Composition and principle of adaptive cruise control system

Fully self-driving cars will surely become popular in the next few years. Google has planned to have 10 million self-driving cars on the road worldwide by 2020. In fact, some basic technology configurations of self-driving cars are already equipped in many of our current models. For example, adaptive cruise control has almost become a standard feature of luxury cars. But what is adaptive? What is the use of radar? What does cruise control control?

In fact, cruise control has been around for a long time. The earliest version of cruise control was born in the 18th century. Its function was to prevent steam engines from running too fast. Later, the cruise control system was connected to the speedometer and drive shaft to calculate the driving speed, and then use the computer to control the throttle to maintain the speed set by the driver. 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.

Cruise control first became popular in the United States, because there are many long, straight and wide interstate highways, and many drivers need to drive long distances. In order to reduce driving fatigue, cruise control became popular. In Europe, because there are many small roads and turns, cruise control was originally seen as a symbol of high-end luxury cars. However, now, cruise control has become popular, and the cost of modern electronic technology has been reduced, making this configuration of luxury cars also equipped in ordinary family cars.

Friends who have used the cruise control function know that it can only be used on highways without traffic jams or on empty streets at 3 a.m. In real life, we often encounter traffic jams, sometimes accelerating and sometimes braking, and cruise control seems to be a decoration, so adaptive cruise control (ACC) came into being.

ACC Adaptive Cruise Control System

ACC (Adaptive Cruise Control) is an intelligent cruise control system based on sensor recognition technology. Compared with traditional cruise control systems that can only cruise at a constant speed according to the speed set by the driver, ACC can identify the vehicle in front, thus achieving the effect of "slow down if the vehicle in front is slow, and speed up if the vehicle in front is fast". At present, it can be divided into basic version ACC (30-150km/h) and full-speed ACC (0-150km/h) according to the speed range. Among them, the sensor of the basic version of ACC is radar, while the full-speed ACC is based on the radar as the main sensor, and other sensors such as the front camera are added to assist in recognition, so as to meet the higher requirements for recognition accuracy and angle at low speeds.

Composition and principle of adaptive cruise control system

1. Radar sensor

In the ACC system, the ranging radar is used to measure the headway, relative speed, and relative acceleration between the vehicle and the vehicle in front. It is one of the key devices in the adaptive cruise control system and 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, etc.

Millimeter wave radar

Principle: Use the reflection of electromagnetic waves by the target to detect the target and determine its position. Millimeter waves have high frequency and wavelength range.

Performance: The detection performance is stable and is not easily affected by the color and shape of the object surface, nor by airflow; it has good environmental adaptability and is less affected by rain, snow, fog, etc.

Monopulse radar

Principle: Every time the radar transmits a pulse, the antenna can form several beams at the same time. The sum of the signals received from each beam can measure the distance of the target, thereby achieving measurement and tracking of the target. (Pulse: A process in which a physical quantity suddenly changes in a short duration and then quickly returns to its initial state)

Performance: All-weather radar can be used in various weather conditions. It has the advantages of long detection distance, large detection angle range, and multiple target tracking, but it is expensive.

Microwave radar

Principle: Microwave radar's accurate speed detection of moving objects is based on the microwave Doppler effect.

The distance is measured by measuring the time delay of the echo signal relative to the transmitted signal.

Performance: Easy to install and maintain, long service life, almost unaffected by light intensity, dust, wind, rain, fog, snow and other weather conditions.

LiDAR

Principle: A laser generates and emits a light pulse, which hits an object and reflects back, and is eventually received by a receiver. The receiver accurately measures the propagation time from the emission of the light pulse to its reflection. Because light pulses travel at the speed of light, the receiver always receives the previous reflected pulse before the next pulse is sent. Since the speed of light is known, the propagation time can be converted into a measurement of distance.

Performance: It has high requirements for the working environment and is sensitive to weather changes. In bad weather such as rainy, snowy, windy and sandy days, the detection range is limited and there are fewer targets to track. However, its biggest advantage is that the detection accuracy is relatively high, the price is low, and it is easy to control and conduct secondary development.

Infrared detection radar

Principle: Different types of objects emit infrared light in specific bands. People can use infrared light in specific bands to detect and track object targets.

Performance: Unstable performance in bad weather conditions, short detection distance, cheapest price.

2. Electronic Control Unit (ECU)

The core part of the ACC system

Composition: Like ordinary single-chip microcomputers, it consists of a microprocessor (CPU), memory (ROM, RAM), input/output interface (I/O), analog-to-digital converter (A/D), and large-scale integrated circuits such as shaping and driving.

Function: Calculate, process and judge the information input by the air flow meter and various sensors according to the programs and data in its memory, and then output instructions.

3. Other components:

Cruise control switch, speed setter, distance setter, status display, alarm...

4. Mutual connections

The radar sensor detects the target vehicle in front of the main vehicle and provides the electronic control unit with information such as the relative speed, relative distance, relative azimuth angle, etc. The electronic control unit determines the driving status of the main vehicle based on the safe vehicle distance and cruising speed set by the driver and the information transmitted by the radar.

1). When there is no vehicle in front of the vehicle, the vehicle will be in a normal cruising state. The electronic control unit can automatically control the power output of the entire vehicle by controlling the electronic throttle (sending instructions to the drive motor, and the drive motor controls the throttle opening to adjust the flow of the combustible mixture) according to the set information.

2). When there is a target vehicle in front of the vehicle and the target vehicle's speed is less than the set speed, the electronic control unit calculates the ratio of the actual vehicle distance to the safe vehicle distance and the relative speed, and selects a deceleration method; at the same time, an alarm is issued to the driver through the alarm to remind the driver to take corresponding measures.

When the distance to the vehicle ahead is too small, the ACC control unit can coordinate with the anti-lock braking system and the engine control system to brake the wheels appropriately and reduce the engine output power, so that the vehicle always maintains a safe distance from the vehicle ahead. The electronic control unit can also control the integrated electronic vacuum booster (EVB) system. When the driver does not brake and the EVB starts to work, the electromagnet in it will replace the driver to operate the vacuum valve and atmospheric valve inside the vacuum booster, thereby achieving the purpose of adjusting the brake pressure.

Advantages of Adaptive Cruise Control

1. Avoid frequent operations, reduce the driver's burden and improve comfort

2. ACC is generally activated when V>40km/h. The active braking function can effectively avoid rear-end collisions at high speeds and improve safety.

When the vehicle distance reaches a safe distance:

1) Reduce power output [by controlling the throttle

2) Active braking

3) Sound and light reminders for drivers

3. Automatically adjust power output according to the driving conditions of the vehicle in front. There is no need to change gears frequently. The engine always works at the best working point, which reduces fuel consumption and the emission of harmful substances.

In general, the application of ACC can improve comfort and safety while being economical and environmentally friendly.

The pitfalls of ACC adaptive system

1. If the car in front of you brakes suddenly, you may suffer losses, including highway emergencies. Why?

The maximum deceleration G value of ACC is 0.35g, while the general consensus is that the deceleration G value of emergency braking is above 0.8, which means that ACC loses control in an emergency;

If there is an emergency brake ahead, don't wait for ACC to help. The correct thing to do is to brake immediately.

Another thing is that when a car is driving in the wrong direction, the speed is too fast;

Driving in the wrong direction is actually the same as emergency braking. The maximum deceleration G-value of the brakes is too small, and the brakes cannot be fully sensitive. Do you understand?