Abstract:
An aircraft flap drive system utilized a variable displacement motor ( 15 ) having a fluid pressure actuated device ( 23 ) to vary the displacement of the motor. The system includes a displacement control valve ( 41 ), and an electrohydraulic control means ( 55,67,85 ) operable in response to an electrical input signal ( 91 ) to communicate pressurized fluid from a source ( 11 ) to the motor. The displacement control valve ( 41 ) includes a load sensing arrangement ( 13,53,49 ) responsive to an increasing load on the motor to bias the displacement control valve toward a position whereby the motor moves toward its maximum displacement (minimum flow). One result is that the conventional fixed displacement motor, of a particular size and weight, may be replaced by a variable motor which is smaller and lighter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     MICROFICHE APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE DISCLOSURE 
     The present invention relates to a fluid pressure operated control system for controlling the position of a vehicle auxiliary device, and more particularly, to such a control system for controlling a device which is subject to varying loads throughout its range of displacements. 
     Although the fluid control system of the present invention may be used advantageously with many different types of vehicles and vehicle auxiliary devices, it is especially suited for use in controlling aircraft flaps and slats, and will be described in connection therewith. 
     Typically, aircraft flap and slat drive systems have been primarily hydraulic systems, and have utilized fixed displacement hydraulic motors as the means for directly actuating or driving the aircraft flaps. 
     Although the prior art systems, utilizing fixed displacement hydraulic motors, have been generally satisfactory in terms of performing the basic function of driving the flaps, the prior art system has had certain inherent drawbacks. It should be noted that these drawbacks are not peculiar to aircraft flap drive systems, but are also applicable to various other hydrostatic drive systems which operate to change the position of a device which is under varying load conditions, as it moves throughout its range of displacement. 
     A key operating criteria for an aircraft flap drive system is the ability to achieve full stroke (i.e., full movement of the flap) within a specified time period, and with the flap subjected to the specified load profile. In a flap drive system utilizing a fixed displacement hydraulic motor, the motor must be sized, in terms of its displacement per revolution, for full break-out torque at the peak load position (as that term will be explained subsequently). At all loads less than the peak load, with motor flow being constant, excess power (fluid pressure) is dissipated within the control system. Thus, in order for the control system to achieve the full stroke of the flap within the specified time, the required size of the hydraulic motor results in the system operating at an excessive flow rate, during most of its operating cycle. 
     The requirement to size the motor to satisfy the peak load situation, while still achieving full stroke in the specified time, requires a hydraulic motor which is larger, more expensive, and heavier than is desirable. As will be understood by those skilled in any of the vehicle arts, excess size and weight of component s is always undesirable, but such is especially true in the case of aircraft. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved control system for driving a vehicle device such as an aircraft flap, wherein the size and weight of the hydraulic motor may be reduced. 
     It is a more specific object of the present invention to provide such a flow control system in which the operation of the hydraulic motor can be tailored to meet the operating parameters of the device being controlled by the system. 
     The above and other objects of the invention are accomplished by the provision of an improved aircraft flap drive system of the type including a source of pressurized fluid hydraulically coupled to a hydraulic motor, the motor including an output operable to drive the aircraft flap, and a brake device associated with the motor output and operable, when applied, to maintain the aircraft flap at a desired position. 
     The improved aircraft flap drive system is characterized by the hydraulic motor comprising a variable displacement motor including fluid pressure actuated means for varying displacement of the motor between a maximum displacement and a minimum displacement. A displacement control valve has an inlet and is operable to communicate pressurized fluid from the source through the inlet to the fluid pressure actuated means, the displacement control valve being normally biased toward a position permitting such communication. An electrohydraulic control means is operable in response to an electrical input signal to communicate pressurized fluid from the source to the hydraulic motor. The displacement control valve includes load sensing means operable in response to an increasing load on the hydraulic motor to bias the displacement control valve toward a position whereby the fluid pressure actuated means varies the displacement of the hydraulic motor toward the maximum displacement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a hydraulic schematic of a hydraulic motor control system made in accordance with the present invention. 
     FIG. 2 is a simplified schematic of an aircraft flap of the type with which the motor control system of FIG. 1 may be utilized, illustrating three different operating positions of the flap relative to the wing profile. 
