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 car companies and suppliers are bound by complex relationships and agreements leading to 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, the automatic transmission is now paramount, and for Europeans, the manual transmission remains the 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 recover from the ruins of war. History shows that in the 2000s, the picture was not very different, although in Europe in some places automation began to appear in more luxurious cars. Only in the 90s, the emergence of electronic government began to change the situation in favor of automatic transmissions and the Old Continent. But even in 80, when the share of automation in new cars in the United States reached 15, and in Japan - 4 percent, only 5 percent of Europeans chose this solution. Of course, in this case, the psychological component and the very purposeful desire of the latter to change gears on their own cannot be underestimated. At the time, they were still predominantly 2002 and 6th gears - it wasn't until year 8 that ZF introduced the first generation of its 8HP six-speed transmission to increase the number to XNUMX, seven years later in the ZF XNUMXHP. The latter becomes a real revolution not only with the number of gears, but also with ideal working comfort, which, thanks to the company's engineers BMW and their precise integration into the seventh series is perfected.
This is truly a period of incredible change because at that 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 to 46 percent in 2014. Despite the increase in the number of gears, the size and weight are decreasing, and there is already something for everyone. Even small cars like Honda The Jazz will also receive dual-clutch transmissions. Mercedes and ZF represent nine staged units in succession. Active joint development of GM and Ford who are working hard on a project for a ten-speed automatic transmission to withstand in America Chrysler, which in the meantime releases the licensed version of the ZF 8HP. While the evolution of manual transmissions is moving towards better gears, easier and more precise gear changes, and some cars to the point where it would be sacrilege to deprive them of them, the automatic now has a huge range of options. Of all automatic transmission vehicles sold in 2014, 49 percent are classic automatic transmissions with 6 or more gears, and only 15 percent have less than 6 gears. CVT transmissions account for 20 percent, dual-clutch transmissions for 9 percent, and automated manual transmissions for just 3 percent, as do hybrid and electric vehicle transmissions. There are some strict specificities behind these numbers: the main share of DSG transmissions, for example, is on the market in Europe, classic - in Europe and the USA, and a high share of CVT transmissions is in Japan. At the same time, the new units are in no way heavier or larger than their predecessors - if the 5-speed automatic transmission of Mercedes in 2004 requires four planetary gears and seven locking devices, then thanks to the intelligent architecture, the new 9G-Tronic is it also controls four planetary gears, but with six clutches as locking elements. One thing is clear - very soon even mid-range brands will follow the luxury brands and now move to high-gear transmissions - a good example of this is the fact that Opel is in the final stages of development for an eight-speed automatic transmission. The idea of a car with an automatic transmission, which makes the engine accelerate unpleasantly and creates a strange synthetic feeling, has now fully entered the annals of history.
Alliances and agreements
However, Mercedes is rather one of the exceptions as an automobile manufacturer that designs and manufactures its own transmissions. Mazda, PSA and Hyundai/ Kia, but in practice most car manufacturers are heavily involved in complex relationships and joint ventures both with each other and with transmission suppliers such as ZF and Aisin. With the 8-speed automatic ZF in different variants, for example, the models are equipped with Audi, BMW and Rolls-Royce... Under the licensing agreement, Chrysler produces the same powertrain for the Evasion, Chrysler, and JeepBut also for Maserati и Fiat... GM makes an eight-speed Hydra-Matic for the Corvette itself, but teamed up with Aisin to develop an eight-speed transmission for Cadillac and supplied automatic transmissions to BMW ten years ago. At the same time, the American giant is working with Ford on a ten-speed transmission, while its European division, Opel, is developing its own eight-speed transmission. Hyundai / Kia have also developed their own eight-speed transmission. Getrag, which in the meantime has gained extensive experience in the production of dual-clutch transmissions, offers its units for both compact Ford models and for Renaultand also for the M-versions of BMW, and two clutches for them in most cases are supplied by LUK. The famous VW and Audi DSG drivetrain was designed with BorgWarner, while the Veyron drivetrain was designed by Ricardo. Transmission with two clutches and seven gears. Porsche PDK is the work of ... ZF, BorgWarner and Aichi Machine Industry jointly develop and manufacture a transmission for 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.
