Abstract:
The invention relates to a cam actuator ( 2 ) for actuating at least one valve ( 3 ) slidably mounted in a mounting ( 1 ), the device comprising a tappet ( 8 ) which is to be mounted on a free end of a stem ( 3   a ) of the valve and which is mobile relative to the mounting ( 1 ); and a resilient return means ( 9 ) for the tappet, which to urge the tappet ( 8 ) against the cam ( 2 ), characterised in that the device comprises an electromagnetic locking means including an electromagnetic actuator ( 22 ) having a coil ( 24 ), preferably outside the tappet ( 8 ), and at least one pin ( 12 ) subjected to the magnetic field of the actuator ( 22 ), such that supplying power to the coil ( 24 ) causes the selective movement of the pin ( 12 ) between a locked position, in which the tappet ( 8 ) is translatably linked to the valve ( 3 ), and an unlocked position, in which the tappet ( 8 ) freely slides on the stem ( 3   a ) of the valve.

Description:
[0001]    The present invention concerns the field of controlling internal combustion engines, in particular four-stroke engines, and, to be more precise, disconnection of the inlet valves of an internal combustion engine, for example a gasoline engine. 
       BACKGROUND OF THE INVENTION 
       [0002]    An engine comprises an engine block delimiting chambers known as combustion cylinders having one end closed by a cylinder head and an opposite end closed by a piston received slidably in the chamber. Each combustion chamber is associated with air and fuel inlet means and with burned gas exhaust means. The efficiency of internal combustion engines depends notably on the amount of air filling the combustion chambers. 
         [0003]    To improve the efficiency of internal combustion engines it is preferable to keep the engine operating within regions in which the filling rate is maximum. In the case of a low load on the engine, a control system of the internal combustion engine allows to pass only the quantity of air necessary to meet the engine load. The consequence of this is to cause hunting of the engine and to degrade the efficiency of the engine. To extend the optimum operating range, notably when the engine is operating at half-load, it is known to deactivate half of the combustion chambers so as to increase the unit load of the combustion chambers remaining active. 
         [0004]    The combustion chambers are deactivated by neutralizing the inlet and exhaust valves of said chambers. 
         [0005]    It is known to use for this purpose a device for actuating at least one valve by means of a cam, as described in the document U.S. Pat. No. 5,878,705. Such a device includes a valve sliding in the cylinder head and maintained in a stable closed position by a valve spring. The valve is used to block an inlet hole feeding air to the combustion chamber to which the inlet hole leads or an exhaust hole through which the burned gases resulting from combustion escape from the combustion chamber. The valve stem is in contact with a hydraulic thrust valve inserted in a sleeve. A tappet is slidably mounted on the sleeve. A camshaft actuates the valve by acting either on the sleeve or on the tappet. Selection is effected by means of a pin that can be moved by an actuator fed with a hydraulic fluid between a connected position in which the sleeve is coupled to the tappet and a disconnected position in which the tappet slides freely on the sleeve. The pin actuator is fed by a hydraulic circuit the pressure in which is produced by a hydraulic pump actuated by the engine. 
         [0006]    It is difficult to use this device, however, because it necessitates the use of hydraulic circuits and a camshaft with multiple cams. Apart from the complexity of developing such a device, the response times of hydraulic actuators are too long for it to be possible to establish efficacious engine management strategies. The response time of a hydraulic actuator depends on the feed pressure in the hydraulic circuit or on temperature and therefore directly on the engine operating conditions. 
       OBJECT OF THE INVENTION 
       [0007]    The object of the invention is to provide a device for actuating at least one valve by means of a cam and enabling at least some of the above drawbacks to be remedied. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    To achieve the above object, the invention proposes a device for actuating by means of a cam at least one valve slidably mounted in a support, the device including a tappet designed to be mounted at a free end of a stem of the valve and mobile relative to the support, and return spring means for the tappet adapted to cause the tappet to bear against the cam, characterized in that the device includes electromagnetic locking means adapted to be selectively actuated between a locked position in which the tappet is coupled to the valve to move in translation therewith and an unlocked position in which the tappet slides freely on the valve stem. 
         [0009]    The actuating device is notably actuated by the cam directly, i.e. by contact of the cam with the actuating device with no intermediary element. The use of electromagnetic locking means enables the response times to be reduced and the hydraulic circuit to be dispensed with. This facilitates integration of the actuating device into a support such as a cylinder head. 
