Apparatus for controlling a fuel injected engine driving a variable pitch propeller
Unlted States Patent 1191 1111 3,876,329  
 Miller 1 1 Apr. 8, 1975 15 1 APPARATUS FOR CONTROLLING A FUEL 1536,1551 1/1951 Chamberlin v. 4l6/28 INJECTED ENGINE DRIVING A VARIABLE 21:32; r l umba.  
  exan fSO11..... PITCH PROPELLER 1796.136 6/1957 Mock 416/29 Inventor: Daniel F. Miller, Beliot, Wis.  
 Assignee: Woodward Governor Company,  
 Rockford. 111.  
 Filed: Aug. 31, 1973 Appl. No.: 393,311  
 US. Cl 416/28; 416/29 Int. Cl. B64c 11/32 Field of Search 416/29, 28, 27, 30  
 References Cited UNITED STATES PATENTS 1,497 (1/1946 Mercier 416/29 1,244 9/1950 Moore 416/28 Primary Examiner-Clarence R. Gordon Atmmey. Agenl, or Firm-Wolfe, Hubbard. Leydig, Voit &amp; Osann 157] ABSTRACT 10 Claims, 4 Drawing Figures PHEHTEE AFR 81875 MAI/F010 fiiifflei VJ 007/705 14/16 7167112 g Z Z 2 g Z .5 Z: W W W W M WM MW WM APPARATUS FOR CONTROLLING A FUEL INJECTED ENGINE DRIVING A VARIABLE PITCH PROPELLER BACKGROUND OF THE INVENTION This invention relates to apparatus by which the pilot of an aircraft may control the power output of an internal combustion engine connected to drive a variable pitch propeller. Such an engine is conventionally equipped with a governor which may be manually set to establish a selected engine speed and which keeps the engine turning at substantially the selected speed under varying flight conditions by adjusting the pitch of the propeller to change the load on the engine. The engine further includes a throttle which may be manually adjusted to change the flow ofcombustion air to the engine. When the engine is running at a given speed and the throttle is opened manually. the pressure in the in take manifold of the engine is increased and the mass flow of fuel and air to the engine also in increased to cause the engine to develop more power.  
  For a giv en engine to develop a given power while still operating safely and economically. the governor and the throttle should he set to cause the engine to run at a particular speed and a particular manifold pressure for each different power level at which it is desired to operate the engine. the particular values being specified by the engine manufacturer. Thus. for each power le\el. there exists a recommended engine speed which the pilot may establish by setting the governor and which remains constant regardless of changes in ambient conditions. Manifold pressure to maintain the set power. however. is dependent not only upon the throt tle setting and engine speed but also upon the pressure of the ambient atmosphere in which the aircraft is flying. Thus. with the engine at given speed and throttle settings. manifold pressure decreases as ambient pressure decreases when the aircraft increases altitude. If the throttle setting is not changed to compensate for the effects of ambient pressure. the engine will not develop power at the desired level.  
  Accordingly. the engine manufacturer recommends that the throttle he adjusted to establish different mani&#39; fold pressures at different altitudes. When altitude is increased. the throttle is opened to pre\ent the mattifold pressure front dropping off sharply but. with pro gressive increases in altitude. is opened to such positions as to establish progressively lower manifold pressures.  
  The engine nninufacturcr also recommends that different manifold pressures be maintained for different ambient temperatures. With progressive temperature increases. the throttle should be opened to establish progressively higher manifold pressures.  
  More particularly. the present invention relates to control apparatus for fulfilling the same general purposes as the control apparatus disclosed in Meyer U.S. application Ser. No. 329.211. filed Feb. 2. 1973 and now abandoned. said application being assigned to the assignee of the present invention. Such apparatus simplifies the tasks of the pilot by enabling the pilot to adjust a single control member to select a desired power level and. as an incident to such adjustment. to automatically establish the correct speed and throttle settings neccssary to properly achieve the desired power level at any temperature or altitude. As a result of the single control member. the pilot is relieved of the hurden of first determining the proper speed and throttle settings for a given power level. temperature and altitude and then manipulating individual controls to establish these settings.  
 SUMMARY OF THE INVENTION The general aim ofthe present invention is to provide new and improved single member control apparatus which is simpler in construction than prior apparatus of the same general type and which. at the same time. more accurately establishes the proper manifold pressure.  
  A more detailed object is to provide novel control apparatus which sets and adjusts the throttle as a function of manifold pressure so that the recommended manifold pressures can be followed more accurately than is the case when the throttle is adjusted to predetermined positions estimated to produce the proper manifold pressure.  
  An important object of the invention is to provide unique single member control apparatus which is especially suitable for use with engines having fuel injection systems.  
