Boost control solenoid operation

[laxplayermjd]

So i did some reading today and learned alot and made a whole lot more sense to me.

http://perrinperformance.com/pages/show/113

Great explinations of how turbo boost is controlled with boost solenoids.Lots of great information for anyone. Yes its alot to read.


So i tried to copy and paste, the pictures did not transfer. You can also go to the linked site. Now everything makes more sense to be because BMW TURBO SYSTEM OPERATE COMPLETELY OPPOSITE. Bmw wastegates are normally open and controlled with vacuum to close and a higher wgdc means more vacuum to hold the wastegate closed.



Boost Control Explained....


This collection of parts above are typical items you will find in a modern boost control system and many aftermarket type system.s Some items may not be reconizable, but after you read this, i think you will be able to pick out any of those parts and understand what they do and how they work.

Modern day boost control systems rely on both mechanical and electrical systems to control boost. The main electronic component is the ECU, which drives an electro-mechanical device that controls the wastegate actuator. Besides the ECU being an important electronic device in controlling boost, the second most important part is the electo-mechanical device known as the boost control Solenoid. Below is the PERRIN EBCS Pro (Electronic, Boost, Control, Solenoid) which replaced the OEM Boost control solenoid to provide better more accurate boost control.



In most turbo applications the boost solenoid is used to bleed boost pressure off the hose that actuates the wastegate actuator. In these applications the boost control solenoid has 2 ports, an IN and an OUT. The PERRIN EBCS Pro can be setup like the stock solenoid, to "BLEED" boost from the system, but that is not where the EBCS Pro has its advantage. The PERRIN 3 port EBCS Pro can be setup to "block" pressure from getting to the wastegate actuator. This makes for a more responsive turbo and for much better boost control, not to mention higher boost levels are possible with proper tuning. In this case 3 is better than 2!

In some cases the EBCS Pro can work with your stock programmed ECU, but to use the EBCS Pro to its fullest, a reprogramming of the ECU must be done. These days this is no big deal as its something that can be done with nearly any car. The EBCS Pro also works very well when using stand alone type ECU's where adjusting boost tables are possible. The EBCS Pro can be used to replace a worn out, or damaged aftermarket solenoid used in a standalone Electronic Boost Control system. In these cases the EBCS Pro will fuction the same, but cost half of a replacement part.

Now included with each PERRIN EBCS Pro is a female harness plug, that plugs right into many OEM wire harnesses. This means no cutting of wires, just simply unplug the OEM one, and plug ours in! Simple as that! Along with this convenient plug we include a set of instructions to show how to install the EBCS Pro in nearly every type of turbo application out there. I say turbo application because I know there are those guys with their normally aspirated Honda's reading this thinking they can add more boost to their car! Sure you can, just like you can add a BOV! If you don't know what a BOV is, that's another article in the works!

How does the boost control system work?
So you are sold our the PERRIN EBCS Pro, but how does it actually work in controlling boost. First understand the mechanical aspect of the boost control system. There is a actuator which turns boost pressure into a mechanical action that pushes the wastegate open on the turbo. The wastegate has a spring in it set to a specified boost pressure. Boost pressure has to exceed the spring pressure before it starts to open the wastegate and control boost. An example, a wastegate actuator set to 10psi will not open the wastegate until it hits 10psi, in turn controlling boost to 10psi. The most basic boost control consists of a hose running from a boost source directly to the wastegate actuator. So what is a wastegate, and wastegate actuator, and how does it actually work?

What is a WASTEGATE?
First thing to understand is what a wastegate is and how it works. On most turbocharged engines there is mechanical system called a wastegate (Turbo diesel engines do not have them a lot of times, but that is a whole other story). The job of the wastegate is the same weather internal or external. Think of the wastegate as a door that opens up and lets exhaust flow around the turbo. Internal type wastegates are built into the turbo, and External Wastegates a separate mechanism that bolts to the exhaust manifold before the turbo. Either system functions the same by by-passing the exhaust around the turbo to control boost.





