Fuel injection system for internal combustion engine
United States Patent [191 Kammerer et a1.  
 [ Apr. 29, 1975 1 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINE [73] Assignee: Robert Bosch G.m.b.l-l., Stuttgart.  
 Germany [22] Filed: Mar. 12, 1973 [21] Appl. NO.: 326,660  
 [30] Foreign Application Priority Data Sept. 21. 1972 Germany 2246373 [52] US. Cl... 123/32 EA; 123/119 R; 123/139 AW [51] Int. Cl F02b 3/00 [58] Field of Search..... 123/32 EA. 139 AW, 119 R 2.982.276 Zcchnallm Harrison 123/32 EA 3.581.723 6/1971 Scholl 123/32 EA 3.683.870 8/1972 .lackson....... 123/32 EA 3.683.877 8/1972 Menncsson.v 123/32 EA 3.710.769 1/1973 Knapp .4 123/139 AW 3.727.081 4/1973 Davis 123/32 EA 3.750.631 8/1973 Scholl et a1 123/32 EA Primary Exmniner-Charles .I. Myhre Assistant EtaminerRona1d B. Cox Attorney, Agent, or Ft&#39;rntMichael S. Striker [57] ABSTRACT A fuel injection system for multi-cylinder internal combustion engines wherein the length of intervals during which the electromagnetic fuel injection valves remain open depends on the rate of air flow in the intake manifold. The flow meter in the manifold employs a pivotable flap which is mounted in the path of inflowing air and is rigid with a damping blade serving to prevent fluctuations in the angular position of the flap. The flap controls a variable resistor which is connected with one input of a control circuit for the coils of fuel injection valves. The position of the flap is further influenced by varying distance of the engine from sea level and by changes in the temperature of inflowmg airv 25 Claims, 14 Drawing Figures rsxnms r SHEET [SW PATENTEC APR 2 9 iii-75 SHEET [380? 10 n mmmmmmmmmm mmmmm SHEU [7 3F 19 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION The present invention relates to improvements in fuel injection systems for internal combustion engines. especially to improvements in intermittently operated electrically controlled fuel injection systems for multicylinder internal combustion engines.  
  Electrically controlled fuel injection systems for internal combustion engines normally comprise an electronic control circuit which regulates the length of intervals during which the fuel injection valves for the respective cylinders of the engine remain open whereby the length of such intervals determines the quantity of injected fuel. The fuel injection valves are located at the outlet of the intake manifold which contains a customary pedal-controlled throttle and preferably an air filter at the inlet end thereof. An input of the control circuit receives signals from a signal generator in synchronism with the RPM of the internal combustion engine. for example, from a signal generator which is actuated by a cam on the crankshaft of the engine. The control circuit employs an energy storing device (e.g., a capacitor or an inductance) which is charged at a controlled rate while the fuel injection valves are closed and discharges in response to aforementioned signals to thereby determine the length of the intervals of opening of fuel inection valves as a function of the RPM of the engine.  
  An important advantage of electrically controlled fuel injection systems for internal combustion engines is that the ratio of the quantity of fuel which is admitted into the cylinders to the quantity of air which is admitted by way of the intake manifold can be regulated with a rather high degree of accuracy. Consequently. the em gine can be operated efficiently and its adjustment can be such that the products of combustion contain a minimum of deleterious substances at all rotational speeds and in all load ranges of the engine.  
  In presently known fuel injection systems, the quantity of air which is being admitted into the cylinders of the internal combustion engine is measured indirectly by a transducer which is mounted in the intake manifold downstream of the throttle. As a rule, the transducer comprises an inductance serving to change the position of an iron core which thereby changes the periods of unstable condition of a multivibrator. The latter receives signals in synchronism with the RPM of the engine. A drawback of such fuel injection systems is that their circuitry must embody a large number of complex and sensitive electronic components which are provided to insure that the intervals of opening of fuel injection valves not only depend on the rate of air flow in the manifold but also accurately reflect the RPM of the engine.  
  It was already proposed to provide a fuel injection system for internal combustion engines with metering means for directly measuring the rate of air flow in the intake manifold and to utilize such metering means for regulating the length of intervals during which the fuel injection valves remain open. The metering means includes a flap which is located downstream of the throttle in the path of the air stream flowing in the manifold and controls a variable resistor which is connected with the control circuit for the fuel injection valves. The resistor can determine the rate of charging or discharge of the aforementioned capacitor or inductance.  
  Just discussed fuel injection system also exhibit a number of drawbacks, particularly as concerns the ac curacy of measurements of the rate of air flow in the intake manifold. This is due to the fact that the current of air flowing in the manifold tends to pulsate, especially if the engine is operated at a medium or high rotational speed. The flap is likely to participate in such pulsating movements of the inflowing air whereby its position does not accurately reflect the momentary rate of air flow. The problem is particularly severe during idling of four-cylinder four stroke cycle engines with properly balanced crankshafts which thus allow for very low idling speeds.  
 SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved fuel injection system for internal combustion engines wherein the length of intervals during which the fuel injection valve or valves remain open is invariably an accurate function of the momentary rate of air flow in the intake manifold regardless of the load upon and/or the RPM of the engine.  
  Another object of the invention is to provide a fuel injection system for internal combustion engines with novel and improved means for measuring the rate of air flow in the intake manifold and with novel and improved means for changing the length of intervals during which the fuel injection valves remain open in dependency on changes in the rate of air flow in the manifold.  
  A further object of the invention is to provide a fuel injection system with novel and improved means which serves to measure the rate of air flow in the intake manifold of an internal combustion engine and whose measurements are not affected by eventual pulsations of the inflowing air stream without, however, affecting the accuracy of measurements and/or the ability of measuring means to react to changes in the rate of air flow without appreciable delay.  
