Braking question

Same, but now with radar, the car can brake in an emergency if it detects a collison.

 

That's not even true for Gen 3, or for any Prius generation.

 

What Chapman said.
The description given in the OP is what I'd say is a misunderstanding of how regenerative braking works in the prius normally as apposed to some of the observations made of what regenerative braking can show at both extremes of use. ie: hypermiling or heavy traffic at freeway speeds......
There is a lot more space inbetween the extremes where regenerative braking works without showing the driver obvious indications of what is happening.

 

No, that's not the case. Where are you getting your information?

 

It's been widely discussed in the Gen 3 sections. Plenty of threads get it right. Are there particular threads or posts you've been relying on to think it works the way you think it works?

 

Some places it has come up before, with the graphs from the Toyota manuals, are here in the Gen 3 section, and here and here in the Prime section.

In that last one, Elektroingenieur kindly posted the Gen 4 graphs in the next post, #32. I typically include the graphs from the Gen 1 and Gen 2 manuals because I haven't personally downloaded the corresponding Gen 3 and Gen 4 ones; certain parameters get adjusted up or down over the generations, and they changed the style of the graph for Gen 4, but none of that ever changes the physics much.

The physics pretty much dictate that very low speed has to be friction, and high speed and/or strong braking has to be significantly friction, and there is kind of a sweet spot in between those regions where regen is able to play its largest role. In any given stop your speed is changing, your pedal effort is changing, your battery SOC and temperature are changing, and the braking computer is recalculating how much of each form of braking to have in the mix, over and over again throughout the process.

 

Bottom line, it's pretty much always a blend of regular friction brakes and regen, sometimes more of one or the other. I'd think 4th gen and 3rd work very similarly.

 

There is still a huge amount of room between "easy" and "hard/sudden" braking, and the regeneration system simply doesn't have the capacity to serve much of that space.

 

That has bits of the right ideas, but to suggest that just "slowly stepping on the brakes lightly" necessarily means you "don't activate" the hydraulics is oversimplified enough to be misleading.

That does get closer. Yes, the brake computer has to calculate how much regen and how much friction to use, every time, and how hard you brake and the vehicle speed are two of the inputs to that calculation. At highway speeds, even quite light braking would exceed the battery's limits if the computer tried to use all regen.

Some people look at the ECO display on the dash and draw conclusions about what the brakes are doing, but there isn't any dash display that really shows exactly that. Old-time member hobbit got curious enough to build one once; one of the earlier threads linked above links to it.

A typical stop from a cruising speed will start out with one mix of friction and regen, bend off in the direction of less friction and more regen as the speed comes down, and then bring the friction back in shortly before stopping.

That's not quite as simple a picture as people sometimes want it to be, but making it sound any simpler than it is wouldn't really be fair to future readers who might come and read the thread.

 

If the brake disks have sat wet for a few days, gotten some surface rust, for the first block or two of driving you will audible confirmation that the friction brakes are being used.

 

I suspect the rotors wouldn't last very long if not used much, it doesn't take much moisture in the air to start them rusting.

 

That was one of the things I was attracted to a PRIUS for - that the rotors are lasting for a very long time - in some cases, the useful life of the car.

But then - they don't salt our roads, and I suspect the precipitation isn't the same here as in UK. We do get an extended wet period - for 2 or 3 whole days. And much of our rain is a fine day followed by an afternoon/evening thunderstorm.

Other parts of the country might be different though.

 

Yeah, unless the car has been sitting for a very long time, and I'm talking years here, its just surface rust that will come off with normal braking. Salted roads though are another matter.

I'm actually surprised that they didn't throw on slotted and drilled rotors. Even with the usage that would be seen on a hybrid, I'd suspect that they would still outlast the car.

 

I had a 2001 Ford Mondeo that had stainless steel rotors (I was told) which showed no signs of rust at all. I don't know why this didn't catch on, could it be something to do with the friction properties of stainless steel or just cost ?