Patent Publication Number: US-7721689-B2

Title: System and method for controlling fluid flow to or from a cylinder of an internal combustion engine

Description:
This application claims the benefit of U.S. Provisional Application No. 60/877,362, filed Dec. 28, 2006. 

   TECHNICAL FIELD 
   The present application relates in general to internal combustion engines, and in particular to a system and a method for controlling fluid flow to or from at least one cylinder of the internal combustion engine. 
   BACKGROUND 
   Internal combustion engines typically have a main body forming cylinders and a cylinder head for closing one end of cylinders. The cylinders, pistons reciprocating in the cylinders, and the cylinder head define a combustion chamber having a variable volume therebetween. A valve is arranged in the internal combustion engine, to provide one of a flow of air and a mixture of air and fuel into the combustion chamber. Typically a separate valve is arranged in the cylinder head to provide exhausting of exhaust gases from the combustion chamber. 
   In most internal combustion engines poppet valves are used to control the inflow and outflow of gases into the combustion chamber. These poppet valves are typically activated by a camshaft, which is rotatably coupled by a drive element to a crankshaft of the internal combustion engine. The rotatable coupling of the crankshaft to the camshaft provides a constant ratio between the speed of rotation of the crankshaft and the speed of rotation of the camshaft. The activation of the individual valves is thus fixed to the rotation of the crankshaft. Sometimes no independent control of the valves is possible even if it is desired to achieve improved engine performance and/or emission characteristics. 
   The poppet valves are typically spring biased to a closed position thereof. To open the valve, the camshaft has to first overcome the bias of the springs, which leads to large energy expenditure for opening of the valves. 
   An alternative internal combustion engine using spherical rotary intake and outlet valves in a cylinder head is shown in U.S. Pat. No. 6,779,504, issued to Coates on Aug. 24, 2004. The Coates cylinder head is formed by two separate body portions. The body portions when assembled to each other define a plurality of spherical valve chambers each conformed to the shape of a single spherical valve to be accommodated therein. The spherical rotary valves are mounted to a drive shaft, which is rotatably coupled to the crankshaft of the internal combustion engine. The rotatable coupling of the crankshaft to the camshaft again provides a constant ratio between the speed of rotation of the crankshaft and the speed of rotation of the camshaft. Again no flexibility is provided for changing the timing of valve opening and closing events with respect to the crankshaft position. 
   Flow of air between the cylinder head and the cylinder is controlled by each of the spherical rotary valves accommodated in the cylinder head. In particular, flow of gases is allowed through an opening in the spherical surface of the rotary valve, which is brought into alignment with a flow opening in the lower body part of the cylinder head, and through the side surfaces of the spherical rotary valves. 
   At the beginning of a valve opening event, the flow through the rotary valve increases gradually. Similarly, at the end of an opening event, the flow through the rotary valve decreases gradually. A fast opening and closing would, however, be desired to optimize the flow of gases through the rotary valves. 
   The present application is directed to overcoming one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present application, a system for controlling fluid flow to or from at least one cylinder of an internal combustion engine includes a rotary valve and a cylinder head. The cylinder head has a valve chamber accommodating the rotary valve, and the rotary valve is arranged to selectively open or close a flow opening in the cylinder head. A drive motor is coupled to the rotary valve to impart rotation thereto. 
   In another aspect of the present application, a method for controlling fluid flow to or from a cylinder of an internal combustion engine includes imparting a rotation to a rotary valve. The rotary valve is arranged in a cylinder head of an internal combustion engine to selectively open or close a flow opening which is associated with the cylinder. The rotation to the rotary valve is imparted by a drive a motor coupled to the rotary valve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of parts of an internal combustion engine having an exemplary cylinder head; 
       FIG. 2  is a perspective view of the cylinder head of  FIG. 1 ; 
       FIG. 3  is a top view of the cylinder head of  FIG. 2 ; 
       FIG. 4  is a perspective view showing the bottom of the cylinder head of  FIG. 1 ; 
       FIG. 5  is a perspective showing the top of the cylinder head of  FIG. 1 , having a cover plate mounted thereon; 
       FIG. 6  is a cross-sectional view of the cylinder head along line VI-VI in  FIG. 3 , having additional elements mounted therein; 
       FIG. 7  is a cross-sectional view along line VII-VII in  FIG. 6 ; 
       FIG. 8  is a cross-sectional view along line VIII-VIII in  FIG. 7 ; 
       FIG. 9  is a partial top view of the cylinder head of  FIG. 2 , having rotary valves arranged therein; 
       FIG. 10  is an end view of an alternative cylinder head; 
       FIG. 11  is a top view of an exemplary rotary valve to be used in a cylinder head of an internal combustion engine; 
       FIG. 12  is a cross-sectional view of the rotary valve along line B-B in  FIG. 11 ; 
       FIG. 13  is a side view of the rotary valve of  FIG. 11 ; 
       FIG. 14  is a cross-sectional view of the rotary valve along line A-A in  FIG. 11 ; 
       FIG. 15  is another side view of the rotary valve of  FIG. 11 ; 
       FIG. 16  is perspective view of the rotary valve of  FIG. 11 ; 
       FIG. 17  is cross-sectional view similar to  FIG. 14  of an alternative rotary valve; 
       FIG. 18  is cross-sectional view similar to  FIG. 12  of an alternative rotary valve; 
       FIG. 19  is cross-sectional view of a drive shaft for rotating rotary valves; 
       FIG. 20  is an enlarged cross-sectional view of a section of the drive shaft according to  FIG. 19 , having a rotary valve mounted thereon; 
       FIG. 21(   a ) is a cross-sectional view of a deflector/bearing assembly; 
       FIG. 21(   b ) is a cross-sectional view of an alternative deflector/bearing assembly; 
       FIG. 22  is a cross-sectional view of a deflector assembly; 
       FIG. 23  is a schematic end view of an internal combustion engine showing a drive mechanism for driving rotary valves arranged in the cylinder head of the internal combustion engine; 
       FIG. 24(   a ) is an end view of an internal combustion engine; 
       FIG. 24(   b ) is a top view of an internal combustion engine, showing an alternative drive mechanism for driving rotary valves arranged within the cylinder head of the engine; 
       FIG. 25  is an end view of an internal combustion engine showing another alternative drive mechanism for driving rotary valves arranged within the cylinder head of the combustion engine; 
       FIG. 26(   a ) is an end view of an internal combustion engine; 
       FIG. 26(   b ) a top view of an internal combustion engine; and 
       FIG. 26(   c ) is an enlarged schematic cross-sectional view through a drive motor; wherein a further alternative drive mechanism for driving rotary valves arranged within the cylinder head is shown. 
   

   DETAILED DESCRIPTION 
   In the following description, relative terms such as top, bottom, side, left right etc. may be used to describe certain elements. These relative terms are used for descriptive purposes only and should not be construed to limit the application. In the following, a flow area will be specified for openings and passages etc. In these instances the term “flow area” will relate to the smallest cross sectional area of the opening, passage etc. 
   Reference signs are used in the following description and drawings to describe the examples shown in the drawings. Throughout the different views and examples, the same reference signs may be used to designate similar parts. 
