Patent Publication Number: US-5836155-A

Title: Sensor arrangement for engine control system

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an engine control system and more particularly an improved sensor arrangement for such a system as particularly applied to two-cycle crankcase compression internal combustion engines. 
     The advantages to two-cycle internal combustion engines because of their simplicity and relatively low cost are well noted. However, the porting arrangement for these engines gives rise to certain problems in connection with exhaust emission control. Because of the overlap between the scavenging action and the exhaust, there is some difficulty in insuring good exhaust emission control. This is because some of the scavenging charge may actually pass out the exhaust port, and thus present the risk of unburned hydrocarbons escaping to the atmosphere. 
     In addition to this problem, because of the fact that the lubricant in a two-cycle engine is normally not recirculated but is consumed in the engine during its running, there is a likelihood of lubricant in the exhaust gases. Thus, this type of engine presents particular problems in controlling exhaust gas emissions. 
     Such features as the use of fuel injection and exhaust gas treatment as well as feedback controls have been proposed so as to permit the continued use of two-cycle engines, even in spite of environmental concerns. However, the use of some of these exhaust control methods also are made difficult by the inherent nature of the two-cycle engine operation. 
     For example, it has been the practice in four-cycle engines to use feedback control systems to maintain the desired air/fuel ratio under all running conditions. These feedback control systems employ oxygen sensors in the exhaust or other sensors to insure that the air/fuel ratio is maintained within the desired range and also to control exhaust emissions. The most commonly used type of sensor senses the presence of oxygen in the exhaust gases in order to provide an indication as to whether or not a stoichiometric mixture is being burned. However, due to the scavenging effect and the likelihood of some air charge in the exhaust gases, oxygen sensors may not be completely practical in these applications. This is because the oxygen sensor may receive some oxygen rather than exhaust gases during the final portions of the exhaust scavenged phase. Devices have been proposed for attempting to overcome these problems, but for a variety of reasons they have not been particularly successful. 
     It is, therefore, a principal object of this invention to provide an improved engine management system particularly adapted for use with two-cycle crankcase compression engines. 
     It is a further object of this invention to provide an improved sensor arrangement for feedback control in such engine management systems. 
     It is a still further object of this invention to provide an improved exhaust sensor arrangement for a two-cycle crankcase compression engine wherein the sensor is mounted and operated in such a way as to insure that primarily exhaust products will be delivered to the sensor. 
     In order to permit more accurate exhaust gas sensing in two-cycle engines, it has been proposed to provide an oxygen sensor arrangement wherein the oxygen sensor receives gases directly from the combustion chamber but only at times when the scavenging process is not at such a stage where the scavenge gases may contact the oxygen sensor. However, the type of systems proposed for this purpose have, for the most part, required some form of valving arrangement for insuring that the oxygen sensor only receives exhaust gases. This provides not only a complicated structure, but also a possible source for malfunction. 
     It is, therefore, a still further object of this invention to provide an improved oxygen sensor arrangement for two-cycle engines wherein it can be insured that the sensor receives exhaust products from the engine but not scavenging gas products. 
     As has been previously noted, the exhaust gases in two-cycle engines may contain amounts of lubricant. The type of exhaust sensors utilized for engine management systems are relatively sensitive and can be easily contaminated if lubricant comes in contact with them. 
     It is, therefore, a still further object of this invention to provide an improved exhaust sensor arrangement for an engine wherein the sensor, per se, is protected from contamination. 
     The type of exhaust sensors used for engine management systems are also sensitive to vibrations and mechanical shock and can be disabled if subjected to an impact force. It is, therefore, a still further object of this invention to provide an exhaust sensor arrangement for an engine wherein the sensor is protected from potentially damaging mechanical shock. 
     SUMMARY OF THE INVENTION 
     A first feature of this invention is adapted to be embodied in a control system for an internal combustion engine having a combustion chamber that varies in volume cyclically during engine operation. An exhaust system receives exhaust gases from the combustion chamber during a cycle of engine operation. A fuel supply system is provided for supplying fuel to the engine for combustion in the combustion chamber. An accumulator chamber is provided that affords a volume in which exhaust gases from the combustion chamber may be accumulated and which communicates with the combustion chamber for at least a portion of the engine operating cycle. A sensor is provided in the accumulator chamber for sensing the air/fuel ratio and providing a control signal for control of the fuel supply system. The inner surfaces of the accumulator chamber may be coated with a catalyst for preventing oil and exhaust gases from contaminating the sensor. A filter may be provided to intercept oil contained in the exhaust gases before reaching the sensor. 
     Another feature of the invention is adapted to be embodied in a control system for a ported engine having at least two combustion chambers, each of which cyclically vary in volume during a single cycle of operation. An accumulator chamber containing an exhaust sensor for sensing the condition of the exhaust gases is provided. This exhaust sensor provides a signal for controlling a fuel supply system that supplies fuel to the combustion chamber for combustion therein. 
     A still further feature of the invention is adapted to be embodied in a control system for a two-cycle internal combustion engine having a combustion chamber that varies cyclically during engine operation. An exhaust system receives exhaust gases from the combustion chamber during a cycle of engine operation. A fuel supply system supplies fuel to the engine for combustion in the combustion chamber. An accumulator chamber provides a volume in which exhaust gases from the combustion chamber may accumulate and communicates with the combustion chamber for at least a portion of the engine operating cycle. A sensor is provided in the accumulator chamber for providing a control signal for control of the fuel supply system. A protective sleeve around the sensor prevents oil in the exhaust gases from contaminating the sensor. The sensor may be mounted in recessed relation to the engine, or may be protected by a cover, to help minimize damaging external impacts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial schematic view showing an outboard boat motor constructed in accordance with an embodiment of the invention in side elevation, in rear plan with a portion of the protective cowling removed and in a schematic cross-sectional view, taken through one cylinder of the engine with the fuel supply system and feedback control system being shown in part schematically; 
     FIG. 2 is an enlarged side elevational view of the engine in the power head portion and looking in the same direction as the lower right-hand side view of FIG. 1; 
     FIG. 3 is a top plan view of the engine depicted in FIG. 2; 
     FIG. 4 is a cross-sectional view taken in the same direction as the rear elevational view of FIG. 1 on an enlarged scale and with portions of the engine broken away to more clearly show the construction; 
     FIG. 5 is a cross-sectional view of the portion of the outboard motor of FIG. 4 below the power head forming a continuation of FIG. 4 with a further part broken away and shown in section; 
     FIG. 6 is an enlarged cross-sectional view looking in the same direction as FIG. 2 with portions broken away and showing the sensor arrangement for the feedback control system of this embodiment; 
     FIG. 7 is a further enlarged cross-sectional view, taken in the same direction as FIG. 6, but shows the sensor element, per se, and its protective arrangement; 
     FIG. 8 is a partial schematic view and shows the relation of the sensor to one of the two cylinders with which it is connected in this embodiment; 
     FIG. 9 is a view, in part similar to FIG. 8, and shows the connection of the sensor to the other cylinder in this embodiment; 
     FIG. 10 is a graph showing the cycle of operation of each of the three cylinders of the engine of this embodiment in relation to crank angle, the condition of the porting communications to the sensor in the sensed cylinder and the controlling cylinder, the pressure in the accumulator chamber where the sensor element is positioned, and the sensor timing interval; 
     FIG. 11 is a view, in part similar to FIG. 4, with other portions being shown schematically, and illustrates another embodiment of the invention; 
     FIG. 12 is a side elevational view, in part similar to FIG. 2, and shows a further embodiment of the invention; 
     FIG. 13 is a rear elevational view, with a portion broken away, of the embodiment of FIG. 12; 
     FIG. 14 is an enlarged side elevational view, in part similar to FIGS. 2 and 12, and shows another embodiment of the invention; 
     FIG. 15 is a top plan view of the embodiment of FIG. 14; 
     FIG. 16 is a rear elevational view of this embodiment, with a portion broken away, and is similar in part to FIGS. 4, 11 and 13; 
     FIG. 17 is a side elevational view, in part similar to FIGS. 2, 12 and 14, and shows yet another embodiment of the invention; 
     FIG. 18 is a top plan view of this embodiment; 
     FIG. 19 is a rear elevational view of this embodiment, with a portion broken away and shown in section, and is in part similar to FIGS. 4, 11, 13 and 16; 
     FIG. 20 is an enlarged partially cross-sectional view, taken through the sensor of this embodiment; 
     FIG. 21 is a side elevational view, in part similar to FIGS. 2, 12, 14 and 17 of a still further embodiment of the invention; 
     FIG. 22 is a rear elevational view of this embodiment, with a portion broken away and shown in cross-section, and is in part similar to FIGS. 4, 11, 13, 16 and 19; 
     FIG. 23 is a cross-sectional view, taken in the area between the power head and drive shaft housing of an outboard motor constructed in accordance with a yet further embodiment of the invention; 
     FIG. 24 is a cross-sectional view, in part similar to FIG. 23, and shows yet another embodiment of the invention; 
