Hydraulic system for moving an aircraft rudder

Abstract

Hydraulic system for moving a rudder of an aircraft, comprising a servo valve, a double-acting rudder actuator with two actuator chambers, two working lines leading from the servo valve to the actuator chambers, and a functional switching valve arranged on the working lines with a valve housing and a valve body movably arranged therein, wherein the functional switching valve comprises three switching positions, wherein in a first switching position of the functional switching valve the actuator chambers are operationally connected to the servo valve, and wherein in a second and a third switching position of the functional switching valve the two actuator chambers are disconnected from the servo valve and short-circuited, characterized in that in the third switching position the two actuator chambers are short-circuited via a throttle with a variable flow cross-section.

Description

The invention relates to a hydraulic system for moving a rudder of an aircraft and to an aircraft comprising such a system. Modern aircraft incorporate multiple control surfaces, such as elevators, rudders, ailerons, trim tabs, flaps, and spoilers, for controlling the aircraft during flight. The movement of these control surfaces is hydraulically controlled in modern aircraft. The hydraulic systems employed include a hydraulic pump, a servo valve, an actuator (typically a double-acting hydraulic actuator with two actuator chambers), and a receiver. Examples of conventional actuators are disclosed, for instance, in EP1795987A2 and WO2018 / 132806A1. The servo valve communicates with the aircraft's electronics and controls the pressurization and ultimately the movement of the actuator. It thus converts an electrical control signal into a control surface movement in a controlled manner. For safety reasons, at least two actuators per control surface are typically used. Mode selector valves (MSVs) are also installed between the servo valve and the actuator to switch the system between an active mode, in which the servo valve is hydraulically connected to the actuator, and a passive mode, in which the connection is interrupted in the event of a malfunction or for maintenance to prevent unwanted rudder movements and structural damage. In passive mode, a damping function is also implemented on these mode selector valves to prevent unwanted rudder vibrations. The construction of a functional switching valve 101, as currently used in the hydraulic system for moving the ailerons of the Airbus A320, is shown schematically in Fig. 3. The valve 101 is connected, on the one hand, to outputs EHSV1 and EHSV2 of a servo valve via working lines 110 and 115, and on the other hand, to the actuator chambers C1 and C2 of a double-acting hydraulic cylinder of the aileron via working lines 120 and 125. The return line 140, which exits at port R, runs past the valve 101 to the manifold of the hydraulic system, which is not shown in the figure. The valve body 102 can be moved axially, i.e. horizontally in the figure, in the valve housing 103 in order to switch the valve 101 between the active and the passive mode. In the figure, the valve 101 is switched in active mode, with the output EHSV1 of the servo valve being operationally connected to the actuator chamber C1 via the open terminals 110a and 120a of the valve 101, and the output EHSV2 of the servo valve being operationally connected to the actuator chamber C2 via the terminals 115a and 125a of the valve 101. The active mode corresponds to a position of the valve body 102 on the left side of the valve housing 103, whereby this position is always assumed when the supply pressure from port P acting on the valve body 102 via the supply line 130 and the input 130a is greater than a threshold value and the chamber pressures in the actuator chambers C1 and C2 acting on the valve body 102 via feedback lines 121 and 126 through the inputs 121a and 126a do not exceed the supply pressure by a certain amount.The scenario in which the supply pressure is greater than the chamber pressures reflects the normal, undisturbed case. In the event of an overload due to a fault, for example, high external loads on the rudder, the chamber pressure in one of the actuator chambers C1 or C2 increases, so that either the chamber pressure of actuator chamber C1 or the chamber pressure of actuator chamber C2 exceeds the supply pressure and the valve body 102 is forced to the right. As a result, ports 110a and 115a are closed, and a short circuit is established between the lines 120 and 125 leading to actuators C1 and C2, namely via connecting line 122, the associated port 122a (which is open in passive mode), and port 125a (which is also open in passive mode). This alternative position corresponds to the passive mode of valve 101. In this passive mode, the valve in Fig. 3 also incorporates a damping function by having a damping element in the form of a through-bore with a constant, defined diameter (port 122a) to slow the flow of the hydraulic fluid. The braking force increases quadratically with increasing flow velocity of the hydraulic fluid through the bore and, correspondingly, with increasing rudder speed. The object of the invention is to provide a generic hydraulic valve that combines a simple design and high robustness with greater variability and, in particular, the possibility of variable damping. Against this background, the invention relates to a hydraulic system for moving a rudder of an aircraft, comprising a servo valve, a double-acting rudder actuator with two actuator chambers, two working lines leading from the servo valve to the actuator chambers, and a functional switching valve arranged on the working lines with a valve housing and a valve body movably arranged therein, wherein the functional switching valve comprises three switching positions, wherein in a first switching position of the functional switching valve the actuator chambers are operationally connected to the servo valve, and wherein in a second and a third switching position of the functional switching valve the two actuator chambers are disconnected from the servo valve and short-circuited. The hydraulic system preferably also includes a pump, a collector for supplying the pump, and return lines leading from the working lines to the collector. The design according to the invention allows for the integration of both overload protection and variable damping via the two passive switching positions into the functional switching valve. This offers advantages in design compared to known functional switching valves with two switching positions. In one embodiment, the switching positions are changed by linear displacement of the valve body within the valve housing. The three switching positions are preferably established in the following sequence upon linear displacement in one direction: first switching position, then second switching position, then third switching position. The functional switching valve can be pressure-controlled and is preferably connected in the hydraulic system such that a supply pressure and the chamber pressures of the first and second actuator chambers act on the functional switching valve. This connection is made via hydraulic lines at the valve housing. The supply pressure is a constant pressure that acts on the functional switching valve during operation. It can, for example, be generated by the hydraulic pump that also generates the working pressures and can be regulated as needed. Preferably, the functional switching valve is connected in the hydraulic system such that it moves into the first switching position when the supply pressure exceeds