Abstract:
The invention relates to an invention combustion engine comprising a cylinder head ( 1 ) with at least one inlet port ( 4 ) and at least one injection device ( 6 ) per cylinder ( 2 ), which extends into the combustion chamber. In order to reduce wear of the injection device while preventing depositions in the region of the injector pocket, the top wall ( 22 ) of the combustion chamber is provided with an injector pocket ( 7 ) in the area of the mouth ( 6   a ) of the injection device ( 6 ). Preferably, at least one scavenging duct arrangement ( 10 ) extends into the injector pocket ( 7 ).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to an internal combustion engine comprising a cylinder head with at least one intake port and at least one fuel injection device per cylinder, which extends into the combustion chamber. The invention also relates to a method for operating an internal combustion engine with at least two exhaust valves per cylinder, where in at least one operating region of the engine exhaust gas is recirculated into the combustion chamber from the exhaust ports via the exhaust valves, and where a swirl flow is generated in the combustion chamber due to differing closing times of the exhaust valves. Furthermore the invention relates to an internal combustion engine comprising a cylinder head with at least two intake and two exhaust valves per cylinder, and with a valve actuating device which permits closing of the exhaust valves at different times. The invention further relates to a cylinder head for an internal combustion engine with at least two intake ports per cylinder opening into the combustion chamber, each intake port being provided with a valve seat in the area where it opens into the combustion chamber, and the openings being partly surrounded by masks formed by material projections of the top face of the combustion chamber. 
   2. The Prior Art 
   From DE 103 26 054 A1 there is known an internal combustion engine with a cylinder head, an injection device injecting fuel directly into the combustion chamber, and two intake ports per cylinder, where the intake openings are provided with rib-shaped masks surrounding the disks of the intake valves semi-circularly and facing the injection nozzle. These masks deflect the combustion air flow approximately in parallel to the lateral fuel jet in order to initiate a tumble flow in the combustion chamber. In the area of the fuel jet at least one of the masks is divided by a gap, exposing the fuel jet immediately to part of the inflowing combustion air. This should increase the efficiency of the internal combustion engine and improve ignition reliability. The gap extending over the whole height of the mask will however impair the effect of the mask. 
   In conventional direct-injection internal combustion engines the injection device extends into the combustion chamber. The exposed situation of the injector tip causes increased wear. 
   From U.S. Pat. No. 6,502,541B2 there is known an internal combustion engine in which exhaust gas can be recirculated into the combustion chamber via the exhaust valves. Internal exhaust gas recirculation is used to improve fuel consumption especially in part-load operation. To generate a swirl of the recirculated exhaust gas in the combustion chamber the exhaust valves are closed at different times. Different closing times are achieved by a phase shift in the timing of the two exhaust valves. The exhaust valves are thus also opened at different times. In order to adjust the valve timing for both valves independently of each other complex technology is required. 
   In U.S. Pat. No. 5,870,993 another internal combustion engine is disclosed with two intake and two exhaust valves per cylinder, in which internal exhaust gas recirculation from the exhaust ports into the combustion chamber can be achieved by shifting the lifting curves of the exhaust valves. By masks in the area of the two exhaust ports a swirl may be imparted to the recirculated exhaust gas in the combustion chamber. The masking of the two exhaust ports is disadvantageous at full load. 
   From EP 0 764 770 B1 there is known a cylinder head which is partially provided with masks in the area where the intake ports open into the combustion chamber, wherein the walls of the intake ports on one side of the opening are configured in such a way that the flow cross-section at low lift of the intake valve is narrowed over an angle region of approximately 180°. At low-load or part-load operation this creates a tumble flow which arises from the intake ports. 
   U.S. Pat. No. 4,974,566A discloses an internal combustion engine with two intake ports opening into the cylinder, whose walls are configured such that at small valve lifts the intake cross-section for the flow through the intake ports is narrowed in a region defined by a certain angle around the movement axis of the intake valve in such a way that at small valve lifts a tumble flow is generated. For large valve lifts the intake cross-section extends along the whole periphery of the valves, which permits satisfactory filling of the cylinder. In the part-load region the engine is operated with small valve lifts, thus giving good thermodynamic conditions for combustion due to the prevailing tumble flow. At full load the engine is operated with full valve lifts, thus achieving sufficient filling of the cylinder and sufficient torque. 
