JPS6325177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for controlling the rotation speed of an internal combustion engine during idling, and more specifically,
Unlike PID (proportional-integral-derivative) control, it considers the internal state of the internal combustion engine, treats the engine as a dynamic system, and estimates the dynamic behavior of the engine using state variables that define the internal state. However, the present invention relates to a method of controlling idle rotation speed using a state variable control technique that determines engine input variables.

(Prior Art) As a conventional method for controlling idle rotation speed in an internal combustion engine, there is a method as shown in FIG. 1, for example. AAC valve 1 for idle speed control
The lift amount changes by duty-controlling the driving pulse width P _A of the control solenoid 3 of the VCM valve 2, and the amount of bypass air passing through the bypass 5 of the throttle valve 4 changes, thereby increasing the idle rotation speed. controlled.

The control unit 6 detects that the engine is in the idle state based on the idle (IDLE) signal from the throttle valve switch 7, the neutral (NEUT) signal from the neutral switch 8, the vehicle speed (VSP) signal from the vehicle speed sensor 9, etc. Then, a basic target value of the idle rotation speed is calculated by a one-dimensional table lookup according to the cooling water temperature (T _w ) detected by the water temperature sensor 10. Then, the target value N r of the idle rotation speed is finally calculated by making corrections according to the air conditioner (A/C) signal, neutral (NEUT) signal, battery voltage (V _B ) signal, etc. from the air conditioner switch _11. In contrast, the pulse width of control solenoid 3 is adjusted so that the deviation SA between the engine's actual idle speed N and its target value N _r becomes small.
Perform proportional and integral (PI) duty control on P _A ,
Perform feedback control to target rotational speed _Nr .

FIG. 2 shows a flowchart of the above control method.

However, such conventional idle speed control methods for internal combustion engines do not perform PI control that effectively utilizes the dynamic characteristics of the engine, actuator, and sensor, and furthermore,
PI control as a control method has become unsuitable for controlling multi-input/output systems, and it is difficult to maintain the same control gain even when loads that can be predicted in advance, such as air conditioners, power steering, clutch engagement, etc., or sustained disturbances are added. Because the engine was configured to perform control, when the engine exhibits dynamic behavior, such as when the engine enters or exits the idle state from another operating state, or immediately after various load disturbances are applied, However, there was a problem of poor control followability, that is, poor transient response. In addition, other control inputs can be added to increase the degree of control freedom.
When trying to improve controllability, there was a problem that it was difficult to apply the PI control method.

(Object of the Invention) The present invention has been made by focusing on the conventional problems as described above. It optimizes the control followability, that is, the transient response when the engine exhibits dynamic behavior, such as immediately after the engine is activated, and also increases the degree of control freedom by adding a large number of control input variables, making it easy to improve controllability. The purpose is to achieve more stable idle rotation speed control.

(Structure and operation of the invention) Therefore, the present invention stores models of the dynamic characteristics of the internal combustion engine, actuator, and sensors in a controller including a microcomputer, etc.
Any one or a combination of two or more of the fuel supply amount (or equivalent amount) and the exhaust gas recirculation (EGR) amount (or equivalent amount) is used as the control input, and the idle rotation speed is used as the control output. From the input and control output, state variables representing the internal state of an internal combustion engine, which is a dynamic model, are estimated, and using the estimated value and the integral value of the deviation between the target value and the actual value of the idle rotation speed, In addition to determining the control input value, when a load or continuous disturbance that can be predicted in advance is added, the optimum gain that determines the control input value is switched to feedback control the idle rotation speed of the internal combustion engine to the target value. Features. This control method uses a multivariable control method that comprehensively controls a large number of input and output variables, instead of the conventional general PID control.

The present invention will be explained below based on the drawings.

FIG. 3 is a block diagram of an apparatus for implementing an embodiment of the method for controlling the idle rotation speed of an internal combustion engine according to the present invention.

