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Supercharger bypass valve operation
5

Supercharger bypass valve operation

Supercharger bypass valve operation

(OP)
Roots superchargers usually have a bypass valve that is open at idle.

I want to start playing with the electric bypass valve that came with my Mercedes kompressor
(mentioned here: thread71-205859: Sound suppression for Lysholm compressor with blow-thru throttles )
and I am wondering which strategy to choose. I can make it TPS or MAP dependent.

I was wondering when it should close.
Should it close gradually from above a certain level of inlet pressure on, or does it shuts close over a fairly short stroke of throttle, located somewhere above the cruise position?

 

RE: Supercharger bypass valve operation

Quote:

Roots superchargers usually have a bypass valve that is open at idle.

No they don't.

Quote:

I want to start playing with the electric bypass valve that came with my Mercedes kompressor

WHY.

Did MB get it that wrong.

Alterations to this may have a deadly impact on safety as discussed in previous threads.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Supercharger bypass valve operation

Is this a turbocharged and blown engine?  I am familiar with a bypass arrangement on the old 2 cycle Detroits where at cruising speeds the turbo would put up more air than the blower could pass so there was a spring loaded bypass around it to let the extra air get into the airboxes.  Only when the pressure between the turbo and the blower started building up would the spring pressure be overcome but what you are describing and wanting to do is diametrically opposite to that situation.

rmw

RE: Supercharger bypass valve operation

3
(OP)
Quote:
No they don't.

Well, err mine has. It's from a MB M271 engine where the throttle is downstream of the charger. Airfilter - AFM - charger with bypass - intercooler - throttle - inlet plenum.
Now that charger is on a Nissan CA18DET engine but with turbo removed.
Driver fro the bypass had to be built from scratch.
As far as I could find out, superchargers are bypassed at idle mainly for sake of fuel economy.
Fourth and fifth generation Eaton chargers have the bypassvalve incorporated.
http://www.capa.com.au/eaton.htm
http://www.magnusonproducts.com/mp1125thgen.htm

Any idea if such bypass closes gradually or not?

Regards,

  Jean
 

RE: Supercharger bypass valve operation

Lysholm compressors (screw compressors) employ internal compression (the trapped volume becomes smaller).  Hence, a bypass will not reduce the work requirement as it does in a roots blower (an air mover with no internal compression).  

RE: Supercharger bypass valve operation

Back to the OP, mechanically operating the bypass valve, obviously is the most simple method, but can lead to some abrupt boost pressure changes, and thus effect driveability.  In a racing application this may be acceptable, but for daily driving, it can get annoying.  The Ford Thunderbird 3.8L supercharged cars had pure MAP actuated bypass valves, and yes, the boost rise was fast giving great throttle response, but you could quite perceptably feel the boost come on, and the cars were a bit "lumpy" to drive.  The ultimate would be to use a pure microprocessor controlled bypass valve and the necessary programming to control it to give smooth operation, and yet reasonable throttle response, but in your particular application you don't indicate the end-use, so I can only relate what experience I've had with Eaton superchargers that have bypass valves.  A pure MAP controlled valve is stone simple, but you may have to slow the valve rate a bit by restricting the sensing line. Yes, the newer cars' bypass valves tend to close "slower", but this is a function of several parameters that the VCM monitors to give the smoothest torque rise.

j79guy

RE: Supercharger bypass valve operation

JCD06

The bypass should normally be operated using a pulse width signal to give proportionality.   The TPS and MAF sensors can both offer an electronic signal that can be sampled and converted into a duty cycle by a simple chip and circuit, or you could use an already interfaced chip with PWM functionality.  It would then be up to you how to control the valve.  Using a linear coefficient over a certain rpm range and TPS signal would be the easiest. Closing the valve at very low MAP levels would offer the supercharger to work when it is needed, but the valve must then stay closed as the pressure rises.  In reality the control is a mix of these two plus other factors.

The old MR2 SC just operated the valve when MAP determined.  It was also fitted with a clutch.

Alternatively, applying full voltage to the actuator will hold it closed.  Using this method would result in a very noticeable moment when the gate changes position and would probably break something eventually.  

Where is your throttle placed?  Do you use the electromagnetic clutch?  What is the car used for?

Pat, which charging systems are you referring to?  All systems use this bypass open at idle, if the SC is clutched.

RE: Supercharger bypass valve operation

I'm talking about all those systems where the supercharger is not clutched and where the throttle is in the inherently safe position upstream of the supercharger.

A roots blower does not consume much power when it runs in a manifold pressure that is typical at closed throttle.