   It is the object of the present invention to minimize the above mentioned wear of the injection device in an internal combustion engine. Furthermore, the forming of deposits in the area around the entry of the injection device into the combustion chamber is to be avoided. A further aim of the invention is to achieve good fuel economy at part load without impairing full load performance. Furthermore it is an object of the invention to design a cylinder head with which combustion conditions especially at part load may be improved and emissions may be further reduced. 
   The invention achieves these aims by providing that the top of the combustion chamber has an injector pocket in the area where the injection device enters the combustion chamber, preferably with at least one arrangement of scavenging passages opening into the injector pocket. Scavenging air enters the injector pocket via the scavenging passage arrangement, thus preventing the formation of deposits. The method of scavenging the injector will not, or only slightly, impair the effectiveness of the masking. 
   In a first variant of the invention, which has no negative influence on the effectiveness of the masking, it is provided that the scavenging passage arrangement is located in the region of at least one squish surface of the combustion chamber top preferably formed by the cylinder head. Preferentially it is provided that the scavenging passage arrangement has at least one scavenging passage which starts from a flat entry area and opens into the injector pocket via a nozzle region. Advantageously the depth of the scavenging passage increases in the direction towards the injector pocket. Preferably the scavenging passage narrows in the form of a nozzle, thus causing the scavenging air to enter the injector pocket with high flow velocity. As the piston approaches upper dead center scavenging air is pressed via the squish surface into the scavenging passage arrangement and further into the injector pocket, thus cleaning out deposits from the injector pocket. 
   In a second variant of the invention it is provided that the scavenging passage arrangement departs from an intake port, preferably from the valve seat area of the intake port. If at least one intake port is furnished with a mask, it is of particular advantage if the scavenging passage arrangement is formed into the mask. Advantageously in this case at least one scavenging passage is positioned essentially radially relative to the intake port between the intake port and the entry point of the injection device. 
   In a particularly simple variant of the invention it is provided that the scavenging passage has a cross-section which is open towards the combustion chamber and is configured preferably as a slot or a groove. The slot or groove may be machined into the cylinder head in a simple manner. It is also possible, however, that the scavenging passage at least partly has a closed cross-section and is preferably formed by a bore. Preferentially it is provided that the scavenging passage arrangement has a certain distance from the bottom of the mask. The effective mechanism of the mask will be much less impaired by this measure than by a gap in the mask extending over its whole height, as shown in DE 103 26 054 A1. 
   It is provided by the invention that the longitudinal axis of at least one scavenging passage forms an angle greater than 0°, preferably between 30° and 60°, with a plane defined by the cylinder axis and the axis of the injection device. 
   To achieve a sufficient swirl effect it is advantageous if the mask extends around the intake port over an angle of 150° to 180°. In this instance the height of the mask should be between 1.5 mm and 4 mm. Preferably it is provided that the distance from the mask to the rim of the valve disk is about 0.3 mm to 0.7 mm. 
   To improve on fuel consumption at part load without impairing full-load performance it is proposed that the two exhaust valves be opened for differing lengths of time, both exhaust valves preferably opening at the same time. Via a phase adjuster the opening point of the exhaust valves may be shifted synchronously. In the case of cam-controlled operation in particular, it may be provided that the exhaust valves have exhaust valve lift curves of differing length. 
   The invention is also suitable for cam-less operation, however. 
   By simultaneously opening both exhaust valves a relatively large volume of exhaust gas may be fed into the exhaust ports at the beginning of the exhaust stroke. In this way a favourable emptying behaviour of the combustion chamber may be achieved with minimal throttling losses. This will result in a high power yield, especially at full load. 
