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Hi All

It’s getting colder as winter approaches and you may or may not have experienced a different feel in regen in colder weather, but you will. As most of you know, I use “L” to slow before I use the brake pedal for a clean regen charge without the brake pads and also to go EV. Many times as the outside temp got below 60 degrees F, I notice no regen effect even here in So. FL, and I had to use the double tap in “N” to go EV. At first, I thought the Traction Battery Control Module prevented charging a cold battery.
Well, I just came upon a Ford patent that explains the reason why this happens.

“The present invention provides a method to reduce the amount of regenerative braking force applied to the wheels of a vehicle when temperatures get cold enough for snow and ice to form. Preferably, an ambient temperature sensor coupled to the vehicle monitors the temperature around the vehicle. Based on the ambient temperature, a determination is made as to the amount of regenerative braking that will be applied to the wheels of the vehicle if compression regenerative braking is needed. If a lift-throttle event is detected, the selected amount of regenerative braking is applied. The amount of regenerative braking is preferably determined by selecting an amount of electrical current that is supplied from an electric motor that controls the braking force on the wheels. For temperatures above a first threshold, the applied regenerative braking force is higher than for temperatures below the first threshold. Hence at lower temperatures, less regenerative braking force is applied, which reduces the likelihood of vehicle slippage due to a road surface with a low coefficient of friction.

The selected regenerative braking force preferably varies as a function of the vehicle's speed. This function is referred to as a map. To determine the amount of regenerative braking to be applied to the wheels of the vehicle, a map is selected based on the ambient temperature. For example, if the temperature is greater than or equal to a first threshold, a standard compression brake regen (CBR) map is selected; or, if a temperature is less than a second threshold, then a cold weather CBR map is selected. If the temperature is less than a first threshold but greater than a second threshold, then there is a linear interpolation between the standard and cold-weather CBR maps. The selected CBR map preferably determines a current that is controlled (as a function of vehicle speed) by the electric motor that is driven by the wheels.

If there is an anti-lock braking system (ABS) event, that is, a slip or lock is detected, then there is a slew out of the compression regenerative braking force to zero. In other words, the compression regenerative braking force is rapidly reduced to zero to permit the anti-lock braking system to control further braking. Reapplication of the throttle ends the application of compression regenerative braking.

A vehicle in accordance with the invention includes a temperature sensor to determine the ambient temperature, an accelerator position sensor that detects the beginning and end of lift-throttle events, and a processor that implements a stored program to perform the method described above.”

Since I have a very little chance of snow and ice here in So FL., I'll be working on a way to get that regen when I need it. So far, after my FEH is warmed up, this problem goes away for me.

Here is the patent http://www.freepatentsonline.com/6588860.html?highlight=5343970 Enjoy!

GaryG

"compression brake regen" ?? What the F are they talking about?
.
_H*

Hi Hobbit

When you let off the accelerator in "D" or "L", you get various degrees of regen, so temp sensors when it get cold can reduce regen to nothing. When you use the brake pedal, it's considered compression regen braking, because you are slowing with both, or if the temp is cold, just the pads. If you have a lock-up of that wheel, both regen and brake pad are released and controlled by the anti-lock system.

The term engine braking means you have compression of the cyclinders with no fuel and friction from the bearing and moving part. There is a one way clutch that can be used to provide engine braking, however, I'm not sure it is involve in this patent. If it was, senors controling the one way clutch would have been discussed I think.

GaryG

from the base note> ... Many times as the outside temp got below 60 degrees F, I notice no regen effect even here in So. FL ...

Hi GaryG,

You're not suggesting that 'below 60 degrees F' is anywhere near the temperature threshold referenced in the patent, are you? i.e. there would be zero likelihood of ice or snow... Wouldn't the decreased regen more likely have to do with lowerered charge current limit when the battery is cold? You may be able to verify that with the CCL XGauge (probably called MxC in the SG II FEH settings) next time you come across those conditions.

cheers,
Bill

from the base note> ... Many times as the outside temp got below 60 degrees F, I notice no regen effect even here in So. FL ...

Hi GaryG,

You're not suggesting that 'below 60 degrees F' is anywhere near the temperature threshold referenced in the patent, are you? i.e. there would be zero likelihood of ice or snow... Wouldn't the decreased regen more likely have to do with lowerered charge current limit when the battery is cold? You may be able to verify that with the CCL XGauge (probably called MxC in the SG II FEH settings) next time you come across those conditions.

cheers,
Bill

No, the battery current issue is also at play till the TBCM has battery temperature under control. I just used the 60F temperature as a starting point where 100% regen can be reduced. We know the ideal temperature of the HV battery is 82F with a desired range of 77F-100F. This would make a 60F temperature outside that range and can effect charging limits. On the other side of the scale, even in cold temperatures of 40F, my A/C compressor is activated to cool the HV battery and regen is canceled to limit the charging limits because of battery heat.

