new c owner and have a question

Hybris System Indicator

The HSI shows you your power demand, and a good driver who knows the optimum power ranges of the engine can use the HSI to get much better MPG. It also is the best tool for zeroing out the power/regen while coasting.

So the real time MPG display is a useful way to learn what your demand is doing to the engine, but only if you can see where your power demands fall at the same time. So you need both displays to really learn and maximize your MPG numbers. Without being able to display both at the same time C drivers need to resort to looking at longer term MPG under various driving styles, possibly with the help of a Scanguage...or, of course, to get tips from others who have their own long term experience.

 

If you have ever been on a trip and wondered if you are going uphill or downhill (sometimes it's hard to tell when the grade changes gradually), just look at the current MPG reading. If it's over 50 mpg, you are going downhill, and if it's under 50 mpg, you are going uphill!

EDIT/UPDATE: I don't understand the relevance of the following post. I rarely use cruise control, and my uphill/downhill "system" works just fine without it.

EDIT/UPDATE#2: Never mind. I think the following post refers to something else, and I just happened to step into the crossfire with my little post!

 

That might work if the cruise control is ON.
If you are using "foot control", then all bets are off.

 

Yes that's what I said. That's why I don't find instantaneous MPG to be useful information.

I really strongly recommend doing some reading about efficiently driving a Prius - there are lots and lots of posts (and YouTube videos) on this topic. Anything that discusses a Gen III (2010-) Liftback or a Prius c or Prius V will talk about the HSI - the Hybrid System Indicator.



It is also discussed in Section 2-2 of your manual. It appears on both the "ECO Score" and "ECO Savings" (in Basic mode) displays, but has its own page in the manual, where you'll find the above illustration.

Well, no, that's not right.

The HSI is your most important tool for knowing where the most important points are for accelerating and braking and for fine tuning your inputs. It's not telling you, nor particularly influenced by, your current "instantaneous" MPG... and that is a good thing if your goal is getting good overall MPG figures. What impresses me most about the HSI is the way Toyota has designed it to succinctly communicate key information about the entire hybrid system in one basic continuum.

I haven't been posting regularly for awhile, but a video that used to be commonly posted was this one:

It is for a Gen III Liftback, and the HSI looks slightly different, but the concepts are very similar and can be applied to driving the c.

 

I think you are assuming WAY too much in your praise of the HSI.

Mine is not labeled HSI; thus my initial question.

So.....if the HSI is so great and really contains SO much more useful information than the instant mileage display does........what ARE those inputs coming from ??

Again, I think you are dreaming. Using your foot to keep the instant MPG graph as high as possible should produce results pretty much identical to using that same foot to keep the HSI instant display as high (to the left) as possible.

If you have some actual engineering documentation that says otherwise, I would really like to see it.

 

They are the same... mostly. The HSI will give you the range up to which your MPGs will start dropping. EG: You are travelling at 50 mph on a flat terrain. If you keep the HSI below the ECO line, your instant mpgs will be 99.9, but if you press the throttle a little bit more it will drop. Knowing where that line is helps out tremendously. Whereas if you were looking at just the mpg in real time, you would only know if you crossed the ECO line by the fact that your mpgs started dropping. HSI is more efficient in this example.

 

And I contend that BOTH displays would "drop" at exactly the same time.
All you are doing is repeating your opinion.......which may or may not be right.
How about some supporting information ??

 

1st off... it's not a repeat, since this is the first I have mentioned it...
2nd... If you think that being able to visually see the line raise and lower to the ECO line is only opinion, then well... I guess you win, as no amount of logic will ever work on you.

I mentioned that both would drop at the same time, I, also, mentioned that with the HSI you would be able to know "before" you were about to drop.

 

Both displays ultimately do give you pretty much the same feedback. I prefer the Eco Score display (aka HSI) over the 5 min. consumption simply because, for me its easier to see, with less distraction from road. Different strokes.

 

That's a pretty good trick.
Does the HSI somehow magically bestow clairvoyant abilities to the driver ??

