Method for setting torque in an internal combustion engine

Internal-combustion engines – Engine speed regulator – Having condition responsive means with engine being part of...

Reexamination Certificate

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C123S494000

Reexamination Certificate

active

06186116

ABSTRACT:

BACKGROUND OF THE INVENTION
This application claims the priority of 198 34 137.7-26, filed Jul. 29, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for setting a specific torque in an internal combustion engine.
In order to achieve a specific motor vehicle driving performance desired, for example, by the driver or set by an electronic motor controller, a very quick and precise establishment of a specific set starting torque (set torque) of an internal combustion engine of the vehicle is necessary. To set the desired torque, first a rate of air flow or mass of air is usually determined which has to be delivered to the internal combustion engine in order to achieve the desired set torque. For a throttle valve situated in an air induction tract, by which the air mass fed to the internal combustion engine can be adjusted, a throttle valve angle is determined from the air mass value and is set at the throttle valve by an appropriate adjusting device.
Because flow processes are involved in the feed of air and fuel to combustion chambers in an internal combustion engine, the term “mass” is used herein to always mean a mass flow, i.e., a mass per unit time. In particular, internal combustion engines which operate by the Otto principle are usually fed air, i.e., the amount of fuel fed for combustion is governed by the amount of air fed for combustion. For this purpose such an internal combustion engine has an air mass sensor by which the air mass fed for combustion is measured in order to feed the internal combustion engine an amount of fuel adapted thereto, for example by a fuel injection system.
The determination of a throttle valve angle from an air mass is usually performed through association with a performance graph, in accordance with, for example, the rotary speed of the internal combustion engine. This association of a torque with an air mass and of an air mass with a throttle valve angle is referred to as a control tract.
As especially the actual conditions in which the internal combustion engine chambers operates are different from the marginal conditions under which such performance graphs were recorded during testing, the air mass actually fed to the combustion chambers often differs from the air mass needed in order to achieve the desired set torque, so that the actual torque differs from the required set torque. To remedy this situation, various control processes are known in which a comparison of the set torque and actual torque is performed. On the basis of the difference thus determined between the set air mass and the actual air mass the throttle valve angle is then adjusted. This comparison followed by adjustment is continued in the sense of a regulation until the actual air mass is the same as the set air mass.
DE 43 15 885 C1 describes a method for torque adjustment in which, based on a set torque, a mass stream set value for the air to be delivered to the combustion chambers and the actual measured value is adjusted to the particular set value by adjusting the throttle valve opening angle. The particular set value is determined by an air mass sensor which is located upstream from a throttle valve in an air induction tube of the internal combustion engine.
The operation of a motor vehicle must, as a rule, be adapted to constantly changing marginal conditions; especially, new values must constantly be set for another necessary set torque. Thus, the need for control to make the actual air mass equal to the set air mass is very great, and therefore an intensive regulation of the throttle valve angle usually is performed constantly. Consequently, very great stress is applied to the throttle valve and the corresponding throttle valve adjusting device. Furthermore, the adjustment of the desired set air mass takes time, and regularly so much time that the desired set air mass changes again between times. Therefore, the throttle valve angle change regularly lags behind the desired set air mass.
Furthermore, the adjustment of a desired set torque depends primarily on the correctness of the reading of the actual air mass. The air mass sensors usually used in determining the air mass are, however, exposed to aging and to contamination, so that the actual air masses that are read differ increasingly over the course of time from the actual air mass. Moreover, fatigue phenomena or the like may induce leakage and other problems in the air intake tract, causing the actually measured air mass to differ from the air mass actually delivered to the internal combustion engine for combustion.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for torque adjustment such that the air mass can be determined with virtually constant accuracy, while especially the cost of the controls for establishing a set torque can be reduced.
This object has been achieved according to the invention by providing a method in which a control tract is provided in which a correlation of a torque with an air mass and of an air mass with a throttle valve position is performed, wherein a set air mass is determined by means of the control tract from a set torque and a corresponding throttle valve position is determined and set. An actual air mass fed to the internal combustion engine for combustion is determined by comparing the set and actual air mass value. Any difference between the set air mass and the actual air mass is determined, along with a correlation value for this difference. The correlation value is used to perform an adaptation of the control tract to the difference such that in the control tract a throttle valve position is associated with a set torque that is to be established which brings about a compensation of the previously determined difference between the set air mass and the actual air mass, in order to determine the actual air mass an actual fuel mass fed to the internal combustion engine for combustion is used as well as a fuel/air mass ratio of a mixture fed to the internal combustion engine for combustion.
The present invention is based on the recognition of adaptively correcting the relationship between the throttle valve angle and the desired set air mass by comparison with the actual air mass delivered for combustion. The adaptation of the control tract can be performed by multiplication or addition. This adaptation acts continuously until another adaptation is performed. If then a set torque follows the adapted control tract, a corrected throttle valve angle is immediately associated with the corresponding set air mass. Therefrom, an actual air mass regularly results which from the outset, i.e., still without any regulation, is closer to the desired set air mass than would be the case if the throttle valve angle were to be determined from the unchanged, i.e., unadapted, control tract. Consequently, the need for regulation is reduced to a considerable extent by this measure, so that the mechanical stress on the components in question is reduced. Furthermore, the desired set value of the air mass and torque is arrived at much more quickly, so that the desired performance of the vehicle can be quickly established.
In order to be independent of aging phenomena, changes in the air intake flow and leakage in the air intake tract, the set air mass actually fed to the combustion is determined according to the fuel/air mass ratio of the mixture fed to the combustion and to the fuel mass contained in this mixture.
Since modern internal combustion engines are equipped, as a rule, with a fuel injection system, in an advantageous embodiment of the method of the invention, the fuel mass is determined with the aid of operating parameters, especially with the aid of the duration of the injection and/or the injection pressure of such a fuel injection system. In this manner, the a method of the present invention can employ a sensing system already present in the internal combustion engine, so that no additional costs and no additional weight are required.
An internal combustion engine is usually de

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