EGAS monitoring concept implementation: TCU

AS you know, EGAS monitoring concept is the best practice or guideline for Automotive ECU. Therefore, many ECUs use this concept. so, I give you some an example. this is about the transmission control unit. it is just Hardware-level.

1. Sensor, communication line

Automatic transmission decides the gear speed according to the relationship between vehicle speed and the opening ratio of the throttle. so TCU(Transmission control unit) need this 2 informations. so speed sensors are needed for this reason. TCU needs to receive the opening ratio of the throttle from ECU as well. This is why TCU has to be in CAN. then, TCU can information to decide gear speed.
in the case of PRND, TCU gets this information from the position sensor. many types of signal application can be used, but for exact signal, generally, TCU get this signal by 2 lines and check the integrity because PRND signal can change the direction of driving and suddenly stop the driving.
so you need to consider how to monitor if sensors are ok or not, for example, open circuit, short to the battery and short to ground. then you will need FMEA or FTA data according to ASIL level.
also the hazard of malfunction, MCU can control the power supply for these sensors. and you better consider fail-safe mode, what if sensors are not working, how to make it is safer.

2. Actuator

once Automatic transmission decided the gear speed, then the core control Actuator to make the actual gear speed, so actuators are moving to fill clutches or grab brakes in transmission. usually, motor or solenoid valves used for the actuator.  they are inductive loads, so you need to think about freewheeling paths. and yeah, Core needs to monitor open circuit, short to the battery and short to ground. mostly Actuators can't be smart, so core must work for them. yes, cut the supply off, fail-safe.

3. Circuit

 when you design a circuit, you need to check the level 3 monitoring concept. the not only main core can cut off the supply, but also something else can cut it off. mostly PMIC does this task while monitoring if the main core is calculating well or not.