Turbo Machine Differential Screw Fastening
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Solution Overview
Problem
Existing turbo machine technologies require excessive work and torque to fasten impellers to shafts due to friction and differential thread diameters, leading to increased stress and energy consumption, and often necessitate complex apparatuses like hydraulic tensioners.
Innovation Solution
A turbo machine utilizing a differential screw with matching thread diameters and pitches on the impeller and shaft screw portions, along with a rotation suppressing member, to securely fasten the impeller to the shaft without rotational movement, reducing the need for extended screw lengths and complex apparatuses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a differential screw with different thread diameters on impeller and shaft sides is used to eliminate relative rotation, then the impeller and shaft can be firmly fastened, but the screw length must be extended causing increased stress concentration and work amount
Solution Approach 1:
The patent applies homogeneity by making both the impeller screw portion and shaft screw portion have the same thread diameter. This eliminates the need for different thread diameters that would require extended screw length and complex step portions, thereby reducing stress concentration while maintaining firm fastening.
2Ease of manufacture
If the impeller is made to perform rotational movement relative to the shaft during fastening, then the male and female threads can engage, but the amount of movement required is vastly greater increasing the work amount
Solution Approach 1:
Instead of making the impeller rotate relative to the shaft during fastening, the patent inverts the approach by using a differential screw mechanism where the screw itself rotates and translates axially. This converts the rotational movement requirement into a controlled axial movement of the screw, significantly reducing the work amount during mounting.
3Stability of the object's composition
If friction force is increased between impeller and shaft to prevent shifting, then relative position stability improves, but a sizable fastening torque is needed increasing the work amount
Solution Approach 1:
The patent introduces the differential screw as an intermediary component between the impeller and shaft. This mediator provides the necessary friction and mechanical advantage to prevent relative shifting while requiring significantly less fastening torque compared to direct impeller-shaft friction, thereby reducing the work amount.
4Reliability
If a tension bolt is used to fasten impeller and shaft firmly, then rotational movement is prevented, but complex apparatus like hydraulic tensioner is required and work amount increases
Solution Approach 1:
The patent extracts the complex hydraulic tensioner apparatus from the fastening system by using a simpler differential screw mechanism. The differential screw achieves firm fastening through its mechanical advantage and self-locking property, eliminating the need for complex external tensioning apparatus while reducing the work amount required.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution minimizes the work required for pretensioning, reduces stress concentration, and eliminates the need for complex apparatuses, enhancing the efficiency and stability of the fastening process while maintaining secure attachment.
Implementation Method 1
it is preferable, once the impeller has been placed in contact with a seating surface (i.e., an end surface of the shaft that is placed in contact with the impeller), for the impeller to then be pushed further in the direction of the shaft so that the impeller becomes elastically deformed. However, in the technology described in Patent document 1 and Patent document 2, because friction force is acting between the impeller and the seating surface after the impeller has been placed in contact with the seating surface, there is an increase in friction resistance.
Implementation Method 2
a structure is disclosed in which an impeller and a shaft can be fastened together using a differential screw in which the pitch of the thread portion on the impeller side is different from the pitch of the thread portion on the shaft side
Implementation Method 3
for the impeller to then be pushed further in the direction of the shaft so that the impeller becomes elastically deformed
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
The present invention is a turbo machine (S1 ∼ S3) that is provided with an impeller (1a) that is rotated, and with a shaft (2) that transmits rotation power to this impeller, wherein there is provided a differential screw (3) having an impeller screw portion (3a) that is provided at one end thereof and that is screwed into the impeller, and having a shaft screw portion (3b) that is provided at another end thereof and that is screwed into the shaft, and that fastens the impeller and the shaft together, and wherein, in the differential screw (3), a thread diameter of thread ridges that are formed on the impeller screw portion is formed the same as a thread diameter of thread ridges that are formed on the shaft screw portion, and a screwing direction of the thread ridges that are formed on the impeller screw portion is formed as the same direction as a screwing direction of the thread ridges that are formed on the shaft screw portion, and a pitch between the thread ridges that are formed on the impeller screw portion is formed smaller than a pitch between the thread ridges that are formed on the shaft screw portion.