Brakes Or "gears" To Slow Down?

[wh05apk]

Since purchase of my is300h I have used the tacho rather than economy gauge, but have gone back to using the economy gauge again and notice when braking or slowing down with the gears the needle goes into the charge section, am I right in thinking initial braking is done by regenerative braking until the needle reaches the bottom of the gauge, then the friction brakes take over?

[ColinBarber]

Yes essentially that is correct. If you use light braking to avoid the needle going beyond the bottom then you will achieve as much energy recovery as possible.

This is one reason why the power gauge is more useful than the tacho.

[wh05apk]

Thanks Colin, since I've had the car I have tended to"play" with the paddles to slow down, is there any benefit to this, such as regenerating more or less brake wear, than just using the brakes and keeping the needle of the bottom?

[ColinBarber]

No benefit in terms of economy. If the braking force can be achieve by the regen system then it is the same as just lightly braking using the pedal. If the 'gear' selected means more braking force is needed over what the regen system can provide then it will turn over the petrol engine to generate an extra load - which is wasting energy.

Benefits to doing what you are is you don't have to press the brake pedal and you may get better performance 'in gear' if you suddenly need to accelerate again.

[PaulWhitt20]

Just a thought. If you are using the gears to slow down then the brake lights will not show. Thus not alerting the drivers behind you are slowing down.

[Deadloak]

True but that would be a case of the driver behind not looking far enough ahead to spot hazards. Which is not very good driving in itself, and that sort of driver is likely to back end you anyway..

[Steve44]

Whilst driving through Switzerland and Italy a few weeks ago, I used S mode when coming down mountain passes, with S2, 3 or 4 selected, keeping the speed down using engine braking and not risking burning out the brakes. Maxed out the Battery charge too more than once. One question, what does the car do when the Battery is full? Disengage the generator or just push out the excess elec as heat?

[Zotto]

When HV batteries are at full charge if you go on braking usual brakes work, so it's time to use engine braking inserting low gears to avoid overheating and wasting brake pads; the energy will be lost in heat.

[michaelH]

and better control on twisting or steep descents

[ToreOe]

Just a thought. If you are using the gears to slow down then the brake lights will not show. Thus not alerting the drivers behind you are slowing down.

Driving at night, I can see the reflections from my brake light in the rear view mirror, and I have noticed something strange. If I go down a hill and use the brakes to keep a constant speed, the brake lights do not show. However, as soon as I reduce speed, ether by using the brakes *or* the paddles, the brake lights light up. Same goes when dynamic cruise is braking.

I find this kindof cool, but also worrying - are the brake light computer/software controlled?

-Tore

[Deadloak]

I find this kind of annoying, when following someone when thier brake lights are contantly being flicked on. I aways say to myself "well don't drive so close, and you wouldn't have to touch them". As mentioned before on the forum, this causes the buffering effect on motorways.

I suppose this a good benefit for ACC, but if the brake lights are twinkling like Christmas lights, then all non-equipped (and some with) drivers will still remain driving in the same manner.

But this is interesting that it could be the programming doing this, and I appologise to those that are not phaffing around with the pedal.

Also I've noticed in the last few years that when on a motorway and you want to change lane. That other cars sometimes take an age to pass. I'd usually ease off or slightly increase to ease their passage. I've come to the conclusion, that in a lot of cars now - across the spectrum - have cruise control. So are not likely to take it off and then inadvertently become impolite drivers.

It will be interesting once I get the IS, if I use the cruise control that much, but I guess I poo-pooed parking sensors too before I had a car with them :).

[wh05apk]

Not noticed the brake lights, but since I have had mine, I have done very little night driving, so will find out soon as the evenings get darker.

It doesn't surprise me if the car only applies the brake lights when actually slowing down, that makes sense, as they are only there to warn other drivers you are slowing down, it would also make sense if they didn't apply them whilst sat at traffic lights, or even used the rear sensors to know when there was traffic behind the car, and turned them off then, maybe that's wishful thinking?

[ColinBarber]

One question, what does the car do when the battery is full? Disengage the generator or just push out the excess elec as heat?

The petrol engine is spun over to create a load. Fuel isn't injected so it doesn't waste fuel but the compression in the cylinders creates a load. Energy recovered from the brakes is used to spin the engine, the faster it spins the more load is generated. It will probably also engage the mechanical brakes.