JP2535007B2 - Engine air-fuel ratio control device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio of an air-fuel mixture used for combustion based on a detection output obtained from an oxygen concentration detector that detects the oxygen concentration in exhaust gas. The present invention relates to an air-fuel ratio control device for an engine that controls

(Prior Art) In engines installed in automobiles, etc., an oxygen concentration detector is installed in the exhaust system to improve exhaust gas purification performance and fuel efficiency, and the detection output obtained from the oxygen concentration detector It is known to control the air-fuel ratio of the air-fuel mixture used for combustion based on the above.

As an oxygen concentration detector used to control such an air-fuel ratio, a platinum electrode is conventionally arranged on the inner and outer peripheral surfaces of zirconia, which is a fixed electrolyte, and the exhaust gas in the exhaust gas due to electromotive force generated between the platinum electrodes is disposed. A zirconia oxygen concentration detector adapted to detect oxygen concentration is widely used.

On the other hand, in recent years, development of a semiconductor oxygen concentration detector using a detection element made of an oxide semiconductor whose electric resistance changes according to the oxygen concentration in exhaust gas has been advanced. This semiconductor oxygen concentration detector has advantages such as a simpler structure and a smaller size than the above-mentioned zirconia oxygen concentration detector.

However, with a semiconductor oxygen concentration detector in which only one type of N-type or P-type oxide semiconductor is used, it is extremely difficult to accurately detect the oxygen concentration in the exhaust gas over the entire air-fuel ratio range used. difficult.

Therefore, in the application of the present application, for example, Japanese Patent Application No. 60-
As disclosed in 198481, it has a first detection element made of an N-type oxide semiconductor and a second detection element made of a P-type oxide semiconductor, and has a first detection element and a first fixed resistor. Are connected in series, the second detection element and the second fixed resistance are connected in series, and a set including the first detection element and the first fixed resistance, a second detection element and a second fixed resistance, A pair of resistors, each of which is connected in parallel to a power source to form a bridge circuit, and which has a voltage and a second voltage obtained at a connection midpoint between the first detection element and the first fixed resistor. Detection element and second
An oxygen concentration detector configured to form a detection output based on the voltage obtained at the connection midpoint between the fixed resistor and the fixed resistor is provided for combustion based on the detection output obtained from the oxygen concentration detector. An air-fuel ratio control device for an engine has been proposed which is designed to control the air-fuel ratio of the air-fuel mixture.

According to the air-fuel ratio control device for such an engine, the oxygen concentration detector can accurately detect the oxygen concentration in the exhaust gas over the entire range of the air-fuel ratio used, so that the air-fuel ratio is feedback-controlled in each air-fuel ratio region. It becomes possible to do.

By the way, the semiconductor oxygen concentration detector as described above is
Since the change in the oxygen concentration in the exhaust gas is detected based on the change in the resistance value of the oxide semiconductor, if the resistance value of the oxide semiconductor changes due to the change in the temperature of the exhaust gas, an appropriate detection output can be obtained. Has the drawback that Therefore, in order to make up for such a defect, an element temperature adjusting means such as a heater is attached to the semiconductor oxygen concentration detector, and by this element temperature adjusting means, the temperature of the detection element made of an oxide semiconductor (hereinafter, referred to as element temperature). It is conceivable to adjust) to a predetermined temperature.

When adjusting the element temperature by the element temperature adjusting means,
Usually, the element temperature is set in a predetermined temperature range, for example, a temperature range in which the response as an oxygen concentration detector is good and durability is not adversely affected (hereinafter referred to as a normal temperature range). It is desirable to keep it within.

(Problems to be Solved by the Invention) In the above-described semiconductor oxygen concentration detector using the N-type and P-type oxide semiconductors, the normal temperature may vary depending on the resistance values of the first and second fixed resistors. The detection output may fluctuate significantly due to temperature changes of the first and second detection elements within the range.

That is, for example, on the vertical axis, the voltage obtained at the connection midpoint between the first detection element and the first fixed resistance and the connection midpoint between the second detection element and the second fixed resistance are shown. In FIG. 6 in which the detection output V which is the difference from the obtained voltage is taken and the horizontal axis represents the element temperature Tx, the resistance value of the first fixed resistor is Ra and the resistance value of the second fixed resistor is The detection output V ₁ obtained from the semiconductor oxygen concentration detector whose resistance value is Rb is a solid line, and
The resistance value of the fixed resistor 'is the resistance value of the second fixed resistor Rb' Ra as the detection output V ₂ obtained from the semiconductor oxygen concentration detector shown respectively in broken lines, the detection output V ₁ Is
It is assumed that the maximum value P ₁ is taken within the range from the temperature α to the temperature β which is regarded as the normal temperature range, and the detection output V ₂ takes the maximum value P ₂ outside the normal temperature range.

