US3755767A

US3755767A - Variable inductance device

Info

Publication number: US3755767A
Application number: US00315342A
Authority: US
Inventors: R Hendrickson
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1972-12-15
Filing date: 1972-12-15
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28

Abstract

In an electronic fuel injection system, a transducer for converting a variable pressure signal to a variable inductance comprises an inductive coil surrounding an axially reciprocable, magnetically permeable plunger. Two opposing sides of one end of the plunger are asymmetrically tapered; and a magnetically permeable flux member attached to the coil has portions adjacent the untapered end of the plunger and both sides of the tapered end of the plunger to create parallel flux paths through the plunger, each of which has a gap defined by one of the tapered sides and has a reluctance which varies with axial movement of the plunger. The portion of the flux member adjacent one side of the tapered end is transversely movable with respect to the plunger by a torque arm and adjusting screw so as to vary the slope of the inductance-plunger position curve.

Description

United States Patent [191 Hendrickson [451 Aug. 28, 1973 VARIABLE INDUCTANCE DEVICE [73] Assignee: General Motors Corporation,

Detroit, Mich.

[221 Filed: Dec. 15, 1972 [21] Appl. No.: 315,342

[56] References Cited UNITED STATES PATENTS 9/1955 Hale et a1. 336/134 12/1966 Lyman..... 336/136 X 2,427,872 9/1947 Newman 336/136 X 2,513,160 6/1950 Friend 336/133 X 1,720,446 7/1929 Sarazin 336/134 X Primary Examiner-Thomas J. Kozma Attorney-Paul Fitzpatrick et a1.

[5 7 ABSTRACT In an electronic fuel injection system, a transducer for converting a variable pressure signal to a variable inductance comprises an inductive coil surrounding an axially reciprocable, magnetically permeable plunger. Two opposing sides of one end of the plunger are asymmetrically tapered; and a magnetically permeable flux member attached to the coil has portions adjacent the untapered end of the plunger and both sides of the tapered end of the plunger to create parallel flux paths through the plunger, each of which has a gap defined by one of the tapered sides and has a reluctance which varies with axial movement of the plunger. The portion of the flux member adjacent one side of the tapered end is transversely movable with respect to the plunger by a torque arm and adjusting screw so as to vary the slope of the inductance-plunger position curve.

4 Claims, 5 Drawing Figures PATENIEMunza ma ll J INDUCTANCE MANIFOLD ABSOLUTE PRESSURE INDUCTANCE MANIFOLD ABSOLUTE PRESSURE a ll VARIABLE INDUCTANCE DEVICE BACKGROUND OF THE INVENTION Many electronic fuel injection systems for engines employ a pressure-inductance transducer in an electronic circuit to vary the duty cycle of a solenoid controlled fuel nozzle in accordance with the pressure in the engine air intake manifold. Such a transducer generally comprises an evacuated bellows in a chamber open to the variable pressure, one end of the evacuated bellows being fixed in the chamber and the other end being adapted to actuate a variable inductance device. The variable inductance device generally comprises a magnetically permeable plunger reciprocable within a coil and mechanically connected to the moving end of the evacuated bellows for co-movement therewith. A magnetically permeable flux member, fixed with respect to the coil, has one portion adjacent one end of the plunger and another portion adjacent the other end of the plunger to form, with the plunger, a magnetic flux path for the coil. One end of the plunger is tapered so that axial movement of the plunger varies the gap between the plunger and flux member; this varies the reluctance of the flux path and thus also the inductance of the device. The parameters of such a transducer are chosen to produce, in conjunction with the rest of the system, a particular desired curve of fuel flow as a function of manifold absolute pressure.

An inherent problem of such a transducer, however, is that very close tolerances have to be met on a number of these parameters in order to keep the desired curve within its tolerance limits. Although an axial adjustment for the fixed end of the evacuated bellows has been shown to be an effective method of adjusting the transducer to match one point on the desired curve, the remaining points on the desired and actual curve may not coincide, since the slopes of the curves may differ. It would be desirable to provide the capability of adjusting the slope of the curve so that expensive close tolerances would no longer have to be met.

An additional feature of most pressure-inductance transducers for electronic fuel injection systems is a power enrichment boost in fuel flow at high manifold absolute pressures. Provision for this feature presently requires additional mechanical devices within the transducer, such as an extra diaphragm with associated spring and stops. A typical design for such a transducer is shown in US. application, Ser. No. 202,760, filed Nov. 29, 1971, of common ownership with this application.

