Who is the dealership and what city are they located in?

 

It seems the brake issue is most in 2008 models for some reason.
As far as I know 2008 models, the brake padel is not adjustable like 2009 models if I am not mistaken. Correct me if I am wrong.
Just my 2 cents

 

Are you referring to the height adjustment on the pedals in the '09's? In the hybrids, there is no memory positions for pedal height or seat position...due to additional weight. A very lacking feature if you ask me.

 

"...I notice that the brakes don't hold without more pressure on the pedal than I am accustomed to having to use. "

in a conventional vehicle you need to rev the engine to pressurize the torque converter to get the vehicle to move (typically) or rev and release the clutch. Remember at idle your ICE is producing a VERY limited (like zero) amount of HP and torque. In our vehicles you have two electric motors that are always producing torque unless they are completely off. I don't know the sequence of the motors when the vehicle is stopped and drive is engaged and perhaps yours needs to have the controller adjusted as it may be feeding too much elec. to the motors. again I don't know. on mine it will creep if I let my foot off the brake, most noticeably when its cold and the ice is running.
Also remember that in a conventional car when you accelerate you are generating MINIMAL horsepower until the RPMs come up. In ours you have 180 HP instantly on tap due to the nature of electric motors as they generate their rated horsepower as soon as engaged, its not linear like an ICE. That's why you need to find the "sweet spot" in the acceleration curve to get max acceleration during your stoplight racin, and flooring the throttle (the conventional ICE style of racin) doesn't work as well as 3/4 or so throttle to use both the ICE and the instant 180 HP in unison. remember also that we have 332 conventional HP AND 180 HP Electric so technocally the HP rating of our cars is 492!
Of course drag racin is for kids as we all know that life begins at 400 knots 50 feet off the deck!

 

Here here, and well said. I needed a little reminder of the principals involved here. And while I think I have a great understanding of the hybrid drivetrain and wisdom involved...wa la, I absolutely overlooked the comparison between conventional and hybrid in this scenario. You are right on. You have abundant torque available with electric motor drive. Something this or any ICE can't hope to ever achieve. The HP/Torque curve...gotta have it in the ICE and it doesn't hardly do anything until you reach 4000RPM's or so depending on the powerplant. MG1/2 give you almost all of their torque instantly.

Your explanation is perfect and I see now why my vehicle (any hybrid or EV) starts to roll without positive brake pressure. And while I recognized it immediately and cautioned my wife (and myself) to pay attention to movement when stopped as well as make sure you firmly apply brake pressure, I did not recognize why. I am not sure my tech's have enough experience to reprogram a controller plus don't you expect that is software driven and may not be adjustable by a normal service tech. Our Prius does not exhibit a tendency to do this creep for lack of a better term.

I have not seen published HP ratings on MG1 and MG2, only that they are 60kW motors. I know you can convert this but it is variable based on other parameters. Is that correct? Our setup is 90HP each, and if so, can you direct me to that information?

Again, thanks for helping me remove my head from my backside so I could see the light and know why my foot is on the brake!

 

Jet: depending on how hard you push on the brake pedal, the electric motor torque is modulated. Light pedal and some torque is still applied to the driveshaft. Just in case you need to move or creep ahead in traffic.

Push real hard and ZERO torque is applied. So from a buried brake pedal... as you release the torque is increased. To mimick the missing torque converter.

Mel: the Prius isn't programmed for the boat either.

I'm sure some of you jet jockeys could measure the current and infer the torque.

Pushing a little harder on the brake pedal at long stop lights can save ~ 400 watts for the time stopped. The brake pump is 12 volts and only kicks in to replenish the accumulator. So a steady hard pedal saves energy.

About the motors and launch power. The 120 kW can not be supported by the battery. So motor launch power is a bit clipped.

 

Marty,
thanks a lot for your feedback very informative indeed.
I guess This explains the connection between the 12v battery and brake failure issue???

 

Oh yeah...look at this! One of my buddies on the yamaha jetboat forum who is a dino power only guy told me the Prius made a poor tow vehicle, so I pimped him with this pic.

Now if I could only figure out how to post a picture on greenhybrid without having to load them to an online forum. I figured out the avatar, the signature, and can post an attachment but not put the photo in the body without having to click an attachment? I pulled back to go up and back farther to go down...what am I doing wrong.

 

There seems to be some variablity not calibrated out at, or near, a stop. Mine is perfect. Not a complaint from the wife or other females that have driven it. And we all know the uterus increases the sensitivity to defects in automobiles.
Mine will roll back on a shallow hill with no foot on any pedal. It does creep nicely in bumper-to-bumper and a light foot on the brakes will hold it still, even on a slight downhill. I can feel the electrics cut in and out when modulating the brake pedal.
I wish we had an extra 180hp added to the ICE, but that battery pack would need to be a lot bigger...
Still, this Tahoe will eat other cars and trucks for lunch. I just wish someone in GM powertrain would fix the 1-2 upshift at full throttle. It feels like you are hitting a wall before it shifts. Even my 7 year old complains about it...

 

I have been re-reading the brake fail issue. Much discussion centering around the vacuum powered hydralic brake booster that we don't have. It is mentioned that we have an electric booster. We do, a 12v electric brake booster. It is not on the master cylinder which we DO have as Jet1 posted 3 pictures of it BUT WITHOUT the normal big round vacuum powered hydraulic brake booster behind it.

When I was questioning the tech yesterday about my possible brake issue, he didn't know where it was and openly admitted that while he had been trained on the hybrids, he didn't remember everything. The other tech might be better than that, I hope. But when we found the booster, it was back under the truck, mounted to the cross frame support just aft of where the driveshaft exits the transmission. It does not look like a brake booster and it basically an electric pump to supply hydraulic boost pressure that is in a large square machined aluminum box. It can be identified by the large hydraulic lines that connect it to the master cylinder on the firewall.

I was thinking about how you could have a loss of boost. Ok, it is 12v, so you need 12v power. trock55 doesn't mention engine fail, just stabiltrack and check engine warning I believe he said. You know the booster is still powered when the ICE is in Autostop, so I suspect that even if the ICE failed, as long as your key is still in RUN, you have brake boost. Heck, if someone has the maintenance manuals, check and see if it is hot in the acc position. That doesn't matter but just curious. I will post a picture of the electric booster if someone will tell me how to put the picture up without an attachment and online photo gallery. Oh, I bet I could load them into the photo garage here and upload from there couldn't I?