Adaptive Cruise Control Description and Operation: Notes

The Adaptive Cruise Control (ACC) system is an enhanced cruise control system with the ability to sense and react to forward traffic. Compared to the common cruise control system found on many vehicles, the main functional enhancement of the adaptive cruise control system is the ability to detect the presence of a vehicle in the path of the adaptive cruise control vehicle. Adaptive cruise control retains the existing cruise control feature that controls the vehicle speed to the driver selected speed. However, adaptive cruise control allows a driver to set and maintain a following distance to the preceding nearest vehicle in the path ahead. The K124 Image Processing Module controller calculates a follow speed limit to ensure an acceptable distance is maintained to the preceding vehicle in front, should one be present. The adaptive cruise control system automatically adjusts the speed when the vehicle comes up behind a slower travelling vehicle in front. The system applies limited automatic braking and throttle control without driver input when necessary to maintain the set following distance. The preceding vehicle's speed and acceleration along with the active cruise control vehicle speed and acceleration and the distance between the two vehicles are factors used by the K124 Image Processing Module controller to determine the follow speed limit. The vehicle speeds up to the original driver selected set speed when the pathway becomes clear without driver input.

The adaptive cruise control functionality depends on various modules on the vehicle to function and each module performs a function that is critical to the proper operation of the adaptive cruise control system. Adaptive cruise control will not operate if any components fail. Communication between modules is via serial data. The following is a functional description of the K124 Image Processing Module and the other associated components:

• K124 Image Processing Module
• B233B Forward Radar Sensor Module - Long Range
• K9 Body Control Module
• K20 Engine Control Module
• K160 Brake System Control Module
• K71 Transmission Control Module
• P16 Instrument Panel Cluster Control Module
• Cruise Control Switch
• Gap Switch

K124 Image Processing Module 

The K124 Image Processing Module analyzes data from various modules, sensors, and switches to provide enhanced safety features. In addition to enhanced safety features, the K124 Image Processing Module provides the adaptive cruise control system functionality. The K124 Image Processing Module analyzes data from the B233B Forward Radar Sensor Module - Long Range to identify and classify objects in the road environment. The system scans the road environment to detect targets within its specified field of view. The K124 Image Processing Module then sends throttle and/or brake commands to the K20 Engine Control Module and K160 Brake System Control Module via serial data in order to control the vehicle acceleration/deceleration based on the data from the modules. The K20 Engine Control Module and K160 Brake System Control Module provide throttle control and automatic braking needed for proper cruise speed adjustment. The following is a list of the K124 Image Processing Module functions pertaining to the adaptive cruise control functionality:

• The K124 Image Processing Module processes the road environment to get data concerning any vehicle ahead of the adaptive cruise control vehicle. Detection, parameter estimation, tracking, object classification and diagnostics are the primary functions. When an object is detected, the controller calculates the object range, range rate, acceleration and azimuth angle parameters.
• The K124 Image Processing Module performs adaptive cruise control state processing automatically - distance control or speed control. The adaptive cruise control operates in two possible states - cruise or follow. The normal operating state is cruise, whereby the vehicle speed is controlled to match the driver selected set speed. When a preceding forward target is identified, the adaptive cruise control system will automatically transition into the follow speed state to provide proper lane spacing behind the target vehicle in front. The preceding vehicle's speed and acceleration, with the adaptive cruise control vehicle speed, acceleration and distance between the two vehicles will be used to determine the adaptive cruise control follow speed limit. The adaptive cruise control follow speed limit will ensure that an acceptable distance is maintained to the preceding vehicle.
• The K124 Image Processing Module determines the follow speed limit for throttle control by the K20 Engine Control Module.
• The K124 Image Processing Module arbitrates the adaptive cruise control system brake and throttle control between the K160 Brake System Control Module and the K20 Engine Control Module.
• The K124 Image Processing Module requests brake light activation during automatic braking.
• The K124 Image Processing Module provides operational feedback to the vehicle driver. The K124 Image Processing Module sends signals for telltales and messages to be displayed on the P16 Instrument Panel Cluster Control Module or driver information center.

