Patent Publication Number: US-2009229560-A1

Title: Internal combustion engine having a reduced cylinder head height

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of international patent application PCT/EP2006/004672 filed May 17, 2006, which claims priority to German patent application DE 102005 023 581.6 filed May 18, 2005. 
    
    
     FIELD OF THE INVENTION 
     The invention concerns an internal combustion engine comprising at least one cylinder and at least one valve provided for a gas exchange. 
     BACKGROUND OF THE INVENTION 
     Numerous configurations of such internal combustion engines are known from prior art. 
     The problem of the invention is to reduce a structural height of a cylinder head as well as, in particular, to reduce a moved mass in controlling a gas exchange valve. 
     SUMMARY OF THE INVENTION 
     This problem is solved by an internal combustion engine with the characteristics of Claim  1 . Advantageous configurations and refinements are indicated in the respective dependent claims. 
     An internal combustion engine according to the invention comprises at least one cylinder and at least one valve provided for a gas exchange and having a first end comprising a valve head, and a second end, characterized in that a valve bearing has a length of a guidance area arranged for the guidance of a valve stem of at most 25%, preferably between 10 and 20%, and particularly preferably of less than 10% of a valve length. 
     The internal combustion engine is, for example, an internal combustion engine operating according to the spark-ignition or the diesel principle. In particular such an internal combustion engine is provided in a vehicle, for example, an automobile. For instance, it may be an internal combustion engine in a passenger car. 
     The valve bearing is preferably designed to be complementary to the valve stem accommodated in it. For a valve stem with a circular cross section, for example, the valve bearing comprises an appropriate circular bore for the guidance of the valve stem. The guidance area here is to be understood, in particular, as the area which is in direct contact with the valve stem. The guidance area is preferably provided to prevent lateral tilting of the valve stem. In particular, the valve is movably guided in its longitudinal direction in the valve bearing, so that a gas intake or gas exhaust port can be opened and closed with the valve disk in a stroke of the valve. Moreover, the valve can be moved back and forth between an open and a closed position by means of at least one reset spring in connection with actuation equipment, for example. In place of a valve closing spring, a forced control of the valve can be provided. Both a mechanical and an electromechanical drive, in particular, an electromagnetic drive can be provided for actuating the valve. 
     The valve bearing can be represented in different ways. For example, the valve bearing may be formed by a guidance machined into the cylinder head. This is preferably provided for a cylinder head of cast iron. In particular, the guidance has a hardened surface. In another variant, a valve bushing can be arranged in the cylinder head as a valve bearing. This variant is preferably used in a light-metal cylinder head of, for example, aluminum or another light metal or a light metal alloy. 
     In a first configuration, it is provided that the guidance area has a length of at most 18 mm, preferably between 18 mm and 10 mm, more preferably between 10 mm and 5 mm, and most preferably between 5 mm and 2 mm. A valve length here is, for example, approximately 85 mm. This data is preferably related to a four-cylinder gasoline engine with a displacement of approximately 2 L. The cylinder head with a reduced valve bearing length expediently has a smaller overall size compared to an ordinary valve bearing length. Additionally, the valve preferably has a smaller length and thus a lower mass than is the case for an ordinary valve bearing length. In particular the moved mass of the valve is reduced. 
     In another configuration it is provided that a valve stem diameter A in an area guided by the valve bearing, a first distance B between a lower edge of the valve disk and an upper edge of the envelope circle described during one revolution of a cam associated with the valve, as well as a second distance C between an end face provided at the second end of the valve for the transmission of an actuating force and a lower edge of the valve bearing are selected such that a product of second distance C and valve stem diameter A, divided by the square of the first distance B, is at most 0.0125, preferably between 0.011 and 0.0125, more preferably between 0.0105 and 0.011, and most preferably less than 0.0105, where the first distance B and second distance C in the direction of a central axis of the cylinder are relative to the closing position of the valve. The valve stem diameter A in the area of valve stem guided by the valve bearing is preferably constant over this area. The valve stem diameter of the valve can also vary over the length of the valve. For instance, a valve stem diameter outside the area guided by the valve bearing can be larger or smaller than inside the area guided by the valve bearing. In particular, the closed position is determined by the fact that the valve head rests against the associated valve seat in the cylinder head and closes off an associated gas intake port. In the case of an overhead valve, the valve is in an upper end position in the closed position. The cam associated with the valve is preferably provided for direct or indirect actuation of the valve. In the rotation of the cam it passes over a circular surface, which is preferably arranged along a valve axis. An axis of rotation of the cam can be arranged such that it forms an intersection with an extension of a longitudinal axis of the valve. It can also be arranged offset thereto, however. The valve is preferably oriented along the main axis of the cylinder. However, a slanted installation and thus an angle to the main axis of the cylinder can also be provided. In case an electromechanical valve drive without a camshaft is used, a distance between the lower edge of the valve head and the upper edge of a volume occupied or passed through during an actuation process with the electromechanical valve drive can be used for the first distance B, instead of the distance between the lower edge of the valve head and the upper edge of the cam&#39;s envelope curve. 