In such a case, the detection output V ₁ has a maximum value P ₁ within the normal temperature range.
Therefore, the fluctuation of the detection output V ₁ with respect to the change of the element temperature Tx in the normal temperature range becomes relatively small, but the detection output V ₂ takes the maximum value P ₂ outside the normal temperature range, The fluctuation of the detection output V ₂ with respect to the change of the element temperature Tx within the normal temperature range becomes extremely large.

As described above, this characteristic is obtained not only when the difference between the voltages obtained at the two connection midpoints is the detection output V, but also when the ratio of the voltages obtained at the two connection midpoints is the detection output V.
If it is set, the same will occur.

If the detection output fluctuates greatly with respect to changes in the element temperature within the normal temperature range, the detection output does not accurately represent the oxygen concentration in the exhaust gas, so the control accuracy of the air-fuel ratio decreases and feedback There is a risk that the operating state of the engine becomes unstable during control.

However, conventionally, the resistance values of the first and second fixed resistors have not been selected based on the above viewpoint.

In view of such a point, the present invention provides a first detection element made of an N-type oxide semiconductor to which a first fixed resistance is connected in series,
Type oxide semiconductor second detection element and a second fixed resistance are connected in series, a set of the first detection element and the first fixed resistance, a second detection element and a second fixed resistance. A pair of resistors, each connected in parallel to a power supply to form a bridge circuit, the voltage obtained at the midpoint of the connection between the first detection element and the first fixed resistor, An oxygen concentration detector configured to form a detection output based on a voltage obtained at a connection midpoint between the second detection element and the second fixed resistor is provided. The air-fuel ratio of the air-fuel mixture used for combustion is controlled based on the obtained detection output, and the fluctuation of the detection output with respect to the change of the element temperature within the normal temperature range is made as small as possible. Engine designed to improve the control accuracy of the air-fuel ratio And to provide an air-fuel ratio control apparatus.

(Means for Solving Problems) In order to achieve the above-mentioned object, the air-fuel ratio control device for an engine according to the present invention comprises a first N-type oxide semiconductor.
Of the detection element and the first fixed resistance element in series, and
The series connection of the second detection element and the second fixed resistance element made of a P-type oxide semiconductor is connected in parallel to the power source, respectively, and the connection between the first detection element and the first fixed resistance element is performed. Oxygen concentration detection means adapted to form a detection output based on the voltage obtained at the connection midpoint and the voltage obtained at the connection midpoint between the second detection element and the second fixed resistance element. When,
Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture used for combustion based on the detection output obtained from the oxygen concentration detection means, and the first and second oxygen concentration detection means
The resistance value of the fixed resistance element is selected so that the detection output has a maximum value within the practical operating temperature range of the first and second detection elements.

(Operation) In the air-fuel ratio control apparatus for an engine according to the present invention configured as described above, the detection output such as the difference or ratio of the voltages obtained at the two connection midpoints is predetermined. Since the resistance values of the first and second fixed resistance elements are selected so as to take the maximum value within the temperature range, the fluctuation of the detection output with respect to the change of the element temperature within the temperature range is extremely small. .

Therefore, the detected output accurately corresponds to the oxygen concentration in the exhaust gas, and the control accuracy of the air-fuel ratio is improved.

(Example) Hereinafter, the Example of this invention is described with reference to drawings.

FIG. 1 shows an example of an air-fuel ratio control system for an engine according to the present invention, together with an engine to which it is applied. In FIG. 2, an air cleaner 11 is provided in a combustion chamber 14 of the engine body 10.
A throttle valve 16 interlocked with an accelerator pedal is arranged in an intake passage 12 that guides the income air from. The opening of the throttle valve 16 is detected by a throttle opening sensor 18, and a detection signal St corresponding to the opening of the throttle valve 16 is obtained from the throttle opening sensor 18, which is a control unit described in detail later. Supplied to 100.

