Patent Publication Number: US-6220216-B1

Title: Four-stroke reciprocating internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     In reciprocating internal combustion engines, a piston is guided for longitudinal movement in a cylinder and the piston drives a crankshaft via a connecting rod. The crankshaft is rotatably journalled in a crankcase which contains lubricating oil for the crank drive. The connecting rod is pivotally held on a crankpin arranged eccentrically to the rotational axis of the crankshaft. 
     If such a reciprocating engine is utilized in a portable handheld work apparatus such as a motor-driven chain saw or the like to drive the work tool, then the engine is regularly moved out of its stand up normal alignment when, for example, the work tool and therefore the drive motor are guided sideways or even overhead. Without suitable countermeasures, the lubricating oil flows in the direction of the piston and can enter the combustion chamber. This can effect the proper operation of the engine especially when the apparatus is put down at engine standstill in the overhead position of the engine. It is even possible that lubricating oil drips out of the engine. 
     German patent publication 197 38 155 discloses a four-stroke internal combustion engine having a chamber next to the cylinder and which chamber contains lubricating oil. The chamber is configured as an oil receptacle with baffle walls within the crankcase in which the lubricating oil is taken up when the cylinder is in an overhead position. An oil catcher is movable with the crankpin about the rotational axis of the crankshaft and projects into the chamber containing the lubricating oil. The oil catcher is intended to catch lubricating oil and spray the lubricating oil onto the components to be lubricated at high rpm of the crankshaft. 
     In the known engine, the crankcase is configured to have a double wall. The inner baffle wall encloses the components of the crank drive and the outer wall of the crankcase surrounds the inner wall. The space, which is formed between the baffle wall and the outer wall, holds the lubricating oil for the crank drive. A slot is formed in the baffle wall and extends on the side of the baffle wall in the peripheral direction. This side of the baffle wall lies opposite the piston. The oil catcher projects through the slot into the chamber containing the lubricating oil and the oil bath contained therein. 
     The outer wall of the lubricating oil chamber is connected to the inner wall above the crankshaft, that is, on the side facing toward the cylinder whereby an oil catch is formed. In the side position and in the overhead position, the oil catch holds the lubricating oil, which flows in the direction of the cylinder, back into the oil chamber. The crank chamber, which is closed off by the baffle wall, is thereby separated from the lubricating oil chamber whereby a wetting of the backside of the piston is precluded in a position of the engine deviating from the normal alignment. The oil catcher is configured radially on the crankpin but enters only segmentwise through the slot into the oil chamber during its revolution and therefore can only catch lubricating oil and move the same to the crank drive when the engine is in its upright position and the lubricating oil is disposed at the base of the lubricating chamber and accessible for the oil catcher. Although the oil is prevented from entering into the crank chamber in the overhead position of the engine, a lubrication is, however, no longer provided so that operating disturbances of the engine can occur very quickly. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to improve a reciprocating piston engine in such a manner that an adequate lubrication of the movable components is ensured in every operating position of the reciprocating piston engine. 
     The reciprocating internal combustion engine of the invention includes: a cylinder defining a longitudinal axis and having a cylinder wall; a piston guided to move longitudinally in the cylinder; a crankcase connected to the cylinder; a crankshaft rotatably journalled in the crankcase and defining a rotational axis; a crank drive including a crankpin operatively connected to the crankshaft and the crankpin being arranged eccentrically to the rotational axis; a connecting rod pivotally connected to the crankpin; the piston being connected to the connecting rod for imparting rotational movement to the crankshaft via the crankpin; the crankcase having a crankcase wall defining an interior space and having a first end configured as a sump for holding lubricating oil in a first spatial orientation of the engine; the crankcase having a second end in the region of the cylinder; the cylinder being connected to the crankcase so as to cause the cylinder wall to extend axially into the interior space at the second end of the crankcase; and, the cylinder wall and the crankcase wall conjointly defining a receptacle for catching oil at the second end of the crankcase in a second spatial orientation of the engine. 
     The crankcase is configured so as to have a trough-like shape and contains the lubricating oil. The cylinder projects axially into the crankcase and forms a wall of the oil receptacle with its outer wall surface. The cylinder and the crankcase are thereby axially pushed one inside the other whereby the space that the piston engine occupies is reduced. The oil receptacle is defined by the crankcase wall and the inwardly projecting wall of the cylinder outside of the region of movement of the crank drive. In this oil receptacle, the lubricating oil collects in the overhead position of the reciprocating piston engine. The oil receptacle is open toward the crank chamber and the crank drive disposed therein whereby the lubricating oil is held in movement by the crank drive also in positions deviating from the upright position of the crankcase. If the reciprocating piston engine is tilted and brought into the overhead position, then the sump oil is lifted from the housing base and caught by the crank drive. 
