Chapter 1: Importance of water-cooled bearing housing in turbocharger assembly

Regardless of how fast and efficient, the engines manufactured by the automobile industry are. The global demand for faster cars is inevitable.

The automobile industry requires more efficient turbochargers in the chase for faster cars. Customer expectations and brand competition drive the industry to develop fast and fuel-efficient engines. It was one of the primary motivations for the invention of TURBOCHARGERS. 

As technology and machinery advance, more efficient turbochargers are developed. These turbochargers reduce fuel consumption by forcing high-pressure air into the piston cylinder.

Reducing losses and forces on turbochargers is one of the simplest strategies to obtain extremely efficient turbochargers. The bearing system of turbochargers is an essential component frequently overlooked by the industry. Even though turbocharger bearings are in charge of delivering turbine energy to the compressor, this single component is exposed to a variety of friction. More efficient engines can be produced by reducing friction at the turbocharger bearing. A well-designed and properly constructed turbocharger bearing can significantly improve engine efficiency and life.

In response to increased pressure to reduce engine fuel consumption and emissions, turbocharger bearing systems are also evolving. The newer engine's expectancy can be increased by developing and producing turbocharger bearing systems that encounter less friction and force.

This article will provide a more in-depth look at the manufacturing process of the turbocharger bearing housing.

Bearing housing: (Image courtesy by TBK Co. Ltd )

 TURBOCHARGER BEARING HOUSING

 The turbocharger improves engine fuel efficiency and power output by using engine   exhaust gasses to rotate the turbine and force additional compressed air into the   engine via the compressor.

 The bearing housing is connected to the turbine and the compressor. The bearing   housing is not only     responsible for the spin of the compressor, but it also cools the     heat transferred from the turbine. High-temperature applications require additional   cooling to function properly. Hence the bearing becomes an essential component of   the turbocharging process.

 The water cooling method is one of the most popular ways to cool the turbocharger.   Water cooling enhances mechanical performance and durability while also extending turbocharger life. Some turbochargers are intended to be oil and water-cooled.

The primary advantage of water cooling happens after the engine has been turned off. It occurs when the water is not pumped properly. After shutting down, the heat stored in the turbine housing and exhaust manifold "socks back" into the turbo charger's central part. This high temperature can damage the bearing system and the oil sealing piston rings behind the turbine wheel.

How does water cooling work in turbocharging?

The turbocharger water cooling mechanism is fascinating, as it operates in a not immediately visible way. True, water flows through the turbocharger during normal engine operation, primarily due to the pressure created by the engine water pump. However, suppose the water lines are properly routed. In that case, a phenomenon known as " Thermal Syphoning " draws water through the turbo's center housing even after the engine is turned off and the water pump is no longer running.

Like transferring heat to water within a standard water-cooled engine, heat in the central housing is transferred to the water by conduction. A water jacket encircles each cylinder, and the water goes through the cylinder head. Suppose the water flowing through a turbocharger can exit after absorbing heat. It will ascend through the cooling system, preventing major damage to the cooler without the assistance of the engine water pump.

A coreless die-casting technology creates the water-cooled turbocharger instead of casting a complete passage in the turbocharger's bearing housing. An open-ended channel is cast into the housing and then sealed off by mating seal plate "o" rings or other sealing materials are used to seal the mating joints to prevent pressurized cooling water from leaking to the outside or into the internal bearing housing section.

Conventionally constructed turbochargers used in automobiles and other high-temperature applications are failing at an alarming rate due to an "Oil Coking" problem. It happens after the engine is turned off and the heat from the exhaust manifold and turbine housing socks returns to the turbocharger bearing housing. The bearing housing temperature rises until it reaches the temperature required to burn the oil. Any residual oil in the bearing housing is subsequently burnt into a thin coating of "coke." The process is repeated until the coke deposits completely plug the small oil passageways. As a result, the bearing becomes oil-starved, and the turbocharger rotating assembly fails.

Previous technology solved this issue by employing water to cool the bearing housing, preventing it from reaching the temperature required to burn the oil. It was achieved by casting a water tunnel into the bearing housing and flowing engine cooling water through it.

It is the working principle and procedure used in the turbocharger bearing housing to cool the turbocharger with water cooling linings.

Now we will look at the technology and machinery required to achieve such bearing housing complexity.

Machine configuration considered for this process:

The horizontal machining center with twin spindle and twin pallet machines. The machine utilized to demonstrate this procedure was set up as shown below.

Machine Configuration: Twin spindle, Twin Pallet Machine HMC

1. X-Axis travel is 320mm, servo axis with rapid travel 60 m/min, with brake motor option.

2. Y-Axis travel is 800mm, servo axis with rapid travel 70 m/min, with brake motor option.

3. Z Axis travel is400mm, servo axis with rapid travel 60 m/min, with brake motor option.

4. The Center distance between two spindles is 320 mm.

5. W Axis servo drive, with 64 tools capacity.

6. A1 Axis is hydraulic with an encoder for pallet positioning of rotary pallets.

7. The A2 Axis is servo with torque motor, 4th axis rotary axis.

8. The A3 Axis is servo with a torque motor, 4th axis rotary axis.

9. Spindle 1 & 2 HSK A63 with 20 KW power and 126 nm torque, 8000rpm, through coolant and high-pressure options for 18 bar.

10. Hydraulic counterbalancing.

The machine has a direct tool change, which occurs when the X, Y, and Z axes are moved simultaneously, resulting in a tool change time of 3 to 5 seconds.

In addition, the chip-to-chip time will be 5 seconds.

The pallets A2 and A3 are rotating axes with servo torque motors, and the rotary drums each have a working envelope of 500 diameters. The A2 axis serves as a servo fourth axis, as does the A3 axis. According to the process sequence, the part can be oriented to the required angular position, which is possible in the fourth axis rotation.

These machines performed flawlessly during roughing, finishing, milling, drilling, rough boring, and finish boring operations on cast alloy components. Two spindles with high power and torque can withstand heavy metal cutting and are mounted on the spindle housing. The through coolant pressure might be as high as 18 bar.

Two clamping settings for the integral manifold with turbine housing are planned on this machine. It is a partial process. The operations that are left out must be planned on another machine; of the two setups, one with the fourth axis for four component loading and the mounting face of exhaust manifold operations are planned. The qualifying steps can be accomplished in this configuration. The second pallet is utilized for the second configuration of the turbine housing operations.

With this, we conclude the introduction of the turbocharger water cooling housing. We may now assert and assume that turbocharger housing is an important component of turbochargers. It contributes significantly to turbocharging efficiency. The key to faster cars is friction reduction and heat deception via water cooling in turbocharger-bearing housing. The machinery must also be sophisticated to have such a complicated part with high precision. 

In the following chapter of this article, we will look closely at the machinery used to make turbocharger bearing housing.
Click here for Chapter 2 >>>>

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