JPS6340263B2 - - 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 by the water temperature sensor 10. Then, the air conditioner (A/C) signal from the air conditioner switch 11, neutral (NEUT)
The deviation between the engine's actual idle rotation speed N and its target value N _r , which is the final idle rotation speed target value N _r calculated by making corrections according to signals, battery voltage V _B signals, etc. Proportional and integral (PI) duty control is performed on the pulse width P _A of the control solenoid 3 so that SA becomes small, and feedback control is performed to the target rotational speed N _r .

The above control method is shown in the form of a flowchart, which is shown in FIG.

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.
When the engine enters the idle state from other operating states,
Alternatively, when the engine exhibits dynamic behavior such as when coming out of an idle state or immediately after various load disturbances are applied, there is a problem of poor control followability, that is, poor transient response. In addition, when trying to increase the degree of freedom of control by adding other control inputs to improve controllability, there was a problem in that it was difficult to apply the PI control method.

In particular, when a predictable disturbance such as an air conditioner load disturbance is added, feedforward information is input in advance by turning on the air conditioner switch 11, and accordingly, feedforward control is added to the feedback control to control the idle speed. This is intended to prevent the rotational speed from decreasing, but the response of the actuator for supplying the control inputs such as air volume, fuel supply volume, or exhaust gas recirculation volume is slow, and there is also a delay time in passing through the intake manifold. It is impossible to prevent the rotation speed from decreasing immediately after the load disturbance is applied. In addition, there was a problem in that when the rotational speed decreased, if other disturbances (for example, electrical load or clutch connection) were added, the engine would stall (the engine would stop).

(Purpose of the Invention) This invention was made by focusing on the conventional problem described above. When the engine enters the idle state from another operating state or exits the idle state, a larger load disturbance is generated. Immediately after joining, etc.
It optimizes control followability, that is, transient response when the engine exhibits dynamic behavior, and also increases the degree of control freedom by adding a large number of control input variables, making it easier to improve controllability and achieve a more stable idle. The purpose is to control rotational speed.
In particular, it is an object of the present invention to improve controllability when a predictable load disturbance is introduced.

(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 consisting of a microcomputer, etc. (or equivalent) and exhaust gas recirculation (EGR)
Any one selected from the amount (or equivalent amount)
or any combination of two or more as the control input, and the idle rotation speed as the control output, and from the control input and control output, estimate the state variable amount representing the internal state of an internal combustion engine, etc., which is a dynamic model. The control input value is determined using the estimated value and the integral value of the deviation between the target value and the actual value of the idle rotation speed, and the idle rotation speed of the internal combustion engine is feedback-controlled to the target value. 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. In particular, when a predictable load disturbance is introduced, the ignition timing is changed with good control response.

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 that is a controlled object. If the control output of the controlled object 12 is the idle rotation speed, the control inputs include air volume (or equivalent amount), ignition timing, fuel supply amount (or equivalent Any one or a combination of two or more selected from the following: (amount) and an exhaust recirculation amount (or equivalent amount) may be adopted. However, when ignition timing is used as a control input, although the response is good compared to other control inputs, there is a large amount of overshoot and undershoot during transients when disturbances are added, making it difficult to stabilize the idle rotation speed. It is not preferable to use ignition timing as a control input, but it is preferable to use ignition timing effectively when the control range is exceeded by other control inputs, or when particularly responsiveness is required.

In this embodiment, the second control input is the pulse width P _A (that is, the amount corresponding to the bypass air amount) that drives the control solenoid (Fig. 1) of the VCM valve 2 for adjusting the amount of bypass air at idle.
and the pulse width that drives the solenoid valve that sub-injects fuel.
P _F (that is, the amount equivalent to the fuel supply amount) is taken. The control output is the idle rotation speed N, which is one output.

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

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 that is the object of control include, for example, the absolute pressure of the intake manifold, the suction negative pressure, the amount of air actually taken into the cylinder, the operational behavior of combustion, the engine torque, etc. It will be done. 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 the detected values 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. In the case of two inputs and one output in this invention, n=4 is appropriate.

Further, when the model is approximated in a low dimension in this way, the influence of the error appears, but this point can be absorbed by adding an I (integral) operation, as will be described later.

In Fig. 3, 14 is an integral (I) operation and a gain block, which is used to control the specified target value of the engine rotation speed.
From the integral of the deviation SA between N _r and the actual value N and the state variable quantity x calculated by the state observer 13, 2
Calculate the values of the two control inputs P _A and P _F (see Figure 5). The above-described 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 is found experimentally, 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 , ΔP _F , 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 represents the vibration component 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, 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 construct a state observer with the following algorithm.

x^(n)=(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, x^(n )→x(n) (8) 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 (P _A ) of the drive pulse width of the control solenoid 3, which is the control input, holds, and the linearity of the fuel injection pulse width from the reference setting value The amount of increase δP _F (·) within the range where the approximation holds is determined, and optimal regulator control of the idle rotational speed N of the engine is performed. Regulator control means constant value control that controls the idle rotation speed N to match the target rotation speed _Nr , which is a constant value.

In this invention, since the experimentally obtained model is a reduced-dimensional approximate model as described above, an I (integral) operation is added to absorb the approximation error. Performs optimal regulator control including operation.

