need to create 0 to 30 pounds linear force

[Paul Hovnanian P.E.]

the reason i need 100ms response time is that this regulator is for a
turbocharged car and the fuel pressure must increase immediately in
response to boost or the mixture will lean out with catastrophic
results.

100ms is just a guess..the faster the better.

controlling the fuel pump sounds interesting but i'm not sure if it
could be controlled fast enough to respond to boost changes..

You are correct. Typical vehicle fuel pumps can't respond that fast.

GOOD POINT:

whoever said that I dont really need 30 psi...you are probably right.
i will do an experiment and see how much force it really takes on the
spring to increase the regulated pressure...this may mean I could use
a much smaller/cheaper/faster/easier solenoid!

You might need to consult with a mechanical engineer to verify the
details, but there are some types of valves where a small 'pilot valve'
is controlled by a solenoid (voice coil). This in turn controls the
flow/pressure in a main line via 'hydraulics' where the hydraulic
working fluid is simply a small amount of the fluid being controlled
tapped off the supply line.

 

[[email protected]]

So for openers, you are talking about pressure, not force. The actual force
is probably far less than a pound depending on the orifice area where the
ball seats, right? No way do you need 30lb of force as originally claimed.

Simple solution: Place a screw behind the spring to adjust the force on the
spring. Attach a gear to the screw. Drive the screw gear with a small DC
motor with a pinion gear on its shaft. The pinion engages the screw gear.
The purpose of the gear and pinion is to give a gear ratio to increase the
motor torque on the screw keeping the motor small and the system simple.

When there is no current in the motor, the pressure will remain at it's
setting and can remain forever consuming no power. Motor current in one
direction will drive the screw toward higher pressure while current in the
other direction will drive the screw to lower pressure.

Connect the motor in your pressure control loop with appropriate
amplification and compensation using pressure as the control variable as you
state.

Privide two limit switches on the screw travel to keep the screw from
bottoming out and stalling the motor at each end of travel.

Don't make this a bigger deal than it needs to be.- Hide quoted text -

- Show quoted text -

Wait a second here.....i'm not so sure I dont need 30 lbs of force if
i want to regulate 30 psi, for instance...the fluid being regulated
has to "lift up" the ball in the orifice, and if there is 30 lbs on
that ball you get 30 psi, yes?

I took apart the fuel pressure regulator that I will be modifying with
the linear force actuator. Its got a 3/4" diameter spring that I could
see easily taking 50 lbs of force to get it to the compressed length
that it was before i sawed open the regulator... (the stock pressure
is 50psi)

it still remains for me to put the opened up regulator on the car and
see if i can modulate the fuel pressure with a much smaller force..but
something tells me no since that same place I will be putting pressure
to modulate the pressure is where that hefty spring was..

 

[Greg Neill]

Wait a second here.....i'm not so sure I dont need 30 lbs of force if
i want to regulate 30 psi, for instance...the fluid being regulated
has to "lift up" the ball in the orifice, and if there is 30 lbs on
that ball you get 30 psi, yes?

30 psi does not mean 30 pounds of force, it means
30 pounds per square inch. What's the cross sectional
area of the ball? How about the orifice in which it
sits?

 

[[email protected]]

Yea verily -- almost.

Not all linear motors are linear induction motors -- there are linear
brushless motors, and I wouldn't be surprised at a linear brushed motor.

The OP wants a force, and a 100ms response time.  He may be able to do
this with a very free-moving rack and pinion (it depends on just how much
parasitic force he can stand), but I'd approach this option carefully.

Other respondents have mentioned that voice coil actuators are $$$ --
they are, but if you wind your own coil and place your own magnets the
purchase price is low.  The _labor_ is high; that plus the fact that
voice coil actuators are generally low-volume items* is what drives up
the price, but rolling your own is a quite viable option.

* Except for disk drives, but those are in-house items.

--
Tim Wescott
Control systems and communications consultinghttp://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html

I think the voice coil is EXACTLY what I am looking for. BEI here in
san diego wants $1000+ for one that can generate about 30 lbs of
force.

Rolling my own sounds good. Any idea where I can find info on making
my own?

 

[Jim Thompson]

I think the voice coil is EXACTLY what I am looking for. BEI here in
san diego wants $1000+ for one that can generate about 30 lbs of
force.

Rolling my own sounds good. Any idea where I can find info on making
my own?

You keep forgetting that your orifice size is NOT 1 SQ.IN. !!

...Jim Thompson

 

[Rich Grise]

I think the voice coil is EXACTLY what I am looking for. BEI here in san
diego wants $1000+ for one that can generate about 30 lbs of force.

Rolling my own sounds good. Any idea where I can find info on making my
own?

If you can buy one off the shelf that meets ALL of your needs, and has
good docs, and if the point of this exercise is to get something working
now, then buy it and be done with it.

You'd never be able to design/build an equivalent from scratch that cheap,
and the other alternatives seem to be basically "If this is a hobby
project, and your time doesn't cost anything..." ;-)

Good Luck!
Rich

 

[[email protected]]

You keep forgetting that your orifice size is NOT 1 SQ.IN. !!

                                        ...Jim Thompson
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         America: Land of the Free, Because of the Brave- Hide quoted text -

- Show quoted text -

OKAY...i'm not forgetting that the orifice is not 1 square inch. I
understand what y'all are saying about 30 lbs not being neccessary to
regulate 30psi in a small orifice.

I took the regulator apart and pumped air through it with a small air
pump i have. It took both of my thumbs pushing as hard as I could on
the diaphragm to get up to 25 psi...however the pump i was using
probably couldnt pump more air than that anyways...

I suppose I will have to try it on the car with the stronger fuel
pump..

The spring that came out is HEFTY. Hefty enough to where I could not
compress it to its compressed (pre sawing open the regulator) length
with my hands! I would not at all be surprised if it took 50+ lbs of
force to compress it to fit back in the regulator, which is what is
leading me to believe that 50 psi takes 50 lbs of pressure.

Are you understanding why I am being misled, apparently?

If the spring I took out was wimpy that would be consistent with the
small orifice/less force required idea.

Still gotta test it...

 

[Glen Walpert]

On Mon, 28 Jan 2008 16:37:59 -0700, Jim Thompson

You keep forgetting that your orifice size is NOT 1 SQ.IN. !!

If the "pressure regulator" is actually a simple relief valve which
returns excess to the tank then the orifice size matters, but not in a
normal pressure regulator where spring (or other) force balances
outlet pressure on the opposite side of a diaphragm, so it is
diaphragm area that matters most, with orifice area having a
relatively small effect, which is good since the orifice area causes
outlet pressure to vary with inlet pressure. "PSRR" ~ diaphragm
area/orifice area.