Patent Publication Number: US-6216658-B1

Title: Engine cylinder block with optimized stiffness

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a cylinder block for an internal combustion engine and more particularly relates to a cylinder block with enhanced structural stiffness. 
     Deflection of a cylinder block of an engine is generally undesirable. Such deflection contributes to undesirable vibrational modes and noise emission levels when an assembled engine is running. It is known to provide stiffened block components in order to generally reduce the level of noise emitted from a running engine. For example, stiffened cylinder block walls are disclosed in U.S. Pat. Nos. 4,470,376; 4,461,247; and 4,627,394. 
     Block deflection can also lead to manufacturing complications. A conventional cylinder block substantially deflects between a free condition and an assembled condition due to the loads and stresses from cylinder head bolts and other components. Such distortion leads to an improper fit of components and unwanted tolerance changes. Accordingly, simulated loads are applied to conventional cylinder blocks during machining operations. An example of such a process is known as torque plate honing, whereby a torque plate is bolted to the conventional block to approximate the loads of a bolted-on cylinder head during honing of the cylinder bores. The bores are thus round when the cylinder head is later mounted to the block. Torque plate honing is necessitated by the degree of deflection of a conventional block. Otherwise, if the cylinder bores were machined while the block was in an unloaded condition, the cylinder bores would deflect from a round shape when the block is in its loaded, assembled condition, resulting in imprecise tolerances, undesirable wear patterns and poor oil consumption. Unfortunately, torque plate honing is costly and difficult to control in a production environment. 
     Conventional cylinder blocks have various openings formed therein to permit the connection of conduits, hoses, and other components. For example, an opening is conventionally formed in the wall of a cylinder block to accommodate the mounting of an oil cooler in fluid communication with the water jacket. A lack of structural material in such an opening leads to undesirable flexibility of the block. Accordingly, a need exists to design such a cavity with improved stiffness. 
     Another component known to emit noise is a cover plate that is bolted to a side of the cylinder block to cover reciprocating pushrods that extend from the crankcase to the cylinder head. The cover plate is known to transmit substantial levels of noise. 
     Accordingly, design features are desirable which provide a stiff block structure in order to reduce noise emission levels and to reduce deflection between free and assembly-loaded conditions. 
     SUMMARY OF THE INVENTION 
     According to the invention, a cylinder block is provided with enhanced stiffness. The cylinder block has an upper portion with a plurality of cylinder bores and a lower portion which forms a portion of the crankcase. Both the upper and lower portions of the block include sculpted outer wall portions. More specifically, the sculpted outer wall portions include a series of curved, non-planar sections. Each section is shaped generally as a partial cylinder so that the sculpted portion has an undulate shape. It has been found that the curved non-planar sections provide substantially greater stiffness relative to conventional planar wall sections. 
     An embodiment of the block may include stiffening ribs which extend between the cylinder bore and the outer wall of the block. The ribs are positioned to optimize cylinder bore stiffness. Bolt bosses may be integrally formed in the ribs having bolt holes to accommodate mounting of the cylinder head. 
     In an embodiment, the cylinder block includes an enclosed closed oil cooler cavity having a wall extending between the cavity and the water jacket. This wall provides structural rigidity to the cavity area, enhancing the stiffness of the block. 
     The cavity wall has an opening, which permits fluid communication between the cavity and the water jacket. A water pump outlet provides a flow of coolant into the cavity; however, the cavity wall opening is distally located relative to the water pump outlet so that coolant is advantageously guided to flow across the oil cooler with enhanced effectiveness. 
     In an embodiment, the block includes a closed tappet cavity, further enhancing stiffness of the block. More specifically, the tappet cavity has an upper wall that extends across the deck of the block. Holes are provided in the upper wall to permit pushrods to protrude upwardly to the cylinder head. The upper wall closing the tappet cavity provides additional stiffness to the block. 
     An advantage of the present invention is to provide a cylinder block with enhanced stiffness. 
     Another advantage of the present invention is to provide a cylinder block that reduces engine noise. 
     A further advantage of the present invention is to provide a cylinder block that eliminates a need for a torque plate honing process. 
     Yet another advantage of the present invention is to provide a cylinder block that reduces oil consumption. 
     A still further advantage of the present invention is to provide a cylinder block that enhances oil-cooling efficiency. 
     Additional features and advantages of the invention are described in, and will be apparent from, the Figures, description, and claims herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a cylinder block embodying features according to the present invention. 
     FIG. 2 is a sectional view as taken generally along line  11 — 11  of FIG. 5 illustrating curved wall portions in the vicinity of the lower portion of the cylinder block. 
     FIG. 3 is a sectional view as taken generally along line III—III of FIG. 5 illustrating curved wall portions in the vicinity of the upper portion of the cylinder block. 
     FIG. 4 is a sectional view as taken generally along line IV—IV of FIG. 3 illustrating one of the reinforcing ribs extending between a respective cylinder bore and the outer wall. 
