WHAT YOU SHOULD KNOW ABOUT ADVANCED DRIVER ASSISTANCE SYSTEMS BY BOB PATTENGALE The driving public may not be quite ready for Google s autonomous vehicle, but other advanced driver assistance systems, designed to improve safety and convenience, are already here. Acustomer calls and says that an image of a coffee cup periodically appears on the dash panel; he wants to know what it means. Another customer claims that the steering wheel shakes occasionally for no apparent reason; it startles him when it occurs. Would you be able to explain what these occurrences mean? The image of the coffee cup? An in-vehicle sys- 34 December 2010
Photoillustration: Harold A. Perry; images: Robert Bosch LLC & Thinkstock December 2010 35
Surround Sensors (radar, video) Brake Control System Occupant Safety Electric Power Steering CAN Bus This ghosted image of a vehicle shows the technologies used in advanced driver assistance systems. Some key components associated with these systems are radar sensors, cameras and various control modules. Images courtesy Robert Bosch LLC; backgrounds: Thinkstock tem sensed that the driver was tired, and flashed that dashboard warning. The shaking steering wheel? Same principle, except more immediate and extreme: Wake up, Buddy! You re drifting out of your lane! These are two examples of advanced driver assistance systems that manufacturers have been rapidly introducing into their vehicles in various combinations to help drivers stay alert and safe behind the wheel. It s a trend that will continue to grow. Advanced driver assistance systems go way beyond enhanced antilock braking or electronic stability control systems. These newest advanced systems are designed to help the driver stay focused on the road and avoid getting into an accident. Some examples of advanced driver assistance systems currently available on today s newer vehicles are: lane departure warning system; adaptive cruise control; adaptive light control; blind spot detection; driver drowsiness detection; traffic sign recognition; predictive emergency braking system; night vision; collision avoidance system; parking aid system; rear-view back-up camera system. Some systems, such as adaptive cruise control, have been around for several years, while others are just being implemented. The key question is: Do you have a plan to deal with these systems when they fail, or will you send your customers back to the dealership to get them repaired? The illustration above shows how these systems are integrated into a vehicle. Advanced driver assistance systems utilize existing components like engine and transmission control modules, antilock brake and/or electronic stability control modules and a variety of shared sensors to monitor and modify vehicle behavior. Depending on the systems built in, the vehicle is surrounded by a combination of simple to advanced distance-measuring sensors, forward- and rearward-looking cameras and miscellaneous driver inputs and displays to keep the driver safe and informed of his surroundings. This article will concentrate on adaptive cruise control and parking assistance systems. 36 December 2010
Fig 1: This flowchart shows that adaptive cruise control (ACC) utilizes a combination of engine, transmission and braking modules to maintain a proper vehicle speed and distance for any given situation. Adaptive cruise control (ACC) can lessen the demands placed on the driver by helping to maintain a predefined minimum distance to the vehicle in front of it. ACC maintains the desired speed set by the driver and can adapt it to the current traffic situation by accelerating or decelerating automatically. The ACC module relies on the distance control radar sensor to monitor the situation ahead of the vehicle. If the vehicle approaches another vehicle, the ACC decelerates slightly to ensure that the defined minimum distance to the vehicle ahead is maintained. This distance can be adapted to individual driving behavior. Once the lane is clear again or the distance between the two vehicles is reestablished, the ACC accelerates to the speed preselected by the driver. Standard ACC is active at speeds between approximately 20 and 125 mph. Some advanced versions incorporate stop & go controls at speeds below 20 mph and can decelerate the vehicle to a standstill. Volvo, for example, refers to this as City Safety Driving Technology. The ACC system needs help from additional components to control the speed of the vehicle being driven and distance to the vehicle ahead (see Fig. 1 above). The ACC sensor and control unit determine the distance to the vehicle ahead (referred to as the time gap) and respond to the driver s desired speed and the time gap from the displays and controls switch. Vehicle distance is maintained using a combination of the drivetrain control, electronic stability program (ESP) and transmission control. For example, if the vehicle ahead slows gradually, the trailing vehicle s speed can be reduced with simple engine speed reduction. But if the vehicle ahead slows more abruptly, the ESP system may need to apply the brakes. The vehicle s controller area network (CAN) connects all these modules together and provides the quick communication needed for proper operation. The flowchart in Fig. 2 on page 40 shows the closed-loop operation of the ACC system. Here s a basic description of operation: The driver inputs the desired vehicle speed and time gap. The ACC system communicates with the engine control module to verify that the minimum vehicle speed has been reached for operation. The radar system at the front of the vehicle provides real-time speed and distance calculations to the ACC controller. If the speed and distance are maintained, the ACC system does not influence vehicle operation. If the vehicle ahead slows down, the ACC controller takes appropriate action to slow the vehicle being driven. At the center of the flowchart is a box labeled Bend detection. ACC works 38 December 2010
