Patent Publication Number: US-2003234002-A1

Title: Modular fuel control apparatus

Description:
[0001] This application is a divisional application of U.S. patent application 09/793,388 filed on Feb. 27, 2001 which claims priority from Provisional U.S. Patent App. Ser. No. 60/217,310, filed Jul. 10, 2000, both of which are hereby incorporated by reference in their entirety. 
    
    
     
       COPYRIGHT NOTICE  
       [0002] This patent document contains information subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent, as it appears in the U.S. Patent and Trademark Office files or records but otherwise reserves all copyright rights whatsoever.  
       FIELD OF THE INVENTION  
       [0003] This invention relates to a fuel injection system, and more particularly to a fuel control apparatus for an internal combustion engine.  
       BACKGROUND OF THE INVENTION  
       [0004] A fuel injection system for an internal combustion, aircraft engine generally includes among other components, a fuel injection servo, a flow divider, and fuel nozzles. Conventional fuel injection servos are shown in FIGS.  1 - 4 . FIGS. 1 and 2 show the RSA-5AD1 and the RSA-5AB1 fuel injection servos, respectively, sold by Precision Airmotive Corporation. FIG. 3 shows the RSA-7AA1 fuel injection servo, which is also sold by Precision Airmotive Corporation.  
       [0005] The major components of a conventional fuel injection servo include the airflow section, the flow metering section, and the fuel regulator section. The RSA-5AB1 servo also includes an automatic mixture control section. Each of these sections cooperates in a known manner to regulate the amount of fuel that is delivered to the engine, which is proportional to the amount of air that flows through the throttle body assembly, i.e., the power produced by the engine. A portion of the internal components of a conventional fuel regulator assembly is shown in FIG. 4, which shows a stack of components that cooperate to separate air and fuel chambers about an air and fuel diaphragm, respectively. The air and fuel diaphragms are also interconnected by the associated components, and each imparts a force on the regulator stem that is connected to the ball, which regulates the position of the ball valve to thereby regulate the metering head across the jetting system (not shown) and thus the amount of fuel delivered to the engine.  
       [0006] A description of the fuel injection systems utilizing the RSA-5AD1 and RSA-5AB1 servos are provided in  RSA- 5 and RSA-10 Fuel Injection Systems, Operation and Service Manual, by The Bendix Corporation and  Training Manual, RSA Fuel Injection System”  by Precision Airmotive Corporation, the entirety of each being incorporated into the present application by reference. A description of the fuel injection systems utilizing the RSA-7AA1 servo is provided in  RSA- 7AA1 Fuel Injection System, Operation and Service Manual, by Precision Airmotive Corporation and  Airflow Performance High Performance Fuel Metering Systems, Installation and Service Manual,  by Airflow Performance, Inc., the entirety of each being incorporated into the present application by reference.  
       [0007] To insure that a fuel injection system operates properly after assembly, the fuel injection servo must be calibrated. In a conventional fuel control system, the fuel servo must he calibrated as a single unit. That is, for example, in the RSA-5AD1 servo of the prior art, the fuel metering and regulator sections must be attached to the airflow section. and the entire servo must then be calibrated as a single unit. Calibration of the unit entails, for example, the application of a pressure signal to the fuel regulator and properly shimming the servo seat, the center body seal, and adjustment of the regulator stem, fastening bolts, and other components. Likewise, the components of the fuel metering section need to be calibrated, ‘which involves pressure testing. Because the calibration of the conventional fuel injector servo must be performed as a single unit, the unit becomes a single, fixed system that cannot be easily modified.  
       [0008] This cumbersome calibration method is somewhat alleviated in the RSA-7AA1 servo. With this servo, the fuel metering and fuel regulator sections are calibrated together as a unit, separate from the air flow section. After calibration of the fuel metering and fuel regulator sections together, they can be installed onto the air flow section without the need to perform further calibration of the servo unit. However, in the RSA-7AA1 servo. once the fuel metering and fuel regulator sections are calibrated together as a unit, it becomes a fixed unit. Any change in either the fuel metering or regulator sections requires recalibration of the two sections as a unit, even if only one section is changed.  
       [0009] This conventional design approach to fuel injection servos does not lend itself to quick turn around time if changes to the fuel metering section or fuel regulator section are required, either for operational purposes or for maintenance. For example, with a conventional fuel injection servo, such as the RSA-5AD1 and RSA-5AB1, in order to make a modification in either the fuel metering section or the fuel regulator section, the entire fuel injection servo would have to be recalibrated as a single unit. Such an operation is extremely time consuming and expensive. Likewise, with the RSA-7AA1 servo, changes in either the fuel metering section or the fuel regulator section require recalibration of the fuel metering fuel regulator unit. Additionally, in a fuel injection servo where the airflow section and fuel metering section are an integral casting, such as in the RSA-5AD1 and RSA-5AB1 servos, a modification in the fuel metering section requires replacement of the airflow section as well.  
       SUMMARY OF THE INVENTION  
       [0010] Therefore, there is a need to provide a fuel injection servo that does not require calibration as a single unit when modifications and/or replacement of the fuel metering section or fuel regulator section is required.  
       [0011] Accordingly, one implementation of the present invention provides a fuel control apparatus (i.e., a fuel injection servo) with a fuel metering section and fuel regulator section that can each be calibrated independently of each other, and independent from the airflow section. The fuel control apparatus of the present invention includes a modular air passage mechanism (i.e., a modular airflow section) and a modular fuel pressure modifying mechanism (i.e., a modular fuel metering section). The modular air passage mechanism has an air intake end and an air outlet end, and is constructed and arranged to accommodate airflow therethrough. The modular fuel pressure modifying mechanism is constructed and arranged ˜o receive fuel from a fuel supply and deliver the fuel at a pressure that is different from the fuel supply to a modular fuel regulator mechanism (i.e., a modular fuel regulator section). The modular fuel regulator mechanism is constructed and arranged to communicate with the airflow in the air passage mechanism and the modular fuel pressure modifying mechanism to regulate an amount of fuel delivered to the engine. Each of the modular fuel pressure modifying mechanism and the modular fuel regulator mechanism are removably mountable to the modular air passage mechanism independently from each other. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] The present invention is further described in the detailed description which follows, by reference to the noted drawings by way of non-limiting exemplary embodiments, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:  
     [0013]FIG. 1 is a perspective view of the RSA-5AD1 fuel injection servo (prior art) sold by Precision Airmotive Corporation;  
     [0014]FIG. 2 is a perspective view of the RSA-5AB1 fuel injection servo (prior art) sold by Precision Airmotive Corporation;  
     [0015]FIG. 3 is a perspective view of the RSA-7AA1 fuel injection servo (prior art) sold by Precision Airmotive Corporation;  
     [0016]FIG. 4 is a schematic of a cross section of the prior art fuel regulator section of FIG. 1;  
     [0017]FIG. 5 is a perspective view of the fuel injection servo of an embodiment of the present invention;  
     [0018]FIG. 6 is another perspective view of the fuel injection servo shown in FIG. 5;  
     [0019]FIG. 7 is another perspective view of the fuel injection servo shown in FIG. 5;  
     [0020]FIG. 8 is another perspective view of the fuel injection servo shown in FIG. 5;  
     [0021]FIG. 9 is a schematic cross-sectional view of the throttle body assembly and regulator assembly of an embodiment of the present invention;  
     [0022]FIG. 10A is a schematic cross-sectional view of the valve body assembly of an embodiment of the present invention;  
     [0023]FIG. 10B is a schematic of the throttle body assembly, regulator assembly, and valve body assembly of an embodiment of the present invention;  
     [0024]FIG. 10C is a schematic diagram of a second embodiment of a valve body assembly, where the valve body includes an enrichment circuit;  
     [0025]FIG. 10D is a schematic diagram of a third embodiment of a valve body assembly, where the valve body includes a bypass circuit;  
     [0026]FIG. 11 is a schematic cross-sectional view of the flow divider used in the fuel injection system of an embodiment of the present invention;  
