Abstract:
An engine comprises a system for variable actuation of the intake valves and is subdivided into a plurality of sub-systems independent with respect to each other, carried by a plurality of respective elements, each mounted on the cylinder head at a respective engine cylinder. Among other things, this considerably facilitates the system maintenance operations.

Description:
The present invention refers to internal combustion engines of the type provided with a system for variable actuation of the intake valves of the engine. 
     Even more particularly, the invention refers to multi-cylinder internal combustion engines which comprise, for each cylinder:
         at least one intake valve and at least one exhaust valve each provided with respective return spring means which push the valve towards a closed position, for controlling respective intake and exhaust conduits,   at least one camshaft, for actuating the intake valves of the engine cylinders by means of respective tappets,   wherein each intake valve is controlled by the respective tappet, against the action of the aforementioned return spring means, by interposing hydraulic means including a pressurised fluid chamber and a hydraulic actuator associated to each intake valve and connected to said pressurised fluid chamber,   said pressurised fluid chamber being adapted to be connected by means of a solenoid valve with an exhaust channel with the aim of decoupling the intake valve from the respective tappet and causing the quick closure of the valve due to the respective return spring means,   said hydraulic actuator further being provided with hydraulic braking means for slowing the final phase of the travel for closing the intake valve controlled thereby when the pressure chamber is connected to the exhaust channel,   electronic control means for controlling each solenoid valve so as to vary the opening and/or closing and/or lift instants of the respective intake valve as a function of one or more engine operative parameters,   wherein the hydraulic means for controlling the intake valves of the engine and the solenoid valves associated thereto are part of a preassembled unit mounted on the engine cylinder head.       

     An engine of the type indicated above is for example described and illustrated in EP 1 338 764 A1 of the applicant. 
     Over the years, the Applicant has developed internal combustion engines comprising a system for variable actuation of the intake valves of the type indicated above, sold under the trademark “MULTIAIR”. The Applicant owns various patents and patent applications regarding engines provided with a system of the type described above. 
     According to what is indicated in the document EP 1 338 764 A1 the entire unit for the variable actuation of the intake valves of the engine is integrated in a single “brick” which can be easily also adapted on an engine initially designed without the system for variable actuation of the intake valves. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is that of improving the abovementioned known system, particularly making system maintenance operations easier and less expensive. 
     A further object of the invention is that of achieving the abovementioned objective by means of a relatively simple and reliable structure. 
     With the aim of attaining such objects, the invention has the object of providing an engine having the characteristics indicated above and further characterised in that the abovementioned preassembled unit is formed by a plurality of separate sub-units, respectively associated to the various engine cylinders and each having an independent support body, mounted on the cylinder head and carrying the hydraulic means and at least one solenoid valve for controlling the intake valves of the respective cylinder. 
