Part 1

Cruise Control Description and Operation (Adaptive Cruise)

Adaptive Cruise Control (ACC)

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 ACC system is the ability to detect the presence of a vehicle in the path of the ACC vehicle. The ACC retains the existing cruise control feature that controls the vehicle speed to the driver selected speed. However, ACC allows a driver to set and maintain a following distance to the preceding nearest vehicle in the ACC vehicle path. The distance sensing cruise control module (DSCC) calculates a follow speed limit to ensure an acceptable distance is maintained to the preceding vehicle in front, should one be present. The ACC system automatically adjusts the speed of an ACC vehicle when the vehicle comes up behind a slower travelling vehicle in front. The ACC system applies limited automatic braking and throttle control without driver input when necessary to maintain the set following distance of the ACC vehicle. The preceding vehicles speed and acceleration along with the ACC vehicle speed and acceleration and the distance between the 2 vehicles are factors used by the DSCC to determine the ACC follow speed limit. The ACC vehicle speeds up to the original driver selected set speed when the pathway becomes clear without driver input.

Adaptive Cruise Control (ACC) System Description

The Adaptive Cruise Control (ACC) System depends on various modules on the vehicle to function and each module performs a function that is critical to the proper operation of the ACC System. ACC will not operate if any components fail. Communication between modules is via the high-speed General Motors local area network (GMLAN) and the class 2 serial data circuit. The body control module (BCM) provides a translating gateway function between the class 2 and the GMLAN data links. The GMLAN utilizes the controller area network (CAN) communications protocol. The following is a functional description of the distance sensing cruise control module (DSCC) and the other associated components:

Distance Sensing Cruise Control Module (DSCC)

The distance sensing cruise control module (DSCC) communicates with the forward looking sensor (FLS) via controller area network (CAN) serial data. The DSCC utilizes the FLS to identify and classify objects in the road environment. The FLS scans the road environment to detect targets within its specified field of view. The DSCC then makes throttle and/or brake commands to the engine control module (ECM) and electronic brake control module (EBCM) via GMLAN serial data circuit to control vehicle acceleration/deceleration based on data from the FLS radar. The ECM and EBCM provide throttle control and automatic braking needed for proper cruise speed adjustment. An internal yaw rate sensor is used by the DSCC to determine the predicted path of the adaptive cruise control (ACC) vehicle. The main power feed for the DSCC is the battery and this signal is always at battery potential. However, the ACC system only activates when the ignition 1 input is active and in the RUN position. The ignition 1 voltage signal to the DSCC has to be 9.2 volts or more to be considered active. When the ignition 1 signal is not active, all ACC functions are disabled. The following is a list of the DSCC functions:

* The FLS radar processes the road environment to get data concerning any vehicle ahead of the ACC vehicle. Detection, parameter estimation, tracking, object classification and diagnostics are the primary FLS functions. When an object is detected, the DSCC calculates the object range, range rate, acceleration and azimuth angle parameters.
* The DSCC performs ACC state processing automatically - distance control or speed control. The ACC system operates in 2 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 by the FLS, the ACC 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 ACC vehicle speed, acceleration and distance between the 2 vehicles will be used to determine the ACC follow speed limit. The ACC follow speed limit will ensure that an acceptable distance is maintained to the preceding vehicle.
* The DSCC determines the Follow Speed limit for throttle control by the ECM.
* The DSCC arbitrates the ACC system brake and throttle control between the EBCM and the ECM.
* The DSCC requests brake light activation during automatic braking.
* The DSCC provides operational feedback to the vehicle driver. The DSCC sends signals for telltales and messages to be displayed on the head-up display (HUD) or driver information center (DIC) via the body control module (BCM). The DSCC will provide audible feedback to the driver via the BCM and the radio amplifier as well.

Body Control Module (BCM)

The following are the ACC system functions provided by the BCM:

* The BCM provides a translating gateway between the class 2 serial data circuit and the high speed GMLAN serial data circuit.
* The BCM reads all cruise control switches and the gap switch. The DSCC monitors a variety of user operated switches from the BCM switch status information sent via the GMLAN serial data circuit.
* The BCM illuminates the brake light based on a GMLAN message from the DSCC during automatic braking.
* The BCM measures the brake pedal position and sends brake pedal travel status via GMLAN serial data circuit to the ECM. The ECM disengages the ACC system when the brake is applied by the driver pressing the brake pedal.
* The BCM serves as a gateway to the display system's (HUD, IPC, DIC and Amplifier) visual and audible warnings. The BCM will generate visual and audible warning class 2 messages based on high speed GMLAN signals from the DSCC.

