Abstract:
Two-stroke engines are particularly prone to piston scuffing due to insufficient oil at some operating conditions. A system and method to precisely deliver oil is disclosed. An oil reservoir groove is formed in the piston with an oil reservoir ring welded to the surface of the piston. A cavity behind the ring forms an oil reservoir. The ring has an inlet gap. The cylinder wall has an oil injector installed therein which sprays oil into the inlet gap when the inlet gap is proximate the oil injector tip. An electronic control unit commands the quantity of oil to provide to the oil reservoir, with the quantity and timing of the injections based on the operating conditions of the engine.

Description:
FIELD OF INVENTION 
       [0001]    The present disclosure relates generally to lubricating the interface between a piston reciprocating within a cylinder. 
       BACKGROUND 
       [0002]    It is important to provide sufficient lubrication for piston reciprocating within a cylinder. In a four-stroke engine, extra lubricant can be splashed around to ensure there is sufficient lubrication on the cylinder liner or bore. Piston-ported two-strokes, however, are particularly prone to lubrication issues due to the tradeoff in providing enough oil for lubrication purposes while simultaneously preventing that oil from exiting the exhaust ports which leads to high oil consumption. Thus, precision lubrication in terms of quantity and coverage is desired. 
         [0003]    Lubrication of the cylinder liner in a two-stroke engine is shown in commonly-assigned, published application, US 2010/0050978, filed 27 Aug. 2009. An inertia reactive oil injector in the piston, in one embodiment, has a tunnel passage and reservoir formed beneath the side surface of a piston. One or more strategically-placed oil reservoirs are provided within the piston. An outlet in the sidewall of the piston allows the mass of the oil within the reservoir(s) to force itself through the outlet in reaction to the deceleration of the piston when it approaches its TDC position. Lubricating oil enters the inlet port, the reservoir, and the tunnel passage during exposure to the pressurized oil below the oil seal. It is desirable to provide a way to fill the reservoir in a controllable manner. 
         [0004]    The oil reservoir disclosed in US 2010/0050978 may be challenging to manufacture. An alternative manufacturing approach to provide a reservoir in the piston is desired. 
       SUMMARY 
       [0005]    According to an embodiment of the present disclosure, an oil injector is provided to inject oil into the reservoir. The oil injector is electronically coupled to an electronic control unit to control the oil injection quantity and frequency as desired. 
         [0006]    To overcome at least one problem in the prior art, a piston-and-cylinder assembly for an internal combustion engine includes: a piston having a crown and a skirt with an outer surface of the crown and outer surface of the skirt forming a substantially cylindrical surface of the piston. The cylindrical surface of the piston has a compression ring groove and an annular oil distribution reservoir defined therein; a compression ring situated in the compression ring groove with the compression ring unattached to the piston; and an oil reservoir ring situated in the oil reservoir groove with the oil reservoir ring fixed to the piston. 
         [0007]    In one embodiment, the compression ring groove and the oil reservoir groove are formed circumferentially into the outside surface of the skirt of the piston. The oil reservoir ring has an inlet gap. The oil reservoir ring is affixed to the cylindrical surface at an upper edge of the reservoir ring and at a lower edge of the reservoir ring. 
         [0008]    The oil delivery passages have an inlet port at the oil reservoir and an outlet port at the cylindrical surface. The outlet ports are located closer to the piston crown than the inlet ports. The oil reservoir ring has an inlet gap. The piston is adapted to reciprocate within the cylinder wall between a top center position and a bottom center position. The assembly further includes an injector disposed through the cylinder wall and aimed at the inlet gap when the piston is at the bottom center position. In an alternative embodiment, such as a piston that was 3-D printed, the oil reservoir is formed in the piston skirt, i.e., no groove is formed in the side of the skirt. No oil reservoir ring is provided. Instead a hole from the outside of the piston skirt to the oil reservoir is provided for the injector to supply oil to the oil reservoir. 
         [0009]    The assembly may further include an engine position sensor and an electronic control unit (ECU) electronically coupled to the injector and the engine position sensor. The ECU commands the injector to open based at least on engine position. In some embodiments, the assembly further include: a heater associated with the injector to raise temperature of oil within the injector and an electronic control unit (ECU) electronically coupled to the heater. The ECU commands the heater to turn on prior to a cold start of the engine. 