  The invention is embodied in an electrically controlled fuel injection system for internal combustion engines, preferably in an intermittently operated fuel injection system for multicylinder internal combustion engines, which comprises an intake manifold having an inlet for admission of atmospheric air and an outlet for discharge of air into the cylinders of the engine, an adjustable throttle mounted in the intake manifold, at least one electromagnetic fuel injection valve provided in the region of the outlet, and an electronic control circuit which is operable to open the fuel injection valve for varying intervals of time which determine the amounts of injected fuel (the pressure of fuel in the conduit controlled by the fuel injection valve is preferably constant). The control circuit includes an energy storing device (such as a capacitor or an inductance) which is charged at a controlled rate between successive openings of the fuel injection valve and discharges during successive openings of the fuel injection valve whereby the duration of discharge determines the length of the intervals during which the valve remains open.  
  The fuel injection system further comprises trans ducer means for changing the duration of discharge of the energy storing device as a function of changes in the quantity of air flowing in the manifold. The transducer means comprises a regulating member (e.g.. a variable resistor) including an output connected with the control circuit and having a plurality of conditions, each of which corresponds to a different length of the intervals. and an air quantity meter or flow meter which is operative to change condition of the regulating member as a function of changes in the rate of air flow in the manifold. The flow meter comprises a flap which is pivotably mounted in the intake manifold between the inlet and the throttle to assume a plurality of positions each corresponding to a different rate of air flow in the manifold. The flap is operatively connected with and can change the condition of the regulating member. and the flow meter further comprises pneumatic damping means which is rigid with the flap and is operative to oppose fluctuations in the position of the flap. The damping means preferably comprises a blade which is rigid with the flap and is pivotable in a damping chamber defined by the manifold downstream of the flap. The flow meter preferably includes a discrete housing which forms part of intake manifold and defines the aforementioned chamber as well as a measuring channel wherein the air flows from the inlet toward the outlet of the manifold and which receives the flap.  
  The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved fuel injection system itself. however, both as to its construction and its mode of operation, together with additional features and advantages thereof. will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.  
 BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic partly sectional view of a four-cylinder internal combustion engine and of a fuel injection system which embodies the invention;  
  FIG. 2 is a diagram of the control circuit in the fuel injection system of FIG. 1;  
  FIG. 3 is a partly elevational and partly sectional view of a transducer which embodies one form of the invention, the section being taken in the direction of arrows as seen from the line IIIIII of FIG. 4;  
  FIG. 4 is a sectional view as seen in the direction of arrows from the line IVIV of FIG. 3;  
  FIG. 5 is a sectional view as seen in the direction of arrows from the line V-V of FIG. 4&#39;,  
  FIG. 6 is a sectional view as seen in the direction of arrows from the line VI-VI of FIG. 4;  
  FIG. 7 is an end elevational view as seen in the direction of arrow VII in FIG. 5;  
  FIG. 8 is a sectional view as seen in the direction of arrows from the line VIII-VIII of FIG. 3;  
  FIG. 9 is a plan view of a portion of the regulating member in the transducer of FIGS. 3 to 8;  
  FIG. 10 illustrates a modified flow meter in a sectional view corresponding to that of FIG. 5;  
  FIG. I] is an elevational view of a further flow meter including an auxiliary valve which is shown in partial section;  
  FIG. 12 is a fragmentary sectional view as seen in the direction of arrows from the line XII-XII of FIG. II;  
  FIG. 13 is an enlarged axial sectional view of the auxiliary valve shown in FIG. 11&#39;, and  
  FIG. 14 is a partially elevational and partially sectional view of still another flow meter.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. I, there is shown a fourcylinder internal combustion engine 10 which is built into an automotive vehicle. The spark plugs 10a of the engine 10 are connected to a receive high-voltage surges from a conventional ignition coil, not shown. The engine I0 further comprises four electromagnetically operated fuel injection valves 11, one for each of the four cylinders, which receive fuel from a receptacle 12. here shown as a distributor. by way of fuel supply conduits 13. The distributor 12 receives fuel from the outlet of a fuel pump 15 (driven by an electric motor. not shown) which draws fuel from a source 150. e.g., a fuel tank. The connection between the outlet of the fuel pump 15 and the distributor 12 contains a relief valve 16 which insures that the fuel pressure in the distributor I2 remains at least substantially constant, e.g. at two atmospheres absolute pressure.  
  The fuel injection system comprises a signal generating device including a rotary cam 18 which is driven by the crankshaft 17 of the engine 10 and produces two signals in response to each revolution of the crankshaft. A transistorized control circuit TS of the fuel injection system furnishes rectangular pulses S which are transmitted to the fuel injection valves ll whereby such valves open for intervals T,- which determine the quantity of injected fuel (as mentioned above, the fuel pressure in the distributor 12 is constant). The coils 19 (one shown) of the fuel injection alves ll are connected in series with discrete decoupling resistors 20 and with a common amplifier stage 21 which includes at least one transistor amplifier 22. The emitter-collector circuit of the transistor amplifier 22 is connected in series with the resistors 20 and hence with the coils 19. Each coil 19 is further connected to the ground.  
  When a cylinder of the engine 10 performs a suction stroke. it should draw a quantity of air corresponding to that amount of pressurized fuel which can be completely combusted during the next-following state of a cycle. In addition, it is desirable to insure that there is no appreciable surplus of air upon completion of a working stroke. In order to insure a satisfactory stochiometric ratio between air and fuel, the intake or suction manifold 25 of the engine I0 accommodates an air quantity meter or flow meter LM which is installed between an adjustable throttle 28 and an air filter 26. The latter is located at the inlet of the intake manifold 25, and the throttle 28 is adjustable by a foot pedal 27. The flow meter LM comprises a flap 30 and serves to change the condition of a regulating member here shown as a variable resistor R whose movable portion 31 is coupled to the flap 30 so that its position relative to the stationary resistor portion 31a varies as a function of changes in the angular position of the flap. The latter is mounted in the path of air flowing in the intake manifold 25 from the filter 26 toward the throttle 28. The resistor R is connected with one input of the transistorized control circuit TS whose output furnishes the pulses S for the amplifier stage 2I. The other input of the control circuit TS is connected with the signal generating means 18, 18a.  