     FIG. 25 is an enlarged cross-sectional view, in part similar to FIGS. 4, 11, 13, 16, 19 and 22 of still another embodiment of the invention; 
     FIG. 26 is a side elevational view, in part similar to FIGS. 2, 12, 14, 17 and 21 of a still further embodiment of the invention; 
     FIG. 27 is a rear elevational view, with a portion broken away, in part similar to FIGS. 4, 11, 13, 16, 19, 22 and 25 for this embodiment; 
     FIG. 28 is a top plan view of this embodiment; 
     FIG. 29 is an enlarged cross-sectional view of the sensor arrangement for this embodiment; 
     FIG. 30 is a graph, in part similar to FIG. 10, showing the operation of this embodiment; 
     FIG. 31 is an enlarged cross-sectional view, taken through a sensor arrangement constructed in accordance with yet another embodiment of the invention; 
     FIG. 32 is a view, with a portion broken away and shown in section, of a sensor arrangement constructed in accordance with still another embodiment of the invention, and is in part similar to FIGS. 6, 20, 29 and 31; 
     FIG. 33 is a side elevational view, in part similar to FIGS. 2, 12, 14, 17, 21 and 26, of still a further embodiment of the invention; 
     FIG. 34 is a rear elevational view, with portions broken away, in part similar to FIGS. 4, 11, 13, 16, 19, 22, 25 and 27 of this embodiment; 
     FIG. 35 is a top plan view of this embodiment; 
     FIG. 36 is an enlarged cross-sectional view, taken through the sensor arrangement of this embodiment; 
     FIG. 37 is a view looking from the direction perpendicular to that of FIG. 36, and shows how the sensor element is mounted in this embodiment; 
     FIG. 38 is a cross-sectional view, in part similar to FIG. 36, and shows a further embodiment of a sensor arrangement; 
     FIG. 39 is a cross-sectional view, in part similar to FIGS. 36 and 37, showing a still further sensor arrangement embodiment; 
     FIG. 40 is a cross-sectional view, in part similar to FIGS. 36, 38 and 39, of a still further sensor arrangement embodiment; 
     FIG. 41 is a cross-sectional view, in part similar to FIGS. 36, 38, 39 and 40, of a still further embodiment of a sensor arrangement, in accordance with the invention; 
     FIG. 42 is a cross-sectional view of another embodiment of a sensor arrangement in accordance with the invention; 
     FIG. 43 is a cross-sectional view of a still further sensor arrangement embodiment; 
     FIG. 44 is a cross-sectional view of another sensor arrangement embodiment; 
     FIG. 45 is a partial schematic view showing the relation of the oxygen sensor to two cylinders with which it is connected, similar to FIGS. 8 and 9 combined; 
     FIG. 46 is a graph illustrating the pressure peaks within the two cylinders to which the sensors shown in FIG. 45 are connected; 
     FIG. 47 is an enlarged side elevational view of an engine showing an oxygen sensor of the present invention mounted within a protective cover; 
     FIG. 48 is an enlarged rear elevational view of the sensor and protective cover of FIG. 47; 
     FIG. 49 is an enlarged top plan view of the sensor and protective cover of FIG. 47; 
     FIG. 50a is a partial vertical cross section through an engine similar to the view of FIG. 4, illustrating yet another sensor mounting arrangement in accordance with the invention; 
     FIG. 50b is a top plan view of the engine depicted in FIG. 50a; 
     FIG. 51 is a side elevational view of an engine showing an oxygen sensor connected to cylinders 1 and 3 and with exhaust communication passages formed integrally with the cylinder block of the engine; 
     FIG. 52 is an enlarged cross-sectional view of the oxygen sensor of FIG. 51 showing exhaust communication passages formed integrally with the cylinder block; 
     FIG. 53 is an enlarged partial sectional view similar to FIG. 6 showing a modified oxygen sensor element sleeve; 
     FIG. 54 is an enlarged cross-sectional view of another oxygen sensor arrangement similar to that shown in FIG. 36; 
     FIG. 55 is a perpendicular view to that of FIG. 54 similar to that of FIG. 37 and illustrates how the sensor element is mounted in this embodiment; 
     FIG. 56 is an enlarged cross-sectional view of a further embodiment of an oxygen sensor arrangement in accordance with the invention having a filter positioned in the inlet conduit; 
     FIG. 57 is an enlarged cross-sectional view of a further embodiment of an oxygen sensor arrangement, similar to that shown in FIG. 36, with a filter positioned within an inlet conduit and having an accumulator chamber coated with a catalyst; 
     FIG. 58 is a view taken perpendicularly to that of FIG. 57, illustrating how the sensor element is mounted in this embodiment; 
     FIG. 59 is a side elevational view of an engine, similar to that shown in FIG. 2, showing yet another oxygen sensor arrangement in accordance with the invention; 
     FIG. 60 is a rear cross-sectional view of the engine of FIG. 59; 
     FIG. 61 is an enlarged cross-sectional view of the oxygen sensor arrangement of FIGS. 59 and 60; 
     FIG. 62 is a partial sectional view of a cylinder head of an engine illustrating an alternative mounting arrangement for an oxygen sensor in accordance with the present invention incorporating a cooling water flow therearound; 
     FIG. 63 is a flow diagram illustrating a typical gas flow into an inlet port of a cylinder leading to an oxygen sensor; 
     FIG. 64 is an enlarged, cross-sectional view showing an improved inlet port in a cylinder of an engine leading to an oxygen sensor arranged in accordance with the present invention; 
     FIG. 65 is an enlarged cross-sectional view of the inlet port of FIG. 64; 
     FIG. 66 is an alternative embodiment of the inlet port of FIG. 65; 
     FIG. 67 is an enlarged, cross-sectional view of an angled inlet port in a cylinder of an engine leading to an oxygen sensor arranged in accordance with the invention; 
     FIG. 68 is a cross-sectional view of a still further embodiment of an inlet port leading to an oxygen sensor arranged in accordance with the invention; and 
     FIGS. 69a and 69b are two views of a cylinder of an engine showing an inlet port for an oxygen sensor opening into a combustion chamber. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     Referring now in detail to the drawings, and to the embodiment of FIGS. 1-10 initially by reference to FIG. 1, an outboard motor is shown in the lower portion of this figure in rear and side elevation and is indicated generally by the reference numeral 21. The invention is shown in conjunction with an outboard motor because the invention has particular utility in conjunction with two-cycle crankcase compression engines. Such engines are normally used as the propulsion device for outboard motors. For these reasons, the full details of the outboard motor 21 will not be described and have not been illustrated. Those skilled in the art can readily understand how the invention can be utilized with any known type of outboard motor. 
     The outboard motor 21 includes a power head that is comprised of a powering internal combustion engine, indicated generally by the reference numeral 22. The engine 22 is shown in the lower left-hand portion of FIG. 3 and in the lower view of FIG. 1, with a portion broken away, and in a schematic cross-sectional view through a single cylinder in the upper view of this figure. The construction of the engine 22 will be described later, but it should be noted that the engine 22 is mounted in the power head so that its crankshaft, indicated by the reference numeral 23, rotates about a vertically extending axis. The engine 22 is mounted on a guide plate 24 provided at the lower end of the power head and the upper end of a drive shaft housing, to be described. Finally, the power head is completed by a protective cowling comprised of a lower tray portion 25 and a detachable upper main cowling portion 26. 
     The engine crankshaft 23 is coupled to a drive shaft (not shown) that depends into and is rotatably journaled within the aforenoted drive shaft housing which is indicated by the reference numeral 27. This drive shaft then continues on to drive a forward/neutral/reverse transmission, which is not shown but which is contained within a lower unit 28. This transmission provides final drive to a propeller 29 in any known manner for propelling an associated watercraft. 
     A steering shaft (not shown) is affixed to the drive shaft housing 27. This steering shaft is journaled for steering movement within a swivel bracket 31 for steering of the outboard motor 21 and the associated watercraft shown in phantom and indicated generally by the reference numeral 30 in a well-known manner. 
     The swivel bracket 31 is, in turn, pivotally connected by a pivot pin 32 to a clamping bracket 33. The clamping bracket 33 is adapted to be detachably affixed to the transom of the associated watercraft 30. The pivotal movement about the pivot pin 32 accommodates trim and tilt-up operation of the outboard motor 21, as is well known in this art. 
     Continuing to refer to FIG. 1 and now primarily to the lower left-hand side view and the upper view, the engine 22 is depicted as being of the two-cycle crankcase compression type and, in the specific illustrated embodiment, is of a three-cylinder in-line configuration. Although this particular cylinder configuration is illustrated, it will be apparent to those skilled in the art how the invention may be employed with engines having other numbers of cylinders and other cylinder orientations. In fact, certain facets of the invention may also be employed with rotary or other ported type engines. 
     The engine 22 includes a cylinder block 34 in which three cylinder bores 35 are formed. Pistons 36 reciprocate in these cylinder bores 35 and are connected by means of connecting rods 37 to the crankshaft 23. The crankshaft 23 is, in turn, journaled for rotation within a crankcase chamber 38 in a suitable manner. The crankcase chamber 38 is formed by the cylinder block 34 and a crankcase member 39 that is affixed to it in any known manner. 
     As is typical with two-cycle crankcase compression engine practice, the crankcase chambers 38 associated with each of the cylinder bores 35 are sealed relative to each other in an appropriate manner. A fuel-air charge is delivered to each of the crankcase chambers 28 by an induction system which is comprised of an atmospheric air inlet device 40 (see also FIGS. 2 and 3) which draws atmospheric air through an inlet 41 from within the protective cowling. This air is admitted to the protective cowling in any suitable manner. 
     A throttle body assembly 42 is positioned in an intake manifold 50 downstream of the air inlet 41 and is operated in any known manner. Finally, the intake system discharges into intake ports 43 formed in the crankcase member 39. Reed-type check valves 44 are provided in each intake port 43 for permitting the charge to be admitted to the crankcase chambers 38 when the pistons 36 are moving upwardly in the cylinder bore 35. These reed-type check valves 44 close when the piston 36 moves downwardly to compress the charge in the crankcase chambers 38, as is also well known in this art. 
