US 4,492,195 A · Method of feedback controlling engine idle speed

Abstract

Engine idle speed is feedback controlled on the basis of multivariable control method by using mathematical dynamic models to determine engine state variables. In the present invention, low-order (e.g. 4 order) dynamic models are adopted for facilitating calculations. The resulting control error is reduced or eliminated by several features as follows: the difference between the target idle speed and the current engine speed is integrated; an appropriate dynamic model is selected according to engine operating condition (coolant temp, O.sub.2 sensor); an appropriate control gain is determined according to engine load condition (air conditioner); the initial integral value of speed difference and the initial state variables are determined according to the engine speed at which the throttle valve is fully closed and the engine speed at which control starts in table look-up method; the target engine idle speed is corrected according to engine conditions; feedforward control is additionally provided, etc.

Claims19

Dependent claims

A method of feedback controlling engine idle speed to a target speed on the basis of mathematical dynamic models to determine engine state variables representative of engine dynamic behavior, which comprises the following step of:

(a) calculating the differences SA between the target engine idle speed N.sub.r and current engine speeds N;
(b) integrating the calculated idle speed differences SA to obtain integral value DUN of speed differences;
(c) selecting an appropriate mathematical engine dynamic model according to at least one of predetermined engine operating conditions;
(d) estimating low-order variables x.sub.i representative of engine internal dynamic states in accordance with the selected dynamic model and on the basis of at least one or two or more combinations of preceding increments of engine idle speed controlling parameters .delta.P.sub.A, .delta.IT and controlled engine idle speed .delta.N;
(e) selecting an appropriate gain K according to external engine load conditions;
and
(f) determining increments of engine idle speed controlling parameters .delta.P.sub.A, .delta.IT on the basis of the estimated state variables x.sub.i, the selected gain K, and the integrated idle speed difference DUN,
whereby engine idle speed is feedback controlled in accordance with low-order engine dynamic state variables.

5 more elements

(a) detecting an engine speed when a throttle valve is fully closed;
(b) detecting that engine idle speed N drops below a predetermined idle speed N* at which engine idle speed control starts;
(c) if the throttle valve is fully closed and further the engine idle speed N drops below a predetermined control start value N*, determining an initial value DUN(0) of integral DUN of speed difference SA between target engine speed value N.sub.r and detected engine speed value N, and initial values x.sub.1 (0) to x.sub.4 (0) of engine dynamic state variables in two dimensional table look-up method, when idle speed control starts;
(d) selecting an appropriate engine internal dynamic model according to engine operating conditions, and an appropriate control gain K according to engine load conditions;
(e) calculating an appropriate target engine idle speed N.sub.r according to engine operating conditions;
(f) detecting that engine speed N exceeds the calculated target value N.sub.r and idle speed controlling values .delta.P.sub.A, .delta.IT are fixed at lower limits;
(g) if engine speed N drops below the target value N.sub.r from the state where engine speed N exceeds the calculated target value N.sub.r and the idle speed controlling values are fixed at the lower limits, cancelling all the values of integral DUN, estimated variables x.sub.1 to x.sub.4, and calculated increments of speed controlling parameters .delta.P.sub.A, .delta.IT and setting all the cancelled values to reference values, respectively;
(h) if engine speed N does not drop below the target value N and the idle speed controlling values are not fixed at the lower limits, calculating difference SA between the target engine speed value N.sub.r and the detected engine speed N;
(i) integrating the difference SA to obtain DUN by the use of the determined initial value DUN(0);
(j) calculating engine speed perturbation .delta.N from designed reference engine speed value Na;
(k) estimating state variables x.sub.1 to x.sub.4 in accordance with the selected engine dynamic model and on the basis of the preceding estimated state variables x.sub.1 * to x.sub.4 *, the calculated engine speed perturbation .delta.N;
and the preceding engine speed controlling values .delta.P.sub.A, .delta.IT;
and
(1) calculating increments of engine controlling values .delta.P.sub.A, .delta.IT on the basis of estimated state variables x.sub.1 to x.sub.4, the calculated speed difference integral DUN and the selected gain K.

11 more elements

Dependencies are inferred from the claim text.

Method of feedback controlling engine idle speed

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Method of feedback controlling engine idle speed

Life of this patent

Abstract

Claims19