No Way

 

What would we need to do?

 

The entire automotive industry seems at the moment to be going through an evolution in that they are striving mightily to find ways to alleviate and/or reduce instances of loss of control due to engine braking of a FWD vehicle on a slippery roadbed surface.

Ford, with the patents on their hybrids, seems to be one of the leaders in this.

 

GaryG — I can tell you what I know about the behavior of the Camry Hybrid (TCH). When coasting at speeds above 64 km/h (~40 mph), under certain conditions fuel-cut is applied to the ICE. One can see this from the FE gauge, which drops to precisely 0 L/100 km in the Canadian (metric) version — the US version then reads 60 mpg, which corresponds to the bottom of the scale. The ICE is, however, still spinning at ~1000 rpm (according to my ScanGaugeII), driven by MG1 (which in turn gets its power from MG2 — this also provides some braking), to prevent MG1 from over-revving. This allows the ICE to apply a small amount of engine braking even when coasting at speeds too high for pure-EV operation. If one puts the gear-shift into the 'B' position, the ICE is spun even faster by MG1, to apply a still greater amount of engine braking. Of course, both of these modes waste the car's kinetic energy as heat in the ICE, rather than storing it in the battery, but at least the ICE isn't consuming any fuel even though it is spinning.

Stan

 

GaryG — Let me elaborate a bit on what the TCH does. The FEH will probably be similar.
There are 3 possible regimes when coasting:
(a) Pure-EV mode up to 64 km/h — the ICE is not spinning, and the moderate regenerative braking power from MG2 flows to the NiMH battery. The FE gauge reads in the blue pure-EV mode area.
(b) Above 64 km/h Toyota do spin the ICE in order to keep the rpm of MG1 within what they consider the safe range — don't forget that, because of the planetary gear ratios, MG1 spins much faster when the ICE is stationary. No fuel is being sent to the ICE (this is called "fuel-cut"), and no battery power is being used, but MG1 is being torqued by electrical power (coming from MG2) to force the ICE to spin — it is spun at ~1000 rpm in the 'D' position. Ignoring losses in the mechanical-to-electrical-to-mechanical conversions taking place in MG2 and MG1, all the power to spin the ICE comes from the wheels in the form of mild braking, comparable to the regenerative braking that is applied in case (a). The FE gauge reads precisely 0 L/100 km (60 mpg in the US version). If the ICE's intake and compression strokes were equal, then in principle no net work would be needed to spin the ICE (assuming adiabatic conditions), and this procedure would therefore not give any braking. This seems to be a point that is not generally understood. [Don't forget that the valves continue to operate normally.] In the Miller/Atkinson-cycle ICE used, however, the expansion stroke is considerably longer than the effective compression stroke (for enhanced thermodynamic efficiency), and so it behaves like a refrigerator — work is done, and the exhaust air is cooler than the intake air. [I guess Toyota need to avoid cooling the catalytic converter too much!] If the gear lever is put into the 'B' rather than the 'D' position, the ICE is spun much faster than 1000 rpm by MG1, and the engine braking effect is then greatly increased. Again, no fuel is being used. ScanGaugeII misreads the situation, and shows that fuel is still being consumed at a rate of ~1 L/h in the 'D' position. Ron DeLong of Linear-Logic (the manufacturer) is aware of this problem, and is trying to figure out a way of correctly nulling ScanGauge's fuel-usage readout (and its associated FE computations) when "fuel-cut" is in effect. The attached document ES-275to288.pdf from the TCH Repair Manual tells you on page 281 how to provoke fuel-cut.
(c) At any road speed if the control systems decide that the ICE should produce mechanical power and/or heat, it may be spun at ~1000 rpm, using fuel, even while regenerative braking power from MG2 is simultaneously being sent to the MiMH battery. The FE gauge reads >0 L/100 km (<60 mpg in the US version).

Indeed, if one starts coasting at a speed well above 64 km/h with fuel-cut applied, then as the car's speed drops below 64 km/h, it will either drop into pure-EV mode [case (a)] or else the ICE will imperceptibly be fired up and will continue spinning at ~1000 rpm but now under gasoline power [case (c)]. The FE gauge will then rise above the 0 L/100 km (60 mpg) mark.

