PDM Installation & Configuration: Step 3: Input and Output Pin Layout
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Step 3: Input and Output Pin Layout
17.20
| 00:00 | - In the third step for our SR86 PMU configuration worked example, we're going to define the physical pins that we're going to use on our PMUs to supply the power to all the loads that we've identified in the vehicle. |
| 00:14 | The flipside of that is we're also going to define the physical pins that we're going to use to get the inputs into those PMUs to drive our controlling functions. |
| 00:22 | Now if we pop over to the laptop here again quickly, you can see our same spreadsheet but we've filled it out a little bit more so we'll go through these and talk about the decisions that have driven each one of these definitions. |
| 00:35 | Now part of this step as well is also defining the current limit that we're going to associate with that output channel and we'll talk about how we do that. |
| 00:43 | So starting off at the top here we've got our ignition coils, so that was our 4 IGN1As, steady state current draw of about 10A and I've defined that those are going to be powered by our PMU1 output channel Now that's a slight added point of complexity in this example is that we've got two PMUs but what you'll see is that it's really no added complexity at all, you can think of it like one power management system with now twice the number of outputs. |
| 01:14 | So we've got PMU1 output channel 12. |
| 01:17 | We're going to define a current limit on that one of 15A. |
| 01:21 | So with our expected steady state draw of 10A in the absolute most extreme scenario, our current limit is going to be 15A, it's going to have to exceed before it will shut that channel down. |
| 01:33 | Now this is a completely system critical channel so we want to make sure that that current limit is never interfering with the normal operation of the vehicle. |
| 01:41 | We don't want it to intermittently trip and give us an unexpected miss that could be a little bit tricky to track down, don't want anything like that. |
| 01:48 | Now that current limit of 15A there is going to drive a little bit of our wiring harness design process as well because we're going to need to size a wire that is capable of handling 15A for a short amount of time in a fault event. |
| 02:05 | So we'll definitely need to take that into consideration. |
| 02:08 | Now it might seem a little bit odd that this is the first element that I have defined an output channel for and I've given it output channel 12. |
| 02:17 | It might seem logical to start at 1 and just work your way through the output channels but that's really not what you want to do and I'll explain why if we pop over to the documentation for our PMU here. |
| 02:28 | So this is in the PMU16 documentation. |
| 02:32 | Hopefully there's a similar diagram in any of the documentation for the PMU you might be working with. |
| 02:37 | This gives us a physical layout for how the physical transistors are arranged inside the PMU that relate to each of the output channels. |
| 02:46 | The larger squares that we can see here on the sides are for the output channels that can handle a higher current, that's 25A maximum for each of those channels. |
| 02:57 | And the smaller transistors here in the middle can handle up to 15A per channel. |
| 03:02 | Now you want to specify your outputs to try and spread them out as much as possible across the PMU and this is physically spreading them out because each of those transistors is going to generate heat and you don't want all of that clustered on one side of the device because it's going to make it much harder for that to be dissipated, you're only using half the heat sinking capability of the device so really not what you want to do. |
| 03:25 | In our situation here when we've got 2 PMUs we're going to have a lot of spare channels so we definitely want to be spreading them out so that's why I've gone with output channel 12 in initially for our coils there. |
| 03:37 | Now back to our spreadsheet. |
| 03:42 | This one here, we've got our injectors, so steady state of 5A, current limit there of 10A and defined output channel 1 for those, that's just a very similar story to what we've done for our coils. |
| 03:57 | We've got in our, we've got 2 devices here, a thermocouple interface and our lambda interfaces, our wideband O2 controllers. |
| 04:06 | That I've both defined as being on output, PMU1 output 2. |
| 04:12 | So combined they have a current draw of 11A so we've defined a current limit of 15A there and we're going to gang those together on output 2. |
| 04:23 | Now having a single output drive multiple electrical loads is absolutely fine and definitely something you will be doing. |
| 04:30 | Two things you need to keep in mind when deciding, making the decision about where to gang those outputs together are that they need to have exactly the same driving function. |
| 04:41 | So we obviously couldn't have two devices on the same output channel that have different control functions, they need to always be on and off in response to exactly the same input conditions so that's one of those things. |
| 04:54 | The other is that I would advise thinking about a priority hierarchy system, definitely at this stage here because we don't want the failure of a non system critical device to pull down a system critical device as well. |
| 05:12 | Say if we had, if we look at our ECU here is a really good example actually, I would always advise putting your ECU on its own output channel because it is a completely system critical device, if it doesn't have power, well nothing's going to work. |
