PISTON MECHANISM WITH PASSAGE THROUGH THE PISTON

Abstract: Piston mechanism with passage through the piston (1), which piston mechanism comprises a cylinder (2) which is provided at one extremity with a conduct (9) which can be closed; a cylinder (1), axially movable in this cylinder (2), which is provided with a conduct (9) which can be closed and which possesses in its outer circumference a groove (7) in which a piston ring (8) is provided for sealing with the cylinder (2); and means (3) to move the piston (1) in the cylinder (2), which means (3) comprise a crank shaft (4) which is mounted in a crank chamber (5) and a piston rod (6) which, on the one hand, by means of a first bearing (18), is hingedly connected to the piston (1) and, on the other hand, by means of a second bearing (20), is hingedly connected to the crank shaft (4), whereby the piston ring (8) is mounted with a certain axial clearance in the groove (7), the passage (12) through the piston (1) extends over this groove (7) and the piston ring (8) forms a valve for closing and opening this passage (12), characterized in that the afore-mentioned passage (12) through the piston (1) gives onto the back side of the piston (1) and thus, medium that flows through this passage (12) also flows over the bearing (18) by which the piston rod (6) is connected to the piston (1).

Description: Piston mechanism with passage through the piston. The invention concerns a piston mechanism with passage or conduct through the piston, whereby the piston mechanism comprises a cylinder which, at one extremity, is provided with a passage which can be closed and, at the other extremity gives onto the inner side of a crank chamber; a piston, axially movable in the cylinder, which equally is provided with a passage or conduct which can be closed, and which comprises in its outer circumference a groove in which a piston ring is situated for the sealing with the cylinder; and means to move the piston in the cylinder, whereby these means comprise a crank shaft which is positoned in the crank chamber and a crank or piston rod which, on the one side, is hingedly connected to the piston by means of a first bearing, and, on the other side, by means of a second bearing, is hingedly connected to the crank shaft, whereby the piston ring is positioned with a clearance in the axial direction in the groove, the passage through the piston extends over this groove and the piston ring forms a valve for closing and opening this passage. Such a piston mechanism allows the sucking in of gaseous medium through the piston without an extra valve in the piston. BE-A-378.946 describes a compressor with a piston mechanism of the type described hereabove. However, the passage in the pistcn only extends partly thereover, namely from the front side up to a opening in the side which, in the utmost extended position, is not yet situated at the back side of the piston. Consequently, this passage does not give onto the back side of the piston. Gaseous medium is sucked in via chambers situated on the outside of the cylinder and consequently not via the crank chamber which is filled with oil. This oil serves to lubricate the bearings with which the piston rod is connected with the crank shaft and the piston. Hereby, the heating of the bearings is avoided, but in the obtained compressed air traces of oil will be present, which is not desirable for certain applications. The presence of chambers at the outside of the cylinder and the use of oil to lubricate do not make the construction simple. The gaseous medium which is sucked in through the passage flows along the wall of the cylinder which can be rather warm during the operation, resulting in the heating of the medium, which dis dvantageously influences the efficiency of the compressor. The invention aims at a piston mechanism which does not present these and other disadvantages and which is not only relatively simple in construction, and possesses a very good efficiency, but which can also operate without oil lubrication and yet is relatively long-lasting. According to the invention this aim is achieved in that said passage through the piston gives onto the back side of the piston and consequently provides that medium, which flows through this passage, also flows over the bearing by which the piston rod is connected to the piston. The medium which is sucked in through the passage originates from the back side of the piston and is to a minimal extent in contact with parts of the pistor- mechanism, that are heated durxng the operation of the piston mechanism. A piston mechanism whereby the piston is provided with a passage which gives onto the back side of the piston and whereby the piston ring forms a valve in this passage, is known from CH-A-30B,083, but this piston mechanism is not of the type concerned by the invention, because the piston is stiffly connected with the piston rod and a crank chamber is not present. A similar piston mechanism does therefore not show the problem of heating of the bearings. in a preferred embodiment of the invention, the piston is provided at its back side with a hole onto which the passage gives, and in which the bearing is situated by which the piston rod is connected to the piston. Thus, a part of the passage extends inwardly through the wall of the piston, whereby the possible heating of the medium, sucked in through the passage, caused by heated parts, is considerably reduced. in a particular embodiment of the invention, the piston mechanism forms part of an oil-free compressor a d a compressed air conduit or a compressed air vessel is connected to the passage in the cylinder, whereby the passage in the piston ta∑ms an inlet during the suckxng in stroke and the piston ring forms an