     Therefore, in the engine according to the invention the system for variable actuation of the intake valves is subdivided into a plurality of sub-systems independent with respect to each other, carried by a plurality of respective “bricks”, each mounted on the cylinder head at a respective engine cylinder. This considerably facilitates the system maintenance operations, for example in case of failure of a single solenoid valve, in that it is sufficient to demount the single brick carrying said solenoid valve. Preferably, each solenoid valve simply rests within a seat arranged in the respective brick and it is locked therein by means of an auxiliary locking plate which is fastened to the brick. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages of the invention will be apparent from the description which follows with reference to the attached drawings, provided by way of non-limiting example, wherein: 
         FIG. 1  is a sectional view of an engine according to the known art, of the type described for example in document EP A 0 803 642 of the applicant, 
         FIG. 2  is a partial perspective view of the cylinder head of a diesel engine according to a first embodiment of the present invention, 
         FIG. 3A  is a perspective view, partially transparent, of a single sub-unit for the variable actuation of the intake valves associated to an engine cylinder of  FIG. 2 , 
         FIG. 3B  is a further perspective view of the support body of the sub-unit of  FIG. 3A , 
         FIGS. 4 ,  5  are sectional views showing the detail of a bracket for locking an injector of the engine of  FIG. 2 , 
         FIG. 6  is a perspective view of a cover associated to the cylinder head of  FIG. 2 , 
         FIG. 7  is a capsized perspective view of the cover of  FIG. 6 , 
         FIG. 8  is a bottom view of the cover of  FIG. 6 , 
         FIG. 8A  is still a perspective view of a single sub-unit for actuating the intake valves associated to an engine cylinder, 
         FIG. 8B  is a sectional view of the sub-unit of the  FIG. 8A , 
         FIG. 9  is a perspective view of a unit associated to the cylinder head of a further embodiment of a diesel engine provided with a system for variable actuation of the intake valves of the engine, which is not part of the present invention, in that it does not include separate sub-units for actuating the intake valves of the different cylinders, 
         FIG. 10  is an enlarged scale perspective view of a component of the unit of  FIG. 9 , 
         FIG. 11  is a sectional view of the unit of  FIG. 9 , and 
         FIG. 12  is a perspective view of a bracket for locking an injector of the engine on which the unit of  FIG. 9  is mounted. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Over the years, the applicant has developed internal combustion engines, petrol or diesel-fuelled, comprising a system for variable actuation of the intake valves of the engine, sold under the trademark “MULTIAIR”. The Applicant owns various patents and patent applications regarding engines provided with a system of the type described above. 
       FIG. 1  of the attached drawings shows a sectional view of a petrol-fuelled engine provided with “MULTIAIR” system, as described in the European patent EP 0 803 642 B1 of the applicant. 
     With reference to  FIG. 1 , the engine illustrated therein is multi-cylinder engine, for example an engine with four in-line cylinders, comprising a cylinder head  1 . The head  1  comprises, for each cylinder, a cavity  2  formed by the base surface  3  of the head  1 , defining the combustion chamber, in which the two intake conduits  4 ,  5  and two exhaust conduits  6  end up. The communication of the two intake conduits  4 ,  5  with the combustion chamber  2  is controlled by two intake valves  7 , of the conventional mushroom type, each comprising a stem  8  slidably mounted in the body of the head  1 . 
     Each valve  7  is returned towards the closed position by springs  9  interposed between an inner surface of the head  1  and an end retaining cap  10  of the valve. The communication of the two exhaust conduits  6  with the combustion chamber is controlled by two valves  70 , also of the conventional type, to which springs  9  for return towards the closed position are associated. 
     The opening of each intake valve  7  is controlled, as described hereinafter, by a camshaft  11  mounted rotatably around an axis  12  within supports of the head  1 , and comprising a plurality of cams  14  for actuating the intake valves  7 . 
     Each cam  14  which controls an intake valve  7  cooperates with the plate  15  of a tappet  16  slidably mounted along an axis  17  which, in the case of the example illustrated in the mentioned prior art document, is substantially directed at 90° with respect to the axis of the valve  7 . The plate  15  is returned against the cam  14  by a spring associated thereto. The tappet  16  constitutes a pumping piston slidably mounted within a bushing  18  carried by a body  19 , or “brick” of a preassembled unit  20 , incorporating all electrical and hydraulic devices associated to the actuation of the intake valves, according to the description outlined hereinafter. 
     The pumping piston  16  is capable of transmitting a thrust to the stem  8  of the valve  7 , so as to cause the opening of the latter against the action of the elastic means  9 , by means of pressurized fluid (preferably oil coming from the engine lubrication circuit) present in a pressure chamber C to which the pumping piston  16  is faced, and by means of a piston  21  slidably mounted in a cylindrical body constituted by a bushing  22  also carried by the body  19  of the sub-unit  20 . 
     Still in the known solution described in  FIG. 1 , the pressurised fluid chamber C associated to each intake valve  7  can be placed in communication with an exhaust channel  23  through a solenoid valve  24 . The solenoid valve  24 , which can be of any known type adapted to the function illustrated herein, is controlled by electronic control means, indicated schematically with  25 , as a function of the signal S indicating the operating parameters of the engine, such as the position of the accelerator and the number of engine revolutions. 
