Test Drive The History of Automotive Transmissions - Part 3
Test Drive

Test Drive The History of Automotive Transmissions - Part 3

Test Drive The History of Automotive Transmissions - Part 3

In this last part, you will find various types of modern solutions in this area.

Today, the world of transmissions is more diverse than ever, and automotive companies and suppliers are bound by complex relationships and agreements leading to the creation of extremely high-tech products, from small CVT transmissions to nine-speed automatic transmissions.

In the 50s, everything seemed to take on a crystal clear picture: for Americans, automatic transmission is now paramount, and for Europeans, manual transmission remains a priority. However, the same statement can be applied to the 70s - we must not forget that the real "motorization" of Europe (Western) began precisely then, because the 80s are still years to rebuild from the ruins of war. History shows that the picture was not much different in the 2000s, although in some places in Europe automatics began to appear in more luxurious cars. It wasn't until the 90s that the advent of e-government began to change the tide in favor of automatic transmissions and the Old Continent. But even in 80, when the share of automation in new cars reached 15 percent in the US and 4 percent in Japan, only 5 percent of Europeans chose this solution. Of course, one cannot underestimate the psychological component in this case and the very purposeful desire of the latter to shift gears on their own. At the time, they were still predominantly 2002 and 6th gear - it wasn't until '8 that ZF introduced the first generation of its 8HP six-speed transmission to take them up to XNUMXHP, seven years later at ZF XNUMXHP. The latter becomes a real revolution, not only with the number of gears, but also with the perfect operating comfort, which thanks to BMW engineers and their precise integration into the seventh series has been brought to perfection.

This is truly a period of incredible change because at the time ZF continued to supply 4HP for the Peugeot 407 and 5HP for VW and Skoda. In fact, over 13 years, the share of automatic transmissions worldwide has skyrocketed, reaching 46 percent in 2014. Despite the increase in the number of gears, the size and weight are reduced, and there is already something for everyone here. Even small cars like the Honda Jazz will also get dual-clutch gearboxes. Mercedes and ZF present nine step units in succession. Active joint development GM and Ford are hard at work on a ten-speed automatic transmission project to counter Chrysler in America, which in the meantime is releasing a licensed version of the ZF 8HP. While the evolution of manual transmissions is moving towards better gears, simplification and more precise shifting, bringing some cars to such perfection that it would be sacrilege to deprive them, automatics now have a huge selection of options. Of all cars with automatic transmissions sold in 2014, 49 percent are classic automatic transmissions with 6 or more gears, and only 15 percent have less than 6 gears. CVTs make up 20 percent, dual-clutch transmissions 9 percent, and automated manual transmissions just 3 percent, as do hybrid and electric vehicle transmissions. These figures hide some strict specifics: the main share of DSG transmissions, for example, is on the market in Europe, classic ones in Europe and the USA, and a high share of CVT transmissions are in Japan. At the same time, the new units are by no means heavier or larger than their predecessors – if the 5 Mercedes 2004-speed automatic transmission requires four planetary gears and seven locking devices, thanks to its intelligent architecture, the new 9G-Tronic is it also manages four planetary gears, but with six clutches as locking elements. One thing is clear - very soon even mid-range brands will follow the luxury goods manufacturers and now move to transmissions with more gears - a good example of this is the fact that Opel is in the final stages of developing an eight-speed automatic transmission. The idea of ​​a car with an automatic transmission that makes the engine accelerate uncomfortably and creates a strange synthetic feel is now completely in the annals of history.

Alliances and agreements

Однако Mercedes – скорее один из исключений как производитель автомобилей, который разрабатывает и производит собственные трансмиссии. На него похожи Mazda, PSA и Hyundai/ Kia, но на практике большинство производителей автомобилей в значительной степени связаны сложными отношениями и совместными предприятиями как друг с другом, так и с такими поставщиками коробок передач, как ZF и Aisin. С 8-ступенчатым автоматом ZF в разных вариантах, например, модели оснащены Audi, BMW и Rolls-Royce. По лицензионному соглашению Chrysler производит такую ​​же трансмиссию для моделей Уклонение, Крайслер, и Jeep, но и для Maserati и Fiat. GM производит восьмиступенчатую Hydra-Matic для самого Corvette, но совместно с Aisin разработала восьмиступенчатую коробку передач для Cadillac, а десять лет назад поставила автоматические коробки передач для BMW. В то же время американский гигант работает с Ford над созданием десятиступенчатой ​​коробки передач, а его европейское подразделение Opel разрабатывает собственную восьмиступенчатую коробку передач. Hyundai / Kia также разработали собственную восьмиступенчатую коробку передач. Компания Getrag, которая тем временем приобрела обширный опыт в производстве коробок передач с двойным сцеплением, предлагает свои агрегаты как для компактных моделей Ford, так и для Renault, а также для M-версий BMW, и два сцепления для них в большинстве случаев поставляет LUK. Знаменитая трансмиссия DSG от VW и Audi была сконструирована с помощью BorgWarner, а трансмиссия для Veyron была разработана Рикардо. Коробка передач с двумя сцеплениями и семью включенными передачами. Porsche PDK – это работа… ZF, BorgWarner и Aichi Machine Industry, которые совместно разрабатывают и производят трансмиссию для Nissan GT-R.

