JPH0515907B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for starting air-fuel ratio feedback in an electronically controlled engine for optimally starting air-fuel ratio feedback in an electronically controlled engine using an O ₂ sensor.

[Prior art] Air-fuel ratio feedback control in an electronically controlled engine is controlled within an extremely narrow range around the stoichiometric air-fuel ratio where the conversion efficiency of the catalyst is highest, in order to optimize the purification rate of exhaust gas by a three-way catalyst. It is used for this purpose.

Such air-fuel ratio feedback control is generally not used during warm-up or the like to improve drivability. Conventionally, the starting point of air-fuel ratio feedback is when the output of the O ₂ sensor exceeds a certain value.
Alternatively, it was assumed that the resistance value of the O ₂ sensor was below a certain value.

[Problems to be Solved by the Invention] However, in this conventional method, feedback control may be started in a state where the O ₂ sensor cannot fully perform its function and the combustion chamber temperature has not risen sufficiently. be. In such a case, the air-fuel ratio control characteristics may become more disturbed than before the feedback started, or a mixture that is richer than the engine's required air-fuel ratio may be supplied, resulting in an increase in emissions such as hydrocarbons. This has led to deterioration in drivability due to the early or late application of feedback control.

In addition, as another method for detecting the completion of warm-up, a method has been proposed in which the engine coolant temperature is continuously measured from the time of engine startup, and when the coolant temperature exceeds a certain value, it is determined that warm-up is complete (Unexamined Japanese Patent Publication No. (Sho 52-18534). This is based on the fact that as the temperature of the engine itself increases, the cooling water temperature (hereinafter also referred to as cooling water temperature or water temperature) also increases due to heat transfer.

However, although it can be said that the cooling water temperature roughly reflects the temperature of the engine itself,
It cannot be said that it accurately reflects the temperature of the intake port. Therefore, when trying to accurately control the increase in volume during warm-up to just the right amount, using the engine coolant temperature to determine the progress and completion of warm-up is insufficient. Satisfactory control is not possible.

For example, when considering the rotational speed of the engine immediately after starting, the conditions differ each time the engine is started, and the engine does not always show the same rotational speed or change pattern of rotational speed.

Therefore, when the rotational speed is high, the number of combustions (explosions) per unit time is large, so heat generation is rapid, and the engine temperature also rises quickly. On the other hand, when the rotational speed is low, the number of combustions per unit time is small, so heat generation is slow, and the rise in engine temperature is also slow.

However, since water has a large heat capacity, the temperature of the cooling water does not rise immediately in response to the engine temperature. Therefore, there is a difference between the engine temperature and the cooling water temperature that cannot be ignored. Furthermore, if the engine speed changes during warm-up, the cooling water temperature will no longer reflect the engine temperature.

Therefore, it is impossible to judge the warm-up state or the completion of warm-up only by tracking the cooling water temperature.

[Means for Solving the Problems] The present invention employs the following means for the purpose of solving the above-mentioned problems.

That is, the method for starting air-fuel ratio feedback for an electronically controlled engine according to the present invention switches between the open control mode and the feedback control that performs air-fuel ratio feedback control based on the output of the O ₂ sensor, depending on the operating state of the engine. In an electronically controlled engine that performs optimal fuel injection, an initial value for warm-up increase is set based on the engine cooling water temperature at startup detected by a water temperature sensor, and this initial value is attenuated by a predetermined amount with each engine rotation. The fuel injection amount is corrected to increase based on the warm-up increase value that is attenuated in this way, and the feedback control is started when the fuel injection amount reaches a value close to a value corresponding to the stoichiometric air-fuel ratio. It is characterized by

[Operation] The initial value of the fuel warm-up increase is set based on the engine cooling water temperature at the time of startup. At startup, the engine temperature and cooling water temperature are usually almost the same. Therefore, a suitable initial value for the warm-up increase can be determined based on the cooling water temperature at the time of startup.

Furthermore, the attenuation of the warm-up increase during warm-up is made to depend on the rotation of the engine. That is, the warm-up increase is attenuated not according to the duration of warm-up or the cooling water temperature, but according to the number of rotations of the engine.

