Hi, folks I'm trying to figure out where the F1 Digital Gear Display gets it's information from. What sensor is responsible? I'm guessing it's not simply the TCU mirroring the paddle/button pushes, but is actually looking at the gear selection actuator on the side of the gearbox. I see there are two sensors on the actuator: Image Unavailable, Please Login One is a gear selection position sensor. The other is a gear engagement position sensor. I don't really understand the differences between the two. Is the engagement just a two position sensor (engaged/not engaged) and the selection is the actual gear selection (N, 1, 2, 3 .... R)? Sensor output goes straight to the TCU, so it's not like I can trace the wiring to the display. Thanks in advance. Cheers.
Hi Ian. The TCU is broadcasting the engaged gear on the CAN bus. That's where the instrument cluster takes the information from. For what regards the selection and engagement sensors, just think to a manual car. The engagement sensor measures the longitudinal position of the gear stick with typically 3 stable positions (even gears, odd gears and N). The selection sensor measures the lateral position of the gear stick, with 4 stable positions (R plane, 1-2 plane, 3-4 plane and 5-6 plane). The TCU has confirmation that the requested gear is well engaged by checking that both sensors have reached the correct values, in fact by checking that both sensors are within the min/max limits calibrated for each gear.
I don't understand why the longitudinal axis is called "engagement" and the lateral axis is called "selection". On a manual car, if you move the gearstick into a certain position, it's the gear you "selected" (requested), but if the linkages are broken between the stick and the gearbox, the gear is not going to be "engaged". The actuator sensor terminology seems strange to me. To confuse the issue, according to the 355 WSM, the actuator only has a position sensor for "selection". Image Unavailable, Please Login The instrument display still shows all the gears. I think my experience with aircraft autopilots is confusing me, where there are sensors on both servo actuators and output linkages. I understand that the 360 TCU is sending the signal to the instruments, but is the readout showing selected gear (input into the TCU from the paddles/buttons) or is it looking at the absolute final output of the actuator before it goes into the gearbox. There is a gentleman on the 348/355 forum whose display is showing the gear he selected (N, R, 1, 2, 3, 4, 5... ), but the car seems to be in neutral. He progressively lost odd and even gear physical engagement, but the digital display was still showing what he selected.
The denomination of the sensors is pretty clear to me. Still imagine a manual car, you are in N and want to go to, let's say, 5th gear : - you move first the stick laterally (toward the right). This movement SELECTs the fork (among the 4) which will be used (fork for 5th or 6th gears) - then you move the stick longitudinally (toward the front). This movement ENGAGEs the synchro rings on the pinion of 5th gear. The 355 works the same. It also have 2 sensors, one for selection and one for engagement. The 360 cluster display the gear in which the actuator is at the end of gear change process. If the values of sensors are out of the expected "boxes" (min/Max limits of both senors), the gear displayed is blinking. I know nothing about the 355 you mentioned, but if there is a mechanical breakage after the output of the actuator (eg. at forks selection level) what he described may happen. Same thing will happen if you remove the actuator from the gearbox, gears selection will continue to work OK but of course the gearbox is not commanded.
Thanks, Eric. Makes more sense now. I've been told that the labels have been swapped on the diagram. i.e. B should be A and vice versa. If so, that also makes the wiring diagrams wrong. I'll have to modify some of my wiring diagrams. The 355 is a bit of a mystery as the sensor is internal and there is only one plug for both axes. 4 wires (plus a shield) though, instead of 3.