     [0027]FIG. 12 is a cross-sectional view of the regulator assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0028]FIG. 13 is a cross-sectional view of the throttle body assembly and the regulator assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0029]FIG. 14A shows a side view of the air diaphragm assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0030]FIG. 14B shows a front view of the air diaphragm assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0031]FIG. 14C shows the air diaphragm retainer used in the air diaphragm assembly of FIGS. 14A and 14B;  
     [0032]FIG. 15A shows a side view of the fuel diaphragm assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0033]FIG. 15B shows a front view of the fuel diaphragm assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0034]FIG. 15C shows the regulator ball used in the fuel diaphragm assembly of FIGS. 15A and 15B;  
     [0035]FIG. 16 shows the center body assembly of the regulator assembly used in the fuel injector. servo of an embodiment of the present invention;  
     [0036]FIG. 17 shows the bellows assembly of the regulator assembly used in the fuel injector servo of an embodiment of the present invention;  
     [0037]FIG. 18 shows the servo seat assembly of the regulator assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0038]FIG. 19A shows a side cross sectional view of the servo seat fitting used in the servo seat assembly of FIG. 18;  
     [0039]FIG. 19B shows an end view of the servo seat fitting used in the servo seat assembly of FIG. 18;  
     [0040]FIG. 19C shows a side view of the servo seat fitting used in the servo seat assembly of FIG. 18;  
     [0041]FIG. 19D shows an end cross sectional view of the servo seat fitting used in the servo seat assembly of FIG. 18;  
     [0042]FIG. 20A shows a side view of the servo seat used in the servo seat assembly of FIG. 18;  
     [0043]FIG. 20B shows an end view of the servo seat used in the servo seat assembly of FIG. 18;  
     [0044]FIG. 20C shows a cross sectional side view of the servo seat used in the servo seat assembly of FIG. 18;  
     [0045]FIG. 20D shows a cross sectional side view of the servo seat used in the servo seat assembly of FIG. 18;  
     [0046]FIG. 21A shows the valve body assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0047]FIG. 21B shows an end view of the idle valve assembly used in the valve body assembly of FIG. 21A;  
     [0048]FIG. 21C shows a side view of the idle valve assembly used in the valve body assembly of FIG. 21A;  
     [0049]FIG. 21D shows an end view of the idle valve assembly used in the valve body assembly of FIG. 21A;  
     [0050]FIG. 22 is a side view of the fuel injection servo of an embodiment of the present invention;  
     [0051]FIG. 23 is a view facing the valve body assembly of the fuel injection servo of an embodiment of the present invention;  
     [0052]FIG. 24 is a view facing the idle link assembly of the fuel injection servo of an embodiment of the present invention;  
     [0053]FIG. 25 is a view facing the idle link assembly of the throttle body assembly of an embodiment of the present invention, without the valve body or regulator assembly attached thereto,  
     [0054]FIG. 26 is a bottom view of the throttle body assembly of an embodiment of the present invention;  
     [0055]FIG. 27 is a cross-sectional view of the throttle body and the venturi assembly used in the fuel injection servo of an embodiment of the present invention;  
     [0056]FIG. 28 is a cross-sectional view of the venturi assembly used in the fuel injection system of an embodiment of the present invention;  
     [0057]FIG. 29 is a graph of carb loss vs. air flow produced by the venturi assembly used in the fuel injection servo of an embodiment of the present invention and of the prior art;  
     [0058]FIG. 30 is a graph of metering suction vs. air flow produced by the venturi assembly used in tie fuel injection servo of an embodiment of the present invention and of the prior art;  
     [0059]FIG. 31 is a graph of gain vs. air flow produced by the venturi assembly used in the fuel injection servo of an embodiment of the present invention and of the prior art;  
     [0060]FIG. 32 is a perspective view of an internal combustion engine having with the fuel injection servo of the present invention mounted thereto; and  
     [0061]FIG. 33 is a cross-sectional view of an internal combustion cylinder of the internal combustion engine of FIG. 32. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0062] Referring now in detail to the Figures, wherein the same numbers are used where applicable, a fuel control apparatus constructed in accordance with an embodiment of the invention is identified generally by the reference numeral  100 , shown in FIG. 5. Although a specific configuration for the fuel control apparatus  100  will be described, it should be readily apparent to those skilled in the art that many facets of the invention are adaptable for use with fuel control apparatuses considerably different than that disclosed. The fuel control apparatus  100  is hereinafter referred to as the fuel injection servo  100 .  
     [0063] The fuel injection servo  100  constructed with the principles of the present invention may be generally installed onto an internal combustion engine  900  (FIG. 32) used primarily for aircraft. The internal combustion engine  900  may include any number of combustion cylinders; however, the typical aircraft engine utilizing the fuel injection servo  100  of the embodiment disclosed has either four, six or eight cylinders. It is contemplated that such engines, and thus the fuel injection servo  100 , could be installed in boats, land-based vehicles, or other internal combustion driven vehicles and/or equipment. The fuel injector servo  100 , when attached to the engine  900  and a flow divider, which distributes the fuel to the combustion chambers of the engine and will be discussed in detail below, becomes part of the aircraft&#39;s fuel injection system. The internal combustion engine  900  will be described in more detail below.  
     [0064] The major components of the fuel injection servo  100  include a modular air passage mechanism  400 , a modular fuel pressure modifying mechanism  200 , and a modular fuel regulator mechanism  300 . The modular air passage mechanism  400  is constructed and arranged to allow air to pass therethrough, with the air ultimately being distributed to the combustion chambers of the engine. The modular air passage mechanism  400  is hereinafter referred to as the throttle body assembly  400 . The modular fuel pressure modifying mechanism  200  is constructed and arranged to receive fuel from the aircraft&#39;s fuel supply and to deliver the fuel at a pressure that is different from the fuel supply to the modular fuel regulator mechanism  300 . The modular fuel pressure modifying mechanism  200  is hereinafter referred to as the valve body assembly  200 . The modular fuel regulator mechanism  300 , hereinafter referred to as the fuel regulator assembly  300 , is constructed and arranged to communicate with both the air that flows through the throttle body assembly  400  and the fuel that is delivered to it from the valve body assembly  200  and to regulate the amount of fuel that the engine receives. The amount of fuel delivered to the engine via the fuel regulator assembly  300  is proportional to the amount of air that flows through the throttle body assembly  400 . Before a detailed description of each of the above assemblies is given, an overview of the fuel injection servo  100  and its general operation within the fuel injection system will be described.  
     [0065] The throttle body assembly  400  comprises, among other things, a throttle body  402  which is essentially the main body section of the fuel injection servo  100 . The valve body assembly  200  and regulator assembly  300  may be removably mounted at adjacent locations to the outer periphery of the throttle body  402 . Thus, the valve body assembly  200  and regulator assembly  300  are removably mountable to the throttle body  402  independently from each other. In an exemplary embodiment, the throttle body  402  has an open ended barrel shape, the two ends of which define an air intake side  403  and an air outlet side  404 . Although shown having a barrel shape, the throttle body  402  can have various cross-sectional shapes. Air enters the throttle body  402  at the air intake side  403 . where the air is represented by number  101  in FIG. 5, and flows through throttle body barrel  435 , which defines an airflow channel. The throttle body barrel  435  is hereinafter to referred to as the throttle body airflow channel  435 . Mounted within airflow channel  435  is a venturi  500 , which the air flows around and through, the details of which are described below. The other end of injection servo  100  air outlet side  404  is connected to the engine via bolts (not shown) that pass through a plurality of holes  432  formed in a flange section at the end of throttle body  402 . Air  101 . after passing through throttle body airflow channel  435 , is distributed to the internal combustion chambers of the engine in a known manner.  
     [0066] Generally, air  101  that flows through throttle body  402  works in combination with venturi  500 , regulator assembly  300 , and the other components to provide the proper amount of fuel to the combustion chambers with respect to the amount of airflow (i.e., engine power setting), thus providing a fuel injection system that ensures efficient combustion within the engine, which is described in detail below.  
