Living with a Jazz Crosstar

[TnTkr]

I agree, all brakes do fade, but not during that small descends.

[Jocko]

I agree, all brakes do fade

But modern brakes don't fade sufficiently to substantially affect their performance. Just releasing the brake for a few a second or two allows them to cool. That is why modern brakes have hard pads and servo assist.

[Kenneve]

I accept what you say about regenerative braking, but I can’t imagine it provides anything like as much ‘resistance’ compared with an engine in 3rd or 2nd gear.
As I understand it, correct me if I’m wrong, there is a direct drive (no reduction gear) between the engine and the motor/generator which is engaged with some form of clutch.

[Kenneve]

I accept what you say about regenerative braking, but I can’t imagine it provides anything like as much ‘resistance’ compared with an engine in 3rd or 2nd gear.
As I understand it, correct me if I’m wrong, there is a direct drive (no reduction gear) between the engine and the motor/generator which is engaged with some form of clutch.

Oops pressed the post button twice🙄🙄

[John Ratsey]

And that is with automatics with virtually nil engine braking.
The B mode offers substantial regeneration, so that covers lack of engine braking.

John, are you saying that a two-mile descent will fully recharge the battery? Is it a AA?

I've been down quite a lot of hills in my various CVT Honda cars and just left the vehicle to do what it wanted. A year or two back I was going down a long hill in Scotland and noticed that the engine revs were quite high so the car must have decided to do some engine braking, but that was the only time I remember it happened.

I know from watching the battery gauge that a medium sized hill will easily fully charge the battery (although the battery charge level might be anywhere between 30% and 60% when starting the descent). One kWh capacity can propel the vehicle for a mile or two on the level but it's the going up hills which need the energy (ask any cyclist) and, conversely, going down a hill makes that energy available for reuse. B mode will cause more aggressive slowing of the vehicle when the accelerator pedal is lifted but I've noticed that in D lifting the pedal causes more slowing of the vehicle than in vehicles with petrol engine + CVT. I find this to be a welcome feature - reduce the accelerator pressure when needing to decelerate for a speed restriction and the vehicle will usually slow down enough without needing to touch the brake pedal.

I accept what you say about regenerative braking, but I can’t imagine it provides anything like as much ‘resistance’ compared with an engine in 3rd or 2nd gear.
As I understand it, correct me if I’m wrong, there is a direct drive (no reduction gear) between the engine and the motor/generator which is engaged with some form of clutch.

There is a direct drive with some intermediate gearing which the vehicle engages at higher speed but it's the equivalent of 5th gear (around 2200rpm at 60mph - details in a previous post). The motor which drives the wheels can work as a generator for the regenerative braking while the generator attached to the engine can work as a motor (that's how the engine gets started) so the capability exists to drive the engine at higher rpm for braking. The unknown is whether Honda has programmed the vehicle to use this capability and in what circumstances to use it. One problem I see is that the vehicle hasn't got a clue how long the hill is. When I get to go down some bigger hills (which may not be this year) then I'll watch what happens.

[Jocko]

I accept what you say about regenerative braking, but I can’t imagine it provides anything like as much ‘resistance’ compared with an engine in 3rd or 2nd gear.

On some vehicles, the Honda-e among them, the regenerative braking is so extreme that one pedal operation is possible. It will bring the car from motorway speeds down to under walking pace without having to touch the brakes. It is like driving a dodgem.

[ColinB]

... reduce the accelerator pressure when needing to decelerate for a speed restriction and the vehicle will usually slow down enough without needing to touch the brake pedal.

On some vehicles ... the regenerative braking ... will bring the car from motorway speeds down to under walking pace without having to touch the brakes.

So if you don't need to touch the brake pedal, is the car clever enough to illuminate the brake lights when regenerating? If not, perhaps the considerate driver ought to lightly touch the brake as a courtesy warning to the following driver.

[equaliser]

... reduce the accelerator pressure when needing to decelerate for a speed restriction and the vehicle will usually slow down enough without needing to touch the brake pedal.

On some vehicles ... the regenerative braking ... will bring the car from motorway speeds down to under walking pace without having to touch the brakes.

So if you don't need to touch the brake pedal, is the car clever enough to illuminate the brake lights when regenerating? If not, perhaps the considerate driver ought to lightly touch the brake as a courtesy warning to the following driver.

Yes, any regenerative braking stronger than 0.5G activates the brake lights.

