Unravelling Engine Braking - pre-'09 and post-'08
#1
09-11-2014, 08:33 AM
Unravelling Engine Braking - pre-'09 and post-'08
In another topic, we got into discussing something that was a diversion of the matter at hand. Rather than further derail that topic, I have opened this one.
https://www.greenhybrid.com/discuss/...reply&p=253938
But doesn't the '09 do exactly this when you use the brake pedal, at any speed, to reduce speed? Within the ev speed range and in "D", given a number of parameters such as having capacity in the battery, braking is done with regeneration when you apply the brake pedal. It does this by itself. (Yes, as it comes to a stop it switches to mechanical brakes only, but that's not my concern here.)
Above the ev speed range, the engine will be running on all FEH's, pre-'09 or post '08. Whether you retard speed by using the brake pedal or "L", the engine will still be turning over whenever you are above the ev speed range.
The '09 has the option of using "L" to reduce speed. Above the ev speed range this will result in the engine going to a higher rpm. In this mode you recapture less energy because you're wasting it pushing all those engine components around more quickly. But if you are in a situation where you are going to exceed the capacity of the hybrid battery, such as descending a long steep hill with a stop sign at the bottom, and while towing a trailer, you will fill up the battery anyway. The sooner the FEH reaches that point, the sooner it switches to mechanical brakes only, and the more wear on the brakes. If you can delay the point where the hybrid battery is full, you will fill up the hybrid battery anyway, and reduce the wear on the brakes. For the same reason, in the same circumstances, using accessories such as the a/c can also reduce wear on the brakes.
Below the ev speed threshold, shifting into "L" causes the engine to be turning over, when it would be shut off in "D". It keeps running until it reaches the point where it switches over to mechanical brakes only, and then the engine shuts off even though it is in "L". In circumstances where the hybrid battery is going to be filled up anyway, but further braking is required, the inefficiency of having the engine parts flailing around translates into reduced use of the friction brakes. I run into this while descending rough steep logging roads in the mountains. It is very easy to overheat the mechanical brakes if you come down these roads too fast, so the less load on the mechanical brakes the better.
While saying this, I can understand why someone living in Florida might not run into this scenario.
I trust you will correct me if I'm wrong, but on the '09 and later, it sounds like there is more control over whether reducing speed is being done by regeneration and/or mechanical brakes and/or engine braking.
My understanding is that this lower limit on the '09 and later is 3mph, or 5kph. I also understand the system is designed this way because an electric motor can't hold a vehicle at a standstill.
So far as I know, the '09 will slow down to the speed where regeneration is cancelled, using "L". But that means the engine is running until speed drops to the point where it switches from regen to mechanical brakes. And if the engine is turning over, even without using gas, it is wasting energy. But to keep from wasting energy, you can just use the brake pedal.
That would be nice to have on the FEH since it would be less necessary to use the brake pedal (or "L") to keep the speed in check on long steep descents.
But this does not address the matter of trailer towing or large descents. At some point, say descending a very steep long hill, the Energi's battery must be filled up. What happens at that point? Does it apply the mechanical brakes to maintain 35mph, or does speed start to build above 35? Is the Energi even rated to tow a trailer?
https://www.greenhybrid.com/discuss/...reply&p=253938
As Gary reminds us, the '08 is different from the '09. Having the '09, my explanation and understanding of what's going on applies to it. When I use the phrase "shut off", I mean the gas engine is not running. I do not mean that I've actually turned the ignition key off.
There are four situations that need to be described:
Shifting into "L" is different if the '09 is above or below the maximum speed for ev-only operation. That limit is 63kph, or about 40mph.
Below that speed, and for the purpose of the discussion, reducing speed can be done by using the brake pedal or shifting into "L". Using just the brake pedal, and nothing special going on (like a panic stop, and above 3mph), all braking is done with the regeneration system. The engine (given it has no reason to be running such as warming up or a/c full on) will be shut off.
