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  1. #1
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    Cabin A/C method and operation

    I've been lurking here for a few months. I have a bunch of tecnical questions I haven't been able to find the answers to. The first one is about the cabin air conditioning.

    At the auto show, I looked through the FEH/MMH the best I could. I would have liked to have taken the engine cover off to see more, but not really possible at a show. I saw the A/C hard lines at the firewall going to/from the evaporator, but I couldn't see down far enough to see the A/C compressor, much less to see whether the A/C compressor was belt driven off of the engine, or whether it was all electrical. I'm assuming it's belt driven off the engine with a clutch like auto A/C has always been.

    If this is true, and we had the A/C on here in hot Texas, will the engine run continuously as long as the A/C is "ON"? Or does the engine start up and shut down as needed just to cycle the compressor on and off if you were stopped, or going slow enough so that otherwise it would be in electrical motor mode?

    About sometime in March we first start using auto A/C here, and depending on the time of day one is out, the auto A/C season can last into November. Good A/C is real important!

    _D

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  3. #2
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    There are two settings for

    There are two settings for the air conditioner in the 2005-07 version. In the economy setting, the internal combustion engine will shut off but the "air conditioned flow can become warm" when this occurs. In the max setting the air condition will cause the internal combustion engine to remain on. The air conditioner system is not electrical driven.

  4. #3
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    There is a econ A/C setting

    There is a econ A/C setting on the '08 and '09 FEH/MMH also that will let the engine shutdown for EV use. The belt driven A/C compressor will stop with the engine off. In this mode, the cabin air will get warm fairly fast unless you do a heater core bypass so hot engine coolant does not circulate in the heater core and the A/C air ductwork. I did this on my '05 FEH and run the A/C in the econ position during the hot summers here in So. FL.

    Your three choices are to use max A/C and run the engine with no EV mode to stay as cold as you want. Run in the econ mode till it gets to warm during EV, and then turn on Max A/C to cool off. Or do a simple heater core bypass to extend the time of keeping the cabin cool.

    Example, today it was over 90 degrees and the Aux battery A/C and compressor would run any time the engine came on to charge the battery in city traffic. When this happens, I run the cabin A/C with the windows up. The battery performs better in the cabin econ A/C mode when temperatures are above 80 degrees (80 OAT - outside air temperature). With the heater core bypassed, the cabin stays cooler longer while in EV. I keep the fan on the #1 speed setting after the cabin has fully cooled down. I drive in EV till I need to get more cooler air and just hit the accelerator to kick the engine back on. I keep the engine ON till the cabin is nice and cold again with a low RPM Pulse in "D" & glide in neutral to maintain speed in traffic. Gliding in neutral with the engine running allows the compressor to run for cooling as well as charging the HV battery. If you stay in "D" while gliding, the engine will be under a higher load trying to push against regen of the traction motor. You will lose speed much quicker and burn much more gas. In other words, run the engine in neutral as much as possible while only the engine load is for the compressor and the generator to recharge the battery. With the SOC high and the cabin cold, I go EV until I need the A/C compressor on again.

    Today I averaged over 42mpg staying cool using this method, and I had three out of vehicle stops and many stopsights. When I need to drive 1-95, I just draft 1.5 seconds behind a big truck with the A/C on and get between 39-45mpg depending on wind direction and vehicle speeds 60 - 70mph. Using neutral at highway speeds is a winner also.


  5. #4
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    Thanks guys. My wife would

    Thanks guys.

    My wife would be the daily driver if we eventually get one. Although I could probably do any routine, I really don't see her having it in anything but "Max" to keep A/C fully functional for most of the year when A/C is needed. She drives into the sun to go to work, and into the sun to get home. This looks like part of the hybrid's efficiency would be negated by our typical use.

    Gary, that's interesting all the tricks you've figured out to boost MPG. I think the wife will be going from Park to Drive, and back to Park She's an intelligent, capable person, but I don't think she's going to want to do all that.

    I did read and see your heater core summer bypass. I needed to cut the heater flow in a car that it wasn't worth me replacing the A/C in, I put a vacuum-operated heater shutoff valve inline in the supply hose. I tee'd into a proper vacuum spot in the climate control system to do it. I spent some time flipping through a book at a parts store to find a valve that had the right size in/outlet, full shutoff, and correct vacuum sense for the application. It turned out to be a valve used in old Caddys.

    Since we're on the topic of cabin, is the battery pack compartment back there ventilated or cooled if so, how?

  6. #5
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    Hi Tex My wife only knows D,

    Hi Tex

    My wife only knows D, R, and P also and she uses Max A/C even during the winter. I mainly posted that information for those serious about saving fuel this summer. You bring up a good point about how a heater core bypass will also cool down the fan vent air.

    The rear HV battery has a vent to the outside near the drivers side rear window. There is a door that opens and closes to control air circulation within the battery unit. There are A/C lines from the main compressor that supplies coolant to the Aux battery A/C system. The battery control module determines if outside venting is enough or to request the PCM to run the compressor and cool the battery with the battery Aux A/C system. The system shuts off while in EV as you can hear the fans stop within the sealed battery. With the cabin A/C off, you can also hear the compressor clutch kicking on and off to cool the battery. This is why I know you might as well run the cabin A/C also when it's hot outside.

