Description

Air Bag Systems

NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus.

SHEET 1 OF 2









SHEET 2 OF 2









PRINCIPLES OF OPERATION
In a collision, the sudden deceleration or acceleration is measured by the impact sensors and the accelerometers in the RCM (restraints control module). The RCM (restraints control module) evaluates the readings to determine the impact point on the vehicle and whether the deceleration/acceleration readings exceed the limits for firing any of the air bags and pretensioners. During a collision, the RCM (restraints control module) only fires the air bags and pretensioners if the safing function confirms that the data from the impact sensor(s) indicates an impact limit has been exceeded.
The RCM (restraints control module) incorporates the following impact thresholds to cater for different accident scenarios:
- Front impact, pretensioners.
- Front impact, driver and passenger air bags stage 1, belt unfastened.
- Front impact, driver and passenger air bags stage 1, belt fastened.
- Front impact, driver and passenger air bags stage 2, belt unfastened.
- Front impact, driver and passenger air bags stage 2, belt fastened.
- Rear impact.
- Driver side impact.
- Passenger side impact.

Firing Strategies
The safety belt pretensioners are fired when the pretensioner impact limit is exceeded. The RCM (restraints control module) only fires the pretensioners if the related safety belt is fastened.
The driver and passenger air bags are only fired in a frontal impact. If an impact exceeds a stage 1 limit, but is less than the corresponding stage 2 limit, only one inflator in each air bag is fired (stage 2 is still fired for disposal after a delay of 100 ms). If an impact exceeds the stage 2 limit, the two inflators in each air bag are fired simultaneously.
The passenger air bag is disabled unless the front passenger seat is occupied by a large person (NAS only), or the passenger air bag deactivation switch is on (all except NAS and Australia).
The stage 2 inflator of the driver air bag is disabled if the driver seat is forward of the switching point of the seat position sensor.
If there is a fault with a safety belt buckle switch, the RCM (restraints control module) assumes the related safety belt is fastened for the pretensioner firing strategy and unfastened for the driver and passenger air bag firing strategies. If there is a fault with the occupant classification sensor, the RCM (restraints control module) disables the passenger air bag. If there is a fault with the passenger air bag deactivation switch, the RCM (restraints control module) disables the passenger air bag.
If a side impact limit is exceeded, the RCM (restraints control module) fires the side air bag and the side head air bag on that side of the vehicle. If the side impact limit on the front passenger side of the vehicle is exceeded, the RCM (restraints control module) also evaluates the input from the occupant classification sensor, and fires the side air bag only if the front passenger seat is occupied by a large person (NAS only).
If multiple impacts occur during a crash event, after responding to the primary impact the RCM (restraints control module) will output the appropriate fire signals in response to any further impacts if unfired units are available.









Crash Signal
When the RCM (restraints control module) outputs any of the fire signals it also outputs a crash signal to the CJB (central junction box) and the ECM (engine control module) on the high speed CAN (controller area network). The crash signal is also hardwired to the ECM (engine control module) and the CJB (central junction box). On receipt of the crash signal, the ECM (engine control module) cuts the power supply to the fuel pump relay and the CJB (central junction box) goes into crash mode. In the crash mode, the CJB (central junction box):
- Activates all of the unlock signals of the vehicle locking system, even if the vehicle is already unlocked.
- Ignores all locking/superlocking inputs until it receives an unlock input, when it returns the locking system to normal operation.
- Activates the interior lamps. The interior lamps remain on permanently until they are manually switched off at the lamp unit, or the CJB (central junction box) crash mode is switched off and they return to normal operation.
- Disables the rear window child lock input until the crash mode is switched off.
- Activates the hazard flashers. The hazard flashers remain on until cancelled by the hazard warning switch or the crash mode is switched off.
The CJB (central junction box) crash mode is switched off by a valid locking and unlocking cycle of the locking system.

