consists of three (or four) electro-hydraulic servo valves to control a power stage
slide valve. The output of each servo valve is algebraically added on the slide
valve to synthesize the displacement of the spool. As long as the gain and
feedback gain of the servo valve are high enough, when the fault output (interference displacement) occurs in one channel, the output can be offset by other
normal working channels through feedback, and the effect of the fault can be
corrected. This form is compact in structure and hardly increases system weight
and power consumption.
According to the polarity and magnitude of input signal, the hydraulic servo
system of missile and spacecraft controls the deflection angle of rocket engine,
rudder, movable nozzle or spoiler of missile, and runner in a proportional or relay
manner, and generates a certain control force or moment to control the movement
and attitude of missile and spacecraft. Early missile hydraulic servo mechanism was
relatively simple, such as V-1 and V-2 missile hydraulic servo mechanism developed in Germany in World War II, which was driven by a DC motor to drive gear
pump as energy source, control signal was input to the wet torque motor, driving a
balance lever, two needle valves were hung at both ends of the lever to control highand low-pressure hydraulic oil, input to the two cavities of actuator. The actuator
outputs a certain moment to drive the load. Dry torque motor and double nozzle
servo valve appeared in the early 1950s, and the electro-hydraulic servo system
became more and more perfect in the 1960s. With the development of aerospace
and missile technology, the requirement for the reliability of launch vehicle is
getting higher and higher. At present, the overall reliability of the advanced launch
vehicle in the world is 0.99, which requires that the reliability of the control system
approaches 0.999. As a key component of the control system, the reliability of the
servo mechanism is above 0.999. Such a level of reliability cannot be achieved by
the conventional hydraulic servo mechanism. Therefore, the reliability of servo
mechanism must be improved essentially. In the early 1960s, when the United
States launched Hercules I missile, the position sensor cable was broken, which
made the servo system in an open-loop state, resulting in the missile out of control,
and ultimately caused the launch failure. In order to improve the reliability of
missile and vehicle servo system afterward, the servo actuator was changed from
electrical feedback to mechanical feedback. The electro-hydraulic servo mechanism
of the space shuttle and the launch vehicle adopts full technology and a redundant
hydraulic servo mechanism. It has been used in Saturn-V S-IVB, Hercules III-M,
and the space shuttle in USA. Figure 9.8 shows the schematic diagram of the four
redundant servo mechanisms of the booster of the US space shuttle.
Compared with the conventional servo mechanism, the characteristics of the four
redundant servo mechanisms of the space shuttle booster shown in Fig. 9.8 are as
follows:
(1) The high-power mechanical parts of the hydraulic servo mechanism have high
reliability, while the low-power electrical and hydraulic amplifiers have low
reliability. The servo amplifiers and servo valves have four redundancies, and
72
9 High-Temperature and High-Speed Gas Turbine Pump …
slide valve. The output of each servo valve is algebraically added on the slide
valve to synthesize the displacement of the spool. As long as the gain and
feedback gain of the servo valve are high enough, when the fault output (interference displacement) occurs in one channel, the output can be offset by other
normal working channels through feedback, and the effect of the fault can be
corrected. This form is compact in structure and hardly increases system weight
and power consumption.
According to the polarity and magnitude of input signal, the hydraulic servo
system of missile and spacecraft controls the deflection angle of rocket engine,
rudder, movable nozzle or spoiler of missile, and runner in a proportional or relay
manner, and generates a certain control force or moment to control the movement
and attitude of missile and spacecraft. Early missile hydraulic servo mechanism was
relatively simple, such as V-1 and V-2 missile hydraulic servo mechanism developed in Germany in World War II, which was driven by a DC motor to drive gear
pump as energy source, control signal was input to the wet torque motor, driving a
balance lever, two needle valves were hung at both ends of the lever to control highand low-pressure hydraulic oil, input to the two cavities of actuator. The actuator
outputs a certain moment to drive the load. Dry torque motor and double nozzle
servo valve appeared in the early 1950s, and the electro-hydraulic servo system
became more and more perfect in the 1960s. With the development of aerospace
and missile technology, the requirement for the reliability of launch vehicle is
getting higher and higher. At present, the overall reliability of the advanced launch
vehicle in the world is 0.99, which requires that the reliability of the control system
approaches 0.999. As a key component of the control system, the reliability of the
servo mechanism is above 0.999. Such a level of reliability cannot be achieved by
the conventional hydraulic servo mechanism. Therefore, the reliability of servo
mechanism must be improved essentially. In the early 1960s, when the United
States launched Hercules I missile, the position sensor cable was broken, which
made the servo system in an open-loop state, resulting in the missile out of control,
and ultimately caused the launch failure. In order to improve the reliability of
missile and vehicle servo system afterward, the servo actuator was changed from
electrical feedback to mechanical feedback. The electro-hydraulic servo mechanism
of the space shuttle and the launch vehicle adopts full technology and a redundant
hydraulic servo mechanism. It has been used in Saturn-V S-IVB, Hercules III-M,
and the space shuttle in USA. Figure 9.8 shows the schematic diagram of the four
redundant servo mechanisms of the booster of the US space shuttle.
Compared with the conventional servo mechanism, the characteristics of the four
redundant servo mechanisms of the space shuttle booster shown in Fig. 9.8 are as
follows:
(1) The high-power mechanical parts of the hydraulic servo mechanism have high
reliability, while the low-power electrical and hydraulic amplifiers have low
reliability. The servo amplifiers and servo valves have four redundancies, and
72
9 High-Temperature and High-Speed Gas Turbine Pump …