   In the context of the invention it is provided that the difference between the closing points of the exhaust valves is 10° to 80° of crank angle, and preferably 20° to 60° of crank angle, a first exhaust valve preferably being closed immediately after upper dead center of the charge exchange process and a second exhaust valve being closed at 20° to 60° crank angle after upper dead center of the charge exchange process. The closing point is here defined as that point in time at which the exhaust valve has a residual lift of 1 mm. Differing closing points will cause swirl to be generated when exhaust gas is sucked back into the cylinder from the exhaust duct. To achieve strong swirl components it is advantageous if the recirculated exhaust gas is guided over a flow guiding surface formed by a mask in the area of at least one exhaust valve. The mask may be provided in the area of one exhaust valve only. In this way flow losses during outflow from the cylinder at full load may be kept small. In order to achieve a sufficient swirl effect it is advantageous if the mask extends around the center of the exhaust port through an angle of approximately 150° to 180°. The height of the mask should be 1.5 mm to 4 mm. Preferably it is provided that the distance of the mask from the rim of the valve disk is 0.3 mm to 0.7 mm approximately. 
   The different closing times of the exhaust valves may be realised by an asymmetrical shape of the cam of at least one exhaust valve. Preferentially it is provided that each exhaust valve is actuated by its own cam, with the cams having different closing flanks. Furthermore it may be provided that the cams have identical opening flanks and/or identical maximal cam lobes. 
   In addition, the swirl in the combustion chamber due to the intake flow from the intake ports can be increased by asymmetrical intake ports, one intake port being preferably configured such that it can be closed down. 
   Combustion conditions and emissions can be improved if the contour of the mask of at least one intake port has a flat main part of maximum height between an ascending and a descending flank and in a developed view is of asymmetrical shape, ascending and descending flanks preferably having different slope angles. 
   It is particularly advantageous if the flank of the profile closer to the combustion chamber wall has a smaller slope than the flank nearer to the center of the combustion chamber. The intake flow may thus be specifically guided to a central cylinder region generating a tumble flow in the direction of the piston axis. 
   It has been found by experiments that a particularly high stability of combustion can be attained if the mask of each port extends over an angle of 120° to 210°, measured around the center of the port opening, and preferably over an angle between 160° and 180°. Preferentially it is provided that at each port a main axis running approximately through the middle of the main part of the mask forms an angle of 70° to 120°, preferably between 80° and 110°, with a straight reference line running through the centers of the port openings. 
   The height of the mask is chosen such that at partial valve lift the opening of each intake port is laterally covered on the intake side. At full valve lift the intake valve is beyond the mask and the full intake cross-section is available. The height of the mask is 1.2 mm to 3.5 mm approximately, and preferably 1.6 mm to 2.5 mm, and even more preferably 1.6 mm to 2.2 mm. In order to avoid heavy throttling of the intake flow especially under full load it is of advantage if a clearance is provided between the mask and the valve disk, which should not exceed a quarter of the height of the mask, preferably. 
   In a particularly preferable variant of the invention it is provided that the depth of the injector recess is at most about equal to the height of the mask. By positioning the injector orifice in the area of the injector recess of the mask, the injector nozzle may extend relatively deeply into the combustion chamber. The depth of the injector recess will thus correspond to the height of the mask at most. It is furthermore of advantage if the injector recess is at a distance from the wall of the mask, this distance being at least 1 mm. This minimum distance between injector recess and wall of the mask will avoid negative influence on the intake flow. 
   The invention will now be described in more detail with reference to the enclosed drawings. 