     FIG. 1  shows a perspective view of an internal combustion engine  1  in accordance with an embodiment of the application. For simplification, an engine main body  3  and crankshaft housing  4  are only schematically shown, while a cylinder head  7  of the engine  1  is shown in more detail. As one of ordinary skill would recognize, engine main body  3  may have at least one cylinder (not shown) formed therein, for accommodating a corresponding number of pistons therein. The exemplary engine main body  3  shown in  FIG. 1  has four cylinders formed therein. The present application, however, is not limited to an engine having four cylinders. 
   The crankshaft housing  4  is adapted to accommodate a crankshaft which is coupled to the pistons as is known in the art. The crankshaft housing  4  has an opening  9  in at least one end thereof to allow part of the crankshaft to extend outside of the crankshaft housing  4 . 
   The cylinder head  7  will now be described in more detail with respect to  FIGS. 2-9  of the drawings which show an exemplary cylinder head. The cylinder head  7  includes a single piece cylinder main body  11  and a cover plate  12  which is best shown in  FIG. 5 . The cylinder main body  11  has a top surface  15  (best seen in  FIGS. 2 and 3 ), a bottom surface  16  (best seen in  FIG. 4 ), opposite end faces  17  and  18  (best seen in  FIGS. 4 and 5 ), and opposite sides  19 ,  20  (best seen in  FIGS. 4 and 5 ). 
   The cylinder main body  11  has a plurality of valve chambers  24  formed therein as is best shown in the cross-sectional views of  FIGS. 6-8 . In particular, eight separate valve chambers  24  are provided. The valve chambers  24  are divided into two groups A and B ( FIG. 7 ) of four valve chambers  24  each. The two groups A and B of valve chambers  24  each form a row of adjacent valve chambers  24 . The valve chambers  24  of group A are air-inlet chambers and the valve chambers  24  of group B are exhaust chambers, as will become more apparent below. A bottom section of the valve chambers  24  (i.e., adjacent the bottom surface  116 ) is shaped to conform to the shape of the rotary valve to be received therein. Passages  27 ,  28  extending between the end faces  17 ,  18  and through the valve chambers of groups A, B, respectively, are formed in the main body  11 . 
   As will be described in more detail herein below, each valve chamber  24  is shaped to accommodate two rotary valves  30  in a side-by-side arrangement, for example, as shown in  FIG. 7 . 
   Insertion passages  32  are provided in the cylinder main body  11  of the cylinder head  7  extending between each of the valve chambers  24  and the top surface  15 . As may be best seen in  FIG. 3 , each of the passages  32  defines a generally heart-shaped opening  33  in the top surface  15 . Each opening  33  and insertion passage  32  is sized to allow a rotary valve  30  to be inserted therethrough into the associated valve chamber  24 . Each insertion passage  32  widens from its respective opening towards its respective valve chamber  24  in a longitudinal direction (see  FIG. 6 ), but has a constant width in a direction normal to the longitudinal direction (see  FIG. 8 ). 
   Flow passages  36  are provided in the main body  11  extending between each valve chamber  24  and the bottom surface  16 . Two flow passages  36  are provided between each valve chamber  24  and the bottom surface  16  (one for each rotary valve to be accommodated therein). In particular, the flow passages  36  extend between the valve chambers  24  and recesses  38  formed in the bottom surface of the main body  11 . In the exemplary cylinder head  7 , four recesses  38  are formed. The recesses  38  are sized to correspond to the cylinders formed in the engine main body and are arranged to be aligned therewith. The recesses  38  form so-called flame faces for the cylinders in the engine main body. Each recess  38  is fluidly connected to two separate valve chambers  24 , one valve chamber  24  of group A and one valve chamber  24  of group B. Each of the flow passages  36  defines an opening  39  in one of the spherical recessions  38 . Each flow passage  36  tapers from its respective valve chamber  24  towards the corresponding opening  39 . 
   In several of the figures, it can be seen that certain of the flow passages  36  and their corresponding openings  39  towards the spherical recessions  38  are of a different size to others. The reason for these different sizes being that the flow passages  36  having smaller dimensions are shown in a pre-finished state, such as a cast state. The flow passages  36 , however, having larger dimensions are shown in a finished state. It should be noted that only the valve chambers  24  having the rotary valves  30  shown therein are shown in a finished state. The other valve chambers  24  (and passages  36 ), however, will be similar to those having the rotary valves  30  therein, once they are finished. 
   The insertion passages  32  and the flow passages  36  are arranged in the engine main body  11  such that there is a substantially straight line of access through the insertion passages  32  towards the flow passages  36 . Circular sealing arrangements  44  are provided within each valve chamber  24  (once they are finished). The circular sealing arrangements are arranged such that they surround each opening of the passage  36  towards the valve chamber  24  and are arranged coaxially thereto. Each sealing arrangement  44  is accommodated in a corresponding seat, machined into a surface of the valve chamber surrounding each passage  36  (see  FIG. 6 ). 
   A longitudinally extending air-duct  47  is provided in the exemplary main body  11 . The air-duct  47  is open towards the end face  18  at opening  48 . The opening  48  may be closed by a cover (not shown), when the cylinder head  7  is assembled. Passages  49  and  50  are provided which extend between the air-duct  47  and the top surface  15 . The air-duct  47  extends adjacent the side  19  of the main body. In the area of the air-duct  47 , the bottom surface  16  is recessed. 
   A flow passage  55  is provided between each valve chamber  24  of group A of the valve chambers  24  and air-duct  47 . The flow area of the flow passage  55  is larger than the combined flow area of the flow passages  36  associated with the valve chamber  24  to which the flow passage  55  is connected. Also, the flow area of the air-duct  47  is larger than the flow area of the flow passage  55 . 
   An exhaust passage  60  is provided between each valve chamber  24  of group B and the side  20  of the main body  11 . Each exhaust passage  60  opens towards the side  20  of the cylinder main body  11  at a corresponding opening  62 . The flow passages  60  each taper from their corresponding valve chamber  24  towards the side  20  of the main body. The flow area of the flow passage  60  at the opening  62 , however, is larger than the combined flow area of the flow passages  32  associated with one of the valve chambers of group B. 
   The cylinder main body  11  also has mounting holes  65  extending between the top surface  15  and the bottom surface  16 . At the top surface  15 , the mounting holes  65  have an enlarged diameter to allow the head of a mounting bolt to be received therein. 
   The cylinder main body  11  also has injector passages  67  which extend between the top surface  15  and the bottom surface  16  thereof. The injector passages are each arranged to open in the center of one of the spherical recessions  38  formed in the bottom surface  16  of the main body  11 . The injector passages  67  extend through a part of the main body which separates the group A of the valve chambers  24  from the group B. As is best shown in  FIG. 8 , the injector passage has multiple steps decreasing in diameter from the top surface  15  towards the bottom surface  16  of the main body  11 . Similarly, the wall portion separating the two valve chambers  24  of groups A and B also decreases in width from the top surface  15  towards the bottom surface  16 . Further, mounting holes  69  and  70  are provided in the top surface  15 . The mounting holes  69  and  70  are provided with internal threads. The mounting holes  70  are arranged on a line with the injector passages  67 . 
