US3828749A

US3828749A - Fuel injection apparatus

Info

Publication number: US3828749A
Application number: US00269175A
Authority: US
Inventors: H Knapp
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1971-07-05
Filing date: 1972-07-05
Publication date: 1974-08-13
Anticipated expiration: 1991-08-13
Also published as: JPS554215B2; IT1001499B; JPS4816021A; FR2145275A6; SE366370B; ES404564A2; BE785833R

Abstract

In a fuel injection apparatus in which an air sensor deflected as a function of the intake air quantities maintains the air-tofuel ratio at a constant value and wherein the return force affecting the air sensor and opposing the deflecting force of the air flow is derived from pressurized liquid, the pressure of said liquid is varied by altering, in response to the oxygen content of the exhaust gas, the energizing current of a solenoid forming part of a pressure control valve.

Description

ilnited Mates Patent 1191 11] 3,828,749 Knapp Aug. 13, 1974- [54] FUEL HNJECTION APPARATUS 3,616,274 11/1971 Eddy 60/276 [751 i g PF G FOREIGN PATENTS OR APPLICATIONS er ermmy 600,895 4/1948 Great Britain 123/32 EA [73] Assignee: Robert Bosch Gmlbill, Stuttgart,

Germany Primary Examiner-Laurence M. Goodridge [22] Filed: July 5, 1972 Assistant Examiner-Ronald B. Cox pp No: 269,175 Attorney, Agent, or Fzrm-Edwm E. Greigg [30] Foreign Application Priority Data [57] ABSTRACT y 5, 1971 Gfirmafly 2133434 In a fuel injection apparatus in which-an air sensor dev I flected as a function of the intake air quantities main- 9 123/139 123/32 tains the air-to-fuel ratio at a constant value and 60/275 wherein the return force affecting the air sensor and [5 i 1 llit. Ci. F02! 39/00, F0219 3/00 pp sing the deflecting force of the air flow is derived Field 0f Search 123/32 276, from pressurized liquid, the pressure of said liquid is 139 32 AE varied by altering, in response to the oxygen content of the exhaust gas, the energizing current of a solenoid [56] Referen Cited forming part of a pressure control valve.

UNITED STATES PATENTS 3,464,801 9/1969 Barstow 60/276 6 Clams 3 Drawmg figures PAIENTED M181 31574 828. 749

sum 1 0F 2 Fig 7.

FUEL INJECTION APPARATUS BACKGROUND OF THE INVENTION This invention relatesto a fuel injection apparatus for continuously injecting fuel into the suction tube of an externally ignited internal combustion engine. In the suction tube there is disposed an air sensor and, spaced therefrom, an arbitrarily operable butterfly valve. The air sensor is deflected by the throughgoing air in proportion to the .air quantities against a constant resetting force which, however, is variable as a function of engine parameters and which, at least partially, is sup plied by pressurized liquid. The air sensor actuates the movable valve member of a fuel metering and distributor valve disposed in the fuel path to meter fuel quantities which are in adesired ratio to the throughgoing air quantities. The change of the resetting force as a function of engine parameters is effected by virtue of an electromagnet, the magnetic force of which is variable as a function of said engine parameters.

In a fuel injection apparatus of the foreoutlined type, as disclosed in Eckert et al, U.S. application Ser. No. 92,345, filed Nov. 24, 1970, now. US. Pat. No. 3,703,888, the return or resetting force of the pressurized liquid is affected by providing an electromagnet which is energized by current intensities characterizing e ngin parameters and the armature of which contacts directly a control plunger. The latter, in turn. is in direct engagement with the air sensor.

In the exhaust gases of internal combustion engines there are contained carbon monoxide, nitrogen oxides and uncombusted or partially combusted hydrocarbons which pollute the air to a significant degree. For the purpose of transforming these harmful components of the exhaust gases into harmless compounds such as can bon dioxide, nitrogen and water, the exhaust gases are guided through catalysts at temperatures over 600 C.

