Automatic Transmission (AT): An automatic transmission uses a planetary gear mechanism to change gears automatically based on the accelerator pedal position and vehicle speed. The driver only needs to operate the accelerator pedal to control the vehicle speed. Generally speaking, the types of automatic transmissions commonly used in automobiles include: hydraulic automatic transmission, hydraulic transmission automatic transmission, electric transmission automatic transmission, stepped mechanical automatic transmission, and continuously variable transmission (CVT). Among them, the most common is the hydraulic automatic transmission. A hydraulic automatic transmission mainly consists of a hydraulically controlled gear transmission system, primarily comprising an automatic clutch and an automatic transmission. It can automatically shift gears according to the accelerator pedal opening and vehicle speed. Continuously Variable Transmission (CVT): A CVT consists of two sets of gear pulleys and a drive belt. Therefore, it is simpler in structure and smaller in size than a traditional automatic transmission. Furthermore, it can freely change the gear ratio, thus achieving stepless speed changes throughout the entire range, resulting in smooth vehicle speed changes without the "jerk" feeling of traditional transmissions. Continuously variable transmissions (CVTs) are a type of automatic transmission, but they overcome the drawbacks of ordinary automatic transmissions, such as sudden gear shifts, slow throttle response, and high fuel consumption. CVTs are lightweight, compact, fuel-efficient, and offer smooth power delivery, and are increasingly being adopted by more manufacturers. However, new technologies also bring new problems. Have you encountered the following situations while driving your CVT-equipped car? For example, the car doesn't move when starting in D mode, making you cautious every time you start, and causing anxiety while waiting at red lights in the morning; or the car lurches forward when you brake while following another vehicle, making your heart race. While the symptoms may not be severe, they can be startling when they suddenly occur. CVTs are a relatively recent type of automatic transmission that has gradually gained popularity in passenger cars. Due to their unique technology and short market entry time, they naturally encounter some new and emerging issues. Recently, I've occasionally heard of domestically produced Audi sedans equipped with Multitronic continuously variable transmissions (CVTs) exhibiting the following symptoms: 1. Braking issues: When braking slowly, the engine speed spikes briefly just before stopping, dropping to a very low level of about 200-300 RPM, before rising again (by about 1/10 of a second). When coasting from idle to slow braking, you can notice the tachometer needle suddenly drop, recovering rapidly in about 1/10 of a second. The vehicle feels like it's suddenly jerking or lurching forward. This phenomenon is more pronounced with gentler braking. 2. Acceleration issues: Audis equipped with Multitronic CVTs feel relatively slow during acceleration. Sometimes, even with significant throttle input, the speed doesn't change much before suddenly lurching forward. 3. Another issue is that when starting in drive (D), the car doesn't move, even with the accelerator. In this case, you need to shift to neutral (N) first, then back to drive (D) to start normally. These problems don't occur constantly but rather randomly, making them quite troublesome. When encountering the above problems, remain calm and avoid panic to prevent misoperation. Take these issues seriously and repair them as soon as possible. If it's within the warranty period, the manufacturer will provide free repairs. (Audi's warranty period is 1 year or 20,000 kilometers, whichever comes first.) The solution is to replace the valve body in the transmission and further reset the control program. The valve body is expensive, costing approximately 16,000 yuan. Adding transmission fluid and other parts, plus labor costs, the total cost will be nearly 20,000 yuan. The repair time is approximately 3 hours. The symptoms may disappear after replacing the valve body, but resetting the program is still recommended. In other countries, some cars equipped with continuously variable transmissions (CVTs) also experience strange problems. For example, a MINI owner reported that when driving his CVT MINI at a steady speed of 60 km/h, the engine speed would suddenly rise to 3200-3400 rpm, and the gear would be in D mode instead of the sport mode S mode. This happened regardless of whether the engine was cold or warm. At a constant speed of 50km/h or 70km/h, the engine speed remained at 2000rpm. This was unsettling, and after a software upgrade and re-identification at a repair shop, the problem was finally resolved. Another owner of a 2003 Audi CVT also encountered the same issue experienced by owners of similar vehicles in China: the engine speed would occasionally spike violently when approaching a stop. CVTs are structurally completely different from automatic transmissions. Internally, they primarily use two variable-diameter pulleys with a drive belt in between to transmit torque. The drive belt is wound around a conical pulley at each end, and the outer diameter of the pulleys changes infinitely, creating a transmission ratio change between the two pulleys from "larger to smaller" to "smaller to larger," thus achieving gear shifting. The electronic commands for gear shifting are executed by an electro-hydraulic control system. If a small part of this control system malfunctions, it will affect vehicle operation. It seems that new technologies also encounter new problems, but every technology must go through a process of development from immaturity to maturity.