   
     BREIF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  a cylinder head of an internal combustion engine according to the invention in a first variant, as seen from the side of the combustion chamber; 
       FIG. 2  a scavenging passage arrangement of an internal combustion engine according to the invention in an oblique view, in a second variant; 
       FIG. 3  a scavenging passage arrangement of an internal combustion engine according to the invention in a third variant; 
       FIG. 4  a scavenging passage arrangement of an internal combustion engine according to the invention in a fourth variant; 
       FIG. 5  a scavenging passage arrangement in a section along line V-V of  FIG. 1  and  FIG. 2 ; 
       FIG. 6  a scavenging passage arrangement of an internal combustion engine according to the invention in a fifth variant, in an oblique view; 
       FIG. 7  the scavenging passage arrangement of  FIG. 6  in a section along line VII-VII of  FIG. 6 ; 
       FIG. 8  a cylinder head of an internal combustion engine according to the invention in a sixth variant, as seen from the side of the combustion chamber; 
       FIG. 9  the cylinder head in a section along line XI-XI in  FIG. 8 ; 
       FIG. 10  a variant of a scavenging passage in cross-section; 
       FIG. 11  another variant of a scavenging passage in cross-section; 
       FIG. 12  a further variant of a scavenging passage in cross-section; 
       FIG. 13  the valves of a cylinder head of an internal combustion engine according to the invention; 
       FIG. 14  the cylinder head in a section along line XIV-XIV of  FIG. 13  with the exhaust valve opened; 
       FIG. 15  the cylinder head in a section analogous to that of  FIG. 14  with the exhaust valve closed; 
       FIG. 16  a valve lift/crank angle diagram; 
       FIG. 17  the developed contour of the mask of an intake port; 
       FIG. 18  the cylinder head according to the invention as seen against the combustion chamber top face; 
       FIG. 19  an oblique view of the openings of two intake ports of the cylinder head; 
       FIG. 20  the cylinder head in a section along line XX-XX of  FIG. 18 ; and in 
       FIG. 21  the mask in a section detail analogous to  FIG. 20 ; 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Parts with identical function are referred to by identical reference numerals. 
     FIG. 1  shows a cylinder head  1  of an internal combustion engine as seen from inside the combustion chamber. The cylinder head  1  has for each cylinder  2  two intake ports  4  served by intake valves  3 . The exhaust ports are not shown in the figures to keep the drawings uncluttered. 
   In the area of a transversal plane  5  between the intake ports  4  an injection device  6  enters the combustion chamber. The axis  6 ′ of the injection device  6  is inclined relative to the cylinder axis  9 . In the entry area or mouth  6   a  of the injection device  6  an injector pocket  7  is located in the cylinder head  1 . An ignition device in the area of the cylinder axis  9  is indicated by reference numeral  8 . 
   The intake ports  4  are partly screened by masks  20  in order to initiate a tumble flow in the combustion chamber. The mask  20  extends through an angle α of between 150° and 180° around the center  4   a  of the intake port  4 . The height HM of the mask  20  is 1.5 mm to 4 mm—as measured from half the height h of the valve disk rim  3   a  of the closed intake valve  3 . The distance a between the mask  20  and the valve disk rim  3   a  is 0.3 mm to 0.7 mm. Due to the mask  20  deposit-prone regions with low local flow velocities occur in the area of the injector pocket  7 , especially between the intake ports  4  and the injector entry  6   a.    
   To combat these deposits an arrangement of scavenging passages  10  is provided for each intake port  4 , which open into the injector pocket  7 . The scavenging passage arrangements  10  presented in  FIGS. 1 to 7  comprise at least one scavenging passage  10   a , an inlet region  11  and a nozzle region  12  each. The inlet region  11  has small depth t but relatively large width b and is located in the area of a squish surface  13  of the top face  22  of the combustion chamber formed by the cylinder head  1 . The width b of the scavenging passage arrangement  10  decreases towards the nozzle region  12  and attains its minimum at the opening into the injector pocket  7 . The depth t increases continuously from the inlet region  11  towards the nozzle region  12  and attains its maximum at the opening into the injector pocket  7 . In plan view the arrangement  10  of scavenging passages may be pear-shaped, club-shaped or bat-shaped as seen in  FIGS. 2 to 4  and  6 . In the variants shown in  FIGS. 2 to 5  the scavenging passage  10   a  of the scavenging passage arrangement  10  has a cross-section that is open towards the combustion chamber. Alternatively, the scavenging passage  10   b  of the scavenging passage arrangement  10  may have a closed cross-section, as shown in  FIGS. 6 and 7 , and may be inclined relative to the plane  21  of the cylinder head gasket. 
   As the piston of the internal combustion engine, which is not shown in the drawings, approaches upper dead center, the gas enclosed in the combustion chamber is pressed by the squish surfaces  13  into the inlet region  11  of the scavenging passage arrangement  10  and flows through the scavenging passage  10   a  or  10   b  into the injector pocket  7 , carrying off deposits due to the high flow velocity. 