The wastegate opens and by-passes the exhaust around the turbo it changes the speed of the turbo. Which in turn controls boost. By opening the door, it slows down the speed of the turbo (making less boost). When it closes it forces the exhaust to flow through the turbo, speeding it up (Making more boost). The system doesn't work as "on or off" as just described. Its not just opened or closed to control boost, but modulated to many varying degrees to divert just enough exhaust around the turbo to create the desired boost. The above diagrams shows an internal wastegate in both the open and closed modes. The first picture illustrates the exhaust passing through the turbo with the wastegate door closed. The second picture illustrates the wastegate door open and it diverting exhaust pressure around turbo.





Tial 44mm External Wastegate Garrett OEM Style Internal Wastegate Actuator

Both internal and external function the same using a "door" to control how much exhaust is diverted around the turbo. But what makes them different is how the "door" works and how its actuated. In an internal wastegate setup the door is a mechanical door that blocks a hole on the turbos exhaust housing. The door is attached to an arm that is then attached to the actuator. The actuator is a separate part that bolts onto the turbo with an arm that opens and closes the door.





Above is a cutaway showing the basic construction of an internal wastegate actuator. Picture 1 is showing it in resting position and picture 2 shows it with boost applied to it. The Red represents the diaphragm, the green represent the spring.

An external wastegate doesn't use a door but rather a valve not much different than an exhaust valve inside your engine. The valve has a seat that it sits on blocking the exhaust pressure. The valve simply lifts off the seat to divert the exhaust around the turbo. The valve is actuated by an actuator like an internal wastegate but the actuator and valve are all one piece.



The above picture shows a cutaway of an external wastegate. Picture 1 shows wastegate in resting postion, and picture 2 shows the wastegate open. The red represents the diaphram, the green represents the spring, and the blue represents the valve. The orange arrows represent exhaust flow.

ACTUATOR what is that?
The actuator for both types is the most important part to understand as it is what ultimately controls boost. Actuators have a pneumatic portion that controlls the mechanical movement, and the movement is resisted by a spring. Using the above diagrams you can see they have chambers divided by a diaphram. Pressure can be applied to either side of the diaphram. As pressure enters these chambers they cause the valve to actuate but only after the pressure exceeds the springs pressure. Meaning if the spring is a 10psi spring, the valve will not start to actuate until the pressure in the chamber goes above 10psi. An internal wastegate typically only has 1 chamber were pressure is applied to (shown above). An external wastegate can have 2 chambers as shown above which we will get into later.

Both types have to work against exhaust pressure. So the design of the wastegate can be very important to ensure that the exhaust back pressure doesn't effect the desired boost. In many OEM setups this is a factor that works against the boost control system. Meaning that maximum boost may not be able to be reached because the exhaust back pressure is opening the wastegate regarless of what the actuator is doing. This is not good for us when trying to make big power, but it is smart for an OEM to design a system with this in mind as this inhearently has some saftey features built into it.

Now that you understand how the wastegate changes the speed of the turbo, and how the wastegate is actuated, the next diagram will make a lot of sense.



This above diagram shows a turbo representing the boost source. As the boost pressure goes up, that pressure is routed to the wastegate actuator (weather internal or external) and when the boost pressure exceeds the spring pressure in the actuator, it will then start to open and control boost. This example is below.







How do you get more boost than the spring pressure in the wastegate?
The above diagrams are somewhat typical setups found in simple aftermarket turbo systems, but not something you would find on a factory turbocharged car, (more on this later). In order to get more boost than the spring pressure in the wastegate actuator, pressure needs to be bled off the hose going to the wastegate actuator. This in turn delays when the wastegate will start to open and control boost. Think of this as tricking the wastegate as to what boost it's seeing. Boost pressure can be bled off in a few ways, using a mechanical bleeder type system with a needle and a seat, a small opening or bleed hole, or the more reliable and accurate way using an electromechanical solenoid.

A solenoid is a simple valve that is mechanically opened (or closed) when battery voltage is applied to it. This is done using a coil winding surrounding a ferrous metal actuator. The battery voltage passes through the coil and causes a magnetic field which moves an actuator that pulls open a valve. Typically these are setup to bleed air from the hose going to the wastegate actuator. But the solenoid doesn't work as on off as describe. In fact the valve is turned on and off very fast to vary the amount of pressure bled from the hose. The speed and length the valve is opened, effects how much pressure is being bled off thus effecting boost!