  A related object is to provide control apparatus in which flow of fuel to the engine is scheduled directly as a function of the position of the control member. the throttle being uniquely controlled to cause mixing of the proper amount of combustion air with the fuel and to establish the proper manifold pressure.  
  Another important object is to automatically reduce the flow of fuel to the engine when the aircraft is flying at such high altitudes that the manifold pressure for obtaining the desired power level cannot be maintained.  
  Still another object is to provide means with which the pilot may optionally select an engine speed diffen ent from the recommended speed while still maintaining the same power level.  
  These and other objects and advantages ofthe invention will become more apparent from the following de tailed description when taken in conjunction with the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic view schematically showing one embodiment of the new and improved control apparatus of the present invention associated with an exemplary aircraft engine.  
  FIG. 2 is a family of curves which show the recommended manifold pressures for various ambient pressures and various constant power levels.  
  FIG. 3 shows several families of curves which illustrate the recommended relationship between outside air temperature and manifold pressure at various power levels and altitudes.  
  FIG. 4 is a diagrammatic view showing another embodiment of the control apparatus.  
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of illustration. the invention is shown in the drawings as embodied in apparatus for controlling a prime mover which herein is a reciprocating piston internal combustion engine 16 of the type commonly used in an aircraft to rotate a variable pitch propeller I7. The engine includes a conventional governor I9 which responds to changes in the engine speed brought about by varying flight conditions such as fluctuations in air speed and density. In response to such changes. the governor causes actuation of a hydraulic servomotor to increase or decrease the propeller blade angle and thus adjust the load on the engine so that the load will keep the engine running at a constant desired speed at a given horsepower setting which is selected by the pilot to suit flight conditions.  
  The governor 19 includes a rotatable head 21 driven by the engine 16 and pivotally supporting flyballs 23 which are connected to a rod 24 urged downwardly by an adjustable speeder spring 25 and actuating a valve (not shown) for regulating the flow of pressure fluid to and from the servo 20. The speed ofthe engine is maintained at a constant desired value determined by the adjustment of the speeder spring. such adjustment being effected by moving a speed setting control element 26 whose position may be adjusted manually by the pilot from inside the cockpit. A gage (not shown) is located in the cockpit to enable the pilot to deter&#39; mine the engine speed.  
  in this instance. the engine 16 is equipped with a fuel injection system with which fuel is delivered into the individual cylinders through injection nozzles (not shown) communicating with fuel lines 30 which. in turn. communicate with a divider valve 31. An enginedrivcn pump 33 delivers fuel to the divider valve through a line 34 at a rate determined primarily by the position ofa rotary metering valve 35 which may be adjusted manually by the pilot.  
  Air for supporting combustion of the fuel is admitted into the intake manifold 36 ofthe engine [6 through an air intake unit 36a having a pivoted butterfly valve 37 which constitutes the throttle of the engine. By manually opening and closing the throttle 37, the pilot may increase and decrease the mass rate of flow of the fuelair mixture and thereby increase and decrease the power developed by the engine. As the throttle 37 is opened and closed. the pressure in the intake manifold 36 increases and decreases. respectively. such pressure being reflected on a gage {not shown) in the cockpit and. when taken with engine speed and fuel flow. providing a measure of the power developed by the engine.  
  If the throttle 37 is at a given setting. the manifold pressure will change when the engine speed is changed and also will change as an incident to changes in the pressure of the ambient atmosphere. That is. if engine speed is reduced. it is necessary to open the throttle and raise the manifold pressure in order to maintain the same power at the reduced speed. When ambient pressure decreases as a result of an increase in altitude. manifold pressure will decrease unless the throttle is opened to compensate for the decreased pressure of the atmosphere. Also. the throttle should be adjusted as the temperature of the ambient atmosphere changes and should be o ened to a greater degree at higher temperatures so as to establish higher manifold pressures and prevent power from dropping off.  
  In order to enable the engine 16 to operate safely and with peak fuel economy at a given power output. the engine manufacturer specifies that the pilot establish a particular engine speed and a particular manifold pressure for each power level at which the pilot desires to run the engine. For one particular engine. the recommended engine speeds and manifold pressures for each power level are shown by the curves of FIGS. 2 and 3. From the curves. it will be seen that a different speed is specified for each different power level but that each speed is of constant value regardless of ambient pressure and temperature. The specified manifold pressure. however. varies as a function of ambient temperature and pressure since different manifold pressures are required to maintain the same power level at different temperatures and altitudes. As shown by the curves. the engine manufacturer specifies progressively higher manifold pressures at progressively higher temperatures and specifies progressively lower manifold pressures for progressively lower ambient pressures. the recommended manifold pressure thus drooping off as altitude is increased and ambient pressure decreases.  