An air flow meter 20 for detecting intake air is provided upstream of the portion of the intake passage 12 where the throttle valve 16 is arranged.
Is provided, and a detection signal Sa corresponding to the detected intake air amount is supplied from the air flow meter 20 to the control unit 100. Further, a surge tank 22 having a relatively large volume is provided on the downstream side of the portion where the throttle valve 16 is arranged in the intake passage 12, and a fuel injection valve 25 is provided on the downstream side of the surge tank 22. It has been established. The fuel injection valve 25 is electronically controlled, and operates to open according to the pulse width of the injection pulse signal Pc supplied from the control unit 100, and the fuel is pressure-controlled and pressure-fed from the fuel supply system. At a predetermined timing toward the intake port portion for the combustion chamber 14, for example, intermittent injection at a timing synchronized with the rotation of the engine,
An air-fuel mixture used for combustion in the combustion chamber 14 is created. The air-fuel mixture is supplied to the combustion chamber 14 via the intake valve 27, ignited by the ignition plug 28, and burned. Then, the exhaust gas generated by burning the air-fuel mixture in the combustion chamber 14 is discharged to the exhaust passage 26 via the exhaust valve 29.

In the exhaust passage 26, a catalytic converter 19 for purifying exhaust gas is arranged and an oxygen concentration detector 30 is also provided. As shown schematically in FIG. 2, the oxygen concentration detector 30 comprises a first detection element 41 made of an N-type metal oxide semiconductor and a P-type metal oxide semiconductor inserted in the exhaust passage 26. The second detection element 43 is provided, and the fixed resistance 42 whose resistance value is selected as described later is connected in series to the first detection element 41, and the second detection element 43 is connected to the fixed resistance 42. Similarly to the fixed resistor 42, a fixed resistor 44 whose resistance value is selected as will be described later is connected in series, and a set of the first detecting element 41 and the fixed resistor 42, a second detecting element 43 and the fixed resistor 44 are connected. And the constant voltage source 45 that supplies the voltage Vc, respectively.
And are connected in parallel to form a bridge circuit. Then, the first detection element 41 and the fixed resistor
The voltage obtained at the midpoint of the connection with 42 is supplied to the subtraction circuit 55 as the detection signal Vsen, and the second detection element
The voltage obtained at the connection midpoint between the 43 and the fixed resistor 44 is supplied to the subtraction circuit 55 as the detection signal Vref, and the detection signal Vsen is subtracted from the detection signal Vref in the subtraction circuit 55 to obtain the detection signal Vout. Then, the detection signal Vout is supplied to the control unit 100.

In this example, as the N-type metal oxide semiconductor, for example, one containing BaSnO ₃ as a main component and an additive such as SiO ₂ or Al ₂ O ₃ added thereto is used. As a semiconductor, for example, TiSrO ₃ as a main component,
A material to which an additive such as SiO ₂ or Al ₂ O ₃ is added is used.

Then, in this example, in order to make the fluctuation range of the detection signal Vout with respect to the change of the element temperature within the normal temperature range as small as possible, the fixed resistance 42 and the fixed resistance 42 in the oxygen concentration detector 30.
The resistance value of 44 is selected so that the maximum value of the change of the detection signal Vout with respect to the temperature change can be obtained under the optimum element temperature.

Specifically, the resistance value of the fixed resistor 42 is R2, the resistance value of the fixed resistor 44 is R4, and the resistance value of the first detection element 41 is R1.
And the resistance value of the second detection element 43 is R3, the resistance value is
R1 and R3 are represented by the following equation: R1 = Ros · f · Exp (−m _S · ΔT) ... R3 = Ror · g · Exp (−m _R · ΔT). In formulas and formulas, Ros and Ror
Is the resistance value of the first and second detection elements 41 and 43 in a state where the air-fuel ratio is set to the target air-fuel ratio under the optimum element temperature,
Further, f and g are functions showing the air-fuel ratio dependence of the first and second detection elements 41 and 43, and are 1 when the air-fuel ratio is the target air-fuel ratio. Furthermore, ΔT is the difference between the optimum element temperature and the actual element temperature, and m _S and m _R are the temperature coefficients of the first and second detection elements 41 and 43, which are made as equal as possible. However, it is difficult to adjust the material to the same value.

Detection as a difference between the voltage obtained at the connection midpoint between the first detection element 41 and the fixed resistance 42 and the voltage obtained at the connection midpoint between the second detection element 43 and the fixed resistance 44 The signal Vout is
Using the formula and the relation of the formula, Vout = Vc · [R4 / {R4 + Ror · g · Exp (-m _R · ΔT)} −R2 / {R2 + Ros · f · Exp (−m _S · ΔT)}]… Be done.