   The top surface  15  has a recessed main part of a rectangular shape. The recessed main part has a finished surface to allow sealing to the cover plate  12 , as will be described below. The insertion openings  33 , the mounting holes  65 , the injector passages  67 , and the mounting holes  69  and  70  are each formed in the recessed main part of the top surface  15 . The top surface  15  also has a finished flat surface surrounding each of the passages  49  and  50 , to allow sealing to air supply ducts, as will be described in more detail below. 
   The bottom surface  16  has a finished flat main surface for sealing to the engine main body. Outside of the sealing surface, the spherical recessions  38  and the recess  53  are provided. 
   The side  20  of the cylinder main body  11  also has finished flat surfaces, at least around the openings  62  of the flow passages  60 , to allow sealing to an exhaust manifold. 
   The cover plate  12  is a substantially flat rectangular plate. The cover plate  12  is dimensioned to sit in the recessed main part of the top surface  15  of the main body  11 . The cover plate  12  has a top surface  80  and a bottom surface  82 . The bottom surface  82  is a flat finished surface, to allow sealing to the recessed main part of the top surface  15  of the main body  11 . Even though not shown, a sealing arrangement may be arranged between the cover plate  12  and the cylinder head  7 , when mounted thereon. 
   The cover plate  12  has a plurality of mounting holes  84  extending between its top surface  80  and its bottom surface  82 . The number of mounting holes  84  and their arrangement corresponds to the number and arrangement of mounting holes  69  and  70  formed in the top surface  15  of the main body  11 . The cover plate  12  also has openings  86  extending between the top and bottom surface thereof. The openings  86  are sized to accommodate part of an injector arrangement (not shown) therein. The openings  86  are arranged such that they are aligned with the injector passages  67  in the main body  11 , when the cover plate  12  is mounted thereon. 
   Having described above an exemplary cylinder head  7 , it should be noted that the application is not limited to the specific cylinder head configuration. In particular, as mentioned above, the valve chamber  24  is shaped to receive two rotary valves  30  therein. The valve chamber  24 , however, may be shaped to receive a single rotary valve or a larger number than two rotary valves  30  therein. Furthermore, if two or more rotary valves  30  are used, these do not necessarily have to be arranged in a side-by-side arrangement as shown. 
   Independent of the number of rotary valves  30  per valve chamber  24 , the several passages arranged within the cylinder head  7  may remain the same. Only the number of flow passages  36  might be adapted. Furthermore, the cylinder head  7  as shown is configured to serve four cylinders of an internal combustion engine. The cylinder head  7  may, however, be adapted to serve any number of cylinders. Especially in large engine applications, one cylinder head may be provided per cylinder of the engine. 
   Even though the cylinder main body  11  of the cylinder head  7  is shown as a single piece cylinder main body  11  having valve chambers  24  formed therein, the cylinder main body  11  could include two or more body parts, such as an upper and a lower body part, which when assembled form the valve chambers  24  and the respective flow passages. In such a split design, the insertion openings  32  may be dispensed, as cylinders may be inserted into the valve chambers  24  before assembly of the body parts. For the same reason, the cover plate  12  could be dispensed. 
   Where the cover plate  12  is used to cover the insertion openings  32  in the cylinder head  7 , the surface of the cover plate  12  facing to the cylinder head  7  may not be flat. It may rather have one or more projections dimensioned to fit into the insertion passages  32  to at least partially fill those. Apart from such projections, the surface of the cover plate  12  facing the cylinder head  7  may again be a flat finished sealing surface. 
   Though not shown, cooling fluid passages may be arranged within the cylinder head main body  11  of the cylinder head  7 . In particular, a cooling fluid passage may be provided within an elevated wall portion between adjacent flow passages  36 , adjacent each valve chamber  24 , and in particular circumferentially around the longitudinally extending passages  27  and  28 . In the one-piece design of the cylinder main body  11  cooling fluid passages may extend substantially from the bottom to the top of the one piece cylinder head main body  11 . 
   In the example shown in  FIG. 7 , longitudinal passages  27 ,  28  are provided in the cylinder head  7 . It would also be possible to provide passages extending transverse in the valve body to accommodate a drive shaft therethrough. In such a case, the drive shaft would extend from the side portions of the cylinder head  7 . The valve chamber  24  may be adapted accordingly and possibly the location of some of the flow passages also may be adapted. Having passages for accommodating drive shafts extending transverse to the valve body may be an option in a cylinder head configured for a single cylinder. 
     FIG. 10  shows schematically an end view of another exemplary cylinder head  107 . The cylinder head  107  has a cylinder head main body  111  having a top surface  115 , a bottom surface  116 , end faces (only one of which is shown), and sides  119  and  120 . Valve chambers  124  are provided within the cylinder head main body  111 . The valve chamber  24  may be of substantially the same shape as in the cylinder head  7  described above. The valve chamber  124  and other internal parts of the cylinder head main body  111 , which will be described herein below, are indicated by broken lines. 
   Longitudinal passages  127  and  128  extend between the end faces of the cylinder head main body  111 . The passages  127 ,  128  are again arranged to extend through separate groups A, B of valve chambers  124 . Rotary valves  130  are schematically indicated, to be received in the valve chambers  124 . Passages  132  are provided in the cylinder head main body  111  extending between each of the valve chamber  124  and the top surface  115 . The bottom surface  116  again has recessions  138  and flow openings between the individual valve chamber  124  and the recessions  138  are provided as in the cylinder head  7 , described with respect to  FIGS. 1-9 . An injector passage  67  is also provided between each recession  138  in the bottom surface  116  and the top surface  115 . 
   One major difference between the cylinder head  107  and the cylinder head  7  described before is that no additional flow passages such as the flow passages  47 ,  55 , and  60  are provided. Fluid flow into or out of the respective valve chamber  124  is provided via the passage  132  which is a combined insertion/flow passage. Furthermore, the shape of the top surface  115  differs from the shape of the top surface  15  described before. 
   The top surface  115  of the cylinder head main body  111  has a longitudinally extending central portion  180  which is horizontally arranged. A part  181  of the top surface  115  is angled with respect to the central part  180  and extends between the central part  180  and the side  119 . A further part  182  of the top surface  115  is also angled with respect to the central part  180  and extends between the central part  180  and the side  120 . 
   Passages  132  extending from valve chambers  124  of group A open towards part  181  of the top surface  115 . Passages  132  extending from valve chambers  124  of group B open towards part  182  of the top surface  115 . The passages  132  have a main extension which is substantially at right angles to its respective part  181 ,  182 . The parts  181  and  182  of the top surface  115  are angled with the same angle with respect to the central part  180 . The part  181  is arranged with respect to the spherical recession  138  in the bottom surface  116 , such that a plane parallel to the part  181  may be tangential to the spherical recession  138  in the area of the valve chamber. The same is true for part  182 . 
