Twin turbo Is the commercial designation for an advanced turbocharging system.
The name Biturbo is also used, but you can also find an incorrect designation by this term of a parallel system with two turbines. This term is understood as a multi-link system for pumping air into the cylinders using two or more compressors driven by exhaust gases, which gives an increase in efficiency, power and reduces the toxicity of emissions.
Twin Turbo system
Twin Turbo was designed to solve the key problem of supercharged engines - the elimination of turbo lag, which manifests itself as a decrease in elasticity and a sharp one at low engine speeds, while the turbine has not yet had time to spin up under the pressure of the exhaust gases to optimal speed. This is due to the fact that the impeller of the supercharger is made of special heat-resistant materials with a considerable margin of safety and therefore has a significant weight and moment of inertia.
Even high-tech lightweight ceramic rotors spin up to 200 thousand revolutions per minute in a quite noticeable time. Turbo lag, or turbo-lag, has an extremely negative effect on the dynamic characteristics of the engine, ultimately affecting the active security driver and passengers.
As it turned out later, the dual one allows you to significantly expand the range of rated torque rpm, increase the maximum power and reduce the specific fuel consumption.
Like any system with more than one element, Twin Turbo can be parallel, sequential or staggered. Each of these schemes differs from the other in geometry, dynamic characteristics and the principle of work. The supercharging is controlled by the microcontroller unit, which receives information from the sensors and controls the valves and actuators on the intake and exhaust manifolds.
Working principle and features
Parallel system
A relatively simple system involving a symmetrical pair of compressors operating simultaneously to evenly distribute the incoming air. Most often, this scheme is used on V-shaped diesel engines where each compressor supplies air to the intake manifold of its cylinder group.
The decrease in inertia is achieved by reducing the mass of the turbine rotor, as you know, two small compressors provide slightly more pressure and spin faster than one, but larger in size and performance. Thus, the width of the turbo lag is significantly reduced, and the engine provides several best performance throughout the entire rev range.
Sequential system
With this arrangement, two comparable compressors (not necessarily the same in characteristics) operate in a complementary mode.
Sequential Twin Turbo circuit:
1 - boost pressure bypass valve; 2 - air supply control valve; 3 - pressure difference sensor; 4 - exhaust gas supply control valve; 5 - secondary turbocharger; 6 - intercooler; 7 - primary turbocharger; 8 - wastegate bypass valve.
One, usually lighter and faster, the supercharger works constantly, eliminating a deep and wide turbo lag, the second, according to the signal from the electronics that monitors the engine speed, is switched on in heavier modes, ensuring maximum power and fuel efficiency. Such a series-parallel scheme (in peak modes, both turbines operate simultaneously) is used on engines of any fuel cycle.
In 2011, German BMW introduced the advanced Triple Turbo sequential charging system.
Step system
The most sophisticated and progressive system providing the widest power range.
Variable two-stage turbocharging scheme:
1 - charge air cooler; 2 - pressure bypass valve (bypass); 3 - turbocharger of the high pressure stage; 4 - stage turbocharger low pressure; 5 - wastegate bypass valve.
To create such a boost, two different-sized compressors are installed, connected to each other by a system of pipes and bypass valves.
This type of turbocharging is called staged due to the fact that in minimum modes the exhaust gases spin up a small turbine, and the engine spins up easily. As the speed rises, the valve opens and the large turbine begins to spin, but the pressure it creates needs to be increased, which is what the small turbine next to it does.
When reaching maximum speed, a large turbine produces so much high pressure that the small supercharger becomes drag. At this moment, the automation opens the bypass valve, and the compressed the air goes into the engine, bypassing the smaller of the turbines.
Rice - the operation of the variable two-stage turbocharging system
The complexity of such a system is more than compensated for by the flexibility of operation and the highest performance of the engine.
Modern Twin Turbo systems use other technical tricks to provide less inertia and more power. Electronic regulation of the volume of exhaust gases on the turbine wheel, variable geometry of the blades, a bleed valve, an unforgettable whistle of which indicates the safe removal of excess air in the intake manifold during gas discharge. The bypass valve is able not only to turn on and off the turbine that is not being used at a given moment, but also to maintain pressure during short-term closing of the throttle, returning the stock to the intake manifold instantly, during the valve closure.
