Abstract:
A system for blocking an output shaft of the engine of an automobile, of a type that includes a toothed wheel coaxially mounted on the shaft, and a first finger mobile between a shaft releasing position and a shaft blocking position in which the first finger is engaged in a gap formed between two teeth of the wheel. The system includes an alignment mechanism capable of aligning a gap between two teeth of the wheel and the first mobile finger, and the first mobile finger is configured to be inserted into the gap without any substantial circumferential clearance.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of motor vehicles and more particularly to the immobilization of a vehicle by locking the output shaft of the motor fitted to the latter. 
     PRIOR ART 
     The locking of the output shaft of a heat engine of a motor vehicle is usually used in an automatic transmission to immobilize the vehicle. To do this, the driver engages a position called the “parking brake” position of the automatic gearbox. A finger then engages between two teeth of a gearwheel, called the “parking gearwheel”, mounted coaxially on the output shaft in order to immobilize the latter. 
     For safety reasons, the engagement of this finger must be able to be carried out when the vehicle is running at a nonzero speed close to 5 km/h. For such an engagement at a nonzero speed to be possible, the width of the finger is substantially less than that of the spaces between two teeth of the parking gearwheel. Thus, once the finger is engaged in the parking gearwheel, there is a circumferential clearance freeing the gearwheel, and therefore the output shaft of the engine, to turn a few degrees. 
     However certain applications, for safety reasons, require the output shaft of the engine to be completely immobilized without it being able to make a rotation when the finger is engaged. 
     For example, in the context of an electric vehicle the motor of which can be of the synchronous or asynchronous type, the inventors have discovered that it is possible to rapidly recharge the array of accumulators of the vehicle by directly powering electrically the windings of the stator of the motor, which then play the role of inductive components. The stator is in effect connected to the output of an inverter generating an alternating electric power supply for the stator from the direct voltage delivered as an input by the accumulator array. As is known per se, an inverter is a reversible device which delivers at its input a rectified voltage when its output is powered with alternating-current voltage. In other words, an inverter operating so as to deliver a rectified voltage at its input is a rectifier. By electrically powering the stator windings, a recharging of the accumulator array is then achieved via the inverter. 
     However, to use such a recharging of the accumulator array, it is necessary to completely lock the rotor in order to immobilize the vehicle. Specifically, the flow of a current in the stator windings generates a motor torque since the rotor tends to align its magnetic field on the magnetic field of the stator caused by the flow of the current (whether it be by phenomena of reluctance in a rotor of a synchronous motor with separate excitation from which the power supply of the rotor has been disconnected, simply by the presence of the permanent magnets on the rotor of a conventional synchronous motor with permanent magnets, or else by the currents induced in the rotor in the case of an asynchronous motor). Because of the multiplying factor of the transmission system, the motor torque delivered to the wheels of the vehicle is considerable. Consequently, the slightest movement of the rotor will result in generating a torque at the wheels in the same direction causing the vehicle to move. In extreme cases, an overspeeding of the electric motor by coupling of the rotor and stator magnetic fields may cause the unintended starting of the vehicle. 
     However, the locking of the rotor, which forms the output shaft of the motor, by means of a finger and of a parking gearwheel as described above is not sufficient to provide optimum safety because of the existing circumferential clearance necessary for the correct operation of the parking brake. Specifically, irrespective of the type of electric power of the stator windings, there is an alternating component in the power supply which has the effect of causing a back-and-forth movement of the rotor, each phase of this back-and-forth movement terminating in a violent abutting of the finger on the side of a tooth of the parking gearwheel. Not only do these violent buttings weaken the teeth of the parking gearwheel and the finger, involving their destruction after a short while, but additionally these vibrating phenomena are propagated throughout the transmission system also weakening the latter and inducing a back-and-forth movement of the vehicle. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to solve the abovementioned problem by proposing a system for locking the output shaft of a motor of a motor vehicle ensuring a complete locking of this shaft. 
     Accordingly, the subject of the invention is a system for locking the output shaft of a motor of a motor vehicle, of the type comprising a gearwheel mounted coaxially on said shaft and a first movable finger that can move between a position of releasing the shaft and a position of locking the latter in which the first finger is engaged in a space formed between two teeth of the gearwheel. 
     According to the invention, the system comprises alignment means able to align a space between two teeth of the gearwheel with the first movable finger, and the first movable finger is designed to engage substantially without circumferential clearance in said space. 