B233B Forward Radar Sensor Module - Long Range 

The B233B Forward Radar Sensor Module - Long Range is located behind the front fascia and is used in the 30 - 200 m (98 - 656 ft) range. The B233B Forward Radar Sensor Module - Long Range communicates with the K124 Image Processing Module via serial data on CAN 8. In addition to the wiring harness ground, the module is grounded through the mounting bracket.

K9 Body Control Module 

The following are the adaptive cruise control system functions provided by the K9 Body Control Module:

• The K9 Body Control Module reads all cruise control switches and the gap switch. The K124 Image Processing Module monitors a variety of user operated switches from the K9 Body Control Module switch status information sent via CAN.
• The K9 Body Control Module illuminates the brake light based on a CAN message from the K124 Image Processing Module during automatic braking.
• The K9 Body Control Module measures the brake pedal position and sends brake pedal travel status via CAN to the K20 Engine Control Module. The K20 Engine Control Module disengages the adaptive cruise control system when the brake is applied by the driver pressing the brake pedal.

K20 Engine Control Module 

The following are the adaptive cruise control system functions performed by the K20 Engine Control Module:

• The K20 Engine Control Module provides the electronic throttle control to the adaptive cruise control System. The K20 Engine Control Module is also responsible for determining when a driver is overriding the adaptive cruise control throttle position by pressing the accelerator pedal.
• The K20 Engine Control Module processes the cruise control switch requests received via CAN from the K9 Body Control Module. Engaging and disengaging the adaptive cruise control system are functions performed by the K20 Engine Control Module.
• The K20 Engine Control Module determines the driver selected vehicle speed. Unless the adaptive cruise control module requests a lower vehicle speed, the K20 Engine Control Module will control the vehicle speed to the driver selected set speed.
• The K20 Engine Control Module allows automatic braking without disengaging the adaptive cruise control.

K160 Brake System Control Module 

The following are the adaptive cruise control System functions performed by the K160 Brake System Control Module:

• The K160 Brake System Control Module controls the operation of the Antilock Brake System.
• The K160 Brake System Control Module provides automatic braking for the adaptive cruise control system. The K124 Image Processing Module will request vehicle deceleration via high speed GMLAN serial data circuit.
• The K160 Brake System Control Module determines when the driver - applied brake pressure is active. The K160 Brake System Control Module will communicate this status via CAN to the K9 Body Control Module.
• The K160 Brake System Control Module releases vehicle automatic braking when there is a throttle override by the driver pressing the accelerator.
• The K160 Brake System Control Module predicts brake temperatures. Due to automatic braking, the brake system may overheat. When the brakes are overheated, the K160 Brake System Control Module requests the adaptive cruise control System to be temporarily shut down by the K20 Engine Control Module until the brakes cool to a normal operating temperature.

K71 Transmission Control Module 

The K71 Transmission Control Module provides a down shift to protect the brakes. When the K71 Transmission Control Module detects some driver braking activity or adaptive cruise control automatic braking activity, the K71 Transmission Control Module down shifts the vehicle transmission to increase engine braking. This helps reduce braking activity, extend brake pad life and reduce brake system overheating.

P16 Instrument Panel Cluster Control Module 

The driver information center is a part of the P16 Instrument Panel Cluster Control Module and displays the adaptive cruise control system warning messages. The K124 Image Processing Module requests messages to be displayed on the driver information center by sending a CAN request to the P16 Instrument Panel Cluster Control Module requesting the display of the warning message. When the message is acknowledged by the driver and the cause of the message resolved, the driver information center turns the message off. The adaptive cruise control system will not operate if the driver information center fails.

Cruise Control Switch 

The cruise control switch, functionally is a common feature that is shared between the adaptive cruise control system and the regular cruise control system. The adaptive cruise control system will not operate if any cruise switch fails. The cruise control switch comprises the following cruise control function switches:

• On/Off switch
• Set/decrease switch
• Resume/increase switch

The cruise control function switches are arranged in a resistive ladder design whereby each switch function is set up with different resistance values. The K9 Body Control Module through the cruise control switch signal circuit detects a predetermined voltage value when any cruise control switch function is activated. The associated cruise control function signal detected by the K9 Body Control Module is then sent to the K20 Engine Control Module as a CAN message. The K20 Engine Control Module on receiving the message provides the cruise control function requested by the K9 Body Control Module. The K20 Engine Control Module is responsible for recognizing and responding to cruise control switch requests sent by the K9 Body Control Module. The cruise control function switches are used by the K20 Engine Control Module to communicate to the K124 Image Processing Module the driver selected vehicle speed. The driver selected vehicle speed is communicated through GMLAN serial data circuit to the K124 Image Processing Module and the K9 Body Control Module. The adaptive cruise control system engages and adjusts vehicle speeds based on the activation of the following cruise control function switches:

Cruise Control On/Off Switch 

The K9 Body Control Module monitors the switch signal circuit in order to determine when the On/Off switch is disabled or activated. The K9 Body Control Module detects a predetermined voltage value on the switch signal circuit. The On/Off switch state is then relayed to the K20 Engine Control Module via CAN. The K20 Engine Control Module sends the On/Off switch input status to the K124 Image Processing Module. When the On/Off switch is turned ON, the adaptive cruise control system enters either a standby enabled or a standby disabled mode. The standby enabled mode indicates that every condition required for the adaptive cruise control system to function has been met, but the adaptive cruise control is not engaged. When the adaptive cruise control is in the standby disabled mode, the conditions necessary for the adaptive cruise control system to function has not been met. When the On/Off switch is turned OFF, the adaptive cruise control will enter the disabled mode. The adaptive cruise control will not activate in the disabled mode.

Cruise Control Set/Decrease Switch 

The adaptive cruise control system is engaged when the adaptive cruise control On/Off switch is turned ON and the set/decrease switch is momentarily pressed and released. To engage ACC the vehicle speed must be at or greater than 5km/h (3mph). When the set/decrease switch is pressed, the selected vehicle speed is set to the greater of the current vehicle speed and the minimum set speed of 25km/h (15mph). The selected vehicle speed is displayed by the driver information center. While in the engaged state, the selected vehicle speed and the following distance can be adjusted. Pressing and holding the set/decrease switch, when the adaptive cruise control system is engaged, will decrease the selected vehicle speed without deactivating the adaptive cruise control. Momentarily pressing and releasing the set/decrease switch, when the adaptive cruise control is engaged, decreased the selected vehicle speed by 1.6 km/h (1 MPH) for each time that the set/decrease switch is pressed.

Cruise Control Resume/Increase Switch 

The resume/increase switch is used in order to increase the selected vehicle speed when adaptive cruise control is active. The amount selected vehicle speed can be increased from the resume/increase switch depends on how long the switch is pressed. The presence of a slower moving vehicle in the path of the adaptive cruise control vehicle will limit the extent to which the selected vehicle speed can be achieved. If there is no preceding vehicle in front, limiting the adaptive cruise control vehicle acceleration, then the vehicle speed that is attained is the new selected vehicle speed. The current selected vehicle speed is displayed by the driver information center. Acceleration is terminated when the resume/increase switch is released. Momentarily pressing and releasing the resume/increase switch will allow the selected vehicle to accelerate in at 1.6 km/h (1 MPH) increments for each time that the resume/increase switch is momentarily pressed.

Gap Switch 

The gap switch allows the driver to determine how closely the adaptive cruise control vehicle follows a target vehicle while adaptive cruise control is engaged. When the adaptive cruise control vehicle speed is being limited due to a slower travelling vehicle, the adaptive cruise control vehicle speed is automatically controlled to the follow speed limit. The gap switch has 3 following distance selections that range from 1 - 2 s. The gap switch following distance between the adaptive cruise control vehicle and the target vehicle is expressed in time as opposed to actual distance. The distance maintained for a selected gap will vary based on vehicle speed. The faster the vehicle speed, the further back you will follow. The gap setting can only be adjusted when the adaptive cruise control system is engaged. The gap switch is hard-wired to the K9 Body Control Module. Based on voltage variations, the K9 Body Control Module is able to read the gap switch selection and communicates the switch status via CAN to the K124 Image Processing Module. The gap switch is a momentary switch.

The initial push of the gap switch recalls the current setting and activates the display. Subsequent pushes of the gap switch will change the gap setting.