Compensating Fuel Metering For Exhaust Gas Recirculation

Abstract

In an internal combustion engine, exhaust gas is recirculated from the intake manifold exhaust gas crossover passage to the induction passage. An exhaust gas recirculation control valve is positioned by the throttle to proportion exhaust gas recirculation flow to induction airflow. In one embodiment, the exhaust gas recirculation passages are cast integrally in the intake manifold. Fuel metering in a timed fuel injection system responsive to manifold absolute pressure is compensated for exhaust gas recirculation.

Description

In a fuel system which relies on manifold pressure as an indication of airflow to the engine and meters fuel flow in accordance therewith, fuel flow may be incorrectly proportioned to airflow when exhaust gas is recirculated to the induction passage unless the fuel metering is compensated for the partial pressure due to exhaust gas. This invention provides means, particularly suited for use with a timed fuel injection system, to adjust the fuel metering in accordance with the position of a valve controlling exhaust gas recirculation to the induction passage.

The details as well as other objects and advantages of this invention are set forth below and shown by the drawings wherein:

FIG. 1 is a top plan view of an induction passage throttle body and an exhaust gas recirculation control valve;

FIG. 2 is a side elevational view of the device shown in FIG. 1 illustrating the configuration of the cam member;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1 illustrating the exhaust gas recirculation control valve;

FIG. 4 is a sectional view along line 4--4 of FIG. 1 illustrating the control valve operating mechanism;

FIG. 5 is a sectional view along line 5--5 of FIG. 2 illustrating the adjustable connection in the linkage between the exhaust gas recirculation control valve and the throttle;

FIG. 6 is a top plan view of the FIG. 1 intake manifold illustrating the exhaust gas crossover passage;

FIG. 7 is a top plan view of an alternative intake manifold having integrally cast exhaust gas recirculation passages;

FIG. 8 is a sectional view taken along line 8--8 of FIG. 7 illustrating the openings from the exhaust gas recirculation passage to the induction passages;

FIG. 9 is a view similar to FIG. 2 illustrating the fuel-metering-compensating mechanism; and

FIG. 10 is a circuit diagram for an electronically controlled timed fuel injection system illustrating two embodiments of variable-impedance devices for compensating the fuel metering.

Referring first to FIGS. 1 and 2, a throttle body assembly 10 is mounted on an intake manifold 12. A pair of induction passages 14 pass through assembly 10 and are controlled by a pair of throttles 16 disposed on a throttle shaft 18.

Inserted between throttle body assembly 10 and manifold 12 is a plate 20 and a base 22 which have extensions of induction passages 14. Plate 20 and base 22 define an exhaust gas recirculation inlet passage 24 leading to a control valve assembly 26 and an exhaust gas recirculation outlet passage 28 leading from control valve assembly 26. Branches 30 connect exhaust gas recirculation outlet passage 28 with induction passages 14 below throttles 16. For simplicity, exhaust gas recirculation inlet passage 24 will be referred to merely as exhaust gas recirculation passage 24, exhaust gas recirculation outlet passage 28 will be referred to as metered exhaust gas passage 28, and the two passages 24 and 28 will be referred to collectively as exhaust gas recirculation passages.

As shown in FIG. 3, exhaust gas recirculation control valve assembly 26 has an inlet bore 32 leading from exhaust gas recirculation passage 24 to an upper cross passage 34. A butterfly valve 36 is disposed on a shaft 38 in an outlet bore 40 leading from cross passage 34 to metered exhaust gas passage 28.

Shaft 38 is journaled on a pair of bushings 42 (FIG. 4) and has a lever 44 (FIGS. 2 and 4) secured on the outer end thereof. A torsion spring 46 (FIG. 4) biases shaft 38 and lever 44 in a counterclockwise direction as viewed in FIG. 2.

The cover 48 for control valve assembly 26 provides a bracket having an upstanding arm 50 (FIGS. 1 and 4) into which a pair of bolts 52 are threadedly secured. As shown in FIG. 2, bolts 52 extend through a slot 54 in a cam member 56, thereby supporting cam member 56 for linear motion.

An additional bolt 58 also extends through slot 54 and is secured to an adjusting nut 60. Adjusting nut 60 threadedly receives a link 62 connected to a throttle lever 64 secured on throttle shaft 18.

A spring 66 biases cam member 56 leftwardly as viewed in FIGS. 1 and 2.