     FIGS. 3,  4  and  5  are graphs of Load, Speed, and Flow Rate, respectively versus Flap Position, comparing the invention with the prior art control system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, which are not intended to limit the invention, FIG. 1 illustrates a hydraulic schematic of a hydraulic motor control system made in accordance with the teachings of the present invention. The system includes a source of pressurized fluid, shown herein as a fixed displacement pump  11 , the output of which is communicated by means of a conduit  13  to the inlet port of a variable displacement hydraulic motor  15 . Although the invention is not so limited, the motor  15  is illustrated herein as being an axial piston motor of the type including a tiltable swashplate  17 . Axial piston devices are well known to those skilled in the art. As is also well known, for a given, constant flow to the motor  15 , movement of the swashplate  17  from the maximum displacement position shown in FIG. 1 toward a minimum displacement position will result in a gradually increasing speed of rotation of an output shaft  19 , and at a gradually decreasing torque. 
     An aircraft flap (shown in FIG. 2) is an example of a vehicle device which must be moved to a desired position and then maintained at that particular, desired position. In order to accomplish such position maintenance, a brake assembly  21  is disposed about the output shaft  19 . Although not an essential feature of the invention, it is preferred that the brake assembly  21  be of the “spring-applied, pressure-released” type, also referred to as the “pressure-off-brake” (“POB”) type, for reasons which will become apparently subsequently. 
     Operably associated with the swashplate  17  is a swashplate actuator, generally designated  23 , including a fluid pressure actuated piston  25  which is linked to the swashplate  17  by any suitable means, such that reciprocation of the piston  25  changes the tilt angle of the swashplate  17 . The piston  25  is biased to the left in FIG. 1 by a spring  27 , toward the maximum displacement position of the swashplate  17  shown in FIG.  1 . Disposed adjacent the spring  27  is a stop piston  29  which is biased to the left in FIG. 1 by fluid pressure in a chamber  31 , as will be described in greater detail subsequently. At the opposite end of the swashplate actuator  23  is another pressure actuated piston  33 , including an actuator portion  35 , the function of which will be described subsequently. 
     The piston  25  can be biased to the right in FIG. 1, from the position shown, by fluid pressure communicated to a chamber  37 , by means of a conduit  39 , from the outlet of a displacement control valve, generally designated  41 . The displacement control valve  41  includes a valve spool  43  which is biased downward in FIG. 1 by a spring  45 , and by fluid pressure communicated into the spring chamber from a conduit  47 . The conduit  47  is teed into a conduit  49 , by means of which fluid flowing out of the outlet port of the motor  15  is communicated to a flow limiter assembly, generally designated  51 . The valve spool  43  is driven upward, in opposition to the force of the spring  45  and the pressure in the spring chamber, by fluid pressure in a conduit  53 , which is teed into the conduit  13 . Thus, the fluid pressures in the conduits  53  and  47  provide a “load sense” signal to the opposite ends of the valve spool  43 , i.e., a fluid pressure differential representative of the load on the motor  15 . 
     Disposed in the conduit  13  is a shut off valve  55  which is preferably a valve of the ON-OFF type, shown in FIG. 1 as being spring biased to the OFF (blocked flow) By position. The OFF position provides a hydraulic lock on the motor  15 , when the motor is under load and the swashplate  17  is “positively” displaced from neutral (i.e., in the direction shown in FIG. 1) The shut off valve  55  is driven toward the ON (flow permitted) position by pressure in a conduit  57 , which extends upstream, by means of a conduit  58 , to the output of a shuttle valve  59 . The output of the shuttle valve  59  is also connected to a conduit  61  which communicates with a brake control valve  63 , the valve  63  preferably being a solenoid operated valve. Communication between the brake control valve  63  and the brake assembly  21  is by means of a conduit  65 . 
     Disposed between the conduits  57  and  58  is a pilot operated pressure maintaining valve  67  which is driven by a pilot pressure from the conduit  58  to the position shown in FIG. 1, communicating conduit  58  to conduit  57 . The pressure maintaining valve  67  is spring biased in the opposite direction, in the absence of a predetermine level of the pilot signal, toward a position in which the conduit  57  would be drained to a conduit  69 . The conduit  69  is teed into a conduit  71 , which is in open communication with a system reservoir R. The conduit  69  is also in communication with a return port  70  of the displacement control valve  41 . 
     In communication with the conduit  13  is a pair of conduits  73  and  75 . The conduit  73  communicates with a solenoid operated flow selector valve  77 , shown in FIG. 1 as being spring biased to a position in which an adjacent conduit  79  is communicated to the conduit  71 , and thus to the system reservoir R. The conduit  79  is teed into a conduit  81 , which communicates with an inlet port  83  of the displacement control valve  41 . 