In such a method of exhaust gas purification the composition of the exhaust gas has to be such that it makes possible a practically total conversion into harmless compounds. Stated differently, the air-to-fuel ratio has to be approximately stoichometrical and is thus designated as A l.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved fuel injection apparatus of the aforenoted type in which the alteration of the resetting force exerted on the air sensor is effected as a function of engine parameters in such a manner that a favorable air ratio A may be set for after-burning.

Briefly stated, according to the invention, the energizing current of an clectromagnet which, as a function of its electromagnetic force, varies the return force excrted on the air sensor, is variable as a function of the oxygen content in the exhaust gas for limiting the maximum value of the concentration of carbon monoxide, nitrogen oxides, and hydrocarbons. More particularly, the electromagnet is associated with the biasing means of a valve which, as a function of this bias, controls the liquid pressure that generates the return force.

The invention will be better understood as well as further objects and advantages become more apparent from the ensuing detailed specification of a preferred, although exemplary embodiment, taken in conjunction with the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning first to FIG. 1, in the fuel injection apparatus shown, the intake air enters into a suction tube portion 1 which comprises a conical portion 3 accommodating an air sensor 2. Th'ercfrom the intake air flows through a coupling hose 4 into a suction tube portion 5 which contains an arbitrarily operable butterfly valve 6. Subsequently, the intake air is admitted to one or more cylinders (not shown) of an internal combustion engine. The air sensor 2 comprises a plate member disposed normal to the direction of air flow and dcflectablc thereby in the conical portion 3 as an approximately linear function of the air quantities passing through the suction tube. Assuming a constant return force affecting the air sensor 2 and a constant air pressure prevailing upstream of the air sensor 2, the air pressure prevailing between the air sensor 2 and the butterfly valve 6 remains constant.

The air sensor 2 directly controls a fuel metering and quantity distributor valve 7. For transmitting the motion of the air sensor 2 to the valve 7, there is provided a lever 8'which is integral with the sensor plate and which is pivotally held at 9. The lever 8 has an integral nose 10 which is in contact with a movable valve component 11 to displace the same. The latter forms part of the fuel metering valve 7 and is shaped as a control plunger. The radial face 12 of the control plunger 11 disposed from the nose 10 is affected by pressurized liquid which serves as the return force for the air sensor 2.

The supply of fuel is effected by a fuel pump 16 which is driven by an clectromotor l5 and which draws fuel from a fuel tank 17 and forces it to the fuel metering valve 7 through a conduit 18. From the conduit 18 there extends, back into the fuel tank 17, a return conduit 19 which contains a pressure limiting valve 20.

From the conduit 18 the pressurized fuel is admitted to a channel 21 provided in the housing of the fuel metering and distributor valve 7. The channel 21 communicates with an annular groove 22 provided in the control plunger 11 and also, with a plurality of chambers 23 (only one shown), each bounded by a portion of a diaphragm 24. Dependent upon the position of the control plunger 11, a bounding or control edge I In of the annular groove 22 covers to a greater or lesser extent a plurality of control slots 25 (only one shown), each of which, through a channel 26, leads to a chamber 27 separated from an associated chamber 23 by the diaphragm 24. From the chamber 27 the fuel is admitted through a channel 28 to an individual fuel injection valve (not shown) disposed in the suction tube in the vicinity of the associated engine cylinder. The diaphragm 24 serves as the movable part of a flat seat valve which, by means of a spring 29', is maintained in an open position. when the fuel injection apparatus is not in operation. The diaphragm boxes, each formed of a chamber 23, a chamber 27 and a portion of the diaphragm 24 separating these two chambers, ensure that independently from the flow passage section at the control slots 25, as determined by the position of the bounding edge 11a, that is, independently from the fuel quantities flowing to the fuel injection valves, the pressure drop at the fuel metering valve 22, is maintained substantially at a constant value. In this manner it is ensured that the extent ofdisplacement of the control plunger 11 and the metered fuel quantities are proportionate to one another.

During the pivotal motion of the lever 8, the sensor plate of the air sensor 2 is displaced in the conical portion 3 of the air intake tube, so that between the periphcry of the plate and the inner wall of the conical portion 3 there occurs a change of the annular flow passage section. This change is proportionate to the extent the air sensor 2 deflects. With this precondition there is ensured a linear dependency of the extent of displacement of the air sensor 2 and the sliding motion of the control plunger 11, so that to the air quantity flowing through the air intake tube there is continuously added a proportionate fuel quantity.

