“With the continuous development of modern automobile technology, people pursue a more comfortable and easy-to-operate driving environment. Therefore, more and more automobiles are equipped with electric windows to realize automatic lifting and lowering of the windows. However, due to the fast rising speed of the power windows, it is easy to cause accidents such as pinching passengers, which is a safety hazard for children in particular. This sets new standards for car safety, requiring power windows to have a certain anti-pinch function.
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With the continuous development of modern automobile technology, people pursue a more comfortable and easy-to-operate driving environment. Therefore, more and more automobiles are equipped with electric windows to realize automatic lifting and lowering of the windows. However, due to the fast rising speed of the power windows, it is easy to cause accidents such as pinching passengers, which is a safety hazard for children in particular. This sets new standards for car safety, requiring power windows to have a certain anti-pinch function.
The anti-pinch function mainly means that when the window encounters an obstacle (such as hand, head, etc.) in the process of rising, it can recognize that the window is in a clamped state, and make it immediately stop rising and descend in the opposite direction, so as to avoid accidents. It is an important embodiment of the humanization of automobiles.
This feature has also been incorporated into legal norms in many countries. The U.S. Department of Transportation has promulgated regulation FMVSSII8 for power window systems, and EU Standard 74/60/EWG also specifies the anti-pinch force that the anti-pinch protection device should ensure. China has also promulgated similar regulations (GB 11552-2009), requiring that from 2012, the electric window regulators of newly added vehicles should have an anti-pinch function, and the anti-pinch force should be less than 100N, that is, when the anti-pinch force reaches Before 100N, when the window glass opening is in the range of 4~200mm, the window should stop rising and fall in the opposite direction.
At present, the anti-pinch function of electric windows is mainly realized through the following two schemes: a Hall sensor scheme and a sensorless scheme based on ripple counting.
1. Hall sensor scheme
In this scheme, a magnetic ring is installed on the motor shaft, and a Hall sensor is installed near the magnetic ring. When the motor rotates, the magnetic ring is driven to rotate, and high and low level pulse signals are induced on the Hall sensor. The number of pulses reflects the motor position, the frequency of the pulses reflects the speed of the motor.
When the power window rises and encounters an obstacle, the resistance will become larger, the motor speed will slow down, and the pulse width of the corresponding pulse signal will become larger. At this time, the system will report information to the ECU module, and the ECU will send a message to the relay or motor driver chip. command to stop or reverse the motor, so as to stop or drop the window to realize anti-pinch judgment.
The DRV5013-Q1 is a bipolar Hall-effect sensor with a wide operating voltage range (2.7 to 38V) and reverse polarity protection up to -22V, making the device suitable for a wide variety of automotive applications. In addition, the device has internal protection features such as load dump, output short circuit, and overcurrent.
This solution requires the installation of magnetic rings and each window requires its own controller, so the cost is high.
Compared with the Hall sensor scheme, the sensorless scheme based on ripple counting can save the cost of the magnetic ring, Hall sensor and related wiring harness. In addition, this solution can use a single controller to control multiple windows at the same time, which can improve the integration of the whole vehicle and further reduce the cost of the controller. Therefore, the sensorless solution based on ripple counting will become the future development trend of electric window anti-pinch.
2. Sensorless scheme based on ripple counting
The sensorless scheme of ripple counting is to use the current ripple generated by the switching of the brushes between the electric stages during the rotor rotation, and to sample, analyze and control this current fluctuation.
This scheme first converts the motor current signal into a voltage signal through a sampling resistor, and filters and amplifies the voltage signal through an operational amplifier. The amplified signal is converted into a digital signal through AD all the way to the MCU, which is used as a judgment of anti-pinch and locked rotor. According to the other way, a square wave signal is obtained through a filter and a comparator, and the frequency of the square wave is proportional to the speed of the motor. The position and speed of the motor can be judged by the number and frequency of square waves.
Reference design TIDA-01421 provides a sensorless anti-pinch solution for ripple. The design is mainly divided into the following parts:
Current Sense Amplification
The INA240-Q1 is a wide common mode range, high precision, bidirectional current sense amplifier. The device has a common-mode range of C4V to 80V, a large common-mode rejection ratio of 120dB, and can provide accurate, low-noise measurements.
Applications can use a simple RC input filter at the input of the INA240-Q1 to reduce high frequency motor brush noise and potential PWM switching noise.
bandpass filter
The output of the current sense amplifier is filtered by an active bandpass filter to remove additional noise and DC components, resulting in a current ripple signal.
The TLV2316-Q1 is a dual, low voltage, rail-to-rail general purpose operational amplifier. The device features unity-gain stable integrated RFI and EMI suppression filters, no phase inversion under overdrive conditions, and high electrostatic discharge (ESD) protection (4kV HBM).
differential amplifier
When the motor starts up, there is a very large initial spike in the motor current known as inrush current. This current spike is large enough and slow enough that it cannot be filtered out by the high pass circuit. With a differential amplifier, this low-speed, high-amplitude current spike can be removed from the signal, resulting in a low-noise AC signal for measurement by the next-stage comparator.
Comparators
The signal output by the differential amplifier passes through the comparator and finally generates a square wave signal of 0V to 3.3V, whose frequency is equal to the motor current ripple frequency. This square wave signal is finally supplied to the MCU for counting.
The LMV7275-Q1 is a rail-to-rail input low power comparator with an open-drain output. The small SC-70 package is ideal for low-voltage, low-power, space-critical designs.
To sum up, this paper introduces the basic principles of two anti-pinch schemes applied to power windows-Hall sensor and ripple anti-pinch technology, and compares the advantages of the ripple scheme compared with Hall in practical applications. Although the Hall solution occupies a dominant position in the current market for window anti-pinch applications with its mature technology and high reliability, with the continuous development of mechanical processing technology and Electronic technology, the market share of ripple technology will increase. obvious.
Hall sensor, electric vehicle, current ripple, window anti-pinch
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