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A system as important as the Twin Turbo can be used in many different ways. It can be one radiator with a common manifold, or separate coolers for each supercharger. A stepped system, for obvious reasons, always dispenses with one radiator.
Turbocharged engines are not as simple as it seems, there are many misunderstandings and uncertainties hovering around this topic. One of these is about two buildings "bi-turbo" and "twin-turbo". Not so long ago, he personally witnessed a conversation between two car owners, one assured that there was a difference, but the other that there were no differences! So what's the truth? Indeed, what is the difference between these two structures of TURBO motors, let's figure it out ...
To be honest, there will be a difference, of course, but it will not be categorical! Only because the names are taken from different manufacturers who install their units with different layouts and structures.
However, system "Bi-turbo" and "Twi-nturbo" - essentially the same thing. If you take the English language and look at the designation, Bi-Turbo and Twin-Turbo, you can see two prefixes « Bi "and" Twin " - if roughly translated, it turns out - "TWO" or "TWO". Nothing else - as the designation of the presence of two turbines on the engine, and one and the other name can be applied to the same engine, that is, they are absolutely - interchangeable. These names do not carry any technical differences, so this is "naked marketing".
Two turbines per engine - how and why?
Now the question may arise, why bother? It's just that there are only two questions that they are designed to solve:
- Elimination, we can say that this is the primary problem.
- Increased power.
- Engine structure.
I'll start with perhaps the simplest point - this is engine structure ... Of course, it's easy to fit a single turbine when you have a 4 or 6 cylinder inline engine. The muffler is one. But here's what to do when you have, say, a V-shaped motor? And three - four cylinders for each side, then there are two mufflers! So they put on each of the turbines, medium or low power.
Elimination of turbo lag - as I wrote above, this is problem number "1". The thing is that the turbocharged engine has a failure - when you press the gas, the exhaust gases need to go through and spin the turbine impeller, it is this time that the power "sags", it can be from 2 to 3 seconds! And if you need to make an overtaking maneuver at speed, this is not safe! So they install various turbines, and often a compressor + turbine. One works at low revs, that is, at the start to avoid "turbo lag", the second - at a speed when you need to leave traction.
Increase in power - this is the most commonplace case. That is, to increase the engine power, another powerful turbine is installed to the low-power turbine, thus they blow two, which significantly increases productivity. By the way, on some racing cars, there are three or even four turbines, but it is very difficult and usually does not go into series production!
Here are the solutions for which "TWINTURBO" or "BITURBO" are used and you know this is a real way out of getting rid of the turbo lag and increasing power.
About the structure
Now, on many cars, only two main structures are used - the location of two turbines. It is parallel and sequential (also known as sequential).
For example, some Mitsubishi have exactly "TWINTURBO", but the parallel operation, as I noted above, is two turbines on the V6 unit, one on each side. They blow into a common collector. But, for example, on some AUDI, there is also a parallel operation on the V6 engine, but the name is "BITURBO".
On Toyota cars, in particular on "SUPRA", there is a straight-six, but there are also two boosts - they work in a tricky order, two can work at once, one can work, the other does not, can be switched on alternately. It all depends on your driving style - they achieve this work with "tricky" bypass valves. Here's a serial-parallel job.
As in some SUBARU cars - the first (small) blows air at low rpm, the second (large) is connected only when the rpm has increased significantly, so you have a parallel connection.
So is there a difference or not at all? You know, behind the scenes, manufacturers still distinguish these two structures, let's take a closer look.
BI-TURBO (BI-TURBO)
As a rule, these are two turbines connected in series. In a striking example, SUBARU - one small and then another large.
The small one spins up much faster, because it does not have a lot of inertial energy - it is logical that it is included in the work at the bottom, that is, the first. For low speeds and up to low revs, this is quite enough. But at high speeds and revs, this "baby" is practically useless, here you need a supply of a much larger volume of compressed air - a second heavier and more powerful turbine is turned on. Which gives you the power and performance you need. What is the benefit of such a consistent placement in BI-TURBO? This is almost the exception of turbo lag (comfortable acceleration) and high performance at high speeds, when traction remains even at speeds over 200 km / h.
