driving in the mountains - 2018 Honda Clarity Forum
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post #1 of 20 (permalink) Old 09-01-2020, 07:30 PM Thread Starter
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driving in the mountains

I finally figured out a sensible way of driving my Clarity Hybrid in the mountains.

My typical trip is a 200-mile, 3-hour drive from Oakland, CA to Tahoe City. The first 2/3 of the trip are flat freeway. The last 70 miles or so consists of steep climbs alternating with downhills. The summit is at 7,000ft, so the total climb is considerably higher. None of the existing drive modes works well:

1. Electric mode runs out of energy very quickly.

2. Hybrid mode works fine at the start of each climb, when both ICE and electric motor work together. But halfway through each climb section, the regulator figures that it's time to recharge the battery. So now the ICE is both pushing the car up, and recharging the battery, and runs at very high RPM, which is less efficient and will shorten its life.

3. Recharge mode is even worse, as the ICE tries to recharge the battery at a higher rate than hybrid.

In both hybrid and recharge mode, it's infuriating that the ICE stops recharging in the downhill sections, when it could recharge with little effort, and instead goes idle.

What Honda should really provide is a "electric with gas assist mode", or "lenient hybrid mode". A driver can emulate it like this:

1. Set the mode to "hybrid".

2. Set the display to show instantaneous MPG (or pay attention to the ICE whine) so you can tell when the ICE starts recharging the battery (usually in the middle of a climb).

3. At that moment, turn hybrid mode off, then turn it back on.

What happens is that cycling out of hybrid mode and back in resets the "target" charge level to the current level. The regulator allows the charge to go below the target level before it takes action again.

On this particular route, one cycle is enough for most climbs. (I don't remember exactly, but it is possible that I used two cycles on one or two particularly long climbs.) Using this technique I was able to reach the summit with about 1/3 charge capacity left. Since the climb takes one good hour, this puts less strain on the battery than driving electric only. It also puts considerably less strain on the ICE.

I really see no downside to automating this mode, and I think it's an engineering failure of Honda for not offering it.
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post #2 of 20 (permalink) Old 09-01-2020, 09:20 PM Thread Starter
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2002, thank you for the interesting information, I had no idea that the Volt had those modes. Also you're probably correct that high-revving the engine is not that terrible (although it sounds like it may be reaching 5000-6000 RPMs), but then again the high whine ruins the greatest feature of driving (mostly) electric: the seemingly effortless power.

It is true that at some point you'll have to rely on ICE only, like when you're going to the top of Haleakala. But there would be a good fraction of trips for which the blended mode would be enough (mine for instance) and that's the philosophy of plug-in hybrids. What saddens me is that supporting this feature would be quite cheap in terms of engineering cost---including UI and documentation. In fact I would find it a lot more useful than the Recharge mode. What is the point of the Recharge mode anyway? To try and do exactly what the Blended mode does, but not as well?

Ah but wait... a Blended mode would mix well with a Recharge mode for going up and down mountains. Except that the Recharge mode would need to be a bit less brain-dead and actually recharge when going downhill.

So I really don't get it.
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post #3 of 20 (permalink) Old 09-01-2020, 09:23 PM
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Mountain mode in the Volt predates Hold Mode by two model years. It allows you to tell the car to shift to hybrid before the battery is depleted. The Volt's hold mode tells the car to switch to hybrid immediately. Honda missed the mark with their HV Charge mode by not allowing the driver to set it early and running electric down to that point before it switches to hybrid mode.

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post #4 of 20 (permalink) Old 09-01-2020, 09:23 PM
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The nickname for what you are doing is called "HV Reset", and it does seem to be the best way to reduce engine noise during a climb. As for reducing stress on the engine, that assumes that there is stress worth worrying about. High revs and the associated loud noise generally bother us more than they bother the engine.

I agree there should be an option for handling this better. Hybrids most of the time run in one of two modes, charge depleting mode (aka EV mode) and charge sustaining mode (aka HV mode). There is another mode at least at the terminology level called Blended Mode where in a high load situation the system will essentially combine charge deplete with ICE usage, using the engine for power to assist the battery in a high load situation rather than trying to maintain battery level. Most hybrids including Clarity have the ability to simultaneously power the wheels with both battery and ICE, however this usually only happens during brief periods of acceleration, and once the SOC starts dropping the system prioritizes ICE for battery charging rather than providing power to the wheels. Or else the engine provides both power to the wheels and battery charging at the same time, resulting in high revs and noise. Blended Mode would be a mode that you can activate for prolonged periods like in a hill climb, where the priority for ICE is to assist the battery in providing power when there is a medium to large power demand.