The pressurized liquid which exerts a constant resetting force on the control plunger 11 is fuel. For this purpose, from the conduit 18 there extends a conduit 32 which merges into a channel which, in turn, is in hydraulic communication with a pressure chamber 33 through a damping throttle 57. The chamber 33 accommodates that terminal portion of the control plunger 11 which includes the radial end face 12 disposed remote from the air sensor lever 8. The conduit 32 contains a throttle 34 which separates the supply circuit 18 of the fuel metering valve 7 from the

control pressure circuit

32, 35. The fuel is admitted through the channel 35 to a pressure regulating valve assembly 36 and is returned therefrom through a return conduit 37 in a depressurized condition to the fuel tank 17. The pressure regulating valve 36 is designed as a flat seat valve in which the metallic diaphragm 24 serves as the movable valve member. When the pressure regulating valve 36 is in its open position, the diaphragm 24 clamped taut between a base 38 and a housing 39 determines, together with a stationary valve seat 40 forming an integral part of the base 38, the flow passage section of the pressure regulating valve. A very small deflection of the diaphragm 24 in a direction away from the valve seat 40 is sufflcient to fully open the valve and to cause the fuel to flow in a depressurized condition through the annular flow passage of the valve 36 from the channel 35 through the return conduit 37 into the fuel tank 17. The diaphragm 24 separates two

chambers

41 and 42 from one another and is loaded by a spring 43, the bias of which may be arbitrarily altered by means of a set screw 44. The spring 43 urges the diaphragm 24 into contact with the valve seat 40 (closed position of valve 36). The spring 43 is disposed in a bore 45 of a magnet core 46 and exerts its force on the diaphragm 24 through an armature 47 (which serves as a spring seat disc) and a force-transmitting member 48. On the core 46 there is mounted a solenoid 51. The armature 47 is suspended in a frictionless manner on a spider 52 which is held between the clamping members 53 and 54. The energizing current is applied to the solenoid 51 through a plug 55. The magnetic circuit is closed by a ring 56 surrounding the solenoid 51.

The aforedescribed fuel injection apparatus operates' as follows:

When the internal combustion engine is running, the fuel pump 16 driven by the electromotor l5 draws fuel from the fuel tank 17 and forces it through the conduit 18 to the fuel metering valve 7. Simultaneously, the internal combustion engine draws air through the

air intake tube

1, 3, 4, 5 and as a result, the air sensor 2 executes a certain deflection from its position of rest. As a function of the extent of this deflection, the control plunger 11 is shifted by virtue of the pressure exerted thereon by the lever 8. Consequently, the flow passage section of the control slots 25 will be enlarged. The direct connection between the air sensor 2 and the control plunger 11 results in a constant ratio of the intake air quantities to the metered fuel quantities.

In order to maintain the air-fuel mixture at a richer or leaner level dependent upon the operational condition of range of the internal combustion engine, the return force exerted on the air sensor 2 has to be altered as a function of engine parameters. This is effected by either measuring these parameters electronically or, after their conversion into electric magnitudes, varying them by means of an electric control apparatus. Then, as corresponding current intensities, they vary the intensity of the magnetic fleld of the solenoid 51. As a result, the armature 47, exposed to the magnetic field, opposes the force of the biasing spring 43 to a greater or lesser extent. Since the diaphragm 24 of the pressure regulating valve 36 requires only a minimum extent of displacement for controlling the pressure of the fuel in the channel 35 and thus the return force exerted on the radial face 12 of the control plunger 11 in the pressure chamber 33, the magnetic force, that is, the magnitude of the energizing current, may be converted directly into a pressure valve. By supporting the armature 47 on the spider 52 and by virtue of designing the pressure control valve as a flat seat valve, the pressure regulating valve operates in a mechanically entirely frictionless manner. The magnetic hysteresis is maintained at a low value in a conventional manner by making the environmental components of nickel-containing iron.