     In other words, the finger is designed to be inserted between two teeth of the gearwheel so that its sides rest on the sides of the teeth. Thus, the rotor has no degree of freedom in rotation. Notably, in the context of recharging an array of accumulators as described above, the back-and-forth movement is prevented. 
     It will quite clearly be understood that the expression “without circumferential clearance” means the absence of functional circumferential clearance to the extent that there is still a minimal circumferential clearance because of the manufacturing tolerances of the mechanical parts. 
     According to one embodiment of the invention, the alignment means comprise a second finger that can move between a position of releasing the shaft and a position of locking the latter in which the second finger is engaged in a space formed between two teeth of the gearwheel, the second movable finger being designed to engage with a large circumferential clearance in said space. 
     In other words, it is possible to add to the first finger a second finger similar to the conventional finger performing the parking brake function in vehicles with automatic transmission. This second finger is then mainly used in the context of the invention as a means for prealigning the first finger but may however retain its first function of parking brake. 
     “Great circumferential clearance” in this instance means a clearance the amplitude of which allows a prealignment of the shaft with the first finger for a nonzero speed of the vehicle of the order of 5 km/h. 
     According to one embodiment of the invention, the system comprises a button able to make a translational movement, and the first finger is able to make a rotary movement about a rotation spindle, the first finger comprising a surface forming a cam on which said button is able to push. More particularly, the second finger is able to make a rotary movement about the rotation spindle and comprises a surface forming a cam on which said button is able to push, the surfaces forming a cam of the first and of the second finger being arranged so that the surface forming a cam of the first finger is able to be engaged once the second finger is engaged in a space between two teeth of the gearwheel. 
     In other words, the first and the second finger engage successively between two teeth of the gearwheel, thus allowing a preliminary locking of the output shaft of the motor, including when the vehicle is moving, followed by a complete locking of the shaft. 
     Preferably, one amongst the first and the second finger comprises a pin able to engage in a circularly arcuate groove of the other finger. The successive engagement of the fingers is thus reinforced and the disengagement of one finger induces the disengagement of the other finger. 
     Preferably, the system comprises an elastomer ring between the rotation spindle of the first finger and the first finger so as to filter the vibrations generated by the reactions on the rotor. 
     According to a particular embodiment of the invention, the alignment means comprise control means able to control the slow rotation of the shaft. 
     In other words, the shaft is turned slowly in order to ensure an engagement of the first finger without circumferential clearance between two teeth of the gearwheel. 
     Advantageously, the present invention finds application in the context of an electric motor of the synchronous type the rotor of which forms the output spindle of the latter, notably when it involves locking the rotor for reasons of recharging the array of accumulators of the vehicle by powering the stator windings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The present invention will be better understood on reading the following description, given only as an example, and made with respect to appended FIGS  1  to  6 , in which identical reference numbers designate identical or similar elements, these figures illustrating schematically a system according to the invention in various operating positions and elements for charging and powering according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIGS. 1 to 5 , a gearwheel  10 , of which only two teeth  12 ,  14  are illustrated, is mounted coaxially on the output shaft  16  of a motor  60  of a motor vehicle, for example an electric motor of the synchronous type of which the rotor  62  forms the output shaft  16 . 
     First and second fingers  18 ,  20  are mounted in rotation on the frame of the motor about one and the same spindle  22 . The end of the first finger  18  has substantially the same shapes and dimensions as the space between the teeth  12 ,  14  of the gearwheel  10  in order to engage in this space substantially without circumferential clearance, the sides  24 ,  26  of the end of the finger  18  then being in contact with the sides  28 ,  30  of the teeth  12 ,  14  (see  FIG. 5 ). 
     The end of the second finger  18  has, for its part, dimensions substantially smaller than those of the space between the teeth  12 ,  14  in order to be able to engage in said space including when the vehicle is running at a speed of approximately 5 km/h. 
     Each of the first and second fingers  18 ,  20  moreover comprises a surface forming a cam  32 ,  34  on which a button  36 , made to move in translation by means of a pressure spring  38 , slides to engage or disengage the fingers  18 ,  20  with or from the gearwheel  10 . 
     The surfaces forming a cam  32 ,  34  are designed so that the surface forming a cam  32  of the first finger comes into contact with the button  36  once the second finger  20  is engaged between the teeth  12 ,  14  (see  FIG. 2 ). 