The only PHEV that I know of that may do this is the Chevy Volt which has something called Mountain Mode, but the way I read it that may just be a more specialized version of HV Mode (known as Hold Mode on the Volt). Hold Mode, like our HV Mode, sustains the battery at whatever SOC it was at when you switched to Hold Mode. Whereas Mountain Mode targets 45% SOC. The idea being that if you know that at some point on your trip you will have a hill climb, you can engage Mountain Mode at the start of the trip then you don't have to think about it as it will burn down the EV charge until it gets to 45% then essentially go into Hold Mode and maintain SOC at that level. The idea being that 45% charge should be enough to make it up most hill climbs with just the battery. Apparently when it later senses a prolonged load it ignores the 45% target allowing the battery to start depleting, but if I understand correctly it's not in blended mode, it just essentially reverts back to EV mode for the hill climb. If I understand correctly on a long hill climb even with Mountain Mode active the Volt can run into the same problem as Clarity, once the battery is depleted then you have to make it up the rest of the way solely on ICE. I don't know this for a fact I am just basing this on something I read from someone who drives a Volt in Kona, Hawaii, they say that for the big hill climbs at high speed they use Hold mode at the start of the trip so that they can start the climb with a full battery. They said this works must better than Mountain Mode. Making me think like I said that Mountain Mode is just a specialized version of HV Mode, it is not a Blended Mode which is what is really needed.

But mountain climbing is a niche requirement, in a type of car that is already very niche (PHEV), so this is just one of many refinements that are lacking in PHEV's that probably won't be addressed unless or until PHEV's become more popular. Actually Blended Mode would be nice even around town, as it would keep the engine quieter while accelerating from a stop light, by using ICE at a lower RPM and being willing to sacrifice some SOC. Then when you reach cruising speed ICE can slightly raise the RPM to recharge the battery prior to the next stop, which you likely won't even notice since you will have more road and wind noise at 45 mph or whatever. Especially if in blended mode the system will be more relaxed about maintaining SOC, allowing SOC to drop if necessary to maintain lower RPM. It wouldn't work perfectly all the time but it would certainly be better than the current situation, where if the SOC is just a hair below the target SOC when the light turns green, you can get an embarrassing growl from the engine, making your passengers wonder if something is wrong with your car.
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post #5 of 20 (permalink) Old 09-01-2020, 09:25 PM
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Originally Posted by obermd View Post
Mountain mode in the Volt predates Hold Mode by two model years. It allows you to tell the car to shift to hybrid before the battery is depleted. The Volt's hold mode tells the car to switch to hybrid immediately. Honda missed the mark with their HV Charge mode by not allowing the driver to set it early and running electric down to that point before it switches to hybrid mode.
No question the Volt set the gold standard for how a PHEV should operate. Although I think even the Volt would have benefited from having an option for Blended Mode.
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post #6 of 20 (permalink) Old 09-01-2020, 09:48 PM
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Originally Posted by semenzato View Post
2002, thank you for the interesting information, I had no idea that the Volt had those modes. Also you're probably correct that high-revving the engine is not that terrible (although it sounds like it may be reaching 5000-6000 RPMs), but then again the high whine ruins the greatest feature of driving (mostly) electric: the seemingly effortless power.

It is true that at some point you'll have to rely on ICE only, like when you're going to the top of Haleakala. But there would be a good fraction of trips for which the blended mode would be enough (mine for instance) and that's the philosophy of plug-in hybrids. What saddens me is that supporting this feature would be quite cheap in terms of engineering cost---including UI and documentation. In fact I would find it a lot more useful than the Recharge mode. What is the point of the Recharge mode anyway? To try and do exactly what the Blended mode does, but not as well?

Ah but wait... a Blended mode would mix well with a Recharge mode for going up and down mountains. Except that the Recharge mode would need to be a bit less brain-dead and actually recharge when going downhill.