     The end face is, for example, a cylinder end face of the valve stem. The end surface can additionally be, for instance, a plate or the like that is mounted on the second end. 
     In another configuration it is provided, additionally or ultimately, that a valve stem diameter in an area guided by the valve bearing, as well as a second distance C between an end face provided at the second end for transmitting an actuation force and a lower edge of the valve bearing are selected such that a product of second distance C and valve stem diameter A is at most 250 mm 2 , preferably between 230 mm 2  and 250 mm 2 , more preferably between 210 mm 2  and 230 mm 2 , and most preferably less than 210 mm 2 , wherein a second distance C in the direction of a main axis of the cylinder is relative to a closed position of the valve. These values can be used, for instance, in an internal combustion engine with a valve length of roughly 85 mm. Preferably, a valve length is between 95 mm and 75 mm. This may be, for example, an internal combustion engine operating according to the spark-ignition principle with four cylinders and a displacement of roughly 2 L. Other internal combustion engines can also be provided, such as a three cylinder internal combustion engine with a displacement of roughly 1000 cm 3  or an internal combustion engine with eight cylinders and a displacement of roughly 4000 cm 3 . 
     Alternatively or additionally, it is provided in an additional configuration that the length of the guidance area divided by the valve stem diameter in an area guided by the valve bearing is at most 4, preferably between 3 and 4, more preferably between 2 and 3, and most preferably less than 2. 
     According to another concept, a second distance C between an end face arranged at the second end of the valve for transmitting an actuation force and a lower edge of the valve bearing, divided by the guidance length of the valve bearing, is at least 3, preferably between 3 and 5, more preferably between 5 and 7, and most preferably greater than 7, relative to a closing position of the valve. 
     According to another configuration, the end face is formed by a cup which is connected via a form fit or a force fit to the second end of the valve. A cup is mounted by means of a clamp connection, for instance, in another variant. The cup is preferably connected to the valve stem so as to be reversibly detachable. A non-reversibly detachable connection can also be provided, however. 
     The cup can preferably be fixed in a longitudinal direction of the valve stem in various positions, which correspond to different end lengths of the valve. The end length of the valve is to be understood as the distance between valve head and cup surface. A fixation in various positions is ensured, for instance, by means of a threaded connection or a clamp connection. 
     According to one refinement, the cup is guided in a cup guide. For a cup with a cylindrical side surface, the cup guide is constructed as a bushing with a complementary shape in cross section, for example. The guide can extend over the entire periphery of the cup; in another variant, however, it can be provided that only certain areas of the cup&#39;s periphery are guided. The cup guide preferably absorbs transverse forces of the valve stem. A stiffening of the cylinder head is also effected by the cup guide, for instance. In particular, the cup guide, in connection with the guidance area of the valve stem, forms a second guidance area which extends from a lower edge of the guidance area of the valve bearing to an upper edge of the cup guide. The second guidance length is preferably between 35% and 65% of the valve length. In particular, a lateral tilting is avoided or at least reduced, despite a smaller valve bearing length. Additionally, a guidance length effective for guidance of the valve is preferably considerably increased in comparison with a guidance without a cup guide. In particular, the arrangement has an a comparatively large effective guidance length despite a small overall height. 
     For improved heat removal it can be provided that a cup of aluminum or an aluminum alloy is used. Accordingly, a suitable friction pairing between cup guide and cup is selected in order to minimize wear. For instance, can be correspondingly selected as a material of the cup guide. The friction partner can additionally be case-hardened or have a wear-protection coating. 
     According to another refinement, the cup guide is directly formed in a cylinder head. For instance, a bushing may be formed in a casting process of the cylinder. Additionally, a bushing for cup guidance can be directly cast into the cylinder head, for example. 
