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Title:
A DIAPHRAGM COMPRESSOR
Document Type and Number:
WIPO Patent Application WO/1999/020903
Kind Code:
A2
Abstract:
A diaphragm compressor, comprising: a connecting road (10) with an end mounted to the eccentric shaft (S) of a motor (M) and with the opposite end in the form of an enlarged head (11); a housing (20) surrounding the connecting rod (10) and having an end upper opening (21), onto which is affixed a cover (30); a diaphragm (40) affixed between the cover (30) and the housing (20) and its median portion being seated and pressed, by a rigid disc (50), onto the enlarged head (11), in order to define with the cover (30) a compression chamber (C) and a discharge chamber (D) which are divided by a valve plate (60) carrying a flexible gasket (70). According to the invention, the suction valve (SV) and the discharge valve (DV) are formed by respective portions (41, 71), of the diaphragm (40) and flexible gasket (70), which are elastically deformable.

Inventors:
Bräscher Filho, Paulo Paim (Rua Ricardo Landmann, 117 Bairro Santo Antônio -000 Joinville, SC, CEP-89219, BR)
Application Number:
PCT/BR1998/000082
Publication Date:
April 29, 1999
Filing Date:
October 08, 1998
Export Citation:
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Assignee:
SCHULZ S.A. (Rua Dona Francisca, 6901 -000 Joinville, SC, CEP-89219, BR)
Bräscher Filho, Paulo Paim (Rua Ricardo Landmann, 117 Bairro Santo Antônio -000 Joinville, SC, CEP-89219, BR)
International Classes:
F04B39/10; F04B45/04; F04B45/047; (IPC1-7): F04B45/04; F04B45/047; F04B45/04; F04B39/10
Foreign References:
GB681397A1952-10-22
US3645651A1972-02-29
GB428632A1935-05-16
GB191000699A1910-10-20
US4278406A1981-07-14
US5145336A1992-09-08
US3771911A1973-11-13
Other References:
PATENT ABSTRACTS OF JAPAN vol. 009, no. 286 (M-429), 13 November 1985 & JP 60 125787 A (ATSUGI JIDOUSHIYA BUHIN KK), 5 July 1985
Attorney, Agent or Firm:
Arnaud, Antonio M. P. (7th floor Rua José Bonifácio, 93 -901 São Paulo, SP, CEP-01003, BR)
Download PDF:
Claims:
CLAIMS
1. A diaphragm compressor, comprising: a connecting rod (10) with an end mounted to the eccentric shaft (S) of a motor (M) and with the opposite end in the form of an enlarged head (11); a housing (20) affixed to the motor (M), surrounding the connecting rod (10) and having an end upper opening (21), onto which is affixed a cover (30); a diaphragm (40) having its peripheral edge hermetically affixed between the cover (30) and the housing (20) and its median portion being seated and pressed, by a rigid disc (50), onto the enlarged head (11), in order to define with the cover (30) a compression chamber (C) of variable volume; and at least one suction valve (SV) provided in the compression chamber (C), characterized in that each suction valve (SV) comprises: a diaphragm portion (41) with a contour partially defined by a slot (42) provided in the diaphragm (40); a throughbore (12) provided in the enlarged head (11); and a respective window (52) provided in the rigid disc (50) and in constant fluid communication with the slot (42), the diaphragm portion (41) being elastically deformable from a closed valve position, in which it remains seated on the enlarged head (11) sealing the throughbore (12) and avoiding the fluid communication between the compression chamber (C) and the atmosphere, to an open valve position, when the pressure inside the compression chamber (C) reaches a certain negative value, in which said diaphragm portion (41) is spaced from the enlarged head (11), allowing the fluid communication between the compression chamber (C) and the atmosphere by means of the throughbore (12), slot (42) and window (52).
2. A diaphragm compressor, as in claim 1, characterized in that the slot (42) of each suction valve (SV) has a fixed edge, disposed between the enlarged head (11) and the rigid disc (50), and a movable edge, disposed under a respective window (52) of the rigid disc (50).
3. A diaphragm compressor, as in claim 1, characterized in that it comprises a plurality of suction valves (SV), whose slots (42) are in the form of arcs of a circle, which are arranged angularly and mutually spaced on the same circular alignment concentric to the diaphragm (40).
4. A diaphragm compressor, as in claim 3, characterized in that each slot (42) has two small radial extensions (42a) turned towards the center of the diaphragm (40) and laterally delimiting the respective diaphragm portion (41).
5. A diaphragm compressor, as in claim 4, characterized in that the throughbore (12) of each suction valve (SV) is located under the region delimited by the radial extensions (42a) of the slot (42).
6. A diaphragm compressor, as in claim 3, characterized in that the windows (52) have a circumferential extension which is substantially equal to that of the respective slot (42), the inner edge of the latter being provided along the inner edge of the window (52), the outer edge of said window being radially outwardly spaced from the slot (42).
