As the name implies, cruise control means that the car cruises at a certain speed and does not require the driver to operate (step on the accelerator). The cruise requires a certain speed to enter (this can be calibrated, for example, some cars can enter at a speed greater than 50). When entering cruise, there will be an initial speed (for example, 50kmh), and the speed can be adjusted by buttons (add, subtract, fast increase, fast decrease). The exit of cruise also has a series of conditions. For example, when the brake is applied, the car will exit the cruise. If the status is inappropriate (there is a problem with the component), it will exit the cruise.
Cruise control is relatively simple (in fact, the logic is quite complicated), but there are no complicated sensors, processors, etc.
Cruise control is only suitable for better road conditions, such as high-speed roads with few cars.
Adaptive cruise
Adaptive cruise (ACC) is more intelligent, and generally can enter the cruise at a lower speed, in addition to high-speed road conditions, it can also be applied to urban road conditions, stop-and-go roads can be used.
The car’s sensor (radar) will send commands to the actuators (throttle, brake, gear) based on the driving state (vehicle distance and speed) of the vehicle ahead and the vehicle (vehicle distance and speed), and then send commands to the actuators (throttle, brake, gear) to determine its own Driving state, whether it is accelerating or decelerating, or exiting cruise.
The most basic function of adaptive cruise is to keep the vehicle running in the longitudinal direction. When there is a danger of collision, the vehicle will prompt the driver and perform active braking intervention.
Speaking of advantages, it is obvious that ACC can reduce driver fatigue to a certain extent.
The composition of the ACC system
The first is the sensor, currently there are radar (long-range radar), ultrasonic ranging sensor, infrared ranging sensor and so on.
The sensor is equivalent to the "eye". For the eyes, the key is to identify the vehicle ahead in the lane and exclude the influence of vehicles in the next lane.
After the eyes receive the signal, it is passed to the ACC cruise control system in the car's brain. The system will query a series of rules and regulations to determine how the car should drive. These rules and regulations are the control strategies in ACC.
The safe distance model (meaning how much distance the car should keep with the car in front) is one of the main control strategies of the ACC system; it cannot be too large, otherwise it will cause protests from the vehicle behind you; it cannot be too small, otherwise there is a risk of rear-end collision; safety The distance between vehicles is a function of the minimum stopping distance and the current vehicle speed.
PS: The safety distance is actually not a fixed length unit, but the so-called TTC, time to collsion, which is the time required for two vehicles to collide with each other assuming the current relative speed is maintained.
After the brain tells the car what to do, the next step is the executive agency. The executive agency is equivalent to the "hands and feet" of the car.
The actuator includes throttle, brake and gear position. Through the actions of these mechanisms, the car is controlled.
It is better to talk about the development of ACC than to talk about the shortcomings.
The development of ACC
Compared with other automotive electronic control technologies, ACC is still slightly immature. The difficulty lies in adaptability to road conditions.
As a driving assistance, adaptive cruise cannot be as intelligent as a human being, able to distinguish all road conditions and respond accordingly. At present, ACC is also mainly used on roads with better road conditions (high-speed or elevated), and it is the judgment of target vehicles in the main lane.
As for the side lanes and the monitoring of multi-target vehicles, the pre-judgment of vehicles with the intention of merging is still insufficient. For example, when the vehicle in front suddenly enters a curve, the vehicle may think that the safety distance is too large, make a misjudgment, and suddenly accelerate into the curve.
The following is an analysis of some typical road conditions:
1. If there is no vehicle in front, ACC will cruise at a certain speed (the cruising speed is within the speed limit set by you);
2. When there is a vehicle within the radar monitoring range, if the speed is too high, the vehicle will slow down and follow the vehicle in front at a certain speed to maintain a safe distance; if the vehicle in front cuts out of the lane, the vehicle will automatically Accelerate to the set speed.
As shown in the picture below (video screenshot) there is no car in the lane ahead, and the speed is 80km/h at this time:
Figure 2 below, there is a vehicle in the front lane, and the vehicle speed drops:
3. When the current car changes direction, the car will change the following target;
4. The ACC stop-and-go function (if available) can be activated when the car is at low speed or even at a standstill. This is more useful in stop-and-go urban conditions;
The system can still maintain the distance to the vehicle in front at low speeds, and can brake the vehicle until it stops. After a few seconds, if the vehicle in front starts, ACC will automatically follow the start;
If the stay time is long, the driver only needs to step on the pedal lightly to enter the cruise mode again.
PS: To achieve ACC with stop-and-go function, the assistance of the camera is usually needed, because although the radar has a strong ability to recognize the target, it is very interfered by clutter, and the image recognition function of the camera is still needed to confirm the target. And Mobileye's products can even use the camera to achieve ACC, of course, it is probably useless if it rains or snows on a cloudy day.
At the same time, after following the car to stop, the strategy of most manufacturers is to start again after confirmation by the driver, which can be confirmed by pressing the button or by pressing the accelerator.
Example of texture map: The following picture shows the urban working condition, and the vehicle speed is 25km/h:
When the red light is waiting as shown in the figure below, the car can automatically brake and the speed drops to 0. After the vehicle in front starts, the car will start automatically:
5. When entering a curve, the car will adjust its speed according to the situation of the curve. The long-range radar has a small field of view, and the target may be lost if the curve radius is too large. Therefore, the current highest-level ACC only has performance requirements for curve radii above 150m.
Summary: As an intelligent driving technology, ACC will be the future direction of automobile development, just like unmanned driving. However, the machine is always a machine and cannot completely replace humans. Intelligent driving is only an assisted driving and cannot be completely relied on and trusted.
