Test drive The history of car transmissions - Part 1

In a series of articles we will tell you about the history of transmissions for cars and trucks - perhaps as a nod to the occasion of the 75th anniversary of the creation of the first automatic transmission.

1993 During pre-race testing at Silverstone, Williams test driver David Coulthard left the track for the next test in the new Williams FW 15C. On wet pavement, the car splashes everywhere, but still everyone can hear the strange monotonous high-speed sound of a ten-cylinder engine. Obviously, Frank William uses a different kind of transmission. It is clear to the enlightened that this is nothing more than a continuously variable transmission designed to meet the needs of a Formula 1 engine. Later it turned out that it was developed with the help of the ubiquitous Van Doorn specialists. transmission of infection. The two conspiring companies have poured huge engineering and financial resources into this project over the past four years to create a fully functional prototype that could rewrite the rules of dynamics in the sports queen. In the YouTube video today you can see the tests of this model, and Coulthard himself claims that he likes her work - especially in the corner, where there is no need to waste time downshifting - everything is taken care of by electronics. Unfortunately, everyone who worked on the project lost the fruits of their labor. Legislators were quick to ban the use of such passes in Formula, allegedly due to "unfair advantage". The rules were changed and V-belt CVT or CVT transmissions were history with only this brief appearance. The case is closed and Williams should return to semi-automatic transmissions, which are still standard in Formula 1 and which, in turn, became a revolution in the late 80s. By the way, back in 1965, DAF with the Variomatic transmission made attempts to enter the motorsport track, but at that time the mechanism was so massive that even without the intervention of subjective factors it was doomed to failure. But that is another story.

We have repeatedly cited examples of how much innovation in the modern automotive industry is the result of old ideas born in the heads of extremely gifted and discerning people. Because of their mechanical nature, gearboxes are one of the prime examples of how they can be implemented when the time is right. Nowadays, the combination of advanced materials and manufacturing processes and e-government has created the opportunity for incredibly effective solutions in all forms of transmission. The trend towards lower consumption on the one hand and the specifics of new engines with reduced dimensions (for example, the need to quickly overcome a turbo hole) lead to the need to create automatic transmissions with a wider range of gear ratios and, accordingly, a large number of gears. Their more affordable alternatives are CVTs for small cars, often used by Japanese automakers, and automatic manual transmissions such as Easytronic. Opel (also for small cars). The mechanisms of parallel hybrid systems are specific, and as part of the emission reduction efforts, drive electrification actually occurs in transmissions.

An engine cannot do without a gearbox

To date, mankind has not invented a more efficient way of direct transmission of mechanical energy (except, of course, hydraulic mechanisms and hybrid electrical systems) than methods using belts, chains and gears. Of course, there are countless variations on this topic, and you can better understand their essence by listing the most outstanding developments in this area in recent years.

The concept of electronic shifting, or electronic indirect connection of the control mechanism to the gearbox, is far from the last cry, because in 1916 the Pullman company of Pennsylvania created a gearbox that shifts gears electrically. Using the same working principle in an improved form, twenty years later it was installed in the avant-garde Cord 812 - one of the most futuristic and wonderful cars not only in 1936, when it was created. It is significant enough that this cord can be found on the cover of a book about the achievements of industrial design. Its transmission transmits torque from the engine to the front axle (!), and the gearshift is direct filigree for the then representation of the steering column, which activates special electrical switches that activate a complex system of electromagnetic devices with vacuum diaphragms, including gears. Cord designers managed to combine all this successfully, and it works great not only in theory, but also in practice. It was a real nightmare to set up synchronization between gear shifting and clutch operation, and, according to the evidence of the time, it was possible to send a mechanic to a psychiatric hospital. However, the Cord was a luxury car, and its owners could not afford the casual attitude of many modern manufacturers to the accuracy of this process - in practice, most automated (often called robotic or semi-automatic) transmissions shift with a characteristic delay, and often gusts.