         [0010]    The tappet advantageously includes an opening designed to receive slidably the valve, the locking means including at least one pin adapted to slide perpendicularly to the valve between an active position in which the pin projects into the opening to constrain the tappet to move in translation with the valve and a deactivation position in which the pin is retracted from the opening to allow the tappet to slide freely on the valve stem, the locking means including an electromagnetic actuator for selectively moving the pin between the activation position and the deactivation position. 
         [0011]    The pin is therefore actuated remotely, i.e. without mechanical contact between the pin that constitutes the active part of the tappet and the electromagnetic actuator. 
         [0012]    For example, the electromagnetic actuator generates a field only when the locking means are no longer actuated. This is notably the case on the back of the cam. 
         [0013]    The electromagnetic actuator is preferably external to the tappet. The electromagnetic actuator therefore does not move in translation with the tappet. There is therefore no mobile connection for energizing an electromagnetic actuator mounted in the tappet. A mobile connection is typically fragile and there is the risk of it breaking over a large number of cycles. The electromagnetic actuator is notably stationary and is designed in particular to be positioned in the support. 
         [0014]    The pin is preferably totally integrated into the tappet. The pin therefore does not come into contact with the support. The actuating device is therefore subject to little friction on actuation of the valve. 
         [0015]    The electromagnetic actuator advantageously includes a magnetic coil perpendicular to the valve so that the axial component of the magnetic field generated moves the pin. 
         [0016]    In particular, said magnetic coil has a coil axis substantially parallel to the direction of movement of the pin. 
         [0017]    The coil is notably integrated into the support and is stationary relative thereto. 
         [0018]    In the activation position, the pin advantageously bears on one end of the valve stem in order to lock the tappet to the valve. 
         [0019]    The locking means advantageously include two diametrally opposite pins sliding in opposite directions to lock or unlock the tappet. 
         [0020]    The electromagnetic actuator advantageously includes a magnetic coil parallel to the valve so that the radial component of the magnetic field generated moves the pin. 
         [0021]    In particular, said magnetic coil has a coil axis substantially perpendicular to the direction of movement of the pin. 
         [0022]    Each pin advantageously includes a flat designed to bear on the end of the valve stem. 
         [0023]    The device advantageously includes a plurality of pins. 
         [0024]    Each pin advantageously has a respective electromagnetic actuator. 
         [0025]    The invention also concerns a device for actuating by means of a cam at least one valve slidably mounted in a support, the device including a tappet designed to be mounted at a free end of a stem of the valve and mobile relative to the support, and return spring means for the tappet adapted to cause the tappet to bear against the cam, characterized in that the device includes electromagnetic locking means including an electromagnetic actuator including a coil, preferably external to the tappet, and at least one pin subjected to the magnetic field of the actuator so that energization of the coil drives selective movement of the pin between a locked position in which the tappet is coupled to the valve so as to move in translation therewith and an unlocked position in which the tappet slides freely on the valve stem. 
         [0026]    This device may have one or more of the features described above. 
         [0027]    In particular, in one embodiment the tappet includes an opening designed to receive the sliding valve and the pin is configured to slide perpendicularly to the valve between an activation position in which the pin projects into the opening to block movement of the tappet in translation on the valve and a deactivation position in which the pin is retracted from the opening to allow the tappet to slide freely on the valve stem, the electromagnetic actuator being configured to move the pin selectively between the activation position and the deactivation position. 
         [0028]    Other features and advantages of the invention will emerge from a reading of the following description of particular nonlimiting embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Reference will be made to the appended drawings provided by way of nonlimiting example and in which: 
           [0030]      FIG. 1  is a diagrammatic partial view of a valve actuating device in accordance with a first embodiment of the invention in a connected mode; 
           [0031]      FIGS. 2 and 3  are diagrammatic views of the complete device shown in  FIG. 1  respectively in the connected mode and in a disconnected mode; 
           [0032]      FIG. 4  is a partial diagrammatic view of a valve actuating device in accordance with a second embodiment of the invention in the disconnected mode; 
           [0033]      FIGS. 5 and 6  are diagrammatic views of the complete device shown in  FIG. 4  respectively in the connected mode and in the disconnected mode. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]      FIG. 1  shows a detail of a device in accordance with a first embodiment of the invention used on an internal combustion engine the structure of which is known in itself and will not be described in more detail here. The device is mounted on a cylinder head  1  forming a support. The device is adapted selectively to transmit the movement of a cam  2  fastened to a rotating shaft to a valve  3  mounted in a well in the cylinder head  1  to slide along an axis X (there can be seen in  FIG. 1  only an end  4  of a stem  3   a  of the valve  3 ). The valve  3  notably enables opening and closing of a combustion chamber or cylinder (not represented). The movement of the cam  2  is transmitted directly. The complete device is more specifically shown in  FIGS. 2 and 3 , which will be described later. 
