Time of Session:
00:36:53 Grosjean reporting issues with gear shifting, asks, “are you sure everything is really right with the gearbox? Downshift don’t seems good.” Engineer confirms they can see the issue occurring over telemetry data, asked to then box and select neutral gear to coast down pit lane into the box. Grosjean responds, “but I can’t pull downshift.” Then the engineer asks him to “try not to shift” gears, but continues to ask him to shift into neutral to coast in the box when he comes in. Finally, the team confirms to Grosjean the issue is “we lost clutch LVDT”, so the team is working on a solution to be able to “keep running.”
** Time of session is the session time at which the message was heard on the television broadcast, as radio communications are delayed from when they actually occur.
What happened? The clutch slave cylinder is instrumented with a displacement sensor that is vital to all clutch operation and that is what failed for Grosjean. There are displacement sensors on the steering wheel clutch paddles as well. The outputs of both sensors are input factors into a multi-dimensional map with clutch slave hydraulic pressure as the dependent function. In a basic sense, the displacement of paddles and slave cylinder are mapped together to control how much the slave is displaced to release the clutch diaphragm. The clutch map is constantly tuned for driver preferences and clutch parameters. Bite point find procedures are fundamental to this tuning, but we’ll discuss those at another time.
What is an LVDT? The acronym stands for “Linear Variable Differential Transformer.” In our basic discussion here, we don’t need to go into how the sensor actual works. Just remember that it outputs physical linear displacement as a voltage to the data system, which is then calibrated to a parameter within the software. For a bit more information on LVDT sensors used in clutch slave instrumentation, please visit Active Sensors site here: http://www.activesensors.com/motorsport-position-sensors/clutch-position-sensors
Active Sensors is one of a few popular suppliers of LVDT sensors for motorsport use and most importantly, will work closely with teams to develop bespoke sensors for specific packaging requirements.
How did they fix the issue for Grosjean to continue? There are many redundant systems and protocols designed into a Formula 1 car to be able to compensate for failures. It would be reasonable to believe that maybe the clutch slave actuation was mapped only to hydraulic pressure, thus eliminating the failed LVDT from closed-loop control.