I thought I would try to describe in a little more detail how I drive for fuel economy in non-highway driving. I have a ScanGauge II installed and mounted on the steering column and I usually have it displaying engine load, engine RPM, and coolant temp. I also have the navi display showing the energy flows.

Of course, the best case scenario is when I am traveling on a slight decline such that I can shift to N and maintain speed. If I just need a little extra, I'll use some battery power to keep me going at the necessary speed. If nobody is behind me, or if there are multiple lanes with low traffic, I don't mind coasting well below the limit.

If I'm going uphill, I try to keep the engine at a relatively high load (above 80) and hopefully charging the battery as well.

If I am driving on relatively level ground and traffic permits, I will pulse and glide between 40 and upper 20s. Personally, I do not like to impede the flow of traffic and do not feel comfortable driving more than a few mph's below the limit if I have traffic behind me.

Overall, I try to keep the battery SoC between 4 and 6 out of 8 bars. If I am going to work and know that the vehicle will be sitting for many hours before driving, I will likely take the SoC down to about 4 bars. This way, when I do finally start back up and the engine is running, at least it will be doing something productive by charging the battery as I'm cruising around at low speeds.

The engine block heater has been a big plus and my tank fuel economy has been going up since I installed it. Here is my current tank.

 

Can you expand on your shift-to-neutral philosophy? I'm hesitant to shift into neutral and back into drive while the car is in motion.

I do appreciate your advice on using the battery as much as possible at the end of the trip in order to maximize the startup engine usage. I hadn't considered that.

As others have said, driving a hybrid properly will force you to alter your driving style. I've made some adjustments (mainly by watching the energy usage graphs, which I think every car should have) but I know that I could do more. Am I happy with my HiHy purchase? Certainly -- compared to what I was driving before, for a similar-sized vehicle, I'm saving anywhere from $20-$35 per comparable mileage fill-up. (On good days, I can get 400+ miles per tank vs 300 miles on old vehicle)

 

To glide in the HSD vehicles, it is really just a matter of letting the engine shut off by taking your foot off the accelerator and then putting enough pressure on the accelerator to stop the regen arrows. If you put too much pressure on the accelerator, you will get assist arrows. If you've tried this, you probably already know that it is very tough getting the "black screen" (no arrows). Apparently, it is difficult in all of the Toyota HSD vehicles except for the Prius II. The easiest way around this is to just shift to Neutral once the engine is off. This just creates an electrical disconnect with the electric motors/generators such that they cannot assist or charge.

When shifting back into Drive from Neutral, you will not notice any transition at all. This is not a true neutral as you would experience in a traditional automatic transmission. With the Toyota HSD, there is no problem shifting back and forth between N and D. You do not even have to press the lock release button when shifting back and forth between N and D.

 

So what you're saying is that as long as I don't see the gas engine icon on my dash display that I should throw the HiHy into neutral and coast, then shift it back into drive in order to maintain speed, then shift back into neutral, etc etc.? How much shifting are we realistically talking about during an average drive to work or to the store?

 

If you need to use a little electric assist to maintain speed, there is no need to shift back and forth between D and N. You should just keep it in D. If you are going down a slight hill such that your speed can be maintained, there really is no need to have regen happening--it just slows you down. Shifting to N can prevent it.

Shifting between N and D is really quite effortless. I use it when I think it can help me. This depends very much on the grade of the roads, the speed limits, the traffic, etc. I imagine your conditions will vary a lot from mine so you will just have to see if these techniques work for you and your conditions.

Do you have navigation on your HiHy? This makes it a little easier to tell when the engine is actually off. If you do not have the navigation, a ScanGauge II would be very beneficial. This way, you can monitor the engine RPMs to see when the engine is off.

 

I have the nav, but I haven't cared for the "energy" screen as I find the graphic too busy to get a good read on with a quick glance. I leave it on "consumption" and watch the graphs to monitor my MPG over time about 80% of the time I'm in the car -- radio/air/map take the other 20%. (or is it vice-versa? I like the graphs, hate the engine graphic). I leave the dash display on the battery/engine graphic almost 100% of the time.

What specifically should I look for on the engine screen other than no lines moving from the engine to the wheels? Is there that significant a difference between that display and what's on the dash display?

When rolling downhill, you're saying I should shift into neutral. When I reach the bottom of the hill and need to accellerate upwards, what type of engine reaction time should I worry about with regards to timing the shift back into drive and then pressing the accellerator?

an additional observation: when I come to a stoplight, the dash display will still display the battery sending power to the wheels unless I press more firmly on the brake. Is this expected activity?