         [0035]    The end  4  of the stem  3   a  of the valve includes a spring cup  5  fixed to the stem  3   a  of the valve by two fixing half-cones  6  in a manner that is known in itself. The spring cup  5  receives on a first face  5   a  a valve spring  7  bearing on the cylinder head  1  so as to hold the valve  3  closed. Such a valve arrangement being moreover known to the person skilled in the art, it will not be described in more detail here. 
         [0036]    The device includes a tappet  8  mounted in the well in the cylinder head  1  to slide along the same axis X as the valve  3  and to be in contact with the cam  2 . A tappet spring  9  is disposed in the tappet  8 , bearing against a second face  5   b  of the spring cup  5  and the tappet  8  in order to maintain the contact between said tappet  8  and the cam  2 . Rotation of the tappet  8  is indexed relative to the cylinder head  1  by a key  10  received in a complementary groove  11  machined in the well of the cylinder head  1 . The tappet  8  is therefore angularly indexed relative to the cylinder head  1  so that it moves only in translation relative to the cylinder head  1 . 
         [0037]    The tappet  8  is pierced at its center by a housing extending along the axis X and containing a sleeve  14  adapted to slide freely in said housing of the tappet  8 . The sleeve  14  includes a key  15  that is received in a complementary groove  16  machined in the tappet  8 . The sleeve  14  is therefore angularly indexed relative to the tappet  8  and can move only in translation along the axis X of the valve  3 . 
         [0038]    The sleeve  14  has at its center a bore into which is inserted a clearance-compensating shim  20  that comes into contact with the end  4  of the stem  3   a  of the valve  3 . The sleeve  14 , the shim  20  and the stem  3   a  form a stack in the direction of the axis X of rigid elements adapted to transmit a force from the sleeve  14  to the valve  3 . 
         [0039]    As shown in  FIG. 1 , the sleeve  14  and the tappet  8  are adapted to define a plane bearing surface for the cam  2 . However, the cam  2 , which here is a double-lobe cam, is adapted to bear only on the tappet  8 . The double-lobe shape of the cam  2  enables the area of contact of the cam  2  on the tappet  8  to be distributed on either side of the axis in order to balance the forces and therefore to limit wear of the parts. 
         [0040]    The device also includes electromagnetic locking means including a ferromagnetic pin  12 . The ferromagnetic pin slides freely in a bore in the tappet  8  along an axis Y perpendicular to the axis X of movement of the tappet  8 . 
         [0041]    The sleeve  14  includes a cylindrical housing  17  on the axis Y adapted to receive the end of the pin  12 . 
         [0042]    The electromagnetic locking means also include an electromagnetic actuator  22  for moving the pin  12  between two extreme positions. The actuator  22  includes a body  23  including a coil  24  and a ferromagnetic core  25  for directing the magnetic field emitted by the coil  24 . 
         [0043]    The body  23  of the actuator  22  is disposed in the cylinder head  1  in line with the pin  12  so that the magnetic field emitted by the coil  24  of the actuator  22  is directed substantially along the axis of movement of the pin  12 , i.e. the axis Y. Energization of the coil  24  therefore drives the movement of the pin  12  subjected to the magnetic field of the actuator  22 . In other words, the pin  12  is moved by virtue of the effect of the axial component of the magnetic force of the electromagnetic actuator  22  produced in particular by the coil  24 . 
         [0044]    In particular, the magnetic coil  24  has a coil axis substantially parallel to the direction of movement of the pin  12 . 
         [0045]    The actuator  22  further includes a pin spring  26  adapted to urge the pin  12  away from the body  23  of the actuator  22 . To be more precise, the pin spring  26  holds the pin  12  in a position projecting into the housing  17  of the sleeve. 
         [0046]    The tappet  8 , the sleeve  14  and the cylinder head  1  are indexed angularly relative to each other in order to enable alignment in the same plane of the body  23  of the actuator  22 , the pin  12  and the opening  17 . 
