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PDM Installation & Configuration: Step 2: Design Required Control Functions

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Step 2: Design Required Control Functions


00:00 - At this stage of the PMU installation process, we're going to design the control functions that will determine when the loads that we have identified in the first stage are going to be powered on or powered off and how that's going to happen.
00:14 So for our SR86 race car here we've got a reasonably conventional power distribution supply scheme where we're going to have a main power stage and an enable power stage.
00:25 So the main power stage will switch basically the electronic devices in the vehicle on, so that's ECUs, dashes, things like that, to allow us to communicate with them but it won't actually allow for the engine to be started.
00:40 For the engine to be started, we need to also turn on the enable power mode, that'll give power to things like our ignition coils and our injectors and mean that if we try to start the motor at that point, it should hopefully start.
00:52 Now if we pop over to my laptop here I've got a spreadsheet up, so this is just working off the spreadsheet from the first step but starting to fill it out a bit, particularly our control functions over here.
01:03 So we'll start at the top of this list, we've got coils and injectors and our control function for that I've written out as main power and enable power and our battery isolator signal.
01:17 So we've got 3 elements here that can control the power to our device in this instance.
01:25 So our main power signal is going to be the ignition key barrel in the vehicle.
01:29 Our enable power signal is going to come from a keypad but the battery isolator also needs to be able to command the system to remove power from these devices because if everything is up and running and the engine's running and something goes wrong and someone trips the battery isolator signal, it needs to be able to tell the PMU to shut the engine down, stall the engine before it actually isolates and removes the battery from the system, this is of course our alternator load dump issue.
01:59 So the way it's going to do that is to remove power from our coils and our injectors, without those the engine is absolutely not going to run so it will stall, no longer spinning, no longer, the alternator's not outputting anymore so when the battery is disconnected from the system, we shouldn't see any issues.
02:15 So control function for both our coils and our injectors here is main power and enable power and our isolator PDM signal there.
02:26 Now there are those other electronic devices in the vehicle that we very well might want to communicate with while the engine is not running, so that would be our lambda interfaces, thermocouple interface, our ECU, our dash logger, keypad and our steering wheel.
02:44 An I've actually got our shift actuator in here as well because it is sometimes advantageous to be able to shift the gearbox without the engine running.
02:55 As a side note, if you're ever doing that, make sure to be rocking the vehicle back and forth, particularly with sequential gearboxes.
03:00 Can be a bit of a bear to shift them with everything completely stationary.
03:05 So for all those devices our control function is going to be main power and our battery isolator signal.
03:13 So all of those devices will be powered up, even when our enable power mode is currently switched off.
03:20 We need to have our battery isolator signal in there as well though as the isolator needs to have control over those being powered up as well.
03:28 Then we've got some of our engine actuators, that's going to be our variable valve control solenoid and our boost control solenoid.
03:35 That is back to the same logic as our coils and our injectors which makes sense, if we're killing the engine that we're not going to need those so they're only going to be on when we are with the enable mode engaged as well and it's the same story for our alternator field.
03:52 We wouldn't want the system to just be in the main power mode because that's going to be there passing a lot of current though that alternator rotor and that could actually lead to a battery drain situation so that also has the enable power in its control logic.
04:10 We've got our starter solenoid next so you can see I've listed our control function there as just start request.
04:17 So this is going to be our PMU controlling our starter motor solenoid, just in response to a start request.
04:25 Now that start request is going to come from our keypad via CAN bus.
04:29 We'll have a little bit of a look at that in just a wee minute.
04:33 A water pump here, I've got our control function as a PWM table based on engine coolant temperature or water pump manual override.
04:44 So this is the first of what we'd call a complex control function.
04:47 So the output to our water pump is going to be pulse width modulated, that's going to deliver varying amounts of power to our water pump which given different conditions will control the speed of that water pump.
04:59 We're going to base that amount of power that we deliver to it on our engine coolant temperature.
05:04 So in the normal operating mode, those two will be related via a table which we will set up in our PMU but there is an or function to that which means that if we command it via a button that's on our keypad again, we can essentially turn that water pump to full on, so you could think of that like 100% duty cycle.
05:26 So our or there is either PWM based on engine coolant temp or 100% on.
05:33 Our fuel system in this vehicle, this is our 3 fuel pumps, is ECU controlled.
05:38 So that is going to be switched via a fuel pump request signal that's going to come from our M150 ECU via CAN.
05:47 We've got our 2 thermofans here, so control function for that is once again what we'd consider to be a complex control function but it's not super complex.
05:58 This is our hysteresis control or often called bang bang control.
06:03 If our engine coolant temperature gets above or equal to 95°C, it's going to turn that coolant fan on.
06:10 When it gets back down below 90°C it's going to turn it off.
06:15 So there's a period between 90 and 95 where the coolant fan could actually be on or off, we don't know which it'll be, it'll depend on what the last state was.
06:23 So that's what a hysteresis is going to do for us there.
06:26 There's a couple of other inputs to this function though and they're "or'd" with that hysteresis, we've got a fans manual override button which is going to be on our keypad as well, so that's a very similar story to our waterpump before.