  The details of the control circuit TS are shown schematically in FIG. 2. This control circuit comprises two transistors T1 and T2 one of which is conductive when the other blocks. and vice versa. The transistor T1 is an input transistor and the transistor T2 is an output transistor. The control circuit TS further comprises an energy storing device here shown as a capacitor C (this capacitor can be replaced with an inductance). The illustrated control circuit operates in such a manner that the energy storing device (capacitor or inductor) undergoes a first change of stored energy (e.g., capacitor charging) alternating with an opposite second change of stored energy (e.g., capacitor discharging). The period during which the capacitor C discharges determines the length of intervals Ti during which the fuel injection valves 11 remain open. Prior to each discharge, the capacitor C is charged in a predetermined manner which will be described below.  
  In order to insure that the length of the interval during which the capacitor C discharges can directly indicate the quantity of air which is allotted for each suction storke, the charging of capacitor C takes place in response to successive signals LJ produced by the cam 18 which is driven in synchronism with the crankshaft 17. The cam 18 insures that the capacitor C is connected with an energy source A while the cam 18 (and hence also the camshaft [7) turns through a predetermined angle. During generation of each charging signal L], the capacitor C receives a charging current J lt is assumed that the cam 18 (which, in actual practice, is preferably replaced by a bistable multivibrator whose condition is changed in response to successive firing pulses) maintains the switch 180 of FIG. 1 in closed position while the crankshaft 17 rotates through 180 degrees and that the switch 180 thereupon opens while the crankshaft rotates through the next 180.  
  The control circuit TS of FIG. 2 renders it possible to initiate a discharging pulse K which is derived from the charging signals LJ immediately upon completion of each charging operation (such charging operation is completed in the 0, 360, 720, etc. positions of the crankshaft 17) and which causes the previously conductive output transistor T2 to block. At the same time, the input transistor T1 becomes conductive because, as a result of blocking of the transistor T2, the base of the transistor T1 can receive sufficient voltage by way of the collector resistor 35 of the transistor T2 and the coupling resistor 36 of the control circuit TS. The charge which the capacitor C accumulates during charging can flow by way of a diode 37 and the collectoremitter circuit of the transistor T1. The discharge current J is maintained at a constant value by a conventional clement E. During discharge, the voltage U at the capacitor C decreases linearly.  
  After elapse of an interval T,, the potential at the right-hand plate of the capacitor C decreases to such an extent that the output transistor T becomes conductive and blocks the transistor T The right-hand plate of the capacitor C is connected with the base of the transistor T by way of a diode 38. The diode 37 prevents the flow of current to the capacitor C by way of a collector resistor 39 when the transistor T, blocks. Consequently, the next charging operation begins in response to the next charging signal LJ when the crankshaft 17 is in the 180 or 540 position so that the capacitor C is again connected to the energy source A. The reference character 40 denotes the lead which connects the resistors 35, 39, the source A and the element E with the positive pole of the main energy source.  
  When the RPM of the engine 10 is less than 2,000, an increase in load upon the engine results in pronounced pulsation of inflowing air. This can cause undesirable vibration of the flap 30 about a neutral position which does not correspond to actual median value of the air quantity QL per unit of time. In order to avoid such misleading indications of the quantity of inflowin g air. the flow meter LM is provided or combined with novel pneumatic damping means which not only prevents the flap 30 from swinging beyond a position corresponding to the median rate of air admission per unit of time but also allows the flap 30 to follow (react to) the changes in the quantity of inflowing air without any appreciable delay. in other words, while not unduly affecting the sensitivity of the flow meter LM, the damping device prevents the flap 30 from furnishing misleading readings or indications, especially when the engine 10 operates under substantial load and a a relatively low RPM.  
  The length of intervals T, is a function of the RPM of the crankshaft l7 and of the condition of the resistor R which, together with the flow meter LM, constitutes a transducer serving to change the duration of discharge of the capacitor C as a function of changes in the quantity of air flowing in the intake manifold 25.  
  The flow meter LM is shown in detail in FIGS. 3 to 8. It comprises a housing 41 which preferably consists of zinc and includes a centrally located base plate or wall 42 and side walls 43, 44. The open side of the housing 41 is closed by a sheet of metal cover 45. The cover 45 defines with the walls of the housing 41 an elongated measuring channel 46 and a damping chamber 62 which communicates with the channel 46 downstream of the flap 30. The flap 30 is pivotably mounted in the housing 41 so as to extend into the channel 46 and is integral with a blade 47 of the damping device As shown in FIG. 5, the parts 30 and 47 make an obtuse angle of approximately I00&#34;. The blade 47 can pivot in the damping chamber 62 whereby one of its free edges faces (i.e., that edge face which is remote from the pivot axis of the flap 30) defines with an arcuate wall 50 of the housing 41 a narrow gap 49. In order to reduce wobbling and friction (and to thus enhance the accuracy of the meter LM). the flap 30 has an integral hub 38 which is rigid with one end of a coaxial rotary shaft 51. The latter is rotable in axially spaced antifriction ball bearings 52, S3 and is adjacent to the path of air flow in the manifold 25. The center of curvature of the internal surface of the wall 50 is located on the axis of the shaft 51 so that, if the flap 30 is held against wobbling and/or other stray movements (i.e., if the flap is confined to rotation about the axis of the shaft 51), the width of the gap 49 remains constant and the damping action of the blade 47 also remains unchanged in each angular position of the flap 30, as long as the one edge face of the blade 47 remains adjacent to the wall 50.  
