Remaining battery gauge vs. EV range - does not really make sense

[Mayjend]

Is 0 EV range and 2 battery bars when the angry bees starts to happen? In other words, running on ICE alone is what makes the angry bees sound happen?

 

[Ray B]

I believe that when you get to 0 charge/2 bars, you ARE running on engine power alone, not hybrid power.

Here is the diagram that I think explains my point of view.

Clarity_CD-CS

• Ray B
• Nov 12, 2018

The green shaded area near the bottom of the chart represents the 0 EV range, but active HV range (0 - 2 bars on the battery meter). So far we've heard from one person who has observed 1 bar, so that would only be possible if it was using the traction battery.

 

[ryd994]

I feel its range is actually 2 bar to full+2 bars
I got ~5miles range for the first bar

 

[MPower]

This ongoing discussion has explained to me something about my old 2012 Prius Plugin. When there was enough charge to run on the electric motor alone, the graphic showed a picture of a full green graduated cylinder with the level slowly reducing until it was totally depleted at which point the cylinder turned pink and was full again but the level fluctuated and the car was running in HV mode. I believe the pink cylinder equated to the bottom two bars of the battery gauge on the Clarity.

This assumption that the bottom 2 bars are just a graphic variation on the same theme reassures me, because I have been there and done that successfully for 6 years and 75,000 miles.

 

[LAF]

I believe that when you get to 0 charge/2 bars, you ARE running on engine power alone, not hybrid power.

no- the car never runs on engine alone- some of the engine power will be used to keep the batter at 2 bars which is good enough for HV driving and 40 mpg

 

[insightman]

no- the car never runs on engine alone- some of the engine power will be used to keep the batter at 2 bars which is good enough for HV driving and 40 mpg

If the Clarity is unwilling to give up its last two bars of battery power, it would seem to me that the electric half of the hybrid system has abdicated, leaving the car to run on engine alone.

Are you saying that the Clarity can always delve into its two-bar reserve when electric power is requested for acceleration or hill-climbing? There has to be a bottom limit, beyond which the Clarity absolutely will not surrender any more battery power in an effort to protect its big, expensive battery.

Or are you saying the Clarity puts itself into HV CHARGE Mode (without displaying this on the dash) when the battery charge is depleted so that it can almost immediately resume powering the car using battery power? In my experience, when the EV range is zero, it stays at zero unless I select HV CHARGE Mode--no power flows from the battery to the wheels so the Clarity is running on engine alone.

There have been a couple of disturbing reports of Clarity drivers experiencing a dangerous lack of power in situations when the battery charge is depleted. None of those drivers has reported seeing less than two bars on the battery charge gauge. Only one poster has seen just a single bar, but didn't also report extremely sluggish performance when that happened. I'm glad that problem has never happened to me and hope this sluggish behavior can be diagnosed and explained.

 

[Ray B]

If the Clarity is unwilling to give up its last two bars of battery power, it would seem to me that the electric half of the hybrid system has abdicated, leaving the car to run on engine alone.

Are you saying that the Clarity can always delve into its two-bar reserve when electric power is requested for acceleration or hill-climbing? There has to be a bottom limit, beyond which the Clarity absolutely will not surrender any more battery power in an effort to protect its big, expensive battery.

Or are you saying the Clarity puts itself into HV CHARGE Mode (without displaying this on the dash) when the battery charge is depleted so that it can almost immediately resume powering the car using battery power? In my experience, when the EV range is zero, it stays at zero unless I select HV CHARGE Mode--no power flows from the battery to the wheels so the Clarity is running on engine alone.

There have been a couple of disturbing reports of Clarity drivers experiencing a dangerous lack of power in situations when the battery charge is depleted. None of those drivers has reported seeing less than two bars on the battery charge gauge. Only one poster has seen just a single bar, but didn't also report extremely sluggish performance when that happened. I'm glad that problem has never happened to me and hope this sluggish behavior can be diagnosed and explained.

As I am not a Honda engineer, I doubt I can answer your question to your satisfaction, but there are some resources you can dig into online to get some of the story. One paper I downloaded on the Sport i-MMD for the Japanese 2014 Accord PHEV (the 13 mile EV range precursor to the Clarity PHEV I guess), describes the system in some detail - in some cases it is very basic, and other aspects are very difficult to comprehend. For instance, the power management control flowchart has nine main elements and 40+ flow arrows and intersections. If you can make sense of half of it, you will be far past me...

It is also not directly applicable since it does not discuss ECON mode vs Normal mode vs Sport mode, but rather just the three key states of EV, Hybrid, and Engine drive.

