US3395855A

US3395855A - Air compressor system employing recirculating means

Info

Publication number: US3395855A
Application number: US592665A
Authority: US
Inventors: Richard B Clark
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1966-11-07
Filing date: 1966-11-07
Publication date: 1968-08-06
Anticipated expiration: 1985-08-06

Description

R. B. CLARK Aug. 6, 1968 AIR COMPRESSOR SYSTEM EMPLOYING RECIRCULATING MEANS Filed Nov. 7, 1966 mm *m I \N.@ @m {Esra Q INVENTOR. RICHARD B. CLARK ited States ABSTRACT OF THE DKSCLOSURE An air compressor system having an engine driven compressor for supplying a receiver, the engine normally operating at idling speeds and accelerating to compressing speeds in response to external demand for air from the receiver. A bypass between the compressor outlet and inlet to permit the free passage of air from the compressor when the engine is idling and substantially eliminating pressure against which the compressor operates so that engine response to external air demands is increased. Means for transferring lubricant from either the receiver or bypass so that lubricant is continuously supplied to the compressor lubricant pump and the receiver remains isolated from the bypass.

The present invention relates to air compressor systems and more particularly to means for reducing the load on the compressor during prime mover acceleration in response to air output demands.

Air compressor systems normally comprise a prime mover driving an air compressor and a receiver from which compressed air is supplied to air driven equipment. Turbocharged engines are commonly employed as the prime mover in industrial air compressor systems to provide increased power within a compact compressor system. A turbocharger is driven by the engine exhaust and in turn supplies intake air to the engine. When air is not being drawn from the receiver, it is desirable to permit the prime mover to operate at idling speed to conserve fuel and to minimize engine wear. When the system is called upon for output air, the engine must be rapidly accelerated to maintain the receiver air pressure at a satisfactory level to meet output demands. However, the reduced air supply to the engine, caused by the turbocharger operating at idling speed along With the engine, and the compressor load on the engine result in a turbocharger lag which limits rapidity of engine response to the compressor system load demands. To decrease the compressor load on the engine and thereby alleviate the above problem, prior art devices valve off the compressor air inlet and provide means for preventing compressed air in the receiver from returning to the compressor. The mass of air entering the compressor is thereby decreased or halted. But, in this arrangement, the compressor outlet up to the receiver is a closed volume containing compressed air from the compressor. Thus, the load on the compressor is still substantial due to the pumping of the compressor, even at idling speeds, against a pressure head in the compressor outlet. The compressor load due to the abovenoted pressure head acts on the engine tending to restrict engine acceleration response to external air demands.

It is accordingly an object of the present invention to provide means, in an air compressor system, forsubstantially eliminating the above-noted pressure head at the compressor outlet, particularly during prime mover acceleration in response to external air demands placed upon the system and thereby improve, i.e., decrease the period of, engine acceleration response.

It is another object of the invention to provide apparatus which permits air from the compressor outlet to bypass the receiver and be recirculated into the closable compressor inlet while the prime mover is operating at idling and accelerating speeds.

It is still another object to provide apparatus adaptable to a turbocharged air compressor system which provides a bypass for compressor outlet air around the receiver into the closable compressor inlet when the turbocharged engine is operating at idling and accelerating speeds and which provides for continuous return of lubricating oil to the compressor.

Further and more specific objects and advantages of the invention are made apparent in the following specification wherein a preferred form of the invention is described by reference to the accompanying drawing which is a schematic illustration of an air compressor system, means for bypassing compressed air from the compressor outlet around the receiver and means for maintaining continu ous return of lubricating oil, entrained in compressed air exiting the compressor outlet, to the compressor.