| 05:27 | If I had ganged something else onto our ECU output here that had similar driving functions, say our CAN switchboard could have a different driving, same driving function if we ganged that onto this output. |
| 05:40 | The vehicle will still operate without the CAN switchboard, you might be able to limp it back to the pits if something goes wrong with that wiring and it shorts but if that failure also pulls down the ECU, well then you're dead on the side of the track so definitely think about some sort of priority hierarchy system. |
| 06:00 | So the ECU there I've got on its own output channel, expected current draw of 10A so a current limit of 15A there, that's out 150% sort of rule. |
| 06:09 | Dash logger keypad and steering wheel are all ganged together on output 7. |
| 06:16 | Combined current draw of approximately 4A so we put a current limit of 6A there. |
| 06:21 | A 2A buffer between current draw and a current limit is actually getting pretty close, I suspect when we do some testing on that one I might end up bumping that current limit up a little bit. |
| 06:33 | That will, we'll think about that, that would be thought about in the wiring harness design as well, possibly running maybe a 20 gauge power wire to those devices as opposed to 22 gauge, making sure we could handle a higher current limit of a failure before there was anything wrong with the wiring harness. |
| 06:52 | So we've got all those on output 7 there. |
| 06:54 | Those are devices that are physically close to one another again as well so it's going to be easier to run a single power wire up to those, making sure it's of an appreciable gauge and then splicing that out in that point to those devices. |
| 07:09 | We've got our shift actuator and our shift actuator is the first device here you can see, hopefully it's reasonably clear that I've got all the outputs linked to, that are on PMU1 in green here and the PMU2 outputs are in blue. |
| 07:29 | Now a shift actuator is the first output here from PMU2 and the reason that I've done that is that our compressor is also powered by PMU2 and we'll talk about the reason that's powered by PMU2 when we get down to that point, but that's going to keep those 2 really closely interlinked and related systems powered by the same PMU which just logically seems like a nice thing to do. |
| 07:57 | We've got our variable valve and our boost control solenoids. |
| 08:00 | So those are both engine actuators that are going to have the same driving function. |
| 08:04 | So they're ganged together on PMU1 output 8 and we've got a current limit of 8A on that channel. |
| 08:12 | Our alternator field, so we've got that on PMU2 output 9 and current limit of 10A on that one. |
| 08:22 | Now we talked about that a little bit in the earlier module, it's actually got quite large gauge wire running to it from the OEM so we'll be following that logic in our wiring harness design, that's why we can have that slightly larger current limit than we might expect there. |
| 08:37 | We've got our starter solenoid here. |
| 08:40 | That's PMU1 output 13, now that's going to be a high current output and once again, just placed to keep that heat dissipation in the PMU as easy as possible. |
| 08:55 | Now that output's actually not going to be used a whole lot hopefully, hopefully the vehicle isn't continually stalling and needing to be restarted on the racetrack but still be thinking about spacing those outputs out physically. |
| 09:07 | Now we've got our electric water pump here, PMU2 output 1. |
| 09:11 | So we've set a current limit of 15A on that one because it's an expected current draw of 10A but large in rush current so we'll look at those settings when we're actually configuring the PMU there but that's going to allow a much larger current to run for a period of time while that PMU's getting up to speed. |
| 09:29 | Our fuel pumps here, we've all kept on the same PMU, just keeping really closely related systems like that on a single device just logically makes sense and makes the system just a bit easier to keep in your mind and grapple with mentally. |
| 09:45 | So we've got output 4, outputs 12 and 13 so that's going to be spreading that current density in that PMU2 out as well. |
| 09:55 | So it's going to keep that heat nice and easy to dissipate. |
| 09:58 | Fan 1 and fan 2 both on PMU 1 so those are quite large draws. |
| 10:02 | So outputs 4 and 5, very similar story to the fuel pumps where we've got current limits set at around about twice the expected current draw but big in rush currents we'll be expecting. |
| 10:13 | And our compressor is our biggest current draw in this system most likely, we've got that on PMU2 output 2. |
| 10:21 | Now the way I have decided which PMU is going to control each device is to try and overall split the load reasonably evenly between the two while keeping really closely interrelated systems on discrete PMUs so like all our control, physical control systems here like our switchboard and our steering wheel and our dash are all powered by one PMU, our fuel pumps are all on one PMU, our shifting system is all on one PMU so keeping that in mind but also trying to split the load between the two PMUs as evenly as possible and I've got the math up here on that and our PMU1 is looking at an expected load of 77A and our PMU2 expected load of 72A. |
| 11:05 | Now once again, not all of these loads are going to be on all the time so this math here is just a guide to make sure we're well below the current handling limit of the PMU and we've hopefully got things split up pretty evenly. |