  The hub 48 is further connected with the flap 30 and blade 47 by pairs of stiffening or reinforcing ribs 54, 55 and this hub has an axially extending cylindrical recess or blind bore for a sleeve 56 which is integral with the base plate or wall 42 of the housing 41. The axial length of the recess may equal or approximate about twothirds of the axial length of the hub 48. The sleeve 56 receives the outer races of the antifriction bearings 52, 53 which are held apart by a distancing cylinder 59. The clearances between the remaining two free edge faces of the blade 47 and the parts 42, 45 are preferably in the range of 0.2 (1.3 millimeter. To this end, the Shaft 51 is held against axial movement relative to the sleeve 56 by a split ring 57 which snaps into a circumferential groove of the shaft and is biased by a resilient washer 58 interposed between the split ring 57 and the inner race of the antifriction bearing 53. Thus, once the clearance between the blade 47 and the parts 42. 45 of the housing 41 are properly selected, the split ring 57 cooperates with the elastic washer 58 to prevent any axial movements of the shaft 51, hub 48, flap 30 and blade 47.  
  The measuring channel 46 has a rectangular crosssectional outline and can form an integral or a separately produced part of the intake manifold 25 shown in FIG. 1. It is assumed that the housing 41 of the meter LM is a separately produced part and has two flanges including a first flange 60 airtightly connected with that portion of the manifold 25 which contains the air filter 26 and a second flange 61 airtightly connected with that portion of the manifold which contains the throttle 28. The configuration of the wall 44 (which is adjacent to the path of pivotal movement of the flap 30) is such that the unobstructed portion of the channel 46 increases exponentially in response to counterclockwise pivoting of the flap 30, as viewed in FIG. 5. This brings about the advantage that the relative indicating error A QL/QL remains constant within the entire range of pivotal movements of the flap 30.  
  The flap 30 is povitable in response to increasing rate of air flow through the manifold 25 against the resistance of a helical spring 65 which offers a practically constant resistance to angular displacement of the flap. The spring 65 is mounted in a centrally located recess 66 of a plastic disk-shaped retainer 67. As shown in FIG. 6, the outer end portion of the spring 65 is secured to the disk 67 by a rivet 68 and the inner end portion 69 of this spring is embedded in a plastic holder or cam 70 is such a way that the spring portion which is adjacent to the end portion 69 extends substantially tangentially of the end portion 71 of the shaft 51 on which the cam 70 is mounted. This insures that the lever arm of the spring 65 does not change in response to relatively angular displacement of the disk 67 and shaft 51. The end portion 71 of the shaft 51 extends beyond the wall 42 and is formed with two flats 72, 73 located opposite each other and insuring that the cam 70 cannot rotate on the shaft 51. The outer portion of the disk 67 has an annulus of gear teeth 75 which can be brought into mesh with a pinion (not shown) whose shaft is insertable into a socket 76 of the housing 41. The pinion can be used to accurately select the angular position of the disk 67 (by rotating the disk in a counterclockwise direction, as viewed in FIG. 6) so that the helical spring 65 is subjected to a predetermined initial stress. The disk 67 is then fixed in the selected angular position by a locking screw 77 or the like (see FIG. 4).  
  The accuracy of the flow meter LM depends on the quality of its finish, on the nature of the bearings for the flap 30 (and hence on the magnitude of hysteresis), and to a considerable extent on the durability of spring 65 and the extent to which the bias of this spring is affected by change in temperature. It was found that a spring which is made of a special nickel-beryllium alloy is particularly suited for use in the improved flow meter.  
  The end portion 71 of the shaft 51 further supports a carrier 78 which consists of synthetic plastic material and is integral with a holder or socket 79 for a weight 80 serving as a means for statically balancing the flow meter. The carrier 78 further supports the loop-shaped movable portion 81 of a potentiometer corresponding to the variable resistor R of FIG. 1. The movable portion 81 is a stamping which is provided with two contacts 82, 83 slidable along an arcuate stationary portion 84 of the potentiometer. The stationary portion 84 is provided on a platelike support 85 best shown in FIG. 9. Referring again to FIG. 3, there is shown (by broken lines) a tongue 86 which is obtained from a blank for the stamping of the movable portion 81 and is thereupon bent twice, both times through appoximately as shown in FIG. 4. The tip of the thus deformed tongue 86 carries a contact 87 which is outwardly adjacent to and registers with the end portion 71 of the shaft 51 and bears against a contact arm 88. Such positioning of the contact 87 in alignment with the shaft 51 insures that the friction between the tongue 86 and contact arm 88 in response to angular displacement of the flap 30 is negligible. The contact arm 88 has a tongue 89 which is received in a plastic socket secured to the housing 41. The median portion of the contact arm 88 is vulcanized into the socket 95, together with five additional contact arms 90, 91, 92, 93 and 94 to establish an electrical connection between the flow meter LM and the control circuit T5 of FIG. L. The control circuit TS has a complementary portion or plug (not shown) which is receivable in the socket 95 and carries contacts engaging with the contact arms 88 and 90-94. The rightmost contact arm 94 of FIG. 3 is connected with an elastic tongue-like element 96 which can engage a complementary contact element 97 of the contact arm 93. The element 96 is disengaged from the element 97 when the engine 10 of FIG. 1 is at a standstill and the flap 30 assumes its neutral position. In such angular position of the flap 30, 3 prong 99 of a supporting plate 98 engages the element 96 and holds it out of contact with the element 97. The supporting plate 98 is mounted on the carrier 78 for limited angular movement relative to the shaft 51. The movable portion 81 of the potentiometer can be adjusted relative to the flap 30 and is then secured to the carrier 78 by a screw 101 or an analogous fastener.  
