Restraints Control Module (RCM)
The RCM is installed on top of the floor tunnel, under the floor console, and controls operation of the SRS. The main functions of the RCM include:
- Crash detection and recording.
- Airbags, pedestrian protection system and seatbelt pretensioners firing.
- Self test and system monitoring, with status indication via the airbag warning indicator, and non volatile storage of fault information.
- Supply of yaw rate and lateral acceleration data for the ABS (Anti-lock Brake System) control module.
The RCM determines which elements of the SRS are to be deployed by using two internal areas:
- Crash severity evaluation.
- Deployment handler.
Crash severity evaluation uses data from the RCM internal accelerometer, the front impact sensors and the seatbelt buckle switches. Based on this data, the RCM decides which level of airbag module deployment is required and forwards the information to the second area, the deployment handler.
The deployment handler evaluates the status of the seat position sensors, seatbelt buckle switches and the occupant classification system, before a final decision is made about which restraints should be deployed.
Data from the side impact and pressure sensors is used by the RCM in conjunction with acceleration data from the RCM internal accelerometer to make a deployment decision. The RCM processes the acceleration data and, subject to an impact being of high enough severity, decides whether the side airbag and air curtain should be deployed.
Yaw rate and lateral acceleration data for the ABS control module is derived from the internal accelerometer and transmitted on the High Speed (HS) Controller Area Network (CAN) chassis and powertrain buses.
On board testing of the airbags, pedestrian protection system and pretensioner firing circuits, the warning indicator circuits and the RCM status is performed by the RCM, together with the storing of fault codes. The impact and pressure sensors perform basic self-tests.
The RCM drives the airbag warning indicator via a HS CAN signal. If the warning indicator fails, a fault code is recorded and a warning tone is sounded in place of the indicator if a further fault occurs. In the event of a crash, the RCM records certain data which can be accessed via the diagnostic connector.
A sensor in the RCM provides confirmation of an impact to verify if airbags, pedestrian protection system and pretensioner activation is necessary. A roll-over sensor monitors the lateral attitude of the vehicle. Various firing strategies are employed by the RCM to ensure that during an accident only the appropriate airbags, pedestrian protection system and pretensioners are fired. The firing strategy used also depends on the inputs from the seatbelt buckle switches and, on NAS vehicles, the occupant classification system.
An energy reserve in the RCM ensures there is always a minimum of 150 milliseconds of stored energy available if the power supply from the ignition circuit is disrupted during a crash. The stored energy is sufficient to produce firing signals for the driver airbag, the passenger airbag and the seatbelt pretensioners.
When the ignition is switched on the RCM performs a self test and then performs cyclical monitoring of the system. If a fault is detected the RCM stores a related fault code and illuminates the airbag warning indicator. The faults can be retrieved by Jaguar approved diagnostic equipment. If a fault that could cause a false fire signal is detected, the RCM disables the respective firing circuit, and keeps it disabled during a crash event.