AIR DRYER PURGE CONTROL FOR TURBOCHARGED COMPRESSORS

Abstract: A compressed air system (10) includes an air compressor (12) the inlet of which is communicated to the vehicle engine turbocharger. The outlet of the air compressor is communicated through an air dryer (22) to a storage reservoir (26). A governor (28) is responsive to the pressure level in the reservoir (26) to generate an unloading signal unloading the air compressor (12) when the pressure in the reservoir (26) attains a predetermined value. The unload­ ing signal is also communicated through a control valve (34, 38) to purge the air dryer during compressor unloading. The control valve closes communication between the governor (28) and the air dryer (22) to trap a predetermined pressure level in the purge volume of the air dryer (22) to prevent the air dryer from purging to atmospheric pressure. Accordingly, a predetermined air pressure level is maintained in the purge volume, so that the outlet of the turbocharger can never be communicated to atmospheric pressure.

Description: This invention relates to compressed air apparatus for an automotive vehicle having a turbocharged engine. Heavy duty vehicles are normally equipped with compressed air braking systems. Since moisture in the compressed air used to operate the braking system is detrimental, it has become increasingly common that such vehicles are also equipped with air dryers, which usually contain a desiccant that dries the air communicated through the air dryer before it is communicated to storage reservoirs, The air compressor used to compress the air is unloaded by a governor which is responsive to the pressure level in the storage reservoirs to generate an unloading signal when the pressure in the reservoirs attains a predetermined level. This unloading signal is also communicated to the air dryer, which causes the latter to back-flush or purge the desiccant during compressor unloading. Furthermore, vehicles equipped with air brakes are normally also equipped with diesel engines, which are commonly turbocharged. The inlet air to the air compressor is often connected to the outlet of the turbocharger. However, when the compressor is unloaded and the air dryer is being purged, the outlet of the turbocharger is communicated to atmosphere when the pressure generated by the turbocharger is greater than the pressure at the discharge valve of the compressor and if the compressor is still unloaded after the air dryer finishes purging. This fact has obvious detrimental consequences, including loss of engine power, increased fuel consumption and an increase in engine emissions. A solution proposed to this problem heretofore is to place a pressure protection valve in the discharge line between the air compressor and the air dryer. However, industry practice discourages use of restrictive valves in the discharge line from the air compressor. Even if such valves were used, they do provide a restriction in the discharge line, and failure of the valve could also fail the air brake system. In the Specification of United States Patent No. 3,937,622 an air dryer system is disclosed wherein a compressor charges a reservoir with compressed air via an air dryer which includes a segregated purge volume for storing air for purging the desiccant of the air dryer when the compressor is switched off on completion of a charging cycle. To achieve this purge a valve is provided which is responsive to a purge volume pressure switched to it via a governor controlled valve to permit discharge of dry air from the purge volume via the desiccant. The purge valve is itself sprang biased to terminate such discharge when the purge volume pressure reaches a predetermined value. Accordingly such a purge valve may need to be specified to have a different spring bias depending upon the fully charged pressure at which the system is required to operate and this can be undesirable especially when the purge valve is integrated into the air dryer. Accordingly, it is an object of the present invention to provide an improved compressed air apparatus. According to the present invention there is provided compressed air apparatus comprising an air compressor, having a discharge lane communicated via a one-way valve to a reservoir, for charging the reservoir to a predetermined pressure level, and to a segregated volume, an air dryer in said discharge line to dry compressed air flowing in one direction therethrough to the reservoir, said air dryer including a purgeable desiccant and a purge valve to regenerate said desiccant by discharging air from said segregated volume through said desiccant in the opposite direction, a governor responsive to said predetermined pressure level in the reservoir to unload the air compressor and to apply a governor signal to a first control valve, to initiate operation of the purge valve, said first control valve comprising a valve member operable by a pressure responsive member which is subject to pressure in said segregated volume in a sense to apply said governor signal as a control signal to a control input of the purge valve and being subject to a bias force in an opposite sense to remove the control signal from the control input of the purge valve when the pressure level in said segregated volume descends to a lower predetermined level determined by said bias. The invention wall now be described by way of examples, with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a portion of one embodiment of a compressed air apparatus made pursuant to the teachings of the present invention; Figure 2 is a schematic illustration similar to Figure 1 but of a different embodiment of the invention; Figure 3 is a view, partly in section, of the air dryer used in the apparatus of Figure 1 or Figure 2; Figure 4 is a longitudinal cross sectional view of a control valve used n the apparatus of Figure 1; and Figure 5 is a longitudinal cross sectional view of another control valve used in the apparatus illustrated in Figure 1 or Figure 2. Referring