gwatpe said:
The PHEV if in SAVE mode and driving may get stuck in series hybrid mode for extended periods, or drain the battery and then fill it back to that level from ICE operation. To force the car into parallel hybrid, I have found that pressing the CHARGE button will speed up the clutch engaging.
What were the weather conditions (temperature wise) during this test? Could it be that the engine was started up to provide heat and not electrical power, when it seemed to be running in Save mode?
My experience is this (at 100 km/h, 62 mph steady driving).
There is no difference between Save and Charge mode. Not in terms of amount of gasoline consumed, not in terms of RPM and not in terms of power produced. The only difference is that in normal or save mode, the car decides when to fire up the engine and when to kill it, while in Charge mode, you do.
When SOC goes above 50%, charging speed slows down, presumable resulting in a less efficient load / fuel economy. So, probably it is most economical not to use charge mode above 50% SOC.
Unfortunately, the engine does not run at it's optimal efficiency, not even when charging. It appears that the system is programmed to burn approx. 11 l / 100 km (9 km / l). At 100 km/h, this translates into 11 l / hour. This burn rate results in a specific amount of power and torque (roughly 30 kW and 100 - 110 Nm).
- Whel 30 kW is more than needed for driving, the surplus power will go to the battery via the generator. So, depending on (the amount of) head or tail wind, the battery will charge slower or faster. You will see the Power needle go up and down a bit (in the green area before where the white scale starts, so less than 30 kW), because that needle only shows what is used for driving. But the total amount of power produced by the engine will be fairly steady at 30 kW. So will the fuel burn rate at 11 l / hour.
- When 30 kW is equal to what is needed for driving, charging stops. This is roughly where the white scale of the Power meeter starts. Again, at 100 km/h.
- When 30 kW is less than what is needed for driving, the engine will burn more fuel at the same RPM, in order to generator more power. The power meter may go up to about 3/4 of the green scale, as the full green scale is 60 kW and at the RPM associated with 100 km/h the engine can produce about 40 something kW max.
- When the max amount of power the engine can produce at the given RPM is less than what is needed for driving, the e-motors will assist, while taking power from the battery. The Power meter will go up further, maybe even out of the green zone, and you will see an energy flow from the battery to the wheels depicted in the dashboard.
- When the max amount of power the engine can produce at the given RPM + 60 kW of e-assistance is less than what is needed for driving, the parallel mode will disengage and only then the engine will rev-up, to produce max 82 mechanical kW @ approx. 4100 RPM, which will be converted by the generator into approx. 70 electrical kW which will be electrically converted to 60 kW usable power for the e-motors. Together with 60 kW of power from the battery (70 kW discharge - electrical conversion losses) this results in the well known 120 kW e-power. The Power meter will definitively be outside the green area.
- When the amount of power the engine can produce at the given RPM is less than what is needed for driving and the battery is depleted, the parallel mode will also disengage, allowing the engine to rev-up and produce more power. Expect the Power meter to be somewhere in the 4th quarter of the green scale. As below that, the engine could still cope in parallel mode and above that the battery would have to assist. Which it can't because it is depleted. I have no idea how you would achieve this state, when driving solo ;-)
What you can see from the above is that there is a fair amount of power reserve, which can be used for driving, but will not used for charging. This is demonstrated by the fact that when you gradually increase acceleration, first charging stops, but only somewhat later e-assistance kicks in.
There seem to be two drawbacks:
- When driving at steady speeds, the engine is not running at optimal efficiency (only 30 kW is produced where the optimal load is at about 40 kW). Most likely, there is a limit to the amount of power you can safely dump on the battery (and indeed, as I said, the amount of power produced by the engine is further reduced when the battery reaches a certain SOC). So, unless you need more power for driving, you cannot simply allow the engine to produce more power. But what if you do need more power for driving? Why not increase fuel burn rate / power output and keep charging? I assume the engine will run more efficiently while doing so.
- As a caravan enthousiast, SOC is a major concern. You want to hang on / enhance SOC as much as possible. Because at some point, you will need to conquer a slope or two and then you need all the SOC you can get. You will understand that you need quite some extra power to maintain a steady speed while towing a caravan. Unless you have no wind at all, or somewhat a tail wind, you will probably burn 11 liters of fuel per hour or more for driving only. That means the battery will recharge very seldom. Even though the engine has plenty of reserve to take on a strong head wind or a mild slope (bridge). I have seen charging stop at 31 kW and power output go up to approx. 40 kW. So apparently, the engine can produce 40 kW at caravan speeds. So, why won't it use that for charging when it doesn't need that for driving?
