GRA
Well-known member
I was referring to the speed at which the Volt allows the engine to drive the 'other' motor. The method Honda is using is what I think is more useful generally, although in cases where your one-way or round-trip commute range is within the Volt's (or any other PHEV's) AER range that is clearly the lowest operating cost (if not usually the lowest total cost of ownership).JeffN said:Huh? I'm not sure what you mean. The Volt has no maximum EV mode speed other than around 100 MPH which is the overall maximum speed. As long as you have usable charge left in the battery the gas engine will stay off under all speeds. If you want to reserve or generate some battery charge for EV driving off the highway at your destination after a trip that is longer than the EV-only battery range then that is also easy.GRA said:From an efficiency/lowest cost point of view, I think Chevy set the max. speed for EV mode a bit high at 70 mph.
First of all, let me correct your misapprehension. I'm not an EV owner, because they don't currently suit my situation and needs. As to my comment about the gas engine being more efficient at freeway cruising speeds, sloppy wording on my part. As you point out, I was comparing it to itself in stop and go, urban driving, not directly comparing it to EV operating efficiency. We are in agreement about the advantages and disadvantages of the various PHEV modes. However, I'm considering lowest lifetime cost as well as reducing emissions where they matter most (built-up urban areas), and taking those two together, the Honda method is superior to the Volt's.JeffN said:That seems like an odd comment coming from an EV owner. What makes you think burning gasoline is more efficient or lower-cost at speeds over 62 mph versus an electric motor? Gas engines are only more efficient at modest highway speeds in the sense that they are much less efficient at lower speed start/stop city driving (Prius etc., excepted). A Volt (or LEAF) driving at 75 MPH on battery is almost certainly running at lower operating cost than any gasoline engine car at that speed. In fact, at higher highway speeds the Volt is slightly more efficient than the LEAF in part because it switches to using both of its electric motors together though the planetary gears so each can run closer to its ideal RPM efficiency. In contrast, the PiP (and apparently the Accord PHEV) force you to use gasoline at speeds above 62 mph even if your entire commute is entirely within your battery range as it is for many people. The PiP's use of gasoline at these speeds is due to power limitations due to its small battery pack and mechanical efficiency limitations due to its transmission design.GRA said:I assume the planetary gear set could be modified to change the ratio slightly and optimize things for the ICE at a lower speed. Some people can certainly use it for their commutes, but my feeling is if you're cruising at 100 km/h (62mph) or faster, traffic is flowing freely and the gas engine is more efficient in that range. I think the Pip or maybe the Accord PHEV (which works more like the Volt than the PiP does) cut-off at 62 makes more sense.
And there's the problem - the Volt only has these benefits because of the way the incentives are structured, indeed, the incentives are what make the car remotely affordable and they won't be around forever, and depending on the results of the election may disappear quite soon. Compare the Volt @ $40K to the base PiP @ $32k, to the base Prius @ $24k. If PHEVs are going to be acceptable to mainstream consumers (with U.S. median family incomes of just under $50k), as opposed to early adopters with far more disposable income (Leaf owner MFI $140k; Volt owner MFI $170k), then initial price and lifetime cost matter, and the only way to get those down is to use the minimum battery that will do the job until gas price increases and battery price decreases change the equation. SeeJeffN said:The PiP can be good for people with 10-12 mile total commutes or 20-24 if they can recharge at work. Otherwise, you are starting the gas engine even at speeds below 62 or with stronger acceleration. A Volt with a battery 3.5 times the size of the PiP battery (4.4 kWh vs 16 kWh) is only $2,500 more when comparing the base models for each car after the tax credit. That's about $215 per kWh of battery at the pack-level which is a good deal if you can put it to good use. PiP is also good if you drive a lot of very long trips where you can take advantage of the 48 mpg EPA highway estimate versus 40 mpg for the Volt.
http://www.cmu.edu/me/ddl/publications/2009-EP-Shiau-Samaras-Hauffe-Michalek-PHEV-Weight-Charging.pdf" onclick="window.open(this.href);return false;
I hope I've clarified my views.