WO1994023202A1 - Systeme d'entrainement pour pistons alternatifs - Google Patents

Systeme d'entrainement pour pistons alternatifs Download PDF

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Publication number
WO1994023202A1
WO1994023202A1 PCT/BR1994/000013 BR9400013W WO9423202A1 WO 1994023202 A1 WO1994023202 A1 WO 1994023202A1 BR 9400013 W BR9400013 W BR 9400013W WO 9423202 A1 WO9423202 A1 WO 9423202A1
Authority
WO
WIPO (PCT)
Prior art keywords
cam
post
reciprocating piston
suction
connecting rod
Prior art date
Application number
PCT/BR1994/000013
Other languages
English (en)
Inventor
Dietmar Erich Bernhard Lilie
Original Assignee
Empresa Brasileira De Compressores S/A. - Embraco
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Empresa Brasileira De Compressores S/A. - Embraco filed Critical Empresa Brasileira De Compressores S/A. - Embraco
Publication of WO1994023202A1 publication Critical patent/WO1994023202A1/fr

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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
    • F04B39/0005—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 adaptations of pistons
    • F04B39/0022—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 adaptations of pistons piston rods
    • 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
    • F04B9/00—Piston machines or pumps characterised by the driving or driven means to or from their working members
    • F04B9/02—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being mechanical
    • F04B9/04—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being mechanical the means being cams, eccentrics or pin-and-slot mechanisms
    • F04B9/042—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being mechanical the means being cams, eccentrics or pin-and-slot mechanisms the means being cams

