anko
Well-known member
I wonder, why is it that I so totally fail when it comes to relaying my message? 
Seriously, I am not talking / thinking about an isolated scenario and I am not simplifying matters. I am not suggesting you should leave the motorway with lower SOC than needed. For argument sake, let's look at the most extreme case: you want to leave the motorway with as much charge as possible so you can cross all of London in EV mode (is that possible?). Then there are basically two approaches to achieve this:
1. Hit Save as soon as you reach the motorway (your approach).
2. Use up the available charge on the motorway and hit Charge well before leaving the motorway, allowing the car to rebuild the so desired SOC (my approach).
The first scenario results in a long series of small oscillations (between the SOC at which you hit Save and that same SOC + 1.5%) . The second scenario results in one huge oscillation (from more than 90% to 30% and back to more than 90%), with maybe (if the stretch of motorway is long enough) a series of small oscillations in the middle section (between 30 and 31.5%). Which approach you take does not make a difference when it comes to the amount of energy needed to travel the distance. In principle, it also does not make a difference when it comes to the amount of time driven in EV mode. In comparison, you can climb 5 flights of stairs at once and then descent 5 flights of stairs (2nd approach) or you can climb and descent 1 flight tof stairs 5 times (1st approach). Or do it totally random. The amount of stairs climbed (time spent in parallel mode) and descended (time spent in EV mode) must be exactly the same in each approach, as you eventually end up at the same level. Also, the amount of energy needed to do this is the same. So far, there is not much difference.
In both scenarios, there are periods of EV driving, at first glance totalling up to the same amount of EV driving. Assuming speed is a fixed parameter on that stretch of motorway, we can not do much to change the efficiency of the vehicle in EV mode. But, as I have tried to explain, I strongly believe that we can impact the efficiency of the vehicle in parallel hybrid mode.
This afternoon, on the way back home from work I did a small test.
- Engaged Save mode at 86.5%. Engine load hovered around 50 - 55%. The power fed into the battery was pretty stable at approx. 3.6 kW.
- Engaged Save mode at 74%. Engine load was a up a few %. The power fed into the battery was more like 5.7 kW.
- Engaged Save mode at 44%. Engine load had gone up to around 75%. Power fed into the battery was as high as 18 kW.
For sure, when the load of the engine went up, so did the instantaneous fuel consumption. But not by the same amount. We all know (I think) that the efficiency of an engine increases when the load increases: the amount of usable mechanical kWh produced per liter of fuel burned increases with the load. So, at lower SOC, the periods of EV driving are equally efficient but during the periods of parallel driving the fuel is spent more efficiently. What does this translate to?
At lower SOC / higher engine load, it takes far less time to increase SOC by 1.5%. Imagine what charging the battery with 18 kW instead of 3.6 kW will do for the time it takes to gain 1.5% SOC. Shorter periods of engine on automatically translate into more periods of engine off.
Seriously, I am not talking / thinking about an isolated scenario and I am not simplifying matters. I am not suggesting you should leave the motorway with lower SOC than needed. For argument sake, let's look at the most extreme case: you want to leave the motorway with as much charge as possible so you can cross all of London in EV mode (is that possible?). Then there are basically two approaches to achieve this:
1. Hit Save as soon as you reach the motorway (your approach).
2. Use up the available charge on the motorway and hit Charge well before leaving the motorway, allowing the car to rebuild the so desired SOC (my approach).
The first scenario results in a long series of small oscillations (between the SOC at which you hit Save and that same SOC + 1.5%) . The second scenario results in one huge oscillation (from more than 90% to 30% and back to more than 90%), with maybe (if the stretch of motorway is long enough) a series of small oscillations in the middle section (between 30 and 31.5%). Which approach you take does not make a difference when it comes to the amount of energy needed to travel the distance. In principle, it also does not make a difference when it comes to the amount of time driven in EV mode. In comparison, you can climb 5 flights of stairs at once and then descent 5 flights of stairs (2nd approach) or you can climb and descent 1 flight tof stairs 5 times (1st approach). Or do it totally random. The amount of stairs climbed (time spent in parallel mode) and descended (time spent in EV mode) must be exactly the same in each approach, as you eventually end up at the same level. Also, the amount of energy needed to do this is the same. So far, there is not much difference.
In both scenarios, there are periods of EV driving, at first glance totalling up to the same amount of EV driving. Assuming speed is a fixed parameter on that stretch of motorway, we can not do much to change the efficiency of the vehicle in EV mode. But, as I have tried to explain, I strongly believe that we can impact the efficiency of the vehicle in parallel hybrid mode.
This afternoon, on the way back home from work I did a small test.
- Engaged Save mode at 86.5%. Engine load hovered around 50 - 55%. The power fed into the battery was pretty stable at approx. 3.6 kW.
- Engaged Save mode at 74%. Engine load was a up a few %. The power fed into the battery was more like 5.7 kW.
- Engaged Save mode at 44%. Engine load had gone up to around 75%. Power fed into the battery was as high as 18 kW.
For sure, when the load of the engine went up, so did the instantaneous fuel consumption. But not by the same amount. We all know (I think) that the efficiency of an engine increases when the load increases: the amount of usable mechanical kWh produced per liter of fuel burned increases with the load. So, at lower SOC, the periods of EV driving are equally efficient but during the periods of parallel driving the fuel is spent more efficiently. What does this translate to?
At lower SOC / higher engine load, it takes far less time to increase SOC by 1.5%. Imagine what charging the battery with 18 kW instead of 3.6 kW will do for the time it takes to gain 1.5% SOC. Shorter periods of engine on automatically translate into more periods of engine off.
