TCH Regenerative Braking Tech - GreenHybrid

vioarc · #1 (**permalink**) 06-26-2006, 10:28 AM

The brakes on my TCH work well, but I'm fuzzy on the tech side.

After reading several references posted here about the TCH's anticipated long brake pad life, I found this link:
http://www.hybridsynergydrive.com/en...e_braking.html

It appears to show that the brakes on each of the TCH's four (4) wheels are typical hydraulic brakes that get used less than in conventional systems.

The "regenerative braking" is actually performed by the Synergy drive, not the brakes.

Controls engage the hydraulic calipers, pads and discs only when needed.

Further clarification / correction will be appreciated.

Droid13 · #2 (**permalink**) 06-26-2006, 02:10 PM

Yup, that's exactly the point. Instead of wasting energy (that's already been put into the car to get it moving) during braking by converting momentum to heat (friction between the brake pads and the rotors), the electric motor is used to slow the car down resulting in the energy being converted back to electricity to charge the battery instead. The car's computer decides how much the generator vs. how much the brake pads control speed for each given situation.

I don't know how efficient it is (how much energy is actually recaptured compared with what went in to get the car moving), probably not a whole lot, but better that heating rotors and making brake dust. Plus, it does sound cool! As I habit, I try to feather the brakes when appropriate in thinking that I'm mostly slowing by the electric motor and not using much, if any, brake pads in the process. When you feel the car just about to come to a stop, I believe you can feel when the motor lets go and only the brakes are working (around 2 or 3mph I think).

Freeze · #3 (**permalink**) 06-26-2006, 08:18 PM

I'm amazed at how smooth the brakes are on the TCH. I'm not a mechanic, but I suspect the TCH is always negotiating a balance between the two systems, thereby elimating a crossover problem. I'd really like to get some miles on the car between brake jobs as I'm always getting new brakes on my Honda Odessey.

lakedude · #4 (**permalink**) 06-26-2006, 09:30 PM

I'm guessing this is one area the TCH has the gen 1 HCH beat completely. The HCH does more and more regen the harder you hit the brakes BUT the regen quits somewhere under 20 miles per hour and it is not smooth. It feels almost like your power brakes quit working. Of course you get used to it but the first couple times are alarming.

Douglas · #5 (**permalink**) 06-26-2006, 09:48 PM

Try this small experiment: (do this on a quiet street with no traffic).

With the display showing the energy transfers...

While gliding (no energy transfer to/from the battery), press the brake pedal (with your left foot).

You will note that you will slow down faster, but no energy is recovered.

This proves (to a point) that there is no regeneration caused by the brakes in the Synergy Drive System.

Regeneration occurs when you lift your foot off the 'go' pedal. (It's not a gas pedal anymore, nor an accelerator pedal, but it does make you 'go'!).

Cheers, Doug

Droid13 · #6 (**permalink**) 06-27-2006, 07:10 AM

I think all this proves is that when you have your foot on the gas and brake pedal at the same time the car's computer is making better choices than the driver. I understand your attempted test criteria, but unless you have source code for the computer to say that regenerative braking algorithms are not affected by gas pedal position, this test doesn't prove anything. Even though you may be gliding, that slight pressure on the gas pedal would still be registered by the computer as a "non-zero" input.

Douglas · #7 (**permalink**) 06-27-2006, 07:53 PM

My point is that the action of pressing on the brake pedal does not cause regen to occur in the Toyota HSD system. It is the action of removing pressure from the accellerator/gas pedal. Unlike other hybrid cars where the brake pedal does indeed cause regen.

Cheers, Doug

TKCamry · #8 (**permalink**) 06-27-2006, 08:19 PM

Quote:

Originally Posted by Douglas

My point is that the action of pressing on the brake pedal does not cause regen to occur in the Toyota HSD system. It is the action of removing pressure from the accellerator/gas pedal. Unlike other hybrid cars where the brake pedal does indeed cause regen.

Cheers, Doug

I'm sorry, but you are wrong. Taking your foot off the gas merely initiates a battery recharge based on the drag of the engine. And then pressing the brake pedal initiates full brake regen and then actual brake application to the brake disks. Here is a Toyota link:

http://72.14.205.104/search?q=cache:...&ct=clnk&cd=26

Quote:

Regenerative Braking System
A regenerative braking system is used which, during engine braking and braking using the foot brake, operates the electric
motor as a generator, converting the vehicle’s kinetic energy into electrical energy, which is used to charge the battery. The
system is particularly effective in recovering energy during city driving, where driving patterns of repeated acceleration and
deceleration are common. When the footbrake is being used, the system controls the coordination between the hydraulic brake
of the ECB and the regenerative brake and preferentially uses the regenerative brake, thereby recovering energy even at lower
vehicle speeds. Furthermore, by improving the battery input performance, more energy is recovered.
Additionally, by reducing the friction loss in the drive system, such as in the transmission, the energy that used to be lost as
driving system loss during deceleration is now recovered, significantly increasing the total amount of recovered energy.

nash · #9 (**permalink**) 06-27-2006, 08:51 PM

Here is a page that shows quite graphically the relationship between brake pedal force and regen/disk brake action: Hybrid Synergy Drive Regenerative Braking

Droid13 · #10 (**permalink**) 06-28-2006, 07:28 AM

Douglas, TKCamry and Nash posts both show the technical backup confirming your assumption is wrong. The point I was trying to explain was why your little experiment was flawed thus leading you to make the wrong assumption.