Patent Publication Number: US-6981476-B2

Title: Internal combustion engine with a single camshaft which controls exhaust valves mechanically and intake valves through an electronically controlled hydraulic device

Description:
SUMMARY OF THE INVENTION 
   The present invention relates to internal combustion engines with multiple cylinders, of the type comprising:
         at least one intake valve and at least one exhaust valve for each cylinder, each provided with respective spring return means which bias the valve towards a closed position, to control respective intake and exhaust conduits,   at least one camshaft, to actuate the intake and exhaust valves of the engine cylinders by means of respective tappets,   in which each intake valve is actuated by the respective tappet, against the action of the aforesaid spring return means, by the interposition of hydraulic means including a pressurized fluid chamber, into which projects a pumping piston connected to the tappet of the intake valve,   said pressurized fluid chamber being able to be connected by means of a solenoid valve with an exhaust channel, in order to uncouple the intake valve from the respective tappet and cause the rapid closure of the valve by effect of the respective spring return means,   electronic control means for controlling each solenoid valve in such a way as to vary the time and travel of opening of the respective intake valve as a function of one or more operative parameters of the engine.       

   Engines of the type specified above have been described and illustrated in various prior patents by the same Applicant. By way of example, see European Patent Application EP 1 344 900 A2. 
   In his European Patent Application EP 0 894 956 A2, the applicant has disclosed an engine of the above indicated type having the features indicated in the pre-characterizing portion of claim  1 . 
   An object of the invention is to provide an engine having the characteristics set out above, having an extremely simple structure with reduced bulk. An additional object is to provide an engine of the type specified above which is characterized by high levels of efficiency and reliability. 
   In view of achieving these and other objects, the invention relates to an engine as defined in the accompanying claim  1 . Additional preferred and advantageous characteristics of the invention are specified in the dependent claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention shall now be described with reference to the accompanying drawings, provided purely by way of non limiting example, in which: 
       FIG. 1  is a section view of an engine according to the prior art, of the type described in European patent EP 0 803 642 B1 by the same Applicant, 
       FIG. 2  shows a first embodiment of the invention, applied to a gasoline engine, 
       FIG. 3  is an enlarged view of a detail of  FIG. 2 , 
       FIG. 4  is an even more enlarged view of a detail of  FIG. 3 , 
       FIG. 5  is a simplified view of a variant, in which for the sake of greater clarity only the various parts of the device for actuating the engine valves are shown, without illustrating the structure that supports them, 
       FIG. 6  shows some of the parts of  FIG. 5  as they are visible from above, 
       FIG. 7 ,  FIG. 8  and  FIG. 9  are a lateral view, a perspective enlarged scale view, and a top view of the parts constituting the valve actuation device, in a second embodiment of the invention, relating to an application to a Diesel engine, and 
       FIG. 10  is a diagram of the device of  FIGS. 7–9 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , the internal combustion engine described in European patent EP 0 803 642 B1 by the same Applicant is a multi-cylinder engine, for instance an engine with four cylinders in line, 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, into which end two intake conduits  4 ,  5  and two exhaust conduits  6 . The communication of the two intake conduits  4 ,  5  with the combustion chamber  2  is controlled by two intake valve  7 , of the traditional 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 cup  10  of the valve. The communication of the two exhaust conduits  6  with the combustion chamber is controlled by two valves  70 , also of a traditional type, whereto are associated springs  9  for the return towards the closed position. The opening of each intake valve  7  is controlled, in the manner described below, by a camshaft  11  rotatably mounted 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  co-operates with the washer  15  of a tappet  16  slidably mounted along an axis  17  which, in case of the example illustrated in the aforementioned prior document, is directed substantially at 90° relative to the axis of the valve  7 . The washer  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  borne by a body  19  of a pre-assembled set  20 , incorporating all the electrical and hydraulic devices associated with the actuation of the intake valves, as described in detail hereafter. The pumping piston  16  is able to transmit a thrust to the stem  8  of the valve  7 , in such a way as to cause the opening thereof against the action of the spring means  9 , by means of pressurized fluid (preferably oil from the engine lubrication loop) present in a pressure chamber C into which projects the pumping piston  16 , and by means of a piston  21  mounted slidably in a cylindrical body constituted by a bushing  22  which is also borne by the body  19  of the subgroup  20 . In the known solution shown in  FIG. 1 , the pressurized fluid chamber C associated to each intake valve  7  can be placed in communication with an exhaust channel  23  by means of a solenoid valve  24 . The solenoid valve  24 , which can be of any known type, suited to the function illustrated herein, is controlled by electronic control means, schematically designated by the number  25 , according to signals S indicative of engine operating parameters, such as the position of the accelerator pedal and the number of engine revolutions per minute. When the solenoid valve  24  is open, the chamber C comes in communication with the channel  23 , so the pressurized fluid present in the chamber C flows into said channel and an uncoupling is obtained of the cam  14  and of the respective tappet  16  from the intake valve  7 , which then rapidly returns to its closed position under the action of the return springs  9 . By controlling communication between the chamber C and the exhaust channel  23 , it is therefore possible to vary at will the time and stroke of the opening of each intake valve  7 . 
