Hydraulic Motor Testing

Application Summary
Hydraulic motors are widely used in many types of heavy-duty, agricultural and construction mobile equipment, such as skid-steer loaders, street sweepers, rock-boring equipment, and golf-course maintenance vehicles. The motors usually occupy less space than electric motors and reciprocating engines with the same torque and speed ratings, and for certain applications, they can provide even more torque and speed.

To ensure that all hydraulic motors that leave the Eaton-Shawnee Hydraulics Division production line meet their intended operating requirements, they undergo a short run-in test and a number of functional tests before shipment. In addition, a few motors are audited to ensure that they meet the full range of performance specifications including maximum reliability and efficiency. This performance testing validates their original design goals — to withstand the real-world rigors of off-road use and abuse. Robert Gear, Reliability Test Technician at the facility, has the responsibility to perform these audits and make sure the equipment and instruments used to test the hydraulic motors are properly calibrated and maintained at all times. In addition, Gear operates the equipment and runs the tests.

Potential Solution
Until recently, the test equipment and data acquisition system that Gear used had a limited number of inputs and other serious drawbacks. Although the acquisition system consisted of a variety of well known, instrumentation-type black boxes, computer-based plug-in cards, signal conditioners, customized interfaces, and strip-chart recorders, much of the equipment was slow, out-dated, and infrequently updated including the DOS-based computer. The data were translated to meaningful information manually, which was extremely tedious and often susceptible to errors. And with an increase in production, it became necessary to purchase more automated and functional test equipment.

IOtech’s Solution
A cross-functional team located at the Eaton Hydraulics design and development facility, Eden Prairie, Minn., investigated and evaluated several data acquisition systems that were available. After a thorough analysis, the team decided upon the IOtech test equipment and recommended a DaqBook^® for the Eaton-Shawnee performance-testing operation.

Gear now has two DaqBook systems that routinely measure several temperatures as well as pressure and flow in hydraulic motors ranging from 250 to 5500 psi. and 0.5 to 50 gpm. The test stands are basically dynamometers, using hydraulics or pneumatics to load the motors during dynamic testing. The hardware connects to three pressure transducers, and two flow meters. Strain-gage pressure transducers measure the input, output, and case pressure, thermocouples measure temperature, and turbine transducers measure flow. The turbines output a dc voltage that is fed directly to the DaqBook. The strain gages connect to DBK43A^™ signal conditioners, and the thermocouples use DBK82^™ signal conditioners. The software interprets flow from turbine rpm measurements, converts the strain-gage outputs to torque in lb-ft at the load, and records pressure in psi in the motor’s case. Differential pressure also is measured between the input and output ports. For example, the input pressure may operate at 5300 psi while the output is 300 psi. Therefore, the software automatically interprets the differential pressure to be 5000 psi.

The DaqBook is handled as a fine instrument. It is located some distance away from the test stand and mounted in a protected instrument cabinet with the test system’s control panel. For most signals, shielded pairs of wires run to single-ended inputs on the DaqBook and the signal conditioners located at the test stand. One exception is the differential measurement for the pressure signal between the input and output ports. No noise or other signal deterioration can be detected during any of the testing programs.

Gear appreciates the DASYLab^® software and Windows^®-based operating environment, particularly in contrast to the previous DOS-based system. It was difficult to translate the DOS information to the more widely used Windows-based computers. The DASYLab software also lets Gear record, in real time, mechanical units of measure and volumetric efficiency. He does not have to manually calculate the values, a huge advantage in saving time and reducing errors compared to the previous equipment.

Gear also wrote a timer program that lets him set up a test and take critical measurement points 30 sec apart — unattended for up to two hours. “The DASYLab software contains a list option that lets me return to the beginning of the test and re-examine every point that I had taken,” says Gear. “That’s an extremely handy and user-friendly feature that the previous data acquisition didn’t have. When you see our Web site and look at our catalogs, you will notice the “bingo” charts for numerous performance points from 0.5 to more than 30 gpm over a pressure range of 250 to 3500 psi. The point list is saved so we can return to the test and examine every point that was recorded when we need to run a trend analysis.”

Conclusion
Numerous DaqBooks collect data from test stands used on the hydraulic motor production line for final performance and durability tests at the Eaton-Shawnee Hydraulics Div., Shawnee, Okla. The combination of DASYLab software and the DaqBook flexibility lets engineers and test technicians run a wide variety of pressure and flow tests on a production line that otherwise would have taken much longer because of the large number of data points needed for final testing.