Electric braking system of a turboprop engine

Abstract

The invention relates to an electric braking system (S) comprising: - a friction element (4) configured to generate a braking torque (CF) to be applied to a rotor; - an actuator (3) of the friction element (4) configured to generate a mechanical force to bring the friction element into contact with the rotor so that it applies the braking torque to the rotor; - an electromechanical member (2) configured to drive the actuator (3) of the friction element (4), the electromechanical member (2) comprising an electric motor (22) and an angular position sensor (23) configured to measure an angle of rotation of the electric motor (22); - a control unit (1) configured to control the electric motor (22) in order to achieve a target braking torque, the control unit (1) implementing a relationship between the angular position of the electric motor and the displacement of the actuator (3) to achieve the target braking torque.Figure for the abbreviation: FIGURE 2.

Description

Title of the invention: Electric braking system for a turboprop engine Technical field

[0001] The invention relates to an electric braking system for a rotor, in particular one driving a propeller of a turboprop in rotation. STATE OF THE ART

[0002] A turboprop engine typically comprises a rotor rotating a propeller to provide thrust. A propeller is fitted to aircraft to propel them.

[0003] On a turboprop, after the engine has stopped, the propellers are kept locked by a braking system called a "propeller brake".

[0004] Such a braking system is illustrated in [Fig.l]. A control unit 1 transmits a current setpoint II to an electromechanical member 2 transforming electrical energy into a mechanical torque CM. Such a current setpoint II is a function of a braking torque CF to be applied to the rotor to be braked (not shown). This is an open-loop system.

[0005] Such an electromechanical member 2 comprises an electric motor 22 which provides the mechanical torque CM and a motor regulation unit 21. The electric motor 22 is a three-phase synchronous motor and the motor regulation unit 21 makes it possible to regulate the motor current 12 applied to each phase of the motor 22 as a function of the rotation angle 0 (between 0 and 360°) of the electric motor 22 measured by an angular position sensor 23. The regulation unit 21 makes it possible to ensure that the motor current 12 is indeed the image of the current setpoint II on each phase of the motor 22.

[0006] The mechanical torque CM generated by the motor makes it possible to actuate an actuator 3 of a friction element 4 which generates the braking torque CF by means of a mechanical force F.

[0007] When braking takes place at high speed, it is possible to use a measurement of the speed of rotation of the rotor (for example of the propeller) to ensure control of the brake. In fact, the observed deceleration of the system to be braked makes it possible to regulate the braking force.

[0008] However, when the speed becomes low or the brake has to be applied to an already stopped propeller (hereinafter called "static braking"), such a method is no longer applicable.

[0009] By means of such a system, a braking torque applied by the brake must be maintained within certain limits. Too low a torque is insufficient to stop the propeller or to keep it locked in case of strong winds for example. Too much torque can damage the mechanical transmission of the engine, braking in this case being brutal.

[0010] One solution would be to be able to directly measure the braking torque applied at the output (using a torque meter for example).

[0011] However, such a solution is not feasible for reasons of cost and mass. Furthermore, such a solution is not optimal in the case of static braking. Indeed, the torque meter measurement depends on the force applied to the propeller due to the wind and is not directly representative of the maximum resistive torque that the brake can provide.

[0012] Thus, the brake control is ensured in an open loop in that there is no feedback on the current setpoint from the control unit 1 even though the electric motor 22 is regulated in a closed loop. Therefore, in such a braking system, one relies on knowledge of the transfer function of the braking system, that is to say the relationship between the current setpoint and the output of the braking system. In the braking system of [Fig.l], the elements involved in the transfer function are: the electromechanical member 2, the unit 3 and the friction element 4.

[0013] Such a system does, however, have drawbacks. In fact, the inaccuracies of electrical regulation and the disparities in the manufacturing of electrical elements constitute a significant factor in the inaccuracy of the braking regulation chain (in addition to the mechanical inaccuracies). Statement of the invention

[0014] The invention makes it possible to overcome the inaccuracies mentioned above and thus improve braking by improving the precision of obtaining the braking torque without having to add an additional member.

