GB2106635A

GB2106635A - Temperature and pressure control for environmental control system for aircraft

Info

Publication number: GB2106635A
Application number: GB08219236A
Authority: GB
Inventors: Robert Bernard Goodman; John Lawrence Warner
Original assignee: United Technologies Corp
Current assignee: RTX Corp
Priority date: 1981-07-20
Filing date: 1982-07-02
Publication date: 1983-04-13
Also published as: SE8204357L; SE446848B; JPS5824736A; FR2509842A1; DE3226337A1; GB2106635B; BR8203800A; FR2509842B1; IT1151924B; SE8204357D0; JPH026975B2; ES8400204A1; IT8222326A0; ES514110A0

Abstract

An environmental control system for an aircraft includes an ambient pressure (altitude) responsive control valve 20 controlling total system flow, an air conditioning package 190 for cooling a portion of the flow and a bypass conduit 185 for bypassing the air conditioning package, the system output flow temperature being regulated by controlling the flows through both the air conditioning package and bypass conduit independently of total system flow. Such independent flow control is achieved by the modulation of synchronized and phased control valves 180, 175, one in the bypass duct and the other disposed serially to the air conditioning package. <IMAGE>

Description

SPECIFICATION Temperature and pressure control for environmental control system Technical Field This invention relates generally to an environmental control system such as a heating, air conditioning and pressurizing system for an enclosed space such as an aircraft cabin and, more particularly, to a temperature and pressure control therefor.

Background An environmental control system for enclosures such as an aircraft cabin or the like must be capable of heating, air conditioning, and pressurizing the cabin for maintenance of passenger comfort throughout the various temperature and pressure climactic conditions encountered by the aircraft. In aircraft powered by gas turbine engines, air for the system is usually provided by bleeding a portion of the output of the engine's compressor section. This compressed air is typically of a temperature in the range of 200"F to 550"F, thereby providing a convenient source of warm air when climactic conditions are such that cabin heating is required.Often, the environmental control system employs a refrigeration system such as an air cycle or freon system for cooling the compressor bleed air when conditions are such that cabin cooling is required.

Heretofor, to provide the environmental control system with both cooling and heating capabilities, it has been the practice to split the compressor bleed flow, a portion of the flow being chilled by the refrigeration system, the remainder of the flow bypassing the refrigeration system, and being recombined with the chilled air and exhausted to the cabin.

Typically, a valve is employed in the bypass air stream for regulating the mass flow thereof, the valve closing to restrict bypass flow to the cabin when cooling of the cabin air is required and opening to allow the bypass to overwhelm the refrigerated air flow when cabin heating is required. A flow limiting venturi is often employed to limit total flow through the system to the cabin to avoid overbleeding the engine.

Such prior art systems exhibit several drawbacks. For example, since the refrigerated air flow is not in and of itself controlled, cabin heating is often quite inefficient, requiring excessive amounts of warm bleed air to bypass the refrigeration section to compensate for the chilling of the air therein. While such excessive flow may be prevented by a flowlimiting device such as a venturi or the like, such a device introduces a substantial pressure drop in the system thereby further contributing to system inefficienies. Also, it will be appreciated that the uncontrolled flow of chilled air to the cabin adversely affects the system's cabin heating capability. By way of example, at low altitudes, considerably more flow is required to cool than to heat at high altitudes.However, with such prior art environmental control systems, if optimum air flow through the system is obtained in cooling at low altitude, heating at higher altitudes may require substantially more flow than would be necessary were it not required to provide warming of previously chilled air, thereby wasting substantial amounts of bleed air, and adversely affecting engine performance.

Certain of the above-named disadvantages of prior art environmental control systems could be alleviated by provision of separate valves for controlling both chilled air flow and warm bypass air flow. United States Patent No. 2,562,918 to Hynes discloses such a provision of separate control valves. However, in the Hynes patent, cabin pressure is regulated by a pressure-regulating valve which, rather than maintaining cabin pressure on the basis of pressure requirements for passenger comfort, maintains a constant pressure at the inlet of the bypass flow control valve such that cabin pressurizing is based solely on temperature demands, a disadvantage associated with the prior art systems discussed herein above.Thus, with systems such as that disclosed in Hynes, it is possible that a decrease in engine compressor discharge pressure for one reason or another, accompanied by an increase in cooling demand could result in an increase in bypass air flow rather than flow through the refrigeration system where an increased flow would me most useful.

