Hydraulic actuation system with integrated heater and aircraft comprising same

Abstract

The invention relates to a hydraulic actuation system (100) comprising at least one tank (104) connected, via a flow restriction, to a pump (103) driven by a motor (101), a hydraulic actuator (112) associated with a control valve (113), a temperature sensor (108) for the hydraulic fluid in the tank (104) and an electronic control unit (102) arranged to implement a heating phase when the temperature of the hydraulic fluid in the tank (104) reaches a first predetermined minimum temperature threshold by activating the motor (101) driving the pump (103) when the control valve (113) is in a state of not supplying the actuator in order to circulate the hydraulic fluid through the restriction. The invention also relates to an aircraft comprising such a system.

Description

[0001]HYDRAULIC ACTUATION SYSTEM WITH INTEGRATED HEATER AND AIRCRAFT COMPRISING SAME The present invention relates to the field of hydraulic actuation, more particularly in the aeronautics sector. BACKGROUND OF THE INVENTION Aircraft are known which are equipped with a hydraulic actuation system, for example for moving the various moving parts of a landing gear or for orienting the propeller blades of a turboprop engine. Such a hydraulic actuation system comprises a reservoir containing a hydraulic fluid, a pump for pumping the hydraulic fluid from the reservoir, a motor for driving the pump, hydraulic actuators each associated with an actuator control valve which is mounted between the pump and the hydraulic actuator and which has a state in which the actuator is supplied by the pump and a state in which the actuator is not supplied. An electronic control unit is connected to the engine and thecontrol valves to control them according to the instructions of the aircraft pilot. Generally, the hydraulic actuation system is installed in one of the areas of the aircraft where the temperature is not controlled, for example in the landing gear hold, which exposes it to extremely low temperatures that can reach -60°C during long high-altitude flights. When the hydraulic actuation system does not actuate elements other than those linked to the landing gear, it is not used during the flight: the pump is therefore unused during the entire flight phase and the fluid does not circulate. The hydraulic fluid therefore risks cooling to the point of reaching ambient temperature and would have a significant viscosity that can have an impact on the operation of the pump, such as an increase in the engine torque required to start the pump, or difficulty priming the pump due to excessive upstream pressure.low (risk of cavitation). This results in a degradation of the reliability and performance of the hydraulic actuation system. To avoid this, it could be considered to oversize the motor and the pump, but this increases the mass of the hydraulic actuation system, the energy consumption of the aircraft and therefore its polluting emissions. Another solution is to place an electrical resistor in the tank to prevent the cooling of the hydraulic fluid. However, unless a large resistor is used which would therefore be heavy, this solution does not allow a uniform temperature of the hydraulic fluid to be obtained. OBJECT OF THE INVENTION The invention aims in particular to guarantee the proper operation of the pump as well as its performance over a wide environmental temperature range and in particular at low temperatures. SUMMARY OF THE INVENTION To this end, according to the invention, an actuation system is providedhydraulic system comprising at least one reservoir containing a hydraulic fluid, a pump for pumping the hydraulic fluid from the reservoir, a pump drive motor, a hydraulic actuator, an actuator control valve which is mounted between the pump and the hydraulic actuator and which has a state of supply of the actuator by the pump and a state of non-supply of the actuator, a temperature sensor of the hydraulic fluid in the reservoir, and an electronic control unit connected to the motor, to the control valve and to the temperature sensor. The actuation system comprises at least one restriction of passage between the pump and the reservoir and in that the electronic control unit is arranged to carry out a heating phase, when the temperature of the hydraulic fluid in the reservoir reaches a first predetermined minimum temperature threshold, by commanding an activation of the pump drive motor while thecontrol valve is in its non-supply state to circulate the hydraulic fluid through the restriction. Thus, actuation of the pump during the heating phase forces the fluid to pass through the restriction. The fluid will heat up as it passes through the restriction and this heating is proportional to the fluid flow rate and the pressure drop caused by the restriction. As the temperature rises, the viscosity of the hydraulic fluid will decrease. This ability to maintain a low viscosity of the hydraulic fluid makes it possible to limit pressure drops in the hydraulic fluid transport circuit and the equipment connected by it in the actuation system during normal operation. The invention makes it possible to guarantee good homogeneity of the temperature of the hydraulic fluid throughout the system. This results in similar performance over a wide range of external temperatures. The inventionalso allows to guarantee the performances of the systems powered by the hydraulic actuation system. The invention is entirely automated and managed by an on-board computer requiring no action on the part of the