a certain amount, and that it moves into the second or third switching position when one of the chamber pressures exceeds the supply pressure by a certain amount. It can therefore be provided that the supply pressure acts on one side of the valve body and the chamber pressures act on the opposite side of the valve. Preferably, the functional switching valve is spring-centered to the second switching position and assumes the second switching position without pressure, or when neither the supply pressure exceeds a threshold value nor any of the chamber pressures exceeds the supply pressure by a certain amount. For example, it can be provided that two mechanical compression springs act on the valve from opposite sides. In one embodiment, the two actuator chambers are short-circuited via a throttle with a constant flow cross-section in the second switching position. This results in a quadratic relationship between the damping braking force acting on the hydraulic fluid, the speed at which the hydraulic fluid flows through the throttle, and consequently the speed of the rudder movement. According to the invention, in the third switching position, the two actuator chambers are short-circuited via a throttle with a variable flow cross-section. Above a certain chamber pressure, this prevents a further quadratic increase in force with the speed of the rudder movement and instead allows for a more extensive movement of the rudder with a nearly constant force. In the given context, it can be provided that every flow cross-section that the variable throttle of the third switching position can assume is at least as large as the constant flow cross-section of the throttle of the second switching position, wherein it is preferably provided that the smallest flow cross-section that the variable throttle of the third switching position can assume corresponds to the constant flow cross-section of the throttle of the second switching position. This ensures a seamless transition between the damping characteristics of the second and third throttles. Regarding the variable throttle of the third switching position, it can be designed such that its flow cross-section expands with increasing difference between the chamber pressures of the first and second actuator chambers. This expansion can be continuous or occur in at least two discrete stages. Against the background mentioned above, the invention further relates to an aircraft comprising a rudder and a hydraulic system according to the invention for moving the rudder. The servo valve of the hydraulic system is preferably located close to the control surface. In principle, placement within the fuselage is also conceivable. The same applies to the hydraulic pump and the receiver. The functional switching valve can be located in the fuselage or on a wing where the control surface to be actuated is situated. The rudder can be an aileron. In this embodiment, the aircraft comprises two wings arranged on opposite sides of the fuselage, each equipped with an aileron. Accordingly, two preferably identical hydraulic systems are provided to actuate the two ailerons. It is also conceivable, and encompassed by the invention, that only one hydraulic system and one electro-hydraulic actuator (EHA) are used. It should be noted here that the term "rudder" can refer to a rudder in the narrower sense, such as an aileron, but can also stand as a representative for any control surface. The aircraft's hydraulic systems, and possibly other hydraulic systems, may share a hydraulic pump, a collector, and possibly other components. Further details and advantages of the invention will become apparent from the exemplary embodiment discussed below with reference to the figures. The figures show: Fig. 1: a circuit diagram of a section of a hydraulic system according to the invention for moving an aileron; Fig. 2: a force-velocity diagram illustrating the damping behavior of such a hydraulic system; and Fig. 3: a schematic representation of a section of a hydraulic system known from the prior art for moving an aileron. The hydraulic system according to the invention, shown in section in Fig. 1, comprises a functional switching valve 1, which is connected on the one hand to the outputs of a servo valve via the working lines 10 and 15, and on the other hand to the actuator chambers C1 and C2 of a double-acting hydraulic cylinder 50 of the aileron via the working lines 20 and 25. A return line 40 or 45 runs from each of the working lines 20 and 25 to a manifold of the hydraulic system, which is not shown in the figure. The functional switching valve 1 is a pressure-controlled, spring-centered hydraulic valve with three switching positions, on which a hydraulic supply pressure transmitted via the supply line 30 and chamber pressures of the actuator chambers C1 and C2 transmitted via feedback lines 21 and 26 act. The switching position 1 shown in the first inset of Fig. 1 corresponds to the active mode of the valve 1, in which the working lines 10 and 20 or 15 and 25, and thus the actuator chambers C1 and C2, are operationally connected to the associated outputs of the servo valve. This switching position is assumed when the supply pressure acting on the valve 1 via supply line 30 is equal to or greater than both the chamber pressure of actuator chamber C1 acting on the valve 1 via feedback line 21 and the chamber pressure of actuator chamber C2 acting on the valve 1 via feedback line 26, which corresponds to the normal, fault-free case. Switching position 2 shown in the main view of Fig. 1, as well as switching position 3 shown in the second inset of Fig. 1, together correspond to the passive mode of the valve 1, in which the working lines 20 and 25, and thus the actuator chambers C1 and C2, are short-circuited and the working lines 10 and 15 coming from the servo valve are blocked. This switching position is assumed in the event of an overload, when the chamber pressure acting on the valve 1 via feedback line 21 or 26 increases in at least one of the actuator chambers C1 or C2. Provided the relevant chamber pressure is still within the range of the supply pressure and does not significantly exceed it, switching position 2 is assumed, whereby the short circuit is conducted via a throttle bore with a constant first diameter. The flow resistance of the hydraulic fluid dampens the rudder movement, with the braking force increasing quadratically with the flow velocity of the hydraulic medium and thus with the rudder's movement speed. This curve is shown in Fig. 2 with line 201. If the relevant chamber pressure increases further, switching position 3 is engaged, whereby the short circuit is routed via a throttle bore with a variable diameter to allow an increased flow of hydraulic fluid compared to switching position 2. Above a certain chamber pressure, this prevents a further quadratic increase in force with the speed of the rudder movement and instead allows for a greater range of rudder movement at a nearly constant force. This is shown in Fig. 2 by line 202. The force reduction and the corresponding advantage in adjusting the size of the rudder are indicated by reference numeral 203. The hydraulic system with variable damping according to the invention can be easily designed for different actuators and rudders and can also be used for large rudders subjected to high forces. The design of the hydraulic system according to the invention is robust and, apart from the servo valve, requires no electrical components. Integration requires no more installation space than known solutions with two switching positions of the function control valve, and the weight is not significantly increased.

