JPS6098142A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To prevent deterioration of air-fuel ratio control and to improve the operationability by comparing the level of flow-in current with predetermined referential level and stopping feedback control of air-fuel upon decision of abnormality through O2 sensor and clamping to specific air-fuel ratio. CONSTITUTION:Comparators 24, 25 constituting a stop command means 23 is provided with upper and lower limits UL, LL from referential level setting means 28, and if the level of flow-in current Is to O2 sensor 1 will deviate from said limits UL, LL, the sensor 1 is decided to be abnormal. Consequently, said means 23 will produce a command signal S4 and feed to air-fuel ratio control means 30 thus to stop feedback control and to maintain the air-fuel ratio at predetermined level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an air-fuel ratio control device for an engine, and more particularly, to an air-fuel ratio controller using an oxygen sensor whose output voltage suddenly changes depending on the air-fuel ratio depending on the value of an injected current. This invention relates to a control device.

[Prior art]

Recently, in order to accurately control the fuel ratio of the engine intake air-fuel mixture to a target value, an oxygen sensor has been installed in the exhaust system to adjust the fuel supply amount according to the oxygen concentration in the exhaust, which has a correlation with the air-fuel ratio. It is under control.

In addition, recently, in order to improve fuel efficiency from the perspective of energy conservation, attempts have been made to control the air-fuel ratio so that the engine burns a lean R17 mixture. An oxygen sensor that can detect lean air-fuel ratios has been developed.

As a conventional oxygen sensor of this kind, for example, Japanese Patent Application Laid-Open No. 56
There is one described in JP-A-89051. and,
An example of a system for controlling the air-fuel ratio using such an oxygen sensor is the air-fuel ratio flI, which was previously filed by the present applicant.
There is a "U control device" (Japanese Patent Application No. 58-79032), which can be shown as shown in FIG.

In Figure 1, 1 is an oxygen sensor, which applies the principle of a kind of concentration battery that generates an electromotive force according to the oxygen concentration. This oxygen sensor 1 is constructed as shown in detail in FIG. An electrode (base 7v"electrode) 3 is provided.

Inner electrode 3 is oxygen ion conductive solid 'l'N, solute 4
An outer electrode (oxygen measurement electrode) 5 is laminated at a position facing the inner electrode 3 with the solid electrolyte 4 sandwiched therebetween. These alumina substrate 2, inner electrode 3, solid electrolyte 4, and outer electrode 5 are covered with a porous protective layer 6, and a heater is installed inside the alumina substrate 2 to heat the solid electrolyte 4 to an appropriate temperature to maintain its activity. 7 is built-in. The inner 'fR axis 3K connects the current supply circuit 8 to the resistor 11. An inflow current Is is supplied via B, and this inflow current IS generates a reference 11 elemental partial pressure Pa at the inner electrode 3. On the other hand, the oxygen partial pressure Pb at the outer electrode 5 is the oxygen partial pressure of the gas to be measured.
Based on these oxygen partial pressures Pa and PbK, ILTI is applied between both electrodes.

E2□・11]□ ・・・・・・・・・■4'Pb However, 1L=gas constant, '1゛: Absolute temperature■°゛: Origin expressed by Nernst's equation, Faraday constant statement Generates 1 electric power bow. And this happened? When switching from the lean side to the rich side at a predetermined air-fuel ratio, the air-fuel ratio changes greatly to the positive side, and the air-fuel ratio at the time of reno change changes depending on the inflow current ISO value. . Further, the oxygen sensor 1 has an internal resistance ILs, and this internal resistance I(,s changes depending on the activation state of the oxygen sensor 1.

16 again, the electromotive force e of the oxygen sensor 1 is taken out to the outside as the oxygen sensor output Vs through the internal resistance JAS, and the upper and lower limits when this output Vs switches and suddenly changes with the air-fuel ratio. The intermediate 1L pressure value (hereinafter referred to as sudden change point output Vsp) increases in proportion to the inflow current IsO value. This is because the lytic element has an internal resistance Rs, and the voltage increase due to this internal resistance S is R,s.
■This is because S is added. That is, the inflow current Is
The sudden change point output Vsp when Vsp is supplied is expressed by the following equation (2).