crew (unlike the solutions of the prior art). According to additional characteristics, usable individually or in whole or in part in combination: - the system comprises a heating valve having an open state for passage of the hydraulic fluid in the restriction and a closed state for the passage of the fluid, the heating valve being controlled by the electronic control unit in its open state to carry out the heating phase; - the restriction is integrated into the heating valve; - the system comprises several actuators and several control valves each associated with one of the actuators; - the electronic control unit is arranged to control the heating phasewhen one of the actuators is powered and the temperature of the hydraulic fluid is between the first predetermined minimum temperature threshold and a second predetermined temperature threshold higher than the first predetermined minimum temperature threshold; - the system comprises a first pressure sensor mounted downstream of the pump to measure a discharge pressure and in which the electronic control unit is connected to the first pressure sensor and is arranged to control the heating phase when the discharge pressure measured by the first pressure sensor reaches a pressure value corresponding to a maximum theoretical discharge flow rate of the pump; - the actuator is servo-controlled in displacement, the pump has a constant displacement, and the electronic control unit is arranged to control the motor in speed and to control the heating valve in its closed state when the motor reaches a speedtheoretical maximum; - the restriction is integrated into a leak drain connecting the pump to the tank; - the system comprises pressure sensors respectively upstream and downstream of the passage restriction and the electronic control unit is arranged to estimate a pump discharge flow rate as a function of a pressure difference between upstream and downstream of the passage restriction when the control valve is in its non-supply state; - the electronic control unit comprises a memory containing a table relating pressure difference values ​​and flow rate values; - the electronic control unit is arranged to determine a theoretical flow rate as a function of a speed of the drive motor, to compare the estimated discharge flow rate with the theoretical discharge flow rate and to issue an alert in the event of exceeding a predetermined threshold corresponding to an insufficiency of the estimated discharge flow rate byrelative to the theoretical discharge flow rate. The invention also relates to an aircraft equipped with such a hydraulic actuation system, in which the electronic control unit is arranged to check that the aircraft is in flight before carrying out the reheating phase. Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Reference will be made to the appended drawings, among which: [Fig. 1] Figure 1 is a schematic view of the actuation system according to the invention; [Fig. 2] Figure 2 is a flowchart illustrating a reheating method implemented by the actuation system according to the invention; [Fig. 3] Figure 3 shows the temperature curve of the hydraulic fluid during the implementation of this reheating method; [Fig. 4] Figure 4 is a representation of the state machine of a first modeof controlling the heating valve of the actuation system according to the invention; [Fig. 5] Figure 5 is a representation of the state machine of a second mode of controlling the heating valve of the actuation system according to the invention; [Fig. 6] Figure 6 shows the pressure curve as a function of the flow rate used for the second control mode; [Fig. 7] Figure 7 is a representation of the state machine of a third mode of controlling the heating valve of the actuation system according to the invention; [Fig. 8] Figure 8 is a flowchart illustrating a method for monitoring the efficiency of the pump implemented by the actuation system according to the invention; [Fig. 9] Figure 9 is a partial schematic front view of an aircraft equipped with the actuation system according to the invention. DETAILED DESCRIPTION OF THE INVENTION With reference to Figures 1 and 9, the hydraulic actuation system according to the invention, bearing the general referencerale 100, is described here in application to an aircraft A provided with main landing gear LGp and a directional front landing gear LGf each comprising a leg L having a free end provided with wheels W and an opposite end articulated to a structure of the aircraft between an extended position illustrated in FIG. 9 and a retracted position in a hold of the aircraft. The hydraulic actuation system illustrated is more particularly used for the actuation of the front landing gear LGf. This same actuation system can be used, with adaptations within the scope of those skilled in the art, for the actuation of the main landing gear or for any other equipment of the aircraft. The hydraulic actuation system 100 comprises a pump 103, driven in rotation by an electric motor 101, having an inlet fluidly connected to a reservoir 104 and an outlet fluidly connected to a supply line 106a comprising in series a filter106a1 and a non-return valve 106a2. The reservoir 104 contains a hydraulic fluid, such as an oil, for example a synthetic oil of type AS1241, and is provided with at least one temperature probe 108 for measuring the temperature of the hydraulic fluid in the reservoir 104. The hydraulic actuation system 100 comprises actuation devices a, b, c each having an inlet connected to the supply line 106a and an outlet connected to a return line 106b connected