     [0067] One aspect of the present invention is that the throttle body assembly  400 , valve body assembly  200 , and fuel regulator assembly  300  of the present invention are of a modular construction. Valve body assembly  200  is a separate structure from throttle body  402 . That is, valve body assembly  200  is specifically constructed and arranged to be easily replaced with an identical valve body or with a valve body that incorporates additional features without the need to replace throttle body assembly  400  and/or without the need to remove the regulator assembly  300  from the throttle body  402 , respectively. Likewise, the fuel regulator assembly  300  is a separate structure from both the throttle body  402  and the valve body assembly  200 . That is, the regulator assembly  300  is specifically constructed and arranger. to be easily replaced and/or maintained without the need to replace the throttle body assembly  400  and/or without the need to remove the valve body assembly  200  from the throttle body  402 . Further, because of this modular construction, the valve body assembly  200  and the regulator assembly  300  can each be preassembled and calibrated separately from the throttle body assembly  400 . Thus, the fuel injection servo  100  does not require calibration as a single unit. Further, the modular construction of valve body assembly  200  and fuel regulator assembly  300  simplifies the manufacturing process of the fuel injection system  100 . The advantages of the modular construction will be further discussed after a description of an exemplary embodiment.  
     [0068] The basic principles underlying the operation of fuel injector servo  100  will now be described. As is generally known in the art, all reciprocating engines operate most efficiently in a very narrow range of air-to-fuel (or fuel/air) ratios. The fuel injection servo  100  uses the measurement of air volume flow to generate a usable force, which is used to regulate the flow of fuel to the engine in proportion to the amount of air being consumed. This is accomplished by channeling the ambient air impact pressure and venturi suction pressure to opposite sides of an air diaphragm in the regulator assembly  300 . The difference between these two pressures becomes a usable force which is equal to the area of the diaphragm times the pressure difference. This force is transmitted through a regulator stem, and is proposed by the force imposed on a fuel diaphragm. The above operation is accomplished within the regulator assembly  300 .  
     [0069] More specifically, referring to FIG. 9, which is a schematic diagram of a cross-section of throttle body assembly  400  and regulator assembly  300 , the regulator assembly  300  comprises, among other things, an air diaphragm  302 , a fuel diaphragm  320 , a regulator stem  308 , and a regulator ball  310  located at the end of the regulator stem  308 . Air diaphragm  302  communicates with air that flows around and through venturi  500 , and fuel diaphragm  320  communicates with ith a fuel s source. Air diaphragm  302  separates and partially defines two air cavities, an ambient air impact side  304  and a venturi suction side  306 . Impact air side  304  experiences an air pressure that is equal to the ambient air impact pressure at the entrance of throttle body  402  (i.e., before the air pressure is influenced by venturi  500 ), which is communicated to it by the impact port  142  and channel  146 . Suction side  306  experiences an air pressure, or suction pressure, that is equal to the pressure at the venturi pressure port  144 , designated as P(suction), which is communicated to suction side  306  by channel  148 . Venturi  500  will be described in detail below. The impact pressure is greater than P(suction), therefore, a net force is exerted on air diaphragm  302  equal to the pressure differential between impact side  304  and suction side  306  multiplied by the area of air diaphragm  302 . The resultant force causes deflection of the air diaphragm to the left, thus pulling regulator stem  308  to the left (as seen in FIG. 9). The application of this force to regulator stem  308  allows the regulator ball  310  to be released from its seat (hereinafter the˜ball valve  311 ), thus allowing fuel to proceed to the engine, as will be discussed below. The fuel diaphragm  320  is used to regulate this flow of fuel.  
     [0070] Fuel diaphragm  320  separates and partially defines two fuel cavities: an unmetered fuel side  312  and a metered fuel side,  314 . An engine driven fuel pump (not shown) receives fuel from the aircraft system (including a booster pump (not shown)) and supplies that fuel at a relatively constant pressure to valve body assembly  200 , where the fuel is split into two paths: an unmetered path  316  and a metered path  318 . Unmetered path  316  and metered path  318  originate in the valve body assembly  200 , shown in FIG. 10A. Valve body assembly  200 , which is mounted adjacent to fuel regulator assembly  300 , communicates with the regulator assembly via unmetered and metered fuel paths  316  and  318 , respectively.  
     [0071]FIG. 10B is a combination of FIGS. 9 and 10A. Unmetered path  316  directly communicates with unmetered fuel side  312 , with the pressure in the unmetered fuel side designated as P(unmetered). Metered fuel side  314  receives fuel from metered path  318 , which has passed through a main metering jet  220  and an idle valve  212  (which are shown in FIG. 10E 3 ) in valve body assembly  200 . which will be described in more detail below. This fuel has a pressure that is designated as P(metered). The pressure in unmetered fuel side  312 . P(unmetered), is greater than the pressure in metered fuel side  314 , P(metered), therefore, a net force is exerted on fuel diaphragm  320  that is equal to the pressure differential between the two sides of the diaphragm multiplied by the area of the diaphragm. The resultant force causes deflection of fuel diaphragm  320  to the right, and thus tends to move regulator stem  308  to the right (as shown in FIG. 9). Thus, the forces applied to stem  308  by air diaphragm  302  and fuel diaphragm  320  oppose each other to provide the proper amount of metered fuel through ball valve  311  that controls an orifice opening  322 , through which fuel flows to the engine.  
     [0072] Further explanation of the above system is facilitated by describing a power change which requires a fuel flow change. This explanation begins with the engine running at a cruise condition. Here, the air velocity through throttle body barrel  435  is generating a pressure differential between the ambient air impact pressure (P(impact)) and the venturi suction pressure (P(suction)), which, for illustrative purposes only, is at a theoretical value of two. This air pressure differential exerts a force to the left as shown in FIG. 9, which is applied to the regulator stem  308 . At the same time, fuel flows to the engine because the ball valve  311  formed by ball  3   10  and opening  322  has opened. This generates a fuel pressure differential (unmetered fuel pressure minus metered fuel pressure), applied a cross fuel diaphragm  320 , that also creates a force with a theoretical of two. That is, the two forces become equal. Because these two opposing forces (fuel and air differentials) are equal, the regulator ball  310  of valve  311  (which is connected to both diaphragms by regulator stem  308 ) is held in a fixed position that allows the discharge of just enough metered fuel to maintain the pressure balance.  
     [0073] If the throttle  410  is opened to increase power, air flow immediately increases. This results in an increase in the pressure differential across air diaphragm  302  to a theoretical value of, for example, three. An immediate result of this increase in pressure is that regulator stem  308  moves to the left (as seen in FIG. 9) to further open ball valve  311 . This increased ball valve  311  opening causes a decrease in pressure in metered fuel side  314 , and since unmetered fuel side  312  pressure remains constant, an increase in fuel pressure differential occurs across the fuel diaphragm. When this increasing fuel differential pressure force reaches a value of three (equaling the air diaphragm force), regulator stem  308  stops moving and the ball valve stabilizes at a position which will maintain the balance of pressure differentials, i.e., air and fuel, each equaling three. Fuel flow to the engine has thus increased, as requested by the pilot (or user), because the ball valve has opened up to a new position. Because the fuel diaphragm force generated by the pressure drop across the main metering jet  220  is equal to the air diaphragm force being generated by venturi  500 , the amount of fuel that is flowing to the engine is the precise amount required for the amount of air intake into the combustion chambers, thus providing the proper fuel/air ratio for efficient combustion. The above sequence of operations is true for all regimes of power operation and all power changes. Ball valve  311  responds to changes in effective air differential pressure forces and adjusts the position of ball valve  311  to regulate unmetered to metered fuel pressure differential forces accordingly. Fuel flow through the metering jet  220 , and to the engine, is a function of the jet&#39;s size and the pressure differential across it. Ball valve 3 lb does riot meter fuel. It only controls the pressure differential across the metering jet  220 .  