     Fuel is added to the air charge inducted into the crankcase chambers 38 by a suitable charge former. In the illustrated embodiments, this charge former includes fuel injectors 45, each mounted in a respective branch of the intake manifold downstream of the respective throttle valve 42. The fuel injectors 45 are preferably of the electronically operated type. That is, they are provided with an electric solenoid that operates an injector valve so as to open and close and deliver high-pressure fuel directed toward the intake port 43. 
     Fuel is supplied to the fuel injectors 45 under high pressure through a fuel supply system, indicated generally by the reference numeral 46. This fuel supply system 46 includes a fuel tank 47 which is positioned remotely from the outboard motor 21 and preferably within the hull of the watercraft 30 propelled by the outboard motor 21. Fuel is pumped from the fuel tank 47 by means of a fuel pump 48, which may be electrically or otherwise operated. This fuel then passes through a fuel filter 49, which preferably is mounted within the power head of the outboard motor 21. Fuel flows from the fuel filter 49 through a conduit into a fuel vapor separator 51, which includes a float controlled valve for controlling the level of fuel in the fuel vapor separator 51. Any accumulated vapor will condense, and excess vapor pressure can be relieved through a suitable vent (not shown). 
     Also mounted, preferably in the power head, is a high-pressure fuel pump 53 which is driven in any known manner as by an electric motor or directly from the engine 22. This fuel pump 53 draws fuel from the fuel vapor separator 51 through a conduit 52 and delivers fuel under high pressure to a fuel rail 54 through a conduit 55. The fuel rail 54 serves each of the injectors 45 associated with the engine. 
     A return conduit 56 extends from the fuel rail 54 to a pressure regulator 57. The pressure regulator 57 controls the maximum pressure in the fuel rail 54 that is supplied to the fuel injectors 45. This is done by dumping excess fuel back to the fuel vapor separator 51 through a return line 58. The regulated pressure may be adjusted electrically along with other controls, as will be described. 
     The fuel-air charge which is formed by the charge-forming and induction system as thus far described is transferred from the crankcase chambers 38 to combustion chambers, indicated generally by the reference numeral 59, of the engine. These combustion chambers 59 are formed by the heads of the pistons 36, the cylinder bores 35, and a cylinder head assembly 61 that is affixed to the cylinder block 34 in any known manner. The charge so formed is transferred to the combustion chamber 59 from the crankcase chambers 38 through one or more scavenge passages 62. 
     Spark plugs 63 are mounted in the cylinder head 61 and have their spark gaps 64 extending into the combustion chambers 59. The spark plugs 63 are fired by a capacitor discharge ignition system (not shown) . This outputs a signal to a spark coil which may be mounted on each spark plug 63 for firing the spark plug 63 in a known manner. 
     The capacitor discharge ignition circuit is operated, along with certain other engine controls such as the regulated fuel pressure, by an engine management ECU, shown schematically and identified generally by the reference numeral 66. 
     When the spark plugs 63 fire, the charge in the combustion chambers 59 will ignite and expand so as to drive the pistons 36 downwardly. The combustion products are then discharged through exhaust ports 67 formed in the cylinder block 34. These exhaust gases then flow through an exhaust manifold, shown in FIG. 4 and identified by the reference numeral 68. The exhaust gases then pass downwardly through an opening in the guide plate 24 to an appropriate exhaust system (to be described later) for discharge of the exhaust gases to the atmosphere. Conventionally, the exhaust gases are discharged through a high-speed under-the-water discharge and a low-speed, above-the-water discharge. The systems may be of any type known in the art. 
     The engine 22 is water cooled, and for this reason, the cylinder block 34 is formed with a cooling jacket 69 to which water is delivered from the body of water in which the watercraft is operating. Normally, this coolant is drawn in through the lower unit 28 by a water pump positioned at the interface between the lower unit 28 and the drive shaft housing 27 and driven by the drive shaft. This coolant also circulates through a cooling jacket formed in the cylinder head 61. After the water has been circulated through the engine cooling jackets, it is dumped back into the body of water in which the watercraft is operating. This is done in any known manner and may involve the mixing of the coolant with the engine exhaust gases to assist in their silencing. This will also be described later. 
     Although not completely shown in the drawings, the engine 22 is also provided with a lubricating system for lubricating the various moving components of the engine 22. This system may spray fuel into the intake passages in proximity to the fuel injector nozzles 45 and/or may deliver lubricant directly to the sliding surfaces of the engine 22. This lubricant is supplied from a tank 70 mounted adjacent the air inlet device 40 (FIG. 3). 
     Referring now primarily to FIGS. 4 and 5, the exhaust system for discharging the exhaust gases to the atmosphere will be described. As has been noted, the exhaust manifold 68 communicates with an exhaust passage, indicated by the reference numeral 71, that is formed in the spacer or guide plate 24. An exhaust pipe 72 is affixed to the lower end of the guide plate 24 and receives the exhaust gases from the passage 71, as shown by the arrows 73. 
     The exhaust pipe 72 depends into an expansion chamber 74 formed within the outer shell 75 of the drive shaft housing 27. This expansion chamber 74 is defined by an inner member which has a lower discharge opening 76 that communicates with an exhaust chamber 77 formed in the lower unit 28 and to which the exhaust gases flow. 
     A through-the-hub, high speed, exhaust gas discharge opening 78 is formed in the hub of the propeller 29 and the exhaust gases exit the outboard motor 22 through this opening below the level of water in which the watercraft 30 is operating when traveling at high speeds. In addition to this high speed exhaust gas discharge, the outboard motor 21 may be provided with a further above-the-water, low speed, exhaust gas discharge (not shown). As is well know in this art, this above-the-water exhaust gas discharge is relatively restricted, but permits the exhaust gases to exit without significant back pressure when the watercraft 30 is traveling at a low rate of speed or is idling, and the through-the-hub exhaust gas discharge 78 will be deeply submerged. 
     As has been previously noted, the cooling water from the engine cooling jacket 69 may also be mixed with the exhaust gases. To accomplish this, the guide plate 24 is provided with a cooling jacket 79 which extends around the exhaust passage 71 and into which the spent cooling water from the engine 22 is returned. This water is then drained through one or more drain openings 81 formed in the lower surface of the guide plate 24. These openings 81 communicate with a water jacket 82 which is formed in the space 83 existent between the outer shell of the expansion chamber 74 and the inner surface of the drive shaft housing outer shell 75. This water flows in the direction of the arrows 85. 
     Finally, a horizontally extending wall 86 formed at a lower portion of the drive shaft housing 27 is provided with one or more water discharge openings 87. The water flows through these openings 87, as also indicated by the arrows 85, so as to mix with the exhaust gas flow 73 and be discharged back into the body of water in which the watercraft is operating. 
     Thus, the existence of the cooling jacket 83 around the expansion chamber 74 provides silencing and cooling. If desired, a cooling jacket may also be formed around the exhaust manifold 68, and this cooling jacket is formed, as shown primarily in FIG. 4, by a cover plate 88 that is affixed to the side of the cylinder block 34 and which defines a cooling jacket 89, as well as a portion of the exhaust manifold 68. Coolant is delivered to this cooling jacket 89 from the engine cooling jacket 69 in an appropriate manner. This water is also then discharged to the guide plate cooling jacket 79. 
     It has been noted that the ECU 66 controls the capacitor discharge ignition circuit and the firing of the spark plugs 63. In addition, the ECU controls the fuel injectors 45 so as to control both the beginning and duration of fuel injection and the regulated fuel pressure, as already noted. The ECU 66 may operate on any known strategy for the spark control and fuel injection control 45, although this system employs an exhaust sensor assembly indicated generally by the reference numeral 91 constructed in accordance with the invention. 
     So as to permit engine management, a number of sensors are employed. Some of these sensors are illustrated either schematically or in actual form, and others are not illustrated. It should be apparent to those skilled in the art, however, how the invention can be practiced with a wide variety of control strategies other than or in combination with those which form the invention. 
     The sensors as shown primarily in FIG. 1 include a crankshaft position sensor 90 which senses the angular position of the crankshaft 23 and also the speed of its rotation. A crankcase pressure sensor 92 is also provided for sensing the pressure in the individual crankcase chambers 38. Among other things, this crankcase pressure signal may be employed as a means for measuring intake air flow and, accordingly, controlling the amount of fuel injected by the injector 45, as well as its timing. 
     A temperature sensor 93 may be provided in the intake passage downstream of the throttle valve 42 for sensing the temperature of the intake air. In addition, the position of the throttle valve 42 is sensed by a throttle position sensor 94. Engine temperature is sensed by a coolant temperature sensor 95 that is mounted in an appropriate area in the engine cooling jacket 69. An in-cylinder pressure sensor 96 may be mounted in the cylinder head 61 so as to sense the pressure in the combustion chamber 59. A knock sensor 97 may also be mounted in the cylinder block 34 for sensing the existence of a knocking condition. 
     Certain ambient conditions also may be sensed, such as atmospheric air pressure by a sensor 98, intake cooling water temperature, as sensed by a sensor 99, this temperature being the temperature of the water that is drawn into the cooling system before it has entered the engine cooling jacket 69. 
     In accordance with some portions of the control strategy, it may also be desirable to be able to sense the condition of the transmission for driving the propeller 29 or at least when it is shifted into or out of neutral. Thus, a transmission condition sensor 100 is mounted in the power head and cooperates with the shift control mechanism for providing the appropriate indication. 
     Furthermore, a trim angle sensor 101 is provided for sensing the angular position of the swivel bracket 31 relative to the clamping bracket 33. 
     Finally, the engine exhaust gas back pressure is sensed by a back pressure sensor 102 that is positioned within the expansion chamber 74 which forms part of the exhaust system for the engine and which is positioned in the drive shaft housing 27. 
