Before autonomous driving reaches Level 5, advanced driver assistance systems (ADAS) have become the best solution for the transition phase. The core of ADAS is assistance; systems like blind spot monitoring and head-up displays primarily assist drivers, making driving easier and safer. However, one ADAS feature has given us a glimpse into the arrival of the autonomous driving era, and it's the technology that allows us to experience autonomous driving firsthand: adaptive cruise control.
cruise control
When discussing adaptive cruise control, we must first understand cruise control. Cruise control is a device installed in a car that allows the car to maintain a set speed. The predecessor of cruise control can be traced back to 1992 when Mitsubishi Motors provided a "distance warning" function in its cars. If the driver gets too close to the car in front, the system will alert the driver, prompting them to apply the brakes to reduce speed.
Cruise control is an improvement on this technology. Drivers can activate the cruise control system while driving, and the car will maintain a set speed without needing to press the accelerator. After activation, the driver can also make minor adjustments to the speed using the manual adjustment device without pressing the accelerator pedal. To overtake, the driver can press the accelerator pedal, and the car will automatically return to the previously set speed after the overtake is complete. To decelerate, pressing the button to cancel or pressing the brake pedal will automatically disengage cruise control. The driver can reset the cruise control by pressing the button again when needed.
Cruise control can only be used on flat, low-traffic roads, such as highways. Using cruise control to keep the car at a constant speed can reduce fuel consumption and free the driver's feet from the accelerator pedal, thus reducing driver fatigue to some extent. It also allows the driver to focus all their attention on the road. However, cruise control has an initial speed and can only be used when the car reaches a certain speed, so it cannot meet the requirements of flexible driving.
Adaptive cruise control
Adaptive cruise control, also known as active cruise control, is an upgraded version of cruise control. It's an intelligent advanced driver assistance system that, like cruise control, allows you to set a predetermined speed and adaptively navigate the road. However, it also upgrades the vehicle by using radar mounted at the front to continuously scan the road ahead and simultaneously collecting wheel speed data from wheel speed sensors to calculate the vehicle's speed. When the vehicle gets too close to the vehicle in front, the adaptive cruise control unit can also control the anti-lock braking system and engine control system to appropriately brake the wheels and reduce engine power, thus maintaining a safe distance from the vehicle ahead.
Adaptive cruise control primarily consists of radar sensors, ultrasonic ranging sensors, infrared ranging sensors, a digital signal processor, and a control module. When activated, it uses low-power radar or infrared beam sensors to fuse multiple sensor data to determine the exact position of the vehicle ahead. If the vehicle ahead slows down or a new target is detected, the adaptive cruise control system sends a signal to the engine or brakes to reduce speed, allowing the car to maintain a safe following distance. When there are no vehicles ahead or the vehicle ahead changes lanes, the adaptive cruise control system will maintain a safe speed according to the set parameters, and the radar will continuously monitor the target ahead and adjust the vehicle speed based on actual road conditions.
Compared to standard cruise control, adaptive cruise control reduces the need for drivers to constantly cancel and reset the function, making it suitable for a wider range of road conditions. In short, besides setting the speed according to the driver's request, adaptive cruise control can also automatically adjust the vehicle without driver intervention by appropriately controlling the engine and brakes. Adaptive cruise control is widely considered a key component of future autonomous vehicles, but its application is still somewhat immature, with the challenge lying in its adaptability. As an advanced driver assistance system, it can never be as intelligent as a human driver, and it may struggle to function effectively in extreme conditions such as congested traffic, rain, or heavy fog.
Currently, adaptive cruise control systems primarily rely on measuring the speed of vehicles ahead to adjust vehicle control. However, their monitoring of vehicles in the adjacent lanes is somewhat inadequate. When vehicles in the adjacent lanes need to change lanes, the adaptive cruise control system struggles to anticipate this. Adaptive cruise control also performs poorly when cornering. If a vehicle ahead suddenly enters a curve, due to inherent hardware limitations in the radar, the adaptive cruise control system may misjudge the distance to the vehicle ahead, leading to speed adjustments and potentially causing accidents.
Cooperative adaptive cruise
Adaptive cruise control has been implemented in many high-end vehicles, but due to its inherent limitations, it cannot fully meet the demands of autonomous driving. In varying road conditions, how to address the monitoring of adjacent lanes and curves by adaptive cruise control systems has become a problem that needs to be solved. With the emergence of intelligent connected vehicles, the concept of cooperative adaptive cruise control has been proposed. Cooperative adaptive cruise control builds upon adaptive cruise control by enabling information exchange between the vehicle and fixed road infrastructure or other vehicles, further achieving more effective driving control. Cooperative adaptive cruise control is a manifestation of intelligent connected vehicles. By integrating information from satellites, road signals, roadside infrastructure, roadside traffic signs, mobile infrastructure, or other vehicles, it can achieve adaptive cruise control in various road conditions and ensure safety during the adaptive cruise process. This will be a future development trend.
Adaptive cruise control has already been commercialized in some vehicles and is considered an essential feature in the development of autonomous driving. Compared to head-up displays, adaptive cruise control is more likely to be fully integrated into the final autonomous driving system. As automotive technology continues to advance, more advanced driver assistance features will gradually be commercialized and incorporated into mid-to-low-end vehicles; this is an indispensable process in the popularization of autonomous driving technology.
