A compressor unit for the production of compressed air for industrial uses

Abstract

 A compressor unit for the production of compressed air for industrial uses, being driven by an electric motor (3), wherein an engagement/disengagement means (38) is interposed between the compressor (2) and the motor (3) which is controlled from an adjustable pressostat (35) to connect and disconnect the motor (3) with/from the compressor (2) on reaching predetermined pressure levels, thereby providing a high frequency of compressor stop/start cycles and optimizing, as by minimization thereof, the amount of energy drawn as a function of the demand for compressed air from the user network (33).

Description

[0001] This invention relates to a compressor unit for the production of compressed air for industrial uses.

[0002] More particularly, the invention relates to a compressor unit which comprises a rotary compressor consisting of a cylindrical rotor with vanes caused to rotate by an electric motor eccentrically within a cylindrical casing, said compressor including a sump with a lower portion adapted to be filled with oil and an upper portion adapted to be filled with compressed air, a pressure tank outside said compressor, an air intake opening for supplying air to said compressor, valve means located in said air intake opening and just comprising a non-return valve, an air outlet opening in the upper portion of said sump, with valve means just including a minimum-pressure valve, circuit means connecting said upper portion of the sump to said pressure tank for supplying compressed air to said pressure tank, circuit means connecting said lower portion of the sump to said cylindrical casing for supplying oil to said rotor, and an adjustable pressostat connected to the upper portion of said sump.

[0003] An air compressor of the kind specified above is disclosed by European Patent Application No. 85830171, and has an advantage in that it can be stopped suddenly and then re-started on command from the adjustable pressostat with no risk of breakage of the rotor vanes and eliminates the conventional procedures for draining the oil out of the rotor casing prior to stopping the rotor.

[0004] In accordance with the provisions made in the compressor unit of European Patent Application No. 85830171 mentioned above, the compressor is stopped and started again by switching off and on the electric power supply to the drive motor for the compressor.

[0005] That operating procedure, while being apparently a convenient one from the energy balance point of view because no electric power would be consumed while the motor is not to drive the compressor, still is less than fully satisfactory from an engineering standpoint, and on account of the problems which it brings about, affects the overall performance of the compressor unit adversely.

[0006] The compressor type with which this invention is concerned will effectively optimize, as by minimizing it, the amount of energy drawn as a function of the demand for compressed air, and this by way of high-frequency stop and start cycles, wherein the frequency may be as high as a command every 20 to 30 seconds.

[0007] However, switching the electric motor off and on to stop and re-start the compressor would require, due to transient electrical and mechanical phenomena, a far lower command frequency, with attendant limitations on full exploitation of the potential which is typical of the compressor unit under consideration here.

[0008] It is, therefore, the object of this invention to solve the problem from the large number of stop/start cycles required to afford full utilization of the capabilities of a compressor of the type specified above.

[0009] The problem is solved by a compressor as indicated being characterized as set forth in Claim 1.

[0010] The invention will be now described in detail with reference to a practical embodiment thereof, as illustrated in the accompanying drawings, where:

Figure 1 is a schematic layout view of a compressor unit according to this invention; and

Figure 2 is a sectional view of the compressor rotor, taken along the line II-II in Figure 1.

[0011] With reference to the drawing views, it may be noticed that, accommodated on a common base 1 are the compressor unit, generally indicated at 2, and its electric drive motor 3. The motor shaft 4 is connected axially to the shaft 5 of the rotor 6 (Figure 2) which is mounted to rotate eccentrically within the cylindrical casing 7 of the compressor, in a manner known per se.

[0012] The rotor 6, which is supported on bearings schematically shown at 8 and 9, has radial vanes 10 which form, in a known manner, variable volume chambers within the cavity 11 of the casing 7.

[0013] That cavity 11 is connected to a suction duct 12 which is communicated externally with a suction intake opening 13.

[0014] The intake opening 13 accommodates a non-return valve, generally denoted by 14.

[0015] That same cavity 11 of the casing 7 is communicated, at a downstream location in the compressive portion, with a delivery duct 15 which opens into a sump 16, of which the lower portion 17 is filled with oil whilst the upper portion 18 is adapted to be filled with compressed air.

[0016] Through an outlet 19, the lower portion 17 of the sump is communicated with a lubricating system, denoted by 20, operative to supply oil, through a filter 21 and a cooler 22, to the bearings 8 and 9 as well as to a plurality of lubrication ducts, not shown, provided within the casing 7.

