JPS637255B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an air-fuel ratio control device capable of measuring and returning the air-fuel ratio of an engine to accurately adjust the air-fuel ratio to a predetermined value. Using an air-fuel ratio sensor that generates an output that is approximately proportional to the air-fuel ratio of the air-fuel ratio, it is possible to stabilize the adjustment control and obtain good characteristics without impairing responsiveness when adjusting the air-fuel ratio to any desired air-fuel ratio. It is something.

[Prior art]

BACKGROUND ART Conventionally, air-fuel ratio sensors (more specifically, oxygen sensors) having characteristics as shown in FIG. 1 have been put into practical use for the purpose of adjusting the air-fuel ratio of an engine to a predetermined value.

In other words, when the fuel is richer than the stoichiometric air-fuel ratio (A/F≒14.7), the output is approximately 0.8V,
Conventionally, oxygen sensors have been used that output approximately 0V when the fuel is leaner than the stoichiometric air-fuel ratio.

Using an air-fuel ratio sensor having such characteristics, it is possible to control the air-fuel ratio so as to draw a limit cycle around the stoichiometric air-fuel ratio.

However, it is impossible to use this for the purpose of adjusting the air-fuel ratio to an arbitrary air-fuel ratio other than the stoichiometric air-fuel ratio.
Therefore, in the past, negative feedback control using an air-fuel ratio sensor was used only when adjusting to the stoichiometric air-fuel ratio, and when adjusting to other air-fuel ratios such as power zone, open loop control without feedback had to be used.

For this reason, for example, in the power zone, inconveniences such as knocking due to insufficient fuel or an abnormal rise in exhaust temperature may occur, so it is necessary to offset the air-fuel ratio setting center slightly to the rich side, which compromises the fuel efficiency. I was forced to do so.

Furthermore, it is necessary to provide individual sensors to correct factors that cause the air-fuel ratio to fluctuate in a complex manner, such as atmospheric pressure and fuel temperature, which inevitably increases the size and cost of the control device.

Even when adjusting to the stoichiometric air-fuel ratio, if you draw a limit cycle and vary the air-fuel ratio, the air-fuel ratio will not be adjusted under operating conditions where the engine speed is strongly controlled by the air-fuel ratio, such as when the engine is idling. Because rotational fluctuations occur in response to the Mitsubishi cycle, which significantly impairs the driver's experience, negative feedback control of the air-fuel ratio was often abandoned during idle conditions.

In order to eliminate the above-mentioned drawbacks, an air-fuel ratio sensor is required that generates an output proportional to the air-fuel ratio and can perform negative feedback control at any air-fuel ratio.

Furthermore, it is desirable to perform control without fluctuations in the air-fuel ratio by using so-called linear control in order to suppress rotational fluctuations.

Under these circumstances, an air-fuel ratio sensor was invented in which an oxygen pump and an oxygen sensor were placed opposite each other with an air gap in between, and it was possible to generate an output approximately proportional to the air-fuel ratio and have good characteristics. This has been clarified through research in various fields.

A conventional air-fuel ratio control device that performs air-fuel ratio control using such an air-fuel ratio sensor will be described below with reference to FIGS. 2 to 4. FIG. 2 is a block diagram showing the configuration of a conventional air-fuel ratio control device, where I _i is a signal corresponding to the target air-fuel ratio and Iφ is a signal corresponding to the measured actual air-fuel ratio, which will be described later. Directly, it is the current value.
ER1 is an error amplifier and outputs an error Ie between the target air-fuel ratio _Ii and the measured air-fuel ratio Iφ.

G _P is a proportional amplifier and generates an output proportional to the error Ie. G _I is an integrator that integrates the error Ie over time and outputs it.

A summing amplifier that combines the outputs of the proportional amplifier G _P and the integrator G _I
SUM is used for addition, and the summing amplifier
The output of SUM is output to a pulse width calculator Gτ. This pulse width calculator Gτ converts the output of the summing amplifier SUM into a pulse width and outputs it to the solenoid valve G _f .

This solenoid valve G _f is opened while a pulse is applied to supply fuel Q _f to the engine G _E. Q _A is the air sucked by engine G _E ,
It is mixed with fuel Q _f and burned to become exhaust (EX).

Further, Gλ is an air-fuel ratio sensor that generates a current signal corresponding to the air-fuel ratio from the composition of the exhaust gas EX, especially the oxygen partial pressure. This air-fuel ratio sensor Gλ is configured as shown in FIG. 3, for example.

In this FIG. 3, 1 and 2 are ion conductive solid electrolytes facing each other with a minute gap in between,
Porous platinum electrodes 3, 4 and 5 are provided on each side.
and 6 are formed, the platinum electrodes 4 and 6 are grounded,
The platinum electrode 3 is connected to a current controller Gc, and the platinum electrode 5 is connected to an error amplifier ER2.