Moreover, the bypass and cooling control valves employed in Hynes exhibit only slight overiap. That is, except in limited circumstances, adjustment of one of the valves fails to adjust the other. Thus, if from a particular setting, increased cooling is desired, such an increase would be effected not by the efficient closing of the bypass control valve with a simultaneous opening of the refrigeration control valve, but rather by a closing of the bypass valve alone, thereby failing to increase the needed cool air flow.

Disclosure of Invention It is, therefore, a principal object of the present invention to provide an environmental control system wherein required system output temperature is maintained substantially independently of system output pressure.

It is another object to provide such an environmental control system wherein adjustments in system cooling are not adversely affected by warm air flow.

It is another object of the present invention to provide such a system wherein adjustments in system heating are not adversely affected by the flow of chilled air through the system.

It is another object of the present invention to provide such a system wherein minimum engine compressor bleed flow is employed to efficiently achieve cabin temperature and pressurization requirements.

In accordance with the present invention, these objects are achieved by provision of control valves, one such valve controlling the flow of air through a refrigeration or air conditioning means, and the other controlling air flow which bypasses the refrigeration means, the valves being phased and synchronized such that a change in setting of one of the valves is accompanied by an opposite proportional change in setting of the other valve.

Thus, when increased heating or cooling is called for, the corresponding valve opens so that an increased flow of the required warm or cold air is achieved with an accompanying decrease in flow of air of the opposite temperature. Another control valve controls total system supply pressure in response to ambient pressure independently of instantaneous cabin temperature requirements such that adjustments in temperature do not adversely affect pressure and vice versa. Accordingly, the environmental control system of the present invention utilizes engine bleed air in a most efficient manner while maintaining both optimum temperature and optimum pressure conditions.

Brief Description of the Drawings Figure 1 is a schematic representation of the environmental control system of the present invention.

Figure 2 is a graphical representation of the operating characteristics of a pressure-regulating control valve employed in the system.

Figure 3 is a graphical representation of the operating characteristics of the temperature control valves employed in the system.

Best Mode of Carrying Out the Invention Referring to Fig. 1, the environmental control system of the present invention is shown generally at 10 and comprises a main supply conduit or duct 1 5 exhausting at the left end thereof to an enclosed space such as an aircraft cabin (not shown), the temperature and pressure of which are to be controlled by this system. Inlet air to the system is provided through duct 1 5 at the right end thereof through a suitable source as the compressor section of a gas turbine engine. The system includes a first (pressure regulating) control valve 20 disposed with duct 15, the setting of this valve controlling the effective cross-sectional area of that duct, and therefore, the amount of flow therethrough from the source.

As shown, valve 20 is a butterfly valve having a pinion 25 on the valve shaft, the pinion engaging with a rack 30 connected to valve actuator 35. Alternatively, valve 20 may be operated from a crank is well known in the art. Actuator 35 comprises first and second cylinders 40 and 45 within which first and second pistons 50 and 55 respectively are received. Pistons 50 and 55 respectively are received. Pistons 50 and 55 are connected by means of rod 60, smaller piston 50 being sealed to cylinder 40 by ring 65 and connected to rack 30 by any appropriate means such as connecting rod 70. Larger piston 55 is sealed to cylinder 45 by a rolling diaphragm 75. The left side of piston 50 communicates with duct 1 5 adjacent the air input to the system through conduit 80.Piston 55 communicates with the system inlet through conduit 85, which communicates with conduit 80 through orifice 90 and ball valve 95 operated by solenoid 100 and normally unseated from valve seat 105. A portion of the air in conduit 85 is continually bled therefrom through branch 105, having a port 110 in the end thereof, the effective area of port 110 being selectively adjusted by flapper 11 5.

