Instant MPG with engine?

Discussion in 'Clarity' started by RobinBrain, Jul 13, 2019.

  1. RobinBrain

    RobinBrain Member

    What MPG do you guys get when the engine is running? Looking at the instant mpg I get around 43ish at 65 MPH. So just engine not engine and battery combined
  2. Mowcowbell

    Mowcowbell Active Member

    The battery is almost always assisting, even when the ICE is running. So, it would be very difficult to produce a gas only MPG reading. 43mpg at 65mph is pretty close to normal for this vehicle.
    jdonalds, ClarityDoc and RobinBrain like this.
  3. fotomoto

    fotomoto Active Member

    Set the center screen to powerflow and you'll see how everything works while in action.
    ClarityDoc and neal adkins like this.
  4. petteyg359

    petteyg359 Active Member

    Which instant MPG? The one on the center screen and the one on the instrument panel are very often different on mine :) I don't bother with the car's MPG measurement at all. I just do the math when I fill up the gas tank, and then the "gas only" MPG happens when I'm on long trips over multiple tanks that are HV all the way.
  5. RobinBrain

    RobinBrain Member

    I wanted to know what readings you guys are getting. So when you have trip a or b on the Center display and look at the tablet display to make sure it engine only
  6. craze1cars

    craze1cars Well-Known Member

    It totally depends if you are going uphill, downhill, upwind, downwind, how heavily loaded, whether gear mode is engaged or not, what the outside temp is and what state of charge the battery is in. Instant MPG reading changes with varying RPMS of the engine, which go up and down with battery drain needs, it does not stay linear with any particular speed. On long road trips I've seen as low as 20 mpg and as high as 65 mpg. It's usually near the 40-ish range, but walks around, at 70 to 75 mph.

    FWIW the car is ALWAYS engine and battery combined, or battery only. There is simply no such thing as driving the Clarity only on engine. Lack of transmission prevents this opportunity. The engine is a generator. So even while cruising with engine running and in gear mode which is the only time the engine is providing SOME power to the wheels, the battery is almost always either expending or receiving energy, depending on the instantaneous load...
    Last edited: Jul 13, 2019
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  7. Clarity Dave

    Clarity Dave Member

    And yet I have seen the energy flow display show energy coming only from the engine, with no flow line between the center and the battery/traction motor at the bottom. In this configuration, the gear icon is present indicating the engine is connected directly to the wheels. It's challenging to photograph it since it's transient and I'm driving at highway speeds when it happens.
  8. RobinBrain

    RobinBrain Member

    Thats what i see also. Do you remember what the instant mpg is at those times?
  9. Clarity Dave

    Clarity Dave Member

    I don't generally have the instant mpg displayed, but that would be interesting to see, so I'll plan on having it up on the next road trip.
  10. craze1cars

    craze1cars Well-Known Member

    Agreed that happens. But the engine is not the exclusive power source to the wheels at this time.

    When this happens it is the moment the engine is indeed coupled to the front wheels, but the engine is also spinning and operating as a low speed generator at the same time, providing an electrical charge into the battery at the same pace the electric traction motor is putting electrical power out to the wheels.

    So even during those times where you see the flow chart balanced out, both the engine AND the electric motor are providing power to the wheels...the car is still not being propelled by only the engine...

    At least that’s my understanding of how this car works. As always, I could be wrong...
    Last edited: Jul 13, 2019
  11. Assuming the “Energy” screen is correct, in HV mode I can see the gear icon in a variety of scenarios:

    1) Engine driving wheels, with battery not involved...

    2) Engine driving wheels, with power flowing to the battery, and...

    3) Engine driving wheels, with power flowing from the battery.
  12. craze1cars

    craze1cars Well-Known Member

    indeed. It does all those things in gear mode depending on load at a given time due to wind, hills, etc. That better illustrates my point that just because the engine is coupled, doesn’t mean the electric motor isn’t also providing supplemental power to the wheels in addition to the engine...sometimes more and sometimes less. Regardless of gear mode being engaged, the car is essentially almost never driving on engine power alone....and any exact moment that might be occurring is never displayed on any screen so that moment can’t be isolated or seen. It is definitely not at the moment flow stops in both directions...the electric is NOT shut “off” during this time as I believe some perceive. The electric motor is still involved and pushing, just the battery is expending the same amount of juice pushing the wheels that it is receiving from the running engine during that time, so the net effect on the battery is still zero. But we have no idea how much torque to the wheels is being split between the coupled engine and the electric motor.