Referring now to the drawing, an air compressor system 10 comprises a prime mover 11 having an air inlet manifold 12 and connected by suitable gearing (not shown) to an air compressor 13. Compressor 13 has an air inlet 14 and a compressed air outlet port 16. A receiver 17 is hermetically communicated with compressor outlet port 16 by pipe 18 and is suitable for containing compressed air under high pressure. A check valve 19 is preferably disposed across pipe 18 to prevent reverse flow of air from receiver 17 to compressor 13. Receiver outlet tube 21 hermetically connects receiver 17 with any suitable external air driven equipment (not shown). Generally, air flow 20 is selectively drawn from outlet 21 by controls on said air driven equipment. Compressor 13 is contemplated to be of a type requiring continuous internal lubrication upon the surfaces of the compressor elements (not shown). Oil present in the compressor interior as a lubricant and coolant is at least partly carried away in the compressed air exiting compressor 13. Receiver 17 is adapted to collect lubricating oil from the compressed air therein. The collected oil is returned to compressor oil pump 22, for example, by flowing through receiver oil return line 23 and continuously supplied to compressor 13 by means of pump 22. The arrangement and interconnection of the above compressor system components is contemplated as in accord with well known prior art practice.

To obtain maximum compressing power within a compact air compressor system, prime mover 11 is preferably a turbocharged engine wherein air is forced into engine inlet manifold 12 at a rate generally proportional to the speed of engine 11. It is desirable to regulate the speed of engine 11, e.g. by means of engine governor 24, and thereby permit engine 11 to idle when air is not being drawn from the compressor system. However, it is neces sary to rapidly accelerate engine 11 when compressed air is withdrawn from the system since the capacity of receiver 17 is limited and substantially constant pressure is usually necessary in outlet 21 to assure proper operation of the air driven equipment. Speed control means to regulate the speed of engine 11 in response to external air demands may comprise a pressure sensor to sense pressure variations in receiver 17 and pressure actuated control means to operate governor 24 in response to sensed pressure variations in receiver 17. However, to provide acceleration of engine 11 as soon as possible after air withdrawal is commenced, the speed control means preferably comprises air fiow sensor means 26, e.g. a venturi tube, having a low pressure sidearm 27, disposed within the channel of outlet 21 as a portion thereof. Pressureactuated, spring-loaded governor control means 28 hermetically communicates with venturi sidearm 27 and is further connected to operate engine governor 24 in response to pressure variations in venturi sidearm 27. When there is no air flow 20 from receiver outlet 21, air pressure in receiver 17 reaches a desired operating level and is communicated to governor control means 28 by venturi sidearm 27. Governor 24 and governor control means 28 are connected such that governor 24 then regulates engine 11 to operate at idling speed. When compressed air is demanded from receiver outlet 21, the air flow through venturi 26 partially evacuates venturi sidearm 27. Springloaded governor control means 23 reacts to the partial evacuation of sidearm 27 by operating governor 24 such that engine 11 operates at compressing speed. The preferred engine speed control means described briefly above and the compressor inlet valve control means described immediately below are more fully described in apiplicants copending patent application, Ser. No. 582,949 for Air Compressor Control System Responsive to Air Flow, filed Sept. 29, 1966.

To regulate the mass of air 29 entering compressor 13 through compressor inlet 14, movable valve means 31 is preferably disposed across compressor inlet passage 14 to be varied between open and closed relation thereto. A valve control means 32 is adapted to operate valve 31 in response to speed variations of engine 11 and thereby prevent or minimize compressor 13 loading upon engine 11. Preferably, valve control means 32 is of a spring-loaded, pressure-actuated type similar to governor control means 28 above. Valve control means 32 communicates with the interior of engine inlet manifold 12 by conduit 33 to permit air pressure, generally equivalent to that in engine inlet manifold 12, to act upon valve control means 32. Control means 32 is linked with valve 31 such that it operates valve 31 between open and closed position relative to compressor inlet 14 in response to pressure variations in engine inlet manifold 12. When the pressure in engine inlet manifold 12, communicated to pressure-actuated valve control means 32 by conduit 33, is high, due to engine 11 operating at compressing speed, valve 31 is operated to open position with respect to compressor inlet 14. As engine 11 is regulated to idling speed, the pressure in manifold 12 and conduit 33 decreases accordingly and valve control means 32 responds by operating valve 31 to close compressor inlet 14. Thus, valve 31 closes olf the air supply to compressor 13 and reduces compressor 13 loading on engine 11 while operating at idling speed and accelerating to compressing speed.

