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Boost Control: Input Configuration

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Input Configuration

16.29

00:00 - You'll notice through this worked example that we've got our car on our mainline chassis dyno. It doesn't really matter if you're tuning boost control on the dyno or out on the road, the procedure and the steps that we're going to take will be identical. Really it just comes down to using the feedback from our data logging to decide how well our boost control system is functioning, and what our next step is, what changes we're going to make next, and then validating those particular changes so on the road or the dyno, the procedure is exactly the same.
00:36 Now we're going to have a look at the actual setup and configuration of the boost control system.
00:41 And we're going to do that in our initial setup two workbook and in our boost control worksheet.
00:49 Now I'm going to, before we get into that, I'm going to just discuss a couple of differences with the way the M1 deals with boost pressure control.
00:58 The first is that we have the option of running an additional boost pressure sensor that's fitted to the inter cooler pipe pre-throttle body.
01:06 Now, this isn't essential but you can fit one if you wish.
01:11 And this will be controlling the boost pressure in the inter cooler pipe pre-throttle body as opposed to inlet manifold as we would do conventionally.
01:21 Now the other difference with the Motec M1 ECU is the way the boost pressure targets are defined.
01:28 The M1 uses gauge pressure, which is the pressure relative to atmospheric pressure. The older 100 series Motec ECUs and a lot of other ECUs on the market will be targeting an absolute boost pressure. If you don't understand the difference between these two, you can end up getting yourself in a lot of trouble targeting more boost than you expect. So if we look at a conventional ECU, perhaps Motec's 100 series ECUs, and let's say we were targeting a boost pressure of 200 kpa.
02:01 So what we meant there was 200 kpa absolute, so that is 100 kpa of positive boost pressure.
02:09 If we wanted to achieve the same target in an M1 ECU, we would actually be wanting to enter the value 100 kpa in our gauge pressure targets. So you can see there's a really big difference there.
02:22 Now I'm going to mention that a couple of times though this worked example because it really is very critical.
02:27 If you get it wrong you could end up in a lot of trouble with the amount of boost pressure your engine is actually seeing.
02:33 Okay, with that being said, let's drop into the software, and we're going to have a look at the configuration.
02:39 And we're going to deal with this in a few different aspects and we're going to start with the input to the ECU.
02:45 In this case we've got our boost pressure sensor setup which we've just discussed. So this is if we want to use an additional boost pressure sensor fitted pre throttle body in the inter cooler plumbing. If we want to do that, we would need to define a voltage resource for that sensor.
03:03 Then we would need to calibrate that particular sensor.
03:07 And we've also got some diagnostic values to let the ECU know if the sensor is in fault. We can also filter the input from that sensor if we wish.
03:19 Now, it's not essential to fit a boost pressure sensor like this to the ECU and if we leave this as not in use, which we've got here, the ECU will use the inlet manifold pressure sensor for its boost pressure targeting as you would have expected in a conventional ECU or Motec's older 100 series ECUs. It also reverts to the inlet manifold pressure sensor if the boost pressure sensor and the inter cooler plumbing is fitted but goes into fault.
03:50 So because we haven't got that setup, we're not using that particular sensor, we can leave all of this set as it is in default and set to Not in Use.
04:01 Now the input we are using though is our inlet manifold pressure sensor. So we've already configured that as part of the basic tuning of the engine, one of our basic configuration aspects. We can filter the boost and this is going to be important particularly if you've got a very noisy boost pressure signal. If you're seeing a lot of noise on that signal, what's going to happen is the ECU will actually be chasing the small peaks and troughs in that signal, so we can apply a small amount of filtering to the boost pressure signal. And it's important here to understand we don't want to use too much filtering or it will actually slow down the response of the system.
04:42 A value of somewhere between 0 and 20 milliseconds is generally an acceptable amount of filtering.
04:50 Now we can move into our activation parameters for our boost control system. And we've got a few here.
04:56 We've got our Boost Activate, which is when the system first becomes active and starts trying to control boost.
05:03 So we want to set this to a relatively low value, somewhere below the pressure at which the waste gate will normally open. So in this case I've selected 10 kpa gauge and I've found this to be a pretty good starting point point. We've also got our Boost Margin and we've got our Boost Maximum. Now these aspects all interact together and I'm just going to explain how they work. So once the boost pressure is above the activate value, what it will do is it will demand maximum duty cycle from our solenoid to try and drive the boost pressure towards our target.
05:42 The margin is the value above and below our current boost target. So when, in this case we've got a margin of 20 kpa. So let's say we were targeting 100 kpa of boost pressure, when we're 20 kpa below that, so in this case 80 kpa, at that point the ECU will go into closed loop boost control.
06:03 So between our activate point of 10 kpa and the lower margin, which would be 80 kpa, the ECU will be driving the solenoid at maximum duty cycle to try and bring the boost on quickly.
06:15 As soon as we come within the margin of our boost control target, then the ECU will actually start controlling boost.
06:22 Likewise, if we end up above our boost target by the same margin, so in our example 120 kpa, the ECU will go to 0 duty cycle in the solenoid to try and bring the boost back down.
06:35 At the same point we also can have a boost maximum.
06:39 So this is our over boost cut and if we hit this point, then the ECU will cut fuel spark to prevent boost increasing further, so this is our safety margin.
06:51 So generally this would be set somewhere above our boost aim plus our boost margin.
06:58 We've also got a Hysteresis on all of these values so it stops the system cycling in and out quickly and I've set this to 5 kpa, which is probably a pretty good default value to use.
07:09 This just stops the system from cycling in and out if we're sitting at one of those particular margin points.
07:17 Next we have our Boost Actuator Output Frequency, which you'll remember from the main body of the course is the frequency that we're going to be pulsing the boost control solenoid at. In this case I've selected 20 hertz and again from the main body of the course somewhere between 15 and 20 hertz is a pretty typical value.
07:36 Another thing that's a little bit unique with the Motec M1 ECU is that we can define the minimum and maximum duty cycles that will be applied to the boost control actuator. So remember again from the main body of the course we found that at very very small duty cycles and also at very large duty cycles the solenoid doesn't really respond properly so what we can do in the M1 we can actually define these values so that the ECU will ignore the bottom end and the top end of the solenoid range, and that means that any time we're targeting a value or asking for a duty cycle it will be within the linear operating area of the boost actuator.
08:18 So I've set our minimum at 15% duty cycle and our maximum at 85% duty cycle.
08:26 Now how this works is that we have a base duty cycle table in the M1 it's called our feed forward table.
08:35 And the value of 0 in that table will equate to our minimum.
08:41 So in this case, while it sounds a little bit complicated, all it's doing is simplifying our tuning because it makes sure that when you're entering numbers into the feed forward table, we're always entering a number that will actually result in the solenoid doing something.
08:55 So when we enter a value of 0 in our feed forward table, this will actually pulse the solenoid at 15% duty cycle. Likewise when we enter a number of 100% duty cycle in the table, it will be pulsing the solenoid at our maximum duty cycle, in this case 85 percent.
09:13 What that means is we can enter a number anywhere between 0 and 100 in our feed forward table and we can expect the solenoid to respond. So that's just another unique aspect of the way the M1 deals with the boost control solenoid.
09:29 We've also go an actuator polarity and this is quite important to make sure that we understand how this works.
09:35 This will depend a little bit on your solenoid as well as how it's been plumbed up.
09:40 So if we've go the solenoid's polarity set normal what this is going to mean is that the output duty cycle will be equal to the requested duty cycle so in that case if we are asking for 20% duty cycle that is what's going to be sent to the solenoid.
09:58 If on the other hand we select inverting, we're going to get the inverted value of that so in that case it would be 80%.
10:05 This is important to get right because if you have this around the wrong way, what's going to happen is our boost control system will work backwards to how you expect it to behave and when you ask for lower duty cycles you're actually going to end up with more boost pressure.
10:21 So it's really important to get that right before we go any further. Now we've also got our boost control mode, which is what tunes the whole boost control system on or off. So if we want to use our boost control system, we need to enable that to start with.
10:38 We've got our feed forward, our proportional gain, our integral gain, and our derivative gain.
10:44 So from the body of the course you'll remember, these are the areas we're actually going to be doing our boost control tuning. We're going to come back and look at that when we get into the tuning part of the course. For the moment we're just going to leave them.
10:58 Now when we have our boost control solenoid wired up and ready to go, we can actually use our boost control mode to test the actuator. So we can click on test actuator and what that's going to do is it's going to pulse our actuator at a duty cycle of 50% and you should be able to audibly hear that solenoid clicking or buzzing away in the engine bay.
11:26 So that's a good way of testing and making sure that our system is wired up correctly and it's actually being powered and working.
11:34 It's going to save the frustration of finding out once you're actually on the dyno that your boost control system isn't working. With the M1, again we have the option of setting up a second boost control solenoid, a boost actuator and we could use this if we want to wire a second solenoid for another turbo charger in a v configuration engine for example.
11:54 So if you do want to use this the second actuator will follow exactly the same as what the first actuator is doing.
12:02 And the setup for the second actuator is basically a mirror of what we've already looked at.
12:09 If we move down further we've also got the ability to control our boost based on a number of different control parameters so we've got a coolant temperature boost limit, we can also add a driver switch so we could use a rotary switch or driver switch here to target different boost pressures. We've got an engine load average boost limit so we can adjust the boost limit depending on the current average engine load.
12:41 We've got a overall engine boost limit, and exhaust temperature boost limit, a gear dependent boost limit, inlet manifold temperature boost limit, launch boost aim, a race time boost limit, and a vehicle speed boost limit.
13:01 Now all of these functions here can be used to control the way the boost system responds, and the way these limits work is worth just discussing for a second here. What they're looking at as you can see we've got a value of 100 applied to all of these boost limits at the moment and what that means is they're effectively going to be doing nothing.
13:24 What we can do is use any of these particular limits to reduce the boost based on whatever conditions as we're trying to control. We'll just discuss briefly how we can use any of these particular limits if we want so if we look at the coolant temperature boost limit for an example.
13:42 So you can see at the moment that's a single zone and it's set to 100, which essentially means it's not doing anything. If we press the A key we can enable our coolant temperature access and we'll just generate a quick table. Let's go between 20 degrees and 120 with 10 degree increments and we'll press okay.
14:02 So again that table automatically fills with 100%.
14:07 Let's say that at 120 degrees we want to reduce our boost, so we can enter a value of 50% in there.
14:15 Now how that's going to work is it's going to look at the difference between our activate boost and our boost aim main. And it's going to give us 50% of that value. Now let's say for simplicity, that our boost aim main is 100 kpa and that our boost activate is 20 kpa. So the difference between those two values is 80 kpa. It's going to give us a result of half of that, which is 40 kpa.
14:45 Plus we've already got our boost activate, which is 20.
14:48 So in this case a value of 50% in our coolant temperature boost aim would give us a boost aim of 60 kpa.
14:56 We can apply that same logic to any of the other boost limit tables if we wish to achieve just about anything we want. We could use that for gear or speed dependent boost control. So it's important to understand how that parameter works because when we hear the term boost limit, we're thinking of an over boost function and that's not how this works. It's a way that we can use the M1 to adjust the boost target based on any of the parameters that we've got input in there.
15:26 There are a lot of controls there that we can use.
15:29 And some of them are a little complex and beyond the scope of this particular course, such as the race time or average load function.
15:39 If you do want more information about those, we go into a lot more detail in our M1 software tutorial course.
15:46 So you can have a look at that.