As mentioned above, the engine to be controlled by this invention is a two-input one-output system, which is optimally controlled by the regulator. It is explained in the book "Linear System Control Theory" (1971) by Shokodo and others, so 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 of equation (11)
The terms are in the differential quadratic form of the control input as shown in equation (9), but this is due to the addition of the I operation 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. In addition, in equation (12), = 1 -CA OA (14) = -CB B (15), and P is P= ^t P- ^t P( ^t P+R
) ^{-1 t} P+ 1 O O O (16) This is the solution to 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, we selected an appropriate R, used a dynamic model (state variable model) of the engine at idle, and calculated using P obtained by solving equation (16).
The optimal gain matrix K in equation (13) is stored in a microcomputer, and from the integral value of the deviation SA between the target value N _r and the actual value N of the idle rotation speed and the estimated state variable x^(k), (12) The optimal control input value u ^* (k) can be easily determined by the formula. Also, as mentioned above, the estimated value of the dynamic state variable of the engine x^(k)
To obtain , the values of matrices A, B, C, and G may be stored in a microcomputer and calculated using equation (6).

Now, predicted disturbances (that is, disturbances that are known in advance to be introduced), such as air conditioner load disturbances, are
With the ON signal of the air conditioner switch 11, disturbance input can be used as feed-forward information, and in addition to normal feedback control, feed-forward control of the amount of air and fuel supply can be added. However, it takes time to adjust the amount of air and fuel supply and obtain a response to the idle speed, and as shown in Figure 6 A and B, a drop in the idle speed immediately after the air conditioner is turned on is unavoidable. (solid line in Figure 6B). Furthermore, if other load disturbances such as power steering, electricity, clutch connection, etc. are added during this period, the rotational speed will further decrease and the engine may stall.

Therefore, when predictable load disturbances such as air conditioners are added, responsive ignition timing IT can be added as feed forward control (Fig. 6 E) to suppress the drop in idle rotation speed (Fig. 6 E).
(Dotted-dotted line in Figure B).

Although there are various ways to change the ignition timing, FIG. 6E shows an example in which the ignition timing is uniformly advanced by a certain value (for example, 8 degrees). In addition, in FIG. 6B, the target value N _r of the idle rotation speed is 650 rpm, the target value N r is set to 800 rpm at the same time as the air conditioner switch 11 is turned on, and the target value N _r is set to 800 rpm at the same time as the air conditioner switch 11 is turned off.
This is an example of returning the speed to 650 rpm.

FIG. 7 shows the procedure of the above idle rotation speed control. When explaining the procedure, the step
30, the target value N _r of the idle rotation speed is determined based on the on/off state of the air conditioner, the value of the water temperature T _W , etc. In step 31, the ignition timing IT is advanced when a predicted disturbance (for example, an air conditioner) is input. In step 32, the deviation SA between the target value _Nr and the actual value N of the idle rotational speed is calculated. In step 33, the rotation speed deviation from the start of control to the previous cycle is calculated.
Adding SA and moving the result to a register called DUN. In step 34, 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 35, the state variable quantities 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 δP _F , Furthermore, the control output value δN is weighted and added to each state variable quantity x ₁
~calculate x ₄ . However, the matrix (A-GC) in equation (6) is of the form A-GC = 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 (18), which is an example of forming a finitely stable observer. . Note that (A, B, C) use visible measurement canonical form.

In step 36, the estimated dynamic internal state variables x ₁ to _{x 4} of the engine and DUN are multiplied by the element k _ji of the optimal gain K and added, and the standard setting value (P _A ) _{a is} calculated.
and (P _F ) Calculate how much to increase the control input value for _a .

The coefficients b _ij , g _i , k _ij, etc. in FIG. 7 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), the fuel supply amount (or equivalent amount), and the exhaust gas recirculation amount (or equivalent amount). ) or a combination of any two or more of them, which in the embodiments described above is the equivalent amount of bypass air. A case has been described in which the pulse width ΔP _A of the control solenoid of the VCM valve and the fuel injection pulse width ΔP _F , which is equivalent to the amount of fuel supplied, are used as control inputs.

(Effects of the Invention) As explained above, according to the present invention, idle rotation speed control is performed by applying a multivariable control method based on a dynamic model of an internal combustion engine,
Moreover, a procedure for estimating the dynamic state of the internal combustion engine is added, and calculation time is shortened by using a low-dimensional version of the engine model in the state observation device, and the approximation error is absorbed by the integral operation. This makes it possible to optimize the control transient response to external disturbances such as misfire disturbances and load disturbances that are problematic in idling conditions, and it is also easy to control by adding multivariable control inputs to increase the degree of control freedom and improve controllability. Therefore, it is possible to realize more stable idle rotation speed control.

In particular, when predictable load disturbances occur, by effectively changing the ignition timing using feedforward control, it is possible to suppress the drop in rotational speed and achieve more stable idling operation. is obtained.

[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 a detailed configuration diagram of the integral operation and gain block in Figure 3, Figures 6A, B, C, D, and E are diagrams showing experimental results of the method according to the present invention, and Figure 7 shows the method according to the present invention. This is a flowchart to explain. 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
... Integral operation and gain block, N _r ... Target value of idle rotation speed, N ... Actual value of idle rotation speed, N _a ... Reference setting value of idle rotation speed,
SA... Deviation between the target value and actual value of idle rotation speed, P _A ... Driving pulse width of the control solenoid that regulates the amount of bypass air, P _F ... Drive pulse width of the injection solenoid valve that regulates the amount of fuel supply, IT...Ignition timing, x _i (=x)...State variable quantity, x^ _i (=x^)...
Estimator of state variables.

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. , one selected from the amount of air supplied to the internal combustion engine or an equivalent amount, which is a control input value for the internal combustion engine, the amount of fuel supplied to the internal combustion engine or an equivalent amount, and the amount of exhaust gas recirculation or an equivalent amount. or any 2
A state variable quantity x _i (i=1, 2,... ...n), and the estimated state variable quantity x _i ^ (i=1, 2, ......n)
and an integral amount of the rotational speed deviation SA, the control input value is determined, and the ignition timing is changed when a predictable continuous disturbance is added.