In the figure, reference numeral 12 denotes an internal combustion engine to be controlled, which performs not only idle speed control but also fuel injection control including air-fuel ratio feedback control. When the control output of the controlled object 12 is the idle rotation speed, the control input can be any one or a combination of two or more of the bypass air amount, ignition timing, fuel supply amount, and exhaust gas recirculation amount. obtain. In this embodiment, as two control inputs,
For adjusting the amount of bypass air at idle
The pulse width P _A (that is, the amount corresponding to the amount of bypass air) that drives the control solenoid of the VCM valve 2 (Fig. 1) and the ignition timing IT are determined. The control output is the idle rotation speed N, which is one output.

Reference numeral 13 denotes a state observer that stores a dynamic model of the engine 12 that is the controlled object and estimates the dynamic internal state of the engine from the above three control input/output information P _A , P _T , and N. Yes, the state variable quantity x (for example, 4
Calculate the estimated value x of the vector representation of the three quantities x ₁ , x ₂ , x ₃ , x ₄ ).

The state observation device 13 simulates the engine to be controlled, and the dynamic internal state is represented by a state variable x (n-th order vector x ₁ to x _o ). Specifically, the state variables representing the internal state of the engine 12, which is the controlled object, include, for example, the absolute pressure of the intake manifold, the suction negative pressure, the amount of air actually taken into the cylinder, the dynamic behavior of combustion, the engine torque, etc. Can be mentioned. If these values can be detected by a sensor, dynamic behavior can be grasped by using the detected values, and control can be performed more precisely by using them for control. However, at present, there are not many practical sensors that can detect these values. Therefore, the internal state of the engine is represented by a state variable x, but the state variable x does not need to correspond to various physical quantities representing the actual internal state, and is used to simulate the engine as a whole. As for the degree n of the state variable x, the larger n is, the more accurate the simulation will be, but on the other hand, the calculation will be more complicated. Therefore, a low-approximation model is used, and approximation errors or errors due to individual engine differences are absorbed by integral operation. In the case of two inputs and one output in this invention, n=4 is appropriate.

In FIG. 3, 14 is an integral operation and a gain block, which is the integral of the deviation SA between the designated target value N _r of the engine rotation speed and the actual value N, and the state variable quantity x calculated by the state observer 13. From this, calculate the values of the two control inputs P _A and IT (see Figure 5).
The state observer 13, integral operation, and gain block 14 constitute a controller.

Next, the action will be explained.

The engine 12 that is the controlled object is a two-input one-output system, and the controlled object 12 is It is possible to estimate the dynamic internal state of
One of the methods is the state observation device 13. Under operating conditions near the idle rotation speed, the controlled object 12
The transfer function matrix T(z) of T(z) is practically found, and becomes T(z)=[T ₁ (z) T ₂ (z)] (1). However, z is the sample value of the input/output signal.
- transformation, where T ₁ (z) and T ₂ (z) are, for example, quadratic transfer functions of z.

FIG. 4 shows a model structure of the controlled object (engine) 12 showing the relationship between input, output, and transfer functions T ₁ (z) and T ₂ (z). However, input and output use deviations ΔP _A , ΔIT, and ΔN from the reference setting values, respectively.

From this transfer function matrix T(z), the state observer 13 can be configured as follows.

First, a state variable model that describes the dynamic behavior of the engine from T(z) x(n)=Ax(n-1)+Bu(n-1) (2) y(n-1)=Cx(n- 1) Derive (3). Here, (n) in each quantity box represents the current time, and (n-1) represents the previous sample time. u(n-1) is a control input vector, which includes the pulse width δP _A (n-1) of the control solenoid 3 and the ignition timing δIT, which represent the perturbation within a range where linear approximation from a certain reference setting value holds. shall be. That is, u(n-1) = δP _A (n-1) δIT(n-1) (4) Also, y(n-1) is the control output, and like the control input vector, a certain reference rotation speed N _a (for example
The element is δN (n-1) representing the perturbation from 650 rpm). That is, y(n-1)=δN(n-1) (5) x(・) is the state variable vector, and the matrix A,
B and C are constant matrices determined from the coefficients of the transfer function matrix T(z).

