JP2016186249A - Control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an air-fuel ratio sensor provided in an exhaust pipe of an internal combustion engine.SOLUTION: The value of a pump current Ip is limited so as not to exceed a prescribed range current value. Thus, a pump current Ip derived based on an excess current cannot control an air-fuel ratio sensor 2. Therefore, even after the excess current is ceased, the air-fuel ratio sensor 2 can be stably controlled rapidly. Since after the excess current is ceased, the period of transition from the excess current state to a normal condition can be reduced through feedback control, so that an erroneous abnormality detection due to an abnormal value during the transition period can be prevented.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for controlling an air-fuel ratio sensor provided in an exhaust pipe of an internal combustion engine.

  In today's internal combustion engines, a three-way catalyst is used for exhaust gas purification. In order to improve the purification rate by the catalyst, the ratio of fuel and air burned in the internal combustion engine is controlled to be close to the theoretical air-fuel ratio.

  For this reason, there is known a method in which an oxygen concentration in exhaust gas is detected by an air-fuel ratio sensor, and a fuel supply amount to an internal combustion engine is feedback controlled. For example, Patent Document 1 discloses a technique for performing feedback control of the fuel supply amount to the internal combustion engine based on the air-fuel ratio detected by the air-fuel ratio sensor.

JP 2001-318074 A

  However, if an overcurrent occurs in the air-fuel ratio sensor or the air-fuel ratio control device due to a ground fault or an inrush current at start-up, feedback control based on the overcurrent is performed, and it is difficult to derive an appropriate fuel supply amount. Become. For example, when the fuel supply amount is derived based on the overcurrent, an excessive or excessive fuel supply amount is derived, which may significantly reduce the exhaust gas purification efficiency. In addition, when feedback control based on overcurrent is performed, the value used in feedback control is calculated to an appropriate value, and the overcurrent ends until it returns to the normal value. There is a possibility that it is erroneously determined that an abnormality has occurred in the air-fuel ratio sensor or the control device.

  In view of the above problems, an object of the present invention is to provide a technique for appropriately feedback controlling the amount of fuel supplied to an internal combustion engine based on an air-fuel ratio.

  In order to solve the above-described problems, the invention of claim 1 is directed to a detection cell unit that generates an air-fuel ratio voltage according to an air-fuel ratio, and an oxygen according to an amount of current that is connected to the detection cell unit and connected to the detection cell unit. A control device for controlling an air-fuel ratio sensor provided in an exhaust part of an internal combustion engine, and an output means for outputting an output voltage based on the air-fuel ratio voltage; and And a constant voltage means for controlling the connection portion voltage generated at the connection portion to have a constant specified voltage value, so that the pump cell portion is supplied with a pump current so that the air-fuel ratio becomes a predetermined ratio. Limiting means for limiting the value of the pump current so as not to exceed a predetermined current value.

  In the control device according to claim 1, in the control device according to claim 1, the limiting means limits the output voltage value so as not to exceed a predetermined voltage value, whereby the pump current value is predetermined. Limit so that the current value is not exceeded.

  The invention according to claim 3 is the control device according to claim 1, further comprising first detection means for detecting the connection portion voltage, wherein the limiting means is based on a value of the connection portion voltage. By controlling the energization means, the pump current value is limited so as not to exceed a predetermined current value.

  According to a fourth aspect of the present invention, in the control device according to the first aspect, a resistor connected between the connection portion and the constant voltage means, and a connection point between the resistor and the constant voltage means. And a second detecting means for detecting a connection point voltage generated at the connection point, and the limiting means controls the energization means in accordance with the value of the connection point voltage so that the value of the pump current is a predetermined current. Limit the value not to exceed.

  According to a fifth aspect of the present invention, in the control device according to any one of the first to fourth aspects, the predetermined current value is a limit voltage value that is a limit of an output of the constant voltage means, and the specified voltage value. It is defined by the difference between

  The invention of claim 6 is the control device according to any one of claims 1 to 5, further comprising a control means for controlling a fuel injection valve for injecting fuel to the internal combustion engine, wherein the control means comprises: Receiving means for receiving the value of the pump current; first derivation means for deriving an air-fuel ratio from the value of the pump current; and second derivation means for deriving the fuel injection amount based on the air-fuel ratio. .

  Further, the invention of claim 7 is a detection cell unit that generates an air-fuel ratio voltage according to the air-fuel ratio, and a pump cell that is connected to the detection cell unit and connected to the connection unit and absorbs and discharges oxygen according to the amount of current that is energized. A control device for controlling an air-fuel ratio sensor provided in an exhaust part of an internal combustion engine, comprising: an output means for outputting an output voltage based on the air-fuel ratio voltage; and the air-fuel ratio based on the output voltage Energizing means for supplying a pump current to the pump cell portion so that the ratio is a predetermined ratio, and a constant voltage means for controlling the connection portion voltage generated at the connection portion to be a constant specified voltage value, The ability of the constant voltage means to energize the connection voltage to make the connecting portion voltage constant is higher than the ability of the energization means to energize the pump current.

