Mechanical air blower for a car: do it yourself

With the development of the internal combustion engine (ICE), the problem of increasing its power arose. The first option is to increase the number of cylinders. But this approach gives rise to problems associated with an increase in the size and weight of the motor. The second option is more promising. This is the installation of a supercharger (supercharger), which allows you to supply additional air volume.

Over time, various versions of such equipment were created:

1. mechanical boost, powered by the crankshaft;
2. turbocharging, powered by exhaust gases;
3. electric blower;
4. Сomprex, powered by exhaust gases;
5. combined, combining elements of mechanical and turbo.

A mechanical air blower (also known as a compressor, Supercharger) increases power by 50%. It takes air from the air pipe and, after compression, forwards it to the manifold.

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The advantages of centrifugals include simplicity of design, compactness and low weight.
There is also no strict need to use intercoolers, since they heat the air much less than vane superchargers and turbochargers. The advantages of centrifugals include simplicity of design, compactness and low weight. There is also no strict need to use intercoolers, since they heat the air much less than vane superchargers and turbochargers.

The idea of ​​​​increasing engine power by pushing an additional portion of air and fuel into it is as old as the world. And this can be achieved if a pressure greater than atmospheric pressure is created at start-up. This is what superchargers are used for. There are many models, but in “Moto” Nos. 8 and 9 (Horex and me with my crazy “gold”) we talked about centrifugal ones. In short, these are high-speed fans, and, figuratively, “boy vacuum cleaners.”

The very idea of ​​forced air injection into the cylinders was proposed shortly after the invention of the internal combustion engine itself. Already in 1885, Gottlieb Daimler received a German patent for the supercharger. The idea was that some external fan, pump or compressor would force an increased charge of air into the engine. In 1902, in France, Louis Renault patented a design for a centrifugal supercharger. But after the release of several cars, all work in this direction was stopped - the imperfection of technologies and materials tipped the scales with more “against” than “for”. The abbreviation PCN (driven centrifugal supercharger) took root in the everyday life of engine mechanics in the 30s of the twentieth century - however, only in aviation. The introduction of monitoring stations made it possible to kill two birds with one stone: to increase specific power and reduce the drop in power at high altitudes. (As altitude increases, the density of air decreases; accordingly, less of it enters the engine, and to maintain power, the oxidizer has to be forced in.) All superchargers installed on internal combustion engines can be divided into two main groups based on their operating principle: centrifugal and positive displacement. And according to the type of drive - drive (driven by the crankshaft) and gas turbine (using the energy of exhaust gases).

What is a monitoring station? Let's plunge into childhood and remember the spinning top. What happens if you splash water on top of a spinning top? That's right, water will splash around under the influence of inertial forces (centrifugal force), and the spinning top will remain almost dry. Likewise, in a centrifugal supercharger, the role of the spinning top is played by the impeller, and the role of water is played by air molecules. I think that as a child, everyone looked inside a vacuum cleaner and saw behind the grate of the dust collector compartment a strange disk with blades and a nut in the middle. This is the simplest centrifugal supercharger, only it works for suction, and not for creating excess pressure. What happens if you connect the hose to the vacuum cleaner, but from the side from which it blows air? And if it is also introduced into the engine intake...

The impeller of a real CN has a rather complex cone-shaped shape, and the blades have a complex profile and bend. The performance and efficiency of the entire supercharger depends on their geometry. (For example, the larger the diameter of the impeller, the more pressure it can produce at the same speed, but at the same time it consumes more power; or when the number of blades increases, the pressure increases, but the performance decreases.) The air, passing through the air channel into the supercharger, falls on the radial blades of the impeller. The blades throw it to the periphery of the casing through a thin slot. There, the air is slowed down in a snail-shaped diffuser, its speed drops, and the pressure rises.

