Automotive drive belts are crucial components of car engines and an integral part of the transmission belt system. Many technological advancements and inventions in drive belts are closely related to the development of the automotive industry. For example, the invention of V-belts, the rapid development of cut-edge V-belts, multi-ribbed belts, and synchronous belts, the application of hydrogenated nitrile butadiene rubber (HNBR) in synchronous belts, and ethylene propylene diene monomer (EPDM) in multi-ribbed belts all stemmed from adapting to the latest technological requirements of the automotive industry. In recent years, due to global warming, environmental protection, and demands for vehicle comfort, energy conservation, emissions, and NVH (noise, vibration, and harshness) have become major topics in the automotive industry. Improving fuel efficiency, reducing emissions, and extending maintenance intervals have always been research goals in the automotive industry. These technologies include multi-valve engines (MVES) and variable valve timing (VVT) technologies, catalytic converters, integrated starter alternators (ISAs) with 42V power generation/starting, direct injection diesel engines, and maintenance intervals of 240,000 km or even 300,000 km. These technological advancements have correspondingly increased and demanding performance requirements for automotive components, including automotive drive belts. To adapt to these changes, some well-known international drive belt manufacturers have made numerous improvements and performance enhancements to automotive drive belts. Toothed Multi-Wedge Belts Toothed multi-wedge belts are similar to toothed V-belts, with teeth cut into the wedges to improve the belt's flexibility and heat dissipation, significantly extending its service life. Goodyear's research shows that for the same neoprene (CR) material, ordinary multi-wedge belts reach 66 hours in high-temperature fatigue tests, while toothed multi-wedge belts can reach 167 hours. Toothed multi-wedge belts also reduce the precision requirements for belt assembly. However, during use, toothed multi-wedge belts draw in and out airflow through the pulleys, generating rhythmic airflow noise. Goodyear addresses this noise with helical teeth, while Dayco uses irregular teeth to reduce noise by approximately 15 dB. These two companies market their products under the "Gatorhark" and "POLYCOG" brands, respectively. Flocked Multi- Wedge Belt One drawback of multi-wedge belt drives is their relatively high transmission noise. When used at low speeds or with rapid changes in angular velocity, and after a period of time, as the wedge surface wears, hardens, and tension relaxes, or after getting wet in rainy weather, a piercing screeching sound will occur during transmission, affecting the vehicle's NVH performance. One solution is to leave 0.1-1.0mm of high-strength short fibers (such as aramid, PBO fibers, etc.) on the wedge surface. Because the fiber has a stable coefficient of friction and sound-absorbing properties, it greatly reduces the noise of the multi-wedge belt drive. Flocked multi-wedge belts are generally achieved using a special grinding process. During grinding, the wedge is first quickly ground into a rough wedge shape, then wet-ground at low speed to remove the rubber, exposing a certain length of fiber on the wedge surface. Elastic Multi-Wedge Belt In recent years, small family cars have also begun to use elastic multi-wedge belts as drive belts to simplify the transmission pulley system structure of the engine front-end accessories. Elastic multi-wedge belts generally use high-twist nylon fibers with a breaking elongation greater than 20% as the strong layer cord. High-performance automotive elastic multi-ribbed belts produced by Continental and other manufacturers reportedly have a service life of 150,000 km. EPDM Multi-ribbed Belts In recent years, engine compartment temperatures have been rising, with some requiring rubber components to withstand 150°C and instantaneous 170°C. Traditional neoprene rubber (CR) clearly cannot meet these requirements. Due to the high cost of HNBR, research has shown that small amounts of oil contamination do not damage the belts at the front of the engine, allowing the use of cheaper, heat-resistant ethylene propylene diene monomer (EPDM) rubber as the main rubber material for multi-ribbed belts. However, EPDM has unsatisfactory wear resistance, high-temperature tear resistance, and dynamic performance, and poor adhesion to other materials. These issues need to be addressed through modification, such as adding ZDA or ZDMA and combining it with other materials. EPDM multi-ribbed belts exhibit significantly