     The lubrication and formation of a lubricating oil mist by the crank drive can be augmented by an oil catcher which is movable about the rotational axis with the crankpin and projects into the interior space of the crankcase. For every revolution, a partial volume of the lubricating oil is caught by the oil catcher and sprayed onto the crank drive parts in the crank chamber which are to be lubricated. The oil catcher reaches into the oil receptacle and thereby catches large amounts of the lubricating oil which have collected in the oil receptacle in side and overhead positions of the reciprocating piston engine. 
     The oil catcher, which rotates about the rotational axis of the crankshaft, either catches the sump oil located at the base in the normal position or the lubricating oil collected in the oil receptacle in the overhead position independently of the alignment of the piston reciprocating engine. Advantageously, the oil catcher is mounted on an end face of a radial crank web of the crankshaft lying opposite the crankpin. The oil catcher is mounted eccentrically to the rotational axis and extends radially into the oil receptacle. The oil catcher rotates freely in the crankcase with the crank web. Preferably, crank webs are mounted on both sides of the crankpin and each crank web is provided with an oil catcher whereby the lubricating capacity is overall increased and is doubled in the overhead operation. Even in the lateral positions of the reciprocating piston engine, the lubrication can always be maintained. 
     The crankcase can advantageously be configured symmetrically to the longitudinal axis of the cylinder and, in this way, the oil receptacle can be configured to have an annular shape about the cylinder. Advantageously, the cylinder is placed with a radial flange on a flange of the crankcase whereby the cylinder wall projects into the crankcase in the built-in position of the cylinder. The radial flange is configured so as to be axially spaced from where the cylinder opens to the crankcase. The interface plane of the cylinder flange and of the crankcase flange purposefully lies orthogonally to the longitudinal axis of the cylinder so that the cylinder can be easily assembled. During assembly, the cylinder is pushed axially into the crankcase and onto the piston, which is already located therein, until the radial flange comes into abutting contact on the crankcase and is thereafter tensioned. The housing wall of the crankcase defines a flange collar on which the cylinder is seated with its radial flange. The flange collar is drawn inwardly. The flange collar of the crankcase delimits the oil receptacle in the longitudinal direction of the cylinder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described with reference to the single figure (FIG. 1) which shows a four-stroke internal combustion engine equipped with a receptacle for lubricating oil according to an embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The four-stroke internal combustion engine  1  shown in FIG. 1 includes a cylinder  2 , a piston  4  and a connecting rod  5 . The piston  4  is longitudinally movable in the cylinder  2  and is journalled so as to be pivotally movable via a piston pin  13  on a connecting rod  5 . The connecting rod  5  is held by a connecting rod bearing  12  on a crankpin  7  which is arranged eccentrically to the rotational axis  16  of the crankshaft  6 . The longitudinal movement of the piston  4  along the cylinder path  15  is converted via the connecting rod  5  into a rotational movement of the crankshaft  6  in the usual manner of a crank drive. The crankpin  7  is held between two crank webs  8  which serve to balance the mass of the crank drive. The crankshaft  6  is held in the crankcase  3  by shaft bearings  28  adjacent respective crank webs  8 . 
     In the embodiment shown, the shaft bearings  28  are configured as roller bearings which are lubricated with the lubricating oil of the crank drive. In addition to the crankshaft bearings, a crankshaft seal is provided which closes off the interior space  27  of the crankcase. This closure is gas tight and oil tight. 
     The crankcase  3  has a trough-like configuration and the housing wall  23  is drawn inwardly to a flange collar  18  at the open end of the crankcase  3 . The cylinder  2  projects axially into the crankcase  3  through the opening delimited by the flange collar  18 . The inwardly projecting part of the cylinder jacket  14  acts as a barrier wall and defines an oil receptacle  11  with the peripheral section of the crankcase housing wall  23 . The oil receptacle  11  is delimited in the axial direction by the flange collar  18  and lies outside of the region of movement of the components of the crank drive. The flange surface of the crankcase  3  can, however, also be advantageously configured on the peripherally extending edge of an upright crankcase wall  23  whereby the inner-lying end face of the cylinder flange  19  lying on the crankcase flange delimits the oil receptacle  11 . The crankcase can comprise three horizontal parts, namely, an upper flange part, the center part having the shaft bearing  28  and a lower part, namely, an oil sump defining the base  25  of the crankcase  3 . 