to the reservoir 104. The return line 106b comprises, downstream of the connection points of the actuation devices a, b, c to the return line 106b, a first non-return valve 106b3, a second non-return valve 106b2 and a filter 106b1. The valves 106b2 and 106b3 are oriented so that the hydraulic fluid exiting the actuating devices a, b, c flows towards the reservoir 104. The valve 106a2 is oriented so that the hydraulic fluid pumped by the pump103 in the reservoir 104 and leaving the pump 103 flows towards the actuating devices a, b, c. Each actuating device a, b, c comprises: - a single-acting hydraulic actuator, namely a braking actuator 112a, having a body receiving, sliding between a retracted position and an extended position, a piston delimiting in the body a variable-volume chamber, the piston being returned by an elastic member to its position defining the smallest volume of the chamber; - double-acting actuators, namely an orientation actuator 112b and an extension / retraction actuator 112c of the leg L, having a body receiving, sliding between a retracted position and an extended position, a piston delimiting in the body a variable-volume chamber; - a monostable control solenoid valve 113a, 113b, 113c, having a three-way / two-position type spool, namely a supply position in which the spool puts intorelation the supply line 106a with the actuator chamber 112a, 112b, 112c respectively and a discharge position in which the spool connects the return line 106b with the actuator chamber 112a, 112b, 112c respectively; - an electronic actuator control unit 114a, 114b, 114c electrically connected to the control terminal of the control solenoid valve 113a, 113b, 113c respectively to send control signals thereto and to the actuator 112a, 112b, 112c respectively to receive status signals from the actuator 112a, 112b, 112c. A pressure relief valve 107 connects the supply line 106a (downstream of the non-return valve 106a2 and upstream of the actuating devices a, b, c) and the return line 106b (between the non-return valves 106b2 and 106b3). A monostable reheating solenoid valve 110, having a two-way / two-position type spool, namely an open position in which the spool activates therelationship via a restriction the supply line 106a with the return line 106b and a closed position in which the spool blocks the passage of the hydraulic fluid between the supply line 106a and the return line 106b. The restriction here consists of a calibrated orifice formed in the spool and through which the fluid flows. The heating solenoid valve 110 is normally closed, that is to say that the spool of the heating solenoid valve 110 is elastically returned to the closed position. An upstream pressure sensor 115 is mounted in the vicinity of the supply port of the reheat solenoid valve 110 and a downstream pressure sensor 116 is mounted in the vicinity of the outlet port of the reheat solenoid valve 110. An electronic control unit 102 is electrically connected to the motor 101, the electronic actuator control units 114a, 114b, 114c, and the control terminal of the reheat solenoid valve 110 to send them signals.control signals. The electronic control unit 102 is electrically connected to the pressure sensors 115, 116, to the temperature probe 108 to receive status signals from them. The electronic control unit 102 is also electrically connected to a pilot unit of the aircraft to receive control signals and transmit status signals, and an electrical power source to receive power signals. The electronic control unit 102 conventionally comprises at least one processor and a memory containing at least one computer program which is executable by the processor and which contains instructions arranged to operate the hydraulic actuation system of the invention. The control of the motor 101 and the control solenoid valves 113a, 113b, 113c and the actuators 112a, 112b, 112c for actuating the landing gear is known in itself and will not be described further here. On the other hand, the method ofheating of the hydraulic fluid will now be described. According to this method (figure 2), the electronic control unit 102 automatically carries out a heating phase, when the temperature of the hydraulic fluid in the tank reaches a first temperature threshold and the aircraft A is in operation. According to a particular embodiment of this method, when the aircraft is powered up, the electronic control unit 102 extracts a measured temperature Tr from the temperature signal from the temperature probe 108 (step 1), checks that the aircraft is indeed in operation (step 2) and, if so, compares the measured temperature Tr to the first temperature threshold (step 3). The first temperature threshold, here equal to -30°C, is a heating activation temperature threshold and corresponds to a minimum temperature at which the viscosity of the hydraulic fluid allows nominal operation of the hydraulic actuation system. Ifthe measured temperature is lower than the first temperature threshold, the electronic control unit 102 controls the heating solenoid valve 110 in the open position (step 4) and the activation of the motor 101 (step 5), which then drives the pump 103, as long as the measured temperature Tr is lower than a second temperature threshold (step 6). The second temperature threshold (here equal to + 30°C) corresponds to a heating stop temperature beyond which it is not useful to go to obtain nominal operation of the hydraulic actuation system 100. When the measured temperature Tr reaches the second temperature threshold, the electronic control unit 102 controls the