Abstract:
A device for actuating the decompression engine brake in an internal combustion engine provided with hydraulic tappets is described, characterized by: an additional rocker arm ( 9 ) for each cylinder, pivoting about an axis ( 4 ) common to the rocker arms of the exhaust valves, and suitable to engage with a corresponding additional cam ( 10 ) arranged on the cam axis ( 7 ) of the cylinders; an actuator system for said additional rocker arm ( 9 ), for each cylinder. In the actuator system of said additional rocker arm ( 9 ) there is a piston ( 15 ) hinged to an end of said rocker arm, said piston ( 15 ) being in its turn moved hydraulically or by a mechanical system comprising an additional arm ( 12 ) controlled by eccentric cams ( 13 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for actuating the engine brake in an internal combustion engine and, more specifically, to a device for actuating the decompression engine brake in an internal combustion engine provided with hydraulic tappets. 
     PRIOR ART 
     Systems are known in the prior art in which an additional exhaust valve or flap is added to increase the pressure, pressurize the engine and increase braking power. 
     However, such systems are inadequate for high power applications. 
     For applications involving high inertia loads, for example in the case of heavy goods vehicles, compression release engine braking systems are used, in which the exhaust valve(s) is (are) opened prematurely with respect to the piston motion. This is effected by additional openings of the exhaust valves by means of specific actuators. 
     For example an additional opening of the exhaust valves can be effected by means of an additional cam lift at the end of the compression stage, with a cam advance of approx. 70 degrees. 
     Therefore the principle of braking the engine inertia is based on the decompression in the combustion chamber during the compression stage stroke is already known in the art. Such systems use the energy accumulated in the form of pressure during the air compression cycle to “brake” the inertia or mass connected to the crankshaft. 
     Some of the decompression engine braking systems known in the art are used in engines provided with mechanical tappets. These however are more robust than hydraulic tappets, and also accept loads with a horizontal component, which simplifies the actuating mechanisms required to actuate the decompression. 
     Engines provided with hydraulic tappets however present an additional problem in that such tappets are more fragile than the mechanical ones. 
     In order to work, hydraulic tappets always require a minimum vertical load, which provides a constant (at least minimum) pressing force, otherwise they expand too much and risk being damaged. 
     Moreover, hydraulic tappets are able to withstand loads with a vertical component, but can only accept loads with a modest horizontal component. A horizontal component could cause permanent damage. 
     Therefore devices and/or actuators must be provided which increase the complexity of the mechanisms, and the problem arises of the need for solutions that are not excessively complicated, bulky or expensive. 
     SUMMARY OF THE INVENTION 
     Therefore the aim of the present invention is to overcome the drawbacks and disadvantages of the prior art with a decompression braking device for an internal combustion engine provided with hydraulic tappets that is extremely simple to produce and thus highly reliable. 
     Another purpose of the present invention is to provide a decompression braking device for an internal combustion engine provided with hydraulic tappets, that is robust, of limited dimensions, requires little maintenance and represents a low cost solution. 
     The present invention relates to a device for actuating the compression release engine brake in an internal combustion engine, said combustion engine comprising: one or more cylinders in line each provided with one or more exhaust valves; respective rocker arms and hydraulic tappets being connected to said exhaust valves; said rocker arms being provided with a common axis for each cylinder; a cam axis for said one or more cylinders in line, characterized in that it comprises: at least one additional rocker arm for each cylinder, pivoting about said common axis and suitable to engage with a corresponding additional cam arranged on said cam axis; at least one actuator system for said additional rocker arm, for each cylinder. Moreover, the device according to the present invention may advantageously comprise at least an additional shaft provided with one or more additional cams, suitable to determine the motion of said actuator system for each cylinder, so that in a first position of said additional shaft, said additional rocker arm does not come into contact with said one or more additional cams, and in a second position of said additional shaft said additional rocker arm comes into contact with said one or more additional cams to determine the actuation of said engine brake. 
     As an alternative, the device for actuating the compression release engine brake according to the present invention, may comprise, instead of said additional shaft provided with one or more additional cams, a hydraulic actuator system of the rocker arm, which exploits the oil pressure in the engine circuit. 