inlet valve. Preferably the crank chamber is provided with an inlet so that the medium which flows through the passage through the piston, also flows over this crank chamber and over the bearing situated therein, by which the piston rod is connected to the crank shaft. Particularly, in the case of oil-free compressors a problem of the heating of the bearing exists♦ Both bearings are cooled in the preceding embodiment by the sucked in gaseous medium. With .a view to better describe the characteristics of the invention, a preferred embodiment of a piston mechanism with passage through the piston according to the invention is described hereafter, as an example without any limitative character, reference being made to the accompanying drawings, in which. figure 1 is a schematic representation of a cross- section of a piston mechanism according to the invention, mounted in a piston compressor; figure 2 is an enlarged view of a crosse-section according to line II-II in figure 1, during the sucking in stroke of the piston mechanism; figure 3 represents the cross-section of figure 2 but during the compression stroke. The piston mechanism represented in figure 1 forms part of an oil-free piston compressor which comprises several such piston mechanisms that essentially are composed of a piston 1, which is axially movable in a cylinder 2 and means 3 to move the piston 1. These means 3 are essentially composed of a crank shaft 4 situated in a crank chamber 5 and driven by a motor, not represented in the figures, and a piston rod 6 which is hingedly connected with the piston 1 and the crank shaft 4. The piston l is provided near its front, in figures 2 and 3 upper, extremity, in other words the extremity directed towards the closed end of the cylinder 2 , with a circumferential groove 7, in which a piston ring 8 is applied which elastically joins the inner wall of the cylinder 2. This piston ring 9 is of the self-lubricating type and is formed by a flat, interrupted ring which is fixed in the groove 7 not only with a radial but with an axial clearance as well. The piston ring could eventually also be formed by an elastic ring. This implies that the thickness of the piston ring 8 is smaller than the width of the groove 7, whereas the depth of the groove 7 is, in radial direction, a little greater than the width of the piston ring. In the closed end cf the cylinder 2 a passage 9 is applied, namely an outlet which, by means of a valve 10, can be closed and to which a pressure conduit 11 is connected. The other end of the cylinder gives onto the above- described crank chamber 5, which is common for ail the piston mechanisms of the piston compressor. As represented in detail in figures 2 and 3, through t he piston 1 a passage 12 is applied, namely an inlet for the medium to be compressed which is sucked in from the crank chamber 5. This passage 12 forming an inlet extends over the groove 7 and is composed of this groove 7 f an additional groove 13 over the piston circumference at the side of the crank chamber 1 relative to the groove 7, a recess 14 over the circumference of t he piston l r which connects the grooves 7 and 13 and where the piston 1 thus has a smaller outside diameter, a number of openings 15 which extend between the groove 3 and the back side, this is in figure 2 and 3 the bottom si d e, of the piston 1, and a number of openings 16 which extend between this groove 7 and the front side of the piston 1. T hese openings 14 and 16 are situated at a distance from the outside of the piston 1. At said back side, the piston 1 is provided with a cavity 17 onto which the openings 15 give. In this cavity 17 is situated the bearing 18 by which an extremity of the crank or piston rod 6 is hingedly connect e d to t he piston 1 and more particularly to the transversal shaft 19 mounted in the cavity 17. This bearing IB, is for instance a needle bearing and is for instance lubricated with grease. The other extremity of the piston rod 6 is hingedly connected in the crank chamber 5 to the crank shaft 4 by a second bearing 20. This bearing 20 can also be lubricated for instance with grease. The crank chamber 5 is provided with an inlet 21. This crank chamber 5 is not filled with oil. The piston mechanism operates as follows. By the movement of the crank shaft 4, the piston 1 executes subsequently a sucking in stroke, this is a movement in the direction of the crank chamber 5, and a compression stroke in the other direction. T he valv e 10 in the passage 9 forming a passage is, in synchronisation with this movement, opened an d close d in a manner known to the craftsman and not further described, in such way that, during the compression, the valve 10 is temporarily open and compressed medium leaves the cylinder 2 via the passage S, but during suction the valve 10 is closed. The valve 10 can be mechanically controlled b ut can for instance also be a recoil valve which automatically opens and closes in the appropriate way. In figure 1 the piston 1 is represented in i t s topmost centre dead, between the sucking in stroke and the compression stroke. During the sucking in stroke the pressure at the front side of the piston 1 is at a certain moment equal to the pressure at the back side, being the pressure in the crank chamber 5. A s soon as this balance is reached, this piston ring 3, on account of the friction of the piston ring β against the inner wall of the cylinder 2, will stay with respect to the moving piston 1 and take t o place which is shown in figure 2, whereby the openings 16 via the groove 7 and the recess 14 are in an open connection with the groove 13 and further via the openings 15 with the cavity 17 of the piston 1. Gaseous medium, for instance air, can flow via the thus formed passage 