7. A diaphragm compressor, comprising: a connecting rod (10) with an end mounted to the eccentric shaft (S) of a motor (M) and with the opposite end in the form of an enlarged head (11); a housing (20) affixed to the motor (M), surrounding the connecting rod (10) and having an end upper opening (21), onto which is affixed a cover (30); a diaphragm (40) which is peripherally and hermetically affixed between the cover (30) and the housing (20) and which is medianly seated and affixed to the enlarged head (11) in order to define with the cover (30) a compression chamber (C) of variable volume; and at least one discharge valve (DV) provided in the compression chamber (C), characterized in that the cover (30) incorporates a tubular axial extension (34) defining, together with a valve plate (60) affixed internally to the cover (30), a discharge chamber (D) provided with an outlet nozzle (31), an elastomeric gasket (70) being seated onto the valve plate (60) and peripherally and hermetically affixed between the latter and the cover (30), each discharge valve (VD) comprising a flexible gasket portion (71) provided with a through opening (72) and being elastically deformable from a closed valve position, in which it remains seated on the valve plate, sealing a respective throughbore (62) of the latter and avoiding fluid communication between the compression chamber (C) and discharge chamber (D), to an open valve position, when the pressure inside compression chamber (C) reaches a certain positive value, in which it is moved away from the valve plate (60), allowing fluid communication between the compression chamber (C) and discharge chamber (D) by means of the throughbore (62) and through opening (72).
8. A diaphragm compressor, as in claim 7, characterized in that it comprises a plurality of discharge valves (DV), whose throughbores (62) and through openings (72) are in the form of arcs of a circle, which are angularly and mutually spaced over two respective concentric circular alignments.
9. A diaphragm compressor, as in claim 7, characterized in that it comprises a stop means (38) internal to the discharge chamber (D) and slightly and axially spaced from said flexible gasket portion (71), in order to limit its displacement and define its open valveposition.
10. A diaphragm compressor, as in claim 9, characterized in that the stop means (38) is defined by the end annular edge of an internal axial tubular projection of the tubular axial extension (34) of the cover (30).
11. A diaphragm compressor, as in claim 7, characterized in that the valve plate (60) is affixed to the cover (30) by a single central screw (61), which is threaded into a central hub (37) and against which is pressed a median region of the flexible gasket (70).
12. A diaphragm compressor, as in claim 11, characterized in that the valve plate (60) is peripherally seated on an inner peripheral step (35) of the cover (30), said step being provided with a continuous annular salience (36) against which is peripherally pressed the flexible gasket (70).
13. A diaphragm compressor, as in claim 12, characterized in that the annular salience (36) is in the form of a small median rib.
14. A diaphragm compressor, as in claim 12, characterized in that the annular salience (36) is in the form of a radially internal rib of a rectilinear triangular crosssection.
15. A diaphragm compressor, comprising: a connecting rod (10) with an end mounted to the eccentric shaft (S) of a motor (M) and with the opposite end in the form of an enlarged head (11); a housing (10) affixed to the motor (M), surrounding the connecting rod (10) and having an end upper opening (21), onto which is affixed a cover (30); a diaphragm (40) which is peripherally and hermetically affixed between the cover (30) and the housing (20) and which is medianly seated and affixed to the enlarged head (11) in order to define with the cover (30) a compression chamber (C) of variable volume, characterized in that the enlarged head (11) of the connecting rod (10) has its upper peripheral region with a convex profile, the inner peripheral profile of the cover (30) being correspondingly concave and similar to that of the enlarged head (11), the curvature of said profiles being defined as a function of the oscillation degree of the enlarged head (11) when the connecting rod (10) is displaced to and from the upper dead point.
16. A diaphragm compressor, as in claim 15, characterized in that at least one of said profiles varies along the periphery of the respective part, so as to minimize the dead volume in the regions of less oscillation of the enlarged head (11).
17. A diaphragm compressor, comprising: a connecting rod (10) with an end mounted to the eccentric shaft (S) of a motor (M) and with the opposite end in the form of an enlarged head (11); a housing (10) affixed to the motor (M), surrounding the connecting rod (10) and having an end upper opening (21), onto which is affixed a cover (30); a diaphragm (40) which is peripherally and hermetically affixed between the cover (30) and the housing (20) and which is medianly seated and affixed to the enlarged head (11) in order to define with the cover (30) a compression chamber (C) of variable volume, characterized in that the enlarged head (11), end upper opening (21 of the housing (20), diaphragm (40) and cover (30) have a contour with a larger extension in the parallel direction to the eccentric shaft (S) and with a smaller extension orthogonal to said direction, the dimensioning of the smaller extension of the contour being defined so as to reduce the dead volume, resulting in a volumetric efficiency gain superior to the volume loss of the compressor chamber (C).
18. A diaphragm compressor, as in claim 17, characterized in that the contour of the enlarged head (11) of the connecting rod (10), end upper opening (21), housing (20), diaphragm (40) and cover (30) are substantially elliptical.
19. A diaphragm compressor, as in claim 17, characterized in that the contour of the enlarged head (11) of the connecting rod (10), end upper opening (21), housing (20), diaphragm (40) and cover (30) are substantially rectangular with rounded corners.
Description:
A DIAPHRAGM COMPRESSOR Field of the Invention The present invention refers to a diaphragm air compressor to be used, for example, in aspirators and nebulizers in patient treatment and also as a pressurized air source for paint guns, for filling balloons and tires, for cleaning electronic equipments, etc..