  In order to allow for adjustments of the engine 10 so that, during idling, the fuel-air ratio is best suited to insure complete or satisfactory combustion of fuel, the housing 41 of the flow meter LM is provided with a bypass channel or passage 105 (see FIG. 5) which com municates with the metering channel 46 by way of an opening 106 located upstream of the flap 30. The opening 106 allows some of the air which flows into the manifold 25 to enter the passage 105 and to reenter the manifold 25 downstream of the flap 30 by way of a second opening 108 whose effective size is adjustable by a flow restrictor 107, e.g., a screw or the like (see FIG. 8).  
  Provision is further made to avoid damage to the flow meter LM in the event of backfiring of fuel-air mixture in the intake manifold 25. To this end, the flap 30 is provided with a relief valve which includes a plate-like valve member 110, a valve spring 111 and a guide pin 112. The spring 111 urges the valve member into a recess in one side of the flap 30 whereby the valve member I 10 overlies and seals two apertures 113, 114 of the flap 30. During backfiring in the manifold 25, the pressure in the downstream portion of the channel 46 rises to such an extent that the valve member 110 is lifted off its seat against the opposition of the spring 111 and allows the combustion products to escape by way of the inlet of the manifold 25, i.e. the relief valve including the parts 110-112 insures an equalization of pressure at both sides of the flap 30 when the pressure at one side rises abruptly as a result of backfiring or for any other reason.  
  The plate 85 of FlG. 9 carries the aforementioned stationary portion 84 of the potentiometer which is applied thereto in accordance with any suitable conven tional procedure, such as laminating process. As mentioned above, the stationary portion 84 is engaged by the slidable contacts 82, 83 of the movable portion 81. In order to insure that the resistance of the potentiom eter including the structure of FIG. 9 and the movable portion 81 will vary as a predetermined function of changes in angular position of the flap 30, the stationary portion 84 is subdivided into eight sections by seven discrete strips S1, S2, S3. S4, S5, S6 and S7. These strips consists of silver which is burned into the ceramic material of the plate 85 and is coated with a thin layer of tin by resorting to a dip-soldering process. The ends of the stationary portion 84 are connected with the contact arms 91 and 92. To this end, the contact arms 91, 92 respectively comprise suitably configurated (stamped) extensions 116 and 115 (see FIG. 3) overlying the fields 118, 119 of FIG. 9.  
  The field 118 is connected with a resistor foil 120 which, in turn, is connected with the adjacent end of the stationary portion 84 by a conductor 121. The resistor 120 is in parallel with a further resistor 122 which is connected with the strip S7. Additional resistors 123, 124, I25, 126, I27, I28. 129 are respectively connected with the strips S7, S6, S5, S4, S3, S2, and S1. The resistors 122-129 are treated by sand blasting so that their width and length indicates a preselected resistance. In this way, the resistance of the potentiometer including the portion 81, 84 (corresponding to portions 31, 31a ofthe resistor R shown in FIG. 1 varies at a predetermined rate in response to changes in angular position of the flap 30.  
  The resistor foil 129 is connected with the strip S1 as well as with the adjacent end of the stationary portion 84, and is in series with a further resistor 130 which is connected with a conductor 131. The latter is further connected to a field 132 which is in current-conducting contact with the tongue-like portion 134 of the contact arm 90. A control resistor 135 is connected with the field 119 and hence with the portion 115 of the contact arm 92. The purpose of the control resistor 135 is to furnish a fixed voltage for determining and (if necessary) adjusting the applied voltage between the fields 118 and 119.  
  All of the resistors shown in FIG. 9 are preferably produced by the cermet method. As known, such method involves the application and firing of a paste in accordance with the screen printing process. It is, however, equally within the purview of the invention (and often preferable) to produce the resistors of FIG. 9 from conductive synthetic plastic material. Such resistors offer a highly satisfactory resistance to wear. The use of resistors in the form of conductive plastics not only results in a reduction of friction between the po tentiometer portions 81 and 84 but also enables the portions 81 and 84 to stand many other stresses which develop when the potentiometer is used in or with an internal combustion engine.  
  The indications which are furnished by the flow meter LM of FIGS. 3 to 9 become less accurate with increasing distance from the sea level. This is attributa&#39; hle to changes in the density of air as a function of changes in distance from zero elevation. Such influence of variations in air density could adversely affect the length of intervals Ti during which the fuel injection valves 11 of FIG. 1 remain open, and hence the fuel-air ratio of the mixture which enters the cylinders of the engine 10. It was found that the richness of the fuel-air mixture increases by about 5 percent whenever the distance between the vehicle and the sea level increases by 1,000 meters. In order to eliminate this error, we provide a modified flow meter which is shown in FIG. 10 and comprises a barometer including a sealed deformable container which is responsive to changes in the pressure of surrounding air and controls a nor mally closed valve 141 serving to regulate the fluid pressure in the damping chamber 62. The valve 141 is mounted in an internal partition 142 of the housing 41A. The partition 142 is located in a plane which is parallel to the axis of the shaft 51. The blade 47 pivots toward the partition 142 when the angular position of the flap 30 changes in response to increasing inflow of air into the intake manifold 25. The container 140 ex pands when the pressure of surrounding air decreases; it is mounted at the end face of the shank of a feed screw 143 which meshes with a wall 144 of the housing 41A and can be fixed in selected axial position by a lock nut 145.  
