Engaging Engine Braking (B) Function

and if you use the regenerative braking correctly, you never actually engage the pads.

 

The pads are always used from 7 MPH to 0.

 

Correct... but at that point, the actual wear is extremely minimal.

 

friction brakes are also used even at speeds above 7mph when really needed to assist regen braking. The computer ultimately decides when to use it.

 

Only if you press the pedal down hard enough. If you just leave it in the regen range it won't come on until below 7 mph.

 

Exactly

 

So the computer doesn't decide... the user does...

 

not really.. the user decides to just step on the brake, the computer decides when to engage the friction brakes depending on the demand and according to many variables. the user doesn't know how soft or how hard one has to step on the brake for it to engage.

i've experienced it many times taking downhill corners at higher speed than normal. even if i step on the brakes just slightly, the friction brakes engage and normal regen braking (not B-mode) rates decrease (less amps taken in than normal) relying more on the friction brakes to do the job. so some variables are at play beyond the user's control.


i have had to engage B for a while then back to D for normal regen rates to come back without assist from the friction brakes. I now take that corner slowly if i want more regen than momentum.

 

It changes force when you get past the regen bar.

 

i don't have a regen bar but i get what you mean as i've driven a gen3 before. so it may now look like that a user can elect to use the pads if he steps on the brakes enough for the regen bar goes past the line. but still, there are instances where the brake pads come alive on their own.

 

The c, like the Gen III, does have the HSI, so we do get the regen bar and we do have a lot of control over when the brakes are and aren't used. They don't have a mind of their own. If you stay in the regen area, are in D and are above the threshold speed, you'll be on regen brakes alone.

 

hi rob, just saying the ECU does play a part in letting friction brakes operate especially when the wheels are turned.

When you happen to pass by Mosman (going north bound) and down that "S" bend to Spit Bridge, try going a little faster (45-50kph) not even at the limit, you'll notice a slight change in pedal feel as you step on the brake slightly to control your descent. Watch the scangauge BTA drop from -30, -40-ish to only -12, -14-ish all the way down as you feel the pads grab the rotors and do most of the braking from there. Try to glance if the regen bar jumps past regen area quickly when the friction brakes jump in or if it still stays within the regen area.

 

Can't say I've noticed that before, but I'll definitely try that next time I'm there or a suitable equivalent.

 

Which is why we're in the "C" forum.

 

Maybe it's different on your 2007.

 

yeah could be.. that's why i'm here in the C forum to find out if the C does it too as it's practically the same drivetrain. wouldn't you like to find out as well? if you have a sharp downhill bend that you usually take in D with a bit of foot on the brake, try going a bit faster around that bend with your foot still on the brake. see if something changed in the way the car feels going down.

 

The user can control how fast he wants to slow down by the pressure on the brake pedal but he has no control on the execution part.

When user depressed the brake pedal, he is just sending a request and the Skid Control ECU will calculate the total braking force needed based on the brake regulator pressure and brake pedal stroke. After calculating the required total braking force, the skid control ECU sends the regenerative braking force request to the power management control ECU (HV CPU). The HV CPU replies with the amount of regenerative braking force that is possible. The HV CPU uses MG2 to create the minus torque (deceleration force), thus carrying out the regenerative braking. The skid control ECU controls the brake actuator solenoid valves and generates the wheel cylinder pressure. The pressure that is generated is what remains after the actual regenerative brake control value has been subtracted from the required total braking force.

Hydraulic Brake Force = Total Brake Force - Regenerative Brake Force

Brake pad will be used if the regenerative brake force is smaller than the total brake force. If user ease up on the brake pedal, the total brake force will be reduced and the braking can be handled entirely by regenerative braking. However, if the SOC is near the upper limit of 80%, HV CPU will restrict regenerative braking and even the slightest brake pressure will cause the brake pad to be used.

If you're on level ground or down a gentle slope, most likely regenerative brake force is enough and ICE may not need to be spun.

If you're on a very steep descent, even on a slow speed, the ICE need to be spun to help to slow down first. If that is still not enough, hydraulic brake may have to make up the shortfall. If you 're in D mode, system will use hydraulic brake directly.

Vincent

 

Contextually, I was saying the user decides when to engage the friction brakes... which is true. If you don't push it down past the regen line, the frictions won't engage until you get below 7 mph. Therefore, if you the user don't allow the line to drop, you are in complete control.

 

great info in this thread. thanks

 

I'm not sure brakes are engaged if you press them hard enough to show "full" regen. Or on the other hand, that they're not being apply when the dash shows less than "full" regen.

First off: the regen display is just rudimentary, may not be showing the full regen range. And there's an unsubstantiated (at least I think) assumption being made: that there's no brakes used if there's only partial regen showing on the display.

All in all though: I've never had a car with front rims anywhere near as clean, the brake pads can't be seeing much use.