GB2477564A

GB2477564A - Turbine wheels with a female tool engagement member

Info

Publication number: GB2477564A
Application number: GB1002077A
Authority: GB
Inventors: George Michael Morrell
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-09
Filing date: 2010-02-09
Publication date: 2011-08-10
Also published as: GB201002077D0

Abstract

A turbine wheel 124 has a co-axially arranged female engaging member 150. The female engaging member forms a cavity in which a corresponding male tool can locate. When a male tool is located within the cavity rotation between the cavity and the male tool is prevented. During assembly of the turbine wheel and shaft, the turbine wheel can be held fast, relative to the shaft by inserting the male tool into the female engaging member 150 (or vice versa). Also, the male member can be used to manipulate the turbine wheel assembly when the compressor wheel is being assembled / disassembled. Consequently, there is provided a turbine wheel having reduced mass as compared to known turbine wheels having male engaging members. Additionally the radial face 152 surrounding the female engaging member provides an area which can be machined to remove material for balancing purposes.

Description

improvements in and re'ating to turbochargers, turbocharger components and turbocharger assembly

BACKGROUND

Technical Field

The present invention relates to a turbocharger for internal combustion engines. More particularly, the present invention relates to improved turbocharger components these being an improved turbine wheel, turbine wheel assembly, rotor assembly and method of assembling and disassembling the same.

Description of Related Art

Turbochargers for internal combustion engines (ICE) are well known. Essentially, turbochargers use the exhaust gas from the ICE to drive a turbine which in turn drives a compressor, the latter compressing atmospheric air and delivering it to the ICE in order to improve its performance. A known turbocharger 10 is shown in Figure 1. Here a housing is formed from a bearing housing 30b, a turbine housing 30t and a compressor housing 30c. A rotor assembly 20 is encased within the bearing housing 30b. The rotor assembly 20 (shown in Figure 2) comprises a compressor wheel 22 and a turbine wheel 24 that are arranged on either end of a shaft 26. The shaft is accurately machined and has two opposed ends. The turbine wheel 24 is welded to one end of the shaft 26 to form a turbine wheel assembly 40 (as shown in Figure 3). The compressor wheel 22 is secured to the turbine wheel assembly by a lock nut 28 that is screwed on to a thread formed on the shaft 26. The turbo wheel 24 and compressor wheel 22 are thus fixed to the shaft and each wheel is constrained from rotating independently.

Referring back to Figure 1, the rotor is carried within the bearing housing 30b by bearings so that it is able to rotate, relative to the housing, about a longitudinal axis of the shaft 26.

Suitably, the bearings are shown in Figure 1 as a pair of free floating plain bearings, indicated as bearings 32 and 33. As an alternative, a minority of turbochargers employ ball bearings, primarily on automotive applications as they have some advantages. The turbine housing 30t directs the exhaust gas from the ICE onto the turbine wheel, which drives the rotor assembly 20 and the compressor housing 30c to deliver the compressed air from the compressor wheel 22 back to the ICE. The exhaust gas can be delivered in radial or axial form. The exhaust gas is shown in Figure 1 as being directed radially, and would be accurately described as an exhaust gas driven, radial flow turbocharger.

The exhaust gas is supplied through a port 34 of the turbine housing which can be single, twin, or even four entry wrapped around the turbine wheel 24, gas passing through the wheel to exit into the exhaust system. Similarly the driven compressor wheel 22 draws in atmospheric air through an intake 36 in the compressor housing 30c and the same housing 30c guides the compressed air across the compressor wheel 22 to exit at 37 into the inlet manifold of the ICE sometimes and often via an after cooler.. It will therefore be appreciated that the turbine wheel 24 extracts energy from the exhaust gas, which is used by the compressor wheel 22 to compress the air.

The bearing housing 30b is sealed at either end of the shaft 26 by piston ring seals. This is to prevent contamination of air and exhaust gas compartments. For instance it prevents any finely filtered pressured engine lubricating oil escaping. A thrust bearing counters end thrust caused by a horizontal component of the wheel gas flows. The turbine housing 30t and compressor housing 30c are made in differing sizes to allow matching of the turbo characteristics to the engine needs.

