How does the HC2018 switch between the gas and electric engines?

R

Rebecca L Feinstein

New Member
Hi there,

I'm new to this forum, my name is Rebecca.

I just bought a used Honda Clarity 2018. I'm wondering how the engines switch from gas to electric and vice versa. I've looked in the owner's manual (which is useless).

Any assistance would be appreciated.
 
It's not really a "switch." Almost all of the time the gas engine is on, it's driving a generator, and the power from the generator is split between going to the motor or the battery. When in pretty specific torque conditions at highway speeds, there's a clutch which may close to connect the gas engine directly to the wheels for a bit better efficiency, but the generator and motor are always in the loop.

That clutch I was just talking about is the only one, and is engaged by activating two redundant valves. The control wires going to one of them got chewed through on my care. It continued to operate perfectly fine, albeit a bit less efficiently and with a strange error message, until I got it fixed.
 
Rebecca L Feinstein said:
Hi there,

I'm new to this forum, my name is Rebecca.

I just bought a used Honda Clarity 2018. I'm wondering how the engines switch from gas to electric and vice versa. I've looked in the owner's manual (which is useless).

Any assistance would be appreciated.
Click to expand...
You mean technically? Depends on what the car is doing. If it is only entering HV drive mode, the basic sequence goes like this: the generator motor spins up the engine to a predetermined speed (around 1000 rpm, I forget the exact number), fuel injection is started, the generator motor quickly transitions over from motoring to generating, and from there the engine is controlled as needed to meet the power requirements. If it's entering engine drive mode, it's a bit more complicated. First few steps are the same as HV drive, so the engine is started the same way, then the engine starts rev matching so there is a smooth engagement of the clutch when it is time to engage. Once the engine is synchronized to the transmission, the generator motor starts loading the engine up, after this step is completed, the shift solenoid starts engaging (technically there are 2, but that isn't relevant), and the ecu starts the tricky process of transitioning torque. The generator is unloaded as the clutch is engaged, and the traction motor also reduces torque. Sorry if I didn't do the greatest job explaining that, but basically it's a very fast dance to maintain constant population torque at the wheels.
 
Not quite sure if you really mean “how” (in which case MeNerdHair’s answer is right on—the car always runs on electric but sometimes is charging the battery at the same time by running the engine, which you could consider “running on gas engine” in a way). There is the one exception at highway speeds where the gas engine if on drives the wheels directly, but you can’t tell that by performance—it’s essentially silent.

If what you meant though is “why” the car switches from having the engine on at times to having the engine off at other times, that is a slightly different topic and let us know if you want some thoughts on that.
 
Rebecca L Feinstein said:
Hi there,

I'm new to this forum, my name is Rebecca.

I just bought a used Honda Clarity 2018.
....
I've looked in the owner's manual (which is useless).
Click to expand...

Welcome to the group and Clarity ownership!

Agree with the other answers, just wanted to add that you may not have received the Owner's Manual, which is thick and informative. You may have instead received the Owner's Guide, which is... less thick and informative. There are multiple posts in this group about how to obtain the manual electronically (free through the Honda owner portal) and in print.
 
MeNerdHair said:
That clutch I was just talking about is the only one, and is engaged by activating two redundant valves.
Click to expand...

Clarification here... the two redundant valves must both operate to engage the clutch. (It would be bad if it got stuck engaged.) My point is that even if that clutch can't engage at all --and that the engine can therefore never directly drive the wheels -- the car will still drive fine. You'll lose ~5 MPG but suffer no performance impairment.
 
It may be helpful to understand that there is only one engine. The majority of the time it is running, in my experience, it is just producing electricity which is sent to either the electric motor, the batteries or both. Even in EDM, the engine can generate electricity. The difference is that the engine is also directly driving the wheels while in EDM.

In EV Mode, electric current is provided by the battery, unless a certain power demand is exceeded, at which point the engine will provide additional current to the electric motor.

In HV Mode, the engine generates electricity which is sent to the motor and batteries as needed. The engine/generator can only provide about 60hp to the wheels. If more than 60hp is required, additional current will be drawn from the battery. Once power demand is reduced, the engine/generator will work to restore (recharge) the battery to the previous level while also sending current to the motor.

Perhaps the answer to the question is that these transitions are controlled by software, based on the driving conditions. Outside of EDM, we are looking at a vehicle where electricity provides the motive power which is provided by either the engine/generator, the battery, or a combination of the two.
 
The easiest way to look at this car is that by default, when first turned on, it is an electric vehicle. If you want to favor using the gas engine, push the HV button. Push it again to return to favoring electric propulsion. But as Landshark has pointed out, the battery management software will ultimately determine how things run based on driving circumstances.
 
rodeknyt said:
The easiest way to look at this car is that by default, when first turned on, it is an electric vehicle. If you want to favor using the gas engine, push the HV button. Push it again to return to favoring electric propulsion. But as Landshark has pointed out, the battery management software will ultimately determine how things run based on driving circumstances.
Click to expand...
And, if for some reason you would like to burn extra gasoline to charge up the battery while driving, press and hold the HV button to active HV Charge. Unlike plugging in, HV Charge stops charging the battery when the Battery Charge Level gauge reaches 12 segments, which represents about 60% of a full charge. HV Charge is discussed on page 17 in the Owners Manual I temporarily made available for downloading).

You could use HV Charge to get your battery up to 60% before your next stop for gas. That scheme would increase your total gas+battery range after that stop for a tankful of gas (a tiny 7 gallons). Another reason to use HV Charge could be to charge your Clarity's battery before entering an urban area where you might prefer to travel on electric power rather than pollute the air.
 
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