Airbag and Safety Belt Pretensioner Supplemental Restraint System (G427717)

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The SRS provides additional protection for occupants in certain vehicle accident conditions. The SRS consists of:

• A driver air bag.
• A passenger air bag.
• A side air bag on each front seat.
• Side air curtains for first and second row seats.
• A pretensioner for each front safety belt.
• A buckle sensor for each front safety belt.
• Front and side impact sensors.
• A passenger air bag deactivation indicator.
• A passenger air bag deactivation switch (all except NAS).
• An occupant monitoring system for the front passenger seat.
• A position sensor for the driver seat.
• An air bag warning indicator.
• A clockspring.
• A RCM.

The SRS features selective activation of the air bags and pretensioners, and two stage driver and passenger air bags. The RCM monitors internal and external sensors and activates the required safety belt pretensioners and air bags if the sensors detect an impact or roll-over above preset limits.

The driver air bag forms the center pad of the steering wheel. Four pins and two latches locate and secure the driver air bag to the steering wheel. The latches consist of wire springs on each side of the driver air bag which engage with hooks in the steering wheel. The driver air bag is released from the steering wheel by pulling on the wire springs with a special tool inserted through a slot on each side of the steering wheel hub. Springs on the locating pins then push the driver air bag away from the steering wheel.

A Lucar connector attaches a ground to the driver air bag.

The driver air bag has a two stage inflator, with separate electrical connectors for each stage. The inflator contains a non-azide propellant as the gas generator.

Lines molded into the inner surface of the driver air bag cover provide weak points that split open in a controlled manner when the air bag deploys. The inflated volume of the air bag is 57 liters (2.01 ft³).

The passenger air bag is located in the instrument panel, behind the upper glove compartment. The bottom of the passenger air bag is attached to a mounting bracket on the in-vehicle crossbeam. The top of the passenger air bag is attached to a chute, which, in turn, is attached to a reinforcement lid in the top of the instrument panel. When the air bag deploys, the chute guides the air bag to the underside of the reinforcement lid. The reinforcement lid incorporates two deployment doors that are forced open, splitting the instrument panel covering, when the air bag deploys.

A Lucar connector attaches a ground to the passenger air bag.

The passenger air bag has a two stage inflator, with separate electrical connectors for each stage. The inflator contains a non-azide propellant as the gas generator. The inflator uses a high pressure mix of air and hydrogen gas as the inflation medium. The inflated volume of the air bag is 130 liters (4.59 ft³).

A side air bag is attached to the outside of each front seat backrest frame, under the backrest cover. In all markets except NAS, the side air bags each consist of a single section, which deploys to protect the thorax region. In NAS markets, the side air bags each consist of two sections, inflated using a common inflator, which deploy to protect both the thorax and the pelvic regions.

The side air bags are handed, and each consist of a molded plastic case which contains the folded air bag and the inflator. In all markets except NAS the side air bags incorporate a cable that connects the igniter of the inflator to a connector in the main seat harness connector block located under the front edge of the seat cushion. In NAS markets the seat harness is connected to an electrical connector in the base of the inflator.

When a side air bag deploys it forces the front edge of the molded plastic case apart and splits open the backrest cover.

The side air bags use compressed argon as the inflation medium. In all markets except NAS the inflated volume of each side air bag is approximately 12 liters (0.42 ft³). In NAS markets the inflated volume of each side air bag is approximately 10 liters (0.35 ft³) for the thorax section and 3 liters (0.11 ft³) for the pelvic section.

The side air curtains are designed to protect the head and upper body of first and second row occupants in side impact and roll-over situations. The side air curtains use compressed argon as the inflation medium.

The side air curtains are installed on the cant rails above the front and rear doors, behind the headliner.

Each side air curtain has an inflator, which is attached to the E pillar by a mounting bracket. The inflator is connected to the air curtain by a gas guide pipe.

The gas guide pipe and air curtain are secured along the cant rail by mounting brackets at each end of the gas guide pipe and two ramps. Tethers attached to the front and rear of the air curtain are anchored to the A pillar and the gas guide mounting bracket respectively. The front of the air curtain is secured to the A pillar by two mounting clips.

When the side air curtain deploys, it breaks out of the two ramps on the cant rail and extends downwards from behind the headliner. The deploying air curtain is tensioned between the tether anchor points on the A pillar and the gas guide mounting bracket. This retains the air curtain in position against the upper part of the doors and the B pillar.

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.

Each pretensioner has a tube containing an inflator and a piston. The inflator is connected to the RCM. The piston is attached to a steel cable, the opposite end of which is attached to the safety belt buckle.

On receipt of a fire signal from the RCM, the inflator generates nitrogen gas that rapidly expands to drive the piston along the tube, pulling the cable and drawing the safety belt buckle downwards.

