Cutoff mechanism for an optical module and an optical module comprising such a mechanism

The invention relates to a cutoff mechanism (5) for an optical module comprising a housing (100) and a driving motor (30) provided with an armature resistance and being arranged to cause the movement of a light beam cutoff shield (10), said housing (100) being made of a plastic material, characterized in that said armature resistance is comprised between 25 and 120 Ohms.The invention also relates to an optical module comprising such cutoff mechanism (5).

The invention relates to a cutoff mechanism for an optical module and an optical module comprising such a cutoff mechanism. Said optical module is particularly intended for being inserted in an automobile projector, especially in an elliptical projector, being arranged in the front of the automobile vehicle.

Such optical modules possess a light source that projects light on a reflector. Light is then reflected on a lens so as to be reverted and returned back outside the vehicle under the form of a light beam. The optical modules also comprise a cutoff mechanism enabling to block out or not a part of the beam.

It is known to use cutoff mechanisms comprising a rotating cutoff shield being electrically operated to be moved, to order, from a first angular position, in which it blocks out a part of the light beam in order to limit the range of the projector to the low beam so as not to dazzle the other drivers circulating in the opposite direction, to a second angular position, in which it does not block out the light beam, the range of the projector then corresponding to the high beam.

There are also so-called multifunction projectors, in which the cutoff shield can assume more than two angular positions so as to block out selectively the light beam.

The shield is electrically operated by an actuator comprising an electric motor. The electric motor comprises a stator and a rotor provided with a set of coils, also called armature windings or armature. The armature presents a conductive wire being wound and thus a resistance, so-called armature resistance, corresponding to the resistance of the conductive wire.

The motor is mounted on a plastic housing of the cutoff mechanism. Due to the reduced space being available within the optical module to position the motor therein, it is known to use motors of small sizes having a reduced volume available for the coils and thus for the conductive wire. The conductive wire length is thus limited. Indeed, the motor torque being proportional to the section of the conductive wire, the section cannot be reduced beyond a threshold enabling the motor to present a sufficient torque to operate the cutoff shield. Now, the resistance of the conductive wire, i.e. the armature resistance being proportional to the length of the conductive wire, such “small” motor thus presents a weak armature resistance, i.e. lower than 25 Ohms.

Consequently, for a given voltage, the current intensity passing through the motor is significant and the latter is thus caused to dissipate much power, which leads to a significant motor self-heating. Such self-heating phenomenon is in particular defined by a so-called self-heating temperature.

Moreover, heat dissipated by the light source and the sun rays entering the optical module through the lens causes the internal environment of the optical module and thus of the motor to be heated. Such heating phenomenon is in particular defined by a so-called environment temperature.

The self-heating of the motor being significant, the temperature reached by the motor, i.e. the sum of the environment and self-heating temperatures, is also significant, which has some chance to damage the plastic housing, on which the motor is mounted.

To remedy such disadvantage, it is known to arrange an electronic board with the motor in the optical module. The electronic board reduces indeed the intensity of the current crossing the motor and thus the power the motor has to dissipate. However, such arrangement is expensive and cumbersome.

Another known solution consists in selecting the housing in metal, in virtue of its resistance to high temperatures, but such material has the disadvantage to be heavy and expensive.

The invention thus aims at improving the situation.

Indeed, it proposes a cutoff mechanism for an optical module comprising a housing and a driving motor provided with an armature resistance and being arranged to cause the movement of a light beam cutoff shield, said housing being made of a plastic material, characterized in that said armature resistance is comprised between 25 and 120 Ohms.

Thus, thanks to the increase of the motor armature resistance beyond 25 Ohms, it is proposed to reduce the intensity crossing the conductive wire and thus to reduce the power the motor has to dissipate. Thus, it is not necessary any more to arrange an electronic board with the motor. The self-heating temperature of the motor is then comprised between 15 and 90° C., more preferably between 30 and 50° C. In such a way, the motor temperature stays lower than 220° C. when the light source of the optical module operates. The motor support housing can then be selected in a plastic material being resistant to such temperatures, for example PES (Polyethylene Sulfide), PET (Polyethylene Terephthalate) or PBT (Polybutylene Terephthalate).

The increase of the conductive wire length is obtained in particular thanks to an increase of the motor size. Such size being limited by the maximum space occupied by the cutoff mechanism, the section of the conductive wire is in particular reduced so as to increase the length thereof. The result of this is a decrease of the motor torque. Beyond an armature resistance of 120 Ohms, the motor then presents a torque being insufficient to drive the cutoff shield and/or a size being incompatible with the space available within the optical module for the cutoff mechanism.

In an advantageous embodiment of the invention, said armature resistance is comprised between 40 and 90 Ohms. In a particularly advantageous way, said armature resistance is substantially equal to 55 Ohms. The term “substantially” means a tolerance of more or less fifteen percent around the target value.

