Thats odd in the sense that I've always felt safer in a front wheel drive on ice where the weight is over the wheels providing more traction. I've certainly passed enough pickup trucks spinning their back wheels and going nowhere in my ZX2 in the winter.

It may be true that RWD is better on ice but it goes against everything I've known.

 

Yes, I know, general public knowledge seems to be that FWD is safer on the slippery stuff, and that's true right up to the point where you enter the "twilight zone".

With RWD, once, if, you lose traction due to "drive" torque you still have the full traction of the front wheels/tires to maintain directional control with. With FWD once "drive" traction is lost there is NO recovery. The AAA is currently recommending that owners of FWD and/or front biased AWD vehicles without a clutch practice shifting quickly into neutral in preparation for when the day comes that the experience is needed in order to regain traction on the front with incurring the detrimental effects of engine compression braking.

Back in my days in MT during the winter I often found myself applying the e-brake ever so slightly to keep the vehicle aligned with the roadbed on a slippery downhill section of the highway.

You may have noticed that fewer and fewer FWD and front biased AWD vehicles now have manual transmissions. IMMHO that is because it is so horribly dangerous to downshift one of these on a slippery roadbed. Not only that but many modern day FWD vehicles with automatics have the controlling firmware written, designed, to quickly upshift the transaxle when you lift the throttle so as to alleviate instances of loss of directional control due to engine compression braking.

 

[QUOTE=
B: Due to my long experience driving/surviving in wintertime conditions I have an inate fear of FWD and front biased AWD vehicles when the roadbed is slippery. There is a really good, sound, reason truckers are required to have a set of "drag" chains on the rearmost wheels of their trailers traveling over our snow and ice covered passes in the wintertime. Greater traction on the front on dry pavement is fine, but that asset quickly turns into a horrible detriment when road conditions become adverse, packed snow or ice.

So the second issue I was addressing was whether or not the rear driveline torque apportioning "method" could be permanently engaged with both front halfshafts removed. Personally I would consider that, RWD only, a much safer configuration in wintertime conditions than the FEH/MMH AWD model even if it already had VSC (PSM, ESC, etc.)and traction control.[/QUOTE]


Hi Willard

After I responded, I now know your complete question.

Sounds like you know what you want in a vehicle, but the modifications your talking about to one of the most advance hybrid vehicles is above my paygrade. I'm afraid the redundant computer systems and software programs in the FEH and MMH would not allow the vehicle to even be started after that kind of mod. The ECVT, PCM, regen braking system and even the battery control module is not design for RWD.

Let me say that engine braking is not you enemy with this eCVT because of the one-way clutch (OWC) design. The OWC is not the axle disconnect BTW. Ford did make provissions for handling regen (the problem you would have) in snow and ice though. Yes, I have another patent for you and other's to look at:

http://www.cleanmpg.com/forums/showthread.php?t=2225

I started that thread at http://www.cleanmpg.com/ the other day while I was doing some research on the FEH & MMH. There is more recent patent info I've posted on that site.

GaryG

 

Ah.... I see. Thanks for the info.... hadn't thought of that particular ramification (which is why I asked).

There can be times when FWD will get you out of situations on ice/snow as well. For example when turning a corner at slow speed sometimes if I've felt the front slip a bit I've given it a little gas to "pull" the front end around. In a way I was kind of working around the issue without knowing precisely what I was doing... Of course that may work when you are turning at 10MPH.... if you are on the freeway instead you'd be hosed when the front end let loose. Really speaks to being safe and driving the conditions. Of course if you are decending a mountain or hit black ice suddenly all the "driving the conditions" goes completely out the window as well.

Gary... from your patent post. How sure are you that the FEH uses the technique of reducing the regen in freezing conditions? I'd like to know so if I ever get into this kind of emergency situation here in Michigan I'll know whether popping into neutral or not is the better plan.

Also..... how does this all apply when one has ABS on any FWD car? Wouldn't the computer sense the front (steering) wheels start to slip and make sure the front end didn't lock up?

 

Wow...Double that, WOW..!

I have NEVER seen a more direct admission of the hazards of engine braking on a FWD or front biased AWD in my life. Good-o.

You should note that the FEH/MMH regenerative braking is significantly reduced ONLY at, near, or below freezing.

Regenerative braking is instantly reduced to zero if ABS needs to release the brakes to prevent lockup. But what about the ICE itself, does it raise the ICE RPM simultaneously to prevent actual engine braking?

Now I am very sure, certain, sure, I never want to drive a FWD or front torque biased AWD in wintertime conditions.

 

I don't see how any current model ECU or ECUs could possibly "know" the front driveline is uncoupled and the rear is always fully coupled. Once VSC/Trac is added, yes, the Trac firmware will expect the front wheels to lose traction first due to engine drive torque and that clearly would NEVER happen. But if the firmware is well designed/written Trac will still react quickly by braking the slipping rear wheels and dethrottling the motive force.