     FIG. 5 is a sectional view as taken generally along line V—V of FIG. 3 illustrating a closed tappet area generally at the right. 
     FIG. 6 is a fragmentary sectional view of a cylinder block of FIG. 3 as taken X generally along line VI—VI, illustrating an embodiment having a closed oil cooler cavity. 
     FIG. 7 is a graph showing the noise level as measured on the right side of a cylinder block according to the invention (solid line) and a conventional cylinder block (dashed line). 
     FIG. 8 is a graph showing the noise level as measured on the left side of a cylinder block according to the invention (solid line) and a conventional cylinder block (dashed line). 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Now referring to the Figures, wherein like numerals designate like parts, FIGS. 1-6 illustrate a cylinder block  20  according to an embodiment of the invention. As illustrated in FIG. 1, the cylinder block  20  has an integrally formed metal body, including a lower portion  22  and an upper portion  24 . The block  20  has an outer casing  40  which is shared by the upper and lower portions  22  and  24 . A plurality of cylindrical parent bores  26  are formed in the block  20  to accommodate reciprocating pistons (not shown). An inner surface of each of the cylinder bores  26  is precisely machined to a smooth finish. The lower portion  22  forms a portion of a crankcase  28 . An oil pan (not shown) is typically mounted to the lower portion of the block  20  to enclose the crankcase. 
     The upper portion  24  of the block  20  forms a deck  30  on which a cylinder head (not shown) is to be mounted. As illustrated, the block  20  is of an in-line six-cylinder configuration, although the features of the invention may be applied to a block having another cylinder configuration as well. 
     The cylinder block  20  includes structural features according to the invention which enhance stiffness and which result in reduced noise emission levels by reducing block deflection. The stiffened block  20  also results in increased manufacturing efficiency and improved oil-cooling performance. 
     According to the invention, to provide improved stiffness, the outer casing  40  of the cylinder block  20  includes curved or sculpted wall portions  42 ,  44  at the lower crankcase portion  22  and at the upper portion  24 , respectively, as illustrated in FIG.  1 . More specifically, each of the sculpted wall portions  42 ,  44  of the block  20  includes a series of undulate, non-planar wall sections  46 ,  48 , respectively. Preferably, each wall section  46 ,  48  is curved, shaped as a partial cylinder, or otherwise non-planar. In an embodiment having cylindrical wall sections  46  and/or  48 , the sections  46 ,  48  may be located coaxially relative to the cylinder bores  26 . It has been found that the non-planar wall sections  46 ,  48  provide substantially greater stiffness relative to conventional planar wall sections without adding weight. 
     Referring particularly to FIG. 2, the lower sculpted wall portion  44  of the block  20  is shown. The non-planar wall sections  48  are concave inwardly relative to the crankcase  28 . Transverse support members  50  extend across the interior of the crankcase  28 , and each of the sections  48  extends between a neighboring pair of the support members  50 . A crank bearing surface  52  is centrally formed in each of the support members  50 . 
     Turning to FIG. 3, the non-planar wall sections  46  of the upper sculpted wall portion  42  are illustrated. On a side of the block  20  opposite the sculpted wall portion  42 , the casing  40  includes a sculpted closed tappet wall  62 . The closed tappet wall  62  is undulate in shape for enhanced stiffness and encloses a plurality of tappet cavities  60  as described in greater detail below in connection with FIG.  5 . Each of the tappet cavities  60  is generally formed by a tubular member having a curved, non-planar inner wall  66  and a curved, non-planar outer wall section  64  of the sculpted closed tappet wall  62 . Shorter sides  68  integrally connect the inner wall  66  and outer wall section  64 . The outer wall sections  64  and the inner walls  66  are concave in a direction generally facing the cylinder bores  26 . 
     For further enhancing stiffness of the cylinder bores  26 , the upper portion  24  of the block  20  may include a plurality of stiffening ribs  70  as shown in FIGS. 3 and 4. Each of the ribs  70  extends between the cylinder bores  26  and a cylinder head bolt boss  72 . More particularly, in the illustrated embodiment, the ribs  70  are connected to a member  71  formed by material shared by adjacent cylinder bores  26 . The ribs  70  also connect the bosses  72  to the sculpted wall portion  46 . The ribs  70  are positioned to optimize stiffness of the cylinder bores  26  and to cause any distortion that does occur to be as cylindrical as possible. 
     Additionally, each of the cylinder head bolt bosses  72  has a bolt hole  74  with threads that extend a greater distance into the block  20  than conventional bolt holes. Providing such lowered threads has been found to result in an improved load distribution in the block  20 , reducing an amount of contact pressure variation on the gasket ring (not shown) around each of the cylinder bores  26 . Specifically, the deep-positioned threads of the invention result in a pressure ratio variation (the ratio between the maximum pressure and minimum pressure) of about 1.6 as compared to a pressure ratio variation of about 3.4 for a conventional block. 