   The exhaust channels  23  of the various solenoid valves  24  all end in a same longitudinal channel  26  communicating with pressure accumulators  27 , only one of which is visible in  FIG. 1 . 
   All the tappets  16  with the associated bushings  18 , the pistons  21  with the associated bushings  22 , the solenoid valves  24  and the related channels  23 ,  26  are borne and formed from the aforesaid body  19  of the pre-assembled set  20 , to the advantage of the rapidity and ease of assembly of the engine. 
   The exhaust valves  70  associated to each cylinder are controlled, in the embodiment illustrated in  FIG. 1 , in traditional fashion, by a respective cam shaft  28 , by means of respective tappets  29 , although in principle, in the case of the prior document mentioned above, an application of the hydraulic actuation system to command the exhaust valves is not excluded. 
   With reference to  FIG. 1 , the variable volume chamber defined inside the bushing  22  and facing the piston  21  (which in  FIG. 1  is shown in its minimum volume condition, the piston  21  being in its upper top stroke end position) communicates with the pressurized fluid chamber C through an opening  30  obtained in an end wall of the bushing  22 . Said opening  30  is engaged by an end nose  31  of the piston  21  in such a way as to obtain a hydraulic braking of the motion of the valve  7  in the closing phase, when the valve is near the closed position, since the oil present in the variable volume chamber is forced to flow into the pressurized fluid chamber C passing through the play existing between the end nose  31  and the wall of the opening  30  engaged thereby. In addition to the communication constituted by the opening  30 , the pressurized fluid chamber C and the variable volume chamber of the piston  21  communicate with other by means of internal passages formed 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 prior art engine illustrated in  FIG. 1 , when the solenoid valve  24  excludes the communication of the pressurized fluid chamber C with the exhaust channel  23 , the oil present in this chamber transmits the motion of the pumping piston  16 , imparted by the cam  14 , to the piston  21  that commands 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 additional passages which place in communication the inner cavity of the piston  21 , which has tubular shape, with the variable volume chamber. After a first displacement of the piston  21 , the nose  31  comes out of the opening  30 , so the fluid coming from the chamber C can pass directly into the variable volume chamber through the opening  30 , which is now free. 
   In the inverse movement of closure of the valve, as stated, during the final phase the nose enters into the opening  30  causing the hydraulic braking of the valve, to prevent any impacts of the body of the valve against its seat, for instance subsequently to an opening of the solenoid valve  24  which causes the immediate return of the valve  7  to the closed position. 
   As an alternative to the hydraulic braking device illustrated in  FIG. 1 , the Applicant has also already proposed (see European patent application EP 1 344 900 A2) an alternative solution in which the piston  21  actuating the engine intake valve lacks the end nose and the check valve  32  instead of being formed in the body of the piston  21 , is formed in a fixed part. Moreover, in the wall of the bushing within which is slidably mounted the piston  21  end one or more passages, directly communicating with the pressure chamber C. Said passages are shaped in positioned in such a way that they are progressively shut by the piston  21  in the final closure phase of the engine valve, to achieve a narrowing of the fluid passage section, with the consequent hydraulic braking effect. In the solution proposed in the European patent application EP 1 344 900 A2, moreover, between the piston  21  which actuates the engine valve and the stem of the engine valve is interposed an auxiliary hydraulic tappet. 
