Jeff Herrin, Director of Advanced Programs at Sauer-Danfoss Inc., Ames, IA, says commercial products based on this technology are in active development and will be available in specific markets in the coming years.
A Digital Displacement pump (DDP) is a hydraulic pump which uses the same core piston pumping principles as many of the commercial pumps currently available in the market, says Herrin
The difference, however, is in how the DDP is controlled.
Output flow of a DDP is controlled by fast-acting electrohydraulic valves paired with each cylinder and piston in the pump.
says a nine piston DDP, for example, will have nine active valves, one per piston, providing control of the pump.
Traditional pumps, on the other hand, control output flow by varying the angle of a single swashplate which controls all of the pistons in the pump simultaneously.
"The electrohydraulic valves which control the pistons have to be very fast in order to provide the pump dynamics needed for most applications of hydraulic pumps," adds Herrin
Designing valves that are both very fast and able to pass a lot of flow through the valve body is not an easy task.
"Those two requirements at the same time are a real challenge," he
In addition, the large number of valves needed for every DDP makes it critical for developers of DDP technology to ensure reliability and robustness of the design in any kind of production environment.
"But by resolving the challenges, there comes a lot of new benefits," says Herrin
Why go DDP?
According to Herrin
, improved operating efficiency is one of the biggest benefits to using DDP technology.
"Digital Displacement pumps themselves, when compared to traditional pumps, offer significant improvements in efficiency, especially at part-load operating conditions," he
Because they provide very fast, dynamic pump control, DDPs offer efficiency at a component level as well as a system level, which leads to overall machine efficiency benefits such as improved fuel economy.
The faster control response of a DDP enables it to provide more precise and repeatable flow and pressure control for applications that require it, such as robotics.
Currently, many of these applications use high fidelity valves to provide precise control.
By using a DDP instead, the high fidelity valve can be simplified which can help reduce costs for customers.
says the potential cost reduction is not a matter of DDPs costing less than traditional pumps but rather their ability to help reduce overall system design costs.
When a DDP is used in place of a traditional pump, other components can be simplified or even removed from the system without sacrificing functionality.
"It's more of the system level bill of material and lifecycle costs comparison that become important and where benefits will be obvious to the OEM
and also the end customer," says Herrin
Because DDPs are such an efficient technology, they are also well suited for use in hydraulic hybrid drivetrains.
"Due to their precise controllability and excellent operating efficiency, Digital Displacement pumps and motors are actually the ideal technology for hybrid drivetrains," says Herrin
Hybrids are designed to provide total operating efficiency of the machine over the duty cycle, and in order to achieve that, the most efficient components must be used.
says at the moment, Digital Displacement is the most efficient pump and motor technology known to the industry.