However, air flow 34 from compressor outlet 16 into pipe 18 is still at a constant head of pressure due to the desired operating pressure in receiver 17. The reaction of compressor 13 to this constant outlet pressure head exerts continued loading on engine 11 during the critical acceleration period. To reduce or eliminate the above noted outlet pressure head and the resulting compressor loading on engine 11 during idling and acceleration, bypass means 36 is disposed in communication with compressor outlet 16. Bypass means 36 is intended to permit air flow from compressor outlet 16 to be freely circulated to inlet 14. In its simplest form, bypass means 36 could comprise merely a port to the atmosphere to thereby provide free circulation of air from compressor outlet 16 to open compressor inlet 14. However, to control the amount of air circulating through the compressor during idling and acceleration of engine 11 and to prevent loss of lubricating oil, in the compressor air output, from the compressor system, bypass means 36 is preferably a conduit having a first end in communication with compressor outlet 16 by means of pipe 18 and a second end in communication with compressor 13 by means of inlet 14 even when valve 31 is closed. To control air fiow from compressor outlet 16 into bypass conduit 30, bypass valve means 37 is disposed in conduit 30 and is operable between a first or open position and a second or closed position.

A bypass valve control means 38 is disposed in communication with said air compressor system to sense variations in engine speed and operate bypass valve 37 in response thereto. Preferably, valve means 37 is an electrically operated, solenoid valve which, when electrically deactivated, permits air how 34 from compressor outlet 16 to bypass receiver 17 and flow through bypass conduit 30 to compressor inlet 14. When electrically activated, solenoid valve 37 closes off bypass conduit 30 and causes air flow 34 from compressor outlet 16 to be directed only toward receiver 17. Bypass valve control means 38 preferably comprises a pressure-controlled switch 39 having an on and off position controlled by elongated member 41 protruding therefrom into a pressure housing 42. Switch 3 9 is connected by electrical conductor 43 to operate solenoid valve 37. Flexible diaphragm 44 is dis posed hermetically across housing 42. An end of member 41 of switch 39 is normally joined to the center of diaphragm 44. Spring 46 is based adjacent switch 39 and acts under compression against diaphragm 44. Tube 47 communicates the interior of engine inlet manifold 12 with the interior of pressure housing 42 on the distal side of diaphragm 44 from member 41. Tube 47 thus acts as a pressure sensing leg for switch 39. When engine 11 is operating at desired compressing speed, increased air pressure in engine inlet manifold 12 is communicated to housing 42 by tube 47. This increased pressure acts against diaphragm 44 overcoming the compression strength of spring 46, moving member 41 toward switch 39, operating switch 39 to the on position and activating solenoid valve 37. When engine 11 returns to idling speed, the pressure in manifold 12 and acting against diaphragm 44 decreases. Spring 46 acts against diaphragm 44, moving member 41 into housing 42, operating switch 39 to the off position and deactivating solenoid valve 37.

Engine 11 may be operating at idling speeds for considerable periods of time according to external air requirements. During operation at idling speeds, it is still necessary to recirculate an adequate amount of lubricating oil to compressor 13 by means of oil pump 22. Since oil laden air fiow 34 from compressor outlet 16 is circulating through bypass conduit 30 at idling speeds, oil collecting means 48 is disposed within conduit 30. Oil collecting means 48 may be, e.g. a sump wherein oil carried by air flow therethrough tends to collect. To return oil from bypass sump 48 to oil pump 22, bypass sump oil return means 49 is disposed to permit recirculation of collected oil in sump 48 to oil pump 22, for example 'by gravity flow. It is necessary to maintain oil return means 49 in noncommunicating relation with receiver 17 at least during operation of engine 11 at idling or accelerating speed. Otherwise, the desired operating pressure maintained in receiver 17 could escape or at least be dissipated into compressor 13. To maintain this noncommunicating relation, sump oil return means 49 could be a separate line communicating with oil pump 22 or even a second compressor oil pump. However, sump oil return means 49 is preferably a line having a first end 51 communicating with sump 48 to receive collected oil therefrom. A second end 52 communicates with receiver oil return line 23 by means of T-junction 53. To permit continued oil recirculation and maintain isolation of receiver 17, T junction 53 preferably comprises an enclosed cylindrical chamber 54. End 52 of sump oil return line 49 communicates with port 56 adjacent a first end 68 of chamber 54 and receiver oil return line 23 with port 57 adjacent the distal end 69 of chamber 54. Line 58 has a first end 59 communicating generally with the linear center of chamber 54 and a second end 61 communicating with oil pump 22. A spring-loaded plunger 62, projecting from a solenoid valve 63 slidably and hermetically penetrates chamber 54 along the axis of cylindrical chamber 54. Plunger 62 has first and second lands 64 and 65, respectively, along its length within chamber 54. Lands 64 and 65 mate with the interior surface of chamber 54 and are disposed such that, when plunger 62 is fully extended into chamber 54, land 64 closes port 57. Land 65 is then positioned past port 56 in chamber end 68 such that oil from bypass sump 48 may flow through line 49, port 56 and chamber 54 into oil pump line 58. When plunger 62 is retracted, land 65 aligns with and closes port 56. Land-64 is then positioned past port 57 toward chamber end 69 such that oil from receiver 17 may flow through line 23, port 57 and chamber 54 into oil pump line 58. Electrically activated solenoid valve 63 is disposed such that when it is deactivated, spring 66 acts in compression against plunger 62 to move plunger land 64 into closing relation with port 57 and land 65 out of alignment with port 56. When solenoid valve 63 is activated, it retracts plunger 62 from chamber 54 and moves plunger land 65 into closing relation with port 56 andland 64 out of alignment with port 57. Electrical conductor 67 connects solenoid valve 63 with pressure-operated switch 39 such that when switch 39 is operated to the on position, valve 63 is activated. When switch 39 is off, valve 63 is deactivated.

