JPH0575904B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling fuel cut when an engine overspeeds, and is particularly applicable to a high-speed rotating automobile engine equipped with an electronically controlled fuel injection device. The present invention relates to an improved method for controlling fuel cut during engine overspeed, which is suitable for preventing overspeed of the engine by cutting off fuel supply when the engine is rotating at high speed.

[Prior Art] One of the methods for supplying an air-fuel mixture at a predetermined air-fuel ratio to the combustion chamber of an internal combustion engine such as an automobile engine uses an electronically controlled fuel injection device. This is achieved by arranging injectors for injecting fuel into the engine, for example, in the intake manifold of the engine for several engine cylinders, and controlling the valve opening time of the injectors according to the operating state of the engine. This is to ensure that an air-fuel mixture with a predetermined air-fuel ratio is supplied to the engine combustion chamber.

In this electronically controlled fuel injection device, normally,
The basic injection amount is determined according to the basic operating conditions of the engine, such as the engine load and engine speed detected from the engine intake air amount or intake pipe pressure, and is input from sensors installed in each part of the engine. Based on the signals, various increases and decreases are added to determine the effective injection amount, and fuel injection is executed. Additionally, in order to reduce hydrocarbons in exhaust gas, improve fuel efficiency, and prevent catalyst heating due to reactions of unburned fuel in the catalyst, it is common to stop fuel injection during deceleration to perform a so-called fuel cut. be. Furthermore, in order to prevent the engine from over-speeding, it is common to cut off the fuel by stopping the fuel supply even when the engine is rotating at high speed.

Conventionally, this fuel cut to prevent overspeed when the engine speed is rotating is performed by stopping fuel injection when the engine speed exceeds a certain fuel cut setting speed. In this method, until the throttle valve is closed, fuel cut and return are repeated near the set fuel cut rotation speed, and the engine continues to rotate at high speed in a hunting state. Therefore, regardless of whether or not this is the driver's intention,
If it continues for a while, it will accelerate the wear and deterioration of various parts of the engine, and especially in cars equipped with catalysts, it has the problem of rapidly increasing the temperature of the catalyst and accelerating its deterioration. Such problems are particularly serious in high-speed rotation type engines that frequently use high-speed rotation ranges.

In order to solve these problems and prevent engine deterioration and catalyst overheating, it is possible to provide a large hysteresis or set a predetermined rotation limit sufficiently low, but it is possible to It is extremely difficult to achieve both practicality and practicality during normal use when driving.

[Purpose of the Invention] The present invention has been made to solve the above-mentioned conventional problems, and is aimed at preventing engine deterioration and catalyst overheating that occur when over-speeding continues, and for normal use in which it is desired to operate at high speeds with good response. It is an object of the present invention to provide a method for controlling fuel cut during engine overspeed, which is compatible with practicality and can effectively prevent overspeed under all operating conditions.

[Structure of the Invention] The present invention provides a fuel cut control method for overspeeding an engine, which prevents overspeeding of the engine by cutting off fuel supply when the engine rotates at high speed, as summarized in FIG. , a procedure for determining whether the engine rotation speed exceeds the fuel cut setting rotation speed, a procedure for cutting off the fuel supply when the engine rotation speed exceeds the fuel cut setting rotation speed, and a procedure for cutting the fuel supply until the fuel cut continues. step of gradually lowering the fuel cut setting rotation speed when
The above object is achieved by including a step of preventing the set fuel cut rotation speed from being lowered below a lower limit value set higher than a normal use rotation range.

[Operation of the Invention] In the present invention, a predetermined fuel cut setting rotation speed for overspeed prevention is changed depending on the overspeed occurrence history, and the engine overspeed continues and fuel cut continues. When the engine is running, the set fuel cut rotation speed is gradually lowered to its lower limit, which is set higher than the normal rotation range.
It is possible to protect the engine and exhaust gas purification device, and prevent engine deterioration and catalyst overheating, without compromising practicality during normal times when you want to operate at high speeds with good responsiveness. Moreover, the fuel cut setting rotation speed does not decrease until it reaches the normal use rotation range, and there is no adverse effect on normal operation.

That is, engine deterioration and catalyst overheating are accelerated when overspeeding is repeated frequently within a short period of time. Under operating conditions where overspeeding occurs repeatedly in a short period of time, it is effective to limit the degree of rotation that can be driven (setting the overspeed limit low), but even if used frequently, the problem described above may occur. It is impossible to set the rotation limit sufficiently low so as not to cause this, as this would greatly impair the practicality of normal use when it is desired to operate the motor at high speeds with good responsiveness. By changing the rotation limit according to the degree of severity of driving as in the present invention, it is possible to prepare for harsh use or careless driving by the user without any loss of practicality during normal use. Good over-speed prevention can be achieved under all driving conditions.