now to the drawings, a compressed air apparatus generally indicated by the numeral 10 includes a conventional automotive air compressor 12 which is powered by the engine of the vehicle. The vehicle further includes a conventional turbocharger 14 which compresses air communicated to the inlet manifold of the engine to increase power. The turbocharger 14 is powered by exhaust gases generated by the vehicle engine. The outlet of the turbocharger 14 is also communicated to the inlet 16 of the air compressor 12. The compressor 12 compresses the air from the turbocharger 14 and communicates compressed air through discharge line 18 to inlet port 20 of air dryer 22. When the compressor 12 is operating, air communicates through outlet or delivery port 24 of the air dryer 22, to a conventional storage reservoir 26. A governor 28 is responsive to the pressure in reservoir 26 which is communicated to the governor 28 through line 30. When the pressure in reservoir 26 attains a predetermined level, the governor 28 generates a governor signal which unloads or disables the compressor 12. The governor signal is also communicated to control port 32 of a control valve (second control valve) 34 and into supply or inlet port 36 of a control valve (first control valve) 38. Referring now to Figure 3, the supply or inlet port 20 of air dryer 22 is communicated to a desiccant canister 40 through a passage 42 and apertures 45. Compressed air flows upwardly through the desiccant canister 40, where the moisture is removed from the air by desiccant pellets contained within the canister 40, in a manner well known to those skilled in the art. Air is communicated from, the desiccant canister 40 into a purge volume 47 which is a segregated volume between the desiccant canister 40 and the outer wall 44 of the air dryer housing. Compressed air is communicated from the purge volume 47 to the outlet port 24 through a one-way check valve 46. Accordingly, compressed air is permitted to flow from the purge volume 47 into the reservoir 26 through the outlet or delivery port 24, but communication in the reverse direction is prevented by check valve 46. Accordingly, the segregated volume 47 contains a predetermined quantity of segregated air that is used to purge the desiccant canister 40 when the compressor is unloaded, as will be described in detail hereinafter. The air dryer 22 may be made pursuant to the teachings of United States Patent Specification Number 4 487 617. Purging of the desiccant canister 40 is controlled by a purge valve generally indicated by the numeral 48. Purge valve 48 includes a valve element 50 which is normally urged against a corresponding valve seat on the housing by a spring 52 acting against a piston 54 which is integral with the valve element 50. Spring 52 urges piston 54, and the valve element 50 upwardly viewing Figure 3, thereby causing the valve element 50 to sealingly engage its valve seat. However, piston 54 is responsive to the fluid pressure level in chamber 56 to be forced downwardly against the bias of spring 52, thereby opening the valve element 50 and permitting air in purge volume 47 to back-flow through the desiccant container 40 and the apertures 45 into passages 58 and from the passages 58 to atmosphere through open purge valve 48. Purging is controlled by a pressure signal which is communicated into the chamber 56 from delivery port 60 of control valve 38, as will be described in detail hereinafter. As can be seen from Figure 3, when the purge valve 48 is forced downwardly to vent the desiccant canister 40 and volume 47 towards atmosphere, the inlet or supply port 20 is also communicated to atmosphere through the passages 42 and 58. Accordingly, following complete discharge of the volume 47, the supply or inlet port 20 would be then communicated to atmosphere for the remainder of the compressor unloading cycle. Since the inlet or supply port 20 is connected to the outlet of the turbocharger 14 through the air compressor 12, the outlet of the turbocharger 14 would also be communicated to atmospheric pressure. This, of course, has undesirable consequences as discussed hereinabove. However, according to the present invention, the pressure level at the outlet of turbocharger 14 is not reduced to atmospheric pressure. Referring to Figure 4, the second control valve 34 includes a housing 62 which slidably receives a piston assembly 64 therewithin. A valve element 66 is adapted to engage a valve seat 68 to control communication between an inlet or supply port 70 of the valve 34 and a delivery port 72 thereof. The piston assembly 64 controls the valve element 66, and the valve element 66 is normally urged away from the seat 68 because the spring 74 acts on the piston 64 to urge the piston assembly 64 against the valve element 66 and to thereafter urge the piston assembly 64 and valve element 66 downwardly viewing Figure 3. The control port 32 of valve 34 communicates effective area 76 of piston assembly 64 to the control pressure at the outlet of the governor 28, so that when the pressure level of control port 32 attains a predetermined level, piston 64 is urged upwardly viewing the Figure, thereby permitting the valve member 66 to sealingly engage valve seat 68, to thereby terminate communication from the supply port 70 to the delivery port 72. However, since the valve member 66 is held against seat 68 by action of a spring 78, pressure can vent back from the delivery port 72 to the supply port 70 even when the valve member 66 is permitted to engage the valve seat 68 by upward movement of the piston assembly 64. The control port 32, as discussed hereinabove, is communicated to the unloader pressure signal generated by the governor 28 during compressor unloading. The delivery port 72 is communicated to the control port 80 of the valve 38, and the supply port 70 of valve 34 is communicated to the purge volume 47 of the air dryer 22, through an appropriate inlet fitting (not shown). Control valve 38 includes a housing 82 which slidably