Abstract:
A latching valve, useable in a multiplexed fluid control system, is switchable between two positions to control working output fluid flow to a corresponding actuator. The valve is latched by deriving a holding force from the working output flow. The latching valve may reside in one of the channels of the multiplexed fluid control system and eliminates the required modulations to hold position and reduces system wear of modulating and multiplexing components. The latching valve includes a working output port coupled with an associated actuator and a control chamber connected to a 3-way multiplexing valve to receive fluid signals. To provide a latching force, the valve includes bleed conduit that bleeds a controlled amount of fluid between the working output port and the control chamber to maintain the pressure in the control chamber. The last position of the latching valve is held until the next selective fluid signal from the modulating valve and multiplexer is received.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to fluid control systems, and more particularly multiplexed hydraulic control systems. 
     BACKGROUND OF THE INVENTION 
     In the art of hydraulic control systems for control of engines, the trend is toward control over more mechanical variables in the engine to attempt an increase in engine efficiency and/or performance. Mechanical variables can include air and fuel valves, variable stator vanes, engine variable geometry, and the like. In prior engines, the common approach of controlling these mechanical variables has been to provide a dedicated hydraulic control for each mechanical variable. However, with the increased number of hydraulic controls has come undesirable increases in weight and size of the overall engine and a decrease in reliability. Such increases in weight and size also decrease the fuel efficiency of engines, particularly for gas turbine aircraft engines. 
     The concept of multiplexing a single hydraulic or pneumatic control to a plurality of channels is known as exemplified by Leeson et al., U.S. Pat. No. 4,984,505, the disclosure of which is hereby incorporated by reference. Multiplexed systems eliminate or reduce the need for several separate hydraulic controls while increasing overall reliability. Leeson illustrates such a multiplexing configuration in which a selectively positioned modulating valve moves linearly with respect to a rotating and multiplexing sleeve. The multiplexing sleeve periodically or sequentially delivers a modulated flow to individual output ports. In other multiplexing schemes, the multiplexer comprises a linearly moving valve as exemplified by McLevige et al., U.S. Pat. No. 5,048,394, the disclosure of which is also hereby incorporated by reference. In both rotary and linear multiplexing configurations, an intermediate second stage valve may be interposed between each multiplexer output and each actuator to integrate and/or amplify the signal to the actuator. 
     While these multiplexing systems reduce the number of hydraulic controls and increase reliability, a drawback with these prior hydraulic multiplexing configurations is that the modulating valve and multiplexer are frequently modulating flow to the second stage valves to correct for error and/or to maintain the last position of the intermediate second stage valves. Such frequent modulated flow may be necessary, for example, to correct for gradual fluid seepage from the control chamber of the second stage valve, which can cause the second stage to fall out of the desired position. These frequent modulations may cause fatigue and wear on the components of the system which may in turn reduce the life-span of the system. Such frequent modulations also can require a large quantity of electrical power. 
     There are also known attempts to configure a multiplexing scheme with latching valves that do not need updating to hold the last valve position. Such a configuration is exemplified in Veilleux, Jr. et al., U.S. Pat. No. 5,551,478. In Veilleux, a plurality of latching second stage valves switch between two positions by application of high pressure signals to one of two control ports corresponding with the two valve positions to change fluid flow to a corresponding actuator. A high pressure pulse on one port switches the valve from a first to a second position and the application of a high pressure pulse to the second port switches the valve back to its first position. The latching valves use internal ports and switches to low and high pressure inputs and an internal spring biasing mechanism to latch the valves in the current position until the appropriate high pressure pulse is delivered to the appropriate control port. However, a problem with this prior latching valve multiplexing system is its size, weight, and complexity, which are a disadvantage in aircraft systems and other systems where smaller size and weight is highly desired. In particular, Veilleux requires a 4-way multiplexing valve that has two control ports for each second stage latching valve. Each latching valve likewise has two control chambers and ports connected by separate conduits to the multiplexing valve. Furthermore, each latching valve requires two high pressure inputs and two low pressure inputs to maintain the latched position and produce an output to an actuator. The numerous ports increase the number of connecting conduits, the overall length or size of the multiplexing and latching valves, and therefore the complexity and weight of the system. Yet another problem with Veilleux is that the disclosed multiplexed fluid control system only provides positive high pressure pulses, and therefore it is not compatible with other variably positioned second stage valves which operate on positive and negative fluid signals. Such variably positioned second stage valves offer better control over mechanical variables which prefer more accurate control. 
     SUMMARY OF THE INVENTION 
     It is a general aim of the present invention to overcome these and other deficiencies existing in the art. 