     Advantageously, the first finger  20  comprises a circularly arcuate groove  40  in which a pin  42  of the second finger is housed, the groove  40  being arranged so that once the pin  42  is in abutment at the top in the groove  40 , the beginning of the surface forming a cam  32  of the first finger is in contact with the button  36  (see  FIG. 2 ). The pin  42  thus forces the engagement of the second finger before the engagement of the first finger between the teeth  12 ,  14  of the gearwheel  10  and obliges a simultaneous return of the two fingers  18 ,  20  when they disengage from the gearwheel  10 . 
     A return spring  44  is moreover provided and simultaneously separates the two fingers  18 ,  20  from the gearwheel  10  when the button  26  retracts in order to disengage the fingers  18 ,  20  from the gearwheel  10 . 
     Finally, means for controlling the rotation of the output shaft of the motor  16 , and therefore of the gearwheel  10 , are provided in order to set the latter rotating slowly, as will be explained in greater detail below. 
     The engagement of the fingers  18 ,  20  between the teeth  12 ,  14  is then achieved in the following manner. 
     From a position in which the fingers are disengaged from the gearwheel  10  ( FIG. 1 ), the button  36  is primed by compressing the pressure spring  38 . The button  38  then acts on the surface forming a cam  34  of the second finger  20  which then pivots toward the gearwheel  10 . 
     If the second finger  20  presses on the outer face of a tooth  12 ,  14 , a slight movement of the vehicle has the consequence of causing the gearwheel  10  to turn, thus allowing the second finger  20 , which has a large circumferential clearance, to engage between the successive teeth  12 ,  14  because of the continuous pressure exerted by the button  36 . 
     Once the engagement of the second finger  20  between two teeth  12 ,  14  of the gearwheel  10  is effective, a prealignment of the first finger  18  with the space formed between the teeth  12 ,  14  is thus achieved. The button  36  then presses on the surface forming a cam  32  of the first finger and the pin  42  is in abutment at the top in the groove  40 . The button  36  then continues its pressure on the surface forming a cam  32  ( FIG. 2 ). 
     In this position, the probability of seeing the first finger  18  coming into contact with the outer surface of a tooth is high ( FIGS. 3 and 4 ). A controlled search of the engagement of the first finger  18  is then applied by setting the output shaft  16  in slow rotation, preferably before a possible charging through a rectifier  66  of the array of accumulators  68  by powering the stator  64 . 
     For example, when the output shaft  16  of the motor  60  consists of the rotor  62  of an electric motor, a current controlling the slow rotation of the rotor  62  is then applied. The output shaft  16  is then aligned with the first finger  18  which then engages between the teeth  12 ,  14  because of the pressure of the button  36  ( FIG. 5 ). The engagement is advantageously detected by means of a stator current sensor for example. Specifically, once the first finger  18  is engaged, the latter presses on the sides of the teeth  12 ,  14  and forms a wedge promoting the absence of circumferential clearance. Via the continuous pressure of the button  36 , the rotor  62  is then completely locked, which results in a current peak that can be detected by means of said sensor. 
     As a variant, when the array of accumulators  68  is charged through the rectifier  66  by the powering of the stator  64  of the electric motor, a back-and-forth movement of the rotor  62  occurs. The preliminary prealignment by means of the second finger  20  then makes it possible to engage in a single back-and-forth movement of the first finger  18  between the teeth  12 ,  14 . 
     As a variant, when the torque applied to the rotor  62  is unidirectional, it is possible to design the second finger  20  so that once in abutment on a tooth, a rotation of the rotor  62  in the direction of the torque engages the first finger  18 , as illustrated for example in  FIG. 4 . 
     Although there has been described an application to the locking of a rotor forming an output shaft of an electric motor of a motor vehicle, the present invention advantageously finds application in the locking of an output shaft of a heat engine. In this type of application, a simple movement of the vehicle allows the first finger to be engaged when the second finger is engaged. 
     Another application of such a system can be directed toward any transmission shaft using epicyclic gear trains to produce discrete (automatic gearboxes) or infinitely variable reduction ratios. 
     The present invention may also be improved by the addition of an elastomer ring  23  between the spindle  22  and the first finger  18  designed to filter possible vibrations generated by the reactions on the rotor  62 .