The buckle of each front safety belt incorporates a Hall effect sensor that provides a safety belt status signal to the RCM. The RCM broadcasts the status of the two front safety belts on the high speed controller area network (CAN) bus for use by the instrument cluster.

Impact sensors are installed in the front and both sides of the vehicle. The use of multiple impact sensors provides shorter air bag trigger times, through faster detection of lateral and longitudinal acceleration, and improves detection accuracy.

There are two front impact sensors attached to brackets on the body front support frame, just above each front longitudinal.

There are six side impact sensors located in the passenger compartment:

• One attached to each front door.
• One attached to the base of each B pillar.
• One attached to the base of each C pillar.

Each impact sensor incorporates an accelerometer and a microcontroller powered by a feed from the RCM. The power feed also provides the interface connection through which the impact sensor communicates with the RCM using serial data messages. Acceleration is evaluated by the microcontroller and transmitted to the RCM, which then makes the decision on whether or not to activate the air bags and pretensioners.

When the ignition is switched on the RCM supplies power to the impact sensors, which perform a self test. After satisfactory self tests the impact sensors continually output 'sensor active' messages to the RCM. If a fault is detected the relevant impact sensor sends a fault message, instead of the sensor active message, to the RCM. The RCM then stores a related fault code and illuminates the air bag warning 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 based on seat occupancy status derived from the occupant classification system (NAS vehicles) or the passenger air bag deactivation switch (all except NAS and Australian specification vehicles).

The RCM illuminates the indicator when:

• The passenger air bag is deactivated with the passenger air bag deactivation switch (where fitted). OR
• Required by passenger seat occupant monitoring (NAS vehicles only).

The passenger air bag deactivation switch provides a method of manually disabling the passenger air bag on all vehicles except Australian specification and those fitted with the occupant classification system. The switch is installed in the front passenger end of the instrument panel and is operated by the ignition key.

When the passenger air bag deactivation switch is operated, it changes a ground connection between two pins in the connectors of the RCM. When the passenger air bag deactivation switch is selected to OFF, the RCM disables the passenger air bag and, if the front passenger seat is occupied, illuminates the passenger air bag deactivation indicator.

There are 2 types of occupant sensing:

• In all markets except North America, vehicles have an occupant detection system to activate the seat belt minder
• On NAS vehicles, an occupant classification system provides signals to the RCM to allow the correct arming of the passenger air bag and corresponding indicator.

Occupant Detection System

The occupant detection system can only determine if the front passenger seat is occupied or unoccupied. The occupant detection system consists of a pressure switch installed between the foam padding and the cover of the front passenger seat cushion.

The pressure switch incorporates a number of load cells connected in series and embedded in a plastic film. Weight on the pressure sensor increases the resistance of the circuit.

The instrument cluster supplies a reference voltage to the pressure switch and measures the current draw to determine the occupancy status. From the occupancy status, and the status of the front passenger safety belt (received from the RCM on the high speed CAN bus), the instrument cluster determines the belt minder status.

Occupant Classification System

Occupant classification system comprises an ECU, attached to the underside of the seat, a silicon filled bladder with a pressure sensor fitted between the cushion foam and the seat pan and a seat belt tension sensor. When an occupant sits on the seat a pressure is created in the bladder and the occupant weight is determined from the pressure generated. The weight is compared against 4 classification thresholds. These are:

• Empty
• Occupied inhibit status (6 year old child, 3 year old child, rear facing/forward facing 12 month infant seats and booster seats)
• Occupied allow status (weight greater than 5th precentile female) and the airbag enabled/disabled as appropriate
• Indeterminate state.

OCS module contains accelerometers and algorithms to compensate for the effects of longitudinal, lateral and vertical forces acting on the vehicle whilst being driven. The belt tension sensor is used to offset loads forced into the seat by 'cinched' child seats (where a child seat load on the seat is increased by a highly tensioned seat belt) and also dynamic belt loading (Off-road/aggressive driving styles).

The belt minder system on cars equipped with the occupant classification system uses the RCM to detect seat occupancy status based on calculations within the RCM, with the instrument cluster then determining whether a seat belt reminder should be activated based on the status of the seat belt buckle switches and vehicle speed.

The seat position sensor allows the RCM 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 and a target plate on the seat base. While the ignition is on, the RCM supplies the sensor with a power supply of 12V nominal, and monitors the return voltage. When the seat frame moves forwards, the sensor moves over the target plate, which changes the reluctance of the sensor. The change of voltage is detected by the RCM 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 target plate.

When the driver seat is forward of the switching point, the RCM 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, uses the normal time delay between firing the two stages.

The air bag warning indicator consists of a red light emitting diode (LED) behind a SRS graphic in the tachometer of the instrument cluster.

