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Use Cases
Use Cases

Fatigue strength measurement on tie rod and axle control arms

Optimization of electric and hybrid vehicles often focuses on components in the electric powertrain. However, to increase range and efficiency, a perfect balance of weight and stability is required for numerous components. This compromise is particularly challenging for heavily stressed components such as the chassis. This application example shows how the measurements of the fatigue strength are carried out on tie rods and axle control arms.

Tie rod and axle guide in vehicle
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Background

As part of the so-called unsprung masses, tie rods and axle control arms have a significant influence on ride comfort and driving dynamics. In order not to endanger safety on the one hand and to allow a comfortable driving experience on the other, a good balance of strength and mass of the components must be achieved.

Simulation models are used during development to simulate the expected forces. To validate the simulations, the forces acting on the axle geometry are measured on the test bench and in road tests and correlated with other values. The forces acting on the control arms and tie rods must be determined in order to measure the fatigue strength. In addition, spring travel, steering angle and speed are to be measured.

Measurement Task

Measurement of forces on control arms and tie rods as well as measurement of spring travel, steering angle and speed.

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Challenge

The acquisition of the required measured values should be carried out in parallel with a single measurement system to allow simple application. In addition, the measurement system should be able to be used in all test scenarios (test bench, road, test track) to avoid long conversion times.

Tie rods and control arms are designed as very stable components, which means that only low strain values are expected in normal driving situations. The measurement technology used must be correspondingly high-resolution in order to be able to precisely acquire even very small signal values.

At the same time, the measurement technology should offer high dynamics in order to be able to measure very high values, such as those that occur during misuse tests.

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The CSM-Solution

Components from the Vector CSM E-Mobility Measurement System are used for the measurements. This allows easy acquisition of all measured values with a coordinated measuring system.

Measurement setup for measuring the fatigue strength of the tie rod and axle control arm

  • The tensile / compressive loads on the tie rods are measured with strain gauges. The strain gauges are applied as a full bridge in pairs opposite each other as a T rosette.
  • Depending on the geometric structure of the axle control arms, strain gages are used to measure individual strains, bends and tensile/compressive loads. Thus, application-specific full, half or quarter bridges are used.
  • The signal values of the strain gauges are acquired with STG6 pro BS20 strain gauge measurement modules. Quarter bridges are supplemented to half bridges directly in the sensor cable. The addition to the full bridge takes place directly in the measurement module. This simple addition means that no further wiring is required and application is accelerated. In addition, a wide range of strain gauge resistance values can be supported very easily.
  • Thanks to the extremely fine input voltage range, even very small measurement signals are recorded accurately. The input voltage range is automatically selected in the measurement module.
  • The spring travel is measured in parallel using suitable distance sensors on an AD4 IG1000 measurement module.
  • The measurement modules are connected to an XCP-Gateway. This converts the EtherCAT® signals to XCP-on-Ethernet and synchronizes all measurement modules.
  • Steering angle and speed are acquired from the vehicle's ECU using a VX1000 Vector interface. The interface is integrated directly into the measurement chain via XCP-on-Ethernet. Using the Precision Time Protocol (PTP, IEEE 1588), the data from the ECU can be synchronized with that of the measurement modules.
  • A data logger or measuring computer is used to record and further process all data.
Fatigue strength measurement on tie rod and axle control arms in the systematics of the Vector CSM E-Mobility Measurement System
Fatigue strength measurement on tie rod and axle control arms in the systematics of the Vector CSM E-Mobility Measurement System
Icon Benefits

Benefits

With this measurement setup, all required measured variables can be acquired easily and in parallel. The robust and compact design of the measurement modules allows them to be installed close to the measurement point, requires only very short analog signal cables and enables them to be used in road tests and on the test bench.

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