     It is provided in another configuration for the cup guide to be formed by a cap placed on a cylinder head. The cap in this case is a socket, for instance. It is preferably attached to the cylinder head by a threaded fastener, by pressing, or the like. 
     In a preferred configuration, a valve is guided with its valve stem in a lower guide formed by the valve bearing, and in an upper guide in the cylinder head with a tappet firmly connected at an upper end and forming an upper spring retainer or with a hydraulic valve clearance compensation element, wherein at least one compression spring is pressed in between the upper spring retainer and a lower spring retainer. 
     According to an additional concept, a length of the valve bearing exceeds the length of the guidance area, preferably by at least 50%. For instance, the valve bearing is formed by a valve bearing bushing which has a larger bore diameter over a first part of its length than in the guidance area. Tilting of the valve bearing in the cylinder head is preferably reduced by a sufficient length of the valve there. A precise orientation of the guidance area with respect to the valve stem is correspondingly improved. In one configuration, an excess of more than 200% can be provided. 
     A seat of the valve bearing in the cylinder head in a preferred configuration has a clearance fit or a transition fit. A press fit is specifically avoided. Preferably, tensions in the cylinder head normally occurring in the case of a press fit are minimized. In particular, this is a tight clearance fit. According to one variant, the valve bearing, in particular a valve bearing bushing, can be held in place by a valve spring. A rotation of the valve bearing is preferably prevented as much as possible. 
     It can be provided in another configuration that a seat of the valve bearing in a cast-iron cylinder head has a fit with an oversize of at least 0.02 mm. In particular, an outside diameter of the valve bearing is dimensioned 0.02 mm larger than an inside diameter of a receptacle provided for the valve bearing in the cast-iron cylinder head. Preferably only slight tensions are induced in the cylinder head in the vicinity of the valve bearing due to the slight oversize. 
     In a cylinder head having a material from the group comprising aluminum, aluminum alloy, magnesium and magnesium alloy, it is provided according to one refinement that a seat of the valve bearing in the cylinder head has an oversize of less than 0.04 mm. Preferably only slight tensions are introduced by the valve bearing in the cylinder head here as well. For an aluminum cylinder head with a valve bearing made of cast iron, an oversize of 30 μm is provided. In particular a bore for accommodating the valve bearing has a tolerance as in conformity with an H7 fit according to DIN Standard 7157. The valve bearing accordingly has an outside diameter tolerance conforming to an s7 fit corresponding to the same standard. These values are preferably relative to room temperature. 
     For an improved cooling, it is preferably provided that the valve has at least one sodium core. For instance, the valve stem has at least one cavity for this purpose. The latter is preferably filled only fractionally with sodium, for example, to about two-thirds. 
     Alternatively or additionally, it is also preferably provided for improved cooling that a wall thickness between the valve bearing and at least one coolant space in the environs of the guidance area of the valve bearing is less than 5 mm in at least one section, preferably between 3 mm and 5 mm, and most preferably between 1 mm and 3 mm. In particular, heat dissipation from the valve stem into the coolant space via the valve bearing is improved. The environs of the guidance area are to be understood in particular as the direct environment of the valve inside roughly one stem diameter. The coolant space preferably carries water from a water-cooling circuit. Oil cooling can additionally be provided. In another configuration, a direct cooling of the valve bearing can be provided in connection with an appropriate seal. 
     Controlling of the valve for carrying out a stroke motion can be realized in various ways. In a first configuration, the internal combustion engine has a rocker arm control. For example, one end of the rocker arm acts on the end face of the valve&#39;s end. The rocker arm is preferably likely driven by the camshaft. 
     In another configuration, the internal combustion engine has a cam lever control. Here, for instance, one end of the cam lever acts on the end face of the second valve, with another end of the cam lever resting against a bearing. The cam lever is again preferably controlled by the camshaft. Lateral forces on the valve stem are preferably minimized with a cam lever control. 
     In another variant, it is provided that the internal combustion engine has a direct camshaft control of the cup. Here, one cam of a camshaft control preferably acts directly on the cup that is mounted at the second end of the valve. In particular, an induction of lateral forces onto the valve is also minimized with a tappet arrangement. 
     In another configuration, the valve is an overhead valve. This preferably allows an optimally simple construction of a valve control. 
