A heart for excavators

A heart for excavators

March 2015

 

With the development of the RS control block platform, compact excavators have gained a sense of energy savings and true responsiveness.

All around the world, urban areas seem to exert an irresistible allure. To accommodate those new residents, housing has to be built. Working efficiently in urban canyons and between city streets demands maneuverable, high-performance, versatile construction equipment. This is why compact-design excavators are found ever more frequently on urban building sites where they dig, hammer and grasp. The demands on the machines are rising continuously. To do their job – comprising many different tasks – in tight spaces, users are asking for more precise control while the law is mandating ever lower emission values. “Significant progress can be achieved only by modifying the entire hydraulic system,” emphasizes Gilles Chetail, Head of Application Center for Compact Excavator at Bosch Rexroth in the French town of Vénissieux. There are massive potentials where the implement hydraulics make use of “flow sharing” (known as LUDV, for short). By its very nature, it improves the utilization of available engine power, the excellence of control response, and the precision of the excavator. In addition, it saves costs in design and maintenance, since the hydraulics are engineered as a single-circuit system. Just one pump is required and the piping layout is considerably simpler.

The SX is a huge legacy

The control block and the pump form the powerful heart of the excavator. And this is also the point where further development of the LUDV system starts. In 2012 Rexroth enhanced the extremely successful SX series of control blocks; the RS12 followed the SX12. With this series the company established the LUDV in compact-design excavators. While only five percent of the mobile working machines used LUDV 15 years ago, in the meantime this has risen to half.

The RS platform which followed thus had to live up to a tremendous legacy. But it made a great impression with its first appearance. “Customer feedback has been very favorable,” says Stephan Brummund, group leader RS development. “This new control block lets users save 10 to 15 percent on energy, depending on the design of the particular excavator, while at the same time increasing productivity.” The RS12 for excavators has now been joined by a big brother: the RS15, which went into production in November of 2014. The RS12 is laid out for three to eight tons, the RS15 for excavators between eight and twelve tons.

“The impetus for this development was the increase in demands put forth by the market,” Chetail explains. In order to achieve greater efficiency and tight control it was necessary to modify the design of the control block. “The challenge was to make these changes within the dimensional limitations imposed by the design,” Brummund adds. Increasing efficiency made it necessary to reduce internal pressure losses. To do this, the developers re-routed the channels within the control block while increasing their diameter. Thanks to their many years of experience in optimizing systems and valves, they could also improve maneuverability.

Greater efficiency

Without having to change the system architecture in their machines, the manufacturers – when making the change to the new control valves – can dispose of a greater volume of oil, at the same pressure level, to power the machine’s movements. The primary sides of both valves can handle up to 350 bar. This opens new perspectives in the design of the hydraulics which, in turn, has a positive influence on the system’s efficiency.

But the pump which works together with the control block is also engineered for even higher efficiency. The small control block is most frequently found in conjunction with the A10VO variable-displacement pump. In parallel to this, and used as an alternative concept, is the A7VO bent-axis hydraulic pump, with which efficiency can be improved even further – and for both brothers.