     As illustrated in FIGS. 1,  3  and  6 , an oil cooler cavity  80  is formed in a side of the cylinder block  20 . The oil cooler cavity  80  is shaped to receive a heat exchanger (not shown) for cooling engine oil. The oil cooler cavity  80  is provided with a flow of coolant, as described below in greater detail. The oil cooler cavity  80  is peripherally defined by four side walls  82  integrally formed as a side of the block  20 , as illustrated. The side walls  82  include bolt bosses  84  with bolt holes to accommodate the securing of a cover plate (not shown) with treaded bolts. 
     The block  20  has a water jacket  34  providing a passage for a flow of coolant around the cylinder bores  26  (FIGS. 4,  5 ). A conventional oil cooler cavity has had an entire side that opens directly into the water jacket. According to an embodiment of the invention, however, for further enhancing stiffness, the oil cooler cavity  80  is substantially closed by a cavity wall  86  extending between the side walls  82 , generally separating the cavity  80  from the water jacket. This cavity wall  86  provides structural rigidity to the region of the cavity  80 , enhancing the overall stiffness of the block  20 . 
     Advantageously, the cavity wall also enhances oil-cooling performance. Specifically, the cavity wall  86  has an opening  88  formed therein to permit fluid communication between the cavity  80  and the water jacket  34 . A water pump outlet  90  (FIG. 6) opens into the cavity  80 , delivering a flow of coolant from a water pump outlet duct across a core of the oil cooler. According to an embodiment of the invention, the opening  88  is distally located relative to the water pump outlet  90  so that coolant is advantageously guided to flow across a substantial area of the oil cooler to enhance cooling efficiency. As shown in FIG. 6, the water pump outlet  90  is generally at an upper portion of the cavity  80  while the opening  88  is located generally at a lower portion of the cavity  80 . It has been found that the cavity wall  86  of the invention results in a 49% improvement in oil cooling efficiency compared to a conventional open oil cooler cavity. 
     FIG. 5 shows the closed tappet cavities  60  mentioned above in connection with FIG.  3 . Each of the tappet areas  60  is enclosed at an outer side by the sculpted closed tappet wall  62  which is integrally cast with the block  20 . In particular, the block  20  includes cam bores  94  formed in the transverse support members  50  positioned in the crankcase  28 . A rotating cam shaft (not shown) is mounted in the cam bores  94 , driving a plurality of pivotably-mounted cam followers which cause a plurality of respective pushrods to reciprocate in a generally known manner. The pushrods extend upwardly through the closed tappet cavity  60  and protrude from the block  20  through holes  98  (FIG. 1) to operate valves in the cylinder head. 
     As shown in FIG. 5, a top of each of the tappet cavities  60  is also closed by an upper tappet cavity wall  96  which is integrally formed with the cylinder head deck  30 . In particular, the upper tappet cavity wall  96  extends across a top of the closed tappet cavity  60  between the pushrod holes  98  (FIG. 1) in the deck  30 , integrally connecting to a top edge of the sculpted closed tappet cavity wall  62 . The sides and bottom of the sculpted closed tappet cavity wall  62  are integrally connecting block  20  also between the cavities  60  and along its edges, in addition to being integrally connected at the upper tappet cavity wall  96 . Accordingly, the cast wall  62  is sturdy and rigid, minimizing vibration and noise transmission from the moving pushrods, cam followers and other components. Moreover, the sculpted wall  62  provides structural rigidity across the entire side of the block  20 , thereby further enhancing the overall stiffness of the block  20 . The tappet cavity wall  62  also eliminates the need for a conventional bolt-on cover and associated gasket, reducing a number of engine components. 
     Due to the enhanced stiffness of the block  20 , it has been found that the conventional practice of torque plate honing is unnecessary. Specifically, the cylinder bores  26  do not deflect substantially between free and loaded conditions, thereby eliminating a need for pre-loading the block  20  during machining of the cylinder bores  26 . The elimination of this processing step advantageously increases manufacturing efficiency and reduces costs. The stiffened block  20  also maintains its close tolerances, resulting in improved oil consumption performance. 
     The above-described features have been found to enhance the stiffness of the block  20 , resulting in substantially reduced noise levels. FIGS. 7 and 8 show noise spectrum data as measured from the left and right sides of the cylinder block  20 , respectively. In particular, the noise level emitted from the cylinder block of the invention (solid line) is substantially lower than the noise level emitted from a cylinder block having conventional structural features (dashed line). In both FIGS. 7 and 8, the peak noise level of the conventional cylinder block is approximately 69 dB, whereas the peak noise level of the cylinder block  20  of the invention is about 61 dB. 
     The present invention is not limited to the exemplary embodiments specifically described herein. To the contrary, it is recognized that various changes and modifications to the embodiments specifically described herein would be apparent to those skilled in the art, and that such changes and modifications may be made without departing from the spirit and scope of the present invention. Accordingly, the appended claims are intended to cover such changes and modifications as well.