Radial turbine
Turbine is a device that converts the energy of engine exhaust into mechanical work.
Radial turbine consists of volute, nozzle, impeller and air outlet. The inlet of the volute 4 is connected with the engine exhaust pipe, and the engine exhaust gas is introduced into the blade nozzle through the volute. The nozzle is a conical flow channel composed of adjacent blades. When the exhaust gas flows through the nozzle, the pressure decreases, the temperature decreases, the speed increases and expands, so that the pressure energy of the exhaust gas can be converted into kinetic energy.
The high-speed airflow from the nozzle impacts the impeller, continues to expand and do work in the flow channel formed by the blades, and pushes the impeller to rotate. Turbine impeller often works under the impact of high temperature exhaust at 900℃ and bears huge centrifugal force, so it is made of nickel-based heat-resistant alloy steel or ceramic materials.
Using lightweight and heat-resistant ceramic materials can reduce the mass of turbine impeller by about 2/3, and the problem of turbo-charging acceleration lag is greatly improved. The nozzle blades are cast or machined from heat-resistant and corrosion-resistant alloy steel. The volute is cast with heat-resistant alloy cast iron, and its inner surface should be smooth to reduce air flow loss.
Vehicle turbocharger consists of centrifugal compressor, radial turbine and intermediate. The supercharger shaft is supported in the intermediate body by two floating bearings. There are oil passages for lubricating and cooling bearings in the intermediate, and sealing devices to prevent oil from leaking into the compressor or turbine.
radial-flow compressor
Centrifugal compressor consists of inlet, compressor impeller, vaneless diffuser and compressor volute. The impeller includes blades and a hub, and is driven to rotate by the supercharger shaft.
When the compressor rotates, air enters the compressor impeller through the air inlet, and under the action of centrifugal force, it flows from the impeller center to the periphery along the flow channel formed between compressor blades. Air gets energy from the rotating impeller, which greatly increases its speed, pressure and temperature, and then enters the vane diffuser.
The diffuser is a gradually expanding flow channel. When the air flows through the diffuser, it slows down and pressurizes, and the temperature also rises. That is to say, in the diffuser, most of the kinetic energy of air is converted into pressure energy.
There are two types of diffusers: vane type and vaneless type. The vaneless diffuser is actually an annular space formed by the volute and the sidewall of the intermediate. The vaneless diffuser is simple in structure, and the change of working conditions has little influence on compressor efficiency, so it is suitable for vehicle supercharger.
Vane diffuser is a flow channel composed of adjacent blades, which has high diffusion ratio and high efficiency, but its structure is complex and the change of working conditions has a great influence on compressor efficiency. The function of the volute is to collect the air flowing from the diffuser and guide it to the compressor outlet. The air continues to decelerate and pressurize in the volute to complete the conversion process from kinetic energy to pressure energy.
Turbocharging system
Turbocharging system is divided into single turbocharging system and double turbocharging system.
Single turbocharging
The supercharging system with only one turbocharger is a single turbocharger system. In addition to the turbocharger, the turbocharger system also includes an intake bypass valve, an exhaust bypass valve and an exhaust bypass valve control device.
Twin turbine engine
Dual turbocharging system of six-cylinder gasoline engine. Wherein two turbochargers are arranged in parallel in the exhaust pipe. According to the working sequence of cylinders, 1, cylinders 2 and 3 are one group, and cylinders 4, 5 and 6 are the other group. The exhaust of three cylinders in each group drives a turbocharger. Because the exhaust intervals of the three cylinders are equal, the supercharger rotates smoothly.
In addition, grouping three cylinders into one group can also prevent exhaust interference between cylinders. The system includes a turbocharger, an intake bypass valve, an exhaust bypass valve and an exhaust bypass valve control device, an intercooler, a resonance chamber and a boost pressure sensor.
Extended data supercharger bearing
The structure of turbocharger bearing is one of the keys to the reliability of vehicle turbocharger. Modern vehicle turbochargers all adopt floating bearings. The floating bearing is actually a ring on the shaft.
There are gaps between the ring and the shaft and between the ring and the bearing seat, forming a double-layer oil film. The piston ring floats between the shaft and the bearing seat. Generally, the internal clearance is about 0.05mm and the external clearance is about 0.1mm. The bearing wall thickness is about 3 ~ 4.5 mm, and the material is tin-lead bronze alloy. The surface of the bearing is coated with a layer of lead-tin alloy or indium with a thickness of about 0.005 ~ 0.008 mm. When the supercharger works, the bearing rotates between the shaft and the bearing seat.
The axial thrust generated by the supercharger during operation is borne by the thrust bearing arranged at one side of the compressor. In order to reduce friction, four oil distribution grooves are respectively machined on the thrust surfaces at both ends of the integral thrust bearing; Oil inlet holes are also machined on the bearing to ensure lubrication and cooling of the thrust surface.
Adjustment of boost pressure
It is the simplest, lowest cost and very effective method to set the intake and exhaust bypass valve in the automobile turbocharger system. Working principle of exhaust bypass valve. The diaphragm in the diaphragm case is controlled to divide the diaphragm case into an upper chamber and a lower chamber. The upper chamber is an air chamber communicated with the compressor outlet through a communication pipe, and the lower chamber is a diaphragm spring chamber. The diaphragm spring acts on the diaphragm, and the diaphragm is connected with the exhaust bypass valve through a connecting rod.
When the outlet pressure of the compressor, that is, the boosting pressure, is lower than the limited value, the diaphragm moves up under the action of the diaphragm spring and drives the connecting rod to close the exhaust bypass valve; When the boost pressure exceeds the limit value, the boost pressure overcomes the diaphragm spring force, pushes the diaphragm downward, and drives the connecting rod to open the exhaust bypass valve, so that part of the exhaust gas is directly discharged into the atmosphere without passing through the turbine, thus achieving the purpose of controlling the boost pressure and the turbine speed.
Resources Baidu Encyclopedia-Turbocharging