         [0047]    The actuator  22  enables movement of the pin  12  between an activation position in which the pin  12  projects into the housing  17  of the sleeve  14  in order to couple together the sleeve  14  and the tappet  8  and a deactivation position in which the pin  12  is retracted from the housing  17  to release the sleeve  14  and the tappet  8 . 
         [0048]      FIG. 2  shows the device with the pin  12  in the activation position to couple together the tappet  8  and the sleeve  14 . The movement of the cam  2  is therefore transmitted successively to the tappet  8 , then to the sleeve  14 , then to the shim  20  and finally to the valve  3 . In the activation position, the cam  2  drives the movement of the valve  3  which then allows exchange of cool gases (inlet) or burned gases (exhaust) between the interior and the exterior of the combustion chamber. 
         [0049]      FIG. 3  shows the device in the disconnected position with the pin  12  in the deactivated position. In this position, the tappet  8  slides freely relative to the cylinder head  1  and relative to the stack comprising the sleeve  14 , the shim  20  and the valve  3 . The tappet spring  9  being sized to be more flexible than the valve spring  7 , the movements of the cam  2  are transmitted only to the tappet  8 , the valve  3  then remaining closed. When the pin  12  is in the deactivation position the cam  2  is therefore disconnected from the valve  3 , which remains closed. 
         [0050]    This embodiment is shown with only one pin  12  and only one electromagnetic actuator  22 . Of course, the device may include a plurality of actuators and pins distributed around the valve at the circumference of the device. 
         [0051]    The clearance-compensating shim  20  may advantageously include a hydraulic thrust bearing to compensate for wear of the parts. Such a thrust bearing being moreover known in itself, it will not be described in more detail here. 
         [0052]    Other embodiments of the invention are equally possible.  FIG. 4  shows in detail a device in accordance with a second embodiment of the invention. This second embodiment includes numerous parts shared with the first embodiment. In this second embodiment, parts identical or similar to those of the first embodiment will therefore be numbered with the same reference increased by  100 . Thus the tappet  8  will be numbered  108  in this second embodiment. 
         [0053]    In this second embodiment, the device is mounted on a cylinder head  101 , as before, forming a support, selectively to transmit the movement of a cam  102  to a valve  103  held closed by a valve spring  107 . In other words, the valve spring  107  exerts a return force on the valve  103  so that the valve  103  closes the inlet port or the exhaust port. 
         [0054]    The device includes a substantially bell-shaped tappet  108  and has cylindrical walls sliding in a bore in the cylinder head and a cover  108   a  on which the cam  102  bears. 
         [0055]    The tappet  108  further includes a sleeve  114 , also substantially bell-shaped, which is inserted into the tappet  108  and rigidly connected to the tappet  108 . The sleeve  114  has a first wall  114   a  that is separated from the cover  108   a  of the tappet  108  by a clearance-compensating shim  120 . The sleeve  114  has a second wall  114   b  separated from the cover  108   a  of the tappet  108  in order to leave a gap between them, the second wall  114   b  being pierced at its center by a housing in which the stem of the valve  3  slides freely. 
         [0056]    The stem  103   a  of the valve can therefore slide freely in the sleeve between the first wall  114   a  and the second wall  114   b  of the sleeve  114  and over a height H. 
         [0057]    The device further includes electromagnetic locking means  122  including two diametrally opposite ferromagnetic pins  112   a  and  112   b  that are received in bores in the sleeve  114 . The bores lead into the housing of the sleeve  114  and extend in a direction perpendicular to the sliding axis X of the valve  103 . 
         [0058]    Each pin  112  can slide in its bore between an activation position in which the pin  112  projects into the housing to block sliding of the valve stem  103   a  in the sleeve  114  and a deactivation position in which the pin  112  is retracted from the housing to allow the stem of the valve  3  to slide freely in the sleeve  114 . 
         [0059]    The locking means  112  include a pin spring  126  for each pin  112 , the pin springs  126  being such that the pins  112  are held in the activation position. 
         [0060]    When the pins  112  are in the activation position, the valve  103  is therefore locked to the tappet  108  so that the movement of the cam  102  is transmitted to the valve  3 . The valve  103  is then connected to the cam  102  (see  FIG. 5 ). 