RESTRAINTS CONTROL MODULE





The RCM (restraints control module) is installed on the top of the transmission tunnel, in line with the B/C pillars, and controls operation of the SRS (supplemental restraint system). The main functions of the RCM (restraints control module) include:
- Crash detection and recording.
- Air bag and pretensioner firing.
- Self test and system monitoring, with status indication via the air bag warning indicator and non volatile storage of fault information.
The RCM (restraints control module) determines which elements of the SRS (supplemental restraint system) are to be deployed by using two internal areas:
- Crash severity evaluation.
- Deployment handler.
Crash severity evaluation uses data from the RCM (restraints control module) internal accelerometer, the front crash sensor and the safety belt buckle switch. Based on this data, the RCM (restraints control module) 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 (restraints control module) in conjunction with acceleration data from the RCM (restraints control module) internal accelerometer to make a deployment decision. The RCM (restraints control module) processes the acceleration data and, subject to an impact being of high enough severity, decides whether the side air bag module and air curtain should be deployed.
On board testing of the air bag modules, front safety belt pretensioner firing circuits, warning indicator circuits and module status is performed by the RCM (restraints control module) together with the storing of fault codes. The impact and pressure sensors perform basic self-tests.
The RCM (restraints control module) drives the air bag warning indicator via a high speed CAN (controller area network) 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. The RCM (restraints control module) 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 safing sensor in the RCM (restraints control module) provides confirmation of an impact to verify if air bag and pretensioner activation is necessary. A roll-over sensor monitors the lateral attitude of the vehicle. Various firing strategies are employed by the RCM (restraints control module) 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 buckle switches and the occupant monitoring system.
An energy reserve in the RCM (restraints control module) 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 (restraints control module) performs a self test and then performs cyclical monitoring of the system. If a fault is detected the RCM (restraints control module) stores a related fault code and illuminates the air bag warning indicator. The faults can be retrieved by Jaguar approved diagnostic equipment over the CAN (controller area network) bus. If a fault that could cause a false fire signal is detected, the RCM (restraints control module) disables the respective firing circuit, and keeps it disabled during a crash event.

CLOCKSPRING





The clockspring is installed on the steering column to provide the electrical interface between the fixed wiring harness of the steering column and the components that rotate with the steering wheel.
The clockspring consists of a plastic cassette which incorporates an outer cover fixed to the steering column and an inner rotor which turns with the steering wheel. Four securing lugs attach the cover to the multifunction switch on the steering column. The rotor is keyed to the steering wheel. A lug on the underside of the rotor operates the self-canceling feature of the turn signal indicator switch. A ribbon lead, threaded on rollers in the rotor, links a connector on the cover to two connectors on the rotor. Link leads for the driver air bag are installed in one of the connectors on the rotor.
To prevent damage to the ribbon lead, both the steering and the clockspring must be centralized when removing and installing the clockspring or the steering wheel.
Replacement clocksprings are fitted with a rotor lock, which locks the cover to the rotor, in the central position. The rotor lock must be removed when the replacement clockspring is installed.

DRIVER AIR BAG





The driver air bag is controlled by the RCM (restraints control module), which chooses between single or dual stage deployment, depending on the occupant position and the crash severity. To reduce the risk of an air bag induced injury to a driver who is positioned close to the steering wheel, the 690 mm diameter air bag deploys radially. The volume of the driver air bag is 57 liters.
The driver air bag has a non-azide propellant that reduces particulates and effluents. It consists of a two stage inflator with separate chambers for the two inflation stages, each being independently activated by the RCM (restraints control module). It has two electrical connectors that are color coded and mechanically keyed to the respective connector on the inflator.