More discussion of some of these ideas can be found in the thread "An Unpalatable Fact (with apologies to Al Gore!)" in the TCH Newsgroup.

Stan

 

I'm not familiar with what data the scangauge collects. Does it not provide information on the injectors themselves? If not, what about other "sensors" that would indicate whether fuel was flowing and being combusted. I'm thinking about indirect measures of fuel usage. What can the SG display with regard to the O2/exhaust sensors? What about fuel/air mixture? What about cylinder/sparkplug firing? What about the fuel pump itself? If the injectors are shut off, the fuel pump should be too. My thinking is this.... if you are coasting with the ICE "running" and there is fuel being combusted in the engine....you will have exhaust gases heading out the tailpipe. If the ICE is "running" solely on spin-up from the motors and the fuel is cutoff, there should be no exhaust gases running through the tailpipes. Same thing goes for an air/fuel mixture....clearly it will be a very different ratio if no fuel is being pumped.

I'm just thinking there has got to be some data provided by the OBD system that can be viewed during a "neutral coast", a D deceleration and an L deceleration to indicate whether fuel is flowing and being combusted or not. That data could be compared to the same data collected during an EV only run. I'm far from a mechanic, but most OBD software sure offers alot of info some of which could be used to answer the question even if indirectly.

 

I'm always curious as to how much info the scanguage knows about fuel usage and how much it infers. As an example.... one of the things that makes me curious as to if it over estimates fuel usage on coasting (as I believe is one of the things you are trying to determine in this thread) is that you hypermilers who I assume coast a great deal of the time, also report that the ScanGuage reads 2MPG less than the NAV.

I'm not a hypermiler, so I don't coast nearly as much I'm sure...my Scanguage reads within 0.3MPG of my NAV all the time (after I ran the calibration on the scanguage suggested in the manual)... Is that because with less coasting there is less overestimating of fuel usage during the coast phase if the fuel is actually cut off and the scan guage doesn't know it?

I do appreciate the information you are trying to gather here.

 

Opps... sorry for the mistaken attribution. Thanks for the rest of the clarification too.

So no one thinks I'm dissing the SG. However much the SG infers or doesn't infer.... I find its extremely accurate and a nice piece of equipment.

 

GaryG — I wasn't aware that the FEH had a clutch to disconnect the ICE/MG1 combination from the wheels when in Neutral. Having perused the thread "Why doesn't ICE cut off automatically when coasting?" I now know better. So, you have an option not open to Toyota hybrid-vehicle owners. I can also tell you that when coasting in 'B' with fuel-cut in effect, the ICE rpm increases to ~3000 (according to ScanGauge, and I'm sure it's correct here) and the fuel usage triples to ~3 L/h (according to ScanGauge, and I'm sure it's wrong here), while the car's FE meter still reads precisely 0 L/100 km. There really is a fuel-cut. See the attached Toyota US Patent #5 914 575. In the Abstract, and also e.g. in Column 2, Lines 47-52, and Column 3, Lines 47-60 you'll see that they specifically discuss this strategy (amongst others). I probably also shouldn't have excluded the possibility that there's also some NiMH battery charging being done by MG2 while coasting above 64 km/h in fuel-cut mode. I can't (yet) confirm or deny this. I'll check out the ICE load factor and open- versus closed-loop operation when in fuel-cut mode, and report back.

Another difference with the TCH appears to be the fact that you say that you can recharge the NiMH battery in Neutral. This is impossible in the Toyota hybrids — both ICE charging via MG1 and regenerative charging via MG2 are locked out in Neutral. [The A/C can continue to discharge the NiMH battery while in Neutral. The FEH uses an ICE driven A/C compressor, you say? That's another difference.] By the way, if you're comparing FEs, it is essential to make sure that you recharge the NiMH battery back to its original SOC before you can legitimately compare FE numbers.

