Something different.

[Jeff15]

Toward the end of a long journey Whilst in B and EV mode the engine starts to rev quite high, didn't last long, about 30 seconds...Strange or what..??

[Marco1979]

Were you going downhill? Looks like the battery was full and the generated electricity had to go somewhere. The generator can drive the engine for additional resistance and you can hear that. No fuel is used however, it’s just engine braking.

[tfw7]

I had that a few weeks ago - it was really revving and sounded like it was straining something! Going downhill on B batter level full.
I pulled over, turned the engine off, waited a minute or so then set off again and all was good.

[Bristol_Crosstar]

I just switch to D when that happens and use the brake, seems to work

[Marco1979]

It can happen in B (strongest regeneration) but also in D when on cruise control and going downhill.
In Switzerland you need a lot of engine braking as I found out during my holidays there. At low speeds the noise is okay and B mode will keep the car in control without having to brake a lot. On highways too; engine braking noise is lost in all other sounds. Most annoying was going downhill at 40 to 60 mph; more revs and no other noise. Better use the brake pedal and D mode under those circumstances…

[GeoffW]

It happened to me not long after we got the car, going down Blue Bank in Yorkshire heading for Whitby. It's a long steep hill and it sounded like the generator was going to burst.

[PaulC]

Yes, another person here who had the engine burst into high revs when going down a steady long incline (3+ miles) and the battery charge level indicator had got to 10 bars.
My guess is that this is some kind of engine braking.

[Lord Voltermore]

Yes it happened to me once when descending a steep mountain pass - but  only because I tried using B mode as an experiment to see if the increased regenerative braking effect of charging the battery was an advantage. It was not. Once the battery is fully charged the car can no longer slow the car by the generator drag  so it goes into 'manic' mode attempting to slow the car by conventional engine braking. The steeper the descent the more manic it becomes.  Like trying to stop a runaway car using a lower gear but no brakes.    As others have said, just select D mode . There will still be some engine braking,and if more retardation is required  gently use the brakes. You have to forget about losing potential 'free energy' regenerative gains in B mode. Once the battery is full  its full. B mode wont be adding more.  And brakes benefit from a bit of use. 

Driven  sensibly even the longest and steepest  descents in europe are unlikely to overheat a mk  4's brakes  Certainly none in the uk  (unless you  race down)   I just stay in D mode.   As part of my 'experiment' I monitored how often the manual transmission cars in front of me on a long descent were  displaying brake lights.  (and potentially overheating them)  Even in D mode I was using brakes significantly less often.

  A few have been startled when the engine starts working much harder than they have experienced before   when climbing a long incline or  doing an unaccustomed fast overtake etc. This illustrates how  rarely it happens for some drivers  and how quiet the car normally is .   The car senses the need to use maximum engine power to immediately  keep the battery topped up ,  rather than suddenly running out of oomph  mid manoeuvre.     In these  circumstances you can sometimes slow the engine speed down by easing back slightly on the throttle.  The car reassesses its needs and sometimes the engine will slow, but with no noticeable difference in road performance.     But dont try it mid overtake     

[Jeff15]

Thanks for all of your views. If it happens again I will have a word with the dealer.

[Kenneve]

Whilst were talking about regeneration and charging, what is your opinion on the following.

When attempting to get the maximum charge from a given downhill slope, is it better to descend at a steady rate, taking longer and presumably at a modest charge rate, or descend quickly and therefore for a shorter time, but at a higher charge rate, (assuming higher speed equals higher charge rate), or is there no difference?

[davejazz]

I know the purists amongst us will say,”he shouldn’t be doing that”, but, if there is a good mechanical reason, please let me know.
 I drive half and half in D and B, and this works for me in both modes. So, I am travelling down a gradient at perhaps 37mph, and the car behind is giving me the impression, with his closeness, that he would rather be doing 42mph. The traffic is a little heavy, and the good soul that he is, does not try to overtake. He is not aggressive, and I give him, in my mind, a bit of help. Perhaps he is late for a date, or needs a p**!

As I said, the car is in mild overrun at 37mph, I move it into N, and within 10 seconds, we are at 42mph.
I then move back to D, where the car will return to its natural momentum. All in petrol or electric mode.

I know that I should be “in full control of my vehicle”, but I would welcome any feedback, if I am compromising anything mechanical or electrical.

With this weather, time to fire up the aircon!

[shufty]

...Is it a 40mph limit?

Your 37 may well be actually 35 and the 42 closer to 40 so you could have gone quicker, in his mind.

[John Ratsey]

Whilst were talking about regeneration and charging, what is your opinion on the following.

When attempting to get the maximum charge from a given downhill slope, is it better to descend at a steady rate, taking longer and presumably at a modest charge rate, or descend quickly and therefore for a shorter time, but at a higher charge rate, (assuming higher speed equals higher charge rate), or is there no difference?

There will be a limit to the rate at which the battery gets charged to avoid it overheating with the brakes being used to absorb the excess energy. I would therefore expect modest deceleration to result in more energy recovery than sudden deceleration.

[Jazzyone]

Just a thought on running in neutral. Does this not damage the electrics? They say you should never tow the Jazz in neutral as it causes the electric motors to run that power the wheels and will damage the system. Always lift the front wheels for a recovery. Is not running in neutral just the same as being towed as the wheels will still rotate the same the car doesn’t know the difference.

[Marco1979]

In D mode while going downhill the Jazz tends to pick up a lot of speed and feels more ‘out of control’, so to say. Nothing compared to the mk3 cvt, btw. In B mode the car will not pick up speed and you as a driver are very much in control. You can even press the accelerator to pick up some speed and decrease engine braking. That feels natural, just as in a manual car where you would descend using the same gear as you would to ascend.

I would not recommend N to go downhill, engine will be off as will generator and electric motor. So no control except your brakes. Choose D or B, it is just a matter of preference.