As illustrated in FIG. 1, it is advantageous to integrate the pressure regulating valve 36 and the fuel metering and distributor valve 7 to simultaneously use the diaphragm 24 as the movable valve member for both valves and to maintain the

control pressure conduits

32, 35 as short as possible. It is to be understood that the pressure regulating valve 36 may be arranged, in a manner not shown, separate from the fuel metering and distributor valve 7.

The fuel injection system may be designed for a predetermined air proportion A by shaping the conical portion 3 accordingly. Preferably, the conical portion 3 is so designed that the air ratio A is approximately 1.1, while the regulation to A l is achieved with the aid of an oxygen sonde 60 to be described hereinafter. Thus, the fuel-air mixture is enriched by starting from a lean mixture.

Turning now to FIG. 2, there is illustrated an electric circuit for the aforenoted regulation of )t. The oxygen sonde 60 is arranged in a wall 59 which separates a chamber 61 from a chamber 62. Through the chamber 61 there pass the exhaust gases, while the chamber 62 is in communication with the ambient atmosphere. The oxygen sonde 60 is bounded by

gas contact members

64, 65 defining a space which is filled, within the wall 59, with an ion-conductive solid electrolyte 63. The member 64 is situated in the chamber 61 and is thus contacted by the exhaust gases, while the member 65 is located in the chamber 62 and is thus exposed to the ambient atmosphere. The oxygen ion conducting solid electrolyte 63 may be stabilized zirconium dioxide, thorium dioxide or mullite (the latter is a fire and high temperature-resistant material having the formula 3 Al- O -2 SiO The

members

64 and 65 are porous, gaspervious foil-like components which are applied in a very thin layer and which may be formed of platinum or high temperature-resistant hard electric material such as tungsten carbide or high temperature-resistant, electrically conductive oxides of the type of Fe;,O.,. Be-

- tween the

foils

64 and 65 there is generated a certain potential difference which is a function of the oxygen content of the exhaust gases. This potential difference is compared with a reference potential which, in turn, is obtained by means of an appropriately highresistance (ohmic) voltage divider formed of two

resistances

66 and 67. The aforenoted comparison of potentials is effected in an operational amplifier 68. The output voltage of the latter is applied to the base of an emitter follower transistor 69 and thus determines the energizing current of the solenoid 51 of the pressure control valve 36.

in order to ensure that at full load the internal combustion engine delivers the highest torque, the butterfly valve 6, shortly before reaching its fully open position, operates a switch 70 having in series a resistance 71. Thus, upon actuation of the switch 70 there is obtained a higher energizing current for the solenoid 51. A higher energizing current flowing through the solenoid 51 means a decrease of the return force exerted on the control plunger 11 and thus an increase of the metered fuel quantities. The air ratio thus adjusts itself to k OB.

Turning now to the diagram of FIG. 3, there is shown the course of the sonde voltage U as a function of the air ratio A. If the fuel injection apparatus, by virtue of an appropriate design of the conical portion 3, has a base setting of lt l 1, then this corresponds to a sonde voltage A. In order to obtain lt l, a voltage comparison to the desired operational point B has to be effected for obtaining a signal for such an adjustment. For this purpose, as mentioned earlier, the potential of the oxygen sonde 60 is compared by means of the operational amplifier 68 with the reference potential which corresponds to point B and which is obtained at the

voltage divider

66, 67. The amplified output signal thus controls the pressure regulating valve 36. It is apparent that a de-energized condition (no current) of the solenoid 51 of the pressure regulating valve 36 corresponds to the operational point A, that is, to a lean base setting of )t 1.1. An adjustment to the operational point B corresponds to A I. For a rich fuel-air ratio under full load conditions, upon the actuation of the switch 70 by means of the butterfly valve 6 in its open position, there is obtained a base current which sets A to 0.9 and thus the operation is shifted to point C that corresponds to the maximum torque.

It is to be understood that it is possible to adapt the fuel injection apparatus closer to A l, for example, by

providing a base setting of k 1.05 and by effecting adjustment with the aid of a two-point regulator, so that an operational point between the points A and B is obtained by means of a flip-flop.

