Back in the time, distinguishing gearboxes was easy; they were either manual or automatic. Manual and automatic are inherently different in structure. The video below would perfectly show the key differences. In general, manual is cheaper, lighter, and more efficient, while automatic is easier and more convenient to drive.
For race cars and sports cars, the manual is the best solution due to its efficiency. The only problem with the stick-shift manual is that it takes more effort to maneuver. To make shifting easier, the sequential manual was introduced firstly to race cars and gradually to streetcars. It can be shifted using the gear lever with “+” and “-” or the shift paddles on the steering wheel. This kind of manual gearbox has no clutch pedal and often comes with an automatic mode, so it is also called semi-automatic. Its structure still resembles that of the traditional manual, though.
The 1989 Ferrari 640 was the first F1 car to have paddle shifting (of course F1 cars have no automatic mode). We see F1 drivers today easily shift down three gears before entering a turn thanks to the paddle shifting and computer assistance. Shift paddles are almost standard equipment for luxury and sports cars now regardless of the actual transmission type, while the traditional three-pedal stick-shift is continuously declining in sales.
If manual-based transmissions are more efficient and could shift automatically with the assistance of the computer, what is the reason for using automatic? The key is the clutch itself. First, the clutch is disengaged and then re-engaged in every gear shift, and this creates the power discrepancy and the bumping push. For those semi-automatic gearboxes, this process is conducted by the computer. Second, whenever a manual car stops, the clutch has to be disengaged from the engine and re-engaged when starts again. This means manual cars are not suitable for crawling in heavy traffic, which is a common situation in metropolitan areas. Some drive manual cars with the clutch half-engaged when crawling, but the clutch will soon be worn out.
Automatic transmission, on the other hand, fits better in urban traffic. Here I refer to any gearbox with a torque converter and planetary gears as automatic even if it has a manual mode. The torque converter allows different turning speeds on both sides, so the whole drive train can be still while the engine is running. Upon a gear shift, the torque converter does not need to be disengaged, so the power transmission is smooth and continuous. Drivers are thus allowed to use “D” gear all the time. Automatic car drivers (like me) can simply use the brake pedal to control the car in the crazy (Asian) traffic: release the brake to let the car crawl; hit the brake to stop; hit the gas pedal only when needed.
The biggest problem for automatics was its efficiency because of the inevitable power loss through the hydraulic system of the torque converter. In the past, the manual version of a model was always faster than its automatic counterpart. Modern torque-converter automatic, however, has significantly improved and is often faster than the manual counterpart. The high-performance automatic transmission will be further introduced later on.
Some prominent manufacturers, including Audi, BMW, and Mercedes, produced only longitudinal engine layouts in the past. Transverse engine placement was considered a cheap solution for small cars and was never regarded as a luxury car layout. In recent years, the transverse layout gains its way into the premium market due to cost concerns and technological progress. Volvo has been using this for more than two decades and even the once RWD-only BMW joins the transverse-FF competition. The gearboxes for transverse vehicles are different from the longitudinal ones, and those luxury brands usually source the transverse automatic from outside suppliers. They source almost from one supplier only.
The AISIN AWF8F Series almost monopolizes the transverse automatic market. BMW, Volvo, and Peugeot all apply the 8-speed auto from the Japanese firm on various transverse models worldwide. Rumor has it that AISIN holds many patents in this realm, so the competing products remain limited. ZF produces a superior 8HP, but its transverse 9HP is not a reputable product. The only notable user of 9HP is Jaguar Land Rover.
This triggers the war of transmission. To break through the monopoly of AISIN, various manufacturers come up with different ideas. The most notable one is Volkswagen AG (VAG), which has been using the dual-clutch transmission (DCT) as an alternative solution to the transverse torque-converter automatic since the 21st century. Following the step of VAG, major European firms also resort to DCT as the full or partial solution to transverse transmission. Notable suppliers of transverse DCT include BorgWarner and Getrag (renamed Magna PT after the merger). Currently, BMW uses both AISIN auto and Getrag DCT in UKL models, and Mercedes uses its own-developed 7G/8G-DCT together with the outsourced Getrag DCT (for the 1.33L engine) in MFA models. The video below shows the basic mechanism of DCT.