Definitions

  • the present invention refers to a reciprocating piston driving system for hermetic compressors of the type used in small refrigerating appliances.
  • the piston moves linearly during each operative stroke, in both directions and with a velocity that varies sinusoidally, as a result of the type of mechanical connection, i.e., the eccentric articulation between the connecting rod of the piston and the crankshaft of the compressor, said crankshaft rotating at a constant speed.
  • the piston starts from a first position of zero instantaneous velocity, towards a second position of zero instantaneous velocity, said second position being displaced from said first position in 180° of the crankshaft rotation.
  • Said displacement is achieved, by initially submitting the reciprocating piston to an acceleration, which will result in a maximum instantaneous velocity, at a position of the stroke thereof that is intermediate relative to said first and second positions of zero velocity, when the motion of said piston begins to be braked, till reaching said second zero velocity, when the process is restarted, till the first zero velocity position is reached again.
  • Said first and second positions of zero instantaneous velocity define, respectively, an upper dead point of compression end and a lower dead point of suction end of the piston operative cycle.
  • the piston operates during its linear movement inside a cylinder presenting an end, which is opposite to the end whereby said piston is articulated to the connecting rod, and which is opened to a valve plate that separates the inner cavity of said cylinder from a cylinder head, inside which the discharge and suction chambers of the compressor are defined.
  • the communication between the inner cavity of the cylinder and each of said chambers is achieved through discharge and suction orifices, which are periodically and selectively closed by respective discharge and suction valves, mounted to said valve plate.
  • the crankshaft drives said piston, in order to impart to said piston an increasing velocity, from its zero velocity position at the upper dead point, till the maximum velocity is reached, when said piston begins to be braked.
  • This drive makes the piston move towards the lower dead point, thus gradually decreasing the pressure inside the inner cavity of the cylinder, till a pressure differential is reached, the sufficient to cause and maintain, while there is a certain minimum pressure differential, the opening of the suction valve, thereby allowing the gas to flow from the inside of the suction chamber towards the cylinder inside.
  • the higher the valve stiffness the longer the time required to reach the differential pressure condition that causes the opening of said valve during the suction stroke. Such longer time means that the opening will occur in a condition of the suction stroke closer to the lower dead point, i.e., closer to the moment of the piston stroke inversion.
  • a second object of the present invention is to provide a piston driving system, as stated above, which allows a better control of the times required for each operative stroke of said piston, particularly at the proximities of the lower dead point and at the upper dead point.
  • a reciprocating piston driving system of the type mounted inside a cylinder, defined in a respective cylinder block and driven by a crankshaft of a hermetic compressor, through a connecting rod, with a first end mounted to the piston and a second opposite end operatively connected with the crankshaft, in order to impart to the piston an operative cycle having a compression stroke and a suction stroke
  • the connection between the crankshaft and the connecting rod comprises: a cam, mounted to the crankshaft, in order to rotate therewith and presenting a peripheral cam surface; a cam follower, mounted from the second end of the connecting rod; and a connecting rod-cam operative connecting means, supported by the cam, keeping the cam follower constantly and operatively connected with the cam surface, the assembly of the connecting rod being made in such a way as to avoid angular displacements thereof, at least on the plane containing the cam surface, said cam surface being designed in such a way as to define during said operative cycle at least a post-compression time during which the
  • Fig. 1 is a longitudinal sectional view of a portion of the compressor inside, in which the cylinder block assembly is mounted, according to the state of the art.
  • Fig. 2 is an upper view of the piston-connecting rod - crankshaft assembly, according to the present invention.
  • Fig. 3 is a cross sectional view of the crankshaft cam, according to the line III-III of figure 2. Best Mode of Carrying- Out the Invention
  • a reciprocating hermetic compressor of the type comprising a cylinder block 1, which is lodged inside a hermetic case (not illustrated) , and which presents a cylindrical cavity, such as a cylinder 2, within which reciprocates a piston 3.
  • the cylinder block 1 presents a pair of opposite faces, towards which the ends of the cylinder 2 are opened.
  • a valve plate 5 and a cylinder head 6 which forms together with said valve plate 5 two internal cavities, each defining a suction chamber 8 and a discharge chamber 9.
  • the cylinder 2 is kept in selective fluid communication with said suction chamber 8 and discharge chamber 9, through respective gas suction orifices 5a and discharge orifices 5b, which are provided at the valve plate 5 and into which are mounted a respective suction valve 10 and a 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 first end 3a, facing the valve plate 5a and a second opposite end 3b, through which said reciprocating piston 3 is driven.
  • the crankshaft 30 While rotating, the crankshaft 30 imparts to said larger eye 22 of the connecting rod 20 a circular movement that will cause a linear movement to the reciprocating piston 3 between points of minimum and maximum distance from the valve plate 5. Said points of minimum and maximum distance from the valve plate 5 represent the points of stroke inversion in the operative cycle of the reciprocating piston, respectively known as upper dead point and lower dead point.
  • the reciprocating piston 3 presents a continuous linear movement, with a suction stroke and a compression stroke, which start, respectively, at the upper dead point and at the lower dead point.
  • Each operative cycle of the reciprocating piston is achieved within a total time T, which corresponds to the sum of a suction time plus a compression time, which are equal. Moreover, the piston stop at the upper dead point and at the lower dead point is instantaneous and of the same duration in both situations.
  • the linear movement of the reciprocating piston 3, between the points of stroke inversion is numerically equal to the diameter of the eccentric and corresponds to an angular displacement from a central portion of the larger eye 22 of the connecting rod 20, according to a regular displacement curve, presenting a single radius that is equal to the eccentricity of the crankshaft 30, i.e., to the distance between the geometrical centers of the crankshaft 30 and said larger eye 22 of the connecting rod 20.
