Open Cut » Health and Safety
The current 'Intelligent Dumper and Hauler Suspension System' (IDHSS) project has evolved from a suspension system concept conceived by Birrana Engineering Pty Ltd. This report documents work conducted to investigate the feasibility of the concept, and discusses the likelihood of the ultimate success of the project.
The ultimate aim of the project is to develop a retrofittable suspension upgrade package compatible with existing oleopneumatic (gas over oil) suspension systems used on off-highway dumpers and haulers in the surface mining industry. The envisaged package would automatically sense the load state of the vehicle and would optimise suspension characteristics accordingly.
If achieved this would have the following benefits:
Reduced harmful low frequency vibrations at the operator's seat.
Reduced peak tyre / haul road forces.
Reduced torsional frame stresses by addressing roll stiffness imbalance.
Initial Stage Objectives
The objectives of the initial stage of the project documented in this report were:
To test the hypothesis of anticipated operator vibration reduction through detailed computer simulation modelling.
To demonstrate the anticipated benefits of the concept through field trials.
To gain an insight into the likelihood of the ultimate success of the project.
The results of computer simulation modelling conducted by BHP Research, Melbourne Laboratories on typical 2-axle dumper and 3-axle
haulers using a detailed vehicle ride model were very encouraging. Clear trends showing a significant reduction in the weighted r.m.s. vertical acceleration at the driver's seat in response to changes in suspension parameters were predicted.
With the co-operation and assistance of Leo and Green Pty Ltd, field trials of an instrumented Cat777 dumper were then conducted at Ebenezer Mine.
Instrumentation of the test vehicle and analysis of subsequently recorded data was conducted by Vipac Engineers and Scientists. Suspension stiffness characteristics were manually tuned by changing the amount of gas and oil within the struts. Suspension displacements, accelerations of the un-sprung vehicle mass and steering inputs were measured and recorded, as were vibration accelerations at the cabin floor and operator's seat. Handling and vibration data was recorded over haul road courses with various suspension settings and at various speeds with the truck loaded and unloaded.
Suspension displacements during normal operation were found to be much smaller than anticipated, which limited the ability of the trials to verify the predicted trends of reduction in operator vibration and tyre forces. Suspension strut friction also appeared to be affecting free movement of the front struts.
At low frequencies, a significant source of vibration appeared to be wheel rotation. Below approximately 3Hz, axle displacements were generally significantly greater than suspension displacement, indicating that the vehicle was bouncing on its tyres. This problem was particularly apparent at vehicle speeds of 41-45 km/hr corresponding to a system resonance at approximately 1.6Hz.
The simulation model for the 'typical' truck requires revision to more accurately represent the vehicle used in the field trials. Further studies are required to investigate the dynamics of the vehicle in more detail. In particular, the effect of strut friction on vehicle dynamics is to be examined.
Conclusions and Recommendations
Birranaremains confident that the project will be successful. The results of the computer simulation were extremely encouraging, with the potential for a significant reduction in operator vibration being predicted.
The trends predicted by the simulation modelling were unable to be validated due to the small suspension displacements observed during the field trials, however there was no evidence that the predicted trends would be incorrect under the harsher operating conditions of principal interest.
Whilst not as conclusive as desired, the field trials were informative and highlighted areas requiring further investigation.
The effect of front strut friction needs to be looked at in detail. A revised vehicle ride model that will allow strut friction to be investigated is required.
In order to develop a working IDHSS prototype, the parameters used in the revised vehicle ride model need to be updated to represent those of the Cat777 dumper used in the field trials. The revised model would be used to investigate the vehicle dynamics in greater detail, and to subsequently determine the required prototype suspension parameters.