     [0074] The metered fuel exits regulator assembly  300  via tube  322  and is delivered from the regulator assembly of the fuel injection system to the engine through a system which includes a flow divider  170  and a set of discharge nozzles  172  (one nozzle per cylinder). The flow divider  170  is shown schematically in FIG. 11. A flow divider  170 , however, is not always required. In those engines that do not use a flow divider, the fuel flow is divided by either a single four-way fitting (not shown), which is used on four-cylinder engines, or a tee (not shown) which divides the fuel flow into two separate paths. Each path incorporates a three-way fitting when used on six-cylinder engines. The flow divider comprises a valve, sleeve, diaphragm and a spring. The valve is spring loaded to the closed position in the sleeve. This effectively closes the path of fuel flow from the fuel regulator assembly  300  to the nozzles and at the same time isolates each nozzle from all the others at engine shut down. The two primary functions of the flow divider are:  1 ) to assure equal distribution of metered fuel to the nozzles at and just above idle; and  2 ) to provide isolation of each nozzle from all the others for clean engine shut down. The area of the fuel discharge jet in the fuel nozzles is sized to accommodate the maximum fuel flow required at rated horsepower without exceeding the available inlet fuel pressure to satisfy all the pressure drops in the fuel injection system. The flow divider  170  operates to deliver metered fuel to the cylinders in a conventional manner as is known in the art and therefore will not be described in detail herein.  
     [0075] The regulator assembly  300 , the valve body assembly  200 , and the throttle body assembly  400  of an embodiment of the present invention will now be described in further detail.  
     [0076] Further detail of the regulator assembly  300  is shown in FIGS.  12 - 20 , noting that the orientation of these figures is reversed from that shown in FIG. 9. Generally, the regulator assembly (i.e., the modular fuel regulator mechanism) is constructed and arranged to communicate with the airflow in the throttle body assembly  400  (i.e., the air passage mechanism) and a fuel supply to regulate an amount of fuel delivered to the engine. The regulator assembly  300  comprises an air diaphragm assembly  340 , a fuel diaphragm assembly  330  a center body assembly  350 , a rear regulator cover assembly  370 , and a servo seat assembly  380 . The center body assembly  350  is mounted between the air and fuel diaphragm assemblies  340 ,  330 , thus separating the air and fuel chambers from each other. Air diaphragm assembly  340  shown separately in FIG. 14, includes air diaphragm  302 , air diaphragm retainer  342 , and diaphragm washers  344 .  346 . Retainer  342  and washers  344 ,  346  are made of metal, but could be made from other material, such as plastic, as long as they 3rd sufficiently strong and rigid. Diaphragm  302  is sandwiched between the two washers  344 ,  346 , which are then mounted to a mounting surface  343  on retainer  342 , shown separately in FIG. 14C. Retainer  342  is positioned at the center of air diaphragm assembly  340 . Air diaphragm  302  is made of a flexible, impermeable, synthetic rubber material. Washers  344   346  have a plurality of holes formed therein for weight reduction, which aids in the overall performance of the regulator section. Specifically, the weight reduction reduces the “g” forces experienced by the fuel diaphragm  320 , resulting in more consistent fuel flow to the engine during aircraft maneuvers.  
     [0077] Fuel diaphragm assembly  330 , shown separately in FIG. 15A, includes the fuel diaphragm  320 , regulator ball  310 , regulator stem  308 , two fuel diaphragm washers  318 ,  319 , and a diaphragm rivet  316 . Like air diaphragm  302 , the fuel diaphragm  320  is made of a flexible, impermeable. synthetic rubber material, and is sandwiched between the two washers  318 ,  319 , which are in turn mounted at their inner periphery to a mounting surface formed on regulator ball  310 . Shown separately in FIG. 15C, regulator ball  310  includes a spherical portion  309  integrally formed on the end of a hollow, cylindrical portion  313 , the outside diameter  315  of which has mounted thereon the two washers  318 ,  319 . A flange portion  317  is also formed on the end of tile cylindrical portion  313  adjacent the spherical portion  309  for providing a stop for washer  319 . Regulator stem  308  is centered within cylindrical portion  313  and is fixedly connected thereto (FIG. 12). Diaphragm rivet  316  is riveted to washers  318 ,  319  near the outer periphery thereof. Rivet  316  has a hole  323  formed therethrough, which allows air that may become trapped in the unmetered fuel side  312  to be vented to the metered fuel side  314  so that the air can be expelled from the fuel regulator. The fuel diaphragm has an annular undulation  321  located radially adjacent to the outside diameter of washers  318 ,  319 .  
     [0078] Center body assembly  350 , shown separately in FIG. 16, includes center body  352 , a bellows assembly  354 . and a shim  339 . Bellows assembly  354 , shown separately in FIG. 17. includes a cup-shaped bellows cage  358 , a bellows  356  located within cage  358 . and a bellows hat  357  for retaining bellows  356  within cage  358 . Bellows assembly  354  is located at the center of center body  352  and press fitted therein at the outer periphery of bellows cage  358 , as shown in FIG. 12. A through hole  361  is formed near the outer periphery of center body  352 , which is used as both a bolt hole for mounting the regulator assembly  300  to throttle body  402  using bolt  368 , shown in FIG. 13, and, because the outer diameter of the hole is larger than the bolt, the hole also is a portion of channel  146 . Channel  146  communicates the ambient air impact pressure of the venturi  500  with the impact pressure side of the air diaphragm  302 . Channel  146  further includes a hole  362  formed in center body  252  that extends from the surface of hole  361  at an intermediate portion thereof to the impact pressure side of the center body. The shim  359  is used to take up any clearances that may exist after assembly of the above components.  
     [0079] The outer periphery of the air and fuel diaphragms have a plurality of through holes that correspond to through holes in center body  352  and rear regulator cover  364 . Thus, the regulator assembly  300  is bolted to throttle body  402  at corresponding holes therein by a co:-responding plurality of bolts, one of which includes bolt  368 , the bolt hole of which is also used as a portion of air channel  146 , as described above. When bolted to throttle body  402 . the synthetic rubber air and fuel diaphragms form a tight seal along the outer periphery of the regulator assembly  300 .  
     [0080] Air diaphragm assembly  340  and fuel diaphragm assembly  330  communicate with each other via regulator stem  308 , which is fixedly interconnected to air diaphragm  302  at one end, and fixedly interconnected to fuel diaphragm  320  at an intermediate portion thereof, adjacent regulator ball  310 . Regulator stem  308  passes through the center of bellows assembly  354 . The bellows assembly and the regulator stem are constructed and arranged such that the regulator stem can freely translate relative to center body  352  during movement of the regulator stem caused by forces generated by the pressure differentials between the two sides of the air and fuel diaphragms. A locating bushing  359  is fitted around the regulator stem, the bushing being in sliding contact with the bellows. One end of the bushing has arm increased outer diameter that is slip-fitted into the center of the air diaphragm retainer  342 , thus establishing a self-centering connection between regulator stem  308  and air diaphragm assembly  340 .  
     [0081] Regulator ball  310  sits pressed against the servo seat of servo seat assembly  380  to form ball valve  311  through which metered fuel flows from metered side  314  of fuel diaphragm  320 . Servo seat assembly  380 , shown separately in FIG. 18, includes a servo seat fitting  382  (shown separately in FIGS.  19 A-D) and a servo seat  384  (shown separately in FIGS.  20 A-D), which are fitted together, with the servo seat placed inside a cavity formed in the servo seat fitting. Servo seat assembly  380  is connected to the regulator assembly  300  by the outside threads formed in servo seat fitting  382  which engage corresponding inner threads  375  formed in bore  371  of rear regulator cover  364 , seen in FIG. 12. Servo seat  384  is fixed to servo seat fitting  382 . A plurality of shims  386 , seen in FIG. 12, are positioned between the hex head of servo seat fitting  382  and the rear surface of regulator cover  364 . These shims  386  are used to make final adjustments during set-up of regulator assembly  300  and during calibration of the regulator assembly, which will be discussed below.  