According to an advantageous embodiment of the invention, said motor comprises at least three coils. The motor comprises in particular three coils. The presence of at least three coils in the motor enables to provide it with a more constant torque, for example, than a motor having two coils. The presence of at least three coils enables to drive a motor shaft connected to a pinion over more than half a turn, i.e. over more than 180°, contrary to a motor only having two coils. The presence of tree coils enables to drive the motor shaft over more than half a turn even starting from a state in which the motor shaft does not turn yet. Thanks to the presence of three coils, the rotation movement transmitted to the shield by the pinion can be geared down while providing a sufficient rotation of the shield between its first and its second angular positions, i.e. a rotation of the shield being higher than 60°. Due to the gearing down, the torque being necessary to drive the shield is less significant, which enables to further reduce the section of the conductive wire and thus to increase the armature resistance, in particular until 120 Ohms.

According to an embodiment of the invention, said mechanism comprises said cutoff shield.

In an interesting embodiment of the invention, said pinion of the motor drives said cutoff shield through a gear, the rotational angle of the shield being lower than the rotational angle of said pinion. The gear is for example an inner tooth gear. The inner tooth gear enables to increase the space being available for the motor within the cutoff mechanism, in particular with respect to a solution presenting an outer tooth gear. It is then possible to select a bigger motor having a more significant armature resistance without increasing the general space occupied by the optical module.

Advantageously, the gearing ratio between the pinion of the motor and the gear is comprised between 1/5 and 1/2. It is in particular equal to 1/3.

In an embodiment of the invention, said shield mainly extends in a first plan, said shield having a tilted portion with respect to such first plan in a rotation according to an axis parallel with a rotational axis of the shield. The tilted portion enables the shield to be driven with no contact with the motor. Thus, it enables to increase the available space for the motor within the cutoff mechanism. It is then possible to select a bigger motor having a more significant armature resistance without increasing the general space occupied by the optical module.

According to an exemplary embodiment of the invention, said shield is arranged to make a rotation of at least 75° between a vertical position and a tilted position.

In an embodiment of the invention, the motor has a length higher than 26 mm. Advantageously, the motor has a diameter higher than 21 mm. The increase in the volume of the motor, i.e. of its length and/or of its diameter makes it possible in particular to increase its armature resistance.

The invention also relates to an optical module comprising a cutoff mechanism such as above described.

FIG. 1enables to illustrate an optical module1according to the invention. In such optical module, there is a light source2generating a light beam reflected by an optical reflector3. The light beam is then projected on a lens4that inverts it and returns it back on the road located in the front of the vehicle, in which the optical module is positioned. The lens4is arranged on a lens carrier7. The light source is here a halogen lamp.

A cutoff mechanism5is arranged between the reflector3and the lens4. Such cutoff mechanism5enables to block out more or less the light beam in reply to an order of the vehicle's user or to an automatic order, so as to propose different lighting modes for the road. The cutoff mechanism5comprises a driving motor, in particular a direct current motor.

As illustrated onFIG. 4, the motor30comprises a stator101also called inductor and a rotor102. When the motor30operates, the stator101generates a magnetic field that drives into rotation the rotor102around a longitudinal axis A. The rotation movement is then transmitted to a motor pinion. The motor30comprises for instance at least three coils103. It is question here of the coils103of the rotor102, otherwise called armature windings or armature. Such coils103comprise a conductive wire104, in particular in copper, and presenting a resistance, the so-called armature resistance. The motor30is thus provided with an armature resistance.

Such cutoff mechanism5will now be described more in details thanks toFIGS. 2 and 3. Further on in the description, the terms front, rear, right, left, upper and lower are defined with respect to the forward direction of the vehicle, i.e. with respect to the arrow direction referenced80onFIG. 2.

The motor30is arranged so as to cause the movement of a cutoff shield10for the light beam. The motor30enables the shield10to be positioned according to various positions, here according to two positions, so as to block out more or less the light beam. For this, the motor30comprises the driving pinion31. Such pinion31is connected to an inner tooth gear14that drives the shield10in movement and particularly in rotation, as explained further on. According to the invention, the armature resistance is comprised between 25 and 120 Ohms, in particular between 40 and 90 Ohms and, more particularly, substantially equal to 55 Ohms. Such armature resistances are obtained in particular thanks to a conductive wire of a section being substantially equal to 0.09 mm. In the case when the motor comprises three coils, each of them comprises for example substantially 700 winding turns of the conductive wire.

The motor operation voltage is for instance comprised between 9 and 16 V. The power to be dissipated by the motor is particularly comprised between 1 and 4 Watts. The self-heating temperature of the motor is then limited to 90° C. and, in particular, to 50° C.