Background of the Invention Different constructive arrangements are known for diaphragm air compressors comprising a drive unit, usually a single phase electric motor, whose shaft incorporates an eccentric end portion, to which is mounted an end eye of a connecting rod, with the opposite end being defined by an enlarged head in the form of a circular flange and provided inside a housing, which is affixed to the motor and which has a circular end upper opening, to whose edge is hermetically attached a removable cover. The attachment of the cover to the housing is carried out bv disposing therebetween a sealing gasket defined by the peripheral edge of a flexible diaphragm, which is medianly seated and affixed by pressing a rigid disc onto the enlarged head of the connecting rod, so as to define with the cover a compression chamber which is selectivelv communicated with the atmosphere and with a nozzle connected to the system to be sucked or pressurized, through suction and discharge valves, respectively.

These known constructions, although being operatively adequate, have inconveniences related to the constructive complexity, to the relatively high cost and also to the volumetric efficiency of the compressor.

Regarding the constructive complexity, it should be noted that in the known compressors the suction and discharge valves are usually in the form of vanes made of a metallic blade, which are affixed by rivets or screws to the rigid disc, which operates as a suction valve plate, as well as to a discharge valve plate, which is mounted inside the cover, separating the compression chamber from a discharge chamber also defined inside the cover.

There are also known constructions with other solutions for the suction and discharge valves, comprising sealing means in the form of additional elements, which are constantly forced to a seating condition against a respective seat by actuation of spring means, which are dimensioned to allow the suction and discharge valves to open when a determined value of underpressure and overpressure, respectively, is achieved in the compression chamber.

These types of construction, employing valves with riveted vanes and provided with opening end stops, or valves provided with separate sealing means and submitted to a spring impelling means, require a relatively large number of components, which are complex to be produced and assembled and which lead to a correspondingly expensive final product.

Another inconvenience of the known diaphragm compressors is related to their volumetric efficiency.

In these compressores, the enlarged head of the connecting rod has a flat upper surface, which is usually provided with a peripheral chamfer, imparting to said enlarged head a frusto-conical aspect, and which is maintained spaced from the cover internal face, which also has a usually frusto-conical shape.

This frusto-conical construction for the enlarged head of the connecting rod and of the cover inside aims to

reduce the space between said parts, thus minimizing the dead space of the compressor chamber, in order to improve the volumetric efficiency of the compressor.

As it is known, this dead space results from the oscillating movement of the head of the connecting rod around a diametral axis parallel to the motor shaft.

This oscillation of the connecting rod head makes the opposite regions thereof, according to a diameter orthogonal to the direction of the motor shaft, come closer to the cover upon the operation of the compressor, requiring a larger gap in relation to the cover than that required in the regions external to the diametral axis of oscillation.

Although the frusto-conical shape already allows said gap to be reduced as compared to a prismatic rectilinear shape, it further results in a dead space which is not achieved by the diaphragm during the displacement of the connecting rod to the upper dead point.

Moreover, these known constructions have a gap, between the connecting rod head and the cover, which is kept constant throughout the periphery of the compressor chamber when the connecting rod reaches its upper dead point and lower dead point positions, resulting in a dead space which is relatively larger in the regions in which there is practically no oscillation of the connecting rod head, this characteristic contributing relevantly to reduce the volumetric efficiency of the compressor.

