NHTSA Tracking Braking Loss on Prius Hybrids

I mentioned the limited slip differential, which can be used on 2wd or 4wd vehicles. There are different designs, but the most basic version uses a "clutch pack" to limit wheel spin.

[ame=http://en.wikipedia.org/wiki/Limited_slip_differential]Limited slip differential - Wikipedia, the free encyclopedia[/ame]

However, these clutches will wear over time, so they will need to be rebuilt to renew the clutches. And the type that works best on FWD (1 way) cars would not help with regen braking (you need 2 way). And they take more space than an open differential (which might not be available in the Prius transaxle). And they cost more than an open differential.

 

Trust your instincts, and save yourself the time by not responding.

 

This thread basically blames the car. I understand that there is an anomaly in the braking system of both the Gen II and the Gen III. I don't want to argue if it is better or worse in either car. What I want to discuss is that a statement an old shop teacher taught me, that as far as I am concerned has stood the test of time, "A poor craftsman blame his tool for subpar workmanship." Don't blame the tool (the car) adjust your driving to compensate. Brake harder the friction brakes will kick in and your stopping distance will not be compromised.

 

Normally, Prius-driver's braking is quite gentle, often using only Regen. It is this Regen that is completely lost for about a second when a micro-skid is detected.

In my opinion, this is NOT good or "best" firmware control of the braking system.

For those drivers who are unaware of this "feature", it could be a significant safety issue.

 

It may not be a "firmware" issue. It may be a mechanical issue. If it is a mechanical issue (due to the open differential) it isn't under active control.

 

"I cannot believe that with Toyota's engineering prowess, they can't solve this without sacrificing the regen braking system in any way."

The solution is called street repair.You're welcome. Call your local government and tell them the streets are dangerously rough.

 

My 4000 + pound CTS stopped much better than my Prius.
I think the stopping distance from 60 to 0 is approx 500 feet on the Prius.

 

"I think the stopping distance from 60 to 0 is approx 500 feet on the Prius."

And you're hyperbole index is off the chart.

 

that is of course, regen stopping distance

 

Except that regen cannot possibly have a "stopping distance" since it disengages below 11 MPH and converts to friction brakes at that point.

"My 4000 + pound CTS stopped much better than my Prius.
I think the stopping distance from 60 to 0 is approx 500 feet on the Prius. "
AJC was making a sarcastic comparison with his Caddy, which of course has NO regen.

 

Tires make a big difference in stopping distance. Brakes are only as good as the friction supplied by the tires. The very same factors that help tires achieve good mileage tend to hurt stopping distance.

Tom

 

u only say that because u have an "old" car. 2010's regen all the time

 

Ummm...no.

Suggest you get it fixed, because the test results on the 2010 Prius are 118 feet from 60mph to 0mph, and NOT close to the 500 feet you estimated. Get your facts right.

2010 Honda Insight vs. 2010 Toyota Prius Comparison Test on Inside Line


Oh, and while we're talking numbers, the CTS has a test stopping distance of 109 feet, from 60mph-0mph. 9 feet difference.

Performance Tested: 2009 Cadillac CTS-V Runs 12.5-Second Quarter-Mile

Coincidentally, the CTS "Sports Wagon" has a stopping distance exactly the same as the 2010 Prius, of 118 feet.


See, this is one of the reasons why web sites like this can be soooo misleading to the average consumer. They see a number like 500 feet, and they actually believe everything they read on the internet. Unfortunately, a great deal of it is simply BS.

 

The brakes on the Prius are not as responsive as the CTS. The Prius feels like the brakes don't respond as fast as the CTS.

"AJC was making a sarcastic comparison with his Caddy" as stated by Darwood. That's correct, only joking - sort of. Still love my Prius.

 

No idea whether the Prius brakes are not as "responsive" as those on the CTS? But who cares about the responsiveness (??), as long as the braking distance is short, and there is no brake fade. That's also why, in most car reviews, any references to "responsiveness" are confined to the handling/steering and to engine gitty-up...and not to the brakes.

CTS sedan 60mph-0; 109 feet
CTS wagon 60-0; 118 ft
Prius G3 60-0; 118 ft

For most consumers, these are the only brake numbers that matter.

 

Regen brakes kick in at the speed of electricity. No mechanical brakes can beat it.

 

And if you really panic brake, the brake assist system kicks in. That will beat human reaction anytime.

Tom

 

I know the the accelerator is by wire. Meaning if electricity is cut there is absolutely no acceleration.

Is braking all by wire too? I assume there is no mechanical connection between the foot pedal and the brake shoe. If the brakes were to fail,and I have not heard of this happening, all the stomping would do no good. Stomping just prepares you to stop again should the electricity comes back up.

Of course, I assume you still have the parking brake. That's connected mechanically, right?

 

It is much more sophisticated than that. Normal braking is by wire. When you press the brake pedal, the master cylinder pushes hydraulic fluid against a "stroke simulator". The presser in the hydraulic line tells the ECU how much braking effort to exert.

If the power brakes fail, solenoid valves in the brake line disconnect the stroke simulator and connect the master cylinder to the front brakes. The rear brakes are cable operated by the parking brake lever.

Tom

 

That's true for Gen 2. On the 2010, the brake accumulator pressure gives power-assist if electronic control fails, and one of the cylinders in the master brake cylinder unit actuates the front brakes while the other operates the rears. That makes the failure mode much better than before (this will be a relief to the few people who experienced fail-safe on Gen 2).

I believe it can also handle a failure in one half of electronic control by allowing manual control of the other half, but I'd have to check the New Car Features again. Someone recently posted the braking section of that document but I can't find it now.

Edit: found the thread, mod had (rightly) deleted the extract from NCF.