  The valve 141 comprises a disk-shaped valve member 146 which is biased against a seat 147 in the partition 142 by a valve spring 153. The seat 147 is externally threaded to mesh with the partition 142 and forms part of a valve body 143 which receives two slotted disk-shaped guides 151, 152 for teh stem of the valve member 146. The spring 153 reacts against the valve body 148 and bears against a washer at the right hand end of the stem 150, as viewed in FIG. 10, so as to urge the stem against or toward the adjacent wall of the container 140. The latter is received in a compartment 155 between the partition 142 and wall 144. A narrow slot or an analogous opening 157 of the housing 41A connects the compartment 155 with the upstream portion of the measuring channel 46. The reference character 156 denotes a further wall of the housing 41A which surrounds a portion of the compartment 155. The wall 156 is parallel with a removable sheet metal cover (not shown) similar to the cover 45 of FIG. 4 and serving to normally close the fourth side of the compartment 155 as well as one side of the channel 46 and chamber 62. The wall 156 is preferably integral with the wall 144.  
  The angular position of the flap 30 of FIG. 10 depends, among others, on the difference between the pressure P, at the upstream tide of the flap and the pressure P; in the damping chambers 62, i.e. the pres sure between the partition 142 and blade 47. As the distance between sea level and the flow meter of FIG. 10 increases, the container 140 expands and opens the valve 141 so that the pressure P increases and the dif ference between P and P decreases. This brings about an automatic compensation for changes in the pressure of atmospheric air. In other words. the angular position of the flap 30 changes as a function of the condition of valve 141 and hence as a function of the distance from sea level.  
  The container 140 can be adjusted and mounted in such a way that it abuts against the stem 150 at sea level. This insures that the compensation for differences between the level of the flow meter and sea level takes place whenever the distance between the sea level and the engine changes. i.e.. all the way between and up to above 3,000 meters above sea level.  
  Alternatively. the container 140 can be mounted in such a way that it expands sufficiently to engage the stern 150 only when the vehicle is driven to an elevation at a fixed distance (e.g.. 1,000 meters) above sea level. In such instances. the minor errors which develop during travel of the vehicle at elevations between 0 and 1.000 meters above sea level are not compensated for. An advantage of such mounting of the container 140 is that eventual malfunctions of the structure including the container 140 and valve 141 cannot adversely affect the rate of fuel injection at elevations at which the vehicle is most likely to be used. Also, the testing of exhaust gases is normally carried out at elevations below 1.000 meters above sea level so that the accuracy of fuel injection during such testing cannot be influenced by corrections involving adjustments to compensate for changes in distance from sea level.  
  Regardless of whether the container 140 is mounted to influence the position of the valve member 146 at any elevation or only above a predetermined distance from sea level. the arrangement of FIG. constitutes a very simple and purely mechanical means which compensates for differences in the distance from sea level and need not consume any electrical or other energy. Moreover, it enables the fuel injection system to compensate for changes in distance from sea level without changing the basic adjustment or setting of the resistor R of FIG. 1 or the resistor including the parts 81, 84 of FIGS. 3-9. Still further. the flow meter of FIG. 10 can be mass-produced for mounting in automotive vehicles so that. once the initial adjustment of the container 140 by means of the feed screw 143 is completed, the housing 41A can be immediately installed in the intake manifold to be electrically connected with the control circuit TS in a manner as described in connection with FIGS. 3 and 4 (see the socket 95).  
  In order to insure a higher rate of filling of cylinders with a combustible mixture. especially in four-cylinder four strike cycle interval combustion engines, the suction system is normally adjusted in such a way that the pressure fluctuates in the higher load range. Thus, when the intake manifold pressure exceeds 700 Torr (i.e., in the range between 700 Torr and maximum manifold pressure), the flap 30 of the flow meter is likely to assume an angular position which is indicative of a higher than actual rate of air flow. such errors in the position of flap 30 are particularly pronounced when the engine is operated at a low RPM; they be come smaller with increasing RPM and become negligible when the RPM exceeds 2,000 revolutions per minute.  
  In order to eliminate errors or inaccuracies in the positioning of flap 30 without additional pressure losses in the suction system, the meter of FIGS. 11 to 13 comprises an auxiliary air valve 160. This valve (best shown in FIG. 13) comprises a cylindrical body or housing 162 receiving a centrally located plunger 161 which is reciprocable in a sleeve 163. The sleeve 163 has external threads 164 mating with the internal threads of a partion 165 in the body 162. This sleeve further serves as a retainer for a helical spring 169 which surrounds the plunger 16]. The upper end portion of the plunger 161 (as viewed in FIG. 13) is provided with external threads 166 meshing with a nut 167. The latter cooperates with a washer 168 to clamp the central portion of an annular diaphragm 170 the marginal position of which is clamped between two separable portions of the body 162. The end portion 187 of the body 162 has one or more openings 188 so that the upper or outer side of the diaphragm 170 is subjected to the pressure of atmospheric air. The partition 165 defines with the diaphragm 170 a pressure chamber 171 which communicates with the intake manifold 25 downstream of the throttle 28 by way of a pipe 172. Thus, the pressure P, in the chamber 171 matches the pressure in the intake manifold 25 between the throttle 28 and the fuel injection valves 11.  
  The other end portion 174 of the plunger 161 (Le. the lower end portion. as viewed in FIG. 13) has a throttling or flow restricting surface 175 which controls the effective area of a passage or port 176 in an end wall 177 of the body 162. The end wall 177 defines with the partition 165 a compartment 178 which communicates with the surrounding atmosphere by way of one or more openings 179 so that the pressure P in compartment 178 matches the air pressure in the com partment surrounded by the end portion 187 of the valve body 162. The port 176 communicates with the interior of a nipple 180 which is connected with one end of a conduit 181 (either directly or by means of a flexible hose. not shown in FIG. 11). The other end of the conduit 181 communicates with the dampling chamber 62 by way of four bores 182 shown in FIGS. 11 and 12. The blade 47 can move into register with selected bores 182 in corresponding angular positions of the flap 30, Le. when the flap 30 is pivoted in a counterclockwise direction. as viewed in FIG. 11.  