Here, we configure a state observer with the following algorithm.

x^=(A-GC)x^(n-1) +Bu(n-1)+Gy(n-1) (6) Here, G is an arbitrarily given matrix and x^(・)
is the estimated value of the internal state variable x(·) of the engine 12. Transforming from equations (2)(3)(6), [x(n)-x^(n)] = (A-GC)[x(n-1)-x^(n-1)]
(7), and if G is chosen so that the eigenvalues of the matrix (A-GC) are within the unit circle, then x^(n)→x(n) (8) when n→large, and the internal state variable quantity x (n) can be estimated from the input u(·) and the output y(·). Also,
It is also possible to appropriately select the matrix G and make all the eigenvalues of the matrix (A-GC) zero, in which case the state observer 13 becomes a finitely stable state observer.

The state variable x^(・) estimated in this way is
Target rotation speed N _r and current actual rotation speed N (・)
Using the information of the deviation SA = (N _r − N (・)),
The increase amount δP _A (・) within the range where a linear approximation from the reference setting value ( _PA ) _a of the drive pulse width of the control solenoid 3 which is the control input holds, and the linear approximation from the reference setting value of the ignition timing are Determine the amount of increase δIT (・) within the range that holds true, and determine the idle rotation speed N of the engine.
performs optimal regulator control. Regulator control means fixed-value control that controls the idle rotational speed N to match the target rotational speed _Nr , which is a constant value. In the present invention, since the experimentally obtained model is a low-dimensional approximate model as described above, an I (integral) operation is added to absorb the approximation error. Performs optimal regulator control including I operation.

As mentioned above, the engine to be controlled by this invention is a two-input one-output system, which is optimally controlled by a regulator. Since it is explained in the book "Linear System Control Theory" (1976) by Shokodo and others, a detailed explanation will be omitted here. Describing only the results, now δu(n)=u(n)−u(n−1) (9) δe(n)=N _r −N(n) (10) and the evaluation function J is J = _∞ 〓 ^K=0 [δe(k) ² +δu ^t (k)Rδu(k)] (11). Here, R is a weight parameter matrix and t is a transposition. k is the number of samples with the control start time being 0, and the second term on the right side of equation (11) represents the square of equation (9) (assuming R is a diagonal matrix). Also, the second term of equation (11) is
The quadratic form of the control input difference as shown in equation (9) is used, but this is because the I operation is added as shown in FIG. The optimal control input u ^* (k) that minimizes the evaluation function J in equation (11) is becomes. If we set K=-(R+ ^tP ) ^-1tP (13) in equation (12), K is the ^optimal gain matrix. Also, in equation (12) and P is is the solution of the Riccati equation.

The meaning of the evaluation function J in equation (11) is that the control input u(・)
The intention is to minimize the deviation SA (rotation fluctuation) of the idle rotation speed N, which is the control output y (・), from the target value N _r while constraining the movement of It can be changed using matrix R. Therefore, by selecting an appropriate R, using a dynamic model (state variable model) of the engine at idle, and using P obtained by solving equation (16), the optimal gain matrix K in equation (13) is micro- The target value of idle rotation speed is stored in the computer.
From the integral value of the deviation SA between N _r and the actual value N and the estimated state variable x^(k), the optimal control input value u ^* (k) can be easily determined by equation (12). Furthermore, as mentioned above, in order to obtain the estimated value x(k) of the dynamic state variable of the engine, the values of matrices A, B, C, and G must be stored in a microcomputer and calculated using equation (6). Bye.

A feature of the present invention is that in the above-described control, when a load or a sustained disturbance is added, the control is performed by switching the optimum gain that determines the control input value.