     According to an additional concept, the internal combustion engine comprises at least one hydraulic clearance compensation element. This is, for instance, a hydraulic tappet. The clearance compensation element is preferably used to compensate the valve clearance. There is preferably an automatic compensation of the valve clearance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in detail below on the basis of the drawing. The characteristics there are not restricted to the individual configurations, however. Rather, the characteristics contained in the specification, including the description of the figures and or the drawing, can be combined for refinements. 
       Shown are: 
         FIG. 1 , a first cylinder head arrangement according to prior art, 
         FIG. 2 , a second cylinder head arrangement, 
         FIG. 3 , a third cylinder head arrangement, 
         FIG. 4 , a fourth cylinder head arrangement, 
         FIG. 5 , a fifth cylinder head arrangement, and 
         FIG. 6 , a plan view onto a cylinder head. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a first cylinder head arrangement  1  according to prior art. A section through first cylinder head arrangement  1  perpendicular to a flame deck  2 , as well as perpendicular to the longitudinal direction of the associated cylinder head  3  is shown. Cylinder head  3  has an overall height  4 . A valve bearing bushing  5  for guiding a gas exchange valve  6  is situated in cylinder head  3 . Gas exchange valve  6  is controlled by means of a cam lever  7 , which is driven by a cam  8 . 
     Below, identically functioning elements are furnished with identical reference numbers and designations. 
       FIG. 2  shows a second cylinder head arrangement  9  according to the invention. This accordingly is a right-hand side of the cylinder head arrangement with a lower overall height  4  provided in comparison to first cylinder head arrangement  1  from  FIG. 1 . The lower overall height  4  is essentially made possible by a modified valve guide. A valve bearing bushing  5  is shorter in construction than in prior art according to  FIG. 1 . Cam lever  7  and cam  8  are accordingly arranged lower. 
       FIG. 3  shows a third cylinder head arrangement  10 . This substantially corresponds to the second cylinder head arrangement  9  shown in  FIG. 2 , third cylinder head arrangement  3  having no cup guide, however. A valve bearing bushing  5 , which has a guidance area  11  for guiding a valve stem  12  of a gas exchange valve  6 , is inserted into cylinder head  3 . An upper spring retainer  14  and a lower spring retainer  15  are provided to clamp in a closing spring  13 . Spring  13  is shown on the left side of valve stem  12  in a position corresponding to an open position. On the right side of the valve stem, spring  13  is shown in the closed position of valve  6 . A valve head  16  lying against a valve seat  17  of a gas intake port  18  represents the closed position. In an open position, not shown, valve head  16  is accordingly moved downwards. Gas exchange valve  6  is actuated by means of a cam lever  7  which is controlled by a cam  8 . In this movement, cam  8  passes over an envelope circle  19  of cam  8 . As cam  8  revolves, cam lever  7  is moved downwards with its oscillating end  20 , so that valve  6  is opened. A fixed end  21  of cam lever  7  is seated on a cam lever bearing  22 . Valve shaft  12  is parallel to a main cylinder axis  23  of a cylinder, not shown. 
     A valve stem diameter A in the guidance area is 4 mm. A first distance B between a lower edge  24  of valve head  16  and an upper edge  25  of oil circuit  19  of cam  8  is 136 mm relative to the cylinder&#39;s main axis  23  in the closed position of the valve as shown. A second distance C between an end face  27  provided at one end  26  of the valve for transferring an actuation force, and a lower edge  28  of valve bearing bushing  5  is 49 mm. Length  29  of the guidance area is 7 mm and thus 8% of the valve length, which is 85 mm. 
     A product of second distance C and valve stem diameter A divided by the square of the first distance B is 0.0106. 
     A product of second distance C and valve stem diameter A is 196 mm 2 . 
     Length  29  of the guidance area divided by valve stem diameter A is 1.75. 
     Second distance C divided by guidance length  29  of the valve bearing bushing is  7 . 
       FIG. 4  shows a fourth cylinder head arrangement  30 , which essentially corresponds to second cylinder head arrangement  10  shown in  FIG. 3 . Differently from the latter, a cup guide  31  is provided in fourth cylinder head arrangement  30 . It guides a spring retainer  14  constructed as a cup  32 . In particular, cup guide  31  counters transverse forces. Additionally, a second guidance length  34  is formed between a lower edge  28  of valve bearing bushing  5  and an upper edge  33  of cup guide  31 . Second guidance length  34  is approximately 52% of valve length  35 . Cup guide  31  is formed directly in cylinder head  3 . In the configuration that is not shown, a guidance cap placed on cylinder head  3  can also be provided. 