[Example] With reference to the drawings, an example of an automobile engine equipped with an intake pipe pressure sensing type electronically controlled fuel injection device, in which the method for controlling fuel cut at engine overspeed according to the present invention is adopted, will be described below. Explain in detail.

In this embodiment, as shown in FIG. 2, an intake air temperature sensor 12 for detecting the temperature of intake air taken in from the outside and a throttle body 14 are provided.
Accelerator pedal located in the driver's seat (not shown)
a throttle valve 16 for controlling the flow rate of intake air, which is opened and closed in conjunction with the flow rate of the intake air; a throttle sensor 18 for detecting the opening degree of the throttle valve 16; Intake pipe pressure sensor 22 for detecting air pressure
, an injector 26 disposed in the intake manifold 24 for intermittently injecting pressurized fuel toward the intake port of each cylinder of the engine 10; The spark plug 28 for ignition and the high-voltage secondary ignition signal generated by the ignition coil 32 are rotated in conjunction with the rotation of the crankshaft of the engine 10 for distributing power to the spark plugs 28 of each cylinder of the engine 10. a crank angle sensor 36 for detecting the rotational state of the engine 10 from the rotational state of the distributor shaft 34A built in the distributor 34, and a crank angle sensor 36 disposed in the cylinder block 10B of the engine 10. A water temperature sensor 38 is installed to detect the engine cooling water temperature, and the fuel injection time is determined according to the engine load detected from the output of the intake pipe pressure sensor 22 and the engine rotation speed determined from the output of the crank angle sensor 36. It calculates and outputs a valve opening time signal to the injector 26, and at the time of deceleration or engine overspeed,
According to the present invention, an electronic control unit (hereinafter referred to as
(referred to as ECU) 40. In the figure, 42 is an exhaust manifold.

The ECU 40, as shown in detail in FIG.
A central processing unit (hereinafter referred to as CPU) 40A consisting of a microprocessor, for example, for performing various calculation processes, and a read-only memory (hereinafter referred to as CPU) for storing control programs and various data, etc.
a random access memory (hereinafter referred to as RAM) 40 for temporarily storing calculation data etc. in the CPU 40A;
C, an analog-to-digital converter (hereinafter referred to as "analog-to-digital converter") equipped with a multiplexer function to convert analog signals inputted from the intake temperature sensor 12, intake pipe pressure sensor 22, water temperature sensor 38, etc. into digital signals and sequentially input them. (referred to as A/D converter)4
0E, and digital signals input from the throttle sensor 18, crank angle sensor 36, etc., and according to the calculation results of the CPU 40A,
For connecting an input/output port (hereinafter referred to as I/O port) 40F with a buffer function for outputting control signals to the injector 26, etc., and each of the component devices to transfer data and instructions. It consists of a common bus 40G.

The effects of the embodiment will be explained below.

In this embodiment, the fuel cut to prevent overspeeding of the engine is executed by a routine in the main routine as shown in FIG.
That is, each time the crank angle detected from the output of the crank angle sensor 36 rotates, for example, 360 degrees, the process proceeds to step 110, and the engine rotation speed is determined.
It is determined whether or not Ne exceeds the set fuel cut rotation speed Nc. The fuel cut setting rotation speed
The initial value of Nc is, for example, its upper limit value Ncmax.

If the determination result in step 110 is positive, that is, if it is determined that it is necessary to cut fuel to prevent overspeeding of the engine,
Proceeding to step 112, the valve opening time signal supplied to the injector 26 is turned off and fuel injection is stopped. Next, the process proceeds to step 114, where the fuel cut set rotation speed Nc is decreased at a constant rate per unit time or at a constant rate per engine revolution, thereby gradually lowering the fuel cut set rotation speed Nc. Next, the process proceeds to step 116, where the lowered fuel cut setting rotation speed Nc is set to its lower limit value, which is set higher than the normal use rotation range.
Determine whether the value is below Ncmin. The lower limit value Ncmin is set, for example, at the beginning of a so-called yellow zone, where a yellow color is displayed on an engine tachometer.

If the judgment result in step 116 is positive, the process proceeds to step 118, where the lower limit value is determined.
Set Ncmin to fuel cut setting rotation speed Nc.
After step 118 or step 116
If the determination result is negative, this routine exits.

