At the client meeting I talked to the engineers in the research department, who had been assigned to create a brochure that would show off their hottest piece of current technology for the next trade show.
The technology was a re-design of the hydraulic pump and motor system that controlled the aim of the Space Shuttle rocket engines. The suggested copy they gave me was a combination of deep Engineerese jargon about their product, and a puffy self- congratulatory section on their research department in general. They knew it wasn't right, but they didn't know what was wrong. Their idea for the cover was to have a bust of Albert Einstein with a human heart on a necklace. A smart pump, get it?
I asked for all the documentation available on the Smart Pump; the ad agency hadn't done that. I took the documentation home and slogged through it, and found a key point: once the new pumps were installed, the cooling system would require 640 fewer gallons of water, because so much less waste heat would be generated.
A quick trip to the calculator showed me that 640 gallons, at 8 pounds per gallon, was over 5,000 pounds. And every ounce on a Space Shuttle is precious. I knew that they'd stopped painting the external fuel tank when they realized that the paint weighed 900 pounds, so 5,000 pounds was a significant benefit. Each Shuttle flight could carry the equivalent of two extra Volkswagens into orbit.
So I made that the headline on the cover of the brochure: With One Intelligent Improvement, Abex Will Make the Space Shuttle 5,000 Pounds Lighter.
Power-Adaptive Hydraulic Control Systems Start With
The Smartpump Innovation
The best example of a power-adaptive hydraulic pump is the human heart. It must be capable of operating at 180 beats per minute for full emergency power, yet also operate at minimum standby demand, (60/minute) and every position between the two as commanded by the brain and sensory system.
To date, the Space Shuttle's hydraulic system has not been power adaptive. At liftoff, the Shuttle's engines develop 7,000,000 pounds of thrust. The thrust vector of the gimbal-mounted rocket motors is controlled by hydraulic servoactuators powered by seven Abex 3000 psi variable flow constant pressure axial piston pumps. This is the biggest use of hydraulic power in the whole bird; all other functions, such as landing gear and flight controls, are minor loads compared to liftoff.
The pumps in the boosters are finished with their job when they're jettisoned, but the three pumps on the orbiter must continue to function for the duration of the mission. When the system pressure is higher than the load requires, unnecessary energy is transferred to the hydraulic fluid in the form of waste heat. This waste heat must be dissipated in heat exchangers and coolant--a serious weight penalty.
NASA asked Abex to investigate a modification to the hydraulic pumps in order to lower this weight penalty.
The Abex solution: a variable flow pump with electronic pressure control which will allow the system pressure to be changed in response to the pressure load demand. Test stand results demonstrate an energy savings of 32% to 40% on the pump alone when the pressure is dropped from 3000 to 1000 psi.
By incorporating the SMARTPUMP modification, NASA engineers estimate the net weight savings after removal of water boilers would be over 5000 pounds.
ABEX: AT THE FRONTIERS OF HYDRAULIC SYSTEMS RESEARCH
The development of the SMARTPUMP variable flow pump opens the door wide for the design of power adaptive control systems, with their attendant energy and weight savings. Abex engineers have been studying the concept of a variable pressure pump for years as part of our ongoing research into sophisticated new hydraulic systems.
ROTARY ACTUATORS Another power adaptive control concept, the rotary actuator, is being developed by Abex engineers, It is basically a variable displacement motor: a servovalve controls a variable cam plate, allowing control of fluid displacement per revolution, and therefore controls torque. This is energy-efficient: torque varies with cam angle at constant supply pressure, and so provides only the torque necessary for a given load. Prototypes are urrently being tested in the DIVADS mobile anti-aircraft system to control turret azimuth. The turret must be able to operate off an accumulator - stored pressurized hydraulic fluid - so that the first shot could be fired before turning the engine on. The Abex rotary actuato Current research is directed at defining its operating characteristics under various load conditions.
INTEGRATED ACTUATOR PACKAGES We are testing performance of hydraulic systems in which electric-motor pumps generate local hydraulic power to operate actuation systems, as opposed to centrally generated hydraulic power. Integrated actuator packages eliminate hydraulic lines running through the ship. They are more reliable and easier to maintain. Presently, Abex has one integrated actuator package flying: an emergency get-home-and-land rudder control system on the F-14. We are now testing performance with emphasis on heat generation and deflection under load.
FAIL-FIXED SERVOVALVES Standard servovalves fail near null, or zero flow, upon loss of electrical power. But electrical failure that sends a spurious high current, either positive or negative, to the valve, could cause the spool to move hard over to the left or right, giving a full flow of fluid into the actuator and potentially leading to high velocity uncontrolled motion. The Fail-Fixed servovalve has three zero-flow positions: the null and the two extremes of spool travel. At exte , riding overstroke conditions, all flow is shut off, thus neutralizing one of the most significant failure modes. Because of pulse width modulation the valve "sees" only zero, full forward, or full reverse signals, time modulated to produce the required output. Therefore the only probable electrical failure modes would be to one of the closed positions. Currently Abex is refining port geometry on the Fail-Fixed valve and extending its utilization to a full range of sizes and fluids.
DIRECT-DRIVE SERVOVALVES Standard servovalves use a hydraulic force amplifying system to control the valve spool's motion. This amplifier is an open-center device and therefore has significant internal leakage. Abex is currently working on a compact, high performance Direct-Drive servovalve that uses a high-force solenoid to give a direct mechanical connection to the spool instead of the hydraulic amplifier. Our research will lead to an efficient and reliable pulse width modulated controller.
8000 PSI PUMPS Hydraulic systems that operate at high pressure can utilize smaller actuators and smaller diameter lines, saving space and weight. Abex has been investigating the practicality of systems at 8000 psi: pumps delivering oil at 8000 psi have operated successfully for 2,200 hours using fluid per MIL-H-5606, with an additional 600 hours using CTFE fluid and 500 hours using Skydrol , phosphate ester fluid. Prototypes of these pumps have flown in a modified T2j aircraft rudder control system for flight evaluation.
EXOTIC FLUIDS Whenever new fluids become available, Abex tests them thoroughly. CTFE halocarbon fluid is nonflammable. Despite its density (1.8g/cc) it is attractive because it provides full protection against hydraulic fires. Abex is testing this fluid for endurance and performance in systems, and for compatibility with our components.