JPS6340929B2 - - 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, the engine is treated as a dynamic system by taking into account the internal state of the engine, and the dynamic behavior of the engine is controlled using state variables that determine the internal state. The present invention relates to a method of controlling idle rotation speed using a state variable control technique that determines engine input variables while estimating them.

(Prior Art) As a conventional method for controlling the idle rotation speed of an internal combustion engine, there is a method as shown in FIG. 1, for example.
In Figure 1, the idle rotation speed control
The lift amount of the AAC valve 1 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, resulting in an idle The rotation speed is controlled.

The control unit 6 controls the engine based on an idle (IDLE) signal from a throttle valve switch (also called an idle switch) 7, a neutral (NEUT) signal from a neutral switch 8, a vehicle speed (VSP) signal from a vehicle speed sensor 9, etc. When the idle state is detected, a basic target value of the idle rotation speed is calculated by a one-dimensional table lookup according to the cooling water temperature ( _TW ) 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 drive pulse width P _A of the control solenoid 3 is proportional and integral (PI) so that the deviation SA between the engine's actual idle rotation speed N and its target value N _r becomes small.
The target idle rotation speed is
Feedback control to _Nr .

FIG. 2 is a flowchart showing 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.
When the engine enters the idle state from other operating states,
Or, when the engine exhibits dynamic behavior such as when coming out of an idle state or immediately after various load disturbances are applied, the control followability, that is, the transient response is poor, and the control transient response until it follows the target rotational speed is poor. In addition, there were problems in that the target rotational speed was greatly reduced and the engine stalled during coasting, and the transient response was poor when revving during idling.

(Object of the Invention) The present invention has been made by focusing on such conventional problems. This system optimizes the control followability, that is, the transient response, when the engine exhibits dynamic behavior, such as immediately after the addition of a large number of control input variables. The purpose is to achieve more stable idle rotation speed control. In particular, the purpose is to prevent coasting engine stall when idle rotational speed control is performed from coasting, and to absorb deterioration in controllability due to changes in the engine over time or manufacturing variations.

(Structure 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 amount and exhaust gas recirculation (EGR) amount or equivalent amount, or any combination of two or more of them as the control input, and the idle rotation speed as the control output, and dynamometer from the control input and control output. Estimating the state variable quantity representing the internal state of the internal combustion engine, etc., which is the Mitsuku model, and determining the control input value using the estimated value and the integral value of the deviation between the target value and the actual value of the idle rotation speed, It is characterized by feedback control of the idle rotational speed of the internal combustion engine to a 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, the initial value that is set immediately after it is determined that idle rotation speed control is to be started from coasting is set so that the amount of undershoot with respect to the target value of idle rotation speed is small, and the initial value is set so that the amount of undershoot with respect to the target value of idle rotation speed is small, and the engine change over time and manufacturing variations are minimized. This method is characterized by modifying the initial value so as to absorb the controllability deterioration caused by this through learning.

(Example) Hereinafter, an example of the present invention will be described with reference to 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 is any one selected from the air amount, ignition timing, fuel supply amount, and exhaust gas recirculation amount, or any combination of two or more of them. obtain. In this embodiment, two control inputs are used to adjust 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 3 (Fig. 1) of the VCM valve 2 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 (observer) which stores a dynamic model of the internal combustion engine 12 to be controlled, and estimates the dynamic internal state of the engine 12 from the above three control input/output information P _A , IT, and N. and the state variable quantity x representing the internal state
(=x _i , i=1, 2, ..., n. For example, four quantities x ₁ ,
The estimated value x^ ₍ =x _{^ i ,} i
=1,2,...,n).

