Damping Force Characteristic Test of Suspension Struts [JASO C611]

Importance of the Topic

The dynamic damping characteristics of suspension struts directly affect vehicle ride comfort, handling stability and component durability. Reliable, standardized measurement of damping force versus piston speed is essential for R&D, quality control, regulatory compliance and comparative evaluation of suspension components. Tests conducted to JASO C611 (and related JASO C602) provide repeatable criteria for manufacturers and test laboratories to verify performance across defined excitation speeds and stroke conditions.

Objectives and Study Overview

This application note documents a JASO C611-compliant damping force characteristic test performed on a commercial front suspension strut using Shimadzu's EMT series electromagnetic fatigue testing machine. Primary goals were to demonstrate: (1) the ability to set and execute tests based on excitation speed, (2) accurate high-speed control and data capture of force and displacement waveforms, and (3) generation of damping force versus stroke and damping force versus speed characterizations for evaluation.

Used Instrumentation

• Electromagnetic dynamic and fatigue testing machine: Shimadzu EMT-1kNV-50 (high-frequency electromagnetic actuator).
• Controller: 4830 controller with Windows Software for 4830.
• Grips: dedicated suspension-strut gripper jigs for mounting the commercial four-wheel front strut specimen.
• Load measurement: 1 kN load cell.
• Stroke capability: ±50 mm.
• Software: Combination test software to chain multiple condition files and a wizard to set test conditions by excitation speed.

Methodology

Tests were performed in displacement-control using a sinusoidal waveform. Key test parameters set according to JASO C611 (and implemented via the software speed-based setup) were:

• Excitation speeds tested: 0.05 m/s, 0.1 m/s, 0.3 m/s, 0.6 m/s (1.0 m/s specified by the standard was not executed because damping force exceeded the EMT-1kNV-50 capacity).
• Amplitude (stroke): ±50 mm; mean: 0 mm.
• Number of cycles (repeats): 10, 20, 60, 100 (set per file and run sequentially by combination software).
• Environment: room temperature (~24 °C).

Data acquisition captured time waveforms of force (damping force) and piston displacement (stroke). Piston speed was obtained by differentiating displacement with respect to time to produce force-versus-speed plots. Test condition files were automated and executed sequentially to cover the required speed points efficiently.

Main Results and Discussion

Key observations from waveform and cycle-peak analyses:

• Force and displacement time traces showed no rattling at zero test force, indicating secure specimen fixation by the dedicated grips.
• Cycle peak force values remained consistent across the recorded cycles, suggesting negligible short-term thermal effects or specimen degradation during the short test durations.
• Damping force increased with excitation speed: Lissajous-type force-versus-stroke plots and force-versus-speed graphs clearly demonstrated higher peak damping at higher speeds.
• Speed control accuracy was high: the plotted left/right edges of force-speed graphs confirm that the actuator reached and maintained the target excitation speeds precisely, validating the controller and software speed-based setup.

The damping force–stroke Lissajous plots were used to inspect hysteresis and linearity, while the damping force–speed characteristic charts (extension vs contraction) provided the principal performance metric used to evaluate the strut per the standard.

Benefits and Practical Applications

The method and instrumentation demonstrated provide several practical advantages:

• Standard-compliant characterization of suspension struts for R&D, supplier acceptance testing, and in-house QA/QC.
• High-frequency, high-precision control (via electromagnetic actuation) supports tests at speeds where conventional hydraulic rigs may be limited.
• Software features that accept excitation speed directly simplify test setup and reduce operator calculation errors (frequency-to-speed conversions).
• Combination test automation enables sequential execution of multiple speed conditions with minimal operator intervention, improving throughput and repeatability.

Future Trends and Applications

Potential developments and expanded applications include:

• Higher-capacity electromagnetic actuators (e.g., EMT-5kNV with 5 kN capacity) to permit testing at the highest standard speeds (1.0 m/s) or with stiffer/more heavily damped components.
• Dedicated shock-absorber test systems with integrated lateral-load mechanisms to perform sliding-resistance tests (per JASO C602/C611) and multi-parameter evaluations in a single automated test file.
• Integration of closed-loop thermal control and long-duration durability protocols to study heat-dependent damping behavior and aging.
• Model-based real-time control and advanced signal processing to extract parameters (e.g., coulomb friction, viscous damping, nonlinearity coefficients) during tests.
• Application of data analytics and machine learning to large test datasets for predictive maintenance, batch acceptance limits, and accelerated design optimization.

Conclusion

The EMT-1kNV-50 electromagnetic fatigue testing machine, combined with the 4830 controller and Windows software, successfully executed JASO C611-style damping force characteristic tests at multiple excitation speeds. The setup provided accurate speed-based control, secure specimen fixation, and consistent force/displacement data suitable for producing damping force–stroke and damping force–speed characterizations. Limitations encountered (exceeding force capacity at 1.0 m/s) are addressable by selecting higher-capacity actuators or dedicated shock-absorber rigs. Overall, the approach supports rigorous performance assessment of suspension struts for development and quality workflows.

References

• JASO C611:93 Suspension Struts.
• JASO C602:2001 Cylindrical Shock Absorbers for Automotive Parts and Suspensions.