Abstract:
A bearing includes at least an inner ring, an outer ring, and rolling bodies arranged between the inner and outer rings, one of the rings being designed to turn and the fixed, and one of the rings including an inducing element is designed to generate an inducing electromagnetic field, the other of the rings including an electrical circuit in which an induced current is generated when one of the rings turns in relation to the other of the rings, and when the inducing element generates an inducing electromagnetic field, wherein the inducing element designed to generate an inducing electromagnetic field includes a module having a piezoelectric effect and/or a module having a thermoelectric effect.

Description:
CROSS-REFERENCE 
     This application claims priority to French Patent Application No. FR1260305 filed on Oct. 29, 2012, the content of which is fully incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a bearing including an inner ring and an outer ring, and rolling bodies arranged between the rings, one of the rings being designed to turn and the other not, and one of the rings including an inducing element designed to generate an inducing electromagnetic field, the other of the rings including an electric circuit in which an induced current is generated when one of the rings turns in relation to the other of the rings, and when the inducing element generates an inducing electromagnetic field. 
     BACKGROUND OF THE INVENTION 
     In such bearings, used for example in diverse equipment, notably in gearboxes, for example, helicopter gearboxes such as that described in document EP0172104, the rotation of the ring carrying the inducing element causes an induced current to be generated in the other ring. 
     Document U.S. Pat. No. 6,892,587 is known, for example, which describes an inducing element incorporating permanent magnets. 
     However, it has been noted that the magnets, providing permanent magnetization, trap the metal particles circulating in the bearing and exterior to it, which can be a cause of failure, notably due to seizing. 
     The present invention aims notably to reduce these drawbacks. 
     SUMMARY OF THE INVENTION 
     To that effect, following a first aspect, the invention proposes a bearing of the aforementioned type, characterized in that the inducing element designed to generate an inducing electromagnetic field includes a module having a piezoelectric effect and/or a module having a thermoelectric effect. 
     Such a bearing, including a thermoelectric or piezoelectric module, transforms variations of the ambient conditions (vibrations and/or temperature) of the bearing into electrical energy. 
     Such a bearing is designed to generate, in an autonomous and integrated manner, an induced current, for example for the purpose of its electric power supply, without giving rise to permanent magnetization that traps the metal particles. In fact, there is no magnetization when the bearing is idle. 
     Such a bearing therefore enables an extension of the service life of the bearing. 
     In embodiments of the invention, the bearing according to the invention furthermore incorporates one or more of the following characteristics:
         it includes a processing module that requires an electric power supply in order to function, in which the current induced in the electric circuit is used to supply the processing module;   at least one part, requiring an electric power supply in order to function, of the processing module, is integral with the ring including the electric circuit;   it includes a capacitor arranged in parallel with the module having the piezoelectric effect and/or a module having a thermoelectric effect;   it includes an inductive resistor on an electric link arranged in parallel with the module having the piezoelectric effect and/or the module having a thermoelectric effect, a switch designed to open or close the electric link and a control device of the switch designed to control the opening or closing of the switch according to the voltage value at the terminals of the module having the piezoelectric effect and/or of the module having the thermoelectric effect;   it furthermore includes a voltage rectifier arranged on the electric link;   the ring includes the inducing element includes terminals arranged on its surface, configured to project towards the other of the rings, and the inducing element includes first windings wound around the terminals and electrically connected to the module having the piezoelectric effect and/or the module having the thermoelectric effect;   a connection of the module having the piezoelectric effect and/or of the module having the thermoelectric effect is connected to one extremity of each of the first windings via respective capacitors;   the other extremity of each of the first windings is connected to one extremity of the first winding arranged on a neighboring terminal via an inductive resistor or is connected to another connection of the module having the piezoelectric effect and/or the module having the thermoelectric effect;   the ring includes the electric circuit includes terminals arranged on its surface, configured to project towards the other of the rings, and the electric circuit includes second windings wound around the terminals;   the extremities of each second winding are connected to a common terminal;   one of the extremities of each second winding is connected to the common terminal via a resistor;   the other of the extremities of each second winding is connected to the common terminal via an inductive resistor.       