Figure 4 shows a turbine wheel 24 in more detail. The turbine wheel has a male engaging member 50. The male engaging member 50 comprises an integral, circular boss 52 and integral nut 54 that are cast to the centre of the turbine wheel 24 at a blade gas exit. The nut 54 may be hexagonal, star, square or other shape. This nut and boss serve no useful operating purpose and the material exists on the turbine wheel for two main reasons. Firstly the material acts to reinforce a hub 25 of the turbine wheel in order to counteract any wheel stress limitations (see below), and secondly for manufacturing purposes.

During manufacture the nut is used to receive a ring or socket spanner for preventing the turbine shaft rotating when the compressor locknut 28 is tightened to the correct torque level when assembling the rotor assembly 20. It is critical not to bend the shaft 26 when performing this operation. Furthermore, the nut 54 is also used as a driver/locating point when machining the shaft 26 and assembling the turbine wheel assembly 40. For instance, the turbine wheel and shaft may be welded and the male engaging member can therefore be used to hold or secure the turbine wheel 24 during this process. The nut 54 and boss 52 are also used as a source of metal to be removed as necessary when a rotor balancing operating takes place.

The basic design and assembly process of a turbocharger, as described above, is used almost universally throughout the relevant industries. However, each manufacturer produces its own variants of wheel geometry, bearing spacing and housing sizing. Even so, the individual differences in the basic design are generally small and externally the turbochargers are hard to distinguish. Turbochargers incorporating this basic design are produced today by several world wide manufactures, with little differences in construction. Moreover the design and assembly process have existed for over fifty years.

For instance, although invented early in the 20th century, exhaust gas driven radial flow turbochargers were introduced to mass production in the late 1950's by several European and US engine producers, notably Caterpillar, Volvo and Saab Scania. Even before this, some marine turbochargers used a combination of radial and axial flow turbochargers. By 1 980 the turbocharger was well established as a means of improving the overall thermal efficiency of an internal combustion engine. Initially used on oil engines further progress was made when Saab introduced a turbocharged petrol engine for use in cars in the nineteen eighties.

Other passenger car manufacturers quickly adopted the device on both petrol and diesel engines throughout the world. Today the basic design turbocharger is a common and well-understood feature on both forms of internal combustion engine.

On introduction in the 1950's turbochargers were equipped with individual turbine nozzle rings and separate compressor diffuser plates. These features were costly and allowed the turbine and compressor performance characteristics to be aligned with those of the engine. By 1965 these components were replaced by today's wrap around turbine and compressor housings in which expansion of exhaust gas and compression of air take place. These changes significantly reduced manufacturing cost and were the last major changes to the basic turbocharger design. There have been improvements, for instance, the use of different materials, and in turbine and compressor blade geometry. However, nothing as radical as the changes in 1965. The lack of basic design change since 1965 was and is due to the focus of development changes as follows.

The focus changed to the development of turbocharger engine systems where the rewards for R & D investment were to be greater than those obtainable by improving the basic design.

The relatively recent advent of passenger car turbos brought pressure upon turbo engineers to take up new challenges for this high volume market and it became clear that the basic turbo design was only a small part of the potential improvement available. Such improvements included variable geometry nozzle vanes, turbine waste gate systems, compounding, and twin and sometimes quadruple turbocharger systems. Also, four entry turbine housings to avail the designer of the exhaust pulse energy and compressor after cooling have been made. These are not the only ideas to be developed some have been around for many years, particularly on large marine engines but the basic design has not changed much in 50 years. Hence, the focus was elsewhere as far as basic design change was concerned.

The radial flow compressor has a relatively narrow performance characteristic and typically high rotational speeds. For example, a 100mm diameter wheel may peak at 80000rpm and a 50mm wheel at 180000. A compressor pressure ratio of 2 bar is not the ideal for low compression ratio petrol engines and initially this level of pressure led to head gasket failures and lower bearing problems for both petrol and diesel motors. Therefore some of the aforementioned systems have been developed to provide lower pressures in the engine cylinder. Such developments include waste gating, variable geometry and twin turbo charging.