     The conduit  75  communicates with the inlet of a solenoid operated extend control valve  85 , while the conduit  75  communicates by means of a conduit  87  to the inlet of a retract control valve  89 . It should be understood by those skilled in the art that the use herein of the terms “extend” and “retract” are not meant to limit the invention, but instead, are by way of explanation, in reference to moving the aircraft flap in either one direction (to extend it) or in another position (to retract it). By way of further explanation, the position of the flap designated F 1  in FIG. 2 is the fully retracted position, the position designated F 2  is an intermediate, extended position, and the position designated F 3  is the fully extended position. 
     The solenoid operated brake control valve  63 , the flow selector valve  77 , the extend control valve  85 , and the retract control valve  89  are all operated by appropriate electrical signals, typically provided by the vehicle or aircraft microprocessor. For simplicity, actuation of any one or more of the valves will be described as occurring in response to an electrical input signal  91 , the electrical leads representing the signal  91  being illustrated in conjunction with only the brake control valve  63  in FIG.  1 . 
     Referring still primarily to FIG. 1, the output of the extend control valve  85  is connected to one inlet  93  of the shuttle valve  59 , while the outlet of the retract control valve  89  is connected to another inlet  95  of the shuttle valve  59 . Teed into the inlet  95  is a conduit  97 , and teed into the conduit  97  is a conduit  99 , communicating pressure to the left end of the pressure actuated piston  33 , the operation of which will be described subsequently. The conduit  97  extends downward in FIG. 1 to the flow limiter assembly  51 , and the pressure in the conduit  97  serves as a pilot pressure tending to drive a piston  98  in an upward direction, the piston  98  in turn driving a flow limiter sense valve  101 . The valve  101  controls the amount of flow in the conduit  49  which bypasses a fixed orifice  103 , and the pressure drop across the orifice  103  and the conducting orifice in the valve  101  is used to control the position of a flow limiting valve  105 . As the pressure drop across the combined orifices in  101  and  103  increases, the flow limiting valve  105  is driven upwardly, in opposition to the biasing force of a spring  107 , to further limit the outlet flow from the motor  15 , through the conduit  49 . Those skilled in the valve art will understand that the larger combined orifice flow area allows a higher flow through the valve  105 . Increasing the restriction to flow through the conduit  49  increases the pressure in the conduit  47 , thus tending to bias the displacement control valve  41  downward, toward a position permitting communication from the inlet  83  to the conduit  39 , thus tending to move the pressure actuated piston  25  to the right in FIG. 1, corresponding to a reduced displacement of the swashplate  17 . 
     With reference now to all of the drawings, the operation of the aircraft flap drive system of the present invention will be described. It will be assumed that an aircraft flap F is initially in the fully retracted position F 1  (see FIG.  2 ). Before any motion of the flap F commences, all of the solenoid type control valves  63 ,  77 ,  85  and  89  are spring biased to the positions shown in FIG. 1, with the solenoids de-energized. In addition, the shutoff valve  55  is in the OFF or closed position shown in FIG. 1, and the flow limiter sense valve  101  is in the low flow position shown in FIG.  1 . Before movement of the flap commences, the flap is being held in the fully retracted position F 1  by the brake assembly  21 , which is applied, in the absence of system pressure in the conduit  65 . 
     In order to extend the flap F away from the fully retracted position F 1  toward an extended position (such as position F 2  in FIG.  2 ), the solenoids of the flow selector valve  77  and the extend control valve  85  are energized, such that pressurized fluid is communicated from the pump  11  through the conduits  73  and  79  to the inlet  83  of the displacement control valve  41 . At the same time, pressurized fluid is communicated through the conduit  75 , and through the valve  85 , to the inlet  93  of the shuttle valve  59 , and from there through the conduit  61  to the inlet of the brake control valve  63  which briefly remains in the closed position as shown. With pressurized fluid being communicated through the shuttle valve  59  to the conduit  61 , there is also pressure in the conduit  58  which pilots the pressure maintaining valve  67  to the position shown in FIG. 1, communicating pressure to the conduit  57 . Pressure in the conduit  57  biases the shutoff valve  55  downward in FIG. 1, opening communication from the pump  11  to the conduit  13  and from there to the inlet of the motor  15 . 
