Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M69/00—Low-pressure fuel-injection apparatus ; Apparatus with both continuous and intermittent injection; Apparatus injecting different types of fuel
  • F02M69/16—Low-pressure fuel-injection apparatus ; Apparatus with both continuous and intermittent injection; Apparatus injecting different types of fuel characterised by means for metering continuous fuel flow to injectors or means for varying fuel pressure upstream of continuously or intermittently operated injectors
  • F02M69/18—Low-pressure fuel-injection apparatus ; Apparatus with both continuous and intermittent injection; Apparatus injecting different types of fuel characterised by means for metering continuous fuel flow to injectors or means for varying fuel pressure upstream of continuously or intermittently operated injectors the means being metering valves throttling fuel passages to injectors or by-pass valves throttling overflow passages, the metering valves being actuated by a device responsive to the engine working parameters, e.g. engine load, speed, temperature or quantity of air
  • F02M69/20—Low-pressure fuel-injection apparatus ; Apparatus with both continuous and intermittent injection; Apparatus injecting different types of fuel characterised by means for metering continuous fuel flow to injectors or means for varying fuel pressure upstream of continuously or intermittently operated injectors the means being metering valves throttling fuel passages to injectors or by-pass valves throttling overflow passages, the metering valves being actuated by a device responsive to the engine working parameters, e.g. engine load, speed, temperature or quantity of air the device being a servo-motor, e.g. using engine intake air pressure or vacuum
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M7/00—Carburettors with means for influencing, e.g. enriching or keeping constant, fuel/air ratio of charge under varying conditions
  • F02M7/12—Other installations, with moving parts, for influencing fuel/air ratio, e.g. having valves
  • F02M7/22—Other installations, with moving parts, for influencing fuel/air ratio, e.g. having valves fuel flow cross-sectional area being controlled dependent on air-throttle-valve position

Definitions

• any fuel-air metering device which is not a positive displacement device will have fuel governed by the incompressible flow equation (Bernoulli's equation) and will have the air flow governed by the compressible flow equation.
• These equations are exact in the same physical sense that the basic equations of Newtonian physics are exact, and in the same sense that the tabulated thermodynamic functions (for instance, entropy, enthalpy, and internal energy) are exact functions.
• the present invention fuel-air metering system involves only the compressible flow equation for air flows, the incompressible flow equation governing the fuel flow, and simple geometry. It is therefore a fundamentally simpler system than that involved with injection systems using solenoid valves, and also a much simpler system than conventional carburetors which have a multiplicity of interlocking air-fuel control systems which interact in complex and analytically intractable ways.
• the inventors have considered a number of practical economic and structural issues.
• the system is designed to be compatible with inexpensive low pressure diaphragm fuel pumps, although it is also compatible with higher fuel pressure systems.
• Any system designed to meter to high accuracy must have parts built to a similarly high level of accuracy, but the inventors have taken pains to make sure that the parts of the system which must be made to close tolerances can be made so by simple manufacturing techniques.
• issues of durability as well as dynamic response have been considered.
• the present invention is adapted to easily connect with either conventional control via diaphragms or with electronic air/fuel ratio controls of one sort or another.
• the interaction of the metering system with its control system is in each case analytically clear and straightforward.
• the parts involved in the control system can be made with relatively large absolute dimensions, so that they can be made to high relative accuracies.
• Figure 1 shows an air flow passage with a specially adapted butterfly valve and with a two orifice in series air flow bypass system which generates, the signal for controlling fuel pressure drop across a fuel control valve.
• Figure 2 shows the fuel flow control arrangement, including a fuel flow control valve linked directly to the butterfly valve throttle shaft and a regulation arrangement which sets the pressure drop across this variable orifice in proportion to the pressure drop across the upstream orifice of the two orifice in series bypass system shown in Figure 1.
• Figure 3 shows a fuel air metering system with several of the fluid mechanical details more clearly shown.
• Figure 3 is partly schematic, and shows the fuel control valve and air throttle in different places, although both of these valves are on the same shaft in the preferred form of the invention.
• Figure 3 particularly shows the shape of the air throttle and details of the design of the pressure regulation system.
• Figure 4 shows a two orifice in series flow system in one of the preferred forms of the invention, illustrating particularly orifice shapes having coefficients of discharge which are insensitive to either Reynold's Number or Mach Number in the operating range of the system.
• Figure 5 is a cross-section of the fuel flow control valve which is linked directly to the air throttle, showing details important in producing a valve which obeys the proper geometrical equations and exhibits insensitivity of coefficient of discharge to Reynold's Number.
• Figure 5A is a sectional view taken on line AA of Figure 5, showing the upstream or convergent portion of the valve of Figure 5.
• Figure 5B is a sectional view taken along line BB of Figure 5, showing the shape of the outlet of the valve producing very sudden expansions for minimum pre.ssure recovery and minimum Reynold's Number sensitivity of the valve. With the minimized pressure recovery downstream of the valve, the flow in the downstream passages is nearly equal to the vena contracta static pressure downstream the variable orifice of Figure 5.
• Figure 6 is a view of the downstream side of the throttle plate of Figure 3, showing a notched section for the idle air flow of the system.