  With most propeller-driven aircraft, the pilot must decide upon the power level and altitude he wishes to maintain and then consult tables. curves or the like to determine the speed and manifold pressure which are specified for the selected power level and altitude and for the then-existing outside temperature. The pilot then must manually set individual controls to set the speed control element 26 and the throttle 37 to the proper positions to maintain the specified speed and manifold pressure. lf the pilot wishes to change altitude while still maintaining the same power level. he must determine the new manifold pressure and then re adjust the throttle to establish the new pressure. Similarly. the throttle should be adjusted if the outside temperature changes by any significant extent.  
  Like the control apparatus disclosed in the aboveidentified Meyer application. the present apparatus simplifies the tasks of the pilot by enabling him to select a desired power level simply by positioning a single adjustable control member 40. As an incident to positioning the control member 40 of the present apparatus. the speed control element 26 is adjusted to establish the specified speed for the selected power level and. at the same time. the throttle 37 is automatically adjusted to establish the manifold pressure which is specified for the particular power level. altitude and temperature. If either altitude or temperature changes. the throttle is automatically adjusted to establish the manifold pressure at the value specified for the changed conditions.  
  The present invention contemplates the provision of new and comparatively simple single member control apparatus which is particularly adapted for use with engines [6 of the fuel injected type and which sets the throttle 37 in such a manner as to make the actual manifold pressure of the engine more accurately corre spond to the value specified by the engine manufacturer. With the present apparatus. both the speed of the engine and the rate of fuel flow are normally scheduled directly as a function of the position of the control member 40. Adjustment of the control member also initiates movement of the throttle to change the manifold pressure and. in carrying out the invention. the ac tual manifold pressure is sensed in order to cause the throttle to be set in a position in which the actual manifold pressure corresponds to the specified pressure. In order that the pressure and temperature of the ambient atmosphere may be taken into account in establishing the manifold pressure. provision is made to sense ambient pressure and temperature and to properly adjust the throttle for different ambient conditions.  
  More specifically. the control member 40 (hereinafter called the power member) is in the form of an elongated rod whose outer end carries a fixed knob 41. The inner end of the power member is pivotally connected at 43 to the lower end of an upright lever 44 whose upper end is supported to swing about a normally fixed pivot 45. An elongated link 46 is connected at its inner end to the lever 44 and is connected at its outer end to the speed control element 26 of the governor 19. As the power member is pushed inwardly or forwardly lie. to the right in FIG. I the speed control element is swung in a clockwise direction to increase the speed setting of the governor. The ratio of the linkage between the power member 40 and the speed control element 26 is such that movement of the power member to each of its various power level positions sets the governor at the speed recommended for that power level. Thus. for the present engine. movement of the power member to tis power position establishes a speed of ZIUO RPM. movement of the power member to its 5571 power position establishes a speed of 2233 RPM and so on.  
  To schedule fuel flow as a function of the position of the power member 40. an arm 47 is coupled to the power member 40 by a pin-and-slot connection 49 and is connected to a fuel control element which herein is shown as being a rotatably supported shaft 50. The shaft 50 is connected to the fuel metering valve 35 and rotates the valve as the power member is moved inwardly and outwardly. inward movement of the power member serving to move the valve clockwise to increase the rate of fuel flow.  
  In order to keep the fuel flow at the rate scheduled by the power member 40. a constant pressure drop is maintained across the inlet and outlet of the metering valve 35 so that the flow rate through the valve is directly related to the position of the valve. For this purpose. a differential pressure valve Sl is located between the fuel pump 33 and the fuel metering valve 35 and includes a chamber which is divided into two compartments 53 and 54 by a flexible diaphragm 55 carrying a valve member 56 having spaced lands 57 and 59. Pump pressure PI is transmitted to the compartment 53 and to one end of the land 59 and is opposed by a spring 60 in the compartment 54 and by the fuel discharge pressure P2 in the line 34. If the pump pressure Pl rises. the valve member 56 is moved to the right to cause the land 57 to open up a bypass port M and divert fuel away from the metering valve 35 and back to the fuel tank through a return line 63. Conversely. a rise in the fuel discharge pressure P2 moves the valve member to the left to close offthe bypass port 6| until the pump pressure Pl rises to a sufficient value to maintain the desired constant pressure drop across the fuel valve 35. the particular drop being determined by the degree of compression in the spring 60. Accordingly. when the spring 60 is set with a given compression. the rate of fuel flow to the engine [6 is directly related to the position of the fuel valve 35.  
