Braking...

I've looked at it only briefly on my Scangauge a few times... It only updates about once a second, but if you're not braking too hard, I think it's basically 100% regen down to 8 mph (which is a known cutover point), and then pretty much 100% friction. If you brake hard enough at any point while stopping to engage the friction brakes, I think they tend to stay on, even if the regen could handle it. At least, those are my rather limited, poor observations. Somebody with a different gauge that is capable of more frequent polling or even graphing would probably be a better source.

Personally, I've always wondered if the system takes advantage of the same sensors that measure acceleration/yaw/etc. for VSC in order to get the transition as smooth as possible - applying the brakes at just the right force to match what the regen was providing. Otherwise, wouldn't there be a little bit of a jerk during the transition if your brake pads had worn down, for example, and took a little bit longer to engage than when the car was new?

 

On the horizontal bar graph the first part shows braking regeneration level. When you max. out that meter friction brakes are also being used. You will regenerate right down to quite low speeds, lower than the GII. I see regen. almost to a stop though it falls off quickly at low speeds. Below a particular speed (8 MPH from the above post) you are using friction brakes. Further, above a certain braking force level you are using a mix (indicated easiest by the left part of the horizontal bargraph). I you enter the "panic stop" zone it's 100% friction brakes at any speed. You don't need a Scangauge to see most of this. I'm not aware of any Scangauge code that would show friction brake use directly. You -can- watch regen current.

 

I have to say, having driven a 2006 Highlander hybrid and a 2013 Prius extensively, Toyota really screwed the brakes on the newer Prius. There's a very distinctive lurch when the Prius switches from regeneration to friction braking. The Highlander has an imperceptible switch. It baffles me that the newer car is worse. Then again, the highlander hybrid is a $40,000+ vehicle...

 

I think it's a proprietary formula the magical gnomes under the hood go by.

I thought the bar graph was a good indicator, but since the whole system is computer controlled, I expect it's some formula that weighs your velocity as compared to how hard you press down on the brake pedal. It employes regen at first, but physical braking kicks in as soon as it known regen can't slow you down fast enough...even if regen braking is present the whole time.

I suppose the regen braking is able to simulate friction braking up to X psi on the brake rotors (like any hydraulic braking system). If the pressure on the pedal would = X + 30 psi, the system would automatically engage the friction brakes to ensure that full braking force is made available.

If anything, I'm sure the Prius' brakes are superior to non-hybrid cars. The friction brakes have to be able to do the job all by themselves in the event of regen braking failure. So, you really have a full friction brake system PLUS the regen braking available to bring you to a stop.

 

On the famous chart Google Sheets - create and edit spreadsheets online, for free. line 74 Friction Brake Sensor.

 

You must have a different Prius. I have a soft touch on the brake for best mpg just like on the gas. Its always a smooth transition.

 

I think if your press hard or fast it would go to and stay on 100% friction brakes for safety reasons.

 

I've not noticed a lurch on ours other than a fraction of second before it stops. This seems to be at a far lower speed than transition from regen to friction.

Reducing pressure at the last moment seems to get rid of this but I guess it would be nice if I didn't have to.

 

I've had rough braking and smooth braking. I think a lot has to do with pedal pressure throughout the braking process. I can do a hard stop, and if I let up on the brake near the end, the stop can be quite smooth. I can gradually press down on the pedal and get smooth braking all the time. I may be a "learning" thing the computer has to do. When in doubt, it applies the friction brakes harder than really desired or needed.

 

Could be I'm not that attentive, but I've never noticed ANY transition.

Maybe cause you have the other vehicle as a base case, but seriously, it's jake by me.

 

I think brakes are usually sufficient to cause a skid on most surfaces for most cars. (Maybe I'm wrong, I don't go around trying to skid cars on clean, dry pavement very often. And cars these days will avoid letting you skid anyway.) So even if the Prius has better brakes, it's still limited by the tires' traction, and wouldn't benefit from the brakes' ability to dissipate kinetic energy more quickly.

 

I find that people I drive with have two different breaking styles that work equally well in a 'traditional vehicle'.

#1 Gradually scrub of speed and then squeeze slightly harder over the last meter
#2 Reduce most of your speed targeting one meter before the stop point, then slightly relax brake pressure towards the end.

I find the Prius' logic can't handle method 1 and causes the famous hybrid lunging, whereas it responds to method 2 really well, it's never lunged once.

Is anyone aware of what style they use?

 

Both.

 

Both and both give nice smooth deceleration to the full stop. The difference is how long you have to stop and how well you aim for that last few feet. Sometimes you can almost come to a full stop with just "coasting" since that includes a small amount of regen braking.

 

I can say from experience in my younger days that all cars with properly functioning brake systems will be able to lock up all 4 tires in a panic stop (ignoring ABS for the moment) and it is the tires that determine stopping distance. Brakes are generally over-designed so they can easily stop a fully loaded car from high speed. If you can push the brake pedal to the floor and the tires don't lock / activate ABS, you have a problem in your brakes.

I'm guessing the regen cuts out in a panic stop so allow better emergency handling. Regen only works on the front tires, while friction brakes work on all 4. The front tires can't steer if they're already at their traction limit due to braking.

 

In the Prius, my braking style is to keep the CHG bar around 80% or so of its capacity, since regen is supposedly ever-so-slightly more efficient at high loads. (Regen reportedly has some fixed amount of efficiency loss, plus loss proportional to the amount of regen; amortizing that fixed loss over a larger amount of regen thus yields a higher percent efficiency.) At highway speeds, filling the CHG bar is relatively gentle braking; as I slow down, I press harder to keep the CHG bar filled. As I'm reaching a stop, I then reverse and let up on the brake a little bit, to come to a nice, gentle stop; by that point, it's all friction anyway.

 

I use B mode when exiting a down ramp. Not all the time, but I felt it would reduce the wear of the brake pads. At least twice, I've forgotten to switch to Drive mode, although not for very far. Does this in any way hurt anything? In addition, is B mode to be used at only certain speeds?

 

Unless it is a Very steep and Very long ramp there is no need to use B. Just keep the HSI in the right 3/4 of the braking area and there will be no friction braking.