JPS6340264B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention considers the internal state of an internal combustion engine, treats the engine as a dynamic system, and uses state variables that define the internal state to evaluate the dynamic state of the engine. This invention relates to a method of controlling idle rotation speed using a state variable control method that determines input variables of an engine while estimating its behavior, and in particular, relates to a control method that improves transient response during coasting and when idling. .

(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, correction is made according to the air conditioner (A/C) signal, neutral (NEUT) signal, battery voltage (VB) signal, etc. from the air conditioner switch 11, and the target value N _r of the idle rotation speed is finally calculated. On the other hand, the deviation SA between the engine's actual idle speed N and its target value N _r
The pulse width of control solenoid 3 is set so that
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, in such a conventional method for controlling the idle rotation speed of an internal combustion engine, control followability is poor when starting from deceleration to idle operation and controlling to the target rotation speed, and the control until the rotation speed follows the target rotation speed is poor. There were problems in that the transient response greatly reduced the target rotational speed, resulting in coasting and engine stalling, and poor transient response when revving during idling.

In particular, if the engine rotation speed range in which idle rotation speed control is started is fixed using the conventional method, when the target rotation speed becomes higher, the difference between the engine rotation speed at which control is started and the target rotation speed becomes smaller.
If control is entered due to coasting or a slight step on the accelerator, the control response may not be in time, resulting in undershoot with respect to the target rotation speed, especially transient control when disturbances are added. There was a problem that sex deteriorated.

For example, if the target rotation speed is set to 650 rpm and the control start range is fixed at 1100 rpm or less to prevent undershoot due to coasting, short pedaling, etc., the target rotation speed becomes 800 rpm when the air conditioner compressor load is applied. In this case, the difference between the start of control and the target rotational speed is 300 rpm, and there is a problem that the rotational speed decreases rapidly during coasting from high rotational speeds, and the control response is not in time, resulting in a large undershoot with respect to the target rotational speed. Ta.

(Objective of the Invention) The present invention has been made in view of these conventional problems, and an object of the present invention is to improve the transient response during coasting and when racing.
The aim is to provide stable control, especially when the cooling water temperature is low or when the air conditioner compressor load is added and the target rotation speed changes.

(Structure and operation of the invention) Therefore, the present invention provides a control input (any one selected from air amount, ignition timing, fuel supply amount, and exhaust gas recirculation amount, or a combination of any two or more of them) and a control output. (idle rotation speed) In a method that performs multivariable control based on a dynamic model between (idle rotation speed), the target rotation speed
The present invention is characterized in that when _Nr changes, the rotational speed range for determining whether to start control is changed in accordance with the target rotational speed _Nr .

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

FIG. 3 is a block diagram of an apparatus for realizing 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 the amount of air (or equivalent amount), ignition timing, fuel supply amount (or equivalent amount), and exhaust gas recirculation amount (or equivalent amount). Any one or a combination of two or more may be used. In this embodiment, the VCM for adjusting the amount of bypass air at idle is used as the two control inputs.
The pulse width P _A (that is, the amount corresponding to the amount of bypass air) that drives the control solenoid of 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 observation device (observer) which stores a dynamic model of the engine 12 to be controlled and estimates the dynamic internal state of the engine from the above three control input/output information P _A , IT, and N. , the state variable quantity x representing the internal state (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 ). Specific examples of state variables that represent the internal state of the engine to be controlled include intake manifold absolute pressure, suction negative pressure, amount of air actually taken into the cylinder, dynamic behavior of combustion, engine torque, etc. . 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. 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 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 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 , 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 matrices A, B,
C is a constant matrix 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, 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 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 driving 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 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 the present invention, as mentioned above, since the experimentally obtained model is a reduced-dimensional approximate model,
An I (integral) operation is added to absorb the homogeneity error, but here optimal regulator control including the I operation is performed.

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.The optimal regulator control algorithm for a general multi-variable system is, for example, proposed by Katsuhisa Furuta. 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 an I (integral) 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), = 1 -CA 0 A (14) = -CB B (15), and P is P= ^t P- ^t P( ^t P +R) ^{-1 t} P+ 1 0 0 0 (16 ) 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.

In particular, when starting the engine or when the target rotation speed N _r increases due to the air conditioner load, the upper limit rotation speed N _L of the rotation speed range in which control is determined to start.
Since the difference between _Nr and There is a problem that transient controllability deteriorates.

For example, assume that the rotation speed at which idle rotation speed control is started is set to 1100 rpm or less, and the target rotation speed changes from 650 rpm to 800 rpm when an air conditioner load is applied. At this time, if you coast from high rpm, the rpm will drop quite quickly, starting from 1100 rpm.
It is difficult to control well within the time it drops to 800rpm.

Therefore, in the present invention, depending on the target rotational speed N _r ,
The engine rotation speed N _L at which control starts is made variable.

For example, when the target rotational speed is 650 rpm, assume that the control start rotational speed is selected to be 1100 rpm so that a large undershoot with respect to the target rotational speed does not occur due to coasting, short stepping, etc. At this time, if the air conditioner and compressor load is added and the target rotational speed becomes 800rpm, the control start rotational speed is set to 1250rpm so that the control response is in time to avoid undershooting the target rotational speed.

