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regenerative brakes vs disc brake life


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41 replies to this topic

#21 OFFLINE   rbort

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Posted 19 January 2015 - 06:58 AM

Hmmm...interesting.  Sounds like what's happening is that when you brake regen the front wheels use the EV motor to slow down if you brake lightly but the rear wheels always engage the brakes with every touch on the brake pedal.  You're regen braking alot (for long times to build charge) so you're dragging the rear brakes lightly with every stop.  If you brake harder than regen then the front pads kick in.

 

In this case if you use L to slow down your brake life is going to be longer than using the brake pedal to slow down in D with regen.  That would be the only way to make the rear brakes last longer.  The fronts will always last longer as long as you don't brake hard.

 

Everyone agree?

 

-=>Raja.









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#22 OFFLINE   drdiesel1

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Posted 19 January 2015 - 08:37 AM

Hmmm...interesting.  Sounds like what's happening is that when you brake regen the front wheels use the EV motor to slow down if you brake lightly but the rear wheels always engage the brakes with every touch on the brake pedal.  You're regen braking alot (for long times to build charge) so you're dragging the rear brakes lightly with every stop.  If you brake harder than regen then the front pads kick in.

 

In this case if you use L to slow down your brake life is going to be longer than using the brake pedal to slow down in D with regen.  That would be the only way to make the rear brakes last longer.  The fronts will always last longer as long as you don't brake hard.

 

Everyone agree?

 

-=>Raja.

 

Not at all :wink:



#23 OFFLINE   rbort

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Posted 19 January 2015 - 02:49 PM

OK, what's your explanation?  I'm all ears  :wink:

 

-=>Raja.



#24 OFFLINE   dr61

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Posted 19 January 2015 - 07:00 PM

Most conventional cars these days have computer control of front-rear brake pressure.  Several people have remarked to me their amazement that their rear brake pads have worn faster than their fronts on their relatively new ICE cars. From what I have read, on many new cars the ABS computer sends more brake pressure to the rear brakes when the driver uses light to moderate brake pedal pressure. When the driver demands quicker stops the computer immediately shifts more pressure to the front pads, as that stops the car more effectively.  Since most drivers brake moderately most of the time, the rear brake pads wear faster.  This is the opposite of the way it used to be with the older brake proportioning valve systems.  The rationale of these newer systems is to keep front brake temperatures lower so there is more reserve for emergency stops.

 

As for how our Energi conventional brake system works along with regen, I have no specific knowledge.



#25 OFFLINE   jdbob

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Posted 19 January 2015 - 09:23 PM

A few items from the workshop manual:

 

Electronic Brake Force Distribution (EBD)

 

On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module uses wheel speed sensor inputs to evaluate rear wheel slip. Once the rear wheel slip exceeds a predetermined threshold, the ABS module commands the HCU to close the appropriate isolation valves to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels. If the rear wheel slip continues and exceeds a second predetermined threshold, the ABS module commands the HCU to open the dump valves to decrease the rear brake pressure and allow the rear wheels to recover. A slight bump may be felt in the brake pedal when EBD is active.

 

Regenerative Braking Mode

 

The ABS module determines the amount of braking torque necessary and sends that information to the PCM along with the current threshold for ABS intervention. The PCM determines how much braking torque the electric motor can provide based on the High Voltage Traction Battery (HVTB) state-of-charge and sends this information back to the ABS module. At the same time, the electric motor is switched to a generator which supplies the determined amount of braking torque. Based on the amount of braking torque the PCM can deliver, the ABS module determines whether it is necessary to apply the friction brakes or if the brake torque from the electric motor is sufficient to safely stop the vehicle.

 

Friction Braking Mode

 

Under some circumstances, the braking torque generated by the electric motor is insufficient to bring the vehicle to a safe, controlled stop and requires the assistance of the conventional friction brakes. Additionally, the state-of-charge in the High Voltage Traction Battery (HVTB) may not allow for regenerative braking to take place or the vehicle may be experiencing an ABS, stability control event.

