Quiet Motor-Pumps Improve Test-Lab Data

Westland, MI -By minimizing noise and vibration, a new hydraulic power system improves a test lab's working environment and the quality of its data.

Capable of operating dozens of single-channel hydraulic stations, the system will serve as the power source for a new road simulator used by the automotive industry. It features a noise level of 81 dB at 3,000 psi operating pressures. In contrast, similar systems operate at 100 to 105 dB.

Engineers at Defiance-STS/SMC test and simulation laboratory say that the new power source eliminates "rumble and pulsation" phenomena in its servo hydraulic test equipment. As a result, test data are cleaner, they say.

The new system will be used to its best advantage when operating road simulators, which automakers employ to test new vehicles. During operation, technicians couple each of a vehicle's wheels to a single hydraulic actuator. The actuator-a hydraulic cylinder-moves each wheel up and down a distance of plus or minus five inches from dead center. By doing so, it simulates the effect of a tire striking a pothole or a large rock. "We're replicating the kinds of linear displacements that take place on the road," notes Lynn C. Benner, supervisor of service and training for Defiance-STS/SMC.

To control the actuator's motion, engineers employ a servo valve, a linear variable displacement transducer (LVDT), and a computer. The servo valve meters hydraulic oil into the cylinder in response to commands from the computer, which employs a stored motion profile. Output from the LVDT consists of a proportional signal that's delivered to the controller. This signal enables the controller to monitor the linear movement of the cylinder. By reducing the vibration ordinarily transmitted through the hydraulic oil, the new power system enables the road simulator to precisely control deflection and force at each wheel.

A 600-gpm, 3,000-psi central hydraulic system will feed oil to the company's proposed new road simulator. When complete, the system will consist of two sub-units, each with a reservoir and five motor-pump assemblies. Each ac motor, rated at 125 hp, is coupled with a 60 gpm pump. An Allen-Bradley programmable logic controller governs the entire system. Designed and constructed by Newton Manufacturing Co., the system will run more than 54 stations of single-channel hydraulics.

Key to the system is the hydraulic power unit, designed by engineers at Vickers, Inc., Maumee, OH. Called the Integrated Motor Pump, it combines an oil-immersed electric motor with a hydraulic pump. ( Design News, 8-29-94, pg. 16 and Design News , 12-5-94, pg. 72)

Bathing the ac motor in hydraulic oil provides it with two important, noise-related advantages. First, this approach eliminates the cooling fan, which typically adds noise to air-cooled motors. Second, because the oil-cooled system needs no air flow, engineers can enclose the entire motor and pump in a sound-absorbing housing. Made of lightweight, polyethylene plastic, the sound shroud retards the transmission of sound to the outside environment. As a result, Defiance-STS' five motor-pumps operate at 81 dB. Single motor-pumps have exhibited noise levels of 71 dB in other 3,000 psi applications, say Vickers engineers.

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