• Figure 7 is a plan view of the passage shown at 111 and 112 of Figure 3, showing how the axial distribution of fuel into the high speed air stream is achieved, and how this distribution varies as the throttle opens.
• Figure 8 is analogous to Figure 4 and shows an upstream orifice arrangement where approximately 50 percent pressure recovery is obtained downstream of the upstream orifice.
• Figure 9 shows important compressible flow relations, plotting particularly both the ratio which shows the fraction of sonic mass flow occuring at a specific pressure drop, and also showing the compressibility function .
• Fig ure 9 is copied from Page 197 of The Internal Combustion Engine in Theory and Practice, Vol. 2 by Charles Fayette Taylor, MIT Press, copyright 1968.
• the metering system air control valve (throttle) and the fuel control valve are on the same throttle shaft (or are otherwise positively linked) and are arranged so that the effective flow areas of the air valve and the fuel valve stay in a fixed proportion as both valves open and close together.
• the fuel flow per unit effective fuel valve area is maintained in fixed proportion to the air flow per unit effective air throttle area. This requires that the pressure drop across the fuel valve be controlled to vary in exact proportion with the square of the mass flow of air per unit area past the air throttle valve.
• This pressure regulation is achieved by a variable restriction servo-valve which controls the pressure drop across the linked fuel valve in proportion to the pressure drop across the upstream orifice of a two orifice in series air flow bypass sytem.
• Figures 1 and 2 show the air circuit and fuel circuit of the metering system in schematic form.
• a throttle plate 1 pivots on shaft 12 in an air flow passage 3.
• Throttle plate 1 is specially shaped with smoothly convergent surfaces and with a vortex stabilizing contour on the upwardly pivoted side.
• This aerodynamic shaping of the throttle valve is required to achieve an air throttle having a coefficient of discharge at each opening position which is relatively insensitive to variations in Mach Number and Reynolds Number which occur due to variations in the pressure drop across the throttle.
• This shaping is important: Conventional throttle plates exhibit variations in coefficient of discharge of as much as 30 percent, and this variation in coefficient of discharge is quite unacceptable in the current metering system.
• a small fraction of the air flow past the carburetor passes through an air flow bypass system which generates a pressure differential used to control the fuel pressure dif ferential across the fuel valve.
• Intake air passes into opening 4 at approximately stagnation pressure with respect to throttle 1 and this flow is sucked past a fixed orifice 5 which discharges into a relatively open passage 6.
• Air from passage 6 is sucked past fixed orifice 7 into passage 8.
• Passage 8 is located in a position where it is in contact with a pressure which approximates the vena contracta static pressure downstream of throttle 1.
• Orifice 7 is significantly smaller than orifice 5.
• the pressure drop across orifice 5 is small, so that air flowing past orifice 5 acts as an approximately incompressible fluid, in good analogy with the incompressible liquid fuel.
• Orifice 7 is designed to have a coefficient of discharge insensitive to Reynolds Number and Mach Number.
• the air flow past orifice 7 varies in almost exact proportion to the air flow per unit area past air throttle 1.
• the air flow past orifice 5 is exactly equal to the flow past orifice 7, and the pressure drop across orifice 5 varies to good approximation with the square of flow through orifice 5.
• the pressure drop across orifice 5 is therefore a good signal for proportional control of fuel pressure drop across the fuel valve. Movement of needle 9 changes the effective flow area of orifice 5 , and changing this flow area is a convenient way of changing the air fuel ratio supplied by the system.
• Figure 2 shows the fuel control arrangement which includes a fuel valve opening in proportion to the air throttle opening and a negative feedback fuel pressure drop regulation system controlling pressure drop across this valve in proportion to the pressure drop across air orifice 5.
• a fuel valve opening in proportion to the air throttle opening
• a negative feedback fuel pressure drop regulation system controlling pressure drop across this valve in proportion to the pressure drop across air orifice 5.
• slotted shaft plug valve 12a On the same shaft as throttle shaft 12 is slotted shaft plug valve 12a, which rotates within a receiving passage so as to have an effective flow area varying in precise proportion to the opening of air throttle 1.
• this slotted shaft is on the throttle shaft, so that there is a zero lag and extremely positive linkage between fuel valve opening and air throttle opening.
• Fuel air metering requires that the pressure drop across slotted shaft valve 12a vary in proportion to the pressure drop across orifice 5.
• the pressure drop across fuel valve 12a is varied in proportion to the pressure differential across air flow orifice 5 by fuel pressure regulator assembly 13, 14, 15, 16.
• a very low friction air piston 13 (which may have to be supported on hydrostatic bearings), is connected on its left face to a connecting passage 22 which connectes to passage 6 at the pressure downstream of orifice 5.
• On the right side of air piston 13 is the pressure upstream of orifice 5, which is communicated by connecting passage 20.
• the pressure drop across orifice 5 therefore produces a leftward force on piston 13 equal to the area of piston 13 times the pressure drop across orifice 5.
• This leftward force is transmitted by a thin cylindrical connecting rod 15 to fuel control piston valve 14 which rides in a cylinder on essentially frictionless hydrostatic gasoline bearings.
