PDM Installation & Configuration: Pit Limiter: Rain Light / Headlight Flash
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Pit Limiter: Rain Light / Headlight Flash
05.52
| 00:00 | - At almost every racetrack in the world the pit lane will have a tightly controlled speed limit which the penalties for exceeding can be quite severe. |
| 00:08 | It's important that this limit is obeyed as the pit lane can be a frantic place, communication is difficult and accidents can have pretty serious outcomes. |
| 00:18 | While races aren't won in the pits, they can certainly be lost in the pits and the fractions of a second that can be gained from entering and exiting the pits as close to the speed limit as possible can really matter. |
| 00:30 | Asking a driver to closely target a particular speed but not exceed it at all isn't a sure thing either as in many racecars this can actually be pretty tricky because of how responsive and peaky they are to drive. |
| 00:43 | This is why you will find almost all modern race cars have a pit limiter mode which when enabled will electronically limit the maximum speed of the vehicle amongst other things. |
| 00:53 | While this mode is engaged the driver can focus on guiding the car into the pits smoothly and stopping in exactly the right spot, knowing they won't be penalised for any accidental speed violations. |
| 01:04 | This pit limiter mode is primarily controlled by the ECU in the vehicle because it's the device directly in control of the engine that can limit its output to control the speed. |
| 01:14 | Setting this up will involve programming the ECU to read some sort of button press or switch input and activate the pit lane limiter mode. |
| 01:22 | This is where we get involved with the PMU as the ECU will send some sort of output to the PMU either over CAN or a direct wire to tell the PMU that the pit limiter mode is currently active. |
| 01:35 | The important element here is that the vehicle ECU reads the button press which enables the pit limiter mode and then communicates to the PMU that the pit limiter mode is active. |
| 01:47 | The PMU does not also read that button press, it only knows about the pit limiter mode from the ECU. |
| 01:54 | This seems like a subtle difference but it is really important in practice as it means there can never be a situation where the ECU and the PMU disagree on whether pit mode is active or not. |
| 02:07 | Alternatively we could have the PMU read the button input and then communicate to the ECU that pit limiter mode should be activated. |
| 02:14 | But the important point is that the physical button press is only read by a single device in the vehicle which then communicates the mode to all the other devices in the vehicle that need to know about it. |
| 02:25 | With all that background out of the way, we can talk about what we actually want to do with the PMU in response to a pit limiter mode being active. |
| 02:32 | Which is to flash the vehicle headlights and rain light to give an external visual cue of the vehicle mode and make it as visible as possible. |
| 02:42 | This is a relatively easy function to set up but we've included it here to really drive home the point about there being only that single device that's reading that button press. |
| 02:51 | The input to this function is therefore obviously going to be a pit mode active request with the outputs being the PMU channels connected to the headlight low beams and the rain light. |
| 03:03 | This would almost always be 2 separate outputs, one for the headlights as there isn't a situation where you'd want a single headlight on and the other off. |
| 03:11 | And one for the rain light as this will need independent control. |
| 03:16 | Let's have a look at a diagram of how we'd set this up now. |
| 03:19 | I'm going to introduce a couple of new symbols, one for a timer and one for a pulse output. |
| 03:23 | The reason for this is that by using those functions, we're able to have the lights flash in a particular pattern which gives a unique visual cue that the vehicle is in pit limiter mode. |
| 03:34 | We have our input on the left here which goes directly into a timer module and that timer module is set to have an on time of 1 second and an off time of 1 second. |
| 03:43 | This means that when the pit limiter mode input is on, the timer will output an on signal for 1 second, followed by an off signal for 1 second. |
| 03:52 | This would be enough to flash our lights if we then sent this signal directly to the output channels controlling them at this stage but we're going to put another element into the chain which is a pulse function. |
| 04:03 | The pulse function will look for a rising edge on its input, meaning its input has switched from off to on. |
| 04:10 | And we've got it configured to output 3, 0.25 second long pulses, spaced 0.25 seconds apart when it sees this. |
| 04:20 | What this means is that when the pit mode enabled input is seen from the ECU, the timer will switch on which will trigger the pulse function to quickly flash the headlights and rain light three times. |
| 04:32 | The timer output switches off or goes low after 1 second and remains low for 1 second and then it switches high again, triggering that pulse output and flashing the lights 3 times again. |
| 04:45 | This will give a distinctive 3 pulses of light then a longer delay and then another 3 pulses of light and that will repeat. |
| 04:52 | It would be important that the vehicle this function is set up on has LED lighting as incandescent lights will not turn on or off fast enough to get the effect that we're after. |
| 05:02 | This might seem needlessly complex when all we really need to do is flash the lights to warn other people in the pits but this particular pattern of flashing can be important in the diagnosis of issues down the line. |
| 05:12 | It might be important to visually check on video that the car was in pit limiter mode. |
| 05:18 | In this module, we've looked at setting up a PMU to flash a race car's headlights and rain light in a unique identifiable pattern when the vehicle is in pit limiter mode. |
| 05:28 | In particular, we've established the importance of the driver input to put the vehicle into pit limiter mode being read by just a single device and that device communicating the vehicle mode out to the other modules that need this information. |
| 05:42 | This is because we never want a situation where modules in the car disagree about which mode the vehicle should be in. |