It should be noted that they can be installed both on the V6 unit (on each side on its own turbine), and on the in-line version (here they can divide the exhaust manifold, for example, one blows from two cylinders, and the other two from the other).
The disadvantages are the high cost and work on setting up such a system. After all, the fine settings of the bypass valves are used here. Therefore, the installation is due to expensive sports cars, such as TOYOTA SUPRA, or on an elite class car - MASERATTI, ASTON MARTIN, etc.
TWIN-TURBO (TWIN-TURBO)
Here, the main task is not to get rid of the "turbo lag", but to maximize productivity (injection of compressed air). As a rule, such a system works on high revs, when one supercharger cannot cope with the increased load on it, therefore another one of the same is installed (in parallel). Together they pump twice as much air for almost the same performance gain!
But what about the "turbo lag" that it is rampant here? But no, she is also effectively defeated only in a slightly different way. As I already said, small turbines spin up much faster, so just imagine - they change 1 big one, for 2 small ones - the performance practically does not decrease (they work in parallel), but the "PIT" leaves because the reaction is faster. Therefore, it turns out, create a normal traction, from the very bottom.
Installation can be both in-line models power units, and V-shaped.
Manufacturing and customization is much cheaper, which is why this structure is used by many manufacturers.
Turbine + compressor
This can also be called "BI-TURBO" or "TWIN-TURBO" - whatever you like. In fact, both the compressor and the turbo version do the same job, only one (mechanical) is much more efficient at the bottom, the other (from exhaust gases) - at the top! ...
I have simplified the wording as much as possible so that the text is available for understanding by a wide range of readers. But for a better understanding of the issue, I recommend reading my past publications about and.
Progress does not stand still, and each new generation of cars must be faster, more economical and more powerful. Combined pressurization systems are often used to increase power, and "conventional" turbines are not at all as simple as it seems at first glance. How did engineers teach turbo engines to be powerful, flexible and fuel efficient at the same time? What technologies make it possible to create mass engines with a specific power of 150 hp? per liter and excellent traction on the bottom, and a thousand monsters?
"Regular" turbine
As I already wrote, a turbocharger is simple at first glance, but it is a high-tech device that works in very harsh conditions. And any complication of it greatly affects the reliability. As an example, I will try to describe in more detail the design of a typical turbocharger without much complication.
The main part of the turbocharger is the middle casing, which houses the sleeve bearings, the thrust bearing and the seal seat with rings. In the case itself there are channels for the passage of oil and coolant through it. On very old structures, they managed only with oil for both lubrication and cooling, but such turbines have not been used on serial machines for a long time. A heat deflector is used to protect the middle housing from hot exhaust gases.
The turbine shaft is installed in the middle housing. This part is not just a shaft; structurally, it is permanently connected to the turbine wheel, most often by friction welding, or is made of a single piece of metal. Sometimes ceramics are used to create the impeller - the strength and corrosion resistance of the best structural steels may not be enough. The shaft itself has a complex shape, it has a thickening for the seal and a thrust ledge, and the shape of the cylindrical part is calculated taking into account thermal expansion during operation.
The compressor wheel is put on the turbine shaft. It is usually made of aluminum and is fixed to the shaft with a nut.
The design of the middle casing, a turbine shaft and a compressor wheel installed in it is called a cartridge. After assembly, this unit is carefully balanced, because it works at very high speeds and the slightest imbalance will quickly disable it.
The turbine also needs two "snails" - a turbine and a compressor. Often they are individual for each machine manufacturer, while the central part is the cartridge and the dimensions of the turbine and compressor wheel are signs of a particular turbine model and its modification.
To protect against too high boost pressure, a gas pressure relief valve is used, it is also a vastegate. It is usually part of a turbine volute and is vacuum operated. It is closed during normal operation of the turbine and opens in case of too high boost pressure or other problems in the operation of the engine, dropping the speed of rotation of the turbine.
And now about how turbines are used and what technologies are used to achieve the highest engine performance.