     The types of sensors which may be utilized for the feedback control system provided by the ECU 66 are only typical of those which may be utilized in conjunction with the invention. As has been noted, the invention deals primarily with the oxygen sensor assembly 91 and its construction and the way in which exhaust gases are delivered to it. For that reason, further details of the description of the components of the engine and outboard motor that have no particular importance in conjunction with the understanding of the construction and operation of the oxygen sensor assembly have been omitted. 
     To be able to understand the construction and operation of the oxygen sensor assembly 91, it is also necessary to identify the various cylinders of the engine since, at least in some embodiments, the oxygen sensor assembly 91 is associated with more than one cylinder of the engine 22, for reasons which will become apparent. In order to permit this description to be more clearly understood, the cylinders of the engine 22 have been numbered from top to bottom as cylinder 1, cylinder 2 and cylinder 3. In conjunction with the description of the exhaust sensor assembly 91, therefore, certain of the components which have been employed to describe the actual physical parts of the cylinders may also be identified as associated with a particular cylinder through the use of a suffix indicating the cylinder number to the individual part number. 
     The cylinders are numbered from top to bottom with cylinder no. 1 being juxtaposed to a flywheel magneto assembly 103 that is affixed to the upper end of the crankshaft 23 in any well known manner. This flywheel magneto assembly 103 supplies electrical power for the aforenoted capacitor discharge ignition system. In addition, it may be provided with a ring gear 104 that cooperates with an electrically operated starter motor 105 (FIG. 3) that is affixed to one side of the cylinder block 34. 
     The sensor assembly 91 has a construction as best shown in FIGS. 6 and 7, although its interaction with the engine will be described later by reference to other figures. The sensor assembly 91 is comprised of an outer housing assembly, indicated generally by the reference numeral 106, and which is comprised, in this embodiment, of an outer housing piece 106a that defines a relatively large accumulator volume 107. 
     A sensor element, in this case an oxygen sensor, indicated generally by the reference numeral 108, has its sensing portion 109 mounted within a fitting 111 which, in turn, has a threaded connection 112 with the outer housing element 106a, so that the sensor portion 109 extends into the accumulator chamber 107. However, the sensor portion 109 is protected by means of a protecting shell 113 that is fitted onto a tubular projection 114 of the mounting fitting 111. A plurality of openings 115 are formed in the shell 113 so as to permit the communication of exhaust gases with the sensor portion 109, but also to protect the sensor portion 109 from damage. 
     The sensor portion 109 is formed as a platinum-plated glass tube having a hollow center 116. An electrical heater 117 extends in the hollow center 116 along the centerline 118 of the sensor 108 and which communicates with the ECU 66 through a shielded conductor 119. As is known, the element 109 will output a signal indicative of oxygen content in the exhaust gas, and thus provides an indicator whether the fuel/air mixture is stoichiometric or not. The actual constituency of the sensor 109 may be of any desired type utilized in this control art. The important features of the invention is that the sensor is positioned in the accumulator chamber 107 in such a manner and is of such a size that it occupies substantially less than one-half of the volume of the accumulator chamber 107. This ensures that the gas actually sensed by the sensor element 109 will be representative of the actual combustion products of the engine. 
     In this and in certain other embodiments, the exhaust gases or combustion products are delivered to the accumulator chamber 107 in a timed relationship from one cylinder of the engine. In this particular embodiment, the cylinder which supplies the exhaust gases to the accumulator chamber 107 is cylinder no. 2. The way in which this is accomplished will now be described by primary reference to FIGS. 6-10, although the structure also appears in certain of the other figures. 
     A first or inlet conduit 121 opens into the accumulator chamber 107 and has an inlet port 122 which opens into the cylinder bore 35-2 of the no. 2 cylinder. This inlet port 122 is disposed at a point approximately equal to the point where the exhaust port 67-2 is opened as the piston 36-2 is moving down at the end of the expansion and the beginning of the scavenge stroke, as shown in FIG. 9. The direction of piston 36-2 travel is indicated by the arrow thereon. Thus, under the condition as shown in FIG. 9, exhaust or combustion gases will flow from the combustion chamber 59-2 into the accumulator chamber 107 through a port 123 formed at the end of the conduit 121, and as shown by the arrow 124. It should be noted that this communication is open at the time when the piston 36-2 first slides past the communication port 122, and this occurs substantially at the end of the combustion and expansion phase and before the scavenge ports 62-2 of this cylinder (2) are opened. 
     A further and exhaust conduit 125 extends from a point in the accumulator chamber 107 that is, in this embodiment, spaced further from the sensor element 109 than the port 123 from cylinder no. 2. This communication passageway 125 has an inlet port 126 which opens into the accumulator chamber 107 and a discharge port 127 which communicates with cylinder no. 1, as shown in FIG. 8. 
     It should be noted that the communication port 127 intersects the cylinder bore 35-1 at a point adjacent where its scavenge port 62-1 will be opened when the piston 36-1 moves downwardly. That is, the ports 122 and 127 of the communication conduits 121 and 125 have a different timing relative to the events in the cylinders with which they are associated. Also, it should be noted that the cylinders are out of phase with each other, as is typical with engine practice, so as to provide more uniform firing impulses. This condition may be best seen in FIG. 10, wherein the timing phase for each cylinder is depicted in relation to crankshaft rotation. 
     It will be seen that the cylinders 1, 2 and 3 reach top dead center position at 120° from each other so as to provide equal firing impulses. It will be also seen from FIG. 10 that because of the spacing of the respective port openings 122 and 127, the port opening 122 will be opened and closed for approximately equal crank angles. However, the port 127 will be opened a shorter time than that of the port 122, and closed for a longer time than it is open. Also, the opening and closing times are staggered from each other, as shown in this figure, due to the difference in timing of the individual cylinders. 
     Thus, beginning at the crankshaft rotation indicated by the point A in FIG. 10, cylinder no. 2 will be at a point slightly after its top dead center position, with the piston 36-2 moving downwardly in the cylinder bore, as shown by the arrow on the piston in FIG. 9. However, the piston 36-2 will be displaced in the cylinder bore 35-2 well above the position shown in FIG. 9 so that the port 122 will be closed and the combustion will have just begun and the gases will be expanding. At this same time, the piston 36-1 in cylinder no. 1 will still be traveling downwardly in a direction opposite to the arrow on the piston shown in FIG. 8, and the piston will be approximately in the position shown in FIG. 8, with the port 127 just about to open. At this time, due to internal leakage the pressure of the gases trapped in the chamber 107 will have fallen to a point A, as shown in the graph of FIG. 10. 
     Upon continued rotation of the crankshaft 23, the port 127 will open, while the port 122 is still closed, and the pressure in the accumulator chamber 107 will fall and the gases will flow from the chamber 107 to the cylinder bore 351. At this point in time, the pressure in the cylinder bore 35-1, and specifically in its combustion chamber 59-1, will be substantially lowered because the exhaust port 67-1 will have been open for some time and the scavenge port 62-1 will have just opened along with the opening of the port 127. Thus, the pressure in the accumulator chamber 107 will be higher than this pressure and flow will occur in the direction of the arrow 125a, as indicated in FIG. 8. FIG. 10 also shows the drop-off of pressure in the accumulator chamber. 
     This movement continues with the piston 36-1 of cylinder 1 reaching its bottom dead center position and then moving upwardly, as shown by the arrow on the piston in FIG. 8, in a direction to close the scavenge port 62-1 and eventually the port 127 communicating with the accumulator chamber 107. However, before the port 127 is closed, the piston in 36-2 in cylinder no. 2 will have moved past the port 122 and it will be opened at approximately the same time the exhaust port 672 of this cylinder opens. As a result, the high pressure gases from the combustion chamber 59-2, which have not had a chance to dissipate through full opening of its exhaust port 67-2, will flow through the conduit 121, as shown by the arrow 124, into the accumulator chamber 107. 
     When the port 122 does open at the point B, then the pressure in the accumulator chamber 107 will build up quite rapidly, and the accumulator chamber 107, which has been purged by the flow when both ports 122, 127 were open, will be charged with the fresh combustion products from combustion chamber 59-2. This build-up pressure occurs until and slightly after the point C when the port 127 closes. This operation continues, although the pressure in the accumulator chamber 107 will then begin to fall, due to the exhaust of gases as its exhaust port 67-2 is opened, until this port again closes at the crank angle D. 
     Hence, the time period C to D is a time period when the exhaust gases in the chamber 107 will represent the instantaneous condition in cylinder no. 2 and the ECU 66 is programmed so as to read the output from the sensor element 109 during this time period. Thus, a very good reading of exhaust gas constituents combustion process can be measured at this time, and then appropriate feedback control initiated by the ECU 66 to provide the appropriate air/fuel ratio and exhaust emission control. 
     In the embodiment thus far described, the exhaust condition sensor assembly 91 has received its inlet of exhaust gases from cylinder no. 2, and exhaust gases were discharged from the accumulator chamber 107 to cylinder no. 1. FIG. 11 shows another embodiment of the invention wherein the sensor assembly 91 receives exhaust gases from cylinder no. 1 and the exhaust gases are discharged not directly back to another cylinder, but back to the induction system, and specifically the intake manifold 50 at a point downstream of the throttle valve of one of the intake runners. This throttle valve is shown in this figure and is identified by the reference numeral 151. Thus, the supply conduit 121 has its inlet port 122 in communication with the cylinder bore 35-1 at a point substantially the same as the communication passageway with cylinder bore 35-2 of the previously described embodiment. The discharge passageway 125, however, has a discharge end 152 in communication with the intake passage of the manifold 50 downstream of the throttle valve 151. Thus, the exhaust gases will be bled back in and mixed with the intake charge. This may, in fact, be utilized to provide a limited amount of exhaust gas recirculation. The operation of this embodiment should be apparent from the foregoing description and, for that reason, further description of this embodiment is not believed to be necessary to permit those skilled in the art to practice the invention. 