heating solenoid valve 110 in the closed position and the deactivation of the motor 101 (step 7). We see in Figure 3 that the measured temperature Tr will thus evolve between the two temperature thresholds. As the passage of the hydraulic fluid in the restrictioninduces a loss of flow, it is not desirable for reheating to take place when the operating devices are in use. The computer program is arranged so that the reheating does not disturb the operation of the connection devices and the electronic control unit 102 checks whether at least one of the connection devices a, b, c is in use before activating a reheating phase and during the reheating phase. Three possible modes of controlling the reheating depending on the use of the actuating devices will now be described. According to the first control mode (illustrated in FIG. 4), each electronic control unit 114a, 114b, 114c of the actuating devices a, b, c transmits to the electronic control unit 102 a signal informing of the active state of the corresponding actuating device a, b, c. In the case where at least one of the actuating devices a, b, c is active thenthe heating solenoid valve 110 is left or brought into its closed position. However, in order to accelerate the heating of the hydraulic fluid when at least one of the actuating devices a, b, c needs to be controlled, the first control mode authorizes the activation of the heating solenoid valve when at least one of the actuating devices a, b, c is active and when the temperature of the hydraulic fluid is within a temperature range, for example T=[-30°C; -20°C], because too low a temperature risks causing a degradation of the performance of the activated actuating device. In the temperature range [-30°C; -20°C], the effect of the temperature will have more impact on the performance of the activated a, b, c actuator device than the loss of flow through the restriction of the heating solenoid valve 110. For example, the activation and deactivation temperatures of the heating are:following: - activation temperature #1 = -20°C; - activation temperature #2 = -30°C; - deactivation temperature #1 = -10°C; - deactivation temperature #2 = +30°C. The second control mode (illustrated in Figure 5) is based on the exploitation of the discharge pressure of the pump 103, measured by the upstream pressure sensor 115. The electronic control unit 102 stops the opening command of the heating solenoid valve 110 when the pressure measured by the upstream pressure sensor 115 is lower than a first predetermined pressure threshold Pr. The pressure profiles as a function of the flow rate at the discharge port of the pump 103 regularly follow a profile such as that given in Figure 6. The pressure threshold Pr for closing the heating solenoid valve 110 is defined in the vicinity of the pressure level corresponding to the maximum flow rate delivered by the pump 103 under the most unfavorable conditions, for example 180 bar. The opening ofthe heating solenoid valve 110 is controlled by the electronic control unit 102 if the measured discharge pressure is greater than a second pressure threshold Ps, for example 200 bar. The third control mode (illustrated in FIG. 7) consists of controlling the heating solenoid valve 110 from the measurement of the rotational speed of the motor 101 actuating the pump 103 in addition to the measurement of the temperature of the hydraulic fluid provided by the temperature sensor 108. This control mode is particularly suitable when: at least one of the actuators 112 is controlled in displacement / speed, the pump 103 has a constant displacement and the motor 101 is controlled in speed. The speed of the motor 101 is automatically adjusted according to a speed / displacement setpoint by means of a PID (or proportional integral derivative) type controller integrated in the electronic control unit 102. The rotation speed of the motor 101, and byConsequently, the delivery flow rate of the pump 103 is limited by the available supply voltage. Opening the heating solenoid valve 110 causes a loss of flow to the actuators, but this loss of flow can be compensated for using the PID controller (this compensation is, however, limited by the maximum rotation speed of the motor 101, so that beyond this maximum rotation speed, there is a degradation in the performance of the actuating devices a, b, c). In order to preserve the performance of the actuating devices a, b, c, the electronic control unit 102 closes the heating solenoid valve 110 when the rotation speed of the motor 101 approaches the maximum speed. The command to open the heating solenoid valve 110 is therefore applied when the fluid temperature is below a certain threshold T=-30°C and if the engine rotation speed is below a first speed threshold Ws. The closingof the heating solenoid valve 110 is conditioned to a fluid temperature higher than the heating deactivation threshold or to a rotation speed of the engine 101 higher than a second speed threshold Wr. The speed thresholds here are as follows: - Ws = 1400 rpm; - Wr = 1500 rpm. The threshold Wr is determined according to a critical speed close to the maximum speed at which the engine is capable of rotating, for example 90% of the maximum theoretical speed. If the engine speed exceeds this threshold then the heating valve closes, thus allowing more flow to the services. This can then lead to a reduction in the engine rotation speed as a result of the control. In order to avoid a "bang-bang" effect on the opening / closing of the reheating valve, reopening of the valve is only permitted if the rotation speed is