12 or inlet in the part of the cylinder at the front side of the piston 1. It is evident that this medium is sucked in via the inlet 21 over the crank chamber 5 and through the part of the cylinder 2 giving onto it, the cavity 17 and the passage 12, which means that this medium flows over the bearing 20 in the crank chamber 5 and over the bearing 18 in the piston 1, These bearings 18 and 20, and the grease that is used for lubrication thereof, are cooled. The crank chamber 5 is also cooled by this medium. The passage 12 itself is rather short and moreover comprises big parts, namely the openings 15 and 16, which are not in direct contact with the hot parts of the piston mechanism, in particular of the cylinder 2. As a result, the medium sucked in through the passage 12 is practically not heated whereby a very good filling degree and a very good efficiency is obtained. When, after its bottommost dead centre the piston 1 moves in the opposite direction, on account of the friction of the piston ring 8 against the inner wall of the cylinder 2, this piston ring will tend to stay. This also occurs as soon as the pressure of the front side of the piston 1 is equal to the pressure at the back side. P revious to the higher pressure arising at the front side of the piston 1, in comparison with the back side of the piston l the piston ring 8 consequently closes the recess 14 in such a way that the connection between the groove 7 and the groove 13 is broken and thus the passage 12 is closed, as represented in figure 3. It is evident that by the friction of the piston ring 8 against the cylinder 2, the closing during the compression stroke and the opening during the suction stroke are accelerated, so that the compression, respectively the suction in starts faster, which results in an ameliorated operation the piston principle. For the same compressed output, less power is hereby lost and a better compression efficiency is obtained. The invention is in no way limited to the embodiment described above and represented in the figures, but such a piston mechanism can be realized in different variants without leaving the scope of the invention. In particular the bearings need not necessarily be needle bearings or similar. They can also be slide bearings, whereby parts of the piston rod surround the corresponding shaft with only a lubricant between them.

Claims: Claims 1.- Piston mechanism with passage through the piston (1), which piston mechanism comprises a cylinder (2) which is provided at one extremity with a conduct (9) which can be closed; a cylinder (1), axially movable in this cylinder (2), which is provided with a conduct (9) which can be closed and which posseses in its outer circumference a groove (7) in which a piston ring (8) is provided for sealing with the cylinder (2); and means (3) to move the piston (1) in the cylinder (2), which means (3} comprise a crank shaft (4) which is mounted in a crank chamber (5) and a piston rod (6) which, on the one hand, by means of a first bearing (18), is hingedly connected to the piston (1) and, on the other hand, by means of a second bearing (20), is hingedly connected to the crank shaft (4), whereby the piston ring (8) is mounted with a certain axial clearance in the groove (7), the passage (12) through the piston (1) extends over this groove (7) and the piston ring (8) forms a valve for closing and opening this passage (12), characterized in that the aforementioned passage (12) through the piston (1) gives onto the back side of the piston (1) and thus medium that flows through this passage (12} also flows over the bearing (IB) by which the piston rod (6) is connected to the piston (1). 2.- Piston mechanism according to claim 1, characterized in that the piston (1) comprises at its back side a cavity (17) onto which the passage (12) in the piston (1) gives, and in which the bearing (18) is situated. 3.- Piston mechanism according to claim 1 or 2, characterized in that it is destined for compressors and in that to the conduct (9) in the cylinder (2) a compressed air conduit (11) or a compressed air vessel 05 is connected, while the passage (12) in the piston (1) forms in inlet during the sucking in stroke and the piston ring (8) forms an inlet valve. 4.- Piston mechanism according to one of the preceding 10 claims, characterized in that the crank chamber (5) is provided with an inlet (21) in such way that the medium, which flows through the passage (12) through the piston (1), also flows over the crank chambei (5) and over the bearing (20) contained therein, by which the piston rod !5 (6) is connected to the crank shaft (4). 5.- piston mechanism according to one of the preceding claims, characterized in that the passage (12) through the piston (1) contains at least one opening (15) / 0 giving onto the back side of the piston (1) and at least one opening (16) extending between the groove (7) and the front side of the piston (1) and at least partially giving onto the groove (7) next to the piston ring (8), whereby these openings (15 and 16) are situated at a 5 distance of the outside of the piston (1) . 6.- Piston mechanism according to claim 5, characterized in that the passage (12) through the piston (1) contains an additional groove (13) over the circumference of the 0 piston (1) and a recess (14) which is formed by a smaller outside diameter of the piston (1) and connects groove (13) to the groove (7), while the opening (15) which gives onto the back side of the piston ( 1 ) , connects to this additional groove (13).

Inventors: TECK MARCEL, TECK, MARCEL
Applicants: ATLAS COPCO AIRPOWER NV, TECK MARCEL, ATLAS COPCO AIRPOWER, NAAMLOZE VENNOOTSCHAP., TECK, MARCEL
Application year: 1996
Main classification: F04B39
IPC codes: F04B39, F04B53