Just ten years ago, their future looked promising ... After they entered motorsport in the 80s and switched to high-speed sequential gearboxes, they are now less common in production cars, giving way to two-speed gearboxes. clutch. Pneumatic and hydraulic shifting manual transmission options remain a priority for trucks, while sequential transmission options for racing cars. The latter is a rather paradoxical fact and is argued by the FIA's desire to cut costs. It got to the point that soon all Formula 1 cars will probably receive transmissions from the same supplier. In addition, they are limited both in materials, and in the number of gears, and in the width of gears - a rather strange decision against the background of the introduction of new turbo engines.
In fact, it all started as a revolution in the extreme incubator of Formula 1, and its concept generator was the chief designer of Ferrari in the mid-80s, John Barnard. Its deep idea in practice is not to find a new way of shifting, but to eliminate complex and heavy mechanisms in the car's cabin. 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 a matter of first removing the clutch pedal. The first prototypes included devices for shifting each gear, and this solution allowed for the shifting of the steering wheel levers. Only then did the idea come up to release the clutch pedal and simultaneously open it with the help of a control electronic brain. This architecture and microprocessor advancements, as well as the introduction of electronically controlled throttle valves, allow for fully automatic gear shifting. Will this not be the last nail in the coffin of the classic automatic transmission - in the nineties such voices began to be heard more and more. Moreover, the automatic transmission is rapidly improving, moving to a completely new architecture with an ordered (sequential) design in which the shift levers are placed in channels or follow the contours of the rotating drum.
Classic automatic now with manual override
But at the same time that semiautomatic transmissions based on manual transmissions took their first steps in the 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 powertrain belongs to ZF, which together with Bosch plays a leading role in the project (Porsche creates the basic idea and leads the project, ZF develops the equipment, and Bosch leads the management). The implementation of the project is shown as optional equipment for the 911 and 968 and later Audi and Mitsubishi buy licenses for the project. The name of this gearbox, tiptronic, comes from the German word tippen (to push) due to the ability to shift by pushing and pulling the lever. This type of transmission already has the function of changing its mode depending on the driving style of the driver.
Meanwhile, John Barnard's creation takes its rightful place in cars - of course, for those with a sporty spirit, or at least with claims to it - such as the Ferrari F360 Modena and the much more modest Alfa 147 Selespeed with sequential transmission (based on a standard five-speed gearbox with an added shift mechanism and Magnetti-Marelli brain.But as we mentioned, the birth of the dual-clutch transmission seemed to inflame the ambitions of automatic transmissions in the large-car world, and the latter turned to more modest models and the possibility of more cheap automation of existing transmissions (such as the Opel Easytronic). meanwhile received its new, third edition). This is realized in simpler ways than a serial architecture - for this, an additional control unit is used, which is already quite compact. Nevertheless, the solution to the long-standing dream of designers of synchronized automatic shifting and decoupling 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 an SMG sequential transmission for the previous generation M5 and converted to a seven-speed DCT for the current one.
With two clutches without interruption of traction
It all started in 2003, when VW introduced the Direct Shift Gearbox (or Direct Schalt Getriebe in German), co-developed with BorgWarner. As soon as it appeared, it demonstrated the ability to shift faster and without the jolt of manual and automatic transmissions, without losing traction and without degrading consumption due to the lack of a converter. However, going back to history reveals that Audi used a similar gearbox in its rally cars back in the mid-80s (like the Sport Quattro S1 Pikes Peak), but the technology has to wait a while before fast enough electronic systems emerge. control for batch production, suitable coupling materials and fast hydraulic actuators. Unlike conventional transmissions, the DSG has two coaxial shafts, each with its own clutch. These connectors are located concentrically with respect to each other, with the outer connected 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 occurs by simultaneously disabling one and engaging the other without interrupting the traction. The gears are driven using classical 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 mechanisms that serve as locking elements in automation - their development has contributed to the evolution of the DSG. However, the two types are similar not only 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 used. DSG transmissions are now a priority mainly for sports models, but are also often used as alternatives for compact and small models such as the Ford Focus and Renault Megane (equipped with Getrag), 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 the automatic transmissions.
