JP2005076499A - Device for controlling fuel cut of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent catalyst deterioration by suppressing hunting of engine speed while preventing output decline of an internal combustion engine, in fuel cut control performed for preventing overspeed of the internal combustion engine. <P>SOLUTION: This fuel control device for the internal combustion engine performs fuel control when the speed of the internal combustion engine exceeds predetermined execution engine speed, and resumes fuel supply when the speed of the internal combustion engine is below reset engine speed. The fuel control device sets the reset engine speed to be a value lowered by a predetermined value, when fuel cut is started. The reset engine speed is controlled so as to be gradually returned from the value lowered by the predetermined value in accordance with passing time after the start of the fuel cut. Preferably, the predetermined value to be lowered is set in accordance with selected gear shift stages. Since the fuel cut is continued until fluctuation of the engine speed caused by the fuel cut is approximately converged, hunting of the engine speed can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus for controlling a fuel cut that is performed to prevent over-rotation of an internal combustion engine.

  In general, in order to prevent engine overspeed, fuel cut is performed when the engine speed exceeds a first predetermined value. If the engine speed falls below a second predetermined value set lower than the first predetermined value, the fuel supply is resumed. Hereinafter, in fuel control for preventing engine overspeed, the first predetermined value at which fuel cut is started is referred to as an execution speed, and the second predetermined value at which fuel supply is resumed is referred to as a return speed. .

  Such fuel control may cause hunting in the engine speed. FIG. 7 shows an example of such hunting of the engine speed. For example, when the engine speed exceeds the effective speed at time t1, fuel cut is started. When the fuel cut is started, the engine speed rapidly decreases. Due to this rapid decrease, the engine speed falls below the return speed at time t2, and the fuel supply is resumed. The engine speed increases rapidly due to the fuel supply. When the engine speed exceeds the effective speed at time t3, the fuel cut is performed again.

  By repeating such fuel cut and fuel supply, hunting with a short cycle occurs in the engine speed. Hunting can raise the temperature of the exhaust gas and thus promote catalyst degradation.

In order to suppress such hunting, an over-rotation preventing device as described in Patent Document 1 below has been proposed. According to this apparatus, when the fuel cut and the fuel supply are repeated at regular time intervals, the effective rotation speed and the return rotation speed are lowered so that the difference between the two gradually increases. The catalyst overheating is prevented by gradually increasing the duration of the fuel cut.
Japanese Patent Publication No. 7-30730

  However, according to the conventional method, since both the execution speed and the return speed are reduced, the engine speed gradually decreases. If the engine speed decreases, the engine output may not increase in response to the driver's depression of the accelerator pedal. In addition, the vehicle speed may decrease due to such a decrease in engine speed.

  Accordingly, an object of the present invention is to provide an apparatus for controlling a fuel cut for preventing over-rotation of an engine so as to suppress hunting while achieving an engine output and a vehicle speed that meet a driver's request. is there. A further object of the present invention is to provide an apparatus capable of preventing the catalyst temperature from being abnormally increased due to suppression of hunting, thereby deteriorating the catalyst.

  According to one aspect of the present invention, the fuel control device for an internal combustion engine performs fuel cut when the rotational speed of the internal combustion engine exceeds a predetermined execution rotational speed, and the rotational speed of the internal combustion engine falls below a predetermined return rotational speed. And restart the fuel supply. When the fuel cut is started, the fuel control device sets the return rotational speed to a value reduced by a predetermined amount. The fuel control device controls the return rotational speed so as to gradually return from the value lowered by the predetermined amount in accordance with the elapsed time from the start of the fuel cut.

  When the fuel is cut, the engine speed fluctuates. If the fuel cut is continued, the fluctuation gradually converges. By gradually returning the return rotational speed from the value once lowered, the fuel cut can be continued until the fluctuation of the engine rotational speed is almost converged. Since the fuel supply is prevented from being resumed due to the fluctuation of the engine speed caused by the fuel cut, it is possible to suppress the occurrence of hunting in the engine speed. Further, since the effective rotational speed is maintained at a predetermined value, it is possible to prevent a decrease in the engine rotational speed, and thus it is possible to avoid a decrease in engine output and a decrease in vehicle speed.

