JP4082231B2 - Engine overspeed prevention control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for controlling a rotational speed so as to prevent over-rotation of an engine.
[0002]
[Prior art]
As a measure to prevent engine overspeed, conventionally, when the engine speed exceeds the predetermined upper limit speed, fuel supply to the engine is temporarily interrupted, and then the upper limit speed is reduced by a predetermined hysteresis speed. A rotation speed limiting method based on fuel supply ON / OFF control, such as restarting fuel supply to the engine when the rotation speed falls below, has been the mainstream (see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 1-167440.
[0004]
[Problems to be solved by the invention]
However, in recent years, the wall thickness of the catalyst has been reduced in accordance with the stricter regulations of the exhaust gas regulations. At that time, the increase in the temperature deviation inside the catalyst due to the ON / OFF of the fuel supply during engine overspeed is the cause of catalyst damage There is concern about becoming.
[0005]
In addition, while the engine speed is limited, the fuel supply ON-OFF control has a large acceleration change in the front-rear direction of the vehicle, which causes discomfort to the passengers.
In view of the above-described present situation, it is required to prevent engine overspeed by adjusting the amount of air supplied to the engine with an electric throttle.
[0006]
As an electric throttle control method, a method of limiting the engine torque by feedback control of the engine speed can be considered. However, compared with the fuel supply ON-OFF control, the air amount control by the electric throttle has a large response delay. If 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 rotational speed as a control parameter is performed for the above problem, the target rotational speed is always constant at the upper limit rotational speed. Even when it is rising, the P component calculation value and I component calculation value act in the torque-up direction until the upper limit rotational speed is exceeded, so it is necessary to cancel with only the remaining D component calculation value. It is difficult to achieve both overshoot regulation and subsequent stability.
[0008]
Even when it is desired to adjust the deceleration at the initial stage of the limiter operation, it takes time because the gains of P, I, and D influence each other.
The present invention has been made paying attention to such a conventional problem, and it is an object of the present invention to appropriately adjust the deceleration at the initial stage 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 a target rotational speed change rate based on the deviation between the upper limit rotational speed and the previous value of the engine rotational speed detected periodically, and calculates the target rotational speed to the previously detected engine rotational speed. The target rotation speed is updated and set by adding the rate of change. And it was set as the structure which controls an engine rotational speed based on the updated target rotational speed.
[0010]
In this way, since the target rotational speed is set to gradually increase as the actual rotational speed increases, the actual engine rotational speed is controlled by controlling the engine rotational speed based on the target rotational speed. Before reaching 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 controlling the air amount without turning on and off the fuel supply, the exhaust purification catalyst is not damaged or the operability is not deteriorated.
Moreover, since it is only necessary to change the setting of the target rotational speed, the deceleration at the start of the rotational speed limit control can be easily adjusted.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a system configuration of 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 occurrences of the position signal 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 the engine coolant temperature.
[0015]
The air-fuel ratio sensor 6 detects the air-fuel ratio of the air-fuel mixture supplied to the engine from the oxygen component or the like in the exhaust gas.
The engine 4 is provided with a fuel injection valve 7 that is driven by a fuel injection signal to supply and inject fuel, and an ignition plug 8 that is attached to the combustion chamber and performs ignition.
[0016]
Further, a throttle valve 10 is interposed in the intake passage 9 of the engine 4, and a throttle control device 11 that electronically controls the opening degree 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]
Detection signals from the various sensors are input to the control unit 13, and the control unit 13 sets a target engine torque based on the signals from the sensors, and the throttle so that the target engine torque is obtained. The opening degree of the throttle valve 10 is controlled via the control device 11 to control the intake air amount, and the fuel injection valve 7 is driven to control the fuel injection amount. The ignition timing is set and the ignition timing is set at the ignition timing. Control to ignite 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 over-rotation of the engine.
FIG. 2 shows a control block for throttle control including such an overspeed prevention function.
[0019]
Based on the accelerator opening detected by the accelerator opening sensor 1 and the engine rotation speed detected by the crank angle sensor 2, the driver request torque calculation unit A searches from the map as shown in FIG. The engine torque required by the driver (driver required torque) is calculated by, for example.
