Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2000-12-22
2001-12-18
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S406380
Reexamination Certificate
active
06330874
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for the cylinder-selective knock control of an internal combustion engine, in which a predetermined cylinder-selective basic ignition angle associated with knock-free operation and a cylinder-selective knock adjustment angle that increases stepwise with a predetermined step size in the retarded direction each time a knock occurs and decreases stepwise with a predetermined step size in the advanced direction after each engine cycle during knock-free operation form a cylinder-selective ignition angle in association with the respective operating point, which is dependent on load and engine speed. A method of that kind is known from German published patent application DE 29 25 770 A1.
When engine knock occurs in a cylinder z of the internal combustion engine, the ignition angle for this cylinder is retarded by a certain amount—step size SK
dec
—thereby reducing the probability that knocking combustion will occur in this cylinder. If the engine then operates without knock, the ignition angle is slowly advanced again by a predetermined amount SK
inc
.
The known total ignition angle ZW(z) for a cylinder z at a particular operating point is made up of a basic ignition angle GZ(z) for knock-free operation, which is dependent on the load L and the engine speed n, is stored in a map and—in the case of a four-cylinder engine—is updated every 180° of crank angle (hence the term “cylinder-selective”), this basic angle being calculated from the ignition dead center position ZOT(z) closest to ignition, and of an additional knock adjustment angle KNK(z) for this cylinder z owing to engine knock: ZW(z)=GZ(z)−KNK(z). It should be noted here that the knock adjustment angle KNK(z) can assume only negative values, in line with the recognition that a positive sign signifies “advance”, while a negative sign signifies “retardation”.
The respective knock adjustment angles KNK(z) are entered in one load- and engine-speed-dependent map per cylinder. As the change from one operating point to the next occurs, the last knock adjustment angle KNK(z) entered is stored at the old operating point. When the engine re-enters this operating point, this value is reused as the knock adjustment angle KNK(z) for knock control. This method has the disadvantage that a relatively random knock adjustment angle will be stored, depending on the time at which the change in the operating point occurs.
This results in the following disadvantages:
the knock limit is not adapted accurately;
the ignition-angle profile in the case of transitions between the adaptation ranges is nonuniform, and the torque profile is therefore not continuous either;
the internal combustion engine is not operated exactly at the knock limit; as a result, optimum torque and optimum specific fuel consumption are not assured.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method for cylinder-selective knock control of an internal combustion engine which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which is improved such that the knock limit is adapted as accurately as possible, that a uniform ignition-angle profile and hence also a continuous torque profile is obtained in the case of transitions between the adaptation ranges, and that optimum torque and optimum specific fuel consumption are established.
With the above and other objects in view there is provided, in accordance with the invention, a cylinder-selective knock control method for an internal combustion engine, in which there is formed, in association with a respective operating point that depends on a load and an engine speed, a cylinder-selective ignition angle from a predetermined cylinder-selective basic ignition angle associated with knock-free operation and a cylinder-selective knock adjustment angle that increases stepwise with a predetermined step size in a retarded direction each time a knock occurs and decreases stepwise with a predetermined step size in an advanced direction after each engine cycle during knock-free operation. The novel method is characterized by the following method steps:
determining a cylinder-selective first adaptation value of a first adaptation circuit from a comparison of the knock adjustment angle with a first and a second threshold value;
wherein the first threshold value is greater than the step size, specified in the retarded direction, of the cylinder-selective knock adjustment angle, and the second threshold value is less than the step size, specified in the retarded direction, of the cylinder-selective knock adjustment angle;
modifying the cylinder-selective adaptation value of the first adaptation circuit in the retarded direction with a predetermined first adaptation step size after each engine cycle for as long as the knock adjustment angle is greater in terms of an absolute value thereof than the first threshold value;
holding the cylinder-selective adaptation value of the first adaptation circuit constant for as long as the knock adjustment angle is less than the first threshold value and greater than the second threshold value in terms of the absolute value; and
modifying the cylinder-selective adaptation value of the first adaptation circuit in the advanced direction with a predetermined second adaptation step size for as long as the knock adjustment angle is less in terms of the absolute value than the second threshold value;
determining a second adaptation value, associated with all the cylinders, of a second adaptation circuit from a comparison of the average value of all the cylinder-selective adaptation values of the current operating point with a predetermined threshold; and
using the cylinder-selective first adaptation value and the second adaptation value associated with all the cylinders to form a cylinder-selective total ignition angle in accordance with the formula
ZW(z)=GZ(z)−KNK(z)−AD
1
(z)−AD
2
where z is a number of the cylinder, ZW is the total ignition angle, GZ is the basic ignition angle, KNK is the knock adjustment angle, AD
1
is the first adaptation value, and AD
2
is the second adaptation value.
In accordance with an added feature of the invention, the second adaptation value of the second adaptation circuit:
is modified in the retarded direction by a predetermined decrement after each engine cycle if the average value of all the cylinder-selective adaptation values of the current operating point has a negative sign and is greater in terms of its absolute value than the threshold; and
is modified in the advanced direction by a predetermined increment after each engine cycle if the average value is less in terms of its absolute value than the threshold.
In accordance with an additional feature of the invention, at least one quantity of the group consisting of the first step size, the second step size, the first adaptation step size, the second adaptation step size, the first threshold value, and the second threshold value, is stored in dependence on the operating point in a map assigned to the quantity.
In accordance with another feature of the invention, an adaptation of the first or second adaptation circuit is blocked for predetermined operating point ranges.
In accordance with a further feature of the invention, there are specified maximum values in the advanced direction or minimum values in the retarded direction for the adaptation values; the values are thereby applicable to all the cylinders.
In accordance with a concomitant feature of the invention, the sum of the knock adjustment angle and the first adaptation value is incremented with the step size if operation is knockfree in a range in which the knock adjustment angle is greater than the first threshold value.
In sum, the invention adds to the known cylinder-selective knock adjustment angle KNK(z) a first adaptation value AD
1
of a first adaptation circuit and a second adaptation value AD
2
of a second adaptation circuit common to all the cylin
Cianciara Wojciech
Fischer Gerhard
Haug Thomas
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
Vo Hieu T.
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