These advances have been beneficial to the basic design too as explained in the next paragraph.

All these systems incorporate the basic design turbo which may have to operate at high speed in an hostile environment. For instance, turbine inlet temperatures of around 550 degrees Celsius, and at the compressor end temperatures of around 100 degrees Celsius. These environments pose some operating limitations for the basic design. A heavier mass at the turbine end compared to the compressor end demands careful shaft balancing, in order to achieve a stable bearing system capable of running for 3 years or 300,000 miles between service whilst being able to offer reasonable warranty performance. Two plane balancing of each wheel is necessary and the machining and concentricity tolerance throughout has to extremely fine. Low cycle fatigue of wheel blades and centrifugal stress of the turbine wheel at high temperature are considerations taken into account during the design stage.

As discussed, the basic design of a turbocharger has not changed from that developed to cope with the stress and fatigue limitations discussed above. However, the improvements obtained with Nickel turbine wheels and Titanium Aluminium compressor wheels have moved the failure boundaries away from the operating range of the basic design turbo. Additionally, waste gated and variable geometry systems have moved the turbo operating points to more efficient positions on the wheel characteristic diagrams. Namely by lowering the shaft speed to give an additional movement away from the troublesome performance and failure areas. These latter developments open the door for the design modification which is the subject of this patent application.

The aforementioned engine/turbo systems when used in conjunction with the coming electronic engine control systems mean that the basic turbo design can be steered even further away from these potential areas of failure. Some field operating conditions have changed to the advantage of turbocharger life. Heavy commercial vehicles are now subjected to a governed 56mph maximum motorway speed (formerly 80mph), and use engines which seek best specific fuel consumptions, nearer to maximum torque speed rather than peak horsepower speed. They are also aided by closer engine/gearbox matching. This condition helps the turbo which consequently does not have to run at its peak operating speed and stress level, as was the case in the past. The single speed marine and industrial/generator engines, and high torque agricultural tractor and earthmoving vehicle engine applications allow the turbo to operate in a zone of performance which is relatively stress free compared to twenty years ago. Summarising, the majority of turbo engine applications have moved in the direction of lower operating turbo speeds. However, despite such a movement away from the failure boundaries there has been a prejudice in the industry not to move away from, change, or alter the basic design developed over fifty years ago.

It is an objective of the present invention to overcome at least one of the above or other identified problems. It is a further aim to provide a turbocharger, turbocharger component and turbocharger assembly process with reduced cost and improved performance characteristics.

SUMMARY OF THE INVENTION

According to the present invention there is provided an improved turbocharger, turbine wheel assembly, and rotor assembly having an improved turbine wheel and a method of assembling the same as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to a first aspect of the present invention there is provided a turbine wheel having a female engagement member. Advantageously, removal of the male engagement member and replacement with a female engagement member provides a turbine wheel having reduced mass.

According to further aspects of the present invention, there is provided a turbocharger, a turbine wheel assembly, and a rotor assembly all having a turbine wheel, wherein the turbine wheel has a female engagement member.

In the exemplary embodiments the turbine wheel has a proximal and distal end through which a rotational axis runs. At the distal end the turbine wheel is arranged to be connected to a shaft. At the proximal end a cavity is provided to act as the female engagement member. The cavity is coaxial with the rotation axis. The cavity in use may be engaged with a male tool.

The cavity may be star shaped, hexagonal, square or slotted, or any other shape which enables torque to be transferred from the tool.

Replacing the prior art nut and boss with a cavity enables a lighter turbo wheel to be used.

Also, because the female member does not, by nature, extend from the proximal end of the turbine wheel, the aerodynamic efficiency of the turbine wheel is improved.

A lighter turbo wheel is advantageous because less material is used. Consequently, large savings in cost can be made as turbine wheels are made from expensive alloys.

