(1) Component Integration
Hydraulic integration blocks have been widely used, reducing or even eliminating
conduits and connectors. The maintainability is improved by using cartridge
components, and the integral combination simplifies the installation and improves
the adaptability to vibration and impact environment.
(2) Replacing Electrical Feedback with Mechanical Feedback
The position feedback of electro-hydraulic servo actuators used by American
militias, Saturn-V rockets, space shuttles, and Apollo lunar simulators is mechanical
feedback. This device has the ability of “failure ! return to zero” and “failure ! safety”. Compared with the feedback of potentiometer and differential
transformer, this device can save a considerable number of connecting cables,
wiring solder joints, and corresponding electronic circuits, and improve the reliability, but its structure requires higher manufacturing accuracy.
(3) Redundancy Design for Key Parts
In general, redundancy design is used in hydraulic energy, electro-hydraulic servo
valve, and actuator.
1. Parallel hydraulic system. Parallel hydraulic system is used in large aircraft and
space shuttle without exception. The American space shuttle orbiter has four
independent hydraulic sources, which supply oil to every single unit of the
control system through a central hydraulic combination to form the whole
system. Each hydraulic power source has 50% (whole hydraulic power source)
working capacity. If one hydraulic energy source fails, the whole system can
still work normally. When the second hydraulic energy source fails, it can
ensure a safe return, that is, it has fault working/fault safety capability.
2. Dual series structure. The dual series structure is used for the electro-hydraulic
servo actuator of the rudder and landing gear of the American space shuttle
orbiter. The rudder surface is driven by four actuators (in double series layout).
Each actuator provides 50% of the required control force for the rudder surface.
When two of the actuators fail, the rudder still has 100% driving force.
3. Detection and correction (error correction) structure. The redundant damped
servo actuator of F-111 fighter bomber is this type of structure. The information
of its three channels, i.e., working, standby, and benchmark, is compared in
pairs to detect the mismatch between channels (e.g., setting zero drift, gain,
working limit, etc.). When the difference exceeds the set value, the system
switches from working (fault) channel to standby channel. This kind of structure
is complex, and its comparison and monitoring components should have high
reliability. It is simpler and more reliable to replace the reference channel and
comparator (hardware) with a single board computer and its software.
4. Redundant electro-hydraulic servo valve. The electro-hydraulic servo system of
American space shuttle adopts four redundant electro-hydraulic servo valves,
three sublevel Saturn-V rocket electro-hydraulic servo systems, and three
redundant electro-hydraulic servo valves, all produced by MOOG Company. It
9.1 Electro-Hydraulic Servo Control Technology of Aircraft Gas Turbine Pump
71
Hydraulic integration blocks have been widely used, reducing or even eliminating
conduits and connectors. The maintainability is improved by using cartridge
components, and the integral combination simplifies the installation and improves
the adaptability to vibration and impact environment.
(2) Replacing Electrical Feedback with Mechanical Feedback
The position feedback of electro-hydraulic servo actuators used by American
militias, Saturn-V rockets, space shuttles, and Apollo lunar simulators is mechanical
feedback. This device has the ability of “failure ! return to zero” and “failure ! safety”. Compared with the feedback of potentiometer and differential
transformer, this device can save a considerable number of connecting cables,
wiring solder joints, and corresponding electronic circuits, and improve the reliability, but its structure requires higher manufacturing accuracy.
(3) Redundancy Design for Key Parts
In general, redundancy design is used in hydraulic energy, electro-hydraulic servo
valve, and actuator.
1. Parallel hydraulic system. Parallel hydraulic system is used in large aircraft and
space shuttle without exception. The American space shuttle orbiter has four
independent hydraulic sources, which supply oil to every single unit of the
control system through a central hydraulic combination to form the whole
system. Each hydraulic power source has 50% (whole hydraulic power source)
working capacity. If one hydraulic energy source fails, the whole system can
still work normally. When the second hydraulic energy source fails, it can
ensure a safe return, that is, it has fault working/fault safety capability.
2. Dual series structure. The dual series structure is used for the electro-hydraulic
servo actuator of the rudder and landing gear of the American space shuttle
orbiter. The rudder surface is driven by four actuators (in double series layout).
Each actuator provides 50% of the required control force for the rudder surface.
When two of the actuators fail, the rudder still has 100% driving force.
3. Detection and correction (error correction) structure. The redundant damped
servo actuator of F-111 fighter bomber is this type of structure. The information
of its three channels, i.e., working, standby, and benchmark, is compared in
pairs to detect the mismatch between channels (e.g., setting zero drift, gain,
working limit, etc.). When the difference exceeds the set value, the system
switches from working (fault) channel to standby channel. This kind of structure
is complex, and its comparison and monitoring components should have high
reliability. It is simpler and more reliable to replace the reference channel and
comparator (hardware) with a single board computer and its software.
4. Redundant electro-hydraulic servo valve. The electro-hydraulic servo system of
American space shuttle adopts four redundant electro-hydraulic servo valves,
three sublevel Saturn-V rocket electro-hydraulic servo systems, and three
redundant electro-hydraulic servo valves, all produced by MOOG Company. It
9.1 Electro-Hydraulic Servo Control Technology of Aircraft Gas Turbine Pump
71