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 the gears are missing and the transmission of torque to the sliding surfaces results in boxing. At the beginning of the 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 a Variomatic in the Dutch car DAF. The main problem with a simple and promising continuously variable changeover in a wide range of designs with axially offset hydraulic actuators and conical elements connected by a bevel belt is their wear. Therefore, in later developments, it was replaced by a segmented metal element made of steel with a high coefficient of friction, in which the movement is not driven by thrust, 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 definitely respects these transmissions, thanks in large part to local manufacturer Jatco, equipped the Murano with a CVT, and the current version of the Subaru Legacy with automatic transmission uses such a transmission from LUK.
At the end of the 19th century, the first variator transmissions were created, in which direct engagement with discs of different diameters was used, and in the 20s Citroen and GM release the first production variants for the first time. Their interest in this technological solution returned in the late 80's, again with the development of materials, and its custodians were the British company Torotrak and the aforementioned Jatco - the latter as the leader in the field of CVT transmissions. Recently, there are more and more new solutions of this kind, such as the Double Rollet CVT Ultimate Transmission, which have not yet demonstrated 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 the so-called hydrodynamic torque converter, which is an extremely complex device, but its principle of operation does not differ from that of the first such devices (see photo). In practice, it consists of a pump connected to the flywheel of an engine, a turbine connected to the gears, and an intermediate piece called a stator. The fluid dynamics in this device is extremely complex, but the oil placed in it is simply pumped around its periphery in a circular motion, similar to the upper part of Figure 8, but in a three-dimensional version in which the intersecting lines are offset. relative to each other. The specific shape of the turbine blades, as a sign of the bracket, is in fact an extremely precisely calculated curvature, which 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 backwards against the pump blades. Here the stator comes to the rescue, the role of which is to change the direction of 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 at this pressure. Because of all of the above, at start-up, the largest increase in torque. Although the flow is directed in the opposite direction at a certain speed, with a gradual increase in its peripheral speed of the turbine in the opposite direction, its net speed becomes the same as in the direction of the turbine. To understand this, imagine that you are driving a tram at a speed of 50 km / h and throw the ball back at a speed of 30 km / h. For you, it is moving backward, but in fact, the direction of travel is forward at a speed of 20 km / h. If the oil flow passes behind the stator blades, its blocking is disengaged 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, soon after starting, the converter is turned off, or rather, its action is blocked using the so-called. locking 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 oil flow, in some cases the stator blades have a variable angle of attack, which changes the torque depending on the situation.
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 a variety of gears without gears or synchronizers. The mechanism consists of a ring gear (crown) with internal teeth, a sun gear and planetary wheels, rubbing it and meshing 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. Locking elements can be clutches or band brakes and are actuated by hydraulic actuators mechanically in old transmissions and electronically in new ones. Even the first automatic transmissions, such as the GM Hydra-Matic or Chrysler Torque-Flite, used composite structures such as Simpson instead of conventional planetary gears. The latter is named after its creator, the American engineer Howard Simpson, and includes two completely identical planetary (epicyclic) gears, in which one of the second parts 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 a direct transmission of torque. A third mechanism providing the so-called overdrive can be added separately to the gearbox. A number of more modern designs use a more sophisticated planetary gear than a conventional planetary gear, such as the Ravigneaux (named after its creator Paul Ravigno), 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. The first 6-speed automatic transmission from ZF, introduced in 2002, uses a Lepelletier mechanism (designed by Paul Lepeletier), which has 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 reach 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