Means For Indicating The Rate Of Air Flow In The Intake Manifold Of An Internal Combustion Engine

Abstract

A potentiometer wherein the sliding contact is pivotable by the flap of an air flow rate metering gauge in the intake manifold of an internal combustion engine with fuel injection into the manifold, and the stationary resistor track of the potentiometer is provided with spaced-apart metallic strips each of which is connected with at least one resistor. The strips are thin enough to be cut by the sliding contact and each thereof extends from a discrete fixed contact adjacent to a convex edge face of the track all the way to a concave edge face of the track. The potentiometer is connected with a control circuit which determines the duration of pulses serving to effect an opening of fuel injection valves.

Description

BACKGROUND OF THE INVENTION

The present invention relates to fuel injection systems for internal combustion engines, and more particularly to improvements in means for regulating the quantities of injected fuel as a function of changes in the rate of air flow into the intake manifold of the engine.

It is already known to install in the intake manifold of an internal combustion engine a flap whose angular position changes in dependency on changes in the quantity of inflowing air and which thereby displaces the sliding contact of a potentiometer. The sliding contact travels along a resistor track which is provided with several contacts for a set of parallel resistors. The resistors enable the resistance of the potentiometer to vary exponentially or in accordance with another suitable pattern in dependency on changes in angular position of the flap.

The manufacture of potentiometers wherein the resistance of the resistor track varies non-linearly in dependency on the position of the sliding contact presents serious problems, especially if the resistance is to vary in exact accordance with a predetermined pattern. In an internal combustion engine with fuel injection into the intake manifold, the air flow metering gauge is preferably designed with a view to insure that the resistance of the potentiometer will vary exponentially as well as that the relative error constituting the difference between actual variations and variations in accordance with an exponential function not only remains constant in each position of the sliding contact but also that such error is minimal. The just discussed error can be compensated for by appropriate adjustment of opening times of fuel injection valves in the engine.

SUMMARY OF THE INVENTION

An object of the invention is to provide a relatively simple and inexpensive potentiometer or rheostat whose sliding contact is controlled by the movable flap of the air flow rate metering gauge in the intake manifold of an internal combustion engine with fuel injection and wherein the resistance which the potentiometer offers in various positions of the flap corresponds exactly to, or deviates negligibly from, a set of predetermined values.

Another object of the invention is to provide a potentiometer wherein the resistance varies exponentially.

The invention is embodied in an internal combustion engine wherein the rate of air flow in the intake manifold is measured by a gauge having a movable member (e.g., a pivotable flap) whose position is a function of the rate of air flow in the intake manifold. More specifically, the invention is embodied in a potentiometer or rheostat comprising an elongated resistor track having an exposed side, a plurality of first contacts each having a narrow metallic web or strip extending across the exposed side of the track, a plurality of resistors connected with the first contacts, and a sliding contact receiving motion from the movable member of the gauge and engaging the exposed side of the track. The thickness of each web or strip is such that the sliding contact cuts thereacross during movement along the respective portion of the exposed side of the track.

The webs or strips can be deposited on the track by evaporation. The first contacts are preferably adjacent to a convex outer edge face and the webs or strips preferably extend all the way from the convex to a concave inner edge face of the track.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved potentiometer 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. 1 is a schematic partly elevational and partly sectional view of an internal combustion engine with fuel injection wherein the gauge which measures the rate of air flow in the intake manifold controls a potentiometer which embodies the invention;

FIG. 2 is an enlarged elevational view of the potentiometer, with the sliding contact omitted; and

FIG. 3 is a sectional view as seen in the direction of arrows from the line III--III of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a four-cylinder four stroke cycle internal combustion engine 10 with fuel injection. The fuel injection system comprises four electromagnetically actuated fuel injection valves 11 which can receive fuel from a distributor 12 by way of discrete fuel lines 13. Fuel is being drawn from a tank 14a by an electromagnetically operated fuel pump 14 which supplies fuel to the distributor 12 by way of a pressure regulator 15. The regulator 15 insures that the pressure of fuel in the distributor 12 equals or closely approximates a predetermined value, e.g., two atmospheres superatmospheric pressure. The surplus fuel delivered by the pump 14 to the pressure regulator 15 is returned to the tank 14a via conduit 15a.