 

I usually keep the nav on the energy screen. It may seem a little busy, but once you get used to it there really aren't that many things you are looking for. Here is something to look for. When you are accelerating using the engine, what is happening to the power that is split to the electric motor? Is it going back to the wheels or is it charging the battery? Or, is the battery providing assist back to the electric motor? In general, you want to avoid the electric motor assisting when the engine is running. These are all good for helping you manage your battery state of charge (SoC).

Also, at the bottom of the energy screen is an instantaneous fuel economy readout that goes all the way to 99.9 mpg. This is more useful than the 60 mpg meter on the chart page. Without a ScanGauge, 99.9 mpg is more helpful to determine if the engine is on or off. Even if your engine is idling and you are coasting, the fuel economy will easily be greater than 60 mpg at pretty low speeds.

I'm not really sure on this, but I have never had any issues. I imagine electric assist would be very fast and the engine power may take a second or so. This is probably no different than if you have it in D and need the engine to kick back on.

A couple of things here. The brake and accelerator combo are meant to simulate a traditional gas only vehicle. At higher speeds, when you let off the accelerator, you get charging. This is analogous to engine braking. When going very slow (as when approaching a red light), assist is occurring to simulate an idling vehicle in gear. The brake has to be pressed harder to stop this assist.

Also, if you come to a stop while your engine is on, I've noticed that the arrows may still be moving for a second or so after coming to a full stop.

 

One thing to think about -- be somewhat mindful of your speed when you put the HiHy back into "D". At speed above around 60 with the engine shut down, there are some pretty radical things that could happen as a result of the ECU trying to get control of the ICE RPM to MG1 relationship.

If you are going downhill in a normal coast in "D" at these higher speeds, the engine may not be shut off (RPM 0), but rather is in fuel cut-off. This is done to avoid overspeeding MG1 (in the case of my Camery, it may be different in the HiHy 4WD because of the twin tranction MG arrangement). But the principle in the HiHy is the same. By putting the car in "N" and building up a high speed, you may have taken away the ability of the ECU to control the ICE/MG1 ratio (it may not shut down the engine in these cases anyway, but I don't know that for sure). If the engine does, in fact shut down to zero RPM in 'N" there could be some nasty mechanical forces when you shift to "D" and the ECU asserts control of MG1.

Some further discussion of that in the latter parts of this thread = https://www.greenhybrid.com/discuss/...t=14215&page=6

 

OK, I checked it last night on my evening commute with my twin tach instumentation, and the ECU does protect MG1 and the ICE in neutral. The conclusion reached are that placing the selector in "N" appears to do (and in some cases not do) the following things:

1. All battery recharge is shut off;
2. ICE ignition and fuel are shut off;
3. MG2 may run open (no electrical currect) at slow speeds or may generate current at high speeds for use by MG1 if required to protect MG1 or the ICE from high RPMs.
4. Regen Braking is shut down except for the amount of current needed by MG1 to apply dynamic braking at high speeds.

So at least for my TCH, about the only thing that "N" acheives is a shutdown of the ICE, either to zero RPM or into fuel cut depending on speed (which will be done the same in a coast anyway) and removal of the traction battery recharge, which will remove some small load on MG2, but that recharge load will be almost insignificant when compared to the current used for MG1 control. Also, the traction battery recharge is not avoided -- you will need to extract energy from the ICE when the coast is over to later recharge the battery, so you have only deferred it.

As for braking, the "N" postion does seem to shut down the regenerative braking -- except when current is require for the RPM proctections mentioned above. Since the ICE is always turning at high speed (in fuel cut), some power generation is needed from MG2 to permit MG1 to add torque (in the positive or negative direction as required) to prevent MG! and/or ICE overspeed. Sot it sort of shuts of regen braking, but not quite.

 

That is the whole idea. Defer the charging until you actually need to have the engine running. In an ideal situation (for maximum fuel economy), you would only have two states. The first state is with the engine running at an efficient state propelling the vehicle and charging the battery as necessary. This would either occur during acceleration or when going up a hill. The second state is coasting with no charging or assisting. This would either occur during deceleration or going down a hill.

Of course this is not practical in most people's normal driving environments, but it is good to know. If you are aware of how to get maximum fuel economy, you can extract what is applicable and apply it to your daily commute.