The platinum electrode 3, the ion-conductive solid electrolyte 1, and the platinum electrode 4 constitute an oxygen pump 7, and when a current Iφ is applied, oxygen O ₂ commensurate with the current Iφ is sent out in the direction of the solid line arrow, reducing the oxygen in the void.

Oxygen O ₂ enters the void from the outside in the direction of the dashed arrow.
diffuses in and replenishes the oxygen in the gap sent out by the oxygen pump 7, so that the oxygen partial pressure in the gap is balanced to a value determined by the oxygen partial pressure outside the gap and the drive current Iφ of the oxygen pump 7.

The platinum electrode 5, the ion-conductive solid electrolyte 2, and the platinum electrode 6 constitute an oxygen sensor 8, which generates superpower Vo commensurate with the oxygen partial pressure ratio inside and outside the gap.

V _ref is a target electromotive force, and closed-loop control is performed so that the superpower V _p becomes equal to the target electromotive force V _ref in an equilibrium state.

ER2 is an error amplifier and outputs an error V _e between the target electromotive force V _ref and the electromotive force V _p . The error V _e is processed by the compensation element G _V and converted into the drive current Iφ of the oxygen pump 7 by the current controller Gc.

The compensation element G _V includes an integral element, and the error V _e
Increase or decrease the output until becomes 0,
The drive current Iφ is increased or decreased to reach an equilibrium state.

In this equilibrium state, the drive current Iφ indicates the oxygen partial pressure outside the air gap, so if the air-fuel ratio sensor shown in Figure 3 is installed in the exhaust gas of the engine, the oxygen partial pressure in the exhaust gas, that is, the air-fuel ratio (A/F) is indicated.

As a typical characteristic is shown in FIG. 4, the air-fuel ratio sensor shown in FIG. 3 has a drive current Iφ proportional to the air-fuel ratio flowing therethrough, so it is possible to detect this and use it as an air-fuel ratio signal.

As mentioned above, the air-fuel ratio control device shown in Figure 2 is an air-fuel ratio sensor that can generate an output proportional to the air-fuel ratio.
Because Gλ is used, the air-fuel ratio can be controlled to any air-fuel ratio suitable for the engine's operating conditions, and basically so-called linear control is possible, so there is no limit cycle, that is, the rotation It has the excellent feature of enabling good air-fuel ratio control without fluctuations.

However, the air-fuel ratio control device shown in FIG. 2 has the following drawbacks and cannot be put to practical use. In other words, the air-fuel ratio sensor Gλ measures the air-fuel ratio by having an oxygen pump and an oxygen sensor facing each other with an air gap in between, and maintaining the oxygen partial pressure in this air gap at a predetermined equilibrium state. ,
Even if the volume of the void is made as small as possible, the delay time cannot be ignored.

For this reason, due to fluctuations in combustion in the engine, especially fluctuations in exhaust gas due to fluctuations in distribution between cylinders, it is not possible to maintain the oxygen partial pressure in the air gap in a strictly balanced state.
The drive current Iφ of the oxygen pump constantly fluctuates.

In this way, when the drive current Iφ fluctuates, the air-fuel ratio control device responds by changing the fuel supply amount, so this, combined with the delay time of each part of the device, aggravates the air-fuel ratio fluctuation, and keeps the air-fuel ratio at a predetermined value. cannot be balanced.

[Summary of the invention]

This invention was made in view of the above-mentioned conventional disadvantages, and provides an excellent air-fuel ratio that can adjust the air-fuel ratio to any value by linear control and does not react unnecessarily to air-fuel ratio fluctuations due to distribution between cylinders, etc. This paper proposes a control device.

[Embodiments of the invention]

Embodiments of the air-fuel ratio control device for an engine according to the present invention will be described below with reference to the drawings. FIG. 5 is a block diagram showing the configuration of an embodiment of the present invention.
Gs has the characteristics shown in Figure 6 (i.e., for error input I _e below a certain level, output I _e ' will not occur;
This operational amplifier has the characteristic of generating an output I _{e ' proportional to an error input I e of} a certain value or more.

This operational amplifier Gs is inserted between the error amplifier ER1 and the proportional amplifier _GP . The other structures and operations are as explained with reference to FIG.

Now, in the air-fuel ratio control system for the engine shown in Fig _. 5, the operational amplifier Gs is provided before the proportional amplifier _GP , so that the proportional amplifier _GP
does not react and does not disturb the equilibrium state of the device.

It is preferable that the dead band provided to the operational amplifier Gs is approximately equal to the range of variation in the oxygen pump drive current Iφ caused by variations in the air-fuel ratio distribution between cylinders.

Note that the integrator G _I is connected to the error amplifier ER1 as before.
Although this is directly connected to the air-fuel ratio due to the air-fuel ratio distribution between cylinders, even if the error _Ie fluctuates under the condition that the target air-fuel ratio is controlled on average, the output of the integrator G _I This is because there is no effect on

In the configuration shown in FIG. 5, no dead zone is provided at the input of the integrator G _I , so the function of making the air-fuel ratio accurately match the target value (that is, Iφ=I _i ) is not impaired.