     FIGS. 12 and 13 show another embodiment which is similar to the embodiment of FIG. 11, and the overall engine construction is similar to the embodiment of FIGS. 1-10. For that reason, where components of this embodiment are the same or substantially the same as those previously described, they have been identified by the same reference numerals. 
     In this embodiment, the accumulator chamber 107, and specifically its discharge conduit 125, is communicated with a crankcase chamber of the engine. The conduit 121 has its port 122 communicating with the cylinder bore 35-1 in the manner previously described. In addition, a pair of one-way check valves, indicated by the reference numerals 171 and 172, are provided in the inlet conduit 121 and exhaust conduit 125, respectively. These check valves 171 and 172 permit flow only in the direction of the arrows illustrated, and, therefore, it will be ensured that reverse flow cannot occur. That is, the accumulator chamber 107 will always be charged from the cylinder bore 35-1 and will discharge always to the crankcase chamber. No reverse flow will be permitted because of the check valves 171 and 172. 
     FIGS. 14-16 show another embodiment of the invention which is generally similar to those embodiments thus far described, and where the components are the same or substantially the same, they have been identified by the same reference numerals and will only be described again as is necessary to understand the construction and operation of this embodiment. 
     In this embodiment, the sensor assembly 91, and specifically its housing 106a, is mounted to the cylinder block 34 by means of a mounting bracket 201. The mounting bracket 201 is appropriately affixed to the cylinder block. 
     In this embodiment, like those of FIGS. 11 and 12 and 13, the pressure supply conduit 121 for the accumulator chamber 107 has its inlet port 122 in registry with the first cylinder bore 35-1 at a location as previously described. With this embodiment, the discharge conduit 127 extends in part through the cylinder block 34 and terminates in a discharge opening 202 that communicates with the exhaust manifold 68, and specifically the portion of the exhaust manifold adjacent the exhaust port 67-1 of cylinder no. 1. In other regards, this embodiment is the same as those previously described and, for that reason, further description of this embodiment is not believed to be necessary to permit those skilled in the art to practice the invention. 
     FIGS. 17-20 show a sensor assembly 91 constructed in accordance with yet another embodiment of the invention. Like those embodiments previously described, many components of this embodiment are the same as those described previously and, for that reason, components which are the same have been identified by the same reference numerals and will not be described again, except insofar as is necessary to understand the construction and operation of this embodiment. 
     Like the embodiment of FIGS. 14-16, the sensor housing 106a is mounted on the cylinder block 34 by a mounting bracket which has a slightly different configuration than that of that embodiment, but since it is the same in function, it has been indicated by the same reference numeral (201). In this embodiment, however, there is provided only an inlet conduit 121 which has its inlet port 122 in communication with the cylinder bore 35-1 at a point adjacent that corresponding to the opening of the exhaust port for this cylinder. In this embodiment, there is, however, no discharge conduit. Thus, the construction is simpler but will not provide as accurate an indication of each firing of the cylinder. However, the leak-down of pressure that occurs will cause sufficient fluctuation to provide good signals and, as noted above, this embodiment is simpler than those previously described. 
     FIGS. 21 and 22 illustrate another embodiment which has the simplicity of the embodiment of FIGS. 17-20, in that it only has one communication passageway, but will also ensure that the accumulator chamber 107 will receive a charge that is indicative of cycle-to-cycle operations. In this embodiment, the sensor assembly 91 is mounted directly on the cylinder head 61 and communicates with an internal passageway 221 formed therein, which communicates with one of the combustion chambers 59, in this instance the combustion chamber 59-1, associated with the no. 1 cylinder. Thus, there will be flow into and out of the accumulator chamber during the entire engine cycle. 
     In all of the embodiments as thus far described, the sensor assembly 91 has been positioned and constructed so as to receive the combustion products directly from the respective combustion chamber 59. Next will be described a series of embodiments wherein the sensor assembly 91 contacts the combustion products at a position in the exhaust system. In each of these embodiments, the structure of the sensor 108, per se, is the same as that previously described. However, the accumulator chamber, which will be identified by a different reference numerals, is formed integrally within either the engine 22 or another component of the outboard motor. 
     Referring first to the embodiment of FIG. 23, in this embodiment, the guide plate 24 is provided with an integral accumulator chamber 241 which is formed on one side of the exhaust passage 71 therethrough. This defines a volume into which the sensor element and its surrounding protective sleeve 113 passes. This chamber 241 is closed by a mounting plate 242 onto which the fitting 111 of the sensor element is threaded so as to provide a good support and yet one that would be well insulated. The sensor element 109 is not shown in this figure, but it may be the same as that shown in FIG. 7. 
     The accumulator chamber 241 communicates with the exhaust passage 71 through an opening 243. Thus, exhaust gases can flow into the accumulator chamber 241 through the opening 243. 
     A smaller vertically downwardly extending passage 244 extends through the guide plate 24 and into the exhaust expansion chamber 74 so that the exhaust gases may discharge. Also, this configuration permits any liquid which may condense in the accumulator chamber 241 also to drain into the expansion chamber 74. 
     This figure also shows small water drain openings 245 that extend from the spacer plate cooling jacket 79 into the expansion chamber 74 so that some water will be mixed directly with the exhaust gases and thus provide additional silencing and cooling therefor. 
     FIG. 24 shows another embodiment which is basically the same as the embodiment of FIG. 23. This embodiment, however, lacks the drain passage 244 and provides a smaller communicating port 251 that communicates the accumulator chamber 241 with the guide plate exhaust passage 71. 
     Another mounting arrangement for the sensor 108 is shown in FIG. 25, and in this embodiment, the engine exhaust cover plate 88 is provided with an integral accumulator chamber 271 which communicates with the exhaust manifold 68 adjacent one of the exhaust ports 67 through a restricted opening 272. Again, the construction of the sensor 108 is the same as that shown in FIG. 7 and, accordingly, this structure will not be described again. 
     This embodiment also employs a drain and discharge passageway 273 that has a discharge end 274 formed in the exhaust manifold 68 and which will create a pressure difference for flow through the accumulator chamber 271 and will also permit liquids to drain away from the sensor element 109. 
     Next will be described a series of embodiments which are generally the same as the embodiment of FIGS. 1-10 in that the accumulator chamber 107 communicates with two cylinders of the engine but with different timing so as to promote a one-way flow through the accumulator chamber 107. The connected cylinders in these embodiments are different from those shown in the embodiment of FIGS. 1 and 10, but because this is the only difference in the basic engine construction and connection of the elements, those elements which are the same or substantially the same as those previously described have been identified by the same reference numerals and will be described again only insofar as is necessary to understand and practice these embodiments. 
     In addition to the aforenoted difference, these embodiments also incorporate an arrangement for ensuring against contamination of the exhaust sensor 109 and other improvements in the sensor unit 91 itself. 
     Referring first to the embodiment of FIG. 26, it will be seen that the inlet conduit 121 that supplies exhaust gases to the sensor assembly 91, and specifically the accumulator chamber 107 thereof, extends from no. 1 cylinder. Therefore, the inlet port 122 is disposed so that it will be located at a point in the cylinder bore 35-1 that is disposed immediately adjacent the top edge of the respective exhaust port 67-1 so that it will open and close at substantially the same timing as the opening and closing of the exhaust port. 
     The return passage 125 extends to the cylinder bore 35-3 of cylinder no. 3 and is disposed so as to be opened and closed later in this cylinder cycle than the inlet opening 122. These openings are at slightly different phases than the previously described embodiment and, for that reason, the opening and closing will be described by reference to FIG. 30. In the embodiment of FIGS. 1-10, cylinders 1 and 2 were 120° out of phase from each other, and thus, the relationship between the port openings of the ports 122 and 127, was as shown in FIG. 10. Basically, the same relationship exists between the cylinders 1 and 3 in this embodiment where the timing of the port openings 122 and 127 are also shown in FIG. 30. 
     As may be seen, starting from the point A, when the inlet port 122 and cylinder bore 35-1 is closed because the piston is still moving downwardly from its top dead center position, the port 127 in the cylinder no. 3 will be open and pressure will fall off in the chamber 107. 
     This fall off in pressure occurs until the point B when the port 122 is opened by the downward movement of the piston 36-1 in the cylinder bore 35-1 when the exhaust port 67-1 first opens. Hence, pressure will build up rather rapidly up to the point C when the port 127 moves to its closed position. At the same time, the pressure at the port 122 will begin to decrease because of the opening of the exhaust port and the pressure will fall off to the point D. As with the previously described embodiment, the actual measurement by the sensor takes place in this time period (C to D). 
     As may be seen from FIG. 29, in this embodiment, the inlet port 123 into the accumulator chamber 107 is disposed at a greater distance from the sensor 109 than the earlier embodiment. In addition, the gases must flow at an angle, as shown by the line 271, to the outlet port 126. This movement is away from the sensor 109 and thus the sensor will be protected against impingement from foreign particles and lubricant in the combustion gases. In addition, any liquids that may condense in the accumulator chamber 107 can drain out of the opened port 126 down to the lowermost cylinder so as to avoid a build-up of contamination in the accumulator chamber. Thus, this embodiment provides the same advantages of the embodiment of FIGS. 1-10, but also the further advantage of better protection from contamination of the sensor 109. 