receives a piston assembly 84 which is urged upwardly viewing Figure 5 by a spring 86. The piston assembly 84 is responsive to the pressure level at control port 80 to move downwardly viewing the Figure. A valve element 88 is yieldably urged into sealing engagement with a valve seat 90 by a spring 92. Accordingly, when the pressure at control port 80 is relatively low, the spring 86 urges the piston assembly 84 to the position illustrated in the drawings, thereby permitting the valve member 88 to sealingly engage valve seat 90 to terminate communication from supply port 36 to delivery port 60 while venting delivery port 60 to exhaust port 94 through passages 96 within the piston assembly 84. When pressure at control port 80 exceeds the predetermined value sufficiently to overcome spring 86, piston assembly 84 moves downwardly, to engage the valve element 88 to thereby close the passage 96 and terminate communication between delivery port 60 and exhaust port 94. Thereafter, the valve member 88 is urged away from valve seat 90, thereby permitting communication from supply port 36 to delivery port 60. As discussed hereinabove, control port 80 is communicated to delivery port 72 of valve 34, delivery port 60 is communicated to the chamber 56 to operate the purge valve 48 of the air dryer 22, and the supply port 36 is communicated to the unloader signal generated by governor 28. In operation, normal operation of the air compressor 12 generates pressure which is communicated through discharge line 18 to the supply reservoir 26 through the air dryer 22. When the pressure in reservoir 26 attains a predetermined level, the governor 28 generates an unloading signal, which unloads the air compressor 12 and which is also communicated to control port 32 of the valve 34 and to supply port 36 of the valve 38. The governor 28 is conventional, and is well known to those skilled in the art. As the reservoir 26 is charged, the pressure level in purge volume 47 increases as the pressure in reservoir 26 increases. This pressure is fed to the control port 80 of valve 38 through the open control valve 34, since the spring 74 urges the valve member 66 to a position permitting communication between the supply and delivery ports of the valve 34. However, even though the valve 38 opens communication between supply port 36 and delivery port 60 due to the high pressure at control port 80, no pressure signal is communicated to the purge valve 48, since the governor is not yet generating an unloading signal. When the governor 28 generates the aforementioned unloading signal, a pressure signal is communicated to control port 32 of valve 34, thereby urging the piston assembly 64 upwardly viewing Figure 4 to permit the valve member 66 to close against valve seat 68, thereby cutting off communication from the supply port 70 to the delivery port 72. Accordingly, the pressure at control port 80 of valve 38 is momentarily trapped by closure of the valve 34, but as the pressure in purge volume 47 decreases during the purge cycle, the pressure at control port 80 bleeds back through the control valve 34, since the decreasing pressure at supply port 70 communicated to the purge volume 47 causes the higher pressure level at delivery port 72 to force the valve member 66 open against the force of spring 78. As long as the pressure at control port 80 of valve 38 is sufficient to overcome the spring 86, a pressure signal from the governor 28 is also communicated through the valve 38 to the purge valve 48 of the air dryer 22, causing the purge valve 48 to open. When the pressure bleeding back from the control port 80 of valve 38 reaches a predetermined level such that the spring 86 urges piston 84 upwardly viewing the Figure, the valve member 88 is urged into sealing engagement with valve seat 90 by spring 92, and the delivery port 60 is open to exhaust port 94 through the passages 96. Accordingly, when this predetermined pressure level is attained, the pressure in chamber 56 is vented, causing the purge valve 48 to close. The valve 38 is designed such that the pressure level at control port 80 at which the spring 86 moves the piston assembly 84 back into the position illustrated on the drawing is somewhat above atmospheric pressure, and approximates the pressure level at the outlet of turbocharger 14. Accordingly, a pressure level somewhat higher than atmospheric pressure is trapped in the purge volume 47 at the conclusion of purging, so that the inlet port 20 is never reduced to atmospheric pressure during operation of the apparatus. The alternate embodiment of Figure 2 is substantially the same as that of Figure 1, except that the control valve 34 has been eliminated and the control port 80 of the valve 38 is communicated directly to the purge volume 47 of the air dryer 22. A one way valve 100 has been added to assure that the pressure-signal controlling purge valve 48 is vented around the control valve 38 at the determination of the governor unloading signal. Accordingly, when the pressure in the purge volume 47 attains the pressure level sufficient to open the valve 38 by forcing piston 84 downwardly while the reservoir 26 is being charged, the valve 38 opens to permit communication between the supply port 36 and delivery port 60 thereof, but since there is no signal from the governor, the purge valve 48 remains closed. However, when a governor unloading signal is generated, this signal is communicated through the valve 38 from the supply port 36 to delivery port 60 thereof, since the pressure at the control port 80 has opened the valve 38, causing the air dryer to purge. As the air dryer purges, pressure at control port 80 of valve 38 decreases. When pressure at port 80 decreases to a predetermined level, spring 86 pushes piston 84 upwardly to allow valve 88 to engage seat 90. The pressure at delivery port 60 is then exhausted and the purge valve 48 closes. This will occur at a purge volume pressure level above atmospheric and before lows of boost pressure from the turbocharger.

