Vehicle Subframe Cast Node Groove Weld Seam Fatigue
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Solution Overview
Problem
Subframes for motor vehicles face challenges in achieving high strength, durability, and low weight, with existing designs often compromising on one or more of these aspects due to limitations in material usage and welding techniques.
Innovation Solution
The subframe design incorporates a cast node with a shoulder that creates a groove-shaped or trench-shaped recess for the weld seam, allowing for a reduced wall thickness of the extruded beams and improved fatigue strength, combined with a lap seam weld and use of lightweight materials like aluminum or magnesium alloys, to enhance both strength and weight reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the wall thickness of extruded beams is reduced to lower subframe weight, then weight decreases, but fatigue strength and structural integrity deteriorate
Solution Approach 1:
The cast node incorporates a groove-shaped recess with specific dimensional ratios (width at least 2.5 times the beam wall thickness) that concentrates structural reinforcement precisely at the weld seam location. This local geometric modification enhances fatigue strength at the critical connection point without requiring increased wall thickness throughout the entire beam, thus maintaining weight reduction while improving local strength.
Solution Approach 2:
The invention changes the geometric parameters of the cast node by introducing a groove-shaped recess with specifically defined width-to-thickness ratios. This parameter modification creates a stress-distributing geometry that improves fatigue strength at the weld connection, allowing thinner beams to maintain adequate strength performance.
2Ease of manufacture
If traditional welding methods are used to connect extruded beams to cast nodes, then manufacturing simplicity is maintained, but fatigue strength at the weld seam is insufficient
Solution Approach 1:
The groove-shaped recess in the cast node creates a localized geometric feature that specifically addresses weld seam fatigue strength. The recess geometry (width at least 2.5 times beam wall thickness) concentrates reinforcement where needed at the connection point, allowing standard welding processes to produce sufficiently strong joints without requiring complex welding procedures or additional reinforcement elements.
3Strength
If the width of the groove-shaped recess is increased to improve fatigue strength, then fatigue strength increases, but manufacturing precision requirements increase
Solution Approach 1:
The invention establishes specific parameter ranges for the groove-shaped recess, particularly that the width should be at least 2.5 times the beam wall thickness. This parameter definition provides a clear manufacturing target that balances fatigue strength improvement with achievable precision tolerances, avoiding overly stringent requirements while ensuring adequate performance.
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 design significantly reduces stress on the weld seams, enabling a substantial weight reduction while maintaining high rigidity and durability, allowing the subframe to absorb dynamic forces effectively.
Implementation Method 1
the extruded beam is connected to the beam connecting element by a weld seam
Data Source
AI summary
The invention relates to a subframe (1) for a motor vehicle, comprising at least three beams, of which, in the assembled state of the subframe, at least two beams (3, 4) extend at a distance from one another, substantially along the longitudinal axis of the motor vehicle and at least one beam (6, 7) extends transversely to the longitudinal axis of the motor vehicle, at least one of the beams being an extruded beam (3, 4), and at least one cast node (11) of aluminium, magnesium or an alloy based on aluminium and/or magnesium, the cast node (11) connecting the extruded beam (4) and at least one of the other beams (6) to another, wherein the cast node (11) has an arm-shaped beam connecting element (11.4), wherein the extruded beam (4) overlaps the beam connecting element (11.4), and wherein the extruded beam (4) is connected to the beam connecting element (11.4) by a weld seam (14). In order to improve such a subframe with regard to high strength and durability and low weight of the subframe, the invention provides that the cast node (11) has on the beam connecting element (11.4) a shoulder which defines a shoulder end face (16), wherein the shoulder end face (16) on the one hand and the extruded support (4) and/or the weld seam (14) on the extruded beam (4) on the other hand define a groove-shaped or trench-shaped recess (17), whose width or average width (W) is at least 2.5 times, preferably at least 3.5 times, particularly preferably at least 4 times, the wall thickness (te) of the extruded beam (4), and wherein the weld seam (14) is designed as a lap seam.