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Hydraulic motor speeds rocket launcher
Vairable displacement, intelligent hydraulic motor improves efficiency
By Charles J. Murray, Senior Regional Editor -- Design News, September 6, 1999
Jackson, MS-- By employing an "intelligent" hydraulic motor, the U.S. Army has improved the speed of a rocket launcher by a factor of up to ten.
The new rocket launcher is so fast that it reportedly can reach its firing point, load, and fire 12 rockets, stow its turret, and leave the firing site in less time than it took for the old system to fire a single rocket.
Significantly, engineers were able to achieve the speed gain without a corresponding ten-fold gain in power consumption. The key was the use of the Intelligent Motor™. By employing it, they reached the ten-fold goal while using only five times as much power. In contrast, a conventional servo- controlled, hydraulic motor-based system would have used 10-15 times as much power, engineers say.
The Intelligent Motor, designed by engineers at Vickers Aerospace Division of Eaton Corp., drives the rocket launcher's turret. They achieved the high-energy, low-power combination by taking a unique approach variable displacement technology. As it operates, the motor uses closed loop feedback signals from sensors, then varies its displacement to match the needs of the rocket launcher.
To vary the motor's displacement, the system changes the angle of the motor's yoke, which pivots on bearings. By increasing the yoke angle in the clockwise direction, output torque increases in the clockwise direction. Similarly, by increasing yoke angle in the counterclockwise direction, counterclockwise torque is increased.
This scheme is a departure from conventional systems, which use motors with fixed yoke angles. To increase output torque in conventional systems, the motor typically works with a throttling valve. The valve reduces the output torque by throttling down the system pressure. As it does so, however, it dumps some of the pressurized fluid energy. That energy is then dissipated as heat. As a result, the larger system must employ big heat exchangers to deal with the dissipated heat.
In contrast, the Intelligent Motor does not need large heat exchangers because it doesn't dump pressurized fluid energy. And because it isn't releasing energy, it's more efficient.
That's particularly important in situations calling for low output torque, but high speed. The reason: Conventional fixed displacement hydraulic motors consume power in proportion to speed. As a result, they often waste prodigious amounts of energy in constant velocity conditions. "If the output power is low, but the input power is high, you're going to waste that energy as heat," notes Rodney L. Case, engineering project specialist for Vickers. "But in variable displacement, the output and input are more closely matched."
Case says that the U.S Army application is the first in the military to use electronic control of a variable displacement hydraulic motor. Software control, in combination with the inherent advantages of variable displacement, enabled engineers to create a far more energy efficient system. "The primary benefit is that it consumes power in proportion to the power delivered," Case says. "So it only consumes as much as it needs."
Additional details...Contact John Ganzerla, Vickers Aerospace Div. of Eaton Corp., 5353 Highland Dr., Jackson, MS 39206; Tel: (601)987-3323; Fax: (601)987-5255.
Typical Applications
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Winch drives
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Leading edge flaps
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Weapons bay doors
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