The motor30comprises an upper side32, a rear side33, a lower side34, a front side35, a right side36and a left side37. The upper side32and the lower side34, being opposite to each other, have curved shapes. They define a cylinder part, the axis of which is located in the centre of the motor30, i.e. here in the centre of the pinion31. The motor30then takes the shape of a cylinder being cut at the level of the front35and rear33sides.

On the right part of the motor30a connection area39is located, being arranged so as to connect the motor30with a power source, for example, a current source (not shown). Thus, the connection area39defines the right side36of the motor30and a part of the upper32, rear33, lower34and front35sides located on the right part of the motor30.

The motor30presents a length of less than 35 mm, in particular substantially equal to 30.5 mm. It presents a diameter of less than 30 mm, for example substantially equal to 24.2 mm. Beyond one and/or the other of such dimensions, the motor presents the disadvantage to be heavy and/or expensive. With the objective of reaching an armature resistance higher than 25 Ohms, the motor has a length higher than 26 mm and/or a diameter higher than 21 mm. The length of the motor is measured along the axis of the motor passing by the pinion31but does not contain the length of the pinion. The length of the motor is then the distance between its left side37and its right side36.

The pinion31is located at the level of the left side37of the motor30. It is mounted on a driving shaft38projecting with respect to the left side37of the motor30and located substantially in the middle of the left side37of the motor30.

The cutoff mechanism5comprises a housing100, in particular in a plastic material. Such housing100comprises a frame50of a substantially rectangular shape so that it presents four interconnected branches, so-called an upper branch51, a left branch52, a lower branch53and a right branch54. The housing100also comprises a motor carrier40.

The motor30is mounted on the housing100, in particular at the level of the motor carrier40. Such motor carrier40is located in the centre and towards the rear side of the frame50, i.e. between the motor and the light source, once the cutoff mechanism5is mounted in the optical module.

The motor carrier40comprises a lower wall41located opposite the lower side34of the motor30, a rear wall or bottom42located opposite the rear side33of the motor30, a rear part of the upper side32and a rear part of the lower side34so that the motor30is in contact with the rear wall42. The motor carrier40also comprises a right wall43with a U-shape, a central branch of the U being arranged backwards vertically and the two side branches of the U being substantially parallel between them, horizontal and oriented forwardly. The right wall43of the motor carrier40thus defines a notch inside which a boss (non visible) of the connection area39, through which the motor is connected with the current source, is inserted and makes integrally part of the motor carrier40. In the same way, the motor carrier40comprises a left wall44in a U-shape, a central branch of the U being arranged rearwards vertically and the two side branches of the U being substantially parallel between them, horizontal and oriented forwardly. The right wall43of the motor carrier40thus defines a notch inside which the shaft38comprising the pinion31can be inserted, the pinion31projecting then beyond the carrier40of the motor30towards the left.

The cutoff mechanism5also comprises a thermal screen60meeting an external side of the rear wall42of the carrier40of the motor30, i.e. a side oriented rearwards. The heat screen60is thus located between the motor carrier40and the light source. It is made of a metal so that it protects the motor carrier40and the motor30from heat dissipated by the light source.

The cutoff shield10is part of the cutoff mechanism5. It is arranged so as to block out more or less the light beam, i.e. to cut more or less the light beam. The shield mainly extends along a first plan. The shield10can be positioned here according two positions, a first position in which it blocks out partially the light beam and corresponding to the low beam, and a second position in which it does not block out the light beam and corresponding to the high beam. In the first position thereof, the cutoff shield10extends according to a substantially vertical plan, whereas, in the second position thereof, it extends in a substantially horizontal plan, for example being substantially tilted of 75° with respect to the vertical. It is here a bi-functional cutoff mechanism5.

The cutoff shield10is positioned opposite the light source. It is mounted on a shield carrier11comprising a first part12provided with the inner tooth gear14, located at the level of a first longitudinal end of the shield10, and a second part13provided with a return spring15tending to bring the shield back in its first position, i.e. in its substantially vertical position, the second part13being located at the level of a second longitudinal end of the shield10. The cutoff shield10is made of steel so as to resist the strong heats emitted by the light source, whereas the first part12and the second part13of the shield carrier11are in plastics, because they are off-centre with respect to the light source and thus less exposed than the shield10to the heat emitted by the light source. The spring15of the second part13is however in metal. The first longitudinal end is located on the left part of the shield10, whereas the second longitudinal end is located on the right part of the shield10.

