Turn your Prius into a EREV (or close)

Discussion in 'Chevrolet Volt' started by scottf200, Jun 27, 2012.

  1. usbseawolf2000

    usbseawolf2000 HSD PhD

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    This discussion assumes that EREV is better and that Prius owners should look to upgrade in order to come close to how Volt operates.

    This notion cares only about EV miles and disregards cost, interior volume, time to recharge, emission beyond tailpipe, etc.

    Blending is a better approach because driving condition (not range) determines which fuel to use. Now that Volt (sort of EREV) has the HOLD mode, the driver can intelligently selects when to use gas depending on the driving condition.

    Prius PHV was designed / optimized (electric motor and battery sized) for EV operation in city traffic condition and blend in highway condition. The blending happens automatically.

    In summary, EREV is a manual two fuel sources plugin but Prius PHV is CVFS (continous variable fuel source) plugin.
     
  2. austingreen

    austingreen Senior Member

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    No, it only assumes that some drivers would like their prius to perform like a erev, and talks about the kit to allow them to do that. No assumptions that's for everyone. Most people don't want to modify their drive train of their car, but if the warranty is up.... many see this path nicer than what this generation of phv gives you.

    Certainly we expect the next generation prius phv to move in the direction of higher rates of acceleration while staying all battery....and greater CD range. Those that want that now and have a higher mileage prius, may want to look at a kit.
     
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  3. drinnovation

    drinnovation EREV for EVER!

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    The discussion presumes that for some people it is better. It is for them to decided the benifits and if they want to choose to upgrade an existing prius. No one here has said its better for everyone or better overall.




    Expanding the EV ability of an existing prius is an owners choice.. they clearly have to make a decision about the cost (already discussed) and giving up the added space for the battery.

    You continue to bemoaned the recharge time which really just shows you have absolutely no idea what you are talking about, and just want to rant against EREV/PHEVs. One can stop charging at any time they want so there is no real advantage so shorter time to full. If you want to get into 3.3kW charging vs 6kw charging, there is meaningful issue, but neither the PHV, the PlugIn Supply or the Volt have a dog in that fight.. that regular BEV stuff right now.



    You keep saying blending is always better with no justification. Its simply not true, no matter how many times you say it. I figured I'd let you go find papers showing its better at least some times, but you did not even do that. I knew they existed as I've read many. For example, below is a chart from a paper on
    Effects of Different PHEV Control Strategies on Vehicle Performance

    [​IMG]
    Which shows the relative MPGe efficiency gains for different strategies in different architectures on different driving tasks. In many of these the EV-frst mode is more efficient, even for a parallel PHEV architecture. For example a parallel PHEV on 3 hyway trips gets 2.2x hybrid efficiency if in EV mode and only 1.95 if in blended mode The differences are much larger for series PHEV, e.g. in City driving. The optimal strategy is complex. The paper concludes concludes

    The optimal fuel usage stragey depends on knowing the intent of the driver as well as the complex issues of the drivetrain and the road load, so no car can do that now. It also depends on the vehicle modes used and if there is more battery than needed, just enough or too little.

    To see how complex these get, there is the "simplified" optimal model for a parallel mode PHEV. First consider the optimal blending strategy, given a battery with just enough power. This swill to use the battery keeps the ICE in its optimal setting (based on BSFC+gearing) and the EV motors manage all the variabilities in road load. If the trip is longer than the battery can sustain that model (i.e. small battery), then the battery would be used only on the most demanding sections (which the car would have to pre-compute). If the battery is larger than needed for that model, the optimal strategy is pure EV to the point the battery reaches a level where battery + ICE can complete the trip using the optimal blending. It become more complex if there is, (as in a Volt) the ability to use parallel and series EV modes as well. It is also much more complex if the trip has different segments, e.g. highway now and city later.

    In practice today's cars cannot see the future load demands or even the driving distance. Since the optimal strategies need information not available to today's car, they all use a reactive strategy. The EREV makes the assumption that most of the time they want to use battery first, since they are likely to return home with some, so it chooses to delay's ice as long as possible. Its a good default strategy with a large enough battery. Since with 35miles EV range, 80% users can complete their day with ZERO Ice, that is a good default -- but not as good on the days with medium trips.

    The reactive blended strategy must presume some range in which to deplete the battery (i.e. default CD range) or some other strategy (e.g. fixed battery % to use in high-load events). After the battery is depleted it then switchs to CS.
    This strategy is fairly good when the battery is fairly small -- as it will likely use all grid energy before they return and got some of the advantages of blending.

    I've not seen a formal analysis of the Prius PHV's default CD range or a formal statement of its actual strategy. But it cannot be the above because the PHV's blended strategy MUST use the ICE for high-demand settings so the car cannot use the optimal fixed distance strategy (and the owner cannot optimize it away). Toyota actually understood that which is part of why there is an EV button.. so users can choose to provide at least 1 bit of input on what they expect to want to do.

    I know (and cited paper that prove) there there are situations where a EV first + blended strategy could be better, but they are infrequent if one has a sufficient battery. They also require full knowledge of the road load for the full trip, making them, at least currently, difficult to automate.