SUMMARY OF THE INVENTION This invention relates to a new and improved variable inductance device that can be used in an otherwise conventional pressure-inductance transducer within a electronic fuel injection system. The device incorporates features to provide adjustment of the slope of the inductance-manifold absolute pressure curve as well as the lateral translation of the curve and a power enrichment modification of the curve at high manifold absolute pressures.

: The device generally comprises a plunger axially reciprocable within a spool around which is wound an inductive coil. One end of the plunger is asymmetrically tapered on opposing sides thereof. A magnetically permeable flux member fixed to the spool has portions passing adjacent the ends of the plunger to provide two parallel flux paths, each of which has an air gap variable by one of the tapered surfaces as the plunger moves axially within the coil. The tapered surfaces of the plunger are designed with such slope and length that one predominates at low manifold absolute pressures and the other predominates at high manifold absolute pressures. A torque arm projecting from the flux member is effective to deform the flux member so that the portion thereof which forms an air gap with the tapered side of the plunger predominating at low manifold absolute pressure is moved transversely away from the plunger to vary the slope of the curve. An adjusting screw threadably mounted in the spool has an end which engages the torque arm to accomplish this result. Further objects and details of the invention will be apparent in the following drawings and description.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical electronic fuel injection system for an engine.

FIG. 2 is a partial cutaway view of a variable inductance device for use in the system of FIG. 1.

FIG. 3 is a view along line 3-3 of FIG. 2.

FIG. 4 is a graph showing typical inductance-pressure curves for the system of FIG. 1.

FIG. 5 is a graph showing typical inductance-pressure curves for the system of FIG. I with power enrichment at high pressures.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an induction passage or manifold 2 has a throttle 4 which controls air flow to the engine. An injector nozzle 6 is disposed to discharge the fuel into induction passage 2 adjacent the inlet valve 8 for the engine combustion chamber. A separate nozzle 6 would ordinarily be provided for each combustion chamber.

A housing 10 defines a transducer chamber 11, which is connected through a conduit 12 to the induction passage 2 downstream from the throttle 4; so that the induction passage pressure downstream from the throttle 4, hereinafter referred to as monifold absolute pressure, is communicated to the transducer chamber 11. Within the transducer chamber 11, an evacuated bellows 14 has one axial end thereof fixed to an axially adjustable member 16 which comprises, for example, an adjusting screw threadably mounted in the housing 10. The other axial end of the evacuated bellows 14, which moves axially in response to the changing manifold absolute pressure, is mechanically linked to the movable member 17 of a variable inductance device 18 to vary the inductance of the latter in accordance with the aforementioned pressure.

The variable inductance device 18 also contains an inductive coil 19 which is connected in an electronic circuit to control the operation of the injector nozzle 6. The circuit includes a pulse generator 20 which applies a negative pulse to a line 22 each time the injector nozzle 6 is to be actuated to inject fuel into the associated combustion chamber. The negative pulse renders an output transistor 24 nonconductive. With the output transistor 24 ofi, current flows through a solenoid winding 26 to actuate nozzle 6 and initiate fuel injection. Nozzle 6 remains actuated for a period of time determined by the remainder of the electronic circuit.

The negative pulse also renders a control transistor 28 nonconductive. With control transistor 28 off, the voltage at a junction 30 between resistors 31 and 32 increases and renders a transistor 34 conductive and a transistor 36 nonconductive. With transistor 36 off,

transistors

38 and 40 are also rendered nonconductive. As long as transistor 40 is off, output transistor 24 remains off and permits current flow through solenoid 26 to actuate the injection nozzle 6.

The aforementioned transistors are maintained in the indicated state for a period of time determined by the L/R time constant provided by the inductance of the transducer coil 19 and the combined resistance of the resistors 31 and 32. When the time constant permits decay of the voltage at junction 30 to a predetermined level, transistor 34 is rendered nonconductive and transistor 36 is thereby rendered conductive. With transistor 36 on,

transistors

38 and 40 are rendered conductive. As transistor 40 becomes conductive output transistor 24 becomes conductive, shorting out the solenoid 26 to de-energize the nozzle 6 and terminate fuel injection.

Thus the duration of fuel injection is controlled by the level of a voltage signal at junction 30 which in turn is controlled by an L/R time constant. In the simplified electronic control circuit shown here for purposes of illustration, this time constant is varied solely by varying the inductance of the transducer coil 19. This inductance is varied in the variable inductance device of this invention in a certain specified manner by the manifold absolute pressure.

