Abstract:
In a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages extending from a plurality of combustion chambers defined in part by the cylinder head, the exhaust passages converging into a converging area also internally defined in the cylinder head, an oxygen sensor for detecting an oxygen concentration in exhaust gas is passed into the converging area substantially in parallel with a cylinder axial line. Thus, the oxygen sensor can be mounted relatively close to the combustion chamber while permitting the sensor to be uniformly exposed to the exhaust gas from the combustion chambers of an entire cylinder bank. Therefore, the oxygen sensor can be activated relatively quickly substantially without any warm-up, and can measure the oxygen concentration of the overall exhaust gas.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages.  
           [0002]    1. Background of the Invention  
           [0003]    It is known to form exhaust passages and a converging area into which the exhaust passages converge internally in a cylinder head as shown in Japanese patent No. 2709815. Japanese UM publication No. 5-44499 discloses engines in which an oxygen sensor for detecting an oxygen concentration is placed in an exhaust manifold and in an exhaust pipe downstream to the exhaust manifold.  
           [0004]    As an oxygen sensor is incapable of operating while the engine is still cold, it is preferable to mount the oxygen sensor as close to a combustion chamber as possible. However, if it is provided upstream of the exhaust manifold, it is exposed only to the exhaust gas produced from one of the cylinders, and incapable of giving the oxygen concentration of the overall exhaust gas. It is conceivable to provide an oxygen sensor for each combustion chamber, but it increases the cost and weight of the engine.  
           [0005]    1. Brief Summary of the Invention  
           [0006]    In view of such problems of the prior art, a primary object of the present invention is to provide a multi cylinder internal combustion engine having a compact exhaust manifold arrangement internally defined in a cylinder head.  
           [0007]    A second object of the present invention is to provide a multi cylinder internal combustion engine which allows an oxygen sensor to be mounted relatively close to the combustion chamber while permitting the sensor to be uniformly exposed to the exhaust gas from the combustion chambers of an entire cylinder bank.  
           [0008]    A third object of the present invention is to provide a multi cylinder internal combustion engine which can activate an oxygen sensor with a minimum warm up time period.  
           [0009]    A fourth object of the present invention is to provide a multi cylinder internal combustion engine which can protect an oxygen sensor from an excessive temperature rise.  
           [0010]    A fifth object of the present invention is to provide a multi cylinder internal combustion engine which provides a favorable mounting position for an oxygen sensor while providing a favorable cylinder head arrangement.  
           [0011]    A sixth object of the present invention is to provide a multi cylinder internal combustion engine which provides a favorable mounting position for an oxygen sensor so as to prevent damages to the oxygen sensor by being hit by an external object.  
           [0012]    According to the present invention, these and other objects can be accomplished by providing a multi cylinder internal combustion engine comprising a cylinder head internally defining exhaust passages extending from a plurality of combustion chambers defined in part by the cylinder head, the exhaust passages converging into a converging area also internally defined in the cylinder head, wherein: an oxygen sensor for detecting an oxygen concentration in exhaust gas is passed into the converging area substantially in parallel with a cylinder axial line.  
           [0013]    Thus, the oxygen sensor can be mounted relatively close to the combustion chamber while permitting the sensor to be uniformly exposed to the exhaust gas from the combustion chambers of an entire cylinder bank. Therefore, the oxygen sensor can be activated relatively quickly substantially without any warm-up, and can measure the oxygen concentration of the overall exhaust gas. By passing the oxygen sensor in parallel with a cylinder axial line, the sensor is protected from the heat of the converging area. In particular, by passing the sensor downwardly into the converging area from above, the assembly work can be simplified.  
           [0014]    In particular, if the converging area and the exhaust passages are defined at least in part by an exhaust passage wall extending laterally from the cylinder head defining an arched profile in a plane perpendicular to a cylinder axial line, and an oxygen sensor for detecting an oxygen concentration in exhaust gas is passed into the converging area, a particularly compact arrangement can be achieved. Also, the mounting position for the oxygen sensor can be gained in a compact manner without requiring any special arrangement.  
           [0015]    According to a preferred embodiment of the present invention for a favorable mounting position for the oxygen sensor, an exhaust outlet is defined adjacent to the converging area, and a hole for receiving the oxygen sensor is formed in a part of the cylinder head interposed between a pair of bosses provided adjacent to the exhaust outlet for supporting threaded bolts for joining an exhaust system component to the exhaust outlet.  