  According to the first to sixth aspects of the present invention, since the limiting means limits the pump current value so as not to exceed the predetermined current value, it is possible to prevent erroneous determination that an abnormality has occurred.

  In particular, according to the invention of claim 2, the limiting means limits the value of the output voltage so as not to exceed the predetermined voltage value, so that the limiting means can limit the value of the pump current by an appropriate method.

  In particular, according to the invention of claim 3, since the limiting means controls the energizing means in accordance with the value of the connecting portion voltage, the limiting means can limit the value of the pump current based on the accurate voltage value.

  In particular, according to the invention of claim 4, the limiting means controls the energizing means in accordance with the value of the connection point voltage, so that the limiting means can limit the value of the pump current based on the voltage value at an appropriate location. .

  In particular, according to the invention of claim 5, the predetermined current value is defined by the difference between the limit voltage value that is the limit of the output of the constant voltage means and the specified voltage value, so the predetermined current value is limited to an appropriate value. can do.

  Further, particularly according to the invention of claim 6, the limiting means limits the value of the pump current so as not to exceed the predetermined current value, so that the control means can derive an appropriate fuel injection amount and inject it from the fuel injection valve. .

  Further, according to the invention of claim 7, the ability of the constant voltage means to pass the current to make the connection voltage constant at a predetermined specified voltage value is higher than the ability of the conduction means to pass the pump current. Therefore, even if the pump current increases or decreases, the connection voltage can be controlled to a constant specified voltage value.

FIG. 1 is a diagram showing an outline of a fuel injection system. FIG. 2 is a diagram showing the configuration of a conventional air-fuel ratio control device. FIG. 3 is a diagram illustrating an example of a correlation between an excessive pump current and a COM voltage. FIG. 4 is a diagram showing the configuration of the air-fuel ratio control apparatus according to the first embodiment. FIG. 5 is a diagram illustrating the configuration of the limiting circuit. FIG. 6 is a diagram illustrating a configuration of an air-fuel ratio control apparatus according to the second embodiment. FIG. 7 is a diagram illustrating a configuration of the voltage monitor unit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<1. First Embodiment>
<1-1. Overview>
FIG. 1 shows an outline of an air-fuel ratio control system 10 that controls the air-fuel ratio of fuel supplied to the internal combustion engine 10a. The air-fuel ratio control system 10 controls the air-fuel ratio sensor 2, the fuel injection device 3 including the air-fuel ratio control device 1, and the fuel injection valve 4, and the fuel burned in the internal combustion engine 10a becomes close to the stoichiometric air-fuel ratio. Control as follows. Note that a lean air-fuel ratio of fuel that is advantageous for fuel efficiency and a rich air-fuel ratio of fuel used at start-up or acceleration are also used, and the air-fuel ratio is properly used depending on the load situation. For this reason, air-fuel ratio feedback control is always performed while the internal combustion engine 10a is being driven.

  First, the fuel injection device 3 detects the intake air amount detected by the intake sensor 10c disposed in the intake pipe 10b, the air-fuel ratio in the exhaust pipe 10d based on the signal from the air-fuel ratio sensor 2 disposed in the exhaust pipe 10d, And the fuel injection amount is calculated from the target air-fuel ratio or the like. The fuel injection device 3 outputs a fuel injection pulse having a pulse width corresponding to the fuel injection amount to the fuel injection valve 4, and fuel is injected from the fuel injection valve 4 and burned in the internal combustion engine 10a. At this time, the air-fuel ratio in the exhaust pipe 10d is fed back to the control device 1, and the fuel injection device 3 repeatedly calculates the fuel injection amount.

  The air-fuel ratio control device 1 detects the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10a based on the signal from the air-fuel ratio sensor 2, and the air-fuel ratio of the fuel burned in the internal combustion engine 10a is the stoichiometric air-fuel ratio. Feedback control is performed so that

  In such feedback control, the air-fuel ratio sensor 2 is disposed in the exhaust pipe 10d and outputs a signal corresponding to the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 2 includes a detection cell portion 2a capable of linearly detecting the air-fuel ratio, and a pump cell portion 2b that absorbs and discharges oxygen, that is, pumps. By pumping the pump cell unit 2b and making the air-fuel ratio detected by the detection cell unit 2a coincide with the stoichiometric air-fuel ratio, a difference between the air-fuel ratio detected by the detection cell unit 2a and the stoichiometric air-fuel ratio can be detected. By detecting such a difference, the air-fuel ratio of the exhaust gas in the exhaust pipe 10d can be detected.

  The control device 1 and the air-fuel ratio sensor 2 are connected to an abnormality detection circuit (not shown). The abnormality detection circuit monitors the voltage value applied to the control device 1 and the air-fuel ratio sensor 2 and the current value supplied. The abnormality detection circuit determines the occurrence of an abnormality or stops the driving of the control device 1 when the voltage value and the current value are larger and smaller than predetermined values.

  FIG. 2 shows a configuration of a conventional air-fuel ratio control apparatus 100. In the conventional air-fuel ratio control apparatus 100, the following air-fuel ratio feedback control is performed.