[0015] To this end, the invention proposes an electric braking system comprising:

[0016] - a friction element configured to generate a braking torque to be applied to a rotor;

[0017] - an actuator of the friction element configured to generate a mechanical force to bring the friction element into contact with the rotor so that it applies the braking torque to the rotor;

[0018] - an electromechanical member configured to drive the actuator of the element of friction, the electromechanical member comprising an electric motor and an angular position sensor configured to measure an angle of rotation of the electric motor;

[0019] - a control unit configured to control the electric motor in order to to achieve a target braking torque, the control unit implementing a relationship between the angular position of the electric motor and the displacement of the actuator to achieve the target braking torque.

[0020] The invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations:

[0021] - the control unit comprises a position regulating device configured to determine a motor current setpoint based on a position setpoint corresponding to the target braking torque.

[0022] - the electric motor is a three-phase synchronous motor.

[0023] - the electromechanical member comprising a regulation unit configured to de terminate the motor current from the current setpoint and the angular position of the electric motor.

[0024] - the actuator of the friction element comprises a member for converting a rotational movement into a translational movement and an elastic member for converting a translational movement into mechanical force;

[0025] - the elastic member is a compression spring;

[0026] - the member for converting a rotational movement into a movement of translation is a ball screw;

[0027] - the friction element comprises brake pads.

[0028] The invention also relates to a turboprop comprising a rotor on which a propeller is mounted, the turboprop comprising a braking system according to the invention.

[0029] The invention also relates to an aircraft comprising a turboprop according to the invention.

[0030] The invention uses the angular position sensor already present to control the electric motor and adds a position regulation stage which determines the electric current setpoint as a function of the position setpoint, which becomes the open-loop control parameter of the braking torque.

[0031] From then on, we move from a motor current / braking torque relationship to an angular position / braking torque relationship. The transfer function used to control the braking is then modified compared to that presented in the introduction.

[0032] Within the framework of the invention, part of the control is now carried out in a closed loop by regulation from the added angular position.

[0033] With this solution, the inaccuracies in regulating the electric current and disparities in manufacturing the electrical elements are removed from the imprecision balance in the braking regulation, as are some of the friction effects. PRESENTATION OF FIGURES

[0034] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and not limiting, and which must be read in conjunction with the attached drawings in which:

[0035] - [Fig.l] illustrates a braking system of known type;

[0036] - [Fig.2] illustrates a braking system according to an embodiment of the invention;

[0037] - [Fig.3] illustrates the details of an actuator of [Fig.2].

[0038] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION

[0039] [Fig.2] illustrates a braking system S according to the invention.

[0040] This braking system comprises, like the system of [Fig. 1], an electromechanical member 2 configured to generate a mechanical torque CM in connection with an actuator 3 of a friction element 4. The friction element 4 makes it possible to generate a braking torque CF to be applied to a rotor. Such a friction element comprises, for example, brake pads.

[0041] A control unit 1 provides a current setpoint II to the electromechanical member 2 to achieve a target braking torque CF. The control unit 1 is for example a computer comprising a processor.

[0042] The actuator 3 makes it possible to convert a mechanical torque CM from the electromechanical member 2 into a mechanical force F to bring the friction element 4 into contact with the rotor so that it applies the braking torque CF to the rotor.

[0043] The actuator 3 comprises a first stage 31 for converting a mechanical torque CM into a translational movement T. This is, for example, a mechanical member for converting a rotational movement introduced by the mechanical torque CM into a translational movement. Such a member 31 is, for example, a ball screw.

[0044] As illustrated in [Fig.3], the actuator 3 also comprises a second stage 32 for converting the translational movement into a mechanical force F. This is, for example, a mechanical, elastic member for converting a translational movement into a mechanical force. Such a member 32 is, for example, a compression spring.

[0045] The electromechanical actuator 2, in addition to the electric motor 22, comprises an angular position sensor 23 and a regulation unit 21 configured to regulate the motor current 12 from the current setpoint II making it possible to achieve a target braking torque CF. The electric motor 22 is a three-phase synchronous motor. The regulation of the electric motor 22 via the angular position sensor is identical to that presented in relation to [Fig.l].