     The lubricating oil  29  is next to the base  25  of the crankcase  3  in the upright normal position of the engine  1  shown in FIG.  1 . If the engine  1  is brought into a side position or if the cylinder  2  is even in overhead position, then the lubricating oil  29  flows on the wall  23  in the direction of the cylinder  2  and collects in the oil receptacle  11 . An oil catcher  10  is mounted on the crank webs  8  on respective end faces  9  lying opposite the crankpin  7 . The oil catchers  10  project into the oil receptacle  11 . The oil catchers  10  are each connected to the crank webs  8  so as to be eccentric to the rotational axis  16  and rotate freely during operation of the engine. The oil catchers  10  are provided as rod-shaped displacing bodies which reach close to the base  26  of the oil receptacle  11 . The oil catchers  10  support the distribution of the lubricating oil in the crank chamber  27  via the moving crank drive parts and the formation of an oil mist. A radially offset oil catcher can also be provided on the connecting rod  5  and project into the oil sump, for example, in the region of the connecting rod bearing  12  which, especially in the start phase of the engine, ensures an immediate lubrication. 
     In the normal orientation of the engine  1  shown, the oil catchers  10  pass through the oil bath  29  at the housing base  25  with each revolution and, in the overhead position, the lubricating oil, which is collected in this case in the oil receptacle  11 , is caught and conveyed to the crank drive. In each possible orientation of the engine  1 , it is thereby ensured that the oil catchers  10  come into contact with the lubricating oil  29  in the interior space  27  of the crankcase  3  with each revolution and ensure the lubrication of the crank drive. In the embodiment shown, the oil catchers are mounted on the side of the crank webs  8  lying opposite to the crankpin  7  and thereby contribute to the mass balance of the crank drive. The oil receptacle  11  is configured symmetrically to the cylinder longitudinal axis  17 . 
     The crankshaft bearings  28  are supported on an inwardly drawn wall section  24  of the housing wall whereby the crankshaft bearings  28  lie directly next to the crank webs  8 . In this way, the volume of the interior space  27 , in which an oil mist must be generated for the purpose of lubrication, is small. The inner-lying surfaces of the inwardly drawn wall sections  24  partition the interior space  27  into two fluid-connected chambers in which the lubricating oil is alternatively collected in dependence upon the orientation of the engine  1 . Both chambers of the interior space  27  are run through by the oil catchers  10  with each revolution of the crankshaft  6 . In the drawing, the crank drive is shown in the position of bottom dead center and the oil catchers  10  project into the chamber of the crank space close to the cylinder and the oil receptacle  11 . At the top dead center of the crank drive, the oil catchers  10  run through the lower base chamber of the crank space  27  as shown by the phantom outline of the oil catchers. The base surface  26  of the oil receptacle  11  is formed by the flange collar  18  and lies somewhat further spaced from the rotational axis  16  of the crankshaft  6  than the base  25  of the crankcase  3  so that the total lubricating oil quantity is accommodated in the oil receptacle  11  and the oil catchers  10  catch lubricating oil with each rotation. 
     The attachment flange  19  of the cylinder  2  can be defined by a cooling rib  21  on the periphery of the cylinder  2 . The flange  19  extends radially further than the cooling ribs  21  in order to make possible an attachment by means of threaded fasteners to the flange collar  18  of the crankcase  3 . The partition plane  20  between the flange  19  and the flange collar  18  lies orthogonally to the longitudinal axis  17  of the cylinder whereby the cylinder  2  is insertable in a simple manner into the crankcase  3  with its cylinder jacket  14 . In the embodiment shown, reference numeral  22  identifies the gas exchange valves of the engine  1  indicated by their valve axes. 
     No axial extension of the cylinder  2  compared to conventional configurations is required to form the barrier wall and therefore the oil receptacle  11 . Rather, the cylinder length corresponds to the dimension, which is necessary for the piston stroke, and the crankcase wall  23  is extended beyond the plane of the open cylinder end. The cylinder  2  and the crankcase  3  are axially inserted one into the other whereby a reduced axial structural elevation of the engine  1  is achieved. 
     The four-stroke internal combustion engine according to the invention is especially suitable for use in portable handheld work apparatus such as motor-driven chain saws, cutoff machines, brushcutters and the like. These apparatus are regularly guided by an operator in a side position or an overhead position. 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.