JPS6079132A - Air-fuel ratio controller for engine - Google Patents

Abstract

PURPOSE:To make the titled controller irresponsive to variation of air-fuel ratio due to distribution between cylinders, when controlling to random air-fuel ratio through a linear air-fuel ratio sensor for producing an output approximately proportional to the engine air-fuel ratio, by providing a band insensitive to an air-fuel ratio error signal. CONSTITUTION:An air-fuel ratio controller will obtain an error Ie between target air-fuel ratio Ii and actual air-fuel ratio Iphi in an error amplifier ERI then an output proportional to said error Ie and an output produced through time integration of said error Ie are added in an adder/amplifier SUM. Thereafter its output is converted by a pulse width operator Gr into pulse width and applied onto a solenoid e valve Gf to feed fuel Qf through said solenoid valve Gf to an engine GE. Here, an operational amplifier GS having such characteristic as to produce a proportional output for an error input Ie higher than predetermined level but not produce an output for lower level error input Ie is provided in the prestage of a proportional amplifier GP for producing an output proportional to said error Ie.

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 and accurately adjusting 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 engine, 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. This is what I did.

[Prior art]

Conventionally, the first
An air-fuel ratio sensor (more specifically, an oxygen sensor) having the characteristics shown in the figure has been put into practical use. .

A - In other words, when the fuel is richer than the stoichiometric air-fuel ratio (/'Fm14.7), the output is approximately 0.8V, and when the fuel is leaner than the stoichiometric air-fuel ratio, the output is #. Conventionally, an oxygen sensor with an open position Ov has been used.

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, conventionally, negative feedback control was performed using an air-fuel ratio sensor 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, inconveniences such as knocking due to insufficient fuel or an abnormal rise in exhaust temperature may occur in the armpit zone. forced to compromise on rates.

In addition, individual sensors should be installed to compensate for factors that cause the air-fuel ratio to fluctuate in a complex manner, such as atmospheric pressure and fuel temperature.
In other words, it was inevitable that the control device would become larger and more expensive.

Even when adjusting to the stoichiometric air-fuel ratio, if you draw a limit cycle and vary the air-fuel ratio, under operating conditions where the rotation speed is strongly controlled by the air-fuel ratio, such as when the engine is idling,
Negative feedback control of the air-fuel ratio was often abandoned in the idling state because rotational fluctuations occur in response to the limit cycle of the air-fuel ratio, significantly impairing the driver's experience.

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 so-called linear control so as to be able to perform control without fluctuations in the air-fuel ratio 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. This has been revealed by research.

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 shows the configuration of a conventional air-fuel ratio control device using a block diagram.
is the target air-fuel ratio, and Iφ is a signal corresponding to the measured actual air-fuel ratio, which is directly a current value as described later.

ERI is an error amplifier and outputs an error Ie between the target air-fuel ratio Ii and the measured air-fuel specific gravity φ.

GP is a proportional amplifier and generates an output proportional to the error Ie. G is an integrator that integrates the error Is over time and outputs the result.

The outputs of the proportional amplifier GP and the integrator G are added to the amplifier SUM.
The output of the summing amplifier SUM is output to the pulse width calculator GT. This pulse width calculator 9τ converts the output of the summing amplifier SUM into a pulse width and outputs it to the solenoid valve GiK.

This solenoid valve Gf opens while a pulse is applied to supply fuel (h) to the engine GE. It becomes exhaust (EX).

Further, Gλ is an air-fuel ratio sensor, and the composition of exhaust EX,
In particular, a current signal corresponding to the oxygen partial pressure to the air/fuel ratio is generated. This air-fuel ratio sensor Gλ is configured as shown in FIG. 3, for example.

In FIG. 3, 1.2 is an ion-conducting solid electrolyte that faces each other with a minute gap in between, and porous platinum electrodes 3, 4.5, and 6 are formed on each surface. 4.6 is grounded, and the platinum electrode 3 is the current controller GC.
The platinum electrode 5 is connected to the error amplifier ER2.