Since engine rotation and the number of fuel injections are in a completely proportional relationship, responding to the number of engine rotations is equivalent to responding to the number of fuel injections.

Since fuel is combusted in the combustion chamber of the engine to generate thermal energy, the number of revolutions of the engine ultimately depends on the amount of heat generated by the engine. Since the amount of heat generated by an engine is directly related to the engine temperature, attenuating the initial value of the warm-up increase by a predetermined amount for each engine revolution means that the warm-up increase is attenuated according to the engine temperature. It's almost the same as going.

Furthermore, the present invention starts feedback control when the fuel injection amount due to the warm-up increase that matches the engine temperature reaches a value close to the value corresponding to the stoichiometric air-fuel ratio.

For this reason, it is possible to achieve the air-fuel ratio in accordance with the engine temperature with sufficient accuracy from the time the engine starts until the fuel injection amount reaches a value close to the stoichiometric air-fuel ratio.

Furthermore, since the above-mentioned warm-up increase value accurately reflects the engine temperature, feedback control is started when the fuel injection amount due to this warm-up increase reaches a value close to the value corresponding to the stoichiometric air-fuel ratio. As a result, feedback control is started when both engine temperature and air-fuel ratio are optimal.

[Example] Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram of an electronically controlled fuel injection engine to which the present invention is applied. Air taken in from the air cleaner 1 is passed through an intake passage 12 including an air flow meter 2, a throttle valve 3, a surge tank 4, an intake port 5, and an intake valve 6 into a combustion chamber 8 of an engine body 7.
sent to. The throttle valve 6 is the accelerator pedal 13 in the driver's cab.
linked to. The combustion chamber 8 is divided by a cylinder head 9, a cylinder block 10, and a piston 11, and the exhaust gas generated by the combustion of the mixture is passed through an exhaust valve 15, an exhaust port 16, an exhaust manifold 17, and an exhaust pipe. 18 to the atmosphere. The bypass passage 21 connects the upstream side of the throttle valve 3 and the surge tank 4, and the bypass flow rate control valve 22 controls the flow cross-sectional area of the bypass passage 21 to maintain a constant engine rotational speed during idling. An exhaust gas recirculation (EGR) passage 23 that guides exhaust gas to the intake system in order to suppress the generation of nitrogen oxides connects the exhaust manifold 17 and the surge tank 4. EGR) control valve 2
4 opens and closes the EGR passage 23 in response to electric pulses. An intake temperature sensor 28 is provided in the air flow meter 2 to detect the intake temperature, and a throttle position sensor 29 detects the opening degree of the throttle valve 3. A water temperature sensor 30 is attached to the cylinder block 10 to detect the cooling water temperature, that is, the engine temperature, and an air-fuel ratio sensor 31, which is a well-known oxygen concentration sensor, is attached to the collecting part of the exhaust manifold 17 to detect the oxygen concentration in the collecting part. The crank angle sensor 32
detects the crank angle of the crankshaft from the rotation of the shaft 34 of the power distributor 33 connected to the crankshaft (not shown) of the engine body 7, and the vehicle speed sensor 35 detects the rotational speed of the output shaft of the automatic transmission 36. do. These sensors 2, 28, 29, 30, 31, 32, 35
and the voltage of the storage battery 37 are controlled by the electronic control unit 4.
Sent to 0. A fuel injection valve 41 is provided near each intake port 5 in correspondence with each cylinder, and a pump 42 supplies fuel from a fuel tank 43 to the fuel injection valve 41 via a fuel passage 44. The electronic control unit 40 calculates the fuel injection amount using input signals from each sensor as parameters, and sends an electric pulse having a pulse width corresponding to the calculated fuel injection amount to the fuel injection valve 41.
The electronic control unit 40 also controls the bypass flow control valve 2.
2. Controls the EGR control valve 24, the solenoid valve 45 (Fig. 2) of the hydraulic control circuit of the automatic transmission, and the ignition coil 46. The secondary side of the ignition coil 46 is connected to the power distributor 33. The charcoal canister 48 accommodates activated carbon 49 as an adsorbent, has an inlet port connected to the upper space of the fuel tank 43 via a passage 50, and an outlet port connected to the barge boat 52 via a passage 51. connected to. The verge port 52 is located upstream of the throttle valve 3 when the throttle valve 3 has an opening smaller than a predetermined opening, and is located downstream of the throttle valve 3 when the throttle valve 3 has a predetermined opening or more. and receive negative pressure in the intake pipe. The on-off valve 53 has a bimetal disc, and closes the passage 49 to stop releasing fuel evaporative gas into the intake system when the engine is at a low temperature lower than a predetermined temperature.