  First, a voltage corresponding to the air-fuel ratio in the exhaust pipe is generated at the VS terminal of the detection cell unit 2a of the air-fuel ratio sensor 2 (terminal provided on the side opposite to the side where the detection cell unit 2a is connected to the pump cell unit 2b). In the case of a voltage corresponding to the theoretical air-fuel ratio, 0.45 [V] is generated at the VS terminal. For this reason, when the inside of the exhaust pipe has a stoichiometric air-fuel ratio, the voltage at the VS terminal is 3.75 [V] due to the addition of the voltage at the connection between the detection cell unit 2a and the pump cell unit 2b.

  The A / F detection circuit 110 detects a voltage generated at the VS terminal and outputs a voltage corresponding to the detected voltage to the VI conversion circuit 120.

  Based on the voltage value output from the A / F detection circuit 110, the VI conversion circuit 120 supplies the pump current Ip to the pump cell unit 2b so that the pump cell unit 2b pumps oxygen and the detection cell unit 2a detects the theoretical air-fuel ratio. Energize. That is, the VI conversion circuit 120 supplies the pump cell unit 2b with a pump current Ip having a value at which the pump cell unit 2b should pump oxygen so as to fill the difference between the detected air-fuel ratio and the stoichiometric air-fuel ratio.

  At this time, in order for the VS terminal of the detection cell portion 2a of the air-fuel ratio sensor 2 to stably generate a voltage corresponding to the air-fuel ratio in the exhaust pipe, the connection terminal com which is a connection portion with the pump cell portion 2b is constant. It is necessary to hold the voltage value. For example, 3.3 [V].

  The constant voltage control unit 130 controls the connection terminal com to have a constant voltage value by passing the COM current Icom through the sense resistor Rs, which is a resistor, and causing a voltage drop in the sense resistor Rs. That is, the constant voltage control unit 14 performs control so that the voltage (COM terminal voltage Vcom; connection unit voltage) generated at the connection terminal com serving as the connection unit between the detection cell unit 2a and the pump cell unit 2b becomes a constant specified voltage value. To do. Note that the current capability by which the constant voltage control unit 14 supplies the COM current Icom and controls the connection terminal com to a constant voltage value is determined by the following arithmetic expression. The current capability is the capability of energizing current, that is, electromotive force.

Current capability of constant voltage control unit 14 = (COM terminal voltage Vcom−constant voltage source output voltage limit) / sense resistor Rs (1)
Here, the “constant voltage source output voltage limit” is the voltage across the sense resistor Rs connected between the constant voltage control unit 14 and the connection terminal com. That is, the current capability is defined by the difference between the limit voltage value that is the limit of the output of the constant voltage control unit 14 and the COM terminal voltage Vcom.

  By detecting the amount of current supplied to the sense resistor Rs, a control unit (not shown) derives the air-fuel ratio and determines the fuel injection amount based on the air-fuel ratio. When fuel is injected into the internal combustion engine and combusted, exhaust gas is discharged into the exhaust pipe, the air-fuel ratio sensor 2 detects the air-fuel ratio again, and air-fuel ratio feedback control is repeated.

  Here, in such an air-fuel ratio control apparatus 100, when an overcurrent Is caused by a ground fault or an inrush current at start-up occurs in the air-fuel ratio sensor 2 or the like, the following problems occur.

  First, when the overcurrent Is flows into the connection terminal com (connection part), the voltage of the connection terminal com rises. As described above, the voltage generated at the VS terminal is the sum of the COM terminal voltage Vcom and the voltage value corresponding to the air-fuel ratio. Therefore, when the COM terminal voltage Vcom increases, the voltage generated at the VS terminal also increases. In this case, an excessive voltage different from the actual air-fuel ratio is input to the A / F detection circuit 110.

  When an excessive voltage is input to the A / F detection circuit 110, the VI conversion circuit 120 receiving the output of the A / F detection circuit 110 derives the pump current Ip based on the excessive voltage value. Will be derived too much.

  When the generation of the overcurrent Is continues or further increases, the pump current Ip becomes further excessive by repeating the air-fuel ratio feedback control.

  As long as the value of the pump current Ip is within the range allowed by the current capability of the constant voltage control unit 140, the constant voltage control unit 140 can hold the COM terminal voltage Vcom at a constant voltage. However, if the pump current Ip is further increased by repeating the feedback control based on the overvoltage, the constant voltage control unit 140 can no longer hold the COM terminal voltage Vcom at a constant voltage.

  When the feedback control is performed after the overcurrent has ended, an excessive pump current Ip is applied to the pump cell portion 2b even though the overcurrent has ended. If an excessive current is supplied to the pump cell unit 2b in a normal state, the air-fuel ratio sensor 2 may be erroneously determined to be in an abnormal state, and control may be hindered.