The bypass valve synchronisation problem does not exist if the blower is not clutched and there is no bypass.

The bent throttle shaft problem does not exist if the throttle is upstream.

I can understand OEM investing huge resources and going to all the trouble to squeeze some extra power out of a restricted space and still retain reasonable economy, but a hot rodder chasing maximum power is really wasting a lot of time and effort and really decreasing safety to save a minimal amount of fuel.

To be frank I really can' be bothered contributing to this.

I also noticed the vast majority of real professional knowledgeable full time working professional engine designers  are not bothering with this thread. You might ask why.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Supercharger bypass valve operation

If one absolutely must put the blower upstream of the throttle, you may do well to copy the throttle body setup as used by VW on the G60 engine.  (The G60 used a remotely mounted positive displacement supercharger)

They employed a bypass throttle that was mechanically coupled to the standard throttle plate.  When the throttle is closed, the bypass is wide open, and vice-versa.  It also appears that the butterfly is biased to blow open with pressure, if the linkage should disconnect.  Certainly, they trusted its operation enough to put it into mass production.

RE: Supercharger bypass valve operation

I just looked at the supercharger on a GM 90 deg V6 Ecotech.

It had no clutch nor visible by pass. I think quite a few of them are out there also.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Supercharger bypass valve operation

Quote:

All systems use this bypass open at idle, if the SC is clutched.

Quote:

Pat said:

To be frank I really can' be bothered contributing to this.

I also noticed the vast majority of real professional knowledgeable full time working professional engine designers  are not bothering with this thread. You might ask why.  

Quote:

Pat said:

It had no clutch nor visible by pass.

Come on Pat,  the original question has some interest and valid discussion.  If you only wish to defend your original unhelpful snappy attitude by backtracking then what you post does not assist the persons original question, does it?  

The GM blower has neither clutch or bypass.  

The VW G-lader system gives good tip-in as the pressure is fed in smoothly, but using electronic controls can give alot more accurate control over the air path.  Some of the G-lader positive pressure is 'wasted' in pusuit of smooth transition, more than would be seen using an electronically controlled bypass.  Although if the point of the system on the OP's project was complete driveability at the expense of some outright performance then it may be a viable approach.  The Mercedes bypass on this particular model is electrically operated though, functionality that might as well be used.

Maybe the OP will chime in with some more details of the project so we can specify what would actually be required.

RE: Supercharger bypass valve operation

My original position was that the OP was acting on a false premise and based on that false premise was wasting his time for little gain at great cost in time, materials and risk.

I stand by that position.

My contribution is why bother.

Remove the throttle blades from the manifold downstream of the blower, add a throttle body before the blower and forget about bypass valves.

You will have a drivable high performance car with no detectable or significant response or fuel economy difference long before you could make the bypass valve work better than an upstream throttle.

I thought that was already strongly implied in this and previous threads.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers for professional engineers
 

RE: Supercharger bypass valve operation

(OP)
j79guy,
What you're telling about the Ford is very useful to me. People who have an aftermarket supercharger kit on their car will not communicate easily about the imperfections and drawbacks. They tend to accept these as inherent.
In my case it is a project car, it will never be a daily driver anymore.
It should allow me to acquire experience in this domain that is not really mine.
This said, that doesn't mean that it should be lumpy smile

The motor shaft is connected to the valve shaft over a gear reduction and the motor has to do several turns before the valve is closed. The other way around, the spring needs some time to rotate the valve shaft and make the motor spin in the other direction.
This makes that it already has a certain delay.

70btdc,
There is a pair of potentiometers connected to the valve shaft, basically making it a servo.
The actual circuit is based on a DRV101 PWM-driver and a MOSFET final.
For the time being, I made the circuit react to the TPS voltage. So obviously it reacts differently then the diaphragm actuated valves but I plan to connect it to my MAP-sensor later and compare both strategies in terms of drivability.
But obviously the valve's "start opening" and "complete open" points need to be different for low and high RPM.
The servo approach could be referred to pressure instead of valve position too.
There is no clutch BTW.

izzmus,
I did consider moving the throttle upstream of the charger. What held me back is the intercooler that is probably not up to the task of being under manifold vacuum. It's a core with plastic end caps and it was made for positive pressure. I'll need an all-aluminium for that.
Also the presence of an OEM bypass valve was challenging smile
Would be interested to see how proportional the VW G60 linkage is.
I'll check out my local VW contact for that.
Installing the throttle before the charger is planned for later.
Corky Bell in "Supercharged" has a bypassvalve even when the throttle is before the charger.
He claims it would avoid the waste of power caused by the charger pulling from the throttle, even partially open.


