Device For Adjusting The Ignition Phase Of An Internal Combustion Engine

Abstract

An automatic ignition advance regulator for an internal combustion engine of the kind in which a lobed cam is mounted on the ignition distributor shaft and controls a switch which sends current sequentially to the ignition system of each engine cylinder and in which means are provided for varying the relative positions of the cam switch and the shaft, the improvement that at least a member sensitive to the working conditions of the engine moves a cam member to which a follower is connected with the movement of the follower controlling the position-varying means.

Description

BACKGROUND OF THE INVENTION

It is known that in internal combustion engines, the ignition of the mixture is caused to take place by the electric spark which flashes in the interior of the explosion chamber, between the two electrodes of the ignition spark plug. It is known that such a spark should be in an appropriate phase relationship with respect to the displacement of the piston and that such a phase angle relationship is expressed in degrees of rotation of the crankshaft, by taking as the reference point of the phase relationship, the upper dead center of the piston between the termination of the compression stroke and the beginning of the expansion stroke. It is known that the spark is caused to flash, as a general rule, before the piston has reached said dead center, and the corresponding phase angle is called the "angle of advance"; in the cases in which the spark is caused to dart after the piston has reached the dead center, the phase angle is defined as the "angle of delay."

As a general rule, especially in the internal combustion engines which equip motor vehicles, the spark is generated in the specially provided electric ignition system, of which an essential component part is the ignition distributor, or current distributor; the basic component part of the ignition distributor is the contact breaker, consisting of an electric contact which is cyclically opened and closed since the timer shaft, driven to rotation by the engine crankshaft, has a cam having lobes: every time that a lobe goes below a pad solid with the movable portion of the electric contact, the latter (which is kept closed by a spring) is opened; the voltage originated by the resulting extra-current, is amplified in a transformer or coil which causes a spark to flash between the spark plug electrodes.

It is known that, as the mixture becomes ignited in the vicinity of the spark plug, a flame front advances in the explosion chamber and, as the flame front reaches the walls of the explosion chamber, the combustion of the mixture is completed. It is also known that the speed at which the flame front is propagated is not very high and that the combustion must be completed in the very first shank of the piston expansion stroke for the efficiency to be maximum or nearly so. The result is that it is necessary to have the spark to be flashed before that the piston reaches its upper dead center, that is, that the spark be timed with a certain advance with respect to said dead center.

PRIOR DEVICES

It is likewise known that the speed of propagation of the flame front does not vary considerably as the engine RPM is varied so that it becomes necessary to increase the angle of advance as the same RPM is increased. This situation has originated a first conventional device for automatically varying the angle of advance: this device is generally embodied by making rotatable with respect to the axis of the timing shaft of the distributor, the component part which carries the lobes, that is, the lobed cam: the connection device (or coupling) between said component part and the distributor shaft is a leverage whose configuration is modified as the RPM is varied, since appropriate springs counteract the centrifugal force acting on portions of said leverage and is variable as the rate of rotation of the engine is varied. This first automatic device is thus capable of supplying an "advance curve" as a function of the RPM of the engine. The RPM number being the same, the operative conditions of the engine are sharply varied, as is known, according to the positions of the accelerator pedal, that is, according to the feeding pressure. The value of the feeding pressure influences, as is known, the occurrence or the absence of particular phenomena such as detonation which occurs at full power rather than under reduced pressures.

Often for these reasons, the ignition distributor has been equipped with a second conventional automatic device which is adopted concurrently with the first one as outlined above; this second device comprises, above all, a small cavity which can be placed into communication with the intake manifold so as to bring the cavity at the negative pressure which obtains in the manifold downstream of the throttle: one of the cavity walls is a deformable diaphragm which is biased by a spring: to every value of the negative pressure, there corresponds a position of the central portion of the diaphragm.

This second conventional device also comprises a dish which forms the base of the contact-breaker and can be rotated through a certain angle with respect to the axis of the distributor shaft inasmuch as a point of the dish, at a certain distance from the axis of rotation, is connected through a rod to the central portion of the diaphragm; such a dish acts as the base of the contact breaker on whose pad are active the lobes of the rotary cam. With such second conventional device, a variation is obtained of the angle of advance of the ignition as a function of the negative pressure obtaining in the intake duct, with said variation being summed to the variation of the angle of advance as a function of the rate of rotation as supplied by said first conventional device.