  When the aircraft is taking off and climbing. it is desirable to supply additional fuel to the engine 16 for cooling purposes but to supply such additional fuel without changing the position of the fuel valve 35 as scheduled by the power member 40. This is achieved through the provision of a mixture control member whose inner end is pivotally connected to a lever 66 which. in turn. is connected to a rod 67. The spring 60 is compressed between the rod 67 and the diaphragm 55 and thus. when the rod is moved to the left. the compression in the spring is increased so as to shift the valve member 56 to the left and increase the flow of fuel to the fuel metering valve 35 so that more fuel is delivered to the engine even though the position of the fuel valve is not changed. Movement of the rod 67 to the right causes the spring 60 to relax to reduce the fuel flow to the engine.  
  As shown. the mixture control member 65 includes two detent notches 69 and 70 which coact with a spring-loaded detent 71 to hold the mixture member in different positions. When taking off and climbing. the pilot may push the mixture member inwardly until the detent 7] seats in the notch 69 and. with the mixture member in this position. the differential pressure valve 51 is set to deliver the desired additional fuel to the engine. After cruising altitude has been reached, the mixture member may be pulled outwardly to seat the detent in the notch 70 and set the differential pressure valve 51 to establish the proper pressure drop for cruising solely under the control of the power member 40.  
  By pulling the mixture member 40 outwardly sufficiently far to seat the detent 71 in a third notch 73. the pilot may shift the valve member 56 to the extreme right to cause the land 57 to fully open the bypass port 61 and the land 59 to fully close the passage leading to the fuel valve 35 and thereby cut off the flow of fuel to the engine 16 and unload the pump 33. As the mixture lever is pulled outwardly to its cut-off position. a button 75 on the end of the rod 67 engages an extension 76 on the diaphragm 55 and shifts the valve member 56 to the right.  
  Movement of the throttle 37 is effected by a throttle servo 80 having a piston 81 slidable in a cylinder 83 and connected to the throttle by means of a pivoted linkage 84. As pressure fluid is admitted into the left end of the cylinder through a line 85. the piston 81 is shifted to the right to open the throttle. When pressure fluid is dumped from the left end of the cylinder. a spring 86 shifts the piston to the left to close the throttle.  
  The throttle servo 80 is controlled by a pilot valve 87 having a valve spool 89 which is adapted to slide downwardly within a bore 90 to connect the servo line 85 with a line 9l leading to a source of pressure fluid such as the pump 33. With the valve spool 89 in its downward position. fuel under pressure is delivered to the throttle servo 80 to open the throttle 37. When the valve spool is shifted upwardly from the position shown in FIG. I. the servo line 85 communicates with a drain line 93 and thus the throttle piston 81 may return to the left to close the throttle.  
  ln keeping with the invention. movement of the power member 40 to a selected power level position serves to adjust the pilot valve 87 to change the setting of the throttle 37 and establish the manifold pressure which is specified for the selected power level. the throttle being moved until the actual manifold pressure corresponds to the pressure dictated by the position of the power member and by ambient pressure and temperature. For these purposes. the arm 47 carries a throttle control element in the form of a cam 94 which rides against a roller follower 95 located at the upper end of a compression spring 96 whose lever end bears against the upper end of the spool 89 of the pilot valve 87. As the power member 40 is pushed inwardly to in crease power. the cam 94 is rocked clockwise and acts through the follower 95 and the spring 96 to shift the valve spool 89 downwardly and cause opening of the throttle to increase the manifold pressure. The cam is shaped to schedule the manifold pressure at values which are properly correlated with the engine speeds ttahlished at different positions of the power member 0. As the cam is adjusted. at pressure signal is transmit- :d from the intake manifold 36 to the pilot valve 87 to ause the throttle to assume a position establishing the etual manifold pressure at a value which corresponds v the commanded value.  
  To transmit the manifold pressure signal. a line 97 :ads from the manifold 36 to a chamber 99 which ouses an evacuated bellows 100 connected to the user end of the valve spool 89 and sealed from the alve bore 90 by a second bellows 101. the latter com iunicating with the drain line 93 through a passage 03 in the valve spool and being filled with fuel at drain ressure. As manifold pressure increases and reases. the bellow I00 contracts and expands. respecvely. to shift the valve spool 89 upwardly and downardly. Accordingly. as the cam 94 is adjusted to shift 1e valve spool downwardly and open the throttle. the ianifold pressure increases and acts through the beliws 100 to cvert a progressbely increasing upward \rce on the valve spool. When the manifold pressure icreases to a sufficient value that the upward force ex rted on the lower end of the spool balances the downard force e\erted on the upper end of the spool. the itter ts moved to its centered position shown in FIG. and the throttle 37 is stopped in a position in which :ie actual manifold pressure coincides \\ith the comianded pressure. l hus. movement of the power memer 40 does not cause the throttle to move to a particuir predetermined position but instead causes the throtlc to move until the commanded manifold pressure is ctually established. Asa result. the manifold pressure pecified for a given power level can be accurately set nd maintained.  