  FIG. 3 shows the correlation between the excessive pump current Ip and the COM terminal voltage Vcom. For example, until the pump current Ip is about 30 [mA], the constant voltage control unit 140 controls the COM terminal voltage Vcom to 3.3 [V]. However, when the pump current Ip exceeds 30 [mA], the COM terminal voltage Vcom increases from 3.3 [V]. This is because the output capability of the constant voltage control unit 140 is exceeded and the constant voltage control unit 140 cannot control the COM terminal voltage Vcom to 3.3 [V]. That is, the constant voltage control unit 140 supplies the COM current Icom to the sense resistor Rs, and the total amount of current including the pump current Ip supplied to the connection terminal com cannot be kept below 30 [mA]. . As a result, the amount of current supplied to the connection terminal com increases, and the COM terminal voltage Vcom rises. When the COM terminal voltage Vcom rises to, for example, about 10 [V], it is necessary to repeat a plurality of operations before returning to 3.3 [V] by feedback control.

  Even after the overcurrent generated in the air-fuel ratio sensor 2 or the like has ended, it is necessary to stably perform the air-fuel ratio feedback control without erroneously determining an abnormal state. The air-fuel ratio control apparatus 1 that performs such air-fuel ratio feedback control will be described below.

<1-2. Configuration>
FIG. 4 shows the configuration of the air-fuel ratio control apparatus 1 according to the first embodiment. The control device 1 is an electronic control device or an integrated circuit, and is connected to the air-fuel ratio sensor 2. The control device 1 detects a voltage value corresponding to the air-fuel ratio output from the air-fuel ratio sensor 2, and performs feedback control so that the air-fuel ratio sensor 2 indicates the stoichiometric air-fuel ratio.

  The control device 1 is provided in the fuel injection device 3 together with a control unit 31 that controls the fuel injection valve 4. The control unit 31 includes a receiving unit 31a, an air-fuel ratio deriving unit 31b, and a fuel deriving unit 31c, and controls the fuel injection valve 4.

  The receiver 31a receives a signal corresponding to the air-fuel ratio from the control device 1.

  The air-fuel ratio sensor 2 is a so-called wide-range air-fuel ratio sensor that can linearly detect the air-fuel ratio of the exhaust gas in the exhaust pipe. The air-fuel ratio sensor 2 is formed in a porous layer with a solid electrolyte material such as zirconia having oxygen ion conductivity, and is disposed in the exhaust pipe. The air-fuel ratio sensor 2 includes a heater, an atmospheric chamber, and a gas diffusion chamber (all not shown). The air-fuel ratio sensor 2 further includes a detection cell unit 2a and a pump cell unit 2b made of a solid electrolyte material such as zirconia having oxygen ion conductivity.

  The heater is energized with current to heat the sensor element. This is because the air-fuel ratio sensor 2 is activated. The atmosphere chamber is formed in communication with the atmosphere outside the exhaust pipe, and takes in the atmosphere as a reference gas into the air-fuel ratio sensor 2. The gas diffusion chamber is formed in communication with the exhaust gas through an exhaust introduction hole formed in the air-fuel ratio sensor 2, and takes in the exhaust gas into the air-fuel ratio sensor 2.

  The detection cell unit 2a is also called a Nernst cell and generates a voltage (air-fuel ratio voltage) corresponding to the air-fuel ratio of the exhaust gas in the exhaust pipe. The detection cell unit 2a generates a voltage corresponding to the oxygen ion concentration in the gas diffusion chamber at the terminal VS. By detecting the voltage generated in the detection cell unit 2a, the difference (deviation) between the air-fuel ratio of the exhaust gas and the stoichiometric air-fuel ratio can be detected.

  The pump cell unit 2b absorbs and discharges oxygen corresponding to the energized current (pump current Ip). The pump cell unit 2b absorbs and discharges oxygen so that the detection cell unit 2a detects the stoichiometric air-fuel ratio. Therefore, if this current is detected, the deviation from the air-fuel ratio of the exhaust gas can be detected, and therefore the air-fuel ratio in the exhaust pipe can be detected from the magnitude of the deviation. The pump cell unit 2b includes a terminal IP on the side opposite to the detection cell unit 2a. A pump current Ip is applied to the terminal IP.

  Note that, by reversing the direction of voltage application to the pump cell unit 2b on the basis of the lean / rich output from the detection cell unit 2a, a wide range is obtained based on the current flowing through the pump cell unit 2b in both the lean region and the rich region. The air-fuel ratio can be detected.

  The detection cell unit 2a and the pump cell unit 2b are connected by a connection terminal com.

  The control device 1 includes a sense resistor Rs, an A / F detection circuit 11, a limiting circuit 12, a VI conversion circuit 13, a constant voltage control unit 14, and a current monitor unit 15.

  The sense resistor Rs is a resistor for detecting the pump current Ip and is, for example, 100 [Ω]. One end of the sense resistor Rs is connected to the connection terminal com, and the other end is connected to a constant voltage control unit 14 described later in the control device 1.

  The A / F detection circuit 11 detects a voltage value based on the air-fuel ratio generated at the terminal VS of the detection cell unit 2a. The detection cell unit 2a amplifies the detected voltage value and outputs the amplified voltage value to the VI conversion circuit 13 via the limit circuit 12 described later. The A / F detection circuit 11 functions as an output unit that outputs an output voltage based on the air-fuel ratio voltage.