Claims

Hydraulic system for moving an aircraft rudder, comprising a servo valve, a double-acting rudder actuator with two actuator chambers, two working lines leading from the servo valve to the actuator chambers, and a functional switching valve arranged on the working lines with a valve housing and a valve body movably arranged therein, wherein the functional switching valve comprises three switching positions, wherein in a first switching position of the functional switching valve the actuator chambers are operationally connected to the servo valve, and wherein in a second and a third switching position of the functional switching valve the two actuator chambers are disconnected from the servo valve and short-circuited, characterized in that in the third switching position the two actuator chambers are short-circuited via a throttle with a variable flow cross-section. Hydraulic system according to claim 1, characterized in that the switching positions are changed by linear displacement of the valve body in the valve housing. Hydraulic system according to one of the preceding claims, characterized in that the function switching valve is pressure-controlled and preferably connected in the hydraulic system in such a way that, on the one hand, a supply pressure and, on the other hand, chamber pressures of the first and second actuator chambers act on the function switching valve. Hydraulic system according to claim 3, characterized in that the functional switching valve is connected in the hydraulic system such that it is moved into the first switching position when the supply pressure exceeds a certain amount, and that it is moved into the third switching position when one of the chamber pressures exceeds the supply pressure by a certain amount. Hydraulic system according to claim 4, characterized in that the functional switching valve is spring-centered to the second switching position and assumes the second switching position without pressure or assumes it when neither the supply pressure exceeds a threshold value nor any of the chamber pressures exceed the supply pressure by a certain amount. Hydraulic system according to one of the preceding claims, characterized in that in the second switching position the two actuator chambers are short-circuited via a throttle with constant flow cross-section. Hydraulic system according to one of the preceding claims, characterized in that each flow cross-section that the variable throttle of the third switching position can assume is at least as large as the constant flow cross-section of the throttle of the second switching position, wherein it is preferably provided that the smallest flow cross-section that the variable throttle of the third switching position can assume corresponds to the constant flow cross-section of the throttle of the second switching position. Hydraulic system according to one of the preceding claims, characterized in that the variable throttle of the third switching position is designed such that its flow cross-section expands with increasing difference between the chamber pressures of the first and second actuator chambers. Aircraft comprising a rudder and a hydraulic system according to any of the preceding claims for moving the rudder.

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