In order to prevent the occurrence of inaccuracies caused by temperature fluctuations when the atmosphere is used as the oxygen reference system, it is expedient to use instead a hermetically closed oxygen reference system whose composition cannot change. As an oxygen reference system there may be considered different mixtures of a metal and a metal oxide or mixtures of two oxides of a metal of two valencies, for example, Ni/NiO, Cu/Cu O, etc. systems, wherein the two components are in a stoichometrical ratio of 1:1.

What is claimed is:

1. In a fuel injection apparatus for the continuous injection of fuel into the suction tube of an internal combustion engine, said suction tube containing an arbitrarily operable butterfly valve, said apparatus being of the known type that has (a) an air sensor disposed in said suction tube spaced from said butterfly valve, said air sensor being deflected by the flow of intake air as a function of the intake air quantities, (b) means generating a return force affecting said air sensor and opposing the deflecting force of the air flow, said return force being independent from the deflected position of said air sensor, (c) a fuel metering and distributor valve having a movable valve member operatively connected to said air sensor to be displaced thereby to an extent proportionate to the deflection of said air sensor for maintaining constant the fuel-to-air ratio for any given return force, ((1) means for applying hydraulic pressure to said movable valve member, said hydraulic pressure forming at least one part of said return force, (e) an electromagnet associated with said means generating said return force and (f) means for varying said return force as a function of the intensity of the energizing current flowing through said electromagnet, the improvement comprising means for varying the intensity of said energizing current as a function of the oxygen content of the exhaust gas for limiting the maximum concentration of pollutants therein, said last-named means including:

A. an electric circuit for supplying said energizing current,

B. a transistor connected in said circuit and having a base,

C. a switch connected in said circuit to affect, dependent on its condition, the base current of said transistor,

D. an oxygen sonde connected in said circuit and having 1. a first member exposed to said exhaust gas,

2. a second member spaced from said first member and exposed to a reference gas,

3. a solid electrolyte disposed in the space defined between said first and second members,

E. means connecting said arbitrarily operable butterfly valve to said switch for actuating the latter when said butterfly valve assumes its full load position to vary said base current and to alter said energizing current for setting a richer air-fuel mixture, and

F. means connected in said circuit, said last-named means varying said energizing current flowing in said circuit as a function of the potential difference between said first and second members.

2. In a fuel injection apparatus for the continuous injection of fuel into the suction tube of an internal combustion engine, said suction tube containing an arbitrarily operable butterfly valve, said apparatus being of the known type that has (a) an air sensor disposed in said suction tube spaced from said butterfly valve, said air sensor being deflected by the flow of intake air as a function of the intake air quantities, (b) means generating a return force affecting said air sensor and opposing the deflecting force of the air flow, said return force being independent from the deflected position of said air sensor, (c) a fuel metering and distributor valve having a movable valve member operatively connected to said air sensor to be displaced thereby to an extent proportionate to the deflection of said air sensor for maintaining constant the fuel-to-air ratio for any given return force, (d) means for applying hydraulic pressure to said movable valve member, said hydraulic pressure forming at least one part of said return force, (e) an electromagnet associated with said means generating said return force and (f) means for varying said return force as a function of the intensity of the energizing current flowing through said electromagnet, the-improvement comprising means for varying the intensity of said energizing current as a function of the oxygen content of the exhaust gas for limiting the maximum concentration of pollutants therein, wherein said hydraulic pressure is supplied by liquid under pressure, said means generating said return force includes a pressure control valve formed of a flat valve having a diaphragm as its movable valve member and means generating a spring bias, the magnitude of which determines the pressure of said liquid, and wherein said electromagnet is connected to said pressure control valve to vary said spring bias as a function of the intensity of said energizing current.

3. An improvement as defined in claim 2, including A. an electric circuit for supplying said energizing current,

B. an oxygen sonde connected in said circuit and havl. a first member exposed to said exhaust gas,

3. a solid electrolyte disposed in the space defined between said first and second members and C. means connected in said circuit, said last-named means varying said energizing current flowing in said circuit as a function of the potential difference between said first and second members.