Classic Automation Competition

In the previous part, we told you in detail about the creation and development of classic automatic transmissions. We will add that in earlier versions, the pressurized hydraulic system activating the locking elements (see below) is mechanically controlled based on vacuum in the manifolds and using a centrifugal regulator. Later everything is based on electronics and parameters related to motor control. It is important to note that the new synthetic oils also make a significant contribution to the precise performance of modern transmissions. However, the rapid development of classic automatic transmissions in recent years has helped them become today unsurpassed in terms of gear shifting comfort with exceptional smoothness and high speed, and so far they are the leaders in the number of gears (already 9). The quick disconnection of the torque converter makes them more efficient and without interruption of traction, which brings them closer to the DSG, the shift times are getting shorter and shorter, and with the help of pressure accumulators the start-stop system is not integrated. question. It is interesting to note that while buses use mostly classic automatic transmissions, the priority for large trucks is a manual transmission with automatic pneumatic gear shifting.

Automatic transmissions

Just a decade ago, their future looked promising… After they entered motorsport in the 80s and switched to high-speed sequential gearboxes, they are now less and less common in production cars, giving way to two-speed gearboxes. clutch. Mechanical transmission options with pneumatic and hydraulic shifting remain the priority for trucks, and sequential ones for racing cars. The latter is a rather paradoxical fact and is argued by the FIA ​​by the desire to cut costs. It's gotten to the point where soon all Formula 1 cars are likely to get gearboxes from the same supplier. In addition, they are limited in materials, and in the number of gears, and in the width of the gears - a rather strange decision against the backdrop of the introduction of new turbo engines.

In fact, it all started as a revolution in the extreme Formula 1 incubator, and its conceptual generator was the chief designer of Ferrari in the mid-80s, John Barnard. His deep idea in practice is not to find a new way to switch, but to eliminate the complex and heavy mechanisms in the cab of the car. Since at that time there was already a technological basis in the form of electro-hydraulic devices (as an element of the active suspension of cars), he decided that such an activator could be used for this purpose. It's not even about removing the clutch pedal first. The first prototypes included devices for shifting each gear, and this solution allowed the steering wheel levers to be moved. Only then did the idea come to release the clutch pedal and simultaneously open it with the help of the control electronic brain. This architecture and microprocessor improvements, as well as the introduction of electronically controlled throttles, allow for fully automatic shifting. Will this be the last nail in the coffin of a classic automatic transmission - in the nineties, such voices began to be heard more and more. What's more, automatic transmissions are rapidly improving, moving towards a completely new architecture with an ordered (sequential) design, in which the levers of the shift systems are placed in channels or follow the contours of a rotating drum.

Classic automatic now with manual override

But at the same time that semi-automatic transmissions based on manual transmissions took their first steps in the big sport, Porsche solved the opposite problem by creating a classic automatic transmission with the ability to shift using levers on the steering wheel. Of course, the transmission belongs to ZF, which together with Bosch plays a leading role in the project (Porsche creates the main idea and leads the project, ZF develops the equipment, and Bosch is the management). The implementation of the project is demonstrated in the form of additional equipment for the 911 and 968, and later Audi and Mitsubishi buy licenses for the project. The name of this tiptronic transmission comes from the German word tippen (to push) because of the ability to shift by pushing and pulling a lever. This type of gearbox already has the function of changing its mode depending on the driving style of the driver.

Meanwhile, John Barnard's creation has its rightful place in cars - of course, for those with a sporty spirit, or at least with pretensions to it - such as the Ferrari F360 Modena and the much more modest Alfa 147 Selespeed with a sequential transmission (based on a standard five-speed transmission with an added shifter and the brain of Magnetti-Marelli But, as we mentioned, the birth of the dual-clutch transmission seemed to scorch the ambitions of automatic transmissions in the world of large cars, and the latter turned to more modest models and the possibility of more cheap automation of existing transmissions (such as the Opel Easytronic has meanwhile received its new, third edition). This is implemented by simpler means than the serial architecture - for this an additional control unit is used, which is already quite compact. However, the solution to the designers' long-held dream of synchronized automatic shifting and disengagement remains only a utopia - in practice this never happens, and all transmissions of this type suffer from a lack of harmonious shifting from one gear to another. . Sports car manufacturers have focused on dual clutch transmissions (DCT or DSG). A typical example in this direction is the collaboration between BMW and Getrag, which materialized as a sequential SMG gearbox for the previous generation M5 and converted to a seven-speed DCT gearbox for the current one.

