GB2505238A - Variable area carburettor throat - Google Patents

Abstract

A variable area carburettor throat comprises a conical plunger 8 and a funnel-shaped tube 2 which are relatively movable axially, the outer cone face of the said plunger and the inner wall of the funnel-shaped tube having gradients, eg 22 and 16 degrees, which differ in a largely fixed relationship along and about their axis. The plunger 8 may be supported by arms 4 inside an outer casing 6 having air holes 1 while the funnel 2 is movable eg by a lever-operated throttle wire connected at 9. Alternatively, the plunger may be movable inside the stationary funnel. A location 5 is provided for fuel injector (10, fig.4). Fuel under pressure is sprayed into the inward flow of air to create a constant fluid admixture downstream to an exit 7 connected to a manifold or engine cylinder, eg of a motorcycle or scooter.

Description

A VARIABLE AREA CARBURETTOR THROAT

Field of the Invention

The present invention relates to a variable area carburettor throat, more particularly for connection to an engine, manifold or cylinder.

Background

According to laws governing fluid dynamics, a fluid's velocity must increase as the fluid passes through a constriction such as a funnel, to satisfy the principle of continuity, while its pressure must decrease to satis4' the principle of conservation of mechanical energy.

Thus any gain in kinetic energy a fluid may accrue due to its increased velocity through a constriction is negated by a drop in pressure.

This effect is known as the Venturi effect and is a jet effect; as accordingly with a funnel velocity of the fluid increases as the cross sectiOnal area decreases, with the static pressure correspondingly decreasing.

In a carburettor the faster air moves, the lower the air's static pressure, and the higher the air's dynamic pressure. A throttle or accelerator linkage of a vehicle does not directly control flow of liquid fuel, the accelerator merely actuates carburettor mechanisms which meter the flow of air being pulled into the vehicle's engina The speed of this flow, and* therefore its pressure, determines the amount of fuel drawn into the airstream, and under correct conditions atomising.

In some embodiments of such engines, carbujrettors may use the Venturi effect to suck gasoline or fuel into the engine's intake air stream.

Jets that are sized for full power tend to starve the engine at lower speed and part throttle. Most commonly this problem has been corrected by using multiple or moveable jets. In movable jet carburettors the problem is corrected by varying the jet size, such as by a slide carburettor.

A slide carburettor has a jet position directly actuated by a physical connection to the throttle cable, controlled by the user's demands rather than demands of the engine.

This means that the metering of the fuel and air and consequent admixture can be inaccurate unless the vehicle is travelling at a constant speed at a constant throttle setting. This inaccuracy results in fuel waste, particularly as the carburettor must be set slightly rich to avoid a lean condition, which condition can cause engine damage.

In order to obtain improved fuel economy and more tractable low-speed behaviour some carburettors feature a variable Venturi controlled by a piston.

This piston has a tapered metering rod, usually referred to as a needle that enters inside an orifice and admits fuel into the airflow passing through the carburettor. The needle is tapered and opens and closes into the orifice across airflow, regulating the input of fuel and flow of admixture, and wherein movement of the piston controls the amount of fuel delivered depending on operatdrf engine demand.

Opposing weight of the piston is a spring, compressed by the piston rising, and such carburetton are known as constant depression.

If the airflow into the engine is increased by opening the throttle, the piston rises, increasing the size of the Venturi. The result is that the pressure drop in the Venturi remains the same regardless of the speed of the airflow, but the piston rises and falls according to the speed of the airflow.

Rate of fuel delivery is fixed to rate of air delivery being possible to obtain good and consistent atomisation of fuel under all operating conditions.

A problem of the constant depression carburettor is in high performance applications.

Since the carburettor relies on restricting air flow in order to produce enrichment during acceleration, the throttle response may be sluggish and imprecise. By contrast a fixed choke design adds extra fuel using a pump.

Prior Art

Accordingly a number of patent applications have been filed in an attempt to resolve the problem or similar, including the following: Granted Japanese patent JP 58 006 057 (WOOD) discloses a fuel distributing apparatus comprising a variable area venturi carburetor having an induction passage open to air at ambient pressure at one end and connected to the intake manifold of an internal combustion engine at the other end to be subject to the changing manifold vacuum or pressure depression therein, the passage having a variable flow area venturi defined by a converging-diverging nozzle having converging and diverging portions joined by a throat therebetween, the venturi having at least one wall movable in opposite directions to contréct or expand the throat and nozzle flow areas, means moving the movable wall, the nozzle being so constructed and designed as to maintain sonic velocity to the flow through the throat over essentially the entire idle speed and part throttle operating range of the engine, with an increase to supersonic velocity downstream of the throat followed by a decrease to subsonic velocity by passage of the flow through a shock wave, the shock wave varying in location between the throat and exit portion of the nozzle as a function of the change in throat area and manifold vacuum levels, means to move the movable wall to change the throat and nozzle flow area, and means introducing fuel into the nozzle below the throat in close proximity to the shock wave and always within an axially extending band including the vertical positions of the shock wave attained in response to changes in nozzle flow area and/or manifold vacuum levels during part throttle operating conditions, the movable wall portion being pivoted adjacent its upper end for a swinging arcuate movement, the wall portion having the profile of one-half of a *convergent-divrg nozzle.

