What exactly happens when you brake?

jamarimutt · 08-27-2004, 08:30 PM

Judging from many posts in this and other forums, it would seem that the brake pads grab the disks only during emergency braking and below 8 mph. If this is true, the brakes pads should last the life of the car.

I suspect that the pads grab the disks almost as frequently as in other cars. Can someone explain what happens in clear and simple English?

DaveinOlyWA · 08-27-2004, 10:19 PM

actually that isnt true. the brakes do engage at first when the brakes are touched. but then the "urgency" is gauged and then the primary stopping force is switched over to the regen motor. (the biggest reason for this is the regen doesnt react quite fast enough therefore in case emergency braking is neccessary, the hydraulics work first.)

here is a chart of what happens during braking.

http://priuschat.com/forums/album_pic.php?pic_id=718

as you can see; initially, the main braking force is friction, but that quickly drops off as the power rises to the regen braking. as you can see very light braking will be all regen. (but we already knew that)

Frank Hudon · 08-27-2004, 10:20 PM

as simple as I can explain it is that MG2 (main drive motor) is a permanent magnet motor which means it's also a permanent magnet generator. When your going down the road and you apply light pressure on the brake pedal the computer see's that as a command to generate electricity and send it to the battery, which it does in increasing amount the more you press on the brake pedal, at a certain point your request for slowing the car down exceeds the amount of torque the motor can generate so the brakes now are assisted with friction braking. That's the clearest I can submit.

DaveinOlyWA · 08-27-2004, 11:15 PM

http://priuschat.com/forums/album_pic.php?pic_id=718

as you can see in this diagram, friction braking to some degree is present most of the time in all but the lightest braking situation.

**efusco** · 08-27-2004, 11:18 PM

Take a look at the PDF for a very detailed description of the braking mechanism and exactly how it works.

DaveinOlyWA · 08-27-2004, 11:25 PM

gee.. rather complicated explanation considering the chart i posted says the same thing but much simpler.

**efusco** · 08-27-2004, 11:35 PM

Quote:

Originally posted by DaveinOlyWA
gee.. rather complicated explanation considering the chart i posted says the same thing but much simpler.

I'll try to keep things in the "colorful pictures and shiny objects" arena for you in the future Dave!! :wink:

:P

DaveinOlyWA · 08-27-2004, 11:43 PM

well thank you!!

actually now that i look at it, i realize that our posts were practically simultaneous.

sooo you take care of the high tech crowd and ill aim for the picture and illustration crowd.

**efusco** · 08-28-2004, 12:10 AM

Oh, and here I'm gonna step right on Dave's turf. I finally located the diagram I was looking for comparing the braking patterns of the classic and new prius and the dramatic improvement in regenerative braking (I think Frank will particularly appreciate this).

Frank Hudon · 08-28-2004, 01:01 AM

I realise that the expanded range exists, never questioned it. The difference is really very small in a practical sense. The major increase comes as a result of the difference of the HV battery terminal voltage I suspect. 500 verses 273 and the increased torque it'll apply to the MG's to get more braking effect. Brake (regen is still limited to 80%BSOC) useage depends on pedal pressure, so I guess I'll have to cut a line and install a pressure switch to see what all is going on.

08-27-2004, 08:30 PM	#1
jamarimutt Join Date: May 2004 Posts: 972 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	What exactly happens when you brake? Judging from many posts in this and other forums, it would seem that the brake pads grab the disks only during emergency braking and below 8 mph. If this is true, the brakes pads should last the life of the car. I suspect that the pads grab the disks almost as frequently as in other cars. Can someone explain what happens in clear and simple English?