Referring to FIG. 2, the variable inductance device 18 is seen to comprise a spool 50, made from a nonmagnetically permeable material, around which is wound the coil 19. The spool 50 has an axial hole 51, in which is disposed a plastic plunger guide 52. A movable member 17, which comprises a magnetically permeable plunger, is axially reciprocable with the plunger guide 52, which may be lined with a low friction substance to facilitate the reciprocation. As shown in FIG. 3, the plunger 17 and plunger guide 52 are rectangular in cross section, although many other shapes could be chosen. A magnetically permeable flux member 54 extends around the coil 19 and spool 50, as shown in FIGS. 2 and 3. The flux member 54 widens at one end, and this wider portion has an opening 56, through which the plunger guide 52 and plunger 17 extend. At the other axial end of the spool, two ends of the flux member 54, not joined, extend to the plunger guide 52. The flux member 54 and plunger 17 thus form two parallel flux paths for the coil 19, the common leg of which is the plunger 17. These flux paths circle the coil through the flux member 54 on opposite sides of the plunger 17. The end of the plunger 17 which projects through the opening 56 is axially constant in cross sectional shape and area; and, therefore, the gap between the flux member 54 and this end of the plunger 17 remains constant with axial movement of the plunger 17. The other end of the plunger 17, however, is tapered on the sides adjacent the two ends of the flux member 54; and these tapered sides produce a variation in the reluctance of the total magnetic flux path as the plunger 17 is moved axially within the spool. The two tapered sides have tapers of different length and depth; one side has a taper both shorter and shallower than the other.

' Flux member 54 has projecting from one side thereof and extending circumferentially part way around the coil 19, a torque arm 58. An adjusting screw 60 is threadably mounted in the spool 50 near the nontapered end of the plunger 17x The adjusting screw 60 extends axially toward the tapered end of the plunger 17 and engages the free end of the torque arm 58.

Prior art variable inductance devices of the moving plunger type have neither the asymmetrical taper nor the torque arm, so far as I am aware. Typical curves of inductance versus manifold absolute pressure for a typical prior art variable inductance transducer are shown as A and B on the graph of FIG. 4. Although curves A and B are similar in general shape, they do not correspond exactly because of differences in various parameters of the variable inductance device. If curve A describes the desired characteristic but the assembled device produces curve B, an axial adjustment for the movable plunger, such as that provided by the axially adjustable member 16, permits the point C where curves A and B intersect to be shifted anywhere along curve A. However, since the slopes of the curves are not changed they will intersect in only one point regardless of where that point is shifted.

In this invention, however, the slope of the inductance-pressurve curve can be changed by the adjusting screw 60. As 17. can be seen in FIG. 2, the side of the plunger 17 having the shortest and shallowest taper is adjacent the side of the flux member 54 from which projects the torque arm 58. As the adjusting screw 60, in contact with the torque arm 58, is moved toward the tapered end of the plunger 17, the torque arm exerts torque on the side of the flux member 54 from which it projects that causes the end of that side of the flux member to move transversely away from the tapered side of the plunger 17. This causes the slope of the inductance-pressure curve to decrease. Once the flux member 54 is deformed in this manner, the opposite movement of the adjusting screw causes the slope of the inductance-pressure curve to increase. The combination of this torque arm 58 and the axially adjustable member 16 allows the entire inductance-pressure curve to be brought within tolerance after manufacture.

It is also desirable, as has been previously mentioned, to provide for an extra boost in fuel supply rate at high manifold absolute pressure by providing for a similar boost in inductance. In FIG. 5, curves E and F show the desired increase in slope in the power enrichment region to the right of the dashed line G. In order to produce such a characteristic, the taper on the nonadjustable gap side of the plunger 17 is made longer and deeper than that on the adjustable gap side of the plunger 17. In operation, at low pressures, the adjustable gap is considerably smaller than the nonadjustable gap and therefore tends to control, since the contribution of the latter to total inductance is negligible. When the pressure increases to the point where the main taper has completely passed the adjustable end of the flux member 54, the adjustable gap no longer decreases with increasing pressure. From this point on, as pressure increases, the non-adjustable gap has an increasing effect upon the total inductance. The result is a curve such as D, E or F in FIG. 5, depending on the relative sizes of the minimum adjustable and nonadjustable gaps. If the minimum adjustable gap is considerably smaller than the minimum non-adjustable gap, very little or no power enrichment boost, such as is shown in curve D, will result. However, higher ratios of minimum adjustable to minimum non-adjustable gap sizes will produce curves such as E or F, wherein the effect of the variable slope disappears at the highest pressures.

