Abstract:
A mechatronic assembly for linearly driving a member includes a control unit and an actuator, the control unit including a control algorithm and a power bridge, the algorithm controlling the power bridge, the power bridge providing a bifilar electrical signal consisting of a torque signal and a direction signal, the actuator including an electric motor which does not have an N-phase multiphase brush, binary probes for detecting the position of the rotor of the motor, a device for transforming the rotational movement of the rotor into a linear movement of the control member, power switches capable of powering the N phases of the motor on the basis of the bifilar electrical signal, and the state of the power switches is controlled directly by a signal from the detection probes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Phase Entry of International Patent Application No. PCT/EP2015/062205, filed on Jun. 2, 2015, which claims priority to French Patent Application Serial No. 1455021, filed on Jun. 3, 2014, both of which are incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of linear electric actuators, for example for controlling rates of fluid circulating in heat engines of cars, and more specifically to the field of reversible actuators requiring a safe return to a reference position, a so-called “fail-safe” function, to control the fluid rate upon power shut-off by the battery. The invention specifically relates to a self-switching reversible linear actuator with a bifilar control with interesting qualities as regards compactness, useful power, endurance, temperature behaviour and cost which are better than the actuators described in the state of the art. 
       BACKGROUND 
       [0003]    Fluid metering valves are already known, which comprise a reversible actuator consisting in the association of a direct current motor or gear motor with a cam transformation system to generate a linear movement and control a regulation rate by more or less pushing a valve away from the seat thereof. Such combinations of the state of the art are based on various solutions for motors or gear motors: 
         [0004]    A first solution consists in using a direct current motor with a brush combined with a reduction gearing and a cam transformation system to generate the axial displacement of the valve, as disclosed, for example, in the U.S. Patent Publication No. 2012/0285411. This first solution has the advantages of a significant movement reduction and thus an interesting power reserve, simple control using a bifilar connection, the absence of any other smart electronic member. Such solution is interesting as regards costs and capacity to work at high temperatures. 
         [0005]    But this solution has two major drawbacks relating to the mechanical switching of electrical signals, which results in the brushes wearing and thus a limited service life, as well as significant electromagnetic emissions which affect the other electronic members nearby. Both drawbacks are more and more a problem for the new specifications of electric actuator for automobiles. On the one hand, always longer service lives are expected from the motors, and on the other hand, the quantity and proximity of electric actuators in motors require a reduction in electromagnetic emissions. Eventually, the spatial configuration of the solution is not very advantageous since it requires positioning the gear motor along an axis perpendicular to the axis of the actuator output member, which leads to a delicate integration on the vehicle engine block. 
         [0006]    A second type of solution is based on a torque motor, which is a second (brushless) direct-current motor, which drives a cam device to generate the translation of a valve as disclosed, for example in patent FR2978998. Such solution has the same advantages, as regards a simple control, relative to the bifilar control of the previous solution since it is also based on a direct-current motor, and it additionally takes advantage of the absence of brushes, which increases their service lives, since no brush wears, as compared to the previous solution. Eventually, such solution is thus interesting because of the extended service life and the low electromagnetic emissions resulting from the absence of brushes, because working at high temperatures is possible thanks to the absence of smart and thus binding (as regards cost) electronic components, and because control, which remains bifilar, is simple. 
         [0007]    But it also has the drawback of being based on an actuator with a limited travel, which prohibits any kind of reduction in the movement upstream of the cam transformation system, which is a significant obstacle, as regards the maximum forces which can be reached. As a matter of fact, the forces obtained with the second solution are half those obtained with the first family of solutions for a higher power consumption. Similarly to the actuators of the previous family, the perpendicular orientation of the torque motor relative to the output member results in a delicate integration of the actuator, because of the transformation by a cam roller. 
         [0008]    Eventually, a third family of known solutions for such reversible actuators for fluid regulation valve control, consists in using an electronically-switched polyphase motor, also currently referred to as a BLOC (for Brushless DC) motor, which corresponds to a brushless polyphase motor, the electronic switching of which, inside the control device, makes it possible to control the electric signals in the phases of the stator, according to the position of the rotor, which is measured by magneto-sensitive sensors. Such motor is associated with a screw-nut transformation system to generate the translation of the valve control member, according to a movement coaxial with that of the motor. In this case, the control device is rather complex, since it works in closed loop, to adapt the signals sent to the stator, according to the actual position of the rotor. Such solution is disclosed in several patents, among which the European patent EP1481459. 