improved high-temperature resistance and fatigue life. For example, CR multi-ribbed belts have a fatigue life of only 50 hours at 107°C, while EPDM multi-ribbed belts can reach 125 hours at 121°C. Continental's EPDM multi-ribbed belts have a service life of 240,000 km. Short Fiber Reinforced Synchronous Belts Since the first patent for HNBR was published in 1975, HNBR has gradually become the preferred standard elastomer material for automotive synchronous belt production worldwide. Honda of Japan first produced a new car equipped with a drive belt made from HNBR in 1985. BMW of Germany also became the first European automaker to use HNBR synchronous belts in 1997, thanks to imports of HNBR synchronous belts from Japan. In the late 1990s, with the rapid development of the global automotive industry and fierce market competition, Continental, an automaker, used HNBR/ZMA combined with aramid short fibers to manufacture HSN-POWER life HNBR synchronous belts for use in gasoline engines. Their lifespan has exceeded 240,000 km, approaching the goal of "the same lifespan as the engine." Automakers are striving to improve engine performance by maximizing the lifespan of camshaft drive synchronous belts. Currently, almost all automakers worldwide are using HNBR synchronous belts to improve the quality of their vehicles. Practice has proven that under normal driving conditions, the service life of HNBR timing belts can reach 100,000-150,000 km. Modern automobiles require timing belts with the following specifications: a service life of 250,000-300,000 km; operating temperature range of -35°C to 150°C, with instantaneous high temperatures reaching 175°C; oil resistance ≥ CR; bench life of up to 3000 hours at 150°C, while maintaining low-temperature performance while improving oil resistance; and a dynamic storage modulus of ≥ 1.4 MPa for the teeth. To achieve such high requirements, only a composite material of peroxide-cured HNBR/zinc methacrylate (ZMA) compound reinforced with aramid short fibers can be used. Continental has manufactured HSN-POWER life HNBR timing belts using a combination of HNBR/ZMA and aramid short fibers for use in gasoline engines, achieving a service life exceeding 240,000 km, approaching the goal of "matching the engine's lifespan." Backed Synchronous Belts Due to manufacturing limitations, automotive synchronous belts typically have a pure rubber backing. However, in modern automotive synchronous belts, the backing needs to simultaneously drive other components such as the oil pump and tensioning mechanism, especially in direct-injection diesel engines. This requires a high tension force, resulting in significant wear on the backing, which pure rubber cannot meet. Making the backing of the belt with fabric greatly improves its wear resistance. The Continental "Conti Diesel Runner" synchronous belt uses this structure. Oil -Resistant Synchronous Belts Since the 1960s, when General Motors first used synchronous belts in its newly developed overhead camshaft (OHC) engine to replace the previously used ball chains, synchronous belts have rapidly gained widespread use in automotive engine timing transmissions, especially in small-displacement engines, due to their numerous advantages such as good synchronization performance, low noise, no lubrication required, light weight, low cost, and easy maintenance. They are almost 100% used in these systems. However, in the new century, with the continuous improvement of modern car engines, increasingly stringent emission regulations, and longer maintenance cycles (240,000 km or even 300,000 km), the load on timing transmission mechanisms has been increasing, and the requirements for valve timing accuracy have become increasingly stringent. Synchronous belts are finding it increasingly difficult to meet the demanding requirements of modern car engines. Furthermore, improvements in chain technology, such as strength, wear resistance, noise reduction, and optimized design, have overcome the inherent shortcomings of chains, highlighting their inherent advantages such as high power output, maintenance-free operation, and heat and oil resistance. Therefore, in recent years, there has been a trend towards using chains in automotive engine timing transmission mechanisms. To compete with chains, foreign transmission belt manufacturers such as Continental, Gates, and TAG have developed oil-resistant synchronous belts. These belts can directly contact lubricating oil like chains, eliminating the need for tensioners and using guide rails for tensioning and guiding. This reduces the belt's friction coefficient by 30%, resulting in a more compact structure. Oil-resistant synchronous belts represent a