  The limiting circuit 12 is a circuit that limits the voltage value based on the air-fuel ratio output from the A / F detection circuit 11 so as not to be higher or lower than a predetermined value. For example, it is limited within a predetermined value range of 6.5 [V] to 1.0 [V]. That is, the limiting circuit 12 functions as a limiting unit that limits the value of the pump current Ip so as not to exceed the predetermined current value by limiting the value of the output voltage to a predetermined voltage value (6.5 [V]) or less. To do. The detailed function and configuration of the limiting circuit 12 will be described later.

  The VI conversion circuit 13 supplies the pump current Ip to the pump cell unit 2b so that the voltage corresponding to the air-fuel ratio output from the A / F detection circuit 11 becomes a voltage value indicating the stoichiometric air-fuel ratio. That is, the pump current Ip is supplied to the pump cell portion 2b so that the pump cell portion 2b discharges or absorbs oxygen so as to fill the gap between the air-fuel ratio of the exhaust gas and the stoichiometric air-fuel ratio. The pump current Ip is energized based on the air-fuel ratio state, that is, rich / lean, and therefore energized from the terminal IP side to the connection terminal com side and from the connection terminal com side to the terminal IP side. There is a case. The VI conversion circuit 13 functions as energization means for energizing the pump current Ip to the pump cell unit 2b so that the air-fuel ratio becomes a predetermined ratio.

  The constant voltage control unit 14 applies a current to the sense resistor Rs to generate a voltage, thereby controlling the connection terminal com to be constant at a constant specified voltage value (for example, 3.3 [V]). This is because it is necessary to control the connection terminal com to a constant voltage in order for the detection cell unit 2a to generate a voltage based on the air-fuel ratio at the terminal VS. Hereinafter, the current that the constant voltage control unit 14 supplies to the sense resistor Rs is referred to as a COM current Icom. Since the COM current Icom is energized based on the voltage (connection voltage) of the connection terminal com, when the current is supplied from the constant voltage control unit 14 side to the connection terminal com side, and the constant voltage from the connection terminal com side. In some cases, power is supplied to the control unit 14 side. The constant voltage control unit 14 functions as a constant voltage unit that controls the connection voltage generated at the connection terminal com to be a constant voltage value.

  The voltage corresponding to the air-fuel ratio input from the A / F detection circuit 11 to the limiting circuit 12 is limited by the limiting circuit 12 within a predetermined upper limit value and lower limit value range and is output to the VI conversion circuit 13. The upper limit value and the lower limit value are values at which the pump current Ip that the VI conversion circuit 13 supplies to the pump cell unit 2b is less than the COM current Icom that the constant voltage control unit 14 supplies to the sense resistor Rs. That is, the limiting circuit 12 limits the voltage value output from the A / F detection circuit 11 to the VI conversion circuit 13 so that the COM current Icom> the pump current Ip. Thereby, even when the feedback control is performed based on the overcurrent and the pump current Ip increases, the pump current Ip can be limited to less than the COM current Icom. After the overcurrent ends, the constant voltage control unit 14 can quickly control the connection terminal com to a predetermined voltage (for example, 3.3 [V] as described above).

  As a result, even if an overcurrent is generated in the control device 1 or the air-fuel ratio sensor 2 and the voltage at the connection terminal com increases, the voltage input to the VI conversion circuit 13 is suppressed to the upper limit of the limit circuit 12. The conversion circuit 13 does not excessively reduce the pump current Ip. As a result, the voltage output from the constant voltage control unit 14 can be kept within an appropriate range, so that the air-fuel ratio feedback control can be stably performed even after the overcurrent is settled.

  The current monitor unit 15 detects the pump current Ip based on the voltage value generated in the sense resistor Rs. The value of the pump current Ip detected by the current monitor unit 15 is transmitted to the control unit 31 described later, and the control unit 31 calculates the air-fuel ratio and the fuel injection amount.

  The control unit 31 acquires the value of the pump current Ip from the current monitor unit 15, calculates the air-fuel ratio and the fuel injection amount, and controls the fuel injection valve 4. That is, the control unit 31 functions as a control unit that controls the fuel injection valve 4.

  The control unit 31 includes a receiving unit 31a that receives the value of the pump current Ip, an air-fuel ratio deriving unit 31b that derives the air-fuel ratio from the value of the pump current Ip, and a fuel deriving unit 31c that derives the fuel injection amount based on the air-fuel ratio. Is provided. The receiving unit 31a functions as “receiving unit”, the air-fuel ratio deriving unit 31b functions as “first deriving unit”, and the fuel deriving unit 31c functions as “second deriving unit”.

  FIG. 5 shows a detailed configuration of the limiting circuit 12. The limiting circuit 12 includes three operational amplifiers OP1, OP2, and OP3. The operational amplifiers (OP1, OP2, OP3) are operational amplifiers that output from the output terminal a voltage that is the difference between the voltage input to the non-inverting input terminal and the voltage input to the inverting input terminal.