Granted European patent EP 0 011 994 (ABBEY) discloses an automatic control system for supplying a fuel-air mixture to the inlet of the intake manifold of the internal combustion engine of a vehicle for regulating the ratio of air to fuel so that this ratio is optimised for prevailing conditions of engine speed and load, said system comprising: A. a variable Venturi structure whose input is coupled to a source of combustion air and whose output is coupled to the inlet of said intake manifold, said structure including a throat and a mechanism to adjust the effective area thereof; B. a servo motor operatively coupled to said mechanism to adjust the area of said throat; C. fuel supply means including a metering valve which controls an auxiliary amount of the fuel to feed fuel into said Venturi structure to be intermixed with said air; D. an auxiliary fuel-control motor operatively coupled to said valve to adjust the auxiliary fuel feed thereof; E. means to sense the difference in air pressure existing between the input to the Venturi structure and its throat to generate a command signal indicative thereof; F. a controller responsive to said command signal.to compare said signal with a servo motor set point to produce an output which is applied to the servo motor to adjust said throat area in a direction and to an extent àausing the velocity of air through said Venturi structure to comply with said set point; said controller, said servo motor and said means to sense air pressure constituting a closed process control loop; G. means to sense the degree of vacuum in said intake manifold to control said auxiliary fuel-control motor to adjust the auxiliary fuel feed accordingly, said degree of vacuum reflecting the prevailing conditions of speed and load; H. a transducer coupled to said auxiliary fuel-control motor to produce an auxiliary signal proportional to the degree of vacuum; and I. means to apply said auxiliary signal to said controller in said loop to modulate said command signal to cause the rate of air flow through said Venturi structure to assume a value relative to the rate of fuel flow at which the resultant ratio is optimised with respect to said prevailing conditions of speed and load.

In contrast the present invention provides a simple and cost-effective means by which a carbureftor may include a variable Venturi throat in conjunction with an injector, so as to provide a sustainably correct ratio of atomised fuel to air, and increase supply of both air and fuel contemporaneously and at high pressure.

Summary of the Invention

According to the present invention there is provided a variable area carburettor throat comprising a plunger moving in a tube; said plunger having an outer cone face predominantly disposed on a first gradient, about an axis, and said tube with an inner funnel wall predominantly, disposed on a second gradient about said axis; and said gradients differing in a largely fixed relationship along and about said axis.

In preferred arrangements an injector is situated prior to the throat, said injector injecting, providing or feeding pulses of fuel into the throat or more particularly stream of air into the throat as required.

The resultant admixture is drawn through the throat and in addition or the alternative the admixture is atomised and increased in velocity, as a result of the Venturi effect.

More particularly the throat thereby mixes and atomises fuel with air in a fixed relationship, as air and fuel passes through the throat past the plunger to a manifold or cylinder, through the tube towards the plunger and past the plunger, with the plunger distance along the axis from the wall being variable so as to increase or decrease velocity of resultant air and fuel admixture.

In preferred embodiments said fixed relationship is stoichiometric, or near to. and variation of the throat area includes control of the tube movement along the axis.

In preferred embodiments the movement may be acting in concert with at least one position sensor to regulate position of the tube and enhance and control feed and atomisation of fuel in relation. The movement may also be regulated with low pressure fuel injector metering devices. Preferably said injector acts under pulses.

The throat position sensor also cooperates an injector metering device within the tube, which device is able to monitor and meter injection or injector action according to user or manufacturer preference, for stoichiometric settings over a whole range.

In preferred embodiments the tube is movable along the axis with respect to the plunger and generally towards the cylinder or manifold. Typically the tube moves with respect to the plunger, wherein the plunger may be fixed at, from or to a manifold or cylinder. In this way vacuum suction downstream on the plunger is irrelevant, wherein the tube is less liable to undesirable movement through suction of the vacuum. As it draws the tube closer, the area increases in between, and less air drag/friction situations occurs.

The variable throat operates under critical flow conditions wherein flow through the throat is at sonic velocity I at or near to Mach 1 and consequently conditions at, in or through the throat are a function of upstream atmospheric conditions and not downstream conditions.

The collaborative design of the plunger and tube are such that the throat is maintained at sonic velocity over most of the engine's range of manifold vacuums and the ratio of vacuum at any position above the throat to the throat is constant.

Fuel input can be metered at any position above the throat and maintained at a constant ratio of air to fuel. This allows easy monitoring of fuel input and effective injection with regards to the stoichiometric ratio and position sensor.

In addition the throat movement increases dynamic pressure, atornising the admixture, leading to a subsequent burn that is more efficient, at or near the stoichiometric range.

