Automotive brake sensors

Discussions related to engineering and its applications. From civil and mechanical to aeronautic and robotics, etc.

Automotive brake sensors

Postby minime on November 25th, 2015, 6:35 pm 

Can anyone explain how an automotive brake sensor works i.e. how does it receive hydraulic pressure and convert it into an electrical signal.
Part number of the particular sensor is 34-52-1-164-458 (34521164458)
It is located on the Brake Master Cylinder.



Pressure sensor bmw.JPG
minime
Member
 
Posts: 114
Joined: 24 Dec 2007


Re: Automotive brake sensors

Postby Eclogite on November 26th, 2015, 3:54 am 

I know nothing about automotive brake sensors, but am familiar with pressure sensing in other fluids. I suspect it is a simple pressure transducer. This consists of a flexible "plate" exposed to the fluid. Deformation of the plate by the hydraulic pressure also deforms a resistor, this deformation changing its electrical resistance. The resistor is one leg of a Wheatstone bridge, so the change in resistance changes the current flow in the bridge. This is proportional to the change in hydraulic pressure. The illustration you provided is consistent with such a device.
Eclogite
Forum Moderator
 
Posts: 1362
Joined: 07 Feb 2007
Location: Around and about


Re: Automotive brake sensors

Postby minime on November 27th, 2015, 3:35 pm 

Thanks Eclogite, I assume the flexible plate would be much the same as a diaphragm, would you know how sensitive these sensors would be to a small air pocket in the region of the diaphragm?
minime
Member
 
Posts: 114
Joined: 24 Dec 2007


Re: Automotive brake sensors

Postby Eclogite on November 27th, 2015, 4:09 pm 

Keep in mind it is a couple of decades since I worked with these, but I do know they are still used in the application I was familiar with.

Unfortunately, that involved pressures in the region of 2,000 - 4,000 psi, so that air pockets would not have been an issue. That said, since the air would necessarily be exerting the same pressure I would not have thought it would be an issue in your case. Again, that is an educated guess rather than a declaration based on current knowledge.

(I'm surprised no one more knowledgeable has chimed in.)
Eclogite
Forum Moderator
 
Posts: 1362
Joined: 07 Feb 2007
Location: Around and about


Re: Automotive brake sensors

Postby Dave_C on November 29th, 2015, 9:20 am 

What Ecloglteis referring to is often called a pressure transducer. It's an analog device that converts pressure to an electrical signal such that the electrical signal is proportional to the pressure.

Chances are, the device you're looking at is actually a brake switch. They only provide an on/off electrical signal as a function of hydraulic pressure. If the pressure is above some minimum value, the switch changes state (closes) and allows electricity to flow from one pole to the other. When pressure is removed, the switch opens. Some typical examples of how they work can be found on the web.
https://www.google.com/?gws_rd=ssl#q=ho ... witch+work
http://www.sw-em.com/hydraulic%20brake% ... 0notes.htm
http://www.huelsmann.us/bugman/brake_li ... h_tech.htm

Regardless of whether the device is a transducer or a switch, the device functions due to pressure, not type of fluid media. So if you have air bubbles in the brake line, it doesn't matter to the device. If it's a transducer, it will measure pressure and if it's a switch, it will change state regardless of what fluid is creating the pressure, air or oil.
User avatar
Dave_C
Member
 
Posts: 331
Joined: 08 Jun 2014
Location: Allentown
TheVat liked this post



Return to Engineering & Electronics

Who is online

Users browsing this forum: No registered users and 6 guests