Autonomous Driving Systems 101: Adaptive Cruise Control (ACC) Explained

  • Author: OPONEO.CO.UK

Since the creation of automobiles, the pursuit for the autonomous car has always captivated the minds of engineers around the world. Indeed, in recent years, cruise control and adaptive cruise control have laid the foundations of future autonomous driving. Back in the 20th century, automakers took inspiration from 17th century engineers, and created the first auto pilot system ever seen in a car: the 1958 Chrysler Imperial.

The 1958 Imperial had an autopilot system connected to the engine pop shaft with a dial on the dashboard to pre-select a speed and an electric motor that adjusted the throttle position to maintain it. Cruise control systems have come a long way since the original imperial design, but their aim has remained the same: to make driving as autonomous as possible.

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Today, adaptive cruise control is the closest system to vehicular autonomy on the market today. The ACC will maintain a preset distance from the vehicle in front, regulating the speed to keep the gap in-between. The driver needs to steer the vehicle but with regards to controlling the speed, the driver doesn’t need to intervene unless there is an emergency.

A Brief Look at Adaptive Cruise Control

Radar and laser sensors, located under the bumper or in the grille enable the car to calculate the distance from the car in front, and to maintain a distance set by the driver. Depending on the speed of the vehicle in front, the ACC will increase or decrease the distance as needed, using the radar or laser sensors to ensure the car doesn’t crash into the back of the car in front. In essence the system regulates the speed on behalf of the driver.

For example, if the distance from the car in front falls below a preset distance, the system will slow the car down to increase the gap between the two vehicles. When there are no vehicles in front of the car, the ACC will accelerate to a speed preselected by the driver, which can be changed at any time. The system makes it easier for drivers to travel without having to constantly alter their speed manually.

How Adaptive Cruise Control Works In Practice

As mentioned above, the key component of ACC is the radar sensor. Most cars on the market make use of radar sensors (although laser sensors are still in use), due to their resistance to poor weather conditions. Whilst driving the radar sensor tacks the distance in front of the car up to 200 meters. If the radar registers a vehicle in front of you within that range, the sensor will slow the speed to maintain the gap between the two vehicles.

To maintain the distance, the radar sensors send a signal to the central control unit which tracks the distance between your vehicle and the car ahead. Once the road is clear of traffic the system will accelerate to a value of your choosing. To set the speed you need to accelerate to your desired speed and press a “Set” button on the dashboard to determine a default speed for the CC to travel at. This means you won’t have to constantly regulate your speed.

On multi-lane roads where several vehicles are registered by the sensor, the ACC will differentiate between the vehicles and prioritize one to track. When a vehicle overtakes a car, the ACC slows down the car utilizing engine management and starting the brakes. If the car needs to slow down rapidly, and the deceleration needed is more than 30% of the car’s maximum stopping power, visual warning signals and a beep will tell the driver to break manually.

Manufacturers That Use ACC

Given the demand for autonomous technology, there are a wealth of ACC packages in cars of all shapes and sizes. These ACC units all vary in their quality and style, with manufacturers like Mercedes, Ford, BMW and Volkswagen all making use of Adaptive Cruise Control, with their own specifications. For example, Ford's ACC technology doesn’t work under 20 mph and can struggle with higher speeds. On the other hand, BMW’s active cruise control ranges from 30 km/h all the way to 180 km/h, either controlled by a paddle or a button on the steering wheel for ease of use.

ACC in Bad Weather

One of the major challenges facing ACC is that its sensors can be sensitive to bad weather. Harsh weather conditions, like heavy rain or snow will shut down the sensor located in the grille or under the bumper. Essentially, the sensors can become blinded by bad weather, and therefore unable to distinguish the distance between you and the vehicle in front (though this is more common with laser sensors than radar sensors).

Limitations of the Cruise Control System

With regards to the cruise control system itself, adaptive cruise control is unable to adjust to changing speed limits. This means that sensors can tell the speed of cars in front of you, but they are unable to adjust to changing speed limits. So whilst ACC is convenient, don’t get too comfortable! At a moments notice you may be required to intervene and press on the brakes to avoid random hazards on the road. The 30% deceleration feature may be useful, but the driver still needs to intervene to brake quickly.

Similarly, the ACC is prone to react to phantom objects or vehicles in other lanes. As technology develops this will be less common, but on winding roads the system can struggle to tell separate lanes apart. On winding lanes the system may register that a vehicle is in front of you when it is actually in another lane. Thankfully, most of these issues can be solved via the use of a preselected speed, but it can take away from the overall autonomy of the system.

Adaptive Cruise Control: A Step Towards Autonomous Driving

At this stage, Adaptive Cruise Control is far from a complete autonomous driving experience, yet it remains an invaluable tool for thousands of drivers around the world. In its current form, the system is good at moderating the distance from vehicles in front, meaning that you don’t have to alternate between the gas and the brakes constantly.

With ACC you can simply pre-select the speed you want and start driving before handing 50% control to the ACC. In future, as these ACC systems become more complex, we can expect to pass over more control to the central control unit. In the meantime, the partial autonomy of ACC will make driving much more comfortable. As autonomous systems become more advance, we can expect that less and less driver oversight will be needed in order to travel safely.

 

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