JP2004245191A - Overspeed prevention controller for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure a satisfactory overspeed prevention function without causing damage to a catalyst and degradation of operability more likely in the ON-OFF control of fuel supply by controlling engine overspeed based on air amount. <P>SOLUTION: A target rotational speed Nt(i) of an engine is updated and set by adding a value, obtained by multiplying a difference between an upper limit rotational speed Nmax and a previous actual rotational speed N(i-1) by a change rate gain Dtg, to the N(i-1). The actual rotational speed N(i) is larger than the target rotational speed Nt(i), a limiter request torque set by a P torque and an I torque set corresponding to a negative difference [Nmax-N(i-1)] decreases from a driver request torque. The rotational speed of the engine is inhibited from rising by torque-controlling with the limiter request torque. The overspeed is prevented by converging to the upper limit rotational speed Nmax while inhibiting overshoot. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for controlling a rotation speed so as to prevent an overspeed of an engine.
[0002]
[Prior art]
As a countermeasure to prevent engine overspeed, conventionally, when the engine speed exceeded a predetermined upper limit speed, fuel supply to the engine was temporarily suspended, and thereafter, the predetermined hysteresis speed was reduced from the upper limit speed. A rotation speed limiting method based on ON-OFF control of fuel supply such as restarting fuel supply to the engine when the rotation speed falls below the mainstream has been the mainstream (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-1-167440.
[0004]
[Problems to be solved by the invention]
However, in recent years, the thickness of the catalyst has been reduced in accordance with the tightening of exhaust gas regulations. There is concern that it will become.
[0005]
Further, during the engine rotation speed limitation, in the ON-OFF control of the fuel supply, the change in the acceleration in the front-rear direction of the vehicle is large, and the occupant is uncomfortable.
In view of the above situation, it is required to prevent the engine from rotating excessively by adjusting the amount of air supplied to the engine with an electronically controlled throttle.
[0006]
As an electronically controlled throttle control method, a method of limiting the engine torque by feedback control of the engine rotational speed can be considered. However, compared with the ON-OFF control of the fuel supply, the air amount control by the electronically controlled throttle has a large response delay, When the engine rotation speed is high, the upper limit rotation speed may be greatly exceeded in time.
[0007]
Even when the PID control having the change speed of the rotation speed as a control parameter for the above problem is performed, the target rotation speed is always kept at the upper limit rotation speed, so that the rotation speed clearly exceeds the upper limit rotation speed. Even when ascending, the calculated value for P and the calculated value for I act in the torque-up direction until the value exceeds the upper limit rotational speed. It is difficult to achieve both overshoot regulation and subsequent stability.
[0008]
Also, when it is desired to adjust the deceleration at the beginning of the limiter operation, it takes time since the gains of P, I, and D affect each other.
SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and has as its object to appropriately adjust the deceleration at the beginning of the limiter operation and to perform stable speed control while suppressing overshoot. And
[0009]
[Means for Solving the Problems]
For this reason, the present invention calculates the target rotation speed change rate based on the difference between the upper limit rotation speed and the previous value of the periodically detected engine rotation speed, and adds the calculated target rotation speed to the previously detected engine rotation speed. The target rotation speed is updated and set by adding the change rate. Then, the engine speed is controlled based on the updated target speed.
[0010]
With this configuration, the target rotation speed is set so as to gradually increase as the actual rotation speed increases. By controlling the engine rotation speed based on the target rotation speed, the actual engine rotation speed is reduced. Before the rotation speed reaches the upper limit rotation speed, control for suppressing the rotation speed increase is started, and excessive rotation increase is suppressed.
[0011]
Since it can be realized by air amount control without turning on and off the fuel supply, there is no possibility that the exhaust purification catalyst is damaged or the operability is deteriorated.
Further, since it is only necessary to change the setting of the target rotation speed, the deceleration at the start of the rotation speed limit control can be easily adjusted.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a system configuration according to an embodiment of the present invention.
[0013]
The accelerator opening sensor 1 detects an operation amount (accelerator opening) of an accelerator pedal depressed by a driver.
The crank angle sensor 2 generates a position signal for each unit crank angle and a reference signal for each cylinder stroke phase difference, and measures the number of the position signals generated per unit time, or measures the reference signal generation cycle. By doing so, the engine speed can be detected.
[0014]
The air flow meter 3 detects the amount of intake air (per unit time) to the engine 4.
The water temperature sensor 5 detects a cooling water temperature of the engine.
[0015]
The air-fuel ratio sensor 6 detects an air-fuel ratio of an air-fuel mixture supplied to the engine from an oxygen component or the like in the exhaust gas.
The engine 4 is provided with a fuel injection valve 7 which is driven by a fuel injection signal and injects fuel, and an ignition plug 8 which is mounted in a combustion chamber and ignites.
[0016]
A throttle valve 10 is provided in the intake passage 9 of the engine 4, and a throttle control device 11 for electronically controlling the opening of the throttle valve 10 by a step motor or the like is provided. A throttle sensor 12 for detecting the opening of the throttle valve 10 is mounted.