     In particular the present invention relates to a device for actuating the decompression engine brake in an internal combustion engine provided with hydraulic tappets, and the relative engine provided with said device, as described more fully in the claims, which are an integral part of this description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be illustrated through the following detailed description of a preferred embodiment of the decompression braking device in an internal combustion engine provided with hydraulic tappets according to the present invention, provided merely by way of example, with the help of the drawings attached hereto in which: 
         FIGS. 1 to 4  are views from different angles of the part of the cylinder head comprising the device for actuating the engine brake object of this invention, according to a first embodiment comprising an actuator system of said additional rocker arm by using shaft and rocker arms; 
         FIGS. 5 and 6  are front and rear perspective views of the device for actuating the engine brake object of this invention according to the first embodiment shown in the figures from  1  to  4 ; 
         FIGS. 7 and 8  are side views of the part of the cylinder head comprising the device for actuating the engine brake object of this invention according to a first embodiment, respectively with the engine brake activated and deactivated; 
         FIGS. 9 and 10  are respectively a rear and side cross-section perspective view of the part of the cylinder head comprising an alternative embodiment of the device for actuating the engine brake according to this invention; 
         FIGS. 11 and 12  show lateral views of the cylinder head part comprising the device for actuating the engine brake object of this invention according to a third embodiment of the actuator system, respectively in case of activated engine brake or deactivated engine brake. 
     
    
    
     In the drawings the same numbers and letters indicate the same parts and components. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The drawings show a part of the engine block  1  comprising a cylinder of a known type provided with a couple of exhaust valves  2 . 1  and  2 . 2 , which are joined to one end of respective rocker arms  3 . 1  and  3 . 2 . 
     A couple of hydraulic tappets  5 . 1  and  5 . 2 . are joined to the other end of the rocker arms. 
     The rocker arms can rotate about a common axis  4  that comprises respective rollers  6 . 1  and  6 . 2 . 
     A cam axis  7  arranged in a conventional manner over the rollers  6 . 1  and  6 . 2  comprises specific eccentric cams  8 . 1  and  8 . 2  for the normal opening/closing of the exhaust valves  2 . 1  and  2 . 2 . 
     In the engine there are normally a given number of cylinders in line (not shown in the drawings), which have the cam axis  7  in common. 
     According to the invention the engine brake function is actuated as follows. 
     An additional element  9  with the function of a rocker arm (hereinafter referred to as the rocker arm) is inserted and pivots centrally about the same axis  4  that is common to the other two rocker arms  3 . 1  and  3 . 2 , in an intermediate position between the latter; a third cam with eccentric  10  is included on the existing common cam axis  7 . 
     At one end of the rocker arm  9  (the end towards the exhaust valves) there is a roller  11 , while the other end  17  of the rocker arm  9  (towards the hydraulic tappets) is joined to an actuator system. According to a first preferred embodiment of the device according to the present invention, said actuator system comprises an additional shaft  12 , provided with a cam  13 . 
     Therefore, according to such first preferred embodiment, in the actuator system an end of a connecting rod  14  is inserted on the cam  13  and the other end of said connecting rod pivots about the end of a piston (or pin)  15 , which can slide inside an appropriate retaining housing (hole or recess)  16  in the engine block. 
     The end  17  of the rocker arm  9  pivots about the piston  15 . In operation, the additional shaft  12  can rotate and assume two different angular positions indicated by letters A and B in the drawings. Thanks to the eccentric cam  13 , the connecting rod end  14  connected thereto can assume two corresponding positions in order to move the piston  15  to a raised position or a lowered position. 
     In the raised position of the piston  15  (angular position A of the axis  12 ,  FIG. 8 ) the rocker arm  9  rotates about the axis  4  so as to move the roller  11  away from the eccentric cam  10 . In this condition the eccentric cam  10  never comes into contact with the roller  11 . In this way the engine brake function is always deactivated. 
     In the lowered position of the piston  15  (angular position B of the axis  12 ,  FIG. 7 ), the rocker arm  9  rotates about the axis  4  and moves the roller  11  so that it comes into contact with the eccentric cam  10 . In this way the engine brake function is activated; in fact the eccentric cam  10  is able to actuate the rocker arm  9  and lower it so as to determine an additional opening of the exhaust valves  2 . 1  and  2 . 2 , besides that determined by the eccentric cams  8 . 1  and  8 . 2  and by the rocker arms  3 . 1  and  3 . 2 . 