         [0010]    In some embodiments, the crown and the skirt are integrally formed. In some embodiments, one or more of the grooves are formed in the crown and one or more of the grooves are formed in the skirt. The cylindrical surface of the piston is made up of the cylindrical outer surface of the crown and the cylindrical outer surface of the skirt. 
         [0011]    Alternatively, an internal combustion engine is disclosed that includes: a cylinder wall and a piston disposed within the cylinder wall and adapted to reciprocate within the cylinder wall between a top center position and a bottom center position. The piston has a crown and a skirt with an outer portion of the crown and an outer portion of the skirt forming a substantially cylindrical surface of the piston. The surface is substantially cylindrical because as well known by one skilled in the art, a piston may be slightly barrel shaped or may be slightly oblong to account for uneven expansion, and may have features in the surface such as an opening for a wrist pin and grooves to accommodate ring. The cylindrical surface has a compression ring groove and an annular oil distribution reservoir defined therein. The annular oil distribution reservoir has at least one outward opening. A compression ring is situated in the compression ring groove. An oil injector is situated in the cylinder wall and located so that the oil injector is aligned with the outward opening of the annular oil distribution reservoir when the piston is proximate a predetermined position. In at least one embodiment, the predetermined position is the bottom center position. 
         [0012]    The annular oil distribution reservoir is a groove formed in the cylindrical surface of the piston. In some embodiments, the groove is a reentrant groove. An oil reservoir ring is disposed in the groove. An upper edge of the oil reservoir ring is affixed to the upper edge of the groove. A lower edge of the oil reservoir ring is affixed to the lower edge of the groove. The oil reservoir ring has at least one circumferential gap, i.e., the outward opening. A plurality of oil distribution passages are defined in the piston with the passages extending between the annular oil distribution reservoir proximate the crown and the cylindrical surface of the piston. The oil distribution passages are angled toward the crown as considered from the annular oil distribution reservoir to the outer surface of the piston. 
         [0013]    When the engine is mounted in a vehicle such that the cylinder wall is oriented at an angle displaced from the vertical such as in horizontal and vee engines, the outward opening of the annular oil distribution reservoir is located substantially at the highest point of the annular oil reservoir groove as mounted in the vehicle. 
         [0014]    The engine also includes an electronic control unit (ECU) electronically coupled to the oil injector. The ECU commands a timing and pulse width to the oil injector. 
         [0015]    The engine may further include a heater coupled to the injector and an electronic control unit electronically coupled to the heater. 
         [0016]    In some embodiments, surfaces of the annular oil distribution reservoir are coated with a non-wetting coating. 
         [0017]    Also disclosed is a method to provide oil to the cylinder wall of an internal combustion engine, including: providing a piston having a crown and skirt with a cylindrical outer surface of the piston having an annular oil distribution reservoir that has an outward opening; installing the piston within the cylinder wall; providing an oil injector in the cylinder wall with a tip of the oil injector aimed at the outward opening of the oil distribution reservoir; providing oil delivery passages having inlets at the annular oil distribution reservoir and outlets at an outer surface of the piston; and commanding the oil injector to open when the outward opening of the annular, reentrant oil distribution reservoir is aligned with the oil injector. The method further includes: placing an oil reservoir ring in the outer portion of the oil distribution reservoir. A gap in the oil reservoir ring is the outward opening. An upper edge of the oil reservoir ring is affixed to an upper edge of the annular, reentrant oil distribution reservoir. A lower edge of the oil reservoir ring is affixed to a lower edge of the annular, reentrant oil distribution reservoir. 