  According to one embodiment of the present invention, the predetermined amount for reducing the return rotational speed is calculated according to the selected gear position.

  The magnitude of the engine speed fluctuation caused by the fuel cut may change depending on the gear position. According to the present invention, since the amount of reduction is determined according to the shift speed, the occurrence of hunting can be suppressed while avoiding a decrease in engine output and a decrease in vehicle speed at any shift speed.

  According to one embodiment of the present invention, the rate at which the return rotational speed returns from the value reduced by the predetermined amount is calculated according to the selected gear position.

  The time for which the fluctuation of the engine speed caused by the fuel cut converges may vary depending on the gear position. According to the present invention, since the rate at which the return rotational speed returns is determined according to the shift speed, the occurrence of hunting is suppressed while avoiding a decrease in engine output and a decrease in vehicle speed at any shift speed. Can do.

  According to one embodiment of the present invention, the detected rotational speed of the internal combustion engine is smoothed. The fuel control device restarts the fuel supply if the smoothed rotation speed falls below the return rotation speed while the fuel cut is being performed.

  Since the engine speed is affected by the operating state of the engine, it may fluctuate greatly instantaneously. Such fluctuations may cause hunting in the engine speed. According to the present invention, since it is determined whether to restart the fuel supply based on the smoothed engine speed, hunting can be suppressed.

  According to one embodiment of the present invention, the degree of smoothing the detected rotational speed is reduced in accordance with the elapsed time since the fuel cut was started.

  When the fuel is cut, the engine speed fluctuates. The magnitude of this variation gradually decreases with the elapsed time since the fuel cut was started. According to the present invention, the degree of smoothing is increased as the fluctuation of the engine speed increases, so that hunting can be prevented from occurring due to the fluctuation of the engine speed caused by the fuel cut.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall system configuration diagram of an internal combustion engine (hereinafter referred to as “engine”) and its control device according to an embodiment of the present invention.

  An electronic control unit (hereinafter referred to as “ECU”) 5 includes an input interface 5a that receives data sent from each part of the vehicle, a CPU 5b that performs calculations for controlling each part of the vehicle, and a read-only memory (ROM) ) And a random access memory (RAM) 5c, and an output interface 5d for sending control signals to various parts of the vehicle. The ROM of the memory 5c stores a program for controlling each part of the vehicle and various data. The program for controlling the fuel according to the present invention, and data and tables used in executing the program are stored in the ROM. The ROM may be a rewritable ROM such as an EPROM. The RAM is provided with a work area for calculation by the CPU 5b. Data sent from each part of the vehicle and control signals sent to each part of the vehicle are temporarily stored in the RAM.

  The engine 1 is an engine having, for example, four cylinders. An intake passage 2 is connected to the engine 1. A throttle valve 3 is provided on the upstream side of the intake passage 2. A throttle valve opening sensor (θTH) 4 connected to the throttle valve 3 supplies an electric signal corresponding to the opening of the throttle valve 3 to the ECU 5.

  A passage 21 that bypasses the throttle valve 3 is provided in the intake passage 2. A bypass valve 22 for controlling the amount of air supplied to the engine 1 is provided in the bypass passage 21. The bypass valve 22 is driven according to a control signal from the ECU 5.

  The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) in the intake passage 2. The fuel injection valve 6 is connected to a fuel pump (not shown) and receives fuel from a fuel tank (not shown) via the fuel pump. The fuel injection valve 6 is driven in accordance with a control signal from the ECU 5.

  The intake pipe pressure (Pb) sensor 8 and the intake air temperature (Ta) sensor 9 are provided on the downstream side of the throttle valve 3 in the intake passage 2. The intake pipe pressure Pb and the intake air temperature Ta detected by the Pb sensor 8 and the Ta sensor 9 are sent to the ECU 5, respectively.

  The engine water temperature (Tw) sensor 10 is attached to a cylinder peripheral wall (not shown) of the cylinder block of the engine 1 filled with cooling water. The engine coolant temperature Tw detected by the Tw sensor 10 is sent to the ECU 5.

  The rotation speed (Ne) sensor 13 is attached around the cam shaft or crank shaft (both not shown) of the engine 1. The Ne sensor 13 outputs a CRK signal pulse at a cycle of a crank angle (for example, 30 degrees) shorter than a cycle of a TDC signal pulse output at a crank angle related to the TDC position of the piston, for example. The CRK signal pulse is counted by the ECU 5, and the engine speed Ne is detected.