   The first embodiment of the invention, illustrated in  FIGS. 2–4 , shall now be described. In these figures, the parts corresponding to those of the known solution illustrated in  FIG. 1  are designated by the same reference number. 
   A first fundamental difference of the solutions illustrated in  FIGS. 2-4  relative to the one in  FIG. 1  resides in the fact that in the latter both the intake valves  7  and the exhaust valves  70  of the engine are controlled by a single camshaft  110 . The camshaft  110  bears a plurality of cams distributed along its length, some of which, designated by reference  7   a , individually control the opening a respective intake valve  7 , whilst the remaining ones, designated by the reference  70   a , individually control the opening of a respective exhaust valve  70 . The cams  70   a  controlling the exhaust valves  70  actuate said exhaust valves mechanically, in the conventional manner. In the example illustrated in  FIGS. 2–4 , each cam  70   a  is in direct contact with a tappet  29  which actuates the opening of a respective exhaust valve  70  against the action of the spring means  9 . Each cam  7   a , instead, actuates the respective intake valve  7  by means of an electronically controlled hydraulic device of the type described above with reference to  FIG. 1 . However, each cam  7   a  is not in direct contact with the washer  15  of the pumping piston  16 , but instead actuates said washer, against the action of a spring  15 a, by means of a rocker arm member  60 . In the example illustrated in  FIGS. 2–4 , the rocker arm members  60  associated to the intake valves  7  are all borne by a shaft mounted oscillating around its axis  61  on the structure of the engine. Each rocker arm member  60  has an end bearing a freely rotating roller  62 , which is in contact with the respective cam  7   a  of the camshaft  110 , whilst the other end  63  of the rocker arm member  60  co-operates with the washer  15 . The fact that the element co-operating with the cam  7   a  is a roller is advantageous, because it avoids the risk, which instead arose in the known solution of  FIG. 1 , that the cam may transmit by friction transverse thrusts which may cause an inclination of the pumping piston  16  relative to its theoretical axis, with consequent difficulties in sliding. 
   The pumping piston  16  controls the opening of the intake valve  7  by means of the electronically controlled hydraulic device. 
   An additional difference of the invention with respect to the prior art solution described above resides in the fact that over the head  2  is mounted a block  190  whereon are borne not only all the elements and parts of the electronically controlled hydraulic device, as in  FIG. 1 , but also the supports within which the camshaft  110  is rotatably mounted, as well as the supports for the rocker arm members  60 . 
   Yet another important characteristic of the invention resides in the fact that each of the solenoid valves  24  associated to the hydraulic means for controlling the engine intake valve is mounted “dry”, outside the block  190 , i.e. each solenoid valve  24  is inserted in a seat obtained in the block  190  and is not exposed to the lubricated environment, defined between the block  190  and a lid  200 , in which are instead contained the camshaft  110 , the rocker arm members  60  and the guide bushings of the pumping pistons  16 . This arrangement is advantageous, since the solenoid valves are thereby cooled by the air and are not directly exposed to the overheating caused by the hydraulic device in its operation. 
   The whole structure constituted by the block  190  and by the various parts mounted thereon can be pre-assembled before the final mounting on the head  2  of the engine. 
   With reference to the electronic hydraulic device which actuates the opening of each intake valve  7 , said device, in accordance with the prior art solution, has a pressure chamber C facing the pumping piston  16 , which communicates with a channel  65  that can be placed in communication with an exhaust channel  23  through the respective solenoid valve  24 . When the solenoid valve  24  is closed the motion of the rocker arm member  60  actuated by a cam  7   a , corresponding to a determined intake valve  7 , determines the motion of the pumping piston  16 , against the action of the spring return means  15   a . The motion of the pumping piston  16  causes a passage of pressurized fluid from the chamber C to the variable volume chamber (designated by the reference  21   a  in  FIG. 4 ) which faces the piston  21  actuating the intake valve  7 . 
   As in the prior art solution, the piston  21  is slidably mounted in a bushing  22 , which is mounted within the block  190 . 
   At the side opposite the chamber  21   a , the piston  21   a  has an end (the lower end in  FIGS. 2–4 ) which actuates (through an auxiliary hydraulic tappet  80 , described below) the stem of valve  7 .  FIGS. 3 ,  4  show the piston  21  in its maximum raised position, corresponding to the closed condition of the intake valve  7 . In this condition, the variable volume chamber  21   a  facing the piston  21  is at its minimum volume and communicates with the pressure chamber C through a conduit  66  formed in the body  190  and a check valve  32 , borne by a fixed body  32   a  (see  FIG. 4 ), which allows only the passage of fluid from the pressure chamber C to the variable volume chamber  21   a  facing the piston  21 . 
