[miken123]

I'm trying to learn more about how the hydraulic part of the braking system in a GM strong (i.e. Two Mode, not BAS) hybrid works.

From my experience with the two mode gmt-900s, there's an electric-powered hydraulic pump that runs as necessary to maintain available hydraulic pressure in a reservoir so that a controller on the vehicle can tell it to apply hydraulic pressure to the friction brakes when needed (I'm not terribly interested in the control strategy as much as I am in the hardware involved).

Note that I am not looking for people to jump in and say "Regen braking works pretty much by running the electric motors in reverse" -- i'm interested in the hydraulic friction aspect of the brakes when used in these GM hybrids.

Anyone have any more details or links to good documentation?

Thanks!

 

[eurohazard]

I found this....

The SCB system replaces traditional boosters, master cylinders and vacuum pumps with an electro-hydraulic control unit (EHCU) and brake pedal simulator unit with a twin master cylinder to supply brake pressure. This offers several advantages: (1) ease of installation with fewer components to fit; (2) improved packaging in the front dash area versus traditional vacuum boosters; (3) a decoupled brake pedal that is ideal for integrationin to autonomous or emergency braking systems; and (4) best-in-class NVH characteristics.

Here's the link.

 

[miken123]

Yup, I was about to post my similar findings. I knew TRW did the brakes on the cars and I think it's safe to assume they use this SBC system you mentioned.

Basically it's an electric vacuum pump that builds up pressure in an accumulator. It does allow for "manual brakes" in case of a loss of electric power. How it does this they don't say (probably for proprietary reasons but what the hell do we care).
Slip Control Boost pdf:
http://www.trw.com/extlink/1,,,00.html?ExternalTRW=/images/Tech_Info_SCB_Eng07.pdf&DIR=2

You'll be wise to note that the unit contains an integrated "Brake Simulator Unit." This, also offered in the past as a separate product from TRW, simulates the pressure on your brake pedal. I'm not 100% on how TRW accomplishes this but other companies do it by having your pedal still activate against a hydraulic fluid in a chamber, and then in that chamber there will be a pressure sensor. In such a case, it would make sense that *the input signal they take from the driver's brake pedal is the pressure.

*To see their PDF on their brake simulator unit (the old stand-alone product that is more or less integrated into their applications used on current GM Two Mode Hybrids: See this link:

http://www.trw.com/extlink/1,,,00.html?ExternalTRW=/images/Tech_Info_ESCR_Eng07.pdf&DIR=2

Thanks for looking into it. I hope this info helps others!

 

[eurohazard]

Sweet finds. This is interesting stuff! I actually forgot about braking in hybrids.....in my own mind more thinking about power-steering, AC, and alternator functions while the engine is off. I think it's a good thread!