     It is another general aim of the present invention to provide a practical and reliable multiplexed fluid control system that utilizes latching type valves. 
     It is therefore an object of the present invention to reduce the complexity and size of a latching valve for use in multiplexed fluid control systems. 
     In that regard, it is another object of the present invention to reduce the number of ports and connections necessary to latch a second stage valve. 
     It is another object to provide a latching valve that operates on negative and positive fluid signals from a 3-way multiplexing valve that alternatively pressures or exhausts a single port. 
     It is therefore a feature of the present invention to provide a latching valve in a channel of a multiplexed fluid control system that derives a holding or latching force from the working output pressure or flow between the latching valve and a corresponding actuator. The latching valve produces a working output flow that is determined by the current state of the valve. The current state of the valve is determined by the last fluid signal received in the channel and is held by the latching force. 
     It is another feature of the present invention to provide a simplified latching valve in a multiplexed fluid control system. The latching valve provides a control chamber for receiving fluid signals from the multiplexing and modulating means. The latching valve is switchable between two states by receipt of fluid signals in the control chamber. The state of the latching valve controls a working output fluid flow to an associated actuator. The latching valve further has a bleed conduit which connects the working output flow to the control chamber to maintain the fluid pressure in the control chamber and thereby latch the valve in its current state. 
     It is an aspect of the present invention that the bleed conduit has a restricted size to limit the flow rate through the bleed conduit so that fluid signals from the multiplexing valve cause the valves to switch states. 
     It is another feature of the present invention to provide a latching valve for a fluid control system that has a movable valve operator translatable between two positions within a valve body for regulating working fluid flow to a corresponding actuator. The valve body defines an inlet, an outlet, a control chamber, and a working output. The valve operator has a first position, which connects the inlet to the working output, and a second position, which connects the outlet to the working output. The position of the latching valve is controlled by fluid pressure in the control chamber. The latching valve also includes a bleed conduit connecting the working output to the control chamber for latching the valve in its current position. 
     It is another feature of the present invention that the latching valve is adapted to use positive or high-pressure fluid signals and negative or lower pressure fluid signals of a 3-way multiplexing valve. The latching valve may therefore be used in a multiplexed control system with other forms of second stage valves which use positive and negative fluid signals. The last fluid signal received in the control chamber determines the current position of the valve operator and therefore the current state of the second stage valve. 
     It is an advantage of the present invention that the valve provides for reduced size and reduced complexity. The latching valve may be of the spool type, or any other appropriate configuration, and can define the bleed conduit internally in the spool. 
     These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial schematic illustration showing a multiplexed fluid control system according to a preferred embodiment of the present invention. 
     FIG. 2 is a cross-sectional fragmentary view of an exemplary latching valve used in FIG. 1 according to a preferred embodiment of the present invention. 
    
    
     While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For purposes of illustration and referring to FIG. 1, a preferred embodiment of the present invention has been illustrated as a multiplexed hydraulic control system  20 , shown in partial schematic form. Although an exemplary multiplexed system  20  is illustrated as the rotary and time division type similar to that shown in U.S. Pat. No. 4,984,505, it will be appreciated by those of skill in the art that the latching valve of the present invention can be used with a number of prior art multiplexed fluid control systems with similar benefits achieved, as will be developed in further detail below. 
     For simplicity of illustration, the exemplary multiplexed hydraulic control system  20  includes only three channels  22 ,  23 ,  24 , each channel having a latching valve  40 - 42  and associated actuator  43   a - 43   c  therein. A preferred embodiment includes an electronic controller  26  that responds to electrical demand inputs to produce electrical commands transmitted by bus  28  to modulating means, shown schematically in FIG. 1 as a modulating valve  30 . In accordance with the electrical commands, the modulating valve  30  selectively connects either a high-pressure hydraulic source (PS) or a lower pressure hydraulic sump (PB) to an input conduit  32  of a multiplexer  33 . The modulating valve uses the hydraulic sump (PB) and the hydraulic source (PS) to produce relatively high magnitude fluid signals which correspond to large fluid flow rates. More specifically, the modulating valve  30  selectively connects the input conduit  32  to the sump (PB) or the source (PS) for short time intervals to provide a selected hydraulic flow rate through the input conduit. Fluid signals include positive fluid signals corresponding to a transitory connection to the higher-pressure hydraulic source (PS) and negative fluid signals corresponding to a transitory connection to the lower-pressure hydraulic sump (PB). The fluid signals that are fed through the input  32  are simultaneously distributed to a channel by a 3-way multiplexing valve  33 , illustrated as a rotary commutator  34  having three control port outputs  36 ,  37 ,  38 , or other suitable multiplexing means. The rotary commutator  34  includes an open segment  35  that sequentially connects the input conduit  32  to each of the outputs  36 - 38  for changing the states of the latching valves  40 - 42 . 