    The new '09 FEH/MMH may have the new variable voltage converter (VVC) which will greatly reduce the heat while charging the HV battery. Ford has said the new hybrid Fusion and Milan will have the new VVC and will eliminate the Aux battery A/C system. As soon as my '09 FEH arrives, I'll be able to tell us for sure if it has the new VVC and if the Aux battery A/C has been removed. If this is true, the '09 should get much better MPG if you drive in EV like I do.

  7. #6
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    Hi Gary Any idea how the A/C

    Hi Gary

    Any idea how the A/C Aux battery cooling is constructed? Is there a small A/C evaporator built into the well that the battery module sits in, and cooled air then ducted in through the module? I am assuming that refrigerant is not piped directly in/out of the battery module itself. If it was, that would sound like a maintenance mess.
    It really would be nice if the battery charging method was more controlled to avoid the need of Aux A/C cooling. I guess you will find out soon!
    I'm equipped to handle all of my family's auto A/C needs, but the simpler, the better! We have a minivan with a dual A/C system, it uses TXV instead of orifice as the expansion device. It works well and has been good, but it doesn't have the raw cooling power that full-sized Ford products have had for years.

    I read the link on the Prius Boost Converter. I understand the underlying concepts fine, but if I was the manager of the engineer who gave the paper, I would have had him re-write it before presentation! Besides lowering resistive losses in wiring and windings due to higher voltage = lower current, the high voltage output of the converter also allows faster di/dt in inductive devices, which speeds them up and increases torque. I used similar techniques about 25 years ago when I was designing for a consulting company, driving low voltage electromechanical parts with a higher voltage source by pulse-width modulating them.

  8. #7
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    Only the fans are located

    Only the fans are located within the battery housing. The Aux evaporator and all lines are located in a Aux Climate Control Housing. The housing is bolted on the left rear corner of the battery's in and out ducts. There is a aux temperature blend door you can see when you remove the battery filter. The filter should be changed at lease every 20,000 miles and checked often if you drive on dirt roads.

    I'm pretty sure the '09 FEH/MMH comes with the new VVC and in addition, a new modified high voltage DC to low voltage DC converter located under the hood. I read a '07 Ford patent where it appeared the FEH/MMH may have problems transferring high voltage DC to the low voltage system and 12V battery during start-ups. I had problems with three relays that cost me ~$1,200 to figure out and replace. The modified system is supposed to eliminate a short that now happens during key-on power switching from the HV battery through the old DC to DC converter to the low voltage system at start-up.

    I stumbled on this patent when doing research on the VVC and I remembered this from an article:

    "High-Efficiency DC-DC Converter. The conventional DC-DC converter, which steps down system voltage to run the vehicle’s 12V accessory bus and charge the auxiliary 12V battery, has been redesigned to operate at higher temperatures. The unit remains liquid cooled, and can switch at higher frequencies."
    http://www.greencarcongress.com/2008...reviews-n.html

    This article has been the best information yet that seems to match-up with what's being reported from test drives. Ford has since released that the '09 FEH/MMH has much more engine stops and restarts switching from EV. I really didn't understand the need to redesign the DC/DC converter until I read the patent about improving a shorting problem. I have a good idea now why my relays went bad. Here is the patent:
    http://www.freepatentsonline.com/7199551.html

    It would be nice if the HV battery does not need the Aux A/C now, but if it operates much cooler and uses it less, that would be nice also.

  9. #8
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    Gary, thanks for all the

    Gary, thanks for all the info! Sounds like the battery cooling is the way I would have done it : ) The air filter too, as anywhere air is used for cooling, comes dust and debris with it.

    I read through the patent and its associated diagram.

    So the modes traversed in start up seem to be:

    1) Pre-charge. The key has been turned to RUN. The contactors that can connect the HV battery to the HV bus are open, but the bus is charged from the HV battery via separate means. There is no path from the HV bus to the step-down DC to DC converter to the LV battery.
    I expect this would be a very quick transitory state.

    2) Pre-start. The HV bus has already been charged to HV battery potential, and now the contactors close to connect the HV battery to the HV bus. Current can be pulled from the HV bus to power the step-down DC to DC converter to charge the LV battery, only if the LV battery needs charging, and only if there is a sufficient state of charge in the HV battery, such that a ICE start could later successfully occur.

    3) I guess the next step would be Start, start the ICE, or enable the HV inverter to power one or more motors to go.

    About step #1, the Pre-charge... there must be quite a bit of decoupling capacitance sitting on the HV bus, or else the pre-charge state would not be needed.