In operation, clockwise opening movement of throttles 16, throttle shaft 18 and throttle lever 64 pulls link 62 and cam member 56 toward the right as viewed in FIG. 2. A cam follower 68 on control valve lever 44 is biased against a cam surface 70 on cam member 56. As is evident from FIG. 2, cam follower 68 successively contacts a first portion 70a in which control valve 36 remains closed, a first ramp 70b in which control valve 36 opens, a peak 70c in which control valve 36 remains open, a second ramp 70d in which control valve 36 closes, and a second portion 70e in which control valve 36 remains closed. The sequence is reversed as throttles 16 are closed and spring 66 returns cam member 56 toward the left.

Cam surface 70 is configured whereby control valve 36 begins opening movement when throttles 16 have been opened about 5.degree., reaches a fully open position when throttles 16 have been opened between 14.degree. and 20.degree., and returns to closed position when throttles 16 have been opened about 34.degree..

As control valve 36 opens, exhaust gas received through exhaust gas recirculation passage 24 is admitted to metered exhaust passage 28 and delivered through branches 30 to induction passages 14.

It will be noted that since control valve 36 and cam member 56 are biased in a valve-closing direction by springs 46 and 66, they exert no opening force on throttles 16. Moreover, even if control valve 36 or cam member 56 were to remain in an open position, throttles 16 would be free to close because bolt 58 rides toward the left in slot 54 as throttles 16 are closed.

Exhaust gas is received by exhaust gas recirculation passage 24 from an exhaust gas riser bore 72 connecting with an exhaust gas crossover passage 74 which passes through intake manifold 12. As may be seen in FIG. 6, intake manifold 12 includes a pair of conventional riser passages 76 which communicate with generally horizontal upper and lower plenum chambers 78 and 79 respectively. Plenum chambers 78 and 79 extend longitudinally from the bottom of riser passages 76 to transverse runner passages 80 at the ends thereof. Exhaust crossover passage 74 extends from an inlet 75 at one side of manifold 12, beneath riser passages 76 and plenum chambers 78 and 79, to exhaust gas riser bore 72.

It will be appreciated, of course, that induction passages 14, manifold riser passages 76, plenum chambers 78 and 79, and runner passages 80 may be collectively referred to as an induction passage.

FIGS. 7 and 8 show a modified intake manifold 12' in which the exhaust gas recirculation and metered exhaust gas passages are cast integrally in the manifold. The FIG. 7 view is schematic and various combinations of dot-dash lines have been used to facilitate visualization of the different passages. As shown in these figures, a pair of riser passages 76 disposed on opposite sides of the manifold centerline connect with upper and lower plenum chambers 78 and 79, respectively, which are generally horizontal and extend longitudinally through the manifold to transversely reaching runner passages 80.

An exhaust gas crossover passage 74' extends from an inlet 75' at one side of the manifold centerline, beneath riser passages 76 and plenum chambers 78 and 79, to the opposite side of the manifold centerline. There exhaust gas crossover passage 74' discharges into an exhaust gas recirculation passage 24'. Passage 24' leads to a pad 82 which is adapted to receive control valve assembly 26. Alternatively, an exhaust gas recirculation control valve of different design could be received in a pocket in manifold 12'. A metered exhaust gas passage 28' extends from pad 82, above exhaust gas recirculation passage 24', above exhaust gas crossover passage 74', and under upper plenum chamber 78 to a pair of ports 84 and 86. Port 84 opens vertically into the bottom of upper plenum chamber 78 and is centered below the associated riser passage 76. Port 86 opens horizontally into lower plenum chamber 79. Thus exhaust gas is recirculated through a crossover passage to heat the induction passages and is then delivered through a control valve assembly into the induction passages.

It will be noted that all exhaust gas recirculated to the engine is delivered through the exhaust gas crossover passage to heat the induction passages, and all exhaust gas delivered through the exhaust gas crossover passage is recirculated to the engine. Thus the exhaust gas recirculation control valve controls both the flow of exhaust gas for heating the induction passages and the flow of exhaust gas recirculated to the engine. This combination proves advantageous under conditions such as wide-open throttle operation where exhaust gas recirculation and induction passage heating should be reduced for maximum power. It should be recognized, however, that the advantages of this manifold structure are not limited to a system in which all exhaust gas flowing through the exhaust gas crossover passage is recirculated to the induction passages.

FIG. 9 illustrates a modification of the FIG. 2 device whereby fuel metering may be compensated for exhaust gas recirculation. The FIG. 9 device is identical to that of FIG. 2, supplemented by an additional cam surface 86 on cam member 56. Concurrently with movement of control valve lever 44 by cam surface 70, cam surface 86 operates a lever 88 through a cam follower 90 carried by lever 88. Lever 88 controls a unit 92 to vary an impedance which controls fuel metering as explained below.