The techniques I use require me to use regen to its full advantage while controlling HV battery temperature for the fastest charge rates possible. The reduction in regen above 60F is limited by the TBCM and PCM and not by the cold weather strategy in the patent I quoted. Like Wayne Gerdes and other hypermilers, we push our vehicles with the knowledge of our vehicles we drive to the max. Many of the Xgauges that Ron and Carl have worked to develop exceed my pay grade, but I know the gauges to set on my SGII that will help my vehicles FE. I choose to monitor gauges till I understand what effect I can use them to my advantage for mileage. So far, I just added SoC to my SGII to monitor. I have to many existing gauges to compare with the detailed SoC gauge Carl has provided. Engine Load and instant MPG compared to SoC is what I'm looking at now.

GaryG

Hi GaryG,

Thanks! Good answer. :-) You also made me realize that there's not that much need for a hv battery warmer except maybe when parking in extreme subzero conditions. The self-heating capabilities of that battery are astonishing.

re: too many possible xgauges to monitor - yup, I hear you on that!

cheers,
Bill

Many times as the outside temp got below 60 degrees F, I notice no regen effect

I notice this happens RIGHT AT 60F here. Does anyone know, is the the MAF/IAT sensor (located right above the air filter) where this temp is measured? I wonder what effect "adjusting" the temp (in this case the resistance) up some would make in other areas of the vehicle operation (especially when it is in the 45 - 60F range outside air temp, fairly common for am temps here in Austin in the Spring and Fall)

The MxC xgauge will let you know when regen is disabled. When MxC goes to zero, there is no regen. It happens frequently in my FEH, many times for no apparent reason that I can discern. When I start out on my commute, I monitor SoC, CHT, MxC and cFE (current fuel economy.) After awhile, I drop CHT in favor of Tav (HV battery temp.) Most of the other 300 or so xgauges for the FEH are really only useful if something is wrong that you're trying to diagnose.

Interesting. I kind of noticed this, because when I bought my FEH, our average daily temperatures were 60-65F. I went away on a business trip for a week, and when I came back, average temperatures were closer to 55-60F, and my EV didn't seem to be engaging at the same point in my commute anymore.

This winter's going to be a big drop-off, I suppose.

Hi Gary:

___Interesting and my question why would Ford drop it out completely (sometimes) at 60 degrees and below. 60 degree external ambient is probably perfect for 75 to 80 internal to the pack? Is this occurring at an intermediate to high range SoC as I have to assume it may be SoC dependant as well? Or maybe not?

___Good Luck

___Wayne

Hi Gary:

___Interesting and my question why would Ford drop it out completely (sometimes) at 60 degrees and below. 60 degree external ambient is probably perfect for 75 to 80 internal to the pack? Is this occurring at an intermediate to high range SoC as I have to assume it may be SoC dependant as well? Or maybe not?

___Good Luck

___Wayne

Hey Wayne

I think the colder temperature is effecting not only regen, but mainly the battery temperature charging limits in colder weather. I leave my battery with a low SoC and as you explained to me a few years ago, the battery takes a much faster charge at lower SoC levels. I've found that the generator will provide most of the charging with a low SoC and until the battery gets to the ideal temperature of 77-82 degrees, regen from the traction motor (MG2) is adjusted to lower levels. In other words, the battery can't take heavy generator charging and heavy regen at the same time.

So yes, it is also occurring at an intermediate to high SoC also until the internal battery temperature rises and can handle a rapid charge. I really don't have many cold days combined with a high SoC experiences with the '05 FEH, but I don't recall any big changes with SoC level. It is pretty much habit that if the '05 FEH loses regen, I shift to neutral and tap the brake pedal to go EV if the battery is too cold or too hot.

The patent I quoted in this thread only addressed regen in weather below 60F. The battery temperature is also a factor in regen outside the traction and ABS concerns in this patent. Combining the two issues I think help people here understand the system for better MPG.

All the rules for the '09 FEH/MMH have changed and do not apply the same as earlier models. I can tell the heat effects of the '09 FEH are much different than the '05 FEH for the better. I'm thinking the '09 will also handle cold weather much better also. The '09 has cut warm-up for EV by at least 25% in hot weather, so I'll assume it will be much better in the winter also.

Hi Gary:

___Thanks for the additional information!

___Good Luck

___Wayne