WO1981001866A1

WO1981001866A1 - Air-fuel ratio control apparatus

Info

Publication number: WO1981001866A1
Application number: PCT/US1980/001686
Authority: WO
Inventors: S Eason
Original assignee: Acf Ind Inc
Priority date: 1979-12-31
Filing date: 1980-12-18
Publication date: 1981-07-09
Also published as: IT1134847B; IT8026860A0; EP0042867A1

Abstract

Apparatus (1) for controlling the air-fuel ratio of a mixture supplied by a carburetor (C) during wide-open throttle conditions. The quantity of fuel or air used to form the mixture sup plied to the engine (E) is controlled and an engine operation parameter is sensed. An electrical signal indicative of wide open is developed and processed by a signal processor (11) together with electrical signals representing other engine operating parameters. The signal characteristics of a control signal are modified so as to vary the air-fuel ratio of the mixture supplied to the engine.

Description

AIR-FUEL RATIO CONTROL APPARATUS Background of the Invention¹

This invention relates to control of internal combustion engines and, more particularly, the control of the air-fuel ratio supplied to an engine at wide-open throttle conditions. Because of the dual need to minimize engine emissions and maximize fuel economy, various schemes have been imple¬ mented to control the air-fuel ratio of the mixture supplied to an engine. Many of■ these schemes employ a feedback technique in which some condition,- for example, the oxygen content in the engine's exhaust is sampled and an electrical signal indicative thereof is generated. Electrical circuitry processes this signal and, in turn, generates a control signal to vary auxiliary air bled into a carburetor's main fuel system. The air-fuel ratio is thus varied to maintain the oxygen content of the exhaust within certain limits.

Schemes such as the one above-described, however, typically do not function during wide-open throttle (WOT) engine operat¬ ing conditions. During these periods, the engine operates open loop, i.e. without feedback control and the control device employed to adjust the bleed air is maintained at some fixed position or duty cycle. "As a consequence, fuel economy and/or emissions may suffer, particularly in those situations where altitude compensation is required. Summary of the Invention Among the several objects of the present invention is the provision of apparatus for controlling the air-fuel ratio of the mixture supplied an internal combustion engine at wide- open throttle conditions; the provision of such^'apparatus which complements existing control schemes to permit control of air-fuel ratio throughout the entire range of engine operating conditions; and the provision of such apparatus which readily permits altitude compensation without the need of auxiliary devices.

Briefly, apparatus of the present invention is for controlling the air-fuel ratio of a mixture supplied by a carburetor to an internal combustion engine when a throttle valve of the carburetor is moved from a closed or intermediate position to its wide-open position. The apparatus comprises

OMPI means for controlling the quantity of fuel or air used to form the mixture supplied to the engine. M^ ns are provided for sensing an engine operating parameter and for developing an electrical signal indicative of the throttle valve being moved to its wide-open position. A signal processor is responsive to the aforesaid electrical signal and other electrical signals representing other engine operating para¬ meters and modifies the signal characteristics of a control signal supplied to the control means. The signal character- istic of the control signal causes the control means to vary the air-fuel ratio of the mixture supplied to the engine. Other objects and features will be in part apparent and in part pointed out hereinafter. Brief description of the Drawings Figure 1 is a schematic representation of the apparatus of the present invention; and

Figure 2 is a graph of "L Duty Cycle versus Engine RPM to aid in illustrating opera'tion of the present invention. Description of a Preferred Embodiment Referring to Figure 1, apparatus of the present invention is indicated generally 1, and is for controlling the air-fuel ratio of a mixture supplied by a carburetor C to an internal combustion engine E. Carburetor C has a throttle valve T movable in a conventional manner from a closed position through a series of intermediate open positions to a fully open position. When throttle valve T -is fully open,^* wide- open throttle (WOT) condition is said to exist.

Apparatus 1 comprises means indicated generally 3 for controlling the quantity of air or fuel forming the mixture supplied to engine E. Means 3 may be of any type, although preferably it is either a variable position solenoid or a stepper motor. A variable position solenoid usable in apparatus 1 is described in United States patent 4,105,726, issued August 8, 1978, to Allen W. Lindberg and assigned to the same assignee as the present application. A stepper motor of the type usable in apparatus 1 is described in patent application 767,914, filed February 11, 1977, and assigned

-_BUREAU

OMPI to the same assignee as the present application. In both instances, the means employed controls an air bleed for bleeding auxiliary air into the main fuel circuit of a carburetor such as carburetor C. Apparatus 1 further includes a means 5 for sensing when throttle valve T is moved to its wide-open position -and for developing an electrical signal indicative thereof. Means 5 may comprise a throttle position switch 7 incorporating a pair of electrical contacts which close when the throttle valve reaches its wide-open position. Closure of the contacts completes an electrical circuit and produces an electrical signal indicative of wide-open throttle. Alternatively, means 5 comprises a vacuum pressure sensor 9 located in the intake manifold M of engine E. Pressure sensors such as sensor 9 are well known in the art. When a wide-open throttle condi¬ tion occurs, the pressure in manifold M drops to approximately 2-3 pounds per square inch. Sensor 9 may be calibrated so when this low vacuum condition occurs a signal is generated.