No one is claiming that synchronization is a much easier task with the simpler and more widespread manual transmissions today, because the question "Why is it necessary to use such a device at all?" Has a fundamental character. The reason for this complex event, but also opening up a business niche for billions, lies in the very nature of the combustion engine. Unlike, for example, a steam engine, where the pressure of the steam supplied to the cylinders can change relatively easily, and its pressure can change during start-up and normal operation, or from an electric motor, in which a strong driving magnetic field also exists at zero speed. per minute (in fact, then it is the highest, and due to the decrease in the efficiency of electric motors with increasing speed, all manufacturers of transmissions for electric vehicles are currently developing two-stage options) an internal combustion engine has a characteristic in which maximum power is achieved at speeds close to maximum, and the maximum torque - in a relatively small range of speeds, in which the most optimal combustion processes occur. It should also be noted that in real life the engine is rarely used on the maximum torque curve (correspondingly on the maximum power development curve). Unfortunately, the torque at low revs is minimal, and if the transmission is directly connected, even with a clutch that disengages and allows for start-off, the car will never be able to perform actions such as starting, accelerating and driving at a wide speed range. Here is a simple example - if the engine transmits its speed 1: 1, and the tire size is 195/55 R 15 (for now, abstracting from the presence of the main gear), then theoretically the car should move at a speed of 320 km. / h at 3000 crankshaft revolutions per minute. Of course, cars have direct or close gears and even crawler gears, in which case the final drive also comes into the equation and must be taken into account. However, if we continue the original logic of reasoning about driving at a normal speed of 60 km / h in the city, the engine will need only 560 rpm. Of course, there is no motor capable of doing such a twine. There is one more detail - because, purely physically, power is directly proportional to torque and speed (its formula can also be defined as speed x torque / a certain coefficient), and the acceleration of a physical body depends on the force applied to it. , understand, in this case, the power, it is logical that for faster acceleration you will need higher speeds and more load (i.e. torque). It sounds complicated, but in practice this means the following: every driver, even one who does not understand anything in technology, knows that in order to quickly overtake a car, you need to shift one or even two gears lower. Thus, it is with the gearbox that it instantly delivers higher revs and therefore more power for this purpose with the same degree of pedal pressure. This is the task of this device - taking into account the characteristics of the internal combustion engine, to ensure its operation in the optimal mode. Driving in first gear at a speed of 100 km / h will be quite uneconomical, and in sixth, suitable for the track, it is impossible to get under way. It is no coincidence that economical driving requires early gearshifts and the engine running at full load (i.e. driving slightly below the maximum torque curve). Experts use the term "low specific power consumption", which is in the middle rev range and close to the maximum load. Then the throttle valve of gasoline engines opens wider and reduces pumping losses, increases cylinder pressure and thereby improves the quality of chemical reactions. Lower speeds reduce friction and allow more time to fill completely. Race cars always run at high speeds and have a large number of gears (eight in Formula 1), which allows for reduced speed when shifting and limits the transition to areas with significantly less power.

In fact, it can do without a classic gearbox, but ...

The case of hybrid systems and in particular hybrid systems such as the Toyota Prius. This car does not have a transmission of any of the listed types. It has virtually no gearbox! This is possible because the aforementioned shortcomings are compensated for by the electrical system. The transmission is replaced by a so-called power splitter, a planetary gear that combines an internal combustion engine and two electric machines. For people who have not read the selective explanation of its operation in books on hybrid systems and especially on the creation of the Prius (the latter are available on the online version of our site ams.bg), we will only say that the mechanism allows part of the mechanical energy of the internal combustion engine to be transferred directly, mechanically and partially, be converted into electrical (with the help of one machine as a generator) and again into mechanical (with the help of another machine as an electric motor). The genius of this creation by Toyota (whose original idea was the American company TRW from the 60s) is to provide high starting torque, which avoids the need for very low gears and allows the engine to operate in efficient modes. at maximum load, simulating the highest possible gear, with the electrical system always acting as a buffer. When simulation of acceleration and downshift is required, the engine speed is increased by controlling the generator and, accordingly, by its speed using a sophisticated electronic current control system. When simulating high gears, even two cars have to switch roles to limit the speed of the engine. At this point, the system enters "power circulation" mode and its efficiency is significantly reduced, which explains the sharp display of fuel consumption of this type of hybrid vehicles at high speeds. Thus, this technology is in practice a compromise convenient for urban traffic, since it is obvious that the electrical system cannot fully compensate for the absence of a classic gearbox. To solve this problem, Honda engineers are using a simple yet ingenious solution in their new sophisticated hybrid hybrid system to compete with Toyota - they simply add a sixth manual transmission that engages in place of the high-speed hybrid mechanism. All this may be convincing enough to show the need for a gearbox. Of course, if possible with a large number of gears - the fact is that with manual control it will simply not be comfortable for the driver to have a large number, and the price will increase. At the moment, 7-speed manual transmissions such as those found in Porsche (based on DSG) and Chevrolet Corvettes are quite rare.

It all starts with chains and belts

So, different conditions require certain values of the required power depending on the speed and torque. And in this equation, the need for efficient engine operation and reduced fuel consumption, in addition to modern engine technology, transmission is becoming an increasingly important challenge.