Disclosure of the Invention As a function of the deficiencies commented above, it is an objective of the present invention to provide a diaphragm compressor of the type considered herein and which has a simple and relatively low cost construction and from which the suction and discharge

valves, which are formed by movable elements affixed onto the walls of the compression chamber through securing means, were completely suppressed.

It is another objective of the present invention to provide a diaphragm compressor, in which the dead space of the compression chamber is substantially reduced, by means of a new configuration for the head of the connecting rod and for the internal portion of the cover, to a value corresponding to that which is effectively necessary to the motion of each peripheral region of the connecting rod head during the compressor operation.

The present diaphragm compressor is of the type comprising: a connecting rod, with an end mounted to the eccentric shaft of a motor and with the opposite end in the form of an enlarged head; a housing, affixed to the motor, surrounding the connecting rod and having an end upper opening, onto which is affixed a cover; a diaphragm having its peripheral edge hermetically affixed between the cover and the housing and its median portion being seated and pressed, by a rigid disc, onto the enlarged head, in order to define with the cover a compression chamber of variable volume; at least one suction valve and at least one discharge valve provided in the compression chamber.

According to a first aspect of the invention, each suction valve comprises a diaphragm portion with a contour partially defined by a slot provided in the diaphragm; a throughbore provided in the enlarged head; and a respective window provided in the rigid disc and in constant fluid communication with the slot, the diaphragm portion being elastically deformable from a closed valve position, in which it remains seated on the enlarged head, sealing the throughbore and avoiding the fluid communication

between the compression chamber and the atmosphere, to an open valve position, when the pressure inside the compression chamber reaches a certain negative value, in which said diaphragm portion is spaced from the enlarged head, allowing the fluid communication between the compression chamber and the atmosphere by means of the throughbore, the slot and the window.

According to a second aspect of the invention, the cover incorporates a tubular axial extension, which defines together with a valve plate affixed inside the cover a discharge chamber provided with an outlet nozzle, an elastomeric gasket being seated onto the valve plate and peripherally and hermetically affixed between the latter and the cover, each discharge valve comprising a flexible gasket portion provided with a through opening and being elastically deformable, from a closed valve position, in which it remains seated on said valve plate, sealing a respective throughbore of the latter and said through opening itself and avoiding fluid communication between the compression and discharge chambers, to an open valve position, when the pressure in the compression chamber reaches a certain positive value, in which it is spaced from the valve plate, allowing fluid communication between the compression and discharge chambers by means of the throughbore and-through opening.

According to a third aspect of the invention, the enlarged head of the connecting rod has its upper peripheral region with a convex profile, the inner peripheral profile of the cover being correspondingly concave and similar to that of the enlarged head, the curvature of said profiles being defined as a function of the oscillation degree of the enlarged head upon displacement of the connecting rod to and from the upper dead point.

According to a fourth aspect of the invention, the end upper opening of the housing, the cover, the diaphragm and the enlarged head of the connecting rod have a substantially elliptical or rectangular contour, with the larger extension being parallel to the direction of the eccentric shaft, the dimensioning of the smaller extension of the contour, in the transversal direction to the eccentric shaft, being carried out so as to reduce the dead volume, resulting in a volumetric efficiency gain which is superior to the volume loss of the compression chamber.

Brief Description of the Drawings The invention will be described below, with reference to the attached drawings, in which: Figure 1 is a partial diametral sectional view of the compressor, taken according to a vertical plane containing the motor shaft and illustrating, in a partial sectional view, the connecting rod in its upper dead point and lower dead point positions; Figure la is an enlarged detail of the upper part of figure 1, defined according to the dash-dot line containing the enlarged head of the connecting rod, the diaphragm, the rigid disc and the cover; Figure 2 is a vertical sectional view of the compressor, taken according to a plane, which is transversal to the motor shaft and which contains the connecting rod; Figure 2a shows an enlarged detail of the upper part of figure 2, illustrating the dead space in the upper dead point position of the connecting rod; Figure 3 shows an enlarged detail of portion"A" defined in a dash-dot line of figure 2, illustrating the operation of the suction and discharge valves;

Figures 4,5 and 6 show top plan views of the enlarged head of the connecting rod, diaphragm and rigid disc, respectively; Figure 7 illustrates a plan view of the assembly formed by the parts of figures 4,5 and 6 in the assembled condition; Figure 8 illustrates a plan view of the end upper opening of the housing, which is designed to operate together with a diaphragm and an enlarged head of the connecting rod of circular contour; Figures 9,10 and 11 are lower views, respectively, of the valve plate, elastomeric gasket and of the cover carrying the valve plate and elastomeric gasket; Figures 12,13 and 14 are upper views of the diaphragm, enlarged head of the connecting rod, and end upper opening of the housing, respectively, having an elliptical contour; and Figures 15,16 and 17 are similar views to those of figures 12,13 and 14, but illustrating another configuration in which the contour of the illustrated parts is substantially rectangular.

