Electromechanical actuator cylinder

The electromechanical actuator cylinder provides a casing, an actuation rod mounted to be movable longitudinally relative to the casing, an electric motor provided with a stator and with a rotating rotor shaft, and a mechanism for converting a rotational movement of the rotor shaft into a linear movement in translation of the actuation rod. The actuator cylinder includes at least one roller bearing for guiding the rotor shaft in rotation relative to the casing and providing at least one row of rolling elements. An inner raceway for the row of rolling elements of the bearing is formed directly on the rotor shaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to French patent application no. 1559018 filed on Sep. 24, 2015, the contents of which are fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of electromechanical actuators or actuator cylinders.

BACKGROUND OF THE INVENTION

More particularly, the invention relates to the field of compact electromechanical actuator cylinders used to provide high performance with a reduced overall size.

An electromechanical actuator cylinder generally provides a casing, an actuation rod mounted so as to be movable longitudinally relative to the casing, an electric motor, and a mechanism, for example of the ball screw type, for converting the rotational movement of the rotor of the motor into a linear movement in translation of the actuation rod.

In order to guide in rotation and support the rotor of the electric motor, a pair of roller bearings mounted axially in abutment against one another is generally mounted at the front of the casing.

This axial stacking of bearings is usually mounted on one side against a radial stop formed on the shaft of the rotor and is axially prestressed by a self-locking clamping nut arranged on the other side.

This solution has the disadvantages in particular of having a considerable axial bulk and of requiring a large number of operations to provide the mounting and fixing of the roller bearings inside the casing of the actuator cylinder.

The present invention aims to overcome these disadvantages.

BRIEF SUMMARY OF THE INVENTION

More particularly, the present invention aims to provide an electromechanical actuator cylinder in which, with the same axial bulk, the loading capacity is increased.

In one embodiment an electromechanical actuator cylinder provides a casing, an actuation rod mounted so as to be movable longitudinally relative to the casing, an electric motor provided with a stator and a rotating rotor shaft, and a mechanism for converting a rotational movement of the rotor shaft into a linear movement in translation of the actuation rod.

The actuator cylinder also provides at least one roller bearing for guiding the rotor shaft in rotation and comprising at least one row of rolling elements. An inner raceway for the row of rolling elements is formed directly on the rotor shaft.

The rolling elements of the bearing roll directly over the rotor shaft of the electric motor supporting the magnets. This bearing is therefore devoid of an inner ring disposed radially between the rolling elements and the rotor shaft.

Thus, in contrast to the prior art, it is not necessary to provide specific means to assure the axial blocking of this bearing or these bearings on the rotor shaft. It is therefore possible to mount an electric motor of greater length within the casing. This makes it possible to increase the loading capacity of the actuator cylinder whilst maintaining the same overall axial bulk. By contrast, for the same loading capacity, it is possible to reduce the overall axial bulk of the actuator cylinder.

The inner raceway is preferably formed on an outer surface of the rotor shaft.

The roller bearing can provide an outer ring mounted in a bore in the casing and provided with an outer raceway for the row of rolling elements of the bearing.

In a preferred embodiment, the actuator cylinder provides at least two roller bearings mounted axially in contact with one another and each comprising a row of rolling elements, an inner raceway for each of the rows of rolling elements being formed directly on the rotor shaft. The rows of rolling elements of the bearings are arranged in an X shape.

In one embodiment the bearing or bearings can be of the angular contact ball bearing type.

The conversion mechanism is preferably a roller screw or ball screw mechanism.

In a variant, the mechanism provides a screw connected to the actuation rod and provided with an external thread, and a plurality of longitudinal rollers engaged with the external thread of the screw and an internal thread of the rotor shaft.

In another variant the roller screw mechanism provides a screw provided with an external thread, a nut disposed around the screw, comprising an internal thread and connected to the actuation rod, and a plurality of longitudinal rollers engaged with the external and internal threads of the screw and the nut. Alternatively, with replacement of the rollers, balls can be engaged with the external and internal threads of the screw and the nut.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1the electromechanical actuator cylinder, referenced10as a whole, extends along a longitudinal axis X-X′, which is intended to be horizontal. The actuator cylinder10provides a casing12, an actuation rod14movable axially and coaxially to the axis X-X′, and also an electric motor16and a roller screw mechanism18disposed inside the casing12. The mechanism18is disposed radially between the electric motor16and the actuation rod14.

The mechanism18allows the conversion of a rotational movement of the electric motor16and a linear movement in translation of the actuation rod14along the axis X-X′. The electric motor16and the mechanism18are housed entirely within the casing12. The actuation rod14extends through the casing12and protrudes axially to the outside.

In the illustrated exemplary embodiment the casing12provides a tubular main body12aand front12band rear12cflanges, each mounted at one end of the body. The actuation rod14extends through the front flange12b.

The electric motor16provides a stator20fixed on the casing12and a rotor22. The stator20is fixed on a bore28in the casing. The rotor22is provided with a tubular rotor shaft24and a plurality of permanent magnets26supported by the shaft. The rotor shaft24extends axially on either side of the stator20. The electric motor16can be of the brushless type.

In order to guide in rotation and support the rotor shaft24, the actuator cylinder10also provides two front roller bearings30,32and one rear roller bearing34. As will be described in greater detail hereinafter, the bearings30,32are each designed so as to limit the overall axial bulk of the actuator cylinder10.

The rear roller bearing34is disposed radially between the rotor shaft24and a rear support36fixed in the bore28in the casing. The roller bearing34is mounted on an outer surface24aof the rotor shaft and in a rear bore in the support36. In addition, sensor and coding means are disposed inside the rear flange12cof the casing in order to know the angular position of the rotor22of the electric motor.