     [0082] Servo seat assembly  380  also includes a constant effort spring  394 , an O-ring  385  an outlet fitting  390 , an outlet fitting O-ring  398 , a spring holder  396 , and two regulator stem lock nuts  399 . Constant effort spring  394  supplements the transition from idle to regulator controlled fuel flow, which is discussed in more detail below. Constant effort spring  94  also assists the air diaphragm to move smoothly from the low air flow idle range to the higher power range of operation. It is also furnished in a selection of strengths to be utilized for proper calibration of the unit.  
     [0083] This servo seat design permits the removal of servo seat assembly  380  without the nee! to remove regulator assembly  300 . This feature reduces the time required to calibrate the regulator servo valve seat because the ball valve seat is not located in the interior of the regulator. To remove the servo seat assembly, the servo fitting is unscrewed from rear regulator cover  364 , thus removing the shims  386 , the servo seat fitting  382 . and the servo seat  381 .  
     [0084] The Valve Body Assembly  200 :  
     [0085] A schematic of the valve body assembly  200  is shown in FIG. 10A, which shows the internal fuel passages thereof Valve body assembly  200  is shown separately in FIGS. 21A and 21B, and its assemblage with the fuel injection apparatus  100  is shown in FIGS.  22 - 24 . Generally, the valve body assembly  200  (i.e., the modular fuel pressure modifying mechanism) is constructed and arranged to receive fuel from the fuel supply and deliver the fuel at a pressure that is different from the fuel supply to the fuel regulator assembly  300  (i.e., the modular fuel regulator mechanism). The major components of valve body section  200  include an idle valve assembly  210  and a manual mixture control valve assembly  240 . Idle valve assembly  210 , which is shown separately in FIGS.  21 B-D, includes an idle valve  212 , which is interconnected to the throttle linkage via an idle valve lever  214 . Idle valve  212  is of a barrel design, i.e. it has a hollow, cylindrical shape, and sits, in a rotationally sliding relation, within a bore  219  formed in valve body  204 . Valve  212  has an opening  216  at an intermediate portion thereof. This opening  216  is essentially a notch cut approximately half way into the side of valve  212 . Opening  216  communicates with channel  318  of regulator assembly  300  for delivering metered fuel to the regulator. At one end of opening  216  is a stepped slot  218 . Idle valve  212  effectively reduces the area of main metering jet  220  for accurate metering of the fuel in the engine idle range. as will be described below. Idle valve assembly  210  also includes an idle valve cover  213 , a thrust washer  215 , an idle lever spacer  217 , and an O-ring  216 , shown in FIGS.  21 A-D.  
     [0086] Shown in FIG. 10A, the fuel path (i.e., the fuel circuit) from fuel inlet  202  to regulator assembly  300  is as follows. Unmetered fuel from the engine fuel pump enters the valve body at fuel inlet  202  and passes through an inlet screen tube  232  of an inlet filter assembly  230 . The fuel is then vented to an unmetered fuel side, which proceeds to the unmetered side  312  of fuel diaphragm  320  via channel  316 , and a metered fuel side, which passes through the main metering jet  220 . The main metering jet  220  is essentially an externally threaded nut formed with a through channel having a constricted throat section  221 . Main metering jet  220  is a screw in part and is easy to access, via the removal of hex-head bolt  223 , and can be removed and replaced very efficiently. Thread section  221  of jet  220  is fabricated utilizing standard drill sizes which provide a wide range of fuel flow in incremental steps. Thus, main metering jet  220  is easy to manufacture while maintaining precise control of fuel flow limits. Passage of the fuel from one side of metering jet  220  to the other side through the constricted throat section  221  causes a pressure drop in the fuel. This lower pressure fuel, i.e. metered fuel, flows through idle valve  212  and its opening  216  and into the metered fuel chamber  314  via channel  318 .  
     [0087] At low engine speed, i.e., the pilot has set the throttle to be very low, idle lever  214  rotates idle valve  212  so that opening  216 , which created a flow path into channel  318 , faces an interior wall of bore  219 . This action permits fuel flow through only stepped slot  218 , which remains in line with channel  318 . At higher engine speeds, i.e., the pilot opens the throttle, idle lever  214  causes rotation of idle valve  212  such that opening  216  again faces channel  318  and thus the metered fuel regulation automatically switches back to regulator assembly  300 . This manual control of the idle mixture is necessary because with very low air flow through the venturi in the idle range, the air metering force is not sufficient to accurately control fuel flow.  
     [0088] An advantage of the barrel-shaped idle valve  212  is that it is easy to manufacture. For instance, the idle valve and the idle valve bore are easily machined with tight tolerances. Thus, matching of each is not required. That is, for example, the idle valve diameter does not have to be machined to a specific diameter determined by the idle valve bore, or vise versa. Rather, each is machined according to predetermined specifications accurately. Thus, the idle valve can be machined and assembled into any valve body assembly  200 . Also, the barrel shaped design is less susceptible to scoring which can lead to unpredictable idle and off-idle engine performance.  
     [0089] The fuel circuit of the valve body assembly  200  of the embodiment shown in FIG. 10A also includes an adjustable jet assembly  270  that is constructed and arranged in parallel with main metering jet  220 . Adjustable jet assembly  270  comprises an adjustable jet body  272 , an adjustable jet valve  274 , a snap ring  276 , a detent spring  278 , and a ball bearing  280 . Adjustable jet assembly  270  operates in parallel with main metering jet  220 , or circuit, and provides adjustment of the fuel mixture at high power settings. That is, when adjustable jet valve  274  is opened, some fuel is diverted to channel  279  in parallel with main metering jet  220 , passes through the adjustable jet valve, and is reunited with the fuel that passes through the main metering jet the metered fuel via a hole (not shown) in adjustable jet body  212  that allows the fuel to pass into idle valve  212 . Adjustable jet valve  274  thus allows for “tweaking” of top end fuel flow on the aircraft. Although shown with an adjustable jet flow path the adjustable jet flow path and thus the adjustable jet assembly are optional.  
     [0090] The other main component of valve body assembly  200  is the manual mixture control assembly, generally designated as reference numeral  240 . The manual mixture control assembly includes a manual mixture valve  242 , which sits within bore  243  formed within the valve body. Manual mixture valve  242  has formed therein channels  244 ,  246  which allows, when orientated as such, fuel to pass from inlet filter assembly  230  and into the unmetered and metered flow paths, respectively. A series of O-rings  247 ,  248 ,  250  prevents seepage of fuel around the manual mixture valve to properly direct the fuel into channel  244 . Channel  244  first runs longitudinally of manual mixture valve  242  delivering fuel to an annular portion. This annual portion directs fuel into channel  316 , thus delivering unmetered fuel to the regulator assembly. Channel  246 , positioned 180 degrees from channel  244 , first. runs longitudinally, delivering unmetered fuel from inlet filter assembly  230  to a second annular portion of manual mixture control valve  242 . which in turn directs the fuel to main metering jet  220 .  
     [0091] When the aircraft is at high altitudes such that the density of the air is appreciably reduced, the fuel regulator may supply too much fuel for a given power setting because. although the regulator causes to the ball valve to open up to according to a differential pressure drop created by the venturi, the air density at such altitudes is decreased, thus, the engine cylinder will be supplied with too much fuel. That is, it will run rich. In this situation, the pilot may use manual mixture control valve  240  to manually reduce fuel flow.  
     [0092] As seen in FIG. 22. the manual mixture control valve  242  is operated by a mixture lever  249 , which is mounted to a jagged-toothed surface  245  of a boomerang-shaped stop bracket  251 . Two wings  246 ,  247  of bracket  251  are limiting points of rotation. so that manual mixture control valve  242  produces a full rich condition when mixture lever  249  is against wing  246 , i.e., the rich stop position, and a progressively leaner mixture as lever  249  is moved toward wing  247 , i.e., the idle cutoff position. Mixture lever  249  is caused to rotate by a cable (not shown) that is connected to the free end of the lever. The cable runs to the cockpit of the airplane and is connected to a pilot control mechanism (not shown), as is known in the art. By rotating manual mixture valve  242  to cut off, the size of the metering jet is effectively reduced. This allows the pilot the option to manually lean the mixture for the best cruise power or the best specific fuel consumption. It also provides the means to shut off fuel flow to the engine at engine shut down.  