major breakthrough in transmission belt technology, changing the traditional concept that transmission belts cannot contact mineral oil. The belt body formulation requires HNBR with a high acrylonitrile content, the tooth cloth coating adhesive needs to contain a large amount of Teflon, and the strong layer cords should use high-strength composite glass fiber or carbon fiber. The herringbone tooth synchronous belt, similar to a human-shaped gear, has the biggest advantages of reduced noise, significantly improved transmission capacity, and increased service life. This type of belt was invented by Goodyear in the 1990s and marketed under the "ENGLE" brand. The successful development of the herringbone tooth synchronous belt is a milestone in the history of synchronous belt development. Compared with the same tooth profile straight tooth synchronous belt, this belt can reduce noise by 10-26 dB, increase service life by 120%, and significantly improve transmission capacity (or reduce bandwidth). It has been tested in automobiles, with a service life exceeding 210,000 km. Non-circular pulley drive technology Currently, automotive engine timing systems commonly use multi-valve and variable valve timing technologies, which multiplies the pulse load on the camshaft, causing increased engine vibration amplitude, affecting the overall vehicle NVH (noise, vibration, and vibration) performance, and also damaging the synchronous belt and other components. To minimize the impact of this vibration, Litens invented SmartSprocket™ non-circular gear transmission technology (CTCcamshaft torque cancellation technology) (Figure 8). This means that the pulleys in the cam section are not traditionally perfectly circular, but rather elliptical or other non-circular. This effectively cancels out most of the amplitude during operation, reducing the force on the belt and its components by 40%, increasing belt life, and saving fuel. Modular and Integrated Drivetrain Systems A modular drivetrain system integrates the timing belt drive system (including the belt, pulleys, and tensioning mechanism) with the engine-side auxiliary drivetrain (which includes the generator, air conditioning, water pump, etc., in addition to the drive components). Users only need to assemble it, simplifying the complex production process to meet the demands of modern automotive intensive manufacturing. Gates' GEM10™ system is an example of this. Gates has also developed an integrated auxiliary drive system (Electro-Mechanical Drive, EMD) that is compatible with both 14V and 42V motor systems, with a service life of 240,000 km and 500,000 start-stop cycles. This system has been applied in newly developed 42V generator/start systems from Peugeot, GM, and other manufacturers. CVT uses composite V-belts. Continuously variable transmissions (CVTs) are ideal for automobiles. They differ significantly from traditional gear and hydraulic automatic transmissions (A/T), consisting of pulleys and belts. There are two types of CVT transmissions in automobiles: friction drive and traction drive. The former includes wet-friction metal belts, dry-friction rubber V-belts, and composite V-belts; the latter is the more recently researched CVT. Friction drive CVTs originally used metal belts. Metal belts require lubrication and a large pulley driving force, which reduces overall transmission efficiency. Using a rubber V-belt eliminates this need, and rubber V-belts are cheaper to manufacture and easier to maintain and use than metal belts, making them a popular research and development target for various manufacturers. However, automotive transmission V-belts need to transmit very high torque, which ordinary rubber V-belts cannot handle. For example, when a 1000cc engine reaches its maximum torque, the V-belt must be able to withstand a lateral pressure of 2.0MPa, while ordinary V-belts can only withstand 0.4-0.5MPa. To achieve such a high modulus, only a composite V-belt composed of a rubber tension belt and a metal block can meet these requirements. Almost all well-known transmission belt manufacturers worldwide are researching and developing composite V-belts for CVTs, representing cutting-edge transmission belt technology. This is not only due to the high technical difficulty of this type of transmission belt but also its vast market potential. It has wide applications in both the automotive and other industries. Composite V-belts have already reached practical application levels abroad; for example, the CVT system jointly developed by Aichi Machinery and Bando Corporation in Japan is installed in the Suzuki Mira car. Samsung, Gates, Goodyear, Continental, and other companies are also developing this type of belt.