lower than the threshold Ws which is set to a value lower than Wr. It should be noted that itIt is possible to combine all or part of the three control modes above. The structure of the hydraulic actuation system according to the invention also makes it possible to monitor the operating state of the pump 103, when it is of constant displacement, and more particularly its delivery flow rate. It is known that the flow rate efficiency of a hydraulic pump deteriorates over time, in particular due to wear of the moving parts such as the piston / liner assemblies. The volumetric efficiency of the pump 103 in new condition is generally of the order of 90% to 95% (if the pump 103 is a piston pump): in fact, a certain quantity of fluid returns to the reservoir 104, in particular via the drain 109, a consequence of internal leaks in the pump 103 resulting from the clearances necessary for its operation. The degradation of the volumetric efficiency with wear causes a loss of energy available for the actuating devices a, b, c, leading to adegradation of their performance. In addition, the "lost" energy dissipates into heat which spreads into the reservoir 104 which can cause an excessive rise in the temperature of the hydraulic fluid and lead to irreversible damage to its properties. Monitoring the volumetric efficiency of the pump 103 therefore makes it possible to prevent excessive degradation leading to a loss of power which would impact the performance of the hydraulic actuation system as a whole. To evaluate the volumetric efficiency, the quotient of the discharge flow rate Q is calculated r by the theoretical flow rate Q th The theoretical flow rate Qth is obtained by the product of the rotation speed of the motor Wm, a quantity measured for the purposes of controlling the motor 101, and the displacement C p of pump 103, known by construction. We therefore have: Q th = W m x C p To know the discharge flow rate Q ra flow sensor could have been installed at the discharge port of the pump 103. However, this type of sensor is bulky, of significant mass, and its measurement may be biased by the effect of the temperature of the hydraulic fluid and the environment. According to the invention, it is proposed to exploit the presence of the restriction and the pressure sensors 115 and 116 upstream and downstream of said restriction to determine the actual flow rate of the hydraulic fluid from the measurement of the differential pressure between the two ports of the heating solenoid valve 110. As indicated previously, the restriction consists of a calibrated orifice through which the hydraulic fluid flows. Actuation of the pump 103 during the heating phase forces the hydraulic fluid to pass through the restriction. The fluid will heat up as it passes through the restriction and this heating is proportional to the fluid flow rate and the pressure drop caused by the restriction.The actual pressure drop across the restriction is within a range of values ​​resulting from manufacturing variations. Thus, for a measured differential pressure, it is possible to determine the corresponding flow rate range in which the actual flow rate lies. The memory of the electronic control unit 102 contains a table relating measured differential pressure values ​​and flow rate value ranges. Therefore, for an estimated pressure differential, it is possible to determine a flow rate range in which the actual flow rate lies. The evaluation of the differential pressure upstream and downstream of the restriction is carried out within the electronic control unit 102 from the pressure measurements provided by the pressure sensors 115, 116 and the flow rate corresponding to the pressure differential is determined from the stored table.For each measured differential pressure, the lower value of the range of flow rate values ​​will be retained because the purpose of the method is to estimate the volumetric efficiency of the pump from which a maintenance operation is required; considering the upper limit would result in an overestimation of the actual flow rate, and therefore of the volumetric efficiency. The calculation of the volumetric efficiency is carried out only when no actuating device is active, so that the entire flow rate at the outlet of the pump 103 passes through the restriction of the reheating solenoid valve 110. This calculation will preferably take place during the flight phase, a phase during which the landing gear actuators are not used. In the case where the volumetric efficiency is below a certain threshold, for example 60%, the electronic control unit 102 warns the aircraft maintenance system of the excessive degradation of the pump 103.The diagram below describes the method for evaluating the volumetric efficiency of the pump. Preferably, the internal geometry of the restriction through which the hydraulic fluid flows is such that the flow is turbulent in order to overcome the effect of the viscosity of the hydraulic fluid on the pressure drop, which is highly dependent on the temperature. Thus, for a fluid temperature above T=0°C, the pressure drop across the restriction is identical regardless of the temperature at a given flow rate. The method for monitoring the efficiency of the pump 103 is therefore carried out at the same time as a warm-up phase when no actuating device is active.After the actuation of the motor 101 and the opening of the reheating solenoid valve 110 (step 45 in FIG. 8), the monitoring method implemented by the electronic control unit 102 comprises the steps of: - checking that the temperature measured by the temperature probe 