Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. The 4/5/6-Post Laboratory Vertical Road Simulation is used to evaluate structural durability performance of various vehicle subsystems using highly repeatable displacement profiles designed to represent proving ground road modules.

Applicability. This procedure can be used to develop or validate the structural durability of vehicle subsystems sensitive to vertical road input and powertrain torque reactions. Body subsystems where the body is mounted to a frame (e.g., pickup trucks, some vans and utility vehicles) can be validated using the 4/5/6-Post Test. Passenger car body and chassis subsystems and truck frame and chassis subsystems typically cannot be validated with this type of testing alone. This is due to the fact that non-vertical inputs contribute to significant fatigue damage in these types of subsystems. Non-vertical inputs cannot be reproduced on the 4-Post Test. Components sensitive to non-vertical road inputs will not experience an adequate level of correlation.

The tests referenced in this procedure do not provide a total vehicle durability test. No powertrain or electrical system operation is included. Degradation modes of rotating components such as wheel bearings are not accurately reproduced. Environmental factors such as elevated temperature, humidity and dust are not typically able to be included. Degradation modes related to exposure time are usually not accurately reproduced.

Additionally, some components are subject to unrealistic wear due to the accelerated nature of the test. Shock absorbers and some elastomers are known to wear prematurely during the test due to excess internal heat generation, which is not dissipated as in normal vehicle operation. Therefore, such components are usually monitored and replaced as necessary during the test. External cooling is usually applied to extend the life of some components during the test.

This procedure can be used for all passenger cars and trucks provided the hydraulic actuators are capable of reproducing the vehicle responses for the proving grounds being simulated. The source data to simulate the proving grounds can come from:

• Physical Road Load Data Acquisition (RLDA) (See GMW15019.)

• A virtual RLDA (vRLDA) or,

• Synthetic Road Drive Files (SynRoad).

Throughout the rest of this document, “desired response files” can be from any of these sources.

Remarks. This test procedure shall be performed according to the requirements stated in the Validation Plan or Activity Request.

The 4-Post Laboratory Vertical Road Simulation serves primarily to represent road-induced vertical loading applied through the four vehicle tires. These loads usually introduce fatigue, interference and wear phenomena to vehicle structures and sub-systems. See Appendix A for considerations in developing a Test Plan for a 4/5/6-Post Test. See Figure B1 in Appendix B for an example 4-Post setup.

The 5-Post and 6-Post designation refers to the addition of powertrain torque input and/or axle torque input to the existing four vertical tire inputs. These additional inputs are sometimes used to evaluate the powertrain mounting system and suspension attachments.

Depending on the GMW Durability Schedule selected, a 4/5/6-Post Laboratory Vertical Road Simulation can reproduce one test equivalent of fatigue exposure for most inertially induced vertical structural inputs in 100 h to 850 h.

For each vehicle, there is preparation time required before durability testing begins. This time may include gathering of desired response files, simulator drive file development, and correlation evaluation. These processes may take several weeks, and must be factored into the test plan. Less time is required if carryover or modified drive files can be used. This test procedure is written for laboratory test engineers and laboratory test technicians. This document is not intended to be used alone as a test specification. The simulation process is intended to produce laboratory road simulations for specific vehicle systems. That is, a set of drive files will closely reproduce measured responses from remote parameters and/or correlation transducers for one vehicle with a specific combination of ballast condition, ballast position, body stiffness distribution, and chassis components. If any of these characteristics are changed, the degree of laboratory-to-road correlation is compromised. However, the test requester and test engineer can together evaluate the risk entailed with a given compromise.

Experience has shown that the compromise is minimized under some conditions, such as a small change in shock absorber damping, mass change, and wheelbase change or body stiffness distribution. If the areas of interest are remote from the suspension-to-body interfaces, the risk can be further reduced. Significant time and cost reductions can be achieved by omitting or condensing the simulation process, if the risk is judged acceptable.