Tim K and TeeSter — According to Ron DeLong, the fuel-injector signal continues to be generated during fuel-cut, even though no fuel is actually being injected. This is what misleads ScanGauge. It computes fuel usage from the injector signal, ICE rpm, and other available information — I don't know precisely what else. ScanGauge doesn't provide injector information to the user, but does show fuel usage rate (in L/h or galUS/h). This is nonzero during fuel-cut, and that's the source of the problem with the FE numbers and overall fuel usage computation. There is a fuel-cut signal issued by the TCH on the CAN bus, and it seems to me that he really needs to read it to suppress these false fuel usage numbers. He's thinking about how to do this. An enormous amount of Toyota hybrid-specific data flows between the sensors and the various ECUs on the CAN bus, but I think Toyota keeps the codes necessary to access these data to themselves. You're right in principle, but we can't yet actually do this with ScanGauge.

Stan

 

GaryG — I did some experiments concerning "fuel-cut" operation in my TCH over the weekend, and this is what I found.

(1) When coasting in 'D' between 65 and 80 km/h when fuel-cut occurs:
(a) TCH's FE gauge says that the FE is 0 L/100 km
(b) SG says (correctly) that the ICE immediately goes OPEN LOOP
(c) SG says (correctly) that the ICE stays at ~1000 RPM
(d) SG says (incorrectly) that fuel consumption is still occurring at ~1 L/h
(e) SG says (incorrectly) that the ICE is at ~30-35 LOAD

(2) When coasting in 'B' between 65 and 80 km/h when fuel-cut occurs:
(a) TCH's FE gauge says that the FE is 0 L/100 km
(b) SG says (correctly) that the ICE immediately goes OPEN LOOP
(c) SG says (correctly) that the ICE stays at ~3000-3300 RPM
(d) SG says (incorrectly) that fuel consumption is still occurring at ~3 L/h
(e) SG says (incorrectly) that the ICE is at ~17-30 LOAD

(3) If from either (1) or (2) I put the gearshift into 'N' while coasting in fuel-cut, the ICE fires up again at around the same rpm (to protect MG1), the FE gauge starts reading >0 L/100 km, and within seconds the ICE is reported by SG to be once again operating CLOSED LOOP. I believe all this to be true.

(4) Of course, when coasting in pure-EV mode (the FE gauge reading <0), the ICE has 0 RPM, and according to SG is OPEN LOOP, 0 LOAD, and using 0 L/h. [Actually, it says 0.1 L/h, but that's a metric readout nulling oversight that I've informed Ron about.]

(5) In cases (1) and (2), charging of the NiMH battery does occur according to the car's display.

(6) As I have said, Toyota lock out NiMH battery charging when in 'N.' I think that this is probably for safety reasons (e.g., during servicing). The Owner's Manuals clearly warn users about this.

(7) The Toyota hybrids have no axle disconnect like the FEH, and so the ICE's and MG1's speeds have to be carefully controlled in relation to the car's speed, even when in 'N.'

If what you are saying about the FEH's fuel injectors is true, namely that they continue to operate in what you call "run-up," and the ICE stays CLOSED LOOP, then the Ford is not applying fuel-cut to the FEH at all.

In the TCH, the NiMH battery's cooling fans draw in air from the passenger compartment. This seems like a sensible idea. This air is clean, and will usually be cooled in summer by the air conditioner, and heated in winter by the heater. This will aid the cooling fans in keeping the battery's temperature in the desired range without additional energy usage. The fans are so quiet in normal operation that I have yet to hear them at all, summer or winter! An interesting question you raise is whether the air conditioning would switch on automatically if the battery needed additional cooling. I doubt it. For example, if the car's windows were open, and the outside air temperature were high, this would be a complete waste of energy, and wouldn't succeed in helping the battery much. Indeed, since the TCH's air conditioning is run by a 3-phase ac compressor from the NiMH battery, you would potentially just be heating the battery up rather than cooling it! The advantage of electric air conditioning, of course, is that the ICE can remain "off." Since it is completely independent of the ICE's crankshaft speed, the electrical air conditioning is also more efficient.

Stan