Forward Collision Warning System: Notes

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

1.	Refer to: MID RANGE RADAR FRONT  - Left (MRRFL) or Right (MRRFR).
2.	Refer to: LONG RANGE RADAR FRONT (LRRF) .
3.	Refer to: BODY CONTROL MODULE (BCM) .
4.	Refer to: LONG RANGE CAMERA FRONT (LRCF) .
5.	Refer to: DISPLAY SCREEN MODULE (DSM) .
6.	Refer to: CENTRAL ADAS DECISION MODULE (CADM) .
7.	Refer to: STEERING WHEEL SENSOR MODULE (SWSM) .
8.	Refer to: INSTRUMENT PANEL CLUSTER (IPC) .
9.	Refer to: BRAKE SYSTEM MODULE (BSM) .

The Autonomous Emergency Braking (AEB) system is the main system comprising the Forward Collision Warning (FCW) system. AEB is a high level feature that encompasses the following sub features:

• FCW / AEB car-to-car
• Pedestrian Emergency Braking (PEB)
• Cyclist Emergency Braking
• Intersection Collision Assist (ICA)

OPERATION 

The AEB system provides the following types of braking features that are based on how the vehicle is equipped:

• Advanced Brake Assist (ABA) - The ABA feature of AEB system provides additional braking during an emergency braking event if the driver provides insufficient braking for the situation. Audible and visual warnings are active during the ABA braking.
• Limited Autonomous Brake Requests (CMS).
• Limited Autonomous Extended Brake Requests (Extended CMS).
• Full Autonomous Brake Requests - This braking feature is only available at low vehicle speeds.
• Pedestrian/Cyclist Emergency Brake Request (PEB).
• Intersection Collision Assist Left Brake Request (ICA-L) - When ICA is activated, the CADM applies the Pre-fill and ABA functions to mitigate any risk of collision evaluated through the obstacle detection by right or left radar.
• Intersection Collision Assist Right Brake Request (ICA-R).

The AEB system is a Driver Assistance System designed to assist the driver in detecting, avoiding and mitigating collisions with vehicles and pedestrians in its forward path. Using a radar paired with a LRCF, the AEB system is able to determine the likelihood of a probable frontal collisions. The AEB system is able to determine the range and speed of a vehicle by using the LRRF. The AEB system also uses the LRRF to determine the range, speed and direction of pedestrian motions in the forward path of the host vehicle. By using the LRCF, the AEB system is able to perform object classification and to determine lane markings. The AEB system uses a sensor fusion algorithm to combine the information from the CADM and the LRCF. This sensor fusion algorithm and logic is contained within the CADM itself.

The AEB system uses the sensor fusion information to determine probable collisions with vehicles, pedestrians, and cyclists in the forward path of the host vehicle. The Cyclist Emergency Braking feature adheres to the Pedestrian Emergency Braking (PEB) system performance. Additionally, the AEB system has the capability of detecting potential intersection collision through the use of the sub-feature Intersection Collision Assist (ICA) system. The ICA system is able to determine probable intersection collisions, particularly in urban areas, at low speeds by utilizing the forward looking radar, LRCF, and corner radars. Based on the sensor fusion algorithm and vehicle dynamic data the AEB system determines a Time To Collision (TTC) between the host vehicle and any target vehicles, objects or pedestrians in its forward path. When the TTC becomes too small the AEB system issues visual, audible and haptic warnings to alert the driver of a probable collision. At low vehicle speeds, in addition to the above mentioned functionality, the AEB system provides full autonomous braking to attempt to mitigate a frontal collision. These AEB FCW events occur as needed in the order of criticality of events. This is determined by the CADM.

Other items of note concerning the AEB systems are:

• The AEB System is only active at vehicle speeds above a calibrated value in a forward gear.
• The AEB System is only active at vehicle speeds above a 5 km/h (3 mph) while in a forward gear.
• AEB is unavailable when the vehicle transfer case is engaged in the 4-Low position.
• The AEB system reacts 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 AEB system reacts 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 AEB system reacts on stationary objects classified by the LRCF as vehicles or pedestrians. A target is considered a stationary object if it has zero velocity the entire time the system is tracking it.

PEB and the Cyclist Emergency Braking Systems

The CADM provides the following PEB/Cyclist functionality based on:

• TTC
• Pedestrian/Cyclist detection
• Detection by radar or LRCF and sensor availability

Scenario	Sub-functionalities
Pedestrian/Cyclist as not in vehicle path.	None
Pedestrian/Cyclist is detected as in vehicle path.	Brake Pre-fill
Pedestrian/Cyclist is detected as in vehicle path with a probability of collision.	The cascading flow is: Brake Pre-fill Visual Warning Audible Warning PED Braking

Brake Pre-fill Operation 

Under normal circumstances, there is space between the brake 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 following are characteristics of brake prefill:

• The CADM requests the BSM to perform the brake prefill.
• The CADM controls the activation and deactivation of the brake prefill with a signal sent to the BSM.
• The brake prefill does not cause audible brake noises.
• The brake prefill does not cause vehicle deceleration.
• The CADM receives the status of the brake prefill from the BSM. When the BSM is performing a brake prefill, the signal sent to the CADM indicates that the system is active.
• The brake lamps are not activated during the pre-fill event.

FCW Warning Indications 

The AEB system has three levels of warning:

1. Visual - The CADM sends a CAN-C signal to the IPC to control the activation and deactivation of the AEB visual warning.
2. Audible - The CADM requests audible tones through the IPC or DSM.
3. Haptic - The haptic warning used by the AEB system is a brake jerk. A brake jerk is a brake pulse or a momentary application of the brakes. The brake jerk warning parameters are contained within and implemented by the BSM. The CADM controls the activation and deactivation of the AEB brake jerk warning. The BSM activates the brake lamps during this event.

During an ignition cycle, the total number of brake jerks or AEB system evens is limited to a maximum of four events. If any brake event counter has reached four, one second after the completion of the fourth brake event, the CADM changes the DSM touchscreen configuration to "Active Braking OFF". The AEB system returns to the last known active braking setting at the next ignition cycle.

LRCF Heating Element:

• This feature is capable of clearing the windshield in front of CADM from fog and frost.
• The CADM module operates the heating element.
• The CADM allows activation of the heating element relay only when the BCM sets the ignition state to run.
• The CADM turns the heating element relay to "Off" if it is "On" when the BCM sets the ignition state to anything other then run.
• The CADM will turn "Off" the heating element relay if a loss of communication condition is determined.
• There is always a timer that is limiting the duration the heating element may be ON. Timers are reset only after an ignition cycle.
• This feature will automatically be activated by the CADM in the case of cold weather when remote starting the vehicle.
• The heating element participates in the load shed strategy. The strategy is managed by the BCM and the BCM will signal the CADM to deactivate the heating element when it is required.