   The cylinder head  107  may thus be formed symmetrical with respect to a longitudinal plane extending normal and through the center of part  180  of the top surface  115 . The parts  181  and  182  are each substantially flat and are finished in order to allow a sealing to respective flow manifolds (not shown) to be mounted thereon and sealed therewith. Respective mounting holes (not shown) are provided in each of the parts  181  and  182  of the top surface  115 . 
   Even though the top surface  115  described above has a central part and two angled parts, it would be possible to dispense with the central part  180  and just to have two angled parts. The angled parts would be angled with respect to each other and with respect to the bottom surface of the cylinder head  107 . An angle included between angled part  181  or angled part  182  is for example in a range between 20 to 50 degrees or in a range between 30 to 40 degrees. 
   As mentioned above, each of the valve chambers  24  or  124  of the cylinder head  7  or  107  is shaped to accommodate two rotary valves  30  therein, but may also be shaped to accommodate a single rotary valve or more than two. 
   An exemplary rotary valve  30  will now be described in more detail with reference to  FIGS. 11-16 . The rotary valve  30  according to the embodiment shown in  FIGS. 11-16  has a body  202  which is made, for example, of a metal, a ceramic or a combination thereof, in the shape of a spherical segment. The body has a spherical zone  204  and two parallel, generally flat side portions  206  and  208 . The side portions  206 ,  208  are equidistant from a midpoint of the spherical zone  204 . 
   The spherical zone  204  is generally rotationally symmetric with respect to an axis of rotation of the rotary valve  30 . Any openings provided in the spherical zone  204  are not considered to break this rotational symmetry even if these openings are not arranged in a rotationally symmetric manner. As used herein, if reference is made to a rotational symmetry of an element or a portion thereof, the rotational symmetry refers to the element or portion in general, disregarding any openings formed in that element or portion, which may break the rotational symmetry. 
   A straight passage  210  is formed through the body  202  between the side portions  206  and  208 . The passage  210  is co-axial to a central axis extending between the two side portions  206 ,  208 , which defines the axis of rotation for the rotary valve  30 . The passage  210  is dimensioned to allow a drive shaft to be inserted therethrough, as will be described in more detail herein below. 
   The body  202  also has a chamber  212  formed therein. The chamber  212  is open towards both side portions  206 ,  208  at respective openings  216 ,  218 . The openings  216 ,  218  are of the same shape and dimensions and, as can be best seen in  FIG. 15 , each of the openings  216 ,  218  has approximately a C-shape, partially surrounding the central passage  210 . Each openings  216 ,  218  may extend more than 180° in a direction of rotation of the rotary valve  30 . 
   Furthermore in the embodiment as shown, openings  226  and  228  are provided in the spherical zone  204  to open the chamber  212  towards the spherical zone  204 . The two openings  226 ,  228  are arranged in a side-by-side arrangement and are symmetrical with respect to a plane extending through the midpoint of the spherical zone and being parallel to both side portions  206 ,  208 . A web  230  is formed between the openings  226 ,  228 . The openings  226 ,  228  are centered with respect to the chamber  212  in a rotational direction of the rotary valve body, i.e., in circumferential direction. Openings  226 ,  228  each widen in a direction away from the plane, which is parallel to the side portions  206 ,  208 . Furthermore, each of openings  226 ,  228  define a curved, concave leading edge  232  and a curved concave trailing edge  233  with respect to a direction of rotation of the valve. The shape of the concave leading edge  232  and the concave trailing edge  233  conforms to a circumferential shape of a flow passage formed in a cylinder head  107 , i.e. if the flow passage is round, the leading edge will have a round shape. 
   A cross-sectional flow area of the opening  216  in the side portion  206  is equal to or larger than a cross-sectional flow area of the opening  226 . Similarly, a cross-sectional flow area of the opening  218  is equal to or larger than a cross-sectional flow area of the opening  228 . The chamber  212  defines a fluid connection between the openings  216 ,  218  in the side portions and the openings  226 ,  228  in the spherical zone. 
   A wall portion of the valve body  202  separating the passage  210  from the chamber  212  has an opening  238  formed therethrough. The opening  238  is aligned and centered with respect to opening  228  in the spherical zone  204 . The wall portion  234  has a raised section  240  extending into the chamber  212  and surrounding the opening  238 . The raised section  240  defines a flat surface  242 . A similar mounting hole may be provided aligned and centered with respect to opening  226 . 
   The rotary valve  30  shown in  FIGS. 11-16  has two side-by-side openings in the spherical zone  204  thereof. It should be noted, that a single opening (e.g., without the web  230 ) or a larger number of openings (i.e., more than two), may be provided in the spherical zone. Furthermore, the chamber  212 , as shown, is open at both side portions  206 ,  208 . Again it should be noted that the chamber  212  might only be open to one of the side portions. It is also possible to provide a separating wall in the chamber  212  to provide two separate chambers, each connected to one of the side portions  206 ,  208  and one of the openings  226 ,  228  in the spherical zone  204 . Indeed, any type of fluid connection between the openings  216 ,  218  in the side portions  206 ,  208  and the openings  226 ,  228  in the spherical zone  204 , such as a straight passage may be provided in the valve body  202 . Although the openings  226 ,  228  in the spherical zone  204  are symmetrical with respect to a plane parallel to the side portions  206 ,  208  as shown, it is possible to offset the two openings in a direction of rotation of the rotary valve or to have openings of different shapes and sizes. An annular protrusion may be provided around the central passage to extend the passage beyond the otherwise flat side portions  206 ,  208 . 
   The rotary valve  30  was described as having a spherical zone  204 , which is rotationally symmetric with respect to the axis of rotation of the rotary valve  30 . Rather than having a spherical zone  204 , it is possible to provide a generally curved portion, which is rotationally symmetric with respect to the axis of rotation of the rotary valve  30 . In other words, the curvature of the surface extending between two side portions in the direction of rotation may differ from the curvature perpendicular to the direction of rotation. The curvature perpendicular to the direction of rotation may be circular or may deviate therefrom, for example, an oval curvature. Although a convex (spherical) curvature is shown in the drawings, a concave curvature or a mixture of concave and convex curvatures is possible. The curvature may be symmetric with respect to a plane which is parallel to the side portions and bisects the rotary valve, but it is also possible to have a non-symmetrical curvature. 
   As indicated by a broken line in  FIGS. 11 and 16 , opening  226  (and/or  228 ) may have a part  250  which extends beyond at least one of the leading edge  232  and the trailing edge  233 . This part  250  may be seen as a secondary part of the openings  226 ,  228 . This secondary part would have a cross-sectional flow area which is substantially smaller than the flow area of the rest of the opening. The part  250  would, for example, have a flow area which is less than 50 percent of the flow area of the other part of the openings  226  and  228 . 
   The interior surfaces of the chamber  212  and/or of the flow passages or openings  260 ,  276 ,  278  in the rotary valve may be made of a heat insulative material. In particular, a coating may be provided on these surfaces. Additionally, heat insulative material may be provided on any surface of the rotary valve, including the central passage. The whole deflector may indeed be made of a heat insulative material. 
