US3589384A

US3589384A - Flow rate-responsive fuel mixture control device with servomechanism

Info

Publication number: US3589384A
Application number: US782689A
Authority: US
Inventors: Konrad Eckert
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1968-01-05
Filing date: 1968-12-10
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29
Also published as: SE338898B; AT293103B; FR1588750A; JPS5114647B1; GB1200041A

Abstract

In the air suction tube of a fuel injection system associated with an internal combustion engine, there is displaceably held a control member which regulates a flow passage section for the air and meters the fuel in response to the change in the flow rate of air in the suction tube. The change in the static air pressure due to the change in the flow rate is utilized as an input force to control a servocircuit whose relatively large output force is used directly to displace said control member.

Description

United States Patent lnventor Konrad Eckert Stuttgart-Bad, Germany Appl. No. 782,689 Filed Dec. 10, 1968 Patented June 29, 1971 Assignee Robert Bosch G.m.b.II.

Stuttgart, Germany Priority Jan. 5, 1968 Germany P 16 01 360.8

FLOW RATE-RESPONSIVE FUEL MIXTURE CONTROL DEVICE WITH SERVOMECIIANISM 9 Claims, 1 Drawing Fig.

US. Cl

Int. Cl Field of Search [56] References Cited UNITED STATES PATENTS 1,550,717 8/1925 Towle .4 137/220 1,620,131 3/1927 Price 137/487 X 2,330,650 9/1943 Weiche 261/50 2,820,364 1/1958 Bevins et al. 261/50 FOREIGN PATENTS 885,821 12/1961 Great Britain 137/220 938,222 10/1963 Great Britain 137/220 Primary Examiner-Robert G. Nilson Attorney-Edwin E. Greigg ABSTRACT: In the air suction tube of a fuel injection system associated with an internal combustion engine, there is displaceably held a control member which regulates a flow passage section for the air and meters the fuel in response to the change in the flow rate of air in the suction tube. The change in the static air pressure due to the change in the flow rate is utilized as an input force to control a servocircuit whose relatively large output force is used directly to displace said I control member.

PATENTFflmmzsmn 3,589,384

Konrad ECKERT his ATTO Y lFLOW RATE-RESPONSIVE FUEL MIXTURE CONTROL DEVICE WITH SERVOMECIIANISM BACKGROUND OF THE INVENTION This invention relates to fuel injection systems associated with externally ignited internal combustion engines for particular use in motor vehicles. Said systems are of the type wherein the supply of air is controlled by an arbitrarily operable throttle member (butterfly valve) disposed in the suction tube and wherein the unmixed air in the suction tube flows past a displaceably held control member at least partially disposed within the suction tube-The control member, by virtue of its displacement, which is a function of the variations in the flow rate of air, varies a flow passage section in the suction tube. The fuel is, at a constant pressure drop, continuously metered at a variable throttle as a function of the position of said control member. a i

The purpose of fuel injection systems of the above type is to provide favorable mixture ratios permitting a complete combustion of the fuel at the highest possible efficiency of the engine with the lowest possible fuel consumption.

In known fuel injection systems of the afore-outlined type, the fuel is metered bya control member which is positioned as a function of the flow rate of air and which automatically regulates an air flow passage section in the suction tube, so that there is maintained a substantially constant static air pressure in the narrowest portion of the flow passage section. Such a device is described in British Pat. No. 1,066,721.

For displacing the control member, one of its sides is exposed to the force of a spring and to the static pressure prevailing at the narrowest portion of the flow passage section and its other side is exposed to the total pressure of the flowing air.

It is, however, disadvantageous to actuate the control member by pneumatic means directly, since the force effect of the air caused by pressure variations is small. Consequently, due to the unavoidable frictional effects, the positioning of the control member is not always an exact function of the flow rate of air.