In operation, governor control means 28 senses air flow through receiver outlet 21 when air is demanded from receiver 17. Control means 28 then operates governor 24 to regulate engine 11 at its desired compressing speed. When turbocharged engine 11 is operating at compressing speed, air pressure in engine inlet manifold 12 increases and acts against spring-loaded valve control means 32. Valve control means 32 operates valve 31 into open position relative to compressor inlet 14. The increased pressure in inlet manifold 12 also acts against diaphragm 44 and spring-loaded switch member 41 by means of line 47 to operate switch 39 to the on position. Solenoid valves 37 and 63 are thereby activated. Valve 37 accordingly closes otf bypass conduit 30 such that air flow 34 from compressor outlet 16 is direced only toward receiver 17. Valve 63, being activated, closes off port 56 by means of plunger land 65 and accordingly closes oif bypass sump 48 from T-junction chamber 54. Oil from receiver 17 is permitted to flow through line 23, chamber 54 and line 58 to compressor oil pump 22.

When air withdrawal from outlet 21 is terminated, compressor 13 output air 34 collects in receiver 17 until desired operating pressure therein is reached. This pressure is communicated to governor control means 28 which, in response thereto, causes governor 24 to regulate engine 11 to its idling speed. With engine 11 operating at idling speed, decreased pressure in engine inlet 12 is communicated to spring-loaded valve control means 32 which then closes valve 31 across compressor inlet 14. Decreased pressure in engine inlet manifold 12 is also communicated to switch diaphragm 44 permitting spring 46 to act on switch member 41 and operate switch 39 to the off position. Valves 37 and 63 are thereby deactivated. Deactivation of valve 37 permits air flow 34 from compressor outlet 16 to enter bypass conduit 30 and be recirculated to compressor 13 by means of closed compressor inlet 14.

Valve 63, being deactivated, closes off port 57 and receiver 17 from chamber 54. Oil from bypass sump 48 is permitted to flow through line 49, chamber 54 and line 58 to compressor oil pump 22. The compression system continues to operate in this mode until a new demand for compressed air is placed on receiver 17 by means of outlet 21 and engine 11 again reaches compressing speed. Thus, during idling and acceleration of engine 11, air flow from compressor outlet 16 freely circulates through bypass 30 back to compressor 13 by means of closed compressor inlet 14. The resistance of air on compressor 13 and the resultant compressor load on engine 11 are greatly minimized if not substantially eliminated during the critical acceleration period of engine 11. Furthermore, by providing oil return means from bypass sump to oil pump 22, in isolation from receiver 17, extended operation of the compressor system at idling speeds is permitted without a compressor lubrication failure. Thus, the preferred embodiment of the present invention provides a simple yet novel air compressor system in which the compressor load on engine 11, due to compressor air interacting with compressor 13, is greatly reduced or substantially eliminated. The ability of engine 11 to rapidly accelerate in response to external air demands is thereby greatly enhanced.