The platinum electrode 3 - the ion-conductive solid electrolyte 1 - the platinum electrode 4 constitute an oxygen pump, and when the electric current φ is applied, the corresponding amount of oxygen is 0! is sent in the direction of the solid line arrow to reduce the oxygen in the void.

Zero oxygen is introduced into 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 bonder 7.

Platinum electrode 5 - Ionic conductive solid electrolyte 2 - Platinum electrode 6
constitutes an oxygen sensor 8, which generates an electromotive force Vo commensurate with the oxygen partial pressure ratio inside and outside the gap.

V ref is the target electromotive force, which is the electromotive force V in the equilibrium state. Closed-loop control is performed so that it becomes equal to the target electromotive force ref.

ER2 is an error amplifier and outputs the error ve't- between the target electromotive force vref and the electromotive force v0. The error ve is processed by the compensation element GV and converted into the drive current Iφ of the oxygen pump 7 by the current controller Gc.

The compensation element GV includes an integral element and increases or decreases the output until the error ve becomes 0, and the drive current
′ increases or decreases to reach an equilibrium state.

In this equilibrium state, the drive current φ indicates the oxygen partial pressure outside the air gap, so if the air-fuel ratio sensor shown in Figure 3 is installed in the engine exhaust gas, the oxygen partial pressure in the exhaust gas will be In other words, the air-fuel ratio (7/F) is indicated.

As a typical characteristic is shown in FIG. 4, the air-fuel ratio sensor shown in FIG. 3 has a driving current φ 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 Fig. 2 uses an air-fuel ratio sensor Gλ that can generate an output proportional to the air-fuel ratio, so it can control the air-fuel ratio at any air-fuel ratio suitable for the engine operating condition. It has the excellent feature of not drawing a limit cycle, that is, enabling good air-fuel ratio control without rotational fluctuations, because it can be controlled and basically so-called linear control is possible. have

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

For this reason, due to fluctuations in engine combustion, especially fluctuations in exhaust gas due to variations in cylinder distribution, the oxygen partial pressure in the air gap cannot be maintained in a strictly balanced state, and the oxygen pump drive current φ constantly fluctuates. .

In this way, when the drive current Iφ fluctuates, the air-fuel ratio control device changes the fuel supply amount in response, which, together 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 has the advantage of being able to adjust the air-fuel ratio to any value by linear control, and not reacting unnecessarily to air-fuel ratio fluctuations caused by distribution between cylinders, etc. This paper proposes a new air-fuel ratio 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, and G8 has the characteristics as shown in FIG. , Crab with an error above a certain level.

For , the output I is proportional to it. ′)
It is an operational amplifier with

This operational amplifier Gs l'i is inserted between the error amplifier ERI and the proportional amplifier CP. The other configurations and operations are the same as those explained with reference to FIG.

Now, in the air-fuel ratio control system for the engine shown in FIG. 5, since the operational amplifier G8 is provided before the proportional amplifier GP,
Error 1. Proportional amplifier CP does not react to minute fluctuations in , and does not disturb the equilibrium state of the device.

The dead band given to the operational amplifier Ga is caused by the oxygen pump drive current φ caused by variations in the air-fuel ratio distribution between cylinders.
It is preferable to make it approximately equal to the fluctuation range of .

Incidentally, the integrator GI is conventionally connected directly to the error amplifier ERI, but this is due to the fact that when the air-fuel ratio is controlled to the target air-fuel ratio on average, the error is Engineering. This is because the output of the integrator GI is not affected even if .

In the configuration shown in FIG. 5, no dead zone is provided at the input of the integrator GI, so the function of making the air-fuel ratio accurately match the target value (that is, setting φ=Ii) 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 G8 as another embodiment, the same effect can be obtained as long as the dead zone is small.

As explained in detail above, in the engine air-fuel ratio control device of the present invention, even if an error occurs due to variations in the air-fuel ratio due to variations in cylinder distribution, etc., a dead band is provided in the error signal so as not to react too sensitively to the error. This enables linear control at arbitrary air-fuel ratios, which was previously impossible, so the air-fuel ratio can be adjusted correctly by feedback control even at non-stoichiometric air-fuel ratios, such as in the no-war zone. Since the air-fuel ratio does not fluctuate by drawing , it is possible to achieve extremely excellent control characteristics, such as no rotational fluctuations even if feedback control is performed during no-load conditions.