    An example application of the pre-charge concept:
    A pre-charge state is used in electronic systems where a circuit module is plugged into a live up and running bus-oriented system. Without a pre-charge state, the module that is being plugged in would appear as an instantaneous short on the power bus voltages. This would blink the power to the other modules that were running. The instantaneous short occurs due to the low impedance of decoupling capacitors on the module, that were at zero volts (discharged) before module insertion. Also input and output capacitors of any DC to DC converter on the module, same issue. Often, "soft start" schemes are used to help alleviate the DC to DC converter inrush current problem.
    A common pre-charge scheme was to have the module's power pin cut back shorter, and the ground and pre-charge pins full length. Both the power pin and the pre-charge pin were fed on the backplane side with the power supply voltage. A resistor on the module connected from the pre-charge pin to the power pin circuitry within the module.
    So upon insertion, the module's ground pin and pre-charge pin connected first. The module's power pin was not connected yet. Current from the power bus, through the pre-charge pin, through the pre-charge resistor (limits in-rush current), charges the module's capacitance via the exponential RC time curve. As the module is continuing to slide in, the actual power pin then contacts and the pre-charge is out of the picture.
    The success of this method required testing as to how fast a module could be inserted, versus the maximum current that could be pulled from the bus worst-case without causing dropouts.

    Anyway, in the FEH, the pre-charge state could be performed with a relay switching in a resistor across the contactors. Or, it could be performed all electronic, via a solid state current source that does the same, where the current source is set to some acceptable value.

    So maybe in your model, there was no pre-charge state, which would cause more arcing on contactor closing. It's funny to be calling an electromechanical device that switches DC a "Contactor". That name was always used for devices switching high current AC. We always called a DC heavy-duty relay... a heavy-duty power relay!

  10. #9
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    Wow Tex You have a much

    Wow Tex

    You have a much better understanding of this stuff than I do. The three relays that went bad happen one after another and caused my FEH to be towed to the dealership each time. The relays are located in the battery junction box where there are a total of 5 that are the same and interchangeable.

    The first that went bad was the injector relay in space 003. It took a week for the tech and Ford Hot Line Engineers to fine the problem because so many codes were found. They opened up the relay and found the coil had a burn spot. Ford claimed they had never seen a relay go bad and thought I had rigged a plug-in for my HV battery. A few days later after driving fine, the power sustain relay went bad and FEH had to be towed back to the dealership. For some reason the FEH started-up when it arrived at the dealership. After the third time of being towed back to the dealership for not starting, Ford replaced the power sustain relay and the PCM power relay. The tech gave me a spare relay to keep in the FEH and showed me how simple they were to replace in case one went bad again. I suspect one technique of turning the key off and back on real fast accelerated the failure of those relays about ten months ago. Still have the spare relay and the FEH has been running fine since.

    Turning the key off in neutral kills the engine for coasting. Returning the key to the ON position right away keeps the power steering, brakes and gauges working like in EV. The engine can be restarted in neutral at any time above 6mph. Below 6mph, the shifter must be placed in Park to restart the engine. I'm guessing this technique caused the relays to go bad early because of this short the patent is talking about. What do you think?

  11. #10
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    Gary, What I got out of the

    Gary,

    What I got out of the patent is that it is all about a method of making sure that the LV battery does not run down if the vehicle is kept in the pre-start condition.
    I guess this problem it solves is similar to what would happen if a person with a gas-engine car turned the ignition switch to Run, but not to Start, and left it in Run while they have the radio on. Eventually, they would run down the battery. But a regular gas engine car has a pretty high Ampere-hour battery to begin with, as that battery (the only battery) is used to power the starter, so the battery charge will stay up for a long time.

    But in the FEH, I'm concluding that the LV battery is small, as it never cranks a starter motor. Since it gets recharged by the HV battery via a DC to DC converter, allowing the DC to DC converter to operate within certain performance guidelines while in Pre-start solves the problem of possibly running down the small LV battery.

    So in a way, I really don't see anything particularly "novel" in this patent. One of the tests of patentability is that it "should not be obvious to one skilled in the art". To me, the application of this idea (to enable the recharging method that is already there) for a patent would fail the test, unless there is something I'm not seeing.

    The patent describes a Figure 2, flowchart of operation, which did not appear for me, but is covered in the text. It makes me wonder if the only way the patent was granted was because of the flowchart, that maybe they are actually patenting a process in software that controls hardware.

    I think the pre-charge concept mentioned in the patent is not part of the patentable idea, but is there for background to establish the sequence of events upon which the "patentable idea" is invoked.

    About your relay problems, I really couldn't say without understanding all of the applicable circuitry. The actual coil of a relay rarely goes bad. The few relays or solenoids that I have had where the coil actually opened up, were usually due to a break in the fine wire at the point where it comes out of the winding on the bobbin, and is tack-welded or soldered onto the pin. In those cases I suspected thermal cycling fatigue, maybe the wire was wound too tight in the beginning or ending of the winding, and it fatigued.
    Burned contacts on a relay are much more common, due to overcurrent, excessive arcing, wear out, or in non-automotive applications here in TX, fire ants! : )
    I'm not sure I would put much belief or accuracy in what I was told at most dealerships, no matter what the make.
    That said, I guess it "might" be possible to burn contacts if your scheme causes some operation beyond the designers original worst-case design.

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