In the illustrated exemplary embodiment the roller screw mechanism18is of the inverted planetary roller screw type. The mechanism18provides a screw40, which is coaxial to the actuation rod14, fixed to the rod and provided with an external thread (not referenced), and a plurality of longitudinal rollers42disposed radially between the screw and the rotor shaft24. The rotor shaft24has a tubular form. The rotor shaft24, coaxial to the screw40, provides an internal thread (not referenced) of which the inner diameter is greater than the outer diameter of the thread of the screw40.

The rollers42are identical to one another and are distributed uniformly around the screw40. Each roller42extends along an axis parallel to the axis of the screw and provides an external thread (not referenced) engaged with the external thread of the screw40and the internal thread of the rotor shaft24. As is known per se, each roller42provides, at each end, an outer toothing engaged with a synchronization toothing of the screw40, and a journal extending axially to the outside from the toothing and housed in a recess in one of the spacer rings44,46mounted on the screw.

The actuation rod14is connected to the screw40of the roller screw mechanism. The rotation of the rotor shaft24of the electric motor is converted into a translation of the screw40and of the actuation rod14along the axis X-X′.

As indicated before, the roller bearings30,32assure the guidance in rotation of the rotor shaft24of the electric motor. Each bearing30,32provides an outer ring30a,32aand a plurality of rolling elements30b,32b, provided here in the form of balls, which are disposed radially between the inner ring and the rotor shaft24. Each bearing30,32also provides a cage (not shown) for maintaining regular circumferential spacing of the rolling elements.

The outer ring30a,32aof each bearing is fixed in the bore28in the casing. An outer raceway50,52is formed on the bore of each ring and has, in cross-section, a concave inner profile adapted to the rolling elements30b,32b, the raceway being directed radially inwardly.

An inner raceway54,56is formed directly on the outer surface24aof the rotor shaft for the row of rolling elements30b,32bof each bearing30,32. The outer surface24aof the rotor shaft delimits the pathways for the rolling elements. Each raceway54,56has, in cross-section, a concave inner profile adapted to the rolling elements30b,32b, the raceway being directed radially outwardly.

The raceways54,56are formed on a radial protrusion58of the rotor shaft24. The protrusion58extends radially outwardly from the outer surface24aof the rotor shaft and is situated axially between the two rows of rolling elements30b,32b. The protrusion58is formed integrally with the rotor shaft24, i.e. in one piece. In the illustrated exemplary embodiment the rolling elements30b,32bare disposed in an X shape.

The rolling elements30b,32bare in direct contact with the outer surface24aof the rotor shaft. Each bearing30,32is therefore devoid of an inner ring disposed radially between the rotor shaft24and the rolling elements30b,32b.

Thus, by contrast with the prior art, it is not necessary to provide specific means in order to assure the axial stop of the bearings30,32on the rotor shaft24. It is therefore no longer obligatory to provide an axial space on the rotor shaft24dedicated specifically to the assembly of such means. Thus, it is now possible to mount an electric motor16of greater length and to therefore increase the loading capacity of the actuator cylinder10, whilst maintaining the same overall axial bulk.

The exemplary embodiment illustrated inFIG. 2, in which identical elements carry the same references, differs from the previous example primarily in that the mechanism18is of the planetary roller screw type. The mechanism18provides a nut60, which is mounted inside the tubular rotor shaft24of the electric motor and on which the actuation rod14is fixed. In this example the actuation rod14is therefore connected to the nut60.

The nut60is mounted coaxially to the screw40and provides an internal thread (not referenced) of which the inner diameter is greater than the outer diameter of the thread of the screw. The rollers42are disposed here radially between the nut60and the screw40and are engaged with the internal and external threads of the nut and of the screw.

The screw40of the mechanism is coupled here to the rotor shaft24of the electric motor. The screw40extends inside the tubular actuation rod14. In order to assure the guidance in rotation of the screw40, the actuator cylinder10provides a housing62provided with a roller bearing64and disposed radially between the screw and the bore in the actuation rod14.

In this exemplary embodiment the rotation of the screw40of the mechanism18, which is connected to the rotor shaft24, is converted into a translation of the nut60and of the actuation rod14along the axis X-X′.

The previous exemplary embodiments relate to an actuator cylinder provided with a mechanism18of the roller screw type. Alternatively, the actuator cylinder10may provide a ball screw mechanism as is illustrated inFIG. 3, in which identical elements carry the same references.

Compared with the previously described exemplary embodiment, the actuator cylinder10differs solely in that the mechanism18provides a plurality of balls66engaged within the external and internal threads of the screw40and of the nut60which are provided specifically for this purpose. Means for recirculating the balls (not shown) are also provided on the nut60.

The invention has been illustrated on the basis of an actuator cylinder comprising bearings30,32of the angular contact ball bearing type. Alternatively, it could be possible to provide other types of rolling elements, for example rollers.

In the illustrated exemplary embodiment, the rolling elements are arranged in an X shape. Alternatively, it could be possible to provide an arrangement in an O shape. However, for reasons of assembly, the inner raceway of one of the two bearings is formed directly on the rotor shaft in this case, the other bearing being provided with its own inner ring.

The invention has been presented on the basis of an actuator cylinder comprising bearings mounted axially in abutment against one another and each comprising a sole row of rolling elements. In a variant, it could be possible for examples to provide a sole bearing comprising at least two rows of rolling elements, or even a greater number of bearings stacked axially and comprising one or more rows of rolling elements.