Steering Column Phasing Optimization
Altair EmployeeOverview
CHALLENGE
Determine the optimal phase and universal joint position to minimize angle difference between the steering wheel and pinion.
PREFACE
Physical vehicle testing is resource intensive. Vehicle modeling and simulation provide an efficient alternative which can be implemented earlier in the design cycle to understand a vehicle’s dynamics. Multibody dynamics software such as Altair MotionSolve allows users to set up and analyze a wide range of dynamic systems, including vehicles. Altair’s MotionSolve allows the simulation of a large selection of vehicle events to analyze vehicle performance parameters. Results can be used to refine vehicle design and improve occupant comfort.
INTRODUCTION
The steering system is pivotal in shaping how a vehicle responds to driver inputs and manages different driving conditions. The configuration of the steering system profoundly influences vehicle dynamics, handling, and the overall driving experience. A critical yet often overlooked aspect is the phasing of the universal joints within the steering column. Proper phasing is essential for smoothening the torque variations perceptible to the driver, enabling a stable straight line (on-center) steering feel, as well as better responsiveness once the steering is turned slightly away from the on-center position. Phasing is a form of tuning, since it allows the steering feel to be symmetric about the on-center position. This isn't always a natural consequence of positioning the steering components. Good steering feel has always distinguished a well-tuned chassis from the rest of the market.
Understanding the Model Definition in MotionView:
The MotionView models leverage the Vehicle Tools Extension to create a front suspension model that includes steering. To focus on optimizing the steering system, the front suspension is deactivated during the simulation.
For precise phasing of the universal joints, three markers are employed per joint. The first marker establishes the correct orientation of the upper or first shaft. The second marker, which is referenced from the first, is adjusted according to the phase angle. The third marker determines the orientation of the lower or subsequent shaft.
The orientation of the universal joints is updated based on the positions of these markers. With the steering wheel operating at a constant radius, the angular displacement and velocity differences between the steering wheel and the rack pinion are recorded.
Understanding the Model Definition in HyperStudy:
In HyperStudy, the model incorporates phase angles ranging from 0 to 180 degrees, alongside Y and Z coordinates for the upper universal joint within a ±100-millimeter range. The primary objective is to minimize the peak to peak value of the angular difference between the steering wheel and the rack pinion. An additional goal was included to make sure the resultant peak to peak value is not 0. An optimization process using the Global Response Surface Method (GRSM) is employed to identify the optimal configuration.
Pre-Requisite
SOFTWARE REQUIREMENTS:
-
- MotionView (2024 or newer)
- MotionSolve (2024 or newer)
- Hyperstudy (2024 or newer)
Model Files
- Steering_U_Joint_Phasing.mdl
- Steering_Study.hstx
Usage/Installation Instructions
Modeling Steps:
- Enable the Vehicle Tools Extension
- Populate a front with Rackpin steering system
- Deactivate Front suspension
- Fix the rack housing to the ground to prohibit free fall
- Apply a motion to the steering wheel joint to drive the steering wheel from -360 to 360 degrees at constant velocity
- Create output to measure the angular difference and angular velocity ratio between the steering wheel and pinion
- Deactivate the inner and outer Tierod ball joints
- Create a Dataset to record the phasing angles for the universal joints
- Include markers to parameterize the orientation of the universal joint from the phasing angles
- Modify the universal joints to set the local cross pin orientation from the created markers
- Create a HyperStudy model to optimize the phasing angles and first Universal joint’s Y and Z positioning. The goal is to minimize the root mean square value of the angle difference between the steering wheel and rack pinion
Post-Requisite
RESULTS
Upon completing the optimization process, the peak to peak value of the angular difference between the steering wheel and rack was recorded at 7.90, significantly improved from the initial value of 22.44. The phase angles from the original design 90°, 35°, and 30° were adjusted to 37.5°, 108.9°, and 9.7°, respectively. Additionally, the coordinates for positioning the first universal joints were updated from (-410, 1325) to (-310 , 1250.03). These modifications have resulted in a noticeably smoother performance of the steering system .
Initial Design
Optimized Design
CONCLUSION
The integration of vehicle modeling and simulation offers a valuable alternative to traditional physical vehicle testing, streamlining the design process and enhancing the efficiency of evaluating vehicle dynamics. By utilizing multibody dynamics software such as Altair MotionSolve, engineers can rigorously simulate and analyze a diverse array of vehicle events, leading to refined design and improved occupant comfort. Specifically, the optimization of the steering system’s universal joint phasing has demonstrated significant improvements in performance. The refinement of phase angles and repositioning of universal joints has reduced the angular difference between the steering wheel and the rack from 22.44 to 7.90, resulting in a markedly smoother steering experience. These advancements underscore the critical role of accurate modeling and simulation in optimizing vehicle systems, ultimately contributing to enhanced driving dynamics and longer-lasting vehicle components.