Simplified design of adaptive steering headlight system

The purpose of the electronic control of the xenon headlights through the stepping motor is to direct the headlight beams, minimize the intensity of the oncoming vehicles, and illuminate the curved road at the same time. However, the position of the vehicle motor driver chip has a great influence on the efficiency of the system.

High-intensity discharge lamps (xenon lamps) vehicle headlights are increasingly becoming the technology of choice for vehicle manufacturers worldwide. In order to maximize the use of high-quality lighting provided by xenon lamps, and at the same time reduce the risk of excessively high xenon lamp intensity caused by improper orientation, the adaptive steering headlight system (AFS) is of increasing importance.

These systems can slightly adjust the beam of the headlights in the vertical direction to compensate for changes in the vehicle's inclination relative to the road surface. At the same time, they can also rotate the headlights of the car according to changes in vehicle steering. Such a light beam can provide the best and safest road lighting ahead, significantly improving the visibility of the road when the driver turns.

1. Automatic leveling-weaken glare

The working principle of the headlight automatic leveling system is to ensure that the lights are level with the road surface when the vehicle is tilted (see the figure below). When the vehicle is at a standstill, it may be tilted for some reason, such as when a passenger gets on the vehicle, loads luggage, or even refuels the fuel tank. Similarly, when the vehicle is traveling, the vehicle may tilt due to braking or acceleration. In both cases, the headlights must remain level with the road. The headlight automatic leveling system adjusts the angle of each headlight based on a series of data from the sensors, especially the suspension compression data from the front and rear axles.

Second, improve safety performance by rotating the headlights

The vehicle's data network includes real-time sensor data about steering angle and wheel speed. Based on this information, the adaptive headlight system equipped with headlights can adapt the light distribution to the vehicle's steering angle, so that oncoming turns and forks—especially the driver ’s gaze point—can be optimized. Lighting (see picture below). This significant enhancement of light can reduce the driver's tension and fatigue, and improve the visibility of obstacles; these obstacles are not even illuminated by the fixed beam headlights. Many studies have shown that when the vehicle turns, the rotating beam headlights increase the illumination of the driver ’s gaze point by 300%.

3. Stepper motor control

The rotation of the headlights of each vehicle is achieved by using a stepper motor, where one stepper motor controls the rotation in the vertical direction and the other one controls the rotation in the horizontal direction (see the following figure). The motor reacts based on data from many sensors around the vehicle. The transmission of information is achieved through the vehicle's data network system. The LIN bus is a practical choice for headlight control, while the CAN bus is able to collect and distribute sensor data to the entire vehicle. Stepper motors are an optimal choice for headlight adjustment applications, because these motors are low cost, rugged, and small in size but can provide a large torque.

As for the placement of the driver IC chip that controls the stepper motor, there are two options available. The first is called direct drive. In this method, the driver chip is mounted on the printed circuit board of the main microcontroller (see top image below). The circuit board is far away from the headlight components and related stepper motors. It may be located in a central electronic control unit (ECU) attached to a vehicle partition (insulation wall), or it may be located in the passenger compartment of the vehicle. "Comfortable" environment. The main shortcomings of this method are the excessive lines required and high-intensity electromagnetic compatibility radiation.

The second method is mechatronics. In this method, the driver chip and the motor are installed together (see the bottom of the figure above). Due to the use of highly integrated single-chip products such as the AMIS-30621 and AIMS-30623 stepper motor controller integrated circuits manufactured by AMI Semiconductor, the electromechanical integration method of the adaptive steering headlight system that can install the chip directly in the motor Becomes more feasible. This method is very beneficial because the interface between the central microcontroller and the mechatronics module requires only a low electromagnetic compatibility bus. The mechatronics method uses a modular design, and the headlight assembly is easy to maintain and maintain, so the benefits are significant.

Four, split hardware and software

The application of stepper motor driver needs to design both hardware and software. This can become very complicated, especially in the case of adaptive steering headlight systems where multiple axes need to be controlled simultaneously. Before the advent of stepper motor controller integrated circuits, the past method was to invest in microcontrollers and develop special software, or use conversion chips (see the figure below, left and middle pictures). The main problem with software-based solutions is that the development costs are high, and there are inherent difficulties in verifying the correct operation of multiple axes under any conditions.

The so-called conversion integrated circuit provides an interface between the microcontroller and the driver chip. The overall solution adds some additional hardware, but it also leads to more difficult to manage complexity and more software requirements (see the following figure, Picture on the right). The disadvantage of using a conversion chip is that it makes the design of the printed circuit board more complicated, while losing some of the advantages of modularity.

Five, single chip method

Compared with other methods, the integrated stepper motor controller reduces the complexity of the multiple-axis adaptive steering headlight system and provides a direct solution that vehicle manufacturers need to support modular and Vehicle integration design.

AMI Semiconductor provides four mixed-signal devices that combine bus connection, positioning, electronic control, and motor driver in a single package with a footprint of 7mm * 7mm. These devices are small in size and high in performance. They can still ensure the modular design of the motion control software and robust motor operation even when they are installed directly inside the stepper motor.

The characteristics of the above two models (AMIS-30621 and AMIS-30623) devices are based on the LIN bus. Compared with a system where the driver is placed at a remote location, this method saves wiring costs and has better electromagnetic compatibility performance. This advantage is the key to solving problems when encountering difficulties in automotive applications. The remaining two improved versions (AMIS-30622 and AMIS-30624) have an I2C serial interface and can be used as a peripheral device adjacent to the microcontroller on a single printed circuit board.

6. Sensorless stop detection

Most automatic headlight systems can make initial position adjustments when the lights are on. This mechanical method basically adjusts the lamp to the lowest possible point within a specified time. There is a problem with this program, that is, noise is generated due to the stepping motor hitting the stop point and the wear is increased. Another solution is to use sensorless stop detection, which features AMIS-30623 and AMIS-30624 components. These components operate quietly and have low wear, yet they can also accurately calibrate the position, and can use semi-closed loop operation when they are close to the electromechanical stop point without the need for external sensors.

7. Summary of this article

The use of a single-chip stepper motor controller integrated circuit can greatly simplify the design of an adaptive steering headlight system and provide high-quality technical performance under conditions that are often difficult to operate. The integrated design greatly improves the overall reliability of the headlights and means that only a few capacitors are needed for external circuit components. Similarly, time to market, design, and overall system cost will be positively affected.

Both the mechatronics and modular methods are supported by single-chip stepper motor controller integrated circuits. These two methods are manufactured for the majority of vehicles when the rapidly growing vehicle electronic system makes the electronic system structure too complicated and expensive. Respected by businessmen.

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