The automotive transmission is one of the most vital components of a vehicle, as it transfers the power from the engine to the wheels. The number of gears in a transmission affects the performance, fuel economy, and emissions of a vehicle. In the past, most transmissions had only three to five gears, but the recent trend is to increase the number of gears to as many as 10. What are the benefits and challenges of having more gears in a transmission? How are the transmission technologies evolving to meet the changing demands of the market and the environment? This article will explore these questions and more.
The primary reasons for vehicles with more transmission speeds are fuel economy and performance. Automakers are under federal mandate to improve their corporate average fuel economy (CAFE) numbers, as well as greenhouse gas and carbon dioxide numbers, while consumers are demanding better performance. Having more gears in a transmission allows the engine to operate at its optimal speed range, which reduces fuel consumption and emissions. More gears also provide smoother acceleration and deceleration, as well as better responsiveness and drivability.
According to a report by Automotive Fleet, a six-speed transmission can improve fuel economy by 4% to 6% compared to a four-speed transmission, while an eight-speed transmission can improve fuel economy by 11% to 14%. A 10-speed transmission can further improve fuel economy by 16% to 18%. These improvements can translate into significant savings for fleet owners and drivers, as well as environmental benefits.
The Challenges of More Gears
However, adding more gears to a transmission is not a simple task. It requires more complex design, engineering, and manufacturing, as well as more space, weight, and cost. More gears also mean more friction losses, more shifting events, and more potential for noise, vibration, and harshness (NVH) issues. Therefore, automakers and transmission suppliers have to balance the trade-offs between the benefits and the challenges of more gears, and find the optimal number of gears for each vehicle type and application.
Another challenge is to ensure the compatibility and integration of the transmission with the engine, the drivetrain, and the vehicle control systems. The transmission has to communicate and coordinate with the engine management system, the transmission control unit, the stability control system, the adaptive cruise control system, and other systems to optimize the performance and efficiency of the vehicle. The transmission also has to adapt to the driver’s behavior, the road conditions, and the driving modes. These require advanced software and hardware solutions, as well as rigorous testing and validation.
The Evolution of Transmission Technologies
To overcome the challenges of more gears, automakers and transmission suppliers have developed and improved various transmission technologies, such as automatic transmission (AT), dual-clutch transmission (DCT), continuously variable transmission (CVT), and hybrid transmission. These technologies have different advantages and disadvantages, and are suitable for different vehicle segments and markets.
- AT: An AT uses a torque converter and a planetary gearset to provide multiple gear ratios and automatic shifting. An AT is easy to use, reliable, and comfortable, but it is also heavy, expensive, and less efficient than other transmission types. To improve the efficiency and performance of ATs, some automakers have added features such as lock-up clutches, electronic controls, adaptive shift logic, and start-stop systems. Some ATs also use more than one planetary gearset to achieve more gears, such as the 10-speed AT developed by Ford and General Motors.
- DCT: A DCT uses two clutches and two sets of gears to provide fast and seamless shifting. A DCT combines the advantages of an AT and a manual transmission (MT), such as high efficiency, high performance, and low weight. However, a DCT also has some drawbacks, such as high cost, high complexity, and low smoothness at low speeds. Some DCTs also use wet clutches to reduce friction and heat, but this increases the oil consumption and the maintenance requirements. Some examples of DCTs are the seven-speed DCT used by Volkswagen and the eight-speed DCT used by Hyundai.
- CVT: A CVT uses a belt or a chain and a pulley system to provide a continuous range of gear ratios, rather than discrete gears. A CVT can optimize the engine speed and the vehicle speed, which improves the fuel economy and the emissions. A CVT also provides smooth and quiet operation, as well as simple and compact design. However, a CVT also has some limitations, such as low durability, low performance, and high noise at high speeds. Some CVTs also use a torque converter or a clutch to improve the responsiveness and the NVH characteristics. Some examples of CVTs are the e-CVT used by Toyota and the Xtronic CVT used by Nissan.
- Hybrid transmission: A hybrid transmission is a transmission that integrates an electric motor and a battery with a conventional transmission, such as an AT, a DCT, or a CVT. A hybrid transmission can provide different driving modes, such as series, parallel, and power-split modes, which can improve the fuel economy, the performance, and the emissions of the vehicle. A hybrid transmission can also provide regenerative braking, start-stop function, and electric-only driving, which can further enhance the efficiency and the functionality of the vehicle. However, a hybrid transmission also adds more complexity, weight, and cost to the vehicle, as well as more challenges for the configuration design, the energy management strategy, the hybrid mode shifting control, and the integration with the vehicle systems.
The Future of Transmission Technologies
The automotive transmission landscape is changing rapidly, as more gears are becoming the norm for most vehicles. However, more gears are not necessarily the ultimate goal, as there are other factors that affect the performance and efficiency of a vehicle, such as the engine type, the vehicle weight, the aerodynamics, and the driver behavior. Therefore, the future of transmission technologies will depend on the development and adoption of other technologies, such as electrification, connectivity, automation, and artificial intelligence.
Electrification is one of the major trends that will shape the future of transmission technologies, as more vehicles are becoming hybrid, plug-in hybrid, or fully electric. Electrification can reduce the dependence on fossil fuels, lower the emissions, and improve the performance of vehicles. However, electrification also poses new challenges and opportunities for transmission technologies, such as the need for single-speed or multi-speed electric vehicle transmissions, the design of distributed electric drive systems, and the optimization of hybrid transmission systems.
Connectivity is another trend that will influence the future of transmission technologies, as more vehicles are becoming connected to each other, to the infrastructure, and to the cloud. Connectivity can provide more information and feedback to the vehicle and the driver, such as the traffic conditions, the road conditions, the driving patterns, and the preferences. Connectivity can also enable more services and functions for the vehicle and the driver, such as remote diagnostics, over-the-air updates, and personalized settings. Connectivity can also enhance the safety and the convenience of the vehicle and the driver, such as collision avoidance, adaptive cruise control, and parking assistance. Connectivity can also improve the efficiency and the performance of the transmission, as it can enable more intelligent and adaptive shifting strategies and control algorithms.
Automation is another trend that will affect the future of transmission technologies, as more vehicles are becoming autonomous or semi-autonomous. Automation can reduce the human errors, increase the comfort, and improve the safety of the vehicle and the driver. However, automation also requires more sensors, actuators, and computers for the vehicle and the transmission, as well as more standards and regulations for the industry and the society. Automation can also change the role and the behavior of the driver, as well as the demand and the expectation for the vehicle and the transmission.
Artificial intelligence is another trend that will impact the future of transmission technologies, as more vehicles are becoming smarter and more capable. Artificial intelligence can provide more learning and reasoning abilities for the vehicle and the transmission, such as self-learning, self-optimization, and self-correction. Artificial intelligence can also provide more interaction and communication abilities for the vehicle and the transmission, such as voice recognition, natural language processing, and emotion detection. Artificial intelligence can also provide more creativity and innovation abilities for the vehicle and the transmission, such as new features, new functions, and new solutions.
The automotive transmission is a dynamic and evolving field, as more gears are changing the landscape. More gears can provide more benefits, but also more challenges, for the vehicle and the transmission. More gears can also stimulate more development and improvement of the transmission technologies, such as AT, DCT, CVT, and hybrid transmission. More gears can also inspire more exploration and integration of other technologies, such as electrification, connectivity, automation, and artificial intelligence. The future of transmission technologies will be more diverse, more intelligent, and more exciting.