  An exhaust passage 14 is connected to the downstream side of the engine 1. The engine 1 exhausts through the exhaust passage 14. The catalyst device 15 provided in the middle of the exhaust passage 14 purifies harmful components such as HC, CO, and NOx in the exhaust gas passing through the exhaust pipe 14.

  The wide area air-fuel ratio sensor (LAF) sensor 16 is provided upstream of the catalyst device 15. The LAF sensor 16 linearly detects the oxygen concentration in the exhaust gas in a wide range of air-fuel ratios ranging from lean to rich. The detected oxygen concentration is sent to the ECU 5.

  A vehicle speed (VP) sensor 17 is mounted in the vicinity of a drive shaft (not shown) of a vehicle on which the engine 1 is mounted, and a pulse is output every time the wheel rotates once, and this is sent to the ECU 5. Based on the output of the VP sensor 17, the ECU 5 detects the vehicle speed.

  The automatic transmission 25 is a transmission provided with, for example, a fifth speed. The input side of the automatic transmission 25 is connected to an output shaft (not shown) of the engine 1, and the output side of the automatic transmission 25 is connected to drive wheels (not shown) of the vehicle. The driving force of the engine 1 is transmitted to driving wheels via the automatic transmission 25. The ECU 5 controls the gear position of the automatic transmission 25 based on the vehicle speed detected by the vehicle speed sensor 17 and the accelerator pedal opening detected by the accelerator pedal opening sensor (illustrated).

  Alternatively, a manual transmission (MT) may be used, or an automatic transmission with a manual (automatic MT) may be used.

  The signal sent to the ECU 5 is transferred to the input interface 5a and converted from analog to digital. The CPU 5b processes the converted digital signal in accordance with a program stored in the memory 5c, and generates a control signal for sending to the vehicle actuator. The output interface 5d sends these control signals to the actuators of the bypass valve 22, the fuel injection valve 6 and other mechanical elements.

  FIG. 2 is a functional block diagram according to one embodiment of the present invention. The execution rotational speed is a predetermined value determined in advance, for example, 6200 rpm. The return rotational speed is set to a value lower than the effective rotational speed, and the reference value is, for example, 6000 rpm. When the fuel cut is not performed, the value of the return rotational speed is maintained at the reference value. While the fuel cut is being performed, the value of the return rotational speed is updated. When the engine speed exceeds the effective speed, fuel cut is started.

  When the fuel cut is started, the reduction amount determination unit 32 determines the reduction amount. The return rotation speed update unit 33 calculates a new return rotation speed by subtracting the reduction amount from the reference value.

  The fluctuation of the engine speed due to fuel cut generally varies according to which gear stage is selected. Therefore, the amount of reduction is preferably determined based on the selected gear position.

  The smoothing unit 34 smoothes the engine speed detected over a predetermined time. The engine speed may fluctuate greatly instantaneously under the influence of the operating state of the engine. If fuel supply is resumed due to such instantaneous fluctuations, hunting may occur. By smoothing the engine speed, it is possible to remove such a large momentary fluctuation, so that hunting can be suppressed.

  The control selection unit 35 resumes the fuel supply by the fuel supply unit 36 if the smoothed engine speed falls below the return speed, and continues the fuel cut otherwise.

  When the fuel cut is continued, the reduction amount is determined again by the reduction amount determination unit 32 in the next cycle. The return rotation speed update unit 33 calculates a new return rotation speed by subtracting the reduction amount from the reference value. Thus, the return rotational speed is updated while the fuel cut is being performed.

  While the fuel cut is in progress, the fluctuations in the engine speed gradually decrease with time. In accordance with such fluctuations in the engine speed, the amount of reduction is reduced with the elapsed time from the start of fuel cut. As the pull-down amount is decreased, the return rotational speed returns toward the reference value. In this way, the fuel cut is continued until the fluctuations in the engine speed due to the fuel cut almost converge. Since the fuel supply is prevented from being restarted due to the fluctuation of the engine speed caused by the fuel cut, hunting can be suppressed.