 

RE: Supercharger bypass valve operation

Is the cost of an intercooler that can handle manifold vacuum that much more than the cost of designing and building a bypass system, especially one that may affect driveability?
Additionally, what is the cost if the bypass system fails?  

RE: Supercharger bypass valve operation

If you are talking about a traditional air-to-air intercooler installed in front of the radiator or some other place equally remote from the engine, then having the entire intercooler system and all connecting pipes under intake vacuum might have some interesting consequences in the event of a leak, and all that "dead volume" behind the throttle might make throttle response a little interesting.

Depending on application, an air-to-water intercooler can be built directly into the intake manifold with relatively minimal volume. It all depends on the layout of the system in question.

RE: Supercharger bypass valve operation

For what it's worth, the Ford Thunderbird bypass type supercharger systems have the throttle upstream of the unclutched supercharger.

"I also noticed the vast majority of real professional knowledgeable full time working professional engine designers  are not bothering with this thread. You might ask why."

Hmmmm, guess that's where the rest of us come in.

j79guy

RE: Supercharger bypass valve operation

(OP)
So far, the bypassvalve starts closing at about 60% TPS and is fully closed around 75% TPS, this means that it's position is dependant of TPS.
I had a look at my logfiles and found out the following: the boost builds up over a much smaller TPS range than over which the valve is closing.
This makes engine operation feel jerky and somewhat uncomfortable because boost always build up at the same point, independent of RPM and driving conditions (uphill-downhill).

So, I'll have to extend the TPS range over which the valve closes or go for the other approach.
That will be to drive the valve so as to deliver a certain boost dependant of TPS.
I'm tending to go for that second one, and in the mean time I'll foresee the necessary wiring for all the relevant parameters to be logged by one device and not by two separate like now, because that makes it awkward and unprecise to reconstitute te data.
 

RE: Supercharger bypass valve operation

My experience on similar systems (Mini Cooper S) has shown that the bypass (operated on purely manifold vacuum with no active control) is continually variable so even at part load there is still some positive pressure effect from the S/C. On the Siemens system used on Mini this was compensated for by using a MAP sensor before and after the S/C which then fed back into the ETC control and torque model. This prevented any drivability/surge issues as the balance of low pressure/high pressure changed through the engine speed and load range.

We tried implementing electronic bypass control in the interests of pursuing part load fuel economy and improving response but the cost out-weighed the benefit and it never made it into production.

Pat makes a good point in saying that OE's spend a lot of time/effort/money getting these systems to work so unless you're prepared to have the potential of some significant compromise you maybe better off focusing your efforts on something else.

What is it you're actually trying to do?

RE: Supercharger bypass valve operation

(OP)
Enginead,
What is so very useful in the experience that you shared here is that you mention the compensation from the two MAP sensors onto the ETC and torque model.
The ECU takes into account what the charger/bypassvalve is doing by sensing the pressure before and after the charger.
How it compensates engine parameters will be load dependent at first because these absolute pressures are load dependent.

It is to note that in principle the ETC hardware is quite similar to the electromechanical bypass valve as used on the MB engine.

The valve control that I described in my previous post and which is used now is load dependant too, albeit in a more crude way because the cable actuated throttle plays a role in it. Anyway it will be more load dependant than my first approach.

Winter was long and the opportunities to test on dry roads were very rare.
The first -short- tests with this system look promising.

The attached picture shows the path to a certain improvement.
X is MAP in bar (scaled to 0 = atmospheric), Y is TPS in volts.
http://files.engineering.com/getfile.aspx?folder=743f055a-8b9f-473d-956c-fb5f2e2cd8b4&file=Image4.jpg
On the second graph, compared to the first one, the gain of the MAF amplifier has been increased what makes boost build up over a wider range of TPS.
Then for the third graph, the offset between the MAF and TPS signals is reduced.
Boost buildup is more "the extension" of the manifold vacuum.
Obviously, that was the setting yielding smoothest throttle response.

What has to be refined? The slope of the positive pressure as function of the throttle position is still steeper than the vacuum as function of throttle. I think drivability might benefit from stretching even more this part of the action.

