new 2010 III - brakes questions

From what I've read on this forum, the majority of your braking is regenerative. That's why the brakes last 100k+. I seem to remember reading that the last5-7mph you are using friction brakes under normal or gentle pressure. Under hard breaking, it's got to be mostly regular brakes and yes the pedal feels different under varied pressures, it is normal.

 

It would be nice if one of our cool geeky members on PC could hack/tap into the ECU and build a DIY LED indicator giving you real time feedback indicating if you are in regen vs regular braking. Like, green if in regen, and red if using regular breaking.

For now, but not as precise, I just monitor the HSI and make sure the CHG bar (that indicates regen) is not a FULL bar, but rather a partial bar.

 

Keep both eyes on the road!

 

Get a ScanGuage... it tells you whether there is a charge or discharge.

 

Getting more squishy as it is depressed doesn't sound right. I'd have a dealer check it.

 

The dealer should verify if the brake recall was performed.

 

In normal operation (not failure fall-back mode), all brake "feel" is produced by a piston and spring. Prius braking is done "by wire", meaning the brake pedal is not mechanically operating the brakes. The hydraulic fluid from the master cylinder doesn't have anywhere to go, so Toyota engineered a "stroke simulator", which is just a piston and spring. You press the brake, the brake moves the hydraulic fluid, and the hydraulic fluid moves the stroke simulator. That's why it feels weird: you aren't really feeling the brakes.

In the even of a system failure, special valves fail over to connect the hydraulics directly to the brakes, reverting to normal mechanical brake operation.

As for the question of how much braking is regenerative, the answer is all of it, up to the limits of the battery to absorb electricity. Gentle braking will almost always be totally regenerative.

There are three exceptions to this general rule: low speed, panic braking, and ABS. At very low speeds (under 10 mph, roughly) there isn't enough electrical generation to effectively regenerate, so the Prius switches to friction braking. This is the funny feeling you get at around four mph.

During a panic stop you don't have time to mess around with regeneration, so the system goes directly to assisted friction braking.

Likewise when you lose traction during braking. Regenerative braking works with only the front wheels, so at the first loss of traction the braking system switches to ABS friction brakes. The loss of traction and ABS action produces the much maligned "brake dropout" or "shooting ahead" that people complain about in numerous posts. If you feel this during braking, keep pressing - you *will* stop.

Tom

 

Tom, does your Michigan winters cause your Prius ABS to activate much? If so, how is the stability,handling and straight line lane control? Here in Carolina I've not yet had a chance to see ABS in action, though we get some ice and snow once in a while.

 

I have a Gen II, so take my answers with the appropriate grain of salt. My model has VSC.

Short answer to your question: yes. I probably should say YES, with all caps, since we slide around all winter.

My 2006 Prius with VSC is the best handling winter car that I have ever owned, and that includes a Jeep C-J5, a four wheel drive Subaru, and a Ford Aerostar with electronic four wheel drive. The Prius can't wade through deep snow, and traction control can be a problem, but when it comes to handling it beats them all, hands down.

I have to remind myself that the roads are slippery. The Prius does such a good job evening out braking and compensating that you don't really feel the conditions.

Obviously you need good tires. The OEM Goodyear Integrity tires were a disaster. I gave those away the first winter and bought some real tires.

Tom