Oval Bore Cam Member for Fuel Pump Driveshaft Stress Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing driveshaft assemblies for high-pressure fuel pumps experience high hoop stresses during assembly due to uneven thermal shrink fitting, leading to cam member failure under high load conditions due to non-uniform deformation and stress concentration.
Innovation Solution
A driveshaft assembly with a cam member featuring a concentric oval bore, where the ovality is within the range of 0.02% to 0.10%, providing a more uniform hoop stress distribution by reducing interference and deformation unevenness during thermal shrink fitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a circular bore is used in the cam member for thermal shrink fitting, then the assembly process is simple, but high hoop stresses and uneven deformation occur leading to cam member failure
Solution Approach 1:
The patent applies asymmetry by changing the bore shape from circular to oval with controlled ovality (0.02%-0.10%). This asymmetric geometry creates non-uniform thermal expansion and contraction during shrink fitting, which redistributes the hoop stresses more evenly across the cam member wall thickness, preventing stress concentration and improving reliability while maintaining manufacturing feasibility
Solution Approach 2:
The patent changes the geometric parameter of the bore from a perfect circle to an oval shape with specific ovality parameters (0.02%-0.10%). This parameter modification alters the thermal stress distribution pattern during shrink fitting, reducing peak hoop stresses and preventing cam member failure under high load conditions
2Ease of operation
If thermal shrink fitting is performed with a circular bore, then the cam member can be assembled on the shaft element, but uneven hoop stress distribution causes failure under high load
Solution Approach 1:
The oval bore with controlled ovality (0.02%-0.10%) creates asymmetric thermal stress distribution during shrink fitting. This asymmetry ensures that the hoop stresses are more uniformly distributed across the cam member wall, preventing stress concentration at specific locations and improving the component's strength under high load conditions while maintaining assembly capability
3Force
If the cam member is shrunk fitted onto the shaft element, then a secure connection is formed, but high peak hoop stresses develop causing potential failure
Solution Approach 1:
The patent modifies the bore geometry parameter from circular to oval with specific ovality (0.02%-0.10%). This parameter change alters the stress distribution pattern during shrink fitting, maintaining sufficient contact pressure for secure connection while redistributing the hoop stresses to reduce peak values and prevent failure
Solution Approach 2:
The oval bore geometry creates local variations in wall thickness and stress distribution around the bore perimeter. This local quality variation ensures that peak hoop stresses are reduced by distributing the thermal shrink fitting loads more evenly across different sections of the cam member wall
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
The oval bore design reduces peak hoop stress by 11% and maintains sufficient contact pressure to prevent relative movement, enhancing the cam member's durability and reducing the risk of failure under high loads.
Implementation Method 1
the cam member is heated up in order to expand an internal bore of the cam member
Implementation Method 2
the cam member is then cooled down to shrink-fit the cam member on the elongate shaft element
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
This invention concerns a driveshaft assembly for a high-pressure fuel pump comprising an elongate shaft element and a cam member comprising a concentric oval bore. The cam member and the concentric oval bore each comprise a major axis of symmetry perpendicular to a minor axis of symmetry. The concentric oval bore is arranged with respect to the cam member such that the major and minor axes of symmetry of the concentric oval bore and the cam member are coaxially aligned.