Downhill driving with full charge engine and brake behavior?

  • Thread starter Thread starter skylines
  • Start date Start date
  • Replies Replies 8
  • Views Views 3K
S

skylines

New Member
There has been plenty of discussion about the optimum way to drive the car with uphill segments. I have a slightly different question. How does the car behave on a long continuous downhill drive starting with a full charge.
I live in a flat part of the country. My question for anyone who has tried this (start at full charge, or get there soon enough) for a long downhill drive is how did the car behave? Did the engine start up (almost certainly we know) and *stay* on for most of the drive? Did the cruise control maintain a set speed on the downhill sections as it does when regeneration is available, or did it gather speed like cruise control often does on "normal" cars? Could you tell if it applied the friction brakes. An issue with EVs is that if they are fully charged they often ride the brakes and that is not good down mountains. If Honda found a way to dump excess energy throughout such a journey essentially mimicking engine braking and saving the brakes then it really is quite brilliant. And one possible answer to the why won't the engine shut off complaints. If you haven't burned enough EV the car assumes that you are going downhill and tries to protect the brakes. Maybe.
 
I have only had the clarity for one week, but i noticed something odd today, at full charge, I was going down a steep hill, and it didn't let me use the paddle regen, it had no affect, and the 'chevrons' just dropped when i pressed the paddles.
 
^^^ This...plus the engine will most likely come on when full charge especially when going downhill or using the brakes to help dissipate the extra regen. The engine will run till it reaches ~150 -160 degrees then shut off. For the Clarity I drive, the engine typically runs ~3-5 mins once it comes on...then returns to "EV". Colder days = longer run time obviously. All perfectly normal.

Hope this helps.
 
ed yagi said:
I have only had the clarity for one week, but i noticed something odd today, at full charge, I was going down a steep hill, and it didn't let me use the paddle regen, it had no affect, and the 'chevrons' just dropped when i pressed the paddles.
Click to expand...

Apologies for not being clear enough with the built in assumptions. As others above have mentioned this is normal in all EVs to protect the battery and not allow it to overcharge. Additionally in the Clarity PHEV if one tries to regenerate by using the paddles or braking too hard the internal combustion engine will sometimes turn on. Sometimes turns off after a short while and sometimes the ICE stays on for a while. Many people don't like this. There has been speculation on whether this is a bug or a feature which allows excess energy to be routed through the engine. I am basically wondering about the latter and suggesting an experiment that might confirm it. How a serial hybrid would do so is unclear because for the overwhelming majority of the time the wheels aren't connected directly to the engine. And having the engine on typically will try to add more charge to the battery not take it off. The closest I have come to testing is to start on a highway right after a full charge. As the ICE came on the EV miles dropped much faster than the EV estimate for a bit. Others have noticed this too. This may simply be the guesstimator adjusting for more EV usage at highway speeds. Or the ICE is actually helping to knock off a bit of the charge of the top. If they did manage this it actually might be a pretty useful feature in the scenario I mentioned in the original post.
 
Last edited:
skylines said:
There has been plenty of discussion about the optimum way to drive the car with uphill segments. I have a slightly different question. How does the car behave on a long continuous downhill drive starting with a full charge.
I live in a flat part of the country. My question for anyone who has tried this (start at full charge, or get there soon enough) for a long downhill drive is how did the car behave? Did the engine start up (almost certainly we know) and *stay* on for most of the drive? Did the cruise control maintain a set speed on the downhill sections as it does when regeneration is available, or did it gather speed like cruise control often does on "normal" cars? Could you tell if it applied the friction brakes. An issue with EVs is that if they are fully charged they often ride the brakes and that is not good down mountains. If Honda found a way to dump excess energy throughout such a journey essentially mimicking engine braking and saving the brakes then it really is quite brilliant. And one possible answer to the why won't the engine shut off complaints. If you haven't burned enough EV the car assumes that you are going downhill and tries to protect the brakes. Maybe.
Click to expand...
My experience and impressions: I live at the top of a hill. I have about two blocks before I hit a half-mile downhill.

(These issues have been discussed and debated in numerous other threads, but AutoCad is getting boring today...)

For me, the ICE (Internal Combustion Engine) starts if I am braking 'too hard' with the charge level above 98%. As the SOC (Battery State of Charge) is reduced, it allows me to brake harder. If I get below 90%, I am able to do my hill without too much concern about starting the ICE.

Even at lower SOC, it seems the engine braking is available for extra braking power. I have had panic stops in EV mode that ended with the ICE running. (Just like extra power is available for acceleration.)

The ICE will run until it is warmed up. It seems to have a couple warmup cycles: The ICE will shut off, then restart in a few minutes. If I am staying in EV, it will shut down completely after 5-10 minutes.

Cruise control does use brakes to maintain speed. SOC over 80% seems to favor the friction brakes over regenerative braking. Automatic panic braking will also start the ICE. Cruise control will activate the brake lights; I am not sure if cruise control activates brake lights when it is using regen braking, or just when using friction brakes.

The system will use regen braking first, then friction brakes, then engine braking.

The brake pedal does immediately activate some friction brakes. This helps a smooth transition from regen brakes to friction brakes. If there is regen space available, the brake pedal will use regen braking, but always uses friction brakes.

The engine braking seems to be the parallel hybrid operating backward. The generator at the wheels makes electricity, and the motor/generator at the ICE spins the ICE like it is trying to start the engine. When the engine braking is complete, the ICE will 'fire up' and run to come up to temperature and circulate oil.
 
Thanks. Long time lurker here and I do remember that you live on a hill. My specific question though is not about a short hill. I pretty much acknowledged all the issues that you mention right at the outset. And those have indeed been discussed to death. But what happens if say one starts at Aspen, or Mt Washington, or similar with a full charge and heads downhill for a long stretch is my question. Most EVs and PHEVs would ride their friction brakes all the way. Does the Clarity do that, or does the engine come on and mostly stay on for most of the trip in that scenario?

The parallel hybrid working backwards explanation is not that obvious for the Clarity given that in the other direction the ICE and wheels can only directly engage within a small band of relatively high speeds. As many people have noted the ICE turning on in a high regeneration scenario seems to happen at pretty low speeds too. One would need gears that this car doesn't have for that to be the full explanation.
 
ClarityBill said:
Oops, My impression would be series hybrid operating in reverse... Sorry.
Click to expand...

Okay. Interesting thought. This should work for the first major regen event at nearly full charge. But once the ICE starts and is warming up this channel would be unavailable if one encounters another major one right afterwards. Definitely a possible answer to my main question. Testable too!
 
You must log in or register to reply here.
Back
Top