EP0333667A2

EP0333667A2 - Improvements in air compressors

Info

Publication number: EP0333667A2
Application number: EP89830054A
Authority: EP
Inventors: Gianfranco Prevosto (It); Giovanni Stantero (It)
Original assignee: CHINOOK SpA
Current assignee: CHINOOK SpA
Priority date: 1988-02-17
Filing date: 1989-02-14
Publication date: 1989-09-20
Also published as: EP0333667A3; IT8867122A0; IT1219027B

Abstract

The improvements concern essentially:
- the presence of a valve-plate (9) through which ventilation channels (16) pass,
- the use of a cooling fan (17) which is driven by the shaft (5) of the compressor and can induce a forced flow of air through the channels (1 6),
- the provision of a lubricating-oil filler duct (36) separate from the oil-vapour discharge duct (32 to 35) which passes through one of the bearings (32) of the shaft,
- the use of a generally tank-shaped lower portion of the casing (25),
- the use of pistons (3) with sealing rings (48) mounted on a head portion (42) which can easily be separated from the rest of the piston (40) so that the rings (48) can be replaced without the need completely to dismantle the piston (3) and the members (4, 5) associated therewith, and
- the provision of annular cavities (39) in the walls of the cylinders (3) which act as sumps for the collection and recovery of the lubricating oil.

Description

The present invention relates in general to air compressors and is particularly concerned with some improvements which are applied to a compressor in order to improve its operating characteristics, particularly as regards the cooling and lubricating functions, and also to simplify the assembly of the compressor and the periodic replacement of some parts (piston rings) which are subject to wear in use.
The characteristics which form the subject of the patent are indicated specifically in the claims which follow.
The invention will now be described, by way of non-limiting example, with reference to the appended drawings, in which;

Figure 1 is a median vertical section of a compressor according to the invention,
Figure 2 is a perspective view of one of the elements illustrated in Figure 1, and
Figure 3 is a view of the element illustrated in Figure 2, in the direction of the arrow III of Figure 2.