   The variants shown in  FIGS. 8 and 9  differ from the variant described above by the scavenging passage arrangement  10  being located in the area of the intake port  4  in the form of an opening in the mask  20 . The scavenging passage arrangement  10  may in this case have at least one scavenging passage with closed cross-section, for instance formed by a bore  10   b  ( FIG. 10 ), and/or at least one scavenging passage  10   a  with a cross-section open towards the combustion chamber ( FIGS. 11 ,  12 ). The open scavenging passage  10   a  may be formed by a slot ( FIG. 11 ) or a groove ( FIG. 12 ) at a certain distance from the bottom  20   a  of the mask  20 . In this variant the scavenging passage arrangement  10  is positioned between the entry  6   a  of the injector device  6  and the intake port  4 . 
   When the intake valve  3  opens scavenging air can flow through the scavenging passage  10   a ,  10   b  from the intake passage into the injector pocket  7 , removing deposits from the injector pocket  7 . 
   The longitudinal axis  10 ′ of the scavenging passage arrangement  10  forms a angle β of 30° to 60° with a transversal plane  5 . 
     FIG. 13  shows a cylinder head  101  in a view from the combustion chamber towards the cylinder head bottom  102  of a cylinder  103 . For each cylinder  103  two intake ports  104 ,  105  and two exhaust ports  106 ,  107  open into the combustion chamber, which is not otherwise visible. Via the intake ports  104 ,  105  the combustion chamber communicates with intake passages and via the exhaust ports  106 ,  107  with exhaust passages, neither of which are shown in the drawing. The intake ports  104 ,  105  respectively the exhaust ports  106 ,  107  are controlled by intake valves  104   a ,  105   a , respectively by exhaust valves  106   a ,  107   a.    
   To improve on fuel consumption, in particular when the internal combustion engine operates at part load, internal exhaust gas recirculation may be used. Such internal exhaust gas recirculation is realized by sucking back exhaust gas from the exhaust passages into the combustion chamber subsequent to the exhaust stroke near upper dead center OTW of the gas exchange phase. In this instance a strong swirl is desirable in the combustion chamber in order to improve combustion conditions and emissions. This swirl is generated by closing the exhaust valves  106   a ,  107   a  at differing points in time. A further increase of swirl may be achieved by a mask  108  in the area of at least one exhaust port  106 . In order to keep the flow losses small at full load during outflow from the cylinder  103 , the mask  108  is placed only in the area of one exhaust port  106 . Preferably the mask  108  is located at the exhaust port  106  of the exhaust valve  106   a  with prolonged opening time. It extends over an angle α of 150° to 180° around the center  106 ′ of the first exhaust port  106 . The height HM of the mask  108  is 1.5 mm to 4 mm, as measured to half the height h of the valve disk rim  106   b . The distance a between the mask  108  and the valve disk rim  106   b  is 0.3 mm to 0.7 mm. 
     FIG. 16  shows a diagram of valve lift H over crank angle KW, in which the valve lift curve of the intake valves  104   a ,  105   a  is designated by E. A 1  is the valve lift curve of the first exhaust valve  106   a , i.e. resulting from asymmetrical lifting, A 2  is the valve lift curve of the second exhaust valve  107   a . The opening flanks RÖ of the first exhaust valve  106   a  and the second exhaust valve  106   a  are identical. The closing point AS 2  of the second exhaust valve  107   a , which differs from that of the first exhaust valve  106   a , is realized by an asymmetrical shape of the closing flank RS 1  of the first exhaust valve  106   a , relative to the opening flank. RS 2  designates the closing flank of the second exhaust valve  107   a . The different closing points AS 1  and AS 2  of the first and second exhaust valve  106   a ,  107   a  together with the common opening point AÖ result in different opening periods Δt 1  and Δt 2 . 
   The valve lift curve A 1 ′ shows a variant in which the closing point AS 1  of the first exhaust valve  106   a  also is later than the closing point AS 2  of the second exhaust valve  107   a . In this case however opening and closing flank RÖ and RS 1 ′ of the valve lift curve A 1 ′ are symmetrical. Here, too, different opening periods Δt 1  and Δt 2  of the first and second exhaust valves lead to swirl formation in the combustion chamber. 