As to your question what I am trying to do I can answer you the following.
This has nothing to do with my job.
I'm working full time professionally, who knows even knowledgeably, doing something completely different. Don't ask me why. Partially it was destiny...
I have been charmed by the technique that I found when I bought this car (Nissan S13 with CA18DET engine), meanwhile ten years ago.
That was quite a difference compared to my old twin-DCOE commuter.
Since then I have walked different ways and meanwhile it became a project car.
After being tired of playing with turbo's I mounted this charger that I had available.
The challenge now is to optimise its control.
A first ECU remapping has been done last year and once I will have satisfactory results with this bypass, I plan to increase the boost.
What will be next? Who knows, I have other hobbies too, and a lack of space and time.
You will understand that given the situation, the potential of significant compromise is virtually inexhaustible :)

 

RE: Supercharger bypass valve operation

JCD06,

I am interested in what you are doing as well.  I am a hobbyist that likes to think "outside of the box".  I am looking into using a Whipple 5.0L supercharger and have thought the same things about the bypass valve.  Naturally their solution is vacuum based (cheapest/easiest solution).  Like you I feel that there has to be a better way (not necessarily cheap or easy).  I was thinking of utilizing a "wastegate" that could be PWM by the PCM to vary the amount being bypassed.  More info on your progress would be greatly appreciated.  

RE: Supercharger bypass valve operation

(OP)
Pokeytemplar,

This project has been on hold for a while because of other priorities and I don't expect it to restart in next couple of weeks...

During summer I had the car for a series of laps on the track and I'm glad that it all held together smile

For increasing the boost I am hesitating to make a larger crank pulley. I might as well decide to go for a second belt and an intermediate shaft.

About your plan.
There was an article somewhere where was explained the differences between these vacuum based bypass valves and turbo bypass valves. I'm talking here about bypass valves for the compressor side where as you're talking about wastegate which is for the turbine side. Perhaps you just confused names.
Anyway, the main difference (that I can remember of) was the spring. So this might need some thinking and tweaking.

The advantage you could have with a vacuum operated valve over an electric actuator like in my setup will most probably be the response time, which I must admit is at the limit for track use.

The inconvenient will be the need for a vacuum tank but these can be cannibalised from stock cars where they are often used for various actuators, for example variable inlet runner length.
On my BMW it's called DISA and I've seen a similar thing in an Audi.

What solenoid valve will you be using for this PWM?
Those used in turbo boost controllers usually work with a frequency in the 10-30Hz range but all specs are top secret. I've always thought that a beefy fuel injector (1000cc/min or so) could do the trick. Response time of such devices is in the ms range.

Good luck and keep us informed about your project.
 

RE: Supercharger bypass valve operation

jcd06,
very interesting project, giving me ideas for mine
I am working on fitting a Mercedes/Eaton M62 supercharger to an old Triumph TR6 engine
This supercharger, from a 2008 car, has a PWM controlled bypass valve and no clutch.
The bypass valve has 2 potentiometers, one to feedback the position of the actuator and the othr to feedback the actual position of the valve.
I am going to control the car ignition/fuel with a 'Megasquirt III' ECU. This kit ECU has progammable PWM ouputs.
I just have to decide which parameters to use to control the bypass valve position. A combination of TPS and MAP, but not sure what algorithm to use.
I look forward to seeing your progress

RE: Supercharger bypass valve operation

(OP)
Mark,
Making this work with a Megasquirt is a nice project.
I've been looking at the Megasquirt ECU at its very beginning but I didn't follow it up. It seems to have very useful features like PWM outputs as you mentioned. I don't know what is the power capability of these outputs. In my setup the valve actuator motor has a resistance of 2ohm and it needs about 2A to open completely.

We might just have the same bypass valve but what you're telling about the potmeters confuses me.
Before mounting it, I have opened the actuator housing and as far as I can remember both potmeters were on the same shaft, one having a longer stroke than the other, probably for some kind of a fail-safe system.
Unfortunately I did not take a picture of the internals, I'll make sure to do so whenever the charger has to come off the engine.
I added a picture of the assembly below

In terms of drivability I have found the pressure/TPS control parameters giving the best results for the valve control.
You can see a couple of graphs in an earlier post. As my approach is completely analog it would drive me too far to define an algorithm but I think the graphs speak for themselves.
 
I still have some reserve about this approach. When accelerating, for the short time that the bypass is partially closed, the valve is regulating pressure and I am not sure about the practical inconvenience this might bring. For that very short period, the engine charge is air that has been bypassed around the compressor and so far I did not pay too much attention at its absolute temperature. A temperature peak high enough might as well start a pinging in the engine.

I want to use a faster logger and check for unwanted temperature rise during this transition.
With a faster logger it will also be possible to monitor the valve reaction time and perhaps try to find a way to speed it up. For normal driving its response is fast enough but for track work it is a noticeable -although not insurmountable- lapse but for a moment I thought I had reinvented turbo lag smile
It's not at all sure that this is caused by the valve response, it might as well be the volume of the intercooler and ducts being taking time to get pressurized or just a combination of both.