  In the operational amplifier OP1, the non-inverting input terminal NI1 is connected to the A / F detection circuit 11, the inverting input terminal II1 is connected to the reference power supply Vref1, and the output terminal OUT1 is connected to the VI conversion circuit 13. The voltage output from the reference power supply Vref1 is, for example, 3.75 [V]. Therefore, the operational amplifier OP1 outputs a voltage value that is the difference between the voltage output from the A / F detection circuit 11 and 3.75 [V]. The A / F detection circuit 11 outputs 3.75 [V] when a voltage corresponding to the ideal air-fuel ratio is generated at the VS terminal.

  The operational amplifier OP2 has an inverting input terminal II2 connected to the output terminal OUT1 of the operational amplifier OP1, a non-inverting input terminal NI2 connected to the reference power supply Vref2, and an output terminal OUT2 connected to the operational amplifier OP1. The voltage output from the reference power supply Vref2 is, for example, 1.0 [V]. The operational amplifier OP2 functions to limit the lower limit of the voltage output from the operational amplifier OP1 to 1.0 [V].

  The operational amplifier OP3 has an inverting input terminal II3 connected to the reference power supply Vref3, a non-inverting input terminal NI3 connected to the output terminal OUT1 of the operational amplifier OP1, and an output terminal OUT3 connected to the operational amplifier OP1. The voltage output from the reference power supply Vref3 is, for example, 6.5 [V]. The operational amplifier OP2 functions to limit the upper limit of the voltage output from the operational amplifier OP1 to 6.5 [V].

  In this way, the voltage input from the A / F detection circuit 11 to the non-inverting input terminal NI1 of the operational amplifier OP1 is output to the VI conversion circuit 13 with the upper limit and lower limit being limited by the limit circuit 12. As a result, even if an overcurrent is generated in the control device 1 or the air-fuel ratio sensor 2 and the COM terminal voltage Vcom is increased, the voltage of the terminal VS thus increased is input to the A / F detection circuit 11. The voltage output from the detection circuit 11 to the VI conversion circuit 13 does not become excessive. Therefore, the pump current Ip output from the VI conversion circuit 13 does not become excessive, and stable air-fuel ratio feedback control can be quickly performed using the pump current Ip even after the end of the overcurrent.

  When the pump current Ip becomes excessive without using the limiting circuit 12 as in the prior art, it is necessary to repeat the feedback control a plurality of times before the pump current Ip is reduced to a normal value. In this case, the feedback control cannot be performed promptly. Further, there is a possibility that the excessive pump current Ip is erroneously determined to be abnormal in spite of the normal state in which the overcurrent has ended before the pump current Ip is reduced to a normal value.

  As described above, the control device 1 according to the first embodiment limits the value of the pump current Ip so that it does not exceed a current value within a predetermined range. For this reason, since the pump current Ip does not become excessively large or small, the air-fuel ratio sensor 2 and the control device 1 are not erroneously determined as abnormal. Moreover, since the period for shifting to the normal state can be shortened by feedback control after the end of the overcurrent, erroneous abnormality detection due to an abnormal value in the transition period can be prevented. In addition, even after the overcurrent generated in the control device 1 or the air-fuel ratio sensor 2 ends, the air-fuel ratio sensor 2 can be controlled quickly and stably based on the value of the pump current Ip.

<2. Second Embodiment>
Next, a second embodiment will be described. The second embodiment includes a configuration similar to that of the first embodiment. For this reason, the difference from the first embodiment will be mainly described.

  FIG. 6 shows the configuration of the air-fuel ratio control apparatus 1 according to the second embodiment. The control device 1 according to the first embodiment described above includes the limiting circuit 12 between the A / F detection circuit 11 and the VI conversion circuit 13. On the other hand, the control device 1 according to the second embodiment does not include the limiting circuit 12 between the A / F detection circuit 11 and the VI conversion circuit 13, and is between the connection terminal com and the VI conversion circuit 13. Includes a voltage monitoring unit 16. The VI conversion circuit 13 includes a limiting circuit 13a. The configuration of the limiting circuit 13a is the same as that of the limiting circuit 12 described above. That is, the limiting circuit 13a outputs the input voltage within a predetermined range.

  The voltage monitor unit 16 monitors the COM voltage Vcom, which is a voltage generated at the connection terminal com, and determines whether or not the COM voltage Vcom is out of a predetermined voltage range (for example, around 3.3 [V]). If the voltage monitor unit 16 determines that the COM voltage Vcom is out of the predetermined voltage range, the voltage monitor unit 16 outputs the limit signal Ls to the VI conversion circuit 13. The voltage monitoring unit 16 functions as a first detection unit that detects the voltage of the connection terminal com (connection unit).

  When the limit signal Ls is input from the voltage monitor unit 16 to the VI conversion circuit 13, the VI conversion circuit 13 performs VI conversion on the voltage value input from the A / F detection circuit 11 via the limit circuit 13a. That is, the VI conversion circuit 13 energizes the air-fuel ratio sensor 2 with the pump current converted based on the voltage value whose upper limit and lower limit are limited by the limit circuit 13a, not the voltage value input from the A / F detection circuit 11. To do. As a result, the pump current does not become too large or too small, and can be kept within a certain range. In other words, the limiting circuit 13a controls the input voltage to the A / F detection circuit 11 when the voltage value at the connection portion between the connection terminal com and the VI conversion circuit 13 exceeds a predetermined voltage value. The pump current value is limited so as not to exceed a predetermined current value.