[0046] The control unit 1 comprises a unit 11 for regulating the position of the friction element 4 allowing, from a position setpoint CP which corresponds to the target braking torque CF, to determine the current setpoint as a function of this position. In particular, the angular position of the electric motor 22 is processed by a position calculator 12 which counts the number of revolutions of the electric motor 22 in order to determine the position of the friction element 4, the latter making the correspondence between the number of revolutions and the displacement induced on the friction element 4.

[0047] The position setpoint CP / target braking torque CF relationship is determined in a unit 10 of the control unit. This is for example a braking logic unit which is for example a computer comprising a processor.

[0048] In this way, the control unit 1 implements a relationship between the angular position of the electric motor 22 and the displacement of the friction element 4 to achieve the target braking torque CF.

[0049] Thus, unlike [Fig. 1], a position regulation stage is added which determines the motor current setpoint as a function of the position setpoint of the moving part of the mechanical member 32, which becomes the open-loop control parameter of the braking torque CF at the end of the chain. The position of the moving part of the mechanical member 32 is regulated from the angular position sensor 23 of the electric motor 22.

[0050] In operation, depending on the conditions of the rotor to be braked, the braking logic unit determines a desired target braking torque CF at the end of the chain and which must be applied to the rotor.

[0051] The logic unit 10 knowing the transfer function of the braking system provides a position setpoint CP which corresponds to the position of the moving part of the mechanical member 32 for this braking torque. The position regulation unit 11 provides the current setpoint II corresponding to the electromechanical member. When the electric motor is powered, the current setpoint II is adjusted according to the position of the moving part of the mechanical member 32 directly linked to the target braking torque. As a result, obtaining the braking torque CF is more precise.

[0052] With such a braking system, the inaccuracies in regulating the electric current and disparities in manufacturing the electrical elements are removed from the imprecision balance in the braking regulation, as are some of the friction effects.

[0053] In the member for converting rotational movement into translational movement, the relationship between rotation and translation is generally well controlled and not affected by friction which acts only on the relationship between torque and force. Only mechanical play intervenes which is small and better controlled.

[0054] At the level of the elastic member, the invention involves the relationship between position and force (stiffness) which was without effect in the previous solution. The advantage of the invention is directly associated with the ability to limit dispersion on this stiffness. This is a mechanical parameter that is generally more stable and better controlled than parasitic effects of the friction type.

Claims

Claims

1. An electric braking system (S) comprising: - a friction element (4) configured to generate a braking torque (CF) to be applied to a rotor; - an actuator (3) of the friction element (4) configured to generate a mechanical force to bring the friction element into contact with the rotor so that it applies the braking torque to the rotor; - an electromechanical member (2) configured to drive the actuator (3) of the friction element (4), the electromechanical member (2) comprising an electric motor (22) and an angular position sensor (23) configured to measure an angle of rotation of the electric motor (22);- a control unit (1) configured to control the electric motor (22) to achieve a target braking torque, the control unit (1) implementing a relationship between the angular position of the electric motor and the displacement of the actuator (3) to achieve the target braking torque, the control unit (1) comprising a position regulating device configured to determine a motor current setpoint as a function of a position setpoint corresponding to the target braking torque.;

2. A braking system according to claim 1, wherein the electric motor (22) is a three-phase synchronous motor.

3. Braking system according to any one of the preceding claims, in which the electromechanical member (2) comprises a regulation unit configured to determine the motor current from the current setpoint and the angular position of the electric motor (22).

4. Braking system according to any one of the preceding claims, in which the actuator (3) of the friction element (4) comprises a member for converting a rotational movement into a translational movement and an elastic member for converting a translational movement into mechanical force.

5. A braking system according to claim 4, wherein the elastic member is a compression spring.

6. Braking system according to any one of claims 4 to 5, in which the member for converting a rotational movement into a translational movement is a ball screw.

7. A braking system according to any one of the preceding claims. preceding, wherein the friction element (4) comprises brake pads

8. A turboprop comprising a rotor on which a propeller is mounted, the turboprop comprising a braking system according to any one of the preceding claims configured to brake the rotor.

9. An aircraft comprising a turboprop engine according to claim 8.

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