Twin-turbo and Bi-turbo
The larger and more powerful the motor, the more air needs to be supplied to the cylinders. To do this, you need to make the turbine larger or faster. With what bigger size turbine, the heavier its impeller and the more inertial it turns out. When you press the gas pedal, the throttle valve opens and more of the combustible mixture enters the cylinders. More exhaust gases are generated and they spin the turbine to a higher speed, which in turn increases the amount of fuel mixture supplied to the cylinders. In order to reduce the time to spin up the turbines and the accompanying "turbo lag", we initially tried methods called twin-turbo and bi-turbo.
These are two different technologies, but the marketers of the manufacturing companies have made a lot of confusion. For example, on the Maserati Biturbo and Mercedes AMG Biturbo actually use twin turbo technology. So what's the difference? Originally Twin Turbo ("twin turbines") was a technology in which the exhaust gases were split into two equal streams and distributed over two identical small turbines. This made it possible to obtain the best time response, and sometimes to simplify the design of the motor, using inexpensive turbochargers, which is very important for V-shaped engines with exhaust manifolds "down".
The designation Biturbo ("double turbine") refers to designs in which two turbines, a small and a large one, are connected in series to the inlet. The small one works well at low load, spins up quickly and provides traction “at the bottom”, and then a large turbine comes into action, which is more efficient at high load. The small turbine is turned off at this moment by the throttle valve system.
The advantage of such a scheme is the greater efficiency of one large turbine at high load: it provides better pressure and less heating of the air with a long resource. And instead of a small turbocharger, you can use a mechanical or electric blower. They heat up the air less than a turbocharger and are not inertial.
But what about the power losses that are needed for their promotion? Losses on their drive at low load are not so significant. But the payback for improving the performance of the turbines is the complication of the intake system, you have to use a lot of pipes and throttle valves switching air flows.
Both technologies are still used by all manufacturers, but all of them significantly increase the cost of the engine, because the number of expensive turbochargers is doubled, and the control system for them is more complicated. For highly forced motors, there is little or no alternative to these technologies. But sometimes you can simply improve the design of a standard turbine.
Thin Wastegate Management
Wastegate is literally a "discharge gate", that is, a bypass valve. On the first turbines, the Vastegate works very simply: when the inlet pressure overcomes the spring tension, it opens, bleeds gases and the pressure drops. Later, the system was complicated: now its discovery was guided not only by the pressure difference, but also by electronics, which takes into account many parameters - mixture enrichment, motion mode, temperature, detonation and which is able to avoid unwanted operating modes of the turbine itself. But he was controlled in the same way - pneumatics. When the pressure needed to be relieved, the valve simply opened.
To obtain a qualitative leap in characteristics, it was possible to smoothly adjust the degree of opening of the bypass valve. In this case, the turbine can often work with maximum efficiency, even at low speeds, and at medium loads, regulation comes into play and the turbine does not go into dangerous modes.
Unfortunately, this method is more complicated. To implement it, it was necessary to place an adjustment electric drive next to the turbine, which reduced its reliability: electronics have to work in very harsh conditions, at high temperatures and high vibrations. But the improvement in performance is worth it and almost all modern turbines of high-powered small motors are of this design.
More efficient turbine wheel. Twinscroll
In search of increasing the efficiency of a single turbine, the design thought came up with a method that made it possible to increase the efficiency of the turbine at both low and high loads. The turbine wheel, which is affected by the exhaust gases, was divided into two parts, hence the name of the technology - twin scroll (“double scroll”), one part of the turbine is more efficient at high load, and the other at low load, but they spin the same compressor wheel on a common shaft. The turbine is not much more complicated, but somewhat more efficient.
In combination with the supply of exhaust gases to different parts of the "snail" from different groups cylinders and fine tuning, this allows you to get a good increase in performance without degrading performance in the low speed zone. Of course, such a turbine will not give maximum possible power, but on the other hand, such a motor will be more high-torque and in practice it is more convenient and faster.
More Efficient Turbine Wheel - Variable Geometry Turbines
In a twin-scroll turbine, the exhaust gas is split into two streams and one always operates at a lower efficiency than possible. But there is another way! The turbine guide vanes can be adjusted and the exhaust gases will always work at maximum efficiency. All this requires a very complex mechanical system located in the hottest part of the turbine - on the exhaust "snail". And a complex control mechanism.