• the fuel control valve piston 14 is connected on its left side to fuel pressure upstream of fuel valve 12a by passage 21, and on its right side is connected downstream of valve 12a by passage 16; the pressure differential across the fuel valve 12a generates a rightward force on piston 14 equal to this pressure drop times the area of piston 14.
• the rightward force from piston 14 balances the leftward force from air piston 13; if the system is not in equilibrium, it will tend to move axially.
• Axial motion of assembly 14, 15, 13 will rapidly change the pressure drop across piston 14, and this change will act to restore equilibrium.
• Axial motion of piston 14 opens and closes fuel flow area to passage 16, and the orifice forced by piston 14 and passage 16 is the only orifice in series with fuel valve 12a. Passage 16 feeds fuel to the engine.
• Assembly 14, 15, 13 acts as a servo controlled valve system controlling the pressure drop across the sleeve of piston 14 (the pressure difference between passage 11 and passage 16). Because passage 16 is the only outlet for fuel which flows past valve 12a, the axial position of piston 14 directly controls the pressure drop across valve 12a, and hence the fuel flow of the metering system. If assembly 13, 15, 14 doesn't stick, piston 14 will move to an axial position producing an exact force balance.
• a force balance between fuel piston 14 and air piston 13 means that the fuel pressure drop across fuel valve 12a is proportional to the pressure drop across air orifice 5, which is what is required to produce a set air-fuel ratio from the analog carburetor
• the fuel flow control system of Figure 2 will work well if details are well handled and if the fuel pressure supplied to passage 10 is sufficient and smooth enough.
• a fuel air me tering system such as that shown on Figures 1 and 2 has oper ated successfully and with excellent accuracy on a test stand at Southwest Research Institute. The function of the system is rather simple and straightforwardly described with exact mathematics. Air flow past an air throttle 1 obeys to excellent approximation the standard compressible flow equation found in engineering textbooks.
• the air flow throttle is positively linked with a fuel flow valve so that the fuel flow metering area is proportional to air throttle opening.
• a two orifice in series air bypass system generates a flow signal closely proportional to the square of the mass flow per unit area past the throttle.
• a negative feedback fuel regulator as sembly controls fuel pressure drop across the fuel metering valve in proportion to the signal generated in this bypass system by regulating the flow resistance of an orifice in series with the fuel valve, thereby varying flow until pressure drop across the fuel control valve is in balance.
• FIG. 3 shows solutions to these problems and has other advantages.
• the air flow passages and fuel flow passages in the metering system of Figure 3 are very closely analogous to those of Figures 1 and 2.
• the air flow passages analogous to Figure 1 are as follows: throttle 42 pivots in generally rectangular passage 40 and forms a variable area air throttle.
• the coefficient of discharge of air throttle 42 has been shown experimentally to be very insensitive to Mach Number and Reynolds Number variations.
• Flow from throttle 42 proceeds to downstream passage 44, and attaches in the form of a coanda wall attached stream to this wall.
• Well upstream of throttle 42 is pick up passage 46, which is shown schematically (in a proper system pick up 46 would be in a large enough passage so that it was picking up air at upstream stagnation pressure).
• Flow from 46 moves through low flow resistance passage 45 and passes through orifice 48, which is analogous to orifice 5.
• Downstream of orifice 48 is relatively large passage 49, which is large enough to dissipate the velocity of flow from orifice 48 and feed a relatively homogenous air flow to downstream orifice 50, which is analogous to orifice 7.
• Orifice 50 feeds passage 51 which is connected to the wall of passage 44 on which the high speed flow from air throttle 42 is attached.
• the downstream corner of the connection between passage 51 and air flow passage 44 is curved at 54, so flow from passage 51 merges smoothly with the main airflow and passage 51 contains a fluid at a pressure very close to the downstream vena contracta static pressure of air throttle 42.
• Variation of the effective open area of orifice 48 as a function of engine intake manifold vacuum is obtained by diaphragm assembly 66, 68, 70, which moves needle 60 in response to variations in the pressure of passage 56, which passage taps passage 51.
• the diaphragm control for needle 60 achieves a controlled enrichment of the mixture at low intake manifold vacuums.
• Diaphragm assembly 66, 68, 70 separates two chambers, chamber 49 is at the upstream pressure of orifice 48 and the other chamber 64 is at the downstream pressure of orifice 48.
• the diaphragm assembly functions analogously to piston 13 in Figure 2.
• Thin diaphragm 66 joins around its outside at peripheral connection 67 and is mounted on diaphragm cup 68.
• Cup 68 is rigidly connected to circular rod 70 which rides in bushing 72 so that rod 70 and bushing 72 provide axial alignment of the diaphragm assembly.
• the rightward side of the diaphragm assembly is at the pressure of chamber 64 which is connected through passage 47 to passage 45, approximately upstream throttle stagnation pressure.
• chamber 49 On the left side of the diaphragm assembly is chamber 49, which is at the pressure directly downstream of orifice 48.