  As mentioned in connection with FIG. 10, the angular position of the flap 30 is a function of the difference between the pressures P. and P Such pressure differential is balanced by the helical spring 65. At a given pressure P the pressure P in the damping chamber 62 increases as a function of difference between the atmospheric pressure P and the suction manifold pressure P, and brings about a less pronounced angular displacement of the flap 30. This can be explained as follows:  
  When the pressure P, in the chamber 171 of FIG. 13 increases, the spring 169 is assisted by the rising pressure P, to move the plunger 161 away from the end wall 177 against the opposition of atmospheric pressure P, in the compartment defined by the end portion 187 and diaphragm 170. The initial stress of the spring 169 is selected in such a way (this stress can be adjusted by rotating the sleeve 163 relative to the partition 165) that. when the pressure P, in the intake manifold 25 equals at least 700 Torr. the flow restricting surface 175 of the plunger 161 begins to allow the flow of fluid between the nipple 180 and the compartment 178. Thus. the atmospheric air is free to flow into the damping chamber 62 by way of the conduit I81 and bores 182 to oppose the counterclockwise pivotal movement of flap 30. as viewed in FIG. 11. The extent to which the plunger 161 can move in a direction away from the end wall 177 of the body 162 can be limited by an adjustable stop screw 185 which meshes with the end portion 187 and extends into the path of movement of the upper end portion of the plunger. The plunger 16] abuts against the stop screw 185 when the engine is operated at full load. Under such circumstances, the pressure losses in the intake manifold 25 are negtigibie. namely, in the range of 1-2 Torr.  
  The positions of bores 182 relative to the blade 47 are selected in such a way that. when the engine is operated at a higher load. the correction in the position of the flap 30 decreases continuously with increasing RPM of the engine. e.g., when the RPM increases be yond 2.000. As the RPM increases, the blade 47 moves into register with and beyond successive bores 182 so that the quantity of air flowing into the damping chamber 62 decreases and the air furnished by the conduit I81 ceases to influence the angular position of the flap 30 when the blade 47 registers with or moves beyond the rightmost bore 182 of FIG. ll. Such positioning of bores [82 renders it possible to influence the angular position of the flap 30 as a function of the RPM of en gine without substantial outlays for additional parts. Furthermore, and depending on the availability of space in the area adjacent to the engine 10, the auxiliary valve 160 can be mounted directly on the flow meter including the flap 30 or the auxiliary valve can be installed at any desired distance from the flow meter by the simple expedient of using a hose which connects the nipple 180 of the valve body 162 with the conduit l8l.  
  FIG. 14 illustrates a further flow meter which is provided with means for influencing the position of the flap 30 as a function of changes in temperature of atmospheric air. Changes in temperature influence the density of air which is being drawn into the intake manifold 25. Moreover, the changes in temperature can influence the elasticity modulus of the spring 65 which opposes the pivotal movement of flap 30. The spring 65 of FIG. 14 is made ofa material which compensates for changes in temperature. Such materials are available on the market. A suitable material is known under the trade name VAC-Thermalast. This elasticity modulus of such material is practically independent from changes in temperature, ie it is at least substantially constant.  
  The compensation for changes in temperature of at mospheric air and resulting changes in density of air can also be effected by resorting to a spring 65 whose material has a negative temperature coefficient. The negative characteristic of the material of spring 65 is then selected in such a way that the changes in modulus of elasticity are balanced by changes in the density of air. To this end. the mounting of spring 65 of FIG. 14 is such that its temperature invariably equals or approx imates the temperature of surrounding air. The housing 41D of FIG. 14 has a bypass duct 205 which communicates with the intake manifold or with the housing 41D upstream of the flap and further communicates with the intake manifold downstream of the flap 30. The spring 65 is mounted in a space or chamber 206 which is traversed by air flowing in the duct 205 whereby such air insures that its temperature equals or closely approximates that of the spring 65.  
  It was found that the accuracy of measurements of air flow rate in the intake manifold is affected not only by changes in temperature which result in changes of air density but also by changes in the modulus of elasticity of the material of spring 65. The errors which are caused by changes in the modulus of elasticity are superimposed on errors which are due to changes in the density of air. The errors which are due to changes in the modulus of elasticity can be eliminated if the material of the spring 65 is a temperature-compensated substance. The errors due to changes in the density of air are eliminated by making the spring 65 of a material having a negative temperature coefficient. As mentioned before. the negative temperature coefficient of the material of spring 65 can be selected in such a way that the changes in density of air are balanced by the influence of temperature on the modulus of elasticity.  
  Without further analysis. the foregoing will so fully reveal the gist of the present invention that others can. by applying current knowledge. readily adapt it for var ious applications without omitting features which fairly constitute essential characterstics of the generic and specific aspects of our contribution to the art, and, therefore. such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.  
  What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:  
  1. In an electrically controlled fuel injection system for internal combustion engines. particularly in an intermittently operated fuel injection system, a combination comprising an intake manifold having an inlet and an outlet; an adjustable throttle mounted in said manifold; at least one electromagnetic fuel injection valve provided in the region of said outlet; a control circuit operable to open said valve for varying intervals of time which determine the amounts of injected fuel. said circuit including an energy storing device which undergoes a first change of stored energy between successive openings of said valve and undergoes an opposite second change of stored energy during successive openings of said valve whereby the duration of the second change of stored energy determines the length of said intervals; transducer means for changing the duration of the second change of stored energy of said device as a function of changes in the quantity of air flowing in said manifold, comprising a regulating member including an output connected with said circuit and having a plurality of conditions each corresponding to a different length of said intervals. and an air quantity meter operative to change the condition of said regulating member as a function of changes in the rate of air flow in said manifold. said meter comprising a flap pivotably mounted in said manifold between said throttle and said inlet to assume a plurality of positions each corresponding to a different rate of air flow in said manifold. said flap being operatively connected with said regulating member, and pneumatic damping means rigid with said flap and operative to oppose fluctuations in the position of said flap. wherein said flow meter further comprises resilient means for opposing the pivotal movement of said flap in response to increasing rate of air flow in said manifold, said flap being pivotable about an axis which is adjacent to the path of air flow in said manifold. wherein said meter further includes a housing forming part of said manifold. said flap being mounted in said housing and said damping means comprising a blade inclined with respect to said flap. said flap having a hub which surrounds said axis.  