     The states of the latching valves  40 - 42  control the working output flows to the associated actuators  43   a - 43   c  in the respective channels  22 - 24 . As will be developed in further detail below, each latching valve  40 - 42  is switchable between two states by application of fluid signals to the channels  22 - 24 . As seen in FIG. 1, latching valve  40  is shown in one of the two states referred to herein as an “ON” state while latching valves  41 - 42  are shown in the other state referred to herein as an “OFF” state. In the preferred embodiment, the “ON” state results from the application of positive fluid signals while the “OFF” state results from the application of negative fluid signals. 
     For control of the system, the electronic controller  26  receives an external demand signal for the demanded position of each actuator  43   a - 43   c  in each of the channels  22 ,  23 ,  24 . Each actuator  43   a - 43   c  may include a position feedback device, such as a linear variable displacement transducer (LVDT)  44 , which sends position feedback signals on a feedback line  46  to the electronic controller  26  for closed loop control if desired. The electronic controller  26  may then process the external demand signals and the position feedback signals on line  46  to determine if any of the corresponding latching valves  40 - 42  need to be switched between states. 
     If any of the latching valves  40 - 42  need to be switched between states, the electronic controller  26  commands the modulating valve  30  to provide an appropriate fluid signal to the associated channel while connected thereto. It will also be appreciated to those of skill in the art that the modulating valve  30  includes an electrical motor, such as a torque motor or a voice coil which is responsive to electric signals and positions the modulating valve in accordance therewith to provide a fluid signal. In the illustrated preferred embodiment, the rotary commutator  34  has a continuous rotational movement with feedback from a position indicator  39  to the electronic controller  26  indicating when a particular channel is open. Under this scheme, the electronic controller  26  sequences commands in time slots as channels  22 - 24  open and close to selectively apply fluid signals to each channel. However, it will be appreciated to those of skill in the art that in an alternative embodiment, the electronic controller may command a motor (not shown) to selectively rotate the commutator to connect the modulating valve to a channel that requires changing. 
     In accordance with the objective of providing a latching valve that operates on positive and negative fluid signals, a preferred embodiment provides simplified latching valves  40 ,  41 ,  42  in individual channels  22 ,  23 ,  24  which are latched in their current position until the next selective update from the modulating valve  30  and multiplexer  33 . Referring now to latching valve  40  as exemplary as illustrated in greater detail in FIG. 2, the latching valve  40  includes a movable spool  54 , or other appropriate valve operator, that rides in a cylindrical bore  56  formed in a valve body  58 . The spool  54  includes an enlarged cylindrical end portion  59  fitted within an accommodating enlarged cylindrical intermediate portion  61  of the bore  56 . The combination of the spool  54  and the bore  56  form a control chamber  60 . As seen in FIG. 1, the control chamber  60  is coupled with a corresponding multiplexer output  36  for receiving respective fluid signals. 
     The valve body  58  defines a working output port  62 , an inlet port  64 , and an outlet port  66 . In the exemplary multiplexed control system  20 , the working output  62  is connected for fluid communication with the associated actuator  43 , the inlet  64  is connected to a high-pressure source (PS), and the outlet  66  is connected to a lower pressure sump (PB). The working output port  62  is selectively connectable in the “ON” state through the bore  56  to the inlet  64  for providing control flow to the associated actuator  43 , and in the “OFF” state to the outlet  66  for venting fluid from the associated actuator  43 . 
     The spool  54  defines a bleed conduit  70  that connects the control chamber  60  with the working output port  62 . The bleed conduit has an annular groove  71  formed on the outer radial periphery of spool  54  so that the angular position of the spool  54  does not affect the connection between the working output port  62  and the control chamber  60 . The bleed conduit  70  also includes a restriction  72  to provide a limited cross-sectional area therein for limiting the flow rate through the bleed conduit  70 , the function of which will be described more fully below. The spool  54  also defines an outer gasket retaining groove  76  with a ring gasket  78  compressed therein for preventing fluid seepage between the control chamber  60  and the inlet port  64 . The spool  54  further defines an annular inlet groove  79  on the outer radial periphery thereof so that the inlet port  64  is connectable to the working output  62 . 
