Control Device For A Fuel Injection System

Abstract

In an internal combustion engine having a throttle in the suction duct a disc is mounted in the duct airstream on the end of a pivotable arm for controlling the fuel valve in proportion to the rate of air intake. A section of the duct between the throttle and the disc is formed by an elastic hose. The disc is mounted in an enlarged section housing the air filter and is of appreciably larger diameter than the throttle.

Parent Case Text

This is a continuation of U.S. Pat. application Ser. No. 80,685, filed Oct. 14, 1970, entitled "Control Device For a Fuel Injection System," now abandoned.

Description

FIELD OF THE INVENTION

The invention relates to a control device for the fuel injection system of an external-ignition engine operating with compression of the fuel mixture and with continuous injection into a suction duct.

BACKGROUND OF THE INVENTION

In a prior art fuel injection system of the type referred to there is provided a sensor member as well as an arbitrarily adjustable throttle mutually spaced in the direction of flow, the sensor member being movable against a return force proportionally to the rate of air flow for controlling a fuel valve so as to measure off a corresponding amount of fuel.

In an embodiment of this system described in German Pat. No. 1,261,701, the deflection of the sensor member is substantially proportional to the rate of air flow so that an amount of fuel proportional to the air flow can be measured off by a simple control of the fuel valve. However, as soon as errors occur in the deflection of the sensor, for instance, owing to vibration of the engine, the proportionality is lost resulting in an unfavorable fuel-to-air ratio. By "vibration" there are meant low-frequency, high-amplitude engine thrusts that occur usually in case of a rapid change in the setting of the butterfly valve, resulting in a sudden change of the pressure conditions in the suction tube. Such thrusts may also occur when in certain rpm ranges the imbalance due to the dynamics of the crank drive substantially increases in an unproportionate manner. Such thrust-like vibrations may further occur when the operator of the vehicle switches from power drive to motor brake, for example, for downhill travel. This thrust-like vibration is to be differentiated from the oscillation type vibration which has a relatively high frequency and a relatively small amplitude. Such engine oscillation is the result of the imbalance of the engine caused by the crank drive. This oscillation type vibration of the engine, unlike the thrust-like vibration, has no appreciable harmful effect on the fuel metering. In contradistinction, the aforenoted thrust-like vibrations may lead to incomplete combustion and the production of poisonous exhausts. To remove this error, the sensor of the known system is actauted by a pneumatic servo motor which responds to the pressures in the suction duct upstream and downstream of the sensor, i.e., to the rate of air flow which in its turn is primarily dependent on the rpm and on the position of the throttle. However, a servo motor of this type is relatively expensive.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a simple device for eliminating or reducing to a minimum the deflectional errors of the sensor referred to.

The invention is characterized in that a section of the suction duct between the sensor and the throttle comprises an elastic connecting tube preferably in the form of an elastic hose section.

The elastic connecting tube prevents the section of the suction duct accommodating the sensor from participating in vibrations of the engine, in which the section accommodating the throttle must necessarily participate, because the throttle cannot be located too far from the cylinders and therefore has to be mounted in the rigid section of the suction duct integrally attached to the engine. The vibrations, which are of different strength according to the rpm and the balancing of the engine, do not detrimentally affect the adjustment of the throttle, since this is done anyway by the driver in an arbitrary manner. However, these vibrations, which are very variable with the rpm, give rise to errors of deflection of the type referred to above and to incomplete filling of the cylinders for the reason that the sensor cannot be constructed without mass. The section accommodating the sensor is therefore preferably attached to the chassis in vehicles having a fuel injection system according to the present invention.

In an embodiment of the invention, the spacing measured along the axis of the suction duct between the sensor in its inoperative position and the axis of the throttle is more than three times the diameter of the throttle, preferably more than four times thereof.

This feature is based on the observation that deflection errors are also caused to an appreciable extent by non-homogeneous or irregular air flow towards the sensor member or away therefrom. This phenomenon is present, for instance, in a known control device without servo motor described in German Pat. No. 1,243,917 and having the sensor and the throttle located relatively close to each other, the sensor being eccentrically supported in the suction duct in order to be actuated by the air flow.

Such unilateral or unsymmetrical actuation by the air flow causes apreciable variation of the flow lines close to the sensor in dependence on the position of the throttle, resulting in the deflection errors referred to.

A sensor member depending for its operation on the flow resistance impairs the filling of the engine owing to two factors. First, there is a pressure drop resulting from the return force which is unavoidable but has to be reduced to a minimum. Second, there is an obstruction or disturbance of the air oscillation in the suction duct obtained by the proportioning or tuning of the length thereof in relation with the response time of the valves and the duration of the exhaust interval (ram effect). In view of this second factor, it is of advantage, according to an embodiment of the invention, for the sensor member to be located at the entrance of the suction duct, where there will certainly be a node of the air oscillation.

In order to obtain a controlling force which is as large as possible for actuating the sensor member, the latter is provided with a large area exposed to the air flow. For the mounting of the sensor, the bottom area of the air filter offers enough space without the requirement of enlarging the remaining portion of the suction duct. In a corresponding embodiment of the invention, the section of the suction duct which houses the sensor, forms an integral part of the housing of the air filter.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows schematically an embodiment of a fuel injection system according to the invention.