Under steady state conditions, the left side of piston 50 is acted upon by air pressure upstream from butterfly valve 20 urging the piston to the right with a force proportional to that pressure. Likewise, piston 55 is acted upon by system air inlet pressure thereby urging that piston to the left, the air bled through branch 105 compensating for the larger diameter of piston 55 so that both pistons exert generally equal and opposite forces on each other. Accordingly, at constant system inlet pressure, the pistons remain in equilibrium and valve 20 remains at a particular setting.

A change in system inlet pressure such as, for example, an increase in pressure is first experienced by piston 50, orifice 90 delaying the effects of the increased pressure on piston 55. Thus, such an increase in pressure unbalances the forces on pistons 50 and 55, the increased pressure first acting on piston 50 to move the pistons to the right thereby causing a translation of rack 30 to partially close valve 20. Eventually, after the delay introduced by orifice 90, the increased pressure also appears within cylinder 45, increasing the force on piston 55 to prevent further movement of both piston 50 and valve 20 thus reestablish ing system equilibrium with the air bled from port 110.

Valve 20 is responsive to ambient pressure (altitude) as well as to system inlet pressure.

Still referring to Fig. 1, flapper 11 5 is mounted on pivot 11 7 and operated by actuator 1 20. Actuator 1 20 comprises cylinders 1 25 and 1 30 within which pistons 1 35 and 140, respectively, are received, each piston being sealed to the corresponding cyclinder by a rolling diaphragm.Flapper 11 5 is also acted upon by spring 1 45 biasing the flapper against both evacuated bellows 150, respon sive to ambient pressure (PAMB) and piston 1 35. Piston 1 35 communicates with system flow downstream from valve 20 through conduit 1 60 while piston 140 communicates with downstream flow through conduit 160, and conduit 165 provided with restriction 1 70 therein.

Under steady state conditions, the regulated system pressure, PREG remains constant at constant ambient pressure (altitude). However, as altitude varies, ambient pressure varies, thereby requiring adjustment in the system output pressure. Accordingly, any change in ambient pressure results in a corresponding change in force on evacuated bellows 150, resulting in an adjustment in flapper 11 5 which effects either an increase or a decrease in the effective opening (bleed flow) of port 110. This adjusts the pressure on piston 55, unbalancing the forces on actuator 35 to adjust pressure regulating valve 20 to a position corresponding to the system output pressure required.The change in regulated pressure appears immediately in cylinder 1 25 and acts on piston 1 35 to offset the force change on flapper 11 5 due to the ambient pressure change. The adjusted regulated pressure subsequently acts on piston 140 through duct 165 and restriction 1 70 to readjust the effective opening of port 110, thereby allowing equilization of forces on opposite sides of pistons 50 and 55 to stablize movement of butterfly valve 20.

The effect of altitude on the operation of valve 20 is illustrated in Fig. 2 wherein PREG, the regulated pressure downstream from valve 20 is shown to decrease with the closing of valve 20 in response to increasing altitude. As set forth hereinabove and as illustrated in Fig.

2, at higher altitudes where cabin air must be warmed, substantially less pressurization is required that at lower altitudes, wherein sufficient cooling may only be attained by elevation of cabin pressure.

Actuation of solenoid 100 to its closed position causes pressure on piston 55 to be dumped through port 110, thus allowing the air pressure in cylinder 40 to bias piston 50 to the right, closing valve 20 for the deactuation of the system.

It is thus seen that the environmental control system of the present invention provides pressure regulation independently of any temperature control by means of first control valve 20 and actuator 35, therefor. Likewise, in the present invention, temperature regulation is achieved independently of pressure regulation by means of second and third control valves 1 75 and 1 80 disposed within cooling duct 183 and bypass duct 185, respectively. As shown, cooling duct 1 83 may comprise an extension of duct 1 5 and includes therein an air conditioning package 1 90 or refrigeration means of any suitable type such as any of the various air cycle or freon refrigeration system known in the art.