FIG. 2 is a block diagram showing details of the electronic control section 40. The electronic control unit 40 includes a CPU (Central Processing Unit) 56 that is made up of a microprocessor and performs calculations and control, and a ROM (read-only) that stores a feedback start processing program to be described later and programs for performing other EGR control processing. RAM (Random Access Memory) 58 for temporarily storing data, a second RAM 59 as a nonvolatile storage element that receives power from the auxiliary power supply and retains essential data even when the engine is stopped, and a multiplexer. With A/D
The (analog/digital) converter 60 and the buffered I/O (input/output) device 61 are connected to the bus 62.
are connected to each other through. The outputs of the air flow meter 2, intake temperature sensor 28, water temperature sensor 30, air-fuel ratio sensor 31, and storage battery 37 are sent to the A/D converter 60. In addition, the outputs of the throttle position sensor 29 and crank angle sensor 32 are sent to the I/O device 61,
2, the EGR control valve 24, the fuel injection valve 41, the solenoid valve 45, and the ignition coil 46 are connected to the I/O device 6.
It receives input from the CPU 56 via 1.

An example of determining a warm-up increase value and starting air-fuel ratio feedback using the above configuration will be described below with reference to a diagram. A program for such processing is stored in the ROM 57.

FIG. 3 is a flowchart showing the startup routine, which is a process for setting the initial value of the warm-up increase. In step 301, the water temperature THW ₀ at the time of engine startup is taken in from the water temperature sensor 30, and in step 302, an initial increase value WL ₀ is determined. This initial increase value WL ₀ is obtained by calculating the increase rate in the temperature range from the lowest temperature the engine encounters (e.g. -30℃) to the warm-up completion temperature (e.g. 80℃) in advance as a map, and interpolating this. Find it by
Then, in step 303, step 302
The initial increase value WL ₀ obtained in step 1 is stored in the RAM 59 as the warm-up increase value FWL. From now on, this warm-up increase value
The FWL is used as a comparison reference value in the processing described later.

Figure 4 is a flowchart showing an interrupt routine for each revolution, which interrupts every revolution of the crankshaft during warm-up to attenuate the warm-up increase (subtraction processing) and set a flag to enable air-fuel ratio feedback control. Processing is in progress. At step 401, A is subtracted from the warm-up increase FWL stored in the memory. This A is a constant or a value depending on the load condition of the engine. In step 402, the new warm-up increase FWL obtained by subtraction is compared with the feedback start value FWL _f (FWL≦FWL _f ). If the determination result is FWL>FWL _f , step 403
Proceed to start feedback flag bit f
[F/B] is set to 0 and the interrupt routine program is terminated. On the other hand, if FWL≦FWL _f is satisfied, the process proceeds to step 404 and the flag f [F/B] is set to 1. In this case, the feedback start value FWL _f is
A value close to the stoichiometric air-fuel ratio value, for example 1.05, is selected. If the content of the flag f [F/B] is 1, proceed to step 405 and increase the warm-up amount FWL.
It is determined whether or not satisfies the relationship (FWL≧1). Since 1 is the subject of comparison here, only the increase in warm-up amount is considered as a problem, and the decrease is impossible. If (FWL≧1), the subsequent processing ends; if (FWL<1), the process proceeds to step 406, sets the content of FWL to 1, and ends the processing.