If, below the ev speed limit, you reduce speed by shifting into "L", and given all the caveats mentioned above etc., the engine will start up. Although it won't be using any gas, it takes some energy for all those mechanical parts to be moving around. This absorbs energy and so there will not be as much left over to send to the hybrid battery.
Now, turning to reducing speed above the ev maximum speed. Whatever else is going on, such as a/c on or off, the engine will be running above that speed. When you're coasting, it isn't consuming gas, but again having all those parts moving around requires energy that isn't going to the hybrid battery. If you use the brakes, the engine will keep turning over, at an rpm that's higher the faster you're going. Applying the brakes won't change the rpm. You'll get regeneration from using the brake pedal, but very little from the engine.
If, instead, above the ev speed limit, you shift to "L" to reduce speed, everything is the same except the engine turns over at a higher rpm. This is how the '09 simulates the engine braking of a non-hybrid. The higher the rpm, the more energy is wasted moving engine parts. I think this is why the hypermilers shift into N in this situation. So to maximize the energy available to the hybrid battery, you want to lower engine rpm, which is "D" instead of "L".
Taking these ideas on the road, I regularly drive roads with such long steepish climbs that on the way down, the hybrid battery gets filled up and I have to keep the speed under control using the brakes and/or shifting into "L".
I can compare at what point during the descents the charge gauge shows that regeneration has ended. At those points, the speed starts to build and I have to use the brakes and, if I'm not already in "L", then also shift into "L" to regulate the speed.
If I have been using "L" from the start of the descent, the point where regeneration ends is lower on the hill. This means there has been less energy being put back into the hybrid battery. It also means I have to use the mechanical brakes less, which is a good thing. Actually, I never come down the hill in "D" because the speed gets out of control right away, and using the brake pedal means I lose regeneration fairly quickly because the battery reaches capacity sooner.
I used to use "L" often to reduce speed, because I was still thinking like a non-hybrid driver. Using the transmission puts more load on the transmission and less on the brakes, and some say: "transmissions are cheaper than brakes". It's also a sign of driver skill to slow without using the brakes, as shown by slowing without the brake lights lit up. However, the hybrid is the opposite of that, and by stopping using "L", I have upped the mileage a notch.
On occasion, below the ev speed with the engine shut off, applying the brakes will cause the engine to start up. I don't know why this happens, but it's pretty rare.
Lately I've tried using the a/c to see what effect it has on the descent. I thought perhaps the FEH would just run the engine more or harder to run the a/c. In fact, doing the descent with a/c turned on, and in "L", I can get farthest down the descent without needing to use the mechanical brakes. Maybe I should try it with all the lights on and blowing the horn:-)
Now, few people with FEH's live in places where the hills are so large they will exceed the hybrid battery capacity. What matters is that it's a convenient way to test what operating mode enhances regeneration.
There are four situations that need to be described:
Shifting into "L" is different if the '09 is above or below the maximum speed for ev-only operation. That limit is 63kph, or about 40mph.
Below that speed, and for the purpose of the discussion, reducing speed can be done by using the brake pedal or shifting into "L". Using just the brake pedal, and nothing special going on (like a panic stop, and above 3mph), all braking is done with the regeneration system. The engine (given it has no reason to be running such as warming up or a/c full on) will be shut off.
If, below the ev speed limit, you reduce speed by shifting into "L", and given all the caveats mentioned above etc., the engine will start up. Although it won't be using any gas, it takes some energy for all those mechanical parts to be moving around. This absorbs energy and so there will not be as much left over to send to the hybrid battery.
Now, turning to reducing speed above the ev maximum speed. Whatever else is going on, such as a/c on or off, the engine will be running above that speed. When you're coasting, it isn't consuming gas, but again having all those parts moving around requires energy that isn't going to the hybrid battery. If you use the brakes, the engine will keep turning over, at an rpm that's higher the faster you're going. Applying the brakes won't change the rpm. You'll get regeneration from using the brake pedal, but very little from the engine.