     FIG. 31 shows another embodiment of the invention, where both the inlet conduit 121 and discharge conduit 125 are extended so as to protrude in part into the accumulator chamber 107. These extending portions are indicated by the reference numerals 281 and 282, respectively. As may be seen, this causes the flow path 283 to be more acute and assist in separation due to the circuitous path that must be followed. In addition, this tends to further protect the sensor 109 from contamination. 
     Another sensor configuration that is constructed to protect the sensor element from contamination is shown in FIG. 32 and is identified generally by the reference numeral 301. This sensor 301 has the same basic construction and operation of the sensor of FIGS. 1-10, and which is shown in most detail in that embodiment in FIG. 6. Therefore, where components have the same construction and operation, they have been identified by the same reference numerals employed in that embodiment and will be described again only insofar as is necessary to understand the construction and operation of this embodiment. 
     It should be noted that this embodiment also reverts to the cylinder no. 2 to cylinder no. 1 connection of the embodiment of FIGS. 1-10, as opposed to the cylinder no. 1 to the cylinder no. 3 connection of the embodiment of FIGS. 26-30 and 31. 
     In this embodiment, protection is provided by placing an orifice plate, indicated generally by the reference numeral 302, at the discharge end 123 of the conduit 121 where it enters the accumulator chamber 107. This control orifice 302 has a restricted central opening 303 defined at the pair of conical sections 304 and 305 which in effect provide a convergent/divergent nozzle. Therefore, the flow along a path 306 will cause some of the air to be turned, as shown at 307, which will tend to reduce the likelihood that oil particles having larger inertia can enter the accumulator chamber 107. Thus, this slows down the flow and provides further assurance that the sensor 109 will not be contaminated. 
     FIGS. 33-37 show a still further embodiment of the invention which connects the sensor, indicated generally by the reference numeral 351 in this embodiment, with the engine in the same manner as with the embodiment of FIGS. 26-30. Because of that similarity, the basic engine and its association with the sensor will not be described again, and the same reference numerals have been applied so as to facilitate the understanding of the operation of this embodiment without necessitating a further description of components which have already been described. 
     In this embodiment, the sensor 351 is constructed in a way so as to further protect the exhaust sensing element, indicated generally by the reference numeral 108, and which has a construction substantially the same as that shown in FIG. 7. However, the protective device is constructed in a different manner, and it is comprised of an outer housing assembly, indicated generally by the reference numeral 352, and which includes a first housing piece 353 which defines a first chamber 354. The conduit 121 has an extending portion 355 which extends into the chamber 354 and which has a plurality of perforate openings 356 which communicate the discharge end 123 with the chamber 354. 
     The end of the extending portion 355 is received in a counterbore 357 formed adjacent the inner end of the chamber 354 and from which a U-shaped passage 358 extends. The passage 358 terminates in a counterbore 359 in which the inlet end 126 of the conduit 125 is press fit. 
     The chamber 354 is formed by a bore 361 that receives a closure plug 362 which is fitted around the inlet tube extension 355. 
     The sensor 108, and specifically its outer protecting sleeve 113, which has the openings 115, extends into a further accumulator chamber 364 formed by an opening 363 in the housing piece 353 and which is closed by a closure plug 365. A small orifice 366 communicates the accumulator chamber 364 with the accumulator chamber 354. These two chambers and, in fact, either one of them, has a volume that is more than one-half of the volume of the sensor element 109 itself. 
     The orifice 366 is surrounded by a conical surface 367 so that any lubricant which may enter the accumulator chamber 364 through the orifice 365 will condense, collect and drain back into the accumulator chamber 354. 
     In a similar manner, a drain port 368 is formed in the lower wall 361 of the accumulator chamber 354 and communicates with the conduit opening 359. The lower surface of this drain opening 368 is also formed with a conical surface 369 so as to assist in the assurance that lubricant or other foreign materials cannot damage the sensor assembly 109. 
     A sensor arrangement constructed in accordance with another embodiment is illustrated in FIG. 38. This embodiment differs from the embodiment of FIGS. 36 and 37 only in that the conduit 125 is not provided with the extension 355 or the apertures 356 and thus freely communicates with the chamber 354. However, this still provides the circuitous flow path and the protection of the sensor 108 from foreign contaminants. Because of its other similarities to the earlier embodiment, it is believed that a further description of this embodiment is not necessary to permit those skilled in the art to practice the invention. 
     FIG. 39 shows yet another embodiment which is similar to the embodiments of FIGS. 36 and 37 and of FIG. 38. In this embodiment, however, the accumulator chamber 354 is eliminated and the supply conduit 121 has an extending portion 401 that extends through an elongated bore 402 formed in the housing piece 353. A first port 403 extends through once side of the tube to the accumulator chamber 364 in which the sensor 108 is positioned and permits the exhaust gases to flow through this and through the restricted passageway 366, as the previously described embodiment. 
     In addition, a further passageway 404 in the tube end 401 communicates with the drain passageway 368 for return of drained or accumulated fluids. Again, the volume of the accumulator chamber 364 is substantially greater than half of the volume displaced by the sensor 109. 
     FIG. 40 shows another embodiment which is similar to the embodiments of FIGS. 36 and 37, FIG. 38 and FIG. 39. This embodiment employs the accumulator chamber 354 as the embodiments of FIGS. 36 and 37 and 38, but incorporates a further arrangement for providing a circuitous flow path therethrough that will help in the separation of lubricant and other foreign contaminants. Thus, the inlet conduit 121 is formed with an extending portion 451 that terminates at an end 454 in the chamber 354 which is spaced from the restricted opening 366 which communicates the accumulator chamber 354 with the accumulator chamber 364. 
     In addition, a discharge tube 455 is pressed into a counterbore 456 in the housing piece 353 and has its inlet end 457 spaced from and offset from the outlet end 454 of the conduit extension 451. As a result, there will be a circuitous flow path that will assist in the separation of oil and contaminants. 
     FIG. 41 illustrates an embodiment which is basically the same as the embodiment of FIGS. 36 and 37. Therefore, the components of this embodiment which are the same as that embodiment have been identified by the same reference numerals and will not be described again. 
     In this embodiment, the housing piece 353 is provided with a drain accumulation chamber 471 into which the gases flow from the passage 358 and also from the drain opening 368 and chamfered surface 369. The lower portion of the drain chamber 471 is provided with a drain opening 472 normally closed by a fitting 473. The fitting 473 may be removed for draining of accumulated fluids. The other cylinder of the engine (cylinder no. 3 in this embodiment) communicates with the drain chamber 471 or some other area upstream of the drain chamber 471. 
     The embodiments for protecting the sensor 108 from contamination thus far described have done this by primarily mechanical means. Now will be described several embodiments of the invention where this protection is achieved by means in addition to mechanical means. In these embodiments, heat is maintained in the accumulator chamber 107 in a variety of fashions. This provides two purposes. First, the sensor element 109 will be maintained at an elevated temperature and one which keeps it at its operating temperature. As know in this art, most exhaust sensors do not become fully operative until they reach an operating temperature that is relatively high. Thus, by maintaining heat in the chamber 107 and on the sensor element 109, it is possible to ensure good operation of the sensor. In addition, by keeping the temperature high, the likelihood of lubricant condensing in the accumulator chamber 107 is avoided. 
     Referring first to the embodiment of FIG. 42, the sensor is provided with an insulating outer housing, indicated generally by the reference numeral 501, which surrounds the housing 106a of the embodiment like that shown in FIG. 6, with an insulating layer, indicated generally by the reference numeral 502. As seen best in the enlarged portion of FIG. 42, the insulating layer 502 comprises a thick insulating layer 503 formed from a suitable material and a thin protective covering 504. Aside from this, this embodiment operates and functions the same as the embodiment of FIG. 6. For that reason, further description of this embodiment is not believed to be necessary to understand the construction and operation. 
     FIG. 43 shows another embodiment which is basically the same as the embodiment of FIG. 42. However, this embodiment additionally provides an electrical heating element, indicated by the reference numeral 531, within the accumulator chamber 107. This heating element 531 not only is in heat exchanging relationship with the outer housing 106a, but also extends around the sensor 109 and its protective sleeve 113. 
     The heating element 531 receives electrical power from a battery 532 and thus maintains the elevated temperature so as to provide oil protection and also to maintain a high temperature for good operation of the sensor 108. 
     FIG. 44 shows another embodiment which maintains heat by providing heat insulating couplings 551 and 552 between the conduits 121 and 125 and the adjacent engine structure. Hence, heat in the accumulator chamber 107 cannot be easily transmitted away from the chamber through the metal-to-metal connection of the previously described embodiments. 
     FIGS. 45 and 46 relate to the embodiment of the present invention shown in FIGS. 1-10 and supplement the disclosure of FIGS. 8-10. Corresponding elements are identified using the same reference number. FIG. 45 is a combination of FIGS. 8 and 9 and illustrates the timing of the pistons 36-1, 36-2 within cylinders 35-1, 35-2 in relation to the respective input ports 122, 127 leading to the oxygen sensor assembly 91. Specifically, as the piston 36-2 descends within cylinder no. 2, the sensor input port 122 opens at point B, at approximately the same time that the exhaust port 67-2 opens. This allows combustion products from the combustion chamber 59-2 to enter the accumulator chamber 107 surrounding the oxygen sensor 108 causing the pressure in the accumulator chamber 107 to build up quite rapidly. Because of the expansion of the gases within cylinder no. 2, and the opening of the exhaust port 67-2, the pressure therein, shown as P2 in FIG. 46, is decreasing. However, the pressure within cylinder no. 2 is higher than the pressure in cylinder no. 1 between the points B and C as best shown in FIG. 46. This causes exhaust gates to flow from the combustion chamber 59-2 into the combustion chamber 59-1 until the sensor outlet port 127 closes. The point C at which the outlet port 127 closes will occur when the piston 36-1 ascends upward sufficiently toward its top dead center position to cover the outlet port 62-1. The upward movement of the piston 36-1 compresses the gases within the combustion chamber and results in a pressure peak indicated by the line P1 in FIG. 46. The ECU 66 is programmed to read the output from the sensor element 109 at a time between points C and D. 
