Forward Collision Warning

Courtesy of CHRYSLER GROUP, LLC

DESCRIPTION 

The Forward Collision Warning Plus (FCW+) system is an enhancement to the current vehicles equipped with Generation 5 Long Range Radar (LRR) (1) and a Forward Facing Camera (FFC) (2). This system uses the FFC video and the Radar for enhanced sensitivity to objects in front of the vehicle and to detect whether the vehicle is approaching another vehicle or large obstacle in its path too rapidly and warn/assist the driver in avoiding the incident. The system communicates with other components on the vehicle to apply the brakes and/or to alert the driver through visual and audible warnings. The FCW Plus function operates regardless of whether Adaptive Cruise Control (ACC) with stop and go is active or not. The system operates down to 0 km/h (0 mph) and provides audible closing/proximity warnings as well as brake pedal vibration.

The FCW+ System shall use three levels of warnings: visual, audible and haptic.

• The visual warning used by the system is displayed in the Instrument Panel Cluster (IPC).
• The audible warning used by the FCW system is generated by the radio/amplifier system.
• The haptic warning used by the FCW is a brake jerk. A brake jerk is a brake pulse or a momentary application of the brakes.

The FCW+ System has four driver selectable settings:

1. FCW+ Far
2. FCW+ Near
3. FCW Far
4. FCW Near

OPERATION 

The FCW+ system is disabled and enabled via a hard switch in the Integrated Center Stack (ICS) (3). There shall be a LED in the ICS to indicate the status of the FCW+ system. When the system is disabled by the user or if the system is disabled due to a fault, the Light Emitting Diode (LED) indicator in the ICS will be illuminated. When the system is enabled, the LED indicator in the ICS will be OFF.

The FCW system is only active when the status of the ignition switch is ON and the PRNDL is in D  (Drive). The system can be manually disabled and enabled by the vehicle operator using hard button on the ICS. The default status of FCW is "ON". The system state is kept in memory from one key cycle to the next. If the system is turned OFF, it will remain OFF when the vehicle is restarted. The minimum speed for FCW activation is 8 km/h (5 mph).

Components that make up the FCW+ system are the FFC, Powertrain Control Module (PCM), ICS and the Generation 5 Radar. The Radar is the component that is responsible for the FCW+, LDW+ and ACC+ decision making. The Radar receives data from the FFC and performs a data fusion with its own sensor data. At this point, the Radar determines if a FCW+, LDW+ or ACC+ event needs to occur.

FCW+ OPERATION 

• The FCW+ system uses the forward looking Radar to determine the range and speed of the vehicle(s) and objects in the forward path of the host vehicle.
• The FCW+ system uses the FFC to perform Object Classification and to determine Lane Markings.
• The FCW+ system uses a sensor fusion algorithm to combine the information from the Radar and the FFC to determine probable collisions with vehicles and objects in the forward path of the host vehicle. The FFC provides the Radar with object information, lane information, FFC sensor status, and the FFC mounting position relative to the host vehicle rear axle. The sensor fusion algorithm and logic is contained within the Radar.
• Based on the sensor fusion algorithm and vehicle dynamic data the FCW+ System determines a time to collision (TTC) between the host vehicle and any target vehicles or objects in its forward path.
• The system will react on moving objects. A target is considered a moving object if it has a velocity greater than zero while the system is tracking it.
• The system will react on stopped objects. A target is considered a stopped object if it has a velocity greater than zero, then comes to a stop while the system is tracking it.
• The system will react on stationary objects. A target is considered a stationary object if it has zero velocity the entire time the system is tracking it.
• When the TTC becomes too small the FCW system issues visual, audible and haptic warning(s) to alert the driver of a probable collision.
• The first warning provided by the system will be a combined audible/visual warning to the driver. This audible/visual warning may be activated at the same time the brake prefill is performed.
• After the first warning, if the driver has not responded and the collision is still probable, the system provides a second warning. The second warning is a haptic warning in the form of a brake jerk. The Radar will request a brake jerk by transmitting a request to the Electronic Stability Control (ESC). The ESC module will respond and execute the brake jerk request. The audible/visual warnings will be active during the brake jerk warning.
• After the brake jerk, if the driver still has not responded and the collision is still probable the system will activate autonomous braking. The autonomous braking will be activated. The Radar makes the deceleration requests for autonomous braking by transmitting the signals to the ESC module. The ESC will respond to the deceleration request for autonomous braking. The audible/visual warnings will be active during the autonomous braking.
• If an Antilock Brake System (ABS) or ESP event is active, the Radar will continuously send an autonomous brake request while the ABS/ESP event is active. Under this condition, the ESC module will honor the autonomous brake request based on the arbitration strategy defined for multiple requests to the ESC system. Autonomous braking may be requested after, at the same time as, or without a brake jerk request, and the request must be honored by the ESC in this condition.

HANDS ON WHEEL ALERT 

The system also monitors the torque sensor inside the Electronic Power Steering (EPS) to verify the driver's hands remain on the wheel. If no driver's steering input is received for 3-5 seconds, the system will alert the driver with audio and visual warning. If the steering wheel continues to receive no torque input from the driver, the FCW+, ACC+ and Lane Departure Warning Plus (LDW+) will deactivate. Once the vehicle has achieved road speeds of 60 km/h (37 mph) and below 160 km/h (100 mph), the system senses the steering wheel input and the FFC can clearly detect the lines in the road, the system will enable again. The system will also disable when the drivers seatbelt is unbuckled while the vehicle is travelling at speeds of 16 km/h (10 mph) or greater.

PRE-FILL OPERATION 

• Under normal circumstances, there is space between the pads and rotors to prevent the pads from wearing out prematurely. This space between the pads and rotors increases the response time during any situation which may require emergency braking. The brake prefill prepares the system for braking by moving the pads closer to the rotor to improve braking response time.
• The brake prefill is performed by the ESC module.
• The Radar controls the activation and deactivation of the brake prefill.
• The brake prefill should cause no audible brake noise.
• The brake prefill should cause no vehicle deceleration.
• The brake lights will not be activated during a brake prefill.

ADVANCED BRAKE ASSIST OPERATION 

• The advanced brake assist feature of FCW+ will provide additional braking during an emergency braking event if the driver provides insufficient braking for the situation.
• The Radar will make deceleration requests for the advanced brake assist feature by transmitting request signals to the ESC.
• Advanced brake assist will be aborted when the driver completely releases the brake pedal.
• If an ABS or ESP event is active, the Radar will continuously send an advanced brake assist request while the ABS/ESP event is active. Under this condition, the ESC will honor the advanced brake assist request based on the arbitration strategy defined for multiple requests to the ESC system.

AUTONOMOUS BRAKE REQUEST OPERATION 

• After the brake jerk, if the driver still has not responded and the collision is still probable the system will activate autonomous braking.
• The Radar will make the deceleration requests for autonomous braking by transmitting the signals ESC module.
• The ESC system will send a Controller Area Network - Chassis (CAN-C) bus request to the BCM to activate the brake lights.

Since there are multiple modules involved in the operation of the FCW system, all faults or diagnostic trouble codes should be checked during diagnosis. The system utilizes the radar sensor in front of the vehicle, so any alignment or configuration issues may cause the system to be inoperative. If the ACC radar detects incorrect or compromised information, the ACC/FCW will function in a limited capacity.