Further the reduced mass turbo wheel will reduce the stress in use on the bearing supporting the shaft.

Yet further, the turbo wheel is the heaviest end of the shaft assembly. Reducing the mass of the heaviest end will improve the balance of the shaft. Consequently in use the stress will be reduced in the wheel hubs. Further when balancing the turbo wheel, due to the reduced mass, less balance shock will be required.

Moreover, the reduced mass of the turbo wheel will reduce the amount of turbo lag. Turbo lag occurs when an engine accelerates from a lower speed, and is a consequence of the inertia of the shaft assembly.

In the exemplary embodiments a radial face is provided on the proximal end of the turbine wheel. The radial face surrounds the female engaging member. Advantageously, the radial face provides an area from which material can be removed. Thus, the turbine wheel can be easily balanced.

According to a further aspect of the present invention there is provided a method of assembly/disassembly of a rotor assembly and a method of forming a turbine wheel assembly.

Here, the method involves the step of inserting a male tool into a female engaging member formed integrally with a turbine wheel. The method comprises the step of using the tool to control the relative rotation of the turbine wheel. For instance, the tool can be used to rotate or restrain the rotation of the turbine wheel relative to a shaft or a fixing that secures a compressor wheel to the shaft.

In the exemplary embodiments the method comprises the step of balancing the turbine wheel by removing material from a radial face that surrounds the female engagement member.

Preferably, the material is removed by machining one or more recesses.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 shows a cross-sectional view through a prior art turbo charger; Figure 2 shows a cross-sectional view through a prior art rotor assembly; Figure 3 shows a cross-sectional view through a prior art turbine wheel assembly; Figure 4 shows a cross-sectional view through a prior art turbine wheel; and Figure 5 shows a cross-sectional view through a turbine wheel embodying a first embodiment of the present invention.

Figure 5 shows a turbine wheel 124. The turbine wheel has a co-axially arranged female engaging member 150. The female engaging member forms a cavity in which a corresponding male tool can locate. When a male tool is located within the cavity, the shape of the cavity is arranged such that relative rotation between the cavity and male tool is prevented. It will therefore be appreciated that the shape of the cavity can be any shape other than substantially circular in cross section. When assembling the turbocharger a bit of a tool can be inserted in to the female engaging member. Subsequent stages in the assembly process can be performed as disclosed in the prior art. For instance, during assembly of the turbine wheel and shaft, the turbine wheel can be held fast, relative to the shaft by inserting the male tool into the female engaging member (or vice versa). Also, the male member can be used to manipulate the turbine wheel assembly when the compressor wheel is being assembled / disassembled.

As discussed, it is necessary to balance the turbine wheel. In the prior art, balancing was done by removing parts of the nut or boss. The replacement of the nut and boss with a female member therefore removes an essential element of the known turbine wheel. It is proposed to balance the turbine wheel having a female member by providing a radial face 152 on the distal end of the hub 125 of the turbine wheel 124. This radial face provides an area which is easy to machine wherein material removal can occur. For instance one or more cavities can be formed in the radial face in order to affect the balancing. This would likely result in a series of circumferentially spaced cavities extending parallel to the longitudinal axis of the shaft and into the hub 125. The cavities can be formed by drilling, milling, or other known techniques. The depth, size and radial location of the cavity can be controlled in order to achieve the desired change of mass.

Consequently there is provided a turbine wheel having reduced mass to the known turbine wheel having a male engaging member, but without loss of important ability to balance the turbine wheel. For instance, the nut and boss of the known turbine wheel are approximately 5% of the weight of the turbine wheel casting. The turbine wheel casting is made from nickel/chrome alloy. Therefore the female engaging member would save a further 5% of metal. Hence a total of 1 0 %. The turbine wheel is the most expensive casting yet 5% of its mass serves no useful operating purpose. Thus a major cost saving is available to the user.

Furthermore, there is an environmental saving of hundreds of thousands of tons of base metals when considered on a world wide usage basis.

