Open Cut » Health and Safety
The objective of this project was to produce a prototype retrofit suspension upgrade package for dumpers and haulers which would allow the suspension characteristics to be optimised according to the load state of the vehicle. The primary aims of the project were to reduce jarring and vibration at the operator's seat in order to reduce vibration related operator injuries, and to increase operator alertness by reducing vibration induced fatigue. Chassis stresses and dynamic tyre/haul road forces are also predicted to decrease, which is anticipated to be beneficial to chassis and tyre life and result in a reduction in haul-road distress.
Results of computer simulation modelling previously conducted in project C3103 were extremely promising, however during subsequent field trials the suspension of an instrumented dumper did not behave entirely as expected. This was attributed to friction locking of the "sliding pillar" front suspension struts. Modelling conducted up until this point had not considered strut friction.
The current project was focused largely on determining the effect of strut friction on suspension performance and operator vibration.
Computer models incorporating strut bearing and seal friction were created in order to determine the effect of strut friction on operator vibration. Additional studies were made to determine sensitivity to damping levels as strut stiffness and friction were varied.
The revised simulation models predicted significant improvements in operator ride would be achievable with the IDHSS concept, however reducing strut friction would be essential for the benefits of the IDHSS to be reealised.
As friction reduces, damping levels were predicted to become of increasing importance. Options for low frction bearings and seals were researched, and prototype bearing and seals were designed, manufactured and tested.
A pair of front struts were upgraded and retrofitted with prototype IDHSS kits and were fitted to a Cat 776 coal hauler prime mover at BHP Mitsui Moura Mine for Prototype trials.
Static friction levels of the prototype strut bearings were unfortunately found to be insufficiently low, and the predicted reduction in operator vibration levels could not be achieved because the prototype IDHSS struts were still friction locking.
Overcoming strut friction to allow the benefits of the IDHSS concept to be realised is believed achievable, and further work to achieve the project objectives is continuing.
Conclusions & Recommendations
The majority of objectives for the project have been met.
There is a clear understanding of the effect of friction on operator vibration, and revised simulation modelling and analysis have indicated that the IDHSS concept combined with a reduction in front sliding pillar strut friction should significantly improve hauler and dumper suspension performance and reduce op-erator vibration levels.
Although most aspects of the prototype struts were successful, static friction levels of the bearings used in the struts did not meet expectations, and the reduction in friction levels achieved in the prototype struts was inade-quate to realise the benefit of the IDHSS concept during the field trials.
We remain confident that the IDHSS concept will be successful. The results of the computer simulation were extremely encouraging, with the potential for a significant reduction in operator vibration being predicted.
Future work is proposed to achieve superior suspension control and minimise or eliminate static friction within the struts. It is believed simple active suspension control will produce the maximum reduction in operator vi-bration exposure and best achieve the objectives of the IDHSS concept.