Here, when it comes to loads and continuous disturbances on devices that have switches such as air conditioners, power steering, clutches, etc., it is possible to detect the start of disturbances as feedforward information. In addition, the optimum servo control gain K when such a load or sustained disturbance is applied is one that provides good controllability (for example, engine misfire, etc.) against general disturbances (such as engine misfires) in the absence of such a load or sustained disturbance. 13) tends to be different from the optimal gain K in equation 13). For example, Figure 6a shows a certain gain.
Servo control when the air conditioner turns on in K ₁
A ₁ and control when a general steady state disturbance is added B ₁
Figure 6b shows the servo control when the air conditioner is turned on at another gain _K2 .
A ₂ and control when a general steady state disturbance is added B ₂
The following shows the case where _A0 in FIG. 6a indicates the target value for idle rotation control when the air conditioner is turned on.
Comparing Figures 6a and 6b, the servo control when the air conditioner is turned on shows better controllability in Figure 6b, while the control when a disturbance is added during normal steady state shows better controllability in Figure 6b. Figure a is better. This indicates that the gain K with good controllability differs depending on each disturbance.
Therefore, controllability can be further improved by controlling the gain _K1 when the air conditioner is not on and switching to the gain _K2 when the air conditioner is on.

Figures 7a and 7b show the state of control of the idle rotation speed when a power steering disturbance is applied. Figure 7a shows the gain _K1 , Figure 7b shows the gain _K2 , and in the figure C
The dots indicate the point at which the power steering is switched off. It can be seen that the gain _K2 in FIG. 7b provides better controllability against power steering disturbances.

Furthermore, FIGS. 8a and 8b show the state of control of the idle rotational speed during clutch engagement and clutch off, where FIG. _{8a shows the gain K 1 and FIG} . is Clutch meat, D ₂
Each dot indicates the clutch-off time. It can be seen that the gain _K2 in FIG. 8b provides better controllability against clutch disturbance.

FIG. 9 shows the procedure of the above idle rotation speed control. To explain the procedure, in step 30, a target value _Nr of the idle rotation speed is determined based on the on/off state of the air conditioner, the value of the water temperature _Tw, etc. In step 31, it is determined whether a disturbance that can be predicted in advance, such as from an air conditioner, power steering, or clutch, has occurred. If there is no disturbance, the optimum gain in that case is determined as kij in step 32. If a disturbance occurs, in step 33, the optimum gain kij corresponding to the disturbance is determined by table lookup or the like. In step 34, the deviation SA between the target rotational speed N _r determined in step 30 and the actual rotational speed N is calculated. In step 35, the rotational speed deviation SA from the start of control to the previous cycle is added, and the result is transferred to a register called DUN. In step 36, the deviation δN of the actual value N of the rotational speed from the reference set value N _a (for example, 650 rpm) is calculated. In step 37, the state variables x ₁ ^* to x ₃ ^* (previously calculated values) representing the dynamic internal state of the engine estimated in the previous control cycle, the calculated control input values δP _A and δIT, and The control output value δN is weighted and added to each state variable quantity x ₁
~calculate x ₄ . However, the matrix (A-GC) of equation (6) is This is an example of forming a finitely settled observer in the form. Note that (A, B, C) uses observable canonical forms.

In step 38, the estimated dynamic internal state variables x ₁ to _{x 4} of the engine and DUN are evaluated for two cases: one in which there is no disturbance, and one in which there is a disturbance that can be predicted in advance due to turning on and off of the air conditioner, power steering, clutch, etc. By multiplying and adding the elements kij of the optimal gain K determined separately, it is calculated how much the control input value should be increased with respect to the reference setting value (P _A ) _a and IT _a .

The coefficients bij, gi, kij, etc. in FIG. 9 are determined in advance and stored in a microcomputer or the like.