It does look like I would need to find a way to disable the ECU's cold climate regenerative braking "map" since only the rear driveline would be in use and that doesn't represent the level of hazard as does the front. In point of fact it would probably be more of an asset at the rear than otherwise.

I'm not sure VSC would be affected in any manner.

 

I should clarify that, it sounds a little misleading as written. It happened in my ZX2, not my 4WD Escape. And also the slipping in those cases was caused by my applying the BRAKES. As of yet, I don't think I've ever felt engine braking cause my front end to come loose. Sometimes releasing the brake didn't feel like enough to recover (and I'm not sure it would have been different in a RWD), so I gave it a little gas. Not saying it can't happen. Just hasn't happened to me personally.

Most of the times I've actually "felt" more secure in the FWD ZX2 because my technique of coming to a corner was to let up on the gas early enough for the vehcile to slow down to a point where I have to apply power to turn the corner so if I slip I'm fine because the vehicle will likely stop on its own or I can pull myself out of it. With a RWD that trick hitting the gas is unavailable and hitting the gas a bit just causes the rear to fishtail making matters worse.

Frankly in any case in the winter I've slipped on ice, I've felt better off with the FWD, but I've never slipped while trying to slow down on a mountain or at high speeds yet, so you still may have a point.

 

I guess I'm not completely convinced its "less safe" to drive a FWD in snow/ice. I believe I've heard the Car Talk guess suggest is safer in most cases. Its a matter of how often. So far I've driven both FWD and RWD in ice and snow. I've always felt more secure in the FWD. In almost 20years of FWD I've yet to encounter engine braking causing me to loose steering on ice (not saying it can't happen--just that it hasn't to me yet). I have encountered loosing steering at low speed and cornering but that has more to do with braking and the fact that one has the wheels turned to the line of travel and the vehicle tends to "snowplow", its inertia thats the enemy there, not engine braking. That occurs whether you are in FWD or RWD. I've encountered that several times and if you are in a FWD you have the option of applying a little gas to pull you out of the slide, in a RWD you are just along for the ride.

If you have ABS the situation seems even less of an issue. When you start to slide your first inclination is to slam on the brakes hard and the ABS should take care of the issue then, engine braking doesn't apply.

It seems more like AAA is trying to make you aware of a situation where you should react differently in a FWD rather than a RWD... not that the situation is frequent or makes the vehicle less safe.

I don't hesitate to say that so far I've been in fewer accidents in my FWD because I haven't slid through any intersections... I've always been able to "pull" myself around the corner rather than finding the ditch.

I've never lost it at high speed on black ice nor decended a mountain on an icy road... so I can't speak to those situations.

As for the 4WD Escape... we'll see, I have yet to drive it on ice/snow.

 

1. How would you know if the "plowing", understearing, events you have experienced were not caused by engine compression braking? Or at least exacerbated by same?

2. "...ABS..." "engine braking doesn't apply..."
One of the main objects of the patent is to remove regenerative braking (or compression braking{??}) when ABS activates so the "brakes" can be fully released by the anti-lock system.

3. I think it is well proven and generally accepted that a problem, a REAL problem, need not be frequent, or even close, to result in a vehicle being labelled UNSAFE by the powers that be.

4: AAA. Think of it this way, what would be your first action in these situations if you had a clutch?

Many years ago back in MT during the winter months I would often apply the e-brake (RWD/automatic) slightly to help keep the vehicle oriented with my desired line of travel when traveling downhill on a slippery roadbed.

The VSC, today, on my 2001 AWD RX300 will automatically apply both rear brakes if understearing, "plowing" is sensed/detected.

 

Ok guys, here is what I have concluded, so correct me if I'm wrong.

With regard to engine braking, the only time the engine is used, is to burn off excess energy with the small generator/motor. It is my understanding that the FEH OWC allows torque with the engine and small generator/motor one way with the traction motor to the wheels. The wheels and the traction motor cannot provide torque back to the engine because of the OWC design. Therefore there is no connection for any of the wheels to recieve engine braking at any time.

I have read that in a single elec motor design, the OWC can be used for engine braking. That clutch design allows for a smooth electronic slip to engage the engine. I've seen no provision for that in the FEH or MMH and think it would decrease it's FE if it had it.

This is why I've always said to shift to neutral when the small generator/motor starts turnning up the ICE to burn energy. There is a small amount of regen coming from the wheels in warm weather, but not enough to make a difference in braking on a downhill condition. Given my choices of ICE run-up, I shift to neutral and use only the brake pads if I need to slowdown. This allows me to stay in EV under 40mph when the run-up is finished, and continue to burn the battery down in EV. Under 40mph with no regen in neutral, the ICE will shutdown by tapping the brake pedal. This is possible because of the axle disconnect.

GaryG