[0020]
The high rotation limiter control unit B calculates a limiter request torque for preventing the engine from over-rotating.
The MIN determination unit C inputs the driver request torque and the limiter request torque, selects a smaller one of them, and outputs it to the throttle opening control unit 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 the 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.
A detailed flow of the throttle control is shown in FIG. Hereinafter, a description will be given with reference to FIG.
[0023]
In step (denoted as S in the figure, the same applies hereinafter) 1, an actual engine rotational speed Ne detected based on a signal from the crank angle sensor 2 is subjected to first-order lag filter processing (as shown in the following equation for noise removal). The rotation speed N (i) is calculated by performing a weighted average calculation process.
[0024]
N (i) = Fg * Ne (i) + (1-Fg) * N (i-1)
N (i): Engine speed after filtering (current value)
N (i-1): Engine speed after filter processing (previous value)
Fg: In engine speed filter gain step 2, the difference between the upper limit speed Nmax and the actual engine speed (previous value) N (i-1) is multiplied by the target speed change rate gain Dtg as shown in the following equation. To calculate the target rotational speed change rate DNt (i).
[0025]
DNt (i) = Dtg × [Nmax−N (i−1)]
In step 3, the target engine speed is changed from the previous engine speed by adding the target engine speed change rate DNt (i) to the actual engine speed (previous value) N (i-1) as shown in the following equation. The current engine speed when the engine speed changes at the change rate is calculated, and this calculated value is used as the current target speed Nt (i).
[0026]
Nt (i) = N (i-1) + DNt (i)
In step 4, the magnitudes of the driver request torque Tac (i) and the limiter request torque (previous value) Trev (i-1) are compared.
[0027]
When the limiter request torque Trev (i-1) is larger than the driver request torque Tac (i), there is no need to operate the limiter (rotational speed limit). The torque Ti (i) is set as the driver request torque Tac (i).
[0028]
When the driver request torque Tac (i) exceeds the limiter request torque Trev (i-1), the process proceeds to step 6 to start the limiter, and the driver request torque Tac (i-1) set in the previous step 5 is set to the initial value. Integral operation starts. Specifically, as shown in the following equation, the deviation between the target engine speed Nt (i) set in step 3 and the actual engine speed N (i) obtained in step 1 is multiplied by an I-component gain Ig. This is added to the previous value Ti (i-1) of the I component torque, and this is the current I component torque Ti (i).
[0029]
Ti (i) = Ti (i-1) + Ig * [Nt (i) -N (i)]
In step 7, a P-minute torque Tp (i) is calculated. Specifically, as shown in the following equation, the deviation between the target rotational speed Nt (i) and the actual engine rotational speed N (i) is multiplied by a P-component gain Pg.
[0030]
Tp (i) = Pg × [Nt (i) −N (i)]
In step 8, the P-part torque Tp (i) and the I-part torque Ti (i) calculated as described above are added to obtain the limiter request torque Trev (i) as shown in the following equation.
[0031]
Trev (i) = Tp (i) + Ti (i)
In step 9, the smaller one of the driver request torque Tac (i) and the limiter request torque Trev (i) is selected as the torque command value Tcom (i). That is, only when the limiter request torque Trev (i) is smaller than the driver request torque Tac (i), the limiter request torque Trev (i) is set as the torque command value Tcom (i), thereby preventing the engine from over-rotating. To prevent.
[0032]
The overspeed prevention operation by the throttle control during acceleration will be described with reference to the time chart of FIG.
When the current engine speed N (i) is less than or equal to the upper limit engine speed Nmax, the value obtained by multiplying the positive engine speed deviation [Nmax-N (i-1)] by the gain Dtg (<1) What is added to the rotational speed N (i-1) is set as the current target rotational speed Nt (i), and for a while after the acceleration starts, the target rotational speed Nt (i) is larger than the current engine rotational speed N (i). Is set.