Anyway, it describes the 'Charge Sustain' mode... "In this mode, when the State of Charge (SOC) of the Li-ion battery falls below the specified value, the vehicle is propelled using gasoline as the energy source so that the SOC stays within the specified range. In other words, the vehicle operates as a hybrid vehicle."

The paper does not address the situation you are concerned about where drivers encounter a serious lack of power on long uphill inclines. But I wonder if in these instances where the car is below 45 mph (no direct mechanical link between the engine and wheels), the car's engine is struggling to run the generator to get enough power to the electric motor, while not pulling too much power from the limited battery supply. I haven't been able to piece it all together yet, as there is little or no available papers which describe the behavior of the Clarity PHEV in these circumstances. I wonder if the car was able to get up to ~45+ mph before the hill, if running in the Engine mode (direct engine link to the wheels) would alleviate the problem at all. I also don't know if the ECON mode would hamper the car's performance in this situation, and maybe normal or sport mode would help.

If I were facing that scenario and had time to prepare, I would run HV charge for a while to build up enough EV battery to manage the hill/mountain. If I couldn't anticipate it I would pull over (if possible) and run HV charge. Otherwise, try the sport or normal mode to see if they would help.

The paper I referenced above is called "Development of SPORT HYBRID i-MMD Control System for 2014 Model Year Accord" by Hirohito Ide, Yoshihiro Sunaga, and Naritomo Higuchi. If you google the title, you will find the pdf pretty easily. As I said, it is not exactly a perfect description of the Clarity PHEV, but it provides a lot of applicable insights (pardon the pun...).

 

[insightman]

"In this mode, when the State of Charge (SOC) of the Li-ion battery falls below the specified value, the vehicle is propelled using gasoline as the energy source so that the SOC stays within the specified range. In other words, the vehicle operates as a hybrid vehicle."

I've come around and now agree that the Clarity is operating as a hybrid vehicle even when the battery is depleted.

The paper I've been scrutinizing for months is "Efficiency Enhancement of a New Two-Motor Hybrid System." My particular interest--how the Clarity PHEV performs pseudo engine-braking by starting the engine--is not addressed in this paper because like the one you referenced, it was written with respect to the previous generation i-MMD Accord Hybrid. That car performs pseudo engine-braking by closing the engine's valves, turning off the fuel-injection system, and then using the deadened engine as a load that enables the starter motor/generator to use up the electricity generated by the traction motor as it slows the car.

Looking at Figure 13 in the Efficiency Enhancement of a New Two-Motor Hybrid System paper, it shows an EV contribution in "Charge Sustaining Mode," abbreviated CS, when the battery's state of charge (SOC) remains constant. If the SOC remains constant, then no battery power is being gained or lost. Therefore, the green EV block at the bottom of the CS mode part of Figure 13 must refer to the electric power being generated by the engine. EV does not necessarily mean EV Drive, when the battery is powering the car.

So I concede that the Clarity is operating "as a hybrid vehicle" even when the battery is so depleted that the i-MMD system will not allow it to contribute to propulsion, leaving the engine alone to provide the electric power that's moving the car.

Vcar is the velocity of the car. F_ENG is a signal that commands the engine to start. SOC is the battery's state of charge.

 

[Bina12834]

This is all waaaaay above my pay grade

 

[Texas22Step]

@V8Power , I did a limited real world test by allowing my EV to go to 0 and 2 bars until it auto entered HV (it was hard to do as I suffer from IAS [ICE Anxiety Syndrome]).
In 20 miles of mixed city and highway driving with speeds of 35 and 55 and no large hills, everything was fine. The 2 bars never increased and I had no loss of power or high reving although I suspect that on a large enough hill I would have. I could not force myself to test longer, but I suspect that you get a little lower MPG since this limits the full range of power flows the algorithm can select from. This observation might support @Ray B ‘s theory that even at the 2 bar buffer limit, the algorithm allows a small amount of back and forth charge/discharge but not as much as in a normal/larger SOC and thus you get the angry bees when calling for more than just limited amounts of power for short durations.