         [0018]    The piston is adapted to reciprocate between a top center position and a bottom center position. The oil injector is located so that the outward opening of the distribution reservoir is aligned with the injector when the piston is at the bottom center position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a cross-sectional representations of a piston with an annular oil distribution reservoir; 
           [0020]      FIGS. 2 and 3  are cross-sectional illustrations of a portion of the piston in  FIG. 1 ; 
           [0021]      FIG. 4  is a cross-sectional representation of a portion of a piston in which the annular oil distribution reservoir is formed in the inner surface of the piston skirt; 
           [0022]      FIGS. 5 and 6  are cross-sectional representations of portions of a piston in which the annular oil distribution reservoir is cast within the piston; 
           [0023]      FIGS. 7 and 8  are cross-sectional representations of portions of a piston in which the annular oil distribution according to embodiments of the present disclosure; 
           [0024]      FIGS. 9-11  are cross-sectional representations of the piston of  FIG. 1  with the cross section taken perpendicular to the central axis of the piston; and 
           [0025]      FIG. 12  is a schematic representation of a piston within a cylinder and components associated with an oil injection system. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0027]    A piston  15  having a crown  12  and skirt  14  is shown in cross section in  FIG. 1 . Crown  12  is affixed to skirt  14  by welding, friction welding, bolting together, or any suitable method. The piston in  FIG. 1  shows a piston crown that is separately formed from the piston skirt and then assembled. Alternatively, the piston is a single piece with the crown and the skirt formed as one integral piece. Groove  16  and  18  are formed in crown  12 . A keystone compression ring  20  is disposed in groove  16 ; a compression ring  22  is disposed in groove  18 . Piston  15  has an opening  24  to support a wrist pin. 
         [0028]    Piston  15  also has an annular oil distribution reservoir  30  defined in skirt  14 . Annular oil distribution reservoir  30  has an oil reservoir ring  32  installed in the outward opening of annular oil distribution reservoir  30 , except for at least one location in which an outward opening  50  remains unobstructed. Annular oil distribution reservoir  30  has a plurality of delivery passages  34  that extend from reservoir  30  to the outer surface of skirt  14 . 
         [0029]    A detail of a portion of piston  15  is shown in  FIG. 2 . The cross section in  FIG. 2  is through outward opening  50  and through a delivery passage  34 . Delivery passage  34  has an inlet port  36  within reservoir  30  and an outlet port  38  at the outer surface of skirt  14 . In  FIG. 3 , a detail of a portion of piston  15  shows a cross section through oil reservoir ring  32 . In the embodiment shown in  FIG. 3 , an upper edge of oil reservoir ring  32  is welded to an upper edge of the opening in piston skirt  14  and a lower edge of oil reservoir ring is welded to a lower edge of the opening in piston skirt  14 . Weld beads  40  and  42  are upper and lower weld beads, respectively. 
         [0030]    In  FIGS. 1-3 , annular oil reservoir  30  is formed with an opening at the outside surface of piston skirt  14 . Alternatively, an annular oil reservoir  130  is formed in an inner surface of piston skirt  114  as illustrated in a cross-sectional view in  FIG. 4 . An oil reservoir  130  has a ring  132  fitted in the opening and welded to piston skirt  114  at weld beads  140  and  142 . The cross section in  FIG. 4  intersects an oil delivery passage  134  that has an inlet port  136  and an outlet port  138 . The portion of the piston shown in  FIG. 4  is one in which the crown  112  and the skirt  114  are integrally formed. 
         [0031]    In  FIGS. 1-4 , an annular oil reservoir is shown with an opening in the inner or outer surface of the skirt. However, an annular oil reservoir  230  formed in during the casting of skirt  224  is shown in  FIG. 5 .  FIG. 6  shows the skirt of  FIG. 5  with an outward opening  250  and an oil delivery passage  234  machined into skirt  224 . 
         [0032]    The annular oil reservoirs  30  in  FIGS. 1-3  and  130  in  FIG. 4  is a reentrant groove. This may prove to be a challenge to machine into the cylindrical surface of the piston. An embodiment in which the groove is not reentrant is shown in  FIG. 7 . Groove  178  is formed in the cylindrical surface of piston  164 . An oil reservoir ring  166  is installed in groove  178 . An annular oil reservoir  180  is defined by groove  178  and oil reservoir ring  166 . An outward opening  168  is defined in oil reservoir ring  166 . As will be described below, an oil injector is provided to inject oil through outward opening  168  to provide oil to oil reservoir  180 . This may be one opening around the periphery or more. A delivery passage  170  is defined in oil reservoir ring  166 . A plurality of such delivery passages may be arranged around the periphery of oil reservoir ring  166 . 