In the drawings, a piston air compressor, generally indicated 1, is intended to be used for producing compressed air in an industrial environment, or possibly for semi-professional amateur use.
The compressor 1 is composed essentially of a casing defining within it two cylinders 2 in which two pistons 3 are sealingly mounted for reciprocal sliding.
According to a widely known arrangement, the pistons 3 are connected by means of connecting rods 4 to the journals of a crankshaft 5 having an end 6 which projects from the casing of the compressor.
A pulley 7 is mounted on the end of the shaft and has two grooves situated remote from and near to the compressor 1 respectively. In use, a belt 8 passes around the outer groove and enables the pulley 7 (and the shaft 5 as a whole) to be rotated by an electric operating motor (not illustrated). The function of the inner groove will be described further below.
A plate 9 is provided in correspondence with the tops of the cylinders 2 and, also according to a widely known arrangement, two pairs of blade valves are mounted therein for regulating the passage of air to and from the cylinders 2 through two intake and delivery ducts 10, 11 in the head 12 of the casing.
More precisely (see also Figure 2), two intake valves 13 are provided which are mounted on the lower face of the plate 9 in corresponding recesses thereof and have the function of enabling the passage of air from the intake duct 10 to the cylinders 2 when the pistons 3 move - alternately - downwards as a result of the rotation of the shaft 5; two delivery valves 14 are provided on the upper face of the plate 9 for enabling the passage of air from the cylinders 2 to the delivery duct 11 when the pistons 3 move - alternately - upwards in a respective cylinders 2 as a result of the rotation of the shaft 5.
The passage of the air through the plate 9, controlled by the valves 13 and 14, takes place through respective holes, such as the holes indicated 15 in Figure 2 (in the case in question, these are the holes through which air is taken into the cylinders 2 under the control of the valves 13).
The plate 9 on which the valves 13 and 14 are mounted (usually by means of driven rivets of a relatively ductile material such as copper) is constituted by a pressure-cast aluminium part traversed by three longitudinal apertures 16 which extend through the entire length of the plate 9 (in the direction of alignment of the cylinders 2).
The apertures 16 are intended to convey a ventilating air flow in order to facilitate the cooling of the head part of the compressor.
The ventilating air flow is generated by a fan 17 mounted on a shaft or pin 18 and rotated by the pulley 7 by means of a belt 19 which passes around the inner groove of the pulley 7.
The fan 17 is mounted on the shaft 18 with the interposition of a bearing 20; more precisely, the shaft 18 is constituted by an S-shaped pin provided with an eccentric central portion 21 which is fixed to the casing of the compressor by the screwing of a threaded end portion 22 into a bush provided in the casing of the compressor 1.
The slackening of a nut 23 which clamps the threaded portion 22 against the casing of the compressor 1, the pin or shaft 18 being kept in a fixed position, allows the eccentric 21 to be pivoted. This causes an orbital movement of the shaft 18 (and of the fan 17 mounted thereon) about the axis of the threaded portion 22, enabling the belt 19 to be tensioned correctly. As well as passing through the apertures 16 which are aligned with the fan 17, the air flow generated by the fan 17 flows over the entire head part of the compressor casing. In addition to the valve plate 9 and the head 12 already described above, the latter also includes a central part 24 in which the cylinders 2 are defined and which is provided with horizontal cooling vanes 24a, and a generally tank-shaped lower portion (crankcase) 25.
The crankcase 25 is therefore closed in correspondence with its base wall and has a main opening which enables the insertion of the shaft 5 and its associated members during the assembly of the compressor and only opens upwards, that is, towards the overlying central part 24.
According to a solution which has found to be particularly advantageous during the assembly of the compressor, the lower part 25 of the casing is provided with a plurality of bosses 26 which project like pillars in the lower part 25 itself (usually six are provided - that is, at the four vertical corners of the part 25, which is generally parallelepipedal in shape, and centrally of its two longer sides). The bosses or pillars 26 are provided with internal sets of threads (only one of which, indicated 27, is visible in Figure 1) for the insertion of respective screws 28 (two of which are shown schematically in Figure 1). The screws 28 extend from the head 12 through the valve plate 9 (which is purposely provided with corresponding through-holes 29, shown in Figure 2) and through the central part 24 of the casing so as to be engaged in the threads 27 provided in the bosses 26 in the lower part 25 of the casing.
The front wall of the part 25, facing the pulley 7, also has a hole with a horizontal axis for the mounting
of a bearing 30 for supporting the shaft 5, with which oil seal members 31 are associated. Another hole with a horizontal axis is provided in a corresponding position on the rear wall of the lower part 25 of the casing and a further bearing 32 is mounted therein, usually by driving, for supporting the rear end of the shaft 5.
The hole in which the bearing 32 is mounted communicates with a lubricant (oil) drainage space or sump 33 provided at the top with a threaded hole 34 in which an oil drainage and collection plug 35 of the type described in European patent application EP-A-0 232 688 is mounted. A duct with a horizontal axis, indicated 36, extends through the upper part of the sump 33 and opens into the lower part 25 of the casing.
When the plug 35 is unscrewed from the hole 34, the duct 36 enables the lubricant to be fed into the lower part 25 of the casing, which serves as a crankcase.
The duct 36 is closed by the threaded shank of the plug 35 when the latter is screwed into hole 34. The lubricant fumes which are generated during the operation of the compressor are therefore discharged from the lower part 25 of the casing through the bearing 32 and the sump 33, until they reach the plug 35. The lubricant which collects in the plug 35 as a result of the trapping action of the latter can thus fall back into the compressor casing to ensure optimum lubrication of the bearing 32.
Finally, two screw plugs 25a and 25b are inserted in corresponding threaded holes provided in the part 25 beneath the aperture into which the bearing 32 is driven. The plug 25a is of transparent material and thus enables the level reached by the lubricant inside the part 25 to be checked. The plug 25b is mounted close to the base wall of the part 25 and - when it is removed - enables all the lubricant to be drained out.
Two lubricant drainage ducts, indicated 37, extend from the cylinders 2 to two corresponding drainage apertures provided at the upper end of the plug 35.
Each of the ducts 37 extends from an intake aperture 38 (only one of which is visible in Figure 1) provided in a respective annular groove 39 in the inner wall of the cylinder, centrally thereof.
The grooves 39 are formed in positions determined in dependence on the geometrical characteristics of the pistons 3. Each of these is constituted essentially by two elements, that is to say, a lower portion 40 connected to the upper end of the corresponding connecting rod 4 by a pin 41, and an upper portion 42 which is fixed to the lower portion 40 by means of a screw 43. The screw 43 extends generally axially of the piston 3 and is kept in position by a locking screw 44.
The lower portion 40 of each piston 3 is tapered at the top so as to form a bevelled shoulder 45 which converges towards the top of the respective cylinder 2.
The upper or head portion 42, however, is generally cylindrical in shape, with a lower axial appendage 46 which is coupled in the manner of a tenon to the narrower top part of the lower portion 40.
The lower end of the latter, which faces the connecting rod 4, has recesses in which respective oil scraper rings 47 are mounted.
Similar rings 48, usually made of polytetrafluoroethylene, are provided in the head portion 42.
The piston structure illustrated enables operation with oil-film lubrication in correspondence with the lower portions of the pistons 2 and operation virtually without lubrication in correspondence with the head portions. This solution minimises the contamination of the compressed air by the lubricating oil.
The fact that the sealing rings 48 are mounted on a head portion 42 which can be separated from the rest of the piston considerably simplifies the periodic replacement of the rings 48 which are subject to wear during the use of the compressor.
In fact, in order to replace the rings 48, it suffices to remove the head 12 and the valve plate 9, so as to make the top regions of the cylinders 2 accessible from the outside , and then to loosen the locking screws 44 and the screws 43 so that the head portions 42 of the pistons 3 can be removed from the cylinders 2.
Once the worn rings 48 have been replaced by new rings, the head portions 42 can be put back in the cylinders and fixed to the respective lower portions 40 by means of the screws 43 and the screws 44; the compressor can then be closed again by the fitting of the valve plate 9 and the head 12.
The rings 48 can thus be replaced without the need to remove the pistons completely from the cylinders, thus avoiding an operation which, in the majority of cases, would require the almost complete dismantling of the compressor 1.
The grooves 39, which are intended to act as traps for the collection and recovery of the lubricating oil 37, to prevent excessive migration of the lubricant towards the top parts of the cylinders 2, are formed so as to open into the annular space between the head portion 42 and the bevelled shoulder 45 of the lower portion 40 of the piston.
More precisely, the annular recesses 39 are formed so as to be slightly above the position reached by the lower end of the shoulder 45 when the piston 3 is in the top dead centre position.