As to the buffer question. We have several observations that with a fully depleted battery (0 EV, 2 bars) only 14.1 to 14.4 kW could be added to the state of charge (SOC). So 14.4/ 7kW = 83 to 85% of the battery is allowed to be usable. So we assume that 15 to 17% is the total buffer but we don’t know how it’s apportioned between top and bottom. But one also has to take into consideration that the charging inverter in the car cannot be 100% efficient and so not all of that 14.1 to 14.4 kW actually makes it to the battery pack. You can’t beat the laws of thermodynamics and so some of the kWs measured at the wall by your EVSE or Killa-Watt meter are lost to inefficiency as heat in the car’s charging inverter. I’ve seen estimates of inefficiency anywhere from 20 to 5% and speculation that Level 2 charges may be more efficient than Level 1. If you assume a around a 90% efficiency, then only 12.5 to 13 kW are allowed to be used. Then that’s a total buffer of 23.5 to 26.5. Holding about 25% of the battery capacity in reserve for battery protection and to mask the unavoidable degradation from the consumer is roughly on par with other EVs and is another indication that our assumptions and speculations are at least in the ball park. Again, what we don’t know is how this assumed, appropriately 25% buffer is split between the top and bottom of the SOC.
Also common sense informs us there must be buffers at top and bottoms since every other large Li-ion battery pack has this and the chemistry/physics dictates that repeated full 100% charge and 100% discharge cycles will destroy any current Li-ion battery no matter what the chemistry or configuration.

Fortunately we have some very intelligent people on the forum and as we build up more observations for them to chew on, we will be able to peel back more of the onion of mystery surrounding our Claritys. Oh what I wouldn’t give to be able to button hole a bunch of Honda engineers and software developers in a locked room for a day!

Are you suggesting Honda should have left the top two segments permanently dark and a "full charge" would not go to the top of the gauge? That would mean that the top 2 and bottom 2 bars are robbing the gauge of more meaningful resolution.

In my opinion, Honda should have not used up the bottom two bars to represent the buffer protecting the battery from becoming completely discharged. The gas gauge can go to zero; the battery-charge gauge should do so, too. Why limit the resolution of the battery-charge gauge by keeping the bottom two bars always lit?

I am not sure about this, but is it possible that the remaining two bars at the bottom are to show a driver that the big (traction) battery still has enough power to charge the 12v battery in order to run the heater, a/c, lights, etc. while the car is running in HV mode? Or is there an alternator that does the charging of the little battery when the ICE is running?

 

[Ray B]

(snip)...
Looking at Figure 13 in the Efficiency Enhancement of a New Two-Motor Hybrid System paper, it shows an EV contribution in "Charge Sustaining Mode," abbreviated CS, when the battery's state of charge (SOC) remains constant. If the SOC remains constant, then no battery power is being gained or lost. Therefore, the green EV block at the bottom of the CS mode part of Figure 13 must refer to the electric power being generated by the engine. EV does not necessarily mean EV Drive, when the battery is powering the car.

Vcar is the velocity of the car. F_ENG is a signal that commands the engine to start. SOC is the battery's state of charge.

Great stuff. It looks like that paper has some overlap with the other one. The chart that you show is similar to Figure 3 in my reference, but in that one it shows a sample plot of power. In CD mode, the power plot stays below the 'engine run' threshold (unless someone mashes the throttle past the click point), and in CS the threshold drops (as shown in your embedded chart), and the power demand triggers the engine in order not to draw too much from the battery. So the green zone is more just to show at what power draw condition is the system just using EV for power, versus the blue range where it will trigger using the engine (and/or battery).

In the other paper it shows a chart that maps the torque vs rpm and shows how in hybrid mode, it tends toward a zone of maximum efficiency, and if that load is too much for what is being asked by via the throttle pedal, then it stores the excess to the battery, and vice-versa - when the demands are pushing beyond what the engine can sustain with good efficiency, it draws energy from the battery via the electric motor. Of course, the regen also assists to maintain the SoC.

So I get the impression it is all very dynamic and with the goal in CS of balancing the gasoline usage and regen to maintain a constant SoC in the traction battery (= two bars, to not only help with hybrid efficiency but also to run the 12V system, etc as mentioned above). Obviously, this is also the case when you have a full battery and switch into HV mode to preserve the battery for later EV usage, though in my experience it is a little more lax about it when there is a high SoC and electric range can drop by several miles in HV mode, but if you drive it long enough it comes back to the EV range starting point (or close).

But all of this doesn't address your question about behavior on long uphill stints. I suspect it has to do with the 45 mph limitation for direct engine traction, and the limited amount of power available when running in ECON mode using the engine as a generator and limiting battery draw. I wonder if anyone has tried similar situations in normal or sport mode, below 45 mph vs above 45 mph.

 

[dstrauss]

Here's a short version of what Ken wrote: the rated sizes the battery is 17 kWh. When the car has 0 EV range and you plug it in to charge, the car will only actually take about 13 kWh. So there's 4 KWh that can be used as a buffer. They are designed to not use up the whole capacity of the battery to have less battery degradation.

It's not only battery degradation, because once you enter hybrid mode you need battery for the bridging (when you stop, etc.) to give you the max effect of hybrid mode.