     FIG. 17  shows a cross-sectional view (similar to  FIG. 14 ) of an alternative rotary valve  30 . The rotary valve  30  shown in  FIG. 17  has all the features of the rotary valve  30  described with respect to  FIGS. 11-16 . The only difference is that an additional opening  260  extending between the chamber  212  and the spherical zone  204  is provided. The additional opening  260  is rotationally offset with respect to the openings  226 ,  228 . The flow area of the additional opening  260  is smaller than the combined flow area of the openings  226 ,  228 . Rather than providing a single additional opening  260  between the chamber  212  and the spherical zone, several additional openings  260  may be provided. These can be in a side-by-side arrangement similar to the openings  226 ,  228  or they can be rotationally offset. The combined flow areas of the openings  260  are smaller than the combined flow areas of openings  226 ,  228 . The openings  226 ,  228  and  260  may be seen as a set of openings. In an alternative rotary valve, a second set of these openings which is rotationally offset by 180° may be provided. In this case, the chamber  212  would have to be adapted accordingly. 
     FIG. 18  shows a cross-sectional view (similar to  FIG. 12 ) of yet another exemplary rotary valve  30 . The rotary valve  30  shown in  FIG. 18  has substantially the same features as the rotary valve  30  described with respect to  FIGS. 11-16 . The rotary valve  30  according to  FIG. 18 , however, differs from the rotary valve  30  shown in  FIGS. 11-16  by having additional flow passages  276  and  278  formed in the body  202  thereof. The flow passages  276 ,  278  extend between the spherical zone  204  and the side portions  206 ,  208  respectively and define respective openings  296 ,  298 ,  286 , and  288 . The flow passages are each angled with respect to the side portions  206 ,  208 . 
   Even though  FIG. 18  shows the flow passages  276 ,  278  being symmetric with respect to a plane, which is parallel to the side portions  206 ,  208  and bisects the rotary valve, they may be asymmetric. Rather than having two flow passages  278 ,  288 , a single flow passage may be provided. Furthermore, a larger number of flow passages may be provided, which may be symmetrically paired, like the ones in the drawings, or which may be asymmetric such as offset with respect to the direction of rotation of the rotary valve. 
     FIG. 19  shows a schematic longitudinal cross-sectional view of a drive shaft  300  for rotating rotary valves mounted thereon. The drive shaft  300  is, for example, suitable to be used with the cylinder head  7  and the rotary valves  30 , as described above, and reference may be made thereto. The drive shaft  300  is dimensioned to pass through the passages  27 ,  28  of cylinder head  7  and any bearing elements provided therein. The drive shaft  300  is made of metal, ceramic, or any other suitable material. 
   The drive shaft  300  has a central flow passage  305  extending longitudinally therethrough, which may be connected to a cooling fluid supply (not shown). Especially in the case of a drive shaft made of ceramic, the flow passage may be dispensed with. The drive shaft  300  has a plurality of mounting holes  310  formed therein, each mounting hole being provided for mounting of a rotary valve to the drive shaft  300 , as will be explained in more detail herein below. The mounting holes  310  are spaced in a longitudinal direction. As shown in  FIG. 19 , the exemplary drive shaft  300  has eight mounting holes  310  formed therein. The first two mounting holes  310  on the left hand side of the drive shaft  300  are formed in the same angular position with respect to the rotational direction of the drive shaft  300 . The first two mounting holes  310  form a first group  312  of mounting holes  310 . 
   The third and fourth mounting holes  310  form a second group  314 , the fifth and sixth mounting holes  310  (which are indicated by a broken line) form a third group  316  and the seventh and eighth mounting holes  310  (which are indicated by a broken line) form a forth group  318 . The mounting holes  310  are rotationally aligned within in each group  312  to  318 , but rotationally offset with respect to the mounting holes of the other groups. In the example shown in  FIG. 19 , each group  312  to  318  is rotationally offset by 90° with respect to two of the other groups and 180° with respect to one of the groups. The centers of the mounting holes  310  in each of the groups are spaced with a distance corresponding to the distance between adjacent flow passages  36  in the above described valve chambers  24 . Adjacent mounting holes of adjacent groups are spaced with a distance corresponding to the distance between adjacent flow passages  36  of adjacent valve chambers  24 . 
   The mounting holes  310  are stepped holes having an outer portion  320  and an inner portion  322 . The outer portion  320  has a larger diameter than the inner portion  322 . The inner portion  322  has an internal thread. Although the drive shaft  30  was described for use with the specific cylinder head and the rotary valves shown above, the number of mounting holes and their relative positions may vary in different applications. Depending on the application, more than two mounting holes  310  may be provided in each group, for example, when more rotary valves are to be grouped together per group or when more than one mounting hole is used to mount a rotary valve on the drive shaft. The rotary valves may be rotationally aligned within the groups or rotationally offset with a predetermined angle. 
     FIG. 20  shows an enlarged sectional view of a rotary valve  30  as described with respect to  FIGS. 11-16  mounted onto the drive shaft  300 . As can be seen in  FIG. 20 , a ring dowel  330  is provided, extending into the opening  238  of the rotary valve  30  and into the outer portion  320  of the mounting hole  310  in the drive shaft  300 . The ring dowel may be made from metal or any material which is strong enough to withstand the stress applied thereto. Furthermore, a screw  335  having a head and a shaft is provided. The shaft extends through the ring dowel  330  into the inner part  322  of the mounting hole  310  where external threads on the shaft come into engagement with the inner threads provided in part  322  of mounting hole  310 . The lower part of the head of the screw  335  is in engagement with the flat surface  242  of the raised section  240  of the rotary valve  30 . 
     FIGS. 21  ( a ) and ( b ) show different examples of a deflector/bearing assembly  400  to be arranged within the cylinder head  7  as, for example, shown in  FIG. 6  and reference may be made thereto. The deflector/bearing assembly  400  has a bearing part  402  and a deflector part  404 . The bearing part  402  is formed by an inner race  406 , an outer race  408 , and a plurality of bearing elements interposed therebetween, such as rollers or balls. Also, any other type of bearing element may be used. Lubrication in the form of a lubricant is provided for the bearing elements and end plates  410  and  412  are provided to seal the lubricant into the bearing part  402 . The inner and outer race  406 ,  408  and/or bearing part  402  may have a surface made of a solid lubricant, in which case sealing of a viscous lubricant is not required. The inner race  406  has a central opening  414  dimensioned to accommodate the drive shaft  300  therein. 
   The deflector part  404  is formed of a one piece deflector body  420 . The deflector body  420  has a central opening  424  extending longitudinally therethrough. The central opening  424  is dimensioned to accommodate the drive shaft  300  therein. The deflector body  402  is rotationally symmetrical with respect to a central axis of the central opening  424 . The deflector body  402  has a diameter which is approximately equal to or larger than a diameter of one of the passages  27 ,  28  formed in the cylinder head  7 . 
   The deflector body  420  has a substantially flat surface  426  facing the bearing part  402 . A deviation from the flat surface is an annular projection surrounding the central opening  424 . The annular projection  428  is dimensioned to come into engagement with the inner race  406  of the bearing part  402 . When the annular projection  428  is in engagement with the inner race  406 , the flat surface  426  is spaced from the rest of the bearing part  402 . 