Claims: Compressed air apparatus comprising an air compressor (14), having a discharge line (18) communicated via a one-way valve (46) to a reservoir (26), for charging the reservoir to a predetermined pressure level, and to a segregated volume (47), an air dryer (22) in said discharge line (18) to dry compressed air flowing in one direction therethrough to the reservoir, said air dryer including a purgeable desiccant (40) and a purge valve (50) to regenerate said desiccant by discharging air from said segregated volume (47) through said desiccant in the opposite direction, a governor (28) responsive to said predetermined pressure level in the reservoir to unload the air compressor (14) and to apply a governor signal to a first control valve (38), to initiate operation of the purge valve, said first control valve comprising a valve member (88) operable by a pressure responsive member (84) which is subject to pressure in said segregated volume (47) n a sense to apply said governor signal as a control signal to a control input of the purge valve and being subject to a bias force (86) in an opposite sense to remove the control signal from the control input of the purge valve when the pressure level in said segregated volume descends to a lower predetermined level determined by said bias. Compressed air apparatus as claimed in claim 1, characterised by said governor signal being a governor pressure signal by a second control valve (34) connected between the segregated volume and the first control valve said second control valve comprising a second valve member (66) with means (74) biasing it to an open condition and second pressure responsive means (64) being operable by said governor pressure signal to move said second valve member (66) to a closed condition whilst permitting the pressure acting on the said first pressure responsive member to respond to a descent of pressure in the segregated volume to said lower predetermined pressure level. Compressed air apparatus as claimed in claim 2, characterised in that said first valve mechanism (38) includes an inlet port (36) communicated with the governor (28), delivery port (60) communicated with the control input of the purge valve (50), a control port (80) communicated to said second valve (34), and an exhaust port (94) communicated to atmosphere, said first valve member controlling communication between said inlet port (36) and said outlet port (60) and said outlet port (60) and said exhaust port (94). Compressed air apparatus as claimed in claim 3, characterised in that said second valve (34) includes an inlet port (70) communicated to said segregated volume (40), delivery port (72) communicated to the control port (80) of the first valve, a control port (32) communicated with said pressure signal, and a valve structure including said second valve member (66) controlling communication between the latter inlet port (70) and delivery port (72). Compressed air apparatus as claimed in claim 1, characterised in that said governor signal is a pressure signal and said first valve (38) includes an exhaust port (94), an inlet port (36) communicated to said governor (28), a delivery port (60) communicated to said purge valve, a control port (80) communicated to said segregated volume (40), and said pressure responsive member (84) being responsive to the pressure level at said control port (80) so that said valve member (88) controls communication between said inlet port (36) and said outlet port (60) and said outlet port (60) and said exhaust port (94) thereby to shift from a first condition communicating the control part of the purge valve with the governor (28) to a second condition terminating this communication and simultaneously venting control pressure signal from said purge valve. Compressed air apparatus as claimed in claim 5, characterised in that said control port (80) of the first valve is communicated directly with said segregated volume (40). Compressed air apparatus as claimed in claim 5 or 6, characterised in that a one-way valve (100) is connected between the inlet port (36) and the outlet port (60) of the first valve affording free passage of air from the outlet port to the inlet port (36).

Inventors: BARTHOLOMEW, ROY EDWIN C/O ALLIED CORPORATION, KNIGHT, DAVID JOHN C/O ALLIED CORPORATION, KOENIG, JAMES PAUL C/O ALLIED CORPORATION, SZUDY, JAMES EDWARD C/O ALLIED CORPORATION, WURST, WILLIAM ROBERT C/O ALLIED CORPORATION
Applicants: ALLIED-SIGNAL INC. (A DELAWARE CORPORATION)
Application year: 1987
Main classification: B01D53
IPC codes: B60T17, B01D53, F04B49