This above diagram shows a typical solenoid used for boost control at rest and also with voltage applied to it. The blue represents the coil that when engergized creates the magnetic field. The Green represents the ferrous metal, the red represents the valve being actuated and the orange arrows indicate the air flowing.

As mentioned above, the speed and length at which the ECU turns the solenoid on and off, effects the amount of air being bled and when the wastegate actuator actually opens. The ECU produces this pulsing (on and off) signal in based on tables in the ECU and many calculations. This pulsing signal is commonly known as the wastegate duty cycle. This duty cycle is a percentage of how long the solenoid is open for a given time. Because the solenoid can open and close only so fast, it has a normal operating frequency. The frequency is how many times it can operate in 1 second, referred to as hertz (not the rent a car company). Typically solenoids work in the 10-30hz range, but this is not what the ECU is changing to increase boost. Back to the duty cycle. The duty cycle is a calculated a percentage of time the solenoid is actually open. Meaning 50% DC (Duty Cycle) means the solenoid on for 50% of the time, and 100% means the solenoid is on all the time. The more time the solenoid is on, the more air is bled from the system, and in turn the longer the wastegate is delayed from opening.





One second of time show above. This example shows a solenoid working at 5hz (turning on and off 5 times in 1 second) and then shows 25%-100% duty cycle. This allows you to visualize the amount of time the solenoid is actually open at different duty cycles. NOTE: the 100% doesn't show it operating 5 times in 1 second because its on all the time.



The ECU can vary this duty cycle signal to the wastegate solenoid to vary the boost higher or lower, to account for temp changes, atmospheric pressure changes, provide a steadier boost curve and even cut boost in situations when a failure has occurred. The ECU has many special maps/tables that determine the DC to use to control boost. This includes target boost tables, min and max DC tables, Boost error trim tables, air temp trims, speed trims gear trims and many more. The ECU uses these with a complicated algorithm to calculate duty cycle and then adjust it to reach its target boost. Here is an example of how this works and an example of the diffent typs of maps used to control boost.







If the ECU sees the driver giving 70% throttle at 4000 RPM it reads a map that says it needs to hit 14psi. The ECU starts with a duty cycle of say 50%. Say it only hits 12psi at 50%, the ECU knows its off by 3psi and adds more duty cycle based on a boost error trim table. Say this equals 5% more duty cycle. Now its running 55% and the ECU is seeing 15psi of boost. Its still a bit high and using this boost error trim table it now pulls some duty cycle from the overall 55%. Lets say it removes 2% and now is at 53%. Now it hits its 14psi target and the ECU is happy until the boost starts to fall as the RPMS rise, or until the driver gives 100% throttle making for a new target boost. The calculations start all over again. This back and forth, and calculating happens many times a second to provide the engine with a steady boost curve. This is a very simple version of what actually happens. There are things like the time it waits to see if the calculated duty cycle actually worked, and start RPM's, gear ratio comps air temp trims, and many other things. This is a pretty complicated process but its what makes modern day turbo cars function so well with little turbo lag and all the safety features.

This duty cycle signal exists in all electronic boost control systems and is very important to understand in order to better use the PERRIN EBCS Pro.



Above is a diagram of a typical OEM boost control setup using a typical 2 port solenoid. First is the system at rest with 10psi of boost coming from the turbo. At this point the solenoid is off and redirecting pressure to the wastegate making it open and in turn controlling boost to 10psi.







Now the solenoid is turned on bleeding pressure from the system. This in turn takes away the pressure that was pushing the wastegate open, and lets the wastegate close increasing boost pressure. Now imagine that happening all very fast on and off varying the degree at which the wastegate is actually open.

Below is an boost control system from a Subaru. This shows a great example of a bleed type system that most all OEM's use. While it does work, its not the most efficient. All main parts of the boost system can be seen here, excetp the solenoid. The solenoid on most system is mounted somewhere off the turbo, and engine. Typically mounted to the chassis away from extreme heat.







In OEM setups, like the one above, the wastegate duty cycle can get maxed out to 100% and still doesn't provide the desired boost. This means in some applications power is being held back because the solenoid can't do its job properly. In many OEM "bleed" applications this is remedied by using a restrictor in the hose coming from the boost source. This are in place to limit the amount of work (Bleeding) the solenoid has to do. While a bleed type system can control boost, they leave a few things on the table that can be improved on.

