Engine start at highway speed while Cold? - 2018 Honda Clarity Forum
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post #1 of 17 (permalink) Old 12-16-2019, 01:20 PM Thread Starter
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Engine start at highway speed while Cold?

I have about a 45 mile commute. In the cold I expect that the batteries won't get me home so the engine will kick on. I'm kind of concerned about it kicking on and needing to support hi way speeds being cold, no warm up, no ease up to speed. Just bam 65 MPH.
Anyone else deal with this concern?


If there is already a thread on this I wasn't able to hone in on the keywords.

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post #2 of 17 (permalink) Old 12-16-2019, 03:17 PM
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If you accelerate past the blue bar on the power curve the engine will come on. Remember the engine at this point acts as a generator and is not directly connected to the drive train. There are other causes for the ICE to come on, They are describe in the owners manual. I would not worry about it. Just drive the car and enjoy it.
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post #3 of 17 (permalink) Old 12-17-2019, 10:50 AM
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First thing to remember - even when the car claims no battery there is still some battery power. Given this I suspect the Clarity's programming will start the engine in time to give it a warm up and then a smooth transition to HV mode where the ICE is propelling the car.

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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post #4 of 17 (permalink) Old 12-17-2019, 12:19 PM
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Originally Posted by obermd View Post
First thing to remember - even when the car claims no battery there is still some battery power. Given this I suspect the Clarity's programming will start the engine in time to give it a warm up and then a smooth transition to HV mode where the ICE is propelling the car.
I think that is correct based on what I have observed. If I switch to HV with a cold engine I notice that for the first mile or two the EV range continues to drop at the normal rate even though the engine light is on (and the EV light is off) so this tells me it is drawing minimal power from the engine while it is warming up. My guess is it does this since I am usually either at cruising speed or mild acceleration, so there is no real rush to start using ICE. After a couple of miles the EV range stabilizes and then (usually) begins climbing back up to the level it was when I first pressed the HV button.

I am pretty sure the same thing happens when it automatically switches from EV to HV when you reach 0 EV range, however it's harder to know for sure since it will not display negative EV range. However when monitoring SOC, EV range of 0 is equal to 10% SOC, and I see it drop down to 7 or 8% so it seems to be doing the same thing.

What I don't know is what it does if you activate ICE with hard acceleration, as far as how much horsepower is provided when the engine is cold compared to the same scenario with a warm engine (like if you had just recently switched to EV). I would think it would limit power somewhat at least until it reaches some minimum operating temperature, although that probably happens pretty quickly so you may not really notice it except for the first few seconds, maybe something a bit like turbo lag. Best way to test would be to try it both with cold engine and warmed up engine, although it would be somewhat subjective whether it feels like it has more power when the engine is warm, it probably would take several tests which would also help eliminate other variables. These type of tests would best be done on an open road with no other cars around since normally in traffic induced hard acceleration situations you have your attention on other things. Unfortunately where I drive it is very rare that there are no other cars around
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post #5 of 17 (permalink) Old 12-17-2019, 02:20 PM Thread Starter
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Thanks all...

What I decided to do is start in HV mode for the first few miles so it could warm up slowly, which helps with the heater as well. Then switch to to EV, and I didn't need the ICE again for the remainder of the trip.
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post #6 of 17 (permalink) Old 12-17-2019, 04:50 PM
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Thanks all...

What I decided to do is start in HV mode for the first few miles so it could warm up slowly, which helps with the heater as well. Then switch to to EV, and I didn't need the ICE again for the remainder of the trip.
Sounds like a plan, then again you have all winter long to try different strategies. Realistically even if you don't touch any buttons at all and just let it use up EV and let it automatically switch to HV for the remainder you will be fine and will likely get nearly identical overall efficiency. That is how many people drive their Clarity which is fine. Others (like me) are button pushers who just can't accept that we are not needed in the process and so we insert our fat thumbs into the proceedings

But seriously the points about seat heating vs. resistance heating are valid so the seat heater is one button you will want to push at least while in EV mode if it will allow a lower set temperature and thus less use of the resistance heater. But no need to go beyond what you are comfortable with. Also as you mentioned it can be worth thinking about what part of your commute you will run ICE, timing it (if possible) that you are in HV mode during periods when you need a lot of cabin heat. That may for example be more when you are leaving work if your car has been sitting outside in the cold, as compared to the morning when your car has been in a garage all night, even if the garage is unheated if it attached to the house it will likely be warmer than outside. Also you can experiment with doing preconditioning in the morning either via the app (easier with L2) or the fob. No need to wrack your brain about all of this but since you are asking, those are some things you can think about as you try different strategies this winter.