         [0009]    Such solution has the advantages of being brushless and thus provides the same guaranteed values of durability and low magnetic emission as the previous solution, but also has a sufficient movement reduction to reach high forces similar to those obtained with the solutions of the first family. Eventually, such configuration is interesting as regards integration since the coaxial nature of the movement of the central screw relative to the motor stator results in a globally axisymmetric construction which greatly facilitates the integration thereof on an engine block and provides an advantageous global compactness of the solution. 
         [0010]    On the contrary, this solution requires using complex control electronics integrating smart equipment which have to interpret information from the rotor position sensor to control the phases of the stator accordingly. This results in an expensive solution implemented at limited temperature since the micro-controller which manages the control of the motor is limited to 140° C., which is too low for the new environmental constraints for the valves under the hood of a car. 
       SUMMARY 
       [0011]    The present invention aims at remedying the drawbacks of the state of the art by providing a compact solution actuation using a brushless motor controlled by a bifilar signal via a simple set of electronic components enabling utilization at high temperatures, above 140° C. One aim of the invention is to enable a linear output along the axis of rotation of the brushless motor, by using a screw movement transformation system, inside the rotor. The invention also aims at enabling the return to a safe position (currently called the fail-safe function) by using a return spring coupled to a reduction gearing of the planetary type. 
         [0012]    For this purpose, the present invention is based on a brushless polyphase motor with electronic switching, integrating a high-performance movement transformation and being able to receive a very compact return device to the reference position, which makes it possible to propose the integration of all the required functions in a coaxial construction. The screw-nut movement reduction device, which may use two nuts and a screw with a double thread, makes it possible to reach a high movement reduction factor as well as high performances to reach a high output power and a good power reserve. The control unit, which is based on a bifilar control from the power bridge to supply the power switches directly controlled by the magneto-sensitive elements for reading the position of the rotor, results in an interesting compromise between conventional self-switching electronics for a brushless motor and a basic control for a motor with a brush. Such an electronic solution is both efficient and inexpensive, and it makes it possible to work at high temperatures since it uses no on-board intelligence. 
         [0013]    Eventually, coupling a planetary reduction gearing and a torsion spring enables a very compact integration of an efficient solution of returning the motor to the reference position. As a matter of fact, the planetary reduction gearing makes it possible to reduce the angular path of the rotor, which may reach several revolutions, to drive a hub over a limited travel and thus operate a torsion spring in good conditions without being affected by the parasitic frictions of the turns which occur when the amplitude of the angular movement is above 270°. The torsion spring consists of a few windings of a wire, on a diameter positioned about the rotor guide and enables integration in the actuator, without extending or expanding its initial size. This also makes it possible to keep a coaxial construction, which can be more easily integrated into the motor environment. 
         [0014]    In its broadest sense, the invention relates to a mechatronic assembly for the linear drive of a member comprising a control unit and an actuator, with the control unit comprising a control algorithm and a power bridge, with said algorithm controlling said power bridge, with the power bridge outputting a bifilar electric signal consisting of a torque signal and a direction signal, with the actuator comprising a polyphase brushless electric motor having N phases, binary probes for detecting the position of the rotor of said motor, a device for transforming the rotary movement of the rotor into a linear movement of the control unit, power switches suitable for supplying the N phases of the motor from the bifilar electric signal, characterised in that the state of the power switches is directly controlled by a signal emitted by the detection probes. “Directly controlled” means the detection probes are electrically connected to the output switches and not to a micro-controller. The electric signal sent to the switches is the detection probes output signal. The only electric components, if any, mounted between one probe and one switch are passive components such as a resistor, a capacitor, or a diode. Advantageously, the N-phase polyphase motor consists of N unipolar or bipolar coils, or N*2 unipolar half-coils. 
         [0015]    According to an alternative solution, the binary probes for detecting the position of the rotor are supplied by the bifilar electric signal. According to another alternative solution, the movement transformation device has at least one nut connected to the rotor of the motor and at least one threaded portion connected to the actuator control member and in that the rotor drives a position-return device through a planetary reduction gearing. According to another alternative solution, the movement transformation device has at least one nut connected to the rotor and a second nut connected to the stator case, with each one cooperating with two portions of the control member having threads in opposite directions and in that the rotor drives the position-return device through a planetary reduction gearing. 
         [0016]    According to another alternative solution, the mechatronic assembly comprises a position sensor comprising a magnet connected to the control member and a magneto-sensitive element connected to the control unit, and the magneto-sensitive element is so designed as to be able to read the axial position of the control member. According to another alternative solution, it comprises a position sensor comprising a magnet connected to the control member and a magneto-sensitive element connected to the control unit and the magnetization pattern of the magnet is so designed as to enable to read the axial position of the control member during the helical movement thereof. Such assembly preferably comprises a position sensor comprising a magnet connected to the control member and a magneto-sensitive element connected to the control unit and the magnetization pattern of the magnet is axisymmetric. 