Although the invention has been described above with particular reference to a single preferred embodiment, the scope of the invention is not limited thereto. For example, bypass 30, bypass sump 48, T-junction 53, valves 37 and 63, switch 39 and the accessory components related thereto are particularly described with reference to a compressor system having a turbocharged engine. These components may also be employed in other compressor systems, e.g. those employing standard combustion engines as prime movers, to minimize wear on the engine during acceleration or to merely permit more rapid acceleration. As a further example, the invention is described with the immediately above-noted components as integral parts of an air compressor system. However, the invention also contemplates use of those noted components for incorporation with existing air compressor systems.

What is claimed is:

1. An air compressor system comprising a compressor having an air inlet and an air outlet for delivering air under pressure,

a prime mover coupled to the compressor and effective to drive the compressor at idling and compressing speeds,

a receiver in communication with the compressor outlet to receive and store air under pressure from the compressor outlet and deliver air under pressure in response to external demands, the system responding to delivery of air from the receiver by accelerating to compressing speeds,

bypass means in communication with the compressor outlet, the bypass means operable to freely receive air from the compressor outlet and substantially eliminate pressure against which the compressor operates, and

control means associated with the bypass means and the prime mover, the control means responsive to operation of the prime mover at idling speeds to operate the bypass means so that compressor loading on the prime mover is materially reduced during acceleration of the system toward compressing speeds and critical prime mover response to the external air demands is increased, the control means further responsive to approach of the prime mover toward compressing speeds to cause closing of the bypass means so that air from the compressor outlet is then directed toward the receiver.

2. The system of claim 1 wherein the bypass means comprise a conduit communicating the compressor output with the compressor input and the control means comprise a valve in said conduit for selectively blocking air flow through said conduit means with means for simutlaneously closing the compressor inlet to form a substantially closed circuit through the compressor and bypass and additional means to assure a constant return of lubricant to the cornpressor from its outlet air through a suitable lubricant pump.

3. In an air compressor system including an internal combustion engine operable at idling and compressing speeds to drive an air compressor for supplying compressed air to a receiver from which air is drawn, the engine having an air inlet manifold, comprising means associated with the compressor and operable for bypassing compressor output around the receiver, and

control means associated with the bypass means and the engine, the control means responsive to pressure in the engine intake manifold when the engine is operating at idling speeds to cause operation of the bypass means so that the engine operates under favorable load conditions.

4. In an air compressor system the combination comprising:

an internal combustion engine having an intake manifold and having an idling speed and a compressing speed;

turbo-charger means operatively associated with said engine for supplying compressed air to the intake manifold thereof and driven by the exhaust gas of said engine;

compressor means in driving connection with said engine and operable to deliver compressed air at its output;

receiver means communicating with the output of said compressor and storing compressed air therefrom for use by air driven devices; and

bypass means between said compressor and said receiver, said bypass means being operatively associated with said engine and responsive to pressure in the engine intake manifold below a preselected pressure to establish a low pressure bypass for the output of said compressor.

5. In :an air compressor system responsive to external air demands, the combination comprising:

a variable speed turbo-charged engine capable of selective operation at compressing and idling speed, said engine accelerating from idling speed to compressing speed in response to said external air demands and having an inlet manifold wherein air pressure is generally proportional to the variable speed of the engine;

a compressor coupled to be driven by said prime mover and having a compressed air outlet for compressed air output an air inlet and an oil pump to recirculate lubricating oil to the compressor;

a receiver disposed to receive and store compressed air from said compressor outlet, said receiver adapted to prevent flow of compressed air from said receiver to said compressor at least when said prime mover is operating at idling speed and having means for collecting oil from the compressed air and recycling the oil to the pump;

a conduit communicating with said compressor outlet and said compressor inlet and permitting compressed air from said compressor outlet to bypass said receiver and be substantially freely recirculated to said compressor inlet;

valve means disposed in relation to said bypass means to control air flow from said compressor outlet through said bypass means, said bypass valve means operable between open :and closed position with relation to said bypass means;

bypass valve control means communicating with said air compressor system to sense variations in said prime mover speed and operate said bypass valve means in response to said speed variations;

means disposed in said conduit to collect oil from compressed air passing through said conduit; and

means communicating with said conduit oil collecting means and said oil pump to recirculate oil from said collecting means to said oil pump, said conduit oil recirculating means in noncommunicating relation; with said receiver at least when said engine is operating at idling and accelerating speeds; and further wherein said sensor means comprises a pressure sensor communicating with said engine inlet manifold and sensing pressure variations therein.