It is known, otherwise, that the timing of the ignition with respect to the dead center of the piston has a considerable bearing not only on the above recalled detonation phenomenon, but also, generally speaking, on the magnitudes of the internal temperatures and pressures, on the combustion, the thermal efficiency, the thermal and mechanical stresses of the internal component parts of the engine, and also the possibility of occurrence of serious irregularities of operation such as pre-ignition and others, but has a considerable influence also on the emission of unburned compounds at the exhaust side; the importance that such emissions have taken in recent years need hardly be mentioned.

It is with special regard to the problem of the emissions (for which the trend is also towards the use of fuels containing no lead and thus having a lower octane) that the second conventional device is inadequate, for the following reasons:

1. It supplies values of the angle of advance which are varied always in the same direction when the variations of the negative pressures are experienced in a certain direction.

(At present, contrarywise, inversions of the direction of variation of the angle of advance may be required, even though the negative pressure is always varied in the same direction).

2. It supplies variations of the angle of advance which have in practice, a constant ratio with respect to the variations of the negative pressure ( at present, such a simple proportion does not fulfil the most recent requirements).

3. It is generally used in certain areas of the field of use of the engine and is not utilized in other areas; this is obtained, as is known, due to the fact that the throttle edge, during its opening stroke, unmasks the bore which establishes a communication between the intake duct (downstream of the throttle) and the small cavity covered by the diaphragm, so that there is a sharp discontinuity in the values of the angle of advance when passing from one area of utilization of the engine to another area. This discontinuous adjustment is now deemed too coarse in order to solve the new problems.

In connection with the inadequacy of the second conventional devices, more sophisticated approaches have been suggested in recent times: for example, a second cavity having a diaphragm (this also connected to the intake duct) has been entrusted with the function of suppressing, under preselected utilization areas, the action of the first diaphragm; or, as an alternative, the dish has been equipped with a second contact-breaker which, in correspondence with certain utilization areas (for example relative to the angular position of the throttle or the accelerator pedal), is inserted, by the agency of appropriate electric contacts, in the ignition circuit instead of the first contact breaker. Both of these more sophisticated approaches, obviously permit the reversal of the direction of variation, but with abrupt discontinuities, rather than in a progressive manner.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is adequately to solve the present problem of a continuous variation of the angle of advance in the entire field of use of the engine as a function of those parameters which are essential, such as the feeding pressure and the rate of rotation, variations of the angle of advance which are not generally required to be proportional to the variations of the parameters; but rather, in certain cases, they are required to invert their algebraic sign as the parameters are varied and anyhow, they are required not to exhibit local discontinuities due to too coarse an approach.

According to the present invention, an internal combustion engine wherein the ignition is controlled by an ignition distributor in which a lobed cam is mounted on a shaft driven to rotation by said engine and controls a switch feeding with current sequentially the ignition system of each cylinder, and in which means are provided for varying the mutual relative positions of said switch, said cam and said shaft to vary the angular position of the shaft in which said cam controls said switch to feed electric ignition current, is characterized in that at least a member responsive to the working conditions of the engine moves a cam member to which a feeler is connected which, with its movement, controls said means.

Such an arrangement permits, consistently with the objects of the present invention, adjusting of the ignition phase according to a law which is any function whatsoever of the signal of said responsive member, with said function being defined by the outline of said cam member.

When a single member is provided which is responsive to the working conditions of the engine (for example to the dispensed power), said cam member is driven (for example to rotation) so that the cam follower is positioned so as to urge the cam on a point of a line; the position taken by the follower, as a function of the cam outline, controls with advantage the positioning of the ignition distributor which carries the circuit-breaker contacts. If it is preferred that the working conditions to which the variation of the angle of advance is two, a cam can be used whose follower is moved along a surface rather than along a line: this is tantamount to saying that the cam member is driven with movements in two directions, each controlled by a member responsive to a working condition of the engine. It is obvious that, by so doing, the adjustment as a function of two parameters still requires the mobility of the contact-breaker-bearing dish with the result being the constructional simplicity of the ignition distributor, since the conventional device which varies the position of the lobed cam relative to the shaft which carries the cam is not required.

