This is a splinter thread from the one I started on the window seal noise. Just so people can find / follow this issue more easily.
So to recap:
I've noticed that on long hill climbs, the IMA battery becomes depleted and stops assisting. This is expected and not a problem.
What happens next is that on part throttle while still climbing the long hill the IMA battery manager decides to start charging the IMA battery (at a rate of up to 50%). This causes the car to slow (as another 3.25hp is drained from the petrol engine on top of losing the 13hp assist).
On a 4% gradient motorway at about 55mph on cruise control in D (ECON on) mode the car started to slow and I had to use more gas and click down the manual gear shift to regain momentum while passing trucks in the crawler lane.
More recently, on a twisty single carriageway road with 4 people in the car and climbing a long 16% gradient, the assist ran out but the car did not force charge this time as I was nearly flooring the throttle. But this meant I accelerated up the hill too much and so I had to back off to about 70% throttle, whereupon the battery manager decided to start force charging the IMA battery and so the car slowed down and I had to increase throttle to nearly maximum again. This caused the force charge to stop but the car speeded up too much and so I backed off... and so on in a cycle.
I took the car to my local dealer and they checked it out and reported "no fault". Talking to the technician, he agreed to escalate it to Honda (UK).
Simultaneously, I sent an e-mail to Honda (UK) about the issue.
The technician confirmed there were no updates / recalls out for the Insight but that if there is a firmware update, it can be downloaded to the car by the dealer with their diagnostic computer.
So, now we're up to date...
I received a couple of calls from Honda today. The genuinely knowledgeable and helpful guy asked me about the details of the phenomenon and said he hadn't come across it but went to talked to a technician about it.
He called back about 20 mins later and the verdict was that it is normal behaviour as the battery manager doesn't
ever want to let the IMA battery stray outside its charge limits of 20-80%. If it gets close to 20% and you aren't at or near 100% throttle, then it will force charge.
This sort of fits with the other discovery that the engine will give you full power even in ECON mode when you floor it (power output is only limited and throttle response smoothed below about 90% throttle position). Following the logic of "if you floor it then temporarily abort ECON mode", it makes sense that it would also temporarily abort force charging to give you maximum power (even if assist isn't available yet).
It can get caught out by lots of light and fairly constant throttle position driving on flat ground followed by continued part throttle gentle hill climbing. If you increase throttle setting dramatically when hill climbing to accelerate, then it may realise that its climbing a hill from the sudden change in engine load (provided you're at or near 100% throttle) and so decide to temporarily abort force charge. If you back off, it assumes that you are reaching flat ground and so resumes force charging until the IMA battery has recovered enough charge to usefully provide assistance again (e.g. for a standing start or another burst of full power assist). If the battery is charged enough, it should stop force charging and either sit at zero for the rest of the hill or resume assisting for a while.
They reckoned that it was more fuel efficient to run the engine at higher load all the time (so use wide open throttle without assist or force charge on part throttle, causing the driver to increase throttle more towards wide-open). This way the engine operates more of the time at its efficient range and the IMA battery can store the excess and save it for later (when the extra hp or torque is required).
So he reckoned it was best to cruise on the flat at 55mph, attack the hill at 60-70mph (in the M25 scenario) to coax the system into not force charging and then ease off back to 55mph at the summit so that then it could force charge on the flat or regen going down the other side (if there is one... the M25 reaches a summit and then there's a plateau).
He said he'd still look into it some more and try out a couple of Insights they have and get a couple of colleagues to try it out too and see if he can investigate the behaviour (what happens at various throttle settings at or near the low battery threshold). They've got a system that can interface to the car while its driving and it can record variables and then store / replay them on time graphs on the laptop to see what the car was doing during a trip.
The fact that you can data log the car while it's running would be an interesting tool to have...
He suggested that I try it again and see if the MID power flow display and the charge/assist gauge agree during the phenomenon. It's a sunny afternoon so it might be time for a test drive
If I can figure a way to fix my little video camera so it can see the dash and the road at the same time I'll post a video. Might be useful if he comes back and says he couldn't replicate the issue.
Forced IMA charging on hill climbs
:
