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Launch Control: E-Throttle Control

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E-Throttle Control

08.54

00:00 - Now the last part of our testing we're going to look at is how we can use the electronic throttle control.
00:05 Now, this is really gonna be a test for the sake of showing you how the function can be used.
00:11 Our Toyota 86, as you've seen through the last test, traction really isn't as much of an issue for this car on today's track.
00:19 We've got a nice warm track, it's a dry day, so we don't have a lot of traction issues.
00:25 For me, the power and the drive by wire throttle control, e-throttle control would be for days when the track is pouring down with water it's got pooling water everywhere, or, alternatively, maybe you've got a very very powerful car where you cannot get the power level low enough in 1st gear to achieve good traction.
00:46 That's, really for me, where I see the value in drive by wire throttle, and feel free to test the system, and I think you'll find quite quickly that if you try to do all of your launch control tuning based on e-throttle position you are going to end up finding it difficult to get really good consistency.
01:05 So, let's have a look at the system anyway.
01:08 We've just finished from our last test with our ground speed based launch control engine speed, and we're going to leave the launch control engine speed table set where we were.
01:20 Now, if we move down, we can see we've got our throttle limit.
01:23 At the moment we've got a single zone for that table set up at 100 percent throttle.
01:30 So, we're gonna start by enabling the vehicle speed axis, and what I'm going to do is generate a table between zero and 50 kilometers an hour, with five kilometer an hour increments.
01:45 You can use as many or as few based on the available sites on this table, which in this case is 21 sites, so we could use a finer resolution, but for the way I would suggest using the throttle position control would be to use a relatively stable throttle position.
02:04 I wouldn't be trying to chase exactly what a driver does with the throttle using this table, because again, you're going to find because it's reactive, it's not proactive, if we get to a position where the car actually does start to grip up and pulls the engine speed down, manually the driver is going to automatically increase the throttle position to keep that momentum and the wheel speed going.
02:28 With this particular system, as it says, it's reactive; there's no ability for it to do that.
02:33 It's just going to provide the e-throttle position based on this table, so there's no feedback loop.
02:40 In our situation here with our Toyota 86, we already know that pretty much from about 25 kilometers an hour in 1st gear, we are actually completely hooked up.
02:51 We have traction and it's not an issue for us.
02:55 Using this table right the way through is only going to, actually, slow us down.
02:59 What we can do though, is through to, let's say, 20 kilometers an hour, we're going to highlight those cells, and let's try setting the throttle position to 70%.
03:09 We might find that we will go too low with it, but there's only one way to find that, and that's with testing.
03:17 One thing to point out with changing the throttle target is the airflow through a throttle body is quite non-linear.
03:23 So, it means that 50% throttle is definitely not going to give us 50% engine torque.
03:29 So, you'll find that initially you actually need to drop the throttle opening quite a bit to actually get any significant effect on the power, or torque, that the engine's producing.
03:41 So, what we're gonna do is just jump it straight up from 70% to 100% from 20 to 25 kilometers an hour.
03:48 Again, that's probably going to work quite happily for our low powered Toyota 86, where we've really got more grip than power.
03:56 If you had a very powerful car what you might find is a really sharp change like that could end up resulting in the car breaking into wheel spin when it was previously hooked up.
04:06 So, in which case, you may want to increase the throttle opening over maybe 5 or 10 kilometers an hour, maybe 10 or 15 kilometers an hour, to smooth out that transition.
04:15 Let's do a launch now and see what our 70% throttle gives us.
04:19 (engine revs) OK, so let's have a look at the time graph and we can see what happened there from the driver's seat that didn't really feel too much different to how we were launching with no throttle control at all.
04:41 There's a couple of reasons for that: first of all, we already had too much power when we were launching with 100% throttle, and we were simply relying on the limiter function to help control that.
04:52 So, essentially, in that area, bringing down the throttle position can actually be helpful because we don't need to be relying so heavily on the launch control limiter to control engine speed, or control engine power.
05:06 If we look at the time graph we can see, again, exactly what's happened during our launch.
05:11 Here you can see this time that during the launch phase our throttle position is sitting at our table value of 70%, even though our foot position is 100%, or 98.8%.
05:23 So, it's doing exactly what we expected.
05:25 Now, based on what we had learnt from the last test, you can see I've increased that throttle position up here.
05:33 Right at that point, 21 kilometers an hour, right at that point where actually have traction, so I'm only trying to reduce the engine power over the period where we've got too much.
05:43 And, you can see that while the engine is still sitting on the RPM limit table, we're actually not relying quite so much on our ignition cut.
05:53 So, it's not relying so heavily on the ignition cut, which is what we'd expect.
05:57 What we're gonna do now is just try dropping that down.
06:02 Let's see, if we go with 45% this should hopefully be a little bit too much, and we should end up with insufficient engine power.
06:11 So, we'll just show you what happens when we've got that situation.
06:15 You'll notice I still have left the zero ground speed position target at 70, because if we drop that down too far, we may not have enough engine power to initially get the car moving.
06:26 (engine revs) OK, we'll just have a quick look at that graph.
06:41 What we've found here, I can feel this really easily through the seat of the pants, and again if we were looking at some acceleration data that would show it.
06:51 What I found was that when we drop the throttle target down to 45, as I'd expect, we didn't have enough power.
07:00 Now, you can see that we're still sitting very close to the RPM limit target, but if we also look at what's happening with our ignition cut, all the way from seven kilometers an hour upwards where essentially we've got two cuts occur.
07:17 So, we're essentially not relying anymore on the launch control function.
07:22 Now, I know from the seat of the pants that ended up slowing the car down.
07:25 Again, we would back this up with hard data.
07:27 The seat of the pants isn't reliable enough to give us the perfect answer, but the purpose of this particular demonstration was just to show you what would happen if we go too far.
07:38 So, for this car, I wouldn't even use the throttle target control at all.
07:43 There's just simply no need because the car isn't that powerful, and we're not that traction limited.
07:49 If we try and use that, it doesn't really achieve anything we can't do with the launch control function on its own.
07:56 But, just be aware that it is there.
07:58 On a wet day this may actually be quite helpful to reduce the load on the launch control system and give us better results.
08:05 Now, again, there's no right or wrong way of setting this up, and it's really going to depend on your particular car, the engine's power delivery torque curve, and also the amount of traction that you've got available.
08:20 This is simply a demonstration on how we can approach setting it up and based on the feedback from the driver, and also the data logging, we can then make adjustments to the engine RPM targets until you've got the optimal set of results.
08:36 So, this brings us to the end of our MoTeC M1 worked example, and I'll trust that this has given some more insight into the practical application of what you have learned in the body of the course.