           [0016]    Once the oxygen sensor has been warmed up to a desired level, it is then desirable to prevent it from an excessively high temperature. To this end, a water jacket may be defined in the cylinder head so as to extend to an adjacent part of the oxygen sensor.  
           [0017]    Preferably, the exhaust system component consists of a catalytic converter, and an outer profile of the oxygen sensor is more inwardly located than an outer profile of the catalytic converter. Thus, the damages to the oxygen sensor by being hit by an external object during transportation and assembly work can be avoided. In the case of a V-type engine, preferably, a dimension between outer ends of oxygen sensors for the respective cylinder banks being smaller than a dimension between outer ends of the catalytic converters. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    Now the present invention is described in the following with reference to the appended drawings, in which:  
         [0019]    [0019]FIG. 1 is a partly broken away front view of a V-type six-cylinder engine embodying the present invention;  
         [0020]    [0020]FIG. 2 is a sectional bottom view of one of the cylinder heads of the engine shown in FIG. 1 taken along a plane passing through the central lines of the exhaust passages  17 ;  
         [0021]    [0021]FIG. 3 is a sectional view taken along line III-III of FIG. 2;  
         [0022]    [0022]FIG. 4 is a sectional view taken along line IV-IV of FIG. 2; and  
         [0023]    [0023]FIG. 5 is a side view of the cylinder head shown in FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    [0024]FIG. 1 generally shows a V-type six-cylinder engine embodying the present invention. This engine  1  comprises a cylinder block  4  defining a crankcase  2  and a pair of cylinder banks  3  arranged in the shape of letter-V, an oil pan  5  attached to the lower surface of the cylinder block  4 , a pair of cylinder heads  6  attached to the respective upper ends of the cylinder banks  3 , and a head cover  7  attached to the upper surface of each cylinder head  6 .  
         [0025]    Each cylinder hank  3  includes three cylinders  8  arranged in a single row, and a piston  9  is slidably received in each cylinder  8 . Each piston  9  is connected to a crankshaft  10  rotatably supported by the crankcase  2  via a connecting rod  11 .  
         [0026]    The cylinder head  6  of each cylinder bank  3  defines three combustion chambers  12  corresponding to the three cylinders  8 , and each combustion chamber  12  is provided with a pair of intake ports each provided with an intake valve  14  and a pair of exhaust ports each provided with an exhaust valve  15 . The intake valves  14  and exhaust valves  15  are actuated by a camshaft  13  which is coupled to the crankshaft  10 . A part of the cylinder head  6  corresponding to each combustion chamber  12  is fitted with a spark plug  18  having an electrode extending into the combustion chamber  12 .  
         [0027]    Between the opposing sides of the cylinder banks  3  is provided an intake manifold  19  which is communicated with the intake ports via intake passages  16  extending inwardly out of the combustion chamber  12 . Fuel injection valves  20  are provided in the intake manifold  19  to inject fuel into the individual intake passages  16 .  
         [0028]    Exhaust passages  17  extend within the corresponding cylinder heads  6  outwardly from the exhaust ports of the combustion chambers  12 , and converge at a converging area  21  defined in each cylinder head  6 . Each converging area  21  directly communicates with an exhaust outlet  26  opening out centrally on a side of the cylinder head  6 . The exhaust outlet  26  is surrounded by a relatively thick-walled annular part whose outer surface defines a mounting surface  27  for a flange  23  of a catalytic converter  22 . Therefore, the cylinder head  6  internally defines an exhaust manifold including the exhaust passages  17  and converging area  21 . An oxygen sensor  24  is passed through an upper wall of the cylinder head  6  located above the converging area  21 . This oxygen sensor  24  is provided with a detecting part which is located centrally in the converging area  21  so as to evenly contact the flow of the exhaust gas from the combustion chambers  12 .  
         [0029]    The distance A between the outer ends of the oxygen sensors  24  provided in the corresponding cylinder banks  3  is smaller than the distance B between the outer ends of the catalytic converters  22  of the corresponding cylinder banks  3  (A&gt;B). In other words, an outer profile of the oxygen sensor is more inwardly located than an outer profile of the catalytic converter. As a result, the outer most part of the lateral profile of the engine is defined by the catalytic converters  22  so that the oxygen sensors  24  are protected from damages that could be caused by hitting other objects during transportation and assembling work even without taking any protective measures.  