  lf the cam 94 is in a given position and the altitude f the aircraft is increased. the manifold pressure dereases as a result of the decreased pressure of the air t the higher altitude. As the manifold pressure dc reases. the bellows I00 evpands and shifts the valve pool 89 downwardly to cause opening of the throttle B7 to obtain the proper manifold pressure. in order to chieve the recommended manifold pressure at the iigher altitude. however. the throttle should not open o far as to bring the manifold pressure back up to its iriginal value. Instead. the throttle should open to a poition establishing a manifold pressure slightly lower han that maintained at the lower altitude. in other rords. the throttle should be positioned to cause maniold pressure to droop at higher altitudes as indicated w the curves shown in FIG. 2. in order to provide such lroop. a bellows 105 which is open to the atmosphere s attached to the upper end portion of the valve spool l9 and is surrounded by a chamber I06 communicating vith the drain line 93 through the passage 103 and illed with fuel at drain pressure. The bellows 101 and 05 serve to seal the ends ofthe valve bore 90 and both ire of equal area so that internal fuel pressure changes lave no effect on the position of the valve spool 89.  
  As the altitude of the aircraft increases and the presure and density of the ambient atmosphere decrease. he bellows )5 tends to contract to raise the valve pool 89. As manifold pressure decreases the bellows .00 tends to lower the valve spool to restore the maniold pressure to its original value but. because of the imbient pressure bias applied by the bellows 105, the nanifold pressure droops and actually takes on a value lightly lower than its original value. The bellows 105 is of smaller area than the bellow I00 and the effect of ambient pressure on manifold pressure is proportional to the ratio of the areas. By properly sizing the bellows I00 and I05. the manifold pressure may be made to droop substantially in accordance with the curves of FIG. 2.  
  To adjust the manifold pressure automatically in response to changes in outside temperature. a cantilevered bimetallic strip I07 is shown as being sandwiched between the compression spring 96 and the upper end of the valve spool 89. As temperature increases, the bimetallic strip flexes downwardly and applies a downward bias to the valve spool so as to open the throttle 37 and cause the manifold pressure to increase substantially in accordance with the curv es shown in FIG. 3. If temperature decreases. the bimetallic strip flexes upwardly and reduces the spring pressure on the valve spool 89. The throttle thus closes to lower the manifold pressure.  
  From the foregoing. it will be apparent that the pres ent invention brings to the art new and improved control apparatus in which a single power member 40 schedules speed and fuel flow directly as a function of the position in which the power member is set. The power member also schedules manifold pressure in accordance with speed and fuel flow while the bias applied by the pressure and temperature sensors I05 and 107 scrv es to trim the manifold pressure so as to establish the latter at the values specified for various altitudes and temperatures. Accordingly. the pilot may select a desired power level simply by setting the power member and. as an incident to such positioning. speed. fuel flow and manifold pressure are automatically and accurately set at the values which are recommended by the engine manufacturer to develop the desired power at a given altitude and with a given temperature.  
  lf the power member 40 of the engine [6 is set for a given power level and the aircraft is flying at an altitude which lies to the right of the diagonal line (1 shown in FIG. 2. the atmospheric pressure is so low that the manifold pressure needed to maintain the desired power setting cannot be obtained even if the throttle 37 is fully opened. Lnder these circumstances. it is desirable to reduce the fuel flow to a rate below that scheduled b the position of the power member so that the actual fuel flow will be correlated with the reduced power which is actually obtained. Such reduction in fuel flow if advantageously achieved by bypassing some of the fuel in the engine line 34 to the drain line 93 by way of a line 108 communicating between the line 34 and a port 109 in the pilot valve 87. the port normally being closed by a land 109a on the valve spool 89. [f the atmospheric pressure is so low that the manifold pressure commanded by the position of the power member and by the outside temperature cannot be obtained. the valve spool 89 will shift downwardly to uncover the port I09 and allow some of the fuel to bypass the engine l6 and flow to the drain line 93. the extent of downward displacement of the spool being proportional to the difference between the commanded manf fold pressure and the actual manifold pressure. As a result. even when the selected power setting cannot be obtained. a fuel mixture ofthe correct fuel/air ratio will be delivered to the engine to avoid the wasting of fuel and to keep the engine operating under safe conditions. The bypass of the scheduled fuel also will occur during throttle bursts. some fuel being bled to drain until the manifold pressure reaches the new setting.  