With two clutches without interruption of traction

It all started in 2003 when VW introduced the Direct Shift Transmission (or Direct Schalt Getriebe in German) co-developed with BorgWarner. As soon as it was introduced, it demonstrated the ability to shift faster and without the jerks of manual and automatic transmissions, without loss of traction and without deterioration in consumption due to the lack of a converter. However, going back to history shows that Audi used a similar gearbox in their rally cars back in the mid-80s (like the Sport Quattro S1 Pikes Peak), but the technology will have to wait a while before fast enough electronic systems are available. control for series production, suitable coupling materials and fast hydraulic actuators. Unlike a conventional transmission, the DSG has two coaxial shafts, each with its own clutch. These connectors are arranged concentrically with respect to each other, with the outer connecting to the inner of the two shafts and the inner to the hollow outer section. One of the shafts accepts odd, and the other - even gears. When, for example, the first gear is engaged, the second is already prepared, and the engagement takes place by simultaneously disengaging one and engaging the other without interrupting traction. The gears are driven using classic synchronizers, but instead of mechanical rods and forks, this is done using hydraulic elements. Multi-plate clutches differ in design from those of mechanical transmissions and in this respect are close to the mechanisms that serve as locking elements in automatics - their development has contributed to the evolution of the DSG. However, the two types are not only similar in terms of opening and closing hydraulic clutches, but also in terms of electronic control based on multiple sensors. In earlier versions, the transmission had oil bath clutches for better heat transfer, but with advances in materials, more efficient dry clutches are now being used. DSG transmissions are now a priority mainly for sports models, but are also often used as an alternative for compact and small models such as Ford Focus and Renault Megane (Getrag equipped), VW Golf, Audi A3, Skoda Octavia (VW-BorgWarner). automatic and automated. So today, with the help of electronics, all types of automatic transmissions have the ability to mechanically switch different modes of operation of automatic machines.

And what happened to the variator in the meantime?

The idea of ​​a continuously variable transmission is as old as the world, and projects include many variations. Their problem is usually that there are no gears and the transfer of torque to the sliding surfaces leads to boxing. Back in the early 20th century, the Swiss Weber had such a transmission, but only in 1955 did the Dorn brothers manage to create a practical solution of this kind - the latter appeared in the form of Variomatic in the Dutch DAF car. The main problem with a simple and promising stepless change in a wide range of designs with axially offset hydraulic actuators and tapered elements connected by a beveled belt is their wear. Therefore, in later designs, it was replaced by a high-friction steel segmented metal element, in which the movement is not by pulling, but by pushing, which provides a higher torque. In the late 80s, many companies such as Ford, Fiat, Subaru and ZF began co-production with Van Doorne, and in order to transmit more torque than in 2000, Audi created a CVT transmission using a chain. In 2003, Nissan, which certainly respects these transmissions, thanks in large part to local manufacturer Jatco, equipped the Murano with a CVT transmission, and the current automatic transmission version of the Subaru Legacy uses one from LUK.

Back in the late 19th century, the first CVT transmissions were created, which used direct engagement with discs of different diameters, and in the 20s, Citroen and GM first produced the first production versions. Their interest in this technological solution returned in the late 80s, again with the development of materials, and its custodians were the British company Torotrak and the aforementioned Jatco - the latter as a leader in CVT transmissions. Recently, more and more new solutions of this kind have appeared, such as the Double Rollet CVT Ultimate Transmission, which have not yet shown their viability.

In a standard CVT transmission, a small planetary gear is usually placed in front of the main gear to provide forward, reverse and neutral gears. Various starting solutions use magnetic connectors or a standard converter (Subaru or ZF Ecotronic CVT). CVT gearboxes, which have been neglected for a long time in recent years, are again attracting increased interest, especially from Japanese manufacturers. They still have a large share in the total production of automatic transmissions. Bosch's transmission technologies are increasingly working in this area. As with others, new materials and electronics come to the rescue.