   The opening point AÖ is the same for both exhaust valves  106   a ,  107   a . By synchronously opening the exhaust valves  106   a ,  107   a  at the beginning of the exhaust stroke, high mass flow through the exhaust ports  106 ,  107  into the exhaust duct is made possible, which is of particular importance at full load operation. Throttling losses can thus be kept small and a power drop at full load is avoided. 
   A cylinder head  201  has for each cylinder  202  two intake ports  203  opening into a combustion chamber  204 . The openings  205  of the intake ports  203  are at least partially surrounded by masks  206  formed by the cylinder head  201 , which are located on the intake side between the openings  205  of both intake ports  203  and the wall of the combustion chamber  207 . The purpose of the mask  206  is to enhance the intake tumble flow and to direct it towards one side of the combustion chamber. 
   In  FIG. 17  the contour  208  of the wall  213  of the mask  206  of an opening  205  is shown in a developed view. Between two flanks  209 ,  210  the contour has a main section  211  with maximum height HM. The contour  208  of the mask  206  is asymmetrical, one of the two flanks  209 ,  210 , i.e. flank  210  nearest to the cylinder rim  207 , having a smaller slope—defined by the angle δ 2 —than the other flank  209  nearer to the cylinder center  212 . The slope angle of the other flank  209  is designated  61 . 
   The main section  211  of the wall  213  of the mask  206  extends around the center  214  of the exhaust port over an angle α between 120° and 210°, with best results being obtained with an angle between 160° to 190°. 
   The direction  215  of the mask  206  is defined by a main axis  215  running through the center M of the main section  211  of the wall  213  and the valve center  214 . The direction angle β 1 , which is formed by the main axis  215  and a reference line  216  through the valve centers  214 , has a value approximately between 70° and 120°, preferably between 80° and 110°. This will achieve an optimally developed tumble flow and particularly good mixture preparation. 
   Reference numeral  217  designates the openings of the exhaust ports. 
   On the intake side an injector recess  218  is provided in the mask  206  between the openings  205  of the intake ports  203 , the distance a′ between recess  218  and wall  213  being at least 1 mm, and with the symmetry axis  219   a  of the injection valve  219  forming an angle γ of 20° to 30° with the cylinder head plane  221 . It is essential that the jet cone  227   b  of the injection jet  227  is distinctly kept away from the combustion chamber top  222  and the cylinder wall. The center line  227   a  of the injection jet  227  may also be slightly inclined against the symmetry axis  219   a  of the injection valve  219 . The angle ε between the symmetry axis  227   a  of the injection jet  227  and the combustion chamber top  222  is roughly 33° to 40°. Due to this configuration the injector tip  220  may extend fairly deeply into the combustion chamber  204 , which will permit precise fuel injection and will avoid wetting of the combustion top face  222 , of the opposite combustion chamber wall and of the intake valves  223 . 
   The maximum height HM of the mask  206  is between 1.2 mm and 3.5 mm approximately and is chosen such that at partial lift of the intake valve  223  the intake opening between valve disk  224  and valve seat  225  is essentially covered laterally except for a clearance  226  forming a gap S. The gap S may have a width of 0.2 mm to 0.6 mm, preferably a quarter of the height HM of the mask  206  at most. When the valve lift h v  of the intake valve  223  exceeds 2.0 mm approximately, the intake opening is freed also on the side of the mask  206 , permitting maximum filling of the cylinder especially at full load. In  FIG. 21  the dotted lines show the maximum possible valve lift of the intake valve  223  at which the intake gap S between valve disk  224  and valve seat  225  will still be just covered by the mask  206 . The height of the valve disk rim is designated h. In the position shown the intake valve  223  extends beyond the mask by e=h/2. The height HM of the mask is thus the predefined valve lift h v  plus half the height h of the valve disk rim. 
   It is of particular advantage if the cylinder head  201  is furnished with a device which permits valve lift to be fully variable, in which case the merits of the mask  206  can be fully exploited.