On the other hand, if the determination result in step 110 is negative, that is, if the engine rotation speed Ne is less than or equal to the fuel cut setting rotation speed Nc, and it is determined that there is no need to perform fuel cut, step 12 is performed.
Proceeding to step 2, a normal valve opening time signal is output to the injector 26 to execute fuel injection. Next, the process proceeds to step 124, where the fuel cut setting rotation speed is set.
Nc is increased at a constant rate per unit time or at a constant rate per engine revolution to gradually increase the fuel cut setting rotational speed Nc. Next, the process proceeds to step 126, where it is determined whether the increased fuel cut setting rotational speed Nc has become equal to or greater than its upper limit value Ncmax. The upper limit value Ncmax is set, for example, at a point slightly beyond the so-called red zone, which is displayed in red on the engine tachometer.

If the judgment result in step 16 is positive, the process proceeds to step 128, where the upper limit value Ncmax is determined.
into the fuel cut setting rotation speed Nc. After step 128 is completed, or if the determination result in step 126 is negative, this routine exits.

FIG. 5 shows an example of the relationship among the engine rotational speed Ne, the fuel cut setting rotational speed Nc, and the fuel injection state in this embodiment. As is clear from the figure, the fuel cut set rotation speed Nc changes depending on the fuel injection state, and if fuel cut continues, the fuel cut set rotation speed Nc is gradually lowered, so that the engine and exhaust gas Purification equipment can be protected. Also, fuel cut setting rotation speed
Since a lower limit value Ncmin and an upper limit value Ncmax are set for Nc, the set fuel cut rotation speed Nc may drop to the normal use rotation range, which may adversely affect drivability or reduce the set fuel cut rotation speed.
Nc does not get too high and become useless.

In this example, the fuel cut setting rotation speed
Since the initial value of Nc is set to its upper limit value Ncmax, when the engine is accidentally over-revved at engine racing value or during sudden acceleration, the first fuel cut will operate on the high-revving side. The engine can be used effectively up to a high speed rotation range. Note that the initial value of the fuel cut setting rotation speed Nc is not limited to this, but considering that it is not desirable to rotate the engine at high speed before the engine is warmed up, the lower limit value Ncmin is used as the initial value. Or,
Alternatively, it is possible to set an intermediate value between the lower limit value Ncmin and the upper limit value Ncmax as the initial value.

In the above embodiments, the present invention was applied to an automobile engine equipped with an electronically controlled fuel injection device that senses intake pipe pressure. However, the scope of application of the present invention is not limited to this, and It is obvious that the present invention can be similarly applied to automobile engines equipped with a sensing electronically controlled fuel injection system, as well as general engines equipped with other fuel supply systems.

[Effects of the Invention] As explained above, according to the present invention, when the engine continues to overspeed, the set fuel cut rotation speed is gradually lowered. without compromising the
It can protect the engine and exhaust gas purification device, prevent engine deterioration and catalyst overheating, and provide excellent overspeed prevention under all driving conditions. Therefore, it is particularly effective for speed rotation type engines that frequently use the speed rotation range and for which it is desired to set the fuel cut setting rotation speed at a high speed. Further, the fuel cut setting rotation speed does not decrease up to the normal use rotation range, and there is an excellent effect that there is no adverse effect on normal operation.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the gist of a method for controlling fuel cut during engine overspeed according to the present invention, and FIG. 2 is a flowchart showing a method for controlling fuel cut at the time of overspeeding of an engine according to the present invention, and FIG. A sectional view including a partial block diagram showing an example of an automobile engine;
FIG. 3 is a block diagram showing the configuration of the electronic control unit used in the above embodiment, and FIG.
Similarly, a flowchart showing a routine in the main routine for cutting fuel when the engine overspeeds;
FIG. 5 is a diagram showing an example of the relationship among the engine rotational speed, fuel cut setting rotational speed, and fuel injection state in the embodiment. 10...Engine, 26...Injector, 34...
Distributor, 36...crank angle sensor,
40...Electronic control unit (ECU), Ne...engine rotation speed, Nc...fuel cut setting rotation speed,
Ncmin...lower limit value, Ncmax...upper limit value.

Claims (1)

[Claims] 1. In an engine overspeed fuel cut control method that prevents engine overspeed by cutting fuel supply when the engine rotates at high speed, it is determined whether the engine speed exceeds a set fuel cut speed. a step of cutting off the fuel supply when the engine speed exceeds the set fuel cut speed; and a step of gradually lowering the set fuel cut speed when the fuel cut continues; A method for controlling fuel cut during engine overspeed, comprising the steps of: preventing a set fuel cut rotation speed from being lowered below a lower limit value set higher than a normally used rotation speed range.