To remedy this disadvantage the solution presents itself to enlarge the surfaces exposed to air pressures. Such an increase of the surfaces, however, would be inconvenient since, in the first place, it would require large volumes and, secondly, the pressure variations at the narrowest portion of the flow passage section would occur only slowly because relatively large volumes of air have to be exchanged. As a result, the control member would assume its position at low speed. Also, the masses to be moved as well as the required space would significantly increase.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved fuel injection system of the afore-outlined type wherein the control member rapidly assumes its new, desired position.

Briefly stated, according to the invention, the control member is displaceable by means of a hydraulic servo mechanism including a servo element which is moved by a pneumatic actuator. The latter operates as a function-of the static air pressure prevailing at the at least approximately narrowest portion of the flow passage section which, in turn, is varied by the control member. The servo element and the pneumatic actuator are interconnected in such a manner that the control member, in case of an increased static pressure of the air, is displaced in a direction to decrease the flow passage section for the air and, conversely, when the static air pressure decreases, the control member is displaced in the opposite direction and thus increases the flow passage section. First, there is provided a closed servo circuit (forming part of the servomechanism) and, secondly, the static pressure regulated by this servocircuit remains substantially constant at the narrowest portion of the flow passage section.

The invention will be better understood as well as other objects and advantages will become more apparent from the ensuing detailed specification of a preferred, although exemplary, embodiment of the invention taken in conjunction with the sole figure showing the embodiment in axial section.

DESCRIPTION OF THE EMBODIMENT The air required for the combustion passes in the direction of the arrow through a two-part suction tube 1 and flows past a control member generally indicated at 2 and an arbitrarily actuated butterfly valve 3 towards the cylinders (not shown) of an internal combustion engine (not shown). The fuel is drawn from a tank 4 through a filter 5 by means of a pump 6 and, flowing past a bypass 7 provided with an overflow valve 8, is led through a pressure conduit 9 under constant pressure to a fuel metering device 10 illustrated only in a schematic manner. A fuel conduit 11 leads from the metering device 10 to one or several nozzles 12 through which the fuel, preferably shortly upstream of the cylinder or cylinders, is injected into the suction tube 1.

The control member 2 comprises a hollow cylinder axially slidably held on a guiding tube 14 and coaxially disposed in a funnel-shaped portion 13 of the suction tube 1. To the cylinder 15 there is internally and axially secured a piston 16 slidably disposed within the guiding tube 14.

The cylinder 15 is provided with an upstream narrowing streamlined conical outer face which, together with the funnel-shaped portion 13, forms a narrow flow passage section 17 for the air. An outer portion of cylinder 15 is formed .as a cam 18 associated with a follower pin 19 which, upon displacement of cylinder 15, actuates a throttle (not shown) in the fuel metering device 10 for controlling the quantity of fuel admitted to conduit 11.

The guiding tube 14, which at its downstream end is closed fluidtight by a threaded screw cap 20, is pressfitted into a sleeve 21 rigidly held coaxially within the suction tube 1 by means of webs 22.

In the space 23 of the guiding tube 14 there is disposed a spring 24 which, at one end, is attached to the piston 16 and, at the other end, is freely rotatably hooked to the screw cap 20. The spring 24 tends to displace the piston 16 together with the cylinder 15 in a downstream direction.

A fuel conduit 25 communicates with space 23 so that the downstream terminal face 26 of the piston 16 is adapted to be exposed to the fuel pressure prevailing in conduit 9, as it will become apparent hereinafter.

The inner space 27 of the cylinder 15 communicates with a conduit 27a through which the fuel, leaking past piston 16 from space 23, is returned to tank 4.

The admission of fuel to the fuel conduit 25 is controlled by means of a servo element formed as a piston plunger 29 disposed in valve block 28 and displaceable by a pneumatically actuated membrane 30 to which it is attached.