| 11:17 | So we're going to have to go through a similar process for the input pin definition on our PMUs now. |
| 11:23 | So back to our spreadsheet we can see we've got our main power input which is that ignition key barrel active high, PMU1 pin A2. |
| 11:30 | We've got our battery isolator signal which is also active high on PMU1 A9. |
| 11:37 | So these are physical wired inputs on the PMU, actual discrete wires going to them. |
| 11:42 | We've chosen A2 and A9 completely arbitrarily, there's no reason behind that. |
| 11:48 | There is actually a small reason behind that in that there was a slightly different design for this system initially that had more wired inputs coming into it, less relying on CAN bus. |
| 11:59 | We've sort of changed things up a bit because CAN bus is awesome and flexible so we really love using it. |
| 12:05 | And that means some of the wired inputs we no longer need but we've left the legacy of those inputs coming into pins A2 and A9. |
| 12:15 | So physical wired inputs there, functionally all the inputs on our Ecumaster PMU16 are exactly the same, they're all the same setup, have the same capabilities so totally arbitrary which wired input you're hooking them to there. |
| 12:30 | Now each PMU also has 2 CAN bus inputs. |
| 12:33 | So we've got PMU1 CAN1 and CAN2 and we've got PMU2 CAN1 and CAN2. |
| 12:39 | Now on our system here we are making good use of CAN bus but it does get slightly confusing because of, it actually comes down to the physical mounting location of the PMUs and the CAN bus wiring that was easily available at those points so we'll have a quick talk about how this is set up now. |
| 12:59 | So our enable power, our start request, our fans manual override and our water pump manual override all come from our 4x2 keypad. |
| 13:10 | They're all going to be wired to the CAN2 port of PMU1 and the reason for that is that 4x2 keypad runs on a 500 Kb speed whereas the rest of the CAN bus in the vehicle runs on a 1Mb speed. |
| 13:24 | Now they're not compatible with one another so PMU1 CAN2 is only talking to that 4x2 keypad, I think they're the only 2 devices that are on that 500 Kb bus. |
| 13:38 | Now some of those signals do need to be sent to other places so our PMU1 is actually going to read that directly from the keypad and then its CAN1 port is 1Mb and connected to the rest of the CAN bus in the vehicle. |
| 13:53 | So it's going to take those inputs coming into its CAN2 and it's going to retransmit them out on its CAN1 port which is going to let us get them into all the other devices that might need them on the vehicle, like our second PMU. |
| 14:05 | Now our second PMU, we've actually wired that 1 Mb bus to the CAN2 port. |
| 14:12 | So that is slightly confusing because on PMU1, CAN2 is 500 Kb and on PMU2, CAN2 is 1Mb. |
| 14:19 | That's because of a slight incompatibility with one of the early model Ecumaster USB to CAN programming modules that we had, we needed to have that just on its own dedicated CAN bus for PMU2 which was the CAN1 port. |
| 14:38 | Functionally it's not going to cause us any issues or cause any major problems and you'll see it being set up in the configuration step of the course. |
| 14:48 | So looking at those CAN inputs, so we've covered off our 4 from our PMU. |
| 14:53 | So those were going to be our, sorry our 4 from our keypad, so that was our enable, our start, our water pump manual override and our fans manual override. |
| 15:02 | So those are all coming into PMU1, CAN2. |
| 15:07 | Then our water pump manual override, because our water pump up here, if I can find our water pump, here it is, is wired to PMU 2, PMU2 needs to know about that override signal. |
| 15:22 | So I've got a note here to myself that the water pump manual override is coming into PMU1 CAN2 and then it has to retransmit that out to PMU2 CAN1. |
| 15:33 | Engine coolant temperature input here is coming from our ECU, PMU1 CAN1, that's our 1Mb bus. |
| 15:43 | Compressor request, compressor is powered by our PMU2, so that is our PMU2 CAN2 port. |
| 15:51 | that's our 1Mb bus in the vehicle. |
| 15:53 | So our PMU1 CAN1 and our PMU2 CAN2 are actually directly wired together. |
| 16:00 | So that's going to be really important for this message passing as well. |
| 16:04 | Fuel pump request, so our fuel pumps are all wired via PMU2, so they're coming in via PMU2 CAN2. |
| 16:12 | So that should give you a good representation of how we go through the process of defining the physical pins that we're going to use on our PMU and our channel current limits. |
| 16:23 | So key things you want to be aware of there is that those current limits need to never interfere with the standard operation of the device but they need to be sized such that a failure could be detected and that channel shut down without any physical wire melting or anything catching on fire. |
| 16:42 | We also want to be making sure that we are spreading the load around a PMU as much as possible. |
| 16:46 | In a situation like this where for one of the PMUs, we're probably only using half the input channels, we've spread that physically around the ECU in relation to where those physical transistors are to spread that heat load out and make sure it's going to be as efficient as possible. |
| 17:02 | And then in a system like this where we've got two PMUs, we've overall tried to split the load fairly evenly between them to make sure they're each working as hard as each other and are both kind of well within their specifications, that's going to give us a really good increase in reliability. |