 

... It's called being aware ... As you press the accelerator, the HSI bar moves up towards the ECO line... when you cross the ECO line your MPGs drop ... Even when you are driving over 45 mph, it still works this way ... You should try it, might make you more efficient ...

 

I'm sorry to burst your bubble but ANY time the HSI bar goes the wrong direction your mileage will suffer.
There is nothing magic about crossing that line.
And I'm not even sure that the ECO label even refers to the line.
It might be a label for the whole part of the graph that is green; IE not in the "power" part.

 

The line is significant. Keeping it below the ECO line at the majority of speeds will allow the ICE to disengage.
ECO is in the middle of the line. There is an entire section that is below "power" and above ECO. I'm telling you, before you argue it further, try it. Drive on a level road (which shouldn't be hard since you live in Florida), drive at 50 MPH. Put your HSI bar just below the ECO line and watch your instant MPGs hit full on the radio screen (you can view this because you have a PC 3 and you will need to hit the car button on your radio). You will drop when you go above the HSI ECO line. This helps you be "clairvoyant" as to when you will be getting bad gas mileage before the instant MPGs tell you that it is going to be so... thus making you more efficient.

Due to our conversation thus far, I feel the need to tell you to pay attention to traffic foremost and don't do this on a crowded road.

It's not rocket science. If you know how much pedal you can give the car before the MPGs start dropping, it's going to be better than being reactive.

 

I quit. You aren't listening.

While there might be a significant drop in efficiency somewhere around that line, it all depends on a lot more inputs than just the gas pedal and EVERY time you push the pedal a tad and the bar goes UP, regardless of where it is on the scale, the fuel consumption also goes up.

And THAT is not rocket science either.

And finally, you can get much the same "feel" by watching the instant MPG display too.
If you are cruising along at ~55-60 MPG on the display, then anything that you do that causes it to drop below....oh say.....40 MPG is down in the significant range and should be avoided......just like avoiding the upper part of the green bar on the other display.

 

I'm sorry, but what Ztanos is saying is widely accepted and agreed upon by the whole PriusChat community - hence, YOU are the one not listening. The ECO line IS significant, as you would see if you read the section of the manual that was pointed out to you and maybe watch some of the videos posted. Learn how the power split device works, that might clear some things up for you.

If you simply want 'keep the mileage as high as possible at all times,' then I suggest you turn on your car, hit the EV button, then get out and push. The HSI lets you know better how to recover mileage after accelerating like a normal person who is not impeding traffic. It gives you more information than an instantaneous mileage indicator, period.

 

I think I understand why you aren't getting it. I'm not saying there is a significant drop in efficiency around that line. I'm saying that watching the line is more efficient than watching the instant MPG meter, which was your original argument. Being reactive won't allow you to be nearly as efficient as prescience.

Again, go out and try it, like I said before.

 

I see that you guys are really serious in your belief.

I have done some limited "testing".
I put the HSI display on the dashboard. I put the 5 minute useage up on the console screen, with it's instant bar on the right.
And then I observe that the two graphs move pretty much exactly in sync (can't be positive because driving is still more important that watching the graphs).

Now if you find it easier or somehow better to watch the bowed HSI graph instead of the MPG one, that is fine but nothing you have said yet convinces me that there is any real difference........except that Toyota has drawn a somewhat arbitrary line on one but not the other in an attempt maybe to make it easier to interpret.

 

Okay... don't go with what all of the youtube videos and the majority of members on this site are saying. You sir are right. Knowing the range of where you can pedal before you drop has absolutely no benefit what-so-ever. Logic doesn't make sense and 4 doesn't come before 5.

Try listening this time... you ready...

YES, THE ECO LINE AND THE INSTANT ARE THE SAME... the fact that you don't know how much pedal you can give by watching just the instant... that's the reason why it's more inefficient of a screen than the HSI. Can you do the same thing with just the Instant screen? Maybe, but the HSI will be easier, every time.