108 is greater than 0°C (step 46); - if so, extracting upstream and downstream pressure values ​​from the upstream and downstream pressure sensors 115 and 116 and acquiring the value of the rotation speed of the motor 101 (step 47); - estimating the actual flow rate (step 48); - calculating the volumetric efficiency (step 49) and comparing it to an efficiency threshold, for example equal to 60% (step 50); - if the volumetric efficiency is lower than the efficiency threshold, issuing an alert (step 51). It should be noted that cases of failure of the heating valve are possible.If the reheat valve remained stuck closed (i.e. making it impossible to reheat the fluid), the consequence would be a degradation of the performance of the controlled systems due to the high viscosity of the fluid if the tank temperature reached a critical threshold (T<-30°C). This failure of the reheat valve does not, however, lead to catastrophic consequences if the aircraft crew is informed that the fluid temperature is below a certain threshold (T<-30°C), based on this information, the crew will then act appropriately to maneuver the aircraft. This failure can be detected by two methods using the components implemented in the system: - by observing the pressure differential across the reheat valve (using pressure sensors 115 and 116).If the differential is greater than a certain threshold (for example 200 bar for a hydraulic generation with a nominal pressure of 206 bar), then the valve is not open; - by observing the temperature of the reservoir fluid. If the temperature rise is less than a certain threshold (for example 5°C) after a certain activation time of the heating valve (for example 1 minute), and if the pressure at the supply port of the heating valve (pressure sensor 115) is greater than a certain threshold (for example 150 bar) then this means that the heating valve has not opened. If the heating valve remained stuck open, the consequences would be as follows: - loss of hydraulic power at the output of the hydraulic generation leading to a degradation of the performance of the supplied systems. However, this degradation may be slight since the flow rate through the heating valve is low.For this, the flow characteristic of the heating valve under a delta P corresponding to the nominal pressure of the pump (for example 206 bar) will be such that it will not exceed 10% of the nominal flow of the pump; - rise in the temperature of the fluid in the tank when the hydraulic generation is activated. An excessive temperature above a certain threshold (for example 130°C depending on the type of fluid used) will cause the pump to stop, depriving the ability to operate the systems. Detection of this stuck open valve failure can be carried out: - by observing the pressure upstream of the pressure sensor 115 for a given engine speed corresponding to a flow rate slightly higher than the characteristic of the heating valve.If the pressure is below a certain threshold when the valve is not controlled (for example 180 bar), and if no pressure variation of the sensor 115 above a certain level (for example 5 bar) over control cycles of opening then closing the heating valve is observed, then the valve is assumed to be stuck open. - by observing the temperature of the reservoir fluid. If the temperature rise is above a certain gradient (for example 1°C / s) when the pump is controlled but the heating valve is not controlled, then the valve is assumed to be stuck open. Knowledge of the degraded state of the valve (stuck open) will make it possible to deactivate the main hydraulic generation and to activate the secondary hydraulic generation system if the aircraft's hydraulic architecture is composed of them.In the event of the absence of complete redundancy of the hydraulic generation, the electronic control unit will inform the crew of this failure in order to limit the maneuvers in order to reduce the rise in the temperature of the fluid. Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.In particular, the actuation system may have a different structure than that described and for example: - comprise a self-regulating variable displacement pump instead of a constant displacement pump; - comprise a different number of actuation devices; - not comprise pressure sensors 115, 116 or comprise only one pressure sensor 115 or comprise a pressure sensor dedicated to measuring the discharge pressure and positioned at the outlet of the pump 103; - the actuators may be single or double acting; - the valves may be monostable or bistable; - comprise a different number of control units... The hydraulic actuation system may be redundant in whole or in part. The restriction could be achieved via a flow restrictor mounted downstream of the reheating solenoid valve 110. The reheating valve is optional.The restriction can be formed by the drain 109 from the moment when the pump 103 has a sufficient internal leak compared to the quantity of hydraulic fluid to be heated. The interest of the drain is to allow the evacuation of calories in the body of the pump thus improving its cooling, to allow appropriate lubrication, as well as to evacuate the pollution particles generated by the organs towards a filtration device. It is generally installed in parallel with the filter mounted on the drainage line, a calibrated valve which acts as protection against overpressures in the event that the drain is blocked. Combining the control modes can be considered in order to ensure better robustness so as not to impact the performance of the actuating devices powered by the pump.