Is there a place where I can follow the progress of your project?

 

RE: Supercharger bypass valve operation

We have indeed got very similar superchargers and bypass valves = hopefully you can see by my photos. Mine has the same electrical characteristics that you quoted. I was mis-informed about the potentiometers -  I took mine a part, as you can see, there are 4 brushes for the pots connected in pairs, shorting the brush for track 1 to the brush for track 2 and likewise for tracks 3 and 4. They are wired so that when one pot gives a max voltage, the ather gives a min, I dont know why. I plotted a graph of the 2 pot values for the complete range of movement of the valve. I am having difficulty accurately controlling the valve. I have built a 2A PWM test circuit, but the positioning is very vague. I will try a different frequency as the 12KHz I have at the moment is probably too high, although DC seemed vague too.
Do you drive the valve with PWM signal or DC and do you find it accurate?
The Megasquirt has a built in fucntion for control of a turbo charger valve which would achieve the same result. The position of the valve can be defined by RPM and Throttle position and you can set a max boost pressure.
I have contacted Bosch in England for some info on the valve and the guy there has in turn applied for info from Germany as he didnt have the data due to it being a 2009 part number. I will pass on the info when I get it.

We haven't progressed much recently due to ill health, but hopefully we will get stuck into it again soon

Mark

RE: Supercharger bypass valve operation

(OP)
Hi Mark,
 
Thanks for the pictures, indeed the chargers are similar.
As for the potmeters, R1 and R2 are 270? and the pots themselves are 1k?.
The reason why there are two pots is most probably for redundancy.
I'll draw a sketch of the circuits used. I'll do this when I'm back home end of April. The first one I built was TPS based and in fact nothing more than just a servo drive. Using an external pot to simulate TPS gives a circuit that allows to check the working of the valve on the bench. Throttle flap follows the pot angle. One wonders why Japanese car builders have problems achieving this.
The PWM driver is the DRV101 with a 24kHz clock. I can't see why 12kHz would prevent accurate positioning.
The valve control was very good in my case but this was probably because I was using other parameters than you.

As you can see in my previous posts, positioning the valve as function of the throttle position did not result in smooth engine operation.
What works well is boost as function of the throttle position. Here absolute valve position is not important but on the other hand in this case the amplification of the differentiator is more important. If it has a wrong value, the reaction to the throttle will be vague (under reacting) and not completely closing the bypass, or oscillating (overreacting).
Unfortunately I can not give you a value for this amplification factor.
 
I seem to remember aftermarket stand-alone boost controllers drive their solenoid with a rather low frequency. I don't think it would be a problem to drive this bypass valve with a low frequency.
I hope for you that the Megasquirt is flexible and transparent enough.


Train dogs,
Teach people.

RE: Supercharger bypass valve operation

(OP)
Hi Mark,
 
I attached the schematics in pdf format.
TPS.pdf is the one I first used for controlling the valve. Although the positioning was very clear and reproducable, this was not the good way to go in terms of drivability. On the drawing I replaced the TPS by a 1Kohm pot on the bench and this makes an easy testcircuit. I must admit that I have been a bit sloppy with taking notes so it might be possible that you'll have to swap the connections #2 and 3 of the valve pot.
MAP.pdf is the circuit that is currently in use.
P1 is set at 13.5Kohm and P2 at 3.7Kohm to give the course from the lower graph attached to my post of 5 May 2009.
MAP sensor gives an output voltage in volt for absolute pressure in bar:  V = 0.5 + (Pabs / 0.6)
In this circuit there is no feedback from the valve position. It controls pressure as function of TPS. I connected the voltage from one of the valve pots to a LM3914 LED dot display driver so at least I have a visual indication of the valve movement.
Let me know if you have questions.
 
I just realised how long this project has been going on and I hope to be able to do some further testing before summer because after August there won't be much time for this kind of fun.
From the calculations I have done sometime ago I could conclude to have reached the limits of this charger. I'll see if discharge temperature will confirm this and if necessary I might go for a LYS1600AX.

Keep us updated.
Regards,

 Jean


Train dogs,
Teach people.