One is boost response. The factory type 2port solenoid bleed type systems are always putting some amount of pressure on the wastegate actuator which means its already starting to open the wastegate (before it hits its boost target) and in turn loosing some turbo response. This may not seem like much pressure pushing it open, but you have to consider the exhaust pressure is also trying to push it open at the same time. The exhaust pressure can be double the boost pressure and also greater than the wastegate actuator spring. Which means even a small amount of pressure can start to open the wastegate and effect boost response. In some cars the exhaust pressure completely blows open the wastegate making for increasing boost nearly impossible.

Secondly a bleed type system may not be able to bleed enough air at higher RPM to reach the desired boost pressure. While changing the size of the restrictor can help this, its still a band-aid for a poorly working solenoid and poorly working system.

The good thing with these types of system is they are simple only a few parts to install and go wrong not to mention they are cheap to make. Also if the solenoid fails it would default to the wastegate spring pressure for boost control. This safety aspect is important in all boost control systems and holds true with the PERRIN EBCS Pro. The PERRIN EBCS Pro (Electronic Boost Control Solenoid) utilizes 3 ports to control boost, which can be setup in many ways other than the stock "Bleeding" type system.

WHY DO I NEED THE EBCS Pro?
Ok you know how a solenoid works to control the wastegate and how the ECU uses it to control boost, why do you need the PERRIN EBCS Pro?

The PERRIN EBCS Pro is designed to work best in our "Fast Response Mode" or "Interrupt mode". In this mode, the solenoid requires less DC (duty cycle) to get the desired boost. This means that in situations were the OEM solenoid is working at 100% to do a given job/boost level, it can be setup to use roughly half the DC% and get the same results. In turn this provides more head room for further tuning or adding more boost. We all want more boost unless you are a Prius, where you want more battery!



EBCS Pro Pro in resting position letting air pass through EBCS Pro Pro above is turned on, blocking boost.

A benefit is the EBCS Pro keeps more boost pressure off the wastegate actuator. It does this by blocking pressure going to the wastegate actuator completely when it turns on and off instead of bleeding pressure. This makes the turbo more responsive and spool quicker. Above is a diagram showing how our solenoid is different on the inside compared to the OEM type. It has a few passageways to allow us to set it up more effectively.

Its works like this: The boost enters the solenoid and passes through to the wastegate actuator when the solenoid is turned off. When the solenoid is turned on by the ECU it blocks boost pressure from getting to wastegate actuator and at the same time relieves any pressure built up in the line going to the actuator. If desired and if programmed to do so the solenoid can be run to completely block pressure getting to the wastegate actuator until that last moment before a boost spike occurs. This makes for a very fast spooling turbo.



System shown with the solenoid off, and passing the boost right through to the actuator making it open at 10psi.



Now the system is showing the solenoid turned on blocking pressure getting to the actuator and in turn bleeding off any built up pressure that was in the actuator. In turn increasing the overall boost pressure.



This is the same setup but using an external type wastegate. You can see in this setup the hose needs to go to the bottom port.




External Wastegate using Top and Bottom Ports
Another benefit is that the EBCS Pro can be used with aftermarket external wastegates as shown above but with a twist. Because of the 3 ports, this enables the use of both top and bottom ports found on most aftermarket external wastegate actuators. In these setups they can provide even better more reliable boost control! While this is not a typical setup, if you are using an external wastegate and can manipulate the tables in the ECU this can make for a powerful setup.





Shown above is the system at rest controlling boost to 10psi, which is the wastegate spring pressure.







With the solenoid turned off the boost pressure pushes the wastegate open at the set spring rate. The top port is vented to the outside air. When the solenoid turns on, pressure is diverted to the top of the wastegate holding the wastegate closed longer and better. This method is great and allows the use of a very light wastegate spring, but still the ability to run huge boost levels. The reason why using a lower rate spring is this allows for better modulation of boost in part throttle situations where you don't want too much boost.