If, instead, above the ev speed limit, you shift to "L" to reduce speed, everything is the same except the engine turns over at a higher rpm. This is how the '09 simulates the engine braking of a non-hybrid. The higher the rpm, the more energy is wasted moving engine parts. I think this is why the hypermilers shift into N in this situation. So to maximize the energy available to the hybrid battery, you want to lower engine rpm, which is "D" instead of "L".
Taking these ideas on the road, I regularly drive roads with such long steepish climbs that on the way down, the hybrid battery gets filled up and I have to keep the speed under control using the brakes and/or shifting into "L".
I can compare at what point during the descents the charge gauge shows that regeneration has ended. At those points, the speed starts to build and I have to use the brakes and, if I'm not already in "L", then also shift into "L" to regulate the speed.
If I have been using "L" from the start of the descent, the point where regeneration ends is lower on the hill. This means there has been less energy being put back into the hybrid battery. It also means I have to use the mechanical brakes less, which is a good thing. Actually, I never come down the hill in "D" because the speed gets out of control right away, and using the brake pedal means I lose regeneration fairly quickly because the battery reaches capacity sooner.
I used to use "L" often to reduce speed, because I was still thinking like a non-hybrid driver. Using the transmission puts more load on the transmission and less on the brakes, and some say: "transmissions are cheaper than brakes". It's also a sign of driver skill to slow without using the brakes, as shown by slowing without the brake lights lit up. However, the hybrid is the opposite of that, and by stopping using "L", I have upped the mileage a notch.
On occasion, below the ev speed with the engine shut off, applying the brakes will cause the engine to start up. I don't know why this happens, but it's pretty rare.
Lately I've tried using the a/c to see what effect it has on the descent. I thought perhaps the FEH would just run the engine more or harder to run the a/c. In fact, doing the descent with a/c turned on, and in "L", I can get farthest down the descent without needing to use the mechanical brakes. Maybe I should try it with all the lights on and blowing the horn:-)
Now, few people with FEH's live in places where the hills are so large they will exceed the hybrid battery capacity. What matters is that it's a convenient way to test what operating mode enhances regeneration.
Above the ev speed range, the engine will be running on all FEH's, pre-'09 or post '08. Whether you retard speed by using the brake pedal or "L", the engine will still be turning over whenever you are above the ev speed range.
The '09 has the option of using "L" to reduce speed. Above the ev speed range this will result in the engine going to a higher rpm. In this mode you recapture less energy because you're wasting it pushing all those engine components around more quickly. But if you are in a situation where you are going to exceed the capacity of the hybrid battery, such as descending a long steep hill with a stop sign at the bottom, and while towing a trailer, you will fill up the battery anyway. The sooner the FEH reaches that point, the sooner it switches to mechanical brakes only, and the more wear on the brakes. If you can delay the point where the hybrid battery is full, you will fill up the hybrid battery anyway, and reduce the wear on the brakes. For the same reason, in the same circumstances, using accessories such as the a/c can also reduce wear on the brakes.
Below the ev speed threshold, shifting into "L" causes the engine to be turning over, when it would be shut off in "D". It keeps running until it reaches the point where it switches over to mechanical brakes only, and then the engine shuts off even though it is in "L". In circumstances where the hybrid battery is going to be filled up anyway, but further braking is required, the inefficiency of having the engine parts flailing around translates into reduced use of the friction brakes. I run into this while descending rough steep logging roads in the mountains. It is very easy to overheat the mechanical brakes if you come down these roads too fast, so the less load on the mechanical brakes the better.
While saying this, I can understand why someone living in Florida might not run into this scenario.
I trust you will correct me if I'm wrong, but on the '09 and later, it sounds like there is more control over whether reducing speed is being done by regeneration and/or mechanical brakes and/or engine braking.
You can slow down to 6mph without using the brake pedal. Below 6mph, regen is cancelled and you are using the brake pads to stop.