08-27-2004, 10:19 PM	#2
DaveinOlyWA Opps !! I Did it Again!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 9,675 My Car: 2006 Prius Package: #4 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 5	actually that isnt true. the brakes do engage at first when the brakes are touched. but then the "urgency" is gauged and then the primary stopping force is switched over to the regen motor. (the biggest reason for this is the regen doesnt react quite fast enough therefore in case emergency braking is neccessary, the hydraulics work first.) here is a chart of what happens during braking. http://priuschat.com/forums/album_pic.php?pic_id=718 as you can see; initially, the main braking force is friction, but that quickly drops off as the power rises to the regen braking. as you can see very light braking will be all regen. (but we already knew that) __________________ My 2006: Last tank 463.1 miles @49.2 pump (49.4 computer) 4.22 cpm winter mpg 50.70 summer mpg 54.59 lifetime: 33,038.3 miles 52.79 mpg pump (54.04 mpg computer) 5.74 cpm My 2007 Zenn Driven 5945 miles, 2.01 cpm/ 105 mpg (at $2.05/gal), 4.04 miles/ Kwh Savings over my Prius $302.66 The Corolla...573.26 The REAL SAVINGS from not driving Corolla 657.39 +Prius= 958.18 (excludes maintenance costs...would be unfair to ICE vehicles) My Plate: DUALPWR (Dual Power)

08-27-2004, 10:20 PM	#3
Frank Hudon Senior Member Join Date: Jan 2004 Posts: 4,144 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	as simple as I can explain it is that MG2 (main drive motor) is a permanent magnet motor which means it's also a permanent magnet generator. When your going down the road and you apply light pressure on the brake pedal the computer see's that as a command to generate electricity and send it to the battery, which it does in increasing amount the more you press on the brake pedal, at a certain point your request for slowing the car down exceeds the amount of torque the motor can generate so the brakes now are assisted with friction braking. That's the clearest I can submit. __________________ You can quote me on this, People who drive vehicles that idle at a traffic light, are idiots. mine 2k3 avg. 5.36 for 46,915Km Best tank 4.4L per 100K 64.2 Imperial 53.4 U.S. gallon, MiniScanner, SilverStars, block heater, winter lips, in as of Oct 15, out on April 25. In again on Sept. 21st. her's 2k4 "B" avg. 6.01 for 42,317 Km Best tank 4.02L per 100K, CAN-view with OBD11 module and flashloader, SilverStars, 06 Chrome grill bar, Michelin HydroEdge, upper and lower grill blocker,upper out as of April 7, lower out on April 28. In again on Sept 21st.

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08-27-2004, 11:15 PM	#4
DaveinOlyWA Opps !! I Did it Again!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 9,675 My Car: 2006 Prius Package: #4 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 5	http://priuschat.com/forums/album_pic.php?pic_id=718 as you can see in this diagram, friction braking to some degree is present most of the time in all but the lightest braking situation.

08-27-2004, 11:18 PM	#5
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,252 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 24	Take a look at the PDF for a very detailed description of the braking mechanism and exactly how it works.

08-27-2004, 11:25 PM	#6
DaveinOlyWA Opps !! I Did it Again!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 9,675 My Car: 2006 Prius Package: #4 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 5	gee.. rather complicated explanation considering the chart i posted says the same thing but much simpler.

08-27-2004, 11:43 PM	#8
DaveinOlyWA Opps !! I Did it Again!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 9,675 My Car: 2006 Prius Package: #4 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 5	well thank you!! actually now that i look at it, i realize that our posts were practically simultaneous. sooo you take care of the high tech crowd and ill aim for the picture and illustration crowd.

08-28-2004, 12:10 AM	#9
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 14,252 My Car: 2004 Prius Package: #9 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 24	Oh, and here I'm gonna step right on Dave's turf. I finally located the diagram I was looking for comparing the braking patterns of the classic and new prius and the dramatic improvement in regenerative braking (I think Frank will particularly appreciate this).

08-28-2004, 01:01 AM	#10
Frank Hudon Senior Member Join Date: Jan 2004 Posts: 4,144 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	I realise that the expanded range exists, never questioned it. The difference is really very small in a practical sense. The major increase comes as a result of the difference of the HV battery terminal voltage I suspect. 500 verses 273 and the increased torque it'll apply to the MG's to get more braking effect. Brake (regen is still limited to 80%BSOC) useage depends on pedal pressure, so I guess I'll have to cut a line and install a pressure switch to see what all is going on.