ECU must be reprogrammed!
The downfall to using the PERRIN EBCS Pro solenoid in any of the above manners is that you HAVE TO REPROGRAM THE ECU! Because the solenoid is blocking pressure getting to the wastegate when its turned on by the ECU, it has to do less work. In turn less DC is needed to get the same boost levels. If used with stock ECU programming over boost, or boost spiking can occur, which can blow up your motor!

So all that talk just to get you buy a PERRIN EBCS Pro, why not just buy a manual boost controller? In todays electronic control engines, and engine systems, being able to utilize the electronics to the fullest is important to keep your engine in the safest working order possible. Most ECU's have over boost protection base on bad fuel or other parts failing, and its important in a high performance engine to keep these safety features working. If a manual boost controller was being used, they are a completely separate mechanical system that has no idea you just filled up with 87octane fuel and your engine is knocking. Not to mention with the ECU controlling boost you can have a smoother delivery of boost. In part throttle situations, the ECU can deliver partial boost levels where a manual boost controller will deliver full boost and act more like a light switch. This can make for a twitchy feeling car typically found in older turbo setups.

So when is the manual boost controller good to use? There are tons of situations where they come into play like in race cars, drag cars, or in boost systems where simplicity is important. Normal road going cars can use them, guys that don't have the ability to reprogram the ECU love these as a few simple twists and more boost! One thing we run into a lot is guys don't have boost gauges. Its very important, no "NECESSARY" when using a Manual boost controller to have a boost gauge! Because its "manual" you have to adjust it to your desired boost level, the boost controller fairies have no idea where you want your boost at. Also for many guys these are fun to have as they like to tinker with their car. It allows for some control over what is going on.

Manual Boost Controllers
You understand how boost control systems in general work but where does a manual boost control fit into the system? Simple! Using the above diagrams replace the solenoid with our manual boost controller.



How does the PERRIN manual boost controller work? There are 4 main components to it, the body, stem, spring and ceramic ball. Boost enters the body but is blocked by the ceramic ball. The spring behind the ball keeps the boost from getting past the ball. The stem gets screwed into the body which changes the pressure needed to move the ball off its seat. When the ball moves off its seat, the boost flows through the boost controller and actuates the wastegate actuator. The ball simply delays when the boost gets to the actuator. One key thing to our MBC (Manual Boost Controller) is our bleed hole. In the stem is a bleed hole that serves 2 purposes. One is to relieve pressure from behind the ball when the turbo is not making boost. If this wasn't there the wastegate would be stuck open after the first time it made boost. The second purpose is to bleed some of the volume of air flowing through the MBC. This helps with keeping a steady boost curve that doesn't drop off severely at higher RPM.



You can see the install is very simple. Hose in on one side and out the other! Another benefit over the EBCS Pro is installation. These can be installed in a few minutes and adjusted and tune in a few more. Overall the Manual boost controller is cheaper easier to install and adjustable by anyone with a boost gauge.

The question that comes to mind is which one is best for me?? That all depends on your intentions, your tuning ability, your mechanical skills, or you budget. You can see the benefits of both, and you just need to weigh those decisions to figure out your best option.



This is an example of an EVO 9 showing stock boost and then the yellow line is the boost curve after ECU tuning and installation of the EBCS Pro. For this application all of our custom tuned AccessPORT maps are tuned specifically to use this EBCS Pro. This decision was made because the OEM boost control system used a 2 port solenoid, and a few restrictors to help control boost. The OEM solenoid had issues with holding more than 18psi beyond 6000. The EBCS Pro in this situation is perfect and provides very good and when required very high boost levels.

Well hopefully this can help everyone better understand what is going on when their turbo starts to sing!

Myths and Misunderstandings
With turbos and their control systems there lots of terms that come up, and also a lot of misunderstandings. One of the more common ones we get with Subaru customers is a strange phenomenon known on the forums as wastegate flutter. People get this strange flutter at a certain RPM then it goes away once past it. The sound leads people to think it's the wastegate door fluttering making this CH CH CH CH CH sound. Not tying to say you are all wrong, but you are all wrong. This sound is compressor surge. Look up the definition and you will find 2 versions. One has to do with blow off valves when they do not function and relief enough boost pressure. This happens only when the throttle is closed and the boost the turbo is making has no where to go. The boost backs up and goes backwards through the turbo. The turbo speed goes from 100,000rpm to nearly a stop and the air rushing backwards out the intake causes the weird fluttering sound. The Blow off valve is in place to vent this boost from the system to keep the turbo spinning.

