The UN52 custom CAN Layer runs at 500kbps. At this time, it is not reconfigurable to run at a different bus speed.
The CAN Layer uses Big Endian (MSB) encoding of data.
Implausible / uninitialized values are set to all 0xFF. You can use this for detection of errors with various sensors on the gearbox.
All data points are either marked with M (Manditory) or O (Optional). Failure to send manditory data may result in weird or inconsistent behaviour by the TCU.
The bit G_SHIFT is used to signal that the user is shifting the gearbox from P or N into either R or D. In this state, the engine should not allow the user to rev the engine, as this can cause damage to the gearbox. Additionally, if the engine is revving higher at idle (For catalyst warm up), the engine should drop its revs to normal idle speed.
TRQ_REQ_TOGGLE is a bit that is toggled at every CAN frame between 1 and 0 (20ms). The engine ECU can use this bit to determine if the gearbox controller is still alive, since the watchdog toggles this bit. If this bit is frozen, the engine ECU can discard this frame entirely, as its contents is no longer valid.
The bits TRQ_REQ_CTRL0, TRQ_REQ_CTRL1, TRQ_REQ_MIN and TRQ_REQ_MAX are used to control how the torque request is handled . Below is the truth table for this
TRQ_REQ_CTRL0
TRQ_REQ_CTRL1
TRQ_REQ_MIN
TRQ_REQ_MAX
Description
0
0
0
0
No request (All other values in the frame can be ignored)
1
0
1
0
Slow reduction in torque
0
1
1
0
Fast reduction in torque
1
1
1
0
Reduction request is ending
If any other combinations other than the above in the table are seen, the engine ECU MUST discard the torque request and ignore it!
Below is an example of how a torque reduction request works:
T0 - The torque request has begun (Slow torque reduction). TRQ_REQ_TRQ starts at the current engine output torque, and is ramped down to the desired torque until T1
T1 - The torque request is in the hold stage, keeping the engine torque reduced.
T2 - The torque ramp is now increasing back the driver demanded torque. The value in TRQ_REQ_TRQ will never exceed driver demand torque.
T3 - Torque request has ended. Control bits are all turned off, and TRQ_REQ_TRQ goes to 0.
Maximum torque is calculated using the current engine RPM and torque output at 100% pedal position. THIS NUMBER CANNOT BE LESS THAN 0!
Minimum torque is calculated using the current engine RPM and torque output at 0% pedal position. This number can be a negative value, indicating the engine can be dragged as it can enter a fuel shutoff condition.
Driver torque is calculated using the engine RPM and throttle angle the driver wishes for (Based on pedal position)
Static torque is calculated using the current power output of the engine. If this number is less than 0, it indicates the engine is not being fueled, and is being dragged by the gearbox (Engine braking).
If using an external speed sensor on the output shaft of the gearbox, this CAN frame can be skipped completely, as the output shaft speed sensor takes care of this.