   In the case of the solution illustrated in  FIGS. 2 ,  3 , the check valve  32 , similarly to what is already proposed in the European patent application EP 1 344 900 A2 is borne by a body  32   a  which is fixed relative to the block  190 . When the piston  21  is sufficiently far away from its end position corresponding to the closed condition of the valve  7 , the variable volume chamber  21   a  facing the piston  21  communicates with the pressure chamber C through an additional conduit  67  and through one or more passages (not shown in the figures) obtained in the wall of the bushing  22 , similarly to what is illustrated in EP 1 344 900 A2. 
   As described above with reference to prior art solutions, in operation, assuming that the solenoid valve  24  is closed and that the intake valve  7  is closed, a rotation of the camshaft  110  causes an oscillation of the rocker arm member  60  and a consequent actuation of the pumping piston  16 . The lower of the piston  16  (with reference to  FIGS. 2–4 ) causes a passage of fluid from the pressure chamber C to the variable volume chamber  21   a  facing the piston  21 . The latter thus moves downwards (with reference to  FIGS. 2–4 ) causing the opening of the valve  7 . In the first phase of the opening motion, the fluid passes only from the chamber C through the passage  66  and the check valve  32 . When the piston  21  has moved a sufficient distance away from its initial position, it frees the openings obtained in the bushing  22  communicating with the passage  67 , so a greater quantity of fluid can pass from the chamber C to the chamber of the piston  21 . During the closing motion of the intake valve  7 , the fluid which is thrust by the piston  21  outside the variable volume chamber  21   a  returns into the pressure chamber C. This passage cannot take place through the check valve  32 , but only through the openings communicating with the passage  67 . Said openings are shaped and arranged for example according to the teachings of EP 1 344 900 A2, in order progressively to reduce the fluid passage section in the terminal closing phase of the valve, to obtain a hydraulic braking effect of the valve. 
   Naturally, in accordance with prior art solutions, the solenoid valve  24  is controlled by an electronic control unit  25  (similar to the one shown in  FIG. 1 ) on the basis of signals S indicating the operating parameters of the engine, to vary the time and amplitude of the opening of the intake valve during the operation of the engine, independently of the profile of the cam  7   a . Every time the solenoid valve  24  is opened, the pressure chamber C is emptied and the intake valve  7  closes rapidly, under the action of the respective return springs  9 , any violent impact of the valve within its seat being in any case prevented by the hydraulic brake effect obtained with the device described above. Also in accordance with EP 1 344 900 A2, to prevent an excessive hydraulic braking effect when the fluid (which is the engine lubricating oil) is too viscous, for instance when starting the engine under low temperature conditions, an additional calibrated hole can be provided which places in communication the variable volume chamber of the piston  21  with the pressure chamber C. 
   An important advantage of the invention described above is that, combining the use of a single camshaft to control both the intake and the exhaust valves, with an electronically controlled hydraulic command to control the intake valves, and providing the rocker arm members  60  to transmit the motion of the cams  7   a  to the pumping pistons  16  which control the intake valves  7 , an engine can be obtained, which, while having all the advantages of an operation of the intake valves that is programmable at will, according to times and openings which may vary as a function of the different operating conditions, also has a relatively simple structure and above all a size that is substantially comparable to that of a traditional engine with two camshafts mechanically controlling the intake valves and the exhaust valves. The additional arrangement of all the elements and parts of the hydraulic system for the variable actuation of the intake valves, as well as of the single camshaft  110  and of the rocker arm members  60  which actuate the intake valves, on a single block  190  separate from the head and mounted over it, provides readily apparent advantages from the viewpoint of simplicity of construction and assembly. 
   The arrangement of the solenoid valves  24  over the block  190 , but outside it, allows to assure a cooling of said solenoid valves, even though the operation of the hydraulic system causes heating. 