The second version is similar but happens under load with the throttle open. The short description is the turbo pushes more air than the engine can consume. When this happens the same type of thing happens like above. The air backs up through the turbo and causes it to slow down (not necessarily stop). This causes the same weird fluttering sound. This only happens at lower RPM where the engine can only flow so much air. This is not a problem on stock cars as they run less boost, have restrictive exhausts and so on. But add free flowing exhaust, and turn the boost up, you will start to hear compressor surge. An example is an STI (2.5l)with a stock turbo. Running 18psi or more, at 3400-3500rpm and higher gears, you will hear the surge/flutter happen then go away once past 3800. This is completely normal happens for such a short period of time, there is generally no ill effects.

Say you have a 2.0L EVO, with a little bigger turbo, and all the free flowing exhaust, intake and other goodies. At low RPM (3500) running 20+psi compressor surge starts to happen. But its doesn't just go away a couple hundred RPM later, but it keeps happening! On these cars it gets so bad that the fluttering (air moving turbulently out of the turbo) causes the whole car to shake, causes crazy MAF sensor readings and the power to significantly drop. This happens much worse on the smaller engine because at lower RPM they consume less air than the 2.5l. The EVO benefits from the turbo being right next to the head which allows it to spool up very fast making more boost at low RPM than say a WRX, which also makes it worse. 2.0L WRX guys may hear the sound but not notice a change in power. This is because the WRX puts the turbo a lot further away from the heads, which causes a loss in turbo spool and means less boost at those low RPMs. To fix this, run less boost! But that is no fun! Seriously a couple of psi less and the problem can be solved. That was a pretty long explanation, but I hope it makes sense so the next time you are out with your friends and they are complaining about wastegate flutter you can correct them! Also look out for some diagrams showing this in our article that explains BOV's and compressor surge.

That might be more than you wanted to know about boost controllers and boost systems. While there are many more aspects about boost control systems, like how to tune them, how the ECU works exactly in conjunction with the sensors, how much boost you should actually run with your turbo, how much boost your engine can take.... I will have to end it there. Keep an eye out for more articles explaining those things in more detail!

Here is that same pic as above, but now its labeled with what the parts really are. If John L actually read this, the secret password for your free lunch is "aquamist".

[Ugnius @ VersaTune]

This is a great article, thanks!
It's best to read it together with images, though.

[fez]

Nice article indeed! Very helpful.

Now here comes the question... Should I redo my system to run in interrupt mode or leave it in bleed mode similar to stock?

[laxplayermjd]

beats me, i still dont know which would be better. but i believe that one is opposite the other so the tune wgdc needs to be modified to work.

When i get mine im sure ill run it bleed mode like stock

[Ugnius @ VersaTune]

Well Perrin article says that interrupt mode has the advantage that much less solenoid duty cycle is required to achieve the same boost pressure. So if you're running close to 100% DC in bleed mode, you might consider switching to interrupt mode.
Interrupt mode can also help achieve faster boost response by preventing premature opening of wastegate by the residual pressure that is in the line.
On the other hand if no pressure pushes the top of the WGA diaphragm, the pressure differential will be bigger and the exhaust pressure will have a tendency to blow the WGA open, so you will need a stiffer WGA spring.

[laxplayermjd]

i guess each way has its pros and cons. lets wait for steve to chime in haha

[Steve @ VersaTune]

Interrupt mode should be more responsive. You need a 3 way valve to do interrupt.

[fez]

ok, looking at the diagrams again I decided to call a guy who did my build. He confirmed that my solenoid is set to interrupt mode - 3 ports (top and bottom of EWG, and boost source).

Steve,
Is there any specific tuning that needs to be done because I have this kind of setup?

[Steve @ VersaTune]

Generally it requires less solenoid duty cycle. Which solenoid and wga do you have?

[fez]

Perrin 3 port like this:
http://www.gstmotorsports.com/store/ind ... cts_id=508

And I'm running a 38mm tial ewg.