In fact, the monitoring station is half of a turbocharger already familiar in the world, but instead of the “hot” (turbine) part, it is mechanically driven from the crankshaft. Due to the very principle of operation, the centrifugal supercharger has one significant drawback. To operate effectively, the impeller must rotate not just quickly, but very quickly. The pressure produced by a centrifugal compressor is proportional to the square of the impeller speed. Accordingly, hence the main disadvantage of centrifugals: a narrow operating range. But this theoretical minus in practice turns out to be a plus. After all, if the supercharger forcibly pumps air into the engine all the time, this will lead to an increase in traction throughout the entire speed range, and it will be difficult to cope with such “fruit” at the bottom. It’s another matter if excess pressure in the intake begins to arise at medium speeds and reaches a peak at high speeds, when the filling of the cylinders deteriorates due to friction losses on the intake tract of the air-fuel mixture (this causes the downward tail of the torque curve in the high speed range at many dino graphs). The centrifugal coolly “inflates” the tops, helping the mixture enter the cylinders in the required volume. That is why there is no need to turn off the supercharger at low speeds, as is necessary with positive displacement compressors.

Supercharger device

To operate the engine in a car, you need a fuel-air mixture; the ratio of elements depends on the load and operating mode. Without additional equipment, fuel assemblies are supplied due to vacuum during inlet and are completely dependent on the volume of the cylinders. The volume can be increased by creating additional pressure. As a result, more fuel assemblies will burn, and the power will increase. This approach saves fuel, since the required power can be obtained with a small cylinder volume.

Mechanical charging consists of:

1. compressor;
2. air filter;
3. intercooler (cooler);
4. two valves (throttle, pipeline);
5. two sensors (temperature, pressure).

   
   Mechanical supercharger operating diagram

The mechanical supercharger is connected to the crankshaft, so work begins simultaneously with the engine starting, the volume of air supplied to the engine is proportional to the speed, which is the main advantage of this equipment. The downside is the loss of engine power.

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The size of the gap between the impeller blades and the housing is the main parameter affecting the efficiency of the compressor.
The size of the gap between the impeller blades and the housing is the main parameter affecting the efficiency of the compressor.

Everything is great, but centrifugal engines also have undeniable shortcomings. The main thing is that you need to spin the impeller to crazy speeds, so you have to use a step-up gearbox, which has 50–150 thousand rpm on the output shaft (for some monitoring stations this figure reaches 250 thousand!). Rare bearings and seals can withstand this, and therefore the issue of service life and efficiency is often more pressing than increasing power. And the overall efficiency of the engine is reduced due to the fact that the supercharger sucks power directly from the crankshaft. But every hole of problems can be climbed out of by a thin rope of technological solutions. For example, BRP on its sports jet skis drives the supercharger directly from the crankshaft flywheel gear, and is saved from gear-damaging jerks by using a friction damper on the supercharger shaft. Yamaha drives the snail through an intermediate shaft. If we look at the tuning units, we see that, for example, Rotrex (which is adored by European motorcycle tuners, including yours truly) uses a friction roller gearbox, in which the impeller shaft is sandwiched between the planetary gears and does not require bearings. The Americans from ProCharger, having brought a kit to the market for Harley-Davidson, focus on the precision of manufacturing the gearbox; their colleagues from Powerdyne like to “supercharge” snowmobiles and use an additional belt drive as a multiplier.

And again we remember our childhood, and also, who remembers, physics. When we inflated our bicycles, mopeds and motorcycles with pumps, remember how the hose going to the wheel got hot? That's right, more pressure means higher temperature, higher temperature means less air density, which means less oxygen molecules per unit volume. To compensate for this decrease in density, the compressed air must be cooled. How? The same as antifreeze or oil - in the radiator, or more precisely, in the intercooler (in scientific terms, charge air cooler). Intercoolers are mainly of the air-to-air type (a seemingly simple radiator with thicker channels) and air-to-liquid, when between the compressor and the intake manifold there is a compact “radiator in reverse”, which takes heat from the compressed air into the liquid, and then discharges it into atmosphere through an additional radiator.

But still, why not turbo? After all, in the world of cars, more and more manufacturers are equipping their cars with turbocharging. Alas, the “turbo” not only increases power, but also creates resistance at the exhaust, greatly heats the air at the intake not only due to its compression, but also due to the proximity of the hot exhaust manifold; in addition, the engine experiences “turbo lag” or “turbo lag” (when the impeller, having no mechanical connection with the crankshaft, does not have time to spin up after the throttle is opened, which causes a short-term dip in traction - the complete antithesis of the expression “follow the handle”). Because of all of the above, the turbo motorcycles that appeared in the early 80s (say, the Yamaha XJ650 Turbo) failed in the market, and now neither the designers of serial vehicles nor the tuners are in a hurry to “stick a snail” into motorcycle engines. The exception is drag racing equipment and other cars for record straight races; there, “turbo lag” is usually compensated by “anti-lag” (a system that allows you to sharply increase the temperature of the gases in front of the turbine - wild barbarity, justified only by complete disregard for the resource). However, let’s not say “never” - the French from Yam74, after experimenting with the Tmax monitoring station, eventually switched to the “turbo”, and not without success. Therefore, we will wait for developments.

