Mechanical blowers. What are

In the process of car production, engineers think not only about the introduction of state-of-the-art technology, modern appearance and first-class safety. Today, automotive internal combustion engines are trying to do less and get more efficiency. The introduction of a mechanical supercharger is one of those ways - to “squeeze out” the maximum, even from a small 3-cylinder engine.

What is a mechanical compressor, how it is arranged and works, what are its advantages and disadvantages - let's talk about this later.

What is a mechanical supercharger

A mechanical blower is a device that forcibly supplies air under high pressure to increase the mass of the fuel-air mixture. The compressor is driven by rotation of the crankshaft pulley, as a rule, the device is communicated through a belt. Forced air compression using a mechanical turbocharger provides an additional 30-50% of the rated power (without a compressor).

How mechanical pressurization works

Regardless of the type of design, all blowers are designed to compress air. The drive compressor starts running as soon as the motor starts. The crankshaft, through a pulley, transmits torque to the compressor, and that, in turn, by rotating the blades or rotors, compresses the intake air, forcibly supplies it to the engine cylinders. By the way, the operating speed of the compressor is many times higher than the speed of the internal combustion engine crankshaft. The pressure generated by the compressor can be internal (created in the unit itself) and external (pressure is created in the discharge line).

Mechanical pressurization device

A typical blower drive system consists of the following:

• directly the compressor;
• throttle valve;
• bypass valve with damper;
• air filter;
• pressure meter;
• an intake manifold temperature sensor; and an absolute pressure sensor.

By the way, for compressors whose operating pressure does not exceed 0,5 bar, the installation of an intercooler is not required - it is enough to improve the standard cooling system and provide a cold inlet in the design.

The air blower is controlled by the throttle position. When the engine is idling, there is a possibility of overpressure in the intake system, which will soon lead to a malfunction of the compressor, so a bypass damper is provided here. Some of this air flows back to the compressor.

If the system is equipped with an intercooler, then the degree of air compression will be higher due to a decrease in its temperature by 10-15 degrees. The lower the intake air temperature, the better the combustion process takes place, the occurrence of detonation is excluded, the engine will work more stably. 

Mechanical pressurization drive types

Over the decades of using a mechanical compressor, car manufacturers have used various types of drive, namely:

• direct drive - directly from rigid engagement with the crankshaft flange;
• belt. The most common type. Cogged belts, smooth belts and ribbed belts can be used. The drive is noted with rapid belt wear, as well as the likelihood of slippage, especially on a cold engine;
• chain - similar to a belt, but has the disadvantage of increased noise;
• gear - there is also excessive noise and large dimensions of the structure.

Centrifugal compressor

Types of mechanical compressors

Each of the types of blowers has an individual performance property, and there are three types of them:

• centrifugal compressor. The most common type, which looks very similar to an exhaust gas turbocharger (snail). It uses an impeller, the rotation speed of which reaches 60 rpm. Air enters the central part of the compressor at high speed and low pressure, and at the outlet the picture is reversed - air is supplied to the cylinders at high pressure, but at low speed. In modern cars, this type of supercharger is used together with a turbocharger to avoid turbo lag. At low speeds and transient conditions, the drive “snail” will supply compressed air stably;
• screw. The main structural elements are two conical screws (screws) installed in parallel. Air, entering the compressor, first passes through the wide part, then it is compressed due to the rotation of two screws that turn inward. They are mainly installed on expensive cars, and the price of such a compressor itself is considerable - the complexity of the design and efficiency affect;
• cam (Roots). It is one of the first mechanical superchargers to be installed on automotive engines. Roots are a pair of rotors with a complex profile section. During operation, air moves between the cams and the housing wall, thereby compressing. The main disadvantage is the formation of excessive pressurization, therefore, the design provides for an electromagnetic clutch for controlling the compressor, or a bypass valve.

Screw compressor

Mechanical compressors can be found on cars from well-known manufacturers: Audi, Mercedes-Benz, Cadillac and others. They are installed on high-volume motors, or in a small car in tandem with a turbine powered by gas energy.

Compressor Roots

Advantages and disadvantages of a mechanical supercharger circuit

As for the disadvantages:

• driving the compressor by means of a drive from the crankshaft, thereby the supercharger takes away part of the power, although it successfully compensates for it;
• high noise level, especially at medium and high speeds;
• at a nominal pressure of over 5 bar, it is necessary to change the design of the engine (install strong pistons with connecting rods, reduce the compression ratio by installing a thick cylinder head gasket, mount an intercooler);
• poor quality of non-standard centrifugal compressors.

On the merits:

• stable torque already from idle speed;
• the ability to operate the car without the need to gain engine speed above average;
• stable work at high speed;
• relative to a turbocharger, the blowers are cheaper and easier to maintain, and there is no need to redesign the oil system to supply oil to the compressor.

Questions and answers:

How does a mechanical blower work? The blower housing has a diffuser. As the impeller rotates, air is sucked in and directed towards the diffuser. From there, it enters the cavity that consumes this air.

What is a mechanical blower intended for and how does it work? This mechanical unit compresses the gas without cooling it. Depending on the type of blower (the design of the gas-collecting mechanism), it is able to create a gas pressure above 15 kPa.

What kind of blowers are there? The most common blowers are centrifugal. There are also screw, cam and rotary piston. Each of them has its own peculiarities of work and the generated pressure.