This application is a continuation in part of my then copending and commonly assigned specifically referenced following U.S. patent application:
1. Ser. No. 101,896 filed Dec. 28, 1970 and issued May 22, 1973 as Pat. No. 3,734,068,
2. Ser. No. 219,275 filed Jan. 20, 1972,
3. Ser. No. 226,486 filed Feb. 15, 1972,
4. Ser. No. 226,498 filed Feb. 15, 1972,
5. Ser. No. 445,411 filed Feb. 25, 1974 as a continuation of Ser. No. 226,498. .Iaddend.
1. Field of the Invention
The present invention is related to the field of electronic fuel control systems for internal combustion engines and particularly to that portion of the above-described field which is concerned with the provision of accurately metered quantities of fuel during transient operating conditions of an internal combustion engine. In particular, the present invention is concerned with that portion of the above-noted field which provides increased quantities of fuel for consumption by the engine when it is operating at a temperature under the normal operating temperature.
2. Description of the Prior Art
The prior art teaches that warm-up enrichment quantities of fuel may be provided through an electronic fuel control system by prolonging the unstable period of a monostable multivibrator in response to an engine temperature sensitive element. However, those systems which make use of the forenoted technique for providing warm-up enrichment are systems which also employ sequentially energized monostable multivibrators in which the unstable period of the second multivibrator in the sequence is a function of the unstable period of the first multivibrator in the sequence as well as the engine temperature. As a consequence, the enrichment quantities of fuel provided thereunder become a complex function of the instantaneous engine temperature as well as the engine parameter which controls the unstable time period of the first monostable multivibrator in the sequence. If the "enrichment factor" is defined as the fuel injection command pulse duration at cold (that is, below normal) temperatures divided by the fuel injection command pulse duration at normal engine operating temperature, the enrichment factor of prior art systems may be shown to be an undesirable decreasing function of intake manifold pressure. However, it is known that the desirable enrichment factor is a value which varies as a function of temperature and which is not a decreasing function of manifold pressure. It is therefore an object of the present invention to provide a warm-up enrichment mechanism for an electronic fuel control system which provides an enrichment factor for the quantities of fuel provided independent of any other engine operating parameter. Since it is normally the case to use engine intake manifold air pressure as the engine operating parameter controlling the first monostable multivibrator in the sequence, it is a still further object of the present invention to provide a warm-up enrichment mechanism which provides an enrichment factor for the quantities of fuel provided substantially independent of the instantaneous intake manifold pressure.
An additional problem with the prior art technique of using successively triggered monostable multivibrators is that, with the number of corrective functions to be inserted in the computational process, the maximum pulse duration obtainable under the most extreme engine operating conditions (i.e. low temperature engine starting) is substantially less than the time period required to provide fuel quantities adequate for engine operation under those conditions. As a consequence, the prior art teaches that it is necessary to provide, through parallel circuitry which may or may not include additional injector valve means, totally independent circuitry for commanding cold starting and the initial warm-up enrichment quantities of fuel which would operate to override the signal generated by the sequentially energized monostable multivibrator main computing circuitry. This solution greatly increased the cost and complexity of the electronic circuitry and also reduced the reliability thereof. It is therefore an object of the present invention to provide a means for generating cold starting and warm-up enrichment compensation which does not greatly increase either the cost or the complexity of the electronic circuitry and which does not represent a significant decrease in the reliability of such circuitry.
It has been proposed by my co-pending commonly assigned patent application identified by Ser. No. 101,896, Fuel Injection Control System, .Iadd.issued May 22, 1973 as U.S. Pat. 3,734,068, .Iaddend.to generate an injection command pulse as a function of the time during which a generated wave form having a specific predetermined shape remains below a variable level, known as a threshold level. It has heretofore been assumed that the prior art cold starting and warm-up enrichment mechanisms and circuits would be readily adaptable for use with an electronic fuel control system according to my above identified co-pending application. However, many of the difficulties which arise from the use of separate and distinct cold starting and warm-up enrichment circuitry in the sequenced monostable multivibrator system also arise in the application of such cold starting and warm-up enrichment networks to electronic fuel control systems according to the above identified application. It is therefore an object of the present invention to provide a cold starting and warm-up enrichment network which is fully compatible with my above identified co-pending application and which does not require parallel circuitry to generate an overriding command pulse. It is a more particular object of the present invention to provide a warm-up enrichment network which controllably alters the shape of the generated wave shape so as to selectively control its time duration at values below the threshold level.