In the explanation of FIG. 5, the characteristics of the operational amplifier G8 were assumed to have a dead zone as shown in FIG.
- It is clear that a similar effect can be obtained with a characteristic having a variable amplification factor in which the amplification factor becomes low in response to an error in footfall.

In addition, although the proportional amplifier Gp and the integrator Gt are used as the error correction calculation means in the configuration shown in FIG. It is also possible to improve the responsiveness of

In this case, it goes without saying that the input of the differentiator is connected to the output of the operational amplifier G8, 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, an output that is approximately proportional to the air-fuel ratio of the engine is generated, and an air-fuel ratio error occurs when performing linear control to an arbitrary air-fuel ratio using a near air-fuel ratio sensor. A dead zone is provided in the signal so that it does not respond to fluctuations due to distribution between cylinders, so the /9 war zone, etc.
The air-fuel ratio can be correctly adjusted by feedback control even when the air-fuel ratio is other than the stoichiometric air-fuel ratio, and rotational fluctuations do not occur even if feedback control is performed during no-load conditions.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of a conventionally used air-fuel ratio sensor, and FIG. 2 is a block diagram of a conventional engine air-fuel ratio control device using an air-fuel ratio sensor having an output approximately proportional to the air-fuel ratio.
FIG. 3 is a diagram showing the configuration of an air-fuel ratio sensor used in the air-fuel ratio control device for the engine shown in FIG. 2 and the air-fuel ratio control device for the engine of the present invention shown in FIG. A characteristic diagram of the sensor, FIG. 5 is a block diagram of an embodiment of the engine air-fuel ratio control device of the present invention, and FIG. 6 is a diagram showing an example of the characteristics of the operational amplifier in the engine air-fuel ratio control device of FIG. be. ERI -- Error amplifier, Ga -- Operational amplifier, GP
...Proportional amplifier %GI...Integrator, GW"・Engine, Gλ0°° Air-fuel ratio sensor Gτ...Pulse width m width unit, Gf...Solenoid valve. In addition, the same symbols in the figures are the same or The corresponding part is shown. Agent Masuo Oiwa Figure 1 Figure 2 Figure 3 Figure 4 Air combustion Figure 5 Figure 6 Ia'

Claims (4)

[Claims] (1) Means for detecting four parameters of engine operation, means for calculating the amount of fuel supplied based on the output of this means, means for supplying fuel to the engine based on the output of this means, and means for supplying fuel to the engine based on the components of engine exhaust An air-fuel ratio sensor that detects the air-fuel ratio and outputs an electrical signal approximately proportional to this air-fuel ratio, receives the output of this air-fuel ratio sensor, calculates a correction amount corresponding to the error from the desired air-fuel ratio, and eliminates the above-mentioned error. An engine comprising means for making the correction calculation ratio different when it is smaller than a predetermined value and when it is larger than a predetermined value, and means for applying the correction amount to the means for calculating the fuel supply amount so as to reduce the error. Air-fuel ratio control device. (2) The means for calculating the correction amount is configured to calculate an amount proportional to the error, an amount obtained by integrating the error, an amount obtained by differentiating the error, or a combination thereof, and output it as the correction amount. When the error is smaller than a predetermined value, an amount proportional to the error or an amount obtained by differentiating the error is suppressed or clamped to O to generate the correction amount. An air-fuel ratio control device for an engine according to item 1. (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 is characterized by outputting a voltage according to the concentration ratio, controlling the driving current of the oxygen pump to maintain this voltage at a predetermined value, and generating an electrical output corresponding to this driving current. An air-fuel ratio control device for an engine according to claims 1 and 2. (4) The air-fuel ratio sensor is composed of an oxygen pump and an oxygen sensor facing each other with an air gap in between.The oxygen pump is driven with a predetermined current to control the oxygen concentration in the air gap, Claims 1 and 2 are characterized in that the voltage is generated according to the oxygen concentration ratio inside and outside the gap, and this voltage is output.
An air-fuel ratio control device for the engine described in Section 2.