     When the solenoid valve  24  is open, the chamber C enters in communication with the channel  23 , hence the pressurised fluid present in the chamber C flows into such channel and thus obtaining the decoupling of the cam  14  and the decoupling of the respective tappet  16  from the intake valve  7 , which thus quickly returns to the closing position thereof under the action of the return springs  9 . Thus, controlling the communication between the chamber C and the exhaust channel  23 , allows varying the opening time and the travel of each intake valve  7  at will. 
     The exhaust channels  23  of the various solenoid valves  24  end up in the same longitudinal channel  26  communicating with pressure accumulators  27 , only one of which can be observed in  FIG. 1 . 
     All tappets  16  with the associated bushings  18 , the pistons  21  with the associated bushings  22 , the solenoid valves  24  and the respective channels  23 ,  26  are carried by and obtained from the abovementioned body  19  of the preassembled unit  20 , to the advantage of an engine that is quick and easy to assemble. 
     The exhaust valves  70  associated to each cylinder are controlled, in the embodiment illustrated in  FIG. 1 , conventionally, by a respective camshaft  28 , through respective tappets  29 , even though, in the case of the mentioned prior art document, an application of the hydraulic actuation system also controlling exhaust valves cannot be excluded generally. 
     Still with reference to  FIG. 1 , the variable volume chamber defined within the bushing  22  and facing the piston  21  (which is illustrated in the minimum volume condition thereof in  FIG. 1 , piston  21  being in the upper end stop position thereof) communicates with the pressurised fluid chamber C through an opening  30  obtained in an end wall of the bushing  22 . Such opening  30  is engaged by an end nose  31  of the piston  21  so as to provide a hydraulic braking of the movement of the valve  7  in the closing phase, when the valve is close to the closing position, in that the oil present in the variable volume chamber is forced to flow into the pressurised fluid chamber C passing through the clearance present between the end nose  31  and the opening wall  30  engaged thereby. Besides the communication constituted by the opening  30 , the pressurised fluid chamber C and the variable volume chamber of the piston  21  communicate with respect to each other through internal passages obtained in the body of the piston  21  and controlled by a check valve  32  which allows the passage of fluid only from the pressurized chamber C to the variable volume chamber of the piston  21 . 
     During the normal operation of the known engine illustrated in  FIG. 1 , when the solenoid valve  24  excludes the communication of the pressurised fluid chamber C with the exhaust channel  23 , the oil present in such chamber transmits the movement of the pumping piston  16 , imparted by the cam  14 , to the piston  21  which controls the opening of the valve  7 . In the initial phase of the opening movement of the valve, the fluid coming from the chamber C reaches the variable volume chamber of the piston  21  passing through the check valve  32  and further passages which place the internal cavity of the piston  21 , which is tubular-shaped, in communication with the variable volume chamber. After a first displacement of the piston  21 , the nose  31  exits from the opening  30 , hence the fluid coming from the chamber C may pass directly into the variable volume chamber through the opening  30 , now free. 
     In the reverse movement for closing the valve, as previously mentioned, during the final phase, the nose  31  enters into the opening  30  causing the hydraulic braking of the valve, so as to avoid impacts of the body of the valve against the seat thereof, for example after an opening of the solenoid valve  24  which causes the immediate return of the valve  7  to the closed position. 
