To enhance automotive comfort, many cars are equipped with power windows, allowing drivers to easily control the raising and lowering of the windows with the push of a button. However, these windows lack intelligence; if the driver is not aware of occupants' hands or objects protruding from the window, they could easily be pinched by the rising glass. For safety reasons, many passenger cars now use anti-pinch window lifters (APWL). Europe and the United States have successively legislated to make APWL a standard feature in automobiles to improve driving safety and user-friendliness. Legislation on APWL is also under discussion in China. Existing APWL systems typically use Hall effect sensors or other optical sensors installed on the motor of the window regulator to detect resistance. These power windows require additional sensors to be installed on existing ordinary window regulators. This paper introduces a window control module that achieves anti-pinch functionality based on existing sensorless power windows. 1. Principle of the Anti-Pinch Window The anti-pinch window designed in this system consists of a power window regulator and a window control module. The power window regulator consists of a lift mechanism and a motor. The lifting mechanism typically employs a rope pulley, gear arm, or flexible shaft type. The key component of an electric window regulator is the motor, which generally uses a reversible permanent magnet DC motor with a built-in reducer. The motor contains a magnetic field coil; by controlling the direction of the voltage applied to the coil, the motor's forward and reverse rotation is controlled, thus raising and lowering the window. In basic car models, the electric window control circuit uses switches and relays to control the window motor, which are prone to problems such as sticking. This system uses intelligent power drive devices to control the window motor, controlling the direction of rotation by controlling the voltage applied to the DC motor. Changes in the current passing through the regulator motor perfectly reflect changes in resistance encountered during the glass's ascent or descent. By sampling the current passing through the window regulator motor and monitoring it, changes in resistance during glass movement can be monitored, allowing for appropriate actions to be taken. The intelligent power drive devices provide overcurrent, overvoltage, and overheat protection for the motor, and automatically identify obstacles encountered during the glass's ascent by monitoring the current, reversing the direction to prevent pinching injuries. The control module can achieve the following functions: (1) Press the door control button (button press time less than 300 ms), the window will automatically rise to the top or fall to the bottom. Press any button on the same switch, and the window will stop rising or falling. (2) Delay the window control button (button press time greater than 300 ms), the window will rise or fall. Release the button during the rising or falling process and the window will stop. (3) The window will automatically stop when it reaches the top or bottom position, and the window motor will be de-energized. (4) If the window glass encounters a certain resistance during the automatic rising process, it will automatically stop and fall a certain distance, which can effectively prevent accidental injury to people or objects. 2 Hardware design principle of the window control module Based on the analysis of the national standard for electric window lifters, the control object of the electric window control module is a permanent magnet DC motor with a power supply voltage of 11~15 V, an operating current of no more than 15 A, and a stall current of no more than 28 A. The door control module mainly consists of the following parts: power supply circuit, microcontroller section, electric window drive circuit, bus interface circuit, etc. The block diagram of the window control module is shown in Figure 1. The microcontroller uses the PIC18F2480 microcontroller, which integrates many practical functions such as A/D, PWM, CAN controller, UART, and SPI. The PIC18F2480 microcontroller controls the switching action of power devices, monitors the system status in real time, receives fault feedback signals, and exchanges fault information and button control information with the central body controller and other door controllers through the vehicle network. This allows for timely display of fault information on the user interface and real-time control of the doors, ensuring driving safety. 2.1 Design of Motor Drive Circuit The window motor is mainly driven by a Freescale intelligent power module MC33486 plus two MOSFETs forming an H-bridge to achieve bidirectional control of the motor. The internal resistance, temperature rise, and voltage of the two MOSFETs are matched with the MC33486. In this design, the STB55NF06T4 in D2PAK package is used. Its normal continuous output current reaches a maximum of 10 A, and the maximum peak current can reach 35 A. It has a wide DC input voltage range of 8–28 V, with overvoltage protection when the voltage exceeds 28 V. It also provides overcurrent protection for both high and low ends. Under chopper control, the frequency can reach 30 kHz, and it exhibits a mirror characteristic for detected high-end output current. These devices provide comprehensive fault detection and protection functions, thus avoiding the use of too many discrete components, greatly reducing the module size, and improving the module's EMC (electromagnetic compatibility) characteristics. 