Vs l) = V(, + R5-1,s -----・
----■ However, Vo: sudden change point output when the injected current is zero. Therefore, for example, inject the current Is into the sensor 1 so that the sensor output Vs is always equal to the change point output ■Sp.
When S is supplied, the value of this injected current [S becomes a magnitude corresponding to the switching air-fuel ratio. That is, the inflow current IS and the switching air-fuel ratio (in other words, the oxygen concentration in the exhaust gas) are expressed in a 1:I relationship as shown in FIG.
The current air-fuel ratio can be detected by detecting the value of the inflow current Is.

Therefore, the abrupt change point output Vsp corresponding to the current air-fuel ratio should be set as the target voltage Va (Va2VSI)), and the inflow current Is is supplied so that the sensor output vS becomes the target voltage Va. By detecting the value, the current air-fuel ratio is detected.

In other words, the value of the injected current θij l s is the resistance 1 (,
The voltage θ1 is detected as a voltage drop between both ends of B by the value detection circuit 9, and the current value detection circuit 9 is detected by the operational amplifier OP.
I, (JP2 and resistor Jtl, I, 2.1, and 3.1 are both 4. This electric current value detection circuit 9 calculates the value of the injected current Is to both sides of the resistor I+, 1.1. Among'
,I.

It measures the pressure drop and outputs the voltage signal ■1. The current supply circuit 8 is composed of operational amplifiers OP3, (Monday) 4, OF2 and a resistor R5, I is 6, I is 7, I is 8.1, I is 9.1 and 10, and the oxygen sensor output Vs is calculated by the following formula: ■
The injected current I is set to the target voltage Va given by
Supply s to ℃・ru.

Va = ■ o' + k Vi ...... ■ However, k: Constant vo2 Output of the current value detection circuit 9 when the inflow current Is is zero ■1 In other words, the current supply circuit 8 Eclipse voltage 15V with resistor R5
, the partial pressure is 1 mole.'' ■ in the formula. The reference voltage V that is adjusted to In addition to setting this reference voltage V. By adding the voltage obtained by multiplying the output Vi of the K current value detection circuit 9 by a constant 1 (1), the target voltage Va is determined, and the operational amplifier OP5
%a IS is controlled so that the oxygen sensor output Vs matches the target voltage Va. In addition, the voltage increase R, s due to the constant I(('' internal resistance It, s
・In order to compensate for the negative multiplication of Is, it is set to a value that satisfies the following equation.

Va=Vo+k Vi=Vo1Rs･IS...
・■On the other hand, the air-fuel ratio control means 1 supplies fuel to the engine.
The air-fuel ratio control means 10 sets the target air-fuel ratio according to the operating conditions, and also controls the supply of fuel from a fuel supply means (for example, an injector, not shown) based on the output Vi of the current value detection circuit 9. The air-fuel ratio is controlled to the target air-fuel ratio by controlling the fuel injection amount. In this case, as described above, jM bft, the output Vi+ of the value detection circuit 9, corresponds to the value of the pouring groove IS, and the pouring current IS
The O value corresponds to the switching air-fuel ratio of the oxygen sensor 1.

Then, this switching air-fuel ratio is injected into the 7114 style IS.
As O increases, the ratio shifts to the leaner side than the theoretical 5 ratio. Once, the sudden change point output Vsp corresponding to the current air-fuel ratio (for example, lean desired fuel-fuel ratio) was set as the target voltage ■;
- Supply the inflow current Is so that the sensor output Vs is equal to the target voltage Va and iA7. This small inflow current Is has a value corresponding to the current air-fuel ratio, and by detecting this value, the current air-fuel ratio is detected. Then, the air-fuel ratio control means 1
0 determines the size of the deviation of the current air-fuel ratio from the target air-fuel ratio σ) based on the current value detection circuit 90 output
The air-fuel ratio is controlled to the target air-fuel ratio by appropriately controlling the fuel supply amount according to the magnitude I, i;.

However, in the air-fuel ratio control device of the prior application, the sudden change point output VSI corresponding to the current desired fuel ratio is set as the target voltage Va, and the sensor output Vs is set to the target voltage Va. An electric IC value detection circuit 9 that supplies the inflow current Is and detects this current value.
Since the configuration was such that the air-fuel ratio was controlled based on the output ■1 of the oxygen sensor 1, for example, as shown in FIG. If the lead wire 11 or heater wire 12 of the sensor 1 is disconnected, the output (1) will no longer accurately correspond to the current air-fuel ratio, and there is a risk that the air-fuel ratio will be incorrectly determined.

