DIY_EFI Digest V5 #718 - knock sensor

[David Hunt]

According to Bosch the primary resonance is 2Hz to 10Hz.  The old 'jerk'
types of sensors were sensitive in that range.  Jerk in this case is the
third derivative type.

Bosch also states that the modern piezo types of sensor are tuned in the
audible range with a Q of about 2.

Yes and engine block 'rings like a bell.' If in the audio range it would
sound badly, but natural harmonic motion just like any other elastic
material.

I would certainly be interested in the Autospeed article also

dh



----- Original Message -----
From: "Mark Agnello" <m_agnello at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, August 29, 2001 2:57 PM
Subject: Re: DIY_EFI Digest V5 #718 - knock sensor


>
> > > TVS wrote:
> > > >
> > > > I assume the frequency has some dependence on
> > variables
> > > > like bore diameter and combustion chamber shape,
> > but is the knock detection
> > > > circuitry likely to 'listen' for a wide range of
> > frequency's or just a
> > > > narrow band?
> > >
>
> These are just educated guesses, but I suspect they
> apply.  Detonation is closely coupled to the pressure
> wave in the combustion chamber.  The pressure wave is
> an acoustic event.  As such, it should be influenced
> by the geometry of the combustion chamber at the
> instant of the event.  The dominant mode's wavelength
> will probably be proportional to the cylinder bore.
>
> If the event timespan is too short to propagate
> laterally, then the dominant mode will probably be
> related to the combustion chamber height at the time
> of the event.  Even if there is a lateral mode, I
> wonder if the high frequency content in a knock signal
> is due to the vertical mode(s)?
>
> WRT the cylinder head and/or block structure
> influencing the dominant frequencies, I agree there
> will be some interaction.  Unlike the 10 Hz bell
> analogy, I don't believe there will be a dominant
> vibrational mode of the engine structure.  These
> structures are too complex to have a primary mode and
> I'll bet auto manufacturers spend a lot of time
> designing engine structures that don't have
> significant vibrational modes.  I know aircraft engine
> manufacturers do this.  If they didn't, the life of
> the engine mounted fuel pumps, actuators, sensors, and
> accessories would be severely shortened.
>
> What do y'all think?  Remember, I'm just a lonely old
> EE that likes to read SF.;)
>
> Autospeed published an article based on an Aussie grad
> student's research into engine knock earlier this
> year.  Does anyone have a copy and does it shed light
> on this issue?
>
>
> =====
> Mark Agnello
> Washington Crossing, PA (USA)
> 88 Toyota Celica All Trac Turbo (restoration project)
> 92 Toyota Celica All Trac Turbo
> 96 Honda VFR
> 89 Honda Hawk GT (restoration project)
>
> __________________________________________________
> Do You Yahoo!?
> Get email alerts & NEW webcam video instant messaging with Yahoo!
Messenger
> http://im.yahoo.com
> --------------------------------------------------------------------------
--
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the
quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
>
>


----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org