     A further embodiment is shown in FIGS. 47-49 which is generally the same as the embodiment of FIGS. 1-10 in that the accumulator chamber 107 communicates with two cylinders of the engine. Elements which are the same or substantially the same as those previously described have been identified by the same reference numerals, and will be described again only insofar as is necessary to understand and practice these further embodiments. 
     This embodiment incorporates a protective cover 600 for guarding against possible damage to the oxygen sensor assembly 91 and its associated conduits 121, 125. The cover 600 may be formed of any suitable material such as aluminum or high-temperature plastic and includes a pair of outwardly extending flanges 602 fastened to corresponding outward extensions 603 of the engine block 34 with bolts 604. The cover 600 is configured to conform to the shape of the sensor assembly 91 and conduits 121 and 125. More specifically, the cover 600 comprises a generally horizontal portion 606 adapted to extend generally around the housing 106a, containing the accumulator chamber, sensor assembly 91 and the shielded conductor 119 extending from the sensor 108. A second vertical portion 608 extends outward to encompass the conduits 121, 125. The first and second portions 606, 608 are disposed generally perpendicular to one another, and provide a space 610 therewithin for the oxygen sensor assembly 91. A hole 607 is provided in one end of the cover 600 for accommodating insertion of the shielded conduit 119. 
     FIGS. 50a and 50b show another embodiment wherein the engine construction and oxygen sensor arrangement are similar to the embodiment of FIGS. 1-10. Again, where components of this embodiment are the same or substantially the same as those previously described, they have been identified by the same reference numerals. 
     In this embodiment, the sensor assembly 91 is protected from possible damage and the overall engine structure is made smaller by mounting the oxygen sensor assembly 91 in a recess formed between adjacent cylinders of the engine block 34. As can be seen by a comparison with FIG. 4, the inlet and outlet conduits 121, 125 include shorter horizontal portions leading to the respective cylinders. The housing 106a of the oxygen sensor assembly 91 fits within a recess formed between the cylinders 1 and 2. The overall engine construction is thus made smaller, and the sensor assembly 91 is less subject to damage from outside forces because it is protected by the linkage 612 for the throttle 614. In this regard, the outward projection of the linkage 612 is indicated by dashed line 616. 
     FIGS. 51 and 52 illustrate a further embodiment wherein an oxygen sensor assembly 618 is mounted integrally with the cylinder block 34 and thus the overall structure is made more durable and compact. The main portion of the sensor 618, is defined by a housing 620 formed from a solid block of material and mounted to the cylinder block 34 with bolts 622. The housing 620 has machined therein an accumulator chamber 107 for housing the sensor element 109. In the embodiment illustrated, the housing 622 is mounted proximally between cylinders 1 and 2. 
     The inlet conduit to the accumulator chamber 107 is defined by a first portion 624 formed in the housing 622 angled upward and toward cylinder No. 1 35-1 and a second portion 626 formed in the engine block 34 and having approximately the same angle as the first portion 624. The second portion 626 extends into the first cylinder 35-1 and terminates at an inlet port 628. 
     The outlet conduit of the accumulator chamber 107 is defined by a short substantially vertical first portion 630 formed in the sensor housing 620, and an elongated second vertical portion 632 formed in the engine block 34. The first and second portions 630, 632 extend generally vertically downward from the accumulator chamber 107 toward cylinder 3. The second portion 632 may be machined directly in the cooling jacket or in an outwardly projecting rib 634 cast on the engine block 34. A short horizontal extension 636 joins the lower end of the second portion 632 to the cylinder wall 35-3. The short horizontal portion 636 terminates in the outlet port 638. 
     In this embodiment, the exhaust gases flow from cylinder 1 past oxygen sensor assembly 618 to cylinder 3. Optionally, a bracket 640 may be mounted on the engine block 34 with bolts 642 provide added strength as needed. Of course, other variations may be utilized. 
     FIGS. 53-55 illustrate variations on the oxygen sensor arrangement of the present invention wherein lubricant contamination of the sensor element is reduced. FIG. 53 shows an oxygen sensor assembly 648 arranged in accordance with another embodiment of the invention. Like the embodiments previously described, many components of this embodiment are the same and, for that reason, will not be described again except insofar as is necessary to understand the construction and operation of this particular embodiment. The oxygen sensor generally indicated by the reference numeral 108 has its sensing portion 109 mounted within a fitting 111 so that the sensing portion 109 extends into the accumulator chamber 107. 
     The sensor portion 109 is protected by a protective sleeve 650 fitted onto a tubular projection (not shown) of the mounting fitting 111. The protective sleeve 650 is defined by a generally cylindrical wall portion 652 having a series of vent openings 654. The protective sleeve 650 includes a non-vented barrier surface 656 on its lower generatrix facing upstream of the inlet port 123. The barrier surface 656 helps reduce the amount of lubricant which may directly contact the sensor element 109. Furthermore, the gas flow 658 within the accumulator chamber 107 is directed away from the sensor element 109 by positioning of the outlet port 126 further away than inlet port 123 with respect to the sensor element 109. In this manner, the gas flow 658 is directed around the terminal end of the protective sleeve 650, and out the outlet port 126, without directly impinging upon the sensor element 109. 
     FIGS. 54 and 55 show a still further embodiment of the invention which is similar in many respects to the embodiment shown in FIGS. 36 and 37. Again, because of the noted similarities, the basic engine design and its association with the sensor will not be described, and the same reference numerals have been used, where applicable, to indicate the same or similar elements. 
     In this embodiment, the sensor 670 comprises an outer housing assembly 353 defining first and second accumulator chambers 354 and 364. The inlet conduit 121 extends into the first accumulator chamber 354 via an extending portion 355 having a plurality of perforated vent openings 356 which are allowed to communicate with the first chamber 354. The terminal end of the extending portion 355 is connected to a U-shaped passage 358 terminating at a lower portion and a counterbore 359 into which the outlet conduit 125 is fitted. The largest lubricant particles will have too much momentum to exit through the small holes 356 provided in the extending portion 355 and, therefore, will exit straight through to the U-shaped passage 358. 
     The first accumulator chamber 354 communicates with the second accumulator chamber 364 via an orifice 366 having a conical upper surface 367. Any lubricant accumulating in the second chamber 364 will condense, collect, and drain back into the first accumulator chamber 354 via the conical surface 367. To prevent lubricant from contaminating the sensor element 109, a protective sleeve 672, similar to the protective sleeve 650 of FIG. 53, is provided. The protective sleeve 672 surrounds the sensor element 109 and is defined by a solid wall portion 674 having a plurality of openings 676. The openings 676 allow exhaust gases to enter and communicate with the sensor element 109 on the side downstream from the inlet orifice 366. A lower barrier wall 678 protects the sensor from upstream flow of exhaust gases and thereby prevents lubricant within the exhaust gases from contacting the sensor element 109. Exhaust gases will travel from the first accumulator chamber 354 into the second accumulator chamber 364 by cyclical flow or diffusion through the orifice 366. This process prevents most contaminants from entering the second chamber 364. Any remaining lubricant particulate matter entering the second accumulator chamber 364 will tend to strike and condense onto the solid wall 678, ultimately dripping downward back through the orifice 366. The threaded fitting 111 allows the sensor 108 to be removed from the housing 353 so that the protective sleeve 672 can be cleaned or replaced. 
     Two further sensor arrangements are illustrated in FIGS. 56-58, and incorporate a catalyst within the accumulator chambers and a lubrication filter in series with the inlet conduit. With specific reference to FIG. 56, a modified oxygen sensor assembly 690 is provided which is similar in many respects to that shown in FIG. 31. Because of the similarities to the earlier embodiment, like elements will be similarly numbered and will not be described further herein. In general the oxygen sensor assembly 690 comprises housing 106a having the inlet conduit 121 and outlet conduit 125 attached thereto. One end of the housing 106a has an opening for the sensor 108. The housing 106a defines the accumulator chamber 107. The inner surface of the housing 106a is coated with a catalyst, such as platinum, which tends to react with unburnt lubricant in the exhaust gases to accelerate oxidation thereof. Thus, a substantial amount of the lubricant which reaches the accumulator chamber 107 will be oxidized, rather than coming into contact with the sensor element. To further prevent lubricant from contaminating the sensor element, the inlet conduit 121 terminates in a short extension portion 694 which extends substantially upward within the accumulator chamber 107. The extension portion 694 extends more than halfway across the center line of the accumulator chamber 107, as shown, and is so positioned to create a bending of the gas flow 696 toward the outlet port 126 and away from the oxygen sensor element. 
     The inlet conduit 121 further incorporates a lubricant filter assembly 698 therein. The lubricant filter assembly comprises a filter housing 700 connected in series with the inlet conduit 121 and with the short extension portion 694. The filter housing 700 provides a flow path between the inlet conduit 121 and extension portion 694. A filter element 702 is placed within an inner chamber 704 of the housing 700 in the flow path of exhaust gas entering the accumulator chamber 107 and is maintained in placed via a spring 707 and cap 708. The gas from the inlet conduit 121 enters the filter housing 700 and the inner chamber 704. The filter element 702 is interposed between the chamber 704 and a second chamber 706. The second chamber 706 is in direct communication with the short extension portion 694. The gas must thus flow into the chamber 704, through the filter element 702 and into the second chamber 706 before reaching the accumulator chamber 107. The cap 708 threadably engages the housing 700 to facilitate periodic cleaning and replacement of the filter element 702. A sealing member 710 has a cylindrical inner opening accommodating the spring 707, for retaining the filter element 702 in place. 