The state observer 13 simulates the engine 12 to be controlled, and the dynamic internal state is represented by a state variable quantity x. The state variables representing the internal state of the engine 12 to be controlled are as follows:
Specifically, examples include 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, and the engine torque. 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. However, at present, there are not many practical sensors that can detect these values. So engine 1
The internal state of the engine 12 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 12 as a whole. As for the order n of the state variable quantity x, the larger n is, the more accurate the simulation will be, but on the other hand, the calculation will be more complicated. Therefore, we use a low-dimensional approximation model and integrate approximation errors or errors due to individual differences between institutions.
(I) Absorb through movement. 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, and as shown in Fig. 4 in detail, the deviation SA between the specified target value N _r of the engine rotation speed and the actual value N
From the integrated quantity and the estimated state variable quantity x^ calculated by the state observer 13, two control inputs P _A and
Calculate the value of IT. Then, the state observation device 1
3, the integral operation, and the gain block 14 constitute a controller.

Next, the effect will be explained.

The engine 12 to be controlled is a two-input one-output system, and from the linearly approximated transfer function matrix T(z) obtained around a certain standard setting value of the rotationally synchronized sample value system between the input and output, the engine 12's It is possible to estimate dynamic internal states. One of the methods is the state observation device 13. The transfer function matrix T(z) of the engine 12 is experimentally determined under operating conditions near the idle rotational speed, and is as follows: 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. 5 shows a model structure of the 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 12 from T(z) −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, and the drive pulse width δP _A (n-1) of the control solenoid 3 (Fig. 1) represents the perturbation within a range where linear approximation from a certain reference setting value holds. The ignition timing δIT is used as an element.
That is, Also, y(n-1) is the control output, which, like the control input vector, is a certain reference rotational 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 matrices A, B,
C is a constant matrix determined from the coefficients of the transfer function matrix T(z).

Here, we configure 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, 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 13 becomes a finitely stable state observer.

The state variable amount x^(・) estimated in this way
, the target rotation speed N _r and the current actual rotation speed N
(・) Using information on the deviation SA = (N _r - N (・)), the range in which linear approximation from the reference setting value (P _A ) _a of the drive pulse width of the control solenoid 3, which is the control input, holds true. Determine the amount of increase δP _A (・) within the range and the amount of increase δIT (・) within the range where linear approximation from the standard setting value IT _a of ignition timing holds, and perform optimal regulator control of the engine's idle rotation speed N. Do the following. 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 addition, in this invention, since the experimentally obtained model is a reduced-dimensional approximate model as described above, an integral (I) operation is added to absorb the approximation error. Perform optimal regulator control including operation.

The engine to be controlled by this invention is a two-input one-output system as described above, which is optimally controlled by a regulator. This is explained in Katsuhisa's ``Linear System Control Theory'' (1973) 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. If k is the number of samples with the control start time being 0, and R is a diagonal matrix, the second term on the right side of equation (11) represents the square of equation (9). Furthermore, the second term on the right side of equation (11) is a quadratic form of the difference in control inputs as shown in equation (9), but this is because an integral action is added as shown in FIG. 4.

The control input u ^* (k) is becomes. In equation (12), ^K =-(R+ ^tP ) ^-1tP (13), then 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 You can change it with 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 quantity x^(k), the optimal control input value u ^* (k) can be easily determined using equation (12). . Furthermore, as mentioned above, in order to obtain the estimated value x^(k) of the dynamic state variable quantity of the engine 12, the matrices A, B,
The values of C and G may be stored in a microcomputer and calculated using equation (6).

By the way, immediately after detecting that the throttle valve 4 (Fig. 1) is fully closed and determining that the operating state of the engine 12 has reached a predetermined state and that idle speed control is to be started, the state observation device Initial value of state variable quantity x required when starting to estimate the state in step 13, target value N _r of idle rotation speed, and actual value N
The initial value of the integral amount of the deviation SA from The initial value of is determined by performing simulations in various situations in advance. On the other hand, for the initial value of the integral amount of the latter deviation SA, it is better to give the apparent actual rotational speed N below the target value _Nr than to give the actual deviation, as shown in Figures 10 A and B described later. In this way, the amount of undershoot is suppressed and the coasting characteristics are improved, so a value with a positive and large apparent deviation SA is determined and given.