[0017]
The detection signals from the various sensors are input to a control unit 13, which sets a target engine torque based on the signals from the sensors and sets the throttle engine so that the target engine torque is obtained. The control device 11 controls the opening of the throttle valve 10 to control the amount of intake air, controls the fuel injection valve 7 to control the fuel injection amount, sets an ignition timing, and sets the ignition timing to the ignition timing. Control for igniting the plug 8 is performed.
[0018]
Here, as a configuration according to the present invention, in the throttle control to the target engine torque, control is performed so as to limit the engine from over-rotating.
FIG. 2 shows a control block of throttle control including such an overspeed prevention function.
[0019]
The driver request torque calculation unit A searches the map as shown in FIG. 3 based on the accelerator opening detected by the accelerator opening sensor 1 and the engine speed detected by the crank angle sensor 2. The engine torque (driver required torque) required by the driver is calculated by the above method.
[0020]
The high-speed limiter controller B calculates a limiter required torque for preventing the engine from over-rotating.
The MIN determination unit C receives the driver required torque and the limiter required torque, selects the smaller one of them, and outputs the smaller one to the throttle opening controller D as a torque command value.
[0021]
The throttle opening control unit D calculates a target throttle opening based on the torque command value, and outputs a target throttle opening signal to the throttle control device 11.
[0022]
The throttle control device 11 controls the opening of the throttle valve 10 based on the actual throttle opening detected by the throttle sensor 12 and the target throttle opening.
FIG. 4 shows a detailed flow of the throttle control. Hereinafter, description will be made with reference to FIG.
[0023]
In step (denoted by S in the figure, the same applies hereinafter) 1, in order to remove noise, the actual engine rotation speed Ne detected based on the signal from the crank angle sensor 2 is subjected to a first-order lag filter processing (see the following equation). Weighted average calculation processing) to calculate the rotation speed N (i).
[0024]
N (i) = Fg × Ne (i) + (1−Fg) × N (i−1)
Here, N (i): engine speed after filtering (current value)
N (i-1): engine speed after filtering (previous value)
Fg: Engine rotation speed filter gain In step 2, the difference between the upper limit rotation speed Nmax and the actual engine rotation speed (previous value) N (i-1) is multiplied by the target rotation speed change rate gain Dtg as in the following equation. Thus, the target rotation speed change rate DNt (i) is calculated.
[0025]
DNt (i) = Dtg × [Nmax−N (i−1)]
In Step 3, the target engine speed is calculated from the previous engine speed by adding the target engine speed change rate DNt (i) to the actual engine engine speed (previous value) N (i-1) as in the following equation. The current engine rotation speed when the engine rotation speed changes at the change rate is calculated, and this calculated value is set as the current target rotation speed Nt (i).
[0026]
Nt (i) = N (i-1) + DNt (i)
In step 4, the magnitude of the driver required torque Tac (i) and the limiter required torque (previous value) Trev (i-1) are compared.
[0027]
When the limiter required torque Trev (i-1) is larger than the driver required torque Tac (i), there is no need to operate the limiter (rotational speed limit). The torque Ti (i) is set as a driver request torque Tac (i).
[0028]
When the driver required torque Tac (i) becomes equal to or more than the limiter required torque Trev (i-1), the process proceeds to step 6 to start the limiter, and the driver required torque Tac (i-1) set in the previous step 5 is initialized to the initial value. To start the integration operation. Specifically, as shown in the following equation, the deviation between the target rotation speed Nt (i) set in step 3 and the current actual engine rotation speed N (i) obtained in step 1 is multiplied by the I component gain Ig. In addition to the previous value of the I-component torque Ti (i-1), the current I-component torque Ti (i) is used.
[0029]
Ti (i) = Ti (i−1) + Ig × [Nt (i) −N (i)]
In step 7, a P-component torque Tp (i) is calculated. Specifically, as shown in the following equation, the difference is calculated by multiplying the deviation between the target rotation speed Nt (i) and the actual engine rotation speed N (i) by a P component gain Pg.
[0030]
Tp (i) = Pg × [Nt (i) -N (i)]
In step 8, the P-component torque Tp (i) and the I-component torque Ti (i) calculated as described above are added to obtain a limiter required torque Trev (i), as in the following equation.
[0031]
Trev (i) = Tp (i) + Ti (i)
In step 9, the smaller of the driver required torque Tac (i) and the limiter required torque Trev (i) is selected and set as the torque command value Tcom (i). That is, the limiter required torque Trev (i) is set as the torque command value Tcom (i) only when the limiter required torque Trev (i) becomes smaller than the driver required torque Tac (i), thereby preventing the engine from overrunning. To prevent.
[0032]
An overspeed prevention operation by the throttle control during acceleration will be described with reference to a time chart of FIG.