Best Mode of Carrying Out the Invention According to the appended drawings, the compressor of the present invention is of the type comprising an electric motor M, whose shaft S incorporates an eccentric end portion, whereto is mounted an end eye of a connecting rod 10 with the opposite end being defined by an enlarged head 11 in the form of a circular, elliptical or substantially rectangular flange, as illustrated in figures 4,13 and 16.

The connecting rod 10 is mounted inside a housing 20, which is secured to the electric motor M and which has an end upper opening 21 which may have a circular, elliptical or substantially rectangular contour, as illustrated in figures 8,14 and 17.

Onto the end upper opening 21 is hermetically affixed a cover 30 provided with an air outlet nozzle 31, to be connected to any system to be pressurized or sucked. Between the cover 30 and the end upper opening 21 is hermetically adapted the peripheral edge of a diaphragm 40, made of a flexible material and which forms with the cover 30 a compression chamber C with a variable volume depending on the movement of the diaphragm 40. This movement results from the fact that the median portion of the diaphragm 40 is seated and pressed onto the enlarged head of the connecting rod 10 by action of a rigid disc 50 provided with a central bore through which passes the screw 51 to be attached to the enlarged head 11. With this known assembly, the movement of the connecting rod 10 by means of shaft S of motor M causes the axial displacement of the diaphragm 40, increasing the volume in the compression chamber C during suction and reducing said volume during compression.

As already mentioned in the beginning of this specification, one of the improvements achieved with the present invention is related to the construction of the suction valves. According to the invention, each suction valve SV comprises a diaphragm portion 41 with a contour which is partially defined by a slot 42 provided in the diaphragm 40 itself, a throughbore 12 provided in the enlarged head 11 and axially aligned with said diaphragm portion 41, and a window provided in the rigid disc 50 in a position such as to maintain a constant fluid communication with the slot 42, and between the latter and the inside of the compression chamber C.

With the above constructive arrangement, the diaphragm portion 41 is elastically deformable from a closed valve position, in which it remains seated on the

enlarged head 11, sealing the throughbore 12 and avoiding fluid communication between the compression chamber C and the atmosphere inside the housing 20, to an open valve position, when pressure inside compression chamber C reaches a certain negative value,-in which said diaphragm portion 41 is spaced from said enlarged head 11, as illustrated in the right half of figure 3, allowing fluid communication to occur between said compressiom chamber C and the atmosphere, by means of throughbore 12, slot 42 and window 52.

Each suction valve SV is designed so that the slot 42 of diaphragm 40 has a fixed edge, which is provided and immobilized between the enlarged head 11 and the rigid disc 50, and a movable edge, which lies under the respective window 52 of the rigid disc, so that it may be elastically deformed towards the inside of said window (figure 3), allowing air to pass to the inside of compressor chamber C when the pressure therein reaches a certain negative value.

In the illustrated embodiment, there is provided a plurality of suction valves SV, whose slots 42 are in the form of arcs of a circle, which are angularly and mutually spaced according to the same circular alignment concentric to the diaphragm 40, the opposite edges of each slot 42 being radially spaced from each other to prevent them from overlapping and interfering with the adjacent edge of the window 52 of the rigid disc 50 during the movement of the diaphragm portion 41.

As illustrated in figures 5,12 and 15, each slot 42 incorporates two small radial extensions 42a, turned towards the center of diaphragm 40, laterally delimiting each respective diaphragm portion 41. In order to guarantee the correct positioning for the

assembly of the rigid disc 50, diaphragm 40 and enlarged head 11 of the connecting rod 10, the rigid disc 50 is provided with two small stamped axial ears 53, which are diametrically opposite and disposed by means of respective throughbores 43 of the diaphragm 40 and which are fittable in recesses 13 provided in the enlarged head 11. With this arrangement, these three parts are mounted in a predetermined radial angular positioning, allowing the throughbore 12 of each suction valve SV to be located under a respective diaphragm portion 41 defined between the two small radial extensions 42a of the respective slot 42.