   The deflector body  420  also defines a deflecting surface  430  facing away from the flat surface  426 . The deflecting surface  430  decreases in diameter in a direction away from the flat surface  426  and defines a curve. At the end of the deflector body  420 , which is opposite to the annular projection  428 , a flat abutment surface  432  is formed for engagement with a part of the rotary valve  30  surrounding the passage  210 , for example, as shown in  FIG. 6 . 
   In  FIG. 21  ( a ), the deflector body and the inner race are shown to be separate parts. As shown in  FIG. 21  ( b ) the deflector body  420  and the inner race  406  may be formed as a single piece. Although  FIG. 21  ( a ) shows the deflector part and the bearing as an assembly, it should be noted that the deflector part and the bearing may indeed be used independently from each other, i.e. a deflector part as shown and described may be used as a deflector independently of the presence of a bearing part and vice versa. The bearing part may, for example, be dispensed with if a rotary shaft (such as drive shaft  300 ) and a passage (such as passage  27  or  28 ) are configured to have complementary bearing surfaces formed thereon. Such complementary bearing surfaces could, for example, be surfaces made of a solid lubricant. In such an arrangement at least one of a surface of the drive shaft and an inner wall surface of the passage should be made of a solid lubricant. 
   The deflecting surface  430  may be a smooth curving surface, as shown, or it may, for example, have guide grooves arranged therein. It is also possible that blades are provided on the deflector in lieu of or in combination with the deflecting surface. Such blades may be configured to facilitate changing a longitudinal fluid flow (with respect to the deflector) to a radial flow or vice versa, in particular upon rotation thereof. The deflecting surface and optionally the other surfaces of the deflector may be made of a heat insulative material. The deflector body as a whole may be made of a heat insulative material or may, for example, be made of metal at least partially coated with a heat insulative material. 
     FIG. 22  shows an assembly of two deflectors, which may each be substantially of the same shape and dimensions as the deflector part  404  shown in  FIG. 21  ( a ). The main difference is, however, that the annular projection  428  is dispensed with so that the deflectors  450  can be arranged in a back-to-back relation as shown in  FIG. 22  without forming a space therebetween. Such an assembly of deflectors may, for example, be used in combination with the cylinder head arrangement shown in  FIG. 6 , where the assembly would be arranged between adjacent rotary valves  30  in the same valve chamber  24 . Although the deflectors  450  are shown as separate parts, they may be integrally formed, to form a deflector having oppositely facing deflector surfaces. 
     FIG. 23  shows a schematic end view of an exemplary internal combustion engine  1 , such as the one previously described. In particular,  FIG. 23  schematically shows a drive mechanism for driving rotary valves arranged in the cylinder head  7  thereof. Reference numeral  500  indicates a crankshaft  500 . Reference numerals  502  and  504  indicate a drive shaft, such as a drive shaft  300  described above and arranged in the cylinder head  7 . 
   Drive elements  512  and  514 , such as, for example, belts, chains, toothed belts, etc., are entrained about the crankshaft  500  and the drive shafts  502 ,  504  respectively. Rotation of the crankshaft  500  is thereby transmitted to the drive shafts  502 ,  504 , respectively. Though not shown, a reduction mechanism may be provided in order to ensure that one rotation of the crankshaft translates into half a rotation of each of the drive shafts  502 ,  504 . Rather than having drive belts directly entrained about the crankshaft  500  and the drive shafts  502 ,  504 , pulleys may be coupled to these members, and the drive belts may extend around the pulleys. Also, a gear mechanism having,, for example circular gears may be used to transmit rotation of the crankshaft  500  to the drive shafts  502 ,  504 . 
     FIG. 24(   a ) shows a schematic end view of an alternative internal combustion engine, and  FIG. 24(   b ) shows a schematic top view thereof. The internal combustion engine may be the same as the one described above with respect to  FIG. 1 . The drive mechanism, however, differs with respect to the previously described drive mechanism. In the drive mechanism according to  FIG. 23 , the drive shafts  502 ,  504  was directly coupled by a corresponding drive elements  512 ,  514  to each of the drive shafts  502 ,  504 . In the Example, as shown in  FIGS. 24(   a ) and  24 ( b ), however, the crankshaft  500  is only directly coupled to drive shaft  504  via the drive element  514 . A separate drive element  520  is provided which is entrained about the drive shafts  502  and  504  to transmit rotation of drive shaft  504  to drive shaft  502 . The crankshaft  500  is thus rotatably coupled to the drive shaft  502  via the drive shaft  504  and the drive elements  514 ,  520 . The drive elements  514  and  520  are provided at opposite ends of the drive shaft  504 . 
     FIG. 25  shows an end view of another exemplary internal combustion engine  1 , such as the one described above. The end view shows yet another alternative drive mechanism for transmitting rotation of a crankshaft  500  to drive shafts  502 ,  504 . The drive mechanism has a rotatable shaft  530  which may, for example, be rotatably supported by the cylinder head  7  of the internal combustion engine  1 , or by any other means. An elliptical gear  32  is mounted on the rotatable shaft  530 . Elliptical gears  534  and  536  are also mounted to driveshaft  502 ,  504 , respectively. The elliptical gears  532 ,  534  and  536  are arranged such that they are in constant engagement. The elliptical gears  534  and  536  are arranged on opposite sides of the elliptical  532 . Furthermore, a drive belt  540  is provided which is entrained about the shaft  530  and the crankshaft  500 . 
   Although the example shown in  FIG. 25  shows a very specific arrangement of elliptical gears, differently shaped elliptical gears may be used. Furthermore, a different arrangement of such elliptical gears may be used. For example, only two elliptical gears may used which would allow transmitting rotation from the crankshaft  500  to one of the drive shafts  502 ,  504 . A drive mechanism may then be provided to rotatably couple the drive shafts, similar to the setup shown in  FIG. 24 . Instead of elliptical gears, it is also possible to provide one or more elliptical pulleys and provide a drive element there around. 
   The characteristics of the elliptical gears or pulleys are that on a constant rotation of one of the elements, the other element will have a varying speed. The speed will vary between a slow and a fast speed. During a single rotation of one elliptical element (such as the one shown), with a constant rotational speed, the other element will have two phases at which it will rotate with a slow speed and two phases at which it will rotate with a fast speed. Depending on the speed changes required during a single rotation, multi-lobe elliptical gears or pulleys may be used. 
   In general, any two non-circular elements, one rotatably coupled to a drive source, such as the crankshaft and the other rotatably coupled to the drive shaft and which are coupled to cause the above speed variation may be used. The above described speed variation may also be achieved, if an elliptical or non-circular element is coupled to a circular element. In the case of a non-circular pulley coupled to a circular pulley, belt tensioning may be provided to take up any slack occurring during the rotation of the pulleys. If a non-circular gear is used in combination with a circular gear, a mechanism may be provided which allows relative movement between the elements. Such a relative movement allows the distance between the centers of rotation of the gears to vary during rotation of the gears. Such a mechanism may also be used for the pulleys to provide belt tensioning as described above. 