When the current engine rotation speed N (i) is equal to or lower than the upper limit rotation speed Nmax, the value obtained by multiplying the positive rotation speed deviation [Nmax-N (i-1)] by the gain Dtg (<1) is used as the value of the previous engine rotation speed. The value added to the rotation speed N (i-1) is set as the current target rotation speed Nt (i), and the target rotation speed Nt (i) is higher than the current engine rotation speed N (i) for a while after the start of acceleration. Is set.
[0033]
At this time, the limiter required torque Trev (i) is calculated as a value obtained by adding the positive P component torque Tp (i) to the I component torque Ti (i) equal to the driver required torque Tac (i). The driver request torque Tac (i) that is larger than the torque Tac (i) and is therefore smaller than the limiter request torque Trev (i) is selected as the torque command value Tcom (i). That is, the rotation speed limitation by the limiter is not started yet, and the vehicle is accelerated with a torque corresponding to the driver's request, so that good acceleration performance can be secured.
[0034]
When controlled by the driver request torque in this way, the actual engine speed N (i) catches up with the target speed Nt (i) (point a in FIG. 5) due to the increase in acceleration. This is because the acceleration is higher than the value obtained by multiplying the gain [Dtg] by the deviation [Nmax-N (i-1)] added to the previous engine rotation speed N (i-1).
[0035]
When the actual engine rotation speed N (i) becomes higher than the target rotation speed Nt (i), the deviation [Nmax−N (i−1)] becomes a negative value, so that the P component torque Tp (i) becomes It becomes a negative value, and the I-component torque Ti (i) also starts to decrease due to the addition of the negative torque component Ig × [Nt (i) -N (i)]. Therefore, the limiter required torque Trev (i) is smaller than the driver required torque Tac (i), the limiter required torque Trev (i) is selected as the torque command value Tcom (i), and the rotation speed limitation by the limiter is started. Is done.
[0036]
Then, with the limiter required torque Trev (i) that is gradually reduced and set by the PI control, the increase in the rotation speed is quickly suppressed, and the upper limit rotation speed Nmax is quickly converged and maintained while suppressing overshoot.
[0037]
As described above, by setting the target rotation speed according to the present invention, before the actual engine rotation speed reaches the upper limit speed, the target rotation speed falls below the actual engine rotation speed, and the limiter operates. Excessive rotation can be prevented.
[0038]
As in the case of the idle speed control, it is also possible to perform feedback control of the engine torque based on the deviation between the target speed and the actual engine speed that are sequentially updated from the initial stage of acceleration. Since the torque is controlled to be smaller than the driver's required torque from the initial stage of acceleration, acceleration performance that meets the requirement cannot be obtained. That is, in the overspeed prevention control to which the present invention is applied, there is not always a target speed in accordance with the request from the beginning, and the control is performed so as not to exceed the upper limit speed.
[0039]
Therefore, as in the present embodiment, the limiter is activated when the actual engine rotation speed exceeds the target rotation speed that is periodically updated and set so as to increase according to the deviation between the upper limit rotation speed and the actual engine rotation speed. By starting the rotation speed limiting control in this way, it is possible to prevent excessive rotation by smoothly converging to the upper limit rotation speed while securing the acceleration performance that meets the demand.
[Brief description of the drawings]
FIG. 1 is a diagram showing a system configuration according to an embodiment of the present invention.
FIG. 2 is a block diagram showing throttle control according to the embodiment.
FIG. 3 is a characteristic map for setting a driver required torque.
FIG. 4 is a flowchart showing details of throttle control according to the first embodiment;
FIG. 5 is a time chart showing an overspeed prevention operation according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Accelerator opening sensor 2 ... Crank angle sensor 4 ... Engine 7 ... Fuel injection valve 9 ... Intake passage 10 ... Throttle valve 11 ... Throttle control device 12 ... Throttle sensor 13 ... Control unit

Claims (5)

The engine rotational speed is periodically detected, and a target rotational speed change rate is calculated based on a deviation between the upper limit rotational speed and the previously detected engine rotational speed. Over-rotation prevention control for preventing over-rotation of the engine during an acceleration operation by updating and setting the target rotation speed by adding the target rotation speed and controlling the engine rotation speed based on the target rotation speed. apparatus. The engine rotation speed control, when the engine rotation speed is equal to or less than the target rotation speed, controls the engine torque to a driver request torque according to the driver's request, after the engine rotation speed exceeds the target rotation speed, 2. The engine overspeed prevention control device according to claim 1, wherein the control is to reduce the engine torque from the driver request torque. After the engine rotation speed exceeds the target rotation speed, control is performed so that the immediately preceding driver request torque is used as an initial value to reduce and correct the engine torque according to the deviation between the target rotation speed and the engine rotation speed. The engine overspeed prevention control device according to claim 2. 4. The engine overspeed prevention control according to claim 3, wherein the engine torque reduction correction amount is calculated by a P component torque and an I component torque according to a deviation between the target rotation speed and the engine rotation speed. 5. apparatus. The engine overspeed prevention control device according to any one of claims 2 to 4, wherein the driver request torque is set based on an accelerator opening and an engine rotation speed.

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