The DCT is structurally closer to traditional manual than automatic. The driving logic should thus be similar to that of semi-automatic (or sequential manual) due to the absence of a torque converter. This leads to a serious problem as most DCTs are marketed as “automatic”. VW offers only DCT (branded as DSG) and manual for its MQB family, so customers naturally assume that DCT is the automatic counterpart of the manual transmission. To force the DCT to behave like an automatic, some weird logic is introduced. For example, the DSG from VW launches from 2nd gear with the clutch half-engaged to avoid the bumping push, and this accelerates the wearing of clutches. Failure of DCT from various brands is always a hot debate all around the world. This does not mean DCTs are bad. They are just applied in the wrong way.
Another solution to the transverse automatic is the continuously variable transmission (CVT). A notable user of CVT should be NISSAN, sourcing the transmission from its compatriot JATCO. All the transverse NISSAN models are equipped with CVT now, compatible with engines up to the VQ35DE. CVT is subject to sustainability issues since its debut in the 1990s, but currently, the problem is not as heated as that of DCT.
Honda implemented the automatic shifting mechanism in a totally different but rather intuitive fashion. Honda simply made the manual gearbox automatic by replacing the clutch with the torque converter and the synchronizers with hydraulic clutches. The clutch for each gear is automatically controlled, shifting gears by disengaging one gear and engaging another simultaneously. Such a gearbox is more robust but requires more gearbox fluid to prevent overheating of clutches. Another obvious drawback is the much larger size compared to the planetary gear gearboxes with the same speeds. Honda managed to make a 6-speed version to the utmost and switched to other types such as CVT and DCT later on. Honda does try to design its gearboxes while avoiding any patent infringement. Transmission products from Honda always feature slightly different structures from mainstream ones.
The war on high-performance longitudinal transmission is as fierce as that on transverse city cars. The torque converter was never welcomed in this class, and the war started with optimizing the manual gearboxes. Ferrari started applying sequential manual “F1-gearbox” on-road cars in the 1990s, and so did BMW, debuting the SMG in the E36 M3. The only exception was the Mercedes-Benz SLR McLaren, which used a traditional 5-speed automatic. In the second decade of the 21st century, longitudinal DCT gained popularity among the class. Audi, BMW, Ferrari, Mercedes, and Porsche are all in the game, and notable suppliers of longitudinal DCT include Getrag and ZF. The PDK from Porsche is one of the most notable applications. Supplied by ZF, PDK can sustain 50 consecutive launches as claimed by Porsche. PDK is also applied on Bentley Continental and Flying Spur now.
The progress of automatic transmission makes the torque converter a feasible option for performance vehicles now. Take the famous ZF 8HP for example. The torque converter of 8HP can be locked up to avoid any power loss at high speed. 8HP sustains higher torque than some DCTs and is especially suitable for high-torque turbocharged sports sedans and GTs. It can now be seen on BMW M models, Alfa Romeo Quadrifoglio, Maserati, Jaguar and Land Rover, Aston Martin, etc.
Mercedes-AMG takes a step further. In its SPEEDSHIFT MCT gearbox, the torque converter is replaced by a multi-disk clutch. That makes it a hybrid transmission between manual and automatic, as shown in the clip. The mechanism of the clutch enables the real launch control just as the sequential manual and the DCT do. Cars with a torque converter gearbox, contrarily, can only use the brakes to simulate the launch. This gearbox is available on selected V8 AMG models.
One has to know that every type of transmission has different specifications catering to different engine outputs. A CVT for high output is still stronger than a traditional automatic for low output. We saw many cases of DCT failure, but that does not mean PDK is bad just because it is also a DCT.
What is the future of car transmissions? The stick-shift manual will remain a low-price solution for city cars and commercial vehicles, with occasional application in some sports cars (e.g. Porsche 911 R). Automatic will become standard equipment for luxury models, whereas some entry-level luxury models may stick to transverse DCT. Longitudinal DCT will be the best solution for street-legal supercars.
The ongoing mania of electrification of automobiles is changing the transmission industry. Gearbox suppliers are offering hybrid transmission solutions as they combine an electric motor with a gearbox. Both PDK and 8HP from ZF can now be mounted with an electric motor. Aisin has been providing Toyota with a hybrid transmission that combines a single-speed reduction gear set with a motor generator, marketed as E-CVT. High-end Lexus hybrid cars receive the “multi-stage hybrid” transmission from Aisin, which combines a 3-speed motor generator and a 4-speed automatic gearbox and provides 10 speeds in total (3 electric speeds multiplied by 3 gear speeds plus one overdrive speed from the gearbox). Whilst most electric cars only need a single-speed gearbox due to the continuous output of the electric motor, Porsche Taycan shows the possibility of a more complicated gearbox layout as it has a single-speed gearbox on the front axle and a two-speed on the rear.
The war of transmission in the electric era is just about to kick off.