FIG. 10 is a schematic diagram of an electronically controlled timed fuel injection system. As shown therein, a fuel injector 94 directs fuel into an intake manifold runner passage 80 at the back of an inlet valve 96 for a combustion chamber 98. Injector 94 is operated by a solenoid 100 during each cycle of the engine, and fuel is metered by controlling the duration of time solenoid 100 is energized to operate injector 94.

To energize solenoid 100, a signal generator 102, which nominally may be considered as a normally open switch, provides a negative voltage pulse during each cycle of the engine. This pulse is differentiated by a capacitor 104 into a negative-going voltage spike which is delivered to the base 106 of a transistor 108. Transistor 108 thus ceases to conduct, and the voltage at its collector 110 increases to render a transistor 112 conductive. The voltage at the collector 114 of transistor 112 then drops and an amplifying transistor 116 stops conducting. The voltage at the collector 118 of transistor 116 is thereby increased, and solenoid 100 is energized to operate injector 94.

As transistor 112 starts conducting, current passes through a primary winding 120. Primary winding 120 is coupled, through a core 122 positioned by a pressure transducer 124, with a secondary winding 126. As current changes in primary winding 120, a voltage is induced in secondary winding 126 which biases base 106 of transistor 108 in a negative direction and holds transistor 108 in a nonconductive state. Over a period of time the rate of change of current in primary winding 120 drops, and the voltage induced in secondary winding 126 reduces sufficiently to render transistor 108 conductive and terminate energization of solenoid 100.

In order to control the duration of time solenoid 100 is energized, unit 92 may control the impedance in the circuit of either primary winding 120 or secondary winding 126. Thus unit 92 could be a potentiometer 92a which, together with resistors 128, 130 and 132, controls the current supplied to primary winding 120. Unit 92 also could be a switch 92b which adds a small resistor 134 to the resistors 136, 138, and 140 controlling the bias voltage on secondary winding 126.

As shown in FIG. 9, pressure transducer 124 is responsive to the absolute pressure in induction passages 14 below throttles 16. It will be appreciated that the induction manifold pressure varies with movement of throttles 16 and with changes in engine load. In addition, as exhaust gas recirculation valve 36 opens and exhaust gas is recirculated to induction passages 14, the absolute pressure in induction passages 14 increases. Manifold absolute pressure transducer 124 then moves core 122 in to increase the inductance between windings 120 and 126 and lengthen the time that solenoid 100 is energized. To compensate for this, the resistance of potentiometer 92a is increased as control valve 36 opens; this reduces the current flow through primary winding 120 to shorten the time that solenoid 100 is energized. Alternatively, switch 92b closes and small resistor 134 permits an increase in the bias voltage on secondary winding 126; thus a shorter period of time is required to render transistor 108 conductive and terminate energization of solenoid 100.

From the foregoing it will be appreciated that fuel metering which is responsive to induction manifold pressure may be incorrectly proportioned to airflow when exhaust gas is recirculated to the induction passages, and further, that such fuel metering may be compensated for recirculation of exhaust gas by additionally controlling fuel metering in response to the position of the exhaust gas recirculation control valve.

Claims

I claim:

1. In an internal combustion engine having an induction passage for airflow to the engine, a throttle in said induction passage controlling airflow therethrough, and an exhaust passage for exhaust gas flow from the engine: a fuel system for delivering fuel to said engine, an exhaust gas recirculation passage extending from said exhaust passage to said induction passage for recirculating exhaust gas to said induction passage, and a valve in said exhaust gas recirculation passage controlling exhaust gas flow therethrough, said fuel system including means controlling fuel delivery to said engine in accordance with the pressure in said induction passage below said throttle whereby the rate of fuel delivery to said engine tends to increase as the absolute pressure in said induction passage downstream of said throttle increases, said fuel system further including means controlling fuel delivery to said engine in accordance with the position of said valve whereby the rate of fuel delivery to said engine tends to decrease as said valve permits increased recirculation of exhaust gas to said induction passage, said fuel system thereby providing an appropriate rate of fuel delivery to said engine as the pressure in said induction passage below said throttle varies with variations both in engine load and in the position of said throttle without providing an inappropriate rate of fuel delivery to said engine as the pressure in said induction passage below said throttle varies with variations in exhaust gas recirculation to said induction passage.