• Diaphragm assembly 66, 68 produces a leftward force on connecting rod 98 carried in bushing 99 to form part of a servo-controlled fuel valve assembly very analogous to the assembly 14, 15 of Figure 2.
• the fuel flow circuit is analogous to Figure 2, and is partly shown schematically with details shown with respect to the fuel control servo valve arrangement.
• Pressurized fuel in relatively large passage 84 is supplied by a pumping arrangement (not shown) and fuel from 84 passes convergently into rectangular passage 82 which is closed off by slotted plug valve 80, which is shown schematically on Figure 3 and is preferred to be on the same shaft as the air throttle 42, in a manner further shown in Figure 5.
• Flow past slotted plug variable area valve 80 flows into a large expansion area 86, in a flow pattern characterized by Reynolds Number insensitivity and approximately complete dissipation downstream flow energy by turbulence, so that the pressure in passage 86 approximates the vena contracta static pressure directly downstream of plug valve 80.
• Passage 86 is large and characterized by low fluid resistance. Passage 86 feeds passage 88, of similarly low resistance.
• Large passage 88 flows from a relatively large area into a piston controlled servo valve area.
• Piston 95 rides on cylinder sleeve 91.
• ports 90 In sleeve 91 are symetrically located ports 90, which ports are arranged so that side forces on piston 95 due to pressure drops from the pressure of passage 88 to the pressure of passage ports 90 do not produce any net side forces tending to stick piston 95.
• Piston 95 has a knife edged shape on its piston skirt, and axial motion of piston 95 in sleeve 91 moves the knife edged skirt opening and closing ports 90 so that the interaction of piston 95 with ports 90 forms a servo controlled valve.
• Ports 90 feed an annular passage 92 around the outside of sleeve 91, and passage 92 feeds passage 110.
• Passage 110 feeds fuel to the airstream (and hence to the engine) via a distribution port arrangement 111, 112 described further in Figure 7.
• Static friction of piston 95 in cylinder sleeve 91 is further balanced by hydrostatic pressure balancing holes 93 symetrically spaced in sleeve 91, which holes serve to center piston 95 in the manner of a hydrostatic bearing.
• Piston 95 opening and closing ports 90 is a servo controlled valve which operates in close analogy to piston 10 of Figure 2.
• On the right side of piston 95 is a pressure very near to the downstream vena contracta static pressure downstream of variable area control valve 80. It has been found experimentally that with piston 95's skirt knife edge as shown, the fluid motion near piston 95 has very small effects on the pressure on this side of the piston.
• On the left side of piston 95 is chamber 100 which connects through a laminar filter 102 positioned in passage 101 with the pressure at pick-up port 104.
• the laminar flow filter 102 (which can be conveniently formed of a conventional cigarette filter) functions well to damp any oscillation in servo-piston valve 95, since any axial motion of piston 95 requires that flow pass through this filter.
• the function of the servo controlled valve assembly 91, 95, 99, 66, 68, 70 is substantially superior to that of the system shown in Figure 2.
• the diaphragm arrangement has been shown to have essentially vanishing hysterisis and static friction. Engine vibration is sufficient to essentially eliminate static friction in connecting rod 98 and compensating rod 70.
• the arrangement of ports 90 and 93 within sleeve 91 substantially eliminates the sticking of piston 95 within the cylinder sleeve 91 if these parts are carefully made.
• the assembly forms an extremely accurate negative feedback servomechanism system, which is well damped by the laminar resistance of the cigarette filter in passage 101. This system has been shown to obey the equations which would be predicted in a free body diagram to an exceptional degree of exactness.
• Air bag accumulator arrangement 115, 116, 118 is shown schematically to show how the two requirements can be satisfied at once.
• Inside container 115 is relatively flexible air bag 116 which contains air under pressure.
• mechanical grid 118 At the connection between air bag 116 and passage 84 is mechanical grid 118, which serves to constrain the expansion of bag 116 toward passage 84.
• Figure 3 also shows a simple and effective evaporative emission control, which closes off flow to passage 110 when the engine stops and fuel pressure in passage 84 drops.
• the system is intended to be used with a fuel pump arranged to leak down pressure when the engine stops. Such a pump is not shown, although many such pumps will occur to those skilled in the art.
• a plug carrier 120 coaxial with piston 95 carries spring-piston arrangement 124, 122, with piston 122 slidably carried within the cylindrical passage 120 and sealed with a relatively low friction 0-ring seal 130. Piston 122 is pushed rightward by spring 124.
• Port 126 and thence the passage containing spring 124 is connected to an engine manifold pressure (connection not shown) .
• engine manifold pressure connection not shown
• the pressure force in chamber 100 forces piston 122 leftward to the position shown.
• pressure in chamber 100 drops and spring 124 pushes piston 122 rightward, until piston 122 contacts piston 95 and pushes piston 95 to a position which fully closes ports 90 as well as ports 93. After this point fuel leakage from the system is negligible. The system therefore controls evaporative emissions.
• the operation of the servo controlled valve depends for its accuracy on a very low friction, low hysteresis and low spring constant characteristic of the diaphragm 66.
• a diaphragm shape we derived analytically has been tested experimentally and has the exceptionally low stiffness characteristics required (stiffness and hysteresis values more than a factor of 10 less than those characteristic of conventional diaphragms).