The geometry of the turbine inlet is changed using guide vanes. At low speeds, when the exhaust gas pressure is low, the blades turn and narrow the channel. The gases pass through the narrow opening at a higher speed, providing a quick cranking up of the turbine. When the engine speed increases, the blades expand the hole in proportion to the increasing gas pressure, and the turbine speed remains stable.
Improving turbine mechanics
Rolling bearings (with balls) have much better characteristics than plain bearings (with oil) - this is practically an axiom. They allow to reduce friction, which means to make the rotation of the turbine easy, to reduce the mass of the shaft, and to reduce the dependence on oil pressure. But high-precision and very "hardy" rolling bearings for huge rotational speeds and temperatures began to be widely used relatively recently.
Turbines on ceramic (rather than metal) rolling bearings are more reliable and durable, they are not afraid of oil pressure loss and stops, and are less sensitive to vibrations and overheating. Of course, they are more expensive than turbines of the previous generation, and serial models of cars with them appeared only recently, but in motorsport their capabilities have been appreciated for a long time. For example, IHI VF series turbines or Garrett GTxxR / RS have been used in tuning cars for many years.
Finally
Gradually, new technologies are becoming cheaper and are being introduced on more and more mass-produced machines. For the latest generation of motors, electronic regulation of the turbine has become an almost mandatory attribute. Twinscroll variants are being used more and more often. On large V-shaped engines, twin-turbo technology is almost always used, but the turbines are not simple, but use all the necessary arsenal of new manufacturing technologies.
In combination with direct fuel injection, this makes it possible to create motors, the characteristics of which would have been considered fantastic ten years ago - with a power of 400-500 Horse power they are content with 95th gasoline, and they do not "eat" much more than small cars of the recent past. As for reliability modern motors, then I already talked about this in another article, because in technology nothing is given just like that.
From the middle of the 20th century, car manufacturers began to produce cars that are equipped with not one turbine, but two. One of the popular such turbocharging systems is the Biturbo.
Let's take a look at why two turbochargers are installed. This contributes to:
- reducing the effect of turbo lagging;
- improving engine performance in transient conditions;
- greater efficiency;
- better environmental friendliness.
What Biturbo looks like
Technically, the biturbo (bi-turbo) turbocharging system looks like this: a small turbine turns into a large one.
The principle of operation of the Biturbo turbocharging system
Biturbo (bi-turbo) are two turbines connected in series different sizes... The system works as follows. A small turbine runs at low revs. The big one is connected when the number of revolutions of the motor increases.
This type of turbocharging system is also called sequential or sequential. That is, the turbines are put into operation one after the other.
On low revs a smaller turbine comes into operation. It works constantly, providing thrust even when the exhaust gas flow is low.
The exhaust gases gradually enter the large turbine. The large compressor spins slowly, pushing air through it. At this point, the small compressor runs at a higher speed. This provides overpressure in the intake system... The higher it is at the input, the higher it is at the output.
It turns out that a slight excess pressure is created at the inlet of the small compressor even when the large compressor is barely working. In such conditions, it is achieved operating pressure boost, the torque increases and the required volume of exhaust gases is created for the operation of the turbines.
On average revs a small turbocharger reaches operating speed, its turbine is hitting the limit of its capacity and performance. The large turbine accelerates noticeably, but there is still potential. The overpressure created by the large compressor is already noticeable. It enters the inlet of the small one, which compresses the mixture even more.
On high revs the exhaust gas flow increases. The bypass valve of the smaller turbine opens slightly (this can also happen at medium speed), and part of the exhaust gases goes directly to the large turbine. Now the large turbine is fully loaded, and the small one is, as it were, protected from twisting. Turbine and compressor parts continue to work fully.
If two turbochargers are installed on the vehicle, a very high boost pressure can be generated that cannot be achieved if only one compressor is running. And at this time, the driver will be able to accelerate smoothly, without jerking, since the effect of turbolag and turbo lag is almost eliminated.
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BITURBO: WHAT IS IT AND THE PRINCIPLE OF WORK
Literally translated from of English language twin-turbo means "double turbo" or "double turbo". Both translations are correct. Now let's leave the linguistic aspect and study in detail the technical side of this type of turbocharging.