RE: Supercharger bypass valve operation

HI just came across this excellent site and this very useful post
I have a audi tvs charger that also uses an electronic bypass that i was going to try to convert to vac control
the tps feedback looks to be magnetic not a swiper , so is a bit different
Now i have found this i just require some one to translate as i have not a clue when it comes to electronic's
I have a DTA S60 ecu but i dont think the low current 'simple' PWM output will power this ? , i was also informed I would require a H bridge but looking here maybe not ?
can an add on module be built that could power this and reference the dta tps / map control ?
regards bob

RE: Supercharger bypass valve operation

(OP)
Hi Bob,
I'm not sure I understand your question and the reason why you want to modify.
Do you want to convert the valve actuator to a diaphragm one or do you want to modify the electronic drive so it takes into account the MAP signal and not only the TPS?
Regards,

  Jean
 

Train dogs,
Teach people.

RE: Supercharger bypass valve operation

Hi Jean
I would want to use the electronic bypass if I can and after showing your diagrams with the DRV101 to an electronic friend ,
we have decided to use the dta ecu via turbo control but with an external drv101 to boost the pwm and with flyback protection
hopefully this will work
bob
 

RE: Supercharger bypass valve operation

(OP)
Hi Bob,


If the DTA ECU has a configurable analog output then it sure can drive the DRV101 input. In that case it might even be possible to incorporate a RPM component in the process.

The point along the TPS axis where the valve starts reacting could be different for low or high RPM.

Personally I don't plan to go that far. I am satisfied with the fact that I found a way to actuate the bypass valve in a more delicate way than the vacuum actuators where only the spring pretention can be adjusted.

I also realise that the latter have the advantage of simplicity and reliability.

Good luck and keep us updated.

 Jean
 

Train dogs,
Teach people.

RE: Supercharger bypass valve operation

(OP)
Here's a brief report of the tests carried out lately.

There is no noticeable rise in charge temperature when the bypass valve is on its way between open and closed.
I feared that this would have been the case for the short time the system is operating on the slope part of the boost graphs posted earlier.
In real world all-day traffic situations this might be happening more than for a short time.
Also I just found out that on the twincharged VW TSI engine there is a "regulating flap" that is bypassing the charger and regulating the boost delivered. So it's probably not such a bad idea.

Air coming out of the charger does not exceed 90°C.
That is at WOT with the M45 spinning at 16200RPM and a boost of 10-11PSI.
I would have expected the air getting hotter when stepping into the lower-efficiency part of the charger performance map.

As for the timing related issue that's where I found it getting particularly interesting.

(average numbers, all counting from start=0)
Time needed to floor the throttle 130ms
Time needed for the bypass valve to close 215ms
Time needed for the boost pressure to rise till 95% of its nominal value in the plenum 510ms
That last one explains the lag that I noticed when testing on the track and I believe this can be improved only by decreasing the volume of the inlet path, in particular intercooler and tubes.


For reference, Kenne Bell states that supercharger reached maximum full boost in approximately the same "split second" (400ms) as the throttle being floored.
http://www.kennebell.net/techinfo/general-info/boost-vs-rpm-comparison.pdf
I could conclude that reaction time of my electric bypass setup is not bad at all and my right foot is almost supersonic because it reaches WOT 3 times faster than his :)
Under these circumstances I don't find it necessary to look for a way to increase the speed of the valve actuator, especially knowing that it's a straight DC motor and not a stepper (these are easier to speed up) and the drive consists of plastic gears.

An air-to-water intercooler might help in decreasing this lag because it has a lower volume.

So what's next? When I have some time I will try to fine tune the response curve of the valve (the graphs posted earlier).
Some fellow members have taken an effort in explaining that placing the throttle downstream of the charger is dangerous.

They are right.
If men didn't do dangerous things, we were probably all driving bicycles (which should certainly not be so bad after all).
I will think about building in some security systems but I'm wondering if this shouldn't be the object of a separate thread.
And last but not least, I'll look out for a larger supercharger because this one is far not dangerous enough smile

 Jean
 

Train dogs,
Teach people.

RE: Supercharger bypass valve operation

Hi jean
I have the Audi V6 TFSI , TVS charger as shown here with in built intercooler
http://www.fourtitude.com/news/publish/Audi_News/article_4110.shtml
this uses a half open boost valve to get its required 10 psi
after market tuners have cracked the audi ecu to close the valve further hence more boost / more power
sadly I may not be fitting this due to frabraction required and where I live ,easy option would be to fit a rotrex
but I will see if I can get this cut and welded and mounted before i give up
the dta should be able to regulate with rpm via turbo control but will be protected with a flyback diode and use an external pwm
I will let you know what happens
bob

RE: Supercharger bypass valve operation

Hi Jean,

I'm in the process of fitting my old Porsche 944 -86 (2.5 litre engine) with an Mercedes Eaton M65 (looks the same as in your pictures) with the same kind of electrically controlled (Bosch) by-pass valve. I want to buid the same kind of circuit that you posted with the signals from the TPS and MAF. I'm not to good on electrics so could you give me a little more information how to build these application and what I should take into account?