Operating principle

A mechanical supercharger for a car is controlled by a valve on the throttle. If the speed is high, it opens when the valve on the pipeline is closed. Air moves freely into the collector. At low speeds, the throttle valve is also open, but at an angle. The pipeline damper opens completely, returning some of the air back to the compressor. The function of the intercooler is to reduce the air temperature by 10 degrees in order to increase the compression ratio.

Torque from the crankshaft to the compressor is transmitted through:

• direct drive (if the supercharger is installed on a shaft flange);
• belt (flat, with teeth or wedges);
• chain;
• gear transmission.

The disadvantage of belts is the likelihood of slipping and short service life. When using a gear, the size of the equipment increases and additional noise is created.

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Rotrex disassembled (top) and its oil system (bottom).
The planetary gearbox with smooth rollers operates mainly due to a special oil circulating through the system. Therefore, unlike their gear counterparts, which are lubricated from the general engine lubrication system, Rotrex has its own oil circuit with a radiator and filter. Rotrex disassembled (top) and its oil system (bottom). The planetary gearbox with smooth rollers operates mainly due to a special oil circulating through the system. Therefore, unlike their gear counterparts, which are lubricated from the general engine lubrication system, Rotrex has its own oil circuit with a radiator and filter.

TURBO NOT TURBO

If you examine the design of such units, you can identify a certain similarity in structure

Namely, such compressors operate from a drive that does not require intervention in the standard engine systems, namely the lubrication and exhaust gas system, which is very important! This design is really very simple - a direct connection is established with the “crankshaft”, which allows the engine and supercharger to interact perfectly during acceleration. That is, the higher the speed, the faster the “crankshaft” rotates, and accordingly the supercharger spins! Thanks to this interaction, there is practically no such thing as “turbo lag”

Also, an additional advantage is the lack of operation at high temperatures, like with TURBO options, which means that the service life is greatly increased - after all, here the “turbine” does not need to cool down, that is, “” or “boost controllers” are not required, we just turn off the car and work stops. The site autoflit.ru recommends doing exactly the same. If you're interested, come in.

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A homemade supercharger, built on the basis of a domestic turbocharger, in which the “hot” part was replaced by a gearbox.
The notch on the impeller is a consequence of balancing: the metal was cut not from the blade, but from where the notch would not create turbulence in the air flow. Our “Kulibins” used an “inside out” gearbox - it’s compact and the oil itself disperses along the teeth due to centrifugal force. The faceplate connects the snail and the gearbox. It also contains a bearing and an impeller shaft seal. A homemade supercharger, built on the basis of a domestic turbocharger, in which the “hot” part was replaced by a gearbox. The notch on the impeller is a consequence of balancing: the metal was cut not from the blade, but from where the notch would not create turbulence in the air flow. Our “Kulibins” used an “inside out” gearbox - it’s compact and the oil itself disperses along the teeth due to centrifugal force. The faceplate connects the snail and the gearbox. It also contains a bearing and an impeller shaft seal.

Driven blowers

Types of turbochargers

Turbine with exhaust gas bypass WGT.

The hot scroll of the turbocharger has a wastegate valve that releases exhaust gases bypassing the turbine rotor in order to limit the increase in turbocharger pressure above a predetermined value. As a result, the flow of gases through the turbine decreases, which reduces both the degree of air compression by the turbine and the excessively high rotation speed of the turbocharger shaft. At low engine loads, the valve closes and the entire exhaust gas flow is directed to the turbine.

Turbine with variable turbine geometry VNT.