  FIG. 7 shows a detailed configuration of the voltage monitor unit 16. The voltage monitor unit 16 includes two operational amplifiers OP4 and OP5.

  In the operational amplifier OP4, the non-inverting input terminal NI4 is connected to the connection terminal com, the inverting input terminal II4 is connected to the reference power supply Vref4, and the output terminal OUT4 is connected to the VI conversion circuit 13.

  The reference power source Vref4 outputs, for example, 3.6 [V]. Therefore, when the voltage input to the inverting input terminal II5 rises and exceeds 3.6 [V], the operational amplifier OP5 outputs a voltage that is the difference between them. This output voltage is the limit signal Ls.

  In the operational amplifier OP5, the inverting input terminal II5 is connected to the connection point C where the sense resistor Rs and the VI conversion circuit 13 are connected, the non-inverting input terminal NI5 is connected to the reference power supply Vref5, and the output terminal OUT5 is the VI conversion circuit. 13 is connected. The reference power supply Vref5 outputs, for example, 3.0 [V]. Accordingly, when the voltage input to the inverting input terminal II5 drops and falls below 3.0 [V], the operational amplifier OP5 outputs a voltage that is the difference between them. This output voltage is the limit signal Ls.

  Accordingly, since the voltage monitor unit 16 monitors the voltage value of the COM terminal voltage Vcom controlled to 3.3 [V] in a normal state, the upper limit is 3.6 [V] and the lower limit is 3 0 [V].

  As a result, the pump current Ip can be kept within a certain range. Even if an overcurrent occurs, the pump current Ip is kept within a certain range so as not to become too large or too small. Therefore, even after the occurrence of the overcurrent ceases, feedback control based on the pump current Ip is quickly performed. Can be done. In addition, since the pump current Ip can be kept within a certain range, it is possible to prevent the pump current Ip from being erroneously determined as abnormal after the overcurrent ends.

  The voltage monitor unit 16 may monitor the voltage value at the connection point C where the sense resistor Rs and the constant voltage control unit 14 are connected, instead of the voltage value at the connection terminal com shown in FIG. Since the voltage value of the COM terminal voltage Vcom can be monitored via the voltage drop at the sense resistor Rs, the occurrence of overcurrent can be monitored at an appropriate location. In this case, the voltage monitor unit 16 functions as a second detection unit that detects the voltage at the connection point C where the sense resistor Rs and the constant voltage control unit 14 are connected.

  When the voltage monitor unit 16 monitors the voltage value at the connection point C, the reference power supply Vref4 outputs 7.0 [V], for example, in consideration of the voltage drop at the sense resistor Rs. Since the connection terminal com is controlled to 3.3 [V] in a normal state without occurrence of overcurrent or the like, the voltage input to the non-inverting input terminal NI4 is 3.3 [V]. Accordingly, when the voltage input to the non-inverting input terminal NI4 rises and exceeds 7.0 [V], the operational amplifier OP4 outputs a voltage that is the difference between them. This output voltage is the limit signal Ls.

  In the operational amplifier OP5, the inverting input terminal II5 is connected to the connection point C where the sense resistor Rs and the VI conversion circuit 13 are connected, the non-inverting input terminal NI5 is connected to the reference power supply Vref5, and the output terminal OUT5 is the VI conversion circuit. 13 is connected. The reference power supply Vref5 outputs, for example, 0.7 [V] in consideration of the voltage drop at the sense resistor Rs. Accordingly, when the voltage input to the inverting input terminal II5 falls and falls below 0.7 [V], the operational amplifier OP5 outputs a voltage that is the difference between them. This output voltage is the limit signal Ls.

  As described above, the voltage monitor unit 16 detects the limit signal when the voltage at the connection point C increases and exceeds 7.0 [V], and when the voltage decreases to 0.7 [V] similarly. Ls is output to the VI conversion circuit 13. When the limit signal Ls is input, the VI conversion circuit 13 converts the voltage value from the A / F detection circuit 11 into the pump current Ip via the limit circuit 13a.

  As described above, the control device 1 according to the second embodiment limits the value of the pump current Ip so as not to exceed or fall below the predetermined current value. For this reason, since the pump current Ip does not become excessively large or small, it is not erroneously determined that the air-fuel ratio sensor 2 and the control device 1 are abnormal. Moreover, since the period for shifting to the normal state can be shortened by feedback control after the end of the overcurrent, erroneous abnormality detection due to an abnormal value in the transition period can be prevented. In addition, even after the overcurrent generated in the control device 1 or the air-fuel ratio sensor 2 ends, the air-fuel ratio sensor 2 can be controlled quickly and stably based on the value of the pump current.

<3. Third Embodiment>
Next, a third embodiment will be described. The third embodiment includes a configuration similar to that of the first embodiment. For this reason, the difference from the first embodiment will be mainly described.