     In the described system, when the solenoid valve  24  is enabled, the valve of the engine follows the movement of the cam (full lift). An early closing of the valve can be obtained by disabling (opening) the solenoid valve  24 , thus emptying the hydraulic chamber and obtain the closing of the valve of the engine under the action of the respective return springs. Analogously, a delayed opening of the valve can be obtained by delaying the opening of the solenoid valve, while the combination of a delayed opening with an early opening of the valve can be obtained by enabling and disabling the solenoid valve during the thrust of the relative cam. According to an alternative strategy, in compliance with the teachings of the patent application EP 1 726 790 A1 of the applicant, each intake valve can be controlled in “multi-lift” mode i.e. according to two or more repeated opening and closing “sub-cycles”. In each sub-cycle, the intake valve opens and then closes completely. The electronic control unit is thus capable of obtaining a variation of the opening instant and/or the closing instant and/or the lift instant of the intake valve, as a function of one or more engine operative parameters. This allows obtaining the maximum efficiency of the engine, and lower consumption of fuel, under any condition of operation. 
     In  FIGS. 2-12 , the common parts or those corresponding to those of  FIG. 1  are indicated using the same reference number. 
     With reference to  FIG. 2 , a body  50  for supporting the camshaft  11 —in which the seats for supporting the rotation of the shaft  11 , on which the latter is held by means of caps  51  fastened on the body  50 —is mounted on the cylinder head  1 . The illustrated example refers to the case of a four-cylinder diesel engine. However, the invention is also applicable to a controlled ignition engine and with any number of cylinders. 
     The main characteristic of the solution illustrated in the  FIG. 2  lies in the fact that the pre-assembled unit for the variable actuation of the intake valves of the engine is constituted by four separate sub-units  20 A,  20 B,  20 C,  20 D, each comprising a respective support independent body or “brick”, respectively indicated with  19 A,  19 B,  19 C,  19 D. 
     As observable in  FIG. 3A , the body  19 A of the sub-unit  20 A, and analogously each of the other bodies  19 B,  19 C,  19 D of the sub-units  20 B,  20 C,  20 D carries all the devices intended to allow actuating the intake valves of the respective engine cylinder. In particular, with reference to the sub-unit  20 A, the sub-unit carries the pumping cylinder  18  whose stem is actuated by a respective cam  14  by means of a rocker arm lever  52 , articulated in  53  to the support body  19 A and carrying a roller  54  for the engagement of the cam  14 . Furthermore, the support body  19 A of the sub-unit  20 A carries the two hydraulic actuators  22  respectively associated to two intake valves of the respective engine cylinder. Furthermore, the body  19 A carries the body of the solenoid valve  24 , which simply rests within a seat arranged in the body  19 A and it is locked by means of a locking plate  52  fixed by means of screws to the body  19 A. Obviously all ducts required for the hydraulic connection of the system for variable actuation of the valves are obtained within the body  19 A. Lastly, an upper cavity of the body  19 A (indicated with  56  in  FIG. 3B ) is closed by means of a cover  570  fastened on the body  19 A. 
     What is indicated above with reference to the unit  20 A obviously also applies for the sub-units  20 B,  20 C and  20 D. 
     The illustrated example, as mentioned, refers to the case of a diesel engine.  FIG. 2  shows one of the injectors associated to the engine cylinders, indicated with the reference I. Each injector I is mounted in the cylinder head through a cup-shaped casing  57 , illustrated more in detail hereinafter and which is made in a single piece with the respective support body  19 A of the respective sub-unit  20 A. 
     The unit for variable actuation of the intake valves of the engine, constituted by the plurality of sub-units  20 A-D is closed at the upper part by a cover  58  with the interposition of a sealing gasket  60 . 
     In the illustrated example, the sealing gasket  60  is received in a corresponding peripheral groove of the cover  58  (see  FIG. 7 ) and respectively provides sealing on the bodies  19 A-D and on the body  50  for supporting the camshaft. 
     However, it should be observed that the architecture of the head described above is provided purely by way of non-limiting example. For example, the body  50  for supporting the camshaft could be made in a single piece with the cylinder head, or it could be made in several pieces respectively integrated in the support bodies of the sub-units  20 A-D. 