 

In these instances, the ABS module activates a mechanical relay which supplies power to a solid state relay that activates a vacuum pump. At the same time, the ABS module sends a PWM voltage to a solenoid mounted on the brake booster. The solenoid allows vacuum from the vacuum pump to enter the brake booster which moves the booster push rod and applies the conventional brakes.

 

During certain braking events, the friction brakes can be applied directly by the driver. The brake booster push rod is equipped with an adjustable stop, once the brake pedal travels far enough to engage the stop, the brake booster push rod is forced into the master cylinder and the conventional friction brakes are applied.


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#26 OFFLINE   rbort

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Posted 19 January 2015 - 09:56 PM

Thanks for the cutout from the manual.  So the question is, does the first sentence always apply?

 

On initial application of the brake pedal, full pressure is applied to the rear brakes

 

If so then it would agree with my assessment as to why the rear brakes are wearing out first.

 

-=>Raja.



#27 OFFLINE   jdbob

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Posted 20 January 2015 - 12:26 AM

I would hope that the rear brakes would only be applied when regenerative braking is not sufficient. But I don't have any information to back up that hope.

 

Here's an article about braking on some of the older Ford hybrids. Of course changes have been made but it might give some idea regarding Ford's thinking: http://www.brakeandf...hybrid-braking/



#28 OFFLINE   fotomoto

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Posted 20 January 2015 - 06:13 AM

Electronic Brake Force Distribution (EBD)

 

On initial application of the brake pedal, full pressure is applied to the rear brakes. 

 

This sure sounds like an absolute statement to me.  No ifs, ands, or buts about it; i.e., no exceptions.   :ohsnap: Rear brakes are always applied anytime you use the brake pedal.   This would also explain the smooth transition from regen to friction braking.



#29 OFFLINE   RubyMax

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Posted 20 January 2015 - 06:40 AM

I had a 2007 Jeep Wrangler Unlimited with 4 wheel disc brakes.  The ABS wasn't what reduced life on the rear brakes first, it was the traction control. The pads were shot at 20K miles.



#30 OFFLINE   rbort

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Posted 20 January 2015 - 06:54 AM

Well, goes back to what I said above, rear brakes are applied with braking, front wheels use regen to brake.  If you press harder front brake friction pads kick in as well and also do so at the end if you don't anyways at 5 mpg in D.

 

This goes on to say if you brake with L all the time, your rear brakes will last longer than using D with light braking to stop each time.  People are experiencing rear brake pad wear, this is the logical explanation for it.  Gary would be a known exception to this, as he "drives without brakes" using L all the time so his rear brakes should last longer than people who drive the car "normally" with D and regular braking as the car expects you to do it.

 

We could probably confirm this if Gary or someone else who uses L all the time to brake would take off the rear tire and just measure the remaining brake pad thickness with a ruler in mm for example (less work than taking the brake caliper off to measure with a vernier caliper).

 

-=>Raja.


Edited by rbort, 20 January 2015 - 06:59 AM.


#31 OFFLINE   stevedebi

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Posted 20 January 2015 - 09:37 AM

Well, goes back to what I said above, rear brakes are applied with braking, front wheels use regen to brake.  If you press harder front brake friction pads kick in as well and also do so at the end if you don't anyways at 5 mpg in D.

 

This goes on to say if you brake with L all the time, your rear brakes will last longer than using D with light braking to stop each time.  People are experiencing rear brake pad wear, this is the logical explanation for it.  Gary would be a known exception to this, as he "drives without brakes" using L all the time so his rear brakes should last longer than people who drive the car "normally" with D and regular braking as the car expects you to do it.

 

We could probably confirm this if Gary or someone else who uses L all the time to brake would take off the rear tire and just measure the remaining brake pad thickness with a ruler in mm for example (less work than taking the brake caliper off to measure with a vernier caliper).

 

-=>Raja.

That is not how I read it Raja. The shop manual has to be read as a whole. The regen braking section specifically talks about determining if the vehicle can stop safely using regen. I believe the first section on the braking distribution only applies after the computer has determined that physical braking is required. At that point the rear pads are used first. So yes, the rear would wear sooner. But the rear pads are only used after regen is completed.

 

It would be vastly wasteful for the system to apply the rear brake pads when the energy could be recaptured via regen. Nobody would do that.