Operation of the air bag warning indicator is controlled by a high speed CAN bus message from the RCM to the instrument cluster. The RCM illuminates 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.

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, i.e. the driver air bag, the horn and the steering wheel switch packs.

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 by a drive peg. A lug on the underside of the rotor operates the self-cancelling feature of the turn signal indicator switch. A ribbon lead, threaded on rollers in the rotor, links two connectors 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. The clockspring is centralized when the drive peg is at six o'clock and 50 - 100% of a yellow wheel is visible in the viewing window.

Replacement clocksprings are fitted with a stopper, which locks the cover to the rotor, in the central position. The stopper must be broken off when the replacement clockspring is installed.

The RCM is installed on the top of the transmission tunnel, in line with the B pillars, and controls operation of the SRS. The main functions of the RCM include:

• Crash detection and recording.
• Air bag and pretensioner firing.
• Self test and system monitoring, with status indication via the air bag warning lamp and non volatile storage of fault information.

A safing sensor in the RCM 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 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 Land Rover approved diagnostic system on a dedicated link between the RCM and the diagnostic socket. 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.

General

In a collision, the sudden deceleration or acceleration is measured by the safing sensor in the RCM and by the impact sensors. The RCM 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 or pretensioners. During a collision, the RCM only fires the air bags and pretensioners if the safing sensor confirms that the data from the remote sensor(s) indicates an impact limit has been exceeded. The RCM also monitors the vehicle for a roll-over accident using the internal roll-over sensor and high speed CAN bus messages from the anti-lock brake system (ABS) module and the steering angle sensor.

The RCM 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 2, belt unfastened.
• Front impact, driver and passenger air bags stage 1, belt fastened.
• Front impact, driver and passenger air bags stage 2, belt fastened.
• Rear impact.
• left-hand (LH) side impact.
• right-hand (RH) side impact.
• Roll-over.

The front impact thresholds increase in severity from pretensioners, through to driver and passenger air bag stage 2, belt fastened.

Firing Strategies

The seat belt pretensioners are fired when either the pretensioner impact limit or the roll-over limit is exceeded. The RCM only fires the pretensioners if the related safety belt is fastened. For the front passenger pretensioner to fire, the seat must also be occupied by a large person, i.e. someone over a given weight (NAS only).

The driver and passenger air bags are only fired in a frontal impact that exceeds the stage 1 threshold. Both stages of the inflator in the driver and passenger air bags are fired. At impacts between the stage 1 and 2 thresholds, the delay between the firing of the two stages varies with the severity of the impact; the more severe the impact the shorter the delay. At stage 2 impact thresholds and above, the two stages of the inflator are fired almost 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). The time delay between firing the two stages of the inflator in the driver air bag is increased if the driver seat is forward of the seat position sensor switching point.

If there is a fault with a safety belt buckle sensor, the RCM 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 detection system, or if there is a fault with the passenger air bag deactivation switch, the RCM increase the time delay between firing the two stages of the inflator in the passenger air bag.

If a side impact limit is exceeded, the RCM fires the side air bag and the side air curtain(s) on that side of the vehicle. If the side impact limit on the front passenger side of the vehicle is exceeded, the RCM also evaluates the input from the occupant classification system, and fires the side air bag only if the front passenger seat is occupied by a large person (NAS only).

The side air curtain(s) on both sides of the vehicle are fired if the roll-over limit is exceeded.

If multiple impacts occur during a crash event, after responding to the primary impact the RCM will output the appropriate fire signals in response to any further impacts if unfired units are available.

Crash Signal

When the RCM outputs any of the fire signals, it also outputs a hard wired crash signal to the engine control module (ECM) and changes the high speed CAN bus output message from 'no crash' to 'crash condition'. The high speed CAN bus message is used by the central junction box (CJB) and the FFBH (fuel fired booster heater).

On receipt of the crash signals:

• The ECM disables the fuel pump.
• Operation of the FFBH is disabled.
• The CJB enters the crash mode and:
  • Activates all of the unlock signals of the vehicle locking system, even if the vehicle is already unlocked. After 3 seconds, the CJB activates the unlock signals again, in case a lock button is pressed during the crash, by flailing limbs for example.
  • Ignores all locking and superlocking inputs until the crash mode is cancelled, when it returns the locking system to normal operation.
  • Activates all of the courtesy lamps, except for the approach lamps. The activated courtesy lamps remain on until they are manually switched off at the lamp unit, or the CJB crash mode is cancelled, when they return to normal operation.
  • Activates the hazard warning lamps. The hazard warning lamps remain on until cancelled by turning the ignition switch from position II to position I or 0, or until the crash mode is cancelled.

The crash mode is cancelled by cycling the ignition switch.