As a result, if the air-fuel ratio is opened to the target air-fuel ratio, the internal angle becomes 1t, which may impair engine drivability. For example, if the air-fuel ratio is controlled to be richer, it will increase the exhaust mission and increase fuel efficiency. On the other hand, if it is controlled to be leaner, combustion will become unstable and in extreme cases (or the engine stalls). .

[Purpose of the invention]

Therefore, the present invention provides pouring 'f11. θ1rθ (iI
It compares it with the standard value to determine whether it is a power or divination that is abnormal, and if it is abnormal, 4111
``A1] When the air-fuel ratio is turned off, clamp the air-fuel ratio to a predetermined air-fuel ratio. σ) Improving the drivability of the 1)-L engine is defined as ff1l (V-J).

[Structure of the invention]

Air-fuel ratio control according to the present invention 1] Device +U detects the oxygen concentration in the engine exhaust gas and injects θ 'Fli,' Mtσ)
%-, and the oxygen sensor output is set to a predetermined value (jQ and)'CZ)-
'E Electricity jib j'i that supplies electricity L to the sea urchin
': Electric bIC value detection that detects the value of fAf L-included current 1: l''-= s role, and 8. 9. air-fuel ratio control means for maintaining the air-fuel ratio at a predetermined air-fuel ratio when a command is given to stop the feedback control; a stop command means for determining whether or not the oxygen sensor is abnormal by comparison, and for commanding to stop the feedback control when it is determined that the oxygen sensor is abnormal; and a standard for setting the predetermined reference value according to operating conditions. and a value setting means, which stops the feedback control of the air-fuel ratio and clamps the air-fuel ratio to a predetermined air-fuel ratio when it is determined that the oxygen sensor is abnormal.

〔Example〕

Hereinafter, the present invention will be explained based on the figures ukjK.

Fig. 5.6 is a diagram showing an embodiment of the present invention, and in explaining this embodiment, the same component parts as those in the previous application will be given the same reference number 1 and the explanation thereof will be omitted. do.

First, to explain the configuration, in FIG. 5, the oxygen sensor 1 is similar to the conventional example shown in FIG. Output. Note that the electrode of the oxygen sensor 1 and the ground wire of the heater are shared and taken out to the outside.The heater of the oxygen sensor 1 is supplied with heater current LH from the heater control circuit 21, and the heater The current iH generates heat and activates the oxygen sensor 1 appropriately.Additionally, the oxygen sensor 1 is supplied with a T-] current supply circuit (current supply means) 8 with a flowing % flow]S. The value of the current Js is determined by the current value detection circuit (current value detection means)
Detected by 9. That is, the current value detection circuit 9 detects the inflow current IsO value and outputs a voltage No. 48 Vi proportional to the electric current θ1 15. The voltage b'(1 value detection circuit 90 output ■1 is manually inputted to the abort command means 23 via the low-pass filter 22, and the abort command means 23 is connected to the comparator 2/I, 25, the OR circuit 26, and the solve flop circuit. The low-pass filter 22 passes only the low frequency component of the output 1, and the output of the low-pass filter 22 is input to the comparator 24.25. Only a voltage signal corresponding to the value of the injected current Is is inputted to the comparator 24.25, and no noise signal (mainly high frequency components) is inputted to the comparator 24.25. (JL and lower limit value LI, are each input. Here, upper limit value UL is the value of the injected current 1.s when the porous protective layer of the oxygen sensor 1 is peeled off, for example) (
At this time, the current value is set to 11 predetermined sections that are even larger than the current value (which becomes very large), and when the inflow current Is exceeds this upper limit value UL, it is determined that the oxygen sensor is abnormal. On the other hand, 1st period (i+J L l, kJ
, for example, the value of the injected current Is when the porous retainer Di Iν・7 of the oxygen sensor 1 is clogged (at this time,
The current value is set to a predetermined value that is even smaller than the current value (which is smaller than normal), and the inflow current 1. s is this lower limit, L
If the value is less than this value, it is determined that the oxygen sensor 1 is abnormal.