         [0017]    The invention also relates to a mechatronic assembly for the linear drive of a member comprising a control unit and an actuator, with the control unit comprising a control algorithm and a power bridge, with said algorithm controlling said power bridge, with the power bridge outputting a bifilar electric signal consisting of a torque signal and a direction signal, with the actuator comprising a polyphase brushless electric motor having N phases, binary probes for detecting the position of the rotor of said motor, a device for transforming the rotary movement of the rotor into a linear movement of the control unit, power switches suitable for supplying the N phases of the motor from the bifilar electric signal, characterised in that the state of the power switches is directly controlled by a signal emitted by the detection probes. The N-phase polyphase motor preferably consists of N unipolar or bipolar coils, or N*2 unipolar half-coils. 
         [0018]    According to an advantageous embodiment, the binary probes for detecting the position of the rotor are supplied by the bifilar electric signal. The movement transformation device advantageously has at least one nut connected to the rotor of the motor and at least one threaded portion connected to the actuator control member and the rotor drives a position-return device through a planetary reduction gearing. The movement transformation device preferably has at least one nut connected to the rotor and a second nut connected to the stator case, with each one cooperating with two portions of the control member having threads in opposite directions and the rotor drives the position-return device through a planetary reduction gearing. 
         [0019]    According to another alternative solution, the mechatronic assembly comprises a position sensor comprising a magnet connected to the control member and a magneto-sensitive element connected to the control unit and the magneto-sensitive element is so designed as to be able to read the axial position of the control member. It preferably comprises a position sensor comprising a magnet connected to the control member and a magneto-sensitive element connected to the control unit, and the magnetization pattern of the magnet is so designed as to enable to read the axial position of the control member during the helical movement thereof. According to another alternative solution, the mechatronic assembly comprises a position sensor comprising a magnet connected to the control member and a magneto-sensitive element connected to the control unit and the magnetization pattern of the magnet is axisymmetric. The winding axis of the torsion spring is advantageously concentric with the axis of rotation of the polyphase engine. According to another alternative solution, the angular path of the torsion spring  20  is mechanically limited by a protrusion connected to the spring itself or to one of the elements of the planetary reduction gearing  18  moving in a limited circular space. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0020]    Other characteristics and advantages of the invention will appear in the description that follows relative to detailed embodiments, and referring to the attached figures that represent respectively: 
           [0021]      FIG. 1 , a typical mechatronic architecture used for controlling via a bifilar control of a motor according to the invention; 
           [0022]      FIG. 2 , the detail of a basic electronic circuit which may be used in the invention; 
           [0023]      FIG. 3 a   , an example of an electronic circuit of the switching logic in a first “120° unipolar” operation mode and its truth table; 
           [0024]      FIG. 3 b   , an example of an electronic circuit of the switching logic in a second “180° unipolar” operation mode and its truth table; 
           [0025]      FIG. 4 , an example of an electronic circuit of the switching logic and its truth table for a bipolar controlling mode, in a first embodiment; 
           [0026]      FIG. 5 , an example of an electronic circuit of the switching logic and its truth table, for a bipolar controlling mode, in a second embodiment; 
           [0027]      FIGS. 6 a  and 6 b   , a first embodiment of the linear actuator integrating a screw-nut system; 
           [0028]      FIGS. 7 a  and 7 b   , a second embodiment of the linear actuator integrating a screw-nut system as well as a reference position-return system; 
           [0029]      FIGS. 8 a  and 8 b   , a partial sectional view and a three-quarter view of a geared motor according to the invention using a third embodiment of  FIGS. 8 a    and  8   b;    
           [0030]      FIGS. 9 a  and 9 b   , a partial sectional view and a three-quarter view of a geared motor according to the invention using the third embodiment of  FIGS. 8 a  and 8 b   ; and 
           [0031]      FIGS. 10 a  and 10 b   , according to the preferred embodiments of  FIGS. 8 and 9 , with the position-return solution coupled to the planetary reduction gearing. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  shows a mechatronic assembly according to the invention consisting of a source of energy  4  supplying a control unit  1  controlling an actuator  2  consisting of a brushless DC motor  8  associated with a mechanical assembly for mechanically transforming  9  the rotation into a linear displacement, and the assembly is symbolized here as a system of the screw-nut type. A sensor  7 , coupled to the mechanical output  12 , here the nut, of the actuator  2 , sends the position information  5  back to the control unit  1  which acts on the control signals  6  grouped in a link connector  3 . The position of the motor rotor  8  is read using N probes  11  which self-switch the N phases of the motor  8 , via a basic electronic circuit  10 . 
