Background Background (FMSS 207 / 210) Background
Rack and Pinion Gear Set
Two steering rack and pinion designs were required to be analyzed for stress studies. Each design was required to withstand two load cases.
To determine the bending and contact stresses in the rack and pinion assemblies under the specified load cases.
Loads & Boundary Conditions
The bearings on the rack and pinion were represented by specific translational and rotational constraints. Two axial moments of different magnitudes were applied to the pinion, one when the pinion was at the end of rack (in-corner), and when the pinion was on rack center (on-center).
Results - von Mises stresses
Von Mises stresses obtained from the analysis show that the stresses were below the yield strength of the material.
Results - Contact Stress Profile
The cutaway views illustrate the distribution of stresses within the rack and pinion at contact Stress continuity can be seen across the contact interfaces.
The stress levels were observed to be well below the critical limit and the rack and pinion gear sets are predicted to endure the loads defined in the analysis without failure.
Laboratory fatigue tests performed on the rear axle determined that the axle will not meet the stipulated durability requirements.
The low cycle fatigue life requirement defined by the customer was 200,000 cycles, while the high cycle fatigue life requirement was 1,000,000 cycles.
A low cycle fatigue laboratory test resulted in a fatigue life of 100,000 cycles, while a high cycle fatigue test resulted in a fatigue life of 500,000 cycles.
To simulate the high and low cycle loading conditions and correlate fatigue life predictions with laboratory results.
To conduct similar analyses on two design iterations (designs provided by the customer) and to compare the durability of the two designs with the baseline design.
Results - Baseline Design
Crack location predicted from Stress Analysis.
Results - Iterations I & II
Iterations I and II consisted of a modification of the baseline design by increasing the radii as shown in the picture Iteration II exceeds the design target.
Design - Iteration I FEA Simulation Laboratory Test Design Target Low Cycle Fatigue Life 128,600 200,000 High Cycle Fatigue Life 562,100 1,000,000
The Finite Element simulation correlated well with laboratory tests, both methods showing that the baseline design of the rear axle will not meet the required design criteria. The design used for Iteration II is the recommended design. The design exceeds the requirements stipulated by the customer.
Federal Motor Vehicle Safety Standards have defined several test that evaluate automotive sub-systems for safety issues in a frontal crash. Two such standards are:
To evaluate the strength of the baseline seat, and make design modifications to improve its strength, in frontal crash simulations.
Loads & Boundary Conditions
Results - Baseline DesignThe outboard recliner bracket failed at 67 % of load
Recommended Design - Iteration I
A reinforcing bracket was welded to the outboard recliner bracket.
Results - Iteration I
The outboard tower bracket failed at 83% of load.
Recommended Design - Iteration II
A reinforcing bracket was welded to the outboard tower bracket.
Results - Iteration II
The outboard recliner and tower brackets pass at 100 % of load The other components of the seat also pass at 100% of load.
Baseline simulation results indicated that the seat would fail at 67 % of the FMVSS 207/210 load due to failure of the outboard recliner bracket.
Design Iteration 1 simulation results indicated that the seat, with the outboard recliner bracket reinforced, would fail at 83 % of the FMVSS 207/210 load due to failure of the outboard tower bracket.
Design Iteration 2 simulation results indicated that the seat, with both outboard recliner and tower brackets reinforced, will not fail under the FMVSS 207/210 loading conditions.
A steering column deformation was simulated through finite element analysis and was correlated with lab test results.
To simulate the collapse of a steering column under a displacement-controlled load.
The top figure shows the displacement contours of the steering column components and its deformed shape.
The simulation result reflects the observed collapse condition during the impact test.
(FMSS 207 / 210)