The membrane 30 serves as a septum separating

spaces

31a and 31b in valve block 28. The membrane 30 is, on its upper side, affected by the static pressure of the air prevailing in the flow passage section 17 and by the force of a compression spring 33 and, on its lower side, by the air pressure prevailing in the space 350 defined by portion 35 of the suction tube 1 downstream of the flow passage section 17. The static pressure prevailing in the approximately narrowest portion of the flow passage section 17 is admitted to space 310 through port 32, while the pressure in space 35a is admitted to space 31b through conduit 34. The flow passage section of space 35a is relatively large; thus the air velocity therethrough is relatively small. As a result, an at least approximately total pressure of the air (static pressure plus dynamic pressure) prevails in conduit 34.

Depending upon the position of the piston plunger 29, the fuel conduit 25 is either connected with the pressure conduit 9 through a conduit 36, or is connected with the tank 4 across a return conduit 37, or is blocked altogether.

OPERATION OF THE EMBODIMENT Any change of the flow rate in the suction tube 1 also causes a variation in the static pressure prevailing in the flow passage section 17. This pressure variation is, due to the interconnecting port 32, followed in space 31a. Membrane 30 yields in response to this pressure variation affecting its upper face and, as a result, the piston plunger 29 is displaced.

Thus, if the static pressure increases in flow passage section 17, the piston plunger 29 travels downwardly from its position shown in the figure, whereby communication is established between

conduits

25 and 36, so that the liquid pressure prevailing in conduit 9 is transmitted to space 23. This pressure in the space 23 causes the piston 16, together with with cylinder 15, to be displaced upstream, decreasing thereby the flow passage section 17.

Should the static pressure fall in flow passage section 17, the piston plunger 29 moves upwardly; as a result, communication is established between the conduit 25 and return conduit 37. Thus, the fuel in the space 23 is now neither confined nor pressurized, so that tension spring 24 can cause a downstream displacement of piston 16 together with the cylinder enlarging thereby the flow passage section 17. The downstream displacement of piston 16 causes a part of the fuel in space 23 to be forced across the conduit 25 and drained through return conduit 37 into tank 4.

As soon as the static pressure attains its original value by virtue of the change of the flow passage section 17, the piston plunger 29 returns into its original position closing conduit 25. The fuel now confined in conduit 25 and space 23 resists the force of spring 24 and, consequently, the piston 16 stops.

It is thus seen that the aforedescribed servomechanism includes a servocircuit controlled by an input force that is constituted by the static pressure of air prevailing in flow passage section 17.

It is to be understood that means may be provided for an arbitrary adjustment of the effective length of spring 33 whereby its force is changed, thus affecting the function between the static pressure in flow passage section 17 and the position of the control member l5, l6.

ADVANTAGES OF THE INVENTION The servo force utilized for that means displacement of the control member 15, 16 is large so that the operation of the device is substantially independent of frictional forces.

The use of the servo force also means an increased camming force for the displacement of follower pin 19 effecting the metering of the fuel.

Further, the throttling losses in the flow passage section 17 may be maintained at a small value since a smaller pressure drop is necessary for the actuation of piston plunger 29 by membrane 30 than would be required were the pressure drop directly applied for the displacement of the cylinder 15.

Since small pressure variations control large output forces, changes in the flow rate of air cause high speed settings.

The system operates independently of the designed structural position of the control member 15, 16.

Accelerating forces (engine vibrations, braking retardations) as well as air vibrations in the suction tube 1 have practically no effect since they are hydraulically dampened by virtue of the piston 16.

lclaim:

1. A fuel injection system associated with an internal combustion engine, comprising A. a suction tube for drawing air,

B. a throttle in said suction tube for arbitrarily controlling the flow rate of air therein,

C. a fuel metering device including a throttle,

D. a control member at least partially disposed in said suction tube and held displaceably therein, said control member being displaced in response to changes in said flow rate; said control member, by virtue of its displacement, simultaneously varying an air flow passage section in said suction tube and controlling the throttle of said fuel metering device, I E. a hydraulic servo mechanism for displacing said control member and including 1. displaceable means responsive to the changes in the static air pressure prevailing in the approximately narrowest part of said flow passage section, and

2. a servocircuit controlled by said displaceable means for moving said control member in a direction of decreasing said flow passage section when said static pressure increases and in a direction of increasing said flow passage section when said static pressure decreases; said servo mechanism tending to maintain constant said static pressure at the approximately narrowest portion of said flow passage section.