#32 OFFLINE   dr61

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Posted 20 January 2015 - 12:46 PM

I agree with stevedebi.  I don't think the rear friction brakes are applied until the regen braking is at max.  The rear friction brakes are the first friction brakes to be activated by the EBD system, hence they will wear faster (unless the driver is typically braking very hard).



#33 OFFLINE   rbort

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Posted 20 January 2015 - 12:55 PM

I hope you guys are right, would certainly be better than wearing the rear brakes all the time.  I guess it would mean that reg braking is only 2 wheel braking per say.

 

-=>Raja.



#34 OFFLINE   GaryG

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Posted 20 January 2015 - 03:58 PM

The article is right on. I've own an '05 Escape Hybrid. Ford made a lot of changes in the '09 Escape Hybrid, so I gave my Son my '05 FEH when I bought my '09 FEH. Ford changed the braking system in the '09 and eliminated L regen, so I had to rely my brake pedal skills. The '13 C-Max Energi has the best regen system out of all of them. My brakes pads on all my Hybrids looked new in the FEH's when I sold them, and my brake pads are still new in my '13 NRG.

 

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#35 OFFLINE   12mile

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Posted 09 February 2015 - 03:40 PM

Followup to my post of 1/19/15. The original PA inspection report listed the front pads at 11/32 and the rear pads at 3/32. Dealer advised to consider rear pad service soon.

I returned to the dealer today for the rear brake work. Dealer called me into the service bay to show me the pads with the wheels pulled off. Pads were good.

The dealer appologized for the error which they chocked up to a transcription error on the inspection report.

I am very happy to learn I am not burning through rear pads every 25 thousand miles. Rear pad wear does not seem to be much of an issue.

Loving our C-Max Energi!
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#36 OFFLINE   rbort

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Posted 09 February 2015 - 08:39 PM

Good to hear 12mile.  I should pull off my rear tire and check the pads --  Well, next time I rotate the tires at 30k miles I'll do that, check the front and rear pads at the same time to see how much looks like if left in there.  

 

I rotate the tires every 10k miles so I should be able to judge by what I see if they will last another 10k miles or not.

 

-=>Raja.



#37 OFFLINE   drdiesel1

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Posted 09 February 2015 - 11:31 PM

Good to hear 12mile.  I should pull off my rear tire and check the pads --  Well, next time I rotate the tires at 30k miles I'll do that, check the front and rear pads at the same time to see how much looks like if left in there.  

 

I rotate the tires every 10k miles so I should be able to judge by what I see if they will last another 10k miles or not.

 

-=>Raja.

 

 

 

Considering you have no idea what measurement you started with, it's nothing more than a guess :wink:

I have a new set of Ford OE front and rear pads for my car. I'll open the box and have a look :camera:



#38 OFFLINE   drdiesel1

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Posted 10 February 2015 - 12:40 AM

Front pad measures just over 7/16 and the rear measures just under.

I had to use a tape measure. All my tools are at work.

 

Here's two images. I would say the difference is about 1/32nd front to rear.

 

 

Attached File  front-pad.jpg   134.11KB   1 downloads

 

Attached File  Rear-pad.jpg   126.99KB   0 downloads



#39 OFFLINE   Tom_NC_1

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Posted 10 February 2015 - 05:53 AM

Thanks drdiesel1 that gives me a good reference point. At my 20k mile free first service, the report from ford service showed 6/32 for all 4 tires. Looks like it could be along time between brake jobs. 


Edited by Tom_NC_1, 10 February 2015 - 03:59 PM.


#40 OFFLINE   rbort

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Posted 10 February 2015 - 11:24 AM

Thanks Dr. Diesel, the pictures are dark need the flashy thingy but you already said what they are so its good to know.

 

Front = 7/16 or 14/32

Rear = 6.5/16 or 13/32

 

Tom, you're at 6/32 now?  That means you're more than half way gone in 20k miles?  Sounds like you'll need to change them by 30k miles if that is the case unless you're talking about tire treads and not brakes?

 

-=>Raja.


Edited by rbort, 10 February 2015 - 11:26 AM.









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