     Regardless of the selected architecture, the sealing gasket  60  has a main portion contained in a general base plane of the cover  58 , and a plurality of portions  61 A-D arranged longitudinally adjacent to each other along one side of the head and associated respectively to the various support bodies  19 A-D of the sub-units  20 A-D. Each of said portions  61 A-D has two lateral portions  62  which extend in planes parallel and orthogonal to the abovementioned general base plane, and a central portion  63  which extends in a parallel plane with respect to the abovementioned general base plane and raised with respect thereto. In particular, as observable in  FIG. 7 , each of the lateral portions  62  has a rectilinear main section which—at the end—extends in two brief sections one respectively contained in the general base plane of the cover and the other in the plane in which the central portions  63  extend. 
     Due to the abovementioned arrangement, the sealing of the fluid of the system for variable actuation of the intake valves (typically engine lubrication oil) at each of the sub-units  20 A- 20 D is ideally guaranteed, even in the area that separates each sub-unit  20  from the one adjacent thereto (also see  FIG. 8A ). 
     A further problem lies in guaranteeing the sealing around each injector I. For such purpose, as previously described, each injector is surrounded by a cup-shaped casing  57 , shaped extended horizontally, obtained in a single piece with the respective body  19 A-D of the respective sub-unit  20 A-D. The cup-shaped casing  57  defines an upper peripheral edge for the engagement of a respective sealing gasket  64  arranged within a respective groove in the lower surface of the cover  58  ( FIG. 7 ). The plane of the upper edge of the cup-shaped casing  57  is parallel but raised with respect to the general base plane of the cover, so that the casing  57  can have the required dimension, without the risk of interference with the actuator cylinders  22  associated to the intake valves of the respective cylinder (see  FIG. 3A ). Actually, should the sealing gaskets  64  of the casings surrounding the injectors I be in the general base plane of the cover, there would be no sufficient room to receive them in the area comprised between the body of the injector and the body of the aforementioned actuators  22 . Therefore, the arrangement described above allows guaranteeing an ideal sealing also at each injector I. 
     Each injector is locked in the seat thereof in the cylinder head (see  FIGS. 4 ,  5 ) by means of a bracket  640  which has an end resting on a support (in the example the head of a screw  65  which is used for fixing the cover  58  on the body  50 ). The opposite end of the bracket  640  is fork-shaped, with two branches  66  which are engaged on two shoulders of the body of the injector. The bracket  640  is pressed in position by means of a screw  67  which engages the cylinder head. The screw  67  traverses the cover with the interposition of sealing rings and it is engaged at the upper end thereof by a nut  68  which presses—from above—the intermediate portion of the bracket  640 , to lock the injector I in the seat thereof. 
       FIGS. 9-12  refer to a different embodiment of a unit for variable actuation of the intake valves, also in this case for a diesel engine, which is not part of the present invention, in that it does not have separate sub-units for actuating the intake valves of the different cylinders. However, also such engine has the characteristic of having cup-shaped casings  57  associated to the injectors of the various engine cylinders defining an upper sealing edge contained in a parallel plane and raised with respect to the general base plane of the cover (not shown in  FIGS. 9-12 ). Such embodiment does not provide for separate sub-units for the system for variable actuation of the intake valves, but two single longitudinal bodies  70 , 71  mounted on the body  50  carrying the camshaft  11 . The first longitudinal body  70  closes—at the upper part—the seat for rotatably supporting the camshaft  11  and integrates the cup-shaped casings  57  associated to the various injectors I. The second longitudinal unit  71  integrates the components of variable actuation of the intake valves of the various cylinders, with the relative solenoid valves  24 . Also in this case (see  FIGS. 11 ,  12 ) each injector is locked in the seat thereof by means of a bracket  65  ( FIG. 12 ) with fork-shaped end, whose branches  66  engage corresponding shoulders provided for in the body of the injector I. Also in this case each bracket  640  has an end resting on the head of a screw  65  and it is pressed in position by a nut  68  engaged on the upper end of a screw  67  which is fastened in the cylinder head and passes through the body  50 , the body  70  and the bracket  640 . 
     Obviously, without prejudice to the principle of the invention, the construction details and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of protection of the present invention.