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Professional Motorsport Data Analysis: TPMS

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TPMS

07.02

00:00 - In both the OEM and motorsport worlds, tyre pressure monitoring systems, often abbreviated to TPMS, have become more and more commonplace.
00:10 The function of a TPMS is simple, it gives you access to real time tyre pressure data when the car is on track.
00:17 The architecture of each system can vary between manufacturers and models but the general layout is made up of a pressure sensing unit mounted inside each wheel, antennas fitted to the chassis to pick up signals from the wheel sensors, and an ECU that's dedicated to receiving and processing the data which can then be sent to the logger over CAN.
00:39 There are 2 main categories for TPMS systems, non flexible and flexible systems.
00:44 Non flexible systems have each wheel sensor programmed to be assigned to a certain corner of the car.
00:51 And that means that rims can only be fitted in a certain position, say front right for example.
00:57 As the sensor is programmed as a front right sensor, the TPMS ECU will always send the data for that sensor as the pressure for the front right tyre regardless of where it's actually physically fitted to the car.
01:10 The sensor position assigned to each sensor can usually be changed relatively quickly but it needs to be done before the data is logged.
01:18 In flexible systems, we can have the sensors fitted to any corner of the car without needing to pre program for position.
01:26 Regardless of which corner of the car the sensor is used on, the system will automatically identify its position which is obviously a big advantage in that we can fit rims to any corner of the car at any point without needing to reprogram the sensors.
01:42 Of course there are downsides too.
01:44 A flexible system is always going to cost more and in some cases, extra wiring is required due to the additional components needed for identifying the sensor positions.
01:55 If our rims are always run in the same position, then a non flexible system won't be a limitation.
02:01 But with that said, having the flexibility of being able to fit rims to whichever corner of side of the car you need to, can be very helpful.
02:10 This is especially true when we have stacks of rim sets with tyre constantly being replaced and swapped around the car which is common in something like endurance racing.
02:20 In some systems, a handheld remote unit is used as part of the package.
02:24 In some non flexible systems, this is what's used to assign the position of each sensor to a corner of the car and it can also be used to check the live pressure of the tyre without needing to be fitted to the car because the remote can act as an antennae.
02:40 It can also be used to return some diagnostics about the sensor like current battery level, sensor temperature, sensor serial number and more.
02:49 Each sensor has an internal battery which in some systems is not rechargeable and not replaceable.
02:56 The batteries in the sensors are often the point of failure in the system so if they do fail, the entire sensor needs to be replaced which can be expensive.
03:05 Keep in mind that the battery level can be checked using the remote which is something that should be done regularly.
03:12 The most common killer of these batteries is heat generated by the brakes, particularly on tracks without much cooling and big braking zones.
03:20 Without having a TPMS system, obviously we're limited to only getting a reading of the tyre pressure once the car is stationary in the pit lane.
03:29 This is definitely still a valid and useful method of checking and setting tyre pressures and even when a car is fitted with a TPMS system we should still be checking the pressures manually with a gauge after each run.
03:42 However having the live data from every point on track gives us a lot more detail about what's happening with the tyre.
03:49 Here in this example we can see the pressure evolution of all four tyres over a single stint.
03:55 Straight away, even just looking at the raw data, we can get a lot of information about what the pressure growth early in the stint looks like.
04:03 And how long it takes for the tyres to reach a stable pressure.
04:07 We can also see a lot of interesting information about how much energy is being absorbed by each tyre by the different amount of pressure growth of each corner of the car.
04:16 This pressure growth split is often more prominent on the driven axle.
04:21 In this example, where the car is mid engined and rear wheel drive, we can see the initial rear cold pressures are similar but they diverge significantly over the first stint of the race.
04:33 Looking at the same data, but over a single lap, we can see how the pressure is changing at different points throughout the circuit.
04:40 The pressure is changing, not just from the loads being experienced by each tyre as well as the heat generated internally from the construction and the tread of the tyre, but also from absorbing heat energy released from the brakes.
04:52 From a reliability and safety perspective, the TPMS system is incredibly useful in its ability to pick up pressure loss and give an early warning of a puncture.
05:03 Warnings based on the minimum pressure and rate of pressure loss can be set and these can be displayed to the driver in the car to give them a heads up and a chance to slow the car.
05:12 As well as back to the engineers in the pits.
05:15 Provided the TPMS data is available over telemetry.
05:19 Being able to display the live tyre pressures to the driver can be a big advantage in the case of a safety car period where the driver is concentrating on keeping suitable pressure in the tyres for the restart.
05:29 Being able to see this for themselves in real time gives them the feedback they need to know they're doing enough to maintain and build pressure sufficiently.
05:38 A TPMS system can also be used to measure temperature from inside the tyre and there are a few different ways this can be done.
05:45 The most basic is to measure the internal air temperature of the tyre.
05:49 As the air temperature is closely related to the internal pressure of the tyre, this is a useful quantity to be able to measure and remember, in extreme temperatures, anything over around 130°C can start to damage the batteries of the TPMS sensor.
06:05 So keeping an eye on the internal air temperature can also give us an indication of the likelihood of an impending sensor failure.
06:13 Another method available in some systems measures the tyre's internal carcass surface temperature using an infrared array.
06:20 In this case, an infrared sensor is imbedded into the TPMS sensor which is pointed at the internal surface of the tyre's carcass, giving us the temperature distribution across its entire span.
06:33 This can be extremely useful for understanding how the energy is being input and distributed throughout the construction of the tyre because the areas of the tyre construction doing the most work will show up as the hottest due to the hysteresis within the construction.
06:48 This gives us another useful tool for understanding both the way the car is being driven and how the setup is affecting the tyres.