     [0093] Valve body  204  is fixedly connected to throttle body  402  with a plurality of bolts  203  and corresponding through holes  203   a.  The throttle body assembly  400  comprises a first surface portion  433  formed on the outer surface of the throttle body  403  (i.e., the main body of the throttle body assembly) and the valve body  204  comprises a second surface portion  233  formed thereon (FIG. 24). The second surface portion  233  is adapted to interface with the first surface portion  433  when the valve body assembly is removably mounted onto the throttle body assembly  400 . In an exemplary embodiment, the first and second surface portions  433 ,  233  are mating planar surfaces. To accurately position valve body assembly  200  onto throttle body  402 , a plurality of dowel pins  205  are rigidly fixed into corresponding dowel pin holes  227  formed in the throttle body, shown in FIGS. 22 and 24. The contact, mating surfaces on the throttle body and the valve body are machined with a low surface roughness and a high degree of flatness to ensure maximum contact between the two surfaces at the interface  209 . Although shown to be in direct contact, a spacer or gasket device may be sandwiched between the first surface portion  433  and second surface portion  233 .  
     [0094] A second embodiment of a valve body assembly  600  is shown schematically in FIG. 10C, which includes an enrichment system  602  in the fuel flow path. Enrichment system  602  includes an enrichment valve diaphragm  604 , a spring  606 , an enrichment valve jet  610 , and an enrichment valve  608 . In this embodiment of valve body assembly  600 , the fuel path is as follows. After the inlet fuel  202  passes through an optional inlet filter assembly (not shown)(which includes an inlet screen tube), the fuel is split into an unmetered and metered path by a manual mixture control assembly  640  (as described earlier in FIG. 10A). The metered path includes, as before, a main jet  620  and an adjustable jet assembly  670  in parallel with main jet  620 . Main jet  620  and adjustable jet  670  operate as described with respect to the embodiment shown in FIG. 10A. Although shown with an adjustable jet flow path, the adjustable jet flow path, and thus the adjustable jet assembly, are optional. The metered fuel and unmetered fuel then enter opposite sides of an enrichment valve diaphragm  604  of enrichment system  602 . The enrichment valve  608  is operated by diaphragm  604  that is vented to the unmetered fuel by enrichment valve jet  610 . When the pressure differential applied across the diaphragm creates a force greater than the enrichment valve spring force, the valve opens to allow unmetered fuel to pass through enrichment valve jet  610  and through diaphragm  604 . Allowing the fuel to flow through chamber  612  and chamber  614  eliminates static chambers, which trap air or require bleed circuits to eliminate the air in the fuel chambers  612 ,  614  around enrichment valve  608  and enrichment valve diaphragm  604 , respectively. The opening point of the valve can be adjusted to a predetermined point by increasing or decreasing the tension on the enrichment valve spring by removing and adding shims  611 . Enrichment valve jet  610 , which can vary in size. controls the amount of fuel enrichment when the valve is open. The metered fuel then passes through a barrel, idle valve  622  and is delivered to metered fuel side  312  of the fuel regulator, and the unmetered fuel is delivered to unmetered fuel side  314 . The enrichment system  602  increases the fuel/air mixture strength to provide for “fuel cooling” of the engine in the high power range. Although this increases fuel consumption, it also increases engine life. The enrichment system  602  can also be used to compensate for fuel/air ratio changes due to changes in air density.  
     [0095] A third embodiment of a valve body assembly  700  is shown schematically in FIG. 10D. which includes a bypass circuit  702  in the fuel flow path. A main function of bypass circuit  702  is to reduce the propensity of vapor formation in the fuel pump and fuel system, which in turn reduces the likelihood of vapor locking. As is known in the art, vapor lock is where fuel in the fuel lines evaporates to vapor instead of maintaining a liquid form, and which is aggravated by elevated fuel temperatures or low inlet fuel pressure to the engine driven pump. If the vapor forms faster that the pump can draw it from the fuel line, because vapor is difficult to pump, the flow of fuel to the fuel injector servo, and thus the engine, is effectively stopped and the engine stalls or is prevented from being started. Also, before locking, the vapor will be passed on into the fuel regulator assembly  300 , which causes the fuel injection servo  100  to meter flow incorrectly. With a given fuel (i.e., Reid vapor pressure number), vapor formation can be minimized by reducing heat in the fuel system, increasing fuel-system pressure, and eliminating sudden changes in cross section or direction of fuel lines. Idle bypass circuit  702  helps prevent vapor locking by enabling more fuel to flow than otherwise would at engine-idle speeds and prior to engine start, thus cooling the fuel injection system components (i.e.. the fuel injection servo, flow divider, etc.) and reducing the fuel temperature, and purging the system of vapor.  
     [0096] Referring to FIG. 10D, idle bypass circuit  702  comprises an idle bypass port  706  incorporated into an idle valve  722 , an idle bypass jet  710 , and an idle bypass channel  704 . In this embodiment of the valve body assembly, the fuel path is as follows. After the inlet fuel  202  passes through an optional inlet filter assembly (not shown)(which includes an inlet screen tube), the fuel is split into an unmetered and metered path by a manual mixture control assembly  740  (as described in FIG. 10A). The metered path includes, as with the prior valve body embodiments, a main jet  720  and an adjustable jet assembly  770  in parallel with the main jet. The metered fuel then passes through a barrel-shaped idle valve  722  and is delivered to metered fuel side  312  of the fuel regulator assembly  200 , and the unmetered fuel is delivered to unmetered fuel side  314  (both seen in FIG. 9). Although shown with an adjustable jet flow path, the adjustable jet flow path and thus the adjustable jet assembly  770  are optional.  
     [0097] The idle bypass circuit  702  comes into operation at engine idle speeds. When idle valve  722  is closed (at idle) the idle bypass port  706  communicates with idle bypass channel  704 , and thus some of the unmetered fuel from fuel inlet  202  bypasses the remainder of the fuel circuit (i.e., the manual mixture control assembly, the main jet and the adjustable jet) and is directed back to the fuel supply, such as the fuel tank. An idle bypass jet  710  in a return channel  715  controls the amount of fuel return when the idle valve is in the idle position. Although shown within return channel  715 , the idle bypass jet  710  can also be positioned within bypass channel  704  between the fuel inlet  202  and the idle valve  722 . Idle  
     [0098] bypass jet  710  is sized for a specific application. i.e., a fuel pump size. A set of o-ring seals  725  are positioned on opposite sides of idle bypass port  706  to prevent the bypassed fuel from seeping into the metered fuel path and from exiting the valve body assembly. At idle speeds, where the fuel flow is low, idle bypass circuit  702  increases the fuel flow from the engine driven pump. This increased fuel flow purges and cools the fuel pump and other fuel system components (i.e., the fuel injection servo and associated hardware and fuel system components upstream of the fuel pump), thus reducing the propensity for vapor formation in the fuel pump and the fuel system. Additionally, before the engine starts, the fuel pump is activated and fuel flows through idle bypass circuit  702 . Thus, the fuel system and associated hardware, including the fuel injection servo, are cooled and purged before the engine starts. This property greatly reduces hot start problems, because hot fuel and vapor are pureed from the fuel injection system prior to engine start. When the throttle is opened, idle valve  722  rotates and closes idle bypass port  706 . At high engine speeds, the higher fuel flow requirements reduce the propensity for vapor formation, and thus fuel flow through the idle bypass circuit is not needed. This also keeps the engine driven fuel pump capacity requirements at high output to a minimum.  
     [0099] The Throttle Body Assembly  400 :  
     [0100] Throttle body assembly  400  is shown in FIGS.  25 - 27 . As briefly mentioned earlier, the throttle body assembly comprises, among other things, throttle body  402 , throttle plate  40 , a throttle stop lever  408 , and venturi assembly  500 . Throttle body  402  is essentially the main body section of the fuel injection servo, the outer surface of which has attached thereto valve body assembly  200  and fuel regulator assembly  300 . To facilitate the attachment of valve body assembly  200 , a first surface  412  is machined at an outside portion of the throttle body. This first surface  412  interfaces with the corresponding mating surface on modular valve body assembly  200 , and the two surfaces are machined to have a surface finish amid flatness that maximizes surface contact of the two mating surfaces. Throttle body  402  hat; an open-ended. barrel shape, the two ends of which define air intake opening  403  and air outlet end  404 . During operation, air  101  enters throttle body  402  at air intake opening  403  and flows through throttle body barrel  435 .  