In preferred embodiments the funnel and plunger have set gradients that typically extend across most of the face and wall, wherein said gradients differ between the plunger and funnel wall, and said gradients are calculated to funnel and/or create a vacuum and/or the Venturi effect, and a consequent high speed of propulsion of admixture into a cylinder or manifold or engine.

Some further embodiments may include incrementally varied gradient faces and walls so as to smoothly direct fluid or admixture through the throat.

The tube thereby features a decrease in inside diameter that in common to the increase in plunger outside diameter is used to increase flow velocity of the air and thereby cause a pressure drop; and draw air and/or fuel from upstream into the stream or throat as appropriate, wherein downstream the mixed fuel/ air is provided at high velocity to the cylinder, or manifold of the engine.

Since sonic velocity at the throat causes the fuel to be atomized to very small particles (about 20 microns) in addition or the alternative this results in a fine fog which flows uniformly to each cylinder or manifold intake, thereby enabling the engine to operate extremely efficiently at lean air fuel ratios.

Advantageously a finely machined or finished outer cone face, and/or plunger, and inner funnel wall, and/or tube, may provide minimal frictional resistance to the admixture and allows the fixed relationship to be as standardised as possible.

In addition or the alternative in all preferred embodiments there is minimal to no interference with the throat to complicate, disturb or alter flow through the throat, and in consequence the ratio may be easily calculated and maintained as close to optimal or stoichiometric at all times. The invention thereby provides an apparatus for atomizing liquid fuel while mixing it with air, and varying the amount of each while maintaining a substantially constant fuel/air ratio stochiometric for the intake manifold of an engine.

Preferably the tube is moved with respect to the plunger. For example in some embodiments arms may be extended through the tube onto which the plunger is mounted, for a fixed position.

In preferred embodiments the plunger is fixed on a stalk centrally supporting the cone face and the tube moves relative to the plunger. This movement is measured, monitored and/or controlled by a position sensor situate within the tube, which sends a signal to an injection control box, which box pulses fuel into the throat upstream.

As the plunger moves in relation to the tube, the plunger is moving against a vacuum, forcing admixture downstream, which magnifies throttle closure, as crude admixture entering the throat is refined and increased in velocity passing through the throat.

A position sensor acts with the injector to remove any lag in fuel metering and additionally an electronic control unit (ECU) also considers and accommodates ambient, and engine temperature, incline, engine rpm and exhaust conditions using a lambda sensor, and other conditions as appropriate.

The invention has been described by way of examples only and it will be appreciated that variation may be made to the above-mentioned embodiments without departing from the scope of invention.

With respect to the above description then, it is to be realised that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Brief Description of Figures

Figures 1 show cross sectional top views of an embodiment of the throat open (1A) and closed (1B) respectively; Figures 2 shows an isometric view of the embodiment and side cross sections shown in Figure 1 plus image of typical injector in situ; Figure 3 shows a sketch of a reverse isometric view of the embodiment of Figure 1; And Figure 4 shows an isometric cross-sectional view of the embodiment of FiOure 1.

Detailed Description of Figures

The pictured embodiment includes an inner (moving) funnel shaped tube with an internal gradient of 22 degree relative to a central axis and a stationary coned shaped plunger with an outer cone gradient of 16 degree relative to the same central axis.

In particular as shown in the Figures the embodiment includes: Air inlet holes 1; inner funnel shape tube 2 movable by lever in an axial direction towards /away from cylinder, manifold or engine to form adjustable passage, the sonic Venturi throat 3; Central plunger support amis 4; A location for injector/ fuel metering device 5; Outer enclosure/casing 6; Exit/outlet towards cylinder 7; Stationary cone shaped plunger 8; Throttle wire connection / position sensor 9 attached to this arm, this setup/design, may be altered to suit different applications/motors; Standard fuel Injector (Figure 3, 10), in location.

The pictured and preferred embodiment is a throttle body injection system with an Venturi which comprises of a stationary conical cylindrical plunger and a movable outer funnel shaped cylindrical tube to form a sonic Venturi throat. In summary the pictured and preferred embodiment provides a less costly enhancement, to replace a standard carburettor, on motorcycles and scooters.

Additionally there is a fixed location for an injector metering device. This device provides a wide angle split cone spray injection.

In some further embodiments the location may be variable or varied according to settings, user or manufacturer preference.

The injector type fuel metering device is ideally located in an upstream atmospheric condition typically within the tube and before the plunger In some embodiments it may be situate outside the throat.

Fuel under pressure is sprayed into the inward flow of air, towards the plunger and/or throat, to create an air and fuel velocity at which the fuel atomizes to a fine mist and to give or create a constant maintained fluid admixture downstream into a manifold or cylinder or engine.

The injector is configured to release pulses of fuel under electronic instruction with relation into the area in-between outer and inner wall controlled by the ECU system.

Compared to the regular injection system this is as well a mass air flow sensor within the throat