Claims

CLAIMS 1. Hydraulic actuation system (100) comprising at least one reservoir (104) containing a hydraulic fluid, a pump (103) for pumping the hydraulic fluid from the reservoir (104), a motor (101) for driving the pump (103), a hydraulic actuator (112), a control valve (113) of the actuator (112) which is mounted between the pump (103) and the hydraulic actuator (112) and which has a state of supply of the actuator (112) by the pump (103) and a state of non-supply of the actuator (112), a temperature sensor (108) of the hydraulic fluid in the reservoir (104), and an electronic control unit (114, 112, 102) connected to the motor (101), to the control valve (113) and to the temperature sensor (108), characterized in that that the actuation system comprises at least one passage restriction between the pump (103) and the tank (104) and in that the electronic control unit (102) is arranged to carry out a heating phase,when the temperature of the hydraulic fluid in the reservoir (104) reaches a first predetermined minimum temperature threshold, by controlling an activation of the motor (101) driving the pump (103) while the control valve (113) is in its non-supply state to circulate the hydraulic fluid in the restriction.

2. System according to claim 1, comprising a heating valve (110) having an open state for passage of the hydraulic fluid in the restriction and a closed state for the passage of the fluid, the heating valve (110) being controlled by the electronic unit, control unit (102) in its open state to carry out the heating phase.

3. System according to claim 2, wherein the restriction is integrated into the heating valve (110).

4. System according to claim 2 or 3, comprising several actuators (112) and several control valves (113) each associated with one of the actuators (112).

5. System according to one of claims 2 to 4, wherein the electronic control unit (102) is arranged to control the heating phase when one of the actuators (112) is powered and the temperature of the hydraulic fluid is between the first predetermined minimum temperature threshold and a second predetermined temperature threshold higher than the first predetermined minimum temperature threshold. 6.System according to any one of claims 2 to 4, comprising a pressure sensor (115) mounted downstream of the pump (103) to measure a discharge pressure and in which the electronic control unit (102) is connected to the pressure sensor (115) and is arranged to control the heating phase when the discharge pressure measured by the pressure sensor (115) reaches a pressure value corresponding to a maximum theoretical discharge flow rate of the pump (103).

7. System according to any one of claims 2 to 4, in which the actuator (112) is servo-controlled in displacement, the pump (103) has a constant displacement, and the electronic control unit (102) is arranged to control the motor (101) in speed and to control the heating valve (110) in its closed state when the motor (101) reaches a theoretical maximum speed.

8. System according to claim 1, wherein the restriction is integrated into a leak drain (109) connecting the pump (103) to the reservoir (104).

9. System according to any one of the preceding claims, comprising pressure sensors (115, 116) respectively upstream and downstream of the passage restriction and the electronic control unit (102) is arranged to estimate a delivery flow rate of the pump (103) as a function of a pressure difference between upstream and downstream of the passage restriction when the control valve (113) is in its non-supply state, the pressure difference being determined as a function of signals from the pressure sensors.

10. System according to claim 9, wherein the electronic control unit (102) comprises a memory containing a table relating pressure difference values ​​and flow rate values. 11.System according to claim 9 or 10, in which the electronic control unit (102) is arranged to determine a theoretical flow rate as a function of a speed of the drive motor (101), to compare the estimated discharge flow rate with the theoretical discharge flow rate and to issue an alert in the event of exceeding a predetermined threshold corresponding to an insufficiency of the estimated discharge flow rate compared to the theoretical discharge flow rate.

12. Aircraft (A) equipped with at least one landing gear (LGf) and a system (100) according to any one of the preceding claims for actuating said landing gear, and the electronic control unit (102) is arranged to verify that the aircraft (A) is in flight before carrying out the. warm-up phase.

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