Basic design of a classic automatic transmission

In its new 9G-Tronic transmission, Mercedes uses a so-called hydrodynamic torque converter, which is an extremely complex device, but the principle of its operation is not different from that of the first such devices (see photo). In practice, it consists of a pump connected to the engine flywheel, a turbine connected to gears, and an intermediate element called a stator. The fluid dynamics in this device are extremely complex, but simply the oil placed in it is pumped around its periphery in a circular motion, similar to the top of Figure 8, but in a 50D version in which the intersecting lines are offset. relative to each other. The specific shape of the turbine blades, as a sign of the arm, is in fact an extremely precisely calculated curvature that optimally absorbs the force of the flow, which, in turn, changes direction abruptly. As a result, the torque increases. Unfortunately, as soon as the direction changes, the flow already has a negative effect, because it is directed back against the pump blades. Here the stator comes to the rescue, whose role is to change the direction of the flow, and it is this element that turns the device into a torque converter. It is designed in such a way that it has a locking mechanism that keeps it stationary under this pressure. As a consequence of all of the above, at start-up, the greatest increase in torque. Although the flow is reversed at a certain speed, as its circumferential speed of the turbine gradually increases in the opposite direction, its net speed becomes the same as in the direction of the turbine. To understand this, imagine you are driving a tram at 30 km/h and you are bouncing a ball back at 20 km/h. In this case, the oil flow passes behind the stator blades, its blocking is disabled and it begins to rotate freely, and when 90 percent of the pump speed is reached, the vortex flow becomes radial and the increase in torque stops. Thus, the car starts and accelerates, but this is always associated with losses, even with modern units. In modern transmissions, shortly after starting, the converter is turned off, or rather, its action is blocked with the help of the so-called. lock-up clutch, which increases the overall efficiency of the transmission. In hybrid versions, such as the ZF 8HP, it is replaced by an electric motor that increases torque, and in some solutions, such as the AMG 7G-DCT, the converter is replaced by a set of plate clutches. And yet - to optimize the dynamics of the oil flow, in some cases, the stator blades have a changing angle of attack, which, depending on the situation, changes the torque.

Set of planetary gears

As mentioned in the previous section, the planetary gear was chosen as the most suitable gear due to its ability to handle various gears without gears or synchronizers. The mechanism is a ring gear (crown) with internal teeth, a sun gear and planetary wheels rubbing it and coupled with the crown ring, which are connected to a common guide. When one of the elements (crown, guide or sun wheel) is locked, torque is transferred between the other two, and the gear ratio depends on the design. The locking elements can be clutches or band brakes and are actuated by hydraulic actuators mechanically in older transmissions and electronically controlled in newer ones. Even early automatic transmissions such as the GM Hydra-Matic or Chrysler Torque-Flite did not use conventional planetary gears but composite designs such as Simpson's. The latter is named after its creator, American engineer Howard Simpson, and includes two completely identical planetary (epicyclic) gears, in which one of the parts of the second is connected to the first (for example, a guide with a sun wheel). In this case, the fixing elements are two multi-plate clutches, two brake belts, as well as a one-way clutch that provides direct transmission of torque. A third mechanism, providing a so-called overdrive, can be added separately to the gearbox. A number of more modern designs use a more complex than conventional planetary gear, such as the Ravigneaux (named after its creator, Paul Ravigneau), which is combined with one and two standard gears to increase the number of gears to five. It includes a common corona and a combination of two different types of satellites and solar wheels, between which even more complex energy flows take place. ZF's first 6-speed automatic transmission, introduced in 2002, uses the Lepelletier mechanism (designer Paul Lepelletier), which resulted in fewer components, less weight and volume. The intelligence of modern solutions lies mainly in the ability, thanks to computer analysis, to integrate more compact locking mechanisms, shafts and gears, allowing more elements to interact and, therefore, to achieve more gears.

At the forefront of 9 gears: Mercedes 9G-Tronic.

The new Mercedes 9G-Tronic transmission has a gear ratio (gear ratio from first to ninth) of 9,15. Thus, equipped with this transmission, the E 350 Bluetec can travel in ninth gear at 120 km / h at just 1350 rpm. The ability to move at lower speeds is also supported by a dual torsion damper replacing the flywheel, combined with a centrifugal pendulum device. Although it can handle up to 1000 Nm of torque, this drivetrain, based on a huge number of computer simulations, is lighter and more compact than before. The two-piece housing is made of aluminum in the hydrodynamic torque converter and magnesium alloys otherwise with a polymer crankcase. Numerous analyzes were performed before the possibility of realizing nine gears with only four planetary gears was achieved. This transmission will be widely used in other transverse-mount models, and the DSG will be used for compact models.

Fantastic recoil ZF: 9HP

The roots of the 9HP can be traced back to 2006 when ZF decided to return to the transverse segment (previous products were four-speed and CVT transmissions, which were discontinued in the late 90s). It usually takes about 4 years to develop, but the company doesn't want them to come back with a 6-speed automatic because they already exist. The fact that the company takes 7 years to complete the goal speaks to the tremendous design work that went into creating this transmission. The solution is an incredibly high-tech solution that, even in the 480 Nm version, weighs only 86 kg. Thanks to the new gearbox, fuel consumption is reduced by about 10 percent compared to a 6-speed gearbox, and at a constant speed of 120 km / h the reduction is 16 percent. Intelligent architecture includes the placement of four planetary gears nested within each other and the addition of additional pin connectors that have less residual friction when open. A multi-stage damping system has been added to the torque converter.

Text: Georgy Kolev

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