    Kinda like net metering on a solar panel. At some moment in time you are getting the exact same amount of energy from the sun as your home is expending. So the battery flow display will say zero. But your refrigerator and TV and lights are still obviously the electricity is not “off”.
    Last edited: Jul 14, 2019
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  13. fotomoto

    fotomoto Active Member

    The power screen is a simple representation of power flow and not a calibrated gauge.


    When my old Gen 2 prius battery failed, Toyota's control logic went into protection mode and took the EV side of the powertrain out of the loop so only the ICE was powering the car (referred to as limp or turtle mode). The car could barely accelerate from a start and maintain 30mph; basically enough to get one off the road and pull over. In the hybrid concept, the ICE in not designed to handle the power needs of the car by itself. It it was it be a 2.5L like most other 4 cylinder FWD cars along with the so-so fuel efficiency to match.
  14. Clarity Dave

    Clarity Dave Member

    That makes sense to me. The energy flow graphic lumps the HV battery, generator(s) and traction motor together, so when the power going into the battery or generator from the gas engine is approximately equal to the power supplied by the traction motor to the wheels, no flow is shown.

    And the traction motor is always coupled to the wheels, so I wouldn't think that it was just along for the ride with the gas engine doing all the work even when the display implies that it is.
  15. Clarity_Newbie

    Clarity_Newbie Active Member


    I have attached a page from the 2018 PLUG-IN HYBRID OWNER’S GUIDE dates 05/17/2018 off the Honda Clarity owners site.

    Perhaps this demonstrates why there is confusion on what drives what when. I can see why folks have differing opinions...depends on what you read.

    Either nice to have one definitive answer instead of conflicting info from the manufacture.

    Attached Files:

  16. KentuckyKen

    KentuckyKen Well-Known Member

    @craze1cars poses some interesting hypotheses. I’ve only done less than 800 mile in HV, but have seen every possible power flow that @Clarity_Newbie referenced.

    The real poser is when the engine is running (engine icon on), and coupled mechanically to the wheels (gear icon on), and there is no power flow to or from the battery. Under those conditions, is the starter-generator providing any power to the traction motor or is the motive force purely mechanical from the engine shaft?

    As I understand it, the starter-generator is coupled to the engine shaft so it’s armature (or whatever you call it) is always turning with the engine. Is that right? But it doesn’t always produce power when spinning since it acts like a motor to start the engine. So how has Honda programmed it and which is more efficient when just engine torque is sufficient; engine mechanical only or engine mechanical plus power to motor from starter-generator? That little Atkinson cycle engine is efficient, not powerful/torquey.

    And while I’m asking, does braking resistance and subsequent regen power to the battery come from the traction motor or the starter-generator? Would that depend on whether the clutch is between the motor and s-gen or between the s-gen and engine. I can’t find @insightman,s and @AnthonyW’s diagrams.

    Inquiring minds want to know!
  17. bpratt

    bpratt Active Member

    The traction motor/generator is connected to the front wheels with a couple of gears and is always turning when the wheels are turning. The motor/generator you call the starter-generator is connected directly to the ICE and is only turning when the ICE is turning. If the clutch is engaged and you step on the brake to slow the car, the clutch will disengage, so the braking resistance and regenerative braking is only from the traction motor.
  18. ClarityBill

    ClarityBill Active Member

    Does the clutch actually disengage with the brake?

    The scan gauge shows the ICE RPM stays the same, when going down a hill and regen kicks in, even when the display shows the gear is turned off. The RPM staying consistent might indicate the clutch is still locked: Seems like RPM would drop to idle speed, or rise, if clutch was disengaged.
  19. Thevenin

    Thevenin Member

    I log my engine miles and fuel purchases manually. I only engage the engine with zero EV miles remaining, and in 90% highway driving. I have spreadsheets with range tests, etc, which I plan to upload here someday.
    For the last three months, I have been getting 45.2 mpg. The dashboard mpg readout varies from 42 to 48 mpg, regardless of my actual mileage. If I drive on back roads (45-50 mph), I can get over 50 mpg, but I don't have many opportunities to do this.
    fotomoto likes this.
  20. insightman

    insightman Well-Known Member

    The traction motor provides all the regen braking. Here's a cutaway of a pre-Clarity i-MMD system:


    And here's my controversial Clarity drive mode diagram

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