The device which carries the cam member and the follower therefor can be constructed as an entity with the ignition distributor, or, as an alternative, it can be an independent mechanical unit which is kinematically connected with the distributor.

The features and objects of the present invention can be better understood from the ensuing description of exemplary embodiments, as illustrated in the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general diagrammatical view of an engine in which the angle of advance is adjusted according to the invention,

FIG. 2 is a cross-sectional view taken along the line II--II of FIG. 1 the view looking in the direction of the arrows,

FIG. 3 is a sectional fragmentary view of a detail of FIG. 1.

FIGS. 4 and 5 are a cross-sectional and a front view, respectively, of an alternative embodiment of the adjustment device according to the invention, and

FG. 6 shows a further embodiment of the device for adjusting the angle of advance as connected, by way of example, to other convention adjustment members in an engine.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the phase adjustment device according to the present invention and a partial cross-sectional view of the ignition distributor: the numeral 1 indicates the carburetor in elevational view (the dotted lines indicate the profile of the inner duct through which the mixture is fed).

The carburetor is flangedly connected to an intake manifold 2 for the mixture to the several cylinders. The manifold, in turn, is flangedly connected to a head 3 of the engine, whereas the engine base is indicated at 4. In the interior of the carburetor 1 there is, shown in dotted lines, a throttle 5 which is fast to a pin 6, to which a lever 7 is keyed. At the end of the lever corresponding to a pivotal point 8 there is pivotally connected one end of a drawbar 9. At the opposite end, the drawbar is connected by a pin 10 to a disc 11, and the disc can be rotated about the axis of a pin 12, with the latter being fast to engine base 4. To the disc 11 there is affixed a planar adjustment cam 13, defined by a plate having a properly shaped profile. On a specially provided groove having a circular outline and solid with the disc 11 (the groove is not shown in the drawing) is wrapped a flexible metallic cable 14 (in dotted lines in the section wrapped around the groove) with an end of the cable being affixed, at 15, to the disc. A spring (not shown in the drawing) tends to rotate the disc 11 with respect to the pin 12 in such a direction as to wind the metal cable in the groove; the opposite end of the metal cable is integrally connected to the accelerator pedal (not shown in the drawings), whereas, in the intermediate section, the cable is properly guided by a flexible sheath according to the conventional methods for this kind of remote control appliances. Thus the displacements of the accelerator pedal correspond to rotations of the disc and thus, through the drawbar 9 and the lever 7, to rotations of the throttle 5. Inasmuch as, as outlined above, the adjustment cam 13 is solid with the disc 11, every position of the accelerator pedal and thus of the throttle 5 corresponds to a particular relative position of the cam 13 with respect to a follower 16 which is maintained in contact with the shaped surface of the cam by a spring 17. The follower 16 is at the end of one arm of a lever 17 fulcrumed at 18, with the pivotal point 18 being integral with the base 4 of the engine. To a pivot 19 which is at the opposite end of the lever 17 is affixed a second flexible metal cable 20 guided by a corresponding flexible sheath 20'. One end of this sheath is affixed to the engine base at 21, whereas the other end is affixed at 22 to the body of an ignition distributor 23. The other end of the flexible metallic cable is solidly affixed to a bushing 24 which is shrunk on a pin 25, with the latter being integral with a dish 26. The dish 26 acts as the base of the contact breaker of the ignition distributor. The pin 25 is solid with the end of a recoil spring (not shown in the drawing) affixed at the other end to the body 23 of the distributor. As a matter of fact, as shown in FIG. 2 (which is a plan view of the distributor, partly in section and deprived of a cap 27) and in FIG. 3 (which is another side view of the distributor, partly in section along an axial plane) there is, solid with the dish, a pin 28 of a hammer 29 and an elbow 30 which carries one of the contacts of the circuit breaker shown at 31. To the hammer 29 there is affixed a pad 32, with which come sequentially in contact the four lobes of a cam 33. In addition, the other of the two contacts of the circuit breaker, shown at 34, is also solid with the hammer 29.