Here, the characteristics of the engine may differ from those at the time of design due to changes in the engine over time or manufacturing errors, but in such a case, it is desirable to correct each control constant determined at the time of design. Control constants include, for example, the model in the condition observation device 13 and the corresponding optimal gain K, but even if the engine characteristics change slightly, these control constants can be absorbed by the integral element introduced into the control system. . Here, we will focus on the initial value of the integral amount of deviation SA given at the time of starting idle rotation speed control, which greatly affects coasting characteristics, and investigate the coasting characteristics due to changes in engine characteristics, especially the undershoot of rotation speed that can lead to engine stalling. Detects the increase in amount and calculates the deviation SA
Correct the initial value of the integral amount to a larger value.

For example, focusing on coasting characteristics immediately after starting idle rotation speed control, in an idle state within a predetermined time T ₀ (for example, 3 seconds) after starting control,
The idle rotation speed is set to a predetermined value N _us (e.g. target value N _r
= 650rpm to 500rpm), or if the undershoot amount U _N with respect to the target value N _r becomes larger than the predetermined value U _r (for example, 150 rpm), the initial value of the integral amount of the deviation SA is increased by a certain value. This corrected value is stored in a backup memory or the like, and the corrected value is used when starting idle rotation speed control next time.

FIG. 6 shows the procedure of the above idle rotation speed control. To explain the procedure, step 3
At 0, the air conditioner on/off status, cooling water temperature
Determine the target value N _r of the idle rotation speed based on the value of T _W , etc. In step 31, the deviation SA between the target value N _r and the actual value N of the idle rotational speed is calculated.

In step 32, it is determined whether the elapsed time from the start of idle rotation speed control is within a predetermined time t _a (for example, 3 seconds), and if the elapsed time is longer than t _a , the process proceeds to step 36. If it is within the predetermined time t _a , then in step 33 the undershoot amount U _N with respect to the target value N _r is calculated, and then in step 34 it is determined whether the undershoot amount is greater than or equal to a predetermined value U _r (for example, 150 rpm), If it is less than or equal to U _r , it is assumed that there is no problem and the process proceeds to step 36. If it is greater than or equal to the predetermined value U _r (that is, if the amount of undershoot within the predetermined time t ₀ = 3 seconds is greater than or equal to the predetermined amount = 150 rpm), in step 35, the initial value table of the integral amount of the deviation SA used is corrected ( Specifically, it increases by a certain amount). Incidentally, instead of steps 33 and 34, it may be determined whether the actual rotation N is smaller than the predetermined rotation N _us . In this case, the aim is to prevent the engine from stalling due to a decrease in rotation.
The amount of undershoot when the target rotation is high, such as when the air conditioner is on, is not a problem unless it reaches N _us .

In step 36, 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 37, the reference setting value N _a of the actual value N of the rotational speed (for example
Calculate the deviation δN from 650rpm). Step 3
8, 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 Each state variable amount x ₁ to x ₄ is calculated by weighted addition of the output value ΔN. However, the matrix (A-GC) in 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 39, the estimated dynamic internal state variables x ₁ to _{x 4} of the engine and DUN are multiplied by the element k _ij of the optimum gain K and added, and the reference setting value (P _A ) is determined.
Calculate how much to increase the control input value for _a and IT _a .

The coefficients b _ij , g _i , k _ij, etc. in FIG. 6 are determined in advance and stored in a microcomputer or the like.

Using the above procedure, we conducted an experiment on the transient response to various disturbances when the idle rotation speed is constant, and the transient response when the target value of the idle rotation speed is changed. Figures 7 to 10 compare
It is a diagram.

Figure 7 shows the transient response of the idle rotation speed N when the clutch is engaged (the clutch is half engaged at the _t0 point, but the brake is being pressed), and A is the conventional PI control;
B is a case of multivariable control according to the present invention. FIG. 8 shows the transient response when the clutch is disengaged (disengaged at point _t0 ), where A is the conventional method and B is the method of the present invention. Figure 9 shows the case when the air conditioner is turned on and the target idle rotation speed N _r is shifted to 800 rpm, and when the air conditioner is turned off and the target idle rotation speed N _r is shifted to 800 rpm.
A transient response is shown when the speed is returned to 650 rpm, with A being the conventional method and B being the method of the present invention. 1st
Figure 0 shows the target value N _r = 650 rpm from the no-load high speed state.
The transient response when coasting is shown, and A
is the case of the conventional method, and B is the case of the method of the present invention.
As is clear from FIGS. 7 to 10, it can be seen that in all cases, the method of the present invention significantly improves the transient response. In addition,
In FIG. 7A, the idle rotation speed does not settle to the target value _Nr .