         [0033]      FIG. 2  shows the basic electronics  10  which may be used in the invention. It consists of a set of control transistors  25  directly controlled by the signals output by the Hall probes  11  detecting the position of the rotor of the motor via a switching logic  26 , consisting of simple electronic elements with no microprocessor. A voltage regulator  28  makes it possible to use the bifilar control signal to supply the  30  Hall probes  11 . 
         [0034]      FIG. 3 a    shows an exemplary control in a first so-called “120 °” unipolar controlling mode of a star-connected three-phase motor. As voltage (PWR+) is positive on the common point, current always circulates in the same direction, in the windings. Voltage from the voltage regulator  28 , output by the bifilar control, supplies the detection block  13  and the Hall probes Ha, Hb, He. Depending on the position of the rotor, the various digital probes are in the low state (equivalent to null voltage) or the high state (5V type voltage). Depending on the state of the probes, the various transistors Q 1  to Q 6  are open or closed and thus enable, or not, the circulation of current in the various phases. The controlling mode which can be obtained with the example of  FIG. 5  is driving in a 120° mode, i.e. each phase is supplied for 120° electrical degrees (one electrical degree is equal to one mechanical degree multiplied by the number of pairs of poles in the motor magnet). 
         [0035]    Similarly,  FIG. 3 b    shows an exemplary “180°” unipolar control. Transistors Q 1  to Q 3  are open or closed, depending on the state of the Hall probes, supplied by the regulated bifilar signal. The transistors are open/closed over 180° electrical degrees. Controlling in 120° or 180° mode can be selected according to the number of authorized control transistors or the profile and torque level expected for the motor. 
         [0036]    Controlling the motor in a bipolar mode (circulation of current in both directions, in each phase) is possible. For this purpose, two different coils just have to be provided per phase, with each one being coiled in one direction. The A+ coil is thus coiled in the direction opposite that of the A− coil, as per the example of  FIG. 4  and the A phase. When transistor Q 1  is open and Q 2  is closed, current circulates in the A− phase and the magnetic field in the phase is oriented in a first direction. On the contrary, when transistor Q 1  is closed and Q 2  is open, current circulates in the A+ phase and the magnetic field in the phase is oriented in a second direction opposite the first direction. The same is true for the two other B and C phases of the example shown in  FIG. 4 . In order to correctly sequence the opening and closing of the transistors Q 1  to Q 6 , the switching logic block  26  must be provided with an adapted control logic  14 , consisting of simple electronic elements such as logic gates which make it possible to obtain the truth table shown. The complete electronic diagram is not shown for reasons of clarity, but can easily be considered by the persons skilled in the art. 
         [0037]    It should be noted that a bipolar connection of the motor coils can be provided, as explained in  FIG. 5 , while keeping 6 power transistors. The control logic  14  is adapted to the corresponding truth table shown in  FIG. 5 . 
         [0038]      FIG. 6 a    shows a sectional view of a linear actuator according to the invention, which comprises a brushless polyphase motor  8 , integrating a rotor and a stator. The front face of the stator case  21  carries an electronic circuit  10  comprising a bifilar controlling device as described above. The rotor  15  carries a magnet  34  so designed as to be able to excite digital probes  11  positioned on the electronic circuit  10 , and integrates a nut  16 , the rotation of which causes the translation of the central axis  17 , the rotation of which is locked using a sliding link with the front flange  29 . According to the control logic disclosed above, the digital probes  11  make it possible to self-switch the stator phases, and the pins linked to the control signals  6  of the motor consist of two power supply leads only. Besides, the central axis  17  which is mobile in translation, carries a magnet  24  so designed as to be able to excite a magneto-sensitive element  30  positioned on the front face of the electronic card  10 , so as to give position information  5  (not shown in  FIG. 6 a   , only in  6   b ) of the control member. The sensor, supplied by two power supply leads separate from those of the motor, issues information  5  on the position of the central axis  17  which enables a control unit outside the actuator, to check the position of the central axis  17  by comparing the actual position thereof with the desired set position. As shown in  FIG. 6 b   , the actuator has a link connector  3  which comprises five electrical connections only: 2 of the connections are the control signals  6  of the motor and the other 3 connections are the position sensor supply, and the output signal thereof, as position information  5 . 
         [0039]      FIGS. 7 a   , showing a separate view of the rotor  15  with a planetary reduction gearing  18 , and  7   b,  showing a sectional view of the complete motor, relate to a second embodiment of the linear actuator according to the invention, wherein the rotor  15  of the polyphase motor integrates a nut  16  which cooperates, on the one hand, with a threaded portion of the central axis  17  composing the control member, and, on the other hand, with a planetary reduction gearing  18  consisting of 3 satellites positioned about the rotor  15  by driving an internal spur gear  19  which itself drives the torsion spring  20 . 