In FIG. 3, there is, indicated at 35, the shaft of the distributor, which rotates in a bushing 36, the latter being solid with the distributor body 23: at the upper end of the shaft is solidly affixed a plate 37 which drives the lobed cam 33 via a coupling 38. In this embodiment of the present device, the coupling 38 contains a centrifugal mechanism which is deformable as the engine RPM is varied and thus, according to the conventional technique, it supplies the variation of the angle of advance of ignition as desired as the rate of engine rotation is varied. To said variation is added the variation of the angle of advance required as a function of the angle of the throttle, by virtue of the device according to the present patent application. This latter variation of the angle of advance is thus obtained since, as the angle of the throttle is varied, due to the mechanism described above, the rotations of the lever 17, correlated with the rises of the cam 13, originate rotations of the contact-breaker carrying dish 26 pivoted at 39 to the bushing 36.

FIGS. 4 and 5 show the device for adjusting the ignition phase embodied according to the further version as described above, which provides the utilization, as the adjusting member, of a spatial adjustment cam (three-dimensional) 40 instead of the planar adjustment cam of the first version, with said adjustment cam being supported by a hollow through shaft 41 with respect to which the cam can effect relative displacements in an axial direction; the shaft 41 is rotatably supported on a body 63 whereas rotations of the cam relative to the shaft are prevented since a pin 49, forcibly introduced into the cam, is guided in two axial grooves 47 and 48, as formed in the shaft in correspondence with the hollow portion thereof.

To the shaft 41 is solidly fastened a sheave or pulley 42 by means of a key 43. On the groove of the sheave is wound a flexible metal cable 45, whose end is affixed to the sheave itself at 65, and the cable (being guided by a flexible sheath 84 in the conventional way), is, at its other end 81, fastened to an accelerator pedal 82 which is pivoted at 83 and undergoes displacements, and thus, is displaced as the position of the accelerator pedal is varied. The spatial cam 49 is thus mechanically connected to the accelerator pedal and carries out displacements (angular) which correspond to the displacements of the pedal.

The axial displacements of the adjustment cam (with respect to the distributor shaft) take place, instead, since the pin 49 is engaged in a cylindrical hollow 46 formed in the interior of the shaft, and can slide axially with respect to the shaft itself. Said axial displacements take place since a spring 68, by acting axially on the spatial cam and thus on the pin 49, urges a piston 50 and a rod 51 solid therewith against a rigid surface 57 which is solid with the central portion of a diaphragm 52. Said diaphragm separates from one another two cavities 53 and 56 whose walls are rigid for the remaining part. Through a flexible tube 55 slipped on a pipe 54, there arrives at a cavity 53 the pressure existing in an intake duct 86 of the centrifugal pump diagrammatically shown at 85 for circulating the cooling liquid, with the pump being driven by the engine 4. To the intake duct 86 of the pump, is connected in fact the other end of the tube 55. Through a tube 59 slipped on mouth 58, the cavity 56 is reached by the pressure obtaining in a delivery duct 87 of said centrifugal pump 85. To said delivery duct of the pump there is connected in fact the other end of the tube 59.

On the two faces of the diaphragm 52 are thus active the two above-mentioned pressures; the resulting load of the differential between the two pressures (a difference which is the head of the centrifugal pump) counteracts, through the kinematic chain formed by the members 57, 51, 50, 49 and 40 the elastic load of the spring 68. It is thus apparent that to every value of the pump head there corresponds a position of the adjustment cam for which an equilibrium is attained between the two counteracting loads aforesaid. Since, as is known, the head of the centrifugal pump is a function of the RPM of the centrifugal pump, since the latter is driven at an RPM which is equal or proportional to that of the internal combustion engine, the relative axial position of the adjustment cam with respect to the shaft is a function of the engine RPM.