The fuel injection system further comprises a signal generator including a normally closed switch 17a and a cam 17 which is driven by the crankshaft 16 of the engine 10 and actuates the switch 17a twice during each revolution of the crankshaft. The switch 17a supplies rectangular pulses LJ to a transistorized control circuit TS which converts the pulses into valve-opening pulses S each having a duration Ti which determines the quantity of fuel injected into the cylinders. This will be readily understood by considering that the pressure regulator 15 maintains the fuel in the distributor 12 at a constant pressure so that the quantity of injected fuel is a direct function of the length of intervals during which the fuel injection valves 11 remain open. The length of intervals Ti varies as a function of many parameters, such as the position of the throttle 25 in the intake manifold 22 of the internal combustion engine 10, the RPM of the crankshaft 16, the pressure in the intake manifold 22, and/or others.

The windings 18 of the fuel injection valves 11 (only one winding 18 shown) are connected to the ground and are in series with discrete buffer resistors 19. The resistors 19 are connected with the output of an amplifier 20 which comprises at least one output transistor 21 having an emitter-collector circuit in series with the resistors 19 and windings 18.

In the internal combustion engine 10 (i.e., in an engine without spontaneous combustion of injected fuel), each piston which performs a suction stroke draws into the respective cylinder a certain amount of air together with a quantity of fuel defined as that quantity of fuel which is completely combusted during the next-following working stroke. As a rule, the operation of the internal combustion engine is considered satisfactory is no appreciable amount of surplus air remains in the cylinder upon completion of the working stroke.

In order to achieve a satisfactory stoichiometric ratio between air and fuel, the engine further comprises an air flow rate metering gauge LM which is installed in the intake manifold 22 between a filter 23 (at the inlet end of the manifold) and the throttle 25. The latter is pivotable by a pedal 24. The gauge LM comprises essentially a movable member or flap 26 which is mounted in the intake manifold 22 upstream of the throttle 25 and is pivotable about a shaft 26a extending tangentially of the intake manifold 22, and a potentiometer R having a sliding contact 27 which is directly or indirectly connected with the flap 26 and is movable along stationary contacts of the potentiometer. The potentiometer R is connected with the transistorized control circuit TS. The latter comprises two transistors and an energy storing device, such as a capacitor. The capacitor is charged with constant current during one-half of each revolution of the crankshaft 16. The discharge immediately follows the charging step and is effected by a discharge current dependent on the resistance of a selected resistor of the potentiometer R. One of the transistors in the circuit TS blocks when the other transistor conducts, and vice versa. The connection between the two transistors is a feedback connection from one transistor to the other, and vice versa.

The construction of the improved potentiometer R is shown in FIGS. 2 and 3. This potentiometer comprises a base plate or carrier 30 which consists of an insulating material and supports an arcuate resistor track 33 whose ends are secured to the carrier by rivets 31 and 32. The track 33 includes a layer of graphite or another material having an accurately defined conductivity. The outer (convex) edge face of the track 33 is adjacent to seven equidistant contacts 34 each having a narrow strip-shaped or web-shaped extension 36 which extends across the track 33, i.e., all the way to the concave inner edge face 35 of the track. The extensions 34 preferably consist of thin layers of silver which are deposited on the track 33 by evaporation. Such thin layers of silver preferably further coat the contacts 34 to insure the making of satisfactory electrical connections with metallic rivets 37 passing through the carrier 30 (see FIG. 3) and connected with discrete conductive strips 38 at the rear side of the carrier 30. The strips 38 may consist of copper and each thereof is connected to a discrete conductor 39 of a nine-strand cable 40 serving to connect the potentiometer R with the control circuit TS. It will be noted that two of the conductors 39 are connected with the rivets 31 and 32.