I claim:

1. A variable inductance device comprising, in combination:

an inductive coil with a central axial hole therethrough;

a magnetically permeable plunger axially reciprocable in the hole, one end of the plunger being tapered on at least one side thereof;

a magnetically permeable flux member fixed to the coil on the outside thereof, the flux member having a first portion adjacent the tapered end of the plunger and a second portion adjacent the other end of the plunger whereby a magnetic flux path is created through the flux member and plunger which varies the inductance of the coil with the axial position of the plunger, the flux member also having a third portion, which third portion comprises a torque arm projecting from the first portion of the flux member, the torque arm being effective, when biased in one direction, to deform the flux member so that the first portion moves transversely with respect to the plunger to further vary the inductance of the coil;

and a member adjustable with respect to the coil, the adjustable member being engageable with the torque arm and effective, when adjusted, to bias the torque arm in the one direction.

2. A variable inductance device comprising, in combination:

an inductive coil with a central axial hole therethrough;

a magnetically permeable plunger axially reciprocable in the hole, one end of the plunger being asymmetrically tapered on two or more sides thereof;

a magnetically permeable flux member fixed to the coil on the outside thereof, the flux member having one portion adjacent each of the tapered sides of the tapered end of the plunger and a further portion adjacent the other end of the plunger whereby the one end of the plunger has a taper on one side that is both longer and deeper than the taper on the other side.

4. A variable inductance device comprising, in com- 10 bination:

an inductive coil with a central axial hole therethrough;

a magnetically permeable plunger axially reciprocable within the hole, one end of the plunger being asymmetrically tapered on opposing sides thereof, the taper on one side being longer and deeper than the taper on the other side;

a magnetically permeable flux member fixed to the coil on the outside thereof, the flux member having a first portion adjacent the one side of the tapered end of the plunger, a second portion adjacent the other side of the tapered end of the plunger and a third portion adjacent the other end of the plunger whereby parallel flux paths are created, one including the first portion of the flux member and the other including the second portion of the flux member, each of the flux paths being dominant in determining the rate of change of inductance of the coil over a different range of axial positions of the plunger, the flux member also having a fourth portion projecting from the second portion thereof, which fourth portion comprises a torque arm effective, when biased in one direction, to deform the flux member so that the second portion moves transversely with respect to the plunger to further vary the inductance of the coil in the range of axial plunger positions in which the second portion is dominant;

t s m k

Claims

1. A variable inductance device comprising, in combination: an inductive coil with a central axial hole therethrough; a magnetically permeable plunger axially reciprocable in the hole, one end of the plunger being tapered on at least one side thereof; a magnetically permeable flux member fixed to the coil on the outside thereof, the flux member having a first portion adjacent the tapered end of the plunger and a second portion adjacent the other end of the plunger whereby a magnetic flux path is created through the flux member and plunger which varies the inductance of the coil with the axial position of the plunger, the flux member also having a third portion, which third portion comprises a torque arm projecting from the first portion of the flux member, the torque aRm being effective, when biased in one direction, to deform the flux member so that the first portion moves transversely with respect to the plunger to further vary the inductance of the coil; and a member adjustable with respect to the coil, the adjustable member being engageable with the torque arm and effective, when adjusted, to bias the torque arm in the one direction.

2. A variable inductance device comprising, in combination: an inductive coil with a central axial hole therethrough; a magnetically permeable plunger axially reciprocable in the hole, one end of the plunger being asymmetrically tapered on two or more sides thereof; a magnetically permeable flux member fixed to the coil on the outside thereof, the flux member having one portion adjacent each of the tapered sides of the tapered end of the plunger and a further portion adjacent the other end of the plunger whereby a pair of parallel flux paths are created through the plunger and the separate portions of the flux member to vary the inductance of the coil with axial movement of the plunger.

3. The variable inductance device of claim 2 wherein the one end of the plunger has a taper on one side that is both longer and deeper than the taper on the other side.

4. A variable inductance device comprising, in combination: an inductive coil with a central axial hole therethrough; a magnetically permeable plunger axially reciprocable within the hole, one end of the plunger being asymmetrically tapered on opposing sides thereof, the taper on one side being longer and deeper than the taper on the other side; a magnetically permeable flux member fixed to the coil on the outside thereof, the flux member having a first portion adjacent the one side of the tapered end of the plunger, a second portion adjacent the other side of the tapered end of the plunger and a third portion adjacent the other end of the plunger whereby parallel flux paths are created, one including the first portion of the flux member and the other including the second portion of the flux member, each of the flux paths being dominant in determining the rate of change of inductance of the coil over a different range of axial positions of the plunger, the flux member also having a fourth portion projecting from the second portion thereof, which fourth portion comprises a torque arm effective, when biased in one direction, to deform the flux member so that the second portion moves transversely with respect to the plunger to further vary the inductance of the coil in the range of axial plunger positions in which the second portion is dominant; and a member adjustable with respect to the coil, the adjustable member being engageable with the torque arm and effective, when adjusted, to bias the torque arm in the one direction.