A signal processing means 11 comprises a signal processor which includes a microprocessor'.^" The signal processor is responsive to the electrical signal from throttle position switch 7 or vacuum pressure sensor 9, whichever is used, and to electrical signals representing other engine operating parameters. For example, signal processor 11 is responsive to an electrical signal from an engine rp sensor 13. The microprocessor- in signal processor 11 is programmed to deter¬ mine the correct air-fuel ratio of the mixture supplied to engine E based upon the information represented by the elec¬ trical signals received. Once a determination has been made, signal processor 11 modifies the signal characteristics of a control signal supplied to control means 3. The control means is responsive, in turn, to a modification in the characteristics of the signal supplied to it to vary the quantity of air or fuel supplied to the engine and thus the air-fuel ratio of the mixture.

The signal characteristic modified by signal processor 11 varies according to the type of control means 3 used in appara-

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OMPI tus 1. Thus, for example, the amplitude, the duty cycle, the frequency, or the pulse repetition rate of the control signal may be variable by the signal processor.

Referring to Figure 2, a graph of % Duty Cycle versus Engine RPM illustrates the increased control achievable with the apparatus of the present invention. As shown, the dashed line IC represents an ideal response curve when control means 3 comprises a variable position solenoid of the type pre¬ viously mentioned. The broken lines UL and LL respectively represent the upper and lower limits which the response curve should fall within. The sinuous line AC represents the actual response attainable with apparatus 1 due to the mechanic and electrical constraints present within the system embodied in apparatus 1. By experimentation, the value of % duty cycle can be determined for each engine rp value at wide-open throttle and the result entered in the memory portion of signal pro- cessor 11. Now, when a wide-open throttle condition is sensed by throttle position switch 7 or vacuum pressure sensor 9, the signal processor combines this information with the engine rpm information provided by sensor 13 to determine the duty cycle of the control signal supplied to control means 3. If the present duty cycle of the control signal is not the determined value, the processor modifies the duty cycle to the proper value. This results in a modification of the air-fuel^' atio of the mixture supplied to the engine to better control emissio and maximize fuel economy. To provide altitude compensation at wide-open throttle, the curve AC is shifted toward the upper or lower limit. It will be understood that in many prior feedback control schemes various techniques are employed to eliminate feedback control during wide-open throttle operation. This requires calibration of the carburetor using traditional metering techniques to develop a fuel flow versus rpm curve for the carburetor. This is not only time consuming, but also requires some compromises to achieve an acceptable calibration. Further additional components such as high speed pullover circuits may

OMPI be needed to achieve calibration. The apparatus of the pre¬ sent invention provides good control to maximize performance and obtain good fuel economy and emissions while eliminating these devices and additional components. In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results obtained.

As various changes could be made in the above construc¬ tions without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. Apparatus for controlling the air-fuel ratio of a mixture supplied by a carburetor to an internal combustion engine when a throttle valve of the carburetor is moved from a closed or intermediate position to its wide-open throttle position comprising: means for controlling the quantity of fuel or air used to form the mixture supplied to the engine; means for sensing when the throttle valve is moved to its wide-open position and for developing an electrical signal indicative thereof; and signal processing means responsive to the aforesaid electrical signal and other electrical signals representing the other engine operating parameters for modifying the signal characteristics of a control signal supplied to the control means, the signal characteristic of the control signal causing the control means to vary the air-fuel ratio of the mixture supplied to the engine.

2. Apparatus as set forth in claim 1 wherein the sensing means comprises a vacuum pressure sensor which develops the electrical signal when the vacuum pressure in an intake mani¬ fold of the engine falls below a predetermined level.

3. Apparatus as set forth in claim 1 wherein the sensing means comprises a throttle position switch which senses the position of the throttle valve and develops the electrical signal when the throttle valve reaches its wide-open position.

4. Apparatus as set forth in claim 2 or 3 wherein the control means comprises a stepper motor.

5. Apparatus as set forth in claim 2 or 3 wherein the control means comprises a solenoid.

6. Apparatus as set forth in claim 1 wherein the signal processing means 'comprises a microprocessor programmed to determine an air-fuel ratio based upon the engine operating conditions represented by the electrical signals received.