     At the same time, the fluid pressure in the conduit  79  biases the flow limiter sense valve  101  in a downward direction to the high flow, extend position H E . The pressure in the conduit  13  biases the displacement control valve  41  upward, through conduit  53 , in opposition to the force of the spring  45 , draining the conduit  39  through the return port  70 , and from there to the system reservoir R. With the chamber  37  of the swashplate actuator  23  thus being drained, the spring  27  biases the pressure actuator piston  25  to the left in FIG. 1, to the maximum displacement position of the swashplate  17 . Next, the electrical input signal  91  is communicated to the brake control valve  63 , opening the valve  63  and permitting communication from the conduit  61  to the conduit  65 , thus releasing the brake and permitting the motor  15  to begin to rotate its output shaft  19 , and to begin to move the flap from the fully retracted position F 1  toward a position of at least some extension. 
     As the flow through the motor  15  and out through the conduit  49  reaches a predetermined flow limit, the pressure drop across the fixed orifice  103  and the high flow orifice H E , begins to increase and, as was explained previously, the pressure drop across the combined orifices will bias the flow limiter valve  105  upward in FIG. 1, restricting flow through the conduit  49  and building up a back pressure in the conduit  47 , thus biasing the displacement control valve  41  downward toward a position opening up communication between the inlet  83  and the conduit  39 . For fairly light loads on the flap, the displacement of the swashplate  17  may already have been biased toward the minimum displacement position. As pressurized fluid is communicated into the conduit  39 , and then into the chamber  37 , the piston  25  is biased to the right in FIG. 1 in opposition to the force of the spring  27 , moving the swashplate  17  toward a minimum (E MIN ) position. This minimum displacement position of the swashplate  17  is determined by the design and configuration of the stop piston  29  which is biased to the left in FIG. 1 to the position shown by pressure in the chamber  31 , which would typically be the pump output pressure in the conduit  75 , as shown in FIG.  1 . 
     As the flap moves from the fully retracted position F 1  toward the fully extended position F 3 , as shown in FIG. 2, the load on the flap, and therefore the load on the motor  15  increases (see also the graph of FIG.  3 ). An increasing load on the motor  15  may be seen in an increasing pressure differential from the conduit  13  to the conduit  49 , thus providing a “load sensing” type of control whereby the displacement of the motor will increase with increasing load and decrease with decreasing load. Those skilled in the flap actuator art will understand that the above statement is true only in regard to operation in the extend mode, in which the loads on the flap inherently oppose the actuation forces applied by the control system. On the other hand, in the retract mode, the loads on the flap are in the same direction as the retraction forces applied by the control system. Thus, in the retract mode, the swashplate actuator  23  merely has a fixed position (see “Ret.” in FIG.  1 ). 
     At some predetermined angle before the flap reaches its desired position, the system will begin to operate in accordance with the following sequence. First, the solenoid of the flow selector valve  77  is de-energized, thus draining the conduit  79  to the system reservoir R, and permitting the flow limiter sense valve  101  to be biased upwardly to the low flow position shown in FIG. 1, blocking the high flow orifices, and reducing the flow through the valve  105 . With the conduits  79  and  81  drained to tank, the conduit  39  is also drained to tank, thus insuring that the piston  25  moves to the left in FIG. 1 to the maximum displacement position of the swashplate  17 . Thus, the motor  15  operates at its lowest speed as the desired stopping point is approached, and the solenoids of the extend control valve  85  and brake control valve  63  are both de-energized. The result is that the conduit  65  is drained to tank and the brake assembly  21  is applied, stopping the rotation of the output shaft  19 . At the same time, the fluid pressure in the inlet  93  and in the conduit  61  is drained to tank. Thus, the flap comes to a stop, at some desired, extended position. 
     As noted previously, the load on the flap during the retract mode is normally much lower than the load on the flap during the extend mode. During the retract mode, the motor  15  may be set for relatively lower power and flow consumption. Therefor, in accordance with one aspect of the invention, retracting the flap is not merely the same process as extending the flap, except in reverse. Instead, the use of a pump  11  which is fixed displacement and a motor  15  which is variable displacement requires that retraction of the flap occur in response to the swashplate  17  of the motor being displaced “over-center”, i.e., such that, as the motor  15  continues to receive pressurized fluid from the conduit  13 , the direction of rotation of the output shaft  19  is reversed, and the flap is retracted. The retraction sequence will now be described. 
     First, the solenoids of the flow selector valve  77  and the retract control valve  89  are energized, thus communicating pressurized fluid through the conduits  73 ,  79  and  81  as described previously and through the conduit  75  as described previously but now also through the conduit  87  and the valve  89  to the inlet  95  of the shuttle valve  59 . With pressurized fluid in the inlet  95 , there is also pressure in the conduit  97  which is communicated to the lower end of the flow limiter sense valve  101 , acting as a pilot signal as was described previously, biasing the piston  98  upward as a mechanical stop. The pressure in the conduit  79  biases the valve  101  downward to an intermediate high flow, retract position H R . In this position H R , the valve  101  provides some bypass around the fixed orifice  103 , but less than in the extend position H E.    
