Restraints Control Module
The RCM is installed on the top of the transmission tunnel, in line with the B pillars, and controls operation of the Supplemental Restraint System (SRS). The main functions of the RCM include:
- Crash detection and recording
- Air bag and pre-tensioner firing
- Self-test and system monitoring, with status indication via the air bag warning lamp and non-volatile storage of fault information.
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 evaluates crash severity by using data from the RCM internal accelerometer, the front crash sensor and the safety belt buckle sensor. Based on this data, the RCM decides which level of air bag module deployment is required and forwards the information to the second area, the deployment handler.
The deployment handler evaluates the status of the seat track position sensor and safety belt buckle sensors before a decision is made about which restraints should finally be deployed.
Data from the side crash 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 air bag module should be deployed.
On board testing of the air bag modules, front safety belt pretensioner firing circuits, warning indicator circuits and module status (the crash and side impact sensors perform basic self-tests) is performed by the RCM together with the storing of fault codes.
The RCM drives the SRS indicator on the instrument pack via a CAN signal. If the warning lamp fails, a fault code is recorded and a warning tone is sounded in place of the lamp if a further fault occurs. It also provides a temporary back-up power supply to operate the air bag modules in the event that in crash conditions, the battery supply is lost. In the event of a crash, it records certain data which can be accessed via the diagnostic connector.
A saving sensor in the RCM provides confirmation of an impact to verify if air bag and pretensioner activation is necessary. Various firing strategies are employed by the RCM to ensure that during an accident only the appropriate air bags and pretensioners are fired. The firing strategy used also depends on the inputs from the safety belt switches and the occupant monitoring 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 switch is disrupted during a crash. The stored energy is sufficient to produce firing signals for the driver air bag, the passenger air bag and the safety belt 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 air bag warning indicator. The faults can be retrieved by the recommended Jaguar diagnostic tool over the CAN bus. 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.