Anyone have ideas to increase HV mileage? I was thinking of trying performance exhaust/muffler/silencer, but I don't know know yet if there is a gain. Accord, Prius, Malibu Hybrids have exhaust heat recovery for faster warm-up and shorter run time during heating season. I like that idea.
Honda Press Kit for 2017 Accord with Exhaust Heat Recovery Device: "The new heat recovery device contributes to the second-generation i-MMD's efficiency by helping to reduce power-robbing friction particularly during initial cold weather operation. Located downstream on the exhaust system, the heat recovery device uses hot exhaust gas to warm engine coolant quicker, especially during cold weather conditions. This brings the engine up to normal operating temperature quicker, reducing internal friction and allowing the i-MMD to operate in electric mode earlier. This helps to achieve improved fuel efficiency during cold weather operation." It's just a valve in the exhaust to direct flow between the bypass pipe and the pipe with the coolant heat exchanger. Coolant goes to the exchanger, heater core, and engine. BTW, Clarity has an electric heater to warm up the cabin and engine faster for the same purpose. Exhaust heat is free and plentiful (well, free after the $800 heat exchanger). Electric heat from the battery, not so much.
I don’t believe the resistance heater in the coolant loop to the heater core is used to heat the engine. Here is a diagram that I think AnthonyW (not sure, apologies to who did if not him) posted showing that this loop has a valve that isolates it from the engine. If it didn’t, it would be quite a large drain on the battery and take a very long time to warm up the cabin.
Surprising, but true (and I am dreading winter for this). The electric resistance heater, water pump, and electric water valve apparently not only are used for cabin heating, but also for "quickly engine warm up". "Engine Warm-Up Mode (from Honda doc 3279 in the words of Japanese engineers) The electric heater coolant pump is operated also used to engine warm up mode to flow the engine coolant from electric coolant heater, as quickly engine warm up. Therefore, it is not failure condition that electric heater coolant pump is operated even when the A/C system is off." The water valve is used to isolate the heater core in the winter when heating the cabin and the engine is off (EV mode). Otherwise, the resistance heater would be heating the cabin and a huge chunk of aluminum sitting in a drafty engine compartment. The water valve is also used to isolate hot engine coolant from the cabin in the summer.
Car and Driver got 46 mpg in HV mode (all gas miles) on their standard test loop going 75 mph. I had gotten 52 mpg average on two 200 mile loops last Spring going 50-55 mph (no heating or A/C used though). For a 2 ton car, I doubt there is anything you can do to improve on that except to make sure you don't have a depleted battery in HV. There seems to be a correlation between a depleted battery in HV mode and poor mileage.
Agreed that MPG is very good for the size and weight. Compare the 2018 Fit with same engine design and displacement. Mileage is about the same, which is amazing. Always room for improvement - at least that's what my wife tells me!
Here is the doc Atkinson is referring to. Bottom of page 4. Also attached is the instructions on how to install a block heater. I imagine that it would be slightly more efficient than allowing the heater core to warm up the engine.
That amazes me. My 2008 Honda Fit usually gets around 30 ... 35 if I drive it like a baby on the highway. And it only has 109 hp.
To Atkinson and AnthonyW: Well, butter my but and call me a biscuit; the resistance heater does prewarm a cold engine! Thanks for the info and I hope I never have to run my ICE in the winter as this must take a lot of juice from the battery for a time.
Easiest mods would be to change the oil to 0W-16 (or as low as 0W-7 if you dare). Studies show that you can gain about 1.5% fuel efficiency by making the switch but that was based on cars whose ICE run all the time. Since our ICE rarely turns on, I just don't think you will see a difference at all. Same thing with a high performance air filter such as K&N, the engine really doesn't run that much to make much difference. Another thing that helps is cold air induction, but our Clarity's already has a basic cold air induction system for both motors. Look under the hood on the drivers side and you will see an a small inlet vent on top of the air filter system extending out to just underneath the lip of the hood. Also check out the air inlet vent underneath the driver's side daytime running lights. The cut out on the passengers side is capped off. As best as I can trace that vent is leading to the electric motor and/or generator.
Thanks for the document, I have been wondering if my Clarity could utilize waste engine heat when the engine is running anyway. Would be more efficient when taking a longer trip in the winter. Would love to see how long the battery warms the engine after the engine starts, I would think it would only be a few minutes. My daughters 4 cylinder Kia gets up to temp in about 5 minutes. No matter, on a 30 degree day it would really make it important to be easy on the throttle so as to not have the engine kick on during my 10 minute commute. Would suck to use battery to heat up the engine just in time to park it for the day.
In HV mode the engine cycles on and off while driving and in cool weather, the heater combined with ambient cold drag coolant temps down during each "off cycle". The engine spends more time each cycle in warm-up mode trying to get back up to 175 degrees, reducing MPG. The answer is to assist warm-up by adding heat somehow. An electric element is cheap has a low capital cost at the expense of electric range, but it works. An exhaust heat recovery device is expensive (maybe $800) and the heat is abundant and free. No electrical parts, just a coolant heat exchanger with an internal thermostat to route exhaust through a bypass pipe when coolant is warmed. Picture attached of an Accord Hybrid "heat collector" which would only bolt up to that specific exhaust, but it has me thinking.
Take a look at the attached file. The valve timing system is optimized to assist in warming the engine in the most efficient way possible when the engine is running.
The computer doesn't call the long duration cam (high efficiency atkinson cycle) until the engine is warmed up. The short duration cam is for high power and warm-up. We want to be out of: 1. warm-up as soon as possible and then avoid 2. high power for best MPG. I don't know how to get into the high power output except maybe with HV Recharge or running the battery low on a hill climb. That leaves warm-up which is a soft spot for hybrids especially in the winter with heat draw for the cabin. Some hybrids have active grill shutters and exhaust heat recovery to mitigate lack of waste heat resulting from greater fuel efficiency. If the engine runs only half the time in HV mode, in cold weather the cabin heater still runs full time (even on low fan). It will be something to watch this winter. So far in the summer on the highway in HV mode, the engine maintains 175 degrees whether running or not.
Are you talking cargo weight or should I be insulted? I’ll have you know, sir, that I am at the perfect weight for some one 7 1/2 ft tall! So I am not over weight I am under tall. Seriously, that’s a valid point. I make sure not to leave anything in the car I don’t need.