  FIG. 3 is a diagram showing control of the return rotational speed according to one embodiment of the present invention. Reference numeral 41 indicates the engine speed. Note that in this example, from time t1 to t2, the engine speed represented by reference numeral 41 represents the smoothed engine speed. Reference numeral 43 indicates the return rotational speed. Reference numeral 45 indicates the number of revolutions executed, and this is maintained at a predetermined value.

  When the fuel cut is started at time t1, the value of the return rotational speed is reduced by the reduction amount D from the reference value. The engine speed rapidly decreases due to the fuel cut. However, since the return speed is updated to a low value, the engine speed does not fall below the return speed. Therefore, fuel supply is not resumed, and fuel cut is continued.

  From time t1 to t2, the fluctuation of the engine speed gradually converges. As the fluctuation range of the engine speed decreases, the amount of reduction is also reduced. At the time point t2 when the return rotational speed almost reaches the reference value, the engine rotational speed falls below the return rotational speed, and fuel supply is resumed.

  The amount of reduction of the return rotational speed and the rate (speed) at which the return rotational speed returns to the reference value are preferably set in consideration of the fluctuation form of the engine rotational speed caused by the fuel cut. The fluctuation form of the engine speed caused by the fuel cut can be measured in advance by, for example, simulation.

  As described above, the fluctuation pattern of the engine speed due to the fuel cut may change according to the selected gear position. In one embodiment, the reduction amount and the rate of returning to the reference value are determined according to the selected gear position. In other embodiments, the reduction amount and the rate of return to the reference value may be determined in consideration of other factors relating to the operating state of the engine.

  The engine speed may vary due to other factors different from the fuel cut. It is not preferable that the fuel cut is undesirably continued due to fluctuations in the engine speed due to such other factors. By controlling the return rotational speed in consideration of the gear position and the like, undesired continuation of the fuel cut can be avoided.

  FIG. 4 is a flowchart showing a process for controlling fuel cut to prevent engine overspeed. This process is performed at predetermined time intervals.

  In step S101, the execution rotational speed is set to a predetermined value, and the return rotational speed is set to the reference value. For example, the execution rotation speed is set to 6200 rpm, and the return rotation speed is set to 6000 rpm.

  In step S102, the current vehicle speed VP is compared with a predetermined lower limit value (for example, 50 km / h). If the vehicle speed VP is equal to or lower than the lower limit value, the process proceeds to step S103, and zero is set to a counter that measures an elapsed time from the start of fuel cut. In step S104, the engine speed detected by the speed sensor 13 (FIG. 1) is set to a variable “NEhrpm”.

  When the vehicle speed is low, there is generally no fear that the catalyst device will be abnormally heated. Therefore, when the vehicle speed is low, the return speed is not reduced in order to achieve the desired drivability as before.

  In step S112, the engine speed set in the variable NEhrpm set in step S104 is compared with the execution speed. If the engine speed set in the variable NEhrpm is greater than the effective speed, fuel cut is performed (S114). In step S113, the engine speed set in the variable NEhrpm set in step S104 is compared with the return speed. If the engine speed set in the variable NEhrpm is equal to or higher than the return speed, fuel cut is performed (S114). If the engine speed set in the variable NEhrpm is lower than the return speed, fuel is supplied (S115) and the process is terminated.

  When the process is started again in the next cycle, if the vehicle speed is larger than the lower limit value in step S102, the process proceeds to step S105, and it is determined whether or not the fuel is being cut. If the fuel is not being cut, the counter is reset in step S103, and the detected engine speed is set in the variable NEhrpm in step S104. As described above, the fuel cut is started (S114) or the fuel supply is continued (S115) according to the determination results of steps S112 and S113. The process is then terminated.

  When the process is started again in the next cycle, if the fuel cut is in progress in step S105, the smoothing coefficient is calculated by referring to the map based on the elapsed time from the start of the fuel cut, that is, the counter value. The smoothing coefficient is a coefficient for smoothing the engine speed. An example of the map is shown in FIG. Immediately after the fuel cut is started, the smoothing coefficient is decreased and the degree of smoothing the engine speed is increased. As a result, it is possible to prevent the fuel supply from being restarted due to an instantaneous change in the engine speed. The fluctuation of the engine speed due to the start of the fuel cut decreases with time. Therefore, the smoothing coefficient is increased and the degree of smoothing is reduced with the elapsed time from the start of fuel cut.