DESCRIPTION OF EMBODIMENT

In the fuel injection system shown, combustion air flows in the direction of the arrows through an air filter 2 provided in a housing 1 to a section 3 of a suction duct having a sensor member 4 provided therein. From section 3, the air flows through a connecting tube 5, a section 6 having an arbitrarily adjustable throttle 7 therein to a manifold 8 having a plurality of tubular sections 9 for supplying air to corresponding cylinders of a combustion engine. Sensor member 4 is shown as comprising a plate perpendicular to the direction of flow, however, it may also be in the form of a piston which is slidable perpendicularly to the direction of flow or of a shutter which is pivotable about a spindle. In any case, sensor member 4 is movable in section 3 according to an approximately linear function of the amount of air flowing through the suction duct. A spring 10 provides a return force, the spring having a very flat characteristic so that on deflection of plate 4 and corresponding shortening of spring 10 there is no appreciable variation in the return force.

To transmit the deflection of plate 4 there is provided a lever 11 journalled with a minimum of friction on an axle 12 and actuating through its pivotal movement by means of boss 13 a movable valve member 14 of a fuel measuring distributor valve 15. The inoperative position of lever 11 is defined by an adjusting screw 16.

As it may be observed from the FIGURE, the pivotal axle 12 of the lever 11, which in turn, carries the sensor plate 4, is held by a housing-like support component an integral part of which constitutes the suction tube portion 3. The support component is affixed to the vehicle chassis C, for example, by means of a clamp 3a. Thus, the sensor number 4 is fixedly supported separate from the engine; the purpose of the connecting tube or hose 5 is to absorb any thrust-like vibration of the engine so that such vibrations will not be transmitted to the suction tube portion 3 and to the sensor member 4.

The fuel is supplied by a fuel pump 18 which is driven from an electromotor 19 and draws fuel from a container 20 and supplies it through a fuel line 21 to valve 15. From line 21 a return line 22 branches off, in which a pressure-limiting relief valve 23 is provided. From measuring valve 15 the measured-off amount of fuel is delivered through fuel lines 24 to the individual tubular sections 9 and via injection valves, not shown, to the engine.

Filter housing 1 and section duct section 3 are an integral unit. The air drawn by the engine exits from filter 2 and impinges directly on plate 4, the latter closing off the suction duct when the engine is stopped. The area of plate 4 can be made appreciably larger than that of throttle 7, whereby plate 4 has a high degree of sensitivity and working capacity. Filter 2 at any rate requires a comparatively large diameter, and this provides the possibility of making plate 4 correspondingly larger. On the other hand, throttle 7 can be comparatively small, so as to require little space. The spacing between plate 4 in its inoperative position and throttle 7 is at least four times the diameter of throttle 7, whereby the air, after having entered the suction duct and passed around plate 4, has time to stabilize before reaching throttle 7. in this manner, adjustment of throttle 7 does not result in errors in the deflection of sensor member 4 and the deflection thereof is always proportional to the change in air rate of flow resulting from the adjustment. In other words, the flow lines have stabilized in the space between plate 4 and throttle 7 and are again parallel. Errors in the deflection of plate 4 would be unavoidable if owing to pivotal movement of plate 4 or adjustment of throttle 7 the flow lines of the air stream, which will always have a somewhat unsymmetrical distribution in the region of restricted passage formed by the throttle or by the plate, do not regain a symmetrical distribution in the region between these two members.

Claims

What is claimed is:

1. In a control device for a fuel injection system of an externally ignited internal combustion engine operating on fuel injected into a multi-part suction duct thereof and mounted in a vehicle having a chassis, said engine having an arbitrarily adjustable throttle member, said contol device being of known type that includes (a) a sensor member displaceable by and in proportion to the air quantities flowing through said suction duct, (b) means for exerting a return force on said sensor member to oppose the displacement thereof in response to air flow, (c) a fuel valve having a fuel control aperture therein, (d) means connecting said sensor member to said fuel valve for the metering of fuel quantities in proportion to said air quantities, the improvement comprising,

A. a support component formed in part of an integral first suction duct portion, said sensor member being carried by said support component and being disposed at least partially in said first suction duct portion,

B. means for securing said support component to said vehicle chassis,

C. a second suction duct portion spaced downstream from said first suction duct portion and containing said arbitrarily adjustable throttle member and

D. a third suction duct portion constituted by an elastic hose interconnecting said first and second suction duct portions to isolate said sensor member from the vibrations of said engine.

2. A control device as defined in claim 1, wherein the spacing measured along said suction duct between said sensor member in the inoperative position thereof and the axis of said throttle member is more than three times the diameter of said throttle member.

3. A control device as defined in claim 1, wherein said sensor member comprises

A. an arm pivotally secured to said support component and

B. a disc affixed to an end of said arm remote from its pivotal attachment and positioned in said first suction duct portion perpendicularly to the direction of air flow.

4. A control device as defined in claim 1, said engine including an intake manifold having a tubular inlet constituting said second suction duct portion.

5. A control device according to claim 2, in which said spacing is more than four times said diameter.

6. A control device according to claim 3, in which the area of said disc is larger than that of said throttle member.

7. A control device according to claim 3, in which said pivotal arm engages a movable valve member of said fuel valve.