So I really don't get it.
I suspect that it's not so much laziness as they are likely worried about making the car too complicated and scaring people away. Even if these modes are optional, the fact that they even exist will cause car pundits to mention them in articles and reviews, usually in a way that makes the car seem complicated. For example HV charge is often mentioned as if it's a normal mode that people need to know how to use, when in reality it's more of a niche feature that some people use but most don't. Another example, I saw a video on a dealer website, one of those videos where a salesperson explains the features of car. This video was about Clarity and was intended for new buyers. As he sat in the car he immediately launched into explanations of how you control the system with HV mode and HV charge, he didn't just mention them he went through it in detail as if you were operating a Learjet and I thought to myself no way anyone watching this video will buy a Clarity. What he should have said "Plug it in when you can, the car will run on electric power, if the electric power runs out it will automatically switch on the gas engine". Which is true, and only nerds like us get into all of the modes, so no need to scare everyone else away by making it sound like you have to do all of that strategizing about switching modes. Another example, I was reading something on a Clarity forum where someone really wanted to get a Clarity as their next car but he had to convince his wife, who wanted I think an Acura or something. He later reported back that he lost the "sale", as when they went on the test drive she liked the car as far as how it rode, the interior, quietness etc. But then he made the big mistake of telling her about the HV button and how you can press it when you get on the freeway to hold battery charge so that when you get off the freeway you can switch back to EV so it will be quieter for city driving. She said "That's stupid, you shouldn't have to do that" and she wouldn't hear any more about the Clarity and they wound up getting an Acura.

Actually that's another feature that would be nice is if you could set a maximum speed for EV, say 50 mph, then if you go over that speed for more than say fifteen seconds it will automatically switch to HV mode, then switch back to EV mode when speed drops below 50 mph. For most trips you would never have to press the HV button as it would do it all automatically. Certainly it would be optional, and should be easily turned on and off. And also the target speed would need to be adjustable based on local speed limits. But again that all gets pretty nerdy if you try and explain it to people it will likely scare them off, so I don't expect to see any features that sophisticated for quite a while.
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post #7 of 20 (permalink) Old 09-02-2020, 02:13 PM
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No question the Volt set the gold standard for how a PHEV should operate. Although I think even the Volt would have benefited from having an option for Blended Mode.
As soon as you put the Volt in Hold Mode you're in what Honda calls Blended or HV mode. The Volt's Hold Mode and Clarity's HV Mode sets a target State of Charge (SOC) and attempts to keep the battery at that level, just like putting the Clarity in HV Mode. If you exceed the target SOC by descending a mountain both the Volt and Clarity will turn the injectors off to the ICE and let the engine continue turning via wheel spin until the battery is depleted back to the target SOC. In the Volt there are a couple of displays via a power meter on the driver information center (dashboard display behind the steering wheel) and a power source graphic in the infotainment area (main radio display). The Clarity can shows the power source graphic in the driver information center and on the infotainment display.

You can tell when the Volt is in hybrid or EV mode by looking at the fuel gauges. The grayed out fuel gauge is the one not being used.

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post #8 of 20 (permalink) Old 09-02-2020, 02:16 PM
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Originally Posted by semenzato View Post
Ah but wait... a Blended mode would mix well with a Recharge mode for going up and down mountains. Except that the Recharge mode would need to be a bit less brain-dead and actually recharge when going downhill.

So I really don't get it.
The Clarity will remain in HV recharge until the HV target state of charge is reached. After this the ICE injectors are turned off and the car uses regenerative braking to continue feeding power into the battery. I tested this driving down the south side of Grand Mesa in Colorado. The only real flaw I see in how Honda implemented HV Charge is the fact that you can't tell the car to use it when you start if there is too much battery left.

2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
2010 Mit Lancer GT MT (traded for ECO @31K miles)
2002 Pont Montana AWD - title to son at college graduation
1990 Pont Transport (traded for Montana @240K miles)
1986 Fiero GT MT (traded for Transport - needed more seats)
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post #9 of 20 (permalink) Old 09-02-2020, 04:24 PM
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If you exceed the target SOC by descending a mountain both the Volt and Clarity will turn the injectors off to the ICE and let the engine continue turning via wheel spin until the battery is depleted back to the target SOC.
Is that documented somewhere? That is absolutely insane. Why would it throw away perfectly good electricity just because you happen to be above the SOC level that it was at when you pressed the HV button? Literally throwing away electricity that could be used later. I understand when the battery is full it cannot regen because there is no place to store the excess electricity, so it is forced to convert the kinetic energy to waste heat either through spinning the cold engine or by using the friction brakes. That makes perfect sense. Or on a long downhill there might be a limitation on regen to avoid excessive heat from what would essentially be a very fast charge. But what possible reason could there be for someone to not want to increase their SOC if the battery is not full, just because they are in HV mode? Pressing the HV mode button means you want to sustain the charge at the current level, i.e. keep it from dropping. Never in a million years could I have imagined that anyone would not want it to increase SOC above that level if there is room in the battery and the electricity is literally free. Or even worse throwing it away as you are saying it does if it is over the target SOC.