Naturally, the first problem that arises is starting - in the first passenger cars, the most common form of gearbox was a chain drive, borrowed from a bicycle, or a belt drive acting on belt pulleys of different diameters. In practice, there were no unpleasant surprises in the belt drive. Not only was it as noisy as its chain partners, but it also couldn't break teeth, which was known from the primitive gear mechanisms that drivers at the time referred to as "transmission lettuce". Since the turn of the century, experiments have been carried out with the so-called "friction wheel drive", which has no clutch or gears, and uses Nissan and Mazda in their toroidal gearboxes (which will be discussed later). However, the alternatives to gear wheels also had a number of serious drawbacks - the belts could not withstand prolonged loads and increasing speeds, they quickly became loose and torn, and the "pads" of the friction wheels were subjected to too rapid wear. In any case, shortly after the dawn of the automotive industry, gears became necessary and remained the only option at this stage for transmitting torque for quite a long period of time.

The birth of a mechanical transmission

Leonardo da Vinci designed and manufactured cogwheels for his mechanisms, but the production of strong, reasonably accurate and durable cogwheels became possible only in 1880 thanks to the availability of appropriate metallurgical technologies for creating high-quality steels and metalworking machines. relatively high accuracy of work. Friction losses in gears are reduced to only 2 percent! This was the moment when they became indispensable as part of the gearbox, but the problem remained with their unification and placement in the general mechanism. An example of an innovative solution is the Daimler Phoenix of 1897, in which gears of various sizes were "assembled" into a real, according to today's understanding, a gearbox, which, in addition to four speeds, also has a reverse gear. Two years later, Packard became the first company to use the well-known positioning of the gear lever at the ends of the letter "H". In the following decades, the gears were no more, but the mechanisms continued to be improved in the name of easier work. Carl Benz, who equipped his first production cars with a planetary gearbox, managed to survive the appearance of the first synchronized gearboxes created by Cadillac and La Salle in 1929. Two years later, synchronizers were already in use by Mercedes, Mathis, Maybach and Horch, and then another Vauxhall, Ford and Rolls-Royce. One detail - all had an unsynchronized first gear, which greatly annoyed the drivers and required special skills. The first fully synchronized gearbox was used by the English Alvis Speed Twenty in October 1933 and was created by the famous German company, which still bears the name "Gear Factory" ZF, which we will often refer to in our story. It wasn't until the mid-30s that synchronizers began to be installed on other brands, but in cheaper cars and trucks, drivers continued to struggle with the gear lever to move and shift gears. In fact, a solution to the problem of this kind of inconvenience was sought much earlier with the help of various transmission structures, also aimed at constantly meshing gear pairs and connecting them to the shaft - in the period from 1899 to 1910, De Dion Bouton developed an interesting transmission in which the gears are constantly meshed, and their connection to the secondary shaft is carried out using small couplings. Panhard-Levasseur had a similar development, but in their development, permanently engaged gears were firmly connected to the shaft using pins. The designers, of course, did not stop thinking about how to make it easier for drivers and protect cars from unnecessary damage. In 1914, Cadillac engineers decided that they could harness the power of their huge engines and equip cars with an adjustable final drive that could shift electrically and change the gear ratio from 4,04: to 2,5: 1.

The 20s and 30s were a time of incredible inventions that are part of the constant accumulation of knowledge over the years. For example, in 1931, the French company Cotal created an electromagnetically shifted manual transmission controlled by a small lever on the steering wheel, which, in turn, was combined with a small idle lever placed on the floor. We mention the latter feature because it allows the car to have exactly as many forward gears as there are four reverse gears. At that time, prestigious brands such as Delage, Delahaye, Salmson and Voisin were interested in Kotal's invention. In addition to the aforementioned bizarre and forgotten "advantage" of many modern rear-wheel drive gears, this incredible gearbox also has the ability to "interact" with a Fleschel automatic shifter that shifts gears as speed drops due to engine load and is in fact one of the first attempts to automate process.

Most cars from the 40s and 50s had three gears, because the engines did not develop more than 4000 rpm. With the increase in revs, torque and power curves, the three gears no longer covered the rev range. The result was a disharmonious movement with a characteristic "stunning" transmission when lifting and excessive forcing when shifting to a lower one. The logical solution to the problem was the massive shift to four-speed gears in the 60s, and the first five-speed gearboxes in the 70s were a significant milestone for manufacturers who proudly noted the presence of such a gearbox along with the model on the car. Recently, the owner of a classic Opel Commodore told me that when he bought the car, it was in 3 gears and averaged 20 l / 100 km. When he replaced the gearbox with a four-speed gearbox, consumption was 15 l / 100 km, and after he finally got a five-speed, the latter dropped to 10 liters.

Today, there are practically no cars with less than five gears, and six speeds are becoming the norm in higher versions of compact models. The sixth idea in most cases is a strong reduction in speed at high revs, and in some cases, when it is not so long and the reduction in speed drops when shifting. Multi-stage transmissions have a particularly positive effect on diesel engines, units of which have a high torque, but a significantly reduced operating range due to the fundamental nature of the diesel engine.

(to follow)

Text: Georgy Kolev