According to the statistics of relevant departments, 41% of all commercial vehicle traffic accidents are side collision accidents, which cause more than 30% of casualties and property losses. Therefore, it is very urgent and very important to solve the side safety problem of commercial vehicles. The newly developed microwave blind spot detection and lane change assist system of Shunhe Company can solve the problem of blind area behind the vehicle side, early warning of potential danger, avoiding traffic accidents and improving driving safety performance.
The lane change assisting system LCA (ISO17387 standard called "change lane assistance system LCDAS", abbreviated as "change lane assist") is to detect the lanes and rear of the adjacent sides of the vehicle through sensors such as radar and camera; The motion information of the side and rear objects is combined with the current state of the vehicle; the driver is finally reminded by sound, light, etc.; the driver is allowed to grasp the optimal lane change timing to prevent traffic accidents caused by lane change; Collisions also have a better preventive effect.
Due to technical maturity and cost, only the lane change decision aid system of 24GHZ microwave radar technology is introduced here. The system uses two 24GHZ microwave radars as sensors to detect the side and rear of the vehicle; the detection distance is 70 meters and the relative speed is 20 meters/second (ie 72Km/H); this can inform the potential danger information 3.5 seconds ahead of time. The driver allows the driver to have enough time to reflect the accident.
The lane change assist system includes three functions: “blind spot monitoringâ€, “close to vehicle warning†and “change lane warningâ€. It can effectively prevent the occurrence of traffic accidents such as rear-end collision, lane change, turning, etc.; greatly improve the safety performance behind the car.
Serial number function category function description
1 Blind spot monitoring BSD according to its judgment of the relative position of the moving object and the relative speed of the car, when in the blind zone of the car, promptly remind the driver to pay attention to the risk of the lane change.
2 The lane change assisted LCA system detects that the target vehicle approaches the vehicle at a relatively large relative speed in an adjacent area, and alerts the driver by visual, audible, or tactile means when the distance between the two vehicles is less than a certain range.
3 After the collision, the RCW system detects that there is a fast moving object behind the same lane, and when there is a risk of collision, the driver of the rear vehicle is reminded by flashing the brake light in time, in case of collision risk, timely warning The occupant seat belt and the like reduce the damage caused by the collision.
2, the technical principle2.1, microwave radar principle
Microwave refers to electromagnetic waves with a wavelength of 1~10mm. It has a large bandwidth, high resolution, and small size of antenna components, which can adapt to harsh environments. The radar antenna emits a series of frequency-modulated continuous wave FMCW, and the frequency changes according to the law of the modulation voltage with time. Generally, it is a continuous triangular wave, and the transmitting and receiving signals are as shown in FIG. 1 . The solid line in the figure is the transmitted signal, and the dashed line is the reflected signal of the relatively stationary and relatively moving objects. The reflection is the same as the waveform of the transmitted signal, except that the delay time is t. t=2R/C (1); In this formula, R is the target distance and C is the speed of light.
The frequency difference between the transmitted signal and the reflected signal at a certain moment is the intermediate frequency f(b) of the mixed output. The reflected signal of a relatively moving object will cause a shift in frequency due to the Doppler effect. The intermediate frequency frequencies outputted at the rising edge and the falling edge of the triangular wave are f(b+) and f(b-), respectively. The following formula holds: thus obtaining the distance R of the target vehicle and the relative movement speed V. The determination of f(b) is mainly through the analysis of the spectrum of the signal; the transform is usually performed by transforming the time domain and the frequency domain of the signal by Fourier transform (FFT).
FMCW transmit and echo signals
2.2, microwave radar structure
Microwave radar mainly includes: antenna, transceiver module, signal processing module and alarm module. The RF transceiver front end is the core component of the radar system. A typical RF front end mainly includes an antenna, a linear VCO, an amplifier, and a balanced mixer. The intermediate frequency signal of the front-end mixing output is sent to the data processing part of the subsequent stage through the intermediate frequency amplification.
The data processing part needs to eliminate unnecessary signals (such as clutter) and interference signals, and process the mixed frequency signals amplified by the intermediate frequency to extract information such as the target distance and speed from the signal spectrum.
2.3, the application of microwave radar
The 24 GHz microwave radar can realize various functions such as blind spot detection, lane departure warning, rear collision warning, parking assistance, and front collision avoidance.
Compared with other technologies, such as video, laser and infrared technology, microwave radar technology has the main advantage that it is not susceptible to weather. The detection data is mainly related to the position and speed of the target. The microwave radar can detect the distance, relative speed, angle and other information of the target object; it can easily identify the relative position of the target object, thereby avoiding the interference and ensuring the validity of the target object recognition and the accuracy of the alarm. By installing a microwave radar, you can provide a full range of protection for your car.
3.1, specifications
The microwave lane change auxiliary system test includes 6 steps of functional test, electrical performance test, electromagnetic compatibility test, reliability test, and load measurement. Electrical performance testing, electromagnetic compatibility testing, and reliability testing are versatile standards for automotive electronics. It is not introduced here. The focus here is on the functional testing of the microwave radar lane change assistance system.
4.1, test preparation:
Divide the area around the car as follows:
A: 30 meters from the rear of the car;
B: 3 meters from the rear of the car;
C: driver's head position;
D: the front part;
N: the rear part;
E: the left side of the body;
J: the right side of the body;
F: the first lane line on the left;
G: the second lane line on the left;
H: the third lane line on the left;
K: the first lane line on the right;
L: the second lane line on the right;
M: the third lane line on the right;
4.2. Blind spot monitoring test standards and requirements:
The rectangular area composed of BCFG and BCKL is a blind zone; if there is a fast approaching vehicle (pedestrian, etc.) in this area, it should be alarmed.
4.3. Approaching vehicle warning standards and requirements:
For adjacent lanes FG and KL, the area after blind zone B is the proximity zone. The test criteria for this area are divided into 3 levels:
Class A: To be able to detect an approaching vehicle (pedestrian, etc.) with a speed greater than 10 m/s, the warning time is greater than 2.5 seconds;
Class B: To be able to detect an approaching vehicle (pedestrian, etc.) with a speed greater than 15 m/s, the warning time is greater than 3.0 seconds;
Class C: To be able to detect an approaching vehicle (pedestrian, etc.) with a speed greater than 20 m/s, the warning time is greater than 3.5 seconds;
5, market trends As early as 1973, AEG-Telefunken and Bosch in Germany began researching automotive anti-collision radar technology and developed a 35 GHz uncorrelated pulse radar. With the maturity of microwave technology, the idea of ​​detecting the surrounding environment of vehicles through sensors to avoid accidents has been re-focused by automakers. In China, more than 100 universities, research institutes and factories have begun to study microwaves. Now, microwave basic components and systems have the technical conditions for engineering applications, especially the modularization of microwave devices, and advances and breakthroughs in microwave monolithic integrated circuit (MMIC) processes, enabling microwave devices to offer batch products at acceptable prices. . By the end of 2016, Hella had shipped more than 10 million 24 GHz microwave radars.
Since Mercedes-Benz in Germany installed the Autonomous Cruise Control System (ACC) on S-Class limousines in 1999, more and more companies and suppliers have invested in microwave radar system development, device development, and algorithm research. The main international microwave radar suppliers are Bosch, Valeo, Hella, Siemens, Delphi and so on.
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