However, it goes without saying that even if the input of the integrator _GI is connected to the output side of the operational amplifier Gs as another embodiment, substantially the same effect can be obtained as long as the dead zone is small.

As explained in detail above, in the air-fuel ratio control device for an engine according to the present invention, even if an error occurs due to fluctuations in the air-fuel ratio due to variations in the distribution between cylinders, a dead band is placed on the error signal so as not to react too sensitively to the error. By providing this, linear control at any air-fuel ratio, which was previously impossible, became possible
The air-fuel ratio can be adjusted correctly using feedback control even when the air-fuel ratio is not stoichiometric, such as in the power zone. Also, since the air-fuel ratio does not fluctuate by drawing a limit cycle, no rotational fluctuations occur even if feedback control is performed during no-load conditions. , very excellent control characteristics can be achieved.

In addition, in the explanation of FIG. 5, the operational amplifier Gs
Although the characteristic has a dead zone as shown in FIG. 6, it is clear that the same effect can be obtained with a characteristic having a variable amplification factor in which the amplification factor decreases when the error is below a certain level.

In addition, as the error correction calculation means, although the proportional amplifier G _P and the integrator G _I are used in the configuration shown in FIG. , it is also possible to improve the responsiveness of air-fuel ratio control.

In this case, it goes without saying that the input of the differentiator is connected to the output of the operational amplifier Gs, similar to the proportional amplifier _GP .

〔Effect of the invention〕

As described above, according to the air-fuel ratio control device for an engine of the present invention, when performing linear control to a desired air-fuel ratio using a linear air-fuel ratio sensor that generates an output approximately proportional to the air-fuel ratio of the engine, an air-fuel ratio error signal is generated. A dead zone is provided in the air-fuel ratio to prevent it from reacting to fluctuations due to the distribution between cylinders, so it is possible to correctly adjust the air-fuel ratio using feedback control even in situations other than the stoichiometric air-fuel ratio, such as in the power zone. This also has the effect that rotational fluctuations do not occur.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram of a conventionally used air-fuel ratio sensor, Fig. 2 is a block diagram of a conventional air-fuel ratio control device for an engine using an air-fuel ratio sensor having an output approximately proportional to the air-fuel ratio, and Fig. 3. is a diagram showing the configuration of an air-fuel ratio sensor used in the air-fuel ratio control device for an engine shown in FIG. 2 and the air-fuel ratio control device for an engine of the present invention shown in FIG. 5, and FIG. 4 shows the characteristics of the air-fuel ratio sensor shown in FIG. 3. figure,
FIG. 5 is a block diagram of an embodiment of the air-fuel ratio control device for an engine according to the present invention, and FIG. 6 is a diagram showing an example of the characteristics of the operational amplifier in the air-fuel ratio control device for the engine shown in FIG. ER1...Error amplifier, Gs...Operation amplifier, G _P
...proportional amplifier, G _I ...integrator, G _E ...engine,
Gλ...Air-fuel ratio sensor, Gτ...Pulse width amplifier,
G _f ...Solenoid valve. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Means for detecting the operating parameters of the engine, means for calculating the fuel supply amount based on the output of this means, means for supplying fuel to the engine in response to the output of this means, An air-fuel ratio sensor that detects a fuel ratio and outputs an electrical signal that is approximately proportional to this air-fuel ratio; and an air-fuel ratio sensor that receives the output of this air-fuel ratio sensor and calculates a correction amount corresponding to the error from the desired air-fuel ratio, and also sets the above error to a predetermined value. Air-fuel ratio control for an engine, comprising: means for making the correction calculation ratio different when it is smaller and larger; and means for applying the correction amount to the means for calculating the fuel supply amount so as to reduce the error. Device. 2. The means for calculating the correction amount is an amount proportional to the error,
It is configured to calculate either an amount that integrates the error, an amount that differentiates the error, or a combination thereof and outputs it as a correction amount, and when the error is smaller than a predetermined value, an amount proportional to the above error or the above error. 2. The air-fuel ratio control device for an engine according to claim 1, wherein the correction amount is generated by suppressing or clamping a differentiated amount to zero. 3 The air-fuel ratio sensor is composed of an oxygen pump and an oxygen sensor that face each other with an air gap in between. The oxygen pump outputs a voltage, controls the driving current of the oxygen pump so as to maintain this voltage at a predetermined value, and generates an electrical output corresponding to this driving current. An air-fuel ratio control device for an engine according to range 1 or 2. 4 The air-fuel ratio sensor is composed of an oxygen pump and an oxygen sensor that face each other across a gap, and this oxygen pump is driven with a predetermined current to control the oxygen concentration in the gap, and this oxygen sensor An air-fuel ratio control device for an engine according to claim 1 or 2, characterized in that the device generates a voltage according to an oxygen concentration ratio and outputs this voltage.