     FIG. 26  shows another alternative drive mechanism for drive shafts  502 ,  504  arranged in a cylinder head  7  of an internal combustion engine  1 . The drive mechanism includes an electric drive motor  550  attached to one end face of the cylinder head  7 . As can be seen in the different views of  FIG. 26 , the electric drive motor  550  is arranged such that the drive shaft  504  partially extends therein. As best seen in  FIG. 26(   c ), permanent magnets  555  are embedded into the drive shaft  504 . The part of the drive shaft  504  in which the permanent magnets  555  are embedded, is surrounded by a stator  560  of the electric motor. The drive shaft  504  thus acts as a rotor of the drive motor  550 . 
   A drive element  570  is provided which is entrained about the drive shafts  502 ,  504 . The drive shaft is provided at an end of the drive shaft  504 , which is opposite to the end, which is accommodated in the electric drive motor  550 . 
     FIG. 26(   a ) shows a sensor  580  for sensing the rotational position and speed of the crankshaft  500 . The detector  580  is connected to the drive motor  550  to provide information with respect to the rotational position and rotational speed of the crankshaft  500  to the drive motor  550 . Alternative sensors, such as a piston position sensor, may be provided. Although the drive motor  550  was described as an electric drive motor, a hydraulic or pneumatic drive motor could be used instead. It is also not necessary that the driveshaft  504  extends into the drive motor  550 . A regular drive motor having a rotor and a stator may be provided and the rotor may be coupled to the drive shaft either within or outside of the drive motor. A separate drive motor may be provided for each of the drive shafts thereby eliminating the need of a drive element to transmit rotation between the drive shafts. 
   The drive motor  550  is arranged to act on the drive shaft  504 , which will have rotary valves attached thereto. Rather than having a drive motor  550  acting on a drive shaft, it would also be possible to provide a drive motor which directly acts upon rotary valves accommodated within a cylinder head of an engine. In this case, the rotary valve may have permanent magnets embedded therein, upon which a stator of the drive motor may act. The rotary valves may be journalled on a respective shaft or could be provided on a shaft journalled within the cylinder head. Alternative means for journaling the rotary valves in the cylinder head may be provided. 
   The stator of such a drive motor may, for example, be attached to the cover plate  12  and in particular to the protrusions described to extend into the insertion passages  32 . The stator of such a drive motor may also be formed by interior walls of the valve chamber for accommodating the rotary valve. 
   With respect to the drive mechanism described hereinbefore, combinations thereof may be formed. It is for example possible to provide a mechanical drive train including gears and/or pulleys between an output of the drive motor and the drive shaft. In particular, non-circular elements may also be used in such a mechanical drive train coupling an output of the drive motor to one or both of the drive shafts. 
   INDUSTRIAL APPLICABILITY 
   The previously described cylinder head  7  and its associated parts may be used for any type of combustion engine, especially engines having direct fuel injection. If no direct fuel injection is used, a fuel-air mixture may be provided via the air-duct  47  and its associated valve chambers  24 . The cylinder head  7  may be a cast part having certain parts thereof machined after the casting process. In particular, the flow passages  36 , the sealing seats surrounding the flow passages  36 , the passages  27 ,  28  and the outside sealing surfaces may be typically machined. 
   In order to prepare the cylinder head  7  for use with an internal combustion engine, the different parts associated therewith are assembled. Such an assembly will now be described with respect to  FIG. 6 , showing a longitudinal cross section through the cylinder head  7 . 
   The view according to  FIG. 6  shows a cross section through group B of the valve chambers  24  and through passage  28 . In the following, reference will thus be made to those valve chambers and to passage  28 . Assembly of the valve chambers  24  and associated parts with respect to group A will be performed in a similar manner. 
   In a first step, bearings will be arranged in the passage  28 . Each part of the passage  28  being arranged between adjacent valve chambers  24  will receive two bearings, such as bearings  402  therein. Additional bearings, which may be of the same shape and design, like the bearings  402 , may be arranged in the parts of the passage  28  extending between the outermost valve chambers  24  and the end faces  17 ,  18 , respectively. 
   In a next step, deflectors, such as deflectors  404  will be arranged adjacent the bearing received in the passage  28 . The deflecting surface of the deflectors is arranged to face towards the inside of the valve chambers  24 . Rather than having separate bearings and deflectors, an integrated deflector bearing assembly as shown in  FIG. 22  could be used instead. 
   In a next step, rotary valves, such as rotary valves  30 , will be inserted into the valve chambers  24  through their respective insertion opening  32 . Next, a drive shaft, such as drive shaft  300  will be subsequently inserted through bearings in the passage  28 , a deflector  404  in a first valve chamber  24 , a first rotary valve  30  in the valve chamber, a second rotary valve  30  in the valve chamber, a second deflector  404  in the valve chamber, bearings in the passage etc. During this assembly, the drive shaft may be cooled via its central cooling passage to cause shrinking thereof, in order to allow a better insertion through the several parts of the assembly. 
   Once the drive shaft is inserted through all the parts of the assembly and exits the opposite end of the cylinder head  7 , the mounting holes  310  in the drive shaft are aligned with the opening  238  in the rotary valves  30 . This alignment will be observed through the insertion opening  32  and will be performed in pairs. Once a opening  238  in a drive shaft  30  is aligned with a corresponding mounting hole  310  in the drive shaft  300 , the dowel pin  330  is inserted through the opening  238  into the top part of the mounting opening  310 . 
   Finally, a screw  335  is inserted into the assembly and is screwed into the inner part of the mounting hole  310  of the drive shaft  300 . 
   In this manner, each of the rotary valves  30  is mounted to the drive shaft  300 . As mentioned above, this final assembly of the rotary valves  30  is done in pairs, as the groups  312  to  318  of mounting holes  310  are rotationally offset. Inasmuch as the alignment of the mounting holes and the insertion of the dowel pin and the screw are performed through the insertion opening  32 , the rotary valves are kept in a constant position, and the drive shaft is to be rotated, to achieve alignment of the mounting holes. It may also be possible to assemble the drive shaft and the componentry associated therewith outside of the cylinder head and to insert such an assembly through a corresponding passage formed either longitudinally or transversely in the cylinder head. In a cylinder head of the split design such an assembly may be inserted before attaching the separate body parts of the cylinder head to each other. 
   Once this assembly is completed, injectors may be mounted to the cylinder head  7  by inserting injectors through the corresponding injector openings  67 . Once the cylinder head  7  is pre-assembled in this manner, it may be mounted to the engine main body, by bolts extending through the mounting holes  65  into corresponding mounting holes in the engine main body. 
   Finally, the cover plate  12  may be placed onto the cylinder head  7  and attached thereto by bolts extending through the mounting holes  69  and  70 . Once the cylinder head  7  is mounted to the engine main body, a drive mechanism is coupled to the drive shafts. Furthermore, an exhaust manifold is attached to side  20  of the cylinder head  7  to fluidly connect each of the passages  60  to the exhaust manifold. Similarly, air inlet pipes are connected to the top surface  15  of the cylinder head  7 , to fluidly connect to passages  49  and  50  connected to the air-duct  47 . The opening  48  in the end face  18  may be closed by a cover plate or plug. Alternatively, another air inlet pipe could be connected to end face  18 , to provide airflow to the air-duct  47 . 