   Moreover, the solution described above allows to position the cams  7   a  actuating the intake valves  7  and the cams  70 a actuating the exhaust valves  70  relatively close to each other along the shaft  110 , without any risk of interference between the parties co-operating therewith (thanks in particular to the use of a hydraulic system to control the intake valves), and maintaining the relative position and the orientation of the intake and exhaust valves, which are necessary for a correct operation of the engine. 
   It should be noted that, in the case of the solution illustrated in  FIGS. 2–4 , the camshaft  110  is in contact on one side with the tappets  29  controlling the exhaust valves  70 , and substantially on the opposite side with the rollers  62  of the rocker arm members  60  which control the intake valves. The interposition of the hydraulic means between the rocker arm member  60  and the intake valves, as stated, allows to maintain exhaust valves and intake valves in the same positions as in a conventional engine, without particular construction complications. 
   An additional advantage of the solution described above derives from the fact that the hydraulic device actuating each intake valve is controlled by a rocker arm member which has a roller  62  co-operating with the respective cam  7   a  of the camshaft  110 . As stated, said solution allows the additional important advantage, with respect to the known solution illustrated in  FIG. 1 , of preventing a rubbing contact of the cam against the washer of the pumping piston of the hydraulic device. Said rubbing contact may cause, by friction, transverse thrusts on the washer which, under particular conditions, may compromise the correct sliding of the pumping piston within the respective guide bushing. 
   Also with reference to  FIG. 4 , it should be noted that between the actuating piston  21  and the stem of the intake valve  7  is interposed an auxiliary hydraulic tappet  80 , which has a first bushing  81 , closed at an end, slidably mounted within the bushing  22  which guides the piston  21 , and a second bushing  82  slidably mounted within the bushing  81 . The first bushing  81  has its closed end in contact with the stem of the intake valve  7 . The second bushing  82  has an end in contact with the lower end (with reference to  FIG. 4 ) of the actuating piston  21 . A first chamber  83  is defined between the second bushing  82  and the piston  21  and is in communication with a passage  84  formed in the body  190  through holes  84   a  (only one of which is shown in  FIG. 4 ) obtained in the wall of the bushing  22 , to feed pressurized oil to said chamber  83 . A second chamber  85  is defined between the first bushing  81  and the second bushing  82 . A check valve  86 , constituted by a ball shutter attached to a return valve  86 , controls a passage  86 a in a transverse wall of the second bushing  82 , to allow the passage of fluid only from the first chamber  81  to the second chamber  82 . 
   During the operation of the engine, the pressurized oil coming from the channel  84  of the lubricating loop arrives into the chamber  83  and from there it passes into the chamber  85  through the check valve  86 , thereby compensating for any play in the chain transmitting thrust from the piston  21  to the valve  7 . 
     FIGS. 5 ,  6  (which are simplified views, showing only the parts of the valve actuation system, without showing the structure of the engine whereon they are borne) refer to a variant which differs from those of  FIGS. 2–4  solely because therein each rocker arm member  60  is pivotally engaged to an end  60   a  on the block  190  by means of yielding supports  60   b , known in themselves, and bears in its intermediate area the rotating roller  62  which co-operates with the cam  7   a . The other end  61  of the rocker arm member actuates the pumping piston  16 .  FIG. 6  clearly shows that the cams  7   a  which control the intake valves of each cylinder of the engine and the cams  70   a  which control the exhaust valves of the same cylinder, axially very close to each other in twos. This notwithstanding, the actuating systems of the intake valves and of the exhaust valves do not interfere with each other. This is due first of all to the fact that the intake valves  7  are actuated by a hydraulic system, which allows to transmit motion from the single camshaft  110  to the intake valves  7 , leaving said valves in their conventional position (with reference in particular to the inclination of their axis which is optimal for a correct operation of the engine). In this case the camshaft  110  is in contact on one side with the tappets  29  of the exhaust valves, whilst it co-operates with the roller  62  of the rocker arm member  60  actuating the intake valve  7  in a position about 90° relative to the tappets  29 . 
   In the case of the solution of  FIGS. 5 ,  6 , moreover, every interference of the cams  7   a  actuating the intake valves with the tappets  29  of the exhaust valves is avoided, in spite of the close position between cams  7   a  and cams  70   a , because along any outgoing radial direction from the axis of the camshaft  110 , the radial dimension of the exhaust cam  70   a  is always greater than the dimension of the cam  7   a . In other words, the section profile of the cam  7   a  is wholly contained within the profile of the cam  70   a  (see  FIG. 5 ). 