         [0030]    The cylinder head  6  is described in more detail in the following with reference to FIG. 2 which shows a section of the cylinder head  6  of one of the cylinder banks (for instance, the right cylinder bank) taken along a plane passing through the central lines of the exhaust passages  17 .  
         [0031]    Each intake passage  16  bifurcates into two sections which directly connect to the intake ports for each combustion chamber  12 , and the inlet end of the intake passage  16  opens out on the intake side of the cylinder head  6 . On the intake side of the cylinder head  6 , four vertical walls are internally defined inside the cylinder head between the adjacent combustion chambers and in the both ends of the cylinder bank  3 , and a head bolt opening  25  is drilled in each of these vertical walls to pass a corresponding one of four head bolts that are used for joining the cylinder head  6  to the cylinder block  4 .  
         [0032]    The exhaust ports for each cylinder are separated from each other by a vertical wall, and merge into the corresponding exhaust passage  17 . The exhaust passage  17  for the central combustion chamber  12  extends straight to the common exhaust outlet  26  via the converging area  21 . The exhaust side of the cylinder head  6  is defined by an exhaust passage wall  33  defining an arched profile in a plane perpendicular to a cylinder axial line. The exhaust passage  17  extending from each of the combustion chambers on an axial end of the cylinder hank  3  extends along the inner side of the corresponding part of the exhaust passage wall  33 . Numeral  21   a  denotes a downstream end of the exhaust passage  17  extending from each cylinder on an axial end of the cylinder bank which opens out into the converging area. A pair of vertical walls  28  are internally formed on the exhaust side of the cylinder head  6  so as to separate the exhaust passages from one another. In other words, the three exhaust passages  16  on each cylinder bank are defined substantially by the vertical walls  28  and exhaust passage wall  33 .  
         [0033]    Each of these vertical walls  28  is formed with a head bolt receiving hole  25  and an oil return passage  29  for communicating the interior of the head cover  7  with the interior of the crankcase  2 . Each axial end portion of the arched exhaust passage wall  33  is formed with a head bolt receiving hole  25  and an oil return passage  29 . These head bolt receiving holes  25  and oil return passages  29  are also formed by drilling.  
         [0034]    Because all of the oil return passages  29  are formed adjacent to the exhaust passages  17 , the lubricating oil can be quickly warmed up after starting the engine, and the time period required for the engine warm-up can be reduced. A mounting hole  30  for the oxygen sensor  24  is formed centrally in the converging area  21 .  
         [0035]    Referring to FIGS. 3 and 4, the cylinder head  6  is provided with a water jacket  31  which extends above and below the exhaust passages  17  as well as above each combustion chamber  12 . The outer periphery of the upper and lower water jackets  31 U and  31 L generally extends along the arched contour of the laterally outer wall or the exhaust passage wall  33  of the cylinder head  6 , but does not quite laterally extend so far as the arched exhaust passage wall  33  of the cylinder head  6 . In this embodiment, the exhaust passages  17  extend along an upwardly slanted plane as seen in the direction of the exhaust gas flow.  
         [0036]    If outer end walls  32  of the upper and lower water jackets  31  and the part of the exhaust passage wall  33  corresponding to the exhaust converging area  21  were given with a uniform wall thickness, there would be a recess  34  (as indicated by the imaginary lines in FIG. 3) along each of the upper and lower ends of the exhaust passage wall  33 . However, according to this embodiment, each of the outer end walls  32  of the upper and lower water jackets  31  and the exhaust passage wall  33  are connected by connecting walls  40 , and the outer profile of the exhaust side of the cylinder head  6  generally presents a smooth surface devoid of such recesses. The connecting walls  40  increase the effective wall thickness of the outer peripheral part of the cylinder head  6 , and can increase both the rigidity and thermal capacity of the converging area  21  without increasing the outer dimensions of the cylinder head  6 .  