• the shape of diaphragm 66 in Figure 3 is the shape of this diaphragm when the diaphragm is undeformed (when the pressure drop across the diaphragm is negligibly small).
• the shape of the diaphragm is significantly different from conventional diaphragm shapes, and points in the diaphragm are shifted outward radially compared to the geometric shapes which are typical of the prior art. For example, consider point 120 on diaphragm 66. When the pressure drop across diaphragm 66 becomes significant, pressure forces will serve to change the shape of the diaphragm so that point 120 shifts radially inward. Virtually all other points on the diaphragm will similarly move inward radially.
• diaphragm stiffness occurs because of circum ferential stretching which occurs as the diaphragm moves axially, and the buckled form of the diaphragm shape 66 totally eliminates these circumferential stress terms, and in consequence, produces a diaphragm which is an order of magnitude less stiff than that of prior art diaphragms.
• the diaphragm shaping of 66 is useful, since it permits diaphragms to be used in devices of much higher precision than has heretofore been possible.
• throttle 42 The resistance of diaphragm 66 to axial motion with in the control range relevant to the servo control valve motion of piston 95 is essentially negligible, so that the diaphragm serves as an effectively zero friction piston which produces a force ideally suited for controlling servo valve piston 95.
• the detailed shape of throttle 42 is important. First it can be clearly seen that the open area of throttle 42 varies as the angle ⁇ increases according to the formula It should be clear that the projected open area of plug valve 80 with respect to its general rectangular passage should be a quite similar equation The Ks can be the same for both the fuel valve and the air valve, in which case the projected open area of both valves will vary in exact proportion. For conventional round butterfly valves, the air projected open area varies according to essentially the same relation, so that for both sorts of throttle valves a close proportioning between fuel flow valve area and air flow valve area is possible with a system which puts both valves on the same shaft.
• throttle 42 the shape of throttle 42 is arranged specifically so that it is very insensitive its coefficient of discharge to variations in Mach Number and
• maximum Mach Numbers may not be higher than .3, while the Mach Number range past the throttle plate will vary from Mach 1 to perhaps Mach .2 when the throttle is more nearly closed.
• Shaping the air throttle for Mach and Reynolds Number insensitivity is important for the practical performance of the present invention metering system.
• the variation of coefficient of discharge with Mach Number is around 30 percent and this variation entails an unacceptable 30 percent variation in air fuel ratio from the metering system.
• Figure 3 also shows an extremely inexpensive and exactly analytic system for enriching the mixture under conditions of very low manifold vacuum operation.
• Connecting Rod 98 has one end at the pressure of chamber 88, and the other end at the typically much lower pressure of chamber 49, so that a rightward error force is produced by con rod 98 equal to the cross sectional area of con rod 98 times the pressure difference between chambers 88 and 49.
• connecting rod 70 is also at the pressure of chamber 88, since it communicates with chamber 88 through passage 87. There is therefore a leftward force on connecting rod 70 equal to the cross sectional area of con rod 70 times the pressure difference between chamber 88 and chamber 64.
• the pressure differential between chamber 49 and and chamber 64 is typically much smaller than the pressure differential between either chamber and chamber 88.
• FIG. 3 shows as many details of the present invention metering system as can be readily placed in one drawing. There are details which, because of graphics, were not shown.
• the pickup of upstream air at 46 and the passages feeding the air orifice 48 are too small, and the pickup at 46 will not pick up air at true upstream stagnation pressure. This imposes an error, but one skilled in fluid mechanics can readily design an pickup analogous to 46 which does read approximately stagnation pressure upstream of the throttle plate.
• a pickup in the air cleaner passage (not shown) will read an excellent approximation of upstream stagnation pressure. In this case as in all others the difference between stagnation and static pressure becomes insignificant as velocities become very small.
• Figure 4 shows a two orifice in series flow system which corresponds closely to that in a metering system developed by the inventors, and particularly shows orifice shapes having coefficients of discharge which are insensitive to either Reynolds Number or Mach Number change in the operating range of the system.
• Block 145 is provided with chamber 146, which has a very large cross sectional area with respect to orifice 148, which corresponds to orifice 48 in Figure 3 and orifice 5 in Figure 1.
• a control needle 160 partly blocks off the cross sectional area of orifice 148. Flow past orifice 148 flows into chamber 149, and it can be seen that the cross section directly downstream of orifice 148 expands very suddenly so as to essentially eliminate pressure recovery of the flow downstream orifice 148.
• orifice 148 The smoothly convergent shape of orifice 148, with its large upstream passage and sudden expansion downstream produces an orifice which has a coefficient of discharge which is extremely constant so that the mass flow past orifice 148 obeys its theoretical flow equation to excellent accuracy.
• Orifice 148 is insensitive to Reynolds Number because the shape of orifice 148 constrains the flow streamlines in a pattern which is essentially invarient over the range of pressure drops relevant to orifice 148.
• the flow pattern downstream of orifice 148 is also effectively uniform over the range of flows relevant to the orifice.