     A cooling space  36  is provided for cooling valve bearing bushing  5 . A first edge  37  according to a first variant is shown. A second edge  38  according to a second variant, which is intended to ensure improved cooling, is shown with a thinner line. A wall thickness  39  in an environment of valve bearing bushing  5  is roughly 2 mm. Contrary to the representation shown, a wall thickness between roughly 1 and 5 mm can be provided. Furthermore, a direct cooling of the valve bearing bushing in conjunction with an appropriate seal can be provided in a configuration that is not illustrated. 
     Mounting of the cup on valve stem  12  is provided by means of a thread  41 . Thereby the distance between a lower edge  24  of valve head  17  and an upper edge  42  of cup  32  can be enlarged or reduced. In one embodiment, not shown, a hydraulic tappet arrangement with an automatic clearance compensation can be provided. 
       FIG. 5  shows a cutout from a cylinder head arrangement  43 . An intake valve  44  and an exhaust valve  45  are provided on a cylinder, not shown. A first valve bearing bushing  46  is provided for guiding intake valve  44 ; a second valve bearing bushing  47  is provided for guiding exhaust valve is  45 . First valve bearing bushing  46  has a first length  48 , and second valve bearing bushing  47  as a second length  49 . Valve bearing bushings  46 ,  47 , as shown, differ essentially in a different design of a first guidance area  50  of the first valve bearing bushing and a second guidance area  51  of the second valve bearing bushing. A third length  52  of first guidance area  50  is approximately as large as fourth length  53  of second guidance area  51 . In the case of first valve bearing bushing  46  and in the case of second valve bearing bushing  47 , a ratio of third length  52  to first length  48  and a ratio of fourth length  53  to second length  49  are roughly 30%. A tilting of valve wearing bushings  46 ,  47  is preferably extensively prevented in cylinder head  3  by sufficient first and second lengths  48 ,  49 . 
     A transition fit is selected for a seat of a first valve bearing bushing  46 . 
     For a seat of second valve bearing bushing  47 , a clearance fit is selected. In another design, not shown, the first valve bearing bushing has an oversize of 0.02 in comparison with the associated bore in cylinder head  3 , not shown in detail. This can be provided for a cast-iron cylinder head. In the case of a cylinder head having a material comprising aluminum, aluminum alloy, magnesium and magnesium alloy, the first valve bearing bushing in one variant, likewise not represented, can have an oversize of up to 0.04 mm in comparison with the associated bore in the cylinder head. 
     In one variant, likewise not shown, a rocker arm control can be provided in place of second cam lever drive  54 . Additionally, likewise not shown, direct controlling of cup  32  with cam  8  can be provided. Furthermore, an upright valve arrangement, likewise not shown, can be provided in place of an overhead valve arrangement. 
     For better cooling of the valve, it is provided that intake valve  44  and preferably exhaust valve  45  each have a sodium core, not shown. This sodium core is provided in a borehole, likewise not shown, in valve stem  12 . This borehole forms a cavity which is approximately two-thirds filled with sodium. 
     In place of the mechanical valve drives shown in  FIGS. 1-5 , electromechanical, in particular electromagnetic, valve drives, could be provided there. Accordingly, a controlling by means of a camshaft and a cam lever shown there would be omitted, for instance, and, in particular, an electromagnetic drive would be arranged alongside the valve stem. 
       FIG. 6  shows a plan view onto a cylinder head  3 . A cutout is shown with the plan view onto a respectively indicated first cylinder bore  55  and a second cylinder bore  56 . Cylinder head  3  belongs to a four-cylinder internal combustion engine, the additional two cylinders not being visible in a cutout shown. Cylinder head  3  as a first intake valve opening  57 , a second one  58 , a third one  59  and a fourth one  60 . Correspondingly, it has a first exhaust valve opening  61 , a second one  62 , a third one  63  and a fourth one  64 . In the area of the intake valve openings, respective cup guides  31  are provided. These cup guides  31  are directly formed in cylinder head  3 . Cup guides  31  serve to guide the valve, not shown. Likewise not shown is the corresponding driving mimicry of the valve. Likewise, first exhaust valve opening  61 , second one  62 , third one  63  and fourth one  64  can have tappet guides, not shown. 
     Furthermore, a number of mounting holes  65  as well as an injector retainer  66  are provided.