Thank You,

Frank
 

RE: Supercharger bypass valve operation

(OP)
Hi Frank,

To be honest if you don't have enough information with a schematic, I don't think you should try to build the circuit. Another engine will have a different behaviour and might need tweaking of some components values. Also you will be using a different MAP sensor and who knows is the TPS fed with another voltage as the 5V on mine.
What I want to say is that there is much chance that even if you blindly copy my circuit you will need to have the insight on how it works to be able to adapt it to your setup.
If you see when this thread has been started and the frequency of my updates you will understand that I am not able to give you much support - just because I don't have enough time, sorry.

I must admit that this was my simple approach to the challenge of making this thing work on my engine. From the electronics point of view you could have a far more performant drive system in terms of stability and ease of adjusting with a more modern design, PIC controller or the like. That's not my branch of electronics, otherwise I would have gone that way myself.

For my new project I will be using this same bypass valve again on another charger but I will make sure that a classic vacuum operated one can be fitted in as well. I have to build the intake and outlet piping from scratch which means there is the opportunity to do so.

Good luck,

 Jean  

Train dogs,
Teach people.

RE: Supercharger bypass valve operation

Jean,

Thanks for your reply. My car have a 0-5 Volt linear signal on the MAP and a 0-5 V signal on the TPS as well. As you have 2 adjustable resistors P1 and P2, are you then able to tune the caracteristics of by-pass valve? How have you physically installed the circuit?

I understand that this circuit will not work on my car necesserly in the same way than your car. But I really like the idea of having this bypass function and that is electrically controlled. So this is the only option I have at the moment because I want to use the original bypass function.

RE: Supercharger bypass valve operation

(OP)
Hi Frank,
The circuit is built in a plastic box laying on the floor at the passengers side. It's connected to the valve with a shielded cable and powered from a plug I installed for that purpose.
The resistors P1 and P2 are 10-turn Bourns potmeters with a dial knob on the front of the box.
Increasing the value of P1 will lower the point on which the bypass starts to close when opening the throttle.
Increasing the value of P2 will lower the angle of the slope but will also increase the point on which the bypass starts to close when opening the throttle. (referring to the graphs in my post of 5 May 09)
 
Depending on what the car is intended for, you might as well control the bypass valve motor with a switch or a TPS threshold. That will be easier but less comfortable for a street car.

Meanwhile I came to the conclusion that this valve has a relative large diameter compared to other butterfly bypass valves used for this purpose. I have no idea why it has been made like this.
 
The exact location of the MAP sensor on the plenum or the length of the hose connecting him to the plenum has an influence on how its output signal is a smoothed image of the absolute pressure which is pulsating. Rough idle with aftermarket ECU's can sometimes be cured by intervening on this point.
I expect it to have an influence on the working of the bypass valve driver as well. I haven't tested this yet but I'll post it here when I have results. That will not before spring anyway.

 

Train dogs,
Teach people.

RE: Supercharger bypass valve operation

Hope I'm not just stating the obvious, but Eaton style bypass valves can be physically adjusted up/down, which affects their function. Push down, boost comes in sooner, push up it comes in later.

Loosen the mounting screws to the blower, there will be a little bit of play. Push all the way up/down, tighten screws, test drive with your calibrated seat-of-the-pants meter (and hopefully a datalogger or scantool.)All the way down can lead to boost before open loop / power enrichment, and cause pinging.

"Egging out" the mounting bracket for more adjustability might not be out of the question.

This is based on experience with L67 series 2 / L32 (GM's 3.8, with M90)


 

RE: Supercharger bypass valve operation

This might be useless (very vehicle specific) but I'll mention it anyway: PCM for those vehicles has a parameter to command bypass open below 1% throttle (comes into play in decel situations.)

If this parameter is changed to say 25% throttle, it will command the valve open until that throttle % is reached. If you physically move the bypass valve down as I described above, and set aggressive boost ramp rates (if you're able to alter the original PCM programming) then the overall effect could be what you are looking for.

This obviously relies on access to the PCM software, which if you had, an external control box wouldn't be needed in the first place. So probably not relevant, but still interesting stuff.

RE: Supercharger bypass valve operation

The project is still alive ?

Has anyone tried the MAP-TPS circuit ?

