correction) IGN, or ignition timing. BAllanJ is correct that the units of measure are degrees before top dead center. In other words it is where in the ignition cycle the piston is relative to its highest point of travel when the ignition spark occurs. How exactly that translates to a given amount of engine loading is beyond me. In fact IGN bounces around quite a bit at times and doesn't track linearly with more intuitive indicators of engine loading (such as RPM). So I don't generally use it and instead use RPM and another surrogate of loading: injector timing. Any of these requires instruments of course.

See this for the most comprehensive -- though rather technical -- discussion on the subject.

 

easier if you have SG

All of this would be less abstract if you had a ScanGauge. If I were still in the Bay Area, I'd give you a demo.

Pulse and glide, in the context of the Prius is typically used at <42 mph (Pulse and Glide plus Warp Stealth in the Prius II for maximum FE … - CleanMPG Forums). One generally wants to pulse w/the ICE to <=42 mph and then glide by dead banding <42 mph (w/the ICE off). Above 42 mph, the ICE must spin. One can monitor ICE on/off state by using the tach built into the SG. It'll read 0 RPM w/ICE off. But, you don't need a SG to P & G.

For SHM, it's used at speeds >42. One simply should accelerate to a certain point that's "highway speed" and then try to maintain IGN 13 to 15 (if the "pioneers" are right). You don't need to know what it means. You'll gradually lose speed though... I suppose you could try to fake it by looking at iMPG, but iMPG doesn't tell you ignition timing.

You might want to look at:
http://priuschat.com/forums/gen-ii-...angauge-best-threads-mileage-improvement.html
New Prius - "Super Highway Mode" Technique (SHM). - CleanMPG Forums

When I was in the Bay Area, I found SHM unsuitable for my former commute, Bay Area highway speeds and terrain. See http://priuschat.com/forums/gen-ii-...y-mode-alternative-65-75-mph-range-hints.html. It requires fair amount of concentration (for me) and thus (to me) is risky to do in heavy traffic, and sometimes impossible due to traffic.

Perhaps my SG is positioned too low? I have mine near the left A pillar slightly above where the power button is but on the left. If it were closer to the speedo and windshield, it'd be more at eye level but the numbers might be too small to read.

I did sometimes SHM on a 45 mph speed limit expressway, but that'd mean I'm usually speeding on it...

IMHO, it's not worth the effort if I want to be limited to those speeds where it does work. I'd rather just use cruise control in that speed range. But then again, I'm no hypermiler.

 

There's another excellent read of what's going on at speed by a fellow in the UK by the name of Graham Davies here. It's not real complex, but not super simple, either. I posted about it some time ago on PC but can't find it at the moment.

Whats Going On As I Drive?

And it has pictures. I like pictures. Especially moving ones.