As mentioned above, when the control output of the internal combustion engine in this invention is the idle rotation speed, the control inputs include the air amount (or equivalent amount), ignition timing,
Either one or any two of fuel supply amount (or equivalent amount) and exhaust gas recirculation amount (or equivalent amount)
Combinations of three or more can be used, and in the above embodiment, a case has been described in which the control inputs are the pulse width of the control solenoid of the VCM valve and the ignition timing, which are equivalent to the amount of bypass air.

(Effects of the Invention) As explained above, according to the present invention, idle rotation control is performed by applying a multivariable control method based on a dynamic model of the internal combustion engine, and a procedure for estimating the dynamic state of the internal combustion engine is performed. , and reduce the calculation time by using a low-dimensional version of the engine model in the observer.
Since the approximation error is absorbed by the integral operation, it is possible to optimize the control transient response to disturbances such as misfire disturbances and load disturbances that are problematic in the idling state, and to increase the degree of control freedom and improve controllability. It is also easy to control by adding multivariable control inputs, and the effect is that more stable idle rotation speed control can be realized.

In particular, when an air conditioner, power steering, clutch, etc. have an ON/OFF switch, the optimal gain is switched by applying a sustained disturbance that can be predicted in advance, so even when a sustained disturbance that can be predicted in advance is applied, The effect is that more stable idling operation can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional idle rotation speed control device for an internal combustion engine, FIG. 2 is a flowchart showing a conventional idle rotation speed control method, and FIG. 3 is a flowchart showing a conventional idle rotation speed control method for an internal combustion engine according to the present invention. Fig. 4 is a block diagram showing the relationship between the control input/output and the engine in Fig. 3, and Fig. 5 is a block diagram of the control device realized.
The figure shows the details of the integral + gain block, Figures 6a and b are diagrams showing the state of the idle rotation speed when air conditioner disturbance and general disturbance are added to different optimal gains, and Figure 7a , b are diagrams showing the state of idle rotation speed when power steering disturbance is applied to different optimum gains, and Figures 8a and b are diagrams showing the idle rotation speed when clutch disturbance is applied to different optimum gains. FIG. 9 is a flowchart illustrating the control method according to the present invention. 1...AAC valve, 2...VCM valve, 3...
...Control solenoid, 4...Throttle valve, 5
... Bypass, 7 ... Throttle valve switch, 8 ... Neutral switch, 10 ... Water temperature sensor, 11 ... Air conditioner switch, 12 ... Internal combustion engine (controlled object), 13 ... Condition observation device, 14
... Controller, N _r ... Target value of idle rotation speed, N ... Actual value of idle rotation speed, N _a
...Standard setting value of idle rotation speed, SA...Difference between target value and actual value of idle rotation speed, P _A ...
...Driving pulse width of the control solenoid that defines the amount of bypass air, IT...Ignition timing, x _i ...Amount of state variable, x _i ...Estimated amount of state variable.

Claims (1)

[Claims] 1. A method for feedback controlling the idle rotation speed based on the deviation SA between the target value N _r and the actual value N of the idle rotation speed when the internal combustion engine is idling, based on the dynamic model of the internal combustion engine stored in the controller. , the amount of air supplied to the internal combustion engine or the amount equivalent to the amount of air, which is a control input value for the internal combustion engine, the ignition timing of the internal combustion engine, and the amount of fuel supplied to the internal combustion engine or the amount equivalent to the amount of fuel supplied. any one or any combination of two or more selected from the amount of exhaust gas recirculation and the amount equivalent to the amount of exhaust gas recirculation;
From the idle rotation speed which is the control output value of the internal combustion engine, a state variable quantity x _i (i=1, 2,
...n), and the estimated state variable amount x^ _i
The control input value is determined from (i = 1, 2,...n) and the integrated amount of the deviation SA of the rotational speed, and when a load or continuous disturbance that can be predicted in advance is added, the control input value is determined. A method for controlling an idle rotation speed of an internal combustion engine, characterized in that control is performed by switching an optimum gain that determines the speed of the engine.