Claims

1. An air compressor including at least one air compression and intake chamber (2) with an associated support (9) for valve means (13, 14) for regulating the intake (13) and delivery (14) of the air to and from the intake and compression chamber (2), characterised in that the support (9) has through-apertures (16) defining flow passages for cooling means.

2. An air compressor including a drive shaft (5) and a rotary pumping element (17) which can generate a flow of cooling means for the compressor (1), characterised in that kinematic coupling means (7, 19) are provided between the drive shaft (5) and the rotary pumping element (17) so that the rotary pumping element (17) is rotated by the drive shaft (5).

3. A compressor according to Claim 2, characterised in that the rotary pumping element is constituted by a fan (17).

4. An air compressor according to Claim 2 or Claim 3, characterised in that the kinematic coupling between the drive shaft (5) and the rotary pumping element (17) is achieved by means of a belt transmission (19), and in that the rotary pumping element (17) is mounted on the compressor (1) so that its mounting position is selectively adjustable (21 to 23) in order to tension the belt transmission (19).

5. An air compressor according to Claim 4, characterised in that the rotary pumping element (17) is mounted on a generally S-shaped pin with a central portion (21) which acts as an eccentric element for tensioning the belt transmission (19) as a result of the displacement of the rotary pumping element (17) relative to the drive shaft (5).

6. An air compressor according to Claim 1 and Claim 2, characterised in that the apertures (16) in the support (9) for the valve means (13, 14) define flow passages for the cooling means which are aligned with the direction of the flow generated by the rotary pumping element.

7. An air compressor including a drive shaft (5) mounted in a part (25) of the casing (1) which is intended to face downwards when the compressor (1) is in use, characterised in that the part (25) of the casing is generally tank-shaped.

8. An air compressor according to Claim 7, characterised in that the part (25) of the casing has a peripheral wall with a plurality of boss formations (26) defining respective screw seats (27) for assembling screws (28) which are intended to extend through the casing (12, 9, 24, 25) of the compressor (1).

9. An air compressor including a casing (12, 9, 24, 25) with at least one part (25) which is intended to house a drive shaft (5) of the compressor and to be filled with lubricant, characterised in that two separate ducts (36; 32, 33, 34, 35) are provided for filling the casing with lubricant and for discharging the lubricant fumes generated during the operation of the compressor, respectively.

10. An air compressor according to Claim 9, characterised in that it includes at least one bearing (32) which is mounted in an aperture in the part (25) of the casing to support the drive shaft (5), and in that the duct (32, 33, 34) for discharging the lubricant fumes extends at least partly through the bearing (32).

11. An air compressor including a casing (12, 9, 24, 25) defining at least one cylinder (2) in which at least one respective piston (3) is mounted for reciprocal movement, characterised in that the at least one piston is constituted by a first portion (42) which faces the top region (9) of the cylinder (2) and carries associated sealing elements (48) for sliding against the wall of the cylinder (2) and by a second portion (40), the first (42) and second (40) portions of the piston (3) being releasably interconnected (43, 44) so that the sealing elements (48) can be replaced by the removal of only the first portion (42) of the piston from the casing of the compressor (1).

12. An air compressor according to Claim 11, characterised in that the first (42) and second (40) portions of the piston are interconnected by screw means (43).

13. An air compressor according to Claim 12, characterised in that the screw means include at least one first screw (43) which extends to connect the first (42) and second (40) portions of the piston and a further screw member (44) which is intended to lock the first screw (43) in the clamping position.

14. An air compressor according to Claim 13, characterised in that the first (42) and second (40) portions of the piston (3) jointly define an annular space in the piston (3) which faces the inner surface of the cylinder (2).

15. An air compressor according to any one of Claims 11 to 14, characterised in that the at least one cylinder (2) has on its inner surface an annular recess (39) which can act as a sump for collecting the lubricant and has associated means (37) for conveying the oil collected in the sump to the casing (25) of the compressor.

16. An air compressor according to Claim 8 and Claim 15, characterised in that a plug (35) is associated with the lubricant-fume discharge duct (32, 33, 34) for collecting the fumes, and in that the conveying means (37) converge towards the plug (35).