JPS6325173B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a method for simultaneously controlling the rotational speed and air-fuel ratio of an internal combustion engine during idling, and more specifically, the present invention relates to a method for simultaneously controlling the rotational speed and air-fuel ratio of an internal combustion engine during idling. differs from that in that it considers the engine as a dynamic system by considering its internal state, and determines the engine's input variables while estimating the engine's dynamic behavior using state variables that define the internal state. This invention relates to a method for simultaneously controlling idle rotation speed and air-fuel ratio using state variable control techniques.

(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 receives an (IDLE) signal from the throttle valve switch 7, a neutral (NEUT) signal from the neutral switch 8,
When it is detected that the engine is in an idling state based on the vehicle speed (VSP) signal etc. from the vehicle speed sensor 9, the idle rotation speed is determined by a one-dimensional table search according to the cooling water temperature (T _w ) by the water temperature sensor 10. Calculate the basic target value. Then, the air conditioner (A/
C) The target value of the idle rotation speed that is finally calculated by making corrections according to the signal, neutral (NEUT) signal, battery voltage (V _B ) signal, etc.
With respect to N _r , the drive pulse width P _A of the control solenoid 3 is controlled by proportional and integral (PI) duty so that the deviation SA between the engine's actual idle rotation speed N and its target value N _r becomes small. , target rotational speed N _r
to control feedback.

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

On the other hand, to control the air-fuel ratio (mixture ratio of fuel and air), first calculate the basic fuel supply amount T _P from the engine rotational speed N and intake air amount Q: T _P = KQ/N (K is a constant)
Find it by. Then, based on the output value of the O ₂ sensor 12 (Fig. 1) which outputs a signal according to the air-fuel ratio according to the oxygen concentration of the exhaust mixture, the correction factor α for the basic fuel supply amount T _P is controlled by PI. By doing this, the actual air-fuel ratio A/F can be adjusted to the target air-fuel ratio (A/F).
F) Feedback control to _r .

However, in such conventional idle rotation speed and air-fuel ratio control methods, idle rotation speed control by manipulating the bypass air amount and air-fuel ratio control by manipulating the fuel supply amount are independent of each other. On the other hand, if the fuel supply amount is increased or decreased to perform air-fuel ratio control, the idle rotation speed will change. Therefore, if the bypass air amount is increased or decreased to perform idle rotation control, This time, the air-fuel ratio changed, and although they were controlled independently, they affected each other, making it difficult to perform stable control of the idle speed and air-fuel ratio.

In particular, when the dynamics of the engine changes due to changes in engine cooling water temperature, etc., there is a problem in that idling operation is difficult to stabilize.

(Purpose of the Invention) The present invention was made by focusing on such conventional problems, and its purpose is to optimally and stably control the idle rotation speed and the air-fuel ratio at the same time. The purpose is to provide stable control even when dynamics change.

(Structure and operation of the invention) Therefore, the present invention aims to reduce the amount of air (or equivalent amount)
and fuel supply amount (or equivalent amount),
Furthermore, based on an engine dynamic model in which the ignition timing or the exhaust gas recirculation amount (or equivalent amount) is the control input, and the idle rotation speed and the air-fuel ratio are the control outputs, the above control inputs and control outputs are calculated. It is characterized by multivariable control, and in particular, by switching the dynamic model and control gain when the dynamics of the engine changes.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 3 shows the configuration of an embodiment of this invention.
In the figure, 13 is the engine to be controlled, and various combinations of control inputs are possible, but here the control input is the drive pulse width P of the control solenoid 3 of the VCM valve 2 that adjusts the amount of bypass air at idle. _A and the fuel injection pulse width P _F that drives the fuel injection valve 14 (see Figure 1) are taken, and the control output is the air-fuel ratio A/F estimated from the engine rotation speed N and the output value of the O ₂ sensor 12. .

Reference numeral 15 denotes a state observation device that stores a dynamic model of the engine 13 that is the controlled object and estimates the dynamic internal state of the engine from the above four control input/output information P _A , P _F , N, A/F. (observer) and state variable quantity x representing the internal state
(For example, a vector representation of six quantities x ₁ , x ₂ , x ₃ , x ₄ , x ₅ , x ₆ ) is calculated.