     Pressurized fluid at the inlet  95  results in pressure in the conduits  61  and  58  and, as was described previously, pressure in the conduit  58  biases the pressure maintaining valve  67  to the position shown in FIG. 1, thus providing pressure in the conduit  57  to move the shutoff valve  55  to the ON (open) position, such that pressure is communicated from the pump  11  through the conduit  13  to the inlet of the motor  15 , in the manner described previously. Pressure at the inlet of the motor will again be communicated through the conduit  53  to bias the displacement control valve  41  in an upward direction in FIG. 1 to a position in which an LVDT  109  is actuated, to indicate pressure as being communicated to the motor. 
     The fluid pressure at the inlet  95  of the shuttle valve  59  and in the conduit  97  is communicated through the conduit  99  to act on the left end of the pressure actuated piston  33 . By means of the actuator portion  35 , the piston  33  moves to the right in FIG. 1, then engages the left end of the piston  25  and biases the piston  25  to the right in FIG. 1 until the piston  25  engages the left end of the stop piston  29 . The fact that the piston  33  is substantially larger than the piston  29  enables the pressure acting on the piston  33  to “overpower” the stop piston  29 , moving the piston  25  and the piston  29  until the piston  29  is bottomed out in the chamber  31 . Thus, the swashplate  17  moves over-center to a predetermined swash angle, and remains in that swash angle, such that during the entire retract movement of the flap, the displacement of the motor  15  is effectively “fixed”. 
     Next, the solenoid of the brake control valve  63  is energized, moving the valve  63  downward in FIG. 1 to pressurize the conduit  65  and release the brake assembly  21 . With the brake released, the motor accelerates, and as flow out of the motor through the conduit  49  reaches the setting of the flow limiter assembly  51 , the outlet flow is limited as described previously and the motor flow remains fairly constant during the high speed portion of the retraction of the flap. 
     While the flap is being retracted, as it approaches the desired position, the solenoid of the flow selector valve  77  is de-energized, thus draining the conduits  79  and  81  to tank and moving the flow limiter sense valve  101  upward to the low flow position shown in FIG. 1, as was described previously. The result will be a smaller pressure drop across the motor  15 , and a smaller flow through the motor, thus reducing motor output speed. 
     Once the desired position of the flap has been achieved, the solenoids of the brake control valve  63  and retract control valve  89  are de-energized, thus draining the conduit  65  and permitting the brake assembly  21  to be engaged, stopping any further rotation of the output shaft  19 . At the same time, the shutoff valve  55  again moves to its OFF (closed) position shown in FIG. 1, and the chamber  37  and conduit  39  are drained, as are the conduits  97  and  99  (through the valve  89 ). With all of these various conduits and chambers drained to tank, the swashplate actuator  23  again moves to the maximum displacement position shown in FIG.  1 . 
     Referring now to the graphs of FIGS. 3 through 5, certain advantages of the present invention will become apparent. The solid line in the graph of FIG. 3 represents the load on the flap F as it moves from the fully retracted position F 1  to the fully extended position F 3 . The drop-off in the flap load near the position F 3  is merely the result of the inherent mechanical advantage in the linkage of the subject embodiment. The purpose of the FIG. 3 graph is to illustrate that, whereas the prior art fixed displacement motor must be sized to match the maximum load on the flap (i.e., the full break-out torque at peak load position), the variable displacement motor  15  of the invention can vary anywhere between the lower and upper load limits (dashed lines) to match the instantaneous load on the flap. 
     In FIG. 4, using the fixed motor of the prior art, the speed of the flap varies generally inversely proportional to the load on the flap. The same is true with regard to the variable motor of the invention, such that the total area under the two curves is identical, indicating equal “travel time” for the fixed and variable motors to move the flap from the position F 1  to the position F 3 . 
     The advantage of the invention is seen in the graph of FIG. 5, showing Flow Rate through the motors, as a function of flap position. It may be seen in FIG. 5 that whereas the fixed motor must be sized for a relatively large flow, the variable motor of the invention may be sized substantially smaller, thus making it possible to meet the objects of the invention, as stated in the BACKGROUND OF THE DISCLOSURE. By way of example only, in developing the present invention it was found that, for a particular system, whereas a fixed motor capable of outputting 32 g.p.m. had been required, the system of the invention made it possible to utilize a variable displacement pump having a peak output flow rate of only 24 g.p.m. The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.