Further potential exists for the GAStrut in other mining applications that require self-contained dampened suspension units such as coal mining shuttle cars. Here, the gas strut could be used as a type of limited suspension, improving operator comfort and reducing stress on the frame and undercarriage to increase unit life.
“Shuttle cars generally last one to three years before serious maintenance is needed,” says Mike Schubert, business development manager at Parker’s Hydraulic Accumulator Div. “By the second maintenance period, a complete overhaul and rebuild is generally required. A gas strut suspension would increase the time period between maintenance and rebuild.”
There is also potential for using the combined cylinder/accumulator technology for track tensioning in bulldozers, excavators, and tractors. There is a specific tension that needs to be maintained on the tracks of these vehicles. If the tension is not high enough, the tracks will fall off. If it is too great, the tracks will snap. Today, this task is generally handled by large springs, which can be difficult to fit within the track widths. A single unit cylinder/accumulator might be a perfect fit.
“Springs can be compressed, or extended, to the point of wearing out or where their tensile strength is changed,” continued Schubert. “With nitrogen, there is no elasticity point. It continues to compress with no change in its physical properties. So, as long as you don’t exceed the working design of the accumulator cylinder, there is greater flexibility in how far the nitrogen gas can be compressed. The benefits are longer life because accumulators can be recharged as necessary, and they allow for the design of smaller, more compact suspensions than possible with springs or air bags.”
Semi-active and active suspensions
The GAStrut is an example of a passive suspension, which has been the traditional standard on construction and mining vehicles. Passive suspensions simply react to the input they receive — namely changes in terrain. Typically, these are leaf springs and strut arrangements, and double coils that attempt to dampen the shocks from terrain changes. Once set, these systems cannot be adjusted. Some designers add multiple dampening or spring rates to suspensions. This can be a cost effective way to vary the spring rate based on the loading the vehicle encounters. Some mining suspensions incorporate air bags to absorb the shock loading. However, these have a short life.
“The other type of suspension is an active suspension, which holds promise for mining applications, due to its many operational benefits,” explains Schubert. “Active suspensions are designed to resist the input received by countering the input force with a second force in the opposite direction. They have been available on automobiles for years, but are rarely, if ever seen on construction and mining vehicles. Yet the benefits from a properly designed active and stable suspension are higher ground speeds, better cornering, reduced rollover, greater operator comfort, increased productivity and lower maintenance costs.”
The new semi-active and active accumulator/ strut suspensions in development will use sensors on the suspension with an auxiliary power unit to measure the impact of ground terrain. Algorithms in the sensors will tell the accumulator valve to open by a given percent to allow the correct fluid discharge to counteract the force being placed on the suspension by the ground. This “active” approach to mining suspensions can reduce the shock amplitude by as much as 66%.
For more information, call BTI at (708) 205-6060 or visit www.rockbreaker.com.
For more informtion from Parker's Accumulator Div., call (815) 621-7024 or click here.