2.2 Current Sampling Circuit Design The anti-pinch function is mainly achieved by monitoring the current change of the window regulator motor, as shown in Figure 2. Freescale's power chip MC33486 has a linear replication function for load current. The CurR output is a current proportional to the load current, where ILoad is the motor current of the window regulator. This current is converted into voltage through sampling resistor R7 and current-limiting resistor R8 and input to the sampling terminal of the microcontroller's ADC. The voltage input to the microcontroller is: After A/D conversion and some calculations, the actual load current can be obtained. Therefore, monitoring the voltage input to the microcontroller port is equivalent to monitoring the motor current during the movement of the car window. During the rising and falling process of the car window, the current passing through the motor when encountering resistance during the rising process changes regularly, and these current changes are reflected in the microcontroller in real time through current sampling. 3 Software Design of the Car Window Control Module 3.1 Start-up and Stopping of the Car Window Start-up refers to the process of the DC motor reaching a stable speed from a standstill. If the motor is started directly (i.e., directly switched on), the starting current U is applied to the motor, and the starting current Ia = (U-0) / Ra = U / Ra is very large, which will cause strong sparking. The current is proportional to the torque, and excessive torque will cause a large impact, and voltage fluctuations will affect the stability of the power supply. In this system design, the motor starts using PWM. A frequency of 2 kHz is used, divided into 10 segments, with the duty cycle gradually increasing from 0% to 100%. Each segment consists of 10 pulses, totaling 5 ms, with a total start-up time of 50 ms for 10 segments. Experiments have shown that this start-up method results in a smoother start-up and better start-up speed. During the window start-up period, the motor current changes significantly, making it impossible to implement the anti-pinch function by monitoring the current change. Furthermore, this period is very short, so the anti-pinch function should be avoided during the start-up period. When stopping, the motor does not stop only when it is detected that it is stalled, but rather when the motor current exceeds a certain range of its normal operating current. In this system experiment, this limit current is defined as 11 A. The motor current change during the rising process is shown in Figure 3, where the motor current shows a gradual increasing trend and continuous change. The motor current change during the falling process is shown in Figure 4, where the current shows a gradual decreasing trend and continuous change. 3.2 Implementation of the Anti-Pinch Algorithm In order to realize the anti-pinch function of the electric glass, the designed and developed window control module must include two functions: (1) It must be able to determine whether an obstacle is encountered; (2) After encountering an obstacle, it must be able to determine whether the glass is rising or has already risen to the top. If the window control module determines that the glass encounters an obstacle during its ascent, it issues a command to reverse the motor, causing the window to descend a certain distance and then stop. If the window control module determines that the glass has reached the top, it issues a command to stop the motor, closing the window. Figures 3 and 5 show the current changes of the DC motor when the window reaches the top and when it encounters resistance during ascent. Comparing Figures 3 and 5 reveals that in both cases—reaching the top and encountering resistance—the motor current increases sharply from its normal operating current. Therefore, monitoring the motor current amplitude can help determine if an obstacle has been encountered. However, the instantaneous current change of the motor may show peak values; therefore, the amplitude must be the average current over a period of time. When the average current A ≥ A_obstacle (A_normalT_top), the window rises to the top; when T ≤ T_top, the window encounters resistance during its ascent. However, different windows of the same model may have slight differences in T_top due to variations in installation. An initial T_top can be determined experimentally, and the time it takes for the window to rise to the top each time can be recorded and stored in an E2PROM. This data serves as the basis for adjusting T_top, thus giving the parameter T_top self-adaptability. Three sets of criteria are used to distinguish between the two situations. When (A ≥ A_obstacle) && (f ≥ f_resistance) && (T ≤ T_top), the window encounters resistance during its ascent; when (A ≥ A_obstacle) && (0 ≤ T_top) When the window reaches its highest point (T), it rises to the top. Three sets of criteria were used to increase the accuracy of the judgment and reduce the false judgment rate. Using these three criteria, the anti-pinch function of the electric window was successfully implemented in a real-vehicle experiment. When encountering resistance during the rising process, the window descends a certain distance, and the current change is shown in Figure 5. 4. Conclusion The PTC microcontroller PIC18F2480 integrates many functions, supports CAN communication and serial communication, and can be programmed online. The intelligent power driver MC33486 not only has a wide voltage input range and large capacity, but also a current mirroring function. Combining these two components, by monitoring the current of the window motor to detect obstacles encountered by the window, the anti-pinch function of the electric window can be easily implemented without adding any sensors, building upon existing electric windows that do not have an anti-pinch function.