     To provide for the “ON” and “OFF” states, the spool  54  has a limited range of movement within the bore  56  between corresponding “ON” and “OFF” positions. In particular, the spool  54  has a limited range of axial movement between two mechanical stops  80 ,  82  defined by the valve body  58 . In the “ON” position, fluid can flow from the inlet  64  past the spool  54  to the working output  62  to drive the associated actuator  43  in a one direction, while, in the “OFF” position, fluid can be vented to the outlet  66  from the working output  62  to move the associated actuator  43  in the opposite direction. 
     The type of fluid signal last received in the control chamber  60  determines whether the working output port  62  is connected to the inlet  64  or the outlet  66 . More specifically, a negative fluid signal from the modulating valve  30  vents fluid from the selected channel to reduce the fluid pressure in the control chamber  60 . The lower pressure causes the spool  54  to axially translate to the “OFF” position wherein the outlet  66  is connected to the working output port  62 . Similarly, a positive fluid signal from the modulating valve  30  adds fluid to the selected channel to increase the fluid pressure in the control chamber  60 . The higher pressure causes the spool  54  to axially translate to the “ON” position wherein the inlet  64  is connected to the working output port  62 . Also shown in the preferred embodiment is a spring  84  which may be used to pre-bias the spool  54  in one axial direction and thereby initialize the spool position at startup. 
     In accordance with the aims, objectives and features of the present invention, a preferred embodiment derives a holding or latching force from the working output flow between the latching valve  40  and the corresponding actuator  43  to latch the spool  54  in its last position. Accordingly, fluid can bleed through the bleed conduit  70  between the control chamber  60  at pressure (Pz) and the working output port  62  at pressure (Pzf) to maintain the last position of the latching valve. The rate at which fluid bleeds through the bleed conduit  70  is controlled by the restriction  72  (the restriction may also be provided integrally by providing a smaller sized bleed conduit). Fluid bleed through the bleed conduit  70  maintains the necessary pressure in the control chamber  60  so that the spool  54  does not drop out of a latched position. It is an advantage that the bleed conduit  70  reduces the number of ports and connections necessary to latch the second stage valve  40  in their current position. Although the bleed conduit  70  could be defined by the valve body or externally on the valve, the spool  54  may define the bleed conduit  70  internally as shown in FIGS. 1 and 2 to further reduce ports needed in the valve body  58 . 
     In the preferred embodiment, the flow through the bleed conduit  70  depends upon the position of the spool  54  in the latching valve  40 . In the “ON” position, the fluid pressure (Pz) in the control chamber  60  is relatively high having received a positive or high pressure (PS) signal from the modulating valve  30 . While in the “ON” position, the inlet  64  is connected to he working output port  62 . As such, the pressure (Pzf) of the working output  62  is also relatively high, as there is only a small pressure drop across the spool  54 . While in this “ON” position, fluid may gradually seep from the control chamber  60  back through the output  36  (see FIG.  1 ). To prevent this seepage from translating the spool  54  out of a latched position, fluid can bleed from the working output port  62  through the bleed conduit  70  to replace lost fluid pressure in the control chamber  60  thereby maintaining the latched position. 
     In the “OFF” position, the fluid pressure (Pz) in the control chamber  60  is relatively low having received a low pressure or negative fluid signal from the modulating valve  30 . While in this position, fluid may seep from multiplexer  33  (see FIG. 1) to the control chamber  60  which tends to cause an increase in fluid pressure. In the “OFF” position, the pressure (Pzf) of the working output port  62  is relatively low as fluid is being drained from the actuator  43  to the outlet  66 . Any pressure build up in the control chamber  60  is released or disposed of by fluid bleed from the control chamber through the bleed conduit  70  and to the working output port  62 . 
     To switch the spool  54  between the “ON” and “OFF” positions, the modulating valve  30  is commanded to give a relatively high magnitude signal to overcome the fluid bleed through the bleed conduit  70 . This axially translates the spool  54  between two positions. To achieve axial translation, the flow rate between the multiplexer output  36  and the control chamber  60  during application of a fluid signal is sufficiently greater than the flow rate through the bleed conduit  70  so that adequate pressure differential exists across the valve to cause the spool  54  to axially translate. To provide adequate pressure differential, the bleed conduit has the restriction  72  that limits fluid flow between the working output port  62  and the control chamber  60 . This restriction  72  is sized large enough so that sufficient fluid bleeds through the bleed conduit  70  to maintain the spool  54  in a latched position but small enough so that the fluid signal provided by the modulating valve  30  switches the spool  54  between positions.