  Means are provided to enable the pilot to trim the engine speed independently of the position of the power member 40 so that the pilot may maintain a given power while running the engine 16 at a speed of his own selection in order to achieve lowest noise conditions. best fuel economy and the like. Herein. these means comprise a manually adjustable speed trim member I I whose inner end is connected to the upper end ofthe lever 44 by the pivot 45. Normally. the speed trim member H0 is held in a cruise position shown in FIG. I by a spring-loaded detent III which seats in a notch 113 in the speed member. With the speed member 110 in the cruise position. the speed of the engine 16 is established in accordance with the position of the power member 40 and is scheduled with respect to power as shown by the can es of FIGS. 2 and 3. If the pilot wishes to develop the same power while running the engine at either a slightly faster or slightly slower speed. he may adjust the speed member 110 inwardly or outwardly. As an incident to such adjustment. the lever 44 is rocked about the lower pivot 43 an acts through the link 46 to change the setting of the speed control element 26 of the governor I).  
  When the speed ofthe engine 16 is trimmed. it is necessary to also adjust the manifold pressure in order to maintain the power called for by the position of the power member 40. For this purpose. a pivoted bellcrank H4 is connected between the speed trim memher I Ill and the upper end of an upright link 115 whose lower end is connected to a lever [[6 adapted to swing upwardly and downwardly about a fixed pivot H7. The bimetallic strip 107 is cantilevered on the inner end portion of the lever llfi and thus the force exerted on the upper end of the alve spool 89 by the compression spring 96 may be adjusted by swinging the lever upwardly and downwardly. If the pilot moves the speed member 110 inwardly to establish a speed slightly higher than dictated by the power member 40. the \al\c spool 89 is lifted to cause closing of the throttle 37 and lowering of the manifold pressure. Conversely. lowering of the speed by the speed trim member Ill) results in the valve spool being shifted downwardly to cause an increase in manifold pressure. Thus. with this arrangement. the manifold pressure is adjusted at the same time engine speed is trimmed so that the engine still will de\elop the power specified by the setting of the power member 40.  
  &#39;l he peed trim member also is used to enable the pilot to override the pilot valve 87 and manually control the throttle 37 in a direct manner if the bellows 100 and I should malfunction or if some other failure should occur in the control apparatus. As shown. a fin ger 120 is carried on the inner end ofthe lever I16 and underlies the upper end of the valve spool 89. When the pilot pushes the speed member [l0 inwardly sufficicntly far to seat the detent 111 into an override notch I21. the finger 120 is swung upwardly and lifts the valve spool 89 so as to port the left side of the throttle servo 80 to drain. Under this condition. the spring 86 shifts the throttle piston 8| to the left until the throttle linkage 84 stops against a screw I23. The latter is adjustably threaded into a plate 124 connected to an arm I which. in turn. is carried on the shaft 50. When the pilot valve 87 is overridden. the pilot may directly move the throttle 37 by adjusting the power member to turn the shaft 50 and cause the screw 123 to shift the throttle linkage 84 and change the throttle setting. In order to permit the throttle to be opened under direct manual control. the linkage 84 is attached to the throt&#39; tle piston 81 by a yieldable connection indicated generally by the reference numeral 126 and having a spring 126a enabling the linkage to move relative to the piston when manually adjusted. the spring 1261: also serving to bias the linkage against the screw 123. The adjusted position of the screw [23 determines the position of the throttle 37 at idle speed while fuel flow to the engine 16 at idle speed is determined by the position of a second adjustable screw 127 adapted to engage the plate 124 and limit the extent to which the power member 40 may be pulled outwardly.  
  Another embodiment ofa control apparatus is shown in FIG. 4 in which parts corresponding to those of the first embodiment are indicated by the same but primed reference numerals. In this instance. the member 110&#39; is not used to trim the speed of the engine 16&#39; during flight but instead is used to purge the prop servo 20&#39; of cold oil when the engine is first started on the ground during cold weather. By pulling outwardly on the member 110&#39; against the bias ofa spring [30. the speed setting of the governor l9 maybe reduced to such a value that all of the cold oil in the prop servo is dumped therefrom through the governor valve associated with the rod 24&#39;. The member Ill) then may be released inwardly to its position shown in FIG. 4 so as to increase the speed setting of the governor l6 and deliver warm oil to the prop servo 20&#39;. It will be noted that movcment of the member 110 has no effect on the position of the pilot valve spool 89&#39; since the control apparatus shown in FIG. 4 does not include a linkage correspond ing to the linkage 14. H5 and H6 ofthe control apparatus shown in FIG. 1. Accordingly. the member 110&#39; may change the speed setting ofthe governor 16&#39; without changing the setting of the pilot valve spool 89&#39;.  
