How does the MINI knock sensor detect knock?
#1
How does the MINI knock sensor detect knock?
I posted this question yesterday, but it disappeared. I see that it is a seemingly solid donut-shaped piece of metal with a bolt going through it's center holding it solidly against the engine block. How can this transmit a signal to retard ignition timing, and also, how not mistake other noises or vibes for pinging or knock? -Jeffy. p.s. I posted this here because only people interested in mods are going to know or care about this question.
#2
Inside the knock sensor is a piezoelectric element. Piezoelectric elements generate a voltage when pressure or a vibration is applied to them. The piezoelectric element in the knock sensor is tuned to the engine knock frequency.
http://www.siemensvdo.fr/NR/rdonlyre...atasheeten.pdf
#3
Piezoelectric crystals translate motion in to electricity, or visa versa. Inside your earbud headphones is a small crystal that has the electricity from your iPod going to it-the electricity causes the crystal to vibrate, making sound from the motion.
You can reverse it, and tune the crystal to vibrate at a certain frequency. So you get an electrical signal out of the crystal when it vibrates due to the knock. A knock is kinda like rapping the block with a hammer-it's a big bang. The frequency of the knock is a known frequency, so the crystal gets tuned to it. That's the reason it doesn't go off due to other noises or vibrations.
You can reverse it, and tune the crystal to vibrate at a certain frequency. So you get an electrical signal out of the crystal when it vibrates due to the knock. A knock is kinda like rapping the block with a hammer-it's a big bang. The frequency of the knock is a known frequency, so the crystal gets tuned to it. That's the reason it doesn't go off due to other noises or vibrations.
#4
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#8
It should also be noted that the sensor is tuned to the knock frequency of a specific engine design as engine block designs will have different resonating characteristics, so while they may look the same they are not necessarily interchangable. Always check part numbers. Note how the relation between frenquencies is shown in the diagrams, but not the actual Hz data.
A very good book about EFI principles (including knock-sensor operation):
http://www.bentleypublishers.com/pro...FIB&subject=25
While the specific systems covered are a bit outdated (and sadly, Charles Probst has passed on...), the principles have not changes and are described in basic terms very well. This book should be mandatory reading for any budding modern-car DIY'er.
A very good book about EFI principles (including knock-sensor operation):
http://www.bentleypublishers.com/pro...FIB&subject=25
While the specific systems covered are a bit outdated (and sadly, Charles Probst has passed on...), the principles have not changes and are described in basic terms very well. This book should be mandatory reading for any budding modern-car DIY'er.
#10
Honestly, I'm not sure... and personally, I wouldn't tap into the wiring as it could change the data the ECU sees. I believe some of the better OBD II monitoring programs can output knock sensor data. Besides, I'm not really sure what you're going to see in real time. The ECU is constantly adjusting the timing to keep the engine on the ragged edge of knocking... and as such knock is sensed and compensated for in fractions of a second.
#12
Well, maybe... but if that happens, the ECU will likely throw a code, although I'll admit not always. However, this usually happens with modified S cars, not on NA Coopers. I'm not sure what you could be doing that would cause this in a Cooper, other than wanting to run really cheap gas which in general is often robbing Peter (engine efficiency & MPG) to pay Paul (cheaper fill up costs)...
By design, the transducer doesn't produce much current. I wouldn't do anything that could possibly steal some of that current. Like I said before, I would look for a program/device that pulls data from the OBD port.
But that's just my admittedly conservative opinion and I'll leave it at that.
By design, the transducer doesn't produce much current. I wouldn't do anything that could possibly steal some of that current. Like I said before, I would look for a program/device that pulls data from the OBD port.
But that's just my admittedly conservative opinion and I'll leave it at that.
#13
#14
i believe that many of the devices on the mini, related to the ECU, use the CAN BUS, and all are sensitive
from Bentley 600-2 -- use digital multimeter only, an analog (swing needle) type may draw enough current to damage components
from Bentley ELE-66 (component B6240) -- plugs directly into the A6000 (DME) computer at PIN locations 7, 8
no info that I can parse on voltage, or signal type (but I rot at schematics)
from Bentley 600-2 -- use digital multimeter only, an analog (swing needle) type may draw enough current to damage components
from Bentley ELE-66 (component B6240) -- plugs directly into the A6000 (DME) computer at PIN locations 7, 8
no info that I can parse on voltage, or signal type (but I rot at schematics)
#15
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Wow, my SES came today and I pulled a code P0326. What do you know, a Knock Sensor thread.
Make: MINI Model: Cooper Year: 2005
VIN: Not Reported MIL: Off
Diagnostic Trouble Codes P0326 Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor)
]Freeze Frame (Frame 0) for DTC P0326
Absolute Throttle Position: 21 %
Calculated Load: 48 %
Coolant Temperature: 190 F
Engine RPM: 2426 r/min
Fuel System Status Bank One: Closed Loop
]Fuel System Status Bank Two: Not Reported
Ignition Timing Advance for #1: 20.0 deg
Intake Air Temperature: 99 F
Intake Manifold Absolute Pressure: 15.9 in.hg
Long Term Fuel Trim Bank One: -0.78 %
Short Term Fuel Trim Bank One: -6.24 %
Vehicle Speed: 48 MPH
Any ideas about my problem - bad sensor or bad gas?
TD
Make: MINI Model: Cooper Year: 2005
VIN: Not Reported MIL: Off
Diagnostic Trouble Codes P0326 Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor)
]Freeze Frame (Frame 0) for DTC P0326
Absolute Throttle Position: 21 %
Calculated Load: 48 %
Coolant Temperature: 190 F
Engine RPM: 2426 r/min
Fuel System Status Bank One: Closed Loop
]Fuel System Status Bank Two: Not Reported
Ignition Timing Advance for #1: 20.0 deg
Intake Air Temperature: 99 F
Intake Manifold Absolute Pressure: 15.9 in.hg
Long Term Fuel Trim Bank One: -0.78 %
Short Term Fuel Trim Bank One: -6.24 %
Vehicle Speed: 48 MPH
Any ideas about my problem - bad sensor or bad gas?
TD
Last edited by Minutia; 05-14-2008 at 06:54 PM.
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