What is Twin-Turbo (Twin Turbo)
In order to achieve a noticeable increase in engine power, a turbine is installed in its design. Twin-Turbo is one of the types of the car's turbo system and it is on it that we will focus our attention. Twin turbo implies installation two identical turbines at once which greatly increase the performance of the entire turbocharging system. This arrangement is much more efficient than a turbo system that uses only one turbine.
Biturbo was originally designed to solve the main problem all inflatable engines - elimination of the so-called "turbo lag". This phenomenon manifests itself in a decrease in elasticity and a sharp drop in engine power at low revs. All this happens at a time when the engine turbine under the exhaust gas pressure does not have time to spin up to optimal speed.
Subsequently, it was observed that twin turbines allowed a significant increase in the range of rated torque rpm, thereby increasing maximum power, while simultaneously reducing overall fuel consumption.
Did you know?The exclusive supercar Bugatti Veyron is equipped with four turbines at once, and such a turbocharging system has received the corresponding name - Quad-Turbo.
Types of turbocharging systems and their principle of operation
There are several main types of Twin-Turbo systems: parallel, serial and stepped... Each type of turbocharging is characterized by its own geometry, operating principle and output dynamic characteristics.
Parallel
This is a relatively simple type of turbo system, the design of which includes symmetrical pair of simultaneously operating compressors. Thanks to this synchronization, an even distribution of the incoming air is achieved.
This scheme is often used in diesel V-shaped engines, where each compressor is responsible for supplying air to the intake manifold of its cylinder group.
The reduction in inertia is achieved by reducing the mass of the turbine rotor, since 2 small compressors create more pressure while spinning up much faster than one large and more efficient compressor. As a result, the turbo lag mentioned above is significantly reduced, and the engine gives out the best performance in the entire rev range.
Consistent
This type implies an arrangement consisting of two commensurate compressors, which at the same time can have different characteristics and work in a complementary mode. The lighter and faster blower runs continuously, eliminating deep and wide turbo lag. The second supercharger controls the engine speed using special signals from the electronics and switches on at heavier engine operating conditions, thus providing maximum power and fuel efficiency.
At peak operating conditions of the engine, 2 turbines are turned on at once, working in pairs. A similar scheme can be applied to engines with any fuel cycle.
Stepped
The most sophisticated and progressive type of turbocharger, providing the widest power range. The creation of the necessary boost is made possible by installing two different-sized compressors interconnected by a special system of bypass-valves and branch pipes.
This type of turbocharging is called staged due to the fact that the exhaust gases spin up a small turbine in minimum modes, and this allows the engine to easily pick up speed and work with greater efficiency. As the speed increases, the valve opens, which in turn drives a large turbine. But the pressure that it creates must be increased, which is what a small turbine does.
After reaching maximum rpm, the large turbine generates tremendous pressure, which converts the small supercharger into aerodynamic drag. At this very moment, the automation opens the bypass valve, and compressed air enters the engine, bypassing the small turbine on its way.
But all the complexity of this system is fully compensated by the flexibility of the engine and its highest performance.
What are the advantages of using Twin-Turbo and are there any disadvantages
The undoubted advantage of the Twin Turbo system is high power with a relatively small engine displacement. This also includes the high torque and excellent dynamics of the Twin-Turbo equipped vehicle. The twin turbine engine is much more environmentally friendly than conventional, because turbocharging allows fuel to be burned much more efficiently in the cylinder system.
The disadvantages of biturbo can be distinguished the complexity of the operation of such a system. Power point becomes more sensitive to the quality of fuel and engine oil. Turbocharged engines need special oil, since without it, the service life is noticeably reduced oil filter... The high temperatures in which the turbines operate have a negative effect on the entire vehicle engine.
The main disadvantage of the Twin-Turbo system is high consumption fuel. To create a fuel-air mixture in the cylinders, a large volume of air is required, which entails an increase in fuel supply.
Turbines wear out rather quickly if you turn off the engine immediately when you stop the car. To prolong the life of the Twin-Turbo, let the engine run for a while. idle, having cooled the turbines in this way, and only after that you can safely take out the ignition key.
Remember! Twin-Turbo is a complex and highly sensitive turbocharging system that requires careful handling and quality components. Compliance with these simple rules allows you to enjoy the speed and dynamics of the car to the maximum.
