ACC Definition

The full English name of ACC is "Adaptive Cruise Control." During vehicle driving, the distance sensor (radar) installed at the front of the vehicle continuously scans the road ahead, while wheel speed sensors collect speed signals. When the distance to the vehicle ahead is too small, the ACC control unit can coordinate with the anti-lock braking system and engine control system to apply appropriate braking and reduce engine output power, maintaining a safe distance from the vehicle ahead. When the distance to the vehicle ahead increases to a safe distance, the ACC control unit controls the vehicle to travel at the set speed.

ACC Working Principle

The radar sensor detects target vehicles ahead of the host vehicle and provides the electronic control unit with information such as relative speed, relative distance, and relative azimuth angle between the host vehicle and the target vehicle. The electronic control unit determines the driving state of the host vehicle based on the safe following distance and cruise speed set by the driver, combined with the information transmitted by the radar.

When there are no vehicles ahead, the vehicle will be in a normal cruise driving state. The electronic control unit, based on the set information, can control the electronic throttle (sending commands to the drive motor, which controls the throttle valve opening to adjust the combustible mixture flow) to achieve automatic control of the vehicle's power output.

When there is a target vehicle ahead and its driving speed is less than the set speed, the electronic control unit calculates the ratio of actual distance to safe distance and the relative speed, and selects a deceleration method; at the same time, it alerts the driver through an alarm, reminding the driver to take appropriate measures.

When the distance to the vehicle ahead is too small,ACC the control unit can coordinate with the anti-lock braking system and engine control system to apply appropriate braking and reduce engine output power, maintaining a safe distance from the vehicle ahead. The electronic control unit can also control the integrated electronic vacuum booster(EVB)  system. When the driver is not braking,EVB  starts working, , the electromagnet replaces the driver in operating the vacuum valve and atmospheric valve inside the vacuum booster, , thereby achieving the purpose of regulating braking pressure.

ACC History

The history of adaptive cruise control systems can be traced back to the 70s. 1971, American companyEATON (Eaton) had already been engaged in development in this area. Its prototype was thePDC (Preview Distance Control) system, which combined radar with other processors to detect distance changes and warn the driver. The system could also control the throttle opening to regulate engine power. Subsequently, Toyota, Honda, General Motors, Ford, Daimler, Bosch and other companies also joined the research and development.

1995, Mitsubishi Motors first offered a system called “Preview Distance Control” system. It was a laser-based ACC system, but the entire system only controlled through the throttle and gears, without braking. Laser-based systems are significantly cheaper than radar-based systems, but laser-based systems are greatly affected in adverse weather conditions. Therefore, radar-based ACC systems are currently widely used.

August 1997, Toyota began using “radar cruise control system”, and in 2000 braking function was added, and in 2004 was added in “low-speed tracking mode”. The low-speed tracking mode is an additional mode that requires driver activation. If the vehicle ahead brakes or stops, this mode can also decelerate or stop the vehicle. However, this system was quickly discontinued, likely due to certain design flaws and imperfections.

1998, Mercedes introduced the S class modelsDistronic distance control system, which is not much different from what we now understand as adaptive cruise control. 2006, Mercedes further improved the system, capable of bringing the vehicle to a complete stop when necessary, hence called Enhanced Distance Control System (DISTRONIC PLUS). This function is similar to the full braking system advocated by Volvo: braking fully when necessary until the vehicle stops. Audi generally uses adaptive systems provided by Bosch abroad, including A4, A6, A8 and Q7 are all equipped with it.

In 2006, Lexus equipped the new generation ACC system on its flagship model LS460. This system can operate within the 0-100 km/h speed range and can repeatedly start and stop, even handling highway traffic congestion.

2010, Audi equipped the A8 with the world's first GPSfunction ACC system.

2015, with the launch of Tesla ModelS, the ACC system began to enter the public eye as a semi-autonomous driving feature.

ACC Functions

1. Through the feedback signals from the distance sensors, the ACC control unit can assess road conditions based on the movement speed of approaching objects and control the vehicle's driving state. Through the feedback-type accelerator pedal, the ACC control unit can determine whether to execute cruise control to reduce driver fatigue.

2. Adaptive cruise control systems generally only function when the vehicle speed exceeds 25km/h, and when the speed drops below 25 km/h, manual control by the driver is required. Through system software upgrades, the adaptive cruise control system can achieve a “stop/start” function to handle frequent stops and starts during city driving. This extended function of the adaptive cruise control system allows the vehicle to maintain the set distance from the vehicle ahead even at very low speeds. When the vehicle ahead starts moving, the adaptive cruise control system alerts the driver, who can then start the vehicle by pressing the accelerator pedal or a button.

3. Adaptive cruise control systems make platoon driving easier. The ACC control unit can set the vehicle to automatically follow. When the host vehicle follows the vehicle ahead, the ACC control unit can adjust the speed to match the vehicle ahead while maintaining a stable distance, and this distance can be selected via the setting button on the control lever near the steering wheel.

ACC as a type of driver assistance system (ADAS), is one of the transitional configurations for future autonomous driving. Many people have a general understanding of ACC: ACC is simply automatic cruise control that can automatically accelerate and decelerate. From various official promotions, we only see ACC bringing convenience to driving, but ACC cannot guarantee effectiveness in all road conditions. You are still responsible for maintaining appropriate distance and speed, and for intervening when potential danger arises. As the end user, it is important to first understand ACC in which situations it may fail or degrade in performance, so as to safely enjoy the convenience brought by the ACC function.