2. The improvement as defined in claim 1, wherein said displaceable means includes an actuator member directly affected by said static pressure and a servo element movable by said actuator member for controlling said servo circuit.

3. The improvement as defined in claim 2, wherein said suction tube includes a funnel-shaped portion, a guiding tube coaxially and fixedly held in said suction tube, said control member includes a hollow cylinder axially slidably held on said guiding tube and a piston fixedly secured to the inside of said cylinder and slidably received in said guiding tube, said piston is directly affected by the opposing forces ofa hydraulic fluid in said servocircuit and of a spring disposed within said guiding tube.

4. The improvement as defined in claim 3, wherein said actuator member is a membrane, one side of which is exposed to said static air pressure, the other side of which is exposed to the total air pressure prevailing in said suction tube.

5. The improvement as defined in claim 4, wherein the force of said static pressure is aided by a spring in engagement with said membrane.

6. The improvement as defined in claim 3, wherein said servo element is formed by a piston plunger attached to and movable by said actuator member; said piston plunger is, when said static pressure increases, adapted to establish communication between the inside of said guiding tube and a means containing hydraulic fluid under pressure, causing thereby to displace said piston and said cylinder in an upstream direction to decrease said flow passage section; said piston plunger is, when said static pressure decreases, adapted to establish communication between the inside of said guiding tube and a tank means, causing thereby said piston and said cylinder to be displaced by said spring in a downstream direction to increase said flow passage section.

7. The improvement as defined in claim 6, wherein said piston plunger is adapted to interrupt communication both between the inside of said guiding tube and said means containing hydraulic fluid and between the inside of said guiding tube and said tank means to confine hydraulic fluid inside said guiding tube for arresting the motion of said piston and said cylinder when said static pressure assumes its original value.

8. The improvement as defined in claim 7, wherein said hydraulic fluid is fuel used for combustion in said engine, said tank means is constituted by a fuel tank and said means containing hydraulic fluid under pressure is a conduit communicating with said fuel tank and containing fuel pressurized by a fuel pump that simultaneously delivers fuel to said fuel metering device.

9. The improvement as defined in claim 3, wherein the outer face of said cylinder is, in its upstream portion, conically shaped and defines, together with said funnel-shaped portion of said suction tube, said flow passage section varied by said control member.

Claims

1. A fuel injection system associated with an internal combustion engine, comprising A. a suction tube for drawing air, B. a throttle in said suction tube for arbitrarily controlling the flow rate of air therein, C. a fuel metering device including a throttle, D. a control member at least partially disposed in said suction tube and held displaceably therein, said control member being displaced in response to changes in said flow rate; said control member, by virtue of its displacement, simultaneously varying an air flow passage section in said suction tube and controlling the throttle of said fuel metering device, E. a hydraulic servo mechanism for displacing said control member and including 1. displaceable means responsive to the changes in the static air pressure prevailing in the approximately narrowest part of said flow passage section, and 2. a servocircuit controlled by said displaceable means for moving said control member in a direction of decreasing said flow passage section when said static pressure increases and in a direction of increasing said flow passage section when said static pressure decreases; said servo mechanism tending to maintain constant said static pressure at the approximately narrowest portion of said flow passage section.

3. The improvement as defined in claim 2, wherein said suction tube includes a funnel-shaped portion, a guiding tube coaxially and fixedly held in said suction tube, said control member includes a hollow cylinder axially slidably held on said guiding tube and a piston fixedly secured to the inside of said cylinder and slidably received in said guiding tube, said piston is directly affected by the opposing forces of a hydraulic fluid in said servocircuit and of a spring disposed within said guiding tube.