In the example, the control start rotation speed for this target rotation speed is a value obtained by adding 450 rpm to the target rotation speed, but it is also possible to perform a table pull-up according to the target rotation speed, or to adjust the control start speed to the target rotation speed in actual control. It is also possible to rewrite the table depending on how much undershoot has occurred.

FIG. 6 shows the procedure of the above idle rotation speed control. When explaining the procedure, the step
At 30, the air conditioner on/off status, cooling water temperature
Determine the target value _Nr of the idle rotation speed based on the value of _Tw , etc. In step 31, set the target rotation N _r to 450 rpm.
The added value is set as the control start upper limit value N _L , and step 32
Now, the actual rotation N and N _L are compared, and if N>N _L , no control is performed, and if N≦N _L , control is started.
In step 33, the target value of idle rotation speed N _r
and the deviation SA of the actual value N is calculated. In step 34, 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 35, 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. Step 36 uses the state variables x ₁ ^* to x ₃ ^* (previously calculated values) estimated in the previous control according to the algorithm that estimates the dynamic internal state of the engine, and the calculated control input values δP _A and δIT.
and ΔN, which is the control output value, are weighted and added to calculate each state variable quantity x ₁ to x ₄ . However, (6)
The matrix (A-GC) of the equation is an example of forming a finitely settled observer in the form A-GC=0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 (18). Note that (A, B, C) uses observable canonical forms.

In step 37, the estimated dynamic internal state variables x ₁ to x ₄ of the engine and DUN= _k 〓 ^j=0 [N _r −N
(j)] is multiplied by the element k _ij of the optimal gain K and added.
Calculate how much the control input value should be increased with respect to the reference setting value (P _A ) _a and IT _a .

The coefficients b _ij , g _i , k _ij, etc. in Fig. 6 are determined in advance, and the microcomputer's ROM (Read Only)
Memory) etc.

Using the above procedure, we compared the results of experiments on transient responses to various disturbances when the idle rotation speed is constant, and transient responses when the target value of the idle rotation speed is changed, using the conventional PI control and the multivariable Figures 7 to 1 show the comparison with the control.
This is figure 0.

Figure 7 shows the transient response of the idle rotation speed N when the clutch is engaged (the clutch is half engaged at the t ₀ 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 where the air conditioner is turned on and the target idle speed is set to 800 rpm, and when the air conditioner is turned off and the target idle speed is set to 650 rpm.
shows the transient response when returning to , A is the conventional method,
B is a case of the method of this invention. FIG. 10 shows the transient response when coasting from a no-load high speed state to a target value of 650 rpm, where A is the conventional method and B is the method of the present invention. As is clear from FIGS. 7 to 10, it can be seen that in each case, the method according to the present invention significantly improves transient controllability. Note that in FIG. 7A, the idle rotation speed does not settle to the target value.

In Fig. 11 A and B, the target rotation N _r is 800 rpm,
These are control results when the control start rotational speed N _L is 1100 rpm and 1250 rpm. It can be seen from the figure that better controllability can be obtained by changing the control start depending on the target rotational speed _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,
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 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 approximation of the engine model in the observer, 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, the configuration changes the rotational speed at which control starts depending on the target rotational speed, so even if the target rotational speed changes, large undershoots do not occur due to coasting, short pedaling, etc., and transient control is maintained. This has the effect of increasing performance and realizing more stable idling.

[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 operation and gain block.
FIG. 6 is a flowchart explaining the control method according to the present invention, FIGS. 7A and B are diagrams showing experimental results of transient response when the clutch is engaged, and FIGS. 8A and B are experimental results of transient response when the clutch is disengaged. Figure showing the results, No. 9
Figures A and B are diagrams showing the experimental results of the transient response when the air conditioner is turned on and off, Figure 10 A and B are diagrams showing the experimental result of the transient response during coasting, and Figure 11 A and B are diagrams showing the experimental results of the transient response when the air conditioner is turned on and off. FIG. 6 is a diagram showing experimental results when the rotational speed at which control is started is not changed and when it is changed. 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,
N _L ...Upper limit rotation speed of the rotation speed range that determines the start of idle rotation speed control, SA...Difference between the target value and actual value of idle rotation speed, P _A ...Drive pulse of the control solenoid that defines the amount of bypass air Width, IT...Ignition timing, x _i ...State variable quantity, x^ _i ...
Estimator of state variables.

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, the ignition timing of the internal combustion engine, and the 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 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 quantity x^ _i (i
= 1, 2, ... n) and an amount obtained by integrating the deviation SA between the target value N _r of the idle rotation speed determined by a predetermined operating state and the actual rotation speed value N, In the method for feedback controlling the idle rotation speed of the internal combustion engine,
It is detected that the throttle is fully closed, the operating status of other engines is in a predetermined state, and the engine rotation speed is within a predetermined range determined based on the target value N _r of the idle rotation speed. When this is detected, it is determined to start idle rotation speed control.
Immediately after this judgment, the initial values of the state variables necessary to start estimating the dynamic state of the engine and the initial value of the integral of the deviation SA are set to the engine rotational speed when the throttle is fully closed, and the idle An idle rotation speed control method characterized in that the idle rotation speed is set according to the engine rotation speed when it is determined to start rotation speed control.