Programming changed in the '09 and newer Ford Hybrids where you must use the brake pedal and judge the point between using the friction brakes and regen.
Programming changed in the '09 and newer Ford Hybrids where you must use the brake pedal and judge the point between using the friction brakes and regen.
So far as I know, the '09 will slow down to the speed where regeneration is cancelled, using "L". But that means the engine is running until speed drops to the point where it switches from regen to mechanical brakes. And if the engine is turning over, even without using gas, it is wasting energy. But to keep from wasting energy, you can just use the brake pedal.
Ford went back to the old way of L programming in the '13 Energi. Ford added a new mode for downhills by controlling regen to maintain your speed. For instance, if the speed limit is 35mph, you can change to this mode at 35mph, and the computer will regulate the speed by using regen on the downhill when required.
But this does not address the matter of trailer towing or large descents. At some point, say descending a very steep long hill, the Energi's battery must be filled up. What happens at that point? Does it apply the mechanical brakes to maintain 35mph, or does speed start to build above 35? Is the Energi even rated to tow a trailer?
#2
09-15-2014, 04:13 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
Wow, long post. I can answer for my 2014 C-Max Energi. When the battery is full it activates the engine, running it without fuel to keep the speed down.
The C-Max also has a "downhill" button that can be pressed that is less powerful than the "L" option, but still provides more braking.
That "L" option will always engage the engine when used on the C-Max, or on 2009 or later FEH.
The C-Max also has a "downhill" button that can be pressed that is less powerful than the "L" option, but still provides more braking.
That "L" option will always engage the engine when used on the C-Max, or on 2009 or later FEH.
#3
09-19-2014, 02:50 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
[quote=xspirit;253954]
But doesn't the '09 do exactly this when you use the brake pedal, at any speed, to reduce speed? Within the ev speed range and in "D", given a number of parameters such as having capacity in the battery, braking is done with regeneration when you apply the brake pedal. It does this by itself. (Yes, as it comes to a stop it switches to mechanical brakes only, but that's not my concern here.)
My understanding is that this lower limit on the '09 and later is 3mph, or 5kph. I also understand the system is designed this way because an electric motor can't hold a vehicle at a standstill.
So far as I know, the '09 will slow down to the speed where regeneration is cancelled, using "L". But that means the engine is running until speed drops to the point where it switches from regen to mechanical brakes. And if the engine is turning over, even without using gas, it is wasting energy. But to keep from wasting energy, you can just use the brake pedal.
Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.
Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?
In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.
Originally Posted by GaryG 
Pre-'09's can use L to separate regen from the friction brakes at any speed. For instance, coming off the highway at 70mph, I just time L to reduce my speed.
Pre-'09's can use L to separate regen from the friction brakes at any speed. For instance, coming off the highway at 70mph, I just time L to reduce my speed.
But doesn't the '09 do exactly this when you use the brake pedal, at any speed, to reduce speed? Within the ev speed range and in "D", given a number of parameters such as having capacity in the battery, braking is done with regeneration when you apply the brake pedal. It does this by itself. (Yes, as it comes to a stop it switches to mechanical brakes only, but that's not my concern here.)
My understanding is that this lower limit on the '09 and later is 3mph, or 5kph. I also understand the system is designed this way because an electric motor can't hold a vehicle at a standstill.
So far as I know, the '09 will slow down to the speed where regeneration is cancelled, using "L". But that means the engine is running until speed drops to the point where it switches from regen to mechanical brakes. And if the engine is turning over, even without using gas, it is wasting energy. But to keep from wasting energy, you can just use the brake pedal.
Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?
In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.
#4
09-20-2014, 10:42 AM
Re: Unravelling Engine Braking - pre-'09 and post-'08
[quote=xspirit;254030]
Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.
Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?
In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.
I used the engine braking when I needed to slow down more rapidly, rather than as a energy capture method. I found the feature useful for slower speeds downhill in the LA canyons, when the engine would stay off, the speed would be kept lower, and the charge would be maximized - until the SOC got above 60 or so, when the engine would come on. So on the 2008 it was useful for slowing down from higher speeds, or keeping the downhill speeds.