    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       These characteristics and advantages of the invention will emerge from reading the description that will follow, given only as an example, and made with reference to the appended drawings, on which: 
         FIG. 1  represents a cutaway view of a helicopter gearbox; 
         FIG. 2  is a view of a bearing in an embodiment of the invention; 
         FIG. 3  is a view of a block diagram of a processing module of a bearing in an embodiment of the invention; 
         FIG. 4  is a flow chart of steps implemented by the processing module of  FIG. 3  in an embodiment of the invention; and 
         FIG. 5  illustrates the electric circuits arranged on the rings of the bearing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , a cutaway view of a helicopter gearbox  1  is represented. This gearbox  1  is designed to perform the transmission of the rotating motion between a primary shaft  4 , which is the engine shaft and a secondary shaft  5 , which is the helicopter rotor, according to several transmission ratios. It includes an outer housing  6 , which incorporates, in addition to the primary and secondary shafts, several bearings  2  and several gears  3 . 
     In an embodiment of the invention, each of these bearings  2  is similar to the mechanical bearing  10  described below with reference to  FIGS. 2 and 3 . 
     With reference to  FIG. 2 , a mechanical bearing  10  in an embodiment of the invention incorporates two coaxial rings: an outer ring  11  and an inner ring  12 . 
     In the space  14  between these coaxial rings  11  and  12 , balls are placed in a lubricant and held apart by a cage (not illustrated). 
     In a known manner, a bearing  10  optimizes the friction between two parts and provides a support for one of these two parts, which is rotating. 
     One of these parts (not illustrated) is fastened to the outer ring  11 . It is, for example, a rotating shaft enclosing the outer ring  11 . In the case of the gearbox  1 , this shaft is, for example, the primary shaft  4 . 
     The other part (not illustrated), for example, a part of the outer housing of the gearbox  1 , is arranged with a tight fit in the receptacle described by the inner ring  12 . It is fixed in relation to the rotating shaft integral with the outer ring  11 . 
     It will be noted that in other bearings  10  according to the invention, this time, it is the inner ring that is fixed with a tight fit to a rotating part, while the outer ring is integral with a fixed part. 
     According to the invention, a processing module  20  is fastened to one of the rings. For example, the processing module  20  is integrated to a housing fixed to a ring of the bearing by screwing or flanging. In another example, a shape is made in a ring of the bearing, this shape acting as a support for the processing module  20 . 
     As illustrated in  FIG. 2 , in the case under consideration, the processing module  20  is fastened to the outer surface of the inner ring  12 . 
     The processing module  20  incorporates for example, in the case under consideration, a microprocessor  21 , a memory  22 , a sensor  23  designed to measure one or more parameter(s), a radio frequency transmitter  24  and an electric power supply module  25 . 
     The electric power supply module  25  is designed to generate an electrical energy induced by the variation of an inducing magnetic flux during the relative rotation of the rings  11 ,  12  and to deliver this electrical energy to the components of the processing module  20 , whose functioning requires an electric power supply. Thus, in the case under consideration, it supplies electrical energy notably to the microprocessor  21 , to the radio frequency transmitter/receiver  24  and possibly to the sensor  23 . 
     With reference to  FIG. 5 , the inner ring  12  includes terminals  120  spaced over its outer surface, cylindrical in shape and projecting towards the outer ring  11 . The number of terminals  120  illustrated is eight, but it can have any value. 
     The electric power supply module  25  incorporates an electric circuit associated with each terminal  120 , including in the case under consideration, a winding  27 , an inductive resistor  28  and a resistor  29 . 
     The winding  27  is wound around each of these terminals  120 . One of the extremities of the winding  27  is connected to an extremity of the inductive resistor  28 . The other extremity of the winding  27  is connected to an extremity of the resistor  29 . The other extremity of the inductive resistor  28  and the other extremity of the resistor  29  are connected to a point X connecting all of the corresponding extremities of the different terminals  120  in a star. 