Also a lot of people including me have one general preference which is that if we know that at least some of the miles will be in HV, we prefer to use EV on surface streets, basically anywhere that acceleration is often needed, and HV when cruising for longer periods at steady speed (like on the highway). This is because the gas engine can be somewhat noisy at times when accelerating from a stop light. Not objectionably so, but in comparison to EV which is silky smooth. Whereas at steady highway speeds I hardly notice the engine. Just personal preference, I really don't think it makes much if any difference in efficiency.

Also being geeky I like to see the "gear" icon come on in the energy display which only happens at steady speeds in HV mode. It is when the gas engine is essentially directly connected to the wheels, or at least more direct than at other times when it is only acting as an electric generator. In fact Honda calls this mode "Direct Drive", although you often hear people refer to it as gear mode because of the icon. We assume that ICE is more efficient in Direct Drive mode than working solely as a generator or they wouldn't have bothered installing the physical hardware which makes this possible. Although I am not aware of any data showing how much more efficient it is in that mode. So it's not really worth trying to make it go into this mode, I'm just pointing out that it often does when you are in HV mode at steady speeds above a certain mph (it's not an exact mph range).

Most of the 60 mph freeway portion of my commute is relatively flat but there is a specific three miles section that has some undulating hills, actually they are overpasses where the freeway goes over surface streets (instead of other way around). During summer the car was just as quiet when going up those "hills", but as the temperature is dropping I notice that ICE can be a bit noisy when climbing those overpasses. So I might start switching momentarily to EV during that section.

Another trick I might try for that section is something called HV Reset which is double geeky It's not a documented feature, but as I mentioned in my previous post the EV range often drops a mile or two when you first select HV mode (as it does at other times as well) and what you do is while the EV range is down before it climbs back up again from engine charging, is you momentarily turn off HV and then turn it on again. This resets the HV target to the lower value, so it will try less hard to charge back up, and is thus less noisy. I heard of this trick from people who do a lot of driving in the mountains so it should work on my trivial little overpasses.

Again the above is in case you think you may want to experiment with the different modes, but it is purely optional and most certainly not necessary, it's just a matter of personal preference.
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post #7 of 17 (permalink) Old 12-17-2019, 10:44 PM
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What I don't know is what it does if you activate ICE with hard acceleration, as far as how much horsepower is provided when the engine is cold compared to the same scenario with a warm engine (like if you had just recently switched to EV). I would think it would limit power somewhat at least until it reaches some minimum operating temperature, although that probably happens pretty quickly so you may not really notice it except for the first few seconds, maybe something a bit like turbo lag. Best way to test would be to try it both with cold engine and warmed up engine, although it would be somewhat subjective whether it feels like it has more power when the engine is warm, it probably would take several tests which would also help eliminate other variables. These type of tests would best be done on an open road with no other cars around since normally in traffic induced hard acceleration situations you have your attention on other things. Unfortunately where I drive it is very rare that there are no other cars around
I'm not sure what the Clarity does, but my 2017 Volt will take up to 65 seconds to transition from BEV to Hybrid. It was rather nerve racking the first time I actually timed this - I was cruising at 75 MPH on a slight uphill on I-76 when the car switched. It's showed no battery range left but no power being pulled from the gas engine and all the power coming from battery.

The engineering challenge for this doesn't change from car to car. You have to give ICE engines a chance to start oil and coolant circulation before putting a load on them. It's a well known issue and I'd be very surprised if Honda's powertrain engineers didn't do it right. Remember, no EV range still has a small amount of battery left. You can see this in the Clarity by the fact that HV kicks on when you have two bars left. The Clarity will drop down to one bar of battery, but the engine will rev to 4500 to 5,000 RPM on one bar, indicating the car is trying to refill the low end buffer.