Engine Control Module (ECM)

The following are the ACC system functions performed by the ECM:

* The ECM provides the electronic throttle control to the ACC system. The ECM is also responsible for determining when a driver is overriding the adaptive cruise control throttle position by pressing the accelerator pedal.
* The ECM processes the cruise control switch requests received via the GMLAN serial data circuit from the BCM. Engaging and disengaging the ACC system are functions performed by the ECM.
* The ECM determines the driver selected vehicle speed. Unless the ACC module requests a lower vehicle speed, the ECM will control the vehicle speed to the driver selected set speed.
* The ECM allows automatic braking without disengaging the ACC.

Electronic Brake Control Module (EBCM)

The following are the ACC system functions performed by the EBCM:

* The EBCM provides automatic braking for the ACC system. The DSCC will request vehicle deceleration via high speed GMLAN serial data circuit.
* The EBCM determines when the driver-applied brake pressure is active. The EBCM will communicate this status via the GMLAN serial data circuit to the BCM.
* The EBCM releases vehicle automatic braking when there is a throttle override by the driver pressing the accelerator.
* The EBCM predicts brake temperatures. Due to automatic braking, the brake system may overheat. When the brakes are overheated, the EBCM requests the ACC system to be temporarily shut down by the ECM until the brakes cool to a normal operating temperature.
* The EBCM calculates yaw rate and provides the yaw rate data to the DSCC for vehicle path predictions.

Refer to ABS Description and Operation.

Transmission Control Module (TCM)

The transmission control module (TCM) provides a down shift to protect the brakes. When the TCM detects some driver braking activity or ACC automatic braking activity, the TCM down shifts the vehicle transmission to increase engine braking. This helps reduce the ABS braking activity, extend brake pad life and reduce brake overheating.

Driver Information Center (DIC)

The DIC is a part of the instrument panel cluster (IPC) and displays the ACC system warning messages. The DSCC requests messages to be displayed on the DIC by sending a GMLAN request to the BCM. The BCM sends a class 2 serial data request to the DIC demanding the display of the warning message. When the message is acknowledged by the driver and the cause of the message resolved, the DIC turns the message off. These displays are accompanied by a chime warning internal to the DIC. The ACC system will not operate if the DIC fails. The following are the 3 ACC messages that can be displayed on the DIC:

* Service Radar Cruise
* Cruise Not Ready
* Clean Radar

Head-Up Display (HUD)

The head-up display (HUD) displays ACC system telltales and status information. The DSCC sends a message to the BCM via the GMLAN serial data circuit requesting the display of a HUD telltale. The HUD displays the telltale when it receives a class 2 message from the BCM demanding illumination of the telltale. Feedback to a driver action takes precedence over other status information sent to the HUD by the BCM. The HUD is enabled in power mode RUN. The driver may have to adjust the position of the HUD or the intensity of the display to see the information being displayed. The ACC system will not operate if the HUD fails. The HUD displays the following telltales and ACC status indicators:

* Cruise Speed Limited Message
* Cruise Engaged Telltale
* Vehicle Ahead Telltale
* Tight Curve Message
* Follow Distance Display
* Set Speed Display
* Driver Alert Telltale
* Vehicle Speed Display

Radio Amplifier

The amplifier receives audible warning commands via a class 2 message from the BCM. The chime alerts the vehicle driver to certain ACC vehicle conditions. The audible chime accompanies a visual indicator as a warning to the driver. The ACC system will not operate if the radio amplifier fails.

Brake Pedal Position (BPP) Sensor

The brake pedal position (BPP) sensor helps the BCM determine when pressure is being applied to the brake by the driver stepping on the brake pedal. The BPP sensor receives a low reference signal and a 5-volt reference from the BCM. When the brake is applied, a signal is applied from the BPP sensor through the BPP sensor signal circuit to the BCM. The BCM utilizes this signal in deciding when to command the activation of the stop lamps. The BCM continuously sends signals via the GMLAN serial data circuit to the EBCM and the ECM reflecting the brake pedal position status. This will include the initial brake travel signal required for the activation of the ACC system. The ACC system will not engage unless the initial brake pedal travel signal is valid and received by the BCM. When the BCM brake pedal position signal indicates that brake pedal pressure is being applied by the driver when the ACC system is engaged, the ECM immediately disengages the ACC system. Re-engaging the ACC system will require the driver pressing the set or resume switch. Refer to Brake Pedal Position Sensor Calibration and Exterior Lighting Systems Description and Operation for more information on the brake pedal pressure sensor.