The state observation device 15 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 13 that 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, the detected values can be used to understand the dynamic behavior of the engine, and can be used for control to perform more precise 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
It is not necessary to correspond to various physical quantities representing the actual internal state, and the engine as a whole is simulated. The order n of the state variable x is
The larger n is, the more accurate the simulation will be.
On the other hand, calculation becomes complicated. Therefore, a reduced-dimensional 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 two outputs in this invention, n=6 is appropriate.

In Fig. 3, 16 is an integral operation and a gain block, which is an integral of the deviation SA between the specified target value _Nr of the engine rotation speed and the actual value N, and the specified target value of the air-fuel ratio (A/F ) From the integral of the deviation SB between _r and the actual value A/F and the state variable quantity x calculated by the state observer 15, two control inputs P _A
and calculate the value of P _F (see Figure 5). Then, the state observer 15, the integral operation, and the gain block 1
6 constitutes a controller.

Next, the action will be explained.

The engine 13 that is the controlled object is a two-input, two-output system, and the control object 13 is It is possible to estimate the dynamic internal state of
One of the methods is the state observation device 15. Under operating conditions near the idle rotation speed, the controlled object 13
The transfer function matrix T(z) of T(z) is practically found, and becomes T(z)=T ₁ (z) T ₂ (z) T ₃ (z) T ₄ (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, second-order transfer functions of z, and T ₃ (z) and T ₄ (z) are first-order transfer functions of z.

Input, output and transfer functions T ₁ (z) to T ₄ (z)
A model structure of the controlled object (engine) 13 showing the relationship is shown in FIG. However, input and output use deviations δP _A , δP _F , δN, and δ(A/F) from the reference setting values, respectively.

From this transfer function matrix T(z), the state observer 15 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 represents the perturbation within a range where linear approximation from a certain reference setting value holds, and the pulse width _δP of the control solenoid 3 (n-1) and the fuel injection pulse width δP _F (n-1)
is an element. In other words, u(n-1)= δP _A (n-1) δP _F (n-1) (4) Also, y(n-1) is the control output vector, and like the control input vector, a certain reference rotation Speed N _a
(for example, 650 rpm) δN (n−
1) and δ(A/F)(n-1) representing the perturbation from the reference air-fuel ratio (A/F) _a . That is, y(n-1) = δN(n-1) δ(A/F)(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 construct 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 13. 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) for 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 15 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 (・)
The current actual air-fuel ratio (A/F) estimated from the information on the deviation SA = (N _r - N (・)), the target air-fuel ratio (A/F) _r , and the output signal of the O ₂ sensor 12 (・) Using the information of deviation SB = ((A/F) _r − (A/F) (・)), the standard setting value of the pulse width of control solenoid 3 (P _A ) _a The amount of increase δP _F (・) within the range where the linear approximation holds from a and the standard setting value of the fuel injection pulse width (P _F ) The amount of increase δP _F (・) within the range where the linear approximation from _a holds. The engine's idle speed N and air-fuel ratio A/F are optimally controlled by the regulator. What is regulator control?
Target rotation speed where idle rotation speed N is a constant value
_Nr means constant value control in which the air-fuel ratio A/F is controlled to match a target air-fuel ratio (A/F) _r , 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, two-output system, and this 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. To describe only the results, now δu(n)=u(n)−u(n−1) (9) δy(n)=y(n)−y(n−) (10) and the evaluation function J Let J= _∞ 〓 ^K=0 [δy ^t (k)Qδy(k)＋δu ^t (k)Rδu(k)] (11). Here, Q, R are weight parameter matrices, t
indicates transposition. k is the number of samples with the control start point as 0, the first term on the right side of equation (11) is the square of equation (10), and the second term is the square of equation (9) (Q, R is a diagonal matrix )
respectively. Furthermore, the second term of equation (11) is made into a quadratic form of the difference in control inputs as shown in equation (9), but this is because an I (integral) operation is added as shown in FIG. Optimal control input that minimizes the evaluation function J of equation (11)
u ^* (k) 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(・)
While restricting the movement of the control output y (・), the deviation SA (rotation fluctuation) of the idle rotation speed N from the target value N _r and the deviation of the air-fuel ratio A/F from the target value (A/F) _r The intention is to minimize SB, and the weighting of the constraints can be changed using weight parameter matrices Q and R. Therefore, by selecting appropriate Q and 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 of equation (13) is calculated. are stored in the microcomputer, and the integral value of the deviation between the target value N _r and the actual value N of the idle rotation speed, the integral value of the deviation between the target value (A/F) _r and the actual value (A/F) of the air-fuel ratio, and From the estimated state variable x(k), the optimal control input value u ^* (k) can be easily determined using equation (12). Also, 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 may be stored in a microcomputer and calculated using equation (6).