By so doing the spatial adjustment cam, due to the effect of the translational and rotation motions aforesaid, will take a position which is a function of the two parameters which characterize the modes of use of the engine; speed of rotation and angle of throttle. In the drawings there is indicated at 60 a feeler member kept in contact with the cam surface by a resilient member 61. The follower, which can only be translated in the direction of its axis, is so guided by a bearing 62 solid with a body 63 of the device. A flexible metal cable 64, properly guided according to the conventional remote control technique, is affixed at one end to the follower and at the other end to the dish of the ignition distributor, a dish which acts as the base of the contact breaker in a way quite similar to that shown in FIG. 1.

As the relative position between the adjustment cam and the follower is varied, the follower is subjected to translational motions and by the mechanism described above causes angular displacements of the dish which acts as the base of the contact breaker thus varying the relative position between the contact breaker hammer and the lobed cam. With this embodiment of the invention, the ignition advance is adjusted by a single device as a function of the engine speed and of the angle of the throttle. The lobed cam of the ignition distributor is directly keyed to its shaft.

FIG. 5 shows a front view of the device of FIG. 4 and is further illustrative of the mounting of a few component parts of the device. At 45 there is shown the flexible metal cable which is fastened to the sheave 42 at 65, the cable being wound in a specially provided semicircular guide of the sheave, and at 44 there is shown a recoil spring which has one end solid with the sheave at 66 and the other is solid with the body of the device at 67.

An additional embodiment of the invention is shown at FIG. 6 which is similar to the one described above in connection with FIGS. 4 and 5.

It is known, in fact, that in gasoline injection engines, it is possible to carry out the regulation of the fuel injected in the individual cylinders with devices essentially based on the use of a spatial cam, whose surface is the engine carburetion plan and of a feeler which engages the cam.

The cam is driven to take several positions by the agency of means which are responsive to the speed of rotation of the engine and the angular position(s) of the throttle(s).

As outlined above also the cam for the adjustment of the ignition phase of the engine is controlled to take several positions by the agency of members which are sensitive to the conditions of use of the engine, so that it is possible to combine into a single mechanical unit the two cams, their followers and the responsive members aforesaid.

In a single substantially cylindrical block there can be formed the shaped surface of the cam which adjusts the injection and the shaped surface of the cam which adjusts the phasing of the ignition: these two surfaces can be arranged on opposite sides with respect to the axis of the block or they can be laid side by side, as in the embodiment shown in the accompanying drawings by way of example.

At 110 there is generally shown the block of the two cams, at 111 the shaped surface of the cam which adjusts the injected fuel and at 112 the shaped surface of the cam which governs the ignition phase.

The block 110 is supported by 2 bushing 113 in bearings 114 and 115 of the carrying and thrust type, with the bushing 113 being keyed by a tongue 116 to a shaft 117 which is rotated at a speed proportional to that of the crank-shaft and is mechanically connected to the latter by a conventional connection (not shown).

At 119 there is shown a centrifugal regulator solid with the shaft 117 and at 118 the axially movable member of said regulator; a member which is solid with the bushing 113.

At 121 there is shown a rod solid with a lever 122 which is solid in turn to a bushing 123 and there is indicated at 124 a groove formed through the block 110 in which the rod 121 is inserted.

The bushing 123 houses a bearing 120 for supporting the shaft 117, with the latter being borne at the opposite end by the a bearing 126.

The bushing 123 is solid with a pin 125 which is rotatably supported in 2 casing 136 of the adjustment unit, and on the pin 125 there is also keyed a bushing 127 equipped with a lever 128, with the latter being mechanically connected to the accelerator pedal (not shown) or to the throttle in a manner similar to that illustrated in the preceding figures of the drawings.

At 135 there is indicated a recoil spring which acts on the block 110 in the sense of counteracting the axial shifts of the block.

There are indicated at 129 and 130 two respective followers in engagement with the shaped surfaces 111 and 112 of the two adjustment cams.

The two followers can slide axially against the bias of respective springs 131 and 132, since they are supported and guided by cups 133 and 134, with the latter being affixed to the casing 136.

As the engine working conditions are varied, the followers 129 and 130 come into contact with different points of the surfaces of the respective cams, the latter being controlled so as to be displaced axially, by the bushing 113 of the member 118 of the regulator 119, through an amount which is proportional to the variations in the engine speed and are driven to rotation about the axis of the block 110, by the rod 121 through an angle which is proportional to the angular variation of the throttle(s).

