Automotive HVAC system: valve control
Foreword The heating, ventilation and air conditioning (HVAC) system can deliver cold or hot air to the cabin, providing a safe, comfortable and relaxing environment for passengers and drivers, improving the visibility of the windows and rearview mirror glass, and filtering out the pollen in the cabin , Dust and odor. Recently, we have seen a sharp increase in the demand for air conditioning systems in cars. In order to ensure that the car rides as comfortable as the sofa at home, the air conditioning system has become more and more complicated, and more and more relevant regulations. In fact, the modern air-conditioning system divides the interior of the car into four different areas, with independent climate control for each area. Therefore, today, there is almost no car with no HVAC system. The output of the air conditioning system is almost equal to the output of the car. Since the beginning of the installation of air conditioners in cars, a number of improved technologies have increased the complexity of modern air conditioning systems. With the development of air-conditioning systems to semi-automatic and fully automated, people predict that the market share of manual air-conditioning will gradually decrease, but considering that manual air-conditioning is the preferred solution for economic cars, we can conclude that manual air-conditioning system will not soon Delisting. In order to comply with the development trend of the automotive air conditioning market and meet the needs of automobile manufacturers for HVAC systems, STMicroelectronics has developed two new intelligent power drivers L99MD01 and L99MD02 for the application of air conditioning system ventilation valve positioning motors. L99MD01 is usually used for high-end air conditioning solutions, while L99MD02 meets the needs of mid-range air conditioning systems. New intelligent power chip driving ventilation valve controller Air conditioning systems can be divided into three major types: manual air conditioning, semi-automatic air conditioning, and fully automatic air conditioning. The ventilation valve of the automatic air conditioning system is controlled by a stepper motor or a DC motor. Which motor depends on the complexity of the system and customer needs. The typical ventilation valve motor configuration is to use the built-in potentiometer DC motor to perform the position detection function; another control method is to use a unipolar stepper motor. The solution using a stepper motor has one major drawback: 5 lines are required to connect the vent valve actuator and the electronic climate control unit. Obviously, in order to adjust the temperature quickly and accurately, it is necessary to increase the number of ventilation valves and motors, which will inevitably cause the wiring harness on the car to become bulky and messy. The electromechanical control method driven by LIN bus is a feasible solution, but the increase in cost makes this solution only suitable for particularly high-end cars. L99MD01 and L99MD02 can meet multiple needs of customers. Both devices are positioned in the mid-to-high-end automotive market, providing complete protection functions and design flexibility for developers of ventilation valve positioning systems. Both products are controlled by the SPI bus, which integrates complete diagnostic and protection functions and can monitor all outputs. Adopt L99MD01 to drive stepper motor L99MD01 is a vehicle driver composed of 6-way half-bridge, capable of driving stepper motor and DC motor. When used as a stepper motor driver, this chip can drive 4 stepper motors at the same time or 3 stepper motors in sequence through the built-in switching power supply module and an external boost converter. This chip saves two wires for each stepper motor driving the ventilation valve, reducing the number of wires from 5 to 3. In addition, L99MD01 can also drive low-cost bipolar winding stepper motors, saving one winding per phase, thus reducing the number of cables. Figure 1: Application diagram of L99MD01 By using the built-in SMPS module, a DC-DC boost converter can be realized, which doubles the power supply voltage and obtains a symmetrical voltage power supply (0V / Vs / 2xVs). The half-bridge circuit is converted to the full-bridge operating mode, allowing bidirectional The current passes through and drives two phases of a stepper motor through two half-bridges. In addition, this symmetrical power supply supplies bidirectional current to each phase winding of the stepper motor, only one line per phase is required, which means that if all motors share a power line, two lines can be driven from the control unit to drive Pole stepper motor (as shown in Figure 1). We can see from Figure 2 the advantages of using L99MD01 stepper motor driver design in terms of wiring and cost. Figure 2: Stepper motor driving bipolar mode saves wire and cost Adopt L99MD0x series products to drive DC motor Compared with stepper motors, DC motors have a lower cost and are the most commonly used control motors in ventilation valve control systems. Both L99MD01 and L99MD02 products can be used to drive DC motor controlled ventilation valve positioning systems. In these two products, the function and technology of L99MD01 is more complicated, mainly used in the high-end automotive market; the chip integrates 8 half-bridge circuits, which can drive 4 DC motors simultaneously or 7 DC motors in sequence, as shown 3 and Figure 4. Figure 3- L99MD01 drives 4 DC motors simultaneously Figure 4- L99MD01 drives 7 DC motors in sequence L99MD02 is a reduced version of L99MD01. The basic structure of the product includes a 6-way half-bridge driver, no SMPS module for external boost converter, and the target application is locked in the mid-range automotive air-conditioning system market. Guangzhou Ehang Electronic Co., Ltd. , https://www.ehangmobile.com