         [0033]    In another embodiment shown in  FIG. 8 , a groove  198  is formed in the cylindrical surface of piston  184 . An annular oil reservoir  200  is defined by groove  198  and an oil reservoir ring  180  that is installed into the outer edge of groove  198 . In this embodiment, delivery passages are defined in piston  184  with an inlet at oil reservoir  200  and an outlet at the surface of the piston. 
         [0034]    A cross section that is perpendicular to a central axis  52  of piston  15  of  FIG. 1  is shown in  FIG. 9 . The cross section in  FIG. 9  is taken through oil reservoir ring  32  and annular oil reservoir  30 . Oil reservoir ring  32  has an outward opening  50 . Alternatively, oil reservoir ring may have a plurality of outward openings. The cross section in  FIG. 10  is taken closer to the piston crown and through oil delivery passages  34 . In the non-limiting example in  FIG. 10 , there are eight evenly space oil delivery passages  34 . The cross section in  FIG. 11  is taken through the outlet ports  38 . 
         [0035]    The embodiments described above show a piston crown and a piston skirt with the compression rings defined in the crown portion of the piston and the annular oil distribution reservoir defined in the skirt. However, in other embodiments, one or more of the compression rings are defined in the piston skirt. In yet other embodiments, the annular oil distribution reservoir is defined in the crown. To describe all these combinations, the grooves may be described as being defined in the outer cylindrical surface of the piston, with the outer cylindrical surface being made up of an outer surface of the crown and an outer surface of the skirt. 
         [0036]    Referring now to  FIG. 12 , piston  15  is shown disposed in a cylinder wall  100 . Piston  15  is shown at its bottom center position in which the top of piston  15  is at position  102  in cylinder wall  100 . Piston  15  has a cranktrain (not shown) that causes piston  15  to reciprocate between position  102 , the bottom center position, and position  104 , the top center position. 
         [0037]    An oil injector  90  pierces through cylinder wall  100 . Injector  90  is supplied oil from an oil reservoir  92  and pressurized by a pump  94 . An electronic control unit (ECU)  150  is electronically coupled to injector  90  to command an injection by causing the injector to open and deliver oil. ECU  150  commands oil injector  90  to inject when oil injector  90  is aligned at the outward opening to annular oil reservoir  30 . In the embodiment in  FIG. 12 , this occurs when piston  15  is in its bottom center position. In alternative embodiments, it could occur at a different time. 
         [0038]    A heating coil  96  is shown on the outside of oil injector  90  in  FIG. 12 . At cold start, the oil in oil injector  90  and the supply lines may be colder than desirable for the desired lubrication. Heating coil  96  is one non-limiting example. Alternatively, a heater within oil injector could be provided, such as an inductive heater. In yet another embodiment, engine coolant is heated prior to engine start. If the block is heated in this manner, oil injector and its contents, may also be heated. 
         [0039]    ECU  150  is electronically coupled to a position sensor  152  and other sensors  154 , such as temperature and pressure sensors. A signal from position sensor  152  can be used by ECU  150  to time injector  90  to provide oil when the outward opening ( 50  in  FIGS. 1 and 2 ) is in the proper position to allow oil to be collected in annular oil reservoir  30 . 
         [0040]    As the piston moves toward top center, acceleration of the piston causes the oil to be pressed into the lower portion of annular oil reservoir  30 . When the piston nears top center and the acceleration of the piston is downward, the oil is pressed into the upper portion of annular oil reservoir  30  causing the oil to be delivered to cylinder wall  100  through delivery passages.  FIG. 12  is insufficiently detailed to show the delivery passages; but these are shown as element  34  in  FIG. 1 . 
         [0041]    In some embodiments, the annular oil reservoir and/or the inside surface of the oil reservoir ring may be coated with an anti-wetting coating. By doing so, the amount of oil in the reservoir is less affected by the amount that adheres to reservoir surfaces. 
         [0042]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.