The sliding contact 27 of the potentiometer R is provided with a preferably pointed tip which travels along the track 33 in response to pivoting of the flap 26 as a result of changes of air pressure in the interior of the intake manifold 22. The path along which the tip of the contact 27 travels along the track 33 is indicated in FIG. 2 by broken lines, as at 41. It will be noted that the width of the path 41 need not exceed the thickness of the extensions 36. When the sliding contact 27 travels along the track 33, its tip cuts across the adjacent extension 36 due to friction between 27 and 33, and thus extablishes an electrical connection between the respective conductor 39 and the conductor 42 which connects the contact 27 with the control circuit TS.

The resistance of the potentiometer R varies in dependency on changes in the angular position of the sliding contact 27, i.e., in dependency on the position of the tip on the contact 27 with respect to the track 33.

The purpose of the web- or strip-shaped extensions 36 is to insure that the resistance varies in accordance with a predetermined pattern. The extensions are shown as being equidistant from each other. Three of the resistors which are connected in parallel between the contacts 34 are shown at A, B and C. Reference may also be had to FIG. 9 of the commonly owned copending application Ser. No. 326,660 filed Mar. 12, 1973 by Kammerer et al., to FIG. 3b of commonly owned abandoned application Ser. No. 128,617 filed Mar. 25, 1971 by Zechnall et al., or to FIGS. 9-10 of commonly owned copending application Ser. No. 164,304 filed July 20, 1971 by Scholl et al. The resistance of the resistors including those shown at A, B and C is selected in such a way that the resistance of the potentiometer R varies exponentially when the sliding contact 27 moves from the rivet 31 toward the rivet 32 or vice versa. It will be noted that the path 41 for the sliding contact 27 is shorter than the distance between the rivets 31, 32.

An important advantage of the potentiometer R is that it is highly resistant to wear as well as that there takes place a uniform distribution of potential at each of the extensions 36.

The track 33 may form part of a circle. The aforementioned distribution of potential is especially satisfactory if the extensions 36 extend all the way across the track 33, i.e., from the convex outer edge face and to the concave inner edge face 35. The fixed contacts 34 are preferably adjacent to the outer edge face of the track 33.

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 various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my 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.

Claims

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In an internal combustion engine with fuel injection wherein the rate of air flow in the intake manifold is measured by a gauge having a movable member whose position with respect to the intake manifold is a function of the rate of air flow therein, a potentiometer comprising an elongated resistor track having an exposed side, a plurality of discrete first contacts each having a narrow metallic strip extending across said exposed side of said track, a plurality of resistors connected with said first contacts, and a sliding contact receiving motion from said movable member and engaging said exposed side of said track, the thickness of said strips being such that said sliding contact cuts across said strips during movement along the respective portion of said exposed side of said track.

2. A potentiometer as defined in claim 1, wherein said strips are deposited on said exposed side of said track by evaporation.

3. A potentiometer as defined in claim 1, wherein said track has a first and a second edge face extending lengthwise of said track, said first contacts being adjacent to one of said edge faces and each of said strips extending from said first and substantially to said second edge face of said track.

4. A potentiometer as defined in claim 3, wherein said second edge face is a concave edge face.

5. A potentiometer as defined in claim 1, wherein said resistors are connected in parallel.

6. A potentiometer as defined in claim 1, further comprising a carrier for said track and said first contacts.

7. A potentiometer as defined in claim 1, wherein said strips consist of silver.

8. A potentiometer as defined in claim 1, wherein said track forms part of a circle.

9. A potentiometer as defined in claim 1, wherein said track contains graphite.

10. A potentiometer as defined in claim 1, wherein said sliding contact and said movable member are pivotable about a common axis.