Considering the condition that the detection signal Vout expressed by the formula has a maximum value, the detection signal Vout is the first and second detection elements.
From the characteristics of 41 and 43, there is no change that takes a minimum value with respect to the temperature change, so the condition that a maximum value is obtained when the differential value is zero is required. Therefore, the following equation by differentiating the equation δVout / δΔT = Vc · [{R4 · Ror · g · Exp (-m R · ΔT) · m R} / {R4 + Ror · g · Exp (-m R · ΔT)} ² − {R2 · Ros · f · Exp (−m _S · ΔT) · m _S } / {R2 + Ros · f · Exp (−m _S · ΔT)} ² ]… and the differential value is set to zero in the equation. When arranged, the relation of the following formula is obtained.

{R2 ・ Ros ・ f ・ Exp (-m _S・ ΔT) ・ m _S } / {R2 ・ Ros ・ f ・ Exp (-m _S・ ΔT)} ² = {R4 ・ Ror ・ g ・ Exp (-m _{R · ΔT) · m R} /} {R4 + Ror · g · Exp (-m R · ΔT)} 2 ... Next, the expression is an element temperature is optimal element temperature, relationship established when the air-fuel ratio is the target air-fuel ratio To obtain the formula Δ
By substituting T = 0 and f = g = 1, (R2 · Ros · m _S ) / (R2 + Ros) ² = (R4 · Ror · m _R ) / (R4 + Ror) ² ... Is obtained.

The resistance values R2 and R4 satisfying such an equation are the detection signal Vout
The maximum value of the change with respect to the temperature change satisfies the condition obtained under the optimum element temperature.

The element temperature Tx is determined to be the optimum element temperature according to FIG. 3 and the formula showing the relationship between the resistance values R1 and R3 and the element temperature Tx.
For example, when the resistance value R2 of the fixed resistor 42 and the resistance value R4 of the fixed resistor 44, at which the detection signal Vout takes the maximum value at 800 ° C., are obtained, for example, the resistance value R2 is 5 kΩ,
The resistance value R4 was selected to be 120 kΩ. Based on the selection result, in this example, the resistance value of the fixed resistor 42 is set to 5 kΩ, and the resistance value of the fixed resistor 44 is set to 120 kΩ.

In this way, the resistance values R2 and R4 of the fixed resistors 42 and 44 are
When is selected, the maximum value of the detection signal Vout is the same as the detection output V ₁ shown in FIG.
The temperature is located at a temperature γ substantially in the center of −β), and the fluctuation of the detection signal Vout is minimized with respect to the change of the element temperature Tx. On the other hand, regardless of the above equation, when the resistance values R2 and R4 of the fixed resistors 42 and 44 are selected, for example, when the resistance value R2 is selected to 1 kΩ, the resistance value R4 is selected to 120 kΩ, respectively The maximum value of the signal Vout is located outside the temperature range (α-β) like the detection output V ₂ shown in FIG. 6 above, and the fluctuation of the detection signal Vout is extremely large with respect to the change of the element temperature Tx. It becomes big.

The ratio of the voltage obtained at the connection midpoint between the first detection element 41 and the fixed resistance 42 and the voltage obtained at the connection midpoint between the second detection element 43 and the fixed resistance 44 is detected. When the signal Vout is used, the detection signal Vout is calculated by using the formula and the relation of the formula, Vout = [R2 ・ {R4 + Ror ・ g ・ Exp (-m _R・ ΔT)}] / [R4 ・ {R2 + Ros + f ・ Exp (−m _S · ΔT)}] is expressed as

In such case also, the differential value of the detection signal Vout by differentiating Equation every zero, it Substituting [Delta] T = 0 and f = g = 1, the following equation _{(R2 + Ros) · m R} · Ror = (R4 + Ror)・ M _S・ Ros… is obtained. The resistance values R2 and R4 satisfying such an expression satisfy the condition that the maximum value of the change of the detection signal Vout with respect to the temperature change is obtained under the optimum element temperature.