The method for estimating the air-fuel ratio deviation SB from the output signal of the _Q2 sensor 12 is as follows. The O ₂ sensor 12 outputs an on signal when the fuel is on the rich side and on the lean side when the fuel is at the stoichiometric air-fuel ratio.
Each side outputs an off signal. Shown in Figure 6
The output signal of the O ₂ sensor 12 is observed at each control period. For example, measure the on time and off time in the first cycle (0 to 1), add the on (rich) signal as (+) and the off (lean) signal as (-), and get SB = -t ₁ The value of SB obtained from +t ₂ -t ₃ +t ₄ (17) can be used as a quantity that represents how much the air-fuel ratio deviates from the target value (A/F) _r within that control cycle. .

In particular, when the cooling temperature of the engine 13 changes, the engine dynamics change. For example, the behavior of the engine changes when the cooling water temperature is 10°C and 60°C. In this way, when the engine dynamics change significantly, the dynamic model based on equations (2) and (3), which were experimentally determined under one predetermined condition of the engine, cannot provide optimal control. It cannot be expected to continue, and it is desirable to adapt in some way.

Therefore, a parameter (for example, cooling water temperature) that detects a change in engine dynamics is determined, a dynamic model is stored according to various values of that parameter, and a dynamic model is changed according to the value of that parameter. Optimal control can be maintained by switching the model and control gain. In this case, the state observer 15
constant matrices A, B, C, G (Equations (2), (3), (6), (7))
Also, the optimal gain K in equation (13) is changed.

FIG. 7 shows the procedure for simultaneous control of the idle rotation speed and air-fuel ratio. To explain the procedure, in step 30, the target value N r of the idle rotation speed is determined based on the on-off status of the air conditioner, the value of the water temperature T _w, etc., and in step 31, the target value N _r of the air-fuel ratio (A/F) _r is determined in the same way. decide. In step 32, the cooling water temperature T _w is detected, and a dynamic model and optimal gain K (b _ij , g _ij ,
k _ij ) from storage. In step 33, the deviation SA between the target value N _r of the idle rotation speed and the actual value N is calculated, and in step 34,
Calculate the deviation SB between the target value (A/F) _r of the air-fuel ratio and the actual value (A/F). 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 DUN1. In step 36, the air-fuel ratio deviation SB from the start of control to the previous cycle is added, and the result is transferred to a register called DUN2. Step 3
In step 7, the deviation of the actual value N of the rotational speed from the standard setting value N _a (for example, 650 rpm) is calculated, and in step 38, the deviation of the actual value A/F of the air-fuel ratio from the standard setting value (A/F) _a is calculated. Calculate each. In step 39, the state variables x ₁ ^* to x ₅ ^* representing the dynamic internal state of the engine estimated in the previous control cycle, the calculated control input values δP _A and δP _F , and the control output value are calculated. Each state variable amount x ₁ to x ₆ is calculated by weighting and adding certain δN and δ(A/F). 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 40, the estimated engine dynamic internal state variables x ₁ to x ₆ and DUN1 and
DUN2 is multiplied by the element k _ij of the optimum gain K and added to calculate how much the control input value should be increased with respect to the reference set values (P _A ) _a and (P _F ) _a .

The coefficients b _ij , g _ij , k _ij, etc. in Fig. 7 are the cooling water temperature T _W
A value corresponding to the value is determined in advance and stored in a microcomputer or the like.

Figures 8A and 8B show the experimental results of A when the dynamic model is the same regardless of the cooling water temperature _TW , and B when the dynamic model is switched depending on the cooling water temperature _TW . . Figure 8A shows that T _W =
The control system was designed based on a model modeled at about 60 to 80℃, and the optimum gain K and state observation model were used at that time, and the results were obtained by dry-blowing when the cooling water temperature T _W was 20℃. , Figure 8B shows the control system designed based on the modeling at T _W = 10 to 30℃, and the optimal gain K and state observation model at that time. This is the result of doing this.
In both cases, the target rotational speed N _r is 1200 rpm. From the figure, it can be seen that better controllability can be obtained by switching the dynamic model according to the cooling water temperature _TW .