  • the transmission of movement between the crankshaft and the reciprocating piston 3 is made through a connecting rod 50, having a first free end 51 and a second opposite end 52, attached to the piston.
  • a connecting rod 50 having a first free end 51 and a second opposite end 52, attached to the piston.
  • the second opposite end 52 need not be articulated to said piston, as in the state of the art.
  • Said first free end 51 carries a roller bearing 51a, the actuation of which will be described ahead.
  • the linear movement of the piston, between the points of stroke inversion corresponds to a linear movement of said first end 51 of the connecting rod 50 and is equal to the largest distance between two diametrically opposite points of a peripheral surface of a cam 40, mounted to the crankshaft 30, in order to rotate with the latter.
  • the roller bearing 51a mounted to the first end 51 of the connecting rod 50 defines a cam follower, which is in permanent contact with the cam peripheral surface 41 of the cam 40, said construction being defined in such a way as to obtain different times of compression and suction, required for a better performance of the compressor, as described below.
  • the best performance of the compressor means the total filling up of the volumetric capacity of the cylinder 2, before the start of the compression stroke, as well as the total flowage of the refrigerant fluid from said cylinder 2 to the discharge chamber 9, before the suction stroke of the reciprocating piston 3 starts, said conditions of total flowage and total filling up with refrigerant fluid to and from the inside of the cylinder 2 occurring even when the pressure differential that is needed to obtain the opening of the respective discharge valve 11 and suction valve 12 is achieved in a time interval close to the instant of the corresponding stroke end.
  • the cam 40 is in the form of a cylindrical tubular body, which is peripherally provided with an annular groove of variable depth, defining a guide rail 4la on the cam surface 41.
  • a connecting rod - cam operative connecting means 60 in the form of a "U" shaped elastic guiding arm, which is mounted upperly relative to the connecting rod-cam assembly and which has a first end 61, attached to the first cam follower end 51 of the connecting rod 50 and a second end 62, positioned at the center of rotation of the cam 40.
  • the elasticity of the guiding arm 60 keeps a constant contact with the connecting rod 50 and the cam surface 40, during the operation of the reciprocating piston 3.
  • the variable profile of the cam surface 40 is obtained in function of the time duration required for each time of the cycle of the reciprocating piston 3.
  • the irregular surface is defined, so that the total time of a cycle of the reciprocating piston 3 corresponds to the sum of the stop times at the end of compression and at the end of suction, i.e., of stroke inversion, as well as to the times of compression and suction motions, as described ahead.
  • the cam 40 is in the form of an irregularly shaped body, defined in function of the required time characteristics mentioned above.
  • the permanent contact between the first free end 51 of the connecting rod 50 and the cam surface 41 can be achieved by action of a cam follower, which is slidably connected with the guiding rail 41a.
  • the operative connecting means is stiff, in order to avoid that during each operative cycle of the piston the free end 51 of the connecting rod 50 provided with the cam follower 51a presents angular displacements during its displacement at least on the plane containing the cam surface 41, there is mounted to the cylinder block 1 a connecting rod guiding element 53 that, during the operation of the reciprocating piston 3, guides a portion of the rod of the connecting rod 50.
  • the cam follower 51a in the form of the roller bearing described above, maintains a permanent sliding contact with the cam surface, this contact being maintained by the guiding arm 60 which, for being elastic, automatically and constantly corrects any attempt of the connecting rod 50 to move away from the cam surface 41, thereby dispensing the use of the connecting rod guide 53.
  • the post- compression time i.e., at the upper dead point, should be long enough to permit that a maximum residual gas, which is present inside said cylinder 2, escapes to the discharge chamber 9, before suction begins.
  • the reciprocating piston 3 should remain at a stationary condition at its upper dead point position.
  • the crankshaft and, therefore, the cam 40 are still moving continuously, the lack of movement is obtained, by maintaining constant the radius of the cam surface 41 during the post compression time.
  • Obtaining a long post compression time corresponds to the relative displacement of the cam follower 51 of the connecting rod 50, along a region of the cam surface 41 presenting an extension long enough to assure a desired stop time for the piston at the upper dead point during a corresponding rotation of the crankshaft.
  • the circumference arc defined by said post compression region of the cam surface presents a radius that is larger than the radius of the suction, post suction and compression regions of said cam surface.
  • the reciprocating piston starts the suction period, which corresponds to a respective suction region of the cam surface, whose curvature radius, or eccentricity, is dimensioned so as to allow a maximum entrance of refrigerant gas into the inside of the cylinder 2, during said suction stroke, until the pressure differential between the suction chamber and the cylinder inside does not maintain the suction valve 10 in an opening condition any more.
  • the variation of the curvature radius during the suction results in a relatively long suction time, but not necessarily of the same duration as the post compression time, in order to allow the inside of the cylinder 2 to be filled up with gas, through small pressure differentials, although not causing turbulence inside said cylinder 2.
  • Such initial acceleration and posterior brake should mean an even transition for the cam follower 51, said transition being achieved with the gradual increase of the radius, from the constant radius of the post suction circular region, till the constant radius of the post compression region is reached, presenting increases by unit of angular pitch, that are variable from said post suction radius up to the post compression radius.
  • said radius increase per unit of angular pitch, at the region of the cam surface 41 adjacent to the region thereof corresponding to the post compression radius should be very small when compared with the cam surface accelerating region 41 of the reciprocating piston 3.
  • the post suction radius that gives origin to a cam surface corresponding to a post suction stop should be smaller than the radius of the suction, compression and post compression regions.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Compressor (AREA)

