well im wondering how does the regenerative braking system work. does the prius use a combination of brakes and regen at the same time, like say 20 % braking and 80 % regen? or does it just use regen.
It uses only regen down to about 7 mph, then switches to friction only. There are two exceptions: 1) a panic stop situation cause the Prius to use friction only, and 2) once the battery state of charge is too high, the Prius will switch to friction. Engine braking occurs in B mode. Tom
<div class='quotetop'>QUOTE(statultra @ Jul 25 2007, 04:20 PM) [snapback]484977[/snapback]</div> Yes, yes, and yes. When the Prius can get enough braking power from regen only, it uses regen only. When the Prius needs friction brakes, it uses friction brakes. When the Prius decides that a combination of friction and regen suits the situation best, it uses the appropriate combination. More specifically: In "panic stop" situations the prius will engage the hydraulic friction brakes. Below 7 mph, the Prius uses friction brakes. In coasting, or soft braking situations when the battery isn't fully charged the Prius will use regen. I've heard that there is some amount of engine braking that occurs as well (especially if the battery is fully charged), but perhaps someone with more knowledge can chime in on that one. <div class='quotetop'>QUOTE(qbee42 @ Jul 25 2007, 04:24 PM) [snapback]484980[/snapback]</div> Is this true? I'm nearly certain that I read somewhere that with a firm enough pressure on the brake the Prius uses Max regen (100 amps?) plus enough friction to make up the difference. Additionally I thought I read somewhere that when the battery SOC is too high, the Prius uses some form of spinning up the ICE to assist in braking. Of course I suppose some of these answers probably depend on whether we are discussing pre 2004 or post 2004 model year.
i believe regen depends upon the position of the brake pedal and deceleration rates, the brake switch also has a part in this im asking these questions because i have issues with the caliper making a noise during deceleration, the regenerative braking noise is a bit higher, sounds like a rotor or something.
Your noise seems abnormal. I would have it checked. I've never had a noise with braking, regardless of pedal pressure. I've had my Prius for over a year and a half and I certainly know about regenerative braking, but it even surprised me the past few days. Part of my trip to Hybridfest was through the mountains of Virginia and West Virginia. I could see on Can-View that continuous moderate brake pressure coming down the mountain increased state of charge by 1% every few seconds. A minute's worth of such braking added 10-15% if the battery had the head room to accept it.
<div class='quotetop'>QUOTE(Danny Hamilton @ Jul 25 2007, 05:32 PM) [snapback]484986[/snapback]</div> I was trying to simplify the answer, just giving the basic cases. Yes, the regen is limited by the capacity of the MGs and the ability of the traction battery to absorb the energy, which will vary by temperature and SOC. The 100 Amp figure is a good rule of thumb. After that, the Prius will apply hydraulic friction brakes if more braking force is needed. I didn't mean to imply that B mode was the only time that engine braking is used. B mode forces engine braking, but the Prius will engage engine braking as needed when regen maxes out. Regen is also limited by traction. Only the front wheels (the driving wheels) are used for regen, so traction can be more of an issue than with friction brakes. Sometimes you will see the traction control engage during regen braking. Bouncing over tracks or a pot hole while braking is a good way to see this happen. Also true about the model year. What I've said applies only to the post 2004 models. Tom
<div class='quotetop'>QUOTE(qbee42 @ Jul 26 2007, 09:20 AM) [snapback]485344[/snapback]</div> I saw this too during my descent from the mountains. SOC got as high as 82%, and B mode was forced until some of that charge was bled off.
could a bent rotor cause noise during regenerative braking? the weird thing is when i shift the car into neutral theres no noise during braking, but ONLY when the vehicle is decelerating with regen the noise occurs, also it has a brand new driveshaft, and wheel alignment was done at the toyota dealer.
<div class='quotetop'>QUOTE(statultra @ Jul 26 2007, 06:30 PM) [snapback]485748[/snapback]</div> "hobbit" in his analysis of braking system operation, noted that as part of the braking action, as soon as you push the brake pedal, there is a "pulse" of hydraulic pressure to get the pads ready for friction breaking, even if they are not used. If you have any distortion in the rotor, this is sure to make a lot of noise on any braking with an uneven rotor. http://techno-fandom.org/~hobbit/cars/bp/ http://techno-fandom.org/~hobbit/cars/brkjob/ is the link to the details. Now the real thing to check is the return pressure springs. Unless they are mounted correct and returning the pads upon brake release, then you are setup for agitating noises.
"Now the real thing to check is the return pressure springs. Unless they are mounted correct and returning the pads upon brake release, then you are setup for agitating noises." Ummmm..... I hate to seem like a know it all but.... There is no such thing as return pressure springs on disc brakes. The pads are pulled back off the rotors by a combination of the rotors pushing the pads back and the square rubber seal around the caliper piston which is slightly distorted upon application and when it returns to its normal position, it pulls the piston back slightly. This is why disc brakes are inherently slef adjusting. The best way to check for an uneven or distorted brake rotor is to drive at 40-50 mph and then (check behind you first!) give the brake pedal a solid hit and hold it tight. If the steering wheel seems to wiggle back and forth in your grasp, have the rotors checked. If the rotors have thickness variation or are warped, the steering wheel will transmit the vibration under hard braking. This works on all disc brake systems. If you feel a vibration more in the "seat of your pants" have the rear brakes checked.
<div class='quotetop'>QUOTE(Bear68 @ Jul 26 2007, 08:43 PM) [snapback]485826[/snapback]</div> Actually a good point. Calling them return springs is a bad term. I am refering to the the springs that clip in and prevent rattling. I've made a mistake once in reinstalling one and was rewarded with rattles.
The rotor-runout test is unlikely to work in a prius, for two reasons. 1> hydraulic braking is entirely by-wire, handled by the apply/release solenoids for each wheel, and there's no way for pressure variations to get back to your foot, and 2> there is very little "road feedback" in the steering system. What might work is hanging a scope off the various pressure sensor inputs at the ECU and watching for a lot of variation, but be really careful there since they're fairly high-impedance devices. . I see a little bit of pressure variation during braking in the rear sensor I tap sometimes, but not enough to worry about, I don't think.. . _H*
<_< Actually, Hobbit, the Prius does still have a mechanical (fluid + metal linkages) connection to your foot pedal in case of catastrophic electrical failure. All Toyotas do. Also, even though the power steering is electric and has a somewhat reduced road feel, you can still feel a pulsation in the wheel if it is severe enough. If the rotor variations are not severe enough to be felt, then you wouldn't have to worry about it anyways. B)
what about if i switched the right side rotor ( the side that makes the noise ) to the left side and see if the noise occurs? is that a possibility?
yes its that whining noise that you get on regenerative braking, its much louder and eminates from the right front of the car, maybe i should take a video so you guys get the idea
