Dual 3-port boost solenoid tuning idea

[bradsm87]

So I finally have an understanding of how 4-port boost solenoids work and their wonderful ability of being able to direct boost to either the top or bottom port on the wastegate.

I started reading into what they are like to tune and there is WAY more negative than positive. Most say that they're way too touchy when trying to control boost accurately. It seems many try then go back to a 3-port setup.

What about run it like this:

One 3-port solenoid to each of the top and bottom ports. The top one is at 100% dc by default, letting the top port stay at ambient pressure by default. The bottom one operates like a traditional 3-port solenoid setup. Run them staggered. For low boost targets, you use the traditional boost control setup and top solenoid remains at 100% dc. You set up a GP PWM output to drive the secondary (top) solenoid with the output of the first boost solenoid as the axis. You then map out the high boost boost target zone that the traditional arrangement can't maintain due to EMAP pushing the valve open (the areas where high DC on the primary boost control solenoid are used) and gradually reduce duty cycle on the top solenoid as primary boost solenoid duty cycle increases to let some boost into the top of the wastegate.

Even if you just use a small range of top solenoid duty cycle right at the top of the range of the primary solenoid where its operation is no longer linear, just to get a bit more range out of it, I think it could work really well.

I'm very tempted to order another 3-port solenoid and try this. That way you get the fine control that the 3-port setup is best for but can add some boost to the top port only when needed.

Better yet (safer) would be to find a secondary solenoid that operates in the reverse manner as the usual ones so that it is closed by default and keeping the top port vented by default in case it gets unplugged or something.

I attached a pic of the secondary (top) solenoid GP PWM DC table. Primary boost solenoid DC is the axis. It does nothing until 50% WGDC then gradually comes in after that.

[Adamw]

It will need to be a bit more sophisticated than your picture above but the control system you describe is what some higher end systems call phase/anti-phase wastegate control.  In theory if you put the time in to linearise the system properly then yes you could potentially get a wide range pressure control that was more linear than a 4 port or two 3 ports just plumbed in reverse NO/NC.  These higher end systems actually even go a bit further and have deadtime and battery voltage correction curves for the solenoids to get it as linear as possible.  

However, in practice in the few maps I have seen set up this way from fairly high end WRC cars, the solenoids were just set up to work in exact inverse of each other - i.e. exactly the same as how a single 4 port would do it...   

[bradsm87]

5 hours ago, Adamw said:

It will need to be a bit more sophisticated than your picture above but the control system you describe is what some higher end systems call phase/anti-phase wastegate control.  In theory if you put the time in to linearise the system properly then yes you could potentially get a wide range pressure control that was more linear than a 4 port or two 3 ports just plumbed in reverse NO/NC.  These higher end systems actually even go a bit further and have deadtime and battery voltage correction curves for the solenoids to get it as linear as possible.  

However, in practice in the few maps I have seen set up this way from fairly high end WRC cars, the solenoids were just set up to work in exact inverse of each other - i.e. exactly the same as how a single 4 port would do it...   

My main concern is that the 4-port is widely seen as extremely touchy and doesn't work well for boost targets close to wastegate pressure (targets I intend to use for accelerator positions around 60%). Many say it doesn't come into a good usable range until you're at least double the wastegate pressure. If I keep the top port completely out of the equation at lower boost targets, I thought operating staged solenoids would fix this, only having the secondary (top port) solenoid slightly come in gradually as WOT boost target approaches.

[Stevieturbo]

On 5/15/2020 at 10:31 PM, Adamw said:

- i.e. exactly the same as how a single 4 port would do it...   

And can easily be done with a 3 port too....

 

It's not rocket science. But the first question is.....do you even need this mode of control ? What issues are you having that you feel the need to do it this way ?

 

But a 4 port solenoid should work too, they just respond a bit slower than a 3 port.

[bradsm87]

41 minutes ago, Stevieturbo said:

And can easily be done with a 3 port too....

 

It's not rocket science. But the first question is.....do you even need this mode of control ? What issues are you having that you feel the need to do it this way ?

 

But a 4 port solenoid should work too, they just respond a bit slower than a 3 port.

The reason I bring it up is I want to purchase things and wire up the car once and right the first time. I've heard way more horror stories about 4-bort boost control being way too touchy than good stories. I'd like accurate boost control anywhere from the 3psi wastegate pressure up to 15psi. I thought using a traditional setup to control the bottom of the actuator only for finer control over the lower targets then only gradually bring a little in to the top port when needed would be the best way to achieve this.

[Stevieturbo]

Can't say I've heard any horror stories, and I know a few guys using 4 ports without issue.

 

But really...a 3 port can do the same job anyway, been doing it on mine for years.

[bradsm87]

4 hours ago, Stevieturbo said:

But really...a 3 port can do the same job anyway, been doing it on mine for years.

Really? 15psi with a 3psi wastegate spring as I mentioned?

[Stevieturbo]

On 5/24/2020 at 3:21 AM, bradsm87 said:

Really? 15psi with a 3psi wastegate spring as I mentioned?

There is no fact that any setup can do that on every application, because every setup is different.

 

But there is pretty much nothing a 4 port can do, that cannot be achieved with a 3 port. Nobody can guarantee you either will allow you that pressure range, and you will not know what it can do, until you try.

[bradsm87]

I ordered a Circuit 7 4-port solenoid with a wider usable duty cycle range than the off-the-shelf 4-port Mac solenoid so that should be a good place to start and that's what I'll try first. I'll chuck another wire in the loom to keep the option of running 2x 3-ports just in case.