On the other hand, the detection signal Vsen supplied to the subtraction circuit 55 is assumed to change according to the oxygen concentration in the exhaust gas, and
When Tx is maintained in the normal temperature range, the voltage V is taken on the vertical axis and the excess air ratio λ is taken on the horizontal axis, as shown by the broken line in FIG. When the air-fuel ratio is set to the rich air-fuel ratio and the excess air ratio λ is smaller than 1, a level near the voltage Vc of the constant voltage source 45 is set and the excess air ratio λ is slightly smaller than 1. When the state changes to a state slightly larger than 1, the level drops sharply, and the level becomes smaller as the air-fuel ratio becomes leaner and the excess air ratio λ becomes larger than 1.

The detection signal Vref supplied to the subtraction circuit 55 is also changed according to the oxygen concentration in the exhaust gas, and its level is the fourth when the element temperature Tx is maintained in the normal temperature range. As indicated by the one-dot chain line in the figure, the larger the excess air ratio λ is smaller than 1, the larger the air excess ratio λ is from slightly smaller than 1 to the state where the excess air ratio λ is slightly larger than 1. When it changes, it increases sharply, and becomes larger as the excess air ratio λ is larger than 1.

Then, as indicated by the solid line in FIG. 4, the detection signal Vout supplied to the control unit 100 has a level at which the excess air ratio λ is 1 when the element temperature Tx is maintained in the normal temperature range. When it is smaller, it takes a negative level, and when the excess air ratio λ changes from slightly smaller than 1 to slightly larger, it changes sharply, and as the excess air ratio λ becomes larger than 1, , Will increase with a relatively large gradient.

Further, the oxygen concentration detector 30 detects the temperature of the heater 47 for adjusting the first and second detection elements 41 and 43 to a predetermined temperature, and the temperature of the first and second detection elements 41 and 43. The element temperature detection sensor 52 that operates is incorporated. The heater 47 includes a constant voltage source 48 and a current controller as shown in FIG.
An operating current I is supplied via 50. The current control unit 50 is
The operating current I is changed according to the control signal Ci supplied from the control unit 100. Element temperature detection sensor 52
A detection signal Sq corresponding to the temperatures of the first and second detection elements 41 and 43 is obtained from the control unit 100.
Is supplied to.

The control unit 100 includes a rotation speed sensor 32 for detecting an engine rotation speed, which is arranged in association with a crank mechanism 33 that changes the reciprocating motion of the piston 31 in the engine body 10 into a rotary motion, and detects the engine speed according to the engine speed. signal
Sn is supplied.

The control unit 100 includes a detection signal corresponding to the cooling water temperature of the engine, which is obtained from a water temperature sensor (not shown), in addition to the above-described detection signals Sn, Sa, St, Vout and Sq. Another detection signal Sx is also supplied.

The control unit 100, based on the various detection signals Sn, Sa, St, Vout, Sq and Sx, based on the air-fuel ratio of the air-fuel mixture used for combustion in the combustion chamber 14, the operating state of the engine, for example, intake air. The fuel injection amount is controlled by changing the pulse width of the injection pulse signal Pc supplied to the fuel injection valve 25 so as to match the target air-fuel ratio set according to the air amount and the engine speed.

At that time, the control unit 100 detects the detection signals Sa and S.
The basic fuel injection amount Tp is set based on the intake air amount and the engine speed, which are respectively represented by n, and the air-fuel ratio correction coefficient C _A , the feedback correction coefficient C _F, and the other correction coefficient C are set.
Set _X. Then, the basic fuel injection amount Tp is added to the air-fuel ratio correction coefficient C _A , the feedback correction coefficient C _F, and the correction coefficient C
_The fuel injection amount Ti is set by multiplying by _X , an injection pulse signal Pc having a pulse width corresponding to this fuel injection amount Ti is formed, and it is supplied to the fuel injection valve 25.

In such a case, the control unit 100, when the target air-fuel ratio T _AF air-fuel ratio correction coefficient C _A is the stoichiometric air-fuel ratio, the reference value, for example, set to 1, the target air-fuel ratio T _AF is larger than the stoichiometric air-fuel ratio When the lean air-fuel ratio is
The target air-fuel ratio T _AF is set smaller than the reference value, and is set larger than the reference value when the target air-fuel ratio T _AF is a rich air-fuel ratio which is smaller than the theoretical air-fuel ratio.

Further, the control unit 100 uses the feedback correction coefficient C _F as a detection signal obtained from the oxygen concentration detector 30.
Set based on Vout as described below.