• Chamber 149 is analogous to chamber 49 in Figure 3 and passage 6 in Figure 1. Chamber 149 is sufficiently large and sufficiently open so that the flow condition of the flow in the chamber as it approaches downstream orifice 150 is quite uniform.
• Orifice 15Q is analogous to ori fice 7 in Figure 1, and connects chamber 149 with chamber 151, which chamber is connected so that it is at the static downstream pressure directly downstream of the air throttle.
• the curvature of orifice 150 is also such as to produce an extremely constant coefficient of discharge, and the cross sectional area of orifice 150 is controlled with control needle 152. Axial motion of either needle 160 or 152 will change the air fuel ratio of a metering system connected to the flow block of Figure 4. It should be noted with respect to orifice 150 that the up stream flow is open and cleanly converging, and the flow from orifice 150 flows into a very expanded cross sectional area of chamber 151.
• Orifice 150 is designed to have a coefficient of discharge of nearly one, which means that the minimum cross sectional area of the flow streamlines occurs quite near the outlet plane of orifice 150 rather than farther downstream. Orifices with coefficients of discharge nearly one and no divergent sections are automatically insensitive to Mach Number, since compressibility effects cannot change the shape of their flow streamlines.
• the shape of orifice 150 should be carefully coordinated with the relatively narrow taper angle of needle 152 to assure that, for the range of needle axial position relevant to the system, the orifice 150 is always a convergent orifice, and never becomes a convergent divergent passage because of the interaction of the areas of the needle 152 and orifice 150.
• a rectangularly slotted shaft 160 rides in a closely fitted receiver sleeve 162 having generally rectangular flow passages in it, and slotted shaft 160 is one part of the throttle shaft which also actuates the air throttle shown in phantom lines as 172.
• the flow in the fuel valve is from left to right, and surface 164 forms a smoothly convergent passage shape which will be characterized by exceptionally thin boundary layers because of the rapid change in static pressure of the flow streamlines as they flow towards the gap between plug slot 160 and bottom surface 166 of sleeve 162.
• the trigonometric relation of the opening gap area to twist angle ⁇ is exactly proportional to the relation of the gap between throttle 172 and air passage surface 174 shown in phantom lines, and it is easy to arrange things so that the projected flow area of both valves varies in exact proportion.
• the shape of air throttle 172 is such that the coefficient of discharge of air throttle 172 is extremely insensitive to variations in Mach Number and Reynolds Number across this throttle. It is required that the coefficient of discharge as a function of shaft angle of the valve formed by 160 and 162 also be characterized by an insensitivity of coefficient of discharge to variations in pressure drop (and hence Reynolds Number) across this valve. Because the fuel flow valve handles an incompressible fluid, Mach number is not relevant, but Reynolds Number insensitivity matters.
• FIG. 5A is a view from the inlet passage.
• Fuel from a relatively large inlet passage 179 flows into the generally rectangular passage of sleeve 162 through rounding entrance curyature 176, and flows through the rectan gular passage until it contacts convergent surface 164, passing through the gap between surface 166 and 164 which forms the projected flow area of the valve.
• a number of issues illustrated in Figure 5A are important. First of all, the relatively large area of the passage 179 is important.
• the upstream pressure tap for the fuel regulator piston assembly for example tap 104 in Figure 3 should be in such a large section so that the pressure pickup will see pressure closely approximating stagnation pressure at surface 164.
• Another important issue is the rounded curvature of entrance surfaces 176, where the flow goes from the much larger passage to the rectangular slot leading to surface 164.
• valve When the valve is in relatively open condition, it behaves as two orifices in series, the first being the fixed orifice formed by curved surfaces 176 and the second being the orifice formed for the gap between surface 166 and the end point of surface 164 on slotted shaft 160.
• curvature of curved surface 176 By changing the curvature of curved surface 176, it is therefore possible to change the coefficient of discharge (and therefore the effective flow area) of the valve of Figure 5 as a function of shaft rotation. This must be done empirically, but it is relatively convenient to shape the rounded surfaces of 176 in such a way that the coefficient of discharge of the fuel valve and the air throttle match closely at all values of shaft angle.
• Reynolds Number insensitivity of the fuel valve also requires that the flow conditions downstream of the valve be properly controlled.
• Figures 5B in combination with Figure 5 shows how this can be done conveniently.
• slotted shaft 160 rotates counterclockwise in Figure 5 the fuel valve opens and there is a gap between surface 166 and surface 164 through which fuel passes.
• the high velocity fuel through this gap rushes downstream, and it is desirable to dissipate the velocity of this flow into turbulence with minimum pressure recovery if the fuel vlave is to show optimal Reynolds Number insensitivity.
• Reynolds Number insensitivity, and minimum pressure recovery are achieved by the most sudden convenient expansion of the fuel in the downstream section, and by arranging flow patterns to prevent wall attached streams from forming.
• Coanda wall attached streams should be avoided since such attached streams are conducive to larger values of pressure recovery than otherwise occur downstream of the fuel valve.
• Downstream of surface 166 is cutaway surface 170 which assures that the high velocity flow stream cannot attach to the lower wall of the downstream passage.