  2. In an electrically controlled fuel injection system for internal combustion engines. particularly in an intermittently operated fuel injection system. a combination comprising an lllfdkt, manifold having an inlet and an outlet; an adjustable throttle mounted in said manifold; at least one electromagnetic fuel injection valve provided in the region of said outlet; a control circuit operable to open said valve for varying intervals of time which determine the amounts of injected fuel, said circuit including an energy storing device which undergoes a first change of stored energy between successive openings of said valve and undergoes an opposite second change of stored energy during successive openings of said valve whereby the duration of the second change of stored energy determines the length of said intervals; transducer means for changing the duration of the second change of stored energy of said device as a function of changes in the quantity of air flowing in said manifold. comprising a regulating member including an output connected with said circuit and having a plurality of conditions each corresponding to a different length of said intervals, and an air quantity meter operative to change the condition of said regulating member as a function of changes in the rate of air flow in said manifold, said meter comprising a flap pivotably mounted in said manifold between said throttle and said inlet to assume a plurality of positions each corresponding to a different rate of air flow in said manifold, said flap being operatively connected with said regulating member. and pneumatic damping means rigid with said flap and operative to oppose fluctuations in the position of said flap, wherein said flow meter further comprises a housing forming part of said manifold and defining a measuring channel wherein the air flows from said inlet to said outlet and a damping chamber communicating with said measuring channel, said flap being located in said channel and said damping means comprising a blade rigid with said flap and located in said damping Chamber.  
  3. A combination as defined in claim 1, wherein said valve comprises a coil and said circuit comprises first and second inputs and an output, said first input being connected with the output of said regulating member, and further comprising amplifier means connected between the output of said control circuit and said coil, and signal generating means connected with said second input and operative to furnish to said circuit signals in synchronism with the RPM of the engine.  
  4. A combination as defined in claim 1, wherein said energy storing device includes a capacitor.  
  5. A combination as defined in claim 1, wherein said energy storing device includes an inductance.  
  6. A combination as defined in claim 1, wherein said regulating member is a variable resistor.  
  7. A combination as defined in claim 4, wherein said flow meter further comprises a shaft rotably mounted in said housing and defining said axis, said hub having an axial bore receiving said shaft and said housing having a sleeve extending into said bore and surrounding said shaft.  
  8. A combination as defined in claim 7, wherein said flow meter further comprises at least one antifriction bearing interposed between said shaft and said sleeve.  
  9. A combination as defined in claim 7, wherein said shaft comprises an end portion extending beyond said sleeve and said flow meter further comprises a holder provided on said end portion, said flow meter further comprising a helical spring arranged to oppose the pivotal movement of said flap in response to increasing rate of air flow in said manifold, said spring having an end portion secured to said holder.  
  l0. A combination as defined in claim 9, wherein said flow meter further comprises a retainer coaxial with said shaft and angularly adjustably secured to said housing, said spring further having a second end portion spaced radially outwardly from said first mentioned end portion thereof and secured to said retainer.  
  ll. A combination as defined in claim 10, wherein said retainer is a disk having a recess for said Spring.  
  12. A combination as defined in claim 10, wherein said retainer is a disk having an annulus of gear teeth.  
  l3. A combination as defined in claim 7, wherein said shaft comprises an end portion extending beyond said sleeve and provided with a carrier, said regulating member including a variable resistor having a movable portion secured to said carrier and a stationary portion which constitutes said output and along which said movable portion slides in response to rotation of said shaft with said flap.  
  ]4. A combination as defined in claim 13, wherein said movable portion of said resistor includes a contact adjacent to and coaxial with the end portion of said shaft.  
  15. A combination as defined in claim 13, wherein said flow meter further comprises a weight secured to said carrier and arranged to statically balance said flap and said blade.  
  16. A combination as defined in claim 13, wherein said flow meter further comprises supporting means provided on said carrier and turnable within limits relative to said shaft, said supporting means having a prong, and two stationary contact elements normally engaging with each other, said prong being arranged to disengage said contact elements in at least one angular position of said supporting means.  
  17. A combination as defined in claim 13, wherein said variable resistor is a potentiometer and said movable portion is the slider of said potentiometer, said resistor further comprising a support for said stationary portion thereofv 18. A combination as defined in claim 17, wherein said stationary portion consists of conductive synthetic plastic material.  
  19. A combination as defined in claim 17, wherein said stationary portion is a laminated structure.  
  20. A combination as defined in claim 17, wherein said support consists of ceramic material and comprises a plurality of current-conducting fields, said flow meter further comprising a plurality of elastic contacts engaging said fields to connect said stationary portion with said circuit.  
  21. A combination as defined in claim 17, further comprising a control resistor connected in series with said stationary portion and maintained on said support.  
  22. A combination as defined in claim 17, further comprising a socket provided on said housing and a plurality of contacts extending into said socket and connected with said circuit, one of said contacts being connected with said movable portion.  
  23. A combination as defined in claim 1, wherein said flow meter further comprises a normally closed relief valve provided in said flap and arranged to open in response to development of a predetermined pressure differential at the opposite sides of said flap.  
  24. A combination as defined in claim I, wherein said flow meter further comprises a housing forming part of said manifold and receiving said flap, said housing 25. A combination as defined in claim 24. further being provided with a bypass channel having end porcomprising adjustable flow restrictor means provided tions communicating with said manifold at the opposite in said bypass channel.  
 sides ofsaid flap.