     The induced voltage V is collected between this common point X and a point V of the winding situated at the outer extremity of a terminal  120 . 
     As also illustrated in  FIG. 5 , the outer ring  11 , designed to be driven in rotation by the shaft with which it is integral, incorporates an inducing block  30 . 
     The outer ring  11  includes terminals  110  spaced over its inner surface, cylindrical in shape and projecting towards the inner ring  12 . The number of terminals  110  illustrated is seven, but it can have any value. 
     Advantageously, these terminals  110  are arranged in such a way as to be facing the terminals  120  of the inner ring  12  during the relative rotation of the rings  11 ,  12 . 
     In the embodiment under consideration, the inducing module  30  includes an electric circuit associated with each terminal  110 , including, in the case under consideration, a winding  31 , a capacitor  32  and an inductive resistor  33 . 
     The winding  31  is wound around each of these terminals  110 . One of the extremities of the winding  31  is connected to an extremity of the inductive resistor  33  and to an extremity of the capacitor  32 . The other extremity of the winding  31  is connected (except in the case of the electric circuit associated with one of the terminals  110 , referenced terminal  110   a ) to the extremity of the inductive resistor  33  of the electric circuit associated with the neighboring terminal  110 . 
     The other extremity of each of the capacitors  31  is connected to a common connector A. 
     The other extremity of the winding  31  associated with the terminal  110   a  is connected to a connector B, while the other extremity of the inductive resistor  33  associated with the neighboring terminal to the terminal  110   a , referenced terminal  110   b , is connected via a resistor to the connector A. 
     In the embodiment of the invention considered with reference to  FIG. 5 , the inducing block  30  furthermore includes a piezoelectric module  35  and a switching stage  34 . 
     The piezoelectric module  35  includes a piezoelectric plate  37  arranged in parallel with a capacitor  38 . One of their common extremities is connected to the connector A, and the other of their common extremities is connected to the connector B. 
     The extremity of the piezoelectric plate  37  connected to the connector A is furthermore connected to an extremity of an inductive resistor  43 . The other extremity of the inductive resistor  43  is connected to an extremity of a voltage rectifier  42 . The other extremity of the rectifier  42  is connected to an extremity of the switch  44  of the switching stage  34 . The other extremity of the switch  44  is connected to that of the extremities of the piezoelectric plate  37  connected to the connector B. 
     In the switching stage, a comparator  39  controls the closing or opening of the switch  44  according to the data supplied to it. 
     The piezoelectric plate  37  is designed to convert ambient vibrations to electrical energy. This electrical energy, which can be weak, and which depends on the piezoelectric plate  37 , is stored in the capacitor  38 , which acts as an energy reservoir and thus allows a more stable voltage u to be delivered to the inducing electric circuits associated with the terminals  110 . 
     In order to increase the energy value delivered by the inducing block  30 , the voltage u between the connectors A, B of the piezoelectric plate  37  is applied at the inductive resistor  42 . This voltage is applied at the inductive resistor  42  when the switch  44  is closed and is not applied at the inductive resistor  42  when the switch  44  is open. The comparator  39  compares the voltage between the connectors A, B of the piezoelectric plate with a fixed minimum threshold and if this voltage is maximum, i.e. higher than the fixed minimum threshold, the comparator  39  controls the closing of the switch  44 . 
     The inductive resistor  43  brakes the drop of the voltage u and thereby enables the capacitor  38  to be charged rapidly according to the principles of exchanges of energy within an oscillating circuit associating an inductive resistor and a capacitor. The voltage rectifier  42  at the output of the inductive resistor  43  enables the charging speed of the capacitor  38  to be improved. 
     The electrical energy generated by the piezoelectric plate because of the ambient vibrations received by the plate is thus supplied to the electric circuits associated with the terminals  110 , which generate an inducing electromagnetic flux. The capacitors  32  associated with the windings  31  enable an appreciably continuous induction to be generated. 
