Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
  • F04B39/12—Casings; Cylinders; Cylinder heads; Fluid connections
  • F04B39/122—Cylinder block

Definitions

• the present invention refers to a cylinder for a reciprocating hermetic compressor of the type used in small refrigerating systems.
• the reciprocating motion of a piston inside a cylindrical cavity such as a cylinder provided in the cylinder block of said hermetic compressors, define suction and compression strokes of refrigerant gas during each operative cycle of the piston.
• the refrigerant gas is aspirated from a suction chamber towards the cylinder inside, through a suction orifice provided on a valve plate, during the suction stroke and it is discharged during the compression stroke from the inside of the cylinder to a discharge chamber, through a discharge orifice provided on said valve plate.
• the suction and compression strokes of the operative cycle of the reciprocating piston are defined by the stroke end positions of said piston, respectively known as upper dead point position and lower dead point position.
• the cylinder within which reciprocates the piston, presents a constant cylindricity throughout its length, said cylindricity defining, in a transversal profile, walls that are parallel to the respective walls of a reciprocating piston mounted inside said cylinder.
• the radial distance between the cylinder wall and the piston wall is calculated in order to be sufficient to receive, by superficial adherence, a lubricant oil film that reduces the friction between the walls of the cylinder and reciprocating piston, mainly when said piston comes closer to the upper dead point, where the pressure rises quickly with the advance of the reciprocating piston.
• a cylinder for a reciprocating hermetic compressor of the type comprising: a cylinder block presenting an internal cylindrical cavity, in which inside reciprocates a piston between a lower dead point and an upper dead point, said reciprocating piston presenting an upper end face, the radial distance between the lateral wall of the reciprocating piston and the adjacent lateral wall of the cylinder, according to a plane containing the upper end face of the reciprocating piston, varying at least along the cylinder length, in order that, at the region of the cylinder adjacent to the portion where there is reached the upper dead point condition, said radial distance is minimum.
• Fig. 1 illustrates, in a longitudinal section view, a reciprocating piston disposed inside a cylinder, which is closed by a valve plate and cylinder head, according to the state of the art
• Fig. 2 illustrates an enlarged view of the assembly of figure 1, without the connecting rod of the piston, the latter being at its upper dead point;
• Figures 3a and 3b illustrate, in an enlarged longitudinal section view, similar views to that of figure 2, but presenting a cylindrical cavity, which is shaped according to two different embodiments of the present invention.
• Reciprocating hermetic compressors comprise a cylinder block 1, which is lodged inside a hermetic shell (not illustrated) and which presents a cylindrical cavity such as a cylinder 2, in which inside reciprocates a piston 3.
• the cylinder block 1 presents a pair of opposite faces, to which are opened the ends of the cylinder 2.
• a valve plate 5 and a cylinder head 6, which forms together with said valve plate 5 two internal cavities, defining a suction chamber 8 and a discharge chamber 9.
• the cylinder 2 maintains a selective fluid communication with said suction chamber 8 and discharge chamber 9, through respective gas suction orifice 5a and gas discharge orifice 5b, provided on the valve plate 5, eccentrically to the geometric axis of the cylinder 2, and onto which are mounted respective suction valve 10 and discharge valve 11, which operate synchronously during the suction and discharge strokes of the operative cycle of the piston 3.
• the reciprocating piston 3 presents a free end face 3a, facing the valve plate 5, and an opposite end 3b, by which said reciprocating piston 3 is driven through a connecting rod 20.
• the reciprocating piston 3 presents a continuous linear movement, having a suction stroke and a discharge stroke, which begin, respectively, at the upper dead point and at the lower dead point.
• the cylinder 2 presents a cylindricity that remains constant throughout its length, from the edge thereof adjacent to the upper dead point region of the reciprocating piston 3 and close to the valve plate 5, up to another opposite edge, which is adjacent to the lower dead point region of said piston 3, defining, in a transversal profile, a parallelism between the adjacent walls of the cylinder 2 and piston 3.
• the diameter of said cylinder 2 is defined so that its lateral wall and the lateral wall of the piston 3 keep a constant minimum mutual radial distance, which is necessary to allow a fine oil film to be retained between the surfaces of the lateral walls of the cylinder and piston, in order to minimize the friction between said cylinder and piston during the motion of said piston inside the cylinder 2.
• This lubrication is mainly required during the final phase of the compression stroke, when the pressure inside the cylinder 2 increases rapidly. Nevertheless, when the piston is close to the upper dead point, this oil film is not enough to avoid the friction wear between the reciprocating piston 3 and the cylinder 2. In order to minimize this wear, it would be necessary to increase the distance between the cylinder 2 and the piston 3. Though the increase of said distance does not alter the results of gas suction during the corresponding cycle of the piston, said distance, during compression, implies an increase of gas leakage to the low pressure region of the refrigerating system. Said gas leakage is even more significant as the reciprocating piston approaches the upper dead point, thereby resulting in efficiency loss for the compressor.
• the cylinder 2 presents, between its opposite ends, a diametral variation calculated in order to optimize the gas pumping inside the cylinder, by action of the reciprocating piston 3, said optimized operation resulting in the minimization of the friction losses between said cylinder and piston, as well as losses due to leakage of the gas being compressed at the low pressure region of the refrigerating system.
• This diametral variation is obtained according to at least a plane containing the free end face 3a of the reciprocating piston 3.
• the cylinder is defined as a conical cavity, whose walls maintain a constant conicality throughout the length of the cylinder, between the upper dead point and lower dead point regions.
• the ideal optimum point is located approximately at the central region of the cylinder 2.
• the ideal optimum point defines a region of the cylinder length, where the piston-cylinder radial distance is such that, during compression, the losses due to friction and to compressed gas leakage are optimum. Above this region, the cylinder 2 presents a radial distance from the reciprocating piston 3 that is smaller than the distance at said ideal optimum point, while, below said region, this distance is larger than said distance at the ideal optimum point.
• the minimum radial distance between the cylinder 2 and reciprocating piston 3 occurs only at the upper dead point region, between the peripheral edge of the free end face of the piston 3 and the wall of the cylinder 2, thereby allowing a certain escape of lubricant oil between the piston and cylinder walls, due to the pressure existing at this region, consequently increasing the gas leakage.
• the region of the cylinder immediately adjacent to the portion thereof where the upper dead point is defined should present a constant radial distance, i.e., a constant cylindrical distance. At this cylindrical portion of reduced radial clearance, the oil forms a barrier against gas flow, thereby avoiding gas leakage even in high pressure conditions.
• the variation of the cylinder- piston radial distance is obtained by varying the profile of said cylinder 2 throughout the length thereof.
• the diameter of the cylinder is calculated, for each position of the piston stroke, in function of some operative parameters of said piston, such as pressure in each said position and motion velocity between each two consecutive positions, i.e., the time that said piston stays in each of said positions.

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• 1993
  • 1993-04-22 BR BR9300994A patent/BR9300994A/pt not_active IP Right Cessation
• 1994
  • 1994-04-22 JP JP6522564A patent/JPH07508333A/ja active Pending
  • 1994-04-22 WO PCT/BR1994/000015 patent/WO1994024436A1/en not_active Application Discontinuation
  • 1994-04-22 EP EP94913458A patent/EP0647292A1/de not_active Withdrawn

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