[0033]
At this time, the limiter request torque Trev (i) is calculated as a value obtained by adding the positive P-part torque Tp (i) to the I-part torque Ti (i) equal to the driver request torque Tac (i). Therefore, the driver request torque Tac (i) that is larger than the torque Tac (i) and smaller than the limiter request torque Trev (i) is selected as the torque command value Tcom (i). That is, the rotational speed limitation by the limiter is not started yet, and the acceleration is accelerated by the torque that meets the driver's request, and good acceleration performance can be ensured.
[0034]
When the control is performed with the driver required torque in this way, the actual engine rotational speed N (i) catches up with the target rotational speed Nt (i) (point a in FIG. 5) due to the increase in acceleration. This is because the acceleration exceeds the value obtained by multiplying the deviation [Nmax−N (i−1)] added to the previous engine speed N (i−1) by the gain Dtg.
[0035]
When the actual engine speed N (i) becomes larger than the target speed Nt (i), the deviation [Nmax−N (i−1)] becomes a negative value, so that the P-part torque Tp (i) is It becomes a negative value, and the I-part torque Ti (i) also starts to decrease when the negative torque part Ig × [Nt (i) −N (i)] is added. Therefore, the limiter request torque Trev (i) is smaller than the driver request torque Tac (i), the limiter request torque Trev (i) is selected as the torque command value Tcom (i), and the limit of the rotation speed by the limiter is started. Is done.
[0036]
Then, the limiter request torque Trev (i) that is set to be gradually decreased by the PI control, the rotational speed increase is quickly suppressed, and the convergence is quickly maintained at the upper limit rotational speed Nmax while suppressing overshoot.
[0037]
Thus, by setting the target rotational speed according to the present invention, the target rotational speed falls below the actual engine rotational speed before the actual engine rotational speed reaches the upper limit speed, so that the limiter operates. Over-rotation can be prevented.
[0038]
As with the idle speed control, it is possible to feedback control the engine torque based on the deviation between the target engine speed that is sequentially updated from the initial acceleration and the actual engine speed. The torque is controlled to be smaller than the driver request torque from the beginning of acceleration, and the acceleration performance corresponding to the request cannot be obtained. That is, in the over-rotation prevention control that is the subject of the present invention, there is no target rotational speed according to the request from the beginning, and it is a control for preventing the upper-limit rotational speed from being exceeded.
[0039]
Therefore, as in this embodiment, the limiter is operated when the actual engine speed exceeds the target engine speed that is periodically updated and set so as to increase in accordance with the deviation between the upper limit engine speed and the actual engine speed. Thus, by starting the rotation speed limit control, it is possible to smoothly converge to the upper limit rotation speed and prevent over-rotation while ensuring acceleration performance that meets the requirements.
[Brief description of the drawings]
FIG. 1 is a diagram showing a system configuration of 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 request torque.
FIG. 4 is a flowchart showing details of the throttle control.
FIG. 5 is a time chart showing an overspeed prevention operation according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Accelerator opening degree 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, a target rotational speed change rate is calculated based on the deviation between the upper limit rotational speed and the previously detected engine rotational speed, and the previously calculated target rotational speed change rate is calculated as the previously detected engine rotational speed. The engine overspeed prevention control is characterized in that the engine speed is controlled by updating the target rotational speed by adding the value and controlling the engine rotational speed based on the target rotational speed. apparatus. In the engine rotation speed control, when the engine rotation speed is equal to or lower than the target rotation speed, the engine torque is controlled to the driver request torque according to the request of the driver, and after the engine rotation speed exceeds the target rotation speed, 2. The engine overspeed prevention control device according to claim 1, wherein the engine torque is controlled to be smaller than the driver required torque. After the engine rotation speed exceeds the target rotation speed, control is performed to reduce the engine torque to be corrected in accordance with the deviation between the target rotation speed and the engine rotation speed with the immediately preceding driver request torque as an initial value. 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 from a P-part torque and an I-part torque according to a deviation between the target rotational speed and the engine rotational speed. apparatus. The engine overspeed prevention control device according to any one of claims 2 to 4, wherein the driver required torque is set based on an accelerator opening and an engine rotation speed.

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