Thanks

Leonidas

RE: Supercharger bypass valve operation

Hi Leonidas,

I built the TPS circuit with the same supercharger and valve as Jean (jcd06).
However, the output oscillated on/off at low frequency with the high frequency PWM signal only present during the on phase.
It did control the valve fairly accurately with feedback but at low frequency and ouside the design specification of the valve (>100Hz)
It was also not PWM, simply switching on when the valve moved out of position due to the return spring, and off when it reached the position required.

Possibly I have incorrectly built the circuit or there is a fault.

However, I opted for another approach. I build a driver circuit controlled with a microcontroller, an Arduino Duemilanove which has PWM outputs and I have written a control program using PID feedback. Eventually, the valve will be controlled by the Engine Management Computer (Megasquirt 3)that also has PWM outputs. I have used the microcontroller to learn the PID parameters characteristic of the valve.

RE: Supercharger bypass valve operation

I passingly followed this thread from way back.  Pat hit on the roots blower and either FI or carbs on the intake side of the blower.

My streetrod had a 355 cu in SBC with a 6-71 and 2 750 cfm carbs on top of it. No bypas or any of that stuff.  This car is as close to a daily driver as you can get. 510 shaft hp at 5500 rpm. I already have well over 13k miles on it in all wether except snow. It's been in the cold down to 10 deg F and heat to 105 deg F the air cond and heat work perfect too.  I get 16+ mpg on the highway and 14 cruising around town.

I get 8 pounds of boost from 2000 rpm up and no detonation (8.4 comp ratio). I can run on 87 octane but usually get 91-93.  Vacuum runs 12 inches at idle and can get up to 19 coasting.  Normal cruise vac is 10-12.

All the parts for the blower are off the shelf items selected on my experience in the hotrod world.

I also had a SC T-Bird which I drove for over 200k with no problems with the motor.  The intercooler allowed a little higher compression and the boost was more gradual up to about 2000rpm.  From there it came on pretty strong up to 13-14 psi.  Ford did a good job on this motor except for head gaskets. Many people blew head gaskets when the blower speed was increased. The fix was to o-ring the block or the heads.  The motro was just a little too small and the car just a bit too heavy to be a real super car. It still got 24 mpg most of the time.

There are lots of questions if you are putting throttle control after the supercharger.  Fuel distribution and air flow are just 2.

99 Dodge CTD dually.

RE: Supercharger bypass valve operation

Is there any way to put a mechanical valve, controlled by vacum ?

Leonidas

RE: Supercharger bypass valve operation

(OP)
Dear all,
 
Yes, this project is still alive.
It is somewhat on hold because of a pending house refurbishment but in my head it goes on :)

There is no means to adjust this valve mechanically.
You can see the valve on a picture posted Januari 11 2010.
 
Mark, it worked for me. It should be possible to have it working over there too but if you have the skills to do it with a microcontroller I wouldn't bother about the opamp stuff. Taking into account the specific valve characteristics is one thing but you still have to tell your system what output you want for a certain set of input parameters. How did you see that?
 
It is still possible to replace this electric valve by a vacuum operated one but that was not the goal.
For the setup with the new charger I will make sure to leave enough clearance so a vacuum actuator can be fitted.

Train dogs,
Teach people.

RE: Supercharger bypass valve operation

Hi Jean,
glad the project is still alive, even if it is only in your head.
I am still playing around with tuning the PID feeback parameters.
(Lots of other stuff going on here too)
I will have to define a look-up table for the boost output. this will be within the ECU program. (Megasquirt III).
I recon TP and MAP as the input parameters, with an overriding max boost limiter (built-in ECU funtion)
I would love to put data-logging on a supercharged Merc engine, to discover how MB do it.
PID feedback control tuning seems to be a black-art but I have a set of parameters that seem to work. Next is the look-up table.
Regards,
Mark

RE: Supercharger bypass valve operation

(OP)
Hi Mark,

Glad to hear about the progress of your project.
PID parameters can be calculated but often this gives useful results only when there is only few external parameters of external influence, which oviously is not the case here.
Time for some trial-and-error engineering and probably being satisfied with some compromises.

If you're wondering how MB did it I can tell you something.
Lately, -finally at last-  I had the opportunity to drive a C230 with a M271 engine with exactly the same kompressor as ours.
The game is not to control the bypass valve only, but to involve the electronic throttle as well.
This way they succeeded in avoiding any surge peaks or unwanted engine reaction.

There was no boost gauge in the car so I couldn't see the pressure build-up but the power comes in very smooth, absolutely no sudden kick-in. The same at throttle release; there is clearly a dashpot effect noticeable in the ETC response.
The compromise is that throttle response is not at all what you would expect from a Bowden cable smile

Regards,

 Jean

 

Train dogs,
Teach people.

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