  In step S107, the amount of reduction is calculated by referring to the map based on the elapsed time from the start of fuel cut, that is, the counter value. An example of the map is shown in FIG. For example, the reference number 51 defines the amount of reduction when the gear stage is the third speed, and the reference number 52 defines the amount of reduction when the gear stage is the fourth speed. As described with reference to FIG. 3, the amount of reduction is reduced with the passage of time from the start of the fuel cut so that the return rotational speed gradually returns to the reference value.

  As shown in FIG. 6, it is preferable to define the amount of reduction for each gear position. For example, for a transmission having a fifth speed, a reduction amount is defined for each of first to fifth speeds. Since the rotational speed tends to increase as the gear position increases, the amount of reduction is increased to avoid hunting, as indicated by the arrows in the figure. Further, since the fluctuation of the rotational speed tends to increase as the gear position increases, the rate of returning to the reference value is lowered (slow) in order to avoid hunting as indicated by the arrows in the figure.

  In step S108, it is determined whether the counter value has reached an upper limit value. If the upper limit has not been reached, the counter value is incremented (S108).

  In step S109, the amount of reduction calculated in step S107 is subtracted from the reference value to calculate the return rotational speed for the current cycle.

  In step S110, the detected engine speed is smoothed using the smoothing coefficient calculated in step S106. Smoothing is performed according to the following formula (1), for example. Here, n is an identifier for identifying a control cycle. (n) represents the current cycle, and (n-1) represents the previous cycle.

Smoothing engine rotational speed = rotational speed NE (n) detected in current cycle x smoothing coefficient + rotational speed NE (n-1) detected in previous cycle x (1-smoothing coefficient)
(1)

Other suitable methods may be used to smooth the engine speed. For example, a moving average method can be used. Further, smoothing can be performed by any appropriate filtering process.

  In step S111, the smoothed engine speed calculated in step S110 is set in a variable NEhrpm. In step S112, the engine speed set in the variable NEhrpm is compared with the execution speed. If the engine speed set in the variable NEhrpm is greater than the effective speed, the fuel cut is continued (S114). If the engine speed set in the variable NEhrpm is equal to or lower than the effective speed and equal to or higher than the return speed, the fuel cut is continued (S114). If the engine speed set in the variable NEhrpm is lower than the return speed, the fuel supply is resumed (S115).

  The present invention can also be applied to a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

1 schematically shows an internal combustion engine and a control device according to one embodiment of the present invention. FIG. The functional block diagram of the fuel control apparatus according to one Example of this invention. The figure which shows control of the return rotation speed according to one Example of this invention. The flowchart of the fuel cut control according to one Example of this invention. The figure which shows the smoothing coefficient table according to one Example of this invention. The figure which shows the amount table of reduction according to one Example of this invention. The figure which shows generation | occurrence | production of the hunting of the engine speed by fuel cut according to the prior art of this invention.

Explanation of symbols

1 Engine 5 ECU
25 Transmission

Claims (5)

A fuel control device that performs fuel cut when the rotational speed of the internal combustion engine exceeds a predetermined execution rotational speed, and resumes fuel supply when the rotational speed of the internal combustion engine falls below a predetermined return rotational speed,
A rotational speed detection means for detecting the rotational speed of the internal combustion engine;
When the fuel cut is started, a setting unit which sets the return rotational speed to a value lowered by a predetermined amount,
A return rotational speed control means for controlling the return rotational speed so as to gradually return from the value reduced by the predetermined amount according to the elapsed time from the start of the fuel cut;
A fuel control device for an internal combustion engine, comprising: The fuel control apparatus according to claim 1, wherein the predetermined amount is calculated according to a selected gear position. The fuel control device according to claim 1, wherein a rate at which the return rotational speed returns from a value reduced by the predetermined amount is calculated according to a selected gear position. Means for smoothing the detected rotational speed of the internal combustion engine;
2. The fuel control device according to claim 1, wherein, while the fuel cut is being performed, the fuel supply is resumed if the smoothed rotation speed falls below the return rotation speed. The fuel control apparatus according to claim 4, wherein the smoothing unit further reduces the degree of smoothing the detected rotational speed in accordance with an elapsed time from the start of the fuel cut.

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