In the preferred constructive form, the windows 52 of each suction valve SV have a circumferential extension which is substantially equal to that of the respective slot 42, the radially internal edge of the latter being disposed along the radially internal edge of the window 52, with the radially external edge of the latter being radially outwardly spaced from the slot 42.

With the aim to assure a better retention of the peripheral edge of the diaphragm 40, said edge is seated on a recessed annular step 22 of the end upper opening 21, said step being defined on a frusto- conical surface cooperating with a corresponding inverted frusto-conical annular projection 32 of the cover (30), said surfaces defining together a retaining means with a dove tail profile for retaining the peripheral edge of the diaphragm 40.

According to another aspect of the present invention, the cover 30 incorporates a tubular axial extension 34, which consists of an extension of the compressor chamber C and which is separated from the latter by a valve plate 60, so as to define a discharge chamber D

provided with the nozzle 31 for discharging the pressurized air.

Valve plate 60 has its peripheral edge seated on an internal peripheral step 35 of the cover 30, said step being preferably provided with a continuous annular salience 36, preferably in the form of a median rib or a radially internal rib, against which is pressed the peripheral region of flexible gasket 70 disposed between the valve plate 60 and the discharge chamber D. The valve plate 60 is affixed to the cover 30 by a single central screw 61, which is threaded into a central hub 37 of the tubular axial extension 34 and agaisnt which is pressed a median region of the flexible gasket 70.

Each discharge valve DV comprises a flexible gasket portion 71 having a through opening 72 preferably in the form of an arc of a circle, said flexible gasket portion 71 being elastically deformable from a closed valve position, in which it remains seated on the valve plate 60, sealing a respective throughbore 62 of the latter and avoiding fluid communication between the compressor chamber C and discharge chamber D, to an open valve position, when the pressure in compressor chamber C reaches a certain positive value, in which it is moved away from the valve plate 60, allowing fluid communication between the compressor chamber C and discharge chamber D by means of the respective throughbore 62 and the respective through opening 72 of the flexible gasket 70, as illustrated in figure 3.

In the illustrated embodiment, there is provided a plurality of discharge valves DV, whose throughbores 62 and through openings 72 are in the form of arcs of a circle, which are angularly and mutually spaced over

two respective circular concentric alignments, as illustrated in figures 9,10 and 11.

In order to limit the elastic deformation of the flexible gasket portions 71 of the discharge valves DV, defining the opening positions thereof, there is internally incorporated into said discharge chamber D a stop 38, which is preferably tubular with an end annular edge which is axially and slightly spaced from each said flexible gasket portion 71.

As it can be observed from figures 1, la, 2 and 2a, the enlarged head 11 of the connecting rod 10 has its upper peripheral region with a convex profile, giving to the enlarged head 11 a frusto-conical shape of reduced height and with a slightly convex lateral surface, the inner peripheral profile of the cover 30 being concave, with the curvature corresponding to that of the upper peripheral region of the enlarged head 11 and defined as a function of the degree of oscillation and of the dimension of the enlarged head 11 upon movement of the connecting rod 10 approaching the upper dead point.

Considering that the oscillation of the enlarged head 11 of the connecting rod 10 occurs in the direction orthogonal to shaft S of motor M, it has been verified that it is more adequate to vary the profile of at least one of the confronting peripheral regions of the enlarged head 11 and cover 30 along the contour of the compressor chamber C, in order to minimize the dead volume in the regions where the enlarged head 11 oscillates less (see figure 2a), resulting in a dead space of variable height. Thus, when the connecting rod 10 is at its upper or lower dead points, i. e., parallel to the cover 30, the free distance between the enlarged head 11 of the connecting rod 10 and the cover 30 has a smaller height at the parallel

positions to the motor shaft and a larger height at the diametral positions orthogonal to the motor shaft.

Aiming to reduce the dead volume inside compressor chamber C and as illustrated in figures 12-17, the diaphragm 40, cover 30, end upper opening 21 of the housing 20 and the enlarged head 11 of the connecting rod 10 may be constructed so as to have a contour with a larger extension disposed in the parallel direction to the shaft S of motor M and with a smaller extension orthogonal to said direction, the dimensioning of the smaller extension of the contour being defined so as to reduce the dead volume, which results in a volumetric efficiency gain superior to the volume loss of the compressor chamber C.

As illustrated in the figures, the contour of the parts described above may be substantially elliptical or rectangular with rounded corners.