     [0101] The pilot (or automated power control user) controls the amount of air that flows through the throttle body barrel by actuation of throttle lever  414 , shown in FIG. 24, which is mounted on a throttle shaft  406  and which is interconnected to a throttle control (not shown) that the pilot operates from within the cockpit. Throttle shaft  406  extends through throttle body  402 . and throttle plate  410  is fixedly mounted thereto within throttle body barrel  435 .  
     [0102] Throttle lever  414  is actuated by a cable (not shown) attached to the free end  411  thereof When more power is desired, i.e., more fuel, the pilot opens the throttle causing rotation of throttle lever  414 , which in turn rotates throttle plate  410 . Throttle plate  410  determines, by its rotated position with respect to throttle body barrel  435 , the amount of airflow that passes through the barrel.  
     [0103] A throttle stop lever  408  (FIG. 25) is interconnected to idle lever  214  via an idle lever assembly  800 , as shown in FIG. 24. When throttle lever  414  is actuated by the pilot, which causes rotation of throttle shaft  406 , idle link assembly  800  causes idle lever  214  to rotate, which in turn rotates idle valve  212  in valve body assembly  200 . The idle link assembly comprises an adjustable length linkage  802  that is used to adjust the idle fuel mixture. When the linkage is adjusted to be lengthened, a richer idle mixture is provided. When adjusted to be shortened, a leaner idle mixture is provided.  
     [0104] Changes in the airflow, as directed by the pilot, are communicated to fuel regulator assembly  300 , as described earlier, which regulates the amount of metered fuel that is delivered to the engine. The amount of airflow is communicated to the regulator assembly by way of a pressure differential created as the air flows around and through the venturi  500 . which is mounted within barrel  435 , shown in FIG. 27 and schematically in FIG. 9. Venturi  500  is shown separately in FIG. 28. As briefly mentioned earlier, venturi  500  of the exemplary embodiment disclosed is a compound venturi. That is, air flows both around and through the venturi, and the air that flows around the venturi influences the pressure of the air that flows through the venturi, as is known in the art. Specifically, as shown in FIG. 28, venturi  500  comprises of an approach section  504  and a recovery section  506  that are separated by three spacers  508 . The venturi is connected to throttle body barrel  435  using a narrow, streamlined strut  502 . Approach section  504  includes a through channel  510  constructed and arranged for air to flow through. The inlet of channel  510  is nozzle shaped, thus, as air enters the venturi, its velocity increases causing a drop in the air pressure. Thus, the inlet of channel  510  is referred to as a boost venturi  512 . The air flowing through the venturi exits via the annular space  514  between the approach and recovery sections. The air that flows over the approach section causes a pressure drop at the end  516  of the approach section  504 . This pressure drop is communicated to boost venturi  512  via channel  510 , which in turn increases the pressure drop created by boost venturi  512 . The pressure created by boost venturi  312 , designated P(suction), is communicated to venturi suction side  306  of regulator assembly  300  via channel  148 . Channel  148  runs from boost venturi  512 , through approaching section  504 , and through the center of a bolt  518  used to attach venturi  500  to throttle body  402 . Bolt  518  passes through strut  502  and screws into threads formed in approach section  504 , as shown in FIG. 27. Ambient air impact pressure. i.e.. air that has not been influenced by the venturi, is communicated to impact air side  304  of regulator assembly  300  via channel  146  formed within strut  502 . Impact air enters this channel  146  at an air impact poll.  142 .  
     [0105] Venturi  500  of the embodiment disclosed is a bullet-type venturi. All components of the venturi are machined from billet material, which produces a venturi with consistent dimensional and surface finish characteristics which in turn results in very consistent venturi performance. This consistent venturi performance, which is characterized below, provides consistent throttle body performance, which in turn enables modularity of the entire fuel injection apparatus because neither the valve body assembly  200  nor the fuel regulator assembly  300  need to be customized (i.e.. calibrated) for a particular throttle body. Additionally, the features of venturi  500 , such as boost venturi  512 , strut  502  configuration. approach section  504  and recovery section  506 , constructed according to the exemplary embodiment described above combine to provide a large pressure signal to regulator assembly  300 . That is, for a given amount of airflow, venturi  500  provides a larger signal to the fuel regulator assembly  300  without decreasing or restricting airflow to the engine. A larger pressure signal from the venturi provides more force in the fuel regulator assembly  300  which improves the overall fuel metering resolution.  
     [0106] These improved characteristics of venturi assembly  500  are shown graphically in FIGS.  29 - 31 . FIG. 29 compares the amount of “carb loss” versus the amount of air flow for venturi  500 , designated as numeral  520 , of the embodiment disclosed and that of a conventional venturi, designated as number  522 . The carb loss is shown graphically as a normalized percentage of inches of water, and the air flow in FIG. 29- 31  is shown graphically as a normalized percentage of PPH. and the density of the air is 0.0765 lb/cu-ft. As the engine speed of the aircraft increases, the air flow increases. The “carb loss” is the pressure loss between inlet opening  403  and outlet discharge  404  of the throttle body, and a higher carb lost; indicates a greater restriction in the airflow path to the engine. As seen if FIG. 29, venturi  500  of the embodiment disclosed has a lower carb loss for a given air flow as compared to a conventional venturi.  
     [0107]FIG. 30 compares the metering suction pressure generated versus the amount of air flow for venturi  500 , designated by numeral  524 , to that of a conventional venturi, designated as numeral  526 . The metering suction, shown graphically as a normalized percentage of inches of water, is the pressure created by boost venturi  512 . The metering suction differential, i.e., the difference between the metering suction pressure and the ambient air impact pressure, is the signal generated by the venturi that is communicated to the air diaphragm inside regulator assembly  300 . As seen in FIG. 30, venturi  500  of the disclosed embodiment produces a larger metering suction pressure for a given air flow. This translates into a larger “gain” that is communicated to regulator assembly  300 .  
     [0108]FIG. 31 is a comparison of “gain” versus air flow for venturi  500 . designated by numeral  528 , and that of a conventional venturi, designated as numeral  530 . The “gain,” shown graphically as a normalized percentage, is the signal generated by the venturi., (i.e. the metering suction differential) and communicated to the regulator assembly  300  divided by the pressure drop across the throttle body as the air flows therethrough, as indicated by curve  520  in FIG. 29. As seen in FIG. 31, venturi  500  of the embodiment disclosed produces a gain that is approximately 2.5 times greater than that of a conventional venturi.  
     [0109] These above venturi performance characteristics combine to provide more force acting on both the air and fuel diaphragms in regulator assembly  300 . These increased forces in turn produce a fuel injection servo  100  that is less sensitive to fluctuations in fuel supply pressure. especially near engine idle speeds. For example, when the engine is running near idle speed, the fuel supply pressure is lower than at higher engine speeds. In a conventional fuel injection servo, the force on the air diaphragm is also relatively low because the venturi gain, or signal, is also relatively low. Likewise, since the air diaphragm force is balanced by the fuel diaphragm force, as described earlier, the forces on the air and fuel diaphragms are relatively low at engine idle speed. For illustrative purposes only, this force is designated as 2 lbs. Under normal conditions, the fuel supply pressure will also fluctuate slightly at engine idle speed. For illustrative purposes only, the fluctuation in fuel supply pressure is designated to produce a force of 1 lb. on the fuel diaphragm. This fluctuation in the fuel supply cause the fuel diaphragm to pulsate as well, and since the magnitude of the force generated by the fluctuation in the fuel supply is, for example, significant relative to the forces on the air and fuel diaphragms at engine idle speed, the fluctuation causes pulsation in the metered fuel that is delivered to the engine. Thus, at low engine speeds, the engine is susceptible to running rough.  