Okay there is a separate topic that some people advocate to not charge to 100% to prolong battery life, and stop at say 80%, which makes sense if you are wall charging or otherwise paying for the electricity because if you stop at 80% you also stop being charged for it. But if you have free charging at work or wherever I question whether it makes sense to not just go ahead and charge to full. To each his own on that one I guess. But in this case we're not talking about 80%, if what you are saying is true then let's say you press the HV button at 40% SOC, then you are saying it will not regen past 40% as long as you remain in HV mode and it will just throw away the energy as waste heat?
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post #10 of 20 (permalink) Old 09-02-2020, 05:44 PM
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Is that documented somewhere? That is absolutely insane. Why would it throw away perfectly good electricity just because you happen to be above the SOC level that it was at when you pressed the HV button? Literally throwing away electricity that could be used later. I understand when the battery is full it cannot regen because there is no place to store the excess electricity, so it is forced to convert the kinetic energy to waste heat either through spinning the cold engine or by using the friction brakes. That makes perfect sense. Or on a long downhill there might be a limitation on regen to avoid excessive heat from what would essentially be a very fast charge. But what possible reason could there be for someone to not want to increase their SOC if the battery is not full, just because they are in HV mode? Pressing the HV mode button means you want to sustain the charge at the current level, i.e. keep it from dropping. Never in a million years could I have imagined that anyone would not want it to increase SOC above that level if there is room in the battery and the electricity is literally free. Or even worse throwing it away as you are saying it does if it is over the target SOC.
Both cars will continue to use regenerative braking to fill the battery until it hits 100% usable SOC. HV/Hold are identical in that they instruct the car to attempt to maintain the current SOC using the gas (ICE) generator/engine. Regenerative braking isn't constrained by this and will fully charge the battery if possible. The car will remain in EV mode until it reaches the HV/Hold SOC point again. As long as the SOC is above the HV/Hold set point the car will operate as an EV. The ICE is still turning via wheel spin; ICE water and oil pumps are pumping to maintain engine temperature and lubrication; and the fuel injectors are turned off. At any time the car is below the HV/Hold SOC the car will use both regenerative braking and ICE to recharge the battery.

Mountain/HV Charge instructs the car to use all available resources (ICE and potential/kinetic energy) to recharge the battery to a pre-programmed SOC.

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Originally Posted by 2002 View Post
Okay there is a separate topic that some people advocate to not charge to 100% to prolong battery life, and stop at say 80%, which makes sense if you are wall charging or otherwise paying for the electricity because if you stop at 80% you also stop being charged for it. But if you have free charging at work or wherever I question whether it makes sense to not just go ahead and charge to full. To each his own on that one I guess. But in this case we're not talking about 80%, if what you are saying is true then let's say you press the HV button at 40% SOC, then you are saying it will not regen past 40% as long as you remain in HV mode and it will just throw away the energy as waste heat?
The Clarity and Volt batteries are both larger than the usable KWh. The car shuts off charging when it reaches the 100% usable SOC point. Likewise it won't regenerate above this point. Both cars also keep a small buffer at the bottom to protect the battery from being completely drained. Bottom line is that the worst thing you can do to a LiOn battery is fully charge it. The second worst is to fully discharge it. Tesla recommends no more than 90% charge and actually has a user setting to control this. The Bolt has a buffer at the top but has a Mountain Top setting to increase the size of the buffer with respect to EVSE (wall or station) charging to allow a driver who starts their daily drive with a long descent to avoid wasting "free" energy.

2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
2010 Mit Lancer GT MT (traded for ECO @31K miles)
2002 Pont Montana AWD - title to son at college graduation
1990 Pont Transport (traded for Montana @240K miles)
1986 Fiero GT MT (traded for Transport - needed more seats)
1985 Fiero 2M4 MT (traded for Fiero GT @8K miles)
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