FIG. 5 is a flowchart showing the air-fuel ratio control routine, and shows the process of selecting either open control (control not based on feedback) or feedback control using the processing results shown in FIG. At step 501, it is determined whether or not step 404 in FIG. 4 has been established. If the flag f [F/B] is 1, the program proceeds to step 502 and starts air-fuel ratio feedback control. Further, if the flag f [F/B] is 0, open control is continued.

FIGS. 6 and 7 show changes in the warm-up increase FWL depending on the engine rotational state. When the engine (E/G) rotational speed is constant as shown in Fig. 6a (such as when the engine is being warmed up by the automatic engine yoke), feedback starts at a constant damping rate as shown in Fig. 6b, and on the other hand , when the engine speed changes to the high side as shown in Figure 7a, the 7th
As shown in Figure b, a change occurs in the attenuation characteristic of FWL, and the time point at which feedback starts becomes earlier.

In this way, since the FWL is attenuated for each rotation, that is, the FWL is attenuated according to the number of rotations,
During warm-up, it is possible to continue increasing the amount in accordance with the actual engine temperature. Furthermore, at the end of damping, that is, when transitioning to feedback control, the air-fuel mixture is at almost the stoichiometric air-fuel ratio and the engine temperature is also optimal for feedback control, so it is possible to optimize the start of air-fuel ratio feedback. can.

In the embodiment of the present invention, the cooling water temperature at the time of startup is taken into account when setting the initial value for the warm-up increase, but the temperature of the cylinder head, the temperature of the cylinder block, etc. may also be used.

Also, set the minimum FWL for the water temperature THW,
The air-fuel ratio feedback may be started based on a FWL value that is not attenuated below the minimum FWL.

[Effects of the Invention] According to the present invention, it is possible to achieve an air-fuel ratio that corresponds to the engine temperature with sufficient accuracy from after startup until the fuel injection amount reaches a value close to the value corresponding to the stoichiometric air-fuel ratio.

Furthermore, since the warm-up increase value accurately reflects the engine temperature, feedback control can be started when the fuel injection amount due to this warm-up increase is close to the value corresponding to the stoichiometric air-fuel ratio. , the feedback control is started when both the engine temperature and the air-fuel ratio are optimal.

For this reason, without installing a temperature sensor near the intake port, we use the output value of a conventional water temperature sensor that detects the engine's cooling water temperature to accurately match the engine temperature (especially the intake port temperature) during warm-up. This allows the start of increase control and feedback control.

Therefore, it is possible to improve the drivability and to improve the emission deterioration that occurs when the air-fuel ratio becomes rough due to the O ₂ sensor and the feedback start is delayed due to insufficient warm-up.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an electronically controlled fuel injection engine to which the present invention is applied, Fig. 2 is a block diagram showing details of the electronic control section 40, Fig. 3 is a flowchart showing a starting routine, and Fig. 4 is a Flowchart showing the interrupt routine for each revolution, Figure 5 is a flowchart showing the air-fuel ratio control routine, Figures 6a and b are warm-up increase change diagrams when the engine rotation speed is constant, Figures 7a and b is a diagram showing a change in warm-up amount when the engine speed is changed. 2, 28, 29, 30, 31, 32, 35...
Sensor, 40...Electronic control unit, 41...Fuel injection valve, 45...Solenoid valve, 46...Ignition coil, 56...CPU, 57...ROM, 58, 59
...RAM, 60...A/D converter, 61...
I/O device, 62... bus.

Claims (1)

[Claims] 1. In an electronically controlled engine that performs optimal fuel injection by switching between open control mode and feedback control that performs air-fuel ratio feedback control based on the output of the O ₂ sensor depending on the engine operating condition, water temperature sensor detects An initial value for the warm-up increase is set based on the engine cooling water temperature at the time of engine startup, and this initial value is attenuated by a predetermined amount each time the engine rotates. A method for starting air-fuel ratio feedback for an electronically controlled engine, comprising increasing the fuel injection amount and starting the feedback control when the fuel injection amount reaches a value close to a value corresponding to a stoichiometric air-fuel ratio.