4. An improvement as defined in claim 3, said suction tube including a conical portion, said air sensor including a plate member disposed and movable within the confines of said conical portion, the periphery of said plate member and the inner wall of said conical portion defining a flow passage section of an area dependent on the position of said plate member, said conical portion being shaped for an air ratio A 1.1, said oxygen sonde adjusting A to 1 when the engine operates at partial load.

5. An improvement as defined in claim 3, said suction tube including a conical portion, said air sensor including a plate member disposed and movable within the confines of said conical portion, the periphery of said plate member and the inner wall of said conical portion defining a flow passage section of an area dependent on the position of said plate member, said conical portion being shaped for an air ratio A 1.05, said improvement including a two-point regulator to adjust A at the partial load range of the engine with the aid of said oxygen sonde.

6. in a fuel injection apparatus for the continuous injection of fuel into the suction tube of an internal combustion engine, said suction tube containing an arbitrarily operable butterfly valve, said apparatus being of the known type that has (a) an air sensor disposed in said suction tube spaced from said butterfly valve, said air sensor being deflected by the flow of intake air as a function of the intake air quantities, (b) means generating a return force affecting said air sensor and opposing the deflecting force of the air flow, said return force being independent from the deflected position of said air sensor, (0) a fuel metering and distributor valve having a movable valve member operatively connected to said air sensor to be displaced thereby to an extent proportionate to the deflection of said air sensor for maintaining constant the fuel-to-air ratio for any given return force, (d) means for applying hydraulic pressure to said movable valve member, said hydraulic pressure forming at least one part of said return force, (e) an electromagnet associated with said means generating said return force and (f) means for varying said return force as a function of the intensity of the energizing current flowing through said electromagnet, the improvement comprising means for varying the intensity of said energizing current as a function of the oxygen content of the exhaust gas for limiting the maximum concentration of pollutants therein, wherein said hydraulic pressure is supplied by liquid under pressure,

wherein said means generating said return force includes a pressure control valve having a closing spring generating a spring bias, the magnitude of which determines the pressure of said liquid, and spider means clamped within said pressure control valve, and wherein said electromagnet is connected to said pressure control valve to vary said spring bias as a function of the intensity of said energizing current, said electromagnet including an armature which opposes said closing spring with a force dependent upon the intensity of said energizing current, said armature being secured to said spider means for frictionless movement.

Claims

1. In a fuel injection apparatus for the continuous injection of fuel into the suction tube of an internal combustion engine, said suction tube containing an arbitrarily operable butterfly valve, said apparatus being of the known type that has (a) an air sensor disposed in said suction tube spaced from said butterfly valve, said air sensor being deflected by the flow of intake air as a function of the intake air quantities, (b) means generating a return force affecting said air sensor and opposing the deflecting force of the air flow, said return force being independent from the deflected position of said air sensor, (c) a fuel metering and distributor valve having a movable valve member operatively connected to said air sensor to be displaced thereby to an extent proportionate to the deflection of said air sensor for maintaining constant the fuel-to-air ratio for any given return force, (d) means for applying hydraulic pressure to said movable valve member, said hydraulic pressure forming at least one part of said return force, (e) an electromagnet associated with said means generating said return force and (f) means for varying said return force as a function of the intensity of the energizing current flowing through said electromagnet, the improvement comprising means for varying the intensity of said energizing current as a function of the oxygen content of the exhaust gas for limiting the maximum concentration of pollutants therein, said last-named means including: A. an electric circuit for supplying said energizing current, B. a transistor connected in said circuit and having a base, C. a switch connected in said circuit to affect, dependent on its condition, the base current of said transistor, D. an oxygen sonde connected in said circuit and having 1. a first member exposed to said exhaust gas, 2. a second member spaced from said first member and exposed to a reference gas, 3. a solid electrolyte disposed in the space defined between said first and second members, E. means connecting said arbitrarily operable butterfly valve to said switch for actuating the latter when said butterfly valve assumes its full load position to vary said base current and to alter said energizing current for setting a richer air-fuel mixture, and F. means connected in said circuit, said last-named means varying said energizing current flowing in said circuit as a function of the potential difference between said first and second members.