That is, the control unit 100 controls the fourth air-fuel ratio corresponding to the stoichiometric air-fuel ratio when the target air-fuel ratio _TAF is set to the stoichiometric air-fuel ratio.
The reference level V _S as shown in the figure is set, the reference level V _S is compared with the detection signal Vout, and when the detection signal Vout is larger than the reference level V _S , the feedback correction coefficient C Decrease _F by a specified value and detect
When Vout becomes smaller than the reference level V _S , the feedback correction coefficient C _F is increased by a predetermined value because it is a lean air-fuel ratio.

Further, the control unit 100 sets a reference level V _R as shown in FIG. 4 corresponding to the target air-fuel ratio T _AF when the target air-fuel ratio T _AF is set to the rich air-fuel ratio,
It compares the detection signal Vout and the reference level V _R, the detection signal
When Vout is larger than the reference level V _R , the air-fuel ratio is on the rich side of the target air-fuel ratio T _AF , so the feedback correction coefficient C _F is decreased by a predetermined value, and the detection signal Vout becomes smaller than the reference level V _R. At this time, the air-fuel ratio is leaner than the target air-fuel ratio T _AF , so the feedback correction coefficient C _F is increased by a predetermined value.

Furthermore, the control unit 100 sets the target air-fuel ratio T _AF
Is set to a lean air-fuel ratio, the reference level V _L corresponding to the target air-fuel ratio T _AF is set as shown in FIG. 4, the reference level V _L is compared with the detection signal Vout, and the detection signal is detected.
When Vout is larger than the reference level V _L , the air-fuel ratio is leaner than the target air-fuel ratio T _AF , so the feedback correction coefficient C _F is decreased by a predetermined value, and the detection signal Vout becomes the reference level V _L.
When it becomes smaller, the air-fuel ratio is on the rich side of the target air-fuel ratio T _AF , so the feedback correction coefficient C _F is increased by a predetermined value.

By doing so, the fuel injection amount Ti is feedback-controlled and the air-fuel ratio converges to the target air-fuel ratio T _AF .

On the other hand, the control unit 100, in addition to performing the air-fuel ratio control as described above, changes the amount of heat generated in the heater 47 and adjusts the temperatures of the first and second detection elements 41 and 43 by controlling the current. The control signal Ci is supplied to the section 50 to control the current flowing through the heater 47 built into the oxygen concentration detector 30.

In the oxygen concentration detector 30 including the heater 47, the first and second detection elements are used from the viewpoint of responsiveness and durability.
The temperature of 41 and 43 is preferably a predetermined temperature α, for example, about 720 ° C. or higher, and a predetermined temperature β, for example, a range of about 870 ° C. or lower, and the normal temperature range (α-β).
Within a temperature γ between the temperatures α and β, for example, 80
At about 0 ° C., the oxygen concentration detector 30 has the best responsiveness.

Therefore, the control unit 100 controls the amount of heat generated by the heater 47 so that the element temperature Tx is close to the temperature γ. At that time, the control unit 100 detects the element temperature Tx based on the detection signal Sq obtained from the element temperature detection sensor 52, compares the element temperature Tx with the temperature γ, and when the element temperature Tx is equal to or higher than the temperature γ, The control value Vh for controlling the current control unit 50 is reduced by a predetermined value Vd, and when the element temperature Tx is equal to or lower than the temperature Tγ or the temperature Tα, the control value Vh
Is increased by a value Vd to be set, a control signal Ci corresponding to the control value Vh is formed, and the control signal Ci is supplied to the current controller 50.
As a result, the current control unit 50 causes the heater to respond to the control signal Ci.
Controls the current flowing through 47. As a result, the amount of heat generated by the heater 47 is increased or decreased, and the element temperature Tx is maintained within a normal temperature range centered on the target temperature γ.

Control unit 100 that performs the control as described above
Is configured by using, for example, a microcomputer. An example of a program executed by the microcomputer in such a case will be described with reference to the flowchart of FIG.

The flow chart of FIG. 5 shows a basic control routine of the fuel supply amount, which is a process after the start.
At 101, the detection signals Sa, St, Sn, Vout and Sx are fetched,
In the subsequent process 102, the basic fuel injection amount Tp is calculated by using the intake air amount Q represented by the detection signal Sa and the engine speed Nx represented by the detection signal Sn to calculate Tp = K × Q / Nx (where K is a constant). Set by performing.