         [0037]    As shown in FIG. 5, the connecting walls  40  are integrally connected to the four bosses  35  each formed with a threaded hole for receiving a threaded bolt for securing the catalytic converter  22 . The four bosses  35  are in turn integrally connected to the annular thick wall surrounding the exhaust outlet  26 . Therefore, the connecting walls  40  in cooperation with the annular thick wall contributes to the increase in the rigidity of the mounting surface  27  for the catalytic converter. Furthermore, the hole  30  for receiving the oxygen sensor  24  is formed between the upper two of the bosses  35 , and this allows the oxygen sensor  24  to be mounted without requiring any special provision or increasing the outer dimensions of the converging area  21 .  
         [0038]    The tangential surface of the bottom of the exhaust passages  17  forms an obtuse angle AG relative to the cylinder axial line as seen from the crankshaft as shown in FIG. 4. The part of the lower water jacket  31 L located under the exhaust passages  17  has a lower wall having a constant thickness and extending in parallel with the mating surface  36  of the cylinder head  6  for the cylinder block  4 . Therefore, the height of the lower water jacket  31 L is greater in the part remote from the combustion chamber  12  than the part adjacent to the combustion chamber  12  (C&gt;D). Also, the lower water jacket  31 L located under the exhaust passages  17  has a greater capacity than the upper water jacket  31 U located above the exhaust passages  17 . The upper and lower water jackets  31 U and  31 L extend from the central part of the cylinder head  6  to either lateral end at least beyond the downstream end  21   a  at which each exhaust passage  17  extending from the combustion chamber  12  on each axial end merges with the converging area  21 .  
         [0039]    Therefore, the water jackets, in particular the lower water jacket  31 L, are given with a large cooling water capacity in the area corresponding to the outer peripheral part of the converging area  21  which tends to have a high temperature. Therefore, this embodiment allows the efficiency of cooling the exhaust passages  17  to be improved without impairing the compact design of the engine. Also, because the upward slanting of the exhaust passages  17  minimizes the thickness of the upper wall of the converging area, the necessary length of the oxygen sensor can be minimized.  
         [0040]    The upper water jacket  31 L extends to either side of the oxygen sensor  24  or, in other words, is provided with a semicircular profile on an outer end thereof so as to partly surround the oxygen sensor  24 . Therefore, the oxygen sensor  24  is placed close to the combustion chamber so as to permit compact design of the cylinder head, and the excessive heating of the oxygen sensor can be avoided by circulating the cooling water close to the oxygen sensor.  
         [0041]    The upper and lower water jackets  31 U and  31 L are communicated with each other by a communication passage  37  provided in each of the vertical walls  28  formed between adjacent combustion chambers and a communication passage  38  provided in a small vertical wall separating the two exhaust ports in each combustion chamber  12 . In each of the vertical walls  28  formed between adjacent combustion chambers, the oil return passage  29  extends immediately next to the communication passage  37  so that the excessive rise in the temperature of the lubricating oil can be avoided, and the quality of the lubricating oil can be maintained over an extended period of time. Also, the oil return passage  29  and communication passage  37  would not cause any increase in the axial dimension of the cylinder head because they are conveniently formed in the walls  28  formed between adjacent cylinder heads.  
         [0042]    When a relatively large water jacket is formed in the cylinder head, there is a need to support the core that is used when casting the cylinder head in a stable manner. In particular, it is desirable to join the core parts defining the upper and lower water jackets by connecting portions having an adequate cross sectional area. In this case, the core parts defining the communication passage between the exhaust ports of each combustion chamber may not provide an adequate rigidity for connecting the core parts defining the upper and lower water jackets  31 U and  31 L. In this embodiment, the additional communication passages  37  are formed between adjacent combustion chambers, and the core parts defining these communication passages provide an additional support for the integrity of the core. Furthermore, because the upper water jacket  31 U is substantially smaller than the lower water jacket  31 L, the load on the core parts joining the core parts defining the upper and lower water jackets  31 U and  31 L is substantially reduced.  
         [0043]    Also, when placing the core parts for the exhaust passages between the core parts for the upper and lower water jackets, it is necessary to avoid any interferences between these core parts in the crankshaft axial direction. However, this arrangement allows it to be accomplished without any difficulty.  
         [0044]    In the foregoing embodiment, each oxygen sensor was passed vertically downwardly into the converting area to facilitate the assembly work, but it is also possible for the oxygen sensor to be passed vertically upward from below if desired.  
         [0045]    Although the present invention has been described in terms of a preferred embodiment thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.