Fully-automated driving cars will surely come to us in the next few years. Google has already planned to have 10 million self-driving cars on the road in the world by 2020. In fact, some basic technology configurations of self-driving cars are already equipped on many of our current models. Such as adaptive cruise system, almost become the standard luxury car. But what is adaptive? What is the use of radar? Cruise control control?
In fact, cruise control was very early, and the earliest version of cruise control was born in the 18th century. Its role was to prevent the steam engine from operating too quickly. Later, the cruise control system was connected to the speedometer and the drive shaft to calculate the speed of the vehicle, and then used the computer to control the throttle to maintain the driver's preset speed. Today, all these actions are integrated into a small black box - ECU. While reducing the driver’s physical exertion, cruise control can also slightly improve fuel economy.
The initial popularity of cruise control was in the United States. Because of the long and wide intercontinental highways, many drivers needed long-distance driving. In order to reduce driving fatigue, cruise control became so popular. In Europe, because of the many trails and more turns, the cruise control configuration was only seen as a symbol of high-end luxury cars. However, nowadays, cruise control is still popular, the cost of modern electronic technology is reduced, so that this year's luxury car configuration is also equipped with ordinary family cars.
Friends who have used cruise control know that they can only use it when they are not congested at high speeds, or in the open streets at 3am. In real life, we often encounter traffic jams. Sometimes it accelerates and sometimes brakes. Cruise control seems to be a device, and adaptive cruise control (ACC) emerges.
ACC adaptive cruise control system
ACC (Adaptive Cruise Control) adaptive cruise control system (hereinafter abbreviated as ACC) is a smart cruise control based on sensor identification technology, compared to a conventional cruise control system that can only perform constant-speed cruise at a speed set by the driver. The ACC can identify the vehicle in front of it, thus achieving the effect of “slowly driving the car ahead and fast as the car is aheadâ€. Currently, the ACC can be divided into the basic ACC (30-150km) according to the use speed section. /h) and full-speed ACC (0-150km/h). Among them, the basic version of the ACC sensor is a radar, while the full-speed ACC is under the premise of the radar as the main sensor, adding the front-view camera and other sensors to assist identification, in order to meet the higher requirements for low-speed identification accuracy and angle.
The composition and principle of adaptive cruise system
1, radar sensor
In the ACC system, ranging radar is used to measure the headway, relative speed, and relative acceleration of the vehicle and the vehicle in front. It is one of the key equipments in the adaptive cruise control system and is the main component that determines the cost of the system. Its main components include transmitting antenna, receiving antenna, DPS (digital signal processing) processing unit, data line and so on.
Millimeter wave radar
Principle: Use the target to reflect the electromagnetic wave to find the target and determine its position. The frequency of the millimeter wave is high and the wavelength segment.
Performance: The detection performance is stable, not affected by the color and shape of the surface of the object, and also not affected by the large airflow; the environment adaptability is good, and the interference of rain, snow, and fog is small.
Monopulse radar
Principle: Each time a radar transmits a pulse, the antenna can form several beams at the same time. From the sum of the signals received by each beam, the distance of the target can be measured, thereby achieving the measurement and tracking of the target. (Pulse: A process in which a physical quantity rapidly returns to its initial state after a sudden change in duration)
Performance: All-weather radar can be applied to a variety of weather conditions, with the advantages of long detection range, large range of detection angles, and multiple targets, but the price is high.
Microwave radar
Principle: The precise speed detection of moving objects by microwave radars is based on the Doppler effect.
The distance is measured by measuring the time delay of the echo signal relative to the transmitted signal.
Performance: easy installation and maintenance, long service life, almost no light, dust and wind, rain, fog, snow and other weather.
Lidar
Principle: The laser generates and emits a pulse of light that hits an object and reflects it back. It is finally received by the receiver. The receiver accurately measures the time of flight of the light pulse from emission to being reflected back. Because the light pulse travels at the speed of light, the receiver always receives the previous reflected pulse before the next pulse. Given that the speed of light is known, the travel time can be converted to a measure of distance.
Performance: high requirements on the work environment, sensitive to weather changes, rain and snow days, wind and sand days and other bad weather detection effect detection range is limited, there are few tracking targets, but its biggest advantage is that the detection accuracy is relatively high, the price Low, easy to control and secondary development.
Infrared detection radar
Principle: The infrared band emitted by different types of objects has its specific band. People can use this specific band of infrared light to realize the detection and tracking of object targets.
Performance: Unstable performance in severe weather conditions, short detection distances, and cheapest prices.
2. Electronic Control Unit (ECU)
The core part of the ACC system
Composition: Like a general-purpose single-chip microcomputer, microprocessor (CPU), memory (ROM, RAM), input/output interface (I/O), analog-to-digital converter (A/D), shaping, driving, etc. Integrated circuit composition.