[madasafish]

I have had brake fade once in 50 odd years of driving: mt second car - a 1946 Rover 16 saloon with drum brakes all round  - on a long downhill (2miles?)  in the Scottish Highlands..

The smell and smoke from hot brake  linings was vile: I opened the front opening windscreen (Yes really!) and the sunroof to get rid of the smell. As the brakes were rod operated, there was no brake fluid to boil. The only way of stopping it was to put the car in second gear and switch off the engine... There were gravel runoff areas on the sharper corners near the bottom.. I never quite needed them..

Subsequent journeys on the same road with more modern disk braked cars (Triumph 2.5PI, MG 1100) had no fade or drama.

[jazzaro]

It occurs to me that there may be a serious problem, when it comes to descending steep hills.
Is there any serious engine braking available?

I have in mind the Devon banks like Countisbury and Porlock hills where there are 1:4 or 1:5 sections, such that with the earlier Jazz cars you would probably change down to 3rd or even 2nd gear + brakes to safely negotiate such slopes.

When you leave the gas pedal and you slightly press the brake, if the battery is not fully charge you will slow down with regenerative braking: the B position is only a stronger standard regenerative level.
If the battery is at 100%, the regenerated electricity will be sent to the electric motor linked to the flywheel, moving the petrol engine with the throttle valve closed so gaining the usual engine braking you would have with a normal car.

[jazzaro]

I have had brake fade once in 50 odd years of driving: mt second car - a 1946 Rover 16 saloon with drum brakes all round  - on a long downhill (2miles?)  in the Scottish Highlands..

Me once with a Fiat Tipo mk1, a car known to have light brakes (its disc rotors were the same of the Uno), first fading and then, when I was able to stop, vapour lock.
And it happened this downhill:
https://www.google.com/maps/place/Passo+dello+Stelvio/@46.5293741,10.4444522,15z/data=!3m1!4b1!4m5!3m4!1s0x47831ae455181c1d:0x1d0709882e83eb60!8m2!3d46.5293602!4d10.453207
In the path between Bormio and Prato allo Stelvio it was easy to see new car prototypes (BMW, Mercedes, VAG, Alfa Romeo) testing their brakes, because the downhill is very very very strong.

[Downsizer]

I've been down quite a lot of hills in my various CVT Honda cars and just left the vehicle to do what it wanted. A year or two back I was going down a long hill in Scotland and noticed that the engine revs were quite high so the car must have decided to do some engine braking, but that was the only time I remember it happened.

I've experienced this on long descents with cruise control on.  I assumed that it kicks in when the speed is exceeding the set cruise speed.

[Kenneve]

On a CVT car, I don't believe that cruise control provides any braking, if you exceed the set limit when going down a hill.
Generally engine speed will rise to circa 3000 rpm to provide some resistance but thats all.
If I'm going down a steep hill, I usually use the down paddle, to force the CVT to change down, probably to an indicated 3rd gear or even 2nd.

So coming back to hybrid car, what happens descending a steep hill, if your battery is already fully charged?
I just can't see how the engine can hold you back. since there is no significant reduction gear (equivalent to the lower gears on a Manual gearbox)  between the engine and the motor/generator, so you are utterly reliant on the brakes alone.

[John Ratsey]

So coming back to hybrid car, what happens descending a steep hill, if your battery is already fully charged?
I just can't see how the engine can hold you back. since there is no significant reduction gear (equivalent to the lower gears on a Manual gearbox)  between the engine and the motor/generator, so you are utterly reliant on the brakes alone.

Under normal driving conditions the generator attached to the engine drive the motor attached to the wheels. However, the generator is capable of functioning as a motor (that's how the engine is started - no other starter motor) and the motor connected to the wheels becomes a generator for regenerative braking, so there's no significant problem I can see with the power from the wheels being used to turn the engine with valves closed to provide additional braking. The electronics will try to spin the engine as whatever speed is deemed appropriate. Until someone reports that this happens we don't know if Honda have enabled this facility. The design challenge as I see it is knowing when to use the engine as a brake to take the load off the discs. Suddenly doing a quick burst of engine braking at the bottom of a medium hill could annoy drivers. I'll put the hypothetical question to my dealer.

[richardfrost]

Well on my RAV4, which is not the current model, has an earlier Toyota hybrid system, but has 6 virtual gears, engine braking just works, whether the battery is showing as full or not. I do this most days as I live up a long steep hill and where I live is a hilly place. I don’t think about how it happens, I just know that it does.