6. In a turbo-charged air compressor, system for supplying compressed air on demand for external requirements, the combination comprising;

a variable speed turbo-charged engine having means for selectively operating said engine at compressing speed and idling speed according to compressed air demand, said engine having an air inlet manifold wherein air pressure varies generally proportionally to said engine speed;

a compressor coupled to be driven by said engine and having a compressed air outlet for compressed air output, an air inlet adapted to be closed when said engine is operating at idling speed and an oil pump disposed to recirculate lubricating oil into said compressor;

a receiver disposed to receive and store compressed air from said compressor outlet, said receiver adapted to prevent flow of compressed air from said receiver to said compressor when said engine is operating at idling speed, said receiver adapted to collect oil from said compressed air therein and having an oil return line to recirculate said collected oil to said oil pump;

a compressor bypass conduit having a first end communicating with said compressor outlet to receive air flow therefrom and a second end communicating with said closable compressor inlet, said conduit having means to collect oil from compressed air therein and an oil return line having a first end communicating with said conduit oil collection means and a second end entering said receiver oil return line by means of a T-junction;

a solenoid valve disposed in said T-junction and electrically operable between a first position permitting only oil from said receiver oil collection means to return to said oil pump and a second position permitting only oil from said conduit oil collection means to return to said oil pump;

a conduit solenoid valve disposed in said first conduit end and electrically operable between a first position preventing compressed air from said compressor outlet from entering said bypas conduit and a second position permitting air flow from said compressor outlet into said bypass conduit;

a pressure controlled switch communicating with said engine inlet manifold to sense air pressure variations therein and electrically connected to said conduit and T-junction solenoid valves, said switch operating said valves to said first positions upon sensing said manifold pressure generally proportional to said engine compressing speed and operating said valves to said second positions upon sensing said manifold pressure generally proportional to said engine idling speed.

7. Control apparatus adaptable to .a turbocharged air compressor having a variable speed turbocharged engine selectively operable at compressing speed and idling speed, an engine air inlet manifold wherein air pressure varies genenally proportionally to said engine speed, a compressor coupled to be driven by said engine, a compressor air outlet, a compressor air inlet which is closed when said engine is operating at idling speed, a compressor oil pump disposed to recirculate lubricating oil into said compressor, a receiver disposed to receive and store compressed air from said compressor outlet, means in said receiver preventing fiow of compressed air from said receive-r to said compressor outlet, means in said receiver to collect oil from compressed air therein, an oil return line to return oil from said receiver oil collection means to said oil pump, the combination comprising:

a compressor bypass conduit disposable to have a first end in communication with said compressor outlet to receive compressed air therefrom and a second end in communication with said closable compressor inlet;

a conduit valve disposable in said first conduit end and electrically operable between a first position to prevent passage of compressed air from said compressor outlet into said bypass conduit and a second position permitting air flow from said compressor outlet into said bypass conduit;

21 valve disposable in said T-junction and electrically operable between a first position permitting only oil from said receiver oil collection means to be recirculated to said oil pump and a second position permitting only oil from said conduit oil collection means to be recirculated to said oil pump;

a pressure controlled switch having a pressure sensing leg, said pressure sensing leg disposable to communicate with said engine inlet manifold and sense air pressure variations therein, said switch electrically connectable to said conduit and T-junction valves to operate said valves to said first positions in response to sensed manifold pressure generally proportional to said engine compressing speed and to operate said valves to said second positions in response to sensed manifold pressure generally proportional to said engine idling speed.

References Cited UNITED STATES PATENTS 2,164,451 7/1939 Fast 230-22 X 10 Caris et a1 23022 X Dodson 23()22 X Lawle-r 230-22 X Simpson 23056 Cox et a1. 23056 X Andersson et al. 23022 X Kitchen 230-22 X 10 FRED C. MATTERN, JR., Primary Examiner.

W. J. KRAUSS, Assistant Examiner.