A turbine with variable geometry TIG (Variable-Nozzle Turbine - VNT, Variable-Turbine Geometry - VTG, Variable-Geometry Turbo - VGT) differs from classic turbochargers by the presence of a ring of special blades (blades). This makes it possible to control the flow of exhaust gases through the turbine. At low engine speeds the blades are in a semi-closed state. Exhaust gases have to “squeeze” into the narrow passages between the blades. The speed of the gas increases (Bernoulli's law) and it spins the turbine faster. At higher engine speeds, the blades open. The cross section for the passage of gases increases, the speed drops, and the turbine rotates more slowly.

Turbine with VST throttling.

Spool-controlled turbines (VST Variable Sliding Turbine) have been used in low-power passenger car engines. The VST turbine operates similarly to a fixed geometry turbine, with the difference that one of the two spool ports is initially opened. When the maximum permissible boost pressure is reached, the spool, continuously moving in the axial direction, opens the second channel. The channels are designed so that the largest part of the exhaust gas flow is directed to the turbine. The remaining part of the exhaust gases, due to further movement of the control valve, is directed to bypass the compressor impeller inside the turbocharger.

Turbine with Twin-scroll (Twinscroll) - double snail. A “twin-scroll” turbine differs from a conventional one in the presence of two channels dividing the turbine’s working chamber in two. Thus, the exhaust gases are supplied to the turbine separately, due to which pulse charging is used more efficiently.

How is the advantage achieved? On a four-stroke engine, the cylinder operating order (for example, ZMZ-409) is 1-3-4-2. Let's imagine that cylinder 1 finishes its cycle and reaches the bottom point, the exhaust valve opens. At the same time, cylinder 2 completes the exhaust cycle by closing the exhaust valve and opening the intake valve. With a conventional single turbo, the exhaust pressure from cylinder 1 will prevent air intake from cylinder 2 since both exhaust valves are open. So, if you separate the cameras, the problem will be resolved. In addition, turbines with variable Twin-scroll have recently appeared: a distribution valve (Quick Spool Valve) is installed at the inlet of the turbine scroll, which redirects the flow of exhaust gases into different channels. And if we take into account that different channels have different geometries, then we actually get a universal, controllable turbine that works well at both low and high engine speeds.

Twin scroll turbocharger Borg Warner EFR-7163-J (VTV) with integrated QSV valve (variable geometry)

Application of compressors on cars

The use of mechanical compressors is especially popular among both expensive cars and sports cars. Such superchargers are often used for auto tuning purposes. Most sports cars are equipped with mechanical compressors or their modifications.

The wide popularity of these units has contributed to the fact that many companies today offer completely ready-made solutions for installation on an atmospheric engine. Such kits contain all the necessary parts suitable for almost all models of power plants.

But mass-produced cars, especially those of medium cost, are rarely equipped with mechanical superchargers.

Cam and screw mechanisms

This type of supercharger is one of the earliest. Similar devices have been installed in cars since the early 90s. They are named after the inventors - Roots.

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These blowers are characterized by rapid pressure generation, but sometimes they can produce higher than normal levels. In this case, air plugs may form in the discharge channel, which will lead to a decrease in the power of the unit.

To avoid problems, when using such devices you need to adjust the inflation pressure.

This can be done in a couple of ways:

1. Turn off the device from time to time.
2. Ensure air passage using a special valve.

Most modern mechanical air blowers for cars are equipped with electronic control systems. They have electronic control units and sensors.

Roots compressors are quite expensive. This is explained by minor tolerances in the production of such products. Additionally, these superchargers need to be maintained regularly as foreign objects or dirt inside the starting system can damage the sensitive unit.

The screw units are reminiscent of the Roots model in their design. They are called Lysholm. In screw blowers, pressure is created inside using special screws.

Such compressors cost more than cam compressors, so they are not used very often and are often installed in exclusive and sports cars.

Centrifugal design

The operation of this type of device is very similar to the operation of a turbocharger. The working element of the unit is the impeller-wheel. It rotates very quickly during operation, sucking air into itself.

It should be noted that this variety is the most popular among all mechanical devices. It has a lot of advantages.

Eg:

• compact dimensions;
• small weight;
• high level of efficiency;
• affordable price;
• reliable fixation on the car engine.

The only disadvantages include the almost complete dependence of performance indicators on the crankshaft speed of the car engine. But modern developers take this fact into account.

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