  When the pump current Ip is excessive with respect to the COM current Icom, the constant voltage control unit 14 cannot absorb or supplement the excessive pump current Ip, and it is difficult to maintain the COM terminal voltage Vcom at a constant voltage value. It becomes.

  Therefore, in the control device 1 according to the third embodiment, the constant voltage control unit 14 sets the COM terminal voltage Vcom to a constant voltage value (specified voltage value), rather than the ability of the VI conversion circuit 13 to pass the pump current Ip. Therefore, the ability to energize the current is set higher. That is, the current capability of the constant voltage control unit 14 is set higher than the current capability of the VI conversion circuit 13 so that the COM current Icom> the pump current Ip. In addition, the current capability for the constant voltage control unit 14 to set the COM terminal voltage Vcom to a constant voltage value is calculated by the above-described arithmetic expression (1).

  As a result, when the pump current Ip exceeding the capability of the constant voltage control unit 14 to pass current is supplied to the connection terminal com, the constant voltage control unit 14 cannot control the connection terminal com to a constant voltage. To prevent. Therefore, the constant voltage control unit 14 can be energized so as to always absorb or supplement the pump current Ip energized to the connection terminal com, and the connection terminal com can be held at a constant voltage.

<4. Modification>
The present invention is not limited to the above embodiment. The present invention can be modified. Hereinafter, modifications of the present invention will be described. The embodiments described above and below can be combined as appropriate.

  In the above embodiment, the air-fuel ratio control device 1 includes either the limiting circuit 12 or the voltage monitoring unit 16. However, the control device 1 may include both the limiting circuit 12 and the voltage monitor unit 16. In this case, the VI conversion circuit 13 may be provided with a limiting circuit 13a.

  In the above embodiment, the limit circuit 12 limits the upper limit and the lower limit of the output voltage of the A / F detection circuit 11. However, the limiting circuit 12 may limit only one of the upper limit and the lower limit.

  Further, the configuration described as hardware may be realized by software. On the other hand, the function described as software may be realized by hardware. Further, hardware or software may be realized by a combination of hardware and software.

DESCRIPTION OF SYMBOLS 1 Control apparatus of air fuel ratio 2 Air fuel ratio sensor 2a Detection cell part 2b Pump cell part 3 Fuel injection apparatus 4 Fuel injection valve

Claims (7)

An exhaust of an internal combustion engine, comprising: a detection cell unit that generates an air-fuel ratio voltage corresponding to the air-fuel ratio; and a pump cell unit that is connected to the detection cell unit and connected to the detection cell unit and absorbs and discharges oxygen according to the amount of current A control device for controlling an air-fuel ratio sensor provided in the unit,
An output means for outputting an output voltage based on the air-fuel ratio voltage;
Energization means for energizing the pump cell with a pump current so that the air-fuel ratio becomes a predetermined ratio based on the output voltage;
Constant voltage means for controlling the connection portion voltage generated in the connection portion to have a constant specified voltage value;
Limiting means for limiting the value of the pump current so as not to exceed a predetermined current value;
A control device comprising: The control device according to claim 1,
The control device restricts the value of the pump current so as not to exceed a predetermined current value by limiting the value of the output voltage so as not to exceed a predetermined voltage value. The control device according to claim 1,
First detecting means for detecting the connection voltage;
Further comprising
The control device limits the pump current value so as not to exceed a predetermined current value by controlling the energization device in accordance with the value of the connection portion voltage. The control device according to claim 1,
A resistor connected between the connection and the constant voltage means;
Second detection means for detecting a connection point voltage generated at a connection point between the resistor and the constant voltage means;
Further comprising
The control device limits the pump current value so as not to exceed a predetermined current value by controlling the energization device according to the value of the connection point voltage. The control device according to any one of claims 1 to 4,
The predetermined current value is defined by a difference between a limit voltage value that is a limit of the output of the constant voltage means and the specified voltage value. The control device according to any one of claims 1 to 5,
Control means for controlling a fuel injection valve for injecting fuel into the internal combustion engine;
Further comprising
The control means includes
Receiving means for receiving the value of the pump current;
First deriving means for deriving an air-fuel ratio from the value of the pump current;
Second deriving means for deriving the fuel injection amount based on the air-fuel ratio;
A control device comprising: An exhaust of an internal combustion engine, comprising: a detection cell unit that generates an air-fuel ratio voltage corresponding to the air-fuel ratio; and a pump cell unit that is connected to the detection cell unit and connected to the detection cell unit and absorbs and discharges oxygen according to the amount of current A control device for controlling an air-fuel ratio sensor provided in the unit,
An output means for outputting an output voltage based on the air-fuel ratio voltage;
Energization means for energizing the pump cell with a pump current so that the air-fuel ratio becomes a predetermined ratio based on the output voltage;
Constant voltage means for controlling the connection portion voltage generated in the connection portion to have a constant specified voltage value;
With
2. A control apparatus according to claim 1, wherein the constant voltage means has a higher ability to pass a current in order to set the connection voltage to a predetermined specified voltage value than the ability of the current supply means to pass the pump current.

Images