  Like the control apparatus of the first embodiment. the control apparatus shown in FIG. 4 includes a mixture control member which may be used to cut off the fuel flow and to richen or lean the fuel-air mixture manually. The mixture control member 65. however. is moved from its normal cruise position shown in FIG. 4 only when special conditions dictate that the fuel-air mixture should be made richer or leaner. During take off and climb. an enrichment orifice 131 in the metering valve 35&#39; automatically richens up the mixture to provide for additional cooling of the engine. Accordingly. it is not necessary to move the mixture control member 65&#39; during normal take off and climb.  
  In the control apparatus shown in FIG. 4. the bellows [00&#39; is located directly in the manifold 36&#39; and is filled with a gas such as helium. When the temperature of the air in the manifold 36&#39; increases. the gas expands the bellows I00 to shift the pilot valve spool 89&#39; downwardly and cause the throttle 37&#39; to open and increase the manifold pressure. The bellows thus is responsive not only to the pressure but also the temperature of the air in the manifold so as to provide a comparatively accurate reflection of the temperature of the air entering the cylinders of the engine 16&#39;.  
  A further difference between the control apparatus shown in FIG. I and that shown in FIG. 4 resides in the manner of positioning the throttle 37&#39;. In the control apparatus shown in FIG. 4, the throttle is set directly by the power lever 40&#39; and then is trimmed by the throttle aervo 80&#39; in accordance with manifold pressure. ambirnt pressure and temperature. As shown. a linkage 140 s connected directly to the shaft 50&#39; and also is coniected at l4! to a differential lever 143. The latter is )ivoted intermediate its ends at I44 and is connected it its lower end to a linkage 145 which is connected to ;he throttle 37. When the shaft 50&#39; is rotated clock ivise by inward movement of the power member 40&#39;. lhL linkages I40 and 145 and the lever H3 cause the :hrottle to open.  
  If the position of the throttle 37&#39; as set by the shaft 50 does not establish the manifold pressure comnanded by the cam 94&#39; and by ambient pressure and :emperature. the pilot valve spool 89 is displaced and :auses the throttle servo 80 to adjust or trim the throtile until the commanded manifold pressure is reached. For this purpose. a link 146 is connected to the servo piston 8| and its outer end defines the intermediate pi\ot 144 for the differential lever [43. When the pis ton 8| is shifted by displacement of the valve spool 89&#39;. the link 146 causes the lever [43 to swing about the upper pivot 141 and adjust the throttle until the actual manifold pressure corresponds with the commanded value.  
 I claim as my invention:  
  1. Control apparatus for an internal combustion engine connected to drive a variable pitch propeller. said engine having:  
 a. a governor adjustable to different speed settings and operable to vary the pitch of the propeller to maintain the actual speed of the engine substantially in agreement with a set speed.  
 b. a fuel valve adjustable to different positions to regulate the rate of flow of fuel to the engine, and  
 c. a throttle adapted to be set in different positions to regulate the flow of combustion air to the engine and to adjust the manifold pressure of the engine.  
 said control apparatus including:  
 a. a speed control element which is operable when moved to change the speed setting of said governor.  
 b, a fuel control element which is operable when moved to change the position of said fuel valve. and  
 c. a throttle control element which is movable to different positions.  
 said control apparatus further including:  
 a. a control member connected to all three of said elements and operable to move all three elements in response to being manually adjusted, thereby to correlate the speed of said engine with the rate of fuel flow and to set said throttle control element in a position correlated both with engine speed and rate of fuel flow.  
 b. first means for sensing variations in the density of the ambient atmosphere.  
 c. second means for sensing variations in the manifold pressure of said engine.  
 d. third means responsive to said first and second means and to the position of said throttle control element and operable to automatically move said throttle in response to variations in the density of the ambient atmosphere and/or the manifold pressure ofsaid engine and/or in response to movement of said throttle control element and operable to locate said throttle in a position causing the manifold pressure to be correlated with the density of the ambient atmosphere and the position of the throttle control element. and  
 . means causing said fuel to flow past said fuel valve with a predetermined constant pressure drop whereby the flow rate of said fuel past said valve is directly proportional to the position of said valve. said last-mentioned means being selectively adjust able to cause said fuel to flow past said valve with a different constant pressure drop whereby the flow rate of the fuel may be changed without changing the position of said valve. and a second control member connected to said last-mentioned means and operable to adjust the latter in response to being manually moved.  
  2. Control apparatus as defined in claim 1 in which said first means includes pressure-responsive means for sensing variations in the pressure of the ambient atmosphere.  
  3. Control apparatus as defined in claim 2 in which said prcssure&#39;responsive means cause said throttle to close when the density of the ambient atmosphere decreases as a result of a decrease in the pressure of the ambient atmosphere and in which said second means cause said throttle to open when manifold pressure decreases as a result of a decrease in the pressure of the ambient atmosphere. said pressureresponsive means and said second means being correlated with one another so the resultant effect of a given decrease in ambient pressure causes opening of said throttle but by a lesser amount than would be the case in the absence of said pressureresponsive means.  
