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Sauer-Sundstrand adds second axial piston open circuit pump.

Sauer-Sundstrand Co. has added a second model to its series 45 axial piston open circuit hydraulic pump line, a move the Ames, Iowa, manufacturer said is the first step in what will be a significant and rapid expansion of its open circuit product group.

New to the series 45 is a 74 cc pump that joins the original 57 cc model, the company's first foray into open circuit piston pumps, introduced in 1996. Sauer-Sundstrand has an established line of open circuit gear pumps, and now in essence is paralleling that with an expanded axial piston open circuit product range.

The new 74 cc pump has a rated speed of 2400 rpm (2800 rpm maximum), with a maximum peak working pressure of 5075 psi; 4060 psi continuous. Flow at rated speed is 47.4 gpm. Both the 57 cc and 74 cc pumps are manufactured in Ames.

This is first step in Sauer-Sundstrand's plan to expand its axial piston open circuit pump line over the next few years. Next up are 100 cc and 130 cc pumps due to be launched in 2000. After that, the company is looking at displacements smaller than 57 cc.

Why this commitment to axial piston open circuit pumps? "In terms of open circuit work function applications, we have a good range of gear products," said Dylan Hayes, market specialist. "But for the higher, more stringent operating conditions of off-highway mobile equipment, we needed more products like the series 45.

"Equipment manufacturers are looking for complete system suppliers. With this range being expanded, plus our gear pumps, hydrostatics and our closed circuit propel products, it gives us a much broader range."

The new 74 cc pump shares many of the design features of the 57 cc model. Both are variable displacement, parallel axial piston/slipper designs that utilize a cradle swashplate design with a hydraulic control piston. Control is provided via a built-in compensator valve. The compensator varies the swashplate angle from maximum displacement to minimum when the set pressure is reached.

The major difference between the two pumps is in the controls. The 57 cc model has an integral single-spool control, while the 74 cc features a bolt-on, two-spool control with one spool for pressure compensation, the other for load sensing. Remote pressure compensation is offered as the third control option. Torque control is also currently under development and is expected to be introduced later this year.

The pressure compensator setting is externally adjustable from 1450 to 4060 psi, with a relief valve installed in the pump outlet line recommended for system protection. In operation the pressure compensator pilot valve consumes a maximum 0.7 gpm.

When system pressure at the pump outlet drops below the compensator setting, the control will increase the pump displacement to maximum flow. When the system reaches the compensator setting, the control regulates pump displacement to produce an output flow that will maintain system pressure at the compensator setting.

A remote pressure compensator control can be added by connecting an external pressure control valve to the remote compensator port, allowing the pressure compensator setting to be controlled mechanically or electronically below the setting in the pilot valve.

The load sensing control is designed to match pump outlet flow and pressure with system demand and is typically used with closed center load sensing directional control valves.

When the control valve is actuated, the load sensing port is connected to the load pressure. The control then adjusts the pump output flow to maintain a constant pressure drop, equal to the load sensing setting, across the control valve.

A pressure compensator pilot valve is built into the control, which when the load sensing pressure increases to the setting of the pressure compensator, the valve opens to limit the load sensing and system pressure. The load sensing setting is also externally adjustable, with a range from 145 to 435 psi.

According to Hayes, the 74 cc pump is expected to find many of the same market applications as the 57 cc model; primarily work functions on agricultural, forestry, railway maintenance and construction equipment. Hayes specifically listed backhoe-loaders, excavators, cranes and pavers, ag tractors and sprayers, and skidders and feller-bunchers as targeted equipment. The larger 74 cc frame is also expected to open up new applications in industrial power packs.

"Adding the large pump just gives us more options," Hayes said. "Typically equipment manufacturers want a supplier that can offer pumps of this type from 45 to 130 cc. This second larger frame size opens this up more for us, and gives us the opportunity to be on larger equipment within the same equipment group. The pumps that follow will obviously open this up even further."

There were four key features for the 74 cc pump that Sauer-Sundstrand identified in its customer surveys, the most import being envelope size. At 6.18 in. wide, 10.08 in. long and 10.47 in. high (for a radial ported pump with through-drive, the largest possible), Hayes said the 74 cc pump is only slightly larger than the 57 cc pump.

"Essentially it fits into the same envelop as the 57 cc pump" Hayes said. "What we've found is that we've been able to replace smaller displacement pumps with this larger pump in the same envelope. It gets used as a high flow option, such as on ag tractors for use on implement functions such as potato or sugar beet harvesting."

The second key feature is noise, increasingly important throughout the mobile hydraulic markets. At one meter, the 74 cc pump generates 76 dB(A) running at 1800 rpm and 3000 psi. At 4060 psi and 2300 rpm, the pump generates 81 dB(A).

Control responsiveness has also been improved, especially important, Hayes said, when the pump is powering a cylinder. The pump can go from its rest position to full flow in 30 to 40 milliseconds and can be destroked in 20 to 30 milliseconds. Hayes said the 74 cc pump is also rated for higher engine speeds, 2400 rpm with a maximum of 2800 rpm.

Tech Specs Sauer-Sundstrand Series 45

Design Variable displacement axial piston open circuit hydraulic pump

Flow 47.4 gpm at rated speed

Speed To 2400 rpm rated/2800 rpm max

Pressure Maximum peak: 5075 psi Continuous: 4060 psi

Mounting SAE C (SAE J744) mounting pad

Auxiliary Mounting Pad Options SAE A, B, B-B, C

Control Options Pressure compensated, load sensing, remote pressure compensation
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Author:Osenga, Mike
Publication:Diesel Progress North American Edition
Date:Mar 1, 1999
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