PASSENGER AIR BAG





The passenger air bag is controlled by the RCM (restraints control module), which chooses between single or dual stage deployment, depending on the occupant status and the crash severity. It consists of a two stage inflator with two air bag electrical connectors to accommodate the two stage inflation. The volume of the passenger air bag is 110 - 120 liters.
The heated gas inflator consists of a high-pressure mix of clean air and hydrogen gas, triggered by two separate ignition squibs. It produces a controlled generation of clean gas to rapidly fill the air bag. It is classified as a stored flammable gas (not as an explosive) and as such, has less restrictive storage and transportation requirements. It produces a very clean burn and almost no particulates and is almost free of any toxins, making disposal or recycling much easier.

SIDE AIR CURTAIN





The side air curtains have a capacity of approximately 29 liters and are fitted along both sides of the car. They deploy from behind the headliner above the doors, and are anchored at their front and rear extremities to maintain tension across the lower edge of the curtain. Their deployment area extends between the A and C pillar trims, passing over the upper B pillar trim. The inflated portion of the curtain provides head protection for outer occupants in both the front and rear of the car, and a significant level of protection against objects such as poles and trees.
The side air curtains have a rapid fill time of less than 25 ms and, when fully inflated, are approximately 150 mm thick. The curtains are internally divided into separate chambers and, when an area of the inflated air bag is impacted, gases transfer through internal vents to chambers further away from the impact, absorbing energy.
The side air curtains use standard hybrid inflators, which inflate the curtains with gas produced from a combination of pyrotechnic charge and compressed gas.

SIDE AIR BAG





The side air bags are mounted in the outer sides of the front seats where they provide thorax, rib and pelvis protection. Each side air bag consists of a folded air bag and a pyrotechnic inflator contained in a nylon fabric cover.
Side air bags inflate in less than 15 ms, and absorb the energy of an impact by venting the inflation gas through a vent in the fabric material of the air bag. The venting used is able to discriminate between small and large sized occupants, and adjust the cushion stiffness to suit.

IMPACT SENSORS





Impact sensors are installed in the front and both sides of the vehicle. A front impact sensor is attached to each headlamp surround panel, below the headlamp. A side impact sensor is attached to the base of each D pillar.
The impact sensors are accelerometers that allow the RCM (restraints control module) to detect the sudden acceleration that occurs during an impact.

IMPACT PRESSURE SENSOR





An impact pressure sensor is installed in each front door, attached to the closure panels. The pressure sensors allow the RCM (restraints control module) to detect the sudden pressure pulse that occurs in the front door during a side impact.

SEAT POSITION SENSOR





The seat position sensor allows the RCM (restraints control module) to detect when the driver seat is forward of a given point on the seat track. The seat position sensor consists of a Hall effect sensor attached to the driver seat frame. While the ignition is on, the RCM (restraints control module) supplies the sensor with power, and monitors the return current. When the seat frame moves forwards, the sensor moves over the edge of the seat track, which changes the reluctance of the sensor. The change of current is detected by the RCM (restraints control module) and used as a switching point. The switching point is when the center of the sensor is 3 ± 4 mm from the leading edge of the seat track.
When the driver seat is forward of the switching point, the RCM (restraints control module) increases the time delay between firing the two stages of the inflator in the driver air bag. When the driver seat is rearward of the switching point, the RCM (restraints control module) uses the normal time delay between firing the two stages.

PRETENSIONERS





The pretensioners are used to tighten the front safety belts during a collision to ensure the occupants are securely held in their seats. A pretensioner is integrated into each front safety belt buckle and attached to a bracket on the inboard side of the seat.

SAFETY BELT BUCKLE SWITCHES
The buckle of each front safety belt incorporates a switch that provides a safety belt status signal to the RCM (restraints control module). The RCM (restraints control module) broadcasts the status on the high speed CAN (controller area network) bus for use by the safety belt reminder and beltminder systems in the instrument cluster.
In the event of a front impact, the RCM (restraints control module) will deploy the pretensioners provided the safety belt buckles are fastened. The pretensioners have a lower deployment threshold than the air bags. Hence it is possible during a minor collision, which exceeds the deployment threshold, that only the pretensioners will deploy.