Axial displacements of the followers 129 and 130 correspond to variations of the adjusted physical units and, respectively, the amount of injected fuel and the ignition angle: as a matter of fact the follower 129 can be mechanically connected to the rack of the injection pump, as diagrammatically shown by 108, and the follower 130 can be mechanically connected to the contact-breaker-carrying dish of the ignition distributor according to the convention technique of remote control, and as illustrated hereinbefore.

Of course, the above described adjustment unit can also be inserted into an electronic injection circuit and in an electronic ignition circuit, since the followers 129 and 130 can be connected to the movable member of a rheostat or a potentiometer or to a plate of a capacitor or the magnetic core of a relay in a manner which is well known to those skilled in the art.

The displacements of the followers originate variation of an electric unit in the circuits and these variations correspond to different values of the regulated magnitudes as a function of the conditions of use of the engine.

Claims

What is claimed is:

1. The combination with an internal combustion engine having cylinders, a carburetor, a throttle for the carburetor, an electrical ignition circuit and an ignition distributor including a driven shaft, a lobed cam mounted on the driven shaft, a plate mounted for movement relative to the driven shaft, a switch for the ignition circuit carried by the plate, and a pad carried by the plate contacting the lobes of the cam during rotation of the cam for controlling the switch, with the current cut-off by the switch causing the initiation in correspondence with each of the cylinders in sequnce, of means for varying the relative positions of the switch and the shaft, said varying means including a disc mounted for rotation on the engine, a planar cam carried by the disc, means connecting the disc to an accelerator pedal, a follower tracking the profile of the planar cam, means operably connecting the follower to the distributor plate, and means operably connecting the disc to the throttle whereby displacements of the accelerator pedal correspond to rotations of the disc and via the connecting means to rotation to the throttle so that every position of the accelerator pedal and hence of the throttle correspond to a particular relative position of the cam with respect to the follower.

2. The combination as claimed in claim 1 in which the means operably connecting the follower to the distributor plate includes a lever fulcrumed intermediate its ends to the engine, the follower being carried at one end of the lever, spring means connected to the lever and engine maintaining the follower in engagement with the profile of the cam, and a flexible cable attached to the other end of the lever and to the distributor plate, so that the displacements of the follower in the direction of the raised portion of the planar cam essentially cause rotations of the distributor plate about the axis of the driven shaft of the distributor.

3. The combination with an internal combustion engine having cylinders, a carburetor, a throttle for the carburetor, a hydraulic circuit, a pump driven by the engine inserted in the hydraulic circuit, said pump having intake and delivery sides, an electrical ignition circuit, and an ignition distributor having a driven shaft, a lobed cam mounted on the driven shaft, a plate mounted for movement relative to the driven shaft, a switch for the ignition circuit carried by the plate, a pad carried by the plate contacting the lobes of the cam during rotation of the cam controlling the switch, with the current cut-off by the switch causing the initiation in correspondence with each of the cylinders in sequence, of means for varying the relative positions of the switch and the shaft, said varying means comprising a three-dimensional cam, means mounting the three-dimensional cam for angular and axial movements, a follower tracking a profile of the three-dimensional cam, means operably connecting the follower to the distributor plate, a first means sensitive to the position of the throttle operatively connected to the throttle and the three-dimensional cam for displacing the cam angularly, a casing, a diaphragm within the casing dividing the casing interior into two spaces, means connecting one space with the pressure of the intake side of the pump, further means connecting the other space with the pressure of the delivery side of the pump, spring means biasing the diaphragm and means operably related to the diaphragm and to the three-dimensional cam for displacing the cam axially.

4. The combination as claimed in claim 3 including an accelerator pedal, a rotatable shaft on which said three-dimensional cam is mounted, and said first means including a pulley fastened to the rotatable shaft, a flexible cable connected to the pulley and means connecting the flexible cable to the accelerator pedal to impart angular displacements to the shaft and hence the cam corresponding to the displacements of the accelerator pedal.