US3047212A - Rotary air compressors - Google Patents

Description

July 31, 1962 c. H. BRISCOE 3,047,212

ROTARY AIR COMPRESSORS Filed March 24, 1958 INVENTOR GEORG-E H. Bm'scog United tates Patent 3,047,212 ROTARY AIR COMPRESSORS George Harold Briscoe, Beddington, Croydon, England,

ass'ignor to Lacy-Hulbert & Company Limited, Beddington, England Filed Mar. 24,1958, Ser. No. 723,158 Claims priority, application Great Britain Apr. 2, 1957 2 Claims. (Cl. 230-210) This invention concerns improvements in air (or gas) compressors and exhausters (hereinafter referred to as compressors) and is especially concerned with the so called dry-type of rotary compressor which employs vanes of special composition working in slots in a drum mounted eccentrically within the compressor casing, though it is also applicable to positive displacement rotary blowers or piston or diaphragm operated compressors.

Air compressors must be effectively cooled if their efficiency is to be maintained and this is particularly true of the dry rotary type. In this type of compressor or exhauster, for example, the vanes are made of material which is liable to lose its strength and form if it is subjected to a temperature above a critical range: the bearings also require efiicient cooling. 7

It has been found possible to cool the smaller sizes of dry rotary machines by fitting a fan to the rotor shaft which directs air over the compressor stator housing. On larger sizes of machines however it is found that the restriction in speed of revolution of the rotor necessitated by consideration of blade rubbing speed is such that no fan of reasonable dimensions fixed to the rotor shaft is capable of passing an appropriate amount of air and overheating necessarily takes place.

. It is the object of the present invention to provide an eilectively cooled air compressor without having recourse to liquid circulation or other expensive and complicated cooling systems.

According to the invention, from one aspect, we provide an air compressor whose rotor shaft or piston crankshaft derives its drive from a motor or prime mover which is arranged to drive a fan (whose outlet is directed over the surface of the compressor) at higher speed than that at which the rotor or piston crankshaft is driven.

The speed increase of the fan drive may be attained by the use of differential pulley sizes or by gearing.

From another aspect the invention provides a rotary vane air compressor having a driving pulley fixed to its rotor shaft and a further pulley mounted for free rotation and carrying a fan whose output is directed over the compressor, said further pulley being arranged to be driven at higher speed than the rotor shaft by the same motor or prime mover that drives that shaft.

The fan pulley is conveniently carried loosely upon the compressor rotor shaft.

In preferred forms of the invention the pulley carrying the fan is arranged to be driven in the same direction of rotation as is the rotor shaft, so that the speed of rotation of its bearing relative to the rotor shaft is reduced.

The fan employed is preferably of the radial-flow type as used for cooling electric motors, and a guide plate with a central air inlet eye is preferably fitted to direct the air flow from the fan over the compressor stator body, which may be formed with cooling fins.

The above and other parts of the invention are embodied in one preferred form of compressor or exhauster which will now be described in greater detail by way of example with reference to the accompanying drawing; which. is a central vertical section.

The compressor comprises a stator casing 1, which is deeply finned as at 2 on its outer surface 2 for cooling ECQ purposes and which is closed at both ends by cover plates 3 and 4 which incorporate bearing housings.

The drum 5 of the compressor is of a type known per se provided with a number of slots in which slide vanes 6 of a special composition as the drum turns eccentrically within the stator housing.

The driving shaft 7 of the drum extends through'the end plate 3 and is provided with a key-way 8 by which is fitted a first pulley 9 for drive by belts 16 and 17 from the pulley 18 of an electric motor 19.

The driving shaft 7, between the driving pulley 9 and the drum 5, carriesthe inner race of a ball-bearing 10 upon which is mounted a second driving pulley 11 of smaller diameter than that which drives the shaft. This second pulley 11 is free to rotate relative to the drum driving shaft and has bolted to it by bolts 12 a multibladed radial-flow fan 13.-

An air guide plate or cowl 14 having a central opening opposite the eye of the fan 13 is carried by brackets (not shown) from the stator 1 in a position to guide the air delivered from the fan outlet 15 axially of that stator.

The pulley 18 on the motor shaft is connected by a belt 20 to the fan driving pulley 11 and this motor pulley may be of the same size as that driving the drum 5 or larger if necessary in order to impart to the fan 13 a rotational speed considerably higher than that of the drum shaft 7.

In experiments carried out with proto-type machines of relatively large size it has been found, that, whereas a fan driven at drum speed is quite incapable of cooling the compressor stator effectively, the high speed fan of the invention is easily capable of maintaining an air flow such that operating temperature conditions are kept within safe limits.

It will be understood that the invention is not restricted to the details of the specific embodiment described which may be varied without departing from the scope of the following claims.

I claim:

1. The combination of an air compressor of the rotary vane type having a casing, fins on the outer surface of said casing, compression means within the casing, a continuous, integral rotary shaft extendin g within and outside of said casing for driving said compression means, a first drive means keyed to said shaft outside said casing, a second drivemeans freely mounted upon said shaft outside of said casing, a fan rotatably mounted on said shaft and directly connected to said second drive means to be driven thereby, said fan having blades arranged to blow cooling air over the finned outer surface of said compressor casing, said second drive means being arranged on the shaft between the casing and said first drive means and constructed to drive said fan at a higher speed than said first drive means drives said compression means.

2. The combination of an air compressor of the rotary van-e type having a casing, fins on the outer surface of said casing, vane compression means within the casing, a continuous, integral rotary shaft extending within and outside of said casing for driving the vane compression means, a first drive pulley keyed to said shaft outside said casing, a second pulley freely mounted upon said shaft outside said casing, and a fan rotatably mounted on said shaft and directly connected to said second pulley means the fan will be driven at higher speed than the compressor.

References Cited in the file of this patent UNITED STATES PATENTS Higham July 9, 1946 Jones Apr. 18, 1950 Willcox Nov. 29, 1955 Hockel Mar. 10, 1959 Scheiterlein Dec. 15, 1959 FOREIGN PATENTS Germany May 19, 1930 Great Britain Apr. 16, 1948

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