     FIGS. 57 and 58 illustrate an oxygen sensor assembly 720 which is in many respects similar to the embodiments of FIGS. 36, 37, and of FIGS. 54-56. This embodiment differs from the previous ones only in that the inlet conduit 121 is provided with a filter 698 therein, and the accumulator chambers are coated with a catalyst material. The sensor 720 comprises a housing 353 forming the lower accumulator chamber 354, and the upper accumulator chamber 364. The inlet conduit 121 terminates in a short extension portion 722 having perforations or apertures 724 therein. The exhaust gas passes from the apertures 724 and through the orifice 366 into the upper accumulator chamber 364. Both the upper and lower accumulator chambers 364, 354 are provided with a coating 726, 728 similar to the coating provided in the embodiment of FIG. 56. The coatings 726, 728 act as catalysts to accelerate oxidation of lubricant and unburned fuel products present in the exhaust gas to protect the sensor element 109. A drain port 730 is formed in the lower wall of the lower accumulator chamber 354. The drain port 730 leads to the outlet conduit 125. 
     A lubricant filter assembly 698, nearly identical to that shown in FIG. 56, is installed in series between the inlet conduit 121 and the short extension portion 722. More particularly, and as described above, the filter assembly 698 comprises a housing 700 which attaches to the respective inlet and outlet tubes. The housing 700 includes the central chamber 704 within which the filter element 702 is positioned. This chamber may also be coated with a suitable catalyst material, as shown, in order to accelerate oxidation of lubricant and unburned fuel products. An angled passageway 732 is provided from the inlet conduit 121 into the chamber 704. Exhaust gas travels through the angled passageway 732 into the chamber 704 and through the filter element 702 into the second chamber 706, whereupon the exhaust gas passes into the short extension portion 722 and through the apertures 724 into the lower accumulator chamber 354. The inclusion of the lubricant filter 698 substantially reduces the lubricant content of the exhaust gases contacting the sensor 108. The provision of the catalytic coatings 726 and 728 within the accumulator chambers further helps to prevent contamination of the sensor element 109. 
     FIGS. 59-61 show another oxygen sensor assembly embodiment which is similar to the embodiment of FIG. 16, and the overall engine construction is similar to the embodiment of FIGS. 1-10. For that reason, where components of this embodiment are the same or substantially the same as those previously described, they have been identified by the same reference numerals. 
     In this embodiment, a modified oxygen sensor assembly 740 is mounted between the first and second cylinders 35-1, 35-2. An L-shaped mounting bracket 742 bolted to the cylinder block 34 is provided for this purpose. As seen best in FIG. 60, the inlet conduit 121 opens at port 122 into the first cylinder 35-1. The outlet conduit 125 opens at port 127 into the exhaust manifold 68. With specific reference to FIG. 61, the oxygen sensor assembly 740 in this embodiment comprises a housing 744 defining an upper chamber 746 and a lower chamber 748. The upper chamber 746 is in communication with the inlet conduit 121 via port 123. The lower chamber 748 is in communication with the outlet conduit 125 via the port 126. The upper and lower accumulator chambers 746, 748 are joined by a small orifice 750 having an upper conical surface 752 adjacent thereto. Exhaust gas follows the path of arrow 754 from the inlet conduit 121 through the sensor 740 and out the conduit 125. Both the upper and lower accumulator chambers 746, 748 are provided with catalytic coatings 756, 758, much as was described previously with reference to FIGS. 56-58. In a preferred embodiment, the upper accumulator chamber 746 is cylindrical in shape having an annular catalytic coating 756 on at least a portion of its inner surface. The catalytic coating 758 surrounds the sensor 108 in the lower chamber 748. As exhaust gas travels along path 754 through the sensor 740, a substantial amount of lubricant therein will be oxidized by the catalytic coatings of the respective accumulator chambers. Furthermore, some of the lubricant within the exhaust gas will be condensed on the conical surface 752. 
     FIG. 62 illustrates a further embodiment of the present invention which provides a cooling flow around an accumulator chamber in which an oxygen sensor element is disposed. More specifically, an oxygen sensor assembly 760 is shown mounted between two cylinders on the cylinder head 61. The oxygen sensor assembly 760 comprises a generally cylindrical housing 762 having a pair of concentric annular walls 764, 766, defining a cooling passage 768 therebetween. The sensor 108 extends within the inner annular wall 766. One or more ports 770 provided in the exterior surface of the housing 762 allow cooling water from cylinder head 61 to flow into the annular cooling passage 768. The arrow 772 illustrates the cooling path of water flowing through the cooling passage 768. Water does not enter the accumulator chamber 107, but cools the inner surfaces of the chamber 107 to help condense saturated gases and lubricants contained within the exhaust gas. Exhaust gas enters through the inlet port 774 from the combustion chamber 776 of cylinder 1. Although not shown in the cross section of FIG. 62, an outlet conduit may be provided from the accumulator chamber 107 to one of the other cylinders in the engine to allow the gas to pass through the accumulator chamber in a substantially unidirectional manner. Alternatively, the outlet conduit may communicate with the exhaust manifold in a manner described previously. In yet another alternative, the flow of exhaust gases through passage 774 may be bidirectional such that exhaust sales enter and exit the accumulator chamber 107 as the relative pressure in the accumulator chamber 107 and the combustion chamber 776 changes them over time. 
     FIGS. 63-69b show various inlet configurations for delivering exhaust gases to an oxygen sensor assembly in accordance with the present invention. It will be appreciated that certain flow patterns are more likely to create contamination problems due to lubricants condensing in the exhaust gas. FIG. 63 shows a conventional inlet conduit 121 having a port 122 opening perpendicular to the cylinder wall 35. The exhaust gas flow 780 typically follows a path down or up along the cylinder wall 35 and then into the port 122. As the flow 780 turns the corner into the port 122, a region 782 of low pressure is created as the boundary layer separates from the wall. This low-pressure region 782 detrimentally encourages condensation of the lubrication therein, sometimes blocking or decreasing the flow through the port 122. 
     FIG. 64 illustrates a cross section of a cylinder 35 having an inlet conduit 121 leading to an oxygen sensor (not shown). The inlet opening 784 of the inlet conduit 121 is flared to improve the flow pattern of exhaust gases therein and reduce undesirable condensation. This is shown in more detail in FIG. 65. As indicated, the streamlines of the gas flow 788 are relatively smooth as they make the transition from the combustion chamber into the inlet conduit 121 without forming a significant low pressure pocket. The amount of lubricant condensation is thus reduced. 
     FIG. 66 illustrates a further embodiment of an inlet conduit opening 790 having an outer flared portion 792 and an inner flared portion 794. The outer flared portion 792 makes a larger angle with the longitudinal axis of the inlet conduit 121. Thus, a &#34;stepped&#34; flare is formed which further helps to smooth the streamlines of the gas flow 796 and prevent low pressure pockets. It can be seen that the outer flared portion 792 is formed in the cylinder wall 786, and partially in the cylinder block 34. The inner flared portion 794 is formed exclusively in the cylinder block 34. Alternatively, additional stepped surfaces may be added as desired, or the opening may be formed continuously like the bell of a horn. 
     FIG. 67 illustrates a still further embodiment of an inlet opening 800 of an inlet conduit 121. The inlet conduit 121 in this embodiment extends at an angle to the cylinder wall 35, and the inlet opening 800 is similarly angled to further smooth the gas flow 802 and reduce condensation. The inlet conduit 121 includes a central axis 804 which is preferably at an acute angle of θ with respect to the cylinder wall 35. The angle θ is preferably approximately 45°, although it is envisioned that other angles θ may be used. 
     In FIG. 68, a further embodiment of an inlet opening of a conduit 121 is shown. In this embodiment, a low pressure region is encouraged so that lubricant within the exhaust gas condenses into a large generally cylindrical chamber 810. The gases enter through a small orifice 812 opening to the cylinder 35. The opening diverges at a surface 814 into the chamber 810, which is preferably formed within the engine block 34. The opening converges at a surface 815 to which the inlet conduit 121 is connected. As shown by the arrow 816, a portion of the gas flow is directed upward into the chamber 810 creating a low-pressure region to facilitate condensation of lubricant therein. Optionally, a drain hole (not shown) may be provided at a lower portion of the chamber 810 to drain condensed lubricant. 
     FIGS. 69a and 69b illustrate a cylinder in two views wherein the inlet conduit 121 leading to the oxygen sensor of the present invention opens into the combustion chamber 59 via a flanged opening 122 provided in the cylinder head 61. A similar arrangement was shown previously with respect to FIG. 62. 
     Although the various inlet openings of conduits 121 are shown opening into various cylinders, these inlets may also open into other portions of the exhaust system of the engine as described previously. More particularly, the sensor assembly 91 may sample combustion gases from various locations in the exhaust system, such as from the exhaust passage 71 as shown in FIGS. 23 and 24, or from the exhaust manifold 68 as shown in FIG. 25. In all of these cases, the preferred shape of the inlet opening 121 either smoothes the exhaust gas flow therethrough to reduce lubricant condensation, or provides a condensation chamber within which the lubricant can condense before it reaches the oxygen sensor element 109. 
     From the foregoing description, it should be readily apparent that the described embodiments of the invention not only provide a very effective exhaust sensor arrangement that can be utilized with two-cycle engines, but also ensures that the sensor will have a long life and be relatively free of contamination and deterioration in output. Of course, those skilled in the art will recognize that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.