Fig 2: This flowchart shows the closed-loop operation of the ACC system. The ACC controller is tasked with maintaining the correct vehicle speed and distance to the vehicle ahead, utilizing a variety of strategies. best on fairly straight stretches of road, but must be able to accommodate slight bends in the road as well. Bend detection utilizes information from the wheel speed, yaw rate and steering-wheel angle sensors to help maintain a proper speed and distance to the vehicle ahead. If the forward-looking radar loses sight of the vehicle ahead due to a curve in the road, ACC will temporarily default to a set speed strategy, similar to standard cruise control without ACC. Once the radar regains sight of the vehicle ahead, the speed and distance will be monitored and modified as necessary. All the ACC system components must work together for proper operation, but one component carries a higher priority: the combined ACC sensor and control unit. It must be calibrated to the vehicle. In the event of a collision, front fascia repair or anything that requires the sensor to be moved, that sensor must be recalibrated. The photo on page 42 shows the calibration fixture and target board for an Audi A7. The ACC sensor has screws for vertical and horizontal adjustment accuracy (see the diagram to the right of the photo). The vehicle must be placed on a level surface with sufficient room in front for the target board. Vehicle tire pressure and height also must be checked prior to adjustment. Next, the target board is adjusted for proper distance and squared with the vehicle. Once everything is in place a scan tool is used to make the final adjustments. The scan tool walks you through the steps. Fig. 3 on page 42 shows the ACC sensor adjustment for a 2008 Audi Q7. Clicking on the ACC sensor adjustment tab begins the process. The ACC control unit will not permit calibration if there are any fault codes present. Correct any fault code issue that arises, then attempt recalibration. The first step is the vertical adjustment, followed by the horizontal adjustment. The readings should be rechecked to make sure the vertical and horizontal are correct. It might take a few attempts to get the readings within tolerance. Patience is the key to success. The scan tool also can be used to perform an ACC system test. Fig. 3 shows the option for performing this test. Here are a few notes from the test. You ll need a second person for the second part of the test, which requires a road test. The first step involves placing two objects at different measured distances in front of the ve- 40 December 2010
1 3 4 The ACC sensor and control unit are critical to the proper operation of the ACC system. The sensor requires recalibration with a special fixture if its position is disturbed. The elements for recalibration are: 1. adjusting screw for vertical alignment; 2. fixed anchor point screw; 3. lens; 4. adjusting screw for horizontal alignment. 2 hicle to determine accuracy. The scan tool will show if the sensor correctly identified the object distances. The second part of the test must be performed at a minimum of 31 mph. The goal is simple: Use the data on the scan tool to determine if the sensor correctly indicates the distance change as you get closer and farther away from the vehicle in front. The other system we ll discuss here goes by many different names and possible configurations, depending on the manufacturer. The system might be referred to as an optical parking system, a parking aid system or a proximity sensor system. The goal is simple: Help the driver determine where the edges of the vehicle are located and avoid running into something. Parking aid systems can be very simple or very advanced. The simple systems might cover only the rear of the vehicle and generally have four radar sensors and a simple parking aid control module. More advanced systems add sensors to the front and cameras to the rear of the vehicle for live video image support. The photo on page 44 shows the locations of the optical sensors in the rear bumper of a 2008 Audi Q7. The control module is normally located near the rear of the vehicle. The vehicle can be equipped with front and rear optical sensors, and the driver has the option of turning the feature on or off. System operation is really very simple. If an obsta- Fig 3: Calibrating the ACC sensor and control unit requires a scan tool. The scan tool will prompt you through the steps, as shown in this screen capture. 42 December 2010
cle is detected within the warning zone, the distance warning begins with a beep. As the vehicle gets closer to the object, the beeping gets faster, until it s almost a solid tone after the critical distance has passed. Audi offers an additional feature called the optical parking system. With this system, a multimedia interface (MMI) display also shows the actual distance from each sensor to the obstacle in question. This provides the driver with a very accurate distance measurement in tight parking areas. Diagnosing any advanced driver assistance system requires a scan tool with enhanced data. The parking aid system also requires a recalibration if any of the sensors are disturbed. The scan tool can be used to perform a quick operational check of the sensors. Fig. 4 on page 45 shows all eight distance sensors (front and rear) on a 2008 Audi Q7. The blue line is the rear left outer sensor, the red line is the rear left inner sensor, the green is the rear right inner sensor and the The arrows indicate the location of the rear parking aid radar sensors on a 2008 Audi Q7. In most cases, they re easy to pick out; just look for the dots on the bumper. purple is the rear right outer sensor. If you don t have a helper, use the recording feature of your scan tool to catch the movement, then come back to the scan tool and replay it. Just make sure you set the scan tool for enough time to allow you to do that. In this example, you can see where the technician passes from the left rear corner of the vehicle to the right rear Circle #21 44 December 2010
Fig 4: This scan tool screen shot shows a quick rear radar sensor operational test. The sensors should respond to a person walking around the back of the vehicle. In this case, all the sensors responded to a person moving past them. corner and back again. All of the rear sensors responded to object movement. It would be very easy to use this method to detect one sensor that s not responding. You ll notice the other graph lines (for the front sensors) remained flat during this test; the front sensors were shown later in the recording. You can also perform a manual distance check by placing an object behind the vehicle and comparing the scan tool data to the actual distance between the sensors and the object. If the readings don t match, you ll need to perform a recalibration procedure. Deployment of advanced driver assistance systems will continue to expand at a rapid pace, capitalizing on advancements in networking technology and the speed of electronic components. Speed limitations of early networking systems placed the focus on protecting vehicle occupants during a crash. The goal now is to avoid the collision entirely, and most of the technology required to accomplish that already exists. Volvo, for one, plans to use this technology to reach an ambitious safety goal: No motorist will die in a Volvo crash after 2020. They ll need your help to keep these systems performing to their full safety potential. This article can be found online at www.motormagazine.com. December 2010 45