     When the eccentric cam  10  is placed in an appropriate angular position, the additional opening of the exhaust valves  2 . 1  and  2 . 2  is effected in a given phase of the engine cycle, towards the end of the compression phase, with a cam advance of approx. 70 degrees with respect to the normal exhaust phase. 
     In the example of the embodiment described here there is a distance of approx. 80 degrees between the two angular positions A and B. 
     In the case of cylinders in line in the engine, the additional shaft  12  is preferably common to all the cylinders in line, and is actuated, for example, by means of a pneumatic actuator, to actuate the engine brake function, by moving it from angular position A to angular position B. 
     According to a second preferred embodiment of the actuator system of the rocker arm  9  of the device according to the present invention, shown in particular in  FIGS. 9 and 10 , instead of the connecting rod  14  and the piston  15 , there is a cylinder arm and spring system, comprising:
         a supporting plate  20  arranged against the eccentric cam  13  of the shaft  12 ;   a first shaped body  21  at the upper end of which said plate  20  is present, and at the other end of which a cavity  22  is present into which a spring  23  is inserted;   a second cylindrical body  24  set in the head, the outer end of which enters the cavity  22  and engages with the contrast spring  23 , which holds the plate  20  against the eccentric cam  13 .       

     The end  17  of the rocker arm  9  pivots about the shaped body  21 . 
     The two angular positions A and B of the eccentric cam  13  determine the lifting or lowering of the plate  20  and of the shaped body  21  contrasted by the spring  23 , and the two consequent positions of the rocker arm  9  to actuate or deactivate the engine brake function. The form of the shaped body  21  is such as to adapt the relative positions of the axes of the second cylindrical body  24  and of the additional shaft  12 , and guarantee the perfect sliding of the two bodies  21  and  24 . 
     Also, according to a third preferred embodiment of the actuator system of the engine brake device according to the present invention, the rocker arm  9  is hydraulically controlled by exploiting the oil in pressure in the oil engine circuit. 
     In this case, as shown in  FIGS. 11 and 12 , neither the additional shaft  12  nor the eccentric cams  13  are present, and the piston  15  is directly activated by the hydraulic circuit. The movement of the piston between a position A of deactivated engine brake, shown in  FIG. 12 , and a position B of activated engine brake shown in  FIG. 11 , corresponds to the movement of the additional rocker arm  9 , as for the embodiments previously described, between a position wherein the roller  11  does not come into contact with the cam ( FIG. 12 , deactivated engine brake) and a position wherein the roller  11  comes into contact with the third cam  10  ( FIG. 11 . activated engine brake). 
     In this case, as said, the movement of the piston  15  between the position A and the position B is directly controlled by a hydraulic actuator system, this results in a further advantage because additional components such as the additional shaft  12  and the eccentric cam  13  are no longer necessary. 
     This last alternative embodiment of the hydraulic brake device according to the present invention has therefore a particularly simple construction and installation, being also less bulky so that it can more easily housed in the cylinder head cover. 
     In the case of engines in which the cylinders have a single exhaust valve, the present invention can be adapted by introducing a few variations within the scope of the invention, for example using the axis  7  of the eccentric cams that control the opening of the exhaust valves, and the axis  4  of the exhaust valve rocker arm, where a double rocker arm can be inserted on said axis  4 , so as to “straddle” the one that is already normally present and control this additional opening phase, acting in exactly the same way as the rocker arm  9  described above. 
     In case of engines with more than one line of cylinders, for example two lines, a device of the type described above is fitted for each line of cylinders. 
     The decompression braking device according to the present invention has several advantages. 
     Firstly, the braking device according to the present invention is extremely simple to produce and highly reliable. It absorbs all horizontal loads, eliminating these on the hydraulic tappets, and uses the same axis as the existing tappets. 
     It introduces a single control axis that is easily installed on the cylinder head, only requiring some slight variations to the production of existing engines, using space that is available on the cylinder head cover. It can be actuated by means of a single control and therefore takes up a limited amount of space, it is robust and requires little maintenance and is therefore a low cost solution. 
     Moreover the actuator can be of any suitable type; one advantage of the present invention is that it can be mounted on the outside of the engine and in particular on the tappet cover. This means there are no particular problems as regards the compatibility of the actuator with the environment in which it is installed, due for example to temperature, vibrations, the presence of oil. 
     The use of the engine braking device with hydraulic tappets according to the present invention avoids the need to adjust valve clearance during the engine&#39;s working life (maintenance free).