Adaptive Cruise Control

Cruise control has been an option on Chrysler Group LLC vehicles for many years to the point where it is a standard feature on many models. It permits the driver to remove the right foot from the accelerator pedal, relaxing the right leg, while driving under steady speed conditions. This is an option that was clearly designed for freeway driving. Slower traffic ahead, however, forces the driver to disable cruise control operation until this traffic moves or is passed. After this happens, the cruise control has to be enabled again by the driver.

Adaptive Cruise Control (ACC) performs the same task as standard cruise control, but with one major added feature. This is the ability to change the set speed and maintain a safe distance from the vehicle ahead without input from the driver. In other words, when the traffic ahead slows down, or a vehicle moves in front of the vehicle from another lane, the driver doesn’t have to do anything (in most cases). Remember that ACC is a convenience feature and not a safety feature. Let’s see how it works.

ACC COMPONENTS

Many of the existing vehicle systems are used with the ACC. These include the Powertrain Control Module (PCM) and the electronic brake control provided by the Electronic Stability Program (ESP) control module.

In addition, there is an infrared unit, which is mounted at the front of the vehicle and inside the grille. It provides the ACC system with information about the lane conditions ahead of the vehicle (Figure 1). This infrared transceiver is combined with an electronic ACC module.

The infrared unit sends out 12 beams which extend across the lane in front of the vehicle. The infrared beams reflect off the vehicle ahead and are received by the receiver in the unit. The ACC module then sends this information over the Controller-Area Network Controller (CAN C) bus. The unit detects objects within a 12-degree angle in front of the vehicle.

In addition to the infrared unit, the system also uses the speed control stalk for driver input and the cluster Electronic Vehicle Information Center (EVIC). The EVIC (the instrument panel display) displays the system settings and lane information. Now let’s see how it works.

ACC OPERATION

The following conditions must be met to activate the ACC system: (1) the vehicle must be traveling at least 25 mph, (2) the ESP must be on, (3) the parking brake is not applied and (4) the transmission must be in Drive.

In order to turn the ACC system on, the driver pushes the cruise control stalk in. The EVIC display will indicate that the system is in Standby mode by displaying ACC Ready (Figure 2). The driver then sets the speed by pulling the stalk down.

The default following distance is based on the distance the vehicle covers in two seconds. It is displayed as three dashes, or bars, in the EVIC. The set vehicle speed, let’s say 43 mph, is displayed as ACC Set: 43 mph, as shown in Figure 3. In addition to the set speed and following distance dashes, the EVIC will display the icon of a full-size car to the left of the dashes if the ACC detects a vehicle in the lane ahead.

The driver can manually set the following distance, corresponding to 1, 1 ½, and 2 seconds, by pulling the stalk rearward either before or after setting the speed. These distances are displayed as 1, 2 or 3 dashes.

Ok, the driver is now cruising along at the desired, set speed at a specific distance from the traffic ahead. What happens if the traffic conditions change? For instance, the traffic ahead slows down or a slower vehicle moves into the lane. With a standard cruise system, the driver must tap the brake to deactivate the system and slow down the vehicle and, possibly, apply the brakes.

Well, with the ACC, the first thing that occurs is the detection of the change in lane conditions by the infrared unit. Next, it sends this information to the PCM and ESP module. Finally, this action initiates a speed reduction by means of the throttle control, then braking, if necessary, to establish the proper following distance. When braking is done, the ESP module will activate the brake lamps.

After the following distance has been re-established, ACC will use throttle control to maintain it. The EVIC will continue to display the original set speed as well as an icon of a car indicating that the system sees a vehicle in the lane ahead.

If the lane conditions change again allowing faster travel, such as the driver moving into a faster lane, traffic accelerates or the slower vehicle moves out of the lane, the system adapts to it. ACC will use throttle control to accelerate the vehicle and resume the set speed, if possible. Also, the car icon, which indicates that a vehicle is ahead, will disappear.

Up to this point, we have discussed automatic changes to the set speed that require no driver input. What if the driver wants to increase the set speed. How is that done? Relatively easily. In fact, it is done in the same manner as on a standard speed control system. Raise the stalk to increase the speed and lower the stalk to lower the speed (this is done in 1-mph increments). If the stalk is held in either position, the change increments are 5-mph.

If the driver uses the accelerator pedal during ACC operation, the system will be overridden and the EVIC will display Driver Override. Pulling the stalk down at this time will establish a new set speed.

To cancel ACC the driver pushes the stalk forward or touches the brakes. This initiates the Cancel function and puts ACC in the Standby mode. Either action also retains the set speed in memory. As a result, if the driver pushes the stalk up, the resume function is initiated, the EVIC display changes to ACC Set plus the speed and ACC accelerates the vehicle to desired speed if lane conditions permit.

Conversely, if the driver pushes the stalk in, this turns ACC off and the system does not retain the set speed in memory.

SPECIAL NOTES ABOUT ACC

Now that we have detailed the operation of ACC, a few special comments are in order. Although the vehicle must be traveling 25 mph to turn ACC on, the vehicle speed can drop to 18 mph before the system transitions to Standby mode.

ACC is not designed to compensate for large differences in speed. If the system does detect such a difference, it will warn the driver by flashing Attention in the EVIC display (Figure 4). An alarm will also sound. Maximum ACC braking will continue, but the driver must intervene.

Weather and driving conditions can affect ACC operation. Mud or dirt on the infrared unit can interfere with the broadcast or reception of the beams. Fog and snow can limit the range. When the system can no longer effectively measure distances due to any of the aforementioned conditions, ACC will automatically shut down. ACC Unavailable will appear in the EVIC display.