         [0061]    When the pins  112  are in the deactivation position, the stem of the valve  3  is unlocked and is able to slide in the sleeve  114  over a height H (see  FIGS. 4 and 6 ). The valve  103  is then disconnected from the cam  102 . To be more precise, the movement of the cam  102  is transmitted only to the tappet  108 , which then slides relative to the cylinder head  101  and to the valve  103 . 
         [0062]    The travel or height H of the stem of the valve  3  in the sleeve  114  is at least equal to the travel imparted to the valve  103  by the cam  102  so that, in the disconnected mode, the movement of the cam  102  never opens the valve  103 . 
         [0063]    The locking means  122  include at least one electromagnetic actuator  122  for moving the pins  112 . As shown in  FIGS. 4 to 6 , the electromagnetic actuator  122  includes a body  123  containing an annular magnetic coil  124 . The coil  124  is integrated into the cylinder head  101  and is wound in the form of a torus around the tappet  108  to generate an electromagnetic field the axis of which is substantially the axis X of movement of the valve  103 . Such a magnetic field enables the pins  112   a  and  112   b  extending radially relative to the coil to be moved without it being necessary to index the pins  112  angularly relative to the cylinder head  101 . In this second embodiment, the tappet  108  is free to rotate. Because the coil  124  is wound around the tappet  108 , electromagnetic actuation is possible whatever the angular position of the tappet  108 . The pins  112  are then moved by virtue of the effect of the radial component of the radial force of the electromagnetic actuator  122  produced in particular by the coil  124 . 
         [0064]    In particular, the magnetic coil  124  has a coil axis substantially perpendicular to the direction of movement of the pins  112 . 
         [0065]    The sleeve  114  may advantageously include a ferromagnetic portion for channeling the magnetic field of the coil  124  along the sliding axis of the pins  112 . 
         [0066]    More advantageously, each pin  112  may have at its end a flat  130  adapted to come into contact with the end of the valve stem  103   a.  The contact between the pin  112  and the valve stem  103   a  is therefore plane-on-plane, which limits the contact pressure between the two parts, also referred to as the Hertz pressure. 
         [0067]    The contact between the two parts can be improved by angularly indexing the pins  112  relative to the sleeve  114  to enable the flats  130  to take up a position facing the end of the valve stem  103   a.  The angular indexing of the pins  112  is effected with a key, for example. 
         [0068]    The second embodiment is shown with two diametrally opposite pins. It is nevertheless possible to use only one pin or to the contrary to use more than two pins. 
         [0069]    As in the first embodiment, the clearance-compensating shim  120  may include a hydraulic thrust bearing for compensating the distribution clearance. The distribution clearance is set between 0.05 and 0.2 mm, for example, thereby ensuring that the valve remains on its seat in all cases, for example all operating temperatures. 
         [0070]    The changes from the connected mode to the disconnected mode and from the disconnected mode to the connected mode are preferably effected when the pin  12 ,  112  is aligned with the opening  17 ,  117 , i.e. when the tappet  14 ,  114  is at the top dead center position, i.e. on the base circle of the cam  102 . The pin  12 ,  112  then has a very short time to engage in and disengage from the opening  17 ,  117 . For example, in an application in which the valve  3 ,  103  contributes to an engine speed of 4000 rpm and for a lift spread over a crankshaft angle of 240°, the pin  12 ,  112  has approximately 20 ms to make the transition between a connected state and a disconnected state. 
         [0071]    Of course, the invention is not limited to the embodiments described but encompasses any variant within the scope of the invention as defined by the claims. 
         [0072]    In particular, the actuators  22 ,  122  may be of the bistable type with a magnetic pin  12 ,  112  so that it is then possible to dispense with the pin spring  26 ,  126 , the pin  12 ,  112  then moving between a stable activation first position and a stable deactivation second position. 
         [0073]    Other electromagnetic actuators may equally be used. Thus it is possible to use rotary actuators (of the stepper motor type) that drive a crank connected to the actuator and enable movement of the pin  12 . The rotation axis of these rotary actuators is preferably parallel to the axis X of the valve. 
         [0074]    Thanks to its features, the device in accordance with the invention is compact and relatively non-intrusive and can be integrated into numerous existing cylinder heads  1 ,  101  subject to simple reboring of the bore for the tappet  8 ,  108 . No oil nut needs to be provided. The device also provides for disconnection systems that are independent from one valve  3 ,  103  to another.