Therefore, the comparator 24 has V i ) U L and 2J
The comparator 25 receives the signal S1 which becomes Vi(ICH).
The OR circuit 26 outputs the signal 2 which becomes [I(] when LL,
Signal S3 that becomes [1-1':l when U L <V i
is output to the solid flop circuit 27.

When the flip-flop circuit 27 receives the [11] signal, it is sorted and outputs a stop command signal S4 that is held at [11] thereafter. That is, the stop command means 23 determines that the oxygen sensor 1 is normal when the value of the injected current 1S is within the predetermined reference range LL-UL, and on the other hand, when the value of the injected current 1S is outside the predetermined reference range, the oxygen sensor 1 is determined to be abnormal, and outputs a stop command signal S, which commands to stop the air-fuel ratio feedback control, as will be described later.

The upper limit value UL and the lower limit values 1 and 11 are set by the reference value setting means 28 to two levels of values, one for cutting and the other for cutting.

That is, 29 is a twin cut circuit, and the twin cut circuit 29 receives an engine rotation signal N and a vehicle speed signal Sp.
and an accelerator opening signal Ac are input. Then, the twin cut circuit 29 receives these signals N, Sp, and A.
It is determined whether or not to perform a twin cut based on c, and when it is determined that a twin cut is to be made (for example, during deceleration), a twin cut signal S is output to the reference value setting means 28. The reference value setting means 28 sets the upper limit value UL to ULl and the lower limit value LL to LLl when the twin cut is not performed, and sets the upper limit value UL to UL when the twin cut is not performed.
The lower limit value LL is set to LJ, 2 (however, January'2>L'l) for LJ, 2 (where, Ul, , <:'Ul, , ), respectively.

The supply of fuel to the engine is performed by an air-fuel ratio control means 30, and the air-fuel ratio control means 30 is controlled by a correction coefficient calculation circuit 31.
and an injection amount control circuit 32. The output Vi of the current value detection circuit 9 is input to the correction coefficient calculation circuit 31, and the above-mentioned stop command signal S4 is input when it is determined that the oxygen sensor 1 is abnormal.

Then, the correction coefficient calculation circuit 31 calculates a correction coefficient α for correcting the air-fuel ratio to the target air-fuel ratio based on the output (1), and when the oxygen sensor 1 is abnormal, the correction coefficient α
is a predetermined value α. Clamp on. In this case, the predetermined value α. is a value for correcting the air-fuel ratio to a predetermined air-fuel ratio, for example, the stoichiometric air-fuel ratio. The injection amount control circuit 32 calculates a basic injection amount based on the operating state of the engine, and multiplies this basic injection amount by a correction coefficient α to determine the final injection amount to control the fuel injection amount supplied by an injector (not shown). do. Further, when the twin cut signal S is input to the twin cut circuit 29 (during the twin cut), the supply of fuel to the engine is stopped. Therefore, the combustion ratio control means 3
0 normally controls the air-fuel ratio to the target air-fuel ratio, and oxygen sensor 1
The difference? 'l; II, '7, the feedback control is stopped and the air-fuel ratio is maintained at a predetermined air-fuel ratio.

Next, the operation will be explained with reference to FIG.

■Oxygen sensor during normal operation (other than when cutting the tube)? The reference plant for determining abnormality 1 has an upper limit of UL and a lower limit of L.
L, respectively. At this time, if the oxygen sensor 1 is normal, the output Vi of the current value detection circuit 9 (hereinafter simply referred to as output Vi) changes as shown by the solid line 1 in FIG. is controlled to the target air-fuel ratio. On the other hand, when the oxygen sensor 1 deteriorates, the magnitude of the output Vi differs from the solid line A depending on the degree of deterioration.