     When the shaft integral with the outer ring  11  rotates, an induced current is generated through the electric circuits associated with the terminals  120  of the inner ring  12  due to the variation of the inducing electromagnetic flux. The resulting induced voltage V in the electric power supply module  25  is then provided, in the case under consideration, to supply the processing module  20 . 
     With a piezoelectric plate having a power density of 1 mW*cm-3/g, the voltage u has an appreciably sinusoidal shape, of amplitude u 0 , equal for example to 15 mV. 
     The value of the induced voltage V is of amplitude V 0 , equal for example to 25 mV, which corresponds to a voltage gain of approximately 40% between the inducing voltage and the induced voltage. 
     Such an inducing circuit enables the inducing voltage to be smoothed to a quasi-sinusoidal voltage when the profile of the vibrations varies. 
     Such a bearing is therefore supplied in an autonomous and integrated manner. Furthermore, the combined functioning of the inducing block  30  and the electric power supply module  25  does not give rise to magnetization when the bearing is idle: the metal particles are not therefore trapped in the bearing in a durable manner, which increases its service life. 
     In another embodiment, the piezoelectric plate  37  is replaced by a thermoelectric cell, to have the Seebeck effect (also called a Peltier effect cell), which enables an electrical energy to be generated in the case where the bearing is situated inside a heat flow. 
     In such a case, it is no longer the vibrations, but a temperature difference between two junctions of the thermoelectric cell, which will provide a voltage used to generate the inducing electromagnetic flux. 
     In an embodiment, the sensor  23  is a sensor designed to measure at least one parameter representative of the vibrations on an axis (for example, the axis radial to the bearing rings) or on two axes or three axes. Such a sensor includes for example an accelerometer or several accelerometers. 
     In an embodiment, the sensor  23  is designed to deliver to the microprocessor  21  a signal, for example analogue, indicating the successive measurements of the parameter taken by the sensor  23 . 
     Further to the execution in the microprocessor  21  of software instructions of a program stored in the memory  22 , the following steps are implemented, with reference to  FIG. 4 : 
     In a step  100 , the signal indicating the successive measurements taken by the sensor  23  is delivered to the microprocessor  21 . 
     In a step  101 , the signal provided by the sensor is processed: it is, for example, sampled and converted to digital data representing the successive values of the parameter measured, and which are stored in the memory  22 . 
     Additional processing is optionally performed based on these successive temporal digital data: averaging, detection of malfunctions, etc. 
     In a step  102 , in an optional embodiment, information derived from digital data, processed if need be, is supplied to the radio frequency transmitter  24 , which is designed to transmit it on a radio frequency channel to a monitoring module  7 . 
     The transmission modalities are as follows, for example: transmission every interval of a fixed duration T or transmission each time data of a fixed volume V are available. 
     In an embodiment, the set of sensors  23  incorporates for example a sensor designed to measure the temperature and/or the angular position of one ring in relation to the other ring, etc. 
     In an embodiment of the invention, the gearbox  1  furthermore incorporates the monitoring module  7  fastened to the outside of the housing  6 . 
     The monitoring module  7  includes a radio frequency receiver capable of receiving radio frequency data transmitted by each of the bearings  2 , similar to the bearing  10  described above. 
     The monitoring module  7  furthermore includes a memory and is designed to memorize these radio frequency data, matching an identifier of the bearing from which the data were transmitted, and optionally matching dating data representative for example of the moment the data were received by the monitoring module. 
     In an embodiment, the monitoring module  7  is designed to perform processing of these data. For example, the monitoring module  7  performs averaging of data transmitted by a bearing and/or is designed to combine data transmitted by different bearings, for the purpose of identifying or characterizing malfunctions on the basis of these combined data. 
     It was considered above that the processing module  20  incorporated, in the case under consideration, the following modules, additional to the electric power supply module  25 : a microprocessor  21 , a memory  22 , a sensor  23  designed to measure one or more parameter(s) and a radio frequency transmitter  24 ; in other embodiments, these modules are replaced and/or enhanced by other modules, some of which are supplied for example by the electric power supply module  25  according to the invention.