[0017] The upper portion 18 of the sump 16 is connected, through an opening 23, to a chamber 24 defined by a tubular oil-drip wall 25. Mounted inside the chamber 24 is a cartridge filter 26 the internal cavity 27 whereof is connected to the compressed air outlet duct 28 leading to the pressure tank 29 through a circuit arrangement shown schematically at 30. The latter also includes an additional heat-exchange cooler 31 and a strainer 32 for separating any residual oil.

[0018] The circuit ducting, schematically shown at 33 and leading out from the pressure tank 29, is to deliver the compressed air to the user network.

[0019] The outlet duct 28 is just equipped with a minimum-pressure valve shown schematically at 34.

[0020] The compressor unit further comprises an adjustable pressostat, shown schematically at 35, which is connected to the upper portion 18 of the sump 16 by the duct 36.

[0021] That adjustable pressostat 35 controls, through a circuit shown at 37, the compressor operation on predetermined pressure levels being reached in the upper portion 18 of the sump 16.

[0022] With particular reference to Figure 1, it may be noticed that the electric motor 3 is connected to the rotor 6 of the compressor by an engagement/disengagement means, generally denoted by 38, and an alignment coupling, known per se and generally indicated at 39.

[0023] The engagement/disengagement means 38 is composed of a driving member 40 fast with the motor shaft 4 and a driven member 41 which is shiftable axially on the rotor shaft 5 by way of a conventional splined fit, between a position of face engagement with the driving member 40 and a disengaged position (position shown in Figure 1). Both members 40 and 41 have juxtaposed surfaces faced with friction material, as respectively denoted by 40a and 41a.

[0024] The axial displacement of the driven member 41 toward the driving member 40, and locking thereof in the engaged position, is accomplished through the magnetic action applied by an electromagnetic device schematically represented by coils 42 jutting out from the motor 3. The energization of coils 42 is controlled by the pressostat 35 through the circuit shown schematically at 37.

[0025] The reverse movement, resulting in the driven member 41 being released from the driving member 40, is provided by the elastic force applied by a leaf spring 43 which reacts on a shoulder 44 formed on one end 45 of the rotor shaft 5, upon the electromagnetic device 42 being de-energized by the pressostat 35.

[0026] In accordance with the invention, with the electric motor 3 kept rotating at all times and entraining the driving member 40 of the engagement/disengagement means 38 therealong, the compressor unit is controlled by engaging and disengaging the movable driven member 41 for a prompt response permitting high frequencies of compressor stop/start cycles.

[0027] Maximum exploitation of the compressor capabilities can thus be achieved.

Claims

1. A compressor unit for the production of compressed air, comprising a rotary compressor consisting of a cylindrical rotor with vanes caused to rotate by an electric motor eccentrically within a cylindrical casing, said compressor including a sump with a lower portion adapted to be filled with oil and an upper portion adapted to be filled with compressed air, a pressure tank outside said compressor, an air intake opening for supplying air to said compressor, valve means located in said air intake opening and just comprising a non-return valve, and air outlet opening in the upper portion of said sump, with valve means just including a minimum-pressure valve, circuit means connecting said upper portion of the sump to said pressure tank for supplying compressed air to said pressure tank, circuit means connecting said lower portion of the sump to said cylindrical casing for supplying oil to said rotor, and an adjustable pressostat connected to the upper portion of said sump, characterized in that it comprises an engagement/disengagement means (38) located between said electric motor (3) and the cylindrical rotor (6) of said rotary compressor, said engagement/disengagement means (38) being operated from said adjustable pressostat (35) to drivingly connect and disconnect the electric motor (3) with/from the compressor (6) on predetermined pressure levels being reached.

2. A compressor unit according to Claim 1, characterized in that said engagement/disengagement means (38) comprises a driving member (40) attached to the shaft (4) of the electric motor (3) and a driven member (41) mounted on the shaft (5) of the compressor rotor (6) and being shiftable axially on said shaft.

3. A compressor unit according to Claims 1 and 2, characterized in that the juxtaposed surfaces of said driving (40) and driven (41) members of the engagement/disengagement means (38) are faced with friction material (41a,40a).

4. A compressor unit according to Claims 1 to 3, characterized in that said driven member (41) is mounted on the compressor shaft (5) by way of an axial splined fit.

5. A compressor unit according to Claims 1 to 4, characterized in that said driven member (41) is shiftable axially on the compressor shaft in the engaging direction with the driving member (40) by the magnetic action applied by an electromagnetic device (42).

6. A compressor unit according to Claims 1 to 5, characterized in that said driven member (41) is shiftable axially on the compressor shaft in the disengage direction by the elastic reaction of a spring (43) which has been biased during the movement in the engage direction and abuts against a shoulder (44) on the end (45) of the compressor shaft (5).