The unnecessary mass detracts from the operating performance as follows. As discussed above the shaft stability is important. The prior art teaches a male engagement member hence a mass of metal at the end of the rotor, thus adding mass to what is already the heaviest end of the rotor system. This is because the rotor system comprises a lightweight aluminium compressor wheel at one end and a heavyweight nickel turbine wheel at the other end. Removing the surplus metal by employing a female engagement member will improve the stability of the rotating system by reducing the mass of the heavy end. Furthermore, the reduced mass of the turbine wheel will be easier to balance, when the rotor balancing operation takes place by stock removal.

Known turbine wheels having male engagement members at the turbine exit interfere with the flow of gas leaving the turbine wheel. This increases the turbulence at the exit. In contrast, by employing a female engagement member, the engagement member does not protrude further than the blades of the turbine in the axial direction. Consequently, removal of the nut and boss from the turbine wheel assembly allows greater flexibility of design of the turbine wheel blade with the potential of improved turbine efficiency.

Reducing the total mass of the turbine wheel also results in reduce operational stress levels and increases the efficiency of the turbo charger. For instance, the turbocharger has long been criticised for its "turbo lag'. This is caused by change in the flow rate of exhaust gasses as the turbo shaft tries to accelerate keep up with the engine speed changes. A lighter rotor assembly would reduce turbo lag by offering improved acceleration of the rotor assembly.

Referring back to Figure 5, the female engaging member 150 is shown as a splined cavity 154.

The shape of the male tool or tool bit is the male equivalent of the female engaging member.

For instance, when the female engaging member is a spline, the male engaging member is a spline drive. The cross-section of the female member could also be hexagonal, star, square or any other shape suitable for transferring axial torque from the tool. It is preferable however if the male tool is a common tool so that repair shops have the tool to hand. The manufacturing processes earlier ascribed to the present nut design can equally be performed with the female engagement member, in star shape, hexagon, square or slotted. With the female engagement member balancing stock removal also remains possible as does welding drive, machine drive and servicing tool application.

The depth of the female member 150 is approximately 20 percent of the axial length of the turbine wheel. The outermost diameter of the female member is approximately 70 percent of the radius of the radial face 152. However it should be appreciated that both these parameters can vary, for instance, according to the magnitude of torque required to be transmitted from the tool.

Although preferred embodiments(s) of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made without departing from the scope of the invention as defined in the claims.

Claims

C'aims 1. A turbine wheel having a female engagement member.
2. The turbine wheel of claim 1, wherein the turbine wheel includes a radial face that surrounds the female engaging member, the radial face providing an area to be machined in order to remove material.
3. The turbine wheel of claim 1 or claim 2 wherein the female engaging member comprises a shaped cavity formed in a proximal end of the turbine wheel and the cavity is coaxial with a rotation axis of the turbine wheel.
4. A turbine wheel assembly comprising a shaft and a turbine wheel, the shaft is fixed to a distal end of the turbine wheel, co-axial with a rotation axis of the turbine wheel and wherein the turbine wheel is as claimed in any of Claims 1 to 3.
5. A rotor assembly comprising a compressor wheel and a turbine wheel assembly, the compressor wheel is attached to a free end of a shaft of the turbine wheel assembly, wherein the turbine wheel assembly is as claimed in Claim 4.
6. A turbocharger comprising a rotor assembly that is rotationally supported within a housing, wherein the rotor assembly is as claimed in Claim 5.
7. A method of manufacturing a turbine wheel assembly, the method comprising inserting a male tool into a female engaging member that is formed integrally with a turbine wheel and using the tool to control the rotation of the turbine wheel relative to a shaft in order to assemble the shaft to the turbine wheel.
8. The method as claimed in claim 7, wherein the method comprises balancing the turbine wheel assembly by machining a radial face of the turbine wheel that surrounds the female engaging member in order to remove material by forming one or more recesses.
9. A method of assembling or disassembling a rotor assembly, the method comprising inserting a male tool into a female engaging member that is formed integrally with a turbine wheel and using the tool to control the rotation of the turbine wheel relative to a fixing in order to secure a compressor wheel to a shaft.