 

The HSI shows the instantaneous power output of the hybrid system (ICE and electric motors). The instantaneous MPG is dependent on the hybrid system power output as well as other factors including road speed (MPH). To maximize fuel mileage, the driver needs to regulate the power output. The instantaneous MPG, which is a secondary parameter, will follow as a result. Therefore, the HSI provides the most direct information for the driver to achieve the best fuel economy, and it is the primary instrument by which the driver controls the hybrid system. My G3 Prius shows the instantaneous MPG on the HSI display where it is always visible to the driver. It is useful to have it there but not necessary to obtain maximum MPG. For whatever reason (cost, space), the Prius C does not display instantaneous MPG on the HSI because it is not as important as the power output. In the lower half of the ECO range, the car is propelled primarily by the electric motors. In the upper half of the ECO range it is propelled primarily by the ICE. The power output is the most important information that the driver needs to know, and it is on the HSI. Based on my understanding of the G3 and Prius C Owner's Manuals, Ztanos is correct.

 

Gee it's interesting being away for awhile.

I, personally, don't assume anything. I started reading PriusChat when I started considering buying a Prius and I joined the forum on the day I signed on the dotted line, a bit under a week before I got my car. I learnt a lot from this forum and things people have linked from these forums - not just the c specific stuff, but about the Prius HSD generally. Taking all that in is in fact overwhelming when you first start driving a Prius, but it's been a couple of years now of taking that knowledge and seeing how it applies when driving the vehicle is part of the learning experience, including learning the little differences in the Australian model compared to the US versions and of course everyone's driving environment is different anyway.

One thing that seems to be pretty much a truism for anyone that's really tested it in detail is quite simply this:

A blind focus on instantaneous MPG will almost certainly harm your overall MPG in the long term.

People often seem to get a Prius and then drive around trying to keep it running in EV, by which I mean driving with the ICE off, because that's best MPG, right? It's an electric car, right?

Wrong. It's a hybrid and it's not designed to be driven that way. All the energy you're using when driving around on electric in a Prius c had to come from somewhere. Yes, you might have come down a hill and generated some energy to store in the battery, but if you came down, either you had to go up it previously or will have to in future. All the driving energy in your c originally comes from the gas station. All of it. Running excessively in EV mode in the chase for instant MPG hurts in the long run.

'But wait!', some people cry, 'I get that, I just mean when you are using the ICE, it's better to keep the instant MPG down, obviously!'.

Wrong again. That logic is taking the essential beauty of the HSD and throwing it away. The Prius has the wonderful ability to mix and match its power use, so for example there will be times where you perhaps need power from the ICE, but not enough to justify running it up in its most efficient power output range. In a normal car that's bad luck. In a Prius the computer can decide to take advantage of this situation, run the ICE harder (but at a more efficient power output for the fuel burn) and direct some of that energy into the HV battery instead of to the drive wheels. In instantaneous MPG terms, this will look bad. But it's not overall, because in the long run, the car has made more efficient use of the petrol.

A driver trying to somehow override this logic while staring at the instantaneous MPG reading just is not going to be making judgements that align with the best operation of the car for overall MPG.

Although the bars going up and down may look similar - and they are similar - the HSI has a big difference in that Toyota has taken the most significant pieces of information about the operation of the HSD and disaplyed it to you on one simple graph. They've given you a huge hint about how to run the engine in the most efficient range when it is running, and that's quite different from what you're trying to do with instantaneous MPG.

Then, for the times when the ICE is off, the instantaneous MPG graph is useless. It shows nothing helpful at all.

The HSI, meanwhile, is continuing to give you important cues about how to drive your car efficiently in this mode.

Once people take the time to learn what the cues on the HSI mean, they very rarely use any other display. Everyone's different, some people make a different choice and yes some people use instantaneous MPG in addition to the HSI, but most drivers do tend to stick with it, for good reason.

Apparently you say you've done some "limited "testing"". Do you record your overall fuel consumption, either manually or with the help of a site like Fuelly? Have you tried different driving styles and monitored the impact?

If you're not sure about these things, why do you believe your non-understanding based on your non-research and non-experience is completely correct? That's the part I really don't follow.

We're only trying to help here. There's nothing in it for us other than trying to help you have a better experience with the car. You should always drive it how you want to drive it, but you opened up this discussion and we're telling you what we know.