• the high velocity jet from the fuel valve expands rapidly, and the passage from the rectangular passage 184 to open passage 186 is also an abrupt opening conducive to small or zero pressure recovery.
• Figures 5, 5A and 5B show a fuel valve with a projected open area which varies in precise proportion with the projected open area of the air throttle valve, the fuel valve is bulit for an extremely constant coefficient of discharge over the range of Reynolds Numbers across which it must operate, and the shaping of curvatures 176 in the valve permits the coefficient of discharge of the fuel valve in relation to the air valve to be programmed as any desirable function of shaft angle ⁇ .
• FIG. 3 and 5 side views of Mach Number insensitive rectangular air throttle have been shown.
• Figure 6 shows a view of the downstream side of the throttle plate of Figure 3, showing a notched section for the idle air flow of the system.
• Throttle 42 is adapted to pivot on a shaft fitting through hole 192, shown in dashed lines. As the throttle pivots open, the open area between edge 194 and the left side of the rectangular passage in which the air throttle pivots opens for air flow. When the throttle is fully closed, there is still need for a minimum idle air flow and this idle flow passes through notch 195, which is adapted to produce a stable wall attached stream air flow downstream of the notch. This high speed stream is useful for downstream mixing purposes.
• Figure 7 is a view of the fuel input passage shown at 111 and 112 of Figure 3, showing how the axial distribution of fuel into the high speed air stream past the air throttle is achieved, and how this distribution varies as the throttle shaft rotates. It is well to look first at Figure 3 to see the fuel introduction ports at 111 and the passage 112, both in the vicinity of the opening edge of air throttle 42. Figure 7 shows an axial cut-away of this passage.
• the passage is characterized by a multiplicity of holes, 111, 200, 201, 202, 203, 204 and 205. When the throttle is fully closed and only the idle flow is passing, only hole 111 is open, and fuel from metering passage 110, shown in Figure 3, feeds directly to hole 111.
• each of holes 200 - 205 is laminar resistance material (which can be either of paper or of finely woven mesh) 206, which serves as a laminar resistance element for flow past holes 200 to 205.
• the throttle As the throttle rotates to open position, (depicted diagramatically by dashed lines 195, 194 in Figure 7) the throttle first uncovers hole 200 then hole 201 then hole 202 then hole 203 then 204 and finally 205, so that after the throttle is part way open fuel is being distributed evenly along the axial length of throttle 42, for even introduction to the downstream passage 40 and to the engine.
• This smooth axial distribution of fuel into the air stream is convenient for mixing arrangements downstream of air throttle 42.
• Figure 8 is analogous to Figure 4 , but shows an upstream orifice arrangement designed to produce 50 percent pressure recovery downstream of the upstream orifice.
• chamber 245 is linked by passage 280 with the upstream pressure side 282 of a diaphragm assembly 270 used in the metering system control assembly, and the pressure in chamber 245 is approximately stagnation pressure upstream of the air throttle. Flow from chamber 245 passes through smoothly convergent nozzle 248, where the flow passes into cylindrical passage 253.
• the ratio of orifice minimum cross sectional diameter to the diameter of cylinder 253 is equal to .62, which is a value taken from Fluid Meters, sixth edition, 1971, the American Society of Mechanical Engineers, New York, New York, Page 221, the value being chosen to produce 50 percent pressure recovery.
• nozzle 248 Directly downstream of nozzle 248 is pressure tap 246, which connects to the low stream pressure side 284 of the diaphragm, shown schematically as assembly 270.
• Flow from cylindrical passage 253 proceeds to open chamber 249, which feeds downstream orifice 250.
• Flow past orifice 250 expands to passage 251, which is strictly analogous to passage 151 in Figure 4, and passage 251 is at the vena con tracta static pressure downstream of the air throttle.
• Figure 9 shows the most important compressible flow relations, plotting particularly the mass flow per unit area versus the mass flow per unit area which would occur at sonic velocity as a function of pressure drop across a perfect orifice.
• the flow relations in Figure 9 are exact, and are used with precision in the two orifice in series passage and for the flow characteristics past the air throttle valve.
• Figure 9 is copied from Page 197 of The Internal Combustion Engine in Theory and Practice, Volume 2 , by Charles Fayette Taylor, MIT Press, copyright 1968.
• the horizontal axis of Figure 9 is plotted in terms of two inversely related variables, the first being Z ⁇ Pacross the orifice, and the second being the pressure ratio across the orifice.
• the vertical axis plots two important functions, the first shows the ratio of mass flow to mass flow at sonic velocity which happens at various pressure drops. It is notable that 50 percent of the mass flow which would occur at sonic velocity already occurs at a pressure drop of 6 percent. Also plotted is the compressibility function ⁇ 2 .
• Reference to Figure 9 may be useful on a number of occasions when considering the mathematical analysis of the metering system, and evaluating its precision.
• M a massflow rate of air
• M f massflow rate of fuel
• IMV intake manifold vacuum
• a f C f opening angle A i C i is a function of throttle angle, ⁇ .
• ⁇ P f fuel pressure differential across fuel valve equals stagnation pressure upstream of valve minus static downstream of valve).
