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Location:
Brisbane
Registered:
July 2003
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Knock sensors.
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Sat, 15 November 2003 12:59
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How do they work? And does a 7MGTE have one?
Regards
Paul
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Knock sensors.
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Sat, 15 November 2003 13:08
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"knock" in a motor generates specific vibrations in the block.
a "knock sensor" is a piezo-electric sensor which is a cermaic that generates an electricla current when it is compressed. this means that it can generate an electrical sugnal that has many of the frequencies in a motor.
what you need to do is to filter out all the frequencies that are NOT associated with knock, in order to detect it.
7MGTE? no idea, sorry.
Cya, Stewart
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Knock sensors.
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Sat, 15 November 2003 13:21
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7mgte has two
and oldcorollas is correct in outlining their function. i should add though, that the sensor is 'tuned' to the harmonic frequency of the 'knock' for each specific engine. which i believe was either 24ooHz - 27ooHz ... i think (i shouldve written that down when i found it out  )
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Knock sensors.
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Sat, 15 November 2003 13:30
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heya Ed,
does the frequency change much with RPM? i know it is mostly based on the cylinder and chamber dimensions, but i imagine that it would change slightly based on the temperature and pressure of gases in the chamber (changing the speed of sound etc)...
any more ideas you wanna share??? have you had any luck setting one up??
i have a couple of piezo sensors, but have not had access to a CRO to look at waveforms (and probably shouldn't be doing that just yet  )
Cya, Stewart
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Knock sensors.
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Sat, 15 November 2003 13:49
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| oldcorollas wrote on Sun, 16 November 2003 00:30 |
have you had any luck setting one up??
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didnt work at all... totally insensitive (even to a ballpein hammer pounding the deck block) 
ive resolved to drill out a spare knock sensor, and mount a samll piezzo microphone in it. then run the lead into the cabin to an Aux audio input on my amp... tune by ear, a much more sensitive device than that shitty circuit!
cheers
ed
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Knock sensors.
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Sat, 15 November 2003 13:54
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| oldcorollas wrote on Sun, 16 November 2003 00:30 |
does the frequency change much with RPM? i know it is mostly based on the cylinder and chamber dimensions, but i imagine that it would change slightly based on the temperature and pressure of gases in the chamber
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i agree it may wander a bit, but id imagine the resonant harmonic is governed mainly by the radius of the cyl, and the material... thus id say you could expect it to occur in a relatively narrow band despite changing conditions
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Club Member
Location:
sydney
Registered:
May 2002
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Re: Knock sensors.
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Sat, 15 November 2003 20:40
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i have a couple of piezo sensors, but have not had access to a CRO to look at waveforms (and probably shouldn't be doing that just yet )
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you can come and borrow my cro if you want Stu
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Location:
Brisbane
Registered:
July 2003
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Re: Knock sensors.
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Sun, 16 November 2003 00:42
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So what does the car do when it detects a 'knock'? Retard the timing, richen up?
'knocking' is pinging is it not?
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Location:
Brisbane
Registered:
February 2003
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Re: Knock sensors.
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Sun, 16 November 2003 01:49
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retard timing (usually in predefined steps) until pinging goes away.
a smart engine mngt system may even go and modify fuel/timing maps to attempt to prevent further pinging - but this behaviour tends to 'detune' cars into safe running modes as opposed to efficient or power modes of operation.
charles.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Knock sensors.
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Sun, 16 November 2003 02:12
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| IRA11Y wrote on Sun, 16 November 2003 07:40 |
you can come and borrow my cro if you want Stu
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cool thanks  will do!!
anyone else want to donate a pinging engine
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Knock sensors.
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Sun, 16 November 2003 07:19
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| oldcorollas wrote on Sun, 16 November 2003 13:12 |
anyone else want to donate a pinging engine
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you have aaprx 3.5weeks of 5M pinging goodness left if you want it 
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