Abstract

Système d'entraînement pour pistons alternatifs du type monté dans un cylindre (2) prévu dans un bloc-cylindres respectif (1), et entraîné par le vilebrequin (30) d'un compresseur hermétique par l'intermédiaire d'une biellette (50) dont la première extrémité (51) est fixée au piston (3) tandis que sa seconde extrémité est associée activement au vilebrequin (30) de manière à imprimer au piston un cycle d'exploitation comprenant une course de compression et une course d'aspiration. Le raccordement entre le vilebrequin (30) et la biellette (50) est assuré par une came (40) montée solidaire en rotation sur le vilebrequin (30) et dotée d'une surface de came périphérique (41); un suiveur de came (51) relié à la seconde extrémité de la biellette (50); et un ensemble (51a, 41a) de liaison active de la biellette et de la came, ensemble assurant en permanence le maintien de la liaison active entre le suiveur de came et la surface de came (41), l'assemblage de la biellette (50) étant réalisé de manière à éviter tout déplacement angulaire de celle-ci, au moins dans le plan dans lequel s'étend la surface de came, et ladite surface de came étant adaptée pour délimiter, pendant ledit cycle d'exploitation, au moins un intervalle suivant la compression et un intervalle suivant l'aspiration, pendant lesquels le piston demeure immobile.
PCT/BR1994/000013 1993-03-29 1994-03-24 Systeme d'entrainement pour pistons alternatifs WO1994023202A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
BRPI9300885 1993-03-29
BR9300885A BR9300885A (pt) 1993-03-29 1993-03-29 Sistema de acionamento de pistão reciprocante

Publications (1)

Publication Number Publication Date
WO1994023202A1 true WO1994023202A1 (fr) 1994-10-13

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/BR1994/000013 WO1994023202A1 (fr) 1993-03-29 1994-03-24 Systeme d'entrainement pour pistons alternatifs

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BR (1) BR9300885A (fr)
WO (1) WO1994023202A1 (fr)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR344266A (fr) * 1904-05-02 1904-10-29 Francois Plancard Fils Pompe à courant continu
DE433695C (de) * 1925-03-03 1926-09-04 Felix Meineke Dr Ing Kolbenpumpe mit Antrieb durch unrunde Scheibe
DE7305570U (de) * 1973-02-14 1973-08-16 Zahnradfabrik Friedrichshafen Ag Federnde Halterung des Kolbens in einer Radialkolbenmaschine
DE2608664A1 (de) * 1976-03-03 1977-09-08 Niepmann Ag Walchwil Vorrichtung zur erzeugung eines gleichfoermigen foerderstromes
US4105371A (en) * 1976-10-15 1978-08-08 General Motors Corporation Cam driven compressor
EP0461943A2 (fr) * 1990-05-15 1991-12-18 L'oreal Dispositif de compression, en particulier pour le remplissage sous pression d'un réservoir

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR344266A (fr) * 1904-05-02 1904-10-29 Francois Plancard Fils Pompe à courant continu
DE433695C (de) * 1925-03-03 1926-09-04 Felix Meineke Dr Ing Kolbenpumpe mit Antrieb durch unrunde Scheibe
DE7305570U (de) * 1973-02-14 1973-08-16 Zahnradfabrik Friedrichshafen Ag Federnde Halterung des Kolbens in einer Radialkolbenmaschine
DE2608664A1 (de) * 1976-03-03 1977-09-08 Niepmann Ag Walchwil Vorrichtung zur erzeugung eines gleichfoermigen foerderstromes
US4105371A (en) * 1976-10-15 1978-08-08 General Motors Corporation Cam driven compressor
EP0461943A2 (fr) * 1990-05-15 1991-12-18 L'oreal Dispositif de compression, en particulier pour le remplissage sous pression d'un réservoir

Also Published As

Publication number Publication date
BR9300885A (pt) 1994-10-18

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