   During operation of the engine, each of the rotary valves  30  will provide successive opening and closing events for its corresponding flow passage  36 . The rotary valves  30  associated with group A of the valve chambers will mainly provide intake of air into the respective engine cylinders during an intake stroke and will prevent fluid flow into the respective valve chambers during a closing event. If an in-cylinder charge dilution (ICCD) is desired, i.e. a mixing of intake air with exhaust gas, for example aimed at reducing emissions such as nitrogen oxides (NOx) during combustion, a certain degree of gas flow from the cylinders to the valve chambers associated with group A may be provided. Such a gas flow may for example be provided by additional flow openings, such as flow opening  260  shown in  FIG. 17  or flow openings  276  to  278  shown in  FIG. 18 . It is also possible, that such a gas flow may be provided by incomplete sealing between the sealing arrangement  44  and the rotary valve  30  at least during a part of a rotation thereof. Such an incomplete sealing could be achieved by providing sections in the spherical zone  204  of each rotary valve deviating from a rotational symmetry thereof. 
   Another alternative is to rotate each of the rotary valves  30  such that two opening events by the openings  226  to  228  occur during a single combustion cycle of the engine i.e. the rotary valve may make two revolutions during a single combustion cycle. In this event, the rotational speed of the rotary valves  30  could be varied, such that the opening events are of a different duration. In some embodiments a longer air intake opening duration may be used. 
   The rotary valves associated with group B of the valve chambers  24  similarly provide opening events to exhaust gas from the respective cylinders through the respective flow passages  36 , the flow passage  226 ,  228  in the rotary valves  30 , into the respective valve chamber  24  and through the respective exhaust passage  60  to the exhaust manifold. 
   In order to achieve ICCD, rather than admitting exhaust gas into the valve chambers  24  of group A, it is also possible to allow exhaust gas from the valve chamber  24  associated with group B to flow into the respective cylinders during an intake stroke. Such an air flow occurring outside of the main opening event of the rotary valves for exhausting gas from the cylinders, may occur in a similar manner as described before. Additional flow openings  260  to  278  may be provided, incomplete sealing between the rotary valves  30  and their corresponding sealing arrangement may be provided or the valves may be driven at a speed to achieve two or more separate valve opening events of the same openings during a single combustion cycle of the engine. Fuel may be injected via the respective injectors in accordance with engine requirements. Alternatively a fuel-air mixture may be provided via valve chambers  24  of group A. 
   The cylinder head  107  shown in  FIG. 10  will be assembled in a similar manner to the cylinder head  7 , and operation thereof will be similar to the one described before. The main difference lies in the fact that an air inlet manifold and an exhaust manifold will be attached to parts  181 ,  182 , respectively, of the top surface  115  of the cylinder head  107 . Air will enter directly through the insertion opening  132  into the respective valve chambers  124  of group A rather than through an air-duct  47  and flow passages  55 . Similarly, exhaust gas will directly exit the respective valve chambers of group B through insertion openings  132  into the exhaust manifold. 
   With respect to  FIGS. 23 to 26  different drive arrangements are shown. In accordance with  FIGS. 23 and 24 , rotation of the crankshaft  500  of the engine  1  is transmitted directly via a mechanical drive train to the respective drive shafts  502 ,  504 , arranged in the cylinder head  7 . The mechanical drive train is designed such that a constant rotation of the crankshaft  500  will translate into a constant rotation of the drive shafts  502 ,  504 . Even though not shown, a speed reduction mechanism may be provided, such that each of the drive shafts  502 ,  504  will run for example at half speed of the crankshaft  500 . In the case of rotary valves having two main flow passages there through, the rotational speed of each of the drive shafts  502 ,  504  may even be reduced to a quarter speed of the crankshaft  500 . 
     FIG. 25  shows an alternative mechanical drive train for transmitting rotation of the crankshaft  500  to the drive shaft  502 ,  504 . This mechanical drive train uses elliptical gears being in engagement with each other. The elliptical gears have the effect, that upon a constant rotation of the crankshaft  500  the rotational speed of each of the drive shafts  502 ,  504  will vary between a low speed and a fast speed. In providing such a speed variation, for example, fast opening and closing of the rotary valves may be achieved. Even though  FIG. 25  shows elliptical gears of the bi-lobe type, multi-lobe elliptical gears may be used. Indeed, any type of non circular gear providing a speed variation such as the one described above could be used. The speed of the drive shaft will vary about a reference speed, which is associated with the rotational speed of the source of rotation. The reference speed will depend on the speed reduction mechanism, if any is used. Without a speed reduction mechanism, the reference speed will be equal to the speed of rotation of the crankshaft. 
   Although  FIG. 25  shows elliptical gears being in engagement, elliptical pulleys being connected by drive belts could be used. They may produce the same effect. The elliptical gears shown in  FIG. 25  will produce during a single rotation of the crankshaft  500  two short periods, in which the rotary shafts  502 ,  504  are rotated at a high speed and two longer periods, at which the rotary shafts  502 ,  504  rotate at a slower speed. Depending on the number of rotary valves attached to the drive shafts and the engine requirements, multi-lobe elliptical gears having a different number of speed changes may be used. 
     FIG. 26  shows an alternative drive mechanism for the drive shafts  502 ,  504 . In the example shown in  FIG. 26 , an electric drive motor is used to drive the drive shaft  504 . Rotation of the drive shaft  504  is then transmitted to the drive shaft  502  via a drive belt  570 . A sensor  580 , which detects the rotational position and speed of the crankshaft  500  is connected to the drive motor  550 , to transmit this information thereto. In accordance with this information, the drive motor  550  can rotate the drive shafts  505 ,  502 , respectively. The drive motor  550  may be driven at varying speeds during a single rotation thereof. This may allow fast opening and closing of the rotary valve. The varying speeds may again vary about a reference speed associated with a crankshaft speed. 
   Rather than providing a drive motor  550  for one of the drive shafts and providing a mechanical drive train between the drive shafts to couple them together, two separate drive motors may be provided. This would add the possibility to independently control rotation of each of the drive shafts. Especially in cases where a single rotary valve is attached to the drive shaft, or where a drive shaft is associated with rotary valves for a single cylinder, individual tailoring of opening, closing and the speed of rotation thereof is possible. In this way, the amount of fluid flow to and from the cylinder may be individually adjusted for the cylinder. Similar control is possible in the application where the drive motor acts directly on the rotary valves, for example, when the rotary valves have magnets embedded therein, as described above. Such an individual tailoring may be particular beneficial in combination with a corresponding tailoring of the amount of fuel to be injected. 
   An electronic control unit may be provided to control operation of the drive motor. Even though  FIG. 26  shows an electric drive motor, similarly a hydraulic drive motor may be provided. 
   The above description describes several examples for a cylinder head of an internal combustion engine and its associated componentry. The present application, however, is not limited to the specific examples shown therein. Features of the different examples for the elements may be combined and/or exchanged. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the cylinder head of the present disclosure. Other embodiments of the cylinder head will be apparent to those skilled in the art from consideration of the specification and practice of the cylinder head disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.