Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Mechanical and Aeronautical Engineering
Selected Highlights from Research Findings
One of the challenges in designing suspension systems for 4X4 vehicles is the fact that such vehicles need to perform well under a variety of road conditions.
A system that works well in some circumstances might compromise performance in others. For instance, soft springs and low damping serve to isolate the vehicle from road input, and therefore improve ride comfort in off-road conditions.
However, such suspension also produces a considerable amount of body roll around corners. Hard springs and high damping, on the other hand, prevent body roll and therefore improve a vehicle’s handing capabilities – but with the consequence that the driver and passengers feel every bump on the road.
In answer to this challenge, researchers in the Dynamic Systems Group designed, developed and tested a novel suspension system that combines a semi-active hydro-pneumatic “spring” with a semi-active damper and ride height control.
Both spring and damper can be switched between two modes, so that the system is theoretically capable of assuming four alternative states. In view of this fact, it has been dubbed the 4-State Semi-active Suspension System (4S4).
Only two of these states are currently employed in practice: soft spring with low damping (the “ride comfort” mode) and stiff spring with high damping (the “handling” mode). Further research is underway to investigate the possible benefits of the remaining two states.
In the 4S4 system, the suspension setting of each of the four wheels is adjusted automatically to respond to changing road conditions. It therefore offers a comfortable ride on rough roads as well as superb handling whenever this is required.
The system has been fully characterised by performing mathematical modelling and computer simulation of the vehicle dynamics. Field-testing results indicate that the system exceeds expectations in terms of handling improvements by more than fifty percent. Prof NJ Theron
Mechanical and Aeronautical Engineering
+27 (0) 12 420 3309
njtheron@postino.up.ac.za
An effective face support system to minimise rockfalls in rockfall-prone mines was developed during a project sponsored by the Safety In Mines Research Advisory Committee (SIMRAC). A technology demonstrator roof support unit was developed and evaluated. Mines with rockfall problems in the face areas can use the roof support system to reduce fatalities and injuries in the face area of stopes.
The steel roof support system consists of two similar support units connected to each other via two crank mechanisms. Each unit consists of a headboard supported by a “wishbone” structure (top and bottom leg). A threaded bar with struts similar to a scissors jack keeps the legs apart. To move the system forward one support unit is collapsed and then hangs from the other. The collapsed unit is manually cranked forward and pre-stressed. If the required position is still not achieved the other unit is released and moved forward. Different models will be used for different stoping heights.
The specification for the system was determined and presented at a workshop with industry participants. Different concepts were developed and evaluated against the system specifications. A technology demonstrator was then developed and tested on surface.
The development process included detail design, building and testing of components and sub-systems, design reviews and the building and commissioning of the technology demonstrator. Its testing was done in a 500-ton hydraulic press, in a mock-up stope and underground.
A risk analysis, in which technical, logistical and economic aspects were assessed, was done to determine the critical areas of the system. During the next phase of the project working prototypes will be developed for underground evaluation. Mr NDL Burger
Mechanical and Aeronautical Engineering
27 (0) 12 420 3764
danie.burger@up.ac.za
A low noise blast hole drilling system was developed to limit the risk of noise induced hearing impairment in mining operations. Noise induced hearing loss has been identified as a major occupational health risk in SA mines.
The noise generated by pneumatic percussion drills is a major contributor to such noise induced hearing loss. This motivated the South African Safety in Mines Research Advisory Committee (SIMRAC) to commission the development of a low noise rock drill system.
The system had to be designed, manufactured, tested and demonstrated in a simulated underground mining environment. The specification required noise levels below 90 dBA. Other important design considerations were ease of manual transport, setting up and operation.
The primary design concept was to encapsulate a standard Seco S215 pneumatic rock drill in a composite material tube. The tube is pushed onto the rock face by a pneumatic cylinder and is sealed at the rock face by an elastic seal.
The drill is pulled towards the rock face by a rope and pulley mechanism fitted inside the tube. This mechanism is powered by a second pneumatic cylinder.
The actions of moving and setting the drill require two persons. However, the team can carry out the drilling function itself on several drills simultaneously because of the self-thrusting design.
The drill is supported by two camlocks. The exhaust (air containing dust, water, rock shavings, oil and grease) is removed from the encapsulating tubes via an exhaust tube to the end of the stope. In this way exhaust noise and air pollutants are disposed of away from personnel.
Tests were conducted in a test stope. Noise levels of under 90 dBA were achieved, thereby attaining the primary design specification. This was achieved without materially compromising ease of handling.
Penetration rate was somewhat improved compared to that of the standard drill, so that productivity could be maintained.
Mr NDL Burger
Mechanical and Aeronautical Engineering
27 (0) 12 420 3764
danie.burger@up.ac.za
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