For example, when the porous retaining layer of the oxygen sensor 1 is partially peeled off, the output Vi changes as shown by the solid line 1 in FIG. 6, and the air-fuel ratio is determined to be leaner than it actually is. As a result, the air-fuel ratio is controlled to the Lynch side compared to the target. Also, when the porous Ai layer of the oxygen sensor 1 becomes clogged, the output 1 becomes as shown by the solid line 1 in Figure 6. As a result, the air-fuel ratio is judged to be richer than it actually is.As a result, the air-fuel ratio is controlled to be leaner than the target.By the way, it is difficult to accurately detect such mild deterioration during normal operation. is actually a difficult IL.Therefore, as described in the next section (■), such mild deterioration can be detected accurately during the 7-hour cut.Furthermore, as deterioration of oxygen sensor 1, the output When the ground wire is broken, the output Vi becomes zero (Vi=O) (see solid line 1 in Figure 6), and when the ground wire is broken, the output Vi becomes a negative value (
Vi<0) (see solid line 1 in Figure 6). When the deterioration is severe like this, V i (L L) as shown in FIG.
(q′27<Sensor 1 abnormality is determined, the air-fuel ratio foot check control is stopped, and the air-fuel ratio is increased to the predetermined enriched fuel ratio by A11J”+. As a result, the oxygen sensor 1 is abnormal. It is possible to operate the engine (deterioration of IJ) despite the sauce.

■Distinguishing the abnormality of oxygen sensor 1 when cutting the tube 1 (111-
The upper limit value is set to UL2, and the lower limit value is set to 1 node 2. At this time, the inside of the exhaust pipe is the atmosphere, the oxygen concentration is 21% of the atmosphere, and the air-fuel ratio is infinite. Therefore, the output ■1 is uniquely determined, It is necessary to have a size that corresponds to the atmosphere.Therefore, by narrowing the normality determination range LL2 to UL2 between the upper and lower limit values UL2 and LIJ2 compared to the previous item (■),
Slight deterioration is detected with high accuracy. That is, when the oxygen sensor 1 deteriorates and the output Vi changes as shown by the solid line B or C in FIG. It is determined that it is abnormal. Therefore,
When Tsuunil Cut is stopped and normal operation resumes,
Air-fuel ratio feedback control is stopped. the result,
Even if the deterioration is mild, it is possible to prevent deterioration of engine drivability, as in the case of item (3) above.

In this embodiment, when it is determined that the oxygen sensor is abnormal, the feedback control is stopped. This will alert the driver and allow them to take appropriate action.

In addition, in this embodiment, two reference values are set for determining whether the oxygen sensor is abnormal, but it goes without saying that the number is not limited to two and may be one.

〔effect〕

According to the present invention, when it is determined that the oxygen sensor is abnormal, it is possible to cancel the air-fuel ratio feedback control t]11 and clamp the air-fuel ratio to a predetermined air-fuel ratio. It is possible to prevent deterioration of fuel ratio control and improve engine drivability.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams of the air-fuel ratio control device of the earlier application, Figure 1 is its circuit 'l'R diagram, Figure 2J&I is a 1jyi side view of the oxygen sensor, and PG:3. Hasonopi 11
- Diagram showing the relationship between the included electric power b1 and the air-fuel ratio, No. 11N-
FIG. 5.6 is a cross-sectional view of the oxygen sensor when it has deteriorated, and FIG. To explain the effect, the output V of the N'fAt value detection circuit is
FIG. 3 is a diagram showing the relationship between i and the air-fuel ratio. DESCRIPTION OF SYMBOLS 1... Oxygen sensor, 8... Current supply means, 9... Current value detection means, 23... Cancellation command means, 28... Standard value setting means, 30... air-fuel ratio control means; Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney Ugagun Part 2, et al. 4, 3

Claims (1)

[Claims] an oxygen sensor that detects the oxygen concentration in the exhaust gas of the engine and whose output voltage suddenly changes at an air-fuel ratio according to the value of the inflow current; and a current supply means that supplies the inflow current so that the output of the oxygen sensor becomes a predetermined value. a current value detection means for detecting the value of the injected current; and foot-knock control of the air-fuel ratio to the target air-fuel ratio based on the output of the current value detection means, and when a command is given to stop the feedback control, the air-fuel ratio is an air-fuel ratio control means that maintains the air-fuel ratio at a predetermined air-fuel ratio; a value of the injected current is compared with a predetermined reference value to determine whether or not the oxygen sensor is abnormal; and when it is determined that the oxygen sensor is abnormal, the feedback control is stopped. 1. An air-fuel ratio control device comprising: a stop command means for commanding a command; and a reference value setting means for setting the predetermined reference value according to operating conditions.