Function: According to its memory program and data, the air flow meter and various sensors input information to calculate, process, determine, and then output instructions.
3. The rest of the components:
Cruise Control Switch, Speed ​​Setter, Distance Setter, Status Indicator, Alarm...
4. Interconnected
The radar sensor detects the target vehicle in front 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 safety distance and cruising speed set by the driver and the information transmitted by the radar.
1). When there is no moving vehicle in front of the vehicle, the vehicle will be in normal cruise driving state. The electronic control unit can control the electronic throttle by issuing the command to the drive motor according to the setting information. The throttle valve is controlled by the drive motor. The degree of opening to adjust the flow rate of the combustible mixture enables automatic control of the power output of the entire vehicle.
2). When there is a target vehicle in front of the host vehicle, and the target vehicle's travel speed is less than the set speed, the electronic control unit calculates the ratio of the actual vehicle distance and the safe vehicle distance and relative speed, and selects the deceleration mode; meanwhile, it passes the alarm device. Alert the driver to remind the driver to take appropriate measures.
When the distance from the preceding vehicle is too small, the ACC control unit can coordinate the brake anti-lock braking system and the engine control system to properly brake the wheel and reduce the output power of the engine to make the vehicle and the vehicle ahead. Always maintain a safe distance. The electronic control unit can also control the integrated electronic vacuum booster (EVB) system. When the driver does not brake, when the EVB starts to work, the electromagnet will replace the vacuum valve and atmosphere inside the vacuum booster of the driver. The valve operates to achieve the purpose of adjusting the brake pressure.
Advantages of Adaptive Cruise System
1, to avoid frequent operation, reduce the burden on the driver, improve comfort
2. ACC is generally started when V>40km/h. The active braking function can effectively avoid rear-end accidents at high vehicle speeds and improve safety.
When the vehicle distance reaches a safe distance:
1) Reduce power output [through control of throttle
2) Active braking
3) Sound and light alert the driver
3. Automatically adjust the power output according to the driving condition of the preceding vehicle, without frequent shifting, the engine always works at the best working point, reduces the fuel consumption, and reduces the emission of harmful substances.
In general, the application of ACC can improve comfort and safety while being eco-friendly.
ACC adaptive system does not adapt to the pit
1. Emergency braking in front of the car, you may suffer losses, including high-speed emergency. Why?
The ACC maximum deceleration G value is 0.35g, and the general consideration is that the emergency braking deceleration G value is 0.8 or more, that is, the emergency ACC runs out of control;
In case of an emergency stop in front of you, don't wait for ACC's help. Stopping the brakes is justified.
There is a time when the car is retrograde; the speed is too fast;
Retrograde is actually a matter of braking and braking. The maximum deceleration G of the brake is too small to be fully braked. Do you understand?
2. When it was a turn, the car lost.
ACC can only identify the vehicle in front of it. It is a straight line scan. When the current side is a turn, it is the vegetable field or ditch that is directly scanned. At this time, we must manually identify the most secure;
3. When you start and stop, do you have a car distance, and when it comes to a stoppage, it may be a potential failure mode?
Before the car moves, your car starts within 3 seconds, 3 seconds can insert a car into it, there will be inevitable rear-end, you have to remember this scene;
4, is the front of the vehicle, when the super-long objects;
ACC intelligently recognizes the car, does not recognize the goods, the goods that come in, is your threat, the parking brake in front of you brakes according to the scheduled distance, you are in danger; it is possible, intimate contact, or even goods KO.
ACC technology trends
1, sensor technology:
Volume: a more compact, more integrated device that is at least half the size
Recognition range: doubled
2, perfect function:
The control performance is more harmonious when changing lanes and crossing corners.
3, high integration:
Reduce costs, enhance the internal links of various systems, improve the information sharing rate, and improve the stability and reliability of the entire system.
4, automatic start technology within the full speed range
Today, ACC automatically shuts down under dense traffic with V<30km/h.
In the future, the automatic launch technology in the full-speed range will enable the ACC to quickly recognize the front obstacle within a short distance. When the current vehicle starts again, the image system can be used to obtain information, so that the driver can automatically start without the participation of the driver.
5, performance requirements:
Better close-range detection capabilities, faster signal processing capabilities, and faster system response.
In this way, even if the traffic jam does not require the driver to participate, there is an unmanned prelude.
Although the ACC (adaptive cruise control system) has become more and more complex, its operation has become more and more simple. As technology becomes more and more mature and the degree of intelligence becomes higher and higher, fully-automated driving of automobiles will certainly become an irreversible trend in the future.
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