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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post #8 of 17 (permalink) Old 12-18-2019, 12:46 AM
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I'm not sure what the Clarity does, but my 2017 Volt will take up to 65 seconds to transition from BEV to Hybrid. It was rather nerve racking the first time I actually timed this - I was cruising at 75 MPH on a slight uphill on I-76 when the car switched. It's showed no battery range left but no power being pulled from the gas engine and all the power coming from battery.
I exactly said that my similar observations were while switching from EV to HV while cruising or mild acceleration. Although I didn't mention the power gauges since they don't really tell you anything about quantity of power going from ICE to wheels, even if they show ICE as providing power. But as I said based on watching the rate of EV range decline I concluded there is very little ICE usage during the transition while cruising. I also don't know what the Volt does but I'll take your word for it since you own and drive one. Sounds like at least in this aspect it operates like the Clarity, and probably for the same reason that I stated, which is that in that driving situation there is no urgency to use a lot of power from ICE while it is warming up.


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Remember, no EV range still has a small amount of battery left.
No need for me to remember since I said that almost verbatim in my post. Although it was in the part of my post prior to what you quoted, so I can only assume you did not read all of my message, which I can understand since both of my posts were lengthy, but that's because both were written for any new Clarity owners who want more detail and will read the entire post. I hope in fact that my post was clear to that audience. I remember when I first got my Clarity I learned a lot from people sharing in detail what they found through experimentation, I didn't get as much from people speculating unless they provide empirical data, like you did in what you said about the Volt and which I tried to do with Clarity, either my own observations or what I hear from other owners who have done experimentation. Although as I mentioned I have no data either on my own or from other Clarity owners if things work differently under the circumstance of activating ICE by putting the pedal to the floor in EV mode with a cold engine.

As for ICE needing time before it can be used in a hard acceleration immediate power demand situation, I said that also, but I left out details like oil pressure because we really don't know, modern engines especially hybrid engines designed for start-stop have much newer technology to handle cold starts and can get full oil pressure and coolant flow in about a second, but there are other aspects that I can't really speculate without knowing, and without empirical data from doing hard acceleration trials with both cold and warm engine which I said is what is needed to better answer the question. As I said I think there is a lag, we just don't know how much, but following my train of thought about the need for power, it might be a different criteria when the owner has made it clear by putting the pedal to the floor that they need maximum power as soon as possible, so the lag may be very brief even with a cold engine. Maybe. Needs some testing. Especially since it is advertised to work that way. I realize the Volt is different as it does not activate ICE in that situation of putting the pedal to the floor. But for Clarity I am not aware of any caveats to not expect absolutely anything from ICE for several minutes even if you floor it. Hard acceleration is usually brief, and also somewhat rare (hopefully) so as I said I think there may be a different criteria than the cruising situation. There may have been a willingness by the engineers to compromise a bit in those situations and start using ICE much more quickly then we might expect. I'm sure it's fine or the system wouldn't allow it.

Now I'm not saying that someone who lives on a rural 70 mph highway, and they come out of their driveway every morning and press the pedal to the floor in order to jump into gaps in traffic is doing any favors long term for their engine if they do that every day. But I don't think most people would do that anyway.
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post #9 of 17 (permalink) Old 12-18-2019, 10:28 PM
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Start/Stop works so quickly because even with the ICE "off", the oil and water pumps are still running and maintaining fluid pressure and movement. All that's really "off" in start/stop is the injectors. Hybrids use their electric motors to restart the engine. Non-hybrids use a heavy duty starter motor. On the other hand, when a car first starts, there is no oil or water pressure, and in fact, both the oil and coolant have drained out of parts of the engine. The coolant isn't so critical because the engine hasn't had a chance to get hot, but the oil is critical and it's all sitting in the oil pan underneath the engine. Oil will drain out of an engine in less than a minute. It takes several seconds to get oil through most of the engine and up to a full minute to get it throughout the entire engine, even on a standard gas or diesel powered vehicle.

I suspect the Clarity may actually start the oil and water pumps at low volume even when running in EV mode, just to lubricate and bring the entire engine to a consistent temperature to safely handle the power surge demands such as flooring the car to get safely to merge speed on a short, uphill entrance ramp to the freeway. My commute has one of these so I frequently pull short bursts of large amounts of power for this purpose. If the oil and water pumps aren't already running to provide some level of lubrication and cooling this would be death on the ICE. Even a "belt" driven system can be operated by the car without starting the ICE with the EV motor providing the power to turn the belt.

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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post #10 of 17 (permalink) Old 12-18-2019, 11:16 PM
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Interesting post. Had thought along these lines as well but you seem well versed in it.

Good post.
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