     [0110] With the improved venturi performance of the present embodiment, the forces imposed upon the air and fuel diaphragms at engine idle speed are greater than that in the conventional fuel injection system. For illustrative purposes only, the force on the air and fuel diaphragms at engine idle speed is designated to be 5 lbs. Thus, the fuel supply pressure fluctuations, which remain the same at 1 lb. (as above), become a smaller percentage of the air and fuel diaphragm force and, therefore, the fuel supplied to the engine contains less pulsation at engine idle speed. As a result, the fuel injection system of the embodiment disclosed is less sensitive to fuel supply pressure fluctuations at engine idle speed and, consequently, the engine runs more smoothly, even at engine idle.  
     [0111] The numeric forces used in the above explanation and elsewhere throughout the disclosure are for illustrative purposes only and are not intended to be limiting or an accurate value experienced by the fuel injection servo  100 . Rather, the numerical values were chosen only to illustrate that the forces imposed on the air and fuel diaphragms of the embodiment disclosed are relatively higher than those imposed on the diaphragms of a conventional fuel injection servo.  
     [0112] An aspect of the present invention is that throttle body assembly  400 , valve body assembly  200  (or valve body assemblies  600 ,  700  of the second and third embodiments, respectively), and fuel regulator assembly  300  are of modular construction. That is, each is a separate structure that can be separately assembled and tested. Also, the valve body assembly  200  and the fuel regulator assembly  300  can be calibrated separately from the throttle body assembly  400 . With this modular design, assembly of the entire unit (i.e., the fuel injection servo  100 ) is as follows. Fuel regulator assembly  300  is individually calibrated on a flow stand for a given engine requirement, i.e., a throttle body size. (A single throttle body will support a horse power range, which corresponds to a range of engine sizes). Calibration of regulator assembly  300  comprises inputting a pressure signal to the regulator to simulate a venturi pressure signal and properly shimming the servo seat, the center body, and bellows cage, adjusting the regulator stem position. and adjusting other various components within the assembly to ensure that the assembly operates as expected for a given pressure signal. Valve body assembly  200  (or valve body assemblies  600 ,  700  of the second and third embodiments. respectively) is also calibrated as a separate unit, which comprises pressure checking the idle and manual mixture control valves and an idle cutoff leakage check. From this point forward, further calibration is not required. After the fuel regulator and valve body assemblies are separately calibrated, they are assembled onto throttle body  402  and the fuel injection servo unit  100  is placed inside an air box for further testing.  
     [0113] This modular design enables interchangeability between throttle body assemblies, valve body assemblies, and regulator assemblies without having to recalibrate the entire fuel injection servo  100  as a unit, or without having to recalibrate an unaffected assembly. Each assembly can be preassembled and precalibrated for an anticipated throttle body size without being assembled as a single fuel injection unit, and each assembly shelved for later use. Thus, when an order for a fuel injection servo is placed, the unit can then be assembled without the need for recalibration, thus shortening the turn around time for an order and effectively eliminating the customization of each valve body assembly  200  and fuel regulator assembly  300  for a specific fuel injection servo unit  100 . Additionally, any single valve body assembly or regulator assembly could be used on a variety of throttle bodies having different sizes by simply calibrating valve body assembly  200  and fuel regulator assembly  300  for the throttle body size desired. Additionally, because all of the components of the venturi are machined from billet material, the venturi has consistent dimensional and surface finish characteristics which in turn results in consistent venturi performance. This consistent venturi performance within the throttle body assembly thus enables modularity of the fuel regulator and valve body assemblies because neither need to be customized (i.e., calibrated) for a particular throttle body assembly. Therefore, a single valve body assembly  200  (or valve body assemblies  600 ,  700  of the second and third embodiments. respectively) or regulator assembly  300  could be used on any throttle body assembly because of the repeatable, consistent venturi performance characteristics.  
     [0114] The above modularity also creates versatility of the fuel injection system of the embodiment disclosed. For example, to make a modification to the valve body, only the casting need be replaced with a modified one, rather than having to replace the entire throttle body. Also, when a modified valve body is installed, regulator assembly  300  does not have to be recalibrated, and vise versa. Thus, if an enrichment circuit (or any other modification within the valve body assembly) were to be added to valve body  204 , which entails more fuel channels arid jets within the valve body, it is not necessary to replace the whole throttle body  402 . as would be necessary with conventional, integral systems, nor is it necessary to recalibrate regulator assembly  300 . Rather, only the new valve body assembly with the modifications desired need be replaced. Thus, the valve body assemblies of FIG. 10C (second embodiment) or FIG. 10D (third embodiment), which include an enrichment system and a bypass circuit, respectively, can simply replace the existing valve body assembly installed on the throttle body assembly without having to recalibrate the fuel regulator assembly. This, of course, saves cost and time. Similarly, if valve body assembly malfunctioned and required replacement in the field, only the valve body assembly would need to be replaced, and regulator assembly  300  would not require recalibration. Likewise, if regulator assembly  300  malfunctioned in the field, it could be replaced without the need to change throttle body assembly  400  and without the need to recalibrate the existing valve body assembly because the valve body assembly and regulator assembly are each mounted to the throttle body  405  at separate locations and each are individually removable. A new regulator assembly  300 . which is already preassembled and precalibrated, could simply be taken from the shelf and installed on the existing fuel injection servo  100  unit.  
     [0115] Furthermore, the modular design reduces the manufacturing costs associated with producing a throttle body  402 . First, because valve body  204  is separate from the throttle body, the intricate fuel channels associated with the valve body are no longer part of the throttle body casting. Thus, the throttle body casting is more cost effective to produce. Secondly, the amount of scrap generated due to manufacturing defects is reduced. In a conventional, integral throttle body, when a manufacturing defect was found in an integrated valve body/throttle body casting, the entire casting had to be discarded, even if the defect occurred in only one portion of the casting. With the modular design, the amount of scrap is reduced, because if a defect is found in a throttle body or a valve body casting, only that particular defective component need be discarded.  
     [0116] As mentioned earlier, the fuel injection servo  100  constructed with the principles of the present invention may be generally installed onto an internal combustion engine, generally indicated as reference numeral  900 , used primarily for aircraft, as shown in FIG. 32. The engine  900  is shown having the fuel injection servo  100  mounted generally at the forward end of the engine such that air  101  enters the airflow channel  435  of the throttle body assembly  400 . The fuel injection servo  100 . however. may be mounted at any location on or proximate the engine. Also seen in FIG. 32 are exhaust manifold pipes  903  and a conventional alternator device  917  that is driven from the engine&#39;s main output shaft  919 , as is known in the art. A propeller (not shown), or other thrust generation device depending on the vehicle or craft to be driven, is typically mounted to output shaft  919 .  
     [0117] Referring to FIGS. 32 and 33, the internal combustion engine, as generally known in the art, includes a cylinder block  902  having at least one cylinder bore  904  therein, a head  906  having an inner wall  908  mounted on the cylinder block, at least one piston  910  reciprocally movable in the at least one cylinder bore, at least one piston having a top face  912 . at least one combustion chamber  914  defined by the inner wall  908  of the cylinder head and the top face  912  of the at least one piston  910 , at least one intake valve  916  movably mounted on the cylinder head  906  in communication with the at least one combustion chamber-  914 , and an exhaust valve  918  movably mounted on the cylinder head in fluid communication with the at least one combustion chamber  914 . The engine  900  also includes at least one ignition device, such as a spark plug  920 , to ignite the fuel mixture within the combustion chamber  914 . The remaining components of an internal combustion engine are generally known in the art and are therefore not described in detail.  
     [0118] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments and elements, but, to the contrary, is intended to cover various modifications, combinations of features, equivalent arrangements, and equivalent elements included within the spirit and scope of the appended claims. Furthermore, the dimensions of features of various components that may appear on the drawings are not meant to be limiting, and the size of the fuel injection servo and components therein can vary from the size that may be portrayed in the figures herein.