06:40 There's another input there also "or'd" which is our pit mode enabled switch.
06:45 Now this was a request from the engineering team and the driver that whenever the pit mode is engaged, those coolant fans come on.
06:52 And the reason for this is that pit lanes have speed limits and you've got to slow down an awful lot coming into the pits and there could be a bit of a taxi way into the pits actually, vehicles running at low speed when it's just come off the race track so not a lot of air going through the radiator, that's the perfect scenerio for a possibly damaging heat spike event that our hysteresis may not kick in in time to actually catch and grab and pull back.
07:18 So whenever that pit mode is engaged, just going to turn our cooling fans on and ensure that we've got adequate airflow over the radiator.
07:26 Now we've mentioned that the vehicle is fitted with a Hollinger sequentially shifted gearbox, it's an air compressor shifting system.
07:33 So we've got our air compressor to control as well.
07:36 Now there is feedback on the system that is going to supply the system pressure via a pressure sensor to the M150 ECU and that's going to control the turning on and off of our compressor.
07:48 So it's going to control that, send that signal to the PMU via CAN, so we're going to call that our compressor request input.
07:55 So that's the design of our control functions, I've got listed down here all the inputs that we're going to need to set up that are going to come into these control functions and a little bit of a note about how those inputs are going to be set up and where they're coming from.
08:10 So starting with our main power, in the vehicle that's actually just going to be the ignition key and barrel.
08:15 So keeping that in place and I've written a note to myself there saying active high.
08:19 So that means when the ignition switch is off, that output wire is going to be grounded and when the ignition switch is on, it's going to be sending a high voltage.
08:30 So this is going to be a discrete wired input to the PMU when it's reading 0 or low, that is going to mean that the system is off and when it's reading a 1 or a high, that's going to mean that our main power should be enabled.
08:43 We've got our MSEL battery isolator PDM signal there, so this is once again a discrete wire coming from our Motorsport Electronics isolater, going to the PMU and it's also active high which means when everything is running normally and the isolator is saying yep everything's fine, keep that battery in the system, it's going to be outputting a high voltage to the PMU saying everything is A OK.
09:06 If for any reason there's a massive current draw 'cause there's a short, someone hits one of the isolation kill switches, it's going to ground that line, the PMU's going to see that, immediately turn off all of those elements that we've linked to that input line, stalling the engine and then our isolator is going to actually isolate the battery out of the system, a discrete period of time after that, there's actually a settable delay in there to ensure that the engine has stalled.
09:35 So once again, discrete wired input on that one.
09:38 We've got our enable power here so that's via CAN bus from our 4x2 keypad.
09:43 I've got button 1 there so that's going to be the top left most button on our keypad and I've written a note to myself just to remind myself that it does have to be latching.
09:53 So that's one push on that button and it will latch into the on state.
09:57 Another push and it will latch into the off state.
09:59 Which sort of makes sense when you think about how that's going to be used.
10:02 Our start request signal coming in, also from our keypad, so exactly the same as before, it's going to be right next to our enable power button.
10:11 But I've noted that one down as being momentary so that is only going to generate an on output when you're holding that button down so that's just like a traditional starter button or starter key switch, only going to run the starter motor while that button is being held down.
10:28 Couple of functions we've included there reference the engine coolant temperature, so we are going to need that data in our PMU, that's going to come over the CAN bus from our ECU, I've got the information around where that data is actually contained and how it's scaled and offset, just in a note there to myself as well which is going to make setting that up in the PMU nice and easy.
10:52 Water pump manual override, once again from our keypad, we've called that button 6, so that's going to end up being the button that is directly below our enable system and that's latching as well.
11:07 Fuel pump request via CAN bus from our ECU, those fuel pumps are ECU controlled.
11:12 We've got our fans manual override, so that's button 5 on our keypad.
11:19 So that's going to be a latching button as well.
11:23 Pit mode enable, so that one also via CAN bus and that's going to come from the CAN switchboard that is on our steering wheel.
11:32 Now I mentioned in the course, 'cause I really wanted to get it in there that when you're reading the state of buttons and then transmitting that data out onto a network, you only want to be reading the state of those buttons in one place and this is where the CAN switchboard on the steering wheel is actually really great because it is the device that is reading the physical state of that button, the physical voltage levels and then it's sending that data out onto the network.
11:58 Having all the other devices that are in the system like the ECU and the PMU and anything else that needs to know that pit mode has been enabled, read that data off a digital network is going to be far more reliable than having each of them reading the voltage level that was on that switch itself.
12:15 So CAN key bus on the steering wheel there, really valuable.
12:18 So I've also got notes there about the PID bus speed and were that bit determining that mode is actually going to be located.
12:27 So that should make setup nice and easy.
12:29 And last input we're going to need is our compressor request.
12:32 This is coming from the ECU over CAN, telling the PMU to turn on that compressor, keep those system pressure levels where we need them.
12:41 So that's the second step in our system there, how we are actually designing those control functions.
12:48 Having this information here is going to once again it seems like a lot of pretty dry definition process up front but when we come to actually configuring the PMU, this is going to be invaluable to really speed up that process, make sure we've got everything correct and make sure nothing gets missed.

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