In the next process 103, the target air-fuel ratio T _AF is set based on the intake air amount Q and the engine speed Nx,
In the following process 105, the air-fuel ratio correction coefficient C _A corresponding to the target air-fuel ratio T _AF is set, and the process proceeds to decision 106. In decision 106, the target air-fuel ratio T _AF is the lean air-fuel ratio,
It is determined which one of the stoichiometric air-fuel ratio and the rich air-fuel ratio, and when the target air-fuel ratio T _AF is determined to be the rich air-fuel ratio, the detection signal Vout and the reference level V _R are set in the process 108. When the comparison is made, the feedback correction coefficient C _F is set based on the comparison result, and the process proceeds to the process 112, and it is determined that the target air-fuel ratio T _AF is the stoichiometric air-fuel ratio,
In the process 109, the detection signal Vout is compared with the reference level V _S , the feedback correction coefficient C _F is set based on the comparison result, the process proceeds to the process 112, and it is determined that the target air-fuel ratio T _AF is the lean air-fuel ratio. If yes, process 111
At, the detection signal Vout is compared with the reference level V _L , the feedback correction coefficient C _F is set based on the comparison result, and the process 112 is proceeded to.

In process 112, another correction value C _X is set based on the detection signals St and Sx, and in the subsequent process 114,
The fuel injection amount Ti is set to the basic fuel injection amount Tp, and the air-fuel ratio correction coefficient C _A ,
Set by multiplying the feedback correction factor C _F and the correction factor C _X and proceed to process 115. In the process 115, an injection pulse signal Pc having a pulse width corresponding to the fuel injection amount Ti is formed, supplied to the fuel injection valve 25, and then returned.

In the above example, the feedback control of the air-fuel ratio is performed when the target air-fuel ratio is any of the rich air-fuel ratio, the stoichiometric air-fuel ratio and the lean air-fuel ratio, but it is not always so. For example, when the target air-fuel ratio is the rich air-fuel ratio,
Compared to when it is stoichiometric or lean air-fuel ratio,
Even if the control accuracy of the air-fuel ratio is lowered to some extent, no serious trouble occurs. Therefore, the air-fuel ratio may be controlled in an open loop.

(Effects of the Invention) As is clear from the above description, in the engine air-fuel ratio control apparatus according to the present invention, the oxygen concentration in which the N-type and P-type oxide semiconductors are used as the first and second detection elements, respectively. Based on the detection output obtained from the detection means, the air-fuel ratio of the air-fuel mixture used for combustion is controlled, and
The resistance values of the first and second fixed resistors connected in series to the first and second detection elements are set so that the detection output obtained from the oxygen concentration detection means has a maximum value within a predetermined temperature range. Since it is selected, the fluctuation of the detection output with respect to the change of the element temperature within the predetermined temperature range is made as small as possible, and as a result, it is possible to improve the driving performance and the control accuracy of the air-fuel ratio. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an engine air-fuel ratio control device according to the present invention together with the main parts of an engine to which it is applied, and FIG. 2 is an equivalent circuit showing the main parts of the example shown in FIG. FIGS. 3, 3 and 4 are characteristic diagrams used for explaining the operation of the example shown in FIG. 1, and FIG. 5 shows a case where a microcomputer is used as the control unit in the example shown in FIG. A flowchart showing an example of a program executed by such a microcomputer,
FIG. 6 is a characteristic diagram for explaining the operation of the semiconductor oxygen concentration detector. In the figure, 10 is an engine body, 12 is an intake passage, 25 is a fuel injection valve, 30 is an oxygen concentration detector, 32 is a rotation speed sensor, and 41 and 43.
Is the first and second detection elements, 42 and 44 are fixed resistors, 100
Is a control unit.

Claims (1)

(57) [Claims] 1. A first detection element made of an N-type oxide semiconductor and a first fixed resistance element connected in series, and a second detection element made of a P-type oxide semiconductor and a second fixed resistance element. And a voltage obtained at a connection midpoint between the first detection element and the first fixed resistance element, and a bridge circuit configured to be connected in parallel to a power source, respectively. Forming a detection output based on the voltage obtained at the connection midpoint between the detection element and the second fixed resistance element, and selecting the resistance values of the first and second fixed resistance elements, Oxygen concentration detection means whose detection output has a maximum value within a predetermined temperature range, and control of the air-fuel ratio of the air-fuel mixture to be burned based on the detection output obtained from the oxygen concentration detection means And an air-fuel ratio control unit for controlling the air-fuel ratio of the engine. Apparatus.