• ⁇ is a compressibility function which constitutes the difference between the air flow function and the fuel flow function.
• O u upstream orifice of two orifice in series airflow analogy system
• O d downstream orifice of two orifice in series airflow analogy system
• the obj ective of a fuel-air metering system is to control air/fuel ratios as a function of engine control variables In notation :
• Bernoulli's equation (the incompressible flow equation) is The mass flow equation for a compressible fluid like air is
• Equation (5) Since the gro are essentially constant, let Equation (5) then becomes
• both A a C a and A f C f vary with rotation angle ⁇ of a shaft Algebraical substituting T and (V) into (V) yields
• Equation (V) Both sides of Equation (V) are proportional to the massflow of air per unit of effective air flow orifice area.
• Equation says that to get a constant air/fuel ratio from a metering system having a constant ratio of effective orifice areas between its fuel metering orifice and its air metering orifice, it is both necessary and sufficient that the pressure drop across the fuel metering orifice, ⁇ P f , be regulated in proportion to the square of the massflow per unit effective area past the airflow orifice.
• Equation (10) should look familiar to anyone who knows carburetors, since a venturi metering system has the suction of fuel into the airstream, ⁇ p fv proportional to the square of massflow of air M divided by ⁇ 2 , with ⁇ 2 a slowly moving function if the air venturi is large in relation to the air throttle opening.
• both A C and A fv C fv are fixed, so that are in constant ratio, in analogy with the requirements of equation
• the present invention metering approach has the airflow metering orifice and the fuel flow metering orifice each varying as engine load is varied, with the ratio held constant The practical advantage of this variation is very great.
• the pressure range required for fuel metering is much less, by the ratio 2 .
• intake manifold vacuum changes from 20" Hg to 1" Hg, there is less than a factor of change in massflow per unit effective butterfly valve area, so that less than a 9-fold variation in ⁇ P f is required.
• This smaller range is a much more practical range of ⁇ P to build hardware for, and it is therefore possible to build a metering system which involves only one basic fuel metering circuit to handle the entire flow range of engine requirements.
• the present invention also has the practical advantage that ⁇ P f varies roughly with intake manifold vacuum, and so is conveniently large under the low load conditions where auto engines operate most of the time.
• ⁇ P f K 5 ⁇ P diaphragm
• the diaphragm can have one side connected to a chamber located between the two orifices, with the downstream orifice O d connecting the chamber to static pressure downstream the air throttle and the upstream orifice O u connecting the chamber with the stagnation pressure upstream of the air throttle valve. On the other side of the diaphragm is the stagnation pressure upstream of the air throttle. With this arrangement, the pressure drop across the diaphragm is equal to the pressure drop across the upstream orifice O u ,
• the massflow equations are: Compressibility effects. exist for flow past both these orifices, but the importance of compressibility effects varies greatly with the magnitude of the ⁇ p across the orifice. For very small pressure drops the compressibility effects are so small that the flow equation for air approximates the incompressible flow equation which governs the fuel flow. If the area of upstream orifice O is much larger than the area of downstream orifice 0,, the great majority of the pressure drop across the system occurs across orifice 0,. For example, if the pressure drop across 0 is about 1% of total pressure at maximum, when the pressure drop across O d is sonic (choked flow).
• Equation for orifice O u is, to good approximation solving for ⁇ P Q u
• M Od is exactly propor tional to r O umax so a x% pressure drop in O u produces an x% reduction in M O d under choked (sonic flow) conditions.
• This condition (7b) can be satisfied by controlling the shape of convergent surfaces 17b shown in Figures 5 and 5A.
• the fuel regulator operates such that is the low case.
• 1 f is exactly proportional to —, which shows that for the low case i.s exactly propo n rtional to n.
• Q is an x% pressure drop, the system produces a uction in and hence a increase in
• air/fuel ratio varies directly J with the effective area of orifice 0u , and varies approximately inversely with the effective area of 0, Control of therefore, can be achieved by varying , by varying , or by varying both in combination.
• Orifices 0, and 0 can be built conveniently large,
• O u or O d could be replaced by two or more or if ices in parallel , for instance
• the equilibration time of the servo controlled fuel valve for example, the time for axial adjust ment of piston rod 95 in Figure 3, is not so fast as adjustment in the air bypass system itself, but can be made extremely fast.
• the rate at which the fuel servo equilibrates is mostly determined by the laminar damping coefficient of cigarette filter 102, which can be readily controlled.
• This equilibration time can be tested with, an arrangement which, puts a quick pulse of fuel into a passage such, as 86 of Figure 3, and which then monitors the time for equilibrium with a piezo electric crystal.
• the system can readily be held below 30 milliseconds and therefore the dynamic response to the current metering system can be exceptionally fast. It is worth noting that with orifice sizes corresponding to diaphragm fuel pump pressures the dynamic errors in the metering system during an acceleration are errors from the rich side (which is the safe side) so that nothing analogous to an accelerator pump is required by the function of the metering system curve per se.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Fuel-Injection Apparatus (AREA)
• Control Of The Air-Fuel Ratio Of Carburetors (AREA)

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• 1981
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