(Effect of the invention) As explained above, according to this invention,
The difference between the drive pulse width P _A of the control solenoid that defines the air amount, which is the control input, and the fuel injection pulse width P _F , and the idle rotation speed N, which is the control output, and the air-fuel ratio A/F detected by the O ₂ sensor. The configuration performs multivariable control based on a dynamic model, and the dynamic model is switched when the dynamics of the engine changes due to changes in the engine cooling water temperature, etc., so it is possible to control the rotational speed when the engine is idling. and air-fuel ratio control can be performed simultaneously and optimally according to the dynamics of the engine, resulting in the effect that more stable idling operation can be realized.

In addition, in the above-mentioned embodiment, the case where the pulse width P _A of the control solenoid that defines the air amount and the fuel injection pulse width P _F are used as control inputs is shown.
If other ignition timing and EGR (exhaust gas recirculation) amount are used as control inputs, the control output is the rotational speed N.
and the air-fuel ratio A/F can be simultaneously and optimally controlled more precisely.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an idle rotation speed control device and an air-fuel ratio control device in a conventional internal combustion engine, FIG. 2 is a flowchart showing a conventional idle rotation speed control method, and FIG. 3 is an idle rotation speed control device in an internal combustion engine according to the present invention. A configuration diagram of a control device that realizes a simultaneous control method for rotational speed and air-fuel ratio, Figure 4 is a block diagram showing the relationship between the control input/output and engine in Figure 3, and Figure 5 is a block diagram of the integral + gain block in Figure 3. Detailed drawing, 6th
The figure is an output waveform diagram of the O ₂ sensor, FIG. 7 is a flowchart explaining the control method according to the present invention, and FIG.
Figures A and B are diagrams showing experimental results when the dynamic model is not switched and when it is switched. 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... O ₂ sensor, 13...Internal combustion engine (controlled object), 14...Fuel injection valve, 15...State observation device, 16...Integrator + gain block, _Nr ...Target value of idle rotation speed, N...Actual value of idle rotation speed , N _a ...Reference setting value of idle rotation speed,
SA...Difference between target value and actual value of idle rotation speed,
(A/F) _r ...Target value of air-fuel ratio, A/F...Actual value of air-fuel ratio, (A/F) _a ...Reference setting value of air-fuel ratio, SB...
Deviation between the target value and actual value of the air-fuel ratio, P _A ...Pulse width of the control solenoid that regulates the amount of bypass air,
P _F …Fuel injection pulse width that defines the fuel supply amount, x _i
...state variable amount, x _i ...state variable estimator.

Claims (1)

[Claims] 1. Deviation SA between target value N _r and actual value N of idle rotation speed and deviation SB between target value (A/F) _r and actual value A/F of air-fuel ratio during idling operation of the internal combustion engine.
The amount of air supplied to said internal combustion engine based on
two control inputs: P _A or an equivalent amount and a fuel amount P _F or an equivalent amount supplied to the internal combustion engine, or the two control inputs are further supplemented with an ignition timing or an exhaust gas recirculation amount or an equivalent amount. In a method of determining a value of a control input and controlling an idle rotation speed N and an air-fuel ratio A/F simultaneously, the control input value and the control output value are determined based on a dynamic model of the internal combustion engine stored in a controller. From the rotational speed N and the air-fuel ratio A/F, a state variable quantity x _i of an appropriate order representative of the dynamic internal state of the internal combustion engine is determined.
(i = 1, 2, ... n), and the estimated state variable quantity x^ _i (i = 1, 2, ... n), the integral value of the deviation SA of the rotational speed, and the air-fuel ratio Determine the control input value from the integral value of the deviation SB, and further,
When the dynamics of the internal combustion engine changes,
Simultaneous control of idle rotation speed and air-fuel ratio in an internal combustion engine characterized by switching to a dynamic model and control gain that match the changed state, estimating the state of the internal combustion engine, and determining a control input value. Method. 2. The method according to claim 1, wherein the dynamic model and the control gain are switched in accordance with the temperature of the cooling water of the internal combustion engine.