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,
Any one or a combination of two or more selected from the fuel supply amount (or equivalent amount) and the exhaust gas recirculation amount (or equivalent amount) can be used, and in the above embodiment, the amount equivalent to the bypass air amount The case where the control inputs are the drive pulse width of the control solenoid of the VCM valve and the ignition timing.

(Effects of the Invention) As explained above, according to the method for controlling the idle rotation speed of an internal combustion engine of the present invention, the idle rotation speed is controlled by applying a multivariable control method based on a dynamic model of the internal combustion engine. Added a procedure for estimating the dynamic state of an internal combustion engine, reduced the calculation time by using a reduced-dimensional version of the engine model in the state observer, and absorbed the approximation error through 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 the idling state.Moreover, in order to increase the degree of control freedom and improve controllability, it is also possible to perform control by adding multivariable control inputs. The effect is that it is easy to realize more stable idle rotation speed control.

In particular, the initial value set immediately after it is determined that idle rotation speed control is to be started from coasting is set so that the amount of undershoot with respect to the target value of rotation speed is small, and the Since the initial values are modified to absorb the deterioration in controllability through learning, it is possible to achieve more stable idling operation.

[Brief explanation of drawings]

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 of the control device to be realized, and Fig. 4 is a detailed block diagram of the integral operation and gain block in Fig. 3.
The figure is a block diagram showing the relationship between the control input/output and the engine in Figure 3, Figure 6 is a flowchart explaining the control method according to the present invention, and Figures 7A and B show experimental results of transient response when the clutch is engaged. Figure 8A,
B is a diagram showing the experimental results of the transient response when the clutch is disengaged, Figures 9A and B are diagrams showing the experimental results of the transient response when the air conditioner is turned on and off, and Figures 10A and B are the diagrams showing the experimental results of the transient response when coasting. FIG. 3 is a diagram showing experimental results. 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 ... Actual value of idle rotation speed, N _r ... Target value of idle rotation speed, N _a ... Reference setting value of idle rotation speed,
SA...Difference between the 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 (=
x _i )...state variable quantity, x^ (= x^ _i )... state variable estimate.

Claims (1)

[Claims] 1 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 the control input amount for the internal combustion engine, the ignition timing of the internal combustion engine, Any one or a combination of two or more selected from the amount of fuel supplied to the internal combustion engine or the amount equivalent to the amount of fuel supplied, and the amount of exhaust gas recirculation or the amount equivalent to the amount of exhaust gas recirculation, and the internal combustion engine. From the _idle rotational speed which is the control output value of state variable quantity x^ _i (i=1, 2,
..., n) and the target value of the idle rotation speed
In the method of feedback controlling the idle rotational speed of the internal combustion engine by determining the value of the control input from the integral of the deviation SA between _Nr and the actual value N,
Immediately after detecting that the throttle valve is fully closed and determining that the operating state of the internal combustion engine has reached a predetermined state and that idle speed control is to be started,
The initial value of the state variable quantity x _i and the initial value of the integral quantity of the deviation SA, which are necessary when starting to estimate the dynamic state of the internal combustion engine, are determined by the engine rotational speed when the throttle valve is fully closed. and the engine rotation speed when it is determined to start idle rotation speed control, and the initial value of the integral amount of the deviation SA is set as if the actual value N is smaller than the target value N _r of the idle rotation speed. When the undershoot amount with respect to the target value N _r exceeds a predetermined value in the transient response immediately after that, or when the actual value N becomes smaller than the predetermined value, the integration of the deviation SA is performed. A method for controlling an idle rotation speed of an internal combustion engine, characterized in that the initial value of the amount is corrected and subsequent idle rotation speed control is continued.