AIR BAG WARNING INDICATOR





The air bag warning indicator consists of a red LED (light emitting diode) behind a SRS (supplemental restraint system) graphic in the instrument cluster.
Operation of the air bag warning indicator is controlled by a high speed CAN (controller area network) bus message from the RCM (restraints control module) to the instrument cluster. The RCM (restraints control module) sends the signal to illuminate the air bag warning indicator if a fault is detected, and for approximately 6 seconds during the bulb check at the beginning of each ignition cycle.

OCCUPANT MONITORING
There are two types of occupant monitoring:
- In all markets except NAS and Australia, vehicles have an occupant detection system.
- In NAS markets, vehicles have an occupant classification system.

Occupant Detection Sensor





For markets which have an occupant detection sensor, this has no interface with the restraints system and only provides the belt reminder function.

Occupant Classification System

Pressure Pad and Sensor





Safety Belt Tension Sensor





Occupant Classification Module





For markets that have an occupant classification system, this provides the RCM (restraints control module) with the occupancy status of the front passenger seat. The restraints control module uses this and the seat buckle status in the evaluation of the firing strategy for the passenger air bag, the passenger side air bag and the front passenger safety belt pretensioner.
The occupant classification system can determine if the front passenger seat is unoccupied, occupied by a small person, or occupied by a large person. The occupant classification system consists of:
- A pressure pad, installed under the cushion of the front passenger seat, which is connected to a pressure sensor.
- A safety belt tension sensor, integrated into the anchor point of the front passenger safety belt.
- An occupant classification module, installed under the front passenger seat.
The pressure pad is a silicone filled bladder. Any load on the pressure pad is detected by the pressure sensor.
The safety belt tension sensor is a strain gauge that measures the load applied by the safety belt anchor to the anchor bolt. The sensor is located in the lower safety belt anchor point.
The occupant classification module supplies a reference voltage to the pressure sensor and the safety belt tension sensor and, from the returned signals, measures the loads acting on the pressure pad and the safety belt tension sensor. The load measurement from the safety belt tension sensor is used to produce a correction factor for the load measurement from the pressure pad. The tightness of the safety belt affects the load acting on the pressure pad, so without the correction factor the occupant classification module cannot derive an accurate occupancy status.
The occupant classification module translates the load readings into a seat occupancy status and transmits the result to the RCM (restraints control module), on a dedicated high speed CAN (controller area network) bus link. The occupant classification module incorporates two load limits for the seat cushion: When the load exceeds the lower limit, but is less than the upper limit, the occupant is classified as small; when the upper limit is exceeded, the occupant is classified as large.

PASSENGER AIR BAG DEACTIVATION INDICATOR





The passenger air bag deactivation indicator is installed on the center switch pack of the instrument panel. When appropriate, the indicator illuminates to advise front seat occupants that the passenger air bag is disabled. Operation of the indicator is controlled by the RCM (restraints control module). The RCM (restraints control module) illuminates the indicator when:
- There is a fault with the passenger air bag firing circuit(s).
- The passenger air bag is deactivated with the PAD (passenger air bag deactivation) switch (where fitted) and the front passenger seat is occupied.
- Required by passenger seat occupant classification (where fitted).

PASSENGER AIR BAG DEACTIVATION SWITCH (ALL EXCEPT NAS)





Where fitted, the PAD (passenger air bag deactivation) switch provides a method of manually disabling the passenger air bag. The switch is installed in the front passenger end of the instrument panel and operated by the emergency key.
When the PAD (passenger air bag deactivation) switch is operated, it changes a ground connection between two pins in the connectors of the RCM (restraints control module). When the PAD (passenger air bag deactivation) switch is selected to OFF, the RCM (restraints control module) disables the passenger air bag and, if the front passenger seat is occupied, illuminates the PAD (passenger air bag deactivation) indicator in the overhead console.