     FIG. 6  also shows that, like the solution of  FIGS. 2–4 , use of the hydraulic device for actuating the intake valve allows to maintain the intake valves and the exhaust valves in twos with their axes in a same plane, orthogonal to the axis of the single camshaft, although the respective actuating cams are axially distanced from each other. 
   Therefore, the cam  7   a  controlling each intake valve  7  and the pumping piston  16  associated thereto are in a plane that is distanced from the plane containing the axis of the respective intake valve and orthogonal to the axis of the shaft  110 . 
     FIGS. 7–10  refer to a second embodiment of the invention, relating to an application to a Diesel engine. 
   In this case, the cams for controlling the exhaust valves  70   a  actuate said valves mechanically, but by means of rocker arm members  90  mounted oscillating at one end  91  on support  92  (known in themselves) mounted in the structure of the engine, each bearing a freely rotating roller  97  in correspondence with their intermediate portion, said roller co-operating with the respective cam  70   a  and having the opposite end to the end  91 , designated by the reference number  93 , acting against the stem of the respective exhaust valve  70   a . The camshaft  110  co-operates with the rocker arm members  60  actuating the intake valves  7  substantially on the side opposite the one co-operating with the rocker arm members  90 . 
   The particular arrangement described above enables to maintain an orientation of the intake valves  7  and of the exhaust valves  70  that is substantially parallel or in any case slightly inclined (at most by an angle of about 2°) relative to the axis of the cylinder, without compromising the complexity of the system and without requiring a large bulk. This arrangement is optimal for the good operation of the Diesel engine. 
   With reference again to said second embodiment, it comprises a system for venting the air that is formed in the hydraulic device for actuating the intake valves as a result for instance of a prolonged stop of the vehicle with its engine shut down. When the engine is started, the oil from the engine lubrication circuit reaches the pressure chamber C (see  FIG. 10 ) after passing through a first supplementary tank or silo  120 , a check valve  121 , a second supplementary tank or silo  122 , communicating with an accumulator  123  and the passage  23  controlled by the solenoid valve  24 . The tanks  120  and  122  respectively have vents  120   a  and  122   a . It should be noted that a system for venting the air present in the valve actuating device has already been proposed in the Applicant&#39;s prior European application EP 1 243 761 B1. However, the system illustrated herein has the novelty of providing a simple capacity (the tank  120 ) upstream of the check valve  121  (with reference to the direction of the flow of fluid when the engine is started, when the oil from the lubrication loop fills the hydraulic loop controlling the intake valves) with the arrival of the inflow channel  230  into the top part of the tank  120  and the outlet from the tank, obtained in its bottom. 
     FIG. 10  of the accompanying drawings is a simplified diagram of the hydraulic loop, which shows the manner in which air is vented when the engine is started. The oil from the channel  230  arrives into the top part of the silo  120  venting through the hole  120   a  communicating with the atmosphere. In the practical embodiment illustrated in  FIGS. 7–9 , said hole  120   a  is obtained in a remote position relative to the silo  120 . The oil fed to the silo  120  flows in the direction of a conduit  130  which branches from the bottom of the silo  120  letting the air contained therein vent into the atmosphere. After passing through the non return valve  121 , the oil arrives into the second silo  122 , where any additional air present therein vents to the atmosphere through an opening  123  (which in the practical embodiments shown in  FIGS. 7–9  is also situated in remote position relative to the silo  122 . The silo  122  is in communication through a channel  124  with a hydraulic accumulator  123 , known in itself, whose capacity is filled displacing a piston  123   b  against the action of a spring  123   a . From the bottom of the silo  122  branches the channel  23 , which can be placed in communication with the pressure chamber C of the device for actuating the intake valve, through the solenoid valve  24 . 
   It should be noted that the arrangement of the silo  120  with the passage  120   a  for venting air to the atmosphere, in an area positioned upstream of the check valve  121  of the hydraulic loop is an innovative element which could also be adopted independently of the arrangement forming the subject of the appended claim  1 . 
   Naturally, without altering the principle of the invention, the construction details and the embodiments may be widely varied relative to what is described and illustrated purely by way of example herein, without thereby departing from the scope of the present invention.