Air supplied through duct 1 80 is cooled in the air conditioning package for exhaust to the aircraft cabin. Air channeled through duct 185 remains substantially at the temperature at which it was input to the system, bypassing the air conditioning package and mixing with the chilled air downstream of the air conditioning package for exhaust to the cabin.

Temperature of the air exausted from the system of the present invention is determined by the setting of second and third control valves 1 75 and 180. A cabin temperature controller 1 95 such as a thermostat or the like senses cabin temperature, compares that temperature to a desired temperature and signals common actuator 200, which sets valves 175 and 1 80 to satisfy the demands of the controller. Valves 1 75 and 1 80 are synchronized by operation from common actuator 200 through linkage 210 comprising valve links 21 5 and 220, each connected rigidly at one end thereof, to the shaft of the corresponding control valve and pivotally at the opposite ends thereof to one of main links 225 and 230.It is seen that operation of actuator 200, in this case, rotation of arm 205, results in generally vertical movement of main link 225 and 230 and pivotal movement of valve links 215 and 220, thereby setting valves 175 and 180. As shown, the valves are not only synchronized by are phased such that adjustment of one of the valves by actuator 200 results in a simultaneous and proportional opposite adjustement of the other.

In accordance with the present invention, and as illustrated in Fig. 3, the valve phasing and synchronization causes the effective flow resistance (sum of the effective areas) of bypass conduit 185, (including valve 180) and cooled air conduit 183, including air conditioning package 1 90 and valve 1 75 to remain almost constant throughout various settings of valves 175 and 180.

In Fig. 3 the effective area of the bypass conduit with valve 1 80 for various actuator positions (valve settings) is indicated by curve 235. The effective area of cooling duct 1 83 with valve 1 75 for various actuator position (valve 175 settings) is indicated by curve 240.

To curve 240 is subtracted the effective restriction of the air conditioning package represented by constant curve 245 to obtain curve 250, which represents the effective area of duct 183, valve 1 75 and air conditioning package 1 90 for all actuator positions. It is noted that the total effective area is the sum of curves 235 and 250 which results in curve 255, representative of a substantially constant valve. Accordingly, for all actuator settings, flow through the system remains substantially constant. Thus, at a constant altitude, adjustments in cabin temperature may be made without a change in cabin inflow. As shown, the valves are set for maximum cooling, valve 1 80 being closed and valve 1 75 being com pletely open.In operation, by way of example, a signal from temperature controller 195 calling for a warmer cabin temperature causes operation of actuator 200 wherein arm 205 is rotated in a counterclockwise direction drawing links 225 and 230 generally upwardly, thereby pivoting links 21 5 and 220 generally counterclockwise. This tends to close valve 1 75 while at the same time opening valve 1 80. Thus, it is seen that a demand for a warmer cabin temperature effects not only an increase in bypass flow but a corresponding proportional decrease in flow through the air conditioning package. Thus, neither of the flows through ducts 1 80 and 1 83 must overwhelm the other and the desired temperature is achieved with conservation of engine bleed air and stabilization of cabin pressure.

Having thus described the invention, what

Claims

is claimed is: CLAIMS

1. An environmental control system comprising a source of pressurized air, a first control valve for controlling total air flow from said pressurized air source in response to altitude, means for cooling a portion of the pressurized air, and a conduit communicating with said pressurized air source for bypassing said cooling means with the remainder of said pressurized air, said system being characterized by: a second control valve being disposed serially with respect to said cooling means for controlling the flow of air thereto, and a third control valve being disposed in said bypass conduit for controlling the flow of air therethrough.

said second and third valves being synchronized and phased such that adjustment of either from any setting thereof effects a simultaneous and proportionally opposite adjustment of the other whereby flow rate and temperature of the combined flow through said cooling means and bypass conduit are independently controllable.

2. The environmental control system of Claim 1 further characterized by the total flow resistance of said cooling means and said second and third control valves is substantially constant for all settings of said second and third control valves.

3. The air conditioning and pressurizing system of Claim 1 further characterized by said second and third control valve phasing being such that one of said control valves is fully open when the other is fully closed.

4. The air conditioning and pressurizing system of Claim 1 further characterized by said second and third control valves being operated by a single actuator.