  4. Control apparatus as defined in claim 1 in which said first means includes temperature-responsive means for sensing variations in the temperature of the ambient atmosphere and for causing said throttle to open when the temperature ofthe ambient atmosphere increases.  
  5. Control apparatus as defined in claim I in which said first means includes pressure-responsive means for sensing variations in the pressure of the ambient atmosphere and further includes temperature-responsive means for sensing variations in the temperature of the ambient atmosphere.  
  6. Control apparatus for an internal combustion engine connected to drive a variable pitch propeller. said engine having:  
 a. a governor adjustable to different speed settings and operable to vary the pitch of the propeller to maintain the actual speed of the engine substantially in agreement with a set speed.  
 b. a fuel valve adjustable to different positions to regulate the rate of flow of fuel to the engine. and  
 c. a throttle adapted to be set in different positions to regulate the flow of combustion air to the engine and to adjust the manifold pressure of the engine.  
 said control apparatus including:  
 a. a speed control element which is operable when moved to change the speed setting of said gover nor.  
 b. a fuel control element which is operable when moved to change the position of said fuel valve. and  
 c. a throttle control element which is movable to different positions.  
 said control apparatus further including:  
 a. a control member connected to all three of said elements and operable to move all three elements in iii response to being manually adjusted. thereby to correlate the speed of said engine with the rate of fuel flow and to set said throttle control element in a position correlated both with engine speed and rate of fuel flow.  
 b. first means for sensing variations in the density of the ambient atmosphere.  
 c. second means for sensing variations in the manifold pressure of said engine.  
 d. third means responsive to said first and second means and to the position of said throttle control element and operable to automatically move said throttle in response to variations in the density of the ambient atmosphere and/or the manifold pressure of said engine and/or in response to movement of said throttle control element and operable to locate said throttle in a position causing the manifold pressure to be correlated with the density of the ambient atmosphere and the position of the throttle control element. and  
 e. means for automatically bypassing fuel away from said engine when manifold pressure drops to a predetermined level.  
  7. Control apparatus for an internal combustion engine connected to drive a variable pitch propeller. said engine having:  
 a. a governor adjustable to different speed settings and operable to vary the pitch of the propeller to maintain the actual speed of the engine substantially in agreement with a set speed.  
 b. a fuel valve adjustable to different positions to regulate the rate of flow of fuel to the engine. and  
 c. a throttle adapted to be set in different positions to regulate the flow of combustion air to the engine and to adjust the manifold pressure of the engine.  
 said control apparatus including:  
 a. a speed control element which is operable when moved to change the speed setting of said governor.  
 b. a fuel control element which is operable when moved to change the position of said fuel valve. and  
 c. a throttle control element which is movable to different positions.  
 said control apparatus further including:  
 a. a control member connected to all three of said elements and operable to move all three elements in response to being manually adjusted. thereby to correlate the speed of said engine with the rate of fuel flow and to set said throttle control element in a position correlated both with engine speed and rate of fuel flow.  
 b. first means for sensing variations in the density of the ambient atmosphere.  
 c. second means for sensing variations in the manifold pressure of said engine.  
 d. third means responsive to said first and second means and to the position of said throttle control element and operable to automatically move said throttle in response to variations in the density of the ambient atmosphere and/or the manifold pressure of said engine and/or in response to movement of said throttle control element and operable to 10 cate said throttle in a position causing the manifold pressure to be correlated with the density of the ambient atmosphere and the position of the throt tle control element. and  
 e. a second control member connected to said speed control element and operable when adjusted manually to move said speed control element without moving said fuel control element whereby engine speed may be changed without changing the rate of fuel flow. and means responsive to movement of said second control member and coacting with said third means to adjust the position of said throttle when said second control member is moved.  
  8. Control apparatus as defined in claim 7 further including means connected to said second control member and operable to disable said third means when said second control member is moved to a predetermined position.  
  9. Control apparatus as defined by claim 8 further including means movable by said first control member and operable to move said throttle when said third means are disabled and said first control member is moved.  
  10. Control apparatus as defined in claim 7 further including means causing said fuel to flow past said fuel valve with a predetermined constant pressure drop whereby the flow rate of said fuel is directly proportional to the position of said valve. said lastmentioned means being selectively adjustable to cause said fuel to flow past said valve with a different constant pressure drop whereby the flow rate of the fuel may be changed without changing the position of said valve. and a third control member connected to said last mentioned means and operable to adjust the latter in response to being manually moved.