2. In a fuel injection apparatus for the continuous injection of fuel into the suction tube of an internal combustion engine, said suction tube containing an arbitrarily operable butterfly valve, said apparatus being of the known type that has (a) an air sensor disposed in said suction tube spaced from said butterfly valve, said air sensor being deflected by the flow of intake air as a function of the intake air quantities, (b) means generating a return force affecting said air sensor and opposing the deflecting force of the air flow, said return force being independent from the deflected position of said air sensor, (c) a fuel metering and distributor valve having a movable valve member operatively connected to said air sensor to be displaced thereby to an extent proportionate to the deflection of said air sensor for maintaining constant the fuel-to-air ratio for any given return force, (d) means for applying hydraulic pressure to said movable valve member, said hydraulic pressure forming at least one part of said return force, (e) an electromagnet associated with said means generating said return force and (f) means for varying said return force as a function of the intensity of the energizing current flowing through said electromagnet, the improvement comprising means for varying the intensity of said energizing current as a function of the oxygen content of the exhaust gas for limiting the maximum concentration of pollutants therein, wherein said hydraulic pressure is supplied by liquid under pressure, said means generating said return force includes a pressure control valve formed of a flat valve having a diaphragm as its movable valve member and means generating a spring bias, the magnitude of which determines the pressure of said liquid, and wherein said electromagnet is connected to said pressure control valve to vary said spring bias as a function of the intensity of said energizing current.

3. An improvement as defined in claim 2, including A. an electric circuit for supplying said energizing current, B. an oxygen sonde connected in said circuit and having

3. a solid electrolyte disposed in the space defined between said first and second members, E. means connecting said arbitrarily operable butterfly valve to said switch for actuating the latter when said butterfly valve assumes its full load position to vary said base current and to alter said energizing current for setting a richer air-fuel mixture, and F. means connected in said circuit, said last-named means varying said energizing current flowing in said circuit as a function of the potential difference between said first and second members.

4. An improvement as defined in claim 3, said suction tube including a conical portion, said air sensor including a plate member disposed and movable within the confines of said conical portion, the periphery of said plate member and the inner wall of said conical portion defining a flow passage section of an area dependent on the position of said plate member, said conical portion being shaped for an air ratio lambda 1.1, said oxygen sonde adjusting lambda to 1 when the engine operates at partial load.

5. An improvement as defined in claim 3, said suction tube including a conical portion, said air sensor including a plate member disposed and movable within the confines of said conical portion, the periphery of said plate member and the inner wall of said conical portion defining a flow passage section of an area dependent on the position of said plate member, said conical portion being shaped for an air ratio lambda 1.05, said improvement including a two-point regulator to adjust lambda at the partial load range of the engine with the aid of said oxygen sonde.

6. In a fuel injection apparatus for the continuous injection of fuel into the suction tube of an internal combustion engine, said suction tube containing an arbitrarily operable butterfly valve, said apparatus being of the known type that has (a) an air sensor disposed in said suction tube spaced from said butterfly valve, said air sensor being deflected by the flow of intake air as a function of the intake air quantities, (b) means generating a return force affecting said air sensor and opposing the deflecting force of the air flow, said return force being independent from the deflected position of said air sensor, (c) a fuel metering and distributor valve having a movable valve member operatively connected to said air sensor to be displaced thereby to an extent proportionate to the deflection of said air sensor for maintaining constant the fuel-to-air ratio for any given return force, (d) means for applying hydraulic pressure to said movable valve member, said hydraulic pressure forming at least one part of said return force, (e) an electromagnet associated with said means generating said return force and (f) means for varying said return force as a function of the intensity of the energizing current flowing through said electromagnet, the improvement comprising means for varying the intensity of said energizing current as a function of the oxygen content of the exhaust gas for limiting the maximum concentration of pollutants therein, wherein said hydraulic pressure is supplied by liquid under pressure, wherein said means generating said return force includes a pressure control valve having a closing spring generating a spring bias, the magnitude of which determines the pressure of said liquid, and spider means clamped within said pressure control valve, and wherein said electromagnet is connected to said pressure control valve to vary said spring bias as a function of the intensity of said energizing current, said electromagnet including an armature which opposes said closing spring with a force dependent upon the intensity of said energizing current, said armature being secured to said spider means for frictionless movement.