Note that on the 2008 it could be engaged without forcing the engine on, so long as the speed was below 40. On the later FEH, it would always engage the engine, although it did not always use gas to the engine.
Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.
Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?
In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.
Note that on the 2008 it could be engaged without forcing the engine on, so long as the speed was below 40. On the later FEH, it would always engage the engine, although it did not always use gas to the engine.
#5
09-24-2014, 03:59 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
im studying Mechatronics and i will try to do something to make my FEH fully Electrical, fuel optional but id rather use a hydrogen based fuel mechanism, so powered with water and self suficient.
#6
09-24-2014, 04:10 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
Hydrogen based? Do you mean running hydrogen? Or do you mean fuel cells, that need hydrogen and oxygen? Neither of these is powered with water...
#7
09-27-2014, 08:32 AM
Re: Unravelling Engine Braking - pre-'09 and post-'08
[quote=xspirit;254030]
Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.
Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?
In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.
In my 06 while braking in L my engine will shut off at a slightly higher speed (35 v 30 MPH) than in D. The reverse is also true...the vehicle will stay in EV mode up to slightly higher speeds in L than in D. Under certain circumstances, there are definite advantages to selecting L in the earlier model years.
Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.
Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?
In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.
#8
09-27-2014, 09:22 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
[quote=stevedebi;254037]
I used the engine braking when I needed to slow down more rapidly, rather than as a energy capture method. I found the feature useful for slower speeds downhill in the LA canyons, when the engine would stay off, the speed would be kept lower, and the charge would be maximized - until the SOC got above 60 or so, when the engine would come on. So on the 2008 it was useful for slowing down from higher speeds, or keeping the downhill speeds.
Note that on the 2008 it could be engaged without forcing the engine on, so long as the speed was below 40. On the later FEH, it would always engage the engine, although it did not always use gas to the engine.
Interesting that the pre-'09 was set up so that when regeneration ceased due to a full battery, the engine was turned on to provide some braking effect by having to move all those engine parts around. I assume this happened in "L", but not in "D". Would I be correct in saying that if you were in the same situation in "D" and using the brake pedal, the same thing would happen as in "L"? Or would the engine just stay off?
I used the engine braking when I needed to slow down more rapidly, rather than as a energy capture method. I found the feature useful for slower speeds downhill in the LA canyons, when the engine would stay off, the speed would be kept lower, and the charge would be maximized - until the SOC got above 60 or so, when the engine would come on. So on the 2008 it was useful for slowing down from higher speeds, or keeping the downhill speeds.
Note that on the 2008 it could be engaged without forcing the engine on, so long as the speed was below 40. On the later FEH, it would always engage the engine, although it did not always use gas to the engine.
Last edited by xspirit; 09-27-2014 at 09:24 PM.
#9
09-27-2014, 09:25 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
[quote=GatorJ;254110]
In my 06 while braking in L my engine will shut off at a slightly higher speed (35 v 30 MPH) than in D. The reverse is also true...the vehicle will stay in EV mode up to slightly higher speeds in L than in D. Under certain circumstances, there are definite advantages to selecting L in the earlier model years.
I'll have to check and see if the ev max speed is the same in "D" and "L" in the '09.
In my 06 while braking in L my engine will shut off at a slightly higher speed (35 v 30 MPH) than in D. The reverse is also true...the vehicle will stay in EV mode up to slightly higher speeds in L than in D. Under certain circumstances, there are definite advantages to selecting L in the earlier model years.
#10
09-27-2014, 09:59 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
This thread should be of interest:
The low gear advantage
https://www.greenhybrid.com/discuss/...dvantage-3733/
It's an old thread and, therefore, applies to the earlier models.
The low gear advantage
https://www.greenhybrid.com/discuss/...dvantage-3733/
It's an old thread and, therefore, applies to the earlier models.