Accelerator Pedal

Deceleration of the ACC vehicle to maintain a certain distance and speed while a slower moving vehicle is in its path is achieved through throttle control by the ECM and the application of light automatic braking by the EBCM. During automatic braking the ECM is commanded to release the throttle by the DSCC. The DSCC via the GMLAN serial data circuit requests the ECM to release the throttle from the currently controlled cruise position. At the end of automatic braking, the ECM will control the vehicle speed to the current set vehicle speed. Driver throttle override occurs when the driver of the ACC vehicle depresses the accelerator pedal with the intention of requesting greater speed than the current throttle position. An example is an ACC vehicle driver stepping on the accelerator for a passing maneuver. The ECM continuously monitors the throttle and reports a throttle override condition. When no throttle override is present, automatic braking is allowed. When throttle override is detected by the ECM, automatic braking in not allowed to affect the vehicle acceleration.

Cruise Control Switch

The cruise control switch, functionally is a common feature that is shared between the Adaptive Cruise Control (ACC) System and the regular cruise control system. The ACC 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 body control module (BCM) 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 BCM is then sent to the engine control module (ECM) as a General Motor local area network (GMLAN) serial data circuit message. The ECM on receiving the message provides the cruise control function requested by the BCM. The ECM is responsible for recognizing and responding to cruise control switch requests sent by the BCM. The cruise control function switches are used by the ECM to communicate to the distance sensing cruise control module (DSCC) the driver selected vehicle speed. The driver selected vehicle speed is communicated through GMLAN serial data circuit to the DSCC and the BCM. The ACC system engages and adjusts vehicle speeds based on the activation of the following cruise control function switches:

On/Off Switch

The BCM monitors the On/Off switch status and makes a determination that the On/Off switch is activated based on a predetermined voltage value at the cruise control switch signal circuit. The On/Off switch state is then relayed to the ECM via the GMLAN serial data circuit. The ECM will recognize and communicate the On/Off switch input to the DSCC. When the On/Off switch is turned ON, it will cause the ACC system to enter either STANDBY ENABLED or STANDBY DISABLED state. The STANDBY ENABLED state indicates that every condition required for the ACC system to function have been met but the ACC is not yet engaged. When in the STANDBY DISABLED state, all conditions necessary for the ACC to function has not been met. When the On/Off switch is turned OFF, ACC will enter the DISABLED state. ACC will not be active in the DISABLED state. When automatic braking is active and the ACC On/Off switch is turned OFF, ACC will delay entering the DISABLED state.

Set/Decrease Switch

The ACC system is engaged when the vehicle driver presses and releases the set/decrease switch. The engaged state of the ACC system can only be entered when the On/Off switch is turned ON. When the set/decrease switch is pressed, the driver selected speed is set to the current vehicle speed by the ECM. The vehicle speed must be above 40 km/h (25 mph). The current driver selected speed is displayed by the head-up display (HUD). While in the engaged state, the driver selected vehicle speed and following distance can be adjusted. Pressing the set/decrease switch when the ACC system is engaged allows the driver to decrease the driver selected vehicle speed. Pressing and holding the set/decrease switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating ACC. The Tap-Down function occurs by momentarily pressing and releasing the set/decrease switch when ACC is engaged. With the Tap-Down function, the driver selected speed is decreased by 1 km/h (1 mph) each time the set/decrease switch is pressed.

The Resume/Increase Switch

When in the resume/increase state, ACC is active and the previously set driver selected speed has not been cleared. The resume/increase switch is used to increase the driver selected speed when ACC is active. The extent to which the driver selected 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 ACC vehicle will limit the extent to which the driver selected speed can be achieved. If there is no preceding vehicle in front limiting the ACC vehicle acceleration, the current vehicle speed attained is the new driver selected speed. The current driver selected speed is displayed by the HUD. Acceleration is terminated when the resume/increase switch is released. Momentarily pressing and releasing the resume/increase switch will result in the Tap-Up function. With the Tap-Up function, the driver selected speed is increased in increments of 1 km/h (1 mph).

Gap Up/Down Switch

The gap up/down switch allows the driver to determine how closely the adaptive cruise control (ACC) vehicle follows a target vehicle while ACC is engaged. When the ACC vehicle speed is being limited due to a slower travelling vehicle, the ACC vehicle speed is automatically controlled to the follow speed limit. The gap switch has 6 following distance selections that range from 1-2 seconds. The gap switch following distance between the ACC 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 up/down switch is hard-wired to the body control module (BCM) and voltage is provided to the switch from the BCM via the gap up/down ignition 1 voltage circuit. Based on voltage variations, the BCM is able to read the selected gap up/down switch selection and communicates the switch status on the GMLAN serial data circuit to the distance sensing cruise control module (DSCC). The gap up/down switch is a 3-position momentary switch - Center, Gap Up and Gap Down - with the following valid signal values:

* No Activation
* Increase Gap
* Decrease Gap

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. Momentarily pressing the gap up/down switch will adjust the switch to the desired gap setting. When the voltage from the gap up/down switch circuit is in an invalid range, the BCM will default to increasing the gap value.