The second part13comprises a clip21pinching the shield through the bottom and on either side of the latter, i.e. it pinches it on a front side and on a rear side of the shield10so as to support it. The clip21of the second part13originates at the level of an arm22, that the second part13comprises, extending parallel to a longitudinal extension axis of the shield10. At the level of a distal end of the arm22located on the right part there is an excrescence23extending beyond the shield10towards the right. The spring15is here wound around the arm22of the second part13and exerts a return force on the clip21of the second part13.

The first part12of the shield carrier11comprises a central body16of a substantially parallelepiped shape from which a clip17originates to pinch the shield10from the bottom so as to support it. The clip17of the first part12is similar to the clip of the second part13, i.e. it pinches the shield10on the front side and on the rear side of the latter. The first part12of the carrier11also comprises an excrescence18projecting with respect to the central body16, towards the left part and extending beyond the shield10towards the left part.

From the central body16two arms also originate, so-called first and second arms19,20. The first arm19extends in a common plan with the shield10, perpendicular to the longitudinal extension direction of the shield10. The second arm extends according to a direction perpendicular to the plan in which the shield10extends, i.e. perpendicular to the first arm19. The inner tooth gear14connects the first arm19with the second arm20and has a substantially circular shape so that it forms a quadrant between the first and the second arms19,20.

The gearing ratio between the pinion31of the motor30and the gear14is here equal to 1/3. The presence of at least three coils enables to drive the pinion on more than 180° around its axis of rotation, so as to drive the cutoff shield on more than 60° around its axis of rotation when the gear ratio is 1/3. With a rotation of 360°, the pinion will be able to drive the cutoff shield in a rotation of 120°. The gear ratio could of course be different, according to the motor torque and/or the desired rotation of the shield. It will be comprised in particular between 1/5 and 1/2.

The fact that the gear14is provided with inner teeth enables the motor30to move back with respect to the frame50and thus to reduce the space occupied by the mechanism cutoff5while keeping a gearing ratio of 1/3 necessary for the rotation driving of the shield10.

The shield carrier11is mounted on the frame50. On the right branch54of the frame50a groove is arranged, having a flared shape towards the front part and presenting an opening56at the level of a rear end, arranged to receive the excrescence23of the second part13of the carrier. The excrescence23of the second part of the shield carrier11is thus inserted into the groove55from the front to the rear up to the moment where it enters the opening56. On a same way, on the left branch52of the frame50there is a groove57of a similar shape as the groove of the right branch54, i.e. with a flared shape towards the front and having an opening (non visible) at the level of a rear end arranged to receive the excrescence18of the first part12of the carrier.

Moreover, the frame50comprises borings being distributed on the branches51,52,53,54thereof and arranged to mount the cutoff mechanism5in the optical module.

It should be noticed here that the shield10comprises a rotation axis defined by the excrescences18,23. Such rotation axis is offset with respect to the rotation axis of the motor30, i.e. the rotation axis of the pinion31. The rotation axis of the shield30is located in particular above the motor rotation axis along a vertical axis.

FIGS. 4 and 5allow a particularly advantageous embodiment of the invention to be illustrated, according to which the shield presents a tilted portion71.FIG. 4illustrates the shield10in its first position, i.e. in its vertical position. The vertical position corresponds to the position in which the cutoff shield blocks out the light beam so as to limit the range of the projector to the low beam.FIG. 5represents the shield10in its second position, i.e. in its tilted position of substantially 75° with respect to the vertical. The tilted position corresponds to the position in which it does not block out or almost not the light beam, the range of the projector then corresponding to the high beam.

The tilted portion71is located on a central area of the shield10. The central area is here located above the motor30. The tilted portion71occupies a lower band of the shield10, i.e. a band being close to the motor30. It is tilted towards the back of the cutoff mechanism. It is tilted according to an axis of rotation parallel with the axis of rotation of the shield. The shield10also comprises a plane wall72extending in the first plan. The plane wall72is here located above the tilted wall71. Parts of the plane wall72, so-called first and second tabs73extend on either part of the tilted wall71, i.e. on each longitudinal end side of the tilted wall71. Fins74connect the longitudinal ends of the tilted wall71with the tabs73. The tabs73are located on either part of the motor30, i.e. beyond the left and right sides of the motor30. When the shield10modifies its position, the tabs73thus do not come into contact with the motor30.

The tilted portion71of the shield10allows, when the shield is in its vertical position, the light beam to be sufficiently blocked out so as to enable the projector to light the road with low beam. It enables the shield to carry out a rotation movement of substantially 75° around its rotation axis without coming into contact with the motor. Such rotation allows the shield10to reach its second position and to let the light beam free so as to allow the projector to light the road with high beam. This slope thus makes it possible to release some space for the motor, whatever the position of the shield.

It is mainly thanks to the inner tooth gearing and/or to the shape of the shield, i.e. thanks to the tilted portion, that it is possible to arrange a motor of greater size within the housing without modifying the space occupied by the optical module.