    The blended strategy is not inherently more a CVFS than an parallel-mode EREV -- both blended and EREV can vary the battery/ICE contributions to driving power. In fact, the blended is more limited CVFS because it MUST use the ice for high-demand situations while an parallel-model EREV can vary from 100% load on EV at any speed/demand to 99% load on ICE, to -85%EV (i.e. ICE doing all work while recharging (note not really sure if recharge is 85% is max or if its 65%.). In a Volt the power split can be anywhere in between.

    I will also note that both the Volt and Prius PHV are still limiting drivers ability to truly optimize fuel usage. Since the best strategy depends on knowledge the car canot have, the Ideal PHEV would have mode selections for the user that would include at minimum 4 modes: Pure EV( pure CD any speed/load), Blended-X (blend to deplete battery after X miles), Hold Mode (save EV for later usage) and CS (charge sustaining, i.e. hybrid mode at current state of charge). While the Blended-X would not have knowledge of road-loads,it could make a decent running average approximation to ensure battery is optimally used and depletes just before arriving at destination.

    I've found no good papers on the PHVs actual strategy/Modes. From what I've ready here, the Prius PHV has only 2 modes. An EV-first blended strategy with EV preference at slow speeds and blending for power/high-speed) followed by CS mode, as well as user selected basic Hold mode (HV). Once can argue the PHV no "EV only" as it cannot operate at highway speeds in EV). One can also ague the PHV is not trying to optimize fuel usage with its blended strategy, its blending out of necessity of the system limitations, but since the battery is so small, its a good initial approximation to load-based blended strategy. (Answering this made me curious, I'm going to start a new thread to get more data on that).


    The Plug-in supply kit discussed in this thread adds "EV-first blended" to a regular Prius at a small fraction of the cost of a new car -- and it adds a more meaningful approximation of EV-only mode (with higher speed and longer range).

    The Volt has a full EV only, followed by CS. It has no real blended strategy. Hold mode is being added for 2013, giving it 2 modes.

    Both the PHV and the Volt (and the Plug-in-supply) could be improved by providing Blended-X, and PHV sould (maybe 2015) provide full capability EV, and the if they don't add Blended-X, the Volt should provide a blended mode (with some default X).
     
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  4. dbcassidy

    dbcassidy Toyota Hybrid Nation, 8 Million Strong

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    You are right. Blending is a much, much better approach. Toyota has over 4 MILLION HSD systems working through out the world. I do have to give credit to the design/engineering team at GM. They were forced to use existing ICE inventory to be coupled with the Volt. This could very well attributed to costs and time constraints to get the Volt finished, tested and ready for production. Had the design team had more time and money in the budget, a better ICE would in in the Volt today, NOT "use whats' on the shelf". The bean counters have the board members' ear and support in this decision. It comes down to PROFITS, and rightfully so. GM NEEDS profits to remain healthy.

    I look forward to the next gen ICE that goes into the Volt. What is needed. is a blend mode - give the driver something that is INNOVATIVE: "FREEDOM OF CHOICE" - a novel approach indeed.

    GM could also lower the costs of the battery = lower Volt purchase price but looking to have the buy lease the battery for, lets' say 10 years at a reasonable monthly price ($100 - $150 range / month). After 10 years, the buyer can still lease or have the option to buy with the monthly lease payments made go to the battery purchase price.

    In regaeds to the EREV. Plug In Supply has a very weak warranty - only 3 years. Toyota PIP has a 10 YEAR /150,000 mile warranty. Toyota WILL be around should one need battery replacement years down the road. The same can NOT be said of Plug In Supply.

    DBCassidy
     
  5. drinnovation

    drinnovation EREV for EVER!

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    What is the basis for asserting blending is better?

    And what does the 4Million hybrids have to do with blended strategy? They are using a charge sustaining hybrid strategy. The Volt and the Plug-in Supply extension also use the same type of strategy in charge sustaining mode. Blended is a strategy for using the stored power from the grid.


    Leasing the battery but owning the car seems to makes little sense to me -- they will have you over a barrel at the end of th lease and there is unlikely to be a market for alternative suppliers or buyers. If you are uncertain, you can just lease the car.

    Agreed.. already been mentioned the the real advantage of the PiP is its toyota through and trough (both quality and warranty). But then again, a 2008 PiP may already be out of warranty and already paid for.
     
  6. Trollbait

    Trollbait It's a D&D thing

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    It did to me at first until EVs started coming to the market.
    EVs have a substantial price difference over an ICE car. Renault is offering battery leasing for their EVs, and it allows them to sell the car for about the same as an ICE model. The battery lease rates still work out ahead of the ICE in terms of fuel cost. So a person who couldn't otherwise afford an EV now can.

    As to why not just lease the entire car? First, GM offered a deal on the lease rate of the Volt. Normally, a person that could only afford to buy a $20k car likely won't be able to lease a $40k one. Then there are the increased lease fees for higher annual miles. With a battery lease, it is only factored over the cost of the battery and not the entire car. With a car lease, there is a risk of being nickeled and dimed over the condition of the car at the end of the lease. Most people don't have to stress over the paint condition of a car they own.

    That is a concern. In the case of a company making battery leasing their business model, it goes against their long term interest to hose customers when the lease or battery change over occurs. They likely aren't the only EV game in town, and by the time the leases are up, battery costs will be down.
     
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