         [0040]    The central axis  17  is slidingly connected to the front flange  21  of the actuator case, so that the rotation of the rotor  15  nut  16  causes the translation of the central axis  17 . The rotation of the rotor  15  results in the loading of the torsion spring  20 , the travel of which is limited by the internal spur gear  19 , which has a pin which circulates inside a notch (not shown in  FIG. 6 b   ) connected to the actuator case. The range of the circular movement of the spring  20  is thus significantly reduced relative to the movement of the rotor  15  thanks to the reduction of such planetary reduction gearing  18  and enables a small deformation of the spring  20  and thus avoids the friction loss of the spring  20  on its chafing sleeve  23 . The rotor  15  torque is transformed in a translation of the control member through the screw/nut link which thus transmits the mechanical power. The planetary reduction gearing can advantageously be made of plastic since it is used for transmitting the return torque stored in the spring, only, so as to ensure the return of the actuator control member to a reference position. The plastic gears of the planetary reduction gearing thus do not transmit the effective mechanical power at the actuator output, but a limited torque, so calculated as to overcome the magneto-static torque of the rotor  15  and ensure the return to the reference position when the motor is no longer powered. A magnet  24  is connected to the rear end of the central axis  17  and cooperates with a magneto-sensitive element  30 , with the magnet  24  and magneto-sensitive element  30  forming a position sensor. The magneto-sensitive element  30  is connected to the motor control device, so that the axial displacement of the control member is read and interpreted by the control device, which can then check that the control member corresponds to the set condition (closed-loop operation). 
         [0041]      FIGS. 8 a  and 8 b    show a third embodiment wherein the movement is transformed using a double-thread screw solution. The rotor  15  has a first nut  16  which cooperates with a first threaded portion of the central axis  17 , whereas a second nut  27  connected to the frame cooperates with a second threaded portion of the central axis  17 , the hand of helix of which is opposed to the first portion. The rotation of the nut  16  connected to the rotor, thus forces the central axis  17  to engage into the second stationary nut  27 , and thus to make an helical movement. The control member of the actuator thus follows an helix and the shape of the valve disk connected to the actuator shall then have to be so designed as to accept such rotation component when dosing the fluid. 
         [0042]    The position sensor making it possible to read the axial position of the control member is similar to the one shown in  FIGS. 7 a  and 7 b   . But it is different therefrom in that the magnet  24  magnetization pattern must be adapted to the relative movement of the magnet  24  relative to the magneto-sensitive element  30  which is helical in the second embodiment. A preferred but not restrictive solution consists in having an axisymmetric magnetization (which is identical during a rotation) on the magnet  24  so that the rotation of the control member is not detected by the magneto-sensitive element  30  forming the sensor. 
         [0043]      FIGS. 9 a  and 9 b    show sectional and perspective views of an actuator according to the embodiment of  FIGS. 8 a  and 8 b   . Such embodiment combines the control device using simplified electronics, the solution of the transformation of the movement using a double helix coupled to a position sensor of the helical movement of the control member, and eventually a reference position-return device using a torsion spring applying a return torque to the rotor through a planetary reduction gearing co-axially distributed about the rotor. The actuator case consists, on the one hand, of an enclosure  21  overmolded about the stator and a front flange  29  which are separated so that the front part of the actuator comprising the planetary reduction gearing and the spring can be easily modified, without changing the rear part which comprises the motor part and the control electronics. 
         [0044]      FIGS. 10 a , 10 b  and 10 c    show in details the original reference position-return solution, which is based on the combination of a torsion spring  20  with a planetary reduction gearing  18 . The spring  20  has a stationary fastener  40  fixed on the stator case  21  and a mobile fastener  41  fixed to the internal spur gear  19 , which comprises a pin  42 , which circulates in a path  43  having a limited length provided in the stator case  21  so as to enable the pre-loading of the spring. The internal spur gear  19  is driven by three planet gears  36  which are driven by the central gear  35  secured to the rotor  15 . The ratio of reduction between the movement of the rotor  15 , which can reach several revolutions, and the reducing crown  19  is so selected as to limit the working angle of the spring  20  to a reduced travel, of the order of 180 to 270 degrees. The spring coils are thus exposed to a low stress and make it possible to provide a return function with a minimum friction. The planetary reduction gearing  18  can be made of plastic materials since it transmits the spring torque only, and not the motor effective torque which is used, in parallel, by the movement transforming device.